Catalyst for dealkylation of c8 aromatics to benzene and toluene, method of preparation and use

Abstract

The application discloses a catalyst for dealkylation of carbon eight aromatic hydrocarbon to prepare benzene and toluene. The catalyst comprises phosphorus-containing aluminum oxide, active metal and silicon oxide; the mass content of the phosphorus-containing aluminum oxide is 80-94% based on the weight of the catalyst, the mass content of the active metal is 5-15%, and the mass content of the silicon oxide is 1-5%. The catalyst provided by the application can maintain high catalytic performance at low reaction temperature, and the catalyst also has high stability.

Description

Technical Field

[0001] This invention relates to the field of aromatic hydrocarbon catalytic conversion, and more specifically to a catalyst for the catalytic hydrogenation and dealkylation of C8 aromatic hydrocarbons to produce toluene and benzene, its preparation method, and its application. Background Technology

[0002] The C8 aromatics dealkylation technology can utilize excess xylene as a raw material to produce benzene and toluene through a side-chain hydrogenation dealkylation reaction. Toluene can then be further converted into benzene through toluene disproportionation technology, achieving the goal of efficiently increasing benzene production and adjusting the product structure of aromatics.

[0003] Currently, aromatic dealkylation technology includes thermal dealkylation and catalytic dealkylation processes. Thermal dealkylation requires an operating temperature of 750–780 °C, while catalytic hydrodealkylation has the advantages of low operating temperature, high liquid yield, and high conversion efficiency, making it widely favored by the market. Existing aromatic catalytic hydrodealkylation catalyst systems include: (1) modified molecular sieve catalysts; (2) composite oxide catalysts. Among them, modified molecular sieves have strong ability to remove C2 and above side chain alkyl groups and have a low reaction temperature, but weak demethylation ability. For example, CN113171793A discloses a hydrodealkylation catalyst and its preparation method, using heavy aromatics as raw materials and NiMo modified hierarchical porous ZSM-5 molecular sieve as catalyst, mainly removing C2 and above side chain alkyl groups, with xylene as the main product. US8168844B2 discloses a Pt-Mo / ZSM-5 catalyst for C8–C 13 The hydrogenation and dealkylation reaction of alkyl aromatics removes side-chain alkyl groups with more than two carbon atoms from the aromatic hydrocarbons, and the mass fraction of the reaction product (benzene + toluene + xylene) reaches 75%.

[0004] Composite oxide catalysts exhibit strong methyl removal capabilities, meeting the requirements for deep demethylation to benzene production. However, the reaction temperature is high (600–650 °C), and high-temperature reaction conditions easily lead to catalyst coking and increased aromatic ring loss. For example, CN94118235.5 discloses a rare earth C9-C... 10 Aromatic dealkylation catalysts and their preparation methods, using C9-C 10 Using aromatics as raw materials and rare earth metal-modified Cr2O3 / Al2O3 as a catalyst, the selectivity for (benzene + toluene + xylene) can reach 95%. This catalyst is also suitable for the catalytic dealkylation of toluene to benzene. UOP's Hydeal aromatic dealkylation process uses a composite oxide catalyst, which can dealkylate toluene and higher aromatic hydrocarbons (C7+) at an operating temperature of 600–650°C. + A) It is converted into benzene.

[0005] Based on π electron cloud density and thermodynamic data, the more carbon atoms in the side-chain alkyl group and the more substituents in the side chain, the easier it is to remove alkylation. The dealkylation reaction of polymethylbenzene proceeds sequentially, with fewer methyl substituents making removal more difficult. This results in the following dealkylation reaction rate pattern: trimethylbenzene > xylene > toluene, butylbenzene > propylbenzene > ethylbenzene > toluene. Therefore, toluene has the highest activation energy and the lowest reaction rate for both activation and demethylation. Achieving direct dealkylation of aromatics to benzene inevitably requires high reaction temperatures (>600℃), and the decreased catalyst stability caused by high temperatures is a problem that is difficult to overcome in this technology. Summary of the Invention

[0006] The technical problem to be solved by this invention is the low catalyst stability caused by the high reaction temperature in the dealkylation of C8 aromatics to benzene and toluene in the prior art. This invention provides a catalyst for the dealkylation of C8 aromatics to benzene and toluene, its preparation method, and its application. Using the catalyst provided by this invention, the above-mentioned problems can be overcome, achieving high catalytic performance even at low reaction temperatures, while also exhibiting high stability.

[0007] The first aspect of the present invention provides a catalyst for the dealkylation of C8 aromatics to produce benzene and toluene, the catalyst comprising phosphorus-containing alumina, an active metal and silicon oxide; based on the weight of the catalyst, the mass content of phosphorus-containing alumina is 80-94%, the mass content of the active metal is 5-15%, and the mass content of silicon oxide is 1-5%.

