JPH043376B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a method for synthesizing acrylamide by reacting acrylonitrile and water in a liquid phase in the presence of a solid catalyst. More specifically, the present invention relates to a highly active solid catalyst useful for this reaction. Acrylamide is a useful monomer that is used in the production of acrylamide-based polymers used as paper strength agents, flocculants, etc., and has many other uses. Currently, acrylamide is synthesized by reacting acrylonitrile, which is industrially produced at low cost, with water. [Prior Art] Many copper-based catalysts are known as solid catalysts used to synthesize acrylamide by reacting acrylonitrile and water, and among them, the following are common. (A) Gas-phase reduced copper obtained by reducing copper oxide with hydrogen gas, etc. (B) Liquid obtained by treating copper salts, copper hydroxide, etc. in the liquid phase with a reducing agent such as formalin or sodium borohydride. Phase-reduced copper (C) Copper salt, copper hydroxide, etc., prepared by reacting with hypophosphite etc. in the aqueous phase, and obtained by decomposing copper hydride by heating etc. (D) Raney copper alloy Raney copper obtained by reacting with a basic compound such as caustic soda.The main catalyst component of these copper-based catalysts is thought to be metallic copper. Next, a hydration reaction of nitrile compounds using metallic nickel as a catalyst has been reported, but the selectivity to acid amide is said to be low in this case.
That is, Watanabe et al. (BULLETIN OF CHEMICAL
SOCIETY OF JAPAN, 37 , 1325 (1964)), the Urushibara nickel catalyst is suitable for synthesizing the corresponding acid amide compound by hydration of aromatic nitriles, but in the case of aliphatic nitriles, it is suitable for synthesizing acidic substances. The selectivity to acid amide is low due to by-products such as. Also, Miura et al. (Journal of the Chemical Society of Japan, 1982, No. 4, 692)
According to the authors, when acrylonitrile is hydrated using a gas-phase reduced nickel catalyst supported on γ-alumina, the selectivity to acrylamide is 42.8%, which is 92.9% for reduced copper obtained in the same way. It is significantly lower than that. Therefore, metallic nickel is considered unsuitable as a catalyst for acrylamide synthesis. Furthermore, many examples of composite catalysts in which nickel is contained in a metallic copper catalyst are known, as shown below. (1) Japanese Patent Publication No. 52-41241 proposes a catalyst obtained by reducing a composition of copper oxide and metal oxides such as nickel, but the appropriate ratio of copper and nickel etc. is not known. No, but merely an example of the catalyst obtained from a mixture of 0.80 mol of copper salt and 0.15 mol of nickel salt is given. (2) U.S. Pat. No. 3,795,629 proposes a copper catalyst obtained by reducing copper oxide with hydrogen in the liquid phase in the presence of a catalytic amount of nickel; this copper catalyst is said to contain a small amount of nickel. However, the amount is not indicated. (3) U.S. Patent No. 4,250,111 describes a catalyst obtained by hydrogen reduction of copper oxide containing oxides of heavy metals such as nickel to copper in a weight ratio of 1/250 to 10/100. has been proposed, and an example is shown in which nickel is contained at 0.48% (weight ratio to copper). (4) Japanese Patent Publication No. 53-3927 states that a copper-based catalyst obtained by treating a mixture of a copper compound and a compound of a second element such as nickel with a borohydride has high activity, high selectivity, and long life. and the second element is 0.05-10%
(atomic ratio to copper). Also, an example containing 0.5% nickel is shown. (5) Japanese Patent Publication No. 53-43924 states that copper-based catalysts containing these second elements by decomposing copper hydride in the presence of compounds of second elements such as nickel are highly active; It is said that the second element is used in a content of 0.05 to 50% (atomic ratio to copper) in the catalyst. However, regarding nickel, no specific explanations such as examples are given. In these examples, a range of 50% (nickel/copper atomic ratio) or less is shown as a suitable nickel content, or examples of even lower contents are described. [Problems to be Solved by the Invention] The various catalysts described above can be used in two ways: using the catalyst itself or supported on a carrier as granules in a fixed bed type; It is broadly divided into two methods: a method in which a supported powder is used in a suspended bed method; Among these, in the suspended bed type, it is difficult to separate the catalyst from the reaction liquid after the reaction, whereas in the fixed bed type, there is no such difficulty, and in the fixed bed type, the deteriorated catalyst can be treated with hydrogen gas. It has the advantage that it can be easily regenerated by known methods such as chemical treatment. Catalysts suitable for fixed beds include those obtained by reducing metal oxides in the gas phase with hydrogen gas or the like, such as the gas-phase reduced copper of the metal copper catalysts mentioned above. Therefore, the present inventors conducted extensive research in order to find a superior catalyst that is different from any of the previously known catalysts as such a gas phase reduction catalyst. [Means for Solving the Problems] As a result, it was discovered that a gas-phase reduced nickel catalyst containing copper has high activity and selectivity in a specific copper content range, and the present invention was completed. That is, in the present invention, when synthesizing acrylamide by reacting acrylonitrile and water in a liquid phase in the presence of a solid catalyst, the copper/nickel atomic ratio is 45/55 to 15/85.
This is a method for synthesizing acrylamide, which is characterized in that reduced copper nickel obtained by reducing a composition of nickel oxide and copper oxide having the following composition with hydrogen or hydrogen-containing gas in the gas phase is used as a catalyst. Until now, metal nickel catalysts had been thought to be impractical due to their extremely low selectivity from acrylonitrile to acrylamide, but this drawback has been completely overcome by incorporating a smaller amount of copper than nickel. This is surprising, and it is also noteworthy that much higher activity than the metallic copper catalyst was obtained by including a higher amount of nickel than copper. The catalyst of the present invention is prepared as follows. A water-soluble salt such as nickel nitrate and copper nitrate is used to make a mixed aqueous solution of both, and a basic substance such as caustic soda is added to this to form a composition of nickel hydroxide and copper hydroxide, or a composition of nickel hydroxide and copper hydroxide is prepared from similar raw materials. After separately preparing nickel hydroxide and copper hydroxide, the two are mixed. The hydroxide composition thus obtained is fired by a conventional method to obtain a composition of nickel oxide and copper oxide. Alternatively, instead of hydroxide, a composition of nickel and copper carbonate, oxalic acid, acetate, and other easily decomposed salts may be prepared and fired to obtain a composition of nickel oxide and copper oxide. When supported on a carrier, for example, the carrier is impregnated in the form of these hydroxides or decomposable salts, and then fired. Or,
As in JP-A-50-12001, the precipitate obtained by adding alkali silicate to an aqueous solution of nickel salt, copper salt, and magnesium salt is filtered and dried, and oxides or hydroxides of nickel and copper are added to magnesium silicate. A method in which it is supported may also be used. Further, in order to form particles of a size suitable for a fixed bed reaction type, it may be formed into tablets. Whichever method is used, the resulting oxide composition is adjusted to have a copper/nickel atomic ratio of 45/55 to 15/85. In order to make the oxide thus obtained into the desired reduced metal type catalyst, it is maintained at a predetermined temperature and reduced with hydrogen gas or a hydrogen-containing gas obtained by diluting it with nitrogen or the like. Reduction temperature is 150~400℃, 200~
350℃ is suitable. Note that it is desirable to avoid contact of the obtained catalyst with oxygen gas and oxygen-containing gas during storage and handling. Oxygen reacts with the catalyst and, within a certain limit, does not impair the activity of the catalyst, or conversely increases its activity, but beyond that it impairs the activity, or it reacts with the target acrylamide, such as ethylene cyanohydrin. This causes the formation of by-products. The method for synthesizing acrylamide by reacting acrylonitrile and water using the catalyst of the present invention is generally as follows. The catalyst is used in powder form as a suspended bed, or preferably in granular form in a fixed bed, and a flow or batch reaction type is adopted. The weight ratio of acrylonitrile and water to be subjected to the reaction is essentially arbitrary, but is preferably 67:
40-5:95, more preferably 50:50-10:
The range is 90. The preferred reaction temperature is 70-150°C. The conversion rate of acrylonitrile to acrylamide is preferably 10 to 98%, more preferably 30 to 95%. At the above-described weight ratio of acrylonitrile to water, reaction temperature, and conversion rate of acrylonitrile, the three components of unreacted acrylonitrile, unreacted water, and produced acrylamide may not form a uniform solution system. In order to avoid this, the synthesized acrylamide may be added again to this reaction system as a solvent, or another inert solvent may be used. The inside of the reactor is maintained at the vapor pressure at the above-mentioned temperature and composition, or at a pressure obtained by adding an inert gas such as nitrogen, and the pressure is usually in the range of normal pressure to 20 atmospheres. Catalyst, acrylonitrile, fed to the reactor
Dissolved oxygen contained in water, solvent, etc. impairs catalyst activity and increases by-products such as ethylene cyanohydrin, as mentioned above, so it is desirable to remove it thoroughly before supplying it to the reactor. . For the same reason, it is desirable to maintain an atmosphere in the reactor that does not contain oxygen gas. Next, it will be further explained by examples. Example 1 [Preparation of catalyst] Copper nitrate and nickel nitrate were each weighed out in 11 weight combinations as shown in the table below and dissolved in 400 ml of pure water.

