A catalyst for methanol aromatization to produce paraxylene and a preparation method and application thereof

Abstract

This invention relates to the field of catalyst technology, and discloses a catalyst for the aromatization of methanol to p-xylene, its preparation method, and its application. The catalyst includes a support and a metal modifier and / or a non-metal modifier supported on the support; the support includes a porous matrix and a shape-selective confinement modification layer disposed on the outer surface and pores of the porous matrix; the porous matrix includes a ten-membered ring channel acidic molecular sieve; the shape-selective confinement modification layer is an amorphous borosilicate glass. When used in the methanol aromatization reaction, the catalyst of this invention can control the reaction pathway and product diffusion behavior, achieving high p-xylene selectivity and resulting in a high p-xylene content in the product. Furthermore, it can reduce the product purification burden when used for the further preparation of terephthalic acid.

Description

Technical Field

[0001] This invention relates to the field of catalyst technology, and in particular to a catalyst for the aromatization of methanol to p-xylene, its preparation method, and its application. Background Technology

[0002] Terephthalic acid (PTA) is a key monomer in the production of polyester materials (such as bottle chips, films, and fiber polyesters). Global industrial production mainly relies on a route that uses petroleum-based mixed xylenes as raw materials, followed by para-xylene (PX) separation, catalytic oxidation, and crystallization purification to obtain high-purity PTA. In this traditional route, the source and purity of PX directly determine the energy consumption, solvent usage, and product yield of downstream oxidation and crystallization units, thus affecting the overall production cost and environmental impact.

[0003] To reduce dependence on petroleum resources and improve overall process efficiency, the direct production of aromatics (including PX) from methanol has become a focus of research and industrialization in recent years. Acidic molecular sieves containing ten-membered ring channels have shown potential for regulating aromatic distribution in methanol shape-selective aromatization (MTA), but several challenges remain in actual scale-up and industrial operation: First, secondary isomerization and cracking induced by acidic sites on the outer surface of the molecular sieve lead to the easy conversion of PX into meta / ortho isomers or higher-carbon aromatics; second, molecular sieves of different sizes and morphologies exhibit insufficient diffusion selectivity for PX and meta / ortho xylenes, making it difficult to stably control the product distribution to a "non-equilibrium" composition with high PX content; third, metal or acidic adjustment methods used to improve catalytic activity are often accompanied by higher side reaction rates (such as carbon deposition, C9...). + This process generates (resulting in) catalysts, thus shortening catalyst lifespan and increasing regeneration costs.

[0004] In the prior art, strategies such as molecular sieve channel design, molecular sieve combination, or surface modification are usually adopted to improve PX selectivity (for example, patent CN103212434B uses ZSM-5 / EU-1 composite molecular sieve and incorporates boron heteroatoms into the composite molecular sieve through hydrothermal synthesis). However, most of these methods are limited to adjusting acid strength or simply relying on pore configuration. Their ability to suppress secondary reactions on the outer surface and to achieve significant PX enrichment while ensuring catalytic activity is still significantly insufficient, resulting in limited effect on improving PX selectivity. Summary of the Invention

[0005] To address the low selectivity of existing catalysts for the aromatization of methanol to p-xylene, this invention provides a catalyst for the aromatization of methanol to p-xylene, its preparation method, and its applications. When used in the methanol aromatization reaction, the catalyst of this invention can regulate the reaction pathway and product diffusion behavior, achieving high p-xylene selectivity and resulting in a high p-xylene content in the product. Furthermore, it reduces the product purification burden when used for further preparation of terephthalic acid.

[0006] The specific technical solution of this invention is as follows: In a first aspect, the present invention provides a catalyst for the aromatization of methanol to p-xylene, comprising a support and a metal modifier and / or a non-metal modifier supported on the support; the support comprises a porous matrix and a shape-selective confinement modification layer disposed on the outer surface and pores of the porous matrix; the porous matrix comprises a ten-membered ring channel acidic molecular sieve; the shape-selective confinement modification layer is an amorphous borosilicate glass.

[0007] In ten-membered ring porous acidic molecular sieves, the diffusion coefficient of p-xylene is higher than that of m-xylene and o-xylene. Constructing a porous matrix using ten-membered ring porous acidic molecular sieves helps to improve the selectivity of p-xylene. Based on this, the present invention modifies the outer surface or pores of a porous matrix with amorphous borosilicate glass, which can exert a shape-selective confinement effect. By regulating the reaction pathway and product diffusion behavior, the selectivity of p-xylene is improved. Specifically, the shape-selective confinement modification layer distributed on the outer surface of the porous matrix can reduce the effective exposure of Brønsted acidic sites on the outer surface through physical shielding and surface passivation, thereby inhibiting side reactions of aromatization products on the outer surface, including isomerization, realkylation, and excessive cracking. The shape-selective confinement modification layer distributed at the pores of the porous matrix can construct a spatially confined structure, which forms a significant diffusion resistance to m-xylene, o-xylene, and trimethylbenzene molecules with larger kinetic diameters, while having a smaller impact on the diffusion behavior of p-xylene molecules with smaller kinetic diameters and more symmetrical configurations. Thus, the apparent selectivity of p-xylene is improved without significantly reducing the methanol conversion rate.

