Behaviour of the Major Resin- and Fatty Acids of Slash
BEHAVIOUR OF THE MAJOR RESIN- AND FATTY ACIDS OF SLASH
PINE (PINUS ELLIOTTII) DURING ORGANOSOLV PULPING
BY
AUGUSTO QUINDE ABAD
B.Sc, National Agrarian University (Lima-Peru), 1973 M.Sc, State University of New York, 1981
A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF
THE REQUIREMENTS OF THE DEGREE
OF DOCTOR OF PHILOSOPHY
in
THE FACULTY OF GRADUATE STUDIES
(Faculty of Forestry)
(Department of Forest Harvesting and Wood Science)
We accept this thesis as conforming
to the required standard
THE UNIVERSITY OF BRITISH COLUMBIA
September, 1990
© Augusto Quinde Abad, 19 90 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, 1 agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission.
Department
The University of British Columbia Vancouver, Canada
Date tk6Ur // jggo
DE-6 (2/88) ABSTRACT
A high extractive-content temperate conifer wood
{Pinus elliottii) was examined as a pulpwood source by organosolv pulping. Particularly, the behavior of the resin- and fatty acids during the lignin solvolysis process was studied in detail. For this purpose the resin- and fatty acids were characterized in the wood, and after pulping trials in order to reveal their fate during pulping, using catalyzed 80% aqueous alcohol (methanol) as solvent.
Wood extractives were removed by both methanolic cold maceration and Soxhlet extraction techniques. The resin- and fatty acid fractions thus collected were saponified and/or methylated and characterized by gas liquid chromatography (GC) and gas chromatography-mass spectrometry (GC-MS). No significant differences were found in regard to extraction efficiencies between the two types of cold extractions. Furthermore, there was no significant difference between these two types of cold extractions in comparison with the procedure described by
TAPPI standard T 204 os-76.
Pulping experiments were performed at 2052C for periods of 5, 20, 40, and 60 min. Lignins, which iii
precipitated on cooling of the black liquor (Lignin
fraction I), were set aside for further extractions and
chemical analyses. The molecular weight distribution of these lignins was determined by size exclusion
chromatography on an HPLC and their quantity was
determined either gravimetrically or volumetrically.
Precipitated Lignin Fraction I, suspected of
containing some adsorbed extractives and some fiber
fragments, was transferred to a tared crucible. The lignin
and extractives were sequentially dissolved by using
tetrahydrofuran (THF), acetone and methanol. This solution
was evaporated, the residue redissolved in methanol-water
(80:20) and the solution liquid-liquid extracted with
diethyl ether in a separatory funnel followed by
methylation prior to GC and GC-MS analysis.
Quantification of the resin- and fatty acids in the
wood and those recovered after organosolv pulping was
performed using an internal standard (methyl
heptadecanoate) added prior to the extraction steps.
The extractives dissolved in the black liquor were
isolated by a ternary liquid-liquid extraction scheme
using diethyl ether, methylated with fresh diazomethane,
and the resin- and fatty acids methyl esters characterized
by GC and GC-MS. The extractives present in the pulp were iv
isolated (removed) by a Soxhlet extraction procedure with methanol and" the resin- and fatty acids fractions characterized as above. Resin- and fatty acids surviving the high-temperature pulping process, were found mainly in the black liquor. After the 60 min cook, the black liquor contained 78.1% and 71.6% of resin- and fatty acids, respectively, while the pulp retained 11.7% and 8.2%, respectively of the extractives originally present in wood. "Lignin fraction I" adsorbed 10.2% and 20.2% of the resin- and fatty acids, respectively. Contrarily, if all of the lignin is precipitated (Lignin fraction II). prior to liquid/liquid extraction of the black liquor with diethyl ether, 98% and 60.4% of the resin- and fatty acids co-precipitate with the lignin and 2.0% and 39.6%, respectively, remain dissolved in the aqueous filtrate.
Industrial organosolv lignin isolated after solvent pulping of pine was thus shown to contain most (98%) of the resin acids and 39.6% of the fatty acids normally found in pines. Although not tested, it is supposed that lignins isolated by precipitation from the black liquor after organosolv pulping of other species cannot be considered as "pristine lignins" as described hitherto in the technical literature, since such lignins are heavily contaminated by the extractives of the wood species. In light of these findings all data on chemical and physical characterization of organosolv lignins and their reactivity will have to be reexamined and reassessed remove the effect of the extractives as contaminants. vi
TABLE OF CONTENTS
ABSTRACT ii
TABLE OF CONTENTS vi
LIST OF FIGURES xi
LIST OF TABLES xiv
ACKNOWLEDGEMENTS xvii
ABBREVIATIONS xix
1. INTRODUCTION 1
2. LITERATURE REVIEW 5
2.1. Wood Extractives 5
2.1.1. Background 5
2.2. Chemical Composition of Wood Extractives 7
2.3. Organosolv Pulping 10
2.4. Effects of Wood Extractives on Pulping 15
2.5. Resin- and Fatty Acids 20
2.5.1. Background 2 0
2.5.2. Chemical Analysis of Resin- and Fatty Acids 23
2.5.3. Resin- and Fatty Acid Characterization in Wood and Black Liquor 26
2.5.4. Characterization of Resin- and Fatty Acids in Pulp and Paper Mill Effluents . . .39
2.6. Utilization of Extractives 44
3 . METHODOLOGY ..49
3.1. Sample Collection and Preparation 4 9
3.2. Chemical Analysis of Wood 49
3.2.1. Wood extractives determination 50
3.2.1.1. Cold methanol maceration 50 vii
3.2.1.2. Methanol Soxhlet extraction 51
3.2.1.3. Ethanol-benzene Soxhlet extraction 51
3.2.2. Acid-insoluble lignin 51
3.2.3. Acid-soluble lignin 52
3.3. Preliminary Studies for the Characterization
of Resin- and Fatty Acids 53
3.3.1. Gas chromatographic studies 53
3.3.1.1. Methylation of resin- and fatty acids 54 3.3.1.1.1. Time of methylation reaction 57 3.3.1.1.2. Solvent selection for methylation .60
3.3.2. Saponification of esterified fatty acids 60
3.4. Characterization of Resin- and Fatty Acids
from Wood 61
3.4.1. Gas chromatographic analysis 61
3.4.2. Preparation of calibration curve 63 3.4.3. Gas chomatography-mass spectrometry (GC-MS) 64
3.5. Organosolv pulping of slash pine 64
3.5.1. Pulping conditions 65
3.5.2. High pressure organosolv pulping 66
3.5.2.1. Resin- and fatty acid removal and characterization from the black liquor 69
3.5.2.1.1. Liquid-Liquid Extraction 70 viii
3.5.2.1.2. Efficiency of the liquid-liquid extraction 73
3.5.2.1.3. Quantification of the resin and fatty acids in the black liquor 74
3.5.2.2. Resin- and fatty acids removal from lignin 75
3.5.2.3. Resin- and fatty acids removal from pulp 75
3.5.2.4. Complementary analysis of the high pressure 60 min pulping.... 77
3.5.3. Normal pressure organosolv pulping 78
3.6. Molecular Weight Distribution of Lignins
After High Pressure Pulping 80
3.6.1. GPC Analysis 81
3.6.1.1. GPC conditions 81
3.6.1.2. Calibration curve 82
3.6.1.3. GPC Injections 82
4. RESULTS AND DISCUSSION 83
4.1. Wood Species 83
4.2. Chemical Analysis of Wood 84
4.2.1. Determination of wood extractives
in the slash pine sample 85
4.2.2. Lignin from wood 87
4.3. Preliminary Studies for the Analysis of
Resin- and Fatty Acids 88
4.3.1. Gas chromatographic studies 88
4.3.1.1. Time selection for methylation..90 4.3.1.2. Solvent selection for methylation 92 ix
4.3.2. Preparation of calibration table 96
4.4. Analysis of Resin- and Fatty Acids in Wood 97
4.4.1. Change of extractives in storage ..102
4.4.1.1. Analysis of resin- and fatty acids after 6 weeks of storage 103
4.4.1.2. Analysis of resin- and fatty acids in wood after 24 weeks of storage Ill
4.4.1.3. Analysis of resin acids in wood after 52 weeks of storage 117
4.5. Organosolv Pulping of Slash Pine 119
4.5.1. Resin- and fatty acids analysis after pulping 121
4.5.1.1. Resin- and fatty acids analysis after 5 min pulping... 130
4.5.1.2. Resin- and fatty acids analysis after 20 min pulping 134
4.5.1.3. Resin- and fatty acid analysis after 40 min pulping 140
4.5.1.4. Resin- and fatty acids analysis after 60 min pulping 142
4.5.1.5. Complementary analyses of the resin- and fatty acid after high pressure 60 min cooks 156
4.6. Characterization of Lignins 157
4.6.1. Quantitative analysis of lignin 157
4.6.2. Molecular weight distribution of lignin 160
4.6.2.1. MWD of lignins from normal pressure cooks 160 X
4.6.2.2. MWD of lignin from high pressure cooks 168
4.6.2.2.1. Soluble lignins in the black liquor.... 168
4.6.2.2.2. Complementary analyses of lignin after a high pressure 60 min pulping 174
5. SUMMARY 180
6. CONCLUSIONS 183
7. BIBLIOGRAPHY 189
APPENDIX A 203
APPENDIX B 212 xi
LIST OF FIGURES Fig # 1 A model for phenol aggregates in neutral resin during kraft pulping of sepetir paya 17
2 Phenolic extractives responsible for the yellow specks from sepetir paya wood 19
3 Chemical structures of the major fatty acids present in slash pine wood 21
4 Main hydrocarbon skeletons for the resin acids..22
5 Resin acid methyl esters of the abietane, pimarane and isopimarane skeletons 24
6 Dissolution and composition changes of ether extractives on acid sulfite pulping of spruce, seasoned by different methods, and of green birchwood 28
7 Changes in the CIQ-IQ fatty acid composition of spruce and birch on acid sulfite pulping after different types of seasoning 30
8 Chemical products derivable from extractives ...45
9 Main distillates obtained from crude tall oil after acidification 47
10 Apparatus used for methylation of the resin and fatty acids 56
11 Flow diagram for the removal, identification and quatitation of the resin- and fatty acids present in slash pine wood. Acids were determined as their methyl ester derivatives.... 62
12a Flow diagram for the recovery, identification and quantification of the resin- and fatty acids in the black liquor and pulp after high pressure organosolv pulping of slash pine wood 68
12b Flow diagram for the recovery, identification and quantification of the resin- and fatty acids in the black liquor and pulp after normal pressure organosolv pulping of slash pine wood 79
13 Calibration curves for resin acids 99
14 Calibration curves for fatty acids 101 xii
15 Gas chromatogram of the Soxhlet methanol extract from wood stored for 6 weeks under CTH room conditions 105
16 Mass spectral total ion chromatogram of the free resin- and fatty acids 113
17 Mass spectral total ion chromatogram of the total resin- and fatty acids 114
18 Relative proportion of resin acids in slash pine wood after 6, 24 and 52 weeks of storage..118
19 Phase diagram of the ternary solvent mixture methanol-water-diethyl ether: X and Y relationship 124
20 Phase diagram of the ternary solvent mixture methanol-water-diethyl ether: Triangular relationship 125
21 Proposed mechanism for the base-catalyzed isomerization of the conjugated dienic resin acids 138
22 GPC calibration curve with polystyrene standards 161
23 Molecular weight distribution curves of lignins isolated after normal pressure organosolv pulping of slash pine 165
24 Molecular weight distribution curve of the dissolved lignin isolated after normal pressure organosolv pulping of slash pine 166
25 Molecular weight distribution of the different lignins (Dissolved, precipitated and trapped lignin) isolated from normal organosolv pulping of slash pine 167
2 6 Distribution curves of the soluble lignins (S-5, S-20) isolated after a high pressure organosolv pulping of slash pine 169
27 Distribution curves of the soluble lignins (S-40, S-60) isolated after a high pressure organosolv pulping of slash pine 170
28 Molecular weight distribution of the soluble lignins (S-5, S-20, S-40 and S-60) isolated from high pressure organosolv pulping of slash pine 171 xiii
29 Distribution curves of the lignins isolated during the complementary analysis after a 60 min high pressure organosolv pulping of slash pine 177
30 Molecular weight distribution of "Lignin II", "Lignin P" and "Lignin S-60" after the 60 min cooking of slash pine 178 xiv
LIST OF TABLES TABLE # 1 Extractives removal by different pulping systems 15
2 Extractives of loblolly pine wood and black liquor 32
3 Resin acids of loblolly pine wood 32
4 Fatty acids of loblolly pine wood ....33
5 Fatty acid composition of southern pine sapwood and kraft black liquor 34
6 Resin acids of slash pine sapwood and kraft black liquor 35
7 Composition of the tall oil precursors of southern pine sapwood and kraft black liquor extractives 36
8 Extractives of Douglas-fir wood and black liquor 38
9 Rates of methylation of dehydroabietic acid with diazomethane in various solvents 58
10 Ratio testing of the response area of dehydroabietic acid relative to the response area of methyl heptadecanoate after 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5 and 5.0 minutes of methylation with diazomethane 91
11 Response factors of dehydroabietic and abietic acids (40 ng/u.L) and palmitic acid (50 ng/jiL) after methylation in diethyl ether-methanol (9:1), dichloromethane- methanol (9:1) and methanol 94
12 Response factors and relative response areas of the individual major resin acids of slash pine with respect to the response area of methyl heptadecanoate 98
13 Response factors, relative response factors and relative response areas of the individual major fatty acids of slash pine with respect to to the response area of methyl heptadecanoate 100
14 Resin- and fatty acid composition of slash pine wood after 6 weeks of storage 106 XV
15 Relative proportion of resin acids in slash pine wood after 6 weeks of storage 108
16 Ratios of the relative intensities of the m/e 239/241 and m/e 301/316 mass peaks of levopimaric and palustric acids on slash pine wood after 6 weeks of storage 110
17 Resin- and fatty acids present in slash pine (Pinus elliottii Engelm.) after a 24 weeks storage 112
18 Resin-and fatty acid composition of slash pine wood after 6 and 24 weeks storage 116
19 Relative proportion of resin acids in slash pine wood after 6, 24 and 52 weeks storage 117
20 Data for the phase diagram separation of the tertiary solvent mixture methanol- water-diethyl ether 123
21 Resin-and fatty acid composition in slash pine wood and black liquor after 5 minutes organosolv pulping 132
22 Resin-and fatty acid proportions following 20 min organosolv pulping of slash pine 135
23 Resin-and fatty acid proportions following 40 min of organosolv pulping of slash pine ....141
24 Resin-and fatty acid composition in slash pine after 60 min organosolv pulping 143
25 Thermal isomerization of neoabietic and levopimaric acid at 2002C for 30 min 149
2 6 Thermal isomerization of levopimaric acid at 155 and 2002C 150
27 Resin-and fatty acid composition of slash pine wood and their recovery after 5, 20, 40 and 60 min organosolv pulping 155
28 Mass balance of lignin, resin and fatty acids of slash pine wood after organosolv pulping 158
2 9 Apparent Mw and Mn of lignins after normal pressure organosolv pulping 162 xvi
30 Molecular weight distribution ranges of the different lignin fractions obtained with normal (autogenous) pressure cooks 164
31 Apparent Mw and M^ of the soluble lignins after the 5, 20, 40 and 60 min organosolv pulping of slash pine wood 172
32 Percentage of the molecular weight ranges of the different soluble lignin fractions from high pressure organosolv cooks of slash pine wood 175
33 Apparent Mw and MQ of Lignin II, Lignin P and Lignin S-60 after the 60 min cooking 176 xvii
ACKNOWLEDGEMENTS
I wish to acknowledge, with gratitude, the expert guidance and invaluable help throughout my graduate studies at UBC, of my Research Supervisor Dr. L. Paszner, Professor,
Faculty of Forestry.
Thanks are also extended to the members of my
Supervisory Committee for reviewing this thesis, especially to Dr. R.W. Kennedy for his corrections, useful suggestions and criticisms. Thanks also go to Dr. A. Kozak for valuable statistical consultations, and to Dr. J.W. Wilson for his assistance and continuous bibliographical supply.
Appreciation is extended to Dr. B. Kosikova for her revisions, criticims and valuable discussions.
Special thanks are due to Dr. S. Ellis, Faculty of
Forestry, for his valuable assistance with the GPC analyses.
Grateful acnowledgement is made to F. Balza, Research
Scientist, Department of Botany, for his help during the mass spectrometric studies and interesting comments and suggestions.
Sincere acknowledgement is made to E. Lee and C. Lai
for their administrative assistance during my stay here at
Forestry.
I express my deepest gratitude to my wife, Roxana, and to my little "Queen", Roxanita, for their patience and endurance throughout my studies.
Finally, I would also like to thank the Canadian
International Developing Agency for their financial support xviii
during my studies at UBC. Many thanks to the National
Agrarian University "La Molina", Lima-Peru, for granting me a leave of absence during this period. xix
ABBREVIATIONS USED
BCR - British Columbia Research
CTH - Control Temperature and Humidity
FFA - Free Fatty Acids
GC - Gas Chromatography
GC-MS - Gas chromatography-Mass spectrometry
GPC - Gel Permeation Chromatography
HPLC - High Pressure Liquid Chromatography
IR - Infrared
Mn - Number Average Molecular Weight
Mw - Weight Average Molecular Weight
MTBE - Methyl Tert-Butyl Ether
MWD - Molecular Weight Distribution
NCASI - National Council of the Paper Industry for
Air and Stream Improvement
RAFA - Resin Acids and Fatty Acids
TAPPI - Technical Association of the Pulp and Paper
Industry
THF - Tetrahydrofuran
TLC - Thin Layer Chromatography
UV/VIS - Ultraviolet/Visible XX
To my wife, Roxana, and to my little "Queen" Roxanita 1
1. INTRODUCTION
Since early days, humans have used extractives of trees such as pigments, resins, turpentine, tannins, phenolics, alkaloids and gums, in many different ways and have developed their own culture. In a modern industrialized society, most of these substances have been replaced by synthetic products and seemingly have come close to losing their value in civilized life (Ohara et al., 1986). Tall oil and pine turpentine products have gained industrial significance recently and besides traditional uses (cosmetics, paints, varnishes and adhesives) have now also been proposed as a source of diesel fuel, and energy for steam and electric power generation (Lipinsky et al., 1985).
Generally, the effect of extractives has been totally ignored in organosolv pulping and they were neither accounted for as neutral solvent-solubles in the pulp nor separated from the lignin and sugars as by-products during recovery of the solvent.
Increased interest concerning pure chemicals and alternate raw materials, derived from lignocellulosic materials, is due mainly to the rise in cost and perceived 2
long-term shortages in fossil and non-renewable raw materials used by the chemical and fuel industries (Suomi,
1983). On the other hand, ever-increasing foreign trade among nations of the world demands careful attention to production economics in which waste utilization and by• product recovery can play a significant role, especially in the pulp and paper industry.
Today, mostly low extractive-content wood species are selected by the pulping industry because of lower chemical
(alkali) consumption, the ease of pulping, bleachability and/or papermaking. Extractives are known to interfere with normal delignification (Rydholm, 1985), cause color reversion in bleaching (Akimoto and Sumimoto, 1980;
Hosokawa et al., 1983; Gullichsen and Soderhjelm, 1984;
Sanusi et al., 1985) and pitch build up on papermachines
(McMillin, 1969; Yatagai and Takahashi, 1980; Tachibana and Sumimoto, 1980; Tachibana and Sumimoto, 1982) and reduce fiber bonding in formation of paper webs (Brandal and Lindheim, 1966; McMillin, 1969) .
Extractives during delignification and subsequent washings and bleaching are largely removed from the fibers. Chemical consumption is an important factor to be considered if a new pulping process is to be selected.
From this perspective, even high extractive-content woods
(i.e. as also in some tropical woods) with suitable fibre properties might be good alternatives if both the 3
lignocellulosic components (pulp, sugars and lignin) and the extractives could be used in the future.
The more than 50 years of organosolv pulping literature was totally silent on the effect of wood extractives during pulping and contained no information whatsoever on the apparent disappearance or chemical changes which may take place when unextracted woods containing notable amounts of extractives are pulped.
Behera (1985) indicated that unbleached Douglas-fir organosolv pulp was low in residual extractives but did not account for the presence of the extractives in his spent liquor. It therefore appears that the extractives are largely removed from the wood substance during pulping, and might be either lost from the spent liquor being adsorbed on the precipitated lignin or undergo high- temperature fragmentation reactions to solvent/water soluble products during pulping.
Since extractives are removed extensively from the fibers during high temperature organosolv pulping, even during short cooking periods it is hypothesized that:
1. ) The pulping conditions are fairly severe and it
appears reasonable to expect chemical and structural
changes in the extractives during organosolv pulping.
2. ) Isolation of the extractives from the spent liquor
must facilitate their handling for further use as by•
products. Furthermore, it would be desirable to 4
recover a cleaner and more reactive lignin suitable for use in its polymeric form (Venter and Van der
Klashorst 1989). Similarly, recovery of extractive- free sugar solutions, ready for fermentation or other applications, appears to be desirable. 5
2. LITERATURE REVIEW
2.1. Wood Extractives
2.1.1. Background
Extraneous materials present in wood are considered extracellular wall constituents. They consist primarily of organic, non-polymeric compounds which can be extracted with water, neutral organic solvents or volatilized by steam (Rowe and Conner, 1979; Fengel and Wegener, 1984) .
In a narrow sense, the term extractives covers those compounds which are soluble in water and organic solvents.
For their removal neutral solvent extraction is used prior to chemical characterization of woods (Fengel and Wegener
1984) . Broadly speaking, water-soluble carbohydrates and inorganic compounds are also included in this group
(Fengel and Wegener, 1984) .
Many wood species are characterized by specific chemical composition of their extractable materials.
Extractives are known to influence utility of wood for pulp and paper (Akimoto and Sumimoto, 1980) and for many other wood-based industries, particularly where decay resistance is of primary concern (Rowe and Conner, 1979).
According to Fengel and Wegener (1984), the amount of soluble material in organic solvents is only a few percent 6
in the wood of trees from the temperate zones, but may be substantial in certain parts of the tree, e.g. in branches, heartwood, roots, and areas of irritation
(wounding) .
Most of the extractives are located in the heartwood and their presence is responsible for the darkening of this portion of the tree. The toxicity of most of the extractive materials present in the heartwood makes this part of the tree relatively resistant to attack by decay organisms (Kollmann and C6te, 1968).
Extractives are important because of their contribution to the properties of wood. Many woods contain extractives which are toxic to bacteria, fungi and termites (Bauch et al., 1977; Sameshima et al., 1978;
Weissmann and Dietrichs, 1975; Yazaki, 1982; Franich and
Gadgil, 1983; MacRae and Towers, 1984). Other extractives can add color and odor to wood, accent the grain pattern and enhance strength properties (Barton, 1976; Wilcox and
Piirto, 1976; Rowe and Conner, 1979) . On the other hand, extractives can cause corrosion of metals in contact with wood (Rowe and Conner, 1979), inhibit setting of concrete, glues, and finishes (Abe and Ono, 1980), prolong paint curing time (Yatagai and Takahashi, 1980), block the reactive groups on the surface of the fibers reducing their bonding capacity (Brandal and Lindheim, 1966;
McMillin, 1969), contribute to color reversion of the 7
pulps (Croon et al., 1966; Venkova Rao et al., 1981), cause pitch problems during papermaking (McMillin, 1969;
Yatagai and Takahashi, 1980; Tachibana and Sumimoto, 1980;
Tachibana and Sumimoto, 1982), and bleed through finishes affecting the color stability of wood to light (Rowe and
Conner, 1979) .
