Catalyst for preparing vinyl acetate, method for preparing the same, and use thereof

Abstract

The application discloses a catalyst for preparing vinyl acetate, a preparation method and application thereof. The catalyst comprises a carrier and Pd, Au and alkali metal acetate supported on the carrier; and the Zeta potential of Pd-Au on the surface of the catalyst is 30-65 mV. The catalyst is suitable for a synthesis reaction of vinyl acetate by using ethylene, and has the advantages of high space-time yield and high selectivity of vinyl acetate.

Description

Technical Field

[0001] This invention belongs to the field of vinyl acetate synthesis, specifically relating to a catalyst for preparing vinyl acetate, its preparation method, and its application. Background Technology

[0002] Vinyl acetate (VAc) is one of the world's 50 most produced chemical raw materials. Through self-polymerization or copolymerization with other monomers, it can produce derivatives such as polyvinyl alcohol (PVA), polyvinyl acetate (PVAc) emulsions, vinyl acetate-ethylene copolymer emulsions (VAE) or copolymer resins (EVA), and vinyl acetate-vinyl chloride copolymers (EVC). These derivatives are widely used in adhesives, architectural coatings, sizing agents for paper or fabrics, paints, inks, leather processing, fiber processing, emulsifiers, water-soluble films, and soil conditioners. Global vinyl acetate production capacity reached 7.79 million tons per year in 2020, with China accounting for 2.75 million tons per year. In recent years, with the rapid development of the downstream product market for VAc, global demand for VAc has been continuously increasing, thus the VAc market has attracted much attention.

[0003] Currently, the gas-phase process for producing vinyl acetate (VAc) is one of the most important industrial methods. Industrially, the gas-phase synthesis of VAc from ethylene primarily uses palladium-gold / potassium acetate / silica as a catalyst, with palladium sites on the catalyst surface being the main active sites. In the reaction, ethylene, oxygen, and acetic acid are used as raw materials, and through gas-phase catalytic reaction, the main products are vinyl acetate, water, and carbon dioxide as a byproduct. The temperature on the reactor shell side can be 100–180°C, while the reaction pressure is 0.5–1.0 MPa, and the gas hourly space velocity (GHSV) is 500–3000 hr. -1 .

[0004] CN106582823A discloses a catalyst for the preparation of vinyl acetate using the ethylene process. The catalyst comprises a support, an active component, and a co-catalyst; the support is SiO2, Al2O3, or a mixture thereof; the co-catalyst is an alkali metal acetate; and the active component includes metal Pd, metal Au, and at least one metal element selected from alkaline earth metals and Group IVB metals. The catalyst can be used in the industrial production of vinyl acetate.

[0005] The catalysts reported above suffer from low selectivity and low yield for vinyl acetate. Therefore, in-depth research on vinyl acetate catalysts is warranted in this field to address these shortcomings. Summary of the Invention

[0006] To address the problems existing in the prior art, this invention provides a catalyst for preparing vinyl acetate, its preparation method, and its application. The catalyst is suitable for the synthesis of vinyl acetate via the ethylene process, and has the advantages of high space-time yield and high selectivity.

[0007] The first aspect of the present invention provides a catalyst for preparing vinyl acetate, the catalyst comprising a support and Pd, Au and alkali metal acetate supported on the support; preferably, the Zeta potential of Pd-Au on the catalyst surface is 30-65 mV, more preferably 35-48 mV.

[0008] According to the present invention, the catalyst contains 1–12 g / L of Pd; and / or 0.1–10 g / L of Au; and / or 10–100 g / L of alkali metal acetate; and / or 250–500 g / L of support. The above description refers to the mass content of Pd, Au, alkali metal acetate, or support per liter of catalyst.

[0009] According to the present invention, the alkali metal acetate includes at least one of potassium acetate and sodium acetate. The support includes at least one of silicon dioxide and aluminum oxide.

