Aerogel negative pressure microwave drying equipment and working method thereof

Abstract

The application discloses an aerogel negative pressure microwave drying equipment and a working method thereof. The heating device and the microwave generator are simultaneously arranged in the drying box. The temperature in the drying box is heated by the heating device. The silica wet gel to be dried is kept at a temperature of 30-50 DEG C before the microwave generator is put into use. The moisture on the outer surface of the wet gel is gradually evaporated through a vacuum degree of-0.03 to-0.06 Mpa. The capillary force in the wet gel is balanced due to the negative pressure, and a layer of nanometer holes is gradually formed. At this time, the microwave generator is started to excite the water molecules in the wet gel. After the water molecules in the wet gel are precipitated, the water molecules are sucked out through the outer layer of nanometer holes due to the negative pressure. The negative pressure balances the capillary force in the wet gel and sucks out the water molecules precipitated in the wet gel, so that the dried silica aerogel full of nanometer holes is obtained.

Description

Technical Field

[0001] This invention relates to the field of new material production technology, and in particular to an aerogel negative pressure microwave drying device and its working method. Background Technology

[0002] The traditional method for drying materials is to heat them to evaporate the moisture, thus obtaining dried materials.

[0003] In conventional heating methods, heat is transferred through convection, conduction, and radiation, penetrating from the outside in. Under negative pressure, the melting and boiling points of the material decrease with increasing vacuum. Simultaneously, a vacuum pump dehumidifies the material, reducing moisture content and allowing water and other solutions within the material to gain sufficient kinetic energy to escape from the surface. However, under vacuum conditions, heat transfer via air convection is difficult; heat is only supplied through conduction and radiation. This results in a high surface temperature and a low internal temperature, leading to a large temperature difference that is difficult to control. Therefore, conventional vacuum drying methods are characterized by slow heat transfer, high energy consumption, low efficiency, and long drying times. Microwave heating, a form of radiative heating, directly acts on the material, heating it simultaneously from the inside out. It eliminates the need for convection or conduction, resulting in rapid heating, high thermal efficiency, short processing time, and uniform internal and external temperatures. This leads to energy savings, high drying efficiency, and good drying quality.

[0004] However, the above method cannot be used to produce silica aerogels because when wet silica aerogels are dried, they are heated both inside and out simultaneously. There is no channel for the internal solvent to precipitate, which would cause the wet gel to pulverize. Therefore, it is necessary to design a device capable of drying silica aerogels. Summary of the Invention

[0005] The purpose of this invention is to provide an aerogel negative pressure microwave drying device and its working method to solve the problems existing in the prior art, and to avoid the collapse of the wet gel skeleton, so as to fully dry the silica aerogel.

[0006] To achieve the above objectives, the present invention provides the following solution: The present invention provides an aerogel negative pressure microwave drying device, comprising...

[0007] A drying oven is provided, in which the silica wet gel is placed. The drying oven has an opening door for sealing the opening.

[0008] A heating device is provided inside the drying oven. The heating device is used to preheat the silica wet gel inside the drying oven, and the heating temperature of the heating device is above 30°C.

[0009] A vacuum pump, used to evacuate the drying chamber; and

[0010] A microwave generator is installed inside the drying oven.

[0011] The monitoring instrument is used to monitor the temperature and vacuum level inside the drying chamber and display the microwave intensity. The monitoring instrument is also used to control the start and stop of the heating device, vacuum pump, and microwave generator.

[0012] Preferably, the heating device is turned on before the vacuum pump and microwave generator are put into operation, and the heating temperature of the heating device is 30-50°C.

[0013] Preferably, the vacuum pump is connected to the drying chamber through a sealed pipe, and the vacuum degree inside the drying chamber is maintained at -0.03 to -0.06 MPa.

[0014] Preferably, the microwave intensity of the microwave generator is determined based on the amount of silica wet gel, and the power of the microwave generator is 300-2000W.

[0015] Preferably, the drying oven door is provided with a transparent observation window, and a door handle is also provided on the side of the drying oven door near the opening.

