JP2001179099A - Vinyl acetate synthesizing catalyst - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a catalyst useful for manufacturing vinyl acetate, which deteriorates in such a small degree that it can be even in a fluidized bed type reactor, excellent in durability and high in activity. SOLUTION: A vinyl acetate synthesizing catalyst is obtained by supporting a palladium component and an alkali metal acetate on a carrier comprising a silicious composition containing aluminum and magnesium to form a layer wherein the palladium component is supported within a range of 0-below 80 μm in the center direction from the outer surface of the carrier and characterized by that the surface area of the palladium metal component calculated from the adsorption of carbon monoxide is 40-300 m2/Pdg.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a catalyst used for producing vinyl acetate from ethylene, oxygen and acetic acid.

[0002]

2. Description of the Related Art There have been many reports on catalysts used for producing vinyl acetate in the gas phase from ethylene, oxygen and acetic acid gas (JP-A-8-40997, JP-A-8-38900, JP-A-8-38899, JP-A-3-24034, JP-B-50-35057, JP-B-47-14209, JP-B-46-17203,
JP-B-54-1283, JP-B-45-7538).
Most of these known catalysts are mainly based on palladium, alkali metals or alkaline earth metals and platinum, gold, silver, copper, iron, manganese, aluminum, titanium, antimony, bismuth, lead, cerium, vanadium, tellurium. , Chromium, molybdenum, and other metals as co-catalyst compounds, and these catalyst components are usually alumina,
A ternary catalyst supported on a carrier such as silica, activated carbon, and titanium oxide.

[0003] It has also been shown that in the supported form of the catalyst, the palladium and the cocatalyst are more or less evenly distributed throughout the support. For example, US Pat.
5,680, 3,743,607 and 3,
950,400 and British Patent 1,333,44.
No. 9 and also South African Patent No. 687,990.
However, the catalytically active components present inside these carriers have a problem that their contribution to the reaction is low because the reaction substrate is unlikely to diffuse into the carriers.

In order to solve this problem, a catalyst has been developed in which the catalytically active component is concentrated near the outermost surface of the carrier. For example, GB 1,500,167 discloses that the catalyst has at least 90% of the palladium and gold distributed from the outermost surface of the support to no more than 30% of the support particle radius. In addition, British Patent Nos. 1 and 2
No. 83,737 teaches that the degree of penetration into the porous support can be adjusted, for example, by pretreatment of the porous support with an alkaline solution of sodium carbonate or sodium hydroxide. JP-A-6-47281 discloses a shell-impregnated catalyst characterized by palladium and gold distributed in the outermost layer having a thickness of 1.0 mm in catalyst support particles. In addition, U.S. Pat.
No. 096 and U.S. Pat. Nos. 4,087,622 and 5,185,308 disclose techniques relating to a method for producing a catalyst. However, these documents relate mainly to the production of catalysts when a fixed-bed reactor is used for the production of vinyl acetate.

It would be economically advantageous if the production of vinyl acetate could be carried out by a fluidized bed process. A typical advantage of the fluidized bed process is that the design of the fluidized bed reactor is simpler than a fixed-bed reactor with multiple tubes, and the fixed-bed reactor does not cause deactivation based on hot spots which cannot be avoided. Life expectancy is expected to improve. Further, since the replenishment of the catalyst can be performed continuously, the exchange of the catalyst can be substantially eliminated. In addition, even at relatively high oxygen levels, it is possible to safely feed into the reactor without the formation of a flammable mixture, and high production rates are possible. Until now, U.S. Pat.
No. 00 discloses that the catalyst can also be used in a fluidized bed reactor. Furthermore, GB 1,266,623 discloses a fluidized bed catalyst for the production of vinyl acetate consisting of palladium promoted with various alkali, alkaline earth or other metals.

However, catalysts used in fluidized bed reactors require catalytic properties, such as mechanical abrasion strength, which were not required in fixed beds, because the particles contact the walls and between the particles. There is no catalyst having high activity and sufficient catalytic properties. That is, until the process of the present invention is found, it can be used in a fluidized bed type reactor,
Moreover, there is no economical palladium catalyst for producing vinyl acetate.

