Separation and purification method and application of beta-methylnaphthalene in mixed methylnaphthalene

Abstract

The invention relates to a beta-methylnaphthalene separation and purification method and application in the field of coal chemical industry. Comprising the following steps: carrying out distillation and multi-side-line gradient rectification on mixed methylnaphthalene, and extracting fractions with the beta-methylnaphthalene content of 80-98% at 3-5 side-line outlets formed in a rectifying tower; performing three-stage crystallization on the crude fraction, with the cooling / heating rate of 10-20 DEG C / h, 0.5-5 DEG C / h and 0.5-2 DEG C / h respectively, and the temperature relationship is that the second crystallization is greater than the third crystallization and the first crystallization is less than the third crystallization; an included angle between a liquid flow channel in the second crystal and the horizontal plane is 15-45 degrees, so that directional separation is realized. Impurities such as alpha-methylnaphthalene and alkylbenzothiophene are removed through gradient rectification pre-enrichment and three-section directional crystallization, a high-purity product with the purity larger than or equal to 99.9% and the yield larger than or equal to 85% is obtained, and the problem that the purity and the yield of a traditional process are difficult to consider at the same time is solved.

Description

Technical Field

[0001] The present invention relates to the technical field of coal chemical industry, and in particular to a method for separating and purifying β-methylnaphthalene from mixed methylnaphthalene and its application, and in particular to a method for separating and purifying high-purity β-methylnaphthalene from mixed methylnaphthalene oil in coal tar wash oil fraction by utilizing a combined process of gradient distillation and directional melt crystallization and its application. Background Art

[0002] Currently, the coal tar wash oil fraction (230-300°C) contains a large amount of valuable polycyclic aromatic hydrocarbons (PAHs), such as β-methylnaphthalene, α-methylnaphthalene, acenaphthene, dibenzofuran, and fluorene. These PAHs can be chemically synthesized into condensed-ring aromatic hydrocarbon derivatives. These derivatives have excellent electrical conductivity and can be excited by light or electric fields to emit strong fluorescence, making them useful as monomer raw materials for organic electroluminescent devices. Furthermore, these condensed-ring aromatic hydrocarbon derivatives exhibit excellent thermal stability, low dielectric constant, and low dielectric loss, making them useful as carbon precursors, high-temperature-resistant and ablation-resistant materials in biosensors and aerospace materials, and as specialty resin materials in 5G copper-clad laminates.

[0003] However, the limitations of existing technologies are analyzed:

[0004] (1) Deficiencies of single distillation technology: Although CN101982523A, CN112933633A, CN102268273A and other patents use distillation technology, the single distillation method has a high demand for the number of theoretical plates (>200) when treating isomers such as α-methylnaphthalene and β-methylnaphthalene due to their extremely close boiling points (a difference of only 3-5°C). This leads to huge energy consumption and low separation efficiency, resulting in a final product purity of only 95-98%.

[0005] (2) Disadvantages of traditional crystallization technology: Patents such as CN101899313A use conventional recrystallization methods. Although the purity can be increased to 98%, the following problems exist: (a) The crystal growth direction is random, and it is impossible to achieve directional removal of impurities; (b) The solubility curves of α-methylnaphthalene and β-methylnaphthalene are similar, making it difficult to achieve effective separation under conventional crystallization conditions; (c) Azeotropic components such as alkylbenzothiophene are prone to form encapsulated crystals, resulting in residual impurities.

[0006] (3) Lack of synergistic effect of process combination: Most existing technologies use a single separation method, lacking the organic combination of distillation and crystallization, and are unable to give full play to the synergistic advantages of different separation mechanisms, resulting in: (a) insufficient pre-enrichment by distillation, which puts a burden on crystallization; (b) improper design of crystallization conditions, which cannot fully utilize the pretreatment effect of distillation; (c) the energy consumption-efficiency balance point of the overall process cannot be optimized.

[0007] The key technical problems to be solved by the present invention are:

[0008] Based on the above analysis of the existing technologies, the core technical problem to be solved by the present invention is: how to achieve efficient separation of β-methylnaphthalene from near-boiling point and azeotropic components such as α-methylnaphthalene and alkylbenzothiophene through an innovative combination of gradient distillation and three-stage directional crystallization, to obtain a high-purity β-methylnaphthalene product with a purity of ≥99.9% and a yield of ≥85%, while significantly reducing energy consumption and process complexity. 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 method for separating and purifying β-methylnaphthalene from mixed methylnaphthalene and its use, so as to solve the defects of low purity and low recovery rate of the product obtained by purifying β-methylnaphthalene due to isomers (α-methylnaphthalene, β-methylnaphthalene, acenaphthene, fluorene) and azeotropic components (alkylbenzothiophene) in the mixed methylnaphthalene, and at the same time solve the technical problem that it is difficult to simultaneously improve the purity and yield of the traditional distillation and crystallization combination process.

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

[0011] In a first aspect, the present invention provides a method for separating and purifying β-methylnaphthalene from mixed methylnaphthalenes, the separation and purification method comprising:

[0012] The mixed methylnaphthalene is sequentially distilled and rectified to obtain a crude β-methylnaphthalene fraction;

[0013] The obtained β-methylnaphthalene crude fraction is sequentially subjected to a first crystallization, a second crystallization, and a third crystallization to obtain high-purity β-methylnaphthalene crystals;

[0014] The temperature of the second crystallization is less than the temperature of the third crystallization and less than the temperature of the first crystallization;

[0015] The angle between the overflow liquid flow channel used in the second crystallization and the horizontal plane along the flow direction is 15-45 degrees.

[0016] The separation and purification method provided by the present invention achieves the enrichment of β-methylnaphthalene through gradient distillation, and then uses a three-stage directional melt crystallization technique to precisely remove trace impurities such as α-methylnaphthalene and alkylbenzothiophene, ultimately obtaining a high-purity β-methylnaphthalene product with a purity of ≥99.9%. This method solves the problem that traditional combined distillation and crystallization processes are difficult to simultaneously improve purity and yield. It has the characteristics of simple process, low energy consumption, and suitability for industrial continuous production. As a preferred technical solution of the present invention, the distillation temperature is 150-200°C.

