DE1643977C3 - Process for the preparation of unsaturated esters of carboxylic acids - Google Patents

Description

Part of the scrubber is the primary pumped washing liquid, while the fresh washing solution is applied to the head of the washer. The used one Washing solution is drawn off at the lower end of the washing tower and enters the distillative desorption. The washing is expediently carried out under the pressure that occurs after the condensation adjusts. It is very advantageous to do this washing before recompressing the cycle gas to the inlet pressure to arrange the reactor.

Often the catalytic reaction is carried out at an excess pressure of a few atm, for example 5 to 10 atm, and the pressure at the inlet of the scrubber is only slightly lower than the pressure in the reactor itself. The loaded washing liquid, which leaves the washer at the lower end, is expediently before going into the desorption to a pressure which is close to normal pressure Pressure in the desorption relaxed.

In the desorption, the loaded solvent is heated to a temperature such that practically table all products absorbed by the solvent are driven off. The expelled Products, i.e. the dissolved esters, the water and the absorbed acids, leave the desorption at the top, are condensed and worked up together with the main products. That of the Dissolved fractions freed and the solvent drawn off at the lower end of the desorber is cooled to the temperature at which the gas enters the laundry, as far as possible, to a slightly lower level Temperature so that the laundry itself takes place close to room temperature.

In the production of the unsaturated carboxylic acid esters, smaller amounts are produced as a by-product Carbon dioxide. It has proven useful to have some of this carbonic acid in the circuit as well the other gases returned to the reactor, in such a way that the carbonic acid content with the Recycle gas is kept at about 20 percent by volume. The amount of newly formed carbon dioxide must then removed from the cycle gas. It has proven to be useful that the cycle gas scrubbing First enter the gas leaving the compressor and a partial flow downstream of the compressor remove, run this over a wash to remove the carbonic acid and then the Re-add main gas flow upstream of the compressor. With this arrangement you come with one Compressor for cycle gas and carbonic acid washing off. The removal of the carbon dioxide from the partial flow can be carried out in a manner known per se. The has proven to be particularly suitable known hot carbonate wash. The laundry is operated in such a way that the carbonic acid content of the through The cycle gas passed through the laundry is reduced from, for example, 20 to, for example, 5% will.

It has been shown that the gas scrubbing according to the invention for the carbon dioxide scrubbing with Hot carbonate liquor is very beneficial. If you do not switch on this laundry, it will be in the cycle gas The esters contained in the hot carbonate wash are saponified and thus lost. About it In addition, the potassium carbonate is converted into potassium carboxylate.

The procedure according to the invention is suitable for the process in which unsaturated esters are obtained by catalytic conversion of an olefin with a carboxylic acid and oxygen. It is in particular the conversion of ethylene with acetic acid and oxygen to vinyl acetate or processes in which the ethylene has been replaced by other olefins such as propylene or butylenes and / or the acetic acid by other carboxylic acids such as propionic acid or butyric acid. The unsaturated esters of the carboxylic acids are prepared in a manner known per se.

example 1

A gaseous mixture of ethylene, acetic acid, oxygen and carbon dioxide was under one Pressure of 6 atm at 170 ° C on a fixed noble metal catalyst implemented, whereby about 12% of the ethylene introduced was converted to vinyl acetate and water and small amounts Carbonic acid. The reaction mixture leaving the reactor was cooled to 40 ° C., whereby Most of the unreacted acetic acid and the vinyl acetate and water formed are liquid taking leave. The condensed products were in one of the products which remained in gaseous form Separator separated without pressure relief, with the liquid products at the bottom of the separator peeled off and relaxed for further processing. The remaining gaseous parts were withdrawn from the top of the separator. This gas had the following composition:

Components by volume

Ethylene 79.0

Carbon dioxide 20.0

Nitrogen 0.1

Vinyl acetate 0.7

Acetic acid 0.1

Water 0.1

100.0

The hourly amount of gas was 8000 Nl. This gas was poured into a with no pressure relief at the bottom Packing filled washing tower introduced, which has a diameter of 90 mm and a height of 2.50 m. Propylene glycol was applied to the head of the scrubber every hour Amount of 2.0 1. In the lower half of the washing tower, the solvent was pumped around in a hourly amount of 5 1. The gas emerging at the top of the scrubber contained <0.02 percent by volume vinyl acetate and less than 0.01 percent by volume each Acetic acid and water. The pressure of the scrubbed gas was 5.4 atmospheres. It became a gas compressor fed, which increased the pressure to 7 atm, so that the gas back into the reaction space could be fed. Before entering the reactor, the circulating gas was used for the implementation the reaction necessary amounts of ethylene, oxygen and acetic acid are supplied.

