Preparation method of high-purity carbazole

Abstract

The invention belongs to the technical field of deep processing of coal tar, and particularly relates to a preparation method of high-purity carbazole. The rectification process of the method mainly comprises the following steps: carrying out two-stage rectification on anthracene carbol oil, adopting a negative pressure rectification mode in the first-stage rectification, extracting a primary light component containing carbazole from the tower top, then carrying out two-stage rectification on the primary light component, and finally extracting high-purity carbazole from a side line. The purity of carbazole prepared through the rectification method can reach 99.5% or above, and the yield is high and reaches 60% or above.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of coal tar deep processing, and particularly relates to a preparation method of high-purity carbazole. BACKGROUND

[0002] Carbazole is a nitrogen-containing heterocyclic compound and one of the components with the highest economic value in coal tar. 90% of the carbazole in the world is obtained from coal tar. Carbazole can be used to produce dyes, pigments, photoconductors, photosensitive materials, special inks and the like. With the development of fine chemical industry and the progress of organic synthesis technology, the demand for high-purity carbazole is increasing. The higher the purity of the product carbazole, the stronger the market competitiveness and the more considerable the economic benefits. However, the content of carbazole in anthracene carbazole oil obtained by the solvent crystallization method is low at present, which limits its application in high-end fields. For example, in the prior art, the Chinese patent application No. 202210369549.2 discloses a production method and system of refined carbazole. The method includes a solvent crystallization process and a rectification process. In the solvent crystallization process, the liquid phase produced in the first washing process is used as raw material anthracene oil, and the liquid phase produced in the Nth washing process is used as the N-1th washing liquid. The last time, the raw material toluene is used for washing to realize multiple continuous washing of anthracene carbazole crystals. Then, the anthracene carbazole oil is heated and melted, and then discharged from the crystallization device for rectification. The purity of carbazole after rectification is 97.5%-98.5%. In order to meet the demand for high-purity carbazole and enhance market competitiveness, the purity of carbazole still needs to be further improved. SUMMARY

[0003] Therefore, the application provides a preparation method of high-purity carbazole to solve the technical problem that the purity of carbazole still needs to be further improved in order to meet the demand for high-purity carbazole and enhance market competitiveness in the prior art.

[0004] The technical scheme for solving the above technical problem of the application is as follows: A preparation method of high-purity carbazole, comprising a rectification process, the rectification process comprising the following steps: S10. The preheated anthracene carbazole crystals are sent into a first rectification column for first-stage negative pressure rectification. After the overhead first light components are condensed, part of them is used as a first reflux liquid, and the other part is taken out from the top of the column. The first heavy components at the bottom are taken out. S20. The first light components are sent into a second rectification column for second-stage rectification. After the overhead second light components are condensed, part of them is used as a second reflux liquid, and the other part is taken out from the top of the column. The second heavy components at the bottom are sent into the inlet of the first rectification column. High-purity carbazole is taken out through a side line.

[0005] Preferably, in the step S10, the pressure of the first-stage negative pressure rectification is-80 kPa to-95 kPa.

[0006] Preferably, in the preparation method of high-purity carbazole, the overhead temperature of the first rectification column is 180-200°C, and the bottom temperature is 280-320°C. Preferably, in the preparation method of high-purity carbazole, the reflux ratio of the first rectification column is controlled to be 0.5-3.

[0007] Preferably, in the preparation method of high-purity carbazole, the overhead temperature of the second rectification column is 260-280°C, and the bottom temperature is 350-370°C.

[0008] Preferably, in the preparation method of high-purity carbazole, the reflux ratio of the second rectification column is controlled to be 0.5-3.

[0009] Preferably, the preparation method of high-purity carbazole further comprises a solvent crystallization process before the rectification process, and the solvent crystallization process comprises: T10. Crystallizing anthracene carbazole from anthracene oil by using a mixture of o-xylene and m-xylene as solvent, wherein the volume ratio of o-xylene to m-xylene is 1: (0.3-3), and the volume ratio of solvent to anthracene oil is (8-15):1.

