Melt crystallization purification method of beta-methylnaphthalene

Abstract

The invention relates to a melt crystallization purification method of beta-methylnaphthalene, and relates to the field of beta-methylnaphthalene purification, and the melt crystallization purification method comprises the following steps: sequentially carrying out first cooling crystallization, second cooling crystallization, third cooling crystallization, sweating operation, melting, recrystallization and devitrification on molten beta-methylnaphthalene to obtain beta-methylnaphthalene with the purity of more than or equal to 99.8%, wherein the second cooling crystallization is assisted by first microbubble treatment. According to the method provided by the invention, by virtue of a specific cooling crystallization process, the uniformity of crystal growth is ensured, the risk that a crystal layer is too thin or too thick in the prior art is avoided, the separation efficiency of the crystal is improved, efficient separation and extraction of high-purity beta-methylnaphthalene are realized, and the purity of the obtained beta-methylnaphthalene is greater than or equal to 99.8%.

Description

Technical Field

[0001] The invention relates to the field of beta-methylnaphthalene purification, in particular to a method for purifying beta-methylnaphthalene by melt crystallization, and in particular to a method for purifying industrial-grade beta-methylnaphthalene (purity ≤98%) by melt crystallization. Background Art

[0002] At present, β-Methyl Naphthalene (β-MN) is an important fine chemical widely used in synthetic resins, dyes, plastic additives, electronic chemicals and pharmaceutical intermediates. Due to its special molecular structure and properties, the purity and crystal form of β-methylnaphthalene have a decisive influence on the quality and performance of its downstream products.

[0003] Traditional β-methylnaphthalene extraction methods usually rely on solvent extraction and distillation, but these methods have problems such as complex operation, high energy consumption, and difficulty in solvent recovery. In comparison, melt crystallization technology, as a method that can be used for efficient separation and purification at lower temperatures, has the advantages of low energy consumption, simple operation, and high purity.

[0004] Although melt crystallization technology has been successfully applied in the purification of many chemicals, such as US265976 discloses a tower crystallizer that can quickly crystallize and uses a combination of crystallization and distillation to purify products, the process is complicated and the equipment is difficult to operate, which poses certain difficulties in industrial scale-up.

[0005] CN101177377A proposes a relatively simple method for refining β-methylnaphthalene by melt crystallization, which realizes the purification of high-purity β-methylnaphthalene through four steps of film formation, crystal growth, sweating and melting, and has the advantages of no waste liquid discharge and improved yield in operation. However, the purity and yield of the purified product still need to be improved.

[0006] However, for compounds with special molecular structures such as β-methylnaphthalene, the existing technology still has many bottlenecks, mainly in terms of rate control during the crystallization process, consistency of crystal morphology, and impurity separation efficiency.

[0007] Therefore, how to efficiently and economically extract and purify β-methylnaphthalene has become a technical problem that needs to be solved urgently in the fields of chemistry, materials and related industries.

[0008] In summary, the existing purification methods for β-methylnaphthalene still have the defects of poor purification effect, low product purity and low recovery rate. Summary of the invention

[0009] In view of the problems existing in the prior art, the object of the present invention is to provide a melt crystallization purification method for β-methylnaphthalene to solve the defects of poor purification effect, low product purity and low recovery rate in the purification method for β-methylnaphthalene.

[0010] To achieve this object, the present invention adopts the following technical solutions:

[0011] The present invention provides a melt crystallization purification method for β-methylnaphthalene, which comprises:

[0012] The molten β-methylnaphthalene is subjected to a first cooling crystallization, a second cooling crystallization, a third cooling crystallization, a sweating operation, melting, recrystallization and crystallization in sequence to obtain β-methylnaphthalene with a purity of ≥99.8%;

[0013] Wherein, the second cooling crystallization is assisted by a first microbubble treatment.

[0014] The method provided by the present invention ensures the uniformity of crystal growth by means of a specific cooling crystallization process, avoids the risk of too thin or too thick crystal layers in the prior art, improves the crystal separation efficiency, and realizes the efficient separation and extraction of high-purity β-methylnaphthalene, and the purity of the obtained β-methylnaphthalene is ≥99.8%.

[0015] As a preferred technical solution of the present invention, the temperature of the molten β-methylnaphthalene is 80-100°C.

[0016] As a preferred technical solution of the present invention, the initial temperature of the first cooling crystallization is 80-100°C.

[0017] Preferably, the cooling rate of the first cooling crystallization is 5-10°C / h.

[0018] Preferably, the endpoint temperature of the first cooling crystallization is 40-60°C.

[0019] Preferably, the first cooling crystallization is cooled to the terminal temperature and maintained for 2-6 hours.

[0020] Preferably, the first cooling crystallization is stirred at 10-20 r / min.

[0021] As a preferred technical solution of the present invention, the initial temperature of the second cooling crystallization is the endpoint temperature of the first cooling crystallization.

