Method for the separation and purification of carbazole and apparatus for the method

Abstract

This invention relates to the field of carbazole purification, and discloses a method for separating and purifying carbazole, as well as an apparatus for using this method. The method includes: performing a first distillation separation on the dehydrogenation product of diphenylamine to obtain an aniline-rich overhead stream and a carbazole-containing bottom stream; performing a second distillation separation on the carbazole-containing bottom stream to obtain a diphenylamine-rich overhead stream and a carbazole-rich bottom stream; performing solution crystallization on the carbazole-rich bottom stream in the presence of a crystallization solvent to obtain crude carbazole; and performing melt crystallization on the crude carbazole under a protective atmosphere. The melt crystallization includes a heating stage, a cooling stage, and a sweating stage. The cooling stage has at least two phases, each with a cooling rate of 0.5-5°C / h, with the cooling rate of the earlier phase greater than that of the later phase along the direction of temperature decrease, and the final temperature of the cooling stage is 210-220°C. This method can separate and purify carbazole to electronic grade.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of carbazole purification, in particular to a method for separating and purifying carbazole and a device used in the method. BACKGROUND

[0002] Carbazole, chemical formula C 12 H9N, is a nitrogen-containing polycyclic aromatic organic compound, which has a structure similar to fluorene. Carbazole has wide application value in industry. It is a key raw material for manufacturing various important dyes, and its derivative, permanent purple RL, is widely used for coloring automobile topcoats and high-temperature-resistant plastics, and has excellent high-temperature resistance and ultraviolet light resistance. In the medical field, carbazole derivatives exhibit biological activities such as antibacterial, antitumor, and anti-dementia, and have become an important direction for medical research and development. In addition, carbazole can also be used to manufacture explosives, pesticides, lubricants, rubber antioxidants, etc., and as a raw material for optoelectronic materials and conductive polymer materials.

[0003] Currently, the production of carbazole mainly relies on the traditional process of extracting from coal tar. However, this process has significant defects. The composition of coal tar is complex, and during the extraction of carbazole, it needs to go through multiple complex processes such as distillation, extraction, and crystallization. Not only is the operation difficult, but it is also very difficult to accurately separate high-purity carbazole, resulting in limited product purity and difficulty in meeting the needs of high-end chemical industries for high-purity carbazole. At the same time, the entire extraction process has high energy consumption and requires the use of multiple chemical reagents, further increasing production costs, making carbazole's competitiveness in the market greatly discounted. It is worth noting that patent CN 116803498B proposes a highly innovative and efficient catalytic synthesis method for carbazole. This method uses diphenylamine as a raw material and, under the action of a specific catalyst, promotes intramolecular dehydrogenation and ring closure of diphenylamine to directly produce carbazole.

[0004] In the process of synthesizing carbazole by dehydrogenation of diphenylamine, the purification of carbazole is a crucial link. However, due to the presence of unreacted diphenylamine, catalyst residues, byproducts, and other impurities in the reaction system, the purification of carbazole becomes extremely difficult. Moreover, carbazole is a white crystalline powder with a melting point of 244.8℃ and a boiling point of 355℃, and is relatively stable, slightly soluble in water, and insoluble in most conventional organic solvents. The above characteristics increase the difficulty of its separation and purification process.

[0005] As a key chemical raw material, the separation and purification of carbazole is of great significance in the production process. Currently, solvent crystallization, rectification purification, and melt crystallization are three commonly used purification methods.

[0006] Solvent crystallization is based on the difference in solubility of carbazole and impurities in the solvent. The carbazole-containing mixture is dissolved in a suitable solvent, the solution is cooled to supersaturation, carbazole is crystallized, and impurities remain in the solution, thereby achieving purification. However, this method requires a large amount of solvent, resulting in waste of resources, and most organic solvents are volatile and toxic. For example, the patent CN 103880732B uses solvent crystallization for purification, and the obtained carbazole purity is only 96%.

[0007] Rectification purification utilizes the different boiling points of carbazole and impurities, through heating vaporization, multiple partial vaporization and condensation in a rectification column. However, rectification has high energy consumption, and may reduce the yield of carbazole due to side reactions or thermal decomposition. For example, in the patent CN 213407767U, the temperature of the column body is above 500℃, and the temperature of the reboiler is as high as 1000℃ or above.

[0008] Melt crystallization is based on the difference in freezing point for purification, but the crystallization is slow and the efficiency is low, such as the patent CN 210340731U purifies carbazole with a purity of only 98%, and the equipment is complex.

[0009] Therefore, it is urgent to develop an efficient and green method for separating and purifying carbazole. SUMMARY

[0010] The purpose of the present application is to overcome the low purity of carbazole in the prior art, and to provide a method for separating and purifying carbazole and a device for the method, which can separate and purify carbazole to an electronic grade.

