Process for producing benzene and durene from xylene

Abstract

This invention relates to the field of mesitylene production technology, specifically a method for producing benzene and mesitylene from xylene. The method comprises the following steps: xylene undergoes an alkyl transfer reaction catalyzed by a catalyst in a reactor; the reaction products are separated to obtain a xylene-mesitylene mixture and toluene; the xylene-mesitylene mixture is then cryogenically crystallized to obtain mesitylene. This method for producing benzene and mesitylene from xylene produces products with stable composition and high selectivity for mesitylene. Under specific catalyst and reaction conditions, benzene and mesitylene can be controllably produced without anhydrous formation. The mesitylene selectivity is between 52% and 64%, and the product composition is stable. This method avoids the problem of acidic water formation caused by using methanol as a raw material, thus improving production efficiency and reducing production costs.

Description

Technical Field

[0001] This invention relates to the field of mesitylene production technology, and is a method for producing benzene and mesitylene using xylene as a raw material. Background Technology

[0002] Mesitylene, also known as 1,2,4,5-tetramethylbenzene or Durone, is an important organic chemical raw material, mainly used in the production of pyromellitic dianhydride or pyromellitic anhydride, PMDA. Currently, it is primarily obtained from C10 aromatic hydrocarbons. Since C10 heavy aromatic hydrocarbons contain a relatively large number of components, mesitylene, the economically valuable component, accounts for only about 8% to 9%. Synthetic methods for mesitylene include methanol alkylation of pseudotrimethylbenzene; isomerization and disproportionation of trimethylbenzene; chloromethylation of pseudotrimethylbenzene; isomerization of tetramethylbenzene; methanol to mesitylene; and methanol-xylene alkylation.

[0003] Chinese patent document CN110627605A discloses a method for producing mesitylene from methanol and xylene. Xylene is mixed with a portion of methanol and fed into the reactor via the top main feed line. The remaining methanol is fed into the reactor via a multi-stage side feed line. The material is converted into a mixed hydrocarbon component rich in mesitylene at a temperature of 250°C to 400°C and a pressure of 0.5 MPa to 2.0 MPa. After separation, heavy aromatics rich in mesitylene are obtained, which are then subjected to a multi-stage freeze crystallization, centrifugal separation, and pressing system to obtain high-purity mesitylene. Xylene and its mixed aromatics (C7 to C9 aromatics and heavy aromatic residues) undergo repeated alkylation reactions with methanol, thereby increasing the selectivity of mesitylene in the oil phase products to 45%. The C7 to C9 aromatics and heavy aromatic residues are returned to the feed storage tank, fully utilizing the reaction byproducts and increasing the mesitylene yield to 35%. The initial reactants in this method are xylene and methanol. The actual reactants are toluene, trimethylbenzene, heavy aromatics generated during the reaction, and unreacted xylene, which are recycled back to the feed tank and reacted with methanol. As the reaction proceeds, the mixed aromatics continuously circulate, making it impossible to maintain a stable feed composition and inevitably leading to changes in the product composition. Furthermore, acidic water is generated during the methanol reaction; with a methanol feed rate of 260 kg / h, the wastewater flow rate is 145 kg / h, and water treatment is also an investment. For xylene disproportionation, the goal is to generate more benzene and mesitylene products through the transfer of methyl groups between benzene rings; however, no process technology for directly producing mesitylene from xylene has been reported. Summary of the Invention

[0004] This invention provides a method for producing benzene and mesitylene from xylene, overcoming the shortcomings of the prior art and effectively solving the problems of high by-products and low yield in the existing mesitylene production process.

[0005] The technical solution of the present invention is achieved through the following measures: a method for producing benzene and mesitylene from xylene as raw material, which is carried out according to the following steps: the raw material xylene undergoes an alkyl transfer reaction catalyzed by a catalyst in a reactor, and the reaction products are separated to obtain a xylene-mesitylene mixture and benzene. The xylene-mesitylene mixture is then frozen and crystallized to obtain mesitylene.

[0006] The following are further optimizations and / or improvements to the above-mentioned technical solution:

[0007] The above alkyl transfer reaction was carried out at a reaction temperature of 300°C to 500°C, a reaction pressure of 0.1 MPa to 5 MPa, and a xylene volume hourly space velocity of 0.5 h⁻¹. -1 up to 6h -1 It is carried out under the following conditions.