[0022] Preferably, the cooling rate of the second cooling crystallization is 10-20°C / h.

[0023] Preferably, the endpoint temperature of the second cooling crystallization is 20-30°C.

[0024] Preferably, the second cooling crystallization is maintained for 0.5-8h after cooling to the end temperature.

[0025] Preferably, the second cooling crystallization is stirred at 20-40 r / min.

[0026] As a preferred technical solution of the present invention, the flow rate of bubbles in the first microbubble treatment is 50-200 L / min.

[0027] Preferably, the diameter of the bubbles in the first microbubble treatment is 20-150 μm.

[0028] As a preferred technical solution of the present invention, the initial temperature of the third cooling crystallization is the endpoint temperature of the second cooling crystallization.

[0029] Preferably, the cooling rate of the third cooling crystallization is 10-20°C / h.

[0030] Preferably, the endpoint temperature of the third cooling crystallization is 0-10°C.

[0031] Preferably, the third cooling crystallization is kept for 0.5-1.5h after cooling to the end temperature.

[0032] Preferably, the third cooling crystallization is stirred at 40-60 r / min.

[0033] As a preferred technical solution of the present invention, the temperature is controlled at 10-30°C during the sweating operation.

[0034] Preferably, the heat preservation time of the sweating operation is 1-5h.

[0035] As a preferred technical solution of the present invention, the temperature during melting is controlled at 40-60°C.

[0036] Preferably, the melting holding time is 1-3h.

[0037] As a preferred technical solution of the present invention, the recrystallization comprises: reducing the temperature to 0-10°C at a cooling rate of 5-20°C / h.

[0038] As a preferred technical solution of the present invention, the crystallization includes: controlling the temperature to 10-30°C and performing a second microbubble treatment, followed by a cooling treatment to obtain β-methylnaphthalene with a purity of ≥99.8%.

[0039] Preferably, the flow rate of bubbles in the second microbubble treatment is 50-200 L / min.

[0040] Preferably, the diameter of the bubbles in the second microbubble treatment is 10-80 μm.

[0041] Preferably, the cooling rate of the cooling treatment is 3-10°C / h.

[0042] Preferably, the terminal temperature of the cooling treatment is 0-2°C.

[0043] Compared with the prior art solutions, the present invention has the following beneficial effects:

[0044] (1) The purification method provided by the present invention adopts a multi-stage cooling curve design, gradually reduces the temperature and adjusts the cooling rate at different stages, thereby avoiding the problem of incomplete crystals or uneven morphology caused by excessively fast or uneven cooling rates in traditional methods, and ensuring high-quality growth of crystals.

[0045] (2) The purification method provided by the present invention combines bubbles and stirring to optimize the growth environment of the crystals, improve the morphology of the crystals, avoid crystal agglomeration and uneven morphology, and further promote the separation of the crystals and the mother liquor through microbubbles, thereby effectively improving the crystallization quality.

[0046] (3) The present invention significantly improves the separation efficiency of crystals and mother liquor through the optimization design of bubble upflow and flow path. The rising effect of bubbles not only accelerates the separation of crystals and mother liquor, but also effectively reduces the redissolution of crystals, thereby improving the crystal yield and the purity of the final product. The purity of the obtained β-methylnaphthalene product is ≥99.97%, and the recovery rate reaches more than 85.3%.

[0047] (4) The purification method provided by the present invention is equipped with a temperature sensor and an automatic control system to monitor the temperature and crystallization state during the crystallization process in real time, automatically adjust the cooling rate, stirring rate and air flow intensity of the bubble generator, thereby achieving precise control of the crystallization process and improving the stability and controllability of the overall operation. DETAILED DESCRIPTION

[0048] To better illustrate the present invention and facilitate understanding of the technical solution of the present invention, typical but non-limiting embodiments of the present invention are as follows:

[0049] This embodiment provides a melt crystallization purification method for β-methylnaphthalene, the melt crystallization purification method comprising:

[0050] The molten β-methylnaphthalene is subjected to a first cooling crystallization, a second cooling crystallization, a third cooling crystallization, a sweating operation, melting, recrystallization and crystallization in sequence to obtain β-methylnaphthalene with a purity of ≥99.8%;

[0051] Wherein, the second cooling crystallization is assisted by a first microbubble treatment.

[0052] In the present invention, the second cooling crystallization is assisted by the first microbubble treatment, and the generated microbubbles help separate the crystals from the mother liquor through the upward flow. The bubble generation rate is adjusted according to the volume of the crystallizer and the crystal precipitation situation to ensure that the number of bubbles is moderate, which can effectively separate the crystals from the mother liquor without excessively interfering with the growth of the crystals, accelerate the separation of the crystals from the mother liquor, and avoid the redissolution of the crystals, thereby ensuring a high product yield.

