Method for producing nanosilica using organosilicon waste catalysts

Abstract

This invention relates to a method for producing nanosilica using organic silicon waste catalysts, and aims to reduce the environmental burden caused by landfill volume and hazardous waste. [Solution] After appropriate pretreatment of the organosilicon waste catalyst, it is acid-leached and purified with HCl, and then the residue is directly reacted with NaOH to obtain Na2SiO3. In the manufacturing process, Na2SiO3 is used as the silicon source and NH4Cl as the precipitant, and the catalytic hydroxyl group self-condensation reaction of Na2SiO3 is carried out in a polyol / low molecular weight alcohol / polyquaternium / aqueous solvent system. The effect of the ratio of polyol, ethanol, and polyquaternium on the particle size, dispersibility, and shape of amorphous SiO2 nanoparticles was investigated. Finally, spherical amorphous SiO2 nanoparticles with excellent dispersibility were produced from silicon-containing solid waste. These nanoparticles have high yield and purity, a particle size controlled to around 100 nm, and uniform particle size dispersion.

Description

[Technical Field]

[0001] This invention belongs to the technical field of recycling hazardous waste resources and environmental protection, and relates to a method for producing nanosilica using organosilicon waste catalysts. [Background technology]

[0002] Silicon naturally accounts for approximately 27.72% of the Earth's crust's total mass. Since the synthesis of organosilicon compounds containing silicon-carbon bonds in the 1960s, organosilicon has entered a period of rapid development. Due to its superior properties, it has become one of the fastest-growing and indispensable commodities in the development of the national economy and people's lives. The most important and complex aspect of its production is the synthesis of methylchlorosilane monomer. The direct method is widely adopted because the process is simple, yields high, does not use solvents, is low-risk, and allows for easy continuous large-scale production. In this method, ternary copper is used as a catalyst and mixed with silicon powder to form an active catalyst, which plays an important role in improving the selectivity and yield of methylchlorosilane. During the continuous reaction, factors such as the accumulation of impurities and catalyst deactivation significantly reduce the conversion rate of silicon powder and the selectivity of dimethylchlorosilane (M2). To maintain stable production, unreacted silicon powder and deactivated catalyst are discharged from the reactor, forming industrial waste residue called organosilicon waste catalyst.

[0003] According to the "China National Hazardous Waste Directory (2021 Edition)," spent organosilicon catalysts are classified as waste organic solvents and organic solvent-containing waste. Because they are prone to spontaneous combustion, proper treatment is necessary to avoid environmental pollution. At the same time, spent catalysts contain valuable resources such as silicon powder, copper compounds, iron, and zinc. Organosilicon spent catalysts account for approximately 3-6% of methylchlorosilane production. Conducting intensive research on the resource utilization of spent catalysts is of urgent and important significance in ensuring the environmentally friendly and sustainable development of the organosilicon industry.

[0004] Traditionally, on-site landfill disposal has been commonly used to treat spent organosilicon catalysts. This method not only causes serious environmental pollution but also results in the loss of large quantities of valuable resources such as silicon and copper. In recent years, research on the resource utilization of spent catalysts has mainly focused on processes that involve forming metal salt solutions through chemical treatment, then producing various metals and their derivatives by means of chemical reduction or electrolysis, and finally obtaining silicon powder after chemically and physically purifying the residues. In this process, the separation conditions greatly affect the solid-liquid phase separation effect, and because the process is relatively complex, new waste is easily generated, increasing the processing load and energy consumption. At the same time, the solid-liquid phase separation process also affects the utilization rate and usability of recovered materials such as silicon. In conventional technology, the recycling of spent organosilicon catalyst resources has mainly focused on the recovery of copper resources, and reports on silicon resources often concern methods for recovering silicon powder.

[0005] CN117416963A discloses a method for producing silicon powder using an organosilicon waste catalyst, comprising the steps of: (1) decoupling an organosilicon waste catalyst to obtain organosilicon waste catalyst decoupling slag; (2) mixing the organosilicon waste catalyst decoupling slag with water to prepare a slurry; (3) performing a two-stage magnetic separation on the slurry to obtain a silicon-rich non-magnetic product; and (4) calcining, pickling, and drying the silicon-rich non-magnetic product to obtain silicon powder.

