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.