Method for separating naphthalene and indane from mixture of naphthalene and indane

Abstract

According to the method for separating the naphthalene and the indane from the mixture of the naphthalene and the indane, the indane product can be obtained from the mixture of the naphthalene and the indane, meanwhile, the refined naphthalene can be co-produced, and the obtained indane product and the refined naphthalene product have good yield and purity. The method comprises the following steps: 1) mixing a mixture of naphthalene and indane with a solvent, then crystallizing the obtained mixed solution, and carrying out solid-liquid separation on the obtained crystallized solution to obtain an impurity-removed mixture of naphthalene and indane, and 2) heating and melting the impurity-removed mixture of naphthalene and indane, and then removing the solvent entrained in the mixture to obtain an impurity-removed mixture of naphthalene and indane; obtaining a mixture of naphthalene and indane without the solvent; 3) taking ethylene glycol as an entrainer, carrying out azeotropic distillation on the mixture of naphthalene and indane without the solvent, and separating to obtain an indane material and a mixed material of naphthalene and the entrainer; and 4) mixing and washing the mixed material of the naphthalene and the entrainer with water, and then performing phase splitting to obtain a light phase component rich in naphthalene.

Description

Technical Field

[0001] The invention relates to a separation technology of naphthalene and thionaphthene, and in particular to a method for separating naphthalene and thionaphthene from a mixture of naphthalene and thionaphthene. Background Art

[0002] Thianaphthene is also known as benzothiophene, with a molecular weight of 134.20, a melting point of 31.3°C, a boiling point of 219.9°C, and is insoluble in water, but soluble in organic solvents such as ethanol, ether, acetone, and benzene. Thianaphthene is an important fine chemical raw material, widely used in the fields of medicine, pesticides, optical materials, and dyes, and is mainly used in the preparation of fungicides, insecticides, herbicides, housefly killers, plant growth hormone raw materials, synthetic dye raw materials, and other intermediates of thiaphthene derivatives.

[0003] Refined naphthalene, with a molecular weight of 128.16, a melting point of 80.1°C, and a boiling point of 217.9°C, is insoluble in water, but soluble in organic substances such as benzene, ether, and anhydrous ethanol. Refined naphthalene is widely used in the preparation of fine chemical products such as water reducers, phthalic anhydride, naphthoquinone, naphthol, dye diffusers, and dye intermediates.

[0004] The thionaphthene resources in tar are mainly concentrated in the naphthalene fraction after tar distillation. The naphthalene residue oil after the industrial naphthalene melt crystallization method is used to produce refined naphthalene contains 10-15% thionaphthene. Due to the difficulty in separation, this part of naphthalene residue oil is generally used as fuel oil, wasting precious naphthalene and thionaphthene resources.

[0005] Since thionaphthene and naphthalene have similar boiling points, it is very difficult to separate and purify thionaphthene using ordinary distillation methods.

[0006] CN101747317A discloses a method for enriching thionaphthene from a mixture containing thionaphthene and naphthalene. The method uses diol as a solvent, enriches thionaphthene in the diol, and recovers the diol to obtain an enriched thionaphthene fraction. In the embodiment, the thionaphthene content of the enriched thionaphthene fraction does not exceed 30%, and a high-purity thionaphthene product cannot be obtained.

[0007] CN114315792A discloses a method for enriching thionaphthene from a mixture containing thionaphthene and naphthalene by a solvent crystallization coupled extraction and distillation method. The method uses triethylene glycol, tetraethylene glycol, MDEA and other solvents to extract thionaphthene from the mixture of thionaphthene and naphthalene, and then extracts and distills to obtain a thionaphthene fraction. In the embodiment, the maximum content of thionaphthene in the extraction and distillation fraction does not exceed 50%, and the purity of thionaphthene is still not high.

