A method for continuously preparing in-situ hydrophobic silica aerogel powder by dual-fluid atomization

Abstract

The present invention relates to the field of aerogel preparation methods, and specifically to a method for continuously preparing in-situ hydrophobic aerogel powder by dual-fluid atomization. The present invention uses dual-fluid atomization technology to spray silica sol containing hydrophobic groups and catalysts through a dual-fluid nozzle. After the two fluids are atomized, they collide and mix with each other to form small droplets; the small droplets are quickly heated in a spray dryer to form small gel particles; the small particles are continuously dried in hot air to gradually form dry, hydrophobic aerogel particles. By gravity separation or centrifugal separation, the particles are collected according to different particle sizes to obtain aerogel powder with uniform particle size.

Description

Technical Field

[0001] The invention relates to the field of aerogel preparation methods, and in particular to a method for continuously preparing in-situ hydrophobic aerogel powder by dual-fluid atomization. Background Art

[0002] Aerogel was invented in the 1830s. Due to its unique three-dimensional network structure composed of nanopores and nano-skeletons, aerogel has many properties that traditional materials cannot match. Its excellent properties such as porosity, specific surface area, refractive index and thermal conductivity determine its wide application in catalysis, insulation and heat insulation materials. In the early 20th century, the United States and China successively realized the industrial production of aerogel and its composite materials, and the production scale continued to increase, and the product quality was further stabilized.

[0003] It is precisely because of the unique nanopore structure of aerogels that when the solvent comes out of the pores, the gel skeleton is subjected to huge surface tension. In order to prevent the pore structure from collapsing, supercritical drying or normal pressure drying is often used. Among them, supercritical drying eliminates the surface tension of the pore liquid and can prevent the pore structure from being deformed due to capillary forces during the drying process. However, supercritical drying usually requires high temperature and high pressure (the critical temperature of CO2 is about 31°C and the pressure is about 7.3 MPa; the critical temperature of ethanol is 243.1°C and the pressure is 6.3MPa; the actual production process parameters are much higher than the critical values). The characteristics of high dependence on process equipment and high cost make it a bottleneck for large-scale production.

[0004] Most existing atmospheric pressure drying processes require modification of the gel skeleton surface and the use of solvents with low surface tension for replacement, thereby reducing the shrinkage stress caused by capillary forces and avoiding skeleton collapse. However, the modification process is lengthy and the replacement process requires a large amount of organic solvents, which is also costly. The biggest problem with supercritical drying and atmospheric pressure drying is that both processes are intermittent production. The wet gel is hoisted into the kettle, the drying process is completed in a sealed state, and then it is hoisted out after drying. This intermittent production method limits the production capacity of aerogels, and it is difficult to control the production process and ensure the consistency of the product. Therefore, the continuous production of aerogel materials has always been one of the research directions of domestic and foreign experts.

[0005] Patent CN 205925659U discloses a continuous production equipment for aerogel powder, including five parts: drying process, solvent recovery process, crushing process, powder collection process and automatic packaging process. The wet gel enters the drying kettle through the feed port, and is evenly dried and preliminarily crushed under the heating effect of the resistance wire and the stirring effect of the stirring paddle; the dried aerogel is transported to the crushing device and crushed by the air flow mill to obtain aerogel powder. During the drying process, after the wet gel enters the drying kettle, the entire kettle material must be dried before it can be transported out. In fact, it is still a semi-continuous process, which only solves the automatic transportation between the kettles. In addition, during the drying process, a large amount of organic matter is heated by the resistance wire and stirred by the stirring paddle, which poses a great safety hazard.

[0006] Patent CN109529735B discloses a method for continuously preparing aerogel composite materials using microwave equipment, wherein aerogel precursors and fibers are compounded to form gel, which is sequentially conveyed to solvent replacement, hydrophobic modification devices, and drying devices through a conveyor belt, and finally a finished product is obtained. This method can realize continuous production of composite materials, but a large amount of flammable and explosive organic solvents are present in both solvent replacement and hydrophobic modification devices, and the gel is introduced into and out of each device by opening a baffle with the material, and the gel material and the conveyor belt are constantly moving. If the contact force between the baffle and the material is too small, the solvent or organic gas is very easy to leak, and if the contact force is too large, the gel is destroyed; in addition, in order to speed up the speed and safety of each process, nano-absorbing factors need to be added to the aerogel, flame retardants need to be added to the solvent, and metal impurities in the fiber material need to be inspected to avoid ignition in the microwave device, which undoubtedly increases the cost and difficulty of aerogel production and cannot be mass-produced.

