Process for the synthesis of m-chlorotoluene by heterogeneous catalytic isomerization

Abstract

The application discloses a method for synthesizing meta-chlorotoluene through heterogeneous catalytic isomerization, and has the advantages of stable catalyst, easy recovery, green sustainability, high selectivity of the product meta-chlorotoluene and the like, and is a method for synthesizing meta-chlorotoluene with wide prospects. The method comprises the following steps: filling modified HZSM-5 molecular sieve into a fixed bed reaction constant temperature area and placing the fixed bed reaction constant temperature area in an inert atmosphere, feeding a mixture of raw material p-chlorotoluene and a diluent into the fixed bed reactor through a constant flow pump for preheating and vaporization, and then performing catalytic isomerization reaction in the fixed bed reaction constant temperature area, and collecting the product meta-chlorotoluene after condensation.

Description

Technical Field

[0001] This invention relates to a method for synthesizing m-chlorotoluene, and more specifically to a method for synthesizing m-chlorotoluene by heterogeneous catalytic isomerization. Background Technology

[0002] The synthesis methods of m-chlorotoluene can be divided into three categories based on the raw materials: direct chlorination of toluene, m-nitrotoluene, and m-cresol. The direct chlorination method uses toluene and chlorine as raw materials and can produce chlorotoluene in one step. However, this method mainly produces o-chlorotoluene and p-chlorotoluene, with a low yield of m-chlorotoluene, less than 1%. The m-nitrotoluene method involves multiple steps, resulting in a long process flow and generating large amounts of wastewater, causing serious environmental pollution. The m-cresol method synthesizes m-chlorotoluene from m-cresol and phosphorus pentachloride, but the raw materials are expensive, leading to high production costs. Currently, the production processes of m-chlorotoluene suffer from low yields, complex processes, high production costs, and serious environmental pollution, necessitating the development of an efficient and environmentally friendly synthesis method.

[0003] Isomerization is a chemical reaction that generally refers to the change in the position of atoms or groups in an organic compound molecule without altering its composition and molecular weight, and is often carried out in the presence of a catalyst. As mentioned earlier, the direct chlorination of toluene to synthesize m-chlorotoluene is a simple process, but the yield is low, and the product is mainly an isomer of m-chlorotoluene. If m-chlorotoluene could be synthesized from chlorotoluene isomers through isomerization, it would solve the problems of low yield, complex process, and high raw material costs associated with the current m-chlorotoluene process. Research on isomerization processes began in the 1970s, initially using alumina as a catalyst. By the 1990s, molecular sieve catalysts were widely studied, and currently, several mature isomerization routes exist, such as isobutene isomerization, xylene isomerization, and C5 / C6 isomerization. Multiple facilities have been built and are being widely applied. Simultaneously, research on isomerization catalysts has become a hot topic, and isomerization technology has experienced rapid development.

[0004] In the prior art, invention patent CN102304011B discloses a method for producing pseudotrimethylbenzene by isomerization of C9 aromatics. The raw materials, methyltrimethylbenzene and mesitylene, are used to prepare pseudotrimethylbenzene in an isomerization reactor under the catalysis of a molecular sieve, achieving a single-pass conversion rate of 45%, thus improving the yield of pseudotrimethylbenzene. Invention patent CN107311837A discloses a method for preparing m-dichlorobenzene by isomerization of o-dichlorobenzene. o-dichlorobenzene is isomerized to o-dichlorobenzene under the action of a modified molecular sieve catalyst, increasing the o-dichlorobenzene conversion rate to over 70%. Invention patent CN115090322A discloses a method for producing m-dichlorobenzene from o-dichlorobenzene catalyzed by rare earth metal-modified molecular sieves. ZSM-5 is modified with rare earth metal gadolinium, and m-dichlorobenzene is generated through an isomerization reaction, where the o-dichlorobenzene conversion rate is increased to over 50%, and the m-dichlorobenzene selectivity reaches 79.4%. Isomerization processes have been studied and applied in various product processes due to their numerous advantages: ① significantly increasing the yield of the target product, ② fully and effectively utilizing by-products to improve economic value, and ③ fewer steps and simpler processes. Researchers have also invented related technologies for the m-chlorotoluene isomer. Patent CN11209417B discloses a method for synthesizing m-chlorotoluene via an isomerization reaction, using p-chlorotoluene as a raw material and isomerizing it in the presence of a homogeneous Lewis acid catalyst to obtain m-chlorotoluene. In this method, the Lewis acid catalyst is AlCl3, which has good catalytic activity, but the catalyst needs to be removed by washing with water after the reaction, generating a large amount of acidic wastewater containing chloride ions, which is difficult to treat and causes serious environmental pollution.

