Method for preparing high-purity nano-silica from silicone waste catalyst

Abstract

The present application relates to a kind of organic silicon waste body preparation nanometer silicon dioxide method, to reduce landfill volume and the harm of hazardous waste to environment.Organic silicon waste body is pretreated properly, then impurity is removed by acid leaching with HCl, then, Na2SiO3 is prepared by direct reaction of NaOH with residue.In the preparation process, Na2SiO3 is used as silicon source, NH4Cl is used as precipitant, and the catalytic hydroxyl self-condensation of Na2SiO3 is carried out in polyhydric alcohol / small molecule alcohol / polyquaternary ammonium salt / aqueous solvent system.The influence of the ratio of polyhydric alcohol, ethanol and polyquaternary ammonium salt on the particle size, dispersibility and shape of amorphous SiO2 nanoparticles is investigated.Finally, the silicon-containing solid waste is prepared into well-dispersed spherical amorphous SiO2 nanoparticles, with high yield and purity, particle size near 100nm, and uniform particle size distribution.

Description

Technical Field

[0001] This invention belongs to the field of hazardous waste resource recycling and environmental protection technology, and relates to a method for preparing nano-silica from organosilicon waste catalyst. Background Technology

[0002] The most important and complex part of the production process is the synthesis of methylchlorosilane monomers. The direct method is widely used due to its simplicity, high yield, solvent-free operation, low risk, and ease of continuous large-scale production. This method uses ternary copper as a catalyst, which is mixed with silicon powder to form an active catalyst catalyst, playing a crucial role in improving the selectivity and yield of methylchlorosilanes. During the continuous reaction, impurity accumulation and catalyst deactivation significantly reduce the conversion rate of silicon powder and the selectivity of dimethylchlorosilane (M2). The industrial waste formed by removing unreacted silicon powder and deactivated catalyst from the reactor to maintain stable production is called organosilicon waste catalyst.

[0003] Traditionally, on-site landfilling was a common method for disposing of waste organosilicon catalysts. This method not only causes significant environmental pollution but also results in the loss of substantial amounts of valuable resources such as silicon and copper. In recent years, research on the resource recovery of waste catalysts has primarily focused on chemically treating them to form metal salt solutions, then using chemical reduction and electrolysis to prepare various metals and their derivatives. The residues are then purified chemically and physically to obtain silicon powder. In this process, separation conditions greatly affect the effectiveness of solid-liquid phase separation, and the process is relatively complex, easily generating new waste and increasing the processing burden and energy consumption. Simultaneously, the solid-liquid phase separation process also affects the utilization rate and performance of recovered materials such as silicon. Current technologies for the recycling of organosilicon waste catalysts mainly focus on recovering copper resources, while reports on silicon resources primarily focus on methods for recovering silicon powder.

[0004] CN117416963A discloses a method for preparing silicon powder from waste organosilicon catalysts, comprising the following steps: (1) removing copper from the waste organosilicon catalysts to obtain copper-removed slag; (2) mixing the copper-removed slag with water to form a slurry; (3) subjecting the slurry to two-stage magnetic separation to obtain a silicon-rich non-magnetic product; and (4) calcining, acid washing, and drying the silicon-rich non-magnetic product to obtain silicon powder.

[0005] CN115181998A discloses a method for recovering silicon powder from waste organosilicon catalysts, comprising the following steps: oxidative acid leaching: adding waste organosilicon catalysts, sulfuric acid solution A, and a modifier to an air-flotation mechanical stirring coupled leaching tank; introducing air into the air-flotation mechanical stirring coupled leaching tank and continuously operating a scraper to remove the surface air-flotation layer; mechanical stirring for oxidative leaching to obtain a leaching slurry; solid-liquid separation: separating the leaching slurry into solid and liquid components to obtain a copper-containing leaching solution and leaching residue; washing, pressing, filtering, and neutralizing the leaching residue to obtain silicon powder.

[0006] CN115058586A discloses a method for recovering silicon powder from waste organosilicon catalysts, comprising the following steps: ball milling the waste organosilicon catalysts to obtain a slurry, then magnetically separating the slurry to remove iron, and pressing and filtering to obtain copper-containing waste silicon powder after iron removal; adding the copper-containing waste silicon powder after iron removal and 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 surface air flotation layer, mechanically stirring to perform oxidative leaching, and after leaching, separating the solid and liquid to obtain leaching residue and copper-containing leaching solution; and washing and pressing and filtering the leaching residue to obtain washing filtrate and silicon powder.

