Distillation contra pervaporation: Comprehensive investigation of isobutanol-water separation

Abstract

Abstract Different research works demonstrate that the pervaporation can replace the distillation or deliver better solutions. It should be, however, accepted with criticism. In our case study, isobutanol-water separation is studied since it is increasingly important in the field of biofuels and process wastewater treatment. There are many options for the separation and they differ in their efficiency, economic features, robustness, development level and environmental impact. Five separation structures are investigated using distillation, both organophilic and hydrophilic pervaporations and hybrid separation units consisting of distillation and pervaporation including heat integrated solutions. The different alternatives are modelled in professional flowsheeting environment. Life cycle assessment, energy evaluation and Multi-Criteria Decision Analysis (MCDA) based on PEST (Political, Economic, Social, and Technological) analysis are completed to evaluate and compare the five alternatives. The feed stream to be separated has the composition of 7 wt% isobutanol 93 wt% water that corresponds to the mixture of the phase split due to the limited solubility. Two product purities are considered, 98.8 and 99.9 wt%. In case of distillation processes, heat integration is also considered, that is, the feed is preheated with its bottom flow. Heat integration significantly improves the efficiency of the distillation and makes it for practically a competitive alternative. The best efficiency can be obtained with heat integrated hybrid separation, that is, the combination of distillation and pervaporation. The pure pervaporation that is the combination of organophilic and hydrophilic pervaporation can be efficient only at sloppy product purities because of the modest separation factor of the organophilic pervaporation membranes. In case of sharp separations, the organophilic pervaporation can be an equally applicable solution as the azeotropic distillation for isobutanol-water separation.