Conditions of stability for (Li2CO3 + Li 2O) melts in air

Valery Kaplan, Ellen Wachtel, Igor Lubomirsky

Research output: Contribution to journalArticle

14 Citations (Scopus)

Abstract

Characterizing the equilibrium between molten (Li2CO3 + Li2O) and CO2 is important for a number of applications ranging from carbonate fuel cells to Li industrial production. The equilibrium pressure of CO2 was measured above (Li2CO3 + Li2O) mixtures containing mole fraction of lithium oxide, xLi 2O, between 0.01 and 0.06 and heated within the temperature range (1073 to 1248) K. These data were used to evaluate the enthalpy and entropy of thermal decomposition of Li2CO3. For 0.02≤xLi 2O≤0.06, both values remain constant to within experimental uncertainty: ΔH = (275 ± 5) kJ · mol-1 and ΔS = (179 ± 4) J · mol-1 · K-1. For mole fraction of lithium oxide 0.01≤xLi2O≤0.02, both ΔH and ΔS decrease considerably with decreasing concentration of the oxide. Nevertheless, they remain much larger than the values calculated for the decomposition of Li2CO3 based on thermodynamic quantities reported for the formation of CO2, Li2O, and Li 2CO3: ΔHs = 148 kJ · mol -1 and ΔSs = 79 J · K-1 · mol-1. We attribute this discrepancy to the solubilization of Li 2O by Li2CO3. Using our derived thermodynamic parameters, we can predict the existence of a range of temperatures and concentrations of Li2O in the Li2CO3 melt that are in equilibrium with atmospheric CO2 or are capable of absorbing CO2 from air. Experimentally, it was verified that, following melting at 1008 K, a Li2CO3 melt is stable in air at 998 K for at least 30 h without signs of Li2O precipitation. The stability of the melt is attributed to partial decomposition of Li2CO3 into Li2O, which decreases the liquidus temperature and reduces the equilibrium partial pressure of CO2. Our findings prompt a revised view of the thermal stability of Li2CO3 melts in air.

Original languageEnglish
Pages (from-to)1623-1627
Number of pages5
JournalJournal of Chemical Thermodynamics
Volume43
Issue number11
DOIs
Publication statusPublished - Nov 2011

Fingerprint

Oxides
Lithium
lithium oxides
air
Air
Thermodynamics
Decomposition
Carbonates
decomposition
Partial pressure
Temperature
thermodynamics
Molten materials
Fuel cells
Enthalpy
liquidus
Melting
Pyrolysis
Thermodynamic stability
Entropy

Keywords

  • Carbon dioxide
  • Lithium carbonate
  • Lithium oxide
  • Molten carbonate
  • Phase equilibrium

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Atomic and Molecular Physics, and Optics
  • Materials Science(all)

Cite this

Conditions of stability for (Li2CO3 + Li 2O) melts in air. / Kaplan, Valery; Wachtel, Ellen; Lubomirsky, Igor.

In: Journal of Chemical Thermodynamics, Vol. 43, No. 11, 11.2011, p. 1623-1627.

Research output: Contribution to journalArticle

Kaplan, Valery ; Wachtel, Ellen ; Lubomirsky, Igor. / Conditions of stability for (Li2CO3 + Li 2O) melts in air. In: Journal of Chemical Thermodynamics. 2011 ; Vol. 43, No. 11. pp. 1623-1627.
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N2 - Characterizing the equilibrium between molten (Li2CO3 + Li2O) and CO2 is important for a number of applications ranging from carbonate fuel cells to Li industrial production. The equilibrium pressure of CO2 was measured above (Li2CO3 + Li2O) mixtures containing mole fraction of lithium oxide, xLi 2O, between 0.01 and 0.06 and heated within the temperature range (1073 to 1248) K. These data were used to evaluate the enthalpy and entropy of thermal decomposition of Li2CO3. For 0.02≤xLi 2O≤0.06, both values remain constant to within experimental uncertainty: ΔH = (275 ± 5) kJ · mol-1 and ΔS = (179 ± 4) J · mol-1 · K-1. For mole fraction of lithium oxide 0.01≤xLi2O≤0.02, both ΔH and ΔS decrease considerably with decreasing concentration of the oxide. Nevertheless, they remain much larger than the values calculated for the decomposition of Li2CO3 based on thermodynamic quantities reported for the formation of CO2, Li2O, and Li 2CO3: ΔHs = 148 kJ · mol -1 and ΔSs = 79 J · K-1 · mol-1. We attribute this discrepancy to the solubilization of Li 2O by Li2CO3. Using our derived thermodynamic parameters, we can predict the existence of a range of temperatures and concentrations of Li2O in the Li2CO3 melt that are in equilibrium with atmospheric CO2 or are capable of absorbing CO2 from air. Experimentally, it was verified that, following melting at 1008 K, a Li2CO3 melt is stable in air at 998 K for at least 30 h without signs of Li2O precipitation. The stability of the melt is attributed to partial decomposition of Li2CO3 into Li2O, which decreases the liquidus temperature and reduces the equilibrium partial pressure of CO2. Our findings prompt a revised view of the thermal stability of Li2CO3 melts in air.

AB - Characterizing the equilibrium between molten (Li2CO3 + Li2O) and CO2 is important for a number of applications ranging from carbonate fuel cells to Li industrial production. The equilibrium pressure of CO2 was measured above (Li2CO3 + Li2O) mixtures containing mole fraction of lithium oxide, xLi 2O, between 0.01 and 0.06 and heated within the temperature range (1073 to 1248) K. These data were used to evaluate the enthalpy and entropy of thermal decomposition of Li2CO3. For 0.02≤xLi 2O≤0.06, both values remain constant to within experimental uncertainty: ΔH = (275 ± 5) kJ · mol-1 and ΔS = (179 ± 4) J · mol-1 · K-1. For mole fraction of lithium oxide 0.01≤xLi2O≤0.02, both ΔH and ΔS decrease considerably with decreasing concentration of the oxide. Nevertheless, they remain much larger than the values calculated for the decomposition of Li2CO3 based on thermodynamic quantities reported for the formation of CO2, Li2O, and Li 2CO3: ΔHs = 148 kJ · mol -1 and ΔSs = 79 J · K-1 · mol-1. We attribute this discrepancy to the solubilization of Li 2O by Li2CO3. Using our derived thermodynamic parameters, we can predict the existence of a range of temperatures and concentrations of Li2O in the Li2CO3 melt that are in equilibrium with atmospheric CO2 or are capable of absorbing CO2 from air. Experimentally, it was verified that, following melting at 1008 K, a Li2CO3 melt is stable in air at 998 K for at least 30 h without signs of Li2O precipitation. The stability of the melt is attributed to partial decomposition of Li2CO3 into Li2O, which decreases the liquidus temperature and reduces the equilibrium partial pressure of CO2. Our findings prompt a revised view of the thermal stability of Li2CO3 melts in air.

KW - Carbon dioxide

KW - Lithium carbonate

KW - Lithium oxide

KW - Molten carbonate

KW - Phase equilibrium

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