JPH1180045A - Production of styrene - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method suppressing the selectivity decrease of hydrogen oxidation of an oxidation catalyst in the production of styrene by oxidative dehydrogenation of ethylbenzene. SOLUTION: Alkaline substance is preliminarily removed from a reaction mixture supplied to a process (2) in the production of styrene by dehydrogenating ethylbenzene at least containing the following (1) to (3) processes. Process (1): the process obtaining the reaction mixture containing styrene and hydrogen by dehydrogenating ethylbenzene in the presence of a dehydrogenation catalyst. Process (2): the process contacting the reaction mixture with the oxidizing catalyst to selectively oxidize hydrogen contained in the mixture to afford water. Process (3): the process contacting the oxidation processed mixture with the dehydrogenation catalyst to dehydrogenate the unreacted ethylbenzene contained in the mixture to obtain styrene.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for producing styrene. More specifically, the present invention relates to a method for producing styrene by an oxidative dehydrogenation method of ethylbenzene, which suppresses a decrease in hydrogen oxidation selectivity of an oxidation catalyst. Styrene is an important compound as a raw material for polystyrene, synthetic rubber, ABS resin, unsaturated polyester resin and the like.

[0002]

2. Description of the Related Art A method for producing styrene by the dehydrogenation of ethylbenzene has been known in the art, for example, as described in many documents. For example, a process using an iron-potassium-based dehydrogenation catalyst has been known in the industry. Has been implemented. However, in the dehydrogenation reaction, the reaction equilibrium is generally strongly restricted, and therefore, even in the case of ethylbenzene, a high conversion cannot be obtained. Further, since the dehydrogenation reaction is an endothermic reaction, in the reaction in the adiabatic reactor, the reaction temperature decreases with the progress of the dehydrogenation reaction, and it is more difficult to obtain a high conversion of ethylbenzene.
Therefore, a so-called oxidative dehydrogenation method using an oxidation catalyst together with a dehydrogenation catalyst in a reaction process has been proposed for the main purpose of “shifting the reaction equilibrium” and “compensating for a decrease in the reaction temperature”.

[0003] For example, JP-A-60-130531 discloses that a dehydrogenating hydrocarbon is brought into contact with a dehydrogenation catalyst comprising an iron compound and an alkali metal, and the resulting reaction mixture is mixed with a Group 8 noble metal and tin. To selectively oxidize the hydrogen contained in the mixture, reheat the treated mixture, subject it to a dehydrogenation reaction again, and recover the dehydrogenated hydrocarbons. How to do is described.

[0004]

As a result of studies made by the present inventors, in the case of the oxidative dehydrogenation method for performing a selective oxidation reaction of hydrogen, an alkaline substance is contained in a mixture of ethylbenzene and hydrogen supplied to the oxidation catalyst. It has been found that the presence of carbon dioxide causes the alkaline substance to adhere to the catalyst, thereby inhibiting its selectivity, causing hydrocarbons such as ethylbenzene to burn on the oxidation catalyst and increasing the amount of carbon dioxide produced.

For example, it is known that a potassium compound is contained in a dehydrogenation catalyst for ethylbenzene, and that the potassium compound is also known to be scattered during the dehydrogenation reaction (BD Herzog et. al., Ind.
Eng. Chem. Prod. Res. Dev. 23,
(2), 187 (1984); Hayasaka et al., Proceedings of the 24th Annual Meeting of the Japan Aromatic Industries Association, p36 (1990)). Therefore, when the dehydrogenation reaction and the selective oxidation reaction of hydrogen are performed alternately in series, if the potassium compound is scattered, the selectivity of the oxidation catalyst is significantly reduced.

On the other hand, carbon dioxide is known to have a function of reducing the dehydrogenation activity of a dehydrogenation catalyst (Hirano,
Catalyst, 29, (8), 641 (1987), etc.). Therefore, an increase in the amount of carbon dioxide generated in the oxidation step means that the conversion rate of the subsequent dehydrogenation reaction is suppressed, which is not preferable in the subsequent dehydrogenation reaction. The purpose of the present invention is
Hydrogen in a reaction mixture containing styrene and hydrogen generated by the dehydrogenation reaction of ethylbenzene is burned by a selective oxidation reaction, and then unreacted ethylbenzene contained in the mixture is dehydrogenated to produce styrene. Another object of the present invention is to provide a method for suppressing a decrease in the hydrogen oxidation selectivity of an oxidation catalyst.

