Synthetic method of p-methyl-ethylbenzene

Abstract

The invention discloses a method for synthesizing p-methyl-ethylbenzene. The method comprises the following steps: mixing methylbenzene, dry gas and water vapor, and then carrying out alkylation reaction under the catalysis of a modified HZSM-5 molecular sieve catalyst, thereby obtaining the p-methyl-ethylbenzene. According to the method, the carbon deposition of the catalyst is slowed down by introducing water vapor to cooperate with dry gas, and meanwhile, the alkylation reaction pressure is reduced and secondary isomerization side reaction is reduced by reducing the strength and the number of strong acid centers of the HZSM-5 molecular sieve catalyst, so that the para-selectivity and the stability of the catalyst are improved.

Description

Technical Field

[0001] The invention relates to a method for synthesizing p-methylethylbenzene, in particular to a method for preparing p-methylethylbenzene by alkylating toluene dry gas, and belongs to the technical field of p-methylethylbenzene preparation. Technical Background

[0002] Para-methylstyrene is a monomer used to prepare polymers and copolymers. Polymethylstyrene synthesized from para-methylstyrene has a lower density than polystyrene (PS), a higher heat resistance, and is easier to mold and process. Its elasticity, transparency, and melt fluidity are all superior to PS. Because the benzene ring contains a methyl group, it is easily brominated and sulfonated, allowing for chemical cross-linking, thereby improving the polymer's oil and flame resistance. It is widely used in the synthesis of thermoplastic elastomers, brominated polyisobutylene-para-methylstyrene rubber, reinforced plastics, coatings, and insulating varnishes.

[0003] p-Methylstyrene can be produced by dehydrogenating p-methylethylbenzene. The key to producing high-purity p-methylstyrene is to produce high-purity p-methylethylbenzene.

[0004] The alkylation of toluene with ethylene or ethanol can be used to produce p-ethylmethylbenzene. However, conventional Friedel-Crafts catalysts produce three isomers in thermodynamic equilibrium, with p-ethylmethylbenzene accounting for approximately 30% and the remainder being m-ethylmethylbenzene and o-ethylmethylbenzene. Therefore, to improve p-ethylmethylbenzene selectivity, a high-performance catalyst is essential. Zeolite catalysts must possess suitable pore size, crystallite size, and intrapore acid site strength, as well as suppressed surface acidity. This allows the toluene alkylation reaction to shift the thermodynamic equilibrium concentration distribution of p-ethylmethylbenzene, m-ethylmethylbenzene, and o-ethylmethylbenzene products, resulting in the primary production of p-ethylmethylbenzene.

[0005] Chinese patent (CN85102828) discloses a method for alkylating toluene with ethylene to produce p-methylethylbenzene using a phosphorus-modified ZSM-5 catalyst. The reaction temperature is 300-380°C, atmospheric pressure, and the hydrocarbon weight space velocity is 6-16h. -1 , toluene / ethylene molar ratio is 2.5 to 5, and the selectivity for methyl and ethyl benzene is greater than 96%.

[0006] Chinese patent (CN93115961) discloses a method for alkylating p-methylethylbenzene by catalytic cracking dry gas and toluene using an antimony (or phosphorus) and magnesium modified pentasil type silica-alumina zeolite catalyst, with a reaction temperature of 290-450°C, a reaction pressure of 0.4-2.5 MPa, and an ethylene weight space velocity of 0.2-1.5 h -1 , toluene / ethylene molar ratio is 2.5 to 10, and the selectivity for methyl and ethyl benzene is greater than 90%.

[0007] Chinese patent (CN201110217577) discloses a method for alkylating toluene with ethylene to produce p-methylethylbenzene using alkaline earth metal and copper modified mordenite catalysts, with a reaction temperature of 380-460°C, a hydrogen partial pressure of 1-3 MPa, and a volume space velocity of 2-5 h -1 , toluene / ethylene molar ratio is 3 to 5, and the selectivity for methyl and ethyl benzene is greater than 95%.

[0008] A Chinese patent (CN201410424434.4) discloses a catalyst obtained by molding a citric acid-modified hydrogen-type EU-1 molecular sieve with alumina and then treating it with steam at 450-600°C for the alkylation of toluene and ethylene, with a selectivity for methyl and ethyl benzene greater than 90%.

