Optimal modes of side-section flow in heat-pump-assisted extractive distillation systems for separating allyl alcohol–allyl acetate mixtures with butyl propionate

Abstract

Objectives.To investigate the influence of side-section flow modes on the energy efficiency of apartially thermally coupled distillation sequence (PTCDS) with a vapor recompression heat pumpfor the extractive distillation of an allyl alcohol–allyl acetate mixture with n-butyl propionate andidentify modes under which the combined use of a PTCDS and heat pump are the most efficient.Methods.Mathematical modeling in the Aspen Plus V10 software package was used as the mainresearch method. The local composition equation of the non-random two-liquid model was usedas a model for describing the vapor–liquid equilibrium, while the Redlich–Kwong model was usedto consider the non-ideal vapor phase. When modeling the conventional extractive distillationscheme and PTCDS, parametric optimization was carried out according to the criterion of the totalenergy costs in the column reboilers. For the economical evaluation, Aspen Process EconomicAnalyzer V10.1 tools were used.Results.For extractive distillation of a mixture of allyl alcohol (30 wt %) and allyl acetate (70 wt %)with n-butyl propionate as an entrainer, the minimum energy consumption was achieved at thesame side-section flow mode for the variants of a PTCDS with and without a heat pump. Thereduction in energy costs relative to the conventional scheme was 20% for the sequence withouta heat pump and 38% for that with a heat pump. An economic assessment was made of thebest options in comparison with the conventional extractive distillation scheme. The PTCDS witha heat pump had an advantage over the sequence without a heat pump only for long periods ofoperation.Conclusions.For the extractive distillation of an allyl alcohol–allyl acetate mixture, the optimalmodes for the combined use of a PTCDS with a vapor recompression heat pump coincide with theoptimal modes for a PTCDS without a heat pump.