JPH0567131B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a method for producing benzoic acids, and more particularly, to a method for producing benzoic acids by directly oxidizing benzene using a specific palladium catalyst. [Prior Art and its Problems] Conventionally, there has been known a method for producing benzoic acid by bringing benzene into contact with carbon monoxide and oxygen in the presence of palladium acetate. In this method, the selectivity of benzoic acid is relatively high, reaching 70-75% by weight, but the conversion rate of benzene is only low, about 1.0-1.5% by weight. Therefore, overall, the yield of benzoic acid is low. [Object of the Invention] An object of the present invention is to overcome the above-mentioned problems and provide a method for directly oxidizing benzene to produce benzoic acid in high yield. [Means for achieving the above object] The gist of this invention for achieving the above object is as follows:
This is a method for producing benzoic acid, which comprises bringing carbon monoxide and oxygen into contact with benzene in the presence of palladium-supported carbon. The benzene is most preferably pure, but crude benzene obtained from various processes such as petroleum reforming process and catalytic cracking process, recovered benzene, etc. can also be used. The carbon monoxide is most preferably pure, but carbon monoxide-containing gases obtained from water gas, generator gas, coke oven gas, etc. can also be used. There are no particular restrictions on the oxygen, but
A mixed gas of oxygen gas and an inert gas such as nitrogen gas may be used if necessary. The carbon monoxide and oxygen capacity ratio is usually
The ratio is 8:2 to 2:8, preferably 5:5. The palladium-supported carbon is a solid catalyst in which at least one palladium component is supported on a carbon support. The amount of the palladium component supported is usually 0.5 to 20% by weight, preferably 1 to 10% by weight as palladium metal. Examples of the form of the palladium component in the palladium-supported carbon that can be suitably used as the catalyst as it is include highly dispersed metallic palladium and a palladium component that can be converted into this by the reaction. The carbon carrier may include amorphous carbon, graphite and mixtures thereof. Among these, graphite ultrafine particles or aggregates thereof, and amorphous carbon are preferable, and amorphous carbon can be particularly preferably used. Examples of the amorphous carbon in the present invention include carbon or carbon compositions generally referred to as amorphous carbon, microcrystalline carbon, amorphous carbon, glassy carbon, and the like. The main component of these amorphous carbons is carbon, but in addition to this, they may also contain heteroatoms such as hydrogen, oxygen, and nitrogen, metal atoms such as iron, and inorganic components such as ash. Are known. Examples of the amorphous carbon include carbon blacks such as furnace black, channel black, thermal black, and acetylene black; cokes such as petroleum coke, petroleum pitch coke, and petroleum coke; coal, peat, cut charcoal, natural grass charcoal, charcoal, Plant charcoal such as grass charcoal, fruit charcoal, nut shell charcoal, starch charcoal, sugar charcoal, molasses charcoal, cellulose charcoal; or mineral charcoal; animal charcoal such as animal charcoal, bone charcoal, blood charcoal; vinyl chloride charcoal, polychlorinated charcoal Various synthetic resin charcoals such as vinylidene charcoal, dimethylphenolaldehyde charcoal, phenol formaldehyde resin charcoal, polyolefin resin charcoal, polyacrylonitrile resin charcoal, polycarbonate resin charcoal; and these charcoals or various other carbon materials or carbon substances. Examples include various activated carbons obtained by activating materials. The starting materials for activated carbon include wood, sawdust, charcoal, rubber charcoal, coconut shell charcoal, palm kernel coal, peat, lignite, bituminous coal, anthracite, petroleum residue, sulfuric acid sludge, oil carbon, pulp waste liquid, petroleum coke, and petroleum. Typical examples include pitch, synthetic resin, and organic waste liquid. Among these various amorphous carbons, porous amorphous carbon, which is usually used as a catalyst carrier or adsorbent, is preferable.
Amorphous carbon of 200 m ² /g or more can be preferably used, and activated carbon can also be preferably used. The shape of the carbon carrier is not particularly limited, and examples thereof include powder, strip, cross, cylindrical, etc.
