Quantitative evaluation of concentration polarization in the permeation of VOCs/water mixtures through PDMS membrane using model equation

The influence of concentration polarization on the pervaporation and separation of VOCs/water mixtures through the PDMS membrane was investigated, using model equation based on the resistance-in-series concept in the boundary layer in feed adjacent to the membrane surface. Dichloromethane, chloroform, 1,2-dichloroethane, and 1,1,2-trichloroethane were used as VOCs. From the permeation data of the mixtures, the overall mass transfer coefficient, mass transfer coefficient of VOCs component across the boundary layer and concentration polarization modulus as a measure of extent of concentration polarization were determined quantitatively with help of the model equations. From the analysis on the determined model parameters, the boundary layer resistance due to the concentration polarization of VOCs component contributed more to the overall permeation process than the membrane resistance did.

The pervaporation of the chlorinated hydrocarbon/water mixtures through PDMS membrane were carried out at various feed flow rates and VOCs concentrations in feed. From the permeation data of the mixtures, the overall mass transfer coefficient, the mass transfer coefficient of VOCs component across the boundary layer and concentration polarization modulus as a measure of the extent of concentration polarization were determined quantitatively with the help of the model equations. From the analysis on the the results, the boundary resistance owing to the concentration polarization of VOCs component was found to be more important when the molar volume of VOCs was greater or VOCs content in the feed mixture was higher. Also, when feed flow rate is slower, it was found that the boundary layer resistance becomes more significant relative to the membrane resistance.