[0008] Furthermore, the total acid content of the phosphorus-containing alumina is 20-40 μmol NH3 / g, wherein the ratio of weak acid content to strong acid content is 3-5:1; and / or, the phosphorus content in the phosphorus-containing alumina, calculated as oxides, is 0.5-5%.

[0009] Furthermore, the active metal is selected from at least one of Co, Ni, and Cr, preferably Cr and Ni, and simultaneously selects Cr and Ni.

[0010] Furthermore, the raw material for the silicon oxide is derived from organosilicon, which is at least one of tetraethyl orthosilicate, silicone ether, and organosilicon oil.

[0011] Furthermore, the catalyst has a total acid content of 2–19 μmol NH3 / g, a weak acid to strong acid ratio of 5–8:1, and a pore volume of 0.45–0.65 cm³. 3 / g.

[0012] A second aspect of the present invention provides a method for preparing the above-mentioned catalyst for the dealkylation of C8 aromatics to benzene and toluene, comprising the following steps:

[0013] (a) Preparation of phosphorus-containing aluminum oxide;

[0014] (b) Take the composite modified alumina obtained in step (a), introduce the modified metal by impregnation, and obtain the metal-modified composite modified alumina by drying and calcination.

[0015] (c) The phosphorus-containing alumina with loaded metal obtained in step (b) is immersed in an organosilicon solution, dried and calcined to obtain a catalyst for the dealkylation of C8 aromatics to produce benzene and toluene.

[0016] Further, in step (a), the method for preparing phosphorus-containing alumina includes the following steps:

[0017] (1) Alumina powder is treated with an aqueous solution of phosphoric acid, followed by drying and calcination;

[0018] (2) The material obtained in step (1) is treated under steam conditions and dried to obtain phosphorus-containing aluminum oxide.

[0019] Furthermore, the total acidity of the C8 aromatic dealkylation catalyst for benzene and toluene is reduced by more than 90% compared to the alumina in step (1), and the pore volume is reduced by only 10-20% compared to the alumina in step (1).

[0020] Further, in step (1), the mass concentration of phosphoric acid in the phosphoric acid aqueous solution is 1-5%, the liquid-solid mass ratio of the phosphoric acid aqueous solution to the alumina powder is 5-20, the treatment temperature is 30-50℃, and the treatment time is 2-6 hours.

[0021] Furthermore, in step (1), after treatment with phosphoric acid aqueous solution, solid-liquid separation is usually performed. The separation method can be filtration, and the filtration adopts conventional methods in the art, such as vacuum filtration.

[0022] Furthermore, the phosphorus oxide content in the phosphorus-containing alumina described in step (1) is 0.5% to 5% by mass.

[0023] Furthermore, the steam treatment temperature in step (2) is 550–700°C and the treatment time is 2–10 hours.

[0024] Furthermore, the drying conditions described in steps (1) and (2) are each independently selected from: a drying temperature of 90 to 150°C and a drying time of 1 to 10 hours; and a calcination temperature of 550 to 700°C and a calcination time of 1 to 10 hours in step (1).

[0025] Furthermore, the impregnation method described in step (b) preferably employs equal-volume impregnation.

[0026] Further, the modified metal in step (b) is at least one of Co, Ni, and Cr, preferably Ni and Cr.

[0027] Further, the organosilicon mentioned in step (c) is at least one of tetraethyl orthosilicate, silicone ether, and organosilicon oil.

[0028] Further, the solvent of the organosilicon solution in step (c) is at least one of saturated alkanes containing 6-8 carbon atoms, preferably at least one of cyclohexane, n-heptane, and n-octane.

[0029] Further, in step (c), the mass concentration of organosilicon in the organosilicon solution is 1-5%, and the mass ratio of the phosphorus-containing alumina loaded with metal to the organosilicon solution is 0.2-1:1.

[0030] Furthermore, the impregnation method described in step (c) is preferably an equal-volume impregnation method.

[0031] Furthermore, the drying conditions described in steps (b) and (c) are each independently selected from: the drying temperature is 90-150°C and the drying time is 1-10 hours; the roasting conditions described in steps (b) and (c) are each independently selected from: the roasting temperature is 550-700°C and the roasting time is 1-10 hours.

[0032] The third aspect of the present invention provides the application of the catalyst for the dealkylation of C8 aromatics to benzene and toluene described in the first or second aspect in the reaction of dealkylation of C8 aromatics to benzene and toluene.

