Preparation method of dibenzofuran

Abstract

The invention discloses a preparation method of dibenzofuran. The preparation method comprises the following steps: melting and charging: heating a dibenzofuran raw material to completely melt the dibenzofuran raw material into liquid, and then filling the liquid into a crystallization tower, the dibenzofuran raw material being a crude product obtained after o-phenylphenol is separated from a product obtained after a dibenzofuran hydrogenation reaction or a dibenzofuran fraction separated from washing oil processing; cooling crystallization: cooling the temperature in the crystallization tower at a preset cooling rate to a crystallization final temperature, keeping the constant temperature for a preset time, and discharging a crystallized liquid; sweating and discharging: fully opening a valve at the bottom of the crystallization tower, and raising the temperature of the crystallization tower to sweating final temperature at a preset temperature raising rate for sweating; and after perspiration is completed, closing a valve at the bottom of the crystallization tower, heating crystals in the crystallization tower until the crystals are completely molten, and collecting the product dibenzofuran. According to the present invention, the dibenzofuran fraction separated from the dibenzofuran hydrogenation reaction by-product or washing oil processing is adopted as the raw material, such that the industrial dibenzofuran product with the purity of more than 99% can be obtained.

Description

Technical Field

[0001] This invention relates to the field of deep processing technology of washing oil, and more specifically, to a method for preparing fluorene oxide. Background Technology

[0002] Fluorene oxide is a heterocyclic compound with two benzene rings and a furan structure, also known as dibenzofuran or biphenyl fluorene oxide, and is one of the products of high-temperature coal tar processing. Coal tar contains approximately 0.5%–1% fluorene oxide, mostly concentrated in the wash oil fraction, where it accounts for about 10%. Fluorene oxide is a relatively abundant component in wash oil, and currently, the development and utilization of components in wash oil products in China is limited to a few substances. Fluorene oxide is a white or light yellow crystal with blue fluorescence. It is a polar molecule with an epoxy structure and is relatively soluble in alcohols and ethers. It is used as a raw material in pharmaceuticals, disinfectants, preservatives, dyes, synthetic resins, and high-temperature lubricants, and also has important applications in animal drugs and materials.

[0003] Currently, the separation of oxygen fluorene from wash oil mainly employs absorption, distillation, extraction, supercritical extraction, adsorption separation, chromatographic separation, or membrane separation. However, these methods typically suffer from drawbacks such as low purity of the separated oxygen fluorene, high cost, or environmental pollution. For example, CN201710125235.7 discloses a refining process for oxygen fluorene. It uses a fraction containing 55%–65% oxygen fluorene obtained from the distillation of residual wash oil or heavy wash oil as raw material. This fraction is directly cooled, crystallized, and centrifuged to obtain crude oxygen fluorene containing approximately 85% oxygen fluorene. The crude oxygen fluorene is then dissolved in a mixed solvent of 95% ethanol and DMF (N,N-dimethylformamide) by heating. A certain amount of water is then added dropwise as a precipitant to precipitate impurities. The hot-filtered solution is cooled, crystallized, and centrifuged to obtain oxygen fluorene with a purity greater than 98%, with a yield greater than 85%. However, a purity of 98% oxygen fluorene often fails to meet application requirements. Summary of the Invention

[0004] The present invention aims to provide a method for preparing fluorene oxide to solve the technical problems of low purity, high cost, or environmental pollution of fluorene oxide isolated in the prior art.

[0005] To achieve the above objectives, according to one aspect of the present invention, a method for preparing fluorene oxide is provided. The method includes the following steps: Melting and charging: heating the fluorene oxide raw material until it is completely melted into a liquid, and then charging it into a crystallization tower. The fluorene oxide raw material is the crude product after separating o-phenylphenol from the product of the hydrogenation reaction of fluorene oxide, or the fluorene oxide fraction separated during wash oil processing; Cooling and crystallization: cooling the temperature inside the crystallization tower at a preset cooling rate until it reaches the crystallization endpoint temperature, maintaining the temperature at a constant temperature for a predetermined time, and then discharging the crystallized liquid; Sweating and discharging: keeping the bottom valve of the crystallization tower fully open, and raising the temperature of the crystallization tower at a preset heating rate to the sweating endpoint temperature for sweating; after sweating is completed, closing the bottom valve of the crystallization tower, heating the crystals inside the crystallization tower until they are completely melted, and collecting the fluorene oxide product.