[0008] Metal modifiers can promote dehydrogenation, regulate acidity, generate Lewis acid sites, and improve the microenvironment of the pores, enabling methanol to react more smoothly along the "dehydrogenation-cyclization-aromatization" pathway, thereby significantly improving aromatic selectivity and reducing carbon deposition. Non-metal modifiers can adjust the electronic environment of acidic centers, weaken the strength of Brønsted acids, thereby reducing side reactions and preventing the loss of framework aluminum in acidic molecular sieves in water-rich environments, further enhancing the stability and catalytic lifetime of the molecular sieves.

[0009] Based on the aforementioned effects of amorphous borooxide glass and metal and / or non-metallic modifiers, the catalyst of this invention employs a design where a porous matrix and amorphous borooxide glass are constructed as a support, and metal and / or non-metallic modifiers are loaded onto this support. Compared to loading metal and / or non-metallic modifiers onto a porous matrix and then modifying it with amorphous borooxide glass, the structural design of this invention can avoid the shape-selective confinement modification layer covering or obscuring the metal and / or non-metallic modifiers, allowing both the amorphous borooxide glass and the metal and / or non-metallic modifiers to fully exert their effects, effectively improving the selectivity of the catalyst.

[0010] Preferably, the shape-selective confinement modification layer has a content of 1-10 wt% in the catalyst; the metal modifier includes one or more of copper, tin, zirconium, cerium, zinc, chromium, calcium, nickel and iron, and has a content of 1-10 wt% in the catalyst; the non-metal modifier includes phosphorus, and has a content of 1-10 wt% in the catalyst.

[0011] Preferably, the ten-membered ring channel acidic molecular sieve includes one or more of ZSM-5, ZSM-22, EU-1, ZSM-35 and NU-87, with a silica-alumina ratio of 10 to 100 and a content of 30 to 60 wt% in the catalyst.

[0012] Preferably, the porous matrix further includes an inert oxide binder; the inert oxide binder is formed by calcination of one or more of silica sol, titanium sol and aluminum sol, and its content in the catalyst is 30-60 wt%; the porous matrix is ​​a microsphere with a particle size of 40-120 μm, or a cylindrical strip with a diameter of 1-3 mm and a length of 2-8 mm.

[0013] Microsphere porous substrates can be used in fluidized bed reactors, while cylindrical strip porous substrates can be used in fixed bed reactors.

[0014] Secondly, the present invention provides a method for preparing the catalyst, comprising the steps of: S1: Prepare a porous matrix from a ten-membered ring-porous acidic molecular sieve; S2: After immersing the porous matrix in a boron source solution for 30-45 min, it is dried, pretreated at 200-300℃ and calcined at 450-550℃ to form a shape-selective confinement modification layer, thus obtaining a support; the boron source includes boric acid and / or metaboric acid. S3: Loading metal modifiers and / or non-metal modifiers on a support.

[0015] The mechanism for forming the shape-selective confinement modification layer in step S2 is as follows: using a boron source solution impregnation method, the boron oxide precursor can preferentially adhere to the outer surface and pores of the porous substrate; drying to remove free water can promote the initial enrichment of the boron source; then, a medium-temperature pretreatment at 200~300℃ can cause partial dehydration and condensation of the boron source, forming oligomeric boron oxide species and anchoring them to the outer surface and pores of the porous substrate; finally, high-temperature calcination at 450~550℃ can further dehydrate and condense the boron oxide species and cause a glass transition, forming a stable amorphous boron oxide glass shape-selective confinement modification layer in situ on the outer surface and pore areas of the porous substrate. The method of this invention (impregnation with boric acid and / or metaboric acid followed by drying → medium-temperature pretreatment → high-temperature calcination in a staged heat treatment process) allows for more controllable thickness and coverage of the shape-selective confinement modification layer. Furthermore, the staged heat treatment method can better control the distribution of boron and oxygen species, ensuring that they are mainly distributed on the outer surface and pores of the porous matrix, while preserving acidic sites inside the pores to a greater extent. This helps to improve the selectivity of the catalytic reaction while ensuring catalytic efficiency.

[0016] Preferably, in step S2, the impregnation, drying and pretreatment at 200~300℃ are repeated 2~4 times before the calcination at 450~550℃ is performed.

[0017] By repeating the impregnation, drying, and pretreatment at 200-300°C an appropriate number of times, the uniformity of the shape-selective confinement modification layer covering the orifice can be improved.

[0018] Preferably, in step S2, the volume ratio of the porous matrix to the boron source solution is 1:0.9~1.2; the drying temperature is 100~120℃ and the time is 3~5 h; the pretreatment at 200~300℃ takes 2~2.5 h; and the calcination at 450~550℃ takes 3~3.5 h.

[0019] Thirdly, the present invention provides the application of the catalyst in the methanol aromatization reaction to produce p-xylene.

[0020] Preferably, the methanol aromatization reaction is carried out at a temperature of 330–500 °C, a pressure of 0.1–3.0 MPa, and a methanol space velocity (WHSV) of 0.3–3 h⁻¹. -1 .