[0053] Wherein, the temperature of the molten β-methylnaphthalene is 80-100°C, for example, it can be 80°C, 82°C, 84°C, 86°C, 88°C, 90°C, 92°C, 94°C, 96°C, 98°C or 100°C, but is not limited to the listed values, and other unlisted values ​​within the range also meet the requirements.

[0054] Among them, the initial temperature of the first cooling crystallization is 80-100°C, for example, it can be 80°C, 82°C, 84°C, 86°C, 88°C, 90°C, 92°C, 94°C, 96°C, 98°C or 100°C, but is not limited to the listed values, and other unlisted values ​​within the range also meet the requirements.

[0055] Among them, the cooling rate of the first cooling crystallization is 5-10℃ / h, for example, it can be 5℃ / h, 6℃ / h, 7℃ / h, 8℃ / h, 9℃ / h or 10℃ / h, but is not limited to the listed values, and other unlisted values ​​within this range also meet the requirements.

[0056] In the present invention, controlling the cooling rate of the first cooling crystallization can help control the size and shape of the crystals, prevent the crystals from being too large or too small to ensure the uniformity of the crystallization, prevent the crystallization from being too fast, promote the formation of crystals, thereby ensuring that the crystals can grow uniformly, and avoid excessive cooling resulting in uneven crystals.

[0057] Among them, the endpoint temperature of the first cooling crystallization is 40-60°C, for example, it can be 40°C, 42°C, 44°C, 46°C, 48°C, 50°C, 52°C, 54°C, 56°C, 58°C or 60°C, but is not limited to the listed values, and other unlisted values ​​within the range also meet the requirements.

[0058] Among them, the first cooling crystallization is maintained for 2-6 hours after cooling to the terminal temperature, for example, it can be 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, 5.5h or 6h, but is not limited to the listed values, and other unlisted values ​​within the range also meet the requirements.

[0059] Wherein, the first cooling crystallization is stirred at 10-20 r / min, for example, it can be 10 r / min, 12 r / min, 14 r / min, 16 r / min, 18 r / min or 20 r / min, but is not limited to the listed values, and other unlisted values ​​within the range also meet the requirements.

[0060] Wherein, the initial temperature of the second cooling crystallization is the endpoint temperature of the first cooling crystallization.

[0061] Wherein, the cooling rate of the second cooling crystallization is 10-20℃ / h, for example, it can be 10℃ / h, 11℃ / h, 12℃ / h, 13℃ / h, 14℃ / h, 15℃ / h, 16℃ / h, 17℃ / h, 18℃ / h, 19℃ / h or 20℃ / h, etc., but is not limited to the listed values, and other unlisted values ​​within the range also meet the requirements.

[0062] In the present invention, the cooling rate of the second cooling crystallization is controlled to ensure that the crystal continues to grow and to gradually remove part of the residual liquid.

[0063] Wherein, the endpoint temperature of the second cooling crystallization is 20-30°C, for example, it can be 20°C, 21°C, 22°C, 23°C, 24°C, 25°C, 26°C, 27°C, 28°C, 29°C or 30°C, but is not limited to the listed values, and other unlisted values ​​within the range also meet the requirements.

[0064] Among them, the second cooling crystallization is maintained for 0.5-8h after cooling to the terminal temperature, for example, it can be 0.5h, 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, 5.5h, 6h, 6.5h, 7h, 7.5h or 8h, but is not limited to the listed values, and other unlisted values ​​within the range also meet the requirements.

[0065] Wherein, the second cooling crystallization is stirred at 20-40r / min, for example, it can be 20r / min, 22r / min, 24r / min, 26r / min, 28r / min, 30r / min, 32r / min, 34r / min, 36r / min, 38r / min or 40r / min, but is not limited to the listed values, and other unlisted values ​​within the range also meet the requirements.

[0066] Among them, the flow rate of bubbles in the first microbubble treatment is 50-200 L / min, for example, it can be 50 L / min, 60 L / min, 80 L / min, 100 L / min, 120 L / min, 140 L / min, 160 L / min, 180 L / min or 200 L / min, but is not limited to the listed values, and other unlisted values ​​within the range also meet the requirements.

[0067] Among them, the diameter of the bubbles in the first microbubble treatment is 20-150μm, for example, it can be 20μm, 30μm, 40μm, 50μm, 60μm, 70μm, 80μm, 90μm, 100μm, 110μm, 110μm, 120μm, 130μm, 140μm or 150μm, etc., and all bubble diameters within a certain range within the example range can be selected, or a uniform bubble diameter can be selected.

[0068] Wherein, the initial temperature of the third cooling crystallization is the endpoint temperature of the second cooling crystallization.

[0069] Among them, the cooling rate of the third cooling crystallization is 10-20℃ / h, for example, it can be 10℃ / h, 11℃ / h, 12℃ / h, 13℃ / h, 14℃ / h, 15℃ / h, 16℃ / h, 17℃ / h, 18℃ / h, 19℃ / h or 20℃ / h, etc., but is not limited to the listed values, and other unlisted values ​​within the range also meet the requirements.

