Method for preparing silica sol by using silicate

Abstract

The invention belongs to the field of fine chemical engineering, and particularly relates to a method for preparing silica sol by using silicate, which comprises the following steps: a) dropwise adding an acidic salt aqueous solution into a silicate aqueous solution under a stirring condition; when the pH value of the mixed system is reduced to 5.5-6, stopping dropwise adding the acidic salt aqueous solution to obtain a silica sol semi-finished product; in the step a), silicate in the silicate aqueous solution is sodium silicate and / or potassium silicate; b) mixing the silica sol semi-finished product with a protective colloid aqueous solution, and defoaming to obtain colloid-protected silica sol; in the step b), the protective colloid in the protective colloid aqueous solution is one or more of polyvinyl alcohol, polyvinylpyrrolidone and polyacrylic acid; the mark of the polyvinyl alcohol is one or more of polyvinyl alcohol (PVA)-1788, polyvinyl alcohol (PVA)-2488 and polyvinyl alcohol (PVA)-0588. The method provided by the invention is simple in process, low in production cost and high in production efficiency, and the prepared silica sol has high stability.

Description

Technical Field

[0001] The invention belongs to the field of fine chemicals, and in particular relates to a method for preparing silica sol by using silicate. Background Art

[0002] Silica sol is a dispersion of nanometer-sized silica particles in water or other solvents. It is amorphous, spherical silica with silanol groups on its surface, resulting in a high specific surface area and high adsorption capacity. It appears as a milky white or colorless, transparent liquid with good fluidity. Silica sol has a wide range of applications in biomedicine, coatings, and surface engineering.

[0003] With increasing environmental protection requirements, chromium-free surface treatment technologies are becoming increasingly popular among existing surface treatment technologies. Chromates contain hexavalent chromium, a toxic and harmful heavy metal with strong oxidizing and carcinogenic properties. The discharge of hexavalent chromium into wastewater can cause serious pollution to water bodies, soil, and other environmental environments, and poses a serious health hazard to humans exposed to it. Silica sol, on the other hand, is primarily composed of silicon dioxide and water and contains no toxic heavy metals. It does not generate heavy metal pollution during use and therefore meets environmental requirements. Silica sol forms a uniform, dense protective film of silicon dioxide on metal surfaces. This film effectively blocks contact with air, moisture, and other corrosive media, thereby improving the metal's corrosion resistance and self-lubricity. Its protective effect is comparable to that of chromic acid passivation, and in some cases, even superior.

[0004] However, silica sol used for chromium-free surface treatment faces the following problems: ① Metal surface treatment liquids are generally acidic. At acidic pH, nano-silica will combine with water to form silicic acid, which undergoes condensation polymerization, forming polysilicic acid or amorphous silica. As the silica particles grow and aggregate, a visible precipitate eventually forms, making the metal surface treatment liquid unstable for storage and unusable. ② Traditional processes generally use silicates as raw materials to synthesize silica sol, such as tetramethoxysilane, propyl silicate, and butyl silicate. Silicates are generally expensive, and the hydrolysis and condensation reactions require strictly controlled conditions, resulting in long reaction times and relatively low production efficiency. In addition, a large amount of alcohol byproducts are produced during the reaction, increasing production costs and process complexity. Summary of the Invention

[0005] In view of this, an object of the present invention is to provide a method for preparing silica sol using silicate, which has simple process, low production cost, high production efficiency, and the prepared silica sol has high stability.

[0006] The present invention provides a method for preparing silica sol using silicate, comprising the following steps:

[0007] a) adding an acid salt solution dropwise to a silicate solution under stirring; stopping the addition of the acid salt solution when the pH of the mixed system drops to 5.5 to 6 to obtain a semi-finished silica sol;

[0008] In step a), the silicate in the silicate aqueous solution is sodium silicate and / or potassium silicate;

[0009] b) mixing the silica sol semi-finished product with a protective colloid aqueous solution and defoaming to obtain a colloid-protected silica sol;

[0010] In step b), the protective colloid in the protective colloid aqueous solution is one or more of polyvinyl alcohol, polyvinyl pyrrolidone and polyacrylic acid; the brand of the polyvinyl alcohol is one or more of PVA-1788, PVA-2488 and PVA-0588.

