BE1017728A5 - METHOD AND DEVICE FOR STEAM DEALKYLATION IN A CATALYTIC CRACKING UNIT OF HYDROCARBONS - Google Patents

Abstract

The present invention describes a process for treating a fraction consisting mainly of hydrocarbons having at least seven carbon atoms (C7 + moiety) as produced in a catalytic cracking unit of a hydrocarbon-containing feed, as well as a device for implementing the method. The C7 + fraction is brought, after a hydrogenation, to a dealkylation with steam or form the recoverable products which are benzene and hydrogen.

Description

The invention relates to a process for treating a fraction consisting mainly of hydrocarbons comprising at least six carbon atoms (C7 + fraction) as it is present in a hydrocarbon-catalyzed cracking unit. forming in a catalytic cracking unit a hydrocarbon-containing feedstock, as well as a device for carrying out the process.

In a catalytic cracking unit of a feed containing hydrocarbons, it is mainly the heavy constituents of the crude oil, as they form during the distillation of crude oil, which are treated.

According to the state of the art, the heavy constituents of the crude oil are fed as filler in a catalytic cracking. In catalytic cracking, the heavy constituents of the crude oil are converted to the presence of a catalyst, mainly paraffins, olefins and shorter chain aromatics. A fraction consisting mainly of hydrocarbons having at least six carbon atoms (C6 + fraction) is separated, among other things, from the reaction products of catalytic cracking. This Ce + fraction contains, as economically valuable product, aromatics, especially benzene, which are used as a starting material for the synthesis of many synthetic materials and to increase the resistance to detonation of gasoline.

In order to arrive at the economically recoverable products of the C6 + fraction, especially with benzene, and to obtain the maximum possible yield, the following process is used according to the state of the art. The C6 + fraction is separated into a fraction consisting mainly of hydrocarbons having six carbon atoms (C6 fraction) and a fraction consisting mainly of hydrocarbons having at least seven carbon atoms (C7 + fraction). The economically valuable product benzene can be directly separated from the C6 fraction. The linear hydrocarbons are separated from the C7 + fraction by means of liquid-liquid extraction and are subsequently treated as raffinate, the raffinate can be returned. for example in the feedstock of catalytic cracking. The C7 + fraction liberated from linear hydrocarbons now mainly contains aromatics comprising from seven to eight carbon atoms and is separated into a fraction consisting mainly of hydrocarbons comprising seven carbon atoms (mainly toluene) and a fraction consisting mainly of hydrocarbons. having at least eight carbon atoms (mainly xylene). The fraction consisting mainly of hydrocarbons having eight carbon atoms is fed as a filler in a process to obtain paraxylene. The fraction consisting mainly of hydrocarbons having seven carbon atoms is fed as a feed in a hydro-dealkylation process.

Such a hydro-dealkylation process is described for example in WO / 2005/071045. The hydrocarbons are contacted with hydrogen in the presence of a catalyst and at a temperature of 400 ° C. to 650 ° C. and at a pressure of between 20 bar and 40 bar, the hydrogen being present in a molar excess. triple to sixfold in relation to hydrocarbons. Under these conditions, the alkyl groups are removed from the respective alkyl aromatics (such as, for example, toluene) so that benzene and the respective alkanes (eg, methane) are formed.

The use of hydrogen during hydro-dealkylation of hydrocarbons has a negative effect on the profitability of this process according to the state of the art for obtaining benzene.

This is why the problem underlying the present invention is to develop an economic variant in the state of the art.

This problem is solved according to the invention, as far as the process is concerned, since the C7 + fraction is subjected to dealkylation with steam, whereby it is mainly formed, in addition to reaction products such as carbon monoxide and carbon dioxide, the two valuable products that are benzene and hydrogen.

The basic idea of the invention consists in the dealkylation of the alkylaromatic compounds by producing benzene by means of a dealkylation with steam. Steam dealkylation only requires cheap water vapor as the feedstock, and in addition to the valuable product of benzene, it also produces the valuable by-product of hydrogen.