[0011] In order to achieve the above-mentioned purpose, the present application provides a method for separating and purifying carbazole from diphenylamine dehydrogenation products, which comprises:

[0012] (1) The diphenylamine dehydrogenation products are subjected to first rectification separation to obtain aniline-rich overhead stream and carbazole-containing column bottom stream;

[0013] (2) The carbazole-containing column bottom stream is subjected to second rectification separation to obtain diphenylamine-rich overhead stream and carbazole-rich column bottom stream;

[0014] (3) The carbazole-rich column bottom stream is subjected to solution crystallization in the presence of a crystallization solvent to obtain crude carbazole;

[0015] (4) The crude carbazole is subjected to melt crystallization under a protective atmosphere;

[0016] The melt crystallization comprises a warming stage, a cooling stage and a sweating stage;

[0017] The cooling stage is at least 2 stages, each stage has a cooling rate of 0.5-5℃ / h, the cooling rate of the former stage is greater than that of the latter stage along the temperature decreasing direction, and the terminal temperature of the cooling stage is 210-220℃.

[0018] Preferably, the cooling stage comprises:

[0019] (S1) performing first-stage cooling at a cooling rate of 2-5℃ / h, a cooling endpoint of 230-235℃, and a stirring rate of 50-200rpm;

[0020] (S2) performing second-stage cooling at a cooling rate of 1-5℃ / h, a cooling endpoint of 220-225℃, and discharging the mother liquor;

[0021] (S3) performing third-stage cooling at a cooling rate of 0.5-1℃ / h, a cooling endpoint of 210-215℃, and maintaining the temperature for 1-5h.

[0022] The second aspect of the present application provides a device for the method of the first aspect, the device comprising a rectification separation unit, a crystallization separation unit, and a melt crystallization unit connected in sequence;

[0023] The rectification separation unit comprises a first rectification column 1, a first delivery pump 3, a second rectification column 6, and a second delivery pump 8 connected in sequence;

[0024] The overhead outlet of the first rectification column 1 is connected to a first condenser 5 and a first reflux tank 4 in sequence, and the reflux outlet of the first reflux tank 4 is connected to the overhead reflux inlet of the first rectification column 1;

[0025] The feed inlet of the first delivery pump 3 is in communication with the column outlet of the first rectification column 1, and the outlet of the first delivery pump 3 is connected to the feed inlet of the second rectification column 6, for feeding the column stream containing carbazole into the second rectification column 6;

[0026] The overhead outlet of the second rectification column 6 is connected to a second condenser 10 and a second reflux tank 9 in sequence, and the reflux outlet of the second reflux tank 9 is connected to the overhead reflux inlet of the second rectification column 6;

[0027] The feed inlet of the second delivery pump 8 is in communication with the column outlet of the second rectification column 6, and the outlet of the second delivery pump 8 is in communication with the crystallization separation unit, for feeding the column stream rich in carbazole into the crystallization separation unit;

[0028] The crystallization separation unit comprises a solution crystallization kettle 11, and the outlet of the solution crystallization kettle 11 is in communication with the melt crystallization unit, for feeding the crude carbazole stream into the melt crystallization unit;

[0029] The melt crystallization unit comprises a melt crystallizer 12, for purifying the crude carbazole stream.

[0030] Compared with the prior art, the above technical solution has the following beneficial effects:

[0031] (1) The separation and purification method provided by the present application can gradually and accurately separate aniline, diphenylamine and carbazole. Diphenylamine can be reused as raw material by being put into the reaction again, thereby effectively reducing the production cost.

[0032] (2) The separation and purification method provided by the present application is simple and easy to operate, easy to realize industrial large-scale production, low in equipment cost and raw material price, and small in environmental pollution in the whole production process, and the purity of the obtained carbazole meets the requirements of electronic grade. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 is a process schematic diagram of the device for the separation and purification method of carbazole in the present application.

[0034] REFERENCE SIGNS

[0035] 1 first rectifying column; 2 first reboiler; 3 first delivery pump;

[0036] 4 first reflux tank; 5 first condenser; 6 second rectifying column;

[0037] 7 second reboiler; 8 second delivery pump; 9 second reflux tank;

[0038] 10 second condenser; 11 solution crystallization kettle; 12 melt crystallizer. DETAILED DESCRIPTION

[0039] The endpoints of the ranges and any values disclosed herein are not limited to the precise values stated. The endpoints of the ranges and the values are approximate values and should be understood as including values approximately near to the stated values. For ranges of values, the endpoints of the ranges are included in the ranges, and the endpoints of the ranges and the individual points included in the ranges can be combined with one another to form one or more new ranges of values, which are to be understood as being specifically disclosed herein.

[0040] In the present application, the pressure is absolute pressure unless otherwise stated.

