HZSM-11 molecular sieve, catalyst containing HZSM-11 molecular sieve, and preparation and application thereof

Abstract

The invention discloses an HZSM-11 molecular sieve catalyst and a preparation method thereof. The catalyst comprises, by weight, 60%-85% of HZSM-11 molecular sieves, 0.1%-6% of sodium oxide and / or potassium oxide and 13%-35% of aluminum oxide. The molar ratio of silicon to aluminum of the HZSM-11 molecular sieve is 40 to 180, and the indication constant k is 100 to 550. The preparation method of the catalyst comprises the following steps: firstly, dissolving cinnamate in benzene to prepare a solution, and enabling the solution to fully fill molecular sieve pores; blowing with hot nitrogen, and carrying out addition reaction on C = C of the cinnamate and benzene to generate a macromolecular salt product, so as to achieve the purpose of modifying an acid center at a pore crossing part; and preparing the catalyst according to a conventional method. The catalyst provided by the invention has proper activity, high p-xylene selectivity and longer one-way operation period.

Description

Technical Field

[0001] The present invention belongs to the technical field of catalytic materials, and specifically relates to a HZSM-11 molecular sieve, a catalyst containing the same, and a preparation method and application thereof, and more specifically to a molecular sieve, a catalyst, and a preparation method and application thereof for synthesizing p-xylene by selective alkylation of toluene and methanol. Background Art

[0002] Para-xylene is an important chemical intermediate. The direct synthesis of para-xylene by selective alkylation of toluene and methanol over a solid acid catalyst is a common method for industrial production. The catalyst used is usually a modified molecular sieve catalyst such as HZSM-5 and ZSM-11. At the acid center, toluene and methanol can generate three isomers, namely para-xylene, meta-xylene and ortho-xylene. The molecular diameters of ortho- and meta-products are larger than those of para-products. The high selectivity of para-products is achieved through the diffusion restriction effect of the selective catalyst pores.

[0003] The following methods are commonly used to modify molecular sieve catalysts: steam treatment to kill the strong acid center of the molecular sieve and reduce the density of the acid center, such as patents CN94110202.5, US4365104, US4128592, CN200310116628.X, etc.; loading Mg oxide or rare earth metal oxide to increase the tortuosity of the molecular sieve pores and adjust the acidity of the molecular sieve, such as patents CN90101436.2, CN94110202.5, CN95118372.9, CN200310116628.X, CN200410020397.9, CN200810246986.5, US4128592, etc.; silanization is used to adjust the pore diameter of the molecular sieve, such as patents US4465886, CN200310116628.X, etc.; phosphorus oxide modification is used to increase the medium and strong acid centers of the molecular sieve, such as patents CN95118372.9, CN200310116628.X, US4128592, etc.

[0004] In the pore structure of HZSM-11 molecular sieve, there are two types of pore space, namely straight-through pores and pore intersections. The pore intersection is where two pores intersect each other at a certain angle (such as 90°) and are connected internally. This kind of pore intersection space is open, and the acid center is denser than the non-intersection, which often becomes an active zone for side reactions or carbon deposit precursors. The above-mentioned modification methods for the pores of HZSM-11 molecular sieves, such as steam treatment, loading Mg oxide, loading rare earth metal oxide and loading phosphorus oxide, not only modify the pore intersections, but also modify the straight-through pores, which is a kind of general modification method that is not targeted. After the above modification, there are still relatively open spaces and a large number of acid centers at the intersection of the pores, which can continue to catalyze the product xylene to continue to react to generate trimethylbenzene, tetralin and phenylcyclohexane with larger molecular weight, which not only affects the selectivity of the product to xylene, but also further forms carbon deposit precursors with a high carbon-hydrogen ratio until carbon deposits are formed, affecting the single-pass operation cycle of the catalyst. If the existing modification means are used to increase the metal oxide loading to achieve the purpose of modifying the acid centers at the intersection of the pores, the loading of the modified material will be too large, which will affect the diffusion of the target product, paraxylene, in the pores, increase the attenuation rate of the catalyst toluene conversion rate, and shorten the single-pass operation cycle. Summary of the invention

[0005] In view of the shortcomings of the prior art, the present invention provides a modified HZSM-11 molecular sieve, a catalyst containing the same and a preparation method thereof. The catalyst provided by the present invention has a suitable active center and pore structure, and can obtain high para-xylene selectivity and excellent stability when applied to the process of producing para-xylene by alkylation of toluene and methanol.

