A crystallization method for purifying fluorene

Abstract

The application provides a crystallization method of refined fluorene, which comprises the following steps: adding a raw material fluorene fraction into a mixed solution, carrying out a first beating and washing at normal temperature, and obtaining crude fluorene through centrifugal separation; mixing the crude fluorene with a solvent A, stirring and heating to 65-85 DEG C, cooling to 5-30 DEG C after the solid part is dissolved, keeping the temperature for 1 h, and obtaining industrial fluorene through centrifugal separation, and the mother liquor is used as a washing agent to participate in the first beating and washing. The method has simple and easy-to-control operation conditions and low cost. Through reducing the high-temperature operation time, using a high-boiling and low-volatility solvent to reduce the solvent loss in the crystallization process, using a single solvent to facilitate solvent recovery, using the mother liquor in the process to increase the yield and reduce the solvent consumption, using the beating and washing mode in the first step operation to operate at normal temperature, reducing the energy consumption and shortening the process cycle, and cooling and crystallizing in the second step operation, the crystal part is dissolved, the remaining solid is used as a crystal seed, so that the crystallization process is controllable, the primary burst nucleation is avoided, and the walling condition is reduced.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of coal tar deep processing, and particularly relates to a crystallization method for purifying and refining a crystallization process for producing industrial fluorene from a fluorene fraction. BACKGROUND

[0002] Fluorene, also known as 9H-fluorene or o-biphenylmethane (CAS No.: 86-73-7), is a white or almost white powdery crystal with a melting point of 114.77℃.

[0003] Fluorene is easily soluble in organic solvents such as ethanol, diethyl ether, benzene and carbon disulfide, and insoluble in water. Its molecular formula is C13H10, and the structural formula is shown below.

[0004]

[0005] Fluorene is one of polycyclic aromatic hydrocarbons purified from coal tar and has a wide range of uses. Fluorene is an important organic synthesis raw material, which can be used to synthesize trinitrofluorenone, aryl transparent nylon, indanthalene, fluorene aldehyde resin, etc.; in the pharmaceutical field, it can be used to synthesize pesticides, herbicides, wetting agents, liquid flash agents and disinfectants, etc.; in the dye industry, it can be used to synthesize fluorescent dyes, vat dyes, etc. In recent years, due to the increasingly wide application of fluorene and its derivatives in the fields of chemical industry, biological engineering, functional polymer materials and polymer synthesis chemistry, the demand for fluorene has greatly increased on the domestic and foreign markets, and the prospect is extremely broad, so it is particularly important to propose a preparation method for purifying high-purity fluorene at a low cost.

[0006] The main components of coal tar are alkanes, arenes, phenolic compounds and a small amount of other oxygen-containing and nitrogen-containing compounds. Fluorene is mainly derived from coal tar wash oil and anthracene oil fraction, accounting for about 1% to 2% of coal tar. The extraction and refining process of fluorene is to first perform batch distillation on the wash oil fraction or the anthracene oil fraction to obtain a fluorene main fraction, and then to refine the fluorene main fraction by a cooling crystallization method or a solvent crystallization method to obtain industrial fluorene. The main impurities in the fluorene fraction obtained by rectification are acenaphthene, oxyfluorene and a small amount of methyl oxyfluorene. To obtain high-purity fluorene, multiple recrystallization or solvent washing steps are required, which is difficult to operate, consumes a large amount of solvent, and is difficult to separate and purify.

[0007] At present, there are some reports on the purification of fluorene in the literatures at home and abroad. Patent CN1884234A discloses a method for crystallizing and purifying fluorene, which selects xylene, toluene, benzene or a mixture of these non-polar solvents as a non-polar solvent for cooling crystallization, and then uses a polar solvent, an alcoholic polar solvent or a ketonic polar solvent to wash the crude crystal of fluorene, and the purity of the product is 97%, but the yield is only 25%. Patent CN101182278A proposes to use a mixture of organic solvents and non-polar organic solvents to centrifugally wash a fluorene fraction containing 50%-80% of fluorene, and then mix the obtained fluorene with an organic solvent to perform cooling crystallization, and the final temperature is 0-25℃. The organic solvent is a single solvent or a mixture of toluene, xylene and benzene. Finally, the same organic solvent mixture as the first washing is used to wash the crystal, and the purity of the obtained product reaches 97%, and the yield is about 65%. The process is complex, consumes a large amount of solvent in the washing process, and the final temperature of cooling crystallization is low, which requires a high-quality cooling source. Patent CN103224441B uses a cooling-solventing coupled crystallization method, and the purity of the fluorene product is more than 99% and the yield is more than 50% after three times of cooling-solventing coupled crystallization. However, the production cycle is long and the yield is low due to multiple crystallizations. Patent CN103382148B pre-crystallizes heavy wash oil, distills and cuts the main fraction of fluorene from the pre-crystallized product, and then crystallizes the main fraction twice to obtain industrial fluorene with a purity of more than 97%. Although the mother liquor of the second crystallization is used in the first crystallization in the process, the yield is still less than 50%.

