Rectification system for preparing 2-(4-methylphenyl) benzoxazole
By using a temperature control system and scraper device in the distillation process for 2-(4-methylphenyl)benzoxazole, the problem of difficult bottom residue cleaning was solved, achieving efficient residue recovery and stable system operation, and reducing processing costs.
Patent Information
- Application Number
- CN202511601784.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-11-04
- Publication Date
- 2025-12-26
AI Technical Summary
In the existing technology, the preparation process of 2-(4-methylphenyl)benzoxazole is difficult to clean the residue at the bottom of the reactor, resulting in high processing costs and low efficiency.
A distillation system is employed, including a temperature control system and a scraper device. The scraper, double-jacket structure, and screw conveyor are hydraulically driven, and combined with heat transfer oil circulation and nitrogen purging, to optimize the temperature and flowability of the residue at the bottom of the vessel, prevent agglomeration, and achieve efficient cleaning and recycling.
It effectively reduces the viscosity of the residue at the bottom of the vessel, prevents agglomeration, improves the efficiency of residue discharge, reduces downtime, ensures the continuous and stable operation of the distillation system, and reduces processing costs.
Smart Images
Figure CN121197831A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of distillation technology, and more particularly to a distillation system for the preparation of 2-(4-methylphenyl)benzoxazole. Background Technology
[0002] 2-(4-methylphenyl)benzoxazole is an intermediate in the synthesis of the fluorescent whitening agent OB-1 (2,2'-(4,4'-stilbene)bisbenzoxazole). Currently, the main method for synthesizing 2-(4-methylphenyl)benzoxazole is recrystallization. Specifically, it uses p-methylbenzoic acid and o-aminophenol as starting materials, solvent oil as the reaction solvent, and boric acid as the catalyst, and undergoes a condensation reaction at around 230 degrees Celsius. After the reaction is completed, the reaction mixture is distilled under reduced pressure. After distilling off the solvent oil and 2-(4-methylphenyl)benzoxazole, the distillation residue is discharged from the bottom valve, forming a distillation residue.
[0003] The recrystallization method requires 12 batches of simple distillation and condensation to obtain a crude product. The crude product is then dissolved in hot ethanol, cooled, crystallized, centrifuged, dried, and packaged for the next process. The mother liquor from centrifugation is then distilled to recover ethanol for reuse in refining. However, the residue at the bottom of the vessel is a solid containing a large amount of the target product. After cooling, the viscosity of the residue in the vessel increases sharply, and it clumps and deposits, making it difficult to discharge. Manual cleaning is required, and the residue at the bottom of the vessel needs to be sent to a qualified unit for harmless treatment, which is expensive.
[0004] Therefore, there is an urgent need for a distillation system for the preparation of 2-(4-methylphenyl)benzoxazole to solve the above problems. Summary of the Invention
[0005] The technical problem to be solved by the present invention is to provide a distillation system for the preparation of 2-(4-methylphenyl)benzoxazole, which can effectively clean the residue at the bottom of the vessel and efficiently recover the residue for the secondary recovery of 2-(4-methylphenyl)benzoxazole.
[0006] To achieve the above objectives, the present invention provides a distillation system for the preparation of 2-(4-methylphenyl)benzoxazole, comprising a temperature control system; the temperature control system includes a heat transfer oil inlet pipe, a heat transfer oil return pipe, a distillation kettle, an oil pump, a high-temperature oil valve, a first valve, a second valve, a third valve, a fourth valve, and a temperature controller; the heat transfer oil inlet pipe is connected to the high-temperature oil valve, the end of the high-temperature oil valve away from the heat transfer oil inlet pipe is fixedly connected to the first valve, and the end of the first valve away from the high-temperature oil valve is fixedly connected to the oil pump; the temperature controller is installed between the oil pump outlet and the high-temperature oil valve; two first valves are respectively provided at both ends of the oil pump; the end of the first valve near the distillation kettle away from the other side of the first valve is connected to the second valve, and the other end of the second valve is connected to the jacket of the distillation kettle; a discharge pipe is connected to one side of the jacket of the distillation kettle, and the discharge pipe is connected to the third valve and the fourth valve respectively, the third valve being normally open.
