CN100413830C - Method for preparing styrene from ethylbenzene dehydrogenation - Google Patents

Abstract

This invention relates to a method for preparing styrene by ethyl benzene dehydrogenation. Styrene is prepared at 450-550 deg.C, normal pressure, space velocity of 0.1-1.0h-1, and CO2/ethyl benzene mol ratio of (10-30): 1 in the presence of Cr2O3/Al2O3 catalyst. The method solves the problems of high energy consumption by steam diluter, or low catalyst performance at low temperatures caused by CO2 diluter. The method can be used for manufacture of styrene by ethyl benzene dehydrogenation.

Description

Method for preparing styrene from ethylbenzene dehydrogenation

technical field

The invention relates to a method for preparing styrene by dehydrogenating ethylbenzene.

Background technique

Styrene is an important organic chemical raw material widely used in the production of plastics, resins and synthetic rubber. It is the fourth largest ethylene derivative product next to PE, PVC, and EO. In recent years, the demand has continued to increase (at a rate of 3-4%). It is expected that the demand in 2004 will exceed 2.1×10 ⁸ tons. In the past 7 years, my country has introduced 8 sets and built 3 sets of styrene production equipment with domestic technology, with an annual production capacity of about 900,000 tons. After China's accession to WTO, the price competition of world chemical products is fierce. Therefore, develop new technological processes and reduce costs. It is of great significance to improve the economic benefits of petrochemical enterprises.

Industrial styrene production methods include ethylbenzene dehydrogenation and styrene-propylene oxide cogeneration. Among them, the co-production method has complicated process, large one-time investment and high energy consumption. Therefore 90% of styrene is produced by dehydrogenation of ethylbenzene. The main reaction of ethylbenzene dehydrogenation is: C ₆ H ₅ -C ₂ H ₅ →C ₆ H ₅ CH=CH ₂ +H ₂ +124 kJ/mol. From a thermodynamic analysis, increasing the temperature and reducing the system pressure are beneficial to the balance. However, the increase of the reaction temperature is greatly limited, because too high reaction temperature not only leads to the cracking of ethylbenzene to produce by-products such as benzene, toluene, CO, CO ₂ , but also consumes a lot of energy. Therefore, most of the industries use a large amount of water vapor as the dehydrogenation medium. Its functions are: (1) heating the reaction raw materials to the required temperature, (2) supplementing heat to avoid cooling due to heat absorption of the reaction, (3) reducing the partial pressure of ethylbenzene, increasing the equilibrium conversion rate, (4) combining with the catalyst The coke formed on the catalyst reacts to maintain the stability of the catalyst. However, the utilization of a large amount of water vapor occupies a large production cost of styrene. The energy consumption per ton of styrene is about 6.3×10 ⁹ kilojoules, and at least 5.4×10 ⁹ kilojoules are needed even considering latent heat recovery.

Through the improvement of the catalyst, the amount of water vapor is reduced. In 1997, Süd Chemie Group developed Styromax-3 and 5 catalysts, which have good low-temperature performance. Its notable feature is that it is suitable for low water ratio (S/O=1:1) operation. Recently, the Criterion Catalyst Company of the United States has developed the C-055 catalyst, which is said to reduce the water ratio (S/O) from 1.7:1 to 1:1, while the selectivity remains unchanged. However, judging from the C-045 catalyst launched in the market, its performance is not outstanding. In addition, DOW Corporation of the United States has developed an adiabatic D-0239E catalyst. The adaptable range of the water ratio is between 1.1 and 1.7. When the operating water ratio is 1:1, the energy consumption can be reduced by 40% without shortening the life of the catalyst. When the water ratio is 1.7, the yield of styrene can be increased by nearly 10%. In short, foreign countries have invested a lot of manpower and material resources in the research and development of the catalyst, and the research technology is highly confidential. At present, the styrene dust production technology is quite mature. Almost all styrene production devices have adopted new reactors with low resistance drop, negative pressure dehydrogenation process, and energy comprehensive utilization measures to reduce the material consumption and energy consumption of styrene production. down to the limit level. Therefore, there is an urgent need to develop new styrene production processes.

