A separation method for a forefraction column in an rt pes production process

Abstract

This invention relates to the field of production technology of RT-based antioxidant intermediates for rubber, and specifically discloses a highly efficient separation method for the pre-distillation column during the RT-based antioxidant production process. This invention utilizes the unique physical property of phenazine, employing aniline, which is already present in the material system, as a carry-out solvent. By continuously introducing aniline into the heavy component system at the bottom of the pre-distillation column, it effectively carries out the phenazine doped in the RT-based antioxidant, achieving complete separation of RT-based antioxidants and phenazine at the bottom of the column. Furthermore, since RT-based antioxidants do not have sublimation properties, the removal of phenazine from the bottom material can effectively reduce the content of RT-based antioxidants at the top of the column, thereby increasing the yield of the final RT-based antioxidant product.

Description

Technical Field

[0001] This invention relates to the field of production technology of 4-aminodiphenylamine (RT-Plast), an intermediate in rubber antioxidants, and particularly to a separation method for the pre-distillation column in the production process of RT-Plast. Background Technology

[0002] 4-Aminodiphenylamine, commonly known as RT-pastosi, is a key intermediate in the synthesis of p-phenylenediamine-based rubber antioxidants. The nitrobenzene process is currently the main industrial production method for RT-pastosi. This method involves using aniline and nitrobenzene as raw materials, undergoing a condensation reaction in the presence of an alkaline catalyst to generate a condensation solution containing p-nitrodiphenylamine and p-nitrosodiphenylamine. This condensation solution is then subjected to catalytic hydrogenation to prepare a hydrogenated feed solution containing the product RT-pastosi. During the condensation reaction, aniline is added in excess, and a series of byproducts, including phenazine, azobenzene, and tar, are inevitably generated, with phenazine being the most abundant. Therefore, the feed solution after the hydrogenation reaction contains not only RT-pastosi but also excess aniline and byproducts such as phenazine, azobenzene, and tar. After separating and recovering the condensation catalyst, the feed solution needs to undergo a subsequent purification process to remove impurities and obtain a high-purity RT-pastosi product.

[0003] Distillation is the primary refining method in the industrial production of RT-Plast. Currently, a continuous distillation operation with two or three columns in series is commonly used. The raw RT-Plast feed liquid containing impurities such as aniline, phenazine, azobenzene, and tar first enters the first column, also known as the fore-fraction column, light component column, or phenazine column. After distillation separation in this column, aniline, azobenzene, and most of the phenazine are collected from the top, while the bottom of the column, containing RT-Plast, a small amount of phenazine, and heavy component impurities such as tar, enters the second column (also known as the product column) for further separation and refining. RT-Plast is collected from the top of the product column, while the bottom of the column is enriched with heavy components such as tar. Phenazine, as a major byproduct in the RT-Plast production process, is generated in large quantities, and its boiling point is close to that of RT-Plast, making separation difficult using conventional distillation methods. This results in the current technology often having a high concentration of RT-Plast in the top liquid of the fore-fraction column, and the bottom liquid also being contaminated with a significant amount of phenazine. This not only reduces the yield of RT-paste from the product column but also significantly increases the separation difficulty in the product column. This increases separation energy consumption and reduces the final product yield. Furthermore, phenazine introduced into the product column, due to its difficulty in separation, often mixes with the final RT-paste product, directly affecting the quality of downstream p-phenylenediamine rubber antioxidants. Therefore, developing a simple, efficient, and advanced pre-fractionation column separation technology to achieve efficient separation of RT-paste and phenazine is of great significance for the high-quality and efficient production of RT-paste. Summary of the Invention

[0004] To overcome the shortcomings of the prior art, this invention provides a highly efficient, convenient, and low-cost separation method for the pre-distillation column in the RT feed production process.

