A process for producing xylene

Abstract

The present application relates to the field of xylene preparation, and discloses a method for producing xylene, which comprises the following steps: (1) performing a hydrocracking reaction on C6+ components in a gas phase reactor to generate product A containing light hydrocarbons, C6-C7 components, C8 aromatic hydrocarbons and C9+ components; (2) performing a transalkylation reaction on the C9+ components in product A with benzene and / or toluene in a liquid phase reactor to generate product B containing xylene. The method combines high-temperature gas phase reaction and low-temperature liquid phase reaction to realize efficient xylene yield increase, and is conducive to improving xylene selectivity due to effective inhibition of high-activation-energy hydrocracking and demethylation side reactions. Through the combined technology, aromatic hydrocarbon loss can be effectively reduced, operating energy consumption can be reduced, and xylene yield can be improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of xylene production, in particular to a method for producing xylene. BACKGROUND

[0002] In recent years, due to the development of plastic, synthetic fiber and synthetic rubber industry, the market demand for xylene (PX) still maintains a high growth rate. Industrially, xylene is mainly produced by aromatic complex device, using naphtha as raw material to obtain xylene through reforming, isomerization, disproportionation and transalkylation and PX adsorption separation processes. Among them, the disproportionation and transalkylation of C9 + A is the raw material, and xylene and benzene are produced by toluene disproportionation, transalkylation and dealkylation. The xylene produced by this technology accounts for 50% of the entire aromatic complex device, and is an important technical unit for increasing xylene production. Generally, this process is a high-temperature gas phase reaction under hydrogenation conditions, the reaction temperature is 350-450℃, the reaction pressure is 2-3MPa, and the hydrogen / hydrocarbon molar ratio is 2-4. High-temperature gas phase reaction has the characteristics of high conversion efficiency, especially high dealkylation efficiency of heavy aromatics, but at the same time, there are problems such as large loss of aromatics and more by-products such as benzene in the product. In addition, high reaction temperature and maintaining a large amount of hydrogen circulation result in high energy consumption of the device.

[0003] CN1067365C discloses a toluene disproportionation and transalkylation process, in which toluene and C9 + A are subjected to transalkylation reaction on a bismuth-containing catalyst under hydrogenation conditions to produce benzene and carbon eight. Among them, benzene and carbon eight aromatics are produced as products, and toluene and unreacted C9 + A are recycled back to the reaction zone. CN103121915B discloses a toluene and heavy aromatics disproportionation and transalkylation method. By introducing hydrogenation metal into the molecular sieve and introducing an additive selected from alkaline earth metal or rare earth metal at the same time, the strong acid centers on the surface of the molecular sieve are reduced, thereby weakening the deep demethylation reaction of the product xylene by the strong acid centers, and the purpose of improving the xylene yield is achieved. CN107759434A discloses a process for treating double-ring or multi-ring heavy aromatics. Different raw materials are treated by two-stage reactors, but all are gas phase reaction conditions. As can be seen from the above, the existing technology all adopts fixed bed gas phase reaction process, and toluene and heavy aromatics in the reformate are mixed and simultaneously introduced into the reactor, and toluene disproportionation, transalkylation and dealkylation and other complex reactions occur on the catalyst simultaneously, but it cannot effectively reduce the loss of aromatics and reduce the operating energy consumption and other problems.

[0004] CN108779047A discloses a liquid-phase alkyl transfer catalyst using an acidic molecular sieve with a twelve-membered ring or larger porous network as the active component. This catalyst is used for the alkyl transfer of 1-cyclic aromatic compounds to xylene, exhibiting lower energy consumption and fewer side reactions compared to traditional gas-phase alkyl transfer methods. CN104230633A discloses a method for liquid-phase alkyl transfer of polyethylbenzene and benzene, using a binder-free Y-type molecular sieve with a SiO2 / Al2O3 molar ratio of 3-20 as the catalyst. This method features high reactivity and good catalyst stability.

[0005] This invention discovers that, based on the activation energy requirements of different reactions, a combination of high-temperature gas-phase reaction and low-temperature liquid-phase reaction can better control side reactions and achieve energy conservation and consumption reduction in the equipment. Specifically, under high-temperature gas-phase reaction conditions, reactions such as fused ring hydrocracking, non-aromatic cleavage, and dealkylation are achieved to produce products rich in methyl aromatics; under low-temperature liquid-phase reaction conditions, alkyl transfer reactions between methyl aromatics are carried out to efficiently increase xylene production. Because the high-activation-energy hydrocracking and demethylation side reactions are effectively suppressed, xylene selectivity is improved. This combined technology can effectively reduce aromatics loss, operating energy consumption, and increase xylene yield. Summary of the Invention

[0006] The purpose of this invention is to overcome the problems of high aromatic hydrocarbon loss and low xylene yield in the prior art, and to provide a method for producing xylene by combining gas-phase reaction and liquid-phase reaction.

