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

Abstract

The invention provides a catalyst for preparing vinyl acetate as well as a preparation method and application of the catalyst. The catalyst comprises a carrier, an active component and an auxiliary agent, wherein the carrier is an oxide at least containing silicon dioxide; the active component comprises at least one of Pd, Cu, Au and Sn, and at least comprises Pd; the auxiliary agent is alkali metal acetate. The catalyst provided by the invention can be applied to preparation of vinyl acetate from C2-C4 olefin, acetic acid and oxygen as raw materials. The method provided by the invention avoids the risk of temperature runaway of the catalyst bed layer and the rapid deactivation of the catalyst caused by temperature runaway, and effectively improves the stability of the catalyst and the operation safety of the device.

Description

Technical Field

[0001] The invention belongs to the field of catalysts, and in particular relates to a catalyst for preparing vinyl acetate, a preparation method and an application thereof. Background Art

[0002] Vinyl acetate is an important organic synthesis intermediate, and typical vinyl acetates include vinyl acetate, allyl acetate, methacrylic acetate, etc. Among them, vinyl acetate is used to produce polyvinyl alcohol, VAE emulsion, PVAC emulsion, plastics, coatings, adhesives, etc.; allyl acetate, as an important chemical raw material, is mainly used to produce important organic synthesis raw materials such as allyl alcohol, epichlorohydrin, glycerol, and is also used in the synthesis of resins and adhesives.

[0003] CN1153755C records a catalyst for producing vinyl acetate. The catalyst preparation process sintered the palladium on the carrier at a temperature higher than 500°C to avoid the initial activity of the catalyst being too high and the reactor's limited heat transfer capacity, which would cause the catalyst to be deactivated, thereby extending the life of the catalyst. However, the high-temperature calcination of the catalyst in industrial production consumes a lot of energy, resulting in high production costs for the catalyst.

[0004] CN1104951C records a catalyst for producing vinyl acetate. The catalyst preparation process includes heating at about 100-600°C in a non-reducing atmosphere for calcination and reducing at 450-500°C. A highly selective catalyst can be prepared. However, the catalyst has high energy consumption due to multiple calcinations in industrial production, resulting in high production costs for the catalyst.

[0005] CN 103120961 B describes an allyl acetate catalyst and a preparation method thereof. The catalyst uses SiO2, Al2O3 or a mixture thereof as a carrier, and carries active components including metal palladium, metal copper and alkali metal acetate, and the average particle size of palladium copper grains is 5-7nm; during the catalyst preparation process, liquid carbon dioxide is used as an impregnation liquid, and the palladium compound used is an acetylacetone group as a ligand. The raw materials used in the preparation method are expensive, resulting in excessively high production costs and lack of economic feasibility for industrial application.

[0006] US3830834A describes a method for continuously preparing vinyl acetate. In order to maintain the activity and selectivity of the catalyst during the continuous preparation of vinyl acetate, it is necessary to continuously replenish alkali metal acetate. Continuous replenishment of alkali metal acetate requires additional equipment investment and increases the complexity of the process, which is not conducive to industrial low-cost application.

[0007] In summary, the current problem in the preparation process of vinyl acetate is that the initial activity of the catalyst is still too high, which easily causes reactor overheating and sintering and deactivation of the active components of the catalyst, and needs to be solved urgently. Summary of the invention

[0008] One of the purposes of the present invention is to provide a catalyst for acetyl oxidation. The acetyl oxidation catalyst preparation process avoids the risk of temperature runaway in the catalyst bed and the rapid deactivation of the catalyst due to temperature runaway, and effectively improves the stability of the catalyst and the safety of the device operation.

[0009] In order to achieve the above-mentioned invention object, the technical solution adopted by the present invention is as follows:

[0010] A catalyst for preparing vinyl acetate, the catalyst comprising a carrier, an active component and an auxiliary agent; wherein the carrier is an oxide containing at least silicon dioxide; the active component contains at least one of Pd, Cu, Au and Sn, and contains at least Pd; and the auxiliary agent is an alkali metal acetate.

