Method for preparing white carbon black by using polycarbosilane synthesis by-product

Abstract

The invention discloses a method for preparing white carbon black by using a polycarbosilane synthesis byproduct, and relates to the field of materials. Liquid polycarbosilane (LPCS) byproducts generated in polycarbosilane (PCS) synthesis are atomized and fully combusted, Si elements in the LPCS are combusted and completely oxidized into white carbon black, the white carbon black is collected through collection, cyclone separation and filtration, and tail gas is purified and emptied. According to the method, by-products in PCS synthesis are used, so that the utilization rate of raw materials in PCS synthesis is increased; compared with the existing method for preparing the white carbon black by adopting a chlorosilane gas phase method, the method has the advantages that the used raw material LPCS does not contain halogen, the tail gas treatment is simple, and the method is environment-friendly.

Description

Technical Field

[0001] This invention relates to the field of materials, and in particular to a method for preparing silica using polycarbosilane synthesis byproducts. Background Technology

[0002] In the field of polymers, especially in rubber and coatings, carbon black is used as a filler to improve the wear resistance, mechanical strength and other properties of polymer materials. However, because carbon black is black, it cannot be used in products where blackness needs to be avoided.

[0003] Screening revealed that porous, ultrafine silica powder can replace carbon black as a filler. Because of its white color, it is commonly known as silica (white carbon black). The advent of silica made it possible to prepare colored rubber, and silica has thus gained widespread application (Wang Baojun, Zhang Peiping, Li Shufa, Ma Liyan, Tian Liyu. Application and preparation methods of silica [J]. World Geology, 2006(01): 100-104). In addition, silica can also be widely used in papermaking, daily chemical industries, and other fields requiring the manufacture of white or translucent products.

[0004] Currently, there are several main methods for preparing precipitated silica. First, precipitated silica is prepared using bentonite. This involves treating naturally occurring bentonite with alkali and then washing it clean [Wang Baojun, Zhang Peiping, Li Shufa, Ma Liyan, Tian Liyu. Application and Preparation Methods of Precipitated Silica [J]. World Geology, 2006(01):100-104.]. However, due to limitations in raw material purity and preparation process, the precipitated silica obtained by this method has a relatively large particle size and low purity. Second, precipitated silica is prepared using a gas-phase method. This method involves burning SiCl4, HSiCl3, or byproducts generated during organosilicon synthesis with H2. The water vapor produced by the combustion of H2 hydrolyzes the above raw materials at high temperature to produce precipitated silica. The prepared silica has small particle size and high purity, and therefore has been widely used. The by-product HCl gas generated during the preparation can be recovered and recycled [Yang Bo, He Hui, Zhou Yangbo, Jia Demin. Research progress of gas-phase silica [J]. Chemical Industry and Engineering Progress, 2005(04):372-377.]; Third, silica is prepared by precipitation method. In this method, CO2 or acidic compounds such as SiCl4 or compounds that produce acidic substances are added to water glass solution. Precipitation is generated by the hydrolysis of silicates in water glass. Finally, silica is obtained by neutralization and washing [Tao Bing, Hou Qinglin, Wang Jiqing. A new process for producing food-grade silica from silicon tetrachloride [J]. Guangdong Chemical Industry, 2015, 42(19):81-83+88.]. In this method, the hydrolysis precipitation of silicates produces large particles, requiring the addition of a precipitating dispersant to the water glass solution to control the particle size of the precipitate [Chen Shuying, A Highly Dispersible Nano-Silica and Its Preparation Method [P]. CN110668450A, 2020]; Fourth, using rice husks to prepare silica. Since rice husks contain a large amount of silicon, and silicon is dispersed in the rice husks as nano-silica, the rice husks are crushed, acid-washed, alkali-washed, and then calcined. The remaining product is then purified to prepare silica [Wang Zichen, Guo Yupeng, Zhao Jingzhe, Tao Nannan. A Method for Preparing High-Purity Nano-Silica from Rice Husks [P]. CN1449996, 2003]. The utilization of rice husks, a byproduct of rice production, is helpful in reducing environmental pressure.

