Subscriber access provided by University of Sussex Library Article Willow lignin oxidation and depolymerization under low cost ionic liquid Raquel Prado, Xabier Erdocia, Gilbert Francesco De Gregorio, Jalel Labidi, and Tom Welton ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.6b00642 • Publication Date (Web): 10 May 2016 Downloaded from http://pubs.acs.org on May 13, 2016
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1 2 3 Willow lignin oxidation and depolymerization under low cost ionic liquid 4 5 a b a b a 6 R. Prado , X. Erdocia , G. F. De Gregorio , J. Labidi , T. Welton 7 8 9 a. Department of Chemistry, Imperial College London, Exhibition Road, SW7 2AZ, London, 10 11 UK 12 13 14 b. Chemical and Environmental Engineering Department, University of the Basque Country, 15 16 Plaza Europa 1, 20018, Donostia San Sebastián, Spain 17 18 19 Corresponding author: r.prado [email protected] 20 21 22 Key words: Catalyst, heterogeneous, lignin, ionic liquids, oxidation. 23 24 25 Abstract 26 27 28 Willow biomass was subjected to different pretreatment conditions with triethylammonium 29 30 hydrogen sulfate as solvent and the produced lignin solutions were treated by oxidation either 31 32 homogeneously using H 2O2 as oxidant, or by heterogeneous catalysis using TiO 2. Lignin, 33 34 residual lignin, oil and the recovered IL were characterized in order to determine the effects 35 36 of each treatment. Lignin was successfully extracted and depolymerized by oxidation and 37 38 39 characterized by ATR IR, HPSEC and py GCMS. The obtained oil was characterized by 40 41 GCMS, it was composed mainly of acids derived from the sugar and lignin fractions, the 42 43 TiO 2 catalyzed oils were richer in phenolic derived compounds than sugar fractions. The final 44 45 ionic liquid was characterized in order to determine its suitability to be reutilized. 46 47 48 Introduction 49 50 51 Recently, the quest for greener technologies that decrease our dependence on fossil fuels has 52 53 become the principal target for many research groups. Efficient utilization of biomass is 54 55 becoming increasingly important as it is the most abundant renewable material on earth, with 56 57 1 58 a yearly global supply of approximately 200 billion metric tons . Lignocellulose consists 59 60 ACS Paragon Plus Environment ACS Sustainable Chemistry & Engineering Page 2 of 37
1 2 3 mainly of plant cell wall material; it is a complex natural composite with three main 4 5 biopolymers: cellulose (ca. 50%), hemicelluloses (ca. 25%) and lignin (ca. 25%) 2. The 6 7 structure and composition of lignocellulose varies greatly, depending on plant species, part of 8 9 1 10 the plant and growth conditions . 11 12 13 Lignin is a phenolic polymer synthesized via the oxidative coupling of three major C6 C3 14 15 phenylpropanoid units, namely, syringyl alcohol, guaiacyl alcohol and p coumaryl alcohol, 16 17 which form a complex and random three dimensional structure inside the cell wall which 18 19 varies depending on the specie 3. Lignin is the main by product in chemical pulping processes, 20 21 amounting to around 100 million tons per year, most of which is burned to generate energy 22 23 24 which is reintegrated into the plant for its own energy supply. However, as lignin is the only 25 26 renewable source of aromatic compounds, it can potentially be an important source of 27 28 different products with a range of applications 4. The diversity of functional groups present in 29 30 lignin allows it to be used as a dispersant in cement and gypsum blends 5, as an emulsifier or 31 32 6 33 chelating agent for removing heavy metals from industrial effluent , as a food additive, in
34 7 35 batteries as a coating for graphite electrodes and it has been added to composites as 36 37 reinforcement 8. 38 39 40 Willow is a commercially cultivated crop that has potential to be a dedicated biomass crop. 41 42 Willow’s leaves and bark are rich in compounds widely used in the pharmaceutical industry, 43 44 well recognized throughout Europe for treating inflammatory conditions and pains of 45 46 47 different origin. There are presently 24 willow varieties available that have been certified by 48 49 the EU. There are 10 of commercial use today and approximately one two varieties are 50 51 developed annually9. 52 53 54 Room temperature ionic liquids (ILs) are receiving a significant amount of interest owing to 55 56 their characteristics as environmentally friendly solvents for a range of chemical processes 57 58 59 60 ACS Paragon Plus Environment Page 3 of 37 ACS Sustainable Chemistry & Engineering
1 2 3 both for catalyzed and uncatalyzed reactions, or as possible constituents in electrochemical 4 5 devices 10,11 . Thus the molecular design, synthesis and characterization of ILs have been the 6 7 focus of many recent scientific investigations. Their unique properties, such as being liquid 8 9 10 over a wide temperature range, having negligible vapor pressure and high thermal, chemical 11 12 and electrochemical stability, allow a wide range of applications and make ILs good 13 14 alternatives to environmentally harmful volatile organic solvents 12 . The properties of ILs vary 15 16 enormously as a function of their molecular structure and considerable effort has been 17 18 19 devoted to identifying and understanding those that have superior properties in any given 20 13,14 21 application . 22 23 24 It is well known that the structure of lignin is affected by the extraction processes, which 25 15 26 cause chemical changes and fragmentation due to the chemical agents and conditions used . 27 28 This fact makes the study of how lignin is affected by each IL of paramount importance. For 29 30 example, Tan et al. observed that after delignification of sugarcane waste using 1 ethyl 3 31 32 33 methylimidazolium alkylbenzenesulphonate ([C2C1im][ABS]), the obtained lignin had a 34 35 lower average molecular weight (MW) than autocatalysis lignin. Both lignins were acetylated 36 37 in order to allow comparison. Acetylated lignin from [C2C1im][ABS] had a lower Mw (3690 38 39 g/mol) than acetylated autohydrolysis lignin (19300 g/mol), polydispersity was also lower for 40 41 the [C C im][ABS] treated lignin (1.66 and 11.4 respectively)16. George et al . studied the 42 2 1 43 44 effect of different ILs (1 ethyl 3 methylimidazolium n hexylsulfate ([C 2C1im][HxSO 4]), 1 45 46 ethyl 3 methylimidazolium diethylphosphate ([C2C1im][Et 2PO4]), 1 ethyl 3 47 48 methylimidazolium n butylsulfate ([C2C1im][BuSO 4]), 1 ethyl 3 methylimidazolium 49 50 dimethylphosphate ([C2C1im][Me 2PO4]), 1 ethyl 3 methylimidazolium lactate 51 52 53 ([C2C1im][lac]), 1 ethyl 3 methylimidazolium chloride [C2C1im]Cl, 1 ethyl 3 54 55 methylimidazolium acetate ([C2C1im][Me 2CO 2]), 1 butyl 3 methylimidazolium chloride 56 57 ([C4C1im]Cl), Cyphos 101, Cyphos 165 and 1 methyl 2 pyrrolidonium chloride ([C1pyr]Cl)) 58 59 60 ACS Paragon Plus Environment ACS Sustainable Chemistry & Engineering Page 4 of 37
