Residual-free ph adjustment process for crude silicon dioxide and application thereof

Abstract

The application discloses a residual-free pH value adjusting process for crude silicon dioxide and application, and comprises the following steps: S1, collecting high-boiling substances generated in a rectification section in the process of synthesizing organosilicon from silicon powder and chloromethane; S2, high-temperature treatment is performed on the high-boiling substances, and organic silicon materials in the high-boiling substances are converted into crude silicon dioxide, wherein hydrogen chloride components are mixed in the crude silicon dioxide; S3, an alkaline substance is added, the obtained crude silicon dioxide is subjected to pH value adjustment, the hydrogen chloride components are consumed, and the alkaline substance is consumed at the same time, so that pure crude silicon dioxide material is obtained. The process breaks through the limitation of traditional treatment ideas, adds a pH value adjusting step, and thus relatively pure crude silicon dioxide material is prepared without adding new impurities, and can be applied to the alternative use of white carbon black in some scenes with relatively low requirements.

Description

TECHNICAL FIELD

[0001] The present application relates to the adjustment of the pH value of crude silicon dioxide, and in particular to the modification and application of crude silicon dioxide used in the preparation of silicone rubber. BACKGROUND

[0002] In the preparation of organosilicon using silicon powder and methyl chloride as raw materials, about 4% of high-boiling substances are generated in the production stage, especially in the rectification stage, accounting for the total amount of crude monomers. Such high-boiling substances cannot obtain high-quality organosilicon materials with chain structure through simple hydrolysis. Therefore, in the industry, the conversion is generally carried out before disposal, thereby reducing the damage to the environment and improving the utilization rate of raw materials.

[0003] The more mainstream conversion method in the industry is mainly wet method and dry method. The wet method is to hydrolyze the high-boiling substances, filter out solid impurities, and separate oil and water by standing to obtain low-quality organosilicon oil. Due to its small molecular weight and strong volatility, it is generally used in low-cost, low-demand situations, or as hazardous waste treatment. The dry method is to spray the high-boiling substances into a directional conversion device composed of a gasification furnace, a conversion kiln, and a dust collector for high-temperature treatment, and convert them into inorganic silicon oxide materials, i.e. crude silicon dioxide, which can be used as inorganic building materials or fine chemical additives.

[0004] And because the equipment used in the dry method is relatively simple, and the processing cost is low, the conversion rate is higher, so generally speaking, production enterprises prefer the dry method for high-boiling substance treatment.

[0005] Furthermore, researchers found that the crude silicon dioxide obtained has similar chemical composition and physical properties to mainstream fumed silica white carbon black. And if the pH value can be further adjusted, it can be more widely used in the preparation of silicone rubber, thereby further broadening the economic value of this byproduct. SUMMARY

[0006] The present application aims to provide a residual-free pH adjustment process for crude silicon dioxide and its application, which relates to a preparation process for adjusting the pH value of crude silicon dioxide, and gives an indication of the application of such crude silicon dioxide in the preparation of silicone rubber.

[0007] To achieve the above-mentioned purpose, the specific technical solutions of the present application are as follows:

[0008] A residual-free pH adjustment process for crude silicon dioxide and its application, comprising the following steps:

[0009] S1, in the process of collecting silicon powder and chloromethane to synthesize organosilicon, high-boiling substances are generated in the rectification section, which are products in the preparation process and account for 1% of the total amount of crude monomers. They are relatively difficult to handle and contain a large amount of substances that need to be treated.

[0010] S2, high-temperature treatment is performed on the high-boiling substances to convert the organosilicon material therein into crude silicon dioxide, wherein the crude silicon dioxide contains hydrogen chloride components;

[0011] S3, adding an alkaline substance to adjust the pH of the obtained crude silicon dioxide, consume the hydrogen chloride components therein, and at the same time consume the alkaline substance, to obtain pure crude silicon dioxide material.

