(230d) Assessment of Polysulfone Membranes Embedded with Carbon Nanotubes and Polyester Non-Woven Fabric Support for the Treatment of Oil and Gas Produced Wastewater

D. N. B. Nkazi, Kwame O-A., Jean Mulopo, S. E. Iyuke,

School of Chemical and Metallurgical Engineering University of the Witwatersrand, PO Box 3, Johannesburg, Wits 2050, South Africa


Abstract

Keywords: Produced oil wastewater; Phase Inversion (PI) membranes; Carbon nanotubes; polyester non-woven fabric; Characterization; permeate flux, oil rejection

With industrial development, there is increase in the amount of oil used, but various technical and management developments lag behind other reasons that are not perfect and make a lot of oil into the water, forming pollution. The use of modified Polysulfone membranes for the treatment of wastewater produced in the oil and gas industry were studied. The micro-porous anisotropic membranes were prepared using the Phase Inversion (PI) method and embedded with carbon nanotubes (CNTs) and/or not supported on a polyester non-woven fabric. The produced membranes were characterized using the Scanning Electron Microscopy (SEM), atomic force microscopy (AFM), Fourier Transform Infrared Spectroscopy (FTIR), and tensile strength analysis.

The multi-walled carbon nanotubes MWCNTs/PSF membrane with 0.4 wt% MWCNTs has the roughest surface and the largest pore size. For membranes containing more than 0.4 wt% MWCNTs, the surfaces become smoother and the pore sizes of cross-section become smaller due to the to the increasing density of functionalized  MWCNTs and van der Waals forces; which cause the steric hindrance between the functionalized MWCNTs to agglomerate inside the polymer matrix during the phase inversion. The pore sizes ranged from 1.598μm for the membranes with the fabric support to 0.191mm for the CNT imbedded membranes without a fabric support. The results showed that the functionalized CNTs interacted with the hydrophobic membranes to enhance its physical, chemical and mechanical properties. The addition of a fabric support decreased the pore sizes of the PI membranes. The membranes were tested for performance and it was shown that increasing pressure increased permeates flux and CNTs increased permeate flux while controlling fouling via pore blockage. The fabric influenced the flux decline by providing further resistance to the flow of permeates through the membrane. Permeates were collected and tested for oil concentrations. The results showed oil rejections ranging between 78% and 90% with the mixed matrix phase inversion membrane supported on a polyester non-woven fabric having the highest oil rejections.

The performance studies with addition of different fractions of MWCNTs on the polymeric membranes produced with different solvents (DMF, CHCL₃ and THF) show an appreciable 48.6 % increase in water flux with DMF as solvent. At values above 0.4 wt% MWCNTs the water flux decreased. The increase in permeability of the membrane was related with the hydrophilicity and adsorption effects of MWCNTs. However, increased viscosity of the casting solution at higher MWCNTs loading (>0.4wt %), retarded the exchange between solvent and non-solvent during phase inversion process, and smoother membrane surfaces and smaller pores appeared as a result. Hence, water flux was severely limited.