Method for separating carbazole from coal tar

Abstract

The invention belongs to the technical field of deep processing of coal tar, and particularly relates to a method for separating carbazole from coal tar, which adopts an o-xylene-m-xylene composite solvent system, adopts a gradient crystallization method in the crystallization process, and can obviously improve the yield of carbazole. Experiments show that by adopting the method for separating carbazole from coal tar, the yield of carbazole can reach 60% or above, especially when the volume ratio of o-xylene to m-xylene is 1: 2, the yield of carbazole is the highest and is 63.28%, the yield is averagely improved by 8.25% and the average improvement rate is 15.00% compared with a single xylene solvent in a contrast ratio.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of deep processing of coal tar, and particularly relates to a method for separating carbazole from coal tar. BACKGROUND

[0002] Carbazole is one of the components with the highest economic value in coal tar, and is an important intermediate for the synthesis of fine chemicals, which can be used in the production fields of fuels, pigments, pesticides, medicines, optoelectronic new materials, special inks and synthetic resins. 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.

[0003] At present, the processes for producing refined anthracene and carbazole at home mainly include solvent washing crystallization, solvent crystallization-distillation, and distillation-solvent method. The solvent crystallization-distillation method is a relatively mature and advanced method for purifying and refining carbazole from coal tar products, and is represented by the technology of the French BEFS company, which can directly process anthracene oil as raw material. The solvent crystallization-distillation method is divided into solvent crystallization (intermittent operation) and distillation (continuous operation) two parts. The key step is solvent crystallization, which adopts the PROABD stepwise directional crystallization process, and the core equipment is the crystallization tank of the BEFS company's patented technology. The heat transfer efficiency is greatly enhanced by the special structure of the tube type crystallization tank, and the temperature difference in the tank is minimized. The crystallization separation efficiency is high, which can fully guarantee the product quality and yield.

[0004] In the prior art, the Chinese invention patent with the application number 202210369549.2 discloses a refined carbazole production method and production system. The method includes a solvent crystallization process and a distillation 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 for the N-1th washing process. The last time is washed with raw material toluene to realize multiple continuous washing of anthracene carbazole crystallization. Xylene is used as a solvent, and the final carbazole yield is 55% to 59%, which is relatively low. The liquid phase produced in the 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 for the N-1th washing process. The last time is washed with raw material toluene to realize multiple continuous washing of anthracene carbazole crystallization. Xylene is used as a solvent, and the final carbazole yield is 55% to 59%, which is relatively low. SUMMARY

[0005] Therefore, based on this, the application provides a method for separating carbazole from coal tar to solve the technical problem of low yield of refined carbazole prepared by the solvent crystallization-distillation method in the prior art.

[0006] The technical solution of the application for solving the above technical problem is as follows: A method for separating carbazole from coal tar, comprising a solvent crystallization process, the solvent crystallization process comprising: S10. Crystallizing the crude anthracene quinoline crystals from the anthracene oil using an o-xylene-m-xylene mixed solvent system as the solvent; wherein the volume ratio of o-xylene to m-xylene in the o-xylene-m-xylene mixed solvent system is 1: (0.3 to 3).

[0007] Preferably, in the method for separating quinoline from coal tar, the volume ratio of o-xylene to m-xylene in the o-xylene-m-xylene mixed solvent system is 1: (0.5 to 2).

[0008] Preferably, in the method for separating quinoline from coal tar, the volume ratio of o-xylene to m-xylene in the o-xylene-m-xylene mixed solvent system is 1:2.

[0009] Preferably, in the method for separating quinoline from coal tar, the volume ratio of the solvent to the anthracene oil is (8 to 15):1.