The C7 + fraction used in the dealkylation with steam contains mainly a) aromatic hydrocarbons containing from seven to ten carbon atoms, b) cyclic paraffins (cycloalkanes) containing from six to ten carbon atoms, c) isoparaffins and n -paraffins having from six to ten carbon atoms; d) alkenes having from seven to ten carbon atoms, or any mixture of the above, the exact composition being a function of the composition of the heavier naphtha concerned which is fed as a feedstock; catalytic cracking. The process according to the invention is however suitable for each of the described compositions of the C7 + fraction.

The hydrocarbons from the C7 + fraction advantageously react with steam in the gaseous phase with the addition of heat to a solid catalyst. The C7 + gas fraction is dealkylated by the presence of water in gaseous form (vapor) on a catalyst with a constant supply of heat, whereby the desired products of benzene and hydrogen are formed in addition to carbon monoxide, carbon monoxide and carbon dioxide. carbon dioxide and other by-products.

The heat required for the dealkylation reaction is preferably produced by the combustion of a filler with air. It is particularly advantageous to use also as gaseous filler by gas reaction by-products from steam dealkylation, in particular carbon monoxide and methane. Some of the gaseous reaction by-products from steam dealkylation, particularly carbon monoxide and methane, are combustible and can thus be used as filler for combustion to produce the necessary heat of reaction. This saves heating gas and this part of the otherwise unused reaction products is used judiciously.

Suitably, the gaseous reaction products are separated, after compression, by hydrogen gas pressure change adsorption and gaseous reaction byproducts, in particular carbon monoxide, carbon dioxide and methane. The valuable hydrogen by-product is also present in gaseous form and can be used in a much smarter way than in combustion. Hydrogen can be readily separated from combustible gas reaction byproducts which can be used as a filler in combustion by prior pressure compression adsorption.

Advantageously, the burnt gases generated during the combustion are cooled by means of a heat exchanger by heating the fillers of the dealkylation with steam. Through the use of flue gas heat to preheat the feedstock (C7 + fraction and vapor) of the dealkylation to steam, the heat still to be supplied, which is necessary to maintain the temperatures required for the reaction of dealkylation, is reduced. This results in an economical use of energy resources.

Advantageously, the C7 + fraction and the steam are guided in pipes, preferably from top to bottom, on the solid catalyst, the catalyst being inside the pipes. Heat is suitably brought from outside into the pipes. The heat required for the dealkylation reaction is preferably transmitted to the pipe by electromagnetic radiation, thermal radiation and / or convection. The dealkylation reaction proper takes place inside the pipes where the catalyst is located. The two reaction partners (C7 + fraction and steam) are guided in the catalyst filled pipes from top to bottom. The heat required for the dealkylation reaction is generated outside the pipes and transmitted by the mechanisms mentioned to the pipe where the heat comes by conduction of heat and convection inside the pipes at the reaction site.

Preferably, a solid catalyst composed of a porous carrier material, in particular γ-Α ^ Οβ, spinel MgAI and / or Cr203, and an active component on the surface of the support material are used. especially Rh with a charge of 0.1 - 1.0% by weight and / or Pd with a charge of 0.2 - 2.0% by weight.

Advantageously, the dealkylation with steam is carried out at a temperature of 400 ° C to 600 ° C, preferably 450 ° C to 550 ° C, particularly preferably 480 ° C to 520 ° C, and pressure of 1 to 15 bar, preferably 1.2 to 10 bar, particularly preferably 1.5 to 8 bar.

Suitably, the dealkylation with steam is carried out at a molar ratio of the water vapor with respect to the hydrocarbons which is, on entering the reactor, of the order of 1 to 20, preferably 2 In another embodiment of the invention, the dealkylation with steam is carried out at a molar ratio of the water vapor with respect to the hydrocarbons which is, upon entry into the reactor, from from 3 to 12, preferably from 5 to 10. In general, the dealkylation with steam is carried out with a molar excess of water, the exact ratio in the different embodiments of the invention being a function of the exact composition of the C7 + fraction.