[0006] The first aspect of the present invention provides a modified HZSM-11 molecular sieve.

[0007] The modified HZSM-11 molecular sieve contains at least one metal oxide of sodium and potassium as an additive, and the additive content is 0.5% to 5%; wherein the silicon-aluminum ratio (SiO 2 / Al 2 O 3 Molar ratio) is 40~180; The indicative constant k of the HZSM-11 molecular sieve is 100-550, preferably 101-500, wherein the indicative constant k is calculated as follows: k=Q / (0.9198×a -0.46 -c) Q-cyclohexane adsorption capacity, in g / 100g; a-silicon-aluminum ratio; c-the number of moles of metal oxides loaded in 100g of molecular sieve.

[0008] Furthermore, the indicator constant k in the present invention is obtained by fitting based on a large amount of data on cyclohexane adsorption, silicon-aluminum ratio, amount of metal oxide substances, etc. measured on HZSM-11 molecular sieves.

[0009] Furthermore, the method for determining the cyclohexane adsorption is as follows: the determination is performed using an intelligent gravimetric analyzer (IGA-002). Before determining the cyclohexane adsorption, a molecular sieve decontamination treatment is performed to remove moisture and impurities such as residual templates. The decontamination treatment is to raise the temperature of the sample to be tested from room temperature to 300°C at a rate of 5°C / min under a vacuum state, and then return it to room temperature after its mass becomes constant, and then the cyclohexane adsorption determination is started. Cyclohexane vapor is passed into the sample chamber after decontamination, and the weight difference is recorded after the sample is completely adsorbed and saturated (i.e., the weight is constant).

[0010] Furthermore, the silicon to aluminum ratio of HZSM-11 molecular sieve is 40~180.

[0011] The second aspect of the present invention also provides a method for preparing the modified HZSM-11 molecular sieve.

[0012] Specifically, the preparation method of the modified HZSM-11 molecular sieve comprises the following steps: (1) Dissolve cinnamate in benzene and stir evenly to fully dissolve; (2) impregnating HZSM-11 molecular sieve with the solution obtained in step (1), and filtering out the HZSM-11 molecular sieve after the impregnation is completed; (3) purging the HZSM-11 molecular sieve filtered out in step (2) with hot nitrogen; (4) Washing the HZSM-11 molecular sieve obtained in step (3) with deionized water, followed by drying and calcining.

[0013] Furthermore, the cinnamate in step (1) can be a soluble carnitine silicate such as sodium cinnamate, potassium cinnamate, etc. The mass fraction of the cinnamate in benzene is 0.5% to 20%, preferably 1% to 15%.

[0014] Furthermore, the liquid-to-solid ratio of the impregnation in step (2) is 4-10 mL / g, preferably 5-8 mL / g; and the impregnation time is 1-10 hours, preferably 1-5 hours.

[0015] Furthermore, the temperature of the hot nitrogen in step (3) is 80°C to 180°C, preferably 85°C to 150°C. The conditions for hot nitrogen purging are conventional operations in the art. For example, the nitrogen volume space velocity is 100h / min. -1 ~3000h -1 , preferably 200h -1 ~2000h-1 The purge time is generally 2 hours to 24 hours, preferably 5 hours to 20 hours. At the end of the purge, the benzene content in the nitrogen after passing through the molecular sieve is not greater than 1μ / L.

[0016] Furthermore, the liquid-to-solid ratio of the washing in step (4) is 4-10 mL / g, preferably 5-8 mL / g; the washing temperature is room temperature-80°C, preferably 40°C-70°C; and the number of washings is 1-10 times, preferably 2-6 times.

[0017] Furthermore, the drying and calcining described in step (4) adopt conventional conditions in the art. The calcination needs to be carried out in an oxygen-containing atmosphere. For example, the drying conditions are generally: the drying temperature is 60°C to 150°C, preferably 80°C to 120°C, and the drying time is 8 hours to 24 hours, preferably 10 hours to 20 hours. The calcination conditions are: the calcination temperature is 300°C to 800°C, preferably 400°C to 700°C, and the calcination time is 2 hours to 24 hours, preferably 4 hours to 8 hours.

[0018] The third aspect of the present invention provides a HZSM-11 molecular sieve catalyst for synthesizing para-xylene, wherein the catalyst contains the modified HZSM-11 molecular sieve described above.

