Method for increasing yield of xylene

Abstract

The invention relates to the technical field of xylene preparation, and discloses a method for increasing the yield of xylene, which comprises the following steps: (1) feeding an aromatic hydrocarbon raw material into a first-stage fixed bed reactor, and contacting with a solid acid aromatic hydrocarbon methylation catalyst in the presence of hydrogen; dividing an alkylating reagent into (n-1) parts, and respectively feeding the (n-1) parts into the first-stage to (n-1)-th-stage fixed bed reactors; a reaction discharge material of the first-stage fixed bed reactor is used as a reaction feed material of the second-stage fixed bed reactor; the aromatic hydrocarbon raw material is benzene and / or methylbenzene; (2) feeding the reaction discharged material of the (n-1) th stage of fixed bed reactor and C9 + heavy aromatics into the nth stage of fixed bed reactor, and contacting with a solid acid transalkylation catalyst in the presence of hydrogen; and (3) separating the product obtained in the step (2). The method can effectively utilize C9 < + > heavy aromatics, obviously improve the raw material conversion rate and xylene selectivity, greatly reduce material circulation, and is beneficial to energy conservation and consumption reduction of the device.

Description

Technical Field

[0001] The invention relates to the technical field of xylene preparation, and in particular to a method for increasing the production of xylene. Background Art

[0002] Paraxylene (PX) is an important basic organic chemical raw material, mainly used to produce purified terephthalic acid (PTA) and dimethyl terephthalate (DMT). PTA is used to manufacture polyester products such as polyethylene terephthalate (PET) and polybutylene terephthalate (PBT). In recent years, the demand for PX has been strong and the growth has been rapid.

[0003] At present, large-scale industrial production of aromatics is achieved through aromatics integrated units. Increasing the yield of xylene is an important goal of aromatics integrated units. Existing technologies mainly include toluene disproportionation and alkyl transfer, C8 aromatics isomerization, toluene selective disproportionation, and heavy aromatics lightening.

[0004] Toluene disproportionation and transalkylation technology is an effective way to convert toluene and C9 and C10 heavy aromatics produced by aromatics complex into mixed xylenes and benzene. More than 50% of mixed xylenes in aromatics complexes are produced by this technology, which is the main means to increase PX production in aromatics complexes. However, toluene disproportionation technology cannot utilize C9 / C10 aromatics produced by aromatics complexes. Although the toluene conversion rate of pure toluene disproportionation technology can reach up to 45-50%, a large amount of benzene is also produced as a by-product while mixed xylene products are obtained, and the xylene selectivity is low. The cost of improving the para-selectivity of toluene shape-selective disproportionation technology is a significant decrease in toluene conversion rate, which is only 25-31%. (Yu Zhengxi et al., Research Progress and Development Trend of Para-Xylene Production Technology, Chemical Industry Progress, 2020, 39(12): 4984-4992)

[0005] The benzene and / or toluene alkylation technology using benzene and / or toluene and methanol as reaction raw materials is a new process route for increasing the production of xylene. This technology achieves the purpose of increasing the production of xylene by introducing methyl groups, breaking the limitation of insufficient methyl groups in toluene disproportionation and transalkylation technology. The disadvantages of this technology are that the toluene conversion rate is low, and in addition to the main methylation reaction, deep alkylation will also occur to produce trimethylbenzenes, tetramethylbenzenes and other polymethylbenzenes. In order to improve the stability of the catalyst, the molar ratio of the feed benzene / toluene to the alkylation agent is usually high. The reaction temperature of the benzene / toluene alkylation technology is relatively high, about 400-600°C (Qi Xiaolan et al., Toluene and methanol alkylation to produce PX technology and industrial application, Petrochemical Technology, 2019(2): 131-132).

[0006] The existing xylene production technologies, whether toluene disproportionation and transalkylation technology or pure toluene disproportionation technology, all have the disadvantages of relatively low toluene conversion rate and low xylene selectivity due to a large amount of benzene in the product, resulting in a large amount of toluene circulating in the system, resulting in excessive energy consumption and other problems, and cannot meet the energy-saving and consumption-reducing needs of aromatics complexes.

[0007] CN102875320A discloses a tandem reaction method for aromatic methylation, wherein benzene and / or toluene are used as raw materials, a carrier gas is mixed with the aromatic raw materials to obtain a reaction mixture, and the reaction mixture flows from the first reactor to the last reactor in sequence; an alkylating agent is divided into at least two streams, which are mixed with the reaction mixture at the entrance of each reactor, and then enter the reactor to contact and react with an alkylation catalyst to obtain a reaction product rich in xylene. Compared with a single reactor, this method can improve the stability of the catalyst, but the toluene conversion rate and methanol utilization rate are still not high, and the C9 / C10 aromatics produced by the aromatics complex cannot be utilized.

[0008] CN104557428A discloses a method for increasing the production of xylene, which uses toluene, C9+ heavy aromatics and an alkylating agent as raw materials, first passes through an alkylation reaction zone under hydrogen conditions, then passes through an alkylation reaction zone, and contacts with a molecular sieve catalyst in the reaction zone. The method has a low conversion rate of aromatics (toluene+C9+ heavy aromatics), and the xylene generated by the alkylation reaction will inevitably be further alkylated in the alkylation reaction zone to generate polymethylbenzenes, resulting in a decrease in the selectivity of xylene.

[0009] CN110678438A discloses a method for producing mixed xylene from heavy reforming product feed, firstly introducing heavy reforming product and hydrogen into a dealkylation reactor to carry out a dealkylation reaction; then introducing the effluent into a splitter unit to separate and obtain a light gas stream, a toluene stream, a benzene stream, a C9 aromatic stream, a C10+ aromatic stream and a mixed xylene stream; then introducing the toluene stream, the C9 aromatic stream and a hydrogen stream into an alkylation reactor for an alkylation reaction; introducing the alkylation effluent into a splitter unit; and separating the alkylation effluent in the splitter unit. Its essence is a combination of a heavy aromatic dealkylation reaction and an aromatic alkylation reaction. Since no methyl groups are introduced from the outside like in a methylation reaction, the xylene yield is limited by the ratio of methyl groups to benzene rings in the heavy reforming product feed. Summary of the invention

[0010] The purpose of the present invention is to overcome the low toluene conversion rate and C 9 + In order to solve the problem of low utilization rate of heavy aromatics, a method for increasing xylene production is provided, which can simultaneously process benzene and / or toluene and C 9 +Heavy aromatics have the characteristics of high conversion rate of benzene and / or toluene and high selectivity of xylene, which is beneficial to energy saving and consumption reduction.

[0011] In order to achieve the above object, the present invention provides a method for increasing the production of xylene, wherein the method is carried out in n-stage fixed bed reactors connected in series, wherein n≥3;

[0012] The method comprises:

[0013] (1) The first to (n-1)th fixed bed reactors are loaded with a solid acid aromatic methylation catalyst, an aromatic raw material is fed into the first fixed bed reactor, and is contacted with the solid acid aromatic methylation catalyst under hydrogenation conditions; an alkylating agent is divided into (n-1) portions and fed into the first to (n-1)th fixed bed reactors respectively;

[0014] The reaction discharge of the first-stage fixed bed reactor is used as the reaction feed of the second-stage fixed bed reactor; the aromatic hydrocarbon raw material is benzene and / or toluene;

[0015] (2) The reaction discharge of the (n-1) stage fixed bed reactor, C 9 + The heavy aromatics are fed into the nth stage fixed bed reactor and contacted with the solid acid transalkylation catalyst under hydrogenation conditions;

[0016] The content of xylene in the reaction discharge of the (n-1) stage fixed bed reactor is 20-60 wt %; the mass of the reaction discharge of the (n-1) stage fixed bed reactor is C 9 + The mass ratio of heavy aromatics is 1:(0.5-2);

[0017] (3) Separating the product obtained in step (2) to obtain xylene.

