Preparation system of silicon dioxide aerogel

Abstract

The present invention relates to a system for preparing silica aerogel, and more particularly, to a system for preparing silica aerogel, which increases the productivity of silica aerogel and improves production efficiency or performance. The silica aerogel preparation system according to the present invention comprises: a raw material supply unit for conveying at least one raw material selected from deionized water, water glass, a surface modifier, an inorganic acid, and an organic solvent to a mixing unit; a mixing unit for preparing a wet silica gel by mixing the raw materials conveyed from the raw material supply unit; a drying part for drying the silica wet gel to prepare a silica aerogel; a recovery unit that recovers a portion of the raw material after evaporation of the raw material used in at least one of the mixing unit and the drying unit; and a heat transfer unit that transfers heat to at least one of the mixing unit and the drying unit, in which the preparation system further includes a crushing unit that crushes the raw material from the raw material supply unit to the mixing unit.

Description

[0001] This case is a divisional application, the parent case of which is an application with an application date of March 7, 2017, application number 201780003199.5, and invention name “System for preparing silica aerogel”. Technical Field

[0002] CROSS-REFERENCE TO RELATED APPLICATIONS

[0003] This application claims the benefit of priority from Korean Patent Application No. 10-2016-0035565, filed on Mar. 24, 2016, the disclosure of which is incorporated herein by reference in its entirety. Technical Field

[0004] The present invention relates to a system for preparing silica aerogel, and more particularly, to a system for preparing silica aerogel, which improves the productivity of silica aerogel and the production efficiency or performance. Background Art

[0005] Silica aerogel has a chemical formula expressed as SiO2·nH2O, a high porosity of 90% to 99.9% and a pore size of 1nm to 100nm. Silica aerogel can be a 600nm 2 / g of super porosity and high specific surface area materials.

[0006] Since silica aerogel has a nanoporous structure and a very large surface area, it can have very excellent water and alcohol absorption capabilities, thereby being used as a very excellent dehumidifier and as an ultralight and ultrathermal insulating material, a catalyst carrier, and a superinsulating material.

[0007] Despite its wide range of applications, silica aerogels have very limited uses.

[0008] The core technology in the preparation of silica aerogels is a drying process that can dry the wet gel without shrinking it while maintaining its original structure. The typical drying method is supercritical drying. However, due to the high production costs and risks associated with high pressures in autoclaves, and the inability to operate continuously, supercritical drying has many limitations in terms of economic efficiency and continuity. Furthermore, the production process not only involves risks but also has the disadvantage of high production costs due to its complexity.

[0009] [Prior art literature]

[0010] Korean Patent Registration No.10-1082982 Summary of the Invention

[0011] Technical issues

[0012] Therefore, the present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a production system of silica aerogel, which increases the productivity of silica aerogel and improves production efficiency or performance.

[0013] Technical Solution

[0014] The silica aerogel preparation system according to the present invention includes: a raw material supply section for conveying at least one raw material selected from deionized water, water glass, a surface modifier, an inorganic acid, and an organic solvent to a mixing section; a mixing section for mixing the raw materials conveyed from the raw material supply section to prepare a wet silica gel; a drying section for drying the wet silica gel to prepare the silica aerogel; a recovery section for recovering a portion of the raw materials used in at least one of the mixing section and the drying section after evaporation; and a heat transfer section for transferring heat to at least one of the mixing section and the drying section. The preparation system further includes a pulverizing section for pulverizing the raw materials conveyed from the raw material supply section to the mixing section.

[0015] Beneficial effects

[0016] The silica aerogel production system according to the present invention may include a raw material supply section, a mixing section, a drying section, a recovery section, and a heat transfer section, and may further include a pulverization section for pulverizing the raw material delivered from the raw material supply section to the mixing section. Thus, the present invention can provide a silica aerogel production system that increases silica aerogel production efficiency and improves production efficiency or performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 is a block diagram illustrating a system for preparing a silica aerogel according to one embodiment of the present invention. DETAILED DESCRIPTION

[0018] Hereinafter, preferred embodiments of the present invention will be described in more detail with reference to the accompanying drawings. However, the present invention is not limited to the following embodiments.

[0019] Figure 1 is a block diagram illustrating a system for preparing a silica aerogel according to one embodiment of the present invention.

[0020] In the following, reference will be made to Figure 1 A system for preparing silica aerogel according to one embodiment of the present invention is described.

[0021] The silica aerogel production system 100 according to one embodiment of the present invention includes a raw material supply unit 110 , a crushing unit 115 , a mixing unit 120 , a drying unit 130 , a recovery unit 140 , and a heat transfer unit 150 .

