Synthetic method of high-purity p-methylstyrene

Abstract

The invention provides a synthetic method of high-purity p-methylstyrene. The method comprises the following steps: carrying out alkylation on toluene and catalytic dry gas in a modified ZSM-5 catalyst to generate methyl-ethylbenzene, carrying out adsorption separation on the methyl-ethylbenzene to obtain high-purity p-methyl-ethylbenzene, and carrying out high-temperature dehydrogenation on the p-methyl-ethylbenzene in the presence of an iron-based catalyst to obtain the high-purity p-methyl styrene. According to the method, based on the synergistic effect of a preparation process and an alkylation reaction catalyst, the para-selectivity of the alkylation reaction catalyst is strictly controlled, so that the selectivity of the catalyst is ensured, the service life of the catalyst is greatly prolonged, and furthermore, a simulated moving bed is utilized to adsorb and separate methyl ethylbenzene isomers, separate, purify and recycle; the raw material utilization rate and the product purity are improved, and the purity of the finally obtained p-methylstyrene is 99% or above.

Description

Technical Field

[0001] The invention relates to a method for synthesizing p-methylstyrene, in particular to a method for preparing p-methylstyrene by dehydrogenating p-methylethylbenzene prepared by alkylation of toluene dry gas. Background Art

[0002] Para-methylstyrene is a monomer used to prepare polymers and copolymers. Polymethylstyrene synthesized with para-methylstyrene as a monomer has a lower density than polystyrene (PS), a higher heat resistance temperature, is easy to mold and process, and has higher elasticity, transparency, and melt fluidity than PS. Since the benzene ring contains methyl groups, it is easy to brominate and sulfonate, and can be chemically cross-linked to improve the oil resistance and flame retardancy of the polymer. It can be widely used in the synthesis of thermoplastic elastomers, brominated polyisobutylene-para-methylstyrene rubber, reinforced plastics, coatings, insulating impregnation varnishes, etc.

[0003] p-Methylstyrene can be prepared by dehydrogenation of p-methylethylbenzene. The key to preparing high-purity p-methylstyrene is to prepare high-purity p-methylethylbenzene.

[0004] The alkylation reaction of toluene with ethylene or ethanol can be used to prepare p-methylethylbenzene, but the methylethylbenzene obtained by conventional Friedel-Crafts catalyst is composed of three isomers in thermodynamic equilibrium, of which p-methylethylbenzene accounts for about 30%, and the rest are m-methylethylbenzene and o-methylethylbenzene. Therefore, in order to improve the selectivity of p-methylethylbenzene, a catalyst with good performance is necessary. The pore size, grain size and acid center strength in the pore of the zeolite catalyst are required to be appropriate, and the acidity of the outer surface is suppressed, so that the toluene alkylation reaction may break the thermodynamic equilibrium concentration distribution of p-methylethylbenzene, m-methylethylbenzene and o-methylethylbenzene products, and mainly produce p-methylethylbenzene.

[0005] Chinese patent (CN85102828) discloses a method for alkylating toluene and ethylene to produce p-methylethylbenzene using phosphorus-modified ZSM-5 catalyst, with a reaction temperature of 300-380°C, normal pressure, and a hydrocarbon weight space velocity of 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 preparing p-methylethylbenzene by alkylation of toluene with antimony (or phosphorus) and magnesium modified Pentasil type silica-alumina zeolite catalyst, reaction temperature 290-450°C, reaction pressure 0.4-2.5 MPa, ethylene weight space velocity 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 catalyst, 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 to 600°C for use in the alkylation process of toluene and ethylene, with a selectivity for methyl and ethyl benzene greater than 90%.

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

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

[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°C, pressure 0.4-0.7 MPa, toluene / ethylene molar ratio 4-7, space velocity 0.3-0.7 h -1 The reaction is carried out under the conditions of , and the para-selectivity of the generated methyl ethyl benzene is about 90%.

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

[0014] Chinese patent (CN202111641309) discloses a method for preparing p-methylethylbenzene by reacting toluene and ethylene. In an alkylation reactor, ethylene is fed in multiple stages to react with toluene to generate m-m ...

[0015] Petrochemicals (1990) 8:511-517 reported the dehydrogenation of p-methylethylbenzene to p-methylstyrene using a multi-component iron-based catalyst in the presence of water vapor, but the prepared p-methylstyrene still contained about 3% of m-methylstyrene. Summary of the invention

[0016] In view of the problems existing in the prior art, the object of the present invention is to provide a method for synthesizing high-purity p-methylstyrene. In the method, toluene and catalytic dry gas are alkylated over a modified ZSM-5 catalyst to produce ethylmethylbenzene, ethylmethylbenzene is adsorbed and separated to obtain high-purity p-methylethylbenzene, and p-methylethylbenzene is dehydrogenated at a high temperature over an iron-based catalyst to obtain high-purity p-methylstyrene. The method has the advantages of stable alkylation catalyst activity, long catalyst life and high purity of p-methylstyrene.