[0011] In one embodiment of the present invention, the Pd loading in the catalyst is 2-8 g / L.

[0012] In one embodiment of the present invention, the active component is an active component pretreated with an oxygen-containing atmosphere and an organic acid; preferably, the organic acid is a small molecule organic acid, preferably comprising a C1-C4 organic acid, more preferably comprising one or more of acetic acid, formic acid, propionic acid, and butyric acid.

[0013] The inventors have found that in the process of preparing vinyl acetate, after the active component is treated with a certain concentration of organic acid and oxygen, the grain distribution of the active component is more uniform, which avoids the active component grains being too small and causing the initial activity of the catalyst to be too high, avoids the risk of temperature runaway in the catalyst bed and the rapid deactivation of the catalyst due to temperature runaway, and can effectively improve the stability of the catalyst and the safety of the device operation.

[0014] In one embodiment of the present invention, the alkali metal acetate comprises one or more of sodium acetate, potassium acetate, and cesium acetate.

[0015] In one embodiment of the present invention, the alkali metal acetate in the catalyst is supported in a molten state or a gaseous state by cooling.

[0016] In one embodiment of the present invention, the alkali metal acetate is distributed on the outer surface of the carrier particles and extends to a depth of no more than 1 / 3 of the dimension from the outer surface to the center of the carrier.

[0017] In one embodiment of the present invention, the loading amount of alkali metal acetate in the catalyst is 10-100 g / L.

[0018] Another object of the present invention is to provide a method for preparing a catalyst. In the preparation process of the acetyl oxidation catalyst, the auxiliary agent alkali metal acetate is cooled in a molten state or a gaseous state and loaded on the outer surface of the carrier particles, extending to a depth not greater than one-third of the dimension from the outer surface to the center of the carrier, and the alkali metal acetate is mainly distributed on the outer surface of the catalyst.

[0019] A method for preparing a catalyst, the method comprising the following steps:

[0020] S1: Loading and fixing active components: Mixing a solution containing an elemental salt of an active component with a carrier, placing the carrier in an alkaline solution to fix the active component, and obtaining a catalyst precursor I;

[0021] S2: Reduction of active components: Reducing agent reduces precursor I, washing and drying to obtain catalyst precursor II;

[0022] S3: Loading auxiliary agent: Precursor II is heated, alkali metal acetate and precursor II are uniformly mixed, alkali metal acetate is cooled and loaded onto the surface of precursor II in a molten state or a gaseous state, and the temperature is lowered to obtain catalyst precursor III;

[0023] S4: Aging treatment: The precursor III is placed in an organic acid and oxygen-containing atmosphere for treatment to obtain the target catalyst.

[0024] In one embodiment of the present invention, the active ingredient element salt described in S1 comprises one or more soluble chloride, nitrate, acetate, and sulfide aqueous solutions.

[0025] In one embodiment of the present invention, the support in S1 is an oxide comprising at least silicon dioxide.

[0026] In one embodiment of the present invention, the base in S1 is an alkali metal-containing base, preferably comprising one or more of sodium metasilicate, potassium metasilicate, sodium carbonate, sodium bicarbonate, potassium carbonate, sodium hydroxide and potassium hydroxide.

[0027] In one embodiment of the present invention, the reducing agent in S2 is a liquid phase reducing agent and / or a gas phase reducing agent, preferably comprising one or more of hydrazine hydrate, sodium borohydride, formaldehyde, glucose, hydrogen, ethylene, and propylene.

[0028] In one embodiment of the present invention, the amount of the reducing agent in S2 is 1-25 times the amount used to reduce the active component to a single substance state.

[0029] In one embodiment of the present invention, the heating temperature in S3 is 100-500°C.

[0030] In one embodiment of the present invention, the alkali metal acetate in S3 comprises one or more of sodium acetate, potassium acetate, and cesium acetate.

[0031] In one embodiment of the present invention, the mixing time in S3 is 10-120 min.

[0032] In one embodiment of the present invention, S3 is carried out in an inert atmosphere; preferably, the inert atmosphere comprises one or more of nitrogen, argon, helium and carbon dioxide.

