Performance limits of isothermal packed bed and perforated monolithic bed reactors operated under laminar flow conditions. I. General optimization analysis

A global optimization analysis of a general class of perforated monolithic bed reactors is presented for the case of an isothermal first-order reaction and for laminar flow conditions. The resulting design rules indicate how a given amount of catalyst material should best be perforated or distributed in space as a function of the available inlet pressure. It is shown that the influence of the different process variables (k,ΔP,V_cata,C_in/C_out,D_mol, S_reac) on the reactor productivity and on the optimal bed design can be grouped into a single dimensionless number E. This number also allows to discuss the sensitive relation between the total and the volumetric productivity of single bed reactors in a very general, compact manner. Two different perforated monolithic bed designs, a slit pore bed (SPB) and a cylindrical pore bed (CPB) are considered. It is found that, when there is an excess inlet pressure (i.e., for E?1), the optimal catalyst layer thickness is given by φ=0.3-0.5 and that the optimal pore diameter is in both cases 1.4-1.45 times smaller than the catalyst layer, independently of the internal catalyst diffusivity (D_int) and the other process variables. When the available inlet pressure is limiting (E>10⁻⁴), and when the absolute reactor productivity is more important than the volumetric productivity, it is found that much more open structures, with much wider pores are needed, i.e., perforated beds show the same behavior as packed beds, where the occurrence of a pressure-drop limitation also induces a shift from the use of full particles to the use of hollow extrudates.