[0017] To achieve the above object, the present invention provides a method for synthesizing high-purity p-methylstyrene, comprising:

[0018] 1) The catalytic dry gas after washing with water to remove the alcohol amine is mixed with toluene and fed into an alkylation reactor for alkylation reaction, 30-80% of the obtained alkylation product is recycled back to the alkylation reactor, and the remaining alkylation product is separated and purified to obtain mixed methyl and ethyl benzene;

[0019] 2) separating the mixed methyl and ethyl benzenes by simulated moving bed adsorption to obtain p-methyl and ethyl benzene with a purity greater than 99.5%;

[0020] 3) After the p-methylethylbenzene and water are gasified, a dehydrogenation reaction is carried out under the catalysis of an iron-based catalyst to separate them;

[0021] The catalyst for the alkylation reaction comprises, by weight, 2 to 5 parts of phosphorus pentoxide, 1 to 3 parts of zinc oxide, and 92 to 97 parts of HZSM-5 molecular sieve;

[0022] The simulated moving bed has 16 to 24 beds, which are divided into an adsorption zone, a purification zone, a desorption zone and a buffer zone according to the bed layers;

[0023] The mixed methyl and ethyl benzene comprises 65-80% of p-methyl and ethyl benzene and 20-35% of m-methyl and ethyl benzene, and the remainder is o-methyl and ethyl benzene.

[0024] As a preferred solution, the preparation process of the catalyst for the alkylation reaction is: phosphorus pentoxide, zinc oxide and HZSM-5 molecular sieve are mechanically mixed and then extruded into a mold, calcined at 500-600° C. for 2-6 hours in a water vapor atmosphere, and naturally cooled to obtain the catalyst.

[0025] As a preferred solution, the silicon-aluminum ratio of the HZSM-5 molecular sieve is 10 to 100. More preferably, the silicon-aluminum ratio of the HZSM-5 molecular sieve is 20 to 50.

[0026] The catalyst provided by the present invention uses HZSM-5 molecular sieve as a substrate, and is subjected to phosphorus modification and hydrothermal treatment to reduce the strength of the strong acid center of the molecular sieve, and zinc oxide covers the strong acid sites on the outer surface to reduce the acidity of the outer surface. The amount of strong acid in the modified molecular sieve is reduced, and the amount of weak acid is increased, thereby reducing the secondary isomerization side reaction and improving the para-selectivity of the catalyst. However, it should be noted that the modification of the catalyst needs to be strictly carried out in accordance with the above requirements, and the para-selectivity of the catalyst cannot be too high. Too high para-selective activity will lead to a decrease in the activity of the catalyst, thereby reducing the life of the catalyst.

[0027] As a preferred solution, the alkylation reaction temperature is 300-450°C, and the space velocity is 3.0-5.0h -1 , the pressure is 1.0-3.0 MPa. Further preferably, the temperature of the alkylation reaction is 360°C-420°C.

[0028] 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.

[0029] As a preferred solution, the remaining alkylation product enters a high separation tank to separate the tail gas and then enters a separation tower for separation. The crude methyl ethyl benzene product discharged from the lower part of the separation tower enters a methyl ethyl benzene heavy component removal tower and a light component removal tower in turn to separate the heavy component and the light component to obtain mixed methyl ethyl benzene; the purity of the mixed methyl ethyl benzene is ≥99%.

[0030] As a preferred solution, the bed configuration of the adsorption zone, purification zone, desorption zone and buffer zone in the simulated moving bed is preferably (5, 6, 3, 2) or (7, 9, 5, 3).

[0031] As a preferred solution, the adsorbent used in the simulated moving bed is X zeolite, and the desorbent is at least one of toluene, p-xylene and p-diethylbenzene.

[0032] As a preferred solution, the adsorbent is RAX-3000A adsorbent produced by Changling Branch of Sinopec Catalyst Company, and the desorbent is p-diethylbenzene.

[0033] As a preferred solution, the operating temperature of the simulated moving bed is 120-170° C. and the pressure is 0.4-1.0 MPa.

[0034] The process of synchronous adsorption separation of methyl and ethyl benzene isomers by simulated moving bed provided by the present invention is as follows: mixed methyl and ethyl benzene is introduced from the entrance of the adsorption tower of the simulated moving bed device, a decomposing agent is introduced from the entrance of the decomposing tower of the simulated moving bed device, a raffinate rich in m-methyl and ethyl benzene is extracted from the outlet of the adsorption tower, and an extract rich in p-methyl and ethyl benzene is extracted from the outlet of the decomposing tower. After the extract is separated by the separation tower, p-methyl and ethyl benzene with a purity of more than 99.5% is obtained, and the separated decomposing agent is reused; the m-methyl and ethyl benzene in the raffinate after the decomposing agent is separated by the separation tower can be sent to the isomerization device for isomerization, and the isomerized product is returned to the adsorption tower as feed.

[0035] As a preferred solution, the iron-based catalyst is calculated by mass percentage as follows: K2O 4-8%; Ce2O3 6-10%; MoO3 1-5%; CaO 1-4%; MgO 1-4%; and the balance is Fe2O3.

