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

The effect of concentration polarization on the pervaporation performa nce was studied for several chlorinated hydrocarbons (Cl-HC's). The fe ed flow rate was varied between 1-5 l/min in a test cell unit, provide d with a flat sheet membrane (plate-and-frame module). For this config uration and for all Cl-HC's studied, the flux decreased below a critic al flow rate of 3 l/min. Cl-HC's with a high permeability showed a con siderable flux decline, while for organic compounds with a low permeab ility like propanol, the decrease in flux was negligible. A model was derived in order to estimate the yield which gave good agreement betwe en the calculated and experimental results. The addition of salts caus ed an important flux decline for trichloroethylene. The effect was rev ersible, could be reduced by an increase of the Re number and could no t 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 mixtu re, but the viscosity of the feed mixture had a considerable effect on both the trichloroethylene and water flux.