Process for the wet preparation of nanometric calcium carbonate

Abstract

The application belongs to the technical field of fine chemical industry, and particularly relates to a process for preparing nano calcium carbonate by a wet method. The process for preparing nano calcium carbonate by a wet method comprises the following steps: polymerizing N-isopropyl acrylamide and vinyl imidazole to generate a copolymer, then adding the copolymer into a calcium hydroxide suspension to form crystal nuclei and disperse, passing in carbon dioxide gas to perform carbonization reaction, after the reaction is completed, passing in nitrogen to restore the copolymer to neutral and desorb from the crystal surface, and finally performing centrifugal separation, collecting the solid product, and obtaining nano calcium carbonate after vacuum drying. The nano calcium carbonate prepared by the process has uniform particle size and good dispersibility. In the process for producing nano calcium carbonate, no toxic and harmful additives need to be introduced, and the production purity is high.

Description

Technical Field

[0001] This invention belongs to the field of fine chemical technology, specifically relating to a wet process for preparing nano-calcium carbonate. Background Technology

[0002] Nano-calcium carbonate, as a functional inorganic filler with high specific surface area, directly determines its application performance in downstream fields such as rubber and plastics, high-end coatings, and electronic packaging due to its particle size uniformity and morphological regularity. Wet preparation of calcium carbonate remains the mainstream industrial process, but this process still faces several core technological bottlenecks.

[0003] During carbonization, the lack of a precise dynamic control mechanism for crystal nucleation and growth stages leads to excessive local supersaturation, which can easily cause crystal nucleus agglomeration, resulting in a wide particle size distribution and irregular morphology, failing to meet the stringent requirements for filler dispersion in high-end applications. Uneven diffusion of carbon dioxide in the gas-liquid two-phase system leads to an imbalance in the crystal nucleation rate between the interface and the liquid phase, resulting in low reaction efficiency and poor product performance consistency. Simply optimizing process parameters can only provide localized relief and cannot achieve precise control throughout the entire process.

[0004] Meanwhile, existing surfactants and polymeric stabilizers have inherent defects: they are difficult to desorb from the crystal surface in the later stages of production, and their residues reduce product purity and pH stability; or their structure is irreversibly damaged after desorption, making them unrecyclable, which increases production costs and easily causes secondary pollution. In addition, there is a lack of a synergistic growth mechanism between the gas-liquid interface crystal nuclei and the liquid phase crystal nuclei. After the interface crystal nuclei are detached by bubbling shearing, they are prone to disordered agglomeration with the liquid phase crystal nuclei, making it impossible to achieve directional crystal growth, which further restricts the improvement of product quality.

[0005] Therefore, it is urgent to solve the synergistic problems of crystal nucleus regulation, agglomeration inhibition, and regulator recovery in the wet preparation of calcium carbonate. Summary of the Invention

[0006] To address the problems of severe agglomeration, wide particle size distribution, poor morphological regularity, and easy residue of regulators in nano-calcium carbonate prepared by existing processes, which cannot meet the requirements for high dispersibility, high purity, and uniform performance of fillers, this invention provides a wet process for preparing nano-calcium carbonate based on synergistic regulation of the gas-liquid interface.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] A wet process for preparing nano-calcium carbonate includes the following steps: S1. N-Isopropylacrylamide and vinyl imidazole were mixed in a molar ratio of 7:3 and polymerized in a solvent under the action of an initiator. The reaction temperature was 60℃ and the reaction time was 4 hours. After the reaction was completed, the copolymer was obtained by precipitation, dialysis purification and freeze drying. S2. The copolymer is added to the calcium hydroxide suspension. The amount of copolymer added is 17% to 25% of the mass of the calcium hydroxide suspension. The temperature is raised to above 35°C and nitrogen gas is introduced to purge. The copolymer precipitates in the liquid phase to form crystal nuclei and disperse. S3. Then carbon dioxide gas is introduced to carry out the carbonization reaction, and the crystal nuclei are carried into the liquid phase by the shear force generated by the bubbling of carbon dioxide gas. S4. When the pH value drops to 7.5, stop the carbon dioxide gas flow and switch to nitrogen gas flow to restore the copolymer to neutrality and desorb it from the crystal surface. S5. Finally, centrifugation is performed to collect the solid product, which is then dried under vacuum to obtain nano-calcium carbonate.

