Method and device for synthesizing diphenylamine

Abstract

The present invention provides a diphenylamine synthesis method, which comprises: (1) carrying out a reaction on aniline under the action of an acid catalyst to generate diphenylamine and ammonia gas, the acid catalyst being in a liquid state at a reaction temperature and a reaction pressure, the reaction temperature being less than or equal to 300 DEG C, and the reaction pressure being 0.5-1.5 MPa; (2) performing gas-liquid separation on the reaction system in the step (1) in the reaction process to obtain ammonia gas and liquid, collecting the ammonia gas, and returning the liquid to the step (1) to continue the reaction; (3) cooling the reaction liquid after the reaction is ended, so that the acid catalyst and aniline are combined to generate solid salt, and then carrying out solid-liquid separation to obtain solid salt and liquid; and (4) distilling the liquid obtained in the step (3) to obtain aniline and diphenylamine. The method is mild in reaction condition, low in production cost, high in conversion rate and selectivity and suitable for industrial popularization, and the catalyst can be recycled.

Description

Technical Field

[0001] The present invention relates to the field of chemical synthesis, and particularly to a method and apparatus for synthesizing diphenylamine. Background Art

[0002] Among the currently disclosed methods for synthesizing diphenylamine, diphenylamine is mainly produced by hydrogenation under the action of a solid acid catalyst, and the reaction temperature is generally > 300°C. In some methods, nitrogen is introduced into the reaction process of aniline and a solid acid catalyst, and subsequent ammonia recovery processes are required to continuously discharge non-condensable tail gases. The continuous discharge of non-condensable gases will inevitably entrain ammonia emissions, causing environmental pollution. There are also some methods for synthesizing diphenylamine that do not require gas introduction, but the reaction temperature is generally still > 300°C, and the catalyst can be recycled fewer times, with lower conversion rates and selectivities.

[0003] Therefore, there is an urgent need to develop a diphenylamine synthesis process with mild reaction conditions, a catalyst that can be recycled, low cost, high conversion rate, and high selectivity. Summary of the Invention

[0004] To solve the deficiencies in the prior art, the present invention provides a process for synthesizing diphenylamine. The process uses an acid catalyst that is liquid at the reaction temperature and reaction pressure as the synthesis catalyst. The entire reaction does not require the introduction of hydrogen or nitrogen. The reaction temperature is ≤ 300°C, and the acid catalyst can be recycled. It has the advantages of mild reaction, high reaction conversion rate and selectivity, and low production cost, and is suitable for industrial promotion and utilization.

[0005] Specifically, the present invention provides a method for synthesizing diphenylamine, which comprises the following steps:

[0006] (1) React aniline under the action of an acid catalyst to produce diphenylamine and ammonia. The acid catalyst is liquid at the reaction temperature and reaction pressure. The reaction temperature is ≤ 300°C, and the reaction pressure is 0.5 - 1.5 MPa;

[0007] (2) During the reaction, perform gas-liquid separation on the reaction system in step (1) to obtain ammonia and a liquid. Collect the ammonia and return the liquid to step (1) for continuous reaction;

[0008] (3) After the reaction, cool the reaction solution to cause the acid catalyst and aniline to combine to form a solid salt, and then perform solid-liquid separation to obtain the solid salt and a liquid;

[0009] (4) Distill the liquid obtained in step (3) to obtain aniline and diphenylamine.

[0010] In one or more embodiments, the acid catalyst is selected from one or more of p-toluenesulfonic acid, 1-propanesulfonic acid, methanesulfonic acid, and ethylsulfonic acid.

[0011] In one or more embodiments, in step (1), no nitrogen or hydrogen is introduced during the reaction.

[0012] In one or more embodiments, in step (1), the mass ratio of aniline to the acid catalyst is (40 - 50):1.

[0013] In one or more embodiments, in step (1), the reaction temperature is 250 - 300 °C.

[0014] In one or more embodiments, in step (1), the reaction time is 3 - 4.5 h.

