Process for preparing white carbon black by precise ammonia release and speed control ammonolysis of gaseous membrane

Abstract

The present application relates to fluorosilicic acid resource utilization, white carbon black wet synthesis, membrane mass transfer controllable reaction technical field, specifically relates to a kind of green preparation process of high specific surface white carbon black using gaseous membrane gas phase slow-release ammonia, precise control ammoniaolysis reaction rate, inhibit ultrafine colloidal generation, significantly improve slurry solid content.The process overcomes the defects of existing technology, such as violent reaction, nucleation out of control, colloid, low solid content, high energy consumption, poor product stability, etc., the product quality is significantly improved, ammonia utilization rate is very high (≥96%), environmental protection is good, process stability is very strong, and can be industrialized continuously.

Description

[0001] This invention belongs to the field of silica preparation technology, specifically relating to a process for preparing silica through precise ammonia release and controlled-rate ammonolysis using a gaseous membrane. Background Technology

[0002] Fluorosilicic acid is a typical silicon- and fluorine-containing intermediate, a byproduct of phosphate fertilizers and fluorochemicals. The mainstream industrial process involves the direct ammonialysis of fluorosilicic acid to produce silica and ammonium fluoride. However, existing traditional processes suffer from critical industry bottlenecks, listed below: 1) Direct addition of ammonia water causes an instantaneous reaction: High-concentration ammonia water is directly mixed with ammonium fluorosilicate liquid phase, resulting in localized instantaneous strong alkali and large-scale nucleation, generating a large amount of ultrafine nano colloidal silica; the colloid has extremely strong suspension properties, is difficult to settle, and is difficult to filter by pressure; 2) Extremely low solid content and limited production capacity: The stable solid content of slurry produced by traditional processes is only 5-8%, the system has extremely high water content, extremely high drying energy consumption, and extremely low equipment capacity, which is a long-standing pain point that the industry has been unable to overcome. 3) Loose particles, high porosity, and low product bulk density: Explosive nucleation leads to loose particles, severe agglomeration, high filtration moisture content, large fluctuations in the specific surface area of ​​the finished product, and poor product stability; 4) Low utilization rate of ammonia water and large amount of volatilization waste: Open ammonia addition reaction results in a large amount of ammonia escape, high environmental pressure and high raw material loss.

[0003] Existing patents and literature employ either a direct liquid-phase ammonia mixing mode or a gas-liquid mixing mode, failing to address the fundamental problems of "uncontrollable reaction, uncontrollable nucleation, and low solids content." Currently, there are no reported processes for preparing high-solids-content silica using precise slow-release of ammonia via a gas-phase membrane, gas-phase mass transfer for rate-controlled ammonolysis, and stepwise crystallization growth. Therefore, this process was developed. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a process for the precise and rate-controlled ammonia release from a gaseous membrane to prepare silica. This process overcomes the defects of existing technologies, such as violent reactions, uncontrolled nucleation, high colloid content, low solid content, high energy consumption, and poor product stability. It significantly improves product quality, has extremely high ammonia utilization (≥96%), good environmental performance, extremely strong process stability, and can be industrialized continuously.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: A process for preparing silica via gaseous membrane ammonia release and rate-controlled ammonolysis includes the following steps: S1. Prepare high-concentration ammonia water as the gas phase supply liquid for ammonia hydrolysis, control the temperature of the ammonia water, and circulate it into the tube side of the gas membrane module. S2. Prepare an aqueous solution of ammonium fluorosilicate as the reaction substrate, control the temperature, and circulate it into the shell side of the gaseous membrane module; S3. A hydrophobic microporous gas membrane is used for molecular-level slow-release mass transfer, allowing ammonia to diffuse across the membrane into the ammonium fluorosilicate solution at a constant rate. S4. The pH of the system is controlled to rise at a constant rate throughout the entire process to achieve a uniform ammonolysis reaction; S5. Under low-speed stirring conditions, react at a constant temperature for 90±30 min to obtain silica slurry; S6. Filter, wash and dry the slurry to obtain the finished silica product.

[0006] More preferably, in step S1, the ammonia concentration is 4-6 mol / L and the ammonia temperature is 20-40℃.

[0007] More preferably, in step S2, the concentration of the ammonium fluorosilicate aqueous solution is 5-30 wt%, and the temperature is 20-55℃.

[0008] More preferably, in step S3, the pore size of the gaseous membrane is 0.1-0.4 μm, and the pressure difference across the membrane is 0.01-0.04 MPa.