[0018] Preferably, in the reaction discharge of the (n-1)th stage fixed bed reactor, the content of xylene is 25-55 wt %, and the content of non-xylene alkylbenzene is 45-75 wt %.

[0019] Preferably, in step (1), the molar ratio of the total molar amount of the alkylating agent introduced into the (n-1) stage fixed bed reactor to the aromatic hydrocarbon feedstock is (0.2-3):1; and the ratio of the feed amount of the alkylating agent in the subsequent stage fixed bed reactor to the feed amount of the alkylating agent in the previous stage fixed bed reactor is (0.5-1.2):1.

[0020] The method for increasing xylene production provided by the present invention couples an aromatic methylation reaction with an aromatic transalkylation reaction. In the prior art, toluene is usually used as a raw material for heavy aromatic transalkylation reactions, which requires additional separation or purification steps, and the yield of xylene is low. The inventors of the present invention have found in their research that the product of the methylation of benzene and / or toluene is reacted with C 9 + Heavy aromatics can be directly used as the raw material for the transalkylation reaction. By controlling the composition of the products of benzene and / or toluene methylation, it is possible to solve the problem that disproportionation and transalkylation technologies are difficult to improve the selectivity of xylenes, and to utilize C 9 + Heavy aromatics can solve the problem that aromatic methylation technology cannot utilize heavy aromatic resources, achieve the effect of increasing xylene production, and greatly reduce material circulation, which is beneficial to energy saving and consumption reduction of the device. In addition, through multi-stage feeding of alkylating agents, compared with single reactor technology, it is also convenient to effectively adjust process parameters, further reduce the occurrence of side reactions, and improve the selectivity of the main reaction products. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a schematic diagram of a reaction system used in one embodiment of the present invention. DETAILED DESCRIPTION

[0022] The endpoints and any values ​​of the ranges disclosed in this article 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 each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0023] The present invention provides a method for increasing the production of xylene, wherein the method is carried out in n-stage fixed bed reactors connected in series, wherein n≥3;

[0024] The method comprises:

[0025] (1) The first to (n-1)th fixed bed reactors are loaded with a solid acid aromatic methylation catalyst, an aromatic raw material is fed into the first fixed bed reactor, and is contacted with the solid acid aromatic methylation catalyst under hydrogenation conditions; an alkylating agent is divided into (n-1) portions and fed into the first to (n-1)th fixed bed reactors respectively;

[0026] The reaction discharge of the first-stage fixed bed reactor is used as the reaction feed of the second-stage fixed bed reactor; the aromatic hydrocarbon raw material is benzene and / or toluene;

[0027] (2) The reaction discharge of the (n-1) stage fixed bed reactor, C 9+ The heavy aromatics are fed into the nth stage fixed bed reactor and contacted with the solid acid transalkylation catalyst under hydrogenation conditions;

[0028] The content of xylene in the reaction discharge of the (n-1) stage fixed bed reactor is 20-60 wt %; the mass of the reaction discharge of the (n-1) stage fixed bed reactor is C 9 + The mass ratio of heavy aromatics is 1:(0.5-2);

[0029] (3) Separating the product obtained in step (2) to obtain xylene.

[0030] The existing xylene production technology, whether it is toluene disproportionation and transalkylation technology or pure toluene disproportionation technology, has the disadvantages of relatively low toluene conversion rate and low xylene selectivity due to a large amount of benzene in the product, resulting in a large amount of toluene circulating in the system, resulting in excessive energy consumption and other problems, and cannot meet the energy saving and consumption reduction requirements of aromatics integrated devices. The method provided by the present invention couples the aromatics methylation reaction and the aromatics transalkylation reaction, and by controlling the composition of the products of benzene and / or toluene methylation, it can not only solve the problem that the disproportionation and transalkylation technology is difficult to improve the xylene yield, but also utilize C 9 + Heavy aromatics can solve the defect that aromatics methylation technology cannot utilize heavy aromatics resources, achieve the effect of increasing xylene production, and at the same time greatly reduce material circulation, which is beneficial to energy saving and consumption reduction of the device.

[0031] According to the present invention, the aromatic hydrocarbon feedstock is fed from the first stage fixed bed reactor to the n-stage fixed bed reactors connected in series, and the alkylating agent is divided into (n-1) portions and fed into the first to (n-1)th stage fixed bed reactors respectively. For the first stage fixed bed reactor, the aromatic hydrocarbon feedstock and the first portion of the alkylating agent may be fed into the reactor separately, or the aromatic hydrocarbon feedstock and the first portion of the alkylating agent may be mixed and then fed into the reactor; the discharge of the first stage fixed bed reactor may be mixed with the first portion of the alkylating agent and then used as the reaction feed of the second stage fixed bed reactor, and so on.

[0032] According to some preferred embodiments of the present invention, the reaction output of the (n-1)th fixed bed reactor includes benzene, xylene and optional non-xylene alkylbenzene. Preferably, the non-xylene alkylbenzene is selected from at least one of toluene, trimethylbenzene and tetramethylbenzene.

[0033] In the present invention, the reaction discharge from the (n-1)th stage fixed bed reactor is directly or optionally fed into the nth stage fixed bed reactor after heat exchange, without any separation or purification process.

[0034] According to the present invention, the content of xylene in the composition of the reaction discharge of the (n-1)th stage fixed bed reactor in step (1) is controlled, and then it is directly used as a reaction raw material to react with C 9 + The transalkylation reaction of heavy aromatics is beneficial to shorten the process, eliminate separation energy consumption, and improve xylene selectivity.

[0035] According to some preferred embodiments of the present invention, in the reaction discharge of the (n-1) stage fixed bed reactor, the content of xylene is 20-60wt%, preferably 25-55wt%, and the content of non-xylene alkylbenzene is 40-80wt%, preferably 45-75wt%. By controlling the composition of the reaction discharge of the (n-1) stage fixed bed reactor within the above preferred range, it is beneficial to achieve an atomic economic chemical reaction and improve the xylene yield. Too high a xylene content may result in the production of C 9 + The amount of heavy aromatics is reduced; the low xylene content indicates that the performance of the alkylation catalyst is not fully utilized, resulting in a decrease in the overall xylene selectivity.

[0036] In the present invention, the method is carried out in n-stage fixed bed reactors connected in series, wherein n≥3, and those skilled in the art can select the number of fixed bed reactors connected in series according to actual conditions, as long as the composition of the reaction discharge of the (n-1)-stage fixed bed reactor is controlled within the above range. Preferably, n is selected from a positive integer of 3-30. The above preferred embodiment is adopted to facilitate the coordinated alkylation reaction and transalkylation reaction, achieve reaction performance with quasi-atomic economy, and maximize the xylene selectivity.

[0037] According to some preferred embodiments of the present invention, in step (1), the molar ratio of the total molar amount of the alkylating agent introduced into the (n-1) stage fixed bed reactor to the aromatic hydrocarbon feedstock is (0.2-3):1, preferably (0.5-2):1.

[0038] In the present invention, in the (n-1) stages of fixed bed reactors connected in series, the molar amount of the alkylating agent introduced into each stage of the fixed bed reactor may be the same or different.

[0039] In a further preferred embodiment, the ratio of the feed amount of the alkylating agent in the subsequent fixed bed reactor to the feed amount of the alkylating agent in the previous fixed bed reactor is (0.5-1.2): 1, preferably (0.6-1): 1. The above preferred alkylating agent feeding method is conducive to exerting the performance of the alkylation catalyst in each fixed bed reactor and controlling the bed temperature rise.