[0007]

SUMMARY OF THE INVENTION The main object of the present invention is to provide a catalyst useful in the production of vinyl acetate, which has low deterioration and excellent durability and is highly active, so that it can be used in a fluidized bed reactor. It is in.

[0008]

As a result of intensive studies on the above-mentioned problems, the present inventors have completed the following invention. 1, a palladium component and an alkali metal acetate are supported on a carrier, and the carrier has a particle size of less than 200 μm and a bulk density of 0.1 μm.
Particles in the range of 7 to 1.5 g / ml, wherein the carrier is a silica-based composition containing aluminum and magnesium, wherein aluminum is 5 to 30% by weight as Al ₂ O ₃ and magnesium is ₃ to 30% by weight as MgO. Wt% silicon to SiO ₂
And the atomic ratio of magnesium to aluminum (magnesium / aluminum)
Is greater than 1/2, and 0 from the outer surface of the carrier toward the center.
a vinyl acetate synthesis catalyst comprising a layer in which a palladium component is supported in a range of more than 80 μm and less than 80 μm, and a surface area of the palladium metal component obtained from adsorption of carbon monoxide is 40 to 300 m ² / Pdg. . 2. The vinyl acetate synthesis catalyst according to 1, wherein the palladium component is a palladium intermetallic compound. 3. The palladium intermetallic compound is palladium and X (X
(3) an intermetallic compound with lead, bismuth, thallium, mercury, and tellurium). 4. A method for producing vinyl acetate from ethylene, oxygen and acetic acid using the vinyl acetate synthesis catalyst described in any one of 4, 1 to 3.

Hereinafter, the present invention will be described in detail. First, the carrier used in the present invention will be described. The particle size (particle size) of the carrier of the present invention is less than 200 μm. Preferably, 1
It is less than 50 μm, more preferably less than 100 μm. In addition, the lower limit of the particle size is not limited by the strength and reactivity of the particles, but if the particles are small, sedimentation is poor and a simple and inexpensive process such as sedimentation cannot be used, and equipment such as a filter is required. It is preferably 10 μm or more, more preferably 20 μm or more due to restrictions on the separation surface of the catalyst. As described above, the range of the minimum particle diameter can be arbitrarily determined depending on the reaction system such as a bubble column, a fluidized bed, and a stirring tank, and the method for separating the catalyst.

Incidentally, in the case of a separation method generally called a cyclone, the average particle diameter is about 60 μm and 20 to 100 μm.
The particles in the range of m are selected because they satisfy both reactivity and separation. The bulk density of the carrier of the present invention is 0.7 to 1.5.
Those in the range of ml / g are selected. 0.7ml bulk density
/ G or less is not preferred because the strength is low and causes cracking and chipping. On the other hand, it is preferable that the bulk density is high in terms of strength, but particles having a volume density of 1.5 ml / g or more generally have low porosity and are not preferable because the palladium carrying performance and the reaction characteristics tend to be low. . More preferably, particles having a bulk density of 0.8 to 1.3 ml / g are selected from strength and porosity.

The silica-based composition containing aluminum and magnesium used for the carrier of the present invention (hereinafter referred to as silica-alumina-magnesia carrier) is obtained by converting aluminum to Al ₂ O ₃
5 to 30% by weight as magnesium and MgO as MgO 3
30 wt%, wherein the silicon in the range of 40 to 92 wt% as SiO _2, silica - the amount of magnesium cations to compensate the charge balance by alumina bonding a bond of tetravalent silica and trivalent alumina In consideration of this, it is possible to use magnesium whose atomic ratio is 1/2 of aluminum, and in order to further develop basicity, the atomic ratio of magnesium to aluminum (magnesium / aluminum) is 1 /.
Preferably greater than 2.

The silica-alumina-magnesia carrier gives a higher wear strength and water resistance than silica gel, which is considered to be relatively strong, due to the silica-alumina bond. Furthermore, since basic magnesium has a function of depositing palladium on a carrier substantially by a stoichiometric reaction, the amount of palladium can be determined by determining the amount of basic magnesium contained in the carrier. In the charging ratio described above, the effect of modifying silica gel is small when aluminum is 5% by weight or less, and the effect tends to be slightly reduced when aluminum is 30% by weight or more. More preferably, aluminum is 5-20.
% By weight.