[0011] Preferably, in step a), the acid salt in the acid salt aqueous solution is one or more of sodium dihydrogen phosphate, zinc dihydrogen phosphate, copper sulfate, aluminum nitrate and aluminum sulfate.

[0012] Preferably, in step a), the mass ratio of silicate to water in the silicate aqueous solution is (1-10):100.

[0013] Preferably, in step a), the mass ratio of acid salt to water in the acid salt solution is (0.5-5):100.

[0014] Preferably, in step a), the stirring speed is 500-2000 r / min.

[0015] Preferably, in step b), the brand of polyvinyl pyrrolidone is one or more of PVP-K30, PVP-K25, PVP-C15 and PVP-C30.

[0016] Preferably, in step b), the mass ratio of protective colloid to water in the protective colloid aqueous solution is (5-20):100.

[0017] Preferably, in step b), the mass ratio of the silica sol semi-finished product to the protective colloid in the protective colloid aqueous solution, calculated based on the raw silicate for preparation, is 1:(1-5).

[0018] Preferably, in step b), a defoaming agent is also added during the mixing process.

[0019] Preferably, the defoaming agent is one or more of an organosilicon defoaming agent, a polyether defoaming agent and a silane coupling agent.

[0020] Compared with the prior art, the present invention provides a method for preparing silica sol using silicate, comprising the following steps: a) adding an acidic salt solution dropwise to a silicate solution under stirring; when the pH of the mixed system drops to 5.5-6, stopping the addition of the acidic salt solution to obtain a silica sol semi-finished product; in step a), the silicate in the silicate solution is sodium silicate and / or potassium silicate; b) mixing the silica sol semi-finished product with a protective colloid solution, defoaming, and obtaining a colloid-protected silica sol; in step b), the protective colloid in the protective colloid solution is one or more of polyvinyl alcohol, polyvinyl pyrrolidone, and polyacrylic acid; the brand of the polyvinyl alcohol is one or more of PVA-1788, PVA-2488, and PVA-0588. The method provided by the present invention has a simple process, low production cost, high production efficiency, and the prepared silica sol has a high stability. More specifically, the method of the present invention has at least the following advantages:

[0021] (1) Using low-cost inorganic silicates to synthesize silica sol, the preparation method is simple and the production efficiency is high;

[0022] (2) Using acid salts for pH adjustment avoids the precipitation of silica sol caused by strong acid, thereby improving production efficiency;

[0023] (3) The semi-finished silica sol is directly mixed into the protective colloid without the need for separate drying and redispersion, which simplifies the production process and improves production efficiency;

[0024] (4) The prepared silica sol is highly stable and has good application prospects in the fields of coating additives, surface treatment agents, etc. DETAILED DESCRIPTION

[0025] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the described embodiments 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 any creative efforts are within the scope of protection of the present invention.

[0026] The present invention provides a method for preparing silica sol using silicate, comprising the following steps:

[0027] a) adding an acid salt solution dropwise to a silicate solution under stirring; stopping the addition of the acid salt solution when the pH of the mixed system drops to 5.5 to 6 to obtain a semi-finished silica sol;

[0028] b) mixing the silica sol semi-finished product with a protective colloid aqueous solution and defoaming to obtain a colloid-protected silica sol.

[0029] In the method provided by the present invention, in step a), the acid salt in the acid salt aqueous solution is preferably one or more of sodium dihydrogen phosphate, zinc dihydrogen phosphate, copper sulfate, aluminum nitrate and aluminum sulfate, more preferably aluminum nitrate.

[0030] In the method provided by the present invention, in step a), the mass ratio of acid salt to water in the acid salt aqueous solution is preferably (0.5-5):100, specifically 0.5:100, 1:100, 1.5:100, 2:100, 2.5:100, 3:100, 3.5:100, 4:100, 4.5:100 or 5:100.

[0031] In the method provided by the present invention, in step a), the silicate in the silicate aqueous solution is sodium silicate and / or potassium silicate, preferably potassium silicate (which has better solubility and chemical stability than sodium silicate).

