Selective transport of gaseous CO through liquid membranes using an iron(II) macrocyclic complex

The equilibrium constant and rate constants for the 1:1 complexation reaction of the iron complex with a tetraimine macrocycle, 2,3,9,10-tetracene (TIM) with CO have been measured in benzonitrile. In CO-saturated solutions, the Fe(II) complex can be oxidized electrochemically to allow the diffusion coefficients of the complex and CO to be determined. The reversible complexation reaction of this Fe(II) complex with CO affords facilitated transport of CO across the benzonitrile liquid membranes. For a membrane with a thickness of 0.072 cm, the transport rate of CO is increased by 14% over the purely diffusional rate. Since the Fe(II) complex does not bind N/sub 2/, O/sub 2/, CO/sub 2/, or H/sub 2/, the facilitated transport will be selective for CO in a variety of gaseous matrices. Selectivity is demonstrated for CO/O/sub 2/ gas mixtures. The rate constants for CO complexation and the diffusion coefficients for the Fe(II) complexes can be used as input parameters for a mathematical model that predicts the magnitude of the facilitated transport. Furthermore, the model and experimental work indicate that low solubility of the Fe(II) complex limits the magnitude of the facilitated transport in this case, as opposed to the thermodynamics or kinetics of the complexation reaction. The experimental and mathematical procedures described herein can be applied to any 1:1 complexation reaction between a soluble nonvolatile carrier and a dissolved gas molecule to predict the magnitude of the facilitated transport across liquid membranes.