[0019] Specifically, the HZSM-11 molecular sieve catalyst for synthesizing paraxylene, based on the weight of the catalyst, comprises: HZSM-11 molecular sieve 60%~85%, preferably 61%~83%; Sodium oxide and / or potassium oxide 0.1%~6%, preferably 0.2%~5%; Alumina: 13% to 35%, preferably 14% to 34%.

[0020] Furthermore, the silicon aluminum (SiO 2 / Al 2 O 3 ) molar ratio is 40~180, preferably 40~150.

[0021] Furthermore, the index constant k of the HZSM-11 molecular sieve is 100-550, preferably 101-500.

[0022] Furthermore, the specific surface area of ​​the catalyst is generally 250-650 m 2 / g, preferably 300~600m 2 / g; the specific pore volume is 0.20~0.50mL / g, preferably 0.25~0.45mL / g.

[0023] Furthermore, the catalyst is generally in the shape of a bar or a sphere. When it is in the shape of a bar, its cross section can be cylindrical, clover-shaped or four-leaf clover-shaped, with a diameter of 0.5-3.0 mm, preferably 1.0-2.0 mm; when it is in the shape of a sphere, its diameter is 0.5-5.0 mm, preferably 1.0-3.0 mm.

[0024] Furthermore, in addition to the metal oxide introduced during the modification of the HZSM-11 molecular sieve, the catalyst may further contain other metal or non-metal oxides as a second additive, such as one or more oxides of Li, La, Ce, Mg, Ca, Ba, Cu, Zn, Zr, Fe, Si, P, B, and C, to further improve the catalyst's acid distribution, pore structure and other physical properties. The content of the second additive oxide in the catalyst is generally 0.1-5%.

[0025] The fourth aspect of the present invention provides a method for preparing the HZSM-11 molecular sieve catalyst.

[0026] Specifically, the preparation method of the HZSM-11 molecular sieve catalyst comprises the following steps: (1) Dissolve an appropriate amount of cinnamate in benzene, stir evenly and fully dissolve; use the solution to impregnate HZSM-11 molecular sieve, and filter out the molecular sieve after impregnation; (2) Purge the filtered molecular sieve with hot nitrogen and cool it naturally to room temperature after the purge is completed; (3) washing the molecular sieve obtained in step (2) with deionized water, drying and calcining the washed molecular sieve to obtain a modified HZSM-11 molecular sieve; (4) The modified HZSM-11 molecular sieve, alumina precursor, extrusion aid and peptizing agent solution obtained in step (3) are fully kneaded, molded, dried and calcined to obtain a catalyst precursor; (5) The molecular sieve obtained in step (4) is loaded with the second auxiliary oxide by conventional impregnation method, and then dried and calcined to obtain a finished catalyst.

[0027] Furthermore, the cinnamate described in step (1) can be a soluble cinnamate such as sodium cinnamate, potassium cinnamate, etc. The mass fraction of cinnamate in benzene is 0.5% to 20%, preferably 1% to 15%. The liquid-to-solid ratio during the impregnation of the molecular sieve is 4 to 10 mL / g, preferably 5 to 8 mL / g; the impregnation time is 1 to 10 hours, preferably 1 to 5 hours.

[0028] Furthermore, the temperature of the hot nitrogen in step (2) is 80°C to 180°C, preferably 85°C to 150°C. The conditions for hot nitrogen purging are conventional operations in the art. For example, the nitrogen volume space velocity is 100h / min. -1 ~3000h -1 , preferably 200h-1 ~2000h -1 The purge time is generally 2 hours to 24 hours, preferably 5 hours to 20 hours. At the end of the purge, the benzene content in the nitrogen after passing through the molecular sieve is no more than 1 μL / L.

[0029] Furthermore, the liquid-to-solid ratio of the washing in step (3) is 4-10 mL / g, preferably 5-8 mL / g; the washing temperature is room temperature-80°C, preferably 40°C-70°C; and the number of washings is 1-10 times, preferably 2-6 times.

[0030] Furthermore, in step (4), the extrusion aid may be sesbania powder, and the peptizing agent solution may be at least one of dilute nitric acid and citric acid. The mass concentration of the dilute nitric acid solution is generally 3% to 15%.

[0031] Furthermore, the proportions and operations of the materials in step (4) are well known to those skilled in the art. For example, the weight ratio of HZSM-11 molecular sieve, alumina precursor, extrusion aid and peptizing agent solution is generally (60-85):(15-40):(3-20):(5-80), preferably (70-80):(20-30):(10-15):(20-50). In the material dosage, HZSM-11 molecular sieve and alumina precursor are weights calculated on a dry basis.

