Ultrafine nanometer calcium carbonate continuous production equipment, production method and product

Abstract

The application relates to the technical field of nano calcium carbonate preparation, in particular to a continuous production equipment and method of ultra-micro nano calcium carbonate and a product. 2+ and CO3 2‑ The high-efficiency nucleation supergravity reactor, and the pipeline reactor for completing uniform growth after nucleation of Ca 2+ and CO3 2‑ The discharge port of the supergravity reactor is in communication with the feeding port of the pipeline reactor. The production method can realize the synergistic control of high-efficiency nucleation of Ca 2+ and CO3 2‑ and uniform growth after nucleation of the two. The product is nano calcium carbonate with a target particle size D50 of 15-20 nm prepared by the production method.

Description

Technical Field

[0001] This invention relates to the field of nano-calcium carbonate preparation technology, and in particular to a continuous production equipment, production method and product for ultra-micro nano-calcium carbonate. Background Technology

[0002] Traditional processes for preparing nano-calcium carbonate typically include bubbling carbonation and spray carbonation. These methods have many inherent drawbacks: they rely heavily on human experience to control reaction parameters, resulting in low automation; they are difficult to precisely control the nucleation and growth process of ultrafine particles, and are prone to explosive nucleation or excessive crystal growth due to local fluctuations in calcium hydroxide supersaturation, ultimately leading to a wide particle size distribution and poor uniformity of the product calcium carbonate.

[0003] In addition, the preparation of nano-calcium carbonate also includes the hypergravity method. The hypergravity method enhances gas-liquid mass transfer by generating a strong shear field through a rotating packed bed, and uses gravitational acceleration to achieve rapid nanoscale mixing of materials. Among them, the hypergravity "one-step method" (i.e., the simultaneous completion of nucleation and crystal growth in a single reactor) intensifies the coupling effect of mass transfer and reaction because the reaction occurs in the same space. The local supersaturation of calcium hydroxide fluctuates drastically, and the lack of independent control space leads to an imbalance between nucleation and growth rates. Excessive supersaturation of calcium hydroxide easily leads to explosive nucleation, while insufficient supersaturation causes excessive crystal growth, making precise control difficult.

[0004] To circumvent the problems of the one-step method using hypergravity, a process combining a hypergravity reactor and a circulating tank was introduced. The crystal nucleus slurry generated by hypergravity is circulated to the circulating tank containing unreacted Ca(OH)2, attempting to balance the effect on Ca. 2+ (i.e., Ca in Ca(OH)2 solution) 2+ ) and CO3 2- (i.e., CO3 produced by the reaction of CO2 with Ca(OH)2 solution) 2- Efficient nucleation and synergistic control over the life cycle of both nuclei and Ca. However, in the cycle, the nucleus and Ca... 2+ Uneven contact leads to fluctuations in secondary nucleation efficiency, abnormal growth of some particles, and exacerbated polydispersity; at the same time, backmixing in the circulating tank disrupts continuity, resulting in a final product with a broad distribution, making it impossible to achieve Ca... 2+ and CO3 2- Efficient nucleation and synergistic control over the growth of both nucleated and unnucleated materials are key aspects. Additionally, a few employ a single-cycle, non-cyclic model, where crystal nuclei are generated under hypergravity and then directly enter the growth stage. However, this method suffers from low CO2 solubility and low Ca2+ solubility under normal pressure. 2+ Insufficient conversion rate, insufficient number of crystal nuclei, residual Ca 2+ Rapid deposition on a small number of crystal nuclei easily leads to the formation of coarse particles, resulting in low raw material utilization and making it impossible to achieve Ca… 2+ and CO3 2-Efficient nucleation and coordinated control over the life cycle of both nucleated organisms.