[0007] To achieve the above objectives, the present invention provides a method for producing xylene, the method comprising:

[0008] (1) The C6+ component is subjected to a hydrocracking reaction in a gas phase reactor to generate product A containing light hydrocarbons, C6-C7 components, C8 aromatic hydrocarbons and C9+ components.

[0009] (2) The C9+ component containing product A is reacted with benzene and / or toluene in a liquid-phase reactor to generate product B containing xylene.

[0010] According to the method provided by this invention, based on the activation energy requirements of different reactions, a combination of high-temperature gas-phase reaction and low-temperature liquid-phase reaction can better control side reactions and achieve energy saving and consumption reduction in the equipment. Specifically, under high-temperature gas-phase reaction conditions, reactions such as fused ring hydrogenation cracking, non-aromatic cleavage, and dealkylation are realized to produce products rich in methyl aromatics; under low-temperature liquid-phase reaction conditions, alkyl transfer reactions between methyl aromatics are carried out to efficiently increase xylene production. Because the high-activation-energy hydrogenation cracking and demethylation side reactions are effectively suppressed, xylene selectivity is improved. This combined technology can effectively reduce aromatics loss, operating energy consumption, and increase xylene yield. Attached Figure Description

[0011] Figure 1 This is a process flow diagram of Embodiment 1 of the present invention;

[0012] Figure 2 This is a process flow diagram of Embodiment 2 of the present invention. Detailed Implementation

[0013] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0014] In this invention, there is no particular limitation on the specific selection of the liquid-phase reactor and the gas-phase reactor. They can be reactors that are conventionally used in the art, each capable of reacting under liquid-phase conditions or under gas-phase conditions.

[0015] This invention provides a method for producing xylene, the method comprising:

[0016] (1) The C6+ component is subjected to a hydrocracking reaction in a gas phase reactor to generate product A containing light hydrocarbons, C6-C7 components, C8 aromatic hydrocarbons and C9+ components.

[0017] (2) The C9+ component containing product A is reacted with benzene and / or toluene in a liquid-phase reactor to generate product B containing xylene.

[0018] According to the present invention, a hydrocracking reaction is first carried out under high-temperature gas-phase reaction conditions to produce a product rich in methyl aromatics; then, an alkyl transfer reaction between methyl aromatics is carried out under low-temperature liquid-phase reaction conditions to efficiently increase xylene production. This can effectively suppress the high-activation-energy hydrocracking and demethylation side reactions, thereby improving xylene selectivity.

[0019] The present invention has a wide range of choices for the specific components of the C6+ component. Preferably, the distillation range of the C6+ component is 70-350℃, more preferably 80-330℃. More preferably, the C6+ component contains at least one of alkanes, alkenes, monocyclic aromatics and polycyclic aromatics.

[0020] According to a preferred embodiment of the present invention, based on the total amount of the C6+ components, the content of alkane is 0-30% by weight, the content of olefin is 0-20% by weight, the content of monocyclic aromatic hydrocarbon is 20-100% by weight, and the content of polycyclic aromatic hydrocarbon is 0-50% by weight; more preferably, based on the total amount of the C6+ components, the content of alkane is 5-25% by weight, the content of olefin is 4-15% by weight, the content of monocyclic aromatic hydrocarbon is 30-50% by weight, and the content of polycyclic aromatic hydrocarbon is 25-45% by weight.

[0021] In this invention, there are no special restrictions on the source of the C6+ component. Preferably, the C6+ component comes from catalytic reforming products, catalytic cracking products, steam cracking products, hydrocracking products, or any mixture thereof.

[0022] According to a preferred embodiment of the present invention, the gas-phase reactor optionally includes a first reaction zone and a second reaction zone, wherein the first reaction zone contains a selective hydrogenation catalyst and the second reaction zone contains a hydrocracking catalyst. For example, the second reaction zone can be set separately in the gas-phase reactor, or the first and second reaction zones can be set in the gas-phase reactor; preferably, when the second reaction zone is set separately in the gas-phase reactor, it is advantageous to independently adjust the reaction parameters of the second reaction zone, which is suitable for processing raw materials with different compositions.

[0023] According to a preferred embodiment of the present invention, the selective hydrogenation catalyst contains a support selected from at least one of Al2O3, SiO2, MgO and diatomaceous earth, and a hydrogenation metal selected from at least one of Ni, Pt, Pd and Mo; more preferably, the support is Al2O3 and / or SiO2, and the hydrogenation metal is Ni and / or Mo.

[0024] According to a preferred embodiment of the present invention, based on the total amount of the selective hydrogenation catalyst, the content of the support is 80-99.9% by weight, preferably 90-95% by weight; and the content of the hydrogenation metal is 0.1-20% by weight, preferably 5-10% by weight.

