Anomalously high reactivity has been observed for microfibrous entrapped particulates used in applications such as hydrogen sulfide adsorption on nano dispersed zinc oxide, low temperature CO oxidation, preferential CO oxidation and VOC adsorption. CFD simulations of H2S adsorption on ZnO have shown enhancements in the activity of entrapped particulates greater than the effect of reducing the size of the particulates. The residence time distribution (RTD) is obtained from streamlines in the unit cell used in the CFD simulation to explain the anomalously high observed activity.

Microfibrous entrapped catalysts and sorbents are a new class of material that consist of micron sized catalyst/sorbent particles (e.g. 25–250 microns) entrapped in a mesh composed of micron diameter fibers (2–20 microns). These fibers can be made out of metals, ceramics or polymers. Microfibrous materials have inherent advantages such as high contacting efficiency, low intra-particle transport resistance, improved heat and mass transfer, and low pressure drop. These materials are engineered to provide specific void volumes and cage dimensions by adjusting the fiber loading and fiber diameter. The resultant cage is used to entrap sorbent/catalyst particulates. The overall void volume of the final structure varies from ca. 50-98%. The drag on the micro fibers in the mesh focus the flow between the fibers resulting in higher interstitial velocities impacting the entrapped particulates resulting in increased mass transfer rates. These materials are sometimes described as a “frozen fluidized bed” since particulates can be fixed in space by entrapment with microfibers. Typical volumetric loadings of particulates are about twenty percent.

CFD using FLUENT has successfully modeled the breakthrough curves for hydrogen sulfide adsorbed by nano-dispersed zinc oxide. In these CFD computations the velocity distribution in a packed bed of particles is accounted for and the residence time distribution (RTD) is implicitly included in the computation. Residence time distributions have been determined from streamlines in the unit cell used in the CFD computations. Effects for several different face velocities corresponding to several orders of magnitude change in Reynolds number have been studied. Comparison to predictions by a plug flow tubular reactor model with axial dispersion will be made.

Extended Abstract Status: Not Uploaded