Liquid-liquid extractions of acrylic acid with tri-n-butyl phosphate dissolved in conventional diluents (benzene, toluene, xylene, hexane, petroleum ether) are analyzed. The results are explained in terms of distribution coefficient, extraction efficacy, equilibrium complexation constant, loading ratio, and coextraction of water. These findings are used to design continuous extraction columns.

Abstract

Separation of carboxylic acids from downstream is a bottleneck in the chemical industry since it takes nearly 30–50 % of the overall production cost. In view of this, an attempt was made for the extraction of acrylic acid from aqueous solution with tri-n-butyl phosphate dissolved in organic diluents like benzene, toluene, xylene, hexane, and petroleum ether. The results are explained in terms of distribution coefficient (σ), extraction efficacy (η%), equilibrium complexation constant (K_ε ), loading ratio (ϕ), and coextraction of water. At lower concentration of acrylic acid and higher concentration of tri-n-butyl phosphate for the acrylic acid-tri-n-butyl phosphate system, maximum extraction efficacy and distribution coefficient for benzene was found as 88.60 % and 7.772, respectively. Coextraction of water in the extract phase and law of mass action were discussed, too. Diffusivity of acrylic acid to the interface of extract (organic) and raffinate (aqueous) phases was calculated using the Wilke-Chang equation and Reddy-Doraiswamy equation. In view of designing a continuous extraction column, the number of theoretical stages and minimum solvent-to-feed ratio were also determined.