JP2003024782A - Carboxylic acid ester producing catalyst excellent in activity - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eminently reduce a catalyst cost by developing high reactivity and using expensive palladium effectively with regard to a catalyst for producing a carboxylic acid ester from an aldehyde, an alcohol, and oxygen. SOLUTION: In the metal catalyst containing palladium supported on active carbon, the active carbon carrier has a specific surface area of 500-1,500 m<2> , a particle size of 75-600 meshes, and a bulk density of 0.3-0.8 g/mL, and a palladium-containing metal supported on the carrier has a specific surface area of at least 50 m<2> /g.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a catalyst for producing a carboxylic acid ester from an aldehyde, an alcohol, and oxygen, which exhibits high reaction activity and effectively uses expensive precious gold palladium. It offers significant cost improvements.

[0002]

2. Description of the Related Art Methods for producing carboxylic acid esters from aldehydes, alcohols and oxygen using a catalyst containing palladium are known. In addition, conventionally, various types of carriers having a relatively high surface area, such as palladium, have generally been selected according to the intended reaction, and noble metals such as palladium have been used by being supported and dispersed on the carrier. For example, it has been reported that various kinds of carriers are selected and used as carriers also in the production of the above-mentioned carboxylic acid ester. Specifically, those using calcium carbonate are disclosed in JP-B-57-35856 and JP-B-57-35860, and those using zinc oxide-alumina, titania-lanthanum oxide, and zinc oxide-titania are particularly fair. The one using zinc oxide is disclosed in Japanese Patent Publication No. 4-72578. Further, from the viewpoint of improving the strength of the catalyst, the one using silica-alumina is disclosed in JP-A-8-332383.
A method using silica-alumina-magnesia is disclosed in Japanese Patent Application Laid-Open No. H9-96952.
-52044 discloses that using zeolite is disclosed in JP-A-9-192495.

[0003]

Noble metals such as platinum and palladium are used in large amounts as catalysts for purifying automobile exhaust gas and as electrode catalysts for fuel cells, and the demand is increasing every year and prices remain stable at high prices. ing. Since precious metals are rare resources and are expensive, achieving high activity and reducing the amount used are becoming more and more important. Therefore, the present invention focuses on palladium among noble metals, and it is an object to realize high activation of a palladium-supported catalyst, reduce the amount used, and significantly reduce the catalyst cost.

[0004]

In view of the present circumstances as described above, the present inventors have made detailed investigations on the high activation of palladium-supported catalysts in order to reduce the amount of precious metal palladium used. As a result, they have found that activated carbon having specific physical properties has high reaction activity. In addition, in the process of catalysis, high reaction activity is achieved by a method in which activated carbon is preheated with nitric acid and used to support the palladium compound, and the supported palladium compound is treated with alkali before reduction treatment. As a result, they have completed the present invention.

That is, the present invention is as follows. An activated carbon-supported palladium-containing metal catalyst having a specific surface area of 500 to 1500 m ² / g and a particle size of 7
5-600 mesh, bulk density 0.3-0.8g / ml
And the specific surface area of the supported palladium-containing metal is 50 m ² / g or more, the activated carbon-supported palladium-containing metal catalyst for producing a carboxylic acid ester. In the present invention, the “palladium-containing metal” means a palladium simple metal and / or a palladium intermetallic compound.

It is generally said that it is preferable that the carrier has a large specific surface area in order to highly disperse the catalytically active component, and activated carbon or graphite used for a fuel cell has a specific surface area of about 3000 m ² / g. Supports with extremely large surface areas are used to develop the high activity of noble metal supported catalysts. The present investigators have extensively studied various types of carriers and carriers having different carrier physical properties. as a result,
In catalysts for producing carboxylic acid esters from aldehydes, alcohols, and oxygen, the bulk density of the carrier is important from the characteristics of the catalyst slurry, and activated carbon with an extremely large specific surface area has low mechanical strength and is not practical. It was clarified that the activity was decreased and the separation of the catalyst and the reaction solution occurred when the particle size was outside the range. That is, it has been found that the use of activated carbon having specific physical properties makes it possible to exhibit higher catalytic activity than conventional catalysts for the first time. It is not clear in detail why the high activation is achieved.

