A method for improving the selectivity of synthesizing diphenylamine from aniline

Abstract

The present invention discloses a method for synthesizing diphenylamine from aniline. The method of the present invention comprises the following contents: (1) providing a reactor, wherein the reactor comprises at least one catalyst bed; (2) introducing aniline into the reactor, passing through the catalyst bed under reaction conditions, and subjecting the reaction effluent to gas-liquid separation and fractionation to obtain a diphenylamine product; wherein, during the reaction, an amine-soluble stabilizer is introduced into the reactor; the amine-soluble stabilizer has a boiling point higher than that of aniline and is stable at high temperatures. By adding the amine-soluble stabilizer, the present invention allows the reaction to be carried out at high temperatures, reduces the large amount of by-products produced and the rapid deactivation of the catalyst, and not only improves the selectivity of diphenylamine, but also prolongs the life of the catalyst.

Description

Technical Field

[0001] The invention belongs to the field of chemical synthesis technology, and specifically relates to a method for synthesizing diphenylamine from aniline. Background Art

[0002] Diphenylamine (N-phenylaniline; DPA for short) is an important organic chemical raw material with a wide range of uses. In industry, it is mainly used for synthetic rubber antioxidants or raw materials for rubber antioxidants, explosive stabilizers, fuels and pharmaceutical intermediates, azo dyes, fruit preservatives, etc. As a raw material for various chemical products, diphenylamine has a good market application prospect.

[0003] There are many methods for synthesizing diphenylamine, and the most valuable method for market application is the continuous synthesis of diphenylamine from aniline. The specific synthesis process is: aniline undergoes condensation and deamination reaction through a catalyst, and some side reactions will occur during this process. The main by-products are: dimethylpyridine, 2-ethylaniline, quinoline, indole, acridine, etc.

[0004] Patent CN1144796A discloses a method for synthesizing diphenylamine from aniline in a continuous process under hydrogen environment. The introduced hydrogen makes the safety of the device worse, and the use of a hydrogen compressor significantly increases the equipment investment.

[0005] Patent CN1363550A converts the introduced hydrogen into nitrogen. Although this reduces the safety risk of the device, the equipment investment is high, the by-product content increases significantly during the high-temperature reaction, and the product selectivity is not ideal.

[0006] Patent CN103044270A is to dissolve hydrogen in the aniline raw material before reacting. Although this method reduces equipment investment, the yield of the product is still not high.

[0007] The synthesis of diphenylamine from aniline can be a gas phase reaction or a liquid phase reaction. Although the gas phase reaction has a higher conversion rate of aniline, it produces more by-products and easily deactivates the catalyst, so the liquid phase reaction is more suitable for industrial production. The suitable conditions for the liquid phase reaction are: the reaction pressure is 1.5~4.0 MPa, the reaction temperature is 250~370℃, and the catalyst used is mostly a solid acid catalyst. Summary of the invention

[0008] In order to solve the problem in the prior art that in the middle and late stages of the reaction of aniline and at a higher reaction temperature (340-370°C), the by-products increase and the selectivity of diphenylamine decreases rapidly, the present invention provides a method for improving the selectivity of synthesizing diphenylamine from aniline.

[0009] The technical purpose of the present invention is achieved through the following technical solutions:

[0010] A method for synthesizing diphenylamine from aniline comprises the following contents:

[0011] (1) providing a reactor, wherein the reactor comprises at least one catalyst bed;

[0012] (2) Aniline is introduced into a reactor and passed through a catalyst bed under reaction conditions. The reaction effluent is subjected to gas-liquid separation and fractionation to obtain a diphenylamine product;

[0013] In the reaction process, an amine-soluble stabilizer is introduced into the reactor; the amine-soluble stabilizer has a boiling point higher than that of aniline, is stable at high temperatures, does not decompose itself at 400°C, and does not react with aniline and the reaction liquid product.

[0014] Further, the amine-soluble stabilizer can be selected from biphenyl, terphenyl, quinoline, acridine, anilino acridine, etc., preferably terphenyl and / or acridine. The amount of the amine-soluble stabilizer added can be 0.2 to 5.0 times the volume of aniline, preferably 0.5 to 2.0 times.

