Chemistry of hydrocarbon compounds – Unsaturated compound synthesis – By dehydrogenation
Reexamination Certificate
1999-09-01
2003-05-20
Dang, Thuan D. (Department: 1764)
Chemistry of hydrocarbon compounds
Unsaturated compound synthesis
By dehydrogenation
C585S660000, C585S656000, C585S621000, C585S624000, C585S625000
Reexamination Certificate
active
06566573
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to the field of catalytic oxidation of hydrocarbons. More particularly, the present invention relates to the catalytic partial oxidation of paraffinic hydrocarbons, such as ethane, propane, and naphtha, to produce olefins, such as ethylene and propylene.
Olefins find widespread utility in industrial organic chemistry. Ethylene is needed for the preparation of important polymers, such as polyethylene, vinyl plastics, and ethylene-propylene rubbers, and important basic chemicals, such as ethylene oxide, styrene, acetaldehyde, ethyl acetate, and dichloroethane. Propylene is needed for the preparation of polypropylene plastics, ethylene-propylene rubbers, and important basic chemicals, such as propylene oxide, cumene, and acrolein. Isobutylene is needed for the preparation of methyl tertiary butyl ether. Long chain mono-olefins find utility in the manufacture of linear alkylated benzene sulfonates, which are used in the detergent industry.
Low molecular weight olefins, such as ethylene, propylene, and butylene, are produced almost exclusively by thermal cracking (pyrolysis/steam cracking) of alkanes at elevated temperatures. An ethylene plant, for example, typically achieves an ethylene selectivity of about 85 percent calculated on a carbon atom basis at an ethane conversion of about 60 mole percent. Undesired coproducts are recycled on the shell side of the cracking furnace to be burned, so as to produce the heat necessary for the process. Disadvantageously, thermal cracking processes for olefin production are highly endothermic. Accordingly, these processes require the construction and maintenance of large, capital intensive, and complex cracking furnaces. The heat required to operate these furnaces at a process temperature of about 900° C. is frequently obtained from the combustion of methane which disadvantageously produces undesirable quantities of carbon dioxide. As a further disadvantage, the crackers must be shut down periodically to remove coke deposits on the inside of the cracking coils.
Catalytic processes are known wherein paraffinic hydrocarbons are oxidatively cracked to form mono-olefins. In these processes a paraffinic hydrocarbon is contacted with oxygen in the presence of a catalyst consisting of a platinum group metal or mixture thereof deposited on a ceramic monolith support. Optionally, hydrogen may be a component of the feed. The process is conducted under autothermal reaction conditions wherein the feed is partially combusted, and the heat produced during combustion drives the endothermic cracking process. Consequently, under these autothermal process conditions there is no external heat source required; however, the catalyst is required to support combustion above the normal fuel-rich limit of flammability. Representative references disclosing this type of process include the following U.S. Pat. Nos. 4,940,826; 5,105,052; 5,382,741; and 5,625,111. Disadvantageously, substantial amounts of deep oxidation products, such as carbon monoxide and carbon dioxide, are produced, and the selectivity to olefins remains too low when compared with thermal cracking.
M. Huff and L. D. Schmidt disclose in the
Journal of Physical Chemistry
, 97, 1993, 11,815, the production of ethylene from ethane in the presence of air or oxygen under autothermal conditions over alumina foam monoliths coated with platinum, rhodium, or palladium. A similar article by M. Huff and L. D. Schmidt in the
Journal of Catalysis
, 149, 1994, 127-141, discloses the autothermal production of olefins from propane and butane by oxidative dehydrogenation and cracking in air or oxygen over platinum and rhodium coated alumina foam monoliths. The olefin selectivity achieved in these processes is not comparable to that achieved by steam cracking and therefore could be improved.
U.S. Pat. No. 5,639,929 teaches an autothermal process for the oxidative dehydrogenation of C
2
-C
6
alkanes with an oxygen-containing gas in a fluidized catalyst bed of platinum, rhodium, nickel, or platinum-gold supported on alpha alumina or zirconia. Ethane produces ethylene, while higher alkanes produce ethylene, propylene, and isobutylene. Again, the olefin selectivity could be improved.
C. Yokoyama, S. S. Bharadwaj and L. D. Schmidt disclose in
Catalysis Letters
, 38, 1996, 181-188, the oxidative dehydrogenation of ethane to ethylene under autothermal reaction conditions in the presence of a bimetallic catalyst comprising platinum and a second metal selected from tin, copper, silver, magnesium, cerium, lanthanum, nickel, cobalt, and gold supported on a ceramic foam monolith. This reference is silent with respect to co-feeding hydrogen in the feedstream. While the use of a catalyst containing platinum and tin and/or copper is better than a catalyst containing a platinum group metal alone, the olefin selectivity should be improved if the process is to be commercialized.
In view of the above, it would be desirable to discover a catalytic process wherein a paraffinic hydrocarbon is converted to an olefin in a conversion and selectivity comparable to commercial thermal cracking processes. It would be desirable if the catalytic process were to produce only small quantities of deep oxidation products, such as, carbon monoxide and carbon dioxide. It would also be desirable if the process were to achieve low levels of catalyst coking. It would be even more desirable if the process could be easily engineered without the necessity for a large, capital intensive, and complex cracking furnace. Finally, it would be most desirable if the catalyst for the process exhibited good stability.
SUMMARY OF THE INVENTION
This invention is a process for the partial oxidation of paraffinic hydrocarbons to form olefins. The process comprises contacting a paraffinic hydrocarbon or mixture thereof with oxygen in the presence of hydrogen and a catalyst. The contacting is conducted under autothermal process conditions sufficient to form the olefin. The catalyst employed in the process of this invention comprises a Group 8B metal and at least one promoter.
The process of this invention efficiently produces olefins, particularly mono-olefins, from paraffinic hydrocarbons, oxygen, and hydrogen. Advantageously, the process of this invention achieves a higher paraffin conversion and a higher olefin selectivity as compared with prior art catalytic, autothermal processes. More advantageously, the process of this invention produces fewer undesirable deep oxidation products, such as carbon monoxide and carbon dioxide, as compared with prior art catalytic, autothermal processes. Even more advantageously, in preferred embodiments, the process of this invention achieves a paraffin conversion and olefin selectivity which are comparable to commercial thermal cracking processes. As a further advantage, the process produces little, if any, coke, thereby substantially prolonging catalyst lifetime and eliminating the necessity to shut down the reactor to remove coke deposits.
Most advantageously, the process of this invention allows the operator to employ a simple engineering design and control strategy, which eliminates the requirement for a large, expensive, and complex furnace like that used in thermal cracking processes. In one preferred embodiment, the reactor simply comprises an exterior housing which contains a monolithic support onto which the catalytic components are deposited. Since the residence time of the reactants in the process of this invention is on the order of milliseconds, the reaction zone operates at high volumetric throughput. Accordingly, the reaction zone measures from about one-fiftieth to about one-hundredth the size of a commercially available steam cracker of comparable capacity. The reduced size of the reactor lowers costs and simplifies maintenance procedures. Finally, since the process of this invention is exothermic, the heat produced can be harvested via integrated heat exchangers to generate electricity or steam credits for other processes.
As noted hereinbefore, thermal energy i
Bearden Mark D.
Bharadwaj Sameer S.
Lazaruk Gerald E.
Maj Joseph J.
Murchison Craig B.
Dang Thuan D.
Dow Global Technologies Inc.
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