[0010] A second aspect of the present invention provides a method for preparing the above-mentioned catalyst, comprising the following steps:

[0011] (a) The support was impregnated in a solution containing palladium and gold to obtain catalyst precursor I;

[0012] (b) Catalyst precursor I was treated with an alkaline compound to obtain catalyst precursor II;

[0013] (c) Catalyst precursor II and reducing agent are mixed to prepare catalyst precursor III;

[0014] (d) Catalyst precursor III was impregnated in a solution containing a long-chain alkyl metal quaternary ammonium salt to prepare catalyst precursor IV;

[0015] (e) The catalyst precursor IV is impregnated in an alkali metal acetate to obtain the catalyst.

[0016] According to the present invention, the palladium- and gold-containing solution in step (a) is a mixed solution of chloropalladium acid and chloroauric acid. The palladium content in the palladium- and gold-containing solution is 1–12 g / L, and the gold content is 0.1–10 g / L. The solid-liquid volume ratio in step (a) is 1:1 to 1:2. The immersion time is 20–60 min. There are no particular limitations on the immersion temperature. The solution can be dried after immersion. The drying can be performed using conventional drying parameters, preferably at 60–120°C for 0.5–2 hours.

[0017] According to the present invention, the alkaline compound in step (b) comprises sodium silicate. The ratio of the molar amount of the alkaline compound to the total molar amount of palladium and gold is 1:1 to 2:1. The alkaline compound exists in solution form. The concentration of the alkaline compound solution is 10 to 500 mmol / L. The treatment can be performed by solution immersion. The immersion time is 20 to 30 hours. There is no particular limitation on the immersion temperature. After immersion, it can be dried. The drying can be performed using conventional drying parameters, preferably 60 to 120°C for 6 to 12 hours.

[0018] According to the present invention, the reducing agent in step (c) comprises hydrazine hydrate. The molar ratio of the reducing agent to palladium and gold is 1:1 to 2:1. The mixing and standing time is 2 to 8 hours. After mixing and standing, washing and drying can be performed. The drying can be carried out using conventional drying parameters, preferably drying at 60 to 120°C for 6 to 12 hours.

[0019] According to the present invention, the long-chain alkyl metal quaternary ammonium salt structure in step (d) is as follows:

[0020]

[0021] According to the present invention, the concentration of the long-chain alkyl metal quaternary ammonium salt solution in step (d) is 10–500 mmol / L, preferably 180–220 mmol / L. The solid-liquid volume ratio in step (d) is 1:0.8–1:2.0, preferably 1:1–1:1.5. The impregnation time is 40–55 h. After impregnation, washing and drying can be performed. The drying can be carried out using conventional drying parameters, preferably drying at 60–120°C for 8–18 hours.

[0022] According to the present invention, drying can be performed after impregnation in step (e). The drying can be carried out using conventional drying parameters, preferably drying at 50-100°C for 1.5-3 hours.

[0023] The third aspect of this invention provides the application of the above-described catalyst or the catalyst prepared by the above-described preparation method in the ethylene-based vinyl acetate synthesis reaction.

[0024] According to the present invention, the raw material gas reacts with the catalyst under the action of a catalyst to obtain the vinyl acetate.

[0025] According to the present invention, in the application described, the raw material gas composition includes oxygen, ethylene, nitrogen, and acetic acid. Preferably, the molar ratio of oxygen:ethylene:nitrogen:acetic acid is 1:(5-7):(4-8):(1-2).

[0026] According to the present invention, in the aforementioned applications, the reaction pressure is 0.5–0.9 MPa; and / or, the reaction temperature is 130–200 °C; and / or, the feed gas volume hourly space velocity is 1600–3000 hr. -1.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] 1. In the vinyl acetate catalyst of the present invention, the catalyst comprises a support and an active component; the active component comprises Pd element, Au element, and alkali metal acetate; the Zeta potential of the Pd-Au nanoparticles on the surface of the catalyst is 30-65 mV, preferably 35-48 mV. The catalyst, when used in the ethylene-based vinyl acetate preparation reaction, has the advantages of high space-time yield and high selectivity of the target product.