[0015] In one or more embodiments, in step (2), gas-liquid separation is performed every 0.5 - 1 h.

[0016] In one or more embodiments, in step (3), the solid-liquid separation time is 0.5 - 1 h.

[0017] In one or more embodiments, in step (3), the temperature of the solid-liquid separation is 60 - 80 °C.

[0018] In one or more embodiments, in step (4), the vacuum degree of the distillation is -0.097 - -0.098 MPa.

[0019] In one or more embodiments, in step (4), the distillation temperature is 120 - 140 °C.

[0020] In one or more embodiments, the method further includes: heating the solid salt obtained in step (3) to obtain the acid catalyst and aniline in a liquid state, and then adding the acid catalyst and aniline to the reaction system of step (1); preferably, the heating temperature is 100 - 130 °C.

[0021] In one or more embodiments, the method further includes: adding the aniline obtained in step (4) to the reaction system of step (1).

[0022] The present invention also provides a device for synthesizing diphenylamine, and the device includes a high-pressure reactor, a gas-liquid separator, a solid-liquid separator, a distillation kettle, and a heater;

[0023] The high-pressure reactor is used to react aniline under the action of an acid catalyst to generate diphenylamine and ammonia, and the acid catalyst is in a liquid state at the reaction temperature and reaction pressure;

[0024] The gas-liquid separator is connected to the high-pressure reactor and is used to perform gas-liquid separation on the reaction system in the high-pressure reactor during the reaction to obtain ammonia gas and liquid, and return the liquid obtained from the gas-liquid separation to the high-pressure reactor;

[0025] The solid-liquid separator is used to perform solid-liquid separation on the cooled reaction liquid to obtain the solid salt formed by the combination of the acid catalyst and aniline and the liquid;

[0026] The distillation kettle is used to distill the liquid obtained from the solid-liquid separation to obtain aniline and diphenylamine;

[0027] The heater is used to heat and decompose the solid salt obtained from the separation by the solid-liquid separator into the acid catalyst and aniline in a liquid state.

[0028] In one or more embodiments, the device further includes an ammonia collection tank for collecting the ammonia gas separated by the gas-liquid separator. Description of the Drawings

[0029] Figure 1 It is a process flow chart for preparing diphenylamine in some embodiments of the present invention. Detailed Embodiments

[0030] To enable those skilled in the art to understand the features and effects of the present invention, the following provides a general description and definition of the terms and phrases mentioned in the specification and claims. Unless otherwise specified, all technical and scientific terms used herein shall have the ordinary meaning understood by those skilled in the art for the present invention. In case of conflict, the definition in this specification shall prevail.

[0031] The theories or mechanisms described and disclosed herein, whether correct or incorrect, shall not limit the scope of the present invention in any way, that is, the content of the present invention can be implemented without being limited by any specific theory or mechanism.

[0032] In this article, terms such as "comprising", "including", "containing" and similar terms cover the meanings of "consisting essentially of" and "consisting of". For example, when this article discloses that "A comprises B and C", it should be considered that "A consists essentially of B and C" and "A consists of B and C" have been disclosed herein.

[0033] In this article, all features defined in the form of numerical ranges or percentage ranges, such as numerical values, quantities, contents and concentrations, are only for the sake of brevity and convenience. Accordingly, the description of the numerical range or percentage range should be regarded as having covered and specifically disclosed all possible sub-ranges and individual numerical values within the range (including integers and fractions).

[0034] In this text, unless otherwise specified, percentages refer to mass percentages and ratios refer to mass ratios.

[0035] In this text, when describing embodiments or examples, it should be understood that they are not used to limit the present invention to these embodiments or examples. On the contrary, all alternatives, modifications, and equivalents of the methods and materials described in the present invention can be covered within the scope defined by the claims.

[0036] In this text, for the sake of concise description, not all possible combinations of all technical features in each embodiment or example are described. Therefore, as long as there is no contradiction in the combination of these technical features, the technical features in each embodiment or example can be combined arbitrarily, and all possible combinations should be considered as the scope described in this specification.

