KR0166965B1 - Process for the preparation of vinyl acetate - Google Patents

Abstract

The present invention contains a SiO ₂ or SiO ₂ -Al ₂ O ₃ mixture having a surface area of 50 to 250 m 2 / g and a pore volume of 0.4 to 1.2 ml / g, having a particle size of 4 to 9 mm, and having a pore volume of 5 to 9 mm. Palladium and / or compounds thereof and optionally further gold and / or are formed on a support on which 20% is formed of pores having a radius of 200 to 3,000 mm 3 and 50 to 90% of the volume of voids is formed of pores having a radius of 70 to 100 mm 3. A process for preparing vinyl acetate in the gas phase from ethylene, acetic acid, and oxygen or an oxygen-containing gas on a gold compound and a catalyst containing an alkali metal compound and optionally further a cadmium compound as activator.

Description

Method for preparing vinyl acetate

It is known that ethylene can be reacted in the gas phase with an oxygen-containing gas or with oxygen and acetic acid on a fixed bed catalyst to give vinyl acetate. The catalyst is suitably containing a noble metal component and an activator component. The precious metal component preferably comprises palladium and / or a compound thereof, and may also exist in the form of gold and / or a compound thereof. See, US Patent No. 3,939,199, German Patent Application Publication No. 2,100,778, US Pat. 4,668,819]. The activator component comprises a compound of group 1 and / or element 2 and / or cadmium. Potassium is preferred as a group 1 element. These active ingredients are applied to the support in finely divided form, and the commonly used support material is silica or alumina.

The specific surface area of the support is generally 40 to 350 m 2 / g. According to US Pat. No. 3,939,199, the total pore volume should be 0.4 to 1.2 ml / g, of which less than 10% of the pore diameter should be formed into fine pores with less than 30 mm 3. Examples of suitable supports having this property include breathable SiO ₂ or SiO ₂ -AlO ₃ mixtures. The support particles in the production of vinyl acetate are generally spherical. However, tablets and cylinders have also already been used.

The present invention comprises a SiO ₂ or SiO ₂ -AlO ₃ mixture having a surface area of 50 to 250 m 2 / g and a pore volume of 0.4 to 1.2 ml / g, having a particle size of 4 to 9 mm, and 5 to 20 of the support pore volume. Palladium and / or the compound and optionally further gold / and / or on a support on which% is formed of pores having a radius of 200 to 3000 mm 3 and 50 to 90% of the volume of voids is formed of pores having a radius of 70 to 100 mm 3 A process for preparing vinyl acetate in a gaseous phase from ethylene, acetic acid, and oxygen or an oxygen-containing gas on a gold compound and a catalyst containing an alkali metal compound and optionally further a cadmium compound as activator.

It is preferable that 8 to 15% of the void volume of the support is formed by voids having a radius of 200 to 3,000 mm 3, and 55 to 75% of the void volume is formed to be voids having a radius of 70 to 100 mm 3.

A support of this type is obtained by the following method: First, microscopic spherical particles in the glass phase are prepared, for example, by flame hydrolysis of a silicon tetrachloride or silicon tetrachloride / aluminum trichloride mixture in an oxygen water flame. United States Patent No. 3,939,199]. Microspherical particles may also be prepared by melting very fine SiO ₂ powder in a sufficiently hot flame and then rapidly cooling the melt. Microspherical particles produced using one of the two methods have a surface area of 100 to 300 m 2 / g. The microspherical particles have a surface area of 150 to 250 m ₂ / g, in particular comprising at least 95% by weight SiO ₂ and at most 5% by weight of Al ₂ O ₃ , in particular at least 99% by weight of SiO ₂ and at most 1% by weight of AlO _3. Suitable. Microspherical particles having the above-mentioned surface area can be purchased, for example, under the trade names Aerosil ( ^(R) Aerosil) or Carbosil ( ^(R) Cabosil), or as highly dispersed silica.

