Process and system for producing xylene

Abstract

The present application relates to the technical field of petroleum chemical industry, and discloses a method and system for generating dimethylbenzene. The method comprises: sequentially performing alkylation reaction and transalkylation reaction; wherein, under alkylation reaction conditions, alkanes are contacted with benzene and hydrogen to perform alkylation reaction; under transalkylation reaction conditions, C9+ heavy aromatic hydrocarbons, toluene and hydrogen from the alkylation reaction are contacted to perform transalkylation reaction; wherein, the alkanes are raffinate oil and / or hydrogenated raffinate oil; wherein, the weight ratio of the benzene to the alkanes is 1-9:1; wherein, the weight ratio of the C9+ heavy aromatic hydrocarbons to the toluene is 1-5:1. The method uses non-aromatic hydrocarbons (C5-C9), especially catalytic reforming or steam cracking by-product non-aromatic hydrocarbons and C9+ heavy aromatic hydrocarbons as raw materials, combines alkylation reaction and transalkylation reaction, and has the characteristics of high non-aromatic hydrocarbon conversion rate and high dimethylbenzene yield.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of petroleum chemical industry, in particular to a method and system for producing dimethylbenzene. BACKGROUND

[0002] Dimethylbenzene is the most important part of basic organic chemical raw materials, and p-xylene is the main raw material for producing terephthalic acid, polyester fiber and engineering plastic. At present, the production of dimethylbenzene mainly comes from the reforming process of oil refinery and the by-product of naphtha steam cracking for producing olefins. In the whole production process, there are a large amount of non-aromatic hydrocarbons (C5-C9) and C9+ heavy aromatic hydrocarbons by-products, which have low added value, narrow use and wide sources. At present, the reforming by-product non-aromatic hydrocarbons are widely used in the production of various types of solvent oil (such as 6# solvent oil), and a small amount is used as blending gasoline and olefin cracking raw material. However, due to the low octane number (RON), low boiling range and low ethylene yield, the economic benefits of its processing and utilization are poor. On the other hand, with the construction and expansion of China's aromatic hydrocarbon combined device and large-scale ethylene device, more and more by-product C9+ heavy aromatic hydrocarbons are produced, which are currently mainly used for extraction of trimethylbenzene and tetramethylbenzene monomers and gasoline blending components. However, due to the complex components, small difference in boiling point and great difficulty in separation, as well as the further restriction of aromatic hydrocarbon content in national gasoline standard.

[0003] Patent application CN106367116A discloses a method for preparing light aromatic hydrocarbons from reforming raffinate oil, which converts the reforming raffinate oil into light aromatic hydrocarbons, and the yield of light aromatic hydrocarbons can reach 50-60%, while producing gasoline blending components with octane number (RON) of 87-90. However, there are still problems such as high energy consumption and low dimethylbenzene yield. Patent application CN104557428A discloses a method for increasing the yield of dimethylbenzene by aromatic hydrocarbon transalkylation and alkylation, but there are problems such as high dry gas yield and low raw material conversion rate. Patent application CN106083512A discloses a device and method for preparing benzene and dimethylbenzene from toluene and heavy aromatic hydrocarbons, but the methyl content is limited, and a large amount of benzene is produced, which has no place to go for the refinery that does not need a large amount of benzene. Therefore, it is urgent to develop a method for directly converting non-aromatic hydrocarbons (C5-C9) and C9+ heavy aromatic hydrocarbons into high value-added products. SUMMARY

[0004] The present application aims to solve the problem of low utilization rate of non-aromatic hydrocarbons (C5-C9) and C9+ heavy aromatic hydrocarbons in the prior art, and provides a method and system for producing dimethylbenzene, which uses non-aromatic hydrocarbons (C5-C9), especially catalytic reforming or steam cracking by-product non-aromatic hydrocarbons and C9+ heavy aromatic hydrocarbons as raw materials, combines alkylation reaction and transalkylation reaction, and has the characteristics of high non-aromatic hydrocarbon conversion rate and high dimethylbenzene yield.

[0005] To achieve the above object, the present application provides a method for producing xylene, which comprises: sequentially performing an alkylation reaction and a transalkylation reaction; wherein the alkylation reaction is performed by contacting an alkane with benzene and hydrogen under alkylation reaction conditions; the transalkylation reaction is performed by contacting C9+ heavy aromatic hydrocarbons, toluene and hydrogen from the alkylation reaction under transalkylation reaction conditions; wherein the alkane is raffinate and / or hydrogenated raffinate; the weight ratio of the benzene to the alkane is 1-9:1; the weight ratio of the C9+ heavy aromatic hydrocarbons to toluene is 1-5:1.

[0006] Preferably, the bromine index of the alkane is ≤500 mgBr / 100 g; further preferably, the bromine index of the alkane is ≤200 mgBr / 100 g.

[0007] Preferably, in the alkylation reaction, the weight ratio of the benzene to the alkane is 4-9:1.

[0008] Preferably, in the transalkylation reaction, the weight ratio of the C9+ heavy aromatic hydrocarbons to toluene is 1-2:1.

[0009] The present application provides a system for producing xylene, which comprises: an alkane supply unit, a benzene supply unit, a hydrogen supply unit, a C9+ heavy aromatic hydrocarbon supply unit, an alkylation reactor and a transalkylation reactor, wherein the alkane supply unit, the benzene supply unit and the hydrogen supply unit are in communication with the alkylation reactor, and the C9+ heavy aromatic hydrocarbon supply unit and the hydrogen supply unit are in communication with the transalkylation reactor.

[0010] The system optionally further comprises a hydrofining reactor, which is arranged between the alkane supply unit and the alkylation reactor.

[0011] The inventors of the present application have found that, by using cheap alkane, especially non-aromatic hydrocarbons by-produced in catalytic reforming or steam cracking, as raw materials, and by catalytically producing toluene and xylene through alkylation of the alkane, and then by using low-value C9+ heavy aromatic hydrocarbons and toluene to perform transalkylation to obtain xylene, and by simply separating the benzene and toluene, the benzene can be recycled to the alkylation reaction, and the toluene can be recycled to the transalkylation reaction, and finally high-yield xylene can be obtained, which has a significant economic value.

