Solubility Of Carbon Dioxide In Li₂O-LiCl And Li₂CO₃-LiCl Molten Salt Systems

With the rapid development of modern industry,a huge amount of fossil fuels,such as coal,oil,and natural gas are consumed.At the same time,increasing amounts of CO2 are released into the atmosphere.The reduction of CO2 emissions and the rational utilization of CO2 have become a research hotspot.The molten salt electrolysis is one of the technologies to decompose CO2 into C and O2.It assimilated the intermittent renewable energy sources into reserved energy effectively.Owing to the lower liquidus temperature and wider electrochemical window than others,Li2O-LiCl and Li2CO3 melts have been widely used as the electrolyte system.Solubility of CO2 affects the electrolysis process deeply.In the present study,the solubility of CO2 in Li2O-LiCl melts and LiCO3-LiCl melts has been measured by Raman spectroscopy and pressure differential method,respectively.Effect of temperature and component of melts has been studied,which has provideed parameters for MSCC-ET in Li2O-LiCl and Li2CO3-LiCl melts.Firstly,a kind of Raman micro heating furnace and the dissolution reactor was designed and constructed which is used to observe the dissolving mechanism of gas in molten salt system at high temperature by Raman spectroscopy.The experimental results has demonstrated that it was suitable to observe the structure and component of molten salt by Raman spectroscopy under 900?.Based on the device mentioned above,the solubility of CO2 in Li2O-LiCl containing 4-8wt%Li2O was studied by Raman spectroscopy.The Li2SO4 was taken as external reference to calculate the content of Li2CO3 transformed from Li2O.The results have shown that the optimal additive amount of Li2SO4 is 13.33wt%,and the solubility of CO2 increases with Li2O content.The CO2 solubility reaches maximum with the value of 0.1105 gCO2/gmelt at 650?,when the content of Li2O is 8wt%,and the conversion efficiency of Li2O in molten salt system reached 94.19%.According to the dissolved gas reaction equation,the thermodynamic data of CO2 dissolved in LiClLi2O melts were calculated.The more content of Li2O was added in the melts,the more negative the dissolution enthalpy of CO2 solubility is,the more heat were released.However,the effect of temperature on enthalpy change is negative.Finally,the solubility of CO2 in Li2CO3-LiCl molten salt system has been studied using pressure differential method.The effects of temperature and Li2CO3 content on CO2 solubility were comprehensively studied.The results have shown that the solubility of carbon dioxide in LiCO3-LiCl melt increased with the content of Li2CO3.With the temperature increasing,the CO2 solubility was decreased.The value of CO2 solubility reaches maximum with the value of 3.965 × 10-7gCO2/gmelt at 600?,when the content of Li2CO3 is 50 mol%.The calculated thermodynamic data for CO2 dissolved in these melts revealed that the process of carbon dioxide dissolved in the Li2CO3-LiCl melt was exothermic and unspontaneous.It is more difficult to dissolve for CO2 when increasing the temperature.The more content of Li2CO3 was added in the melts,the more heat was released.