As the physical properties of activated carbon, the specific surface area is 500 to 1
The range is preferably 500 m ² / g, more preferably 60.
It is in the range of 0 to 1300 m ² / g. When it is less than 500 m ² / g, the dispersibility of palladium is deteriorated and the activity is lowered, and when it is more than 1500 m ² / g, the activity tends to be high, but it is not preferable because it may lower the mechanical strength and the fluidity. The particle size of the activated carbon is preferably 75 to 600 mesh. If it is smaller than 600 mesh, there is no problem in terms of reaction activity, but it is not preferable because the sedimentation property is poor, and the catalyst is difficult to separate from the reaction solution because clogging of the filter is likely to occur. On the other hand, if it is larger than 75 mesh, the reaction activity tends to decrease, which is not preferable. From the viewpoint of the balance between the separation property from the reaction solution and the reaction activity, the range of 100 to 500 mesh is more preferable.

The bulk density of activated carbon is an important factor from the catalyst slurry state, and 0.3 to 0.8 g / ml is preferable,
If it is less than 0.3 g / ml, the amount of the catalyst is large and the bulk becomes high, and the viscosity of the reaction solution increases, which is not preferable. On the other hand, 0.8
When it is larger than g / ml, the specific surface area is small as a result, and the pore volume is small, so that the activity tends to be low. Therefore, the range of the bulk density is more preferably 0.35 to 0.6 g / ml in view of the balance between reaction characteristics and activity. The specific surface area of the palladium-containing metal supported on activated carbon is one of the important factors for the activity expression of the catalyst and is required to be 50 m ² / g or more. More preferably 70m ² / g or more, more preferably 100 m ² /
It is preferably as large as g or more.

The palladium-containing metal supported on the activated carbon may be a palladium simple metal, but a palladium intermetallic compound is preferable for the production of carboxylic acid ester. For example, Pd ₃ Pb ₁ consisting of palladium and lead
Intermetallic compounds, as well as palladium intermetallic compounds of palladium with bismuth, thallium, mercury, gold, etc. are preferred. Furthermore, in some cases, nickel, chromium, cobalt, indium, tantalum, copper, zinc, zirconium, hafnium, tungsten, manganese, silver,
Rhenium, antimony, tin, rhodium, ruthenium,
It may contain iridium, platinum, titanium, aluminum, boron, silicon and the like. These foreign elements are usually 5% by weight, preferably 1% by weight, based on the total amount of catalyst species after reduction.
It can be included in the range of weight percent.

Examples of the palladium compound or the lead compound used for preparing the catalyst include organic acid salts such as formate salts and acetate salts, inorganic acid salts such as sulfates, hydrochlorides and nitrates, ammine complexes and benzonitrile complexes. It is appropriately selected from organic metal complexes such as, oxides, and hydroxides. Palladium compounds such as palladium chloride and palladium acetate are preferred. In the present invention, it is essential that the activated carbon is heat-treated with an aqueous nitric acid solution, and further treated with an alkaline substance before the reduction treatment of the palladium compound supported by the activated carbon. Treatment of activated carbon is 3
A nitric acid concentration of 0 to 60% and a temperature range of room temperature to 100 ° C., but a temperature of about 90 ° C. is usually selected as a general temperature from the viewpoint of time and effect. The treatment time is generally 30 minutes to 48 hours, though it varies depending on the nitric acid concentration and the treatment temperature.

In the alkali treatment before the reduction of the palladium compound carried on the activated carbon, Li as an alkaline substance,
It is possible to select and use from alkali compounds such as alkali metals such as Na, K, Rb, Cs, Mg, Ca, Sr and Ba, and hydroxides of alkaline earth metals, carbonates and metal alkoxides. The amount and concentration used for the alkali treatment of the palladium compound before reduction varies depending on the amount of the palladium compound supported on the activated carbon and the type of the alkaline compound used,
A stoichiometric amount or more, preferably 2 to 3 times / Pd mole, necessary for converting the amount of the supported palladium compound into a hydroxide is used. The concentration of a general alkaline solution is, for example, 0.1 to 10 mol / l, which can be selected and used according to the amount of palladium supported. Although water is mainly used as a solvent for the alkali treatment solution, an alkali-soluble solvent having methanol or the like as a solvent can also be used.

