CN113563225A - Method for synthesizing cyanobenzene by recycling benzoguanamine byproduct - Google Patents
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- C07C253/20—Preparation of carboxylic acid nitriles by dehydration of carboxylic acid amides
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- C07C253/00—Preparation of carboxylic acid nitriles
- C07C253/22—Preparation of carboxylic acid nitriles by reaction of ammonia with carboxylic acids with replacement of carboxyl groups by cyano groups
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Abstract
The invention provides a method for synthesizing cyanobenzene by recycling benzoguanamine byproducts, which takes byproducts 2, 4, 6 triphenyl-1, 3, 5-triazine, benzamide and the like dissolved in water washing and recovered in the production process of benzoguanamine as main raw materials. Firstly, carrying out acidolysis on 2, 4, 6-triphenyl-1, 3, 5-triazine to obtain benzamidine, benzoic acid and ammonia gas, and generating ammonium benzoate on the spot by the benzoic acid and the ammonia gas; then heating and dehydrating the components such as the benzamidine, the ammonium benzoate, the benzamide and the like under the chelation of the nickel chloride to generate cyanobenzene; finally, the high-purity benzonitrile is prepared through rough distillation and rectification. A plurality of byproducts and intermediates are converted into benzonitrile and high-boiling residues through ingenious design. The invention obviously reduces the treatment difficulty and cost of the wastewater in the benzoguanamine production and has higher economic effect; the whole reaction process is simple, the separation design for recovering the effective components is reasonable, the conversion rate of the recovered by-products is high, and the purity of the synthesized cyanobenzene is high.
Description
Technical Field
The invention relates to the technical field of chemical synthesis, in particular to a method for synthesizing cyanobenzene by recycling benzoguanamine byproducts.
Background
Benzonitrile, also known as benzonitrile, is a colorless oily liquid with the odor of almond. The cyanobenzene derivative is slightly soluble in cold water, soluble in hot water, and easily soluble in ethanol and ether, can be used as a solvent for nitrile rubber, resin, polymers, coatings and the like, and meanwhile, cyanobenzene is an important organic synthesis intermediate, and is mainly used as an intermediate for synthesizing high-grade coatings such as pesticides, veterinary drugs, fluorine-containing liquid crystal materials, aliphatic amine, benzoic acid, benzoguanamine and the like. With the wide application of high-grade coatings such as benzoguanamine and the like, the gradual increase of the usage amount of efficient fluorine-containing pesticides and the expansion of the market of high-end fluorine-containing liquid crystal materials, the demand of cyanobenzene is increased, the content requirement of downstream products on cyanobenzene is higher and higher, and particularly the market demand of cyanobenzene with the content of more than or equal to 99.9% is gradually increased.
The traditional method for synthesizing the benzonitrile comprises ammoxidation of toluene, Rosenmund reaction and Sandmeyer reaction, and classical functional group conversion, and the like, and the method for preparing the benzonitrile has the problems of high temperature and high pressure, use of a measured cyanide salt, low yield, low purity and the like. When the benzoic acid and the ammonia gas are utilized to synthesize the benzonitrile, the benzoic acid and the ammonia gas are polymerized at high temperature to generate a 2, 4, 6-triphenyl-1, 3, 5-triazine byproduct.
In recent years, researchers have proposed that benzonitrile synthesis using catalytic halobenzonitrile of transition metals such as Pd, Cu, Ni, Rh, and Ir show relative superiority, but such reactions still require the use of cyanide salt poisons with the formation of large amounts of salts after the reaction. Synthetic methods for the conversion of halogenated hydrocarbons to nitriles in the aqueous ammonia and iodine system have been reported by lida et al (Iida S, Ohmura R, Togo H.direct oxidative conversion of alkyl halides into nitriles with molecular iodine and 1, 3-diodo-5, 5-dimethylhydatoin in aq ammonia [ J ]. Tetra-hydro, 2009.65: 6257-. The method has the advantages of no need of transition metal catalysis, simple reaction reagent, mild reaction condition, unchanged carbon number of the substrate before and after the reaction, and the deficiency of needing to use a large amount of iodine, so the preparation cost is higher and the reaction condition is stricter.
