JPH0544451B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention relates to a method for producing indole from aniline and ethylene glycol. More specifically, the present invention relates to a method for preventing a decrease in catalyst activity when producing indole by reacting aniline and ethylene glycol in the gas phase in the presence of a catalyst.

(Prior Art and Problems to be Solved by the Invention) Indole is widely used as a raw material for chemical industries such as perfumes and dyes, and has particularly attracted attention in recent years as a raw material for the synthesis of amino acids. Traditionally, indole has been manufactured using expensive raw materials or through long and complicated processes. However, recently, a gas phase catalytic reaction of aniline and ethylene glycol has been discovered as a method for producing indole using inexpensive raw materials and in a simple process.

Various solid acid catalysts and metal catalysts have been proposed as catalysts for the reaction. These catalysts are
When the reaction is carried out over a long period of time, the activity decreases, although the extent varies depending on the type of catalyst and reaction conditions, and periodic regeneration operations by heating and calcination in an oxygen atmosphere are required. Regeneration operations are complicated, and if performed too frequently, they may impair the economics of the process. The details of the cause of this decrease in activity are not clear, but since reactivation is possible using conventional methods, the main cause is organic matter becoming carbonaceous and depositing on the catalyst surface under the reaction conditions. This is thought to be due to coating the active sites of the catalyst. The reduction in activity can be reduced by carrying out the reaction in a hydrogen atmosphere or by adding water to the reaction system, but this is not always sufficient.

On the other hand, it is known that in order to obtain indole in good yield, it is necessary to have a large excess of aniline present in the reaction system. Therefore, when producing indole industrially by this method, it is essential to separate and recover a large amount of aniline contained in the resulting reaction mixture and use it again as a raw material in the reaction. However, in this case, a problem arises in that the activity of the catalyst is significantly reduced compared to the case where recovered aniline is not used. In other words, if the reaction is carried out without recycling the recovered aniline, the catalyst can maintain sufficient reaction activity for several hundred hours, but if the recovered aniline is supplied with other conditions being exactly the same, the catalyst The activity of this product decreases significantly, and the frequency of regeneration operations increases significantly. Therefore, it is presumed that the recovered aniline contains impurities that are harmful to the catalyst.

The reaction liquid obtained by condensing the gaseous reaction mixture exiting the reactor contains not only the produced indole and water, unreacted ethylene glycol, and excess aniline, but also small amounts of various side reaction products. exists. Some of them have been isolated and identified, but many of the side reaction products are
Its chemical structure, physical compound properties, etc. have not been clarified. If these side reaction products are recycled to the reactor without being separated from the recovered aniline, they may become carbonaceous and deposit on the catalyst surface, causing a decrease in its activity. It is thought that there are.

Moreover, since the aniline recovered by distillation according to the conventional method has an adverse effect on the catalyst activity, the side reaction products that cause the decrease in activity are due to the vapor-liquid equilibrium relationship between aniline and aniline in the distillation operation. It is considered that it is difficult to separate.

The problem of the present invention is to effectively remove side reaction products that are harmful to the catalyst and difficult to separate by distillation, and to effectively remove side reaction products that are harmful to the catalyst and difficult to separate by distillation.
The object of the present invention is to provide a method that can avoid adverse effects on the activity of a catalyst.

(Means for Solving the Problems) As a result of intensive studies to solve the above-mentioned problems, the inventors of the present invention discovered that before separating and recovering aniline by distillation and supplying it to the reaction apparatus again, We have discovered that it is extremely effective to heat-treat a solution containing the reaction product and aniline to convert the side reaction product into a non-volatile substance to facilitate distillation separation from the aniline, The method of the present invention has been achieved.

That is, the present invention is a method for producing indole by using an excess amount of aniline with respect to ethylene glycol and carrying out a gas phase reaction in the presence of a catalyst. This is a method for producing indole, characterized in that the recovered aniline-containing aniline is obtained by treatment and subsequent distillation separation.

