Comparative heterogeneous contacting efficiency in fixed bed reactors: Opportunities for new microstructured systems

Abstract

Novel microstructured heterogeneous contacting systems called microfibrous entrapped catalysts (MFEC) were prepared by entrapping small particles of γ-alumina (150–180μm) in sinter-locked network of metal (SS-304) microfibers (8 and 12μm). These materials are in the form of thin flexible sheets (0.5–2.0mm) and have uniform structures of high and variable voidages. Head-to-head theoretical comparisons of the performance efficiencies of flow-through pleated MFEC structures of various pleat factors (PF=face area of MFEC/cross-sectional area of the reactor) were made with packed bed reactors of various particle sizes (0.16–2.0mm) and monolith reactors of various cpsi (100–900 cells per square inch). These comparisons showed that while packed beds produced high pressure drops, monoliths resulted in low fluid-solid mass transfer rates. On the other hand, MFEC structures with high PF (≥4) showed remarkable improvements in terms of conversion along with significant reduction in pressure drops and catalyst requirements compared to monoliths and packed beds. While small particles used in MFEC improved interphase and intraparticle mass transport rates, high voidages and ease of pleating helped lower the pressure drops in MFEC. To further ascertain these results, pleated structures of MFEC containing Pd/γ-alumina were tested for application in catalytic aircraft cabin air purification (ozone decomposition). Pressure drop and ozone conversion efficiency of pleated MFEC designs were measured at various flow rates and temperatures, and compared with those of a commercial monolith based ozone catalytic converter. The experimental results substantiated the mathematical findings.