A process for converting heavy aromatics to light aromatics

Abstract

The application discloses a method for converting heavy aromatic hydrocarbons into light aromatic hydrocarbons, and the method comprises the following steps: contacting heavy aromatic hydrocarbons and toluene with a catalyst under heavy aromatic hydrocarbon lightening reaction conditions, wherein the active component of the catalyst is a nickel-cobalt alloy, and the carrier of the catalyst is ZrO2 modified USY molecular sieve. The catalyst used in the application exhibits good conversion rate, mixed xylene selectivity and anti-coking performance in heavy aromatic hydrocarbon lightening. The alloy formation of Ni and Co can improve the anti-coking performance of the catalyst, and improve the conversion rate and mixed xylene selectivity. The ZrO2 modified USY molecular sieve has a large specific surface area and mesopore volume. The ZrO2 modified USY molecular sieve as the carrier can improve the dispersity and stability of the nickel-cobalt alloy, and improve the anti-sintering performance of the catalyst, so that the catalyst exhibits good catalytic activity, stability and anti-coking performance.

Description

Technical Field

[0001] This invention relates to the field of heavy aromatic hydrocarbon hydrogenation dealkylation catalysts, and particularly to a method for converting heavy aromatic hydrocarbons into light aromatic hydrocarbons. Background Technology

[0002] Heavy aromatics are a general term for aromatic compounds with 9 or more carbon atoms (C9). They are primarily C9 and C10 aromatics produced as byproducts in petroleum and coal processing. Heavy aromatics mainly originate from catalytic reforming units in oil refineries, cracked gasoline and ethylene tar produced as byproducts of ethylene plants, and coal tar produced as a byproduct of high-temperature coal coking.

[0003] Currently, there are two main methods for the comprehensive utilization of heavy aromatics. One method is direct physical separation and utilization, which generally involves distillation to extract high-value products such as trimethylbenzene, mesitylene, naphthalene, methylnaphthalene, and high-boiling-point aromatic solvents. However, due to the large number of isomers and similar boiling points in heavy aromatics, ordinary distillation is quite difficult. The other method is the hydrodealkylation technology for heavy aromatics, which aims to reduce the carbon number of heavy aromatics and convert them into basic chemical raw materials such as benzene, toluene, and xylene (BTX). Compared with physical separation and utilization, the advantage of hydrodealkylation technology is that it can convert low-value heavy aromatics into high-value-added fine chemical products.

[0004] Catalytic hydrodealkylation exhibits high reactivity and selectivity for light aromatic hydrocarbons (benzene, toluene, xylene). The key to this method lies in the development of efficient catalysts and catalytic processes. Current catalysts primarily use molecular sieves as supports and supported noble metals as active components. However, catalysts using inexpensive metals or metal oxides as active components exhibit lower catalytic activity, resulting in higher catalytic costs. A major problem with non-noble metal catalysts is their susceptibility to deactivation due to carbon deposition, sintering, and oxidation. Carbon deposition is the leading cause of catalyst deactivation. Therefore, developing an inexpensive catalyst resistant to carbon deposition and sintering is of paramount importance. Summary of the Invention

[0005] In view of this, the present invention proposes a method for converting heavy aromatics into light aromatics to solve the above problems.

[0006] The technical solution of this invention is implemented as follows:

[0007] A method for converting heavy aromatics into light aromatics, the method comprising: contacting heavy aromatics, toluene, hydrogen and a catalyst under heavy aromatics lightening reaction conditions; wherein the active component of the catalyst is a nickel-cobalt alloy and the catalyst support is a ZrO2-modified USY molecular sieve.

[0008] Preferably, in the catalyst active component nickel-cobalt alloy, the mass of nickel is 5-10% of the carrier mass, and the mass of cobalt is 5-10% of the carrier mass.

[0009] Preferably, ZrO2 accounts for 20% to 40% of the mass of the ZrO2-modified USY molecular sieve.

[0010] Preferably, ZrO2 accounts for 30% of the mass of the ZrO2-modified USY molecular sieve.

[0011] Preferably, the specific surface area of ​​the ZrO2-modified USY molecular sieve is 359-386 m². 2 / g.

[0012] Preferably, the pore volume of the ZrO2-modified USY molecular sieve is 0.35-0.46 cm³. 3 / g.

