A green integrated process for the efficient preparation of ammonium fluoride and by-product white carbon black

Abstract

The present invention relates to the field of inorganic chemical technology and discloses a green integrated process for the efficient preparation of ammonium fluoride and by-product white carbon black. In order to solve the problems of high energy consumption, heavy pollution and low added value of by-products in traditional processes, the present invention adopts ultrasonic cavitation combined with membrane filtration to pre-treat fluorosilicic acid, combined with microwave staged temperature control technology, to achieve precise control of NH4F nucleation and crystal growth, shortening the reaction time by 66.7% and achieving a product purity of ≥99.8%. High-purity NH4F solution and white carbon black slurry are obtained synchronously by dynamic centrifugation. After the mother liquor is purified by supercritical CO2, Cl ‑ The content is ≤5ppm and can be recycled ≥10 times; NH3 and CO2 in the tail gas are catalyzed into urea through a microchannel reactor with a purity of ≥99.5%. ‑ Emissions meet national first-level standards, energy consumption is reduced by 50%, and it is suitable for large-scale applications in the electronics, rubber and fertilizer industries.

Description

Technical Field

[0001] The present invention relates to the technical field of inorganic chemical industry, and more particularly to a green integrated process for efficiently preparing ammonium fluoride and producing by-product white carbon black. Background Art

[0002] Ammonium fluoride is an important raw material in the fields of electronics and glass etching. The traditional preparation process mostly uses the neutralization method of hydrofluoric acid and ammonia water, which has the problems of strong raw material corrosiveness, low by-product utilization rate, and great environmental pollution. In addition, it has the problems of high energy consumption and chloride ion (Cl - ) exceeds the standard (>500ppm) and other defects. In addition, the by-product silica is mostly discharged as low-value waste, resulting in serious waste of resources.

[0003] Therefore, it is necessary to propose a green integrated process for the efficient preparation of ammonium fluoride and by-product white carbon black to solve the above problems. Summary of the Invention

[0004] The purpose of the present invention is to solve the problem of high energy consumption in the preparation of ammonium fluoride and the chloride ion (Cl - ) exceeds the standard (>500ppm). In addition, the by-product silica is mostly discharged as low-value waste, which is a serious waste of resources.

[0005] In order to achieve the above-mentioned purpose, the present invention specifically adopts the following technical solutions:

[0006] A green integrated process for efficiently preparing ammonium fluoride and by-product white carbon black comprises the following steps:

[0007] (a) Fluorosilicic acid was pretreated by ultrasonic cavitation and membrane filtration to obtain a fluosilicic acid filtrate with a turbidity of ≤5 NTU;

[0008] (b) subjecting the filtrate from step a to a microwave-controlled reaction in stages to generate ammonium fluoride crystal nuclei and silicon dioxide particles, wherein the NH4F concentration in the mixture after the reaction is ≥12 wt%;

[0009] (c) subjecting the mixed solution of step b to dynamic centrifugation to obtain a solution of ammonium fluoride having a purity of ≥99.8% and a white carbon black slurry, wherein the white carbon black has a specific surface area of ​​≥250 m² / g;

[0010] (d) Purify the mother liquor from step c by supercritical CO2 to obtain Cl - Recyclable mother liquor with a content of ≤5ppm;

[0011] (e) catalytically converting the tail gas produced in step b to synthesize a solid product having a urea purity of ≥99.5%.

[0012] Furthermore, the ultrasonic cavitation treatment conditions in step a are 40 kHz, 60% amplitude, and a treatment time of 25-35 minutes, and the suspended matter content of the fluorosilicic acid filtrate after treatment is ≤0.01 wt%.

[0013] Furthermore, the step b includes the following staged control:

[0014] The first stage: 30 ± 0.5 ° C, pH 6.0-6.5, microwave power 180-220 W, forming NH4F crystal nuclei with a particle size of 10 ± 2 nm;

[0015] The second stage: 50±0.5℃, pH 7.0-7.5, microwave power 280-320W, NH4F grains grow to 50±5nm, and SiO2 particles are generated simultaneously;

[0016] The third stage: 70±0.5℃, pH 7.5-8.0, microwave power 230-270W, to obtain a stable NH4F-SiO2 mixed system.

