Thermogravimetric Analysis of Modified Hematite by Methane (CH4) for Chemical-Looping Combustion: A Global Kinetics Mechanism

Iron oxide (Fe 2 O 3 ), known in its natural form as hematite, is potentially able to capture CO 2 through the chemical-looping combustion (CLC) process. Magnesium (Mg) is an effective methyl-cleaving catalyst, and as such it was combined with hematite to assess any possible enhancement to the kinetic rate of the reduction of Fe 2 O 3 with methane. Therefore, in order to evaluate the effectiveness of Mg as a hematite promoter, the behaviors of Mg-modified hematite samples (hematite–5% Mg(OH) 2 ) were assessed for any enhancement to the kinetic rate of the CLC process. The Mg-modified hematite was prepared by hydrothermal synthesis. The reactivity experiments were conducted in a thermogravimetric analyzer using a continuous stream of CH 4 (at concentrations of 5, 10, and 20%) at temperatures ranging from 700 to 825 °C over 10 oxidation–reduction cycles. The mass spectroscopic analysis of the product gas indicated the presence of CO 2, H 2 O, H 2, and CO in the gaseous product. The kinetic data obtained by isothermal experiments at the reduction step are well fitted by two parallel rate equations. The modified hematite samples showed higher reactivity than the unmodified hematite samples during reduction at all the investigated temperatures.