(225ah) Adsorption of Carbon Monoxide for Magnesium Production | AIChE

(225ah) Adsorption of Carbon Monoxide for Magnesium Production


Arndt, L. - Presenter, University of Minnesota - Duluth
Xie, W., University of Minnesota - Duluth
Davis, R., University of Minnesota Duluth
The world’s demand for magnesium continues to be on the rise. This creates the perfect
opportunity to introduce new forms of production. One proposed method first developed in late 1800,
is the carbothermic reduction of magnesium oxide. Magnesium oxide is heated in the presence of
carbon resulting in the release of carbon monoxide and magnesium vapor. However, it needs to be
operated under low pressure and high temperature. Of particular interest is the possibility of using a
solar reactor to react carbon directly with dolomite, allowing Mg to be produced with less energy and
fewer emissions than current approaches.

Unfortunately, immediately after the temperature begins to decrease, the magnesium vapor is
reverted to magnesium oxide by carbon monoxide at an extremely rapid rate. Over the years numerous
techniques have been developed to condense magnesium before it can be oxidized but none have been
a commercial success. One new technique currently under consideration is the use of a fluidized bed of
molecular sieves. The effluent vaper leaving the reactor could pass directly into the bed still at a high
temperature. Molecular sieves would be selected for their ability to adsorb the high-temperature
carbon monoxide allowing the magnesium to pass through the column. If this process can take place at
or above the reaction temperature, the magnesium vaper will not be oxidized. If any of the magnesium
forms magnesium oxide, the solid particles can be trapped in the bed. This will allow the magnesium
vapor to be condensed into pure Mg on the other side.

Currently, little research has been done into molecular sieves’ ability to adsorb gas at such
extreme temperatures. Doing so creates several challenges. Adsorption generally becomes less efficient
as the temperature increases. At a temperature as high as 2000 K many molecular sieves would be
destroyed. Despite these challenges, further research into this magnesium production technique should
be conducted. Figure 1 shows a schematic of our experimental setup. This work intends to determine
what type of molecular sieves are best suited for the task and what other variables will be of significance
in the design. To accomplish this, several molecular sieves have been purchased and will be used inside
a high-temperature furnace. Their ability to adsorb carbon monoxide will be monitored at different
temperatures, pressure, and column sizes. The results will be assessed and summarized for the next
phase of the research.