Survey of Renewable Chemicals Produced from Lignocellulosic Biomass During Ionic Liquid Pretreatment
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Lawrence Berkeley National Laboratory Recent Work Title Survey of renewable chemicals produced from lignocellulosic biomass during ionic liquid pretreatment. Permalink https://escholarship.org/uc/item/71d9d3rw Journal Biotechnology for biofuels, 6(1) ISSN 1754-6834 Authors Varanasi, Patanjali Singh, Priyanka Auer, Manfred et al. Publication Date 2013-01-28 DOI 10.1186/1754-6834-6-14 Peer reviewed eScholarship.org Powered by the California Digital Library University of California Varanasi et al. Biotechnology for Biofuels 2013, 6:14 http://www.biotechnologyforbiofuels.com/content/6/1/14 RESEARCH Open Access Survey of renewable chemicals produced from lignocellulosic biomass during ionic liquid pretreatment Patanjali Varanasi1,2, Priyanka Singh1, Manfred Auer1, Paul D Adams1, Blake A Simmons1,2 and Seema Singh1,2* Abstract Background: Lignin is often overlooked in the valorization of lignocellulosic biomass, but lignin-based materials and chemicals represent potential value-added products for biorefineries that could significantly improve the economics of a biorefinery. Fluctuating crude oil prices and changing fuel specifications are some of the driving factors to develop new technologies that could be used to convert polymeric lignin into low molecular weight lignin and or monomeric aromatic feedstocks to assist in the displacement of the current products associated with the conversion of a whole barrel of oil. We present an approach to produce these chemicals based on the selective breakdown of lignin during ionic liquid pretreatment. Results: The lignin breakdown products generated are found to be dependent on the starting biomass, and significant levels were generated on dissolution at 160°C for 6 hrs. Guaiacol was produced on dissolution of biomass and technical lignins. Vanillin was produced on dissolution of kraft lignin and eucalytpus. Syringol and allyl guaiacol were the major products observed on dissolution of switchgrass and pine, respectively, whereas syringol and allyl syringol were obtained by dissolution of eucalyptus. Furthermore, it was observed that different lignin-derived products could be generated by tuning the process conditions. Conclusions: We have developed an ionic liquid based process that depolymerizes lignin and converts the low molecular weight lignin fractions into a variety of renewable chemicals from biomass. The generated chemicals (phenols, guaiacols, syringols, eugenol, catechols), their oxidized products (vanillin, vanillic acid, syringaldehyde) and their easily derivatized hydrocarbons (benzene, toluene, xylene, styrene, biphenyls and cyclohexane) already have relatively high market value as commodity and specialty chemicals, green building materials, nylons, and resins. Keywords: Lignin valorization, Ionic liquid pretreatment, Renewable chemicals, Biofuels Background phenylpropanoid-based biopolymer, and provides mech- Lignocellulosic biomass is primarily composed of three anical support and water transport to the plant and inhi- biopolymers: cellulose, hemicelluloses and lignin [1]. bits the action of various biological agents (e.g., insects) Holocellulosic biopolymers are considered the most on the plants [6]. It is estimated that 50 million tons of lig- valuable components of lignocellulose and are utilized nin is produced annually from pulp and paper industries for the production of various products including paper worldwide [7]. The high energy content of lignin, the pres- and biofuels [2-4]. Lignin constitutes roughly a third of ence of highly reactive groups, and the fact that it will be the biomass and is typically burned to produce waste heat generated in large quantities as second generation biorefi- and/or electricity within paper mills and biorefineries neries are deployed represents a significant opportunity [1,5]. Lignin is a naturally occurring heterogeneous for the production of a wide range of renewable chemicals and materials that can be sold as co-products (Figure 1). * Correspondence: [email protected] For example, lignin sulfonates produced from kraft 1Joint Bioenergy Institute, Physical Biosciences Division, Lawrence Berkeley pulping are currently utilized as phenol-formaldehyde National Laboratory, Emeryville, CA, USA 2Sandia National Laboratories, Biological and Materials Science Center, plastics, binders, adhesives, mud-sand cements in dril- Livermore, CA, USA ling oil-wells, dispersants, or flotation agents, emulsifiers © 2013 Varanasi et al.; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Varanasi et al. Biotechnology for Biofuels 2013, 6:14 