JPS6287552A - Method of purifying vinyl acetate reaction formed gas - Google Patents

Abstract

PURPOSE:To purify in high purity vinyl aceate-containing reaction formed gas obtained by reaction of ethylene, acetic acid and oxygen, by setting a scrubber in a purifying process, circulating and reusing anhydrous vinyl acetate. CONSTITUTION:A reaction formed gas of ethylene, acetic acid and oxygen in the presence of a catalyst is fed to a distillation column 1, a distilled mixed gas from the top of the column is cooled, a condensate is separated by a decanter 8, an organic layer is circulated through the distillation column 1 and a mixture of acetic acid/water/vinyl acetate taken out from the bottom of the distillation column 1 is fed to a distillation column 4. A mixture of vinyl acetate/water is distilled from the top of the column, sent to a distillation column 2, crude vinyl acetate is obtained from the bottom of the column and distilled by a distillation column 3 to give pure vinyl acetate from the top of the column. On the other hand, an uncondensed gas separated from the condensate is subjected to counter-current contact with anhydrous vinyl acetate, part of distillate at the bottom of the distillation column 2 so that water in the gas is absorbed in vinyl acetate and it is circulated through the distillation column 2.

Description

[Detailed Description of the Invention] [Industrial Application Field 1] The present invention provides a method for obtaining vinyl acetate free of dull substances by purifying a vinyl acetate-containing reaction product obtained by reacting ethylene, acetic acid, and oxygen. Regarding.

[Prior art 1] Vinyl acetate is produced by reacting ethylene, acetic acid, and oxygen in the gas phase using palladium or a palladium salt as the main catalyst, and in addition to the reaction mixture, unreacted ethylene, unreacted oxygen, unreacted acetic acid, water, and carbonic acid are produced. Since the gas chamber contains inert gas and the like, the reaction product gas is purified to remove these impurities. That is, as a typical purification method in an industrial method, a reaction product gas mixture is cooled in multiple stages,
This removed condensate is subjected to distillation, while uncondensed components are recycled to the reactor. In the distillation operation, the vinyl acetate/water mixture is first distilled off from the top in a first distillation column, while the acetic acid is distilled off from the bottom. Acetic acid is reused in the reaction. After the above mixture is separated into two layers, an organic layer and an aqueous layer, the organic layer is introduced into a second distillation column and is separated into a water/low-boiling component mixture from the top and a vinyl acetate/high-boiling component mixture from the bottom. Separated. The mixture consisting of vinyl acetate and high-boiling components is separated in the distillation column 3 into pure vinyl acetate, which is distilled out from the top, and high-boiling components (including polymers, etc.) which are taken out from the bottom. As a result, vinyl acetate can be obtained.

[Problems to be Solved by the Invention] Approximately 60 to 80% of the total energy required for this is consumed.

Now that we are entering an era of resource and energy conservation,
It goes without saying that in a distillation method that requires a large amount of expensive thermal energy, it is necessary to reconsider how to save labor.

As one such countermeasure, for example, Japanese Patent Application Laid-Open No. 52-11151
The proposal was made in Publication No. 1, and although the thermal energy saving effect is quite large, approximately 2(2) to 35% compared to the conventional method, more advanced methods are required for industrial implementation. There is a need to save heat energy.

[Means for Solving the Problem 1] However, as a result of the inventors' extensive research into methods to solve this problem, the inventors have found that the thermal energy is approximately 40% lower than that of the conventional method.
% or more, in some cases 50% or more -1: IJfJ can be reduced, and the vinyl acetate with significantly reduced content of water, an impurity, can be obtained, which is an extremely useful effect industrially. In a method for purifying a reaction product gas containing vinyl acetate, the reaction product gas coming out of a reaction zone is introduced into a distillation column 1, the mixture exiting from the top of this column is also cooled, and the condensate is supplied to a decanter. After separating into two layers, an organic layer and an aqueous layer, the organic layer is circulated to the distillation column 1, and the acetic acid/water/vinyl acetate mixture taken out from the bottom of the distillation column 1 is introduced into the distillation column 4. A vinyl acetate/water mixture is distilled from the top, acetic acid is distilled from the bottom, and the top mixture is then introduced into the distillation column 2 to obtain crude vinyl acetate containing low-boiling components from the top and high-boiling components from the bottom. The vinyl is introduced into a distillation column 3 to obtain purified vinyl acetate, while the uncondensed gas separated from said condensate is introduced into a scrubber to obtain substantially water-free vinyl acetate, in particular the bottom of the distillation column 2. A method for purifying a vinyl acetate reaction product gas, which comprises bringing the gas into countercurrent contact with a portion of the distillate to absorb water in the gas into vinyl acetate, and supplying the vinyl acetate that has absorbed ascites to the distillation column 2. It is.