[0021] More preferably, the methanol aromatization reaction is carried out at a temperature of 380~480℃, a pressure of 0.1~2.4 MPa, and a methanol space velocity (WHSV) of 0.3~1.5 h⁻¹. -1 .

[0022] Fourthly, the present invention provides the application of the catalyst in the preparation of terephthalic acid from methanol, the steps of which include: 1) Under the action of the catalyst, methanol aromatization reaction is carried out, and the product is separated by distillation to obtain mixed xylene containing p-xylene; 2) Catalytic oxidation of the mixed xylenes yields a mixed phthalic acid containing terephthalic acid; 3) After separating the mixed terephthalic acid by suspension crystallization, it is washed with pure terephthalic acid, filtered by pressure, and purified terephthalic acid is obtained.

[0023] The methanol aromatization reaction using the catalyst of this invention achieves high selectivity, resulting in a high para-xylene content in the product, thereby reducing the burden on downstream purification. Besides para-xylene, the methanol aromatization reaction product may also contain low-carbon light hydrocarbons, benzene, toluene, o-xylene, m-xylene, and trimethylbenzene. Purification yields a mixture of para / o / m-xylenes, which can be directly catalytically oxidized to obtain a mixture of terephthalic acid, o-, and isophthalic acid. Subsequent separation of these phthalic acids, achieved through suspension crystallization, elution with pure terephthalic acid, and pressure filtration, yields high-purity terephthalic acid.

[0024] Preferably, in step 3), the terephthalic acid content in the product obtained after suspension crystallization separation is not less than 97 wt%, and the purity of the refined terephthalic acid is not less than 99.5 wt%.

[0025] Compared with the prior art, the present invention has the following advantages: (1) In the catalyst of the present invention, by modifying the outer surface and pores of the porous matrix constructed by the ten-membered ring channel acidic molecular sieve with amorphous boron-oxygen glass, the shape-selective confinement effect can be achieved. By reducing the effective exposure of the Brønsted acidic sites on the outer surface and forming diffusion resistance to by-products with large kinetic diameters, the dual regulation of reaction pathway and product diffusion behavior can be achieved, thereby greatly improving the selectivity of xylene.

[0026] (2) In the catalyst of the present invention, by adopting a design of using a support constructed from a porous matrix and amorphous boron-oxygen glass, and loading metal and / or non-metal modifiers onto this support, it is possible to avoid the shape-selective confinement modification layer composed of amorphous boron-oxygen glass covering or shielding the metal and / or non-metal modifiers, which helps to improve the selectivity of the catalyst.

[0027] (3) In the preparation process of the catalyst, the present invention adopts a staged heat treatment method of drying → medium-temperature pretreatment → high-temperature calcination after impregnation with boric acid and / or metaboric acid. This method can control the generated amorphous borooxy glass to be mainly distributed on the outer surface and pores of the porous matrix, which helps to improve the selectivity of the catalytic reaction while ensuring catalytic efficiency. Detailed Implementation

[0028] The present invention will be further described below with reference to embodiments.

[0029] First, the present invention relates to a catalyst for the aromatization of methanol to p-xylene, comprising a support and a metal modifier and / or a non-metal modifier supported on the support; the support comprises a porous matrix and a shape-selective confinement modification layer disposed on the outer surface and pores of the porous matrix; the porous matrix comprises a ten-membered ring channel acidic molecular sieve; the shape-selective confinement modification layer is an amorphous borosilicate glass.

[0030] In some specific embodiments, the content of the shape-selective confinement modification layer in the catalyst is 1~10 wt%.

[0031] In some specific embodiments, the metal modifier includes one or more of copper, tin, zirconium, cerium, zinc, chromium, calcium, nickel and iron, and its content in the catalyst is 1 to 10 wt%.

[0032] In some specific embodiments, the non-metallic modifier includes phosphorus, which is present in the catalyst at a content of 1 to 10 wt%.

[0033] In some specific embodiments, the ten-membered ring channel acidic molecular sieve includes one or more of ZSM-5, ZSM-22, EU-1, ZSM-35 and NU-87, with a silica-alumina ratio of 10 to 100 and a content of 30 to 60 wt% in the catalyst.

[0034] In some specific embodiments, the porous matrix further includes an inert oxide binder; the inert oxide binder is formed by calcining one or more of silica sol, titanium sol and aluminum sol, and its content in the catalyst is 30-60 wt%.

[0035] In some specific embodiments, the porous matrix is ​​a microsphere with a particle size of 40~120 μm, or a cylindrical strip with a diameter of 1~3 mm and a length of 2~8 mm.

[0036] Second, the present invention relates to a method for preparing the catalyst, comprising the following steps: S1: Prepare a porous matrix from a ten-membered ring-porous acidic molecular sieve; S2: After immersing the porous matrix in a boron source solution for 30-45 min, it is dried, pretreated at 200-300℃ and calcined at 450-550℃ to form a shape-selective confinement modification layer, thus obtaining a support; the boron source includes boric acid and / or metaboric acid. S3: Loading metal modifiers and / or non-metal modifiers on a support.

[0037] In some specific embodiments, step S1 includes: mixing a ten-membered ring porous acid molecular sieve, a binder precursor, and water to form a porous matrix, and calcining it at 450~550℃ for 2~5 h to obtain a porous matrix; the binder precursor includes one or more of silica sol, titanium sol, and aluminum sol.