[0009] More preferably, in step S4, the pH rise rate of the ammonium fluorosilicate ammonolysis solution is ≤0.03 pH / min.

[0010] More preferably, the solid content of the silica slurry obtained in step S5 is 6-10%.

[0011] More preferably, in step S5, the reaction is carried out at a constant temperature for 90 minutes under low-speed stirring at 40-80 rpm.

[0012] As a preferred technical solution, the present invention provides a process for preparing high-solids-content silica by precise ammonia release and rate-controlled ammonolysis via gaseous membrane, which specifically includes the following steps: S1. Prepare 4-6 mol / L high-concentration ammonia solution as the ammonia hydrolysis gas phase supply liquid, control the ammonia solution temperature at 20-40℃, and circulate it into the tube side of the gas membrane module; S2. Prepare an aqueous solution of ammonium fluorosilicate with a mass concentration of 5-30 wt% as the reaction substrate liquid, control the temperature at 20-55℃, and circulate it into the shell side of the gaseous membrane module; S3. A hydrophobic microporous gaseous membrane is used for molecular-level slow-release mass transfer. The membrane pore size is 0.1-0.4 μm and the pressure difference across the membrane is 0.01-0.04 MPa, so that ammonia gas diffuses across the membrane into the ammonium fluorosilicate solution at a constant rate. S4. The pH of the entire system is controlled to rise slowly and uniformly, with a pH rise rate ≤ 0.03 pH / min, to achieve a uniform ammonolysis reaction without shock or explosion. S5. Under low-speed stirring at 40-80 rpm, the reaction is carried out at a constant temperature for 90 min to obtain silica slurry; S6. Filter, wash and dry the slurry to obtain high-purity silica.

[0013] The innovative aspects of this invention are reflected in the following aspects: 1) Abandoning the direct addition of ammonia in the liquid phase, the gaseous membrane molecular-level slow release of NH3 is adopted to achieve a uniform, controllable, and mild ammonolysis reaction; 2) Suppressing instantaneous burst nucleation, reducing ultrafine colloids, and promoting orderly grain growth and particle densification; 3) Increase the stable solids content of silica slurry from the traditional 5-7% to 7-10%; improve filtration performance, reduce drying load, and significantly increase production capacity; 4) Ammonia water utilization rate ≥96%, no ammonia escape, green and environmentally friendly, suitable for industrial continuous production.

[0014] Compared with the prior art, the method of the present invention has the following significant advantages and beneficial effects.

[0015] 1) Significantly increased solid content: In traditional ammonia addition processes, the ammonia concentration is generally 7-10 mol / L, and the ammonium fluorosilicate concentration is at most 10-30%, with a solid content of about 3-7%. However, in this invention, ammonia is added to the ammonium fluorosilicate solution through a gaseous membrane, which reduces the amount of water added to the final slurry and increases the solid content to 6-10%.

[0016] 2) Product quality has been significantly improved: In this invention, ammonia is released uniformly through a gaseous membrane, maintaining low supersaturation throughout the process. This results in a large number of crystal nuclei with primary crystal grains of approximately 7-10 nm, which then accumulate to form aggregates of hundreds of nanometers, ultimately creating a high specific surface area white carbon black with pore sizes of 15-20 nm. In contrast, traditional processes involving adding ammonia water or ammonia gas produce instantaneous high saturation, generating a massive number of primary particles that rapidly dehydrate and condense, forming relatively dense aggregates with a lower proportion of micropores and a lower specific surface area.

[0017] 3) Ammonia utilization rate is extremely high, and it is environmentally friendly: In this invention, ammonia is released at a uniform rate through a gaseous membrane, which can precisely control the pH of the final silica slurry to 8.4-8.5, reducing the volatilization of excess ammonia when the local pH is high and improving the ammonia utilization rate.

[0018] 4) Extremely stable process, capable of continuous industrialization: In this invention, no liquid ammonia is added directly throughout the process. The ammonia source is supplied entirely by gaseous membrane molecular diffusion. The ammonia hydrolysis reaction rate is completely limited by the gaseous membrane mass transfer rate, which completely avoids local over-alkali and explosive nucleation. This achieves precise and controllable reaction rate and significantly improved batch stability, making it suitable for large-scale continuous production. Detailed Implementation

[0019] The technical solution of the present invention will be further described in detail below with reference to the embodiments, but the scope of protection of the present invention is not limited thereto.

