Tert-Butanol–water mixture separation by extractive distillation: Application of experimental data in process simulations

Abstract

Effect of two solvents on the tert-butanol–water azeotropic mixture separation efficiency and economy has been studied. As solvents, two imidazolium ionic liquids (ILs), namely 1-ethyl-3-methylimidazolium bromide [EMim]Br and 1-butyl-3-methylimidazolium bromide [BMim]Br, were selected. For the original diluted tert-butanol (TBA) mixture separation, a separation unit composed of pre-concentration and extractive distillation columns was proposed. Simulations of separation equipment were carried out based on the equilibrium stage model of a distillation column implemented in ASPEN+. Regarding phase equilibrium description, the original NRTL excess Gibbs energy equation was used for the components’ activity coefficients calculation. Phase equilibrium data of IL-containing binaries were measured experimentally in a broad range of ILs’ concentrations and original binary parameters of the NRTL equation were evaluated from these data. To avoid ILs decomposition, regeneration of extraction solvents, ILs, in a vacuum film evaporator was considered. The effect of temperature and pressure in the vacuum film evaporator on the purity of the recovered ILs was tested experimentally in laboratory equipment and the results were applied in separation unit design simulations. For the proposed separation unit, operation costs were evaluated using the ASPEN+ software. Influence of the state of feed entering the extractive distillation column on operation costs was also investigated. By replacing the total condenser at the pre-concentration column head for a partial one, overall operation costs of the separation unit were reduced by about 20%.