Preparation method for regulating and controlling dispersity of nano calcium carbonate based on nucleation process

Abstract

The invention discloses a preparation method for regulating and controlling dispersity of nano calcium carbonate based on a nucleation process. The preparation method comprises the following steps: (1) preparing slurry A; (2) preparing slurry B; (3) guiding a crystal form; according to the invention, by accurately controlling the introduction opportunity of the modifier, optimizing the synergistic effect of the nucleating agent and the crystal form directing agent, and combining with a composite modifier system, the dispersibility and morphology uniformity of the nano calcium carbonate and the compatibility of the nano calcium carbonate with an organic matrix are significantly improved.

Description

Technical Field

[0001] The present invention relates to the technical field of nano-calcium carbonate preparation, and in particular to a preparation method for nano-calcium carbonate based on regulating the dispersibility of the nano-calcium carbonate during a nucleation process. Background Art

[0002] As an important functional inorganic material, nano-calcium carbonate has been widely used in rubber, plastics, papermaking, daily chemicals, medicine and environmental protection due to its excellent physical and chemical properties, including high specific surface area, good biocompatibility and environmental friendliness. It is worth noting that more than 90% of application scenarios require good interfacial compatibility between nano-calcium carbonate and organic matrices. However, the surface of unmodified nano-calcium carbonate is rich in hydrophilic hydroxyl groups, which has significant surface property differences from non-polar or weakly polar organic materials. This incompatibility often leads to interfacial defects in composite materials.

[0003] In the existing technology, surface modification is the main method to improve the compatibility of inorganic fillers / organic matrices. Current research focuses on post-modification processes, including dry modification and wet modification, but there are common problems such as high energy consumption and uneven modification. In contrast, in-situ modification technology is increasingly attracting attention from academia and industry due to its advantages in modification uniformity, production efficiency and cost control. However, in the gas-liquid-solid heterogeneous system for the preparation of nano-calcium carbonate by carbonization, traditional in-situ modification methods face the following technical bottlenecks: (1) low gas-liquid mass transfer efficiency; (2) serious particle agglomeration; (3) difficulty in morphology control; and (4) uneven particle size distribution.

[0004] For example, the patent with publication number CN 110128851A, entitled "A Method for Preparing Hydrophobic Nano-Calcium Carbonate," achieved in-situ modification in a microreactor. However, due to the premature addition of the surface modifier to the calcium hydroxide solution, that is, its introduction before nucleation, the modification reaction was incomplete, resulting in abnormal product morphology, with irregular morphologies such as elliptical and spindle shapes appearing simultaneously, and insufficient crystal structure stability.

[0005] In view of the above technical deficiencies, the present invention achieves efficient dispersion modification and morphology control of nano-calcium carbonate by precisely controlling the timing and conditions of introducing the modifier during the nucleation process. Summary of the Invention

[0006] In view of the shortcomings of the existing technology, the main purpose of the present invention is to provide a preparation method for nano-calcium carbonate based on the nucleation process to regulate the dispersibility, which solves the problems of incomplete modification, abnormal morphology (coexistence of elliptical / spindle shapes) and unstable crystal structure in the traditional in-situ carbonization method for preparing nano-calcium carbonate.

[0007] Another object of the present invention is to provide a nucleating agent, whereby the nucleating agent can promote heterogeneous nucleation, refine the initial grains, and form a stable lattice structure of nano-calcium carbonate crystals.

[0008] Another object of the present invention is to provide an innovative order of adding surface modifiers so that the added modifiers act only on the particle surface and do not interfere with the intrinsic growth direction of the crystals, thereby ensuring uniform product morphology.

[0009] The present invention provides a preparation method for nano-calcium carbonate based on the regulation of its dispersibility during the nucleation process, which solves the problems of incomplete modification, abnormal morphology (coexistence of elliptical and spindle shapes), and unstable crystal structure in the traditional in-situ carbonization method for preparing nano-calcium carbonate.