Of the circulating gas downstream of the gas compressor 10% were branched off and added to a washing with saturated potassium carbonate solution at 100 ⁰ C. The washing was operated in such a way that the gas leaving the washing contained 5 percent by volume of carbonic acid. The scrubbed gas was fed back into the cycle gas upstream of the gas compressor

The enriched solvent leaving the ester wash was let down to normal pressure and fed to a distillation in which the parts of the circulating gas taken up by the solvent were aborted again. The bottom temperature of this laundry was 185 ° C, the head temperature 70 to 80 ° C. The removed products were condensed by cooling to room temperature and added to the relaxed condensates from the cooling of the reaction products and with then processed this together. The solvent drawn off at the lower end of the distillation was returned to the gas scrubber after cooling to near room temperature.

With this procedure it was achieved that in the compression and reheating of the washed cycle gas-j no blockages occurred due to polymerization of the vinyl acetate and that practically no impairment occurred to the potassium carbonate wash to remove CO ₂ by saponification of vinyl acetate.

Example 2

Under a pressure of 8 atm and at a temperature of 180 ° C, it became a gaseous mixture from essentially Ethya; Acetic acid, oxygen and carbon dioxide on a fixed noble metal catalyst implemented. The reaction mixture leaving the reactor was cooled to 40.degree. The majority of the liquid reaction products (vinyl acetate, excess acetic acid, formed water) condenses. The separation was carried out in a fully pressurized separator made into gaseous and "liquid products."

The gas mixture escaping from the separator had the following composition:

g / h

Ethylene 20 837.90

• Ethane 1321.50

Nitrogen 1832.20

Oxygen 1080.10

Carbon dioxide 9 911.50

Acetic acid 366.35

Water 62.70

Vinyl acetate 1,180.00

Ethyl acetate 0.40

Acetaldehyde 1.10

Acrolein 0.60

Methyl acetate 0.60

The cycle gas leaving the laundry had the following composition:

g / h

Ethya 20665.40

Ethane 1,309.50

Nitrogen 1831.90

Oxygen 1079.00

Carbon dioxide 9,733.10

Acetic acid 350.07

Water 5.00

34 973.97

This gas, which was now free from vinyl acetate, was fed to a compressor which contained the cycle gas brought back to full reaction pressure. Then the converted ethylene and the converted oxygen is replenished and acetic acid is added and the mixture is again over the catalyst guided.

The solvent withdrawn from the laundry below had the following composition:

g / h

_a , ethylene 172.50

Ethane 12.00

Oxygen 1.10

Carbon dioxide 178.40

Nitrogen 0.30

Acetic acid 7,689.93

Water 215.70

Vinyl acetate 1180.00

Ethyl acetate 0.40

Acetaldehyde 1.10

Acrolein 0.60

Methyl acetate 0.60

9,452.63

The loaded solvent was let down in an intermediate tank. The liquid reaction product from the first separator was also depressurized into the same intermediate tank. The gases occurring during this expansion were compressed to 8 atm in a residual gas compressor. Downstream of the residual gas compressor, the gas was cooled to 20 to 25 ° C. in a water cooler and again washed in a small acetic acid wash to remove the vinyl acetate. The following table shows the inlet and outlet of the gas:

36 594.95

To remove the vinyl acetate, this cycle gas was passed through a scrubbing tower 2.50 m high and 90 mm in diameter, which was filled with Raschig rings. The acetic acid recovered in the distillative work-up of the liquid reaction products served as the washing agent. It was added to the top of the column in an amount of 7831 g / h. The laundry was designed in two stages to dissipate the heat of reaction. In the lower part, the temperature of 40 ° C. was maintained by pumping the detergent through an external water cooler. The pressure in the laundry was 7.5 atmospheres.

input
g'l exit
gl 55 ethylene
Ethane
nitrogen
oxygen
Carbon dioxide
⁶⁰ acetic acid
Water ·
Vinyl acetate
acetaldehyde 371.58
13.21
1.60
6.00
601.75
8.80
1.75
109.60
1.87 368.50
13.00
1.60
6.00
592.40
8.80
0.14 1116.16 991.91

618 g of acetic acid were added to the laundry every hour from the recovery in the distillative up-

work used. The loaded detergent had the following composition:

g / h

Ethylene 3.08

Athan 0.21

Carbon dioxide 9.35

Acetic acid 612.80

Water 19.86

Vinyl acetate ■ 109.60

Acetaldehyde 1.87

756.77 The vinyl acetate-free gas leaving the residual gas scrubber was now used to remove the in the reac Wash the carbonic acid formed with potassium carbonate as described in Example 1.

The gas leaving the carbonic acid wash has the following composition:

g / h

Ethylene 359.37

Ethane 13.00

Nitrogen 1.60

Oxygen 6.00

Water 2.30

Carbon dioxide 85.18

467.45

This loaded acetic acid was also depressurized in the above-mentioned pressureless container. the Liquid products arising there, i.e. the crude reaction condensate, the detergent for the cycle gas scrubbing and the detergent for the Reslgas

scrubbing, were combined together in a distillation on ao main cycle gas and returned to the reactor worked. guided.