1 2 3 with lignin from different sources (organosolv, alkali (NaOH) and moderately sulfonated 4 5 alkali lignin). It was observed that the anion had more influence on the lignin structure than 6 7 the cation. The effect of the anion in modifying lignin’s molecular weight follows the order: 8 9 10 sulfate>lactate>acetate>chloride>phosphate. It must be highlighted that the rate of 11 12 modification of lignin by the action of IL also depends on its source, with organosolv lignin 13 14 being more susceptible to structural changes than moderately sulfonated lignin and alkali 15 16 lignin 17,18 . 17 18 19 20 Due to its complex structure, few investigations using lignin directly as a substrate have been 21 22 23 conducted to study its reactivity. However, many studies have been carried out using lignin 24 25 model compounds in order to elucidate the reaction mechanisms and the proper conditions to 26 27 extend the reaction to lignin 15 . The depolymerization of lignin model compounds and lignin 28 29 in ILs have been studied under both reductive and oxidative conditions. The reductive 30 31 32 conditions were achieved by adding Lewis and Brönsted acids as a catalyst; however, these 33 34 reactions were only briefly studied because of the low reactivity shown by lignin itself, 35 36 despite the high yields obtained with lignin model compounds. Oxidation has been studied 37 38 more extensively, in most cases coupling a metal catalyst such as Fe, Mn, Co, V, Pd, Mg and 39 40 an oxidizing agent such as O , H O or other peroxide acids with many different solvents and 41 2 2 2 42 15,19 43 under different conditions . The role of the ILs in this case was to be the reaction solvent 44 45 and/or catalyst 20 . 46 47 Three different species of willow (Resolution, Terranova and Endurance) were delignified by 48 49 [Et NH][HSO ] following the best conditions observed in previous experiments for 50 3 4 51 21 52 Miscanthus . In previous experiments, it was observed that [Et3NH][HSO 4] showed lower 53 54 overall yield than butylimidazolium hydrogensulphate [HC 4im][HSO 4] for lignin oxidation 55 56 depolymerisation. In addition, the composition of the oil was different for both ILs. In this 57 58 59 60 ACS Paragon Plus Environment Page 5 of 37 ACS Sustainable Chemistry & Engineering
1 2 3 work we sought to improve the [Et 3NH][HSO 4] performance by adding a heterogeneous 4 5 catalyst, as is less toxic than [HC 4im][HSO 4]. The obtained lignin was characterized and the 6 7 most suitable specie was treated for different times and at different temperatures. The aim of 8 9 10 the study was to establish which lignin was the best for oxidative depolymerization under 11 12 different conditions using low cost ILs. The influence of heterogeneous and homogeneous 13 14 conditions was studied by adding TiO 2 and H 2O2 for the lignin obtained from each chosen 15 16 willow specie and pretreatment conditions. 17 18 19 20 21 22 Instruments 23 24 25 All lignin samples were characterized by attenuated total reflectance infrared spectroscopy 26 27 (ATR IR) by direct transmittance in a single reflection ATR System (ATR top plate fixed to 28 29 an optical beam condensing unit with ZnSe lens) with an MKII Golden Gate SPECAC 30 31 1 32 instrument. Spectral data was acquired over 30 scans in the range of 4000 700 cm and 4 cm 33 1 34 resolution. 35 36 37 The isolated lignin products were subjected to High Performance Size Exclusion 38 39 Chromatography (HPSEC) to obtain lignin MW and M W distribution (MWD) using a JASCO 40 41 instrument equipped with an interface (LC NetII/ADC) and a reflex index detector (RI 42 43 2031Plus). Two PolarGel M columns (300 x 7.5 mm) and PolarGel M guard (50 x 7.5 mm) 44 45 46 were employed. Dimethylformamide + 0.1% lithium bromide was used as the eluent. The 47 1 48 flow rate was 0.7 mL min and the analyses were carried out at 40 °C. Molecular weight 49 50 calibration was carried out using polystyrene standards (Sigma Aldrich) ranging from to 266 51 52 to 70,000 g mol 1. 53 54 55 GC MS analysis was performed to identify and to quantify the monomers present in the oil. 56 57 The oil was dissolved in ethyl acetate (HPLC grade) and was injected into an Agilent GC 58 59 60 ACS Paragon Plus Environment ACS Sustainable Chemistry & Engineering Page 6 of 37
1 2 3 (7890A) MS (5975C inert MSD with Triple Axis Detector) equipped with a capillary column 4 5 HP 5MS ((5% Phenyl) methylpolysiloxane, 60 m x 0.32 mm). The temperature program 6 7 started at 50 °C raised to 120 °C at a rate of 10 °C min 1, held for 5 min, raised to 280 °C at a 8 9 1 1 10 rate of 10 °C min , held for 8 min, raised to 300 °C at a rate of 10 °C min and finally held 11 12 for 2 min. Helium was used as carrier gas. Calibration curves were established using 13 14 commercially available compounds with purity >99% (Sigma Aldrich) –phenol, o cresol, m 15 16 cresol, p cresol, guaiacol, catechol, 4 methylcatechol, syringol, acetovanillone, 17 18 19 syringaldehyde, acetosyringone and 4 hydroxy 3 methoxyphenylacetone. 20 21 In order to determine the influence of the process on the nature of the IL and elucidate how 22 23 24 the chemical structure of the IL is affected, ATR IR spectral data was acquired over 30 scans 25 1 1 26 in the range of 4000 700 cm and 4 cm resolution and NMR spectra were recorded at 30 °C 27 28 on a Bruker Avance 600 MHz equipped with a z gradient BBI probe. Typically, 40 mg of 29 30 sample were dissolved in DMSO d6. The spectral widths were 5,000 and 25,000 Hz for the 31 32 1 13 33 H and C spectra, respectively. 34 35 High performance liquid chromatography (HPLC) analysis was performed on a Shimadzu 36 37 38 Prominence HPLC with a photodiode array (PDA) detector. Detection of substrates was 39 40 carried out at 280 nm using a Purospher STAR RP 18 end capped column. A 20% 41 42 Acetonitrile, 80% water isocratic method lasting 10 min was employed. 43 44 45 HSQC NMR spectra were recorded at 30 ºC on a Bruker Avance 600 MHz equipped with a 46 47 z gradient BBI probe. Typically, 20 mg of sample was dissolved in 0.6 ml of DMSO d6. 48 49 50 51 52 Synthesis of ionic liquid 53 54 [Et 3NH][HSO 4] was synthesized by drop wise addition of 5 M H 2SO 4 to Et 3N using an 55 56 acid:base ratio of 1:1. An ice bath was used to maintain the temperature. The mixture was 57 58 59 60 ACS Paragon Plus Environment Page 7 of 37 ACS Sustainable Chemistry & Engineering