[0009] A Chinese patent (CN201611227350) discloses that a ZSM-5 / ZSM-11 molecular sieve catalyst modified with aluminum, cerium, and phosphorus is used in the alkylation process of toluene and ethylene, with a selectivity for methyl and ethyl benzene greater than 95%.

[0010] A Chinese patent (CN201710469627) discloses a ZSM-5 / ZSM-11 co-crystallized molecular sieve catalyst that is first treated with acid and then modified with silicon, magnesium (or phosphorus, calcium) for the alkylation of toluene with ethylene, with a selectivity for methyl and ethylbenzene greater than 95%.

[0011] Chemical Reaction Engineering and Technology (2020) 6:491-497 reported the case of modifying the binderless ZSM-5 catalyst with chemical liquid deposition of polyphenylmethylsiloxane modifier to catalyze the shape-selective alkylation of toluene and ethylene to synthesize p-ethylmethylbenzene, with a selectivity of 97% for p-ethylmethylbenzene.

[0012] Petroleum Refining and Chemical Industry (1998) 10:5-9 reported the alkylation of catalytic cracking dry gas with toluene using La / ZSM-5 shape-selective zeolite catalyst to produce p-methylethylbenzene at 350-400℃, pressure 0.4-0.7MPa, toluene / ethylene molar ratio 4-7, space velocity 0.3-0.7h -1 The reaction is carried out under the conditions of , and the para selectivity of the generated ethylbenzene is about 90%.

[0013] The above-mentioned documents have made various modifications to the catalysts, improving the selectivity of p-ethylmethylbenzene in the reaction of toluene and ethylene to varying degrees. However, the catalyst life is short and it cannot operate stably for a long period of time; the product still contains 3 to 10% of m-ethylmethylbenzene, and the prepared p-methylstyrene still contains about 3% of m-methylstyrene, which affects the properties of the polymer.

[0014] A Chinese patent (CN202111641309) discloses a method for producing p-ethylmethylbenzene by reacting toluene with ethylene. In an alkylation reactor, ethylene is fed in multiple stages and reacts with toluene to produce a m-to-p-mixed ethylmethylbenzene with a m-to-p ratio of 0.6. The m-to-p-mixed ethylmethylbenzene is then fed into an ethyl position shift reactor to convert the m-to-p-ethylmethylbenzene. However, the method fails to break through thermodynamic equilibrium and completely convert the m-to-p-ethylmethylbenzene. Summary of the Invention

[0015] In view of the shortcomings of the prior art methods for synthesizing p-methylethylbenzene, the present invention aims to provide a method for synthesizing p-methylethylbenzene. The method produces p-methylethylbenzene by alkylating toluene with catalytic dry gas over a modified ZSM-5 catalyst. The catalyst prepared by the method has the advantages of stable activity, long life, and high selectivity for p-methylethylbenzene.

[0016] In order to achieve the above technical objectives, the present invention provides a method for synthesizing high-purity and durable p-methylethylbenzene, comprising mixing toluene, dry gas and water vapor and then subjecting the mixture to an alkylation reaction under the catalysis of a modified HZSM-5 molecular sieve catalyst; the modified HZSM-5 molecular sieve catalyst is prepared from the following raw materials, in parts by mass: 2 to 5 parts of phosphorus pentoxide, 2 to 5 parts of magnesium oxide, 1 to 3 parts of zinc oxide, 3 to 6 parts of silicon dioxide, and 81 to 92 parts of HZSM-5 molecular sieve.

[0017] The present invention creatively introduces water vapor into the alkylation reaction. The synergistic effect of water vapor and hydrogen in the dry gas slows down catalyst carbon deposition, thereby improving catalyst stability and catalyst life. Furthermore, the modified HZSM-5 molecular sieve catalyst used in the present invention is a modified shape-selective catalyst. The catalyst uses HZSM-5 molecular sieve as a substrate and is modified with phosphorus, magnesium, zinc, and silicon and subjected to hydrothermal treatment to reduce the strength of the molecular sieve's strong acid centers. Zinc oxide covers the strong acid sites on the outer surface, reducing the number and strength of the outer surface acid centers. The phosphorus, magnesium, and silicon-modified molecular sieve reduces the amount of strong acid and increases the amount of weak acid, thereby reducing secondary isomerization side reactions. Furthermore, the phosphorus, magnesium, and silicon-modified molecular sieve pores improve the catalyst's para-selectivity, thereby producing p-methylethylbenzene with high selectivity and high stability.

