Mineral oils: processes and products – Chemical conversion of hydrocarbons – With preliminary treatment of feed
Reexamination Certificate
1999-04-05
2001-01-16
Myers, Helane E. (Department: 1764)
Mineral oils: processes and products
Chemical conversion of hydrocarbons
With preliminary treatment of feed
C208S133000
Reexamination Certificate
active
06174428
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATION
This application is related to applicants' concurrently filed application Attorney Docket No. Pet-1747, entitled “Process For Converting Hydrocarbons By Treatment In A Distillation Zone Comprising Withdrawing A Stabilised Distillate, Associated With A Reaction Zone, And Its Use For Hydrogenating Benzene”, based on French Application 98/04.351 filed Apr. 6, 1998, said applications being incorporated by reference herein.
The invention relates to a process for converting hydrocarbons. The process of the invention associates a distillation zone with a hydrocarbon conversion reaction zone which is at least partially external to the distillation zone. Thus this process can selectively convert hydrocarbons separated from a hydrocarbon feed by means of the distillation zone.
In particular, the process of the invention is applicable to selective reduction of the quantity of light unsaturated compounds (i.e., containing at most six carbon atoms per molecule) including benzene in a hydrocarbon cut essentially comprising at least 5 carbon atoms per molecule, with no substantial loss of octane number, said process comprising passing said cut into a distillation zone associated with a hydrogenation reaction zone.
BACKGROUND OF THE INVENTION
The general trend now is to reduce the quantity of benzenes and olefins (unsaturated compounds) in gasolines, because of their known toxicity.
Benzene has carcinogenic properties and thus the possibility of it polluting the air must be limited as far as possible, in particular by practically excluding it from automobile fuels. In the United States, reformulated fuels must not contain more than 1% by volume of benzene; in Europe, it has been recommended that a gradual decrease towards that value be made.
The benzene content of a gasoline is very largely dependent on that of the reformate component in that gasoline. The reformate results from catalytic treatment of naphtha intended to produce aromatic hydrocarbons, principally comprising 6 to 9 carbon atoms per molecule and the octane number of which is very high endowing the gasoline with antiknock properties.
Because of the toxicity described above, the amount of benzene in the reformate must be reduced to acceptable levels.
The benzene in a reformate can be hydrogenated to cyclohexane. Since it is impossible to selectively hydrogenate benzene in a mixture of hydrocarbons also containing toluene and xylenes, that mixture must first be fractionated to isolate a cut containing only benzene, which can then be hydrogenated.
International patent application WO 95/1 5934 describes a reactive distillation which aims to selectively hydrogenate diolefins and C2-C5 acetylenic compounds. The distillate can be separately recovered from the light compounds. The catalytic hydrogenation zone is completely internal to the distillation column, which means that the hydrogen cannot dissolve properly in the feed and the pressure cannot be increased.
A process has been described in which the catalytic benzene hydrogenation zone is internal to the distillation column has been described which separates benzene from other aromatic compounds (Benzene Reduction—Kerry Rock and Gary Gildert CDTECH—1994 Conference on Clean Air Act Implementation and Reformulated Gasoline—October 94), which cuts the cost of the apparatus. It appears that the pressure drop across the catalytic bed(s) in that process means that an intimate mixture between the liquid phase and the gaseous stream containing the hydrogen cannot be obtained. In that type of technology where the reaction and distillation proceed simultaneously in the same physical space, the liquid phase descends through every catalytic bed in the reaction zone in a trickle flow, and thus in threads of liquid. The gaseous fraction containing the fraction of vaporised feed and the gas stream containing hydrogen rise through the catalytic bed in columns of gas. In that arrangement, the entropy of the system is high and the pressure drop across the catalytic bed(s) is low. As a result, operating that type of technique cannot easily promote dissolution of hydrogen in the liquid phase comprising the unsaturated compound(s).
European published patent application EP-A-0 781 830 assigned to Institut Francais du P{acute over (e)}trol describes a process for hydrogenating benzene using a distillation column associated with a reaction zone which is at least partially external. The feed for the reaction zone is withdrawn from the distillation zone then the effluent from the reaction zone is re-introduced into the distillation zone. The hydrogenation reaction can also take place in the distillation zone. This process does not envisage a circulating reflux in the column with the result that no heat is extracted from the reaction zone.
SUMMARY OF THE INVENTION
The process of the present invention is an improvement over patent application EP-A-0 781 830, the features of which are hereby included in the present description.
The invention provides a process for converting a hydrocarbon feed associating a distillation zone and a reaction zone which is at least partially external to the distillation zone producing a vapour distillate and a bottom effluent. At least one reaction for converting at least a portion of at least one hydrocarbon takes place in a reaction zone comprising at least one catalytic bed, in the presence of a catalyst and a gas stream comprising hydrogen. The feed for the reaction zone is drawn off at the height of a draw-off level and represents at least a portion of the liquid flowing in the distillation zone, and at least a portion of the effluent from the reaction zone is re-introduced into the distillation zone at the height of at least one re-introduction level, so as to ensure continuity of distillation. The invention is characterized in that the temperature of the portion of the effluent from the reaction zone re-introduced into the distillation zone is lower than that of the feed for the reaction zone drawn off at the height of a draw-off level located below the re-introduction level.
The Applicant has surprisingly discovered that carrying out at least one circulation of a liquid drawn off from the distillation zone at a draw-off level and re-introduced at a re-introduction level located above said draw-off level, the temperature of said liquid at the re-introduction level being lower than the temperature of said liquid at the draw-off level, improves the performance of the process.
More particularly, the process of the present invention is applicable to hydrogenation of benzene and other unsaturated compounds in a hydrogenation zone associated with a distillation zone. In a particular application, the process of the invention is a process for treating a feed, the major portion of which is constituted by hydrocarbons containing at least 5, preferably 5 to 9, carbon atoms per molecule, and comprising at least one unsaturated compound, comprising benzene and possibly olefins in which said feed is treated in a distillation zone associated with a hydrogenation reaction zone which is at least partially external and comprises at least one catalytic bed, in which hydrogenation of at least a portion of the unsaturated compounds contained in the feed, containing at most six carbon atoms per molecule, i.e., containing up to six (inclusive) carbon atoms per molecule, is carried out in the presence of a hydrogenation catalyst and a gas stream comprising hydrogen, preferably in the major portion, the feed for the reaction zone being drawn off from the height of a draw-off level and representing at least a portion, preferably the major portion, of the liquid flowing in the distillation zone, at least a portion, preferably the major portion, of the effluent from the reaction zone being re-introduced into the distillation zone at a height of at least one re-introduction level, so as to ensure continuity of distillation, and so that a distillate which is highly depleted in unsaturated compounds is recovered, said process being characterized in that the te
Ambrosino Jean-Louis
Didillon Blaise
Marache Pierre
Viltard Jean-Charles
Witte G{acute over (e)}rald
Institut Francais du Pe'trole
Millen White Zelano & Branigan P.C.
Myers Helane E.
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