[0006] CN115181998A discloses a method for recovering silicon powder from an organosilicon waste catalyst, comprising: an oxidation-acid leaching step in which an organosilicon waste catalyst, sulfuric acid solution A and a adjusting agent are added to an air flotation-mechanically agitated integrated leaching tank, air is introduced into the air flotation-mechanically agitated integrated leaching tank, a scraper device is continuously operated to remove the air flotation layer on the surface, and oxidation leaching is performed by mechanical agitation to obtain a leaching slurry; and a solid-liquid separation step in which the leaching slurry is subjected to solid-liquid separation to obtain a copper-containing leaching liquid and a leaching slag, and the leaching slag is washed, pressure filtered, and neutralized to obtain silicon powder.

[0007] CN115058586A discloses a method for recovering silicon powder from an organosilicon waste catalyst, which includes the steps of: crushing an organosilicon waste catalyst with a ball mill and slurring it to obtain a slurry; then removing iron from the slurry by magnetic separation and pressure filtration to obtain copper-containing waste silicon powder after iron removal; adding the copper-containing waste silicon powder after iron removal and a sulfuric acid solution to a flotation machine to form a mixed slurry; then drawing air into the flotation machine and continuously operating a scraper device to remove the air-floating layer on the surface; performing oxidation leaching by mechanical stirring; and after leaching, performing solid-liquid separation to obtain leached slag and copper-containing leaching liquid; and subjecting the leached slag to a washing and pressure filtration process to obtain a washed filtrate and silicon powder.

[0008] The conventional technology described above recovers silicon powder from organosilicon waste catalysts, but it does not have high economic value. A search reveals that there are currently very few reports on producing nano-sized silica using organosilicon waste catalysts as a raw material. [Overview of the Initiative] [Problems that the invention aims to solve]

[0009] To address the challenge of producing nano-sized silica from organosilicon waste catalysts, the present invention separates impurities from the organosilicon waste catalyst, performs acid leaching and suction filtration without adding an oxidizing agent such as hydrogen peroxide, then separates the solid and liquid with sodium hydroxide, performs a titration reaction, filters again by suction, and finally dries the gel-like material to remove volatile impurities by calcination, thereby obtaining nano-sized silica with uniformly dispersed particle size. This simplifies the recovery process, reduces the amount of waste generated, reduces the impact of the recovery process on the recovered material, and lowers energy consumption and costs, thereby improving the effective recovery of silicon in organosilicon waste catalysts, increasing market value, and mitigating environmental impact. The present invention achieves the above objectives through the following technical solutions. [Means for solving the problem]

[0010] A method for producing nanosilica using organosilicon waste catalysts, wherein the method is: Step S1 involves calcining an organosilicon waste catalyst under a mixed gas of oxygen and nitrogen to obtain a calcined waste catalyst product. Step S2 involves mixing the calcined waste catalyst with concentrated hydrochloric acid, continuously stirring under ultrasonic conditions while heating to obtain an acid leaching slurry, and then repeatedly washing with water and suction filtration until the filtrate becomes neutral to obtain the filtrate. Step S3 involves uniformly mixing the filtrate obtained in S2 with sodium hydroxide and sodium fluoride, adding water and mixing uniformly, heating and stirring to allow the reaction to occur, and then filtering to obtain a sodium silicate solution. Step S4 involves adding a polyol, a C1-3 monohydric alcohol, and polydimethyldiallylammonium chloride to a sodium silicate solution to obtain solution A, slowly adding ammonium chloride solution to solution A, adjusting the amount of ammonium chloride solution used so that the pH of the mixed solution is 6-7, and obtaining a gel substance. The process includes step S5, in which a gel-like substance is allowed to mature, followed by washing, suction filtration, drying, calcination, and pulverization to obtain nano-sized silica.

[0011] Preferably, in step S1, the volume percentage of oxygen gas in the mixed gas is 5-20%, the firing temperature is 600-1000°C, and the firing time is 30-90 min.