It is important to secure the amount of magnesium to make the charge generated by the silica-alumina bond neutral and to maintain the amount as the base component. Therefore, the optimum range varies depending on the amount of aluminum, the amount of palladium carried, and the like. However, when the amount is less than 3% by weight, the palladium carrying characteristics generally decrease. Next, the palladium component carried on the carrier of the present invention will be described.

In the present invention, the palladium component is contained in a carrier,
It is expected that the larger the thickness of the layer not existing on the outer surface of the particles, that is, the more the palladium component exists inside the carrier, the less the palladium peeling due to abrasion. However, the more the palladium component is present inside the support, the greater the resistance of the reaction substrate to diffusion into the pores, and the lower the reaction rate. In other words, the position where the palladium component is distributed inside the carrier is selected from the optimum distribution position based on the abrasion and the reaction speed. Specifically, the range in which the palladium component does not exist from the outer surface of the carrier is 10 μm or less, preferably 5 μm, and more preferably 2 μm in the depth direction from the outer surface of the carrier (hereinafter, referred to as A layer). The range in which the palladium component is present (hereinafter referred to as the layer B) is within 80 μm, preferably within 50 μm, more preferably within 30 μm, and more preferably within 20 μm from the outer surface of the carrier including the layer A.

The palladium component has a specific surface area of palladium metal in the carrier determined from carbon monoxide of 300 m ² / Pd.
Although g greater than preferred from the reaction surface, that difficulties on preparation increases, also bake faster particle growth by agglomeration, since the activity decreases in the following 40m ² / Pdg, 40~300m ² / A range of Pdg is chosen. Further, the present invention is characterized in that an alkali metal acetate is added in addition to the palladium component.

The kind of alkali metal constituting the alkali metal acetate of the present invention can be selected from sodium, potassium, rubidium and cesium. Preferably, potassium is selected. The amount of addition varies depending on the type of alkali metal. For example, potassium acetate is used in an amount of 0.1 to 10% by weight, preferably 1 to 4% by weight, based on the total weight of the catalyst.
Used in. Next, the synthesis of the silica-alumina-magnesia carrier of the present invention will be described using specific examples.

A silica sol solution and alkoxides are used as a silica source, alumina sol, aluminum nitrate and aluminum acetate are used as an aluminum source, and magnesium nitrate and magnesium acetate are used as a magnesium source. This mixed solution is heated to 110 to 280 ° C, preferably 130 to 24 ° C.
It is prepared by spray drying at 0 ° C. and then calcining the spray dried particles at a temperature of preferably 500-700 ° C., preferably 600-660 ° C. to form a carrier. In this case, the bulk density of the carrier obtained by firing is 0.7
The solid content concentration and slurry viscosity of the slurry are adjusted so as to be 1.5 g / ml. Alternatively, an inorganic compound, an organic substance, a polymer, or the like that decomposes into a gas under the above-mentioned firing conditions can be added as a bulk density regulator.

The specific surface area of the carrier is 10 to 700 m ² / g as measured by the nitrogen adsorption method, preferably 20 to 350 m ² / g, more preferably 50 to ³ m ² / g.
A material of 00 m ² / g is used. Specific surface area is 10m ² / g
In the following, it is not preferable because the palladium component is hardly supported or is easily peeled off even if it is supported. Further, the reaction activity of the obtained catalyst is low. From the viewpoint of catalyst preparation, there is no particular problem that the specific surface area of the support is large. However, when the specific surface area is large, the mechanical strength and the corrosion resistance tend to decrease. For this reason, the specific surface area is most preferably selected from the range of 50 to 250 m ² / g.

Next, a general method for producing a catalyst in which the distribution of the palladium component is controlled will be described below. The method of the present invention is a method in which fine particles of a silica-alumina-magnesia carrier containing basic magnesium are reacted in advance with a palladium-containing solution, and immobilized inside the carrier. Although the principle is unknown, for example, when an aluminum chloride solution is allowed to coexist with a palladium chloride-containing solution and reacted with a silica-alumina-magnesia carrier, the palladium component can not be carried on the outer surface of the carrier. By changing the amount of aluminum chloride to be added, the thickness of the layer A where no palladium component is present can be controlled. This is thought to be because aluminum selectively reacts with basic magnesium in the carrier over palladium, and remains on the internal surface of the carrier because basic magnesium on the outer surface of the carrier reacts with aluminum first and is consumed. It is presumed that the basic magnesium and palladium react to form a layer B in which the palladium component is fixed inside the carrier.

