Catalyst for preparing vinyl acetate as well as preparation method and application of catalyst

Abstract

The invention relates to a catalyst for preparing vinyl acetate and a preparation method and application thereof, and the preparation method comprises the following steps: mixing and kneading superfine silica powder, superfine diatomite, silica sol and a boron compound according to the weight ratio of 100: (5-20): (10-60): (0.1-1), drying, molding, and roasting at 150-650 DEG C for 1-6 hours to prepare a boron-doped composite SiO2 carrier; according to the molar ratio of Pd / (Au + Pd) being 0.76-0.93 and the mass of the carrier being 0.5%-1%, carrying out isovolumetric rolling impregnation by using a palladium and gold compound solution, and then drying; treating for 0.5-30 hours by using an alkaline solution, drying, reducing for 1-6 hours at the temperature of 300-650 DEG C in a nitrogen-hydrogen atmosphere, washing with water until no chlorine exists, and drying; mixing copper acetate and rhenium oxide with 0.5%-3% of aluminum phosphate according to the molar ratio of Cu / (Re + Cu) of 0.93-0.97 and 0.3%-1% to prepare dilute sol, dipping, coating and drying; dipping in a potassium acetate solution according to the proportion of 0.2%-7.5%, and carrying out negative pressure heat treatment at 60-200 DEG C for 1-6 hours; the obtained high-stability long-life catalyst is high in strength and few in by-products.

Description

Technical Field

[0001] The present invention relates to the field of chemical engineering technologies, and relates to a catalyst for preparing vinyl acetate, a preparation method thereof and an application thereof, and particularly relates to a long-life catalyst containing palladium and gold supported on silicon for the process of preparing vinyl acetate by the ethylene method, a preparation method thereof and an application thereof. Background Art

[0002] Vinyl acetate is one of the 50 most produced chemical products in the world. As a raw material for vinyl acetate resin and polyvinyl alcohol, and as a comonomer for copolymerization with ethylene, styrene, acrylate, methacrylate, etc., it is widely used in the fields of adhesives, paints, coatings, films, laminating materials, fiber treating agents, etc. It is an important industrial material and has high economic value.

[0003] In the 1970s, the ethylene method for preparing vinyl acetate was discovered. Vinyl acetate is produced by reacting ethylene, acetic acid and oxygen together in the gas phase in the presence of a palladium / gold catalyst and an alkali metal promoter, and has become a commonly used process method, such as USP3725680 and USP3743607. The active components are usually supported on a porous inorganic carrier material such as silica (aluminum), such as USP3775342 and USP3822308.

[0004] In the early prior art, the palladium and gold active components of these catalysts were more or less evenly distributed throughout the carrier, GB1333449. Due to the limitation of the diffusion rate of the reactants into the interior of the carrier, a large number of catalytic active components palladium and gold in the interior of the carrier have a great influence on contacting the reactants, and the role played in the reaction is quite limited. To solve this problem, in the early technology, GB1283737 also used an alkali solution to pretreat the porous carrier to control the penetration of the active components into the interior of the carrier.

[0005] USP4048096 and USP4087622 disclose very effective and widely used catalyst preparation methods. An outer layer impregnated catalyst is produced. The carrier is impregnated with an aqueous solution of palladium and gold compounds, soaked in a solution of alkali metal silicate for precipitation, and then the palladium and gold compounds are converted into metallic palladium and gold with a reducing agent, washed with water, contacted with an alkali metal acetate, and dried; a high specific activity (83 gVAM / g(Pd+Au)h -1 ) can be obtained. This eggshell-type catalyst is well-known and constitutes the most typical ethylene method catalyst preparation technology.

