Assessing the Accuracy of Selectivity as a Basis for Solvent Screening in Extractive Distillation Processes

Abstract

An important parameter for consideration in the screening of solvents for an extractive distillation process is selectivity at infinite dilution. The higher the selectivity, the better the solvent. This paper assesses the accuracy of using selectivity as a basis for solvent screening in extractive distillation processes. Three types of binary mixtures that are usually separated by an extractive distillation process are chosen for investigation. Having determined the optimum solvent feed rate to be two times the feed rate of the binary mixture, the total annual costs of extractive distillation processes for each of the chosen mixtures and for various solvents are carried out. The solvents are ranked on the basis of the total annual cost (obtained by design and costing equations) for the extractive distillation processes, and this ranking order is compared with that of selectivity at infinite dilution as determined by the UNIFAC method. This matching of selectivity with total annual cost does not produce a very good correlation.

Extractive distillation with the mixture of ionic liquid and solid inorganic salt as entrainers

“…It is known that extractive distillation is an energyintensive process, and the use of an entrainer with a higher relative volatility (or selectivity) usually corresponds to a lower total annual cost. 33 Furthermore, both IL and solid salt are nonvolatile, rendering entrainer recovery by simple flash distillation or gas stripping feasible. In this sense, the mixed entrainers can still be taken on as environmentally friendly "green solvents.…”

Extractive Distillation: A Review

“…When solvents are ranked in the order of relative volatility (or selectivity), the solvent with the highest relative volatility is always considered to be the most promising solvent for a given separation task. This may indicate that, from the viewpoint of economic consideration, the use of the solvent with the highest relative volatility (or selectivity) will always give the lowest total annual cost (TAC) of the extractive distillation process (Momoh, 1991). The economic evaluations were carried out by using many different solvents for separating three different binary mixtures: 2-methyl-butene/isoprene (Mixture A), n-butane/ trans-2-butene (Mixture B), and n-hexane/benzene (Mixture C).…”

“…The effect of solvent selectivity on the total annual cost of an extractive distillation operation (2-methyl-1-butene/isoprene); adapted from Momoh (1991). The effect of solvent selectivity on the total annual cost of an extractive distillation operation (n-butane/trans-2-butene); adapted from Momoh (1991). 126 Lei , Li, and Chen Class II: Other liquids composed of molecules containing both active hydrogen atoms and donor atoms (oxygen, nitrogen and fluorine), e.g.…”

“…The effect of solvent selectivity on the total annual cost of an extractive distillation operation (n-hexane/benzene); adapted fromMomoh (1991).…”

Conceptual Design of Azeotropic Distillation Processes

“…19 Extractive Distillation Process for Acetone/Methanol Separationconsider the effort for the recovery of the entrainer, which can be critical if it comes to the selection of an optimal solvent[137].…”