Graduated loading of catalyst on reticulated ceramic foam.

摘要

Reticulated ceramic foams have properties that make them ideal as structured catalyst support. The highly porous, tortuous foam results in lower pressure drop and improved heat transfer characteristics in comparison to conventional pellet-packed reactors. A new advantage introduced here is the ability to fabricate a variable catalyst loading axially and/or radially within the reactor bed.;Catalyst components are often dispersed on the support surface by exposure to precursor solutions. If catalyst loading is a function of exposure time, by exposing sections of the foam to these solutions for different times the concentration of the catalyst on the foam will vary in a predetermined manner, thereby making catalyst activity a function of axial and radial position in the reactor. Recommended procedures for producing graduated catalyst loading on the ceramic foam are presented. For example, if the reactor catalyst bed comprises a cylinder of ceramic foam, the loading profile may be adjusted to increase from inlet to outlet along the axial direction according to any desired function. Alternatively, concentration may decrease or increase from the outer radius to the center point.;Two-dimensional pseudo-homogeneous computer simulations for reactor beds are developed to compare the performance of conventional pellet-packed reactors, uniformly loaded foam-packed reactors and gradually loaded foam-packed reactors, using examples of industrially important highly exothermic and endothermic processes such as partial oxidation of o-xylene and ethylene, methanation of carbon dioxide, and steam reforming of methane.;Graduated loading is designed to improve the temperature distribution within the reactor by minimizing the hotspot temperature (for exothermic reactors) or cold spot temperatures (for endothermic reactors) in the reactor while increasing the average bed temperature. The result is a more stable reactor with higher conversion rates and improved selectivity. Proper temperature control prolongs the life of the catalyst and maintains the integrity of the catalyst. Alleviation of temperature constraints also allows for larger tube diameters, which reduces the number of tubes and therefore the capital cost of the reactor or for greater productivity, which reduces operating costs.