[0005] This invention is achieved through the following technical solution:

[0006] A separation method for a pre-distillation column in the production of RT-RT feedstock, taking the material entering the pre-distillation column as the processing object, specifically includes the following steps:

[0007] (1) The material is preheated and continuously fed into the column from the middle of the front fractionation column, and is separated by distillation under reduced pressure.

[0008] (2) A stream of preheated aniline material is continuously introduced from the reboiler of the front fractionation column or the bottom of the column to assist in the distillation and carry out the phenazine in the bottom of the column;

[0009] (3) Control the temperature of the top and bottom of the pre-distillation column and the reflux ratio to continuously separate the feed. Aniline, azobenzene, phenazine and other light components are collected from the top of the column and transported to the aniline column for aniline recovery. The bottom liquid is transported to the subsequent RT product column for further separation and purification.

[0010] Through long-term research on the RT-plast production process, the inventors discovered that phenazine, as a major byproduct in the RT-plast production process, is generated in large quantities. Furthermore, phenazine and RT-plast have similar boiling points, making complete separation through conventional distillation very difficult. However, their research on the physical properties of phenazine revealed that although it has a high boiling point, it is sublimable. Targeted verification studies confirmed that the sublimability of phenazine applies even in the presence of water vapor or organic solvent vapor, and that phenazine is carried away by the sublimation of water vapor or organic vapor.

[0011] By utilizing the unique physical property of phenazine, aniline, which is originally present in the material system, is used as a carry-out solvent. By continuously introducing it into the heavy component system at the bottom of the pre-fractionation column, the phenazine doped in RT-p ...

[0012] A more preferred technical solution of the present invention is as follows:

[0013] The mass ratio of each component in the material is as follows: aniline 10-30%, phenazine 0.5-2%, azobenzene 0.1-1%, tar 0.2-1%, and the remainder is RT-based esters.

[0014] In step (1), the pressure at the top of the tower is controlled at 2-15 kPa.

[0015] In step (2), the amount of aniline material introduced is 5-30% of the mass of the material feed in the pre-distillation column, and the aniline preheating temperature is 100-180℃; more preferably, the aniline is fresh aniline or aniline recovered by the aniline column.

[0016] In step (3), the top temperature of the fore-distillation column is controlled at 110-160℃, the bottom temperature is controlled at 270-295℃, and the reflux ratio is controlled at 1-15.

[0017] Further preferably, the mass fraction of RT-pes in the top product of the fore-distillation column is less than 0.2%, the mass ratio of phenazine in the bottom product is less than 0.1%, and the mass content of aniline is 0.1-0.2%.

[0018] After the bottom product liquid of the pre-distillation column enters the RT-paste product column, RT-paste and a small amount of aniline can be separated by either side-streaming RT-paste or by connecting a simple distillation column in series at the top of the product column, to obtain high-purity RT-paste product.

[0019] Compared with the prior art, the beneficial effects of this invention are mainly reflected in:

[0020] By cleverly utilizing the unique physical property of the main byproduct phenazine, which can be sublimated, and its property difference with RT peroxide, the two can be separated efficiently in the pre-distillation column in a simple and quick manner, reducing separation energy consumption while improving the final efficiency of RT peroxide products.

[0021] This invention improves the separation efficiency of the pre-distillation column in the RT feedstock production process efficiently, conveniently, and at low cost without adding additional separation equipment, thus significantly increasing the economic efficiency of the process. Detailed Implementation

[0022] To enable those skilled in the art to better understand the technical solutions of this invention, the technical solutions in the embodiments of this invention will be clearly and completely described below.

[0023] Example 1: A separation method for the pre-distillation column in the RT-Purpose production process.

[0024] The material entering the pre-fractionation column during RT feedstock production is used as the processing target. The content of each component in this material (by mass fraction) is as follows: aniline 15%, phenazine 1%, azobenzene 0.5%, tar 0.5%, and RT feedstock 83%. The specific steps include the following:

[0025] (1) The above materials are preheated at a flow rate of 100 kg / h and continuously fed into the column from the middle of the front fractionation column. The pressure at the top of the column is controlled at 8 kPa for distillation separation.

