Thermodynamic Analysis and Reduction of Bismuth Oxide by Ethanol

In this study, ethanol (C₂H₅OH) was used as an alternative reducing agent for Bi₂O₃ because ethanol is renewable, increasingly available, and low in toxicity. Thermodynamic analysis was performed to predict experimental conditions for Bi formation in the Bi₂O₃-C₂H₅OH-Ar system at Ar/C₂H₅OH molar ratio of 10.5. Ar was used as a carrier gas for ethanol. Bi₂O₃ reduction kinetics was investigated at 600 K to 800 K (327 °C to 527 °C) at Ar flow rate 85 sccm. Ar flow rate was also varied at 600 K and 800 K (327 °C and 527 °C) in order to clarify the mechanism controlling the process. Mass measurements and XRD analyses were carried out to determine the extent of reduction. Fractional conversion increased with time and temperature. Full reduction time decreased from ~180 minutes at 600 K (327 °C) to ~30 minutes at 700 K and 800 K (427 °C and 527 °C). The reduction process was external mass transfer limited (Q _a = 7.2 kJ/mole) above 700 K (427 °C). It was controlled by intrinsic chemical kinetics (Q _a = 54.7 kJ/mole) below 700 K (427 °C). In the mass-transport-controlled regime, the extent of reduction increased with flow rate as predicted by a mass-transport theory. Possible reaction pathways were discussed using the thermodynamic and experimental results.