[0015] Further, the soluble amine stabilizer can be added throughout the reaction process, or at any time point throughout the process, preferably in the middle and late stages of the operation cycle. In the present invention, the middle and late stages of the operation cycle refer to: as the operation time increases, the catalyst performance gradually decreases, so the reaction temperature is continuously increased to meet the diphenylamine single-pass molar yield ≮19.0%. The middle and late stages of operation refer to the device operation time reaching more than 40% of the total operation time, and the late stages of operation refer to the device operation time reaching more than 70% of the total operation time.

[0016] Furthermore, the catalyst is a β zeolite catalyst. Furthermore, the β zeolite catalyst comprises the following components by mass fraction: 45-90% Hβ zeolite, preferably 60-70%, 0-5.0% alkali metal, preferably 0.2-4.5%, and 5-50% γ-Al2O3. Silicon in the Hβ zeolite is calculated as SiO2, aluminum is calculated as Al2O3, and the molar ratio of SiO2 / Al2O3 is 20-100, preferably 28-68.

[0017] The preparation method of the β zeolite catalyst is well known to those skilled in the art. For example, the β zeolite catalyst can be prepared by the following method: mixing the β zeolite with a soluble salt solution containing an alkali metal (the alkali metal may be potassium, calcium, magnesium, etc.), performing ion exchange, and then filtering, washing, and drying; then mixing the ion-exchanged β zeolite with aluminum hydroxide powder, adding nitric acid and deionized water, extruding into strips, drying, and calcining to obtain the β zeolite catalyst.

[0018] Further, the reaction conditions are: reaction pressure of 1.5-8.0 MPa, preferably 2.0-6.0 MPa, reaction temperature of 250-370°C, preferably 280-360°C, aniline volume space velocity of 0.1 h -1 ~0.5h -1 , preferably 0.1 h -1 ~0.3h -1 .

[0019] Furthermore, the reactor comprises two beds, and the catalyst loading volume ratio of the two beds is generally 1:0.5 to 1:2, preferably 1:0.8 to 1:1.5.

[0020] Furthermore, the amine-soluble stabilizer is introduced only into the second catalyst bed but not into the first catalyst bed.

[0021] The inventor of the present application unexpectedly discovered through a large number of experiments that in the reaction process of synthesizing diphenylamine from aniline, adding a soluble amine stabilizer to the second bed layer can improve the selectivity of the main reaction. It is speculated that the reasons may include two aspects. First, from a thermodynamic point of view, it is found that in the reaction of synthesizing diphenylamine from aniline, when the reaction temperature is 250~370℃, the equilibrium constant of the liquid phase reaction is much larger than the equilibrium constant of the gas phase reaction. At the same time, the side reaction of generating 2-methylpyridine and acridine is that the equilibrium constant of the gas phase reaction is much larger than the equilibrium constant of the liquid phase reaction, and the equilibrium constant of 2-methylpyridine decreases slowly with the increase of temperature under liquid phase conditions. Therefore, it is necessary to ensure that the reaction is carried out under liquid phase conditions as much as possible, which can reduce the generation of by-products. However, under a certain pressure, especially in the middle and rear sections of the reactor, as the reaction temperature increases, the vaporization rate of the reaction raw materials and products increases, and the by-products increase. Based on the above findings, in the present invention, an amine-soluble stabilizer that can dissolve the raw materials and products is introduced into the reactor (preferably in the rear section of the reactor). At the same time, due to the high boiling point of the amine-soluble stabilizer, it can form an azeotropic effect with some by-products to a certain extent, thereby increasing the boiling point of the azeotrope and relatively reducing the vaporization rate of the reaction system, so that the reaction in the entire reactor is as liquid phase as possible.

[0022] Second, from a kinetic perspective, the study found that most of the main reaction occurred in the front half of the reaction bed, and the main by-products such as lutidine and acridine had a longer reaction process and were mainly produced in the back half of the bed. As the temperature in the back half of the bed increases, the generated ammonia and by-products with lower molecular weight are easily used as raw materials to promote the generation of by-products with larger molecular weight, and are not easy to fall off from the catalyst, resulting in accelerated catalyst deactivation. After adding amine stabilizers that can dissolve raw materials and products, it can not only reduce vaporization, but also remove by-products with lower molecular weight from the back half of the bed in time, reducing the generation of by-products with larger molecular weight. More importantly, the deactivation of the catalyst in the synthesis of diphenylamine from aniline is mainly caused by carbon deposition. Adding a high-boiling point solvent with strong solubility can dissolve carbon deposition, slow down the deactivation rate of the catalyst, and extend the life of the catalyst.