[0032] In the method provided by the present invention, in step a), the mass ratio of silicate to water in the silicate aqueous solution is preferably (1-10):100, specifically 1:100, 2:100, 3:100, 4:100, 5:100, 6:100, 7:100, 8:100, 9:100 or 10:100.

[0033] In the method provided by the present invention, in step a), the dropping speed of the acidic salt solution is preferably 0.5 to 5 mL / min, specifically 0.5 mL / min, 1 mL / min, 1.5 mL / min, 2 mL / min, 2.5 mL / min, 3 mL / min, 3.5 mL / min, 4 mL / min, 4.5 mL / min or 5 mL / min.

[0034] In the method provided by the present invention, in step a), the stirring speed is preferably 500-2000 r / min, specifically 500 r / min, 600 r / min, 700 r / min, 800 r / min, 900 r / min, 1000 r / min, 1100 r / min, 1200 r / min, 1300 r / min, 1400 r / min, 1500 r / min, 1600 r / min, 1700 r / min, 1800 r / min, 1900 r / min or 2000 r / min.

[0035] In the method provided by the present invention, in step b), the protective colloid in the protective colloid aqueous solution is one or more of polyvinyl alcohol (PVA), polyvinyl pyrrolidone (PVP) and polyacrylic acid (PAA); wherein the brand of the polyvinyl alcohol is one or more of PVA-1788, PVA-2488 and PVA-0588, preferably PVA-1788; the brand of the polyvinyl pyrrolidone is preferably one or more of PVP-K30, PVP-K25, PVP-C15 and PVP-C30, more preferably PVP-K30. In the present invention, the above protective colloids all have excellent water solubility and a certain viscosity, which can thicken and disperse the nanocolloids to avoid precipitation and aggregation.

[0036] In the method provided by the present invention, in step b), the mass ratio of protective colloid to water in the protective colloid aqueous solution is preferably (5-20):100, specifically 5:100, 6:100, 7:100, 8:100, 9:100, 10:100, 11:100, 12:100, 13:100, 14:100, 15:100, 16:100, 17:100, 18:100, 19:100 or 20:100.

[0037] In the method provided by the present invention, in step b), the mass ratio of the silica sol semi-finished product to the protective colloid in the protective colloid aqueous solution, calculated on the basis of the raw silicate for preparation, is preferably 1:(1-5), specifically 1:1, 1:1.5, 1:2, 1:2.5, 1:3, 1:3.5, 1:4, 1:4.5 or 1:5.

[0038] In the method provided by the present invention, in step b), a defoaming agent is preferably further added during the mixing process; the defoaming agent is preferably one or more of an organosilicon defoaming agent, a polyether defoaming agent, and a silane coupling agent; the organosilicon defoaming agent is preferably a polydimethylsiloxane (PDMS) emulsion, which is suitable for aqueous systems and high viscosity systems; the polyether defoaming agent is preferably a GPE-type polyether defoaming agent, which is suitable for high temperature and strong acid and strong alkali environments; the silane coupling agent is preferably silane coupling agent KH-550 or KH-560, which has a lower cost.

[0039] For the purpose of greater clarity, the present invention is described in detail with reference to the following examples and comparative examples.

[0040] Example 1

[0041] (1) Utilizing the easy hydrolysis property of silicate to prepare silica sol semi-finished product, the specific steps are as follows:

[0042] 5 g of potassium silicate was added to 100 g of deionized water and stirred to dissolve to obtain a potassium silicate solution; 3 g of zinc dihydrogen phosphate was added to 100 g of deionized water and stirred to dissolve to obtain a zinc dihydrogen phosphate solution; the zinc dihydrogen phosphate solution was slowly added dropwise to the above potassium silicate solution at a drop rate of 2 mL / min and maintained at a high-speed stirring of 1000 r / min. The solution gradually turned milky white. Since the addition of zinc dihydrogen phosphate would lower the pH and induce silicic acid polymerization, continuous high-speed stirring was required to avoid the formation of silicate colloidal precipitation, and the pH change of the solution was monitored in real time. When the pH dropped to 5.5, the addition of zinc dihydrogen phosphate solution was stopped to obtain Zn(OH)2-SiO2 silica sol.

