A catalyst for the production of vinyl acetate by the ethylene method and a method for preparing the same

Abstract

The application discloses a catalyst for preparing vinyl acetate by an ethylene method and a preparation method thereof. The catalyst is prepared by the following steps: obtaining a catalyst carrier by performing hydrothermal aging treatment and surface modification on a catalyst carrier, and impregnating an active component on the modified catalyst carrier to obtain the catalyst. The modification of the catalyst carrier improves the stability of the catalyst carrier, and the modified silica carrier reduces the migration of the active component on the surface of the catalyst carrier. The catalyst prepared by the method has more uniform active component distribution, and has better performance in reaction activity and catalyst life during the catalytic reaction process.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of vinyl acetate preparation, and particularly relates to a catalyst for preparing vinyl acetate by the ethylene method and a preparation method thereof. BACKGROUND

[0002] Vinyl acetate (VAc) is one of the world's largest fifty basic organic chemical raw materials, and is mainly used for producing polyvinyl alcohol (PVA), polyvinyl acetate emulsion (PVAC), vinyl acetate-ethylene copolymer emulsion (VAE), ethylene-vinyl acetate copolymer resin (EVA), and vinyl acetate-chloroethylene copolymer (PVAC) and other derivatives. These derivatives are widely used in construction, textiles, machinery, medicine and soil improvers and other aspects.

[0003] More than 60% of the world's vinyl acetate production capacity is concentrated in the Asian region, and China's vinyl acetate production capacity accounts for about 40% of the world's total production capacity, making it the world's largest vinyl acetate producing country. Internationally, vinyl acetate production is divided into acetylene method and ethylene method. Compared with the acetylene method, the ethylene method has the characteristics of economic environmental protection, high product purity, etc. Using ethylene, acetic acid and oxygen as raw materials, vinyl acetate is prepared under the action of a catalyst in the gas phase, which is a known mature process. Usually such catalysts use silicon dioxide or aluminum oxide as a carrier, and a catalyst composed of palladium and gold supported thereon. The catalyst has high activity, but the instability of the catalyst and the generation of by-products such as carbon dioxide and acetaldehyde are the shortcomings of the catalyst. Research shows that the activity of the catalyst is closely related to the composition and distribution form of the active component on the carrier. The more uniform the distribution of the active component on the carrier surface, the higher the dispersion degree of the active component, which has an important influence on the activity and service life of the catalyst. At present, many researchers have proposed various methods for depositing active palladium, gold and other metals on the surface of the catalyst carrier to form a narrow metal belt. For example, US3,775,342, US5,347,046A, US4,048,096A, etc. The results show that the use of such methods is beneficial to improving certain properties of the catalyst.

[0004] In the preparation of the catalyst in the past, the specific surface area of the catalyst carrier material can be varied within a wide range, such as the specific surface area of most catalyst carriers being 100-200 m 2The water-soluble metal salt solution is mixed with the porous carrier, and the metal ions are simply adsorbed on the surface of the carrier. The specific surface area of the porous carrier is provided by the microporous structure. When the surface of the carrier is in contact with the metal salt solution, the metal salt solution cannot quickly enter the microporous structure of the carrier due to the surface tension. Most of the solution is concentrated on the outer surface layer. With the extension of the immersion time, part of the metal salt enters the inside of the carrier under the action of the pore structure of the carrier, and uneven concentration of the immersion solution occurs, resulting in accumulation of the active metal component on the outer surface of the carrier. This not only reduces the active sites of the catalyst, but also easily causes loss of the active component, thereby reducing the service life of the catalyst. SUMMARY

[0005] The present application is proposed to overcome the shortcomings in the prior art, and aims to provide a catalyst for preparing vinyl acetate by the ethylene method and a preparation method thereof.