[0037] As Figure 1 shown, the present invention provides a method for synthesizing diphenylamine, which specifically includes the following steps:

[0038] (1) React aniline under the action of an acid catalyst to generate diphenylamine and ammonia. The acid catalyst is in a liquid state at the reaction temperature and reaction pressure. The reaction temperature is ≤ 300 °C, and the reaction pressure is 0.5 - 1.5 MPa;

[0039] (2) During the reaction, perform gas-liquid separation on the reaction system in step (1) to obtain ammonia and a liquid. Collect the ammonia and return the liquid to step (1) to continue the reaction;

[0040] (3) After the reaction is completed, cool the reaction solution to cause the acid catalyst and aniline to combine to form a solid salt, and then perform solid-liquid separation to obtain the solid salt and the liquid;

[0041] (4) Distill the liquid obtained in step (3) to obtain aniline and diphenylamine.

[0042] In the present invention, the catalyst is an acid catalyst that is in a liquid state at the reaction temperature and reaction pressure. The acid catalyst that can be used in the present invention can be one or more selected from p-toluenesulfonic acid, 1-propanesulfonic acid, methanesulfonic acid, and ethylsulfonic acid.

[0043] The present invention uses an acid catalyst that is in a liquid state at the reaction temperature and reaction pressure. During the reaction, the catalyst is in a liquid state, which is conducive to full contact with the reactants and improves the reaction rate. After the reaction is completed, by cooling, the solid salt formed by the combination of the acid catalyst and aniline can be precipitated, so that the acid catalyst can be recovered by solid-liquid separation and reused in the reaction system to catalyze the synthesis of diphenylamine from aniline, realizing the recycling of the catalyst.

[0044] In some embodiments, the acid catalyst used in the present invention is p-toluenesulfonic acid.

[0045] In step (1), nitrogen or hydrogen is not introduced during the reaction. This is beneficial for recovering high-quality ammonia and increasing economic efficiency.

[0046] In step (1), the mass ratio of aniline to the acid catalyst can be (40 - 50):1, such as 42:1, 45:1, 58:1. In some embodiments, aniline and the acid catalyst are added using a metering pump, which is beneficial for controlling the dosage of the reactants and the reaction rate.

[0047] In step (1), the reaction temperature can be 250 - 300 °C, such as 260 °C, 270 °C, 280 °C, 290 °C. On the one hand, under this temperature condition, the reaction is mild; on the other hand, at this temperature, the catalyst can maintain a liquid form, increasing the contact area of the catalyst and improving the reaction rate and the reaction yield.

[0048] In step (1), the reaction time can be 3 - 4.5 h, such as 3 h, 3.5 h, 4 h, 4.5 h.

[0049] In step (1), the reaction pressure can be 0.5 - 1.5 MPa. In the present invention, since ammonia is continuously generated during the reaction, the reaction pressure is within a range. In the present invention, it is difficult for the reaction pressure to exceed 1.5 MPa. When the pressure is 1.5 MPa, there is too much ammonia in the reactor and the reaction is difficult to proceed; at the same time, the reaction pressure is not less than 0.5 MPa because part of the aniline is vaporized, which is the pressure of gaseous aniline.

[0050] In step (2), it is preferred to perform gas-liquid separation every 0.5 - 1 h. Performing gas-liquid separation in multiple times can avoid ammonia dissolving in the liquid under high pressure and is also beneficial for avoiding excessive gas pressure resulting in cylinder burst.

[0051] In step (3), the solid-liquid separation time can be 0.5 - 1 h, such as 0.6 h, 0.7 h, 0.8 h, 0.9 h, 1 h.

[0052] In step (3), the solid-liquid separation temperature can be 60 - 80 °C, such as 60 °C, 65 °C, 70 °C, 75 °C, 80 °C. In the present invention, the acid catalyst and aniline will form a solid salt insoluble in organic matter at 60 - 80 °C, and basically all the salt can precipitate within this temperature range. Therefore, selecting the above temperature range for solid-liquid separation is beneficial for the recycling of the acid catalyst.

