A method for preparing high-concentration active silicic acid

Abstract

The present invention provides a method for preparing high-concentration active silicic acid, belonging to the field of silica sol technology. Water glass is diluted with water to the desired SiO2 content, and then an inorganic salt is dissolved in the solution to obtain a mixed solution. The mixed solution is then subjected to cation exchange while stirring to obtain crude silicic acid. The crude silicic acid is then subjected to a second cation exchange by column chromatography to remove metallic impurities, thereby obtaining an acidic silicic acid intermediate. An inorganic salt is then added to the acidic silicic acid intermediate and an anion exchange is performed to obtain an alkaline silicic acid product. The optional addition of a dispersant to the alkaline silicic acid product can improve the storage stability of the silicic acid. The present invention achieves a silicic acid concentration of 9% without a dispersant and 14% with a dispersant. The prepared silicic acid is suitable for preparing silica sols.

Description

Technical Field

[0001] The invention relates to a method for preparing high-concentration active silicic acid, belonging to the technical field of silica sol. Background Art

[0002] The ion exchange method is currently the most widely used method for preparing silica sol. This method uses water glass as the raw material and produces active silicic acid through ion exchange. The silica sol product undergoes nucleation and particle growth. The cost of the ion exchange method is directly related to the concentration of active silicic acid. This is because the liquid level in the reactor must be maintained constant during the silica sol particle growth process. This requires that the water in the silicic acid be distilled off as the silicic acid is added. Otherwise, the liquid level in the reactor rises, reducing the particle density and slowing the reaction rate. The silicic acid concentration that is not able to react increases, forming new small-sized seed crystals, resulting in a wide particle size distribution. Producing high-concentration silicic acid can reduce water evaporation and energy consumption. For example, if growing a silica sol seed crystal to 100 nm requires 20 tons of 2% silicic acid, using 4% silicic acid instead only requires 10 tons, halving the amount of water required for evaporation and significantly reducing energy consumption.

[0003] In conventional ion-exchange silicate production, a single cation exchange reaction with a water glass solution yields the final silicate at a pH of approximately 5-6. At this pH, the silicate carries very little charge, making the active silicate less stable and prone to aggregation, forming a gel. Consequently, it is difficult to achieve a solids content exceeding 4% and maintaining stability. Attempts to produce 5% silicate using conventional methods resulted in gelation within the ion-exchange column, leading to production failure. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for preparing high-concentration silicic acid. The silicic acid concentration reaches 9% without using a dispersant and can reach 14% with a dispersant. The prepared silicic acid is suitable for preparing silica sol.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] A method for preparing high-concentration active silicic acid comprises the following steps:

[0007] (1) diluting water glass with water to a desired SiO2 content, and then dissolving inorganic salt A in the solution to obtain a mixed solution;

[0008] (2) performing a first cation exchange on the mixed solution by stirring to maintain the pH of the silicic acid at 1 to 4, thereby obtaining crude silicic acid;

[0009] (3) subjecting the crude silicic acid to a second cation exchange reaction by column chromatography to obtain an acidic silicic acid intermediate having a pH of 1 to 4;

[0010] (4) Adding inorganic salt B to the acidic silicic acid intermediate, and then performing anion exchange by stirring to obtain an alkaline silicic acid product with a pH of 8 to 10.

[0011] Furthermore, the water glass contains SiO2 25%, SiO2:Na2O=3.3.

[0012] Furthermore, the mass ratio of water to water glass is (0.5-3.5):1.

[0013] Furthermore, the inorganic salt A is selected from one or more of sodium sulfate, potassium sulfate, sodium chloride, potassium chloride, ammonium chloride, sodium nitrate, and lithium chloride.

[0014] Furthermore, the mass fraction of the inorganic salt A relative to the glass is 5% to 6.5%.

[0015] Furthermore, the cation exchange resin used in the first cation exchange was an activated cation exchange resin, and the mixture was stirred for 10 minutes.

[0016] Furthermore, the mass ratio of the cation exchange resin to the water glass used in the first cation exchange is (5-11):1.

[0017] Furthermore, the mass ratio of the cation exchange resin to the water glass used in the second cation exchange is (0.5-1.1):1.

[0018] Furthermore, the inorganic salt B is selected from one or more of sodium sulfate, potassium sulfate, sodium chloride, potassium chloride, ammonium chloride, sodium nitrate, and lithium chloride.

[0019] Furthermore, the mass fraction of the inorganic salt B relative to the water glass is 2.5% to 4.2%.

[0020] Furthermore, a dispersant is added to the alkalized silicic acid product prepared in step (4), and the dispersant is selected from a polymer carboxylic acid alkali metal salt or a polymer carboxylic acid ammonium salt.

[0021] Furthermore, the dispersant is selected from sodium polyacrylate, potassium polyacrylate, ammonium polyacrylate, sodium polymethacrylate, potassium polymethacrylate or ammonium polymethacrylate.

[0022] Furthermore, the mass fraction of the added dispersant is 0.002% to 0.02%.