[0006] The present application is implemented by the following technical scheme:

[0007] A preparation method of a catalyst carrier for preparing vinyl acetate by the ethylene method, comprising the following steps:

[0008] (I) preparation of a gel

[0009] (i) batching: industrial sodium silicate with a modulus of 3.3-3.4 is prepared into a 15wt%-20wt% sodium silicate aqueous solution by adding water;

[0010] (ii) gel preparation: deionized water is added into a reaction tank as a bottom liquid, and 15-20wt% sodium silicate aqueous solution and sulfuric acid aqueous solution are added into the reaction tank in a parallel flow mode. Under stirring, the pH value of the parallel flow process is controlled to be 7-8. After the parallel flow is completed, the gel is aged at 20°C-60°C for 2h-3h to obtain the gel;

[0011] (II) acidification: the gel obtained in step (I) is adjusted to pH 2-3 by adding an inorganic acid, and the obtained product is soaked for 4h-8h. After washing, filtering and drying, a powder is obtained;

[0012] (III) molding: the powder obtained in step (II) is prepared into a spherical carrier with a diameter of 0.5-1.5mm by rolling, drying and calcining;

[0013] (IV) hydrothermal treatment: the spherical carrier obtained in step (III) is kept at 150°C-170°C for 2h-6h, and then naturally cooled to room temperature to obtain a silica sphere;

[0014] (V) surface modification: the silica sphere obtained in step (IV) is treated with an organic silane containing an ortho-hydroxyl group, a double-hydroxyl group or an ortho-hydroxyl or double-hydroxyl organic silane at room temperature for 4h-8h, and then dried to obtain the modified silica carrier, which is the catalyst carrier.​

[0015] A method for preparing a catalyst for preparing vinyl acetate by ethylene method, comprising the following steps:

[0016] (I) impregnating a modified silica carrier with a solution of water-soluble salt containing palladium and gold, drying the carrier after impregnation by rotating / turning operation, and the drying condition is 40-120 DEG C for 4-6 h;

[0017] (II) selecting a fixing solution to fix the metal ions on the carrier, and the fixing time is at least 1 h;

[0018] (III) washing with deionized water to remove impurity ions, and reducing the product after washing to change the fixed metal palladium and gold ions into reduced metal;

[0019] (IV) impregnating the reduced product with acetate, and drying under the condition of isolating oxygen to obtain the catalyst.

[0020] In the above technical solution, the mass percentage of palladium in the water-soluble salt solution containing palladium is 0.6-3.0%, and the mass percentage of gold is 0.1-2.0%.

[0021] In the above technical solution, the soluble salt containing palladium is chloropalladic acid, palladium acetate, palladium chloride, palladium nitrate, sodium chloropalladic acid or potassium chloropalladic acid.

[0022] In the above technical solution, the soluble salt containing gold is gold chloride, chloroauric acid, sodium chloroauric acid or potassium chloroauric acid.

[0023] In the above technical solution, the fixing solution is sodium hydroxide, sodium carbonate, sodium silicate, potassium hydroxide, potassium carbonate or potassium silicate solution.

[0024] In the above technical solution, the reaction condition of the reduction process is: using hydrogen / nitrogen atmosphere in a quartz tube, reducing at 350-550 DEG C for 2-8 h, or reducing at room temperature for 4-10 h by using hydrazine hydrate.

[0025] In the above technical solution, the acetate is potassium acetate.

[0026] In the above technical solution, the mass percentage of potassium acetate in the catalyst is 5.0-20.0%.

[0027] In the above technical solution, the drying condition after impregnating the acetate is: drying at 40-60 DEG C under nitrogen atmosphere.

[0028] The beneficial effects of the present application are:

[0029] The present application provides a kind of catalyst and its preparation method, for with ethylene, acetic acid and oxygen as reaction raw material gas phase synthesis vinyl acetate in;First by hydrothermal aging treatment and surface modification of catalyst carrier obtain modified silica carrier, improve the stability of carrier;Then on the basis of modified silica carrier impregnation active component, reduce the migration phenomenon of active component on the surface of carrier.The catalyst prepared by the method of the present application has more uniform active component distribution, and has better performance in reaction activity and catalyst life during the catalytic reaction process. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 It is the catalyst cross-sectional view prepared by example 1 of the present application.

[0031] For those skilled in the art, other related drawings can be obtained from the above drawings without creative labor. DETAILED DESCRIPTION

[0032] In order to enable those skilled in the art to better understand the technical solutions of the present application, the technical solutions of the present application will be further described below in combination with the drawings of the specification and through specific embodiments.