[0033] In one embodiment of the present invention, the organic acid in S4 is a small molecule organic acid, preferably comprising C1-C4 organic acids, more preferably comprising one or more of acetic acid, formic acid, propionic acid, butyric acid; preferably, the concentration of the organic acid is 3-20 mol%, based on the total molar amount of the gas. The reason why the present invention is based on the total molar amount of the gas is that, in some embodiments, the organic acid is gasified to form a gas, and the gas composition includes organic acid, oxygen and nitrogen.

[0034] In one embodiment of the present invention, the oxygen-containing atmosphere in S4 comprises one or more of pure oxygen, air, and a nitrogen-oxygen mixture; preferably, the oxygen concentration is 1-10 mol%, based on the total molar amount of the gas.

[0035] In one embodiment of the present invention, the temperature of the treatment in S4 is 100-200° C., and the treatment time is 1-48 h.

[0036] Another object of the present invention is to provide a use of a catalyst.

[0037] A use of a catalyst, wherein the catalyst is the above catalyst, or is a catalyst prepared by the above method, and the catalyst is used to prepare alkenyl acetate, preferably to prepare allyl acetate.

[0038] Another object of the present invention is to provide a method for preparing alkenyl acetate. Under the action of the catalyst provided by the present invention, no alkali metal acetate needs to be added during the preparation of alkenyl acetate, thereby simplifying the preparation process of alkenyl acetate and reducing production costs.

[0039] A method for preparing alkenyl acetate, the method adopts the above catalyst, or adopts the catalyst prepared by the above method, and the method uses C2-C4 olefin, acetic acid and oxygen as raw materials to catalyze the preparation of alkenyl acetate.

[0040] In one embodiment of the present invention, the molar ratio of C2-C4 olefin: acetic acid: oxygen: water = 1: (0.1-0.5): (0.1-0.5): (0-0.6);

[0041] In one embodiment of the present invention, in the method for preparing vinyl acetate, the raw material volume space velocity is 1000-3000h -1 .

[0042] In one embodiment of the present invention, in the method for preparing vinyl acetate, the reaction temperature is 120-180° C. and the pressure is 0.1-1.5 MPaG.

[0043] In one embodiment of the present invention, in the process for preparing alkenyl acetate, no additional alkali metal acetate is added during the process.

[0044] Compared with the prior art, the present invention has the following beneficial effects:

[0045] 1) It avoids the risk of temperature runaway in the catalyst bed and the rapid deactivation of the catalyst caused by temperature runaway, and effectively improves the stability of the catalyst and the safety of the device operation.

[0046] 2) In the process of preparing alkenyl acetate, no alkali metal acetate needs to be added, thus optimizing the preparation process of alkenyl acetate and reducing production costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 This is the distribution of potassium acetate elements in the catalyst cross section of Example 1, where the darker part on the shell side is the distribution area of ​​potassium acetate. DETAILED DESCRIPTION

[0048] The present invention is further described below by means of specific examples. The examples described in the present invention are only used to illustrate the present invention and do not limit the scope of the present invention.

[0049] The calculation method and test method used in the embodiments or comparative examples are as follows:

[0050] 1. Use gas chromatography and Agilent GC 8890A chromatograph to analyze the content of each component in the reaction product, and calculate the activity and selectivity of the catalyst according to the following formula:

[0051]

[0052] 2. Determination method of catalyst element distribution

[0053] The catalyst was cut into two halves using a slicer to obtain a cross section of the catalyst, which was then observed and measured using a Hitachi High-Tech S-4800 scanning electron microscope (SEM).

[0054] 3. Determination of particle size of active components of catalyst

[0055] A certain amount of catalyst was crushed with a mortar to obtain uniform powder, and then the catalyst powder was ultrasonically dispersed in anhydrous ethanol and measured with a JEOL 2100plus transmission electron microscope (TEM).

[0056] Main raw material information:

[0057] Silica gel balls: Qingdao Haiwan Chemical Co., Ltd., model: FNG-II

[0058] Unless otherwise specified, other raw materials are commercially available.

