Towards electrifying cement production : electrochemically-enhanced dissolution of CaCO3 during water electrolysis under a pH-gradient

Details

Supervisors

Proost, Joris

Faculty

Ecole polytechnique de Louvain

Degree label

Master [120] : ingénieur civil en chimie et science des matériaux, à finalité spécialisée

Abstract

In 2019, the concept of a new type of reactor for the production of cement has been highlighted : the hybrid electrolyser. This new hybrid reactor idea is a step forward toward the decarbonization of the cement industry which is one of the most polluting ones. A neutral water electrolyser is used to convert CaCO3 into Ca(OH)2 while also producing H2 and a pure mix of O2 and CO2. The reviewed process is perfectly in line with the actual trend to electrify industrial processes and store excess renewable energy in the form of hydrogen. In this work, a laboratory-scale setup has been developed to study the operation of the hybrid electrolyser. A set of potentiostatic and galvanostatic experiments have been carried out with different couples of anode/cathode (DSA/Ni, DSA/Graphite, Ti/Ni) and two electrolytes (NaNO3, NaClO4). Especially, the results show that a pH gradient is formed in the electrolyser with a pH = 1 at the anode and pH = 11.5 at the cathode. The acidic anodic pH allows a complete dissolution of 500mg of CaCO3 at a current higher than 0.4A. However, the cathodic pH is not high enough to start the precipitation of Ca(OH)2. Still, the migration of calcium ions toward the cathode has been proven and an approached value for their mobility in 1M NaNO3 has been derived : µ = 9.63 +/- 3.52[10e−8m²/Vs]. The experiments also prove the simultaneous production of the gaseous streams but highlighted that the parasitic reduction of NO3- from NaNO3 prevents the production of H2 at the cathode. Moreover, estimations of the Faraday efficiencies highlighted a lack in the production of O2 with only 70% of the theoretical amounts produced. The quantity of CaCO3 which can be dissolved in water is greatly improved by the pH gradient created by the electrolyser. Finally, the design of the reactor must be modified to accommodate its main limitations, i.e. the slow migration of Ca2+ and the difficulty to precipitate Ca(OH)2 directly inside the setup.