[0008] As can be seen from the above methods, the current methods for purifying fluorene mainly use solvent crystallization and solvent washing methods. The solvent crystallization method has the problems of high toxicity of the selected solvent, large solvent consumption, long production cycle, low product yield and high production cost due to multiple recrystallizations. In the production process, a large amount of solvent is lost due to the long operation time at high temperature and the strong volatility of the solvent, and the crystallization process is not well controlled, which causes problems such as walling and pipe blocking. The solvent washing method has the problems of low product yield and high solvent recovery cost due to the consumption of a large amount of solvent in the washing process. Based on these problems in the process, a new process for preparing industrial fluorene with high content at a low cost is urgently needed to meet the growing demand for fluorene at home and abroad. SUMMARY

[0009] The present application provides a crystallization method for purifying fluorene, which takes a fluorene fraction as a starting product and comprises the following steps: step 1, adding the fluorene fraction into a washing solution to perform beating and washing, and separating to obtain crude fluorene; step 2, mixing the crude fluorene with a solvent A, stirring and heating, cooling and constant-temperature standing after the solid part is dissolved, and separating to obtain industrial fluorene and a mother liquor. The solvent A in step 2 acts as a crystallization solvent.

[0010] Preferably, the beating and washing is carried out at room temperature for 10-60 minutes after the fluorene fraction is added to the washing solution. The preferred time is 10, 20, 30, 40, 50, 60 minutes. The preferred beating temperature is obtained by comprehensively considering various factors, and is preferably room temperature, which is conducive to accelerating the mass transfer process and improving the impurity removal effect. A high temperature is conducive to the impurity removal effect, but affects the yield. A low temperature is conducive to the yield, but affects the impurity removal effect. The beating and washing can effectively remove the fluorene front fraction and other impurities.

[0011] Preferably, in any of the above, the mother liquor separated in step 2 is used as the washing solution for the beating and washing in step 1. The crystallization mother liquor mainly contains acenaphthene, fluorenone and methylfluorenone, and has a low content. As the washing solution for the first step, the crystallization mother liquor can significantly improve the yield without affecting the product content.

[0012] Preferably, in any of the above, the washing solution further comprises solvent A, wherein the amount of solvent A is 0-20% of the washing solvent. The beating and washing preferably uses a mixed solution of the mother liquor and solvent A as the washing solution. The fluorene product has a higher purity when a certain amount of fresh solvent is added. In the beating and washing, the temperature is maintained at room temperature without the process of temperature reduction, thereby reducing the energy consumption and shortening the crystallization period. The amount of solvent A is preferably 0, 5, 10, 15, 20% of the washing solvent. The crystallization mother liquor mainly contains acenaphthene, fluorenone and methylfluorenone, and has a low content. The crystallization mother liquor can be mixed with pure solvent A, and used as the washing solution for the first step, thereby significantly improving the yield without affecting the product content. Solvent A has an impurity removal effect, and the solvent A present in the mother liquor also has an impurity removal effect. Adding solvent A to the mother liquor can improve the impurity removal effect. Solvent A can dissolve fluorene and impurities, but reduces the yield. Therefore, the amount of solvent A is preferably 0-20% of the washing solvent.

[0013] Preferably, in any of the above, in step 1, the mass ratio of the fluorene fraction to the washing solution is 1:0.8-1.2. A too high amount of washing solvent results in a low yield and a large amount of solvent consumption, and a too low amount of washing solvent results in an insufficient impurity removal effect. Further preferably, the mass ratio is 1:0.8, 1:0.9, 1:1.0, 1:1.1, 1:1.2.

[0014] Preferably, in any of the above, in step 1, the content of fluorene in the fluorene fraction is 50-80%. Further preferably, the content is 50, 50, 70, 80%.

[0015] It is preferred that the solvent A is selected from one of benzyl alcohol, DMAC (N,N-dimethylacetamide), 1-methylnaphthalene, chlorobenzene, DMF (N,N-dimethylformamide). In step 2, the solvent A has the function of dissolving fluorene, and the preferred solvent A has the characteristics of high boiling point and low volatility, and low loss in the crystallization process.

