Chapter 17 - Cellulose hydrolysis in supercritical water to recover chemicals

Abstract

This chapter investigates the cellulose decomposition in subcritical and supercritical water (25 MPa, 320–400°C, and 0.05–10.0 s). To understand the change of product distributions around the critical temperature, kinetic studies were conducted for reactions of cellulose, cellobiose, and glucose in subcritical and supercritical water. Below 350°C, the cellulose hydrolysis rate was slower than the glucose or cellobiose decomposition rate. However, above 350°C, the cellulose hydrolysis rate drastically increased and became higher than the glucose or cellobiose decomposition rate. The direct observation of the reaction field by using a diamond anvil cell was conducted to understand the change of cellulose hydrolysis rate around 350°C. Below 280°C, cellulose particles became gradually smaller with time. However, the shrinking rate of the particles increased greatly around 300°C. In the range of temperature from 300 to 320°C, cellulose disappeared without changing its particle shape. After cooling the produced solutions at room temperature for two hours, white precipitates came out from the solutions, which were found to be cellulose-like materials that had been solubilized in high-temperature water.