[0009] Specifically, the initiator is azobisisobutyronitrile; based on the total amount of N-isopropylacrylamide and vinylimidazole monomers, the amount of azobisisobutyronitrile added is 0.1 mol% to 2.0 mol% of the total amount of monomers.

[0010] Specifically, the solvent is tetrahydrofuran.

[0011] Specifically, the concentration of calcium hydroxide in the calcium hydroxide suspension is 1.5 mol / L to 2.5 mol / L.

[0012] Specifically, in step S2, the nitrogen purging time shall be no less than 30 minutes.

[0013] Specifically, in step S2, the temperature is raised to 36℃~38℃.

[0014] Specifically, nitrogen gas is introduced in step S4 for no less than 15 minutes.

[0015] Specifically, after the copolymer is desorbed, it is separated by centrifugation at 36℃-38℃.

[0016] Compared with the prior art, the present invention has the following beneficial effects: In this invention, copolymer microspheres encapsulate crystal nuclei in the liquid phase through electrostatic interaction, directly inhibiting agglomeration; subsequently, nitrogen gas is introduced to desorb the copolymer, releasing crystals for directional growth, ultimately obtaining nano-calcium carbonate with uniform particle size and regular morphology.

[0017] The nano-calcium carbonate prepared by this process exhibits uniform particle size and good dispersibility. This invention utilizes the temperature and carbon dioxide / nitrogen response characteristics of the copolymer to control the timing and state of nucleation and crystal growth. A gas-liquid interface synergistic carbonation mechanism ensures uniform nucleus generation and dispersion, avoiding irregular growth caused by localized supersaturation. Copolymer desorption guarantees directional crystal growth. The combination of these three process steps fundamentally solves the problems of mismatched nuclei and crystal growth, and low reaction efficiency in traditional processes.

[0018] In this invention, the copolymer can be recycled through adsorption and desorption. The copolymer and nano-calcium carbonate are separated by centrifugation, achieving a recovery rate of over 93%. No copolymer residue remains in the finished nano-calcium carbonate product. The entire nano-calcium carbonate production process requires no toxic or harmful additives, resulting in high purity. Attached Figure Description

[0019] Figure 1 This is a scanning electron microscope image of the nano-calcium carbonate prepared in Example 1. Detailed Implementation

[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] The technical solution adopted in this invention is as follows.

[0022] A wet process for preparing nano-calcium carbonate includes the following steps: S1. N-Isopropylacrylamide and vinylimidazole were mixed in a molar ratio of 7:3, using azobisisobutyronitrile as the initiator. Based on the total molar amount of N-isopropylacrylamide and vinylimidazole monomers, the amount of azobisisobutyronitrile added was 0.1 mol%–2.0 mol% of the total monomer amount. Polymerization was carried out in tetrahydrofuran at 60 °C for 4 h. The reaction product was precipitated with methanol, purified by dialysis, and freeze-dried to obtain the copolymer.

[0023] S2. The copolymer is added to a calcium hydroxide suspension, wherein the concentration of calcium hydroxide in the suspension is 1.5 mol / L to 2.5 mol / L. The amount of copolymer added is 17% to 25% of the mass of the calcium hydroxide suspension. The temperature is raised to above 35°C, preferably 36°C to 38°C. Nitrogen gas is then introduced for purging for at least 30 minutes. The copolymer precipitates in the liquid phase, forming crystal nuclei and dispersing.

[0024] S3. Then carbon dioxide gas is introduced to carry out the carbonization reaction, and the crystal nuclei are carried into the liquid phase by the shear force generated by the bubbling of carbon dioxide gas.

[0025] S4. When the pH value drops to 7.5, stop the carbon dioxide gas flow and switch to nitrogen gas flow for at least 15 minutes to allow the copolymer to return to neutral and desorb from the crystal surface.

