Abstract
Steam gasification of cellulose was studied using a newly developed continuous cross-flow moving bed type differential reactor. In this apparatus, a quartz glass half tube reactor is divided into six compartments in order to collect gas and tar separately and analyze their compositions while biomass sample (cellulose) is continuously fed into the reactor. Steam with Ar carrier gas is fed into each of the compartment that is heated by an image furnace. Char is also collected at the end of the reactor. It was found that there is an induction period for 15-20 s before weight decrease of cellulose begins in steam gasification at 673 K, suggesting the existence of intermediate products. Produced tar was cellulose with low degree of polymerization whose elemental compositions and FT-IR spectra were quite similar to those of original cellulose. The main components were levoglucosan, cellobiosan, and cellotriosan. When evolution of tar was completed, dehydration of the intermediate products took place, producing char. Based on the results, we proposed a new mechanism of steam gasification of cellulose and calculated the first-order kinetic parameters using experimental data obtained by a thermobalance reactor in our previous reports. The parameter fitting quite agreed with the experimental data. The time profile of each intermediate was also calculated using the parameter. It was found that the rate-determining step of cellulose steam gasification with slow heating is the reaction that decreases the degree of polymerization of cellulose.