[0070] In the present invention, controlling the cooling rate of the third cooling crystallization helps to further refine the crystals, improve the purity and quality of the crystals, and ensure that the crystals are uniformly precipitated and form an ideal crystal form.

[0071] Among them, the endpoint temperature of the third cooling crystallization is 0-10°C, for example, it can be 0°C, 1°C, 2°C, 3°C, 4°C, 5°C, 6°C, 7°C, 8°C, 9°C or 10°C, but is not limited to the listed values, and other unlisted values ​​within the range also meet the requirements.

[0072] Among them, the third cooling crystallization is maintained for 0.5-1.5h after cooling to the terminal temperature, for example, it can be 0.5h, 0.6h, 0.7h, 0.8h, 0.9h, 1h, 1.1h, 1.2h, 1.3h, 1.4h or 1.5h, but is not limited to the listed values, and other unlisted values ​​within the range also meet the requirements.

[0073] Wherein, the third cooling crystallization is stirred at 40-60r / min, for example, it can be 40r / min, 42r / min, 44r / min, 46r / min, 48r / min, 50r / min, 52r / min, 54r / min, 56r / min, 58r / min or 60r / min, but is not limited to the listed values, and other unlisted values ​​within the range also meet the requirements.

[0074] Among them, the temperature controlled during the sweating operation is 10-30℃, for example, it can be 10℃, 12℃, 14℃, 16℃, 18℃, 20℃, 22℃, 24℃, 26℃, 28℃ or 30℃, but is not limited to the listed values, and other unlisted values ​​within the range also meet the requirements.

[0075] Among them, the insulation time of the sweating operation is 1-5h, for example, it can be 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h or 5h, but is not limited to the listed values. Other unlisted values ​​within this range also meet the requirements.

[0076] In the present invention, when the crystallization process is nearly finished and most of the crystals have been precipitated, sweating begins. The temperature in the crystallizer is slowly raised to a temperature close to the melting point, so that impurities in the crystallized crude crystals gradually melt and seep out from the inside of the crystals. The heating is continued and the temperature is kept, and the temperature gradient is used to cause the impurities on the surface and inside of the crystals to gradually dissolve and separate, thereby further purifying the crystals.

[0077] Among them, the controlled temperature during melting is 40-60°C, for example, it can be 40°C, 42°C, 44°C, 46°C, 48°C, 50°C, 52°C, 54°C, 56°C, 58°C or 60°C, but is not limited to the listed values, and other unlisted values ​​within the range also meet the requirements.

[0078] Among them, the melting insulation time is 1-3h, for example, it can be 1h, 1.2h, 1.4h, 1.6h, 1.8h, 2h, 2.2h, 2.4h, 2.6h, 2.8h or 3h, but is not limited to the listed values, and other unlisted values ​​within the range also meet the requirements.

[0079] In the present invention, the crystals obtained by sweating are heated again to a molten state, so that the trace impurities involved in the crystals are precipitated and separated again, further improving the purity of the crystals. The crystals are kept warm for a certain period of time to ensure that all residual trace impurities have been released. The purpose of this process is to remove trace impurities by melting again and further purify.

[0080] Wherein, the recrystallization comprises: reducing the temperature to 0-10°C at a cooling rate of 5-20°C / h.

[0081] In the present invention, the cooling rate of recrystallization is 5-20°C / h, for example, it can be 5°C / h, 6°C / h, 8°C / h, 10°C / h, 12°C / h, 14°C / h, 16°C / h, 18°C / h or 20°C / h, but is not limited to the listed values, and other unlisted values ​​within the range also meet the requirements.

[0082] In the present invention, the terminal temperature of recrystallization cooling is 0-10°C, for example, it can be 0°C, 1°C, 2°C, 3°C, 4°C, 5°C, 6°C, 7°C, 8°C, 9°C or 10°C, but is not limited to the listed values, and other unlisted values ​​within the range also meet the requirements.

[0083] In the present invention, the melted material is slowly cooled again to further precipitate or dissolve the impurities, thereby promoting crystals to precipitate again to improve the purity of the crystals.

[0084] The crystallization comprises: controlling the temperature to be 10-30° C. and performing a second microbubble treatment, followed by a temperature reduction treatment to obtain β-methylnaphthalene with a purity of ≥99.8%.

[0085] In the present invention, the temperature during crystallization is controlled at 10-30°C, for example, it can be 10°C, 12°C, 14°C, 16°C, 18°C, 20°C, 22°C, 24°C, 26°C, 28°C or 30°C, but is not limited to the listed values, and other unlisted values ​​within the range also meet the requirements.

[0086] Among them, the flow rate of bubbles in the second microbubble treatment is 50-200 L / min, for example, it can be 50 L / min, 60 L / min, 80 L / min, 100 L / min, 120 L / min, 140 L / min, 160 L / min, 180 L / min or 200 L / min, but is not limited to the listed values, and other unlisted values ​​within the range also meet the requirements.