[0018] In the present invention, the reaction raw materials can be contacted with the alkylation catalyst to react to generate p-methylethylbenzene, and the alkylated product obtained by the alkylation reaction can be separated and purified to obtain high-purity p-methylethylbenzene.

[0019] As a preferred solution, the conditions for the alkylation reaction are: temperature of 280-420° C. and pressure of 50-200 KPa.

[0020] As a preferred solution, the conditions for the alkylation reaction are: temperature of 310-380° C. and pressure of 80-100 KPa.

[0021] The alkylation reaction of the present invention adopts low pressure, which reduces the residence time of the product p-methylethylbenzene, reduces the secondary isomerization side reaction, and improves the para-selectivity of the reaction.

[0022] As a preferred solution, the dry gas is washed with water to remove alcoholamine. The present invention uses the dry gas after washing with water to remove alcoholamine to reduce the risk of catalyst deactivation.

[0023] As a preferred solution, the dry gas comprises, by volume, 10-15% ethylene, 20-30% hydrogen, 20-30% nitrogen, 20-30% methane, and 10-20% ethane.

[0024] As a preferred solution, the molar ratio of toluene to ethylene in the dry gas is (4-8):1.

[0025] As a preferred solution, the molar ratio of water vapor to toluene is (0.25-2):1. If the water ratio is too low, or no water vapor is introduced, the catalyst will rapidly deposit carbon, the catalyst activity will decrease rapidly, and the catalyst life will be shortened; if the water ratio is too high, the catalyst life will be limited, a large amount of wastewater will be generated, and production costs will increase.

[0026] As a preferred solution, the volume space velocity of toluene is 0.3 to 1.0 h -1 .

[0027] As a preferred solution, the change in the alkylation reaction temperature is negatively correlated with the change in the ethylene conversion rate of the system. When the ethylene conversion rate decreases by 0.5 to 1 percentage point, the alkylation reaction temperature increases by 1 to 2°C.

[0028] As a preferred solution, the modified HZSM-5 molecular sieve catalyst is obtained by mixing phosphorus pentoxide, magnesium oxide, zinc oxide, silicon dioxide and HZSM-5 molecular sieve, extruding and then calcining the mixture.

[0029] As a preferred solution, the calcination treatment conditions are: temperature of 500-600°C, time of 2-6 hours, and calcination in a steam atmosphere. The present invention utilizes steam calcination to reduce the strength of the catalyst active center and improve the catalyst's para-selectivity.

[0030] As a preferred solution, the silicon-aluminum ratio of the HZSM-5 molecular sieve is 10-100.

[0031] As a preferred solution, the silicon-aluminum ratio of the HZSM-5 molecular sieve is 20 to 50. The present invention uses a molecular sieve with a low silicon-aluminum ratio, which can provide more active sites and improve the conversion rate.

[0032] The catalyst provided by the present invention uses HZSM-5 molecular sieve as a substrate, is modified with phosphorus, magnesium, zinc, and silicon, and is subjected to hydrothermal treatment, thereby reducing the strength of the strong acid centers of the molecular sieve. Zinc oxide covers the strong acid sites on the outer surface, reducing the number and strength of the acid centers on the outer surface. The modified molecular sieve has a reduced amount of strong acid and an increased amount of weak acid, thereby reducing secondary isomerization side reactions and improving the para-selectivity of the catalyst.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] 1) The HZSM-5 molecular sieve used in the alkylation reaction catalyst of the present invention is modified with phosphorus, magnesium, zinc, and silicon and subjected to hydrothermal treatment, thereby reducing the strength of the strong acid center of the molecular sieve and the acidity of the outer surface of the molecular sieve, reducing the amount of strong acid and increasing the amount of weak acid, reducing secondary isomerization reactions, and improving para-selectivity.