In this sense, extractives are part and package of wood formation; their specific composition is controlled by biological activity during wood formation and subsequent maturing of the woody cells. Thereby, the wood industry has to learn how to deal with them and utilize them to the best possible advantage.
2.2. Chemical Composition of Wood Extractives
There is a part of the extractives termed resins that does not characterize certain chemical compounds, but must rather be considered a physical condition (Fengel and
Wegener, 1984). According to Sandermann (1960), the term
"resin" seems to be a mixture of different compounds which mutually inhibit crystallization.
Extractives from both softwoods and hardwoods can be classified into groups like: terpenes and terpenoids, fats, waxes, and their components, phenolic and 8
polyphenolic compounds and others (Fengel and Wegener,
1984) .
Most of the secondary extractives are located in the resin canals and the ray parenchyma cells (Mutton, 1959;
Back, 1960). In lower amounts they are found in the middle lamella, intercellular spaces and the cell walls of tracheids and libriform fibres (Back, 1960; Paasonen,
1967) . In no case are they chemically linked to the cell wall matrix components (cellulose, hemicelluloses and lignin). This allows their solubilization in suitable solvents without disturbing the cell wall.
The content and composition of wood extractives varies among wood species. This variation may be partially controlled and modified by environmental conditions including season, nutritional state, particular tissue being studied, and further varied if the tree is under attack by decaying microorganisms that will provoke response reactions (Swan, 1968; Dahm, 1970; Rowe and
Conner, 1979).
Variations in chemical composition and amount of wood extractives have been extensively studied on many species like spruces, pines or birches. It has been shown that softwood log seasoning involves slow enzymatic ester hydrolysis and oxidation of unsaturated acids (Donetzhuber and Swan, 1965). Conversely, the extractives content in birch remains constant during seasoning and is as high 9
after two years of storage, as in fresh wood (Donetzhuber and Swan, 1965).
According to Assarsson (1969), during outside chip storage some undesirable microbiological and chemical processes may occur, causing a serious deterioration in the quality of the chips. It was also found that the resin composition is modified by biochemical and chemical reactions. In this regard, fats and waxes (esters) are enzymatically hydrolyzed to fatty acids and higher alcohols, which can be metabolized by microbial respiration to carbon dioxide and water (Selleby, 1965).
According to Assarsson (1969) the amount and chemical structure of the wood extractives change during seasoning, and these changes are more drastic at the beginning and subsequently slow down after five or six months. He also stated that outside chip storage influences the resin composition by biochemical and organic chemical reactions in which esters, like fats and waxes are enzymatically hydrolyzed to fatty acids and higher alcohols, respectively (Assarsson 1969).
After four weeks of outside storage of chips, the tall oil yield is reduced by 40 - 50 % of that originally obtainable from the green wood. This decrement might be due to biological activity and autoxidation reactions
(Chalk, 1968) . 10
2.3. Organosolv Pulping
In general, during a chemical pulping process wood is treated with chemicals at high temperature in pressurized vessels. The main goal of any chemical pulping process is to degrade lignin (lignin solvolysis) leaving the
cellulosic material as the major fraction of the resulting pulp. The extractives, which are a minor extracellular extraneous fraction of the organic compounds in the wood,
are also subject to the severe conditions and are largely
removed during the pulping process.
Most chemical pulping processes can be grouped
according to the main chemical which is used to delignify wood. Thereby, there will be two groups of processes if
organic or inorganic chemicals are used as delignifying
agents. If organic solvents are used, these chemical processes are refered to as "organosolv" pulping processes. The leading inorganic pulping processes are the
kraft and sulfite processes.
In general, industrial pulping developments are motivated by economical and environmental considerations
(Lora and Aziz, 1985; Aziz and McDonough, 1987) . The
established pulp and paper industry would like to increase
pulp yield, improve pulp quality, and reduce both water
and air pollution (Kleinert, 1974) . Other considerations
such as energy, raw material, and economy provide 11
incentives for introduction of alternative processes in order to improve the world market position of chemical pulps (Saul, 1979; Casey, 1983; Paszner and Behera, 1985).
Lately, new, more effective and cheaper pulping processes have been suggested (Cox and Worster, 1971; Paszner and
Behera, 1985; Saul, 1979).
These same considerations motivated organosolv pulping trials by Kleinert and Tayenthal in 1931 using aqueous ethanol as the pulping solvent for woods at temperatures similar to those used in kraft pulping. In
Q later experiments with ethanol-water experiments at 185 C at a concentration of (50:50 ethanol-water), it was shown that aqueous organic solvents are powerful agents for delignification of both hardwoods and softwoods (Kleinert,
1974).
Subsequently, during the last 50 years several non- conventional solvent pulping methods have been investigated. Organic solvents as delignifying agents can be grouped as low and high boiling point solvents (Aziz and Sarkanen, 1989). Among the most common organic solvents are: a) aliphatic alcohols: methanol (Paszner,
1989), ethanol (Kleinert, 1974; Faass et al., 1989), butanol (K611 and Lenhardt, 1987), chloroethanol (Nimz et al., 1986), ethylene glycol (Nelson, 1977, K611 and
Lenhardt, 1987); b) amines: ethanolamine (Enkvist and
Moilanen, 1949), ethylenediamine (Kubes and Bolker, 1978; 12
Zargarian et al., 1988); c) ketones: acetone, methyl ethyl ketone, cyclohexanone (DeHaas and Lang, 1974), d) organic acids: formic acid (Ede and Brunow, 1989), acetic acid
(Young et al., 1986); e) esters: ethyl acetate (Young and
Baierl, 1985); f) phenols: phenol (Schweers, 1974), cresols (Sano et al., 1989; Sano, 1989).
Several catalysts have been used in aqueous methanol and ethanol but only few possess specific advantages as catalysts (Aziz and Sarkanen, 1989). Fleming (1985) gives the following list of catalysts used in combination with
different organic solvents: a) methanol: CaCl2, Mg(N03)2,
MgS04 , b) ethanol: Al salts, (NH4)2S, NH3, HCOOH, NaOH,
NaHC03 + methyl anthraquinone (AQ), c) isopropanol:
NaHS03, Na2S03, d) butanol: HN03, AQ, e) phenol: HC1, f) acetone: NH3, g) cyclohexanone: NH3, h) sulfolane:
Na2S, H2S04.
Young and Davis (1986), working with aspen chips in aqueous acetic acid (50-87.5%) for up to two hours at temperature between 160-185°C, achieved good delignification (Kappa numbers 10-40) with pulp yields ranging between 50-60%. A liquor-to-wood ratio of 4:1 to
8:1 was adequate for this purpose. They also found that lignin removal could be done with as low as 50% acetic acid and that the delignification selectivity was improved at higher solvent concentrations. 13
Young et al. (1985) described an alternate pulping process based on ethyl acetate/acetic acid/water. During this process ethyl acetate is proposed as the substitute solvent for water in the acetic acid pulping which shows the following advantages: Reduced cooking time, lower pulping temperatures for given cooking pressures, higher strength pulps, higher yields, enhanced solubility of lignin in the pulping solvent, and simplified recovery of organic chemicals.
Organosolv pulping of Eucalyptus regnans, Pinus radiata and Pinus elliottii was performed by treatment with ethylene glycol solutions of salicylic acid derivatives at 170 and 195°C (Nelson, 1977). It was found that Eucalyptus wood (E. regnans) was easily delignified with a three percent solution of aspirin or salicylic acid in glycol at 170°C. When methyl salicylate or glycol salicylate were used, more vigorous conditions were required. Furthermore, it was found that P. radiata was more difficult to delignify than E. regnans, and also that
P. elliottii was even more difficult to pulp than P. radiata.
Intensive development programs are underway at laboratories throughout the world to improve the organosolv pulping processes (Katzen et al., 1980; Marton and Granzow, 1982; Lipinsky, 1983). A major drawback of these processes has been their inability to pulp softwoods 14
adequately (Sarkanen et al., 1978) and to produce high yield pulps with small amount of rejects (Paszner and
Behera, 1985).
Organosolv pulping for all wood species has been possible by using alkaline-earth-salt-catalysts in aqueous methanol (75-85 %) as the solvent (Paszner and Behera,
1985). Advantages of this process include high pulp yield, ease of bleaching, high cellulose viscosity and good paper strength (Paszner and Behera, 1985; Behera, 1985).
The behavior of extractives during these organosolv pulping studies has apparently been completely ignored to date. The extractives content of organosolv pulps made from spruce (Behera, 1985) and Douglas-fir (Paszner and
Behera, 1985) chips was found to be lower than customary for chemical pulps (kraft and sulfite). Further, no interference from the dissolved extractives was noted during lignin and solvent recovery. In other words, the presence of extractives during organosolv pulping did not present any of the common pulping problems (high chemical comsumption, inhibition of delignification and pitch), nor was their presence notably interfering in any way with recovery of the by-products or the alcohol solvent. It is, therefore, apparent that the alkaline-earth-salt-catalyzed organosolv process is particularly suited for pulping of high resin content softwoods and hardwoods. 15
2.4. Effects of Wood Extractives on Pulping
It was suggested that the extractives suffer several changes during pulping (Sanusi et al., 1985). They studied the effect of wood extractives on pulping and bleaching of red lauan by three pulping processes. The red lauan chips were subjected to kraft, alkali-methanol, and cresol-water digestions to produce chemical pulps. These processes were shown to remove varying percentages of extractives as compared to the cold extraction by ethanol-benzene solvent system (100%) from the original wood (See Table 1).
Table 1. Extractives Removal by Different Pulping Systems (Sanusi et al., 1985)
Pulping method Extractives Removed (%)
Kraft 53 - 61
Alkali-methanol 62 - 80
Cresol-water 78 - 90 16
These results showed that the presence of solvents in the cooking liquor reduced the amount of residual wood extractives in the fibers (pulp) following cooking. From the point of view of efficiency of extractives removal, the cresol-water pulping was more effective than the kraft and alkali-methanol processes, although the former pulp showed inferior strength properties (Sanusi et al., 1985).
Thus the pulp properties and rates of extractives removal by the various solvents may be unrelated.
Tachibana and Sumimoto (1982) studied the chemical composition of neutral extractives from sepetir paya
(Pseudosindora palustris Sym.) and concluded that the extractives functioned as phenol carriers in formation of colored specks on paper sheets. They found that the phenolic compounds, responsible for the colored specks, were protected from alkaline attack during cooking by a membrane containing these neutral compounds .
Tachibana and Sumimoto (1982) suggested that the aggregation of phenolics can be aided by the enclosing action of fi-sitosteryl glucoside which is accompanied, or occluded by the neutral compounds. The 15-sitosteryl glucoside may act as interfacial substance between a resin particle and the cooking liquor as illustrated in Fig. 1. G » a glucosidic part of fi-sitosteryl glucoside A - an aglycon part of fi-sitosteryl glucoside
Figure 1. A model for phenol aggregates in neutral resin during kraft pulping of sepetir paya (Tachibana and Sumimoto, 1982) 18
According to McMillin (1969) it is not unreasonable to expect extractives present in the pulp to have detrimental effect on pulp color and handsheet properties.
He found that burst and tear strength of handsheets tend to decrease with increasing extractive content. This can be attributed to a lessened bond strength owing to lowered surface tension forces, blocking of reactive sites on the fiber surface, and the reduction of the number of the effective hydrogen bonds.
Detailed analysis by Tachibana and Sumimoto (1980) show that six phenolic extractives were responsible for the yellow specks that appear on the surface of bleached sulfate pulp. These new types of pitch problems were also isolated from the wood of sepetir paya and identified as the following compounds: methyl ferulate (I), methyl p- coumarate (II), butein (III), pseudosindorin (IV) , sulphuretin (V) and rengasin (VI) (See Fig. 2) . Due to their conjugated structures these extractives would be expected to be highly colored due to the quinone methide products they are capable of forming under suitable conditions. These structures would also be expected to be susceptible to UV (photo) degradation. 19
COOCH3 COOCH3 I I CH CH II II CH CH
OCH3
OH OH Methyl fendate (I) Methyl p-coumarate (II)
OH OH
HC -^-OH HO HC- II HO II ^CH xx •CH OH OH 0 OH l But ein (III) Psevdosindorin (IV)
OH OH HO
OHj H3CO «
Szdphuretin (V) Rengasin (VI)
Figure 2. Phenolic extractives responsible for the yellow specks from sepetir paya wood (Tachibana and Sumimoto, 1980) 20
2.5. Resin- and Fatty Acids
2.5.1. Background
The resin and fatty constituents of pulpwoods are a very important source of by-products. The resin- and fatty
acids are the main components of the tall oil* obtained
from the kraft pulping.
The fatty acid fraction is composed of either
saturated and/or unsaturated entities. The most valuable
fatty acid components of tall oil are those that belong to
the unsaturated group (dienoic and trienoic acids). Among
the most common fatty acids present in wood are the
following: palmitic (Cig.g)/ stearic (C^Q.Q), oleic
(C]_8:i)f linoleic (CJ^Q^) and linolenic (Ci8:3)* (See Fig.
3) .
Resin acids are organic compounds that belong to the
diterpene group. Diterpenes, are compounds composed of
four isoprene units (Streitwieser and Heathcock, 1981).
Almost all the resin acids can be classified into four
skeletal classes: abietane, pimarane, isopimarane and
labdane. (See Fig. 4). Among these resin acids the most
*Tall oil consists of a mixture of 40 to 50% each of fatty acids (i.e. oleic and linoleic) and resin acids (i.e. abietic and pimaric) with about 10% unsaponifiables. Hexadecanoic (palmitic) acid
-COOH Octadecanoic (stearic) acid
.COOH
Octadecaenoic (oleic) acid
.COOH
Octadecadienoic (linoleic) acid
.COOH
Octadecatrienoic (linolenic) acid
Figure 3. Chemical structures of the major fatty acids present in slash pine wood 22
18
Abietane Labdane
Figure 4. Main hydrocarbon skeletons for the resin acids (Zinkel et al., 1971) 23
important are: pimaric, sandaracopimaric, isopimaric,
levopimaric, palustric, dehydroabietic, abietic and neoabietic (See Fig. 5) .
2.5.2. Chemical Analysis of Resin- and Fatty Acids
Since the introduction of chromatography for separation by Tswett in 1906 there have been many changes or variations to this technique. Among the modifications, plane chromatography (paper and thin-layer chromatography
(TLC)), column chromatography, gas chromatography (GC) , and high performance liquid chromatography (HPLC) are widely used today. It was around 1952 that the modern era of chromatography began with the publication on the separation of volatile fatty acids by gas-liquid partition chromatography (James and Martin, 1952). The first gas chromatographic studies were performed on packed columns.
Later with the introduction of the open tubular columns by
Golay in 1957, these became the most common columns used for separation analysis (Freeman, 1981) .
Resin- and fatty acids present in wood, black liquors and pulp and paper mill effluents have been characterized by using a combination of chromatographic (TLC, GC and/or
HPLC) and spectrometric (UV, IR, NMR and/or MS) 24
Palustrate Levopimarate Dehydroabietate
Abietate Neoabietate
Figure 5. Resin acid methyl esters of the abietane, pimarane, and isopimarane skeletons 25
techniques. Among the chromatographic techniques, gas liquid chromatography (GLC or GC) is the most widely used.
Due to the excellent research and development carried out by the suppliers, it is possible to obtain open tubular (capillary) columns in sizes from 10 up to 100 m long, as reasonably strong, inert and durable tubing
(fused-silica) and with cross-linked bonded-phases in order to avoid bleeding and to allow rinsability of the columns. Nowadays, very complex samples can be easily separated by using these types of chromatographic columns.
Different stationary phases have been studied for the separation of resin- and fatty acids. A list of the stationary phases used for packed columns is as follows:
100% dimethyl polysiloxane (Zinkel, 1975), diethylene glycol succinate or DEGS (Zinkel, 1975; Fourie and Basson,
1990), 10% Silar 10C (Leach and Thakore, 1976; Lie Ken Jie and Chan, 1985), ethylene glycol-silicone copolymer or
EGSS-X (Zinkel and Foster, 1980; Zinkel and Han, 1986).
Stationary phases used with capillary columns are:
100% dimethyl polysiloxane or SE-30 (Holmbom et al., 1974;
Holmbom, 1977; Holmbom and Ekman, 1978; Lorbeer and
Kratzl, 1985), 95% dimethyl-(5%)-diphenyl-polysiloxane or
SE-54 (Turner and Wallin, 1985; Ayorinde et al., 1988),
1,4-Butanediol succinate, BDS (Holmbom et al., 1974;
Holmbom, 1977; Yildirim and Holmbom, 1977b; Holmbom and
Ekman, 1978; Ekman, 1979; Anas et al., 1983; Zinkel and 26
Han, 1986) . Other stationary phases offered by the
suppliers are: nitroterephthalate modified polyethylene glycol (FFAP or SP-1000) and 50% cyanopropylmethyl-(50%)- methylphenyl-polysiloxane (DB-225). These were also used to analyze the fatty acids subject of the experiments of this thesis.
Methyl esters are still the most universal derivatives for the gas chromatographic analysis of resin-
and fatty acids. The most popular derivatization techniques for methyl esters are: diazomethane, boron trifluoride, hydrochloric acid/methanol, sulfuric
acid/methanol, perchloric acid/methanol, and also
transesterification with either sodium methoxide in methanol or tetramethylammonium hydroxide in methanol
(Fourie and Basson, 1990) .
2.5.3. Resin- and Fatty Acid Characterization in Wood and
Black Liquor
Lately, the composition of the resin- and fatty acids present in softwoods has been fairly completely
established (Yildirim and Holmbom, 1977b; Ekman, 1979;
Lorbeer and Kratzl, 1985).
Analytical procedures for determining the resin- and
fatty acids present in wood might comprise all or some of
the following steps: (a) isolation and concentration, (b) 27
separation and removal of neutral interfering substances,
(c) methylation of the resin- and fatty acids, (d)
identification and determination of the different
components present in the extract.
Removal of the wood extractives has been performed by using different organic solvents. 7Among the most common
solvents used for these extractions are: Petroleum ether
(Yildirim and Holmbom, 1977b; Ekman, 1979; Lorbeer and
Kratzl, 1985), diethyl ether (Zinkel, 1975; Zinkel and
Foster, 1980; Foster et al., 1980), acetone (Yildirim and
Holmbom, 1977a), methanol (Lorbeer and Kratzl, 1985) .
According to Yildirim and Holmbom (1977b), the petroleum ether extractives of Pinus brutia Henry comprise
around 1.1 to 1.5% of the dry wood. Interesting findings were: i) the lack of pimaric acid (a resin acid) and ii) the presence of oleic and linoleic acids as the major
fatty acids.
Kahila and Rinne (1957) demonstrated that changes in
the resin composition during storage of sprucewood were
reflected in the resin of the unbleached pulp as outlined
in Fig. 6.
Sulfite pulping of both softwoods and some hardwoods
(Kahila, 1957; Kahila and Rinne, 1957; Mutton 1958), may be inhibited by their resins (Rydholm, 1985). Under acid
pulping conditions, the fatty and resin acids are not 2.0r- -, 2.0
1.5 - 1.5 o o 5
o 1.0 1.0
nmol Unsopo— c — ntfiables "55
Figure 6. Dissolution and composition changes of ether extractives on acid sulfite pulping of spruce, seasoned by different methods, and of green birchwood (Kahila, 1957) 29
converted into hydrophilic soaps as is the case in alkaline pulping (Rydholm, 1985) .
It has been pointed out (Kahila, 1957, Kahila and
Rinne, 1957) that the amount of resin acids decreases during the sulfite cooking process. It also seems that the amount of unsaponifiable matter in the extracts decreases to a considerably lesser degree (See Fig. 6) . Furthermore, they found that the content of unsaturated C 16-18 fatty acids, containing two double bonds (i.e. linoleic acid) decreases considerably as compared with the oleic acid. On the other hand, saturated fatty acids remain largely unchanged during the cook (Fig. 7).
Lorbeer and Kratzl (1985) when working with the
Austrian black pine {Pinus nigra var. Austriaca), examined the difference between the removal of the wood extractives with methanol and petroleum ether. They found that during the extraction with methanol, esterification of the free fatty acids took place, as opposed to the non reactivity of the resin acids. They also reported that there was no isomerization of the conjugated fatty acids during the treatment with methanol over different lengths of time.
According to Holmbom and Ekman (1978), the content of the tall oil precursors in common spruce [Picea abies (L.)
Karst] was about 30 to 50% of that of Scots pine {Pinus silvestris L.). They found that during kraft pulping, the 0=Saturated acids 1 =Monounsaturated acids 2=Diunsaturated acids -1 1.00 3=Triunsaturated acids
O TJ O O 0.30 r- o 0.75 o Q) O D l_ QL o (0 0.20 0.50 &^ o to TJ 7ZZ2. to* 'o U) 'o O o 0.10 1 0.25 D OO
00 r r 0 O 0 (£) 0.00 0 0.00 O Wood Pulp Wood Pulp Wood Pulp Wood Pulp Spruce Spruce Spruce Birch 4 Months 8 months 7 months no land land water seasoning seasoning seasoning seasoning
Figure 7. Changes in the Cjg.jg fatty acid composition of spruce and birch on acid sulfite pulping after different types of seasoning (Kahila and Rinne, 1957) 31
dienoic and trienoic fatty acids are isomerized to acids with conjugated double bonds of the cis-trans configuration type. Further, they found that the main change in the resin acid composition during pulping was the isomerization of levopimaric into abietic acid.
Data of Zinkel (1975) on the extractives of loblolly pine wood (Pinus taeda L.) and in the black liquor after kraft pulping is presented in Tables 2, 3 and 4. During their chromatographic analyses, they were unable to resolve properly levopimaric and palustric acids when using DEGS or SE-30/EgiP as stationary phases. The data are presented as a combined figure in Table 3. Analysis of the nonsaponifiable fraction showed that the main components were sitosterol (48% of total nonsaponifiables), trans-pinosylvin dimethyl ether (8.3%), tetracosanol (2.5%), pimaral (2.3%), pimarol (2.4%) and agathadiol (0.7%) (Zinkel, 1975).
Zinkel and Foster (1980) determined the composition of the tall oil precursors in the sapwood and black liquors after kraft pulping of four southern pine woods: slash (Pinus elliottii Engelm.), longleaf (Pinus palustris
Mill.), shortleaf (Pinus echinata Mill.), and Virginia
(Pinus virginiana Mill.) pines (See Tables 5, 6 and 7).
They found that during kraft pulping of these species isomerization reactions and significant losses of the resin and fatty acids resulted. The losses were shown to 32
Table 2. Extractives of Loblolly Pine Wood and Black Liquor (Zinkel, 1975)
Extract, mg/g of o.d. wood
Ether soluble Black extractives Wood Liquor
Total extract 20.0 19.7 Neutrals 14.9 2.5 Saponifiable 12.2 Nonsaponifiables 2.2 2.5 Glycerol 0.3a 0.3a
Free acids 5.0 17.0 Resin 3.9 3.6 Fatty 0.3 12 . 4 Oxidized 1. 0 0.9 Strong 0.1 0.2
Total fatty acids 12.0 12 . 4 Not accounted for 0.2
a = Calculated assuming all wood saponifiables are triglycerides.
