Effects of process parameters on isobutane/2-butene alkylation using a solid acid catalyst Original Research Article

Alkylation processes based on solid acid catalysts have been studied with varying degrees of urgency for the last three decades. Work has focused on developing both catalysts and processes. Unfortunately, much of the catalyst development work was done under conditions where catalyst deactivation was rapid and possibly accelerated by the test equipment chosen to compare catalysts and conditions. Under these circumstances, the true performance of the catalyst for alkylation was not measured. This paper reports a study of the effect of time-on-stream, olefin concentration, feed olefin residence time, temperature, and catalyst loading for isobutane/2-butene alkylation using a continuous stirred reactor (CSR) system. A CSR system has been shown to give relatively constant activity over much greater times than conventional fixed-bed or batch reactor systems. The effects of these parameters on olefin conversion, useful catalyst lifetime and product quality are reported and initial rate constants, catalyst deactivation rates and an energy of activation for olefin conversion are calculated. In summary, these experiments show the dramatic effect of time-onstream for the reaction of isobutane and 2-butene, which exhibits four distinct stages of activity and selectivity. The first stage is the “initial activity”, which is never actually observed due to experimental limitations but is important in kinetic treatment of the data. The second stage is the “useful lifetime of the catalyst”, which is characterized by high olefin conversion and relatively slow catalyst deactivation. The third stage is the “rapid deactivation” region where a rapid loss of catalyst activity for olefin conversion coupled with a change in selectivity from C5–C8 products to C9+ products occurs. The fourth stage is where the product of olefin conversion is primarily C9+ products and the deactivation is again rather slow. These experiments also show that most changes in experimental conditions which increase the concentration of unreacted olefin (e.g., decreasing olefin conversion by increasing feed olefin concentration, decreasing feed olefin residence time, etc.) decreases the catalyst lifetime and product quality. The experiments also show that there is an optimum reaction temperature which balances the low olefin conversion at low temperature and the high oligomerization activity at high temperature. A set of performance equations from kinetic parameters were derived to describe the conversion of 2-butene under various experimental conditions using a USY catalyst. These performance equations allowed the calculation of initial conversion activity, change in conversion activity over time and an estimate of the useful lifetime of the catalyst.