[0005] As a precursor to silicon carbide ceramics, polycarbosilane (PCS) has been successfully applied. In the synthesis of PCS, dichlorodimethylsilane is first prepared into polydimethylsilane (PDMS) via the Wurtz reaction. PDMS is then converted into PCS through pyrolysis, synthesis, and de-mineralization. During the synthesis process from PDMS to PCS, approximately 15 wt% of liquid polycarbosilane (LPCS) is generated as a byproduct. This byproduct contains 50 wt.% Si [Xie Kai, Zhang Changrui, Pan Yi, Zhou Anchen, Chen Yimin, Xu Jing. Preparation of Si-CN composite ultrafine powder from low molecular weight polycarbosilane [J]. Journal of the Chinese Ceramic Society, 1998, 26(5): 668-672]. The current method of treatment is to dispose of it as hazardous chemical waste. If the byproduct LPCS generated during PCS synthesis can be converted into silica, achieving waste utilization, it will generate considerable economic value. Summary of the Invention

[0006] The purpose of this invention is to overcome the difficulties in the disposal of existing LPCS by-products and the shortcomings of traditional silica preparation processes, and to provide a method for preparing silica using polycarbosilane synthesis by-products. Through an integrated process of atomization combustion and multi-stage separation, silicon in LPCS is efficiently converted into high-quality silica.

[0007] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0008] A method for preparing silica using polycarbosilane synthesis byproducts includes the following steps:

[0009] 1) Atomized combustion: Liquid polycarbosilane (LPCS), a byproduct of polycarbosilane (PCS) synthesis, is pressurized and atomized through an atomizing nozzle and burned in a burner. The Si element in LPCS is oxidized to generate white carbon black.

[0010] 2) Preliminary sedimentation: Hot air carrying silica enters a sedimentation and accumulation cylinder equipped with a cooling device and a stirring scraper. After the silica particles agglomerate and settle, they are collected by the stirring scraper. The hot air is cooled by the cooling device and then discharged.

[0011] 3) Deep separation: The air discharged from the sedimentation and accumulation cylinder passes through a cyclone separator and an exhaust gas filter in sequence to separate the residual silica. The exhaust gas is then purified and discharged into the air.

[0012] In step 1), the burner has an inner and outer channel structure. Air is preheated to 800-1000°C by combustion heat in the outer channel, and then evenly distributed by the air distribution plate before entering the inner channel to participate in combustion. In the burner, LPCS is pressurized and atomized through a nozzle. It is then ignited by a resistance wire installed next to the nozzle and heated by electricity, and continues to burn. After the LPCS is fully combusted, the Si element in the LPCS is oxidized into silica, while the C and H elements become CO2 and H2O. Preferably, the weight average molecular weight of the raw material LPCS can be 200-800, and the Si content ≥50wt.%.

[0013] In step 1), the pressurization pressure of LPCS can be 0.2 to 5 MPa, the atomizing nozzle is a pressure atomizing nozzle, and the atomized particle size can be ≤50 μm.

[0014] In step 1), the number of burners can be 1 to 5, and the burners can be uniformly installed circumferentially on the top or side wall of the precipitation accumulation cylinder; in the burners, the air fed into the burners can be preheated by the burning LPCS, and the preheated air can increase the combustion temperature of LPCS, so that the combustion temperature is ≥1200℃, to ensure that the combustion of LPCS is complete and to avoid residual free carbon and other impurities in the prepared silica; preferably, the combustion temperature is controlled at 1200 to 1500℃.

[0015] In step 2), the rotation speed of the stirring scraper can be 1 to 5 r / min. Preferably, the cooling device can be a cooling water jacket, which can cool the air to 150 to 200°C.

[0016] In step 2), the precipitation and accumulation cylinder is equipped with a slowly rotating stirring scraper, which is used to scrape off the silica deposited on the inner wall of the precipitation and accumulation cylinder and collect it in the silica collection tank at the bottom of the precipitation and accumulation cylinder; the precipitation and accumulation cylinder is equipped with a cooling device, which is used to remove the heat generated by combustion and cool down the hot air inside the precipitation and accumulation cylinder.

