Catalyst for synthesis of 2, 6-dichlorotoluene and preparation method thereof

Abstract

The invention discloses a catalyst for synthesis of 2, 6-dichlorotoluene and a preparation method of the catalyst, and belongs to the technical field of production of 2, 6-dichlorotoluene. According to the catalyst, ZSM-5 zeolite is used as a matrix, firstly, mesoporous-microporous graded pore channels are constructed in the ZSM-5 zeolite through selective etching of an alkali solution to improve mass transfer; then loading iron and cerium bimetallic active components by adopting an equivalent-volume impregnation method, and accurately regulating and controlling a reaction path through the synergistic effect of acidity and oxidation-reduction characteristics of the iron and cerium bimetallic active components; and finally, coating the outer surfaces of the catalyst particles with a layer of amorphous silicon dioxide thin shell through a chemical vapor deposition technology, and selectively passivating non-shape-selective acidic sites on the outer surfaces. According to the design, the chlorination reaction is forced to be mainly carried out in an internal pore channel with shape selectivity, so that the selectivity and yield of 2, 6-dichlorotoluene as well as the recyclability are remarkably improved while the high activity is maintained.

Description

Technical Field

[0001] This invention belongs to the field of 2,6-dichlorotoluene production technology, specifically relating to a catalyst for the synthesis of 2,6-dichlorotoluene and its preparation method. Background Technology

[0002] 2,6-Dichlorotoluene is a key intermediate in the synthesis of high-performance polymers, pharmaceuticals, and pesticides, and its downstream products, such as 2,6-dichlorobenzonitrile and 2,6-dichlorobenzaldehyde, have extremely high market value. However, the efficient and selective synthesis of this molecule has always been a major challenge in the field of fine chemicals. The core difficulty lies in how to precisely introduce a second chlorine atom into the 6-position, where steric hindrance is greatest and electron cloud density is affected by two adjacent substituents, on a benzene ring already containing a methyl and a chlorine atom, thereby obtaining a high-purity 2,6-isomer and maximally suppressing the formation of other positional isomers (such as 2,4-, 2,3-, and 2,5-dichlorotoluene).

[0003] Currently, the main industrial and research routes for synthesizing 2,6-dichlorotoluene revolve around the electrophilic chlorination reaction using o-chlorotoluene as a raw material. The core technology and bottleneck of this route lie entirely in the selectivity and stability of the catalyst system.

[0004] First-generation traditional catalysts are represented by Lewis acids. While these catalysts can efficiently activate chlorine molecules to achieve the chlorination of o-chlorotoluene, their fatal flaw lies in their extremely poor regioselectivity. The reaction they catalyze is essentially a non-shape-selective electrophilic attack, and the products are a complex mixture of multiple dichlorotoluene isomers under thermodynamic equilibrium. Because the physical properties (such as boiling points) of the isomers are extremely similar, the subsequent separation and purification processes are extremely energy-intensive and have extremely low yields, resulting in huge production costs and environmental pressures, making it difficult to meet the requirements of modern green chemical engineering.

[0005] Second-generation catalysts, represented by zeolite molecular sieves, represent a leap from "strong catalysis" to "shape-selective catalysis." Their regular micropores can utilize steric hindrance to preferentially allow the formation and diffusion of 2,6-dichlorotoluene molecules with higher linearity, thereby significantly improving reaction selectivity. However, conventional zeolite catalysts still suffer from two inherent drawbacks: The single microporous structure (pore size is usually <1nm) causes severe diffusion resistance to larger molecules such as o-chlorotoluene, resulting in a low reaction rate and rapid deactivation of the catalyst cavity due to carbon buildup.

[0006] Non-selective active sites on the outer surface: Non-shape-selective acid sites on the outer surface of catalyst particles can non-selectively catalyze chlorination reactions, generating a large number of unwanted byproducts such as 2,4-dichlorotoluene.

[0007] Therefore, it is necessary to develop a novel catalyst to achieve a balance between high activity, high selectivity, and high stability in the synthesis of 2,6-dichlorotoluene. Summary of the Invention

[0008] In view of this, the present invention aims to provide a catalyst for the synthesis of 2,6-dichlorotoluene and a method for preparing the same. The catalyst obtained by the present invention significantly improves the selectivity and yield of 2,6-dichlorotoluene, as well as its recyclability, while maintaining high activity.