[0041] The first aspect of the present application provides a method for separating and purifying carbazole from diphenylamine dehydrogenation product, which comprises:

[0042] (1) The diphenylamine dehydrogenation product is subjected to first rectification separation to obtain aniline-rich overhead stream and carbazole-containing column bottom stream;

[0043] (2) The carbazole-containing column bottom stream is subjected to second rectification separation to obtain diphenylamine-rich overhead stream and carbazole-rich column bottom stream;

[0044] (3) The carbazole-rich column bottom stream is subjected to solution crystallization in the presence of a crystallization solvent to obtain crude carbazole;

[0045] (4) under a protective atmosphere, subjecting the crude carbazole to melt crystallization;

[0046] The melt crystallization comprises a temperature rising stage, a temperature dropping stage and a sweating stage;

[0047] The temperature dropping stage is at least two stages, each stage has a dropping rate of 0.5-5 ℃ / h, the dropping rate of the former stage is greater than that of the latter stage along the temperature dropping direction, and the terminal temperature of the temperature dropping stage is 210-220 ℃.

[0048] The method adopts a combined process of "double rectification pre-separation + solution crystallization preliminary purification + multi-stage melt crystallization deep purification", and the combined process can gradually and accurately separate aniline, diphenylamine and carbazole, further, a multi-stage temperature dropping melt crystallization process is innovatively invented, and through the strategy of fast temperature dropping at first and slow temperature dropping later, electronic-grade carbazole is obtained.

[0049] According to the present application, preferably, the diphenylamine dehydrogenation product comprises carbazole, diphenylamine, aniline, benzene and other components.

[0050] According to the present application, preferably, the content of the carbazole is 40-80 wt% based on the total mass of the diphenylamine dehydrogenation product; the content of the diphenylamine is 5-25 wt%; the content of the aniline is 2-20 wt%; the content of the benzene is 3-10 wt%; and the content of the other components is 0.01-5 wt%.

[0051] According to a preferred embodiment of the present application, the content of the carbazole is 55-80 wt% based on the total mass of the diphenylamine dehydrogenation product; the content of the diphenylamine is 15-25 wt%; the content of the aniline is 10-20 wt%; the content of the benzene is 3-8 wt%; and the content of the other components is 0.01-2 wt%.

[0052] The step (1) of the present application further comprises subjecting the aniline-rich overhead stream to first cooling.

[0053] According to the present application, preferably, the temperature of the first cooling is 0-30 ℃.

[0054] According to the present application, preferably, the content of the carbazole in the carbazole-containing bottom stream is 60-80 wt%.

[0055] According to the present application, preferably, when the mass content of the aniline in the carbazole-containing bottom stream is >20%, the carbazole-containing bottom stream is subjected to first heating, and then is subjected to first rectification separation until the content of the carbazole in the carbazole-containing bottom stream is 60-80 wt%.

[0056] According to the present application, preferably, the temperature of the first heating is 60-150℃, preferably 60-120℃.

[0057] The step (2) of the present application further comprises second cooling the overhead stream rich in diphenylamine.

[0058] According to the present application, preferably, the temperature of the second cooling is 40-120℃.

[0059] According to the present application, preferably, the content of carbazole in the carbazole-rich bottom stream is 80-95wt%.

[0060] According to the present application, preferably, when the mass content of diphenylamine in the carbazole-rich bottom stream is >20%, the carbazole-rich bottom stream is further subjected to second heating and then second rectification separation until the content of carbazole in the carbazole-rich bottom stream is 80-95wt%.

[0061] According to the present application, preferably, the temperature of the second heating is 150-250℃, preferably 180-220℃.

[0062] According to the present application, preferably, the content of carbazole in the crude carbazole is 95-99wt%.

[0063] In the present application, the content of carbazole is determined by a gas chromatograph.

[0064] According to the present application, preferably, the conditions of the first rectification separation comprise: the overhead pressure is 0.01-0.1MPa; the overhead temperature is 60-80℃; and the reflux ratio is 1-10:1.

[0065] According to the present application, preferably, the conditions of the first rectification separation comprise: the overhead pressure is 0.01-0.05MPa; the overhead temperature is 65-75℃; and the reflux ratio is 1-5:1.

[0066] In the present application, the conditions of the first rectification separation adopt the above-mentioned preferred ranges, which are more conducive to the effective separation of aniline, carbazole and diphenylamine, and the high-efficiency separation can be realized by using the difference in boiling points. Aniline, as a light component, is preferentially vaporized, and carbazole and diphenylamine are effectively enriched in the bottom of the column due to their high boiling points.

[0067] According to the present application, preferably, the number of trays of the rectification column for the first rectification separation is 10-30, more preferably 15-20, which is more conducive to the separation of aniline.