[0008] The aforementioned xylenes are o-xylene, m-xylene, a mixture of o-xylene and m-xylene, or a mixture of o-xylene, p-xylene, and m-xylene.

[0009] The catalysts mentioned above are modified zeolite molecular sieves, including one or more of mordenite, β molecular sieve, ZSM-11 molecular sieve, MCM-22 molecular sieve, HZSM-5 molecular sieve, and MCM-49 molecular sieve.

[0010] The modified metals of the above catalysts are Co, Mg, Ni, Zn, Cu, Mo, and Ga.

[0011] The metal content in the above catalyst is from 0.1 wt% to 6 wt%.

[0012] The silica-alumina molar ratio of the above-mentioned modified zeolite molecular sieves is 15 to 300.

[0013] The above-mentioned method for producing benzene and mesitylene from xylene is implemented using the following apparatus, which includes a reactor, a separator, and a crystallizer. A raw material pipeline is fixedly installed at the feed end of the reactor. A first product pipeline is fixedly installed between the discharge end of the reactor and the feed end of the separator. A second product pipeline is fixedly installed between the first discharge end of the separator and the feed end of the crystallizer. A third product pipeline is fixedly installed at the second discharge end of the separator. A mesitylene product pipeline is fixedly installed at the first discharge end of the crystallizer. A reflux pipeline is fixedly installed between the second discharge end of the crystallizer and the raw material pipeline. A catalyst bed is provided inside the reactor.

[0014] In summary, the method for producing benzene and mesitylene using xylene as a raw material according to the present invention produces products with stable composition and high selectivity for mesitylene. Under certain catalyst and reaction conditions, benzene and mesitylene can be produced in a controllable manner without the formation of anhydrous substances. Compared with existing technologies, the present invention uses xylene directly for the reaction to produce benzene and mesitylene, with a mesitylene selectivity between 52% and 64%, stable product composition, and avoids the problem of acidic water formation caused by using methanol as a raw material, thereby improving production efficiency and reducing production costs. Attached Figure Description

[0015] Appendix Figure 1 This is a schematic diagram of the process flow of the present invention.

[0016] The codes in the attached diagram are as follows: 1 is the reactor, 2 is the separator, 3 is the crystallizer, 4 is the feed line, 5 is the first product line, 6 is the second product line, 7 is the third product line, 8 is the mesitylene product line, 9 is the reflux line, and 10 is the catalyst bed. Detailed Implementation

[0017] This invention is not limited to the following embodiments, and specific implementation methods can be determined according to the technical solution of this invention and the actual situation. Unless otherwise specified, all chemical reagents and chemical products mentioned in this invention are well-known and commonly used chemical reagents and chemical products in the prior art; unless otherwise specified, all percentages in this invention are mass percentages; room temperature in this invention generally refers to a temperature between 15°C and 25°C, and is generally defined as 25°C.

[0018] Unless otherwise specified, all equipment and devices used in this invention are existing and commonly known in the art.

[0019] The present invention will be further described below with reference to embodiments:

[0020] Example 1: The method for producing benzene and mesitylene from xylene is carried out according to the following steps: the raw material xylene undergoes an alkyl transfer reaction catalyzed by a catalyst in reactor 1, and the reaction products are separated to obtain a xylene-mesitylene mixture and benzene. The xylene-mesitylene mixture is then frozen and crystallized to obtain mesitylene.

[0021] In this invention, the xylene separated from the xylene-meta-tetramethylbenzene mixture can be recycled as a raw material.

[0022] Example 2: As an optimization of the above example, the alkyl transfer reaction was carried out at a reaction temperature of 300°C to 500°C, a reaction pressure of 0.1 MPa to 5 MPa, and a xylene volume hourly space velocity of 0.5 h⁻¹. -1 up to 6h -1 It is carried out under the following conditions.

[0023] Example 3: As an optimization of the above examples, xylene is an o-xylene, m-xylene, a mixture of o-xylene and m-xylene, or a mixture of o-xylene, p-xylene, and m-xylene.

[0024] In this invention, the reaction effect is better when the content of p-xylene is less than 15% when a mixture of o-xylene, p-xylene, and m-xylene is used as a raw material.

[0025] Example 4: As an optimization of the above examples, the catalyst is a modified zeolite molecular sieve, including one or more of mordenite, β molecular sieve, ZSM-11 molecular sieve, MCM-22 molecular sieve, HZSM-5 molecular sieve, and MCM-49 molecular sieve.