Table 3. Resin acids of loblolly pine wood (Zinkel, 1975)
Black Resin acid Wood, Liquor, methyl ester % %
Pimarate 8.0 7.7 Sandaracopimarate 1.8 1.8 Communate tr. ? . . Levopimarate-palustrate 59.5 45 . 1 Isopimarate 1. 6 1.3 Abietate 12. 6 19.2 Dehydroabietate 8 . 4 14 . 6 Neoabietate 8.1 10.4 Table 4. Fatty Acids of Loblolly Pine Wood (Mole %)(Zinkel 1975) Fatty acid Black Methyl ester3 r18:0 Free Esterified Liquor Unsaturation
14:0 0.33 1.9 tr tr U 0.43 0.7 tr tr U 0.50 tr tr tr 16:0 0.57 20.9 6.4 6.1 16:1 0.67 3.6 1.1 1.0
17:0? 0.74 1.3 # # tr U 0.88 tr tr tr 18:0 1.00 24.2 2.0 1.8 18:1 1.18 15.0 39.7 38.4 9 c U 1.30 0.7 0.7 0.7 18:2 1.45 10.8 39.2 23.7 9, 12 cc 18:3 1.64 3.6 3.6 1.2 5, 9, 12 U 1.75 1.5 1.0 * . 18:2 1.94 • • • • 15.0 9, 11 ct U 2.11 • • • • 2.5 18:2 2.23 • • 1.9 9, 11 ? U 2.44 • • • • 1.3 20:3 2.80 0.0 4.7 3.5 5, 11, 14 22:0 3.19 10.2 0.8 U 3.66 • • 1.1 24:0 5.70 10.0 0.8 aU, unidentified; tr, trace. Table 5. Fatty acid composition of southern pine sapwood and kraft black liquor. (Zinkel and Foster 1980)
Fatty acid (normalized % of fraction) Pines fatty acid 16:0 16:1 17:0 18:0 18:1 18:29'12 18:35'9'12 18:39'12'15 18:29'n fraction
Slash Free 11.6 0.8 1.6 3.5 32.1 30.1 2.3 1.6 Esterified 6.9 0.3 1.1 1.7 42.8 36.3 2.7 1.4 Black liq. 6.4 0.4 0.7 1.2 42.9 24.1 1.1 1.4 12 .la Longleaf Free 8.3 0.6 1.2 3.6 37.6 34.2 4.0 0.9 • • Esterified 4.9 0.3 0.6 0.8 40.8 39.6 2.9 1.3 » • • Black liq. 5.0 0.3 0.7 1.1 42.6 27.1 1.1 1.3 10 5 Shortleaf b Free 14.9 0.7 0.9 3.3 33.4 25.2 2.0 0.5 • • Esterified 6.3 0.3 1.0 1.2 32.4 41.9 5.2 0.8 • • Black liq. 6.7 0.2 1.8 1.6 34.3 25.5 2.4 0.8 13 5 Virginia Freec 16.7 1.5 1.2 4.4 15.7 24.5 3.1 0.9 Esterified 4.9 0.4 0.9 1.0 30.2 44.1 9.3 1.5 • • Black liq. 4.7 0.4 0.6 1.1 30.2 20.4 2.3 1.5 19 6 a= The 18:39'12'15 (a 18 carbon fatty acid with 3 double bonds occurring at bond positions 9, 12/ and 15) and 18:29'1:L peaks were not resolved on GLC. The 18:29'13- was estimated by subtracting the 18:39'^2/^^ content found in the esterified fraction from the combined peak of the black liquor. b= contained 12.8% 20:0. c= Contained 3.8%, 8.8% and 7.0% of 20:0, 22:0 and 24:0, respectively. Table 6. Resin acids of slash pine sapwood and kraft black liquor (Zinkel and Foster, 1980)
Slash Shortleaf Longleaf Virginia Black Black Black Black Resin acids* Wood liq. Wood liq. Wood liq. Wood liq. % % % % % % % %
Pimarate 7.4 7.7 6.0 6.4 6.6 7.4 6.3 6.8 Sandaracopimarate 2.0 2.4 1.8 2.2 2.0 2.0 1.4 1.9 Communate 2.7 2.1 —. - Levopimarate 9.6 3.7 27 . 9 12.7 27.8 12.0 34.6 17.7 Palustrate 19.4 19.3 15.2 26.5 19.0 27.5 12.0 14.9 Isopimarate 23.7 26.2 5.0 5.7 8.3 8.3 3.5 4.9 Abietate 12.0 13.2 15.1 14.7 13.5 15.7 17.1 22.0 Dehydroabietate 4.8 8.8 15.3 16.6 10.5 12.8 2.6 6.1 Neoabietate 18.4 16.5 13.7 15.2 12.1 14.2 22.5 25. 6
* Resin acids were determined as their methyl esters. Table 7 . Composition of the tall oil precursors of southern pine sapwood and kraft black liquor extractives (mg/g of o.d. extractives-free wood). (Zinkel and Foster, 1980)
Slash Shortleaf Longleaf Virginia Ether-soluble Black Black Black Black extractives Wood liquor Wood liquor Wood liquor Wood liquor
Neutrals (saponified) 20.1 1.4 20.1 1.2 22.7 1.4 10.6 1. 0 Fatty acids 17. 6 18.3 20.3 9.5 Nonsaponifiables 2.5 1.4 1.8 1.2 2.4 1.4 1.1 1.0 Free acids 5.9 20.4 6.6 22.5 6.0 24.9 3.4 11.5 Resin 5.7 3.5 6.5 4.4 5.8 4.7 3.3 2.9 Total fatty acids 17.8 16.9 18.4 18 .1 20.5 20.2 9.6 8.6 Total tall oil precursors8 26.0 21.8 26.7 23. 6 28.7 26.1 14.0 12.5
aTall oil precursors = total fatty acids + resin acids + nonsaponifiables 37
be reproducible between repetitive experiments, and only
80 to 90 % of the original tall oil precursors were recovered from the black liquors.
It can be seen from the data in Table 6 that the resin acid composition of these four pines is quite similar. Slash pine was a noticeable exception because of its relatively high proportion of isopimaric acid and low fraction of levopimaric acid.
Foster et al. (1980), characterized the sapwood and heartwood extracts of Douglas-fir [Pseudotsuga menziesii
(Mirb.) Franco] and the tall oil from the kraft black liquor. They found that the yield of heartwood diethyl ether extractives, (mg/g oven-dried extract-free
(o.d.e.f.) wood basis) was nearly three times that of the sapwood (See Table 8), and that the amount of tall oil precursors was only 80% of that of sapwood. Furthermore, they reported that during kraft pulping, isomerization reactions and a reduction of the total amounts of conjugated resin acids, with formation of dehydroabietic acid occur. Foster et al.'s (1980) tall oil precursor content was lower by about 15% than that reported by
Zinkel et al. (1980) for southern pines.
Therefore, under acid or alkaline conditions, considerable transformation of the extractive components can be expected. Such changes alter their chemical and physical characteristics. These changes may be beneficial Table 8. Extractives of Douglas-fir wood and black liquor (Foster et al., 1980)
Extractives, mg/g of o.d. wood
Sapwood Heartwood
Black Black Wood3 Liquor Wood3 Liquor
Neutrals 5.5 0.7 7.0 1.1 . . .Non-saponifiables 1.7 0.7 1.6 1.1 . . .Saponifiables (fatty acids) 3.5 1.6 . . .Not recovered13 0.3 3.8
Free Acids 2.1 2.6 2.8 2.2 . . .Fatty acids 0.1 1.4 0.1 0.7 . . .Resin acids 2.0 1.2 2.7 1.4
Strong acids 0.1 tr. 0.1 0.1
Tall oil precursors0 7.3 3.3 6.0 3.3
a) Total diethyl ether extractives from sapwood was 7.7 mg/g, and from heartwood 21.2 mg/g (11.3 mg/g was not eluted from DEAE- Sephadex by acetic acid). b) Not recovered from saponification. c) Tall oil precursors = non-saponified neutrals and saponified neutrals and free acids. 39
technically (by-products) or detrimental environmentally
(toxicity and pollution).
2.5.4. Characterization of Resin- and Fatty Acids in Pulp and Paper Mill Effluents
Resin- and fatty acids (RAFA) have been established to be the major contributors to fish toxicity by softwood pulp and paper mill effluents (Rogers et al., 1972;
Rogers, 1973; Leach and Thakore, 1973; Leach and Thakore,
1976; Leach et al., 1978; Chung et al., 1979; Holmbom,
1980; Walden and Howard, 1981; Wearing et al., 1984;
Sameshima et al., 1986). Control of these compounds in the discharges from pulp and paper mills is important in controlling their impact on the environment and assessing their biological effect. The effectiveness of the control measures depends on the availability of adequate analytical methods.
Several investigators have been using high performance liquid chromatography (HPLC) for the analysis of resin- and fatty acids (RAFA) in pulp mill effluents and/or tall oil rosins (Mortimer, 1979; Fatica, 1989).
However, analysis by gas chromatography still remains the selected choice for the characterization of RAFA constituents in pulp and paper mill effluents as described 40
by Holmbom (1977), Chung et al. (1979), Holmbom (1980),
Turoski (1981), Voss and Rapsomatiotis (1985).
Almost all of the efforts for the analysis of the pulp and paper mill effluents in North America have been developed in the USA (National Council of the Paper
Industry for Air and Stream Improvement - NCASI) and
Canada (British Columbia Research - BCR) . The main difference between these two procedures (NCASI and BCR) is the method of isolation. The NCASI procedure uses diethyl ether as the solvent for extraction of an acidified (pH 2
- 3) effluent, while the BCR procedure removes the resin- and fatty acids from the effluent under alkaline (pH 9-10) conditions by adsorption onto a porous "polymeric resin"
(XAD-2) (Voss and Rapsomatiotis, 1985).
Most of the latest innovations in analytical methods for the characterization of RAFA present in pulp and paper mill effluents have been directed to their chromatographic separation and detection. In this regard, the most important developments have been the use of high- resolution capillary gas chromatography (Chung et al.,
1979; Holmbom, 1980) and the combination of gas chromatography and mass spectrometry (GC-MS) (Turoski et al., 1981; Claeys et al., 1983).
The isolation of resin- and fatty acids from pulp and paper mill effluents is the most important and critical step during a given procedure. It defines the maximum 41
recovery of the analytes of interest; as well it can limit the amount of co-extractives that might interfere with their quantitative determination. Isolation can be performed either by adsorption onto a porous "polymeric resin" or by solvent extraction using a single solvent or a combination of solvents.
Among the "polymeric resins" used for isolation of resin- and fatty acids from the effluents, only three of them have been found to be of great interest and these resins are: XAD-2 (Rogers, 1973; Leach and Thakore, 1976;
Rogers et al., 1979; Chung et al., 1979; Wearing et al.,
1984; Voss and Rapsomatiotis, 1985), XAD-4 (Rogers et al.,
1979) and XAD-8 (Button, 1971). Out of these three polymeric resins, XAD-2 is the most commonly used for resin- and fatty acids analysis in pulp and paper mill effluents.
Several solvents or mixtures have been suggested for solvent extraction of the resin- and fatty acids from black liquors and pulp and paper mill effluents. The most important solvents are as follows: Petroleum ether- acetone-methanol (Saltsman and Kuiken, 1959; McMahon,
1980) ; diethyl ether (Anon. NCASI, 1972; Anon. NCASI,
1975; Holmbom, 1980); methylene chloride (Turoski et ai.,
1981; Turner and Wallin, 1985); hexane-acetone-methanol
(Wearing et al., 1984); methyl tert-butyl ether (Voss and
Rapsomatiotis, 1985). 42
Several problems have been encountered during the removal of the resin- and fatty acids from the black liquors and mill effluents. Among the most common ones are the precipitation of the lignin and formation of emulsions during the extraction steps where acidified lignin fragments are present. These residues may induce the adsorption of the resin- and fatty acids leading to erroneously low results. McMahon (1980) using a ternary solvent system (petroleum ether-acetone-methanol) solved this problem by keeping the lignin in solution; no loss of resin- and fatty acids took place because no emulsion was formed.
Emulsion difficulties have been addressed in different ways. Voss and Rapsomatiotis (1985) eliminated this problem by adding equal or greater amounts of methyl tert-butyl ether to the effluents during their extraction procedure. Turoski et al. (1981), when extracting an acidified (pH 2) effluent sample with dichloromethane,
found severe emulsion difficulties which were broken primarily by using a heat gun to gently boil the dichloromethane in the bottom layer of the separatory
funnel. When all else failed, the entire emulsion
interface was either filtered or drawn off and
centrifuged. To obtain phase separation Turner and Wallin
(1985) used ultrasonic dispersion for breaking up emulsions. 43
In addition to the procedures mentioned above for the characterization of resin- and fatty acids by gas chromatography and/or gas chromatography-mass spectrometry, some procedures involve colorimetric techniques for the determination of the resin and/or fatty acids. McDonald (1978) reported on the quantitative determination of the abietic-type resin acids present in kraft effluents. He found that the recovery of these acids by extraction was not quantitative, but could be calculated for a given set of conditions and the analytical results adjusted accordingly. The main drawback of this method is the interference of unsaturated fatty acids and sterols commonly present in pulp and paper mill effluents.
Kwon and Rhee (1986) developed a simple and rapid colorimetric method for determining the free fatty acids produced by lipase from triacylglycerides. Their method used a cupric acetate-pyridine mixture as a color developing reagent. The sensitivity and reproducibility of this method was good for caproic, caprylic, capric, lauric, palmitic, stearic and oleic acids.
Another spectrophotometry determination of fatty acids as a new assay for lipases is proposed by Walde
(1990) . This simple method for fatty acid determinations in vegetables oils can be carried out with samples of less than 100 mg. 44
2.6. Utilization of Extractives
Wood extractives comprise a large number of chemical entities which have been utilized for different purposes, e.g. dyes, tanning agents and perfumes, or naval stores
(Fengel and Wegener, 1984). Currently, extractives of wood and bark are valuable sources of phenols for the manufacture of naturally based phenol-formaldehyde adhesives and of special products derived from the main wood components.
Division of the extractives present in living trees, wood, bark and foliage can be formulated as follows:
1. Bark extractives obtained by solvent extraction.
2. Wood extractives obtained by means of solvent
extraction or pulping (e.g, kraft).
3. Foliage extractives.
/An overview of these low-molecular-weight silvichemicals is given in Fig. 8 (Fengel and Wegener,
1984) .
Extractives present in the foliage have long been used for their medicinal, nutritive and relaxant values .
The essential oils that can be extracted by steam distillation of foliage are primarily used in the preparation of fragances, perfumes and cosmetics (Keays,
1976) . Rosin Rosin Turpentine ^^Stump extraction j TREE j Topping ^> Turpentine Maple syrup
Solvent Solvent extraction extraction
Tannins Tannins Phenolic Terpenes acids Lignans Waxes Colouring matter
Figure 8. Chemical products derivable from extractives (Fengel and Wegener, 1984) 46
Extractives present in pulp-mill waste liquors also deserve attention both because of their importance in waste treatment and for their insecticidal (toxic) effects
(Sameshina et al., 1980; Sameshina et al., 1986). Several pulping waste-liquors have been reported to have termiticidal activity (Sameshina et al., 1978; Sameshina et al., 1980) or in high enough concentrations to be toxic to fish (Sameshina et al., 1986).
Very important by-products from kraft pulping are sulfate turpentine and tall oil which are used in the paint and lacquer industry and for some other purposes
(Sjostrom, 1981). Tall oil consists of a mixture of 40-50
% each of fatty acids (i.e. oleic and linoleic) and resin acids with about 10 % unsaponif iables. Most of the crude tall oil is purified and fractionated by vacuum distillation to yield a fatty acid fraction and a resin acid fraction (Sjostrom, 1981). (See Fig. 9).
The most important fields of applications for the fatty acids are: soaps, esters, fatty alcohols, amines, metal soaps, emulsifiers, polyol esters, amides, additives for plastics and others (Knaut and Richtler, 1985).
Currently, an over supply of fatty acids exists due to the fact that world demand for fatty acid methyl esters has declined in recent years. Methyl ester derivatives have better storage stability; they are readily fractionated due to their lower boiling point; they require less 47
Figure 9. Main distillates from crude tall oil after acidification (Sj6str6m, 1981) 48
energy for their production, and are less corrosive. On the other hand, the investment costs associated with their processing are higher than for the fatty acids (Knaut and
Richtler, 1985) .
Numerous studies have been conducted in the United
States on the potential use of fats and oils as fuel for farm equipment and trucks. These studies demonstrated that this is an attractive application in principle and from a market viewpoint, but a very difficult application from a practical viewpoint (Lipinsky et al., 1985).
A very exciting area of application for fatty acids and their derivatives is the cosmetic and drug or pharmaceutical industries. Palmitic, stearic, myristic and short chain fatty acids are of a particular interest in this respect. A list of applications is as follows: shaving creams, bath oils, aerosol hair conditioners, fluid hair conditioners, hand creams, antiperspirants, eye make-up, nail whiteners, shampoos, and face powders
(Kalustian, 1985). 3. METHODOLOGY
3.1. Sample Collection and Preparation
Wood samples were obtained from three living trees of slash pine (Pinus elliottii Engelm.) from Florida. Logs 25 cm long taken at 1.5 m height above the ground were debarked manually and sawn into 1.5 cm disks. The disks were air dried for various periods (24 to 52 weeks) in a
CTH room at 23°C, 65%RH and chipped by hand as required.
Chip samples were ground in a Wiley mill to pass 40 mesh (425 |lm) and to be retained on a 60 mesh (250 |lm) screen. The wood meal was allowed to air dry in the CTH room at 23+ 2°C and 65± 2% relative humidity.
3.2. Chemical Analysis of Wood
Air dried wood meal samples were taken for determining the extractive content, acid-insoluble lignin
(Klason lignin) and acid-soluble lignin (UV lignin) according to TAPPI standards T 204 os-76, T 222 os-76 and
TAPPI UM-250, respectively. 50
3.2.1. Wood extractives determination
To determine the effect of heat upon the degradation of extractives, cold methanol maceration extraction was compared with a standard Soxhlet extraction using methanol as the solvent. Furthermore, both the maceration and the
Soxhlet extraction results were compared against the extraction method recommended by TAPPI standard T 204 os-
76.
3.2.1.1. Cold methanol maceration
50 g of wood meal was placed in a 1 L Erlenmeyer flask with a drain hole at the bottom and covered with 300 ml of anhydrous methanol containing known amount of methyl heptadecanoate as an internal standard (concentration ~ 30 ng/fiL) . The mixture was allowed to steep for 54 h at room temperature. The solvent was decanted and filtered on a millipore filter system. The filtrate was concentrated to about 5 mL under reduced pressure in a rotary evaporator at 40°C, transferred quantitatively to a tared evaporation dish and evaporated to dryness in a fume hood. Finally, the dish was placed in a freeze-drier for 48 h and finally weighed. 51
3.2.1.2. Methanol Soxhlet extraction
Wood meal samples were extracted in a Soxhlet apparatus for 54 h with anhydrous methanol containing known amounts of methyl heptadecanoate as an internal standard (concentration ~30ng/|xL) . For samples weighing approximately 40 g, about 300 mL of anhydrous methanol and some boiling stones were used. Extraction was performed at a siphoning rate of 4 cycles per hour.
The extract was evaporated under reduced pressure in a rotary evaporator at 40°C, transferred quantitatively to a tared evaporation dish and evaporated in a fume hood to dryness. Subsequently, the samples were dried in a freeze drier for 48 h and finally quantified.
3.2.1.3. Ethanol-benzene Soxhlet extraction
Ethanol-benzene extraction was carried out according to TAPPI standard T 204 os-76.
3.2.2. Acid-insoluble lignin
Air-dried, extractive-free wood meal was used for determination of the acid-insoluble lignin (Klason lignin) content according to a modified TAPPI standard T 222 os-76 52
method. A modification of the secondary hydrolysis was used in this procedure. After dilution with water to 3%
concentration of sulfuric acid, the solution was treated
in an autoclave under steam pressure of 1.5 bar (20 psi) and at 127.5°C for 1 h.
The insoluble material was allowed to settle
overnight. Then, the clean supernatant was carefully decanted through a medium porosity filtering crucible.
Finally, the lignin was quantitatively collected by vacuum
filtration onto the crucible and oven-dried at 105± 3°C
for 1 h. The acid filtrate was saved for the acid-soluble
lignin (UV lignin) content determination.
3.2.3. Acid-soluble lignin
Though lignin is insoluble in strong acids, small
amounts are dissolved during Klason lignin determination.
This acid-soluble lignin (UV lignin) was determined
according to TAPPI UM 250 in combination with T 222 os-74
(Klason lignin).
UV absorption measurements of the acid filtrate were performed at 2 05 nm wavelength on a Shimadzu UV-Visible
recording spectrophotometer (UV-160).
The acid soluble lignin content was calculated by using the following equation: 53
Lignin (%) = B x V x 100 1000 x W
where: B = lignin content (g/1000 mL),
V = total volume of solution,
W = oven-dry weight of wood meal
B can be calculated from:
B = A x D 110 .
where : A = UV absorbance at 205 nm D = dilution factor 110 = absorptivity, e
3.3. Preliminary Studies for the Characterization of
Resin- and Fatty Acids
3.3.1. Gas chromatographic studies
Gas chromatography was carried out with a Hewlett-
Packard 5890A gas chromatograph equipped with a flame ionization detector and a HP 3396A integrator. The reports generated on the HP 3396A printer, after each chromatographic run, were transferred to a computer for data storage.
After several trials using different stationary phases, HP-5 was chosen as the stationary phase due to its best resolution for the resin acids and DB-225 for its best resolution of the fatty acids. For identification and 54
quantification of resin- and fatty acids these two capillary columns were used.
Resin acids were analysed on a HP-5 fused-silica cross-linked bonded phase capillary column (25 m, 0.2 mm,
0.33 (lm) . The temperature program was set for 5 min at
40°C, for 30 min at 15°C/min to 215°C and for 30 min increase at 3°C/min to 250°C. The temperature of the injector was set at 200°C and that of the detector at
300°C. The injection volume was 1.4 |1L in the splitless mode. Helium was used as the carrier gas at a flow rate of
1.7 mL/min.
Fatty acids were resolved on a DB-225 J&W fused- silica megabore column (15 m, 0.537 mm, 1.0 Jim). The runs were performed isothermally at 170°C. The temperatures of the injector and detector were 200°C and 300°C, respectively. The injection volume was 1.4 (IL in the splitless mode. Helium was used as the carrier gas at a flow rate of 5.0 mL/min.
3.3.1.1. Methylation of resin- and fatty acids
Methylation of both resin- and fatty acids were carried out with fresh diazomethane (CH2N2) prepared according to de Boer and Backer (1963). The diazomethane generating system was constructed according to de Boer 55
and Backer (1963) from common components available in the laboratory which can be easily dismantled for storage.
The generator system was clamped in a fume hood behind an explosion proof shield. The esterification apparatus is a modification of the one proposed by Levitt
(1973) and consists basically of a diazomethane generator, source of inert gas and the esterification receptacle
(Fig. 10). The generator is a 360 mm long x 20 mm diameter test tube equipped with a ground joint which is joined to a glass bulb having three side arms. One of these side arms is used to connect the bulb to a nitrogen gas source, another one holds a small dropping tube with a stopcock and the third side arm connects to the esterif ication receptacle. In the test tube 10 mL of each of diethyl ether and 2-ethoxyethanol and the appropriate amount of N- methyl-N-nitroso-p-toluenesulfonamide* are placed. The test tube is then connected to the bulb. Inert gas (i.e. nitrogen) is passed through the system for approximately
30 seconds, while at the same time 2 mL of 60% aqueous potassium hydroxide is added to the dropping tube. The gas
flow is then interrupted and the stopcock is opened to allow the KOH to drain into the generator. The test tube
is heated in a water bath to 70°C. After closing the
stopcock the gas flow is resumed at a rate of 1-2
*. The amounts of diazomethane generator used for individual and mixed samples were 0.6 and 2.5 g , respectively. 56
Figure 10. Apparatus used for methylation of the resin and fatty acids 57
bubbles per second. At this point, the ethereal diazomethane generated is swept out of the generator by the nitrogen gas and is introduced into the sample by means of a Pasteur pipet during a fixed time (Section
3.3.1.1.1). The sample is dissolved in an appropriate solvent (Section 3.3.1.1.2)
The sample is then set aside for 1 to 2 min to allow the esterification to be completed. Finally, the esterified solution is purged with nitrogen gas in order to sweep out the excess diazomethane. At this point the sample is ready for GC and GC-MS analysis.