[0033] Furthermore, the reaction conditions are as follows: reaction temperature of 450–750 °C, and C8 aromatic weight hourly space velocity of 0.5–2 h⁻¹. -1 The molar ratio of hydrogen to C8 aromatics is 2–8, and the reaction pressure is 2–6 MPa; preferably, the reaction temperature is 500–550 °C, and the weight hourly space velocity (WHSV) of the C8 aromatics is 0.5–1 h⁻¹. -1 The molar ratio of C8 aromatic hydrocarbons is 3–5, and the reaction pressure is 3–4 MPa.

[0034] Compared with the prior art, the present invention has the following advantages:

[0035] (1) The catalyst provided by the present invention includes phosphorus-containing alumina, active metal and silicon oxide, especially phosphorus-containing alumina, which is modified by phosphorus and water vapor, effectively suppressing acidity and opening up the pores, reducing the alkyl transfer of C8 aromatics to generate heavy aromatics. When combined with modified metal and silicon oxide, it still maintains high catalytic performance at low reaction temperature, and the catalyst also has high stability.

[0036] (2) The preparation method provided by the present invention is simple and easy to operate. First, the alumina is modified by phosphorus and water vapor to obtain phosphorus-containing alumina. Then, active metal and organosilicon are impregnated to obtain the C8 aromatic hydrocarbon dealkylation to benzene and toluene catalyst.

[0037] (3) The dealkylation catalyst for benzene and toluene from C8 aromatics provided by this invention balances the catalyst's demethylation capability and reaction temperature. When used for the dealkylation of C8 aromatics to benzene and toluene, it can selectively convert C8 aromatics into toluene and a small amount of benzene at low reaction temperatures, avoiding the high reaction temperature and low stability associated with deep demethylation to benzene. The produced toluene can be converted into benzene through toluene disproportionation technology, thus achieving the same high-efficiency benzene production from C8 aromatics. Furthermore, this catalyst effectively improves the problem of rapid catalyst deactivation caused by high temperatures, significantly enhancing the catalyst's high-temperature stability. Attached Figure Description

[0038] Figure 1 The graph shows the C8 aromatic conversion rate over time for Example 1 and Comparative Example 1. Detailed Implementation

[0039] The present invention will now be described in detail with reference to specific embodiments. It should be noted that the following embodiments are only used to further illustrate the present invention and should not be construed as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the content of the present invention are still within the scope of protection of the present invention.

[0040] The raw materials used in the specific embodiments of the present invention are commercially available and have an analytical grade (AR) purity.

[0041] In this invention, the acid content is characterized by ammonia desorption under programmed temperature rise, using a Micrometrics AutoChem2920 fully automated programmed temperature rise chemisorption analyzer. For weak acids, the amount of NH3 desorbed is measured at desorption temperatures below 300℃; for strong acids, the amount of NH3 desorbed is measured at desorption temperatures between 300℃ and 600℃.

[0042] In this invention, the pore volume is characterized by a low-temperature nitrogen adsorption method, using a Micromeritics 3Flex-Physisorption fully automated specific surface area and pore size distribution analyzer.

[0043] Example 1

[0044] Alumina powder (with a total acid content of 124 μmol NH3 / g and a pore volume of 0.63 cm³) was used. 3The modified alumina (g) was placed in a 1% phosphoric acid aqueous solution, with the liquid-to-solid mass ratio of the phosphoric acid solution to alumina controlled at 20. It was treated at 50°C for 3 hours, filtered, dried at 150°C for 1 hour, and then calcined at 700°C for 1 hour. The modified alumina was then treated with steam at 700°C for 5 hours, followed by drying at 120°C for 5 hours to obtain phosphorus-containing alumina, wherein the phosphorus oxide content in the phosphorus-containing alumina was 1.2%. The phosphorus-containing alumina was then impregnated with an equal volume of chromium nitrate, dried at 120°C for 5 hours, and then calcined at 700°C for 5 hours to obtain Cr-modified composite alumina. The Cr-modified phosphorus-containing alumina was placed in a tetraethyl orthosilicate solution of hexane, with a silicone concentration of 5% by weight. The mass ratio of the Cr-modified phosphorus-containing alumina to the silicone solution was 0.8. After drying at 120°C for 10 hours, the alumina was calcined at 600°C for 10 hours. The resulting catalyst for the dealkylation of C8 aromatics to benzene and toluene contained 4% SiO2, 81% phosphorus-containing alumina, and 15% active metal.

[0045] The total acid content of the phosphorus-containing alumina is 39 μmol NH3 / g, and the ratio of weak acid content to strong acid content is 3.5.

[0046] The total acidity of the catalyst for the dealkylation of C8 aromatics to benzene and toluene is only 10 μmol NH3 / g, with a weak acid / strong acid ratio of 6.8, representing a 92% decrease compared to the raw material alumina (124 μmol NH3 / g); its pore volume is 0.54 cm³. 3 / g, compared to raw material alumina (0.63cm) 3 / g) decreased by only 14.2%.