The microspheres are then compressed using organic fillers (e.g. sugars, ureas, higher fatty acids, long chain paraffins, microcrystalline celluloses) and lubricants (e.g. kaolin, graphite, metal soaps), for example Moldings are obtained by extrusion or tableting (after precompression). This molding is burned in an O ₂ -containing base to remove the adjuvant again. The surface area, pore volume, and ratio of pore volume (pore-radius distribution) formed to pores of a particular radius, the type of deformation (tablets, extrudates, etc.), the temperature and duration of combustion, fillers, lubricants and microspheres It is determined by the relative amounts of and the surface area of the microspherical particles. The most suitable value for these parameters can determine a simple preliminary experiment.

In addition, silica sol may be added to the missec particles instead of lubricant and filler, followed by drying and burning. This method is particularly suitable for extrudates. In this method, the surface area, pore volume and pore-radius distribution are determined by the type of silica sol used (measured by the size of the major particles, the tindle effect), the type of microspheres used, the drying rate and temperature, and the duration of combustion. And the parameters of the temperature. In addition, the most suitable values for these parameters can also be determined by simple preliminary experiments.

The finished support prepared by one of the two methods has a surface area of 50 to 250 m 2 / g and a pore volume of 4 to 9 mm (adjustable by purification or extrusion) of 0.4 to 1.2 ml / g.

By using a support having the specific pore-radius distribution mentioned above, it is possible to significantly increase the space-time yield of the catalyst compared to other conventional supports under the same conditions (the same content of the active substance on the support and the same reaction conditions) while at the same time the main side reaction That is, it is possible to reduce the combustion of ethylene forming CO ₂ by 30% or more. Similarly, the formation of ethyl acetate, which occurs as another side reaction, is substantially reduced. The advantage of the process according to the invention is that it allows considerable savings when the selectivity is increased from about 92% to about 95%, and the improvement in performance that significantly increases the selectivity with performance in new installations is due to the amount of catalyst and This means that the volume of the reactor can be reduced, which can substantially increase the capacity of the existing equipment without reducing or rebuilding the equipment cost, thereby saving the investment cost of the equipment expansion.

The surface area of the aforementioned support is in all cases the BET surface area measured by the method of Brunauer, Emmett and Teller. This refers to the total surface area of 1 g of the supporting material, ie the sum of the outer surface area of the support and the inner surface area of all open pores. The ratio of the total pore volume and the pore volume by the pore of a particular size (for example, a pore diameter of 70 to 100 mm 3) can be measured using a mercury porosimetry. Suitable measuring devices are produced, for example, from Carlo Erba or Micromeritics Company.

The catalytically active material is applied to the support in a conventional manner, for example by impregnation of the support with a solution of the active material, followed by drying and, if necessary, reduction. However, the active material may also be applied to the support by methods such as precipitation, spraying, deposition or dipping.

Suitable solvents for the catalytically active substance are, in particular, unsubstituted carboxylic acids having 2 to 10 carbon atoms in the molecule, such as propionic acid, n- and iso-butyric acid and various valeric acids. For physical and economic reasons, acetic acid is preferably used as the solvent. If the active substance is not sufficiently soluble in the carboxylic acid, it is convenient to add an inert solvent. That is, for example, palladium chloride is actually better dissolved in aqueous acetic acid than in glacial acetic acid. Another suitable solvent is a solvent which is inert and easily miscible with the carboxylic acid. For example, in addition to water, ketones such as acetone, acetylacetone, ethers such as tetrahydrofuran or dioxane, and hydrocarbons such as benzene are mentioned.

The catalyst contains palladium and / or a compound thereof as the precious metal component and an alkali metal compound as the activator component. It may contain gold and / or compounds thereof as further precious metal components and may contain cadmium compounds as additional activator components.

