(501d) A Comparison between Ceramic Foam Catalyst and Packed-Beds for Methanol Steam Reforming

Ceramic foams are sponge-like materials with open cells that are connected to each other through openings or windows that are formed from ceramic struts. The open cells collectively form tortuous continuous passages that are interrupted by the web of struts. The foam can accept a washcoat and thus becomes an attractive catalytic support. The foam has high porosity and offers little resistance to flow (low pressure drop). The tortuous flow path generates disturbances in the flow that enhances the heat and mass transfer between the pores in the washcoat and the flow. Recent work by Richardson and co-workers note the attractions of ceramic foam catalysts and their advantages over conventional porous pellets. In addition, they have measured rates of heat & mass transfer in ceramic foams and presented them as correlations suitable for reactor design & simulation.

The objective of this work is to examine the advantages of ceramic foams versus packed beds for steam reforming of methanol. Two reactors are simulated: one that is filled with either a ?cartridge' of catalytic foam or a bed of commercial pellets. The reactor geometry is designed to mimic a semi-commercial methanol reformer of about 1L volume, which has been studied in other publications from our labs. The pseudo-homogenous methodology, with appropriate modification, is used to simulate the two reactors.

A key assumption of the comparison is that the commercial catalyst can be deposited onto the ceramic foam support as a washcoat without altering the nature of the active sites and the associated pore structure. This implies that the reaction mechanism and kinetic expressions remains the same for the foam and porous pellet and that the ratio of active sites per unit surface area (BET) is constant. Since the BET surface area of the washcoat and porous pellet are different, the total number of active sites per unit volume of reactor is different between the two reactors.