[0012] In order to obtain as much silicon component in the high-boiling substances as possible, high-temperature treatment includes passing the high-boiling substances into a gasification furnace, wherein the temperature of the gasification furnace is 600±50℃, and then passing into a conversion kiln after gasification is completed, wherein the temperature of the conversion kiln is 1150±50℃.

[0013] The temperature of 600±50℃ can gasify the organosilicon substance and separate it from other solid impurities, and the temperature of 1150±50℃ can convert the organosilicon substance into inorganic crude silicon dioxide by adding combustion air.

[0014] In order to further improve the quality of the crude silicon dioxide, the process of adjusting the alkaline substance includes the following steps:

[0015] After the conversion of the conversion furnace is completed, the crude silicon dioxide material is cooled and passed into a treatment tower in a fluidized state under the protection of nitrogen, wherein the treatment tower includes an inlet at the bottom, a low-temperature treatment section, a high-temperature treatment section, and an outlet at the top from bottom to top. The low-temperature treatment section is provided with sufficient ammonia gas, which reacts with hydrogen chloride to generate ammonium chloride and residual ammonia gas. The high-temperature treatment section is provided with combustion air to decompose ammonium chloride and unreacted ammonia gas. The outlet at the top discharges pure crude silicon dioxide raw material.

[0016] The selection of ammonia gas for adjustment and the selection of nitrogen gas as the protective gas are mainly based on the following considerations:

[0017] 1. In the traditional treatment process, some researchers have attempted to adjust the pH of this part of the silicon dioxide. However, since the purity of the silicon dioxide substance needs to be maintained, the general technical personnel believe that if an alkaline substance is added, it will bring new residues, which may include reaction products or both reaction products and alkaline substances, and thus cannot prepare pure crude silicon dioxide products.

[0018] At the same time, due to the fact that hydrogen chloride is extremely soluble in water, more research is placed on water washing or other treatment methods, which do not require the addition of new substances and do not produce new substances, and can meet the purity requirements, but will damage the physical size of the crude silicon dioxide, so the effect is not very good.

[0019] 2. Ammonia can decompose hydrogen at high temperature, which can accelerate the combustion reaction to maintain high temperature, and the ammonium chloride product generated by ammonia and hydrogen chloride can also decompose into gaseous products at high temperature, so that no residue can be achieved, and the decomposition itself can maintain the necessary process conditions for no residue.

[0020] In order to further collect the obtained crude silicon dioxide material, the discharged crude silicon dioxide raw material is captured to obtain a crude silicon dioxide raw material that can be used for production.

[0021] The crude silicon dioxide is applied to the preparation raw material of silicone rubber, thereby replacing the use of white carbon black and other materials.

[0022] Beneficial effects:

[0023] The process breaks through the limitations of traditional processing ideas by adding an acid-base adjustment step, thereby obtaining relatively pure crude silicon dioxide material with appropriate acid-base value without adding new impurities, which can be used to replace white carbon black in some low-performance scenarios in the silicone rubber industry.

[0024] This treatment process can better handle high-boiling substances and convert silicon elements in high-boiling substances for use, achieving economic value recycling of waste. The energy consumption and environmental impact during production are within a controllable range, making it suitable for industrial promotion. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 is a performance comparison table of the crude silicon dioxide, a certain fumed white carbon black (HB-615), and crude silicon dioxide without ammonia gas treatment;

[0026] Figure 2 is a ratio table when the crude silicon dioxide is applied in civilian single-component room temperature vulcanized silicone rubber;

[0027] Figure 3 is a performance comparison table of silicone rubber prepared based on Figure 2 . DETAILED DESCRIPTION

[0028] In order to better understand the purpose, structure and function of the present application, a further detailed description of a residue-free acid-base adjustment process for crude silicon dioxide and application method is given.

[0029] Example:

[0030] The liquid high-boiling-point substance is fed into the gasifier, heated and vaporized, and then enters the conversion kiln. Under the action of combustion air, it is directionally converted from organic silicon to inorganic silicon, namely crude silicon dioxide.

[0031] Crude silica is cooled and then fluidized in a nitrogen atmosphere before entering an ammonia treatment tower. After high-temperature collection, crude silica treated with ammonia can be obtained.