[0047] The above-mentioned catalysts for the dealkylation of C8 aromatics to benzene and toluene were used in the catalytic hydrogenation dealkylation reaction of C8 aromatics at a reaction temperature of 550 °C and a C8 aromatic weight hourly space velocity of 0.5 h⁻¹. -1 The molar ratio of C8 aromatics to hydrogen was 3, the reaction pressure was 3 MPa, the catalyst performance is shown in Table 1, and the stability test results after 200 hours of continuous operation are shown in [Table 1]. Figure 1 The results showed that the catalyst was very stable, with no significant decrease in activity, and the C8 aromatic conversion rate decreased by only 1.1 percentage points.

[0048] Example 2

[0049] Alumina powder (with an acid content of 135 μmol NH3 / g and a pore volume of 0.54 cm³) was used. 3Alumina (g) was placed in a 5% phosphoric acid aqueous solution, with the liquid-to-solid mass ratio of the phosphoric acid solution to alumina controlled at 10. The solution was treated at 40°C for 2 hours, filtered, dried at 90°C for 10 hours, and then calcined at 600°C for 5 hours to obtain phosphorus-modified alumina, wherein the phosphorus oxide content in the phosphorus-modified alumina was 4.1%. The phosphorus-modified alumina was then treated with steam at 600°C for 10 hours, and then dried at 150°C for 1 hour to obtain composite-modified alumina. The composite-modified alumina was then impregnated with cobalt nitrate in equal volumes, dried at 90°C for 10 hours, and then calcined at 650°C to obtain Co-modified composite alumina. The Co-modified composite alumina was placed in a heptane-based silicone oil solution with a silicone concentration of 2.3% by weight. The mass ratio of the Co-modified composite alumina to the silicone solution was 1. After drying at 100°C for 5 hours and then calcining at 650°C for 1 hour, a catalyst for the dealkylation of C8 aromatics to produce benzene and toluene was obtained. The catalyst contained 2.3% SiO2 modification by mass, 91.7% composite modified alumina by mass, and 6% modified metal by mass.

[0050] The total acid content of the phosphorus-containing alumina is 21 μmol NH3 / g, and the ratio of weak acid content to strong acid content is 4.9.

[0051] The total acidity of the catalyst for the dealkylation of C8 aromatics to benzene and toluene is only 14 μmol NH3 / g, with a weak acid / strong acid ratio of 7.1, representing a 90% decrease compared to the raw material alumina (135 μmol NH3 / g); its pore volume is 0.48 cm³. 3 / g, compared to raw material alumina (0.54cm) 3 / g) decreased by only 11.1%.

[0052] The above-mentioned catalysts for the dealkylation of C8 aromatics to benzene and toluene were used in the catalytic hydrogenation dealkylation of C8 aromatics at a reaction temperature of 500 °C and a C8 aromatic weight hourly space velocity of 1 h⁻¹. -1 The molar ratio of C8 aromatics to hydrogen was 5, the reaction pressure was 3 MPa, and the catalyst performance is shown in Table 1. The stability test results after 200 hours of continuous operation showed that the catalyst was very stable, the activity did not show a significant downward trend, and the C8 aromatic conversion rate decreased by only 2.3 percentage points.

[0053] Example 3

[0054] Alumina powder (with an acid content of 106 μmol NH3 / g and a pore volume of 0.76 cm³) was used. 3Alumina (g) was placed in a 3% phosphoric acid aqueous solution, with the liquid-to-solid mass ratio of the phosphoric acid solution to alumina controlled at 5. The solution was treated at 30°C for 6 hours, filtered, dried at 120°C for 5 hours, and then calcined at 550°C for 10 hours to obtain phosphorus-modified alumina, wherein the phosphorus oxide content in the phosphorus-modified alumina was 2.7%. The phosphorus-modified alumina was then treated with steam at 550°C for 10 hours, and then dried at 90°C for 10 hours to obtain composite-modified alumina. The composite-modified alumina was then impregnated with an equal volume of nickel nitrate, dried at 90°C for 10 hours, and then calcined at 600°C to obtain Ni-modified composite-modified alumina. The above-mentioned Ni-modified composite alumina was placed in a silane ether of n-octane, with a weight concentration of 5% for organosilicon in the solution and a mass ratio of 0.2 between the Ni-modified composite alumina and the organosilicon solution. After drying at 150°C for 2 hours, it was then calcined at 550°C for 10 hours to obtain a catalyst for the dealkylation of C8 aromatics to produce benzene and toluene. The catalyst contained 1% SiO2 modification by mass, 94% composite alumina by mass, and 5% modified metal by mass.

