Method for preparing white carbon black with high specific surface area from fluorosilicone raw material

Abstract

The invention provides a method for preparing white carbon black with a high specific surface area from fluorosilicone raw materials, and belongs to the technical field of chemical product preparation. The preparation method of the white carbon black with the high specific surface area comprises the following steps: adding a dispersing agent into a fluorosilicone raw material, reacting with ammonia water, always keeping the pH value of the system at 9.3-9.4 in the reaction process, carrying out solid-liquid separation after the reaction, drying the solid to obtain the white carbon black with the high specific surface area, and concentrating and drying the filtrate to obtain an ammonium fluoride product. The specific surface area of the prepared white carbon black is greater than 300 m < 2 > / g, and the oil absorption value is gt; the concentration of F <-> is less than 50 ppm, and the yield of the obtained ammonium fluoride is greater than 95%. The preparation method is low in raw material cost, simple and environment-friendly in process and suitable for industrial production.

Description

Technical Field

[0001] The present invention belongs to the technical field of chemical product preparation, and particularly relates to a method for preparing white carbon black with a high specific surface area from fluorosilicon raw materials. Background Art

[0002] White carbon black with a high specific surface area has characteristics such as small particle size, large specific surface area, high surface energy, strong adsorption capacity, high purity, and high stability, making it exhibit unique properties in aspects such as light absorption, magnetism, thermal resistance, catalytic property, and melting point. White carbon black can significantly improve the physical properties of rubber materials and at the same time reduce the rolling resistance of tires without affecting the wet skid resistance of the tires. In particular, ultrafine white carbon black, as a reinforcing filler, is widely used in the production of green tires. It can replace carbon black for the tire sidewall, effectively improving the tear strength of the sidewall and the ability to resist crack propagation. Compared with the rubber compound filled with ordinary carbon black, the rolling resistance of the rubber compound filled with white carbon black can be reduced by about 30%. In the paint field, white carbon black with a high specific surface area also performs excellently. It can form a paint film with a good matting effect. In addition, white carbon black can also be surface-treated with organic coatings (mainly polymer waxes) to improve the dispersibility and enhance the scratch resistance of the paint film. It can also be used in multiple fields such as electronic packaging materials and daily necessities, demonstrating its unique properties and broad application prospects.

[0003] The production methods of white carbon black are mainly two categories: the gas-phase method and the precipitation method. The precipitation method has relatively simple process equipment and significant cost advantages, so it has become the main preparation method. The by-product fluorosilicic acid (H2SiF6 + 6NH3+(n + 2)H2O→6NH4F+SiO2·nH2O) generated in the production of wet-process phosphoric acid and the solid waste fluorosilicate slag (SiO2+6NH4F→(NH4)2SiF6+4NH3+2H2O(NH4)2SiF6+4NH3·H2O→6NH4F+SiO2·nH2O) generated in the process of preparing hydrogen fluoride from fluorosilicic acid are high-quality raw materials for preparing white carbon black. However, since the precipitated white carbon black is generated in the liquid phase, it usually undergoes agglomeration due to the hydroxyl groups on its own surface, making it impossible to obtain a high specific surface area.

[0004] Chinese Patent Document CN107840341A discloses a method for preparing a seed solution by adding fluosilicic acid or ammonium fluosilicate and ammonia in a three-stage series reaction kettle, and continuously producing silica by controlling the molar ratio of materials in different reaction kettles. Chinese Patent Document CN 117303375A discloses a method for obtaining gel seeds by reacting fluosilicic acid with an ammoniating agent in a plug flow reactor, and then obtaining silica by controlling the aging and pressure of pressure filtration. Chinese Patent Document CN101376500B discloses a method for preparing seeds using water glass, and further reacting fluosilicic acid and water glass in the seeds to generate silica. The processes of silica obtained by the methods introduced in the above patents are relatively complex, and the industrialization difficulty is relatively large. Based on this, there is an urgent need for a method for simply and efficiently preparing high specific surface area silica with a simple process flow. Summary of the Invention

[0005] In order to solve the above problems, the present invention provides a method for preparing high specific surface area silica from fluosilicon raw materials.

