Decomposition of Formic Acid in Supercritical Water^†

Abstract

The decomposition of 0.05−0.7 M formic acid in supercritical water was investigated in a temperature range of 550−650 °C and a pressure range of 24−30 MPa for residence times of 16−46 s. The gaseous products were composed of H2 and CO2 as major components, and CO as a minor one, which indicates that decarboxylation is the dominant reaction pathway and dehydration is secondary. High temperature increased hydrogen production. Compared with temperature, pressure had less effect on hydrogen production. Carbon gasification efficiency reached 94.5% at a residence time of 20 s, and extending the residence time had very little effect. High concentration of formic acid led to side-reactions, which caused a great decrease of hydrogen production. The mechanisms for formic acid decomposition were studied computationally using the GAUSSIAN 03 suite of programs. Results show that water takes part in the formic acid decomposition reaction as a catalyst, which promotes both the decarboxylation and dehydration, and the promoting effect on decarboxylation is more apparent.