[0010] Preferably, in the method for separating quinoline from coal tar, step S10 is specifically: S11. Providing a crystallization device and feeding the anthracene oil and the solvent into the crystallization device; S12. Cooling the anthracene oil and the solvent to a first crystallization temperature; S13. Cooling the anthracene oil and the solvent to a second crystallization temperature to obtain crude anthracene quinoline crystals and a crystallization mother liquor; wherein the second crystallization temperature < the first crystallization temperature; S14. Discharging the crystallization mother liquor; S15. Heating to a sweating temperature to make the crude anthracene quinoline crystals sweat and discharge the sweat; S16. Repeating steps S11 to S15 until the crude anthracene quinoline crystals in the crystallization device reach a first predetermined volume.

[0011] Preferably, in the method for separating quinoline from coal tar, the first crystallization temperature is 10°C to 20°C and the second crystallization temperature is 0°C to 5°C.

[0012] Preferably, in the method for separating quinoline from coal tar, in step S15, the sweating temperature is 35°C to 50°C.

[0013] Preferably, the method for separating quinoline from coal tar further comprises: S20. Inputting a washing liquid into the crystallization device to wash the crude anthracene quinoline crystals at least once.

[0014] Preferably, the method for separating quinoline from coal tar further comprises: S30. Inputting a washing liquid into the crystallization device, performing an N-th washing process on the crude carbazole crystals, 2≤N≤5, wherein the liquid phase obtained from the first washing is mixed with the raw material, the liquid phase obtained from the i-th washing is used as the washing liquid for the (i-1)-th washing, 2≤i≤N; S40. Inputting an i-th washing liquid into the crystallization device in sequence, performing an (i-1)-th washing process on the crude carbazole crystals; S50. Inputting a solvent into the crystallization device, performing an (N+1)-th washing process on the crude carbazole crystals, using the liquid phase obtained from the washing as the N-th washing liquid, and using the solid phase obtained after the washing as the carbazole crystals; S60. Discharging the crystallization device after the carbazole crystals are heated and melted.

[0015] Preferably, in the method for separating carbazole from coal tar, the N-th washing process in step S40 comprises the following steps: S41. Adding the N-th washing liquid into the crystallization device, and heating to 55-75℃ to melt the carbazole oil; S42. Cooling to 10-20℃ to preliminarily crystallize the carbazole oil; S43. Cooling to 0-5℃ to further crystallize the carbazole oil; S44. Discharging the liquid phase that has not been crystallized.

[0016] Compared with the prior art, the present application has at least the following advantages: In the method for separating carbazole from coal tar, the use of the o-xylene-m-xylene composite solvent system can significantly improve the yield of carbazole. Experiments show that the yield of carbazole is significantly improved by using the method for separating carbazole from coal tar. When the volume ratio of o-xylene to m-xylene is 1: (0.5-2), 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, reaching 63.28%, which is 8.25% higher than the average of the single xylene solvent used in the comparative example, and the average increase rate is 15.00%. During the entire washing process, when the liquid phase obtained from the i-th washing is recovered and used as the washing liquid for the (i-1)-th washing, the yield of carbazole can be further improved, reaching 66.76%, which is 11.76% higher than the average of the comparative example, and the increase rate is 21.38%. DETAILED DESCRIPTION

[0017] 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.

[0018] 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 describing specific embodiments only and is not intended to be limiting. As used in this document, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0019] In an embodiment of the present application, a method for separating carbazole from coal tar comprises a solvent crystallization process, the solvent crystallization process comprising: S10. Crude anthracene carbazole crystals are obtained by crystallization using an anthracene oil as a raw material and an o-xylene-m-xylene composite solvent system as a solvent, wherein the volume ratio of o-xylene to m-xylene in the o-xylene-m-xylene mixed solvent system is 1:(0.3 to 3).

[0020] In the technical solution of the present application, the anthracene oil is produced in the process of producing various coal chemical products from coal tar, and its components include 6.5% to 8.3% anthracene, 4.0% to 5.2% carbazole, 23.6% to 27.8% phenanthrene, and 3.6% to 5.4% naphthalene. The o-xylene-m-xylene composite solvent system used in the present application can significantly improve the yield of carbazole compared to a single raw material solvent. Experiments show that when the volume ratio of o-xylene to m-xylene is 1:2, the yield of carbazole is the highest, reaching 63.28%, which is 8.25% higher than the average yield of the comparative examples using single xylene solvent, and the average increase rate is 15.00%.

