Microwave-Assisted Hydrolysis of Cotton Waste to Glucose in Combination with the Concentrated Sulfuric Acid Impregnation Method

Direct hydrolysis of a towel to glucose was investigated using microwave-assisted (MW) treatment combined with impregnation in concentrated sulfuric acid (SA) solution (51 wt% for 30 min) before the MW treatment. The maximum glucose yield by direct hydrolysis of an untreated towel was 30.9%, obtained at a heating temperature of 200 °C for 2 min. The maximum total glucose yield (from both direct hydrolysis and enzymatic hydrolysis of treated residue) was 74.2%, attained at a microwave heating temperature of 180 °C for 3 min. This condition is milder than that of MW treatment without impregnation in concentrated SA (our previous study, heating temperature of 200 °C for 7 min required). As shown by XRD of the unimpregnated and impregnated towels (in 9 and 36 wt% SA solution), the crystallinity index value decreased with the increase in SA concentration. Finally, 22.4 g of ethanol could be produced using the supernatant (containing glucose) and the microwave-treated residue as a carbon source for Saccharomyces cerevisiae , with less fermentation inhibition. Thus, impregnation in concentrated SA before MW treatment is effective for the production of glucose from cellulosic material and has low energy input.