The facilitated transport of carbon monoxide through cuprous chloride solution

Abstract

The facilitated transport of carbon monoxide through thin, immobilized films of cuprous chloride solutions is investigated, using a tracer C140 technique. Steady-state tracer flux measurements are used to determine the second-order forward rate constant and equilibrium constant for the reversible reaction of CO with cuprous ion. The enhanced results at low CO partial pressures can be interpreted in terms of a consecutive reaction model. The cuprous ion is remarkably effective as a carrier for CO. The CO permeation rate in the presence of cuprous ion can be increased by two orders of magnitude over the nonfacilitated flux. As such, the cuprous ion is an attractive facilitating agent for use in a membrane separation system. SCOPEImmobilized liquid membranes which contain a mobile reactive carrier have been used to separate mixtures containing acid gases, for example, CO, and H2S (Ward and Robb 1967, Winnick et al. 1974, Matson et al. 1977. Due to the reversible chemical reaction which occurs in the liquid layer, high membrane permeability and selectivity for a specific permeant can be achieved at atmospheric pressure. In addition, since the complex formed near the upstream (high concentration) boundary dissociates near the downstream (low concentration) boundary, no net reaction occurs in the membrane, eliminating the need for a regeneration step in this type of separation scheme.The complexation reaction of CO with cuprous ion has been widely used for CO removal in industrial absorbers (Kohl and Riesenfeld 1960). In our study, the reaction has been adapted for use in a membrane geometry. Two comp!ementary experiments were conducted to evaluate this reaction system. Using the tracer technique of Donaldson and @inn (1975), the reaction kinetics are explored by measuring the steady-state flux of C'4O through cuprous chloride solutions equilibrated with equal partial pressures of untagged CC). The transport data are compared to an analytical model for simultaneous reaction and diffusion. The net flux of CO through these membranes was also monitored, by the parallel flux of tracer C14O. The extent of flux enhancement was measured as a function of CO partial pressure, total copper concentration, and membrane thickness. CONCLUSIONS AND SIGNIFICANCEThe carrier-mediated transport of CO by cuprous chloride anion, Cu(Cl)3-2, through thin (190 pm) liquid membranes lies intermediate between the two limiting regimes of very fast and very slow reaction rates. At high CO partial pressures (100% CO), the CO flux is well described by a simple bimolecular reaction model, with an equilibrium constant of 1,600 M-1 and a second-order forward rate constant of 8,400 M-1 s-l at 25OC. As the CO partial pressure is reduced, the measured enhancement is higher than anticipated. This additional facilitation is discussed in terms of a consecutive reaction model, where the product of the primary reaction can further react with the carrier, forming a second CO-containing species.Carbon monoxide transport with a 5% CO upstream concentration is m...

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