The patent with publication number CN103012204A proposes that after benzoic acid leftovers are used as raw materials and react with ammonia gas under heating to obtain a crude product, the crude product is separated, rectified and purified to obtain the final benzonitrile product with a content of 99.5% and a yield of 75% -80%, which has the problems of low yield and content, and also has the disadvantages of incomplete reaction due to short reaction time and obviously increased impurities due to long reaction time.
In order to solve the technical problems, the patent with publication number CN103664696A proposes a method for synthesizing benzonitrile, which uses toluene, ammonia gas and air as raw materials, wherein the ratio of the raw materials is toluene to hydrogen to air is 1:2-10:10-50, the reaction temperature is 300 ℃ and 500 ℃, the reaction pressure is 0.01-0.1Mpa, the benzonitrile is generated in the presence of a catalyst, and the yield of the benzonitrile is about 83%. However, the method still has the problems of low yield and great difficulty in treating the three wastes generated in the synthetic process of the benzonitrile.
Another noteworthy problem is that various domestic and foreign production enterprises take high-purity benzonitrile and dicyandiamide as raw materials and inorganic salt as a catalyst to react in an alcohol solvent to produce the benzoguanamine. In the whole conversion process, benzonitrile is trimerized under a strong alkaline condition to generate a small amount of 2, 4, 6-triphenyl-1, 3, 5-triazine, and meanwhile, benzonitrile is hydrolyzed with trace water in a system under the alkaline condition to generate a benzamide byproduct. Therefore, in the whole process of producing the benzonitril and then producing the benzoguanamine by using the benzonitril, the organic wastewater mainly comprises the benzoguanamine, 2, 4, 6-triphenyl-1, 3, 5-triazine, benzamide, melamine, biuret and other organic solid byproducts. The purification process of the crude benzoguanamine product comprises a process of leaching with a large amount of hot water, and the benzoguanamine purification process is realized after the organic wastes are dissolved in the hot water. The organic matters dissolved in the wastewater are discharged to a sewage treatment station for harmlessness after the washing process is finished, which results in huge sewage amount of benzoguanamine and high wastewater treatment cost.
In view of the above, there is a need to design an improved method for recycling benzoguanitrile by-product of benzoguanamine to solve the above problems.
Disclosure of Invention
In order to overcome the defects of the prior art, the invention provides a method for recycling and reusing benzoguanamine by-products to synthesize benzonitrile, which takes the by-products, such as 2, 4, 6 triphenyl-1, 3, 5-triazine, benzamide and the like, which are dissolved in water washing during the production process of benzoguanamine as main raw materials. In the process design, firstly, carrying out acidolysis on effective components such as 2, 4, 6-triphenyl-1, 3, 5-triazine and the like to obtain benzamidine, benzoic acid and ammonia gas, and generating ammonium benzoate on the spot from the benzoic acid and the ammonia gas; then heating and dehydrating the components such as the benzamidine, the ammonium benzoate, the benzamide and the like under the chelation of the nickel chloride to generate cyanobenzene; finally, the high-purity benzonitrile is prepared through rough distillation and rectification. A plurality of byproducts and intermediates are converted into benzonitrile and high-boiling residues through ingenious design. The invention obviously reduces the treatment difficulty and cost of the wastewater in the benzoguanamine production and has higher economic effect; the whole reaction process is simple, the separation design for recovering the effective components is reasonable, the conversion rate of the recovered by-products is high, and the purity of the synthesized cyanobenzene reaches a high level.
In order to realize the aim, the invention provides a method for synthesizing cyanobenzene by recycling benzoguanamine byproducts, which comprises the following steps:
s1, adding a recovered byproduct of benzoguanamine into a reaction vessel, sequentially adding an alkyl alcohol organic solvent, an acid solution and a transition metal salt catalyst, heating to a first preset temperature, stirring for a preset time, and carrying out acidolysis; then, removing the alkanol organic solvent and water under reduced pressure, continuously heating to a second preset temperature, dehydrating, performing reduced pressure crude distillation after the preset time, collecting the distillate to obtain a benzonitrile reaction crude product; the effective components of the recovered by-product of the benzoguanamine comprise 2, 4, 6-triphenyl-1, 3, 5-triazine and benzamide;
s2, transferring the benzonitrile reaction crude product obtained in the step S1 into a crude distillation tower, carrying out reduced pressure distillation to collect a tower top product to obtain a benzonitrile crude product, and treating a high boiling point mixture in a tower kettle as a solid waste;
s3, feeding the crude benzonitrile obtained in the step S2 into a rectifying tower of the existing benzonitrile production line in a mode of intermittent rectification to directly obtain a finished product with the content of 99.9% or feeding a small amount of raw material continuously, and removing impurities to obtain high-quality benzonitrile with the content of 99.9%.