Suitable palladium compounds are all salts and complexes that are soluble (and also reducible, if necessary) and do not leave deactivating substances such as halogens or sulfur in the finished catalyst. Particularly suitable are carboxylates, preferably salts of aliphatic monocarboxylic acids having 1 to 5 carbon atoms, such as acetate, propionate or butyrate. Also suitable are, for example, nitrates, nitrites, oxide hydrates, oxalates, acetyl acetonates or hydrates, oxalates, acetyl acetonates or acetoacetates. However, if care is taken to remove sulfates or halogen anions, such as by precipitating the sulfate radicals with barium acetate or the like, or by precipitating the halogens with nitric acid, etc. Compounds such as halides can also be used. Palladium acetate is particularly preferred because the palladium compound is soluble and easy to purchase.

In general, the content of palladium in the catalyst is from 1.0 to 3% by weight, preferably from 1.5 to 2.5% by weight, in particular from 2 to 2.5% by weight, wherein the proportion of metal is based on the total weight of the supported catalyst.

In addition to palladium and / or compounds thereof, gold and / or compounds thereof may further be present. Barium acetoaurate is particularly suitable as a gold compound. Generally, when using gold or one of its compounds, it is added in a ratio of 0.2 to 0.7% by weight, and the proportion of metal is based on the total weight of the supported catalyst.

The catalyst contains an alkali metal compound and optionally further a cadmium compound as activator. Examples of suitable compounds include alkali metal carboxylates such as potassium acetate, sodium acetate, lithium acetate and sodium propionate. Also suitable are alkali metal compounds, such as hydroxides, oxides and carbonates, which are converted to carboxylates under the reaction conditions. Suitable cadmium compounds are halogen or sulfur free compounds, such as carboxylate (preferably), oxides, hydroxides, carbonates, citrate, tartrate, nitrates, acetacetonates, benzoylacetonates and acetyl Acetate. Cadmium acetate is particularly suitable. It is also possible to use mixtures of different activators. The proportion of each activator addition is generally from 0.5 to 4% by weight and the proportion of metal in these activators is based on the total weight of the supported catalyst.

The catalyst may be palladium / alkali metal element / cadmium and palladium / gold / alkali metal element [where palladium or gold may be present in the form of metals or compounds in the finished catalyst, with the preferred alkali metal element being potassium (carboxylate form) ] Is preferable.

Here, the ratio K: Pd or K: (Pd + Au) is preferably 0.7: 1 to 2: 1. The Cd: Pd or Cd: (Pd + Au) ratio is preferably between 0.6: 1 and 2: 1, in particular between 0.6: 1 and 0.9: 1. Pd, Au, Cd and K are always calculated as elements, ie only the metal proportions of Pd acetate, Cd acetate and K acetate on the support are compared with one another. Particular preference is given to palladium acetate / potassium acetate / cadmium acetate and palladium acetate / barium acetoalurate / potassium acetate catalyst.

The process of impregnating the catalyst support with the solution of the active ingredient is preferably a method of coating the support material with the solution, followed by pouring or filtration of the excess solution. In view of the loss of the solution, it is advantageous to carefully mix it using only an amount of the solution corresponding to the total pore volume of the catalyst support so that the particles of the support material are uniformly wetted. Such mixing can be carried out, for example, by stirring. The impregnation process and mixing are convenient because they can be immediately dried at the same time in a rotary drum or drum dryer. It is also convenient to adjust the amount and composition of the solution for impregnating the catalyst support so that it corresponds to the pore volume of the support material and the desired amount of active material is applied by one impregnation.

The catalyst support impregnated with a solution of the active substance is preferably dried under reduced pressure. During drying the temperature should be below 120 ° C, preferably below 90 ° C. It is also generally suitable to dry in a stream of inert gas (eg nitrogen stream or carbon dioxide stream). After drying, the remaining solvent content should preferably be less than 8% by weight, in particular less than 6% by weight.

