Book Description

A reactive distillation column for the alkylation of benzene with long chain linear olefin was studied. The study involved design, construction, experimentation, and simulation of the column. Establishing the design required study of reaction rates, thermodynamic relationships, and packing structures. A heuristic was developed for the design of such columns. This heuristic involved estimating an amount of catalyst loading and subsequently determining the operating parameters for a column. This method is particularly applicable to systems with high concentrations of inert feeds. A column was constructed following the design. Data was collected from the column and compared to simulations. The simulations were performed with Aspen Plus RADFRAC. In this manner, the data was used to validate the commercial steady state models for reactive distillation. In addition, dynamic simulations of the system were performed. These dynamic simulations provided insight into more design considerations. For example, steady state simulations indicated an optimal feed stage based on steady state conversion of the olefin. However, the dynamic simulations showed a potential disadvantage to the utilization of the optimal feed stage. With some disturbances, a column configured with the feed stage with the highest steady state conversion also deviated from the steady state faster and with greater amplitude than other configurations. These considerations were further explored in developing a control scheme for reactive distillation columns. Control of reactive distillation differs from traditional distillation in that one control variable is conversion. Traditional distillation generally focuses on production rates and product purity. To this end, control schemes were analyzed and dynamic simulations were performed. These simulations showed an advantage to a variable pairing in which duty is paired with conversion. The conversion was inferred from a stage temperature in the reactive zone. In addition, distillate rate may be paired with product composition. In conclusion, the reactive distillation column design for long chain olefin alkylation of benzene requires careful estimation of catalyst requirements and valid simulation tools. In addition, dynamic response should be considered in the design. Finally, a simple inferential control scheme may be adequate.