[0035] 2) The present invention creatively introduces water vapor into the alkylation reaction. The synergistic effect of water vapor and hydrogen in the dry gas slows down the carbon deposition of the catalyst, improves the stability of the catalyst, and greatly increases the life of the catalyst. The single-pass life of the catalyst exceeds 3000 hours.

[0036] 3) The present invention adopts low pressure in the alkylation reaction, which reduces the residence time of the product p-methylethylbenzene, reduces the isomerization side reaction, and improves the para-selectivity of the reaction. The p-methylethylbenzene selectivity reaches 99.0%, and the m-methylethylbenzene selectivity is less than 1.0%. DETAILED DESCRIPTION

[0037] The present invention is further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments. Obviously, the embodiments described below are only a part of the embodiments, and all other embodiments obtained by professionals in this field without making creative efforts are still within the scope of protection of the present invention.

[0038] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or prepared by existing methods.

[0039] The HZSM-5 molecular sieve used in the examples and comparative examples of the present invention was produced by Nankai University Catalyst Company.

[0040] The dry gas compositions in the examples of the present invention and the comparative examples are as follows by volume: 13% ethylene, 25% hydrogen, 21% nitrogen, 30% methane, and 11% ethane.

[0041] Example 1

[0042] This embodiment is a method for synthesizing high-purity and durable p-methylethylbenzene, which is as follows:

[0043] 1) Preparation of alkylation reaction catalyst

[0044] 5 parts of phosphorus pentoxide, 3 parts of magnesium oxide, 2 parts of zinc oxide, 3 parts of silicon dioxide, and 87 parts of HZSM-5 molecular sieve are mechanically mixed and then extruded. The silicon-aluminum ratio of the HZSM-5 molecular sieve is 35. Then, the mixture is calcined at 550°C for 4 hours in a water vapor atmosphere and naturally cooled to obtain a modified alkylation catalyst.

[0045] 2) Catalytic alkylation of dry gas and toluene to synthesize methyl and ethyl benzene

[0046] The alkylation reaction of toluene dry gas is carried out in a tubular reactor. A phosphorus-magnesium-zinc modified HZSM-5 molecular sieve catalyst is loaded into the Φ25 mm reactor. The catalyst bed height is 1.5 m. Both ends of the catalyst in the reactor are filled with quartz sand. The temperature is raised. When the temperature reaches 500°C, water vapor is passed through the reactor for hydrothermal treatment at normal pressure for 2 hours to reduce the initial activity of the catalyst and improve the catalyst selectivity. Then, when the temperature is lowered to 310°C, the reactor pressure is adjusted to 100 kPa, and toluene, catalytic dry gas that has been washed with de-alcoholamine, and water vapor are mixed and introduced into the reactor. The molar ratio of toluene to ethylene is 6:1, the molar ratio of water vapor to toluene is 0.6:1, and the toluene volume space velocity is 0.6 h-1. -1 Under the above conditions, the p-ethylmethylbenzene synthesis reaction is carried out to obtain an alkylated product. The reaction conditions can be appropriately adjusted as the ethylene conversion rate changes. For example, when the ethylene conversion rate decreases significantly, the reaction temperature can be increased. For example, the reaction temperature can be increased by 1-2°C for every 0.5-1 percentage point decrease in the ethylene conversion rate.

[0047] Example 2

[0048] 1) Preparation of alkylation reaction catalyst

[0049] 3 parts of phosphorus pentoxide, 2 parts of magnesium oxide, 1 part of zinc oxide, 6 parts of silicon dioxide, and 86 parts of HZSM-5 molecular sieve are mechanically mixed and then extruded. The silicon-aluminum ratio of the HZSM-5 molecular sieve is 20. Then, the mixture is calcined at 550°C for 4 hours in a water vapor atmosphere and naturally cooled to obtain a modified alkylation catalyst.