[0012] Further, the present application can convert alkane (C5-C9), especially non-aromatic hydrocarbons by-produced in catalytic reforming or steam cracking, and C9+ heavy aromatic hydrocarbons into xylene, greatly increasing the added value of the xylene, and the xylene has a high yield, and at least one high-quality olefin cracking material, such as ethane or propane, can be by-produced; the method has the characteristics of simple process flow and product upgrading, successfully solves the problem of outlet of alkane (C5-C9) and C9+ heavy aromatic hydrocarbons, and can fully utilize the methyl source in the alkane, and has a significant direct economic benefit. Attached Figure Description

[0013] Figure 1 This is a schematic diagram of the system provided by the present invention.

[0014] Explanation of reference numerals in the attached figures

[0015] 1- Hydrogenation refining reactor; 2- Alkylation reactor; 3- Stripping tower

[0016] 4-Benzene fractionation tower; 5-Toluene fractionation tower; 6-Xylene fractionation tower

[0017] 7-Alkyl transfer reactor; 8-Alkane supply unit; 9-Benzene supply unit

[0018] 10- Hydrogen supply unit; 11- C9+ heavy aromatics supply unit Detailed Implementation

[0019] 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.

[0020] The first aspect of the present invention provides a method for producing xylene, the method comprising: sequentially performing an alkylation reaction and an alkyl transfer reaction; wherein, under alkylation reaction conditions, an alkane is contacted with benzene and hydrogen to carry out an alkylation reaction; wherein, under alkyl transfer reaction conditions, at least a portion of C9+ heavy aromatics derived from the alkylation reaction, toluene, and hydrogen are contacted to carry out an alkyl transfer reaction; wherein the alkane is raffinate and / or hydrogenated raffinate; wherein the weight ratio of benzene to alkane is 1-9:1; wherein the weight ratio of C9+ heavy aromatics to toluene is 1-5:1.

[0021] By employing the above method, using inexpensive alkanes and benzene as raw materials, toluene and xylene are catalytically produced through alkane alkylation technology. Then, low-value-added C9+ heavy aromatics are used to undergo alkyl transfer with toluene to obtain benzene and xylene. Through simple separation, benzene is recycled to the alkylation reaction, and toluene is recycled to the alkyl transfer reaction, finally yielding high-yield xylene, which significantly improves the xylene yield.

[0022] In the present application, the C9+ heavy aromatic hydrocarbons "at least partially from the alkylation reaction" can be understood as that the C9+ heavy aromatic hydrocarbons can all come from the alkylation reaction, and when the amount of the alkylation reaction is insufficient to provide the C9+ heavy aromatic hydrocarbons required by the transalkylation reaction, it can be understood that the source of the C9+ heavy aromatic hydrocarbons contains two parts, one part is the C9+ heavy aromatic hydrocarbons from the alkylation reaction, that is, the "C9+ heavy aromatic hydrocarbons at least partially from the alkylation reaction" described above; the other part is provided from outside the system, for example, the C9+ cut fraction from catalytic reforming and / or steam cracking.

[0023] In the present application, it can be understood that toluene is all from the alkylation reaction.

[0024] According to the present application, preferably, the bromine index of the alkane is ≤500 mgBr / 100g, further preferably, the bromine index of the alkane is ≤200 mgBr / 100g. The inventors further found that the alkane satisfying the bromine index under the preferred scheme of the present application is beneficial to the alkylation reaction, especially has a great influence on the catalyst activity, so that the alkane makes the catalyst have better reaction performance.

[0025] In the present application, the raffinate oil is the raffinate oil commonly defined in the art, which is not described here again. Preferably, the raffinate oil is the raffinate oil from catalytic reforming and / or steam cracking.

[0026] In the present application, it is worth noting that the "non-aromatic" in the present application means that the component contains substantially no aromatic hydrocarbons, rather than absolutely no aromatic hydrocarbons. When the raffinate oil contains trace amounts (less than 1% by weight) of aromatic hydrocarbons, it can be referred to as a non-aromatic component.

[0027] In the present application, the raffinate oil is mainly composed of alkane and a small amount of unsaturated hydrocarbon, the alkane is selected from at least one of normal alkane, isomeric alkane and cycloalkane, and the unsaturated hydrocarbon is at least one of, for example, olefin and aromatic hydrocarbon. Preferably, the raffinate oil contains 95-99.99% by weight of C5-C9 alkane and 0.01-5% by weight of C5-C9 unsaturated hydrocarbon.

[0028] Further, the "C5-C9 alkane" in the present application represents an alkane with a total number of carbon atoms of 5-9, including straight-chain alkane, branched-chain alkane or cycloalkane, and specifically can be straight-chain alkane, branched-chain alkane or cycloalkane with a total number of carbon atoms of 5, 6, 7, 8 and 9, for example, n-pentane, n-hexane, n-heptane, methylcyclohexane, ethylcyclopentane, etc. The "C5-C9 unsaturated hydrocarbon" represents an unsaturated hydrocarbon with a total number of carbon atoms of 5-9, including olefin or aromatic hydrocarbon, and specifically can be olefin or aromatic hydrocarbon with a total number of carbon atoms of 5, 6, 7, 8 and 9, for example, hexene, heptene, methylhexene and benzene, etc.

[0029] In the present application, it can be understood that when the composition of the raffinate oil does not satisfy the required bromine index, the raffinate oil can be hydrogenated to satisfy the required bromine index after hydrogenation saturation; when the unsaturated hydrocarbon content in the composition of the raffinate oil is low and satisfies the required bromine index, the raffinate oil can be directly used as the alkane for subsequent alkylation reaction without hydrogenation.

[0030] According to the present application, preferably, the alkane is the raffinate oil after hydrogenation, and the hydrogenation conditions are such that the raffinate oil satisfies the bromine index after hydrogenation. Preferably, the hydrogenation is carried out in the presence of hydrogen, and the hydrogen oil volume ratio of the hydrogen (notably, the hydrogen refers to the hydrogen in the hydrogenation process) to the alkane is 100-500:1, more preferably 150-200:1.

[0031] In the present application, preferably, the hydrogenation is carried out in the presence of a hydrogenation catalyst.

[0032] In a preferred embodiment, the hydrogenation conditions include that the mass space velocity of the alkane is 1-8h -1 , more preferably 1-5h -1 , the temperature is 150-200℃, more preferably 165-180℃, and the pressure is 1-5MPa, more preferably 3-5MPa.

[0033] In the present application, any hydrogenation catalyst conventionally defined in the art is suitable for the present application as long as the alkane satisfies the required bromine index after hydrogenation saturation. Preferably, the hydrogenation catalyst includes a carrier and a metal active component supported on the carrier, and the metal active component is selected from at least one of Group VIII elements, Group VIB elements, Group IIB elements and Group IIA elements.