[0007] The distillation vessel adopts a cylindrical structure with a cone at the bottom, and a hydraulically driven scraper is installed inside the cone. The cone is set with a cone angle of 60° to effectively optimize the gravity flow of residue at the bottom of the vessel. It adopts a double-layer jacket structure with an inner layer of 316L stainless steel and an outer layer of heat insulation.
[0008] The temperature control system uses heat transfer oil circulation, and its specific implementation method is as follows: high temperature heat transfer oil is introduced into the double-layer jacket structure to maintain the temperature of the cone.
[0009] In a preferred embodiment of the present invention, the hydraulically driven scraper uses 316L as the raw material.
[0010] In a preferred embodiment of the present invention, the insulation layer is made of carbon steel wound pipe.
[0011] In a preferred embodiment of the present invention, a screw conveyor is provided below the distillation vessel, and the screw conveyor is powered by a twin-screw motor.
[0012] In a preferred embodiment of the present invention, the discharge port of the distillation kettle is equipped with a DN200 valve, heat transfer oil is used for insulation, and nitrogen is used for purging.
[0013] In a preferred embodiment of the present invention, when the temperature control system is in the normal distillation stage, the hydraulically driven scraper runs at a low speed to prevent local overheating of the material; before the residue at the bottom of the vessel is discharged, the speed of the hydraulically driven scraper is increased to fully stir and reduce the viscosity before the discharge valve is opened.
[0014] In a preferred embodiment of the present invention, a high-temperature resistant sight glass is provided on the side of the bottom of the distillation vessel, and a sampling and detection port is provided next to the sight glass.
[0015] In a preferred embodiment of the present invention, an internal reflux condenser and a reflux distributor collection tank are installed inside the distillation kettle, and an outlet is provided at the lower part of the reflux distributor collection tank.
[0016] The technical principle of this invention lies in the fact that the residue at the bottom of the vessel comprises the following components: The pyrolysis product of boric acid is B2O3; Polymer, wherein the polymer has a softening point greater than 250°C; Carbonized materials, i.e., solid particles; The residue at the bottom of the vessel exhibits rheological behavior, forming a high-viscosity melt at high temperatures (220°C) and rapidly solidifying upon cooling. A temperature control system is added to the bottom of the vessel to prevent sticking to the wall, prevent clumping, and promote flow, effectively cleaning the residue at the bottom of the distillation vessel cone. The working principle of the temperature control system is as follows: Generally, a single thermal oil heater can only provide oil at a single temperature. However, distillation kettles made of special materials, such as enamel, cannot operate above 200 degrees Celsius. The thermal oil inlet pipe connects to the thermal oil heater, containing 280-degree thermal oil supplied by the heater. The return pipe contains cooled oil after heat exchange, returning to the thermal oil heater. Normal operation of the distillation kettle is provided by an oil pump, and the third valve is normally open. When the insulation layer temperature of the distillation kettle meets the requirements, the thermal oil circulation becomes oil pump-second... The process involves a valve-distillation kettle jacket-fourth valve-oil pump, where the heat transfer oil circulates in a single loop without exchanging heat transfer oil with the oil furnace, ensuring the normal operation of the distillation kettle. When it is necessary to increase the temperature of the distillation kettle, the high-temperature oil valve is automatically opened to introduce high-temperature oil from the oil furnace to participate in the circulation. The excess high-temperature oil introduced is returned to the oil furnace through the third valve after heat exchange, thus ensuring the normal operation of the distillation kettle and ensuring the cleaning efficiency of the bottom residue. In conjunction with the screw conveyor, the bottom residue is effectively recovered for secondary recovery treatment of 2-(4-methylphenyl)benzoxazole.