[0029] 2. In the preparation method of the vinyl acetate catalyst of the present invention, the preparation method includes impregnation, reduction and other steps to obtain the vinyl acetate catalyst. A long-chain alkyl metal quaternary ammonium salt solution is added to the impregnation solution, preferably a quaternary ammonium salt with a specific structure and a limited amount of the quaternary ammonium salt. The catalyst prepared by this method, when used in the ethylene-based vinyl acetate production reaction, has the advantages of high space-time yield and high selectivity of the target product.

[0030] 3. The vinyl acetate catalyst of the present invention is suitable for the vinyl acetate preparation reaction in the ethylene process, and has the advantages of high space-time yield and high selectivity of the target product. Detailed Implementation

[0031] In this invention, the zeta potential of the catalyst in each example was measured using a Malvern zeta potential meter. The parameters were: test solution volume 0.75–1.5 mL, measurement time 1–2 min / run, and test temperature 25°C. The test method is as follows:

[0032] (1) Place the catalyst sample in deionized water and sonicate for 1 hour; wherein the volume ratio of the catalyst sample to deionized water is 1:100.

[0033] (2) Take the above-mentioned ultrasonically treated mixture and place it in the sample cell. Select a saturated potassium acetate solution as the reference sample, measure the Zeta potential of the sample and record the value.

[0034] In this invention, the content of each component in the product in each example was analyzed by gas chromatography using an Agilent gas chromatograph. The test parameters were: injection volume: 1 μL, flow rate: 1 mL / min, column temperature rise rate: 20 °C / min.

[0035] In this invention, the structural formulas of the long-chain alkyl metal quaternary ammonium salts (denoted as quaternary ammonium salt M) in each example are as follows:

[0036]

[0037] The preparation method of the long-chain alkyl metal quaternary ammonium salt is as follows:

[0038] (1) Add dodecyltrimethylammonium bromide, ferric chloride, and 2-hydrazyl-2-imidazoline hydrobromide in equimolar proportions to a methanol solution, wherein the total mass ratio of dodecyltrimethylammonium bromide, ferric chloride, and 2-hydrazyl-2-imidazoline hydrobromide to methanol is 5:95. Stir at 80°C for 24 hours (400 rpm).

[0039] (2) The solid sample was obtained by filtration and then vacuum dried at 60°C for 12 hours. The result is the target product.

[0040] Example 1

[0041] 1. Catalyst Preparation

[0042] (a) Take 1100 mL of spherical silica carrier (5 mm in diameter, with a specific surface area of ​​175 m²) 2 / g, pore volume 0.8cm 3 The catalyst precursor I was prepared by impregnating a mixture of chloropalladic acid and chloroauric acid in an aqueous solution with a solid-liquid volume ratio of 1:1.2. The palladium content in the solution was 2.75 g / L and the gold content was 0.625 g / L. After impregnation for 30 minutes, the catalyst was dried at 80 °C for 1 hour.

[0043] (b) Add an aqueous sodium silicate solution (60 mmol / L) to catalyst precursor I, wherein the ratio of the total molar amount of palladium and gold to the molar amount of sodium silicate is 1:1.2. After mixing thoroughly, let stand for 24 hours, and then dry at 80°C for 8 hours to obtain catalyst precursor II;

[0044] (c) The reducing agent and the total molar ratio of palladium and gold were 1:1.5. The hydrazine hydrate solution (concentration of 85wt%) was added for reduction, and the mixture was allowed to stand for 4 hours. Then it was washed with deionized water and dried at 100°C for 6 hours to obtain catalyst precursor III.

[0045] (d) The catalyst precursor III was impregnated in an aqueous solution of quaternary ammonium salt M (solution concentration of 200 mmol / L) for 48 hours with a solid-liquid volume ratio of 1:1.2, and then dried at 100 °C for 12 hours to obtain the catalyst precursor IV.

[0046] (e) The catalyst precursor IV was impregnated with an aqueous solution of potassium acetate and dried at 80°C for 2 hours to obtain the finished catalyst, so that the potassium acetate content in the catalyst was 30 g / L.

[0047] The catalyst composition in this example includes: 2.75 g / L Pd, 0.625 g / L Au, 30 g / L alkali metal acetate, and 400 g / L support. The surface zeta potential of the Pd-Au catalyst in this example is 42 mV.