[0034] In a preferred embodiment, the content of the metal active component in terms of elements is 10-20wt% based on the total amount of the catalyst, and the content of the carrier is 80-90wt%.

[0035] In the present application, the selection range of the carrier is wide. Preferably, the carrier is selected from at least one of alumina, titania, zirconia and silica; more preferably, the carrier is alumina.

[0036] In the present application, the selection range of the metal active component is wide. Preferably, the metal active component is selected from at least one of Group VIII metal elements, Group VIB metal elements, Group IIB metal elements and Group IIA metal elements. More preferably, the metal active component is selected from at least one of Ni, Mo, W, Zn and Mg.

[0037] In the present application, the hydrogenation catalyst can be commercially available, such as RN-1 catalyst, purchased from Sinopec Catalyst Company, or can be prepared by existing methods, which will not be described here.

[0038] In the present application, the alkylation reaction can convert more alkanes (preferably C5-C9 alkanes) in alkanes to alkylbenzene (mainly toluene and xylene). Preferably, the weight ratio of benzene to alkanes is 4-9:1.

[0039] In the present application, the conditions for the alkylation reaction are selected in a wide range. Preferably, the alkylation reaction conditions include: temperature is 450-550℃, pressure is 1-7MPa, weight hourly space velocity of benzene and alkanes is 1-10h -1 , hydrogen to oil volume ratio is 500-2000:1; further preferably, the alkylation reaction conditions include: temperature is 480-520℃, pressure is 3-5MPa, weight hourly space velocity of benzene and alkanes is 4-8h -1 , hydrogen to oil volume ratio is 1000-2000:1. In the present application, the use of appropriate amount of hydrogen can better hydrogenate the unsaturated hydrocarbons existing in the alkylation reaction, so as to avoid the adverse effects of the polymerization or polycondensation of the unsaturated hydrocarbons (including the unsaturated hydrocarbons in the alkanes, the unsaturated hydrocarbons produced by the hydrogen transfer side reaction in the alkylation reaction, etc.) in the alkylation reaction to form carbon deposition.

[0040] In the present application, preferably, the alkylation reaction is carried out in the presence of an alkylation catalyst, which includes a molecular sieve, a binder and optionally an active metal component, further preferably, the alkylation catalyst includes a molecular sieve and a binder. The use of the above alkylation catalyst has the advantages of high benzene single-pass conversion rate and high toluene and xylene yield.

[0041] In the present application, the type of molecular sieve is selected in a wide range. Preferably, the molecular sieve is selected from at least one of ZSM-5 molecular sieve, MCM-22 molecular sieve, ZSM-12 molecular sieve, Beta molecular sieve and MOR zeolite molecular sieve, further preferably ZSM-5 molecular sieve.

[0042] In a preferred embodiment, the silicon to aluminum molar ratio of the molecular sieve is 20-70, preferably 20-50. The use of this preferred scheme has the advantages of high raw material conversion rate and good selectivity of target product.

[0043] In the present application, the molecular sieve can be an acid-modified molecular sieve or an unmodified molecular sieve, preferably the molecular sieve is an acid-modified ammonium type molecular sieve, and the acid modification method is a method known in the art. Preferably, the acid is at least one selected from the group consisting of citric acid, phosphoric acid, hydrochloric acid and oxalic acid, which can be selected by those skilled in the art according to the needs, and will not be described here.

[0044] In the present application, the type of binder is not particularly limited, and the binder defined conventionally in the art is suitable for the present application. Preferably, the binder is alumina and / or silica.

[0045] In a preferred embodiment, the metal component is at least one selected from the group consisting of Mg, Re, Cu, Mo, La, K, Na and Pt, and is further preferably at least one selected from the group consisting of Re, Pt and Mo.

[0046] In the present application, the amount of each substance in the alkylation catalyst is not particularly limited, as long as it is beneficial to the alkylation reaction. Preferably, the content of the metal component is 0-0.5 parts by weight based on 100 parts by weight of the alkylation catalyst, and the content of the binder is 10-40 parts by weight.

[0047] In the present application, the preparation method of the alkylation catalyst has a wide selection range, as long as the above-mentioned alkylation catalyst can be obtained. In a particularly preferred embodiment, the alkylation catalyst is prepared by the following method: the molecular sieve is mixed with the binder to form a shape, and then dried and calcined, and then optionally impregnated with the metal component. In the present application, the forming method is not particularly limited, for example, it can be a standard forming method known in the art, and specifically, the molecular sieve powder and the binder can be mixed, and then the material can be added to the extruder with the mold, and the powder can be extruded into a strip-shaped extrudate. In the present application, the impregnation method is not particularly limited, as long as the metal component is impregnated on the calcined product, for example, the impregnation method can be carried out according to any impregnation method known in the art, for example, at least one selected from the group consisting of co-impregnation, stepwise impregnation and equal volume impregnation, and the present application does not limit this. In the present application, the timing of introducing the metal component is also not particularly limited, for example, it can be carried out after the preparation of the molecular sieve. Specifically, for example, it can be carried out before the forming and calcining, or it can be carried out after the forming and calcining; the metal component can also be introduced during the preparation of the molecular sieve, for example, the metal component can be previously loaded on alumina, and then mixed with the molecular sieve to form a shape, which can be selected by those skilled in the art according to the actual needs.

[0048] According to one specific embodiment of the present application, the alkylation catalyst is obtained by the following method: after mixing the molecular sieve with a binder, the mixture is added to an extruder with a mold, the powder is extruded into a strip-shaped extrudate, and then dried and calcined, and then, after optionally introducing a metal component by impregnation, dried and calcined to obtain the alkylation catalyst.

[0049] In the present application, the types and amounts of the various substances in the alkylation catalyst have been described above and will not be repeated here.

[0050] In the present application, the preparation method of the transalkylation catalyst includes introducing an extrusion aid and / or a peptizing agent during the molding process.

[0051] In the present application, the types and amounts of the extrusion aid and the peptizing agent are not specifically limited, and those skilled in the art can select the types and amounts of the extrusion aid and the peptizing agent within a reasonable range according to the specific situation of the extrusion molding. Preferably, the extrusion aid is selected from at least one of sesbania powder, dextrin, and methyl cellulose. Preferably, the peptizing agent is selected from at least one of nitric acid, acetic acid, and citric acid.