[0005] In summary, isomerization is a promising process for the synthesis of m-chlorotoluene. However, current research on catalytic isomerization for m-chlorotoluene is limited, and existing techniques suffer from challenges such as difficulties in separating homogeneous catalysts, high post-processing costs, and environmental pollution. Therefore, there is a need to develop an efficient, green, and sustainable method for the synthesis of m-chlorotoluene. Summary of the Invention

[0006] This invention addresses the problems and shortcomings of existing technologies by providing a heterogeneous catalytic isomerization method for synthesizing m-chlorotoluene. This method has advantages such as stable and easily recoverable catalyst, green and sustainable production, and high selectivity for the product m-chlorotoluene, making it a promising method for synthesizing m-chlorotoluene.

[0007] This invention is achieved through the following technical solution:

[0008] The method for heterogeneous catalytic isomerization synthesis of m-chlorotoluene according to the present invention includes the following steps:

[0009] Modified HZSM-5 molecular sieves were packed into the isothermal zone of a fixed-bed reactor under an inert atmosphere. A mixture of p-chlorotoluene and diluent was first pumped to the preheating of the fixed-bed reactor for vaporization, and then carried out a catalytic isomerization reaction in the isothermal zone of the fixed-bed reactor. After condensation, the product m-chlorotoluene was collected.

[0010] The method for synthesizing m-chlorotoluene via heterogeneous catalytic isomerization described above in this invention further comprises an ion exchange method for modifying the HZSM-5 molecular sieve, including the following steps: preparing a 0.5–5 wt% metal nitrate solution; placing the molecular sieve in the prepared solution; stirring in a constant temperature water bath at 70–100°C for at least 2 hours to perform ion exchange; repeating the exchange three times; washing away nitrate ions with deionized water after filtration; drying after filtration at 60–120°C; and finally calcining at 300°C–600°C for 1–6 hours to obtain the modified HZSM-5 molecular sieve. A further technical solution is that the metal is one or a combination of Zn, Ce, and La.

[0011] The method for heterogeneous catalytic isomerization synthesis of m-chlorotoluene described above in this invention may further include the carrier gas of the inert atmosphere being one of N2, Ar, or He; and the diluent being one of benzene, toluene, or chlorobenzene.

[0012] A further technical solution of the heterogeneous catalytic isomerization method for synthesizing m-chlorotoluene described above in this invention may be that the mass ratio of the raw material p-chlorotoluene to the diluent is 0.5:1 to 2:1; the preheater temperature is 150 to 300°C; the fixed-bed reaction temperature is 250 to 400°C; and the constant flow pump delivers the reaction liquid at a volume hourly space velocity of 0.3 to 1 h⁻¹. -1 The isomerization reaction pressure is slightly positive; the condensation method is a 25°C circulating water condensation method.

[0013] Compared with the prior art, the present invention has the following advantages:

[0014] (1) The present invention uses p-chlorotoluene as raw material to catalytically isomerize to obtain m-chlorotoluene. The p-chlorotoluene conversion rate and m-chlorotoluene selectivity are high, with the p-chlorotoluene conversion rate reaching more than 69% and the m-chlorotoluene selectivity reaching more than 80%.

[0015] (2) The catalyst of the present invention is a heterogeneous solid catalyst. Compared with the homogeneous catalytic process, the catalyst of the present invention is easy to separate, has less corrosiveness to equipment, has high reaction safety, and can be continuously produced.

