Kinetic Modeling and Optimization of the Rh/C-Catalyzed Continuous Green Synthesis of Acetic Acid from Methanol in a Two-Phase Fixed Bed Tubular Reactor

Acetic acid is an important organic chemical product and starting material for numerous organic syntheses. According to estimates, around 5 million metric tons of acetic acid is produced per year. Its industrial preparation involves transition-metal-based catalysts and high pressure and temperature. Because of the paradigm shift of the last decades, a higher accent in research and development is given to greener syntheses. Here a continuous Rh-catalyzed synthesis of acetic acid from methanol and carbon monoxide is presented, which requires significantly lower pressures (similar to 10-15 bar) than the industrially applied homogeneous technologies (similar to 30 bar). A simplified first-principles mathematical model is developed for the continuous steady-state isotherm and isobar tubular reactor involving the microkinetics of catalytic reactions. The model is calibrated using experimental data, and satisfactory agreement between the simulated and experimental results is achieved. On the basis of the calibrated model, a process optimization is carried out involving the inlet concentrations as well as reactor operating conditions (temperature, pressure, and mean residence time) as decision variables. The acetic acid productivity and the total productivity (acetic acid and methyl acetate) were maximized. According to the results, the process presents significant potential for productivity improvement with respect to both objectives. This highlights the importance and exploitable potential offered by process optimization.