Effects of lignin on the ionic-liquid assisted catalytic hydrolysis of cellulose: chemical inhibition by lignin

The production of cellulose-derived biofuels and biochemicals, such as bioalcohols and bioplastics, from lignocellulose requires the isolation of cellulose by lignin removal or delignification processes. While the remaining lignin and its phenolic fragments have been reported to inhibit the biological conversion of cellulose, we observed that the catalytic hydrolysis of cellulose also can be inhibited most likely because of an associative interaction between cellulose and lignin. The associative interaction between cellulose and the functional groups of lignin was proven by gel-permeation-chromatography measurement of regenerated mixtures of lignin and cellulose which simulate the lignocellulose-derived cellulose containing lignin as an impurity. Chemical bonds between cellulose and lignin were hypothesized using lignin model compounds containing known functionalities such as hydroxyl, methoxy, phenyl, allyl, and carboxyl groups in order to explain the effects of lignin on the hydrolysis of cellulose. The yield of glucose from cellulose dropped when carboxylic and hydroxyl groups were present possibly because of the formation of ether and ester bonds between the lignin and cellulose. These observations may help develop the chemical processes and therefore convert the inedible biomass resource of lignocellulose-based cellulose containing lignin and its derivatives to the valuable fuels and chemicals.