[0087] Among them, the diameter of the bubbles in the second microbubble treatment is 10-80μm, for example, it can be 10μm, 20μm, 30μm, 40μm, 50μm, 60μm, 70μm or 80μm, etc., and all bubble diameters within a certain range within the example range can be selected, or a uniform bubble diameter can be selected.

[0088] Among them, the cooling rate of the cooling treatment is 3-10℃ / h, for example, it can be 3℃ / h, 4℃ / h, 5℃ / h, 6℃ / h, 7℃ / h, 8℃ / h, 9℃ / h or 10℃ / h, but is not limited to the listed values, and other unlisted values ​​within the range also meet the requirements.

[0089] The terminal temperature of the cooling treatment is 0-2°C, for example, 0°C, 1°C, 1.5°C or 2°C, but is not limited to the listed values, and other values ​​not listed within the range also meet the requirements.

[0090] In the present invention, the gas used to form microbubbles includes inert gases and other gases that do not react with β-methylnaphthalene, such as nitrogen, helium, neon, argon, etc.

[0091] In the present invention, microbubbles are generated at the bottom of the melt and then move upward, and may also be generated at the side of the melt.

[0092] Further, in order to illustrate the good purification effect that the purification method provided by the present invention can achieve for β-methylnaphthalene, the following actual example is used for exemplary description, as follows:

[0093] Example 1

[0094] This embodiment provides a melt crystallization purification method for β-methylnaphthalene, the melt crystallization purification method comprising:

[0095] The molten β-methylnaphthalene (with a purity of 97.5%) is subjected to a first cooling crystallization, a second cooling crystallization, a third cooling crystallization, a sweating operation, melting, recrystallization and crystallization in sequence to obtain a purified β-methylnaphthalene product;

[0096] The temperature of the molten β-methylnaphthalene is 90° C.

[0097] The initial temperature of the first cooling crystallization is 90°C, the cooling rate is 10°C / h, the end temperature is 50°C, and the temperature is kept at the end temperature for 4 hours after cooling to the end temperature, and the stirring is carried out at 15r / min during the process;

[0098] The initial temperature of the second cooling crystallization is the endpoint temperature of the first cooling crystallization, the cooling rate is 15°C / h, the endpoint temperature is 25°C, and the temperature is kept for 4 hours after cooling to the endpoint temperature, assisted by the first microbubble treatment, the bubble flow rate is 100L / min, the bubble (nitrogen) diameter is 50μm, and stirring is performed at 30r / min during the process;

[0099] The initial temperature of the third cooling crystallization is the endpoint temperature of the second cooling crystallization, the cooling rate is 15°C / h, the endpoint temperature is 5°C, and the temperature is kept at the endpoint temperature for 1h, and stirring is performed at 50r / min during the process;

[0100] The temperature during the sweating operation is controlled at 20°C and the insulation time is 3 hours;

[0101] The temperature during the melting process is controlled at 50°C and the insulation time is 2h;

[0102] The recrystallization comprises: lowering the temperature to 5°C at a cooling rate of 10°C / h;

[0103] The crystallization includes: controlling the temperature to 20°C and performing a second microbubble treatment, followed by a cooling treatment to obtain β-methylnaphthalene; the flow rate of the bubbles (nitrogen) in the second microbubble treatment is 150 L / min, and the diameter of the bubbles is 40 μm; the cooling rate of the cooling treatment is 5°C / h, and the terminal temperature is 1°C.

[0104] Example 2

[0105] This embodiment provides a melt crystallization purification method for β-methylnaphthalene, the melt crystallization purification method comprising:

[0106] The molten β-methylnaphthalene (with a purity of 85.3%) is subjected to a first cooling crystallization, a second cooling crystallization, a third cooling crystallization, a sweating operation, melting, recrystallization and crystallization in sequence to obtain a purified β-methylnaphthalene product;

[0107] The temperature of the molten β-methylnaphthalene is 95° C.

[0108] The initial temperature of the first cooling crystallization is 95°C, the cooling rate is 5°C / h, the end temperature is 55°C, and the temperature is kept at the end temperature for 5h after cooling to the end temperature, and the stirring is carried out at 18r / min during the process;

[0109] The initial temperature of the second cooling crystallization is the endpoint temperature of the first cooling crystallization, the cooling rate is 18°C / h, the endpoint temperature is 25°C, and the temperature is kept for 6 hours after cooling to the endpoint temperature, assisted by the first microbubble treatment, the flow rate of the bubble (argon gas) is 150L / min, the diameter of the bubble is 70μm, and stirring is performed at 30r / min during the process;

[0110] The initial temperature of the third cooling crystallization is the endpoint temperature of the second cooling crystallization, the cooling rate is 12°C / h, the endpoint temperature is 2°C, and after cooling to the endpoint temperature, it is kept for 1.2h and stirred at 50r / min;

