Cellulose hydrolysis in subcritical and supercritical water

Abstract

In this paper we propose a new method to hydrolyze cellulose rapidly in supercritical water (SCW) to recover glucose, fructose and oligomers (cellobiose, cellotriose, cellotetraose, etc.). Cellulose decomposition experiments were conducted with a flow type reactor in the range of temperature from 290 to 400°C at 25 MPa. A high pressure slurry feeder was developed to feed the cellulose–water slurries. Hydrolysis product yields (around 75%) in supercritical water were much higher than those in subcritical water. At a low temperature region, the glucose or oligomer conversion rate was much faster than the hydrolysis rate of cellulose. Thus, even if the hydrolysis products, such as glucose or oligomers, are formed, their further decomposition rapidly takes place and thus high yields of hydrolysis products cannot be obtained. However, around the critical point, the hydrolysis rate jumps to more than an order of magnitude higher level and becomes faster than the glucose or oligomer decomposition rate. This is the reason why we obtained a high yield of hydrolysis products in supercritical water.