Performance of polyphenylsulfone/copper benzenetricarboxylate framework nanofiltration membrane for organic solvents separation

Abstract

Over the years, the importance of solvent separation emerges to minimize the energy consumption and provide better solvent recovery. The limitation of current technologies has called for new solvents recovery using membrane technology. Hence, the primary focus of this study was to prepare and evaluate the performance of polyphenylsulfone (PPSU) nanofiltration (NF) membranes for organic solvents separation. In the first phase, PPSU membranes with different polymer concentrations in the range of 17 to 25 wt% were fabricated. The experimental results showed that the polymer concentration has great impact not only on the membrane morphology but also its separation characteristics. The obtained results revealed that the PPSU membrane made of 17 wt% polymer concentration (PPSU 17) was the best performing membrane (molecular weight cut off (MWCO) 612 g/mol) due to its promising methanol flux (16.8 L/m2.h) coupled with good rejection of dye (Methyl Blue dye: 92%) at 6 bar. Further investigation using different solvents such as ethanol and isopropanol showed that apart from viscosity, molecular weight and molecular size of the solvent, the affinity between the solvent and the membrane plays a significant role in affecting the transport rate of the solvent through the membrane. In the second phase, PPSU 17 was used to investigate the influence of membrane pretreatment conditions on the membrane properties and performance. It was found that the membrane performance was negatively affected with longer immersion period in methanol solution (14 days) prior to separation experiment, attributed to the rearrangement of the polymer chain which result in membrane swelling and/or change of membrane surface hydrophilicity. In the third phase, the performance of PPSU 17 membrane was further enhanced by incorporating the membrane with copper-1,3,5-benzenetricarboxylate (Cu-BTC) particles at different loadings (0.5 to 3 wt%). The results indicated that when 0.8 wt% Cu-BTC was incorporated into PPSU membrane (designated as PPSU/0.8Cu- BTC), the methanol flux increased by 43% while membrane MWCO decreased by 18% in comparison with the neat PPSU membrane, when both were tested using 10 ppm of methanol-dyes solution at 6 bar. The improvement in membrane flux and dye rejection could be attributed to the good dispersion of the Cu-BTC particles in the membrane matrix coupled with their improved interfacial contact with the membrane. In addition, the incorporation of Cu-BTC showed a great improvement in terms of resistance to compaction, indicating the importance of Cu-BTC in increasing membrane rigidity and strength.