It is advantageous to subject the C7 + fraction, prior to the dealkylation with steam, to a dienes and styrenes conversion process, hydrogenation processes using hydrogen being especially used for this purpose. It is also advantageous to subject the C7 + fraction, prior to the dealkylation with steam, to a process for converting and removing components containing sulfur, nitrogen and / or oxygen, hydrogen being especially used for this purpose. Through the use of hydrogenating processes, diolefins optionally present in the C7 + fraction can be converted to their corresponding olefins or styrene to ethylbenzene, just as components containing sulfur, nitrogen or oxygen can be converted. and eliminated. The deactivation of the catalyst is thereby reduced and the life of the catalyst substantially increased.

The reaction products of the dealkylation with steam are preferably cooled and separated during a 3-phase separation into gaseous reaction products, hydrocarbons and water. The reaction products from the dealkylation with steam contain not only the desired valuable products of benzene and hydrogen but also reaction products such as carbon monoxide and carbon dioxide and reaction by-products. . To obtain the desired products of value, the reaction products must be separated. This is done through a 3-phase separation of the cooled reaction products into the gaseous reaction products, in particular hydrogen, carbon monoxide, carbon dioxide and methane, into the hydrocarbons, especially benzene, and water.

Suitably, the hydrogen forming during the dealkylation with steam of the C7 + fraction is fed in whole or in part into the feedstock for processes using hydrogen. The hydrogen produced during the dealkylation with steam can be used in whole or in part for the hydrogen-using processes described in the previous section, so that the need for hydrogen to be supplied from the outside is reduced.

In one embodiment of the invention, the hydrogen forming during the dealkylation with steam of the C7 + moiety is fed as a feedstock in any process using hydrogen, preferably in a process for conversion. and removing sulfur-containing components or a process for cracking a hydrocarbon-containing feedstock with hydrogen in the oil refinery.

For a good yield of the desired reaction product benzene from steam dealkylation, reducing the sulfur content of the C7 + fraction, prior to the dealkylation with steam, to less than 10 ppm, preferably less from 3 ppm, particularly preferably to less than 1 ppm, is advantageous.

Benzene is preferably separated from the hydrocarbons of the reaction products by rectification. After rectification, benzene is advantageously subjected to adsorption purification to dry and remove the trace components, the benzene being brought over an adsorbent on which the trace components are adsorbed unlike benzene. By applying the process according to the invention, benzene can be obtained from the reaction products by simple rectification and further processed or marketed. Extractive extraction or extractive rectification, such as when using a method according to the state of the art, is not necessary, which reduces investment and process costs.

Advantageously, components of the C7 + fraction whose boiling point is very close to that of benzene and which form azeotropes are converted by the dealkylation with steam. All higher boiling reaction products than benzene which originate from the rectification and which consist mainly of unconverted feedstock of the dealkylation with steam are appropriately returned via optional hydrogenation as feedstock. in the dealkylation with steam. In another embodiment of the invention, all higher boiling reaction products than benzene from the rectification and consisting mainly of unconverted feedstock from the dealkylation with steam are returned. , before the dealkylation with steam, hydrogenation of a C7 + fraction, a Ce + fraction and hydrogenation of a fraction consisting mainly of hydrocarbons having at least five carbon atoms. By returning the unconverted fillers to hydrogenation or dealkylation with steam, circulation is achieved without loss of valuable fillers.

In another embodiment of the invention, before the dealkylation with steam, a fraction consisting mainly of hydrocarbons having at least eight carbon atoms (Cs + fraction) is separated by distillation from the C7 + fraction, the separated Ce + fraction being fed as a filler in a process to obtain paraxylene or is removed for treatment as gasoline.