[0006] The preparation method of the outer layer impregnation adopted by GB1500167 has at least 90% of palladium and gold distributed in the carrier particles in the part not exceeding 30% of the particle radius from the outer surface, so as to obtain a catalyst with the active components concentrated in the outermost layer of the carrier; while GB1521652 attempts to distribute and fix the gold and palladium active components as evenly as possible into a narrow area on the carrier surface, in order to obtain a vinyl acetate catalyst with high yield, good selectivity and long life. In the subsequent patent documents EP565952A1, EP643214A1, EP643208A1, EP643209A1, in the disclosed technical content, there is almost no noble metal in the more internal area of the catalyst; in the particularly effective improvement measures with high activity disclosed in USP5314858 and USP5332710, the preparation method of uniformly fixing noble metals to a narrow area on the carrier surface by impregnation, precipitation and reduction is also adopted.

[0007] Changing the elemental composition of the catalyst is the first method that comes to mind in the improvement research. USP4668819 and USP4902823 introduce a palladium-potassium-cadmium catalyst. EP0565952A1 adopts a palladium-potassium-cadmium or palladium-potassium-barium catalyst. USP5567839 adopts a method of precipitation with barium salt instead of sodium silicate, and the barium element also remains in the catalyst; in CN1076875A of British BP Company, the yield is increased by controlling the weight ratio of gold to palladium and the potassium acetate content. In USP5179056, USP5189004 and USP5342987, it is also disclosed that the presence of free sodium can increase the space-time yield. USP5347046 contains metal elements such as copper, nickel, cobalt, silver, manganese, iron, lead, etc. in addition to palladium and gold in the catalyst; USP5968869 loads copper first before loading other active components to reduce the by-product carbon dioxide, but the activity is somewhat lost. EP1102635B1 adopts an active component of Pd / Au / HfO2; USP6605739 uses MoVNbX (X is selected from phosphorus, boron, hafnium, tellurium, arsenic or their compounds) to prepare VAM; USP6849243B1 describes barium and cadmium as additional promoters; while in USP2006 / 0135809A1, neodymium, titanium, magnesium, zirconium, yttrium, praseodymium, lanthanide elements and rubidium and their binary compositions are specifically disclosed as additional promoters.

[0008] In addition to element improvements, adjustments in the preparation method are also often used. EP0464633 discloses various non-spherical shaped catalysts. The use of hollow catalyst carriers offers advantages such as good heating distribution and low pressure drop. Generally speaking, spherical catalysts often have better service strength and handling convenience. USP5274181 uses hydrazine to reduce palladium and gold active elements, while EP0637209 uses hydrogen for reduction. USP5693586 reduces with ethylene at 150°C and modifies with potassium acetate, which can reduce CO2 by-products. USP5990344 discloses a preparation method of palladium on a sintered support above 500°C, which promotes significant growth of palladium metal particles, thereby suppressing the problem of excessive initial activity of the catalyst. USP6022823 calcines the support impregnated with palladium and gold salts before metal reduction to enhance catalyst activity. USP6420308 believes that the order of preparation steps is also important and cleans the catalyst before reduction to obtain higher space-time yield and product selectivity.

[0009] In addition to the technical content disclosed in the above foreign patent documents, with the implementation of the Chinese patent system in 1985, both foreign companies like Hoechst Artificial Gas Company and domestic research institutions such as Shanghai Research Institute of Petrochemical Technology have applied for a large number of patents with the same or similar content, such as the content related to the modification of the same elements involved in CN1068104A, CN1078199C, CN1090534C, CN1093775C, CN1104281C, CN1107538C, CN1117619C, CN1127472C, CN1129481C, CN1215353A, CN1281385A, and CN112642480B, CN 114425445 B, CN1084219C, CN100336593C.

[0010] Although a large number of improved existing technologies have been reported, unfortunately, due to reasons such as diffusion limitations of reactants, morphology and distribution of active components, and side reactions caused by excessive initial activity, the catalytic efficiency and reaction results of this type of catalyst have been unstable, affecting the service life, and usually forming a small amount of CO2 and high-boiling by-products. The use of precious metals leads to higher catalyst costs and losses due to limitations in service strength, and the catalytic efficiency that should be fully exerted has not been achieved.

