Method for synthesizing m-chlorotoluene through heterogeneous catalytic isomerization

Abstract

The invention discloses a method for synthesizing m-chlorotoluene through heterogeneous catalytic isomerization, and the method has the advantages of stable and easy recovery of a catalyst, greenness, sustainability, high selectivity of the product m-chlorotoluene, and the like, and is a m-chlorotoluene synthesis method with a wide prospect. The method for synthesizing m-chlorotoluene through heterogeneous catalytic isomerization comprises the following steps: filling a fixed bed reaction constant-temperature area with a modified HZSM-5 molecular sieve, in an inert atmosphere, conveying a mixture of raw materials parachlorotoluene and a diluent to a fixed bed reactor through a constant-flow pump, preheating, and vaporizing; and carrying out catalytic isomerization reaction in a constant-temperature area of the fixed bed reactor, condensing, and collecting to obtain the product m-chlorotoluene.

Description

Technical Field

[0001] The invention relates to a method for synthesizing meta-chlorotoluene, and more specifically to a method for synthesizing meta-chlorotoluene by heterogeneous catalytic isomerization. Background Art

[0002] The synthesis method of m-chlorotoluene can be divided into toluene direct chlorination method, m-nitrotoluene method and m-cresol method according to different raw materials. Among them, the toluene direct chlorination method uses toluene and chlorine as raw materials, and can produce chlorotoluene in one step, but the products of this method are mostly o-chlorotoluene and p-chlorotoluene, and the yield of m-chlorotoluene is low, less than 1%; the m-nitrotoluene method produces m-chlorotoluene through a multi-step process, the process is long and produces a large amount of wastewater, and the environmental pollution is serious; the m-cresol method synthesizes m-chlorotoluene by reacting m-cresol and phosphorus pentachloride, but the raw materials used are expensive and the production cost is high. At present, the production process of m-chlorotoluene has problems such as low yield, complex process, high production cost and serious environmental pollution. It is urgent to develop an efficient and green and environmentally friendly synthesis method of m-chlorotoluene.

[0003] Isomerization is a chemical reaction, generally referring to the change of the position of atoms or groups in the molecules of organic compounds without changing their composition and molecular weight, and is often carried out in the presence of a catalyst. As can be seen from the previous article, the process of synthesizing meta-chlorotoluene by direct chlorination of toluene is simple, but the yield is low, and the product is mainly the isomers of meta-chlorotoluene. If meta-chlorotoluene can be synthesized from chlorotoluene isomers through isomerization reaction, the current problems of low yield of meta-chlorotoluene process, complex process and high cost of raw materials will be solved. The research on isomerization process started in the 1970s, and alumina was used as a catalyst. By the 1990s, molecular sieve catalysts began to be widely studied. At present, there are many mature routes for isomerization process, such as isobutylene isomerization, xylene isomerization and C5 / C6 isomerization, and many sets of equipment have been built and promoted. At the same time, the research on isomerization catalysts has gradually become a hot topic, and isomerization technology has also ushered in a booming development.

[0004] In the prior art, the invention patent with publication number CN102304011B discloses a method for producing trimethylol from C9 aromatics by isomerization. Trimethylol and mesitylene are used as raw materials to prepare trimethylol in an isomerization reactor under the catalytic action of molecular sieves. The single-pass conversion rate reaches 45%, which improves the yield of trimethylol. The invention patent with publication number CN107311837A discloses a method for preparing meta-dichlorobenzene by isomerization of o-dichlorobenzene. o-dichlorobenzene is isomerized to produce o-dichlorobenzene under the action of modified molecular sieve catalyst, and the conversion rate of o-dichlorobenzene is increased to more than 70%. The invention patent with publication number CN115090322A discloses a method for preparing meta-dichlorobenzene by catalyzing o-dichlorobenzene with rare earth metal modified molecular sieves. ZSM-5 is modified with rare earth metal gadolinium and isomerized to produce meta-dichlorobenzene. The conversion rate of o-dichlorobenzene is increased to more than 50%, and the selectivity of meta-dichlorobenzene can reach 79.4%. The isomerization process has many advantages: ① significantly improve the yield of the target product, ② fully and effectively utilize the by-products to improve the economic value, ③ few steps and simple process, and has been studied and applied in multiple product processes. For meta-chlorotoluene isomers, researchers have also invented related technologies. The invention patent with publication number CN11209417B discloses a method for synthesizing meta-chlorotoluene by isomerization reaction, using para-chlorotoluene as a raw material, and isomerizing meta-chlorotoluene in the presence of a homogeneous catalyst Lewis acid. In this method, the Lewis acid catalyst is AlCl3. Although it has good catalytic activity, the catalyst needs to be removed by washing with water after the reaction, producing a large amount of acidic wastewater with chloride ions, which is difficult to handle and seriously pollutes the environment.

[0005] In summary, the preparation of m-chlorotoluene by isomerization process is a promising process route, but there are few studies on the preparation of m-chlorotoluene by catalytic isomerization. The main research technology has problems such as difficulty in separating homogeneous catalysts, high post-processing costs, and environmental pollution. Therefore, it is necessary to develop an efficient, green, and sustainable method for synthesizing m-chlorotoluene. Summary of the invention

[0006] In view of the problems and shortcomings of the prior art, the present invention provides a method for synthesizing meta-chlorotoluene by heterogeneous catalytic isomerization. The method has the advantages of stable and easy recovery of the catalyst, green and sustainable, high selectivity of the product meta-chlorotoluene, etc., and is a method for synthesizing meta-chlorotoluene with broad prospects.