With regard to the device, the problem is solved because the device comprises an oven with a fireplace and pipes in the fireplace. The actual dealkylation with steam takes place in the pipes which are again in the furnace hearth where the heat required for the dealkylation with steam can be generated.

Advantageously, the pipes are placed vertically in the hearth and have compensating elements for thermal expansion at the lower and / or upper end. The thermal expansion compensating elements at the lower and / or upper end of the vertical pipes prevent mechanical stresses due to temperature differences which can lead to increased wear of the pipes.

Suitably each pipe has an inlet for the C7 + fraction and water vapor and an evacuation of the reaction products.

It is also advantageous for each pipe to be filled internally with a catalyst, the catalyst being composed of a porous support material, in particular γ-Α Οβ, spinel MgAl and / or O 2 () 3, and an active component on the surface of the support material, particularly Rh with a charge of 0.1 - 1.0 wt% and / or Pd with a charge of 0.2-2.0 % in weight.

The oven preferably has at least one burner on the wall, the lid and / or the bottom. Suitably the hoses are suitable for an internal pressure of 1 to 15 bar, preferably 1.2 to 10 bar, particularly preferably 1.5 to 8 bar, and for charging in an oven with temperatures of flames up to 1400 ° C.

With the present invention, it is possible to produce in particular an economical variant in the state of the art for the treatment of a C7 + fraction in a catalytic cracking unit of a feed containing hydrocarbons. The use of the method according to the invention and the device according to the invention makes it possible to produce, in addition to the economically valuable product that is benzene, the precious by-product that is hydrogen.

Claims (26)