[0007]

Means for Solving the Problems The present inventors have made intensive studies to solve the above-mentioned problems, and as a result, selected hydrogen on the downstream side of the dehydrogenation catalyst layer of ethylbenzene and in the dehydrogenation reaction product. The present inventors have found that by removing a small amount of an alkaline substance contained in the dehydrogenation reaction product on the upstream side of the oxidation reaction catalyst layer, the oxidation reaction proceeds without inhibiting the selectivity of the selective oxidation catalyst for hydrogen. Was completed.

That is, the gist of the present invention is to provide a method for producing styrene by a dehydrogenation reaction of ethylbenzene comprising at least the following steps (1) to (3): A method for producing styrene, which is removed in advance.

Step (1): a step of dehydrogenating ethylbenzene in the presence of a dehydrogenation catalyst to obtain a reaction mixture containing styrene and hydrogen. Step (2): a step of bringing the reaction mixture into contact with an oxidation catalyst to selectively oxidize hydrogen contained in the mixture into water. Step (3): a step of bringing the oxidized mixture into contact with a dehydrogenation catalyst to dehydrogenate unreacted ethylbenzene contained in the mixture to obtain styrene. It is in. Hereinafter, the present invention will be described in detail.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The method for producing styrene used in the present invention is, for example, as follows. In the case of "dehydrogenation reaction + oxidation reaction + dehydrogenation reaction": Ethylbenzene (which may contain styrene) may be used at a temperature of 500 to 700 ° C and a pressure of 4.9 to 981 kP.
In (a), the mixture is passed through a dehydrogenation reactor (catalyst layer) in the former stage to obtain a mixture of styrene, hydrogen, unreacted ethylbenzene, and the like by a dehydrogenation reaction. The obtained mixture is passed through an oxidation reactor (catalyst layer), and selective oxidation of hydrogen is performed using a newly introduced oxygen-containing gas in the presence of a selective oxidation catalyst for hydrogen. Further, the mixture generated from the oxidation reactor (catalyst layer) is passed through a subsequent dehydrogenation reactor (catalyst layer),
Unreacted ethylbenzene is dehydrogenated to obtain styrene.
At this time, in the oxidation reactor, the temperature rises due to the heat generated by the internal combustion of hydrogen, and the hydrogen is oxidized (burned) and reduced, so that there is an advantage that the equilibrium inhibition of the subsequent dehydrogenation reaction is reduced.

Here, after the step of dehydrogenating ethylbenzene, ie, downstream of the reaction catalyst layer and before the step of selective oxidation of hydrogen in the dehydrogenation reaction product, ie, upstream of the reaction catalyst layer By removing a small amount of alkaline substances contained in the dehydrogenation reaction product, the hydrogen selectivity of the oxidation reaction in the hydrogen selective oxidation reaction catalyst layer is improved, and as a result, the carbon dioxide generated from the combustion of other hydrocarbons is reduced. Since the increase in the amount of generated carbon can be suppressed, a high conversion rate can be obtained in the dehydrogenation reaction in the dehydrogenation reaction catalyst layer at the rear of the oxidation reaction catalyst layer.

It is a preferable method to include water vapor in the supplied ethylbenzene. It is said that water vapor has a function of reducing the partial pressure of ethylbenzene and styrene produced in the dehydrogenation reaction and suppressing the production of coke. Here, the ratio of steam to ethylbenzene is not particularly limited, but the molar ratio of steam and ethylbenzene to be fed is preferably 15 or less, more preferably 1 to 14.

If necessary, the above dehydrogenation reactor (catalyst layer) and hydrogen oxidation reactor (catalyst layer) may be combined in multiple stages to carry out the reaction. Of course, it is necessary to remove the alkaline substance between the dehydrogenation reactor (catalyst layer) and the oxidation reactor (catalyst layer). However, when the dehydrogenation reactor (catalyst layer) is a combination of five or more stages, investment is large for the obtained effect, which is not practical.