[0005] Therefore, it is necessary to provide a continuous production equipment, method, and product for ultra-micro nano-calcium carbonate to address the limitations of existing technologies that combine centrifugal reactors and circulating tanks in achieving the desired calcium carbonate production. 2+ and CO3 2- The issues include efficient nucleation and the coordinated control of the life cycle of both nucleated organisms. Summary of the Invention

[0006] The purpose of this invention is to provide a continuous production equipment, production method, and product for ultra-micro nano-calcium carbonate. The specific technical solution is as follows:

[0007] In a first aspect, the present invention provides a continuous production equipment for ultra-micro nano calcium carbonate, including a storage tank, a gas storage tank, a supergravity reactor, a pipeline reactor, a stirring component, a first pressure sensor, a temperature sensor, and a second pressure sensor.

[0008] The storage tank is connected to the top inlet of the supergravity reactor via a feeding assembly;

[0009] The gas storage tank is connected to the bottom air inlet of the hypergravity reactor through the first air inlet assembly;

[0010] The gas storage tank is connected to the feed inlet of the pipeline reactor via a second air inlet assembly;

[0011] The outlet of the supergravity reactor is connected to the inlet of the pipeline reactor;

[0012] The stirring end of the stirring component is disposed inside the storage tank, while the end of the component away from the stirring end extends through the outside of the storage tank and is connected to the driving component.

[0013] Both the first pressure sensor and the temperature sensor are installed inside the hypergravity reactor;

[0014] The second pressure sensor is installed inside the pipeline reactor.

[0015] Optionally, the pipeline reactor is an integrally formed continuous S-shaped curved pipeline structure; the inner diameter of the pipeline reactor is 80~125mm, and the length is 30~50m.

[0016] Optionally, the continuous production equipment for ultra-micro nano calcium carbonate further includes a gas-liquid separator; the feed end of the gas-liquid separator is connected to the discharge port of the supergravity reactor, and its discharge end is connected to the feed port of the pipeline reactor through a discharge component.

[0017] The discharge assembly includes a discharge pipeline and a discharge pump; the two ends of the discharge pipeline are respectively connected to the inlet of the gas-liquid separator and the pipeline reactor; the discharge pump is installed on the discharge pipeline.

[0018] A pH meter is installed on the pipeline between the gas-liquid separator and the hypergravity reactor;

[0019] The feeding assembly includes a feeding pipeline and a feeding pump; the two ends of the feeding pipeline are respectively connected to the top inlet of the storage tank and the supergravity reactor; the feeding pump is installed on the feeding pipeline;

[0020] The first air intake assembly includes a first air intake pipe, a first flow meter, and a first regulating valve; both ends of the first air intake pipe are connected to the bottom air inlet of the gas storage tank and the supergravity reactor, respectively; the first flow meter and the first regulating valve are both installed on the first air intake pipe;

[0021] The second air intake assembly includes a second air intake pipe, a second flow meter, and a second regulating valve; the two ends of the second air intake pipe are respectively connected to the inlet of the gas storage tank and the feed port of the pipeline reactor; the second flow meter and the second regulating valve are both installed on the second air intake pipe.

[0022] In a second aspect, the present invention provides a continuous production method for ultra-micro nano-calcium carbonate, comprising:

[0023] Step S1: The CaO raw material is pretreated to obtain a mass concentration of 6.0% ± 0.3% and a specific surface area of ​​[missing information]. S 比 Not less than 85m 2 / kg of Ca(OH)2 suspension;

[0024] Step S2: The Ca(OH)2 suspension is continuously reacted using the aforementioned ultra-micro nano calcium carbonate continuous production equipment;