As a further improvement of the present invention, in step S1, the acid solution includes hydrochloric acid and acetic acid, and the transition metal salt catalyst is a nickel salt catalyst.
As a further improvement of the present invention, in step S1, the mass contents of the 2, 4, 6-triphenyl-1, 3, 5-triazine and the benzamide in the recovered by-product of the benzoguanamine are 30% to 40% and 30% to 40%, respectively.
As a further improvement of the invention, the mass ratio of the recovered by-product of the benzoguanamine to the acid solution is (150-2000): (10-50); the mass ratio of the recovered by-product of the benzoguanamine to the nickel salt catalyst is 1 (0.005-0.04).
As a further improvement of the present invention, in step S1, the first preset temperature is 100 ℃, and the preset reaction time is 5 hours; the second preset temperature is 120-180 ℃, and the preset time is 12-18 h.
As a further improvement of the invention, in step S2, the content of benzonitrile in the crude product of benzonitrile is between 95% and 98%, and the bottom of the column is a high boiling point mixture. The crude benzonitrile product and the high boiling point mixture in the tower bottom can be separated only by rough distillation, the content and impurity components of the crude benzonitrile product distilled from the top of the rough distillation tower are close to those of the crude benzonitrile product in the existing production line, the crude benzonitrile product can be directly merged at the feed end of the existing rectifying tower in a small quantity continuous feeding mode, and the finished benzonitrile product with the content of 99.9% can be obtained after rectification. The ingenious design of the whole recovery process ensures that the cyanobenzene prepared from the benzoguanamine byproduct is easy to realize industrialization and has high economic value.
The invention has the beneficial effects that:
1. the invention provides a method for synthesizing cyanobenzene by recycling benzoguanamine byproducts, which takes byproducts dissolved in water washing in the production process of benzoguanamine as raw materials, wherein the effective components in the byproducts mainly comprise a small amount of 2, 4, 6-triphenyl-1, 3, 5-triazine generated by trimerization of the cyanobenzene under strong alkaline conditions, and benzamide generated by hydrolysis of the cyanobenzene under alkaline conditions when the cyanobenzene is used for preparing the benzoguanamine. Firstly carrying out acidolysis on 2, 4, 6-triphenyl-1, 3, 5-triazine in the by-product in an alkanol solvent to obtain benzamidine, benzoic acid and ammonia gas; the benzoic acid reacts with the ammonia gas decomposed in the system on site to generate ammonium benzoate; after reducing pressure to remove alkanol and water, continuously heating the kettle to a preset reaction temperature, respectively forming chelates by coordination of nickel salt, benzamidine, ammonium benzoate and benzamide under the action of a nickel chloride catalyst, and dehydrating under a heating condition to generate cyanobenzene; under the catalytic action of a nickel salt catalyst, the temperature for synthesizing cyanobenzene by dehydrating the benzamide and the benzamide at the high temperature is also reduced from 200-250 ℃ to 120-180 ℃. And finally, obtaining the high-purity benzonitrile through rough distillation and rectification. According to the invention, the conversion of byproducts 2, 4, 6-triphenyl-1, 3, 5-triazine and benzamide into the product benzonitrile in the production process of the benzoguanamine is realized through a one-pot method, the cyclic utilization of the byproducts is realized, the types and COD of organic matters in the wastewater after the benzoguanamine byproducts are recovered are greatly reduced, the difficulty and the cost of wastewater treatment are obviously reduced, and therefore, the high economic effect is achieved; and the whole reaction process is simple, the raw material conversion rate is high, the crude product is easy to separate, the generated benzonitrile crude product can be connected with a rectifying tower of the existing benzonitrile production line, and finally the high-quality benzonitrile with the content as high as 99.9 percent is produced. Therefore, the method has important economic value for the whole industrial production line of the benzoguanamine.
2. The method for synthesizing cyanobenzene by recycling benzoguanamine byproducts can be used for preparing cyanobenzene with the boiling point of 189.5-191.1 ℃ and the refractive index of 1.5280-1.5289, and the content of the cyanobenzene is more than 99.9% through gas chromatography analysis. Meanwhile, the content and the components of organic impurities in the wastewater are as low as below 30 percent of the prior post-treatment process, and the wastewater treatment difficulty and the cost are greatly reduced.