[0026] Example 5: As an optimization of Example 4 above, the modifying metal of the catalyst is Co, Mg, Ni, Zn, Cu, Mo, or Ga. In this invention, the catalyst modification can be carried out using oxides of the above-mentioned metals or their soluble salts, and the preferred modifying metals of the catalyst are Mg, Zn, and Mo.

[0027] Example 6: As an optimization of Example 4 above, the metal content in the catalyst is 0.1 wt% to 6 wt%.

[0028] Example 7: As an optimization of Example 4 above, the silica-alumina molar ratio of the modified zeolite molecular sieve is 15 to 300.

[0029] The modified zeolite molecular sieve in this invention is prepared by modifying the zeolite molecular sieve with metal and then modifying its outer surface acidity and pores with siloxane reagent. The preparation process is as follows: (1) The molecular sieve powder is subjected to NH4 + (1) Ion exchange, washing, and calcination are used to prepare acidic zeolite molecular sieves; (2) A certain concentration of soluble metal salt solution is prepared to impregnate and modify the acidic zeolite molecular sieves to obtain metal-modified zeolite molecular sieves. The impregnation time is 3h to 12h; (3) The surface of the metal-modified zeolite molecular sieves obtained in step (2) is modified with siloxane reagent to modulate the acidity and pore structure of the catalyst surface to obtain a metal and silanization co-modified catalyst; (4) The modified catalyst prepared in step (3) is extruded, calcined, and then used.

[0030] Example 8: As Figure 1As shown, the apparatus for producing benzene and mesitylene from xylene includes a reactor 1, a separator 2, and a crystallizer 3. A raw material pipeline 4 is fixedly installed at the feed end of the reactor 1. A first product pipeline 5 is fixedly installed between the discharge end of the reactor 1 and the feed end of the separator 2. A second product pipeline 6 is fixedly installed between the first discharge end of the separator 2 and the feed end of the crystallizer 3. A third product pipeline 7 is fixedly installed at the second discharge end of the separator 2. A mesitylene product pipeline 8 is fixedly installed at the first discharge end of the crystallizer 3. A reflux pipeline 9 is fixedly installed between the second discharge end of the crystallizer 3 and the raw material pipeline 4. A catalyst bed 10 is provided inside the reactor 1.

[0031] In this invention, reactor 1 can be a fixed-bed or moving-bed reactor. Xylene, the raw material, enters reactor 1 via feed line 4, reacts with the catalyst, and completes the alkyl transfer process. The resulting reaction product enters separator 2, and the separated toluene is discharged via third product line 7. The mixture of xylene and mesitylene enters crystallizer 3 via second product line 6, where it is freeze-crystallized to obtain mesitylene product. Unreacted xylene enters reactor 1 via a circulation line to continue the reaction.

[0032] Example 9:

[0033] HZSM-5 molecular sieve catalyst with a silica-alumina molar ratio of 30 and 2% Ni loading was used in alkylation reactor 1 with o-xylene as feedstock. The reaction temperature was 380℃, the pressure was 0.5 MPa, and the total feed space velocity was 1 h⁻¹. -1 In reactor 1, o-xylene undergoes an alkyl transfer reaction, yielding a mixture of toluene, xylene, and mesitylene. This mixture is then cryogenically crystallized to obtain mesitylene, while the unreacted xylene is used as a raw material for further reaction. The product distribution during stable catalyst operation in this embodiment is shown in Table 1.

[0034] Example 10:

[0035] HZSM-5 molecular sieve catalyst with a silica-alumina molar ratio of 60 and 3% Zn loading was used in alkylation reactor 1 with m-xylene as feedstock. The reaction temperature was 400℃, the pressure was 1.0 MPa, and the total feed space velocity was 1 h⁻¹. -1 In reactor 1, m-xylene undergoes an alkyl transfer reaction, yielding a mixture of benzene, xylene, and mesitylene. This mixture is then cryogenically crystallized to obtain mesitylene, while unreacted xylene is used as a raw material for further reaction. The product distribution during stable catalyst operation in this embodiment is shown in Table 1.

