A method for isobaric drying of aerogels using supercritical ethanol

Abstract

The present invention discloses a method for isobaric drying of aerogels using supercritical ethanol, comprising a loading step, a drying step, and a discharging step. In the drying step, after sealing a material tank and a drying kettle, the gap between the material tank and the drying kettle is used as a pressure balance chamber. A supercritical fluid discharge channel is established from the material tank to the outside of the kettle, and a balancing gas channel is established outside the kettle to the pressure balance chamber. Balancing gas is filled into the pressure balance chamber through the balancing gas channel, and the pressure of the balancing gas in the pressure balance chamber is dynamically controlled to maintain a consistent pressure inside and outside the material tank. The material tank is heated by the drying kettle to cause the ethanol to enter a supercritical state, and the liquid material in the gel material is displaced and discharged from the material tank. This drying method can shorten the time the gel stays in the drying kettle, improve the utilization efficiency of the drying kettle, save energy consumption during the cooling and heating processes of the drying kettle, and reduce the drying cost of the gel product.

Description

Technical Field

[0001] The invention relates to a drying method in the production process of an aerogel thermal insulation material, in particular to a method for performing supercritical isobaric drying on a gel material by using ethanol as a solvent. Background Art

[0002] During the production of aerogel thermal insulation materials, a drying process is required to remove liquid ethanol and other substances from the gel, resulting in a dry state. The existing aerogel supercritical ethanol drying method typically involves placing the gel material in a drying kettle, injecting liquid ethanol into the kettle and heating it. The temperature and pressure within the kettle increase simultaneously, causing the ethanol to reach a supercritical state, typically at 260-270°C and 14-16 MPa. After a certain period of insulation, the supercritical ethanol is slowly discharged at a constant temperature. Once all the ethanol has been discharged, the drying kettle is cooled. When the temperature within the drying kettle drops below 70°C, the lid is opened and the material is discharged. During the production process, if the drying kettle uses natural cooling, it takes at least 5-6 hours to reduce the temperature from 260°C to 70°C to reach the opening temperature. The material stays in the drying kettle for a long time, and the utilization efficiency of the drying kettle is low. If the drying kettle uses water cooling, it also takes 3-4 hours, and a special cooling circulation system needs to be installed outside the drying kettle. Not only is the equipment manufacturing cost high, but the cooling circulation system also consumes electricity when working, which increases the cost of aerogel production. In addition, when one batch of gel products is dried, the next batch of gel materials is placed in the drying kettle during the heating process. The cooled drying kettle needs to be reheated, and the heating time requires at least 4-5 hours, which is inefficient and causes energy waste. Summary of the Invention

[0003] The technical problem to be solved by the invention is to provide a method for isobaric drying of aerogels using supercritical ethanol, which can shorten the residence time of the gel in the drying kettle, improve the utilization efficiency of the drying kettle, save energy consumption during the cooling and heating processes of the drying kettle, and reduce the drying cost of the gel product.

[0004] The technical solution adopted to solve the technical problem is: a method for drying aerogels in supercritical ethanol isobaric pressure, comprising:

[0005] a loading step of loading the gel material to be dried and ethanol into a material tank;

[0006] In the drying step, the material tank is moved into a drying kettle, which is used to heat the material tank to make the ethanol enter a supercritical state, displacing the liquid substance in the gel material and then discharging it from the material tank;

[0007] The unloading step is to remove the material tank from the drying kettle after depressurization, and then take out the dried gel material from the material tank after cooling;

[0008] In the drying step, after the material tank and the drying kettle are closed, the gap between the material tank and the drying kettle is used as a pressure balance chamber, and a supercritical fluid discharge channel from the material tank to the outside of the kettle and a balance gas channel from the outside of the kettle to the pressure balance chamber are established. The balance gas is filled into the pressure balance chamber through the balance gas channel, and the pressure of the balance gas in the pressure balance chamber is dynamically controlled to ensure that the pressure inside and outside the material tank is always consistent.

[0009] As a further improvement of the present invention: the balance gas is nitrogen or an inert gas.

[0010] As a further improvement of the present invention: in the unloading step, the material tank is purged with safety gas before opening the tank.

[0011] As a further improvement of the present invention: before the material tank is moved out of the drying kettle, the supercritical fluid discharge channel is closed to make the material tank in a completely closed state.

[0012] As a further improvement of the present invention: the safety gas is nitrogen, carbon dioxide, argon or other inert gases.