[0008] CN108558591B discloses a naphthalene residual oil separation and recovery method, wherein the light components are removed by a light removal tower, the bottom materials of the light removal tower are sent to a naphthalene removal tower, naphthalene and thionaphthene are separated by the naphthalene removal tower, the naphthalene components are obtained at the top of the naphthalene removal tower, the bottom materials are sent to a benzothiophene tower, the top components of the benzothiophene tower are sent to a static crystallizer, and the thionaphthene products are obtained by crystallization in the static crystallizer. In this method, naphthalene and thionaphthene are separated by ordinary distillation of the naphthalene removal tower, the energy consumption is high, and the naphthalene content of the naphthalene removal tower top discharge material is only 85.6%; the benzothiophene tower bottom discharge material is a byproduct, and its benzothiophene content is as high as 29.2%, and the thionaphthene recovery rate is low, only reaching 70%.

[0009] CN115504960A discloses a method for extracting thionaphthene from naphthalene residual oil, which uses naphthalene residual oil after preparing refined naphthalene by melting and crystallizing industrial naphthalene as raw material, firstly adopts a double solvent extraction method, utilizes the different distribution coefficients of naphthalene and thionaphthene in solvent ether and ethanolamine, dissolves naphthalene in ether, and dissolves thionaphthene in ethanolamine, realizes the preliminary separation of naphthalene and thionaphthene; then utilizes the azeotropic property of naphthalene and ethanolamine, performs intermittent azeotropic distillation on the ethanolamine solution of thionaphthene, makes ethanolamine and a small amount of naphthalene in the solution azeotropically distill out first, then obtains thionaphthene fraction, and washes the thionaphthene fraction with ether to obtain 98% thionaphthene product. The embodiment of this method shows that the recovery rate of thionaphthene is only 75.3%. Summary of the invention

[0010] The invention provides a method for separating naphthalene and thionaphthene from a mixture of naphthalene and thionaphthene. The method can obtain a thionaphthene product from the mixture of naphthalene and thionaphthene, and can also co-produce refined naphthalene, and is conducive to obtaining a thionaphthene product and a refined naphthalene product with good yield and purity.

[0011] To achieve the purpose, the present invention provides the following technical solutions:

[0012] The present invention provides a method for separating naphthalene and thionaphthene from a mixture of naphthalene and thionaphthene, the method comprising the following steps:

[0013] 1) mixing the mixture of naphthalene and thiophanate with a solvent, then crystallizing the obtained mixed solution, and performing solid-liquid separation on the obtained crystal solution to obtain a mixture of naphthalene and thiophanate from which impurities are removed; the solvent is n-butanol;

[0014] 2) heating and melting the mixture of the naphthalene and thionaphthene of the impurity removal, and then removing the solvent carried secretly therein to obtain the mixture of naphthalene and thionaphthene of the removal of solvent;

[0015] 3) taking ethylene glycol as entrainer, the mixture of naphthalene and thionaphthene of the desolvation is subjected to azeotropic distillation, and separation obtains the mixture of thionaphthene material and naphthalene and entrainer;

[0016] 4) mixing and washing the mixture of the naphthalene and the entrainer with water, and then carrying out phase separation with the obtained mixed solution to obtain a light phase component rich in naphthalene.

[0017] In the present invention, n-butanol is first used as a solvent to mix with a mixture of naphthalene and thionaphthene, and then crystallization is performed, which is beneficial to removing impurities (such as dimethylphenol, etc.) carried therein, and then the crystallized product is heated and melted, the solvent is removed, and ethylene glycol is used for azeotropic distillation, so that thionaphthene and naphthalene can be separated more efficiently and thoroughly, and subsequently the thionaphthene product can be obtained by simple drying, and the refined naphthalene product can be obtained by washing with water and phase separation.

[0018] In some embodiments, in step 1), the mixture of naphthalene and thionaphthene is industrial naphthalene, or a naphthalene fraction after tar distillation separation, or a naphthalene residual oil after melt crystallization of the industrial naphthalene or the naphthalene fraction. In some embodiments, in step 1), the thionaphthene content in the mixture of naphthalene and thionaphthene is 10-15wt%, the naphthalene content is 80-85wt%, and it also contains impurities such as dimethylphenol. By the method of the present invention, high-quality refined naphthalene products and thionaphthene products can be obtained synchronously from this type of naphthalene and thionaphthene mixture.