[0025] Specifically, the Ca(OH)₂ suspension is stored in the storage tank, and CO₂ gas is stored in the gas storage tank; the Ca(OH)₂ suspension is fed into the top inlet of the supergravity reactor using the feeding assembly, and the feed flow rate of the Ca(OH)₂ suspension is controlled to be 4-6 m³ / s. 3 / h; CO2 gas is introduced into the bottom inlet of the supergravity reactor using the first inlet assembly, and the CO2 gas flow rate is controlled to be 300~400 Nm³. 3 The inlet air pressure is 0.6~1.0 MPa per hour; the rotational speed of the centrifugal reactor is controlled. The pressure inside the hypergravity reactor is controlled at 1800~2200 r / min.P The pressure is 0.30~0.45MPa, and the reaction temperature inside the hypergravity reactor is controlled at 20±2℃; the residence time of the reaction system formed by the convective mixing of the Ca(OH)2 suspension and CO2 gas inside the hypergravity reactor is... t The homogeneous nucleation reaction is completed in 5-7 seconds, yielding the first reaction solution; wherein, the Ca(OH)2 suspension contains Ca... 2+ Conversion rate after the homogeneous nucleation reaction is completed X It ranges from 30% to 42%;

[0026] The first reaction solution is conveyed to the pipeline reactor, and the conveying flow rate is controlled at 0.27~0.62m / s; CO2 gas is introduced into the pipeline reactor using the second air inlet assembly, and the pressure inside the pipeline reactor is controlled. The pressure is 0.2~0.3 MPa; the reaction temperature inside the pipeline reactor is controlled at 20±2℃; the residence time of the first reaction liquid and CO2 gas inside the pipeline reactor is... The uniform crystal nucleus growth reaction is completed in 105~130s, yielding the second reaction solution;

[0027] Step S3: After the second reaction liquid is subjected to the first post-treatment, ultrafine nano-calcium carbonate with a target particle size D50 of 15~20nm is obtained; the CO2 tail gas discharged from the supergravity reactor and the pipeline reactor is discharged after the second post-treatment.

[0028] Optionally, in step S2, the Ca in the Ca(OH)2 suspension is determined using equation (1-1) according to the heat balance equation. 2+ Conversion rate after the homogeneous nucleation reaction is completed X :

[0029] Equation (1-1);

[0030] in, ρ This indicates the density of the Ca(OH)2 suspension in the supergravity reactor. c p This represents the specific heat capacity of the Ca(OH)2 suspension in the supergravity reactor. This indicates the flow rate of the Ca(OH)2 suspension in the supergravity reactor. ΔT This indicates the temperature increase caused by the reaction of the Ca(OH)₂ suspension with CO₂ gas to produce calcium carbonate in the hypergravity reactor. ΔT ≤1.2K; n aThis represents the molar flow rate of the Ca(OH)₂ suspension in the centrifugal reactor. ΔH| This represents the absolute value of the enthalpy of calcium carbonate produced by the reaction of the Ca(OH)2 suspension with CO2 gas in the supergravity reactor.

[0031] From equation (1-1) and ΔT ≤1.2K, determine the conversion rate X The upper limit is no higher than 42%;

[0032] To control the standard deviation of primary nucleus particle size in the first reaction solution after the homogeneous nucleation reaction is completed. σ ≤2nm, determine conversion rate X The lower limit is no less than 30%.

[0033] Optionally, in step S2, the rotational speed of the hypergravity reactor is determined using equation (1-2). :

[0034] Equation (1-2);

[0035] in, β Indicates the supergravity factor; g Represents gravitational acceleration; This represents the radius of the core reaction zone in the rotor packing region of the supergravity reactor.

[0036] β The lower limit is determined using equations (1-3) and (1-4):

[0037] Equation (1-3);

[0038] Equation (1-4);

[0039] in, The mass transfer coefficient in the liquid phase; The specific surface area of ​​the gas and liquid phases;

[0040] Solving equations (1-3) and (1-4) simultaneously, we obtain 900≤ β ;

[0041] β The theoretical upper limit value is β ≤1300;

[0042] according to β The lower limit and theoretical upper limit are used to determine the rotational speed using equation (1-2). The speed is 1800~2200 r / min.

[0043] Optionally, in step S2, the pressure inside the hypergravity reactor is determined by simultaneously using equations (1-5), (1-6), and (1-7). P The pressure is 0.30~0.45MPa.

