Solvents extractive distillation

Impurity to be removed Extractive distillation solvent Reference... 

Extraction and Extractive Distillation. The choice of an extraction or extractive distillation solvent depends upon its boiling point, polarity, thermal stabiUty, selectivity, aromatics capacity, and upon the feed aromatic content (see Extraction). Capacity, defined as the quantity of material that is extracted from the feed by a given quantity of solvent, must be balanced against selectivity, defined as the degree to which the solvent extracts the aromatics in the feed in preference to paraffins and other materials. Most high capacity solvents have low selectivity. The ultimate choice of solvent is deterrnined by economics. The most important extraction processes use either sulfolane or glycols as the polar extraction solvent. 

Dimethylacetamide (DMAc), cellulose solvent (with lithium chloride), 5 384 N, N-Dimethylacetamide (DMAc), 23 703 extractive distillation solvent, 8 802 solvent for cotton, 8 21 N, AA-Dimethylacrylamide (DMA), 20 487 P,P-Dimethyl acrylic acid, physical properties, 5 35t Dimethylallylamine, 2 247... 

Earlier explorations for appropriate solvents may have been conducted by the Edisonian technique of trying whatever was on the laboratory shelves. An extensive list of mixtures and the extractive distillation solvents that have been studied is in the book of Kogan (Azeotropic and Extractive Distillation, Leningrad, 1971, pp. 340-430, in Russian). 

The use of digital computers to carry out complete calculations in the design of separation processes has been the goal of many. To do this effectively, suitable methods for phase equilibria and tray-to-tray distillation calculations are required. Results calculated by the application of such methods to dehydrate aqueous ethanol mixtures using ethylene glycol as the extractive distillation solvent is discussed below. A brief review of the methods used for phase equilibria and enthalpies is followed by a discussion of the results from distillation calculations. These are compared for extractive distillation with corresponding results obtained by azeotropic distillation with n-pentane. 

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. 

The obtained values of FX2 for these samples are plotted against time from solvent injection to establish the maximum value for the separation factor, F12 (max). Further details about the experimental technique are in the original paper (35). The larger the value of FX2 (max), the better the solvent can separate the mixture, indicating a better extractive distillation solvent. This was verified by comparing values for FX2 (max) and infinite dilution relative volatilities (a°i2) for the system n-hexane-benzene with six different solvents. The results presented in... 

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