[0021] Preferably, the volume ratio of o-xylene to m-xylene in the o-xylene-m-xylene mixed solvent system is 1:(0.5 to 2), and further 1:2.

[0022] Preferably, the volume ratio of the solvent to the anthracene oil is (8 to 15):1. Compared with the prior art, the present application uses less solvent to obtain a better yield of carbazole, which is beneficial to reduce the production cost.

[0023] In an embodiment of the present application, the method for separating carbazole from coal tar described above, the step S10 is specifically: S11. A crystallization device is provided, and the anthracene oil and the solvent are fed into the crystallization device; S12. The anthracene oil and the solvent are cooled to a first crystallization temperature; S13. The anthracene oil and the solvent are cooled to a second crystallization temperature to obtain crude anthracene carbazole crystals and a crystallization mother liquor; wherein the second crystallization temperature < the first crystallization temperature; S14. The crystallization mother liquor is discharged; S15. warming to sweating temperature to sweat the crude carbazole crystals and discharge the sweat; S16. repeating steps S11 to S15 until the crude carbazole crystals in the crystallization device reach a first predetermined volume.

[0024] Specifically, a crystallization device is provided, which can be a crystallizer with fins or tubes inside. Batch feeding of anthracene oil and solvent into the crystallization device is performed, and the crystals are cooled and crystallized, and then the mother liquor is discharged. Then the temperature is raised for sweating, and after the sweat is discharged, crude carbazole crystals are obtained. The above process is referred to as the feeding process. The above process is repeated about 6-8 times until the crude carbazole crystals reach the preset capacity of the crystallization device, and the feeding is stopped. This process is referred to as the feeding and supplementing process.

[0025] The "feeding and supplementing process" is specifically as follows: anthracene oil and solvent are fed into the crystallization device, and first cooled to a first crystallization temperature for preliminary crystallization. Preferably, the first crystallization temperature is 10-20°C. Then the anthracene oil and solvent are cooled to a second crystallization temperature for deep crystallization. Preferably, the second crystallization temperature is 0-5°C. After crystallization, the mother liquor is discharged, and the temperature is raised to a sweating temperature to make the carbazole crystals sweat and discharge the sweat. Preferably, the sweating temperature is 35-50°C. The above process is referred to as the feeding process. After the feeding process is completed, the generated carbazole crystals are left in the crystallization device, and anthracene oil and solvent continue to be fed into the crystallization device, and the above process is repeated until the last sweating is completed, and the crude carbazole crystals in the crystallization device reach a predetermined volume (first predetermined volume), and the supplementing process is completed.

[0026] In one embodiment, the medium for cooling the anthracene oil and solvent to the first crystallization temperature, and for cooling the crystallization material A to the second crystallization temperature is tetrahydronaphthalene.

[0027] In some cases, steps S12 to S14 can be repeated until the crude carbazole crystals in the crystallization device reach a predetermined volume, and then directly enter the S20 process. In some cases, sweating can not be performed in the later stage of supplementing, so as to ensure the yield of carbazole. That is, when the volume of carbazole in the crystallization device reaches the first predetermined volume, only steps S12 to S14 are repeated, and sweating is not performed, so that the crude carbazole crystals in the crystallization device reach a second predetermined volume.

[0028] It is worth noting that in the technical solution provided by the present application, two-step cooling crystallization is adopted. First, the anthracene oil and solvent are cooled to 10-20°C and kept for a period of time, so that the crude carbazole crystals are formed and grown. Then the anthracene oil and solvent are further cooled to 0-5°C, so that the crude carbazole crystals grow, thereby facilitating the increase of the yield of carbazole.

[0029] S20. Input washing liquid into the crystallization device to wash the crude carbazole crystals at least once.