[0044] Equation (1-5);

[0045] Equation (1-6);

[0046] Equation (1-7);

[0047] in, This represents the mass transfer rate of CO2 within the supergravity reactor. Indicates the volumetric mass transfer coefficient within the hypergravity reactor; CO [2] indicates the solubility of CO2 within the supergravity reactor; K H Represents the Henry's constant; c 0 represents the initial molar concentration of the Ca(OH)2 suspension in the supergravity reactor.

[0048] Optionally, in step S1, the specific surface area of ​​the Ca(OH)2 suspension is determined using formula (1-8). S 比 The lower limit is not less than 85m 2 / kg:

[0049] Equation (1-8);

[0050] in, This represents the dissolution rate constant of calcium hydroxide in the Ca(OH)₂ suspension within the hypergravity reactor. This indicates the saturation concentration of the Ca(OH)2 suspension within the supergravity reactor. c This indicates the concentration of the reaction system within the hypergravity reactor; This indicates the solid mass of calcium hydroxide in the Ca(OH)2 suspension within the supergravity reactor.

[0051] Optionally, in step S1, the pretreatment includes first grinding the CaO raw material to a particle size ≤10μm, then digesting and removing impurities to obtain refined lime milk, then adding water to adjust to obtain a Ca(OH)2 suspension with a mass concentration of 6.0%±0.3%, and finally adding a dispersant to the Ca(OH)2 suspension, and after stirring and mixing, obtaining the specific surface area. S 比 Not less than 85m 2 / kg of Ca(OH)2 suspension;

[0052] The dispersant includes sodium polyacrylate, which is added at a rate of 0.2% to 0.6% of the mass of the Ca(OH)2 suspension.

[0053] In step S3, the first post-processing includes sequentially performing solid-liquid separation, washing to remove impurities, and drying and classifying the second reaction solution to obtain the ultrafine nano calcium carbonate.

[0054] The solid-liquid separation includes performing hydrocyclone separation on the second reaction liquid to obtain a first underflow; centrifuging the first underflow to obtain a second underflow; and dehydrating the second underflow at 0.6~0.8MPa to obtain a wet material with a moisture content of 32%~38%.

[0055] The washing and impurity removal process includes washing the wet material with water until the conductivity of the filtrate is ≤50μS / cm;

[0056] The drying and grading process includes first drying the washed and cleaned wet material to a moisture content of <1%, and then grading and purifying it.

[0057] The second post-treatment includes absorbing the CO2 tail gas through a water scrubbing tower before discharging it in compliance with emission standards.

[0058] In a third aspect, the present invention provides an ultrafine nano calcium carbonate product, which is produced by the aforementioned continuous production method for ultrafine nano calcium carbonate.

[0059] The application of the technical solution of the present invention has at least the following beneficial effects:

[0060] (1) The present invention provides a continuous production equipment for ultra-micro nano calcium carbonate, which is used to achieve the production of Ca²⁺ and CO₃²⁻. 2- It provides the equipment foundation for efficient nucleation and the coordinated control of the life cycle of both nucleated nuclei.

