DE1768412B2 - Process for the production of vinyl acetate - Google Patents

Description

acidity more than 90 ° / ₀ . This bottom product is distilled z. B. worked up in a thin film evaporator: the concentrated polymer is obtained as a residue, the recovered acetic acid is returned to the process.

Together with the polymer-containing stream from the reaction evaporator, the bottom of the Pure vinyl acetate column containing the polymers dissolved in vinyl acetate and formed during redistillation contains, be worked up on the thin-film evaporator mentioned. But you can also go to the swamp Introduce the pure vinyl acetate column into the azeotrope column and thus introduce the vinyl acetate contained therein win as a distillate.

From the water obtained in the first aeotrope column, the then dissolved organic Products are distilled off and returned to the work-up system, so that then a waste water is discharged from the system, which contains traces of acetic acid as the only impurity.

The crude, liquid \ inyl acetate obtained as a condensate by cooling the reaction products is before use in the azeotropic distillation expediently relaxed to normal pressure, and the The dissolved gases released in the process can be fed back into the cycle gas in a suitable manner will.

The small amounts of gases, which remain dissolved in the liquid reaction product even after the expansion, go overhead in the azeotropic distillation and are separated from the condensed products in the condenser. These gases can then be ^{cooled to temperatures of about 0} ° C., with acetaldehyde and other low-boiling components condensing together with vinyl acetate. This condensate is added to the above-mentioned column to separate off the low-boiling products.

However, it is also possible to remove those which have remained dissolved in the condensate from the reaction product Separate gases in a scraper upstream of the azeotrope column.

In the procedure according to the invention, the acetic acid is not returned as practically anhydrous acetic acid to the vinyl acetate production, which would be desirable because of the evaporation and condensation energies to be applied there, but it is with a water content of about 0.5 to 6 ° / _{0 worked} in the circulatory acetic acid. (The amount of water to be effectively removed from the reaction product is of course constant, since the water newly formed in the reaction must be removed in each case.)

The acetic acid obtained in the bottom of the azeotrope column has a content of about 100 to 1000 ppm Ethyl acetate (based on the separated vinyl acetate). You can use the evaporator already described this acetic acid without further purification of the vinyl acetate production be fed back.

It was surprisingly found that practically no new formation of ethyl acetate is observed, if you use this ethyl acetate-containing acetic acid for the production of vinyl acetate from ethylene, Acetic acid and oxygen used in the presence of catalysts. The reaction evidently arises a balance between the formation and degradation of ethyl acetate.

So if you recycle the acetic acid worked up according to the invention for vinyl acetate production used, a vinyl acetate is obtained, which is poor in ethyl acetate, and also avoided a new formation of ethyl acetate in the reaction itself. This eliminates the extraordinarily expensive and lossy separation of the ethyl acetate from the vinyl acetate by distillation.

All percentages are percentages by weight.

B e i s ρ i e 1 1

The figures given below relate to the figures.
The reaction was carried out in a manner known per se over a fixed noble metal catalyst on a support at 185 ^{° C. and a pressure of 8 atm}

from ethylene, oxygen and acetic acid to vinyl acetate carried out 1.

The reaction mixture 2 was cooled to 30 ^c C after leaving the reactor 1, the oxygen are zugef'hrt immediately above la and acetic acid s'> -ie the ethylene from the Reaktionsverdampfer7 and transferred into a separator la in which the separation between the condensed liquid and the remaining gaseous portions was made. The gases 3 were returned to the process. The condensate 2a was let down to atmospheric pressure 2 b and fed to the distillative work-up via 2 c. The gases 39a released during the expansion were brought back to reaction pressure and likewise fed back into the reactor.

The feed product 2 b in the distillation 4 had the following composition

Ethylene

Carbon dioxide

Vinyl acetate

acetic acid

water

Ethyl acetate

acetaldehyde

Low-boiling components

Weight percent

0.19

0.49

21.38

70.85

6.81

0.04

0.23

0.01

100.00

kg / h

0.041 0.104 4.534 15.034 1.443 0.008 0.048 0.002

In the distillation 4, the water newly formed in the reaction was together with the water formed Vinyl acetate removed as top product 5. the

Bottom temperature was 125 ^C C _t the head temperature 70 ⁰ C, the reflux ratio is 1: 5.

At the bottom of the column, the acetic acid 6 to be reused in the reaction was immediately obtained deducted. It had the following composition:

Acetic acid.
water
Polymers ..
Ethyl acetate

Weight percent

97.64 1.98 0.34 0.04

100.00

kg / h

15.034 0.305 0.053 0.007

The acetic acid got hot in the reaction evaporator ?, the fresh acetic acid and ethylene over

7 α or Ib are supplied, are used. In order to avoid an accumulation of polymers in this evaporator, a return flow 8 of 1.851 kg / h was fed to a thin-film evaporator 9. In this thin-film evaporator, 10 1.605 kg / h of the acetic acid used were recovered. The remainder was discarded as polymer 11.