[0016] (3) The process of this invention will not generate metal pollution or wastewater, thus meeting the standards of green chemistry and conforming to the strategic goal of sustainable development. Detailed Implementation

[0017] Example 1 (HZSM-5 molecular sieve modification)

[0018] HZSM-5 molecular sieve was modified by ion exchange. A 0.076 mol / L zinc nitrate solution was prepared, and the HZSM-5 molecular sieve was added to the prepared solution. The mixture was stirred at 80°C for 2 hours for ion exchange. 100 ml of metal salt solution was taken for each exchange, and the process was repeated three times. The mixture was dried in an oven at 110°C and then calcined in a muffle furnace at 450°C. After cooling to room temperature, the mixture was removed and stored to prepare a 0.5% Zn / HZ molecular sieve catalyst.

[0019] Example 2 (HZSM-5 molecular sieve modification)

[0020] HZSM-5 molecular sieve was modified by ion exchange. A 0.153 mol / L zinc nitrate solution was prepared, and the HZSM-5 molecular sieve was added to the prepared solution. The mixture was stirred at 90°C for 2 hours for ion exchange. 100 ml of metal salt solution was taken for each exchange, and the process was repeated three times. The mixture was dried in an oven at 120°C and then calcined in a muffle furnace at 500°C. After cooling to room temperature, the mixture was removed and stored to prepare a 1% Zn / HZ molecular sieve catalyst.

[0021] Example 3 (HZSM-5 molecular sieve modification)

[0022] HZSM-5 molecular sieve was modified by ion exchange. A 0.383 mol / L zinc nitrate solution was prepared, and the HZSM-5 molecular sieve was added to the prepared solution. The mixture was stirred at 100°C for 1 hour for ion exchange. 100 ml of metal salt solution was taken for each exchange, and the process was repeated three times. The mixture was dried in an oven at 80°C and then calcined in a muffle furnace at 400°C. After cooling to room temperature, the mixture was removed and stored to prepare a 3% Zn / HZ molecular sieve catalyst.

[0023] Example 4 (HZSM-5 molecular sieve modification)

[0024] HZSM-5 molecular sieve was modified by ion exchange. A 0.071 mol / L cerium nitrate solution was prepared, and the HZSM-5 molecular sieve was added to the prepared mixed solution. The mixture was stirred at 80°C for 3 hours for ion exchange. 100 ml of metal salt solution was taken for each exchange, and the process was repeated three times. The mixture was dried in an oven at 100°C and finally calcined in a muffle furnace at 550°C. After cooling to room temperature, the mixture was removed and stored to prepare a 1% Ce / HZ molecular sieve catalyst.

[0025] Example 5 (Synthesis of m-chlorotoluene)

[0026] The modified HZSM-5 molecular sieve prepared in Example 1 was used as a catalyst for the isomerization synthesis of m-chlorotoluene, wherein the mass ratio of p-chlorotoluene to chlorobenzene was 1:1, and the liquid hourly space velocity (LHSV) was 0.3 h⁻¹. -1 The gas is heated and vaporized in a preheater at a vaporization temperature of 200℃, and the reaction temperature is 350℃. N2 is used as the carrier gas, and the carrier gas space velocity is 360 h⁻¹. -1 The isomerization reaction was carried out, with a conversion rate of 69.49% for p-chlorotoluene and a selectivity of 70.09% for m-chlorotoluene.

[0027] Example 6 (Synthesis of m-chlorotoluene)

[0028] The modified HZSM-5 molecular sieve prepared in Example 1 was used as a catalyst for the isomerization synthesis of m-chlorotoluene, wherein the mass ratio of p-chlorotoluene to chlorobenzene was 1.5:1, and the liquid hourly space velocity (LHSV) was 0.5 h⁻¹. -1 The gas is heated and vaporized in a preheater at a vaporization temperature of 200℃, and the reaction temperature is 310℃. N2 is used as the carrier gas with a carrier gas space velocity of 360 h⁻¹. -1 The isomerization reaction was carried out, with a conversion rate of 59.45% for p-chlorotoluene and a selectivity of 74.34% for m-chlorotoluene.

[0029] Example 7 (Synthesis of m-chlorotoluene)

[0030] The modified HZSM-5 molecular sieve prepared in Example 2 was used as a catalyst for the isomerization synthesis of m-chlorotoluene, wherein the mass ratio of p-chlorotoluene to chlorobenzene was 1:1, and the liquid hourly space velocity (LHSV) was 0.5 h⁻¹. -1 The gas is heated and vaporized in a preheater at a vaporization temperature of 200℃, and the reaction temperature is 330℃. N2 is used as the carrier gas with a space velocity of 360 h⁻¹. -1 The isomerization reaction was carried out, with a conversion rate of 48.96% for p-chlorotoluene and a selectivity of 80.24% for m-chlorotoluene.

