Pervaporation of dilute alcoholic mixtures using PDMS membrane

Pervaporation (PV) of methanol/water and ethanol/water mixtures through PDMS membrane was investigated using a PV cell (in laboratory scale). PDMS membrane is a well-known hydrophobic membrane for removing organics from aqueous mixtures. Experimental results were obtained at different initial alcohol (methanol and ethanol) concentrations (0.3–3 wt%) and temperatures (30–50∘C). Recirculation flow rate was kept constant at a value of 15.6 l/h. Average permeation flux (j)(j), separation factor (α)(α) and activation energy of permeation (EP)(EP) were calculated. Separation factor of PDMS membrane for methanol was greater than that for ethanol. Total flux for methanol/water and ethanol/water mixtures was observed to vary from 0.37 to 0.56 (kg/m2h) and 0.52 to 0.90 (kg/m2h) at 30∘C, respectively, as alcohol concentration changed from 0.3 to 3 wt%. Separation of alcohols depends on both their selective sorption in polymeric membrane and their diffusivity. The most important observation was that separation factor of methanol/water mixtures is greater than that of ethanol/water mixtures and it is because of different molecular size of alcohols. Different behavior of alcohol/water mixtures can also be explained in the entire concentration range studied using relative values of solubility parameters of the alcohols. It can be due to the fact that activation energy of alcohol permeation increases as solubility parameter difference between alcohol and membrane increases.