[0048] 2. Catalyst Evaluation

[0049] The evaluation was conducted using a fixed-bed reactor, under the following conditions:

[0050] Catalyst loading volume: 60 ml;

[0051] Composition of reaction raw materials (in molar ratio): Oxygen: Ethylene: Nitrogen: Acetic acid = 1:6:7.5:1.5;

[0052] Reactant feed volume hourly space velocity: 2000 hr -1 ;

[0053] Reaction pressure: 0.7 MPa;

[0054] Reaction temperature: 150℃;

[0055] Reaction time: 130 hours;

[0056] The content of each component in the reaction product was analyzed by gas chromatography, and then the space-time yield and selectivity of vinyl acetate were calculated.

[0057] For ease of comparison, the experimental results are listed in Table 1.

[0058] Example 2

[0059] 1. Catalyst Preparation

[0060] (a) Take 1100 mL of spherical silica carrier (5 mm in diameter, with a specific surface area of ​​175 m²) 2 / g, pore volume 0.8cm 3 The catalyst precursor I was prepared by impregnating a mixture of chloropalladic acid and chloroauric acid in an aqueous solution with a solid-liquid volume ratio of 1:1.2. The palladium content in the solution was 2.75 g / L and the gold content was 0.625 g / L. After impregnation for 30 minutes, the catalyst was dried at 80 °C for 1 hour.

[0061] (b) Add an aqueous sodium silicate solution (60 mmol / L) to catalyst precursor I, wherein the ratio of the total molar amount of palladium and gold to the molar amount of sodium silicate is 1:1.2. After mixing thoroughly, let stand for 24 hours, and then dry at 80°C for 8 hours to obtain catalyst precursor II;

[0062] (c) The reducing agent and the total molar ratio of palladium and gold were 1:1.5. The hydrazine hydrate solution (concentration of 85wt%) was added for reduction, and the mixture was allowed to stand for 4 hours. Then it was washed with deionized water and dried at 100°C for 6 hours to obtain catalyst precursor III.

[0063] (d) The catalyst precursor III was impregnated in an aqueous solution of quaternary ammonium salt M (solution concentration of 200 mmol / L) for 48 hours with a solid-liquid volume ratio of 1:1.0, and then dried at 100 °C for 12 hours to obtain the catalyst precursor IV.

[0064] (e) The catalyst precursor IV was impregnated with an aqueous solution of potassium acetate and dried at 80°C for 2 hours to obtain the finished catalyst, so that the potassium acetate content in the catalyst was 30 g / L.

[0065] The catalyst composition in this example includes: 2.75 g / L Pd, 0.625 g / L Au, 30 g / L alkali metal acetate, and 400 g / L support. The surface zeta potential of the Pd-Au catalyst in this example is 35 mV.

[0066] 2. Catalyst Evaluation

[0067] The catalyst evaluation method is the same as in Example 1.

[0068] For ease of comparison, the experimental results are listed in Table 1.

[0069] Example 3

[0070] 1. Catalyst Preparation

[0071] (a) Take 1100 mL of spherical silica carrier (5 mm in diameter, with a specific surface area of ​​175 m²) 2 / g, pore volume 0.8cm 3 The catalyst precursor I was prepared by impregnating a mixture of chloropalladic acid and chloroauric acid in an aqueous solution with a solid-liquid volume ratio of 1:1.2. The palladium content in the solution was 2.75 g / L and the gold content was 0.625 g / L. After impregnation for 30 minutes, the catalyst was dried at 80 °C for 1 hour.

[0072] (b) Add an aqueous sodium silicate solution (60 mmol / L) to catalyst precursor I, wherein the ratio of the total molar amount of palladium and gold to the molar amount of sodium silicate is 1:1.2. After mixing thoroughly, let stand for 24 hours, and then dry at 80°C for 8 hours to obtain catalyst precursor II;

[0073] (c) The reducing agent and the total molar ratio of palladium and gold were 1:1.5. The hydrazine hydrate solution (concentration of 85wt%) was added for reduction, and the mixture was allowed to stand for 4 hours. Then it was washed with deionized water and dried at 100°C for 6 hours to obtain catalyst precursor III.