The top product 5 of the azeotrope column 4 was separated into lower aqueous 12 and upper organic phase 13 in a phase separator. According to the analysis, the organic phase has the following composition:

Weight
percent kg / h Vinyl acetate
water 98.29
1.05
0.02
0.59
0.05
100.00 4.274
0.046
0.001
0.026
0.002 Ethyl acetate
acetaldehyde
Low boilers

This upper phase (crude vinyl acetate) was used in a further column 14 for further dehydration and to separate off all low-boiling components. The top product 15 of this column contained about 10% acetaldehyde, the remainder essentially Vin ^v lacet? It.

This overhead product 15 was distilled in column 16. The vinyl acetate 17 obtained as the bottom product was returned to the distillation 14 . The low boilers 18 , which were removed from the process, were drawn off overhead.

The vinyl acetate 19 obtained as the bottom product in column 14 was now dry and freed from all low-boiling products, but it still contained small amounts of acetic acid and polymers. It was freed from these compounds by redistillation. The vinyl acetate 21 thus obtained as the end product meets all specifications. It has an ethyl acetate content of max. 0.02%

The bottom product 22 of the vinyl acetate redistillation 20 was also passed over the aforementioned thin-film evaporator 9 in order to recover the vinyl acetate contained therein from the polymer-containing product, which was returned to the distillation 4 through line 10.

A lower aqueous phase 12 falls in the phase separator for the distillate in the first azeotrope column 4 at. In addition to small amounts of other impurities, this aqueous phase contains about 1% vinyl acetate in solution. By stripping this water in a column 23 all volatile constituents 24 were driven off, so that for the entire process wastewater 25 is obtained which contains practically only acetic acid as an impurity.

The driven off organic compounds 24 were returned to the column 16, in which all low-boiling components are withdrawn via the top 18.

In the azeotrope column 4, the gases 26 are released which, after the expansion of the cold liquid reaction products, still remain dissolved in the liquid. These gases escape overhead from the aforementioned phase separator 12/13. To isolate entrained acetaldehyde and vinyl acetate, they were ^{cooled to O 1} C by brine I3a and then added to the remaining residual gas in order to be returned to the process.

The small amounts of liquid products 27, which are condensed out by the cooling, were introduced into the column 16 , in which all the low boilers 18 are removed overhead.

Example 2

In a laboratory bell-shaped tray column made of glass with ίο 60 trays were on the 30th tray 2000 g / h of a mixture added with the following composition:

Weight percent

Vinyl acetate 15.98

Ethyl acetate 0.02

Water 6.00

Acetic acid 78.00

The top product was condensed, cooled to 40 ⁰ C and passed into a phase separator. From ao the vinyl acetate phase, 2400 g / h were pumped as reflux to the top of the column, the remainder was taken off as crude vinyl acetate. His concentration was low

Weight percent

Vinyl acetate 98.59

Ethyl acetate 0.01

Water 1.40

The bottom product of the column had the following composition:

Weight percent

Vinyl acetate 0.01

Ethyl acetate 0.02

Water 2.00

Acetic acid 97.97

Example 3

In the test column of Example 2, 2000 g / h of a mixture are added, the ethyl acetate content of which is three times higher than in Example 2. The composition was

Weight percent

Vinyl acetate 15.94

Ethyl acetate 0.06

Water, 6.00

Acetic acid 78.00

After condensation and cooling of the head

ducts from the separator were 2,200 g / h of the

Vinyl acetate phase as reflux to the top of the column

pumped. The crude vinyl acetate on the head then contained

Weight percent Vinyl acetate 98.55 Ethyl acetate 0.05

Water 1.40

The bottom product had the end of the experiment

Composition:
Weight percent

Vinyl acetate 0.02 Ethyl acetate 0.06

Water 2.75

Acetic acid 97.17

. .

Example 4

With the same feed conditions as in Example 3, 14 g / h were obtained from the 15th tray of the test kettle

a liquid side stream with the following composition is drawn off:

Weight percent

Vinyl acetate 1.0

Ätb \ 'acetate 5.0

Water 11.0

Acetic acid 83.0

In this procedure, the crude vinyl acetate was present at the top of the column

Weight percent

Vinyl acetate 98.58

Ethyl acetate 0.02

Water 1.40

The bottom product had the following composition:

Weight percent

Vinyl acetate 0.02

Ethyl acetate 0.03

Water 2.00

Acetic acid H7.95

The side stream was then passed into a second column in which the vinyl as contained therein acetate and ethyl acetate as an azeotrope with the water was distilled overhead. The acetic acid that am The bottom of this column was withdrawn, was added to the bottom product of the first column.