[0111] The temperature during the sweating operation is controlled at 25°C and the insulation time is 2h;

[0112] The temperature during the melting process is controlled at 45°C and the holding time is 2.5 hours;

[0113] The recrystallization comprises: lowering the temperature to 2°C at a cooling rate of 15°C / h;

[0114] The crystallization includes: controlling the temperature to 25°C and performing a second microbubble treatment, followed by a cooling treatment to obtain β-methylnaphthalene; the flow rate of the bubbles (argon) in the second microbubble treatment is 100 L / min, and the diameter of the bubbles is 60 μm; the cooling rate of the cooling treatment is 8°C / h, and the terminal temperature is 1.5°C.

[0115] Example 3

[0116] This embodiment provides a melt crystallization purification method for β-methylnaphthalene, and the melt crystallization purification method comprises:

[0117] The molten β-methylnaphthalene (with a purity of 84.6%) is subjected to a first cooling crystallization, a second cooling crystallization, a third cooling crystallization, a sweating operation, melting, recrystallization and crystallization in sequence to obtain a purified methylnaphthalene product;

[0118] The temperature of the molten β-methylnaphthalene is 80° C.

[0119] The initial temperature of the first cooling crystallization is 80°C, the cooling rate is 8°C / h, the end temperature is 40°C, and after cooling to the end temperature, it is kept for 6 hours and stirred at 20r / min;

[0120] The initial temperature of the second cooling crystallization is the endpoint temperature of the first cooling crystallization, the cooling rate is 10°C / h, the endpoint temperature is 20°C, and the temperature is kept for 0.5h after cooling to the endpoint temperature, assisted by the first microbubble treatment, the flow rate of the bubble (neon gas) is 200L / min, the diameter of the bubble is 60μm, and stirring is performed at 20r / min during the process;

[0121] The initial temperature of the third cooling crystallization is the endpoint temperature of the second cooling crystallization, the cooling rate is 10°C / h, the endpoint temperature is 0°C, and after cooling to the endpoint temperature, it is kept for 0.5h and stirred at 40r / min;

[0122] The temperature during the sweating operation is controlled at 10°C and the insulation time is 5 hours;

[0123] The temperature during the melting process is controlled at 40°C and the insulation time is 3 hours;

[0124] The recrystallization comprises: lowering the temperature to 10°C at a cooling rate of 5°C / h;

[0125] The crystallization includes: controlling the temperature to 10°C and performing a second microbubble treatment, followed by a cooling treatment to obtain β-methylnaphthalene; the flow rate of the bubbles (neon gas) in the second microbubble treatment is 50 L / min, and the diameter of the bubbles is 50 μm; the cooling rate of the cooling treatment is 3°C / h, and the terminal temperature is 2°C.

[0126] Example 4

[0127] This embodiment provides a melt crystallization purification method for β-methylnaphthalene, the melt crystallization purification method comprising:

[0128] The molten β-methylnaphthalene (with a purity of 75.8%) is subjected to a first cooling crystallization, a second cooling crystallization, a third cooling crystallization, a sweating operation, melting, recrystallization and crystallization in sequence to obtain a purified β-methylnaphthalene product;

[0129] The temperature of the molten β-methylnaphthalene is 100° C.

[0130] The initial temperature of the first cooling crystallization is 100°C, the cooling rate is 5°C / h, the end temperature is 60°C, and after cooling to the end temperature, it is kept for 2h and stirred at 10r / min;

[0131] The initial temperature of the second cooling crystallization is the endpoint temperature of the first cooling crystallization, the cooling rate is 20°C / h, the endpoint temperature is 30°C, and the temperature is kept for 8 hours after cooling to the endpoint temperature, assisted by the first microbubble treatment, the flow rate of the bubble (helium) is 50L / min, the diameter of the bubble is 70μm, and stirring is performed at 40r / min during the process;

[0132] The initial temperature of the third cooling crystallization is the endpoint temperature of the second cooling crystallization, the cooling rate is 20°C / h, the endpoint temperature is 10°C, and after cooling to the endpoint temperature, it is kept for 1.5h and stirred at 60r / min;

[0133] The temperature during the sweating operation is controlled at 30°C and the insulation time is 1 hour;

[0134] The temperature during the melting process is controlled at 60° C. and the holding time is 1 hour;

[0135] The recrystallization comprises: lowering the temperature to 0°C at a cooling rate of 20°C / h;

[0136] The crystallization includes: controlling the temperature to 30°C and performing a second microbubble treatment, followed by a cooling treatment to obtain β-methylnaphthalene; the flow rate of the bubbles (helium) in the second microbubble treatment is 200L / min, and the diameter of the bubbles is 40μm; the cooling rate of the cooling treatment is 10°C / h, and the end temperature is 0°C.