[0016] Preferably, the drying chamber is provided with an operation panel, and the monitoring instrument is installed on the operation panel. The monitoring instrument includes a touch screen, a display, and key indicator lights. The display is used to show the objects to be dried in the drying chamber. The touch screen is used to operate and control the start and stop of the heating device, vacuum pump, and microwave generator, and to display the temperature, vacuum level, and microwave intensity in the drying chamber. The key indicator lights are used to indicate the working status of the heating device, vacuum pump, and microwave generator.

[0017] Preferably, the heating device is one or more of the following: resistance temperature detector (RTD), infrared heater, hot water heater, steam heater, or thermal oil heater.

[0018] The present invention also provides a method for operating an aerogel negative pressure microwave drying device, applicable to the above-mentioned aerogel negative pressure microwave drying device, comprising the following steps:

[0019] First, place the silica wet gel to be dried into the drying oven, close the drying oven door to make the drying oven a sealed state, and at the same time, power on the negative pressure microwave drying equipment to make all monitoring instruments work; turn on the heating device to gradually raise the temperature of the silica wet gel to be dried in the drying oven to above 30°C.

[0020] Turn on the vacuum pump to gradually reduce the air pressure inside the drying chamber to below -0.03 MPa and maintain it within the range of -0.03 to -0.06 MPa; after 1-3 hours, a layer of nanopores will form on the surface of the silica wet gel to be dried.

[0021] Turn on the microwave generator and control the microwave intensity in the drying oven at 300-2000W. After 30-60 minutes, the silica wet gel will dry into a nanoporous silica aerogel.

[0022] The present invention achieves the following beneficial technical effects compared to the prior art:

[0023] The aerogel negative pressure microwave drying equipment and its working method of the present invention simultaneously install a heating device and a microwave generator inside the drying chamber. The heating device heats the temperature inside the drying chamber, and before the microwave generator is activated, the wet silica gel to be dried is kept at a temperature of 30-50°C.

[0024] A vacuum of -0.06 MPa is used to gradually evaporate the moisture on the outer surface of the wet gel. Due to the negative pressure, the capillary forces within the wet gel are balanced. As the water molecules on the outer surface evaporate, the space originally occupied by the water molecules does not collapse due to the capillary forces, gradually forming a layer of nanopores. These pores provide channels for the precipitation of internal water molecules. At this point, a microwave generator is activated to excite the water molecules inside the wet gel. After precipitation, the water molecules are drawn out through the outer nanopores by the negative pressure. This negative pressure balances the capillary forces within the wet gel while simultaneously drawing out the precipitated water molecules, resulting in a dry silica aerogel filled with nanopores. If a microwave generator is used on a silica wet gel before a layer of nanopores has formed on its surface, the water molecules inside the gel will have no channels to escape and will break up the wet gel, causing it to collapse and preventing the formation of a nanopore-filled aerogel. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 Internal structural layout of the aerogel negative pressure microwave drying equipment Figure 1 ;

[0027] Figure 2 Internal structural layout of the aerogel negative pressure microwave drying equipment Figure 2 ;

[0028] Figure 3 Internal structural layout of the aerogel negative pressure microwave drying equipment Figure 3 ;

[0029] Figure 4 A schematic diagram showing the location of the infrared heater when it is used in the heating device;

[0030] Figure 5 A schematic diagram showing the installation location of the heating device when a resistance temperature detector, hot water heater, steam heater, or thermal oil heater is used;

[0031] The components include: 1. Drying oven; 2. Drying oven door; 3. Vacuum pump; 4. Door handle; 5. Transparent observation window; 6. Button indicator light; 7. Display; 8. Touch screen; 9. Microwave generator; 10. Heating device; 11. Negative pressure space. Detailed Implementation

[0032] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] The purpose of this invention is to provide an aerogel negative pressure microwave drying device and its working method to solve the problems existing in the prior art, and to avoid the collapse of the wet gel skeleton, so as to fully dry the silica aerogel.

