MXPA01001152A - Method for producing supported catalysts and their use for producing vinyl acetate monomer - Google Patents

Abstract

The invention relates to a supported catalyst containing palladium and doped with hafnium for the heterogeneously catalyzed gas-phase oxidation of ethylene and acetic acid into vinyl acetate. To this end the porous support, for example on a SiO2 basis, during or after coating with the active metals and promoters is exposed to suitable hafnium compounds, for example by saturation with soluble hafnium compounds. The advantage of this hafnium-doped catalyst system is its improved activity and long-term stability in comparison with undoped catalysts.

Description

PROCEDURE FOR PRODUCING SUPPORTED CATALYSTS AND THEIR USE TO PREPARE VIN1LO ACETATE MONOMER DESCRIPTIVE MEMORY 5 The present invention describes a supported catalyst containing palladium doped with Hf, a process for producing it and its use for the synthesis of vinyl acetate. It is known that vinyl acetate (VAM) can be prepared in the gas phase from ethylene, acetic acid and oxygen; the supported catalysts used for this synthesis comprise Pd as the active metal and an alkaline element as a promoter, preferably K. Additional additives used are Cd, Au or Ba. The metal salts can be applied to the support by soaking, impregnation, spraying, vapor deposition, immersion or precipitation. US-A-3 743 607 and GB-1 333 449 describe the production of supported Pd / Au catalysts for the synthesis of VAM by impregnation with Pd / Au salts and subsequent reduction. However, this method does not give impregnated catalysts on the surface, but rather the noble metals are evenly distributed over the entire cross section of the pellet. GB-1 283 737 discloses the production of a noble metal catalyst impregnated on the surface by prepreg of the carrier with j ^^^^^^^^^^^^ e ^ g an alkaline solution and saturation with 25-90% water or alcohol. Subsequent impregnation with Pd salts and reduction of the precipitated salts to the metal gives surface impregnated catalysts in which it is said that the penetration depth of the noble metals is up to 50% of the radius of the pellet. In the case of Pd / Au / K catalysts, it has been found that it is favorable to apply the two noble metals to the support in the form of a shell, that is, the noble metals are distributed only over a zone close to the surface while the regions of the shaped support body that are contained therein are virtually free of noble metal. The thickness of these catalytically active shells is approximately 0.1-2 mm. According to US-A-3 775 342 and US-A-3 822 308, the impregnated catalysts on the surface are impregnated with a solution of Pd / Au salts and with an aqueous base, preferably NaOH, being impregnated. the insoluble palladium and gold hydroxides precipitated in the pellets in a shell-like surface area. The hydroxides that have been fixed in the shell in this way are then reduced to metals. GB 1 521 652 uses the same procedure (pre-impregnation with Pd / Au salts, drying, precipitation with base, reduction) to obtain catalysts impregnated on the egg-type surface, ie only an internal ring of the spherical SiO2 support understands the F g < - ^ "- h * at ^^ - '^. - - - noble metals, while the inner core and a thin outer shell remain virtually free of noble metals.According to EP-A-0 723 810, a support preferably doped with Al, Zr, Ti is produced by pretreatment (impregnation) of the support with metal salt solutions and is subsequently used for the base precipitation described above to form a Pd / Au / K catalyst impregnated on the surface. The starting materials used for impurities are, in particular, expensive alkoxides, for example, zirconium alkoxides Finally, the obtained catalysts must be dried at elevated temperatures and calcined at temperatures up to 800 ° C. Accordingly, an object of the present invention is to provide a simple and inexpensive process for producing active and selective VAM catalysts, in particular catalysts impregnated on the surface, based on Pd and with a long operating life. Accordingly, the present invention provides a process for producing a supported catalyst for the production of vinyl acetate monomer by impregnation of the support with a basic solution and a solution comprising palladium salts, wherein the impregnation is carried out simultaneously or consecutively, with or without intermediate drying, washing the support to remove any chloride present and reducing the insoluble compounds precipitated on the support before or after washing, drying the catalyst precursor obtained in this way and impregnation thereof with alkali metal compounds that are converted complete or - *. **** - ** .. *. * ^^, f fffttfH'f r- * - '"" - - ~~ ^^^ partially in alkali metal acetates under the reaction conditions in the production of vinyl acetate monomer, wherein the support is impregnated with one or more hafnium compounds either simultaneously with the impregnation of noble metal or in a subsequent treatment and is dried at a temperature of < 160 ° C and is not subsequently calcined. Now it has been found that the impurification with Hf is favorable for the activity and the selectivity and guarantees a better adherence of the noble metal to the support. Furthermore, it has been found that when the catalysts of the invention are produced using hafnium as an activator, the additional calcination step. The hafnium-doped catalysts of the invention also have a more uniform distribution of active metal of Pd or Pd / Au and a better dispersion of the noble metals than the non-contaminated VAM catalysts. The high degree of dispersion is also retained mostly in long-term operation due to the reduced agglomeration of the noble metal particles, as a result of which the deactivation of the catalysts of the invention is delayed and long operating lives are obtained. According to the invention, a porous support, preferably a configured SiO2 support, is doped with Hf by treating the support porous with a suitable Hf precursor during or after loading with a Pd precursor or the fixation / reduction of the Pd precursor. The support is preferably impregnated with a solution comprising palladium salts or palladium and gold salts and one or more hafnium compounds.

