Pressure dependent kinetics of magnesium oxide carbothermal reduction

• Published in: Thermochimica acta Vol. 636; no. C; pp. 23 - 32
• Main Authors: Chubukov, Boris A., Palumbo, Aaron W., Rowe, Scott C., Hischier, Illias, Groehn, Arto J., Weimer, Alan W.
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 20.07.2016; Elsevier
• Subjects: Carbon dioxide; Carbothermal reduction; Contact; Conversion; Gas analysis; Isoconversional; Kinetics; Magnesium oxide; Model-free; Reduction; Stoichiometry; Unity; Isoconversional; Model-free; Carbothermal reduction; Kinetics
• ISSN: 0040-6031; 1872-762X
• DOI: 10.1016/j.tca.2016.03.035

•Maximum reaction rate observed experimentally at low vacuum conditions.•Model developed for continuous prediction of reaction rate with T & P.•Reaction mechanism consists of two parallel reactions.•High yield of Mg metal obtained experimentally. The rate of MgO carbothermal reduction was studied at temperatures from 1350 to 1650°C and pressures from 0.1–100kPa based on product gas analysis at near isothermal conditions. For all temperatures the initial rate of carbothermal reduction increased inversely with pressure, and between conversions of 20–35% a transition occurred after which the reaction rate was maximum at 10kPa. Analysis of reacted pellets showed that the reaction stoichiometry, the ratio of C to MgO reacted, was less than unity and decreased with pressure indicating CO2 generation was more prevalent at elevated pressures. SEM imaging revealed the dissolution of C and MgO contact with conversion, and isoconversional analysis points to a change in the rate determining step between 1 and 10kPa. The given experimental observations argue the importance of mass transfer and gaseous intermediates. A kinetic model is formulated based on a macroscopic species balance with CO2 as the reaction intermediate.