Effect of acidity on hydrolysis and depolymerization of lignocellulose in one-pot lignin-first biorefinery

Abstract

In lignin-first biorefinery, extraction and depolymerization of lignin from lignocellulosic materials provide value-added lignin monomers. In this study, a mixture of acid-containing water and ethylene glycol was introduced to the lignin-fist biorefinery for simultaneously improving lignin cleavage, together with the depolymerization of cellulose and hemicellulose within one-pot. The experiments were conducted at 180-250°C under the hydrogen pressure of 30 bar for 1-6 h using oil palm empty fruit bunch (OPEFB) as a biomass source. The presence of acid and mixed solvent in the reaction provided the lignin oil yield up to 60 wt% comprising of the main monomers such as phenol, guaiacyl, and syringyl. Moreover, the acidity at pH 4 leads to the lignin monomer yield of 4.5 wt%. Glucose, xylose, and arabinose from hydrolysis of cellulose and hemicellulose in water phase were identified to clarify that the one-pot lignin-first biorefinery simultaneously depolymerize lignin and hydrolyze carbohydrate. The effects of temperature and reaction time were investigated. The results revealed that the harsh conditions result in high potential of lignin depolymerization but diminish the sugar units of carbohydrate. This study demonstrate that ethylene glycol participates in the extraction of lignin from OPEFB, while acid-containing water participates not only in depolymerization of carbohydrate but also in depolymerization of lignin. On the other hand, acid-catalyst stabilizes the reactive lignin.