[0010] Preferably, the preparation method of high-purity carbazole further comprises a solvent crystallization process before the rectification process, and the solvent crystallization process comprises: T11. Providing a crystallization device, and feeding the anthracene oil and the solvent into the crystallization device; T12. Cooling the anthracene oil and the solvent to a first crystallization temperature, wherein the first crystallization temperature is 10-20°C; T13. Cooling the anthracene oil and the solvent to a second crystallization temperature to obtain crude anthracene carbazole and a crystallization mother liquor, wherein the second crystallization temperature is 0-5°C; T14. Discharging the crystallization mother liquor; T15. Heating to a sweating temperature to make the crude anthracene carbazole sweat, and discharging the sweat, wherein the sweating temperature is 35-50°C; T16. Repeating steps T11-T15 until the crude anthracene carbazole in the crystallization device reaches a first predetermined volume.

[0011] Preferably, the preparation method of high-purity carbazole further comprises: T20. Inputting a washing liquid into the crystallization device to wash the crude anthracene carbazole at least once; T30. Input the washing liquid into the crystallization device, and perform N washing processes on the anthracene carbazole crystals, 2≤N≤5, wherein the liquid phase obtained by the first washing is mixed with the raw material, and the liquid phase obtained by the i-th washing is used as the washing liquid for the (i-1)-th washing, wherein 2≤i≤N; T40. Input the i-th washing liquid into the crystallization device in sequence, and perform the (i-1)-th washing process on the anthracene carbazole crystals; T50. Input the solvent into the crystallization device, and perform the (N+1)-th washing process on the anthracene carbazole crystals, wherein the liquid phase obtained by the washing is used as the N-th washing liquid, and the solid phase obtained after the washing is used as the anthracene carbazole crystals; T60. After the anthracene carbazole crystals are heated and melted, the crystallization device is discharged.

[0012] Preferably, in the step T40 of the preparation method of the high-purity carbazole, the i-th washing process comprises the following steps: T41. Add the i-th washing liquid into the crystallization device, and heat to 55-75℃ to melt the anthracene carbazole oil; T42. Cool to 10-20℃ to preliminarily crystallize the anthracene carbazole oil; T43. Cool to 0-5℃ to further crystallize the anthracene carbazole oil; T44. Discharge the liquid phase which is not crystallized.

[0013] Compared with the prior art, the present application has at least the following advantages: The preparation method of the high-purity carbazole disclosed in the present application comprises mainly two-stage rectification of the anthracene carbazole oil, wherein the negative pressure rectification is used in the first-stage rectification, the first-stage light component containing carbazole is collected from the top of the column, and the first-stage light component is subjected to the second-stage rectification, and finally the high-purity carbazole is collected. The purity of the carbazole prepared by this rectification method can reach 99.5% or more, and the yield is relatively high, which is more than 60%. DETAILED DESCRIPTION

[0014] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict. The technical solutions of the present application will be further described below in combination with the embodiments of the present application, and the present application is not limited to the following specific embodiments.

[0015] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in the description herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0016] In one specific embodiment of this application, a method for preparing high-purity carbazole includes a distillation process, wherein the distillation process includes the following steps: S10. The preheated anthracite crystals are fed into a first-stage distillation column for first-stage negative pressure distillation. The light components at the top of the column are condensed and part of them are used as reflux liquid, while the other part is collected from the top of the column. The heavy components at the bottom of the column are collected. The anthracene-carbazole crystals in this scheme are obtained by solvent crystallization using anthracene oil as raw material. The main components include: anthracene 65-68.5%, carbazole 25-28.5%, and phenanthrene 0.1-2%. The anthracene-carbazole crystals are then fed to a preheater and preheated to a suitable temperature to reduce heat consumption in the distillation column and improve distillation efficiency. Preferably, the preheating temperature is 100°C to 150°C.