[0032] Furthermore, the drying conditions in steps (3), (4) and (5) are generally as follows: the drying temperature is 60°C to 150°C, preferably 80°C to 120°C, and the drying time is 2 hours to 24 hours, preferably 5 hours to 20 hours; the roasting conditions are generally as follows: the roasting temperature is 300°C to 800°C, preferably 400°C to 700°C, and the roasting time is 2 hours to 24 hours, preferably 3 hours to 8 hours. During roasting, the molecular sieve or molecular sieve catalyst is purged with air flow, and the air volume space velocity is 100h -1 ~3000h -1 , preferably 200h -1 ~2000h -1 .

[0033] Furthermore, step (4) is preferably performed by naturally drying in the shade for 10 to 48 hours before drying.

[0034] Furthermore, the conventional impregnation method for loading the second additive oxide in step (5) is an operation well known to those skilled in the art.

[0035] A fifth aspect of the present invention provides a method for producing p-xylene by alkylation of toluene and methanol, wherein the HZSM-11 molecular sieve catalyst described above is used.

[0036] A method for producing paraxylene by alkylation of toluene and methanol comprises the following steps: raw materials toluene and methanol are subjected to selective alkylation reaction in the presence of a HZSM-11 molecular sieve catalyst under reaction conditions.

[0037] Further, the reaction conditions include: reaction pressure of 0.1MPa~4.0MPa, preferably 0.11MPa~3.5MPa; reaction temperature of 300℃~550℃, preferably 350℃~500℃; toluene mass space velocity of 1h -1 ~10h -1 , preferably 2h -1 ~8h -1 ; The molar ratio of toluene and methanol is 10~1:1, preferably 8~2:1; the water-to-hydrocarbon ratio (the molar ratio of water to a mixture of toluene and methanol) is 1~5:1, preferably 1.5~4:1; the hydrogen-to-hydrocarbon molar ratio is 1~10:1, preferably 1.5~8:1.

[0038] Based on the research on the reaction of toluene and methanol alkylation to produce p-xylene, the inventors of this application have made the following findings: the toluene alkylation reaction is a typical acid-catalyzed selective catalytic reaction, and the acid properties and pore structure of the catalyst affect the selectivity of the para-position product and the stability of the catalyst. The commonly used catalyst for the alkylation of toluene and methanol to produce p-xylene is a modified HZSM-5 or HZSM-11 molecular sieve catalyst. In the pore structure of the HZSM-11 molecular sieve, there are two types of pore spaces, namely straight-through pores and pore intersections. The pore intersection is that two pores are interpenetrating at a certain angle (such as 90°) and are connected internally. This kind of pore intersection space is open, and the acid center is more dense than the non-intersection, which often becomes an active zone for side reactions or carbon deposit precursors. The existing modification methods for the HZSM-11 molecular sieve pores, such as steam treatment, loading Mg oxide, loading rare earth metal oxides, and loading phosphorus oxides, not only modify the pore intersections, but also modify the straight-through pores, which is a general modification method that is not targeted. After the above modification, there are still relatively open spaces and a large number of acid centers at the intersection of the pores, which can continue to catalyze the product xylene to continue to react to generate trimethylbenzene, tetralin and phenylcyclohexane with larger molecular weights, which not only affects the selectivity of the product p-xylene, but also further forms carbon deposit precursors with a high carbon-hydrogen ratio until carbon deposits are formed, affecting the catalyst's single-pass operation cycle. If the existing modification means are used to increase the metal oxide loading to achieve the purpose of modifying the acid centers at the intersection of the pores, the loading of the modified material is too large, which affects the diffusion of the target product p-xylene in the pores, increases the catalyst toluene conversion rate attenuation rate, and shortens the single-pass operation cycle.

