JPS6011442A - Production of vinyl acetate - Google Patents

Abstract

PURPOSE:To reduce the load of azeotropic distillation and improve the efficiency, in the continuous vapor-phase production of vinyl acetate from ethylene, oxygen and acetic acid, by using a specific amount of acetic anhydride in place of the whole or a part of the continuously supplied acetic acid. CONSTITUTION:In the continuous production of vinyl acetate by the vapor-phase reaction of ethylene, acetylene and oxygen in the presence of a VIII-group metal catalyst (e.g. Pd) under normal pressure-20atm at 50-200 deg.C, acetic anhydride is supplied to the system in an amount to satisfy the formula x<=0.138y+6.59z [x is feeding rate of acetic anhydride (pt.wt./hr); y is feeding rate of acetic acid (pt.wt./hr); z is feeding rate of water (pt.wt./hr)]. Since the water produced by the reaction and the water contained in the supplied raw material are consumed by the hydrolysis of acetic anhydride, the distillation load can be reduced without leaving acetic anhydride in the reaction system nor inhibiting the production of vinyl acetate.

Description

Detailed Description of the Invention The present invention relates to a method for continuously producing vinyl acetate by a gas phase method using ethylene, acetic acid, and oxygen as raw materials, and in particular, the separation and purification of the reaction product is easier than in conventional methods. , relating to improvements in continuous production methods for efficiently obtaining vinyl acetate.

It is known that vinyl acetate can be produced by reacting ethylene, acetic acid, and oxygen as reaction raw materials in the gas phase in the presence of a catalyst in which, for example, metallic palladium and potassium acetate are supported on a carrier such as 7-lika or alumina. There is. However, in general, solid catalysts are susceptible to the effects of catalyst poisons, and their activity decreases significantly over time due to side-reactants.Also, the catalytic activity of metal palladium in this reaction is not very large, so it is difficult to increase its activity. Research on carriers, cocatalysts, etc., and research on preventing a decrease in initial activity are currently being conducted.

In addition, the continuous gas-phase production method of vinyl acetate that is currently being used industrially requires an extremely heavy distillation load for post-treatment of the reaction product, especially azeotropic distillation, and requires a large amount of energy. There is a big drawback. This solution is desperately needed for a continuous production method of vinyl acetate using a gas phase method, and has been a technical problem that must be overcome in particular industrially.

A conventionally known method for producing vinyl acetate by a gas phase method using ethylene as a reaction raw material can be explained, for example, by an example of a flow sheet as shown in FIG. 1 of the accompanying drawings.

In FIG. 1, raw material components acetic acid, ethylene and oxygen are fed through their respective inlet pipes to a reactor 1 filled with a catalyst, usually from the top thereof. Reactor l is 50
The reaction conditions are maintained at a temperature of ~200°C and a pressure of between 20 and 20 atm, and the raw material mixture reacts catalytically on the catalyst surface to produce vinyl cyanoacetate according to the following formula (1), and at the same time Produces moles of water.

02 H4+ CHs C0OH+ t/202-→C
HsCOOCxHs+H20 (1) Also, along with this reaction, ethylene and oxygen react to generate carbon dioxide gas and water as shown in the following formula (n) Ic.

CHx = Cf(z +3Qz→2COz +2H2
0(11) As a result, the crude vinyl acetate-containing reaction product obtained in reactor 1 contains approximately 5% by weight of water produced by these reactions. The presence of this amount of water not only takes part in side reactions and adversely affects the recovery and yield of vinyl acetate, but also impairs the isolation of vinyl acetate and the recovery of acetic acid for recycling. This makes the operation complicated, especially azeotropic distillation, which imposes a heavy distillation load and requires a large amount of energy.

