Device and method for continuous production of benzonitrile and full recycling of ammonia gas from benzoic acid

Abstract

The application provides a device and a method for continuous production of benzonitrile and full recycling of ammonia from benzoic acid, the device comprising an ammonia supply system, a gas mixing system, a continuous ammoniation system, a continuous dehydration system and an intermittent dehydration system connected in sequence, the continuous ammoniation system being connected with a benzoic acid supply system, and a liquid outlet of the intermittent dehydration system being connected with a rectifying tower; and further comprising a deamination recycling system to realize recycling and recycling of ammonia. The method uses high-pressure excess ammonia as input to provide power for recycling of ammonia in the device; and the yield and purity of benzonitrile are improved by grading control of process parameters. The device and the method can produce benzonitrile with high yield, high purity and low color number through the cooperation of the systems in the device and the grading control of the process parameters, and the benzonitrile can directly enter a rectification process, thereby reducing the difficulty and energy consumption of rectification; and the ammonia is used and recycled in multiple stages, thereby reducing the ammonia consumption and improving the economic benefits of preparation of benzonitrile.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of benzyl cyanide preparation process, and particularly relates to a device and method for continuous production of benzyl cyanide and full recycling of ammonia gas from benzoic acid. BACKGROUND

[0002] The preparation methods of benzyl cyanide mainly include: benzoic acid method, benzoic acid is obtained by ammoniation, and a commonly used catalytic method is high-temperature catalysis or an alumina catalyst; ammonia oxidation method, benzyl cyanide is obtained by oxidizing toluene with air in the presence of ammonia; there is also a method of reacting aniline hydrochloride with diazotization of nitrous acid, and then reacting with cuprous cyanide to obtain benzyl cyanide; benzamide reacts with dichlorosulfoxide to obtain benzyl cyanide; among the above methods, the benzoic acid method and the ammonia oxidation method are more commonly used in industrial production.

[0003] In the production process of preparing benzyl cyanide from benzoic acid products, due to the high reaction temperature and long residence time of intermediates, the intermediates ammonium benzoate and benzamide are prone to hydrolysis and deamination to regenerate benzoic acid in the subsequent dehydration process; therefore, there is a problem of difficult balance between the dehydration degree of the product and the decomposition of the intermediate, which may cause the final prepared benzyl cyanide to contain part of unreacted benzoic acid or benzamide, increasing the difficulty of subsequent rectification and purification process. At the same time, due to the ammonia separation process in the high-temperature dehydration stage, the consumption of ammonia is large, the ammonia nitrogen index in the tail gas and wastewater is high, the amount of waste gas and wastewater is large, and the treatment is difficult. Therefore, the current production process for synthesizing benzyl cyanide from benzoic acid has a series of problems such as low yield, difficult further improvement of product quality, large amount of wastewater, high ammonia nitrogen and COD, and difficult treatment.

[0004] In addition, a large amount of ammonia gas is required in the ammoniation reaction process of preparing benzyl cyanide from benzoic acid products, and the amount of ammonia gas required at different stages and different temperatures is also different. If the ammonia gas generated in the reaction kettle is not treated and recovered in stages, not only will the ammonia concentration in the reaction kettle be too high or too low, causing many side reactions and affecting the normal operation of the device, but also the purity and quality of the final product will be affected. In addition, the allocation and centralized recovery of ammonia gas in different kettles have a great influence on the control of product raw material consumption, production cost, and treatment of waste water and waste gas.

[0005] At present, there are two methods for recovering ammonia generated in the ammonia process of organic matter: one is to use a condenser to pass ammonia into the condenser, and then to separate the gas and liquid after condensation to recover the liquid ammonia, but this method has low recovery efficiency, high requirements for process conditions, and low universality; the other is to set up an ammonia absorption device to absorb ammonia with water. The utility model patent (application number CN201920236390.0) discloses an ammonia reaction device for optimizing ortho-aminobenzoic acid, which realizes the absorption of tail gas by setting a tail gas absorption tank and an anti-back suction device at the end of the exhaust pipe connected with the reaction kettle; however, the device uses softened water in the tail gas absorption tank to absorb a large amount of ammonia, and then discharges the wastewater, which causes resource waste, increases the preparation cost of ortho-aminobenzoic acid, and pollutes the environment.

[0006] Therefore, it is necessary to design an improved device and method for continuous production of benzonitrile and ammonia from benzoic acid and full recycling of ammonia to solve the above problems. SUMMARY

[0007] The device and method for continuous production of benzonitrile and ammonia from benzoic acid and full recycling of ammonia provided by the present application can realize high yield, high purity, and low color number of benzonitrile products through the coordinated operation of various systems in the device and the hierarchical control of process parameters in the preparation of benzonitrile, and the prepared benzonitrile can be directly fed into a rectification process, which can reduce the difficulty and energy consumption of the rectification process; and the ammonia can be recycled and reused, which can reduce the consumption of ammonia and thus reduce the production cost.

