synopsisThe transport of twelve organic liquids through a highly swollen rubbery membrane has been studied. The transport was caused by a pressure applied to the liquid above the membrane (reverse osmosis). The flux waa found to be a highly nonlinear function of the driving pressure. Detailed thermodynamic and diffusion theories are proposed to describe the transport in terms of the concentration gradient of the swelling liquid within the membrane induced by the applied pressure. The data and the theory appear to be in very good agreement. The diffusion coefficients deduced from the data are explained in terms of a hydrodynamic mechanism of diffusion. Highly swollen membranes can yield very high liquid fluxes at moderate pressure and consequently may have applicat>ions for performing certain separations.

synopsisThe pressuredriven transport of liquids employed in reverse osmosis has been shown to occur by a solution-diffusion mechanism in highly swollen polynier membranes. A theory based on this mechanism was successfully used earlier to correlate permeation fluxes for such membranes. Positive confirmation of this theory is provided here by direct measurement of the proposed concentration gradient. A study of the temperature dependence of the liquid diffusion coefficient in the polymer membrane has provided additional evidence of a hydrodynamic regime of diffusion in highly swollen membranes. It is also shown that the proposed ceiling flux in reverse osmosis is equal to the pervaporation flux.

synopsisThe hydraulic permeation of toluene-cyclohexanone and isooctane-CCl4 mixtures through a membrane, a rubber network, was studied. No separation of components occurred in this mode. The mixture flux data were successfully analyzed using a solution-diffusion theory by treating the mixture as if it were a single component with properties of the mixture. Diffusion coefficients determined in this way appear to be governed by frictional forces having a hydrodynamic origin. Slight separation of the components did occur when the pervaporation mode of operation was used. The significance of this is discussed.

SynopsisAn approximate equation was developed that permits calculation of the solvent tracer diffusion coefficient in a homogeneous swollen membrane from the measured hydraulic permeability coefficient. This relation was applied to data for 28 polymer-solvent systems that included 15 different organic solvents and 5 hydrocarbon polymer networks whose equilibrium swellings ranged from 16.1 to 91.5% polymer on a volume basis. The calculated tracer diffusion coefficient divided by the pure solvent self-diffusion coefficient for these systems formed a unique correlation when plotted versus the polymer volume fraction in the membrane. This relation agreed well with tracer diffusion coefficient data in the literature for the benzene-natural rubber system measured by radioactive tagging. Discussion centers on the evidence for the validity of the equation developed and the role of hydrodynamics on diffusion in swollen membranes.

SynopsisPoly(viny1 alcohol) membranes were prepared by crosslinking with terephthalaldehyde. Hydraulic permeation of wat+er through this network structure was measured as a function of pressure for temperatures ranging from 18" to 35.8'C. The data were analyzed via a previously developed solution-diffusion theory for hydraulic permeation to give mutual diffusion coefficients. The activation energy for diffusion was found to be 6.5 kcal/mole which compared to the value of 4.3 kcal/mole for viscous flow of water indicates an influence of polymer-liquid interaction on the energetics of the diffusion process.