Energy saving schemes for separation of benzene-cyclohexane-toluene mixture with different initial compositions by extractive distillation

Abstract

Benzene is one of the important raw materials for organic synthesis. Extraction and extractive distillation (ED) are used to recover benzene from petroleum and coking coal products. Application of the systems with partially thermally coupled distillation columns (PTCDC) is one of the effective ways to reduce the energy consumption of ED. In this paper, evaluation is considered of the energy efficiency of ED schemes with PTCDC (PTCEDS) to separate benzene (B)-cyclohexane (CH)-toluene (T) mixture with two different initial feed compositions and N-methylpyrrolidone (NMP) as entrainer. The mixture #1 is some equivalent of the product of catalytic dealkylation of the gasoline fraction of hydrocracking with B, CH, T concentrations 40, 20, 40 mass %, respectively, and mixture #2 is a some equivalent of product of the hydrocracking and hydropurification of vapor cracking gasoline with B, CH, T concentrations 50, 5, 45 mass %, respectively. Three conventional ED schemes and five ED schemes with PTCDC were considered. All 8 schemes were compared by the total boiler heat duties criterion under optimal values of operating parameters. Optimization was carried out by using sensitivity analysis and the SQP (sequential quadratic programming) optimization tools of Aspen Plus. It was determined that the scheme where toluene is separated in the first column as the bottom product had the lowest energy consumption among the conventional schemes in all cases of the initial feed compositions. The best solution with PTCDC in the both cases is the scheme where CH is recovered in the first ED column as a distillate, B is a distillate of the main column and T is a bottom product of the complex column side stripper section. The power consumption reduces by 19.8% and 22% for mixture #1 and mixture #2, respectively, compared to the conventional ED schemes with two outlets columns