[0033] Example 1

[0034] A preparation method of a catalyst for preparing vinyl acetate by ethylene method, comprising the following steps:

[0035] (I) preparation of modified silica

[0036] Industrial sodium silicate with a modulus of 3.3-3.4 is prepared into a 15wt% sodium silicate aqueous solution by adding water, and industrial sulfuric acid is prepared into a 25wt% sulfuric acid aqueous solution by adding water; deionized water is added as a bottom liquid in a reaction tank, and the 15wt% sodium silicate aqueous solution and the 25wt% sulfuric acid aqueous solution are added to the reaction tank in a parallel flow manner, the pH is controlled to be 8 at a stirring speed of 150 revolutions per minute during the parallel flow process, and the gel is obtained after aging at 30℃ for 3h after the parallel flow process is completed; the obtained gel is adjusted to pH 3 by adding inorganic acid, and the obtained product is soaked for 4h, then washed with deionized water until the conductivity of the washing water is less than 500μs / cm; the obtained filter cake after washing is dried in a drying oven with air blowing at 120℃, and then rolled into a φ5.0mm spherical carrier after rolling and drying at 120℃; the obtained spherical carrier is kept at 160℃ for 5h under the condition of 20% water vapor content and 10% ammonia content, and then naturally cooled to room temperature to obtain silica balls, which are then treated with double-hydroxyl organosilane at room temperature for 4h, and then dried to obtain the modified silica carrier.

[0037] (II) preparation of a catalyst for preparing vinyl acetate by ethylene method

[0038] The modified silica carrier is impregnated with a solution of 1.0 wt% palladium chloride and 0.3 wt% of an aqueous soluble salt of chloroauric acid, and after rotation / turning operation, the carrier is dried at 50°C for 6h; the metal ions on the carrier are fixed by using sodium silicate solution, and the fixing time is 2h; the fixed metal palladium and gold ions are reduced to reduced state metal by using hydrogen / nitrogen=1:10 atmosphere at 450°C for 4h in a quartz tube; then the carrier is impregnated with 10% potassium acetate solution, and dried at 60°C in nitrogen atmosphere to obtain a catalyst with active components in the form of protein type distribution and in reduced state.

[0039] The cross-section of the obtained catalyst is shown in Figure 1 The active components of the catalyst are in the form of shell type distribution structure, wherein the middle part is the carrier of the catalyst, and the active components are distributed on the surface of the carrier.

[0040] Example 2

[0041] A method for preparing a catalyst for preparing vinyl acetate by ethylene method, comprising the following steps:

[0042] (I) Preparation of modified silica

[0043] Industrial sodium silicate with a modulus of 3.3-3.4 is prepared into 15 wt% sodium silicate aqueous solution by adding water, and industrial sulfuric acid is prepared into 25 wt% sulfuric acid aqueous solution by adding water; deionized water is added into a reaction tank as a bottom liquid, and the 15 wt% sodium silicate aqueous solution and the 25 wt% sulfuric acid aqueous solution are added into the reaction tank in a parallel flow mode, the pH is controlled to be 7 at a stirring speed of 150 rpm during the parallel flow process, and the obtained gel is aged at 30°C for 3h after the parallel flow process; the obtained gel is adjusted to pH 2 by adding inorganic acid, and the obtained product is soaked for 4h, then washed with deionized water until the conductivity of the washing water is less than 500 μs / cm; the obtained filter cake after washing is dried in a drying oven with air blowing at 120°C, and then rolled into a spherical carrier with a diameter of 5.0 mm by rolling and drying at 120°C; the obtained spherical carrier is treated at 170°C for 5h under the conditions of 10% water vapor content and 10% ammonia content, and then naturally cooled to room temperature to obtain silica balls; the obtained silica balls are treated by rotating at room temperature for 4h using an organic silane containing terminal amino group, and then dried to obtain a modified silica carrier.

[0044] (II) Preparation of a catalyst for preparing vinyl acetate by ethylene method

[0045] The modified silica carrier is impregnated with a solution of 2.0 wt% palladium chloride and 0.3 wt% of an aqueous soluble salt of chloroauric acid, and after rotation / turning operation, the carrier is dried at 60°C for 6 hours; the metal ions on the carrier are fixed by using sodium silicate solution, and the fixing time is 3 hours; the fixed metal palladium and gold ions are reduced to reduced metal by using hydrogen / nitrogen atmosphere at 450°C for 4 hours in a quartz tube; then the carrier is impregnated with 10% potassium acetate solution, and dried at 60°C under nitrogen atmosphere to obtain a catalyst with protein-type distribution of active components, reduced palladium, gold and acetate.

