Deoxygenation of propionic acid: Thermodynamic equilibrium analysis of upgrading a bio-oil model compound

The thermodynamic equilibrium of gas-phase deoxygenation of propionic acid was studied over a wide range of reaction conditions (T = 200-600 degrees C, P = 1-10 bar and H-2/acid = 0-10 mol/mol) using non-stoichiometric equilibrium models. The effect of catalyst type on equilibrium composition was incorporated by applying different combinations of the reactions involved, including decarboxylation, decarbonylation, hydrogenation/hydrogenolysis and water-gas shift reactions. It was implemented by using appropriate constraining component balance equations in minimization of Gibbs free energy of the system. Accordingly, four reaction models were used, the results of which were compared with each other and with the relevant experimental data. The results illustrate that high equilibrium conversions of propionic acid (>85%) are possible for all models. It was found that reactions leading to saturated hydrocarbons (that is, ethane and propane) are highly favorable while those including oxygenates interconversions are equilibrium limited. The results fit favorably with experimental data obtained by employing selective catalysts. (C) 2017 Elsevier Ltd. All rights reserved.