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 °C, pressures of up to 25 MPa and residence times of between 0.004 s and 10 s 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 °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 °C, respectively. Above 330 °C the low density and ionic product of the medium would disfavor the 5-HMF formation.