[0040] According to some preferred embodiments of the present invention, the SiO 2 / Al 2 O 3 The molar ratio is the SiO 2 / Al 2 O 3 The molar ratio is 2-15, preferably 2.5-12. The present invention controls the ratio of the silicon-aluminum molar ratio of the first solid acid zeolite molecular sieve in the solid acid aromatic methylation catalyst and the silicon-aluminum molar ratio of the second solid acid zeolite molecular sieve in the solid acid transalkylation catalyst, so that the acidity of the two catalysts is mutually matched, thereby controlling the degree of the alkylation reaction and the transalkylation reaction, which is beneficial to further improve the conversion rate of the reaction raw materials and the yield of the target product xylene, and reduce the energy consumption of the reaction device.

[0041] According to some preferred embodiments of the present invention, the method further comprises: using C 9 + The heavy aromatics are used to exchange heat with the discharge of the (n-1) stage fixed bed reactor, and then fed into the n-stage fixed bed reactor. The inventors of the present invention have found in their research that the discharge temperature of the (n-1) stage fixed bed reactor is relatively high due to the continuous exothermic reaction of the alkylation reaction. 9 + The heat exchange of heavy aromatics with the reaction discharge of the (n-1) stage fixed bed reactor can reduce the temperature of the reaction feed of the n-stage fixed bed reactor, which is beneficial to the effective use of heat in the device to reduce energy consumption, and is also beneficial to the transalkylation reaction to reduce possible side reactions.

[0042] Preferably, the temperature of the reaction feed of the nth stage fixed bed reactor is 10-100°C lower than the temperature of the reaction discharge of the (n-1)th stage fixed bed reactor, preferably 30-90°C.

[0043] According to some preferred embodiments of the present invention, relative to the total mass of the solid acid aromatic methylation catalyst loaded in the first to (n-1)th stage fixed bed reactors, the mass space velocity of the aromatic feedstock is 1-15h -1 , preferably 2-10h -1 .

[0044] Preferably, the conditions of the fixed bed reactors of the first to (n-1) stages independently include: the reactor inlet temperature is 300-480°C, preferably 320-460°C, and the pressure is 0.1-4MPa, preferably 0.1-3MPa. In the present invention, in the (n-1) stages of fixed bed reactors connected in series, the reaction conditions in each stage of the fixed bed reactor may be the same or different, and all meet the above preferred ranges, and those skilled in the art may adjust according to actual needs.

[0045] According to some preferred embodiments of the present invention, hydrogen is introduced into the n-stage fixed bed reactors connected in series through the first stage fixed bed reactor to provide the hydrogenation conditions. Preferably, the molar ratio of the aromatic hydrocarbon feedstock to hydrogen is 1-6, preferably 1-4.

[0046] In a further preferred embodiment, in the aromatic hydrocarbon feedstock, the molar ratio of methyl to benzene ring is 0.1-4:1, preferably 0.2-2:1. The use of the above preferred aromatic hydrocarbon feedstock composition is conducive to further improving the selectivity of xylene products.

[0047] In the present invention, the selection range of the alkylating agent is relatively wide, and any alkylating agent that can introduce a methyl group conventionally used in the art can be used. Preferably, the alkylating agent is selected from at least one of methanol, dimethyl ether, methyl bromide and carbon monoxide, more preferably methanol.

[0048] In the present invention, the composition of the solid acid aromatic hydrocarbon methylation catalyst can be selected in a wide range. Preferably, the solid acid aromatic hydrocarbon methylation catalyst comprises a first solid acid zeolite molecular sieve, a first binder and an optional first active component; the first solid acid zeolite molecular sieve is selected from at least one of MFI type, MEL type, FER type and TON type topological structure molecular sieves, preferably an MFI type topological structure molecular sieve; for example, a ZSM-5 molecular sieve. With this preferred embodiment, the molecular sieve has a suitable acid strength, which is conducive to further improving the activity of catalyzing the aromatic hydrocarbon methylation reaction.

[0049] Preferably, the SiO 2 / Al 2 O 3 The molar ratio is 80-300, preferably 85-200; under the above preferred circumstances, it is beneficial to improve the stability of the catalyst while maintaining a relatively high catalytic activity.

[0050] In the present invention, there is no particular limitation on the type of the first binder. Preferably, in step (1), the first binder is aluminum oxide and / or silicon oxide.

[0051] In the present invention, preferably, the solid acid aromatic methylation catalyst optionally contains an active component. Preferably, in step (1), the first active component is selected from at least one of rare earth elements and Group VIII metal elements, and more preferably, the active component is selected from at least one of La, Ce, Fe, Co and Ni.

[0052] In a further preferred embodiment, the first active component includes rare earth elements and Group VIII metal elements, more preferably La and Ni.

[0053] Preferably, the mass ratio of the rare earth element to the Group VIII metal element is 1:(0.5-2).

[0054] In some preferred embodiments, relative to 100 parts by weight of the first solid acid zeolite molecular sieve, the content of the first binder is 15-400 parts by weight, preferably 20-200 parts by weight, and the content of the first active component is 0-80 parts by weight, preferably 10-75 parts by weight.

[0055] In the present invention, there is no particular limitation on the preparation method of the solid acid aromatic hydrocarbon methylation catalyst, which may be a method conventionally defined in the art. For example, it may be prepared by the following method: an ammonium-type first solid acid zeolite molecular sieve powder and a first binder are mixed, and the mixture is molded, dried and calcined, and then the first active component is optionally loaded to obtain a solid acid aromatic hydrocarbon methylation catalyst, wherein the content of the first binder is 15-400 parts by weight relative to 100 parts by weight of the first solid acid zeolite molecular sieve.

[0056] Preferably, the method further comprises: optionally introducing an active component before or after the catalyst is extruded. In the present invention, there is no particular limitation on the molding method, for example, it can be extrusion molding. In the present invention, there is no particular limitation on the drying conditions, preferably, the drying temperature is 100-140°C and the time is 1-8h. In the present invention, there is no particular limitation on the calcination conditions, preferably, the calcination temperature is 450-600°C and the time is 2-8h.

[0057] In the present invention, the type and properties of the first solid acid zeolite molecular sieve, the type of the first binder and the type of the active component have been described in the foregoing content and will not be repeated here.

[0058] In the present invention, the first binder is preferably a material that can be converted into oxides by calcination, for example, pseudo-boehmite and / or silica sol.

[0059] In the present invention, the preparation method of the solid acid aromatic methylation catalyst also includes introducing a first extrusion molding aid and / or a first peptizing agent during the molding process. Those skilled in the art can select the type and amount of the first extrusion molding aid and the first peptizing agent within a reasonable range according to the specific circumstances of the extrusion molding. Preferably, the first extrusion molding aid is selected from at least one of sesbania powder, dextrin and methylcellulose. Preferably, the first peptizing agent is selected from at least one of nitric acid, acetic acid and citric acid.

[0060] In a preferred embodiment, relative to 100 parts by weight of the first solid acid zeolite molecular sieve, the amount of the first extrusion molding aid is 1-30 parts by weight, and the amount of the first peptizing agent is 1-8 parts by weight.

[0061] In the present invention, there is no special requirement for the loading method of the first active component, and a conventional method can be used, such as impregnating the calcined product with a solution of a soluble precursor compound containing the first active component, and then drying and calcining. The present invention also has no special restrictions on the conditions of the drying and calcining, and those skilled in the art can choose according to actual conditions. Preferably, the drying temperature is 100-140°C and the time is 1-8h. Preferably, the calcination temperature is 450-600°C and the time is 2-8h.

[0062] Preferably, the precursor of Fe is selected from at least one of ferric nitrate, basic iron carbonate and ferric acetate. Preferably, the precursor of Co is selected from at least one of cobalt nitrate, basic cobalt carbonate and cobalt acetate. Preferably, the precursor of Ni is selected from at least one of nickel nitrate, basic nickel carbonate and nickel acetate. Preferably, the precursor of the rare earth element is selected from the water-soluble salts of each, for example, it can be at least one of lanthanum nitrate, lanthanum sulfate, lanthanum chloride, lanthanum acetate, lanthanum carbonate, lanthanum oxalate, cerium nitrate and cerium chloride.

