Experimental Study of Polyamide-Silica Nanoparticles Membrane Performance in Reduction of Chemical Oxygen Demand (COD) of Produced Water (A Mixture of Xylene-Water) by Using Reverse Osmosis

In oil and gas production, large amounts of water are injected into the reservoir to achieve a high recovery level. When this liquid returns to the surface, it is enriched with valuable hydrocarbons and is called “produced water”. Membrane operations are used to separate this liquid mixture and reuse the produced water. One of the important factors in the treatment of produced water is the reduction of chemical oxygen demand (COD). The maximum COD limit for crude oil that comes to the surface through oil wells is 60 ppm for surface water discharge. In this study, the reverse osmosis process was used and the effect of pressure, weight percentage of polymer and nanoparticle parameters on the flow rate and COD reduction of effluent was investigated using polyamide membrane with silica nanoparticles. According to SEM images, it was observed that the membrane consists of three layers and the polyamide layer, which is responsible for the main separation, is a dense layer and has an uneven surface morphology, and polyether sulfone (middle layer) has finger like porosity. In this study, xylene and distilled water were used as produced water. The response surface method and central composite design were used for designing the experiments and statistical analysis of the results. In order to select the optimum membrane, maximum flux and separation percentage were considered. The optimum conditions with concentration of 10.05 wt.% polyether sulfone polymer, 2.09 wt.% silica nanoparticles and the operating pressure of 10 bar were predicted. The optimum laboratory results for flux, separation rate and COD in the effluent were 39.11 kg.m-2.h-1, 98.65% and 30 ppm, respectively, which was even better than the standards for discharging petroleum effluents into surface water.