[0017] Compared with the prior art, the technical solution of this application has the following beneficial effects: This invention discloses a distillation system for the preparation of 2-(4-methylphenyl)benzoxazole. By adding a wall-scraping and stirring device to the conical body of the distillation vessel, and incorporating a hydraulically driven scraper made of 316L stainless steel, the system effectively breaks up static residue deposition, prevents localized overheating and scaling, and enhances residue uniformity through forced stirring, thereby reducing overall viscosity. It can scrape away residue adhering to the vessel wall, preventing clumping. A mechanical seal at the top of the stirring shaft ensures that the vacuum inside the vessel does not leak.
[0018] By adding an auxiliary temperature control system at the bottom of the vessel, high-temperature heat transfer oil is circulated into the double-layer jacket structure to maintain the cone temperature at 250-260℃. The temperature is precisely controlled by an independent temperature controller to ensure stable residue temperature, prevent local overheating that could lead to residue carbonization, and ensure that the residue temperature at the bottom of the vessel is above the "softening flow threshold," thereby reducing residue viscosity and preventing cooling agglomeration.
[0019] By optimizing the discharge system, the bottom discharge port is positioned at the lowest point of the distillation vessel, and the cone is set with a 60° cone angle, effectively optimizing the gravity flow of distillation residue and avoiding dead zones at the bottom of the vessel. A screw conveyor is installed below the bottom discharge port, using a twin-screw motor to improve discharge efficiency. A heated jacketed discharge valve is selected, and the discharge port of the distillation vessel uses DN200 valve heat transfer oil insulation to maintain the residue temperature in the pipeline at ≥220℃, preventing cooling and agglomeration, ensuring smooth valve opening and closing, and avoiding blockage. A nitrogen purging interface is installed before the distillation vessel discharge valve. During discharge, 0.3MPa nitrogen is introduced for purging, using nitrogen pressure to assist in residue transport and reduce residue in the pipeline. In case of blockage, the discharge valve is closed, and 0.4-0.5MPa nitrogen is introduced for reverse purging (short-time pulse type) to clear the pipeline blockage.
[0020] By adding a high-temperature resistant sight glass and a sampling port on the side of the vessel bottom, the liquid level and flow state of the residue at the bottom of the vessel can be observed through the high-temperature resistant sight glass to determine in advance whether there is clumping; the residue composition can be sampled and analyzed through the sampling port to adjust the heating temperature or solvent oil rinsing frequency.
[0021] This invention optimizes the distillation kettle and temperature control system by reducing residue viscosity, preventing agglomeration and deposition, assisting in conveying and discharging, and facilitating cleaning and maintenance. Through the above equipment settings, the problem of difficult residue discharge can be solved from the entire process of "generation-conveyance-cleaning", ensuring the continuous and stable operation of the distillation system and reducing downtime caused by residue blockage. Attached Figure Description
[0022] Figure 1 This is a schematic diagram of the process flow of a distillation system for the preparation of 2-(4-methylphenyl)benzoxazole according to this application.
[0023] In the diagram: 1. Heat transfer oil return pipe; 2. Heat transfer oil inlet pipe; 3. High temperature oil valve; 4. Temperature controller; 5. Third valve; 6. Distillation kettle; 7. Oil pump outlet; 8. Fourth valve; 9. Oil pump; 10. First valve; 11. Second valve; 12. Screw discharge machine. Detailed Implementation
[0024] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below in conjunction with specific embodiments.
[0025] Example 1:
[0026] A distillation system for the preparation of 2-(4-methylphenyl)benzoxazole, including a temperature control system; such as Figure 1 As shown, the temperature control system includes a distillation kettle 6; the distillation kettle 6 is equipped with an internal reflux condenser and a reflux distributor collection tank, and the lower part of the reflux distributor collection tank is provided with a collection outlet. The distillation kettle 6 adopts a cylindrical structure with a cone at the bottom, and a hydraulically driven scraper is installed inside the cone; the hydraulically driven scraper uses 316L as raw material, which can effectively break up static residue deposition, avoid local overheating and scaling, and force stirring to improve the uniformity of residue and reduce the overall viscosity. It can scrape off the residue attached to the kettle wall to prevent it from sticking and clumping; a mechanical seal is provided at the top of the stirring shaft to ensure that the vacuum inside the kettle does not leak.
