Hydrolysis of cellulose in supercritical water: reagent concentration as a selectivity factor

In this work, the influence of reagent concentration on hydrolysis reactions of cellulose in supercritical water was analyzed. The hydrolysis was carried out at 400 °C and 25 MPa with reaction times between 0.07 and 1.57 s and feeding cellulose concentrations between 5 and 20 % w/w (1.5–6 % w/w at reactor inlet). Also, a flash separator was used to separate vapor in the product stream in order to increase the final concentration. The best result for sugar production (79 % w/w) was obtained working with a cellulose concentration of 5 % w/w and 0.07-s reaction time. For glycolaldehyde production, the best result (42 % w/w) was obtained with a concentration of 20 % w/w and 1.57 s. The employment of a flash separator allowed reducing the water content by 50 %. It was also observed that by increasing the cellulose concentration in the reactor up to 4 % w/w, the hydrolysis took place with a similar kinetic as that in the heterogeneous media, thus reducing the conversion rate of cellulose in supercritical water.