[0023] Compared with the prior art, the method of the present invention has the following beneficial effects:

[0024] 1. The present invention introduces an amine-dissolving stabilizer into the reactor (especially the second bed layer), thereby changing the reaction atmosphere in the rear section of the reactor for continuous synthesis of diphenylamine from aniline, increasing the liquid phase content of the reaction system, and maintaining the liquid phase system required for the main reaction of synthesizing diphenylamine from aniline as much as possible. The maintenance of the liquid phase system can maintain a high equilibrium constant for the main reaction of aniline to generate diphenylamine, while reducing the equilibrium constants of 2-methylpyridine and acridine, thereby making the reaction proceed more in the direction of the main reaction.

[0025] 2. The study found that the side reactions such as the formation of 2-methylpyridine and acridine mainly occurred in the second half of the reaction. The amine stabilizer introduced at this time can effectively dissolve the small molecular by-products generated during the reaction due to its good solubility, avoiding their attachment to the catalyst and further aggregation and coking, that is, reducing the generation of larger molecular weight by-products; moreover, the solvent also has a good dissolving effect on carbon deposits in the reaction system, which can effectively strip carbon deposits from the catalyst, thereby slowing down the deactivation rate of the catalyst, maintaining the activity and selectivity of the reaction, and extending the life of the catalyst.

[0026] 3. The amine-soluble stabilizer introduced into the reactor of the present invention reduces the amount of by-products generated at a higher reaction temperature at the end of the operation cycle and improves the selectivity of diphenylamine. At the same time, the improvement of diphenylamine selectivity also helps to reduce the difficulty of subsequent separation of the by-product part. DETAILED DESCRIPTION

[0027] The following non-limiting embodiments may enable a person skilled in the art to more fully understand the present invention, but are not intended to limit the present invention in any way.

[0028] Preparation of catalyst: The catalyst used in the experiment is a catalyst composed of β zeolite, activated alumina and alkali metal. The specific preparation method is as follows:

[0029] (1) Take 200g Hβ zeolite (SiO2 / Al2O3 molecular ratio is 28) and 1500mL (0.1mol / L) potassium chloride aqueous solution, place them in a 2000mL four-necked flask with a stirrer, and perform ion exchange. The exchange reaction temperature is 75℃, the stirring speed is 200n / min, and the time is 5.0h. Afterwards, the zeolite and potassium aqueous solution after the exchange are filtered, washed, and dried; the washing process is: washing until there is no chlorine. The drying process is: drying at 60℃ for 4.0h and drying at 110℃ for 4.0h.

[0030] (2) 70 g of the above-exchanged zeolite was mixed with 10 g of aluminum hydroxide powder, and nitric acid and an appropriate amount of deionized water were added, wherein the amount of nitric acid added was 0.5 wt% of the dry material, and after kneading on an extruder, extrusion and molding were performed to obtain catalyst strips with a diameter of 1.5 mm, and then dried at 60°C for 4.0 h and at 110°C for 4.0 h. Then, the catalyst was calcined in a muffle furnace at 520°C for 8.0 h to obtain the catalyst used, which contained 1.1 wt% potassium, 80 wt% Hβ zeolite, and the rest was γ-Al2O3.

[0031] In the embodiment, the calculation method of aniline conversion and diphenylamine selectivity is:

[0032] Aniline molar conversion rate = (the number of moles of aniline in the raw material - the number of moles of aniline in the product) / the number of moles of aniline in the raw material;

[0033] Diphenylamine molar selectivity = (the number of moles of diphenylamine in the product × 2) / (the number of moles of aniline in the raw material - the number of moles of aniline in the product).

[0034] Examples 1-3

[0035] The reactor is a catalyst bed, and the amine-soluble stabilizer terphenyl and aniline enter the reactor from the reactor inlet to react. The reaction conditions and test results are shown in Table 1.

[0036] Comparative Example 1

[0037] The existing process was adopted, the reactor included a catalyst bed, the process conditions were the same as in Example 1, and no soluble amine stabilizer was introduced during the reaction. The reaction conditions and results are shown in Table 1.

[0038] Table 1 Process conditions and test results

[0039]

[0040] Embodiment 4-6

[0041] The reactor includes two catalyst beds, and the high boiling point solvent biphenyl and aniline enter the reactor from the inlet of the second bed of the reactor to react. The reaction conditions and results are shown in Table 2.