[0009] To achieve the above objectives, the present invention provides the following technical solution: This invention provides a method for preparing a catalyst for the synthesis of 2,6-dichlorotoluene, comprising the following preparation steps: S1. Disperse ZSM-5 zeolite in NaOH aqueous solution and stir, then filter and wash until neutral; then dry and calcine to obtain mesoporous ZSM-5 support; S2. Mix and soak the mesoporous ZSM-5 carrier, water, Fe(NO3)3 and Ce(NO3)3, then filter, dry and calcine to obtain Ce-Fe / mZSM-5; S3. Place Ce-Fe / mZSM-5 in a quartz boat and put it into a tube furnace; introduce nitrogen as a carrier gas and heat the system to 300-400℃; bubble nitrogen through a TEOS liquid bottle to carry TEOS vapor into the reaction zone for 30-40 min; after the reaction is completed, cool to room temperature under a nitrogen atmosphere; finally, treat the sample in dry air at 400-500℃ for 2 hours to completely convert the deposited silicon species into amorphous SiO2, and obtain the target catalyst Ce-Fe / mZSM-5@SiO2.

[0010] ZSM-5 zeolite was dispersed in NaOH aqueous solution and stirred, then filtered and washed until neutral; then dried and calcined to obtain mesoporous ZSM-5 support.

[0011] Preferably, the ratio of ZSM-5 zeolite to NaOH aqueous solution in S1 is (1-10) g: 100 mL.

[0012] Preferably, the concentration of the NaOH aqueous solution is (0.2-0.5) mol / L.

[0013] Preferably, the stirring temperature in step S1 is 65-75℃ and the stirring time is 30-40 min.

[0014] Preferably, the calcination temperature in S1 is 500-600℃ and the time is 3-5 hours.

[0015] While conventional ZSM-5 micropores (<2 nm) offer good shape selectivity, the high diffusion resistance of reactants and products within the pores easily leads to catalyst deactivation due to carbon buildup. This invention employs the aforementioned technical solution, using post-treatment alkaline etching to create a mesoporous network (2-50 nm) within the ZSM-5 crystal. This promotes the entry of o-chlorotoluene molecules and chlorine gas into the active sites, as well as the rapid diffusion of the product 2,6-dichlorotoluene, thereby significantly improving the reaction rate and resistance to carbon buildup.

[0016] ZSM-5, water, Fe(NO3)3, and Ce(NO3)3 were mixed and soaked, then filtered, dried, and calcined to obtain Ce-Fe / mZSM-5. Preferably, the mass ratio of ZSM-5, water, Fe(NO3)3 and Ce(NO3)3 in S2 is (1-10):100:0.2:0.1.

[0017] Preferably, the soaking time in S2 is 10-12 hours.

[0018] Preferably, the calcination temperature in S2 is 500-550℃ and the time is 3-5h.

[0019] Current catalysts typically involve single Fe modification or direct use of FeCl3, resulting in excessively strong acidity that is difficult to control, easily leading to deep chlorination and isomerization. This application employs bimetallic modification with iron (Fe) and cerium (Ce), where Fe... 3+ Provides the main Lewis acid sites, activating chlorine molecules; Ce 4+ / Ce 3+ Its unique redox properties are key; it can rapidly recycle byproducts generated in the reaction or small amounts of adsorbed Cl· radicals produced by overchlorination, stabilizing the reaction environment. Simultaneously, CeO2 itself possesses moderate Lewis acidity, which can synergistically work with Fe to modulate the overall acid strength distribution of the catalyst, ensuring it is "sufficient to activate the reactants without being too strong and causing side reactions."

[0020] Ce-Fe / mZSM-5 was placed in a quartz boat and then placed in a tube furnace. Nitrogen was introduced as a carrier gas, and the system was heated to 300-400°C. Nitrogen was bubbled through a TEOS liquid bottle to carry TEOS vapor into the reaction zone for 30-40 minutes. After the reaction was completed, the mixture was cooled to room temperature under a nitrogen atmosphere. Finally, the sample was treated in dry air at 400-500°C for 2 hours to completely convert the deposited silicon species into amorphous SiO2, thus obtaining the target catalyst Ce-Fe / mZSM-5@SiO2.

