(Ni-based oxygen carriers obtained by different synthesis methods for use in the chemical looping reforming of methane process)

Abstract

Oxygen carriers containing Ni, La, Al and Mg were synthesized successfully by microwave assisted self-combustion (N6C), microwave assisted self-combustion followed by wet impregnation (N6CI) and co-precipitation (N6CP), for their application in the production of hydrogen from methane chemical recirculation systems with CO₂ capture. The materials were prepared following the general formula Ni_x/La₂O₃/Al₂O₃/MgO, where x = 60% by weight, the remainder being related to lanthanum (8%), aluminum (30%) and magnesium (2%) oxide. The obtained solids were characterized by X-ray diffraction), temperature programmed reduction and activity through methane reforming process with chemical recirculation. Reactivity tests were conducted at 900 ºC, where the sample was initially subjected to 8 cycles of OSC (oxygen storage capacity), and finally were carried out two reaction cycles, with each cycle containing 15 pulses of methane and 15 pulses of oxygen. The results of the characterizations indicate that the methods used were appropriate for obtaining different materials with different properties. Generally, the carriers showed excellent percentage of CH₄ conversion, and high hydrogen production. The carrier N6CP exhibited the best performance to syngas production with H₂/CO ratio equal to 2 on the 15^th pulse, as well as being appointed as being the most resistant to deactivation by coke and higher oxidation potential, consuming 100% O₂ up to the 12^th pulse. In turn, the N6CI lost enough performance throughout the cycles and the N6C formed larger amount of coke, revealing the peculiarities of the synthesis methods employed. According to the reaction products formed in the reduction step with CH₄, it can be concluded that the most frequent reactions were catalytic cracking, reforming and combustion.

Keywords:
oxygen carriers; microwave-assisted combustion; co-precipitation; chemical looping reforming