Novel Adsorbents For The Removal Of Oil From Produced Water

Abstract

Produced water is water that is brought up to the surface of the well during oil and gas operations. Almost all oil and gas wells generate huge amounts of produced water as part of the production process. These large volumes of water are estimated to be over 437 million barrels per day. This number most likely will continue to rise due to the increase in energy demand. For the sustainable development of oil and gas fields, managing produced water in an effective manner is a key issue. There are several methods explored for produced water management including recycle, reinjection and disposal back into the environment and all of which require an effective treatment method prior to reuse. Adsorption, a prominent method for water treatment due its high efficiency at low concentrations, is implemented widely for tertiary treatment. Due to its high adsorption capacity, activated carbon has always been the most commonly used adsorbent in the industries worldwide. However, due to its high cost of regeneration, it is becoming a less attractive option. Recently, synthetic resins are showing potential as an alternative to activated carbon adsorbents. In this study, the application of four commercial synthetic resins for the removal of emulsified oil from produced water was investigated. Key experimental parameters such as adsorbent dosage, contact time, initial oil concentration and pH were evaluated for Optipore L493, Amberlite IRA 958, Amberlite XAD 7 and Lewatit AF 5. Oil removal rates upwards of 98% were achieved using AF 5, XAD 7 and L493. IRA 958 recorded very modest removal rates of less than 25%. Isotherm data werefurther investigated and fitted using Langmuir, Freundlich, Toth, Flory Huggins and Dubinin-Radushkevich models. The Freundlich model showed the best representation of the adsorption process onto XAD 7. The Toth model presented the best illustration of the adsorption process onto L 493 while Dubinin-Radushkevich best described the removal using AF 5 resin. Kinetic studies assessing the rate of removal for each resin were conducted and results fitted using pseudo-first and second order equations in addition to intraparticle diffusion models. Experimental results were best fitted using pseudo second order kinetics. The study confirmed the applicability of the resins for the removal of oil from produced water. Chemical regeneration is conducted to study the synthetic resin’s ability for regeneration and reuse. Solvents used for this part of the study include two organic solvents (methanol and ethanol), 1 M NaOH and D.I. water heated to 65 °C. Experimental results indicate that XAD 7 was completely regenerated using both organic solvents. AF 5 was also completely regenerated using methanol and D.I. water, while NaOH completely regenerated L493. To further support this data, resins were further analyzed at a clean state and after regeneration using an organic elemental analyzer.