Degradation And Removal Of Lignin In Pretreatment Of Corn Stover By ScCO₂-Ethanol-Water

In recent years, people paid much attention on the cellulosic ethanol technology.Lignin, as the main component of lignocellulosic biomass, functions as a matrixbetween the cellulose fbers and is a barrier to effcient enzymatic hydrolysis ofcellulose to sugars. The main aim of the pretreatment stage is to destroy thelignocellulosic matrix, remove lignin from the surface of cellulose and improve theenzyme hydrolysis efficiency of cellulose. Supercritical pretreatment has beenclaimed to be a promising and environmentally friendly chemical process. In thisstudy, scCO₂-ethanol-water ternary mixtures were used to pretreat cron stover. Thedegradation and removal behavior of lignin was studied.Firstly, Van Soest method, GC-MS, thermal property analysis and FTIRcharacterization were conducted to study the degradation and removal behavior oflignin. The results showed that the scCO₂-ethanol-water pretreatment could removelignin from corn stover effectively. During the scCO₂-ethanol-water pretreatment,depolymerization and condensation of corn stover lignin competed with each other.The ether bonds cleavage was the main form of lignin depolymerization. Thepretreatment temperature and time had important effect on the degradation andremoval behavior of lignin.Residual lignin which can not be removed during the pretreatment was studied.Residual lignin unevenly distributed on thefber surface as spherical particles afterpretreatment, with lignin-carbohydrate complex on the surface. Some lignin particlesgathered and fused to form large size particles. The residual lignin was formed fromthe large size lignin and the readsorption of dissolved lignin. Large size particles andlignin-carbohydrate complex made residual lignin hardly to be removed. Ethanolwashing and NaOH solution washing were used to remove the residual lignin. Thedelignification rates for residual lignin were19.2%and22.2%for ethanol and NaOHwashing respectively. In the production of cellulosic ethanol, using ethanol washingfor the removal of residual lignin, ethanol can be recycled by distillation and usedrepeatedly, improving the efficiency and avoiding environment pollution.