Stepwise pretreatment of aqueous ammonia and ethylenediamine improve enzymatic hydrolysis of corn stover

It is a trade-off between sugar loss in pretreatment and sugar release in hydrolysis for most pretreatment. Here, a stepwise mild pretreatments of aqueous ammonia pretreatment and ethylenediamine was developed to reduce the sugar loss during pretreatment process and improve the sugar release in enzymatic hydrolysis of corn stover. Among four parameters of stepwise pretreatment (NH3 loading, aqueous ammonia pretreatment time, ethylenediamine loading and ethylenediamine pretreatment time), aqueous ammonia pretreatment time and ethylenediamine loading played the key roles in the improving enzymatic hydrolysis. More than 95% glucan and 85% xylan were reserved in the pretreated solid after stepwise pretreatment. The glucan and xylan conversion reached 94.18% and 72.81%, respectively, with a low enzyme loading of 10 mg cellulase/g glucan. The characterization of the pretreated solid suggested that in stepwise pretreatment process, aqueous ammonia pretreatment increased the specific surface area of pretreated solid by 26.4%, while ethylenediamine pretreatment resulted in the collapse of the biomass porous structure and hence reduced the specific surface area. Crystalline index of the biomass increased after aqueous ammonia pretreatment, while the crystalline index was decreased from 53.22% to 32.13% after ethylenediamine pretreatment. Results implied that aqueous ammonia pretreatment enhanced productive enzyme adsorption on biomass mainly by increasing specific surface area, while ethylenediamine pretreatment improved productive enzyme adsorption by the coalescence and re-localization of lignin to expose more accessible surface. As a result, these interactive effects provided by the stepwise pretreatment improved the accessibility of the pretreated corn stover to enzymes and thus increased sugar release significantly.