In a preferred embodiment of the invention, the HF doping is performed by impregnation with a soluble Hf precursor to an aqueous solution or acetic acid solution or alcohol solution. Preference is given to a water soluble precursor. Between treatment with Hf and loading with the other elements, it is possible to insert additional pre-treatment or post-treatment steps such as washing, drying, oxidation or reduction. As support materials, it is possible to use all commonly used support materials, for example, SiO2 or AI2O3, their mixtures of oxide and mixed oxides (aluminosilicates) or C. Preference is given to SiO2. The SiO2 support is preferably used as a shaped body and is in the form of spheres, pellets, rings, stars or other industrial shaped bodies. The diameter or length and thickness of the support particles is generally from 3 to 9 mm. The surface area of the supports, measured by the BET method (Brunnauer, Emmet and Teller), is generally 10-15 500 m2 / g, preferably 20-250 m2 / g. The pore volume is generally from 0.3 to 1.2 ml / g. The hafnium content of the catalysts of the invention is in the range of 0.01 to 50% by weight. Preference is given to a Hf content in the range of 0.05 to 25% by weight. Suitable Hf precursors for doping the S0O2 are all the inorganic Hf salts and organometallic Hf compounds which are soluble and do not contain catalyst poisons such as sulfur. Preferred precursors are hafnium oxychloride = HfOCI2, hafnium chloride = ^ ¡^ ^ ^ *. HFCI4, substituted hafnocene dichlorides, substituted cyclopentadienyl-hafnium trichlorides, hafnium acetylacetonate, hafnium alkoxides such as ethoxide or butoxide or propoxide, hafnium oxide, hafnium hydroxide, hafnium nitrate, Hf-thd (= Hf (C11H19O2) 4). By further post-treatments of the catalyst loaded with the precursor or Hf precursors, for example, washing and drying steps, calcination steps, fixation and reduction of the active Pd component, subsequent impregnation with alkali metal acetate promoters, etc., the Hf precursor can be converted into the final compound, for example, the oxide or oxychloride, which is then present in the ready-to-use catalyst. The loading with the active component Pd and the other promoters such as Au, Cd, Ba, K can be carried out by the methods known from the prior art. In general, catalyst systems based on Pd / Cd / K, Pd / Ba / K or Pd / Au / K have been established for the synthesis of vinyl acetate. The catalysts produced using the process of the invention generally have the following metal content: the Pd content of the Pd / K Cd and Pd / K / Ba catalysts is generally from 0.6 to 3.5% by weight, preferably from 0.8 to 3.5% by weight. 3.0% by weight, in particular from 1.0 to 2.5% by weight. The Pd content of the Pd / Au / K catalysts is generally 0.5 to 2.0% by weight, preferably 0.6 to 1.5% by weight. The content of K is generally 0.5 to 4.0% by weight, preferably 1.5 to 3.0% by weight.