[0026] S5. Finally, centrifuge at room temperature to collect the solid product, and then vacuum dry to obtain nano-calcium carbonate.

[0027] The copolymer described in this invention becomes positively charged upon the introduction of carbon dioxide gas due to the protonation of the vinylimidazolium matrix, and returns to neutral after degassing with nitrogen gas. Utilizing the low critical dissolution temperature of N-isopropylacrylamide, the copolymer precipitates as microspheres above 35°C and dissolves in water at room temperature. During the initial carbonization with carbon dioxide gas, the copolymer at the gas-liquid interface first comes into contact with the high concentration of carbon dioxide gas. The vinylimidazolium matrix becomes positively charged due to protonation, rapidly adsorbing Ca²⁺ ions diffused from the liquid phase to the interface, forming crystal nuclei at the interface. The shear force generated by the bubbling of carbon dioxide gas peels off the crystal nuclei at the interface and carries them into the liquid phase, where they combine with Ca²⁺ ions adsorbed on the surface of the microspheres to form nuclei. Simultaneously, the microspheres encapsulate the crystal nuclei through electrostatic interaction, inhibiting aggregation. When the pH drops to 7.5, degassing with nitrogen gas for 10 minutes restores the copolymer to neutrality, causing it to desorb from the crystal surface and release crystals for growth. Finally, the copolymer dissolves in water at room temperature, and centrifugation ensures that the copolymer does not remain in the nano-calcium carbonate.

[0028] To verify the beneficial effects of the present invention, several sets of embodiments were designed for verification.

[0029] Example 1 A wet process for preparing nano-calcium carbonate includes the following steps: S1. N-Isopropylacrylamide and vinylimidazole were mixed in a molar ratio of 7:3, using azobisisobutyronitrile as the initiator. Based on the total molar amount of N-isopropylacrylamide and vinylimidazole monomers, the amount of azobisisobutyronitrile added was 0.15 mol% of the total monomer amount. Polymerization was carried out in tetrahydrofuran at 60°C for 4 hours. The reaction product was purified by methanol precipitation, dialysis, and freeze-drying to obtain the copolymer.

[0030] S2. The copolymer is added to a calcium hydroxide suspension, wherein the concentration of calcium hydroxide in the suspension is 2 mol / L. The amount of copolymer added is 20% of the mass of the calcium hydroxide suspension, and the temperature is raised to 36°C. Nitrogen gas is then introduced to purge the solution for 35 minutes. The copolymer precipitates in the liquid phase, forming crystal nuclei and dispersing.

[0031] S3. Then carbon dioxide gas is introduced to carry out the carbonization reaction, and the crystal nuclei are carried into the liquid phase by the shear force generated by the bubbling of carbon dioxide gas.

[0032] S4. When the pH value drops to 7.5, stop the carbon dioxide gas flow and switch to nitrogen gas flow for 20 minutes to allow the copolymer to return to neutral and desorb from the crystal surface.

[0033] S5. Finally, centrifuge at room temperature to collect the solid product, and then vacuum dry to obtain nano-calcium carbonate.

[0034] Example 2 A wet process for preparing nano-calcium carbonate includes the following steps: S1. N-Isopropylacrylamide and vinylimidazole were mixed in a molar ratio of 7:3, using azobisisobutyronitrile as the initiator. Based on the total molar amount of N-isopropylacrylamide and vinylimidazole monomers, the amount of azobisisobutyronitrile added was 0.1 mol% of the total monomer amount. Polymerization was carried out in tetrahydrofuran at 60°C for 4 hours. The reaction product was precipitated with methanol, purified by dialysis, and freeze-dried to obtain the copolymer.

[0035] S2. The copolymer is added to a calcium hydroxide suspension, wherein the concentration of calcium hydroxide in the suspension is 1.5 mol / L. The amount of copolymer added is 17% of the mass of the calcium hydroxide suspension, and the temperature is raised to 37°C. Nitrogen gas is then introduced to purge the solution for 33 minutes. The copolymer precipitates in the liquid phase, forming crystal nuclei and dispersing.