[0043] (2) Adding PVA resin to prepare colloid-protected silica sol, the specific steps are as follows:

[0044] Slowly add 10g of PVA-1788 powder to 100mg of deionized water, stir and dissolve at 80°C at a speed of 400-600rpm, and after the PVA powder is completely dissolved, cool to room temperature to obtain a PVA protective colloid solution; slowly add the PVA protective colloid solution to the above-mentioned Zn(OH)2-SiO2 silica sol and stir evenly at a speed of 400-600rpm to obtain PVP-protected Zn(OH)2-SiO2 silica sol.

[0045] Example 2

[0046] (1) Utilizing the easy hydrolysis property of silicate to prepare silica sol semi-finished product, the specific steps are as follows:

[0047] Add 5g of potassium silicate to 100g of deionized water and stir to dissolve to obtain a potassium silicate solution; add 2g of copper sulfate to 100g of deionized water and stir to dissolve to obtain a copper sulfate solution; slowly add the copper sulfate solution dropwise to the above potassium silicate solution at a drop rate of 2mL / min and maintain high-speed stirring at 1000r / min. The solution gradually turns into a blue emulsion. Since the addition of copper sulfate will lower the pH and induce silicate polymerization precipitation, continuous high-speed stirring is required to avoid the formation of silicate colloidal precipitation, and the pH change of the solution is monitored in real time. When the pH drops to 5.5, stop adding the copper sulfate solution to obtain Cu(OH)2-SiO2 silica sol.

[0048] (2) Add PVP resin to prepare colloid-protected silica sol, the specific steps are as follows:

[0049] Add 10g of PVP-K30 to 100g of deionized water, stir and dissolve at 80°C at a speed of 400-600rpm, and after the PVP is completely dissolved, cool to room temperature to obtain a PVP protective colloid solution; slowly add the PVP protective colloid solution to the above-mentioned Cu(OH)2-SiO2 silica sol and stir evenly at a speed of 400-600rpm to obtain PVP-protected Cu(OH)2-SiO2 silica sol.

[0050] Example 3

[0051] (1) Utilizing the easy hydrolysis property of silicate to prepare silica sol semi-finished product, the specific steps are as follows:

[0052] Add 5 g of potassium silicate to 100 g of deionized water and stir to dissolve to obtain a potassium silicate solution; add 3 g of aluminum nitrate to 100 g of deionized water and stir to dissolve to obtain an aluminum nitrate solution; slowly add the aluminum nitrate solution dropwise to the above potassium silicate solution at a drop rate of 2 mL / min and maintain high-speed stirring at 1000 r / min. The solution gradually turns milky white. Since the addition of aluminum nitrate will lower the pH and induce silicic acid polymerization, continuous high-speed stirring is required to avoid the formation of silicate colloidal precipitation, and the pH change of the solution is monitored in real time. When the pH drops to 5.5, stop adding the aluminum nitrate solution to obtain Al(OH)3-SiO2 silica sol.

[0053] (2) Adding PAA resin to prepare colloid-protected silica sol, the specific steps are as follows:

[0054] 10 g of acrylic acid monomer was added to 100 g of deionized water, and the acrylic acid solution was poured into a polytetrafluoroethylene container autoclave. The temperature was set to 110° C. and a thermal polymerization reaction was carried out for half an hour. After cooling, a viscous PAA protective colloid solution was obtained. The PAA protective colloid solution was slowly added to the above-mentioned Al(OH)3-SiO2 silica sol and stirred evenly at a speed of 400-600 rpm. Finally, 0.5 mL of defoamer KH-560 was added, and the mixture was slowly stirred at 100 rpm for 1 minute and then allowed to stand for defoaming to obtain PAA-protected Al(OH)3-SiO2 silica sol.

[0055] Comparative Example 1

[0056] The main difference from the embodiment is that the order and method of adding the silicate aqueous solution are different, as follows:

[0057] 1g of zinc dihydrogen phosphate was added to 100g of deionized water and stirred to dissolve to obtain a zinc dihydrogen phosphate solution. Under stirring conditions of 1000r / min, 1.5g of potassium silicate was added to the above zinc dihydrogen phosphate solution, and the solution immediately turned milky white. Since silicate is added to zinc dihydrogen phosphate, excessive acid will cause silicic acid to polymerize and precipitate. If there is no time to adjust the pH, a white colloidal particle suspension visible to the naked eye will be generated prematurely, and PVA colloid cannot be added further, resulting in test failure.

