Enhancement of enzymatic hydrolysis of sugarcane bagasse by pretreatment combined green liquor and sulfite

•Sugarcane bagasse is pretreated by combination with green liquor (GL) and sulfite.•GL-sulfite pretreatment could protect carbohydrates and selectively remove lignin.•Enzymatic hydrolysis efficiency is improved by GL-sulfite pretreatment.•Pretreatment using Kraft-GL allows higher glucose yield than that using Soda-GL.•GL-sulfite pretreatment could couple with a pulp mill for biorefinery.

Green liquor (GL) is readily available in any pulp mills which could be recycled. Alkaline sulfite pretreatment process was developed for non-woody biomass biorefinery. In this study, GL combined with sulfite was effectively utilized to improve the enzymatic hydrolysis of sugarcane bagasse by selectively removing lignin. Compare to conventional alkaline sulfite pretreatment, the solid yield could be higher with low degradation of polysaccharide. With the increment of the pretreatment temperature from 100 to 140 °C, the enzymatic hydrolysis efficiency was improved. And a higher glucose yield was achieved under pretreatment condition of 0.4 g/g-DS Na2SO3 and 1.5 mL/g-DS GL due to the higher degradation of xylan. The highest glucose yield of 96.8% could be reached with 3.36 g/(L·h) of initial rate after Kraft GL-sulfite pretreatment at 140 °C. The superior performance of Kraft GL allows conversion of cellulose to glucose more significantly than Soda GL. In addition, surface tension test indicated that a part of lignin was dissolved in the pretreatment liquor as lignosulfonate. The results showed that GL combined with sulfite is a promising way for sugarcane bagasse pretreatment.