[0036] S3. Then carbon dioxide gas is introduced to carry out the carbonization reaction, and the crystal nuclei are carried into the liquid phase by the shear force generated by the bubbling of carbon dioxide gas.

[0037] S4. When the pH value drops to 7.5, stop the carbon dioxide gas flow and switch to nitrogen gas flow for 18 minutes to allow the copolymer to return to neutral and desorb from the crystal surface.

[0038] S5. Finally, centrifuge at room temperature to collect the solid product, and then vacuum dry to obtain nano-calcium carbonate.

[0039] Example 3 A wet process for preparing nano-calcium carbonate includes the following steps: S1. N-Isopropylacrylamide and vinylimidazole were mixed in a molar ratio of 7:3, using azobisisobutyronitrile as the initiator. Based on the total molar amount of N-isopropylacrylamide and vinylimidazole monomers, the amount of azobisisobutyronitrile added was 2.0 mol% of the total monomer amount. Polymerization was carried out in tetrahydrofuran at 60°C for 4 hours. The reaction product was precipitated with methanol, purified by dialysis, and freeze-dried to obtain the copolymer.

[0040] S2. The copolymer is added to a calcium hydroxide suspension, wherein the concentration of calcium hydroxide in the suspension is 2.5 mol / L. The amount of copolymer added is 25% of the mass of the calcium hydroxide suspension, and the temperature is raised to 38°C. Nitrogen gas is then introduced to purge the solution for 40 minutes. The copolymer precipitates in the liquid phase, forming crystal nuclei and dispersing.

[0041] S3. Then carbon dioxide gas is introduced to carry out the carbonization reaction, and the crystal nuclei are carried into the liquid phase by the shear force generated by the bubbling of carbon dioxide gas.

[0042] S4. When the pH value drops to 7.5, stop the carbon dioxide gas flow and switch to nitrogen gas flow for 25 minutes to allow the copolymer to return to neutral and desorb from the crystal surface.

[0043] S5. Finally, centrifuge at room temperature to collect the solid product, and then vacuum dry to obtain nano-calcium carbonate.

[0044] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A wet process for preparing nano-calcium carbonate, characterized in that, Includes the following steps: S1. N-Isopropylacrylamide and vinyl imidazole were mixed in a molar ratio of 7:3 and polymerized in a solvent under the action of an initiator. The reaction temperature was 60℃ and the reaction time was 4 hours. After the reaction was completed, the copolymer was obtained by precipitation, dialysis purification and freeze drying. S2. The copolymer is added to the calcium hydroxide suspension. The amount of copolymer added is 17% to 25% of the mass of the calcium hydroxide suspension. The temperature is raised to 36℃ to 38℃ and nitrogen gas is introduced for purging. The copolymer precipitates in the liquid phase to form crystal nuclei and disperse. S3. Then carbon dioxide gas is introduced to carry out the carbonization reaction, and the crystal nuclei are carried into the liquid phase by the shear force generated by the bubbling of carbon dioxide gas. S4. When the pH value drops to 7.5, stop the carbon dioxide gas flow and switch to nitrogen gas flow to restore the copolymer to neutrality and desorb it from the crystal surface. S5. Finally, centrifugation is performed to collect the solid product, which is then dried under vacuum to obtain nano-calcium carbonate. The initiator is azobisisobutyronitrile; based on the total molar amount of N-isopropylacrylamide and vinylimidazole monomers, the amount of azobisisobutyronitrile added is 0.1 mol% to 2.0 mol% of the total molar amount of monomers. The concentration of calcium hydroxide in the calcium hydroxide suspension is 1.5 mol / L to 2.5 mol / L; The nitrogen purging time in S2 shall not be less than 30 minutes; Nitrogen gas should be introduced into S4 for at least 15 minutes.

2. The wet process for preparing nano-calcium carbonate according to claim 1, characterized in that, The solvent is tetrahydrofuran.

3. The wet process for preparing nano-calcium carbonate according to claim 1, characterized in that, After desorption, the copolymer is separated by centrifugation at room temperature.

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