DECOMPOSITION OF FORMIC-ACID UNDER HYDROTHERMAL CONDITIONS

The thermal decomposition of formic acid was studied in dilute aqueous solutions and in the absence of added oxygen at temperatures between 320 and 500 degrees C and pressures between 178 and 303 atm for reside nce times between 1.4 and 80 s. Under these conditions, the formic aci d conversion ranged from 38% to 100%, and the major products were alwa ys CO2 and H-2, which indicates that decarboxylation is the preferred reaction path for formic acid decomposition under hydrothermal conditi ons. CO also appeared as a product, which shows that a dehydration pat h is available, but the CO yield was always at least an order of magni tude lower than the yields of Co-2 and H-2. The kinetics of formic aci d disappearance and product formation at temperatures above 320 degree s C are consistent with a reaction rate law that is first order in for mic acid. The implications of the present results to the generally acc epted molecular decomposition mechanism are discussed, as are the alte rnative free-radical, ionic, and surface-catalyzed reaction mechanisms proposed in the literature.