[0016] It is preferred that in step 2, the mass ratio of the crude fluorene to the solvent A is 1:0.8-1.2. If the amount of the solvent A is high, the yield is low and the consumption is large; if the amount of the solvent A is low, the impurity removal ability is low, and the suspension density in the crystallization process is too high, resulting in small particle size of the obtained crystal. Further preferred mass ratios are 1:0.8, 1:0.9, 1:1.0, 1:1.1, and 1:1.2.

[0017] It is preferred that in step 2, the heating temperature is 65-85℃. The selected heating temperature is beneficial to the formation of fluorene crystals and ensures the purity of the crystals: if the temperature exceeds 85℃, the crystals are completely dissolved, and the crystallization process is equivalent to no seed, which is easy to burst into nucleation, resulting in small particle size of the product and easy to form a crust in the crystallization process; if the temperature is lower than 65℃, a large amount of crystals are not dissolved and do not participate in the recrystallization, resulting in high impurity content of the product. Further preferred temperatures are 65℃, 70℃, 75℃, 80℃, and 85℃.

[0018] It is preferred that in the cooling process, the temperature is lowered to 5-30℃ after the solid part is dissolved and kept constant for 1h. If the temperature is too high, the yield is reduced, and if the temperature is too low, the energy consumption is high, and the yield cannot be improved. Further preferred temperatures are 5℃, 10℃, 15℃, 20℃, 25℃, and 30℃.

[0019] It is preferred that the cooling rate is 0.1-0.5℃ / min. If the cooling rate is too fast, the supersaturation degree is large, resulting in small particle size of the product; if the cooling rate is too low, the crystallization period is long, and the grown crystals may be broken. Further preferred cooling rates are 0.1℃ / min, 0.2℃ / min, 0.3℃ / min, 0.4℃ / min, and 0.5℃ / min.

[0020] It is preferred that in steps 1 and 2, the separation is performed by centrifugal separation.

[0021] It is preferred that the crystallization mother liquor is recycled and mixed with the solvent A to participate in the beating and washing operation in the first step.

[0022] The preferred specific technical solutions of the present application are as follows:

[0023] The fluorene fraction is added to the mixed solution, and once washing is carried out at normal temperature to obtain crude fluorene through centrifugal separation; the crude fluorene is mixed with the solvent A, stirred and heated to 65-85℃, and after the solid part is dissolved, the temperature is lowered to 5-30℃, and constant temperature is maintained for 1h, and then separation is carried out to obtain industrial fluorene and crystallization mother liquor; wherein the crystallization mother liquor is used as the washing solution to participate in the first step of beating and washing.

[0024] The content of the raw fluorene fraction is 50%-80%.

[0025] The mass ratio of the fluorene fraction to the washing solution is 1:0.8-1.2.

[0026] The washing solution is a mixed solution of the solvent A and the crystallization mother liquor, wherein the solvent A accounts for 0%-20% of the washing solvent.

[0027] The solvent A is selected from one of benzyl alcohol, DMAC, 1-methylnaphthalene, chlorobenzene and DMF.

[0028] The mass ratio of the crude fluorene to the solvent A is 1:0.8-1.2.

[0029] After the fluorene fraction is added to the washing solution, stirring is carried out at normal temperature for 10-60min.

[0030] The cooling rate is 0.1-0.5℃ / min.

[0031] The separation step adopts centrifugal separation.

[0032] The crystallization method for purifying fluorene provided by the application is a method for preparing industrial fluorene from fluorene fraction through secondary crystallization, and industrial fluorene products with a content of more than 96% are obtained; the crystallization mother liquor is used in the first step of beating and washing to reduce the amount of pure solvent used in washing and recover fluorene in the mother liquor, so that the yield is improved, and the yield of industrial fluorene reaches about 80% (calculation method: industrial fluorene product mass x fluorene content / (fluorene fraction crude product mass x fluorene content)). The method reduces the operation time at high temperature, uses high-boiling and low-volatility solvent as the crystallization solvent to reduce the solvent loss in the crystallization process, and the solvent loss in the crystallization process is about 0.2kg / kg product when using xylene as the crystallization solvent, while the solvent loss in the process provided by the application can be reduced to about 0.05kg / kg product when treating the same fluorene fraction. In addition, the use of a single solvent is beneficial to solvent recovery; the use of the mother liquor in the process increases the yield and reduces the amount of solvent; the first step operation adopts the beating and washing mode, and the operation is carried out at normal temperature, so that the energy consumption can be reduced and the process cycle can be shortened; the second step operation is cooling and crystallization, the crystal part is dissolved, no seed is added, and the operation condition is simple and easy to control. As can be seen from the microscope picture of fluorene (see Figures 1-2 ), the crystal habit of the product is good, the particle size is large, and the product is easy to filter and dry. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 Microscope picture of the crude fluorene product after washing for the preferred embodiment 1 of the present application.