The Cd content of the Pd / K / Cd catalysts is generally 0.1 to 2.5% by weight, preferably 0.4 to 2.0% by weight. The Ba content of the Pd / K / Ba catalysts is generally from 0.1 to 2.0% by weight, preferably from 0.2 to 1.0% by weight. The Au content of the Pd / K / Au catalysts is generally 0.2 to 1.0% by weight, preferably 0.3 to 0.8% by weight. In a preferred embodiment of the invention, the catalyst comprises the following composition: PdxAuyHfz wherein x = 0.7-1.3% by weight, in particular from 0.9 to 1.1% by weight, y = 0-1% by weight, preferably 0.5- 1% by weight, in particular from 0.6 to 0.9% by weight, z = 0.05-5% by weight, in particular from 0.1 to 2% by weight. Suitable salts are all palladium, cadmium, barium, gold and potassium salts that are soluble and do not contain catalyst poisons such as sulfur. Preference is given to acetates and chlorides. In the case of chlorides, PdCl2, NaPdC and HAuCI4 are particularly preferred precursors. However, in the case of chlorides it must be ensured that the chloride ions are removed before the catalyst is used. This is achieved by washing the doped support, for example, with water, after the Pd and, if used, the Au have been fixed to the support by reduction to the metals. Suitable solvents are all the compounds in which the selected salts are soluble and which can be eliminated easily again by drying after impregnation. Solvents which are especially suitable for acetates are unsubstituted carboxylic acids, in particular acetic acid. Water is especially suitable for chlorides. The additional use of another solvent 5 is favorable when the salts are not sufficiently soluble in the acetic acid or in the water. Suitable additional solvents are those which are inert and miscible with acetic acid or water. Examples of additional solvents that can be added to acetic acid are ketones such as acetone and acetylacetone, also ethers such as tetrahydrofuran or dioxane, acetonitrile, dimethylformamide and also hydrocarbons such as benzene. At least one salt of each of the elements (Pd / K / Au / Hf, Pd / K / Cd / Hf, Pd / K / Ba / Hf) to be applied to the SiO2 support particles must be applied. . It is possible to apply a plurality of salts of an element, but in general exactly one salt of each of the three elements is applied. The required amounts of the salts can be applied in one step or by multiple impregnation. The salts can be applied to the support by known methods such as soaking, impregnation, spraying, vapor deposition, immersion or precipitation. Suitable reducing agents are all compounds which are capable of reducing the salts of Pd and Au used in metals. Possible reducing agents are, therefore, for example, citrates, formations, hydrazine, hydroxylamine and alkali metal borohydrides. Reducing agents Gaseous mixtures such as H2 or CO or ethylene can also be used, but in the case of surface impregnated catalysts only when a shell structure has already been produced in the impregnation with the metal salts. The vinyl acetate preparation is generally carried out by passing acetic acid, ethylene and oxygen or oxygen containing gases over the finished catalyst at temperatures of 100 to 220 ° C, preferably 120 to 200 ° C, and pressures of 1 to 25 bar, preferably from 1 to 20 bar, being able to circulate the components that do not react. Result favorable to keep the oxygen concentration below 10% by volume (based on the mixture of gas without acetic acid). However, dilution with inert gases such as nitrogen or carbon dioxide can also be favorable in some cases. Carbon dioxide is particularly suitable as a diluent, since it is formed in small amounts during the reaction. The following examples illustrate the invention.

EXAMPLE 1 (Hf at 1%, not calcined) 20 1.67 g of palladium dichloride PdCI2, 1.40 g of tetrachloroauric acid trihydrate HAuCI * 3H2O and 2.29 g of hafnium oxide dichloride octahydrate HfOCI2 * 8H2O are dissolved in 75 ml of water and HE MÜÜ ^ - «- ÉÉ? AttíHÉÍ added to 100 g of SiO2 support pellets of type KA-160 (Südchemie) (pore filling method). After the solution has been absorbed, the impregnation mixture is dried uniformly in a rotary evaporator while air is passed over the pellets at 70 ° C and the impregnated pellets are further dried overnight at 110 ° C in a drying oven. 2.70 g of KOH are then dissolved in 75 ml of water and added to the dried pellets, mixed thoroughly for 30 minutes on a rotary evaporator, allowed to stand overnight and then washed to be free of chloride in a Soxhiet using approximately 10 I of water. After standing overnight, the pellets are dried at 110 ° C in a drying oven. The catalyst is reduced in 10% ethylene / 90% N2 at 150 ° C for 2 hours. Subsequently, 2.6 g of potassium acetate are dissolved in 25 ml of water, added to the pellets and mixed well. The pellets are dried overnight at 110 ° C. The finished catalyst comprises 1% Pd, 0.7% Au and 1% Hf. f ^^ gsg ^^^^^^^^^^^^ g EXAMPLE 2 (Comparative Example) (Hf at 1%, calcined in air for 4 hours at 300 ° C) The catalyst was produced by a method similar to Example 1, with the only difference that after the KOH precipitation and before the removal of chloride by washing, the pellets were calcined in air for 4 hours at 300 ° C.

EXAMPLE 3 (Comparative Example) (1% HF, calcined in air for 4 hours at 400 ° C) The catalyst was produced by a similar method to Example 15, with the only difference that after the KOH precipitation and before the removal of chloride by washing, the pellets were calcined in air for 4 hours at 400 ° C.

EXAMPLE 4 (Hf at 5%, not calcined) The catalyst was produced using a method similar to Example 1 (HAWE 65), except that 11.47 g of HfOCI2 * 8H2O were introduced instead of 2.29 g of HfOCI2 * 8H2O. The catalyst was not calcined. The finished catalyst comprises 1% Pd, 0.7% Au and 5% Hf.