[0006] Furthermore, the mass concentration of the fluorene feedstock is 50%–95%.

[0007] Furthermore, in the melting and charging step, the oxygen fluorene raw material is heated to above 80°C to completely melt it into a liquid.

[0008] Furthermore, in the cooling crystallization step, the cooling rate is 0.5–3 °C / h, and the final crystallization temperature is 55–60.5 °C.

[0009] Furthermore, in the cooling crystallization step, the temperature is reduced to 66-69℃ at a cooling rate of 0.5-1.5℃ / h, and then reduced to 55-60.5℃ at a cooling rate of 1.5-3℃ / h.

[0010] Furthermore, in the cooling crystallization step, after cooling to the final crystallization temperature, maintain a constant temperature for 60–120 minutes.

[0011] Furthermore, perspiration is achieved through gravity flow or intermittent vacuum, with constant-temperature vacuum perspiration until no sweat drips out.

[0012] Furthermore, the final temperature of sweating was 65.5–78.5℃.

[0013] Furthermore, in the sweating and discharging steps, the temperature is increased to 60.5-65.5℃ at a rate of 1.5-3℃ / h, and then increased to 65.5-78.5℃ at a rate of 0.5-1.5℃ / h.

[0014] Furthermore, when the mass concentration of the fluorene raw material is less than 80%, the preparation method is repeated multiple times.

[0015] By applying the technical solution of this invention, using the byproduct of the hydrogenation reaction of fluorene oxide as raw material, the main components of which are fluorene oxide (approximately 85%) and biphenyl (approximately 10%), an industrial fluorene oxide product with a purity greater than 99% can be obtained through melt crystallization. This invention has the advantages of high selectivity, low energy consumption, low operating temperature, no solvent, no waste liquid, and no gas phase. Attached Figure Description

[0016] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0017] Figure 1 The gas chromatogram of the fluorene oxide product obtained in Example 1 is shown;

[0018] Figure 2 The gas chromatogram of the fluorene oxide product obtained in Comparative Example 1 is shown.

[0019] Figure 3 The gas chromatogram of the fluorene oxide product obtained in Example 2 is shown; and

[0020] Figure 4 The gas chromatogram of the fluorene product obtained in Comparative Example 2 is shown. Detailed Implementation

[0021] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0022] In view of the technical problems of low purity, high cost, or environmental pollution of oxygen fluorene separated in the prior art, the present invention proposes the following technical solutions.

[0023] According to a typical embodiment of the present invention, a method for preparing fluorene oxide is provided. The method includes the following steps: Melting and charging: Fluorene oxide raw material is heated until it is completely melted into a liquid, and then charged into a crystallization tower. The fluorene oxide raw material is the product of the hydrogenation reaction of fluorene oxide, and the crude product after separating o-phenylphenol by chemical separation is used as the reaction raw material, including but not limited to fluorene oxide fraction from wash oil processing; Cooling and crystallization: The temperature inside the crystallization tower is lowered at a preset cooling rate until it reaches the crystallization endpoint temperature. After maintaining the temperature at a predetermined time, the crystallized liquid is discharged; Sweating and discharging: The bottom valve of the crystallization tower is kept fully open, and the temperature of the crystallization tower is increased at a preset heating rate to the sweating endpoint temperature for sweating; After sweating is completed, the bottom valve of the crystallization tower is closed, and the crystals inside the crystallization tower are heated until they are completely melted, and the fluorene oxide product is collected.

[0024] Compared to existing technologies, this invention employs a completely different technical solution, using melt crystallization to increase the purity of fluorene oxygen to over 99%. Through a single enrichment of the fluorene oxygen fraction and a single recrystallization, a finished product with a fluorene oxygen content of over 99% can be obtained. This achieves continuous industrial production while overcoming the drawbacks of existing technologies, such as multiple recrystallization steps and high solvent consumption. It boasts advantages such as fewer process steps, lower production costs, and a better product appearance and color, demonstrating promising market application prospects.

[0025] Furthermore, the melting and crystallization process generates no gas, making leaks easy to control. The entire equipment can also be sealed, further enhancing environmental safety. Melting and crystallization requires no additives, thus eliminating waste liquid and other chemical substances (solvents). Since solvent recovery costs often constitute a large portion of the overall crystallization cost, the technical solution of this invention significantly reduces production costs.