Drawings
FIG. 1 is a colorless oily liquid of benzonitrile obtained in example 11H NMR(400MHz，CDCl3) Spectra.
FIG. 2 is a colorless oily liquid of benzonitrile obtained in example 113C NMR(100MHz,CDCl3) Spectra.
FIG. 3 is a HPLC-MS spectrum of a benzonitrile colorless oily liquid obtained in example 1.
FIG. 4 is an infrared spectrum of a benzonitrile colorless oily liquid obtained in example 1.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in detail below with reference to specific embodiments.
It should be noted that, in order to avoid obscuring the present invention with unnecessary details, only the structures and/or processing steps closely related to the scheme of the present invention are shown in the specific embodiments, and other details not closely related to the present invention are omitted.
In addition, it is also to be noted that the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus.
The invention provides a method for synthesizing cyanobenzene by recycling benzoguanamine byproducts, which comprises the following steps:
s1, adding recovered byproduct solid of benzoguanamine into a reaction vessel, sequentially adding an alkyl alcohol organic solvent, an acid solution and a transition metal salt catalyst, heating to a first preset temperature, stirring for a preset time, and carrying out acidolysis; then, removing the alkanol organic solvent and water under reduced pressure, continuously heating to a second preset temperature, dehydrating, performing reduced pressure crude distillation after the preset time, collecting the distillate to obtain a benzonitrile reaction crude product; the effective components of the recovered by-product of the benzoguanamine comprise 2, 4, 6-triphenyl-1, 3, 5-triazine and benzamide. The mass contents of the 2, 4, 6-triphenyl-1, 3, 5-triazine and the benzamide in the recovered by-product of the benzoguanamine are respectively 30-40% and 30-40%. The other components are organic solid byproducts such as melamine, biuret and the like, and can provide an ammonia source for synthesizing the ammonium benzoate from the benzoic acid in the reaction process. The alkanol organic solvent is preferably butanol.
In step S1, the acid solution includes hydrochloric acid and acetic acid, and the transition metal salt catalyst is preferably a nickel salt catalyst, and more preferably a nickel chloride catalyst.
The mass ratio of the recovered by-product of the benzoguanamine to the acid solution is (150-2000): (10-50); the mass ratio of the recovered by-product of the benzoguanamine to the nickel salt catalyst is 1 (0.005-0.04).
The first preset temperature is 100 ℃, and the preset reaction time is 5 hours; the second preset temperature is 120-180 ℃, and the preset time is 12-18 h.
Through the step, the 2, 4, 6-triphenyl-1, 3, 5-triazine in the by-product is firstly subjected to acidolysis in alkanol solvent to obtain benzamidine, benzoic acid and ammonia gas; the benzoic acid reacts with ammonia gas on site to generate ammonium benzoate; after reducing pressure to remove alkanol and water, continuously heating the kettle to a preset reaction temperature, forming chelates by respectively coordinating nickel salt with benzamidine, ammonium benzoate and benzamide under the action of a nickel chloride catalyst, and removing water to generate benzonitrile under a heating condition; under the catalytic action of a nickel salt catalyst, the temperature for synthesizing cyanobenzene by dehydrating the benzamide and the benzamide at the high temperature is also reduced from 200-250 ℃ to 120-180 ℃. And finally, obtaining the high-purity benzonitrile through rough distillation and rectification. Therefore, the method better realizes the recovery of the by-product in the production process of the benzoguanamine, the converted crude product is easy to separate due to huge difference of boiling points, the crude cyanobenzene product obtained by crude distillation can be continuously transferred to the existing cyanobenzene rectifying tower, the operation is convenient, and the economic benefit is obvious.
S2, transferring the crude cyanobenzene reaction product obtained in the step S1 into a crude distillation tower, carrying out reduced pressure distillation to collect a tower top product to obtain a cyanobenzene crude product (comprising 95-98 wt% of cyanobenzene and other small amount of low-boiling-point impurities), cooling a high-boiling-point mixture in a tower kettle to obtain a high-viscosity oily substance, wherein the high-boiling-point mixture is complex in components and has no recycling value, and the high-boiling-point mixture is treated as solid waste.