[0034] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0035] like Figures 1-5 As shown, this invention provides an aerogel negative pressure microwave drying device and its operating method. In particular, it provides a device and its operating method suitable for large-scale, mass production of silica aerogel. The aerogel negative pressure microwave drying device of this invention consists of a drying chamber 1, a drying chamber door 2, a microwave generator 9, a vacuum pump 3, a heating device 10 (including a resistance thermometer, infrared heater, hot water heater, steam heater, thermal oil heater, etc.), and monitoring instruments.

[0036] A heating device 10 is installed inside the negative pressure microwave drying oven 1, enabling it to heat the internal temperature of the drying oven 1 without using microwaves. Current related equipment uses microwaves as a heating method to address the problems of slow heat conduction, high energy consumption, low efficiency, and long drying time associated with conventional vacuum drying methods. However, microwave heating is a type of radiative heating, where microwaves directly act on the material, heating it simultaneously from the inside out. Silica wet gels are quite brittle; when microwaves are applied, the solvents inside and outside the wet gel evaporate simultaneously. Since there are no channels for the internal solvents to precipitate after evaporation, they will break the wet gel skeleton, causing the silica wet gel to be dried to pulverize. This invention uses the heating device 10 to first raise the temperature inside the drying oven 1 to above 30°C. Before applying microwaves inside the negative pressure microwave drying oven 1, the wet gel to be dried is placed in an environment with a temperature above 30°C so that its external solvents are heated and precipitated. At this point, the vacuum pump 3 of the drying oven 1 generates a negative pressure of -0.03 to -0.06 MPa, balancing the capillary forces generated in the pores left after the outer solvent of the dried wet gel evaporates. This ensures that the wet gel skeleton will not break or collapse under the influence of capillary forces. The space left after the solvent molecules precipitate from the wet gel is filled with air, forming a layer of nanopores about 3 mm thick, providing a channel for the solvent to precipitate from the inside of the wet gel. Simultaneously, the nanopores formed in the outer skeleton of the wet gel gradually harden. Then, microwaves are applied to the wet gel to stimulate the evaporation of its internal solvent, which is extracted through the nanopores already formed in the outer layer of the wet gel by the negative pressure. Similarly, the space occupied by the solvent molecules inside the wet gel does not collapse due to the negative pressure and is entirely occupied by air. Thus, a dried silica aerogel filled with nanopores is obtained.

[0037] Specifically, the drying chamber 1 is a sealed chamber, with a sealed connection between the drying chamber door 2 and the drying chamber 1. The drying chamber 1 is connected to the vacuum pump 3 via a sealed pipe. A microwave generator 9 and a heating device 10 are installed inside the drying chamber 1. Monitoring instruments can test the temperature and vacuum level inside the drying chamber 1, display the microwave intensity, and control the start and stop of the heating device 10, vacuum pump 3, and microwave generator 9 according to a program. The drying chamber door 2 is equipped with a transparent observation window 5 and a door handle 4, which allows the drying chamber door 2 to be opened.

[0038] In one embodiment, the monitoring instrument includes a display 7, a touch screen 8, and key indicator lights 6. The display 7 is used to display the status of the dried material in the drying chamber 1. The touch screen 8 is used to operate and control the start and stop of the heating device 10, the vacuum pump 3, and the microwave generator 9, and to display the temperature, vacuum level, and microwave intensity in the drying chamber 1. The key indicator lights 6 are used to indicate the working status of the heating device 10, the vacuum pump 3, and the microwave generator 9.

[0039] The present invention installs a heating device 10 inside the drying chamber 1 of the aerogel negative pressure microwave drying equipment. This heating device 10 ensures that the temperature inside the drying chamber 1 of the aerogel negative pressure microwave drying equipment reaches above 30°C and is maintained between 30°C and 50°C before the negative pressure and microwave devices are put into operation.

[0040] In one embodiment, after the temperature inside the drying chamber 1 of the aerogel negative pressure microwave drying equipment reaches above 30°C, the vacuum pump 3 is turned on to form a negative pressure space 11 inside the drying chamber 1. The vacuum degree of the negative pressure space 11 gradually reaches -0.03MPa over 30 minutes and is maintained between -0.03 and -0.06MPa.