[0059] Example 1

[0060] 1) Preparation of catalyst

[0061] Take 1L of silica gel beads (average particle size 5mm, specific surface area 269m 2 / g, pore volume of 0.82 mL / g, average pore size of 11.3 nm), prepare 352 mL of an aqueous solution of sodium chloropalladate and copper chloride containing 5.0 g Pd and 0.9 g Cu, mix them evenly with silica gel balls, then put the silica gel balls loaded with active components into an aqueous solution containing 800 mL of 42 g sodium metasilicate nonahydrate, soak for 20 h, and obtain precursor I;

[0062] Slowly add 12.5 g of 80 wt% hydrazine hydrate solution to precursor I, reduce for 4 h, wash thoroughly with deionized water, and dry at 120° C. to obtain precursor II;

[0063] Precursor II and 55 g of potassium acetate were placed in a rotary drying furnace, nitrogen was introduced, the temperature was raised to 300°C, the mixture was fully mixed for 0.5 h, and the mixture was cooled to room temperature to obtain catalyst precursor III;

[0064] Precursor III was loaded into a 316L stainless steel fixed bed reactor with an inner diameter of 4.5cm and a length of 150cm and an oil bath jacket. Acetic acid was heated and gasified at 150℃ and then introduced into the reactor. The total gas volume was 3L / min, the acetic acid concentration was 12mol%, the oxygen concentration was 4.0mol%, and the remaining gas was nitrogen. The finished catalyst was obtained after treatment at 140℃ for 12h. According to analysis, the average particle size of the active component was 5.3nm, and there were no active component grains with a particle size less than 2nm; the depth of potassium acetate distributed from the outer surface of the carrier to the center was 125μm, and the depth was 1 / 20 of the size from the outer surface to the center of the carrier.

[0065] 2) Preparation of allyl acetate

[0066] 500 mL of catalyst was placed in a fixed bed reactor with an inner diameter of 3 cm and a height of 150 cm. Inert porcelain balls were loaded at the upper and lower ends of the catalyst. After leak testing with nitrogen, the reaction system was heated up and then the reaction raw materials were introduced. The reaction temperature was 150 ° C, the reaction pressure was 0.65 MPaG, and the volume space velocity was 1900 h -1 The raw material composition is propylene: acetic acid: oxygen: water = 1: 0.4: 0.2: 0.35. After 24 hours of stable reaction, the hot spot temperature is 162.5°C. The mixture obtained by the above reaction is cooled, separated by gas and liquid, and analyzed by gas chromatography. According to the analysis, the catalyst activity is 422g / L·h, and the selectivity of allyl acetate is 97.2%; without adding potassium acetate, after continuous evaluation for 2000 hours, the catalyst activity is 386g / L·h, and the selectivity of allyl acetate is 96.8%. The catalyst activity and selectivity can still meet the requirements of industrial use.

[0067] Example 2

[0068] Take 1L of silica gel beads (average particle size 5mm, specific surface area 269m 2 / g, pore volume of 0.82 mL / g, average pore size of 11.3 nm), prepare 352 mL of an aqueous solution of sodium chloropalladate, copper chloride and chloroauric acid containing 6.0 g Pd, 0.7 g Cu and 0.5 g Au, mix well with silica gel balls, then put the silica gel balls loaded with active components into 900 mL of an aqueous solution containing 19.7 g sodium hydroxide, soak for 10 h, and obtain precursor I;

[0069] The precursor I was reduced in a hydrogen and nitrogen mixed gas at 300°C for 4 hours, washed thoroughly with deionized water, and dried at 120°C to obtain the precursor II;

[0070] Precursor II and 70 g of sodium acetate were placed in a rotary drying furnace, nitrogen was introduced, the temperature was raised to 350°C, the mixture was fully mixed for 1 h, and the mixture was cooled to room temperature to obtain catalyst precursor III;

[0071] Precursor III was loaded into a 316L stainless steel fixed bed reactor with an inner diameter of 4.5cm and a length of 150cm and an oil bath jacket. Acetic acid was heated and gasified at 150℃ and then introduced into the reactor. The total gas volume was 3L / min, the acetic acid concentration was 6.5mol%, the oxygen concentration was 3.0mol%, and the remaining gas was nitrogen. The finished catalyst was obtained after treatment at 150℃ for 24h. According to analysis, the average particle size of the active component was 5.8nm, and there were no active component grains with a particle size less than 2nm; the depth of sodium acetate distributed on the outer surface of the carrier to the center was 203μm, and the depth was 1 / 12 of the size from the outer surface to the center of the carrier.