[0053] In step (4), the vacuum degree (relative pressure) for distilling the liquid obtained by solid-liquid separation can be -0.097 to -0.098 MPa. In step (4), the distillation temperature can be 120 to 140 °C, such as 120 °C, 125 °C, 130 °C, 135 °C, 140 °C. Under this vacuum degree and temperature, diphenylamine product and recyclable aniline can be separated, and such distillation conditions are beneficial to improving the purity of diphenylamine.

[0054] The method for synthesizing diphenylamine of the present invention may further include: heating the solid salt obtained in step (3) to obtain a liquid acid catalyst and aniline, and then adding them to the reaction system of step (1); preferably, the heating temperature can be 100 to 130 °C, such as 100 °C, 115 °C, 120 °C, 125 °C, 130 °C. Under this temperature condition, the solid salt obtained by solid-liquid separation can be decomposed into a liquid acid catalyst and aniline, so as to be recycled as a catalyst and raw material for re-reaction.

[0055] The method for synthesizing diphenylamine of the present invention may further include: adding the aniline obtained in step (4) to the reaction system of step (1).

[0056] The present invention also provides a device for synthesizing diphenylamine, which specifically includes a high-pressure reaction kettle, a gas-liquid separator, a solid-liquid separator, a distillation kettle and a heater;

[0057] The high-pressure reaction kettle is used to react aniline under the action of an acid catalyst to generate diphenylamine and ammonia, and the acid catalyst is in a liquid state under the reaction temperature and reaction pressure;

[0058] The gas-liquid separator is connected to the high-pressure reaction kettle and is used to perform gas-liquid separation on the reaction system in the high-pressure reaction kettle during the reaction to obtain ammonia and a liquid, and return the liquid obtained by gas-liquid separation to the high-pressure reaction kettle;

[0059] The solid-liquid separator is used to perform solid-liquid separation on the cooled reaction liquid to obtain a solid salt formed by the combination of an acid catalyst and aniline and a liquid;

[0060] The distillation kettle is used to distill the liquid obtained by solid-liquid separation to obtain aniline and diphenylamine;

[0061] The heater is used to decompose the solid salt separated by the solid-liquid separator into a liquid acid catalyst and aniline.

[0062] Preferably, the device for synthesizing diphenylamine of the present invention further includes an ammonia collection tank for collecting the ammonia separated by the gas-liquid separator.

[0063] In the present invention, the reaction can be carried out in a high-pressure reactor. The high-pressure reactor can provide a high-temperature and high-pressure environment, and can control the reaction process to ensure the smooth progress of the reaction. In the present invention, a heater is used to heat and decompose the solid salt into a liquid acid catalyst and aniline, which is beneficial to the transfer of substances in the industrial production process. In the present invention, the ammonia gas collected by the ammonia gas collection tank can be used as a new product, reducing environmental pollution while increasing economic benefits.

[0064] The present invention has the following advantages compared with the prior art:

[0065] (1) In the present invention, the reaction temperature ≤ 300 °C, and the reaction conditions are mild and easy to control;

[0066] (2) In the present invention, an acid catalyst in a liquid state under the reaction temperature and reaction pressure is used as the catalyst, achieving a very high conversion rate and selectivity at a relatively low reaction temperature. The conversion rate is as high as 45-53%, and the selectivity is still as high as over 99.5% after the catalyst is recycled;

[0067] (3) In the present invention, the acid catalyst can be recovered by cooling to form a solid salt and then separating the solid and liquid. By this method, recycling can be achieved, reducing production costs;

[0068] (4) In the present invention, after the acid catalyst is recycled multiple times, the reaction still has a very high conversion rate and selectivity;

[0069] (5) In the present invention, no hydrogen or nitrogen gas is introduced, which is convenient for recovering high-quality ammonia gas and increasing economic benefits.

[0070] The present invention will be described below by way of specific examples. It should be understood that these examples are merely illustrative and are not intended to limit the scope of the present invention. The methods, reagents, and materials used in the examples are conventional methods, reagents, and materials in the art unless otherwise specified. The raw material compounds in the examples can be obtained through commercial channels.