[0013] Preferably, the ZrO2-modified USY molecular sieve is prepared by dissolving zirconium nitrate in deionized water, immersing the USY molecular sieve in the zirconium nitrate aqueous solution for 6-8 hours, drying the immersed sample, and calcining the dried sample at 600-800℃ for 5-6 hours to obtain the ZrO2-modified USY molecular sieve.

[0014] Preferably, the catalyst is prepared by: taking ZrO2-modified USY molecular sieve, performing ion exchange on the support with NH4Cl solution at 85-95℃, filtering, washing, drying at 110-120℃ for 6-8h, then impregnating with nickel nitrate and cobalt nitrate solution for 4-6h, filtering, drying at 120-130℃ for 6-8h, calcining in air at 700-800℃ for 4-6h to obtain the catalyst, and reducing with hydrogen at 550-650℃ for 3-5h to obtain a nickel-cobalt alloy catalyst supported on ZrO2-modified USY molecular sieve.

[0015] Preferably, the reaction conditions for the heavy aromatic hydrocarbon lightening process are: a reaction temperature of 280–320°C, a reaction pressure of 2.5–3 MPa, and a feed space velocity of 2.5–3.5 h⁻¹. -1 Toluene and C10 + The mass ratio of heavy aromatics is 3:2, and the volume ratio of hydrogen to heavy aromatics is 1000.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0017] (1) The present invention provides a method for converting heavy aromatics into light aromatics. The catalyst active component is a nickel-cobalt alloy, and the catalyst support is a ZrO2 modified USY molecular sieve. It exhibits good conversion rate, xylene selectivity and anti-coking performance in the conversion of heavy aromatics into light aromatics. The alloying of Ni and Co can improve the anti-coking performance of the catalyst and increase the conversion rate and xylene selectivity.

[0018] (2) ZrO2 has both oxidizing and reducing properties. The oxygen atoms on the surface of ZrO2 can react with carbon species on the surface of active metals, effectively inhibiting the formation of carbon deposits.

[0019] (3) The ZrO2 modified USY molecular sieve of the present invention has a large specific surface area and mesoporous pore volume. The ZrO2 modified USY molecular sieve as a support improves the dispersibility and stability of nickel-cobalt alloy, improves the anti-sintering performance of the catalyst, and makes the catalyst exhibit good catalytic activity, stability and anti-carbon deposition performance. Detailed Implementation

[0020] To better understand the technical content of this invention, specific embodiments are provided below to further illustrate the invention.

[0021] Unless otherwise specified, the experimental methods used in the embodiments of this invention are all conventional methods.

[0022] Unless otherwise specified, all materials and reagents used in the embodiments of this invention are commercially available.

[0023] Example 1

[0024] Preparation method of ZrO2 modified USY molecular sieve: 120.9g of zirconium nitrate pentahydrate was dissolved in deionized water to form a zirconium nitrate aqueous solution. 100g of USY molecular sieve was immersed in the zirconium nitrate solution to fully absorb the zirconium nitrate precursor. The immersion time was 6h. The immersion sample was dried to remove the solvent. The dried sample was calcined at 600℃ for 5h to obtain ZrO2 modified USY molecular sieve. ZrO2 accounted for 30% of the mass of USY molecular sieve.

[0025] Catalyst preparation method: Dissolve 12.4 g of nickel nitrate hexahydrate and cobalt nitrate hexahydrate in deionized water. Take 50 g of the above ZrO2 modified USY molecular sieve, and perform ion exchange on the support with 10 mL of 0.5 g / mL NH4Cl solution at 90±5℃ for 4 hours. Filter, wash, and dry at 115±5℃ for 6 hours. Impregnate in nickel nitrate and cobalt nitrate solution, let stand for 4 hours, filter, dry at 125±5℃ for 6 hours, calcine in air at 700℃ for 4 hours, and reduce in hydrogen at 550℃ for 3 hours to obtain the nickel-cobalt alloy catalyst supported on ZrO2 modified USY molecular sieve (the mass of metallic nickel is 5% of the mass of the support, and the mass of metallic cobalt is 5% of the mass of the support).