[0038] In some specific embodiments, in step S2, the impregnation, drying and pretreatment at 200~300℃ are repeated 2~4 times before the calcination at 450~550℃ is performed.

[0039] In some specific embodiments, in step S2, the volume ratio of the porous matrix to the boron source solution is 1:0.9~1.2.

[0040] In some specific embodiments, in step S2, the drying temperature is 100~120℃ and the time is 3~5 h; the pretreatment at 200~300℃ takes 2~2.5 h; and the calcination at 450~550℃ takes 3~3.5 h.

[0041] In some specific embodiments, step S3 includes: vacuum impregnating the carrier in a metal source and / or non-metal source solution, drying it, and then calcining it at 480~550℃ for 2~5 h.

[0042] Third, the present invention relates to the application of the catalyst in the methanol aromatization reaction to produce p-xylene.

[0043] In some specific embodiments, the methanol aromatization reaction is carried out at a temperature of 330–500°C, a pressure of 0.1–3.0 MPa, and a methanol space velocity (WHSV) of 0.3–3 h⁻¹. -1 .

[0044] Fourth, this invention relates to the application of the catalyst in the preparation of terephthalic acid from methanol, the steps of which include: 1) Under the action of the catalyst, methanol aromatization reaction is carried out, and the product is separated by distillation to obtain mixed xylene containing p-xylene; 2) Catalytic oxidation of the mixed xylenes yields a mixed phthalic acid containing terephthalic acid; 3) After separating the mixed terephthalic acid by suspension crystallization, it is washed with pure terephthalic acid, filtered by pressure, and purified terephthalic acid is obtained.

[0045] In some specific implementations, in step 1), the impurities separated by distillation are returned to the methanol aromatization reaction.

[0046] In some specific embodiments, in step 2), the catalytic oxidation process is carried out under the action of a main catalyst and a co-catalyst; the main catalyst includes one or more of transition metal chloroacetates, tartrates and lactates, and the transition metal includes one or more of copper, nickel, iron, tin, cobalt and manganese; the co-catalyst includes lanthanide halides; the amounts of the main catalyst and the co-catalyst are 30-400 ppm and 100-900 ppm respectively, based on the weight of the mixed xylene.

[0047] In some specific embodiments, in step 2), the oxidant used in the catalytic oxidation process is oxygen, and the reaction solvent includes two or more of water, acetic acid, tartaric acid or lactic acid.

[0048] In some specific embodiments, in step 2), the catalytic oxidation process is carried out in a series of 3-5 batch reactors or a multi-layer tower reactor with 3-8 layers, at a temperature of 150-220°C, a pressure of 1.5-2.5 MPa, and a reaction residence time of 0.8-3.0 h.

[0049] In some specific embodiments, in step 3), the terephthalic acid content in the product obtained after suspension crystallization separation is not less than 97 wt%, and the purity of the refined terephthalic acid is not less than 99.5 wt%.

[0050] The present invention will now be described with reference to specific embodiments and comparative examples. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Example 1

[0051] The methanol aromatization catalyst used in this embodiment was prepared according to the following steps: S1: ZSM-5 molecular sieve with a silicon-to-aluminum ratio of 25 and aluminum sol are dispersed in water, spray-dried to form microspheres, and calcined at 500℃ in air atmosphere for 3 h to obtain a porous microsphere matrix with a particle size of 60~90 μm.

[0052] S2: The porous matrix was mixed with an equal volume of boric acid solution, impregnated under normal pressure for 30 min, dried at 120℃ for 4 h, pretreated at 250℃ for 2 h, and then calcined at 480℃ in air atmosphere for 3 h to obtain the support.

[0053] S3: The support was mixed with an equal volume of a mixed aqueous solution of zinc nitrate, copper nitrate and phosphoric acid, vacuum impregnated for 30 min, dried at 110 °C for 4 h, and then calcined at 550 °C in an air atmosphere for 3 h to obtain a methanol aromatization catalyst for the production of p-xylene, wherein the mass ratio of ZSM-5, Al2O3, amorphous borosilicate glass, zinc, copper and phosphorus was 45:42:5:4:1:3.

[0054] Using the catalyst of this embodiment, terephthalic acid was prepared according to the following steps: Step 1: Methanol aromatization reaction and distillation A catalyst for the aromatization of methanol to p-xylene was loaded into a fluidized bed reactor. Methanol was then introduced into the reactor to carry out the methanol aromatization reaction under the following conditions: reaction temperature 460℃, reaction pressure 0.3 MPa, and methanol space velocity 0.5 h⁻¹. -1 The methanol conversion rate was 100%, the total selectivity of aromatics in the product was 75%, and the selectivity of xylene among the aromatics was 87%.

[0055] The methanol aromatization reaction products were separated by distillation to remove components other than p-xylene, m-xylene, and o-xylene, resulting in a mixed xylene with a p-xylene content of 86 wt%. The separated C1-C5 low-carbon light hydrocarbons, benzene, and toluene were recycled back to the fluidized bed reactor and mixed with fresh methanol feedstock to continue the reaction.

