Extractive distillation of tetrahydrofuran–ethyl acetate–water mixture in schemes including columns with side sections and side draws

Objectives. The work set out to evaluate the energy efficiency of using schemes including columns with side sections and side draws in the extractive distillation of tetrahydrofuran–ethyl acetate–water mixture with dimethyl sulfoxide as an entrainer. Methods. The main research method consisted of a computational experiment with the Aspen Plus v. 12 software package. The local composition UNIQUAC equation model was used for describing vapor–liquid equilibrium. Parametric optimization of initial scheme and schemes, including columns with side sections and side draws, was carried out according to the criterion of energy consumptions in distillation columns reboilers. Results. Two variants ofschemes including partially thermally coupled distillation columns and two variants ofschemes including columns with side draws were synthesized on the basis of the conventional scheme of double extractive distillation consisting of two-withdrawal columns using the graph method. The optimal operating parameters of the conventional scheme and all schemes obtained on its basis were determined. The schemes, including columns with side draw, were modeled in two variants, namely, in the vapor phase with side draw, and in the liquid phase. The energy efficiency of the proposed schemes was evaluated in comparison with the conventional scheme. Conclusions. The phase state of the side draw is shown to have little effect on the total energy consumption in column reboilers, the amount of liquid-phase side draw being 1.4–5.2 times greater than that of vapor-phase draw. Among the schemes including complex columns with a side section, the maximum reduction of energy consumption by 5.9% in relation to the scheme of two-withdrawal columns is provided by the scheme according to which the thermal coupling between the second extractive column and the regeneration column of the entrainer is realized. Thermal coupling of extractive columns provides a significantly lower energy saving (1.36%). Among the schemes including complex columns with side draw, the greatest energy efficiency (5.9%) is characterized by the scheme in which the draw in the vapor phase is taken from the second extractive column to the regeneration column.