RU2093506C1 - Method of preparing vinyl acetate - Google Patents

Abstract

FIELD: manufacture of polymeric materials. SUBSTANCE: synthesis of vinyl acetate is carried out at oxygen content of 7.5-10 vol % in vapor-gas mixture (calculated by dry gas) by counterflow supply of potassium acetate into reactor which uses prising, as silicon oxide carrier, silica gel containing 25-45 wt % diatonite and 15-25 wt % bentonite, the ratio of active components being as follows (wt %): 0.5-1.5 palladium; 0.2-0.7 gold; 5-10 potassium acetate 5-10, and the carrier balance. In addition, catalyst comprises, as catalytically active component, tetraaminouronitrate of formula: [Au(NH₃)₄](NO₃)₃, the ratio of components being as follows: 1.0-3.0 palladium acetate; 0.5-1.5 tetraaminouronitrate; 5-10 potassium acetate; and the carrier balance. The catalyst silicon oxide carrier is silica gel subjected to hydrochemical treatment, and corroded surfaces are used for carbonate cleaning of gas. EFFECT: more efficient preparation method.

Description

 The invention relates to a method for producing ethylene-based vinyl acetate.

It is known that vinyl acetate is produced by reacting ethylene, oxygen and acetic acid in the gas phase at 120-250 ^° C, a pressure of 1-10 atm, followed by condensation of the resulting reaction gas and vinyl acetate from the condensate. The residual reaction gas containing ethylene, oxygen and carbon dioxide (the main by-product of the vinyl acetate synthesis reaction) is partially or completely subjected to carbonate purification from carbon dioxide and returned to the beginning of the process.

The synthesis of vinyl acetate is carried out on a catalyst containing palladium with the addition of various metals, in particular gold and alkali metal acetates. As a carrier, silicic acid, alumina, silica gel, activated carbon, etc. are used [2,3]
Also known are catalysts containing palladium, gold and potassium acetate salts as catalytically active components.

As salts of the active components, palladium acetate, barium acetate, potassium acetate are used. Silicic acid is used as a carrier [4]
The main disadvantage of this method of producing vinyl acetate is the low removal of vinyl acetate.

The closest in technical essence to the invention is a method for producing vinyl acetate, carried out by gas-phase interaction of ethylene, oxygen and acetic acid at a temperature of 140-200 ^o C, a pressure of 8 atm, a space velocity gas-vapor mixture of 2000 nl / h with an oxygen content of up to 0.7 vol. (in terms of dry gas) [1] The synthesis process is carried out on a fixed catalyst bed containing 0.52-0.57 wt. palladium, 0.24-26 wt. gold, 5.0 wt. potassium acetate deposited on a silica ball carrier.

 Vinyl acetate, unreacted acetic acid, water and other impurities are isolated from the resulting reaction gas after cooling.

 The condensate is subjected to multi-stage distillation with the release of pure vinyl acetate. Unreacted acetic acid is isolated and returned to the synthesis process.

 Uncondensed reaction gas containing unreacted ethylene, oxygen, and carbon dioxide, after adding fresh ethylene, oxygen, and acetic acid vapor in the form of a circulating gas, is returned to the vinyl acetate synthesis reactor.

 To maintain the activity of the catalyst, a solution of potassium acetate is continuously added to the synthesis reactor at a rate equal to their entrainment from the surface of the catalyst. Make-up with potassium acetate is carried out by direct flow into the initial vapor-gas mixture.

 Isolation of acetic acid from the bottom residue of the evaporator of the synthesis of vinyl acetate-mixture of acetic acid-water ethyl ethyl diacetate-polymer is carried out by distillation in an evaporator with external boilers, then in a thin-film evaporator, the distillation of the mixture is carried out: acetic acid-water-ethylidene diacetate, which is recycled to the vinyl acetate production cycle and the bottom residue of the polymer solution in the mixture: acetic acid-ethylidene diacetate with the content of acetic acid 25-30% of the system withdrawn for combustion.

 The specified process for the production of vinyl acetate has several disadvantages, the main of which is the insufficiently high activity, selectivity and catalyst life.

 In addition, direct-feed feed of potassium acetate to the initial vapor-gas mixture in the synthesis reactor contributes to the uneven distribution of potassium acetate along the height of the catalyst layer, which leads to a decrease in vinyl acetate removal and catalyst life.

 The disadvantage of this method is that it does not provide the output from the system of ethylidene diacetate, which is formed as a by-product in the process of vinyl acetate synthesis, as a result of which it accumulates in the evaporator of the vinyl acetate synthesis unit.

 The content of ethylidene diacetate in the bottom residue of the evaporator of the vinyl acetate synthesis unit is allowed to be no more than 2.5%; with a higher content of ethylidene diacetate, they enter the vapor-gas mixture sent to the synthesis and deactivates the catalyst.