[0017] As a preferred technical solution of the present invention, the number of plates of the distillation tower used in the distillation is 80-100.

[0018] Preferably, during the distillation, 3-5 side outlets are provided at different heights of the tower body to extract fractions with a β-methylnaphthalene content of 80-98%.

[0019] As a preferred technical solution of the present invention, the reflux ratio of the distillation is 10-20.

[0020] Preferably, the top pressure of the distillation tower is 10-30 kPa.

[0021] Preferably, the top temperature of the distillation tower is 180-220°C.

[0022] As a preferred technical solution of the present invention, the bottom pressure of the distillation tower is 30-50 kPa.

[0023] Preferably, the bottom temperature of the distillation tower is 230-260°C.

[0024] As a preferred technical solution of the present invention, the temperature of the crude β-methylnaphthalene fraction fed into the first crystallization is 110-130°C.

[0025] Preferably, the first crystallization includes a first heat preservation and a first temperature reduction performed sequentially.

[0026] Preferably, the first heat preservation temperature in the first crystallization is 80-100°C.

[0027] Preferably, the first insulation time in the first crystallization is 2-4 hours.

[0028] Preferably, the first cooling in the first crystallization comprises: cooling to 70-80° C. at a cooling rate of 10-20° C. / h.

[0029] As a preferred technical solution of the present invention, the second crystallization includes: a second heat preservation and a second cooling performed sequentially.

[0030] Preferably, the second heat preservation temperature in the second crystallization is 50-70°C.

[0031] Preferably, the second insulation time in the second crystallization is 6-10 hours.

[0032] Preferably, the second cooling in the second crystallization comprises: cooling to 50-53° C. at a cooling rate of 0.5-5° C. / h.

[0033] As a preferred technical solution of the present invention, the third crystallization includes: a third heat preservation and a first temperature increase performed sequentially.

[0034] Preferably, the holding temperature of the third crystallization is 60-80°C.

[0035] Preferably, the heating rate of the third crystallization is 0.5-2°C / h.

[0036] Preferably, the holding time of the third crystallization is 4-8 hours.

[0037] In a second aspect, the present invention provides a use of high-purity β-methylnaphthalene crystals obtained by the separation and purification method as described in the first aspect, the use comprising: using the high-purity β-methylnaphthalene crystals after drying as a monomer raw material for an organic electroluminescent device (OLED), a raw material for preparing a carbon matrix material, a raw material for preparing a high-temperature resistant material, a raw material for preparing an ablation-resistant material, or a raw material for preparing a special resin material.

[0038] As a preferred technical solution of the present invention, the drying method includes: vacuum drying.

[0039] Preferably, the absolute vacuum degree of the drying is ≤0.5 kPa.

[0040] Preferably, the drying temperature is 70-80°C.

[0041] Preferably, the drying time is 2-5 hours.

[0042] Compared with the existing technical solutions, the present invention has the following beneficial effects:

[0043] (1) The separation and purification method provided by the present invention uses a multi-side gradient distillation process to accurately control the enrichment degree of β-methylnaphthalene, significantly reduce the content of α-methylnaphthalene and alkylbenzothiophene, and provide high-quality raw materials for subsequent crystallization separation.

[0044] (2) In the separation and purification method provided by the present invention, an inclined flow channel structure is adopted during the second crystallization. By precisely controlling the cooling rate and the crystal growth direction, the spatial separation of the target crystals and the impurity crystals is achieved, thereby fundamentally solving the problem of separation of azeotropic systems and isomers.

[0045] (3) The separation and purification method provided by the present invention has significantly reduced energy consumption and is suitable for industrial continuous and stable production. It can obtain a high-purity β-methylnaphthalene product with a purity of ≥99.9%, and the economic benefits are significantly improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 Schematic diagram of the overflow liquid flow channel in the second crystallization in an embodiment of the present invention.

[0047] In the figure: 100 is an overflow liquid flow channel, 200 is an inlet for β-methylnaphthalene crude fraction, 300 is an outlet for β-methylnaphthalene crystal product, and 400 is an outlet for crystallization mother liquor.

[0048] The present invention is further described in detail below. However, the following examples are merely simplified examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention shall be subject to the claims. DETAILED DESCRIPTION

[0049] To better illustrate the present invention and facilitate understanding of the technical solutions of the present invention, typical but non-limiting embodiments of the present invention are as follows:

[0050] Currently, when β-methylnaphthalene is extracted from mixed methylnaphthalene in coal tar wash oil fractions, the purity and yield of the obtained β-methylnaphthalene product are poor due to the influence of isomers (such as α-methylnaphthalene, β-methylnaphthalene, acenaphthene, fluorene, etc.) and the azeotropic component alkylbenzothiophene, which is not conducive to the efficient and high-quality utilization of β-methylnaphthalene. Based on this, the present invention provides a method for separating and purifying β-methylnaphthalene from mixed methylnaphthalene. By adopting the precise coupling of gradient distillation pre-enrichment and melt crystallization, β-methylnaphthalene is completely separated from trace impurities such as α-methylnaphthalene and alkylbenzothiophene, and finally a high-purity β-methylnaphthalene product with a purity of ≥99.9% is obtained. The details are as follows:

[0051] This embodiment provides a method for separating and purifying β-methylnaphthalene from mixed methylnaphthalene, the separation and purification method comprising:

[0052] The mixed methylnaphthalene is sequentially distilled and rectified to obtain a crude β-methylnaphthalene fraction;

[0053] The obtained β-methylnaphthalene crude fraction is subjected to first crystallization, second crystallization and third crystallization in sequence to obtain high-purity β-methylnaphthalene crystals.

[0054] In the present invention, the mixed methylnaphthalene used includes: β-methylnaphthalene, α-methylnaphthalene, alkylbenzothiophene, benzene, toluene, etc., and the mass percentage of β-methylnaphthalene can be selected to be 30-70%.

[0055] The temperature of the second crystallization is less than the temperature of the third crystallization and less than the temperature of the first crystallization.