[0019] In a preferred embodiment, in step 1), the mass ratio of the solvent to the mixture of naphthalene and thiophanate is 1:1 to 4:1, preferably 1.5 to 3:1, for example 1.5:1, 2:1, 2.5:1, 3:1, etc. The preferred mass ratio is used for mixing and then cooling and crystallizing, which is conducive to more complete and thorough removal of impurities. If the mass ratio is too low, some impurities will precipitate during the crystallization process, which may cause incomplete removal of impurities; if the mass ratio is too high, the cooling and crystallization refrigeration energy consumption is high, and it is easy to cause increased losses of the target products thiophanate and naphthalene during the crystallization process, and the energy consumption of solvent recovery is also high.

[0020] In a preferred embodiment, in step 1), the crystallization temperature for crystallization is 8-30°C, preferably 10-25°C (for example, 10, 15, 20, 25°C, etc.); the crystallization time is 15-45min, preferably 20-40min (for example, 20, 25, 30, 35, 40min, etc.). Preferably, when performing the crystallization, the temperature is lowered to the crystallization temperature at a cooling rate of 1-3°C / min (for example, 1°C / min, 2°C / min, 3°C / min, etc.) for crystallization. The preferred cooling crystallization conditions are used to facilitate the full crystallization and precipitation of the target products thionaphthene and naphthalene, as well as the removal of impurities, and to facilitate the acquisition of thionaphthene and refined naphthalene products with high purity and product recovery rate.

[0021] In a preferred embodiment, in step 2), the temperature for heating and melting is 82-90°C, for example, 82, 84, 85, 86, 88, 90°C, etc.

[0022] In a preferred embodiment, in step 2), the removed solvent is recycled as the solvent required for the mixing in step 1).

[0023] Preferably, in step 2), the entrained solvent is removed by distillation separation. The conditions for distillation separation are not particularly limited, and those skilled in the art can determine the required conditions according to the needs of separating the solvent. In one embodiment, the conditions for distillation separation are, for example: the top pressure of the distillation tower is 22 kPa, the top temperature is 80° C., and the reflux ratio is 0.8.

[0024] In some embodiments, in step 1), the solid-liquid separation may be performed by filtration separation, for example, the crystallization liquid is sent to a filter for solid-liquid separation, and the obtained filter cake (ie, the solid phase component) is a mixture of naphthalene and thionaphthene from which impurities have been removed.

[0025] The inventors have found that ethylene glycol and naphthalene can form a minimum azeotrope, and naphthalene and thionaphthene can be effectively separated through azeotropic distillation. In a preferred embodiment, in step 3), the mass ratio of the amount of the entrainer to the mixture of naphthalene and thionaphthene from which the solvent is removed is 0.53 to 0.62:1, preferably 0.55 to 0.62:1, more preferably 0.55 to 0.60:1 (e.g. 0.55:1, 0.56:1, 0.57:1, 0.58:1, 0.59:1, 0.60:1, etc.). The preferred mass ratio is used to facilitate ethylene glycol and naphthalene to form an azeotrope at the top of the tower, to facilitate obtaining a thionaphthene product of higher purity in the tower bottom, and to avoid causing higher energy consumption. If the mass ratio is too low, the amount of residual naphthalene in the bottom product may increase, resulting in a decrease in the purity of the bottom thionaphthene product; if the mass ratio is too high, although the bottom product can obtain a high-purity thionaphthene product, energy consumption is increased because ethylene glycol also needs to be distilled out of the bottom product.

[0026] In a preferred embodiment, in step 3), the conditions for performing the azeotropic distillation include: the top pressure of the azeotropic distillation tower is 5 to 15 kPa, the top temperature is 110 to 125° C., and the reflux ratio is 5 to 10. The preferred azeotropic distillation conditions are beneficial to the efficient separation of naphthalene and thionaphthene, and to the acquisition of high-purity, high-recovery refined naphthalene products and thionaphthene products.

