Electrochemical Synthesis of Slaked Lime Utilizing a Diaphragm Flow Cell

Abstract

Slaked lime (Ca(OH)2) is one of the most widely utilized chemicals, with applications in diverse industries including construction, mining, water treatment, and chemical manufacturing. Currently, Ca(OH)2 is synthesized by coal-fired calcination of CaCO3 to make CaO, followed by exothermic hydration. Converting CaCO3 into Ca(OH)2 using electrochemically generated acid and base has attracted great interest because it could be powered by renewable electricity and would generate the CO2 byproduct in a pure form. Previous electrochemical Ca(OH)2 syntheses have incorporated the processing of calcium salts within the electrochemical cell to avoid acid–base recombination losses, but these cells have poor stability and high energy demand. Herein, we show that production of high-salinity acid and base solutions using a diaphragm flow cell (DFC) coupled with ex situ processing of CaCO3 substantially improves the efficiency of electrochemical Ca(OH)2 production. Using a closed loop with a simple KCl salt solution, we demonstrate the synthesis of >99% pure Ca(OH)2 for 0.088 to 0.10 kWh per mole at productive current densities of 158 to 334 mA cm–2.