[0056] Wherein, the angle α between the overflow liquid flow channel 100 and the horizontal plane along the flow direction in the second crystallization is 15-45°, such as Figure 1 As shown, for example, it can be 15°, 20°, 25°, 30°, 35°, 40° or 45°, but is not limited to the listed values. Other unlisted values ​​within this range also meet the requirements, thereby achieving spatially oriented separation of β-methylnaphthalene crystals from α-methylnaphthalene and alkylbenzothiophene impurities.

[0057] For example, Figure 1As shown, in the second crystallization, the crude β-methylnaphthalene fraction is fed from the crude β-methylnaphthalene fraction inlet 200 of the crystallization device, and then the liquid flows along the overflow liquid flow channel 100 inclined at 15-45 degrees. During the flow process, due to temperature control and the channel inclination design, β-methylnaphthalene crystals (white circles in the figure) are gradually formed and flow along the overflow liquid flow channel 100. At the same time, impurities (such as α-methylnaphthalene and alkylbenzothiophene impurities represented by small red dots in the figure) are spatially separated from the β-methylnaphthalene crystals. Finally, the β-methylnaphthalene crystals flow out from the β-methylnaphthalene crystal product outlet 300, and the crystallization mother liquor flows out from the crystallization mother liquor outlet 400.

[0058] The distillation temperature is 150-200°C, for example, 150°C, 155°C, 160°C, 165°C, 170°C, 175°C, 180°C, 185°C, 190°C, 195°C or 200°C, but is not limited to the listed values. Other values ​​not listed within this range also meet the requirements.

[0059] Among them, the number of plates of the distillation tower used in the distillation is 80-100, for example, it can be 80, 82, 84, 86, 88, 90, 92, 94, 96, 98 or 100, etc., but is not limited to the listed values. Other values ​​not listed within this range also meet the requirements.

[0060] In the distillation, 3-5 side outlets are set at different heights of the tower body to extract fractions with a β-methylnaphthalene content of 80-98%, for example, 80%, 82%, 84%, 86%, 88%, 90%, 92%, 94%, 96% or 98%, etc., but are not limited to the listed values. Other values ​​not listed within this range also meet the requirements.

[0061] In the present invention, 3-5 side outlets are arranged at different heights of the tower body, and multiple extraction ports are arranged within the tower body height range of the fraction with a β-methylnaphthalene content of 80-98%. The fraction containing β-methylnaphthalene within the extraction range is extracted, thereby realizing gradient pre-enrichment of the raw material. The specific location of the side outlet can be reasonably designed according to the distribution range of the fraction in the tower during actual operation. The extraction amount of each side outlet is dynamically adjusted according to the composition of the raw material. The fraction with a β-methylnaphthalene content of 95% or more is directly fed into the three-stage crystallization process as a high-quality raw material.

[0062] In this invention, a multi-side distillation column is operated in stages, utilizing the boiling point difference between β-methylnaphthalene and α-methylnaphthalene (Δt = 3-5°C) to form fractions of varying concentrations at different column heights. This multi-side design avoids the high energy consumption of a single distillation column while providing high-quality, graded pre-treated raw materials for the crystallization system.

[0063] The reflux ratio of the distillation is 10-20, for example, it can be 10, 11, 12, 13, 14, 15, 16, 17, 18, 19 or 20, but is not limited to the listed values. Other values ​​not listed within this range also meet the requirements.

[0064] The top pressure of the distillation tower is 10-30 kPa, for example, it can be 10 kPa, 12 kPa, 14 kPa, 16 kPa, 18 kPa, 20 kPa, 22 kPa, 24 kPa, 26 kPa, 28 kPa or 30 kPa, but is not limited to the listed values. Other values ​​not listed within this range also meet the requirements.

[0065] The top temperature of the distillation tower is 180-220°C, for example, it can be 180°C, 185°C, 190°C, 195°C, 200°C, 205°C, 210°C, 215°C or 220°C, but is not limited to the listed values. Other values ​​not listed within this range also meet the requirements.

[0066] The bottom pressure of the distillation tower is 30-50 kPa, for example, it can be 30 kPa, 32 kPa, 34 kPa, 36 kPa, 38 kPa, 40 kPa, 42 kPa, 44 kPa, 46 kPa, 48 kPa or 50 kPa, but is not limited to the listed values. Other values ​​not listed within this range also meet the requirements.

[0067] The bottom temperature of the distillation tower is 230-260°C, for example, it can be 230°C, 235°C, 240°C, 245°C, 250°C, 255°C or 260°C, but is not limited to the listed values. Other values ​​not listed in this range also meet the requirements.

[0068] The temperature of the crude β-methylnaphthalene fraction fed into the first crystallization is 110-130°C, for example, 110°C, 112°C, 114°C, 116°C, 118°C, 120°C, 122°C, 124°C, 126°C, 128°C or 130°C, but is not limited to the listed values. Other values ​​not listed within this range also meet the requirements.

[0069] In the present invention, in the three-stage directional crystallization, the first crystallization (coarse separation stage) is to quickly form crystal nuclei at a relatively high temperature (80-100°C), and to achieve preliminary separation by utilizing the difference in crystallization rates between β-methylnaphthalene and impurities; the second crystallization (fine separation stage) is to achieve directional growth of β-methylnaphthalene crystals and spatial exclusion of impurities through directional flow in a 15-45° inclined flow channel at a moderate temperature (50-70°C); and the third crystallization (ultra-purification stage) is to perform sweating treatment at a moderate temperature (60-80°C), and to promote the diffusion and discharge of residual impurities to the crystal surface by slowly increasing the temperature.

[0070] Wherein, the first crystallization includes a first heat preservation and a first cooling performed in sequence.

[0071] The first heat preservation temperature in the first 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. Other values ​​not listed within this range also meet the requirements.

[0072] The holding time of the first holding in the first crystallization is 2-4 hours, for example, it can be 2 hours, 2.2 hours, 2.4 hours, 2.6 hours, 2.8 hours, 3 hours, 3.2 hours, 3.4 hours, 3.6 hours, 3.8 hours or 4 hours, but is not limited to the listed values. Other values ​​not listed within this range also meet the requirements.