[0068] According to the present application, preferably, the conditions of the second rectification separation comprise: the overhead pressure is 0.001-0.1MPa; the overhead temperature is 80-180℃; and the reflux ratio is 1-30:1.

[0069] According to a preferred embodiment of the present application, the conditions of the second rectification separation include: a tower top pressure of 0.001-0.02 MPa, a tower top temperature of 80-120℃, and a reflux ratio of 2-30:1.

[0070] In the present application, the conditions of the second rectification separation adopt the above-mentioned preferred ranges, which are more beneficial to the separation of diphenylamine and the preliminary enrichment of carbazole.

[0071] According to the present application, preferably, the number of plates of the rectification tower of the second rectification separation is 10-50, more preferably 20-40, which is more beneficial to the separation of diphenylamine.

[0072] The present application does not particularly limit the type of the crystallization solvent of the solution crystallization, and the crystallization solvent of the solution crystallization is selected from at least one organic solvent system in alcohol, benzene, ether and alkane, preferably the crystallization solvent of the solution crystallization is C1-C4 alcohol, more preferably ethanol and / or diethyl ether.

[0073] The C1-C4 alcohol in the present application includes but is not limited to methanol, ethanol, propanol and butanol.

[0074] According to the present application, preferably, the mass ratio of the crystallization solvent to the carbazole-rich tower bottom stream is 2-10:1, more preferably 2-5:1.

[0075] According to the present application, the conditions of the solution crystallization include: a temperature of 80-190℃, a stirring rate of 50-800 r / min, and a cooling rate of 10-100℃ / h.

[0076] Further preferably, the conditions of the solution crystallization include: a temperature of 100-150℃, a stirring rate of 50-500 r / min, and a cooling rate of 50-100℃ / h.

[0077] In the present application, the conditions of the solution crystallization adopt the above-mentioned preferred ranges, which can control a suitable dissolution temperature to ensure complete dissolution, make the crystal grow uniformly, and improve the purity.

[0078] It should be noted that the present application does not particularly limit the number of times of the solution crystallization, as long as the content of the carbazole product can meet the needs, and the person skilled in the art can select according to the actual needs, preferably 1-5 times.

[0079] According to the present application, preferably, the warming-up stage includes:

[0080] (Q1) performing first-stage warming-up at a warming-up rate of 5-15℃ / h and a final warming-up temperature of 200-230℃, and a stirring rate of 50-400 rpm;

[0081] (Q2) the second temperature rising stage is performed at a temperature rising rate of 0.5-5℃ / h and a terminal temperature of 240-260℃.

[0082] In the temperature rising stage, the above conditions are adopted, the temperature is raised in stages, and stirring is performed in the first temperature rising stage, so that the mass transfer and heat transfer are strengthened, the crystal structure is optimized, and higher purity carbazole can be obtained in subsequent solid-liquid separation.

[0083] According to a preferred embodiment of the present application, the temperature rising stage comprises:

[0084] (Q1) the first temperature rising stage is performed at a temperature rising rate of 10-15℃ / h and a terminal temperature of 220-230℃, and the stirring rate is 50-150rpm;

[0085] (Q2) the second temperature rising stage is performed at a temperature rising rate of 0.5-2℃ / h and a terminal temperature of 240-250℃.

[0086] According to the present application, preferably, the temperature rising rate of the step (Q1) stage is greater than the temperature rising rate of the step (Q2) stage, and more preferably, the absolute value of the difference between the temperature rising rate of the step (Q1) stage and the temperature rising rate of the step (Q2) stage is 8-10℃ / h, so that the differentiated temperature rising control helps to form a more complete and dense crystal structure, which is not only higher in purity, but also facilitates subsequent solid-liquid separation, and finally, the ideal crystal yield is maintained while ensuring high purity.

[0087] According to the present application, preferably, the temperature lowering stage comprises 3-5 stages, the temperature lowering rate of each stage is 0.5-5℃ / h, the absolute value of the difference between the temperature lowering rate of the former stage and the temperature lowering rate of the latter stage is 0.5-4℃ / h along the temperature lowering direction, and the terminal temperature of the temperature lowering stage is 210-220℃.

[0088] According to the present application, preferably, the last stage of the temperature lowering stage is subjected to heat preservation, and the heat preservation time is 1-5h.

[0089] In the present application, the above multi-stage temperature lowering conditions are adopted, so that the carbazole crystallization process can be accurately controlled, and the impurities can be effectively prevented from being wrapped in the crystal due to too fast growth of the carbazole crystal, which is beneficial to significantly improving the purity of the carbazole.

[0090] According to the present application, preferably, the temperature lowering stage comprises:

[0091] (S1) the first temperature lowering stage is performed at a temperature lowering rate of 2-5℃ / h and a terminal temperature of 230-235℃, and the stirring rate is 50-200rpm;

[0092] (S2) the second temperature lowering stage is performed at a temperature lowering rate of 1-5℃ / h and a terminal temperature of 220-225℃, and the mother liquor is discharged.