The operation of alkali treatment before the reduction of the palladium compound can be carried out at a temperature of room temperature to 100 ° C. It is also possible to apply the pressure required to maintain the liquid phase even at a temperature of 100 ° C. or higher, and it can be carried out under the conditions of room temperature to 160 ° C. and atmospheric pressure to several atmospheres. The time required for the alkali treatment varies depending on the amount of the palladium compound supported and the amount of the catalyst to be prepared, but is generally in the range of 30 minutes to 6 hours. The amount of palladium supported on the activated carbon carrier is not particularly limited, but is usually 0.1 to 20% by weight, preferably 1 to 10% by weight based on the weight of the carrier. The amount of other metals is usually 0 to 20% by weight, preferably 1 to 5% by weight.

A general reduction method can be applied to the reduction of the palladium compound or other metal compound for forming the palladium intermetallic compound. It can be carried out in any form of gas phase and liquid phase using a reducing agent such as hydrogen, formalin, alcohol, hydrazine, NaBH ₄ . The optimum reduction method is selected depending on the amount of the palladium compound supported and the combination with a promoter metal other than palladium. When reducing in the gas phase, it is common to use hydrogen as a reducing agent at a temperature of 200 to 400 ° C. Further, in the case of reduction in the liquid phase, a general reduction method which is performed by blowing hydrogen at a temperature of room temperature to 200 ° C. or by adding formalin, NaBH ₄ , and hydrazine is adopted. It is possible to carry out the treatment at a temperature of 100 ° C. or higher by applying a pressure necessary to keep the liquid phase. It is preferably carried out under the conditions of room temperature to 160 ° C. and atmospheric pressure to several atmospheres. The time required for the reduction treatment varies depending on the treatment conditions such as the combination and type of the palladium compound and other constituent catalysts, the amount supported, and the amount of catalyst, but it is generally 0.5 to 50 hours. Usually, it is convenient from the operability to set the conditions so that the treatment is completed within 24 hours.

In the production of the carboxylic acid ester of the present invention, the amount of the catalyst used depends on the type of reaction raw material, the composition and preparation method of the catalyst,
Although it can be widely changed depending on the reaction conditions, the reaction format, etc., it is not particularly limited, but when the catalyst is reacted in the slurry state, it is preferable to use 0.04 to 0.5 kg in 1 l of the reaction liquid. More preferably 0.1-0.3K
It is in the range of g. Examples of alcohols used in the present invention include aliphatic saturated alcohols such as methanol, ethanol, isopropanol, butanol, 2-6 hexanol, and octanol; alicyclic alcohols such as cyclopentanol and cyclohexanol; ethylene glycol; Examples thereof include diols such as propylene glycol and butanediol; aliphatic unsaturated alcohols such as allyl alcohol and methallyl alcohol; aromatic alcohols such as benzyl alcohol; and hydroxyoxetanes such as 3-alkyl-3-hydroxymethyloxetane. These alcohols can be used alone or as a mixture of two or more kinds.

There is no particular limitation on the ratio of aldehyde to alcohol used in the reaction of the present invention.
It can be carried out in a wide range such as a molar ratio of alcohol of 10 to 1/1000, but is generally carried out in a range of 1/2 to 1/50. The oxygen used in the present invention is molecular oxygen,
That is, the oxygen gas itself or a mixed gas obtained by diluting the oxygen gas with a reaction-inert diluent such as nitrogen or carbon dioxide gas can be used, and air can also be used. The amount of oxygen supplied to the reaction system is controlled so that the oxygen partial pressure on the outlet side of the reactor is 0.8 atm or less. It is preferably 0.4 atm or less. On the other hand, it is advisable to set the total pressure so that the oxygen concentration of the reactor outflow gas does not exceed the explosion range (8%).

