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

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.