[0006] The technical solution of the present invention is: a method for preparing high specific surface area silica from fluosilicon raw materials, the method comprising the following steps: S1. Take ammonia water with a certain concentration and add it to a reaction kettle equipped with a stirring paddle, a peristaltic pump and a condenser; S2. Under the condition of stirring, respectively dropwise add fluosilicon raw materials and ammonia water to react, and carry out aging after the addition is completed; S3. Filter the reaction solution, cool and crystallize the filtrate, and dry it after filtration to obtain ammonium fluoride finished product; S4. Adjust the pH of the filter cake and make it into a slurry, filter, wash the filter cake with pure water, and dry the filter cake in a dryer to obtain silica finished product.

[0007] To ensure the precipitation of silica under alkaline conditions, preferably, in step S1, ammonia water is added to the reaction kettle as a bottom layer, so that the pH of the reaction system is always maintained at 9.3 - 9.4.

[0008] Preferably, in step S2, a dispersant is added before the addition of fluosilicon raw materials. The dispersant is a composition of urea and formaldehyde, and the addition amounts of urea and formaldehyde are respectively 0.1 - 0.3% of the mass of the added fluosilicon raw materials. To ensure the uniform dispersion of the prepared silica, further preferably, the temperature at which the dispersant is added is 25 - 35°C, preferably 30°C. The fluosilicon raw material, fluosilicic acid or ammonium fluosilicate solution, is weakly acidic, and urea and formaldehyde added under acidic conditions will polymerize to form polymer chains. During the subsequent formation of silica, the precipitated silica adheres to the polymer chains, making the generated silica have good dispersibility. Preferably, in the step S2, the fluorosilicon raw material is fluorosilicic acid or fluorosilicate slag; when the fluorosilicon raw material is fluorosilicic acid, in the preparation method of the white carbon black of the present invention, urea and formaldehyde are first added to fluorosilicic acid and stirred to form a mixed solution of urea-formaldehyde resin and fluorosilicic acid, and then the mixed solution reacts with ammonia water, and then silica white is obtained through aging and solid-liquid separation. The experimental results show that during the reaction process, the pH of the solution has a significant impact on the specific surface area of the white carbon black, and it is necessary to always maintain the pH between 9.3 and 9.4. Under alkaline conditions, fluorosilicic acid is added to the reaction system for reaction: H2SiF6 + 2NH3 → (NH4)2SiF6 (NH4)2SiF6 + 4NH3 + (n + 2) H2O → 6NH4F + SiO2·nH2O Fluorosilicic acid first reacts with ammonia water to form an intermediate product ammonium fluorosilicate, and ammonium fluorosilicate further reacts with ammonia water immediately to form white carbon black and ammonium fluoride. This requires the reaction bottom material to be maintained under the condition of excessive ammonia water, that is, to control the pH of the reaction solution between 9.3 and 9.4, so that the ammoniation reaction proceeds more completely. Under rapid stirring, fluorosilicic acid is added to the alkaline system, and the white carbon black generated by the reaction precipitates and disperses rapidly with extremely small particle size, ensuring that the added fluorosilicic acid quickly generates white carbon black without adhering to the surface of the precipitated white carbon black, preventing particle agglomeration, and thus greatly improving the specific surface area of the white carbon black.

[0009] When the fluorosilicon raw material is fluorosilicate slag, it needs to be pretreated before performing the operation of step S2. The pretreatment steps are as follows: Take a certain amount of fluorosilicate slag in a reaction vessel, add water and a cosolvent with a feeding pump and stir, and then dropwise add a previously prepared ammonium fluoride solution with a peristaltic pump. The equivalent amount of ammonium fluoride used is 1.2 to 1.5. Then introduce nitrogen, the reaction temperature is 130 to 150 °C, the reaction stirring speed is 100 to 300 rpm. Wait until the reaction solution is clarified, stop stirring, cool, and the reaction solution is ammonium fluorosilicate solution.