[0022] Reference Figure 1 The raw material supply part 110 may deliver at least one raw material of deionized water, water glass, a surface modifier, an inorganic acid, and an organic solvent to the mixing part 120. Only one organic solvent may be used, or two or more organic solvents may be used.

[0023] The raw material supply part 110 may mix a portion of raw materials such as deionized water, water glass, a surface modifier, an inorganic acid, and an organic solvent with one another and transfer the remaining raw materials as they are.

[0024] Deionized water is water from which all ions have been removed. Waterglass is a dark aqueous solution of sodium silicate (liquid phase) obtained by fusing silicon dioxide and alkali. Waterglass can be produced by melting a mixture of silica sand and soda ash at a temperature of 1,300°C to 1,500°C and then treating the resulting mixture in a low-pressure steam boiler.

[0025] There is no particular limitation on the water glass, but the water glass solution may contain 28 to 30 wt% of silicon dioxide (SiO 2 ). Furthermore, the water glass solution may contain 0.1 to 10 wt% of silicon dioxide.

[0026] Deionized water and water glass are stored in corresponding storage containers. Then, deionized water and water glass can be transported from the storage containers to the mixing unit 120 through pipelines. When valves are installed in the middle of each connecting pipeline, the amount of deionized water and water glass can be adjusted.

[0027] Typically, wet silica gels prepared using water glass have hollow spaces filled with water. These wet silica gels are also referred to as silica hydrogels. However, when the solvent is removed through a drying process, the liquid solvent evaporates into a gas phase, causing shrinkage and rupture of the porous structure due to the high surface tension of water at the gas / liquid interface. As a result, the resulting silica aerogel exhibits a decrease in specific surface area and a change in its porous structure.

[0028] Therefore, in order to maintain the porous structure of the wet gel, not only must the water with a relatively high surface tension be replaced with an organic solvent with a relatively low surface tension, but the wet gel must also be dried without shrinking while maintaining its original structure. When the hollow space of the wet silica gel is filled with a non-polar organic solvent, the wet silica gel can be called a silica lyogel.

[0029] The non-polar organic solvent can replace the water present in the hollow space of the prepared wet silica gel, thereby preventing the shrinkage and rupture of the pores that occur during evaporation of the water present in the hollow space of the wet silica gel when the silica is dried. As a result, it is possible to prevent a decrease in specific surface area and a change in the porous structure that occurs when the wet silica gel is dried.

[0030] The organic solvent may include at least one selected from hexane, heptane, toluene, and xylene, but is not limited thereto. In more detail, the organic solvent may be hexane.

[0031] Dried silica aerogels maintain low thermal conductivity immediately after drying. However, the hydrophilic silanol groups (Si-OH) on the silica surface absorb water from the air, gradually increasing the thermal conductivity. Therefore, to maintain low thermal conductivity, the surface of the silica aerogel must be modified to be hydrophobic.

[0032] An organosilicon compound can be used as a surface modifier that can be used when preparing a wet silica gel. In particular, a silane compound, a siloxane compound, a silanol compound, or a silazane compound can be used as a surface modifier. Here, one of these can be used alone, or a mixture of two or more of them can be used.

[0033] Specific examples of the silane compound may include dimethyldimethoxysilane, dimethyldiethoxysilane, methyltrimethoxysilane, vinyltrimethoxysilane, phenyltrimethoxysilane, tetraethoxysilane, dimethyldichlorosilane, 3-aminopropyltriethoxysilane, and the like.

[0034] Specific examples of the siloxane compound may include polydimethylsiloxane, polydiethylsiloxane, octamethylcyclotetrasiloxane, and the like.

[0035] Specific examples of the silanol compound may include trimethylsilanol, triethylsilanol, triphenylsilanol, tert-butyldimethylsilanol, and the like.

[0036] In addition, specific examples of the silazane compound may include 1,2-diethyldisilazane, 1,1,2,2-tetramethyldisilazane, 1,1,3,3-tetramethyldisilazane, hexamethyldisilazane, 1,1,2,2-tetraethyldisilazane, 1,2-diisopropyldisilazane, and the like.

[0037] Alternatively, the surface modifier may be a hydrated organosilicon compound. When a hydrated organosilicon compound is used as described above, its reactivity with silica increases, allowing for more efficient surface modification. As a result, a hydrophobic silica aerogel can be prepared having significantly improved tap density characteristics and specific surface area while maintaining excellent hydrophobicity.