[0030] After the feeding and supplementing process is completed, the crude carbazole crystals in the crystallization device are washed to reduce the content of phenanthrene in the final obtained carbazole oil as much as possible, thereby improving the purity of carbazole. The washing liquid is preferably the same substance as the solvent, and the washing is performed a total of 2 to 5 times. The liquid phase generated in the process is directly mixed with the raw material, anthracene oil, and then recycled, thereby reducing the loss of carbazole and improving the yield of carbazole.

[0031] In another specific embodiment of the present application, the following is further included: S30. Input washing liquid into the crystallization device to perform N washing processes on the crude carbazole crystals, 2≤N≤5, wherein the liquid phase obtained in the first washing is mixed with the raw material, and the liquid phase generated in the i-th washing is used as the washing liquid for the (i-1)-th washing, 2≤i≤N; wherein the first washing process is repeated 2 to 3 times, the first washing liquid for the first washing is from the liquid phase generated in the second washing process, and the liquid phase generated in the washing process is directly mixed with the anthracene oil and then recycled as the raw material.

[0032] S40. Input the i-th washing liquid into the crystallization device in sequence to perform the (i-1)-th washing process on the crude carbazole crystals; In the entire washing process, the liquid phase generated in the i-th washing is used as the washing liquid for the (i-1)-th washing, thereby on the one hand, the carbazole lost with the solvent can be crystallized again to improve the yield of carbazole, and on the other hand, the carbazole lost with the solvent is finally used as the raw material oil, further reducing the loss of carbazole and improving the yield of carbazole. It should be noted that under the guidance of the technical solution of the present application, those skilled in the art can understand that by increasing the number of single-step solvent crystallization, the purity of the prepared refined carbazole can be further improved, and the yield of carbazole will not be greatly affected.

[0033] As a preferred, the i-th washing process includes the following steps: S41. Add the i-th washing liquid into the crystallization device, and heat to 55°C to 75°C to melt the carbazole oil; S42. Cool to 10°C to 20°C to preliminarily crystallize the carbazole oil; S43. Cool to 0°C to 5°C to further crystallize the carbazole oil; S44. Remove the uncrystallized liquid phase.

[0034] The N+1 washing process, i.e. the last washing process, uses solvent as the washing liquid to further reduce the content of phenanthrene and the like in carbazole and improve the purity of carbazole. As preferred, after the last washing process, the content of phenanthrene in the anthracene carbazole oil obtained is ≤0.5%.

[0035] S50. Inputting raw material solvent into the crystallization device, performing the N+1 washing process on the crude anthracene carbazole crystal, and taking the obtained liquid phase as the N washing liquid and the obtained solid phase as the anthracene carbazole crystal after washing; S60. After the anthracene crystal is heated and melted, the crystallization device is discharged.

[0036] The anthracene carbazole oil obtained after the washing process is heated and melted, and the crystallization device is discharged for rectification.

[0037] For example, the above steps S30 to S60 perform the following steps: after the feeding and replenishing process is completed, a proper amount of the first washing liquid is first added into the crystallization device, the crude anthracene carbazole crystal is heated and melted, and is fully mixed, and then is cooled and crystallized, after the crystallization is completed, the liquid phase is discharged, and the discharged liquid phase is taken as the raw material anthracene oil. After the first washing process is repeated once, a proper amount of the second washing liquid is added into the crystallization device, the crude anthracene carbazole crystal is heated and melted, and is fully mixed, and then is cooled and crystallized, after the crystallization is completed, the liquid phase is discharged, and the discharged liquid phase is taken as the first washing liquid. After the second washing process is completed, a proper amount of the third washing liquid is added into the crystallization device, the crude anthracene carbazole crystal is heated and melted, and is fully mixed, and then is cooled and crystallized, after the crystallization is completed, the liquid phase is discharged, and the discharged liquid phase is taken as the second washing liquid. After the third washing process is completed, a proper amount of the fourth washing liquid is added into the crystallization device, the crude anthracene carbazole crystal is heated and melted, and is fully mixed, and then is cooled and crystallized, after the crystallization is completed, the liquid phase is discharged, and the discharged liquid phase is taken as the third washing liquid. After the fourth washing process is completed, a proper amount of the solvent o-xylene-m-xylene is added into the crystallization device, the anthracene carbazole crystal is heated and melted, and is fully mixed, and then is cooled and crystallized, after the crystallization is completed, the liquid phase is discharged, and the discharged liquid phase is taken as the fourth washing liquid.