The amount of carbon dioxide washed out corresponds to the formation of new CO ₂ . After the CO ₂ wash, this scrubbed residual gas was with the

309682/203

Claims (3)

ι ^κ 2 Blockages occur as a result of polymer formation. It has also been shown that for the Claims: Production of the unsaturated esters required catalysts have a longer lifespan if the I. Process for the production of unsaturated esters 5 cycle gases according to the invention Vtrvon carboxylic acids by reaction of olefins are subjected to a scrubbing,
With organic acids and oxygen when washing the cycle gas with the higher temperature and normal or higher-boiling, liquid, organic solution with high pressure in the presence of a catalyst, the solvent is loaded with lighter components, with cooling of the reaction products. A substantial part of the carboxylic acid formed can be driven off from the solvent by heating, whereupon the esters, the acids and the water are deposited, the solvent after cooling is returned to the, making it possible to use laundry. The products obtained when stripping the non-condensed portions of the fully or partially charged solvent are circulated back into the inlet of the reactor. It is expedient to list the products before the gas scrubbing, adding the condensates produced by the condensed condensates so that they can disperse with them freed circulating gas are processed further together before entry,
the reactor of a wash with a liquid. The solvent used is preferably an organic solvent which has a higher boiling point than those organic liquids to which at least the carboxylic acid ester formed is subjected. Boil ao 20 ° C higher than those produced in the process 2. The method according to claim 1, characterized by carboxylic acid esters and the acids used. the indicates that one is washing with an upper boiling limit without process-related loading solvents carried out ^ this at least 20 ° C interpretation. It is expedient to use such solvents boils higher than the carboxylic acid esters formed. in which the gas to be removed from the cycle 3. The method according to claims 1 and 2 »5 washing compounds are sufficiently soluble, characterized in that part of the solvent is particularly advantageous Washed cycle gases before the introduction of oxygen-containing compounds of the type of in the reactor by a wash in whole or in part- glycols or their ethers and esters proved. When wisely released from carbonic acid. have proven particularly useful as solvents 30 glycol esters of the organic acids used in the reaction have been shown, for example in the case the use of acetic acid to produce Vinyl acetate, propylene glycol diacetate. Expedient The easily accessible glycols, e.g. 35 propylene glycol, as a solvent. It shows that in the course of use the glycol through the absorbed carboxylic acid, e.g. B. acetic acid, It is known that unsaturated esters of carboxylic acids can be converted into the carboxylate, in this case the diacetate, by converting mono-. To the extent that the olefin used is converted into the ester with organic acids and oxygen at 40% glycol, the increased temperature improves in the presence of noble metals, the detergent effect of the solvent. Otherwise has as catalysts; Preferably, the shown that the glycol esters are also in permanent precious metals on carriers and contain alkali salts. operation are very suitable for this process.
In particular, one works here at temperatures. The cycle gas is washed - w ".e from 50 to 300 ° C and said ordinary or increased 45 - after deposition the slightly condensing pressure. In the continuous implementation of this the proportions through. It has proven to be expedient to process the recycle gases to separate the condensing fractions that are not easily converted through the reactor before entering the parts of the olefins, acids and oxygen in the wash at temperatures <50 ° C , more expediently returned to the reactor. 50 wise <40 ° C to cool down. An essential further process has now been developed for the production of continuous cooling of the gases, generally saturated esters of carboxylic acids by reaction does not bring any advantages, which the greater energetic expenditure of olefins with organic acids and oxygen for the cooling and the later return to elevated temperature and ordinary or justify heating. If, for example, a higher pressure is cooled in the presence of a catalyst, the circulating gases from the production of vinyl acetate being reduced to about 40 ° C. by cooling the reaction products, they contain a substantial part of the carboxylic acid ester formed, about 0.7 percent by volume vinyl acetate . Through which the acids and water are separated, this content is found to be <0.02 percent by volume, which is characterized by the fact that it is reduced. The inflow of the solvent to the non-condensed fractions wholly or partially in the washing tower is advantageously set up in such a way that the circuit is returned to the inlet of the reactor, the solvent is raised in a single pass, the condensed fractions being about 10 percent by weight with the Esters, e.g. B. Vinyl-free circulating gas before entering the reactor acetate, enriches. To carry out this one wash with a liquid, organic wash process, it has proven to be useful "to work in a solvent that has a higher boiling point than the tower-like aggregate formed. This is subjected to carboxylic acid ester. The gas according to the invention is then used to enter the bottom Into the scrubbing tower and proper scrubbing of the cycle gas is achieved that leaves it at the upper end, while the scrubbing during its compression and reheating does not lead any liquid in countercurrent