[0011] Therefore, in the field of the activity and selectivity of silicon-supported catalysts for the preparation of vinyl acetate by the ethylene method, especially in terms of stability and service life, continuous improvement is still needed to further improve the catalytic efficiency of the catalyst, especially stability and long-cycle service life, reduce by-products, and increase mechanical strength. Summary of the Invention

[0012] In view of the above problems, the present invention aims to provide an improved method for preparing a catalyst for vinyl acetate production, and enable the catalyst obtained thereby to have better reaction stability, reduce by-products, and improve service intensity.

[0013] The present invention provides a method for preparing a catalyst for vinyl acetate production, comprising the following steps:

[0014] (1) Mix, knead, dry, form, and calcine at 150 - 650 °C for 1 - 6 h according to the weight ratio of ultrafine silica powder:ultrafine diatomaceous earth:silica sol:boron compound of 100:(5 - 20):(10 - 60):(0.1 - 1) on a dry basis to prepare a boron-doped composite silica support;

[0015] (2) Carry out equal-volume rolling impregnation and drying with a solution of palladium- and gold-containing compounds according to the molar ratio of Pd / (Au + Pd) of 0.76 - 0.93 and 0.5% - 1% of the support mass;

[0016] (3) Treat with an alkaline solution for 0.5 - 30 h and then dry, reduce in a nitrogen-hydrogen atmosphere at 300 - 650 °C for 1 - 6 h, wash with water until chlorine-free and then dry;

[0017] (4) According to the molar ratio of Cu / (Re + Cu) of 0.93 - 0.97 and 0.3% - 1% of the total catalyst weight, use copper acetate and rhenium oxide, and mix evenly with a dilute sol of aluminum phosphate accounting for 0.5% - 3% of the total catalyst weight, then carry out rolling impregnation coating and drying;

[0018] (5) Impregnate with a potassium acetate solution according to 0.2% - 7.5% of the total catalyst weight, and carry out heat treatment at 60 - 200 °C and a negative pressure of -0.01 - -0.1 MPa for 1 - 6 h to obtain the catalyst.

[0019] In the present invention, the catalyst support is composed of particles with any regular or irregular shape such as spherical, granular, columnar, annular, star-shaped or other shapes, and can have a scale of about 1 - 10 mm, such as diameter, length, or width. So far, a spherical shape of about 4 - 8 mm is preferred, and a spherical shape of 5 - 7 mm is most preferred.

[0020] In the present invention, the dry basis calculation method of silica sol is as follows: the silica sol contains 10% silicon dioxide, and its dry basis is 10% of the total weight.

[0021] In the present invention, the temperature of the roasting in step (1) is any value among 150°C, 200°C, 250°C, 300°C, 350°C, 400°C, 450°C, 500°C, 550°C, 600°C, 650°C or the range value between any two of them; the time of the calcination is any value among 1 h, 2 h, 3 h, 4 h, 5 h, 6 h or the range value between any two of them.

[0022] In the present invention, the boron compound in step (1) is boric acid and / or alkali metal borate; the alkali metal borate is selected from sodium tetraborate, sodium tetraborate pentahydrate, sodium tetraborate decahydrate, potassium tetraborate, potassium tetraborate pentahydrate, potassium tetraborate decahydrate.

[0023] In the present invention, in step (2), the equal-volume impregnation means estimating the pore volume of the carrier by the water drop method and obtaining the volume amount of the required impregnating solution, so that the impregnating solution just meets the needs of completely wetting the carrier and fully adsorbing the impregnation, without leaving any remaining impregnating solution unadsorbed by the carrier, which is a conventional operation familiar to those skilled in the art.