[0038] More specifically, the surface modifier may include at least one selected from hexamethyldisilazane, tetramethyldisilazane, and hydrates thereof, more specifically hexamethyldisilazane (HMDS), considering surface modification efficiency and thereby hydrophobicity-increasing effect on the silica wet gel.

[0039] The inorganic acid that can be used to prepare the silica wet gel may include at least one acid selected from nitric acid, hydrochloric acid, acetic acid, sulfuric acid, and hydrofluoric acid. In particular, the inorganic acid may be nitric acid (HNO 3 ).

[0040] Inorganic acids can rapidly react with surface modifiers to decompose them. Therefore, they can promote the reaction between the water glass solution and the surface modifier to form a surface-hydrophobic silica sol. Furthermore, inorganic acids can promote the gelation of the hydrophobic silica sol by adjusting its pH. Therefore, hydrophobic silica wet gels can be prepared by simultaneously inducing surface modification and gelation.

[0041] The mixing section 120 can mix the raw materials delivered from the raw material supply section 110 to prepare a wet silica gel. The mixing section 120 may include a motor (not shown) and a mixing tank (not shown). In the mixing tank, the raw materials delivered from the raw material supply section 110 can be mixed by a stirring blade rotated by the motor. A temperature sensor for measuring temperature can be provided in the mixing tank. The wet silica gel prepared in the mixing section 120 can be transported to the drying section 130. To this end, the mixing section 120 and the drying section 130 can be connected to each other by a pipeline.

[0042] Before describing the drying part 130, the pulverizing part 115 will be described first. Figure 1 The silica aerogel preparation system 100 according to one embodiment of the present invention may further include a pulverizing unit 115 for pulverizing the raw material supplied from the raw material supply unit 110 to the mixing unit 120 .

[0043] The pulverization unit 115 can crush or pulverize the raw material particles to produce small-sized raw material particles. This finer pulverization of the raw material particles increases the surface area of the particles per unit volume, further increasing the reaction area. This increased reaction area per unit volume further improves surface modification and solvent replacement performance. Consequently, the production rate of the silica aerogel can be increased, thereby improving production efficiency and performance.

[0044] The drying unit 130 dries the wet silica gel prepared in the mixing unit 120 to generate a silica aerogel. The drying unit 130 may include a motor (not shown) and a drying tank (not shown). In the drying tank, the wet silica gel may be dried by rotating a stirring blade rotated by the motor. In this case, a silica aerogel in a powdered form may be prepared.

[0045] The silica aerogel preparation system 100 according to one embodiment of the present invention may further include a collecting unit 160 for collecting the silica aerogel powder prepared in the drying unit 130 .

[0046] The drying section 130 and the collecting section 160 may be connected to each other via a pipe. A valve may be installed in the middle of the connecting pipe. The amount of silica aerogel delivered from the drying section 130 to the collecting section 160 may be adjusted by switching the control valve.

[0047] The recovery unit 140 recovers a portion of the raw material after evaporation of the raw material used in at least one of the mixing unit 120 and the drying unit 130. In particular, the recovery unit 140 may mainly recover the organic solvent evaporated in the mixing unit 120 and the drying unit 130. The recovery unit 140 may include a condenser (not shown), a storage tank (not shown), and a vacuum pump (not shown).

[0048] The condenser can liquefy the evaporated and recovered raw material, and the storage tank can store the raw material such as the organic solvent liquefied in the condenser. A vacuum pump can be used to control the pressure in each of the condenser and the storage tank.

[0049] When the organic solvent evaporated while the drying process is performed is recovered through the recovery part 140 , a filter may be provided in the drying part 130 so that the silica aerogel powder is not recovered.

[0050] The silica aerogel production system 100 according to one embodiment of the present invention may further include a heat transfer unit 150 for transferring heat to at least one of the mixing unit 120 and the drying unit 130. The heat transfer unit 150 is a heater for transferring hot air to the mixing unit 120 and the drying unit 130.

[0051] The solvent replacement and gelation in the mixing unit 120 are affected by the ambient temperature. Here, the solvent replacement and gelation are preferably performed in an atmosphere of 30° C. to 40° C. The heat transfer unit 150 may provide a heat medium or hot air as a medium for heating the mixing unit 120 .

[0052] The drying process performed in the drying section 130 is affected by temperature. Generally, the drying process can be most efficient at room temperature to 150° C. The heat transfer section 150 can also transfer heat to the drying section 130 .

[0053] The above-mentioned pulverizing portion 115 will be described in more detail.