Example 5

2000 g / h of the same mixture that was used in Examples 3 and 4 was one on the 30th tray Trial column with 60 trays added. As in Example 3, the return flow was 2200 g / h

ίο the vinyl acetate phase from the separator is used. In this experiment, the amount withdrawn at the top and bottom of the column was adjusted so that on At the bottom a larger amount of vinyl acetate was removed with the acetic acid.

is The composition of the vinyl acetate at the top of the column was with this driving style

Weight percent

Vinyl acetate 98.57

Ethyl acetate 0.03

Water 1.40

“O The sump concentration was

Weight percent

Vinyl acetate 2.00

Ethyl acetate 0.07

Water 2.50

1 sheet of drawings

Claims (1)

1 2 molecular oxygen or air at 10 to 4O ⁰ C Claim: if a condensate is obtained which essentially z. B. about 45 to 80% from acetic acid, 15 to 35% from Method / ₀ consists of water for the recovery of vinyl acetate of vinyl acetate and from 3 to 20 °. It c ^ m resulting mixture, 5 also contains varying amounts of ethyl acetate which essentially still acetic acid, water z. B. 500 to 2500 ppm, based on vinyl acetate, and contains small amounts of ethyl acetate, through This reaction mixture is brought into an azeotropic azeotropic distillation, where one takes by re-distillation and in this distillation the leadership of the condensation and phases in the mixture vinyl acetate contained and separation of the top product available vinyl ίο a part of the water present, which corresponds to the amount of water formed in the ecetats, the main amount of water together reaction, is withdrawn overhead with vinyl acetate, thereby top. The reflux of vinyl acetate in the azeotrope is characterized by the fact that vinyl acetate is regulated in the distillation column in such a way that an amount such that an average water content is obtained in the bottom product in the acetic acid drawn off in the bottom, about 0.5 to 15 percent acetic acid from about 0.5 to 6 percent by weight of 6% water is adhered to tion, a reflux ratio - based on the withdrawn vinyl acetate - of 3 to 8 is advantageous. the vinegar drawn off at the bottom of the azeotrope column 20 acid can e.g. B. 0.05 to 1.0% polymers containing z. B. Ent-Bei by polymerization of vinyl acetate Processes for the production of vinyl acetate are available. one often obtains a crude, liquid vinyl acetate, which is obtained overhead in the azeotrope distillation. Essentially acetic acid, water and small amounts of vinyl acetate are also used, which also contains over amounts of ethyl acetate. Such a product was separated from the water at the top. In another z. B. in the production of vinyl acetate by distillation, cFeses vinyl acetate is azeotropically freed from the reaction of ethylene with acetic acid and mole-dissolved water and low-boiling components - precular oxygen or air in the gas phase with acetaldehyde. The vinyl acetate obtained at this elevated temperature and usually or erlonne as a bottom product is elevated under pressure in the presence of a catalyst, e.g. B. 30 by redistillation of small amounts of polymeric noble metal catalyst, obtained by cooling and freed from traces of acetic acid and is then available to the reaction products leaving the reaction space as pure vinyl acetate with ethyl acetate products to near room temperature. ^D:; se vinyl acetate ppm kept between about 20 and not more than 300th Production is carried out with excess acetic acid. The top product of the low boiler column mentioned and the unconverted acetic acid still consists essentially of vinyl acetate, in the circuit back to the vinyl acetate production - In a further column this is now guided. The vinyl acetate is recycled as a bottom product from the acetic acid before its return product in the reaction the contained vinyl acetate, recovered and in the beginning of the distillation back-water as well as the polymers, which - be it led, while the low-boiling components in the reaction or in the work-up - arise through 40 as the top product of this column and from Polymerization of vinyl acetate has formed ent- the process can be removed. far away. The vinegar containing water and ethyl acetate It has been now found a process for the recovery of acid corresponding to the azeotropic column obtained at the bottom with a vinyl acetate from the resulting in the production temperature of about 12O ⁰ C, substantially still acetic acid, 45 tinuierlicher operation can at kon mixture immediately contains in the pressure water and small amounts of ethyl acetate, are introduced through the evaporator of the reaction system, azeotropic distillation, whereby one by recirculation the main vaporizer hot acetic acid removes the previously heated amount of water together with vinyl acetate over 50 of the stream of essentially ethylene overhead, found, which passes through the existing cycle gas. This is because vinyl acetate is recycled in such an amount, the evaporation can take place at relatively low temperatures of about 110 to 140 ° C., which contains about 0.5 to 6% water, so that acetic acid is obtained as the bottom product. This as a sump to avoid corrosion is very beneficial. Acetic acid obtained from the product, which may also contain the polymers for the reformed, fresh acetic acid required for the vinyl formation can also be introduced into the evaporator, acetate production can be used and z. B. at con- As an advantageous embodiment, continuous operation has been given directly via the evaporator, in the upper part of the evaporator, in which are returned to the vinyl acetate production. if the gases and vapors are, a spray-By the measures according to the invention is 60 protection, z. B. in the form of a defogger, achieved that a vinyl acetate is obtained as the top product and the fresh acetic acid is used on this defogger, which is practically free of ethyl acetate. To give rinse to avoid poly- The inventive method can, for. B. entrained in mers of the gas stream and into the be carried out in the following way: reactor are introduced. By cooling the reaction products from the 65 From the bottom of the evaporator one can get liquid at elevated temperature and normal or greater amounts of acetic acid that it becomes more polycyclic Pressure in the presence of a catalyst has a diameter content of about 1 to 5%, i.e. one seduced Implementation of ethylene, acetic acid and steam from the water-containing vinegar