Production of Mg and Al using concentrated solar energy for future fuel applications

Dr. Jean Puig, Dr. Marianne Balat-Pichelin

A high energetic sustainable fuel must be produced, used and recycled in clean ways for future means of transportation. The combustion in air of magnesium or aluminum fine powders is highly energetic, produces only solid phases and thus does not emit greenhouse gases during transportation. The aim of this study is to prove that MgO and Al2O3 formed after combustion can be reduced to their native metals with high yield using concentrated solar energy. Thermodynamic calculations have already shown that the use of carbon agents mixed with MgO or Al2O3 and low pressures make the reduction process feasible at temperatures lower than 2000 K. In a preliminary work, the carbothermal reduction of MgO and Al2O3 using concentrated solar energy with an argon flow at 1000 Pa was carried out using the “Heliotron” reactor and allowed to obtain nanostructured powders with 70 – 80 wt.-% Mg. Taking these results into account, a new reactor “Sol@rmet” has been designed and by controlling reaction parameters (solar flux, temperature, time, CO emission…), Mg yield greater than 80 – 95 wt.-% in the collected powders has been reached. The main problems occurring in the carbothermal reduction of MgO have been attributed to a backward reaction reforming MgO powder and to a sintering process of MgO particles at high temperature. Reaction mechanisms and kinetics have been studied in order to improve Mg yield rates. First investigations on the carbothermal reduction of Al2O3 are also presented. Notably, a challenge in the aluminum production is to avoid the formation of some undesired by-products.