KR100642658B1 - Method for improving the performance of a catalyst for manufacturing styrene - Google Patents

Abstract

The present invention relates to a method for improving the performance of a catalyst for preventing the degradation of the catalyst according to the progress of the process, that is, the reduction of the catalyst efficiency in the process of preparing the styrene monomer by the catalytic dehydrogenation of ethylbenzene in the presence of steam. It is about.

In the method of the present invention, while supplying steam and ethyl benzene as a raw material to the reactor, while injecting KOH into the reactor through a separate supply line, it is characterized in that the KOH is very difficult to evaporate directly under reduced pressure. According to the catalyst performance improving method of the present invention, since the KOH can be easily evaporated even at low temperatures, there is an effect that can solve various problems due to the high temperature in the conventional method that requires a high temperature for the supply of KOH.

Description

Method for improving the performance of a catalyst for manufacturing styrene

1 is a conceptual diagram showing a KOH injection process according to the present invention.

2 is a cross-sectional view of the reactor used in the embodiment of the present invention.

3 is a schematic diagram of a styrene manufacturing apparatus used in the embodiment of the present invention.

* Description of the major symbols in the drawings

1. reservoir, 2. thickener,

3. evaporator, 4. vacuum pump,

a. Catalyst layer,

11.heater, 12. 1 reactor,

13. reactor 2, 14. exhaust gas absorption tower,

15. exhaust gas degassing tower, 16. exhaust gas compressor,

17. crude styrene separation tank, 18. separation tank degassing tower,

19. benzene-toluene separation tower, 20. ethylbenzene recovery tower,

21. styrene purification tower, 22. residual styrene purification tower,

23. Styrene reservoir.

The present invention relates to a process for improving the performance of a catalyst in a process for producing styrene monomers by catalytic dehydrogenation of ethylbenzene in the presence of steam.

Styrene is widely used as a raw material for producing elastic resins such as various resins such as polystyrene and ABS resins and synthetic rubber, and the production is increasing every year as the use thereof is expanded.

It is well known that styrene is prepared by dehydrogenation of ethylbenzene on the catalyst in the presence of superheated steam, ie steam, in a reactor with a dehydrogenation catalyst layer, which is important in this dehydrogenation process. And high selectivity to inhibit the production of by-products. Conventionally, researches on dehydrogenation catalysts have been actively conducted in order to achieve high conversion and high selectivity, and various catalysts including Fe and K and other alkali metals have been developed.

On the other hand, the dehydrogenation catalyst used in the manufacturing process of styrene, even if the catalyst with a high initial activity, the activity is gradually reduced when the use is continued, thereby reducing the conversion rate and selectivity of the dehydrogenation reaction. For this reason, dehydrogenation catalysts typically last about two years, and at the end of their lifetime, reactors operating at high temperatures must be shut down and replaced with new catalysts. This is a significant increase in manufacturing costs, such as the cost of a fuel cell and the cost of supplying calories to restart the reactor.

Several methods have been proposed to extend the life of the catalyst, but there have been problems such as stopping the operation of the reactor, adversely affecting the conversion rate and selectivity, and US Pat. No. 5,686,369. Has been proposed a method of continuously or intermittently feeding alkali metal compounds, in particular KOH, to the reaction stream. This is because the content of other metal components in the catalyst does not change significantly during the dehydrogenation reaction, but the content of K component is greatly reduced, and as a result, the activity of the catalyst gradually decreases. This technique aims to prolong the life of the catalyst by preventing the decrease of activity.

However, there is no detailed description of the method of injecting KOH in the U.S. patent, but it is described as being injected in a dried solid state, or in a liquid state or in a vapor state, and in the case of injecting in a vapor state, KOH is used in Examples Is illustrated by heating to a high temperature and evaporating to inject. However, since KOH is a material having a very low vapor pressure, the commercialized process has been evaporating at a high temperature of about 800 ^o C or higher for the evaporation of KOH, and such high temperature is difficult to select the material of the evaporator when it is applied in actual field. If the inner wall material is weak, the KOH may be deteriorated due to the sublimation of the metal at high temperatures, and it is difficult to maintain the high temperature of the evaporator, and the fittings of valves and measuring devices of all lines through which high temperature steam passes. There are various process and equipment problems such as this difficulty, and the improvement is urgently needed.

Accordingly, an object of the present invention is to inject KOH into the reaction stream to improve the performance of the catalyst without stopping the reaction process and without adversely affecting the conversion and selectivity of the dehydrogenation reaction, but by directly evaporating KOH at low temperature. It is to provide a method for improving catalyst performance that can solve the problem of evaporating KOH at high temperature by injection into the reaction stream.

In the catalyst performance improving method of the present invention, in the preparation of styrene monomers by catalytic dehydrogenation of ethylbenzene, while supplying steam and ethylbenzene as raw materials to the reactor, KOH is injected into the reactor through a separate supply line, and evaporated. This very difficult KOH is characterized by being injected directly under reduced pressure.

In the method of the present invention, the injection of KOH will be described with reference to the accompanying drawings.