[0073] Wherein, the first cooling in the first crystallization includes: cooling to 70-80°C at a cooling rate of 10-20°C / h. The cooling rate can be, for example, 10°C / h, 11°C / h, 12°C / h, 13°C / h, 14°C / h, 15°C / h, 16°C / h, 17°C / h, 18°C / h, 19°C / h or 20°C / h, and the end temperature of the cooling can be, for example, 70°C, 72°C, 74°C, 76°C, 78°C or 80°C, but is not limited to the listed values. Other values ​​not listed within this range also meet the requirements.

[0074] In the present invention, the starting temperature of the first cooling is the temperature of the first heat preservation.

[0075] Wherein, the second crystallization includes: a second heat preservation and a second cooling performed in sequence.

[0076] The second heat preservation temperature in the second crystallization is 50-70°C, for example, it can be 50°C, 52°C, 54°C, 56°C, 58°C, 60°C, 62°C, 64°C, 66°C, 68°C or 70°C, but is not limited to the listed values. Other values ​​not listed within this range also meet the requirements.

[0077] The holding time of the second holding in the second crystallization is 6-10 hours, for example, it can be 6 hours, 6.5 hours, 7.0 hours, 7.5 hours, 8.0 hours, 8.5 hours, 9.0 hours, 9.5 hours or 10 hours, etc., but is not limited to the listed values. Other values ​​not listed within this range also meet the requirements.

[0078] Wherein, the second cooling in the second crystallization includes: cooling to 50-53°C at a cooling rate of 0.5-5°C / h. The cooling rate can be, for example, 0.5°C / h, 1°C / h, 1.5°C / h, 2°C / h, 2.5°C / h, 3°C / h, 3.5°C / h, 4°C / h, 4.5°C / h or 5°C / h, and the cooling endpoint temperature can be, for example, 50°C, 50.5°C, 51°C, 51.5°C, 52°C, 52.5°C or 53°C, but is not limited to the listed values. Other values ​​not listed within this range also meet the requirements.

[0079] In the present invention, the starting temperature of the second cooling is the temperature of the second keeping warm.

[0080] Wherein, the third crystallization includes: a third heat preservation and a first temperature increase performed sequentially.

[0081] Among them, the insulation temperature of the third insulation in the third crystallization is 60-80°C, for example, it can be 60°C, 62°C, 64°C, 66°C, 68°C, 70°C, 72°C, 74°C, 76°C, 78°C or 80°C, but is not limited to the listed values. Other values ​​not listed within this range also meet the requirements.

[0082] Among them, the holding time of the third insulation in the third crystallization is 4-8h, for example, it can be 4h, 4.5h, 5h, 5.5h, 6h, 6.5h, 7h, 7.5h or 8h, but is not limited to the listed values. Other values ​​not listed in this range also meet the requirements.

[0083] Wherein, the first heating in the third crystallization includes: heating to 70-80°C at a heating rate of 0.5-2°C / h. The heating rate can be, for example, 0.5°C / h, 0.6°C / h, 0.7°C / h, 0.8°C / h, 0.9°C / h, 1°C / h, 1.1°C / h, 1.2°C / h, 1.3°C / h, 1.4°C / h, 1.5°C / h, 1.6°C / h, 1.7°C / h, 1.8°C / h, 1.9°C / h or 2°C / h, and the heating end temperature can be, for example, 70°C, 72°C, 74°C, 76°C, 78°C or 80°C, but is not limited to the listed values. Other values ​​not listed within the range also meet the requirements.

[0084] In the present invention, the starting temperature of the first heating is the temperature of the third heat preservation.

[0085] In the present invention, gradient distillation reduces the impurity load of the crystallization system, enabling the crystallization process to achieve efficient separation under relatively mild conditions; the temperature gradient design of the three-stage crystallization fully utilizes the differences in the solubility and crystallization kinetics of each component at different temperatures. The synergistic effect of the two achieves dual optimization of purity and yield.

[0086] Furthermore, the obtained high-purity β-methylnaphthalene crystals can be selected as monomer raw materials for organic electroluminescent devices (OLEDs), raw materials for preparing carbon matrix materials, raw materials for preparing high-temperature resistant materials, raw materials for preparing ablation-resistant materials, or raw materials for preparing special resin materials after drying.

[0087] Wherein, the drying method includes: vacuum drying.

[0088] The absolute vacuum degree of drying is ≤0.5 kPa, for example, it can be 0.5 kPa, 0.4 kPa, 0.3 kPa, 0.2 kPa or 0.1 kPa, etc., but is not limited to the listed values. Other values ​​not listed in this range also meet the requirements.

[0089] The drying temperature is 70-80°C, for example, 70°C, 71°C, 72°C, 73°C, 74°C, 75°C, 76°C, 77°C, 78°C, 79°C or 80°C, but is not limited to the listed values. Other values ​​not listed within this range also meet the requirements.

[0090] The drying time is 2-5 hours, for example, 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, 4.5 hours or 5 hours, but is not limited to the listed values. Other values ​​not listed within the range also meet the requirements.

[0091] Furthermore, in order to illustrate that the high-purity β-methylnaphthalene crystals obtained by the separation and purification method provided by the present invention reach a high-purity level, the following actual example is used for illustrative purposes, as follows:

[0092] Example 1

[0093] This embodiment provides a method for separating and purifying β-methylnaphthalene from mixed methylnaphthalene, which is as follows:

[0094] Raw material composition: The composition of the mixed methylnaphthalene raw material is 50.2% of β-methylnaphthalene, 30.5% of α-methylnaphthalene, 4.8% of alkylbenzothiophene, and 14.5% of other impurities (benzene, toluene, dimethylnaphthalene, etc.).

