Carbocation scavenger enhanced pretreatment of wood for enzymatic saccharification – Experimental study and review

The suppression of lignin repolymerization by carbocation scavengers in lignocellulosic biomass pretreatment improves both the bioconversion of cellulose and the quality of the obtained lignin. However, the effects of the various known scavenger compounds on the enzymatic cellulose saccharification of different biomass substrates have not yet been systematically investigated. We reviewed the effects of the frequently studied pretreatment additives 2-naphthol, 2-naphthol-7-sulfonate, mannitol and syringic acid on the pretreatment of different wood species. The review shows that carbocation scavengers can be effective for enhancing the pretreatment of various soft- and hardwoods. The reported effects on enhancing cellulose bioconversion are however very case specific, depending on pretreatment additive, biomass species, pretreatment method, and other factors. Therefore, it is not possible to specify a single best additive for the pretreatment of woody biomass, but it should be selected specifically for each individual case. This insight was further confirmed by a complementary experimental study of the mentioned compounds in the autohydrolysis pretreatment of softwood (spruce) and hardwood (beech). 2-Naphthol-7-sulfonate proved very effective for enhancing both the enzymatic saccharification of softwood and hardwood cellulose. 2-Naphthol improved the pretreatment of softwood, but was hardly effective for hardwood. Vice versa, mannitol and syringic acid enhanced hardwood pretreatment, but were not effective for softwood. An analysis of the additive consumption in autohydrolysis pretreatment further revealed that the aromatic compounds 2-naphthol, 2-naphthol-7-sulfonate and syringic acid are highly reactive, reaching a consumption of 86–100 % in spruce and 71.9–97.7 % in beech pretreatment, whereas mannitol was hardly consumed. • Review of different carbocation scavenger pretreatment additives. • Review of carbocation scavenger effect on woody biomass pretreatment. • Study of carbocation scavengers in soft- and hardwood pretreatment for enzymatic saccharification. • Study on the consumption of carbocation scavengers in soft- and hardwood pretreatment.