[0017] In step 3), the exhaust gas filter may use PTFE membrane filter media, sintered stainless steel filter screen, filter accuracy ≤1μm, or other filter media that can withstand 150~200℃.

[0018] Compared with the prior art, the outstanding advantages and technical effects of the present invention are as follows:

[0019] 1. This invention prepares high-quality silica by burning the liquid byproduct LPCS generated during PCS synthesis, thereby increasing the utilization rate of PDMS raw material in PCS synthesis and significantly reducing the production cost of PCS.

[0020] 2. Compared with the existing gas-phase method for preparing silica using raw materials such as chlorosilanes, the raw material LPCS of this invention does not contain halogens, and the combustion exhaust gas contains only CO2, H2O and trace amounts of dust. After multi-stage separation, it can meet emission standards without additional deacidification process. Compared with the chlorosilane gas-phase method, it has greater environmental advantages and is more environmentally friendly.

[0021] 3. The silica obtained by this invention has a purity of ≥99.5%, an average particle size of 50–200 nm, and a specific surface area of ​​80–150 m². 2 / g, which can meet the needs of high-end applications such as silicone rubber reinforcement; adopting integrated equipment, the process is short and easy to operate, and continuous production can be realized. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the equipment flow for this method. Wherein, 1 - burner; 2 - sedimentation and accumulation cylinder; 3 - silica collection tank; 4 - cyclone separator; 5 - silica collection tank; 6 - exhaust gas filter.

[0023] Figure 2 This is a schematic diagram of the burner structure. 11 - Air inlet; 12 - Outer channel; 13 - Inner channel; 14 - Ignition resistance wire; 15 - LPCS atomizing nozzle; 16 - Air distribution plate. Detailed Implementation

[0024] The following embodiments will be described in detail with reference to the accompanying drawings, but they are not intended to limit the scope of protection of the present invention. Equipment, reagents, operating procedures, etc., not specifically described in this embodiment can all be achieved using conventional techniques existing in the art.

[0025] The method embodiment of the present invention involves atomizing and burning the byproduct LPCS generated during PCS synthesis. After complete combustion, the Si element in LPCS is burned to produce silica particles. After collection, cyclone separation, and filtration, high-quality silica is obtained, and the exhaust gas is also purified before being discharged into the air.

[0026] The specific process is as follows:

[0027] (1) In the burner, after the LPCS is pressurized, it is sprayed out and atomized through the atomizing nozzle of the burner. The LPCS is ignited and burned. The Si element is oxidized into white carbon black, and the C and H elements are converted into CO2 and H2O respectively.

[0028] The burners are installed on the sedimentation and accumulation cylinder, and there are 1 to 5 of them;

[0029] In the burner, the LPCS is atomized by the nozzle and ignited by the electrically heated ignition resistance wire installed next to the nozzle, and then continues to burn.

[0030] In the burner, the air supplied to the burner can be preheated by the heat of LPCS combustion. The preheated air can increase the combustion temperature of LPCS and adjust the injection speed of LPCS. The final combustion temperature is higher than 1200℃ to ensure complete combustion of LPCS and avoid residual free carbon and other impurities in the prepared silica.

[0031] (2) After the LPCS is burned, the hot air carrying the silica enters the sedimentation and accumulation cylinder. The silica particles agglomerate and are deposited on the inner wall of the sedimentation and accumulation cylinder. After the hot air is cooled, it is discharged from the sedimentation and accumulation cylinder and enters the cyclone separator.

[0032] The precipitation and accumulation cylinder is equipped with a slowly rotating stirring scraper, which can scrape off the silica deposited on the inner wall of the precipitation and accumulation cylinder and collect it in the silica collection tank at the bottom of the precipitation and accumulation cylinder.

[0033] The precipitation and accumulation cylinder is equipped with a cooling device, which carries away the heat generated by combustion and cools down the hot air inside the precipitation and accumulation cylinder.

[0034] (3) The hot air coming out of the sedimentation and accumulation cylinder passes through a cyclone separator and an exhaust filter to further separate the residual silica particles in the air.

