Modeling, simulation and analysis of the liquid-phase catalytic oxidation of toluene

The liquid-phase, catalytic oxidation of toluene with air in a continuous stirred tank reactor has become the main technology for producing benzoic acid. Designs are aimed at obtaining high product conversion rates but the reaction is strongly exothermic and therefore it is also important to maintain stable operation to guarantee product quality. However, there is currently no suitable process simulation model available for study. In this paper, a mathematical model of the reaction system is established and validated by comparison to literature data. Steady-state variables were calculated for a series of the operating conditions, using the homotopy continuation method, revealing the existence of multiple steady-state solutions. Two steady-state solutions were found for each operating condition, which had different conversion rates and sensitivities to changes in operating conditions. The operating point having the highest conversion rate was the most sensitive to changes in operating conditions, thus requiring a superior control system. A trade off must be carried out between conversion rate and production stability. Consequently, in practice, a number of factors must be considered simultaneously to select a compromise design.