S3, intermittently rectifying the crude benzonitrile obtained in the step S2 to directly obtain a finished product with the content of 99.9%, or feeding the finished product into a rectifying tower of the existing benzonitrile production line for vacuum rectification in a small quantity continuous feeding mode (the mass ratio of the crude benzonitrile obtained in the step S2 to the benzonitrile of the existing benzonitrile production line is about 1: 10; the benzonitrile of the existing benzonitrile production line is that benzoic acid leftovers react with ammonia gas to obtain ammonium benzoate, then dehydrating at high temperature to generate a crude benzonitrile, and performing crude rectification and rectification to obtain a finished benzonitrile with the content of 99.9%), and removing impurities to obtain the high-quality benzonitrile with the content of 99.9%.
The method can obviously reduce the treatment difficulty and cost of the wastewater in the benzoguanamine production, has higher economic effect, and has simple reaction process, high raw material conversion rate and high benzonitrile product purity.
Example 1
A method for synthesizing cyanobenzene by recycling benzoguanamine byproducts comprises the following steps:
s1, adding 140g of benzoguanamine byproduct (containing about 42g of 2, 4, 6-triphenyl-1, 3, 5-triazine and 52g of benzamide) into a reaction vessel, adding 500mL of butanol, 25g of hydrochloric acid, 15g of acetic acid and 1.4g of nickel chloride catalyst, heating to 100 ℃ for reaction for 5 hours, and removing butanol and water under reduced pressure after the raw materials are completely acidolyzed; continuously heating the reaction materials to 150 ℃, stirring and reacting for 15h until the reaction is complete, carrying out rough distillation under reduced pressure, collecting distillate, and obtaining a benzonitrile reaction crude product;
s2, transferring the crude cyanobenzene reaction product obtained in the step S1 into a crude distillation tower, carrying out reduced pressure distillation to collect a tower top product to obtain 86.8g (gas phase content is 97.8%) of a cyanobenzene crude product, and treating a high-boiling-point mixture in a tower kettle as a solid waste, wherein the high-boiling-point mixture is complex in composition;
s3, mixing 86.8g of the benzonitrile crude product obtained in the step S2 with 868g of the benzonitrile crude product on the existing production line (the content of the benzonitrile gas phase is 96.5 percent) according to a new process: the prior art is 1: the 10 mass ratios are mixed and then the mixture is rectified under reduced pressure, 859.3g (gas phase content is 99.93%) of high-quality benzonitrile is obtained after rectification and impurity removal (on the existing production line, the benzonitrile crude products recovered and converted by the new process enter the mode of the feeding end of the existing rectifying tower in a small quantity continuous feeding mode in a parallel mode, so that the benzonitrile crude products of the two processes are integrated and enter the existing rectifying tower for purification, and the existing device and equipment are fully utilized).
FIG. 1 shows a colorless oily liquid of benzonitrile obtained in this example1H NMR(400MHz，CDCl3) The characterization result shows that the kinds and contents of hydrogen atoms in molecules can be determined by delta 7.66-7.59 (m, 3H) and 7.49-7.45 (m, 2H) from the chemical shift and peak area integral of hydrogen in the figure, so that the cyanobenzene prepared by the embodiment has a correct structure and no other miscellaneous peaks, and the cyanobenzene product prepared by the method has high purity.
FIG. 2 shows a colorless oily liquid of benzonitrile obtained in this example13C NMR(100MHz,CDCl3) Delta 132.7,132.0,129.0,118.8,112.3, from the chemical shift and peak area integration of carbon in the figure, the kind and content of carbon atoms in the molecule can be determined, thereby further confirming that the present example produces benzonitrile with higher purity.
FIG. 3 shows the HPLC-MS characterization of benzonitrile obtained in the present example, and M is measured+The molecular weight of 104, which is consistent with the theoretical molecular weight of benzonitrile, further confirms that the structure of the product is correct.
FIG. 4 shows benzonitrile obtained in this exampleThe infrared characterization spectrum of the oily liquid can be seen in 2230cm-1Characteristic absorption of cyano group, 1448cm-1、769cm-1、688cm-1It is the vibration absorption peak of hydrogen on the benzene ring, thus further confirming that the benzonitrile product obtained in this example has a correct structure.
