(55a) Solute-Solvent NRTL: A Novel Approach to Model Amino Acid Solubility

Solution thermodynamic models are extensively used to describe fluid phase equilibria and thermodynamic properties for liquid mixtures. The Nonrandom Two-liquid (NRTL) activity coefficient model proposed by Renon and Prausnitz (1968) has been one of the most practiced solution thermodynamic models accurately describing the solution nonideality in liquid mixtures. However, the requirement of two binary interaction parameters per binary system with the NRTL model proves to be excessive when applied to multicomponent solute-solvent systems such as amino acid solubilities in various pure and mixed-solvents. This work presents a simplified NRTL formulation that reduces the number of binary interaction parameters from two to one for solute-solvent binary pairs and applies it to describe the fluid phase equilibria of different amino acid and solvent solutions. The model gives good predictions for the solubility of glycine, DL-alanine, DL-methionine, aminobutyric acid, isoleucine, leucine, norleucine, phenylalanine, serine, tryptophan, tyrosine, valine, diglycine, N-succinyl-L-phenylalanine-p-nitroanilide (SPNA), and L-phenylalanine-p-nitroanilide (HPNA) in various solvents. Furthermore, the simplified NRTL formulation can be employed in wide varieties of solution systems involving solutes, such as aqueous electrolyte solutions, CO2 solubility, and membrane sorption, showing a critical potential for the application of the new formulation