[0023] The principles adopted by the present invention and the beneficial effects produced are as follows:

[0024] The present invention adopts pH control means during the preparation and storage of silicic acid, so that the silicic acid remains stable at a concentration of up to 9.0%, and is ultimately used for silica sol growth, as described in detail below:

[0025] (1) Before the first cation exchange, a small amount of inorganic salt is pre-dissolved in water glass. During the cation exchange process, the inorganic salt is converted into the corresponding acid, keeping the pH of the silicate at a low level of 1 to 4. Under acidic pH conditions, the silicate is partially protonated and positively charged. The mutual repulsion of positive charges prevents the polymerization of silicates, thereby improving their stability. At the same time, the low pH value also converts impurities such as aluminum oxide and iron oxide in the silicate into corresponding cations, which can be removed by the subsequent cation exchange process.

[0026] The first ion exchange must be performed by mixing the resin and water glass, rather than using an ion exchange column. This is because water glass is highly alkaline, while crude silicic acid is highly acidic. If a column method is used, water glass and crude silicic acid will diffuse and mix at the interface where the ion exchange occurs, resulting in a continuously changing pH gradient. Within this gradient, there is a region with a pH close to neutral. Both water glass and high-concentration crude silicic acid are unstable at neutral pH and gel, causing the resin to agglomerate.

[0027] (2) The second cation exchange removes the residual sodium ions from the first exchange. Because water glass contains a large amount of sodium ions, the sodium ion exchange efficiency is low at a low pH. The first cation exchange alone cannot effectively remove all the sodium. At the same time, most of the iron and aluminum impurities in the silicate are also removed.

[0028] (3) The third anion exchange: a small amount of inorganic salt is added before the exchange. During the anion exchange, the inorganic salt is converted into hydroxide, bringing the pH of the silicic acid product to 8-10. Under such weak alkaline conditions, the silicic acid molecules are partially ionized and carry negative charges. The repulsion between the negative charges allows the silicic acid to remain stable at a higher solid content. For the same reasons as (1), this ion exchange step also uses stirring.

[0029] (4) After the ion exchange is complete, a certain amount of polymer carboxylate dispersant can be added to the silicic acid to improve its storage stability. The dispersant contains a large number of negatively charged carboxyl anions that can form hydrogen bonds with the silanol groups, so that the active groups of the silicic acid are surrounded by polymer chains, preventing the mutual polymerization of the silicic acid. After using the dispersant, the concentration of silicic acid can be increased from 9% to 14%.

[0030] (5) Although the present method uses three ion exchanges to prepare silicate acid, the resin consumption in the last two ion exchanges is minimal, and the added cost is essentially negligible. The cost savings from subsequent silica sol growth far outweigh the increased cost of the three exchanges. Since the prepared silicate acid contains a small amount of alkali, the amount of alkali added to the reactor can be appropriately reduced during the silica sol growth process.

[0031] (6) The content of high-valent metal impurities in the silicate prepared by the method of the present invention is lower than that in the conventional method. The silicate prepared by the present invention is used for silica sol seed growth, and eventually a large-particle silica sol with a particle size of 60 to 120 nm can be obtained. The prepared silicate is suitable for silica sol preparation. DETAILED DESCRIPTION

[0032] In order to make the various technical features and advantages or technical effects of the above technical solutions of the present invention more obvious and easy to understand, they are described below in conjunction with embodiments.

[0033] Example 1:

[0034] Dissolve 900g of water glass (containing 25% SiO2, SiO2:Na2O = 3.3) in 3000g of water, then add 50g of potassium chloride and stir to dissolve. Add 10kg of activated cation exchange resin and stir rapidly for 10 minutes to obtain crude silicic acid with a pH of 1.0. Pass the crude silicic acid through an exchange column containing 1kg of cation exchange resin to obtain an acidic silicic acid intermediate with a pH of approximately 1.0. Dissolve 30g of potassium chloride in the acidic silicic acid intermediate, then perform anion exchange to obtain finished silicic acid with a pH of 9.3, a SiO2 concentration of 5.25%, and a viscosity of 1.50mPa·s. After standing for one week, the viscosity reaches 1.97mPa·s. The metal content of the silicate is shown in Table 1.

[0035] Example 2:

[0036] Dissolve 1900g of water glass (containing 25% SiO2, SiO2:Na2O = 3.3) in 3100g of water, then add 120g of sodium chloride and stir to dissolve. Add 10kg of activated cation exchange resin and stir rapidly for 10 minutes to obtain crude silicic acid with a pH of 2.5. Pass the crude silicic acid through an exchange column containing 1kg of cation exchange resin to obtain an acidic silicic acid intermediate with a pH of approximately 2.5. Dissolve 80g of sodium chloride in the acidic silicic acid intermediate, followed by anion exchange, to obtain finished silicic acid with a pH of 9.9, a SiO2 concentration of 9.05%, and a viscosity of 2.88mPa·s. After standing for one week, the viscosity reaches 4.24mPa·s. The metal content of the silicate is shown in Table 1.