[0074] (d) The catalyst precursor III was impregnated in an aqueous solution of quaternary ammonium salt M (solution concentration of 200 mmol / L) for 48 hours according to a solid-liquid volume ratio of 1:1.4, and then dried at 100 °C for 12 hours to obtain the catalyst precursor IV.

[0075] (e) The catalyst precursor IV was impregnated with an aqueous solution of potassium acetate and dried at 80°C for 2 hours to obtain the finished catalyst, so that the potassium acetate content in the catalyst was 30 g / L.

[0076] The catalyst composition in this example includes: 2.75 g / L Pd, 0.625 g / L Au, 30 g / L alkali metal acetate, and 400 g / L support. The surface zeta potential of the Pd-Au catalyst in this example is 48 mV.

[0077] 2. Catalyst Evaluation

[0078] The catalyst evaluation method is the same as in Example 1.

[0079] For ease of comparison, the experimental results are listed in Table 1.

[0080] Example 4

[0081] 1. Catalyst Preparation

[0082] (a) Take 1100 mL of spherical silica carrier (5 mm in diameter, with a specific surface area of ​​175 m²) 2 / g, pore volume 0.8cm 3 The catalyst precursor I was prepared by impregnating a mixture of chloropalladic acid and chloroauric acid in an aqueous solution with a solid-liquid volume ratio of 1:1.2. The palladium content in the solution was 2.75 g / L and the gold content was 0.625 g / L. After impregnation for 30 minutes, the catalyst was dried at 80 °C for 1 hour.

[0083] (b) Add an aqueous sodium silicate solution (60 mmol / L) to catalyst precursor I, wherein the ratio of the total molar amount of palladium and gold to the molar amount of sodium silicate is 1:1.2. After mixing thoroughly, let stand for 24 hours, and then dry at 80°C for 8 hours to obtain catalyst precursor II;

[0084] (c) The reducing agent and the total molar ratio of palladium and gold were 1:1.5. The hydrazine hydrate solution (concentration of 85wt%) was added for reduction, and the mixture was allowed to stand for 4 hours. Then it was washed with deionized water and dried at 100°C for 6 hours to obtain catalyst precursor III.

[0085] (d) The catalyst precursor III was impregnated in an aqueous solution of quaternary ammonium salt M (solution concentration of 200 mmol / L) for 48 hours with a solid-liquid volume ratio of 1:0.9, and then dried at 100 °C for 12 hours to obtain the catalyst precursor IV.

[0086] (e) The catalyst precursor IV was impregnated with an aqueous solution of potassium acetate and dried at 80°C for 2 hours to obtain the finished catalyst, so that the potassium acetate content in the catalyst was 30 g / L.

[0087] The catalyst composition in this example includes: 2.75 g / L Pd, 0.625 g / L Au, 30 g / L alkali metal acetate, and 400 g / L support. The surface zeta potential of the Pd-Au catalyst in this example is 30 mV.

[0088] 2. Catalyst Evaluation

[0089] The catalyst evaluation method is the same as in Example 1.

[0090] For ease of comparison, the experimental results are listed in Table 1.

[0091] Example 5

[0092] 1. Catalyst Preparation

[0093] (a) Take 1100 mL of spherical silica carrier (5 mm in diameter, with a specific surface area of ​​175 m²) 2 / g, pore volume 0.8cm 3 The catalyst precursor I was prepared by impregnating a mixture of chloropalladic acid and chloroauric acid in an aqueous solution with a solid-liquid volume ratio of 1:1.2. The palladium content in the solution was 2.75 g / L and the gold content was 0.625 g / L. After impregnation for 30 minutes, the catalyst was dried at 80 °C for 1 hour.

[0094] (b) Add an aqueous sodium silicate solution (60 mmol / L) to catalyst precursor I, wherein the ratio of the total molar amount of palladium and gold to the molar amount of sodium silicate is 1:1.2. After mixing thoroughly, let stand for 24 hours, and then dry at 80°C for 8 hours to obtain catalyst precursor II;

[0095] (c) The reducing agent and the total molar ratio of palladium and gold were 1:1.5. The hydrazine hydrate solution (concentration of 85wt%) was added for reduction, and the mixture was allowed to stand for 4 hours. Then it was washed with deionized water and dried at 100°C for 6 hours to obtain catalyst precursor III.