[0071] Equipment Example 1

[0072] This equipment example provides a device that can be used for synthesizing diphenylamine, as Figure 1As shown in the figure, the device includes a high-pressure reactor, a gas-liquid separator, a solid-liquid separator, a distillation kettle, an ammonia collection tank and a heater. The high-pressure reactor is used to react aniline under the action of an acid catalyst in a liquid state at a reaction temperature and a reaction pressure to generate diphenylamine and ammonia. The gas-liquid separator is connected to the high-pressure reactor and is used to perform gas-liquid separation on the reaction system in the high-pressure reactor during the reaction to obtain ammonia and liquid, and return the liquid obtained by gas-liquid separation to the high-pressure reactor. The solid-liquid separator is used to perform solid-liquid separation on the cooled reaction liquid to obtain a solid salt formed by the combination of an acid catalyst and aniline and a liquid. The distillation kettle is used to distill the liquid obtained by solid-liquid separation to obtain aniline and diphenylamine. The ammonia collection tank is used to collect the ammonia separated by the gas-liquid separator. The heater is used to heat and decompose the solid salt separated by the solid-liquid separator into an acid catalyst in a liquid state and aniline, and the liquid acid catalyst and aniline can be re-introduced into the high-pressure reactor to catalyze the reaction of aniline to synthesize diphenylamine.

[0073] Example 1

[0074] In this example, the device of Equipment Example 1 was used to synthesize diphenylamine according to the following steps:

[0075] (1) Aniline and p-toluenesulfonic acid were respectively pumped into the high-pressure reactor by a metering pump according to a mass ratio of 40:1. The reaction pressure was 0.5 - 1.5 MPa, and the reaction temperature was 250 °C. During the reaction, the gas-liquid separator valve was opened every 0.5 h for gas-liquid separation. The ammonia obtained by gas-liquid separation entered the ammonia collection tank, and the liquid returned to the high-pressure reactor to continue the reaction. After reacting for 3 h, the liquid in the high-pressure reactor was put into a solid-liquid separator at a temperature of 80 °C and allowed to stand for 0.5 h to precipitate a solid salt formed by the combination of aniline and p-toluenesulfonic acid, and then solid-liquid separation was performed. The solid salt obtained by solid-liquid separation was heated to 110 °C to obtain liquid aniline and p-toluenesulfonic acid that could be re-introduced into the reaction. The liquid obtained by solid-liquid separation was distilled in a distillation kettle under a vacuum of -0.097 MPa and a kettle temperature of 120 °C to obtain an aniline fraction and a diphenylamine kettle liquid. The purity of diphenylamine was 99.3%. The conversion rate of the reaction raw materials was 50%, and the product selectivity was 99.15%.

[0076] (2) Use a metering pump to re-inject the p-toluenesulfonic acid and aniline obtained by heating and melting after solid-liquid separation and the aniline fraction obtained by distillation into the high-pressure reactor, and add aniline to make the mass ratio of aniline to p-toluenesulfonic acid 40:1. The reaction pressure is 0.5 - 1.5 MPa, and the reaction temperature is 250 °C. During the reaction, open the valve of the gas-liquid separator every 0.5 h for gas-liquid separation. The ammonia gas obtained from the gas-liquid separation enters the ammonia gas collection tank, and the liquid returns to the high-pressure reactor to continue the reaction. After reacting for 3 h, put the liquid in the high-pressure reactor into a solid-liquid separator at 80 °C and let it stand for 0.5 h to precipitate the solid salt formed by the combination of aniline and p-toluenesulfonic acid, and then perform solid-liquid separation. Heat the solid salt obtained from the solid-liquid separation to 110 °C to obtain the liquid aniline and p-toluenesulfonic acid that can be re-injected into the reaction. Distill the liquid obtained from the solid-liquid separation in a distillation kettle with a vacuum degree of -0.097 MPa and a kettle temperature of 120 °C to obtain an aniline fraction and a diphenylamine kettle liquid. The purity of diphenylamine is 99.2%. The conversion rate of the reaction raw materials is 49.8%, and the product selectivity is 99.13%.