[0025] According to a preferred embodiment of the present invention, the hydrocracking catalyst contains a silica-alumina molecular sieve having ten-membered or twelve-membered ring channels, more preferably at least one of ZSM-5, MOR, Beta, ZSM-12, and MCM-22 molecular sieves; more preferably ZSM-5 and / or Beta molecular sieves. The silica-alumina molecular sieve used in the present invention can be commercially available or prepared by conventional methods.

[0026] According to a preferred embodiment of the present invention, the hydrocracking catalyst further contains at least one hydrogenating metal selected from Mo, Pt, Re, Co, and W, more preferably a Mo-Pt bimetallic catalyst. This preferred embodiment has suitable hydrogenation activity and is more conducive to suppressing deep hydrogenation side reactions of monocyclic aromatic hydrocarbons.

[0027] According to a preferred embodiment of the present invention, based on the total amount of the hydrocracking catalyst, the content of the silica-alumina molecular sieve is 50-80% by weight, and the content of the hydrogenated metal is 0.1-20% by weight; more preferably, the content of the silica-alumina molecular sieve is 60-70% by weight, and the content of the hydrogenated metal is 5-10% by weight. The hydrocracking catalyst also preferably contains a binder, and the content of the binder is selected from a wide range, aiming to meet the 100% principle.

[0028] The present invention allows for a wide range of choices of the type of adhesive. Preferably, the adhesive is alumina and / or silicon dioxide.

[0029] According to a preferred embodiment of the present invention, before use, the selective hydrogenation catalyst, the hydrocracking catalyst, and the liquid-phase alkyl transfer catalyst further include a step of reducing each of them separately. The reduction conditions preferably each independently include: carried out under a hydrogen atmosphere at a temperature of 300-600°C for 1-5 hours.

[0030] According to a preferred embodiment of the present invention, the reaction conditions in the first reaction zone include: a reaction temperature of 150-400°C, a reaction pressure of 0.5-5 MPa, and a feed mass hourly space velocity of 2-20 h⁻¹. -1 The hydrogen-to-hydrogen volume ratio is 200-2000; specifically, the reaction temperature is preferably 300-400℃, the reaction pressure is preferably 1-3MPa, and the feed mass hourly space velocity is preferably 2-5h. -1 The hydrogen-to-hydrogen volume ratio can preferably be 500-1000.

[0031] According to a preferred embodiment of the present invention, the reaction conditions in the second reaction zone include: a reaction temperature of 300-500°C, a reaction pressure of 2-7 MPa, and a feed mass hourly space velocity of 1-4 h⁻¹. -1 The hydrogen-to-hydrogen volume ratio is 200-2000. Specifically, the reaction temperature is preferably 350-400℃, the reaction pressure is preferably 5-7MPa, and the feed mass hourly space velocity is preferably 1-3h. -1 The hydrogen-to-hydrogen volume ratio can preferably be 800-1700.

[0032] According to a preferred embodiment of the present invention, the liquid-phase reactor is provided with a liquid-phase alkyl transfer catalyst to catalyze the alkyl transfer reaction between methyl aromatics to produce xylene under low-temperature liquid-phase reaction conditions.

[0033] According to a preferred embodiment of the present invention, the liquid-phase alkyl transfer catalyst contains a molecular sieve and an acidic modifying component, wherein the acidic modifying component is at least one of phosphomolybdic heteropoly acid, phosphotungstic heteropoly acid, or sulfate, more preferably phosphomolybdic heteropoly acid and / or phosphotungstic heteropoly acid. Under the above preferred conditions, it is beneficial to further improve the yield of xylene.

[0034] According to a preferred embodiment of the present invention, the molecular sieve is a silica-alumina molecular sieve with twelve-membered ring channels, more preferably at least one of MCM-22, Y, Beta, and MOR; more preferably at least one of MCM-22, Y, and Beta molecular sieves. Using the above preferred embodiment facilitates the diffusion of reactants to the desired reactive sites under liquid phase conditions. The molecular sieve used in the present invention can be commercially available or prepared using conventional methods.

[0035] According to a preferred embodiment of the present invention, based on the total amount of the liquid-phase alkyl transfer catalyst, the content of molecular sieve is 30-80% by weight, and the content of acidic modifying component is 5-50% by weight; more preferably, the content of molecular sieve is 40-70% by weight, and the content of acidic modifying component is 20-40% by weight; the hydrocracking catalyst also preferably contains a binder, and the content of the binder is selected from a wide range, as long as it can meet the 100% principle. In the present invention, the liquid-phase alkyl transfer catalyst may contain a binder or not, and the selection range of the type of binder is wide. Preferably, the binder is alumina and / or boehmite. Using the above preferred embodiment is more conducive to promoting the alkyl transfer reaction under low temperature and liquid phase conditions.

