Sulfate removal from water produced during CO2 enhanced oil recovery, coal-bed methane recovery, and mining operations using anion exchange resins

Limited freshwater resources and expected increases in water demand are causing electric utilities to explore more non-traditional water sources, such as produced water from CO2 enhanced oil recovery (EOR), coal-bed methane recovery, and mining operations. Electric utilities, including coal-fired power plants, are the second largest users of freshwater in the United States. Produced water from EOR is variable in composition; it is dominated by high total dissolved solids composed mainly of sodium and chloride ions, on the order of 100,000 mg/L, and also high sulfate concentrations (up to 900 mg/L). Dissolved sulfate can cause stress corrosion cracking in steam turbine blades at concentrations as low as 8 mg/L. A certain level of treatment must be done before reuse in power plants is a viable option. This study focuses on sulfate removal from synthetic produced water and produced water from EOR and mining operations in the Illinois Basin using anion exchange resins. Equilibrium batch studies were conducted to compare commercially available strong base and weak base anion exchange resins of different type. Our results indicate that for optimal sulfate removal in high chloride solutions, (i.) weak base resins perform better than strong base resins, (ii.) resins with an epoxy polyamine matrix perform better than those with a divinylbenzene matrix, and (iii.) resins with secondary/tertiary amines perform better than those with pyridine functionality, and even better than those with quaternary ammonium. Reasons for better performance among resins include more closely spaced anion exchange sites and less steric hindrance. Sorption isotherms showed that weak base resins, pretreated with hydrochloric acid, significantly outperformed strong base resins, which had negligible sulfate removal at typical resin loadings. Resin titration curves coupled with experimental data were used to identify optimal pretreatment conditions for the weak base resins studied. Our results suggest that sulfate removal significantly decreases above 10,000 mg/L chloride, and that more moles of sulfate can be removed at high chloride concentrations when the chloride:sulfate ratio is lower. Sulfate removal was challenging for produced water from EOR and mining operations, with 576 and 918 mg/L sulfate, and 87,364 and 13,009 mg/L chloride, respectively. Measured sulfate removals were 8 and 70%, respectively. For practical use, weak base resins were able to be regenerated and their large retardation values allow for reasonable reactor dimensions