[0024] In some specific embodiments of the present invention, the solution containing palladium and gold compounds in step (2) is prepared by mixing palladium salts and gold salts; further, the palladium salts are selected from one or more of sodium chloropalladate, chloropalladic acid, palladium chloride, palladium acetate, sodium palladium chloride, potassium palladium chloride, palladium sulfate, palladium nitrate solution.

[0025] In some specific embodiments of the present invention, the gold salts are selected from one or more of gold chloride, gold acetate, chloroauric acid, sodium tetrachloroaurate, potassium tetrachloroaurate solution.

[0026] In the present invention, the treatment with the alkaline solution, water washing, drying and reduction in step (3) are to fully precipitate and solidify the active components of palladium and gold elements on the carrier and reduce them to the metallic state; wash with water until there is no chlorine in the wash liquor and no precipitate occurs when tested with 0.1 mol / L silver nitrate solution; the drying conditions are to keep at 20 - 160°C for 1 - 30 h in air or nitrogen atmosphere.

[0027] In the present invention, the alkaline solution is selected from inorganic bases and / or organic bases; among them, the inorganic bases are preferably one or several of hydroxides, meta-aluminates, carbonates, bicarbonates, ammonium carbonate, ammonia water of alkali metals. Preferably, the inorganic bases are selected from one or more of the aqueous solutions of sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, sodium silicate, potassium silicate.

[0028] In the present invention, the dilute aluminum phosphate sol is obtained by carrying out a dissolution reaction between phosphoric acid and one or more of aluminum oxide, aluminum hydroxide, boehmite, pseudo-boehmite at an equimolar ratio of phosphorus to aluminum.

[0029] In the present invention, in steps (1) to (4), the drying can be carried out under air conditions or under an inert gas, and the drying temperature is 80°C to 120°C; preferably, in steps (3) and (4), drying is carried out under a nitrogen atmosphere at 100°C for 4 hours.

[0030] In some specific embodiments of the present invention, the temperature of the drying is any value among 60°C, 70°C, 80°C, 90°C, 100°C or a range value between any two of them; the time of the drying is any value among 3h, 4h, 5h, 6h, 7h, 8h or a range value between any two of them.

[0031] In the present invention, the dilution with deionized water involved in the preparation process is mainly to meet the requirements and convenience of operation, and has no influence on the performance of the final finished catalyst; when the convenience of operation implementation is not affected, the minimum amount of water is preferably used for dilution, which can greatly reduce the energy consumption.

[0032] The present invention also provides a catalyst for preparing vinyl acetate, which is prepared by the method described above.

[0033] In the present invention, the catalyst prepared above is applied to the reaction process of preparing vinyl acetate by the ethylene method, especially in the operation process with a long life cycle; preferably, during the 20,000-hour use process, the unit output rate is greater than 320 g / Lcat·h and the product selectivity is greater than 91%.

[0034] In the present invention, the pore volume of the catalyst is 0.2 to 1.5 mL / g; the surface area is 50 to 300 m 2 / g; the bulk specific gravity is 0.5 to 0.65 g / mL; the compressive strength is 16 to 21 KN / grain.

[0035] The present invention provides a method for preparing vinyl acetate. Ethylene, acetic acid and an oxygen-containing gas react to obtain vinyl acetate under the action of the catalyst prepared by the method described above.

[0036] In some specific embodiments of the present invention, the preparation conditions for vinyl acetate further include: temperature 140 to 200°C, pressure 0.75 to 0.85 MPa, the volume space velocity of the mixed gas is 1800 to 2200 h -1 , the molar ratio of ethylene to acetic acid is 1:(0.2 to 0.3), and the oxygen content based on the dry gas is 7% to 8%.

[0037] The chemicals involved in the present invention are common industrial chemical products and experimental reagents, and can be easily obtained by commercial purchase.

[0038] The chemical unit operations involved in the present invention are conventional operation techniques in the art, well-known to those of ordinary skill in the art, and are routinely used in chemical experiments and industrial production processes.