 In order to maintain the ethylidene diacetate content in the bottom residue of the evaporator of the vinyl acetate synthesis unit not more than 2.5%, bottoms in large quantities must be removed from the evaporator and thin-film evaporator, while the output of acetic acid with bottom residue from the thin-film evaporator for burning increases.

 A significant drawback is that in the process of carbonate purification of the circulating gas, toxic potassium metavanadate is used, the neutralization of which is associated with high material costs.

 The objective of the invention is to increase the activity, selectivity and service life of the catalyst, as well as improving the environmental friendliness of the process.

 The task, according to the invention, is achieved as follows.

 1. The synthesis of vinyl acetate is carried out at an oxygen content in the gas-vapor mixture of 7.5-10.0 vol. (when converted to dry gas) when countercurrent feed of potassium acetate to the reactor, on catalysts containing silica gel as a silica support, including 25-45 wt. diatomite and 15-25 wt. bentonite in the following content of active components, wt. palladium 0.5-1.5; gold 0.2-0.7; potassium acetate 5-10; carrier rest. The proposed method leads to an increase in the removal of vinyl acetate by more than 50%, an improvement in the selectivity of the formation of vinyl acetate over ethylene and an increase in the service life of the catalyst.

 2. Countercurrent feed of feed-in potassium acetate to the vinyl acetate synthesis reactor promotes a uniform distribution of potassium acetate along the height of the catalyst bed and thereby maintains a stable catalyst activity. The use of these catalysts, in which silica gel containing diatomite and bentomite is used as a carrier, also leads, in turn, to an increase in vinyl acetate removal and catalyst service life, while maintaining the optimal porous structure of the catalyst during the synthesis of vinyl acetate.

 3. The use of a catalyst in which tetraamine auronitrate is used as the catalytically active component of gold. The specified catalyst is easy to manufacture compared to existing industrial catalysts consisting of more than ten stages using toxic products such as hydrazine hydrate.

 4. The use of corrosion-resistant surfaces of the carbonate treatment unit of the circulating gas.

 The proposed method eliminates the use of toxic potassium metavanadate from the process and greatly simplifies the disposal of waste products that do not already contain potassium metavanadate.

 The invention is illustrated by the following examples.

Example 1 (comparative). 1 l of a silica carrier in the form of spheres (bulk density 550 g / l) is impregnated with an aqueous solution containing 3.3 g of palladium in the form of sodium tetrachloropalladate and 1.5 g of gold in the form of hydrochloric acid. The amount of impregnating solution is determined by the moisture capacity of the carrier. Drying the wet catalyst intermediate is carried out in a stream of air at 90-100 ^o C. After drying, the intermediate is impregnated with an aqueous solution containing 6.0 g of sodium hydroxide and incubated for 24 hours at room temperature. palladium and gold hydroxides formed on the support are reduced with a 5% aqueous solution of hydrazine hydrate.

The intermediate product of the catalyst containing palladium and gold is washed with distilled water to the absence of chlorine ions and dried in a stream of air at a temperature of 90-100 ^o C, then impregnated with an aqueous solution containing 30 g of potassium acetate and again dried in a stream of air at 90-100 ^o C , the finished catalyst contains, by weight. palladium 0.56; gold 0.26; potassium acetate 5.0; carrier rest.

900 cm ^{3 of} catalyst are placed in a reaction tube with an inner diameter of 25 mm and a height of 2700 mm.

A vapor-gas mixture consisting of 1300 nl / l ethylene, 98 nl / h oxygen (7.0 vol. In terms of dry gas) and 800 nl / h acetic acid is passed through a reaction tube at a temperature of 150 ^° C, a pressure of 8.0 atm. .

 100 ml / h of acetic acid (of the total amount of acetic acid supplied) containing 0.05% potassium acetate was fed to the top of the reactor.

 The potassium acetate solution is supplied by direct-flow supply with the initial vapor-gas mixture.

 The vapor-gas mixture exiting the reaction tube is condensed in water-cooled refrigerators.

 The test duration is 120 hours.

The resulting condensate and purge gas are analyzed chromatographically. The average removal of vinyl acetate is 300 g VA / l cat, the selectivity of the formation of vinyl acetate for ethylene 92.2%
Example 2. The catalyst according to example 1 is tested under the conditions of example 1, when the content in the vapor-gas mixture is 105 nl / h of oxygen (7.5 vol. In terms of dry gas).

The removal of vinyl acetate is 350 g VA / l cat • h, the selectivity of the formation of vinyl acetate for ethylene 92.8%
Example 3. The catalyst according to example 1 was tested under the conditions of example 1, with a content of 130 nl / h of oxygen in the vapor-gas mixture (9.0 vol. In terms of dry gas).