[0021] The outer surface of the catalyst also contains non-shape-selective acidic sites, which can non-selectively chlorinate, generating unwanted isomers and reducing overall selectivity. In the final stage of preparation, this invention uses chemical vapor deposition to uniformly coat the outer surface of the catalyst particles with an ultrathin, amorphous silica shell. This shell selectively passivates the strongly acidic sites on the outer surface, and due to its porosity, it does not hinder reactant molecules from entering the internal mesoporous-microporous shape-selective channels, allowing the target reaction to occur only within the shape-selective internal pores.

[0022] This invention provides a catalyst for the synthesis of 2,6-dichlorotoluene, which is prepared by the above-described preparation method.

[0023] Preferably, the catalyst has a specific surface area >350 m². 2 / g, total pore volume >0.25 cm³ 3 / g, mesoporous pore volume >0.13cm 3 / g, micropore volume is 0.12-0.15 cm³ 3 / g.

[0024] It contains at least the following beneficial technical effects: The catalyst of this invention achieves a significant increase in the yield of 2,6-dichlorotoluene through a triple innovative design: constructing a hierarchical "mesoporous-microporous" pore structure, introducing an "iron-cerium" bimetallic synergistic system, and encapsulating a "silica" selective passivation shell. Compared with traditional catalysts, this represents a substantial increase. At the same time, its unique structure endows it with excellent selectivity, reactivity, and potential long-term operational stability, fundamentally solving the technical bottlenecks of low yield, poor selectivity, and easy deactivation in traditional processes. Detailed Implementation

[0025] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0026] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0027] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0028] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be obvious to those skilled in the art. This application specification and embodiments are merely exemplary.

[0029] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0030] Unless otherwise specified, "room temperature" and "normal temperature" in this invention refer to 25±2℃.

[0031] Unless otherwise specified, all raw materials or instruments used in the following embodiments of the present invention are commercially available.

[0032] Example 1 This invention provides a method for preparing a catalyst for the synthesis of 2,6-dichlorotoluene, comprising the following preparation steps: S1. Disperse 5g of ZSM-5 zeolite in 100mL of 0.3mol / L NaOH aqueous solution and stir at 70℃ for 35min. Then filter and wash until neutral. Then dry and calcine at 550℃ for 4 hours to obtain mesoporous ZSM-5 support. S2. Mix mesoporous ZSM-5 carrier, water, Fe(NO3)3 and Ce(NO3)3 in a ratio of 5:100:0.2:0.1 and soak for 11 hours. Then filter, dry and calcine at 500-550℃ for 4 hours to obtain Ce-Fe / mZSM-5. S3. Place Ce-Fe / mZSM-5 in a quartz boat and put it into a tube furnace; introduce nitrogen as a carrier gas and heat the system to 350°C; bubble nitrogen through a TEOS liquid bottle to carry TEOS vapor into the reaction zone for 35 min; after the reaction is completed, cool to room temperature under a nitrogen atmosphere; finally, treat the sample in dry air at 450°C for 2 hours to completely convert the deposited silicon species into amorphous SiO2, and obtain the target catalyst Ce-Fe / mZSM-5@SiO2.

[0033] Example 2 This invention provides a method for preparing a catalyst for the synthesis of 2,6-dichlorotoluene, comprising the following preparation steps: S1. Disperse 1g of ZSM-5 zeolite in 100mL of 0.2mol / L NaOH aqueous solution and stir at 70℃ for 35min. Then filter and wash until neutral. Then dry and calcine at 550℃ for 4 hours to obtain mesoporous ZSM-5 support. S2. The mesoporous ZSM-5 carrier, water, Fe(NO3)3 and Ce(NO3)3 were mixed and soaked in a ratio of 1:100:0.2:0.1 for 10 h, then filtered, dried and calcined at 500℃ for 3 h to obtain Ce-Fe / mZSM-5; S3. Place Ce-Fe / mZSM-5 in a quartz boat and put it into a tube furnace; introduce nitrogen as a carrier gas and heat the system to 400°C; bubble nitrogen through a TEOS liquid bottle to carry TEOS vapor into the reaction zone for 40 min; after the reaction is completed, cool to room temperature under a nitrogen atmosphere; finally, treat the sample in dry air at 500°C for 2 hours to completely convert the deposited silicon species into amorphous SiO2, and obtain the target catalyst Ce-Fe / mZSM-5@SiO2.