[0026] (2) Fresh aniline preheated to 150°C was continuously injected from the reboiler of the pre-distillation column at a flow rate of 10 kg / h using a centrifugal pump to assist in the distillation and removal of phenazine from the heavy components in the column bottom.

[0027] (3) The temperature at the top of the pre-distillation column is controlled at 140°C, the temperature at the bottom of the column is controlled at 275°C, and the reflux ratio is controlled at 5. The feed is continuously separated. Aniline, azobenzene, phenazine and other light components are collected from the top of the column and transported to the aniline column for aniline recovery. The bottom liquid is transported to the subsequent RT product column for further separation and purification.

[0028] Samples were taken from the top and bottom of the above-mentioned column and analyzed by gas chromatography-external standard method. The analytical results of the components in the top product were as follows: aniline 94.31%, azobenzene 1.86%, phenazine 3.75%, and RT-pestos 0.08%; the analytical results of the components in the bottom product were as follows: phenazine 0.062%, RT-pestos 98.9%, and aniline 0.13%.

[0029] The gas chromatography analysis method involved in the above embodiments is as follows:

[0030] Agilent 7820A gas chromatograph; FID detector; HP-5 column (30m × 0.32mm × 1.0μm); detector temperature: 300℃; vaporization chamber temperature: 280℃; combustion gas (hydrogen) flow rate: 35mL / min; combustion gas (air) flow rate: 350mL / min; split ratio: 30:1; injection volume: 10μL; sample preparation solvent: dichloromethane; temperature program: initial column temperature 90℃, ramp to 280℃ at a rate of 15℃ / min, hold for 18min.

[0031] Example 2: A separation method for the pre-distillation column in the RT-Purpose production process

[0032] The material entering the pre-distillation column during RT product production is the subject of treatment, and its material composition is the same as in Example 1.

[0033] The specific implementation steps are the same as in Example 1. The only difference compared to Example 1 is that the aniline introduced into the reboiler of the pre-distillation column is the aniline recovered from the aniline column.

[0034] The gas chromatography-external standard method, the same as in Example 1, was used to sample and analyze the above-mentioned top and bottom products. The analytical results for the components in the top product were as follows: aniline 94.29%, azobenzene 1.88%, phenazine 3.74%, and RT-pestos 0.086%; the analytical results for the components in the bottom product were as follows: phenazine 0.07%, RT-pestos 99.0%, and aniline 0.14%.

[0035] Example 3: A separation method for the pre-distillation column in the RT-Purpose production process

[0036] The material entering the pre-distillation column during RT product production is the subject of treatment, and its material composition is the same as in Example 1.

[0037] The specific implementation steps are the same as in Example 2. The difference from Example 2 is that the recovered aniline material is introduced from the lower part of the pre-distillation column near the first theoretical plate.

[0038] The gas chromatography-external standard method, the same as in Example 1, was used to sample and analyze the above-mentioned top and bottom products. The analytical results for the components in the top product were as follows: aniline 94.22%, azobenzene 1.85%, phenazine 3.82%, and RT-pestos 0.1%; the analytical results for the components in the bottom product were as follows: phenazine 0.073%, RT-pestos 98.8%, and aniline 0.13%.

[0039] Example 4: A separation method for the pre-distillation column in the RT-Plast production process

[0040] The material entering the pre-distillation column during RT product production is the subject of treatment, and its material composition is the same as in Example 1.

[0041] The specific implementation steps are the same as in Example 1. The only difference compared to Example 1 is that the fresh aniline continuously fed into the reboiler of the pre-distillation column is 20 kg / h.

[0042] The gas chromatography-external standard method, the same as in Example 1, was used to sample and analyze the above-mentioned top and bottom products. The analytical results for the components in the top product were as follows: aniline 95.86%, azobenzene 1.34%, phenazine 2.73%, and RT-pestos 0.07%; the analytical results for the components in the bottom product were as follows: phenazine 0.056%, RT-pestos 99.0%, and aniline 0.18%.