EXAMPLE 5 (Comparative Example) (5% HF, calcined in air for 4 hours at 300 ° C) The catalyst was produced by a method similar to Example 4, the only difference being that after the KOH precipitation and before chloride removal by washing, the pellets were calcined in air for 4 hours at 300 ° C.

EXAMPLE 6 (Comparative Example) (Hf at 5%, calcined in air for 4 hours at 400 ° C) The catalyst was produced by a method similar to example 4, with the only difference that after the KOH precipitation and before the chloride removal by washing, the pellets were calcined in air for 4 hours at 400 ° C.

EXAMPLE 7 (Comparative Example) Example 7 corresponds to Example 1 except that the doping with Hf was omitted.

EXAMPLE 8 (Hf at 2%, with Cl content) 0. 84 g of palladium chloride, 0.70 g of tetrachloroauric acid and 2.29 g of hafnium oxide dichloride are dissolved together in 35 ml of water and added to the pellets; the impregnation mixture is dried at 60 ° C for 3 hours in an oil pump aspirator. gMta ^ = f ^^^ 1.35 g of KOH dissolve in 35 ml of water and add to the dried pellets. The mixture is left to rest overnight. The pellets are washed with approximately 8 I of water, dried overnight at 110 ° C and reduced by C2H4 at 170 ° C. 4 g of potassium acetate are dissolved in 40 ml of water and added to the pellets and the mixture is then dried overnight at 110 ° C.

EXAMPLE 9 (Hf at 2%) 2. 29 g of hafnium oxide dichloride are first dissolved in 35 ml of water and added to the pellets. The impregnation mixture is dried in an oil pump aspirator. 1.06 g of palladium acetate and 0.81 g of gold acetate are dissolved in 35 ml of glacial acetic acid and added to the pellets. The impregnation mixture is allowed to dry as described above. 1.35 g of KOH are dissolved in 40 ml of water and added to the pellets and the mixture is allowed to stand overnight. The pellets are washed in a Soxhiet using approximately 8 I of water and after washing they are dried overnight at 110 ° C and reduced with C2H4 at 170CC for 3 hours. 4 g of potassium acetate are dissolved in 40 ml of water and added to the pellets. The pellets are dried overnight at 110 ° C in a drying oven.

X Uj Mi? A. -te ^ -. -. ,,. - * »** - A ^ s EXAMPLE 10 (Hf at 0.5%) 1. 06 g of palladium acetate and 0.81 g of gold acetate are dissolve in 40 ml of glacial acetic acid, 0.58 g of hafnium oxide dichloride are added and after 2 minutes the solution is added to the pellets. As much glacial acetic acid as possible is removed at 60 ° C in an oil pump aspirator and the pellets are dried overnight at 60 ° C in a vacuum drying oven. 1.40 g of KOH are dissolved in 40 ml of water and added to the pellets and the mixture is left to rest overnight. The pellets are washed in a Soxhiet using approximately 6 I of water, dried overnight 110 ° C in a vacuum drying oven and reduced in 10% C2H4 at 170 ° C for 2 hours. 4 g of potassium acetate are dissolved in 40 ml of water and added to the pellets. The pellets are dried overnight at 110 ° C. 15 EXAMPLE 11 (Hf at 0.25%) 1. 06 g of palladium acetate and 0.81 g of gold acetate are dissolve in 40 ml of hot glacial acetic acid, 0.29 g of hafnium oxide dichloride are added and after 2 minutes the solution is added to the pellets. As much glacial acetic acid as possible is removed at 60 ° C in an oil pump aspirator. 1.40 g of KOH dissolve in 40 ml of water ^^ gg¡ = j | gg ^!. ^^ ± j ^ ¡^^ ¡¡¡¡^ ^ ^^ and they are added to the pellets and the mixture is allowed to stand overnight. The pellets are washed in a Soxhiet using approximately 8 I of water, dried overnight at 110 ° C in a vacuum drying oven and reduced in 10% C2H at 170 ° C for 2 hours. 4 g of potassium acetate are dissolved in 40 ml and added to the pellets. The pellets are dried overnight at 110 ° C. The following table provides an overview of the catalysts doped with Hf produced: Example Charge of Hf Calcination 5 5% 4 hours at 300 ° C in air 10 6 5% 4 hours at 400 ° C in air 4 5% uncalcined 2 1% 4 hours at 300 ° C in air 3 1% 4 hours a 400 ° C in air 1 1% unburned 7 0 uncalcined 8 2% unburned 15 9 2% uncalcined 10 0.5% unburned 11 0.25% uncalcined Reaction tests in the gas phase oxidation of ethylene and acetic acid to give vinyl acetate: The catalysts are tested in a fixed bed tube reactor having a tube diameter of 2 cm. The reactor is heated externally using oil jacket heating. 15 ml of the catalyst pellets are placed in the reactor. The rising reactor volume and ^^^^^^^^^ * í? ^^^ ^^^ | The downstream of the catalyst bed is filled with glass spheres. The test apparatus is controlled by a procedure control system and is operated continuously. The catalyst is first activated and then tested under constant reaction conditions. 5 The activation comprises a plurality of steps: heating under N2, addition of ethylene, increase the pressure, addition of acetic acid, maintenance of the conditions, addition of oxygen. The reaction conditions in the tests are: reaction temperature = 160-170 ° C, pressure = 8-9 bar gauge pressure. The The feed is composed of 64.5% by volume of ethylene, 16.1% by volume of N2, 14.3% by volume of acetic acid and 5.1% by volume of 02. A complete analysis of the reactor product is carried out directly at the outlet of the reactor. reactor by gas chromatography in line (2-column arrangement). 15 The gas chromatography data were used to determine the selectivities of VAM S (= moles of VAM / (moles of VAM + 0.5 * moles of COx) and STY (space-time yield = g of VAM / I of cat. . * h): Example% Load TPS STY No. of Hf CC) (bar) (%) g / l * h 1 1 160 9 79 700 1 1 165 9 78 740 1 1 170 9 77 750 2 1 170 9 70 150 4 5 170 9 84 690 5 5 170 9 96 320 7 0 170 9 88 850 8 2 170 9 93 330 9 2 170 9 88 670 10 0.5 170 9 89 1100 11 0.25 170 9 90 820 As can be seen from the table, the catalysts doped with Hf that have not been calcined have better performance than the non-contaminated catalyst. All calcined catalysts are deficient. The calcination leads to the concretion and, consequently, to the deactivation of the noble metal particles in the support.