[0026] Fluorene has a low melting point (82℃), and the impurities in crude fluorene are mostly biphenyl and its derivatives, which have even lower melting points. They are suitable for separation by melt crystallization. Compared with the distillation and refining methods used in existing fluorene preparation technologies, melt crystallization has the advantages of low energy consumption, low material consumption, low emissions, and high product purity.

[0027] In the melting and charging step of this invention, the raw material must be heated to complete melting before entering the crystallization tower, and must not contain any solids. Preferably, the fluorene oxygen raw material is heated to above 80°C to completely melt it into a liquid. In the cooling crystallization step, the cooling rate is 0.5–3°C / h, and the final crystallization temperature is 55–60.5°C. During the cooling crystallization process, the cooling rate is initially slow and then accelerates, decreasing to 66–69°C at a cooling rate of 0.5–1.5°C / h, and then decreasing to 55–60.5°C at a cooling rate of 1.5–3°C / h.

[0028] In a typical embodiment of the present invention, in the cooling crystallization step, after cooling to the crystallization endpoint temperature, the temperature is maintained at a constant temperature for 15 to 30 minutes; sweating is carried out by gravity flow or intermittent vacuum, and constant temperature vacuum sweating is carried out until no sweat drips out; the sweating endpoint temperature is 65.5 to 78.5°C; in the sweating and discharge step, the temperature is raised to 60.5 to 65.5°C at a rate of 1.5 to 3°C / h, and then raised to 65.5 to 78.5°C at a rate of 0.5 to 1.5°C / h.

[0029] According to a typical embodiment of the present invention, for raw material fluorene with a mass concentration of 80% to 90%, a high-purity fluorene product with a concentration of 99% can be obtained through a single static melt crystallization process using the method of the present invention. When the raw material concentration is lower than 80%, multiple static melt crystallization processes are required. Experiments show that by separately recovering the crystallization mother liquor and sweat for use as raw materials, the process yield of the refining process can be improved. Following the above method, static melt crystallization of fluorene raw material with a mass concentration of 80% to 90% can yield a high-purity fluorene product of 99%, with a single-pass yield ranging from 26% to 53%.

[0030] In one embodiment of the present invention, the method for preparing fluorene oxide, using the byproduct of the hydrogenation reaction of fluorene oxide as raw material, employs a static melt crystallization method, and includes the following steps:

[0031] (1) Melting and charging: Heat the oxygen fluorene raw material with a mass concentration of 80% to 90% to above 80°C in the preheating tank until it is completely melted into liquid; close the bottom valve of the crystallization tower and add the molten oxygen fluorene raw material in the preheating tank into the crystallization tower at once;

[0032] (2) Cooling crystallization: Cooling medium is introduced into the jacket of the crystallization tower and the cooling rate is maintained at a rate of 0.5 to 3℃ / h. After the temperature of the material in the crystallization tower is reduced to the crystallization endpoint temperature, the temperature is kept constant for 60 to 120 minutes. Then, the bottom valve of the crystallization tower is opened to discharge the remaining uncrystallized mother liquor, and then the valve is closed.

[0033] (3) Sweating and discharge: Keep the bottom valve of the crystallization tower fully open, and heat the crystallization tower at a rate of 0.5 to 3℃ / h to sweat; the sweating method is gravity flow or intermittent vacuum sweating, and constant temperature vacuum sweating until no sweat drips out; close the bottom valve of the crystallization tower, introduce heating medium into the crystallization tower jacket to melt all the crystals, and then open the bottom valve of the crystallization tower to collect the product oxygen fluorene.

[0034] This invention utilizes a melt crystallization method to prepare high-purity fluorene products from crude fluorene. It optimizes the preparation and purification process of fluorene, enabling the production of high-purity fluorene products with a purity of 99%, thus improving product quality and yield. The process is simple, energy-efficient, operates at low temperatures, and is easily implemented industrially. It requires no solvents, resulting in minimal pollution, making it a low-cost and environmentally friendly method for preparing fluorene.

[0035] The beneficial effects of the present invention will be further illustrated below with reference to embodiments.