[0096] (d) The catalyst precursor III was impregnated in an aqueous solution of quaternary ammonium salt M (solution concentration of 200 mmol / L) for 48 hours with a solid-liquid volume ratio of 1:1.8, and then dried at 100 °C for 12 hours to obtain the catalyst precursor IV.

[0097] (e) The catalyst precursor IV was impregnated with an aqueous solution of potassium acetate and dried at 80°C for 2 hours to obtain the finished catalyst, so that the potassium acetate content in the catalyst was 30 g / L.

[0098] The catalyst composition in this example includes: 2.75 g / L Pd, 0.625 g / L Au, 30 g / L alkali metal acetate, and 400 g / L support. The surface zeta potential of the Pd-Au catalyst in this example is 63 mV.

[0099] 2. Catalyst Evaluation

[0100] The catalyst evaluation method is the same as in Example 1.

[0101] For ease of comparison, the experimental results are listed in Table 1.

[0102] Example 6

[0103] 1. Catalyst Preparation

[0104] (a) Take 1100 mL of spherical silica carrier (5 mm in diameter, with a specific surface area of ​​175 m²) 2 / g, pore volume 0.8cm 3 The catalyst precursor I was prepared by impregnating a mixture of chloropalladic acid and chloroauric acid in an aqueous solution with a solid-liquid volume ratio of 1:1.2, wherein the palladium content in the solution was 1.0 g / L and the gold content was 0.1 g / L. After impregnation for 30 minutes, the catalyst was dried at 80 °C for 1 hour.

[0105] (b) Add an aqueous sodium silicate solution (60 mmol / L) to catalyst precursor I, wherein the ratio of the total molar amount of palladium and gold to the molar amount of sodium silicate is 1:1.2. After mixing thoroughly, let stand for 24 hours, and then dry at 80°C for 8 hours to obtain catalyst precursor II;

[0106] (c) The reducing agent and the total molar ratio of palladium and gold were 1:1.5. The hydrazine hydrate solution (concentration of 85wt%) was added for reduction, and the mixture was allowed to stand for 4 hours. Then it was washed with deionized water and dried at 100°C for 6 hours to obtain catalyst precursor III.

[0107] (d) The catalyst precursor III was impregnated in an aqueous solution of quaternary ammonium salt M (solution concentration of 200 mmol / L) for 48 hours with a solid-liquid volume ratio of 1:1.2, and then dried at 100 °C for 12 hours to obtain the catalyst precursor IV.

[0108] (e) The catalyst precursor IV was impregnated with an aqueous solution of potassium acetate and dried at 80°C for 2 hours to obtain the finished catalyst, so that the potassium acetate content in the catalyst was 30 g / L.

[0109] The catalyst composition in this example includes: 1.0 g / L Pd, 0.1 g / L Au, 30 g / L alkali metal acetate, and 400 g / L support. The surface zeta potential of the Pd-Au catalyst in this example is 42 mV.

[0110] 2. Catalyst Evaluation

[0111] The catalyst evaluation method is the same as in Example 1.

[0112] For ease of comparison, the experimental results are listed in Table 1.

[0113] Example 7

[0114] 1. Catalyst Preparation

[0115] (a) Take 1100 mL of spherical silica carrier (5 mm in diameter, with a specific surface area of ​​175 m²) 2 / g, pore volume 0.8cm 3 The catalyst precursor I was prepared by impregnating a mixture of chloropalladic acid and chloroauric acid in an aqueous solution with a solid-liquid volume ratio of 1:1.2, wherein the palladium content in the solution was 12.0 g / L and the gold content was 10.0 g / L. After impregnation for 30 minutes, the catalyst was dried at 80 °C for 1 hour.