[0027] In a preferred embodiment, in step 4), the mass ratio of the water to the mixture of the naphthalene and the entrainer is 0.8 to 1.5:1, for example, 0.8:1, 1.0:1, 1.2:1, 1.4:1, 1.5:1, etc.; in step 4), the temperature for phase separation is 80 to 85°C, for example, 80°C, 82°C, 84°C, 85°C, etc. The preferred washing and phase separation conditions are used to further improve the recovery rate of naphthalene and the recovery rate of ethylene glycol entrainer; if the mass ratio is relatively low, the aqueous phase may be difficult to fully dissolve and recover the ethylene glycol entrainer; and if the mass ratio is relatively high, more naphthalene will be dissolved in the aqueous phase, resulting in a reduced recovery rate of naphthalene; when the phase separation temperature is high, the evaporation loss of naphthalene will increase, and when the temperature is low, naphthalene may crystallize and precipitate. In step 4), a light phase component and a heavy phase component are obtained by phase separation, wherein the light phase component is a component rich in naphthalene, and the heavy phase component is mainly a mixture of water and entrainer.

[0028] Preferably, in step 4), the temperature of the water used for the washing is 70-80°C, for example, 70°C, 72°C, 75°C, 77°C, 80°C, etc. The preferred washing water temperature is used to obtain a preferred temperature of the mixture required for phase separation in the phase separator, so that naphthalene and the entrainer are phase-separated under milder conditions. If the water temperature is high, the evaporation loss of naphthalene will increase. If the water temperature is low, naphthalene may crystallize.

[0029] In some embodiments, in step 3), the thionaphthene material is cooled to obtain a thionaphthene product, for example, cooled to 40° C. to obtain a thionaphthene product;

[0030] In step 4), the naphthalene-rich light phase component is dried to obtain a refined naphthalene product, for example, by drying at 40 kPa and 95° C. to obtain a refined naphthalene product.

[0031] In some preferred embodiments, in step 1), the mass ratio of the solvent to the mixture of naphthalene and thionaphthene is 1.5 to 3:1, the crystallization temperature for crystallization is 10 to 25°C, and the crystallization time is 20 to 40 minutes; in step 3), the mass ratio of the amount of the entrainer to the mixture of naphthalene and thionaphthene from which the solvent is removed is 0.55 to 0.60:1. The above preferred method is used to separate naphthalene and thionaphthene from the mixture of naphthalene and thionaphthene, and can give consideration to obtaining refined naphthalene products and thionaphthene products with higher purity and yield.

[0032] The technical solution provided by the present invention has the following beneficial effects:

[0033] (1) The method of the present invention is adopted to first mix a mixture of naphthalene and thionaphthene with a n-butanol solvent for crystallization and impurity removal, and then carry out azeotropic distillation with ethylene glycol after solvent removal to separate thionaphthene material and a mixture of naphthalene and an entrainer, wherein the mixture of naphthalene and the entrainer can obtain a refined naphthalene product after washing and phase separation; the method of the present invention can separate a thionaphthene product and refined naphthalene with good yield and purity from the mixture of naphthalene and thionaphthene. In a preferred embodiment, by further optimizing the process conditions, the yield and purity of the thionaphthene product and refined naphthalene can be further improved.

[0034] (2) The method of the present invention has the characteristics of simple process flow, required operating conditions and temperature, good product quality, etc., and the process operation and control are simple and easy. DETAILED DESCRIPTION

[0035] In order to facilitate the understanding of the present invention, the present invention will be further described below in conjunction with examples. It should be understood that the following examples are only for a better understanding of the present invention and do not mean that the present invention is limited to the following examples.

[0036] Where specific experimental steps or conditions are not specified in the examples, the corresponding conventional experimental steps or conditions in the art can be used. The reagents or instruments used without specifying the manufacturer are all conventional products that can be purchased commercially.

