Parameters Optimization Of Isopropanol Dehydration By Hybrid Distillation-Vapor Permeation Process Using Response Surface Methodology

Isopropanol (IPA) is an important organic solvent used in the chemicals and pharmacy industries. It forms an azeotrope with water at atmospheric condition, which cannot be separated by conventional distillation. Vapor permeation (VP) is a promising process for azeotropic separation because it is not limited by the vapor-liquid equilibrium. However, VP itself still encounters some challenges such as the membrane productivity, their insufficient thermal, mechanical resistance, and so on. Then application of VP alone in industry is not an optimal choice. Hybrid distillation and VP membrane processes (D-VP) could offer economically attractive alternatives by simplifying process structure as well as reducing energy consumption. There are a large number of parameters and a strong coupling among them in D-VP hybrid systems, it is necessary to find an effective approach to achieve this multi-variable optimization. Response surface methodology (RSM) is proved to be an effective way for parameters optimization, it was widely used to analyze the effects of multiple factors and their interactions. For the above reasons, RSM was selected to optimize the D-VP hybrid systems parameters in this study, then an economic analysis was performed comparing different processes for IPA purification to get the most attractive process from economic point of view.(1) Simulation models of IPA dehydration systems were built with UniSim Design. Three different processes:traditional azeotropic distillation, D-VP hybrid systems and distillation-VP membrane-distillation(D-VP-D) hybrid systems were performed. In the hybrid combinations VP with both PVA/PVDF polymeric composite membrane and NaA type zeolite membrane were used. According to the process simulation, brief stream characteristics were made to test the accuracy of the simulation results as well as comprehensively investigate coupling separation process.(2) RSM was used to optimize the D-VP hybrid systems parameters. The D-VP hybrid systems with ceramic NaA type zeolite membrane (HDCM) and PVA/PVDF polymeric composite membrane (HDPM) for IPA dehydration were used. Firstly, Plackett-Burman (PB) design was used to screen the factors essential for TAC. Then steepest ascent method was employed to approach the vicinity of the optimal conditions. Subsequently, Box-Behnken design was used to estimate the relationship between a response and optimal parameters for minimum TAC. With the optimal values of the parameters, we got the minimum TAC of HDCM and HDPM systems which were48.54∈/t IPA and56.50∈/t IPA, respectively.(3) An economic analysis was performed comparing different processes. The TACs of the IPA purification systems were split into operation costs and investment costs. The operation costs included the energy costs and maintenance costs, the investment costs included the distillation columns and the vapor permeation units depreciated costs. Firstly, the economic analysis was performed comparing optimized and pre-optimized parameters for HDCM and HDPM systems, the optimized TAC could be saved17.13%and18.34%for HDCM and HDPM systems compared to the literature data for the same process, respectively. Then a brief comparison of stream characteristics and economic analysis for unit operation was made among all the three separation processes. It was found that D-VP hybrid system was the most attractive process from economic point of view, HDCM and HDPM systems could lead to a saving in total costs of58.94%and55.11%compared to azeotropic distillation, respectively.