Influence of spray drying suspension on the morphology of Fe-based oxygen carriers for chemical looping

Chemical looping reforming (CLR) and chemical looping combustion (CLC) are promising technologies with inherent CO2 capture for transforming fuels into syngas and energy respectively. Circulating oxygen carriers (OC) are used to transfer oxygen from mostly air to the fuel inside the process. Over the past years a variety of materials have been proposed for the role of oxygen carriers, ranging from bulk mineral powders to oxygen carrier particles engineered for shape, size and composition. Iron based materials are very promising and cost effective candidates with minor impact on the environment as compared to the toxic Ni-based OCs. Granulation by the industrial spray-drying technique is suitable for producing oxygen carrier particles with high sphericity and dimensions fit for the fluidized-bed reactors of the CL-process. The lifetime of the oxygen carriers in these reactors however strongly depends on their mechanical properties (as measured by the crushing strength and the attrition resistance) which is related with their morphology and porosity. As this morphology depends on the spray drying suspension, the relation between the additives used in the iron-based suspension and the morphology of the spray-dried particles is investigated in this work [1]. The influence of the concentration of the binder, dispersing agent and solids in the spray-drying suspensions and the intensity of the milling procedure on the morphology and microstructure of the resulting particles is studied by Hg-porosimetry, tapped density, optical microscopy and SEM. A controlled sintering treatment is used during post-processing of these spray-dried particles in order to further improve their mechanical properties before investigating their performance as oxygen carriers in the chemical looping process

Development of stable oxygen carrier materials for chemical looping processes : a review

This review aims to give more understanding of the selection and development of oxygen carrier materials for chemical looping. Chemical looping, a rising star in chemical technologies, is capable of low CO2 emissions with applications in the production of energy and chemicals. A key issue in the further development of chemical looping processes and its introduction to the industry is the selection and further development of an appropriate oxygen carrier (OC) material. This solid oxygen carrier material supplies the stoichiometric oxygen needed for the various chemical processes. Its reactivity, cost, toxicity, thermal stability, attrition resistance, and chemical stability are critical selection criteria for developing suitable oxygen carrier materials. To develop oxygen carriers with optimal properties and long-term stability, one must consider the employed reactor configuration and the aim of the chemical looping process, as well as the thermodynamic properties of the active phases, their interaction with the used support material, long-term stability, internal ionic migration, and the advantages and limits of the employed synthesis methods. This review, therefore, aims to give more understanding into all aforementioned aspects to facilitate further research and development of chemical looping technology

Developing sustainable iron-based oxygen carriers for chemical looping processes

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Robocasting of porous alumina hollow fibre monoliths by non-solvent induced phase inversion

3D printed hollow fibre structures are of interest for different separation processes. However, the preparation of such structures using robocasting is not evident due to their poor self-supporting properties after printing. We propose a method based upon non-solvent induced phase inversion to overcome this issue, and use this method for preparing porous alumina hollow fibre structures. The method uses a paste that contains alumina powders, polyetherimide as polymeric binder and N-Methyl-2-pyrrolidone as solvent, that is extruded through a concentric nozzle. A humid atmosphere is used to further solidify these extruded hollow fibres enabling the printing of both hollow 2D patterns and 3D monolithic structures. The resulting green samples are mechanically strong and can be easily handled without any shape deformation before thermal treatment

Processing and characterization of Fe-based oxygen carriers for chemical looping for hydrogen production

Until now various oxygen carrier particles have been proposed for use in chemical looping processes. Their chemical performance is determined not only by their composition and their microstructure/morphology but also by the reaction condition of the processes in which they are utilized. In the present work, iron based oxygen carriers supported on Al2O3 and MgAl2O4 were spray dried and heat treated to have a suitable morphology and sufficient mechanical properties for chemical looping. The MgAl2O4-support was in situ generated from MgO and Al2O3 by reaction sintering. After physical characterization and determining their compressive strength the oxygen carriers were tested in the chemical looping reforming process for producing syngas in a lab-scale batch fluidized-bed reactor. The suitability of utilizing steam regeneration was investigated for both oxygen carriers by relating their chemical performance to their composition. It was shown that the Al2O3-supported oxygen carrier deactivated after 9 cycles of steam regeneration because of the accumulation of an in-situ formed FeAl2O4-phase due to an irreversible reaction between support and the active phase. This deactivation was successfully avoided by replacing the Al2O3-support with MgAl2O4. This Fe2O3/MgAl2O4 oxygen carrier could be subsequently regenerated by steam, making it suitable for chemical looping for hydrogen generation