1 2 3 stirred for 24 h and dried under vacuum. The H 2SO 4 was titrated prior to use in order to 4 5 determine its concentration as acid base ratio has a large impact on pretreatment and the 6 7 synthesis was performed in the way that deviation from 1:1 ratio was the minimum 8 9 22 10 possible . 11 12 Pretreatment 13 14 Willow, water and [Et 3NH][HSO 4] were mixed in a 1:2:8 mass ratio. First the 3 different 15 16 species of willow were pretreated at 120 °C for 22h21 . The mixtures were subjected to 17 18 19 different time and temperature conditions (150 °C 2 h, 120 °C 8 h and 120 °C 22 h) to 20 21 establish the best conditions to obtain the most suitable lignin for oxidative depolymerization. 22 23 The resulting solution (black liquor) was filtered using Whatman 542 filter paper and washed 24 25 with 3 volumes of ethanol. The ethanol of the black liquor was evaporated under vacuum at 26 27 55 °C. 28 29 30 Depolymerization 31 32 In lignin depolymerization the performance of the heterogeneous and homogeneous 33 34 conditions were compared. The black liquor was treated under oxidizing conditions with 35 36 either 5% H2O2 which acted as oxidant, or 1% TiO 2 as catalyst with 1% H 2O2, which was 37 38 39 required to initiate the reaction, for 1 h at 120 °C. The H 2O2 percentages were referred to an 40 41 exact H 2O2 weight percent added from 30% H 2O2 commercially available solution. 42 43 The residual lignin was precipitated by the addition of 2 volumes of distilled water and then 44 45 centrifuged at 4000 rpm for 15 min. The residual lignin was washed with distilled water and 46 47 dried at 70 °C overnight. 48 49 50 The liquid phase was subjected to a liquid/liquid extraction process with MeTHF, in order to 51 52 extract the small phenolic compounds. Extraction was repeated three times and the MeTHF 53 54 was evaporated and resulting oil was characterized by GC MS. The [Et 3NH][HSO 4] ionic 55 56 liquid was recovered after centrifugation and dried by evaporation. 57 58 59 60 ACS Paragon Plus Environment ACS Sustainable Chemistry & Engineering Page 8 of 37
1 2 3 4 5 6 Results and discussion 7 8 9 The main aim of this study was to establish which willow specie and pretreatment conditions 10 11 provided the best lignin for being depolymerized under oxidative conditions, using either 12 13 homogeneous or heterogeneous conditions. Three different willow species were treated by 14 15 the same pre treatment conditions. The lignin was characterized to establish which variety 16 17 18 was the most suitable for its depolymerization and obtaining a higher quantity of phenolic 19 20 monomers. Lignin was pretreated with the optimun conditions obtained before for 21 22 Miscanthus 21 . The obtained lignin was characterized by HPSEC, py GC MS and HSQC 23 24 NMR. Table 1 shows the yields obtained for the 3 species, the lignin yield was not 25 26 27 significantly different acording to the aplication of a one way ANOVA test with significance 28 29 level of 0.05, as the variance coefficient was found to be 0.04. The parameters that we took 30 31 into account for determining which was the best specie to be depolymerized were: the MW 32 33 and the phenolic proportion of the lignin composition determined by py GCMS (Figure 1). 34 35 The M is important as higher M is normally associated with condensed structures that 36 W W 37 38 make lignin depolymerisation more dificult, as charge is delocalised along the aromatic 39 40 structure of the lignin building strong internal linkages (Figure 2). 41 42 43 The heteronuclear single quantum coherence (HSQC) NMR spectra of different lignin 44 45 species are depicted in Figure 3 and the assigned structures are depicted in Figure 4, side 46 47 chain region (δC/δH 50–95/2.5–6.0 ppm) and the aromatic region (δC/δH 95–160/5.5–8.0 48 49 ppm). 2D HSQC is a powerful tool for lignin structural characterization providing 50 51 52 information of the structure of the inter unit linkages present and was used to determine the 53 54 differences in lignin structure depending on willow specie. The most common aromatic 55 56 structures in lignins are those of phenylpropane origin, namely guaiacol alcohol, syringol 57 58 59 60 ACS Paragon Plus Environment Page 9 of 37 ACS Sustainable Chemistry & Engineering
1 2 3 alcohol and p hydroxyphenyl alcohol. In Table 2 all the characteristic samples observed and 4 5 their assignments are described. Table 3 shows the different proportion of the linkages 6 7 observed for the different species, it was observed that Resolution showed of higher 8 9 10 proportion of methoxyl groups and β O 4 linkages which are more suitable for being 11 12 oxidised, on the other hand S/G ratio showed the same tendency observed by py GCMS, 13 14 where Resolution showed the lowest S/G ratio and Terranova the highest. 15 16 17 18 19 20 The M W was determined by HPSEC, Table 1 shows the results obatined for the MW for the 21 22 diferent willow species. It was oberved that lignin derived from Resolution has lower M W 23 24 compared to Terranova and Endurance; The MWD was also different for the three species; 25 26 27 for Endurance a fragment was observed with a very high MW and Resolution showed a 28 29 narrower peak. The chromatograms were divided into 3 different regions depending on the 30 31 nature of the compounds that were identified. The retention times are approximately related 32
33 to the MW of the fraction detected and its complexity. Products with a retention time between 34 35 3 to 11 min were identified as sugar fragmentation derived compounds, from 7 to 24.5 min, 36 37 38 aromatic or phenolic fragmentation derived compounds were identified and finally long chain 39 40 fatty acids fragments were identified post 24.5 min (Table 4). It was observed that Resolution 41 42 willow had a higher proportion of phenolic derived compounds in its structure and Endurance 43 44 and Terranova were richer in fatty acids and complex structures composed of more than one 45 46 47 ring, such as 2 hydroxy 4 (phenylmethoxy) benzaldehyde and condensed structures such as 48 49 1 phenanthrenecarboxylic acid. Overall it was decided to apply the consecutive 50 51 depolymerization treatment for Resolution, as it had lower MW and also a higher proportion 52 53 of phenolic small fractions that can be easily extracted, or more easily broken down. 54 55 56 57 58 59 60 ACS Paragon Plus Environment ACS Sustainable Chemistry & Engineering Page 10 of 37