[0036] As a preferred solution, the dehydrogenation reaction process is: preheating p-methylethylbenzene and water vapor and entering the dehydrogenation reactor, condensing the product into an oil-water separator to separate the gas phase and water, and then sequentially undergoing purification separation, light component removal and heavy component removal to obtain the p-methylstyrene. The purity of the p-methylstyrene is above 99.0%.

[0037] As a preferred solution, the purification and separation process also requires the addition of a polymerization inhibitor, and the amount of the polymerization inhibitor added is 50 to 100 ppm of the p-methylstyrene content.

[0038] As a preferred solution, the process conditions of the dehydrogenation reaction are: the temperature of the dehydrogenation reactor is 560°C to 630°C, the liquid volume space velocity of methyl ethyl benzene is 0.5h -1 ~2.0h -1 , the mass ratio of water to p-methylethylbenzene is 2 to 4, and the dehydrogenation reaction pressure is 30 to 100 KPa.

[0039] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0040] 1) In the alkylation reaction of the present invention, the HZSM-5 molecular sieve used as the alkylation reaction catalyst is modified with phosphorus and zinc 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, increasing the amount of weak acid, improving the para selectivity, and reducing the secondary isomerization reaction. Furthermore, by strictly controlling the para selectivity of the catalyst, the meta- and para-selectivities are kept in an appropriate ratio, with 20-35% of meta-ethylmethylbenzene and 65-80% of para-ethylmethylbenzene, without affecting the stability of the catalyst and improving the catalyst life.

[0041] 2) The simulated moving bed of the present invention separates methyl and ethyl benzene isomers by adsorption, optimizes the configuration of the simulated moving bed bed layers, increases the number of bed layers in the purification zone, and improves the separation efficiency of the simulated moving bed, thereby obtaining p-methyl and ethyl benzene with a purity greater than 99.5%. The p-methyl and ethyl benzene are subjected to high-temperature catalytic dehydrogenation to obtain p-methylstyrene with a purity greater than 99.0%, thereby solving the current problem that the purity of p-methylstyrene is less than 98.0%.

[0042] 3) The present invention designs an adaptive and matching process flow and process parameters, and the production cost of p-methylstyrene is low and the purity is high, and it can be used for the industrial production of p-methylstyrene. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 It is a schematic diagram of the process flow of the present invention:

[0044] In the figure: 1-water washing tower; 2-drying tower; 3-alkylation reactor; 4-high separation tank; 5-separation tower; 6-methyl and ethylbenzene heavy tower; 7-methyl and ethylbenzene light tower; 8-toluene heavy tower; 9-toluene light tower; 10-simulated moving bed device; 11-p-methyl and ethylbenzene separation tower; 12-m-methyl and ethylbenzene separation tower; 13-dehydrogenation reactor; 14-condenser; 15-oil-water separator; 16-separation tower; 17-p-methylstyrene light tower; 18-p-methylstyrene heavy tower; 19-p-methyl and ethylbenzene light tower; 20-p-methyl and ethylbenzene heavy tower DETAILED DESCRIPTION

[0045] The present invention will be further described below in conjunction with specific embodiments, but the present invention is not limited thereto.

[0046] Figure 1In the process, the catalytic dry gas enters the water washing tower 1 for washing, the catalytic dry gas is discharged from the upper part of the water washing tower and enters the drying tower 2 to remove water and solid impurities, and is mixed with toluene dried by molecular sieve and enters the alkylation reactor 3 for alkylation reaction. The alkylation product flows out of the reactor and is cooled and divided into two parts. One part returns to the inlet of the alkylation reactor and enters the alkylation reactor 3 after being mixed with the reaction materials, and the other part of the alkylation product enters the high separation tank 4 to separate the tail gas and then enters the separation tower 5. The crude methyl and ethyl benzene product discharged from the lower part of the separator enters the methyl and ethyl benzene heavy component removal tower 6 and the light component removal tower 7 in turn to separate the heavy component and the light component, so as to obtain 99.8% of m-methyl and ethyl benzene isomers.

[0047] The product discharged from the upper part of the alkylation product separation tower 5 is separated into light and heavy components by a toluene removal tower 8 and a light removal tower 9 to obtain recovered toluene, which is returned to the alkylation reactor 3 for repeated use.

[0048] The methyl and ethyl benzene isomers are introduced from the entrance of the adsorption tower of the simulated moving bed device 10, and the analytical agent is introduced from the entrance of the analytical tower of the simulated moving bed device 10. The raffinate rich in m-methyl and ethyl benzene is extracted from the outlet of the adsorption tower, and the extract rich in p-methyl and ethyl benzene is extracted from the outlet of the analytical tower. The extract is separated by the p-methyl and ethyl benzene separation tower 11 to obtain p-methyl and ethyl benzene with a purity of more than 99.5%, and the separated analytical agent is reused; the raffinate is separated by the m-methyl and ethyl benzene separation tower 12 to obtain m-methyl and ethyl benzene with a purity of more than 95.0%, and the m-methyl and ethyl benzene can be sent to the isomerization device for isomerization, and the isomerized product is returned to the adsorption tower as feed.