[0013] Beneficial effects: The aerogel supercritical ethanol isobaric drying method of the present invention uses the gap between the material tank and the drying kettle as a pressure balance chamber in the drying step, establishes a supercritical fluid discharge channel from the material tank to the outside of the kettle, and a balance gas channel from the outside of the kettle to the pressure balance chamber, and fills the pressure balance chamber with balance gas through the balance gas channel, and dynamically controls the pressure of the balance gas in the pressure balance chamber, so that the pressure inside and outside the material tank is always consistent, so that the drying kettle is not in direct contact with ethanol throughout the whole process, thereby realizing the high-temperature opening of the kettle to remove the dried hot material tank and load the cold material tank to be dried, so that the hot material tank is naturally cooled outside the kettle. This method can shorten the residence time of the material tank in the drying kettle and improve the utilization efficiency of the drying kettle. Moreover, this aerogel supercritical ethanol isobaric drying method does not require the setting of a drying kettle cooling circulation system, which not only saves equipment investment but also reduces the operating cost of the equipment. In addition, this method can also make full use of the residual temperature of the drying kettle after unloading, shorten the heating time of the next batch of drying kettles, and save energy consumption. During the unloading process, the material tank is purged with a safety gas before it is opened, further removing any residual ethanol gas from the tank and ensuring safe unloading operations. The technical feature of completely enclosing the supercritical fluid discharge channel during the removal of the material tank from the drying kettle prevents ethanol from overflowing from the supercritical fluid discharge channel into the drying kettle during the process, further improving operational safety. The technical feature of using nitrogen, carbon dioxide, argon, or other inert gases ensures that the safety gas isolates oxygen during the high-temperature drying process, ensuring that the ethanol in the material tank does not come into contact with the drying kettle at all. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 The present invention is a schematic diagram of the structure of the equipment used in the method for isobaric drying of aerogels using supercritical ethanol. Implementation Method

[0015] A method for isobaric drying of aerogel using supercritical ethanol, comprising:

[0016] a loading step of loading the gel material to be dried and ethanol into a material tank;

[0017] In the drying step, the material tank is moved into a drying kettle, which is used to heat the material tank to make the ethanol enter a supercritical state, displacing the liquid substance in the gel material and then discharging it from the material tank;

[0018] In the unloading step, the material tank is depressurized and moved out of the drying kettle as a whole, and the dried gel material is taken out from the material tank after cooling.

[0019] In the drying step, after the material tank and the drying kettle are closed, the gap between the material tank and the drying kettle is used as a pressure balance chamber, and a supercritical fluid discharge channel from the material tank to the outside of the kettle and a balance gas channel from the outside of the kettle to the pressure balance chamber are established. The balance gas is filled into the pressure balance chamber through the balance gas channel, and the pressure of the balance gas in the pressure balance chamber is dynamically controlled to keep the pressure inside and outside the material tank consistent.

[0020] Preferably, in the unloading step, the material tank is purged with safety gas before opening the tank.

[0021] Preferably, the supercritical fluid discharge channel is closed during the process of moving the material tank out of the drying kettle, so that the material tank is in a completely closed state.

[0022] The balance gas is nitrogen or an inert gas.

[0023] The safety gas is nitrogen, carbon dioxide, argon or other inert gases, preferably nitrogen.

[0024] Figure 1A schematic diagram shows the schematic structure of the equipment used in the supercritical ethanol isobaric drying method for aerogels according to the present invention. The material tank 2 is a closed, cylindrical, pressure-bearing material tank. It is coaxially positioned within the drying vessel 1. The distance D between the cylindrical outer wall of the material tank and the tubular inner wall of the drying vessel is 5-7.5 mm, with an optimal distance of 5 mm. This creates a pressure equilibrium chamber 7 between the material tank and the drying vessel. An ethanol pipe 3 is located at the bottom of the material tank. It can pass through the bottom nozzle of the drying vessel and sealably engages with the nozzle 4 at the bottom of the drying vessel, forming a supercritical fluid discharge channel. After the material tank is loaded into the drying vessel, the ethanol pipe 3 passes through the drying vessel, forming a supercritical fluid discharge channel. A nitrogen pipe 6 is connected to the upper wall of the drying vessel, forming a balancing gas channel. Externally, a liquid ethanol inlet pipe 8, a material tank temperature sensor 9, and an ethanol condensation pipe 5 are located, connected to the ethanol pipe 3. The drying vessel is preferably an induction-heated drying vessel.

[0025] The supercritical drying process comprises the following steps:

[0026] Loading: Load the gel material to be dried into the material tank, close the loading port of the material tank, hoist the material tank into the drying kettle, and inject liquid ethanol into the material tank from the outside of the drying kettle through the ethanol pipe. When the injected liquid ethanol reaches the specified amount, close the liquid ethanol injection pipeline valve and the ethanol condensation pipeline valve; in this step, the gel material and ethanol can also be loaded into the material tank outside the kettle body, and then the material tank is closed and moved into the drying kettle.