The reaction mixture coming out of the reactor 1 is cooled by a condenser 2 and led to a gas-liquid separator 3, where unreacted ethylene gas and oxygen gas are recovered from the top, and a large amount of unreacted gas is recovered from the bottom. A crude vinyl acetate liquid containing water produced by the reaction with acetic acid is taken out and put into a receiver 4, and then a certain amount of it is introduced into an azeotropic distillation column 5 where it is subjected to azeotropic distillation treatment. . In this azeotropic distillation column 5, vinyl acetate and water are distilled out as an azeotropic fraction from the top of the column by azeotropic distillation, and acetic acid remains in the column. The azeotropic mixture of vinyl acetate and water distilled from the top of the azeotropic distillation column 5 is cooled and separated into an upper layer of vinyl acetate and a lower layer of water, and the upper layer of vinyl acetate is introduced into the dehydration distillation column 6. The resulting product is subjected to distillation and dehydration treatment to remove low-temperature impurities, and then purified in a vinyl acetate distillation column 7.

In addition, in order to recover the high-boiling point fraction remaining at the bottom of the distillation column 7 and the vinyl acetate remaining without being separated,
It is returned to the azeotropic distillation column 5 and azeotropically distilled together with the crude vinyl acetate liquid to be subjected to the next azeotropic distillation. The liquid remaining at the bottom of the column 5 that has been subjected to the azeotropic distillation treatment is led to the acetic acid distillation column 8 where it is rectified, and the acetic acid fraction is circulated to the reactor 1 as a reaction raw material component. The high-boiling component liquid taken out from the bottom of the distillation column 8 is led to a separation column 9 where acetic acid is recovered and added to the crude vinyl acetate receiver 4, where high-boiling impurities at the bottom of the column are discarded. .

The load was extremely heavy, and reducing that load as much as possible was a major improvement issue in continuous vinyl acetate production.

The present inventors have conducted research on reducing the distillation load in the method for continuously producing vinyl acetate by subjecting ethylene, acetic acid, and oxygen to a gas-phase reaction as described above. We discovered that the objective could be achieved efficiently by supplying acetic anhydride to 4 and/or the mutual aid distillation column 5 and allowing it to react with the by-produced water, and proposed it earlier (Japanese Patent Application No. 57-216475). .

However, as a result of further research into an improved method for producing vinyl acetate more effectively, the present inventors discovered a method for continuously producing vinyl acetate using a gas phase method using ethylene, oxygen, and acetic acid as raw materials. In place of all or part of the continuously replenished acetic acid, K is used to satisfy specific conditions.
have found that when acetic anhydride is used, the azeotropic distillation load can be significantly reduced without inhibiting the production of vinyl acetate.

That is, the present invention continuously produces vinyl acetate by subjecting ethylene, acetic acid, and oxygen to a gas phase reaction in the presence of a metal catalyst from Group 11 of the periodic table at a pressure of normal pressure to 20 atm and a temperature of 50 to 200°C. In this method, y (parts by weight/hour) of acetic acid and 2 (parts by weight/hour) of water are supplied to the reaction zone.
In this case, there is provided a continuous method for producing vinyl acetate, characterized in that acetic anhydride is supplied so that the acetic anhydride supply iX (parts by weight/hour) satisfies the following formula 1 %.

The present invention is not essentially involved in the synthesis reaction of vinyl acetate,
In addition, acetic acid is replenished in a specific range of amount conditions that can substantially completely hydrolyze acetic anhydride, which if present in large quantities in the reaction zone has a negative effect on the formation of vinyl acetate, in the reaction zone during the synthesis reaction of vinyl acetate. This is based on the discovery that industrially desirable improvement effects can be obtained when added in place of at least a portion of The present invention utilizes the phenomenon that acetic anhydride easily hydrolyzes in the presence of water to form acetic acid, which is a reaction raw material. Despite the technical concept, on the contrary, when added to the reaction zone under certain lid range conditions, it does not interfere with the production of vinyl acetate, yet it has a significant distillation load on the reaction liquid, which is desirable for continuous vinyl acetate production. It was a serious discovery that the reduction of

In addition, in such a reaction method, if an excess of acetic anhydride is supplied to the reaction zone beyond the specified ht range, the production of vinyl acetate will be significantly inhibited, and acetic anhydride will remain in the crude vinyl acetate solution. I also found out that it does.

