Extraction of amino acids by emulsion liquid membranes containing di (2-ethylhexyl)phosphoric acid as a carrier biotechnology; coupled, facilitated transport; diffusion

Abstract

An experimental and analytical study on the batch extraction of amino acids such as tryptophan (Trp) and phenylalanine (Phe) was performed with emulsion liquid membranes containing di (2-ethylhexyl)phosphoric acid (D2EHPA) as a carrier. A series of preliminary experiments on the extraction equilibria for aqueous-organic two-phase systems showed that the complex formation reaction can be expressed as follows: A + + 2 (HL) 2 = AL (HL) 3 + H +, K ex = ( [ AL(HL) 3 ] [ H +]/[ A +] [ (HL) 2 ] 2) Here, A + is the cation of the amino acid, and (HL) 2 is the dimer of D2EHPA. The distribution ratio of the amino acid is given by D= K ex [(HL) 2] 2/( K a + [ H +]) where K a is the acid dissociation constant of the carboxylic group in the amino acid. The rate of extraction of Trp with D2EHPA, measured by using a Lewis-type stirred cell, in a two-phase system suggested that the complex formation reaction is so fast that the extraction equilibrium is established at the aqueous-organic interface. On the basis of the above results, the mechanism and the rate of extraction of the amino acids with emulsion liquid membranes are discussed, and a permeation model is proposed which takes into account the mass transfer in both the external aqueous phase and the organic membrane phase, and also the extraction equilibria. It was found that the effects of various experimental conditions on the extraction rate and the extent of recovery were satisfactorily explained by the proposed model. The results of the permeation of β-phenethylamine (β-PhA) and tryptophan methyl ester (TrpMe) are also discussed.