[0017] Specifically, the solvent crystallization method for obtaining anthracite crystals means that a solvent crystallization process is included before the distillation process. This solvent crystallization process includes: T10. Using anthracene oil as raw material, anthracene-carbamate crystals are obtained by crystallization using an o-xylene-m-xylene composite solvent system; in the o-xylene-m-xylene mixed solvent system, the volume ratio of o-xylene to m-xylene is 1:(0.3 to 3); the volume ratio of solvent to anthracene oil is (8 to 15):1.

[0018] In this technical solution, the anthracene oil is produced during the production of various coal chemical products using coal tar as raw material. Its components include: 6.5%–8.3% anthracene; 4.0%–5.2% carbazole; 23.6%–27.8% phenanthrene; and 3.6%–5.4% naphthalene. The o-xylene-m-xylene composite solvent system used in this solution can significantly improve the yield of carbazole compared to a single raw material solvent.

[0019] Preferably, in the above-mentioned method for preparing high-purity carbazole, the solvent crystallization process specifically comprises: T11. A crystallization apparatus is provided, wherein the anthracene oil and the solvent are fed into the crystallization apparatus; T12. Cool the anthracene oil and the solvent to a first crystallization temperature; the first crystallization temperature is 10°C to 20°C; T13. Cool the anthracene oil and the solvent to a second crystallization temperature to obtain crude anthracene crystals and crystallization mother liquor; wherein, the second crystallization temperature is 0°C to 5°C; T14. Drain the mother liquor from the crystallization solution; T15. Heat to the sweating temperature to induce sweating of the crude anthracite crystals and release sweat; the sweating temperature is 35°C to 50°C; T16. Repeat steps T11 to T15 until the crude anthracite crystals in the crystallization apparatus reach a first predetermined volume.

[0020] T17. Repeat steps T11 to T14 until the crude anthracite crystals in the crystallization apparatus reach a second predetermined volume.

[0021] Specifically, a crystallization apparatus is provided, which may be a crystallizer with internal fins or tubes. Anthracene oil and solvent are fed into the crystallization apparatus in batches, cooled for crystallization, and the mother liquor is discharged. Then, the mixture is heated to induce sweating, and after the sweating is discharged, anthracene-cak crystals are obtained. This process is considered the feeding process. The above process is repeated approximately 6-8 times until the anthracene-cak crystals reach the preset capacity of the crystallization apparatus, at which point feeding is stopped. This process is considered the replenishment process. The complete process described above is considered the "feeding and replenishment process".

[0022] The aforementioned "feeding and replenishing process" specifically involves introducing anthracene oil and solvent into the crystallization apparatus. First, the mixture is cooled to a first crystallization temperature for preliminary crystallization. Preferably, the first crystallization temperature is 10°C to 20°C. Then, the anthracene oil and solvent are cooled to a second crystallization temperature for deep crystallization. Preferably, the second crystallization temperature is 0°C to 5°C. After crystallization, the mother liquor is drained, and the temperature is raised to a sweating temperature to induce sweating in the anthracene crystals, releasing the sweat. Preferably, the sweating temperature is 35°C to 50°C. This process is considered the feeding process. After the feeding process, the generated anthracene crystals remain in the crystallization apparatus. Anthracene oil and solvent are then continuously introduced into the crystallization apparatus, and the above process is repeated until the final sweating occurs. Once the anthracene crystals in the crystallization apparatus reach a predetermined volume (first predetermined volume), the replenishing process is completed.

[0023] In some cases, steps T12 to T14 can be repeated until the anthraquinone crystals in the crystallization device reach a predetermined volume, after which the process directly proceeds to step T20. In other cases, during the later stages of feeding, sweating can be discontinued to ensure the yield of carbazole. That is, once the volume of carbazole in the crystallization device reaches the first predetermined volume, steps T12 to T14 can be repeated without further sweating, allowing the anthraquinone crystals in the crystallization device to reach the second predetermined volume.

[0024] In one embodiment, the medium used to cool anthracene oil and solvent to a first crystallization temperature and to cool the material A to be crystallized to a second crystallization temperature is tetrahydronaphthalene.