[0043] Example 5: A separation method for the pre-distillation column in the RT feedstock production process.

[0044] The material entering the pre-distillation column during RT product production is the subject of treatment, and its material composition is the same as in Example 1.

[0045] The specific implementation steps are the same as in Example 1. The only difference compared to Example 1 is that the reflux ratio of the fore-distillation column is controlled at 3.

[0046] The gas chromatography-external standard method, the same as in Example 1, was used to sample and analyze the above-mentioned top and bottom products. The analytical results for the components in the top product were as follows: aniline 94.30%, azobenzene 1.84%, phenazine 3.75%, and RT-pestos 0.11%; the analytical results for the components in the bottom product were as follows: phenazine 0.084%, RT-pestos 98.8%, and aniline 0.15%.

[0047] Example 6: A separation method for the pre-distillation column in the RT-Purpose production process

[0048] The material entering the pre-fractionation column during RT feedstock production is used as the processing target. The content of each component in this material (by mass fraction) is as follows: aniline 12%, phenazine 1.5%, azobenzene 0.8%, tar 0.7%, and RT feedstock 85%. The specific steps include the following:

[0049] (1) The above materials are preheated at a flow rate of 200 kg / h and continuously fed into the column from the middle of the front fractionation column. The pressure at the top of the column is controlled at 3 kPa for distillation separation.

[0050] (2) Fresh aniline preheated to 130°C was continuously injected from the reboiler of the pre-distillation column at a flow rate of 30 kg / h using a centrifugal pump to assist in the distillation and removal of phenazine from the heavy components in the column bottom.

[0051] (3) The temperature at the top of the pre-distillation column is controlled at 120°C, the temperature at the bottom of the column is controlled at 280°C, and the reflux ratio is 5. The feed is continuously separated. Aniline, azobenzene, phenazine and other light components are collected from the top of the column and transported to the aniline column for aniline recovery. The bottom liquid is transported to the subsequent RT product column for further separation and purification.

[0052] The gas chromatography-external standard method, the same as in Example 1, was used to sample and analyze the above-mentioned top and bottom products. The analytical results for the components in the top product were as follows: aniline 92.14%, azobenzene 2.7%, phenazine 5.08%, and RT-pestos 0.08%; the analytical results for the components in the bottom product were as follows: phenazine 0.065%, RT-pestos 98.7%, and aniline 0.18%.

[0053] Example 7: A separation method for the pre-distillation column in the RT-Plast production process

[0054] The material entering the pre-distillation column during RT product production is the subject of treatment, and its material composition is the same as in Example 6.

[0055] The specific implementation steps are basically the same as in Example 6. The only difference compared to Example 6 is that the reflux ratio of the fore-distillation column is controlled at 7.

[0056] The gas chromatography-external standard method, the same as in Example 1, was used to sample and analyze the above-mentioned top and bottom products. The analytical results for the components in the top product were as follows: aniline 92.12%, azobenzene 2.72%, phenazine 5.09%, RT-pes 0.07%; the analytical results for the components in the top product were as follows: phenazine 0.06%, RT-pes 98.8%, aniline 0.17%.

[0057] Example 8 (Comparative Example 1):

[0058] Similarly, the material entering the pre-distillation column in the RT feed production is used as the processing object, and the same feed composition as in Example 1 is adopted.

[0059] In the specific implementation steps, the temperature, pressure, and reflux ratio in the pre-distillation column are controlled in the same manner as in Example 1. The difference from Example 1 is that no aniline material is introduced into the bottom of the column during the operation.

[0060] The gas chromatography-external standard method, the same as in Example 1, was used to sample and analyze the above-mentioned top and bottom products. The analytical results for the components in the top product were as follows: aniline 93.28%, azobenzene 1.48%, phenazine 3.32%, and RT-pestos 1.89%; the analytical results for the components in the bottom product were as follows: phenazine 0.48%, and RT-pestos 98.2%.