The reaction of the present invention can be carried out by any conventionally known method such as a bubble column, a stirring tank, an irrigation reactor and the like. Further, the oxygen partial pressure of the outlet gas of each reactor may be changed for each reactor as long as it is within the range of the conditions of the present invention. In the reaction of the present invention, the pH of the reaction system is maintained at 6 to 9 by adding an alkali metal or alkaline earth metal compound (eg, oxide, hydroxide, carbonate, carboxylate, etc.) to the reaction system. It is preferable. These alkali metal or alkaline earth metal compounds can be used alone or in combination of two or more. The reaction of the present invention can be carried out at a high temperature of 100 ° C. or higher, but preferably 30 to 100 ° C.
Is. The reaction pressure can be carried out in any wide pressure range from reduced pressure to increased pressure, but it is usually 1 to 20 Kg / c.
It is carried out at a pressure of m ² . The reaction time is not particularly limited and cannot be uniquely determined because it varies depending on the set conditions, but it is usually 1 to 20 hours.

The present invention will be described in more detail with reference to the following examples and comparative examples, but the present invention is not limited thereto. In the following examples and comparative examples, the physical properties, specific surface area, bulk density, particle size, and palladium specific surface area of the catalyst of the activated carbon carrier were measured by the following methods. [Measurement of Specific Surface Area of Activated Carbon Carrier] A nitrogen gas adsorption method (manufactured by Yuasa Ionics Inc., Autosorb: 3AG type) was used. [Measurement of Bulk Density] As a pretreatment, the carrier was dried in a vacuum dryer for 8 hours.
After drying at 0 ° C for 6 hours and cooling, 50.0 g of the carrier was weighed at room temperature, transferred to a graduated cylinder, and the graduated cylinder was shaken for 1 hour.
Tap and fill for 5 minutes. Flatten the sample surface and read the fill volume. Bulk density is the weight of the carrier divided by the fill volume. [Preparation of particle size] 75-60 obtained by classifying 600-mesh and 75-mesh sieve in a shaker and classifying activated carbon
The one with 0 mesh was used. [Measurement of specific surface area of metal containing palladium] CO gas adsorption method (manufactured by Okura Riken Co., Ltd., fully automatic CO gas adsorption amount measuring device R60
15-G) was used.

[0018]

[Example 1] Activated carbon (Takeda Pharmaceutical Co., Ltd., trade name: X7)
100-3) is crushed with a ball and classified by a sieve,
Particles of 75-600 mesh were obtained. 60% nitric acid solution
Put it in the tube and treat it at 90 ° C for 30 minutes, and after filtering, distilled water
It was washed 10 times with. Then, in a vacuum dryer at 80 ° C for 6 hours
After drying, the specific surface area of the activated carbon was measured and found to be 978 m. ²
/ G, and the bulk density was 0.35 g / ml. Pretreated
100 g of activated carbon was weighed and used for preparation of the catalyst. salt
Palladium chloride is used as palladium per 100 parts by weight of the carrier.
3 parts by weight of palladium chloride so that the carrier is 3 parts by weight.
% And 2% by weight sodium chloride in water at room temperature
Stir at room temperature for 1 hour to allow palladium chloride to be completely adsorbed on the carrier.
Let Then, decant the liquid and adsorb palladium chloride.
The carrier thus obtained was washed 10 times with distilled water.

