A method of producing a catalyst for the synthesis of vinyl acetate (options)

 

(57) Abstract:

The invention relates to a new method of preparation of the catalyst for vapor-phase reaction of ethylene, oxygen and acetic acid to form vinyl acetate, wherein said catalyst comprises metallic palladium and gold deposited on a suitable porous carrier. Describes how to obtain a catalyst (option) on the basis of a combination of palladium-gold, ending in a separate impregnation and fixation (fixation) of palladium and gold with the subsequent recovery of fixed solids to the state free of metal on a suitable carrier, the catalyst used for the synthesis of vinyl acetate from ethylene and acetic acid. Embodiments of the method include applying the first or palladium, and then gold or beginning of gold, and then palladium. Effect: increase the activity, selectivity and increase the service life of the catalyst. 2 C. and 10 C. p. F.-ly, 2 tab.

The connection with previous applications

This application is a partial continuation of application USSN 08/823592 from 3/25/97, now repealed, which is a continuation application USSN 08/489541 filed 6/12/95, which on the voided.

The technical field to which the invention relates

The present invention relates to a new method of preparation of the catalyst for vapor-phase reaction of ethylene, oxygen and acetic acid, with formation of vinylacetate. Primarily, the present invention relates to a new method of forming the catalyst used for the catalytic synthesis of vinyl acetate, wherein said catalyst comprises metallic palladium and gold deposited on a suitable porous carrier.

Description of the prior art

It is known in the art that vinyl acetate can be obtained by the reaction of ethylene, oxygen and acetic acid in the gas phase in the presence of a catalyst comprising palladium, gold and alkali metal acetate, printed on some of the material-carriers, such as silicon dioxide. Usually, this catalytic system is characterized by high activity. Unfortunately, when using such catalysts based on palladium and gold were obtained contradictory results. Apparently, these contradictions to some extent depend on the type of distribution or profile of the catalytic component deposited on the substrate, and their quantitative so porous media with palladium and gold, metal components are deposited in the Central and inner parts of the medium, not take a significant participation in the mechanism of the reaction, since the reagents are unable to easily diffuse into the Central or inner region of the porous mesh catalyst. Consequently, much of the reaction proceeds only on the most remote from the centre or on the surface sites of the catalyst. The catalytic components in the internal areas of the media, do not take a substantial stake in the reaction scheme, resulting in reduced catalytic efficiency per unit weight of the catalytic component. In addition, the use of highly active catalyst over time gives rise to side reactions with the corresponding decrease in the selectivity to vinyl acetate.

Were granted various patents, the purpose of which was smoother distribution and attachment of gold and palladium catalyst components in a narrow zone on the surface of the carrier to obtain a catalyst for the synthesis of vinyl acetate, providing a high yield of the target product, a high reaction selectivity to vinyl acetate and having a long service life. When the s U.S. patents issued in the name of Hoechst Celanese Corporation, U.S. patent 5314858 and 5332710, as well as their PCT and foreign equivalents describe and claim improvements in the underlying technology.

The basic method of forming a catalyst for the synthesis of vinyl acetate containing palladium and gold on the catalytic carrier, includes (1) impregnation of the support with aqueous solutions of water-soluble compounds of palladium and gold, (2) deposition of water-insoluble compounds of palladium and gold on the catalytic media in contact impregnated catalyst carrier with a solution of compounds able to react with vodorastvorimami compounds of palladium and gold with the formation of insoluble compounds of precious metals, (3) washing the treated catalyst with water to remove anions, which are released from impregnating compounds of palladium and gold in the course of the deposition, and (4) the conversion of water-insoluble compounds of palladium and gold available in metals as a result of processing regenerating agent. Final processing typically includes (5) impregnation of recovered catalyst with an aqueous solution of acetate of an alkali metal and (6) drying the final catalyst product.

Described which the manipulation in the implementation of the above stages and/or the use of media materials with different pore sizes.

U.S. patent 5314858 relates to a method that includes (1) simultaneous or sequential impregnation of the catalytic carrier with aqueous solutions of such salts of palladium and gold, as a mixed sodium chloride and palladium chloride, gold (III), (2) fixation of noble metals on the carrier by deposition of water-insoluble compounds of palladium and gold, as a result of processing the impregnated carriers such reactive basic solutions, as an aqueous solution of sodium hydroxide, which reacts with the formation of hydroxides of palladium and gold on the surface of the carrier, (3) washing with water to remove chloride ion (or other anion), and (4) recovery of hydroxides of precious metals available in palladium and gold, and the improvement is that at the stage of fixation (2) use two separate stages of deposition, while the number of reactive compounds in contact with saturated salt carrier, at each stage does not exceed the quantity required for reaction with a water-soluble compounds of precious metals, which saturated the media. Between the individual stages of fixation or precipitation carrier impregnated with reactive primary process is orodnik metals before carrying out the second stage of fixation, where the media adds extra reactive primary connection.

