Visualized Kinetic Aspects of a Wood Block in Sub- and Supercritical Water Oxidation

Abstract

Reaction of a wood block of “hinoki” (a coniferous tree, Chamaecyparis obtusa) was studied in the presence of O2 in sub- and supercritical water by observing the change in the size and shape of the block in a flow-type reaction cell, to understand the kinetic aspects of the whole reaction progress. The employed temperature was 573−698 K, the pressure was 25 MPa, and the O2 concentration was 0−3.0 mass %. The phenomenological rate value was evaluated on the basis of the size change. In the subcritical water, O2 promoted the size decrease rate almost linearly up to its solubility limit. Its temperature dependence was weaker than in the absence of O2. The recovered amount of total organic carbon was smaller in the presence of O2 and became richer in organic acids such as formic acid. The reaction rate increased with increasing the flow rate. These results indicated that a certain mass-transfer process was involved in the promotion of the reaction. On the other hand, in the supercritical region, the wood bloc...