Preparation and characterization of pelletized Mn-based sulfur sorbents

The global energy situation is changing slowly into new sustainable patterns of production and consumption. However, fossil fuels still lead the world energy outlook, covering more than 80% of the energy mix. Between other alternatives, biomass gasification and its derived energy forms such as biofuels, biogas, or low carbon hydrogen, will contribute to the energy transition, playing a major role in the next decades. Biomass gasification-derived syngas presents a major challenge regarding cleaning and conditioning steps due to the undesired components such as tar, particulate matter, nitrogen or sulfur compounds. Conventional methods for sulfur removal are not efficient in terms of energy, mainly due to low operation temperatures and large investments. Therefore, high-temperature desulfurization with solid sorbents is considered one of the alternatives. Within this project, Mn-based/γ-Al2O3, Mo-promoted sorbents are being developed to achieve a chemical looping desulfurization with sorption-regeneration cycles. The objective of this project is to synthesize and characterize a series of sorbents with different compositions (15% Mn and 2,5-10% Mo), in the form of egg-shell pellets. Three synthesis methods have been performed, namely using ethylene glycol as a hydrophobic solvent for both sequential and co-impregnation (EG-SQ and EG-Co) or glycerol as the precursor’s solvent for co-impregnation (GL-Co). GL-Co method presented the highest time efficiency results. Additionally, XRF analysis showed the highest loading with one impregnation can be achieved with this method. However, the preparation step needs to be further upgraded, due to the challenging handling of glycerol and deficient material properties in the final sorbents. On the other hand, both ethylene glycol methods showed a high standard in material properties. Time efficiency improved in EG-Co in comparison with EG-SQ. Despite being very similar for the three approaches, XRD patterns clearly displayed a higher formation of the mixed oxide MnMoO4 in both co-impregnation methods, which could entail an enhancement in the desulfurization efficiency, as MnMoO4 was previously found to play a role in the promotion mechanism. Sorbent textural properties such as surface area and pore volume were studied by N2 physisorption. Neither pore blockage nor large surface area decrease were reported. The egg-shell profile distribution was confirmed by SEM/EDS analysis, performing both line scans and elemental mapping. The egg-shell thickness was higher in ethylene glycol sequential impregnation (200µm) than co-impregnation (100µm). Besides, it also showed a dependency with impregnation time for the GL-Co approach