[0010] The technical solution is as follows:

[0011] A preparation method for regulating the dispersibility of nano-calcium carbonate based on a nucleation process comprises the following steps:

[0012] (1) Preparing slurry A: uniformly mixing calcium hydroxide slurry and nucleating agent, and stirring at high speed to obtain slurry A; the concentration of the calcium hydroxide slurry is 5 wt%~10 wt%;

[0013] (2) Preparation of slurry B: Continuously introduce mixed gas into slurry A to perform carbonization reaction. When the slurry begins to gel and become viscous, add a surface modifier into the reaction system to obtain slurry B;

[0014] (3) Crystal guidance: When the pH of slurry B is 10±0.5, add the crystal guidance agent and stir until the pH reaches 6.5±0.5, then stop aeration;

[0015] (4) Preparation of modified nano-calcium carbonate: directly drying the solution after crystal orientation to obtain modified nano-calcium carbonate.

[0016] Preferably, the nucleating agent is zinc chloride, and the content of zinc chloride is 0.1 wt% to 5 wt% of the total amount of calcium hydroxide slurry.

[0017] Preferably, in steps (1) to (3), the mixed gas is continuously introduced during the reaction process and high-speed stirring is continuously performed.

[0018] Preferably, the carbonization reaction temperature is 0°C to 50°C.

[0019] Preferably, the mixed gas is a mixture of carbon dioxide and an inert gas, and the flow rate ratio of carbon dioxide to inert gas in the mixed gas is 1:3.

[0020] Preferably, the surface modifier is a composite modifier of copolymer salt and saponified sodium stearate, and the mass ratio of the copolymer salt to saponified sodium stearate is 5~1:5~1;

[0021] The copolymer salt is one of a polystyrene-carboxylic anhydride functional group copolymer, a polystyrene-N-phenylmaleimide-carboxylic anhydride functional group terpolymer, a polyacrylonitrile-styrene-butadiene rubber-carboxylic anhydride functional group terpolymer, and a polybutadiene-acrylonitrile-styrene-carboxylic anhydride functional group tetrapolymer, and the salt is obtained by ring-opening under alkaline conditions;

[0022] The alkali solution is sodium hydroxide solution.

[0023] Preferably, the saponified sodium stearate is a product obtained by saponifying stearic acid in a sodium hydroxide solution at a molar ratio of 1:1.

[0024] Preferably, the amount of the surface modifier is 0.1 wt% to 2 wt% of the total amount of the calcium hydroxide solution.

[0025] Preferably, the crystal directing agent is sulfuric acid, and the molar ratio of sulfuric acid to calcium ions is 0.01:1 to 0.001:1.

[0026] Preferably, the high-speed stirring has a rotation speed of 800 rpm to 1200 rpm.

[0027] Preferably, the drying temperature is 50-80° C., and the drying time is 24-48 hours.

[0028] The present invention also provides a nucleating agent, which can promote heterogeneous nucleation, refine the initial grains, and form a stable lattice structure of nano-calcium carbonate crystals. The technical solution is as follows:

[0029] The nucleating agent is zinc chloride, and the content of the zinc chloride is 0.1wt% to 5wt% of the total amount of the calcium hydroxide slurry.

[0030] The nucleating agent is uniformly mixed with calcium hydroxide slurry and stirred at high speed to obtain slurry A; the concentration of the calcium hydroxide slurry is 5 wt% to 10 wt%.

[0031] The high-speed stirring has a rotation speed of 800 rpm to 1200 rpm.

[0032] The present invention also provides an innovative order for adding surface modifiers, so that the added modifiers act only on the particle surface and do not interfere with the intrinsic growth direction of the crystals, thereby ensuring uniform product morphology. The technical solution is as follows:

[0033] The surface modifier is added after the nucleation stage;

[0034] In the nucleation stage, the calcium hydroxide slurry and the nucleating agent are uniformly mixed and stirred at high speed to obtain slurry A, and then the mixed gas is continuously introduced into the carbonization reaction. When the conductivity value of the slurry is the lowest and the reaction system is in a gelled state, a large number of highly active nano-calcium carbonate crystals are generated in the reaction system, and nucleation is completed at this time.