Claims (2)

1. NOVELTY OF THE INVENTION CLAIMS 1. A process for producing a supported catalyst by impregnation of the support with a basic solution and a solution comprising palladium salts, where the impregnation is carried out simultaneously or consecutively, with or without intermediate drying, washing the support to remove any chloride present and reduction of insoluble compounds 10 precipitates on the support before or after washing, drying of the catalyst precursor obtained in this way and impregnation thereof with alkali metal compounds which are completely or partially converted into alkali metal acetates under the reaction conditions in the production of monomer of vinyl acetate, where the support is 15 impregnated with one or more hafnium compounds either simultaneously with the impregnation of noble metal or in a subsequent treatment and is dried at a temperature of < 160 ° C and is not subsequently calcined.
2. 2. The process according to claim 1, further characterized in that the support is impregnated with a solution that 0 further comprises Au, Cd and / or Ba compounds as activators in addition to the palladium salts and the hafnium compound or compounds . jrirna ihri i < ap * ~ «^ 3. The process according to claim 1 or 2, further characterized in that hafnium compounds are used which are soluble in water, acetic acid or alcohol. 4. The process according to claim 3, further characterized in that the hafnium compounds are selected from the following group: HfOCI2, HfCL4, substituted hafnocene dichlorides, substituted cyclopentadienylhafnium trichlorides, hafnium acetylacetonate, hafnium alkoxides, HfO2, Hf (OH) 4, Hf (NO3), Hf (CnH18O2) 4). 5. The process according to any of claims 1 to 4, further characterized in that the catalyst has a hafnium content in the range of 0.01 to 50% by weight. 6. A supported catalyst comprising palladium and one or more alkali metal compounds and one or more hafnium compounds as catalytically active components in a porous support material, and which can be obtained by the process according to claim 1 7 '.- The supported catalyst according to claim 6, further characterized in that the catalyst has a hafnium content in the range of 0.01 to 50% by weight. 8. The supported catalyst according to claim 6 having the following composition: PdxAuyHfz, wherein x = 0.7-1.3% by weight, y = 0.5-1% by weight and z = 0.05-5% by weight. | te4j ^^ í agg ^ u ^ | ^^^^ Mj & ^ i? ^ & ^^ n li ^ ¿£ 9. The catalyst supported according to any of claims 6 to 8 for preparing vinyl acetate. ^^^^^^ g ^ wtt ^^^^^^^^^^^^^^^^^^^^ g ^ gg ^ g ^^^ l ^^^^^^^^^^^^ ^^^^^