Therefore, it can be seen that the use of the method of the present invention can control the distribution of the palladium component in the particles by the amount of the basic magnesium of the carrier, the amount of the supported palladium, and the amount of the added aluminum. It is considered that the palladium reacted with the basic magnesium of the carrier is deposited as hydroxide in the pores inside the carrier. Since the solubility of palladium hydroxide is extremely low, it is considered that the position is fixed by the reaction with basic magnesium. Finally, in order to convert to palladium metal which acts as a catalyst, palladium metal is converted by a reduction operation using a reducing agent.

The temperature at which the palladium solution contacts and reacts with the basic magnesium in the carrier varies depending on the amount of palladium to be supported. Cloth width becomes narrow.
It is preferably at least 80 ° C, more preferably at least 90 ° C. Although it is possible to carry out the process even at 100 ° C. or higher, the effect is generally not so different from 90 ° C. It is carried out at temperatures up to 100 ° C., which is a safe temperature for operation. The weight ratio of palladium to the carrier in the catalyst of the present invention is 0.1 to 0.1.
It is 5.0% by weight, preferably 0.2 to 4.0% by weight, particularly preferably 0.3 to 2.0% by weight.

The palladium compound used for supporting the palladium component of the present invention may be any palladium compound that can be dissolved in a solvent such as water or an organic solvent.
Palladium nitrate and palladium acetate are mentioned, but palladium chloride having high solubility and easy to use industrially is preferable. In the present invention, the palladium component may form a palladium intermetallic compound composed of palladium and another metal. The palladium intermetallic compound is specifically palladium-X (X = lead, bismuth,
(Thallium, mercury, tellurium).

In the method for producing a palladium intermetallic compound, for example, a palladium intermetallic compound (Pd-Pb) composed of palladium and lead is reduced by impregnating a carrier with a palladium solution as described above. The lead is impregnated with an aqueous solution such as lead acetate or lead nitrate, and lead is added. Thereafter, the lead is reduced to form an intermetallic compound of Pd-Pb. An organic solvent can be used for bismuth or the like, which does not easily exist as an aqueous solution even with a metal forming an intermetallic compound with palladium. Solvents useful for the preparation include, specifically, water and the following volatile organic solvents. A carboxylic acid having 4 or less carbons,
Alcohols, ethers, esters and aromatics.

In the case of a palladium intermetallic compound, X is defined by a stoichiometric combination with palladium. For example, Pd ₃ Pb ₁ , Pd ₃ Tl ₁ , Pd ₄ Te ₁ , Pd ₅ H
The approximate value can be determined by the ratio at which g ₃ and Pd ₅ Bi ₂ are formed. In terms of the catalyst structure, the palladium intermetallic compound is stable under the reaction conditions, such as being difficult to grow crystallites due to oxidation and reduction, and is preferable from the viewpoint of catalyst life, in addition to changing the catalyst performance as compared with palladium metal. The approximate amount of X to be added to add X is greater than 0 and 5.0% by weight based on the carrier.
Or less, preferably 0.1% by weight or more and 4.0% by weight or less,
Particularly preferably, the content is 0.1% by weight or more and 3.0% by weight or less.

The present invention is characterized by adding an alkali metal acetate in addition to the above-mentioned palladium component. Hereinafter, the method of addition will be described. The alkali metal acetate is, for example, a method of dissolving a predetermined amount of potassium acetate in water or an organic solvent, impregnating the carrier carrying a palladium component, and removing and fixing the solvent component by drying or the like. Preferably, a method in which potassium acetate is absorbed into a solution having a pore volume equal to or slightly smaller than the pore volume of the carrier, impregnated, and dried. Alternatively, the catalyst particles can be immobilized by a method in which predetermined potassium acetate is sprayed and supported while stirring at a temperature of 80 ° C. The drying can be carried out at a temperature of room temperature or lower to 150 ° C., except for the solvent water and the organic solvent. When it is usually carried out at normal pressure, it is dried at a temperature of 60C to 150C, preferably 70C to 120C.

