NiO/Al2O3 oxygen carriers for chemical-looping combustion prepared by impregnation and deposition–precipitation methods

Abstract

Ni-based oxygen carriers (OC) with different NiO content were prepared by incipient wet impregnation, at ambient (AI), and hot conditions (HI) and by deposition-precipitation (DP) methods using -Al 2 O 3 and -Al 2 O 3 as supports. The OC were characterized by BET, Hg porosimetry, mechanical strength, TPR, XRD and SEM/EDX techniques. Reactivity of the OC was measured in a termogravimetric analyzer and methane combustion selectivity towards CO 2 and H 2 O, attrition rate, and agglomeration behaviour were analyzed in a batch fluidized bed reactor during multicycle reduction-oxidation tests.XRD and TPR analysis showed the presence of both free NiO and NiAl 2 O 4 phases in most of the OC. The interaction of the NiO with the alumina during OC preparation formed NiAl 2 O 4 that affected negatively to the OC reactivity and methane combustion selectivity towards CO 2 and H 2 O during the reduction reaction. The NiO-alumina interaction was more affected by the support type than by the preparation method used. The NiO-alumina interaction was stronger in the OC prepared on -Al 2 O 3 . 2The OC were evaluated in the fluidized bed reactor with respect to the agglomeration process.OC prepared by the AI and HI methods with NiO contents up to 25 wt%, OC prepared by the DP method on -Al 2 O 3 with NiO content lower than 30 wt%, and OC prepared by the DP method on -Al 2 O 3 with a NiO content lower than 26 wt% did not agglomerated. OC that agglomerated showed an external layer of NiO over the particles. It seems that the most important factor affecting to the formation of the external NiO layer on the OC, and so to the agglomeration process, was the metal content of the OC. The attrition rates of the OC prepared using -Al 2 O 3 as support were higher than the ones prepared using -Al 2 O 3 as support, and in general the attrition rates of all the OC were low.The OC prepared by AI, HI or DP methods on -Al 2 O 3 as support had appropriated characteristics to be used in the chemical-looping combustion process.

Syngas combustion in a chemical-looping combustion system using an impregnated Ni-based oxygen carrier

“…Attrition data obtained during these tests were similar to that obtained by Gayán et al [34] for an impregnated OC using CH 4 as fuel gas. After 20 cycles, the attrition rates decreased and were almost constant, with a weight loss about 0.01% per cycle.…”

“…A nickel-based oxygen carrier was prepared by the hot incipient wet impregnation (HIWI) method on -Al 2 O 3 to be used in this work [34]. Previous studies showed that the highest reactivity of the Ni-based OC using …”

Progress in Chemical-Looping Combustion and Reforming technologies

“…Boudouard reaction. The carbon formation has been systematically observed in batch mode reactors -TGA, fixed bed or fluidized bed-for Ni-based particles because both reactions can be catalyzed by metallic nickel [144][145][146][147][148][149][150][151][152][153][154][155][156][157][158]. Carbon formation was strongly dependent on the availability of oxygen.…”

“…To increase the reactivity and regenerability of the oxygen-carrier particles, a number of Ni-based solid particles fashioned by different preparation methods and using different compounds as support material have been tested. Spray drying [181], incipient impregnation [151], and mechanical mixing [37] has been used considering the capability of scaling-up for industrial application and the potential to reduce particle production costs. [165,211], which has poor reactivity for CLC [212].…”

“…For Ni-based oxygen-carriers the unconverted products were H 2 and CO when the temperature was low [160] or the oxygen in the particles was depleted [145][146][147]153,162,172,215]. In some cases, even though methane was fully converted, H 2 and CO can be significantly high for low reactive oxygen-carriers [150,151,157].…”