The method for producing indole, which is the subject of the present invention, is as follows:
This is a method in which aniline and ethylene glycol are reacted in the gas phase in the presence of a solid acid catalyst or metal catalyst.
Among the catalysts used in this method, the solid acid catalysts include (1) Si, Al, B, Sb, Bi, Sn, Pb,
Ga, Ti, In, Sr, Ca, Zr, Be, Mg, Y, Cu,
A catalyst containing an oxide or hydroxide of at least one element selected from Ag, Zn, Cd, and lanthanide elements (hereinafter referred to as catalyst substance (1)), such as CdO, ZnO, PbO ₂ , Al ₂ O ₃ −B ₂ O ₃ , SiO ₂ −
ZnO, _SiO2 -CaO, _{SiO2 - In2O3} , _SiO2 -SrO,
_SiO2 -CdO, _{SiO2 - Al2O3} , _SiO2 -MgO, TiO
−SnO ₂ , TiO ₂ −ZrO ₂ , CdO ₂ −Bi ₂ O ₃ , SiO ₂ −
_Y2O3 , _SiO2 , _{Bi2O3 -} BeO, _{SiO2 - Ga2O3 ,}
SiO ₂ −La ₂ O ₃ , SiO ₂ −Ce ₂ O ₃ , SiO ₂ −ZnO−
AgO, _SiO2 -MgO-CuO, etc. can be mentioned. Also, (2) Pd, Pt, Cr, Fe, Ni, Co, Zn,
A catalyst containing a sulfide or selenide of at least one element selected from Mo, Cd, and W (hereinafter referred to as catalyst material (2)), such as PdS, PtS,
CrS, FeS, NiS, CoS, ZnS, _MoS2 , CdS,
Examples include WS ₂ , ZnSe, and CdSe.
Also, (3) Fe, Tl, Ca, Mn, Bi, St, Y, Al,
Inorganic salts of at least one element selected from Zn, Cd, Ni, Mg, In, Be, Co, Ga and lanthanide elements, i.e. halides, carbonates, nitrates, sulfates, phosphates, pyrophosphates, phosphomolybdate,
Silica tagstate (hereinafter referred to as catalyst material (3))
Catalysts containing, for example, ferric sulfate, thallium sulfate, calcium sulfate manganese sulfate, bismuth sulfate, strontium sulfate, yttrium sulfate, cadmium bromide, aluminum sulfate, zinc sulfate, nickel sulfate, cadmium chloride, magnesium sulfate, indium sulfate , beryllium sulfate, cadmium nitrate, cobalt sulfate, aluminum zinc sulfate,
Examples include magnesium chloride and cadmium sulfate.

Furthermore, as metal catalysts, Cu, Ag, Pt, Pd,
Examples include catalysts containing at least one element selected from Ni, Co, Fe, Ir, Os, Ru, and Rh (hereinafter referred to as catalyst material (4)).

Among the above-mentioned groups of catalyst materials, the group of catalyst materials (1) is most preferably used.
SiO ₂ −ZnO−AgO, in the group of catalyst materials (2), cadmium sulfide, in the group of catalyst materials (3), cadmium sulfate, and in the group of catalyst materials (4), supported on a large surface area carrier. An example of this is Ag.

These catalysts can be manufactured by any known method. That is, the catalyst substance (1) can be prepared by hydrolyzing a water-soluble salt of a catalyst constituent element to form a hydroxide, and drying and calcining the resulting gel;
It can be produced by a method such as thermally decomposing an easily decomposable salt in the air.

The catalyst substance (2) is produced by adding sodium sulfate or potassium selenide to a water-soluble salt of a catalyst constituent element, or by catalyzing a catalyst constituent element or its salt with hydrogen sulfide gas or hydrogen selenide gas, etc. You can.

Furthermore, the catalyst substance (4), which is a metal catalyst, can be produced by a method in which a salt, hydroxide or oxide of a catalyst constituent element is reduced with a reducing agent such as hydrogen, formalin formic acid, phosphorous acid, or hydrazine.

These solid acid catalysts or metal catalysts are each of the above-mentioned catalyst substances (1), (2), (3), and (4) alone, or a mixture of two or more thereof, or they are supported on a carrier. It's okay. As the carrier, any commonly used carrier can be used, and diatomaceous earth, pumice, titania, silica alumina, alumina, magnesia, silica gel, activated carbon, activated clay, asbestos, etc. are usually used. A supported catalyst is prepared by supporting the catalyst substance on these carriers by a conventional method.

The amount of the catalyst substance supported on the carrier is not particularly limited, and is usually an appropriate amount depending on the carrier, for example, 1 to 50
% of said catalyst material may be supported.

In the method for producing indole of the present invention, the reaction between aniline and ethylene glycol is carried out in the gas phase in the presence of the above-mentioned catalyst, but it may be carried out in a fixed bed, fluidized bed or moving bed reactor.

Aniline and ethylene glycol to be introduced into the reactor are in the range of 0.01 to 1 mol of ethylene glycol per 1 mol of aniline, preferably 0.05 to 1 mol.
It is in the range of 0.5 mole.

The amounts of aniline and ethylene glycol that are introduced as raw materials are in the range of 0.01 to 10 hr ^-1 in terms of liquid hourly space velocity (LHSV), and are introduced into the reaction apparatus after being vaporized in an evaporator in advance. Also, in that case, water vapor, hydrogen,
Carbon monoxide, carbon dioxide, methane, nitrogen, neon, argon, etc. may be accompanied as a carrier gas. In particular, water vapor, hydrogen, and carbon monoxide are preferred because they increase the catalyst life.

The reaction temperature ranges from 200 to 600℃, preferably 250℃
~500℃ range.

The reaction pressure can be selected from any pressure above standard atmospheric pressure and below the pressure at which the raw materials or components contained in the reaction mixture form a condensed phase at the reaction temperature, but in practice it is 1.1 x 10 ⁵ to 1.0. A range of ×10 ⁷ Pa is preferred, and a range of 2.0 × 10 ⁵ to 5.0 × 10 ⁶ Pa is more preferred.