1 2 3 Different pre treatment conditions were tested and the obtained yields relating to lignin are 4 5 detailed in Table 5. The ANOVA statistics test was applied to the obtained yields to 6 7 determine whether the pre treatment conditions had any influence on depolymerization of 8 9 10 lignin with a significance level of 0.05. The variance coefficient for biomass solubility was 11 12 0.01, implying that yield was not significantly affected. The lignin recovery variance 13 14 coefficient was 0.05, so lignin extraction was also not affected by pre treatment conditions. 15 16 17 Results from the pretreatment yields did not indicate that lignin itself was affected. The 18 19 obtained lignins were characterized by HPSEC, ATR IR spectroscopy and py GCMS. It was 20 21 observed that the proportion of char was higher with lower reaction times and higher 22 23 24 temperatures. Furthermore, the S/G ratio determined by py GCMS was not significantly 25 26 affected as the variance coefficient was 0.04. 27 28 29 Both lignin and residual lignin of all the different treatments were characterized by HPSEC, 30 31 ART IR spectroscopy and py GCMS. 32 33 34 35 36 37 Oxidative depolymerization 38 39 40 The three black liquors were subjected to oxidation. All the lignin samples were degraded 41 42 under oxidizing conditions. Once again, the ANOVA statistics test with a significance level 43 44 of 0.05 was applied to the lignin degradation yields and the oil extraction yields (Table 6). 45 46 Lignin degradation was not significantly affected by pre treatment conditions using H2O2 47 48 under homogeneous conditions, as the obtained covariance coefficient was 0.05, but using 49 50 51 TiO 2/H 2O2 the covariance coefficient was 2, implying that pre treatment conditions affected 52 53 the degradation of lignin. It was also observed that the highest degradation was obtained for 54 55 Lig 2. On the contrary, comparing oil yields, for both conditions there was no significant 56 57 difference in oil yield obtained, using H O the covariance coefficient was 0.04, but with 58 2 2 59 60 ACS Paragon Plus Environment Page 11 of 37 ACS Sustainable Chemistry & Engineering
1 2 3 TiO 2/H 2O2 the covariance coefficient was 0.07, and the best oil yield was obtained for Lig 2. 4 5 To summarize, pre treatment conditions affected the activity of heterogeneous catalysis with 6 7 TiO and the best results were obtained for Lig 2 conditions. 8 2 9 10 The S/G ratio decreased after treatment under oxidizing conditions, meaning that syringyl 11 12 13 units are easier to degrade than guaiacyl units. As observed in fig 1, syringyl units are linked 14 15 to lignin through ether linkages whereas coniferyl units are linked by ethers and 5 5’ 16 17 linkages, which are harder to break under oxidizing conditions. 18 19 20 21 22 23 Spectroscopic characterization of lignin 24 25 26 Lignin and residual lignin were characterized by ATR IR (Figure 5) in order to identify any 27 28 changes in the chemical structure of lignin due to the pretreatment conditions or oxidation 29 30 reactions. The spectra of the pretreated lignin samples (Lig 2, Lig 8 and Lig 22) showed the 31 32 characteristic bands assigned to lignin structure. The bands were assigned to their 33 34 corresponding functional groups as described in Table 7. 35 36 37 38 39 40 According to the ATR IR spectra, pre treatment conditions did not affect the chemical 41 42 functionality observed in the lignins. However, when each lignin was compared to the 43 44 45 corresponding residual lignin after oxidation, in both cases some changes were observed that 46 1 47 are related to the oxidation of the groups present in lignin. The stretch at 1703 cm was 48 49 slightly displaced to a higher wavenumber with an increase in intensity, primarily due to the 50 51 formation of carboxylic acids and esters. Also a new band appeared at 1369 cm 1 which was 52 53 54 assigned to the aliphatic CH stretch found exclusively in aliphatic methyl groups and OH 55 56 stretches in phenols. Finally a significant relative decrease in intensity of the band at 1100 57 58 59 60 ACS Paragon Plus Environment ACS Sustainable Chemistry & Engineering Page 12 of 37
1 2 3 cm 1 was observed and assigned to the combination between syringyl and guaiacyl rings 4 5 which agrees with the decrease of S/G ratio after oxidation measured by py GCMS 23,24. 6 7 8 Pyrolysis 9 10 11 The pretreated and oxidized lignin samples were subjected to py GCMS. The pretreated 12 13 lignin showed the same peaks in the chromatogram so they were composed of the same 14 15 fractions but with different relative abundance (Figure 6). As was mentioned in the initial part 16 17 18 of the discussion, the chromatograms of the lignins can be divided in three parts (Table 4). 19 20 Lig 22 showed a higher proportion of fatty acids whereas Lig 8 showed a higher proportion 21 22 of sugar derived fractions. However for all lignin samples the phenolic and aromatic peaks 23 24 were the most intense. When the lignin samples were subjected to oxidation it was observed 25 26 27 that through the use of hydrogen peroxide without added catalyst, both the sugar and phenolic 28 29 components degraded approximately in the same proportion. However, with TiO 2/H 2O2 the 30 31 phenolic signals were less intense than the sugar signals, which could mean that the phenolic 32
33 components were degraded selectively by the action of TiO 2. 34 35 36 37 38 39 HPSEC 40 41 42 The MW of the obtained lignin and residual lignin samples were measured by HPSEC. The 43 44 obtained results are detailed in Table 9 and MWD profiles are depicted in Figure 7. 45 46 Comparing MWD of the lignin samples obtained from different pretreatment conditions, it 47 48 was observed that they had the same profile but were displaced to longer retention times, 49 50 51 which means lower M W as shown in Table 9. In accordance with the integrated results, higher 52 53 reaction time leads to a higher MW, which can be due to the self condensation of lignin or due 54 55 to interactions with the IL since longer reaction times promote lignin reactivity with the IL 56 57 anion 25,26. All lignin samples were degraded after oxidation, with both the catalyzed and 58 59 60 ACS Paragon Plus Environment Page 13 of 37 ACS Sustainable Chemistry & Engineering
1 2 3 uncatalyzed conditions. The extent of degradation was generally higher for Lig 22. 4 5 Comparing both conditions, the degradation was observed to be higher for TiO 2 catalyzed 6 7 conditions for Lig 2 and Lig 22 but not for Lig 8. The obtained residual lignins showed high 8 9 27,28 10 polydispersity . 11 12 13 Oil Characterization 14 15 The oils were characterized by GC MS, the chromatograms showed a complex mixture of 16 17 18 aromatic products derived from lignin with some sugar derived compounds (Figure 8, Figure 19 20 9). Several monomers were determined quantitatively, and vanillic acid was the main product 21 22 of the oils (Table 10). Oxidation with both H2O2 and TiO 2/H2O2 treatments leads to 23 24 overoxidation to the acid with no selectivity observed towards the aldehyde. Butanoic acid 25 26 27 and pentanoic acids were obtained as the main products from hemicellulose, whilst a range of 28 29 substituted benzoic acids was obtained from lignin as well as the calibrated benzoic acid 30 31 (Table 11). The presence of fatty acids was also observed. Comparing oxidation treatments, 32