[0010] Preferably, the cosolvent for accelerating the dissolution of fluorosilicate slag includes fluosilicic acid or ammonium bifluoride or others, and the addition amount of the cosolvent is 5%; in this preparation process, the addition of the cosolvent is mainly to promote the surface dissolution of fluorosilicate slag and make the silicon in the fluorosilicate slag dissolve in ammonium fluoride solution faster. The method of dropping ammonium fluoride solution into the reaction solution can solve two problems. On the one hand, it can avoid a large amount of ammonium fluoride and fluorosilicate slag reacting rapidly at 140 °C to release a large amount of ammonia gas, which will make the solution become alkaline. Under alkaline conditions, ammonium fluorosilicate in the solution reacts with the released ammonia gas to form silica white, and the newly formed silica white will be mixed with the fluorosilicate slag that has not fully reacted, making it impossible to effectively separate and utilize the silicon in the fluorosilicate slag. By adopting the method of dropping ammonium fluoride solution, the degree of the reaction can be controlled, and thus the amount of ammonia gas released can be controlled. A small amount of ammonia gas generated in the reaction will quickly volatilize from the system under heating conditions, and the dissolution amount of ammonia gas in the system is adjusted by introducing nitrogen gas to maintain the weak acidity of the reaction system and prevent the formation of silicon dioxide. On the other hand, it can avoid a large amount of ammonium fluoride and fluorosilicate slag quickly generating SiF4. The reaction of SiF4 with water to form silicon dioxide easily causes pipeline blockage. The dropping method can effectively slow down the reaction progress and reduce the release amount of SiF4. Preferably, in the step S2, the reaction stirring speed is 600 - 800 rpm, and the reaction temperature is 30 - 50 °C.

[0011] Preferably, in the step S2, the feeding method is to slowly pump ammonia water and fluorosilicon raw materials simultaneously, the feeding time is 0.4 - 0.6 h, and the stirring speed is 600 - 800 rpm.

[0012] Preferably, in the step S2, after the reaction ends, the aging time of the reaction solution is 6.0 - 8.0 h, and the stirring speed is 600 - 800 rpm.

[0013] Preferably, in the step S4, the pH during the repulping of the filter cake is 6.8 - 7.3.

[0014] The beneficial effects of the present invention are as follows: The silica white product prepared by the present invention has good performance, and the by - product ammonium fluoride can be sold as a product. The raw materials used have low cost, and the process is simple, which is suitable for industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a schematic process flow diagram for the preparation of silica white in Example 1 of the present invention.

[0016] Figure 2 It is a SEM diagram of silica white prepared from reaction solutions with different pH values in Table 2 of Comparative Example 2 of the present invention (a is Comparative Example 2 - 1 and b is Example 1). DETAILED DESCRIPTION OF THE INVENTION

[0017] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in combination with specific embodiments of the present invention. The described embodiments are only a part of the embodiments of the present invention, rather than all embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts belong to the protection scope of the present invention.

[0018] In the embodiments of the present invention, Example 1 S1. Add ammonia water with a concentration of 25% which is one-twentieth of the volume of fluorosilicic acid and water which is one-tenth of the volume of fluorosilicic acid into a reaction kettle equipped with a stirring paddle, a peristaltic pump and a condenser.

[0019] S2. Slowly pump in a mixed solution of fluorosilicic acid (concentration of 18%), urea (the addition amount is 0.1% of the total mass of the reaction solution), formaldehyde (the addition amount is 0.1% of the total mass of the reaction solution) and ammonia water (concentration of 25%) with a planned amount under the conditions of a stirring speed of 700 rpm and a temperature of 30°C. Control the addition amount of ammonia water so that the pH is 9.3 - 9.4, and control the end-point pH of the reaction solution to be 9.3 - 9.4 during the reaction process. After the reaction is completed, stir and age for 7 h.

[0020] S3. Filter the reaction solution, cool and crystallize the filtrate, filter it and then dry it to obtain ammonium fluoride finished product.