[0036] According to a preferred embodiment of the present invention, the liquid-phase alkyl transfer catalyst further comprises a hydrogenation metal component, wherein the hydrogenation metal component is selected from at least one group VIB, VIIB, and VIII metals; preferably, the hydrogenation metal component is selected from at least one group Cr, Mo, W, Mn, Re, Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, and Pt; more preferably, at least one group Pt, Pd, Ni, and Cu; and even more preferably, Pt. The liquid-phase alkyl transfer catalyst modified by the combined hydrogenation metal component and the acid-modifying component exhibits a superior effect in increasing xylene production.

[0037] According to a preferred embodiment of the present invention, based on the total amount of the liquid-phase alkyl transfer catalyst, the content of the hydrogenation metal component is 0.05-1% by weight, more preferably 0.1-0.5% by weight. Under the above preferred conditions, it is helpful to achieve a highly efficient synergistic effect between the metal hydrogenation site and the acidic site.

[0038] According to a preferred embodiment of the present invention, the method for preparing the liquid-phase alkyl transfer catalyst includes:

[0039] a) Acidic modified components are immobilized on the surface of a molecular sieve in a non-aqueous solution or an aqueous solution to obtain a modified molecular sieve;

[0040] b) The modified molecular sieve from step a) is immobilized with hydrogenated metal components to prepare a modified catalyst.

[0041] In this invention, there are no specific limitations on the immobilization methods described in steps a) and b), and they can be selected from any conventional immobilization method. Preferably, the immobilization methods described in steps a) and b) are each independently selected from impregnation, precipitation, or ion exchange methods.

[0042] The impregnation, precipitation, or ion exchange methods can be carried out in accordance with conventional techniques in the field, and will not be described in detail here.

[0043] According to a preferred embodiment of the present invention, when the impregnation method is used for immobilization, the preparation method of the liquid-phase alkyl transfer catalyst includes: impregnating a molecular sieve in a non-aqueous or aqueous solution of an acidic modifying component, and drying it to obtain a modified molecular sieve; molding the modified molecular sieve with an optional binder, and calcining it to obtain a modified molecular sieve support; impregnating the modified molecular sieve support with a hydrogenated metal component, and drying and calcining it to obtain a liquid-phase alkyl transfer catalyst. Preferably, the non-aqueous solution can be selected from at least one of ethanol, propanol, acetone, and aromatic hydrocarbons; preferably, the drying temperature is 100-150°C; preferably, the calcination includes calcining at 450-550°C for 2-4 hours; the present invention has a wide range of choices for the molding method, for example, it can be kneading molding; preferably, a binder can be added during the kneading molding or molecular sieve impregnation process.

[0044] According to a preferred embodiment of the present invention, the reaction conditions of the liquid-phase reactor include: a temperature of 150-400°C, a pressure of 2-6 MPa, and a feed mass hourly space velocity of 0.5-8 h⁻¹. -1 The hydrogen-to-hydrogen molar ratio is 0-2; more preferably, the reaction conditions of the liquid-phase reactor include: a temperature of 200-300℃, a pressure of 2-5MPa, and a feed mass hourly space velocity of 1-4h. -1 The hydrogen-to-hydrogen volume ratio is 10-500; more preferably, the hydrogen-to-hydrogen volume ratio is 10-50.

[0045] According to a preferred embodiment of the present invention, the molar ratio of C9+ component to benzene and / or toluene is 0.1-5:1, more preferably 0.3-3:1; under the above preferred conditions, it is beneficial to increase the yield of xylene in the product.

[0046] According to a preferred embodiment of the present invention, in step (2), the xylene content in product B is increased by more than 20% compared to the xylene content in the feed to the liquid-phase reactor. The yield of xylene is significantly improved through the alkyl transfer reaction in the liquid-phase reactor.

[0047] According to a preferred embodiment of the present invention, the method further includes fractionating the product A to obtain light hydrocarbons, C6-C7 components, C8 aromatic hydrocarbons, C9-C10 aromatic hydrocarbons, and C10+ components; the light hydrocarbons include one or more of methane, ethane, propane, butane, and pentane; the C6-C7 components include benzene and / or toluene; the C8 aromatic hydrocarbon components include xylene and ethylbenzene; the C9-C10 aromatic hydrocarbon components include one or more of trimethylbenzene, methyl ethylbenzene, tetramethylbenzene, and dimethyl ethylbenzene; and the C10+ components include one or more of fused-ring aromatic hydrocarbons such as pentamethylbenzene, methylnaphthalene, dimethylnaphthalene, anthracene, and biphenyl, as well as gums.

[0048] According to a preferred embodiment of the present invention, the obtained C6-C7 component provides at least a portion of the benzene and / or toluene described in step (2). Utilizing a portion of the product from step (1) as a reaction raw material in step (2) is beneficial for improving the utilization rate of the reaction raw materials and reducing material consumption in the xylene preparation process.