After the esterification is finished, the excess ethereal diazomethane in the generator is vented into the fume hood and 10% acetic acid is added dropwise to destroy any traces of unreacted nitrosoamide and/or diazomethane and to neutralize the base.
3.3.1.1.1. Time of methylation reaction
The extractives had to be derivatized to increase their volatility for GC analysis. Methyl ester derivatives of resin- and fatty acids are the most common derivatives for gas chromatographic analysis (Fourie and Basson,
1990) . Most of the published techniques for methylation suggest the dropwise addition of freshly prepared ethereal 58
solution of diazomethane into the sample until it just
attains a faint yellow color (Levitt, 1973; Zinkel and
Han, 198 6) . The amount of diazomethane delivered to the
sample during methylation depends on factors such as: the
flow of the nitrogen gas (carrier of the diazomethane produced) , the length of time of exposure to the gas
stream (bubbling), the temperature of the water bath of the generator, and the amount of nitrosoamide added.
Generally, 1.5 to 2 min are needed for the pale yellow color to show up in the sample solution to indicate
an excess of diazomethane. According to Zinkel and Han
(1986) methylation of dehydroabietic acid in ether/methanol (9:1) was fully completed after 1 min (See
Table 9).
Table 9. Rates of methylation of dehydroabietic acid with diazomethane in various solvents.(Zinkel and Han, 1986)
Reaction Time* Solvents 5 min 3 min 1 min
Benzene 97 % 91 % Toluene 95 % 96 % Ether 95 % 34 % 11 "5 Ether/MeOH (9:1) 100 % 100 % 100
* Add 5 to 15 sec for evaporation of diazomethane. 59
When working with colorless model standards, it is easy to monitor the methylation reaction since an excess of diazomethane is detected by the yellowing of the solution. However, in the case of colored solutions (i.e. wood extracts) the appearance of the yellow color is camouflaged by the coloring materials in solution. For this reason, it was necessary to devise an alternate means of sensing the completion of the methylation reaction. As an alternative, methylation of colored solutions (i.e. wood extracts) was performed at fixed times.
Thus a series of experiments were performed in order to determine the optimum time for complete methylation of the resin- and fatty acids. Known amounts of dehydroabietic acid and methyl heptadecanoate (internal standard) were dissolved in dichloromethane-methanol (9:1) and refluxed with freshly prepared diazomethane for 1.5,
2.0, 2.5, 3.0, 3.5, 4.0, 4.5 and 5 min periods. After the indicated time, the reaction was stopped by evaporating the excess of diazomethane under a stream of nitrogen gas.
The samples were transferred to a 25 mL volumetric flask and the final volume made up with dichloromethane and then analyzed by gas chromatography (GC). 60
3.3.1.1.2. Solvent selection for methylation
In this experiment, palmitic, dehydroabietic and abietic acids were methylated in three different solvents: ether-methanol (9:1), dichloromethane-methanol (9:1) and methanol. Known amounts of methyl heptadecanoate were added to these solutions as internal standards.
During these experiments the only variable was the reaction time, while all other parameters for methylation remained constant.
3.3.2. Saponification of esterified fatty acids
Saponification was carried out according to Ekman
(197 9) and the products analysed by GC and GC-MS.
Fractions to be saponified were evaporated to dryness prior to the addition of a 0. 4N KOH solution in 90% ethanol. This mixture was allowed to stand for 4 h at 702C to allow saponification of the esters. At the end of the reaction, the mixture was diluted with water (1:1 v/v) and
acidified with 0. 4N H2S04. The acid constituents were isolated by successive extractions with diethyl ether. The combined extracts were evaporated and redissolved with a dichloromethane-methanol (9:1) mixture prior to methylation. The resulting resin- and fatty acids were analysed by GC as described above. 61
3.4. Characterization of Resin- and Fatty Acids from Wood
Characterization of resin- and fatty acids were performed in a similar way for the cold methanol maceration, methanol Soxhlet, and ethanol-benzene Soxhlet
extractions. Crude extracts were taken after freeze-drying
and divided into two portions. The first part was methylated directly for the analysis of resin acids and
free fatty acids, and the second sample was saponified and
later methylated in order to account for the total fatty
acid content of the wood.
The analytical procedure for the determination of
resin- and fatty acids present in wood consisted of three major steps: 1) removal, concentration and quantification
of the total extractives, 2) saponification and/or
methylation of resin- and fatty acids, and 3)
identification and quantification of individual resin- and
fatty acids by GC and GC-MS. An abbreviated sequence is
shown in Fig. 11.
3.4.1. Gas chromatographic analysis
Analysis of resin acids was performed on a HP-5
fused-silica cross-linked bonded phase capillary column
(25 m, 0.2 mm, 0.33 p:m) and that of the fatty acids on a
DB-225 fused-silica megabore column (15m, 0.537mm, 1. Ofim) . Wood Wood Meal
Maceration Soxhlet
CH3OH CH3OH 54 h. 54 h.
1.Rotary Evaporator Extract ' 2.Freeze—Drying Extract
WE=Total Extractives
1 .Methylation 1 .Saponification 1 .Methylation 1 .Saponificatio 2.GC/GC-MS 2. Methylation 2.GC/GC—MS 2. Methylation 3. GC/GC—MS 3. GC/GC—MS
Resin Acids Resin Acids Resin Acids Resin Acids + + + + Free Total Free Total Fatty Acids Fatty Acids Fatty Acids Fatty Acids
Figure 11. Flow diagram for the removal, identification and quantification of the resin and fatty acids present in slash pine wood. Acids were determined as their methyl ester derivatives 63
Conditions for both determinations were given earlier
(See section 3.3.1).
3.4.2. Preparation of calibration curve
Resin acids were obtained from Helix Biotech
Scientific Ltd. and the fatty acids were secured from
Aldrich Chemicals Company, Inc. Linoleic and linolenic acids were obtained as free acids while palmitic, stearic and oleic acids were bought as their methyl ester derivatives. Methylation of the different acids was carried out by refluxing them with a freshly prepared diazomethane solution during a 4 min reaction time. All samples were dissolved in dichloromethane-methanol (9:1) prior to methylation.
Calibration curves were prepared by using standard solutions of resin- and fatty acid methyl esters at three different concentration levels, all containing the same amount of methyl heptadecanoate as internal standard.
Response factors for all resin- and fatty acids were calculated by the integrator. 64
3.4.3. Gas chomatography-mass spectrometry (GC-MS)
The mass spectra were recorded with a Finnigan 1020 mass spectrometer coupled to a Perkin Elmer 3B gas chromatograph. The temperature program was similar to that used in GC. The temperature of the injection port was set at 250°C, and the ion source was kept at 95°C. Split injection mode at a (100:1) ratio was used with an injection volume of 1.0 u,L. The ionization voltage was
70eV and the resolution was set at 1000. The scanning mass range was 40 to 450 in 1 sec.
3.5. Organosolv pulping of slash pine
Manually debarked disks of slash pine wood were stored for 24 weeks in the controlled temperature and humidity (CTH) room at 23± 2°C and 65± 2% relative humidity. Chips were prepared by hand cutting on a guillotine to a standarized chip size: 2.5 cm x 1.5 cm x
0.3-0.5 cm. Chip moisture content was determined before cooking. 65
3.5.1. Pulping conditions
Series of pulps were prepared from slash pine chips by treatment with a pulping liquor and the conditions
(Chang and Paszner, 1982; Paszner and, Chang 1983) given below:
Wood slash pine
Charge of A.D. chips, g ....13 - 14
Pulping liquor
Methanol-H20, % 80 : 20
Liquor-to-wood ratio ..10 : 1
Catalysts
CaCl2, M 0.025
Mg(N03)2, M 0.025
Cooking temperature, °C ....205
Cooking time, min 5, 20, 40 and 60
Pressure, bar a) High pressure (197)
b) Normal pressure* (40)
*Normal pressure pulping is accomplished without pressurizing the vessels prior to immersion into the boiling bath. 66
3.5.2. High pressure organosolv pulping
Four different pulping times were set to determine the rate of extractives removal together with that of residual lignin and also to determine the pulp yield.
Cooks were made in a 175 mL vessel which was purged with argon at elevated pressure prior to its immersion into a preheated glycerol bath which was maintained at 205°C. At each cooking time three or four cooks were performed in order to get statistically representative results.
After each cooking trial, the vessel was quenched in a cold water bath until the inside pressure was low enough to open it. The pulping liquor was carefully decanted and the cooked chips removed from the vessel, washed with fresh cooking liquor and rinsed with methanol. All the solvent fractions were collected as the "initial black liquor".
The cooked chips were disintegrated in a 250 mL
Waring blender with fresh methanol for one minute and the disintegrated fibers were collected on a 15 cm Buchner funnel (pre-weighed filterpaper was used) and washed twice with methanol (60 mL) , once, with water (25 mL) and then with methanol (30 mL). The filtrate, containing additional resin- and fatty acids and dissolved lignin from the pulp, was combined with the "initial black liquor" to give the
"mother black liquor". 67
Lignins, which precipitated on cooling from their respective mother black liquors ("Lignin I"), were set aside for quantitative analysis, and also for identification and quantification of the resin- and fatty acids adsorbed onto their surface. (See section 3.5.2.2)
Removal of "Lignin I" from the "mother black liquor" left the "black liquor A" containing most of the extractives and a soluble lignin. The final volume of the filtrate, containing the internal standard, was made up to
250 mL in a volumetric flask and saved for GC and GC-MS analysis. An analytical scheme is outlined in Fig. 12a.
Aliquots from "black liquor A" were taken for resin- and fatty acid characterization (50 mL) and also taken for the quantitative analysis of the lignin solubilized in the black liquor. An aliquot of 150 mL of "black liquor A" was diluted in 1500 mL of water to provoke precipitation of the soluble lignin designated as "Lignin S"* . The precipitate was allowed to settle overnight, then vacuum filtered, transferred to a tared aluminum dish and finally freeze-dried for 24 h. This lignin was quantified and also taken for Gel Permeation Chromatography (GPC) molecular weight analysis on an HPLC (Section 3.6.1).
*"Lignin S" recovered by direct precipitation of the cooking liquor (i.e. before liquid-liquid extraction of the extractives) it will be contaminated by proportional amounts of the coprecipitating extractives removed during pulping. Decant/ Blending/ Washing Black Liquor Chips Washing Pulp + Lignin (Lignin + Entrapped Lignin + Extractives + + Extractives) 4- Extractives
Pulping Filtration/ Washing
Yield
Mother Black Liquor Pulp ^Lignin — lij -< + Lignin (Fibers) + Extractives + Extractives Kappa Number Soxhlet Lignin—P Filtration CH3OH Lignin— I + Fibers + Extractives Extractives
Dissolution co Fibers THF/Acetone/ Black Liquor "A" CHjOH + Extractives Lignin— S + Dissolved Lignin
Lignin Liq-Liq Ext. + Extractives (Et20) Extractives Liq-Liq Ext.
Extractives (Et20)
Residual Lignin Black Liquor "F"
Figure 12a. Flow diagram for the recovery, identification and quantification of the resin and fatty acids in the black liquor and pulp after high ^pressure organosolv pulping of slash pine wood Lignin II is total recoverable lignin after pulping 69
The resulting pulps were air dried in the CTH room
and samples taken for pulp yield (unscreened) , Kappa number and residual resin and fatty acid content determinations. Kappa numbers were obtained according to
TAPPI standard T 236 os-76.
3.5.2.1. Resin- and fatty acid removal and
characterization from the black liquor
The analytical procedure for determining the resin-
and fatty acids present in the black liquor, lignin and pulp consisted of three major steps: 1) isolation and
concentration, 2) saponificatio-n and/or methylation of the
resin- and fatty acids, and 3) identification and quantification of the resin- and fatty acids by GC and/or
GC-MS. Reference to the various samples is made as
outlined in Fig. 12a.
"Black liquor A" collected after removal of "Lignin
I" was transferred to a 250 mL volumetric flask and 10 mL
of methyl heptadecanoate (-30 ng/u.L) was added as an
internal standard. The recovery of the resin- and fatty
acids was carried out by liquid/liquid extraction with
diethyl ether using a 250 mL separatory funnel.
Since the pulping black liquor (methanol-water phase)
contained both the extractives and the soluble lignin a 70
solvent was required for the selective removal of the resin- and fatty acids (extractives in general), leaving the lignin and sugars in solution. In addition to this consideration, it was necessary to look for a solvent system that would enable the removal of the extractives without emulsification and precipitation of the dissolved lignin and thus to avoid loses of the extractives by adsorption to the precipitated lignin or any other artifact. Lignin precipitation follows removal (recovery) of the methanol from the black liquor. Therefore, it was necessary not only to selectively remove the extractives from the black liquor, but also to determine the proper proportions of the solvents at which selective polar/non- polar phase separation took place, without solvent emulsification and precipitation of the lignin. The solvent also had to be a poor lignin solvent. The extractives were usually carried by the non-polar solvent, while the lignin remained soluble in the polar (methanol- water) phase.
After testing different solvents (i.e. petroleum ether, chloroform and diethyl ether), diethyl ether was chosen as the solvent for the extraction due to its good dissolving power for the resin- and fatty acids. 71
3.5.2.1.1. Liquid-Liquid Extraction
No suitable phase diagram was available for the ternary water-methanol-ether mixture, and thus first a proper phase diagram had to be prepared. Selective liquid phase separation of the ternary mixture (methanol-water- diethyl ether) was difficult to attain. A phase diagram was constructed based on an equilateral triangle. In turn, the corners were assigned 100% concentration (or 0%) for each of the three solvents. On each side of the triangle the percent ratios of the percentages of the two solvents joined by that particular side were plotted .
During initial experiments, known proportions of the water-methanol mixture were placed in 25 mL beakers and diethyl ether was added from a 10 mL buret (0.01 mL) until phase separation was observed to occur. Since all three solvents were colorless, accurate visual perception of the phase separation was very difficult. In order to overcome this difficulty it was necessary to select a dye such that at the point of separation it should be present either in the ether phase or in the water-methanol phase. Several dyes were tested. The best dyes for this purpose proved to be "Fuchsin" and "Aniline Blue Black", the latter being selected as the more appropriate for these experiments.
A series of different proportions of the water- methanol mixture were placed in a 25 mL beaker together 72
with two drops of a water solution of aniline black blue and mixed together before the addition of the diethyl ether. After addition of known amounts of ether, the mixture was mixed with a glass rod for 5 sec and left standing for about 5 to 7 sec to see if phase separation took place. Five to seven attempts were made for each trial before finding the minimal amount of ether needed for phase separation with a minimum of intersolubility of the solvent phases.
By taking the obtained volumes of the diethyl ether and by knowing the initial volumes of the water and methanol solvents, the three ratios of the combinations of water/methanol, ether/water and ether/methanol were plotted on the respective side of the triangle.
Perpendicular lines were drawn from these three points and their intersection plotted as the point of phase separation for that particular combination. Joining all of these points gave a curve which represented all the points at which phase separation takes place. This curve could be used to predict the proper proportions of these three solvents if phase separation were required. Predictions for phase separation from any point on this curve can be obtained by drawing perpendiculars to each side of the triangle originating from that point on the curve.
Similar attempts were made with different starting combinations of ether/water and ether/methanol mixtures 73
and adding to these mixtures methanol and water, respectively, to reconstruct the phase separation curve.
These tests provide confirmation and new points on the phase separation curve. Further, this approach also allows liquid/liquid extraction to be approached from any water/methanol or ether/methanol ratio and provides further opportunity to purify the extractives by washing.
3.5.2.1.2. Efficiency of the liquid-liquid extraction
Recovery of the resin- and fatty acids from the black liquor, by liquid-liquid extraction, were studied by taking water-methanol mixtures with ratios in the range of
1.0 (50:50) to 1.5 (60:40) with known concentrations of the resin- and fatty acids. Aliquots of 50 mL of these solutions were placed in a separatory funnel and extracted with diethyl ether. The volume of diethyl ether needed for phase separation for each particular ratio was determined and plotted in Fig. 19 and 20. One minute shaking was followed by 3 min standing to allow phase separation. This extraction was followed by three additional extractions with 30 mL each of diethyl ether. Then, the combined ethereal extracts were evaporated to almost dryness on a vacuum rotary evaporator under reduced pressure and later dried in a freeze-drier for about 24 h before methylation.
Prior to methylation the freeze-dried extracts were 74
redissolved first with methanol and then in dichloromethane so that the final solution was a mixture of dichloromethane-methanol (9:1). The methylated samples were transferred to a 25 mL volumetric flask and the final volume made up with dichloromethane. These samples were ready for GC analysis.
3.5.2.1.3. Quantification of the resin and fatty acids in the black liquor
When working with the black liquor, and in order to obtain the right proportions, aliquots of 50 mL of black liquor (~ methanol-water, 80:20) were combined with 40 mL of water and 50 mL of diethyl ether (Omnisolv grade) in a
250 mL separatory funnel. The final proportions of methanol-water-diethyl ether were adjusted to 40-50-50.
Funnel extraction, drying, methylation and GC analysis were performed as before (Section 3.5.2.1.2.). During these extractions no emulsions were formed and therefore losses of the resin and/or fatty acids were very unlikely to happen. 75
3.5.2.2. Resin- and fatty acids removal from lignin
Lignin that precipitated on cooling of the black liquor ("Lignin I") , which was assumed to contain some adsorbed extractives and some fiber fragments, was transferred to a tared medium porosity crucible. Lignin and extractives were dissolved by using tetrahydrofuran
(THF), acetone and methanol, sequentially and the remaining fibers were oven dried at 105+ 2°C for mass balance calculation (yield correction). The organic lignin- and extractives solution (THF, acetone, methanol) were evaporated and the residue redissolved in methanol- water (80:20), transferred to a 250 mL volumetric flask containing a known amount of internal standard (-30 ng/|j.L) . An aliquot (50 mL) of this solution was taken for resin- and fatty acid identification and quantification as described before (See Section 3.5.2.1.3). A 150 mL portion of this lignin solution was diluted in 1500 mL of water in order to precipitate the lignin and quantified it in a similar manner as for "Lignin S" (See Section 3.5.2).
3.5.2.3. Resin- and fatty acids removal from pulp
Resin- and fatty acids left in the pulp were extracted by air-drying the pulp first,' followed by 76
Soxhlet extraction for 54 h using anhydrous methanol
(Omnisolv grade).
On removal of the resin- and fatty acids from the pulp, some lignin was co-removed together with the extractives, which was designated "Lignin P". The total extract, containing extractives plus "Lignin P", was redissolved in methanol (10 mL) and the final volume made up to 250 mL with methanol-water (80:20) in a volumetric flask. An aliquot of 50 mL of this solution was analyzed for resin- and fatty acids as described before (Section
3.5.2.1.3) for wood analysis above. Another aliquot of 150 mL was diluted in 1500 mL of water in order to precipitate the lignin. This lignin was quantified in a similar way as for "Lignin S" (See Section 3.5.2) and also taken for GPC analysis.
During this Soxhlet extraction with methanol , the extractives and lignin were refluxed for 54 h. Due to the possibility of lignin recondensation a known lignin sample was taken for comparison. A sample of 300 mg of the
"Lignin S-20" (Mw= 1390 and Mn= 678) was refluxed with 160 mL of methanol as mentioned above. The resulting lignin solution was concentrated under vacuum to ~15 mL and then diluted with 150 mL of water in order to provoke precipitation of the lignin. This lignin was filtered on a micropore filter, air dried over night, then freeze-dried for 24 h and finally taken for GPC analysis. Comparison of 77
the original "Lignin S-20" and the one after refluxing
showed the same Mw and Mn values, i.e., no recondensation occurred due to heating (refluxing) in methanol.
3.5.2.4. Complementary analysis of lignin from the high pressure 60 min pulping
Complementary analyses were performed on the resin-
and fatty acid samples of the mother black liquor, the precipitated lignin and the pulp obtained after 60 min
cooking. Contrary to the fractionation procedure followed
for the extractives analyses after the 20, 40 and 60 min cooking, a dilution of the mother black liquor with water
(1:10 ratio) rendered another type of lignin ("Lignin
II") . This "Lignin II" was isolated, freeze-dried (Section
3.5.2.) and taken for further molecular weight distribution analysis by size exclusion chromatography on an HPLC (Section 3.6.1).
Resin- and fatty acids were isolated, identified and quantified in the black liquor (Section 3.5.2.1.3) and in the lignin (Section 3.5.2.2). These extracts were ready
for GC and GC-MS analyses. 78
3.5.3. Normal pressure organosolv pulping
Normal pressure pulping performed at autogenous pressures developed by the 80:20 cooking liquor was conducted as a complementary experiment to the high pressure trials. Both normal and high pressure pulping were conducted in a similar manner. The black liquor and the pulp were handled as described before (Sections
3.5.2.1. and 3.5.2.3.). An analytical scheme is outlined in Fig. 12b.
For the normal pressure pulping, the cooked chips were removed from the vessel, washed with acetone (30 mL), and then with methanol (30 mL) and water (40 mL) . The black liquor and the wash fractions were collected as the
"initial black liquor". On standing overnight a lignin
("Precipitated Lignin") precipitated from this black liquor which was isolated and saved for GPC analysis. The residual black liquor was called "Black Liquor R".
The cooked chips were disintegrated in a 250 mL
Waring blender with acetone (80 mL) for one minute and the resulting fibers were collected on a 15 cm Buchner funnel
(pre-weighed filter paper was used) and washed twice with acetone (40 mL) and water (30 mL) and finally with 30 mL of acetone. On standing of this filtrate a new amount of lignin precipitated ("Entrapped Lignin") which was isolated and taken for GPC analysis. Decant/ Blending/ Washing Black Liquor Chips Washing Pulp + Lignin (Lignin + Entrapped Lignin + Extractives + + Extractives) + Extractives
Pulping Filtration/ Washing ^/'^Washing
Washings Pulp "Initial Black Liquor" + Extractives + Extractives + Lignin + Extractives + Lignin
Filtration Filtration Precipitated Trapped Lignin Lignin
GPC " Black Liquor R" Residual GPC + Lignin Washings + Extractives + Extractives
Liq-Liq Ext.
(Et20) Extractives
Dissolved Lignin GPC
Fiaure 12b Flow diagram for the recovery, identification and quantification of Figure HD. *XO ^ ^ ^ LIQUQR AND PULP AFFCER NORMAL
pressure organosolv pulping of slash pine wood 80
After the liquid-liquid extraction of the resin- and fatty acids from the "Black Liquor R", a small fraction of lignin ("Dissolved Lignin") precipitated out of the solvent system. Precipitation of this lignin type may be caused in part by the higher water concentration present at the end of the extraction. Again, this lignin was isolated and taken for GPC analysis.
