Insight into understanding sequential two-stage pretreatment on modifying lignin physiochemical properties and improving holistic utilization of renewable lignocellulose biomass

Abstract

The key to obtain the full benefits of renewable lignocellulosic biomass is to develop sustainable and economical fractionation technology of lignocellulosic components. Acidic pretreatment usually solubilizes the majority of hemicellulose, but also aggravates lignin repolymerization which would intensify lignin inhibition on cellulose hydrolysis. Thus, in this work, two approaches were utilized to modify the lignin physiochemical properties and synergistically improve holistic utilization of lignocellulose biomass. Firstly, the addition of 2-naphthol in dilute acid (DA) pretreatment largely suppressed lignin repolymerization and mitigated lignin inhibition, resulting in increased cellulose hydrolysis yield from 46.81% to 55.74%. Secondly, it was found that the phenolic groups of lignin played a pivotal role in determining the ease of cellulose hydrolysis, thus a second-stage treatment with acid-chlorite (CHL) or poly(ethylene glycol) diglycidyl ether (PEE) was introduced to selectively oxidize/block phenolic groups of lignin, which further improved cellulose hydrolysis to theoretically maximum yield. In addition to enhanced cellulose hydrolysis, the lignin residues recovered after PEE modification and enzymatic hydrolysis could be used as high-capacity adsorbents for lead ions removal from wastewater, while xylose was utilized for xylonic acid production. Results showed that the biorefinery process based on DA pretreatment and PEE post-treatment could enable a holistic utilization of renewable lignocellulosic biomass.