[0049] The p-ethylmethylbenzene obtained from the separation tower 11 is mixed with water vapor and heated in a preheater and enters the dehydrogenation reactor 13 for dehydrogenation reaction; the dehydrogenation product is condensed by the condenser 14 and enters the oil-water separator 15, and the dehydrogenated liquid obtained after dehydration and tail gas removal in the oil-water separator enters the separation tower 16; the crude p-methylstyrene product discharged from the lower part of the separation tower 16 enters the p-methylstyrene light component removal tower 17 and the heavy component removal tower 18 in turn to separate the light component and the heavy component, so as to obtain more than 99.0% of p-methylstyrene.

[0050] The components discharged from the upper part of the separation tower 16 are successively passed through the p-methylethylbenzene light removal tower 19 and the heavy removal tower 20 to obtain the recovered p-methylethylbenzene, which is returned to the dehydrogenation reactor 13 for repeated use.

[0051] Example 1

[0052] 1) Preparation of alkylation catalyst

[0053] 5 parts of phosphorus pentoxide, 2 parts of zinc oxide, and 93 parts of HZSM-5 molecular sieve (Nankai University Catalyst Company) were mechanically mixed and then extruded. The silicon-aluminum ratio of the HZSM-5 molecular sieve was 28. Then, they were calcined at 550°C for 4 hours in a water vapor atmosphere and naturally cooled to obtain a modified alkylation catalyst.

[0054] 2) Preparation of dehydrogenation catalyst

[0055] 78 parts of Fe2O3, 5 parts of K2O, 6 parts of Ce2O3, 4 parts of MoO3, 4 parts of CaO and 3 parts of MgO are mechanically mixed and then extruded.

[0056] 3) Catalytic alkylation of dry gas and toluene to synthesize methyl and ethyl benzene

[0057] The alkylation reaction of toluene dry gas is carried out in a tubular reactor. A phosphorus-zinc modified HZSM-5 molecular sieve catalyst is loaded into a Φ25mm reactor. The catalyst bed height is 1.5m. Both ends of the catalyst in the reactor are filled with quartz sand. After the reactor system is filled with toluene, the temperature and pressure are gradually increased. When the reaction temperature reaches 370°C and the pressure reaches 2.0MPa, the toluene dried by the molecular sieve and the catalytic dry gas dried by water-washed dealcoholamine are mixed and enter the reactor. The molar ratio of toluene to ethylene is 6:1, and the toluene volume space velocity is 3.0h -1 Under the above conditions, the methyl ethyl benzene synthesis reaction is carried out. The reaction conditions are appropriately changed as the ethylene conversion rate changes. For example, the reaction temperature can be increased when the ethylene conversion rate decreases significantly. For example, the reaction temperature can be increased by 1 to 2°C when the ethylene conversion rate decreases by 0.5 to 1 percentage point. The composition of the alkylation product is analyzed by online chromatography. The ethylene conversion rate, methyl ethyl benzene selectivity and production time are shown in Table 1. The crude reaction product is cooled and divided into two parts. 40% of the crude product is recycled and returned to the inlet of the alkylation reactor. After mixing with the reaction materials, it enters the alkylation reactor. The other part of the alkylation product enters the separation tower. The crude methyl ethyl benzene product discharged from the lower part of the separation tower enters the methyl ethyl benzene heavy removal tower and the light removal tower in turn to separate the heavy component and the light component, and obtains 99.8% of methyl ethyl benzene isomers, including 20.1% of m-methyl ethyl benzene, 79.5% of p-methyl ethyl benzene, and 0.3% of o-methyl ethyl benzene.

[0058] 4) Methyl and ethyl benzene adsorption separation

[0059] A simulated moving bed with 16 adsorption beds was used. The bed configurations of the adsorption zone, purification zone, desorption zone, and buffer zone were (5, 6, 3, 2). The adsorption separation operation temperature was 140°C and the pressure was 0.6MPa. Each adsorption bed was a Φ30×1000mm column filled with RAX-3000A adsorbent (Changling Branch of Sinopec Catalyst Company). Methyl and ethyl benzene isomers were introduced from the inlet of the adsorption tower of the simulated moving bed device, and the desorbent p-diethylbenzene was introduced from the inlet of the desorption tower of the simulated moving bed device. The raffinate rich in m-methyl and ethyl benzene was extracted from the outlet of the adsorption tower, and the extract rich in p-methyl and ethyl benzene was extracted from the outlet of the desorption tower. The flow rates of the injected and extracted logistics were: 850ml / h for the raw material methyl and ethyl benzene isomers, 4200ml / h for the desorbent p-diethylbenzene, 2122ml / h for the extract, 2928ml / h for the raffinate, and 2975ml / h for the circulation volume.

[0060] The extract is separated by a p-methylethylbenzene separation tower to obtain p-methylethylbenzene with a purity of 99.6%, and the separated analytical agent p-diethylbenzene is reused; the residual liquid is separated by a m-methylethylbenzene separation tower to obtain m-methylethylbenzene with a purity of 95.3%, and the separated analytical agent p-diethylbenzene is reused.