33 it was observed that the oil obtained with H2O2 without added catalyst showed higher 34 35 concentrations of sugar derived acids. However, as Lig 22 showed high concentrations of 36 37 38 fatty acids (as observed by py GCMS), oil 22 is a response of the initial composition of Lig 39 40 22 showing high concentration of fatty acids with H2O2 alone , but with TiO 2/H2O2 it showed 41 42 higher concentrations of phenolics, suggesting that phenolics were oxidising first followed by 43 44 fatty acids. For oils 8 and 22 obtained with TiO 2/H 2O2 the main peak of the chromatogram 45 46 47 was assigned to 1 (2,4,5 trihydroxyphenyl) 1 butanone, whereas for oil 2 the main peak was 48 49 assigned to butylated hydroxytoluene, an impurity from the solvent. It was observed that the 50 51 relative abundance for butylated hydroxytoluene in oil 8 and 22 was 7 % and 6 % 52 53 respectively. As the concentration is the same for all the samples, the proportion of 54 55 compounds derived from lignin depolymerization was higher in oil 8 and oil 22 than in oil 2. 56 57 58 For oils obtained with H2O2 alone the main product was pentanoic acid for oil 2 and the 59 60 ACS Paragon Plus Environment ACS Sustainable Chemistry & Engineering Page 14 of 37
1 2 3 proportion of pentanoic acid, 1 (2,4,5 trihydroxyphenyl) 1 butanone and butylated 4 5 hydroxytoluene was similar in oil 8, whereas oil 22 was composed mainly of butylated 6 7 hydroxytoluene and fatty acids. In sumary, both oil 8 and oil 22 obtained with TiO /H O 8 2 2 2 9 29 31 10 showed a higher concentration of lignin derived compounds . 11 12 13 Ionic liquid characterization 14 15 Spectroscopic characterization 16 17 18 The IL was characterized by ATR IR before and after pre treatment and oxidation (Figure 10, 19 20 Figure 11). ATR IR spectra of [Et NH][HSO ] did not show evidence of moisture 21 3 4 22 23 contamination and observed bands were assigned to the different groups present in 24 1 25 [Et 3NH][HSO 4] structure. Bands at 3037, 2998, 2951, 2888, 2818, 2717, 2558 and 2505 cm 26 27 were assigned to asymmetric and symmetric stretching vibrations of CH 2 and CH 3 on the 28 29 ammonium salt, the band at 1478 cm 1 was assigned to the NH deformation vibration, the 30 31 1 32 band at 1440 cm was assigned to the S CH 3 asymmetric deformation vibration, bands at 33 1 34 1401, 1291, 1233, 1061 and 1034 cm were assigned to the HOSO 3 asymmetric and 35 36 symmetric stretching vibrations, the band at 1364 cm 1 was assigned to alkyl chain 37 38 deformation on the ammonium salt and the band at 838 cm 1 corresponded to CH in plane 39 40 vibration. These bands are modified only by the addition of water to the IL, whereby some 41 42 43 bands assigned to the anion overlapped with adjacent bands. The bands at 1289 and 1233 cm 44 45 1 overlapped with the band at 1149 cm 1 and the band at 1062 cm 1 overlapped with the band 46 1 32,33 47 at 1031 cm , all of these bands were assigned to HOSO 3 . A new band was also observed 48 49 at 1644 cm 1 and was assigned to water itself. Taking into account that the IL is mixed with 50 51 52 water during pre treatment to establish whether the IL was contaminated by biomass waste, 53 54 the obtained spectra were compared with the spectrum from the IL and water mixture. The 55 56 only difference observed among the spectra of the IL after pre treatment and oxidation, was 57 58 59 60 ACS Paragon Plus Environment Page 15 of 37 ACS Sustainable Chemistry & Engineering
1 2 3 the appearance of a new band at 1731 cm 1, which increases in intensity with increased pre 4 5 treatment time. Moreover, after oxidation using TiO2/H 2O2 the intensity of the band was 6 7 comparatively higher than for oxidation with H O alone. This band was assigned to the C=O 8 2 2 9 10 of the acetate group, which is formed during the degradation stages of hemicellulose. As this 11 12 band is more intense for TiO 2/H 2O2 samples it is postulated that hemicelluloses are not 13 14 completely degraded to CO 2 and H 2O, as happens with H 2O2 alone where release of pressure 15 16 was observed when the tube was opened after the treatment, which cannot be due to IL as it 17 18 19 has low vapor pressure nor water as it was opened at room temperature. The acetic acid was 20 34,35 21 not extracted by MeTHF and remained in the IL . 22 23 24 25 26 27 HPLC characterization 28 29 [Et NH][HSO ] was characterized by HPLC to determine the impurities which remained after 30 3 4 31 32 oxidation. As observed in the chromatograms (Figure 12), after pre treatment some 33 34 impurities remained in solution after lignin precipitation. After oxidation via both 35 36 homogeneous and heterogeneous conditions, the chromatogram only showed one small peak 37 38 apart from the one assigned to [Et 3NH][HSO 4]. After oxidation and extraction processes 39 40 [Et NH][HSO ] was also purified and was ready to be reused. 41 3 4 42 43 Conclusion 44 45 46 Resolution willow specie was chosen as best source of lignin for being depolymerized. Pre 47 48 treatment conditions had no influence on lignin solubility and recovery but affected the 49 50 51 further reactivity of lignin as its composition was different as well as its MW. Lignin was 52 53 successfully depolymerized under oxidizing conditions either with H2O2 or TiO 2/H 2O2 54 55 treatments. However whilst the composition of the obtained oils was different, oxidation via 56 57 hydrogen peroxide alone leads to an oil rich in sugar derived acids whereas oxidation with 58 59 60 ACS Paragon Plus Environment ACS Sustainable Chemistry & Engineering Page 16 of 37
1 2 3 TiO 2 catalysis leads to an oil rich in phenolic derived fragments, derived from lignin. The 4 5 addition of TiO 2 enhanced the selectivity of the reaction and the yields of phenolic 6 7 monomers, the main target when lignin is depolymerizing. 8 9 10 References 11 12 13 01, Zhang, Y.H.P.; Ding, J.R.; Mielenz, S.Y.; Cui, J.B.; Elander, R.T.; Laser M.; Himmel, 14 15 M.E.; McMillan, J.R.; Lynd, L.R. Fractionating Recalcitrant Lignocellulose at Modest 16 17 18 Reaction Conditions. Biotechnol. Bioeng. 2007, 97 , 214 223. 19 20 02, Fang, Z.; Fang, C. “Complete dissolution and hydrolysis of wood in hot water.” Aichen J. 21 22 2008, 54 , 2751 2758. 23 24 03, Garcia, A.; Toledano, A.; Serrano, L.; Egües, I.; Gonzalez, M.; Martín, F.; Labidi, J.. 25 26 27 Characterization of lignins obtained by selective precipitation. Sep. Purif. Technol. 2009, 68, 28 29 193 198. 30 31 04, Kilpeläinen, I.; Xie, H.; King, A.; Granstrom, M.; Heikkinen, S.; Argylopuolos, D.S.. 32 33 Disolution of wood in ionic liquids. J. Agric. Food Chem. 2007, 55 , 9142 9148. 34 35 05, Yang, D.; Qiu, X.; Zhou, M.; Lou, H. Properties of sodium lignosulfonate as dispersant of 36 37 38 coal water slurry. Energy Convers. Manage. 2007, 48 , 2433–2438. 39 40 06, Sena Martins, G.; Almeida Vara, E.; Duarte, J.C. Eco friendly new products from 41 42 enzymatically modified. Ind. Crops Prod. 2008, 27 , 189–195. 43 44 07, Agrwal, A.; Kaushik, N.; Biswas, S. Derivatives and Applications of Lignin – An Insight. 45 46 47 the scitech journal. 2014, 1 (7), 30 36. 48 49 08, Thakur, V. K.; Thakur, M. K.; Raghavan, P.; Kessler M. R. Progress in Green Polymer 50 51 Composites from Lignin for Multifunctional Applications: A Review. ACS. Sust. Chem. Eng. 52 53 2014, 2, 1072 1092. 54 55 09, ESCOP. Willow varietal identification Guide. Carlow: teagasc.n.d. 1997. 56 57 58 59 60 ACS Paragon Plus Environment Page 17 of 37 ACS Sustainable Chemistry & Engineering
