Alkaline Degradation of Cellobiose with Kraft Green Liquor

U. S. Department of Agriculture * Forest Service * Forest Products Laboratory * Madison, Wis. ALKALINE DEGRADATION OF CELLOBIOSE WITH KRAFT GREEN LIQUOR U.S.D.A. FOREST SERVICE RESEARCH PAPER FPL 153 1971 SUMMARY The products were determined from oxidative alka line degradation of cellobiose in laboratory-prepared kraft green liquor, a solution of sodium carbonate and sodium sulfide. The major degradation product was 3,4-dihydroxybutyric acid and only minor amounts of isosaccharinic acid were produced in the presence of oxygen. The amount of carbohydrate undergoing an oxidative stopping reaction was 22.2 percent in oxygen, and the glycosyl-aldonic acids formed were D arabiononic, D-mannonic, and D-erythronic acids. ALKALINE DEGRADATION OF CELLOBIOSE WITH KRAFT GREEN LIQUOR1 By ROGER M. ROWELL JESSE GREEN Chemists and MARTHA A. DAUGHERTY Forest Products Laboratory,2 Forest Service, U.S. Department of Agriculture INTRODUCTION reactive sites, and side reactions with other wood components . In kraft pulping, spent black liquor is burned in In this work, cellobiose was degraded in solu- chemical recovery furnaces, and the dissolution tions of sodium carbonate, sodium sulfide, and of the smelt results in green liquor. The green laboratory-prepared kraft green liquor M liquor is composed primarily of sodium carbonate Na CO and 0.096 M Na S) for varyingtimes in the 2 3 2 and sodium sulfide; it acquires the green color presence of and in the absence of oxygen. from the presence of colloidal iron sulfide. The Two previous investigations by the author and green liquor is treated with lime (causticization) others (2, 3) dealt with the oxidative alkaline de- that converts the carbonate to hydroxide and the gradation of cellobiose in both barium and sodium new white liquor is then hydroxide. Under those strongly alkaline conditions, cellobiose was degraded in the absence of oxygen preferentially to D-glucoisosaccharinic acid by an endwise depolymerization reaction clarified and used again in another pulping cycle. (peeling reaction). In that reaction scheme, the Kraft green liquor has recently been found (5) 3 reducing end is eliminated in the form of 4-deoxy- effective in controlling fungal deterioration of D-glycero-2,3-hexodiulose, which is rearranged wood substances in fresh wood pulp chips stored to 2-glucoisosaccharinic acid by abenzil-benzilic outdoors in piles. The treatment, dippingthe chips acid type rearrangement or fragmented to glycolic in green liquor, stopped fungal attack and pre- and 3,4-dihydroxybutyric acids if an oxidant is vented the initial temperature rise caused by res- present, In the absence of oxygen the nonreducing piration of the living cells and by microbial oxida- D-glucose end is converted mainly to lactic acid or tions. Thus, the green liquor seemed to serve as a in oxygen it follows an oxidative pathway to gly- fungicide and an enzyme inhibitor. Because these ceric and arabinonic acids. treated piled chips may be exposed to the atmos- In inert atmospheres, the endwise depolymeri- phere for extended periods of time, it was of in- zation occurs without termination and accounts for terest to determine the effects of this oxidative the total depolymerization of the sugar units pres- alkaline medium on the carbohydrates in the chips. ent. In oxygen, however, termination of this reac- Using a soluble sugar as a model system, a tion is attained by the formation of glucosyl- sugar such as cellobiose instead of cellulose or aldonic acids, which are resistant to further alka- wood chips gives an indication of the maximum line degradation at the low temperatures used effects the alkaline mediumwill have on the carbo- (25°C.). The aldonic end units are mainly D- hydrates. This is possible because no complica- arabinonic acid, lesser amounts of D-mannonic tions are involved such as penetration of chemi- and D-erythronic acids, and traces of D-gluconic cals, accessibility of wood sugars, solubility of and 2-deoxy-D-ribonic acids. 1 Presented in part at the 160th National American Chemical Society Meeting, Chicago, Ill., 1970. 2 Maintained at Madison, Wis., in cooperation with the University of Wisconsin. 