[0049] According to a preferred embodiment of the present invention, the C9+ component in step (2) is a C9-C10 aromatic hydrocarbon, preferably derived from the C9-C10 aromatic hydrocarbon obtained by the above fractionation.

[0050] The present invention will be described in detail below through embodiments.

[0051] The following preparation examples illustrate the preparation of liquid-phase alkyl transfer catalysts.

[0052] In the following preparation examples, HY, MCM-22, and Beta molecular sieves were all prepared in-house, with silicon-aluminum molecular ratios (Si / Al2) of 25, 30, and 50, respectively.

[0053] Preparation Example 1

[0054] A 20% by weight phosphomolybdic acid heteropoly acid ethanol solution was prepared, and a certain amount of HY type molecular sieve was added and stirred at room temperature for 4 hours. Then, it was spray-dried at 120℃ and calcined at 450℃ for 3 hours to obtain a heteropoly acid modified molecular sieve. The modified molecular sieve was kneaded with alumina and calcined at 500℃ for 3 hours to obtain a modified molecular sieve support. An equal volume of the modified molecular sieve support was impregnated with a certain amount of chloroplatinic acid, dried at 120℃, and then calcined at 500℃ for 3 hours to obtain a liquid-phase alkyl transfer catalyst C1. The composition and properties of the obtained catalyst are shown in Table 1.

[0055] Preparation Example 2

[0056] A 20% by weight phosphotungsten heteropolyacid ethanol solution was prepared, and a certain amount of HY-type molecular sieve was added and stirred at room temperature for 4 hours. Then, it was spray-dried at 120°C and calcined at 500°C for 3 hours to obtain a heteropolyacid modified molecular sieve. The modified molecular sieve was kneaded with alumina and calcined at 500°C for 3 hours to obtain a modified molecular sieve support. An equal volume of the modified molecular sieve support was impregnated with a certain amount of chloroplatinic acid, dried at 120°C, and then calcined at 500°C for 3 hours to obtain a liquid-phase alkyl transfer catalyst C2. The composition and properties of the obtained catalyst are shown in Table 1.

[0057] Preparation Example 3

[0058] A 20% by weight phosphotungsten heteropolyacid ethanol solution was prepared, and a certain amount of MCM-22 molecular sieve was added and stirred at room temperature for 4 hours. Then, it was spray-dried at 120℃ and calcined at 500℃ for 3 hours to obtain a heteropolyacid modified molecular sieve. The modified molecular sieve was kneaded with alumina and calcined at 500℃ for 3 hours to obtain a modified molecular sieve support. An equal volume of the modified molecular sieve support was impregnated with a certain amount of chloroplatinic acid, dried at 120℃, and then calcined at 500℃ for 3 hours to obtain a liquid-phase alkyl transfer catalyst C3. The composition and properties of the obtained catalyst are shown in Table 1.

[0059] Preparation Example 4

[0060] A 20% by weight phosphomolybdic acid heteropolyacid ethanol solution was prepared, and a certain amount of Beta molecular sieve was added and stirred at 70°C for 4 hours. Then, it was spray-dried at 120°C and calcined at 450°C for 3 hours to obtain a heteropolyacid modified molecular sieve. The modified molecular sieve was kneaded with alumina and calcined at 500°C for 3 hours to obtain a modified molecular sieve support. An equal volume of the modified molecular sieve support was impregnated with a certain amount of chloroplatinic acid, dried at 120°C, and calcined at 500°C for 3 hours to obtain a liquid-phase alkyl transfer catalyst C4. The composition and properties of the obtained catalyst are shown in Table 1.

[0061] Preparation Example 5

[0062] A 20% by weight phosphotungsten heteropolyacid ethanol solution was prepared, and a certain amount of MCM-22 molecular sieve was added and stirred at room temperature for 4 hours. Then, the solution was spray-dried at 120°C to obtain a heteropolyacid modified molecular sieve. The modified molecular sieve was kneaded with alumina and calcined at 500°C for 3 hours to obtain a modified molecular sieve support. An equal volume of the modified molecular sieve support was impregnated with a certain amount of chloroplatinic acid, dried at 120°C, and then calcined at 500°C for 3 hours to obtain a liquid-phase alkyl transfer catalyst C5. The composition and properties of the obtained catalyst are shown in Table 1.

[0063] Preparation Example 6

[0064] A 20% by weight phosphotungsten heteropoly acid ethanol solution was prepared, and a certain amount of MCM-22 molecular sieve and pseudoboehmite were added. The mixture was stirred at room temperature for 4 hours, and then spray-dried at 120°C to obtain a heteropoly acid modified molecular sieve. The modified molecular sieve was kneaded into a shape and calcined at 550°C for 3 hours to obtain a modified molecular sieve support. An equal volume of the modified molecular sieve support was impregnated with a certain amount of chloroplatinic acid, dried at 120°C, and then calcined at 500°C for 3 hours to obtain a liquid-phase alkyl transfer catalyst C6. The composition and properties of the obtained catalyst are shown in Table 1.

