Microwave assisted transition metal salt and orthophosphoric acid pretreatment systems: Generation of bioethanol and xylo-oligosaccharides

In the present work, the transition metal compounds i.e. CoCl2, NiCl2, and CrO3 were used as microwave sensitizer's chemicals in combination with H3PO4. The efficiency of the pretreatment process was assessed based on sugar and ethanol generation potential from pretreated rice straw (RS). The in-house produced crude cellulase (Cr-Cell) and xylanase (Cr-Xyl) alone and in combination was used for hydrolysis of pretreated RS. The efficiency of the in-house enzyme against the commercial cellulase (ComCell) and xylanase (Com-Xyl) was also examined. The structural characteristics of the pretreated RS were studied using FTIR and XRD. Based on the above studies, NiCl2+H3PO4 and CrO3+H3PO4 mediated microwave pretreatment system were found to be the suitable methods with maximum sugar yield of 65.2 +/- 1.01% and 70.76 +/- 0.87% using a cocktail of the commercial cellulase and xylanase (Com(CK)-CellXyl) which are comparable to the in-house enzyme cocktail (Cr-CK-CellXyl). The FTIR and XRD analysis of the pretreated and untreated RS also suggested that there is a change in biomass crystallinity resulting in enhanced accessibility of enzyme to the biomass. The maximum ethanol yield of 14.39 +/- 0.44 g/L and 12.41 +/- 0.33 g/L was obtained for simultaneous sacchariflcation and fermentation (SSF) of CrO3+H3PO4 pretreated RS using Com(CK)-CellXyl and Cr-CK-CellXyl. The pretreated RS when subjected to hydrolysis using in-house and commercial xylanase, several xylo-oligosaccharides i.e. xylotriose (X3), xylotetraose (X4) and xylopentoses (X5) were generated with major contribution of X5. (C) 2020 Elsevier Ltd. All rights reserved.