Solvay process

Abstract: DUAL ALKALI APPROACHES FOR THE CAPTURE AND SEPARATION OF CO 2 H.P. Huang † , Y. Shi # , W. Li # , and S.G. Chang * Environmental Energy Technology Division Lawrence Berkeley National Laboratory University of California Berkeley, CA 94720 Abstract The Solvay process utilizes two alkalis in sequential order to convert CO 2 to sodium carbonate for commercial use. The ability to transform CO 2 into sodium carbonate cost- effectively would be a breakthrough in CO 2 sequestration by providing benign long-term storage of CO 2 . However, the Solvay process was not designed for CO 2 sequestration and is not practical for use in the sequestration of CO 2 from fossil fuel power plants. This paper investigates methods to modify the process in order to make it effective for the control of power plant CO 2 emissions. The new modified process, called the Dual Alkali Approach, attempts to replace either or both bases, ammonia and lime, in the Solvay process with other compounds to make CO 2 capture and separation efficient. Ammonia was replaced with different amines in aqueous solutions of salts and it was found that bicarbonate precipitation did occur. A method to regenerate the amine in the second step has not been implemented. However, the second step in Solvay Process has been implemented without using lime, namely, ammonia has been regenerated from an ammonium chloride solution using activated carbon. The HCl adsorbed in the activated carbon was removed by water to regenerate the activated carbon. Introduction Existing techniques to sequester CO 2 from stationary power plants involve two steps. The first step uses an amine, as an alkali, to capture CO 2 from flue gas. The captured CO 2 is then stripped by steam at high temperatures. In the second step, the concentrated CO 2 gas is pressurized to supercritical CO 2 liquid and disposed of in geologic formations and/or the deep ocean. Although the pressurization of CO 2 is energy intensive, the first step accounts for two thirds to three fourths of the entire cost. In addition to the energy required for both steps, when large amounts of SO 2 and NOx are present in the flue gas reagent loss also occurs. The reagent loss arises due to the formation of heat stable salts such as amine sulfates and nitrates. As well as the extensive energy required to implement existing CO 2 sequestration techniques, there are also ecological concerns regarding the consequences of storing CO 2 in the ocean and in geological formations. Corresponding author, Email: SGChang@lbl.gov On leave from the College of Chemistry and Environmental Sciences, Wuhan University, P. R. China # On leave from the Department of Environmental Engineering, Zhejiang University, P.R. China

Abstract: Typically, CO2 electroreduction is coupled with oxygen evolution reaction (OER), which is highly energy consuming, and also costs alkalis formed at the cathode. Here, we use chlorine evolution reaction (CER), instead of OER, to integrate with CO2 electroreduction mediated by an efficient metal-nitrogen doped carbon catalyst derived from the mixture of nickel porphyrin and commercial carbon black. The combined system was evaluated in two electrolyzer configurations that have been adopted in the chlor-alkali process to produces CO, Cl2, and KHCO3 simultaneously. To allow continuous operation, we designed a continuously operating system to collect produced KHCO3 in a precipitate tank with improved techno-economics and efficient CO2 utilization. Also, it could serve as an environmental-friendly alternative to the Solvay process for soda production. This work may provide a new strategy for the design of CO2 electrolysis systems with better economic viability.