The catalyst of the present invention can be produced by the above method. Next, conditions for producing vinyl acetate using the catalyst of the present invention will be described. First, when ethylene, oxygen, acetic acid and water are reacted in the gas phase to produce vinyl acetate, the reaction temperature is 100 to 250 ° C, preferably 140 to 200 ° C. The reaction pressure is 0.5 × 10 ⁵ Pa to 3.3 from the viewpoint of equipment.
Although it is practically advantageous to be 0 × 10 ⁶ Pa, it is more preferably in the range of 1.0 × 10 ⁵ Pa to 1.0 × 10 ⁶ Pa.

In the method of the present invention, the gas supplied to the reaction system comprises ethylene, oxygen, acetic acid and water. If necessary, nitrogen, carbon dioxide or a gas inert to the reaction can be used as a diluent. . Ethylene is 2-80% by volume, preferably 5%, based on the total amount of the supplied gas.
Oxygen in an amount of 1 to 15% by volume, preferably 3 to 10% by volume, and acetic acid in an amount of 2 to 30% by volume, preferably 3 to 10% by volume. The proportioning amount of water is 0.5 to 50% by volume, preferably 0.1 to 50% by volume.
It is supplied to the reaction system at 5 to 30% by volume.

In carrying out the process of the present invention, it is advantageous to use high-purity ethylene as a raw material.
A small amount of lower saturated hydrocarbon such as methane, ethane and propane may be mixed. Oxygen can also be supplied in a form diluted with an inert gas such as nitrogen or carbon dioxide gas, for example, in the form of air. However, when circulating a reaction gas, oxygen having a high concentration, preferably 99% or more is generally used. Is more advantageous. The reaction mixture gas can be supplied in principle at a rate higher than the rate at which the catalyst forms a fluid state. In a reactor with a diameter of several mm to several cm, such as a lab device, there is no particular problem if the linear velocity is higher than the minimum fluidization speed, but in a large reactor with a diameter of several meters, the inside of the fluidized bed The decomposition of the product may occur due to the growth of air bubbles and the increase in the residence time due to back mixing. Therefore, it is important to select a flow rate according to the size of the reactor. The optimum speed is selected according to the diameter of the reactor and the capacity of the cyclone for separating the catalyst. Normally linear velocity 0.0
It is selected from the range of 1 m / sec to 2.0 m / sec. Preferably, it is generally performed in the range of 0.02 to 1.5 m / sec.

[0029]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described more specifically with reference to embodiments. In the present invention, the catalyst activity evaluation test and the abrasion test using a reactor were measured by the following methods. (Catalyst activity evaluation test using a reactor) A SUS sintered filter with a mesh size of 10 μm was installed at the bottom with 50 g of catalyst, and the same mesh size as the bottom was used at the top to separate the catalyst and the reaction gas. It is charged into a 1-inch diameter SUS fluidized-bed reactor equipped with a 10-μm SUS sintered filter, and a reaction raw material gas is supplied from the filter side at the bottom to perform an evaluation test of catalytic activity. Typically, the reactant gas is supplied such that the contact time between the catalyst layer and the reactant gas is 3 seconds.

The product gas generated by the reaction is analyzed by gas chromatography. The gas reactor effluent was analyzed online using a Shimadzu Model 14B gas chromatograph equipped with a thermal conductivity detector (TCD) and a combustion ion detector (FID). Oxygen, nitrogen, ethylene, and carbon dioxide consist of molecular sieve (13X) and chromosolve 101 having a carrier particle diameter of 80/100 mesh.
And quantified by TCD. Vinyl acetate and acetic acid are separated by gas chromatography-56 and quantified by FID. The reactor pressure is then controlled, and all piping is maintained at about 180 ° C. to prevent condensation of liquid feed or product.