1 2 3 10, Plechkova, N.V.; Seddon, K.R. Application of IL in the chemical industry. Chem. Soc. 4 5 Rev. 2008, 37 , 123 150. 6 7 11, Seddon, R.D.; Rogerds, K.R. Ionic Liquids solvents of the future. Science. 2003, 302 , 8 9 10 792 793. 11 12 12, Marszall, M. P.; Kaliszan, R. Application of ionic liquids in liquid chromatoghraphy. 13 14 Crit. Rev. Anal. Chem. 2007, 37 , 127 140. 15 16 13, Nockemann, P.; Binnemans, K.; Driesen, K. Purification of imidazolium ionic liquids for 17 18 19 spectroscopic applications. Chem. Phys. Lett. 2005, 415 , 131 136. 20 21 14, MacFarlane, D. R.; Tachikawa, N.; Forsyth, M.; Pringle, J. M.; Howlett, P.C.; Elliott, G. 22 23 D.; Davis, J. H.; Watanabe, M.; Simon, P.; Angell, A. Energy applications of ionic liquids. 24 25 Energy Environ. Sci. 2014, 7, 232 250. 26 27 15, Xu, C.; Arancon, R. A. D.; Labidi, L.; Luque, R.; Lignin depolymerization strategies: 28 29 30 towards valuable chemicals and fuels. Chem. Soc. Rev. 2014, 43 , 7485 7500. 31 32 33 16, Tan, S. S. Y.; MacFarlane, D. R.; Upfal, J.; Edye, L. A.; Doherty, W. O. S.; Patti, A. F.; 34 35 Pringle, J. M.; Scott, J. L. Extraction of lignin from lignocellulose at atmospheric pressure 36 37 using alkylbenzenesulfonate ionic liquid. Green Chem. 2009, 11 , 339–345. 38 39 17, George, A.; Tran, K.; Morgan, T. J.; Benke, P. I.; Berrueco, C.; Lorente, E.; Wu, B. C.; 40 41 Keasling, J. D.; Simmonsa, B. A.; Holmes, B. M. The effect of ionic liquid cation and anion 42 43 44 combinations on the macromolecular structure of lignins. Green Chem. 2011, 13 , 3375 3385. 45 46 18, Behling, R.; Valange, S.; Chatel, G.; Heterogeneous catalytic oxidation for lignin 47 48 valorization into valuable chemicals: what results? What limitations? What trends? Green 49 50 Chem. 2016, 18 , 1839 1854. 51 52 53 19, Ma, R.; Xu, Y.; Zhang, X. Catalytic oxidation of biorefinery lignin to value added 54 55 chemicals to support sustainable biofuel production. Chem. Sus. Chem . 2015, 8, 24 51. 56 57 58 59 60 ACS Paragon Plus Environment ACS Sustainable Chemistry & Engineering Page 18 of 37
1 2 3 20, Chatel, G.; Rogers. R. D. Review: Oxidation of lignin using ionic liquids an innovative 4 5 strategy to produce renewable chemicals. ACS Sustainable Chem. Eng. 2013, 2 (3), 322–339. 6 7 21, Prado, R.; Brandt, A.; Erdocia, X.; Hallett, J.; Welton, T.; Labidi, J. Lignin oxidation and 8 9 10 depolymerisation in ionic liquids. Green Chem. 2016, 18 , 834 841. 11 12 22, Verdia, P.; Brandt, A.; Hallett, J. P.; Ray, M. J.; Welton, T. Fractionation of 13 14 lignocellulosic biomass with the ionic liquid 1 butylimidazolium hydrogen sulfate. Green 15 16 Chem. 2014, 16 , 1617 1627. 17 18 19 23, García, A.; Toledano, A.; Serrano, L.; Egüés, I.; González, M.; Martín, F.; Labidi, J.. 20 21 Characterization of lignins obtained by selective precipitation. Sep. Purif. Technol. 2010, 68 , 22 23 193 198. 24 25 24, Lau, S.; Ibrahim, R. FT IR spectroscopic studies on lignin from some tropical woods and 26 27 rattan. Pertanika. 1992, 14 (1), 78 81. 28 29 30 25, Yinghuai, Z.; Yuanting, K. T.; Hosmane, N. S. Applications of Ionic Liquids in Lignin 31 32 Chemistry,. Ionic Liquids - New Aspects for the Future. Edited by J. Kadokawa. Intech. 33 34 doi:10.5772/51161. 2013 35 36 26, Pu, Y.; Jiang, N.; Ragauskas, A.J.; Ionic liquid as a green solvent for lignin. J. Wood 37 38 39 Chem. Technol. 2007, 27 , 23 33. 40 41 27, Buranov, A.U.; Ross, K.A.; Mazza, G. Isolation and characterization of lignins extracted 42 43 from flax shives using. Bioresour. Technol. 2010, 101 , 7446–7455. 44 45 28, El Hage, R.; Brosse, N.; Chrusciel, L.; Sanchez, C.; Sannigrahi, P.; Ragauskas, A. 46 47 Characterization of milled wood lignin and ethanol organosolv lignin from miscanthus. 48 49 50 Polym. Degrad. Stab. 2009, 94 , 1632 1638. 51 52 29, Lanzalunga, O.; Bietti, M. Photo and radiation chemical induced degradation of lignin 53 54 model compounds. J. Photochem. Photobiol. B. 2000, 56 , 85 108. 55 56 57 58 59 60 ACS Paragon Plus Environment Page 19 of 37 ACS Sustainable Chemistry & Engineering
1 2 3 30, Toledano, A.; Serrano, L.; Pineda, A.; Romero, A. A.; Luque, R.; Labidi, J. Microwave 4 5 assisted depolymerisation of organosolv lignin via mild hydrogen free hydrogenolysis: 6 7 Catalyst screening. Appl. Catal. B. 2014, 145 , 43 55. 8 9 10 31, Pandey, M. P.; Kim, C. S. “Lignin depolymerization and conversion: a review of 11 12 thermochemical methods.” Chem. Eng. Technol. 2011, 34 , 29 41. 13 14 32, Shi, F.; Deng, Y. Abnormal FT IR and FTRaman spectra of ionic liquids. Spectrochim. 15 16 Acta A. 2005, 62 , 239 244. 17 18 19 33, Pretsch, E.; Bühlmann, P.; Affolter, C.; Herrera, A.; Martínez, A. Structure determination 20 21 of organic compounds. New York: Springer Verlag. 2000 22 23 34, Fanf, J. M.; Sun, R. C.; Tomkinson, J. Isolation and characterization of hemicelluloses. 24 25 Cellulose. 2000, 7, 87 107. 26 27 35, Peng, F.; Bian, J.; Peng, P.; Guan, Y.; Xu, F.; Sun. R.C.; Fractional separation and 28 29 30 structural features of hemicelluloses from sweet sorghum leaves. Bioresource. 2012, 7 (4) 31 32 4744 4759. 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 ACS Paragon Plus Environment ACS Sustainable Chemistry & Engineering Page 20 of 37
1 2 3 List of tables 4 5 6 Table 1: Different willow lignin properties 7 8 9 Table 2: Assignements of 13C-1H cross signals in the (HSQC) of lignin and fibres 10 11 Table 3: HSQC-NMR characterization of different species 12 13 14 Table 4: py-GCMS determined compounds 15 16 17 Table 5: Pre-treatment yields 18 19 20 Table 6: Yields after oxidation of lignin 21 22 23 Table 7: ATR-Ir band assignment 24 25 26 Table 8: py-GCMS identified compounds of Lignin 27 28 29 Table 9: HPSEC results for lignins 30 31 Table 10: Phenolic calibrated compounds determined by GCMS 32 33 34 Table 11: Oil composition non calibrated compounds identified by GCMS 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 ACS Paragon Plus Environment Page 21 of 37 ACS Sustainable Chemistry & Engineering
1 2 3 Table 1: Different willow lignin properties 4 5 6 Sample Lignin S/G Pre treatment M Polydispersity 7 name yield py GCMS W 8 Resolution 22 h at 120 °C 20±1 1.35±0.08 35111 13.50 9 10 Terranova 22 h at 120 °C 18.83±0.9 1.92±0.06 48056 16.67 11 Endurance 22 h at 120 °C 17.8±0.8 1.56±0.1 70456 31.58 12 13 14 15 Table 2: Assignements of 13C-1H cross signals in the (HSQC) of lignin and fibres 16 17 Lable δC/δ H (ppm) Assignments 18 56.359/3.759 C H in methoxyls groups 19 59.777/3.257 20 A 60.538/3.661 C H in β O 4’ substructures 21 γ γ 60.305/4.051 22 23 A’ 63.017/3.693 Cγ Hγ in β O 4’ substructures 24 A 71.657/4.181 Cα Hα in β O 4 linked to a G unit 25 A 71.657/3.804 Cα Hα in β O 4 26 A 72.241/4.866 Cα Hα in β O 4 linked to a S unit 27 A 85.662/4.632 Cα Hα in resinol structure 28 B 86.747/4.092 C H in β O 4 in dibenzodiocoxin 29 β β 30 C 87.540/5.449 Cα Hα in resinol structure 31 S 104.273/6.616 C2,6 H2,6 in S units 32 S’ 106.967/7.334 C2,6 H2,6 in oxidized (C α=O) S units 33 110.957/7.378 E C H in p coumarate 34 112.691/6.656 8 8 35 G 110.458/7.157 C2 H2 in guaiacyl units 36 G’ 111.195/6.919 C H in oxidised guaiacyl units 37 2 2 38 G 115.754/6.762 C5 H5 in guaiacyl units 39 E 115.959/6.261 C3,5 H3,5 in p coumarate 40 E 126.927/6.993 Cβ Hβ in cinnamyl aldehyde end groups 41 C H in p hydroxybenzoate F 131.332/7.627 2,6 2,6 42 substructures 43 44 45 46 Table 3: HSQC-NMR characterization of different species 47 48 49 S/G MeOH β O 4 50 NMR 51 52 Resolution 1.16 12.81 1.77 53 Terranova 1.71 10.50 1.27 54 55 Endurance 1.40 9.21 1.40 56 57 58 59 60 ACS Paragon Plus Environment ACS Sustainable Chemistry & Engineering Page 22 of 37
