MODELING AND SIMULATION OF REACTIVE DIVIDING WALL DISTILLATION COLUMN USING RATE BASED APPROACH

Abstract

Distillation is one of the most important separation technology adopted in the chemical process industries. All the petrochemicals units use at least one distillation column for the separation and purification of the products. However, the distillation process accounts for more than 50 % of the plant operating cost. Dividing wall distillation column (DWDC) is a powerful process intensification technology used in the distillation process. Using the reaction and separation within a DWDC makes the process intensification more alternative and thus resulted, reactive dividing wall distillation column (RDWDC). Since the reactions are time dependent and the RDWDC uses Sulzer- zx packing, the present work uses rate-based approach for modeling and simulation of a RDWDC. For easy group of the methodology and the analysis of the results, a case study has been adopted, as reported earlier by Mueller and Kenig (2007). This case study deals with the production and purification of Diethyl Carbonate (DEC) from the reaction of Dimethyl Carbonate (DMC) with ethanol. The input parameters for the reaction kinetics were taken from the work of Keller et al. (2011). The analysis has been carried out using ASPEN Plus (Version: 6.0). The parameters reflux ratio (r), liquid split rate (l) and vapor split rate (v) were optimized by using the results obtained from simulation with the optimization software Design Expert (Version:6.0) using the Box-Behnken design under response surface methodology (RSM). Synthesis of the DEC in a RDWDC previously carried by Mueller and Kenig (2007). The reflux ratio obtained by them for the RDWDC was 11.67, which is very high. This requires 201342 Btu/hr of energy for the reboiler for the specified distillation operation. Using the optimization technique, the reflux ratio has been found to be 9.8. At this reflux ratio, the energy requirement is 173435 Btu/hr for the distillation operation as against 201342 Btu/hr for r=11.67. This means a reduction of 13.86 % in the reboiler duty has been effected by the optimization technique. However, it can be seen that the RDWDC can be operated in a wide range from 5.2 to 9.8. The composition and temperature profiles in the pre and post fractionator of the DWDC are found to be similar as those given by Mueller and Kenig (2007). This shows that the methodology adopted by the kinetics of the overall reaction as proposed works well with the case problem and that the proposed methodology for the RDWDC can be used with confidence.