[0027] The cone of the distillation vessel 6 is set with a cone angle of 60° to effectively optimize the gravity flow of residue at the bottom of the vessel. It adopts a double-layer jacket structure, with an inner layer of 316L stainless steel and an outer layer of carbon steel coiled pipe as a heat insulation layer. A screw conveyor 12 is installed below the distillation vessel 6, and the screw conveyor 12 adopts a twin-screw power. The discharge port of the distillation vessel 6 adopts a DN200 valve, uses heat transfer oil for heat insulation, and uses nitrogen purging.
[0028] To avoid multiple batches of processing using the recrystallization method, this distillation system removes most of the solvent oil and then performs a single distillation operation on the reaction product. 650 kg of solvent oil, 390 kg of boric acid, 325 kg of excess p-toluic acid, approximately 7000 kg of the target product, and approximately 1800 catties of other impurities are added to distillation vessel 6 in one batch. The distilled 2-(4-methylphenyl)benzoxazole is collected from the reflux distributor collection tank at the top of distillation vessel 6 and then cooled and crystallized in a rotary slicer before packaging.
[0029] The remaining residue at the bottom of the vessel was a solid substance containing a large amount of the target product, including the following components: The pyrolysis product of boric acid is B2O3; Polymer, wherein the polymer has a softening point greater than 250°C; Carbonized materials, i.e., solid particles; The residue at the bottom of the distillation vessel exhibits rheological behavior, forming a high-viscosity melt at high temperatures (220°C) and rapidly solidifying upon cooling. To effectively clean the residue inside the cone-shaped body of the distillation vessel, a temperature control system that prevents sticking, agglomeration, and promotes flow needs to be added to the bottom of the vessel.
[0030] like Figure 1As shown, the temperature control system uses heat transfer oil circulation and also includes a heat transfer oil inlet pipe 2, a heat transfer oil return pipe 1, an oil pump 9, a high-temperature oil valve 3, a first valve 10, a second valve 11, a third valve 5, a fourth valve 8, and a temperature controller 4. The heat transfer oil inlet pipe 2 is connected to the high-temperature oil valve 3. The end of the high-temperature oil valve 3 away from the heat transfer oil inlet pipe 2 is fixedly connected to the first valve 10, and the end of the first valve 10 away from the high-temperature oil valve 3 is fixedly connected to the oil pump 9. The temperature controller 4 is installed between the oil pump outlet 7 and the high-temperature oil valve 3. Two first valves 10 are respectively provided at both ends of the oil pump 9. The end of the first valve 10 near the distillation kettle 6 away from the other side is connected to the second valve 11, and the other end of the second valve 11 is connected to the jacket of the distillation kettle 6. A discharge pipe is connected to one side of the jacket of the distillation kettle 6, and the discharge pipe is connected to the third valve 5 and the fourth valve 8 respectively. The third valve 5 is normally open. The specific implementation method is as follows: the heat transfer oil inlet pipe 2 is connected to the heat transfer oil furnace, and the inside of the heat transfer oil is provided by the heat transfer oil furnace. The heat transfer oil return pipe 1 contains the cooled oil after heat exchange and returns to the heat transfer oil furnace. The normal working circulation of the distillation kettle 6 is provided by the oil pump 9, and the third valve 5 is normally open. When the temperature of the insulation layer of the distillation kettle 6 meets the requirements, the heat transfer oil circulation is oil pump 9-second valve 11-distillation kettle 6 jacket-fourth valve 8-oil pump 9. At this time, it is a single circulation of heat transfer oil, and there is no heat transfer oil exchange with the oil furnace, ensuring the normal use of the distillation kettle 6. When it is necessary to increase the temperature of the distillation kettle 6, the high temperature oil valve 3 needs to be automatically opened to introduce high temperature oil from the oil furnace to participate in the circulation. The excess high temperature oil introduced is returned to the oil furnace through the third valve 5 after heat exchange, thereby ensuring the normal use of the distillation kettle 6 and ensuring the cleaning efficiency of the bottom residue. With the help of the screw discharge machine 12, the bottom residue is effectively recovered for secondary recovery treatment of 2-(4-methylphenyl)benzoxazole.