[0054] The raw materials delivered from the raw material supply unit 110 to the mixing unit 120 may be in a state where solids and liquids are mixed. Alternatively, the raw materials may be in a sol state where solids are dispersed in a liquid. Therefore, the pulverizing unit 115 may pulverize the raw materials using a homogenizer to make the mixed raw materials smaller and more uniform. Here, the homogenizer may be a device that vigorously stirs two immiscible liquid substances to form an emulsion.

[0055] In the silica aerogel production system 100 according to one embodiment of the present invention, the raw material supplied to the mixing unit 120 may be in a state where solid and liquid are mixed with each other. In this case, the pulverizing unit 115 may pulverize the raw material particles using a jet mill to produce finer particles.

[0056] Here, the jet mill may refer to a fine pulverizer that jets compressed air or steam having a predetermined pressure or higher from a specific nozzle and draws the raw material into a high-speed jet flow to sufficiently accelerate the raw material, thereby causing the accelerated particles to collide with each other or with an impact plate, thereby pulverizing the particles.

[0057] The crushing unit 115 may also include a blade (not shown) for crushing the raw material particles. Here, the blade may have an upwardly upright shape. The raw material particles tend to fall under the action of gravity. Therefore, when the blade rotates with the blade facing upward, the falling particles and the blade can effectively collide with each other. As a result, the blade of the crushing unit 115 can crush the particles more strongly to improve the crushing performance.

[0058] In addition, in the silica aerogel production system 100 according to one embodiment of the present invention, the pulverizing unit 115 may include a blade unit (not shown) for pulverizing raw material particles. The blade unit may include a plate member (not shown) and a protruding blade member (not shown).

[0059] The plate member is provided below the pulverizing portion 115 and has a flat plate shape. In addition, the protruding blade member may have a blade shape protruding upward from an upper surface of the plate member.

[0060] The raw material particles may be accumulated at the bottom due to gravity, and the accumulated raw material particles may be accumulated on a plate member provided below the pulverizing unit 115 .

[0061] Then, when the plate member rotates, the protruding blade member protruding upward from the plate member can rotate together with the plate member. Therefore, the raw material particles accumulated on the plate member can be more effectively and finely crushed by the rapidly rotating protruding blade member.

[0062] When raw material particles are accumulated and dense on the upper surface of the plate member, the protruding blade member can more strongly and reliably perform a pulverizing operation while passing through the accumulated and dense raw material particles. Therefore, pulverization can be performed more efficiently.

[0063] As described above, when the pulverizing unit 115 finely pulverizes the raw material particles, the reaction surface area is increased, thereby significantly increasing the reaction rate. As a result, the surface modification and solvent replacement performance can be further improved.

[0064] Therefore, the productivity of silica aerogel can be increased, thereby significantly improving production efficiency and performance.

[0065] In addition, to produce a product with an ideal particle size distribution, the dried silica aerogel can be subjected to a grinding process and a screening process (an operation of classifying particles according to particle size through a sieve). As in one embodiment of the present invention, when a pulverizing unit 115 is provided between the raw material supply unit 110 and the mixing unit 120, a product with an ideal particle size distribution can be produced without performing grinding and screening processes after drying, thereby reducing production costs.

[0066] While embodiments of the present invention have been described with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the invention as defined in the following claims.

Claims

1. A system for preparing silica aerogel, comprising: a raw material supply section, which delivers at least one raw material selected from the group consisting of deionized water, water glass, a surface modifier, an inorganic acid, and an organic solvent to a mixing section; a mixing section for mixing the raw materials delivered from the raw material supply section to prepare a silicon dioxide wet gel; a drying section for drying the wet silica gel to prepare a silica aerogel; a recovery section for recovering a portion of the raw material evaporated from the raw material used in at least one of the mixing section and the drying section; as well as a heat transfer section that transfers heat to at least one of the mixing section and the drying section, The preparation system further comprises a crushing section for crushing the raw materials transported from the raw material supply section to the mixing section. The crushing part includes a blade unit for crushing raw material particles, and The blade unit includes a plate member disposed below the pulverizing portion and having a flat plate shape, and a protruding blade member protruding upward from an upper surface of the plate member.

2. The preparation system according to claim 1, wherein: The pulverizing section includes a blade for pulverizing raw material particles. The blade stands upright upward.

3. The preparation system according to claim 1, wherein: The inorganic acid is nitric acid, i.e., HNO3, The organic solvent is hexane, The surface modifier is hexamethyldisilazane, ie, HMDS.

4. The preparation system according to claim 1, wherein: preparing silica aerogel powder in the drying section, and The preparation system further includes a collecting portion for collecting the silica aerogel powder.

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