First, KOH is dissolved in water to a certain concentration to make an aqueous solution, and then stored in the storage tank (1), by sending a certain amount of KOH aqueous solution from the storage tank (1) to the concentration tank (2) to evaporate a certain amount of water to concentrate. . Then, the concentrated aqueous KOH solution is sent to the evaporator 3 and evaporated under reduced pressure. At this time, by evaporating the KOH under reduced pressure in the evaporator, the KOH is easily evaporated to a gaseous state even at a low temperature of about 700 ^o C or less. Evaporated gaseous KOH is continuously supplied to the reactor using a means such as a vacuum pump (4).

While injecting KOH into the reactor according to the method of the present invention, ethylbenzene and steam as raw materials are supplied to dehydrogenate ethylbenzene to prepare a styrene monomer. The production process of styrene monomer is known gas phase catalytic dehydrogenation process using a conventional production apparatus equipped with steam superheater, reactor, heat exchanger, evaporator, exhaust gas recovery system, benzene-toluene column, ethylbenzene recovery tower, styrene The purification column, the styrene recovery column, is carried out by a known purification process using a conventional purification device equipped with a styrene storage tank, which will be described below.

Ethylbenzene made by alkylating benzene with ethylene is mixed with steam and this mixed steam is injected into the reactor. The reactor uses a plurality of adiabatic reactors or isothermal reactors that are commonly used, preferably two or three, in series or in parallel. In the case of ethylbenzene injection, steam is mixed and injected as a heat source for the reaction because the dehydrogenation reaction of ethylbenzene is an endothermic reaction, and steam acts as an oxidizing agent to oxidize the dehydrogenation catalyst in the reactor and is produced during the reaction. It reacts with C to prevent coking of the catalyst surface and lowers partial pressure of ethylbenzene to induce an equilibrium shift to styrene.

A ratio of steam to ethylbenzene, ie, a molar ratio of steam to ethylbenzene, is suitable from about 7: 1 to about 13: 1, and the mixture of these ratios is brought to a temperature of about 500 ^o C to about 700 ^o C at the inlet of the first reactor. Heated and injected into the reactor. In this case, the total space velocity, which is the injection rate of liquid ethylbenzene, is preferably 0.20 h ⁻¹ to 0.40 h ⁻¹ . The reaction temperature in the reactor is maintained at about 500 ^° C. to about 700 ^° C., preferably 550 ^° C. to 650 ^° C., and the pressure is maintained at 0.4 kg / cmk ² to 1.5 kg / cm ² .

Catalysts used for the dehydrogenation of ethylbenzene include Fe-K-based, Fe-K-Mg-based, Fe-K-Cr-based, Fe-K-Ce-based, Fe-K-Mg-based Fe and K. Well-known catalysts, such as -Cr system and Fe-K-Ce-Mo system, can be selected and used.

The reaction effluent after the dehydrogenation reaction contains crude styrene, unreacted ethylbenzene, a small amount of benzene and toluene by-products, and a small amount of phenylacetylene, methyl styrene, tar, etc., and gaseous products include hydrogen, carbon dioxide, and carbon monoxide. , Methane and the like. The reaction effluent is sent to a styrene purification device to purify and separate the styrene monomer.

Hereinafter, the present invention will be described in detail through Examples and Comparative Examples.

Example

Gas phase KOH evaporated under reduced pressure in accordance with the method of the present invention using an existing production facility consisting of a dehydrogenation device and a purification device connected in series with two adiabatic reactors having a structure as shown in FIG. Was injected into the reactor through a separate feed line at the time of mixed steam injection of ethylbenzene and steam, and the dehydrogenation process of ethylbenzene was performed. Fe ₂ O ₃ / K ₂ O catalyst was used as a catalyst. The reaction conditions for dehydrogenation are shown in Table 1 below. As a result of the reaction, conversion of ethylbenzene to styrene showing catalytic performance was 65%, and selectivity was 96%.

Process variables Reaction condition Steam: ethylbenzene molar ratio 9: 1 Reactor Inlet Temperature First Reactor Second Reactor 608 ^o C 618 ^o C Reactor Outlet Temperature First Reactor Second Reactor 538 ^o C 568 ^o C Total Space Velocity of Liquid Ethylbenzene 0.38 h ^-1 Average Pressure First Reactor Second Reactor 0.78 kg / cm ² 0.62 kg / cm ²

Comparative example

A styrene monomer was prepared by catalytic dehydrogenation of ethylbenzene in the same manner as in Example except that KOH was not injected.

According to the catalyst performance improvement method of the present invention, by directly evaporating the KOH that requires extremely high temperature to evaporate under reduced pressure, it is possible to easily evaporate KOH even at low temperatures, thereby solving the problems of high temperature evaporation, reactor injection It has the advantage that the flow rate control at the time becomes easier.

Claims (2)

In the process of producing styrene monomer by catalytic dehydrogenation of ethylbenzene in the presence of steam, while supplying steam and ethylbenzene as raw materials to the reactor, KOH is directly evaporated at low temperature under reduced pressure through a separate supply line. Method for improving the performance of the dehydrogenation catalyst, characterized in that the injection into the cabin. The method for improving performance of a dehydrogenation catalyst according to claim 1, wherein the aqueous KOH solution is concentrated to a certain concentration, and then the concentrate is evaporated under reduced pressure.

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