MODELING AND SIMULATION OF HYBRID DISTILLATION COLUMN

Abstract

Distillation is an energy intensive process and is extensively used in process industry to separate liquid mixtures. For industries dealing with liquid products such as alcohol, ether, and close boiling liquid mixtures like propane-propylene, benzene — cyclohexane, etc the problem is more acute. If one focuses on world scenario of file's he will find than with the depletion of petroleum products ethyl alcohol is being projected as the next generation fuel. Its large-scale production at low cost will help us to cut down our fuel bills. The, increasing worldwide competitiveness in production has forced industry to improve current process design. Consequently, the development of new process design and reorganization of present process designs with the possible integration of new technologies is a growing importance to industry. Pervaporation / Vapor-permeation with distillation in form of a hybrid separation unit are one such developing technology that can be used for various industrial applications. An analysis shows that the operating cost of the Pervaporation unit are about 66% less than the costs of the entrainer based distillation process (in the case of dehydrating ethanol from 94 to 99.8 wt%). The same fact is also true for isopropanol production. Further, it has also been found than cost savings in the case of a 100,000 kg/day plant are claimed to be about 48% less in overall cost compared to azeotropic distillation in the case of dehydration of isopropanol from 85 to 99.0 wt%. This Thesis work focuses on Pervaporation based hybrid processes. Hybrid configurations and their economic evaluation available till now are also present in this work. A critical review, of various types of membrane, membrane — modules has also been made a part of this thesis. Based on the vapor liquid equilibrium in membrane unit the selection criterion between pervaporation — distillation and vapor-permeation-distillation are also included. A simple steady state pervaporation model is developed using log mean diffusivity coefficients and simulated in visual Basic 6.0. Based on this model "user defined unit" is developed in HYSYS 3.0 and for dehydration of ethanol from 20 wt% to 95.53wt °A) hybrid system is designed similar to I — 211A configuration iii except that permeate is not recycled back to column. It is found that the proposed model and its log mean approximation of diffusivity can be used successfully to calculate the composition and flux for lower and higher ethanol content feed. iv