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Conversion of CO₂ and saline water to value-added chemicals and desalinated water Dara, Mohammad Saad

Abstract

Two electrochemical approaches that simultaneously convert carbon dioxide and high salinity brines to desalinated water and value-added chemicals in the form of inorganic acids and carbonate salts were demonstrated. In the first method, a multi-compartment electrodialysis cell module using anion exchange and cation exchange membranes, and a Pt/Ir-coated Ti anode and Ti mesh cathode was used to produce HCl and NaHCO₃ products from a carbonic acid and sodium chloride solution. Under an applied voltage inorganic carbon salts and acids were produced. A mathematical model for this electrodialysis cell configuration was developed to better understand limitations within the cell which were not available from experimental data including concentration profiles within the intra-membrane channels. In the second method, a first of a kind 5-compartment electrochemical cell including an anode, cathode and three electro-dialytic compartments was used. Water was converted to oxygen and protons at the anode while gaseous O₂ and CO₂ were converted to bi(carbonate) or hydroxide ions at the cathode. The three central electrodialysis compartments combine the ions present in the saline water with the products of the anode and cathode to produce value-added chemicals and desalinated water. A custom-built electrochemical cell with an active area of 3.24 cm² containing an array of two anion and cation exchange membranes each, Pt/C catalyzed cathode and titanium anode electrodes were used. The cell was investigated to understand the different factors affecting cell performance. Increasing concentrations of hydrochloric acid and bi(carbonate)/hydroxide salts was observed in the respective compartments over 24-hour periods of testing. Current efficiencies of alkaline (bicarbonate, carbonate or hydroxide) ions and proton production were as high as 71% and 96%, respectively. Polarization losses across the different compartments of the electrochemical cell were mapped to determine the source of overpotentials with different gas compositions. The new electrochemical cell platform is scalable and was used to successfully desalinate and convert carbon dioxide to chemicals. The process shows considerable commercial potential and has been scaled-up to a commercial module for deployment with different industrial operations within the oil and gas, and mining sectors.

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Attribution-NonCommercial-NoDerivatives 4.0 International

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