Liquefaction kinetics of cellulose treated by hot compressed water under variable temperature conditions

Abstract

In this study, we investigate a process for liquefaction of cellulose with hot compressed water as a pre-treatment for a compact gasification process of cellulose. Experiments were carried out using a batch reactor with a temperature controller. The temperature profile for heating was controlled in a proportional relationship with time. Cellulose was drastically decomposed and liquefied when the maximum temperature was set at over ∼513 K. It decomposed to oligosaccharides, monosaccharides and pyrolysis products such as glyceraldehydes and 5-hydroxymethyl-2-furaldehyde. Theoretical treatment was investigated by considering the following stepwise processes: decompositions of I. cellulose to oligosaccharides, II. oligosaccharides to monosaccharides and pyrolysis products and III. monosaccharides to pyrolysis products. In these steps, step I is a heterogeneous reaction consists of: (a) Diffusion of water monomer to a cellulose surface and (b) Hydrolysis reaction of water monomer with a cellulose molecule at the surface. The temperature dependence of the rate constants was expressed by the Arrhenius relationship. The calculated result showed good correlation to the experimental data. The results suggest that it is possible to estimate the decomposition of cellulose by hot compressed water in a batch reactor that requires slow heating process.