[0063] According to the present invention, preferably, the mass of the reaction discharge of the (n-1) stage fixed bed reactor is 9 + The mass ratio of heavy aromatics is 1:(0.5-2), preferably 1:(0.6-1.5). By controlling the mass of the reaction discharge of the (n-1) stage fixed bed reactor and C 9 + The mass ratio of heavy aromatics is within the above preferred range, which is beneficial to exerting the performance of the transalkylation catalyst and improving the overall selectivity of xylene.

[0064] According to some preferred embodiments of the present invention, in step (2), the contacting conditions include: the reactor inlet temperature is 300-480°C, 9 + The mass space velocity of heavy aromatics is 1-8h -1, pressure is 0.5-5MPa, hydrogen-to-oil molar ratio is 1-6. Preferably, the reactor inlet temperature is 320-450°C, C 9 + The mass space velocity of heavy aromatic hydrocarbons is 1-6h -1 , pressure is 1-4 MPa, and hydrogen to oil molar ratio is 1-4. Under the above preferred reaction conditions, the main transalkylation reaction is favorable.

[0065] In the present invention, unless otherwise specified, the pressures described in the present invention are gauge pressures.

[0066] According to the present invention, preferably, the C 9 + Heavy aromatics selected from C 9 + Monocyclic aromatic hydrocarbons and / or condensed-ring aromatic hydrocarbons, the present invention is for the C 9 + There is no specific requirement for the specific composition of heavy aromatics. For example, the heavy aromatics may contain at least one of trimethylbenzene, tetramethylbenzene, methylethylbenzene and dimethylethylbenzene.

[0067] Preferably, the C 9 + Among heavy aromatics, C 10 The content of aromatic hydrocarbons is 1-75wt%, preferably 5-60wt%. In the above preferred case, it is beneficial to improve the efficiency of transalkylation reaction.

[0068] According to some preferred embodiments of the present invention, the solid acid transalkylation catalyst comprises a second solid acid zeolite molecular sieve, a second binder and an optional second active component; the second solid acid zeolite molecular sieve is selected from at least one of MFI type, MWW type, BEA type, MOR type, FAU type topology structure molecular sieves and BEA / MOR symbiotic molecular sieves, preferably at least one of BEA type, MOR type topology structure molecular sieves and BEA / MOR symbiotic molecular sieves, and further preferably BEA / MOR symbiotic molecular sieves.

[0069] In the present invention, it is understood that the BEA / MOR symbiotic molecular sieve refers to a two-phase symbiotic molecular sieve formed by the intergrowth of twins of two phases with different structural types of BEA and MOR. The BEA type and MOR type molecular sieves have conventional definitions in the art, the BEA type molecular sieve is, for example, a beta zeolite molecular sieve, and the MOR type molecular sieve is, for example, a mordenite molecular sieve.

[0070] Preferably, in the BEA / MOR symbiotic molecular sieve, the mass ratio of the BEA type to the MOR type molecular sieve is 95:5-5:95, preferably 85:15-35:65.

[0071] In a preferred embodiment, the molar ratio of silicon oxide to aluminum oxide in the second solid acid zeolite molecular sieve is 10-80, preferably 15-60. The advantage of adopting this preferred embodiment is that its acid properties are more suitable for catalyzing aromatic hydrocarbon transalkylation reactions.

[0072] Preferably, the second binder is at least one of aluminum oxide, silicon oxide, titanium oxide, zinc oxide and zirconium oxide.

[0073] Preferably, the second active component is selected from at least one of Group VA metal elements and Group VIB metal elements, for example, it can be selected from at least one of Sb, Bi, Cr, Mo and W.

[0074] In a further preferred embodiment, the second active component includes any one of the metal elements of Group VA and any one of the metal elements of Group VIB.

[0075] Preferably, in the second active component, the mass ratio of the Group VA metal element to the Group VIB metal element is 10:1-1:10. In the above preferred case, the activity, selectivity and stability of the transalkylation catalyst can be further improved through the synergistic effect of the molecular sieve and the second active metal component.

[0076] Preferably, the Group VA metal element is selected from Sb and / or Bi, more preferably Bi.

[0077] Preferably, the Group VIB metal element is at least one selected from Cr, Mo and W, and more preferably Mo.

[0078] Preferably, relative to 100 parts by weight of the second solid acid zeolite molecular sieve, the content of the second binder is 15-200 parts by weight, preferably 20-150 parts by weight; the content of the second active component is 2-160 parts by weight, preferably 10-80 parts by weight.

[0079] According to some preferred embodiments of the present invention, the solid acid transalkylation catalyst is prepared by the following method, comprising:

[0080] S1, subjecting the second solid acid zeolite molecular sieve raw powder to at least one acid treatment;

[0081] S2, exchanging the product obtained by acid treatment with ammonium to obtain an ammonium-type second solid acid zeolite molecular sieve;

[0082] S3, mixing and molding the ammonium type second solid acid zeolite molecular sieve and the second binder precursor, and drying and calcining to obtain a catalyst molded body;

[0083] S4, treating the catalyst shaped body with ammonia-containing water vapor to obtain a catalyst precursor;

[0084] The method further comprises: introducing metal active components into the mixing in step S3, or introducing metal active components into the catalyst precursor by an impregnation method.

[0085] According to some preferred embodiments of the present invention, the acid treatment in step S1 comprises: contacting the second solid acid zeolite molecular sieve with an acid solution. The acid solution may be an aqueous solution of an organic acid and / or an inorganic acid, preferably, the acid solution is selected from at least one of citric acid, acetic acid, glycolic acid, oxalic acid and ethylenediaminetetraacetic acid. Preferably, the concentration of the acid solution is 0.2-4.5 mol / L.

[0086] Preferably, the acid treatment is performed 1-4 times, more preferably 1-2 times.

[0087] Preferably, the acid treatment conditions include: temperature of 50-90° C. and time of 2-15 h.

[0088] According to some preferred embodiments of the present invention, those skilled in the art can reasonably select the type and amount of ammonium salt used and the solid-liquid ratio of ammonium exchange according to the specific circumstances of ammonium exchange to obtain ammonium-type solid acid zeolite.

[0089] According to some preferred embodiments of the present invention, in step S3, relative to 100 parts by weight of the ammonium type second solid acid zeolite molecular sieve, the amount of the second binder is 15-200 parts by weight, preferably 20-150 parts by weight; preferably, the second binder precursor refers to any substance that can be calcined to obtain the second binder, which is well known to those skilled in the art.

[0090] In the present invention, the preparation method of the transalkylation catalyst further comprises introducing a second extrusion molding aid during the molding process. Those skilled in the art can select the type and amount of the second extrusion molding aid within a reasonable range according to the specific conditions of the extrusion molding. Preferably, the second extrusion molding aid is selected from at least one of sesbania powder, dextrin and methylcellulose.

[0091] In a preferred embodiment, the amount of the second extrusion molding aid is 1-20 parts by weight relative to 100 parts by weight of the second solid acid zeolite molecular sieve.

[0092] In the present invention, the type and properties of the second solid acid zeolite molecular sieve and the type and amount of the second binder have been described in the above content and will not be repeated here.

[0093] In the present invention, the selection range of the loading method of the second active component is relatively wide. According to the present invention, the precursor compound of the second active component can be added during the mixing process in step S3, and then the molding can be performed; or after the catalyst precursor is obtained in step S4, the second active component can be loaded on the catalyst precursor by impregnation. Preferably, after the catalyst precursor is obtained in step S4, the second active component is loaded on the catalyst precursor by impregnation. The above preferred embodiment is conducive to better matching of the metal component and the acid center of the molecular sieve, and the synergistic effect is better.