[0007] Patent CN103408028B provides a production process for super insulating material silica gel, including the preparation of hydrogel, the generation of organic gel, double tower distillation, hydrophobic treatment, spray drying, product testing and other steps. Its main technology is to cut the hydrogel into pieces, put it into a distillation kettle, and replace the water in the hydrogel with azeotropic organic matter by distillation; the gel containing organic azeotropes is filtered to recover organic matter, and the filter cake is pulped and then added with silane coupling agent for hydrophobic treatment, and then pumped into a spray dryer for drying. The problems of this technology are: 1) the process of filtration and pulping contains a large amount of organic solvents, which need to be carried out in an oxygen-free environment, otherwise the risk factor is high, the equipment must be customized explosion-proof equipment, and the investment is high; 2) during the filtration process, the organic solvent comes out of the nanopores of the gel, and the capillary force also exists, and the skeleton structure of the gel will still be destroyed; 3) the feeding and discharging of the distillation process are also intermittent, and continuous production is not possible; 4) the gel slurry is easy to block the feed port of the dryer. Summary of the invention

[0008] The present invention hopes to provide a method for continuously preparing in-situ hydrophobic silica aerogel powder by dual-fluid atomization, and the specific scheme is as follows:

[0009] A method for continuously preparing in-situ hydrophobic silica aerogel powder by dual-fluid atomization comprises the following steps:

[0010] a) mixing a methyl-containing organic silicon source with ethyl orthosilicate or methyl orthosilicate in a mass ratio of 1:(0-2), adding water, a solvent and an acid to form a silica sol containing a hydrophobic group;

[0011] b) preparing a gel catalyst;

[0012] c) mixing the silica sol containing hydrophobic groups and the gel catalyst uniformly through a two-fluid nozzle and atomizing them into small droplets;

[0013] d) The atomized droplets form gel particles;

[0014] e) drying the solvent in the gel particles under a reduced oxygen environment.

[0015] The methyl-containing organic silicon source in step a) is one or more of methyltriethoxysilane, methyltrimethoxysilane, dimethyldimethoxysilane, dimethyldiethoxysilane, trimethylmethoxysilane, trimethylethoxysilane, and / or prepolymers thereof.

[0016] The solvent in step a) is one or more of methanol, ethanol, acetone, butanone, n-hexane and hexamethyldisiloxane.

[0017] The pH of the small droplets in step c) is 9.0-10.5, and the gelation time in step c) is 1-120s.

[0018] In step c), atomization is performed in an environment where the oxygen concentration is lower than 3%.

[0019] In the step e), the drying temperature is 30-200° C. and the pressure is normal pressure.

[0020] The drying method in step e) is hot air circulation drying, which includes a fluid heating unit, a hot air circulation unit, a powder separation unit and a fluid recovery unit.

[0021] The main components of the hot air circulating and drying in the hot air circulation unit are carbon dioxide or nitrogen.

[0022] The present invention uses a dual-fluid atomization technology to spray the silica sol containing hydrophobic groups and the catalyst through a dual-fluid nozzle. After the two fluids are atomized, they collide and mix with each other to form small droplets. The small droplets are quickly heated in the spray dryer to form small gel particles. The small particles are continuously dried in the hot air to gradually form dry, hydrophobic aerogel particles. The particles are collected according to different particle sizes by gravity separation or centrifugal separation to obtain aerogel powder with uniform particle size.

[0023] The present invention has the following advantages:

[0024] 1. Realize true continuous production.

[0025] 2. The present invention only requires normal pressure, so the equipment only requires normal pressure equipment, and the material inlet and outlet can be easily sealed by flange connection.

[0026] 3. The production process is simple, and better aerogel particle size distribution and drying effect can be obtained.

[0027] 4. The production equipment is in an inert gas environment, with a small amount of reagents, low energy consumption and high production efficiency.

[0028] 5. By selecting the appropriate atomizer and using process parameters, the droplet size range can be controlled between 10 and 500 μm, which can meet the needs of different fields and applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 The present invention is a schematic diagram of a method for continuously preparing in-situ hydrophobic silica aerogel powder by dual-fluid atomization. DETAILED DESCRIPTION

[0030] Example 1

[0031] Methyltrimethoxysilane and methyl orthosilicate were mixed in a mass ratio of 1:0.8, water, methanol, and nitric acid were added in a mass ratio of 0.2:8:0.01 to methyltrimethoxysilane, respectively, and heated to 60°C for hydrolysis for 2 hours to form a silica sol containing hydrophobic groups;