[0021] S4. Adjust the pH of the filter cake to 7 with HF and re-slurry it, filter it, wash the filter cake three times with pure water, and place the filter cake in a dryer at 120°C and dry it for 3 h to obtain precipitated silica finished product.

[0022] The precipitated silica yield obtained in this example is greater than 96% (96.5%), the specific surface area is 355 m 2 / g, the oil absorption value is 291 mL / 100 g, the fluoride ion concentration is 39 ppm, and the ammonium fluoride yield is 96.3%.

[0023] Example 2 S0. Take fluorosilicate slag (40 g) in a reaction vessel, add water which is 1.5 times the mass of the fluorosilicate slag and ammonium bifluoride (a co-solvent) which is 5% of the mass of the fluorosilicate slag, introduce nitrogen to make the pH of the reaction system 6.3, and add 1.2 equivalents of 35% ammonium fluoride solution to the reaction vessel in a dropping manner using a peristaltic pump under stirring, heat to 140°C, and stir at 200 rpm for 0.6 h until the reaction system becomes clear to obtain an ammonium fluorosilicate reaction solution. Add urea (the addition amount is 0.1% of the total mass of the reaction solution) and formaldehyde (the addition amount is 0.1% of the total mass of the reaction solution) respectively, and stir for standby.

[0024] S1. Then, add ammonia water (25%) which is one-twentieth of the volume of ammonium fluorosilicate and water which is one-tenth of the volume of ammonium fluorosilicate into a reaction kettle equipped with a stirring paddle, a peristaltic pump and a condenser.

[0025] S2. Under the conditions of a stirring speed of 700 rpm and a temperature of 30 °C, slowly pump in ammonia water and the cooled ammonium fluorosilicate reaction solution simultaneously. The feeding time is controlled within 0.5 h, and the pH of the reaction solution is controlled at 9.3 - 9.4 and the pH at the end point of the reaction is 9.3 - 9.4. After the reaction is completed, stir and age for 7 h.

[0026] S3. Filter the reaction solution, cool the filtrate for crystallization, and dry it after filtration to obtain the finished product of ammonium fluoride or directly recycle it.

[0027] S4. Adjust the pH of the filter cake to 7 with HF and re-slurry it, filter it, wash the filter cake three times with pure water, and place the filter cake in a dryer at 120 °C for drying for 3 h to obtain the finished product of silica white.

[0028] The yield of silica white obtained in this example is 96.7%, the specific surface area is 365 m 2 / g, the oil absorption value is 289 mL / 100g, and the yield of ammonium fluoride is 95.8%.

[0029] Comparative Example 1 The difference between the preparation method of silica white in this comparative example and the preparation method of silica white in Example 1 is only that in the preparation process of silica white in this comparative example, the initial pH of the reaction is not controlled by adding ammonia water as a base. After the experiment, the performance values of the silica white product are shown in Table 1.

[0030] Table 1 Performance values of silica white

[0031] The results of the performance values of the silica white obtained in Comparative Example 1 show that when no ammonia water is added as a base, the generation rate of silica white is slow, the particles agglomerate, and both the specific surface area and the oil absorption value are significantly reduced.

[0032] Comparative Example 2 The difference between the preparation method of silica white in this comparative example and the preparation method of silica white in Example 1 is only that in step S2 of the preparation process of silica white in this comparative example, the pH of the reaction solution is maintained within different ranges all the time. After the experiment, the performance values of the silica white product are shown in Table 2: Table 2 Performance values of silica white

[0033] The results of the performance values of the silica obtained in Comparative Example 2 show that during the preparation process, when the pH of the reaction solution is always maintained at 9.3 - 9.4, it is most conducive to the formation of silica, with the highest specific surface area, oil absorption value, and yield. To observe the microscopic morphology of the prepared silica, the silica prepared in Comparative Example 2 - 1 and Example 1 was subjected to SEM testing, as Figure 2 . The results show that when the pH is 9.3 - 9.4, the microscopic morphology of the prepared silica is uniform and regular. Comparative Example 3 The preparation method of the silica in this comparative example is different from that of the silica in Example 1 only in that different dispersants are added in step S2 of the preparation process of the silica in this comparative example. After the experiment, the performance values of the silica products were measured as shown in Table 3. Table 3 Silica Performance Values

[0034] The results of the performance values of the silica in Comparative Example 3 show that using urea - formaldehyde as a dispersant can quickly disperse the generated silica and avoid agglomeration, while adding urea or formaldehyde alone does not have a dispersing effect.