[0056] Step 2: Xylene oxidation reaction and terephthalic acid purification The oxidation of mixed xylenes was carried out in a three-stage series reactor under the following conditions: the main catalysts were cobalt chloroacetate and copper chloroacetate, at amounts of 200 ppm and 100 ppm respectively (by weight of the mixed xylenes); the co-catalyst was lanthanum bromide, at 500 ppm (by weight of the mixed xylenes); the reaction solvent was a mixture of acetic acid and water in a 9:1 mass ratio, at 50% (by weight of the mixed xylenes); oxygen was supplied to the reactors; the reaction temperature was 180 °C; the reaction pressure was 2.0 MPa; and the reaction residence time was 2.0 h. After the reaction, a mixed phthalic acid with a terephthalic acid content of 86 wt% was obtained.

[0057] After suspension crystallization separation of mixed terephthalic acids, the terephthalic acid content was increased to 97.5 wt%. Then, it was washed with molten pure terephthalic acid and then separated by pressure filtration to obtain purified terephthalic acid with a terephthalic acid content of 99.5 wt%. Example 2

[0058] The methanol aromatization catalyst used in this embodiment was prepared according to the following steps: S1: EU-1 molecular sieve with a silicon-to-aluminum ratio of 30, aluminum sol and water are mixed evenly, and then extruded and crushed to obtain cylindrical strip particles. The particles are then calcined at 500℃ in an air atmosphere for 3 h to obtain a cylindrical strip porous matrix with a diameter of 2 mm and a length of 2~4 mm.

[0059] S2: The porous matrix was mixed with an equal volume of boric acid solution, impregnated at atmospheric pressure for 40 min, dried at 120℃ for 4 h, pretreated at 280℃ for 2 h, and then calcined at 490℃ in air atmosphere for 3 h to obtain the support.

[0060] S3: The support was mixed with an equal volume of a mixed aqueous solution of zinc nitrate and phosphoric acid, vacuum impregnated for 30 min, dried at 110℃ for 4 h, and then calcined at 550℃ in an air atmosphere for 3 h to obtain a catalyst for the aromatization of methanol to p-xylene, wherein the mass ratio of EU-1, Al2O3, amorphous borosilicate glass, zinc and phosphorus was 45:43:3:6.5:2.5.

[0061] Using the catalyst of this embodiment, terephthalic acid was prepared according to the following steps: Step 1: Methanol aromatization reaction and distillation A catalyst for the aromatization of methanol to p-xylene was loaded into a fixed-bed reactor. Methanol was then introduced into the reactor to carry out the methanol aromatization reaction under the following conditions: reaction temperature 480℃, reaction pressure 0.15 MPa, and methanol space velocity 0.4 h⁻¹. -1 The methanol conversion rate was 100%, the total selectivity of aromatics in the product was 80%, and the selectivity of xylene among the aromatics was 85%.

[0062] The methanol aromatization reaction products were separated by distillation to remove components other than p-xylene, m-xylene, and o-xylene, resulting in a mixed xylene with a p-xylene content of 89 wt%. The separated C1-C5 low-carbon light hydrocarbons, benzene, and toluene were recycled back to the fixed-bed reactor and mixed with fresh methanol feedstock to continue the reaction.

[0063] Step 2: Xylene oxidation reaction and terephthalic acid purification The oxidation reaction of mixed xylenes was carried out in a three-tiered tower reactor under the following conditions: the main catalysts were cobalt lactate and manganese lactate, at amounts of 300 ppm and 100 ppm respectively (by weight of the mixed xylenes); the co-catalyst was cerium iodide, at an amount of 450 ppm (by weight of the mixed xylenes); the reaction solvent was a mixture of acetic acid, lactic acid, and water in a mass ratio of 8:1:1, at 55% (by weight of the mixed xylenes); oxygen was supplied to the three-tiered tower reactor; the reaction temperature was 180℃; the reaction pressure was 2.0 MPa; and the reaction residence time was 2.0 h. After the reaction, mixed phthalic acid with a terephthalic acid content of 89 wt% was obtained.

[0064] After suspension crystallization separation of mixed terephthalic acids, the terephthalic acid content was increased to 98.6 wt%. Then, molten pure terephthalic acid was used for rinsing, followed by solid-liquid separation by pressure filtration to obtain purified terephthalic acid with a terephthalic acid content of 99.8 wt%. Example 3

[0065] The only difference between this embodiment and Example 1 is that the content of amorphous borosilicate glass in the methanol aromatization to p-xylene catalyst is increased. Specifically, the steps for preparing the methanol aromatization to p-xylene catalyst in this embodiment are as follows: S1: ZSM-5 molecular sieve with a silicon-to-aluminum ratio of 25 and aluminum sol are dispersed in water, spray-dried to form microspheres, and calcined at 500℃ in air atmosphere for 3 h to obtain a porous microsphere matrix with a particle size of 60~90 μm.

[0066] S2: The porous matrix was mixed with an equal volume of boric acid solution, impregnated under normal pressure for 30 min, dried at 120℃ for 4 h, pretreated at 250℃ for 2 h, and then calcined at 480℃ in air atmosphere for 3 h to obtain the support.

