Toward electrochemical synthesis of cement-An electrolyzer-based process for decarbonating CaCO3 while producing useful gas streams.

Cement production is currently the largest single industrial emitter of CO2, accounting for ∼8% (2.8 Gtons/y) of global CO2 emissions. Deep decarbonization of cement manufacturing will require remediation of both the CO2 emissions due to the decomposition of CaCO3 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 CaCO3 is decarbonated at low pH and Ca(OH)2 is precipitated at high pH, concurrently producing a high-purity O2/CO2 gas mixture (1:2 molar ratio at stoichiometric operation) at the anode and H2 at the cathode. We show that the solid Ca(OH)2 product readily decomposes and reacts with SiO2 to form alite, the majority cementitious phase in Portland cement. Electrochemical calcination produces concentrated gas streams from which CO2 may be readily separated and sequestered, H2 and/or O2 may be used to generate electric power via fuel cells or combustors, O2 may be used as a component of oxyfuel in the cement kiln to improve efficiency and lower CO2 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.