[0050] 2) Catalytic alkylation of dry gas and toluene to synthesize methyl and ethyl benzene

[0051] The alkylation reaction of toluene dry gas is carried out in a tubular reactor. A phosphorus-magnesium-zinc modified HZSM-5 molecular sieve catalyst is loaded into the Φ25 mm reactor. The catalyst bed height is 1.5 m. Both ends of the catalyst in the reactor are filled with quartz sand. The temperature is raised. When the temperature reaches 500°C, water vapor is passed through the reactor for hydrothermal treatment at normal pressure for 2 h. When the temperature is lowered to 310°C, the reactor pressure is adjusted to 90 kPa. Toluene, catalytic dry gas after water washing and dealcoholization, and water vapor are mixed and introduced into the reactor. The molar ratio of toluene to ethylene is 8:1, the molar ratio of water vapor to toluene is 1:1, and the volume space velocity of toluene is 1.0 h -1 Under the above conditions, the p-ethylmethylbenzene synthesis reaction is carried out to obtain an alkylated product. The reaction conditions can be appropriately adjusted as the ethylene conversion rate changes. For example, when the ethylene conversion rate decreases significantly, the reaction temperature can be increased. For example, the reaction temperature can be increased by 1-2°C for every 0.5-1 percentage point decrease in the ethylene conversion rate.

[0052] Example 3

[0053] 1) Preparation of alkylation reaction catalyst

[0054] 2 parts of phosphorus pentoxide, 5 parts of magnesium oxide, 3 parts of zinc oxide, 4 parts of silicon dioxide, and 86 parts of HZSM-5 molecular sieve are mechanically mixed and then extruded. The silicon-aluminum ratio of the HZSM-5 molecular sieve is 50. Then, the mixture is calcined at 550°C for 4 hours in a water vapor atmosphere and naturally cooled to obtain a modified alkylation catalyst.

[0055] 2) Catalytic alkylation of dry gas and toluene to synthesize methyl and ethyl benzene

[0056] The alkylation reaction of toluene dry gas is carried out in a tubular reactor. A phosphorus-magnesium-zinc modified HZSM-5 molecular sieve catalyst is loaded into the Φ25 mm reactor. The catalyst bed height is 1.5 m. Both ends of the catalyst in the reactor are filled with quartz sand. The temperature is raised. When the temperature reaches 500°C, water vapor is passed through the reactor for hydrothermal treatment at normal pressure for 2 h. When the temperature is lowered to 310°C, the reactor pressure is adjusted to 80 kPa. Toluene, catalytic dry gas that has been washed with alcohol deamine, and water vapor are mixed and introduced into the reactor. The molar ratio of toluene to ethylene is 4:1, the molar ratio of water vapor to toluene is 1.5:1, and the volumetric space velocity of toluene is 0.3 h -1 Under the above conditions, the p-ethylmethylbenzene synthesis reaction is carried out to obtain an alkylated product. The reaction conditions can be appropriately adjusted as the ethylene conversion rate changes. For example, when the ethylene conversion rate decreases significantly, the reaction temperature can be increased. For example, the reaction temperature can be increased by 1-2°C for every 0.5-1 percentage point decrease in the ethylene conversion rate.

[0057] Comparative Example 1

[0058] The conditions of this comparative example are the same as those of Example 1, except that the reactor pressure is replaced with 0.3 MPa to obtain an alkylated product.

[0059] Comparative Example 2

[0060] The conditions of this comparative example were the same as those of Example 1, except that the reactor pressure was replaced with 0.5 MPa to obtain an alkylated product.

[0061] Comparative Example 3

[0062] The conditions and steps of this comparative example are consistent with those of Example 1, except that zinc oxide is not added during the preparation of the alkylation reaction catalyst. Instead, 5 parts of phosphorus pentoxide, 3 parts of magnesium oxide, 3 parts of silicon dioxide, and 89 parts of HZSM-5 molecular sieve are prepared to obtain an alkylation product.

[0063] Comparative Example 4

[0064] The conditions and steps of this comparative example are consistent with those of Example 1, except that silicon dioxide and magnesium oxide are not added during the preparation of the alkylation reaction catalyst. Instead, 5 parts of phosphorus pentoxide, 3 parts of zinc oxide, and 92 parts of HZSM-5 molecular sieve are prepared to obtain an alkylation product.

[0065] Comparative Example 5

[0066] The conditions of this comparative example were the same as those of Example 1, except that no water vapor was introduced into the reaction system to obtain an alkylated product.