[0008] To achieve the above-mentioned purposes, the present application provides a device for continuous production of benzonitrile and ammonia from benzoic acid and full recycling of ammonia, which comprises an ammonia supply system, a gas mixing system, a continuous ammoniation system, a continuous dehydration system, and an intermittent dehydration system connected in sequence, wherein the continuous ammoniation system is connected with a benzoic acid supply system, the liquid outlet of the intermittent dehydration system is connected with a rectification tower, and the obtained product benzonitrile is directly fed into the rectification tower; the continuous ammoniation system is provided with a top outlet connected with the intermittent dehydration system, and excess ammonia is fed into the intermittent dehydration system to realize the complete conversion of intermediates and the full recycling and reuse of ammonia.

[0009] The device further comprises a deamination recycling system, which is connected with the top outlets of the continuous dehydration system and the intermittent dehydration system, and the top outlet of the deamination recycling system is further connected with the gas mixing system to realize the recycling and reuse of ammonia.

[0010] As a further improvement of the present application, the gas mixing system is provided with a Venturi mixer, which mixes the low-pressure ammonia gas output by the ammonia removal recycling system with the high-pressure ammonia gas output by the ammonia gas supply system, and inputs the mixture into the continuous amination system for full reaction with benzoic acid.

[0011] As a further improvement of the present application, the top outlet of the continuous amination system, the continuous dehydration system, the intermittent dehydration system and the ammonia removal recycling system is provided with a condenser, which condenses the output material in the respective system, prevents the output material from entering the ammonia removal recycling system, and collects the excess ammonia gas in the respective system into the ammonia removal recycling system for recycling and recycling of ammonia gas.

[0012] As a further improvement of the present application, the intermittent dehydration system is provided with a first dehydration unit and a second dehydration unit, which are arranged in parallel.

[0013] The present application also provides a method for realizing continuous production of benzonitrile and full recycling of ammonia gas, which uses the device for continuous production of benzonitrile from benzoic acid and full recycling of ammonia gas as described above, and comprises the following steps:

[0014] S1, the benzoic acid supply system provides benzoic acid for the continuous amination system, and the ammonia gas output by the ammonia gas supply system is input into the continuous amination system through the gas mixing system, mixed with the benzoic acid therein to generate ammonium benzoate, which is continuously input into the continuous dehydration system in a high-temperature molten state, and the excess ammonia gas is output from the top outlet of the continuous amination system and input into the intermittent dehydration system after being condensed;

[0015] S2, the ammonium benzoate in the continuous dehydration system is converted into a mixture of intermediate benzamide and final product benzonitrile through two times of dehydration, the mixture of benzamide and benzonitrile enters the intermittent dehydration system, and the water vapor generated by the reaction carries the unreacted ammonia gas, which is output from the top outlet of the continuous dehydration system and enters the ammonia removal recycling system after being condensed;

[0016] S3, the benzamide and benzonitrile in the intermittent dehydration system are mixed with the ammonia gas input from the continuous amination system, and the complete conversion and dehydration of the intermediate are realized by controlling the reaction temperature, so as to obtain the final product benzonitrile and input it into the rectifying tower, and the water vapor carrying the residual ammonia gas is output from the top outlet of the intermittent dehydration system and enters the ammonia removal recycling system after being condensed;

[0017] S4, the deamination circulating recovery system rectifies the liquid input from the continuous dewatering system and the intermittent dewatering system, ammonia gas obtained is continuously extracted from a condenser at the top of the deamination circulating recovery system and is mixed into the gas mixing system by the negative pressure effect of a venturi mixer, mixed with ammonia gas output by the ammonia gas supply system, re-input into the continuous amination system for preparation of benzonitrile, and remaining waste water is input into a sewage treatment device from the bottom of the deamination circulating recovery system.

[0018] As a further improvement of the present application, in step S3, the reaction temperature of the intermittent dewatering system is 240-270 DEG C, and the time is 6-10 h, the unreacted ammonium benzoate and benzamide are completely dewatered at high temperature, and the ammonia gas input from the continuous amination system inhibits the reverse decomposition of benzamide, so that it is all converted into benzonitrile, and the reaction yield is improved.

[0019] As a further improvement of the present application, in step S1, the temperature of the continuous amination system is controlled to be 190-210 DEG C, so as to ensure the conversion of the benzoic acid, and the generated ammonium benzoate is kept in a molten state, facilitating material conveying, and the reaction residence time is 2-4 h.

[0020] As a further improvement of the present application, in step S2, the temperature of the continuous dewatering system is controlled to be 210-240 DEG C, and the treatment time is controlled to be 4-6 h.

