Screening of extractive distillation solvents

D. P. Tassios, Rapid Screening of Extractive Distillation Solvents. Predictive and Experimental... 

Tassios, D.P., Rapid screening of extractive distillation solvents Predictive and experimental techniques, in Extractive and Azeotropic Distillation, Advances in Chemistry Series No. 115, American Chemical Society, Washington, DC, 1972. Chapter 4. 

D. P. Tassios, R M Screening of Extractive Distillation Solvents. Predictive and Experimental Technk]ues, in Earaciive and Azeotropic Distillation, Cliap. 4, American Cberttical Swieiy Advances in CTiemistty Series No. 115. Washington, DC, 19. ... 

Rapid predictive and experimental techniques for screening extractive distillation solvents are reviewed. In preparing a list of potential solvents the method of Scheibel is recommended for non-hydrocarbon systems for hydrocarbon systems solvents of high polar cohesive density should be considered. For screening the potential solvents the method of Pierotti, Deal, and Derr is recommended. If it is not applicable, the method of Helpinstill and Van Winkle should be considered next. Finally, reliable screening is accomplished through a simple, rapid technique recently developed that uses gas-liquid chromatography. 

T xtractive and azeotropic distillation in different types of chemical industry has become more important as more separations of close-boiling mixtures and azeotropic ones are encountered. Extractive distillation is used more because it is generally less expensive, simpler, and can use more solvents than azeotropic distillation. Solvent selection for azeotropic distillation has recently been discussed by Berg (I). Therefore, solvent screening for extractive distillation is discussed here. 

In the area of extracting solutes from aqueous solutions, many systems have been screened in feasibility tests that have used carbon dioxide as a solvent. A partial list of the solutes includes ethanol, acetic acid, dioxane, acetone, and ethylene glycol. The reason for these efforts has been potential low energy costs compared with distillation and the environmental advantages of using carbon dioxide. 

Since the type of solutions encountered in extractive distillation involve mixtures of polar compounds or polar with nonpolar ones, the solutions are usually nonideal, and predicting the phase equilibrium from pure component data only is practically impossible. Theoretical and experimental studies through the years, however, have established certain trends which are used to search for and screen potential solvents. 

The extractive distillation was used for those components which were difficult to separate by ordinary distillation. Therefore, in order to screen out the best solvent of extractive dwastillation, the VLB date between hydrogenated Cg arenes and solvents (sulfolane, glycerol, dioctyl phthalate)... 

Phase-equilibrium calculations were discussed for vapor-liquid equilibria (VLB), liquid-liquid equilibria (LLE), and solid-solid equilibria (SSE). Results from VLE calculations often take the form of K-factors and relative volatilities, especially when thermodynamic calculations serve as intermediate steps in computer-aided process-design programs. In those situations, K-factors are routinely provided to subprograms that size distillation columns and gas-liquid absorbers. Similarly, the distribution coefficients computed for LLE serve as bases for sizing solvent-extraction columns moreover, liquid-liquid distribution coefficients may be helpful in screening candidate solvents for use in an extraction. 

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