[0025] Preferably, the above-mentioned method for preparing high-purity carbazole further includes: T20. Introduce washing solution into the crystallization apparatus to wash the crude anthracite crystals at least once; After the feeding and replenishment processes are completed, the anthraquinone crystals in the crystallization device are washed to minimize the phenanthrene content in the final anthraquinone oil, thereby improving the purity of carbazole. The washing solution is preferably the same substance as the solvent, and washing is performed 2 to 5 times. The liquid phase generated during the process is directly mixed with the raw material—anthraquinone oil—and recycled, thereby reducing carbazole loss and increasing carbazole yield.

[0026] T30. Input washing liquid into the crystallization device to perform N washing process on the anthracite crystals, where 2≤N≤5, wherein the liquid phase obtained from the first washing is mixed with the raw material, and the liquid phase generated from the i-th washing is used as the washing liquid for the (i-1)-th washing, where 2≤i≤N; The first washing process is repeated 2 to 3 times. The first washing liquid in the first washing process comes from the liquid phase generated in the second washing process. The liquid phase generated in the washing process is directly mixed with anthracene oil and then recycled as a raw material.

[0027] T40. The i-th washing solution is sequentially input into the crystallization device to perform the i-1-th washing process on the anthracite crystals; Throughout the washing process, the liquid phase produced in the i-th wash serves as the washing liquid for the (i-1)-th wash. This allows for secondary crystallization of the carbazole lost with the solvent, increasing the carbazole yield. Furthermore, the carbazole lost with the solvent is ultimately used as the feed oil, further reducing carbazole loss and increasing the yield. It should be noted that, as understood by those skilled in the art, increasing the number of single-step solvent crystallization steps can further improve the purity of the prepared refined carbazole without significantly affecting the carbazole yield.

[0028] Preferably, the i-th washing process includes the following steps: T41. Add the i-th washing liquid to the crystallization apparatus and heat it to 55°C to 75°C to melt the anthracite oil; T42. Cool to 10°C to 20°C to allow the anthracite oil to begin crystallizing; T43. Cool to 0°C to 5°C to allow the anthracite oil to crystallize further; T44. Exclude the uncrystallized liquid phase.

[0029] The N+1th washing process, i.e., the final washing process, uses a solvent as the washing liquid to further reduce the content of phenanthrene and other substances in carbazole and improve the purity of carbazole. Preferably, after the final washing process, the phenanthrene content in the obtained anthraquinone oil is ≤0.5%.

[0030] T50. A solvent is introduced into the crystallization apparatus to perform the N+1 washing process on the anthracite crystals. The liquid phase obtained after washing is used as the Nth washing liquid, and the solid phase obtained after washing is used as anthracite oil. T60. After heating and melting the anthracite oil, remove it from the crystallization device.

[0031] The anthracite oil obtained after the washing process is heated and melted, and then discharged from the crystallization device for distillation.

[0032] For example, steps T30 to T60 above perform the following steps: After the feeding and replenishment process is completed, an appropriate amount of first washing liquid is first added to the crystallization device, heated to melt anthraquinone crystals, and thoroughly mixed. Then, the mixture is cooled to crystallize. After crystallization, the liquid phase is discharged, and the discharged liquid phase is used as the raw material anthraquinone oil. After the first washing process is repeated once, an appropriate amount of second washing liquid is added to the crystallization device, heated to melt anthraquinone crystals, and thoroughly mixed. Then, the mixture is cooled to crystallize. After crystallization, the liquid phase is discharged, and the discharged liquid phase is used as the first washing liquid. After the second washing process is completed, an appropriate amount of third washing liquid is added to the crystallization device, heated to melt anthraquinone crystals, and thoroughly mixed. Then, the mixture is cooled to crystallize. After crystallization, the liquid phase is discharged, and the discharged liquid phase is used as the second washing liquid. After the third washing process is completed, an appropriate amount of fourth washing liquid is added to the crystallization device, heated to melt anthraquinone crystals, and thoroughly mixed. Then, the mixture is cooled to crystallize. After crystallization, the liquid phase is discharged, and the discharged liquid phase is used as the third washing liquid. After the fourth washing process is completed, an appropriate amount of solvent o-xylene-m-xylene is added to the crystallization device, heated to melt anthracite crystals, and mixed thoroughly. Then the mixture is cooled to crystallize. After crystallization is completed, the liquid phase is discharged, and the discharged liquid phase is used as the fourth washing liquid.