[0093] (S3) third-stage cooling at a cooling rate of 0.5-1℃ / h and a final temperature of 210-215℃, and holding for 1-5h.

[0094] In the present application, the above-mentioned three-stage cooling conditions are adopted, and the cooling rates in different temperature zones are precisely controlled to optimize the whole process simultaneously. This scheme can induce the growth of high-purity crystals, effectively improve the production efficiency of the main stage, guarantee the final yield, and avoid impurity eutectics. Finally, the best balance between the purity of carbazole products, the crystal morphology, and the process economy is achieved.

[0095] According to the present application, preferably, the cooling rate in step (S1) is greater than the cooling rate in step (S2), and more preferably, the absolute value of the difference between the cooling rate in step (S1) and the cooling rate in step (S2) is 1-4℃ / h.

[0096] According to the present application, preferably, the sweating stage includes: a temperature rising rate of 0.5-1℃ / h and a final temperature of 215-220℃.

[0097] It should be noted that the present application does not particularly limit the number of melt crystallization, as long as the content of carbazole products meets the needs. Those skilled in the art can select according to actual needs, and preferably 1-3 times.

[0098] The protective atmosphere according to the present application is selected from at least one of nitrogen, argon, and helium.

[0099] The present application provides a device for the above-mentioned method of the first aspect, which comprises a rectification separation unit, a crystallization separation unit, and a melt crystallization unit connected in sequence.

[0100] The rectification separation unit comprises a first rectification column 1, a first delivery pump 3, a second rectification column 6, and a second delivery pump 8 connected in sequence.

[0101] The overhead outlet of the first rectification column 1 is connected to a first condenser 5 and a first reflux tank 4 in sequence, and the reflux outlet of the first reflux tank 4 is connected to the overhead reflux inlet of the first rectification column 1.

[0102] The feed inlet of the first delivery pump 3 is communicated with the column outlet of the first rectification column 1, and the outlet of the first delivery pump 3 is connected to the feed inlet of the second rectification column 6, for feeding the column stream containing carbazole into the second rectification column 6.

[0103] The overhead outlet of the second rectification column 6 is connected to a second condenser 10 and a second reflux tank 9 in sequence, and the reflux outlet of the second reflux tank 9 is connected to the overhead reflux inlet of the second rectification column 6.

[0104] The inlet of the second delivery pump 8 is connected to the outlet of the bottom of the second distillation column 6, and the outlet of the second delivery pump 8 is connected to the crystallization separation unit, which is used to send the carbazole-rich bottom stream into the crystallization separation unit.

[0105] The crystallization separation unit includes a solution crystallization vessel 11, the outlet of which is connected to the melt crystallization unit for feeding crude carbazole into the melt crystallization unit.

[0106] The melt crystallization unit includes a melt crystallizer 12 for purifying the crude carbazole stream.

[0107] According to the present invention, the system further includes a first reboiler 2 connected to the first distillation column 1.

[0108] According to the present invention, the system further includes a second reboiler 7 connected to the second distillation column 6.

[0109] The following combination Figure 1 The method and apparatus for separating and purifying carbazole from diphenylamine dehydrogenation products of the present invention will be described below:

[0110] like Figure 1 As shown, the dehydrogenation product of diphenylamine first enters the first distillation column 1, where it is separated by distillation under the heating action of the first reboiler 2. The low-boiling-point components rise with the steam and are discharged from the top outlet of the column. After being cooled by the first condenser 5 and distributed by the first reflux tank 4, part of it is returned to the top of the column as reflux liquid, and the other part is output as aniline-rich product. Meanwhile, the carbazole-containing stream in the bottom of the column is sent to the second distillation column 6 by the first transfer pump 3.

[0111] The second distillation column 6 is connected to the second reboiler 7. The heating drives the vaporization of the carbazole-containing bottom stream. The low-boiling-point diphenylamine component is discharged from the top outlet of the column and cooled and distributed by the second condenser 10 and the second reflux tank 9. Part of it is returned to the top of the column as reflux liquid, and the other part is output as a diphenylamine-rich product. The bottom stream is further enriched and becomes a carbazole-rich bottom stream, which is sent to the crystallization separation unit by the second transfer pump 8.

[0112] The crystallization separation unit includes a solution crystallization vessel 11, in which the carbazole-rich column feed is mixed with a crystallization solvent and crystallized in solution to obtain crude carbazole; the crude carbazole is then sent to the melt crystallization unit.

[0113] The melting crystallization unit includes a melting crystallizer 12. The crude carbazole crystals undergo a heating stage, a cooling stage, and a sweating stage under a protective atmosphere to further remove impurities and finally obtain a high-purity carbazole product.