[0039] Advantages of the present invention over the prior art: The preparation method of the catalyst provided by the present invention and the catalyst obtained therefrom have good space-time yield and selectivity of vinyl acetate during the reaction for preparing vinyl acetate, can enable the expensive noble metal per unit mass to exert higher catalytic performance, especially have very good stability in catalytic reaction performance, so as to adapt to a long service life cycle, such as stable operation for a long period of more than 20,000 h, and have low carbon dioxide and high-boiling by-products, and have good mechanical strength during use, and are particularly suitable for the industrial production process with a long service life cycle. Detailed implementation manners

[0040] The technical solutions of the present invention will be described clearly and completely below. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0041] In the examples, the content of elements was determined by atomic emission spectroscopy and X-ray fluorescence, and the composition analysis of raw materials and reaction products was completed by a gas chromatograph. Other analysis and detection can refer to the relevant analysis methods in (National Standards for Test Methods of Petroleum and Petroleum Products, published by China Standard Press in 1989) and (Analysis Methods of Petrochemical Industry (RIPP Test Methods), published by Science Press in 1990).

[0042] Materials and reagents used in the present invention:

[0043] Coarse pore silica powder: industrial product, Qingdao Ocean Chemical Industry;

[0044] Boric acid: chemically pure, Beijing Chemical Reagent Company;

[0045] Diatomite: industrial product, Jilin Yuantong Mining Industry;

[0046] Silica sol: industrial product, SiO2 10%, Qingdao Ocean Chemical Industry;

[0047] Sodium palladium chloride: chemically pure, Beijing Chemical Reagent Company;

[0048] Tetrachloroauric acid: chemically pure, Beijing Chemical Reagent Company;

[0049] Sodium silicate: industrial product, SiO2 20 wt%, Sichuan Runhe Catalyst Co., Ltd.;

[0050] Phosphoric acid: chemically pure, 85%, Beijing Chemical Reagent Company;

[0051] Pseudoboehmite: industrial grade, 70% Al2O3, Shandong Aluminum Industry;

[0052] Copper acetate: chemically pure, Beijing Chemical Reagent Company;

[0053] Rhenium oxide: chemically pure, Beijing Chemical Reagent Company.

[0054] Example 1

[0055] A preparation method of a vinyl acetate catalyst, comprising the following steps:

[0056] (1) Grind 1 kg of coarse pore silica powder, 150 g of washed diatomaceous earth and 5 g of boric acid in a stirring mill to 200 mesh, add 1.5 L of silica sol, and roll it into spherical carriers with a diameter of 6 mm on a laboratory rolling disc machine. Dry it in air at 25 °C for 16 h, dry it in an oven at 80 °C for 4 h, and then calcine it in a muffle furnace at 400 °C for 3 h.

[0057] (2) On a laboratory rolling disc machine, adopt the equal-volume impregnation method to prepare an aqueous solution of 20 g of sodium palladium chloride and 6 g of tetrachloroauric acid in 1 L, and roll and impregnate it on the surface of the above spherical carriers, and dry it in an oven at 100 °C for 4 h.

[0058] (3) Place the above-mentioned palladium- and gold-impregnated carriers in a 1 L solution containing 100 g of sodium silicate and let them stand at room temperature for 12 h. Then, use a nitrogen-hydrogen mixed gas with 5 v% hydrogen to reduce it at 450 °C for 4 h to completely reduce the palladium and gold compounds loaded on the carriers to elemental palladium and gold; then wash it with deionized water until there is no Cl - in the washing solution. When tested with 0.1 mol / L silver nitrate solution, no precipitation occurs, and then dry it in a nitrogen atmosphere at 100 °C for 4 h.

[0059] (4) React 12 g of phosphoric acid, 4 g of pseudoboehmite and deionized water and stir to form a sol; mix it with 7 g of copper acetate and 0.5 g of rhenium oxide to prepare a dilute sol, and evenly roll and coat and impregnate it on the above-mentioned palladium- and gold-containing carriers on a laboratory rolling disc machine, and place it in an oven and dry it in a nitrogen atmosphere at 100 °C for 4 h.