3.6. Molecular Weight Distribution of Lignins After High
Pressure Pulping
In summary, different lignins were obtained after pulping based on their solubility. A lignin which precipitates on standing of the "mother black liquor" was called "Lignin I". A second type of lignin, which remained in solution after the filtration of "Lignin I", was designated "Lignin S". These soluble lignin types were the lignins S-20, S-40 and S-60 obtained after the 20, 40 and
60 min pulping experiments. A third type of lignin
("Lignin P") was co-removed from the pulp after Soxhlet extraction of the pulp extractives with methanol. Finally, by using a different procedure for precipitation of the lignin in the black liquor, namely a dilution of the whole black liquor in water (1:10 ratio), rendered the new type
"Lignin II" . Lignin II contains Lignin I and Lignin S. 81
Molecular weight distributions of these lignins were determined by size exclusion chromatography on an HPLC.
3.6.1. GPC Analysis
3.6.1.1. GPC conditions
The molecular weight distribution (MWD) of the different lignins obtained after organosolv pulping was estimated by using a size exclusion chromatographic method. All lignin samples were dissolved in tetrahydrofuran (THF) at 0.5% (w/v) for injections into the HPLC.
The instrument setting was as follows: A HPLC system equipped with an Isocratic Spectra Physics H8810 Pump, a
Rheodyne 7125 injector loop, a GH8P guard column, and four
30 cm long analytical TSK H columns in series (1000H,
2500H, 3000H and 4000H containing spherical, cross-linked polystyrene/divinyl benzene particles of 8 to 10 |im diameter,packed in tetrahydrofuran).
Tetrahydrofuran was the eluent, and the eluting lignin fractions were monitored by measuring the absorbance at 280 nm wavelength using a Kratos Spectroflow
757 UV/VIS detector. Output signal was transferred to a
Spectra Physics 4290 integrator-plotter. 82
3.6.1.2. Calibration curve
Calibration of the size exclusion chromatography
columns based on relative elution time (VR) was obtained by using the polystyrene standards of different molecular weights. Out of the measured values of molecular weight
distribution, weight average molecular weight (Mw) and
number average molecular weight (Mn) were calculated by instrument procedure.
Replotting of the detector responses by using the MTS mainframe graphics package TELLAGRAF, enables easier interpretation and differentiation of the various lignin types.
3.6.1.3. GPC Injections
All organosolv lignins obtained were readily soluble in tetrahydrofuran (THF). Therefore, there was no need to derivatize the lignin samples. Each injection sample consisted of a 20 UX of the 0.5% (w/v) lignin solution in
THF. All analyses were performed at a flow rate of 1.0 mL/min of THF. A minimum of three replicates for each individual lignin type was taken for these analyses. 83
4. RESULTS AND DISCUSSION
4.1. Wood Species
The generic composition of slash pine (Pinus eliottii
Engelm.) wood extractives has been described earlier in the literature by Zinkel and Foster (1980) . Accordingly, confirmatory qualitative and quantitative analyses were performed on the wood extractives of this species.
Although considerable work has been done on the chemical composition of the extractives of most conifers, nothing has been published on the behaviour of such extractives during organosolv (solvent) pulping thus far.
The baseline chemical composition of the wood sample used for this study was investigated. Thereby, the chemical composition of its fatty acid and resin acid fractions could be compared to those found in the literature (Table
5 and 6, respectively). For comparison the tall oil composition of southern pine sapwood and black liquor extractives is also reproduced in Table 7.
The information thus derived was very helpful in further assessing the extractive values for the experimental wood sample and comparing them to those reported in the literature. Particularly, confirmatory analyses were performed on the wood extractives of slash pine to validate earlier findings of Zinkel and Foster 84
(1980) and to study the behaviour of its extractives during organosolv pulping. The known chemical composition of extractives of this species facilitated adequate control in following the fate of extractives noted for this species. This fact also aided in selection and development of the appropriate isolation methodology from the cooking liquor.
4.2. Chemical Analysis of Wood
The major portion of wood in general is comprised of polysaccharides and lignin. Accompaning these components, small amounts of extracellular, so called "extraneous" components are also found in practically all woods. These extraneous components comprise substances that can be removed from the wood by neutral organic solvents. During chemical pulping, wood is treated with chemicals
(inorganic or organic) at high temperature and pressure in order to dissolve as much lignin as possible from the cell wall and the connecting (middle lamella) zones. This leaves the cellulosic portion (pulp) as the raw material for papermaking.
Dissolution of the lignin during pulping is accompanied also by solubilization of the extractive components present in wood. In order to strike a mass 85
balance of the lignin and extractives present in wood, it was required to implement quantitative determinations of the various entities in the slash pine sample.
4.2.1.Determination of wood extractives in the slash pine sample
Since study of the behaviour of the extractives during organosolv pulping was of interest, it was necessary to characterize the resin- and fatty acids in particular before and after the pulping process. Further, it was also necesary to find a proper procedure for their quantitative removal from both the wood and spent cooking liquor without influencing their content and/or chemical structure.
The first concern during the qualitative and/or quantitive determination of the extractives was the effect of heat upon their degradation. It was first expected that elevated temperatures might degrade (change) some of the extractives. For this reason, cold methanol maceration extraction was compared with Soxhlet extraction in which hot methanol is cycled between the boiling reservoir flask and the extraction chamber (barrel). Thus the extractives removed from the wood are exposed to boiling solvent in the solvent reservoir or round bottom flask. 86
The total extractives content of the wood after 6 weeks of storage obtained by the methanol maceration extraction was 4.2% (average of three replicate determinations) and by the methanol Soxhlet extraction
4.3%. From these experiments it was found that the method of extraction had no significant effect on the quality and quantity of extractives in the sample as determined by the maceration and hot Soxhlet extraction techniques.
Therefore, it can be stated that heating did not cause degradation of the extractives during their removal from wood.
Furthermore, both the methanol maceration and methanol Soxhlet extractions were compared against a standard ethanol-benzene (1:2) Soxhlet extraction, conducted according to TAPPI standard T 204 os-76. The content from the latter extraction was 3.9%, which is slightly lower than that found in the previous extraction modalities.
Quantification of the extractives present in wood is a very difficult task. It must consider not only factors which can affect their content in the standing tree, but also factors that can influence the methodology used for their quantification. It is known that biological factors like the month of felling (Bishop and Marckworth, 1933), environment, genetic variations (Stanley, 1969), geographical location (Swan, 1968) , seasoning (Assarsson, 87
1969; Springer, 1978) , part of the tree (Lorbeer and
Kratzl, 1985) and age (Stanley, 1969) have noticeable effects on the extractive content in different woods. In addition to the previous considerations, it is very important to know the conditions of storage and the elapsed time between the cutting and the execution of the chemical analysis.
4.2.2. Lignin from wood
The average acid-insoluble lignin (Klason lignin) content of a representative sample found in slash pine wood was 2 6.8 %. The lignin content was determined according to TAPPI standard T 222 os-76. Since some lignin is also solubilized in highly concentrated acids (i.e.
H2S04 at 72%), the total lignin was determined by adding the acid-soluble lignin (UV lignin) to the Klason lignin.
The acid-soluble lignin was 1.4%. Therefore, the total lignin, which is the sum of Klason and UV lignin, was
28.2%. 88
4.3. Preliminary Studies for the Analysis of Resin- and
Fatty Acids
4.3.1. Gas chromatographic studies
During splitless injection, the solvent selected for injection must fulfill some basic considerations. These should include the ability to dissolve the sample, to provide a good "solvent effect", and to be compatible with the column stationary phase. The most widely used solvents for splitless injection are: dichloromethane, chloroform, carbon disulfide, diethyl ether, n-hexane and iso-octane
(Freeman, 1981). In addition to the basic considerations, selection of CH2CI2 as the solvent for injection was based on its lower boiling point (40QC). This characteristic rendered good chromatograms with minor solvent tailing and was suitable for quantitative calculations by the integrator. It must be added that quantification of resin acids was not jeopardized by the solvent tailing since these acids elute quite late in the chromatogram (after 40 minutes in the HP-5 capillary column). In the case of the fatty acids, even though they emerge quite early in the chromatogram (after 5 min in the DB 225 megabore column), no interference by the solvent peak was detected.
Quantitative analyses were performed by using the internal standard method. This method does not require 89
either exact or consistent sample volume nor consistent response factors since the latter are built into the method. This method is very useful if reproducibility is a problem, and in situations where one does not want to perform frequent recalibrations. The internal standard chosen for this method cannot be a component of the sample, and a known amount of it is added to each sample.
According to Miller (1988) every internal standard should meet several criteria:
"-It should elute near the peaks of interest, -It must be well resolved from them, -It should be chemically similar to the analytes of interest and not react with any sample components, and -Like any standard, it must be available in pure form".
Chromatographic analyses were based on the process of measuring the peak areas which consisted of integrating the area under the peaks. This process also converts analog signals into a digital signal necessary for computer calculations.
All resin- and fatty acids were methylated before GC and GC-MS analysis. There is a choice of a number of reagents for methylation but specifications for quantitative conversions have not been defined. Among these specifications, time of reaction and solvent for methylation were inconsistent, and investigations for 90
ascertaining the best conditions were necessary to fully develop a reliable and reproducible method.
4.3.1.1. Time selection for methylation
Preparation of methyl esters (complete methylation) is an important aspect of identification and characterization of the wood extractives. Considerable efforts were expanded in this study to select the optimum conditions for derivatization of the extractives at hand.
The method of de Boer and Backer (1963) has been confirmed to give good results when diazomethane was used as the methylation agent.
In order to ascertain the time for completion of the methylation reaction for the resin- and fatty acids, a series of methylations were performed where the reaction was allowed to proceed for 1.5, 2.0, 2.5, 3.0, 3.5, 4.0,
4.5, and 5.0 min. Dehydroabietic acid was chosen as the test resin acid for this experiment. Comparisons were based on the ratios of the response areas of the test resin acid relative to the response area of an internal standard (methyl heptadecanoate). Results of these ratio comparisons are reported in Table 10.
From this table it can be seen that at reaction times longer than 3.0 min the ratio testing show no further increase and hence methylation can be considered as being 91
complete. Thus to ensure complete methylation of all future samples a reaction time of 4.0 min was chosen.
Table 10. Ratio testing of the response area of dehydroabietic acid relative to the response area of methyl heptadecanoate after various times of methylation with diazomethane
Time (min) A* resin acid A int. std.
1.5 1.20
2.0 1.20
2.5 1.22
3.0 1.28
3.5 1.28
4.0 1.32
4.5 1.31
5.0 1.32
A= Response area. 92
4.3.1.2. Solvent selection for methylation
According to Zinkel and Han (1986), methylation of resin acids carried out in a single solvent is not as efficient as methylation performed in a mixture of solvents. They found that methylation in either benzene, toluene or ether alone was not completed in a short time period, but the addition of methanol to diethyl ether resulted in an instantaneous reaction (See Table 9).
Esterification with CH2N2, like other reactions, is greatly influenced by solvents (Eistert et al., 1951).
Among the publications to date describing the methylation reaction, several have dealt with the use of ether-methanol (9:1) as the solvent for this reaction.
Intrigued by the speed of the reaction, an attempt was made to extend the number of solvents suitable for methylation to shorten the methylation time and assure complete derivatization.
Methanol/dichloromethane was chosen as an alternative. Methanol was chosen because it was the solvent used for organosolv pulping and because of the good results that Zinkel and Han (1986) and Schlenk and
Gellerman(1960) had with it as a co-solvent. On the other hand, dichloromethane was chosen because it is included among the good solvents for splitless injection (Freeman, 93
1981) . Dichloromethane has also been suggested as good solvent for methylation (Hopps, 1974) .
From the above information, it was decided to test the best solvent effect (or mixture) of ether-methanol
(9:1), dichloromethane:methanol (9:1) and methanol alone.
Results of these methylation studies are given in Table
11.
Inspection of Table 11 reveals that the best response factors for the dehydroabietate, abietate and palmitate methyl esters were those obtained when the methylation was carried out in dichloromethane-methanol (9:1). A low response factor indicates a higher reaction rate.
The results of the three acid models chosen clearly demonstrate that the mixture of dichloromethane-methanol
(9:1) is a better choice as a solvent mixture for methylation of resin- and fatty acids than the ether- methanol previously reported in the literature (Zinkel and
Han, 1986) . Since it was also found that dichloromethane is the best alternative as the solvent for injection Table 11 . Response factors of palmitic-, dehydroabietic- and abietic acids after methylation in 3 solvents
Response Factors
Cone. Et20-CH3OH CH2CI2-CH3OH CH3OH (ng/jiL) (9:1) (9:1)
Palmitic 50 4.70 x 10~4 4.45 x 10"4 4.74 x 10"4
Dehydroabietic 40 3.47 x 10~4 3.25 x 10"4 3.56 x 10~4
Abietic 40 4.51 x 10~4 4.28 x 10"4 4.69 x 10~4
* the known amount (or concentration) Response actor - ^ Measured Response (area or height) 95
(See section 4.3.1) it can be concluded that the mixture of dichloromethane-methanol (9:1) not only allows faster and more complete methylation of the resin- and fatty acids, but also facilitates direct analysis by GC- injections without isolation of these methyl esters.
Zinkel and Han (1986) suggested that proper precautions should be observed in handling methylated samples to prevent oxidative changes. They suggested methyl tert-butyl ether (MTBE) as a good polar solvent, accompanied by additional flushing of the vial with nitrogen before closing it even for very short periods before the GC analysis. They also mention that storage in a nonpolar solvent can provoke oxidation-dehydration reactions of levopimarate and palustrate methyl esters and lead to formation of dehydroabietate.
Nestler and Zinkel (1963) pointed out that methyl levopimarate, though quite labile both chemically, e.g. in acid medium, and thermally, has been found to pass through the column unchanged both chemically and reproducibly in the chromatographic sense. Also they found that when this acid was stored in capped vials as a solution in n-hexane, slow conversion to methyl dehydroabietate took place as the major change and four additional peaks having retention times shorter than methyl levopimarate were observed. One of these peaks showed a retention time similar to that of pimaric acid. 96
Under alkaline pulping conditions the predominant change in the resin acid composition was the partial isomerization of levopimaric to abietic acid (Holmbom and
Ekman, 1978).
4.3.2. Preparation of calibration table
Quantification of resin- and fatty acids was conducted on two different columns and two calibration curves were constructed. A three-level calibration curve was built into the integrator and calculations for individual quantitations were made by the same integrator.
The response factors and relative response areas of the individual resin acids with respect to the internal standard (methyl heptadecanoate) are given in Table 12 and their calibration curves constructed in Fig. 13.
Data for the construction of the calibration curve for the fatty acids is given in Table 13 and the calibration curves are found in Fig. 14. Both resin- and fatty acids provide linear responses within the ranges expected for P. elliottii. 97
4.4. Analysis of Resin- and Fatty Acids in Wood
A high extractive-content, temperate southern conifer wood (Pinus elliottii Engelm.) was examined as a pulpwood source by organosolv pulping. Since it was of interest to investigate the behaviour of the resin- and fatty acids during the lignin solvolysis process, it was necessary to characterize these entities not only in the wood sample, but also in the black liquor, pulp, and the lignin which may precipitate on cooling of the black liquor.
Direct analysis of the resin- and fatty acids was performed without previous separation (purification) from a very complex mixture since numerous other extractives are also present in the wood. This became feasible due to the excellent characteristics of the capillary columns
(fused-silica cross-linked bonded phase i.e. HP-5, 25 m x
0.2 mm x 0.33 Jim) and may have been a result of the appropriate time programming for the GC analysis.
Substantial time was spent on manipulating the chromatogram for achieving such separations. Time- temperature programming turned" out to be an excellent means for separating the major and minor extractive constituents in the samples. By this procedure it became possible to obtain better separation of the major components of interest. Thus each analysis took in excess of 67 min to complete the separation required. Table 12 . Response factors and relative response areas of the individual major resin acids (as methyl esters) of slash pine with respect to the response area of methyl heptadecanoate
Levels 45 ng/ L 68 ng/ L 90 ng/ L RF A ratio* RF A ratio* RF A ratio*
Pimaric 4.10 E-04 1.19 4.22 E-04 1.92 4.79 E-04 2.55
Sandaracopimaric 3.10 E-04 1.59 3.73 E-04 2.29 4.03 E-04 3.15
vO Isopimaric 3.40 E-04 1.55 3.66 E-04 2.45 3.89 E-04 3.18 CO
Palustric 2.73 E-04 . 1.65 3.06 E-04 2.45 4.05 E-04 3.25
Dehydroabietic 3.21 E-04 1.50 3.32 E-04 2.23 4.46 E-04 2.84
Abietic 3.86 E-04 0.84 4.13 E-04 1.27 5.55 E-04 1.57
Neoabietic 3.93 E-04 1.10 4 .54 E-04 1.57 5. 93 E-04 2.12
*A ratio= Response area of resin acid Response area of methyl heptadecanoate Concentration ng/>L
Figure 13. Calibration curves for resin acids (as methyl esters) Table 13 . Response factors, relative response factors and relative response areas of the individual major fatty acids (as methyl esters) of slash pine with respect to the response area of methyl heptadecanoate
Levels
32 ng/ L 45 ng/ L 65 ng/ L
Acids RF R.RF A ratio* RF R.RF A ratio* RF R.RF A ratio
Palmitic 2.16 E-4 1.02 1.22 2.28 E-4 1.02 1.63 2.86 E-4 1.04 2.25
Stearic 2.12 E-4 1.00 1.04 2.24 E-4 1.00 1.38 2.74 E-4 1.00 1.94
Oleic .2.85 E-4 1.34 0.80 3.03 E-4 1.35 1.06 3.72 E-4 1.36 1.48
Linoleic 2.13 E-4 1.01 0.95 2.26 E-4 1.01 1.26 2.79 E-4 1.02 1.75
Linolenic 3.89 E-4 1.83 0.62 4.11 E-4 1.83 0.83 5.04 E-4 1.84 1.16
Response area of fatty acid *A ratio= Response area of methyl heptadecanoate Concentration ng//iL
Figure 14. Calibration curves for fatty acids (as methyl esters) 102
In essence, in spite of the long chromatographic times, these direct analyses saved time, prevented losses of sample components that might occur during separation and reduced the risk of possible chemical alterations
(oxidation and/or isomerization) of the components by reactions with acids, bases or other chemicals customarily used during extraction or separation of compounds of interest in mixed solutions.
4.4.1. Change of extractives in storage
Earlier, researchers found that the composition of extractives in pine wood changed with prolonged storage time, in that concentrations of individual extractives species decreased while others increased due to autooxidation and/or isomerization (Lawrence, 1959) .
In order to validate earlier findings on the fate of the extractives during seasoning, and to study the behaviour of the resin- and fatty acids during pulping, it became necessary to characterize the resin- and fatty acids content of the wood after different time periods of sample storage.
With the purpose of determining the fate of these extractives during storage, an initial characterization of 103
the resin- and fatty acids in processed wood samples was performed after 6 and 24 week exposure in the CTH room. An additional analysis of only the resin acids in wood samples after 52 weeks storage allowed estimation of the isomerization tendencies of the major resin acid constituents after three different storage intervals, i.e., 6, 24 and 52 weeks. Finally, pulping experiments were carried out with wood samples stored for 24 weeks
(almost 6 months). The delay in pulping (storage for 24 weeks) was chosen to produce a seasoned material, thus level the changes which occur with seasoning (Assarsson,
1969). Thus the pitfall of ascribing changes in the extractives, not necessarily brought about by the pulping procedure per se, and misleading interpretation of the results normally obtained with fresh wood samples, was avoided. It can be assumed that at this stage (after 24 weeks) the resin- and fatty acids were in their more stable forms.
4.4.1.1. Analysis of resin- and fatty acids after 6 weeks of storage
Seven resin acids and five fatty acids present in slash pine wood were identified on the basis of comparison of their GC-retention times with those of model compounds and by GC-MS spectra. Oleic, linoleic and linolenic acids 104
were not included in the GC-MS spectral identification and their identification was based only on GC retention times.
Mass spectra of resin- and fatty acids were compared with spectra found in the literature (Zinkel et al., 1971).
Mass spectra of the resin- and fatty acids are given in
Appendix A and B, respectively.
The GC-chromatogram of the Soxhlet methanol extracts from wood stored for 6 weeks is shown in Fig. 15. This chromatogram was taken with an HP-5 column which properly resolved the following resin acids: pimaric, sandaracopimaric, isopimaric, palustric, dehydroabietic, abietic and neoabietic acids. Among the fatty acids only palmitic and stearic were separated properly while oleic, linoleic and linolenic failed to be resolved on this column. Further studies of the fatty acids were performed on wood samples after 24 weeks of storage by using a DB-
225 capillary column which was puchased later.
The GC quantitative analysis of the resin- and fatty acids were related to an internal standard added at an early stage in the extraction procedure. Therefore, minor sample losses were not detrimental during the handling of the extracts due to the presence of the internal standard.
Results are presented in Table 14. Figure 15. Gas chromatogram of the Soxhlet methanol extract from wood stored for 6 weeks under CTH room conditions (Resin and fatty acids: 1. Palmitic, 2 heptadecanoic, 3 + 4 = mixture of oleic, linoleic and linolenic acids', 5! pxmaric, 6. sandaracopimaric, 7. isopimaric, 8. palustric, 9 dehydroabietic, 10. abietic and 11. neoabietic acids). All acids were detected as their methyl ester derivatives 106
Table 14. Resin- and fatty acid composition of slash pine wood after 6 weeks of storage (%)a
Acids13 Free Combined Total
Fatty acidsc:
16:0 0.03 0.14 0.17
18:1, 18:2, 18:3d 0.29 0.84 1.13
18:0 0.02 0.06 0.08
TOTAL 0.34 1.04 1.38
Resin acids:
Pimaric 0 .11
Sandaracopimaric 0.04
Isopimaric 0.23
Palustric 0.35
Dehydroabietic 0.08
Abietic 0.14
Neoabietic 0 .09
TOTAL 1. 04
a= Percentages are based on oven-dried wood. b= Acids were determined as their methyl esters. c= Abbreviated notation of fatty acids: 16:0= Palmitic acid; 18:1= oleic acid, 18:2 linoleic acid, 18:3= linolenic acid, 18:0= stearic acid. d= Mixture of oleic, linoleic and linolenic acids. 107
It is evident from the information given in Table 14 that the free fatty acid content is almost 25% of the total fatty acid content (free plus combined -esterified- fatty acids) present in slash pine wood. It can also be observed that the main fat components were of the unsaturated type, i.e., oleic, linoleic and linolenic acids.
/Among the resin acids, 63.5% belong to the abietane type (abietic, neoabietic, palustric and dehydroabietic),
25.9% to the isopimarane type (isopimaric and sandaracopimaric) and 10.6% to the pimarane type (pimaric)
(for chemical structures see Fig. 4 and 5). Palustric and isopimaric acids accounted for almost 56% of the total content of the resin acids, while sandaracopimaric was present only in 4% of their combined weight.
The relative proportion of the most common resin acids present in slash pine wood after 6 weeks storage is given in Table 15. 108
Table 15. Relative proportion of resin acids in slash pine wood after 6 weeks of storage
10.6
3.8
22.1
33. 6
7.7
13.5
8.7
100.0
* Percentages are based only on the total amount of the seven resin acids characterized in this study.
The resin acid composition in the combined Soxhlet extracts shows the presence of the most common acids, except levopimaric acid. This finding seems to be contradictory to previous reports (Zinkel and Foster,
1980) which gives a relative proportion of 9.6% for 109
levopimaric acid. Confirmatory tests were performed in order to corroborate finding of the lack of levopimaric acid in the wood extract. Individual samples of levopimaric and palustric acids, as well as the mixture of the two acids, were analyzed by GC-MS, since these two resin acids could not be resolved on the HP-5 capillary column. Spectral patterns for these two resin acids are significantly different and the ratio of the relative intensities of two pairs of mass peaks were taken as parameters for their differentiation.