[0041] In one embodiment, the negative pressure inside the drying chamber 1 of the aerogel negative pressure microwave drying device is maintained at -0.03 to -0.06 MPa for more than 1 hour to 3 hours.

[0042] In one embodiment, the negative pressure inside the drying chamber 1 of the aerogel negative pressure microwave drying equipment is maintained at -0.03 to -0.06 MPa for more than 1 hour to 3 hours. Then, the microwave generator 9 is turned on and the microwave intensity is controlled at 300 to 2000W according to the amount of wet gel to be dried (the microwave intensity is determined according to the amount of silica wet gel; the greater the amount, the greater the microwave intensity, and the smaller the amount, the smaller the microwave intensity).

[0043] In one embodiment, inside the drying chamber 1 of the aerogel negative pressure microwave drying equipment, after the microwave generator 9 is turned on, the temperature is maintained at 30-50°C, the negative pressure at -0.03--0.06 MPa, and the microwave power at 300-2000 W. Depending on the amount of wet gel to be dried, the drying time is typically 30-60 minutes. After this time, all devices in the drying chamber 1 are turned off, stopping the aerogel negative pressure microwave drying equipment from operating. This produces a product with a thermal conductivity of 0.013 W / mK and a density of 50 kg / m³. 3 Specific surface area: above 900 m² / g; Porosity: above 95% silica aerogel.

[0044] Example 1

[0045] An aerogel negative pressure microwave drying device and its working method include the following steps:

[0046] Step 1: Manufacturing an aerogel negative pressure microwave drying device:

[0047] like Figure 1 As shown, the negative pressure microwave drying equipment is divided into three parts: upper, middle and lower. The upper part is equipped with monitoring instruments; the middle part is where the negative pressure microwave drying chamber 1 is arranged; and the lower part is where the vacuum pump 3 is installed.

[0048] Step 2, Instrument installation in drying oven 1:

[0049] like Figure 4 As shown, the negative pressure microwave drying oven 1 is a sealed chamber with a door at the front. The door 2 is sealed to the oven. The oven 1 is connected to a vacuum pump 3 via a sealed pipe. Inside the oven 1 are a temperature sensor, a camera, a pressure sampling tube, a microwave generator 9, and an infrared heater, with the infrared heater's heating direction aligned with the position where the silica wet gel is placed. A rotatable tray is installed inside the oven 1 to hold the silica wet gel to be dried.

[0050] Step 3, Working Method:

[0051] First, place the silica wet gel to be dried into drying chamber 1 and close drying chamber door 2 to seal drying chamber 1. Then, power on the negative pressure microwave drying equipment to activate all monitoring instruments. Third, turn on the infrared heater to gradually raise the temperature of the wet gel to above 30°C. Fourth, turn on vacuum pump 3 to gradually reduce the air pressure inside drying chamber 1 to above -0.06 MPa and maintain it within the range of -0.05 to -0.06 MPa. Fifth, after more than 2 hours, a layer of nanopores approximately 3 mm thick will form on the surface of the silica wet gel. Sixth, turn on microwave generator 9 and control the microwave intensity inside drying chamber 1 at 600W. After 60 minutes, the silica wet gel will be dried into a nanoporous silica aerogel.

[0052] Example 2

[0053] An aerogel negative pressure microwave drying device and its working method include the following steps:

[0054] Step 1: Manufacturing an aerogel negative pressure microwave drying device:

[0055] like Figure 2 As shown, the negative pressure microwave drying equipment is divided into three parts: upper, middle and lower. The upper part is where the negative pressure microwave drying chamber 1 is arranged; the middle part is where the monitoring instruments are installed; and the lower part is where the vacuum pump 3 is installed.