[0058] Not only zinc dihydrogen phosphate, but also adding silicate to other acidic solutions such as sulfuric acid, nitric acid, phosphoric acid, etc. will prematurely generate large-particle silicic acid precipitates, so this addition order is not advisable.

[0059] Comparative Example 2

[0060] The main difference from the embodiment is that PVA uses 1799 brand, which is as follows:

[0061] (1) Utilizing the easy hydrolysis property of silicate to prepare silica sol semi-finished product, the specific steps are as follows:

[0062] 5 g of potassium silicate was added to 100 g of deionized water and stirred to dissolve to obtain a potassium silicate solution; 3 g of zinc dihydrogen phosphate was added to 100 g of deionized water and stirred to dissolve to obtain a zinc dihydrogen phosphate solution; the zinc dihydrogen phosphate solution was slowly added dropwise to the above potassium silicate solution at a drop rate of 2 mL / min and maintained at a high-speed stirring of 1000 r / min. The solution gradually turned milky white. Since the addition of zinc dihydrogen phosphate would lower the pH and induce silicic acid polymerization, continuous high-speed stirring was required to avoid the formation of silicate colloidal precipitation, and the pH change of the solution was monitored in real time. When the pH dropped to 5.5, the addition of zinc dihydrogen phosphate solution was stopped to obtain Zn(OH)2-SiO2 silica sol.

[0063] (2) Adding PVA resin to prepare colloid-protected silica sol, the specific steps are as follows:

[0064] Slowly add 10g of PVA-1799 powder to 100mg of deionized water, stir and dissolve at 110°C at a speed of 400-600rpm, and after the PVA powder is completely dissolved, cool to room temperature to obtain a PVA protective colloid solution; slowly add the PVA protective colloid solution to the above-mentioned Zn(OH)2-SiO2 silica sol and stir evenly at a speed of 400-600rpm to obtain PVP-protected Zn(OH)2-SiO2 silica sol.

[0065] Due to its high alcoholysis degree, PVA-1799 requires a higher temperature to dissolve and the dissolution process is slow and inefficient. After dissolution, lumpy transparent colloids will remain. There are also problems such as excessive solution viscosity, increased bubbles, and difficulty in defoaming. Therefore, PVA1799 should be avoided when choosing PVA brands.

[0066] Comparative Example 3

[0067] The main difference from the embodiment is that PVA uses 0388 brand, which is as follows:

[0068] (1) Utilizing the easy hydrolysis property of silicate to prepare silica sol semi-finished product, the specific steps are as follows:

[0069] 5 g of potassium silicate was added to 100 g of deionized water and stirred to dissolve to obtain a potassium silicate solution; 3 g of zinc dihydrogen phosphate was added to 100 g of deionized water and stirred to dissolve to obtain a zinc dihydrogen phosphate solution; the zinc dihydrogen phosphate solution was slowly added dropwise to the above potassium silicate solution at a drop rate of 2 mL / min and maintained at a high-speed stirring of 1000 r / min. The solution gradually turned milky white. Since the addition of zinc dihydrogen phosphate would lower the pH and induce silicic acid polymerization, continuous high-speed stirring was required to avoid the formation of silicate colloidal precipitation, and the pH change of the solution was monitored in real time. When the pH dropped to 5.5, the addition of zinc dihydrogen phosphate solution was stopped to obtain Zn(OH)2-SiO2 silica sol.

[0070] (2) Adding PVA resin to prepare colloid-protected silica sol, the specific steps are as follows:

[0071] Slowly add 10g of PVA-0388 powder to 100mg of deionized water, stir and dissolve at 60°C at a speed of 400-600rpm, and after the PVA powder is completely dissolved, cool to room temperature to obtain a PVA protective colloid solution; slowly add the PVA protective colloid solution to the above-mentioned Zn(OH)2-SiO2 silica sol and stir evenly at a speed of 400-600rpm to obtain PVP-protected Zn(OH)2-SiO2 silica sol.