[0046] Example 3

[0047] A method for preparing a catalyst for preparing vinyl acetate by ethylene method, comprising the following steps:

[0048] (I) Preparation of modified silica

[0049] An industrial sodium silicate with a modulus of 3.3-3.4 is prepared into a 20 wt% sodium silicate aqueous solution by adding water, and an industrial sulfuric acid is prepared into a 30 wt% sulfuric acid aqueous solution by adding water; deionized water is added into a reaction tank as a bottom liquid, and the 15 wt% sodium silicate aqueous solution and the 25 wt% sulfuric acid aqueous solution are added into the reaction tank in a parallel flow mode, the pH is controlled to be 7 at a stirring speed of 150 rpm during the parallel flow process, and the obtained gel is aged at 30°C for 3 hours after the parallel flow process to obtain a gel; the obtained gel is adjusted to pH 2 by adding an inorganic acid, and the obtained product is soaked for 4 hours, then added into a water washing tank, and washed with deionized water until the conductivity of the washing water is less than 500 μs / cm; the obtained filter cake after water washing is dried in a drying oven with air blowing at 120°C, and then rolled into a spherical carrier with a diameter of 5.0 mm by rolling and drying at 120°C; the obtained spherical carrier is treated at 160°C for 5 hours in a steam atmosphere with a steam content of 25% and an ammonia content of 10%, and then naturally cooled to room temperature to obtain silica balls; the obtained silica balls are treated by rotation at room temperature for 4 hours with an organic silane containing terminal amino groups, and then dried to obtain a modified silica carrier.

[0050] (II) Preparation of a catalyst for preparing vinyl acetate by ethylene method

[0051] The modified silica carrier is impregnated with a solution of 2.0 wt% palladium chloride and 0.3 wt% of an aqueous soluble salt of chloroauric acid, and after rotation / turning operation, the carrier is dried at 60°C for 6 hours; the metal ions on the carrier are fixed by using sodium silicate solution, and the fixing time is 3 hours; the fixed metal palladium and gold ions are reduced to reduced metal by using hydrogen / nitrogen atmosphere at 450°C for 4 hours in a quartz tube; then the carrier is impregnated with 10% potassium acetate solution, and dried at 60°C under nitrogen atmosphere to obtain a catalyst with protein-type distribution of active components, reduced palladium, gold and acetate.

[0052] Example 4

[0053] A method for preparing a catalyst for preparing vinyl acetate by ethylene method, comprising the following steps:

[0054] (I) Preparation of modified silica

[0055] An industrial sodium silicate with a modulus of 3.3-3.4 is prepared into a 20wt% sodium silicate aqueous solution by adding water, and an industrial sulfuric acid is prepared into a 30wt% sulfuric acid aqueous solution by adding water; deionized water is added into a reaction tank as a bottom liquid, and the 15wt% sodium silicate aqueous solution and the 25wt% sulfuric acid aqueous solution are added into the reaction tank in a parallel flow mode, the pH is controlled to be 7 at a stirring speed of 150 rpm during the parallel flow process, and the gel is obtained by aging at 30°C for 2h after the parallel flow process; the obtained gel is adjusted to pH 2 by adding an inorganic acid, and the product obtained by soaking for 4h is washed with deionized water until the conductivity of the washing water is less than 500μs / cm; the filter cake obtained by washing is dried in a drying oven with air blowing at 120°C, and a spherical carrier with a diameter of 5.0mm is prepared by rolling and drying at 120°C; the obtained spherical carrier is kept at 160°C for 5h under the conditions of a water vapor content of 25% and an ammonia content of 15%, and is naturally cooled to room temperature to obtain silica balls, and the obtained silica balls are treated by rotating at room temperature for 4h with isobutyl organosilane, and the modified silica carrier is prepared after drying.