[0021] As a further improvement of the present application, in step S1, the pressure of the ammonia gas output by the ammonia gas supply system is 0.5-1.0 MPa, so as to realize the flow of the ammonia gas through each system under the driving of pressure and fully participate in the reaction.

[0022] As a further improvement of the present application, in step S4, the deamination circulating recovery system carries out deamination treatment on the liquid therein by heating; the deamination circulating recovery system is a normal-pressure rectification device, the overhead of the kettle is ammonia gas, the ammonia nitrogen content in the aqueous solution at the bottom of the kettle is less than 200 ppm, and the full recovery and utilization of the ammonia gas in the whole system is realized.

[0023] The present application has the following beneficial effects:

[0024] 1. The device and method for continuous production of benzonitrile and ammonia gas full recycling of benzoic acid according to the present application, which comprises an ammonia gas supply system, a gas mixing system, a continuous ammoniation system, a continuous dehydration system and an intermittent dehydration system connected in sequence, the continuous ammoniation system is connected with a benzoic acid supply system, and the liquid outlet of the intermittent dehydration system is connected with a rectifying tower; and the device further comprises a deamination recycling system communicated with the continuous dehydration system, the intermittent dehydration system and the gas mixing system, so as to realize recycling and utilization of ammonia gas. Through the cooperation of various systems in the device and the hierarchical control of process parameters such as temperature and ammonia gas amount in the preparation process of benzonitrile, the high yield, high purity and low color number benzonitrile product can be prepared without adding catalyst, the prepared benzonitrile can directly enter the rectification process, the difficulty and energy consumption of the rectification process are reduced; and the ammonia gas is continuously rectified and recycled, the utilization rate of ammonia gas in the whole preparation process is improved, the consumption is reduced, and the preparation cost of benzonitrile is reduced.

[0025] 2. In the preparation method of benzonitrile according to the present application, high-pressure excess ammonia gas is input, which can provide power for the recycling of ammonia gas in the whole device and realize self-operation; the input of excess ammonia gas ensures the conversion rate of benzoic acid to ammonium benzoate, and the remaining ammonia gas is input into the intermittent dehydration system, so that the intermediate that is not completely reacted is all converted into benzonitrile, and the presence of ammonia gas atmosphere can also inhibit the hydrolytic deamination reaction of the intermediate in high temperature and large amount of water vapor, so that the problem of difficult balance between dehydration degree of the product and decomposition of the intermediate is solved, the yield of benzonitrile is improved, and the impurity content of the product is reduced. In addition, by controlling the reaction temperature and time in the intermittent dehydration system, complete conversion and dehydration of the intermediate are realized, the purity of the prepared benzonitrile product is high, which can be directly input into the rectifying tower without intermediate process treatment, and the process is saved.

[0026] 3. The reaction dehydration process is divided into continuous reaction dehydration and intermittent reaction dehydration according to the present application, the continuous reaction dehydration process is used to evaporate a large amount of water vapor in the initial and middle stages of the reaction, reduce the residence time of the material and reduce the reaction temperature in this stage; then the intermittent reaction dehydration is used to ensure that benzoic acid ammonium and benzamide are all converted into benzonitrile at a higher temperature, so as to improve the conversion rate and yield of the reaction. In addition, the present application does not input ammonia gas in the continuous reaction dehydration stage, but inputs ammonia gas in the intermittent reaction dehydration stage in the later stage of the reaction, which avoids the problem that a large amount of ammonia gas is entrained in a large amount of water vapor generated in the continuous reaction dehydration reactor and escapes from the condenser, resulting in that the ammonia nitrogen content in the waste water is too high and the waste water amount is too large to be treated.

[0027] 4、The present application carries out deamination treatment through the deamination circulating recovery system, realizes automatic suction and mixing of the high-pressure ammonia gas in the main road and the normal-pressure ammonia gas discharged in the recovery system through the Venturi mixer, makes the recovered ammonia gas re-enter the production system of the benzonitrile, realizes the recycling of the ammonia gas, obviously reduces the consumption of the ammonia gas in the whole process, and reduces the ammonia content in the waste water. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 It is the schematic diagram of the device for the continuous production of benzonitrile and the full recycling of ammonia gas of the benzoic acid of the present application.

[0029] Figure 2 It is the schematic diagram of the device for the continuous production of benzonitrile and the full recycling of ammonia gas of the benzoic acid of another embodiment of the present application.

[0030] REFERENCE NUMERALS

[0031] 100 - the device for the continuous production of benzonitrile and the full recycling of ammonia gas of the benzoic acid; 110 - ammonia gas supply system; 120 - gas mixing system; 130 - continuous ammoniation system; 140 - continuous dehydration system; 150 - intermittent dehydration system; 151 - liquid outlet; 152 - first dehydration unit; 153 - second dehydration unit; 160 - deamination circulating recovery system; 170 - condenser; 200 - rectifying column; 300 - waste water treatment device. DETAILED DESCRIPTION

[0032] In order to make the purpose, technical scheme and advantages of the present application more clear, the present application is described in detail below in combination with the drawings and specific embodiments.