The reaction product gas leaving the reactor 5 (substantially vinyl acetate, unreacted ethylene, unreacted acetic acid, unreacted oxygen, carbon dioxide,
water, inert gas, etc.) are introduced into the distillation column 1.

Preferably, the gas is cooled by heat exchange in the city into which it is introduced.

Distillation column 1 and distillation columns 2, 3, . 1 may be any of a plate tower, a packed tower, a spray tower, etc. The gas coming out of the column 1 is led to a gas-liquid separator 7 via a condenser 6, where it is separated into uncondensed gas and condensate. The condensate is separated into two layers, an organic layer 9 and an aqueous layer 1 () in a decanter 8. The aqueous layer 10 is then drained. The organic layer 9 is recycled to the distillation column 1. A mixture based on acetic acid/water/vinyl acetate is obtained from the bottom of the distillation column 1, which is then fed to the distillation column 4. The separated acetic acid obtained from the bottom is reused in the reaction. The vinyl acetate/water mixture that is the distillate from the top is fed to the distillation column 2, where low-boiling components and water are obtained from the top, and crude vinyl acetate containing small amounts of high-boiling components and polymer components is obtained from the bottom. Ru. Crude vinyl acetate is introduced into the distillation column 3, and pure vinyl acetate can be obtained from the top or at a higher rate from the bottom, resulting in the effect of saving thermal energy.

On the other hand, the unagglomerated gas separated from the condensate in the gas-liquid separator 7 is led to the scrubber 11 and brought into countercurrent contact with vinyl acetate, which is a part of the bottom distillate of the distillation column 2 and is substantially free of water. The moisture in the gas is absorbed by vinyl acetate. The vinyl acetate that has absorbed ascites is circulated to the distillation column 2.

In the present invention, installing a scrubber during the purification process as described above to recycle and reuse the anhydrous vinyl acetate is the most important point, and the bottom liquid from the scrubber contains almost acetic acid. Therefore, the distillation column 2 can carry out distillation using a low-temperature heat source, and this operation saves energy compared to conventional methods.

During the circulation, the vinyl acetate may be fed mixed with the vinyl acetate/water mixture or crude vinyl acetate from the distillation column 4, or may be fed separately.

The gas exiting from the top of the scrubber is purified by known means such as washing with acetic acid and recycled to the reaction as recycled gas. Furthermore, in the present invention, in which vinyl acetate is absorbed in the acetic acid cleaning solution, the uncondensed gas separated into gas and liquid is brought into contact with substantially anhydrous vinyl, which is a part of the bottom distillate from the distillation column 2. By circulating the water-absorbed vinyl acetate through the distillation column 21, it is possible to use more energy than in conventional purification methods.

[Example 1] Next, the method of the present invention will be explained in more detail with reference to Examples. "r%" is based on weight unless otherwise specified in I).

Example 1 (See Figure 1) Ethylene, acetic acid and oxygen were reacted in the gas phase in the presence of a palladium main catalyst supported on silica in a reactor 5.

The resulting reaction product gas (f-s composition; vinyl acetate, 1.4
Volume %, unreacted acetic acid 10 volume %, unreacted ethylene 11
% by volume, 2.5% by volume of unreacted oxygen, 5.7% by volume of water, 18% by volume of carbon dioxide, and 18% by volume of inert gas) is cooled to 100°C in a condenser 12 and sent to a gas-liquid separator 13. The mixed gas separated from the condensate containing acetic acid as the main component is transferred to the distillation column 1. The condensate is put into a decanter 8, and an organic layer 9 and an aqueous layer 1 are separated.
It was separated into o. The aqueous layer was discarded at a rate of 0.551/H, and the organic layer was recycled to distillation column 1 at a rate of 20.91/H.