[0007] The existing technology described above recovers silicon powder from waste organosilicon catalysts, but its economic value is not high. Through research, there are currently few reports on the preparation of nano-sized silicon dioxide using waste organosilicon catalysts as raw materials. Summary of the Invention

[0008] To overcome the difficulty of preparing nano-sized silica from waste organosilicon catalysts, this invention, after separating impurities from the waste organosilicon catalysts, does not add oxidants such as hydrogen peroxide. Instead, it uses only acid leaching and filtration, followed by solid-liquid separation with sodium hydroxide, titration, and further filtration. Finally, the gel is dried and calcined to remove volatile impurities, yielding uniformly dispersed nano-sized silica. This simplifies the recycling process, reduces waste generation, minimizes the impact of the recycling process on the recovered materials, and reduces energy consumption and costs. It also improves the effective recovery of silicon from waste organosilicon catalysts and increases their market value, thus alleviating environmental pressure. This invention achieves the above objectives through the following technical solution:

[0009] A method for preparing nano-silica from organosilicon waste includes the following steps:

[0010] S1. Under a mixed gas of oxygen and nitrogen, the waste silicone catalyst is calcined to obtain the waste catalyst calcination material.

[0011] S2. The waste catalyst roasting material and concentrated hydrochloric acid are mixed, heated and stirred continuously under ultrasonic conditions to obtain acid leaching slurry. The slurry is washed and filtered multiple times until the filtrate is neutral to obtain filter residue.

[0012] The filter residues obtained from S3 and S2 are mixed evenly with sodium hydroxide and sodium fluoride, water is added and mixed evenly, heated and stirred to carry out the reaction, and filtered to obtain sodium silicate solution.

[0013] S4. Polypolyol, C1-3 monohydric alcohol, and polydimethyldiallylammonium chloride are added to sodium silicate solution to obtain solution A. Ammonium chloride solution is slowly added to solution A, and the amount of ammonium chloride solution is adjusted to make the pH of the mixed solution 6-7, thus obtaining a gel-like substance.

[0014] S5. After the gel-like substance is left to stand and age, it is washed, filtered, dried, calcined, and ground to obtain nano-sized silica.

[0015] Preferably, in step S1, oxygen accounts for 5-20% of the volume of the mixed gas, the calcination temperature is 600-1000℃, and the calcination time is 30-90 min.

[0016] Preferably, in step S2, the concentration of hydrochloric acid is 6–12 mol·L⁻¹. -1 Preferably 10–12 mol·L -1 The acid leaching time is 60–180 min, the heating temperature is 40–60℃, the ultrasonic power is 100–300 W, and the ultrasonic frequency is 60–180 kHz. The solid-liquid ratio of the waste catalyst roasting material to the hydrochloric acid solution is 1–2 kg:1 L. Under ultrasonic and heating conditions, thorough acid leaching of the waste catalyst roasting material with concentrated hydrochloric acid can effectively remove impurities and increase the silicon content.

[0017] Preferably, in step S3, the mass ratio of filter residue, sodium hydroxide, and sodium fluoride is 1:5-6:0.005-0.01. Excess sodium hydroxide ensures complete reaction of silicon. The inventors also discovered that adding a small amount of fluoride ions to the system promotes the reaction and increases the yield of sodium silicate.

[0018] Preferably, in step S3, the amount of water added is not particularly limited; for example, the water can be 10-20 times, or even 15 times, the mass of the filter residue. The heating and stirring reaction is carried out at 70-95°C for 1-3 hours. Filtration is performed using a 0.3-0.5μm ultrafine filter membrane.

[0019] Preferably, in step S4, the polyol is selected from at least one of polyethylene glycol and polypropylene glycol, and the number average molecular weight of the polyol is 400-800; the C1-3 monohydric alcohol is selected from at least one of methanol, ethanol, and isopropanol; and the number average molecular weight of polydimethyldiallylammonium chloride is 40,000-60,000.

[0020] The inventors unexpectedly discovered that during the titration reaction of ammonium chloride with sodium silicate, the presence of a certain amount of polyol, C1-3 monohydric alcohol, and quaternary ammonium salt cationic surfactant in the system could reduce the particle size of the resulting nano-sized silica to below 80 nm, and the resulting nano-sized silica particles were uniformly dispersed. However, it is necessary to reasonably control the relative amounts of polyol, C1-3 monohydric alcohol, and quaternary ammonium salt cationic surfactant, the chain length (i.e., molecular weight) of the polyol, and the concentration of sodium silicate.