[0033] Here, it also needs to be explained that, in order to avoid the unnecessary details from blurring the present application, only the structures and / or processing steps closely related to the scheme of the present application are shown in the drawings, and other details not closely related to the present application are omitted.

[0034] In addition, it also needs to be explained that the term "comprising", "including" or any other variant thereof is intended to cover the non-exclusive inclusion, so that the process, method, article or equipment including a series of elements not only includes those elements, but also includes other elements not explicitly listed, or includes the elements inherent to such process, method, article or equipment.

[0035] Please refer to Figure 1As shown, a device 100 for continuous production of benzonitrile and ammonia gas full recycling of benzoic acid, comprising an ammonia gas supply system 110, a gas mixing system 120, a continuous ammoniation system 130, a continuous dehydration system 140 and an intermittent dehydration system 150 connected in sequence, the continuous ammoniation system 130 is connected with the benzoic acid supply system, the liquid outlet 151 of the intermittent dehydration system 150 is connected with the rectifying tower 200, and the obtained product benzonitrile is directly input into the rectifying tower 200; the continuous ammoniation system 130 is provided with a top outlet communicated with the intermittent dehydration system 150, and the excess ammonia gas is introduced into the intermittent dehydration system 150 to realize the full conversion of the intermediate and the full recycling of the ammonia gas. The device further comprises a deamination circulating recovery system 160, which is respectively communicated with the top outlet of the continuous dehydration system 140 and the intermittent dehydration system 150, and the top outlet of the deamination circulating recovery system 160 is further communicated with the gas mixing system 120 to realize the recycling and recycling of the ammonia gas. Through the cooperation of each system in the device, not only can the benzonitrile product with high yield, high purity and low color number be prepared, and the prepared benzonitrile can directly enter the rectification process, reducing the difficulty and energy consumption of the rectification process; the ammonia gas can also be continuously rectified and recycled, improving the utilization rate of ammonia gas in the preparation process, reducing the ammonia nitrogen content in the wastewater, and achieving good economic and environmental benefits.

[0036] Specifically, the gas mixing system 120 is provided with a venturi mixer, which mixes the low-pressure ammonia gas output from the deamination circulating recovery system 160 with the high-pressure ammonia gas output from the ammonia gas supply system 110 and inputs them into the continuous ammoniation system 130 for sufficient reaction with benzoic acid. The venturi mixer can mix the low-pressure ammonia gas evaporated in the deamination circulating recovery system 160 with the high-pressure ammonia gas from the ammonia gas supply system 110, so that the ammonia gas can be fully recycled, and the use of excess equipment is reduced.

[0037] In some specific embodiments, the top outlet of the continuous ammoniation system 130, the continuous dehydration system 140, the intermittent dehydration system 150 and the ammonia stripping recycling system 160 is provided with a condenser 170, which can purify the ammonia gas in the ammonia stripping recycling system 160 and pump it to the main pipeline through the Venturi mixer under negative pressure. The condenser 170 can condense the materials in the mixed gas output by each system, avoid the reaction materials from being taken into the ammonia stripping recycling system 160 with ammonia gas and water vapor, relieve the pressure of high COD of waste water in the subsequent ammonia stripping recycling system 160, and collect the excess ammonia gas of the corresponding system into the ammonia stripping recycling system 160 for recycling and cyclic utilization of ammonia gas. The condenser 170 at the top outlet of the ammonia stripping recycling system 160 removes the water in the recycled ammonia gas. It should be noted that the entire device 100 for continuous production of benzonitrile and full cyclic utilization of ammonia gas is a sealed device, the ammonia gas is completely recycled and utilized, there is no gas phase emission, the ammonia nitrogen index in the liquid phase emission reaction waste water is very low, and the continuous device and environmental protection are realized.

[0038] Referring to Figure 2 In some specific embodiments, the intermittent dehydration system 150 is provided with two sets of intermittent units, i.e. a first dehydration unit 152 and a second dehydration unit 153, which are arranged in parallel in an intermittent manner and can be switched and used alternately to realize the whole continuous process by switching. Because the reaction temperature of the intermittent dehydration system 150 is high and the reaction time is strictly required, the first dehydration unit 152 and the second dehydration unit 153 are arranged to be used alternately to realize the continuity of the process, so that the conversion rate and the yield of benzonitrile can be ensured, and the balance of energy consumption and operation can be realized.