[0007] The present invention is achieved through the following technical solutions:

[0008] The method for synthesizing meta-chlorotoluene by heterogeneous catalytic isomerization of the present invention comprises the following steps:

[0009] The modified HZSM-5 molecular sieve is filled in the fixed bed reaction constant temperature area and placed under an inert atmosphere. The mixture of the raw material para-chlorotoluene and the diluent is first transported to the preheating of the fixed bed reactor by a constant flow pump for vaporization, and then a catalytic isomerization reaction is carried out in the constant temperature area of ​​the fixed bed reactor. After condensation, the product meta-chlorotoluene is collected.

[0010] The method for synthesizing meta-chlorotoluene by heterogeneous catalytic isomerization of the present invention has a further technical solution that the modification method of 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 70-100°C constant temperature water bath for more than 2 hours for ion exchange, exchanging three times in total, filtering and washing nitrate ions with deionized water after exchange, drying after separation by suction filtration, the drying temperature is 60-120°C, and finally roasting at a temperature of 300°C-600°C for 1-6h to obtain the modified HZSM-5 molecular sieve. A further technical solution is that the metal is one of Zn, Ce, La or a combination thereof.

[0011] The method for synthesizing m-chlorotoluene by heterogeneous catalytic isomerization of the present invention may further include the following technical solutions: the carrier gas of the inert atmosphere is one of N2, Ar or He; and the diluent is one of benzene, toluene or chlorobenzene.

[0012] The method for synthesizing m-chlorotoluene by heterogeneous catalytic isomerization of the present invention can also be further technically provided that the mass ratio of the raw material p-chlorotoluene to the diluent is 0.5:1-2:1; the temperature of the preheater is 150-300°C; the fixed bed reaction temperature is 250-400°C; the constant flow pump transports the reaction liquid at a volume space velocity of 0.3-1h -1 ; The isomerization reaction pressure is a slightly positive pressure; and the condensation method is a 25°C circulating water condensation method.

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

[0014] (1) The present invention uses p-chlorotoluene as a raw material to catalyze isomerization reaction to prepare m-chlorotoluene, and the p-chlorotoluene conversion rate and m-chlorotoluene selectivity are high. The p-chlorotoluene conversion rate is as high as more than 69%, and the m-chlorotoluene selectivity is 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 low corrosion to equipment, has high reaction safety, and can be produced continuously.

[0016] (3) The process of the present invention will not generate metal pollution and wastewater, meet the standards of green chemistry, and comply with the strategic goal of sustainable development. DETAILED DESCRIPTION

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

[0045] Comparative Example 1

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

[0047] Table 1 Summary of application effects

[0048] Serial number Example Conversion rate of parachlorotoluene % m-Chlorotoluene selectivity % Meta-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 Embodiment 11 46.23 80.57 37.24 8 Example 12 44.95 81.60 36.67 9 Embodiment 13 50.84 76.68 38.98 10 Embodiment 14 50.23 77.66 39.00 11 Comparative Example 1 51.35 70.16 36.03

Claims

1. A method for synthesizing meta-chlorotoluene by heterogeneous catalytic isomerization, characterized in that: The following steps are involved: The modified HZSM-5 molecular sieve is filled in the fixed bed reaction constant temperature area and placed under an inert atmosphere. The mixture of the raw material para-chlorotoluene and the diluent is first transported to the preheating of the fixed bed reactor by a constant flow pump for vaporization, and then a catalytic isomerization reaction is carried out in the constant temperature area of ​​the fixed bed reactor. After condensation, the product meta-chlorotoluene is collected.

2. The method for synthesizing meta-chlorotoluene by heterogeneous catalytic isomerization according to claim 1, characterized in that: The modification method of the modified HZSM-5 molecular sieve is an ion exchange method, which comprises 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°C for more than 2 hours to carry out ion exchange, and carrying out three exchanges in total. After the exchange, the nitrate ions are washed away by suction filtration with deionized water, and then dried after separation by suction filtration at a drying temperature of 60-120°C. Finally, the modified HZSM-5 molecular sieve is calcined at a temperature of 300-600°C for 1-6 hours to obtain the modified HZSM-5 molecular sieve.

3. The method for synthesizing meta-chlorotoluene by heterogeneous catalytic isomerization according to claim 2, characterized in that: The metal is one of Zn, Ce, La or a combination thereof.

4. The method for synthesizing meta-chlorotoluene by heterogeneous catalytic isomerization 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.

5. The method for synthesizing meta-chlorotoluene by heterogeneous catalytic isomerization according to claim 1, characterized in that: The mass ratio of the raw material p-chlorotoluene to the diluent is 0.5:1-2:1; the temperature of the preheater is 150-300°C; the fixed bed reaction temperature is 250-400°C; the volume space velocity of the reaction liquid transported by the constant flow pump is 0.3-1h -1 ; The isomerization reaction pressure is a slightly positive pressure; and the condensation method is a 25°C circulating water condensation method.