JPH0611730B2 - Method for purifying vinyl acetate reaction product gas - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for purifying vinyl acetate-containing reaction product gas obtained by reacting ethylene, acetic acid and oxygen to obtain vinyl acetate free from impurities.

[Prior Art] It is known to produce vinyl acetate by reacting ethylene, acetic acid and oxygen in the gas phase using palladium or a palladium salt as a main catalyst.

The reaction product gas obtained in the above reaction contains unreacted ethylene, unreacted oxygen, unreacted acetic acid, water, carbon dioxide gas and further an inert gas, which is unexpectedly contained in vinyl acetate. The reaction product gas is purified to remove it. That is, as a typical refining method in the industrial method, the reaction product gas mixture is cooled in multiple stages,
The condensate obtained in this case is subjected to distillation, while the uncondensed components are recycled to the reactor. The distillation operation is carried out by first distilling the vinyl acetate / water mixture from the top and acetic acid from the bottom in the first distillation column. 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 to form a water / low-boiling point mixture from the top and a vinyl acetate / high-boiling point mixture from the bottom. To be separated. The mixture of vinyl acetate and high-boiling component is separated into pure vinyl acetate distilled from the top and high-boiling components (including polymer etc.) taken from the bottom in the distillation column 3 to reduce the amount of target impurities. Vinyl acetate is obtained.

[Problems to be Solved by the Invention] However, in such a known purification method, a huge amount of energy is required for distillation, and in particular, about 60 to 80% of the total energy required for distillation is required only for separating water. It is consumed.

Needless to say, it is necessary to reexamine the labor saving in the distillation method which requires a great deal of expensive heat energy at the present time of the age of resource saving and energy saving.

As one of such measures, for example, Japanese Patent Application Laid-Open No. 52-11151
The proposal is made in Japanese Patent Publication No. 1 and the saving effect of heat energy is about 20 to 35%, which is considerably large as compared with the conventional method. Savings are being requested.

[Means for Solving Problems] However, as a result of intensive studies by the present inventors for solving such problems, the heat energy is about 40 as compared with the conventional method.
%, Or even 50% or more in some cases, and a purification method capable of exerting an extremely useful effect industrially that vinyl acetate having a significantly reduced content of water as an impurity can be obtained. He came up with an invention.

That is, the present invention provides a method for purifying a reaction product gas containing vinyl acetate obtained by reacting ethylene with acetic acid and oxygen in a gas phase in the presence of a catalyst, wherein the reaction product gas emerging from the reaction zone is distilled. 1, the gas mixture discharged from the top of this column is cooled, and the condensate is supplied to a decanter to separate the organic layer and the aqueous layer into two layers, and the organic layer is circulated to the distillation column 1 and the distillation column is The acetic acid / water / vinyl acetate mixture taken out from the bottom of 1 is introduced into the distillation column 4 and vinyl acetate /
Acetic acid was distilled from the bottom of the water mixture, and then the top mixture was introduced into the distillation column 2 to obtain crude vinyl acetate containing a low boiling point component from the top and a high boiling point component from the bottom, and the crude vinyl acetate was further distilled from the distillation column 3. To obtain purified vinyl acetate,
On the other hand, the uncondensed gas separated from the condensate is introduced into a scrubber and brought into countercurrent contact with vinyl acetate containing substantially no water, particularly a part of the bottom distillate of the distillation column 2 to remove water in the gas from acetic acid. The method for purifying a vinyl acetate reaction product gas is characterized in that vinyl acetate is adsorbed on vinyl and the water-absorbed vinyl acetate is supplied to the distillation column 2.

The basic steps of the present invention are as shown in FIG.

The method of the present invention will be described with reference to FIG.

Reaction product gas leaving the reactor 5 (substantially vinyl acetate, unreacted ethylene, unreacted acetic acid, unreacted oxygen, carbon dioxide,
Water, including inert gas, etc.) is introduced into the distillation column 1.
The gas is preferably cooled by heat exchange before it is introduced.