[0020] In the following embodiments, all raw materials used are common commercially available products that can be purchased directly, or can be prepared using conventional techniques in the art. For example, the gaseous membrane module (micro 2040) and the hydrophobic microporous gaseous membrane (4040) used were purchased from Anhui Konano Membrane Technology Co., Ltd. Example 1

[0021] A process for preparing silica via gaseous membrane ammonia release and rate-controlled ammonolysis includes the following steps: (1) Prepare 1000ml of 5mol / L high-concentration ammonia water as the ammonia hydrolysis gas phase supply liquid, control the temperature of the ammonia water at 30℃, and circulate it into the tube side of the gas membrane module. (2) Prepare 1000 ml of 20 wt% ammonium fluorosilicate aqueous solution as the reaction base liquid, control the temperature at 40℃, and circulate it into the shell side of the gas membrane module; (3) A hydrophobic microporous gaseous membrane is used for molecular-level slow-release mass transfer. The membrane pore size is 0.2 μm and the pressure difference across the membrane is 0.025 MPa, so that ammonia gas diffuses across the membrane into the ammonium fluorosilicate solution at a constant rate. (4) The pH of the system was controlled to rise slowly and uniformly throughout the process, with a pH rise rate of 0.022 pH / min; (5) Under low-speed stirring at 60 rpm, the mixture was reacted at a constant temperature for 90 min to obtain a silica slurry. (6) The slurry is filtered, washed and dried to obtain high-purity silica.

[0022] Experimental results: The system pH increased uniformly from 5.3 to 8.7 without any abrupt changes; the final slurry pH was 8.5, and the stable slurry solid content was 6.7%; the specific surface area of ​​the silica was 370 m². 2 / g, pore size 15.3nm. Example 2

[0023] A process for preparing silica via gaseous membrane ammonia release and rate-controlled ammonolysis includes the following steps: (1) Prepare 1000ml of 6mol / L high-concentration ammonia water as the ammonia hydrolysis gas phase supply liquid, control the temperature of the ammonia water at 30℃, and circulate it into the tube side of the gas membrane module. (2) Prepare 1000 ml of 30 wt% ammonium fluorosilicate aqueous solution as the reaction base liquid, control the temperature at 40℃, and circulate it into the shell side of the gas membrane module; (3) A hydrophobic microporous gaseous membrane is used for molecular-level slow-release mass transfer. The membrane pore size is 0.2 μm and the pressure difference across the membrane is 0.015 MPa, so that ammonia gas diffuses across the membrane into the ammonium fluorosilicate solution at a constant rate. (4) The pH of the system was controlled to rise slowly and uniformly throughout the process, with a pH rise rate of 0.018 pH / min; (5) React at a constant temperature for 90 min under low-speed stirring at 60 rpm; (6) The slurry is filtered, washed and dried to obtain high-purity silica.

[0024] Experimental results: The system pH increased uniformly from 5.3 to 8.5 without any abrupt changes; the slurry pH was 8.4, and the stable slurry solid content was 10.0%; the specific surface area of ​​the silica was 386 m². 2 / g, pore size 16.7nm. Example 3

[0025] A process for preparing silica via gaseous membrane ammonia release and rate-controlled ammonolysis includes the following steps: (1) Prepare 1000ml of 4mol / L high-concentration ammonia water as the ammonia hydrolysis gas phase supply liquid, control the temperature of the ammonia water at 40℃, and circulate it into the tube side of the gas membrane module. (2) Prepare 1000 ml of 25 wt% ammonium fluorosilicate aqueous solution as the reaction base liquid, control the temperature at 35℃, and circulate it into the shell side of the gas membrane module; (3) A hydrophobic microporous gaseous membrane is used for molecular-level slow-release mass transfer. The membrane pore size is 0.2 μm and the pressure difference across the membrane is 0.04 MPa, so that ammonia gas diffuses across the membrane into the ammonium fluorosilicate solution at a constant rate. (4) The pH of the system was controlled to rise slowly and uniformly throughout the process, with a pH rise rate of 0.026 pH / min; (5) React at a constant temperature for 90 min under low-speed stirring at 60 rpm; (6) The slurry is filtered, washed and dried to obtain high-purity silica.

[0026] Experimental results: The system pH increased uniformly from 5.3 to 8.7 without any abrupt changes; the slurry pH was 8.5, and the solid content of the stable slurry was 8.4%; the specific surface area of ​​the silica was 355 m². 2 / g, pore size 17.2nm.

