Chemistry of hydrocarbon compounds – Unsaturated compound synthesis – With measuring – sensing – testing – or synthesis operation...
Patent
1992-12-31
1994-11-15
McFarlane, Anthony
Chemistry of hydrocarbon compounds
Unsaturated compound synthesis
With measuring, sensing, testing, or synthesis operation...
585500, 585654, 585658, 585659, 585310, 585312, 585324, 585910, 585911, 422139, 422140, 422144, 502 38, 502 41, 502 44, C07C 200, C07C 5327, C07C 5373
Patent
active
053650069
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a process and an apparatus for dehydrogenating alkanes. The invention also relates to an integrated combination process for the simultaneous production of olefins and catalytically cracked hydrocarbons, and to apparatus for performing the process.
BACKGROUND OF THE INVENTION
Olefins are produced by the thermal and/or catalytic dehydrogenation of alkanes. In the thermal cracking processes, alkanes are passed through tubes which are maintained at a temperature which is sufficiently high to cause dehydrogenation of alkanes to alkenes. A by-product of thermal cracking is "coke", which is a material of high carbon to hydrogen atomic ratio. The coke forms a deposit which reduces heat transfer from outside the tubes to the alkane stream passing through the interior of the tubes. A common expedient to reduce coke deposition is to pass steam through the tubes with the alkane stream. The steam reduces the vapour pressure of the alkanes and tends to reduce polymerization side-reactions involved in the formation of coke. Processes wherein alkanes are dehydrogenated to alkenes in the presence of steam are known as steam cracking processes, and are widely used in the chemical industry for the manufacture of ethene and propene, inter alia.
PRIOR ART
GB-A-2104094 describes a steam cracking process wherein a feed mixture containing alkane and steam is passed through reaction tubes from a feed header, and a product mixture containing steam, unconverted alkane and alkenes is recovered from the reaction tubes in a product header. The reaction tubes contain a specified dehydrogenation catalyst, and the feed mixture is passed through some of the total available tubes, the other tubes receiving a mixture containing steam and air which remove carbonaceous deposits therefrom. The pressure in the operative tubes is in the range of from 2 to 25 atmospheres (0.203 to 2.534 MPa) and the temperature in the tubes is in the range of from 450.degree. to 700.degree. C., preferably 500.degree. to 650.degree. C. The tubes are heated by burning fuel in a fuel-combustion zone from which high temperature radiant, convective and conductive heat-transfer to the exteriors of the tubes is effected. After passing across the exteriors of the tubes, the combustion gases have considerable enthalpy, and some is recovered in superheated-steam generation equipment, some is recovered in saturated-steam generation equipment, and some is recovered in air-preheaters. A portion of the superheated steam is used as the process-steam in the steam-cracking operation. There is no disclosure regarding usage of the remaining steam, and it is conceivable that at least some of it would be surplus to the requirement at the plant site. Moreover, much of the heat is lost in the combustion gas discharged to atmosphere. Thus, a steam-cracking plant of the type described in GB-A-2104094 is likely to be thermally inefficient in terms of the energy consumed to olefin-production. Fuel must be burned to maintain the high temperatures essential for the dehydrogenation reactions, but much of the heat value of the fuel is either not utilized or is not efficiently utilized.
In the fluidized catalytic cracking (FCC) of a cracker feedstock, the cracker feedstock is brought into contact with hot particles of active cracking catalyst in a reaction zone. During this period of contact, the feedstock is converted to lower molecular weight hydrocarbons and hydrogen and higher molecular weight by-products. The former include hydrocarbon distillates and hydrocarbon gases which are recovered from the reaction zone after separation from catalyst. The latter include materials of relatively high carbon to hydrogen ratio which are associated with the catalyst. The catalyst particles and associated material are subjected to the action of a stripping gas (usually steam) to remove strippable materials, and the latter are recovered with the lower molecular weight products. The stripped catalyst has associated therewith unstripped material
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Exxon Research and Engineering Company
Irzinski E. D.
McFarlane Anthony
Ott Roy J.
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