[0039] The preparation method of the catalyst of the present invention is as follows: firstly, cinnamate is dissolved in benzene to prepare a solution, and then the solution is filled with the molecular sieve pores. Hot nitrogen is used for purging, and C=C in the cinnamate at high temperature reacts with benzene to generate a macromolecular salt product with two benzene rings. Since the molecular size of the reaction product is larger than the diameter of the molecular sieve straight-through pore, even if there is an acid center required for the reaction in the straight-through pore, it cannot be generated in the straight-through pore, but can only be generated at a location where there is both sufficient space and an acid center, such as the intersection of the pores. The hot nitrogen will also gasify the excess benzene in the pores and take out the molecular sieve, and the remaining unreacted cinnamate in the pores will be taken away during water washing, while the macromolecular product generated by the reaction cannot be taken out of the pores due to the limitation of the molecular size, and continues to remain at the intersection of the pores. The calcination process fully oxidizes and burns the carbon and hydrogen components in the macromolecular product, turning them into carbon dioxide and water vapor and escaping the molecular sieve. The remaining metal oxides continue to adhere to the intersection of the molecular sieve channels, covering the acid centers and adjusting the size of the intersection of the channels, but will not affect the acid centers in the straight channels, nor will it affect the smooth flow of the channels. Combined with the modification of La oxide, the strong acid centers inside and outside the channels are further modified, and a catalyst with suitable activity, high para-xylene selectivity, and a long single-pass operation cycle is obtained. Implementation

[0040] The technical scheme of the present invention is described in detail below in conjunction with the examples, but the present invention is not limited to the following examples. In the material dosage, the HZSM-11 molecular sieve and the alumina precursor are all measured by weight on a dry basis.

[0041] In the examples of the present invention and the comparative examples, the concentration of the product was analyzed by liquid chromatography, and the conversion rate and selectivity were obtained by calculation.

[0042] Toluene conversion rate = number of moles of toluene involved in the reaction / total number of moles of toluene feed × 100%; Para-xylene selectivity = number of moles of para-xylene in the product / number of moles of xylene in the product × 100%. Example 1

[0043] This embodiment provides a method for preparing a HZSM-11 molecular sieve catalyst, comprising the following steps: (1) Dissolve an appropriate amount of potassium cinnamate in benzene, stir evenly, fully dissolve, and prepare a solution with a mass percentage of 5%; use the solution at a liquid-to-solid ratio of 6 mL / g to impregnate 200 g of HZSM-11 molecular sieve with a silicon-aluminum ratio of 40, and filter out the molecular sieve after impregnation for 3 hours; (2) The filtered molecular sieve was heated with 120℃ hot nitrogen for 1000h -1 The air velocity was purged for 3 hours, and then naturally cooled to room temperature after the purging; (3) washing the molecular sieve obtained in step (2) with deionized water at a liquid-to-solid ratio of 6 mL / g, drying the washed molecular sieve at 110° C. for 4 hours and calcining at 560° C. for 5 hours to obtain a modified HZSM-11 molecular sieve; (4) The modified HZSM-11 molecular sieve, alumina precursor, extrusion aid and peptizing agent solution obtained in step (3) are fully kneaded, molded, dried at 110° C. for 5 hours, and calcined at 550° C. for 5 hours to obtain a catalyst precursor; (5) The catalyst precursor obtained in step (4) was loaded with La oxide by conventional impregnation method, and then dried at 110°C for 5 hours and calcined at 550°C for 5 hours to obtain a finished catalyst, which was denoted as A. Example 2

[0044] This embodiment provides a method for preparing a HZSM-11 molecular sieve catalyst, comprising the following steps: (1) Dissolve an appropriate amount of potassium cinnamate in benzene, stir evenly, fully dissolve, and prepare a solution with a mass percentage of 4.5%; use the solution at a liquid-to-solid ratio of 5 mL / g to impregnate 200 g of HZSM-11 molecular sieve with a silicon-aluminum ratio of 80, and filter out the molecular sieve after impregnation for 3 hours; (2) The filtered molecular sieve was heated with 110℃ hot nitrogen for 1200h -1 The air velocity was purged for 3 hours, and then naturally cooled to room temperature after the purging; (3) washing the molecular sieve obtained in step (2) with deionized water at a liquid-to-solid ratio of 8 mL / g, drying the washed molecular sieve at 120° C. for 5 hours and calcining at 530° C. for 5 hours to obtain a modified HZSM-11 molecular sieve; (4) The modified HZSM-11 molecular sieve, alumina precursor, extrusion aid and peptizing agent solution obtained in step (3) are fully kneaded, molded, dried at 120° C. for 5 hours, and calcined at 550° C. for 3 hours to obtain a catalyst precursor; (5) The catalyst precursor obtained in step (4) was loaded with Ca oxide by conventional impregnation method, and then dried at 110°C for 5 hours and calcined at 550°C for 3 hours to obtain a finished catalyst, which was denoted as B. Example 3

