Effect of combined inorganic with organic acids pretreatment of rice straw on its structure properties and enzymatic hydrolysis

Abstract

Rice straw was pretreated with sulfuric acid combined with five organic acids (oxalic acid, acetic acid, tartaric acid, succinic acid, and fumaric acid) at 121°C for 90 min with five different blending ratios. The concentrations of glucose, xylose, arabinose and inhibitors such as acetic acid, furfural and HMF (5‐hydroxymethylfurfural) in the prehydrolysate were analyzed. It demonstrated that the concentrations of both sugars and inhibitors in prehydrolysate decreased with increasing organic acids blending ratio. The different solid residues from pretreatments were subjected to enzymatic hydrolysis process. The results showed that pretreating rice straw using combined sulfuric acid with oxalic acid or fumaric acid resulted in the maximum glucose yield (∼66%) after 72 h enzymatic hydrolysis in sharp contrast to ∼58% glucose yield obtained from pretreatment only with sulfuric acid under the same conditions. Furthermore, the structure of the raw material and the pretreated rice straw were characterized by scanning electron microscopy (SEM) and Fourier transformer infrared (FTIR) spectrum to clarify the effects of the combined sulfuric acid with oxalic or fumaric acid pretreatment on disrupting the fibers, removing hemicellulose and making the cellulose structure loose. © 2017 American Institute of Chemical Engineers Environ Prog, 37: 808–814, 2018