The nonideal mixing effect on the selectivity dynamic of consecutive-parallel reactions in an isothermal continuous stirred tank reactor based on Cholette’s model

Abstract This work presents the mixing conditions and kinetic reaction constant effects on a continuous stirred tank reactor (CSTR) consecutive-parallel reactions selectivity dynamics in an isothermal CSTR based on Cholette’s model. The mixing condition effect is accounted for using the parameter μ = n / m , where n is the flow fraction to the reactor and m is the dead space fraction in the reactor. μ = 1 and μ ≠1 represent, respectively, the ideal and nonideal mixing operations. The final desired product yield steady state in the phase plane is first constructed under reaction constant and mixing condition combinations, μ = 0.5, μ = 1 and μ = 2. The simulation results reveal that the larger the μ parameter, the higher the reactant final steady state values, a s , and the desired product, b s . For μ = 0.5 < 1, the short circuit flow or channeling effects were less than that of the dead volume in a real CSTR, leading to lower both final steady state values, a s and b s , than those under ideal mixing, μ = 1. On the other hand, under the nonideal mixing condition μ = 2 > 1, i.e., the short circuit flow effect or channeling larger than the dead volume in the reactor, resulted in a higher final steady state ( a s , b s ) than those under ideal mixing. A comparative analysis of the mixing condition effects reveals that a higher μ value reduces the transient maximum selectivity regions while increasing the transient minimum selectivity regions. In the selectivity dynamic simulations, the phase plane is divided into a transient extreme yield region and monotonic yield variation region. It is observed, for the first time, that a higher μ value diminishes the transient maximum selectivity region area while expanding the transient minimum selectivity region area in the phase plane. Additionally, the trajectory from the start up to the final steady state is altered due to nonideal mixing. These novel findings, which have not been previously published, hold direct relevance for the design and operation of real reactors. Given that ideal mixing is rarely achievable in practical CSTRs, our results offer valuable insights for optimizing reactor design and start-up policies to enhance the desired product transient yield.