[0072] Due to its low molecular weight and low viscosity, PVA-0388 has limited effect on dispersing and preventing silicic acid. Silica sol will precipitate and aggregate after being left for a period of time, so PVA0388 should be avoided when choosing PVA brands.

[0073] Comparative Example 4

[0074] The main difference from the embodiment is that the silicon source is a silicate with poor solubility, such as magnesium silicate, calcium silicate, aluminum silicate, etc.

[0075] The results show that the silicate aqueous solution will have poor dispersion and cannot form a stable colloid, so the above-mentioned silicates should be avoided.

[0076] Performance Comparison

[0077] The performance effects of Examples 1 to 3 and Comparative Examples 1 to 4 are summarized in Table 1.

[0078] Table 1 Silica sol properties

[0079] Silicon Source Protective colloid Acidic pH adjustment Feature Description Example 1 Potassium silicate PVA-1788 Zinc dihydrogen phosphate relatively stable Example 2 Sodium silicate PVPK30 copper sulfate relatively stable Example 3 Potassium silicate PAA Aluminum nitrate Very stable Comparative Example 1 Potassium silicate / Zinc dihydrogen phosphate precipitation Comparative Example 2 Potassium silicate PVA-1799 Zinc dihydrogen phosphate Difficult to remove foam Comparative Example 3 Potassium silicate PVA-0388 Zinc dihydrogen phosphate precipitation Comparative Example 4 magnesium silicate / / precipitation

[0080] As can be seen from Table 1, the silica sols of the examples all have good dispersibility and stability. Comparative Example 1 produces silicic acid precipitation due to the different order of adding silicate and acidic liquid; Comparative Example 2 uses PVA-1799 that requires high temperature dissolution, and the system viscosity is high, dissolution is difficult, defoaming is difficult, and efficiency is low; Comparative Example 3 uses low molecular weight PVA-0388 that dissolves at room temperature, but the colloidal protection effect is limited, and the silica sol will precipitate after being left for a period of time; Comparative Example 4 uses slightly soluble or insoluble silicate, and silica sol cannot be prepared.

[0081] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for preparing silica sol using silicate, characterized in that: The following steps are involved: a) adding the acid salt solution dropwise to the silicate aqueous solution under stirring; When the pH of the mixed system drops to 5.5-6, stop adding the acid salt solution to obtain a semi-finished silica sol; In step a), the silicate in the silicate aqueous solution is sodium silicate and / or potassium silicate; b) mixing the silica sol semi-finished product with a protective colloid aqueous solution and defoaming to obtain a colloid-protected silica sol; In step b), the protective colloid in the protective colloid aqueous solution is one or more of polyvinyl alcohol, polyvinyl pyrrolidone and polyacrylic acid; the brand of the polyvinyl alcohol is one or more of PVA-1788, PVA-2488 and PVA-0588.

2. The method according to claim 1, characterized in that In step a), the acid salt in the acid salt aqueous solution is one or more of sodium dihydrogen phosphate, zinc dihydrogen phosphate, copper sulfate, aluminum nitrate and aluminum sulfate.

3. The method according to claim 1, characterized in that In step a), the mass ratio of silicate to water in the silicate aqueous solution is (1-10):

100.

4. The method according to claim 1, wherein In step a), the mass ratio of acid salt to water in the acid salt solution is (0.5-5):

100.

5. The method according to claim 1, wherein In step a), the stirring speed is 500 to 2000 r / min.

6. The method according to claim 1, characterized in that In step b), the brand of polyvinyl pyrrolidone is one or more of PVP-K30, PVP-K25, PVP-C15 and PVP-C30.

7. The method according to claim 1, characterized in that In step b), the mass ratio of protective colloid to water in the protective colloid aqueous solution is (5-20):

100.

8. The method according to claim 1, characterized in that In step b), the mass ratio of the silica sol semi-finished product to the protective colloid in the protective colloid aqueous solution is 1:(1-5) based on the raw silicate for preparation.

9. The method according to claim 1, characterized in that In step b), a defoaming agent is also added during the mixing process.

10. The method according to claim 9, characterized in that The defoaming agent is one or more of an organosilicon defoaming agent, a polyether defoaming agent and a silane coupling agent.