[0094] Preferably, the precursor compound of the second active component can be an organic salt or an inorganic salt containing the second active component, preferably at least one of nitrate, acetate, basic carbonate, chloride, acetate, carbonate, oxalate and sulfate. The amount of the precursor compound of the second active component is based on the composition of the prepared catalyst.

[0095] The present invention has no particular limitation on the specific operation of the impregnation method, which can be the same as the loading method and operating conditions of the active components in the solid acid aromatic methylation catalyst described above, and will not be described in detail here.

[0096] In the present invention, there is no particular limitation on the drying conditions of the solid acid transalkylation catalyst. Preferably, in step S3, the drying conditions include: a temperature of 100-140° C. and a time of 2-24 hours.

[0097] According to the present invention, preferably, the calcination conditions in step S3 include: a temperature of 200-600° C. and a time of 3-10 h.

[0098] In the present invention, it can be understood that as long as the ammonia-containing water vapor can be brought into contact with the catalyst molded body, the specific method of providing the ammonia-containing water vapor and the contact form with the catalyst molded body are not particularly limited. Preferably, the treatment conditions include: bringing the ammonia water into contact with the catalyst precursor under conditions that satisfy the vaporization of ammonia and water. In this preferred embodiment, the specific operation can be to introduce an ammonia-containing aqueous solution into a container containing the catalyst precursor, and then increase the temperature to vaporize the ammonia and water.

[0099] In the present invention, there is no particular limitation on the concentration of the aqueous ammonia. Preferably, the aqueous ammonia has an ammonia content of 5-25% by weight, more preferably 10-20% by weight.

[0100] In the present invention, there is no particular limitation on the contact conditions between the aqueous ammonia and the catalyst molding. Preferably, the contact conditions include: a temperature of 200-600°C, a time of 1-12 hours, a mass space velocity of the aqueous ammonia of 0.5-10 h -1Further preferably, the contact conditions include: temperature of 250-550°C, time of 2-10h, mass space velocity of ammonia water of 1-6h -1 .

[0101] The method for preparing a solid acid transalkylation catalyst using the above preferred embodiment has the advantages of optimizing the pore structure of the catalyst and improving diffusion, which is beneficial to further improve the selectivity of xylene.

[0102] According to some preferred embodiments of the present invention, the separation in step (3) also obtains dry gas and gas containing benzene, toluene, C 9 + A further stream of at least one of the heavy aromatic hydrocarbons.

[0103] Preferably, the method further comprises: returning the mixture containing benzene and / or toluene to step (1) for reuse, so as to provide at least part of the aromatic hydrocarbon feedstock in step (1). 9 + The heavy aromatics are returned to step (2) for reuse to provide at least part of the C 9 + Heavy aromatics. The preferred implementation method of logistics recycling can improve resource utilization and reduce material loss.

[0104] The present invention will be described in detail below through examples.

[0105] Unless otherwise specified, the pressures described in the following embodiments are all gauge pressures.

[0106] The conversion of each reactant and the selectivity of xylene are defined as follows:

[0107]

[0108]

[0109] The following preparation examples are used to illustrate the preparation of the solid acid aromatic methylation catalyst in the present invention.

[0110] Preparation Example A1

[0111] (1) Take 100 parts by weight of ammonium ZSM-5 molecular sieve powder (silicon-aluminum molar ratio SiO 2 / Al 2 O 3 150), 107 parts by weight of silica sol (containing 40wt% SiO 2 ) and 15 parts by weight of sesbania powder, mixed evenly and extruded into strips, dried at 120°C for 3 hours, calcined at 550°C in air for 4 hours, and sheared to obtain a cylindrical carrier with a diameter of 2.0 mm and a length of 2.0 mm.

[0112] (2) The obtained cylindrical carrier was impregnated with a mixed aqueous solution of lanthanum nitrate and nickel nitrate (with respect to 100 parts by weight of ammonium ZSM-5 molecular sieve, lanthanum content was 20 parts by weight, and nickel content was 20 parts by weight), allowed to stand for 4 hours, dried at 120°C for 3 hours, and calcined at 550°C in an air atmosphere for 4 hours to obtain a solid acid aromatic methylation catalyst M1.

[0113] Preparation Example A2

[0114] (1) Take 100 parts by weight of ammonium ZSM-5 molecular sieve powder (silicon-aluminum molar ratio SiO 2 / Al 2 O 3 123), 100 parts by weight of silica sol (containing 40wt% SiO 2 ) and 15 parts by weight of sesbania powder, mixed evenly and extruded into strips, dried at 120°C for 3 hours, calcined at 550°C in air for 4 hours, and sheared to obtain a cylindrical carrier with a diameter of 2.0 mm and a length of 2.0 mm.

[0115] (2) The obtained cylindrical carrier was impregnated with a mixed aqueous solution of lanthanum nitrate and nickel nitrate (relative to 100 parts by weight of ammonium-type ZSM-5 molecular sieve, the lanthanum content was 10 parts by weight and the nickel content was 10 parts by weight), allowed to stand for 4 hours, dried at 120°C for 3 hours, and calcined at 550°C in an air atmosphere for 4 hours to obtain a solid acid aromatic methylation catalyst M2.

[0116] The following preparation examples are used to illustrate the preparation of the solid acid transalkylation catalyst of the present invention.

[0117] Preparation Example B1

[0118] (1) Take the BEA / MOR symbiotic molecular sieve raw powder (silicon aluminum molar ratio SiO 2 / Al 2 O 3 25, the mass ratio of beta zeolite to mordenite phase composition is BEA / MOR=35 / 65), and at a temperature of 80°C, it is contacted with 0.5 mol / L glycolic acid, and acid treatment is performed twice, each time for 4 hours;

[0119] (2) exchanging the BEA / MOR symbiotic molecular sieve obtained by acid treatment with ammonium to obtain an ammonium-type BEA / MOR symbiotic molecular sieve;

[0120] (3) 100 parts by weight of ammonium-type BEA / MOR symbiotic molecular sieve powder, 25 parts by weight of alumina binder and 15 parts by weight of extrusion molding aid sesbania powder were mixed and uniformly extruded into strips. The mixture was dried at 140° C. for 3 hours and then calcined at 550° C. for 3 hours to obtain a catalyst molded body A1;

[0121] (4) The catalyst molded body A1 was treated with water vapor containing aqueous ammonia (specifically, an aqueous solution containing 20 wt% aqueous ammonia was brought into contact with A1 at a temperature of 250° C. for 10 h and a mass space velocity of the aqueous ammonia solution of 1 h -1 ), to obtain a solid acid transalkylation catalyst precursor PA1;

[0122] (5) The obtained catalyst precursor PA1 was impregnated with a mixed aqueous solution of bismuth nitrate and ammonium heptamolybdate (containing 20 parts by weight of bismuth and 20 parts by weight of molybdenum relative to 100 parts by weight of ammonium-type BEA / MOR symbiotic molecular sieve), allowed to stand for 4 hours, dried at 120°C for 3 hours, and calcined at 550°C in an air atmosphere for 4 hours to obtain a solid acid transalkylation catalyst T1.