[0061] (2) The present invention provides a continuous production method for ultrafine nano-calcium carbonate, which can realize the production of Ca²⁺ and CO₃²⁻. 2- This invention achieves efficient nucleation and synergistic control over the growth of both nucleated and unnucleated calcium carbonate particles, thereby enabling continuous production of ultrafine nano-calcium carbonate with a target particle size D50 of 15-20 nm. Specifically, to achieve continuous production of ultrafine nano-calcium carbonate, this invention limits the feed flow rate of the Ca(OH)₂ suspension in the hypergravity reactor to 4-6 m³ / h. 3 / h, and the CO2 gas inlet flow rate is 300~400Nm 3 / h; further, the rotational speed in the hypergravity reactor. nWith a speed of 1800~2200 r / min, it can provide a hypergravity environment, thereby generating centrifugal force with accelerations hundreds to thousands of times greater than gravity. This forcefully compresses the reaction system into the tiny gaps of the packed bed, maximizing "micro-mixing" and "uniformity of reaction conditions." This avoids back-mixing phenomena such as "partial material backflow" and also prevents the formation of "explosive" crystal nuclei caused by excessive local Ca(OH)2 supersaturation. Furthermore, this invention limits the pressure within the hypergravity reactor. P The pressure is 0.30~0.45 MPa, driving the Ca in the entire reaction system. 2+ With CO3 2- The concentration becomes instantly uniform, completely eliminating local supersaturation differences. All crystal nuclei are generated synchronously under the same "critical supersaturation," thus ensuring the consistency of initial size and efficiently completing the uniform crystal nucleus formation reaction. In addition, to ensure the smooth and continuous completion of the uniform crystal nucleus formation reaction and avoid fluctuations in nucleation conditions, this invention also limits the reaction temperature to 20±2℃ and the residence time of the reaction system in the hypergravity reactor. t The rotational speed is 5-7 seconds. Furthermore, the strong shear force generated by the limited rotational speed in the hypergravity reactor continues to act on the newly formed micro-nuclei, preventing their aggregation. On the other hand, the shear force also inhibits the "non-uniform growth" of the nuclei in the early stages of formation (e.g., preventing some nuclei from preferentially adsorbing ions and growing abnormally), ensuring that all nuclei grow slowly at the same rate, achieving uniformity in nuclei size. Further, this invention uses a tubular reactor to complete the uniform nucleus growth reaction, rather than generating new nuclei. Specifically, if new nuclei are generated in the tubular reactor, a higher Ca(OH)₂ supersaturation is required to overcome the surface energy barrier, while completing the uniform nucleus growth reaction only requires a lower Ca(OH)₂ supersaturation. 2+ It can then attach and grow on the surface of the crystal nucleus, therefore Ca 2+ The growth will preferentially attach to the surface of the crystal nucleus rather than spontaneously forming new crystal nuclei; furthermore, in order to ensure the continuous and smooth completion of the uniform crystal nucleus growth reaction, this invention limits the flow rate of the feed liquid into the pipeline reactor to 0.27~0.62m / s, controls the reaction temperature in the pipeline reactor to 20±2℃, and limits the residence time of the first reaction feed liquid and CO2 gas in the pipeline reactor. tʹ The time frame is 105-130 s, ensuring that the crystal nuclei at any position in the tubular reactor have similar growth reaction conditions, facilitating uniform crystal nuclei growth and avoiding abnormal growth or stagnation. Therefore, this invention combines a hypergravity reactor and a tubular reactor, along with appropriate control parameters, to achieve continuous production of ultrafine nano-calcium carbonate with a target particle size D50 of 15-20 nm.

[0062] In addition to the objectives, features, and advantages described above, the present invention has other objectives, features, and advantages. The invention will now be described in further detail with reference to the figures. Attached Figure Description

[0063] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0064] Figure 1 This is a schematic diagram of the structure of a continuous production equipment for ultra-micro nano calcium carbonate during operation, as described in the embodiment.

[0065] Figure 2 This is the particle size distribution of nano-calcium carbonate prepared by the supergravity method in existing literature.

[0066] The following are the reference numerals: 1. Storage tank, 2. Gas storage tank, 3. Hypergravity reactor, 4. Pipeline reactor, 5. Gas-liquid separator, 6. Discharge pump, 7. pH meter, 8. Feed pump, 9. First flow meter, 10. First regulating valve, 11. Second flow meter, 12. Second regulating valve, 13. Conductivity meter. Detailed Implementation

[0067] 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 a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0068] Example:

[0069] See Figure 1 A continuous production line for ultra-micro nano-calcium carbonate includes a storage tank 1, a gas storage tank 2, and a high-gravity reactor 3 (using a pressure-resistant rotating packed bed as the high-gravity reactor 3, with a processing capacity of 4~6 m³ / s). 3 / h, pressure resistance ≥1.0MPa), pipeline reactor 4, stirring component, first pressure sensor (not shown in the figure), temperature sensor (not shown in the figure) and second pressure sensor (not shown in the figure);

