Kinetic and Equilibrium Study on Formic Acid Decomposition in Relation to the Water-Gas-Shift Reaction

Abstract

Kinetics and equilibrium are studied on the hydrothermal decarbonylation and decarboxylation of formic acid, the intermediate of the water-gas-shift (WGS) reaction, in hot water at temperatures of 170-330 degrees C, to understand and control the hydrothermal WGS reaction. (1)H and (13)C NMR spectroscopy is applied to analyze as a function of time the quenched reaction mixtures in both the liquid and gas phases. Only the decarbonylation is catalyzed by HCl, and the reaction is first-order with respect to both [H(+)] and [HCOOH]. Consequently, the reaction without HCl is first and a half (1.5) order due to the unsuppressed ionization of formic acid. The HCl-accelerated decarbonylation path can thus be separated in time from the decarboxylation. The rate and equilibrium constants for the decarbonylation are determined separately by using the Henry constant (gas solubility data) for carbon monoxide in hot water. The rate constant for the decarbonylation is 1.5 x 10(-5), 2.0 x 10(-4), 3.7 x 10(-3), and 6.3 x 10(-2) mol(-1) kg s(-1), respectively, at 170, 200, 240, and 280 degrees C on the liquid branch of the saturation curve. The Arrhenius plot of the decarbonylation is linear and gives the activation energy as 146 +/- 3 kJ mol(-1). The equilibrium constant K(CO) = [CO]/[HCOOH] is 0.15, 0.33, 0.80, and 4.2, respectively, at 170, 200, 240, and 280 degrees C. The van't Hoff plot results in the enthalpy change of DeltaH = 58 +/- 6 kJ mol(-1). The decarboxylation rate is also measured at 240-330 degrees C in both acidic and basic conditions. The rate is weakly dependent on the solution pH and is of the order of 10(-4) mol kg(-1) s(-1) at 330 degrees C. Furthermore, the equilibrium constant K(CO2) = [CO(2)][H(2)]/[HCOOH] is estimated to be 1.0 x10(2) mol kg(-1) at 330 degrees C.

Efficient Catalytic Decomposition of Formic Acid for the Selective Generation of H2 and H/D Exchange with a Water‐Soluble Rhodium Complex in Aqueous Solution

“…In addition, formic acid is a valuable raw material in organic syntheses and also an important intermediate in the water gas shift reaction. [17,18] Thus, the combination of CO 2 reduction by H 2 and selective decomposition of HCOOH to H 2 and CO 2 under mild conditions is a carbon-neutral process and provides an overall environmentally benign system. There have been extensive studies on the decomposition of formic acid in the gas phase (in supercritical water), [19][20][21][22] on the surface of metals and metal oxides, [23,24] and in the homogeneous phase with metal complexes.…”

Wet Air Oxidation of Benzene

“…In both experiments, almost an of the formic acid disappeared before the addition of the oxygen (Table 5.2), which suggests that decomposition of the forrnic acid took place either by decarbonylation or decarboxylation [73].…”

Controlling the Equilibrium of Formic Acid with Hydrogen and Carbon Dioxide Using Ionic Liquid

“…Additional 13 C NMR measurements of the IL phase after the decomposition reaction of FA in the IL (10 days at 60°C) showed two broad peaks designated as CO 2 (126 ppm) and H 2 CO 3 /HCO 3 -(159 ppm) with an intensity ratio of 3:1; note that H 2 CO 3 and HCO 3 -is indistinguishable in NMR due to the fast proton transfer. This observation gives that c CO 2 (liq) : (c H 2 CO 3 (liq) + c H 2 CO 3 -(liq) ) ) 3:1 and that c CO 2 (liq) calculated by eq 7 may differ from the real value of c CO 2 (liq) by a factor of ∼3/4. Nevertheless, the following discussions on the solvent effect on the equilibrium constant are unaffected by such a relatively small error.…”