The method of the present invention may be a reaction liquid obtained by condensing a gaseous reaction mixture exiting a reactor for indole production under the above conditions, or an aniline fraction after indole is separated from this reaction liquid. .

The treatment temperature in the heat treatment is 100 to 350°C, preferably 150 to 250°C. On the other hand, the treatment time may be selected to be a necessary and sufficient time to achieve the object of the present invention depending on the treatment temperature. Usually 10 minutes to 10
About an hour is enough.

The operating pressure may be a pressure equal to or higher than its saturated vapor pressure depending on the composition of the processing solution and the processing temperature. This heat treatment may be carried out either batchwise or continuously. In the case of a continuous type, complete mixing, extrusion flow, or intermediate fluid mixing may be used; however, the volumetric efficiency is improved when the flow is closer to extrusion flow.

In the reaction product liquid or recovered aniline that has been heat-treated as described above, side reaction products harmful to the catalyst are converted into non-volatile substances by the heat treatment.
These are removed by conventional distillation separation. The aniline thus obtained is reused in the reaction as is or mixed with fresh aniline.

(Operation and Effects of the Invention) According to the method of the present invention, aniline in excess of the stoichiometric amount relative to ethylene glycol is introduced into the reaction apparatus, and the excess aniline is separated and recovered from the reaction product and used again as a raw material. Then, by subjecting this to heat treatment, side reaction products harmful to the catalyst can be converted into non-volatile substances and removed.

Therefore, the activity of the catalyst can be maintained for a long time and indole can be produced in good yield.

That is, the present invention provides an industrial method for producing indole using aniline and ethylene glycol as raw materials.

(Example) Hereinafter, the method and effects of the present invention will be explained in more detail with reference examples, comparative examples, and examples.

Reference example 1 In a stainless steel reaction tube with an inner diameter of 25 mm, a particle size of 3~
500 ml of 4 mm catalyst was charged and subjected to reaction. The catalyst is compression molded powdered cadmium sulfide. Under a pressure of 7Kg/ ^cm2 , hydrogen gas is
The temperature of the catalyst layer was gradually raised from room temperature to 350°C and maintained at 350°C. Next, aniline and 33% ethylene glycol aqueous solution were mixed at 234 g/hr and 48 g/hr, respectively, and then vaporized.
The reaction was started by supplying it to the reaction tube. Immediately after the start of the reaction, the indole yield was 74.8% based on ethylene glycol. This yield gradually decreased with the passage of time, and was 52.0% at 310 hours after the start of the reaction. In this case, the aniline used in the reaction is commercially available industrial aniline.

Comparative Example 1 In Reference Example 1, the reaction mixture exiting the reaction tube was cooled to room temperature, the resulting condensate was separated into an aqueous phase and an organic phase, and aniline was separated and recovered from the latter by distillation. In other words, a distillation pot with an internal volume of 30 mm, an internal diameter of
25 kg of the organic phase was charged into a glass distillation apparatus consisting of a packed bed of 1/4 inch Raschig ring with nominal dimensions of 80 mm and a height of 2000 mm and a condenser, and the operating pressure was 10 Torr.
Batch distillation was performed at a reflux ratio of 0.2. Initial distillation amount is 0.4Kg,
Then, 20.3 kg of aniline fraction was distilled out. Similar batch distillation was repeated to obtain approximately 80 kg of recovered aniline. As a result of the analysis, the purity of recovered aniline was 99%.
That's all.

Using this recovered aniline, an indole synthesis reaction was carried out under exactly the same conditions as in Reference Example 1. Immediately after the start of the reaction, the indole yield based on ethylene glycol was 75.2%, almost the same as in Reference Example 1, but it had already decreased to 43.6% 195 hours after the start of the reaction.

Example 1 Approximately 100 kg of the organic phase obtained in the indole synthesis reaction under the same conditions as in Reference Example 1 was placed in a stainless steel stirring tank equipped with a jacket for a heat medium, and the mixture was heated by a heat medium while being gently stirred. Heated. The internal temperature
After reaching 200°C, it was held at this temperature for 2 hours. At this time, the vapor pressure was approximately 6 Kg/cm ² .

Approximately 80 kg of aniline was recovered from this heat-treated liquid by batch distillation using the same distillation apparatus and operating conditions as in Comparative Example 1, and subjected to the same indole synthesis reaction as in Reference Example 1. Immediately after the start of the reaction, the indole yield based on ethylene glycol was 75.0%, which is approximately the same as in Reference Example 1. After that, the reaction continued for 320 hours, but the yield was 50.5%.
Therefore, reaction results comparable to those of Reference Example 1 were obtained.

Claims (1)

[Claims] 1 In a method for producing indole by using an excess amount of aniline with respect to ethylene glycol and performing a gas phase reaction in the presence of a catalyst, the aniline to be reused is heat-treated as a reaction product or the aniline separated from the reaction product, and then A method for producing indole, characterized in that the aniline contains recovered aniline obtained by distillation separation.