BACKGROUND Rice straw (RS), one of the most plentiful lignocellulosic wastes worldwide, has been considered a potential candidate to produce bioethanol. The object of this work was to develop an efficient and feasible pretreatment process for RS with alkaline peroxide combined with ionic liquid (IL)–water mixtures, reveal the mechanism, and achieve biomass valorization. RESULTS Alkaline peroxide pretreatment under mild conditions combined with IL–water mixtures pretreatment at a water content of 30 wt% was established, leading to a maximum lignin removal of 63.8% with an enzymolysis efficiency of 92.1% and a simultaneous saccharification and co‐fermentation efficiency of 91.0%. Furthermore, the recycled IL also showed good performance with the established pretreatment process, resulting in 251.6 g L−1 of reducing sugar and 91.9 g L−1 ethanol at high solid loading. The alkaline peroxide pretreatment enhanced lignin extraction and disrupted the RS structure to facilitate the dissolution of amorphous components by the IL–water mixtures. CONCLUSION A simple and efficient pretreatment was successfully established. The IL was successfully recycled for further pretreatments, and high concentrations of reducing sugars and ethanol were achieved using the pretreated RS. The effectiveness of the pretreatment process suggested potential application in future biorefineries. © 2018 Society of Chemical Industry
An efficient ionic liquids (ILs) recycle technology will increase the economic viability of lignocellulosic biorefinery. The availability of recycling 1‐butyl‐3‐methylimidazolium chloride for rice straw (RS) pretreatment was conducted. The kosmotropic salt K3PO4 (TKP) solution was used as antisolvent for cellulose precipitation and forming a three‐phase system consisting of biomass, ILs‐rich, and salt‐rich phases. The upper ILs phase and the bottom TKP phase were recycled without additional purification, which significantly simplifies the process for recovering ILs. Subsequently, the RS pretreated with multiple reusing ILs (RPRS) were investigated by components analysis, structure evolution, enzymatic hydrolysis, and fermentation experiments. The results showed that unpurified reusing ILs led to further delignification and improvement of enzyme accessibility of the pretreated RS. The reducing sugar yield of RS pretreated with 8th reusing IL (8th RPRS) could still reach 98.9%, and the ethanol and succinic acid concentrations achieved 91.9 and 29.3 g/L by simultaneous saccharification and cofermentation. The present study demonstrated that the ILs recovered by phase‐separation process could be used for RS pretreatment, and achieving high titer ethanol fermentation.
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