[0052] In one preferred embodiment, the amount of the extrusion aid is 2.5-10 parts by weight and the amount of the peptizing agent is 2.5-5 parts by weight, based on 100 parts by weight of the molecular sieve.

[0053] In the present application, the drying conditions during the molding and impregnation processes have a relatively wide selection range and can be the conventional drying conditions in the art. Preferably, the drying conditions for the molding and impregnation are each independently selected from a drying temperature of 100-120°C and a drying time of 12-24h.

[0054] In the present application, the calcination conditions during the molding and impregnation processes have a relatively wide selection range and can be the conventional calcination conditions in the art. Preferably, the calcination conditions for the molding and impregnation are each independently selected from a calcination temperature of 500-600°C and a calcination time of 2-12h, and further preferably, the calcination temperature is 500-550°C and the calcination time is 2-5h.

[0055] In the present application, the amounts of the various substances in the transalkylation reaction are not specifically limited. Preferably, in the transalkylation reaction, the weight ratio of the C9+ heavy aromatic hydrocarbons to toluene is 1-2:1. By limiting the amounts of toluene and C9+ heavy aromatic hydrocarbons, the yield of xylene can be improved.

[0056] In the present application, the conditions of the transalkylation reaction have a relatively wide selection range. Preferably, the conditions of the transalkylation reaction include a temperature of 250-450°C, a pressure of 1-7MPa, and a weight hourly space velocity of toluene and C9+ heavy aromatic hydrocarbons of 1-6h -1, the hydrogen to oil volume ratio is 500-2000:1; further preferably, the temperature is 300-450℃, the pressure is 2-4MPa, the weight hourly space velocity of toluene and C9+ heavy aromatic hydrocarbon is 1-4h -1 , the hydrogen to oil volume ratio is 1000-2000:1. By adopting the above preferred embodiments, the catalyst has the advantages of stable operation and high xylene yield.

[0057] In the present application, preferably, the transalkylation reaction is carried out in the presence of a transalkylation catalyst, the transalkylation catalyst comprising a transalkylation molecular sieve, a binder and optionally an active component, further preferably, the transalkylation catalyst comprising a transalkylation molecular sieve, a binder and an active component.

[0058] In the present application, the type of the transalkylation molecular sieve is selected from a wide range, for example, the transalkylation molecular sieve is selected from at least one of ZSM-5 molecular sieve, MCM-22 molecular sieve, ZSM-12 molecular sieve, Beta molecular sieve and MOR zeolite catalyst, further preferably, the MOR zeolite molecular sieve.

[0059] In a preferred embodiment, the transalkylation molecular sieve has a silicon to aluminum molar ratio of 20-70, preferably 20-50. Under this preferred scheme, the yield of xylene can be further improved.

[0060] In the present application, the transalkylation molecular sieve is an ammonium type molecular sieve modified by acid, the method and type of the acid have been described in the foregoing, which will not be repeated here.

[0061] In a preferred embodiment, the binder is alumina and / or silica.

[0062] In a preferred embodiment, the active component is selected from at least one of Mo, Re, Bi, Sn and Pt elements, further preferably, at least one of Mo, Bi and Pt. By adopting the above preferred embodiments, the C9+ heavy aromatic hydrocarbon conversion rate is high, and the xylene yield is high.

[0063] In the present application, the content of each substance in the transalkylation catalyst is not specifically limited. Preferably, the content of the active component is 0.01-1 parts by weight based on 100 parts by weight of the transalkylation catalyst, and the content of the binder is 10-45 parts by weight, further preferably, the content of the active component is 0.01-0.8 parts by weight based on 100 parts by weight of the transalkylation catalyst, and the content of the binder is 20-45 parts by weight. In the present application, the preparation method of the transalkylation catalyst is selected from a wide range, as long as it is beneficial to the transalkylation reaction, for example, the same preparation method as the alkylation catalyst can be used to prepare the transalkylation catalyst, and the specific preparation method has been described in the foregoing, which will not be repeated here.

[0064] To further optimize the alkylation reaction and direct the conversion to alkylbenzenes (mainly toluene and xylene), such as... Figure 1 As shown, in one specific embodiment, the method for producing xylene includes: (1) optionally hydrogenating raffinate under hydrogenation conditions to obtain alkane (hydrogenated raffinate); (2) alkylating the alkane with benzene and hydrogen under alkylation reaction conditions, wherein the weight ratio of benzene to alkane is 1-9:1, the alkylation reaction is carried out in the presence of an alkylation catalyst at a temperature of 450-550°C, a pressure of 1-7 MPa, and a weight hourly space velocity (WHSV) of 1-10 h⁻¹ for benzene and alkane. -1 The hydrogen-to-oil volume ratio is 500-2000:1; (3) Under alkyl transfer reaction conditions, at least part of the C9+ heavy aromatic hydrocarbons obtained from the alkylation reaction, toluene, and hydrogen are contacted for alkyl transfer reaction, wherein the weight ratio of the C9+ heavy aromatic hydrocarbons to toluene is 1:5-1, the alkyl transfer reaction is carried out in the presence of an alkyl transfer catalyst, at a temperature of 250-450℃, a pressure of 1-7 MPa, and a weight hourly space velocity of 1-6 h⁻¹ for toluene and C9+ heavy aromatic hydrocarbons. -1 The hydrogen-to-oil volume ratio is 500-2000:1. Under this preferred scheme, the conversion rates of benzene and C9+ heavy aromatics and the yield of xylene are optimal, with a benzene conversion rate of 38.85%, a C9+ heavy aromatics conversion rate of 58.23%, and a xylene yield of over 32.17%.

[0065] According to a preferred embodiment of the present invention, such as Figure 1 As shown, the method further includes: optionally cooling the aromatic product obtained from the alkylation reaction and alkyl transfer reaction, followed by gas-liquid separation to obtain a gaseous material (e.g., Figure 1 The light hydrocarbons shown (such as ethylene, propane, etc.) and liquid materials. In this invention, the cooling is preferably performed to below 25°C.

[0066] According to a preferred embodiment of the present invention, such as Figure 1 As shown, the method further includes: fractionating the liquid phase material to obtain benzene, toluene, xylene and C9+ heavy aromatics.