Therefore, in the process of the present invention, it is important that the acetic anhydride fed to the reaction zone is added under specific amount range conditions, specifically, the proportion of acetic anhydride fed to the reactor is
[to the acetic acid containing circulating acetic acid supplied to the reactor]-, 1
M is required to be within 3.8w%. in this way,
In the method of the present invention, acetic anhydride reactive with water is added to the reaction zone, so even if a certain amount of water is contained in the reaction raw materials, it is only necessary to supply a proportionate excess amount of acetic anhydride. It is acceptable for some water to be included in the recycled materials. In this case, the water fed to the reaction zone immediately reacts with acetic anhydride in the reaction zone, so
In this case, the number of acetic anhydrides that can be supplied is greater than 13.8 w% based on acetic acid when water is not supplied.

In the method of the present invention, the amount of acetic anhydride that can be fed to the reaction zone is the amount of acetic anhydride, acetic acid, and water that are fed to the reaction zone, respectively, by X (parts by weight/hour).

When y (parts by weight/hour) and 2 (parts by weight/hour), it is expressed by the following formula.

That is, X≦0.1381 + 6.59 z, and the acetic anhydride supply amount X needs to satisfy the above inequality.

The method of the present invention uses substantially the same reaction temperature and pressure conditions as the conventional method of producing vinyl acetate using ethylene, acetic acid, and oxygen as raw materials in the presence of a metal scrap catalyst of Group 1 of the periodic table. Adopted conveniently. The reaction temperature is 50-2
50'C range, preferably 100-200°C
It is. The reaction pressure is in the range of normal pressure to 20 atm, preferably 5 to 15 atm. The catalyst is one of the noble metals of the periodic table group, for example, palladium can be cited as a representative example. Further, the catalyst can be prepared by a conventionally known method. The catalyst used in the method of the present invention is prepared, for example, as follows.

First, the surface area is 140-160m/! i': After immersing a silica sphere with a diameter of 5 mm in an aqueous solution of sodium salt of tetrachloropalladate, it is subjected to a usual reduction treatment using formalin and hydrogen isobarically. Further, this is prepared by immersing it in an aqueous solution of potassium acetate and then drying it at 120'C for several hours. The catalyst Pd6 degree obtained in this way is about 0.5W%
, the potassium acetate concentration is about 5W%.

In addition, the ethylene and oxygen gas used as reaction raw materials are both of the highest possible purity of 99% or more,
The ratio of both gas components is ethylene:oxygen 99-70:1
~30 volumes, preferably 98 to 80 volumes, and 2 to 20 volumes. In addition, acetic acid used as a reaction raw material is
A compound containing as few impurities as possible is preferably used, and the amount thereof is 1 to 100 mol, preferably 2 to 20 mol, per mol of oxygen.

According to the method of the present invention, the reaction product liquid taken out from the reaction vessel is separated from dissolved ethylene and oxygen, and then passed through an azeotropic distillation column to form an azeotropic mixture of vinyl acetate and water and unreacted acetic acid. and can be easily separated. The post-processing of this reaction solution is significantly reduced compared to the distillation load in the conventional gas phase continuous production of vinyl acetate, and the industrial resolution is extremely high.

Hereinafter, the present invention will be explained in more detail with reference to Examples and Comparative Examples.

In the following specific example, a small experimental manufacturing apparatus as shown in sheet 70 in FIG. 2 was used. The reactor 1 in the figure is a reaction tube with an inner diameter of 2.54 mm and a length of 200 degrees Fahrenheit, and all of the accompanying equipment is of a scale corresponding to this.

Example 1 A solid catalyst (Nijirica spheres as carrier, Pd concentration: 0.5 w), which is usually used for vinyl acetate synthesis, was placed in the reaction tube of a vapor phase vinyl acetate synthesis reaction apparatus as shown in FIG.

Fill with potassium acetate concentration: 5W%) 0.96 1-1
Reaction pressure: 8 kg/cItG reaction temperature: 140°C
ethylene at 1300 Nl 1 hour and oxygen at ci
oN//hour, acetic acid 790g/hour, acetic anhydride 85g/hour
Supply at the rate of time. The ratio of acetic anhydride to acetic acid traps is 1.8w, which satisfies the inequality requirement of the present invention.

phase two convergence 1-. The yt-rat reaction solution was collected from the crude reaction solution receiver and analyzed by gas chromatography.