[0031] By adding an auxiliary temperature control system at the bottom of the vessel, high-temperature heat transfer oil is introduced into the double-layer jacket structure to maintain the cone temperature at 250-260℃. The temperature is precisely controlled by an independent temperature controller 4 to ensure stable residue temperature, prevent local overheating that could lead to residue carbonization, ensure that the residue temperature at the bottom of the vessel is above the "softening flow threshold", reduce residue viscosity, and avoid cooling and agglomeration.
[0032] Furthermore, when the temperature control system is in the normal distillation stage, the hydraulically driven scraper operates at low speed to prevent local overheating of the material; before the bottom residue is discharged, the speed of the hydraulically driven scraper is increased to fully stir and reduce viscosity before the discharge valve is opened.
[0033] Furthermore, a high-temperature resistant sight glass is provided on the side of the bottom of the distillation vessel 6, and a sampling and detection port is provided next to the sight glass; the liquid level and flow state of the residue at the bottom of the vessel are observed through the high-temperature resistant sight glass to determine in advance whether there is agglomeration; the residue composition is sampled and analyzed through the sampling and detection port to adjust the heating temperature or solvent oil rinsing frequency.
[0034] Furthermore, the bottom discharge port is located at the lowest point of the bottom of the vessel, and the cone is set with a 60° cone angle to effectively optimize the gravity flow of distillation residue and avoid dead zones at the bottom of the vessel. A screw conveyor 12 is installed below the bottom discharge port, and the screw conveyor 12 adopts a twin-screw power to improve discharge efficiency. A heated jacketed discharge valve is selected, and the discharge port of the distillation vessel 6 adopts a DN200 valve. Heat transfer oil is used for insulation to maintain the temperature of the residue in the pipeline ≥220℃, prevent cooling and agglomeration, ensure smooth valve opening and closing, and avoid blockage. A nitrogen purging interface is set in front of the discharge port valve of the distillation vessel 6. During discharge, 0.3MPa nitrogen is introduced for purging, and nitrogen pressure is used to assist in the transport of residue and reduce residue in the pipeline. In case of blockage, the discharge valve is closed, and 0.4-0.5MPa nitrogen is introduced for reverse purging (short-time pulse type) to clear the pipeline blockage.
[0035] This invention optimizes the distillation kettle 6 and temperature control system by reducing residue viscosity, preventing agglomeration and deposition, assisting in conveying and discharging, and facilitating cleaning and maintenance. Through the above equipment settings, the problem of difficult residue discharge can be solved from the entire process of "generation-conveyance-cleaning", ensuring the continuous and stable operation of the distillation system and reducing downtime caused by residue blockage.
[0036] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.
Claims
1. A distillation system for the preparation of 2-(4-methylphenyl)benzoxazole, characterized in that: It includes a temperature control system; the temperature control system includes a distillation vessel (6); the distillation vessel (6) adopts a cylindrical structure and has a cone at the bottom, and a hydraulically driven scraper is provided in the cone.
2. The distillation system for preparing 2-(4-methylphenyl)benzoxazole according to claim 1, characterized in that: The cone of the distillation vessel (6) is set with a cone angle of 60° and adopts a double-layer jacket structure. The inner layer is made of 316L stainless steel and the outer layer is made of carbon steel coiled tube as a heat insulation layer.