(Abrasion test) The abrasion strength of the catalyst particles is determined by using a conventional test method for a fluid contact catalyst (FCC). That is, 50 g of particles are accurately weighed and charged into a 1.5-inch inner diameter vertical tube equipped with a perforated disk having three orifices of 1/64 inch at the bottom, and air is blown at a speed that is sonic at the hole. The sink particles were run vigorously. The abrasion strength of the catalyst particles was determined as a percentage of the initial charge of particles that were refined during 5-20 hours and escaped from the top of the vertical tube. <Reference Manufacturing Example> Aluminum nitrate and magnesium nitrate were respectively added to Al / Si + A in Snowtex N-30 (SiO ₂ content: 30% by weight) manufactured by Nissan Chemical Industries as a silica sol aqueous solution.
A solution having a solid content of 26% by weight was prepared by adding l = 10 mol% and Mg / Si + Mg = 10 mol%. 1
The dried particles were obtained by spray drying with a spray dryer set at a temperature of 30 ° C. The dried particles are heated from room temperature to 400 ° C. over 2 hours and kept for 1 hour while blowing air, and then heated up to 600 ° C. for 1 hour and calcined at 600 ° C. for 2 hours, and sieved at 150 μm or more and 20 μm or less. After removal, a spherical silica-alumina-magnesia carrier having an average particle diameter of 60 μm was obtained. When the bulk density was measured, it was 0.91 g / ml.
Met.

[0032]

EXAMPLE 1 1.0 palladium per 100 parts by weight of the spherical silica-alumina-magnesia carrier of Reference Production Example
A 15% by weight aqueous solution in which palladium chloride sodium salt (Na ₂ PdCl ₄ ) and aluminum nitrate are dissolved is heated to 90 ° C. and prepared with stirring so that the weight becomes 0.35 parts by weight of aluminum. Next, 100 parts by weight of the carrier is instantaneously charged in a dry state, and the mixture is further stirred at 90 ° C. for 60 minutes. After the palladium in the solution was completely adsorbed, the liquid was decanted and the carrier supporting palladium was washed several times with distilled water.

Next, the above-mentioned palladium carrier was added to an aqueous solution in which sodium acetate was added in a molar amount 6 times the amount of palladium, and the mixture was stirred. The temperature was raised to 60 ° C. and then Pd
A lead acetate solution corresponding to /Pb=3/1.3 (molar ratio) was added and maintained for 30 minutes. Next, a hydrazine aqueous solution having a molar ratio of 4 times the amount of palladium was slowly added dropwise over about 30 minutes while stirring, and a reduction treatment was performed for 3 hours. Continue using distilled water until chlorine ions are no longer detected.
Washed 0 times. After the washing is completed, the substrate is dried in a forced air oven at 60 ° C. overnight, cooled, and then dried.
An aqueous solution of 3.5 parts by weight of potassium acetate was added to 0 parts by weight, and the mixture was impregnated while rotating so that the mixture was dispersed and supported as uniformly as possible. Then, it was dried again at 60 ° C. in a forced air oven on a stainless steel screen to obtain a catalyst of the present invention.

The obtained catalyst was embedded in a resin and polished to form a cross section of catalyst particles, and JXA-8800R manufactured by JEOL Ltd.
The measurement was performed using an X-ray macro analyzer (EPMA). Acceleration voltage: 15 KV, electron beam diameter: 0.1 μm, spectral crystals: Pd = PETH, Pb = PETH, Si = TA
Performed with P. From the image analysis of the cross section of the particles, it was observed that palladium was not present in the depth direction of 2 μm from the outer surface of the particles and almost 100% was dispersed and supported within 10 μm from the outer surface. The specific surface area (MAS) of palladium metal determined from adsorption of carbon monoxide was 103 m ² / Pdg. When the wear strength of the catalyst was measured,
The 20 hour weight loss was 1.2%. Further, the sample after the measurement of the wear strength was dissolved in aqua regia and the reduction ratio of palladium was measured to be 0.1% or less.

[0035]

Example 2 Example 1 was applied to a 1-inch diameter SUS reactor.
Of 8.0 × 10 ^FivePa and 150
An evaluation test of the catalyst activity was conducted at ℃ in a reactor. Touch
As a pretreatment of the medium, the catalyst was placed in a nitrogen stream at 160 ° C. for 3 hours.
8.0 × 10 minutes at 150 ° C. in a stream of ethylene.
10^FiveHeated at Pa. The acetic acid vapor is then combined with ethylene.
At least 1 mixture of 15: 1 gas mixture
Feeded over time.