The removal of vinyl acetate is 440 g VA / l cat • h, the selectivity of the formation of vinyl acetate for ethylene 93.4%
Example 4. The catalyst according to example 1 was tested under the conditions of example 1, with a content of 145 nl / h of oxygen in the vapor-gas mixture (10.0 vol. In terms of dry gas).

The removal of vinyl acetate is 460 g VA / l cat • h, the selectivity for the formation of vinyl acetate over ethylene is 94.2%
Example 5. The catalyst according to example 1 is tested under the conditions of example 1, however, the test duration is 200 hours. After the test, the content of potassium acetate on the catalyst in the upper and lower zones of the reactor is determined. Determine the average removal of vinyl acetate after every 100 hours of testing.

 A similar experiment is carried out with countercurrent supply of potassium acetate to the initial vapor-gas mixture.

Example 6. 300 g of wide-pore silica gel, 125 g of diatomite and 75 g of bentonite are ground to 70 μm, mixed, 750 cm ^{3 of} distilled water are added.

Balls with a diameter of 4-5 mm are formed from the obtained paste, dried at a temperature of 200 ^{° C.} and calcined at a temperature of 700 ^{° C.} for 3 hours.

 The resulting carrier contains 25 wt. diatomite, 15 wt. bentonite, the rest is silica gel.

 Based on 1 l of the carrier, the catalyst is prepared according to example 1.

 The finished catalyst contains, by weight. palladium 0.8; gold 0.3; potassium acetate 7.0.

 The test catalyst is carried out under the conditions of example 1.

The removal of vinyl acetate is 350 g VA / l cat • h, the selectivity of the formation of vinyl acetate for ethylene 92.2%
Example 7. From 250 g of wide-pore silica gel, 125 g of diatomite and 125 g of bentonite receive the carrier of example 6. The resulting carrier contains 25 wt. diatomite, 25 wt. bentonite. The rest is silica gel.

 The catalyst according to Example 1 is prepared from 1 l of the indicated support, however, the precious metals impregnation solution contains 5.0 g of palladium in the form of sodium tetrachloropalladate, 2.3 g of gold in the form of hydrochloric acid, and the aqueous alkali solution contains 9.0 g of sodium hydroxide.

 The finished catalyst contains, by weight. palladium 1.0; gold 0.49; potassium acetate 6.0; carrier rest.

 The test catalyst is carried out under the conditions of example 1.

The removal of vinyl acetate is 390 g VA / l cat • h, the selectivity of the formation of vinyl acetate for ethylene 92.4%
Example 8. From 150 g of wide-pore silica gel, 225 g of diatomite and 125 g of bentonite receive the carrier of example 6. The resulting carrier contains 45 wt. diatomite, 25 wt. bentonite. The rest is silica gel.

 The catalyst according to Example 1 is prepared from 1 l of the indicated support, however, the impregnation solution contains 6.6 g of palladium in the form of sodium tetrachloropalladate, 3.0 g of gold in the form of hydrochloric acid, and the aqueous alkali solution contains 12.0 g of sodium hydroxide.

 The finished catalyst contains, by weight. palladium 1.5; gold 0.7; potassium acetate 7.0; carrier rest.

 The test catalyst is carried out under the conditions of example 1.

The removal of vinyl acetate is 480 g VA / l cat • h, the selectivity of the formation of vinyl acetate for ethylene 92.1%
Example 9. The catalyst according to example 8 was tested under the conditions of example 1, however, when the potassium acetate solution was countercurrently fed into the reactor.

The removal of vinyl acetate is 680 g VA / l cat • h, the selectivity of the formation of vinyl acetate for ethylene 94.1%
Example 10. 1 liter of silica gel grade KSS-2 is placed in an autoclave pre-filled with water (filling factor 0.25). The autoclave is heated to 200 ^o C and kept at this temperature for 8 hours. During processing, the silica gel in the autoclave is in an atmosphere of water vapor.

 The catalyst according to example 1 is prepared from 1 liter of the obtained support. The finished catalyst contains, by weight. palladium 0.6; gold 0.28; potassium acetate 5.6; carrier rest.

 The test catalyst is carried out under the conditions of example 1.

The removal of vinyl acetate is 350 g VA / l cat • h, the selectivity of the formation of vinyl acetate for ethylene 92.5%
Example 11. From 1 l of the carrier obtained according to example 10, prepare the catalyst according to the description of example 7.

 The test of the catalyst is carried out under the conditions of example 3, however, with countercurrent flow of a solution of potassium acetate into the reactor.

The removal of vinyl acetate is 460 g VA / l cat • h, the selectivity of the formation of vinyl acetate for ethylene 93.6%
Example 12. 1 l of the carrier obtained according to example 10, is impregnated with a 50% aqueous solution of acetone containing 7.0 g of palladium acetate (3.3 g of palladium), 3.4 g of tetraamineuronitrate (1.5 g of gold), 30 g of potassium acetate.