[0035] Comparative Example 4 The preparation method of the silica in this comparative example is different from that of the silica in Example 2 only in that in step S0 of the preparation method of the silica in this comparative example, the feeding method is to add ammonium fluoride drop - by - drop or add ammonium fluoride and fluorosilicate slag together. After step S0 is completed, the remaining situation of the filter residue in the reaction and the yield of the prepared silica are compared, as shown in Table 4.

[0036] Table 4 Yield of Silica Prepared by Different Feeding Methods of Ammonium Fluoride

[0037] In Comparative Example 4, in the preparation of silica from fluorosilicate slag, the feeding method of raw materials will affect the dissolution of fluorosilicate slag. A large amount of ammonia gas generated by simultaneous feeding will make it difficult to completely dissolve the fluorosilicate slag, and the slow drop - by - drop method can accelerate its dissolution.

[0038] Comparative Example 5 The preparation method of the silica in this comparative example is different from that of the silica in Example 2 only in that different cosolvents are added during the reaction process in step S0 of the preparation method of the silica in this comparative example. The time for complete dissolution of fluorosilicate slag was compared, and the results are shown in Table 5.

[0039] Table 5 Cosolvent and Dissolution of Fluorosilicate Slag

[0040] According to Comparative Example 5, during the preparation of silica from fluorosilicate slag, the addition of a cosolvent can accelerate the dissolution of fluorosilicate slag. The cosolvent can rapidly dissolve the surface layer of fluorosilicate slag and accelerate the dissolution of fluorosilicate slag in ammonium fluoride solution. Among them, the effect of the cosolvent ammonium bifluoride is more likely to promote the dissolution of fluorosilicate slag than fluorosilicic acid.

[0041] Comparative Example 6 The difference between the preparation method of silica in this comparative example and the preparation method of silica in Example 2 is only that nitrogen is not introduced during the reaction process in step S0 of the preparation method of silica in this comparative example. Comparing the dissolution time of fluorosilicate slag, the results are shown in Table 6.

[0042] Table 6 Dissolution of nitrogen and fluorosilicate slag

[0043] According to Comparative Example 6, during the preparation of silica from fluorosilicate slag, the introduction of nitrogen can accelerate the dissolution of fluorosilicate slag. During the dissolution process of fluorosilicate slag, nitrogen can carry out the ammonia gas released during the reaction process out of the reaction system, avoiding the precipitation of silica due to ammonia gas dissolving in the solution and prolonging the reaction time.

[0044] Comparative Example 7 The difference between the preparation method of silica in this comparative example and the preparation method of silica in Example 2 is only that different reaction temperatures are used during the reaction process in step S0 of the preparation method of silica in this comparative example. After the experiment, record the time for complete dissolution of equal mass of silica and the yield of silica, as shown in Table 7 below.

[0045] Table 7 Time for complete dissolution of equal mass of fluorosilicate slag at different temperatures and yield of silica

[0046] According to Comparative Example 7, the reaction process between fluorosilicate slag and ammonium fluoride is accompanied by the overflow of ammonia gas. Reacting under high temperature conditions is beneficial to the overflow of ammonia gas from the system and reduces the precipitation of silica. Through the screening of temperature, it is found that the reaction rate is slower at 130°C. When the reaction temperature reaches 140°C, the reaction dissolution time is 0.6 h, and the energy consumption is lower compared with 150°C. Therefore, the optimal reaction temperature is 140°C.

[0047] In summary, through the optimization of various aspects such as the feeding method, preparation temperature, preparation pH, and dispersant during the preparation process of silica, the prepared silica has lower preparation cost, higher specific surface area, oil absorption value, purity and other indicators of the product, and has a larger application market.