[Table] A sodium carbonate aqueous solution having a concentration of 5% by weight was added dropwise to the obtained solution over 1.5 hours to adjust the pH to 9.5. Thereafter, stirring was continued for 1.5 hours to age the mixture, and after being allowed to stand for an additional 19 hours, the resulting precipitate was suction-filtered. This was poured into 2000 ml of pure water, stirred vigorously for 30 minutes to suspend it, and was suction-filtered. More new pure water 200
Suspension and filtration were repeated using ml. This washing operation was repeated until the pH of the filtrate became 8.0 to 8.5. The obtained precipitate was dried in an evaporating dish at 120°C for 8 hours, and the dried product was pulverized and calcined at 300°C for 3 hours to obtain copper oxide, nickel oxide, or a composition thereof.
Weigh out the stoichiometrically calculated amount to obtain 2.5 g of metal from these metal oxides,
The mixture was placed in a reaction tank and reduced at 300° C. for 3 hours in a hydrogen flow of 100 c.c./min. [Synthesis of acrylamide] After reduction, add 100 ml of deoxygenated pure water to the reaction tank while preventing air from entering the reaction tank, attach a reflux condenser to the top of the reaction tank, and seal the top with nitrogen. , to prevent air from entering the reaction tank. This reaction tank was immersed in a 75°C hot bath, and when the contents reached 75°C, 8.5 ml of acrylonitrile, which had been deoxygenated in advance, was poured into the tank. The contents were stirred and kept at approximately 75°C for 6 hours to react. 6
After a period of time, the reaction solution was cooled, and acrylonitrile, acrylamide, and by-products such as ethylene cyanohydrin, β-hydroxypropionamide, and biscyanoethyl ether were determined by gas chromatography. The conversion rate of acrylonitrile was determined from the total amount of acrylamide and by-products, and the selectivity to acrylamide was determined from the ratio of acrylamide to by-products. Through the above experiments, the results shown in the following table were obtained.

