Study Of Pretreatment On Lignocellulose By Ionic Liquids For Enhancing Its Enzymatic Hydrolysis

As a kind of potential biomass resource,lignocellulose can be utilized to reduce the reliability on fossil resource.This study focuses on the pretreatment on lignocellulose by aqueous tetrabutylammonium hydroxide(TBAOH)and tetramethylammonium hydroxide(TMAOH)for enhancing its enzymatic hydrolysis.Herein,two kind of raw materials,corn stalk and corn cob,were studied,respectively.First of all,effects of pretreatment temperature(20-80°C),concentration of aqueous solution(10-40wt%),pretreatment time(5-80 min)and ratio of liquid to solid(3-8,wt/wt)were investigated with the enzymatic hydrolysis sugar yield taken as indicator.Then,the optimum pretreatment conditions were determined.For corn stalk,the optimum conditions of aqueous TBAOH and TMAOH pretreatment were identified as pretreatment temperature 20°C,concentration of TBAOH 30%,pretreatment time 20 min,ratio of liquid to solid 5 and pretreatment temperature 20°C,concentration of TMAOH 10%,pretreatment time 60 min,ratio of liquid to solid 5,respectively.The corresponding enzymatic hydrolysis sugar yield were 68.2% and 72.6%.Compared to the enzymatic hydrolysis sugar yield 17.7% of unpretreated corn stalk,they were significantly increased to around 4 times.For corn cob,when pretreated by two aqueous ionic liquids,the optimum conditions were identified as pretreatment temperature 30°C,concentration of TBAOH 20%,pretreatment time 60 min,ratio of liquid to solid 5 and pretreatment temperature 20°C,concentration of TMAOH 10%,pretreatment time 60 min,ratio of liquid to solid 5,respectively.The corresponding enzymatic hydrolysis sugar yield were 88.9% and 92.2%,which were significantly increased to around 3 times of 32.4% of unpretreated corn cob.Besides,the lignocellulose samples before and after pretreatment were characterized by HPLC,FTIR,XRD and SEM to illustrate the contents of components,functional groups,crystal structure and surface morphology,respectively.The results of these characterizations showed that hemicellulose and lignin in corn stalk and corn cob raw materials were significantly removed by aqueous TBAOH and TMAOH pretreatment.Meanwhile,cellulose was not dissolved and therefore relatively purified.Moreover,the complex structure of raw material was deconstructed and cellulose was exposed consequently.As a result,the accessibility to cellulose increased significantly.Finally,based on the results of enzymatic hydrolysis and characterizations,the pretreatment mechanism was demonstrated as follows: during the pretreatment,hemicellulose and lignin in lignocellulose raw material were removed or degraded by the combination of cation together with its hydrate and the strong basicity of anion hydroxide.Consequently,the complex microstructure of lignocellulose was deconstructed,the accessibility to cellulose of enzyme was increased and the enzymatic hydrolysis was enhanced significantly.