Impact of Shape and Size of Catalysts on the Physical Properties and Pressure Drop in Fixed Bed Catalytic Systems

Catalyst shape and size selection is an important aspect of the industrial catalyst design. Shapes of different sizes were made using alumina and characterized using standard methods used in the industry. Tableting machine, extruder and granulating equipment were used for forming different catalytic shapes. The samples were characterized by BET surface area, pore volume (N2 adsorption and water pick-up) and the sphericity & voidage calculations were performed for different alumina shapes. The physical strength and bulk density of the shapes were analyzed using ASTM methods. Spheres exhibited highest pore volume as the forming process exert minimum external force to the material. BET Surface area of all the samples were found comparable. The impact of different shapes and sizes on the pressure drop across the bed was studied for different gas flow rates using a fixed bed reactor set-up. Sphericity & voidage were calculated for different shapes and sizes and a modified Ergun equation was used for theoretical evaluation of the pressure drop. The experimental & theoretical results were compared and the relative error was noted. The study showed how the theoretical and experimental values differ as non-ideality in the flow across the packed bed increases. For special shapes like trilobe extrusions, improved voidage helps to minimise the pressure drop across the bed.