Using recyclable pH-responsive lignin amphoteric surfactant to enhance the enzymatic hydrolysis of lignocelluloses

In order to enhance the enzymatic hydrolysis of lignocelluloses and recycle surfactants after enzymatic hydrolysis, a pH-responsive lignin amphoteric surfactant (SLQA) was prepared by the quaternization of sulfonated lignin (SL). Compared with SL, SLQA could much more effectively enhance the enzymatic hydrolysis of lignocelluloses. With an increase in the quaternization degree, enhancement of the enzymatic hydrolysis of lignocelluloses by the SLQA gradually increased. Adding 2 g L-1 SLQA-80 (mass radio of quaternizing agent to SL was 80%) could increase the enzymatic digestibility of pretreated eucalyptus and corncob residues (CCR) from 36.7% and 37.8% to 84.3% and 90.5%, respectively. The adsorption of SLQA on lignin film was larger than that of SL, and the lignin film became more hydrophilic after adsorbing SLQA. Thus, SLQA could cause more effective steric hindrance and form a hydration layer to reduce the non-productive adsorption of cellulase on lignin. The purified SLQA-80 exhibited sensitive pH-responsive property, and 90.8% of SLQA-80 could be recycled by adjusting the pH of hydrolysate after enzymatic hydrolysis. Adding recyclable SLQA could not only obviously enhance the enzymatic hydrolysis of lignocelluloses, but could also enable the comprehensive utilization of lignocelluloses. This method is of great significance to reducing the cost of cellulosic ethanol.