[0077] (3) According to the reaction conditions in step (2), recycle the p-toluenesulfonic acid and conduct the reaction 8 more times. The purity of diphenylamine, the conversion rate of raw materials, and the product selectivity of each reaction are shown in Table 1.

[0078] In Table 1, Reaction No. 1 refers to the reaction using p-toluenesulfonic acid for the first time, and Reactions No. 2 - 10 refer to the reactions using the recycled p-toluenesulfonic acid for the 1st - 9th times respectively.

[0079] Table 1: Experimental Results of Recycling p-Toluenesulfonic Acid in the Reaction

[0080] Reaction number Diphenylamine purity Raw material conversion rate Product selectivity 1 99.3％ 50.3％ 99.15％ 2 99.2％ 50.1％ 99.13％ 3 99.4％ 50.2％ 99.12％ 4 99.1％ 49.9％ 99.14％ 5 99.3％ 50.0％ 99.13％ 6 99.5％ 49.9％ 99.12％ 7 99.1％ 49.8％ 99.13％ 8 99.2％ 49.7％ 99.09％ 9 99.1％ 49.8％ 99.10％ 10 99.1％ 49.7％ 99.05％

[0081] Example 2

[0082] In this example, use the device of Equipment Example 1 to synthesize diphenylamine according to the following steps:

[0083] Aniline and 1 - propanesulfonic acid were respectively pumped into a high - pressure reactor by metering pumps at a mass ratio of 40:1. The reaction pressure was 0.5 - 1.5 MPa, and the reaction temperature was 250 °C. During the reaction process, the gas - liquid separator valve was opened every 0.5 h for gas - liquid separation. The ammonia gas obtained from the gas - liquid separation entered the ammonia collection tank, and the liquid returned to the high - pressure reactor to continue the reaction. After 3 h of reaction, the liquid in the high - pressure reactor was put into a solid - liquid separator at 60 °C and left to stand for 0.5 h to precipitate the solid salt formed by the combination of aniline and 1 - propanesulfonic acid. Then, solid - liquid separation was carried out. The solid salt obtained from the solid - liquid separation was heated to 100 °C to obtain liquid aniline and 1 - propanesulfonic acid that could be reused in the reaction. The liquid obtained from the solid - liquid separation was distilled in a distillation kettle with a vacuum degree of - 0.097 MPa and a kettle temperature of 120 °C to obtain aniline fraction and diphenylamine kettle liquid. The purity of diphenylamine was 99.02%. The conversion rate of the reaction raw materials was 47.5%, and the product selectivity was 99.08%.

[0084] Example 3

[0085] In this example, the device of Equipment Example 1 was used to synthesize diphenylamine according to the following steps:

[0086] Aniline and ethylsulfonic acid were respectively pumped into a high - pressure reactor by metering pumps at a mass ratio of 50:1. The reaction pressure was 0.5 - 1.5 MPa, and the reaction temperature was 250 °C. During the reaction process, the gas - liquid separator valve was opened every 0.5 h for gas - liquid separation. The ammonia gas obtained from the gas - liquid separation entered the ammonia collection tank, and the liquid returned to the high - pressure reactor to continue the reaction. After 3 h of reaction, the liquid in the high - pressure reactor was put into a solid - liquid separator at 60 °C and left to stand for 0.5 h to precipitate the solid salt formed by the combination of aniline and ethylsulfonic acid. Then, solid - liquid separation was carried out. The solid salt obtained from the solid - liquid separation was heated to 100 °C to obtain liquid aniline and ethylsulfonic acid that could be reused in the reaction. The liquid obtained from the solid - liquid separation was distilled in a distillation kettle with a vacuum degree of - 0.097 MPa and a kettle temperature of 120 °C to obtain aniline fraction and diphenylamine kettle liquid. The purity of diphenylamine was 99.0%. The conversion rate of the reaction raw materials was 48.3%, and the product selectivity was 99.03%.

