Study On The Characterization Of Dilute HCl And HNO₃ Co-hydrolysis Of Corn Stover At Low Temperature

It is an effective and practical way to alleviate energy crisis and avoid environment problems for industrial-scale biogas production utilizing the corn stover especially agriculture waste. However, there are a few problems such as higher cost and lower fermentation efficiency in the bioconversion of corn stover. Thus, a higher efficient and feasible pretreatment method is necessary. By using HCl, H₂SO₄ and HNO₃ in the hydrothermal hydrolysis of corn stover, the characterization of dilute mixed acid hydrolysis of corn stover at low temperature was investigated and the optimal conditions were obtained from the theoretical analysis, which offered a novel pretreatment method to realize industrially the conversion from corn stover to biogas.The effect of hydrochloric acid, sulfuric acid and nitric acid alone on the hydrolysis characterization of corn stover at low temperature was investigated. The results showed that there was a decreasing order that firstly nitric acid, followed by sulfuric acid, and finally the hydrochloric acid for improving hydrolysis efficiency of corn stover. At 120℃, using nitric acid, sulfuric acid and hydrochloric acid of 1% for 60 min, the hydrolysis efficiency of cellulose were respectively 60.5%, 60.0%, 58.8%, while the hydrolysis efficiency of hemicellulose were 83.6%, 82.5%, 74.2%, respectively. Moreover, it was found that at 120℃when hydrochloric acid and sulfuric acid was alone used, the xylose and arabinose amount in the hydrolysate decreased with increasing acid concentration and reaction time. While nitric acid was used, the xylose and arabinose concentration in the hydrolysate increased with the increase of acid concentration, and longer reaction time was beneficial for enhancing the xylose concentration, but it led to lower arabinose amount.Hydrochloric acid and nitric acid, as a mixed acid, were selected to hydrolysis the corn stover at low temperature. The results showed that the hydrolysis efficiency of corn stover using a mixed acid of hydrochloric acid and nitric acid was superior to that of using individual acid in case of the same acid concentration. At 120℃, total acid concentration of 1% and the ratio between hydrochloric acid and nitric acid of 3, the hydrolysis efficiency of hemicellulose was 95.0%, while 83.6% for using nitric acid of 1% alone and 74.2% for using hydrochloric acid of 1% alone at 60 min. Comparison of the micro-morphology and crystallinity analysis of corn stover pretreated by mixed acid and acid alone, using mixed acid pretreatment better than that of acid alone was proved. By means of response surface methodology, the conditions using hydrochloric acid and nitric acid mixed was optimized. 120℃, the ratio between hydrochloric acid and nitric acid of 3.02, the xylose and arabinose yields were respectively 18.0 g/100gDM and 3.4 g/100gDM at 92.1 min.