[0095] Step 1: Pre-enrichment by gradient distillation

[0096] (1) Preliminary distillation: The mixed methylnaphthalene raw material is preliminarily distilled at 150°C and normal pressure to remove low-boiling components (such as benzene, toluene, etc.) with a boiling point below 150°C to obtain an intermediate fraction;

[0097] (2) Distillation enrichment: The intermediate fraction after the preliminary distillation is sent to a distillation tower for distillation separation. The distillation process parameters are set as follows: number of distillation tower plates: 90; reflux ratio: 15:1; tower top pressure: 20 kPa; tower top temperature: 195°C; tower bottom pressure: 40 kPa; tower bottom temperature: 245°C; side line outlet setting: three side line outlets are set at 20%, 50% and 80% height from the top to the bottom of the tower body, and fractions with β-methylnaphthalene contents of 85%, 90% and 95% are extracted respectively;

[0098] Through the above distillation process, a β-methylnaphthalene crude fraction is obtained, wherein the β-methylnaphthalene content is 95.2%, the α-methylnaphthalene content is 3.6%, the alkylbenzothiophene content is 0.8%, and the other impurities content is 0.4%.

[0099] Step 2: Directional melt crystallization separation

[0100] (1) First crystallization: The crude β-methylnaphthalene fraction was heated to 120°C, injected into the first crystallization apparatus, and maintained at 90°C for 2.5 hours to form crystal nuclei. The temperature was then cooled to 75°C at a rate of 15°C / hour, and allowed to stand for separation to obtain first crystals and mother liquor.

[0101] (2) Second crystallization: After the first crystal is heated and melted, it is injected into a special second crystallization device with an overflow liquid flow channel of the device at an angle of 30° to the horizontal plane. The temperature is maintained at 65°C for 8 hours, and then slowly cooled to 55°C at a cooling rate of 2°C / h. The second crystal and mother liquor are separated by standing.

[0102] (3) Third crystallization: After the second crystal is heated and melted, it is transferred to the third crystallization device and kept at a constant temperature of 70°C for 6 hours. Then, the temperature is slowly raised to 75°C at a heating rate of 1°C / h for fine sweating treatment. The final crystals and mother liquor are obtained by standing and separating.

[0103] Step 3: Product drying and quality inspection

[0104] The final crystals were dried at 75° C. and 0.3 kPa vacuum conditions for 3 h to obtain high-purity β-methylnaphthalene crystal products.

[0105] Analysis by gas chromatography-mass spectrometry (GC-MS) and high performance liquid chromatography (HPLC) showed that the content of β-methylnaphthalene in the product was 99.98%, the content of α-methylnaphthalene was 0.01%, the content of alkylbenzothiophene was undetectable (<0.001%), the content of other impurities was 0.009%, and the product yield was 88.0% (based on the β-methylnaphthalene in the raw material).

[0106] Example 2

[0107] This embodiment provides a method for separating and purifying β-methylnaphthalene from mixed methylnaphthalene, which is as follows:

[0108] Raw material composition: The composition of the mixed methylnaphthalene raw material is 70.3% of β-methylnaphthalene, 20.2% of α-methylnaphthalene, 3.1% of alkylbenzothiophene, and 6.4% of other impurities (benzene, toluene, dimethylnaphthalene, etc.).

[0109] Step 1: Pre-enrichment by gradient distillation

[0110] (1) Preliminary distillation: The mixed methylnaphthalene raw material is preliminarily distilled at 180°C and normal pressure to remove low-boiling components (such as benzene, toluene, etc.) with a boiling point below 180°C to obtain an intermediate fraction;

[0111] (2) Distillation enrichment: The intermediate fraction after the preliminary distillation is sent to a distillation tower for distillation separation. The distillation process parameters are set as follows: number of distillation tower plates: 100; reflux ratio: 20:1; tower top pressure: 30 kPa; tower top temperature: 210 °C; tower bottom pressure: 45 kPa; tower bottom temperature: 255 °C; side line outlet setting: 5 side line outlets are set at 15%, 30%, 50%, 70% and 85% height from the top to the bottom of the tower body, and fractions with β-methylnaphthalene contents of 80%, 85%, 90%, 95% and 98% are extracted respectively;

[0112] Through the above distillation process, a β-methylnaphthalene crude fraction is obtained, wherein the β-methylnaphthalene content is 98.1%, the α-methylnaphthalene content is 1.5%, the alkylbenzothiophene content is 0.3%, and the other impurities content is 0.1%.

[0113] Step 2: Directional melt crystallization separation

[0114] (1) First crystallization: The crude β-methylnaphthalene fraction was heated to 125°C, injected into the first crystallization apparatus, and maintained at 95°C for 3 h to form crystal nuclei. The temperature was then cooled to 80°C at a cooling rate of 18°C / h, and allowed to stand for separation to obtain first crystals and mother liquor.

[0115] (2) Second crystallization: After the first crystal is heated and melted, it is injected into a special second crystallization device with an overflow liquid flow channel of the device at an angle of 35° to the horizontal plane. The temperature is maintained at 60°C for 9 hours, and then slowly cooled to 53°C at a cooling rate of 1°C / h. The second crystal and mother liquor are separated by standing.

[0116] (3) Third crystallization: After the second crystal is heated and melted, it is transferred to the third crystallization device and kept at a constant temperature of 75°C for 7 hours. Then, the temperature is slowly raised to 80°C at a heating rate of 1.5°C / h for fine sweating treatment. The final crystals and mother liquor are obtained by standing and separating.

[0117] Step 3: Product drying and quality inspection

[0118] The final crystals were dried at 80° C. and 0.5 kPa vacuum conditions for 5 h to obtain high-purity β-methylnaphthalene crystal products.

[0119] Analysis by gas chromatography-mass spectrometry (GC-MS) and high performance liquid chromatography (HPLC) showed that the content of β-methylnaphthalene in the product was 99.97%, the content of α-methylnaphthalene was 0.015%, the content of alkylbenzothiophene was undetectable (<0.001%), the content of other impurities was 0.014%, and the product yield was 90.0% (based on the β-methylnaphthalene in the raw material).

[0120] Example 3

[0121] This embodiment provides a method for separating and purifying β-methylnaphthalene from mixed methylnaphthalene, which is as follows:

[0122] Raw material composition: The composition of the mixed methylnaphthalene raw material is 30.6% of β-methylnaphthalene, 40.2% of α-methylnaphthalene, 9.8% of alkylbenzothiophene, and 19.4% of other impurities (benzene, toluene, dimethylnaphthalene, etc.).