[0042] Comparative Example 2

[0043] The reactor includes two catalyst beds, and the process conditions are the same as those in Example 5, except that no soluble amine stabilizer is introduced during the reaction. The reaction conditions and results are shown in Table 2.

[0044] Table 2 Process conditions and test results

[0045]

[0046] Example 7

[0047] The catalyst used was conventional commercially available Hβ molecular sieve: the Hβ molecular sieve content was 75.0% and the alumina content was 25.0%.

[0048] The reactor is a catalyst bed, and the amine-soluble stabilizer biphenyl and aniline enter the reactor from the reactor inlet to react. The reaction conditions and results are shown in Table 3.

[0049] Comparative Example 3

[0050] The catalyst used was conventional commercially available Hβ molecular sieve: the Hβ molecular sieve content was 75.0% and the alumina content was 25.0%.

[0051] The reactor includes a catalyst bed, and no soluble amine stabilizer is introduced during the reaction. The reaction conditions and results are shown in Table 3.

[0052] Table 3 Process conditions and test results

[0053]

[0054] Example 8

[0055] The reactor is a catalyst bed, the catalyst and process conditions are the same as in Example 3, and the amine-soluble stabilizer biphenyl enters the reactor from the reactor inlet together with aniline to react. The reaction conditions and results are shown in Table 4.

[0056] Comparative Example 4

[0057] The reactor is a catalyst bed, and the catalyst and process conditions are the same as those in Example 7, except that no soluble amine stabilizer is introduced during the reaction. The reaction conditions and results are shown in Table 4.

[0058] Table 4 Process conditions and test results

[0059]

[0060] It can be seen from the results of the embodiments and comparative examples that the method of the present invention can reduce the large amount of by-products produced in the middle and late stages of operation when synthesizing diphenylamine, effectively slowing down the reduction in diphenylamine selectivity, thereby reducing the catalyst deactivation rate and extending the catalyst's one-way life.

Claims

1. A method for synthesizing diphenylamine from aniline, comprising the following contents: (1) providing a reactor, wherein the reactor comprises at least one catalyst bed; (2) Aniline is introduced into a reactor and passed through a catalyst bed under reaction conditions. The reaction effluent is subjected to gas-liquid separation and fractionation to obtain a diphenylamine product; in, During the reaction, an amine-soluble stabilizer is introduced into the reactor; the amine-soluble stabilizer has a boiling point higher than that of aniline, does not decompose itself at 400° C., and does not react with aniline and the reaction liquid product; The amine-soluble stabilizer is selected from at least one of biphenyl and terphenyl.

2. The method according to claim 1, characterized in that The amount of the amine-soluble stabilizer added is 0.2 to 5.0 times the volume of aniline.

3. The method according to claim 2, characterized in that The amount of the amine-soluble stabilizer added is 0.5 to 2.0 times the volume of aniline.

4. The method according to claim 1, characterized in that The amine-soluble stabilizer is selected from terphenyl.

5. The method according to claim 1, characterized in that The amine-soluble stabilizer is added throughout the reaction process.

6. The method according to claim 1, characterized in that The amine-soluble stabilizer is added in the middle and late stages of the operation cycle, and the middle and late stages of the operation cycle refer to the time when the device operation time reaches more than 40% of the total operation time.

7. The method according to claim 1, characterized in that The catalyst is a beta zeolite catalyst.

8. The method according to claim 7, characterized in that The beta zeolite catalyst comprises the following components by mass fraction: 45-90% H beta zeolite, 0.1-5.0% alkali metal and 5-50% gamma-Al2O3; wherein the SiO2 / Al2O3 molar ratio of the H beta zeolite is 20-100.

9. The method according to claim 1, characterized in that: The reaction conditions are: reaction pressure of 1.5-8.0 MPa, reaction temperature of 250-370°C, aniline volume space velocity of 0.1 h -1 ~0.5h -1 .

10. The method according to claim 9, characterized in that The reaction conditions are: reaction pressure of 2.0-6.0 MPa, reaction temperature of 280°C-360°C, aniline volume space velocity of 0.1 h -1 ~0.3h -1 .

11. The method according to claim 1, characterized in that: The reactor comprises two catalyst beds, and the filling volume ratio of the two catalyst beds is 1:0.5-1:

2.

12. The method according to claim 11, characterized in that The filling volume ratio of the two catalyst beds is 1:0.8~1:1.

5.

13. The method according to claim 11 or 12, characterized in that: The amine stabilizer is introduced only into the second catalyst bed but not into the first catalyst bed.

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