[0056] (II) Preparation of a catalyst for preparing vinyl acetate by ethylene method

[0057] The modified silica carrier is immersed with a 1.67wt% palladium chloride solution and a 0.15wt% chloroauric acid aqueous salt solution, and the carrier is dried at 70°C for 6h after rotating / turning operation; the metal ions on the carrier are fixed by selecting a sodium silicate solution, and the fixing time is 3h; the fixed metal palladium and gold ion oxygen-containing catalyst is washed with deionized water to remove impurity ions, and is reduced to a reduced metal by using hydrogen / nitrogen atmosphere at 450°C for 4h in a quartz tube; then, the above carrier is immersed with a 10% potassium acetate solution, and is dried at 60°C in a nitrogen atmosphere to obtain a catalyst with a protein type distribution of active components, a reduced state of palladium and gold, and acetate.

[0058] Example 5

[0059] A method for preparing a catalyst for preparing vinyl acetate by ethylene method, comprising the following steps:

[0060] (I) Preparation of modified silica

[0061] An industrial sodium silicate with modulus of 3.3-3.4 is dissolved in water to form a 15wt% sodium silicate solution, and an industrial sulfuric acid is dissolved in water to form a 25wt% sulfuric acid solution; deionized water is added into a reactor as a bottom liquid, and the 15wt% sodium silicate solution and the 25wt% sulfuric acid solution are added into the reactor in a parallel flow mode, the stirring speed is 150 rpm, the pH value is controlled to be 8 during the parallel flow process, and the gel is obtained after aging at 30°C for 3h; the obtained gel is adjusted to pH 3 by adding an inorganic acid, and the obtained product after soaking for 4h is washed with deionized water until the conductivity of the washing water is less than 500μs / cm; the filter cake obtained by washing is dried in a drying oven with air blowing at 120°C, and then is rolled and formed, and dried at 120°C to prepare a spherical carrier with a diameter of 5.0mm; the obtained spherical carrier is treated at 160°C for 5h in a steam atmosphere with a steam content of 20% and an ammonia content of 15%, and then is naturally cooled to room temperature to obtain silica spheres, and the obtained silica spheres are rotated at room temperature for 4h in an organic silane solution containing double hydroxyl groups, and then are dried to obtain a modified silica carrier.

[0062] (II) Preparation of a catalyst for preparing vinyl acetate by ethylene method

[0063] The modified silica carrier is impregnated with a 1.67wt% palladium chloride solution and a 0.3wt% chloroauric acid solution, and then is dried at 80°C for 6h after rotation / turning operation; a sodium silicate solution is selected to fix the metal ions on the carrier, and the fixing time is 2h; the carrier is washed with deionized water to remove impurity ions, and the fixed palladium and gold ions are reduced to reduced metal in a quartz tube in a hydrogen / nitrogen atmosphere at 450°C for 4h; then, the carrier is impregnated with a 10% potassium acetate solution, and is dried at 60°C in a nitrogen atmosphere to obtain a catalyst with a protein-type distribution of active components, reduced palladium, gold and acetate.

[0064] Catalyst evaluation

[0065] A 20ml catalyst is added into a tubular fixed bed reactor, the ethylene flow is adjusted to 1.5mol / h, and the reactor is heated; when the temperature of the catalyst bed is 130°C, acetic acid is added, and the acetic acid feed amount is 0.25mol / h; when the temperature of the catalyst bed is 142°C, oxygen is gradually introduced, and the flow rate reaches 0.08mol / h after 1h.

[0066] The temperature of the catalyst bed is controlled to be 142-145°C during the reaction, and the inlet pressure of the reactor is 0.8MPa. The reaction gas is condensed by a condenser and then is discharged, the amounts of vinyl acetate and acetic acid in the reaction liquid are analyzed, and the amounts of byproduct carbon dioxide, uncondensed vinyl acetate and oxygen in the tail gas are analyzed.

[0067] The evaluation results of the examples are shown in Table 1

[0068]

[0069]

[0070] wherein: activity = generated vinyl acetate / (volume of catalyst * reaction time);

[0071] selectivity = (amount of ethylene for generating vinyl acetate / amount of ethylene consumed in the reaction) * 100%.

[0072] The applicant states that the above description is only a specific embodiment of the present application, but the protection scope of the present application is not limited thereto. It should be understood by those skilled in the art that any changes or replacements within the technical scope disclosed by the present application can be easily thought out by any person skilled in the art, and all of them fall within the protection scope and disclosure scope of the present application.