[0123] Step 1: Pre-enrichment by gradient distillation

[0124] (1) Preliminary distillation: The mixed methylnaphthalene raw material is preliminarily distilled at 200°C and normal pressure to remove low-boiling components (such as benzene, toluene, etc.) with a boiling point below 200°C to obtain an intermediate fraction;

[0125] (2) Distillation enrichment: The intermediate fraction after the preliminary distillation is sent to a distillation tower for distillation separation. The distillation process parameters are set as follows: number of distillation tower plates: 80; reflux ratio: 10:1; tower top pressure: 10 kPa; tower top temperature: 185°C; tower bottom pressure: 35 kPa; tower bottom temperature: 235°C; side line outlet setting: three side line outlets are set at 25%, 55% and 75% height from the top to the bottom of the tower body, and fractions with β-methylnaphthalene contents of 80%, 85% and 90% are extracted respectively;

[0126] Through the above distillation process, a β-methylnaphthalene crude fraction is obtained, wherein the β-methylnaphthalene content is 90.5%, the α-methylnaphthalene content is 7.2%, the alkylbenzothiophene content is 1.3%, and the other impurities content is 1.0%.

[0127] Step 2: Directional melt crystallization separation

[0128] (1) First crystallization: The crude β-methylnaphthalene fraction was heated to 115°C, injected into the first crystallization apparatus, and maintained at 85°C for 3.5 hours to form crystal nuclei. The temperature was then cooled to 70°C at a cooling rate of 12°C / hour, and allowed to stand for separation to obtain first crystals and mother liquor.

[0129] (2) Second crystallization: After the first crystal is heated and melted, it is injected into a special second crystallization device with an overflow liquid flow channel of the device at an angle of 25° to the horizontal plane. The temperature is maintained at 55°C for 10 hours, and then slowly cooled to 50°C at a cooling rate of 0.8°C / h. The second crystal and mother liquor are separated by standing.

[0130] (3) Third crystallization: After the second crystal is heated and melted, it is transferred to the third crystallization device and kept at a constant temperature of 65°C for 5 hours. Then, the temperature is slowly raised to 70°C at a heating rate of 0.5°C / h for fine sweating treatment. The final crystals and mother liquor are obtained by standing and separating.

[0131] Step 3: Product drying and quality inspection

[0132] The final crystals were dried at 70° C. and 0.1 kPa vacuum conditions for 2 h to obtain high-purity β-methylnaphthalene crystal products.

[0133] Analysis by gas chromatography-mass spectrometry (GC-MS) and high performance liquid chromatography (HPLC) showed that the content of β-methylnaphthalene in the product was 99.97%, the content of α-methylnaphthalene was 0.02%, the content of alkylbenzothiophene was 0.001%, the content of other impurities was 0.009%, and the product yield was 85.0% (based on the β-methylnaphthalene in the raw material).

[0134] Comparative Example 1

[0135] The only difference from Example 1 is that no distillation was performed.

[0136] In this case, the mixed methylnaphthalene feedstock was directly fed into the distillation column. Under the same distillation and crystallization conditions, the resulting β-methylnaphthalene product had a purity of 97.50% and a yield of 62.0%. This indicates that the lack of distillation pretreatment allows low-boiling-point components to enter the distillation system, increasing distillation energy consumption and interfering with the distillation separation of β-methylnaphthalene, significantly increasing the difficulty of subsequent crystallization, and ultimately leading to a significant reduction in product purity and yield.

[0137] Comparative Example 2

[0138] The only difference from Example 1 is that no rectification is performed.

[0139] Directly feeding the distilled mixed methylnaphthalene into the crystallization system, under the same distillation and crystallization conditions, the resulting β-methylnaphthalene product had a purity of 96.80% and a yield of 65.0%. This demonstrates that the distillation process, through multi-side fractionation technology, can effectively enrich β-methylnaphthalene and initially remove most impurities, providing high-quality raw materials for subsequent crystallization separation. Without the distillation step, near-boiling-point impurities such as α-methylnaphthalene and alkylbenzothiophenes cannot be effectively removed, seriously affecting the quality of the final product.

[0140] Comparative Example 3

[0141] The only difference from Example 1 is that the first crystallization is not performed. In this case, the crude β-methylnaphthalene fraction obtained by distillation is directly subjected to the second crystallization.

[0142] Under the same distillation and other crystallization conditions, the final β-methylnaphthalene product had a purity of 98.50% and a yield of 70.0%. It can be seen that the lack of the first crystallization step will lead to a decrease in product purity, which shows that the first crystallization plays an important role in the entire process. It can form a large number of crystal nuclei through a faster cooling rate and preliminarily remove some impurities, providing purer raw materials for subsequent crystallization.

[0143] Comparative Example 4

[0144] The only difference from Example 1 is that the second crystallization is not performed. In this case, the crystals obtained from the first crystallization are directly subjected to the third crystallization.

[0145] Under the same distillation and other crystallization conditions, the final β-methylnaphthalene product had a purity of 98.70% and a yield of 75.0%. It can be seen that the lack of this step will significantly reduce the purity of the product, which shows that the second crystallization is the core step of the entire process. In particular, the design of the inclined liquid flow channel and the slow cooling rate can achieve efficient separation of β-methylnaphthalene from impurities such as α-methylnaphthalene and alkylbenzothiophene.

[0146] Comparative Example 5

[0147] The only difference from Example 1 is that the third crystallization is not performed, and the crystals obtained from the second crystallization are directly dried.

[0148] Under the same distillation and other crystallization conditions, the final β-methylnaphthalene product had a purity of 99.30% and a yield of 76.0%. It can be seen that the lack of this step will significantly reduce the purity of the product, which indicates that the sweating process of the third crystallization plays an important role in removing residual trace impurities, especially by slowly increasing the temperature, which can promote the migration of residual trace impurities in the crystals to the surface and be discharged, thereby further improving the purity of the product.

[0149] Comparative Example 6

[0150] The only difference from Example 1 is that in the second crystallization, the angle between the overflow liquid flow channel and the horizontal plane along the flow direction is 10°.