A process for treating a fraction consisting mainly of hydrocarbons having at least seven carbon atoms (C7 + moiety) as formed in a catalytic cracking unit of a hydrocarbon-containing feed, characterized in that the C7 + fraction is subjected to a dealkylation with steam, whereby it is formed mainly, in addition to reaction products such as carbon monoxide and carbon dioxide, the two valuable products that are benzene and hydrogen and in that hydrogen is separated from gaseous reaction products by pressure swing adsorption after compression of all gaseous reaction by-products of the dealkylation with steam. 2. Process according to claim 1, characterized in that the C7 + fraction contains mainly a) aromatic hydrocarbons containing from seven to ten carbon atoms, b) cyclic paraffins (cycloalkanes) containing from six to ten carbon atoms, c) isoparaffins and n-paraffins having from six to ten carbon atoms; d) alkenes having from seven to ten carbon atoms, or any mixture of the above. 3. Process according to claim 1 or 2, characterized in that the hydrocarbons from the C7 + fraction react with water vapor in the gas phase with the addition of heat to a solid catalyst. 4. Process according to any one of claims 1 to 3, characterized in that the heat required for the dealkylation reaction is produced by the combustion of a filler with air. 5. Process according to any one of claims 1 to 4, characterized in that the gaseous reaction by-products from the dealkylation with steam, in particular carbon monoxide and methane, are also used as filling material. for combustion with air. 6. Method according to any one of claims 1 to 5, characterized in that the burnt gases generated during the combustion -cooled by means of a heat exchanger by heating the fillers from the dealkylation to the steam. 7. Method according to any one of claims 1 to 6, characterized in that the C7 + fraction and the steam are guided in pipes, preferably from top to bottom, on a solid catalyst, the catalyst being inside the pipes. 8. Method according to any one of claims 1 to 7, characterized in that heat is supplied from the outside in the pipes. 9. The method of claim 8, characterized in that the heat required for the dealkylation reaction is transmitted to the pipes by electromagnetic radiation, heat radiation and / or convection. 10. Process according to any one of claims 1 to 9, characterized in that a solid catalyst composed of a porous support material, in particular γ-ΑΙ203, spinel MgAl and / or Cr2C> 3, and an active component on the surface of the support material, in particular Rh with a charge of 0.1-1.0 wt.% and / or Pd with a load of 0.2 - 2.0 % by weight, is used. 11. Process according to any one of claims 1 to 10, characterized in that the dealkylation with steam is carried out at a temperature of 400 ° C to 600 ° C, preferably 450 ° C to 550 ° C, so particularly preferred from 480 ° C to 520 ° C. 12. Process according to any one of claims 1 to 11, characterized in that the dealkylation with steam is carried out at a pressure of 1 to 15 bar, preferably from 1.2 to 10 bar, particularly preferably from 1 to 1 bar. , 5 to 8 bar. 13. Process according to any one of claims 1 to 12, characterized in that the dealkylation with steam is carried out at a molar quotient of the water vapor with respect to the hydrocarbons which is, when entering the reactor , of the order of 1 to 20, preferably 2 to 15. 14. Process according to any one of Claims 1 to 13, characterized in that the dealkylation with steam is carried out at a molar ratio of the water vapor with respect to the hydrocarbons which is, on entering the reactor. , of the order of 3 to 12, preferably 5 to 10. 15. Process according to any one of Claims 1 to 14, characterized in that the C7 + fraction is subjected, prior to the dealkylation with steam, to a process for converting dienes and styrenes, hydrogenation processes with the use of hydrogen. being especially used for this purpose. 16. Process according to any one of Claims 1 to 15, characterized in that the C7 + fraction is subjected, prior to the dealkylation with steam, to a process for the conversion and elimination of sulfur-containing, nitrogen-containing components. and / or oxygen, hydrogenation processes using hydrogen being especially used for this purpose. 17. Process according to any one of claims 1 to 16, characterized in that the reaction products of the dealkylation with steam are cooled and separated during a 3-phase separation into gaseous reaction products, hydrocarbons and water. . 18. Process according to any one of claims 1 to 17, characterized in that the hydrogen forming during the dealkylation with steam of the C7 + fraction is fed wholly or partly into the filler for the processes using hydrogen according to claim 15 or 16. 19. Process according to any one of Claims 1 to 18, characterized in that the hydrogen forming during the dealkylation with steam of the C7 + fraction is introduced as a filler in any process using hydrogen. preferably in a process for the conversion and removal of sulfur-containing components or a process for cracking a hydrocarbon-containing feedstock with hydrogen in the oil refinery. 20. Process according to any one of claims 1 to 19, characterized in that the sulfur content of the C7 + fraction is reduced, before the dealkylation with steam, to less than 10 ppm, preferably less than 3 ppm, particularly preferably at less than 1 ppm. 21. Process according to any one of claims 1 to 20, characterized in that the benzene is separated from the hydrocarbons of the reaction products by a rectification. Process according to Claim 21, characterized in that the benzene is subjected, after rectification, to an adsorption treatment to dry and remove the trace components, the benzene being fed over an adsorbent on which the trace components are adsorbed. Process according to any one of Claims 1 to 22, characterized in that components of the C7 + fraction whose boiling point is very close to that of benzene and which form azeotropes are converted by the dealkylation with steam. Process according to any one of claims 21 to 23, characterized in that all reaction products with a boiling point higher than that of benzene which come from the rectification and which consist mainly of unconverted Steam dealkylation is suitably returned via optional hydrogenation as feedstock in the dealkylation with steam. 25. Process according to any one of claims 21 to 23, characterized in that all the reaction products with a boiling point higher than that of benzene which come from the rectification and which consist mainly of unconverted the dealkylation with steam are returned to a hydrogenation of a C7 + fraction, a 0β + fraction or a hydrogenation of a fraction consisting mainly of hydrocarbons having at least five carbon atoms before the dealkylation with steam. 26. Process according to any one of claims 1 to 25, characterized in that, prior to the dealkylation with steam, a fraction consisting mainly of hydrocarbons comprising at least eight carbon atoms (Cs + fraction) is separated by distillation of the fraction C7 +, the separated Ce + fraction being fed as a filler in a process to obtain paraxylene or discharged to be treated as gasoline.