[0114] By cooperation of the device and the method, the present application can realize high-efficiency separation of aniline, diphenylamine and carbazole in sequence, and the carbazole obtained after solution crystallization and melt crystallization processes has the advantages of high purity, low energy consumption and industrialization.

[0115] The present application will be described in detail below through examples.

[0116] In the following examples and comparative examples, the conventional methods are used unless otherwise specified; the reagents, materials and instruments used are commercially available and / or prepared by methods known in the art unless otherwise specified.

[0117] In the following comparative examples and examples, the diphenylamine purity calculation formula is as follows:

[0118] ;

[0119] In the following comparative examples and examples, the aniline purity calculation formula is as follows:

[0120] ;

[0121] In the following comparative examples and examples, the carbazole purity calculation formula is as follows:

[0122] .

[0123] Example 1

[0124] (1) Rectification: the carbazole content in the diphenylamine dehydrogenation product is 60.2%, the diphenylamine content is 19.8%, the aniline content is 14.3%, the benzene content is 5.5%, and the remaining components are 0.2%. The dehydrogenation product enters the first rectification tower, the number of plates of the first rectification tower is 15, the temperature of the first reboiler is 80°C, the reflux ratio is 2, the tower top pressure is 0.01 MPa, the tower top temperature is 65°C, and the temperature of the first condenser is 10°C; the mixture in the first rectification tower is transferred into the second rectification tower through the first conveying pump, the number of plates of the second rectification tower is 30, the temperature of the second reboiler is 180°C, the reflux ratio is 10, the tower top pressure is 0.01 MPa, the tower top temperature is 105°C, and the temperature of the second condenser is 80°C.

[0125] The products collected at the tower top and the material flow at the tower bottom of the first rectification tower and the second rectification tower are analyzed for material components.

[0126] (2) Crystallization: the mixture in the second rectification tower is transferred into the solution crystallization kettle, 99% ethanol is added as the crystallization solvent, the ratio of ethanol to the carbazole-rich mixture is 2, the crystallization temperature is 150°C, the crystallization stirring speed is 500 r / min, and the crystallization cooling rate is 80°C / h. The crystallization is repeated twice.

[0127] The crystallized stream was analyzed for composition.

[0128] (3) Melting crystallization: The melting crystallization of carbazole from the mixture containing impurities was carried out in three stages of temperature rising, temperature falling and sweating. Nitrogen was introduced into the melting crystallizer during the whole process.

[0129] In the temperature rising stage, the mixture was placed in a heating device and slowly heated to 230°C at a rate of 10°C / min, with a stirring rate of 80 rpm during the process. Then, the temperature was raised to 245°C at a rate of 1°C / min.

[0130] The temperature falling stage was divided into three stages. In the first stage, the temperature was lowered from the melting temperature to 230°C at a rate of 3°C / h, with a stirring rate of 80 rpm during the process. In the second stage, the temperature was lowered from 230°C to 220°C at a rate of 2°C / h, with the mother liquor being periodically discharged. In the third stage, the temperature was lowered from 220°C to 210°C at a rate of 0.5°C / h, and the temperature was maintained for 2 h.

[0131] In the sweating stage, the crystalline layer was heated to 218°C at a rate of 0.5°C / h to melt and discharge the impurities. The sweat was collected in time to prevent secondary pollution, and the melting crystallization was repeated twice.

[0132] The material after melting crystallization was analyzed for composition. The results are shown in Table 1.

[0133] Example 2

[0134] This example provides a method for separating and purifying carbazole, which has the same process steps as Example 1, but the key operating parameters are different, as follows:

[0135] The starting material was the dehydrogenation product of diphenylamine, containing 70.6% carbazole, 15.6% diphenylamine, 10.6% aniline, 2.7% benzene, and 0.5% other components.

[0136] The operating conditions of the first rectifying column were as follows: the number of trays was 20, the temperature of the reboiler was 120°C, the reflux ratio was 2:1, the pressure at the top of the column was 0.05 MPa, the temperature at the top of the column was 75°C, and the temperature of the first condenser was 10°C.

[0137] The operating conditions of the second rectifying column were as follows: the number of trays was 20, the temperature of the reboiler was 220°C, the reflux ratio was 20:1, the pressure at the top of the column was 0.05 MPa, the temperature at the top of the column was 120°C, and the temperature of the second condenser was 80°C.

[0138] The operating conditions of the solution crystallization were as follows: the ratio of ethanol to carbazole-rich solution was 5:1, the crystallization temperature was 100°C, the stirring rate during crystallization was 400 r / min, and the cooling rate during crystallization was 70°C / h. The crystallization was repeated twice.

[0139] The operating conditions of the melting crystallization were as follows:

[0140] Ramp-up stage: ramp up to 220°C at a rate of 15°C / min, with stirring rate of 100 rpm during the process; and then ramp up to 250°C at a rate of 2°C / min.