1 2 3 Table 4: py-GCMS determined compounds 4 5 6 r.t Fraction Resolution Terranova Endurance 7 4.311 1 (2 Phenylsulfanyl ethyl) X 8 pyrrolidine 9 10 4.594 1H Pyrrole, 1 ethyl X X X 11 4.854 Furfural X X X 12 5.501 Thiophene X X 13 7.014 2 Furancarboxaldehyde, 5 methyl X 14 15 7.26 Phenol X X X 16 7.655 Acetamide, N,N diethyl X X 17 8.192 Benzyl Alcohol X 18 9.116 Phenol, 2 methoxy (guaiacol) X X X 19 20 9.497 2 Furanmethanol X 21 9.509 Phenol, 3,4,5 trimethyl X 22 9.607 Levoglucosenone X X 23 9.859 2,5 Pyrrolidinedione, 1 ethyl X 24 25 10.243 Benzene, 1 ethenyl 4 methoxy X 26 10.422 Phenol, 4 ethyl X 27 11.085 Phenol, 2 methoxy 4 methyl X 28 11.421 1,4:3,6 Dianhydro .alpha. d X X X 29 glucopyranose 30 31 11.548 Benzofuran, 2,3 dihydro X X 32 13.442 Phenol, 4 ethyl 2 methoxy X 33 14.608 2 Methoxy 4 vinylphenol X X X 34 15.683 Phenol, 2,6 dimethoxy (syringol) X X X 35 36 16.878 Vanillin X X 17.895 Benzoic acid, 4 hydroxy 3 37 X X X 38 methoxy 39 17.964 Phenol, 2 methoxy 4 (1 propenyl) X X 40 18.38 1 Decene X 41 18.669 Ethanone, 1 (4 hydroxy 3 42 X X 43 methoxyphenyl) 44 19.079 Phenol, 2,4 bis(1,1 dimethylethyl) X 45 19.356 Ethanone, 1 (2,6 dihydroxy 4 X X 46 methoxyphenyl) 47 19.448 Homovanillyl alcohol X X X 48 19.985 Ethanone, 1 (3,4 49 X 50 dimethoxyphenyl) 51 20.101 2,5 dimethoxy 4 ethylamphetamine X X 52 20.343 2,4' Dihydroxy 3' X X X 53 methoxyacetophenone 54 20.442 Diethyl Phthalate X X 55 20.563 Phenol, 2,6 dimethoxy 4 (2 56 X 57 propenyl) 58 21.255 Phenol, 2,6 dimethoxy 4 (2 X 59 60 ACS Paragon Plus Environment Page 23 of 37 ACS Sustainable Chemistry & Engineering
1 2 3 propenyl) 4 21.655 Cyclododecane X 5 21.909 Phenol, 2,6 dimethoxy 4 (2 6 X X X 7 propenyl) 22.324 Ethanone, 1 (4 hydroxy 3,5 8 X X X 9 dimethoxyphenyl) 10 22.775 Desaspidinol X X X 11 23.069 Aspinidol X 12 13 23.526 4 dimethylamino salicylic acid X X 23.959 Benzaldehyde, 2 hydroxy 4 14 X X 15 (phenylmethoxy) 16 24.504 Hexadecanoic acid, methyl ester X X 17 24.773 n Hexadecanoic acid X X 18 19 24.975 n Hexadecanoic acid X X 20 25.097 Hexadecanoic acid, ethyl ester X X X 21 26.200 9,12 Octadecadienoic acid X 22 26.714 Linoleic acid ethyl ester X X X 23 24 27.066 Octadecanoic acid X X 25 27.950 Tricosane X 26 28.325 6,6 Dimethylhepta 2,4 diene X 27 28.515 Dodecamide, N,N diethyl X X 28 29 28.550 1 Phenanthrenecarboxylic acid, 1,2 30 ,3,4,4a,9,10,10a octahydro 1,4a di 31 methyl 7 (1 methylethyl) , methyl X 32 ester, [1R (1.alpha.,4a.beta.,10a. 33 alpha.)] 34 28.793 Tetracosane X 35 Pentacosane 36 29.601 X 29.965 1,2 Benzenedicarboxylic acid, 37 X X X 38 mono (2 ethylhexyl) ester 39 30.254 Decosanoic acid, ethyl ester X 40 30.375 Eicosane X 41 Octadecane 42 31.218 X X 43 32.206 Octadecane X 44 33.361 Nonacosane X 45 36.613 Stigmastan 3,5 diene X X X 46
47 48 49 Table 5: Pre-treatment yields 50 51 52 Sample Solved Lignin Residual S/G 53 54 name Pre treatment biomass yield Char % Lignin 55 % % % 56 Lig 2 2 h at 150 °C 60±1 20±1 56±1 40.3±0.9 2.16±0.08 57 Lig 8 8 h at 120 °C 61.0±0.9 19.7±0.3 56.6±0.5 39.5±0.7 2.2±0.1 58 59 60 ACS Paragon Plus Environment ACS Sustainable Chemistry & Engineering Page 24 of 37
1 2 3 Lig 22 22 h at 120 °C 64.2±0.6 20.1±0.4 11.8±0.2 61.3±0.5 2.26±0.06 4 5 6 7 8 9 10 Table 6: Yields after oxidation of lignin 11 12 13 Sample Lignin % Oil % S/G 14 Lig 2 20 ± 1 2.16±0.08 15 Lig 2 H O 7.6 ± 0.4 15.9 ± 0.6 1.62 16 2 2 17 Lig 2 TiO 2/H 2O2 2.6 ± 1 22.3 ± 0.4 1.71 18 Lig 8 19.7 ± 0.3 2.2±0.1 19 Lig 8 H 2O2 6.3 ± 0.4 14.9 ± 0.8 1.71 20 Lig 8 TiO 2/H 2O2 5.4 ± 0.1 16.3 ± 0.7 1.83 21 Lig 22 20.1 ± 0.6 2.26±0.06 22 Lig 22 H 2O2 5.35 6.9 ± 0.2 1.18 23 ±0.05 24 25 Lig 22 TiO 2/H 2O2 2 ± 1 11.10 1.16 26 ±0.7 27 28 29 30 Table 7: ATR-IR band assignment 31 32 33 Band 1 Functional group 34 cm 35 3346 –OH stretch 36 2932 CH stretches in methyl and methylene groups 37 2851 38 39 1703 C=O stretches in unconjugated ketones, carbonyl and ester groups 40 1604 Aromatic skeletal vibrations and C=O stretch 41 1513 Aromatic skeletal vibrations 42 1454 CH deformation in methyl and methylene groups 43 1428 Aromatic skeletal vibrations combined with C H in plane deformation 44 1209 Guaiacyl ring breathing plus C=O stretch 45 1110 Etherified guaiacyl ring plus syringyl unit and secondary alcohol plus C=O stretch 46 C O deformation in primary alcohol plus C=O stretch in unconjugated ketones 47 1028 48 and the aromatic C H in plane deformation 49 913 C H out of plane deformation 50 834 C H out of plane deformation in 2 and 6 positions on syringyl ring 51 52 53 54 55 56 57 58 59 60 ACS Paragon Plus Environment Page 25 of 37 ACS Sustainable Chemistry & Engineering
1 2 3 4 5 6 Table 8: py-GCMS identified compounds of Lignin 7 8 9 r.t Fraction 10 4.311 1 (2 Phenylsulfanyl ethyl) pyrrolidine 11 12 4.594 1H Pyrrole, 1 ethyl 13 4.854 Furfural 14 7.014 2 Furancarboxaldehyde, 5 methyl 15 7.26 Phenol 16 17 7.655 Acetamide, N,N diethyl 18 8.192 Benzyl Alcohol 19 9.116 Phenol, 2 methoxy (guaiacol) 20 9.497 2 Furanmethanol 21 22 9.509 Phenol, 3,4,5 trimethyl 23 9.859 2,5 Pyrrolidinedione, 1 ethyl 24 10.243 Benzene, 1 ethenyl 4 methoxy 25 10.422 Phenol, 4 ethyl 26 27 11.085 Phenol, 2 methoxy 4 methyl 28 11.421 1,4:3,6 Dianhydro .alpha. d glucopyranose 29 11.548 Benzofuran, 2,3 dihydro 30 13.442 Phenol, 4 ethyl 2 methoxy 31 32 14.608 2 Methoxy 4 vinylphenol 33 15.683 Phenol, 2,6 dimethoxy (syringol) 34 16.878 Vanillin 35 17.895 Benzoic acid, 4 hydroxy 3 methoxy 36 37 17.964 Phenol, 2 methoxy 4 (1 propenyl) 38 18.38 1 Decene 39 18.669 Ethanone, 1 (4 hydroxy 3 methoxyphenyl) 40 19.079 Phenol, 2,4 bis(1,1 dimethylethyl) 41 42 19.356 Ethanone, 1 (2,6 dihydroxy 4 methoxyphenyl) 43 19.448 Homovanillyl alcohol 44 19.985 Ethanone, 1 (3,4 dimethoxyphenyl) 45 20.343 2,4' Dihydroxy 3' methoxyacetophenone 46 47 20.442 Diethyl Phthalate 48 20.563 Phenol, 2,6 dimethoxy 4 (2 propenyl) 49 21.255 Phenol, 2,6 dimethoxy 4 (2 propenyl) 50 21.655 Cyclododecane 51 52 21.909 Phenol, 2,6 dimethoxy 4 (2 propenyl) 53 22.324 Ethanone, 1 (4 hydroxy 3,5 dimethoxyphenyl) 54 22.775 Desaspidinol 55 23.959 Benzaldehyde, 2 hydroxy 4 (phenylmethoxy) 56 57 24.404 Hexadecanoic acid, methyl ester 58 25.097 Hexadecanoic acid, ethyl ester 59 60 ACS Paragon Plus Environment ACS Sustainable Chemistry & Engineering Page 26 of 37
