Kinetic analysis of cellulose depolymerization reactions in near critical water

Abstract

In this work, a kinetic analysis of cellulose depolymerization in hot pressurized water is presented. An experimental facility that works with temperatures up to 400°C, pressures of up to 25MPa and residence times of between 0.004s and 10s was used for the experimental study. A mathematical model was developed in order to predict the evolution of the cellulose concentration and its derivatives. To do so, a reaction scheme was proposed, and kinetic parameters currently unavailable in literature were adjusted, using the experimental data obtained in this work. The kinetics for cellulose hydrolysis showed a change around the critical point of water, the activation energy being 154.4±9.5kJ/mol and 430.3±6.3kJ/mol below and above the critical point, respectively. The activation energy for oligosaccharide hydrolysis was 135.2±9.2kJ/mol and 111.5±9.1kJ/mol for the glucose to fructose reaction. The kinetics of 5-hydroxyl-methyl-furfural formation showed a drastic change at 330°C. The activation energy for 5-HMF formation is 285±34kJ/mol and −61.3±15.7kJ/mol at temperatures below and above 330°C, respectively. Above 330°C the low density and ionic product of the medium would disfavor the 5-HMF formation.