Morphological Characterization of Open-Cell Solid Foams

Reactors with a fixed-bed of catalyst particles are widely applied for continuous multi-phase processes in the petrochemical, chemical, and biochemical industry. However, the performance of these reactors often suffers from some drawbacks, such as energy consuming high-pressure drop and mass and heat transfer limitations. One solution is to replace randomly packed catalysts with structured packings, e.g open-cell solid foam catalysts as they provide high specific surface area of up to 2000 m2/m3 at high open porosities between 75 - 97%. As result, the pressure drop of the gas-liquid two-phase flow is comparatively low (Mohammed et al. 2013). Studies argued that both the bulk material and the foam morphological properties like the number and shape of the pores and struts have a strong impact on heat transfer rates and on the hydrodynamic behavior (Tekog˜lu et al., 2011). Thus, a key factor in the foam characterization is to properly define foam structural parameters and to choose an appropriate predictive morphological model. Due to the highly random, irregular and non-ideal solid foam structure it is difficult to specify one geometrical property. At same time, although several models and correlations have been proposed to calculate morphological properties, each of these correlations was proposed for specific materials and pore shape. Therefore, the goal of this study is to characterize the solid foam, and find the most suitable morphological model for the characterization of the packing, which is applicable for different solid foam shape, material, and structure. In order to distinguish the influence of the foam materials, foam samples of different materials (polyurethane, carbon, and nickel) but same foam density are investigated. Different measurements techniques (light microscopy, electron scanning microscopy, and X-ray micro tomography) were used to reveal the impact of the material. The morphological analysis indicated that polyurethane foam mimics both the carbon and the nickel foam. Furthermore, all solid foams show similar strut properties (see Fig 1) which is confirmed by tomographic measurements of window (pore) diameter and specific surface area. In the contribution, the methodology of the foam characterization and the comparison between the foam morphologies will be shown.