Study on the effect of fractionation pretreatment process on the enzymatic hydrolysis of switch grass for bioenergy and biorefinery

Abstract

Lignocellulosic biomass is the world's most abundant renewable resource. Conversion of lignocellulosic biomass to bioenergy, such as the second generation bioethanol or biobutanol is viable because of its broad availability. Switch grass was developed as a pioneer energy crop in USA with great industrial prospect. It contains about 60% sugars and 18% lignin. An intergrated pretreatment process was developed to fractionate cellulose, hemicellulose and lignin from switch grass, consisting of dilute acid pretreatment (DAP) coupled with organic solvent (organosolv) pretreatment of water/ethanol (OWEP). In the coupled dilute acid -organosolv process, hemicellulose sugars were recovered in the first residual liquid while a varied amount of cellulose was retained in the residual solid and the lignin fraction was obtained by simply adjusting the pH from the second liquid. The optimal two-stage process consisted of the first stage DAP at 428K for 7min with 0.8% sulfuric acid, resulting in 79.82% glucose recovery yield and 98.74% xylose removal and the second stage OWEP at 468K for 20min in 45%(v/v) ethanol with 0.4% NaOH, resulting in 62% total glucose yield 99% xylose and 80% lignin removal. After enzymatic hydrolysis, the glucose yield was up to 92.6%, compared with 16% yield from untreated switch grass. The intergrated process has great promising.