Page 2 of 9 http://www.biotechnologyforbiofuels.com/content/6/1/14 Figure 1 Schematic depiction of the different routes to convert lignin into renewable materials and chemicals. and stabilizers, grinding agents, electrolytic refining like benzene, phenol, guaiacol, vanillic acid, methanol, agents, protein precipitants, tanning agents, sequestering acetic acid, and dimethyl sulfoxide (DMSO) [17,18]. These agents, storage battery plates, lime plaster, crystal growth lignin products are considered “value-added” chemicals inhibitor, ingot mold wash and as flame retardants [8,9]. (Figure 2) that could substantially impact the profit mar- Starch-based films incorporated with lignin have higher gins of a lignocellulosic biorefinery, but significant hurdles water resistance and increased elongation that make remain before they can be fully realized. One of the most them effective packaging materials [10]. Lignin is also used significant of these is the realization of an efficient, cost- in the production of conducting polymer lignosulfonic effective, and scalable means of fractionating lignocellu- acid-doped polyamine [11]. Carbon fibers produced from lose into polysaccharide- and lignin-rich streams that lignin based materials require a lower amount of thermo- enable downstream conversion into fuels and chemicals. stabilization and possess high tensile strength [12]. Lignin Recently, some ionic liquids (ILs) have been shown to be has been used to produce various polymers like very effective in the delignification of lignocellulosic ARBOFORM, polyesters and polyurethanes and various biomass and depolymerization of lignin [19-23]. While polymer blends with PVC, polyolefins, and rubbers are much of the focus on ILs in the biomass field has been on being currently developed [13-15]. Lignin has also been their impact on the crystalline nature of cellulose, little at- used as slow release nitrogenous fertilizers for soil and tention has been paid in their potential utility as a means catalyst for the Kraft pulping process [10,16]. Due to its to valorize lignin. hydrophobic nature, lignin can be used in the manufac- Recent efforts in converting lignin to its monomeric ture of gypsum wallboards [10]. products using ILs have focused on the technical lignins In addition to these applications, lignin is a potential re- extracted from lignocellulosic biomass [25-27]. Cox and newable source for many low molecular weight chemicals Ekerdt have shown that during IL dissolution, lignin Varanasi et al. Biotechnology for Biofuels 2013, 6:14 Page 3 of 9 http://www.biotechnologyforbiofuels.com/content/6/1/14 Figure 2 Market price vs. demand for lignin-derived products [24]. depolymerization occurs through breakdown of alkyl-aryl pine, and eucalyptus respectively) and technical lignins ether linkages [26]. But no lignin breakdown products were (kraft and low sulfonate alkali) were treated with reported to be observed during this process. Through [C2mim][OAc] at 160 and 120°C for 6 hrs. Since IL and electro-catalytic oxidative cleavage of lignin, Reichert et al. water are both polar, recovery of polar lignin breakdown produced various aromatic compounds like guaiacol, vanilic products posed significant challenges. Our choice of acid, vanillin, acetovanillone, syringol, syringaldehyde, and extraction solvents for non-polar products included syringic acid from alkali lignin [25]. Though a total yield of pentane, hexane, heptane and benzene. Out of the sol- 6% was observed, no information about the relative quan- vents tried, benzene enabled the most recovery and hence tities of each compound was reported. Stark et al. produce we have included the data on benzene extracted products syringaldehyde and 2,6-dimethoxy-1,4-benzoquinone from in this report. Although yields were not the same using oxidative depolymerization of Beech lignin. Although an different solvents, patterns of lignin degradation and re- impressive yield (66.3%) of the products was obtained the covery were similar for all the solvents tested. Table 1 process utilized high pressure (84 × 105 Pa of air) and very shows the percent biomass recovered for various types long reaction times (24 h) [27]. Lignin cleavage to mono- of biomass pretreated at 160°C. For all the conditions mers has also been accomplished using Bacillus sp. LD003 studied there is a loss of mass observed, indicating that by Bandounas et al., but the incubation times for microbial lignin and other biomass constituents remain solubi- degradation were very long (1–2 days) [28]. In this work, lized in the supernatant. At low biomass loading levels, we investigate the ability of the IL 1-ethyl-3-methylimidazo- low sulfonate alkali lignin showed the maximum lium acetate