CONCENTRATION POLARIZATION AND OTHER BOUNDARY-LAYER EFFECTS IN THE PERVAPORATION OF CHLORINATED HYDROCARBONS

The effect of concentration polarization on the pervaporation performance was studied for several chlorinated hydrocarbons (Cl-HC's). The feed flow rate was varied between 1-5 l/min in a test cell unit, provided with a flat sheet membrane (plate-and-frame module). For this configuration and for all Cl-HC's studied, the flux decreased below a critical flow rate of 3 l/min. Cl-HC's with a high permeability showed a considerable flux decline, while for organic compounds with a low permeability like propanol, the decrease in flux was negligible. A model was derived in order to estimate the yield which gave good agreement between the calculated and experimental results. The addition of salts caused an important flux decline for trichloroethylene. The effect was reversible, could be reduced by an increase of the Re number and could not be explained by pore-blocking of the zeolite pores. Different salts caused the same decrease of trichloroethylene flux but did not affect the water flux. Fluxes were not influenced by the pH of the feed mixture, but the viscosity of the feed mixture had a considerable effect on both the trichloroethylene and water flux.