[0035] Since the present invention adopts the above technical solution, it has the following beneficial effects:

[0036] By precisely controlling the timing of modifier introduction, optimizing the synergistic effect of nucleating agents and crystal-directing agents, and combining a composite modifier system, the present invention significantly improves the dispersibility, morphological uniformity, and compatibility of nano-calcium carbonate with organic matrices. Compared to existing technologies, the present invention has the following advantages:

[0037] 1. Significantly improve the dispersibility of nano calcium carbonate and reduce agglomeration

[0038] When preparing nano-calcium carbonate by traditional in-situ carbonization, the introduction of surface modifiers before nucleation can easily lead to incomplete modification, abnormal morphology (coexistence of elliptical and spindle shapes), and unstable crystal structure. The present invention effectively inhibits agglomeration by the following means:

[0039] (1) Accurately control the timing of introducing the modifier: add the modifier when the conductivity is lowest (i.e., the system is gelled and a large number of nano-calcium carbonate crystals are generated). At this time, the surface activity of the particles is the highest, and the modifier can be evenly coated to reduce subsequent agglomeration.

[0040] (2) High-speed stirring to enhance mass transfer: Combined with the mixed flow rate ratio of CO2 and inert gas (1:3), the gas-liquid mass transfer efficiency is improved and agglomeration caused by excessive local concentration is avoided.

[0041] 2. Improve the compatibility of nano-calcium carbonate with organic matrix

[0042] The surface of unmodified nano-calcium carbonate is rich in hydrophilic hydroxyl groups (-OH), which makes it poorly compatible with non-polar organic materials (such as rubber and plastics). The present invention achieves efficient surface hydrophobization through the use of a composite modifier (copolymer salt + saponified sodium stearate):

[0043] (1) Copolymer salts (such as polystyrene-carboxylic anhydride functional group copolymers): After the polystyrene-carboxylic anhydride functional group copolymer is ring-opened under alkaline conditions, the carboxylate (—COO⁻) strongly binds to Ca²⁺ to form a chemical bonding layer, thereby improving the modification stability.

[0044] (2) Saponified sodium stearate: long chain alkyl (C 17 H 35 —) Provide hydrophobicity, synergistically coat the particles with the copolymer, and significantly reduce the interfacial energy with the organic matrix.

[0045] (3) Modification uniformity: Post-nucleation modification avoids the problem of incomplete coating caused by premature addition of modifiers in traditional in-situ modification.

[0046] 3. Achieve precise control of crystal shape and avoid abnormal morphology: After nucleation, the nano-calcium carbonate microcrystals have initially formed a stable lattice structure. At this time, the addition of modifiers only acts on the particle surface and will not interfere with the intrinsic growth direction of the crystal, thereby ensuring uniform product morphology.

[0047] 4. Carbonization and modification are carried out simultaneously, eliminating the need for subsequent modification steps and reducing energy consumption and production costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Attachment Figure 1 The present invention is a flow chart for preparing nano calcium carbonate.

[0049] Attachment Figure 2 This is a TEM image of Example 1 of the present invention.

[0050] Attachment Figure 3 This is the TEM image of comparative example 1 of the present invention.

[0051] Attachment Figure 4 This is the TEM image of comparative example 2 of the present invention.

[0052] Attachment Figure 5 This is the TEM image of comparative example 3 of the present invention. DETAILED DESCRIPTION

[0053] The following describes the technical solutions in the embodiments of the present invention in detail with reference to several embodiments and accompanying drawings. It is apparent that the embodiments described are only some of the embodiments of the present invention, not all of them. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without inventive effort are considered to fall within the scope of protection of the present invention.

[0054] Example 1

[0055] A preparation method for regulating the dispersibility of nano-calcium carbonate based on a nucleation process comprises the following steps:

[0056] (1) Preparation of slurry A: Calcium hydroxide slurry and zinc chloride (0.1 wt% of the total amount of calcium hydroxide slurry) were uniformly mixed and stirred at 800 rpm to obtain slurry A; the concentration of the calcium hydroxide slurry was 5 wt%; the mixed gas was continuously introduced and stirred at high speed.