The distillation column 1 and the distillation columns 2, 3 and 4 described below may be any of tray columns, packed columns, spray columns and the like. The gas discharged from the tower 1 is introduced into a gas-liquid separator 7 via a condenser 6 and separated into an uncondensed gas and a condensate. The condensate is separated into two layers, an organic layer 9 and an aqueous layer 10, in the decanter 8. Then, the water layer 10 is discharged. The organic layer 9 is circulated to the distillation column 1. A mixture containing acetic acid / water / vinyl acetate as a main component is obtained from the bottom of the distillation column 1, and the mixture is then supplied to the distillation column 4. The separated acetic acid obtained from the bottom is reused in the reaction. The vinyl acetate / water mixture, which is a distillate from the top, is supplied to the distillation column 2, and low-boiling components and water are obtained from the top, and crude vinyl acetate containing a small amount of high-boiling components and polymer components from the bottom is obtained. Crude vinyl acetate is a distillation column 3
Is introduced into the top to obtain pure vinyl acetate from the top, a high boiling point component and a polymer component from the bottom, and the purification is completed. In the present invention, this distillation column 2 is a low-temperature heat source that has been conventionally discarded, for example, a top vapor (60 to 80) of the distillation column 4.
It is possible to operate the bottom of the column at a pressure of 200 to 760 mmHg) under reduced pressure by using the temperature of (° C.) And the like, and a heat energy saving effect can be obtained.

On the other hand, the uncondensed gas separated from the condensate in the gas-liquid separator 7 is guided to the scrubber 11, and is brought into countercurrent contact with vinyl acetate, which is a part of the bottom distillate of the distillation column 2 and contains substantially no water. The water in the gas is absorbed by vinyl acetate. The vinyl acetate that has absorbed the water is circulated to the distillation column 2.

In the present invention, the greatest feature is that the scrubber is installed and the anhydrous vinyl acetate is circulated and reused during the purification process as described above, and the bottom liquid from the scrubber contains almost no acetic acid. Since the distillation column 2 can perform distillation with a low-temperature heat source, such an operation saves energy as compared with the conventional method.

The gas discharged from the top of the scrubber is purified by a known means such as washing with acetic acid, and is reused as a circulating gas in the reaction. Further, since vinyl acetate is absorbed by the above-mentioned acetic acid cleaning liquid, it is circulated to the distillation column 4.

[Operation] In the present invention, the non-condensed gas that has been vapor-liquid separated is brought into contact with substantially anhydrous vinyl that is a part of the bottom distillate from the distillation column 2, and the vinyl acetate distillation column 2 that has absorbed water. It is possible to save energy as compared with the conventional refining method by circulating it into the.

[Example] Next, the method of the present invention will be described more specifically with reference to Examples. "%" Is based on weight unless otherwise specified.

Example 1 (see FIG. 1) In the reactor 5, ethylene was reacted with acetic acid and oxygen in the gas phase in the presence of a palladium main catalyst supported on silica. The resulting reaction product gas (gas composition: vinyl acetate 4.4% by volume, unreacted acetic acid 10% by volume, unreacted ethylene 41% by volume, unreacted oxygen 2.5% by volume, water 5.7% by volume, carbon dioxide 18) % By volume, 18% by volume of inert gas) in the condenser 12
The mixture gas cooled to 100 ° C. is introduced into the gas-liquid separator 13, and the mixed gas separated from the condensate containing acetic acid as the main component is distilled in the distillation column 1.
(A diameter of 100 mm, a height of 10 m and a 5/8 "pole ring packed tower).
It was cooled to 5 ° C. and introduced into the gas-liquid separator 7. The condensate from the separator 7 is put into the decanter 8, and the organic layer 9 and the aqueous layer 1
It was separated into 0 and. The water layer was discarded at a rate of 0.55 / H, and the organic layer was circulated to the distillation column 1 at a rate of 20.9 / H.