[0072] 2) Preparation of allyl acetate

[0073] 500 mL of catalyst was placed in a fixed bed reactor with an inner diameter of 3 cm and a height of 150 cm. Inert porcelain balls were loaded at the upper and lower ends of the catalyst. After leak testing with nitrogen, the reaction system was heated up and then the reaction raw materials were introduced. The reaction temperature was 155 ° C, the reaction pressure was 0.80 MPaG, and the volume space velocity was 2100 h -1 The raw material composition is propylene: acetic acid: oxygen: water = 1: 0.3: 0.22: 0.4. After 24 hours of stable reaction, the hot spot temperature is 166.8 ° C. The reaction mixture is cooled, the gas-liquid separation is carried out and then analyzed by gas chromatography. According to the analysis, the catalyst activity is 409g / L / h and the selectivity of allyl acetate is 98.1%. Without the addition of sodium acetate, after 2000 hours of continuous evaluation, the catalyst activity is 377g / L / h and the selectivity of allyl acetate is 97.3%. The catalyst activity and selectivity can still meet the requirements of industrial use.

[0074] Example 3

[0075] Take 1L of silica gel beads (average particle size 5mm, specific surface area 269m 2 / g, pore volume of 0.82 mL / g, average pore size of 11.3 nm), prepare 352 mL of an aqueous solution of sodium chloropalladate and copper chloride containing 4.5 g Pd and 0.8 g Cu, mix them evenly with silica gel balls, then put the silica gel balls loaded with active components into an aqueous solution containing 19 g sodium metasilicate nonahydrate (1200 mL), soak for 16 h, and obtain precursor I;

[0076] Slowly add 40 g of 80% hydrazine hydrate solution to precursor I, reduce for 4 h, wash thoroughly with deionized water, and dry at 120° C. to obtain precursor II;

[0077] Precursor II and 50 g of potassium acetate were placed in a rotary drying furnace, nitrogen was introduced, the temperature was raised to 250°C, the mixture was fully mixed for 2 h, and the mixture was cooled to room temperature to obtain catalyst precursor III;

[0078] Precursor III was loaded into a 316L stainless steel fixed bed reactor with an inner diameter of 4.5cm and a length of 150cm and an oil bath jacket. Propionic acid was heated and gasified at 200℃ and then introduced into the reactor. The total gas volume was 3L / min, the concentration of propionic acid was 10mol%, the concentration of oxygen was 3.8mol%, and the remaining gas was nitrogen. The finished catalyst was obtained after being treated at 160℃ for 8h. According to analysis, the average particle size of the active component was 4.8nm, and there were no active component grains with a particle size less than 2nm; the depth of potassium acetate distributed from the outer surface of the carrier to the center was 248μm, and the depth was 1 / 10 of the size from the outer surface to the center of the carrier.

[0079] 2) Preparation of allyl acetate

[0080] The catalyst evaluation conditions were the same as those in Example 1. After 24 hours of stable reaction, the hot spot temperature was 163.0°C. The mixture obtained by the reaction was cooled, separated into gas and liquid, and analyzed by gas chromatography. After analysis, the catalyst activity was 439 g / L / h, and the selectivity of allyl acetate was 97.0%. Without supplementing potassium acetate, after continuous evaluation for 2000 hours, the catalyst activity was 392 g / L / h, and the selectivity of allyl acetate was 96.5%. The catalyst activity and selectivity can still meet the requirements for industrial use.

[0081] Comparative Example 1

[0082] During the catalyst preparation process, no organic acid and oxygen atmosphere treatment were used, and the remaining preparation conditions were the same as in Example 1.