[0137] Comparative Example 1

[0138] The only difference from Example 1 is that the first microbubble treatment is not performed in the second cooling crystallization.

[0139] Comparative Example 2

[0140] The only difference from Example 1 is that the first microbubble treatment is not performed in the second cooling crystallization, but is performed in the first cooling crystallization.

[0141] Comparative Example 3

[0142] The only difference from Example 1 is that the first microbubble treatment is not performed in the second cooling crystallization, but is performed in the third cooling crystallization.

[0143] Example 5

[0144] The only difference from Example 1 is that the cooling rate of the first cooling crystallization is 20° C. / h.

[0145] Example 6

[0146] The only difference from Example 1 is that the cooling rate of the first cooling crystallization is 2° C. / h.

[0147] Example 7

[0148] The only difference from Example 1 is that no stirring is performed during the first cooling crystallization.

[0149] Example 8

[0150] The only difference from Example 1 is that the cooling rate of the second cooling crystallization is 25° C. / h.

[0151] Example 9

[0152] The only difference from Example 1 is that the cooling rate of the second cooling crystallization is 5° C. / h.

[0153] Example 10

[0154] The only difference from Example 1 is that stirring is not performed during the second cooling crystallization.

[0155] Embodiment 11

[0156] The only difference from Example 1 is that the cooling rate of the third cooling crystallization is 25° C. / h.

[0157] Example 12

[0158] The only difference from Example 1 is that the cooling rate of the third cooling crystallization is 5° C. / h.

[0159] Embodiment 13

[0160] The only difference from Example 1 is that no stirring is performed during the third cooling crystallization.

[0161] Embodiment 14

[0162] The only difference from Example 1 is that the flow rate of bubbles in the first microbubble treatment is 20 L / min.

[0163] Embodiment 15

[0164] The only difference from Example 1 is that the flow rate of bubbles in the first microbubble treatment is 250 L / min.

[0165] Example 16

[0166] The only difference from Example 1 is that the second microbubble treatment is not performed during crystallization.

[0167] Embodiment 17

[0168] The only difference from Example 1 is that the flow rate of bubbles in the second microbubble treatment is 20 L / min.

[0169] Embodiment 18

[0170] The only difference from Example 1 is that the flow rate of bubbles in the second microbubble treatment is 250 L / min.

[0171] The β-methylnaphthalene product obtained in the above example was tested for purity by high performance liquid chromatography and the recovery rate of β-methylnaphthalene was calculated. The results are shown in Table 1.

[0172] Table 1

[0173]

[0174]

[0175] From Table 1, we can see that:

[0176] (1) Examples 1-4

[0177] ① Purity: The purity of all examples reached above 99.97%, which means that the melt crystallization purification method of the present invention can effectively remove impurities and obtain highly pure β-methylnaphthalene.

[0178] ② Recovery rate: The recovery rate is between 94% and 95%, which indicates that during the purification process, although the purity is extremely high, some β-methylnaphthalene cannot be completely recovered. This is because the improvement of purity often requires more crystallization steps and higher separation efficiency, resulting in certain losses.

[0179] Analysis: Examples 1-4 show that the purity of β-methylnaphthalene can be significantly improved by optimizing the methods of gradual cooling crystallization, microbubble treatment, etc. The recovery rate is relatively high, but since the purity is already very close to the theoretical limit (100%), the recovery rate cannot be further significantly improved.

[0180] (2) Comparative Examples 1-3

[0181] ① Purity: The purity is about 98%, which is significantly lower than that of Examples 1 to 4. This indicates that the process without microbubble treatment or using only low-flow bubbles has poor effect, resulting in the retention of impurities and a decrease in purity.

[0182] ② Recovery rate: The recovery rate is generally low, below 90%, especially the recovery rate of Comparative Example 1 is only 90%. This situation shows that the lack of effective microbubble treatment or poor crystallization conditions resulted in the failure of successful recovery of some β-methylnaphthalene, further affecting the overall recovery effect.

[0183] Analysis: The crystallization process in these comparative solutions is not as optimized as that in Examples 1-4. The microbubble flow rate is too small or microbubble treatment is not used, resulting in reduced purity and reduced recovery rate. The lack of crystallization and the auxiliary effect of bubbles reduces the separation efficiency, and impurities cannot be effectively removed, and the target product cannot be recovered to the maximum extent.

[0184] (3) Embodiment 5-18

[0185] ① Purity: The purity of these examples is generally higher than 98%, ranging from 99.80% to 99.90%, which is closer to Examples 1-4, but mostly lower than 99.95%. The change in purity is mainly affected by the cooling rate, crystallization steps and microbubble flow rate.

[0186] ② Recovery rate: The recovery rate varies widely, ranging from 89% to 94%. Specifically:

[0187] Fast cooling rate (such as Examples 8, 9, and 11): In these examples, due to too fast crystallization, the target product and impurities may not be fully separated, thereby affecting the recovery rate and reducing it to about 89%.