[0026] Example 2

[0027] Preparation method of ZrO2 modified USY molecular sieve: 120.9g of zirconium nitrate pentahydrate was dissolved in deionized water to form a zirconium nitrate aqueous solution. 100g of USY molecular sieve was immersed in the zirconium nitrate solution to fully absorb the zirconium nitrate precursor. The immersion time was 8h. The immersion sample was dried to remove the solvent. The dried sample was calcined at 600℃ for 6h to obtain ZrO2 modified USY molecular sieve. ZrO2 accounted for 30% of the mass of USY molecular sieve.

[0028] Catalyst preparation method: Dissolve 19.8g of nickel nitrate hexahydrate and 19.8g of cobalt nitrate hexahydrate in deionized water. Take 50g of the above ZrO2 modified USY molecular sieve, and perform ion exchange on the support with 10ml of 0.5g / ml NH4Cl solution at 90±5℃ for 4 hours. Filter, wash, and dry at 115±5℃ for 8 hours. Add it to the nickel nitrate and cobalt nitrate solution for impregnation, let stand for 5 hours, filter, dry at 125±5℃ for 8 hours, calcine in air at 800℃ for 6 hours, and reduce in hydrogen at 600℃ for 4 hours to obtain the nickel-cobalt alloy catalyst supported on ZrO2 modified USY molecular sieve (the mass of metallic nickel is 8% of the mass of the support, and the mass of metallic cobalt is 8% of the mass of the support).

[0029] Example 3

[0030] Preparation method of ZrO2 modified USY molecular sieve: 120.9g of zirconium nitrate pentahydrate was dissolved in deionized water to form a zirconium nitrate aqueous solution. 100g of USY molecular sieve was immersed in the zirconium nitrate solution to fully absorb the zirconium nitrate precursor. The immersion time was 8h. The immersion sample was dried to remove the solvent. The dried sample was calcined at 800℃ for 6h to obtain ZrO2 modified USY molecular sieve. ZrO2 accounted for 30% of the mass of USY molecular sieve.

[0031] Catalyst preparation method: Dissolve 24.8g of nickel nitrate hexahydrate and 24.8g of cobalt nitrate hexahydrate in deionized water. Take 50g of the above ZrO2 modified USY molecular sieve, and perform ion exchange on the support with 10ml of 0.5g / ml NH4Cl solution at 90±5℃ for 4 hours. Filter, wash, and dry at 115±5℃ for 8 hours. Add it to the nickel nitrate and cobalt nitrate solution for impregnation, let stand for 6 hours, filter, dry at 125±5℃ for 8 hours, calcine in air at 800℃ for 6 hours, and reduce in hydrogen at 650℃ for 5 hours to obtain the nickel-cobalt alloy catalyst supported on ZrO2 modified USY molecular sieve (the mass of metallic nickel is 10% of the mass of the support, and the mass of metallic cobalt is 10% of the mass of the support).

[0032] Example 4

[0033] Example 4 is basically the same as Example 1 in terms of active metal components and preparation method, except that ZrO2 accounts for 10% of the mass of USY molecular sieve in ZrO2 modified USY molecular sieve.

[0034] Example 5

[0035] Example 5 is basically the same as Example 1 in terms of active metal components and preparation method, except that ZrO2 accounts for 20% of the mass of USY molecular sieve in ZrO2 modified USY molecular sieve.

[0036] Example 6

[0037] Example 6 is basically the same as Example 1 in terms of active metal components and preparation method, the difference being that ZrO2 accounts for 40% of the mass of the ZrO2-modified USY molecular sieve.

[0038] Example 7

[0039] Example 7 is basically the same as Example 1 in terms of active metal components and preparation method, except that ZrO2 accounts for 50% of the mass of USY molecular sieve in ZrO2 modified USY molecular sieve.

[0040] Comparative Example 1

[0041] The support components and preparation method in this example are basically the same as those in Example 1. The difference is that cobalt nitrate is replaced with copper nitrate. After reduction, a nickel-copper alloy catalyst supported on ZrO2 modified USY molecular sieve is obtained (the mass of metallic nickel is 5% of the mass of the support, and the mass of metallic copper is 5% of the mass of the support).