Claims

1. A process for the preparation of a catalyst support for the production of vinyl acetate by the ethylene method, characterized in that: It comprises the following steps: (I) gel preparation The sodium silicate aqueous solution and the sulfuric acid aqueous solution are added to the bottom liquid in a parallel flow mode, and the pH value during the parallel flow process is controlled under stirring, and the gel is obtained after aging after the parallel flow process is completed; The aging condition is 20-60℃ for 2-3h; (II) acidification An inorganic acid is added to the gel to adjust the pH value, and the product obtained after soaking for 4-8h after the inorganic acid is added is washed, filtered and dried to obtain a powder; (III) shaping The powder obtained in step (II) is rolled and shaped, and dried at 60-120℃ to prepare a spherical carrier; (IV) hydrothermal reaction The spherical carrier obtained in step (III) is subjected to a hydrothermal reaction, and then cooled to obtain a silicon sphere; The hydrothermal condition is 150-170℃ for 2-6h; (V) surface modification The silicon sphere obtained in step (IV) is treated with an organic silane containing a specific group, and then dried to obtain a catalyst carrier; The organic silane containing a specific group is an ortho-hydroxy organic silane, a double-hydroxy organic silane or an ortho-hydroxy and double-hydroxy organic silane; The bottom liquid is deionized water; the mass fraction of the sodium silicate aqueous solution is 15-20%; the mass fraction of the sulfuric acid aqueous solution is 10-30%; and the pH value during the parallel flow process is controlled at 7-8. In the acidification step, the inorganic acid adjusts the pH value of the gel to 2-3, and the inorganic acid is hydrochloric acid, sulfuric acid or nitric acid.

2. A process for the preparation of a catalyst for the production of vinyl acetate by the ethylene process, characterized in that: It comprises the following steps: (I) impregnation The catalyst carrier of claim 1 is impregnated with a water-soluble metal salt solution, and the catalyst carrier is dried at 40-120℃ for 4-6h after impregnation; (II) fixing metal ions A fixing solution is selected to fix the metal ions on the carrier, and the carrier is washed after fixing; (III) reduction The carrier treated in step (II) is subjected to reduction; (IV) acetate impregnation and drying The product after reduction in step (III) is impregnated with an acetate and dried in an oxygen-free condition to prepare a catalyst.

3. The process for the preparation of a catalyst for the production of vinyl acetate by the ethylene method according to claim 2, characterized by the fact that: The water-soluble metal salt solution is a water-soluble salt solution containing palladium and a water-soluble salt solution containing gold; the mass percentage of palladium in the water-soluble salt solution containing palladium is 0.6-3.0%; the mass percentage of gold in the water-soluble salt solution containing gold is 0.1-2.0%; the water-soluble salt containing palladium is chloropalladic acid, palladium acetate, palladium chloride, palladium nitrate, sodium chloropalladic acid or potassium chloropalladic acid; the water-soluble salt containing gold is gold chloride, chloroauric acid, sodium chloroauric acid or potassium chloroauric acid; and the fixing solution is sodium hydroxide solution, sodium carbonate solution, sodium silicate solution, potassium hydroxide solution, potassium carbonate solution or potassium silicate solution.

4. The process for the preparation of a catalyst for the production of vinyl acetate by the ethylene method according to claim 2, characterized by the fact that: The metal ion fixing time is ≥1h; the reaction condition for reduction in step (III) is that the carrier is reduced in a quartz tube under a mixed gas atmosphere of hydrogen and nitrogen with a volume ratio of 1:10 at 350-550℃ for 2-8h, or reduced with hydrazine hydrate at room temperature for 4-10h; the acetate is potassium acetate, and the mass percentage of potassium acetate in the catalyst is 5.0-20.0%.

5. The process for the preparation of a catalyst for the production of vinyl acetate by the ethylene method according to claim 2, characterized by the fact that: The drying condition after impregnation with the acetate is 40-60℃ under a nitrogen atmosphere.

6. A catalyst for the production of vinyl acetate by the ethylene method, prepared by the process according to any one of claims 2 to 5, characterized in that, The active component of the catalyst is in a protein type distribution.

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