Designing of polyethylene-based material modified by plasma discharge for water/oil separation

Abstract

Produced water (PW) from petrochemical industries is one of the largest wastewaters generated in Qatar. Soluble and insoluble oil contaminants occur in this water and must be removed if water will be used or discharged into the land or sea. Adsorption is a common procedure used in the industry for a wastewater treatment and oily components removal. It is a simple, cost effective process. Currently there are many available natural and synthetic, particularly polymeric adsorbents. Polyolefins are pure hydrocarbon polymers, which due to an appropriate sorption efficiency of lowmolecular weight hydrocarbons can be used as suitable sorbents. However, polyolefins' based sorbents are commercially used only for removal of free oil. In this work, we have investigated a potential use of polyethylene as a filtration media in tertiary filtration of emulsified oil/water mixtures with respect to key parameters determining their adsorption ability. Polyethylene powders of various size and physical treatment were used. Emulsion formed from distilled water and commercial Diesel oil (DO) with a concentration below 200 ppm was used as a model of PW. The emulsions were prepared without emulsifier, and emulsification was insured by ultrasonication. The relationships between the sorption properties and surface composition and morphology of modified and unmodified PE powders were evaluated. Characterizations include the neat oil sorption, and sorption from emulsions, scanning electron microscopy, and profilometry. The PE adsorbents were further characterized by Brunauer-Emmett Teller surface area analysis, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy were employed in order to characterize the porosity, crystallinity and chemical composition of PE, respectively. Sorption experiments were carried out as a function of different weight dosage, initial oil concentrations, and contact time to obtain the optimum conditions for the adsorption process. The results showed that LDPE powder, at a dosage of 3 g treated with plasma, using initial oil concentration of 100 ppm and 720 min of contact time presented the most suitable conditions for the adsorption of oil from emulsified DO. The adsorption process renders LDPE a suitable adsorbent for the removal of oil from diluted oil emulsions with an oil removal efficiency exceeding 93.5%. Equilibrium studies have been carried out to determine the sorption capacity of LDPE for the adsorption of oil from diluted DO emulsions using the optimum conditions. Langmuir and Freundlich adsorption models were applied to describe the experimental isotherms. Equilibrium data were fitted very well with the Freundlich model. The pseudo first- and second-order kinetic models were used to describe the kinetic data and the rate constants of sorption were evaluated. The experimental data were fitted well with the pseudo-second-order kinetic model. The study confirmed the feasibility of using oil adsorbents based on plasma treated PE powders as potential adsorbents media for the removal of oil contaminants from PW