[0067] S3: The support was mixed with an equal volume of a mixed aqueous solution of zinc nitrate, copper nitrate and phosphoric acid, vacuum impregnated for 30 min, dried at 110 °C for 4 h, and then calcined at 550 °C in an air atmosphere for 3 h to obtain a catalyst for the aromatization of methanol to p-xylene, wherein the mass ratio of ZSM-5, Al2O3, amorphous borosilicate glass, zinc, copper and phosphorus was 40.3:37.6:15:3.6:0.9:2.7.

[0068] Using the catalyst of this embodiment, methanol aromatization and distillation were carried out under the same conditions as in Example 1. The specific steps are as follows: A catalyst for the aromatization of methanol to p-xylene was loaded into a fluidized bed reactor. Methanol was then introduced into the reactor to carry out the methanol aromatization reaction under the following conditions: reaction temperature 460℃, reaction pressure 0.3 MPa, and methanol space velocity 0.5 h⁻¹. -1 The methanol conversion rate was measured to be 76%, the total selectivity of aromatics in the product was 89%, and the selectivity of xylene among the aromatics was 67%. The methanol aromatization reaction product was subjected to distillation to remove components other than p-xylene, m-xylene, and o-xylene, yielding a mixed xylene with a p-xylene content of 90 wt%. The separated C1-C5 low-carbon light hydrocarbons, benzene, and toluene were recycled back to the fluidized bed reactor and mixed with fresh methanol feedstock for further reaction.

[0069] Data Analysis: Compared to Example 1, Example 3 showed a significant decrease in methanol conversion and xylene selectivity under the same methanol aromatization reaction conditions. This indicates that excessively high content of amorphous borosilicate glass in the catalyst leads to a decrease in catalytic efficiency and xylene selectivity. The reasons are as follows: excessive amorphous borosilicate glass can overly cover acidic sites in the catalyst, resulting in decreased catalytic efficiency. Furthermore, excessive amorphous borosilicate glass can enter the pores, causing pore narrowing, which facilitates the formation of smaller molecular diameter byproducts (benzene and toluene), thus reducing xylene selectivity in the products.

[0070] Comparative Example 1 The only difference between this comparative example and Example 1 is that the methanol aromatization to p-xylene catalyst is not modified with an amorphous borooxide glass shape-selective confinement layer. Specifically, the steps for preparing the methanol aromatization to p-xylene catalyst in this comparative example are as follows: S1: ZSM-5 molecular sieve with a silicon-to-aluminum ratio of 25 and aluminum sol are dispersed in water, spray-dried to form microspheres, and calcined at 500℃ in air atmosphere for 3 h to obtain a porous microsphere matrix with a particle size of 60~90 μm.

[0071] S2: The porous matrix was mixed with an equal volume of a mixed aqueous solution of zinc nitrate, copper nitrate and phosphoric acid, vacuum impregnated for 30 min, dried at 110 °C for 4 h, and then calcined at 550 °C in an air atmosphere for 3 h to obtain a methanol aromatization catalyst for the production of p-xylene, wherein the mass ratio of ZSM-5, Al2O3, zinc, copper and phosphorus was 45:42:5:4:1:3.

[0072] Using the catalyst of this comparative example, methanol aromatization and distillation were carried out under the same conditions as in Example 1, with the specific steps as follows: A catalyst for the aromatization of methanol to p-xylene was loaded into a fluidized bed reactor. Methanol was then introduced into the reactor to carry out the methanol aromatization reaction under the following conditions: reaction temperature 460℃, reaction pressure 0.3 MPa, and methanol space velocity 0.5 h⁻¹. -1 The methanol conversion rate was 100%, the total selectivity of aromatics in the product was 74%, and the selectivity of xylene among the aromatics was 62%. The methanol aromatization reaction product was subjected to distillation to remove components other than p-xylene, m-xylene, and o-xylene, yielding a mixed xylene with a p-xylene content of 57 wt%. The separated C1-C5 low-carbon light hydrocarbons, benzene, and toluene were recycled back to the fluidized bed reactor and mixed with fresh methanol feedstock for further reaction.

[0073] Data Analysis: Compared to Example 1, Comparative Example 1 showed a significant decrease in p-xylene selectivity under the same methanol aromatization reaction conditions. This indicates that introducing a shape-selective confinement modification layer onto a porous matrix constructed from a ten-membered ring-channel acidic molecular sieve can effectively improve p-xylene selectivity. The reason for this is that the shape-selective confinement modification layer distributed on the outer surface of the porous matrix can reduce the effective exposure of Brønsted acidic sites on the outer surface through both physical shielding and surface passivation, thereby inhibiting side reactions of the aromatization product on the outer surface, including isomerization, realkylation, and excessive cracking. Furthermore, the shape-selective confinement modification layer distributed at the pore openings of the porous matrix can construct a spatially confined structure, significantly hindering the diffusion of m-xylene, o-xylene, and trimethylbenzene molecules with larger kinetic diameters, while having less impact on the diffusion behavior of p-xylene molecules with smaller kinetic diameters and more symmetrical configurations. Therefore, the apparent selectivity of p-xylene is improved without significantly reducing methanol conversion.