[0055] The total acid content of the composite modified alumina is 30 μmol NH3 / g, and the ratio of weak acid content to strong acid content is 4.2.

[0056] The total acid content of the catalyst for the dealkylation of C8 aromatics to benzene and toluene is only 9 μmol NH3 / g, and the weak acid / strong acid ratio is 6.3, which is 91.5% lower than that of the raw material alumina (106 μmol NH3 / g); its pore volume is 0.64 cm³. 3 / g, compared to raw material alumina (0.76cm) 3 / g) decreased by only 15.8%.

[0057] The above-mentioned catalysts for the dealkylation of C8 aromatics to benzene and toluene were used in the catalytic hydrogenation dealkylation of C8 aromatics at a reaction temperature of 550 °C and a C8 aromatics weight hourly space velocity of 1 h⁻¹. -1 The molar ratio of C8 aromatics to hydrogen was 4, the reaction pressure was 4 MPa, and the catalyst performance is shown in Table 1. The 200-hour stability test results showed that the catalyst was very stable, and the activity did not show a significant downward trend. The C8 aromatic conversion rate decreased by only 1.9 percentage points.

[0058] Example 4

[0059] Alumina powder (with an acid content of 180 μmol NH3 / g and a pore volume of 0.69 cm³) was used. 3Alumina (g) was placed in a 5% phosphoric acid aqueous solution, with the liquid-to-solid mass ratio of the phosphoric acid solution to alumina controlled at 20. The solution was treated at 40°C for 5 hours, filtered, dried at 120°C for 6 hours, and then calcined at 600°C for 5 hours to obtain phosphorus-modified alumina, wherein the phosphorus oxide content in the phosphorus-modified alumina was 5%. The phosphorus-modified alumina was then treated with steam at 600°C for 8 hours, and dried at 150°C for 1 hour to obtain composite-modified alumina. The composite-modified alumina was then impregnated with an equal volume of chromium nitrate, dried at 120°C for 4 hours, and then calcined at 700°C to obtain Cr-modified composite-modified alumina. The Cr-modified composite alumina was placed in a hexane-based silicone oil solution, with a silicone concentration of 5% by weight. The mass ratio of the Cr-modified composite alumina to the silicone solution was 1. After drying at 120°C for 10 hours, it was calcined at 600°C for 10 hours to obtain a catalyst for the dealkylation of C8 aromatics to produce benzene and toluene. The catalyst contained 5% SiO2 modification by mass, 83% composite alumina by mass, and 12% modified metal by mass.

[0060] The total acid content of the composite modified alumina is 20 μmol NH3 / g, and the ratio of weak acid content to strong acid content is 5.0.

[0061] The total acid content of the catalyst for the dealkylation of C8 aromatics to benzene and toluene is only 18 μmol NH3 / g, and the weak acid / strong acid ratio is 7.9, which is 90% lower than that of the raw material alumina (180 μmol NH3 / g); its pore volume is 0.57 cm³. 3 / g, compared to raw material alumina (0.69cm) 3 / g) decreased by only 17.4%.

[0062] The above-mentioned catalysts for the dealkylation of C8 aromatics to benzene and toluene were used in the catalytic hydrogenation dealkylation reaction of C8 aromatics at a reaction temperature of 550 °C and a C8 aromatic weight hourly space velocity of 0.5 h⁻¹. -1 The molar ratio of C8 aromatics to hydrogen was 3, the reaction pressure was 3 MPa, and the catalyst performance is shown in Table 1. The 200-hour stability test results showed that the catalyst was very stable, and the activity did not show a significant downward trend. The C8 aromatic conversion rate decreased by only 1.8 percentage points.

[0063] Example 5

[0064] Alumina powder (with an acid content of 111 μmol NH3 / g and a pore volume of 0.58 cm³) was used. 3Alumina (g) was placed in a 1% phosphoric acid aqueous solution, with the liquid-to-solid mass ratio of the phosphoric acid solution to alumina controlled at 10. The solution was treated at 30°C for 4 hours, filtered, dried at 100°C for 10 hours, and then calcined at 550°C for 8 hours to obtain phosphorus-modified alumina, wherein the phosphorus oxide content in the phosphorus-modified alumina was 0.5%. The phosphorus-modified alumina was then treated with steam at 700°C for 2 hours, followed by drying at 120°C for 6 hours to obtain composite-modified alumina. The composite-modified alumina was then impregnated with cobalt nitrate in equal volumes, dried at 120°C for 10 hours, and then calcined at 700°C to obtain Co-modified composite-modified alumina. The Co-modified composite alumina was placed in a tetraethyl orthosilicate solution of cyclohexane, with a silicone weight concentration of 4% and a mass ratio of Co-modified composite alumina to silicone solution of 0.5. After drying at 120°C for 10 hours and then calcining at 650°C for 5 hours, a catalyst for the dealkylation of C8 aromatics to produce benzene and toluene was obtained. The catalyst contained 2% SiO2 modification, 90% composite alumina, and 8% modified metal.