[0017] Furthermore, the dynamic centrifugal separation control parameters in step c include:

[0018] Input data: online viscosity sensor detection value, accuracy ±0.1mPa·s;

[0019] Output command: centrifuge speed 8000-15000rpm, adjustment response time ≤50ms;

[0020] Separation product indicators: water content of ammonium fluoride solution ≤ 0.5%, solid content of white carbon black slurry ≥ 25wt%.

[0021] Furthermore, the conditions for supercritical CO2 purification in step d are:

[0022] Pressure 18-22MPa, temperature 48-52℃, ethanol entrainer addition amount 4.8-5.2vol%;

[0023] The purified mother liquor was recycled to step b for ≥10 times, and the NH4F yield was maintained at ≥99.3%.

[0024] Furthermore, the conditions for urea synthesis in step e are:

[0025] The flow channel diameter of the microchannel reactor is 0.4-0.6 mm, and the catalyst is ZnO with a particle size of 20-50 nm;

[0026] Ammonia conversion rate ≥95%, urea product nitrogen content ≥46.3wt%, moisture ≤0.3%.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] The present invention uses supercritical CO2 purification technology to remove Cl - The content is significantly reduced from 500ppm in traditional processes to ≤5ppm, meeting the first-level discharge standard for industrial wastewater; microwave-assisted reaction technology combined with dynamic centrifugal separation reduces the overall energy consumption from 120kWh / ton in traditional processes to 60kWh / ton, with an energy saving effect of 50%, and no fluorine-containing waste gas emissions. DETAILED DESCRIPTION

[0029] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0030] A green integrated process for the efficient preparation of ammonium fluoride and by-product white carbon black.

[0031] Example 1

[0032] 1. Raw material pretreatment.

[0033] (a) Fluosilicic acid pretreatment: Ultrasonic cavitation and membrane filtration. Industrial-grade fluosilicic acid typically contains colloidal silicate, metal ion flocculants, and mechanical impurities. The pretreatment utilizes a synergistic mechanism of "ultrasonic cavitation-membrane filtration";

[0034] Reaction Mechanism: Industrial-grade fluosilicic acid (H2SiF6) often contains colloidal impurities (such as silica gel and metal oxides) and suspended particles. Ultrasonic cavitation uses high-frequency vibration (40kHz) to generate microjets and localized high temperature and high pressure, destroying the colloid's stability. Fluosilicic acid is introduced into a specially designed cavitation reaction tank, where the transducer generates mechanical vibration waves of a specific frequency. The sound waves form periodic high-pressure / low-pressure zones in the liquid. These low-pressure zones generate microbubbles that rapidly collapse (cavitation effect), releasing shock waves and microjets. This physical action effectively tears apart the colloidal agglomeration structure, destabilizing and precipitating submicron-sized impurities. It also inhibits abnormal polymerization of silicone gel in subsequent processes, causing impurities to aggregate.

[0035] Micron-sized particles are further retained through membrane filtration (0.2μm PTFE). The cavitated feed liquid enters the cross-flow membrane filtration unit. A surface hydrophobic filter membrane is selected. Under the action of tangential flow, micron-sized suspended matter is retained on the membrane surface. The filtrate passes through the filter membrane and enters the clean storage tank. The key control point at this stage is the transmittance of the filtrate to ensure that the subsequent reaction is not interfered with by impurities.

[0036] Parameters based on:

[0037] The ultrasonic frequency is set to 40kHz: high frequency has a strong cavitation effect and can disperse colloids efficiently.

[0038] The amplitude was set to 60%: too low an amplitude would result in insufficient cavitation, while too high an amplitude would increase energy consumption. 60% was the experimentally optimized value.

[0039] The treatment time was set to 30 minutes: it was determined by dynamic monitoring of turbidity that the turbidity was stable at ≤3 NTU after 30 minutes.

[0040] Data verification: The suspended matter content dropped from 0.5wt% to 0.008wt%, and the colloid removal rate was 96.3%.

[0041] 2. Microwaves control the reaction in stages. This step uses the three-dimensional coordinated regulation of the reaction path through "temperature-pH-microwave energy". A microwave resonant cavity reactor is equipped with a platinum electrode pH probe and a fiber optic temperature sensor to achieve real-time closed-loop control. Ammonia is injected in a gradient manner through a metering pump to avoid local over-alkalinity that causes side reactions.

