Influence of Acetic Acid as a Catalyst in Ethanol Organosolv Pretreatment of Wheat Straw for the Production of Colloidal Lignin Particles and Enzymatic Hydrolysis

Abstract

Ethanol organosolv pretreatment of lignocellulosic biomass produces high quality lignin and an enriched cellulose fraction while enabling a completely renewable-based process. However, optimization of this process is still necessary to be economically competitive. During autocatalytic pretreatment, acetic acid is released from hemicellulose and acts as catalyst for delignification. In this study, up to 4.4 wt% of acetic acid was added to ethanol organosolv pretreatment of wheat straw to determine its influence on delignification, enzymatic hydrolysis, and lignin yield, and compare the results to autocatalytic pretreatment. The results show that the addition of acetic acid significantly improves all of these parameters. Up to 48.5 % of delignification were achieved when 4.4 wt% of catalyst was added compared to 40.5 % in autocatalytic pretreatment. Glucose release in enzymatic hydrolysis slightly increased from 52.0 to 56.7 %, and a maximum lignin yield of 36.1 % was reached compared to 23.2 % when no catalyst was added. However, the addition of more than 0.6 wt% catalyst resulted in significantly darker lignin and a drastic increase in particle size after precipitation of the extracts into colloidal lignin particles. It can be concluded that acetic acid offers a promising possibility to improve ethanol organosolv pulping while maintaining a completely renewable-based process.