[0067] The compositions of the alkylated products of Examples 1 to 3 and Comparative Examples 1 to 5, ethylene conversion, ethylmethylbenzene selectivity, the ratio of p-ethylmethylbenzene to m-ethylmethylbenzene in ethylmethylbenzene, and production time were analyzed by online chromatography. The results are shown in Tables 1 and 2.

[0068] Table 1 Alkylation reaction test results of Examples 1 to 3 and Comparative Examples 1 to 4

[0069]

[0070]

[0071] Table 2 Alkylation reaction test results of Comparative Example 5

[0072]

[0073] As can be seen from Tables 1 and 2, the selectivity of p-methylethylbenzene in the methylethylbenzene produced by the alkylation reaction of toluene with dry gas in Example 1 is 99%, and the process can operate stably for 3000 hours continuously. However, in Comparative Examples 1 and 2, the proportion of p-methylethylbenzene in the methylethylbenzene produced by the reaction at elevated reaction pressure drops to 95%. In Comparative Example 3, the proportion of p-methylethylbenzene in the methylethylbenzene produced by the reaction in which the catalyst is modified with phosphorus, magnesium, and silicon drops to 95%. In Comparative Example 4, the proportion of p-methylethylbenzene in the methylethylbenzene produced by the reaction in which the catalyst is modified with phosphorus and zinc drops to 68%. In Comparative Example 5, no water vapor is introduced into the reaction system, and the catalyst is deactivated after 400 hours of reaction.

Claims

1. A method for synthesizing p-methylethylbenzene, characterized in that: Toluene, dry gas and water vapor are mixed and then subjected to an alkylation reaction under the catalysis of a modified HZSM-5 molecular sieve catalyst; the modified HZSM-5 molecular sieve catalyst is prepared from the following raw materials in parts by mass: 2 to 5 parts of phosphorus pentoxide, 2 to 5 parts of magnesium oxide, 1 to 3 parts of zinc oxide, 3 to 6 parts of silicon dioxide, and 81 to 92 parts of HZSM-5 molecular sieve.

2. A method for synthesizing p-methylethylbenzene according to claim 1, characterized in that: The conditions of the alkylation reaction are: temperature of 280-420° C. and pressure of 50-200 KPa.

3. A method for synthesizing p-methylethylbenzene according to claim 2, characterized in that: The conditions of the alkylation reaction are: temperature of 310-380° C. and pressure of 80-100 KPa.

4. The method for synthesizing p-methylethylbenzene according to any one of claims 1 to 3, wherein: The dry gas is washed with water to remove the alcohol amine.

5. A method for synthesizing p-methylethylbenzene according to claim 4, characterized in that: The dry gas comprises, by volume fraction, 10-15% ethylene, 20-30% hydrogen, 20-30% nitrogen, 20-30% methane, and 10-20% ethane.

6. A method for synthesizing p-methylethylbenzene according to claim 5, characterized in that: The molar ratio of the toluene to the ethylene in the dry gas is (4-8):1; the molar ratio of the water vapor to the toluene is (0.25-2):

1.

7. A method for synthesizing p-methylethylbenzene according to claim 1 or 5, characterized in that: The volume space velocity of toluene is 0.3~1.0h -1 .

8. A method for synthesizing p-methylethylbenzene according to claim 7, characterized in that: The change in the alkylation reaction temperature is negatively correlated with the change in the ethylene conversion rate of the system. When the ethylene conversion rate decreases by 0.5 to 1 percentage point, the alkylation reaction temperature increases by 1 to 2°C.

9. A method for synthesizing p-methylethylbenzene according to claim 1, characterized in that: The modified HZSM-5 molecular sieve catalyst is obtained by mixing phosphorus pentoxide, magnesium oxide, zinc oxide, silicon dioxide and HZSM-5 molecular sieve, extruding and then calcining the mixture.

10. The method for synthesizing p-methylethylbenzene according to claim 9, wherein: The calcination treatment conditions are: temperature of 500-600° C., time of 2-6 hours, and calcination atmosphere of water vapor.

11. The method for synthesizing p-methylethylbenzene according to claim 10, wherein: The silicon-aluminum ratio of the HZSM-5 molecular sieve is 10-100.

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