[0039] The application further discloses a method for realizing continuous production of benzonitrile and full cyclic utilization of ammonia gas, which is implemented by using the device 100 for continuous production of benzonitrile and full cyclic utilization of ammonia gas, and comprises the following steps:

[0040] S1, the benzoic acid supply system provides benzoic acid for the continuous ammoniation system 130, the ammonia gas output by the ammonia gas supply system 110 is input into the continuous ammoniation system 130 through the gas mixing system 120, and the benzoic acid in the continuous ammoniation system 130 continuously generates ammonium benzoate, the ammonium benzoate is continuously input into the continuous dehydration system 140 in a high-temperature molten state, and the excess ammonia gas is output from the top outlet of the continuous ammoniation system 130 and input into the intermittent dehydration system 150 after the condenser 170;

[0041] The temperature control of the continuous ammoniation system 130 is 190-210 DEG C, so as to ensure the conversion of benzoic acid and keep the generated benzoyl ammonium in a molten state, facilitating the material delivery, and the reaction residence time is 2-4 h; the pressure of the ammonia gas output by the ammonia gas supply system 110 is 0.5-1.0 MPa, so as to realize the flow of the ammonia gas through the systems under the pressure driving and the full participation in the reaction.

[0042] S2, the ammonium benzoate in the continuous dehydration system 140 is converted into a mixture of intermediate benzamide and final product benzonitrile through two times of dehydration, the mixture of benzamide and benzonitrile enters the intermittent dehydration system 150, and the water vapor generated in the reaction and carrying the unreacted ammonia gas is output from the top outlet of the continuous dehydration system 140, enters the ammonia removal recycling system 160 after the condenser 170;

[0043] The process of the two times of dehydration is that the ammonium benzoate first loses one molecule of water to obtain benzamide, and the benzamide loses one molecule of water to become benzonitrile. The temperature control of the continuous dehydration system 140 is 210-240 DEG C, and the residence time control is 4-6 h; since a large amount of water generated in the process will take away part of the heat, a continuous temperature rising dehydration process is required to ensure the temperature of the reaction kettle, so as to evaporate a large amount of water in the material;

[0044] S3, the benzamide and benzonitrile in the intermittent dehydration system 150 are mixed with the ammonia gas input from the continuous ammoniation system 130, and the complete conversion and dehydration of the intermediate are realized by controlling the reaction temperature, so as to obtain the final product benzonitrile which is input into the rectifying tower 200, and the water vapor carrying the residual ammonia gas generated is output from the top outlet of the intermittent dehydration system 150, enters the ammonia removal recycling system 160 after the condenser 170;

[0045] The reaction temperature of the intermittent dehydration system 150 is 240-270 DEG C, and the time is 6-10 h, so as to completely dehydrate the unreacted benzoic acid, ammonium benzoate and benzamide at high temperature, and the ammonia gas atmosphere inhibits the reverse hydrolysis and deamination decomposition reaction of the benzamide, so that the benzamide is completely converted into benzonitrile, the reaction yield is improved, the reaction temperature and time in the intermittent dehydration system 150 are controlled, the complete conversion and dehydration of the intermediate are realized, the prepared benzonitrile product has high purity, can be directly input into the rectifying tower, and does not need to be treated by an intermediate process, thereby saving the process;

[0046] S4, the deamination circulating recovery system 160 carries out deamination treatment on the liquid input from the continuous dehydration system 140 and the intermittent dehydration system 150 through a rectifying tower, ammonia gas obtained is continuously extracted from a condenser 170 at the top of the deamination circulating recovery system 160, and the ammonia gas is mixed into the gas mixing system 120 by the negative pressure effect of the Venturi mixer, mixed with ammonia gas output by the ammonia gas supply system 110 after passing through the Venturi mixer, and re-input into the continuous amination system 130 to prepare benzonitrile, so that the ammonia gas is fully recycled, and the remaining waste water is input into the sewage treatment device 300 from the bottom of the deamination circulating recovery system 160.

[0047] In particular, the present application inputs excess ammonia gas at high pressure, which can provide power for the circulation of ammonia gas in the entire device, and realizes self-operation; the input of excess ammonia gas ensures the conversion rate of benzoic acid to ammonium benzoate, and the remaining ammonia gas is input into the intermittent dehydration system 150, so that the intermediate that is not completely reacted is further converted into benzonitrile, and the presence of ammonia gas atmosphere can also inhibit the hydrolytic deamination reaction of the intermediate in the high-temperature and large amount of water vapor, solving the problem of difficult balance between the dehydration degree of the product and the decomposition of the intermediate, improving the yield of benzonitrile, and reducing the proportion of by-products at high temperature.