[0070] The storage tank 1 is connected to the top inlet of the supergravity reactor 3 via a feeding assembly;

[0071] The gas storage tank 2 is connected to the bottom air inlet of the supergravity reactor 3 through the first air inlet assembly;

[0072] The gas storage tank 2 is connected to the feed inlet of the pipeline reactor 4 through the second air inlet assembly;

[0073] The outlet of the supergravity reactor 3 is connected to the inlet of the pipeline reactor 4;

[0074] The stirring end of the stirring component is located inside the storage tank 1, while the end of the component away from the stirring end extends through the outside of the storage tank 1 and is connected to a driving component (such as a motor).

[0075] Both the first pressure sensor and the temperature sensor are installed inside the hypergravity reactor 3;

[0076] The second pressure sensor is installed inside the pipeline reactor 4.

[0077] The pipeline reactor 4 is an integrally formed continuous S-shaped curved pipeline structure; the inner diameter of the pipeline reactor 4 is 80~125mm (specifically 106mm), and the length is 30~50m (specifically 40m).

[0078] The continuous production equipment for ultra-micro nano calcium carbonate also includes a gas-liquid separator 5; the feed end of the gas-liquid separator 5 is connected to the discharge port of the supergravity reactor 3, and its discharge end is connected to the feed port of the pipeline reactor 4 through the discharge component.

[0079] The discharge assembly includes a discharge pipeline and a discharge pump 6; the two ends of the discharge pipeline are respectively connected to the inlet of the gas-liquid separator 5 and the pipeline reactor 4; the discharge pump is installed on the discharge pipeline.

[0080] A pH meter 7 is installed on the pipeline between the gas-liquid separator 5 and the supergravity reactor 3;

[0081] The feeding assembly includes a feeding pipeline and a feeding pump 8; the two ends of the feeding pipeline are respectively connected to the top inlet of the storage tank 1 and the supergravity reactor 3; the feeding pump is installed on the feeding pipeline;

[0082] The first air intake assembly includes a first air intake pipe, a first flow meter 9, and a first regulating valve 10; the two ends of the first air intake pipe are respectively connected to the bottom air inlets of the gas storage tank 2 and the supergravity reactor 3; the first flow meter 9 and the first regulating valve 10 are both installed on the first air intake pipe;

[0083] The second air intake assembly includes a second air intake pipe, a second flow meter 11, and a second regulating valve 12; the two ends of the second air intake pipe are respectively connected to the inlet of the gas storage tank 2 and the feed port of the pipeline reactor 4; the second flow meter 11 and the second regulating valve 12 are both installed on the second air intake pipe.

[0084] A continuous production method for ultrafine nano-calcium carbonate includes:

[0085] Step S1: The CaO raw material is pretreated to obtain a mass concentration of 6.0% ± 0.3% and a specific surface area of ​​[missing information]. S 比 Not less than 85m 2 / kg of Ca(OH)2 suspension;

[0086] Step S2: The Ca(OH)2 suspension is continuously reacted using the aforementioned ultra-micro nano calcium carbonate continuous production equipment;

[0087] Specifically, the Ca(OH)₂ suspension is stored in the storage tank 1, and CO₂ gas (purity ≥ 99.5%) is stored in the gas storage tank 2. The Ca(OH)₂ suspension is fed into the top inlet of the supergravity reactor 3 using the feeding assembly, and the feed flow rate of the Ca(OH)₂ suspension is controlled to be 4~6 m³ / s. 3 / h; CO2 gas is introduced into the bottom inlet of the supergravity reactor 3 using the first inlet assembly, and the CO2 gas inlet flow rate is controlled to be 300~400 Nm³. 3 / h, with an inlet air pressure of 1.0 MPa; control the rotational speed of the hypergravity reactor 3. The pressure inside the hypergravity reactor 3 is controlled at 1800~2200 r / min. P The pressure is 0.30~0.45MPa, and the reaction temperature inside the hypergravity reactor 3 is controlled at 20±2℃; the residence time of the reaction system formed by the convective mixing of the Ca(OH)2 suspension and CO2 gas inside the hypergravity reactor 3 is... t The homogeneous nucleation reaction is completed in 5-7 seconds, yielding the first reaction solution; wherein, the Ca(OH)2 suspension contains Ca... 2+ Conversion rate after the homogeneous nucleation reaction is completed X It ranges from 30% to 42%;