[0123] Preparation Example B2

[0124] (1) Take the BEA / MOR symbiotic molecular sieve raw powder (silicon aluminum molar ratio SiO 2 / Al 2 O 3 33, the mass ratio of β zeolite to mordenite phase composition is BEA / MOR=48 / 52), and at a temperature of 70°C, it is contacted with citric acid with a concentration of 1.0 mol / L, and acid treatment is performed twice, each time for 6 hours;

[0125] (2) exchanging the BEA / MOR symbiotic molecular sieve obtained by acid treatment with ammonium to obtain an ammonium-type BEA / MOR symbiotic molecular sieve;

[0126] (3) 100 parts by weight of ammonium BEA / MOR symbiotic molecular sieve powder, 25 parts by weight of pseudo-boehmite and 15 parts by weight of extrusion molding aid sesbania powder were mixed, and a mixed aqueous solution of bismuth nitrate and chromium nitrate (containing 40 parts by weight of bismuth and 20 parts by weight of chromium relative to 100 parts by weight of ammonium BEA / MOR symbiotic molecular sieve) was added, mixed evenly, and extruded into strips. The mixture was dried at 140°C for 3 hours and then calcined at 550°C for 8 hours to obtain a catalyst molded body A2;

[0127] (4) The catalyst molded body A2 was treated with water vapor containing aqueous ammonia (specifically, an aqueous solution containing 10 wt % aqueous ammonia was brought into contact with A2 at a temperature of 350° C. for 3 h and a mass space velocity of the aqueous ammonia solution of 2 h -1 ), to obtain a solid acid transalkylation catalyst precursor PA2;

[0128] (5) The obtained catalyst precursor PA2 was dried at 120° C. for 3 hours and calcined at 550° C. for 4 hours in an air atmosphere to obtain a solid acid transalkylation catalyst T2.

[0129] Preparation Example B3

[0130] The method of Preparation Example B1 was followed, except that the active component loading in step (5) was not performed, and the solid acid transalkylation catalyst precursor PA1 was used as the solid acid transalkylation catalyst T3.

[0131] Preparation Example B4

[0132] The method of Preparation Example B1 is followed, except that in step (5),

[0133] The obtained catalyst precursor PA1 was impregnated with an aqueous solution of ammonium heptamolybdate (containing 20 parts by weight of molybdenum relative to 100 parts by weight of ammonium-type BEA / MOR symbiotic molecular sieve), allowed to stand for 4 hours, dried at 120°C for 3 hours, and calcined at 550°C in an air atmosphere for 4 hours to obtain a solid acid transalkylation catalyst T4.

[0134] Preparation Example B5

[0135] The method of Preparation Example B1 is followed, except that the molar ratio of SiO2 in the BEA / MOR symbiotic molecular sieve raw powder used in step (1) is 2 / Al 2 O 3 is 75, the mass ratio of β zeolite to mordenite phase composition is BEA / MOR=50 / 50, and the other conditions and steps are the same as B1, which is recorded as solid acid transalkylation catalyst T5.

[0136] The following examples are used to illustrate the method for increasing xylene production in the present invention.

[0137] Example 1

[0138] like Figure 1 As shown, five fixed bed reactors are connected in series, each with a volume of 50 ml. The first four fixed bed reactors are respectively filled with 15 ml of solid acid aromatic methylation catalyst M1, and the fifth fixed bed reactor is filled with 15 ml of solid acid transalkylation catalyst T1.

[0139] The ratio of the molar ratio of silicon oxide to aluminum oxide of the first solid acid zeolite molecular sieve ZSM-5 in the solid acid aromatic methylation catalyst M1 to the molar ratio of silicon oxide to aluminum oxide of the second solid acid zeolite molecular sieve BEA / MOR intergrowth molecular sieve in the solid acid transalkylation catalyst T1 is 6.

[0140] Toluene and hydrogen are fed into the first fixed bed reactor and flow from the first reactor to the fourth reactor in sequence. The alkylation agent methanol is divided into four equal parts and introduced into four fixed bed reactors respectively. It is mixed evenly with toluene before entering the first reactor; it is mixed evenly with the outlet stream of the previous reactor before entering the second, third and fourth reactors, and then contacted with the solid acid aromatic methylation catalyst M1 in each reactor for reaction. The fourth stream flowing out of the fourth reactor and C 9 + The heavy aromatics are mixed at the inlet of the fifth fixed bed reactor and then enter the fifth reactor to react with the solid acid transalkylation catalyst T1 in the reactor.

[0141] The alkylation conditions include:

[0142] The molar ratio of toluene to the total amount of methanol introduced into the four reactors: 2.0;

[0143] Inlet temperature of the first four reactors: 400 °C;

[0144] Reaction pressure of the first four reactors: 1.0 MPa;

[0145] The hydrogen to oil molar ratio of hydrogen and toluene introduced into the first reactor is 2.0;

[0146] Mass space velocity of toluene relative to the total mass of solid acid aromatic methylation catalyst: 4.0 h -1 ;

[0147] The outlet temperature of the fourth reactor was 432°C.

[0148] The reaction output of the fourth reactor includes benzene, toluene, xylene, C 9 + Aromatic hydrocarbons, etc., wherein the content of xylene is 40wt%, and the content of non-xylene alkylbenzene is 60wt%.

[0149] The transalkylation reaction conditions include:

[0150] The fifth reactor inlet temperature is 360°C;

[0151] Reaction pressure: 3.0MPa;

[0152] The reaction discharge of the fourth reactor and C 9 + The mass ratio of heavy aromatics is 1:1;

[0153] C 9 + Heavy aromatics composition: C 10 The mass percentage of aromatic hydrocarbons is 20%;

[0154] C9 + Mass space velocity of heavy aromatics: 2.0h -1 ;

[0155] Hydrogen to oil molar ratio: 3.

[0156] The reaction product at the outlet of the fifth reactor was cooled by an air condenser and separated by a gas-liquid separator to obtain a liquid product. The liquid product was sampled and analyzed every 12 hours, with a total of 6 samples taken. The average toluene conversion rate (mass) after the initial reaction for 72 hours was 53.6%, and the average xylene selectivity (mass) was 88.2%.

[0157] Example 2

[0158] Five fixed bed reactors were connected in series, each with a volume of 50 ml. The first four fixed bed reactors were respectively filled with 15 ml of solid acid aromatic methylation catalyst M2, and the fifth fixed bed reactor was filled with 15 ml of solid acid transalkylation catalyst T2.

[0159] The ratio of the molar ratio of silicon oxide to aluminum oxide of the first solid acid zeolite molecular sieve ZSM-5 in the solid acid aromatic methylation catalyst M2 to the molar ratio of silicon oxide to aluminum oxide of the second solid acid zeolite molecular sieve BEA / MOR symbiotic molecular sieve in the solid acid transalkylation catalyst T2 is 4.

[0160] Toluene flows from the first reactor to the fourth reactor in sequence. The alkylation agent methanol is divided into four equal parts and introduced into four fixed bed reactors respectively. It is mixed evenly with toluene before entering the first reactor; it is mixed evenly with the outlet stream of the previous reactor before entering the second, third and fourth reactors, and then contacted with the solid acid aromatic methylation catalyst M2 in each reactor for reaction. The fourth stream flowing out of the fourth reactor and C 9 + The heavy aromatics are mixed at the inlet of the fifth fixed bed reactor and then enter the fifth reactor to react with the solid acid transalkylation catalyst T2 in the reactor.

[0161] The alkylation conditions include:

[0162] The molar ratio of toluene to the total amount of methanol introduced into the four reactors: 1.5;

[0163] Inlet temperature of the first to fourth reactors: 450°C;

[0164] Reaction pressure of the first to fourth reactors: 3.0 MPa;

[0165] The hydrogen to oil molar ratio of hydrogen and toluene introduced into the first reactor is 2.0;

[0166] Mass space velocity of toluene relative to the total mass of solid acid aromatic methylation catalyst: 4.0 h -1 ;

[0167] The fourth reactor outlet temperature: 494°C.

[0168] The reaction output of the fourth reactor includes benzene, toluene, xylene, C 9 + Aromatic hydrocarbons, etc., wherein the content of xylene is 55wt%, and the content of non-xylene alkylbenzene is 45wt%.