[0048] Specifically, the present application divides the reaction dehydration process into continuous reaction dehydration and intermittent reaction dehydration, first, through continuous reaction dehydration at a lower temperature, a large amount of reaction generated water vapor is evaporated in the early and middle stages of the reaction, the residence time of the material is reduced, the reaction temperature in this stage is reduced, and the equipment efficiency is improved; then, through intermittent reaction dehydration, the residual ammonium benzoate and benzamide in the later stage of the reaction are completely converted into benzonitrile at a higher temperature, so as to improve the conversion rate and yield of the reaction. In addition, the present application does not input ammonia gas in the continuous reaction dehydration stage, but inputs ammonia gas in the intermittent dehydration stage after a large amount of reaction generated water vapor is removed from the material, which reduces the problem that a large amount of reaction generated water vapor takes away ammonia gas in the continuous dehydration stage, causing the load of the deamination circulating recovery system 160 to be too large. In the intermittent dehydration stage, the reaction generates less water and the temperature is higher, so that the input of ammonia gas does not significantly increase the load of the deamination circulating recovery system 160.

[0049] In some specific embodiments, the deamination circulating recovery system 160 carries out deamination treatment on the liquid therein by heating; the deamination circulating recovery system 160 is a normal pressure rectifying device, the overhead of the kettle is ammonia gas, and the ammonia nitrogen content in the aqueous solution at the bottom of the kettle is less than 200 ppm, so that the ammonia gas in the entire system is fully recycled.

[0050] The present application carries out deamination treatment through the deamination cycle recovery system 160, the obtained ammonia gas is mixed with the ammonia gas output by the ammonia gas supply system 110 through a Venturi mixer to realize automatic suction and mixing of the high-pressure ammonia gas in the main path and the normal-pressure ammonia gas discharged in the recovery system, so that the recovered ammonia gas reenters the production system of the benzonitrile, realizes recycling of the ammonia gas, significantly reduces the consumption of the ammonia gas in the whole process, and reduces the ammonia content in the waste water, facilitating treatment of the sewage treatment device 300.

[0051] Embodiment 1

[0052] The present embodiment provides a method for realizing continuous production of benzonitrile and full recycling of ammonia gas, which is carried out by using the aforementioned device 100 for continuous production of benzonitrile from benzoic acid and full recycling of ammonia gas, and includes the following steps:

[0053] S1, the benzoic acid supply system provides benzoic acid for the continuous ammoniation system 130, the ammonia gas output by the ammonia gas supply system 110 is input into the continuous ammoniation system 130 through the gas mixing system 120, mixed with the benzoic acid therein to generate ammonium benzoate, the ammonium benzoate is input into the continuous dehydration system 140, and the excess ammonia gas is output from the top outlet of the continuous ammoniation system 130, input into the intermittent dehydration system 150 after being condensed by the condenser 170; wherein the temperature of the continuous ammoniation system 130 is controlled to be 200℃, and the time is 3.5h; the pressure of the ammonia gas output by the ammonia gas supply system 110 is 0.6MPa;

[0054] S2, the ammonium benzoate in the continuous dehydration system 140 is dehydrated twice to generate benzoamide and benzonitrile, the benzoamide and benzonitrile are input into the intermittent dehydration system 150, and the generated gas is output from the top outlet of the continuous dehydration system 140, input into the deamination cycle recovery system 160 after being condensed by the condenser 170; wherein the temperature of the continuous dehydration system 140 is controlled to be 230℃, and the processing time is controlled to be 5h;

[0055] S3, the benzoamide and benzonitrile in the intermittent dehydration system 150 are mixed with the ammonia gas input from the continuous ammoniation system 130, and the reaction temperature is controlled to realize complete conversion and dehydration of the intermediates, the obtained product benzonitrile is input into the rectifying tower 200, the generated gas is output from the top outlet of the intermittent dehydration system 150, input into the deamination cycle recovery system 160 after being condensed by the condenser 170; wherein the reaction temperature of the intermittent dehydration system 150 is 260℃, and the time is 7h;

[0056] S4, the deamination recycling system 160 deaminates the liquid input from the continuous dehydration system 140 and the intermittent dehydration system 150 by heating, and the obtained ammonia gas is input into the gas mixing system 120 from the top outlet and mixed with the ammonia gas output from the ammonia gas supply system 110, and then re-input into the continuous amination system 130 for preparation of the benzonitrile, and the remaining waste water is input into the waste water treatment device 300.

[0057] Comparative Example 1

[0058] Comparative Example 1 provides a method for realizing continuous production of benzonitrile and full recycling of ammonia gas, which is different from Example 1 in that the continuous amination system 130 of the device is directly connected to the continuous dehydration system 140, and the excess ammonia gas is transported into the continuous dehydration system 140, and the rest is substantially the same as Example 1, which is not repeated here.

[0059] Comparative Example 2

[0060] Comparative Example 2 provides a method for realizing continuous production of benzonitrile and full recycling of ammonia gas, which is different from Example 1 in that the reaction temperature of the intermittent dehydration system 150 in step S3 is 230°C, and the rest is substantially the same as Example 1, which is not repeated here.

