JPH027939B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing acrylamide by hydrating acrylonitrile. More specifically, it relates to a method for maintaining the concentration of water in a reaction solution within a specific range when producing acrylamide by hydrating acrylonitrile in the presence of an oxide catalyst consisting of titanium and zinc. . As a method for producing acrylamide, a method is known in which acrylonitrile is reacted with water in the presence of a metal copper-containing catalyst. However, when using a metallic copper-based catalyst, increasing the nitrile concentration in the reaction solution reduces the reaction rate to amide, so a dilute nitrile concentration of about 30% or less is usually used (Tokuko Showa). (According to Publication No. 55-27898). The present inventors have previously discovered that a composite oxide catalyst containing titanium exhibits a good catalytic effect on the hydration reaction of nitrile. After that, we conducted intensive research on the relationship between reaction conditions and amide yield using an oxide catalyst consisting of titanium and zinc, and found that the region with high nitrile concentration was better than the region with low concentration at a constant temperature. We have discovered the surprising fact that the yield of amide increases per unit time and per unit catalyst weight, and the selectivity to undesirable by-products such as acrylic acid and ethylene cyanohydrin decreases significantly. I was able to complete it. The present invention aims to provide an industrially useful method for hydrating nitriles to produce the corresponding amides. According to the present invention, when acrylonitrile is hydrated in the presence of an oxide catalyst consisting of titanium and zinc to produce acrylamide, the concentration of water in the reaction solution in the reactor is adjusted to the concentration of water in the reaction solution. This can be achieved very easily by keeping the content at 15% by weight or less and 0.1% by weight or more. Next, the present invention will be explained in more detail. The oxide catalyst composed of titanium and zinc used in the method of the present invention contains oxides of titanium and zinc as essential components, and includes solid solutions and non-stoichiometric oxides. This also includes physical mixtures of single oxides, such as titanium dioxide and zinc oxide. The term "oxide" is also defined to include hydrated oxides or hydroxides. The oxide catalyst used in the present invention can be prepared in any convenient manner that can be employed in the preparation of catalysts of this type. As a preparation method, a precipitation method can be preferably employed. i.e. salts of titanium and zinc, such as sulfates, nitrates, oxylates, halogenates,
Adding a solution, especially an aqueous solution, of an alkaline substance such as aqueous ammonia, alkali hydroxide, alkali carbonate, organic amines, etc. to a solution of an organic acid salt, especially an aqueous solution, or heating and stirring in the presence of urea, etc.
A commonly used method is to generate a precipitate of a corresponding metal hydroxide or hydrous oxide by a so-called homogeneous precipitation method, and to sinter the resulting precipitate at an appropriate temperature. The oxide catalyst thus obtained is preferably calcined to stabilize the catalyst structure. The firing temperature of the above catalyst is in the range of 50℃ to 600℃,
More preferably, the temperature range is from 100°C to 300°C. Such an oxide catalyst can be used by being supported on a carrier, as is customary for this type of catalyst. Therefore, suitable supports such as silica, alumina, silica/alumina, diatomaceous earth,
Alundum, corundum, activated carbon, naturally occurring silicates, etc. can be supported on the metal compound at any stage of the catalyst preparation process described above. The hydration reaction of acrylonitrile is carried out in a fixed bed or suspended bed in the presence of the above catalyst. Depending on the type of reactor, there may be a spatial or temporal distribution of the water concentration within the reactor. For example, in a fixed bed reactor, the inlet moisture concentration is higher than the outlet moisture concentration. Furthermore, in the case of a batch reaction, the concentration of water changes with time, regardless of the type of reactor. When the water concentration changes spatially or temporally, the water concentration in the present invention refers to the maximum water concentration in the reactor, or the initial water concentration in the case of a batch reaction. The concentration of water defined in this way is preferably 15% by weight or less of the reaction solution, and more preferably 7% by weight or less. When the water concentration exceeds 15% by weight, the activity and selectivity of the catalyst decreases. Furthermore, since the presence of a free aqueous phase reduces selectivity, it is desirable that the water concentration be below the solubility of water at the reaction temperature. Sufficiently high reaction rates cannot also be achieved if the water concentration is too low. Therefore, it is necessary that the water concentration be at least 0.1% by weight. The hydration reaction of nitrile according to the method of the present invention is usually carried out at a temperature of room temperature to 300°C using the above-mentioned catalyst, but it may be carried out at a temperature of 20°C to 150°C in order to increase the reaction rate and suppress side reactions. Particularly preferred. The reaction is usually carried out in the liquid phase. In order to inhibit polymerization during the reaction, suitable polymerization inhibitors such as hydroquinone, phenothiazine, p
-tert-butylcatechol etc. can be added as necessary. It is also possible to suppress polymerization by dissolving oxygen in the reaction feed solution. In carrying out the method of the present invention, a stable solvent that can withstand use at the reaction temperature can also be used together with water. Examples of solvents used in the present invention include alcohols, ketones, amides, sulfoxides, and specific examples include methanol, ethanol, isopropanol, acetone, dimethylformamide, dimethylsulfoxide, formamide, acetamide, and the like. Next, the present invention will be explained using Examples, but these Examples do not limit the present invention. (Catalyst Preparation) Slowly drop 2.5 mol of titanium tetrachloride (TiCl _{4 )} into 500 ml of ion-exchanged water while cooling with ice. zinc chloride
2.5 moles of ZnCl ₂ are dissolved in 1 part of ion-exchanged water. Add both solutions to the separable flask in Step 5, and then add 1 kg of urea and 2 ounces of ion-exchanged water. While stirring, raise the temperature of the contents to 92°C. Maintain this state for approximately 10 hours until the pH of the internal solution reaches 6.5. Stop stirring and let stand overnight. The generated precipitate is filtered under suction, washed with a large amount of ion-exchanged water until no chlorine ions are detected, and then calcined in air at 110°C for 10 hours. This is ground into fine powder and used as a catalyst. Example 1 5 g of the catalyst prepared by the above method, 97 g of acrylonitrile and 3 g of water were placed in a container with a Liebig condenser.
The mixture was placed in a 200 ml flask and heated at 70° C. for 2 hours with stirring under atmospheric pressure. After the reaction, the reaction mixture is filtered to remove the catalyst,
When analyzed by gas chromatography,
11.8 g of acrylamide in the filtrate (conversion rate of water 100
%) was confirmed to be included. Trace amounts of ethylene cyanohydrin were also detected. Examples 2 to 4 The hydration reaction of acrylonitrile was carried out in the same manner as in Example 1, except that the amount of the charged liquid was kept constant at 100 g and the ratio of acrylonitrile to water was changed. The results are shown in Table 1. Comparative Examples 1-2 The hydration reaction of acrylonitrile was carried out in the same manner as in Example 1, except that the amount of liquid to be charged was kept constant at 100 g and the concentration of water was increased. The results are shown in Table 1. 【table】

Claims (1)

[Claims] 1. When producing acrylamide by hydrating acrylonitrile in the presence of an oxide catalyst consisting of titanium and zinc, the concentration of water in the reaction solution in the reactor should be 15% by weight or less based on the reaction solution. A method for producing acrylamide, characterized in that the content is 0.1% by weight or more.