[0087] Example 4

[0088] In this example, the device of Equipment Example 1 was used to synthesize diphenylamine according to the following steps:

[0089] Aniline and methanesulfonic acid were respectively pumped into a high-pressure reactor by metering pumps according to a mass ratio of 40:1. The reaction pressure was 0.5 - 1.5 MPa, and the reaction temperature was 300 °C. During the reaction, the gas-liquid separator valve was opened every 0.5 h for gas-liquid separation. The ammonia gas obtained from the gas-liquid separation entered the ammonia gas collection tank, and the liquid returned to the high-pressure reactor to continue the reaction. After reacting for 3 h, the liquid in the high-pressure reactor was put into a solid-liquid separator at 60 °C and left to stand for 0.5 h to precipitate the solid salt formed by the combination of aniline and methanesulfonic acid. Then, solid-liquid separation was carried out. The solid salt obtained from the solid-liquid separation was heated to 100 °C to obtain liquid aniline and methanesulfonic acid that could be reused in the reaction. The liquid obtained from the solid-liquid separation was distilled in a distillation kettle with a vacuum degree of -0.097 MPa and a kettle temperature of 120 °C to obtain an aniline fraction and a diphenylamine kettle liquid. The purity of diphenylamine was 99.1%. The conversion rate of the reaction raw materials was 46.8%, and the product selectivity was 99.02%.

[0090] Comparative Example 1

[0091] In this comparative example, alumina, a solid catalyst, was used to catalyze the synthesis of diphenylamine from aniline:

[0092] (1) Aniline and alumina were put into a high-pressure reactor according to a mass ratio of 40:1. The reaction pressure was 0.5 - 1.2 MPa (because the catalytic performance of the alumina catalyst was weak, less ammonia gas was generated, so the pressure was lower), and the reaction temperature was 250 °C. During the reaction, the gas-liquid separator valve was opened every 0.5 h for gas-liquid separation. The ammonia gas obtained from the gas-liquid separation entered the ammonia gas collection tank, and the liquid returned to the high-pressure reactor to continue the reaction. After reacting for 3 h, solid-liquid separation was carried out on the substances in the high-pressure reactor. The liquid obtained was distilled in a distillation kettle with a vacuum degree of -0.097 MPa and a kettle temperature of 120 °C to obtain an aniline fraction and a diphenylamine kettle liquid. The purity of diphenylamine was 97.1%. The conversion rate of the reaction raw materials was 30.0%, and the product selectivity was 96.8%.

[0093] (2) The alumina obtained after solid-liquid separation and the aniline fraction obtained from the distillation were re-put into the high-pressure reactor, and aniline was added to make the mass ratio of aniline to alumina 40:1. The reaction pressure was 0.5 - 1.2 MPa, and the reaction temperature was 250 °C. During the reaction, the gas-liquid separator valve was opened every 0.5 h for gas-liquid separation. The ammonia gas obtained from the gas-liquid separation entered the ammonia gas collection tank, and the liquid returned to the high-pressure reactor to continue the reaction. After reacting for 3 h, solid-liquid separation was carried out on the substances in the high-pressure reactor. The liquid obtained was distilled in a distillation kettle with a vacuum degree of -0.097 MPa and a kettle temperature of 120 °C to obtain an aniline fraction and a diphenylamine kettle liquid. The purity of diphenylamine was 97.0%. The conversion rate of the reaction raw materials was 30%, and the product selectivity was 96.7%.

[0094] (3) Under the reaction conditions of step (2), the alumina was recycled and the reaction was carried out 8 more times. The purity, reaction conversion rate, and selectivity of diphenylamine in each reaction are shown in Table 2.

[0095] In Table 1, Reaction No. 2 refers to the reaction using alumina for the first time, and Reactions No. 2-10 refer to the reactions using recycled alumina for the 1st-9th times, respectively.

