Maleic acid hydrotropic fractionation of wheat straw to facilitate value‐added multi‐product biorefinery at atmospheric pressure

Abstract

Abstract Wheat straw was rapidly fractionated using maleic acid (MA) as an acid hydrotrope at atmospheric pressure under a range of conditions. MA hydrotropic fractionation (MAHF) was very selective in dissolving lignin and hemicelluloses resulting in a cellulose‐rich water insoluble solids (WIS), which was evaluated for producing fibers through bleaching and cellulosic nanofibrils by fibrillation, as well as glucose through enzymatic saccharification. The residual lignin (RL) within the WIS has a low degree of condensation, which eased bleaching. The RL was also carboxylated through MAHF, which facilitated nanofibrillation to produce lignin‐containing cellulose nanofibrils. The carboxylation also aided enzymatic saccharification of WIS by decreasing nonproductive cellulase binding to RL through electrostatic repulsion between carboxylated (charged) RL and the cellulase at elevated pH (>cellulase isoelectric point). The dissolved lignin (DL) from MAHF also has a low degree of condensation, making it favorable for further catalytic conversion. Carboxylation improved DL antioxidant capability. MA is an FDA‐approved indirect food additive (21CFR175‐177) and is much less corrosive than other acids typically used for cellulosic fractionation. It is also less soluble which is a distinct and very promising advantage for acid recovery. Therefore, MAHF has notable advantages and significant potential for sustainable biorefinery.

Keywords

• 2D NMR analysis
• enzymatic hydrolysis
• lignin antioxidant activity
• lignin esterification/carboxylation
• lignin‐containing cellulose nanofibrils (LCNFs)
• maleic acid hydrotropic fractionation (MAHF)