1 2 3 26.714 Linoleic acid ethyl ester 4 29.965 1,2 Benzenedicarboxylic acid, mono (2 ethylhexyl) 5 ester 6 7 30.254 Docosanoic acid, ethyl ester 8 36.613 Stigmastan 3,5 diene 9 10 11 12 Table 9: HPSEC results for lignins 13 14 15 Mw Mn Polydispersity 16 Lig 2 19,744 2,001 9.87 17 18 Lig 2 H 2O2 13,041 1,505 8.66 19 Lig 2 TiO 2/H 2O2 10,622 1,441 7.37 20 Lig 8 24,555 2,549 9.63 21 9,820 1,138 8.63 22 Lig 8 H 2O2 23 Lig 8 TiO 2/H 2O2 13,612 1,437 9.47 24 Lig 22 35,111 2,601 13.50 25 Lig 22 H 2O2 8,463 1,091 7.75 26 27 Lig 22 TiO 2/H 2O2 5,028 770 6.52 28
29 30 31 32 33 34 35 36 37 Table 10: Phenolic calibrated compounds determined by GCMS 38 39 40 r.t. standards Oil 2 Oil 2 Oil 8 Oil 8 Oil Oil 41 H2O2 TiO 2 H2O2 TiO 2 22 22 42 H O TiO 43 2 2 2 44 5.57 Phenol (a) 0.07 0.16 0.06 0.06 0.22 0.13 45 7.27 Guaiacol (b) 0.04 0.11 0.04 0.04 0.12 0.09 46 9.15 Catechol (c) 0.19 0.49 0.24 0.18 0.58 0.49 47 10.94 3 methoxycatechol (d) 0.23 0.27 0.13 0.15 0.22 0.24 48 49 11.71 4 methylcatechol (e) 0.03 0.02 0.02 0.02 0.00 0.00 50 13.71 Syringol (f) 0.06 0.15 0.08 0.06 0.06 0.11 51 14.90 Vanillin (g) 0.00 0.00 0.00 0.00 0.00 0.01 52 16.77 Acetovanillone (h) 0.00 0.01 0.00 0.01 0.03 0.01 53 18.02 Vanillic acid (3 Hydroxy 4 54 27.92 39.72 31.71 14.25 32.96 43.41 55 methoxy benzoic acid) (i) 56 17.47 4 hydroxy 3 methoxyphenil (j) 0.00 0.01 0.03 0.03 0.00 0.01 57 20.33 Acetosyringone (k) 0.00 0.01 0.00 0.00 0.00 0.01 58 59 60 ACS Paragon Plus Environment Page 27 of 37 ACS Sustainable Chemistry & Engineering
1 2 3 4 5 6 Table 11: Oil composition non calibrated compounds identified by GCMS 7 8 9 n Non calibrated compounds 10 1 Maleic anhydride 11 2(3H) Furanone, 5 methyl 12 2 13 3 Butyrolactone 14 4 Butanoic acid, 3 hydroxy , ethyl ester 15 5 2(3H) Furanone, dihydro 5 methyl 16 Ethylene glycol diglycidyl ether 17 6 18 7 Succinic anhydride 19 8 2 Furancarboxylic acid, ethyl este 20 9 Pentanoic acid, 4 oxo , ethyl este 21 Pentanoic acid, 4 oxo 22 10 23 11 Butanedioic acid, ethyl methyl ester 24 12 4 Isopropylbenzenethiol, S methyl 25 13 Ethyl hydrogen succinate 26 Butanedioic acid, diethyl ester 27 14 28 15 Ethyl hydrogen fumarate 29 16 Acetic acid, 2 phenylethyl ester 30 17 Salicylic acid 31 1 Methyl 3 piperidinemethanol 32 18 33 19 2,5 Cyclohexadiene 1,4 dione, 2,6 bis(1,1 dimethylethyl) 34 20 Butylated Hydroxytoluene 35 21 1,2 Dimethoxy 4 (2 propenyloxy)benzene 36 1 Butanone, 1 (2,4,5 trihydroxyphenyl) 37 22 38 23 Benzoic acid, 4 hydroxy 3 methoxy 39 24 Naphthalene, 1 isocyanato 40 25 Pentanoic acid, 4 oxo , phenylmethyl ester 41 26 Azelaic Acid 42 43 27 3 Methoxydiphenylamine 44 28 Benzoic acid, 4 hydroxy 3,5 dimethoxy 45 29 Benzoic acid, 2 hydroxy , phenylmethyl ester 46 30 Hexadecanoic acid, ethyl ester 47 48 31 Octadecanoic acid, ethyl ester 49 32 (E) 9 Octadecenoic acid ethyl este 50 33 Octadecanoic acid, 2 (acetyloxy) 1 51 [(acetyloxy)methyl]ethyl ester 52
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1 2 3 4 5 6 7 List of figures 8 9 10 Figure 1: a) MWD of different species b) py-GCMS Chromatogram of the different species 11 12 13 Figure 2: Lignin structure 14 15 16 Figure 3: HSQC-NMR spectra of the different species a) Resolution, b) Terranova, c) 17 18 Endurance 19 20 21 Figure 4: Lignin detected structures 22 23 24 25 Figure 5: ATR-IR of lignin and residual lignin 26 27 28 Figure 6: py-GCMS chromatograms of different samples 29 30 31 Figure 7: MWD of different lignins 32 33 34 Figure 8: oil Chromatogram 35 36 37 Figure 9: Oil chromatograms obtained by GCMS 38 39 40 Figure 10: ATR-IR spectra of the IL and its mixture with water 41 42 43 Figure 11: ATR-IR spectra of IL after the different treatments 44 45 46 Figure 12: HPLC results for IL after the different conditions a) after pretreatment b) after 47 48 treatment with H 2O2 alone c) after treatment with TiO 2/H2O2 49 50 51 52 53 54 55 56
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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 Figure 1: a) MWD of different species b) py-GCMS Chromatogram of the different species 17 18 19 20 coniferyl alcohol 21 O OH O 22 HO OH 23 HO 24 O 25 O OH synapyl alcohol 26 27 28 Figure 2: Lignin structure 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 Figure 3: HSQC-NMR spectra of the different species a) Resolution, b) Terranova, c) 56 57 Endurance 58 59 60 ACS Paragon Plus Environment ACS Sustainable Chemistry & Engineering Page 30 of 37
1 2 3 4 A A’ 5 6 7 8 9 10 11 12 13 14 15 16 B 17 C 18 G 19 20 21 22 23 24 25 G’ 26 27 28 29 30
31 32 33 34 E 35 F S S’ 36 37 38 39 40 41
42 43 44 45 Figure 4: Lignin detected structures 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 ACS Paragon Plus Environment Page 31 of 37 ACS Sustainable Chemistry & Engineering
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 Figure 5: ATR-IR of lignin and residual lignin 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 Figure 6: py-GCMS chromatograms of different samples 57 58 59 60 ACS Paragon Plus Environment ACS Sustainable Chemistry & Engineering Page 32 of 37
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 Figure 7: MWD of different lignins 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 Figure 8: oil Chromatogram 58 59 60 ACS Paragon Plus Environment Page 33 of 37 ACS Sustainable Chemistry & Engineering
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 Figure 9: Oil chromatograms obtained by GCMS 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 ACS Paragon Plus Environment ACS Sustainable Chemistry & Engineering Page 34 of 37
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Figure 10: ATR-IR spectra of the IL and its mixture with water 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 ACS Paragon Plus Environment Page 35 of 37 ACS Sustainable Chemistry & Engineering
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 Figure 11: ATR-IR spectra of IL after the different treatments 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 ACS Paragon Plus Environment ACS Sustainable Chemistry & Engineering Page 36 of 37
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 Figure 12: HPLC results for IL after the different conditions a) after pretreatment b) after 19 20 / 21 treatment with H 2O2 c) after treatment with TiO 2 H2O2 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 ACS Paragon Plus Environment Page 37 of 37 ACS Sustainable Chemistry & Engineering
1 2 3 For Table of contents only 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 Authors 23 24 25 Raquel Prado 26 27 28 Xabier Erdocia 29 30 31 Gilbert Francis De Gregorio 32 33 Jalel Labidi 34 35 36 Tom Welton 37 38 39 Sypnopsis 40 41 42 Reusable ionic liquids are used as solvents and biomass as the feedstock to obtain chemicals 43 44 from renewable resources. 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 ACS Paragon Plus Environment