Abstract
Efficient cellulose depolymerization is a major bottleneck for economical production of second‐generation biofuels. In this work, crystalline cellulose was subjected to sequential ball milling and ethanolysis as a mild and selective depolymerization approach. Ball milling and ethanolysis resulted in 38±1 % cellulose conversion, with 24 % ethyl‐glucopyranoside as the main identified and quantified product and negligible side reaction of the ethanol solvent to form diethyl ether. In comparison, ethanolysis of the original cellulose resulted in only 3±1 % conversion. Additional soluble products from cellulose ethanolysis included carbohydrate isomers and oligomers, differing from the products obtained from hydrolysis. X‐ray diffraction and nuclear magnetic resonance spectroscopy revealed increased crystallinity post‐reaction, retarding further depolymerization. Hot liquid water extracted soluble oligomers from the ethanolyzed cellulose, suggesting formation of a nanoscale barrier of crystalline cellulose that traps soluble products during ethanolysis. Use of cellulose‐swelling co‐solvents and repeated mechanical decrystallization both proved effective at increasing cellulose conversion and soluble product yields. Repeated ball milling and ethanolysis resulted in 62±1 % cellulose conversion. Ethanolysis of decrystallized cellulose has potential for rapid (<2 h) de‐polymerization at mild conditions.
Rapid depolymerization: The success of lignocellulosic biofuels and chemicals depends on the economic conversion of cellulose. Here, decrystallized cellulose is depolymerized by ethanolysis at mild conditions. Ethyl‐glucopyranoside is the main product; however, additional isomers were also detected. A crystalline solid residue remained that is resistant to conversion but contains trapped soluble oligomers. Strategies for preventing trapping oligomers are proposed.