[0061] Comparative Example 3

[0062] Comparative Example 3 provides a method for realizing continuous production of benzonitrile and full recycling of ammonia gas, which is different from Example 1 in that the reaction temperature of the intermittent dehydration system 150 in step S3 is 280°C, and the rest is substantially the same as Example 1, which is not repeated here.

[0063] The products of benzonitrile obtained from the intermittent dehydration system 150 in Example 1 and Comparative Examples 1-3 are tested for purity, color, and yield, and the ammonia content of the waste water is tested, and the results are shown in the following table.

[0064] Table 1 Test results of various indexes in Example 1 and Comparative Examples 1-3

[0065]

[0066] As can be seen from Table 1, when ammonia gas is directly input into the continuous dehydration system 140, a large amount of reaction water is generated due to dehydration of ammonium benzoate and benzamide at high temperature, and the water entrains a large amount of ammonia gas and volatile benzoic acid from the condenser at the top of the tower, resulting in a significant increase in the yield of the product and the consumption of ammonia gas. At the same time, a large amount of ammonia gas enters the ammonia recycling system, resulting in excessive load of the system, decreased ammonia recovery efficiency, and significantly increased ammonia nitrogen content in the waste water. In addition, when the kettle temperature in the batch dehydration system is too low or too high, it will affect the dehydration of ammonium benzoate and benzamide in the later stage of the reaction. If the kettle temperature is too low, the reaction will be incomplete, and a certain proportion of benzamide will be left in the crude product, resulting in a low content, and affecting the yield and content after rectification. If the kettle temperature is too high, the proportion of by-products such as rearrangement and polymerization at high temperature will increase, affecting the yield of the reaction. However, the by-products at such high temperature have very high boiling points and will not significantly affect the content of the product.

[0067] In summary, the present application provides a device and method for continuous production of benzonitrile and full recycling of ammonia gas from benzoic acid, which comprises an ammonia gas supply system, a gas mixing system, a continuous ammoniation system, a continuous dehydration system and a batch dehydration system connected in sequence, the continuous ammoniation system is connected with a benzoic acid supply system, and the liquid outlet of the batch dehydration system is connected with a rectification tower. The device further comprises a deamination recycling system connected with the continuous dehydration system, the batch dehydration system and the gas mixing system, to realize recycling and utilization of ammonia gas. In the method, high-pressure excess ammonia gas is input to realize flow of ammonia gas through each system under pressure driving and full participation in the reaction. By controlling the process parameters, the problem of difficult balance between dehydration degree of the product and decomposition of the intermediate is solved, complete conversion and dehydration of the intermediate are realized, the yield of benzonitrile is improved, and the impurity content of the product is reduced. The prepared benzonitrile product has high purity and can be directly input into the rectification tower without intermediate process treatment, saving the process. The ammonia gas obtained from the deamination recycling system and the ammonia gas output from the ammonia gas supply system can be mixed and reused in the preparation process of benzonitrile, realizing recycling and reuse of ammonia gas, significantly reducing the consumption of ammonia gas in the whole process, basically close to the theoretical value, and reducing the ammonia content in the waste water. The present application prepares benzonitrile product with high yield, high purity and low color number through the synergistic cooperation of each system in the device and the hierarchical control of process parameters in the preparation process of benzonitrile. The prepared benzonitrile can be directly input into the rectification process, reducing the difficulty and energy consumption of the rectification process. Recycling and reuse of ammonia gas reduces the consumption of ammonia gas in the preparation process, thereby reducing the production cost and improving the economic benefit of benzonitrile preparation.

[0068] The above examples are only used to illustrate the technical solutions of the present application but not limit the present application. Although the present application is described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can be modified or equivalent replaced without departing from the spirit and scope of the technical solutions of the present application.

Claims

1. A device for the continuous production of benzoic acid to benzonitrile and the complete recycling of ammonia, characterized in that, The system comprises, in sequence, an ammonia supply system, a gas mixing system, a continuous ammoniation system, a continuous dehydration system, and an intermittent dehydration system. The continuous ammoniation system is connected to the benzoic acid supply system, and the outlet of the intermittent dehydration system is connected to a distillation column, whereby the resulting product, benzonitrile, is directly fed into the distillation column. The continuous ammoniation system has a top outlet connected to the intermittent dehydration system, allowing excess ammonia to be introduced into the intermittent dehydration system, thus achieving complete conversion of the intermediate and full recovery and reuse of ammonia. The device also includes an ammonia desulfurization and recycling system, which is connected to the top outlets of the continuous dehydration system and the intermittent dehydration system, respectively. The top outlet of the ammonia desulfurization and recycling system is also connected to the gas mixing system to realize the recovery and recycling of ammonia.