[0045] This embodiment provides a method for preparing a HZSM-11 molecular sieve catalyst, comprising the following steps: (1) Dissolve an appropriate amount of potassium cinnamate in benzene, stir evenly, fully dissolve, and prepare a solution with a mass percentage of 5.5%; use the solution at a liquid-to-solid ratio of 6.5 mL / g to impregnate 200 g of HZSM-11 molecular sieve with a silicon-aluminum ratio of 120, and filter out the molecular sieve after impregnation for 4 hours; (2) The filtered molecular sieve was heated with 120℃ hot nitrogen for 1400h-1 The air velocity was purged for 4 hours, and then naturally cooled to room temperature after the purging; (3) washing the molecular sieve obtained in step (2) with deionized water at a liquid-to-solid ratio of 8 mL / g, drying the washed molecular sieve at 120° C. for 3 hours and calcining at 540° C. for 6 hours to obtain a modified HZSM-11 molecular sieve; (4) The modified HZSM-11 molecular sieve, alumina precursor, extrusion aid and peptizing agent solution obtained in step (3) are fully kneaded, molded, dried at 120° C. for 5 hours, and calcined at 550° C. for 3 hours to obtain a catalyst precursor; (5) The catalyst precursor obtained in step (4) was loaded with Fe oxide by conventional impregnation method, and then dried at 120°C for 3 hours and calcined at 550°C for 3 hours to obtain a finished catalyst, which was denoted as C. Example 4

[0046] This embodiment provides a method for preparing a HZSM-11 molecular sieve catalyst, comprising the following steps: (1) Dissolve an appropriate amount of potassium cinnamate in benzene, stir evenly, fully dissolve, and prepare a solution with a mass percentage of 6.5%; use the solution at a liquid-to-solid ratio of 4 mL / g to impregnate 200 g of HZSM-11 molecular sieve with a silicon-aluminum ratio of 150, and filter out the molecular sieve after impregnation for 4 hours; (2) The filtered molecular sieve was heated with 110℃ hot nitrogen for 800h -1 The air velocity was purged for 3 hours, and then naturally cooled to room temperature after the purging; (3) washing the molecular sieve obtained in step (2) with deionized water at a liquid-to-solid ratio of 7 mL / g, drying the washed molecular sieve at 120° C. for 5 hours and calcining at 530° C. for 4 hours to obtain a modified HZSM-11 molecular sieve; (4) The modified HZSM-11 molecular sieve, alumina precursor, extrusion aid and peptizing agent solution obtained in step (3) are fully kneaded, molded, dried at 120° C. for 4 hours, and calcined at 540° C. for 3 hours to obtain a catalyst precursor; (5) The catalyst precursor obtained in step (4) was loaded with Zn oxide by conventional impregnation method, and then dried at 100°C for 6 hours and calcined at 520°C for 3 hours to obtain a finished catalyst, which was denoted as D.

[0047] Comparative Example 1 This comparative example provides a method for preparing a HZSM-11 molecular sieve catalyst, comprising the following steps: (1) Using potassium nitrate as a precursor, a HZSM-11 molecular sieve with a silicon-aluminum ratio of 40 was impregnated by a conventional impregnation method. After impregnation for 5 hours, the molecular sieve was filtered out, dried at 110°C for 7 hours, and calcined at 550°C for 3 hours; (2) After fully mixing HZSM-11 molecular sieve with a silicon-aluminum ratio of 40, alumina precursor, an extrusion aid and a peptizing agent solution, the mixture was shaped, dried at 110° C. for 5 hours, and calcined at 550° C. for 5 hours to obtain a catalyst precursor; (3) The catalyst precursor obtained in step (2) was loaded with La oxide by conventional impregnation method, and then dried at 110°C for 5 hours and calcined at 550°C for 5 hours to obtain a finished catalyst, which was recorded as E1.

[0048] Comparative Example 2 This comparative example provides a method for preparing a HZSM-11 molecular sieve catalyst, comprising the following steps: (1) Using potassium nitrate as a precursor, a HZSM-11 molecular sieve with a silicon-aluminum ratio of 80 was impregnated by a conventional impregnation method. After impregnation for 5 hours, the molecular sieve was filtered out, dried at 110°C for 7 hours, and calcined at 550°C for 3 hours; (2) The HZSM-11 molecular sieve, alumina precursor, extrusion aid and peptizing agent solution obtained in step (1) are fully kneaded, molded, dried at 110° C. for 5 hours, and calcined at 550° C. for 5 hours to obtain a catalyst precursor; (3) The catalyst precursor obtained in step (2) was loaded with Cu oxide by conventional impregnation method, and then dried at 110°C for 5 hours and calcined at 550°C for 5 hours to obtain a finished catalyst, which was recorded as E2.