[0012] Preferably, in step S2, the hydrochloric acid concentration is 6-12 mol·L. -1 Preferably 10-12 mol·L -1 The acid leaching time is 60-180 min, the heating temperature is 40-60°C, the ultrasonic output is 100-300 W, the ultrasonic frequency is 60-180 kHz, and the solid-liquid ratio of the calcined waste catalyst to the hydrochloric acid solution is 1-2 kg:1 L. Under ultrasonic and heating conditions, the calcined waste catalyst can be effectively purified by thoroughly acid leaching it with concentrated hydrochloric acid, thereby improving the silicon content.

[0013] Preferably, in step S3, the mass ratio of the filtrate, sodium hydroxide, and sodium fluoride is 1:5 to 6:0.005 to 0.01. Using an excess amount of sodium hydroxide allows the silicon to react sufficiently. The inventors have further discovered that adding a small amount of fluoride ions to the system accelerates the reaction and improves the yield of sodium silicate.

[0014] Preferably, in step S3, the amount of water added is not particularly limited; for example, the amount of water is 10 to 20 times the mass of the filtrate, for example, 15 times, and the reaction by heating and stirring is carried out for 1 to 3 hours under conditions of 70 to 95°C. Filtration is carried out using an ultrafine filtration membrane of 0.3 to 0.5 μm.

[0015] Preferably, in step S4, the polyol is at least one selected from polyethylene glycol and polypropylene glycol, the number average molecular weight of the polyol is 400 to 800, the C1-3 monohydric alcohol is at least one selected from methanol, ethanol and isopropanol, and the number average molecular weight of polydimethyldiallylammonium chloride is 40,000 to 60,000.

[0016] The inventors unexpectedly discovered that when performing a titration reaction of sodium silicate with ammonium chloride, the presence of a certain amount of polyol, a C1-3 monohydric alcohol, and a quaternary ammonium ion surfactant in the system reduces the particle size of the resulting nano-sized silica to 80 nm or less, and also uniformly disperses the resulting nano-sized silica particles. However, it is necessary to appropriately control the relative amounts of polyol, C1-3 monohydric alcohol, and quaternary ammonium ion surfactant used, the chain length (i.e., molecular weight) of the polyol, and the concentration of sodium silicate.

[0017] Preferably, in step S4, in solution A, the concentration of the polyol is 3-5 wt%, the concentration of the C1-3 monohydric alcohol is 30-40 wt%, the concentration of the polydimethyldiallylammonium chloride is 0.2-0.3 wt%, and the concentration of the sodium silicate is 0.4-1.0 mol / L, preferably 0.4-0.6 mol / L. The operation of slowly adding the ammonium chloride solution to solution A is performed by adding the ammonium chloride solution to solution A using a peristaltic pump, and the concentration of the ammonium chloride solution is 1-2 mol / L. The molecular weight and amount of polydimethyldiallylammonium chloride used must be strictly controlled in relation to the amounts of polyol and the C1-3 monohydric alcohol used; otherwise, the effect of small particle size and uniform particle dispersion cannot be achieved.

[0018] Preferably, in step S5, the standing time is 12 to 24 hours, washing is performed by multiple suction filtration and washing with deionized water, drying until a constant weight is reached, and then calcining is performed at 600 to 700°C for 5 to 10 hours. [Effects of the Invention]

[0019] The beneficial effects of this invention are as follows:

[0020] Firstly, this invention produces high-purity nano-sized silica simply by treating calcined organic silicon waste catalyst with acid and alkali, simplifying the process flow, improving recovery rates, reducing the impact of the separation process on the recovered material, as well as energy consumption and costs, and reducing waste generated in the recovery process. At the same time, since no oxidizing agents such as hydrogen peroxide are added, the corrosion resistance requirements of the equipment can be lowered, facilitating industrial adoption.

[0021] Second, when using the manufacturing process of the present invention, especially when performing the titration of ammonium chloride with sodium silicate in step S4, by adding a combination of polyol, a monohydric alcohol with C1-3, and a polymeric polyquaternary ammonium, the obtained nano-sized silica has an average particle size of less than 100 nm, excellent particle size dispersibility, and a span value of 0.5 or less.

