Combined Severity during Pretreatment Chemical and Temperature on the Saccharification of Wheat Straw using Acids and Alkalis of Differing Strength

Acids and alkalis are considered important catalysts in biomass pretreatment, which is essential to overcome the recalcitrance of lignocellulose for sugar release. In this study, the effects of various chemicals and temperatures on the pretreatment and subsequent enzymatic hydrolysis of wheat straw were investigated. The conversions of glucan and xylan during pretreatment and enzymatic hydrolysis were examined. The temperature and different ions in pretreatment govern the dissociation constant and hydrogen ion concentration. Due to higher dissociation at higher temperature, weak acids and weak alkalis can produce high glucose yields, similar to strong acids and alkalis. The concept of modified combined severity for weak acid pretreatment was explored. The pH value and real combined severity of weak acids at reaction temperatures were estimated according to xylan recovery during pretreatment. Glucose yield in enzymatic hydrolysis is mainly decided by xylan recovery for acidic pretreatment and by total content of xylan and acid-insoluble-lignin in solids for alkaline pretreatment.