[0038] It is worth mentioning that in the above embodiments, the process temperature and the process time involved are all a temperature or a time adopted in the experiment, and those skilled in the art can make reasonable adjustments within the error range on the basis of the process temperature and the process time provided by the present application, which should be included in the protection scope of the present application.

[0039] The technical solutions and technical effects of the present application are further illustrated by specific experimental examples below.

[0040] 1. Main reagents In the embodiment of the present application, the anthracene oil is produced in the process of producing various coal chemical products by Ningxia Xitai Coal Chemical Co., Ltd. using coal tar as raw material. The components of the anthracene oil include 7.4% anthracene, 4.6% carbazole, 25.7% phenanthrene, and 4.5% naphthalene. Other reagents and solvents are commercially available and can be used without further purification.

[0041] 2, Comparative Example 1 The feeding and supplementing process is as follows: 200 ml (224 g) of the anthracene oil is taken and mixed with 2000 ml of o-xylene (solvent) and then fed into a crystallization reactor. First, the temperature is lowered to 15°C and kept for 1 h, and then the temperature is lowered to 5°C and kept for 1 h. The crystallization mother liquor is discharged, and then the temperature is raised to 45°C for sweating. The above process is repeated 7 times, and the last two times do not have sweating. The solvent crystallization process is as follows: the solvent o-xylene is added to the crystallization reactor for the washing process. The temperature is raised to 60°C to melt the crude anthracene carbazole crystals. First, the temperature is lowered to 15°C and kept for 1 h, and then the temperature is lowered to 5°C and kept for 1 h, and the liquid phase is discharged. The above washing process is repeated three times, and the crude anthracene carbazole crystals are washed three times. The anthracene carbazole crystals after the third washing are collected.

[0042] 3, Comparative Example 2

[0043] The other conditions are kept the same as in Comparative Example 1, and m-xylene is used as the solvent.

[0044] The components in the anthracene carbazole crystals are analyzed by gas chromatography. The anthracene carbazole crystals after the third washing are measured, and the yield of carbazole in the anthracene carbazole crystals is calculated. The calculation method is shown in the following formula:

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

[0046] Table 1: Test results of comparative examples

[0047] Comparative Example 1 and Comparative Example 2 use a single xylene solvent, and the quality of the obtained anthracene carbazole crystals is comparable, and the yield of carbazole is about 55%, which is relatively low.

[0048] 4, Experimental Example 1 The other conditions are kept the same as in Comparative Example 1, and the o-xylene-m-xylene composite solvent system is used as the solvent, and the volume ratio of o-xylene to m-xylene is shown in the following table.​

[0049] The components in the anthracene carbazole crystals were analyzed by gas chromatography, the anthracene carbazole crystals after the third washing were measured, and the yield of carbazole in the anthracene carbazole crystals was calculated.

[0050] Table 2 Test Example 1 test results

[0051] As shown in the above table, the raw material solvent is 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, which is 63.28%, which is 8.25% higher than the average of the single xylene solvent used in the comparative example, and the average increase rate is 15.00%.

[0052] 4. Test Example 2 The other conditions were kept the same as in Test Example 1, and the conditions of the feeding and the feeding process were unchanged.

[0053] In the early stage of production, the liquid phase produced in the first washing process in Test Example 1 was collected and discharged into the raw material anthracene oil, the liquid phase produced in the second washing process was used as the first washing liquid, and the liquid phase produced in the third washing process was used as the second washing liquid.

