Experimental evaluation of chemical systems for CO₂ capture by CaO in eutectic CaF₂-CaCl₂

Abstract

CO2 capture by CaO in molten salts is a variant of calcium looping in which the active substances (CaO/CaCO3) are dissolved or in a slurry with inorganic molten salts. One of the main advantages is the nonexistence of degradation in the reactivity between the active material and CO2. Previous research has revealed good absorption and desorption characteristics with CaO contents up to 20 wt% in eutectic CaF2-CaCl2. The hypothesis is that the formed CaCO3 continuously dissolves in the melt, leaving highly reactive CaO readily available for the incoming CO2. In the present study, the CaO content is increased to 40 wt%, and the absorption characteristics is investigated with focus on the sorption capacity and CO2 removal rate. The chemical system is also evaluated experimentally with regards to viscosity and solubility of the formed CaCO3 during CO2 absorption, with the aim of determining chemical upscaling limitations. The results show that the practical CaO content limit is 30 wt%, in which a sorption capacity of 20 g CO2/100 g sorbent is observed, without any deterioration of the reaction kinetics. For 40 wt% CaO, the sorption capacity is higher, but on the expense of the CO2 removal rate and CaO conversion. This is attributed to a significant increase in viscosity and the solubility limit of CaCO3 being exceeded.

Keywords

• co₂ capture
• calcium looping
• molten salts
• phase diagram
• viscosity