[0022] Third, the method for manufacturing nano-silica using the waste organosilicon catalyst of the present invention shows stable performance, realizes effective recovery of silicon in the waste organosilicon catalyst, and improves the market added value of the product.

Brief Description of the Drawings

[0023] [Figure 1] XRD pattern of the nano-sized silica powder obtained in Example 1, PDF#01-082-1555. [Figure 2] SEM image of the nano-sized silica powder obtained in Example 1. [Figure 3] FTIR spectrum of the nano-sized silica powder obtained in Example 1.

Modes for Carrying Out the Invention

[0024] Hereinafter, referring to the drawings of the embodiments of the present invention, the technical solution means of the embodiments of the present invention will be clearly and completely described.

[0025] The organosilicon waste catalyst sample used in the embodiment of the present invention was obtained from an industrial silicon company in Xinjiang. Since Cu had already been recovered and the sample contained carbon, it was first calcined in a muffle furnace at 1000°C for 6 hours, then pulverized in a planetary ball mill, and finally passed through a 200-mesh sieve. The sieved organosilicon waste catalyst was detected and analyzed using an Agilent 5900 plasma emission spectrometer and a Bruker Tiger II X-ray fluorescence analyzer from Germany. Its chemical composition is shown in Table 1, and although all substances except Ag are expressed in oxide form, in reality, silicon in the organosilicon waste catalyst existed almost entirely in elemental form.

[0026] JPEG0007850405000002.jpg5170JPEG0007850405000003.jpg21170

[0027] <Example 1> In S1, the organosilicon waste catalyst was placed in an electric resistance furnace under a mixed gas of oxygen and nitrogen (the volume ratio of oxygen gas to nitrogen gas was 1:9) and calcined at 600°C for 75 minutes to obtain the calcined waste catalyst product.

[0028] In S2, the volume is 12.0 mol·L. -1 A 1 L hydrochloric acid solution was prepared and mixed with 1 kg of spent catalyst calcined material. The mixture was heated to 50°C and continuously stirred for 120 minutes at a rotation speed of 120 rpm under ultrasonic conditions of 200 W and 80 kHz to obtain an acid leaching slurry. The acid leaching slurry was repeatedly washed with a circulating water vacuum pump until the pH of the washing solution became neutral, and then the leaching residue was obtained by suction filtration.

[0029] In step S3, the filtrate, sodium hydroxide, and sodium fluoride were charged in a mass ratio of 1:5:0.01 and mixed uniformly. Then, water equivalent to 15 times the mass of the filtrate was added, the mixture was heated to 90°C, and the reaction was stirred for 100 minutes while maintaining the temperature at 90°C to obtain a sodium silicate solution. This solution was then filtered through a 0.45 μm membrane to obtain a sodium silicate filtrate.

[0030] In S4, PEG400, methanol, and polydimethyldiallylammonium chloride (molecular weight 40000) were added to the sodium silicate filtrate and diluted with water to obtain solution A. The concentration of sodium silicate in solution A was 0.4 mol / L, the concentration of PEG400 was 3 wt%, the concentration of ethanol was 40 wt%, and the concentration of polydimethyldiallylammonium chloride was 0.2 wt%. Under stirring conditions, a 2.0 mol / L ammonium chloride solution was added to solution A using a peristaltic pump. During the dropwise addition process, the pH was monitored in real time, and when the pH of the system reached 7, the addition of ammonium chloride was stopped to obtain a gel-like substance.

[0031] In S5, the gel-like substance was allowed to mature for 24 hours, then repeatedly washed using a circulating water vacuum pump, filtered by suction, and subsequently dried at 105°C in an electric blast dryer. The dried product was then pulverized, and subsequently baked in a muffle furnace at 600°C for 4 hours, followed by pulverization in a planetary ball mill to obtain nano-sized silica powder with a purity of 98.72% and a yield of 96.13%. The purity was measured using an X-ray fluorescence analyzer, and the yield y was calculated according to the following formula: m1 was the mass of the organosilicon waste catalyst that can theoretically be converted to SiO2, and m2 was the mass of the final product, nano-sized silica powder. JPEG0007850405000004.jpg11170

[0032] The composition of nano-sized silica powder was measured using a Bruker Tiger II X-ray fluorescence analyzer from Germany. The results are shown in Table 2 below.