[0056] Step 2, Instrument installation in drying oven 1:

[0057] like Figure 5 As shown, the negative pressure microwave drying oven 1 is a sealed chamber with a door installed at the front. The door 2 is sealed to the drying oven 1. The drying oven 1 is connected to a vacuum pump 3 via a sealed pipe. Inside the drying oven 1 are a temperature sensor, a camera, a pressure sampling tube, a microwave generator 9, and an electric heater. The electric heater is installed in the lower part of the drying oven 1. A rotatable tray is installed inside the drying oven 1 to hold the dried silica wet gel.

[0058] Step 3, Working Method:

[0059] First, place the silica wet gel to be dried into drying chamber 1 and close drying chamber door 2 to seal drying chamber 1. Then, power on the negative pressure microwave drying equipment to activate all monitoring instruments. Third, turn on the electric heater to gradually raise the temperature inside drying chamber 1 to above 40℃. Fourth, turn on vacuum pump 3 to gradually reduce the air pressure inside drying chamber 1 to above -0.05MPa and maintain it within the range of -0.04 to -0.05MPa. Fifth, after more than 1.5 hours, a layer of nanopores approximately 3mm thick will form on the surface of the silica wet gel to be dried. Sixth, turn on microwave generator 9 and control the microwave intensity inside drying chamber 1 at 500W. After 50 minutes, the silica wet gel will be dried into a nanoporous silica aerogel.

[0060] Example 3

[0061] An aerogel negative pressure microwave drying device and its working method include the following steps:

[0062] Step 1: Manufacturing an aerogel negative pressure microwave drying device:

[0063] like Figure 3 As shown, the negative pressure microwave drying equipment is divided into three parts: upper, lower left, and lower right. The upper part is where the negative pressure microwave drying chamber 1 is arranged; the lower left part is where the monitoring instrument is installed; and the lower right part is where the vacuum pump 3 is installed.

[0064] Step 2, Instrument installation in drying oven 1:

[0065] like Figure 5 As shown, the negative pressure microwave drying oven 1 is a sealed chamber with a door installed at the front. The door 2 is sealed to the drying oven 1. The drying oven 1 is connected to a vacuum pump 3 via a sealed pipe. Inside the drying oven 1 are a temperature sensor, a camera, a pressure sampling tube, a microwave generator 9, and a hot water heater, which is installed in the lower part of the drying oven 1. A rotatable tray is installed inside the drying oven 1 to hold the dried silica wet gel.

[0066] Step 3, Working Method:

[0067] First, place the silica wet gel to be dried into drying chamber 1 and close the drying chamber door 2 to seal the chamber. Then, power on the negative pressure microwave drying equipment to activate all monitoring instruments. Third, turn on the hot water heater to gradually raise the temperature inside drying chamber 1 to below 50℃. Fourth, turn on the vacuum pump 3 to gradually reduce the air pressure inside drying chamber 1 to above -0.04MPa and maintain it within the range of -0.03 to -0.04MPa. Fifth, after more than 3 hours, a layer of nanopores approximately 3mm thick will form on the surface of the silica wet gel. Sixth, turn on the microwave generator 9 and control the microwave intensity inside drying chamber 1 at 800W. After 50 minutes, the silica wet gel will be dried into a nanoporous silica aerogel.

[0068] The aerogel negative pressure microwave drying equipment and its working method of this invention involve first heating the wet gel to above 30°C before applying microwaves, allowing the external solvent to precipitate and providing a channel for the internal solvent to precipitate. To prevent the wet gel skeleton from collapsing due to capillary forces during external solvent precipitation, a certain negative pressure is applied to balance the internal capillary forces. The temperature also allows the outer layer of solvent to evaporate and precipitate. After the external solvent precipitates, the gel skeleton remains intact, and the space filled with air forms a layer of nanopores. This provides a channel for the internal solvent to precipitate. Simultaneously, the outer skeleton of the wet gel gradually hardens. Microwaves are then applied to the wet gel to stimulate internal solvent evaporation, which is then extracted through the channels formed on the outer layer by the negative pressure. The space occupied by the internal solvent molecules does not collapse due to the negative pressure and is entirely filled with air, resulting in a dried aerogel product filled with nanopores.