[0036] Example 11:

[0037] HZSM-5 molecular sieve and ZSM-11 molecular sieve with a silica-alumina molar ratio of 60 were graded as catalysts. o-Xylene was used as the feedstock in alkylation reactor 1, with a reaction temperature of 320℃, a pressure of 2.0 MPa, and a total feed space velocity of 1 h⁻¹. -1 In reactor 1, o-xylene undergoes an alkyl transfer reaction, yielding a mixture of benzene, xylene, and mesitylene. This mixture is then cryogenically crystallized to obtain mesitylene, while unreacted xylene is used as a raw material for further reaction. The product distribution during stable catalyst operation in this embodiment is shown in Table 1.

[0038] Example 12:

[0039] HZSM-5 molecular sieves with a silica-alumina molar ratio of 60 and β-molecular sieves were used as catalysts. In alkylation reactor 1, m-xylene and p-xylene were used as feedstocks in a 1:1 mass ratio. The reaction temperature was 360℃, the pressure was 2.0 MPa, and the total feed space velocity was 1 h⁻¹. -1 In reactor 1, xylene undergoes an alkyl transfer reaction, yielding a mixture of benzene, xylene, and mesitylene. This mixture is then cryogenically crystallized to obtain mesitylene, while the unreacted xylene is used as a raw material for further reaction. The product distribution during stable catalyst operation in this embodiment is shown in Table 1.

[0040] Example 13:

[0041] HZSM-5 molecular sieve catalyst with a silica-alumina molar ratio of 80 was used in alkylation reactor 1 with m-xylene and o-xylene in a mass ratio of 1:1 as raw materials. The reaction temperature was 420℃, the pressure was 3.0 MPa, and the total feed mass hourly space velocity was 1 h⁻¹. -1 In reactor 1, xylene undergoes an alkyl transfer reaction, yielding a mixture of benzene, xylene, and mesitylene. This mixture is then cryogenically crystallized to obtain mesitylene, while the unreacted xylene is used as a raw material for further reaction. The product distribution during stable catalyst operation in this embodiment is shown in Table 1.

[0042] Example 14:

[0043] Using a 6% magnesium-modified ZSM-11 molecular sieve catalyst, m-xylene and o-xylene were used as feedstock in alkylation reactor 1 at a mass ratio of 1:2. The reaction temperature was 380℃, the pressure was 2.5 MPa, and the total feed space velocity was 1 h⁻¹. -1 The raw materials undergo an alkyl transfer reaction in reactor 1, yielding a mixture of benzene, xylene, and mesitylene. This mixture is then cryogenically crystallized to obtain mesitylene, while the unreacted xylene is used as a raw material for further reaction. The product distribution during stable catalyst operation in this embodiment is shown in Table 1.

[0044] Example 15:

[0045] HZSM-5 molecular sieve with a silica-alumina molar ratio of 150 and ZSM-11 were graded and used as catalysts. In alkylation reactor 1, o-xylene and m-xylene were used as feedstocks in a 1:1 mass ratio. The reaction temperature was 400 °C, the pressure was 2.0 MPa, and the total feed space velocity was 1 h⁻¹. -1 The raw materials undergo an alkyl transfer reaction in reactor 1, yielding a mixture of benzene, xylene, and mesitylene. This mixture is then cryogenically crystallized to obtain mesitylene, while the unreacted xylene is used as a raw material for further reaction. The product distribution during stable catalyst operation in this embodiment is shown in Table 1.

[0046] Example 16:

[0047] HZSM-5 molecular sieve with a silica-alumina molar ratio of 150 and MCM-22 were graded and used as catalysts. In alkylation reactor 1, m-xylene, o-xylene, and p-xylene were used as feedstocks in a mass ratio of 1:1:1. The reaction temperature was 440℃, the pressure was 3.0 MPa, and the total feed space velocity was 1 h⁻¹. -1 In reactor 1, xylene undergoes an alkyl transfer reaction, yielding a mixture of benzene, xylene, and mesitylene. This mixture is then cryogenically crystallized to obtain mesitylene, while the unreacted xylene is used as a raw material for further reaction. The product distribution during stable catalyst operation in this embodiment is shown in Table 1.

