Thermodynamics of gas phase chromium species: The chromium oxides, the chromium oxyhydroxides, and volatility calculations in waste incineration processes

Abstract

The thermodynamics of three gaseous chromium oxides and twelve gaseous chromium oxyhydroxides are assessed for application to chromium volatility calculations in waste incineration processes. For the oxyhydroxides, the thermodynamic properties, S 0(298), H 0(298) − H 0(0), −(G 0(T) − H 0(298)) T , and C p 0(T), are calculated by the molecular constant method using estimated molecular parameters. The enthalpies of formation, ΔH f 0(298), of the chromium oxides and the chromium oxyhydroxides are determined either from vapor pressure data when available or from bond energy correlations which use available data on the gaseous chromium oxyhalides. The thermodynamic constants, S 0(298), ΔH f 0(298), and H 0(298) − H 0(0), are tabulated for all fifteen gaseous species. Likewise, the thermodynamic functions, −(G 0(T) − H 0(298)) T and C p 0(T), are given in polynomial form as a function of temperature for ranges from 298 to 1000 K and 1000 to 3000 K. Equilibrium vapor compositions over Cr 2O 3(s) at fixed partial pressures of oxygen (0.10 atm) and water (0.10 atm) and temperatures in the range of 800 to 1600 K show that CrO 2(OH) 2(g) is the dominant vapor species with small contributions from CrO(OH) 3(g), CrO 3(g), CrO 2OH(g), and CrO(OH) 2(g).