The mass fragmentation pattern of levopimaric acid reveals higher intensity of the m/e 239 peak (77.71%) compared to the m/e 241 peak (32.99%) giving a ratio of
2.4, while the m/e 301 peak (29.86%) shows lower relative intensity than the m/e 316 peak (84.66%), giving a ratio of 0.35. On the other hand, palustric acid generates a lower intensity of the m/e 239 peak (36.80%) than the m/e
241 peak (100%) with a ratio of 0.37; and the m/e 301 peak
(88.55%) greater than the m/e 316 peak (64.54%) with a ratio of 1.37.
The ratios of the relative intensities of the m/e 239 peak against the m/e 241 peak, and the m/e 301 peak against the m/e 316 peak, are shown in Table 16. 110
Table 16. Ratios of the relative intensities of the m/e 239/241 and m/e 301/316 mass peaks of levopimaric and palustric acids on slash pine wood after 6 weeks of storage
m/e
ACIDS: 239/241 301/316
Levopimaric 2.4 0.35
Palustric 0.37 1.37
Extract a 0.37 1.37
a These values correspond to the peak which was obtained for'the wood sample.
Comparison of the mass fragmentation patterns of palustric acid, levopimaric acid and the extract reveals that palustric acid is the only resin acid present in the methanolic extract of the wood sample after 6 weeks of storage (See Appendix A). While levopimaric acid could not be detected the possibility exists that it might have been present in fresh wood, and that it might have disappeared during storage. This supposition can be supported by Ill
Lawrence's study (1959) who found that oxidation of resin acids in the chips was quite rapid and that in a few hours the content of levopimaric acid was approximately one-half of that of the original pine oleoresin.
4.4.1.2. Analysis of resin- and fatty acids in wood after 24 weeks of storage
Characterization of the resin- and fatty acids in slash pine wood after 24 weeks of storage was performed in a similar fashion as that for wood after 6 weeks of storage. Gas chromatographic analyses of the resin acids were performed on the HP-5 fused-silica cross-linked bonded-phased capillary column, while the fatty acids were analyzed on the newly acquired DB-225 megabore capillary column. Quantitative results of the resin- and fatty acids present in the wood after a 24 weeks storage are given in
Table 17.
The mass spectral total ion chromatogram of the methylated wood extract (free fatty acids and resin acids) and the saponified-methylated wood extract (total fatty acids and resin acids) are shown in Fig. 16 and 17. It can be seen from these two chromatograms that the peak areas 112
Table 17. Fatty and resin acid composition of slash pine wood after 24 weeks of storage (%)a
Acids53 Free Combined Total
Fatty acids:
Palmitic 0.015 0.118 0.133
Stearic 0.009 0.033 0.042
Oleic ' 0.019 0.105 0.124
Linoleic 0.005 0.010 0.015
Linolenic N.D. 0.002 0.002
TOTAL 0.048 0.268 0.316
Resin acids:
Pimaric 0.028
Sandaracopimaric 0.008
Isopimaric 0.050
Palustric 0 . 037
Dehydroabietic 0.059
Abietic 0. 017
Neoabietic 0 . 007
TOTAL 0.206
a= Percentages are based on oven-dried wood. b= Acids were determined as their methyl esters. loo n
RIC .
CO
500 1000 1500 2000 SCAN 8:45 17:30 26:15 35:00 TIME
Figure 16. Mass spectral total ion chromatogram of the free fatty and resin acids (Methylated wood extract) Figure 17. Mass spectral total ion chromatogram of the total fatty and resin acids (Saponified and methylated wood extract) 115
of the fatty acids increase considerably after saponification of the fats present in slash pine wood.
A comparison of the resin- and fatty acid compositions of slash pine wood after 6 and 24 weeks storage is given in Table 18.
Extracts for both storage periods gave similar qualitative results, but the acid quantities were different. The proportion of free fatty acids (FFA) to resin acids (RA) was greater after 6 weeks storage
(FFA/RA= 0.33) than after 24 weeks (FFA/RA= 0.23). The amounts of both free fatty acids and resin acids were reduced significantly from the former values to about
14.1% and 19.8%, respectively. The change in resin- and fatty acid concentrations were earlier explained as the result of metabolic and/or degradative reactions of fatty and resin acids in seasoned wood (Assarsson and Akerlund,
1967). Greater reduction of fatty acids might be the result of additional autoxidation reactions of free fatty acids, especially those of oleic, linoleic and linolenic acids (Lawrence, 1959; Miyashita and Takagi, 1986). It was found in this study that within the 6 to 24 weeks, almost
50% of the esterified fatty acids are hydrolyzed and probably metabolized by microbial respiration to carbon dioxide and water. Table 18. Resin and fatty acid composition of slash pine wood after 6 and 24 weeks storage (%)
Storage time (Weeks)
6 24
Free Combined Total Free Combined Total
Fatty Acids: 0.340 1.040 1.380 0.048 0.268 0.316
Resin Acids 1.040 — — _ 1.040 0.206 — — — 0.206
AA11 values are percentages on O.D. wood basis. 117
4.4.1.3. Analysis of resin acids in wood after 52 weeks of storage
Resin acids were characterized in wood samples after
52 weeks of storage. The resin acid composition after this period of storage shows considerable change from that determined after 6 and 24 weeks storage. It was found that the relative proportion of these resin acids may decrease, increase or mantain almost the same values. On one hand, palustric acid is reduced from 33.7 to 2.5%, abietic acid from 13.1 to 1.6%, and neoabietic acid from 8.4 to 1.2%.
On the other hand, increases for sandaracopimaric from 3.9 to 15.6%, and dehydroabietic from 7.6 to 48.5% were observed, while pimaric and isopimaric acids showed little change. The relative proportions of resin acids in slash pine wood after 6 , 24 and 52 weeks storage are given in
Table 19 and Fig. 18.
Table 19. Relative proportion (%) of resin acids in slash pine wood after 6, 24 and 52 weeks storage
Storage time (weeks) Resin Acids: 6 24 52
Pimaric 10.7 13.6 11.7 Sandaracopimaric 3.9 3.9 15. 6 Isopimaric 22. 6 24.3 18.9 Palustric 33.7 18.0 2.5 Dehydroabietic 7.6 28.6 48.5 Abietic 13.1 8.3 1.6 Neoabietic 8.4 3.4 1.2 TOTAL 100.0 100.0 100.0
^Percentages are based only on the total amount of the seven resin acids characterized in this study. 118
50-|
0 6 24 52 Weeks
Figure 18. Relative proportion of resin acids in slash pine wood after 6, 24 and 52 weeks of storage 119
Variations in the relative proportions of these acids may be due to isomerization and/or autodegradation, and/or oxidation reactions. The exact mechanisms by which these resin acids are converted into products is unclear. Most resin acids found in pine species have structures which could be readily converted to dehydroabietic by simple mechanistic processes such as isomerization and dehydrogenation, but how this occurs is not fully understood. Bacterial populations, existing in wood, may have a role.
4.5. Organosolv Pulping of Slash Pine
In the last decade, a lot of effort and money has been put into research and development on organosolv pulping leading to a better understanding of its chemistry and to overcome most of its drawbacks. For example, the
ALCELL company has spent up to $5 million to develop its solvent pulping process, while ORGANOCELL reported a cost of 45 million DM ($32.5 million CDN) to acheive a production of 5T/day (Pappens, 1990; Dahlmann and
Schroeter, 1990). Some process disadvantages relate to the difficulty of pulping mixed wood species, the extremely efficient control needed to handle the volatile pulping 120
chemicals, and the proper pulp washing procedure to avoid reprecipitation of lignin onto the pulp fibers.
It seems that during organosolv pulping, most of the extractives are removed from the wood, based on their solubility characteristics in methanol. In addition to this assumption, due to the short pulping periods (i.e. 15 to 60 min) it can be expected that the extractives may suffer only mild changes to their chemical structures.
Although, side reactions might occur (i.e. fragmentation, isomerization, condensation and/or oxidation) and the extent of these organic reactions might be less pronounced than those found during the actual commercial chemical pulping processes, i.e., sulfite or kraft processes.
It was also expected that the extractives after pulping might be either dissolved in the black liquor
(methanol-water phase), adsorbed onto the lignin which precipites on cooling out of the black liquor, or entrapped in the resulting pulp. Therefore, it was necessary to isolate, concentrate and characterize the resin- and fatty acids from the fractions mentioned above.
As the main objective of this work, it was important to characterize the resin- and fatty acids in the wood before and after pulping. Furthermore, due to the drastic structural (chemical) and/or content variations of these acids in the green state, as compared to the composition following 20 or 24 weeks of storage (Assarsson, 1967) 121
(section 4.4.1), all pulping experiments were performed on wood stored for 24 weeks in order to avoid changes unrelated to pulping and to minimize the risk of misinterpretation of the pulping results when using fresh wood.
4.5.1. Resin- and fatty acids analysis after pulping
There is a large body of information available on how lignin and cellulose are degraded during the course of the chemical pulping processes (Clayton, 1969; Gellerstedt and
Lindfors, 1984; MacLeod et al., 1984; Buchwalter, 1985;
Ohi and Ishizu, 1989) . Some of these studies were also extended to organosolv pulping (Garves, 1988; Paszner and
Cho, 1989) . However, almost no efforts have been made to study the changes which extractives may suffer during high temperature organosolv pulping.
Judging from the low extractive content of organosolv pulps (Behera, 1985) both the extractives and lignin are dissolved in the black liquor (methanol-water at 80:20 ratio). Therefore, it was necessary to remove selectively the resin- and fatty acids (extractives in general) from the black liquor by using a third solvent leaving the lignin and sugars in solution. The resin- and fatty acids were isolated by using liquid-liquid extraction. Several 122
solvents (petroleum ether, chloroform, and diethyl ether) were studied as possible solvents with sufficient selectivity in order to accomplish these goals by simple liquid-liquid extraction. Due to its good dissolving power of the extractives and the poor solubility of the lignin, diethyl ether was selected as the best solvent to perform such extractions.
It is known that ether is slightly soluble in water and vice versa. A saturated water solution contains 8.43%
(w/w) of ether at 152C and 6.05% (w/w) at 252C. Ether saturated with water contains 1.2% at 20aC. Ether is miscible with lower aliphatic alcohols, benzene, chloroform, petroleum ether, other fat solvents, and many oils (Anon., 1983).
Table 20 shows the number of mL of the initial water- methanol mixture, the minimal volumes of diethyl ether needed to provoke phase separation and the ratio of the
percentages of the resulting mixtures Et20/MeOH, Et20/H20 and the starting I^O/MeOH mixture.
Plotting of this data is depicted in the phase diagrams presented in Fig. 19 and 20. A more practical phase diagram to use is the x and y relationship depicted in Fig. 19. By plotting the water-methanol proportions on the "X" axis (black liquor composition) and the number of mL of diethyl ether needed for phase separation Table 20 . Data for the phase diagram separation of the tertiary solvent mixture methanol-water-diethyl ether
Solvent (mL) Ratio Mixture
* H20 Me OH Et20 H20/MeOH Et20/H20 Et20/MeOH
1 9,. 0 1.. 0 1.0 9..0 0 0,.1 1 1..0 0 2 8.. 5 1.. 5 1.3 5,.7 0 0,.1 5 0..8 7 3 8,. 0 2.. 0 1.6 4,.0 0 0..1 9 0..8 5 4 7.. 0 3.. 0 2.1 2..3 3 0..3 0 0..7 0 5 6,. 0 4.. 0 2.5 1..5 0 0,.4 2 0..6 3 6 5.. 7 4.. 3 3.4 1..3 3 0,.6 0 0..8 0 7 5.. 5 4.. 5 4.2 1..2 2 0..7 6 0..9 3 8 5.. 2 4.. 8 5.2 1..1 0 1,.0 0 1..1 0 9 5,. 0 5.. 0 6.0 1,.0 0 1,.2 0 1..2 0 10 4,. 8 5.. 2 7.0 0..9 2 1..4 6 1..3 5 11 4.. 6 5.. 4 9.0 0,.8 5 1..9 6 1..6 7 12 4.. 5 5.. 5 10.4 0,.8 2 2..3 1 1..9 0 13 4,. 3 5.. 7 13.5 0..7 5 3,.1 4 2..3 7 14 4,. 0 6.. 0 17.0 0..6 7 4..2 5 2..8 3 15 3,. 8 6.. 2 21.0 0..6 1 5..5 3 3..3 9 16 3.. 0 7.. 0 * 0..4 3 * *
* At H20/MeOH ratio lower than 0.45 there is no phase separation. J I I I I 2 4 6 8 10 Hater/MeOH Ratio
Figure 19. Phase diagram of the ternary solvent mixture methanol-water-diethyl ether: X and Y relationship Ether (100%)
Water Me OH
Figure 20. Phase diagram of the ternary solvent mixture methanol-water-diethyl ether: Triangular relationship 126
on the "Y" axis, then by using this chart, starting with any black liquor composition (water-methanol ratio), it is possible to find the proper amount of extracting organic solvent (diethyl ether) which would give the right proportions for selective phase separation. Accordingly,
Fig. 19 becomes a practical chart to use in solvent purification of the black liquor of an organosolv pulp mill.
Attempts to derive an equation that would represent the curve presented in the triangle of Fig. 20 and thus facilitate the calculation of the proportions seems to be quite complex and examples for such exercises were not found in the literature. However, for the less complex curve in Fig. 19 an equation for the relationship of the x and y parameters is presented below:
Y = 5.248 - 0.355 CX) - 11.948 (1/X) + 13.328 U/X)2
SOURCE SUM-OF-SQUARES DF MEAN-SQUARE
REGRESSION 1,256.895 4 -314.224 RESIDUAL 1.665 11 0.151
TOTAL 1,258.560 15 CORRECTED 520.757 14
RAW R-SQUARED (1-RESIDUAL/TOTAL) 0.999 CORRECTED R-SQUARED (1-RESIDUAL/CORRECTED 0.997 127
From both of these phase diagrams (Fig. 19 and 20) it can be seen that when working with equal volumes of and MeOH (ratio of 1.0, 5 mL of water - 5 mL of methanol), the minimal amount of diethyl ether (6 mL) needed for phase separation is higher than indicated by the initial volumes of water and methanol. However, if the initial amount of methanol is reduced (i.e. at ^O/MeOH of a ratio of 4.0, 8 mL of water and 2 mL of methanol) then the amount of Et20 needed decreases to 1.6 mL, and hence the number of extractions must be increased if the same extraction efficiency is to be obtained. Furthermore, at this ratio, because of the higher amount of water, precipitation of lignin is more likely to happen, a condition clearly undesirable for such a system to function efficiently.
On the other hand, if the amount of methanol is increased (^O/MeOH ratio 0.82, i.e. water 4.5 mL and methanol 5.5 mL) , then phase separation of the black liquor takes place giving water containing the dissolved sugars in solution as one phase, and an ethereal Et20/Me0H phase with the lignin and extractives due to the high solubility of the ether in methanol and low solubility in water.
Therefore, if solvent extractions of the organosolv black liquor are to be performed for removal of extractives, lignin or sugars, then it is necessary to 128
know which one of these entities has to be removed or extracted, and a compromise of factors must be accepted such as: a. ) The time or effort required to remove the extractives
by solvent extraction. In going from a H20/MeOH= 1.0
to a higher ratio (i.e. H20/MeOH= 4.0), less ether is
needed for phase separation, but the number of
extractions must be increased to obtain complete and
selective removal of the extractives. b. ) The proper proportions of the solvents in order to get
the correct phase separation. In this case, the ether
had to be separated from the water-methanol mixture in
order to selectively remove the extractives from the
cooking liquor, and to avoid precipitation of the
lignin.
b.l.At H20/MeOH ratio lower than 0.82 (i.e. H20/MeOH ratio
of 0.67, water= 4.0 mL and methanol= 6.0 mL) the
minimal amount of Et20 needed for phase separation is
quite large (Et20= 17 mL). Because of the high
solubility of the methanol in ether, the water
separates from the Et20-methanol mixture. Therefore,
it is very likely that lignin and extractives will be
found in the ether-methanol phase, while the sugars
must be in solution in the water phase. This approach
would be suitable if extractives- and lignin-free 129
sugars were to be obtained, leaving the mixture of
extractives and lignin in the organic phase. b.2.If the lignin removal is performed after removal of
the extractives from the black liquor, as stated
above, then it is feasible to obtain extractive-free
fermentable sugars in the water whereas the lignin is
separated in the Et20/methanol phase.
b.3.At H20/MeOH ratio higher than 1.5 (i.e. H20/MeOH ratio
of 4.0, water= 8 mL and methanol= 2 mL) the amount of
Et20 needed for phase separation is 1.6 mL. Under
these conditions, there is enough water (to promote
separation from the ether) but insufficient methanol
to keep the lignin in solution. Therefore, for
efficient extractives removal, a great number of ether
(only 1.6 mL) extractions are needed and the low
methanol content and high water content will promote
precipitation of the lignin.
A short investigation on the efficiency of the recovery was conducted in order to estimate the margin of error for this procedure. Nearly 100% of the resin- and fatty acids were quantitatively recovered when performing the extractions at the water-methanol-ether (50:40:50) ratio or the equivalent water:methanol= 1.25 (50:40) ratio. Extractives recoveries of no less than 95-96% are obtained when the water-methanol ratios go closer to 1.0
(50:50) or 1.375 (55:40). 130
It can be concluded that removal of the extractives by liquid-liquid extraction of a water-methanol mixture with diethyl ether must be performed within the water- methanol range between 1.0 to 1.4. Within this range the ideal water-methanol ratio for the best extraction efficiency is 1.25.
4.5.1.1. Resin- and fatty acids analysis after 5 min pulping
Due to the use of methanol (an excellent organic solvent with high dissolving power for extractives) at high temperature and high pressure, it was expected that most of the extractives would be removed at early stages of the pulping process. A 5 min pulping time was chosen as the shortest time since the estimated rate of heating of the stainless steel vessel was about 262C/min. Extractives removal was studied only for the industrially relevant temperature of 2052C. Delignification of softwoods is largely incomplete at temperature under 200SC and prolonged cooking leads to a rapid loss of cellulose viscosity and poor pulp (Paszner and Chang,1983).
In the 5 min cooks, characterization of the extractives was performed only on those present in the black liquor since no defiberization (fiber liberation) occurs on such short cooking. Quantitative values for the 131
resin- and fatty acids following 5 min cooking are given in Table 21. These results show that even after such short cooking, about 90% of the resin acids and 25% of the fatty acids were found in the cooking liquor and apparently survived the high temperature extraction.
The differences in degree of removal of the two types of acids are difficult to explain. However, it is possible to rationalize that their different solubility in methanol and/or their different location in the wood, may be responsible for the differences in solubility/removal by hot methanol. Total fatty acids represent the free fatty acids originally present in wood (0.048%) plus a fraction of fatty acids resulting from fats, which must have been hydrolyzed during the pulping process. The percentage of saturated fatty acids found in the black liquor is lower than that determined in the wood as free acids. Therefore, it seems that saturated fatty acids are less soluble in hot methanol and more difficult to remove than unsaturated ones (Palmitic= 0.009% and Stearic= 0.002%). On the other hand, oleic and linoleic acids were removed in higher amounts (0.047% and 0.022%) due to the hydrolysis of fats present in the wood. 132
Table 21. Resin- and fatty acid composition in slash pine wood and black liquor after 5 minutes of organosolv pulpinga
Wood Black Liquor
Fatty Acids: Free Total Free
Palmitic 0.015 0.133 0.009
Stearic 0.009 0.042 0.002
Oleic 0.019 0.124 0.047
Linoleic 0.005 0.015 0.022
Linolenic N.D.b 0.002 0.001
TOTAL 0.048 0.316 0.081
Resin Acids:
Pimaric 0.028 0.029
Sandaracopimaric 0.008 0.009
Isopimaric 0.050 0.051
Palustric 0.037 0.005
Dehydroabietic 0.059 0.051
Abietic 0.017 0.038
Neoabietic 0.007 0.002
TOTAL 0.206 0.185
a All values are percentages on O.D. wood basis. b N.D.= Not detected. 133
Among the resin acids it seems that those of the pimarane (pimaric) and isopimarane (isopimaric and sandaracopimaric) type are almost completely removed from wood and their chemical structure remains unchanged on organosolv pulping. However, with the exception of abietic acid, resin acids of the abietane type (palustric, dehydroabietic and neoabietic) were found in lower amounts in the cooking liquor than those originally present in wood. It seems that a portion of palustric and neoabietic acid isomerizes into a more "thermostable" form like abietic acid. The reduction of dehydroabietic acid can be explained in terms of incomplete removal by the methanol from the wood.
Since resin- and fatty acids can be easily removed even after short pulping periods (5 min), it might be inferred that short cooks of this type can be used as pre- treatments (for extractive removal) whenever a high extractive content wood might be a problem (i.e. in preparing dissolving pulps). 134
4.5.1.2. Resin- and fatty acids analysis after 20 min pulping
Quantitative results of the resin- and fatty acids after 20 min pulping are shown in Table 22. This table
reveals that after 20 min of organosolv pulping about 60%
of the total fatty acids were removed* from the wood. Most
of these fatty acids were found in the black liquor
(44.0%). Almost equal amounts of extractives were
distributed between the precipitated lignin (Lignin I) and the pulp at 16.5% and 15.5%, respectively.
A comparison between the total fatty acids after pulping (fatty acids in the black liquor, lignin and pulp)
with those found in the wood before pulping (free and
total fatty acids), is as follows: Total saturated fatty
acids found after pulping -palmitic (0.055%) and stearic
(0.023%)- are present in lower percentages than those
found in wood -palmitic (0.133%) and stearic (0.042%). The
amount of unsaturated fatty acids after pulping is equal
to that found in wood with respect to oleic and linolenic
acid, but higher for linoleic acid. However, oleic acid
remains the predominant fatty acid component of fats in
slash pine wood.
* Removed extractives are either dissolved in the black liquor or adsorbed onto the precipitated lignin ("Lignin I"). The rest of the extractives remain in the pulp. Table 22. Resin-and fatty acid composition in slash pine wood after 20 min of organosolv pulping3
Wood Black Precip Pulp Liquor Lignin Fatty Acids: Free Total Total Total Total TOTAL Palmitic 0. 015 0 .133 0.028 0.007 0.020 0.055 Stearic 0. 009 0 .042 0.004 0.002 0.017 0.023 Oleic 0. 019 0 .124 0.078 0.034 0.011 0.123 Linoleic 0. 005 0 .015 0.028 0.008 0.001 0.037 Linolenic N .D. 0 .002 0.001 0.001 0.002 TOTAL 0. 048 0 .316 0.139 0.052 0.049 0.240
Resin acids: Pimaric 0. 028 0.024 0.005 0.029 Sandaracopimaric 0. 008 0.006 0.002 • • • 0.008 Isopimaric 0. 050 0.035 0.008 • • • 0.043 Palustric 0. 037 0.010 0.001 • • • 0.011 Dehydroabietic 0. 059 0.035 0.004 0.031 0.070 Abietic 0. 017 0.022 0.006 0.012 0.040 Neoabietic 0. 007 0.001 0.001 0.002 TOTAL 0. 206 0.134 0.027 0.043 0.203
3 All values are percentages on O.D. wood basis. 136
Summation of the percentages of the fatty acids found after pulping (black liquor + precipitated lignin + pulp) accounts for only 76% of the original total fatty acids present in wood. An explanation of this gap might be attributed to an incomplete hydrolysis of the esterified fatty acids (fats) during this short cooking period.
The total amount of resin acids removed from the wood after 20 min pulping was about 78.8% of the total resin acids present in the wood. Most of the resin acids were found in the black liquor (65.5 %) , and the rest in the precipitated lignin (13.3%) and the pulp (21.2%).