[0083] 1) Preparation of catalyst

[0084] After analysis, the average particle size of the active component is 4.2nm, and the active component grains smaller than 2nm account for 16.6%; the depth of potassium acetate distributed on the outer surface of the carrier to the center is 120μm, and the depth is 1 / 21 of the size from the outer surface to the center of the carrier.

[0085] 2) Preparation of allyl acetate

[0086] The catalyst evaluation conditions were the same as in Example 1. After 24 hours of stable reaction, the hot spot temperature was 172.4°C. The mixture obtained by the reaction was cooled, separated into gas and liquid, and analyzed by gas chromatography. After analysis, the catalyst activity was 392 g / L / h, the selectivity of allyl acetate was 90.2%, and the main by-product was carbon dioxide. After continuous evaluation for 2000 hours, the catalyst activity was 313 g / L / h, the selectivity of allyl acetate was 93.4%, and the catalyst activity could not meet the requirements for industrial use.

[0087] Comparative Example 2

[0088] During the catalyst preparation process, potassium acetate was loaded by a conventional potassium acetate aqueous solution impregnation method, and the remaining preparation conditions were the same as in Example 1.

[0089] 1) Preparation of catalyst

[0090] The analysis showed that the average particle size of the active component was 5.5 nm, and there were no active component grains with a particle size less than 2 nm; potassium acetate was evenly distributed on the inner and outer surfaces of the carrier.

[0091] 2) Preparation of allyl acetate

[0092] The catalyst evaluation conditions were the same as those in Example 1. After 24 hours of stable reaction, the hot spot temperature was 160.8°C. The mixture obtained by the above reaction was cooled, separated into gas and liquid, and analyzed by gas chromatography. After analysis, the catalyst activity was 382g / L / h, and the selectivity of allyl acetate was 96.9%; without supplementing potassium acetate, after continuous evaluation for 1000 hours, the catalyst activity was 302g / L / h, and the selectivity of allyl acetate was 91.3%. The catalyst activity and selectivity could not meet the requirements for industrial use; after supplementing potassium acetate and continuing to operate for 1000 hours, the catalyst activity was partially restored, and the activity was 336g / L / h, and the selectivity of allyl acetate was 93.2%.

[0093] Comparative Example 3

[0094] During the catalyst preparation process, organic acid and oxygen treatment and carrier surface treatment are not used, and potassium acetate is not loaded by molten state or gaseous cooling. The remaining preparation conditions are the same as those in Example 1.

[0095] 1) Preparation of catalyst

[0096] After analysis, the average particle size of the active component is 4.0nm, and the active component particles smaller than 2nm account for 19.2%; potassium acetate is evenly distributed on the inner and outer surfaces of the carrier.

[0097] The catalyst evaluation conditions were the same as those in Example 1. After 24 hours of stable reaction, the hot spot temperature was 173.2°C. The mixture obtained by the reaction was cooled, separated from the gas and liquid, and analyzed by gas chromatography. After analysis, the catalyst activity was 365g / L / h, and the selectivity of allyl acetate was 90.0%. Without supplementing potassium acetate, after continuous evaluation for 1000 hours, the catalyst activity was 288g / L / h, and the selectivity of allyl acetate was 88.7%. The catalyst activity and selectivity could not meet the requirements for industrial use; after continuous supplementation of potassium acetate for 1000 hours, the catalyst activity was partially restored, the activity was 304g / L / h, and the selectivity of allyl acetate was 90.6%. The catalyst activity and selectivity could not meet the requirements for industrial use.

[0098] Comparative Example 4

[0099] During the catalyst preparation process, the catalyst was calcined at 600° C. for 8 h in a nitrogen atmosphere instead of the organic acid and oxygen atmosphere treatment. The remaining preparation conditions were the same as in Example 1.

[0100] 1) Preparation of catalyst

[0101] After analysis, the average particle size of the active component is 5.6nm, and the active component grains smaller than 2nm account for 4.1%; the depth of potassium acetate distributed on the outer surface of the carrier to the center is 129μm, and the depth is 1 / 19 of the size from the outer surface to the center of the carrier.

