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Biorefinery approach for lignocellulosic biomass valorisation with an acidic ionic liquid

da Costa Lopes, André M., Lins, Roberto M. G., Rebelo, Ricardo A., Łukasik, Rafał M.
Green chemistry 2018 v.20 no.17 pp. 4043-4057
aqueous solutions, arabinose, biobased products, biomass, biorefining, cellulose, commercialization, enzymatic hydrolysis, experimental design, feedstocks, fuels, glucose, green chemistry, hemicellulose, hydrolysis, ionic liquids, lignin, lignocellulose, pentoses, pulp, recycling, saccharification, sulfates, value added, wheat straw, xylose
The commercialisation of the biorefinery approach involving the integration of the multi-step valorisation of low value biomass feedstock into a variety of chemicals, fuels and bioproducts is still very limited. In this context, the present work proposes an advanced methodology that comprises a cascaded approach towards wheat straw valorisation. The studied concept lies in the employment of an aqueous solution of the acidic 1-ethyl-3-methylimidazolium hydrogen sulfate ionic liquid in a selective and efficient hydrolysis of the hemicellulose fraction of wheat straw into pentoses, namely xylose and arabinose. An experimental design was utilised to search for the optimisation parameters, resulting in a maximum 80.5 wt% pentose yield in the liquor. Furthermore, the remaining solid, which contained practically all of the initial cellulose and lignin, was processed by considering two scenarios: (i) a direct enzymatic hydrolysis of the reaction solid, which yielded 75.8 mol% glucose; or (ii) a preceding extraction of lignin followed by enzymatic saccharification of the cellulose pulp, which yielded 91.3 mol% glucose. For both scenarios, lignin-rich solid fractions were obtained with distinct purities and yields. Additionally, the second scenario allowed producing a stream of value-added aromatic (phenolic) compounds. This work also overcame the challenges in IL recycling and reuse, with a simultaneous recovery of the pentoses from the reaction liquor as high as 88.6 mol%.