NUMERICAL STRATEGIES IN SOLVING GAS-LIQUID REACTOR MODELS .2. TRANSIENT FILMS AND DYNAMIC TANK REACTORS

Two numerical strategies were compared in solving isothermal dynamic gas-liquid tank reactor models. The simultaneous strategy consists of the solution of the partial differential equation (PDE) system arising from the dynamic reactor bulk phase mass balances combined with the transient film model according to the film-penetration theory. In the simultaneous strategy the PDEs were converted to ODEs using a finite-difference discretization scheme for the gas and liquid films. The ODEs created were solved by the backward difference method. In the sequential strategy the solution was obtained computing the bulk phase mass balances and the stagnant film model separately in a sequence. Thus the sequential model consists of ODEs and a two-point boundary value problem. In the sequential approach the film model was solved using spline collocation and the bulk phase balances were solved using the backward difference algorithm for ODEs. The example simulations of a dynamic continuous stirred tank reactor and a batch reactor model with a reaction scheme of two consecutive-competitive second-order reactions indicate that the simultaneous solution strategy is a more robust and reliable method. The sequential strategy suffers from problems in selection of suitable integration intervals between updating the concentration gradients obtained from the stagnant film solution.