[0065] Preparation Example 7

[0066] A 20% by weight aqueous solution of phosphotungsten heteropoly acid was prepared, and a certain amount of MCM-22 molecular sieve was added. The mixture was stirred at 80°C for 4 hours and then spray-dried at 120°C to obtain a heteropoly acid modified molecular sieve. The modified molecular sieve was kneaded with alumina and calcined at 500°C for 3 hours to obtain a modified molecular sieve support. The modified molecular sieve support was exchanged with a dichloroplatinum ammonium solution at room temperature for 6 hours, dried at 120°C, and then calcined at 500°C for 3 hours to obtain a liquid-phase alkyl transfer catalyst C7. The composition and properties of the obtained catalyst are shown in Table 1.

[0067] Preparation Example 8

[0068] A certain amount of MCM-22 molecular sieve was weighed, impregnated with ammonium sulfate, and then dried at 120℃ to obtain a modified molecular sieve. The modified molecular sieve was kneaded with alumina and calcined at 500℃ for 3 hours to obtain a modified molecular sieve support. An equal volume of the modified molecular sieve support was impregnated with a certain amount of chloroplatinic acid, dried at 120℃, and then calcined at 500℃ for 3 hours to obtain a liquid-phase alkyl transfer catalyst C8. The composition and properties of the obtained catalyst are shown in Table 1.

[0069] Preparation Example 9

[0070] A certain amount of MCM-22 molecular sieve was weighed and kneaded with alumina to form a modified molecular sieve support. The modified molecular sieve support was calcined at 500℃ for 3 hours to obtain a modified molecular sieve support. An equal volume of the modified molecular sieve support was impregnated with a certain amount of chloroplatinic acid, dried at 120℃, and then calcined at 500℃ for 3 hours to obtain a liquid-phase alkyl transfer catalyst C9. The composition and properties of the obtained catalyst are shown in Table 1.

[0071] Preparation Example 10

[0072] A 20% by weight phosphotungstic heteropoly acid ethanol solution was prepared, and a certain amount of MCM-22 molecular sieve was added and stirred at room temperature for 4 hours. Then, it was spray-dried at 120℃ and calcined at 500℃ for 3 hours to obtain a heteropoly acid modified molecular sieve. The modified molecular sieve was kneaded with alumina and calcined at 500℃ for 3 hours to obtain a liquid-phase alkyl transfer catalyst C10. The composition and properties of the obtained catalyst are shown in Table 1.

[0073] Preparation Example 11

[0074] A certain amount of MCM-22 molecular sieve was kneaded with alumina and calcined at 500℃ for 3 hours to obtain liquid-phase alkyl transfer catalyst C11. The composition and properties of the obtained catalyst are shown in Table 1.

[0075] Table 1. Composition of catalysts obtained in each preparation example

[0076]

[0077]

[0078] Note: The remainder in Table 1 is binder.

[0079] The following examples illustrate the method for producing xylene according to the present invention.

[0080] Example 1

[0081] For reference Figure 1 To provide a more comprehensive description of this application, a 100-ton / hour catalytic cracking gasoline and light diesel oil mixture (distillation range: 70-300℃) undergoes desulfurization and denitrogenation pretreatment before being sequentially fed into a hydrogenation saturation unit. This unit undergoes olefin saturation and selective hydrogenation of polycyclic aromatic hydrocarbons (PAHs). The reaction products then enter a hydrocracking unit for non-aromatic cracking, cycloalkane ring-opening, and dealkylation reactions, generating a product rich in methyl aromatics. This product then enters a separation unit for sequential separation, yielding C1-C5 light hydrocarbons, C6-C7 components, C8 components, C9-C10 components, and C10+ components. Among these, C5... -Light hydrocarbons are collected as feedstock for cracking, C8 fraction is collected as product, and C6-C7 and C9-C10 fractions enter the liquid-phase reactor for liquid-phase alkyl transfer reaction. At least a portion of the C10+ fraction is recycled back to the hydrocracking unit. The reaction products from the liquid-phase reactor are recycled back to the separation unit for sequential separation. The hydrocracking saturated catalyst is a Ni-Mo / alumina catalyst (Ni content 2wt%, Mo content 6wt%, the remainder alumina), and the hydrocracking catalyst is a Pt-Mo / (ZSM-5+Beta) catalyst (Pt content 0.1wt%, Mo content 8wt%, ZSM-5 molecular sieve content 15wt%, Beta molecular sieve content 50wt%, the remainder alumina). Before feeding, the catalysts are reduced for 3 hours in a hydrogen atmosphere at 450°C. The liquid-phase alkyl transfer catalyst is C1, and before feeding, the catalyst is reduced for 3 hours in a hydrogen atmosphere at 300°C.