3. The distillation system for preparing 2-(4-methylphenyl)benzoxazole according to claim 1, characterized in that: A screw feeder (12) is provided below the distillation vessel (6), and the screw feeder (12) adopts a twin-screw power.
4. The distillation system for preparing 2-(4-methylphenyl)benzoxazole according to claim 1, characterized in that: The temperature control system uses heat transfer oil circulation and also includes a heat transfer oil inlet pipe (2), a heat transfer oil return pipe (1), an oil pump (9), a high-temperature oil valve (3), a first valve (10), a second valve (11), a third valve (5), a fourth valve (8), and a temperature controller (4); the heat transfer oil inlet pipe (2) is connected to the high-temperature oil valve (3), and the first valve (10) is fixedly connected to one end of the high-temperature oil valve (3) away from the heat transfer oil inlet pipe (2), and the oil pump (9) is fixedly connected to one end of the first valve (10) away from the high-temperature oil valve (3); the first valve (10) is fixedly connected to one end of the first valve (10) away from the high-temperature oil valve (3); the first valve (10) is fixedly connected to one end of the first valve (10) away from the high-temperature oil valve (3). An oil pump outlet (7) is provided at one end; the temperature controller (4) is installed between the oil pump outlet (7) and the high-temperature oil valve (3); two first valves (10) are respectively provided at both ends of the oil pump (9); the first valve (10) near the distillation vessel (6) is connected to a second valve (11) at one end away from the other side of the first valve (10), and the other end of the second valve (11) is connected to the jacket of the distillation vessel (6); a discharge pipe is connected to one side of the jacket of the distillation vessel (6), and the discharge pipe is connected to a third valve (5) and a fourth valve (8) respectively, and the third valve (5) is normally open.
5. The distillation system for preparing 2-(4-methylphenyl)benzoxazole according to claim 4, characterized in that: The discharge port of the distillation kettle (6) is equipped with a DN200 valve, which is kept warm by heat transfer oil and purged with nitrogen.
6. The distillation system for preparing 2-(4-methylphenyl)benzoxazole according to claim 4, characterized in that: The heat transfer oil inlet pipe (2) is connected to the heat transfer oil furnace. The heat transfer oil inside is supplied by the heat transfer oil furnace. The heat transfer oil return pipe (1) contains the cooled oil after heat exchange, which returns to the heat transfer oil furnace. The normal working cycle of the distillation kettle (6) is oil pump (9) - second valve (11) - distillation kettle (6) jacket - fourth valve (8) - oil pump (9). At this time, it is a single circulation of heat transfer oil, and there is no heat transfer oil exchange with the oil furnace.
7. The distillation system for preparing 2-(4-methylphenyl)benzoxazole according to claim 6, characterized in that: When it is necessary to increase the temperature of the distillation vessel (6), the high-temperature oil valve (3) is automatically opened to introduce high-temperature oil from the oil furnace to participate in the circulation. The excess high-temperature oil introduced is returned to the oil furnace through the third valve (5) after heat exchange.
8. The distillation system for preparing 2-(4-methylphenyl)benzoxazole according to claim 7, characterized in that: When the temperature control system is in the normal distillation stage, the hydraulically driven scraper runs at low speed; before the residue at the bottom of the vessel is discharged, the speed of the hydraulically driven scraper is increased to fully stir and reduce the viscosity before the discharge valve is opened.
9. The distillation system for preparing 2-(4-methylphenyl)benzoxazole according to claim 1, characterized in that: The bottom side of the distillation vessel (6) is provided with a high-temperature resistant sight glass, and a sampling and detection port is provided next to the sight glass.
10. The distillation system for preparing 2-(4-methylphenyl)benzoxazole according to claim 9, characterized in that: The discharge valve of the distillation kettle (6) is equipped with a nitrogen purging interface. When discharging, nitrogen is introduced for purging; when blocked, the discharge valve is closed and nitrogen is introduced for short-term pulse reverse purging.