[0074] Comparative Example 2 The only difference between this comparative example and Example 1 is that the pretreatment at 250°C was not performed in step S2. Specifically, the steps for preparing the methanol aromatization catalyst to p-xylene in this comparative example are as follows: S1: ZSM-5 molecular sieve with a silicon-to-aluminum ratio of 25 and aluminum sol are dispersed in water, spray-dried to form microspheres, and calcined at 500℃ in air atmosphere for 3 h to obtain a porous microsphere matrix with a particle size of 60~90 μm.

[0075] S2: The porous matrix was mixed with an equal volume of boric acid solution, impregnated under normal pressure for 30 min, dried at 120℃ for 4 h, and then calcined at 480℃ in air atmosphere for 3 h to obtain the support.

[0076] S3: The support was mixed with an equal volume of a mixed aqueous solution of zinc nitrate, copper nitrate and phosphoric acid, vacuum impregnated for 30 min, dried at 110 °C for 4 h, and then calcined at 550 °C in an air atmosphere for 3 h to obtain a methanol aromatization catalyst for the production of p-xylene, wherein the mass ratio of ZSM-5, Al2O3, amorphous borosilicate glass, zinc, copper and phosphorus was 45:42:5:4:1:3.

[0077] Using the catalyst of this comparative example, methanol aromatization and distillation were carried out under the same conditions as in Example 1, with the specific steps as follows: A catalyst for the aromatization of methanol to p-xylene was loaded into a fluidized bed reactor. Methanol was then introduced into the reactor to carry out the methanol aromatization reaction under the following conditions: reaction temperature 460℃, reaction pressure 0.3 MPa, and methanol space velocity 0.5 h⁻¹. -1 The methanol conversion rate was measured to be 96%, the total selectivity of aromatics in the product was 64%, and the selectivity of xylene among the aromatics was 86%. The methanol aromatization reaction products were then subjected to distillation to remove components other than p-xylene, m-xylene, and o-xylene, yielding a mixed xylene with a p-xylene content of 85 wt%. The separated C1-C5 low-carbon light hydrocarbons, benzene, and toluene were recycled back to the fluidized bed reactor and mixed with fresh methanol feedstock for further reaction.

[0078] Data analysis: Compared with Example 1, Comparative Example 2 showed a significant decrease in p-xylene selectivity and methanol conversion rate under the same methanol aromatization reaction conditions. This indicates that by adopting a staged heat treatment method of drying → medium-temperature pretreatment → calcination during the preparation of the amorphous borosilicate glass shape-selective confinement modification layer, the catalyst prepared can achieve higher p-xylene selectivity and catalytic efficiency when used in the methanol aromatization reaction. The reason for this is that, in the above-mentioned staged heat treatment process, the first step of drying to remove free water promotes the initial enrichment of the boron source. Then, the medium-temperature pretreatment at 200-300℃ allows the boron source to undergo partial dehydration and condensation, forming oligomeric boron oxide species that are anchored on the outer surface and pores of the porous substrate. Finally, the high-temperature calcination at 450-550℃ allows the boron oxide species to further dehydrate and condense, undergoing a glass transition. This results in the in-situ formation of a stable, amorphous boron oxide glass shape-selective confinement modification layer on the outer surface and pore areas of the porous substrate. Through this method, the distribution of boron oxide species can be better controlled, ensuring that they are mainly distributed on the outer surface and pores of the porous substrate, and allowing for a more complete glass transition of the boron oxide, thereby improving catalytic efficiency and para-xylene selectivity.

[0079] Comparative Example 3 The only difference between this comparative example and Example 1 is that the order of steps S2 and S3 is reversed. Specifically, the steps for preparing the methanol aromatization catalyst to p-xylene in this comparative example are as follows: S1: ZSM-5 molecular sieve with a silicon-to-aluminum ratio of 25 and aluminum sol are dispersed in water, spray-dried to form microspheres, and calcined at 500℃ in air atmosphere for 3 h to obtain a porous microsphere matrix with a particle size of 60~90 μm.

[0080] S2: The porous matrix is ​​mixed with an equal volume of a mixed aqueous solution of zinc nitrate, copper nitrate and phosphoric acid, vacuum impregnated for 30 min, dried at 110 °C for 4 h, and then calcined at 550 °C in an air atmosphere for 3 h to obtain the modified porous matrix.

[0081] S3: The modified porous matrix was mixed with an equal volume of boric acid solution, impregnated under normal pressure for 30 min, dried at 120℃ for 4 h, pretreated at 250℃ for 2 h, and then calcined at 480℃ in air atmosphere for 3 h to obtain a methanol aromatization catalyst for the production of p-xylene, wherein the mass ratio of ZSM-5, Al2O3, amorphous borooxy glass, zinc, copper and phosphorus was 45:42:5:4:1:3.