[0042] (a) Staged reaction mechanism:

[0043] The first stage (nucleation): The system maintains a weakly acidic environment, and the microwave field radiates at a moderate power. Fluorosilicic acid molecules dissociate under the action of directional electromagnetic energy and combine with ammonia ions to form ammonium fluoride embryos. Low temperature conditions inhibit the Ostwald ripening of the embryos to ensure uniform size of the crystal nuclei.

[0044] Fluorosilicic acid is neutralized with ammonia (NH3·H2O) to generate NH4F and SiO2 particles:

[0045] H2SiF6+6NH3→6NH4F+SiO2↓.

[0046] The low temperature of 30 °C and weak acidity of pH 6.2 inhibited side reactions such as NH3 volatilization and promoted the uniform nucleation of nano-sized NH4F nuclei of 10±2 nm.

[0047] The second stage (crystal growth): The temperature is raised in a step-by-step manner and the alkalinity of the system is increased. The microwave power is simultaneously enhanced, and the ammonium fluoride crystal nuclei preferentially grow along specific crystal planes to form a regular morphology. The silica precursor dehydrates and condenses under alkaline conditions, gradually constructing a three-dimensional network structure to form white carbon black primary particles. The non-thermal effect of microwaves accelerates molecular diffusion and shortens the phase change induction period.

[0048] The temperature was raised to 50°C, the pH value was raised to 7.3, and the microwave power was increased to 300W to accelerate the growth of NH4F grains to 50±5nm, and SiO2 particles were generated simultaneously.

[0049] The third stage (system stabilization): The temperature is raised to near the boiling point and the pH is adjusted to the weak alkaline threshold. Under this condition, the surface energy of the ammonium fluoride crystal is reduced, reducing ion dissolution; the silanol groups on the silica surface condense, the colloidal stability is enhanced, and the microwave power is adjusted back to avoid lattice defects caused by local overheating.

[0050] Raise the temperature to 70℃ and adjust the pH to 7.8 to inhibit the hydrolysis of NH4F. Side reactions:

[0051] NH4F+H2O→NH3↑+HF, the hydrolysis path of ammonium fluoride is blocked through precise pH control, and the side reaction inhibition rate is ≥97.5%. In addition, microwave selective heating suppresses ammonia escape and improves the utilization rate of nitrogen atoms.

[0052] (b) Parameter design basis:

[0053] Microwave-assisted heating: Compared with traditional conduction heating, microwaves act directly on polar molecules such as NH4 + 、F - , shortening the reaction time by 66.7%, from the original 120 minutes to 40 minutes.

[0054] Purpose of pH gradient control:

[0055] First stage pH 6.2: Avoid excessive NH3 volatilization (≤0.5%).

[0056] The second stage pH 7.3: promotes the stable precipitation of SiO2 colloid.

[0057] The third stage is pH 7.8: close to the isoelectric point of NH4F, reducing ion residues.

[0058] Data verification: NH4F concentration is 12.5wt%, while the traditional process is only 8wt%, and the purity is ≥99.8%.

[0059] 3. Dynamic centrifugation.

[0060] (a) Separation mechanism: The density difference between NH4F solution (1.1 g / cm³) and white carbon black SiO2 (2.2 g / cm³) is utilized to dynamically adjust the centrifugal speed according to the viscosity. However, the Brownian motion of nanoparticles is strong, and traditional centrifugation easily leads to backmixing. In-line viscosity sensing is introduced as a process variable. The viscosity change directly reflects the particle dispersion state and concentration gradient. The target speed is 8500-10000 when the viscosity is set at 70-90, 11000-12500 when the viscosity is set at 91-110, and 13000-14500 when the viscosity is set at 111-130. Efficient solid-liquid separation and graded viscosity control are achieved:

[0061] The viscosity sensor collects the rheological data of the material in real time, and the signal is transmitted to the PLC controller. The control system has a built-in viscosity-speed mapping algorithm. As mentioned above, the ratio of viscosity to speed is as follows: the low viscosity range corresponds to a moderate centrifugal force field to prevent the crushing of silica; the high viscosity range activates a strong centrifugal force to overcome the colloid resistance, so that the centrifuge speed responds to instructions in milliseconds, achieving dynamic matching of separation strength and material state.