[0151] Using the same raw materials and other process conditions, the final β-methylnaphthalene product had a purity of 98.60% and a yield of 72.0%. This indicates that the inclination angle of the liquid flow channel has a significant impact on the crystallization effect. When the angle is too small (10°), the liquid flow and convection are insufficient, the spatial separation of impurities and target crystals is poor, and the product purity is reduced.

[0152] Comparative Example 7

[0153] The only difference from Example 1 is that in the second crystallization, the angle between the overflow liquid flow channel and the horizontal plane along the flow direction is 60°.

[0154] Using the same raw materials and other process conditions, the final β-methylnaphthalene product had a purity of 98.20% and a yield of 70.0%. This indicates that when the liquid flow channel is tilted too sharply (60°), the liquid flows too fast, crystal growth becomes unstable, impurities are easily trapped inside the crystals, and some fine crystals are washed away, thereby reducing product purity and yield.

[0155] Comparative Example 8

[0156] The only difference from Example 1 is that the temperature of the second crystallization is 80°C.

[0157] Using the same raw materials and other process conditions, the final β-methylnaphthalene product had a purity of 97.80% and a yield of 75.0%. This indicates that the second crystallization temperature has a significant impact on product purity. When the temperature is too high (80°C), the β-methylnaphthalene and impurities mostly remain in liquid form, making effective separation impossible, resulting in reduced product purity.

[0158] Comparative Example 9

[0159] The only difference from Example 1 is that the temperature of the second crystallization is 40°C.

[0160] Using the same raw materials and other process conditions, the final β-methylnaphthalene product had a purity of 98.00% and a yield of 68.0%. This indicates that when the second crystallization temperature is too low (40°C), although β-methylnaphthalene can fully crystallize, the excessively rapid cooling causes impurities to be trapped within the crystals. Furthermore, the β-methylnaphthalene crystals do not grow perfectly and have an uneven particle size distribution, which is detrimental to subsequent separation and purification, thereby affecting product quality and yield.

[0161] Comparative Example 10

[0162] The only difference from Example 1 is that the holding temperature of the third crystallization is 40°C.

[0163] Using the same raw materials and other process conditions, the final β-methylnaphthalene product had a purity of 98.30% and a yield of 74.0%. This indicates that when the third crystallization holding temperature is too low (40°C), the sweating process is insufficient, the migration rate of impurities within the crystals is slow, and they cannot be effectively expelled from the crystals, thereby reducing the product purity.

[0164] Comparative Example 11

[0165] The only difference from Example 1 is that the holding temperature of the third crystallization is 60°C.

[0166] Using the same raw materials and other process conditions, the resulting β-methylnaphthalene product had a purity of 98.50% and a yield of 76.0%. This indicates that while a high third crystallization holding temperature (90°C) facilitates the rapid migration of impurities, it also causes a large amount of β-methylnaphthalene crystals to melt, increasing the risk of impurities reintroducing, affecting product purity, increasing β-methylnaphthalene losses, and reducing yield.

[0167] Example 4

[0168] The only difference from Example 1 is that the cooling rate of the first crystallization is 5° C. / h.

[0169] Using the same raw materials and other process conditions, the final β-methylnaphthalene product had a purity of 99.80% and a yield of 83.0%. This indicates that the cooling rate of the first crystallization has a certain impact on the purity and yield of the product. Although a slower cooling rate is conducive to the formation of higher-quality crystals, it also reduces production efficiency and may cause some loss of β-methylnaphthalene in the solution, thereby reducing the yield.

[0170] Example 5

[0171] The only difference from Example 1 is that the cooling rate of the second crystallization is 10° C. / h.

[0172] Using the same raw materials and other process conditions, the final β-methylnaphthalene product had a purity of 99.75% and a yield of 82.0%. This indicates that the cooling rate of the second crystallization significantly affects the purity of the product. Excessively fast cooling rates are detrimental to the effective separation of impurities from the target product, resulting in some α-methylnaphthalene and alkylbenzothiophene impurities being trapped within the crystals, making them difficult to remove in the subsequent crystallization step, thereby reducing the product purity.

[0173] Example 6

[0174] The only difference from Example 1 is that the cooling rate of the third crystallization is 5° C. / h.

[0175] Using the same raw materials and other process conditions, the resulting β-methylnaphthalene product had a purity of 99.70% and a yield of 80.0%. This indicates that the heating rate of the third crystallization affects both the purity and yield of the product. Excessively fast heating rates lead to an inadequate sweating process, preventing impurities from effectively diffusing to the crystal surface and being expelled, thereby reducing product purity. This also results in some β-methylnaphthalene being carried over, reducing yield. The purity and recovery of the β-methylnaphthalene products obtained in the above examples and comparative examples are detailed in Table 1 below.

[0176] Table 1

[0177] β-Methylnaphthalene purity / % β-Methylnaphthalene recovery rate / % Example 1 99.98 88.0 Example 2 99.97 90.0 Example 3 99.97 85.0 Comparative Example 1 97.50 62.0 Comparative Example 2 96.80 65.0 Comparative Example 3 98.50 70.0 Comparative Example 4 98.70 75.0 Comparative Example 5 99.30 76.0 Comparative Example 6 98.60 72.0 Comparative Example 7 98.20 70.0 Comparative Example 8 97.80 75.0 Comparative Example 9 98.00 68.0 Comparative Example 10 98.30 74.0 Comparative Example 11 98.50 76.0 Example 4 99.80 83.0 Example 5 99.75 82.0 Example 6 99.70 80.0

[0178] As shown in Table 1, the complete "distillation-rectification-three-stage crystallization" process route proposed in the present invention (Examples 1-3) can obtain high-purity β-methylnaphthalene products with a purity of ≥99.97% and a recovery rate of ≥85%, demonstrating that the present invention has good adaptability and stability and is suitable for industrial promotion and application. However, the lack of any key step (Comparative Examples 1-5) will significantly reduce the product purity and yield, demonstrating the scientific nature and necessity of the process design of the present invention.