The purpose of the present invention is to develop a method of preparation of catalyst for the synthesis of vinyl acetate containing palladium and gold on a porous carrier, whereby the fixation of the water-soluble compounds of noble metals in the form of water-insoluble compounds on the surface of the carrier can be achieved by contacting the impregnated carrier with so many reactive compound that is sufficient to complete the deposition and fixation of compounds of noble metals on the media in the implementation of the multiple stages of the commit.

Summary of the invention

The inventors found that applied particularly active catalysts containing palladium and gold intended for production of vinyl esters of ethylene, lower carboxylic acids containing 2-4 carbon atoms, and oxygen, in the implementation of the gas-phase reactions at elevated temperatures and normal or increased pressure can be obtained by modification of stages (1) and (2) of the above process. Usually, at the stage asadero connection what contributes to the simultaneous deposition of oxide (hydroxide) of each component during the time required for the complete precipitation of insoluble compounds of noble metals. As noted earlier, during a typical stage of the deposition in accordance with known methods, palladium is deposited at a greater rate than gold, resulting in an increasing number neozhidannogo gold can vydeliajutsia of the catalytic carrier prior to its immobilization by deposition or at a subsequent stage of leaching. This fact is caused by changes in the ratio between the amounts of palladium and gold in the transition from the impregnation stage to the stage of deposition. Although there is a problem when the number of precipitant solution is equal to the pore volume of the carrier, an even more serious problem occurs when the deposition is carried out by immersing the impregnated carriers in diluted precipitators.

To overcome this problem, in accordance with the present invention, a suitable catalyst is formed by (1) inconsistent catalytic impregnation of the carrier with aqueous solutions of such salts of palladium and gold as sodium chloride-palladium and gold chloride (III), (2) naposledy the s palladium and gold as a result of processing the impregnated carriers such reactive solutions as an aqueous solution of sodium hydroxide, which reacts with components of the system with the formation of hydroxides of palladium and gold on the surface of the carrier, (3) flushing the system with water to remove chloride ion (or other anion), and (4) recovery of the noble metal hydroxides to free palladium and gold.

Detailed description of the invention

In the preparation of the improved catalysts of the present invention suitable catalytic carrier is first impregnated with an aqueous solution containing or water-soluble compound of palladium, or a water-soluble compound of gold. Examples suitable for this purpose is a water-soluble palladium compounds can serve as palladium (II) chloride, mixed sodium chloride-palladium (II) nitrate, palladium (II), then as a water-soluble gold compounds can be used chloride of gold (III) or tetrachlorotoluene (II) acid and its alkali metal salts. Usually, I prefer to use available tetrachlorosilane (III) acid and mixed sodium chloride-palladium (II), due to their high solubility in water. Usually use so much of these compounds, which provides content in 1 l goto the re, will be 10-70% of palladium. Preparation of catalyst for the synthesis of vinyl acetate from ethylene, oxygen and acetic acid, in accordance with the method of the present invention, provide catalyst containing at least 17 wt.% more palladium and at least 12% more gold than when using the method according to U.S. patent 5332710. The method of the present invention provides a catalyst containing an equivalent or greater quantity of gold than the catalyst obtained by the method of U.S. patent 5314858.

Comparative examples was performed on the catalysts prepared by the above method of the present invention (technology separate commit) and the method of double fixation, in accordance with the method of U.S. patent 5314858. In table. 2 shows the results of these examples. The results show that the method of the present invention provides greater holding gold than the method of U.S. patent '858.

An important factor is the volume of solution used for impregnation of the carrier of noble metals. For the effective application of the volume of the impregnating solution should be 95-100% of the adsorption capacity catalic the congestion can have a variety of geometrical shapes. So, for example, the media may be molded in the form of pellets, tablets or cylinders. The geometric dimensions of the material media are usually 1-8 mm Most suitable geometric configuration is a spherical shape, for example, beads with a diameter in the range of 4-8 mm, Such media are usually referred to as granules.

