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      Efficient biomass pretreatment using ionic liquids derived from lignin and hemicellulose.

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          Abstract

          Ionic liquids (ILs), solvents composed entirely of paired ions, have been used in a variety of process chemistry and renewable energy applications. Imidazolium-based ILs effectively dissolve biomass and represent a remarkable platform for biomass pretreatment. Although efficient, imidazolium cations are expensive and thus limited in their large-scale industrial deployment. To replace imidazolium-based ILs with those derived from renewable sources, we synthesized a series of tertiary amine-based ILs from aromatic aldehydes derived from lignin and hemicellulose, the major by-products of lignocellulosic biofuel production. Compositional analysis of switchgrass pretreated with ILs derived from vanillin, p-anisaldehyde, and furfural confirmed their efficacy. Enzymatic hydrolysis of pretreated switchgrass allowed for direct comparison of sugar yields and lignin removal between biomass-derived ILs and 1-ethyl-3-methylimidazolium acetate. Although the rate of cellulose hydrolysis for switchgrass pretreated with biomass-derived ILs was slightly slower than that of 1-ethyl-3-methylimidazolium acetate, 90-95% glucose and 70-75% xylose yields were obtained for these samples after 72-h incubation. Molecular modeling was used to compare IL solvent parameters with experimentally obtained compositional analysis data. Effective pretreatment of lignocellulose was further investigated by powder X-ray diffraction and glycome profiling of switchgrass cell walls. These studies showed different cellulose structural changes and differences in hemicellulose epitopes between switchgrass pretreatments with the aforementioned ILs. Our concept of deriving ILs from lignocellulosic biomass shows significant potential for the realization of a "closed-loop" process for future lignocellulosic biorefineries and has far-reaching economic impacts for other IL-based process technology currently using ILs synthesized from petroleum sources.

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          Most cited references43

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          Features of promising technologies for pretreatment of lignocellulosic biomass.

          N. Mosier (2005)
          Cellulosic plant material represents an as-of-yet untapped source of fermentable sugars for significant industrial use. Many physio-chemical structural and compositional factors hinder the enzymatic digestibility of cellulose present in lignocellulosic biomass. The goal of any pretreatment technology is to alter or remove structural and compositional impediments to hydrolysis in order to improve the rate of enzyme hydrolysis and increase yields of fermentable sugars from cellulose or hemicellulose. These methods cause physical and/or chemical changes in the plant biomass in order to achieve this result. Experimental investigation of physical changes and chemical reactions that occur during pretreatment is required for the development of effective and mechanistic models that can be used for the rational design of pretreatment processes. Furthermore, pretreatment processing conditions must be tailored to the specific chemical and structural composition of the various, and variable, sources of lignocellulosic biomass. This paper reviews process parameters and their fundamental modes of action for promising pretreatment methods.
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            Is Open Access

            Cellulose crystallinity index: measurement techniques and their impact on interpreting cellulase performance

            Although measurements of crystallinity index (CI) have a long history, it has been found that CI varies significantly depending on the choice of measurement method. In this study, four different techniques incorporating X-ray diffraction and solid-state 13C nuclear magnetic resonance (NMR) were compared using eight different cellulose preparations. We found that the simplest method, which is also the most widely used, and which involves measurement of just two heights in the X-ray diffractogram, produced significantly higher crystallinity values than did the other methods. Data in the literature for the cellulose preparation used (Avicel PH-101) support this observation. We believe that the alternative X-ray diffraction (XRD) and NMR methods presented here, which consider the contributions from amorphous and crystalline cellulose to the entire XRD and NMR spectra, provide a more accurate measure of the crystallinity of cellulose. Although celluloses having a high amorphous content are usually more easily digested by enzymes, it is unclear, based on studies published in the literature, whether CI actually provides a clear indication of the digestibility of a cellulose sample. Cellulose accessibility should be affected by crystallinity, but is also likely to be affected by several other parameters, such as lignin/hemicellulose contents and distribution, porosity, and particle size. Given the methodological dependency of cellulose CI values and the complex nature of cellulase interactions with amorphous and crystalline celluloses, we caution against trying to correlate relatively small changes in CI with changes in cellulose digestibility. In addition, the prediction of cellulase performance based on low levels of cellulose conversion may not include sufficient digestion of the crystalline component to be meaningful.
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              Ionic liquids as electrolytes

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                Author and article information

                Journal
                Proc. Natl. Acad. Sci. U.S.A.
                Proceedings of the National Academy of Sciences of the United States of America
                1091-6490
                0027-8424
                Sep 2 2014
                : 111
                : 35
                Affiliations
                [1 ] Deconstruction Division, Joint BioEnergy Institute, Emeryville, CA 94608; Center for Sustainable Energy and Department of Chemistry and Chemical Technology, Bronx Community College, City University of New York, Bronx, NY 10453;
                [2 ] Deconstruction Division, Joint BioEnergy Institute, Emeryville, CA 94608; Biological and Materials Science Center, Sandia National Laboratories, Livermore, CA 94551;
                [3 ] Complex Carbohydrate Research Center, University of Georgia, Athens, GA 30602; and The BioEnergy Science Center, Oak Ridge National Laboratory, Oak Ridge, TN 37831.
                [4 ] Deconstruction Division, Joint BioEnergy Institute, Emeryville, CA 94608;
                [5 ] Biological and Materials Science Center, Sandia National Laboratories, Livermore, CA 94551;
                [6 ] Complex Carbohydrate Research Center, University of Georgia, Athens, GA 30602; and.
                [7 ] Deconstruction Division, Joint BioEnergy Institute, Emeryville, CA 94608; Biological and Materials Science Center, Sandia National Laboratories, Livermore, CA 94551; seesing@sandia.gov.
                Article
                1405685111
                10.1073/pnas.1405685111
                25136131
                3da11bd7-172a-4e3d-a157-334b1c9a91d3
                History

                bioenergy,green chemistry,lignocellulose conversion,renewable chemicals,saccharification

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