[0032] Prepare ammonia water as a gel catalyst; after nitrogen replacement and heating in the spray dryer, the oxygen concentration is less than 3% and the temperature is 120±5°C; atomize the silica sol containing hydrophobic groups and ammonia water in a ratio of 1:0.08 through a double-fluid nozzle, mix them evenly to form small droplets with a diameter of 200~500μm, and ensure that the pH of the small droplets is 9.6±0.3;

[0033] The atomized droplets form gel particles, and the gelation time is 6~12s;

[0034] The oxygen concentration in the spray dryer is maintained below 3%. The temperature of the heated nitrogen is maintained at 120±5℃ and the pressure is normal pressure through hot air circulation heating. The heated nitrogen enters the spray dryer and forms a mixed gas with nitrogen and methanol vapor after passing through the spray dryer. The mixed gas is condensed to remove the solvent, and then recycled for heating and drying.

[0035] The catalyzed sol droplets form small gel particles within 12 seconds, and the vaporized methanol and nitrogen form a mixed gas. Due to the effect of gravity, the gel particles continue to fall while being dried, gradually forming dry hydrophobic aerogel powder, which falls to the bottom of the dryer. Due to the influence of airflow, small particles of powder come out from powder outlet 1; relatively larger particles of powder come out from powder outlet 2, and aerogel powders of different particle sizes are obtained, with a specific surface area of ​​500~550m 2 / g, density 55kg / m 3 , the average diameter of powder 1 is 10~30μm, and the average diameter of powder 2 is 50~60μm.

[0036] Embodiment 2-4

[0037] The following examples are used to study the effects of parameters on product performance, and the other parameters are the same as those in Example 1, with specific differences as shown in the following table:

[0038] Sol raw materials and ratio Gel Catalyst pH value of small droplet Gel time Experimental Results Example 2 Trimethylethoxysilane: ethyl orthosilicate: water, ethanol, nitric acid = 1:1.7:0.15:6:0.01 Sodium hydroxide aqueous solution 10.0 10s <![CDATA[Specific surface area is 500 - 550 m 2 / g, density is 50 kg / m 3 , the average diameter of powder 1 is 20 - 35 μm, and the average diameter of powder 2 is 50 - 80 μm.]]> Example 3 Dimethyldiethoxysilane:ethyl orthosilicate:water,hexamethyldisiloxane,nitric acid=1:1.5:0.2:8.5:0.02 Ammonia solution 10.5 5s <![CDATA[Specific surface area is 450 - 600 m 2 / g, density is 35 kg / m 3 , the average diameter of powder 1 is 10 - 20 μm, and the average diameter of powder 2 is 40 - 60 μm.]]> Example 4 Dimethyldimethoxysilane: methyl orthosilicate: water, methanol, nitric acid = 1:1:0.15:6:0.015 Sodium hydroxide aqueous solution 9.5 60s <![CDATA[Specific surface area is 550 - 650 m 2 / g, density is 65 kg / m 3 , the average diameter of powder 1 is 30 - 40 μm, and the average diameter of powder 2 is 60 - 100 μm.]]>

[0039] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for continuously preparing in-situ hydrophobic silica aerogel powder by dual-fluid atomization, characterized in that: The steps include: a) mixing a methyl-containing organic silicon source with ethyl orthosilicate or methyl orthosilicate in a mass ratio of 1:(0-2), adding water, a solvent and an acid to form a silica sol containing a hydrophobic group; b) preparing a gel catalyst; c) mixing the silica sol containing hydrophobic groups and the gel catalyst uniformly through a two-fluid nozzle and atomizing them into small droplets; d) The atomized droplets form gel particles; e) drying the solvent in the gel particles under a reduced oxygen environment; the methyl-containing organic silicon source in step a) is one or more of methyltriethoxysilane, methyltrimethoxysilane, dimethyldimethoxysilane, dimethyldiethoxysilane, trimethylmethoxysilane, trimethylethoxysilane, and / or prepolymers thereof; the solvent in step a) is one or more of methanol, ethanol, acetone, butanone, n-hexane, and hexamethyldisiloxane; the pH of the small droplets in step c) is 9.0-10.5, and the gelation time in step c) is 1-120s; In step c), atomization is performed in an environment where the oxygen concentration is less than 3%; In step e), the drying temperature is 30-200°C and the pressure is normal pressure; The drying method in step e) is hot air circulation drying, which includes a fluid heating unit, a hot air circulation unit, a powder separation unit and a fluid recovery unit; The main components of the hot air circulating and drying in the hot air circulation unit are carbon dioxide or nitrogen; Drying is performed using a spray dryer, and inert gas enters from the bottom of the spray dryer.

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