[0141] The ramp-down stage is divided into four stages: the first stage is to reduce the temperature from the melting temperature to 235°C at a rate of 5°C / h; the second stage is to reduce the temperature from 235°C to 225°C at a rate of 2°C / h, with stirring rate of 100 rpm during the process; the third stage is to reduce the temperature from 225°C to 215°C at a rate of 1°C / h, with periodic removal of mother liquor; and the final stage is to reduce the temperature from 215°C to 210°C at a rate of 0.5°C / h, with keeping the temperature for 3 h.

[0142] The sweating stage is to further purify the material, and the crystalline layer is heated to 220°C at a rate of 1°C / h to melt and remove the impurities, and the sweat is collected in time to prevent secondary pollution. The melting and crystallization process is repeated once.

[0143] The component analysis of the material after melting and crystallization is carried out. The results are shown in Table 1.

[0144] Example 3

[0145] According to the method of Example 1, except that the temperature reduction stage during the melting and crystallization process of the material is divided into two stages: the first stage is to reduce the temperature from the melting temperature to 220°C at a rate of 5°C / h, with stirring rate of 80 rpm during the process and periodic removal of mother liquor; and the final stage is to reduce the temperature from 220°C to 210°C at a rate of 1°C / h, with keeping the temperature for 2 h. The results are shown in Table 1.

[0146] Example 4

[0147] According to the method of Example 1, except that the temperature increase stage during the melting and crystallization process of the material is divided into one stage: to increase the temperature to 245°C at a rate of 15°C / h, with stirring rate of 80 rpm during the process. The results are shown in Table 1.

[0148] Comparative Example 1

[0149] According to the method of Example 1, except that the temperature reduction stage during the melting and crystallization process of the material is divided into one stage: the first stage is to reduce the temperature from the melting temperature to 210°C at a rate of 5°C / h, with periodic removal of mother liquor and keeping the temperature for 2 h. The results are shown in Table 1.

[0150] Comparative Example 2

[0151] According to the method of Example 1, except that the temperature reduction stage during the melting and crystallization process of the material is divided into two stages: the first stage is to reduce the temperature from the melting temperature to 220°C at a rate of 2°C / h, with stirring rate of 80 rpm during the process and periodic removal of mother liquor; and the final stage is to reduce the temperature from 220°C to 210°C at a rate of 10°C / h, with keeping the temperature for 2 h. The results are shown in Table 1.

[0152] Comparative Example 3

[0153] According to the method of Example 1, except that a two-stage cooling procedure was used in the temperature reduction stage during the melt crystallization process, the preliminary cooling was reduced from the melting temperature to 220℃ at a rate of 10℃ / h, the stirring rate was 80 rpm during the period, and the mother liquor was discharged regularly; the final cooling was reduced from 220℃ to 210℃ at a rate of 3℃ / h, and the temperature was maintained for 2h. The results are shown in Table 1.

[0154] Comparative Example 4

[0155] According to the method of Example 1, except that after the material passed through the second rectifying tower, the material in the tower kettle directly underwent the melt crystallization process, and the melt crystallization process was the same as that of Example 1. The results are shown in Table 1.

[0156] Table 1 Purity of each substance

[0157]

[0158] From the above results, it can be seen that compared with the comparative examples, the examples show that the method provided by the present application can gradually and accurately realize the efficient separation of aniline, diphenylamine and carbazole, and purify the electronic-grade carbazole, solving the problem of low purity of carbazole in the prior art.

[0159] The preferred embodiments of the present application are described in detail above, but the present application is not limited thereto. Within the technical concept of the present application, various simple modifications can be made to the technical solutions of the present application, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be considered as disclosed by the present application, and all belong to the protection scope of the present application.

Claims

1. A method for separating and purifying carbazole, characterized by, The method comprises: (1) subjecting a diphenylamine dehydrogenation product to first rectification separation to obtain aniline-rich overhead stream and a carbazole-containing column bottom stream; (2) subjecting the carbazole-containing column bottom stream to second rectification separation to obtain diphenylamine-rich overhead stream and carbazole-rich column bottom stream; (3) subjecting the carbazole-rich column bottom stream to solution crystallization in the presence of a crystallization solvent to obtain crude carbazole; the crystallization solvent for the solution crystallization is C1-C4 alcohol and / or diethyl ether; (4) subjecting the crude carbazole to melt crystallization under a protective atmosphere; the melt crystallization comprises a warming-up stage, a cooling-down stage and a sweating stage; the cooling-down stage comprises at least two stages, each stage has a cooling-down rate of 0.5-5 ℃ / h, the cooling-down rate of the former stage is greater than that of the latter stage along the temperature decreasing direction, and the terminal temperature of the cooling-down stage is 210-220 ℃.

