Kinetic and thermodynamic study of the aqueous Kolbe–Schmitt synthesis of beta-resorcylic acid
Detailed thermodynamic and kinetic study of the aqueous Kolbe-Schmitt synthesis of beta-resorcylic acid has been carried out in a laboratory-scale batch reactor operated under ambient pressure. The dependence of the conversion on partial pressure of carbon dioxide (4 x 10(-4) - 1 bar), initial concentration of resorcinol (0.4-0.8 M), initial concentration of potassium bicarbonate (0.4-6 M) and temperature (348-428 K) was studied. The reaction was found to be reversible and exothermic (Delta H = -30.4 kJ/mol). Partial pressure of carbon dioxide does not influence the reaction kinetics when carried out in the excess of potassium bicarbonate (C-KHCO3,C-0/C-R,C-0 > 1). Increase of the initial concentration of potassium bicarbonate accelerates drastically the rate and shifts the equilibrium conversion to higher values. For the first time a reliable kinetic model has been proposed based on two reversible reactions of pseudo first order towards resorcinol and beta-resorcylic acid. The kinetic constants showed Arrhenius dependencies on the reaction temperature with the apparent energies of activation 105 and 125 kJ/mol for the forward and the reversed reactions, respectively. Pre-exponential factors increased with the initial concentration of potassium bicarbonate indicating a complexity of the reaction mechanism involved. The kinetic model was successfully validated against experimental data obtained under high pressure and temperature using a micro-plant. Finally, the model was found consistent with the literature data available for this reaction. (C) 2012 Elsevier B.V. All rights reserved.