[0035] Example 1

[0036] like Figure 1 and 2 As shown, three burners 1 are installed on the sedimentation and accumulation cylinder 2. The raw material LPCS has a weight average molecular weight of 500 and a Si content of 52 wt.%. In the burner 1, the raw material LPCS is burned to form silica. The hot air carrying silica enters the sedimentation and accumulation cylinder 2, which is equipped with a cooling water jacket and a slowly rotating stirring scraper. In the sedimentation and accumulation cylinder 2, silica particles agglomerate into larger particles and deposit on the inner wall of the sedimentation and accumulation cylinder 2. After being scraped off by the stirring scraper, they are collected in the silica collection tank 3 at the bottom of the sedimentation and accumulation cylinder 2. The hot air is also cooled in the sedimentation and accumulation cylinder 2. The hot air carrying a small amount of silica exits the sedimentation and accumulation cylinder 2 and enters the cyclone separator 4. Under the separation of the cyclone separator 4, most of the silica remaining in the air is deposited in the silica collection tank 5. Finally, the hot air is filtered by the exhaust gas filter 6 to remove the remaining silica before being discharged into the atmosphere.

[0037] In burner 1, LPCS is pressurized to 0.3MPa and then sprayed from LPCS atomizing nozzle 15 into inner channel 13 for atomization. The atomized LPCS is ignited by ignition resistance wire 14 and continues to burn in inner channel 13. Air entering from air inlet 11 passes through outer channel 12 of burner 1. The air in outer channel 12 is heated by the LPCS burning in inner channel 13. The preheated air is distributed by air distribution plate 16 and enters inner channel 13 at a uniform speed. The preheated air can increase the combustion temperature of LPCS to ensure complete combustion of LPCS and avoid residual free carbon in silica.

[0038] In this embodiment, 1 kg of LPCS was burned to obtain 1.05 kg of silica. Analysis showed that the obtained silica had an average particle size of 153 nm, a purity of 99.8%, and a specific surface area of ​​130 m². 2 / g.

[0039] Example 2

[0040] Similar to Example 1, the difference lies in that a burner 1 is installed circumferentially on the side wall of the precipitation and accumulation cylinder 2. The raw material LPCS (weight-average molecular weight 200, Si content 50 wt.%) is pressurized to 0.2 MPa and then atomized through a pressure atomizing nozzle (particle size 50 μm). Air is preheated to 800°C through the outer channel and enters the inner channel to participate in combustion, with the combustion temperature controlled at 1200°C. The stirring scraper of the precipitation and accumulation cylinder 2 rotates at 1 r / min, and the hot air is cooled to 150°C by a cooling water jacket before being discharged. The air is then further processed by a cyclone separator and a PTFE membrane filter.

[0041] In this embodiment, 1 kg of LPCS was burned to obtain 1.02 kg of silica. The product had an average particle size of 185 nm, a purity of 99.5%, and a specific surface area of ​​85 m² / g.

[0042] Example 3

[0043] Similar to Example 1, the difference lies in that five burners 1 are evenly installed circumferentially on the top of the sedimentation and accumulation cylinder 2. The raw material LPCS (weight-average molecular weight 800, Si content 55 wt.%) is pressurized to 0.5 MPa and then atomized through a pressure atomizing nozzle (atomizing particle size 20 μm). Air is preheated to 1000°C through the outer channel and enters the inner channel to participate in combustion at a combustion temperature of 1500°C. The stirring scraper of the sedimentation and accumulation cylinder 2 rotates at 5 r / min, and the hot air is cooled to 200°C by a cooling water jacket before being discharged. The air is then further processed by a cyclone separator and a PTFE membrane filter.

[0044] In this embodiment, 1 kg of LPCS was burned to obtain 1.06 kg of silica. The product had an average particle size of 110 nm, a purity of 99.6%, and a specific surface area of ​​150 m² / g.

[0045] Comparative Example 1

[0046] Silica was prepared using the traditional SiCl4 gas-phase method. The raw materials SiCl4 and H2 were mixed at a volume ratio of 1:2 and burned at 1800℃. The exhaust gas was then treated in a water absorption tower to recover HCl, and finally neutralized in an alkali washing tower before being discharged.