When the palladium compound (and optionally a gold compound) is reduced (which may sometimes be useful), it can be carried out in vacuum, atmospheric pressure or at elevated pressures of 10 bar or less. At this time, it is preferable to further dilute the reducing agent with a high pressure inert gas. The reduction temperature is 40 to 260 ° C, preferably 70 to 200 ° C. It is generally convenient to use inert gas / reducing agent mixtures containing from 0.01 to 50% by volume of reducing agent, preferably from 0.5 to 20% by volume of reducing agent. Examples of inert gases that can be used include nitrogen, carbon dioxide or noble gases. Examples of suitable reducing agents include hydrogen, methanol, formaldehyde, ethylene, propylene, isobutylene, butylene and other olefins. The amount of reducing agent depends on the amount of palladium, and in some cases, on the amount of gold used, but the reducing equivalent should be 1-1.5 times or more of the oxidative equivalent, but the greater the amount of reducing agent there is no adverse effect. For example, at least 1 mole of hydrogen per mole of palladium should be used. After drying, it can be reduced in the same facility.

Vinyl acetate generally passes acetic acid, ethylene and oxygen or oxygen-containing gas through the finished catalyst at a temperature of 100 to 220 ° C., preferably 120 to 200 ° C. and a pressure of 1 to 25 bar, preferably 1 to 20 bar. It can be prepared by, where the unreacted components can be circulated. It is appropriate to maintain the oxygen concentration at 10% by volume or less (based on acetic acid-free gas mixture). In some cases, however, it may be advantageous to dilute with an inert gas (eg nitrogen, carbon dioxide). In particular, since CO ₂ is formed in a small amount during the reaction, it is suitable for dilution in the circulation process.

The following examples illustrate the invention.

Comparative Example 1

(Spherical Support Particles Containing Ordinary Silica Gel)

200 g of silica support containing conditioned (80 ° C.) silica gel spherical particles having a radius of 5 to 8 mm are used. A support (commercially available) containing such spherical particles is formed of 8% voids with a radius of 70 to 100 mm 3 and 29% of voids with a radius of 200 to 3,000 mm 3, with a BET surface area of 169 m 2 / g and 0.48 ml / g It has a void volume. Impregnated the support with a solution of 11.5 g of Pd acetate, 10.0 g of Cd acetate and 10.8 g of K acetate (corresponding to the pore volume above) in 66 ml of glacial acetic acid, at 60 ° C., 200 mbar, so that the residual solvent content was 2% by weight. The support is dried under nitrogen at a pressure of. This process doped 2.3 wt% Pd, 1.8 wt% Cd and 2.0 wt% K (Cd: Pd = 0.78: 1, K: Pd = 0.77: 1).

50 ml of the completed catalyst is introduced into a reaction tube of 1.5 m in length and 8 mm in inner diameter. The gas to be reacted is then passed through the catalyst at a pressure of 8 bar (reactor inlet) and a catalyst temperature of 150 ° C. This gas contains 27% by volume ethylene, 55% N ₂ , 12% acetic acid and 6% O ₂ at the reactor inlet. The results are shown in the table below.

Comparative Example 2

(Spherical Support Particles Containing Ordinary SiO ₂ )

Bentonite is squeezed, roasted, and then washed with HCl (SiO ₂ content after washing is 96% by weight) to use 200 g of a silica support having a radius of 5 to 6 mm. The support containing these spherical particles has a BET surface area of 121 m 2 / g and a void volume of 0.66 ml / g, and is formed from 21% of pores with a radius of 70 to 100 mm 3 and 42% of pores with a radius of 200 to 3,000 mm 3. The support particles are impregnated and dried as in Comparative Example 1 so that the doping is the same (different except that 114 ml is used instead of 66 ml of glacial acetic acid). The catalyst is then tested as in Comparative Example 1. The results are shown in the table below.