[0042] Comparative Example 2

[0043] The support components and preparation method in this example are basically the same as those in Example 1. The difference is that cobalt nitrate is replaced with iron nitrate. After reduction, a nickel-iron alloy catalyst supported on ZrO2 modified USY molecular sieve is obtained (the mass of metallic nickel is 5% of the mass of the support, and the mass of metallic iron is 5% of the mass of the support).

[0044] Comparative Example 3

[0045] The active metal components and preparation method in this example are basically the same as in Example 1, except that the ZrO2-modified USY molecular sieve is replaced with a TiO2-modified USY molecular sieve, with TiO2 accounting for 30% of the mass of the USY molecular sieve. After reduction, a nickel-cobalt alloy catalyst supported on TiO2-modified USY molecular sieve is obtained (the mass of metallic nickel is 5% of the mass of the support, and the mass of metallic cobalt is 5% of the mass of the support).

[0046] Comparative Example 4

[0047] The active metal components and preparation method in this example are basically the same as in Example 1, except that the ZrO2-modified USY molecular sieve is replaced with a CeO2-modified USY molecular sieve, with CeO2 accounting for 30% of the mass of the USY molecular sieve. After reduction, a nickel-cobalt alloy catalyst supported on CeO2-modified USY molecular sieve is obtained (the mass of metallic nickel is 5% of the mass of the support, and the mass of metallic cobalt is 5% of the mass of the support).

[0048] Comparative Example 5

[0049] This example is basically the same as Example 1 in terms of active metal components and preparation method, except that the ZrO2-modified USY molecular sieve is replaced with USY molecular sieve. After reduction, a nickel-cobalt alloy catalyst supported on USY molecular sieve is obtained (the mass of metallic nickel is 5% of the mass of the support, and the mass of metallic cobalt is 5% of the mass of the support).

[0050] Comparative Example 6

[0051] The active metal components and preparation methods in this example are basically the same as those in Example 1. The difference is that the catalyst is prepared without H2 reduction treatment to directly obtain the nickel oxide and cobalt tetroxide catalyst supported on ZrO2 modified USY molecular sieve (the mass of nickel is 5% of the mass of the support, and the mass of cobalt is 5% of the mass of the support).

[0052] Experimental Example 1

[0053] Weigh 0.3g of the catalyst from Examples 1-7 and Comparative Examples 1-6 and load it into the isothermal zone in the middle of the reaction tube. Fill the upper and lower parts of the reaction tube with 30g of 20-40 mesh quartz sand each. Purge the reaction apparatus with nitrogen gas for 40 minutes, then proceed with the heavy aromatic hydrocarbon hydrogenation and dealkylation reaction under the following conditions: temperature 280-320℃, pressure 2.5-3MPa, and toluene reacting with C10... +The mass ratio of heavy aromatics is 3:2, and the heavy hourly space velocity is 2.5-3.5 h⁻¹. -1 The volume ratio of hydrogen to heavy aromatics was 1000; after 24 hours of reaction, the composition of the liquid product was analyzed by gas chromatography, and the C10 was calculated. + Conversion rate of heavy aromatics, selectivity of mixed xylenes (PX, MX and OX); carbon deposition results after 500 h of reaction.

[0054] Table 1. Different catalysts used for C10 + Reaction conditions and results of hydrogenation dealkylation of heavy aromatics

[0055]

[0056]

[0057] Table 1 shows that the nickel-cobalt alloy catalysts supported on ZrO2-modified USY molecular sieves prepared in Examples 1-3 of this invention exhibit good conversion rates, xylene selectivity, and anti-carbon deposition properties in the heavy aromatic hydrocarbon lightening reaction. Examples 4-7 reflect the effect of ZrO2 content on the quality of modified USY molecular sieves. The addition of ZrO2 can improve thermal stability and anti-carbon deposition properties; too little ZrO2 will affect its effect, while too much ZrO2 may clog the pore structure of the USY molecular sieve, reducing the active surface area and the number of available active sites of the catalyst, thereby reducing catalytic activity and selectivity. In Comparative Examples 1-2, replacing the nickel-copper alloy with a nickel-copper and nickel-iron alloy significantly reduced the xylene selectivity. In Comparative Examples 3-4, replacing ZrO2 with TiO2 and CeO2 reduced the conversion rate, selectivity, and anti-carbon deposition properties of the catalyst to some extent. In Comparative Example 5, using USY molecular sieves without added ZrO2 as the support, the catalyst's anti-carbon deposition properties were significantly weakened, and the conversion rate of heavy aromatic hydrocarbons and the selectivity of xylene were also significantly reduced. The catalyst in Comparative Example 6, which was not pretreated with hydrogen reduction, showed a significant decrease in activity.