[0082] Using the catalyst of this comparative example, methanol aromatization and distillation were carried out under the same conditions as in Example 1, with the specific steps as follows: A catalyst for the aromatization of methanol to p-xylene was loaded into a fluidized bed reactor. Methanol was then introduced into the reactor to carry out the methanol aromatization reaction under the following conditions: reaction temperature 460℃, reaction pressure 0.3 MPa, and methanol space velocity 0.5 h⁻¹. -1 The methanol conversion rate was 100%, the total selectivity of aromatics in the product was 68%, and the selectivity of xylene among the aromatics was 83%. The methanol aromatization reaction product was subjected to distillation to remove components other than p-xylene, m-xylene, and o-xylene, yielding a mixed xylene with a p-xylene content of 87 wt%. The separated C1-C5 low-carbon light hydrocarbons, benzene, and toluene were recycled back to the fluidized bed reactor and mixed with fresh methanol feedstock for further reaction.

[0083] Data analysis: Compared with Example 1, Comparative Example 2 showed a significant decrease in the selectivity of p-xylene under the same methanol aromatization reaction conditions. This indicates that by first modifying the amorphous borosilicate glass and then loading metal and non-metal modifiers during catalyst preparation, the selectivity of p-xylene during the catalytic reaction can be improved. The reasons for this are as follows: Metal modifiers can promote dehydrogenation, regulate acidity, generate Lewis acid sites, and improve the microenvironment of the pores, enabling methanol to react more smoothly along the "dehydrogenation-cyclization-aromatization" pathway, thereby significantly improving aromatic selectivity and reducing carbon deposition. Non-metal modifiers can weaken the strength of Brønsted acids by regulating the electronic environment of acidic centers, thereby reducing side reactions. In this invention, the amorphous borosilicate glass achieves improved xylene selectivity by forming a shape-selective confinement modification layer on the outer surface and pore openings of the porous matrix. If the order of first loading metal and non-metal modifiers and then modifying the amorphous borosilicate glass is adopted, the shape-selective confinement modification layer of the amorphous borosilicate glass is easy to cover or shield the introduced metal and non-metal modifiers, weakening their effect and thus causing a decrease in xylene selectivity during the catalytic reaction.

Claims

1. A catalyst for the aromatization of methanol to p-xylene, characterized in that, The invention includes a support and a metal modifier and / or a non-metal modifier loaded on the support; the support includes a porous matrix and a shape-selective confinement modification layer disposed on the outer surface and pores of the porous matrix; the porous matrix includes a ten-membered ring channel acidic molecular sieve; the shape-selective confinement modification layer is an amorphous borosilicate glass.

2. The catalyst according to claim 1, characterized in that, The shape-selective confinement modification layer has a content of 1-10 wt% in the catalyst; the metal modifier includes one or more of copper, tin, zirconium, cerium, zinc, chromium, calcium, nickel and iron, and has a content of 1-10 wt% in the catalyst; the non-metal modifier includes phosphorus, and has a content of 1-10 wt% in the catalyst.

3. The catalyst according to claim 1, characterized in that, The ten-membered ring channel acidic molecular sieve includes one or more of ZSM-5, ZSM-22, EU-1, ZSM-35 and NU-87, with a silica-alumina ratio of 10 to 100 and a content of 30 to 60 wt% in the catalyst.

4. The catalyst according to claim 1, characterized in that, The porous matrix further includes an inert oxide binder; the inert oxide binder is formed by calcination of one or more of silica sol, titanium sol and aluminum sol, and its content in the catalyst is 30~60 wt%; the porous matrix is ​​a microsphere with a particle size of 40~120 μm, or a cylindrical strip with a diameter of 1~3 mm and a length of 2~8 mm.

5. A method for preparing a catalyst according to any one of claims 1 to 4, characterized in that, step include: S1: Prepare a porous matrix from a ten-membered ring-porous acidic molecular sieve; S2: After immersing the porous matrix in a boron source solution for 30-45 min, it is dried, pretreated at 200-300℃ and calcined at 450-550℃ to form a shape-selective confinement modification layer, thus obtaining a support; the boron source includes boric acid and / or metaboric acid. S3: Loading metal modifiers and / or non-metal modifiers on a support.

6. The preparation method according to claim 5, characterized in that, In step S2, the impregnation, drying and pretreatment at 200~300℃ are repeated 2~4 times, and then the calcination at 450~550℃ is carried out.

7. The preparation method according to claim 5 or 6, characterized in that, In step S2, the volume ratio of the porous matrix to the boron source solution is 1:0.9~1.2; the drying temperature is 100~120℃ and the time is 3~5 h; the pretreatment at 200~300℃ takes 2~2.5 h; and the calcination at 450~550℃ takes 3~3.5 h.

8. The application of the catalyst according to any one of claims 1 to 4 in the methanol aromatization reaction to produce p-xylene.

9. The application according to claim 8, characterized in that, The methanol aromatization reaction is carried out at a temperature of 330–500 °C, a pressure of 0.1–3.0 MPa, and a methanol space velocity of 0.3–3 h⁻¹. -1 .

10. The application of the catalyst according to any one of claims 1 to 4 in the preparation of terephthalic acid from methanol, characterized in that, step include: 1) Under the action of the catalyst, methanol aromatization reaction is carried out, and the product is separated by distillation to obtain mixed xylene containing p-xylene; 2) Catalytic oxidation of the mixed xylenes yields mixed phthalic acid containing terephthalic acid; 3) After the mixed terephthalic acid is separated by suspension crystallization, it is washed with pure terephthalic acid, filtered by pressure, and purified terephthalic acid is obtained.