[0102] 2) Preparation of allyl acetate

[0103] The catalyst evaluation conditions were the same as those in Example 1. After 24 hours of stable reaction, the hot spot temperature was 166.3°C. The mixture obtained by the reaction was cooled, separated into gas and liquid, and analyzed by gas chromatography. After analysis, the catalyst activity was 412 g / L / h, the selectivity of allyl acetate was 95.6%, and the main by-product was carbon dioxide. After continuous evaluation for 2000 hours, the catalyst activity was 346 g / L / h, and the selectivity of allyl acetate was 94.2%. The catalyst activity and selectivity can still meet the requirements for industrial use.

[0104] From the above test results we can see that:

[0105] (1) It can be seen from Example 1 and Comparative Example 1 that the catalyst of Example 1 was treated with organic acid and oxygen during preparation, while the catalyst of Comparative Example 1 was not treated with organic acid and oxygen. The proportion of active component grains smaller than 2 nm in the catalyst of Comparative Example 1 was significantly higher, resulting in excessive oxidation reaction, high hot spot temperature, high selectivity of byproduct carbon dioxide, and the risk of excessive exothermic temperature rise. The long-term activity and selectivity of the catalyst in Comparative Example 1 were significantly lower than those of the catalyst in Example 1;

[0106] (2) It can be seen from Example 1 and Comparative Example 2 that Comparative Example 2 does not use molten state or gaseous state cooling to load potassium acetate. Without replenishing potassium acetate, the catalyst in Comparative Example 2 is operated for a long time for 1000 hours. The long-term activity and selectivity of the catalyst in Example 1 are significantly lower than those of the catalyst in Example 1. After the subsequent replenishment of potassium acetate, the activity and selectivity of the catalyst in Comparative Example 2 are partially restored, but are still lower than those of the catalyst in Example 1.

[0107] (3) By comparing Example 1 with Comparative Example 3, it can be seen that in the catalyst preparation process, organic acid and oxygen treatment are not used, and potassium acetate is not loaded on the carrier surface by molten state or gaseous cooling. The initial hot spot of the catalyst in Comparative Example 3 is high, the side reaction of over-oxidation is obvious, the selectivity of the main reaction is low, and there is a risk of excessive exothermic temperature rise; the long-term activity and selectivity of the catalyst in Comparative Example 3 are significantly lower than those of the catalyst in Example 1.

[0108] (4) By comparing Example 1 with Comparative Example 4, it can be seen that after the high-temperature treatment of the catalyst, the active components can be sintered, and there are still 4.1% active component grains smaller than 2 nm. The hot spots are reduced, but over-oxidation reaction still exists. The selectivity of the catalyst sintered at high temperature is lower than the selectivity of the catalyst treated with organic acid and oxygen; the long-term activity and selectivity are also lower than the activity and selectivity of the catalyst in Example 1.

[0109] The above is only a preferred embodiment of the present invention. It should be pointed out that ordinary technicians in this field can make several improvements and supplements without departing from the method of the present invention. These improvements and supplements should also be regarded as the scope of protection of the present invention.

Claims

1. A catalyst for preparing vinyl acetate, characterized in that: The catalyst comprises a carrier, an active component and an auxiliary agent; Wherein, the carrier is an oxide containing at least silicon dioxide; the active component contains at least one of Pd, Cu, Au, and Sn, and contains at least Pd; and the auxiliary agent is an alkali metal acetate.

2. The catalyst according to claim 1, characterized in that The Pd loading in the catalyst is 2-8 g / L; and / or, the active component is an active component pretreated with an oxygen-containing atmosphere and an organic acid; Preferably, the organic acid is a small molecule organic acid, preferably comprises a C1-C4 organic acid, and more preferably comprises one or more of acetic acid, formic acid, propionic acid, and butyric acid.