2. The apparatus for continuous production of benzoic acid to benzonitrile and full recycling of ammonia according to claim 1, characterized in that, The gas mixing system is equipped with a Venturi mixer, which mixes the low-pressure ammonia gas output from the deammoniation cycle recovery system with the high-pressure ammonia gas output from the ammonia supply system, and then inputs it into the continuous ammoniation system to fully react with benzoic acid.

3. The apparatus for continuous production of benzoic acid to benzonitrile and full recycling of ammonia according to claim 1, characterized in that, The top outlets of the continuous ammoniation system, continuous dehydration system, intermittent dehydration system, and ammonia desulfurization and recycling system are all equipped with condensers. The condensers condense the materials output from the aforementioned systems to prevent them from entering the ammonia desulfurization and recycling system, and collect excess ammonia from the corresponding systems into the ammonia desulfurization and recycling system for ammonia recovery and recycling.

4. The apparatus for continuous production of benzoic acid to benzonitrile and full recycling of ammonia according to claim 1, characterized in that, The intermittent dehydration system is provided with a first dehydration unit and a second dehydration unit, which are connected in parallel.

5. A method for the continuous production of benzoic acid to benzonitrile and the complete recycling of ammonia, characterized in that, This method is carried out using the apparatus for continuous production of benzonitrile and full recycling of ammonia from benzoic acid as described in any one of claims 1 to 4, and includes the following steps: S1. The benzoic acid supply system provides benzoic acid to the continuous ammoniation system. The ammonia gas output from the ammonia supply system is input into the continuous ammoniation system through the gas mixing system, where it mixes with the benzoic acid to generate ammonium benzoate. The ammonium benzoate is continuously input into the continuous dehydration system in a high-temperature molten state. Excess ammonia gas is output from the top outlet of the continuous ammoniation system, passes through a condenser, and is then input into the intermittent dehydration system. S2. In the continuous dehydration system, ammonium benzoate is dehydrated twice to form a mixture of intermediate benzamide and final product benzonitrile. The mixture of benzamide and benzonitrile enters the intermittent dehydration system. At the same time, the water vapor generated by the reaction carries unreacted ammonia gas and is output from the top outlet of the continuous dehydration system. After passing through the condenser, it enters the ammonia removal and recycling system. S3. The benzamide and benzonitrile in the intermittent dehydration system are mixed with ammonia gas input from the continuous ammonia system, and the intermediate is completely converted and dehydrated by controlling the reaction temperature to obtain the final product benzonitrile, which is then fed into a distillation column. The water vapor carrying residual ammonia generated is output from the top outlet of the intermittent dehydration system, and enters the deammoniation recycling system after passing through a condenser. S4. The ammonia removal and recycling system distills the liquid input from the continuous dehydration system and the intermittent dehydration system. The resulting ammonia gas is continuously extracted from the condenser at the top of the ammonia removal and recycling system and incorporated into the gas mixing system by the negative pressure effect of the Venturi mixer. It is mixed with the ammonia gas output from the ammonia gas supply system and then reintroduced into the continuous ammoniation system for the preparation of benzonitrile. The remaining wastewater is discharged from the bottom of the ammonia removal and recycling system and enters the wastewater treatment device.

6. The method for continuous production of benzoic acid to benzonitrile and full recycling of ammonia according to claim 5, characterized in that, In step S3, the reaction temperature of the intermittent dehydration system is 240-270°C, and the time is 6-10 hours. The unreacted ammonium benzoate and benzamide are completely dehydrated at high temperature, and the ammonia gas input from the continuous ammoniation system inhibits the reverse decomposition of benzamide, so that it is completely converted into benzonitrile, thereby improving the reaction yield.

7. The method for continuous production of benzoic acid to benzonitrile and full recycling of ammonia according to claim 5, characterized in that, In step S1, the temperature of the continuous ammonia system is controlled at 190-210°C to ensure the conversion of benzoic acid and to keep the generated ammonium benzoate in a molten state for easy material transport. The reaction residence time is 2-4 hours.

8. The method for continuous production of benzoic acid to benzonitrile and full recycling of ammonia according to claim 5, characterized in that, In step S2, the temperature of the continuous dehydration system is controlled at 210–240°C, and the residence time is controlled at 4–6 hours.

9. The method for continuous production of benzoic acid to benzonitrile and full recycling of ammonia according to claim 5, characterized in that, In step S1, the pressure of the ammonia gas output by the ammonia gas supply system is 0.5 to 1.0 MPa, so that the ammonia gas can flow through each system under pressure and fully participate in the reaction.

10. The method for continuous production of benzoic acid to benzonitrile and full recycling of ammonia according to claim 5, characterized in that, In step S4, the ammonia removal and recycling system is an atmospheric distillation device. The top product is ammonia gas, and the ammonia nitrogen content in the aqueous solution at the bottom of the vessel is less than 200 ppm, thus achieving full recovery and utilization of ammonia gas in the entire system.

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