[0037] Thianaphthene purity detection method: quantitative analysis by GC-MS.

[0038] Purity detection method of refined naphthalene: quantitative analysis by GC-MS.

[0039] The calculation formula of the yield of thionaphthene is: the mass of thionaphthene in the refined thionaphthene product / the mass of thionaphthene contained in the crystallization residual oil*100%;

[0040] The calculation formula of refined naphthalene yield is: the mass of naphthalene contained in the refined naphthalene product / the mass of naphthalene contained in the crystallization residual oil*100%.

[0041] Example 1

[0042] The mixture of naphthalene and thiophanate used in this example is the residual oil obtained by crystallization after extracting refined naphthalene from the naphthalene fraction obtained from a tar processing device through melt crystallization. The raw material contains 12.68wt% of thiophanate, 83.28wt% of naphthalene, and 4.04wt% of impurities such as dimethylphenol.

[0043] Naphthalene and thionaphthene are separated from the above-mentioned crystallization residual oil according to the following steps:

[0044] 1) mixing n-butanol solvent and crystallization residual oil in a mass ratio of 1.9:1 to obtain a mixed solution at 53.5° C.; then crystallizing the obtained mixed solution, wherein the crystallization conditions include: cooling at a rate of 2° C. / min, cooling to 20° C. for crystal growth, and a crystal growth time of 30 min; filtering the obtained crystal solution for solid-liquid separation, and obtaining a filter cake, which is a mixture of naphthalene and thiophanate from which impurities are removed (the mixture includes 54.18wt% of naphthalene, 8.25wt% of thiophanate, and 37.57wt% of solvent).

[0045] 2) The filter cake obtained in step 1) is heated and melted at 85° C., and then sent to a distillation tower for distillation separation, wherein the distillation tower has a top pressure of 22 kPa, a top temperature of 80° C., a reflux ratio of 0.8, a theoretical plate number of 20, a bottom temperature of 164° C., and a bottom pressure of 25 kPa. Through distillation separation, the solvent is extracted from the top of the tower, and the mixture of naphthalene and thionaphthene from which the solvent is removed is extracted from the bottom of the tower.

[0046] 3) The solvent-free mixture of naphthalene and thionaphthene obtained in step 2) is fed into an azeotropic distillation tower, and ethylene glycol is used as an entrainer to perform azeotropic distillation, wherein the mass ratio of the amount of the entrainer to the solvent-free mixture of naphthalene and thionaphthene is 0.55:1; the tower top pressure of the azeotropic distillation tower is 10 kPa, the tower top temperature is 115° C., and the reflux ratio is 8. The mixture of naphthalene and the entrainer is extracted at the top of the azeotropic distillation tower, and the thionaphthene material rich in 156° C. is extracted from the tower bottom. The thionaphthene material is cooled to 40° C. to obtain a refined thionaphthene product.

[0047] 4) the mixed material of naphthalene and entrainer obtained in step 3) is mixed and washed with 75 ℃ of water in a mixing tank, wherein the mass ratio of the consumption of water and the mixed material of the aforementioned naphthalene and entrainer is 1:1. Then the mixed solution obtained by mixing and washing is phase-splitting in a phase separator, and phase-splitting is carried out under a temperature of 82 ℃ and a pressure of 101.325 kPa, and a light phase component and a heavy phase component are obtained by phase-splitting, wherein the light phase component is a component rich in naphthalene, and the heavy phase component is mainly water and entrainer. The light phase component is dried in a drying device (pressure 40 kPa, temperature 95 ℃) to obtain a refined naphthalene product.

[0048] Experimental results: the purity of the obtained thionaphthene product was 99.1%, and the yield was 95.7%; the purity of the obtained refined naphthalene product was 99.5%, and the yield was 97.8%.

[0049] Example 2

[0050] The process is carried out in accordance with Example 1, except that in step 1), the mass ratio of n-butanol to the crystallized residual oil is 1:1.

