Desalination of produced water via CO2 + C3H8 hydrate formation

Abstract

Recent years have seen increased interest in gas hydrate production as a viable saline water desalination technique. Produced water is the liquid that is extracted from oil and gas fields and is typically salty. The management of produced water is a significant aspect of the petroleum industry because of its potential to serve as a source of fresh water for oil-producing nations with limited access to clean water, growing environmental concerns, and the strict laws governing the discharge of produced water into the environment. In this study, the effect of mixed gas (CO2 + C3H8 (70:30)) hydrate formation in treating produced water and kinetic studies on induction time, moles of gas consumed, rate, water recovery, and water-to-hydrate conversion were experimentally investigated. An aqueous solution with the same ion concentrations was prepared and experiments were performed at 275.15 K/277.15 K, 2.0 MPa, and 450 rpm. The findings unveiled that with an increase in salinity, the water recovery decreased showing the hindering effect of salts on mixed hydrate formation by reducing the solubility of mixed gas due to the strong electrostatic force of attraction between salt ions and water. A maximum of 67.3% water recovery was observed in 2.8 wt% produced water solution at 275.15 K, 2.0 MPa, and 450 rpm. Furthermore, the induction time increased by 52.64% in treating 2.8 wt% and a decrease in moles of gas consumed, water recovery, and water-to-hydrate conversion by 6.99%, 2.08%, and 9.69% compared to the deionized water system at 275.15 K. A removal efficiency of 47%-63% is achieved by using CO2 + C3H8 and the sequence of metal cation removal is in the order K+ > Na+ > Mg2+ > Ca2+ and anions SO42− > Cl− at 275.15 K. The results also showed that with a rise in the experimental temperature to 277.15 K the removal efficiency increased though the amount of hydrate formed is less. This study illustrates that the formation of mixed gas (CO2 + C3H8) hydrate can be used for treating produced water based on the water recovery, removal efficiency, electrical conductivity, and total dissolved solids results with lower energy consumption.