[0049] Comparative Example 3 This comparative example provides a method for preparing a HZSM-11 molecular sieve catalyst, comprising the following steps: (1) Using potassium nitrate as a precursor, a HZSM-11 molecular sieve with a silicon-aluminum ratio of 120 was impregnated by a conventional impregnation method. After impregnation for 4 hours, the molecular sieve was filtered out, dried at 120°C for 5 hours, and calcined at 540°C for 5 hours; (2) The HZSM-11 molecular sieve, alumina precursor, extrusion aid and peptizing agent solution obtained in step (1) are fully kneaded, molded, dried at 120° C. for 5 hours, and calcined at 550° C. for 3 hours to obtain a catalyst precursor; (3) The catalyst precursor obtained in step (2) was loaded with Fe oxide by conventional impregnation method, and then dried at 120°C for 3 hours and calcined at 550°C for 3 hours to obtain a finished catalyst, which was recorded as E3. Example 5

[0050] The properties of the HZSM-11 molecular sieve and the HZSM-11 molecular sieve catalyst obtained in the above examples and comparative examples are shown in Tables 1 and 2.

[0051] Catalyst performance evaluation: The catalysts of the above examples and comparative examples were used in a small evaluation device to conduct an evaluation experiment on the alkylation of ethylbenzene to synthesize p-xylene, using toluene and methanol as raw materials, and the mass space velocity of toluene was 5h -1 The molar ratio of toluene to methanol was 3:1, the water-to-hydrocarbon ratio was 3:1, the hydrogen-to-hydrocarbon ratio was 4:1, the reaction temperature was 450°C, the reaction pressure was 2.0 MPa, and the reaction results are shown in Table 3, where the single-pass operation cycle is the operation time from the start of the reaction to the time when the toluene conversion rate drops to 10%.

[0052] Table 1 Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 Comparative Example 3 HZSM-5 molecular sieve Silicon to aluminum ratio, molar ratio 40 80 120 150 40 80 120 Cyclohexane adsorption g / 100g 16.35 15.91 15.11 14.54 8.45 8.23 4.45 Additives <![CDATA[K 2 O content*]]> 0.03 0.02 0.04 0.05 0.03 0.02 0.05 Indicative constant, k 126 159 252 365 61 80 85 *, the number of moles of metal oxide loaded per 100g of molecular sieve.

[0053] Table 2 Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 Comparative Example 3 Molecular sieve catalyst Modified HZSM-5 molecular sieve, wt% 67.5 72.3 70.0 76 67 71.5 69.4 Additives Second additive oxide, wt% 3.6 1.4 2.0 1.5 3.5 1.6 2.0 Alumina, wt% 28.9 26.3 28.0 22.5 29.5 26.9 28.6 Table 3 Catalyst No. Average conversion of toluene, mol% Average selectivity for para-xylene, mol% One-way operation cycle, h A 13.45 98.32 720 B 13.26 98.67 654 C 12.77 99.03 735 D 12.64 98.79 685 E1 14.23 93.17 254 E2 13.81 94.52 312 E3 12.56 94.39 287

Claims

1. A modified HZSM-11 molecular sieve, It is characterized in that The modified HZSM-11 molecular sieve contains at least one metal oxide of sodium and potassium as an additive, and the additive content is 0.5% to 5%; Among them, the silicon-aluminum ratio of HZSM-11 molecular sieve is 40~180; The indicative constant k of the HZSM-11 molecular sieve is 100-550, preferably 101-500, wherein the indicative constant k is calculated as follows: k=Q / (0.9198×a -0.46 -c) Q-cyclohexane adsorption capacity, in g / 100g; a-silicon-aluminum ratio; c-the number of moles of metal oxides loaded in 100g of molecular sieve.

2. The method for preparing the modified HZSM-11 molecular sieve according to claim 1, It is characterized in that The following steps are involved: (1) Dissolve cinnamate in benzene and stir evenly to fully dissolve; (2) impregnating HZSM-11 molecular sieve with the solution obtained in step (1), and filtering out the HZSM-11 molecular sieve after the impregnation is completed; (3) purging the HZSM-11 molecular sieve filtered out in step (2) with hot nitrogen; (4) Washing the HZSM-11 molecular sieve obtained in step (3) with deionized water, followed by drying and calcining.