[0021] 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 polydimethyldiallyl ammonium chloride is 0.2-0.3 wt%, and the concentration of sodium silicate is 0.4-1.0 mol / L, preferably 0.4-0.6 mol / L. The ammonium chloride solution is slowly added to solution A using a peristaltic pump, and the concentration of the ammonium chloride solution is 1-2 mol / L. The amount of C1-3 monohydric alcohol used, relative to the polyol, requires strict control of the molecular weight and amount of polydimethyldiallyl ammonium chloride; otherwise, the effect of small particle size and uniform particle dispersion cannot be achieved.

[0022] Preferably, in step S5, the standing time is 12-24 hours, the washing is performed by multiple filtrations with deionized water, the product is dried to constant weight, and then calcined at 600-700℃ for 5-10 hours.

[0023] The beneficial effects of this invention are:

[0024] I. This invention prepares high-purity nano-sized silica by treating organosilicon waste catalyst calcination material with acids and alkalis. It simplifies the process, improves the recovery rate, reduces the impact of the separation process on the recovered material, as well as energy consumption and costs, and minimizes waste generated during the recycling process. Furthermore, the absence of oxidants such as hydrogen peroxide reduces the requirements for equipment corrosion resistance, facilitating industrial-scale application.

[0025] 2. Using the preparation process of this invention, especially during the titration of sodium silicate with ammonium chloride in step S4, a combination of polypolyol, C1-3 monohydric alcohol and high molecular weight polyquaternary ammonium salt is added. The resulting nano-sized silica has an average particle size of less than 100 nm and good particle size dispersibility with a span value of less than 0.5.

[0026] Third, the preparation method of this invention is stable, effectively recovers silicon from organosilicon waste catalysts, and improves the market added value of the product. Attached Figure Description

[0027] Figure 1 The XRD patterns are those of the nano-sized silica powder obtained in Example 1 and PDF#01-082-1555.

[0028] Figure 2 This is a SEM image of the nanoscale silica powder obtained in Example 1.

[0029] Figure 3 This is the FTIR image of the nanoscale silica powder obtained in Example 1. Detailed Implementation

[0030] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

[0031] The organosilicon waste catalyst samples used in this embodiment of the invention came from an industrial silicon enterprise in Xinjiang. Cu had already been recovered. Because it contained carbon, it was first calcined in a muffle furnace at 1000℃ for 6 hours, then ground using a planetary ball mill and passed through a 200-mesh sieve. The sieved organosilicon waste catalyst was analyzed using an Agilent 5900 plasma atomic emission spectrometer and a Bruker Tiger II X-ray fluorescence spectrometer. Its chemical composition is shown in Table 1. Except for Ag, all substances are expressed in oxide form. In fact, in organosilicon waste catalyst, silicon mostly exists in elemental form.

[0032] Table 1 Chemical composition of organosilicon waste catalyst

[0033] composition <![CDATA[SiO2]]> <![CDATA[Fe2O3]]> <![CDATA[Al2O3]]> CaO <![CDATA[SO3]]> <![CDATA[TiO2]]> Ag <![CDATA[Na2O]]> <![CDATA[P2O5]]> CuO content(%) 89.000 3.683 2.570 2.375 1.360 0.416 0.219 0.060 0.053 0.051

[0034] Example 1

[0035] S1. Under a mixed gas of oxygen and nitrogen (the volume ratio of oxygen to nitrogen is 1:9), the waste silicone catalyst is placed in a resistance furnace and roasted at 600°C for 75 minutes to obtain the waste catalyst roasting material.

[0036] S2, prepare 12.0 mol·L -1 1L of hydrochloric acid solution was mixed with 1kg of waste catalyst calcination material, heated to 50℃, and stirred continuously at 120rpm for 120min under ultrasonic conditions of 200W and 80kHz to obtain acid leaching slurry; the acid leaching slurry was repeatedly washed with a circulating water vacuum pump until the pH of the washing liquid was neutral, and the leaching residue was obtained by vacuum filtration.