[0051] Experimental results: the purity of the obtained thionaphthene product was 94.1%, and the yield was 94.2%; the purity of the obtained refined naphthalene product was 97.3%, and the yield was 97.2%.

[0052] Example 3

[0053] The process is carried out in accordance with Example 1, except that in step 1), the mass ratio of n-butanol to the crystallized residual oil is 4:1.

[0054] Experimental results: the purity of the obtained thionaphthene product was 98.8%, and the yield was 92.3%; the purity of the obtained refined naphthalene product was 99.0%, and the yield was 93.9%.

[0055] Example 4

[0056] The process is carried out in accordance with Example 1, except that in step 1), the crystal growing temperature is 8°C.

[0057] Experimental results: the purity of the obtained thionaphthene product was 98.3%, and the yield was 94.8%; the purity of the obtained refined naphthalene product was 98.9%, and the yield was 97.9%.

[0058] Example 5

[0059] The process is carried out in accordance with Example 1, except that in step 1), the crystal growing temperature is 30°C.

[0060] Experimental results: the purity of the obtained thionaphthene product was 98.4%, and the yield was 92.5%; the purity of the obtained refined naphthalene product was 98.4%, and the yield was 92.3%.

[0061] Example 6

[0062] The process is carried out in accordance with Example 1, except that in step 1), the crystal growing time is 15 min.

[0063] Experimental results: the purity of the obtained thionaphthene product was 98.8%, and the yield was 91.3%; the purity of the obtained refined naphthalene product was 99.2%, and the yield was 93.5%.

[0064] Example 7

[0065] The process is carried out in accordance with Example 1, except that in step 1), the crystal growing time is 45 min.

[0066] Experimental results: the purity of the obtained thionaphthene product was 98.6%, and the yield was 94.8%; the purity of the obtained refined naphthalene product was 98.6%, and the yield was 97.6%.

[0067] Example 8

[0068] The method is carried out with reference to Example 1, except that in step 3), the mass ratio of the amount of the entrainer to the mass ratio of the mixture of naphthalene and thionaphthene from which the solvent is removed is 0.53:1.

[0069] Experimental results: the purity of the obtained thionaphthene product was 80.1%, and the yield was 93.8%; the purity of the obtained refined naphthalene product was 99.2%, and the yield was 86.7%.

[0070] Example 9

[0071] The method is carried out with reference to Example 1, except that in step 3), the mass ratio of the amount of the entrainer to the mass ratio of the mixture of naphthalene and thionaphthene from which the solvent is removed is 0.62:1.

[0072] Experimental results: the purity of the obtained thionaphthene product was 98.9%, and the yield was 94.2%; the purity of the obtained refined naphthalene product was 99.0%, and the yield was 97.3%.

[0073] Table 1 Summary of experimental results

[0074]

[0075] It can be seen from the above experimental results that the method of the present invention can be used to simultaneously separate the thionaphthene product and the refined naphthalene product from the crystallization residual oil, while taking into account good purity and product yield.

[0076] From the comparison between Examples 2 and 3 and Example 1, it can be seen that in Examples 2 and 3, the mass ratio of n-butanol to the crystallization residual oil is not controlled within the preferred range of 1.5 to 3:1. Compared with Example 1, the yield and purity of the thionaphthene product, as well as the yield and purity of the refined naphthalene product are inferior to those of Example 1.

[0077] Comparison between Examples 4 and 5 and Example 1 shows that Example 1 controls the crystal growing temperature within the preferred range of 10 to 25° C., which can better obtain thiophanate products and refined naphthalene products with both high purity and yield.

[0078] Comparison between Examples 6 and 7 and Example 1 shows that Example 1 controls the crystal growing time within the preferred range of 20 to 40 minutes, which can better obtain thiophanate products and refined naphthalene products with both high purity and yield.