[0065] The total acid content of the composite modified alumina is 37 μmol NH3 / g, and the ratio of weak acid content to strong acid content is 3.2.

[0066] The total acid content of the catalyst for the dealkylation of C8 aromatics to benzene and toluene is only 7 μmol NH3 / g, and the weak acid / strong acid ratio is 7.2, which is 93.6% lower than that of the raw material alumina (111 μmol NH3 / g); its pore volume is 0.47 cm³. 3 / g, compared to raw material alumina (0.58cm) 3 / g) decreased by only 18.9%.

[0067] The above-mentioned catalysts for the dealkylation of C8 aromatics to benzene and toluene were used in the catalytic hydrogenation dealkylation reaction of C8 aromatics at a reaction temperature of 500 °C and a C8 aromatic weight hourly space velocity of 0.5 h⁻¹. -1 The molar ratio of C8 aromatics to hydrogen was 5, the reaction pressure was 3 MPa, and the catalyst performance is shown in Table 1. The 200-hour stability test results showed that the catalyst was very stable, and the activity did not show a significant downward trend. The C8 aromatic conversion rate decreased by only 1.3 percentage points.

[0068] Example 6

[0069] Alumina powder (with an acid content of 106 μmol NH3 / g and a pore volume of 0.76 cm³) was used. 3Alumina (g) was placed in a 3% phosphoric acid aqueous solution, with the liquid-to-solid mass ratio of the phosphoric acid solution to alumina controlled at 5. The solution was treated at 30°C for 6 hours, filtered, dried at 120°C for 5 hours, and then calcined at 550°C for 10 hours to obtain phosphorus-modified alumina, wherein the phosphorus oxide content in the phosphorus-modified alumina was 2.7%. The phosphorus-modified alumina was then treated with steam at 550°C for 10 hours, and dried at 90°C for 10 hours to obtain composite-modified alumina. The composite-modified alumina was then impregnated with equal volumes of nickel nitrate and chromium nitrate, dried at 90°C for 10 hours, and then calcined at 600°C to obtain Ni / Cr-modified composite alumina. The amounts of nickel nitrate and chromium nitrate were controlled to ensure that the Ni content in the Ni / Cr-modified composite alumina was 2% and the Cr content was 3.2%. The above-mentioned Ni / Cr modified composite alumina was placed in a silane ether of n-octane, with a silicone concentration of 3% by weight in the solution. The mass ratio of Ni / Cr modified composite alumina to silicone solution was 1. After drying at 150°C for 2 hours, it was calcined at 550°C for 10 hours. The resulting catalyst for the dealkylation of C8 aromatics to produce benzene and toluene contained in the catalyst was 3% by mass of SiO2 modification, 92% by mass of composite modified alumina, and 5% by mass of modified metal, of which Ni accounted for 2% and Cr accounted for 3% by mass.

[0070] The total acid content of the composite modified alumina is 28 μmol NH3 / g, and the ratio of weak acid content to strong acid content is 4.6.

[0071] The catalyst for the dealkylation of C8 aromatics to benzene and toluene has an acid content of only 11 μmol NH3 / g, a weak acid / strong acid ratio of 8.0, which is 90% lower than that of the raw material alumina (106 μmol NH3 / g); its pore volume is 0.62 cm³. 3 / g, compared to raw material alumina (0.76cm) 3 / g) decreased by only 18.4%.

[0072] The above-mentioned catalysts for the dealkylation of C8 aromatics to benzene and toluene were used in the catalytic hydrogenation dealkylation of C8 aromatics at a reaction temperature of 550 °C and a C8 aromatics weight hourly space velocity of 1 h⁻¹. -1 The molar ratio of C8 aromatics to hydrogen was 4, the reaction pressure was 4 MPa, and the catalyst performance is shown in Table 1. The 200-hour stability test results showed that the catalyst was very stable, and the activity did not show a significant downward trend. The C8 aromatic conversion rate decreased by only 1.9 percentage points.