Processing and characterization of Fe-based oxygen carriers for chemical looping for hydrogen production

Chemical looping reforming (CLR) and chemical looping combustion (CLC) are promising technologies with inherent CO2 capture for transforming fuels into syngas and energy respectively. Circulating oxygen carriers (OC) are used to transfer oxygen from mostly air to the fuel inside the process. Over the past years a variety of materials have been proposed for the role of oxygen carriers, ranging from bulk mineral powders to oxygen carrier particles engineered for shape, size and composition. A lot of attention has been focused towards the development of Ni-based oxygen carriers due to their good reactivity, conversion and mechanical stability. However the cost, susceptibility towards S-containing impurities and their toxicity are key drivers to develop Ni-free materials. Oxygen carriers based on Fe-oxides are promising because of their lower cost and diminished impact on health and environment. Nevertheless, they also need good thermo-chemo-mechanical properties and thus a sufficient lifetime to be applicable in industrial CL-processes. The longevity of the oxygen carriers in the coupled fluidised bed reactors can be limited by two factors, such as their fragmentation and attrition leading to smaller particles inhibiting their fluidisation as well as their chemical deactivation. Granulation by the industrial spray drying technique appears to yield oxygen carrier particles with high sphericity and good fluidization properties. In addition, a microstructure is obtained that on the one hand aims at thermo-chemo-mechanical integrity and high attrition resistance, and on the other hand at intimate contact between the solid and gaseous phases. However, spray-drying does not appear to be used for producing Fe-based OC thus far. This work emphasises the colloid chemistry of concentrated suspensions used for spray-drying, the development of Fe-based OC by granulation of primary raw materials and the subsequent processing and heat treatment of the oxygen carriers for hydrogen production by chemical looping. To reach the objectives, a systematic approach is used. At first the role of the preparation of the spray dry suspension and the granulation conditions on the morphology of the particles has been investigated. Secondly, the effect of the sinter process was studied. A correlation between tapped density, strength and attrition resistance of the heat-treated materials was observed. Finally, the chemical performance of these Fe-based oxygen carriers was examined in a small scale batch reactor. The chemical composition of the OC was (ex situ) monitored in view of the enhancement of the chemical properties and long term stability thereof by altering the composition and microstructure of synthesised oxygen carriers

3D printed Ni/Al2O3 based catalysts for CO2 methanation : a comparative and operando XRD-CT study

Ni-alumina-based catalysts were directly 3D printed into highly adaptable monolithic/multi-channel systems and evaluated for CO2 methanation. By employing emerging 3D printing technologies for catalytic reactor design such as 3D fibre deposition (also referred to as direct write or microextrusion), we developed optimised techniques for tailoring both the support's macro-and microstructure, as well as its active particle precursor distribution. A comparison was made between 3D printed commercial catalysts, Ni-alumina based catalysts and their conventional counterpart, packed beds of beads and pellet. Excellent CO2 conversions and selectivity to methane were achieved for the 3D printed commercial catalyst (95.75% and 95.63% respectively) with stability of over 100 h. The structure-activity relationship of both the commercial and in-house 3D printed catalysts was explored under typical conditions for CO2 hydrogenation to CH4, using operando 'chemical imaging', namely X-Ray Diffraction Computed Tomography (XRD-CT). The 3D printed commercial catalyst showed a more homogenous distribution of the active Ni species compared to the in-house prepared catalyst. For the first time, the results from these comparative characterisation studies gave detailed insight into the fidelity of the direct printing method, revealing the spatial variation in physico-chemical properties (such as phase and size) under operating conditions