[0096] Table 2: Experimental results of recycling alumina in the reaction

[0097] Reaction number Diphenylamine purity Raw material conversion rate Product selectivity 1 97.1％ 30.0％ 96.8％ 2 97.0％ 30.2％ 96.7％ 3 97.1％ 30.1％ 96.3％ 4 97.2％ 29.7％ 95.7％ 5 97.0％ 29.8％ 95.6％ 6 96.7％ 29.6％ 95.9％ 7 96.9％ 29.7％ 95.3％ 8 96.8％ 29.1％ 95.2％ 9 96.7％ 29.2％ 95.0％ 10 96.2％ 29.0％ 95.0％

Claims

1. A method for synthesizing diphenylamine, characterized in that, the method comprises the following steps: (1) Reacting aniline under the action of an acid catalyst to produce diphenylamine and ammonia. The acid catalyst is in a liquid state at the reaction temperature and reaction pressure. The reaction temperature is ≤ 300 °C, and the reaction pressure is 0.5 - 1.5 MPa; (2) During the reaction, performing gas-liquid separation on the reaction system in step (1) to obtain ammonia gas and a liquid, collecting the ammonia gas, and returning the liquid to step (1) for continuous reaction; (3) After the reaction, cooling the reaction solution to cause the acid catalyst and aniline to combine to form a solid salt, and then performing solid-liquid separation to obtain the solid salt and a liquid; (4) Distilling the liquid obtained in step (3) to obtain aniline and diphenylamine.

2. The method according to claim 1, characterized in that, the acid catalyst is selected from one or more of p-toluenesulfonic acid, 1-propanesulfonic acid, methanesulfonic acid, and ethylsulfonic acid.

3. The method according to claim 1, characterized in that, the method has one or more of the following characteristics: In step (1), nitrogen or hydrogen is not introduced during the reaction process; In step (1), the mass ratio of aniline to the acid catalyst is (40 - 50):1; In step (1), the reaction temperature is 250 - 300 °C; In step (1), the reaction time is 3 - 4.5 h.

4. The method according to claim 1, characterized in that, in step (2), gas-liquid separation is performed every 0.5 - 1 h.

5. The method according to claim 1, characterized in that, in step (3), the time for solid-liquid separation is 0.5 - 1 h; and / or in step (3), the temperature for solid-liquid separation is 60 - 80 °C.

6. The method according to claim 1, characterized in that, in step (4), the vacuum degree of the distillation is -0.097 - -0.098 MPa; and / or in step (4), the temperature of the distillation is 120 - 140 °C.

7. The method according to claim 1, characterized in that, the method further comprises: heating the solid salt obtained in step (3) to obtain the acid catalyst and aniline in a liquid state, and then adding the acid catalyst and aniline to the reaction system in step (1); preferably, the heating temperature is 100 - 130 °C.

8. The method according to claim 1, characterized in that, the method further comprises: adding the aniline obtained in step (4) to the reaction system in step (1).

9. An apparatus for synthesizing diphenylamine, characterized in that, the apparatus comprises a high-pressure reactor, a gas-liquid separator, a solid-liquid separator, a distillation kettle, and a heater; the high-pressure reactor is used for reacting aniline under the action of an acid catalyst to produce diphenylamine and ammonia, and the acid catalyst is in a liquid state at the reaction temperature and reaction pressure; the gas-liquid separator is connected to the high-pressure reactor and is used for performing gas-liquid separation on the reaction system in the high-pressure reactor during the reaction to obtain ammonia gas and a liquid, and returning the liquid obtained by gas-liquid separation to the high-pressure reactor; The solid-liquid separator is used for solid-liquid separation of the cooled reaction liquid to obtain a solid salt formed by the combination of the acid catalyst and aniline and a liquid; The distillation kettle is used for distilling the liquid obtained by solid-liquid separation to obtain aniline and diphenylamine; The heater is used for heating and decomposing the solid salt separated by the solid-liquid separator into the acid catalyst in liquid state and aniline.

10. The device according to claim 9, characterized in that, the device further includes an ammonia collection tank for collecting the ammonia separated by the gas-liquid separator.

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