[0069] It should be noted that, for those skilled in the art, it is obvious that the present invention is not limited to the details of the above exemplary embodiments, and that the present invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered exemplary and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention, and no reference numerals in the claims should be construed as limiting the scope of the claims.

[0070] Specific examples have been used to illustrate the principles and implementation methods of this invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of this invention. Furthermore, those skilled in the art will recognize that, based on the ideas of this invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of this invention.

Claims

1. A method for operating an aerogel negative pressure microwave drying device, applicable to an aerogel negative pressure microwave drying device, characterized in that, Drying equipment includes A drying oven is provided, in which silica wet gel is placed. The drying oven has a door on its open side, which is used to seal the opening of the drying oven. as well as The heating device is installed inside the drying oven. The heating device is used to preheat the silica wet gel inside the drying oven. The heating temperature of the heating device is above 30°C. The heating device is turned on before the vacuum pump and microwave generator are put into use. as well as A vacuum pump, used to evacuate the drying chamber; as well as A microwave generator is installed inside the drying oven. The monitoring instrument is used to monitor the temperature and vacuum level inside the drying oven and display the microwave intensity. The monitoring instrument is also used to control the start and stop of the heating device, vacuum pump, and microwave generator. The working method includes the following steps: First, place the silica wet gel to be dried into the drying oven, close the drying oven door to make the drying oven sealed, and at the same time, power on the negative pressure microwave drying equipment to make all monitoring instruments work; turn on the heating device, and before applying microwaves into the negative pressure microwave drying oven, gradually raise the temperature of the silica wet gel to be dried in the drying oven to above 30°C so that the external solvent is heated and precipitated. The vacuum pump is turned on, and the air pressure in the drying chamber is gradually reduced to below -0.03 MPa and maintained within the range of -0.03 to -0.06 MPa. This balances the capillary force generated in the pores left after the solvent on the outer layer of the wet gel evaporates, ensuring that the wet gel skeleton will not break or collapse due to capillary force. The space left after the solvent molecules of the wet gel precipitate are filled with air. After 1-3 hours, a layer of 3 mm thick nanopores is formed on the surface of the silica wet gel to be dried, providing a channel for the solvent to precipitate from the inside of the wet gel. Turn on the microwave generator and control the microwave intensity in the drying oven at 300-2000W. After 30-60 minutes, the internal solvent will evaporate and be extracted by negative pressure through the nanopores already formed on the outer layer of the wet gel. The silica wet gel will then dry into a nanoporous silica aerogel.

2. The working method of the aerogel negative pressure microwave drying device according to claim 1, characterized in that: The heating temperature of the heating device is 30-50℃.

3. The working method of the aerogel negative pressure microwave drying device according to claim 1, characterized in that: The vacuum pump is connected to the drying chamber through a sealed pipe, and the vacuum level inside the drying chamber is maintained at -0.03 to -0.06 MPa.

4. The working method of the aerogel negative pressure microwave drying device according to claim 1, characterized in that: The microwave intensity of the microwave generator is determined based on the amount of silica wet gel, and the power of the microwave generator is 300-2000W.

5. The working method of the aerogel negative pressure microwave drying device according to claim 1, characterized in that: The drying oven door is equipped with a transparent observation window, and a door handle is also provided on the side of the drying oven door near the opening.

6. The working method of the aerogel negative pressure microwave drying device according to claim 1, characterized in that: The drying chamber is equipped with an operation panel, and the monitoring instrument is installed on the operation panel. The monitoring instrument includes a touch screen, a display, and key indicator lights. The display is used to show the objects to be dried in the drying chamber. The touch screen is used to operate and control the start and stop of the heating device, vacuum pump, and microwave generator, and to display the temperature, vacuum level, and microwave intensity in the drying chamber. The key indicator lights are used to indicate the working status of the heating device, vacuum pump, and microwave generator.

7. The working method of the aerogel negative pressure microwave drying device according to claim 1, characterized in that: The heating device is any one or more of the following: resistance temperature detector (RTD), infrared heater, hot water heater, steam heater, or thermal oil heater.

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