Examples 2 to 7
The method for recycling and reusing the benzoguanitrile from the benzoguanamine byproduct provided in examples 2-7 is different from that in example 1 in that the mass ratio of the benzoguanamine byproduct to hydrochloric acid and acetic acid in step S1 is shown in table 1, except for the above differences, other operations are substantially the same, and are not repeated herein. Specific experimental condition parameters and measurement results are shown in table 1.
As can be seen from the results in table 1, changing the amount ratio of 2, 4, 6-triphenyl-1, 3, 5-triazine and benzamide to hydrochloric acid and acetic acid in step S1 has a significant effect on the quality yield and purity of the produced benzonitrile product. When hydrochloric acid or acetic acid is used alone, benzonitrile can also be obtained by acidolysis, but the quality yield and purity are lower. According to the invention, the mixed acid of hydrochloric acid and acetic acid is adopted to carry out acidolysis on the 2, 4, 6-triphenyl-1, 3, 5-triazine, the hydrochloric acid and the acetic acid have a synergistic effect, the improvement of the quality yield and the purity of the benzonitrile product is facilitated, and the quality yield and the purity of the benzonitrile prepared under the condition of the dosage ratio in the embodiment 1 are highest.
TABLE 1 preparation conditions and Experimental results parameters for examples 1-7
| Examples | Mass ratio of | Mass yield (%) | Purity of crude productDegree (%) |
| 1 | 140:25:15 | 62 | 97.8 |
| 2 | 140:15:25 | 63 | 97.2 |
| 3 | 140:20:10 | 60 | 97.1 |
| 4 | 140:25:0 | 26 | 96.6 |
| 5 | 140:0:15 | 21 | 96.0 |
| 6 | 140:0:0 | 10 | 96.8 |
| 7 | 140:35:20 | 54 | 97.6 |
In the table, the mass yield of the benzonitrile crude product refers to the mass ratio of the benzonitrile crude product to the benzoguanamine byproduct as the raw material. Since the total mass content of 2, 4, 6-triphenyl-1, 3, 5-triazine and benzamide in the benzoguanamine by-product is about 60-80%, the mass yield of the raw benzonitrile product relative to the conversion rate of the useful components 2, 4, 6-triphenyl-1, 3, 5-triazine and benzamide is about 80-90%.
Examples 8 to 10
Examples 8 to 10 provide a method for recycling and reusing a benzoguanitrile by-product from a benzoguanamine, which is different from example 1 in that the mass ratio of 2, 4, 6-triphenyl-1, 3, 5-triazine to nickel chloride in step S1 is changed, and other operations are substantially the same except for the above differences, and thus, the description thereof is omitted. Specific experimental condition parameters and measurement results are shown in table 2.
TABLE 2 preparation conditions and Experimental results parameters for examples 1, 8-10
Comparing the results of examples 1 and 8-10, it is known that the mass yield and purity of benzonitrile after reaction tend to increase and decrease with the increase of the amount of the transition metal nickel catalyst, when the amount ratio of the recovered benzoguanamine byproduct to nickel chloride is controlled within the range of 1 (0.005-0.04), the benzonitrile obtained after catalytic reaction has higher yield and purity, and when the molar amount ratio of the recovered benzoguanamine byproduct to nickel chloride is 1: 0.01-0.02, the mass yield and purity of benzonitrile are highest.
Examples 11 to 18
Examples 11 to 18 provide a method for recycling and reusing a benzoguanitrile by using a benzoguanamine byproduct, which is different from example 1 in that the second heating and stirring reaction condition in step S1 is changed, and other operations are substantially the same except for the above differences, and thus, the details are not repeated herein. Specific experimental condition parameters and measurement results are shown in table 3.
TABLE 3 preparation conditions and Experimental results parameters for examples 11-18
Comparing the results of examples 1 and 11 to 18, it can be seen that the mass yield and purity of benzonitrile after reaction tend to increase and decrease with the increase of reaction temperature, and when the high-temperature dehydration reaction temperature after the completion of acidolysis is controlled within the range of 120 to 180 ℃, benzonitrile obtained after dehydration reaction has high yield and purity, and when the reaction temperature is 160 ℃, the mass yield and purity of benzonitrile are optimal. This is probably because when the temperature is too low, the catalytic reaction activity is not high, resulting in a lower mass yield of benzonitrile; however, when the reaction is too high, the catalytic reaction is too fast, and the occurrence probability of other side reactions is accelerated, so that the quality yield of the benzonitrile is reduced. However, from the results of examples 11 to 16, it is understood that the change in the reaction temperature affects the mass yield of benzonitrile, but the content of benzonitrile distilled from the crude distillation is very stable, and is between 95% and 98%. The process is ingenious in design, the effective component which can be distilled through rough distillation after reaction and conversion is basically benzonitrile, impurities generated by other side reactions and by-products can not be distilled through rough distillation, and the content of a crude product is not influenced.