[0037] S3, filter residue, sodium hydroxide, and sodium fluoride are added in a mass ratio of 1:5:0.01, mixed evenly, and then 15 times the mass of water is added to the filter residue. The mixture is heated to 90°C and stirred for 100 minutes to obtain a sodium silicate solution. The solution is then filtered through a 0.45μm membrane to obtain a sodium silicate filtrate.

[0038] S4. PEG400, methanol, and polydimethyldiallyl ammonium 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 PEG600 was 3 wt%, the concentration of ethanol was 40 wt%, and the concentration of polydimethyldiallyl ammonium 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. The pH was monitored in real time during the dropwise addition process. When the pH of the system reached 7, the addition of ammonium chloride was stopped, and a gel-like substance was obtained.

[0039] S5. The gel-like substance was allowed to stand for 24 hours, then repeatedly washed and filtered using a circulating water vacuum pump. Afterward, it was dried at 105℃ in an electric heating drying oven. The dried product was then ground and calcined in a muffle furnace at 600℃ for 4 hours. Finally, it was ground using a planetary ball mill to obtain nano-sized silica powder with a purity of 98.72% and a yield of 96.13%. Purity was measured using X-ray fluorescence spectrometry. The yield y was calculated using the following formula: m1 is the mass of the organosilicon waste that can theoretically be converted into SiO2, and m2 is the mass of the final nano-sized silica powder.

[0040]

[0041] The composition of nano-sized silica powder was determined using a Bruker Tiger II X-ray fluorescence spectrometer (Germany). The results are shown in Table 2 below:

[0042] Table 2 12 mol·L -1 XRF analysis of nano-silica samples prepared by hydrochloric acid leaching

[0043]

[0044] If 6 mol·L⁻¹ is used in step S2 -1 Acid leaching with hydrochloric acid results in nano-sized silica with a SiO2 content of 96.04%. Without acid leaching in step S2, the final product has a SiO2 content of 91.72%. Therefore, the acid leaching step significantly improves product purity, using 10⁻¹² mol·L⁻¹. -1 Hydrochloric acid is preferred.

[0045] Figure 1 This is the XRD pattern of the standard PDF card #01-082-1555 for the nano-sized silica powder and amorphous SiO2 obtained in Example 1. A large, broad, and flat peak was observed at 2θ = 23°, therefore, the sample is considered to be amorphous nano-silica.

[0046] Figure 2 This is a SEM image of the nanoscale silica powder obtained in Example 1.

[0047] Figure 3 This is the FTIR spectrum of the nanoscale silica powder obtained in Example 1. (At 3471 cm⁻¹) -1 There is a relatively wide absorption band at 1635cm. -1 There is a sharp absorption band at 802 cm⁻¹, which is attributed to the OH bonds in the SiO₂ precursor particles. -1 and 462cm -1A strong absorption band was observed at 1091 cm⁻¹, and these absorption peaks indicate the formation of Si-O-Si bonds, which is characteristic of silicon dioxide materials. -1 The peak value indicates the formation of Si-O-Si asymmetric vibrations. Therefore, FTIR spectroscopy confirms the formation of nano-silica material, and FTIR analysis supports the XRD results.

[0048] Example 2

[0049] The other conditions are the same as in Example 1, except that in step S3, the filter residue, sodium hydroxide, and sodium fluoride are fed in a mass ratio of 1:6:0.005.

[0050] Example 3

[0051] The other conditions are the same as in Example 1, except that in step S4, PEG400 is replaced with PEG800, and the concentration of PEG800 in solution A is 5 wt%; the concentration of ethanol is 30 wt%.

[0052] Example 4

[0053] The other conditions are the same as in Example 1, except that in step S4, the molecular weight of polydimethyldiallyl ammonium chloride is 60,000, and the concentration of polydimethyldiallyl ammonium chloride in solution A is 0.3 wt%.

[0054] Example 5

[0055] The other conditions are the same as in Example 1, except that in step S4, the concentration of polydimethyldiallylammonium chloride in solution A is 0.1 wt%.

[0056] Example 6

[0057] The other conditions are the same as in Example 1, except that in step S4, the concentration of polydimethyldiallylammonium chloride in solution A is 0.4 wt%.

[0058] Comparative Example 1

[0059] The other conditions are the same as in Example 1, except that sodium fluoride is not added in step S3.

[0060] Comparative Example 2

[0061] The other conditions are the same as in Example 1, except that PEG400 is not added in step S4.

