An integrated process for the simultaneous desalination of reject brine and CO2 mineralization

The State of Qatar has seen considerable expansion in its gas industry in recent years, becoming the largest exporter of liquefied natural gas (LNG) globally, with about 31% of the market share in 2014. Qatar further plans to expand its LNG export from 77 MMT per annum to 110 MMT in next 5 years. Qatar's economic success is a story of 'Gas Monetization'' resulting in immense progress and prosperity of the country and in line with the vision statement laid out in the 'Qatar National Vision 2030'. While natural exploration and monetization has had a great contribution and growth to the economy of Qatar, it has resulted in significant amount of CO2 emissions as well. In addition to CO2 emissions, another challenge in terms of managing waste in Qatar and in the region is 'Reject Brine' which is generated by the desalination of seawater to generate potable water for domestic as well as various industrial consumption. It is estimated that Qatar generates about 6 million m3 of reject brine per day, which is often sent back to the same source of the intake seawater. In spite of the development of new and highly efficient desalination processes, the management of reject brine still needs improvement. Managing reject brine is often a major economic and environmental challenge to most desalination plants, especially those involving thermal desalination. Conventional management methods have proved to be ineffective and often lead to adverse impacts on the environment. This research project focuses on the, 'Development of an Integrated System for Simultaneous Treatment of Reject Brine and Mineralization of CO2'. The novel, three-step integrated system will involve the combination of an inert-particles spouted bed reactor (IPSBR) and a membraneless electrolyzer to sequester CO2, reduce the salinity of the reject brine and, at the same time, convert these wastes into useful products. The research will be carried out through several work packages, starting with the collection and characterization of various reject brine samples from different sources in Qatar. The proposed process consists of three primary steps. First, the reject brine is contacted with a gas stream containing different concentrations of CO2 to reduce the concentration of magnesium and calcium ions in the brine by converting them into valuable carbonates (additives to cement). The reaction will be carried out in a newly patented, inert-particles spouted bed reactor system, which is specially designed for gas-liquid contact and is characterized by systematic intense mixing due to the motion of the inert particles within the bed. Excellent mixing is generated by the gas jet injected through an orifice in the bottom of the reactor, while the inert particles also provide a high gas-liquid interfacial area for effective mass transfer between the gas and liquid phases. In the second step, the pretreated brine is then fed to a membraneless electrolyzer that converts a portion of the aqueous brine solution into an alkaline effluent stream containing sodium hydroxide (NaOH) and another portion into an acidic effluent stream containing hydrochloric acid (HCl). Simultaneously, the electrolysis process generates valuable clean and green hydrogen and oxygen, which may be recombined in a fuel cell to recuperate electrical power and produce high purity fresh water (alternate way to produce water from brine and/or sea-water). The electrolyzer will employ selective electrocatalysts developed at Columbia University to allow for oxygen evolution at the anode in the chloride-containing environment. Finally, the alkaline stream is then sent to another spouted bed reactor, where CO2 reacts with NaOH to form sodium bicarbonate. Experimental design will be carried out to determine the optimum conditions for all three key steps and the results will be used to design a bench-scale prototype of the system for continuous operation. Demonstration of the integrated system will represent the final work package of the proposed research where the efficiency and stability of the designed integrated system will be evaluated and optimized. The proposed combination of IPSBR and the membraneless electrolyzer has never been reported in the literature, and for the first time such an approach will be evaluated for the desalination of reject brine and mineralization of CO2. The investigators are uniquely positioned to successfully carry out the proposed research and are confident this project will lead to a breakthrough in the simultaneous treatment of reject brine, capture and mineralization of CO2, and generation of clean/green hydrogen fuel. The successful outcome of this project will lead to the development of an effective, patentable technology that will contribute to mitigating the negative impact of CO2 emissions and, at the same time, significantly reduce the salinity of reject brine so that it can be reused for irrigation purposes or low salinity flooding for enhanced oil recovery, thus addressing two key waste management challenges in Qatar. It is also worth noting that the State of Qatar is moving forward to accomplish its ambitious goals of the National Vision 2030, which focuses on human development, social development, economic development and environmental development. Research in brine management and reduction of CO2 emissions can contribute effectively to achieving at least three of the main pillars of the Qatar Vision 2030, namely social development, economic development and environmental development.