[0060] (5) After cooling to room temperature, impregnate it with an equal volume of an aqueous solution containing 100 g of potassium acetate. After taking it out, place it in an oven with vacuum pumping, and keep it at -0.09 MPa negative pressure at 150 °C for 4 h to obtain a catalyst for preparing vinyl acetate, which is a catalyst with relatively low palladium and gold contents.

[0061] Comparative Example 1

[0062] The catalyst for comparison is a commercial vinyl acetate catalyst with similar palladium, gold, and potassium contents to the catalyst of Example 1 of the present invention. Its active component distribution is an eggshell-type structure impregnated on the surface, with a silica support. Its preparation process and steps are similar to the preparation content in the examples of the classic patent literature USP4048096 for preparing vinyl acetate catalysts.

[0063] Example 2

[0064] This example is used to illustrate the reaction process of the catalyst of the present invention and the comparative catalyst for comparison.

[0065] The vinyl acetate catalyst prepared in Example 1 of the present invention was placed in a 1-liter small side-stream experimental reactor attached to an industrial production device of a certain overseas chemical plant. The pore volume of the catalyst in Example 1 is 0.65 ml / g, the surface area is 130 m 2 / g, the bulk density is 0.59 g / ml, and the compressive strength is 21 KN / particle.

[0066] The commercial catalyst for preparing vinyl acetate in Comparative Example 1 used for comparison has a pore volume of 0.68 ml / g, a surface area of 160 m 2 / g, a bulk density of 0.56 g / ml, and a compressive strength > 16 KN / particle.

[0067] Composition of the feed gas: By volume, the ethylene content is not less than 99.9%, by mass, the acetic acid content is not less than 99.5%, and the oxygen content in oxygen is not less than 99.7% by volume.

[0068] Process conditions during the reaction: The temperature range during the reaction life cycle is 140 - 200 °C, and the temperature slowly increases during the operation according to the unit productivity of vinyl acetate; the reaction pressure is 0.8 MPa; the supply volume rate of the vapor mixture is 2000 h -1 , the molar ratio of ethylene to acetic acid is 4:1, and the oxygen content based on dry gas is 7%.

[0069] Example 3

[0070] This example is used to illustrate the comparison of the reaction process and results of the catalyst of the present invention and the comparative catalyst.

[0071] Through the evaluation test of a small side-stream experimental reactor with an operating cycle of 2 years, the vinyl acetate synthesis process is carried out under the condition that the initial reactants are not completely converted. The single-pass conversion rate of ethylene is ~8%, the conversion rate of acetic acid is ~18%, and the conversion rate of oxygen is ~45%; the content of the stable product vinyl acetate by weight is ~99.90%; the unit output rate is greater than 320 g / Lcat·h, and the relative rate of yield decline is 0.9.

[0072] In terms of selectivity: The selectivity of vinyl acetate formation to ethylene is not less than 91% during its service life, and the average selectivity is 92.0%; the selectivity of vinyl acetate formation to acetic acid is 99.5%; the CO2 selectivity is ~7%; the amount of by-products formed does not exceed 1.0% of the amount of the product vinyl acetate.

[0073] Compared with the operation of the commercial comparative catalyst during the same service life, in terms of activity and selectivity, the relative ratio of yield decline, and the yields of carbon dioxide and by-products, etc., it is 3 - 10 percentage points better than the comparative agent.

[0074] It shows that the catalyst obtained by the preparation method of the catalyst of the present invention has better space-time yield and selectivity of vinyl acetate, stability in catalytic reaction performance, low carbon dioxide and high-boiling by-products, good mechanical strength during use, and is more suitable for the industrial production process with a long service life cycle.