[0062] Comparative Example 3

[0063] The other conditions are the same as in Example 1, except that ethanol is not added in step S4.

[0064] Comparative Example 4

[0065] The other conditions are the same as in Example 1, except that polydimethyldiallyl ammonium chloride is not added in step S4.

[0066] Comparative Example 5

[0067] The other conditions are the same as in Example 1, except that in step S4, a 1.0 mol / L sulfuric acid solution is added to solution A by a peristaltic pump.

[0068] The specifications of the nanoscale silica products obtained from the above embodiments and comparative examples are listed in Table 3 below.

[0069] Table 3. Indicators of Nanoscale Carbon Dioxide Products

[0070]

[0071]

[0072] Span represents the particle size distribution of microparticles; a smaller span value indicates a narrower particle size distribution. The span value is calculated using the following formula:

[0073] The large quantities of silicon-containing waste generated by various silicon production enterprises have the potential to produce nano-silica. By first calcining the organosilicon waste and then ultrasonically leaching it with 12 mol / L hydrochloric acid, the purity of SiO2 is improved, and the yield can reach over 94%. Using NH4Cl as a precipitant, and modifying it with polyethylene glycol, small molecule alcohols, and polyquaternary ammonium salts, nano-silica particles with a particle size around 100 nm, spherical shape, good dispersibility, and amorphous structure were successfully prepared. This invention effectively reduces resource waste and landfill costs, and also avoids environmental pollution caused by landfilling.

Claims

1. A method for preparing nano-silica from organosilicon waste catalyst, characterized in that, Includes the following steps: S1. Under a mixed gas of oxygen and nitrogen, the waste silicone catalyst is calcined to obtain the waste catalyst calcination material. S2. The waste catalyst roasting material and concentrated hydrochloric acid are mixed, heated and stirred continuously under ultrasonic conditions to obtain acid leaching slurry. The slurry is washed and filtered multiple times until the filtrate is neutral to obtain filter residue. The filter residues obtained from S3 and S2 are mixed evenly with sodium hydroxide and sodium fluoride, water is added and mixed evenly, heated and stirred to carry out the reaction, and filtered to obtain sodium silicate solution. The mass ratio of filter residue, sodium hydroxide, and sodium fluoride is 1:5-6:0.005-0.01; S4. Polypolyol, C1-3 monohydric alcohol, and polydimethyldiallyl ammonium chloride are added to sodium silicate solution to obtain solution A. Ammonium chloride solution is slowly added to solution A, and the amount of ammonium chloride solution is adjusted to make the pH of the mixed solution 6-7, resulting in a gel-like substance. In solution A, the concentration of polypolyol is 3-5 wt%, the concentration of C1-3 monohydric alcohol is 30-40 wt%, the concentration of polydimethyldiallyl ammonium chloride is 0.2-0.3 wt%, and the concentration of sodium silicate is 0.4-1.0 mol / L. S5. After the gel-like substance is left to stand and age, it is washed, filtered, dried, calcined, and ground to obtain nano-sized silica.

2. The method according to claim 1, characterized in that, In step S1, oxygen accounts for 5-20% of the volume in the mixed gas, the calcination temperature is 600-1000℃, and the calcination time is 30-90min.

3. The method according to claim 1, characterized in that, In step S2, the concentration of hydrochloric acid is 6~12 mol•L. -1 The acid leaching time is 60-180 min, the heating temperature is 40-60℃, the ultrasonic power is 100-300W, and the ultrasonic frequency is 60-180kHz; the solid-liquid ratio of the waste catalyst roasting material to the hydrochloric acid solution is 1-2 kg: 1 L.

4. The method according to claim 3, characterized in that, In step S2, the concentration of hydrochloric acid is 10~12 mol•L. -1 .

5. The method according to claim 1, characterized in that, In step S3, the amount of water added is 10-20 times the mass of the filter residue; the reaction is carried out by heating and stirring at 70-95℃ for 1-3 hours; and filtration is performed using a 0.3-0.5μm ultrafine filter membrane.

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

7. The method according to claim 1, characterized in that, In solution A, the concentration of sodium silicate is 0.4-0.6 mol / L.

8. The method according to claim 1, characterized in that, In step S5, the standing time is 12-24 hours, the washing is done by multiple filtrations with deionized water, the drying is done to constant weight, and the calcination is carried out at 600-700℃ for 5-10 hours.

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