In the reaction, a mixed gas of helium and oxygen is gradually added while supplying the above-mentioned mixed gas of acetic acid vapor and ethylene to which water has been added.
The ratio of oxygen, acetic acid, water and helium is 60: 4: 15: 1
The mixing ratio was 5: 6. The flow rate at which the contact time between the mixed gas of ethylene, oxygen, acetic acid, water and helium and the catalyst was 3 seconds was maintained, and vinyl acetate was synthesized at 150 ° C. As a result of analyzing the generated gas by gas chromatography, the selectivity of vinyl acetate was 85.2%, the selectivity of carbon dioxide (carbon dioxide) was 14.5%, and the conversion of ethylene was 16.7%. The selectivity was recalculated to ethylene required to generate vinyl acetate and carbon dioxide in the reaction product, and calculated from the ratio. All the numerical values shown are the results of measuring the reaction gas 8 hours after the mixing ratio of ethylene, oxygen, acetic acid, water, and helium became the above.

[0037]

Comparative Example 1 Commercially available silica gel (average particle diameter 100 μm)
m) was used as a carrier, and impregnated with magnesium acetate having a magnesium content of 4 wt%, and calcined at 600 ° C. Carrier 10
A 15% by weight aqueous solution of sodium palladium chloride (Na ₂ PdCl ₄ ) is prepared at room temperature with stirring so that the amount of palladium becomes 1.0 part by weight per 0 parts by weight, and then 100 parts by weight of the carrier is instantaneously dried. And stirred at room temperature for another 120 minutes. After the palladium in the solution was completely adsorbed, the liquid was decanted and the carrier supporting palladium was washed several times with distilled water.

Next, the above-mentioned palladium carrier was added to an aqueous solution in which sodium acetate was added in a molar amount 6 times the amount of palladium, and the mixture was stirred. The temperature was raised to 60 ° C and then Pd /
A lead acetate solution corresponding to Pb = 3 / 1.3 (molar ratio) was added and 3
Hold for 0 minutes. Next, a hydrazine aqueous solution having a molar ratio of 4 times the amount of palladium was slowly added dropwise over about 30 minutes while stirring, and a reduction treatment was performed for 3 hours. Continue with distilled water until chlorine ions are no longer detected.
Washed twice. After the washing, the catalyst is dried in a forced air oven at 60 ° C. overnight, cooled, and then dried.
An aqueous solution of 3.5 parts by weight of potassium acetate was added to 0 parts by weight, and the mixture was impregnated while rotating so that the mixture was dispersed and supported as uniformly as possible. Then, it was dried again at 60 ° C. in a forced air oven on a stainless steel screen to obtain a catalyst using silica gel as a carrier.

The obtained catalyst was subjected to image analysis in the same manner as in Example 1. As a result, from the results of image analysis of the particle cross section,
It was found that palladium was uniformly present in the depth direction from the outer surface of the particles. Lead also showed the same distribution as palladium. The specific surface area (MAS) of palladium metal determined from the adsorption of carbon monoxide was 31 m ² / Pdg. When the same evaluation as in Example 2 was performed using the obtained catalyst, the selectivity for vinyl acetate was 82.2%, the selectivity for carbon dioxide was 17.5%, and the conversion of ethylene was 6.3%. there were. When the wear strength of the catalyst was measured, the weight loss in 5 to 20 hours was 5.8%, and the sample after the wear strength measurement was dissolved in aqua regia and the reduction rate of palladium was measured to be 5.3%. Was.

[0040]

EXAMPLE 3 1.3 as palladium per 100 parts by weight of the spherical silica-alumina-magnesia carrier of Reference Production Example.
A 15% by weight aqueous solution in which palladium chloride sodium salt (Na ₂ PdCl ₄ ) and aluminum nitrate are dissolved is heated to 90 ° C. and prepared with stirring so that the weight becomes 0.35 parts by weight of aluminum. Next, 100 parts by weight of the carrier is instantaneously charged in a dry state, and the mixture is further stirred at 90 ° C. for 60 minutes. After the palladium in the solution was completely adsorbed, the liquid was decanted and the carrier supporting palladium was washed several times with distilled water.