3 Underlined numbers In parentheses refer to Literature Cited at the end of this report. ammonium acetate (0.1 M) to separate and elute EXPERIMENTAL the acids. The eluate from the bottom of the column was analyzed by the automated periodate-pentane- 2,4-dione assay (4) employing the Technicon auto- Reaction Conditions analyzer. The yellow color developed in the assay by the formation of 3,5-diacetyl-l,4-dihydro-2,6- Solutions of cellobiose (0.2 milligrams per lutidine was recorded at 420 nanometers. The milliliter) were degraded in a (a) 0.096 M aqueous amount of each compound was determined by com- sodium sulfide, (b) 0.28 M sodium carbonate, or parison of areas under peaks relative to standard (c) green liquor (0.28 MNa CO and 0.096 M Na S) 2 3 2 runs (tables 1 and 2). at 25°C. in 100-milliliter bubbling towers equipped with reflux condensers. Degradations in oxygen were made by bubbling oxygen gas through the Oxidation of Inorganic Sulfur Compounds solutions during the reaction. All other degradations were carried out by stoppering the towers A solution of sodium sulfide (0.096 M) was without adding or removing gases. oxidized at 25° C. by bubbling oxygen gas through the solution. Samples were removed every 24 hours, the pH determined, and the samples ana- Detection of Products lyzed for sulfide, sulfite, thiosulfate, sulfate, and total sulfur, by TAPPI methods T624 M-44 A sample after degradation (3.6 milliliters) was (1) and T624 OS-68 (6) (table 3 and figure 1). pumped (0.6 milliliter per minute), by a peristaltic Solutions of sodium sulfite (0.096 M), sodium pump, onto a column (0.6 centimeter x 28 centi- thiosulfate (0.096 M), and sodium sulfate (0.096 M) meters, resin bed) of Bio-Rad AG 1-X8 (200-400 were treated with oxygen, as described, and ana- mesh) resin in the acetate form The column was lyzed at time of solution and after 24 hours for washed with water (1.8 milliliters) and then with sulfur oxidation products (table 4). Table 1.-- Retention times of compounds on 1 Bio-Rad AG 1- X8 (200-400 mesh) 1 6 x 28 centimeters of resin in the acetate form. FPL 153 -2- Table 2.--Oxidative alkaline degradation of cellobiose1 1Reported as molar percentage yield from cellobiose. 2 0.096 M aqueous sodium sulfide; 0.28 M sodium carbonate; and green liquor, 0.096 M aqueous sodium sulfide plus 0.28 M sodium carbonate. 1,2 Table 3.--Oxidation of sodium sulfide with oxygen at 25°C. 1 Milligrams of sulfur per milliliter. 2 pH of solutions was 11.6 throughout the oxidations. 1 Table 4.--Products of ,sulfur oxidation- 1 Reported as milligrams of sulfur per milliliter. FPL 153 -4- Figure 1.--Oxidation of 0.096 M sodium sulfide with molecular oxygen. M 138 764 -5- DISCUSSION It can be seen from table 1 that there is good separation in the 0.1 M ammonium acetate system for neutral sugars, bound acids, isosaccharinic and glyceric acids; however, no separation is achieved for arabinonic acid from 3,4- dihydroxybutyric acid. To overcome this diffi- culty, the 3,4-dihydroxybutyric acid was analyzed in the 0.5 M acetic acid systemwhere there The concentration of the hydroxyl ion formed in is good separation of these two acids. the equilibrium accounts for the pH of 11.6 and The two major differences between the degrada- the acids produced from the carbohydrate de- tion of cellobiose in barium or sodium hydrox- gradation are not sufficient to affect the pH. The ide (2) and in green liquor is in the percentage same is true for the sodium carbonate solution: yield of isosaccharinic acid compared to 3,4- dihydroxybutyric acid and in the total amount of degradation takingplace per unit of time. In barium hydroxide (24 hours at 25° C.) under nitrogen, 50 percent of the molar yield was isosaccharinic acid with a total degradation yield of 73.4 per- Hydrogen sulfide can be detected with lead ace- cent @. In green liquor, under the same condi- tate during the sugar degradation that may be due tions, 4.84 percent is isosaccharinic acid with a to the equilibrium between the hydrosulfide ion - = total degradation yield of only 18.5 percent. The (HS ) and the sulfide ion (S ), data show that as long as oxygen is excluded from solutions of sodium sulfide, sodium carbonate, or green liquor, very little happens to the carbohydrates present. The high yields of 3,4-dihydroxybutyric acid in green liquor (42.7 percent at 5 days +O ) indi- 2 cate that the 4- deoxy-D-glycero-2,3-hexodiulose intermediate undergoes extensive oxidative frag- mentation and does not participate in a benzil- which gives a proton to react with the hydro- benzilic acid type rearrangement to isosaccha- sulfide ion to give hydrogen sulfide. The rinic acid. In barium hydroxide (24 hours ), might also come from the ionization of the car- 2 boxylic acids produced in the alkaline degrada- the yield of 3,4-dihydroxybutyric acid was 19.7 tion percent (2). It is interesting that the amount of sugar undergoing the oxidative stopping reaction is about the same in green liquor (22.2 percent) as it was in barium hydroxide (27.2 percent) (2). In both, the aldonic end units are D-arabinonic, D-mannonic, and D-erythronic acids. It might be expected that while sodium sulfide Table 3 and figure 1 indicate the oxidation solution underwent oxidation, there would be a pathway of the sulfide ion is via the thiosulfate drop in the pH (sodium sulfide, pH 11.7; sodium to sulfate.

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