[0075] Although the embodiments of the present invention have been shown and described, for those of ordinary skill in the art, it can be understood that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a catalyst for vinyl acetate production, characterized in that, It includes the following steps: (1) Ultrafine silica powder, ultrafine diatomaceous earth, silica sol, and boron compound are mixed and kneaded, dried, formed, and calcined at 150 - 650°C for 1 - 6 h according to the weight ratio of 100:(5 - 20):(10 - 60):(0.1 - 1) on a dry basis to prepare a boron-doped composite silica support; (2) According to the molar ratio of Pd / (Au + Pd) of 0.76 - 0.93 and the proportion of 0.5% - 1% of the support mass, an equal-volume rolling impregnation is carried out with a solution containing palladium and gold compounds and then dried; (3) After being treated with an alkaline solution for 0.5 - 30 h and then dried, it is reduced at 300 - 650°C in a nitrogen-hydrogen atmosphere for 1 - 6 h, washed with water until chlorine-free and then dried; (4) According to the molar ratio of Cu / (Re + Cu) of 0.93 - 0.97 and the proportion of 0.3% - 1% of the total catalyst weight, copper acetate and rhenium oxide are used, and mixed evenly with a dilute aluminum phosphate sol accounting for 0.5% - 3% of the total catalyst weight, and then subjected to rolling impregnation coating and drying; (5) Impregnated with a potassium acetate solution according to the proportion of 0.2% - 7.5% of the total catalyst weight, and heat-treated at 60 - 200°C under a negative pressure of -0.01 - -0.1 MPa for 1 - 6 h to obtain the catalyst.

2. The preparation method according to claim 1, characterized in that, The boron compound is boric acid and / or alkali metal borate.

3. The preparation method according to claim 1, wherein In step (2), the solution containing palladium and gold compounds is prepared by mixing palladium salts and gold salts; further, the palladium salt is selected from one or more of sodium chloropalladate, chloropalladic acid, palladium chloride, palladium acetate, sodium palladium chloride, potassium palladium chloride, palladium sulfate, palladium nitrate solution.

4. The preparation method according to claim 1, characterized in that, The gold salt is selected from one or more of gold chloride, gold acetate, chloroauric acid, sodium tetrachloroaurate, potassium tetrachloroaurate solution.

5. The preparation method according to claim 1, characterized in that, The alkaline solution is selected from inorganic bases and / or organic bases; further, the alkaline solution is an inorganic base; More specifically, the inorganic base is selected from one or more of the aqueous solutions of sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, sodium silicate, potassium silicate.

6. The preparation method according to claim 1, characterized in that, The dilute aluminum phosphate sol is obtained by a dissolution reaction of phosphoric acid and one or more of aluminum oxide, aluminum hydroxide, boehmite, pseudo-boehmite at an equimolar ratio of phosphorus to aluminum.

7. A catalyst for preparing vinyl acetate, characterized in that, It is prepared by the method as described in any one of claims 1 - 6.

8. The catalyst according to claim 7, characterized in that, The pore volume of the catalyst is 0.2 - 1.5 mL / g; The surface area is 50 - 300 m 2 / g; the bulk specific gravity is 0.5 - 0.65 g / mL; the compressive strength is 16 - 21 KN per piece; during the 20,000-hour usage process, the selectivity of vinyl acetate is greater than 91% and the unit yield is greater than 320 g / Lcat·h.

9. A method for preparing vinyl acetate, characterized in that, Ethylene, acetic acid, and an oxygen-containing gas react to obtain vinyl acetate under the action of the catalyst prepared by the method as described in any one of claims 1 - 6.

10. The preparation method according to claim 9, characterized in that, The preparation conditions of the vinyl acetate also include: temperature of 140 - 200 °C, pressure of 0.75 - 0.85 MPa, volume space velocity of the mixed gas of 1800 - 2200 h -1 , molar ratio of ethylene to acetic acid of 1:(0.2 - 0.3), and oxygen content of 7% - 8% based on dry gas.