[0057] (2) Preparation of slurry B: Continuously introduce mixed gas into slurry A and conduct carbonization reaction at 0°C. When the slurry begins to gel and become viscous, add 0.1 wt% of the total amount of calcium hydroxide solution as a surface modifier to the reaction system to obtain slurry B; continue to introduce mixed gas and continue to stir at high speed;

[0058] Preparation method of a surface modifier: a. Ring-opening a polystyrene-carboxylic anhydride functional group copolymer under sodium hydroxide conditions; b. Saponifying stearic acid in a sodium hydroxide solution at a molar ratio of 1:1; c. Mixing the products of step a and step b at a ratio of 1:5 to prepare a surface modifier;

[0059] (3) Crystal guidance: Continue to introduce mixed gas and stir at high speed. When the pH of slurry B reaches 9.5, add sulfuric acid with a molar ratio of sulfuric acid to calcium ion of 0.01:1. Stir until the pH reaches 6, then stop aeration.

[0060] The mixed gas is a mixture of carbon dioxide and argon gases, and the flow rate ratio of the carbon dioxide to the argon gases in the mixed gas is 1:3.

[0061] (4) Preparation of modified nano-calcium carbonate: The crystal-guided solution was dried at 50 °C for 24 h to obtain modified nano-calcium carbonate.

[0062] Example 2

[0063] A preparation method for regulating the dispersibility of nano-calcium carbonate based on a nucleation process comprises the following steps:

[0064] (1) Preparation of slurry A: Calcium hydroxide slurry and zinc chloride (5 wt% of the total amount of calcium hydroxide slurry) were uniformly mixed and stirred at 1200 rpm to obtain slurry A; the concentration of the calcium hydroxide slurry was 10 wt%; the mixed gas was continuously introduced and stirred at high speed.

[0065] (2) Preparation of slurry B: Continuously introduce mixed gas into slurry A and perform carbonization reaction at 50°C. When the slurry begins to gel and become viscous, add a surface modifier (2 wt% of the total amount of calcium hydroxide solution) into the reaction system to obtain slurry B; continue to introduce mixed gas and continue stirring at high speed;

[0066] Preparation method of a surface modifier: a. Ring-opening a polybutadiene-acrylonitrile-styrene-carboxylic anhydride functional group quaternary copolymer under sodium hydroxide conditions; b. Saponifying stearic acid in a sodium hydroxide solution at a molar ratio of 1:1; c. Mixing the products of step a and step b at a ratio of 5:1 to prepare a surface modifier;

[0067] (3) Crystal guidance: Continue to introduce mixed gas and continue stirring at high speed until the pH of slurry B reaches 10.5, then add sulfuric acid with a molar ratio of sulfuric acid to calcium ion of 0.001:1, stir until the pH reaches 7, and then stop aeration;

[0068] The mixed gas is a mixture of carbon dioxide and helium, and the flow rate ratio of the carbon dioxide to helium in the mixed gas is 1:3.

[0069] (4) Preparation of modified nano-calcium carbonate: The crystal-guided solution was dried at 60 °C for 48 h to obtain modified nano-calcium carbonate.

[0070] Example 3

[0071] A preparation method for regulating the dispersibility of nano-calcium carbonate based on a nucleation process comprises the following steps:

[0072] (1) Preparing slurry A: Calcium hydroxide slurry and zinc chloride (3 wt% of the total amount of calcium hydroxide slurry) were uniformly mixed and stirred at 1000 rpm to obtain slurry A; the concentration of the calcium hydroxide slurry was 8 wt%; the mixed gas was continuously introduced and stirred at a high speed;

[0073] (2) Preparation of slurry B: Continuously introduce mixed gas into slurry A and perform carbonization reaction at 25°C. When the slurry begins to gel and become viscous, add a surface modifier of 1 wt% of the total amount of calcium hydroxide solution into the reaction system to obtain slurry B; continue to introduce mixed gas and continue to stir at high speed;

[0074] Preparation method of a surface modifier: a. Ring-opening a polystyrene-N-phenylmaleimide-carboxylic anhydride functional group terpolymer under sodium hydroxide conditions; b. Saponifying stearic acid in a sodium hydroxide solution at a molar ratio of 1:1; c. Mixing the products of step a and step b at a ratio of 2:1 to prepare a surface modifier;

[0075] (3) Crystal guidance: Continue to introduce mixed gas and continue stirring at high speed until the pH of slurry B reaches 10, then add sulfuric acid with a molar ratio of sulfuric acid to calcium ion of 0.005:1, stir until the pH reaches 6.5, and then stop aeration;

[0076] The mixed gas is a mixture of carbon dioxide and helium, and the flow rate ratio of carbon dioxide to helium in the mixed gas is 1:3.