 The finished catalyst contains, by weight. palladium acetate 1.0; tetraamine auronitrate 0.5; potassium acetate 5.0.

 The test catalyst is carried out under the conditions of example 1.

The removal of vinyl acetate is 410 g VA / l cat • h, the selectivity of the formation of vinyl acetate for ethylene 92.4%
Example 13. 1 l of silica gel KSK is placed in an autoclave and subjected to hydrothermal treatment at a temperature of 150 ^o C for 6 hours as described in example 10.

1 l of the carrier obtained according to example 10 is impregnated with a 50% aqueous solution of acetone containing 10.55 g of palladium acetate (5.0 g of palladium), 5.3 g of tetraamineuronitrate (2.3 g of gold), 30 g of potassium acetate . Drying the wet catalyst is carried out in a stream of air at a temperature of 80-85 ^o C.

 The finished catalyst contains, by weight. palladium acetate 2.0; tetraamineuronitrate 1.0; potassium acetate 5.0.

 The test catalyst is carried out under the conditions of example 1.

The removal of vinyl acetate is 450 g VA / l cat • h, the selectivity of the formation of vinyl acetate for ethylene 92.3%
Example 14. Based on 1 liter of KCC-3 grade silica gel, subjected to hydrothermal treatment at 300 ^{° C.} for 5 hours as described in Example 10, a catalyst was prepared as described in Example 12, however, a 50% aqueous solution of acetone contains 14 g of palladium acetate ( 6.6 g of palladium), 6.8 g of tetraamineuronitrate (3.0 g of gold), 30 g of potassium acetate.

 The finished catalyst contains, by weight. palladium acetate 3.0; tetraamine auronitrate 1.5; potassium acetate 5.0.

 The test of the catalyst is carried out under the conditions of example 3 with a countercurrent flow of a solution of potassium acetate into the reactor.

The removal of vinyl acetate is 690 g VA / l cat • h, the selectivity for the formation of vinyl acetate over ethylene is 94.2%
Example 15. On the basis of the support described in Example 7, a catalyst is prepared as described in Example 12. However, the aqueous acetone impregnation solution contains 12.2 g of palladium acetate, 6.0 g of tetraamineuronitrate and 30 g of potassium acetate.

 The finished catalyst contains, by weight. palladium acetate 2.4; tetraamineuronitrate 1.2; potassium acetate 6.0.

 The test of the catalyst is carried out under the conditions of example 1, however, when the content in the vapor-gas mixture of 113 nl / h of oxygen (8.0 vol.) And countercurrent flow of potassium acetate into the reactor.

The removal of vinyl acetate is 510 g VA / l cat • h, the selectivity of the formation of vinyl acetate for ethylene 93.6%
Example 16. The process of carbonate purification of the circulating gas is carried out when the potash metavanadate potassium content in the solution is 10 g / l to prevent corrosion of the working surface of the equipment.

 The spent potash solution annually in the amount of 50 tons with a potassium metavanadate content of 500 kg is stripped and sent for disposal in special concrete bins to prevent the release of highly toxic potassium metavanadate into groundwater.

 When using equipment with corrosion-resistant surfaces, the use of potassium metavanadate is excluded, which allows the disposal of spent potash solution by conventional methods.

Claims (3)

 1. The method of producing vinyl acetate by the interaction of ethylene, oxygen and acetic acid in the vapor-gas phase in the presence of a catalyst containing palladium, gold, potassium acetate supported on a silica carrier as active components, while continuously feeding a potassium acetate feed solution into the reactor, followed by cooling and condensation reaction products and condensate rectification to separate vinyl acetate from by-products, with the separation of acetic acid from the bottom residue of the synthesis unit evaporator, its purification th and reuse in the process, with the carbonate purification of the circulating reaction gases from carbon dioxide and their return to the synthesis stage, characterized in that the process is carried out with an oxygen content of 7.5 to 10.0% in the vapor-gas mixture, calculated on the dry gas volume, the feed solution of potassium acetate to the reactor is countercurrent, use as a silica carrier, wt. Diatomite 24 45
Bentonite 15 25
Silica gel Else up to 100%
the following content of active components, wt. Palladium 0.5 1.5
Gold 0.2 0.7
Potassium Acetate 5 10
Carrier Else up to 100%
2. The method according to claim 1, characterized in that the process is carried out in the presence of a catalyst containing, as active components, gold and palladium, respectively, tetraamineuronitrate [Au (NH ₃ ) ₄ ] (NO ₃ ) ₃ and palladium acetate.  3. The method according to PP.1 and 2, characterized in that they use a silica carrier containing silica gel, subjected to hydrothermal treatment.  4. The method according to claim 1, characterized in that the carbonate purification of the circulating gases is carried out in apparatus with a corrosion-resistant surface.

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