Promoting the Reduction Reactivity of Ilmenite by Introducing Foreign Ions in Chemical Looping Combustion

A new kind of ilmenite oxygen carrier was prepared by impregnating the raw ilmenite particles with K2CO3, Na2CO3, or Ca(NO3)(2). The cyclic reduction reactivity of the new oxygen carrier was investigated in a fluidized bed reactor. It has been found that the addition of foreign ions can significantly promote the reduction reactivity of ilmenite. The effect of foreign ions on enhancing the reduction reactivity of ilmenite is in the sequence of K+ > Na+ > Ca2+. The effect of the loading amount of K+ on increasing the ilmenite reactivity is in the sequence of 15 wt % K+ > 10 wt % K+ > 5 wt % K+. The reduction reactivity of the ilmenite impregnated with 15 wt % K+ can be improved similar to 8 times faster than that of the activated raw ilmenite. This reactivity reaches up to the same level of the synthetic Ni-based carrier. The modified ilmenite obtains a porous structure caused by the migration of K or Na ions. One possible explanation for the reactivity enhancement of ilmenite with the addition of foreign ions, especially K+ and Na+, is the migration of K+ or Na+. Another explanation may be the active principle of the alkali-rich phase formed between the foreign ions and titanium iron oxides, that is, K1.46Ti7.2Fe0.8O16 or Na2Fe2Ti6O16. This study proves that the reduction reactivity of the natural ilmenite can be promoted significantly by impregnating ilmenite with K+.