It can be used in various shapes or molded products. The palladium-supported carbon in this invention is
For example, commercially available activated carbon-supported palladium catalysts, palladium carbon catalysts, activated carbon-supported palladium hydroxide catalysts, etc. can be used in the reaction as they are, or after being subjected to activation treatment such as reduction treatment. It can be newly prepared and used by various methods from various palladium compounds and metallic palladium. The palladium compounds include palladium halides such as palladium fluoride, palladium chloride, palladium bromide, and palladium iodide; inorganic acid salts of palladium such as palladium nitrate, palladium sulfate, palladium acetate, palladium acetylacetonate, and palladium sulfide; Organic acid salts; palladium inorganic complex compounds such as tetraamminepalladium dichloride, hexachloropalladate, hexachloropalladate sodium salt, tetrachloropalladate, dinitrodiamminepalladium dichloride;
Palladium oxide, palladium hydroxide; [Pd(CO)
Palladium carbonyl complexes such as Cl ₂ ] ₂ , [Pd(CO) ₂ Cl] ₂ , palladium diisonitrile complexes, [PdCl ₂
(Olefin)] ₂ , [Pd(PPh ₃ ) ₂ (Olefin)],
Palladium olefin or allyl complex such as [PdCl(η ₃ −C ₃ H ₅ )] ₂ , [Pd(η ₃ −C ₃ H ₅ ) ₂ ], [η ₅ −
Palladium cyclopentadienyl complexes such as [C ₅ H ₅ PdCl] ₂ , palladium phosphine complexes such as [Pd(PPh ₃ ) ₄ ], [(CH ₃ ) ₂ PdPPh ₃ ], [CH ₃ PdOCOCH ₃ ]
Examples of palladium compounds include various organic palladium compounds such as palladium alkyl complexes, palladium aryl complexes, and palladium acyl complexes. In addition, examples of the metallic palladium include colloidal palladium, ultrafine particulate palladium, and the like. Among these various palladium compounds and metallic palladium, halogenated palladium such as palladium chloride, tetrachloropalladium, hexachloropalladium acid, palladium hydroxide, and colloidal palladium are preferable, and palladium dichloride and tetrachloropalladium acid are preferable. The various palladium compounds and metallic palladium may be used singly or in combination of two or more in preparing the catalyst.
Further, the various palladium compounds may be anhydrous or hydrated, and may be an aqueous solution, suspension,
It can be used in various forms such as acidic solutions, alkaline solutions, and dissolved forms in organic solvents. Examples of methods for preparing the catalyst include adsorption from a solution such as an ordinary aqueous solution, impregnation, immobilization, dry mixing, wet kneading, vapor phase sublimation adsorption, vapor deposition, and grinding. Support can be prepared by various methods. For example, as a method for supporting palladium chloride, an impregnation method using an acidic aqueous solution of palladium chloride in hydrochloric acid is preferably used. The solid prepared as a support by the above method can be used as a catalyst in a reaction as it is, but usually,
It is preferable to activate the catalyst by reduction or decomposition treatment to produce a highly dispersed metallic palladium or highly dispersed palladium hydroxide component on a carbon carrier, and use it in the reaction as a so-called supported palladium catalyst. Examples of the reduction method include a wet reduction method using an aqueous or alkaline solution of aldehydes such as sodium formate and formaldehyde, oxalic acid, and hydrazine, or a dry reduction method using a reducing gas such as carbon monoxide, hydrogen, and ethylene. Conventional reduction methods can be used. The wet reduction treatment can be generally carried out at a temperature of 0 to 100°C, preferably room temperature to 90°C. In addition,
This wet reduction treatment may be carried out simultaneously with the preparation of the palladium compound on the support, or may be carried out before drying the prepared solid on the support. The solid obtained through this wet reduction treatment is usually separated from the solution by a separation method such as filtration, and then dried by a normal drying method such as vacuum drying, heat drying, gas flow drying, etc. It can be used as a catalyst in reactions. On the other hand, the dry reduction treatment or thermal decomposition treatment
After separating the liquid such as a solution or solvent from the supported solid, usually by filtration or impregnation to dryness, if necessary, further drying by a conventional drying method, and the obtained solid is For example, 100-500
It can be carried out by heat treatment at a temperature of 150 to 300°C, preferably in the reducing gas or an inert gas such as nitrogen or helium, or under vacuum. By such treatment, highly dispersed metallic palladium is produced on carbon support, and a so-called carbon-supported palladium catalyst can be prepared. The carbon-supported palladium thus prepared can be used in the reaction as it is, or as a catalyst after being subjected to pretreatment such as reduction treatment or steam treatment, if necessary, before the reaction. As mentioned above, this palladium-supported carbon catalyst can be prepared from various raw materials by various methods, but among them, palladium chloride is dissolved in an acid such as an aqueous hydrochloric acid solution, and amorphous carbon is added thereto. Then a predetermined temperature, for example 60-100
Preference is given to the preparation method by heating to 0.degree. C., followed by addition of a formate, such as sodium formate, and a carbonate, such as sodium carbonate, followed by reduction treatment with heating. In the method of the present invention, benzoic acid can be produced by bringing the benzene, carbon monoxide, and oxygen into contact with the palladium-supported carbon to carry out the reaction. In the reaction, the amount of each component cannot be absolutely specified, but usually, the amount of the palladium-based catalyst is 0.05 to 30.0 g per mole of benzene in terms of palladium metal.