[0077] (4) Preparation of modified nano-calcium carbonate: The crystal-guided solution was dried at 80 °C for 30 h to obtain modified nano-calcium carbonate.

[0078] Example 4

[0079] A preparation method for regulating the dispersibility of nano-calcium carbonate based on a nucleation process comprises the following steps:

[0080] (1) Preparing slurry A: Calcium hydroxide slurry and zinc chloride (0.1 wt% of the total amount of calcium hydroxide slurry) were uniformly mixed and stirred at 1200 rpm to obtain slurry A; the concentration of the calcium hydroxide slurry was 7 wt%; the mixed gas was continuously introduced and stirred at a high speed;

[0081] (2) Preparation of slurry B: Continuously introduce mixed gas into slurry A and perform carbonization reaction at 30°C. When the slurry begins to gel and become viscous, add a surface modifier (0.8 wt% of the total amount of calcium hydroxide solution) to the reaction system to obtain slurry B; continue to introduce mixed gas and continue stirring at high speed;

[0082] Preparation method of a surface modifier: a. Ring-opening a polyacrylonitrile-styrene-butadiene rubber-carboxylic anhydride functional group terpolymer under sodium hydroxide conditions; b. Saponifying stearic acid in a sodium hydroxide solution at a molar ratio of 1:1; c. Mixing the products of step a and step b at a ratio of 3:4 to prepare a surface modifier;

[0083] (3) Crystal guidance: Continue to introduce mixed gas and continue stirring at high speed until the pH of slurry B reaches 10, then add sulfuric acid with a molar ratio of sulfuric acid to calcium ion of 0.01:1, stir until the pH reaches 6, and then stop aeration;

[0084] The mixed gas is a mixture of carbon dioxide and argon gas, and the flow rate ratio of carbon dioxide to argon gas in the mixed gas is 1:3

[0085] (4) Preparation of modified nano-calcium carbonate: The crystal-guided solution was dried at 70 °C for 40 h to obtain modified nano-calcium carbonate.

[0086] Example 5

[0087] A preparation method for regulating the dispersibility of nano-calcium carbonate based on a nucleation process comprises the following steps:

[0088] (1) Preparing slurry A: Calcium hydroxide slurry and zinc chloride (0.32 wt% of the total amount of calcium hydroxide slurry) were uniformly mixed and stirred at 1100 rpm to obtain slurry A; the concentration of the calcium hydroxide slurry was 5 wt%; the mixed gas was continuously introduced and stirred at high speed;

[0089] (2) Preparation of slurry B: Continuously introduce mixed gas into slurry A and perform carbonization reaction at 40°C. When the slurry begins to gel and become viscous, add a surface modifier (2 wt% of the total amount of calcium hydroxide solution) to the reaction system to obtain slurry B; continue to introduce mixed gas and continue stirring at high speed;

[0090] Preparation method of a surface modifier: a. Ring-opening a polystyrene-N-phenylmaleimide-carboxylic anhydride functional group terpolymer under sodium hydroxide conditions; b. Saponifying stearic acid in a sodium hydroxide solution at a molar ratio of 1:1; c. Mixing the products of step a and step b at a ratio of 4:1 to prepare a surface modifier;

[0091] (3) Crystal guidance: Continue to introduce mixed gas and continue stirring at high speed until the pH of slurry B reaches 9.5, then add sulfuric acid with a molar ratio of sulfuric acid to calcium ion of 0.01:1, stir until the pH reaches 6.5, and then stop aeration;

[0092] The mixed gas is a mixture of carbon dioxide and helium, and the flow rate ratio of carbon dioxide to helium in the mixed gas is 1:3;

[0093] (4) Preparation of modified nano-calcium carbonate: The crystal-guided solution was dried at 60 °C for 35 h to obtain modified nano-calcium carbonate.

[0094] Comparative Example 1: The same as Example 1, except that a surfactant was added to slurry A.

[0095] Comparative Example 2: The same as Example 1, except that the surfactant was changed to commercially available sodium stearate.