On the other hand, another route for styrene production is the oxidative dehydrogenation process. Heat is provided by the hydrogen oxidation reaction inside the reaction to reduce energy consumption. However, due to the increase in side reactions such as deep oxidation and oxygen molecule insertion, the selectivity of styrene is not high enough to be industrialized. In recent years, the research on the oxidative dehydrogenation of ethylbenzene to styrene using _CO2 as a mild oxidant has attracted the attention of scientists all over the world. Tower's paper published in Chem.Eng.Prog. magazine reported that at 600°C, the ratio of CO ₂ to ethylbenzene is 5:1, and the equilibrium conversion rate of ethylbenzene can reach 95%. Without _CO , the equilibrium conversion was only 67%, and similar conversions have been obtained industrially. As a diluent, _CO2 itself has a high heat capacity, which is very beneficial to reduce the hot spots on the surface of the catalyst and maintain the stability and life of the catalyst. In addition, the substitution of CO ₂ for steam oxidative dehydrogenation to styrene may open up a new way for the utilization of CO ₂ (especially for the hydrogen production process of methane steam reforming, a large amount of CO ₂ has not been effectively utilized), which has a great impact on reducing greenhouse gas emissions. Gas emissions are significant. However, commercial Fe-K-Ce-Mo catalysts are not suitable for the dehydrogenation of ethylbenzene in the presence of _CO2 . Some new catalysts have been developed, with Al ₂ O ₃ , ZnO, SiO ₂ , ZrO ₂ , zeolite and activated carbon as supports, different transition metals Fe, V, Cr, Co oxides as active components, alkali metals Li, Na etc. as auxiliaries. For example, Park Sang Yon of Korea Research Institute of Chemical Industry reported in Japanese Patent JP11165069 A2 and US Patent USP6037511, USP6034032 that in the temperature range of 500-700 ° C, in (Fe(II)) _x (Fe(III)) _y O On _z /S and 5% Fe ₃ O ₄ /ZSM-5 catalyst, use CO ₂ as diluent to carry out mild oxidative dehydrogenation of ethylbenzene to styrene, and 48% styrene can be obtained. However, the key to hindering the industrialization of this technology is the activity and stability of the catalyst. Under high conversion conditions, the catalyst deactivates significantly within 10 hours.

Contents of the invention

The technical problem to be solved by the present invention is that in the prior art, the energy consumption of the water vapor diluent is large or the low temperature performance of the catalyst is poor when _CO is used as the diluent. A new method for preparing styrene by dehydrogenation of ethylbenzene is provided Methods. The method is used in the dehydrogenation reaction of ethylbenzene, and when _CO2 is used as the diluent, it has the advantages of low reaction energy consumption, high catalytic activity of the catalyst at low temperature, and high selectivity of the product styrene.

In order to solve the above-mentioned technical problems, the technical scheme adopted in the present invention is as follows: a method for preparing styrene by ethylbenzene dehydrogenation, using ethylbenzene as raw material, in _CO Atmosphere, reaction temperature is 450～550 ℃, reaction pressure is Under normal pressure, space velocity of 0.1 to 1.0 hours ^-1 , and CO ₂ : ethylbenzene molar ratio of 10 to 30:1, ethylbenzene passes through the catalyst bed to generate styrene, wherein the catalyst used includes the following group by weight percentage: point:

a) 10-30% _{Cr2O3 ;}

b) 60-75% Al ₂ O ₃ ;

c) 0.1-20% of at least one transition metal oxide selected from V, Ce, Mn, Mo, Zn or Sb.

In the above technical solution, the Cr ₂ O ₃ catalyst is preferably used in a range of 15-25% by weight, and the transition metal oxide is preferably used in a range of 5-15%. The preferred version of the catalyst used is to also include 0.01 to 1.5% noble metal or its oxide in terms of weight percentage, the preferred version of the noble metal is at least one selected from Pd or Pt, the preferred range of the noble metal or its oxide is 0.2- 0.8%.

The preparation method of the catalyst used in the method of the present invention is as follows: at first with the required amount of noble metal element compound solution, transition metal element compound solution, salt solution of chromium, impregnated on alumina with equal volume impregnation method, kneading molding, in Drying at 80-150°C for 1-10 hours, and then calcining at 450-650°C for 0.5-12 hours to obtain the desired catalyst.