Dehydroabietic and abietic acids were the only detectable resin acids present in the pulp.
The resin acids of the pimarane and isopimarane
(pimaric, isopimaric and sandaracopimaric acids) type were detected in the black liquor and precipitated lignin.
Their total percentages were very close to the ones found in the wood before pulping. Within the resin acids of the abietane type, palustric and neoabietic acids show a reduction from their original percentages in the wood.
Palustric acid was reduced from 0.037% to 0.011% and neoabietic from 0.007% to 0.002%. On the other hand, dehydroabietic and abietic acids show an increase from their initial contents in the wood. The amount of abietic acid increased from 0.017% in wood to 0.040%, and 137
dehydroabietic acid increased from 0.059 in wood to 0.070% after pulping.
From this data it appears that the resin acids of the pimarane and isopimarane type are recovered completely after pulping and that their chemical characteristics remained unchanged. However, palustric and neoabietic acid are not recovered totally, while abietic and dehydroabietic acids apparently increase in quantity.
This last finding can be explained as the result of probable isomerization of palustric and neoabietic acid into dehydroabietic and/or abietic acids. There is evidence that dienic resin acid under acid or base catalyzed conditions undergoes isomerization. Schuller and
Lawrence (1965) proposed a mechanism for these isomerizations which is given in Fig. 21. The pulping experiments were performed under acid conditions (20 min cook, pH 4.2), and it can be assumed that palustric and neoabietic acids may undergo the same acid catalyzed reactions of dienic resin acids as shown by Baldwin et al.
(1956), Lawrence (1959) and Schuller et al. (1960). 138
Figure 21. Proposed mechanism for the base-catalyzed isomerization of the conjugated dienic resin acids (Schuller and Lawrence, 1965) 139
Isomerization reactions of resin acids during organosolv pulping seem to be different from those that occur during seasoning of the wood. Under the latter conditions the relative proportions of dehydroabietic and sandaracopimaric acid increase substantially as end products of the isomerization reactions. Meanwhile, under organosolv pulping conditions, dehydroabietic and abietic acids seem to be the major end products. It appears that during storage under natural conditions, in the presence of enzymes, the isomerization reaction leads to formation of dehydroabietic and sandaracopimaric acids. However, under the conditions of pulping at pH 4.2 to 5.0 in methanolic medium at high temperature (2052C) and elevated pressure, palustric acid together with neoabietic acid and/or any other unidentified dienic abietane resin acid type, all isomerize-into abietic or dehydroabietic acid as suggested in Fig. 21 . From these data it can be concluded that among the resin acids of the abietane type, abietic and dehydroabietic acids, under the severe conditions of our organosolv pulping conditions, are the more stable end products from isomerization reactions and more probably originate from palustric and neoabietic acids. A mechanism for these isomerizations (Fig. 21) was proposed earlier by Schuller and Lawrence (1965). 140
4.5.1.3. Resin- and fatty acid analysis after 40 min pulping
Quantitative results of resin- and fatty acids after
40 min organosolv pulping are given in Table 23. It can be
seen that around 80% of the original total fatty acids present in wood are removed after this cooking period. Out
of this portion, 60.4% are dissolved in the black liquor,
19.0% are adsorbed onto the precipitated lignin ("Lignin
I") and 11.7% are entrapped in the pulp.
Although after 40 min pulping the percentage of
palmitic acid is higher than that found after 20 min
pulping (while the stearic acid concentration remains
about the same) these values are still lower than their
total amounts present originally in wood.
Around 82.5% of the resin acids are removed from the
wood. Most of the acids were extracted in the black liquor
(69.4%), adsorbed onto the precipitated lignin (13.1%) and
entrapped in the pulp (17.5%). Again, the more stable
dehydroabietic and abietic acids were the only resin acids
found in the pulp. Table 23. Resin-and fatty acid composition in slash pine wood after 40 min of organosolv pulping8
Wood Black Precip Pulp Liquor Lignin Free Total Total Total Total TOTAL Fatty acids: Palmitic 0.015 0.133 0.051 0.008 0.015 0.074 Stearic 0.009 0.042 0.006 0.003 0.012 0.021 Oleic 0.019 0.124 0.099 0.036 0 . 009 0.144 Linoleic 0.005 0.015 0.034 0.012 0.001 0.047 Linolenic N.D. 0.002 0.001 0.001 0.002 TOTAL 0.048 0.316 0.191 0.060 0 . 037 0.288
Resin Acids: Pimaric 0.028 0.024 0.005 • • • 0.029 Sandaracopimaric 0.008 0.007 0.002 ... 0.009 Isopimaric 0.050 0.037 0.007 • . . 0.044 Palustric 0.037 0.010 0.002 • • • 0.012 Dehydroabietic 0.059 0.042 0.004 0 . 024 0.070 Abietic 0.017 0.022 0.006 0.012 0.040 Neoabietic 0.007 0.001 0.001 0.002 TOTAL 0.206 0.143 0.027 0.036 0.206
a All values are percentages on O.D. wood basis. 142
Comparing these data with those obtained after 2 0 minutes pulping, again the concentration of pimaric, isopimaric and sandaracopimaric acids was nearly the same as that found in the wood. However, the contents of palustric and neoabietic acids decreased, while the percentages of abietic and dehydroabietic acids increased due to the high temperature, treatment. Again, this might be explained in terms of the isomerization reactions of both palustric and neoabietic acids leading to their conversion into abietic (See Fig. 21) and/or dehydroabietic acid.
4.5.1.4. Resin- and fatty acids analysis after 60 min pulping
Quantitative results of the resin- and fatty acids after 60 min pulping are given in Table 24. Organosolv pulping for 60 min permits substantial removal of the fatty acids (91.8%) and resin acids (88.3%) from the wood.
Most of the fatty acids were detected in the black liquor (71.6%)* and the rest proportioned between the precipitated lignin (20.2%)* and the pulp (8.2%)*.
* These values are based on the total fatty acid content detected after pulping. Table 24. Resin-and fatty acid composition in slash pine wood after 60 min of organosolv pulping3
Wood Black Precip Pulp Liquor Lignin Free Total Total Total Total TOTAL Fatty acids: Palmitic 0.015 0.133 0.078 0.009 0.011 0.098 Stearic 0.009 0.042 0.005 0.003 0.009 0.017 Oleic 0.019 0.124 0 .108 0.041 0.007 0.156 Linoleic 0.005 0.015 0.053 0.015 0.001 0.069 Linolenic N.D. 0.002 0.001 0.001 • • • • 0.002 TOTAL 0.048 0 .316 0.245 0.069 0.028 0.342
Resin Acids: Pimaric 0.028 0 . 031 0.004 • • • 0.035 Sandaracopimaric 0.008 0 . 012 0.002 • • • 0.014 Isopimaric 0.050 0.038 0.006 • • • 0.044 Palustric 0.037 0.014 N.D. • • • 0.014 Dehydroabietic 0.059 0.044 0.006 0.021 0.071 Abietic 0.017 0.021 0.003 0.003 0.027 Neoabietic 0.007 N.D • • • • • • • • N.D. TOTAL 0.206 0.160 0.021 0.024 0.205
a All values are percentages on O.D. wood basis. 144
Palmitic , oleic and linoleic acids are detected in higher amounts and followed the same trend as found earlier with the 40-minute pulping. Again, even though the palmitic acid recovery after the 60 min pulping is greater than after 40 min, the total amount recovered (0.098%) represents only 75% of its original content in the wood
(0.133%).
Oleic and linoleic acids are found in higher concentrations after pulping than originally detected in wood. Again, it might be speculated that these increments could be either the result of better hydrolysis of the fats after pulping than by saponification or that some un• identified fatty acids may have isomerized into these two acids.
Pulping trials of the respective model compounds for the methyl derivatives of stearic, oleic, linoleic and linolenic acids were performed in order to clarify some of these above results. All these methyl derivatives were treated at 2052C for 60 min. Stearic acid, as an example of a saturated fatty acid, did not suffer any chemical change under the above conditions. On the other hand, unsaturated fatty acids (i.e. oleic, linoleic and linoleic) manifested some chemical changes. Oleate (C^.^) and linoleate methyl esters suffered reductions from their original contents of 20% and 90%, respectively.
Furthermore, organosolv pulping of, linolenate (Ci8*3) 145
methyl ester revealed that under the present conditions it is completely degraded.
The trend of degradation for these three fatty acid methyl ester derivatives is similar to the one observed during their autooxidation reactions. According to Holman
(1965), the methylene-interrupted polyunsaturated acids, because of their activated methylene groups, are very easily attacked by oxygen. He suggested that this autooxidation reaction goes through a free radical formation and that its rate is dependent upon the degree of unsaturation of the fatty acids. He added that the rate of oxidation for linoleate is approximately 20 times that of oleate due to the double activation of the methylene group in the former.
From the previous information it is possible to propose that the degradation of the unsaturated fatty acids is related to the number of reactive sites (double bonds) in the molecule. Since linoleic acid has more double bonds, this molecule must show greater degradation.
In our experiments, methyl linolenate (C18*3^ was completely destroyed after organosolv pulping at 2052C for
60 min.
From the total resin acids detected after pulping, only 11.7% remained in the pulp; the bulk was distributed between the black liquor (78.1%) and the precipitated lignin (10.2%). Dehydroabietic and abietic acids were the 146
only resin acids left in the pulp. These residual acids in the pulp can be explained in terms of their lower solubility in methanol and also because of the higher content in the wood. Considering the initial contents, it is very likely that there must remain some residues of the other resin acids in the pulp, but the amounts are too low to be detected.
Pimaric and sandaracopimaric acids both increased by the same amounts, while isopimaric acid decreased by the same amount. In this case it would be more appropriate to assume that isopimaric acid isomerized into sandaracopimaric acid instead of pimaric acid.
Isomerization of isopimaric acid into sandaracopimaric acid suggests only a shift in the double bond from the 7 position in isopimaric acid to the 8(14) position in sandaracopimaric acid. Isomerization of isopimaric acid into pimaric acid includes not only the migration of this double bond , but also the change in the configuration of carbon C-13.
Pulping experiments of the isopimarate methyl derivative (model compound) showed that this acid isomerizes into pimaric (1.8%), sandaracopimaric (1.4%), dehydroabietic acid (3.8%) and other minor compounds not identified. Also, additional cookings of pimaric and sandaracopimaric acid demonstrated that these two acids do 147
not suffer any chemical changes under the present
conditions (60 min at 2052C).
Furthermore, cooking of methyl sandaracopimarate, which contained methyl isopimarate as impurity in a 8:1
ratio, rendered a final sandaracopimarate-pimarate-
isopimarate ratio of (12:1:1). From these results it is possible to conclude that organosolv pulping provokes the
isomerization of isopimaric acid into pimaric and
sandaracopimaric acids.
Among the abietane resin acids type, dehydroabietic
and abietic acid show the highest contents among the major
resin acids found after pulping. Dehydroabietic acid
increased from 0.059% in the wood to 0.071% after pulping, while abietic acid presented a noticeable increment from
0.017 to 0.027%. This latter value is lower than that
after the 40 min cook which can be explained in terms of
degradation of the abietic acid because of longer
residence time (60 min) during the pulping process.
However, palustric and neoabietic acids exhibit the lowest
contents among the resin acids. Palustric acid was reduced
from 0.037% in the wood to 0.014% after pulping, while neoabietate dissappeared completely after pulping.
Organosolv pulping of the model compound of methyl
dehydroabietate for 60 min at 205°C reveals that this acid
does not suffer any chemical change during these
conditions. However, pulping of methyl palustrate and 148
methyl abietate rendered their comprehensive isomerization into methyl dehydroabietate. And surprisingly, methyl neoabietate was completely degraded under the same organosolv pulping conditions.
Loeblich et al. (1955b) found that palustric acid on treatment with mineral acid is isomerized to abietic acid.
They indicated that the isomerization of palustric acid into abietic acid was approximately 90% complete. They also found that levopimaric acid isomerized into palustric acid after heating at 155 2C for about 5 h. The amount of palustric acid was 29.0% of the isomerized products.
Furthermore, they postulated that palustric acid is an intermediate product in the acid and that heat isomerization of levopimaric to abietic acid also occurs.
The present findings seem to contradict the results obtained in the past, in which abietic acid was the end product of thermal, acid and base catalyzed isomerization of palustric, neoabietic and levopimaric acids (Loeblich et al., 1955a; Loeblich et al., (1955b); Baldwin et al.,
1956; Loeblich and Lawrence, 1957; Schuller et al., 1960;
Schuller and Lawrence, 1965).
It has been shown that the end products formed by thermal isomerization of neoabietic acid at 2002C consist primarily of palustric and abietic acid. After a 72 h reaction, the products approached an equilibrium mixture of 13% palustric acid, 82% abietic acid and 5% neoabietic 149
acid (Loeblich and Lawrence, 1957) . It was also found that neoabietic acid is more readily isomerized to abietic acid than to palustric acid, whereas levopimaric acid forms both of these acids with equal ease. (See Table 25) .
Furthermore, analysis of the products after a 30 min isomerization of neoabietic and levopimaric acids at 2002C showed that neoabietic acid is more stable to heat than levopimaric acid (Loeblich and Lawrence, 1957). (See Table
25) .
Table 25. Thermal Isomerization of Neoabietic and Levopimaric acid at 200fiC for 30 min (Loeblich and Lawrence, 1957)
Palustric Abietic Neoabietic % % %
Levopimaric Acid 34 52 14 Neoabietic Acid 5 11 84
According to Loeblich et al. (1955a), thermal isomerization of levopimaric acid between 155 and 200QC gives palustric, abietic and neoabietic acids as the end products. These analyses were performed in order to understand the reactions that take place when oleoresin is processed into rosin by distillation. They found that very little, if any, isomerization of the crystalline acid occurred below its melting point (m.p. 150-1522). 150
Furthermore, they discovered that isomerization of levopimaric acid at 200 eC was found to be about eight times as fast as the isomerization at 1552C. (See Table
26) .
Table 26. Thermal Isomerization of Levopimaric Acid at 155 and 200&C (Loeblich et al., 1955a)
Temp., Time Palustric Abietic Neoabietic oc. h. % % %
155 4 35 52 14
200 0.5 34 52 14
Contrary to the findings given in the literature above (acid, base and heat catalyzed isomerizations), organosolv pulping of the model compounds of methyl abietate at 200SC during 60 min reveals its complete isomerization into dehydroabietic acid. This result not only contradicted those results given in the literature, but also those obtained after organosolv pulping of slash pine wood samples. It was observed that the abietic acid content increased from 0.017% in the wood to 0.040% after
20 and 40 min cooks and to 0.027% after a 60 min cook. It was assumed (See sections 4.5.1.2 and 4.5.1.3) that those increments were produced because of isomerizations of palustric and neoabietic acids into abietic acid. Since it was found that organosolv pulping of the model compounds 151
of abietic and palustric acids isomerized into dehydroabietic acid and that neoabietic acid was destroyed, it was necessary to find an explanation for the survival of abietic acid after pulping of slash pine wood.
It was expected that pulping of abietic acid in combination with similar resin acids of the abietane (i.e. neoabietic and palustric acids) type may induce or favor a strange mechanism for their isomerization into abietic acid. With this in mind, abietic acid was pulped with palustric and levopimaric acids in a (1:1:1) ratio, and again the main product was dehydroabietic acid.
Further attempts were performed in order to understand the different behaviour of abietic acid not only as a model compound but also as a component of the wood during pulping. In order to simulate part of the wood environment, a 5 g sample of pure AVICEL (Hercules Co.) was added to the methyl abietate sample and pulped at 2052 at pH 3.3 for 60 min. The pH was adjusted with 10% acetic acid solution. Again, the end product of this reaction was dehydroabietic acid.
The final trials from these series of experiments were the pulping of model abietic acid (free acid) at 20 and 60 min. The purpose of these trials was to compare the different behavior of the free acid against its methyl derivative and also to investigate the effect of two 152
cooking periods (residence time) on the isomerization of abietic acid.
GC analyses of abietic acid after a 20 min cook revealed the presence of dehydroabietic acid. The original amount of abietic acid was reduced to 55%, while the remainder (45%) was converted to dehydroabietic acid.
However, pulping for 60 min again showed the complete disappearance of abietic acid. These results indicate that about half of the abietic acid during a 20 min pulping is depleted (isomerized) , while after a 60 min cook, it is completely isomerized into dehydroabietic acid.
These findings may contradict all previous assumptions that abietic acid could have been the end product from isomerization of palustric and neoabietic acids during organosolv pulping of slash pine wood. These results suggest that organosolv pulping of the methyl ester and free form of abietic acid after a 60 min. cooks provokes its isomerization into dehydroabietic acid.
Furthermore, it is possible to conclude that isomerization of abietic acid into dehydroabietic acid during organosolv pulping is a time dependent reaction.
Even though organosolv pulping of the model compound for abietic acid evidences its isomerization into dehydroabietic acid, organosolv pulping of slash pine wood does not give the same results. The following arguments 153
may explain the high percentages of abietic acid observed after organosolv pulping of the wood:
a) . During the pulping process, wood may protect this acid from the severity of the high temperature and pressure of the pulping experiments. This possibility is supported by the fact that abietic and dehydroabietic acids are the only acids left in the pulp.
b) . One wood constituent or a group of the wood constituents may induce the selective or stereospecific formation of an adduct which is resistant to the pulping conditions. This possibility suggests that a further series of experiments should be conducted with abietic acid under the pulping conditions with the addition of a single or multiple components of the wood constituents of slash pine wood.
c) . There may be a small steric difference between the natural and synthetic forms of abietic acid, and these two forms may behave differently during pulping.
Therefore, one can speculate that the natural form is more thermostable than the synthetic one.
Fatty and resin acids surviving the high-temperature pulping process were found mainly in the black liquor
(78.1% and 71.6%, respectively).The remaining fractions were detected in the pulp (11.7% and 8.2%, respectively) and adsorbed onto the lignin (10.2% and
20.2%,respectively). However, it is not unreasonable to 154
suggest that at the cooking temperature used, all extractives removed were dissolved in the cooking liquor and that Lignin I (precipitate) merely entrapped some of the extractives. Originally, it was assumed that this lignin precipitated because of a side reaction with extractives, however since the extractives are readily removed from the lignin with non-polar solvents, it is apparent, that the extractives are merely adsorbed on the porous, hollow globular precipitated lignin particles
(Paszner and Cho, 1988).
Summative results of the resin- and fatty acid composition after 5, 20, 40 and 60 minutes pulping are given in Table 27. The total of the resin- and fatty acids contents in the pulp were as follows: after 20 min=
0.092%, after 40 min= 0.073% and after 60 min= 0.052%.
The total resin acids removed from the wood are as follows: after 5 min= 0.185%, after 20 min= 0.161%, after
40 min= 0.170% and after 60 min= 0.181%. It is quite clear that the resin acids are easily removed even after a very short cooking time (5 min).
On the other hand, removal efficiency of the fatty acids was low after the 5 min cook (25.0%), but increased rapidly after the 20 min cook (60.0%), 40 min cook (80.0%) and the 60 min cook (92.0%). In all of these cases it must be assumed that the rest of the fatty acids remain in the pulp. Table 27. Fatty-and resin acid composition* of slash pine wood and their recovery after 5, 20, 40 and 60 min organosolv pulping
Wood Pulping Time (min) 5 20 40 60 Fatty acids: FA TA TA TA TA TA Palmitic 0 . 015 0 .133 0 .009 0 .055 0 .074 0 .098 Stearic 0 . 009 0 .042 0 .002 0 .023 0 .021 0 .017 Oleic 0 . 019 0 .124 0 .047 0 .123 0. 0144 0 .156 Linoleic 0 .005 0 .015 0 .022 0 .037 0 .047 0 .069 Linolenic N.D. 0 .002 0 .001 0 .002 0 .002 - 0 .002 TOTALS 0 .048 0 .316 0 .081 0 .240 0 .288 0 .342
Resin Acids: Pimaric 0 .028 0 .029 0 .029 0 .029 0 .035 Sandaracopim. 0 .008 0 .009 0 .008 0 .009 0 .014 Isopimaric 0 .050 0 .051 0 .043 0 .045 0 .044 Palustric 0 .037 0 .005 0 .011 0 .012 0 .014 Dehydroabietic 0 .059 0 .051 0 .070 0 .070 0 .071 Abietic 0 .017 0 .038 0 .040 0 .040 0 . 027 Neoabietic 0 . 007 0 .002 0 .001 0 .002 N.D. TOTALS 0 .206 0 .185 0 .202 0 .207 0 .205
* Values correspond to percentages (%) based on O.D. wood. ** N.D.= not detected, signal peaks too small to be detected by the integrator. 156
4.5.1.5. Complementary analyses of the resin- and fatty acid after high pressure 60 min cooks
Contrary to the fractionation procedures followed for the extractive analyses after 5, 20, 40 and 60 min cookings as described above, when the total lignin in a 60 min black liquor is precipitated with an excess amount of water (1:10 ratio) another type of lignin (Lignin II) was obtained.
On quantitative analysis of the diluted black liquor
(See section 3.5.2.1.3) and the precipitated lignin (See section 3.5.2), it was found that 98.2% of resin acids and
60.4% of fatty acids were adsorbed onto the lignin. The rest of these compounds.remained dissolved in the aqueous filtrate. This has important connotations as to the expected pollution loads from softwood extractives in the aqueous residue following removal of the lignin by filtration/centrifugation from the organosolv black liquor. Thereby, lignin precipitation effectively removes these toxic substances (particularly the more toxic resin acids) from the pulping effluents. Some recently published results by Organocell (MD Papier) (Dahlmann and Schroeter,
1990; Pappens, 1990) confirm these findings. Conversely, organosolv lignins directly precipitated from black liquor will be contaminated by extractives unless removed by
solvent extraction. 157
4.6. Characterization of Lignins
It has been proven that organosolv lignin is uncondensed, low molecular weight and free of sulfur (Nimz and Casten, 1985; Young et al., 1985). Therefore, a suitable extraction and purification technique will not only ensure the yield of another high value by-product in the form of the extractives, but also the procedure will produce a purer residual lignin which might be considered as a convenient material as a phenol substitute in adhesives for particleboards, and other resin-type products (polyurethanes), or as a chemical feedstock
(manufacture of aromatics and liquid fuels).
4.6.1. Quantitative analysis of lignin
Due to the different cooking times used during the pulping experiments, establishment of a mass balance was necessary in order to follow possible losses during the whole pulping analysis procedures. Mass balances were detailed specifically for lignin, resin- and fatty acids, and routine pulp yield analyses were also undertaken.
Quantitative results for pulp yield, lignin, resin acids and fatty acids are given in Table 28.
From this table, it can be seen that even after 60 min of cooking, a high pulp yield of 54.5% is obtained. Table 28. Mass balance of lignin, resin and fatty acids of slash pine wood after organosolv pulping3
Pulping Time (minutes) 20 40 60 WOOD
Pulp yield 71.0 59.0 54.5 100.0
Lignin a) Organosolv lignin: Lignin I,% 4.91 7.14 7.61 Lignin S,% 7.06 7.09 8.85 Lignin P, % 3.16 2.54 2.39 Lignin left in pulp (K No)b, % 12.50 11.05 8.80
b) Lignin from wood 28.2° Acid-insoluble, % 26.8 Acid-soluble, % 1.4
Resin Acids 0.204 0.206 0.205 0.206c Black liquor, % 0.134 0.143 0.160 Lignin I, % 0.027 0.027 0.021 Pulp, % 0.043 0.036 0.024
Fatty Acids 0.240 0.288 0.342 0.342d Black liquor, % 0.139 0.191 0.245 Lignin I, % 0.052 0.060 0.069 Pulp, % 0.049 0.037 0.028
a All values are percentages on O.D. wood basis. b Kappa number (K No) multiplied by 0.15 = Lignin (%). c These values were obtained by chemical analyses of the wood. This fatty acid content was determined after organosolv pulping. 159
Pulp yields after 20 min (71%), 40 min (59%) and 60 min
(54.5%) are comparable with those found by Behera and
Paszner (1985).