[0036] Example 1

[0037] A method for purifying fluorene oxide through melt crystallization specifically includes the following steps:

[0038] (1) Fluorene Oxygen Melting: Under normal pressure, fluorene oxygen crystals with a purity of 75% are added to the reactor, and the reactor temperature is controlled at 85℃ to melt the crystals;

[0039] (2) Cooling: Control the reactor temperature to reduce it to 67℃ at a cooling rate of 1.5℃ / h, and then reduce it to 58℃ at a cooling rate of 3℃ / h.

[0040] (3) Crystallization: Crystallization was carried out at a temperature of 58℃ for 2 hours;

[0041] (4) Separation and extraction: The liquid that has not grown into crystals is released, and the melting crystallizer is raised by 3°C each time. After each temperature is raised to this temperature, the liquid is allowed to sweat until no liquid drips out, and then the temperature is raised again. Finally, the temperature is raised to 75°C. After sweating is completed, the remaining crystals are melted to obtain the fluorene oxide product.

[0042] Fluorene oxide was purified using the method described in Example 1, yielding a product with a first-pass yield of 37.8% and a purity of 99.25%. The gas chromatogram of the product is shown below. Figure 1 As shown.

[0043] Comparative Example 1

[0044] A method for purifying fluorene oxide through melt crystallization specifically includes the following steps:

[0045] (1) Fluorene Oxygen Melting: Under normal pressure, fluorene oxygen crystals with a purity of 80% are added to the reactor, and the reactor temperature is controlled at 90℃ to melt the crystals;

[0046] (2) Cooling: Control the reactor temperature and reduce it to 67℃ at a cooling rate of 3.5℃ / h, and then reduce it to 43.5℃ at a cooling rate of 2℃ / h.

[0047] (3) Crystallization: Crystallization was carried out at a temperature of 43.5℃ for 2.5 hours;

[0048] (4) Sweating: Release the liquid that has not grown into crystals, raise the melting crystallizer by 5°C each time, and after each temperature increase, sweat until no liquid drips out, and then raise the temperature again. Finally, raise the temperature to 77.5°C. After sweating is completed, melt the remaining crystals to obtain the fluorene oxide product.

[0049] The method described in Comparative Example 1 was used to purify fluorene oxide. The yield of the fluorene oxide product was 46.5% in one pass, and the purity of the product was 96.69%. The gas chromatogram of the product is shown below. Figure 2 As shown, compared with Example 1, the lower crystallization temperature and the faster heating rate led to a decrease in product purity.

[0050] Example 2

[0051] A method for purifying fluorene oxide through melt crystallization specifically includes the following steps:

[0052] (1) Oxyfluorene melting: Under normal pressure, 90% pure fluorene crystals are added to a melting crystallizer, and the reactor temperature is controlled at 90°C to melt the crystals;

[0053] (2) Cooling: Control the reactor temperature and reduce the temperature of the molten oxygen fluorene to 58.5℃ at a cooling rate of 1℃ / h;

[0054] (3) Crystallization: Crystallization was carried out at a temperature of 58.5℃ for 1.5 hours;

[0055] (4) Sweating: Release the liquid that has not grown into crystals, raise the melting crystallizer by 0.8°C each time, and after each temperature increase, sweat until no liquid drips out, and then raise the temperature again. Finally, raise the temperature to 70.5°C. After sweating is completed, melt the remaining crystals to obtain the fluorene oxide product.

[0056] The method described in Example 2 was used to purify fluorene oxide, resulting in a first-pass yield of 46.5% and a purity of 99.14%. The gas chromatogram of the product is shown below. Figure 3 As shown.

[0057] Comparative Example 2

[0058] A method for purifying fluorene oxide through melt crystallization specifically includes the following steps:

[0059] (1) Fluorene Oxygen Melting: Under normal pressure, 90% pure fluorene oxygen crystals are added to the reactor, and the reactor temperature is controlled at 90℃ to melt the crystals;

[0060] (2) Cooling: Control the reactor temperature and reduce the temperature of the molten oxygen fluorene to 55℃ at a cooling rate of 3.5℃ / h;

[0061] (3) Crystallization: Crystallization was carried out at a temperature of 55℃ for 2.5 hours;

[0062] (4) Sweating: Release the liquid that has not grown into crystals, raise the melting crystallizer by 3.5°C each time, and after each temperature increase, sweat until no liquid drips out, and then raise the temperature again. Finally, raise the temperature to 65°C. After sweating is completed, melt the remaining crystals to obtain the fluorene oxide product.