On the other hand, a mixture of acetic acid / water / vinyl acetate at a ratio of 9.6 / H from the bottom of the distillation column 1 (composition: acetic acid 44%, vinyl acetate 5
0%, water 5.7%, ethyl acetate 0.053%) was taken out, and then the mixture was introduced into the distillation column 4. From the bottom of the distillation column (set at 125 ° C), 2% of acetic acid containing 2% water
Obtained at a rate of 5.8 / H. Top (set to 70 ° C)
The distillate from was cooled to 35 ° C. in a condenser, introduced into a decanter, and separated into an organic layer and an aqueous layer. The water layer is 1.
The organic layer (composition of the main components; vinyl acetate 98.5%, water 1.5%) was discarded at a ratio of 4 / H and supplied to the distillation column 2 at a ratio of 9.4 / H. From the top of the distillation column 2 (set to 45 ° C.), low boiling point components (composition: vinyl acetate 87.8)
%, Water 9.2%, acetaldehyde 2.7%, methyl acetate 0.3%) was distilled off at a ratio of 1.7 / H. Crude vinyl acetate containing 50 ppm and 120 ppm of ethyl acetate was obtained from the bottom of the distillation column 2 (set at 56 ° C.). Part of the crude vinyl acetate was cooled to 35 ° C. in a cooler,
It is introduced into the scrubber 11 at a ratio of 6 / H, and the remaining crude vinyl acetate is sent to the distillation column 3 at a ratio of 6.8 / H,
Pure vinyl acetate was taken out from the top (set to 50 ° C),
High boiling components were separated from the bottom. Further, the uncondensed gas leaving the gas-liquid separator 7 is a scrubber 11 (tower diameter 100 mm, diameter 10
mm aluminum Raschig ring (1.5 m) and introduced in countercurrent contact with the bottom distillate (crude vinyl acetate) from the distillation column 2 and the bottom effluent from the scrubber 11 (composition;
Vinyl acetate (98.5%, water 1.5%) was circulated to the distillation column 2 at a ratio of 11 / H. The gas from the top of the scrubber 11 was washed with acetic acid and reused as a circulating gas in the reaction. Along with this, the cleaning liquid was introduced into the distillation column 4.

[Brief description of drawings]

 FIG. 1 is a process system diagram for carrying out the present invention. 1; Distillation tower 1, 8; Decanter 2; Distillation tower 2, 9; Organic layer 3; Distillation tower 3, 10; Water layer 4; Distillation tower 4, 11; Scrubber 5; Reactor, 12; Condenser 6; Condensation Vessel, 13; gas-liquid separator 7; gas-liquid separator

Claims (3)

[Claims] 1. A method for purifying a reaction product gas containing vinyl acetate obtained by reacting ethylene, acetic acid and oxygen in a gas phase in the presence of a catalyst, wherein the reaction product gas coming out of the reaction zone is a distillation column. 1, the gas mixture discharged from the top of this column is cooled, and the condensate is supplied to a decanter to separate the organic layer and the aqueous layer into two layers, and the organic layer is circulated to the distillation column 1 and the distillation column is The acetic acid / water / vinyl acetate mixture taken out from the bottom of 1 is introduced into the distillation column 4 to distill the vinyl acetate / water mixture from the top and acetic acid from the bottom, and then the top mixture is introduced into the distillation column 2 from the top. Crude vinyl acetate containing low-boiling components from the bottom containing high-boiling components is obtained, and the crude vinyl acetate is further introduced into the distillation column 3 to obtain purified vinyl acetate, while uncondensed gas separated from the condensate. To the scrubber Then, the vinyl acetate reaction produced by countercurrently contacting vinyl acetate containing substantially no water so that the water content in the gas is absorbed by the vinyl acetate and the vinyl acetate having absorbed the water is supplied to the distillation column 2. Gas purification method. 2. A process according to claim 1, characterized in that the substantially water-free vinyl acetate which is brought into countercurrent contact with the scrubber is part of the bottom distillate of the distillation column 2. 3. The method according to claim 1, wherein the distillation of the distillation column 2 is performed under reduced pressure.