3. The preparation method according to claim 1, It is characterized in that The cinnamate described in step (1) is selected from sodium cinnamate and / or potassium cinnamate.

4. The preparation method according to claim 3, It is characterized in that The mass fraction of cinnamate in benzene is 0.5%~20%.

5. The preparation method according to claim 3, It is characterized in that The liquid-to-solid ratio of the impregnation in step (2) is 4-10 mL / g, and the impregnation time is 1-10 hours.

6. The preparation method according to claim 3, It is characterized in that The temperature of the hot nitrogen in step (3) is 80°C to 180°C.

7. The preparation method according to claim 3, It is characterized in that The liquid-to-solid ratio of the cleaning in step (4) is 4-10 mL / g.

8. A HZSM-11 molecular sieve catalyst for synthesizing paraxylene, It is characterized in that The catalyst contains the modified HZSM-11 molecular sieve according to claim 1.

9. The HZSM-11 molecular sieve catalyst according to claim 8, It is characterized in that The HZSM-11 molecular sieve catalyst comprises, based on the weight of the catalyst: HZSM-11 molecular sieve 60%~85%, preferably 61%~83%; Sodium oxide and / or potassium oxide 0.1%~6%, preferably 0.2%~5%; Alumina, 13% to 35%, preferably 14% to 34%; The silicon-aluminum molar ratio of the HZSM-11 molecular sieve is 40-180, preferably 40-150; the index constant k of the HZSM-11 molecular sieve is 100-550, preferably 101-500.

10. The HZSM-11 molecular sieve catalyst according to claim 9, It is characterized in that The specific surface area of ​​the catalyst is 250-650m 2 / g, and the specific pore volume is 0.20~0.50mL / g.

11. The HZSM-11 molecular sieve catalyst according to claim 9, It is characterized in that The catalyst also contains one or more oxides of Li, La, Ce, Mg, Ca, Ba, Cu, Zn, Zr, Fe, Si, P, B, and C as a second auxiliary agent, and the content of the second auxiliary agent oxide in the catalyst is 0.1-5%.

12. A method for preparing the HZSM-11 molecular sieve catalyst according to any one of claims 8 to 11, It is characterized in that The steps include: (1) Dissolve an appropriate amount of cinnamate in benzene, stir evenly and fully dissolve; use the solution to impregnate HZSM-11 molecular sieve, and filter out the molecular sieve after impregnation; (2) Purge the filtered molecular sieve with hot nitrogen and cool it naturally to room temperature after the purge is completed; (3) washing the molecular sieve obtained in step (2) with deionized water, drying and calcining the washed molecular sieve to obtain a modified HZSM-11 molecular sieve; (4) The modified HZSM-11 molecular sieve, alumina precursor, extrusion aid and peptizing agent solution obtained in step (3) are fully kneaded, molded, and then dried and calcined to obtain a catalyst precursor; (5) The molecular sieve obtained in step (4) is loaded with metal or non-metal oxide by conventional impregnation method, and then dried and calcined to obtain a finished catalyst.

13. The preparation method according to claim 12, It is characterized in that The cinnamate described in step (1) is selected from sodium cinnamate and / or potassium cinnamate.

14. The preparation method according to claim 12 or 13, It is characterized in that The mass fraction of the cinnamate in benzene is 0.5% to 20%.

15. The preparation method according to claim 12, It is characterized in that The liquid-to-solid ratio of the impregnation in step (1) is 4-10 mL / g, and the impregnation time is 1-10 hours.

16. The preparation method according to claim 12, It is characterized in that The temperature of the hot nitrogen in step (2) is 80°C to 180°C.

17. A method for producing p-xylene by alkylation of toluene and methanol, It is characterized in that The HZSM-11 molecular sieve catalyst described in any one of claims 8 to 11 is used.

18. The method according to claim 17, It is characterized in that The method comprises the following contents: raw materials toluene and methanol are subjected to selective alkylation reaction in the presence of HZSM-11 molecular sieve catalyst under reaction conditions.

19. The method according to claim 18, It is characterized in that The reaction conditions include: reaction pressure of 0.1 MPa to 4.0 MPa, reaction temperature of 300° C. to 550° C., toluene mass space velocity of 1 h -1 ~10h -1 , the molar ratio of toluene and methanol is 10~1:1, the molar ratio of water to toluene and methanol mixture is 1~5:1, and the molar ratio of hydrogen to hydrocarbon is 1~10:1.