Kinetic analysis of cellulose depolymerization reactions in near critical water

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 degrees C, pressures of up to 25 MPa 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 +/- 9.5 kJ/mol and 430.3 +/- 6.3 kJ/mol below and above the critical point, respectively. The activation energy for oligosaccharide hydrolysis was 135.2 +/- 9.2 kJ/mol and 111.5 +/- 9.1 kJ/mol for the glucose to fructose reaction. The kinetics of 5-hydroxyl-methyl-furfural formation showed a drastic change at 330 degrees C. The activation energy for 5-HMF formation is 285 +/- 34 kJ/mol and -61.3 +/- 15.7 kJ/mol at temperatures below and above 330 degrees C, respectively. Above 330 degrees C the low density and ionic product of the medium would disfavor the 5-HMF formation. (c) 2012 Elsevier B.V. All rights reserved.