EXPERIMENTAL AND MODELING STUDIES OF A PARASITIC BINDING MECHANISM IN FACILITATED MEMBRANE-TRANSPORT

A "parasitic binding" reaction mechanism in facilitated transport was studied theoretically and experimentally. An example of this mechanism is CO (solute) transport through CuCl (carrier) solutions. In this process, after the first binding of solute with a carrier molecule, the second reaction step takes place between the solute-carrier complex and a second carrier molecule. The steady state mass transport equations were solved numerically for the facilitation factor, F. Modeling results indicated a "cross-over" point in a plot of F vs. the ratio of total carrier to feed solute concentration, theta, for certain values of K1 and K2. An explanation for this cross-over point was found when F and the ratio of concentration values of carrier-solute complexes were plotted vs. K2 with theta as a parameter. The concentration ratio of first step's solute-carrier complex to the second step's is approximately equal to 1 at the cross-over point. An experimental apparatus was designed and set up to conduct the experimental study. Laboratory experiments related to CO transport through CuCl containing immobilized liquid membranes (ILMs) were performed. Experimental values were consistently lower than the modeling results based on previously reported physical properties. An improved value for the diffusivity ratio of carrier-solute complex to the solute, gamma, was obtained by minimizing the difference between experimental results and modeling results.