The specific surface area of the material of the carrier may vary within wide limits. So, for example, can be applied to the media area of the inner surface of 50-300 m2/g and, particularly, 100-200 m2/g (in accordance with the measurement by the BET method).

Examples of suitable for the use of media materials may be silicon dioxide, aluminum oxide, aluminum silicates or spinel. The preferred material of the carrier is silicon dioxide.

After each impregnation the carrier water-soluble compounds of palladium or gold impregnated carrier may be subjected to drying prior to fixation of the compounds of palladium or gold on the surface of the carrier in the form of water-insoluble compounds. The fixing solution may be a system containing an alkali solution such as an aqueous solution containing hydroxides of alkaline metallogenia solutions of sodium hydroxide or potassium hydroxide. As a result of processing an alkaline solution of salts of noble metals into water-insoluble compounds, presumably in the hydroxides and/or oxides, at least in the case where the alkaline solution is a sodium hydroxide solution or potassium hydroxide.

In accordance with known methods, alkaline fixing solution was dispersed on the surface of the impregnated carriers and thus treated the native stand for 24 hours or more during deposition. The used amount of the fixing solution is equal to the absorption capacity of the dry media, and the applied amount of the alkaline compound exceeds, in molar terms, the quantity required for reaction with all of impregnating salts of noble metals.

In the method of the present invention, each stage of fixing the amount of the alkaline compound contained in the fixing solution should be such that the ratio of the alkali metal and the anion of the water-soluble salt of the noble metal was 1:1-1,8:1 in molar terms.

The volume of solution at each stage of fixation may be equivalent to the pore volume of the carrier, or impregnated carrier Moriyama media. On the other hand, the carrier may be impregnated on one or both stages separate fixing in accordance with the method, denoted as "rotary dip", a term that is listed in a recognized application for U.S. patent 5332710. According to this method, the impregnated catalyst carrier is dipped in an alkaline fixing solution and subjected to Galloway or rotate it, at least in the initial stages of deposition of water-insoluble compounds of noble metals. Such rotation or hartowanie carriers in the alkaline fixing solution should be at least for 0.5 h initial processing, preferably for at least 2,5 hours Processing rotary dip can last up to 4 h and then processed media can be cured in the fixing solution to ensure complete precipitation of water-soluble compounds of noble metals.

Can be used any equipment for Saltovka or rotation and the concrete type of the device used is not critical. However, the decisive factor may be the intensity of the rotational motion. The rotation should be sufficient to ensure that all surfaces are impregnated with the m intensive, since in this case can appear abrasive action of the particles of insoluble compounds of precious metals, resulting in insoluble compounds can ground the surface of the carrier. Usually the intensity of rotation must be 1-50 rpm and maybe even higher depending on the type of media and the amount of noble metal to be applied to the media. Apply the rotational speed, expressed in revolutions per minute, is variable and may also depend on the type of machine used, the size and shape of media, media type, number of deposited metal, etc , but this option must be set in the above range, providing a slight abrasive action, it should exclude the situation when insoluble compounds grated surface of the carrier to an unacceptable degree.

Before each stage of fixation of the impregnated catalyst carrier may be subjected to drying to remove the absorbed water. In the case where the fixation is conducted by a method that takes into account pore volume, drying the impregnated carrier is required to achieve full contact of the noble metal with locking rarepattern, do not expose the impregnated carrier is dried before fixation.

On the other hand, the impregnating solution containing the compound of gold, and the fixing solution may be mixed immediately prior to impregnation, thus eliminating the need for the implementation of individual stages of fixation. The possibility of this interpretation is based on a fairly slow formation of insoluble salts of gold at room temperature.

After stages of fixing the media is washed, for example, distilled water in order to remove such anions, such as chlorides, which are still present in the media and stand out from the source impregnating solution. Washing is continued until complete removal of anions from the media. In the ideal case, the catalyst should not remain anions in more than 1,000 h/million For guarantees almost complete removal of the catalyst such anions as chloride, water effluent should be tested with silver nitrate. Then the catalyst is dried at temperatures not exceeding 150oC.

Further, fixed and washed material is treated regenerating agent to present salts and compounds of precious metals in use is hydrazine, or in the gas phase, for example, using hydrogen or hydrocarbons, for example ethylene. If the recovery is carried out in the presence of hydrazine hydrate, the reaction is preferably carried out at normal temperature. In the case of the implementation of the recovery in the gas phase reaction is conveniently carried out at elevated temperatures, for example at 100-200oIn the case of recovery of ethylene. Usually use an excess of the reducing agent in order to ensure full transfer of all salts and compounds of precious metals in metallic form.

