Effect of carrier type on coupled transport kinetics of thiocyanate ions through liquid membranes

Coupled transport of thiocyanate ions through a liquid membrane containing quaternary ammonium chloride salts in chloroform was examined. The influences of the carrier type in the membrane phase on the coupled transport of thiocyanate ions were investigated. The kinetics of the coupled transport were analyzed in the formalism of two , tmax, , ) were also consecutive irreversible first-order reactions and the kinetic parameters (k1d, k2m, k2a, calculated. For the coupled transport of thiocyanate ions, quaternary ammonium chloride salts having different carbon atom numbers (Cn) used as carriers were found to increase thiocyanate ions transport efficiency with increasing carbon atom numbers. Tetradecyl trimethylammonium chloride (TDTMACl), hexadecyl trimethylammonium chloride (HDTMACl), and tetraoctyl ammonium chloride (TOACl) were found to be the most effective carrier types for transport of thiocyanate ions when Cn is greater than 16. The activation energies for maximum membrane entrance and exit fluxes were calculated as 32.45 kJ/mol and 34.75 kJ/mol, respectively. The values of the activation energy indicate that the process is controlled by species diffusion.

As carbon atom numbers of the carrier salts increase, tmax decreases, and thiocyanate ions are rapidly transported into the membrane where less accumulation appears. TEACl salt has a minor effect on transportation of thiocyanate ions. The transport kinetic parameters obtained with this carrier salt have lower values when compared — k2 k1d — — k2a — k2m — K — Thiocynate ion concentration in acceptor phase, mol/l Thiocynate ion concentration in donor phase, mol/l Thiocynate ion concentration in membrane phase, mol/l Carbon atom numbers of carrier molecules Mean diffusion coefficient of the complex in a membrane with thickness l, cm2/s Maximum value of membrane exit flux, mol.m2/min Maximum value of membrane entrance flux, mol.m2/min Membrane entrance rate constant, 1/min Membrane exit rate constant, 1/min Membrane entrance or leak to membrane rate constant, 1/min Acceptor phase exit rate constant, 1/min Membrane phase exit rate constant, 1/min Equilibrium constant l R — — Ra — Rd — Rm — — Sd/m — Sa/m — t tinf — — Distance between phases, m Reduced thiocyanate ion concentration Reduced thiocyanate ion concentration in acceptor phase Reduced thiocyanate ion concentration in donor phase Reduced thiocyanate ion concentration in membrane phase Reduced thiocyanate ion concentration in acceptor phase corresponding to inflection point of function Interface surface of donor phase over per unit of membrane, m2 Interface surface of acceptor phase over per unit of membrane, m2 Time, min Time corresponding to inflection point of the function, min