Organic compounds -- part of the class 532-570 series – Organic compounds – Heterocyclic carbon compounds containing a hetero ring...
Reexamination Certificate
1999-09-29
2002-07-09
Dentz, Bernard (Department: 1625)
Organic compounds -- part of the class 532-570 series
Organic compounds
Heterocyclic carbon compounds containing a hetero ring...
C549S534000, C549S259000, C562S532000, C568S472000, C568S475000, C568S479000, C502S209000, C502S305000, C502S348000, C502S350000
Reexamination Certificate
active
06417376
ABSTRACT:
This invention relates to chemical products that are made via selective oxidation. More particularly, this invention relates to selective oxidation in the presence of a catalyst which is supported on a mesh-like structure.
In the petrochemical industry there are produced products that are made via selective oxidation. By selective oxidation is meant that the feed component is reacted with molecular oxygen or molecular oxygen containing streams such as air with the reaction being stopped before complete oxidation to carbon dioxide and water.
For example, phthalic anhydride is produced by a selective oxidation process. Most plants for producing phthalic anhydride employ a multi-tubular reactor filled with inert (Raschig) rings or beads coated with an active catalyst. The reaction is highly exothermic and often excessive oxidation of the product, phthalic anhydride, occurs due to poor temperature control or heat removal. Conversion of o-xylene is virtually complete, but selectivity to phthalic anhydride is well below 100%. The best commercial processes are known to have a yield of about 80%.
Ethylene oxide also is commercially produced by a selective oxidation process involving the epoxidation of ethylene over a catalyst which catalyzes the production of ethylene oxide. In general, the catalyst which is employed for such production is a silver containing catalyst, which is supported on a suitable support.
The production of ethylene oxide is an exothermic reaction and. in general, in order to remove the heat of reaction ethylene oxide is produced in a tubular reactor in which the gaseous ethylene, and a gas containing oxygen are reacted in the gaseous phase over a bed of supported catalyst in a plurality of tubes, with the exothermic heat of reaction being removed by use of a circulating coolant which surrounds the tubes.
The yield of ethylene oxide is dependent upon both the rate of conversion of ethylene to ethylene oxide, and the selectivity of such conversion. In general, higher temperatures increase conversion and decrease selectivity, whereby conversion is balanced against selectivity in order to obtain an appropriate yield. In general, there have been attempts to improve the yield of ethylene oxide by employing a variety of promoters in combination with the silver containing catalyst which is commercially employed for such ethylene oxide production.
The yield of acrylic acid is dependant upon the conversion and selectivities in the oxidation of propylene or propane to acrolein and the further oxidation of acrolein to acrylic acid. In general, higher temperatures increase conversion and decrease selectivity, whereby conversion is balanced against selectivity in order of obtain an appropriate yield. Attempts have been made to increase selectivity by modifications to the mixed oxide catalyst normally used.
As a result, there is a need for improvements in processes for the selective oxidation of organic compounds by the use of molecular oxygen.
In accordance with one aspect of the present invention there is provided a selective oxidation process wherein an organic compound is reacted with molecular oxygen in the presence of a suitable oxidation catalyst, with such catalyst being supported on a particulate support wherein such supported catalyst is supported on a non-particulate catalyst support structure that is a mesh-like material. The term “supported on the mesh” includes coating the supported catalyst on the mesh as well as entrapping the supported catalyst in the interstices of the mesh.
The supported catalyst supported on the mesh is used as a fixed bed. The reaction is preferably in the gas phase.
More particularly, the mesh like material is comprised of fibers or wires, such as a wire or fiber mesh, a metal felt or gauze, metal fiber filter or the like. The mesh like structure may be comprised of a single layer, or may include more than one layer of wires (e.g. a knitted wire structure or a woven wire structure), and is preferably comprised of a plurality of layers of wires or fibers to form a three-dimensional network of materials. In a preferred embodiment, the support structure is comprised of a plurality of layers of fibers that are randomly oriented in the layers. One or more metals may be used in producing a metal mesh. Alternatively the mesh fibers may be formed from or include materials other than metals alone or in combination with metals; e.g. carbon, metal carbides, metal oxides, or a ceramics.
In a preferred embodiment wherein the mesh-like structure is comprised of a plurality of layers of fibers to form the three-dimensional network of materials, the thickness of such support is at least five microns, and generally does not exceed ten millimeters. In accordance with a preferred embodiment, the thickness of the network is at least 50 microns and more preferably at least 100 microns and generally does not exceed 2 millimeters.
In general, the thickness or diameter of the fibers which form the plurality of layers of fibers is less than about 500 microns, preferably less than about 150 microns and more preferably less than about 30 microns. In a preferred embodiment, the thickness or diameter of the fibers is from about 8 to about 25 microns.
The three-dimensional mesh-like structure may be produced as described in U.S. Pat. Nos. 5,304,330; 5,080,962; 5,102,745; or 5,096,663. It is to be understood, however, that such mesh-like structure may be formed by procedures other than as described in the aforementioned patents.
The mesh-like structure that is employed in the present invention (without supported catalyst on the mesh) has a void volume which is at least 45%, and is preferably at least 55% and is more preferably at least 65% and still more preferably is at least about 85% (for example, at least 90%). In general, the void volume does not exceed about 98%. The term “void volume” as used herein is determined by dividing the volume of the structure which is open by the total volume of the structure (openings and mesh material) and multiplying by 100. In general, the average void opening is at least 10 microns and preferably at least 20 microns.
The catalyst support on which the catalyst is supported, with such supported catalyst then being supported on a mesh like structure, is a support that is in particulate form. The term particulate as used herein includes and encompasses spherical particles, elongated particles, fibers, etc. In general, the average particle size of the particulate on which the selective oxidation catalyst is supported does not exceed 200 microns and is typically no greater than 50 microns with the average particle size in the majority of cases not exceeding 20 microns. In general, the average particle size of such particulates is at least 0.002 micron and more generally at least 0.5 microns. When the catalyst supported on the particulate support is coated on the mesh, the average particle size of the catalyst support generally does not exceed 10 microns and, when entrapped in the mesh, generally does not exceed 150 microns.
In accordance with a preferred aspect of the present invention, the selective oxidation is effected in a fixed bed and the particulate support has an average particle size as hereinabove described, which size is significantly smaller than those used in prior art fixed bed processes.
In an embodiment of the invention, the mesh-like structure, that functions as a support for the oxidation catalyst supported on a particulate support is in the form of a shaped structured packing. This packing can be configured to provide for turbulence of the gas phase flowing over the catalyst in the selective oxidation reactor. The mesh-like catalyst support structure may be provided with suitable corrugations in order to provide for increased turbulence. Alternatively, the mesh-like structure may include tabs or vortex generators to provide for turbulence. The presence of turbulence generators permits mixing in the radial (and longitudinal) direction and permits improved heat transfer at the wall compared to the processes know in the
Barner Herbert E.
Ercan Cemal
Huang Chiung Y.
Murrell Lawrence L.
Overbeek Rudolf A.
ABB Lummus Global Inc.
Dentz Bernard
Lillie Raymond J.
Olstein Elliot M.
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