【table】

[Table] Example 2 [Preparation of catalyst] Eleven types of metal oxides obtained in the same manner as in Example 1 were made into cylindrical tablets with a diameter of 5 mm and a length of 5 mm, and weighed 300 g each. Inner diameter 30mm
The mixture was packed in a stainless steel reaction tube and reduced at 300°C for 3 hours in a hydrogen stream diluted with nitrogen. [Synthesis of acrylamide] After the reduction, the reaction tube was installed at a predetermined location in the reaction equipment while preventing air from entering the reaction tube. This reaction equipment consists of a reaction tube, a deoxygenated acrylonitrile storage tank and its supply pump, a deoxygenated pure water storage tank and its pump, and a reaction liquid circulation pump. Acrylonitrile and pure water respectively
The reaction solution was supplied to the bottom of the reaction tube at a rate of 300 g/hr and 700 g/hr, and 1000 g/hr of the reaction solution was drawn out from the top of the reaction tube, and 60 g/hr of the reaction solution was circulated to the bottom of the reaction tube. The reaction was continued by wrapping it around the outside of the reaction tube and keeping the reaction temperature at 120°C using a heating wire. After 3 hours, the reaction solution was sampled and
The conversion rate and selectivity were determined by analysis in the same manner as above. Through the above experiments, the results shown in the following table were obtained.

【table】

[Table] [Effects of the Invention] According to the present invention, when synthesizing acrylamide through the reaction of acrylonitrile and water, a gas phase reduction metal type catalyst suitable for a fixed bed reaction type and suitable for hydrogen gas treatment and chemical liquid treatment is used. A highly active and highly selective catalyst can now be easily prepared.

Claims (1)

[Claims] 1. When synthesizing acrylamide by reacting acrylonitrile and water in a liquid phase in the presence of a solid catalyst, a composition of nickel oxide and copper oxide having a copper/nickel atomic ratio of 45/55 to 15/85 is used. A method for synthesizing acrylamide, characterized in that reduced copper nickel obtained by reduction with hydrogen or hydrogen-containing gas in the gas phase is used as a catalyst.