The raw material used in the catalyst used in the inventive method is as follows: the raw material of Pd is selected from palladium acid or its salt; The raw material of Pt is selected from chloroplatinic acid or its salt; The raw material of Mo is selected from ammonium molybdate; The raw material of Ce is selected from Cerium nitrate; the raw material of Cr is selected from chromium nitrate; the raw material of Al is selected from alumina, the raw material of vanadium is selected from ammonium metavanadate, and the rest are selected from its nitrate.

The catalyst used in the method of the present invention is owing to adopt Cr ₂ O ₃ and Al ₂ O ₃ form catalytic system, support transition metal oxide or/and noble metal or its oxide compound to form catalyst simultaneously, be used for ethylbenzene catalytic dehydrogenation reaction, in Under the condition of CO as the _diluent , the inventors have surprisingly found that the conversion rate of ethylbenzene can reach 74.6% and the selectivity of styrene can reach more than 98% at the reaction temperature of 500 DEG C and the normal pressure condition, and at the same time Due to the use of _CO2 as diluent and the reaction at a temperature of 500 ° C, a large amount of energy consumption can be saved, and a good technical effect has been achieved.

The evaluation condition of the catalyst obtained by the method of the present invention is that the temperature is controlled at 450～550° C., the reaction pressure is normal pressure, the mol ratio of carbon dioxide and ethylbenzene is maintained at 10～30: 1, and the space velocity of ethylbenzene is 0.1～1.0 hours ^-1 . The reaction products were directly analyzed by on-line gas chromatography.

Below by embodiment the present invention will be further elaborated.

Detailed ways

【Example 1】

0.1 gram of weight composition 20%Cr ₂ O ₃ /80%Al ₂ O ₃ catalysts are packed into a stainless steel reactor with a diameter of 5 mm, the temperature is programmed to 500 ° C, and the heating rate is 20 ° C / min, and the catalyst is pre-heated under N2 atmosphere. After 2 hours of treatment, ethylbenzene is vaporized by a saturated steam generator, and then mixed with _CO2 to form a feed gas that enters the catalyst bed for reaction. The reaction was carried out at 500°C, the pressure was normal pressure, the molar ratio of _CO2 to ethylbenzene was 20:1, and the flow rate of ethylbenzene was 0.42 mmol/h. The weight composition and performance were shown in Table 1 and Table 2.

[Embodiments 2-4]

Prepare and evaluate the catalyst according to the steps and conditions of Example 1, only changing the content of _Cr2O3 and _Al2O3 components, the weight percent composition of the catalyst, the _{dehydrogenation performance} and the stability of the catalyst under the carbon dioxide atmosphere, see respectively Table 1, Table 2.

The weight percent composition of table 1 catalyst

Table 2 Catalyst dehydrogenation performance under carbon dioxide atmosphere

Example Conversion rate% Selectivity % Example 1 57.5 99.0 Example 2 48.6 99.2 Example 3 59.3 98.9 Example 4 56.4 98.7

【Example 5】

The composition of 0.1 gram weight percentage composition is the catalyst of 5% CeO ₂ /20% Cr ₂ O ₃ /75% Al ₂ O ₃ , packs in the stainless steel reactor of a diameter 5 millimeters, heats up to 500 ℃ by programming, the heating rate At 20°C/min, the catalyst was pretreated under _N2 atmosphere for 2 hours. Ethylbenzene was vaporized by a saturated steam generator, and then mixed with _CO2 to form a feed gas that entered the catalyst bed for reaction. The reaction is carried out at 500°C, the pressure is normal pressure, the molar ratio of CO to ethylbenzene is 20:1, and the flow rate of ethylbenzene is 0.42 mmol/hour. The weight composition, evaluation results and performance are shown in Table 3 _, Table 4 and Table 4. 5.

[Embodiments 6-11]

Prepare and evaluate catalyst according to each step and condition of embodiment 5, just change the type of transition metal element, each component content, the weight percent composition of catalyst, the dehydrogenation performance under the carbon dioxide atmosphere and the stability of catalyst are shown in Table 3, respectively. Table 4, Table 5.

