Wheat straw, with an estimated annual production over 170 million tons,
1, 2 has been considered the most promising agricultural residue for the production of bio-products and 2
nd generation bioethanol in Europe. The processing of wheat straw into fermentable sugars represents a great challenge, mainly due to its complex and highly recalcitrant architecture. In this work, the conversion of wheat straw into pentoses using supercritical CO
2 followed by an enzymatic saccharification of cellulosic fraction is for the first time investigated. This technology benefits from the
in-situ formation of carbonic acid. Without an additional chemical, this technology outperformed liquid hot water pretreatment allowing to produce total sugars yield as high as 84 % in comparison to 67 % with liquid hot water (and under more severe reaction conditions). Both chemical and physical effects of supercritical CO
2 resulted in a glucan to glucose conversion yield of 82 mol% representing a 26 % improvement over those achieved in liquid hot water.
3 Firstly, the effect of various process conditions, such as temperature, residence time and initial CO
2 pressure on conversion of hemicelluloses into pentoses (in both oligomeric and monomeric form) were scrutinised in an effort to define the optimal operational conditions. Then, several material characterisation techniques were used to investigate thoroughly the physical influence of supercritical CO
2on the processed solids.
Acknowledgment
This work was supported by the Fundação para a Ciência e a Tecnologia (FCT/MEC, Portugal) through SFRH/BD/94297/2013, IF/00471/2015 grants and by BBRI - Biomass and Bioenergy Research Infrastructure (ROTEIRO/0189/2013) and the Associated Laboratory for Sustainable Chemistry−Clean Processes and Technologies−LAQV which is financed by national funds from FCT/MEC (UID/QUI/50006/2013) and co-financed by the ERDF under the PT2020 Partnership Agreement (POCI-01-0145-FEDER-007265).
References
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3. A. R. C. Morais, A. C. Mata and R. Bogel-Lukasik, Green Chem., 2014, 16, 4312-4322.