[0034] Figure 2 Microscope picture of the industrial fluorene product after crystallization for the preferred embodiment 1 of the present application.

[0035] Figure 3 Process flow chart of the crystallization process for the preferred embodiment 1 of the present application DETAILED DESCRIPTION

[0036] The present application is described more clearly and completely by the following examples, but the described examples are only a part of the embodiments of the present application, not all. The examples are to help understanding the present application, and should not limit the protection scope of the present application.

[0037] Example 1.

[0038] As Figure 3 The process flow chart of the crystallization process is shown, and 500g of fluorene fraction with content of 68.00% is used as raw material. The fluorene fraction is added into the mixed solution of DMAC and crystallization mother liquor according to the mass ratio of washing solution: fluorene fraction = 1:1, in which DMAC accounts for 10% of the amount of washing solvent, and the washing is carried out at room temperature for 40min. Then, the wet crude fluorene product is obtained by centrifugal filtration. Then, the wet crude fluorene product is added into DMAC according to the mass ratio of solvent: crude fluorene = 1:1, and heated to 80℃ to dissolve the solid part. The solution is cooled to 5℃ at a cooling rate of 0.02℃ / min, and kept at constant temperature for 1h. Then, the product is obtained by centrifugal filtration and dried at 60℃ under vacuum degree of 0.094Mpa. The purity of the obtained industrial fluorene product is 96.62%, and the yield is 78.74%. The solvent loss is calculated to be 0.054kg / kg product by evaporating and recovering the solvent from the washing mother liquor. Figure 1 The microscope picture of the crude fluorene product after washing is shown. Figure 2 The microscope picture of the industrial fluorene product after crystallization is shown. It can be seen that the crystal habit of the product is good, and the particle size is large, which is easy to filter and dry.

[0039] Example 2.

[0040] 450 g of a 66.83% fluorene fraction was added to the crystallization mother liquor at a mass ratio of washing solution to fluorene fraction of 0.8:1. The mixture was stirred at room temperature for 30 minutes and centrifuged to obtain a crude wet fluorene product. Benzyl alcohol was then added to the product at a mass ratio of solvent to primary alcohol of 1:1. The product was heated to 75°C to dissolve the solids. The solution was cooled to 10°C at a rate of 0.01°C / min and held at that temperature for 1 hour. After centrifugation and drying at 60°C under a vacuum of 0.094 MPa, 255.03 g of industrial fluorene with a 96.06% content was obtained, yielding 81.46%. The solvent was recovered by evaporation of the slurry-beating washing mother liquor, resulting in a calculated solvent loss of 0.044 kg / kg of product. The crystallized industrial fluorene product exhibited good crystal habit and large particle size, making it easy to filter and dry.

[0041] Example 3.

[0042] 600 g of a fluorene fraction with a 71.83% content was used as the starting material. A mixture of benzyl alcohol and a crystallization mother liquor was added at a mass ratio of washing solvent to fluorene fraction of 0.65:1, with benzyl alcohol accounting for 10% of the washing solvent. The mixture was stirred at room temperature for 40 minutes and centrifuged to obtain a wet crude fluorene product. Benzyl alcohol was then added at a mass ratio of solvent to crude fluorene of 1:1. The mixture was heated to 70°C to dissolve the solids. The solution was cooled to 10°C at a rate of 0.05°C / min and held at that temperature for 1 hour. After centrifugation, the mixture was dried at 60°C under a vacuum of 0.094 MPa to obtain 356.28 g of industrial fluorene with a 96.81% content, for a yield of 80.03%. The solvent was recovered by evaporation of the washing mother liquor, with a calculated solvent loss of 0.042 kg / kg of product. The crystallized industrial fluorene product exhibited good crystal habit and large particle size, making it easy to filter and dry.

[0043] Example 4.