[0062] (b) Parameter basis:

[0063] Viscosity feedback control: When the viscosity is 100 cP, 12000 rpm can separate SiO2 with a particle size of ≤50 nm.

[0064] Silica index, specific surface area index is achieved through crystal control in the growth stage to avoid damage to the pore structure during post-processing. Its specific surface area is ≥250m² / g: high specific surface area requires control of grain growth rate, and the microwave power in the second stage is 300W.

[0065] Oil absorption value 2.0mL / g: related to the surface hydroxyl (-OH) content, excessive agglomeration should be avoided, washing temperature 80℃.

[0066] Data verification: white carbon black D50 particle size 45±3nm, specific surface area 255m 2 / g.

[0067] 4. Supercritical CO2 mother liquor purification to build a closed loop of deep removal of ionic impurities and resource recycling.

[0068] (a) Purification mechanism: Supercritical CO2 (scCO2) has high diffusivity and solubility at 20 MPa and 50°C, forming liquid-like density and gas-like diffusivity, which can penetrate into the ion solvation layer. Ethanol, as a polar entrainer, can selectively extract Cl - 、SO4 2- Plasma impurities exist in the form of hydrated ions, and their hydroxyl groups form hydrogen bond associations with impurity ions and are entrained and extracted by the supercritical fluid.

[0069] (b) Parameter basis:

[0070] Pressure 20MPa: higher than the critical pressure of CO2 7.38MPa. CO2 is pressurized to a supercritical state by a compressor and premixed with a certain amount of ethanol to form a homogeneous solvent to ensure the supercritical state.

[0071] Ethanol 5vol%: Experiments show that 5% ethanol can make Cl - The removal rate increased from 90% to 99.5%.

[0072] Cycle number ≥ 10: Regularly monitor the accumulation trend of mother liquor ions to ensure that the product purity meets the standard within the upper limit of the cycle number. It has been verified that the NH4F yield after mother liquor reuse is still ≥ 99.3%, proving that impurity accumulation is controllable.

[0073] Data verification: Cl - The content dropped from 100ppm to 4.2ppm, SO4 2- From 50ppm to 2.8ppm.

[0074] 5. Catalytic synthesis of urea from tail gas to achieve waste gas resource utilization and eliminate terminal pollution.

[0075] Ammonia and carbon dioxide in the exhaust gas form laminar flow in the micron-sized flow channel, eliminating the macroscopic mixing dead zone. In addition, the high specific surface area promotes gas-solid mass transfer and significantly shortens the reaction path length.

[0076] (a) Reaction mechanism: Unreacted NH3 and CO2 are catalyzed by ZnO to produce urea in a microchannel reactor:

[0077] 2NH3+CO2→NH2CONH2+H2O.

[0078] (b) Parameter basis:

[0079] Microchannel diameter 0.5mm: increases specific surface area, shortens mass transfer path, and increases reaction rate.

[0080] Nano ZnO catalyst: Nano ZnO catalyst is loaded on the inner wall of the microchannel, exposing highly active crystal faces. When the particle size is 20nm, the active site density is the highest, and the BET specific surface area is 120m² / g.

[0081] NH3 / CO2 molar ratio 2:1: Ammonia and carbon dioxide undergo adsorption-activation-condensation process on the catalyst surface to generate urea intermediate and dehydrate and solidify, avoiding excessive NH3 leading to by-products such as biuret.

[0082] The reaction heat is efficiently discharged through the microchannel to avoid catalyst sintering and deactivation.

[0083] Data verification: urea purity 99.6%, ammonia conversion rate 96.2%.

[0084] Example 2 (Process Optimization Verification)

[0085] Comparative experiment: Effect of microwave power on NH4F grain size:

[0086]

[0087] The experiment verified the optimal process parameters by comparing the grain sizes under different microwave powers:

[0088] Microwave power 180W: The grain size is 15±3nm. The low power leads to uneven growth of the crystal nucleus.

[0089] Microwave power 200W (preferred): The grain size is 10±2nm, achieving the optimal nucleation conditions and meeting the process design requirements.

[0090] Microwave power 220W: grain size is 12±3nm. Too high power causes local overheating and affects crystal uniformity.

[0091] Conclusion: 200 W microwave power is an ideal condition for nucleation, which can precisely control the NH4F crystal size within the nanoscale range of 10 ± 2 nm and ensure the product purity ≥ 99.8%.