Comparing the results of examples 1, 13, 17 and 18, it can be seen that the mass yield of benzonitrile after reaction tends to decrease with the increase of reaction time, and when the high temperature dehydration time after the completion of acidolysis is controlled within the range of 12 to 18 hours, the benzonitrile obtained after catalytic reaction has high yield and purity, and when the reaction time is 15 hours, the mass yield and purity of benzonitrile can be optimized. This is probably due to the fact that, due to the prolonged time, benzonitrile reacts with incompletely reacted raw materials and intermediates to increase the content of byproducts, thereby reducing the quality yield and purity of benzonitrile.
In summary, the method for synthesizing benzonitrile by recycling and reusing the benzoguanamine byproduct provided by the invention uses byproduct 2, 4, 6 triphenyl-1, 3, 5-triazine in the production process of benzoguanamine and recycled benzamide and the like as raw materials, and obtains benzonitrile by acidolysis and metal catalysis. And the 99.9 percent of benzonitrile is prepared by rough distillation and rectification. The whole reaction process is simple, the conversion rate of raw materials is high, the types and COD of organic matters in the wastewater after the benzoguanamine preparation reaction are obviously reduced, the difficulty and the cost of wastewater treatment are obviously reduced, and therefore, the method has higher economic effect.
Although the present invention has been described in detail with reference to the preferred embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the spirit and scope of the present invention.
Claims (6)
1. A method for synthesizing cyanobenzene by recycling benzoguanamine byproducts is characterized by comprising the following steps:
s1, adding a recovered byproduct of benzoguanamine into a reaction vessel, sequentially adding an alkyl alcohol organic solvent, an acid solution and a transition metal salt catalyst, heating to a first preset temperature, stirring for a preset time, and carrying out acidolysis; then, removing the alkanol organic solvent and water under reduced pressure, continuously heating to a second preset temperature, dehydrating, performing reduced pressure crude distillation after the preset time, collecting the distillate to obtain a benzonitrile reaction crude product; the effective components of the recovered by-product of the benzoguanamine comprise 2, 4, 6-triphenyl-1, 3, 5-triazine and benzamide;
s2, transferring the benzonitrile reaction crude product obtained in the step S1 into a crude distillation tower, carrying out reduced pressure distillation to collect a tower top product to obtain a benzonitrile crude product, and treating a high boiling point mixture in a tower kettle as a solid waste;
s3, intermittently rectifying the crude benzonitrile obtained in the step S2 to directly obtain a finished product with the content of 99.9 percent or feeding the finished product into a rectifying tower of the existing benzonitrile production line in a small quantity continuous feeding mode to remove impurities to obtain high-quality benzonitrile with the content of 99.9 percent.
2. The method for recycling and synthesizing benzonitrile as claimed in claim 1, wherein in step S1, the acid solution includes hydrochloric acid and acetic acid, and the transition metal salt catalyst is a nickel salt catalyst.
3. The method for recycling and synthesizing benzonitrile according to claim 1, wherein, in step S1, the mass contents of the 2, 4, 6-triphenyl-1, 3, 5-triazine and the benzamide in the recycling byproduct of the benzoguanamine are 30% to 40% and 30% to 40%, respectively.
4. The method for recycling and synthesizing benzonitrile as claimed in claim 1, wherein a mass ratio of the recycled byproduct of benzoguanamine to the acid solution is (150-2000): (10-50); the mass ratio of the recovered by-product of the benzoguanamine to the nickel salt catalyst is 1 (0.005-0.04).
5. The method for recycling and synthesizing benzonitrile as claimed in claim 1, wherein in step S1, the first preset temperature is 100 ℃, and the preset reaction time is 5 hours; the second preset temperature is 120-180 ℃, and the preset time is 12-18 h.
6. The method for synthesizing benzonitrile as claimed in claim 1, wherein in step S2, the content of benzonitrile in the crude benzonitrile product is between 95% and 98%, and the bottom of the column is a high boiling point mixture, which is a high viscosity oil after cooling.
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