Reverse micellar extraction of amino acids using the two-tailed cationic surfactant DODMAC

Reverse micelles have been formed for the first time with a two tailed cationic surfactant, dioctyldimethyl ammonium chloride (DODMAC), in alcohol/isooctane mixtures. The effect of different alcohols and salts on water uptake of the DODMAC reverse micelles has been studied.The effects of pH and of the concentrations of amino acid, NaCl, DODMAC and l-decanol on the reverse micellar extraction of aspartic acid, glutamic acid and threonine from aqueous salt solutions were determined by phase contact experiments. The concentrations of all ionic species in the aqueous phase were measured and the corresponding concentrations inside the reverse micelles were obtained by material balances and the condition of electrical neutrality. The results show that the amino acids were mainly extracted through an ion exchange mechanism. Important factors which dominate the amino acid extraction are the net charge of amino acid, the competition among anions, the dissociation equilibrium of DODMAC and the water uptake in the reverse micelles. The ionic species in the reverse micelles tend toward their undissociated states as the water uptake by the reverse micelles decreases.The renormalization of Guggenheim's canonical partition function to satisfy the limits of order and disorder has been used to generate excess Gibbs energy models for liquid mixtures. Under well defined assumptions, the contributions to the activity coefficients arising from the new partition function correspond exactly with those given by existing semi-empirical models.A thermodynamic model has been developed to calculate the concentrations of all ionic species in both the aqueous and the reverse micellar phases. With this model it is possible to study the effect of changes of extraction variables, such as the concentrations of salt, surfactant and cosurfactant, in the extraction of amino acids by reverse micelles. The model has been tested by performing flash calculations for the system DODMAC, l-decanol isooctane, NaCl an amino acid and water. Three different amino acids were considered. The calculated results are in good agreement with the experimental data