SELECTION OF EXTRACTIVE AGENTS FOR THE SEPARATION OF CHLOROFORM - METHANOL - TETRAHYDROFURAN MIXTURE

Abstract

Variants of the extractive distillation of chloroform - methanol - tetrahydrofuran equimolar mixture with industrial separating agents are considered. The basic system shows opposite deviations from the ideal behavior, because it contains binary azeotropes with minimum and maximum boiling points (3.3.1-4 system according to Serafimov’s classification). The choice of selective substances for extractive distillation was carried out taking into account the concentration dependences of the excess molar Gibbs energy of the binary constituents of the derivative system “chloroform - methanol - tetrahydrofuran - industrial test agent (ethylene glycol (EG), dimethyl sulfoxide (DMSO), N-methylpyrrolidone (N-MP))” at 101.32 kPa. Based on the results of the evaluation of the thermodynamic criterion, DMSO and N-MP are recommended. Both agents show selective effect when separating two binary constituents. EG is selective only with respect to chloroform-tetrahydrofuran mixture. Since the tested agents show different selective effects, the final agent choice determines the qualitative composition of the product flows in the column for the extractive distillation of the three-component mixture (the first column of the flowsheet) and, accordingly, the structure of the total flowsheet. The schemes consist of two two-column complexes for extractive distillation (for the basic three-component mixture and for the binary mixture). The maximum contribution to the total reboiler energy consumption of the distillation columns is made by the first extractive distillation column: 65% (EG), 53% (N-MP) and 24% (DMSO). The use of the most selective agent reduces the energy consumption of this column: the reboiler load is maximal in the case of EG, in comparison with which the load is 47% lower in the case of N-MP and 76% lower in the case of DMSO.