Claims

1. A method for preparing white carbon black with high specific surface area from fluorosilicon raw materials, characterized in that, The method includes the following steps: S1. Take ammonia water with a certain concentration and add it into a reaction kettle equipped with a stirring paddle, a peristaltic pump and a condenser; S2. Under the condition of stirring, dropwise add fluorosilicon raw materials and ammonia water respectively for reaction, and carry out aging after the addition is completed; S3. Filter the reaction solution, cool and crystallize the filtrate, and dry it after filtration to obtain ammonium fluoride finished product; S4. Adjust the pH of the filter cake and make it into a slurry, filter it, wash the filter cake with pure water, and dry the filter cake in a dryer to obtain precipitated silica finished product.

2. The method for preparing white carbon black with high specific surface area from fluorosilicon raw materials according to claim 1, wherein In the step S1, ammonia water is added to the reaction kettle as a base to keep the pH of the reaction system at 9.3 - 9.4 during the reaction process.

3. The method for preparing white carbon black with high specific surface area from fluorosilicon raw materials according to claim 1, characterized in that, In the step S2, a dispersant is added before the fluorosilicon raw materials are dropwise added. The dispersant is a composition of urea and formaldehyde, and the addition amounts of urea and formaldehyde are respectively 0.1 - 0.3% of the mass of the added fluorosilicon raw materials.

4. The method for preparing white carbon black with high specific surface area from fluorosilicon raw materials according to claim 1, characterized in that, In the step S2, the temperature for adding the dispersant is 25 - 35°C. Preferably, the addition temperature is 30°C. Under acidic conditions at 30°C, formaldehyde and urea form a urea-formaldehyde resin polymer, and this polymer has a good dispersing effect during the crystallization process of precipitated silica.

5. The method for preparing precipitated silica with high specific surface area from fluorosilicon raw materials according to claim 1, characterized in that, In the step S2, the fluorosilicon raw material is fluosilicic acid or fluorosilicate slag; when the fluorosilicon raw material is fluorosilicate slag, it needs to be pretreated before the operation of step S2. The pretreatment step is to take the fluorosilicate slag in a reaction vessel, add ammonium fluoride solution and a cosolvent and stir, heat and react. When the reaction solution becomes clear, stop stirring. The reaction solution is ammonium fluosilicate solution; the reaction temperature is 130 - 150°C, the reaction stirring speed is 100 - 300 rpm, and the equivalent of the used ammonium fluoride is 1.2 - 1.

5.

6. The pretreatment method of fluorosilicate slag according to claim 5, characterized in that, The cosolvent for accelerating the dissolution of fluorosilicate slag includes fluosilicic acid or ammonium bifluoride or others. The addition amount of the cosolvent is 4 - 8%; preferably, ammonium fluoride is used to dissolve the fluorosilicate slag during the dissolution process, and the ammonium fluoride solution is added to the reaction system in a way of dropwise addition by a peristaltic pump, and the concentration of ammonium fluoride is 32 - 37%.

7. The pretreatment method of fluorosilicate slag according to claim 5, characterized in that, During the stirring process, the pH of the reaction system is made to be 6.0 - 6.5 by introducing nitrogen until the reaction solution becomes clear.

8. The method for preparing white carbon black with high specific surface area from fluorosilicon raw materials according to claim 1, characterized in that, In the step S2, the feeding method is that ammonia water and fluorosilicon raw materials are simultaneously pumped in by peristaltic pumps, and the feeding time is 0.4 - 0.6 h.

9. The method for preparing precipitated silica with high specific surface area from fluorosilicon raw materials according to claim 1, characterized in that, In the step S2, after the reaction is completed, the aging time of the reaction solution is 6.0 - 8.0 h, and the stirring speed is 600 - 800 rpm.

10. The method for preparing precipitated silica with high specific surface area from fluorosilicon raw materials according to claim 1, characterized in that, In the step S4, the pH during the re-slurrying of the filter cake is 6.8 - 7.3.

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