[0061] Example 9 (Comparative Example 2):

[0062] Similarly, the material entering the pre-distillation column in the RT feed production is used as the processing object, and the same feed composition as in Example 1 is adopted.

[0063] The specific implementation steps are basically the same as those in Example 8. The difference is that the reflux ratio is adjusted to 10 during the operation.

[0064] The gas chromatography-external standard method, the same as in Example 1, was used to sample and analyze the above-mentioned top and bottom products. The analytical results for the components in the top product were as follows: aniline 93.57%, azobenzene 1.58%, phenazine 3.43%, and RT-pestos 1.41%; the analytical results for the components in the bottom product were as follows: phenazine 0.42%, and RT-pestos 98.1%.

[0065] Example 10 (Comparative Example 3):

[0066] The material entering the pre-distillation column during RT product production was used as the processing object, and the same feed composition as in Example 6 was adopted.

[0067] In the specific implementation steps, the temperature, pressure, and reflux ratio in the pre-distillation column are controlled in the same manner as in Example 6. The difference from Example 6 is that no aniline material is introduced into the bottom of the column during the operation.

[0068] The gas chromatography-external standard method, the same as in Example 1, was used to sample and analyze the above-mentioned top and bottom products. The analytical results for the components in the top product were as follows: aniline 91.03%, azobenzene 2.25%, phenazine 4.67%, and RT-pestos 2.04%; the analytical results for the components in the bottom product were as follows: phenazine 0.52%, and RT-pestos 98.0%.

[0069] Obviously, the embodiments described above are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort should fall within the scope of protection of the present invention.

Claims

1. A separation method for a pre-distillation column in the production of RT-RT feedstock, wherein the material entering the pre-distillation column in the production of RT-RT feedstock is the processing object, characterized in that, Specifically, the steps include the following: (1) After being preheated, the material is continuously fed into the column from the middle of the pre-distillation column and is separated by distillation under reduced pressure. The mass ratio of each component in the material is: aniline 10-30%, phenazine 0.5-2%, azobenzene 0.1-1%, tar 0.2-1%, and the remainder is RT-based product. (2) A stream of preheated aniline material is continuously introduced from the reboiler of the front distillation column or the bottom of the column to assist in the distillation and carry out the phenazine in the bottom of the column. The amount of aniline material introduced is 5-30% of the mass of the material in the front distillation column, and the aniline preheating temperature is 100-180℃. (3) Control the temperature of the top and bottom of the fore-distillation column and the reflux ratio to continuously separate the feed. Aniline, azobenzene and phenazine are collected from the top of the column as light components and sent to the aniline column for aniline recovery. The bottom liquid is sent to the subsequent RT-peptide product column for further separation and purification. The temperature of the top of the fore-distillation column is controlled at 110-160℃, the temperature of the bottom of the column is controlled at 270-295℃, and the reflux ratio is controlled at 1-15. The mass fraction of RT-peptide in the top liquid of the fore-distillation column is less than 0.2%, the mass ratio of phenazine in the bottom liquid is less than 0.1%, and the mass content of aniline is 0.1-0.2%.

2. The separation method of the pre-distillation column in the RT feedstock production process as described in claim 1, characterized in that: In step (1), the pressure at the top of the tower is controlled at 2-15 kPa.

3. The separation method of the pre-distillation column in the RT feed production process as described in claim 1, characterized in that: The aniline is fresh aniline or aniline recovered by an aniline tower.

4. The separation method of the pre-distillation column in the RT feed production process as described in claim 1, characterized in that: After the bottom product liquid of the pre-distillation column enters the RT-plast product column, RT-plast and aniline are separated by either side-streaming RT-plast or by connecting a simple distillation column in series at the top of the product column, to obtain high-purity RT-plast product.