[0054] In the subsequent production process, the first washing liquid was first used to wash the crude anthracene carbazole crystals, the liquid phase produced was discharged into the raw material anthracene oil, then the second washing liquid was used to wash the crude anthracene carbazole crystals, the liquid phase produced was used as the first washing liquid, and finally the solvent was used to wash the crude anthracene carbazole crystals, and the liquid phase produced was used as the second washing liquid.

[0055] The components in the anthracene carbazole crystals were analyzed by gas chromatography, and the yield of carbazole in the anthracene carbazole crystals was calculated.

[0056] Table 3 Test Example 2 test results

[0057] As shown in the above table, in the entire washing process, when the liquid phase produced in the i-th washing is recovered as the washing liquid for the i-1-th washing, the yield of carbazole can be further improved, which can reach 66.76%, which is 11.76% higher than the average of the comparative example, and the increase rate is 21.38%.

[0058] The above embodiments only express several implementation ways of the present application, and the description is specific and detailed, but it should not be understood as a limitation to the patent scope of the application. It should be pointed out that for ordinary skilled in the art, without departing from the concept of the present application, several modifications and improvements can be made, which all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application should be subject to the appended claims.

Claims

1. A method for separating carbazole from coal tar, characterized by, The solvent crystallization process comprises: S10. Crude anthracene is obtained by crystallization of anthracene oil 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).

2. The method for separating carbazole from coal tar as described in claim 1, characterized in that, The volume ratio of o-xylene to m-xylene in the mixture of o-xylene and m-xylene is 1: (0.5-2).

3. The method for separating carbazole from coal tar as described in claim 2, characterized in that, The volume ratio of o-xylene to m-xylene in the mixture of o-xylene and m-xylene is 1:

2.

4. The method for separating carbazole from coal tar as described in claim 1, characterized in that, The volume ratio of the solvent to the anthracene oil is (8-15):

1.

5. The method for separating carbazole from coal tar as described in claim 1, characterized in that, The step S10 specifically comprises: S11. A crystallization device is provided, and the anthracene oil and the solvent are fed into the crystallization device; S12. The anthracene oil and the solvent are cooled to a first crystallization temperature; S13. The anthracene oil and the solvent are cooled to a second crystallization temperature to obtain crude anthracene crystals and a crystallization mother liquor, wherein the second crystallization temperature is lower than the first crystallization temperature; S14. The crystallization mother liquor is discharged; S15. The temperature is raised to a sweating temperature to make the crude anthracene crystals sweat, and the sweat is discharged; S16. The steps S11-S15 are repeated until the crude anthracene crystals in the crystallization device reach a first predetermined volume.

6. The method of separating carbazole in coal tar according to claim 5, wherein The first crystallization temperature is 10-20°C, and the second crystallization temperature is 0-5°C.

7. The method for producing precarbazole according to claim 5, wherein In step S15, the sweating temperature is 35-50°C.

8. The process for separating carbazole from coal tar as claimed in claim 1 wherein, Further comprising: S20. A washing liquid is input into the crystallization device to wash the crude anthracene crystals at least once.

9. The process for separating carbazole from coal tar as claimed in claim 1 wherein, Further comprising: S30. A washing liquid is input into the crystallization device to wash the crude anthracene crystals for N times, 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, 2≤i≤N; S40. The (i-1)-th washing liquid is input into the crystallization device in sequence to wash the crude anthracene crystals; S50. A solvent is input into the crystallization device to wash the crude anthracene crystals for the (N+1)-th time, and the liquid phase obtained by the washing is used as the washing liquid for the N-th washing, and the solid phase obtained after the washing is used as anthracene crystals; S60. After the anthracene crystals are heated and melted, the crystallization device is discharged.

10. The method for separating carbazole from coal tar as described in claim 9, characterized in that, In step S40, the i-th washing process comprises the following steps: S41. The i-th washing liquid is added to the crystallization device, and the temperature is raised to 55-75°C to melt the anthracene oil; S42. The temperature is lowered to 10-20°C to preliminarily crystallize the anthracene oil; S43. The temperature is lowered to 0-5°C to further crystallize the anthracene oil; S44. The liquid phase that is not crystallized is discharged.

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