[0179] Comparative Examples 1-5 omitted key steps, including distillation, rectification, first crystallization, second crystallization, and third crystallization. The results showed that the omission of any of these steps resulted in a significant decrease in product purity and yield. This demonstrates the necessity and synergistic effect of the present invention's integrated "gradient rectification + three-stage crystallization" process.

[0180] Comparative Examples 6-11 verify the scientific nature of the parameter range determined by the present invention by changing key parameters such as liquid flow channel angle and crystallization temperature. In particular, the liquid flow channel angle of 15-45 ° can achieve the best directional separation effect within this range. Specifically, the angle between the liquid flow channel and the horizontal plane in the second crystallization is a key factor affecting product purity. When the angle is less than 15 ° (Comparative Example 6) or greater than 45 ° (Comparative Example 7), product purity is significantly reduced. The 15-45 ° range determined by the present invention is the optimal interval for achieving efficient separation. Within this range, liquid flow and crystal growth reach an optimal balance, which is conducive to the spatial separation of impurities and target product.

[0181] Crystallization temperature significantly affects product purity and yield. A second crystallization temperature that is too high (Comparative Example 8) or too low (Comparative Example 9) will reduce separation efficiency; a third crystallization temperature that is too low (Comparative Example 10) or too high (Comparative Example 11) will also affect the efficiency of the sweating process, thereby reducing product purity.

[0182] The cooling / heating rates during the crystallization process have a significant impact on product quality (Examples 4-6). Compared with Example 1, changing the rates of the first, second, or third crystallizations will result in a decrease in product purity and yield, but the degree of impact is relatively small, indicating that the process of the present invention has a certain degree of operational flexibility.

[0183] In summary, the steps of the present invention exhibit significant synergistic effects. Distillation and rectification provide high-quality raw materials for crystallization, while the three-stage crystallization achieves a gradient removal of impurities through different temperature gradients and flow conditions. This synergistic effect is key to achieving high-purity and high-yield separation of β-methylnaphthalene.

[0184] Furthermore, the method for separating and purifying β-methylnaphthalene from mixed methylnaphthalene proposed in the present invention successfully solves the technical problem that traditional processes are difficult to simultaneously improve purity and yield through the innovative combination of gradient distillation and directional melt crystallization, especially the design of a 15-45° inclined liquid flow channel and a strictly controlled temperature gradient in the second crystallization, thereby achieving efficient separation and purification of β-methylnaphthalene and providing a new technical solution for related chemical fields. Compared with the existing technology (purity 95-98%, yield 60-75%), the present invention achieves a technical breakthrough of purity ≥99.97% and yield ≥85%, and has obvious advantages in key technical indicators.

[0185] 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, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the scope of protection of the present invention.

[0186] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any appropriate manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0187] In addition, the 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 method for separating and purifying β-methylnaphthalene from mixed methylnaphthalenes, characterized in that: The separation and purification method comprises: The mixed methylnaphthalene is sequentially distilled and rectified to obtain a crude β-methylnaphthalene fraction; The obtained β-methylnaphthalene crude fraction is sequentially subjected to a first crystallization, a second crystallization, and a third crystallization to obtain high-purity β-methylnaphthalene crystals; The temperature of the second crystallization is less than the temperature of the third crystallization and less than the temperature of the first crystallization; The angle between the overflow liquid flow channel used in the second crystallization and the horizontal plane along the flow direction is 15-45 degrees.

2. The separation and purification method according to claim 1, wherein The distillation temperature is 150-200°C.

3. The separation and purification method according to claim 1 or 2, wherein: The number of plates of the distillation tower used in the distillation is 80-100; Preferably, during the distillation, 3-5 side outlets are provided at different heights of the tower body to extract fractions with a β-methylnaphthalene content of 80-98%.

4. The separation and purification method according to any one of claims 1 to 3, wherein The reflux ratio of the distillation is 10-20; Preferably, the top pressure of the distillation tower is 10-30 kPa; Preferably, the top temperature of the distillation tower is 180-220°C.

5. The separation and purification method according to any one of claims 1 to 4, wherein The distillation bottom pressure is 30-50 kPa; Preferably, the bottom temperature of the distillation tower is 230-260°C.

6. The separation and purification method according to any one of claims 1 to 5, wherein: The temperature of the crude β-methylnaphthalene fraction fed into the first crystallization is 110-130° C.; Preferably, the first crystallization comprises a first heat preservation and a first temperature reduction performed sequentially; Preferably, the first heat preservation temperature in the first crystallization is 80-100° C.; Preferably, the first heat preservation time in the first crystallization is 2-4 hours; Preferably, the first cooling in the first crystallization comprises: cooling to 70-80° C. at a cooling rate of 10-20° C. / h.

7. The separation and purification method according to any one of claims 1 to 6, wherein: The second crystallization comprises: a second heat preservation and a second cooling performed sequentially; Preferably, the second heat preservation temperature in the second crystallization is 50-70° C.; Preferably, the second heat preservation time in the second crystallization is 6-10 hours; Preferably, the second cooling in the second crystallization comprises: cooling to 50-53° C. at a cooling rate of 0.5-5° C. / h.

8. The separation and purification method according to any one of claims 1 to 7, wherein: The third crystallization comprises: a third heat preservation and a first temperature rise performed sequentially; Preferably, the third heat preservation temperature in the third crystallization is 60-80° C.; Preferably, the holding time of the third holding in the third crystallization is 4-8 hours; Preferably, the first temperature increase in the third crystallization comprises: increasing the temperature to 70-80° C. at a heating rate of 0.5-2° C. / h.

9. Use of high-purity β-methylnaphthalene crystals obtained by the separation and purification method according to any one of claims 1 to 8, characterized in that: The uses include: using the high-purity β-methylnaphthalene crystals after drying as monomer raw materials for organic electroluminescent devices, raw materials for preparing carbon matrix materials, raw materials for preparing high-temperature resistant materials, raw materials for preparing ablation-resistant materials, or raw materials for preparing special resin materials.

10. The use according to claim 9, characterized in that The drying method includes: vacuum drying; Preferably, the absolute vacuum degree of drying is ≤0.5kPa; Preferably, the drying temperature is 70-80°C; Preferably, the drying time is 2-5 hours.

Images