Depending on the destination thus obtained catalyst may be introduced traditional additives. For example, adding acetates of alkali metals beneficial in the case when the catalyst is intended for producing unsaturated esters from olefins, oxygen, and organic acids. In this case, the catalyst may be impregnated, for example, an aqueous solution of potassium acetate and then dried.

The catalysts according to the invention with particular success can be applied to obtain the vinyl acetate from ethylene, oxygen and acetic acid in the gas phase. Especially suitable for this purpose, the catalysts of nastojashego. In the above-mentioned synthesis of vinyl acetate such a catalyst is also characterized by high activity and selectivity and long life.

EXAMPLES 1-4

The catalysts of examples 1-4 were prepared in accordance with the method of the present invention. Specific examples are given in table. 1. Unless otherwise noted, in each example used catalytic media on the basis of silicon dioxide, manufactured by Sud Chemie having a spherical shape and a diameter of about 7,3 mm In each of the examples 250 cm3media impregnated with an aqueous solution containing sufficient sodium chloride-palladium to ensure the availability of 1.65 g (6.6 g/l) of palladium on the carrier. Used in the table. 1 the term "initial wettability" is known from the literature as indicating the volume of solution equal to the volume of the pores of the support. Then the processed media recorded with an aqueous solution of sodium hydroxide according to the method described in table. 1. The amount of sodium hydroxide used in the first stage of fixation, defined as the molar ratio of sodium cations to the anions of chlorine, was 1.2:1. Variations in the time of fixation is also reflected in the table. 1. After the first fixation of the processed material tatel the efficiency of the water supply was 200 cm3/min for approximately 5 hours After washing, the catalyst was dried for one hour at 100oC. thereafter, the dried catalysts were impregnated 0.75 g (3.0 g/l) of gold used in the form of an aqueous solution of chloroaurate sodium. Then the processed media recorded with an aqueous solution of sodium hydroxide in accordance with the method described in table. 1. The amount of sodium hydroxide used in the second phase of the commit specified in the molar ratio of sodium to chloride anion, was 1.2:1. Variations in the time of fixation is also provided in table. 1. After the second fixation processed base material was thoroughly washed with distilled water to remove chloride ions. Unless specifically stated, the volumetric rate of water was 200 cm3/min for approximately 5 hours After washing the catalysts were air dried in nitrogen atmosphere at 150oC. Then, each of the obtained catalyst was recovered gaseous ethylene at a temperature of 150oC. Regenerating gas contained 5% ethylene in nitrogen, and it was passed over the catalyst for 5 hours at atmospheric pressure. The recovered catalyst was impregnated with an aqueous solution containing 10 g (40 g/l) of potassium acetate, use is SUP>C.

The catalysts of examples 4-6 were prepared in accordance with the method described in U.S. patent 5314858. The catalysts of examples 7 to 11 were prepared according to the method of the present invention. The source and destination of the load on the metal are shown in table. 2. From the presented results one can see that the average holding metal for Pd according to the method of U.S. patent '858 was 88%, and for Au - 77%, while the average holding metal for Pd in accordance with the method of the invention was 88%, and for Au - 85%. The catalysts of examples 1-11 were used for the synthesis of vinyl acetate by reaction of ethylene, oxygen and acetic acid in accordance with methods well-known in this technical field.

1. A method of producing a catalyst comprising a porous support containing thereon palladium and gold in the form of metals, including impregnation specified media, water-soluble compounds of these noble metals, the transformation of these absorbed water-soluble compounds of noble metals in water-insoluble compounds of noble metals by contacting the impregnated carrier at the stage of fixing solution containing a compound reactive with respect to these the compounds of precious metals and restore these water-insoluble compounds of precious metals regenerating gas with formation of free of noble metals on the specified media characterized in that it includes the stages of (1) contacting the specified media with one of these water-soluble compounds of precious metals for the purpose of impregnation of the carrier water-soluble compounds, (2) the conversion of the specified water-soluble noble metal in the water-insoluble compound of the noble metal in the contact specified impregnated carrier at the first stage of fixing with a solution containing a compound reactive in relation to a specified water-soluble compounds, with the aim of deposition on the specified media specified water-insoluble compound of a noble metal, (3) contact the specified pre-impregnated and fixed media with the second of these water-soluble compounds of noble metal in order impregnation of the carrier water-soluble compounds, (4) the conversion of the specified second water-soluble compound of a noble metal in a water-insoluble compound of a noble metal in contact specified impregnated carrier at the second stage of fixation with a second solution containing a compound reactive with respect to the second water soluble solla, with the subsequent recovery of water-insoluble compounds of noble metals with formation of free of noble metals on the specified media.

