Systematic kinetic modeling of the propyl tert-butyl ether synthesis reaction

The kinetics of the liquid-phase addition of 1-propanol to isobutene to produce propyl tert-butyl ether (PTBE) has been studied using the ion-exchange resin Amberlyst (TM) 35 as the catalyst. Reaction rates free from mass transfer limitations have been experimentally determined in the temperature range 303-352 K, for different initial proportions of alcohol and isobutene, and using two different reactor types (i.e., a batch stirred tank reactor, to obtain most of the experimental data, and a tubular reactor, to validate those results). To find out the best kinetic model, a systematic approach has been adopted. The overall etherification reaction has been decomposed as the result of elementary steps based on Langmuir-Hinshelwood-Hougen-Watson or Eley-Rideal mechanisms. Candidate kinetic equations have been originated from all possible combinations of adsorbed and non-adsorbed compounds, and rate-determining step. The possible effect of the interaction between the reaction medium and the resin on reaction rates has been also examined. Since all experimental data have been used at once in the fit of the kinetic equations, all combinations of significant or non-significant temperature dependence of model parameters have been also considered. As a result, 1404 candidate kinetic equations have been fitted separately to experimental data. Discrimination among models is based on mathematical and physico-chemical criteria. The final choice of the best kinetic model involves multimodel inference. It corresponds to an Eley-Rideal mechanism where one 1-propanol molecule adsorbed on the catalyst reacts with one isobutene molecule from the liquid phase to form one adsorbed PTBE molecule, the surface reaction being the rate-determining step.