2. The method of claim 1, wherein, the diphenylamine dehydrogenation product comprises carbazole, diphenylamine, aniline, benzene and other components; based on the total mass of the diphenylamine dehydrogenation product, the content of the carbazole is 40-80 wt%, the content of the diphenylamine is 5-25 wt%, the content of the aniline is 2-20 wt%, the content of the benzene is 3-10 wt%, and the content of the other components is 0.01-5 wt%.

3. The method of claim 1, wherein, the content of the carbazole in the carbazole-containing column bottom stream is 60-80 wt%; the content of the carbazole in the carbazole-rich column bottom stream is 80-95 wt%; the content of the carbazole in the crude carbazole is 95-99 wt%.

4. The method of claim 1, wherein, the conditions for the first rectification separation comprise: the overhead pressure is 0.01-0.1 MPa; the overhead temperature is 60-80 ℃; and the reflux ratio is 1-10:1; the rectification column for the first rectification separation has 10-30 plates.

5. The method of claim 1, wherein, the conditions for the second rectification separation comprise: the overhead pressure is 0.001-0.1 MPa; the overhead temperature is 80-180 ℃; and the reflux ratio is 1-30:1; the rectification column for the second rectification separation has 10-50 plates.

6. The method of claim 1, wherein, the mass ratio of the crystallization solvent to the carbazole-rich column bottom stream is 2-10:

1.

7. The method of claim 1, wherein, the conditions for the solution crystallization comprise: the temperature is 80-190 ℃, the stirring rate is 50-800 r / min, and the cooling-down rate is 10-100 ℃ / h.

8. The method of any one of claims 1-7, wherein, the warming-up stage comprises: (Q1) the first-stage warming-up is performed at a warming-up rate of 5-15 ℃ / h, a warming-up terminal temperature of 200-230 ℃, and a stirring rate of 50-400 rpm; (Q2) the second-stage warming-up is performed at a warming-up rate of 0.5-5 ℃ / h and a warming-up terminal temperature of 240-260 ℃.

9. The method of any of claims 1-7, wherein, the cooling-down stage comprises 3-5 stages, each stage has a cooling-down rate of 0.5-5 ℃ / h, the absolute value of the difference between the cooling-down rate of the former stage and that of the latter stage along the temperature decreasing direction is 0.5-4 ℃ / h, and the terminal temperature of the cooling-down stage is 210-220 ℃.

10. The method of any one of claims 1-7, wherein, the cooling-down stage comprises: (S1) the first-stage cooling-down is performed at a cooling-down rate of 2-5 ℃ / h, a cooling-down terminal temperature of 230-235 ℃, and a stirring rate of 50-200 rpm; (S2) a second temperature decreasing stage with a temperature decreasing rate of 1-5℃ / h and a terminal temperature of 220-225℃, and discharging mother liquor; (S3) a third temperature decreasing stage with a temperature decreasing rate of 0.5-1℃ / h and a terminal temperature of 210-215℃, and keeping the temperature for 1-5h.

11. The method of any one of claims 1-7, wherein, The sweating stage includes a temperature increasing rate of 0.5-1℃ / h and a terminal temperature of 215-220℃.

12. An apparatus for use in the method of any one of claims 1-11, characterized by The device comprises a rectification separation unit, a crystallization separation unit and a melt crystallization unit connected in sequence; The rectification separation unit comprises a first rectification tower (1), a first delivery pump (3), a second rectification tower (6) and a second delivery pump (8) connected in sequence; The top outlet of the first rectification tower (1) is connected with a first condenser (5) and a first reflux tank (4) in sequence, and the reflux outlet of the first reflux tank (4) is connected with the top reflux inlet of the first rectification tower (1); The feed inlet of the first delivery pump (3) is communicated with the outlet of the tower kettle of the first rectification tower (1), and the outlet of the first delivery pump (3) is connected with the feed inlet of the second rectification tower (6) for feeding the tower kettle stream containing carbazole into the second rectification tower (6); The top outlet of the second rectification tower (6) is connected with a second condenser (10) and a second reflux tank (9) in sequence, and the reflux outlet of the second reflux tank (9) is connected with the top reflux inlet of the second rectification tower (6); The feed inlet of the second delivery pump (8) is communicated with the outlet of the tower kettle of the second rectification tower (6), and the outlet of the second delivery pump (8) is communicated with the crystallization separation unit for feeding the tower kettle stream rich in carbazole into the crystallization separation unit; The crystallization separation unit comprises a solution crystallization kettle (11), and the outlet of the solution crystallization kettle (11) is communicated with the melt crystallization unit for feeding the crude carbazole into the melt crystallization unit; The melt crystallization unit comprises a melt crystallizer (12) for purifying the crude carbazole.

Images