Solvent selection for extractive distillation processes to separate close-boiling polar systems

Influence of Solvent and Acid Properties on the Relative Volatility and Separation Selectivity for Extractive Distillation of Close-Boiling Acids

“…For the OA−LA and PA−BA mixture experiments, molar ratios of 3.0 were used, leading to x LA,f = 0.25 and x BA,f = 0.25, respectively. For the OA−LA mixture, experiments at higher pressures were done using x LA,f = 0.12 and 0.05 to facilitate comparison with results from Sprakel et al 16 Vapor and liquid compositions under isobaric equilibrium conditions were obtained using a Fisher Scientific model Labodest VLLE 602. The equilibrium vessel is a dynamic recirculating still, equipped with a Cottrel circulation pump.…”

“…Examples are the separation of monochloroacetic acid (MCA) and dichloroacetic acid (DCA) with a relative volatility of 1.25, 14 the separation of octanoic acid (OA) and levulinic acid (LA, also called 4-oxo pentanoic acid) with a relative volatility of 1.2, 15 and the separation of 2-methyl butyric acid (2MBA) and valeric acid (VA) with a relative volatility of 1.30−1.35. 16,17 Blahusǐak et al 18 have shown that for mixtures with a relative volatility below 1.3, affinity separations appear to be proper alternatives for distillation, and even for relative volatilities between 1.3 and 3, the use of a solvent to increase the relative volatility is worth considering. Thus, one of the options to improve the separation efficiency for the organic acid separations mentioned earlier is extractive distillation, where a solvent or extractive agent is added to the acid mixture.…”

“…10−17 This added solvent either needs to show preferential affinity for one of the molecules to be separated through, e.g., hydrogen-bonding or acid−base interaction, thus showing a negative deviation from Raoult's law, or needs to preferentially repel one of the components more than the other, thus showing a positive deviation from Raoult's law. 16 For the improved separation of organic acids using extractive distillation, different approaches were reported in the open literature. For the separation of DCA from MCA, 14 LA from OA, 15 and VA from 2MBA, 16,17 Lewis bases were considered as the solvent.…”

“…The feasibility of the use of Lewis base solvents to create higher relative volatilities for the MCA−DCA separation case is based on the difference in acidity between MCA and DCA, which is reflected by a difference in pK a between the two acids of ΔpK a ≥ 1.5. 14,19 However, the use of Lewis base solvents for the separation of the other acid mixtures with ΔpK a = 0.25−0.4 for OA and LA 15,20,21 and ΔpK a = 0−0.1 for 2MBA and VA 15,16 appeared to be less successful. Based on the available information, we hypothesize that for mixtures with a relatively low ΔpK a , a relatively strong Lewis base and a relatively high solvent-to-feed ratio would be required to obtain a sufficiently high separation efficiency.…”

Ternary Liquid–Liquid Equilibrium of Toluene + Dimethyl Carbonate + ILs at 298.15 K and Atmospheric Pressure

“…Boudreau et al used fatty acid as a solvent to separate the ethanol–water system by liquid–liquid extraction, and the results showed that the energy consumption of the extraction process was 38% less than that of the distillation process. Due to pinch points or close boiling points, many mixtures are difficult to separate by distillation based on the report of Smith et al and Sprakel et al Liquid–liquid extraction process was widely employed in the chemical industry due to its simplicity, low cost, and ease of scaling up . Therefore, the separation of toluene and dimethyl carbonate mixture with pinch point is studied by liquid–liquid extraction in this work.…”