[0033] The anthracene-carbazole crystals obtained by the solvent crystallization method are preheated and then fed into a first-stage distillation column. Inside the column, heat is provided by a reboiler to partially vaporize the material. During the vapor's ascent, mass and heat transfer occur between the rising vapor and the descending liquid. Based on the differences in boiling points of the components, the lighter components with lower boiling points (mainly containing anthracene, carbazole, and other light components) are preferentially vaporized and distilled off from the top of the column. After condensation in the top condenser, a portion is used as primary reflux. Preferably, the reflux ratio of the first-stage distillation column is controlled between 0.5 and 3. The remaining lighter components are collected from the top of the column and sent to a second-stage distillation column for further distillation. The heavier components with higher boiling points are enriched at the bottom of the column and collected therefrom. Because a negative pressure distillation method is used, the reboiler temperature of the first-stage distillation column can be reduced, improving operational safety. Preferably, the top temperature of the first-stage distillation column is 180°C to 200°C, and the reboiler temperature is 280°C to 320°C.

[0034] S20. The primary light component is fed into a two-stage distillation column for two-stage distillation. After the secondary light component at the top of the column is condensed, part of it is used as secondary reflux liquid, and the other part is collected from the top of the column. The secondary heavy component at the bottom of the column is sent to the inlet of the primary distillation column. High-purity carbazole is collected through a side stream.

[0035] The primary light component collected from the top of the first-stage distillation column enters the second-stage distillation column, where carbazole is further separated from other components. The vapor distilled from the top (mainly containing anthracene) is condensed in the top condenser; a portion is refluxed as secondary reflux, and the remainder is collected and returned to the top of the column as secondary reflux. The carbazole fraction is collected via a side stream, and anthracene residue oil is collected from the bottom of the distillation column. Preferably, the reflux ratio of the second-stage distillation column is controlled between 0.5 and 3 to ensure distillation efficiency. The secondary heavy component (anthracene residue oil) from the bottom of the column is sent to the inlet of the first-stage distillation column for distillation along with the anthracene-carbazole oil, achieving material reuse. High-purity carbazole product is collected via a side stream at a temperature controlled between 310℃ and 330℃. The collection rate is adjusted according to product quality requirements to ensure that the carbazole purity meets production requirements, such as 99% or higher. Preferably, the top temperature of the two-stage distillation column is 260°C to 280°C, and the bottom temperature is 350°C to 370°C.

[0036] In this scheme, based on the differences in boiling points of components such as anthracene, carbazole, and phenanthrene in anthracene-carb oil, a two-stage distillation method is adopted for separation. The first-stage distillation initially separates the components, collecting the primary light component rich in carbazole from the top of the column. The second-stage distillation further purifies the components, again collecting the high-purity carbazole product via a side stream, while the bottom material of the second-stage column is recycled, achieving resource recycling. It is worth noting that the type and specifications of the primary and secondary distillation columns can be selected according to actual production needs, such as plate columns or packed columns. The primary distillation column operates under negative pressure, with an operating pressure of -80 to -95 kPa; the secondary distillation column operates under normal pressure, with pressure sensors installed to monitor the pressure inside the column in real time, ensuring that pressure fluctuations are within the allowable range (±5 kPa) to prevent abnormal pressure from affecting the distillation effect.

[0037] It is worth noting that the process temperature and process time involved in the above embodiments are all temperatures or times used in the experiment. Any adjustments made by those skilled in the art based on the process temperature and process time provided by the present invention within a reasonable error range should be included within the protection scope of the present invention.

