Saccharification of the Pretreated Corn Stover by Microwave Assisted DMSO/AmimCl Co-solvents

Abstract

In order to enhance the enzymatic saccharification efficiency of corn stover, microwave assisted treatment with dimethyl sulfoxide (DMSO) and 1-ally-3-methylimidazolium (AmimCl) co-solvents was designed to break up the complicated chemical structure of corn stover. The pretreatment conditions were studied to increase the dissolution ratio, extraction ratio and cellulose I crystallinity index (Crl) variation. With the increase of AmimCl concentration, time and temperature of the pretreatment, the dissolution ratio, extraction ratio increased and Crl decreased. Considering the costs of high AmimCl concentration, degradation of biomass at high temperature and long time, the optimum conditions were DMSO/AmimCl co-solvents with a DMSO concentration of 15% (w) and 4 g corn stover per 100 g co-solvents. The optimum temperature and time were 110 degrees C and 60 min, respectively. Under the optimal conditions, the ratios of corn stover dissolution and extraction were as high as 46.6% and 22.9%, respectively. The cellulose saccharification ratio had a great increase within 14 h of enzymatic hydrolysis with an enzyme loading amount of 14 FPU/g solids. The saccharification ratio for the extracts was 71.4% in 14 h, while the ratio was only 12.5% for the raw corn stover in 20 h. Powder X-ray diffraction was used to determine the cellulose crystal structure. The cellulose I crystallinity index of corn stover residues decreased obviously and the crystal form of AmimCl extracts were transformed from I to II. From the SEM pictures of the materials, it could be seen that the outer surface of corn stover residues became rough, which was good for enzyme accessibility and saccharification. The AmimCl extracts had lost their natural status completely. By simple vacuum distillation, AmimCl could be recycled and its solubility kept almost constant. According to H-1 NMR spectroscopy analysis, the structures of fresh and recycled AmimCl were almost the same. From the results mentioned above, it can be concluded that microwave assisted treatment with DMSO AmimCl co-solvents was a feasible method for corn stover pretreatment.