Comparison of effects of carbocation scavengers assisted acid pretreatment on improving enzymatic digestibility of masson pine and poplar

To investigate the disparate effects of carbocation scavengers on promoting the enzymatic hydrolysis of softwood and hardwood, five carbocation scavengers were supplemented during acid pretreatment of masson pine and poplar in this study, including 2-naphthol (2 N), 2-naphthol-7-sulfonate (NS), p -hydroxybenzoic acid (PB), vanillic acid (VA) and syringic acid (SA). The results showed that naphthols (2 N and NS) with only one nucleophilic site enhanced delignification and enzymatic hydrolysis more significantly than the monophenols with several reactive sites. Adding 2 N and NS increased the hydrolysis yield of acid-pretreated masson pine (AM) from 14.87% to 20.58% and 35.52%, respectively. Correspondingly, the hydrolysis yield of acid-pretreated poplar (AP) improved from 56.54% to 80.47% and 86.9%, respectively. Moreover, as pretreatment severity increased, the enzymatic digestibility of AM and AP first increased and then decreased. However, the naphthols modification retarded this decline, especially for the enzymatic hydrolysis of pretreated poplar. The structure of carbocation scavengers and the lignin unit composition jointly determined the improvement on enzymatic hydrolysis of woody biomass by carbocation scavengers. Furthermore, the naphthols promoted the enzymatic hydrolysis mainly by alleviating enzyme non-productive binding.