[0031] Example 8 (Synthesis of m-chlorotoluene)

[0032] The modified HZSM-5 molecular sieve prepared in Example 2 was used as a catalyst for the isomerization synthesis of m-chlorotoluene, wherein the mass ratio of p-chlorotoluene to chlorobenzene was 1.5:1, and the liquid hourly space velocity (LHSV) was 0.5 h⁻¹. -1 The gas is heated and vaporized in a preheater at a vaporization temperature of 200℃, and the reaction temperature is 310℃. N2 is used as the carrier gas with a carrier gas space velocity of 360 h⁻¹. -1 The isomerization reaction was carried out, with a conversion rate of 50.35% for p-chlorotoluene and a selectivity of 77.82% for m-chlorotoluene.

[0033] Example 9 (Synthesis of m-chlorotoluene)

[0034] The modified HZSM-5 molecular sieve prepared in Example 2 was used as a catalyst for the isomerization synthesis of m-chlorotoluene, wherein the mass ratio of p-chlorotoluene to chlorobenzene was 1:1, and the liquid hourly space velocity (LHSV) was 0.8 h⁻¹. -1 The gas is heated and vaporized in a preheater at a vaporization temperature of 200℃, and the reaction temperature is 310℃. N2 is used as the carrier gas with a carrier gas space velocity of 360 h⁻¹. -1 The isomerization reaction was carried out, with a conversion rate of 46.86% for p-chlorotoluene and a selectivity of 75.23% for m-chlorotoluene.

[0035] Example 10 (Synthesis of m-chlorotoluene)

[0036] The modified HZSM-5 molecular sieve prepared in Example 2 was used as a catalyst for the isomerization synthesis of m-chlorotoluene, wherein the mass ratio of p-chlorotoluene to chlorobenzene was 1:1, and the liquid hourly space velocity (LHSV) was 0.5 h⁻¹. -1 The gas is heated and vaporized in a preheater at a vaporization temperature of 200℃, and the reaction temperature is 330℃. N2 is used as the carrier gas with a space velocity of 300 h⁻¹. -1 The isomerization reaction was carried out, with a conversion rate of 51.65% for p-chlorotoluene and a selectivity of 75.28% for m-chlorotoluene.

[0037] Example 11 (Synthesis of m-chlorotoluene)

[0038] The modified HZSM-5 molecular sieve prepared in Example 3 was used as a catalyst for the isomerization synthesis of m-chlorotoluene, wherein the mass ratio of p-chlorotoluene to chlorobenzene was 1:1, and the liquid hourly space velocity (LHSV) was 0.5 h⁻¹. -1 The gas is heated and vaporized in a preheater at a vaporization temperature of 200℃, and the reaction temperature is 310℃. N2 is used as the carrier gas with a carrier gas space velocity of 360 h⁻¹. -1 The isomerization reaction was carried out, with a conversion rate of 46.23% for p-chlorotoluene and a selectivity of 80.57% for m-chlorotoluene.

[0039] Example 12 (Synthesis of m-chlorotoluene)

[0040] The modified HZSM-5 molecular sieve prepared in Example 3 was used as a catalyst for the isomerization synthesis of m-chlorotoluene, wherein the mass ratio of p-chlorotoluene to chlorobenzene was 1:1, and the liquid hourly space velocity (LHSV) was 0.5 h⁻¹. -1 After being heated and vaporized in a preheater at a vaporization temperature of 200℃, the reaction temperature was 310℃, with N2 as the carrier gas and a carrier gas space velocity of 240 h⁻¹. -1 The isomerization reaction was carried out, with a conversion rate of 44.95% for p-chlorotoluene and a selectivity of 81.60% for m-chlorotoluene.