[0033] JPEG0007850405000005.jpg31170

[0034] In step S2, 6 mol·L -1When acid leaching with hydrochloric acid, the SiO₂ content in the finally obtained nano-sized silica was 96.04%. When the acid leaching in step S2 was not carried out, the SiO₂ content in the finally obtained product was 91.72%. Therefore, the acid leaching step can significantly improve the purity of the product, and it was desirable to use 10 - 12 mol·L -1 of hydrochloric acid.

[0035] Figure 1 is the XRD pattern of the nano-sized silica powder obtained in Example 1 and the standard PDF card #01 - 082 - 1555 of amorphous SiO₂. Since a large, broad and flat peak was observed at 2θ = 23°, the sample was considered to be amorphous nano-silica.

[0036] Figure 2 is the SEM image of the nano-sized silica powder obtained in Example 1.

[0037] Figure 3 is the FTIR spectrum of the nano-sized silica powder obtained in Example 1. A relatively broad absorption band was observed at 3471 cm -1 and a sharp absorption band was observed at 1635 cm -1 which was due to the O - H bond in the SiO₂ precursor particles. Strong absorption bands were observed at 802 cm -1 and 462 cm -1 and these absorption peaks indicated the formation of the Si - O - Si bond, which were characteristics of the silica material. The peak value at 1091 cm -1 indicated the formation of the Si - O - Si asymmetric vibration. Therefore, the FTIR spectrum indicated the formation of the nano-silica material, and the FTIR analysis supported the XRD results.

[0038] <Example 2> Other conditions were the same as in Example 1, and the difference was that in step S3, the filter residue, sodium hydroxide and sodium fluoride were charged at a mass ratio of 1:6:0.005.

[0039] <Example 3> The other conditions were the same as in Example 1, the only difference being that in step S4, PEG400 was replaced with PEG800, and the concentration of PEG800 in solution A was set to 5 wt% and the concentration of ethanol to 30 wt%.

[0040] <Example 4> The other conditions were the same as in Example 1, the only difference being that in step S4, the molecular weight of polydimethyldiallylammonium chloride was set to 60,000 and the concentration of polydimethyldiallylammonium chloride in solution A was set to 0.3 wt%.

[0041] <Example 5> The other conditions were the same as in Example 1, the only difference being that in step S4, the concentration of polydimethyldiallylammonium chloride in solution A was set to 0.1 wt%.

[0042] <Example 6> The other conditions were the same as in Example 1, the only difference being that in step S4, the concentration of polydimethyldiallylammonium chloride in solution A was set to 0.4 wt%.

[0043] <Comparative Example 1> The other conditions were the same as in Example 1, the only difference being that sodium fluoride was not added in step S3.

[0044] <Comparative Example 2> The other conditions were the same as in Example 1, the only difference being that PEG400 was not added in step S4.

[0045] <Comparative Example 3> The other conditions were the same as in Example 1, the only difference being that ethanol was not added in step S4.

[0046] <Comparative Example 4> The other conditions were the same as in Example 1, the only difference being that polydimethyldiallylammonium chloride was not added in step S4.

[0047] <Comparative Example 5> Other conditions were the same as in Example 1, the only difference being that in step S4, a 1.0 mol / L sulfuric acid solution was added to solution A using a peristaltic pump.

[0048] The indicators for the nano-sized silica products obtained in the above examples and comparative examples are shown in Table 3 below.

[0049] JPEG0007850405000006.jpg67170

[0050] The span value indicates the particle size dispersion, and it was explained that a smaller span value indicates a narrower particle size dispersion. The span value was calculated using the following formula. JPEG0007850405000007.jpg13170

[0051] Large quantities of silicon-containing waste generated from various silicon production companies have the potential to be used to produce nanosilica. By calcining organosilicon waste catalysts and then performing sonication and acid leaching treatments with 12 mol / L hydrochloric acid, the purity of SiO2 was improved, achieving a yield of over 94%. By using NH4Cl as a precipitating agent and modifying it with polyethylene glycol, low molecular weight alcohols, and polyquaternium, we succeeded in producing nanosilica particles with a particle size of approximately 100 nm, a spherical shape, excellent dispersibility, and an amorphous structure. The method of the present invention not only effectively reduces resource waste and landfill costs, but also avoids environmental pollution caused by landfill.