[0044] 450.0 g of a 76.06% fluorene fraction was used as the starting material. This was added to a mixture of DMF and crystallization mother liquor at a mass ratio of 1:1 (washing solvent: fluorene fraction), with DMF comprising 15% of the washing solvent. The mixture was washed at room temperature for 60 minutes and centrifuged to obtain a wet crude fluorene product. DMF was then added to the mixture at a mass ratio of 1:1 (solvent:crude fluorene). The mixture was heated to 80°C to dissolve the solids. The solution was cooled to 30°C at a rate of 0.02°C / min and held at that temperature for 1 hour. After centrifugation, the mixture was dried at 60°C under a vacuum of 0.094 MPa to yield 275.67 g of industrial fluorene with a 96.77% content, representing a yield of 77.94%. The crystallization mother liquor was recycled and used in a single washing operation. The solvent was recovered by evaporation of the slurry-washing mother liquor, resulting in a calculated solvent loss of 0.053 kg / kg of product. The crystallized industrial fluorene product exhibited good crystal habit and large particle size, making it easy to filter and dry.

[0045] Example 5.

[0046] Example 1. With 600 g of fluorene fraction having a content of 68.00%, it was added into the mixed solution of chlorobenzene and crystallization mother liquor at a mass ratio of washing solution: fluorene fraction = 1:1, wherein chlorobenzene accounted for 6% of the amount of washing solvent, and washed for 40 min at room temperature. After centrifugal filtration, 85.82 g of crude fluorene was obtained. With the crude fluorene as raw material, it was added into chlorobenzene at a mass ratio of solvent: crude fluorene = 1:1, and heated to 80°C to dissolve the solid part. The solution was cooled to 30°C at a cooling rate of 0.01°C / min, and kept constant for 1 h. After centrifugal filtration, drying was performed at 60°C and a vacuum degree of 0.094 MPa to obtain 328.53 g of industrial fluorene having a content of 97.03% and a yield of 78.13%. Through evaporation of the washing mother liquor to recover the solvent, the solvent loss was calculated to be 0.055 kg / kg of product. After crystallization, the industrial fluorene product had good crystal habits, large particle size, and was easy to filter and dry.

[0047] Example 6.

[0048] With 500 g of fluorene fraction having a content of 62.00%, it was added into the mixed solution of 1-methylnaphthalene and crystallization mother liquor at a mass ratio of washing solution: fluorene fraction = 1.2:1, wherein 1-methylnaphthalene accounted for 10% of the amount of washing solvent, and washed for 60 min at room temperature. After centrifugal filtration, the wet crude fluorene was obtained, and then it was added into 1-methylnaphthalene at a mass ratio of solvent: crude fluorene = 1:1, and heated to 75°C to dissolve the solid part. The solution was cooled to 5°C at a cooling rate of 0.02°C / min, and kept constant for 1 h. After centrifugal filtration, drying was performed at 60°C and a vacuum degree of 0.094 MPa to obtain 252.48 g of industrial fluorene having a content of 96.79% and a yield of 78.83%. Through evaporation of the washing mother liquor to recover the solvent, the solvent loss was calculated to be 0.046 kg / kg of product.

[0049] The microscope images of the industrial fluorene products obtained in Examples 2-6 were basically consistent with the example, and are not provided again.

Claims

1. A crystallization method for purifying fluorene, using a fluorene fraction as a starting product, characterized in that: The following steps are involved: The method comprises the following steps: adding a fluorene fraction to a washing solution at a mass ratio of the fluorene fraction to the washing solution of 1:0.8-1.2, stirring at room temperature for 10-60 minutes, performing pulping and washing, and separating to obtain crude fluorene; mixing the crude fluorene with a solvent A, stirring and heating, cooling the crude fluorene after the solid portion is dissolved, and standing at a constant temperature at a cooling rate of 0.1-0.5°C / min to obtain industrial fluorene and a mother liquor; the mother liquor separated in step 2 is used as a washing solution in the pulping and washing in step 1; in step 1, the washing solution comprises the mother liquor separated in step 2 and 0%-20% of solvent A; in step 2, the mass ratio of the crude fluorene to solvent A is 1:0.8-1.2, and the solvent A is selected from one of benzyl alcohol, DMAC, and 1-methylnaphthalene.

2. The method according to claim 1, wherein In step 1, the fluorene content in the fluorene fraction is 50% to 80%.

3. The method according to claim 1, wherein In step 2, the heating temperature is 65-85° C.; the cooling process is to cool the mixture to 5-30° C. and keep the temperature constant for 1 hour after the solid part is dissolved.

4. The method according to claim 1, wherein In step 1 and step 2, the separation is performed by centrifugation.

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