[0073] Comparative Example 1

[0074] Alumina powder (with an acid content of 124 μmol NH3 / g and a pore volume of 0.63 cm³) was used. 3 Alumina (g) was placed in a 1% phosphoric acid aqueous solution, with the liquid-to-solid mass ratio of the phosphoric acid solution to alumina controlled at 20. The solution was treated at 50°C for 3 hours, filtered, dried at 150°C for 1 hour, and then calcined at 700°C for 1 hour to obtain phosphorus-modified alumina, wherein the phosphorus oxide content in the phosphorus-modified alumina was 1.2%. The phosphorus-modified alumina was then treated with steam at 700°C for 5 hours, and then dried at 120°C for 5 hours to obtain composite-modified alumina. The composite-modified alumina was then impregnated with an equal volume of chromium nitrate, dried at 120°C for 5 hours, and then calcined at 700°C for 10 hours to obtain Cr-modified composite alumina, wherein the amount of chromium nitrate was controlled so that the mass content of modified metal Cr in the catalyst was 15%, and the mass content of the composite-modified alumina was 85%.

[0075] The composite modified alumina has an acid content of 39 μmol NH3 / g and a weak acid content / strong acid content ratio of 3.5.

[0076] The catalyst for the dealkylation of C8 aromatics to benzene and toluene has an acidity of only 54 μmol NH3 / g, a weak acid / strong acid ratio of 4.2, representing a 57% decrease compared to the raw material alumina (124 μmol NH3 / g); its pore volume is 0.50 cm³. 3 / g, a decrease of 21% compared to the raw material alumina (0.63).

[0077] The above-mentioned catalysts for the dealkylation of C8 aromatics to benzene and toluene were used in the catalytic hydrogenation dealkylation reaction of C8 aromatics at a reaction temperature of 550 °C and a C8 aromatic weight hourly space velocity of 0.5 h⁻¹. -1 The molar ratio of hydrogen to C8 aromatics was 3, the reaction pressure was 3 MPa, and the catalyst performance is shown in Table 1. The results of the 200-hour continuous operation stability test are shown in [Table 1]. Figure 1 The results showed that the catalyst activity decreased significantly, with the C8 aromatic conversion rate decreasing by 23.2 percentage points.

[0078] Comparative Example 2

[0079] Alumina powder (with an acid content of 124 μmol NH3 / g and a pore volume of 0.63 cm³) was used. 3Alumina (g) was placed in a 1% phosphoric acid aqueous solution, with the liquid-to-solid mass ratio of the phosphoric acid solution to alumina controlled at 20. The solution was treated at 50°C for 3 hours, filtered, dried at 150°C for 1 hour, and then calcined at 700°C for 1 hour to obtain phosphorus-modified alumina, wherein the phosphorus oxide content in the phosphorus-modified alumina was 1.2%. The above phosphorus-modified alumina was then impregnated with an equal volume of chromium nitrate, dried at 120°C for 5 hours, and then calcined at 700°C to obtain Cr-modified phosphorus-modified alumina. The Cr-modified phosphorus-modified alumina was placed in a tetraethyl orthosilicate solution of hexane, with a silicone concentration of 5% by weight. The mass ratio of the Cr-modified phosphorus-modified alumina to the silicone solution was 0.8. After drying at 120°C for 10 hours and then calcining at 600°C for 10 hours, a catalyst for the dealkylation of C8 aromatics to benzene and toluene was obtained. The catalyst contained 4% SiO2 modification by mass, 81% composite modified alumina by mass, and 15% modified metal by mass.

[0080] The total acid content of the composite modified alumina is 42 μmol NH3 / g, and the ratio of weak acid content to strong acid content is 3.6.

[0081] The total acid content of the catalyst for the dealkylation of C8 aromatics to benzene and toluene is only 14 μmol NH3 / g, and the weak acid / strong acid ratio is 5.3, which is 89% lower than that of the raw material alumina (124 μmol NH3 / g); its pore volume is 0.34 cm³. 3 / g, compared to raw material alumina (0.63cm) 3 / g) decreased by 46%.

[0082] The above-mentioned catalysts for the dealkylation of C8 aromatics to benzene and toluene were used in the catalytic hydrogenation dealkylation reaction of C8 aromatics at a reaction temperature of 550 °C and a C8 aromatic weight hourly space velocity of 0.5 h⁻¹. -1 The molar ratio of C8 aromatics to hydrogen was 3, the reaction pressure was 3 MPa, and the catalyst performance is shown in Table 1. The 200-hour stability test results showed a significant decrease in catalyst activity, with the C8 aromatic conversion rate decreasing by 16.1 percentage points.