[0079] From the comparison between Example 8 and Examples 1 and 9, it can be seen that Example 8 does not adopt the preferred mass ratio of the amount of the entrainer to the mixture of naphthalene and thionaphthene from which the solvent is removed of 0.55 to 0.62:1, and the purity of the obtained thionaphthene product decreases significantly, and the yield of the refined naphthalene product also decreases significantly. From the comparison between Examples 1 and 9, it can be seen that when other conditions are substantially the same, the mass ratio of the amount of the entrainer to the mixture of naphthalene and thionaphthene from which the solvent is removed is controlled within a more preferred range of 0.55 to 0.60:1 in Example 1, which can further improve the yield and purity of thionaphthene and refined naphthalene products.

[0080] It is easy to understand that the above embodiments are only examples for clear explanation and do not mean that the present invention is limited thereto. For ordinary technicians in the relevant field, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from this are still within the protection scope of the present invention.

Claims

1. A method for separating naphthalene and thionaphthene from a mixture of naphthalene and thionaphthene, characterized in that: The method comprises the following steps: 1) mixing the mixture of naphthalene and thiophanate with a solvent, then crystallizing the obtained mixed solution, and performing solid-liquid separation on the obtained crystal solution to obtain a mixture of naphthalene and thiophanate from which impurities are removed; the solvent is n-butanol; 2) heating and melting the mixture of the impurity-removed naphthalene and thionaphthene, and then removing the solvent carried secretly therein to obtain the mixture of naphthalene and thionaphthene removed from the solvent; 3) taking ethylene glycol as entrainer, the mixture of naphthalene and thionaphthene of the desolvation is carried out azeotropic distillation, and separation obtains the mixture of thionaphthene material and naphthalene and entrainer; 4) mixing and washing the mixture of the naphthalene and the entrainer with water, and then carrying out phase separation with the obtained mixed solution to obtain a light phase component rich in naphthalene.

2. The method according to claim 1, characterized in that In step 1), the mixture of naphthalene and thionaphthene is industrial naphthalene, or a naphthalene fraction obtained after tar distillation separation, or naphthalene residual oil obtained after melt crystallization of the industrial naphthalene or the naphthalene fraction.

3. The method according to claim 1, characterized in that In step 1), the mass ratio of the solvent to the mixture of naphthalene and thiophanate is 1:1 to 4:1, preferably 1.5 to 3:

1.

4. The method according to claim 3, characterized in that In step 1), the crystal growth temperature of the crystal is 8-30°C, preferably 10-25°C; the crystal growth time is 15-45min, preferably 20-40min; Preferably, when the crystallization is performed, the temperature is lowered to the crystal growing temperature at a cooling rate of 1 to 3° C. / min for crystal growing.

5. The method according to any one of claims 1 to 3, characterized in that: In step 2), the temperature for heating and melting is 82-90°C.

6. The method according to any one of claims 1 to 3, characterized in that: In step 2), the removed solvent is recycled as the solvent required for the mixing in step 1); Preferably, in step 2), the entrained solvent is removed by distillation separation.

7. The method according to any one of claims 1 to 3, characterized in that: In step 3), the mass ratio of the amount of the entrainer to the mixture of naphthalene and thionaphthene from which the solvent is removed is 0.53 to 0.62:1, preferably 0.55 to 0.62:1, and more preferably 0.55 to 0.60:

1.

8. The method according to claim 7, characterized in that In step 3), the conditions for carrying out the azeotropic distillation include: the top pressure of the azeotropic distillation tower is 5-15 kPa, the top temperature is 110-125° C., and the reflux ratio is 5-10.

9. The method according to any one of claims 1 to 3, characterized in that: In step 4), the mass ratio of the water to the mixture of the naphthalene and the entrainer is 0.8 to 1.5:1; In step 4), the temperature for phase separation is 80-85°C; Preferably, in step 4), the temperature of the water used for the washing is 70-80°C.

10. The method according to any one of claims 1 to 3, characterized in that: In step 3), the thionaphthene material is cooled to obtain a thionaphthene product; In step 4), the naphthalene-rich light phase component is dried to obtain a refined naphthalene product.

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