[0067] The present invention does not limit the conditions for the fractionation, as long as the desired materials can be obtained. Preferably, the fractionation process includes: first, performing a first fractionation to obtain benzene, with a distillation range of 65-85℃; then, performing a second fractionation to obtain toluene, with a distillation range of 85-105℃; and then performing a third fractionation to obtain xylene and C9+ heavy aromatics, with a distillation range of 105-145℃ for xylene.

[0068] According to the present application, preferably, the method further comprises: recycling the benzene obtained by the fractionation into the alkylation reaction, and recycling the toluene and C9+ heavy aromatic hydrocarbons obtained by the fractionation into the transalkylation reaction. The advantage of using this preferred embodiment is that the methyl groups of the alkanes in the raffinate can be fully utilized, thereby maximizing the utilization of the methyl groups.

[0069] The second aspect of the present application provides a system for producing dimethylbenzene, as shown in the figure, the system comprises: an alkanes supply unit 8, a benzene supply unit 9, a hydrogen supply unit 10, a C9+ heavy aromatic hydrocarbon supply unit 11, an alkylation reactor 2, a transalkylation reactor 7, the alkanes supply unit 10, the benzene supply unit 9 and the hydrogen supply unit 10 are respectively communicated with the alkylation reactor 2, the C9+ heavy aromatic hydrocarbon supply unit 11 and the hydrogen supply unit 10 are respectively communicated with the transalkylation reactor 7, and the alkylation reactor 2 and the transalkylation reactor 7 are communicated. Figure 1

[0070] The system further optionally comprises a hydrofining reactor 1, which is arranged between the alkanes supply unit 8 and the alkylation reactor 2.

[0071] In the present application, it is worth noting that the alkanes supply unit 8 and the alkylation reactor 2 can be directly communicated; alternatively, a hydrofining reactor 1 can be arranged, that is, the alkanes supply unit 8 and the alkylation reactor 2 are respectively communicated with the hydrofining reactor 1.

[0072] According to the system provided by the present application, preferably, the system further comprises a stripping column 3, which is used for gas-liquid separation to obtain gas-phase materials and liquid-phase materials.

[0073] According to the system provided by the present application, preferably, the system further comprises a benzene fractionation column 4, which is used for first fractionation of the liquid-phase materials obtained by the stripping column 3 to obtain benzene, the inlet of the benzene fractionation column 4 is communicated with the liquid outlet at the bottom of the stripping column 3, and the benzene material outlet at the top of the benzene fractionation column 4 is communicated with the benzene supply unit 9 for recycling of the unreacted benzene in the alkylation reaction.

[0074] According to the system provided by the present application, preferably, the system further comprises a toluene fractionation column 5, the inlet of the toluene fractionation column 5 is communicated with the outlet at the bottom of the benzene fractionation column 4 for second fractionation of the liquid-phase materials obtained by the outlet at the bottom of the benzene fractionation column 4 to obtain toluene, and the toluene material outlet at the top of the toluene fractionation column 5 is communicated with the transalkylation reactor 7 for providing toluene for the transalkylation reaction.

[0075] ​According to the system provided by the present application, preferably, the system further comprises a xylene fraction column 6, an inlet of the xylene fraction column 6 being communicated with a column bottom outlet of the toluene fraction column 5; and a third fraction column for performing a third fraction on a liquid phase material obtained from the column bottom outlet of the toluene fraction column 5 to obtain xylene and C9+ heavy aromatic hydrocarbon.

[0076] According to the system provided by the present application, the system further comprises that a column bottom C9+ heavy aromatic hydrocarbon material outlet obtained by separating the xylene fraction column 6 is communicated with the transalkylation reactor 7.

[0077] The system provided by the present application can realize the method of the first aspect, and the combination of the alkylation reaction and the transalkylation reaction. The present application can effectively convert benzene into toluene and xylene by performing the alkylation reaction on the system by using alkanes as a methyl source reagent, and the introduction of hydrogen can reduce the carbon deposition rate of the catalyst and improve the stability of the catalyst, and further performing the transalkylation reaction can further improve the yield of xylene.

[0078] The present application will be described in detail below by way of examples.

[0079] Example 1

[0080] (1) 47.05 g of ammonium type ZSM-5 zeolite with a SiO2 / Al2O3 molar ratio of 25 (purchased from Sinopec Catalyst Co., Ltd.) and 14.3 g of γ-Al2O3 were uniformly mixed, and then a certain amount of sesbania powder and dilute nitric acid were added, and then extruded into strips, dried at 120°C for 12 h, and then placed in a muffle furnace at 550°C for calcination for 4 h to obtain an alkylation catalyst W-1.

[0081] (2) 47.05 g of ammonium type Beta zeolite with a SiO2 / Al2O3 molar ratio of 50 (purchased from Sinopec Catalyst Co., Ltd.) and 35 g of γ-Al2O3 were uniformly mixed, and then a certain amount of sesbania powder and dilute nitric acid were added, and then extruded into strips, dried at 120°C for 12 h, and then placed in a muffle furnace at 550°C for calcination for 4 h to obtain a transalkylation catalyst precursor, and then a certain amount of chloroplatinic acid solution was impregnated, dried at 120°C for 12 h, and then placed in a muffle furnace at 550°C for calcination for 4 h to obtain a transalkylation catalyst V-1 (0.5 wt% Pt / catalyst V-1).

[0082] (3) The alkylation reaction was performed by using the alkylation catalyst W-1 and the transalkylation reaction was performed by using the transalkylation catalyst V-1. Figure 1The system shown, take 3g alkylating catalyst W-1, loaded in the alkylating reactor 2, and take 5g transalkylation catalyst V-1 loaded in the transalkylation reactor 7. Hydrogen and material containing benzene and alkane (from steam cracking, composition as shown in Table 1, the bromine index of alkane is 125mgBr / 100g) are introduced into the top of the alkylating reactor 2 to contact with the alkylating catalyst inside the alkylating reactor 2 to evaluate the reaction, hydrogen and material containing toluene and C9+ heavy aromatic hydrocarbon (composition as shown in Table 2) are introduced into the top of the transalkylation reactor 7 to contact with the transalkylation catalyst inside the transalkylation reactor 7 to evaluate the reaction.

[0083] The alkylating reaction conditions are: weight space velocity 7h -1 -1, temperature 500℃, pressure 3MPa, hydrogen to oil volume ratio 1000, reaction raw material benzene:alkane = 4:1 (weight ratio). The transalkylation reaction conditions are: weight space velocity 2h -1 -1, temperature 370℃, pressure 2.7MPa, hydrogen to oil volume ratio 1000, reaction raw material toluene:C9+ heavy aromatic hydrocarbon = 1:1 (weight ratio).