[0038] 1. Main reagents In this embodiment of the invention, the anthracene oil is anthracene oil produced by Ningxia Xitai Coal Chemical Co., Ltd. in the process of producing various coal chemical products using coal tar as raw material. Its components include: 7.4% anthracene, 4.6% carbazole, 25.7% phenanthrene, 4.5% naphthalene, and 0.6% acridine.

[0039] The other reagents and solvents are commercially available and can be used without further purification.

[0040] 2. Preparation of anthracene-carbide crystals 2.1 Anthracene-Carbide Crystallization Feeding and replenishment process: Take 200ml (224g) of anthracene oil and mix it with 2000ml of o-xylene (solvent). The solution was fed into a crystallization reactor, first cooled to 15°C and held for 1 hour, then cooled to 5°C and held for 1 hour. The mother liquor was drained, and then heated to 45°C for sweating. This process was repeated 7 times, with the last two times omitting the sweating step.

[0041] Solvent crystallization process: o-xylene solvent is added to the crystallization reactor for washing. The mixture is heated to 60°C to melt the crude anthracite crystals. First, the temperature is lowered to 15°C and held for 1 hour, then lowered to 5°C and held for 1 hour, at which point the liquid phase is discharged. This washing process is repeated three times, and the crude anthracite crystals are collected after the third wash.

[0042] 2.2 Anthracene-carbamate crystals Keep all other conditions the same as in 2.1, and use m-xylene as the solvent.

[0043] 2.3 Anthracene-carbamate crystals Keeping other conditions the same as in 2.1, the solvent used is an o-xylene-m-xylene composite solvent system, where the volume ratio of o-xylene to m-xylene is shown in the table below.

[0044] The components in anthraquinone crystals were analyzed by gas chromatography, and the yield of carbazole in the anthraquinone crystals was calculated. The calculation method is shown in the following formula:

[0045] Where: β is the carbazole yield (%); m is the mass (g) of anthracite crystals; q represents the mass percentage (%) of carbazole in the anthraquinone crystals; M represents the mass (g) of anthracene oil; Q represents the mass percentage (%) of carbazole in anthracene oil.

[0046] Table 1. Experimental data on anthracite crystallization prepared with different solvents.

[0047] As can be seen from the table above, when using xylene as a single solvent, the quality of the anthraquinone crystals obtained is quite similar (anthraquinone crystal one and anthraquinone crystal two), and the carbazole yield is also around 55%, which is too low.

[0048] The raw material solvent adopts an o-xylene-m-xylene composite solvent system. When the volume ratio of o-xylene to m-xylene is 1:(0.5 to 2), the average yield of carbazole is greater than 60%. In particular, when the volume ratio of o-xylene to m-xylene is 1:2, the yield of carbazole is the highest, at 63.28%, which is 8.25% higher than that of the control group using a single xylene solvent, with an average improvement rate of 15.00%.

[0049] Therefore, subsequent experiments can use an o-xylene-m-xylene composite solvent system with a volume ratio of o-xylene to m-xylene of 1:2 to prepare carbazole.

[0050] 2.4 Experimental Example 2 Keep all other conditions the same as in Experiment 4, including the conditions for feeding and replenishing.

[0051] In the initial stage of production, the liquid phase generated in the first washing process of Experiment 1 was collected and discharged into the raw material anthracene oil. The liquid phase generated in the second washing process was used as the first washing liquid, and the liquid phase generated in the third washing process was used as the second washing liquid.

[0052] In subsequent production, the crude anthraquinone crystals were first washed with a first washing solution, and the resulting liquid phase was discharged into the raw material anthraquinone oil. Then, the crude anthraquinone crystals were washed a second time with a second washing solution, and the resulting liquid phase was used as the first washing solution. Finally, the crude anthraquinone crystals were washed a third time with a solvent, and the resulting liquid phase was used as the second washing solution. Gas chromatography was used to analyze the components in the anthraquinone crystals, and the yield of carbazole in the anthraquinone crystals was calculated.