- From the bottom of the force-free column 1, acetic acid/
A water/vinyl acetate mixture (composition: 44% acetic acid, 50% vinyl acetate, 5.7% water, 0.053% ethyl acetate) was taken out, and then the mixture was introduced into distillation column 4. Acetic acid containing 2% water was obtained from the bottom of the distillation column (set at 125°C) at a rate of 25.8 n/h. The distillate from the top (set at 70°C) was cooled to 35°C in a condenser, led to a decanter, and separated into two layers: an organic layer and an aqueous layer. The aqueous layer is discarded at a rate of 1.4 n/h, and the organic layer (composition of main components: vinyl acetate 98.5%, water 1.5%) is discarded at a rate of 9.4 n/h.
was supplied to distillation column 2 at a ratio of . Top of distillation column 2 (45
°C) to low boiling point components (composition: vinyl acetate 87
．． 8% of water, 9.2% of water, 2.7% of acetaldehyde, and 0.3% of methyl acetate) were distilled off at a rate of 1°7/h.

Vinyl mono-acid containing 50 ppm of water and 120 ppm of ethyl acetate was obtained from the bottom of distillation column 2 (precipitated at 56° C.). A part of the crude vinyl acetate was cooled to 35°C at a temperature of A;:)' -7, .
．． It is sent to the distillation column 3 at a ratio of 81/H, and the top (50'
: ') purer vinyl acetate was taken out and high boiling pre-components were separated from the bottom. In addition, the uncondensed gas exiting the gas-liquid separator 7 is passed through a scrubber 11 (column diameter 100 mm, diameter 10 mm).
The bottom distillate (crude vinyl acetate) from the distillation column 2 is brought into countercurrent contact with the bottom distillate (crude vinyl acetate) from the scrubber 11 (composition: vinyl acetate 98.5). %, water 1°5%) is 111 /
The gas from the top of the scrubber 11, which was recycled to the distillation column 2 in a proportion of H, was washed with acetic acid and reused in the reaction as a circulating gas, while the cleaning liquid was introduced into the distillation column 4.

[Brief explanation of drawings]

FIG. 1 is a process flow diagram for carrying out the present invention. 1; Distillation column 1 8; Decanter 2; Distillation column 2
9; Organic layer 3; Distillation column 310; Aqueous layer 4; Distillation column 411; Scrubber procedure amendment October 2S, 1986 Commissioner of the Japan Patent Office Black □ Yo”lf'1% 10.127B
Submission 1, Indication of the case Patent Application No. 227554, 1932 () 2, Name of the invention Method for purifying vinyl acetate reaction product gas 3, Person making the amendment Relationship to the case Amount of patent, applicant address Kita-ku, Osaka City Nozakicho 9-6 (zip code 530)
4. Column 1 of the detailed description of the invention in the specification to be amended - rτ7%" -di 5. Contents of the amendment (1) Delete [Tower Top 760IIIIIIHg et seq."] at the end of page 6 of the specification. (2) "Collection" in the first line of page 7 of the specification is corrected to "shuku". (3) “00 for circulation” on page 7, lines 12 to 14 of the specification
．． No problem. ” to be deleted. that's all

Claims (1)

[Claims] 1. In a method for purifying a reaction product gas containing vinyl acetate obtained by reacting ethylene, acetic acid, and oxygen in the gas phase in the presence of a catalyst, the reaction product gas emerging from a reaction zone is introduced into distillation column 1, the gas mixture exiting from the top of this column is cooled, and the condensate is fed to a decanter to separate into an organic layer and an aqueous layer, and then the organic layer is circulated to distillation column 1 and The acetic acid/water/vinyl acetate mixture taken out from the bottom of the distillation column 1 is introduced into the distillation column 4, the vinyl acetate/water mixture is distilled from the top, and the acetic acid is distilled from the bottom, and then the top mixture is introduced into the distillation column 2. to obtain crude vinyl acetate containing low-boiling components from the top and high-boiling components from the bottom, and further introduce the crude vinyl acetate into a distillation column 3 to obtain purified vinyl acetate, while being separated from the condensate. The uncondensed gas is introduced into the scrubber, brought into countercurrent contact with vinyl acetate substantially free of water, so that the water in the gas is absorbed by the vinyl acetate, and the vinyl acetate that has absorbed the water is supplied to the distillation column 2. Characteristic method for purifying vinyl acetate reaction product gas. 2. Process according to claim 1, characterized in that the substantially water-free vinyl acetate brought into countercurrent contact in the scrubber is part of the bottom distillate of the distillation column (2). 3. The method according to claim 1, wherein the distillation in the distillation column 2 is carried out under reduced pressure.