[0083] Comparative Example 3

[0084] Alumina (with an acid content of 124 μmol NH3 / g and a pore volume of 0.63 cm³) was used. 3 / g) was treated with steam at 700℃ for 5 hours, and then dried at 120℃ for 5 hours to obtain steam-treated alumina. The above steam-treated alumina was then impregnated with chromium nitrate in equal volumes, dried at 120℃ for 5 hours, and then calcined at 700℃ to obtain Cr-modified steam-treated alumina. The above Cr-modified steam-treated alumina was placed in a tetraethyl orthosilicate solution of n-hexane, with an organosilicon weight concentration of 5%, and the mass ratio of Cr-modified composite alumina to organosilicon solution was 0.4. After drying at 120℃ for 10 hours and then calcining at 600℃ for 10 hours, a catalyst for the dealkylation of C8 aromatics to benzene and toluene was obtained, wherein the catalyst contained 2% SiO2 modification, 83% alumina, and 15% modified metal.

[0085] The composite modified alumina has an acid content of 103 μmol NH3 / g and a weak acid content / strong acid content ratio of 2.5.

[0086] The catalyst for the dealkylation of C8 aromatics to benzene and toluene has an acid content of only 65 μmol NH3 / g, a weak acid / strong acid ratio of 3.9, which is 47.6% lower than that of the raw material alumina (124 μmol NH3 / g); its pore volume is 0.46 cm³. 3 / g, compared to raw material alumina (0.63cm) 3 / g) decreased by 27%.

[0087] The above-mentioned catalysts for the dealkylation of C8 aromatics to benzene and toluene were used in the catalytic hydrogenation dealkylation reaction of C8 aromatics at a reaction temperature of 550 °C and a C8 aromatic weight hourly space velocity of 0.5 h⁻¹. -1 The molar ratio of C8 aromatics to hydrogen was 3, the reaction pressure was 3 MPa, and the catalyst performance is shown in Table 1. The 200-hour stability test results showed that the catalyst activity decreased significantly, and the C8 aromatic conversion rate decreased by 10.3 percentage points.

[0088] Table 1. Catalytic hydrodealkylation reaction performance of C8 aromatics in each embodiment.

[0089]

Claims

1. A catalyst for the dealkylation of C8 aromatics to produce benzene and toluene, said catalyst comprising phosphorus-containing alumina, an active metal, and silicon oxide; based on the weight of the catalyst, the phosphorus-containing alumina has a mass content of 80-94%, the active metal has a mass content of 5-15%, and the silicon oxide has a mass content of 1-5%; said active metal is selected from at least one of Co, Ni, and Cr; The total acidity of the phosphorus-containing alumina is 20~40 μmolNH3 / g, and the phosphorus content in the phosphorus-containing alumina, calculated as oxides, is 0.5~5%. The catalyst has a total acid content of 2-19 μmol NH3 / g, a weak acid to strong acid ratio of 5-8:1, and a pore volume of 0.45-0.65 cm³. 3 / g.

2. The catalyst for the dealkylation of C8 aromatics to benzene and toluene according to claim 1, characterized in that, The ratio of weak acid to strong acid in the phosphorus-containing alumina is 3~5:

1.

3. The catalyst for the dealkylation of C8 aromatics to benzene and toluene according to claim 1, characterized in that, The active metals are Cr and Ni.

4. The preparation method of the catalyst for the dealkylation of C8 aromatics to benzene and toluene according to any one of claims 1-3, comprising the following steps: (a) Preparation of phosphorus-containing aluminum oxide; (b) Take the phosphorus-containing alumina obtained in step (a), introduce active metal by impregnation, and then dry and calcine to obtain phosphorus-containing alumina loaded with metal; (c) The phosphorus-containing alumina with metal loading obtained in step (b) is immersed in an organosilicon solution, dried and calcined to obtain a catalyst for the dealkylation of C8 aromatics to produce benzene and toluene.

5. The preparation method according to claim 4, characterized in that, In step (a), the preparation method of phosphorus-containing alumina includes the following steps: (1) Alumina powder is placed in an aqueous solution of phosphoric acid, then dried and calcined; (2) The material obtained in step (1) is treated under steam conditions and dried to obtain phosphorus-containing aluminum oxide.

6. The preparation method according to claim 4, characterized in that, The organosilicon mentioned in step (c) is at least one of tetraethyl orthosilicate, silicone ether, and organosilicon oil.

7. The preparation method according to claim 4, characterized in that, The organosilicon solution in step (c) has a mass concentration of 1-5% and a mass ratio of phosphorus-containing alumina loaded with metal to organosilicon solution of 0.2-1:

1.

8. The use of the catalyst according to any one of claims 1-3 in the dealkylation of C8 aromatics to produce benzene and toluene.

9. The application according to claim 8, characterized in that, The reaction conditions are as follows: reaction temperature 450~750℃, C8 aromatic weight hourly space velocity 0.5~2h. -1 The molar ratio of hydrogen to C8 aromatics is 2~8:1, and the reaction pressure is 2~6 MPa.

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