2. The method according to p. 1, wherein the reactive compound used in the first and second stages of fixation, is an alkaline compound.

3. The method according to p. 2, characterized in that the alkaline compound includes potassium hydroxide or sodium.

4. The method according to p. 1, characterized in that the volume of the reaction solution in contact with the specified impregnated carrier at the first stage of fixation is equal to the absorption capacity of the specified media in the dry state.

5. The method according to p. 1, characterized in that the volume of the solution in contact with the impregnated carrier in the first phase commit sufficient for immersion media.

6. The method according to p. 1, characterized in that the volume of the reaction solution in contact with the impregnated carrier at the second stage of fixation is equal to the absorption capacity of the specified dry media.

7. The method according to p. 1, characterized in that the volume of the reaction solution in contact with saturated n is the action scene themes that specified the first stage of fixation carried out by rotational dive.

9. The method according to p. 8, characterized in that the noble metal which is in contact with the carrier first and which is subjected to the first phase commit is a PD.

10. The method according to p. 1, wherein the stage includes: (1) the contacting of the solution of water-soluble Pd with a porous media with a view to its impregnation with a water-soluble compound Pd; (2) the conversion of the specified water-soluble metallic Pd in the water-insoluble compound Pd in contact connections Pd and the media in the first phase commit with an alkaline compound, and the carrier is dipped in a solution of alkaline compounds and subjected to Galloway, at least during the initial stages of the deposition of water-insoluble compounds of Pd; (3) contacting the pre-impregnated and fixed media with a water-soluble compound of a metal Au order impregnation of the carrier water-soluble compounds Au; (4) the conversion of the specified water-soluble metal Au in water-insoluble compound Au in the contact connection Au and media in the second stage fixation with alkaline sopostanovlenije compounds of Pd and Au using a reducing agent with formation of free Pd and Au in the form of metals on the media.

11. The method according to p. 1, wherein the stage includes: (1) the contacting of the solution of water-soluble Pd with a porous media with a view to its impregnation with a water-soluble compound Pd; (2) the conversion of the specified water-soluble metallic Pd in the water-insoluble compound Pd in the contact connections Pd and the media in the first phase commit with the alkaline compound, and the carrier is dipped in a solution of alkaline compounds and subjected to Galloway during at least the initial stages of the deposition of water-insoluble compounds of Pd; (3) the contacts are initially impregnated and fixed media with water-soluble compounds Au metal and alkaline connection with the purpose of impregnation of the carrier water-soluble Au and simultaneous implementation of the second stage of fixation; and (4) recovery of the compounds of Pd and Au regenerating agent with formation of free Pd and Au in the form of metals on the media.

12. A method of producing a catalyst comprising a porous carrier containing palladium and gold in the form of metals, comprising a carrier impregnated with water-soluble compounds of these noble metals, conversion of absorbed water-soluble soapymassage media in at least one stage of fixing solution, containing a compound reactive in relation to water-soluble compounds of the noble metal to be deposited on the carrier water-insoluble noble metal compounds and recovery of water-insoluble noble metal compounds regenerating gas from education to the media free of noble metals, characterized in that it includes the stages of (1) contacting the carrier with water-soluble compounds of palladium for impregnation of water-soluble compounds of palladium on a carrier, (2) the conversion of water-soluble palladium compounds in water-insoluble compound of palladium by contacting the impregnated carrier at the first stage of fixing with a solution containing a compound reactive in relation to water-soluble palladium compounds for deposition on the carrier water-insoluble palladium compounds, (3) contact first impregnated and fixed media with a water-soluble compound of gold for impregnation of water-soluble gold compounds on the carrier, (4) the transformation of water-soluble gold compounds in water-insoluble compound of gold by contacting the impregnated carrier at the second stage of fixation with the second solution, sodetel water-insoluble gold compounds and subsequent recovery of water-insoluble compounds of palladium and gold with formation of free metals palladium and gold on the media.

 

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