Examples of the catalyst for dehydrogenating ethylbenzene used in the present invention include, for example, the aforementioned JP-A-60-13053.
No. 1 entitled "Iron compounds and the first of the periodic table"
A dehydrogenation catalyst comprising an alkaline metal selected from the group consisting of Group A and Group 2A "is preferably used. As used herein, "alkaline metal" refers to lithium,
Refers to metals of Groups 1A and 2A of the periodic table, including sodium, potassium, rubidium, cesium, beryllium, magnesium, calcium, strontium and barium. Further, in a preferred embodiment of the present invention, the dehydrogenation catalyst comprises a group 4B, a group 5B, or a group 6B of the periodic table.
It may contain a group B metal. Also, JP-A-4-27
The catalyst of "Consisting mainly of iron oxide and potassium oxide" described in Japanese Patent No. 7030 is also a preferred example. The composition of the preferred dehydrogenation catalyst used in the process of the present invention is substantially 70-80% by weight ferric oxide, 10-20% by weight potassium oxide and contains small amounts of other components. May be.

The catalyst for selective oxidation of hydrogen used in the present invention is a catalyst containing at least one metal selected from metals of Groups 4, 5 and 8 of the periodic table or a catalyst of the periodic table. The catalyst includes both at least one metal selected from Group 4 and Group 5 and at least one metal selected from Group 8 metal of the periodic table. For example,
“An oxidation catalyst comprising a noble metal of Group VIII of the periodic table and tin, more preferably an inorganic catalyst having a surface area in the range of 1 to 500 m ² / g” described in the above-mentioned JP-A-60-130531 Oxidation catalyst composed of a noble metal of Group VIII of the periodic table and tin compounded on a support ”;
No. 1-225140, "An oxidation catalyst comprising a Group 8 noble metal, a Group 4A metal and a Group 1A or Group 2A metal, more preferably about 900 to 1500
An oxidation catalyst comprising a Group 8 noble metal, a Group 4A metal and a Group 1A or Group 2A metal formed on an alumina support calcined at a temperature in the range of ° C. Further, "a catalyst containing tin or tin and an alkali metal" described in JP-A-6-298678 and Group 4 of the periodic table as described in JP-A-9-29095, Group 5 such as Sn, Ti, Ta, N
A catalyst containing b or the like and Group 8 of the periodic table, for example, Pt or Pd can also be used as a preferable catalyst. Alkaline substances scattered from the dehydrogenation catalyst are not specified, but since they are generated in the presence of high-temperature steam and carbon dioxide, for example, alkali metal carbonates such as potassium carbonate or potassium hydroxide, etc. Hydroxides and the like of alkaline substances are estimated as scattering substances.

The term "alkaline substance" used in the present invention is a general term for compounds containing alkaline metals such as oxides, carbonates and hydroxides of the above-mentioned alkaline metals. In the present invention, removing the alkaline substance means that the alkaline substance is contained in the reaction mixture supplied to the step (2) to such an extent that the operation can be stably continued without causing deterioration of the oxidation reaction catalyst. Say reduce the amount. As a method of removing the alkaline substance, a method of providing a removal layer composed of a dust collecting device such as a cyclone, a bag filter, a scrubber or the like between the step (1) and the step (2), or filling the adsorbent is used. Fixed layer type,
A method of providing an adsorbing layer comprising an adsorbing device of a moving bed type, a fluidized bed type or the like can be used. Here, step (1) and step (2)
Means between the downstream side of the ethylbenzene dehydrogenation catalyst layer in the step (1) and the upstream side of the selective oxidation catalyst layer of hydrogen contained in the dehydrogenation reaction mixture in the next step (2). means.