[0084] Specifically, Example 1 uses the system shown in Figure 1 , hydrogen is provided by the hydrogen supply unit 10, and alkane and benzene are provided by the alkane supply unit 8 and the benzene supply unit 9 respectively, which are then introduced into the alkylating reactor 2 to perform the alkylation reaction (the alkylating reaction conditions are as described above), to obtain the alkylation reaction product, which is cooled and then introduced into the stripping column 3 to perform gas-liquid separation, to separate out light hydrocarbon (as shown in Figure 1 ), and the bottom material of the stripping column 3 is introduced into the benzene fraction column 4 to perform the first fractionation (distillation range 65-85℃), to separate out benzene, part of which is returned to the alkylating reactor 2 to perform the alkylation reaction, and the bottom material of the benzene fraction column 4 is introduced into the toluene fraction column 5 (distillation range 85-105℃), to separate out toluene. The bottom material of the toluene fraction column 5 is introduced into the xylene fraction column 6 (distillation range 105-145℃), to separate out xylene and C9+ heavy aromatic hydrocarbon. The toluene is introduced into the transalkylation reactor 7 to perform the transalkylation reaction with C9+ heavy aromatic hydrocarbon provided by the C9+ heavy aromatic hydrocarbon supply unit 11 and C9+ heavy aromatic hydrocarbon separated out from the xylene fraction column 6, and hydrogen is provided by the hydrogen supply unit 10, and the transalkylation product can be returned to the alkylating reactor 2 for reuse after the transalkylation reaction.

[0085] The product content is tested by gas chromatography, and the benzene conversion rate, C9+ heavy aromatic hydrocarbon conversion rate and xylene yield are calculated, as shown in Table 3.

[0086] The calculation formula of the benzene conversion rate is = (raw material benzene mass - remaining benzene mass) / raw material benzene mass * 100%.

[0087] The formula for calculating the conversion rate of C9+ heavy aromatics is = (mass of raw material C9+ heavy aromatics - mass of remaining C9+ heavy aromatics) / mass of raw material C9+ heavy aromatics * 100%.

[0088] The formula for calculating the yield of xylene is = mass of xylene in products / (total mass of raw material benzene and C9+ heavy aromatics) * 100%, wherein the xylene refers to a mixture of o-xylene, p-xylene and m-xylene.

[0089] Example 2

[0090] (1) 47.05 g of ammonium-type ZSM-5 zeolite with a SiO2 / Al2O3 molar ratio of 25 (purchased from Sinopec Catalyst Co., Ltd.) was uniformly mixed with 14.3 g of γ-Al2O3, and then a certain amount of sesbania powder and dilute nitric acid were added, and then extruded into a strip, dried at 120°C for 12 h, and then placed in a muffle furnace at 550°C for calcination for 4 h to obtain an alkylation catalyst precursor, and then a certain amount of chloroplatinic acid solution was impregnated, dried at 120°C for 12 h, and then placed in a muffle furnace at 550°C for calcination for 4 h to prepare an alkylation catalyst W-2 (0.5 wt% Pt / catalyst W-2).

[0091] (2) The same transalkylation catalyst V-1 (0.5 wt% Pt / Beta) as in Example 1 was selected.

[0092] (3) The system as shown in Figure 1 was used, 3 g of the alkylation catalyst W-2 was loaded into the alkylation reactor 2, and 5 g of the transalkylation catalyst V-1 was loaded into the transalkylation reactor 7. The same alkylation reaction raw materials and conditions and transalkylation reaction raw materials and conditions as in Example 1 were selected, the product content was tested by gas chromatography, and the benzene conversion rate, C9+ heavy aromatics conversion rate and xylene yield were calculated, as shown in Table 3.

[0093] Example 3

[0094] (1) The method of Example 1 was followed, except that ammonium-type ZSM-5 zeolite with a SiO2 / Al2O3 molar ratio of 38 (purchased from Sinopec Catalyst Co., Ltd.) was selected to obtain an alkylation catalyst W-3.

[0095] (2) The same transalkylation catalyst V-1 as in Example 1 was selected.

[0096] (3) The system as shown in Figure 1 was used, 3 g of the alkylation catalyst W-3 was loaded into the alkylation reactor 2, and 5 g of the transalkylation catalyst V-1 was loaded into the transalkylation reactor 7. The same alkylation reaction raw materials and conditions and transalkylation reaction raw materials and conditions as in Example 1 were selected, the product content was tested by gas chromatography, and the benzene conversion rate, C9+ heavy aromatics conversion rate and xylene yield were calculated, as shown in Table 3.

[0097] Example 4

[0098] (1) The same alkylating catalyst W-3 as in Example 3 was selected and used.

[0099] (2) 47.05 g of ammonium type MOR zeolite with SiO2 / Al2O3 molar ratio of 30 (purchased from Sinopec Catalyst Co., Ltd.) was uniformly mixed with 35 g of γ-Al2O3, then a certain amount of sesbania powder and dilute nitric acid were added, extruded into strips, dried at 120°C for 12 h, then placed in a muffle furnace at 550°C for calcination for 4 h to obtain an alkyl transfer catalyst precursor, then a certain amount of chloroplatinic acid solution was impregnated, dried at 120°C for 12 h, then placed in a muffle furnace at 550°C for calcination for 4 h to prepare the alkyl transfer catalyst V-2 (0.5 wt% Pt / catalyst V-2).

[0100] (3) The system as shown in Figure 1 was used, 3 g of the alkylating catalyst W-3 was loaded into the alkylating reactor 2, and 5 g of the catalyst V-2 was loaded into the alkyl transfer reactor 7. The same alkylating reaction raw materials and conditions and alkyl transfer reaction raw materials and conditions as in Example 1 were selected, the product content was tested by gas chromatography, and the benzene conversion rate, C9+ heavy aromatic hydrocarbon conversion rate, and xylene yield were calculated, as shown in Table 3.

[0101] Example 5

[0102] (1) 47.05 g of ammonium type ZSM-5 zeolite with SiO2 / Al2O3 molar ratio of 38 (purchased from Sinopec Catalyst Co., Ltd.) was uniformly mixed with 14.3 g of γ-Al2O3, then a certain amount of sesbania powder and dilute nitric acid were added, extruded into strips, dried at 120°C for 12 h, then placed in a muffle furnace at 550°C for calcination for 4 h to obtain an alkylating catalyst precursor, then a certain amount of ammonium molybdate solution was impregnated, dried at 120°C for 12 h, then placed in a muffle furnace at 550°C for calcination for 4 h to prepare the alkylating catalyst W-4 (0.5 wt% Mo / catalyst W-4).

