[Abstract]

Rapid depolymerization of cellulose into processable monomers (e.g., sugars) using solid acid catalysts is an important step for cost-effective biofuel and biochemical production, but has not yet been achieved due to the limited contact between solid cellulose and solid catalysts. Herein, the unique roles of supercritical CO₂ (i.e., scCO₂) as an in-situ acid catalyst and reaction solvent in achieving the ultra-fast full solid catalytic hydrolysis of cellulose are disclosed for the first time. When the ball-milling pretreated cellulose was hydrolyzed using oxidized carbon catalysts at 150 ℃ and 100–300 bar-CO₂, the hydrolysis kinetics remarkably increased by 3X for conversion and 5X for glucose, resulting in ∼90% conversion and ∼85% total sugar selectivity at 20 min. The hydrolysis rate obtained with scCO₂ here was higher than conventional ones with toxic and unrecyclable homogeneous catalysts (e.g., HCl) under harsh reaction conditions (i.e., 180–220 ℃ and pH of 1–2). A comprehensive reaction engineering study (e.g., temperature, CO₂ pressure, stirring speed, catalyst acid properties) combined with the in-situ and ex-situ monitoring of the phase behavior of the H₂O/scCO₂ solution revealed that scCO₂ and water form a water-in-scCO₂ (W/O) Pickering emulsion mediated by the carbon catalysts, and  this in turn substantially increase physical contact between cellulose and catalyst, thereby leading to the enhanced hydrolysis rate.

* Reference

- Authors (Pusan National University): Han Ung Kim and Jungho Jae (School of Chemical Engineering)

- Title of original paper: Highly efficient hydrolysis of cellulose to sugars using supercritical CO₂ as a green acid catalyst and solvent

- Journal: Chemical Engineering Journal

- DOI: https://doi.org/10.1016/j.cej.2024.152336