[0169] The transalkylation reaction conditions include:

[0170] The fifth reactor inlet temperature is 420°C;

[0171] Reaction pressure: 3.0MPa;

[0172] The reaction discharge of the fourth reactor and C 9 + The mass ratio of heavy aromatics is 1:1.25;

[0173] C 9 + Heavy aromatics composition: C 10 The mass percentage of aromatics is 55%;

[0174] C 9 + Mass space velocity of heavy aromatics: 2.0h -1 ;

[0175] Hydrogen to oil molar ratio: 4.

[0176] The reaction product at the outlet of the fifth reactor was cooled by an air condenser and separated by a gas-liquid separator to obtain a liquid product. The liquid product was sampled and analyzed every 12 hours, with a total of 6 samples taken. The average toluene conversion rate (mass) after the initial reaction for 72 hours was 65.6%, and the average xylene selectivity (mass) was 90.3%.

[0177] Example 3

[0178] The method of Example 1 is followed, except that the solid acid aromatic methylation catalyst is M1 and the solid acid transalkylation catalyst is T3.

[0179] The reaction was carried out under the same reaction conditions as in Example 1. The reaction product at the outlet of the fifth reactor was cooled by an air condenser and separated by a gas-liquid separator to obtain a liquid product. The liquid product was sampled and analyzed every 12 hours. A total of 6 samples were taken. The average toluene conversion rate (mass) after the initial reaction for 72 hours was 45.5%, and the average xylene selectivity (mass) was 84.8%.

[0180] Example 4

[0181] The method of Example 1 is followed, except that the solid acid aromatic methylation catalyst is M1 and the solid acid transalkylation catalyst is T4.

[0182] The reaction was carried out under the same reaction conditions as in Example 1. The reaction product at the outlet of the fifth reactor was cooled by an air condenser and separated by a gas-liquid separator to obtain a liquid product. The liquid product was sampled and analyzed every 12 hours. A total of 6 samples were taken. The average toluene conversion rate (mass) after the initial reaction for 72 hours was 50.9%, and the average xylene selectivity (mass) was 83.1%.

[0183] Example 5

[0184] The method of Example 1 is followed, except that the solid acid aromatic methylation catalyst is M1 and the solid acid transalkylation catalyst is T5. The molar ratio of silicon oxide to aluminum oxide of the first solid acid zeolite molecular sieve ZSM-5 in the solid acid aromatic methylation catalyst M1 and the molar ratio of silicon oxide to aluminum oxide of the second solid acid zeolite molecular sieve BEA / MOR intergrowth molecular sieve in the solid acid transalkylation catalyst T5 is 1.6.

[0185] The reaction was carried out under the same reaction conditions as in Example 1. The reaction product at the outlet of the fifth reactor was cooled by an air condenser and separated by a gas-liquid separator to obtain a liquid product. The liquid product was sampled and analyzed every 12 hours. A total of 6 samples were taken. The average toluene conversion rate (mass) after the initial reaction for 72 hours was 34.6%, and the average xylene selectivity (mass) was 78.9%.

[0186] Example 6

[0187] According to the method of Example 1, the difference is that

[0188] The alkylation conditions include:

[0189] The molar ratio of toluene to the total amount of methanol introduced into the four reactors: 3.5;

[0190] Inlet temperature of the first to fourth reactors: 400°C;

[0191] Reaction pressure of the first to fourth reactors: 1.0 MPa;

[0192] The hydrogen to oil molar ratio of hydrogen and toluene introduced into the first reactor is 2.0;

[0193] Mass space velocity of toluene relative to the total mass of solid acid aromatic methylation catalyst: 4.0 h -1 ;

[0194] The fourth reactor outlet temperature: 425°C.

[0195] The reaction output from the fourth reactor includes benzene, toluene, xylene, C9+ aromatics, etc., wherein the content of xylene is 38wt%, and the content of non-xylene alkylbenzene is 62wt%.

[0196] Then, the transalkylation reaction was carried out according to the method of Example 1.

[0197] The reaction product at the outlet of the fifth reactor was cooled by an air condenser and separated by a gas-liquid separator to obtain a liquid product. The liquid product was sampled and analyzed every 12 hours, with a total of 6 samples taken. The average toluene conversion rate (mass) after the initial reaction for 72 hours was 45.6%, and the average xylene selectivity (mass) was 82.9%.

[0198] Example 7

[0199] According to the method of Example 1, the difference is that

[0200] The transalkylation reaction conditions include:

[0201] The fifth reactor inlet temperature is 490°C;

[0202] Reaction pressure: 3.0MPa;

[0203] The reaction discharge of the fourth reactor and C 9 + The mass ratio of heavy aromatics is 1:0.85;

[0204] C 9 + Heavy aromatics composition: C 10 The mass percentage of aromatic hydrocarbons is 20%;

[0205] C 9 + Mass space velocity of heavy aromatics: 2.0h -1 ;

[0206] Hydrogen to oil molar ratio: 3.

[0207] The reaction product at the outlet of the fifth reactor was cooled by an air condenser and separated by a gas-liquid separator to obtain a liquid product. The liquid product was sampled and analyzed every 12 hours, with a total of 6 samples taken. The average toluene conversion rate (mass) after the initial reaction for 72 hours was 57.3%, and the average xylene selectivity (mass) was 75.6%.

[0208] Comparative Example 1

[0209] A fixed bed reactor with a reactor volume of 50 ml was used, and 15 ml of solid acid aromatic methylation catalyst M1 was loaded. Toluene and alkylating agent methanol were fed into the fixed bed reactor to contact with the catalyst.

[0210] Alkylation conditions include:

[0211] Toluene to methanol molar ratio: 2.0;

[0212] Reaction temperature: 400°C;

[0213] Reaction pressure: 1.0MPa;

[0214] Hydrogen to oil molar ratio: 2.0;

[0215] Liquid volume space velocity of toluene: 4.0 hours -1 ;

[0216] The reaction product was cooled by an air condenser and separated by a gas-liquid separator to obtain a liquid product. The liquid product was sampled and analyzed every 12 hours, for a total of 6 samples. The average toluene conversion rate (mass) after the initial reaction time of 72 hours was 33.5%, and the average xylene selectivity (mass) was 72.6%.

[0217] Comparative Example 2

[0218] Four fixed bed reactors connected in series were used, each reactor had a volume of 50 ml, and each reactor was filled with 15 ml of solid acid aromatic methylation catalyst M1.

[0219] Toluene flows from the first reactor to the fourth reactor in sequence, and the alkylation agent methanol is divided into four equal parts and introduced into four fixed bed reactors respectively, and is evenly mixed with toluene before entering the first reactor; before entering the second, third and fourth reactors, it is evenly mixed with the outlet flow of the previous reactor, and then contacted and reacted with the solid acid aromatic methylation catalyst in each reactor respectively.

[0220] The alkylation conditions include:

[0221] The molar ratio of toluene to the total amount of methanol introduced into the four reactors: 2.0;

[0222] Inlet temperature of the first to fourth reactors: 400°C;

[0223] Reaction pressure of the first to fourth reactors: 1.0 MPa;

[0224] The hydrogen to oil molar ratio of hydrogen and toluene introduced into the first reactor is 2.0;

[0225] Mass space velocity of toluene relative to the total mass of solid acid aromatic methylation catalyst: 4.0 h -1 ;

[0226] The reaction product was cooled by an air condenser and separated by a gas-liquid separator to obtain a liquid product. The liquid product was sampled and analyzed every 12 hours, for a total of 6 samples. The average toluene conversion rate (mass) after the initial reaction for 72 hours was 36.2%, and the average xylene selectivity (mass) was 76.1%.