[0103] (2) The same alkyl transfer catalyst V-2 as in Example 4 was selected and used.

[0104] (3) The system as shown in Figure 1 was used, 3 g of the alkylating catalyst W-4 was loaded into the alkylating reactor 2, and 5 g of the alkyl transfer catalyst V-2 was loaded into the alkyl transfer reactor 7. The same alkylating reaction raw materials and conditions and alkyl transfer reaction raw materials and conditions as in Example 1 were selected, the product content was tested by gas chromatography, and the benzene conversion rate, C9+ heavy aromatic hydrocarbon conversion rate, and xylene yield were calculated, as shown in Table 3.

[0105] Example 6

[0106] The method is the same as in Example 4, except that the alkane is hydrogenated raffinate oil. Using... Figure 1 In the aforementioned system, in hydrorefining reactor 1, alkanes (derived from catalytic reforming with a bromine index of 1200 mgBr / 100g) are contacted with a hydrotreating catalyst (i.e., RN-1 catalyst, 13.05 wt% Mo - 2.75 wt% Ni / RN-1 catalyst, purchased from Sinopec Catalyst Co., Ltd.). After hydrotreating to remove unsaturated hydrocarbons, the composition of the hydrotreated raffinate oil with a bromine index of 165 mgBr / 100g is shown in Table 1. The hydrotreating conditions are: a hydrogen-to-oil volume ratio of 150:1 and a mass hourly space velocity (HHSV) of 5 h⁻¹ for the raffinate oil. -1 The temperature was 165℃, the pressure was 3MPa, and other conditions were the same as in Example 4. The product content was tested by gas chromatography, and the benzene conversion rate, C9+ heavy aromatic hydrocarbon conversion rate and xylene yield were calculated, as shown in Table 3.

[0107] Example 7

[0108] Following the method of Example 4, except that the active components in the alkyl transfer catalyst are Mo and Bi, alkyl transfer catalyst V-3 (0.3 wt% Mo / 0.5 wt% Bi-MOR) was prepared. Other conditions were the same as in Example 4. The product content was tested by gas chromatography, and the benzene conversion rate, C9+ heavy aromatic hydrocarbon conversion rate and xylene yield were calculated, as shown in Table 3.

[0109] Example 8

[0110] The method of Example 4 was followed, except that the weight ratio of benzene to alkanes was 1:1, the weight ratio of C9+ heavy aromatics to toluene was 1:1, the alkyl transfer catalyst used was alkyl transfer catalyst V-3 from Example 7, and other conditions were the same as in Example 4. The product content was tested by gas chromatography, and the benzene conversion rate, C9+ heavy aromatic conversion rate and xylene yield were calculated, as shown in Table 3.

[0111] Example 9

[0112] The method of Example 4 was followed, except that the weight ratio of benzene to alkanes was 9:1, the weight ratio of C9+ heavy aromatics to toluene was 5:1, the alkyl transfer catalyst used was alkyl transfer catalyst V-3 from Example 7, and other conditions were the same as in Example 4. The product content was tested by gas chromatography, and the benzene conversion rate, C9+ heavy aromatic conversion rate and xylene yield were calculated, as shown in Table 3.

[0113] Comparative Example 1

[0114] The method of Example 4 was followed, except that the weight ratio of benzene to alkane was 20:1, the weight ratio of C9+ heavy aromatic hydrocarbon to toluene was 20:1, the transalkylation catalyst was transalkylation catalyst V-3 of Example 7, and other conditions were the same as in Example 4. The product content was tested by gas chromatography, and the benzene conversion, C9+ heavy aromatic hydrocarbon conversion, and xylene yield were calculated, as shown in Table 3.

[0115] Table 1 Content of each component in hydrocarbon (wt%)

[0116]

[0117]

[0118] Note: "-" in Table 1 means not containing.

[0119] Table 2

[0120]

[0121] Table 3

[0122]

[0123]

[0124] As can be seen from Table 3 above, the method of the present application can use non-aromatic hydrocarbons (C5-C9), especially catalytic reforming or steam cracking by-products, as raw materials, combine alkylation and transalkylation reactions, and has the characteristics of high non-aromatic hydrocarbon conversion and high xylene yield.

[0125] The preferred embodiments of the present application are described in detail above, but the present application is not limited thereto. Within the technical concept of the present application, various simple modifications can be made to the technical solutions of the present application, including combining each technical feature in any other suitable manner, and these simple modifications and combinations should also be considered as disclosed by the present application and fall within the protection scope of the present application.

Claims

1. A method for producing xylene, the method comprising: The reaction involves a sequential alkylation reaction and an alkyl transfer reaction; wherein, under alkylation reaction conditions, an alkane is contacted with benzene and hydrogen to carry out the alkylation reaction; under alkyl transfer reaction conditions, at least a portion of the C9+ heavy aromatic hydrocarbon from the alkylation reaction, toluene, and hydrogen are contacted to carry out the alkyl transfer reaction; wherein the alkane is raffinate oil and / or raffinate oil after hydrogenation; wherein the weight ratio of benzene to alkane is 1-9:1; wherein the weight ratio of C9+ heavy aromatic hydrocarbon to toluene is 1-5:

1. The raffinate contains 95-99.99% by weight of C5-C9 alkanes and 0.01-5% by weight of C5-C9 unsaturated hydrocarbons. The alkylation reaction is carried out in the presence of an alkylation catalyst, which includes a molecular sieve, a binder, and optionally a metal component. The molecular sieve is selected from at least one of ZSM-5 molecular sieve, MCM-22 molecular sieve, ZSM-12 molecular sieve, Beta molecular sieve and MOR zeolite molecular sieve.

2. The method according to claim 1, wherein, The bromine index of the alkane is ≤500mgBr / 100g.

3. The method according to claim 2, wherein, The bromine index of the alkane is ≤200mgBr / 100g.

4. The method according to claim 1, wherein, The raffinate is the raffinate from catalytic reforming and / or steam cracking.

5. The method according to claim 1, wherein, In the alkylation reaction, the weight ratio of benzene to alkanes is 4-9:

1.