[0041] Example 13 (Synthesis of m-chlorotoluene)

[0042] The modified HZSM-5 molecular sieve prepared in Example 3 was used as a catalyst for the isomerization synthesis of m-chlorotoluene, wherein the mass ratio of p-chlorotoluene to chlorobenzene was 1:1.5, and the liquid hourly space velocity (LHSV) was 0.5 h⁻¹. -1 The gas is heated and vaporized in a preheater at a vaporization temperature of 200℃, and the reaction temperature is 330℃. N2 is used as the carrier gas with a space velocity of 360 h⁻¹. -1 The isomerization reaction was carried out, with a conversion rate of 50.84% ​​for p-chlorotoluene and a selectivity of 76.68% for m-chlorotoluene.

[0043] Example 14 (Synthesis of m-chlorotoluene)

[0044] The modified HZSM-5 molecular sieve prepared in Example 4 was used as a catalyst for the isomerization synthesis of m-chlorotoluene, wherein the mass ratio of p-chlorotoluene to chlorobenzene was 1:1, and the liquid hourly space velocity (LHSV) was 0.5 h⁻¹. -1 The gas is heated and vaporized in a preheater at a vaporization temperature of 200℃, and the reaction temperature is 310℃. N2 is used as the carrier gas with a carrier gas space velocity of 360 h⁻¹. -1 The isomerization reaction was carried out, with a conversion rate of 50.23% for p-chlorotoluene and a selectivity of 77.66% for m-chlorotoluene.

[0045] Comparative Example 1

[0046] Isomerization evaluation experiments were conducted using Lewis acid AlCl3 as a catalyst. The isomerization reaction was carried out in a three-necked flask in a constant temperature oil bath, with a mass ratio of p-chlorotoluene to chlorobenzene of 1:1, a reaction temperature of 120℃, and a catalyst amount of 3%. After two hours of reaction, the conversion rate of p-chlorotoluene was 51.35%, and the selectivity of m-chlorotoluene was 70.16%.

[0047] Table 1 Summary of Application Results

[0048] Serial Number Example p-Chlorotoluene conversion rate % m-Chlorotoluene selectivity % m-Chlorotoluene yield % 1 Example 5 69.54 70.09 48.74 2 Example 6 59.45 74.34 44.19 3 Example 7 48.96 80.24 39.28 4 Example 8 50.35 77.82 39.18 5 Example 9 46.86 75.23 35.25 6 Example 10 51.65 75.28 38.88 7 Example 11 46.23 80.57 37.24 8 Example 12 44.95 81.60 36.67 9 Example 13 50.84 76.68 38.98 10 Example 14 50.23 77.66 39.00 11 Comparative Example 1 51.35 70.16 36.03

Claims

1. A method for heterogeneous catalytic isomerization to synthesize m-chlorotoluene, characterized in that, Includes the following steps: Modified HZSM-5 molecular sieves were packed into the isothermal zone of a fixed-bed reactor under an inert atmosphere. The mixture of p-chlorotoluene and diluent was first pumped to the preheating of the fixed-bed reactor for vaporization via a constant flow pump. Then, a catalytic isomerization reaction was carried out in the isothermal zone of the fixed-bed reactor. After condensation, the product m-chlorotoluene was collected. The modification method for the modified HZSM-5 molecular sieve is an ion exchange method, comprising the following steps: preparing a metal nitrate solution with a content of 0.5~5wt%; placing the molecular sieve in the prepared solution; stirring in a constant temperature water bath at 70-100℃ for more than 2 hours to carry out ion exchange; repeating the exchange three times; after the exchange, washing away nitrate ions with deionized water; drying after filtration separation at 60~120℃; and finally calcining at 300℃~600℃ for 1~6 h to obtain the modified HZSM-5 molecular sieve. The metal is one or a combination of Zn, Ce, and La; the mass ratio of the raw material p-chlorotoluene to the diluent is 0.5:1~2:1; the preheater temperature is 150~300℃; the fixed bed reaction temperature is 250~400℃; and the constant flow pump delivers the reaction liquid at a volume hourly space velocity of 0.3~1 h. -1 The isomerization reaction pressure is slightly positive; the condensation method is a 25°C circulating water condensation method.

2. The method for heterogeneous catalytic isomerization synthesis of m-chlorotoluene according to claim 1, characterized in that, The carrier gas of the inert atmosphere is one of N2, Ar or He; the diluent is one of benzene, toluene or chlorobenzene.