[0116] (b) Add an aqueous sodium silicate solution (60 mmol / L) to catalyst precursor I, wherein the ratio of the total molar amount of palladium and gold to the molar amount of sodium silicate is 1:1.2. After mixing thoroughly, let stand for 24 hours, and then dry at 80°C for 8 hours to obtain catalyst precursor II;

[0117] (c) The reducing agent and the total molar ratio of palladium and gold were 1:1.5. The hydrazine hydrate solution (concentration of 85wt%) was added for reduction, and the mixture was allowed to stand for 4 hours. Then it was washed with deionized water and dried at 100°C for 6 hours to obtain catalyst precursor III.

[0118] (d) The catalyst precursor III was impregnated in an aqueous solution of quaternary ammonium salt M (solution concentration of 200 mmol / L) for 48 hours with a solid-liquid volume ratio of 1:1.2, and then dried at 100 °C for 12 hours to obtain the catalyst precursor IV.

[0119] (e) The catalyst precursor IV was impregnated with an aqueous solution of potassium acetate and dried at 80°C for 2 hours to obtain the finished catalyst, so that the potassium acetate content in the catalyst was 30 g / L.

[0120] The catalyst composition in this example includes: 12 g / L Pd, 10 g / L Au, 30 g / L alkali metal acetate, and 400 g / L support. The surface zeta potential of the Pd-Au catalyst in this example is 42 mV.

[0121] 2. Catalyst Evaluation

[0122] The catalyst evaluation method is the same as in Example 1.

[0123] For ease of comparison, the experimental results are listed in Table 1.

[0124] Comparative Example 1

[0125] 1. Catalyst Preparation

[0126] (a) Take 1100 mL of spherical silica carrier (5 mm in diameter, with a specific surface area of ​​175 m²) 2 / g, pore volume 0.8cm 3 The catalyst precursor I was prepared by impregnating a mixture of chloropalladic acid and chloroauric acid in an aqueous solution with a solid-liquid volume ratio of 1:1.2. The palladium content in the solution was 2.75 g / L and the gold content was 0.625 g / L. After impregnation for 30 minutes, the catalyst was dried at 80 °C for 1 hour.

[0127] (b) Add an aqueous sodium silicate solution (60 mmol / L) to catalyst precursor I, wherein the ratio of the total molar amount of palladium and gold to the molar amount of sodium silicate is 1:1.2. After mixing thoroughly, let stand for 24 hours, and then dry at 80°C for 8 hours to obtain catalyst precursor II;

[0128] (c) The reducing agent and the total molar ratio of palladium and gold were 1:1.5. The hydrazine hydrate solution (concentration of 85wt%) was added for reduction, and the mixture was allowed to stand for 4 hours. Then it was washed with deionized water and dried at 100°C for 6 hours to obtain catalyst precursor III.

[0129] (d) Catalyst precursor III was impregnated in an aqueous solution of dodecyltrimethylammonium bromide (solution concentration of 200 mmol / L) for 48 hours with a solid-liquid volume ratio of 1:1.0, and then dried at 100 °C for 12 hours to obtain catalyst precursor IV.

[0130] (e) The catalyst precursor IV was impregnated with an aqueous solution of potassium acetate and dried at 80°C for 2 hours to obtain the finished catalyst, so that the potassium acetate content in the catalyst was 30 g / L.

[0131] The catalyst composition in this example includes: 2.75 g / L Pd, 0.625 g / L Au, 30 g / L alkali metal acetate, and 400 g / L support. The surface zeta potential of the Pd-Au catalyst in this example is 18 mV.

[0132] 2. Catalyst Evaluation

[0133] The catalyst evaluation method is the same as in Example 1.

[0134] For ease of comparison, the experimental results are listed in Table 1.

[0135] Comparative Example 2

[0136] 1. Catalyst Preparation

[0137] (a) Take 1100 mL of spherical silica carrier (5 mm in diameter, with a specific surface area of ​​175 m²) 2 / g, pore volume 0.8cm 3 The catalyst precursor I was prepared by impregnating a mixture of chloropalladic acid and chloroauric acid in an aqueous solution with a solid-liquid volume ratio of 1:1.2. The palladium content in the solution was 2.75 g / L and the gold content was 0.625 g / L. After impregnation for 30 minutes, the catalyst was dried at 80 °C for 1 hour.