[0061] 5) Catalytic dehydrogenation of methyl and ethyl benzene

[0062] The p-methylethylbenzene obtained from the separation tower is mixed with water vapor in a preheater for preheating and gasification, and then enters the tube-in-tube dehydrogenation reactor for catalytic dehydrogenation reaction. The modified iron-based catalyst is loaded into the Φ32mm reactor, the catalyst bed height is 1.5m, and both ends of the catalyst in the reactor are filled with quartz sand. The reaction temperature of the p-methylethylbenzene raw material is 600℃, the water-oil mass ratio is 3:1, and the space velocity is 0.8h -1 , the reaction pressure is 50KPa. Under the above conditions, the dehydrogenation reaction of p-methylethylbenzene is carried out. The composition of the dehydrogenation product is analyzed by online gas chromatography, and the selectivity of p-methylstyrene is 95.78%. The crude reaction product is condensed by a condenser, and after the oil-water separator is drained, the oil phase enters the p-methylstyrene separation tower, and the p-methylstyrene crude product discharged from the lower part of the separation tower enters the p-methylstyrene light removal tower and the heavy removal tower in turn, and 99.2% of p-methylstyrene is obtained at the top of the heavy removal tower.

[0063] Example 2

[0064] 1) Preparation of alkylation catalyst

[0065] 4 parts of phosphorus pentoxide, 3 parts of zinc oxide and 93 parts of HZSM-5 molecular sieve are mechanically mixed and then extruded. The silicon-aluminum ratio of the HZSM-5 molecular sieve is 28. Then, they are calcined at 600°C in a water vapor atmosphere for 2 hours and naturally cooled to obtain a modified alkylation catalyst.

[0066] 2) Preparation of dehydrogenation catalyst

[0067] 79 parts of Fe2O3, 4 parts of K2O, 10 parts of Ce2O3, 2 parts of MoO3, 1 part of CaO and 4 parts of MgO are mechanically mixed and then extruded.

[0068] 3) Catalytic alkylation of dry gas and toluene to synthesize methyl and ethyl benzene

[0069] The alkylation reaction of toluene dry gas is carried out in a tubular reactor. A phosphorus-zinc modified HZSM-5 molecular sieve catalyst is loaded into a Φ25mm reactor. The catalyst bed height is 1.5m. Both ends of the catalyst in the reactor are filled with quartz sand. After the reactor system is filled with toluene, the temperature and pressure are gradually increased. When the reaction temperature reaches 380°C and the pressure reaches 3.0MPa, the toluene dried by the molecular sieve and the catalytic dry gas dried by water-washed alcohol removal amine are mixed and enter the reactor. The molar ratio of toluene to ethylene is 8:1, and the toluene volume space velocity is 5.0h -1 , the methyl ethyl benzene synthesis reaction was carried out under the above conditions, and the reaction conditions were appropriately changed with the change of ethylene conversion rate. For example, the reaction temperature can be increased when the ethylene conversion rate decreases significantly, such as increasing the reaction temperature by 1-2°C for every 0.5-1 percentage point decrease in the ethylene conversion rate. The composition of the alkylation product was analyzed by online chromatography, and the ethylene conversion rate, methyl ethyl benzene selectivity and production time are shown in Table 2. The crude reaction product was cooled and divided into two parts, 50% of the crude product was recycled and returned to the inlet of the alkylation reactor, mixed with the reaction materials and then entered the alkylation reactor, and the other part of the alkylation product entered the separation tower, and the crude methyl ethyl benzene product discharged from the lower part of the separation tower entered the methyl ethyl benzene heavy removal tower and the light removal tower in turn to separate the heavy component and the light component, and 99.8% of methyl ethyl benzene isomers were obtained, of which m-methyl ethyl benzene was 22.1%, p-methyl ethyl benzene was 77.5%, and o-methyl ethyl benzene was 0.3%.

[0070] 4) Methyl and ethyl benzene adsorption separation

[0071] A simulated moving bed with 24 adsorption beds is used. The bed configurations of the adsorption zone, purification zone, desorption zone, and buffer zone are (7, 9, 5, 3). The adsorption separation operation temperature is 120°C and the pressure is 0.5MPa. Each adsorption bed is a Φ30×1000mm column loaded with RAX-3000A adsorbent. Methyl and ethyl benzene isomers are introduced from the inlet of the adsorption tower of the simulated moving bed device, and the desorbent p-diethylbenzene is introduced from the inlet of the desorption tower of the simulated moving bed device. The raffinate rich in m-methyl and ethyl benzene is extracted from the outlet of the adsorption tower, and the extract rich in p-methyl and ethyl benzene is extracted from the outlet of the desorption tower. The flow rates of the injected and extracted logistics are: 1260ml / h of raw material methyl and ethyl benzene isomers, 5290ml / h of desorbent p-diethylbenzene, 2824ml / h of extract, 3726ml / h of raffinate, and 4500ml / h of circulation volume.