[0058] Experimental Example 2

[0059] The mesoporous specific surface area and mesoporous pore volume were determined by low-temperature nitrogen adsorption method. The following are the structural parameters of the molecular sieve supports of Examples 1-7 and Comparative Examples 3-5.

[0060] Table 2. Structural properties of catalysts in Examples 1-7 and Comparative Examples 1-5

[0061] Example <![CDATA[Specific surface area (m 2 / g)]]> <![CDATA[Pore volume (cm 3 / g)]]> Example 1 378 0.42 Example 2 386 0.46 Example 3 372 0.38 Example 4 369 0.31 Example 5 373 0.37 Example 6 359 0.35 Example 7 337 0.26 Comparative Example 3 364 0.34 Comparative Example 4 348 0.28 Comparative Example 5 361 0.32

[0062] As shown in Table 2, the catalysts provided in Examples 1-3 of this invention have a large specific surface area and pore volume. A larger specific surface area can provide more active sites, increasing the contact area between reactants and catalysts, thereby improving the reaction rate and catalytic activity. A larger mesopore volume can provide larger diffusion channels, which helps the mass transfer of reactants and products, facilitates the diffusion and dispersion of carbon deposits, slows down the formation of carbon deposits, and thus extends the service life of the catalyst.

[0063] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for converting heavy aromatics into light aromatics, characterized in that, Under the conditions of heavy aromatic hydrocarbon lightening reaction, heavy aromatic hydrocarbons, toluene, hydrogen and catalyst are contacted; the active component of the catalyst is nickel-cobalt alloy, and the catalyst support is ZrO2 modified USY molecular sieve. The preparation method of the ZrO2 modified USY molecular sieve is as follows: dissolve zirconium nitrate in deionized water to obtain zirconium nitrate aqueous solution; immerse USY molecular sieve in zirconium nitrate aqueous solution for 6-8 h; dry the immersed sample; calcine the dried sample at 600-800℃ for 5-6 h to obtain ZrO2 modified USY molecular sieve. The catalyst is prepared as follows: ZrO2 modified USY molecular sieve is subjected to ion exchange with NH4Cl solution at 85-95℃, filtered, washed, dried at 110-120℃ for 6-8 h, then impregnated with nickel nitrate and cobalt nitrate solution for 4-6 h, filtered, dried at 120-130℃ for 6-8 h, calcined in air at 700-800℃ for 4-6 h, and reduced with hydrogen at 550-650℃ for 3-5 h to obtain the catalyst, namely, the nickel-cobalt alloy catalyst supported on ZrO2 modified USY molecular sieve. In the catalyst active component nickel-cobalt alloy, the mass of nickel is 5-10% of the carrier mass, and the mass of cobalt is 5-10% of the carrier mass.

2. The method for converting heavy aromatics into light aromatics according to claim 1, characterized in that, In the ZrO2-modified USY molecular sieve, ZrO2 accounts for 20% to 40% of the mass of the USY molecular sieve.

3. The method for converting heavy aromatics into light aromatics according to claim 2, characterized in that, In the ZrO2-modified USY molecular sieve, ZrO2 accounts for 30% of the mass of the USY molecular sieve.

4. The method for converting heavy aromatics into light aromatics according to claim 1, characterized in that, The specific surface area of ​​the ZrO2-modified USY molecular sieve is 359-386 m². 2 / g.

5. The method for converting heavy aromatics into light aromatics according to claim 1, characterized in that, The ZrO2-modified USY molecular sieve has a pore volume of 0.35-0.46 cm³. 3 / g.

6. The method for converting heavy aromatics into light aromatics according to claim 1, characterized in that, The specific reaction conditions for the lightening of heavy aromatics are as follows: reaction temperature of 280~320℃, reaction pressure of 2.5~3MPa, and weight hourly space velocity of 2.5-3.5h⁻¹. -1 The mass ratio of toluene to heavy aromatics is 3:2, and the volume ratio of hydrogen to heavy aromatics is 1000.

Images