6. The method according to any one of claims 1-5, wherein, The alkylation reaction conditions include: a temperature of 450-550℃, a pressure of 1-7 MPa, and a weight hourly space velocity (WHSV) of 1-10 h⁻¹ for both benzene and alkanes. -1 The hydrogen-to-oil volume ratio is 500-2000:

1.

7. The method according to claim 6, wherein, The alkylation reaction conditions include: a temperature of 480-520℃, a pressure of 3-5 MPa, and a weight hourly space velocity (WHSV) of 4-8 h⁻¹ for both benzene and alkanes. -1 The hydrogen-to-oil volume ratio is 1000-2000:

1.

8. The method according to claim 1, wherein, The alkylation catalyst includes a molecular sieve and a binder.

9. The method according to claim 1, wherein, The molecular sieve is ZSM-5 molecular sieve.

10. The method according to claim 1 or 8, wherein, The silicon-aluminum molar ratio of the molecular sieve is 20-70.

11. The method according to claim 10, wherein, The silicon-aluminum molar ratio of the molecular sieve is 20-50.

12. The method according to claim 1 or 8, wherein, The binder is aluminum oxide and / or silicon oxide.

13. The method according to claim 1, wherein, The metal component is selected from at least one of the elements Mg, Re, Cu, Mo, La, K, and Pt.

14. The method according to claim 1, wherein, Based on 100 parts by weight of alkylation catalyst, the content of the metal component, calculated as an element, is 0-0.5 parts by weight, and the content of the binder is 10-40 parts by weight.

15. The method according to any one of claims 1-5, wherein, In the alkyl transfer reaction, the weight ratio of the C9+ heavy aromatic hydrocarbon to toluene is 1-2:

1.

16. The method according to any one of claims 1-5, wherein, The alkyl transfer reaction conditions include: a temperature of 250-450℃, a pressure of 1-7 MPa, and a weight hourly space velocity (WHSV) of 1-6 h⁻¹ for toluene and C9+ heavy aromatics. -1 The hydrogen-to-oil volume ratio is 500-2000:

1.

17. The method according to claim 16, wherein, The alkyl transfer reaction conditions include: a temperature of 300-450℃, a pressure of 2-4 MPa, and a weight hourly space velocity (WHSV) of 1-4 h⁻¹ for toluene and C9+ heavy aromatics. -1 The hydrogen-to-oil volume ratio is 1000-2000:

1.

18. The method according to any one of claims 1-5, wherein, The alkyl transfer reaction is carried out in the presence of an alkyl transfer catalyst, which includes an alkyl transfer molecular sieve, a binder, and optionally an active component.

19. The method according to claim 18, wherein, The alkyl transfer catalyst comprises an alkyl transfer molecular sieve, a binder, and an active component.

20. The method according to claim 19, wherein, The alkyl transfer molecules are screened from at least one of ZSM-5 molecular sieve, MCM-22 molecular sieve, ZSM-12 molecular sieve, Beta molecular sieve and MOR zeolite molecular sieve.

21. The method according to claim 20, wherein, The alkyl transfer molecular sieve is a MOR zeolite molecular sieve.

22. The method according to claim 19, wherein, The silicon-to-aluminum molar ratio of the alkyl transfer molecular sieve is 20-70.

23. The method according to claim 22, wherein, The silicon-to-aluminum molar ratio of the alkyl transfer molecular sieve is 20-50.

24. The method according to claim 19, wherein, The binder is aluminum oxide and / or silicon oxide.

25. The method according to claim 19, wherein, The active component is selected from at least one of the elements Mo, Re, Bi, Sn and Pt.

26. The method according to claim 19, wherein, Based on 100 parts by weight of alkyl transfer catalyst, the active component has an elemental content of 0.01-1 parts by weight, and the binder has an elemental content of 10-45 parts by weight.

27. The method according to claim 26, wherein, Based on 100 parts by weight of alkyl transfer catalyst, the active component has an elemental content of 0.01-0.8 parts by weight, and the binder has an elemental content of 20-45 parts by weight.

28. The method according to any one of claims 1-5, wherein, The method further includes: optionally cooling the aromatic products obtained from the alkylation reaction and alkyl transfer reaction, and then performing gas-liquid separation to obtain gaseous and liquid phase materials.

29. The method according to claim 28, wherein, The method further includes fractionating the liquid phase material to obtain benzene, toluene, xylene and C9+ heavy aromatics.

30. The method according to claim 29, wherein, The fractionation process includes: first, a first fractionation to obtain benzene, with a distillation range of 65-85℃; then, a second fractionation to obtain toluene, with a distillation range of 85-105℃; and then, a third fractionation to obtain xylene and C9+ heavy aromatics, with a distillation range of 105-145℃ for xylene.

31. The method according to claim 30, wherein, The method further includes: recycling the benzene obtained from fractionation to the alkylation reaction, and recycling the toluene and C9+ heavy aromatics obtained from fractionation to the alkyl transfer reaction.

32. The method according to claim 1, wherein, The method is carried out using the following system, which includes: an alkane supply unit, a benzene supply unit, a hydrogen supply unit, a C9+ heavy aromatics supply unit, an alkylation reactor, and an alkyl transfer reactor. The alkane supply unit, the benzene supply unit, and the hydrogen supply unit are respectively connected to the alkylation reactor. The C9+ heavy aromatics supply unit and the hydrogen supply unit are respectively connected to the alkyl transfer reactor. The alkylation reactor and the alkyl transfer reactor are connected together. The system may also optionally include a hydrorefining reactor disposed between the alkane supply unit and the alkylation reactor.

33. The method according to claim 32, wherein, The system also includes a stripping tower for gas-liquid separation to obtain gaseous and liquid materials.

34. The method according to claim 33, wherein, The system also includes a benzene fractionation tower, the inlet of which is connected to the bottom liquid material outlet of the stripping tower, and the top benzene material outlet of the benzene fractionation tower is connected to the benzene supply unit, for recycling unreacted benzene as a raw material for alkylation reaction.

35. The method according to claim 34, wherein, The system also includes a toluene fractionation tower, the inlet of which is connected to the bottom outlet of the benzene fractionation tower, and the top toluene material outlet of the toluene fractionation tower is connected to the alkyl transfer reactor to provide toluene for the alkyl transfer reaction.

36. The method according to claim 35, wherein, The system also includes a xylene fractionation tower, the inlet of which is connected to the bottom outlet of the toluene fractionation tower.

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