Design/optimization of energy-saving extractive distillation process by combining preconcentration column and extractive distillation column

Abstract

In extractive distillation, the addition of entrainer may reverse the relative volatility of the feed components causing the component with higher-boiling point to be removed as the distillate from the extractive column. In this study, the energy saving possibility of a three-column extractive distillation system was studied when this phenomenon occurred. Based on a three-column conventional extractive distillation system, an innovative energy-saving extractive distillation process with lower capital investment was developed by combining preconcentration column and extractive distillation column. Two important case studies were investigated to verify the above-mentioned energy and economic advantages: the separation of n-propanol-water using N-methyl-2-pyrrolidone (NMP) as entrainer and the separation of ethyl acetate–ethanol using furfural as entrainer. In order to separate these two mixtures, first a three-column extractive distillation sequence including a preconcentration column was applied to diluted fresh feedstock. Then, based on this three-column conventional extractive distillation system, an innovative energy-saving distillation process was developed. For the two separated mixtures, based on the method of global economic optimization, a scheme with optimum design variables was developed for both of the conventional distillation and the new proposed distillation processes. Results revealed that the new process offered 22.76% and 17.25% energy-savings respectively. Similar percentage of reduction in total annual costs (TAC) can also be obtained when compared to the conventional distillation process.