Graphene Oxide Membranes for High Salinity, Produced Water Separation by Pervaporation

Abstract

Oil and gas industries produce a huge amount of wastewater known as produced water which contains diverse contaminants including salts, dissolved organics, dispersed oils, and solids making separation and purification challenging. The chemical and thermal stability of graphene oxide (GO) membranes make them promising for use in membrane pervaporation, which may provide a more economical route to purifying this water for disposal or re-use compared to other membrane-based separation techniques. In this study, we investigate the performance and stability of GO membranes cast onto polyethersulfone (PES) supports in the separation of simulated produced water containing high salinity brackish water (30 g/L NaCl) contaminated with phenol, cresol, naphthenic acid, and an oil-in-water emulsion. The GO/PES membranes achieve water flux as high as 47.8 L m−2 h−1 for NaCl solutions for membranes operated at 60 °C, while being able to reject 99.9% of the salt and upwards of 56% of the soluble organic components. The flux for membranes tested in pure water, salt, and simulated produced water was found to decrease over 72 h of testing but only to 50–60% of the initial flux in the worst-case scenario. This drop was concurrent with an increase in contact angle and C/O ratio indicating that the GO may become partially reduced during the separation process. Additionally, a closer look at the membrane crosslinker (Zn2+) was investigated and found to hydrolyze over time to Zn(OH)2 with much of it being washed away during the long-term pervaporation.

Metal cation crosslinked, partially reduced graphene oxide membranes with enhanced stability for high salinity, produced water treatment by pervaporative separation

“…This work shows a novel approach to improve GO membrane stability, increase its permeability and selectivity for produced water membranes via the new process of pervaporation separation that was introduced in our previous study [46]. The innovation lies in integrating partial reduction and metal cation cross-linking to improve GO stability.…”

Exemplar Mixtures for Studying Complex Mixture Effects in Practical Chemical Separations

“…They note that produced water has levels of chloride as high as 380,000 mg/L, 20 times higher than that of seawater, a pH as low as 3, and potential “items of concern” including Al, As, Ba, B, Br, Cd, Cu, Fe, Pb, Li, Ni, Zn, H 2 S, sulfate, sulfide, and bicarbonate. As interest grows in extracting value-added products from produced water, , it seems likely that developing a set of exemplar mixtures that can be adopted by the research community will greatly aid in the comparison of experiments.…”

Preparation of 2D Materials and Their Application in Oil–Water Separation

“…In contrast, graphene oxide (GO) with many oxygen-containing functional groups on its surface has a better application prospect in oil–water separation [ 89 , 90 ]. First, these oxygen-containing functional groups are almost all hydrophilic, which can efficiently and selectively separate water under the action of hydrogen bonds and possess a high water flux [ 91 ]. For example, Cai et al prepared a GO-based membrane capable of separating oil-in-water emulsions, and the membrane water flux was as high as 4600 L m 2 h −1 bar −1 [ 92 ].…”