[0072] The extract is separated by a p-methylethylbenzene separation tower to obtain p-methylethylbenzene with a purity of 99.8%, and the separated analytical agent p-diethylbenzene is reused; the residual liquid is separated by a m-methylethylbenzene separation tower to obtain m-methylethylbenzene with a purity of 95.8%, and the separated analytical agent p-diethylbenzene is reused.

[0073] 5) Catalytic dehydrogenation of methyl and ethyl benzene

[0074] The p-methyl and ethyl benzene obtained from the separation tower is mixed with water vapor in a preheater for preheating and gasification, and enters the tube-in-tube dehydrogenation reactor for catalytic dehydrogenation reaction. The modified iron-based catalyst is loaded into the Φ32mm reactor, the catalyst bed height is 1.5m, and both ends of the catalyst in the reactor are filled with quartz sand. The reaction temperature of the p-methyl and ethyl benzene raw material is 560℃, the water-oil mass ratio is 2:1, and the space velocity is 0.5h -1 , the reaction pressure is 30KPa. Under the above conditions, the p-methylethylbenzene dehydrogenation reaction is carried out. The composition of the dehydrogenation product is analyzed by online gas chromatography, and the selectivity of p-methylstyrene is 95.81%. The crude reaction product is condensed by a condenser, and after draining the oil-water separator, the oil phase enters the p-methylstyrene separation tower, and the p-methylstyrene crude product discharged from the lower part of the separation tower enters the p-methylstyrene light removal tower and the heavy removal tower in turn, and 99.5% of p-methylstyrene is obtained at the top of the heavy removal tower.

[0075] Example 3

[0076] 1) Preparation of alkylation catalyst

[0077] 2 parts of phosphorus pentoxide, 1 part of zinc oxide, and 97 parts of HZSM-5 molecular sieve are mechanically mixed and then extruded. The silicon-aluminum ratio of the HZSM-5 molecular sieve is 28. Then, they are calcined at 500°C in a water vapor atmosphere for 6 hours, and then naturally cooled to obtain a modified alkylation catalyst.

[0078] 2) Preparation of dehydrogenation catalyst

[0079] 79 parts of Fe2O3, 8 parts of K2O, 8 parts of Ce2O3, 1 part of MoO3, 3 parts of CaO and 1 part of MgO are mechanically mixed and then extruded.

[0080] 3) Catalytic alkylation of dry gas and toluene to synthesize methyl and ethyl benzene

[0081] The alkylation reaction of toluene dry gas is carried out in a tubular reactor. A phosphorus-zinc modified HZSM-5 molecular sieve catalyst is loaded into a Φ25mm reactor. The catalyst bed height is 1.5m. Both ends of the catalyst in the reactor are filled with quartz sand. After the reactor system is filled with toluene, the temperature and pressure are gradually increased. When the reaction temperature reaches 360°C and the pressure reaches 1.0MPa, the toluene dried by the molecular sieve and the catalytic dry gas dried by water-washed dealcoholamine are mixed and enter the reactor. The molar ratio of toluene to ethylene is 5:1, and the toluene volume space velocity is 4.0h -1Under the above conditions, the methyl ethyl benzene synthesis reaction is carried out. The reaction conditions are appropriately changed as the ethylene conversion rate changes. For example, the reaction temperature can be increased when the ethylene conversion rate decreases significantly. For example, the reaction temperature can be increased by 1 to 2°C when the ethylene conversion rate decreases by 0.5 to 1 percentage point. The composition of the alkylation product is analyzed by online chromatography. The ethylene conversion rate, methyl ethyl benzene selectivity and production time are shown in Table 3. The crude reaction product is cooled and divided into two parts. 60% of the crude product is recycled and returned to the inlet of the alkylation reactor. After mixing with the reaction materials, it enters the alkylation reactor. The other part of the alkylation product enters the separation tower. The crude methyl ethyl benzene product discharged from the lower part of the separation tower enters the methyl ethyl benzene heavy removal tower and the light removal tower in turn to separate the heavy component and the light component, and obtains 99.7% of methyl ethyl benzene isomers, of which m-methyl ethyl benzene is 30.5%, p-methyl ethyl benzene is 69.1%, and o-methyl ethyl benzene is 0.3%.

[0082] 4) Methyl and ethyl benzene adsorption separation

[0083] A simulated moving bed with 16 adsorption beds is used. The bed configurations of the adsorption zone, purification zone, desorption zone, and buffer zone are (5, 6, 3, 2). The adsorption separation operation temperature is 170°C and the pressure is 1.0 MPa. Each adsorption bed is a Φ30×1000mm column filled with RAX-3000A adsorbent. Methyl and ethyl benzene isomers are introduced from the inlet of the adsorption tower of the simulated moving bed device, and the desorbent p-diethylbenzene is introduced from the inlet of the desorption tower of the simulated moving bed device. The raffinate rich in m-methyl and ethyl benzene is extracted from the outlet of the adsorption tower, and the extract rich in p-methyl and ethyl benzene is extracted from the outlet of the desorption tower. The flow rates of the injected and extracted logistics are: 1020 ml / h of raw material methyl and ethyl benzene isomers, 4080 ml / h of desorbent p-diethylbenzene, 2142 ml / h of extract, 2958 ml / h of raffinate, and 3570 ml / h of circulation volume.