3. The catalyst according to claim 1 or 2, characterized in that The alkali metal acetate comprises one or more of sodium acetate, potassium acetate, and cesium acetate; And / or, the alkali metal acetate in the catalyst is supported in a molten state or a gaseous state by cooling; and / or, the alkali metal acetate is distributed on the outer surface of the carrier particles and extends to a depth no greater than 1 / 3 of the dimension from the outer surface to the center of the carrier; And / or, the loading amount of alkali metal acetate in the catalyst is 10-100 g / L.

4. A method for preparing the catalyst according to any one of claims 1 to 3, characterized in that: The method comprises the following steps: S1: Loading and fixing active components: Mixing a solution containing an elemental salt of an active component with a carrier, placing the carrier in an alkaline solution to fix the active component, and obtaining a catalyst precursor I; S2: Reduction of active components: Reducing agent reduces precursor I, washing and drying to obtain catalyst precursor II; S3: Loading auxiliary agent: Precursor II is heated, alkali metal acetate and precursor II are uniformly mixed, alkali metal acetate is cooled and loaded onto the surface of precursor II in a molten state or a gaseous state, and the temperature is lowered to obtain catalyst precursor III; S4: Aging treatment: The precursor III is placed in an organic acid and oxygen-containing atmosphere for treatment to obtain the target catalyst.

5. The preparation method according to claim 4, characterized in that: S1: the active component element salt comprises one or more of soluble chloride, nitrate, acetate and sulfide aqueous solutions; And / or, the carrier in S1 is an oxide containing at least silicon dioxide; And / or, the base in S1 is an alkali containing an alkali metal, preferably comprising one or more of sodium metasilicate, potassium metasilicate, sodium carbonate, sodium bicarbonate, potassium carbonate, sodium hydroxide and potassium hydroxide.

6. The preparation method according to claim 4, characterized in that: The reducing agent in S2 is a liquid phase reducing agent and / or a gas phase reducing agent, preferably comprising one or more of hydrazine hydrate, sodium borohydride, formaldehyde, glucose, hydrogen, ethylene, and propylene; And / or, the amount of the reducing agent in S2 is 1-25 times the amount used to reduce the active component to a single substance state.

7. The preparation method according to claim 4, characterized in that: The heating temperature in S3 is 100-500° C. And / or, the alkali metal acetate in S3 comprises one or more of sodium acetate, potassium acetate, and cesium acetate; And / or, the mixing time in S3 is 10-120 min; and / or, S3 is carried out in an inert atmosphere; Preferably, the inert atmosphere comprises one or more of nitrogen, argon, helium and carbon dioxide.

8. The preparation method according to claim 4, characterized in that: The organic acid in S4 is a small molecule organic acid, preferably a C1-C4 organic acid, more preferably one or more of acetic acid, formic acid, propionic acid, and butyric acid; Preferably, the concentration of the organic acid is 3-20 mol%, based on the total molar amount of the gas; And / or, the oxygen-containing atmosphere in S4 comprises one or more of pure oxygen, air, and a nitrogen-oxygen mixture; Preferably, the oxygen concentration is 1-10 mol%, based on the total molar amount of the gas; And / or, the treatment temperature in S4 is 100-200° C., and the treatment time is 1-48 h.

9. Use of a catalyst, wherein the catalyst is the catalyst according to any one of claims 1 to 3, or is a catalyst prepared by the method according to any one of claims 4 to 8, and the catalyst is used to prepare alkenyl acetate, preferably to prepare allyl acetate.

10. A method for preparing vinyl acetate, the method using the catalyst according to any one of claims 1 to 3, or the catalyst prepared by the method according to any one of claims 4 to 8, characterized in that: The method uses C2-C4 olefins, acetic acid and oxygen as raw materials for catalytic preparation of vinyl acetate.

11. The method for preparing vinyl acetate according to claim 10, characterized in that: In terms of molar ratio, C2-C4 olefin: acetic acid: oxygen: water = 1: (0.1-0.5): (0.1-0.5): (0-0.6); And / or, the raw material volume space velocity is 1000-3000h -1 ; and / or, the reaction temperature is 120-180° C. and the pressure is 0.1-1.5 MPaG; And / or, no alkali metal acetate is added during the process.

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