[0047] The results showed that 1 kg of SiCl4 yielded only 0.3 kg of silica with a purity of 99.7% and an average particle size of 120 nm. It required an HCl absorption tower, hydrochloric acid purification equipment, and an alkali washing tower, and the equipment investment cost was 40% higher than that of Example 1. Furthermore, the inner wall of the reactor needed to be replaced every 6 months due to HCl corrosion.

[0048] This invention utilizes the atomized liquid polycarbosilane (LPCS) byproduct generated during polycarbosilane (PCS) synthesis for complete combustion, oxidizing the Si element in the LPCS to form precipitated silica. The silica is then collected, separated by cyclone separation, and filtered, while the exhaust gas is purified and discharged. This method uses a byproduct from PCS synthesis, improving the raw material utilization rate. Compared to existing methods using chlorosilane gas-phase methods to prepare precipitated silica, this method uses halogen-free LPCS, simplifies exhaust gas treatment, and is environmentally friendly. It solves the hazardous waste disposal problem of LPCS and reduces the raw material cost of precipitated silica, possessing both economic and environmental value.

[0049] The above embodiments are merely preferred embodiments of the present invention and should not be considered as limiting the scope of the present invention. All equivalent variations and improvements made within the scope of the present invention should still fall within the patent coverage of the present invention.

Claims

1. A method for preparing white carbon black using a polycarbosilane synthesis by-product, characterized by It comprises the following steps: 1) atomized combustion: pressurized liquid polycarbosilane (LPCS) byproduct of polycarbosilane (PCS) synthesis is atomized through an atomizing nozzle and combusted in a burner, with a combustion temperature of ≥1200℃, so that Si elements in the LPCS are completely combusted and oxidized to generate white carbon black; 2) preliminary precipitation: hot air carrying the white carbon black enters a precipitation accumulation cylinder with a cooling device and a stirring scraper, and the white carbon black particles are deposited and collected by the stirring scraper after agglomeration, and the hot air is cooled by the cooling device and then discharged; 3) deep separation: the air discharged from the precipitation accumulation cylinder is sequentially separated from residual white carbon black by a cyclone separator and a tail gas filter, and the tail gas is then discharged after purification.

2. The method for preparing silica using polycarbosilane synthesis byproducts as described in claim 1, characterized in that... In step 1), the burner has an inner and outer channel structure, air is preheated to 800-1000℃ by combustion heat through the outer channel, then uniformly distributed by an air distribution plate and enters the inner channel to participate in combustion; the atomized LPCS is ignited and combusted by the bypass heating of the nozzle resistance wire, and C and H elements are converted into CO2 and H2O, respectively, with a combustion temperature of 1200-1500℃ to ensure sufficient combustion of LPCS and avoid residual free carbon impurities in the prepared white carbon black.

3. The method for preparing silica using polycarbosilane synthesis byproducts as described in claim 1, characterized in that... In step 1), the number of burners is 1-5, and the burners are arranged at the top or sidewall of the precipitation accumulation cylinder.

4. The method for preparing silica using polycarbosilane synthesis byproducts as described in claim 1, characterized in that... In step 1), the pressurized pressure of LPCS is 0.2-5MPa, the atomizing nozzle is a pressure atomizing nozzle, and the atomized particle size is ≤50μm.

5. The method for preparing silica using polycarbosilane synthesis byproducts as described in claim 1, characterized in that... In step 2), the precipitation accumulation cylinder is provided with a slowly rotating stirring scraper, which is used to scrape the white carbon black deposited on the inner wall of the precipitation accumulation cylinder and collect it in the white carbon black collection tank at the bottom of the precipitation accumulation cylinder; the stirring scraper has a rotating speed of 1-5r / min; the precipitation accumulation cylinder is provided with a cooling device for removing the heat generated by combustion and reducing the temperature of the hot air in the precipitation accumulation cylinder to 150-200℃.

6. The method of claim 5, wherein the white carbon black is prepared using a polycarbosilane synthesis byproduct. The cooling device uses a cooling water jacket.

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