[0053] Table 3 Detection results of Experiment Example 2

[0054] As can be seen from the table above, during the entire washing process, when the liquid phase generated from the i-th wash is recycled as the washing liquid for the (i-1)-th wash, the yield of carbazole can be further improved, reaching 66.76%, which is an average increase of 11.76% compared to the control group, representing an improvement rate of 21.38%.

[0055] 3. Carbazole purification 3.1 Comparative Example The preparation conditions for anthracene-carb crystals are the same as those in Group 4 of Section 2.3.

[0056] Distillation Process: Anthracite crystals are fed to a preheater and preheated to 120°C. The preheated anthracite oil is then fed into a plate distillation column, where it is heated by a reboiler to maintain a top temperature of 180°C and a bottom temperature of 345°C. Lighter components are distilled off from the top of the column, condensed in a top condenser, and a portion is used as primary reflux at a reflux ratio of 2.5. The system operates at atmospheric pressure, with pressure sensors monitoring the pressure within the column in real time to ensure fluctuations are within ±0.05 MPa. Carbazole is collected via a side stream at a controlled temperature of 290°C. After the system stabilizes, gas chromatography is used to detect the collected carbazole and calculate its yield.

[0057] 3.2 Experimental Example 1 Maintaining other conditions identical to Comparative Example 1, the distillation process is as follows: Preheated anthraquinone oil is fed into a single-stage distillation column (plate distillation column). Inside the column, heating is achieved via a reboiler, controlling the top temperature at 180°C and the bottom temperature at 280°C. The light component is distilled off from the top of the column, condensed in the top condenser, and used as primary reflux liquid at a reflux ratio of 1.5. The operation is carried out at a pressure of -90 kPa, with pressure sensors monitoring the pressure in real time to ensure pressure fluctuations are within ±0.5 kPa. The carbazole-rich intermediate is collected via a side stream at a temperature controlled at 290°C.

[0058] The intermediate product collected from the first-stage distillation column enters the second-stage distillation column, where carbazole is further separated from other components. The top temperature is 260℃, and the bottom temperature is 350℃. The vapor distilled at the top is condensed by the top condenser, and a portion is returned to the top as secondary reflux (reflux ratio 1.5). The secondary heavy components at the bottom are sent to the inlet of the first-stage distillation column for distillation along with the anthracene-carbazole oil. High-purity carbazole product is collected via a side stream at a controlled temperature of 320℃. The operation is under atmospheric pressure, with pressure sensors monitoring the pressure inside the column in real time to ensure pressure fluctuations are within ±0.5 kPa.

[0059] After the system is running stably, gas chromatography is used to detect the extracted carbazole and calculate its yield.

[0060] 3.3 Experimental Example 2 Keeping all other conditions the same as in Experiment 1, the difference is that the first-stage distillation column is operated with a top temperature of 200℃, a bottom temperature of 320℃, and an internal pressure of -80kPa; while the second-stage distillation column has a top temperature of 280℃ and a bottom temperature of 370℃.

[0061] After the system is running stably, gas chromatography is used to detect the extracted carbazole and calculate its yield.

[0062] Table 2 Summary of Experimental Results

[0063] As can be seen from the table above, Experimental Examples 1 and 2, which used a two-stage distillation method, compared to the control group which used only a single-stage distillation, showed a significant improvement in the purity of carbazole, reaching 99.5% to 99.6%, an increase of 1.2% to 1.3% compared to the control group which used only a single-stage distillation. Furthermore, the yield of carbazole also showed a significant improvement, reaching 60.51% to 61.4%, an increase of 9.89% to 10.9% compared to the control group, representing an improvement rate of 19.53% to 21.53%.