[0082] The raw material composition is shown in Table 2, the reaction conditions of each unit are shown in Table 3, and the product yield of the unit is shown in Table 4.

[0083] Example 2

[0084] For reference Figure 2 This application will be described more fully. A mixture of reformed gasoline and light diesel oil (distillation range: 80-330℃) at a capacity of 100 tons / hour undergoes desulfurization and denitrogenation pretreatment before being fed into a hydrogenation saturation unit. Olefin saturation and selective hydrogenation of polycyclic aromatic hydrocarbons occur. The reaction products then enter a hydrocracking unit for non-aromatic cracking, cycloalkane ring-opening, and dealkylation reactions, producing a product rich in methyl aromatics. This product then enters a separation unit for sequential separation, yielding C1-C5 light hydrocarbons, C6-C7 components, C8 components, C9-C10 components, and C10+ components. Among these, C5... - Light hydrocarbons are collected as feedstock for cracking, C8 fraction is collected as product, and C6-C7 and C9-C10 fractions enter the liquid-phase reactor for liquid-phase alkyl transfer reaction. At least a portion of the C10+ fraction is recycled back to the hydrocracking unit. The reaction products from the liquid-phase reactor are recycled back to the separation unit for sequential separation. The hydrocracking saturated catalyst is a Ni-Mo / alumina catalyst (2wt% Ni, 6wt% Mo, remainder alumina), and the hydrocracking catalyst is a Pt-Mo / (ZSM-5+Beta) catalyst (0.1wt% Pt, 8wt% Mo, 15wt% ZSM-5 molecular sieve, 50wt% Beta molecular sieve, remainder alumina). Before feeding, the catalysts are reduced for 3 hours in a hydrogen atmosphere at 450°C. The liquid-phase alkyl transfer catalyst is C1, and before feeding, the catalyst is reduced for 3 hours in a hydrogen atmosphere at 300°C.

[0085] The raw material composition is shown in Table 2, the reaction conditions of each unit are shown in Table 3, and the product yield of the unit is shown in Table 4.

[0086] Table 2 Composition of raw materials used in each embodiment

[0087]

[0088]

[0089] Table 3 Operating conditions for Examples 1-2

[0090]

[0091] Table 4. Test results of Examples 1-2

[0092]

[0093]

[0094] The following examples illustrate the processing method of this application using the liquid-phase alkyl transfer catalyst of this application.

[0095] Example 3-12

[0096] The raw materials were processed according to the method of Example 2, except that the liquid phase alkyl transfer catalyst C1 was replaced with the liquid phase alkyl transfer catalysts C2-C11 obtained in Preparation Examples 2-11, and the results are shown in Table 5.

[0097] Comparative Example 1

[0098] The raw materials were processed according to the method of Example 2, except that the liquid-phase alkyl transfer unit was replaced with a conventional gas-phase alkyl transfer unit, the gas-phase alkyl transfer catalyst was Mo / MOR (1% molybdenum content), and the reaction conditions were: reaction temperature 370°C, reaction pressure 3.0 MPa, H2 / HC = 3, WHSV = 3.0 h. -1 With all other operating conditions unchanged, the results are shown in Table 5.

[0099] Table 5. Product Yield of the Unit

[0100]

[0101]

[0102] As shown in Table 5, the combined gas-phase reaction and liquid-phase alkyl transfer process of this invention achieves a higher xylene yield and a lower yield of heavy components compared to the traditional gas-phase alkyl transfer process. In the optimized scheme, the liquid-phase alkyl transfer catalyst modified with a composite of heteropolyacid and hydrogenated metal promoter exhibits even better xylene production enhancement.

[0103] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for producing xylene, the method comprising: (1) The C6+ component is subjected to a hydrocracking reaction in a gas phase reactor to produce product A containing light hydrocarbons, C6-C7 components, C8 aromatic hydrocarbons and C9+ components; (2) The C9+ component containing product A is reacted with benzene and / or toluene in a liquid-phase reactor to generate product B containing xylene; The liquid-phase reactor is equipped with a liquid-phase alkyl transfer catalyst; The liquid-phase alkyl transfer catalyst contains a molecular sieve and an acidic modifying component, wherein the acidic modifying component is a phosphomolybdic heteropolyacid, a phosphotungstic heteropolyacid, or a sulfate. The molecular sieve is a silica-alumina molecular sieve with twelve-membered ring channels; In the liquid-phase alkyl transfer catalyst, based on the total amount of catalyst, the content of molecular sieve is 30-90% by weight, and the content of acidic modifying component is 5-50% by weight.

