THE SEPARATION OF DISSOLVED ORGANICS FROM WATER BY PERVAPORATION

The ability of thin composite membranes to separate dissolved organic solvents from water by pervaporation has been examined. The separation performance of a pervaporation process was considered as a combination of an evaporation step and a diffusion step. For the experimental work, poly (dimethylsiloxane) and polyolefin composite membranes were incorporated into 0.1-0.3 m2, 2-inch diameter laboratory spiral-wound test modules. Typical fluxes were in the range 0.2-1.5 L/m2-h, depending on the operating conditions and the feed solution. The membranes used in this work were non-selective for polar solvents such as ethanol (αmem< 1) so that the overall enrichment of polar solvents in the permeate was typically 5-10 fold. With non-polar solvents such as ethyl acetate, chloroform and 1,1,2-trichloroethane, where the membrane selectivity, αmem, is greater than 1, organic enrichment in the permeate of 50-400 fold was obtained. Pervaporation therefore appears to be an economically viable method of removing non-polar solvents from dilute aqueous streams. Preliminary calculations show plant capital costs in the range $2-5/gal of feed water per day and operating costs of $2-10/1,000 gal of feed water treated. © 1990.