Claims

1. A method for producing nanosilica using organosilicon waste catalysts, Step S1 involves calcining an organosilicon waste catalyst under a mixed gas of oxygen and nitrogen to obtain a calcined waste catalyst product. Step S2 involves mixing the calcined waste catalyst with concentrated hydrochloric acid, continuously stirring under ultrasonic conditions while heating to obtain an acid leaching slurry, and then repeatedly washing with water and suction filtration until the filtrate becomes neutral to obtain the filtrate. Step S3 involves uniformly mixing the filtrate obtained in S2 with sodium hydroxide and sodium fluoride, adding water and mixing uniformly, heating and stirring to allow the reaction to occur, and then filtering to obtain a sodium silicate solution. Step S4 involves adding a polyol, a C1-3 monohydric alcohol, and polydimethyldiallylammonium chloride to a sodium silicate solution to obtain solution A, slowly adding ammonium chloride solution to solution A, and adjusting the amount of ammonium chloride solution used so that the pH of the mixed solution becomes 6-7 to obtain a gel substance. A method for producing nanosilica using an organosilicon waste catalyst, characterized by comprising step S5, which involves allowing a gel-like substance to mature, followed by washing, suction filtration, drying, calcination, and pulverization to obtain nano-sized silica.

2. The method for producing nanosilica using an organosilicon waste catalyst according to claim 1, characterized in that in step S1, the volume percentage of oxygen gas in the mixed gas is 5 to 20%, the calcination temperature is 600 to 1000°C, and the calcination time is 30 to 90 min.

3. In step S2, the hydrochloric acid concentration is 6-12 mol·L. －１ The method for producing nanosilica using an organosilicon waste catalyst according to claim 1, characterized in that the acid leaching time is 60 to 180 min, the heating temperature is 40 to 60°C, the ultrasonic output is 100 to 300 W, the ultrasonic frequency is 60 to 180 kHz, and the solid-liquid ratio of the calcined waste catalyst to the hydrochloric acid solution is 1 to 2 kg:1 L.

4. The method for producing nanosilica using an organosilicon waste catalyst according to claim 1, characterized in that in step S3, the mass ratio of the filtrate, sodium hydroxide, and sodium fluoride is 1:5 to 6:0.005 to 0.

01.

5. The method for producing nanosilica using an organosilicon waste catalyst according to claim 1, characterized in that in step S3, the amount of water added is 10 to 20 times the mass of the filtrate, the reaction by heating and stirring is carried out for 1 to 3 hours under conditions of 70 to 95°C, and filtration is carried out using an ultrafine filtration membrane of 0.3 to 0.5 μm.

6. The method for producing nanosilica using an organosilicon waste catalyst according to claim 1, characterized in that, in step S4, the polyol is at least one selected from polyethylene glycol and polypropylene glycol, the number average molecular weight of the polyol is 400 to 800, the C1-3 monohydric alcohol is at least one selected from methanol, ethanol and isopropanol, and the number average molecular weight of polydimethyldiallylammonium chloride is 40,000 to 60,000.

7. The method for producing nanosilica using an organosilicon waste catalyst according to claim 1, characterized in that in step S4, the concentration of polyol in solution A is 3 to 5 wt%, the concentration of monohydric alcohol C1-3 is 30 to 40 wt%, the concentration of polydimethyldiallylammonium chloride is 0.2 to 0.3 wt%, and the concentration of sodium silicate is 0.4 to 1.0 mol / L.

8. The method for producing nanosilica using an organosilicon waste catalyst according to claim 7, characterized in that the concentration of sodium silicate in solution A is 0.4 to 0.6 mol / L.

9. The method for producing nanosilica using an organosilicon waste catalyst according to claim 1, characterized in that in step S5, the standing time is 12 to 24 hours, washing is performed by multiple suction filtration and washing with deionized water, drying until a constant weight is reached, and then calcining at 600 to 700°C for 5 to 10 hours.

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