[0048] Example 17:

[0049] Using a 1% nickel-modified MCM-49 catalyst, alkylation reactor 1 employed m-xylene, o-xylene, and p-xylene as feedstocks in a mass ratio of 6:2:1. The reaction temperature was 350℃, the pressure was 4.0 MPa, and the total feed space velocity was 0.8 h⁻¹. -1 Xylene undergoes an alkyl transfer reaction in reactor 1, yielding a mixture of benzene, xylene, and mesitylene. This mixture is then cryogenically crystallized to obtain mesitylene, while unreacted xylene is used as a raw material for further reaction. The product distribution during stable catalyst operation in this embodiment is shown in Table 1.

[0050] Example 18:

[0051] Using a 2% magnesium-modified MCM-22 catalyst, alkylation reactor 1 was used with m-xylene, o-xylene, and p-xylene as feedstock in a mass ratio of 6:2:1. The reaction temperature was 320℃, the pressure was 4.0 MPa, and the total feed space velocity was 0.8 h⁻¹. -1In reactor 1, xylene undergoes an alkyl transfer reaction, yielding a mixture of benzene, xylene, and mesitylene. This mixture is then cryogenically crystallized to obtain mesitylene, while the unreacted xylene is used as a raw material for further reaction. The product distribution during stable catalyst operation in this embodiment is shown in Table 1.

[0052] This invention provides a method for producing benzene and mesitylene from xylene. The product generated by this method has a stable composition and high selectivity for mesitylene. As shown in Table 1, the selectivity for mesitylene is between 52% and 64%.

[0053] In summary, the method for producing benzene and mesitylene using xylene as a raw material according to the present invention produces products with stable composition and high selectivity for mesitylene. Under certain catalyst and reaction conditions, benzene and mesitylene can be produced in a controllable manner without the formation of anhydrous substances. Compared with existing technologies, the present invention uses xylene directly for the reaction to produce benzene and mesitylene, resulting in stable product composition. It avoids the problem of acidic water formation caused by using methanol as a raw material, thereby improving production efficiency and reducing production costs.

[0054] The above technical features constitute the embodiments of the present invention, which have strong adaptability and implementation effect. Unnecessary technical features can be added or removed according to actual needs to meet the needs of different situations.

[0055]

Claims

1. A method for producing benzene and mesitylene from xylene, characterized in that... The process is as follows: xylene, the raw material, undergoes an alkyl transfer reaction catalyzed by a catalyst in a reactor. The reaction products are separated to obtain a xylene-meta-tetramethylene mixture and benzene. The xylene-meta-tetramethylene mixture is then frozen and crystallized to obtain meta-tetramethylene. The alkyl transfer reaction was carried out at a reaction temperature of 300°C to 500°C, a reaction pressure of 0.1 MPa to 5 MPa, and a xylene volume hourly space velocity of 0.5 h⁻¹. -1 up to 6h -1 Under the conditions; The catalyst is a modified zeolite molecular sieve, including one or more of ZSM-11 molecular sieve, MCM-22 molecular sieve, HZSM-5 molecular sieve, and MCM-49 molecular sieve, with the modified metal being Mg, Ni, or Zn; or the catalyst is obtained by grading HZSM-5 molecular sieve with ZSM-11 molecular sieve, β molecular sieve, or MCM-22 molecular sieve; or the catalyst is HZSM-5 molecular sieve with a silica-alumina molar ratio of 80.

2. The method for producing benzene and mesitylene from xylene according to claim 1, characterized in that... Xylene is a mixture of o-xylene, m-xylene, o-xylene-m-xylene, or o-xylene-p-xylene-m-xylene.

3. The method for producing benzene and mesitylene from xylene according to claim 1 or 2, characterized in that... The metal content in the catalyst ranges from 0.1 wt% to 6 wt%.

4. The method for producing benzene and mesitylene from xylene according to claim 1 or 2, characterized in that... The silica-alumina molar ratio of the modified zeolite molecular sieve is 15 to 300.

5. The method for producing benzene and mesitylene from xylene according to claim 1, characterized in that... The following apparatus is used: a reactor, a separator, and a crystallizer. A raw material pipeline is fixedly installed at the feed end of the reactor. A first product pipeline is fixedly installed between the discharge end of the reactor and the feed end of the separator. A second product pipeline is fixedly installed between the first discharge end of the separator and the feed end of the crystallizer. A third product pipeline is fixedly installed at the second discharge end of the separator. A mesitylene product pipeline is fixedly installed at the first discharge end of the crystallizer. A reflux pipeline is fixedly installed between the second discharge end of the crystallizer and the raw material pipeline. A catalyst bed is provided inside the reactor.

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