The above-mentioned adsorption layer is a layer made of an adsorbent which physically or chemically adsorbs an alkaline substance. The adsorbent is not particularly limited as long as it has a property of adsorbing an alkaline substance. Specific examples thereof include, for example, silica compounds, alumina compounds, silica-
Compounds obtained by calcining an alumina-based mixture at a high temperature (called ceramics), inorganic oxides (single) such as iron oxide, titanium dioxide, calcium oxide, and magnesium oxide, or a mixture of these, or a composite thereof No. Further, the shape may be any shaped body such as a ball-shaped, honeycomb-shaped shaped body, an extruded shaped body (a columnar shape, a pipe shape, etc.), an irregular shaped shaped body, and the like. The amount of the adsorbent used is not particularly limited, but usually, the volume of the adsorbent is in the range of 0.001 to 2 times, preferably 0.005 to 2 times the volume 1 of the dehydrogenation catalyst. It is desirable to use in the range of 1 time. Even if the adsorbent is used in excess of the above amount, the effect is not increased, and conversely, the equipment becomes large and the equipment cost increases. On the other hand, if the amount of the adsorbent is less than the above, the adsorbent will break through in a short period of time, and the period of stable operation will be short.

[0018]

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples unless it exceeds the gist.

Example 1 An oxidation catalyst was produced according to Example 1 of JP-A-9-29095. Specifically, first, 44.1 g of concentrated nitric acid and 7.6 g of tin chloride were added to 623.6 g of water, the obtained solution was added to 1139.6 g of α-alumina hydrate, and this solution was gradually mixed for 15 seconds. And mixed more vigorously for another 5 minutes. The resulting gel was extruded using an extruder and dried in an oven at 95 ° C. for 2 hours. This operation was repeated, and 2943 g of the obtained oven-dried product was heated to 350 ° C.
For 1 hour and further at 600 ° C. for 3 hours, and then cooled to room temperature. After heating 535 g of the extruded product which had been calcined in advance in a dry atmosphere to a temperature of 1040 ° C. over 6 hours, the temperature was maintained at the same temperature for further 3 hours, and then cooled to room temperature over 6 hours. Next, 142.5 g of water was added to 2.5
12.9 g of a chloroplatinic acid solution containing 4% by weight, 37.3 g of a lithium nitrate solution containing 0.88% by weight of lithium, and 7.3 g of concentrated nitric acid were added, and the mixture was transferred to a glass evaporator with mixing. 163.6 g (200 cc) of the calcined extruded product was added to the solution, and an impregnation operation was performed at 95 ° C. Extruded product impregnated in oven at 150 ° C
After drying at a temperature of 650 ° C. for a further 2 hours in a quartz tube, and then cooling to room temperature,
A Pt-Sn-based oxidation catalyst was obtained.

(Reaction) A commercially available dehydrogenation catalyst (Nissan Gardler catalyst: G-84C) as shown in FIG. 1 was placed in a reaction tube having an inner diameter of 21 mm equipped with a thermocouple insertion tube having an outer diameter of 6 mm.
Then, 10 cc of a silica-alumina-based ceramic ball-1 (3 mm sphere, manufactured by Tipton Corp.) as an adsorbent for an alkaline substance was filled in the lower part of the sphere. The lower part was filled with 21 cc of the above-mentioned oxidation catalyst, and the lower part of the oxidation catalyst was further filled with 36 cc of the same dehydrogenation catalyst. The temperature of the dehydrogenation catalyst inlet was raised to 600 ° C. while flowing nitrogen while controlling the temperature with a split heater. Then, a mixture of styrene / ethylbenzene, water and hydrogen were fed from the top of the reaction tube, and air and nitrogen were mixed. The reaction was started by introducing the mixed gas into the lower part of the adsorbent of the alkaline substance. During the reaction, the dehydrogenation catalyst layer and the adsorbent layer were kept at approximately 600 ° C. isothermally.
The temperature rise in the oxidation catalyst layer was 30 to 40 ° C. The composition ratio of the entire feed to the catalyst layer is styrene / ethylbenzene / water / hydrogen / oxygen / nitrogen =
0.4 / 1 / 11.5 / 0.36 to 0.48 / 0.18
/2.05 (molar ratio). Further, pressure: 65 kPa, LHSV for a mixture of styrene / ethylbenzene with respect to a dehydrogenation catalyst: 2.0
/ Hr. After the start of the reaction, samples of the liquid and gas at the outlet of each catalyst layer and at the outlet of the reaction tube were sampled, and their compositions were analyzed by gas chromatography, and the results shown in Table 1 were obtained.