[0034] Example 3 This invention provides a method for preparing a catalyst for the synthesis of 2,6-dichlorotoluene, comprising the following preparation steps: S1. Disperse 10g of ZSM-5 zeolite in 100mL of 0.5mol / L NaOH aqueous solution and stir at 75℃ for 40min. Then filter and wash until neutral. Then dry and calcine at 600℃ for 5 hours to obtain mesoporous ZSM-5 support. S2. The mesoporous ZSM-5 carrier, water, Fe(NO3)3 and Ce(NO3)3 were mixed and soaked in a ratio of 10:100:0.2:0.1 for 12 hours, then filtered, dried and calcined at 550℃ for 5 hours to obtain Ce-Fe / mZSM-5; S3. Place Ce-Fe / mZSM-5 in a quartz boat and put it into a tube furnace; introduce nitrogen as a carrier gas and heat the system to 400°C; bubble nitrogen through a TEOS liquid bottle to carry TEOS vapor into the reaction zone for 40 min; after the reaction is completed, cool to room temperature under a nitrogen atmosphere; finally, treat the sample in dry air at 500°C for 2 hours to completely convert the deposited silicon species into amorphous SiO2, and obtain the target catalyst Ce-Fe / mZSM-5@SiO2.

[0035] Comparative Example 1 This invention provides a method for preparing a catalyst for the synthesis of 2,6-dichlorotoluene, comprising the following preparation steps: S1. Disperse 5g of ZSM-5 zeolite in 100mL of 0.3mol / L NaOH aqueous solution and stir at 70℃ for 35min. Then filter and wash until neutral. Then dry and calcine at 550℃ for 4 hours to obtain mesoporous ZSM-5 support. S2. The mesoporous ZSM-5 carrier, water, Fe(NO3)3 and Ce(NO3)3 were mixed and soaked in a ratio of 5:100:0.2:0.1 for 11 hours, then filtered, dried and calcined at 500-550℃ for 4 hours to obtain Ce-Fe / mZSM-5.

[0036] Comparative Example 2 This invention provides a method for preparing a catalyst for the synthesis of 2,6-dichlorotoluene, comprising the following preparation steps: S1. Mix ZSM-5, water, Fe(NO3)3 and Ce(NO3)3 in a ratio of 5:100:0.2:0.1 and soak for 11 hours. Then filter, dry and calcine at 500-550℃ for 4 hours to obtain Ce-Fe / ZSM-5. S2. Place Ce-Fe / ZSM-5 in a quartz boat and put it into a tube furnace; introduce nitrogen as a carrier gas and heat the system to 350°C; bubble nitrogen through a TEOS liquid bottle to carry TEOS vapor into the reaction zone for 35 min; after the reaction is completed, cool to room temperature under a nitrogen atmosphere; finally, treat the sample in dry air at 450°C for 2 hours to completely convert the deposited silicon species into amorphous SiO2, and obtain the target catalyst Ce-Fe / ZSM-5@SiO2.

[0037] Experimental Example 1 The Ce-Fe / mZSM-5@SiO2 prepared in Example 1 was tested, and the results are shown in Table 1.

[0038] Table 1

[0039] This catalyst possesses a high specific surface area and suitable pore volume, providing abundant active sites and reactant transport space for the reaction. The hierarchical pore structure greatly improves mass transfer, which is the structural basis for the catalyst's high activity and resistance to carbon deposition, and successfully passivates non-selective acid sites on the outer surface.

[0040] Experimental Example 2 Catalyst performance testing experimental protocol 1. Experimental setup and procedure Reaction apparatus: Atmospheric pressure fixed-bed continuous flow reactor.

[0041] Reaction tube: Quartz tube, inner diameter 10 mm.