Next, the solution was replaced with a 50% 1-propanol aqueous solution, and sodium acetate was added in a molar amount 6 times the amount of palladium. After heating to 90 ° C., Pd / Bi = 5 /
A triphenylbismuth / 1-propanol solution equivalent to 2.5 (molar ratio) was added dropwise with stirring and maintained for 30 minutes. Next, a hydrazine aqueous solution having a molar amount of 4 times the amount of palladium was slowly added dropwise over about 30 minutes while stirring, and a reduction treatment was performed for 6 hours. Next, it was washed about 10 times with distilled water until no chlorine ion was detected. After the washing is completed, the catalyst is dried in a forced air oven at 60 ° C. overnight, cooled, and then 3.2 parts by weight of an aqueous solution of potassium acetate is added to 100 parts by weight of the carrier to disperse and support as uniformly as possible. The mixture was impregnated while rotating as it did. The catalyst was then dried again at 60 ° C. in a forced air oven on a stainless steel screen to obtain a catalyst.

The obtained catalyst was subjected to image analysis in the same manner as in Example 1. As a result, from the image analysis of the obtained particle cross section, it was observed that palladium was not present in the depth direction of 2 μm from the outer surface of the particle, and almost 100% was dispersed and supported within 10 μm from the outer surface. The distribution of bismuth also showed the same distribution as palladium. The specific surface area (MAS) of palladium metal determined from adsorption of carbon monoxide is 98 m ² /
The value of Pdg was obtained. When the same evaluation as in Example 2 was performed using this catalyst, the selectivity of vinyl acetate was 84.8.
%, The selectivity of carbon dioxide was 15.1%, and the conversion of ethylene was 14.9%.

[0043]

Comparative Example 2 In the step of supporting palladium of Example 1,
A catalyst was prepared by the same operation except that aluminum nitrate was not added. As a result of performing image analysis by performing the same processing as in Example 1, all palladium was supported within 10 μm from the outer surface of the particles. The specific surface area (MAS) of palladium metal determined from adsorption of carbon monoxide was 88 m ² / Pdg. The evaluation results performed in the same manner as in Example 2 showed that the selectivity for vinyl acetate was 85.4%, the selectivity for carbon dioxide was 14.5%, and the conversion of ethylene was 17.1%. When the wear strength was evaluated, the weight loss in 5 to 20 hours was 1.3%. Further, this sample after the evaluation of abrasion strength was dissolved in aqua regia and the reduction ratio of palladium was measured. As a result, a high value of 5.5% was shown.

[0044]

Industrial Applicability The catalyst of the present invention can be used in a fluidized bed reactor, and has high activity, so that vinyl acetate can be efficiently synthesized.

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Claims (4)

[Claims] 1. A palladium component and an alkali metal acetate supported on a carrier, wherein the carrier has a particle size of less than 200 μm and a bulk density of 0.7 to 1.5 g / ml, and the carrier is aluminum. And a magnesium-containing silica-based composition, wherein aluminum is 5 to 30% by weight as Al ₂ O ₃ ,
Comprises magnesium 3-30% by weight MgO, silicon in the range of 40 to 92 wt% as SiO _2, and,
Atomic ratio of magnesium to aluminum (magnesium /
Aluminum) having a layer in which the palladium component is supported in a range from 0 μm to less than 80 μm from the outer surface of the carrier toward the center from the outer surface of the carrier, and the surface area of the palladium metal component determined from the adsorption of carbon monoxide. Is 40 to 300 m ² /
A vinyl acetate synthesis catalyst, which is Pdg. 2. The vinyl acetate synthesis catalyst according to claim 1, wherein the palladium component is a palladium intermetallic compound. 3. The palladium intermetallic compound is composed of palladium and X (X = lead, bismuth, thallium, mercury, tellurium).
The vinyl acetate synthesis catalyst according to claim 2, which is an intermetallic compound of 4. A process for producing vinyl acetate from ethylene, oxygen and acetic acid using the vinyl acetate synthesis catalyst according to claim 1.