Example 1

The support is prepared from SiO ₂ microspheres with a surface area of 200 m 2 / g and fillers and lubricants. The finished support is formed from 62% of pores with a radius of 70 to 100 microns and 9% of pores with a radius of 200 to 3000 microns and has a void volume of 0.80 ml / g. The support particles are cylindrical with a curved surface (6 mm high by 6 mm in radius, similar in shape to known pharmaceutical capsules). The surface area of the support particles is 185 m 2 / g.

200 g of the support particles are impregnated and dried as in Comparative Example 1 to obtain the same doping (except that 141 ml of glacial acetic acid is used instead of 66 ml). The catalyst is then tested as in Comparative Example 1. The results are shown in the table below.

Example 2

The support is prepared from SiO ₂ / Al ₂ O ₃ microspherical particles (97 wt% SiO ₂ , 3 wt% Al ₂ O ₃ ) and fillers and lubricants having a surface area of 170 m ₂ / g. The finished support is formed from a void of 58% with a radius of 70 to 100 mm 3 and a void of 12% with a radius of 200 to 3000 mm 3 and has a void volume of 0.75 ml / g. The support particles have the same shape and size for Example 1 but the surface area is 132 m 2 / g. 200 g of the support particles are impregnated and dried as in Comparative Example 1 to obtain the same doping (except that 131 ml of glacial acetic acid is used instead of 66 ml). The catalyst is then tested as in Comparative Example 1. The results are shown in the table below.

Example 3

The silica sol is mixed with glassy SiO ₂ microspheres (surface area 200 m 2 / g), then dried and roasted to prepare a support. The finished support has a void volume of 0.64 ml / g and is formed from 65% of pores with a radius of 70 to 100 mm 3 and 9% of pores with a radius of 200 to 3000 mm 3. The support particles are extrudate pieces (radius, 6 mm in height) obtained by extrusion and have a surface area of 170 m 2 / g.

The support particles (200 g) are impregnated and dried as in Comparative Example 1 to achieve the same doping (except that 110 ml of glacial acetic acid is used instead of 66 ml). The catalyst is then tested as in Comparative Example 1. The results are shown in the table below.

Example 4

The support is prepared from SiO ₂ microspheres with a surface area of 300 m 2 / g, fillers and lubricants. The finished support has a void volume of 0.91 ml / g and is formed from 56% of voids with a radius of 70 to 100 mm 3 and 10% of voids with a radius of 200 to 3,000 mm 3. The support particles have the same shape and size as in Example 1. However, the surface area of the support particles is 184 m 2 / g.

200 g of the support particles are impregnated and dried as in Comparative Example 1 to obtain the same doping (except that 163 ml of glacial acetic acid is used instead of 66 ml). The catalyst is then tested as in Comparative Example 1. The results are shown in the table below.

In the table, the distribution (%) means the distribution ratio of the void volume formed by the pores having a radius of 70 to 100 mm 3 or 200 to 3,000 mm 3. STY stands for space time yield. Combustion (%) means the percentage of ethylene reacted, converted to CO ₂ , and ethyl acetate content means the amount of ethyl acetate obtained as a by-product in the condensed portion of the reaction product.

Claims (2)

It contains a SiO ₂ or SiO ₂ -Al ₂ O ₃ mixture having a surface area of 50 to 250 m 2 / g and a pore volume of 0.4 to 1.2 ml / g, having a particle size of 4 to 9 mm, and 5 to 20% of the pore volume. Palladium and / or compounds thereof and optionally further gold and / or gold compounds on supports formed from pores with a radius of 200 to 3,000 mm 3 and 50 to 90% of the volume of voids are formed with pores with a diameter of 70 to 100 mm 3, And a process for producing vinyl acetate in the gas phase from ethylene, acetic acid, and oxygen or an oxygen-containing gas on a catalyst containing an alkali metal compound and optionally further a cadmium compound as activator. The method of claim 1, wherein the void volume is formed by voids having a radius of from 8 to 15% with a radius of 200 to 3,000 mm 3, and wherein 55-75% of the void volume is formed with voids with a radius of 70 to 100 mm 3.