A novel experimental method to study metal vapor condensation/oxidation: Mg in CO and CO2 at reduced pressures

Abstract

A novel method is presented to study magnesium metal vapor condensation/oxidation in CO and CO 2 atmosphere at reduced pressures. Mg(s) was evaporated and mixed with an equimolar amount of CO or CO 2 at 1000°C after which the gaseous mixture flowed through an air cooled tubular condenser. Measurements of the axial temperature profile, calculation of partial pressures and analysis of deposits within the condenser allowed for identification of deposition/condensation onset temperatures, supersaturation ratio and reaction mechanism. In the presence of CO 2 , rapid oxidation of Mg(g) has been observed. In the presence of CO, no Mg(g) oxidation was found above 950°C. Mg(g) oxidation observed at lower temperatures is believed to be initiated by CO disproportionation. The proposed mechanism is able to explain the increase in Mg metal yield with decreasing CO partial pressure. At a CO partial pressure <3 mbar, high Mg metal mass yields of >90w% were found. The presented method is applicable to the study of a variety of metal vapor/oxidizer combinations e.g. of interest in metal and solar fuel production.

Experimental carbothermal reduction of MgO at low pressure using concentrated solar energy

“…Considering T pyro minus 200 K (Table 2), the maximum temperature reached in experiments 32 and 33 was close to 2000 K. The high Mg content obtained in these two experiments with adequate physico-chemical parameters and heat treatment proved that the reversion reaction during the experiments and the oxidation during the collection are weak. This is mainly due to low partial pressure of CO and CO 2 during the whole duration of the experiments (< 10 Pa and < 1 Pa respectively for PCO and PCO 2 ) [27]. Using an improved collection process of the powders (collection on all the metallic sections, better system to filter the particles…), higher metallic yields close to 65-70 m% could be obtained.…”

“…The Magsonic TM process used a Laval nozzle at temperature above 1970 K and at atmospheric pressure with reversion below 10%, which demonstrated the possibility to obtain high Mg yields [26]. Finally, it had been recently demonstrated that rapid oxidation of Mg (g) occurred in the presence of CO 2 and that it is necessary to have low CO and CO 2 partial pressures to obtain high metal yield [27] .…”

On the prevailing reaction pathways during magnesium production via carbothermic reduction of magnesium oxide under low pressures

“…  (see Fig. 2) were estimated combining balance eqns (12), (14), and (16) for the O 2 -Ar sweep and eqns (13) and (15) for the CO 2 -Ar sweep as…”

“…This scenario would impose the equality of the extents of the reverse reactions (4) and (5), i.e.   4 5  * * , thereby making the Boudouard reaction only a step of the reverse overall reaction (1), as suggested by Hischier et al 15…”

“…In addition, it has been demonstrated that lower CO partial pressures drastically decrease the severity of the reverse reaction (1), which takes place during cooling of the product mixture. 14,15 These benefits thus present a strong incentive for investigating the CTR under vacuum, as they may compensate for the additional pumping work required to maintain low reaction pressures.…”