Superhydrophobic-superoleophilic kaolin based microfiltration membrane for oil recovery from oilfield produced water

Abstract

The discharge of oilfield produced water (OPW) causes disruption of the ecosystem and environmental degradation. Herein, novel hybrid membrane coupled absorption-filtration technology is proposed for the recovery of oil from OPW. The present study aims to develop a superhydrophobic-superoleophilic kaolin-based hollow fibre ceramic membrane using phase inversion and sintering technique for the recovery of oil from synthetic OPW. To achieve the superhydrophobic-superoleophilic modification, organosilanes sol-gel coating was performed on kaolin-based hollow fibre ceramic membranes. Membrane morphology and surface roughness was analysed using field emission scanning electron microscopy (FESEM) and atomic force microscopy. The membrane surface functionality was studied using Fourier transform infrared, X-ray photoemission spectroscopy (XPS) and X-ray diffraction analysis. The membrane filtration performance was evaluated using cross flow module. In the first stage of the work, feasibility studies of Malaysian kaolin (MK) and Nigerian kaolin (NK) were studied on fabrication of kaolin-based hollow fibre membrane by varying the loading composition (34 to 37 wt.%) and sintering temperature (1200 to 1500˚C). Experimental results show that increase of kaolin concentration and sintering temperatures decreases the flux rate. The physiochemical and performance analysis showed that 34 wt.% MK ceramic membrane exhibits better water flux (565.06 L/m2h) with desired pore size and stability than 34 wt.% NK membrane. It owes to the MK which hold higher degree of crystallinity and smaller particle size. In the second stage, for effective oil absorption-filtration, organosilane agents such as methyltriethoxysilane (MTES), fluoroalkylsilane, octadecyltrimethoxysilane, chlorotrimethylsilane chlorotrimethylsilane, and trichloro(octadecyl)silane were used for the modification of superhydrophobic-superoleophilic kaolin hollow fibre membrane. XPS and FESEM analysis clearly indicated that the organosilanes are bound firmly on the surface of kaolin membranes. The effect of coating cycle and oil concentration were also studied. Among the coated membranes, MTES coated kaolin membrane showed the maximum water contact angle of 161.3° and lowest oil contact angle of 0o. Resultantly, this depicts that the superhydrophobic-superoleophilic property were attained. In the third stage of the study, the oil recovery performance of the kaolin membranes with different organosilane agents were evaluated and compared. MTES-coated membranes showed maximum oil absorption capacity of 10 g/g, oil flux of 80 L/m2h, and oil separation efficiency 90%. The optimized MTES coated membranes were adopted to further optimization of process condition (oil concentration, feed flow and feed pH) in cross flow module for the effective oil flux and separation efficiency using response surface methodology (RSM). From the central composite design, maximum oil flux of 97.67 L/m2h and separation efficiency 98.41% were observed at oil concentration of 50 mg/L, feed flow of 300 mL/min, and feed pH of 4. The RSM model was good coherent with experimental data. Overall, this study portrays the development of economically viable superhydrophobic-superoleophilic kaolin hollow fibre membrane for the absorption combined filtration process for the separation of oil from produced water. This study would pave the way for researchers to eliminate the pollutants using hybrid absorption-filtration process.