[0092] Example 3 (Environmental Analysis)

[0093] Waste comparison:

[0094]

[0095] Conclusion: Wastewater chloride ion (Cl - ) content is reduced from 500ppm to ≤5ppm. NH3 and CO2 in the tail gas are efficiently converted into urea with a purity of ≥99.5% through the microchannel reactor, realizing waste gas resource utilization.

[0096] The overall comprehensive energy consumption has dropped from 120kWh / ton to 60kWh / ton, a 50% reduction, mainly due to the coordinated optimization of microwave staged temperature control technology and dynamic centrifugal separation.

[0097] The specific surface area of ​​the by-product of the present invention is ≥250m 2 The by-product white carbon black with a purity of ≥99.5% and urea with a purity of ≥99.5% both have high added value and completely solve the problem of by-product waste in traditional processes.

[0098] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. The scope of patent protection of the present invention shall be based on the claims. Any equivalent structural changes made using the contents of the description of the present invention shall also be included in the scope of protection of the present invention.

Claims

1. A green integrated process for efficiently preparing ammonium fluoride and by-product white carbon black, characterized in that: The following steps are involved: (a) Fluorosilicic acid was pretreated by ultrasonic cavitation and membrane filtration to obtain a fluosilicic acid filtrate with a turbidity of ≤5 NTU; (b) subjecting the filtrate from step a to a microwave-controlled reaction in stages to generate ammonium fluoride crystal nuclei and silica particles by reacting fluorosilicic acid with aqueous ammonia, wherein the concentration of NH4F in the mixture after the reaction is ≥12 wt%; The step b includes the following staged control: The first stage: 30 ± 0.5 ° C, pH 6.0-6.5, microwave power 180-220 W, forming NH4F crystal nuclei with a particle size of 10 ± 2 nm; The second stage: 50±0.5℃, pH 7.0-7.5, microwave power 280-320W, NH4F grains grow to 50±5nm, and SiO2 particles are generated simultaneously; The third stage: 70±0.5℃, pH 7.5-8.0, microwave power 230-270W, to obtain a stable NH4F-SiO2 mixed system; (c) subjecting the mixed solution of step b to dynamic centrifugation to obtain a solution of ammonium fluoride having a purity of ≥99.8% and a white carbon black slurry, wherein the white carbon black has a specific surface area of ​​≥250 m² / g; (d) Purify the mother liquor from step c by supercritical CO2 to obtain Cl - Recyclable mother liquor with a content of ≤5ppm; (e) catalytically converting the tail gas produced in step b to synthesize a solid product having a urea purity of ≥99.5%.

2. The green integrated process for efficiently preparing ammonium fluoride and by-product white carbon black according to claim 1, characterized in that: The ultrasonic cavitation treatment conditions in step a are 40 kHz, 60% amplitude, and a treatment time of 25-35 minutes. After the treatment, the suspended matter content of the fluorosilicic acid filtrate is ≤0.01 wt%.

3. The green integrated process for efficiently preparing ammonium fluoride and by-product white carbon black according to claim 1, characterized in that: The dynamic centrifugal separation control parameters in step c include: Input data: online viscosity sensor detection value, accuracy ±0.1mPa·s; Output command: centrifuge speed 8000-15000rpm, adjustment response time ≤50ms; Separation product indicators: water content of ammonium fluoride solution ≤ 0.5%, solid content of white carbon black slurry ≥ 25wt%.

4. The green integrated process for efficiently preparing ammonium fluoride and by-product white carbon black according to claim 1, characterized in that: The conditions for supercritical CO2 purification in step d are: Pressure 18-22MPa, temperature 48-52℃, ethanol entrainer addition amount 4.8-5.2vol%; The purified mother liquor was recycled to step b for ≥10 times, and the NH4F yield was maintained at ≥99.3%.

5. The green integrated process for efficiently preparing ammonium fluoride and by-product white carbon black according to claim 1, characterized in that: The conditions for urea synthesis in step e are: The flow channel diameter of the microchannel reactor is 0.4-0.6 mm, and the catalyst is ZnO with a particle size of 20-50 nm; Ammonia conversion rate ≥95%, urea product nitrogen content ≥46.3wt%, moisture ≤0.3%.

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