Toward electrochemical synthesis of cement—An electrolyzer-based process for decarbonating CaCO ₃ while producing useful gas streams

Abstract

Cement production is currently the largest single industrial emitter of CO ₂, accounting for ∼8% (2.8 Gtons/y) of global CO ₂ emissions. Deep decarbonization of cement manufacturing will require remediation of both the CO ₂ emissions due to the decomposition of CaCO ₃ to CaO and that due to combustion of fossil fuels (primarily coal) in calcining (∼900 °C) and sintering (∼1,450 °C). Here, we demonstrate an electrochemical process that uses neutral water electrolysis to produce a pH gradient in which CaCO ₃ is decarbonated at low pH and Ca(OH) ₂ is precipitated at high pH, concurrently producing a high-purity O ₂/CO ₂ gas mixture (1:2 molar ratio at stoichiometric operation) at the anode and H ₂ at the cathode. We show that the solid Ca(OH) ₂ product readily decomposes and reacts with SiO ₂ to form alite, the majority cementitious phase in Portland cement. Electrochemical calcination produces concentrated gas streams from which CO ₂ may be readily separated and sequestered, H ₂ and/or O ₂ may be used to generate electric power via fuel cells or combustors, O ₂ may be used as a component of oxyfuel in the cement kiln to improve efficiency and lower CO ₂ emissions, or the output gases may be used for other value-added processes such as liquid fuel production. Analysis shows that if the hydrogen produced by the reactor were combusted to heat the high-temperature kiln, the electrochemical cement process could be powered solely by renewable electricity.