[0096] Comparative Example 3: The same as Example 1, except that the surfactant is changed to polystyrene-carboxylic anhydride functional group copolymer and commercially available sodium stearate.

[0097] Morphology Dispersed state Average particle size / nm <![CDATA[Specific surface area / m 2 / g]]> Activation Example 1 oval Good dispersibility 30.6 38.8 95.3％ Example 2 oval Good dispersibility 35.4 37.8 98.6％ Example 3 oval Good dispersibility 33.5 38.1 98.2％ Example 4 oval Good dispersibility 28.2 39.3 97.5％ Example 5 oval Good dispersibility 40.1 28.9 99.8％ Comparative Example 1 Oval and spindle-shaped Slight reunion 556.8 13.4 92.8％ Comparative Example 2 oval Slight reunion 46.2 30.1 73.2％ Comparative Example 3 oval Slight reunion 44.3 30.8 83.2％

[0098] The results of the implementation and comparative cases show that the post-nucleation dispersant addition process and the type of dispersant used in this patent have significant advantages. The strategy of introducing a specific dispersant after nucleation effectively regulates the crystallization behavior of nano-calcium carbonate. The modified nano-calcium carbonate particles prepared by this patent have uniform morphology, narrow particle size distribution, high activation, and good dispersibility. The modified nano-calcium carbonate prepared by this process has excellent overall performance and provides a reliable technical path for the industrial production of highly stable and easily dispersible nanomaterials.

Claims

1. A preparation method for regulating the dispersibility of nano calcium carbonate based on the nucleation process, characterized in that: The following steps are involved: (1) Preparing slurry A: uniformly mixing calcium hydroxide slurry and nucleating agent, and stirring at high speed to obtain slurry A; the concentration of the calcium hydroxide slurry is 5 wt%~10 wt%; (2) Preparation of slurry B: Continuously introduce mixed gas into slurry A to perform carbonization reaction. When the slurry begins to gel and become viscous, add a surface modifier into the reaction system to obtain slurry B; (3) Crystal guidance: When the pH of slurry B is 10±0.5, add the crystal guidance agent and stir until the pH reaches 6.5±0.5, then stop aeration; (4) Preparation of modified nano-calcium carbonate: directly drying the solution after crystal orientation to obtain modified nano-calcium carbonate.

2. The preparation method according to claim 1, wherein The nucleating agent is zinc chloride, and the content of the zinc chloride is 0.1wt% to 5wt% of the total amount of the calcium hydroxide slurry.

3. The preparation method according to claim 1, wherein In the steps (1) to (3), the mixed gas is continuously introduced during the reaction and high-speed stirring is continuously performed.

4. The preparation method according to claim 1, wherein The carbonization reaction temperature is 0°C to 50°C.

5. The preparation method according to claim 1 or 3, wherein The mixed gas is a mixture of carbon dioxide and inert gas, and the flow rate ratio of carbon dioxide to inert gas in the mixed gas is 1:

3.

6. The preparation method according to claim 1, wherein The surface modifier is a composite modifier of copolymer salt and sodium stearate saponification solution, and the mass ratio of the copolymer salt to sodium stearate is 5~1:5~1; The copolymer salt is one of a polystyrene-carboxylic anhydride functional group copolymer, a polystyrene-N-phenylmaleimide-carboxylic anhydride functional group terpolymer, a polyacrylonitrile-styrene-butadiene rubber-carboxylic anhydride functional group terpolymer, and a polybutadiene-acrylonitrile-styrene-carboxylic anhydride functional group tetrapolymer, and the salt is obtained by ring-opening under alkaline conditions; The alkali solution is sodium hydroxide solution.

7. The preparation method according to claim 6, wherein The sodium stearate saponification solution is a product obtained by saponifying stearic acid in a sodium hydroxide solution at a molar ratio of 1:

1.

8. The preparation method according to claim 1 or 6, wherein The amount of the surface modifier is 0.1wt% to 2wt% of the total amount of the calcium hydroxide solution.

9. The preparation method according to claim 1, wherein The high-speed stirring has a rotation speed of 800 rpm to 1200 rpm.

10. The preparation method according to claim 1, wherein The drying temperature is 50-80° C., and the drying time is 24-48 hours.

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