atoms, particularly preferably 0.30 to 3.00 g atoms. Reaction conditions such as reaction temperature and reaction pressure cannot be unconditionally defined as they vary depending on the type of palladium-supported carbon, but in general, the following conditions can be employed. The reaction temperature is usually 50 to 300°C, preferably
The temperature is 80-200℃. If the reaction temperature is lower than 50℃,
Benzene conversion may be low and productivity may be low. On the other hand, if the reaction temperature is higher than 300°C, the selectivity to benzoic acid may be low or the catalyst activity may be significantly deteriorated. The reaction pressure is usually 0 to 50 kg/cm ² G, preferably 5 to 30 kg/cm ² G. This reaction pressure depends on the autogenous pressure of the reaction system, that is, the pressure of carbon monoxide and oxygen, the vapor pressure of benzene, the vapor pressure of the product, or the vapor pressure of the inert solvent or inert gas used as the case requires. It can be prepared by However, when carrying out this reaction, an inert solvent,
An inert gas is not necessarily required, and it may be preferable not to use it. When the reaction pressure is lower than 0 Kg/cm ² G, that is, when the pressure of carbon monoxide is low, the selectivity of benzoic acid may decrease significantly. Carbon monoxide is essential in the reaction. while the pressure is 50
If it is higher than Kg/cm ² G, that is, if the pressure of carbon monoxide is too high, the yield of benzoic acid may become low. That is, in order to improve the yield of benzoic acid, there is an appropriate range for the pressure of carbon monoxide. The reason for this is not clear, but for example,
By coordinating carbon monoxide to palladium in the catalyst in an appropriate proportion, the selectivity of the reaction between benzene and water improves; on the other hand, if the pressure is too high, palladium may be coated with more carbon monoxide than necessary. It can be considered that this decreases the number of active sites and lowers the yield of benzoic acid. The reaction time of the above reaction is usually 0.5 to 30 hours, preferably 1 to 20 hours. This reaction time is 0.5
If the reaction time is shorter than 30 hours, the conversion rate of benzene may decrease, while if the reaction time is longer than 30 hours, the yield of benzoic acid cannot be expected to increase to the extent that the reaction time is increased, and the productivity may decrease. It may decrease. The reaction can be carried out by various reaction methods and reaction operations, such as a batch method, a semi-batch method, and a continuous method. Further, the catalyst may be used in a slurry state, a fixed bed, a moving bed, or a fluidized bed. There is no particular restriction on the order of contacting each component of the reaction raw material with the catalyst. After the reaction, the reaction product can be separated from solids such as the catalyst automatically or by conventional separation methods such as filtration and distillation. This recovered reaction product contains benzoic acid, which is the target product, and this benzoic acid can be processed by sequential treatments such as distillation, solvent extraction, alkaline water treatment and acid treatment, or by appropriate treatment. The recovered reaction product can be separated and purified by conventional separation and purification methods such as operations combined with the above. Also,
A portion of the reaction product and/or unreacted benzene after separating benzoic acid can be recycled to the reaction system and used again. When the above reaction is carried out by a batch operation method, the catalyst recovered by separating the reaction products after the reaction can be used as it is, or after regenerating a part or all of it, repeatedly as a catalyst for the reaction. I can do it. When the above reaction is carried out in a continuous manner, the catalyst which has been partially or completely deactivated by being subjected to the reaction can be regenerated and used in the reaction after stopping the reaction, or can be continuously carried out. Alternatively, a portion of the catalyst may be intermittently taken out from the reactor during the reaction, regenerated in a catalyst regenerator, and recycled to the reactor again for use in the reaction. [Effects of the Invention] According to the present invention, benzoic acid can be easily produced in high yield by directly oxidizing benzene by using a specific palladium catalyst.
This is something that could not be expected from conventional palladium acetate catalysts. Thus, the present invention can provide a novel method for producing benzoic acids that is industrially extremely advantageous. [Example] Examples 1 to 3 Preparation example of Pd/carbon catalyst 0.82 g of palladium chloride, 2.0 ml of 2N hydrochloric acid and 5.0 ml of water
ml of the mixture, add 14 ml of water, and make 80
After heating to .degree. C., 9.2 g of powdered amorphous carbon was added thereto, and the mixture was stirred at 80.degree. C. for 5 minutes. Next, add 2 g of sodium formate and 3 g of sodium carbonate to 40
℃ for 10 minutes, filtered and dried at 100℃ for 1 hour to obtain a palladium-supported carbon (hereinafter sometimes referred to as 5% palladium-supported carbon) catalyst containing 5% by weight of palladium metal. Obtained. Reaction Example A stainless steel autoclave equipped with a magnetic stirring device was charged with benzene in the amount shown in Table 1 and the 5% by weight palladium-supported carbon catalyst obtained in the catalyst preparation example, and carbon monoxide and oxygen (50% by weight) were charged.
A direct oxidation reaction of benzene was carried out under the indicated conditions using a mixed gas (50, volume ratio) at the indicated pressure. The reaction product was subjected to gas chromatography to confirm benzoic acid and determine its yield. The results are shown in Table 1. Comparative Example 1 The same procedure as in Example 1 was carried out except that palladium acetate was used in the amount shown in Table 1 instead of palladium-supported carbon. The results are shown in Table 1.

【table】

[Table] As shown in Table 1, under the same reaction conditions,
The yield of benzoic acid is much higher when using palladium-supported carbon as a catalyst than when using palladium acetate as a catalyst.

Claims (1)

[Claims] 1. A method for producing benzoic acid, which comprises bringing carbon monoxide and oxygen into contact with benzene in the presence of palladium-supported carbon. 2. The method for producing benzoic acid according to claim 1, wherein the catalyst is palladium-supported amorphous carbon. 3. The method for producing benzoic acid according to claim 1 or 2, wherein the catalyst is a catalyst prepared from palladium halide and amorphous carbon.