[0027] Drying: Close the lid of the drying kettle, use the gap between the drying kettle and the material tank as a pressure balance chamber, add nitrogen from the outside of the drying kettle through the nitrogen pipe to the pressure balance chamber, use the drying kettle to heat the material tank, monitor the pressure in the pressure balance chamber and the pressure and temperature in the material tank in real time, and when the pressure in the material tank increases, inject nitrogen into the pressure balance chamber to ensure that the pressure in the pressure balance chamber is always equal to the pressure in the material tank; when the temperature at the bottom of the material tank reaches 265°C, control the temperature in the material tank to be stable at 263°C-267°C, so that the ethanol enters a supercritical state, open the valve on the supercritical fluid discharge channel, discharge the ethanol in the material tank, and maintain the ethanol in the material tank in a supercritical state; when the valve on the supercritical fluid discharge channel is closed and the pressure in the material tank no longer increases, the drying is completed;

[0028] Unloading, maintain the temperature of the material tank not lower than the supercritical temperature of ethanol, open the valve on the supercritical fluid discharge channel, slowly release the pressure, when the pressure of the material tank and the pressure balance chamber reaches normal pressure, the pressure relief ends, inject nitrogen into the pressure balance chamber through the nitrogen pipe, purge the pressure balance chamber, inject nitrogen into the material tank through the supercritical fluid discharge channel, purge the material tank, after the purge is completed, close the supercritical fluid discharge channel, open the kettle cover, lift the material tank out of the kettle, cool naturally, take out the aerogel felt, and complete a drying work cycle.

[0029] Taking a 650-liter drying kettle as an example, the supercritical drying method of aerogels according to the present invention saves 5-6 hours of cooling time in the drying kettle compared to the conventional process of cooling the drying kettle to 70°C before unloading because the material is discharged at a high temperature. Since the next batch of gel is directly loaded into the drying kettle at a high temperature after unloading, the residual heat of the drying kettle is fully utilized, reducing the heating time in step 4) by 3-4 hours. A single drying batch can reduce the gel's residence time in the drying kettle by 8-10 hours. This not only improves the utilization efficiency of the drying kettle but also saves energy consumed by cooling and heating. Furthermore, since the cooling step is omitted, the drying kettle does not need a dedicated cooling system, reducing equipment investment.

Claims

1. A method for isobaric drying of aerogels using supercritical ethanol, comprising: a loading step of loading the gel material to be dried and ethanol into a material tank; In the drying step, the material tank is moved into a drying kettle, which is used to heat the material tank to make the ethanol enter a supercritical state, displacing the liquid substance in the gel material and then discharging it from the material tank; The unloading step is to remove the material tank from the drying kettle after depressurization, and then take out the dried gel material from the material tank after cooling; The invention is characterized in that: in the drying step, after the material tank and the drying kettle are sealed, the gap between the material tank and the drying kettle is used as a pressure balance chamber, a supercritical fluid discharge channel is established from the material tank to the outside of the kettle, and a balance gas channel is established outside the kettle to the pressure balance chamber, and the balance gas is filled into the pressure balance chamber through the balance gas channel, and the pressure of the balance gas in the pressure balance chamber is dynamically controlled to ensure that the pressure inside and outside the material tank is always consistent; An ethanol pipe is provided at the bottom of the material tank, which passes through the bottom pipe opening of the drying kettle and is inserted and sealed with the bottom pipe opening of the drying kettle to form a supercritical fluid discharge channel. After the material tank is loaded into the drying kettle, the ethanol pipe passes through the drying kettle to form a supercritical fluid discharge channel; A nitrogen pipe for forming a balance gas channel is connected to the upper part of the drying kettle wall; A liquid ethanol injection pipeline connected to the ethanol connecting pipe, a material tank temperature sensor, and an ethanol condensation pipeline are arranged outside the drying kettle.

2. The aerogel supercritical ethanol isobaric drying method according to claim 1, characterized in that: The balance gas is nitrogen or an inert gas.

3. The aerogel supercritical ethanol isobaric drying method according to claim 2, characterized in that: During the unloading step, the material tank is purged with safety gas before opening.

4. The aerogel supercritical ethanol isobaric drying method according to claim 3, characterized in that: Before the material tank is removed from the drying kettle, the supercritical fluid discharge channel is closed to make the material tank completely closed.

5. The aerogel supercritical ethanol isobaric drying method according to claim 3 or 4, characterized in that: The safety gas is nitrogen, carbon dioxide or inert gas.

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