Next, 300 ml of distilled water was added. Na
An alkaline aqueous solution prepared by dissolving 6.5 g of OH in 75 ml of water was added dropwise over about 10 minutes while stirring, and then maintained for 15 minutes. Next, the supernatant was decanted and washed with distilled water 10 times. Next, the solution was prepared by adding Na acetate to 6 wt% and stirred. Next, lead acetate is added to Pd to P
An equivalent amount of d / Pb = 3 / 1.3 (molar ratio) was added, and the mixture was stirred at 60 ° C. for about 30 minutes. Next, a palladium-lead intermetallic compound was reduced by slowly dropping an aqueous solution of NaBH _{4 in a} 3-fold molar amount with respect to Pd + Pb over about 30 minutes while stirring. After the dropping, it was kept for another 30 minutes. Next, wash with water 10
I went there. Then, it was dried in a vacuum dryer at 80 ° C. for 6 hours to obtain a palladium-lead intermetallic compound catalyst supporting activated carbon. The obtained catalyst was measured by the CO gas adsorption method, and the specific surface area of the palladium-lead intermetallic compound was determined to be 109 m.
A value of ² / g was obtained.

As a condition for evaluating the activity of the reaction, the catalyst amount was set in advance by an experiment so that the conversion was 20% or less of the low conversion rate, which is less likely to be affected by the orders of methacrolein and methanol. 1.0 g of the obtained catalyst was placed in a 100 ml flask equipped with a condenser on the top, 80 g of a 10 wt% methacrolein / methanol solution was added, and a Teflon (registered trademark) -coated rotor was put therein while stirring with a magnetic stirrer. 82% 7vol% oxygen / helium gas
It was blown at a rate of ml / min and reacted at 45 ° C. for 2 hours. After the reaction, the conversion rate of methacrolein was 16.5 from the analysis values of the product in the reaction solution and the vent gas by gas chromatography.
%, Selectivity of methyl methacrylate (MMA) 89.2%
Met. The productivity of MMA per g of palladium-lead intermetallic compound was 0.28 mol / h · g.

[0021]

Comparative Example 1 A palladium-lead intermetallic compound-supported catalyst was obtained in the same manner as in Example 1 except that the silica-alumina-magnesia carrier described in Example 1 of JP-A-9-52044 was used. When the specific surface area of the palladium-lead intermetallic compound was determined, a value of 88 m ² / g was obtained. The reaction was carried out at 45 ° C. for 2 hours under the same conditions except that the catalyst amount of Example 1 was changed to 1.0 g and the catalyst amount was doubled to 2.0 g. After the reaction, the product was analyzed by gas chromatography to find that the conversion of methacrolein was 9.5% and methyl methacrylate (MM
The selectivity of A) was 88.5%. The productivity of MMA per g of palladium-lead intermetallic compound is 0.08 mol /
It was h · g.

[0022]

[Comparative Example 2] Activated carbon (Takeda Pharmaceutical Co., Ltd., trade name: X7)
100-3) is crushed with a ball and classified by a sieve,
Particles of 75-600 mesh were obtained. 60% nitric acid solution
It is put into a container and treated at 90 ° C for 24 hours, filtered and distilled water.
It was washed 10 times with. Then, in a vacuum dryer at 80 ° C for 6 hours
After drying, the specific surface area of activated carbon was measured and found to be 439 m. ²
/ G, and the bulk density was 0.46 g / ml. This activated carbon
A catalyst was obtained in the same manner as in the example except that was used. Para
When the specific surface area of the indium-lead intermetallic compound was calculated, it was 66.
m²A value of / g was obtained. Example 1 except that the catalyst was changed
The reaction was carried out under the same conditions at 45 ° C. for 2 hours. After reaction
When the product was analyzed by means of
In conversion of 10.2%, methyl methacrylate (MM
The selectivity of A) was 88.7%. MMA Palladium
-Productivity per g of lead intermetallic compound is 0.17 mol /
It was h · g.

[0023]

Comparative Example 3 Activated carbon (Kureha Chemical Co., Ltd., trade name: B
AC-MP, particles having an average particle size of 500 microns (30 mesh) were used, and pre-treatment with nitric acid was not performed, followed by washing with distilled water 10 times. Then, after drying in a vacuum dryer at 80 ° C. for 6 hours, the specific surface area of the activated carbon was measured and found to be 823 m.
² / g, and the bulk density was 0.54 g / ml. A catalyst was obtained in the same manner as in Example 1 except that this activated carbon was used.
When the specific surface area of the palladium-lead intermetallic compound was determined, a value of 73 m ² / g was obtained. The reaction was carried out at 45 ° C. for 2 hours under the same conditions as in Example 1 except that the catalyst was changed. After the reaction, the product was analyzed by gas chromatography to find that the conversion of methacrolein was 5.1% and methyl methacrylate (M
The selectivity for MA) was 89.4%. The productivity of MMA is 0.087mo per g of palladium-lead intermetallic compound.
It was 1 / h · g.