[0188] Microbubble treatment effect: When the second microbubble flow rate is large (such as in Examples 14, 15, and 17), the recovery rate is high, reaching more than 94%. This is because appropriate microbubble treatment can promote the removal of impurities and the purification of the target substance during the crystallization process.

[0189] Synergistic effect of stirring and bubbling treatment: In Examples 10 and 13, the lack of stirring or microbubble treatment caused the recovery rate to drop to about 89%. This shows that the effect of stirring and bubbling is very critical for the uniform distribution of crystals and the removal of impurities.

[0190] Analysis: The purity of Examples 5-18 is generally high, but the difference in recovery reflects the significant impact of process conditions (such as cooling rate, stirring speed, microbubble treatment, etc.) on the recovery. Appropriate microbubble flow and moderate cooling rate can improve the recovery, but the improvement in purity is often accompanied by a certain loss in recovery. In particular, when the process conditions are too harsh (such as too fast cooling or insufficient bubble treatment), the recovery may be negatively affected even if the purity is high.

[0191] The preferred embodiments of the present invention are described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, a variety of simple modifications can be made to the technical solution of the present invention, and these simple modifications all belong to the protection scope of the present invention.

[0192] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0193] In addition, various embodiments of the present invention may be arbitrarily combined, and as long as they do not violate the concept of the present invention, they should also be regarded as the contents disclosed by the present invention.

Claims

1. A melt crystallization purification method for β-methylnaphthalene, characterized in that: The melt crystallization purification method comprises: The molten β-methylnaphthalene is subjected to a first cooling crystallization, a second cooling crystallization, a third cooling crystallization, a sweating operation, melting, recrystallization and crystallization in sequence to obtain β-methylnaphthalene with a purity of ≥99.8%; Wherein, the second cooling crystallization is assisted by a first microbubble treatment.

2. The melt crystallization purification method according to claim 1, characterized in that: The temperature of the molten β-methylnaphthalene is 80-100°C.

3. The melt crystallization purification method according to claim 1 or 2, characterized in that: The initial temperature of the first cooling crystallization is 80-100°C; Preferably, the cooling rate of the first cooling crystallization is 5-10°C / h; Preferably, the endpoint temperature of the first cooling crystallization is 40-60°C; Preferably, the first cooling crystallization is cooled to the end temperature and maintained for 2-6 hours; Preferably, the first cooling crystallization is stirred at 10-20 r / min.

4. The melt crystallization purification method according to any one of claims 1 to 3, characterized in that: The initial temperature of the second cooling crystallization is the endpoint temperature of the first cooling crystallization; Preferably, the cooling rate of the second cooling crystallization is 10-20°C / h; Preferably, the endpoint temperature of the second cooling crystallization is 20-30°C; Preferably, the second cooling crystallization is cooled to the end temperature and maintained for 0.5-8h; Preferably, the second cooling crystallization is stirred at 20-40 r / min.

5. The melt crystallization purification method according to any one of claims 1 to 4, characterized in that: The flow rate of bubbles in the first microbubble treatment is 50-200 L / min; Preferably, the diameter of the bubbles in the first microbubble treatment is 20-150 μm.

6. The melt crystallization purification method according to any one of claims 1 to 5, characterized in that: The initial temperature of the third cooling crystallization is the endpoint temperature of the second cooling crystallization; Preferably, the cooling rate of the third cooling crystallization is 10-20°C / h; Preferably, the endpoint temperature of the third cooling crystallization is 0-10°C; Preferably, the third cooling crystallization is maintained for 0.5-1.5h after cooling to the end temperature; Preferably, the third cooling crystallization is stirred at 40-60 r / min.

7. The melt crystallization purification method according to any one of claims 1 to 6, characterized in that: The temperature during the sweating operation is controlled at 10-30°C; Preferably, the heat preservation time of the sweating operation is 1-5h.

8. The melt crystallization purification method according to any one of claims 1 to 7, characterized in that: The temperature during the melting process is controlled at 40-60°C; Preferably, the melting holding time is 1-3h.

9. The melt crystallization purification method according to any one of claims 1 to 8, characterized in that: The recrystallization comprises: reducing the temperature to 0-10°C at a cooling rate of 5-20°C / h.

10. The melt crystallization purification method according to any one of claims 1 to 9, characterized in that: The crystallization comprises: controlling the temperature to 10-30° C. and performing a second microbubble treatment, followed by a temperature reduction treatment to obtain β-methylnaphthalene with a purity of ≥99.8%; Preferably, the flow rate of bubbles in the second microbubble treatment is 50-200 L / min; Preferably, the diameter of the bubbles in the second microbubble treatment is 10-80 μm; Preferably, the cooling rate of the cooling treatment is 3-10°C / h; Preferably, the terminal temperature of the cooling treatment is 0-2°C.

Images