Evaluation of ilmenite, manganese ore, LD slag and iron sand oxygen carriers for chemical looping gasification with microalgae

Microalgae could be a sustainable feedstock for production of liquid biofuels. However, as such fuels contain significant fractions of reactive ash species, it is necessary to deploy synthesis routes which can handle such “dirty” fuels. Chemical-looping gasification (CLG) has the potential to convert such feedstocks and generate a concentrated syngas stream, a common precursor for liquid fuel production. Suitable functional oxygen carriers are key for CLG, and herein we report our new work in fluidized-bed tests with four oxygen carriers, namely ilmenite, MnGBhne, LD slag and iron sand. These materials are economically viable natural ores or industrial by-products. The oxygen carrier is reduced to different oxidation degrees (0.2, 0.5, 1) at typical temperatures (850, 900, 950 °C) to define equal material states prior to the gasification. We found that the LD slag and iron sand had the highest gasification rate and fluidized well without agglomeration, thus they are selected as suitable oxygen carriers for the process. Several factors including catalysis, water splitting and water-gas shift are comprehensively discussed with regard to the outstanding performance of LD slag and iron sand. Calcium catalysis is deemed as a key reason for the fast gasification and a mechanism of this is proposed.