[0024]

Comparative Example 4 A catalyst was obtained by the same procedure as in Example 1 except that the alkali treatment after carrying the palladium compound was not carried out. When the specific surface area of the palladium-lead intermetallic compound was determined, a value of 112 m ² / g was obtained. Reaction was carried out at 45 ° C. for 2 hours under the same conditions as in Example 1 except that this catalyst was used. When the product was analyzed by gas chromatography after the reaction, the conversion rate of methacrolein was 3.2% and the selectivity of methyl methacrylate (MMA) was 86.7%. MMA
The productivity per g of the palladium-lead intermetallic compound is 0.
It was 053 mol / h · g.

[0025]

Example 2 Using the catalyst obtained in Example 1, reaction was carried out at 45 ° C. for 2 hours under the same conditions and operations except that methacrolein was changed to acrolein as a reaction raw material. After the reaction, the product was analyzed by gas chromatography to find that the acrolein conversion rate was 20.1% and methyl acrylate (M
The selectivity of A) was 90.7%. MA Palladium-
Productivity per g of lead intermetallic compound is 0.454 mol /
It was h · g.

[0026]

[Effect of the Invention] When carboxylic acid ester is produced by reacting aldehyde and alcohol with molecular oxygen, activated carbon having specific physical properties is used as a carrier, pretreatment of activated carbon with nitric acid and alkali treatment after supporting palladium compound. The palladium-containing metal catalyst obtained by carrying out the above can obtain a high carboxylic acid ester forming activity. A significant reduction in catalyst cost can be achieved compared to conventional palladium catalysts.

Front page continuation (51) Int.Cl. ⁷ identification code FI theme code (reference) C07C 69/54 C07C 69/54 Z // C07B 61/00 300 C07B 61/00 300 F term (reference) 4G069 AA03 AA08 BA08A BA08B BB02A BB02B BC21B BC72A BC72B CB75 DA08 EA01Y EB18X EC02X EC03X EC04X EC05X EC21X FA01 FA02 FB14 FB17 FB20 FB43 4H006 AA02 AC48 BA25 BA55 BA56 BA81 BA85 BE30 KA35 4H039 CA66 CC30 CD10 CE10 CD30 CD10 CE10

Claims (3)

[Claims] 1. An activated carbon-supported palladium-containing metal catalyst for producing a carboxylic acid ester from an aldehyde, an alcohol, and oxygen, wherein the activated carbon carrier has a specific surface area of 500 to 1500 m ² / g and a particle diameter of 75 to 600. Mesh with a bulk density in the range of 0.3-0.8 g / ml,
And the specific surface area of the supported palladium-containing metal is 50 m
An activated carbon-supported palladium-containing metal catalyst for producing a carboxylic acid ester, which has a content of ² / g or more. 2. The activated carbon is pretreated with an aqueous nitric acid solution and then loaded with a palladium compound, and then the loaded palladium compound is treated with an alkaline substance and then reduced, or the palladium compound and a palladium metal-metal compound by reduction thereof are used. The method for producing an activated carbon-supported palladium-containing metal catalyst for producing a carboxylic acid ester according to claim 1, wherein the metal compound forming a compound is reduced together. 3. A method for producing a carboxylic acid ester from an aldehyde, an alcohol, and oxygen in the presence of a catalyst, wherein the aldehyde is acrolein or methacrolein, and the catalyst is a palladium-containing metal supported on activated carbon according to claim 1. A method for producing a carboxylic acid ester, which is a catalyst, wherein the obtained carboxylic acid ester is an acrylic acid ester or a methacrylic acid ester.