[0063] The method described in Comparative Example 2 was used to purify fluorene oxide. The yield of the fluorene oxide product was 46.5% in one pass, and the purity of the product was 97.12%. The gas chromatogram of the product is shown below. Figure 4 As shown, the lower temperature at the end of the sweating process compared to Example 2 resulted in lower purity of the finished product.

[0064] Compared with conventional chemical separation methods (absorption, distillation, extraction, supercritical extraction, adsorption separation, chromatographic separation, membrane separation), the embodiments of the present invention achieve the following technical effects:

[0065] 1) High-purity products can be separated: The purity of products processed by general distillation and recrystallization is around 99%, while the purity of products processed by melt crystallization can reach 99.9% or even 99.99%, thus meeting the high-purity requirements of pharmaceutical products, food additives, fragrances, biochemical products, and reagent products.

[0066] 2) The method is suitable for special systems: such as materials with similar boiling points, isomers, chiral substances, etc., which are extremely difficult to separate by conventional distillation, but sometimes melt crystallization is quite simple; melt crystallization is also very suitable for heat-sensitive substances, dilute solutions, and substances with very high boiling points.

[0067] 3) Low temperature operation: Generally, it is operated at normal pressure and low temperature. The operation is simple and safe, and there are no high requirements for the equipment because the corrosivity decreases at low temperatures. There are no high requirements for the heat source, and there is no need to invest heavily in heating furnaces and high vacuum equipment systems, thus reducing costs and equipment investment.

[0068] 4) Environmentally friendly: Compared with recrystallization using solvents, the product does not need to be dried to remove the solvent, thus reducing the drying steps and avoiding increased costs, environmental pollution, and low-temperature freezing operations caused by solvent introduction.

[0069] 5) Energy saving: The energy consumption of melting crystallization is generally only 10% to 30% of that of distillation.

[0070] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing fluorene oxide, characterized in that, Includes the following steps: Melting charge: The oxygen fluorene feedstock is heated until it is completely melted into a liquid, and then charged into the crystallization tower. The oxygen fluorene feedstock is the crude product after the separation of o-phenylphenol from the product of the hydrogenation reaction of oxygen fluorene or the oxygen fluorene fraction separated in the washing oil process. Cooling crystallization: The temperature inside the crystallization tower is cooled down at a preset cooling rate until it reaches the crystallization endpoint temperature. After maintaining the temperature at a constant temperature for a predetermined time, the crystallized liquid is discharged. Sweating and discharge: Keep the bottom valve of the crystallization tower fully open, and raise the temperature of the crystallization tower at a preset heating rate to the sweating endpoint temperature for sweating; after sweating is completed, close the bottom valve of the crystallization tower, heat the crystals in the crystallization tower until they are completely melted, and collect the product oxygen fluorene.

2. The preparation method according to claim 1, characterized in that, The mass concentration of the fluorene feedstock is 50% to 95%.

3. The preparation method according to claim 1, characterized in that, In the melting and charging step, the oxygen fluorene raw material is heated to above 80°C to completely melt it into a liquid.

4. The preparation method according to claim 1, characterized in that, In the cooling crystallization step, the cooling rate is 0.5–3 °C / h, and the final crystallization temperature is 55–60.5 °C.

5. The preparation method according to claim 4, characterized in that, In the cooling crystallization step, the temperature is reduced to 66-69℃ at a cooling rate of 0.5-1.5℃ / h, and then reduced to 55-60.5℃ at a cooling rate of 1.5-3℃ / h.

6. The preparation method according to claim 4, characterized in that, In the cooling crystallization step, after the temperature drops to the final crystallization temperature, it is kept constant for 60 to 120 minutes.

7. The preparation method according to claim 1, characterized in that, The perspiration is achieved through gravity flow or intermittent vacuum, with constant temperature vacuum perspiration until no sweat drips out.

8. The preparation method according to claim 1, characterized in that, The endpoint temperature for sweating is 65.5–78.5℃.

9. The preparation method according to claim 8, characterized in that, In the sweating and discharging steps, the temperature is raised to 60.5-65.5℃ at a rate of 1.5-3℃ / h, and then raised to 65.5-78.5℃ at a rate of 0.5-1.5℃ / h.

10. The preparation method according to claim 1, characterized in that, When the mass concentration of the fluorene raw material is less than 80%, the preparation method is repeated multiple times.

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