[0084] The extract is separated by a p-methylethylbenzene separation tower to obtain p-methylethylbenzene with a purity of 99.7%, and the separated analytical agent p-diethylbenzene is reused; the residual liquid is separated by a m-methylethylbenzene separation tower to obtain m-methylethylbenzene with a purity of 95.2%, and the separated analytical agent p-diethylbenzene is reused.

[0085] 5) Catalytic dehydrogenation of methyl and ethyl benzene

[0086] The p-methylethylbenzene obtained from the separation tower is mixed with water vapor in a preheater for preheating and gasification, and then enters the tube-in-tube dehydrogenation reactor for catalytic dehydrogenation reaction. The modified iron-based catalyst is loaded into the Φ32mm reactor, the catalyst bed height is 1.5m, and both ends of the catalyst in the reactor are filled with quartz sand. The reaction temperature of the p-methylethylbenzene raw material is 610℃, the water-oil mass ratio is 4:1, and the space velocity is 2.0h -1, the reaction pressure is 100KPa. Under the above conditions, the dehydrogenation reaction of p-methylethylbenzene is carried out. The composition of the dehydrogenation product is analyzed by online gas chromatography, and the selectivity of p-methylstyrene is 95.16%. The crude reaction product is condensed by a condenser, and after draining the oil-water separator, the oil phase enters the p-methylstyrene separation tower, and the p-methylstyrene crude product discharged from the lower part of the separation tower enters the p-methylstyrene light removal tower and the heavy removal tower in turn, and 99.2% of p-methylstyrene is obtained at the top of the heavy removal tower.

[0087] Comparative Example 1

[0088] 1) Catalytic alkylation of dry gas and toluene to synthesize methyl and ethyl benzene

[0089] The other conditions were the same as those in Example 1, and the catalyst used was a silicon-magnesium-modified ZSM-5 / ZSM-11 co-crystallized molecular sieve catalyst prepared according to Chinese patent CN201710469627. The ethylene conversion, methylethylbenzene selectivity, and production time are shown in Table 4. The crude reaction product was separated to obtain methylethylbenzene containing 4.4% of m-methylethylbenzene, 95.1% of p-methylethylbenzene, and 0.3% of o-methylethylbenzene.

[0090] 2) Catalytic dehydrogenation of methyl and ethyl benzene

[0091] Methyl ethyl benzene containing 4.4% m-ethyl ethyl benzene, 95.1% p-ethyl ethyl benzene and 0.3% o-ethyl methyl benzene was mixed with steam in a preheater for catalytic dehydrogenation reaction, and the dehydrogenation conditions were consistent with those in Example 1. The composition of the dehydrogenated product was analyzed by online gas chromatography, and the selectivity of p-methyl styrene was 95.58%. After separation of the dehydrogenated product, methyl styrene with a purity of 99.5% was obtained, which contained 4.3% m-methyl styrene and 95.3% p-methyl styrene.

[0092] Table 1

[0093] Production time, h 200 500 1000 2000 3000 3500 Ethylene conversion, % 75.2 74.8 74.3 73.7 73.2 72.3 Methyl and ethyl benzene selectivity, % 95.1 95.2 94.3 94.1 93.8 91.3 Selectivity to methyl and ethyl benzene, % 76.1 78.2 79.4 79.5 79.5 79.4 Selectivity of m-ethylbenzene, % 23.1 21.0 19.8 19.7 19.7 19.8

[0094] Table 2

[0095] Production time, h 200 500 1000 2000 3000 3500 Ethylene conversion, % 75.8 75.6 75.3 74.7 74.2 72.1 Methyl and ethyl benzene selectivity, % 95.0 95.2 94.6 94.3 93.8 92.3 Selectivity to methyl and ethyl benzene, % 73.1 76.2 77.2 77.4 77.0 76.4 Selectivity of m-ethylbenzene, % 26.2 23.1 22.1 21.9 22.3 22.9

[0096] Table 3

[0097]

[0098]

[0099] Table 4

[0100] Production time, h 100 200 300 400 Ethylene conversion, % 65.7 64.2 50.9 20.5 Methyl and ethyl benzene selectivity, % 95.2 95.0 92.1 90.3 Selectivity to methyl and ethyl benzene, % 95.1 95.5 95.4 95.3 Selectivity of m-ethylbenzene, % 4.6 4.2 4.3 4.2

[0101] The products obtained in Examples 1 to 3 are all above 99%, which is due to the synergistic effect of the preparation process and the alkylation reaction catalyst. The para-selectivity is strictly controlled by the alkylation reaction catalyst, part of the alkylation product is refluxed, and the remaining part is simultaneously adsorbed and analyzed by a moving bed, thereby efficiently separating p-ethylmethylbenzene and m-ethylmethylbenzene. M-ethylmethylbenzene can be isomerized, reconstructed and recycled, and high-purity p-ethylmethylbenzene is directly used for dehydrogenation to prepare p-methylstyrene. The present invention greatly improves the catalyst life and product purity through multiple separation and purification and cyclic recovery.