[0027] Comparative Example 1

[0028] A process for preparing silica includes the following steps: (1) Prepare 6 mol / L high concentration ammonia water as ammonia hydrolysate, control the temperature of ammonia water at 40℃, and add it at a constant speed to a reaction tank containing a 25 wt% ammonium fluorosilicate solution. (2) React at a constant temperature for 90 min under low speed stirring at 60 rpm to obtain silica slurry. (3) Filter, wash and dry to obtain silica product.

[0029] Experimental results: The system pH jumped abruptly from 5.3 to 9.2, with the final slurry pH at 8.7 and a solid content of 5.3%; the specific surface area of ​​the silica was 236 m². 2 / g, pore size 21.8nm.

[0030] Comparative Example 2

[0031] A process for preparing silica includes the following steps: (1) Control the outlet pressure of the liquid ammonia cylinder to 0.06 MPa and the gas volume flow rate to 80 L / h. Pass the ammonia gas into the reaction tank containing a 25 wt% ammonium fluorosilicate solution. (2) Stir and circulate the gas at a constant temperature for 60 min under low-speed stirring at 500 rpm. At this time, the pH is 9.2. Stop circulating the gas and continue stirring for 1 h. The reaction ends and the silica slurry is obtained. (3) Filter, wash and dry to obtain the finished silica product.

[0032] Experimental results: The system pH gradually increased from 5.3 to 9.2, with the final slurry pH at 9.2 and a solid content of 8.3%; the specific surface area of ​​the silica was 282 m². 2 / g, pore size 23.5nm.

[0033] Table 1 Performance data of the silica products obtained in each example

[0034] As can be seen from the table above, both adding ammonia water and introducing ammonia gas will lead to local supersaturation, instantly generating a large number of primary grains. These grains mature and grow in an overly alkaline environment, bridging together, causing micropore collapse, increased pore size, decreased specific surface area, and increased bulk density. In contrast, the gaseous membrane ammonia release process can achieve uniform supply of ammonia gas at the molecular level and throughout the entire process, maintaining a stable low supersaturation and constant pH throughout the system, eliminating local overly alkaline areas, and relying on the electrostatic repulsion of particles to inhibit grain maturation and chemical bond bridging, thus completely preserving the microporous structure between particles, and finally obtaining fluffy white carbon black powder with fine and uniform particle size, high specific surface area, and low bulk density.

Claims

1. A process for preparing silica via gaseous membrane ammonia release and rate-controlled ammonolysis, characterized in that, Includes the following steps: S1. Prepare high-concentration ammonia water as the gas phase supply liquid for ammonia hydrolysis, control the temperature of the ammonia water, and circulate it into the tube side of the gas membrane module. S2. Prepare an aqueous solution of ammonium fluorosilicate as the reaction substrate, control the temperature, and circulate it into the shell side of the gaseous membrane module; S3. A hydrophobic microporous gas membrane is used for molecular-level slow-release mass transfer, allowing ammonia to diffuse across the membrane into the ammonium fluorosilicate solution at a constant rate. S4. The pH of the system is controlled to rise at a constant rate throughout the entire process to achieve a uniform ammonolysis reaction; S5. Under low-speed stirring conditions, react at a constant temperature for 90±30 min to obtain silica slurry; S6. Filter, wash and dry the slurry to obtain the finished precipitated silica.

2. The process for preparing silica by precise ammonia release and rate-controlled ammonolysis via gaseous membrane as described in claim 1, characterized in that, In step S1, the ammonia concentration is 4-6 mol / L and the ammonia temperature is 20-40℃.

3. The process for preparing silica by precise ammonia release and rate-controlled ammonolysis via gaseous membrane as described in claim 1, characterized in that, In step S2, the concentration of the ammonium fluorosilicate aqueous solution is 5-30 wt%, and the temperature is 20-55℃.

4. The process for preparing silica via gaseous membrane ammonia release and rate-controlled ammonolysis as described in claim 1, characterized in that, In step S3, the gaseous membrane has a pore size of 0.1-0.4 μm and a pressure difference of 0.01-0.04 MPa across the membrane.

5. The process for preparing silica by precise ammonia release and rate-controlled ammonolysis via gaseous membrane as described in claim 1, characterized in that, In step S4, the pH rise rate is ≤0.03 pH / min.

6. The process for preparing silica by precise ammonia release and rate-controlled ammonolysis via gaseous membrane as described in claim 1, characterized in that, The solid content of the silica slurry obtained in step S5 is 6-10%.

7. The process for preparing silica via gaseous membrane precise ammonia release and rate-controlled ammonolysis as described in claim 1, characterized in that, In step S5, the reaction is carried out at a constant temperature for 90 minutes under low-speed stirring at 40-80 rpm.

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