The weight percent composition of table 3 catalyst

Table 4 Catalyst dehydrogenation performance under carbon dioxide atmosphere

Conversion rate% selectivity% Example 5 69.9 99.1 Example 6 65.8 98.7 Example 7 65.7 98.8 Example 8 55.5 99.3 Example 9 49.0 99.8 Example 10 41.1 98.9 Example 11 69.6 99.0

The stability performance of table 5 embodiment 5 catalysts

Response time, hours Conversion rate selectivity 50 69.9 99.1 100 69.6 99.3 150 69.0 99.3 200 68.8 99.5

[Example 12]

0.1 gram weight percent is composed of 0.4%Pd/5%CeO ₂ /20%Cr ₂ O ₃ /74.6%Al ₂ O ₃ The catalyst is loaded into a stainless steel reactor with a diameter of 5 mm, and the temperature is raised to 500 ° C, The heating rate was 20°C/min, and the catalyst was pretreated under _N2 atmosphere for 2 hours. Ethylbenzene was vaporized by a saturated steam generator, and then mixed with _CO2 to form a feed gas that entered the catalyst bed for reaction. The reaction was carried out at 500°C, the pressure was normal pressure, the molar ratio of CO to ethylbenzene was 20:1, and the ethylbenzene flow rate was 0.42 mmol/hour. The catalyst composition and dehydrogenation performance were listed in Table 6 _, Table 7 and Table 8.

[Examples 13-19]

According to each step of embodiment 12, only change the type and weight percentage content of noble metal in the catalyst composition, the type and weight content of transition metal oxide, the weight content of chromium oxide and the weight content of aluminum oxide, the weight percentage composition of the obtained catalyst, The dehydrogenation performance and stability under a carbon dioxide atmosphere are shown in Table 6, Table 7, and Table 8, respectively.

The weight percent composition of table 6 catalyst

Table 7 Catalyst dehydrogenation performance under carbon dioxide atmosphere

Conversion rate% selectivity% Example 12 74.6 98.6 Example 13 69.9 99.1 Example 14 70.4 98.8 Example 15 74.2 98.0 Example 16 73.1 98.8 Example 17 74.1 98.9 Example 18 74.4 98.6 Example 19 74.5 98.7

The stability performance of table 8 embodiment 12 catalysts

Response time, hours Conversion rate selectivity 50 74.6 98.6 100 74.4 98.6 200 74.3 98.7 300 74.2 98.8 400 74.0 98.0

[Example 20]

Prepare and evaluate the catalyst according to the steps and conditions of Example 12, except that the reaction temperature is changed to 450° C., the space velocity is 0.1 hour ⁻¹ , and the CO ₂ : ethylbenzene molar ratio is 28: 1. The reaction result is: conversion of ethylbenzene The yield was 71.8%, and the styrene selectivity was 99.4%.

[Example 21]

Prepare and evaluate the catalyst according to the steps and conditions of Example 12, except that the reaction temperature is changed to 550° C., the space velocity is 1.0 hours ⁻¹ , and the CO ₂ : ethylbenzene molar ratio is 12: 1. The reaction result is: conversion of ethylbenzene The yield was 76.1%, and the styrene selectivity was 97.3%.

Claims (6)

1. A method for preparing styrene by ethylbenzene dehydrogenation, using ethylbenzene as raw material, in _CO Atmosphere, reaction temperature is 450～550 ℃, reaction pressure is normal pressure, and space velocity is 0.1～1.0 hours ^-1 , CO ₂ : Under the condition that the molar ratio of ethylbenzene is 10～30:1, ethylbenzene generates styrene through the catalyst bed layer, wherein the catalyst used comprises the following components in weight percent: a) 10-30% _{Cr2O3 ;} b) 60-75% Al ₂ O ₃ ; c) 0.1-20% of at least one transition metal oxide selected from V, Ce, Mn, Mo, Zn or Sb. 2. The method for preparing styrene by dehydrogenating ethylbenzene according to claim 1, characterized in that the amount of Cr ₂ O ₃ used as catalyst is 15-25% in weight percentage. 3. The method for preparing styrene by ethylbenzene dehydrogenation according to claim 1, characterized in that the consumption of transition metal oxides is 5-15% in weight percent. 4. The method for preparing styrene by dehydrogenation of ethylbenzene according to claim 1, characterized in that the catalyst used also contains 0.01 to 1.5% of noble metals or oxides thereof in terms of weight percent. 5. The method for preparing styrene by dehydrogenation of ethylbenzene according to claim 4, wherein the noble metal is selected from at least one of Pd or Pt. 6. The method for preparing styrene by ethylbenzene dehydrogenation according to claim 4, characterized in that the amount of noble metal or its oxide is 0.2-0.8% by weight.