[0064] The above embodiments merely illustrate several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A method for preparing high-purity carbazole, characterized in that, The process includes a distillation process, which comprises the following steps: S10. The preheated anthracite crystals are fed into a first-stage distillation column for first-stage negative pressure distillation. The light components at the top of the column are condensed and part of them are used as reflux liquid, while the other part is collected from the top of the column. The heavy components at the bottom of the column are collected. S20. The primary light component is fed into a two-stage distillation column for two-stage atmospheric distillation. After the secondary light component at the top of the column is condensed, part of it is used as secondary reflux liquid, and the other part is collected from the top of the column. The secondary heavy component at the bottom of the column is sent to the inlet of the primary distillation column. High-purity carbazole is collected through the side stream.

2. The method for preparing high-purity carbazole as described in claim 1, characterized in that, In step S10, the pressure of the negative pressure distillation section is -80 kPa to -95 kPa.

3. The method for preparing high-purity carbazole as described in claim 1, characterized in that, In step S10, the top temperature of the first-stage distillation column is 180°C to 200°C, and the bottom temperature is 280°C to 320°C.

4. The method for preparing high-purity carbazole as described in claim 1, characterized in that, In step S10, the reflux ratio of the first-stage distillation column is controlled between 0.5 and 3.

5. The method for preparing high-purity carbazole as described in claim 1, characterized in that, In step S20, the top temperature of the two-stage distillation column is 260°C to 280°C, and the bottom temperature is 350°C to 370°C.

6. The method for preparing high-purity carbazole as described in claim 1, characterized in that, In step S20, the reflux ratio of the two-stage distillation column is controlled between 0.5 and 3.

7. The method for preparing high-purity carbazole as described in claim 1, characterized in that, The distillation process is preceded by a solvent crystallization process, which includes: T10. Using anthracene oil as raw material, anthracene-carbamate crystals are obtained by crystallization using an o-xylene-m-xylene composite solvent system; in the o-xylene-m-xylene mixed solvent system, the volume ratio of o-xylene to m-xylene is 1:(0.3 to 3); the volume ratio of solvent to anthracene oil is (8 to 15):

1.

8. The method for preparing high-purity carbazole as described in claim 7, characterized in that, The solvent crystallization process is specifically as follows: T11. A crystallization apparatus is provided, wherein the anthracene oil and the solvent are fed into the crystallization apparatus; T12. Cool the anthracene oil and the solvent to a first crystallization temperature; the first crystallization temperature is 10°C to 20°C; T13. Cool the anthracene oil and the solvent to a second crystallization temperature to obtain crude anthracene crystals and crystallization mother liquor; wherein, the second crystallization temperature is 0°C to 5°C; T14. Drain the mother liquor from the crystallization solution; T15. Heat to the sweating temperature to induce sweating of the crude anthracite crystals and release sweat; the sweating temperature is 35°C to 50°C; T16. Repeat steps T11 to T15 until the crude anthracite crystals in the crystallization apparatus reach a first predetermined volume.

9. The method for preparing high-purity carbazole as described in claim 7, characterized in that, Also includes: T20. Introduce washing solution into the crystallization apparatus to wash the crude anthracite crystals at least once; T30. Input washing liquid into the crystallization device to perform N washing process on the anthracite crystals, where 2≤N≤5, wherein the liquid phase obtained from the first washing is mixed with the raw material, and the liquid phase generated from the i-th washing is used as the washing liquid for the (i-1)-th washing, where 2≤i≤N; T40. The i-th washing solution is sequentially input into the crystallization device to perform the i-1-th washing process on the anthracite crystals; T50. A solvent is introduced into the crystallization apparatus to perform the N+1 washing process on the anthracite crystals. The liquid phase obtained after washing is used as the Nth washing liquid, and the solid phase obtained after washing is used as anthracite oil. T60. After heating and melting the anthracite oil, remove it from the crystallization device.

10. The method for preparing high-purity carbazole as described in claim 9, characterized in that, In step T40, the i-th washing process includes the following steps: T41. Add the i-th washing liquid to the crystallization apparatus and heat it to 55°C to 75°C to melt the anthracite oil; T42. Cool to 10°C to 20°C to allow the anthracite oil to begin crystallizing; T43. Cool to 0°C to 5°C to allow the anthracite oil to crystallize further; T44. Exclude the uncrystallized liquid phase.

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