[0102] It can be seen from Tables 1 to 4 that the selectivity of the catalyst provided by the present invention for methyl and ethyl benzene is 70%, and it can operate stably for 4000 hours continuously, while the selectivity of the catalyst used in Comparative Example 1 for methyl and ethyl benzene is 95%. The high selective activity causes it to be deactivated after 400 hours of reaction, and the purity of the obtained product is only 94.8%, which cannot meet the performance requirements of high-purity para-methylstyrene.

Claims

1. A method for synthesizing high-purity p-methylstyrene, characterized in that: include: 1) The catalytic dry gas after washing with water to remove the alcohol amine is mixed with toluene and fed into an alkylation reactor for alkylation reaction, 30-80% of the obtained alkylation product is recycled back to the alkylation reactor, and the remaining alkylation product is separated and purified to obtain mixed methyl and ethyl benzene; 2) separating the mixed methyl and ethyl benzenes by simulated moving bed adsorption to obtain p-methyl and ethyl benzene with a purity greater than 99.5%; 3) After the p-methylethylbenzene and water are gasified, a dehydrogenation reaction is carried out under the catalysis of an iron-based catalyst to separate them; The catalyst for the alkylation reaction comprises, by weight, 2 to 5 parts of phosphorus pentoxide, 1 to 3 parts of zinc oxide, and 92 to 97 parts of HZSM-5 molecular sieve; The simulated moving bed has 16 to 24 beds, which are divided into an adsorption zone, a purification zone, a desorption zone and a buffer zone according to the bed layers; The mixed methyl and ethyl benzene comprises 65-80% of p-methyl and ethyl benzene and 20-35% of m-methyl and ethyl benzene, and the remainder is o-methyl and ethyl benzene.

2. The method for synthesizing high-purity p-methylstyrene according to claim 1, characterized in that: The preparation process of the catalyst for the alkylation reaction is as follows: phosphorus pentoxide, zinc oxide and HZSM-5 molecular sieve are mechanically mixed and then extruded, calcined at 500-600° C. for 2-6 hours in a water vapor atmosphere, and naturally cooled to obtain the catalyst; the silicon-aluminum ratio of the HZSM-5 molecular sieve is 10-100.

3. The method for synthesizing high-purity p-methylstyrene according to claim 1, characterized in that: The temperature of the alkylation reaction is 300-450°C, and the space velocity is 3.0-5.0h -1 , pressure is 1.0~3.0MPa.

4. A method for synthesizing high-purity p-methylstyrene according to claim 3, 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.

5. The method for synthesizing high-purity p-methylstyrene according to claim 1, characterized in that: The remaining alkylation product enters a high separation tank to separate tail gas and then enters a separation tower for separation. The crude methyl ethyl benzene product discharged from the lower part of the separation tower enters a methyl ethyl benzene heavy component removal tower and a light component removal tower in turn to separate heavy components and light components to obtain mixed methyl ethyl benzene; the purity of the mixed methyl ethyl benzene is ≥99%.

6. The method for synthesizing high-purity p-methylstyrene according to claim 1, characterized in that: The bed configuration of the adsorption zone, purification zone, desorption zone and buffer zone in the simulated moving bed is preferably (5, 6, 3, 2) or (7, 9, 5, 3).

7. The method for synthesizing high-purity p-methylstyrene according to claim 1, characterized in that: The adsorbent used in the simulated moving bed is X zeolite, and the desorbent is at least one of toluene, p-xylene and p-diethylbenzene.

8. The method for synthesizing high-purity p-methylstyrene according to claim 1, characterized in that: The operating temperature of the simulated moving bed is 120-170° C., and the pressure is 0.4-1.0 MPa.

9. The method for synthesizing high-purity p-methylstyrene according to claim 1, characterized in that: The iron-based catalyst is calculated by mass percentage as follows: K2O 4-8%, Ce2O3 6-10%, MoO3 1-5%, CaO 1-4%, MgO 1-4%, and the balance is Fe2O3.

10. The method for synthesizing high-purity p-methylstyrene according to claim 1, characterized in that: The dehydrogenation reaction process is: preheating ethylparamethylbenzene and water vapor and entering the dehydrogenation reactor, and after condensation, the product enters the oil-water separator to separate the gas phase and water, and then sequentially undergoes purification separation, light component removal and heavy component removal to obtain the product.

11. The method for synthesizing high-purity p-methylstyrene according to claim 10, characterized in that: The purification and separation process also requires the addition of a polymerization inhibitor, the amount of which is 50 to 100 ppm of the p-methylstyrene content.

12. The method for synthesizing high-purity p-methylstyrene according to claim 1, characterized in that: The process conditions of the dehydrogenation reaction are: the temperature of the dehydrogenation reactor is 560°C to 630°C, the liquid volume space velocity of methyl ethyl benzene is 0.5h -1 ~2.0h -1 , the mass ratio of water to p-methylethylbenzene is 2 to 4, and the dehydrogenation reaction pressure is 30 to 100 KPa.

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