Process Simulation Based on Experimental Investigations for 3-Methylthiophene Alkylation with Isobutylene in a Reactive Distillation Column

A new approach that substitutes the original two-step olefinic alkylation of thiophenic sulfur (OATS) technology with a reactive distillation (RD) column was proposed to remove sulfur compounds from fluid catalytic cracking (FCC) gasoline. 3-Methylthiophene (3MT) and isobutylene (IB) were designated as the model compounds for sulfide and olefin, respectively; NKC-9 cation exchange resin mixed with the 2 mm X 2 mm theta ring packing was used as the catalyst bed. The process parameters such as feed composition, molar ratio of 3MT to IB, and reflux ratio were investigated experimentally in the RD column. Simulation for this process was carried out by using the equilibrium stage model-the RADFRAC module of Aspen Plus. The multicomponent vapor-liquid equilibria were predicted by an UNIQUAC method, and the kinetics model that is essential in the RD process was obtained from our previous work. The key design factors (e.g., number of reactive and nonreactive stages, location of feed stage, column pressure, mass ratio of distillate to feed, and catalyst weight) were optimized. The theoretical calculations from the equilibrium stage model matched well with the experimental results. Optimization of the process revealed that applying RD technology into OATS process offers higher alkylation selectivity and better catalytic stability, and the sulfur content in FCC gasoline declined by more than 99%.