Diffusion of phenol in the presence of a complexing agent, tetrahydrofuran

The effect of a complexing agent, tetrahydrofuran, on the diffusion of phenol across a stagnant fluid layer has been studied. At a given activity of free phenol, the steady-state flux of phenol appearing in an acceptor phase was greatly enhanced. However, as the fraction of phenol associated with the complexing agent increased, the flux of phenol decreased, since the transport was then controlled by the diffusion of the complex, a larger structure. A mathematical model of simultaneous association and diffusion was derived to determine whether the diffusional behavior of two associating species could be accounted for in terms of the association equilibrium constant and Fick's second law. Experimental results supported the model. It was concluded that the presence of a complexing agent tends to reduce the rate of diffusion, the effect being more pronounced at high concentrations of complexing agent.