Unified Kinetic Model for Cellulose Deconstruction via Acid Hydrolysis

Abstract

Kinetics of cellulose acid hydrolysis is reported to be very different under dilute acid–high temperature and concentrated acid–low temperature conditions due to the heterogeneous and homogeneous nature of the reactions, respectively. This work aims at unifying the kinetics of cellulose deconstruction by developing a mechanistic model that includes formation and decomposition of glucose and cellulo-oligomers under extremely low (0.07%) to high (70%) acid concentrations and high (225 °C) to low (25 °C) temperatures. A continuous distribution kinetic model that includes (i) random mid-chain and specific end-chain scission of cellulose to form cellulo-oligomers and glucose; (ii) specific scission of cellulo-oligomers to form glucose, cellobiose, cellotriose, cellotetraose, and cellopentaose; and (iii) degradation of glucose was developed. The model predicted reasonably well the experimental data of concentration of cellulose, glucose, and other oligomers obtained from different studies in a broad range of acid concentrations and temperatures. The effects of initial concentration and degree of polymerization on cellulose conversion and glucose yield were evaluated using this model. Moreover, the model also predicted various reported physical effects on cellulose deconstruction and, importantly, manifested its applicability for cellulose hydrolysis in lignocellulosic biomasses like walnut green skin and yellow poplar wood.