[0037] Example 3:

[0038] 2000g of water glass (containing 25% SiO2, SiO2:Na2O = 3.3) was diluted with 1333g of water, and 100g of sodium sulfate was added and stirred to dissolve. 20kg of activated cation exchange resin was added and rapidly stirred for 10 minutes to obtain crude silicic acid with a pH of 2.0. The crude silicic acid was passed through an exchange column containing 1kg of cation exchange resin to obtain an acidic silicic acid intermediate with a pH of approximately 1.0. 50g of sodium sulfate was dissolved in the acidic silicic acid intermediate, followed by anion exchange, to obtain finished silicic acid with a pH of 9.0 and a SiO2 concentration of 14.0%. A sodium polyacrylate dispersant (1 / 10,000th of the weight of the silicic acid) was added and stirred thoroughly, resulting in a viscosity of 1.28mPa·s. After standing for one week, the viscosity reached 3.33mPa·s. The metal content of the silicate is shown in Table 1.

[0039] Comparative Example:

[0040] In this example, a conventional method was used to prepare silicic acid with a target concentration of 4%. 1000g of water glass (containing 25% SiO2, with a SiO2:Na2O ratio of 3.3) was dissolved in 6250g of water. The solution was passed through a cation exchange column containing 10kg of cation exchange resin. The resulting silicic acid had a pH of 5.4, a SiO2 concentration of 3.93%, a viscosity of 1.56mPa·s, a 24-hour viscosity of 3.63mPa·s, and a gel after 72 hours. The metal content of the silicate is shown in Table 1.

[0041] Table 1 High-valent metal impurity content in silicic acid prepared in each embodiment (ppm)

[0042] Metal Example 1 Example 2 Example 3 Comparative Example calcium 11.5 9.8 16.5 23.9 magnesium 6.7 5.0 5.4 16.6 aluminum 67 72 68 389 iron 13 10 11 38 copper ＜0.035 ＜0.035 ＜0.035 ＜0.035

[0043] Note: The metal impurity content has been converted to the value under the condition of 40% SiO2 content (i.e. the typical SiO2 content of silica sol products).

[0044] As can be seen from Table 1, Examples 1 to 3, due to the use of the method of the present invention, can more thoroughly remove high-valent metal impurities such as calcium, magnesium, aluminum, and iron contained in water glass than Comparative Document 1, thereby producing purer silicic acid.

[0045] Although the present invention has been disclosed as above by way of embodiments, they are not intended to limit the present invention. Any appropriate modification or equivalent substitution of the technical solution of the present invention by a person skilled in the art should be included in the protection scope of the present invention. The protection scope of the present invention shall be based on that defined in the claims.

Claims

1. A method for preparing high-concentration active silicic acid, characterized in that: The following steps are involved: (1) diluting water glass with water to a desired SiO2 content, and then dissolving an inorganic salt A in the solution, wherein the inorganic salt A is selected from one or more of sodium sulfate, potassium sulfate, sodium chloride, potassium chloride, ammonium chloride, sodium nitrate, and lithium chloride to obtain a mixed solution; (2) The mixed solution is subjected to a first cation exchange by stirring to maintain the pH of the silicic acid at 1-4 to obtain crude silicic acid; (3) The crude silicic acid is subjected to a second cation exchange by column flow to obtain an acidic silicic acid intermediate with a pH of 1 to 4; (4) Adding an inorganic salt B to the acidic silicic acid intermediate, wherein the inorganic salt B is selected from one or more of sodium sulfate, potassium sulfate, sodium chloride, potassium chloride, ammonium chloride, sodium nitrate, and lithium chloride, and then performing anion exchange by stirring to obtain an alkaline silicic acid product with a pH of 8 to 10.

2. The method according to claim 1, wherein Water glass contains 25% SiO2, SiO2:Na2O = 3.

3.

3. The method according to claim 1, wherein The mass ratio of water to water glass is (0.5~3.5):

1.

4. The method according to claim 1, wherein The mass fraction of the inorganic salt A relative to the glass is 5% to 6.5%.

5. The method according to claim 1, wherein The cation exchange resin used in the first cation exchange was an activated cation exchange resin, and the mixture was stirred for 10 minutes.

6. The method according to claim 1, wherein The mass ratio of the cation exchange resin to the water glass used in the first cation exchange is (5~11):

1.

7. The method according to claim 1, wherein The mass ratio of the cation exchange resin to the water glass used in the second cation exchange is (0.5~1.1):

1.

8. The method according to claim 1, wherein The mass fraction of inorganic salt B relative to water glass is 2.5%~4.2%.

9. The method according to claim 1, wherein A dispersant is added to the alkalized silicic acid product prepared in step (4). The dispersant is selected from a polymer carboxylic acid alkali metal salt or a polymer carboxylic acid ammonium salt, and the mass fraction of the dispersant added is 0.002% to 0.02%.

10. The method according to claim 9, wherein The dispersant is selected from sodium polyacrylate, potassium polyacrylate, ammonium polyacrylate, sodium polymethacrylate, potassium polymethacrylate or ammonium polymethacrylate.