Applying filled and unfilled polyether-block-amide membranes to separation of toluene from wastewaters by pervaporation

One of the methods of achieving high selectivity or high flux for specific compounds is the modification of membrane such as filling, grafting or coating. The most common is adding fillers, especially high aspect ratio fillers. It improves physical properties such as increased stiffness or reduced creep and a variety of other purposes: improves thermal stability, high voltage resistance, electrical conductivity, radiation shielding and optical and aesthetic effects. In many cases, filled polymeric membranes show permeabilities much lower than the conventional unfilled membranes, and hence can serve as barriers for oxygen, water and other solutes. In the area of organophilic pervaporation membranes mostly tree types of fillers have been used: zeolite, silicate and carbon sieve. This study focused on the removal of toluene from the wastewaters. The concentration of that solvent in the feed solution was close to its solubility in water — 500 ppm. The tests were carried out on a polyether-block-amide (PEBA) membrane filled with carbon black (PEBA + cb) and another without the filling (PEBA). Both membranes were made in a laboratory and were characterized by the same thickness (75 μm). The removal of toluene from wastewaters for PEBA membrane after 5 h of the process was satisfactory, reaching approx. 65%. However, special attention should be paid to very high toluene concentration indicated by high enrichment factor and selectivity of the process. The final concentration of toluene in the retentate after 5 h of pervaporation with use of PEBA + cb membrane was about 100 ppm, (80% of removal), but much higher fluxes accomplished for that membrane (especially water flux) worsened the concentration of toluene in the permeate.

The results yielded by the pervaporation of wastewater produced by the chemical industry using PEBA and PEBA + cb membranes are very promising. Although the wastewater was characterized by a very high toluene concentration (500 mg/dm3), PEBA and PEBA + cb membranes removed 67 and 81% of toluene during one 5 h experiment. Moreover, the high enrichment factors and selectivity coefficients which indicate good separation properties of the membranes