As a result, the composition of the crude reaction solution was 75.9 w% acetic acid.
.

Vinyl acetate 20.9 <v%, water 4. IW was observed, and acetic anhydride was not detected. The space-time convergence of vinyl acetate is 25
It was 4.5'/cat-dx.

The ratio of by-product water to vinyl acetate was 19.6 W%.

Comparative Example 1 In the reaction of Example 1, 790 g/h of acetic acid and 8
When acetic acid was supplied at 86:1/hour in place of acetic anhydride at 5'97, the composition of the crude reaction solution was 72.4W% acetic acid,
The space-time yield of vinyl acetate was 262 g/cat-7X hour.

The ratio of by-product water to vinyl acetate was 26.3 w%. Ivy.

Example 2 In the reaction of Example 1, the amount of acetic anhydride supplied was 102.9
The reaction was carried out in the same manner except that the reaction temperature was increased to 150=C. In this case, the ratio of acetic anhydride to acetic acid was 12.9 W%, which satisfies the requirements of the present invention.

Obtained. As a result of analyzing the crude reaction solution, its composition was acetic acid 6
At a concentration of 9.3 w%, vinyl acetate 25.9 w%, and water 4.8 W, no acetic anhydride was detected.

The space-time yield of vinyl acetate was 3759/Cat4X hours.

The ratio of by-product water to vinyl acetate was 18.5 w%.

Comparative Example 2 In the reaction of Example 1, the amount of acetic acid supplied was 757 y/hour,
The reaction was carried out in the same manner as (-) except that acetic anhydride was supplied at a rate of 125 g/hour (the ratio of acetic anhydride to acetic acid was 1 asw%).
). However, in this case, the composition of the condensate is 86.8W acetic acid.
%, acetic anhydride was 10.9W, and water was extremely small.

Vinyl acetate was only 2.3 W% and its space-time yield was 22 ji/cat-d x hours.

Example 3 The reaction was carried out in the same manner as in Comparative Example 2 except that water was supplied at a rate of 11/hour. (x=tz5(g/hour) <A=o
, t 38 x 757 (g/hr) x 6.59 x 8U
'/hour) = 157 (9/hour), which satisfies the acetic anhydride supply amount requirement. ) As a result of analysis, the composition of the crude reaction solution was 75.0W of acetic acid and 21.4W of vinyl acetate. W%, water was 3.6 w%, and the space-time yield of vinyl acetate was 2399/cat-1x hour.

The ratio of by-product water to vinyl acetate is 17. It was IW Chi.

The above Examples 1 to 3 are compared with Comparative Example 1.As is clear, the ratio of water to vinyl acetate is A25~7m.
It can be seen that the distillation load has been reduced significantly by 35 w%.

[Brief explanation of the drawing]

FIG. 1 is a flow sheet of a normal vinyl acetate manufacturing method, and FIG. 2 is a flow sheet used in Examples and Comparative Examples of the present invention. Symbols in the diagram: 1... Reactor, 2... Condenser, 3... Gas-liquid separator, 4... Receiver, 5... Azeotropic distillation column, 7
... Vinyl acetate distillation column, 10 ... Acetic acid evaporator, 11
···vinegar! #Superheater. Patent application 7 Shin-Etsu Vinyl Acetate Co., Ltd. Shin-Etsu Chemical Co., Ltd.

Claims (1)

[Claims] Vinyl acetate is continuously produced by a gas phase reaction of ethylene, acetic acid and oxygen in the presence of a metal catalyst from Group I of the periodic table at a pressure of normal pressure to 20 atm and a temperature of 50 to ZOO°C. In the method for producing acetic acid fed to the reaction zone, y (parts by weight/
A continuous method characterized in that acetic anhydride is supplied such that when water is 2 (parts by weight/hour) and water is 2 (parts by weight/hour), the acetic anhydride supply amount A method for producing vinyl acetate.