2. The method according to claim 1, wherein, The distillation range of the C6+ component is 70-350℃; And / or, the C6+ component contains at least one of alkanes, alkenes, monocyclic aromatics and polycyclic aromatics; And / or, the C6+ component is derived from catalytic reforming products, catalytic cracking products, steam cracking products, hydrocracking products, or any mixture thereof.

3. The method according to claim 2, wherein, The distillation range of the C6+ component is 80-330℃; And / or, based on the total amount of the C6+ components, the content of alkanes is 0-30% by weight, the content of olefins is 0-20% by weight, the content of monocyclic aromatic hydrocarbons is 20-100% by weight, and the content of polycyclic aromatic hydrocarbons is 0-50% by weight.

4. The method according to claim 1, wherein, The gas-phase reactor is optionally provided with a first reaction zone and a second reaction zone, wherein the first reaction zone contains a selective hydrogenation catalyst and the second reaction zone contains a hydrocracking catalyst.

5. The method according to claim 4, wherein, The selective hydrogenation catalyst contains a support selected from at least one of Al2O3, SiO2, MgO and diatomaceous earth, and a hydrogenation metal selected from at least one of Ni, Pt, Pd and Mo.

6. The method according to claim 5, wherein, Based on the total amount of the selective hydrogenation catalyst, the content of the support is 80-99.9% by weight, and the content of the hydrogenation metal is 0.1-20% by weight.

7. The method according to claim 4, wherein, The hydrocracking catalyst contains a silica-alumina molecular sieve with ten- or twelve-membered ring channels.

8. The method according to claim 7, wherein, The molecules are screened from at least one of ZSM-5, MOR, Beta, ZSM-12, and MCM-22.

9. The method according to claim 7 or 8, wherein, The hydrocracking catalyst also contains at least one hydrogenation metal selected from Mo, Pt, Re, Co and W.

10. The method according to claim 9, wherein, The hydrogenated metal is a Mo-Pt bimetal.

11. The method according to claim 9, wherein, Based on the total amount of the hydrocracking catalyst, the content of the silica-alumina molecular sieve is 50-80% by weight, and the content of the hydrogenated metal is 0.1-20% by weight.

12. The method according to claim 4, wherein, The reaction conditions in the first reaction zone include: a reaction temperature of 150-400℃, a reaction pressure of 0.5-5MPa, and a feed mass hourly space velocity of 2-20h. -1 The hydrogen-to-hydrogen volume ratio is 200-2000; and / or, The reaction conditions in the second reaction zone include: a reaction temperature of 300-500°C. o C, the reaction pressure is 2-7 MPa, and the feed mass hourly space velocity is 1-4 h⁻¹. -1 The hydrogen-to-hydrogen volume ratio is 200-2000.

13. The method according to claim 1, wherein, The molecules in the liquid-phase alkyl transfer catalyst are screened from at least one of MCM-22, Y, Beta, and MOR.

14. The method according to any one of claims 1-8, wherein, The liquid-phase alkyl transfer catalyst also contains at least one hydrogenation metal component selected from group VIB, VIIB and VIII metals.

15. The method according to claim 14, wherein, The hydrogenated metal component is selected from at least one of Pt, Pd, Ni and Cu.

16. The method of claim 14, wherein, Based on the total amount of catalyst, the content of hydrogenated metal components is 0.05-1% by weight.

17. The method of claim 14, wherein, The preparation method of the liquid-phase alkyl transfer catalyst includes: a) Acidic modified components are immobilized on the surface of a molecular sieve in a non-aqueous solution or an aqueous solution to obtain a modified molecular sieve; b) The modified molecular sieve from step a) is supported on hydrogenated metal components to prepare a liquid-phase alkyl transfer catalyst.

18. The method according to claim 17, wherein, The immobilization methods described in steps a) and b) are each independently selected from impregnation, precipitation, or ion exchange methods.

19. The method according to claim 1, wherein, The reaction conditions of the liquid phase reactor include: temperature of 200-300℃, pressure of 2-5MPa, and feed mass hourly space velocity of 1-4h. -1 The hydrogen-to-hydrogen volume ratio is 10-500.

20. The method according to claim 1, wherein, The molar ratio of C9+ component to benzene and / or toluene is 0.1-5:

1.

21. The method according to claim 1, wherein, The molar ratio of C9+ component to benzene and / or toluene is 0.3-3:

1.

22. The method according to any one of claims 1-8, wherein, In step (2), the xylene content in product B is more than 20% higher than the xylene content in the feed to the liquid phase reactor.

23. The method according to any one of claims 1-8, wherein, The method also includes fractionating the product A to obtain light hydrocarbons, C6-C7 components, C8 aromatics, C9-C10 aromatics and C10+ components.

24. The method according to claim 23, wherein, The resulting C6-C7 component provides at least a portion of the benzene and / or toluene described in step (2).

25. The method according to any one of claims 1-8, wherein, The C9+ component in step (2) is a C9-C10 aromatic hydrocarbon.

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