The total lignin content present in slash pine wood was 28.2%. The lignin recovered after pulping was directly quantified gravimetrically through precipitation from the black liquor (i.e. "Lignin I", which precipitates on cooling of the black liquor, "Lignin S" that remains in solution in the black liquor after filtration of Lignin I) and "Lignin P" (which is a lignin co-removed during the
Soxhlet methanol removal of the extractives from pulp), or indirectly ascertained volumetrically by an oxidation reaction with potassium permanganate (Kappa number). The degree of delignif ication of the wood (Lignin I plus
Lignin S) after 20, 40 and 60 min cooking was about 42.5%,
50.5% and 58.4%, respectively.
On removal of the extractives with methanol by
Soxhlet extraction from the organosolv pulps, some lignin was co-removed with the extractives and subsequently precipitated. The amount of this lignin (Lignin P) after the 20, 40 and 60 min cooks was 3.16%, 2.54% and 2.39%, respectively. This indicated that washing with cooking liquor removed the free lignin incompletely from the pulp.
In addition to the quantification analysis of lignin, additional work was designed to determine the molecular 160
weight distribution of the different lignins obtained at the different pulping conditions.
4.6.2. Molecular weight distribution of lignin
Molecular weight distributions of the different lignin types were determined by size exclusion chromatography. A calibration curve obtained using polystyrene standards is given in Fig. 22.
Molecular weight distribution studies were performed on lignins obtained for both normal (autogenic) pressure and high pressure during pulping.
4.6.2.1. MWD of lignins from normal pressure cooks
A series of cooks was performed at normal pressure, that is without pressurizing the vessels prior to their immersion into the hot oil bath. The apparent weight
average (Mw) and the number average (Mn) molecular weight values were calculated from the elution profiles at constant absorptivity 280 nm wavelength. The results are shown in Table 29. 161
18.'
4J 10. A 0» •H ffl 3 U 4. (TJ H 19. 3 CJ CD H 51 O 2 10.
10.
1. J I I L 10 16. 9 22. 6 28. 31 34. 82 29. 73 45. 43 19.75 25.46 31.16 36. 87 42. 58 Elution Volume (mL)
Figure 22. GPC calibration curve with polystyrene standards 162
Table 29. Apparent Mw and Mn of lignins after normal pressure organosolv pulping
Lignin Type: Mw Mn Mw/Mn
Dissolved* 1474 631 2.34
Precipitated** 4218 1076 3.92
Entrapped*** 5525 1134 4.87
From this table it can be seen that the "entrapped lignin" shows the highest weight average molecular weight
(Mw=5525). This indicates a high proportion of higher molecular weight lignin molecules remaining in the pulp as
"entrapped lignin" in comparison to the other lignins. The procedure for calculation of weight average molecular weight places a greater emphasis on the fraction of high molecular weight molecules than that of the number average molecular weight. The fractions of "entrapped lignin" molecules with molecular weights in the range of 150,000 to 50,000 and 50,000 to 8,000, are 6% and 11%, respectively. These fractions are higher than those given for the "precipitated lignin" with 10% of the lignin molecules falling in the range of 50,000 to 8,000, and 0%
*Dissolved lignin, is the lignin that remains in solution even after the liquid-liquid extraction of the extractives from the black liquor. **Precipitated lignin, is the lignin that precipitates on cooling of the "initial black liquor". ***Entrapped or trapped lignin, is the free lignin left in the pulp which is removed from it by successive acetone- water-acetone washings and precipitates from this solution. 163
for the "dissolved lignin" which does not show molecules with Mw higher than 10,000. (See Table 30 and Fig. 23 and
24) .
On the other hand, the "dissolved lignin" shows the lowest Mn value (Mn=631). This reflects a high proportion of low molecular weight (dimers, trimers and tetramers) lignin fragments in the soluble lignin. Almost 45% of the soluble lignin molecules fall in the range of molecular weight below 1000. However, the precipitated and entrapped lignins contain only 22% each of low molecular weight product.
A comparison of the molecular weight distribution of these three (dissolved, precipitated and entrapped) lignins is presented in Fig. 25.
An interesting observation is that fairly well separated peaks are observed in the chromatograms for each lignin fraction at molecular weight lower than 400. The most prominent low molecular weight peak is observed in the dissolved lignin chromatogram and indicates the presence of monomeric components (molecular weight 160 to
190). Assumptions for structures at higher molecular weights are less feasible due to the large number of condensation pathways by which the phenyl-propane units might be joined to form either dimers, trimers, tetramers, etc. These may be more profitably studied by solid state NMR. Table 30. Molecular weight distribution ranges of the different lignin fractions obtained with normal (autogenous) pressure cooks
Molecular Weight Ranges
Lignin 150000-50000 50000-8000 8000-5000 5000-1000 1000-200 < 200 Type % % % % % %
Dissolved 0 0 3 52 38 7
Precipitated 0 10 12 56 20 2
Entrapped 6 11 16 51 20 2 Figure 23. Molecular weight distribution curves of lignins isolated after normal pressure organosolv pulping of slash pine 166
Figure 24. Molecular weight distribution curve of the dissolved lignin isolated after normal pressure organosolv pulping of slash pine 167
D i ss ol V e d L ig n i r
Pr e c i pi t< ted L i< i i n
T r a P P e d L g n i n
1 ' i i i i i ,; i , i i i i i i i | i i i i i i i i , ^T- i i III." 100 1000 10000 100000 1000001 Molecular Weight
Figure 25. Molecular weight distribution of the soluble lignins (Dissolved, precipitated and trapped lignins) isolated from normal organosolv pulping of slash pine 168
4.6.2.2. MWD of lignin from high pressure cooks
As mentioned in Section 4.5.1.1., the 5 minute cook did not result in fiber liberation, but caused removal of extractives and some lignin. On cooling of the black liquor, a small amount of "Lignin I" precipitated and separated, and only the soluble lignin (Lignin S-5) was taken for GPC analysis. A molecular weight distribution of
"Lignin S-5" is presented in Fig. 26a.
4.6.2.2.1. Soluble lignins in the black liquor
After the 20, 40 and 60 min cooking at high pressure, ready fiber liberation took place. The lignins, which precipitated on cooling ("Lignin I") from the respective black liquors, were isolated only for quantitative analysis. Their respective soluble lignins (Lignins S-20,
S-40 and S-60) were taken for GPC analysis. The respective molecular weight distribution curves are shown in Fig. 26 and 27, and a comparison of their molecular weight distributions is given in Fig. 28.
Looking at the distribution curves of these soluble lignins, a discernible shift of these curves toward the lower molecular weight region can be seen as the cooking times are extended (Table 32). This can be explained 169
"b"
o _J
Figure 26. Distribution curves of the soluble lignins isolated after a high pressure organosolv pulping of slash pine: a) S-5 lignin b) S-20 lignin 170
E
"a"
3
o
£ CJ
> 3 "b II in
r-i
Figure 27 Distribution curves of the soluble lignins isolated after a high pressure organosolv pulping of slash pine: a) S-40 b) S-60 171
S - 5 1h JV
S - 201
S - 40
S - 6C>
I I I I I ! I I | I I I I I I I I | I I I I I I I I | I 1 1 1—I—I I > | 100 1000 10000 100000 1000000 Molecular Weight
Figure 28. Molecular weight distribution of the soluble lignins (S-5, S-20, S-40 and S-60) isolated from high pressure organosolv pulping of slash pine 172
in terms of degradation of the higher molecular weight lignin molecules into lower molecular weight fragments. The same degradation trend is also evident on looking at the decrease of the weight average molecular weight of these fractions and the increase of the number average molecular weight, as the cooking times are prolonged. Numerical molecular weight values are presented in Table 31.
Table 31. Apparent Mw and Mn of the soluble lignins after the 5, 20, 40 and 60 min organosolv pulping of slash pine wood
Cooking time Mw Mn Mw/Mn
5 min 1041 407 2.6
20 min 1390 678 2.1
4 0 min 1211 685 1.8
60 min 988 618 1.6
The decreasing polydispersity numbers demonstrate that the degradation of lignin is continued by extending the cooking time under the present conditions. However, contradictory results have been reported by Kondo and
McCarty (1985) on kraft pulping of western hemlock wood
[Tsuga heterophylla (Raf.) Sarg.]. They reported that in
incremental delignification of hemlock wood, the latter 173
increments show much increased proportions of higher molecular weight lignins. Kondo and McCarty (1985) concluded that the formation of higher molecular weight lignin molecules was likely due to recondensation reactions.
Hagstrom-Nasi and Sjostrom (1988) working with dioxane lignin and oxidizing it under alkaline conditions, found that by increasing the concentration of ethanol from
0, 20, 50 and 80%, degradation of lignin was accelerated.
Clare and Steelink (1973) and Katuscak et al. (1971) mention that during the oxidation of lignin under ethanolic conditions it is very likely that the ethanol solvent retarded repolimerization reactions. Hagstrom-Nasi and Sjostrom (1988) in order to clarify this possibility, performed an alkaline oxygen oxidation of creosol at various ethanol concentrations. Creosol was used as a model compound which is known to undergo coupling reactions during alkaline autoxidation (Kratzl, 1966;
Kratzl, 1974). Hagstrom-Nasi and Sjostrom (1988) found that creosol was stabilized by ethanol toward the alkaline oxygen oxidation as ethanol concentration was increased.
They explained this phenomena as a result of coupling reactions of radicals from ethanol with phenoxy radicals, causing a decrease in the generation of dimers.
Consequently, inhibition of repolymerization of the lignin fragments can be explained in terms of the retardant 174
effect of the solvent (ethanol) towards the oxidative coupling reactions.
Therefore, it is possible to infer that working with very high methanol concentrations (i.e. 80%, Paszner and
Cho, 1989) and elevated pressures (Chang and Paszner,
1982), lignin is degraded extensively (Mw=988, at 60 min) and is inhibited from recondensation reactions. These findings can be well supported by the data given in Tables
31 and in Table 32 and emphasized by Paszner and Cho
(1989) as advantages of the N7AEM catalyzed organosolv process.
4.6.2.2.2. Complementary analyses of lignin after a high pressure 60 min pulping
Complementary lignin analyses were performed after a high pressure, 60 min cook. Contrary to the fractionation procedure followed for the extractive analyses after the
5, 20, 40 and 60 min cooks, extensive dilution of the mother black liquor with water (1:10 ratio) rendered another type of lignin ("Lignin II") by precipitating the bulk of the dissolved lignin (Lignin S plus Lignin I) .
This "Lignin II" was isolated and dried as described in
Section 3.6.2.1. The molecular weight distribution of this Table 32. Percentage of the molecular weight ranges of the different soluble lignins fractions from high pressure organosolv cooks of slash pine wood
Molecular weight, M, w
Lignin type 8000 - 5000 5000 - 1000 1000 - 200 < 200 % % % % s 5 0.5 24.5 72.0 3.0 s 20 2.0 48.0 47.5 2.5 s 40 1.0 46.0 51.0 2.0 s 60 0.5 42.5 55.5 2.0 176
lignin was determined by size exclusion chromatography with the aid of an HPLC. (See Fig. 29a).
After Soxhlet removal of the extractives from the pulp with methanol as the solvent, another fraction of lignin ("Lignin P") was co-extracted and used for GPC analysis (See Fig. 29b) . This lignin was compared with
"Lignin II" and "Lignin S-60", all originally from the same 60 min cook. The molecular weight distributions of these three lignins are compared in Fig. 30 and their apparent Mw and Mn are given in Table 33.
Table 33. Apparent Mw and Mn of Lignin II, Lignin P and Lignin S-60 after the 60 min cooking
Mw Mn Mw/Mn
Lignin II 4395 759 5.8
Lignin P 23999 2019 11.9
Lignin S-60 988 618 1.6
From these data, it can be seen that "Lignin P" has an unusually high polydispersivity number and weight average molecular weight, while "Lignin S-60" has both the lowest polydispersivity number and number average molecular weight. Trapped lignin fragments in the il <£> in r-i cO a *n ,© © © CD © CD CD ©
Figure 29. Distribution curves of the lignins isolated during the complementary analysis after a 60 min high pressure organosolv pulping of slash pine: a) Lignin-II-60 b) Lignin-P 178
LIGNIN II
LIGNIN P
Figure 30. Molecular weight distribution of "Lignin II", "Lignin P" and "Lignin S-60" after the 60 min cooking of slash pine 179
secondary wall require further degradation before they can escape by diffusion into the cooking liquor. Thus limited solvent accessibility in the cell wall may partly be responsible for the relatively large amount of high molecular weight residual lignin in organosolv pulps.
Due to the fact that "Lignin P" was co-extracted together with the extractives during the Soxhlet extraction of the pulp, it was first suspected that this lignin might undergo recondensation because of the long refluxing process (54 h) required for removal of the extractives. In order to elucidate this intriguing result,
300 mg of a low molecular weight lignin ("Lignin S-20, Mw=
1390 and Mn= 678) was refluxed in methanol for 54 h. The weight and number average molecular weights obtained after this treatment were the same as the the original values.
This confirms that refluxing in methanol did not provoke recondensation of the organosolv lignin, and therefore the initial high molecular weights of pulp residual lignin are indeed valid. 180
5. SUMMARY
The behaviour of the extractives present in slash pine wood (Pinus elliottii) during pulping using catalyzed
80% aqueous methanol, was studied in detail.
Resin- and fatty acids were characterized before and after the pulping trials. Total wood extractives were determined gravimetrically by methanolic cold maceration and Soxhlet extraction, and by the TAPPI standard T 204 os-76. No significant differences were found between the efficiencies of these three types of extractions.
The resin- and fatty acids thus collected were saponified and/or methylated and characterized by gas liquid chromatography (GC or GLC) and gas chromatography- mass spectrometry.
Pulping experiments were performed at 2052C for periods of 5, 20, 40 and 60 min.
Chemical characterization of the resin and fatty acid extractives revealed only minor qualitative changes in the form of limited isomerizations of certain components .
Resin- and fatty acids surviving the high temperature pulping process, were found mainly in the black liquor.
The extractives were recovered from the cooking liquor by a selective tertiary component liquid/liquid extraction procedure. The water/methanol ratio of the black liquor was adjusted prior to extraction with diethyl ether 181
according to a phase diagram developed for this purpose.
The liquid/liquid extraction was nearly 100% effective in removing the extractives from the black liquor.
In the cooking liquor, substantial quantities of resin acids (89.8%) and fatty acids (25.6%) were detected after 5 min cooking (less than the actual time to temperature). After a 60 min cook the black liquor contained 78.1% and 71.6% resin- and fatty acids, respectively, while the pulp retained 11.7% and 8.2%, respectively.
Effective extractives removal from the black liquor was observed on precipitation of the lignin (Lignin II) by dilution with 10 times volume of water. Lignin II carried
98% and 60.4% of resin- and fatty acids(respectively) leaving minor amounts of resin acids (2%) and some fatty acids (39.6%) dissolved in the aqueous filtrate. A small fraction of lignin which precipitates on cooling of the black liquor ("Lignin I") adsorbed and carried 10.2% and
20.2% of the resin- and fatty acids, respectively. It is, thereby, demonstrated that outright lignin precipitation from organosolv black liquor usually yield lignin powders substantially contaminated with extractives and the aqueous filtrate still contains extractives residues which may be toxic to fermenting organisms. The residual extractives in the aqueous filtrate after precipitating the lignin did not show structural differences from the 182
components normally removed with the precipitated lignin and thus extractives removal from the black liquor by lignin precipitation may depend on the extractive binding capacity of the lignin or limited by concentration
(solubility) in the aqueous filtrate.
Different lignins were obtained from the black liquor and pulp, based on their solubility. A lignin fraction which precipitates on cooling of the black liquor was designated "Lignin I", the lignin that remains in solution was named "Lignin S" and the lignin that required further extraction from the pulp was called "Lignin P". Their molecular weight distributions were determined by size exclusion chromatography on an HPLC. Quantification of these lignins involved both gravimetric and volumetric methods. 183
6. CONCLUSIONS
Removal of the wood extractives was not affected by
heat, since extraction by both cold methanol
maceration and Soxhlet methanol extraction gave the
same qualitative and quantitative results.
Efficiencies of the cold methanol maceration, methanol
Soxhlet extraction and the TAPPI extraction of the
wood extractives from slash pine were very similar.
Quantitative results of the slash pine wood extractives
after 6 weeks of storage were almost the same by the
three methods used: cold methanol maceration (4.2%),
methanol Soxhlet extraction (4.3%) and the TAPPI
standard T 204 os-76 (3.9%).
Methylation of the resin- and fatty acids dissolved in
dichloromethane-methanol (9:1) was faster and more
complete than in diethyl ether-methanol (9:1) or
methanol alone.
Methylation of the resin- and fatty acids present in
the colored wood extracts solutions was found to be
complete after bubbling freshly prepared diazomethane
for about 4 min.
Determinations of the resin- and fatty acids (RAFA)
from wood, pulping liquor and pulp were performed
without fractionation of the extracts before the gas
chromatographic analysis. Good resolution of these 184
compounds was due to the proper temperature
programming and characteristics of the columns used.
7. The HP-5 capillary column was able to clearly resolve
pimaric, sandaracopimaric, isopimaric, palustric,
dehydroabietic, abietic and neoabietic acids. However,
it did not separate the pair levopimaric-palustric
acids. Among the fatty acids of the study only
palmitic and stearic acids were resolved on this
column.
8. The DB-225 megabore column resolved palmitic, stearic,
oleic, linoleic and linolenic acids properly .
Direct analysis of the resin- and fatty acids without
separation from the other wood extractives, was due to
the excellent characteristics of the capillary columns
(fused-silica cross-linked bonded phase) and to the
appropriate time programming for the GC analysis.
9. The total content of the 7 major resin acids present
in slash pine wood after 6 weeks of storage (1.040%)
was notably reduced after 24 weeks of storage
(0.206%) .
Comparison of the mass fragmentation patterns of
palustric acid, levopimaric acid and their
corresponding peaks in the wood extract chromatograms,
revealed that levopimaric acid is not present in the
methanolic extract of the wood sample after 6 weeks of
storage. However, the possibility could exist that it 185
might be present in fresh wood and that it might have
disappeared during storage.
10. The total content (1.389%) of the 5 major fatty acids
present in slash pine wood after 6 weeks of storage
was greatly reduced after 24 weeks of storage
(0.316%).
11. Relative proportions of the resin acids after 6, 24
and 52 weeks of storage show that after long periods
of storage, dehydroabietic acid is the most stable
form among the resin acids.
12. Selective removal of the extractives from the black
liquor (methanol-water at 80:20 ratio) was
accomplished using liquid-liquid extraction with added
diethyl ether. The ternary solvent system that gave
good solvent separation (diethyl ether and water-
methanol) had the following final proportions:
Methanol-water-ether (40:50:50).
13. Most of the extractives removed from the wood after
the 60 min pulping were found in the black liquor (RA=
0.160% and FA= 0.245%) and precipitated lignin
(RA=0.021% and FA=0.0 69%). Some residual resin- and
fatty acids were left in the pulp (RA=0.024% and
FA=0.028%) .
14. Organosolv pulping of fatty acid model compounds
demonstrated that their survival was closely related
to their chemical structures. Stearic acid did not 186
suffer any chemical change after organosolv pulping.
On the other hand, oleic and linoleic acids were
reduced from their original contents by as much as 20
and 90%, while linolenic acid was completely degraded
during pulping. The more unsaturated the acid, the
more vulnerable it was to destruction.
15. The total resin acid content does not suffer
quantitative changes after organosolv pulping, but
instead qualitative modifications occur as a result of
either isomerization and/or oxidation reactions.
16. Model compounds for palustric and levopimaric acids
during organosolv pulping (60 min at 2052C) are almost
completely isomerized into dehydroabietic acid.
17. Methyl neoabietate model compound is completely
destroyed (disappears) after organosolv pulping.
18. Organosolv pulping of isopimaric acid (model compound)
renders isopimaric acid (88%), pimaric acid (1.8%),
sandaracopimaric acid (1.4%), dehydroabietic acid
(3.8%) and 5.0% of other non-identified compounds.
19. Model compounds of pimaric, sandaracopimaric and
dehydroabietic acids do not suffer any chemical change
during organosolv pulping at 2052 during 60 min.
20. Isomerization or oxidation reactions of the resin
acids during storage of wood samples, lead to
formation of dehydroabietic acid, while during 187
organosolv pulping abietic and dehydroabietic acids
are the preferred end products.
21. The average fatty acid content of wood samples stored
for 24 weeks (samples used for pulping) was 0.316%,
and after 60 min of organosolv pulping all (0.342%)
fatty acids were removed. This increment can be the
result of better hydrolysis (solvolysis) of the fat
material at high temperature or the end result of
isomerization reactions of unidentified fatty acids
into the five major fatty acids studied.
22. Quantitative analysis of lignin in slash pine wood
gives an insoluble-lignin content of 26.8% and a
soluble-lignin content of 1.4%. Therefore, its total
lignin content was 28.2%.
23. Extensive dilution of the pulping black liquor with
water (1:10 ratio) rendered a precipitated lignin
("Lignin II") which adsorbed 98% of the resin acids
and 60% of the fatty acids, leaving the residual
resin- and fatty acids dissolved in the aqueous phase.
24. GPC analyses of the precipitated soluble lignin
("Lignin S-5"), obtained from a 5 min cook, showed the
presence of a high proportion (75%) of low molecular
weight lignin (less than 1000).
25. GPC analyses of the soluble lignins after the 20, 40
and 60 min cooks show that the weight average
molecular weight (Mw) decreases as the cooking time is 188
prolonged. These results indicate a virtual absence of
any lignin recondensation reactions during organosolv
pulping.
26. Soluble lignins do not suffer recondensation after
refluxing them for 54 h in methanol.
27. Precipitation of the soluble lignin from the black
liquor by dilution apparently cannot remove all the
toxic wood extractives from aqueous solution. 189
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APPENDIX A
Mass spectra of the most common resin acids present in pine species Figure Al. Mass spectrum of 8(14),15-pimaradien-18-oate (methyl pimarate) Figure A2 . Mass spectrum of 8 (14),15-isopimaradien-18-oate (methyl sandaracopimarate) Figure A3. Mass spectrum of 7,15-isopimaradien-18-oate (methyl isopimarate)
Figure A5. Mass spectrum of 8 (14),12-abietadien-18-oate (methyl levopimarate) Figure A6 . Mass spectrum of 8,11,13,-abietatrien-18-oate (methyl dehydroabietate)
Figure A8. Mass spectrum of 8 (14),13(15)-abietadien-18-oate (methyl neoabietate) 212
APPENDIX B
Mass spectra of the most common fatty acids present in pine species Figure Bl. Mass spectrum of hexadecanoate (methyl palmitate) in
l 1 ill 1)1. 11 nil ll. Ljjjdi 1 L.Jt.i,L, ...-Jut," ll* J^W 1 - \- J L L
Figure B2. Mass spectrum of octadecanoate (methyl stearate) Figure B3. Mass spectrum of 9-octadecenoate (methyl oleate) Figure B4. Mass spectrum of 9,12-octadecadienoate (methyl linoleate) Figure B5. Mass spectrum of 9,12,15-octadecatrienoate (methyl linolenate)