[0138] (b) Add an aqueous sodium silicate solution (60 mmol / L) to catalyst precursor I, wherein the ratio of the total molar amount of palladium and gold to the molar amount of sodium silicate is 1:1.2. After mixing thoroughly, let stand for 24 hours, and then dry at 80°C for 8 hours to obtain catalyst precursor II;

[0139] (c) The reducing agent and the total molar ratio of palladium and gold were 1:1.5. The hydrazine hydrate solution (concentration of 85wt%) was added for reduction, and the mixture was allowed to stand for 4 hours. Then it was washed with deionized water and dried at 100°C for 6 hours to obtain catalyst precursor III.

[0140] (d) The catalyst precursor III was impregnated with an aqueous solution of potassium acetate and dried at 80°C for 2 hours to obtain the finished catalyst, so that the potassium acetate content in the catalyst was 30 g / L.

[0141] The catalyst composition in this example includes: 2.75 g / L Pd, 0.625 g / L Au, 30 g / L alkali metal acetate, and 400 g / L support. The surface zeta potential of the Pd-Au catalyst in this example is 11 mV.

[0142] 2. Catalyst Analysis and Evaluation

[0143] The catalyst evaluation method is the same as in Example 1.

[0144] For ease of comparison, the experimental results are listed in Table 1.

[0145] Table 1

[0146]

[0147] The specific embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combining the various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A catalyst for preparing vinyl acetate, characterized in that, The catalyst comprises a support and Pd, Au and alkali metal acetate supported on the support; the Zeta potential of Pd-Au on the catalyst surface is 30~65 mV.

2. The catalyst according to claim 1, characterized in that, The Zeta potential of Pd-Au on the catalyst surface is 35~48 mV.

3. The catalyst according to claim 1, characterized in that, The content of Pd is 1~12 g / L; and / or, the content of Au is 0.1~10 g / L; and / or, the content of alkali metal acetate is 10~100 g / L; and / or, the content of the carrier is 250~500 g / L.

4. The catalyst according to claim 1, characterized in that, The alkali metal acetate includes at least one of potassium acetate and sodium acetate; and / or the support includes at least one of silicon dioxide and aluminum oxide.

5. A method for preparing the catalyst according to any one of claims 1 to 4, comprising the following steps: (a) The support was impregnated in a solution containing palladium and gold to obtain catalyst precursor I; (b) Catalyst precursor I was treated with an alkaline compound to obtain catalyst precursor II; (c) Catalyst precursor II and reducing agent are mixed to prepare catalyst precursor III; (d) Catalyst precursor III was impregnated in a solution containing a long-chain alkyl metal quaternary ammonium salt to prepare catalyst precursor IV; (e) The catalyst precursor IV is impregnated in an alkali metal acetate to obtain the catalyst; the long-chain alkyl metal quaternary ammonium salt in step (d) has the following structural formula: 。 6. The method according to claim 5, characterized in that, In step (d), the concentration of the long-chain alkyl metal quaternary ammonium salt solution is 10 to 500 mmol / L; and / or, the solid-liquid volume ratio in step (d) is 1:0.8 to 1:2.

0.

7. The method according to claim 5, characterized in that, In step (d), the concentration of the long-chain alkyl metal quaternary ammonium salt solution is 180~220 mmol / L; and / or, the solid-liquid volume ratio in step (d) is 1:1~1:1.

5.

8. The method according to claim 5, characterized in that, The alkaline compound mentioned in step (b) includes sodium silicate; and / or, the ratio of the molar number of the alkaline compound to the total molar number of palladium and gold is 1:1 to 2:

1.

9. The method according to claim 5, characterized in that, The reducing agent mentioned in step (c) includes hydrazine hydrate; and / or the ratio of the reducing agent to the total molar amount of palladium and gold is 1:1 to 2:

1.

10. The application of the catalyst according to any one of claims 1 to 4 or the catalyst prepared by the preparation method according to any one of claims 5 to 9 in the ethylene-based vinyl acetate synthesis reaction.

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