Solubility of CO_2 in the Molten Li_2CO_3 + Na_2CO_3 + K_2CO_3 Eutectic Mixture at 973 K

摘要

The solubility of carbon dioxide in the molten Li_2CO_3 + Na_2CO_3 + K_2CO_3 mixture at 973 K has been determined by potentiometric titration of samples of the melt saturated with carbon dioxide at a pressure of 1 atmosphere. The solubility value deduced in this way amounts to 10~(-1) mol.l~(-1) which is surprisingly high if it is compared with the low current densities observed for the electrochemical reduction of CO_2 in saturated melts. In order to explain this controversial situation it is proposed that CO_2 dissolves in molten carbonates principally as dicarbonate ions C_2O_5~(2-). This assumption is strengthened by a theoretical investigation which allows to calculate a free enthalpy value of - 142kJ.mol~(-1) for the production of C_2O_5~(2-) by the reaction of CO_2 with CO_3~(2-).