[0042] Catalyst loading: 1.0 g (40-60 mesh), fixed at the top and bottom with quartz wool.

[0043] Reactants: o-chlorotoluene and chlorine (N2 is used as carrier gas and dilution gas).

[0044] Reaction conditions: Reaction temperature: 250-300℃; o-chlorotoluene feed rate: 0.1 mL / min (via micro-injection pump); Cl2 / N2 mixed gas flow rate: 30 mL / min (Cl2 volume fraction: 10%); Molar ratio (Cl2: o-chlorotoluene): 1.2:1 (a slight excess of chlorine gas to ensure complete reaction); Product Analysis: Instrument: Gas chromatograph equipped with a flame ionization detector.

[0045] Chromatographic column: Capillary column with a highly polar stationary phase (HP-INNOWax) to achieve complete separation of all dichlorotoluene isomers.

[0046] Catalytic experiments were conducted on the catalysts of Examples 1-3 and Comparative Examples 1-2 respectively (the amount of o-chlorotoluene was 100 mL and the amount of catalyst was 100 mg). The products were detected and the results are shown in Table 2.

[0047] Table 2

[0048] The catalyst was then subjected to the above method 10 times, and the change in relative yield was detected, as shown in Table 3.

[0049] Table 3

[0050] As can be seen from the above, the catalyst prepared by this invention has enhanced resistance to carbon deposition: the hierarchical pore structure avoids the retention of reactants and products in narrow channels, reducing the formation of carbon precursors at the source. The synergistic effect of Fe and Ce helps maintain the stability of the active sites, and the redox capacity of Ce may help delay catalyst deactivation. By optimizing the "conversion-selectivity" balance, the yield of 2,6-dichlorotoluene was doubled, and the production efficiency was significantly improved.

[0051] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A process for the preparation of a catalyst for the synthesis of 2,6- dichlorotoluene, characterized in that, The preparation method comprises the following steps: S1. stirring ZSM-5 zeolite in NaOH aqueous solution, then filtering and washing to neutral, then drying and calcining to obtain mesoporous ZSM-5 carrier; S2. mixing and soaking the mesoporous ZSM-5 carrier, water, Fe(NO3)3 and Ce(NO3)3, then filtering, drying and calcining to obtain Ce-Fe / mZSM-5; S3. placing the Ce-Fe / mZSM-5 in a quartz boat and putting it into a tube furnace; passing nitrogen as a carrier gas to heat the system to 300-400℃; bubbling nitrogen through a TEOS liquid bottle to bring TEOS vapor into the reaction zone for 30-40min; after the reaction, cooling to room temperature under a nitrogen atmosphere; finally, treating the sample in dry air at 400-500℃ for 2 hours to completely convert the deposited silicon species into amorphous SiO2 to obtain the target catalyst Ce-Fe / mZSM-5@SiO2.

2. The production method according to claim 1, characterized by, The ratio of ZSM-5 zeolite to NaOH aqueous solution in S1 is (1-10) g:100 mL.

3. The method of claim 3, wherein, The concentration of the NaOH aqueous solution is (0.2-0.5) mol / L.

4. The method of claim 1, wherein, The stirring temperature in S1 is 65-75℃, and the time is 30-40min.

5. The preparation method according to claim 1, characterized in that, The calcination temperature in S1 is 500-600℃, and the time is 3-5 hours.

6. The method of claim 1, wherein, The mass ratio of ZSM-5, water, Fe(NO3)3 and Ce(NO3)3 in S2 is (1-10):100:0.2:0.

1.

7. The preparation method according to claim 1, characterized in that, The soaking time in S2 is 10-12h.

8. The method of claim 1, wherein, The calcination temperature in S2 is 500-550℃, and the time is 3-5h.

9. A catalyst for the synthesis of 2,6-dichlorotoluene, characterized in that, The catalyst is prepared by the preparation method of any one of claims 1-8.

10. The catalyst of claim 9, wherein The catalyst has a specific surface area > 350 m 2 / g, a total pore volume > 0.25 cm 3 / g, a mesopore volume > 0.13 cm 3 / g, a micropore volume of 0.12 cm 3 / g.

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