Example 2 As an adsorbent, a commercially available silica-alumina-based ceramic ball-2 (manufactured by Tipton Co., Ltd.
The same operation as in Example 1 was performed except that a composition ratio of silica / alumina different from 1) was used, and the results shown in Table 1 were obtained.

Comparative Example 1 The same operation as in Example 1 was carried out except that the adsorbent was not charged, and the results shown in Table 1 were obtained. From these reaction examples, in the method using the adsorbent according to the method of the present invention,
It can be seen that the production of carbon dioxide does not increase and the activity of the second layer dehydrogenation catalyst is stable.

[0023]

[Table 1]

[0024]

As described above, according to the method of the present invention,
By eliminating poisoning of the oxidation catalyst due to scattering of the alkaline substance, the selectivity of the oxidation catalyst is stabilized without lowering. Therefore, combustion of hydrocarbons such as styrene and ethylbenzene is suppressed, and an increase in carbon dioxide generation is suppressed. As a result, a decrease in the activity of the dehydrogenation catalyst placed behind the oxidation catalyst layer over time can be suppressed. In addition, in the multi-stage dehydrogenation reaction, since the reaction temperature does not decrease and the restriction of equilibrium is reduced, it is possible to obtain styrene in a significantly higher yield as a whole as compared with the case where no adsorbent is used. it can.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a reaction tube used in an embodiment of the present invention.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Makoto Takiguchi 8-3-1 Chuo, Ami-cho, Inashiki-gun, Ibaraki Prefecture Inside the Tsukuba Research Laboratory, Mitsubishi Chemical Corporation (72) Inventor Takashi Fujita 17-17 Towada, Kamisu-cho, Kashima-gun, Ibaraki Prefecture 1 Mitsubishi Chemical Corporation Kashima Office

Claims (10)

[Claims] 1. At least the following steps (1) to (3)
A method for producing styrene by a dehydrogenation reaction of ethylbenzene comprising: removing an alkaline substance in the reaction mixture supplied to the step (2) in advance. Step (1): a step of dehydrogenating ethylbenzene in the presence of a dehydrogenation catalyst to obtain a reaction mixture containing styrene and hydrogen. Step (2): a step of bringing the reaction mixture into contact with an oxidation catalyst to selectively oxidize hydrogen contained in the mixture into water. Step (3): a step of bringing the oxidized mixture into contact with a dehydrogenation catalyst to dehydrogenate unreacted ethylbenzene contained in the mixture to obtain styrene. 2. The method for producing styrene according to claim 1, wherein the alkaline substance is a potassium compound. 3. The dehydrogenation catalyst used in the step (1) and the step (3) is a catalyst comprising an iron compound and an alkaline metal selected from the group consisting of Groups 1A and 2A of the periodic table. 3. The method for producing styrene according to 1 or 2. 4. The method for producing styrene according to claim 3, wherein the dehydrogenation catalyst contains iron oxide and potassium oxide as main components. 5. The method according to claim 1, wherein the oxidation catalyst used in the step (2) is a catalyst containing at least one metal selected from metals of Groups 4, 5, and 8 of the periodic table. A method for producing styrene according to any one of the preceding claims. 6. The oxidation catalyst used in the step (2) is at least one metal selected from Group 4 and Group 5 of the Periodic Table and at least one metal selected from Group 8 of the Periodic Table. 5. The catalyst according to claim 1, which is a catalyst containing both metals.
The method for producing styrene according to the above item. 7. The production of styrene according to claim 1, wherein the removal of the alkaline substance is carried out by providing a layer for removing the alkaline substance between the step (1) and the step (2). Method. 8. The production of styrene according to claim 1, wherein the removal of the alkaline substance is performed by providing an adsorption layer of the alkaline substance between the step (1) and the step (2). Method. 9. The method for producing styrene according to claim 8, wherein the adsorption layer of the alkaline substance comprises at least one adsorbent selected from the group consisting of a silica-based compound, an alumina-based compound, and a silica-alumina-based composite compound. 10. The method for producing styrene according to claim 8, wherein an amount of the adsorbent used is in a range of 0.001 to 2 times as a volume ratio with the dehydrogenation catalyst.