[0227] It can be seen from the comparison between the above embodiments and comparative examples that the present invention couples the aromatic methylation reaction and the aromatic transalkylation reaction, and by controlling the composition of the product of the methylation of benzene and / or toluene, it can solve the problem that the disproportionation and transalkylation technology is difficult to increase the xylene yield, and significantly improve the toluene conversion rate and xylene selectivity; and it can also utilize C 9 + Heavy aromatics can solve the defect that aromatics methylation technology cannot utilize heavy aromatics resources, achieve the effect of increasing xylene production, and at the same time greatly reduce material circulation, which is beneficial to energy saving and consumption reduction of the device.

[0228] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A method for increasing xylene production, characterized in that: The method is carried out in n-stage fixed bed reactors connected in series, wherein n≥3; The method comprises: (1) The first to (n-1)th fixed bed reactors are loaded with a solid acid aromatic methylation catalyst, an aromatic raw material is fed into the first fixed bed reactor, and is contacted with the solid acid aromatic methylation catalyst under hydrogenation conditions; an alkylating agent is divided into (n-1) portions and fed into the first to (n-1)th fixed bed reactors respectively; The reaction discharge of the first-stage fixed bed reactor is used as the reaction feed of the second-stage fixed bed reactor; the aromatic hydrocarbon raw material is benzene and / or toluene; (2) The reaction discharge of the (n-1) stage fixed bed reactor, C9 + The heavy aromatics are fed into the nth stage fixed bed reactor and contacted with the solid acid transalkylation catalyst under hydrogenation conditions; The content of xylene in the reaction discharge of the (n-1) stage fixed bed reactor is 20-60 wt %; the mass of the reaction discharge of the (n-1) stage fixed bed reactor is about the same as that of C9 + The mass ratio of heavy aromatics is 1:(0.5-2); (3) Separating the product obtained in step (2) to obtain xylene.

2. The method according to claim 1, wherein: The reaction output of the (n-1)th stage fixed bed reactor includes xylene, optional benzene, and optional non-xylene alkylbenzene; Preferably, in the reaction discharge of the (n-1)th stage fixed bed reactor, the content of xylene is 25-55 wt %, and the content of non-xylene alkylbenzene is 45-75 wt %.

3. The method according to claim 1 or 2, wherein: The method is carried out in n-stage fixed bed reactors connected in series, wherein n is selected from a positive integer of 3-30; Preferably, in step (1), the molar ratio of the total molar amount of the alkylating agent introduced into the (n-1) stage fixed bed reactor to the aromatic hydrocarbon feedstock is (0.2-3):1; Preferably, the ratio of the feed amount of the alkylating agent in the subsequent fixed bed reactor to the feed amount of the alkylating agent in the previous fixed bed reactor is (0.5-1.2):

1.

4. The method according to any one of claims 1 to 3, wherein: The ratio of the SiO2 / Al2O3 molar ratio of the first solid acid zeolite molecular sieve contained in the solid acid aromatic methylation catalyst to the SiO2 / Al2O3 molar ratio of the second solid acid zeolite molecular sieve contained in the solid acid transalkylation catalyst is 2-15, preferably 2.5-12.

5. The method according to any one of claims 1 to 4, wherein: The method also includes: using C9 + The heavy aromatics exchange heat with the reaction discharge of the (n-1)th stage fixed bed reactor and then feed it into the nth stage fixed bed reactor; Preferably, the temperature of the reaction feed of the nth stage fixed bed reactor is 10-100°C lower than the temperature of the reaction discharge of the (n-1)th stage fixed bed reactor, preferably 30-90°C.

6. The method according to any one of claims 1 to 5, wherein: Relative to the total mass of the solid acid aromatic methylation catalyst loaded in the first to (n-1)th stage fixed bed reactors, the mass space velocity of the aromatic feedstock is 1-15h -1 , preferably 2-10h -1 ; Preferably, in step (1), hydrogen is introduced into n-stage fixed bed reactors connected in series through the first-stage fixed bed reactor to provide the hydrogenation conditions. Preferably, the molar ratio of the aromatic hydrocarbon feedstock to hydrogen is 1-6; Preferably, the conditions of the first to (n-1)th fixed bed reactors independently include: the reactor inlet temperature is 300-480°C, and the pressure is 0.1-4MPa; Preferably, in the aromatic hydrocarbon raw material, the molar ratio of methyl group to benzene ring is 0.1-4:1, preferably 0.2-2:1; Preferably, the alkylating agent is selected from at least one of methanol, dimethyl ether, methyl bromide and carbon monoxide, preferably methanol.

7. The method according to any one of claims 1 to 6, wherein: The solid acid aromatic methylation catalyst comprises a first solid acid zeolite molecular sieve, a first binder and an optional first active component; the first solid acid zeolite molecular sieve is selected from at least one of MFI type, MEL type, FER type and TON type topological structure molecular sieves, preferably an MFI type topological structure molecular sieve; Preferably, the SiO2 / Al2O3 molar ratio of the first solid acid zeolite molecular sieve is 80-300, preferably 85-200; Preferably, the first active component is selected from at least one of rare earth elements and Group VIII metal elements, preferably at least one of La, Ce, Ni, Co, Rh, Pd and Pt, preferably La and Ni; Preferably, the first binder is aluminum oxide and / or silicon oxide; Preferably, relative to 100 parts by weight of the first solid acid zeolite molecular sieve, the content of the first binder is 15-400 parts by weight, and the content of the first active component is 0-80 parts by weight.

8. The method according to any one of claims 1 to 7, wherein: The quality of the reaction discharge of the (n-1) stage fixed bed reactor is similar to that of C9 + The mass ratio of heavy aromatics is 1:(0.6-1.5); Preferably, in step (2), the contacting conditions include: the reactor inlet temperature is 300-480°C, C9 + The mass space velocity of heavy aromatics is 1-8h -1 , pressure is 0.5-5MPa, hydrogen-to-oil molar ratio is 1-6; Preferably, the C9 + Heavy aromatics selected from C9 + Monocyclic aromatic hydrocarbons and / or condensed-ring aromatic hydrocarbons; Preferably, the C9 + Among heavy aromatics, C 10 The content of aromatic hydrocarbons is 1-75 wt%, preferably 5-60 wt%.

9. The method according to any one of claims 1 to 8, wherein: The solid acid transalkylation catalyst comprises a second solid acid zeolite molecular sieve, a second binder and an optional second active component; the second solid acid zeolite molecular sieve is selected from at least one of MFI type, MWW type, BEA type, MOR type, FAU type topological structure molecular sieve and BEA / MOR symbiotic molecular sieve, preferably at least one of BEA type, MOR type topological structure molecular sieve and BEA / MOR symbiotic molecular sieve, and more preferably BEA / MOR symbiotic molecular sieve; Preferably, the molar ratio of silicon oxide to aluminum oxide of the second solid acid zeolite molecular sieve is 10-100, preferably 15-80; Preferably, the second binder is at least one of aluminum oxide, silicon oxide, titanium oxide, zinc oxide and zirconium oxide; Preferably, the second active component is selected from at least one of Group VA metal elements and Group VIB metal elements, preferably including any one of Group VA metal elements and any one of Group VIB metal elements; Preferably, in the second active component, the mass ratio of the Group VA metal element to the Group VIB metal element is 10:1-1:10; Preferably, the Group VA metal element is selected from Sb and / or Bi; Preferably, the Group VIB metal element is selected from at least one of Cr, Mo and W; Preferably, relative to 100 parts by weight of the second solid acid zeolite molecular sieve, the content of the second binder is 15-200 parts by weight, and the content of the second active component is 2-160 parts by weight.

10. The method according to any one of claims 1 to 9, wherein: The separation in step (3) also yields dry gas and gas containing benzene, toluene, C9 + other streams of at least one of the heavy aromatics; Preferably, the method further comprises: returning the mixture containing benzene and / or toluene to step (1) for reuse, and / or returning C9 + The heavy aromatics are returned to step (2) for reuse.

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