[0032] The process parameters are as follows:

[0033] Specifically: the gasifier operates at a temperature of 600±50℃, aiming to gasify organosilicon materials and separate them from other solid impurities; the conversion kiln operates at a temperature of 1150±50℃, aiming to convert organosilicon materials into inorganic crude silica. The ammonia treatment tower is divided into two parts according to different operating temperatures:

[0034] The low-temperature section operates at 415℃, aiming to consume the hydrogen chloride carried in the crude silica and reduce its content; the ammonia gas ratio is 2.07 times the equivalent of hydrogen chloride in the acid value of the crude silica without ammonia treatment.

[0035] The high-temperature section operates at 870℃ and is designed to decompose the ammonium chloride and unreacted ammonia produced by the reaction into a gaseous phase to achieve gas-solid separation. This high-temperature section requires combustion air, which can react with the hydrogen produced after the ammonia decomposition to maintain the temperature.

[0036] After preparation, according to Figure 2 Silicone rubber was prepared, and a comparative lateral experiment was conducted. According to... Figure 3 The data shows that, regardless of whether the crude silica has been treated with ammonia, its performance is still somewhat inferior to that of mainstream fumed silica. However, in the industry of single-component room temperature vulcanizing silicone rubber with relatively low performance requirements, the treated silica material can be used as a substitute for mainstream fumed silica. Different performance requirements can be achieved by adjusting the substitution ratio. The performance of crude silica treated with pH is improved, especially with a significant change in the pH value of the suspension. Therefore, it can also achieve good application results with a large substitution amount.

[0037] It is to be understood that the present application is described by way of example only, and that modifications or alterations can be made to the features and embodiments described without departing from the spirit and scope of the application. In addition, modifications can be made to the features and embodiments described to accommodate specific situations and materials without departing from the spirit and scope of the application. Accordingly, the application is not limited to the specific embodiments disclosed herein, but rather, the scope of the application includes all embodiments falling within the scope of the claims.

Claims

1. A process for pH adjustment of crude silicon dioxide without residual acid, characterized in that, The method comprises the following steps: S1, collecting high-boiling residues generated in a rectification section during synthesis of organosilicon from silicon powder and methyl chloride; S2, high-temperature treatment of the high-boiling residues to convert organosilicon materials therein into crude silicon dioxide, wherein the crude silicon dioxide contains hydrogen chloride; S3, adding an alkaline substance to adjust the pH of the obtained crude silicon dioxide, consume the hydrogen chloride therein, and consume the alkaline substance at the same time, to obtain pure crude silicon dioxide material; The high-temperature treatment comprises passing the high-boiling residues into a gasification furnace, wherein the temperature of the gasification furnace is 600±50℃, and then passing the high-boiling residues into a conversion kiln for treatment after the gasification is completed, wherein the temperature of the conversion kiln is 1150±50℃; The process of adjusting the alkaline substance comprises the following steps: After the conversion is completed, the crude silicon dioxide material is cooled and passed into a treatment tower in a fluidized state under the protection of nitrogen, wherein the treatment tower comprises, from bottom to top, an inlet at the bottom, a low-temperature treatment section, a high-temperature treatment section, and an outlet at the top, wherein sufficient ammonia gas is passed into the low-temperature treatment section, the ammonia gas reacts with the hydrogen chloride to generate ammonium chloride and residual ammonia gas, combustion-supporting air is passed into the high-temperature treatment section to decompose the ammonium chloride and the unreacted ammonia gas, and pure crude silicon dioxide raw material is discharged from the outlet at the top.

2. A process for pH adjustment of crude silicon dioxide without residual acid, according to claim 1, characterized in that, The discharged crude silicon dioxide raw material is captured to obtain crude silicon dioxide raw material that can be used for production.

3. Use of the crude silicon dioxide obtained according to any one of claims 1, characterized in that, The crude silicon dioxide is applied to the preparation of single-component room-temperature vulcanized silicone rubber.

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