JPH0611731B2 - Method for dehydrating vinyl acetate reaction product gas - Google Patents

Description

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

[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.

In addition to vinyl acetate, the reaction product gas obtained in the above reaction contains unreacted ethylene, unreacted oxygen, unreacted acetic acid, water, carbon dioxide gas and an inert gas. 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, while 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 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 the high-boiling component is separated into pure vinyl acetate distilled from the top and the high-boiling component (including the polymer) taken out from the bottom in the distillation column 3 to reduce the amount of impurities of interest. Thus, vinyl acetate can be 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 effect of saving thermal energy is about 20 to 35%, which is considerably large as compared with the conventional method, but in industrial implementation, a higher thermal energy is required. 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. I completed the invention.

That is, the present invention provides a method for removing water from 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, After introducing the mixture into the distillation column 1, cooling the gas mixture from the top of the column and supplying the condensate to the decanter to separate the organic layer and the aqueous layer into two layers, the organic layer is circulated to the distillation column 1. , Introducing uncondensed gas separated from the former condensate into a scrubber, and bringing it into countercurrent contact with vinyl acetate containing substantially no water so that the water content in the gas is absorbed by vinyl acetate,
And supplying the vinyl acetate that has absorbed the water to the dehydration tower 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 dehydration column 2 described below may be any of a plate column, a packed column, a spray column 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.

On the other hand, the uncondensed gas separated from the condensate by the gas-liquid separation gas 7 is guided to the scrubber 3 and brought into countercurrent contact with vinyl acetate containing substantially no water, and the water content in the gas is absorbed by the vinyl acetate. . The vinyl acetate that has absorbed the water is supplied to the dehydration tower 2.

In the present invention, the biggest feature is that the uncondensed gas and the anhydrous vinyl acetate are brought into countercurrent contact by installing the clubber during the refining process as described above, and almost no acetic acid is contained in the bottom liquid from the scrubber. Since it is not included, the dehydration column 2 can perform distillation with a low-temperature heat source, for example, a low-temperature vapor that has been conventionally discarded from a distillation column 4 as described below. By the above operation, the water in the vinyl acetate reaction gas is almost completely removed, but in order to obtain pure vinyl acetate as the final product, the bottom distillate from the dehydration column 2 is separated into a higher boiling fraction. Introduce into the column for purification.

Since a mixed product containing acetic acid / water / vinyl acetate as a main component is obtained from the bottom of the distillation column 1, it is purified by a conventional method.
That is, the mixture 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, which is a distillate from the top, is supplied to the dehydration tower 2, and crude vinyl acetate containing a low boiling point component and water from the top and a small amount of high boiling point components and polymer components from the bottom is obtained. The crude vinyl acetate is introduced into the above-mentioned high boiling separation column, pure vinyl acetate is obtained from the top to obtain a high boiling point component and a polymer component from the bottom, and the purification is completed.

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 in the above-mentioned acetic acid cleaning liquid, it is circulated to the distillation column.

[Operation] In the present invention, in order to process the non-condensed gas that has been separated into gas and liquid,
By providing a scrubber during the refining process and bringing it into contact with substantially anhydrous vinyl acetate, and supplying vinyl acetate that has absorbed water to the dehydration tower 2, it is possible to save energy compared to the conventional dehydration method. Of.

[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 40% 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 11, and the mixed gas separated from the condensate containing acetic acid as a main component is distilled in the distillation column 1.
It was charged into a 5/8 "Pall ring packed column with a diameter of 100 mm and a height of 10 m. From the bottom of the column, a distillate containing 50% vinyl acetate, 5.7% water, and 44.3% acetic acid at a ratio of 15 / H. The mixed gas discharged from the top was cooled to 35 ° C. by the condenser 6 and introduced into the gas-liquid separator 7. The condensate from the separator 7 was put into the decanter 8, and the organic layer 9 and the aqueous layer were obtained. The water layer was discarded at a rate of 0.50 / H,
The organic layer was circulated in the distillation column 1 at a ratio of 22 / H.

In addition, the uncondensed gas leaving the gas-liquid separator 7 is a scrubber 3 (aluminum Raschig ring with a tower diameter of 100 mm and a diameter of 10 mm is 1.5 m
The bottom effluent from the scrubber 3 (composition; vinyl acetate 98.5%, water 1.5%) is introduced at a ratio of 12 / H. It was supplied to the dehydration tower 2.

The distillate from the top of the column was cooled and separated into an organic layer and an aqueous layer by a decanter. The water layer was discarded at a rate of 0.15 / H to complete dehydration.

The gas from the top of scrubber 3 was washed with acetic acid and reused in the reaction as a circulating gas.

[Brief description of drawings]

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

Claims (1)

[Claims] 1. A method for removing water from a reaction product gas containing vinyl acetate obtained by reacting ethylene with acetic acid and oxygen in the gas phase in the presence of a catalyst, wherein the reaction product gas coming out of the reaction zone is After introducing the gas mixture into the distillation column 1 and cooling the gas mixture from the top of the column and supplying the condensate to a decanter to separate the organic layer and the aqueous layer into two layers, the organic layer is distilled.
The uncondensed gas separated from the condensate is introduced into the scrubber and is brought into countercurrent contact with vinyl acetate containing substantially no water so that the water in the gas is absorbed by the vinyl acetate and the water is absorbed. The vinyl acetate reaction product gas dehydration method, characterized in that the vinyl acetate is supplied to the dehydration tower 2.