[0088] The first reaction liquid is conveyed to the pipeline reactor 4 (it should be noted that the first reaction liquid can also flow into the gas-liquid separator 5 first, and then the liquid processed by the gas-liquid separator is conveyed to the pipeline reactor 4 using the discharge component), and the conveying flow rate is controlled to be 0.27~0.62m / s; CO2 gas is introduced into the pipeline reactor 4 using the second air inlet component, and the pressure inside the pipeline reactor 4 is controlled. The pressure is 0.2~0.3 MPa; the reaction temperature inside the pipeline reactor 4 is controlled at 20±2℃; the residence time of the first reaction liquid and CO2 gas inside the pipeline reactor 4 is... The uniform crystal nucleus growth reaction is completed in 105~130s, yielding the second reaction solution;

[0089] Step S3: The second reaction liquid is collected through the discharge pipeline (a pH meter 7 and a conductivity meter 13 are installed on the discharge pipeline), and then subjected to the first post-treatment to obtain ultrafine nano calcium carbonate with a target particle size D50 of 20 nm; the CO2 tail gas discharged from the supergravity reactor 3 and the pipeline reactor 4 is discharged after the second post-treatment.

[0090] In step S2, the Ca in the Ca(OH)2 suspension is determined using equation (1-1) according to the heat balance equation. 2+ Conversion rate after the homogeneous nucleation reaction is completed X :

[0091] Equation (1-1);

[0092] in, ρ This represents the density of the Ca(OH)₂ suspension in the supergravity reactor 3, and is taken as 1050 kg / m³. 3 ; c p This represents the specific heat capacity of the Ca(OH)2 suspension in the supergravity reactor 3. Q The value represents the flow rate of the Ca(OH)₂ suspension in the supergravity reactor 3, and is taken as 1.39 × 10⁻⁶. -3 m 3 / s; ΔT This indicates the temperature increase caused by the reaction of the Ca(OH)₂ suspension with CO₂ gas to produce calcium carbonate in the hypergravity reactor 3. ΔT ≤1.2K; n a The value represents the molar flow rate of the Ca(OH)₂ suspension in the supergravity reactor 3, and is 1.13 mol / s; ΔH |This represents the absolute value of the enthalpy of calcium carbonate generated by the reaction of the Ca(OH)2 suspension with CO2 gas in the supergravity reactor 3, and is 15.6 kJ / mol.

[0093] From equation (1-1) and ΔT ≤1.2K, determine the conversion rate X The upper limit is no higher than 42%;

[0094] To control the first reaction solution to complete the uniform crystal nucleation reaction in the pipeline reactor 4 and determine the conversion rate X satisfy: Therefore, the conversion rate can be obtained. X The final upper limit shall not exceed 40%;

[0095] To control the standard deviation of primary nucleus particle size in the first reaction solution after the homogeneous nucleation reaction is completed. σ ≤2nm, determine conversion rate X The lower limit is no less than 30%.

[0096] It can be seen that 30%≤ X ≤40%.

[0097] when X When the concentration is >38%, due to changes in the concentration distribution of substances in the reaction system and reaction kinetic parameters, the supersaturation of the secondary reaction S <20, the growth rate is insufficient, and the actual particle size is <19nm, therefore the conversion rate is low. X The upper limit is 38%. Therefore... X The range is 30% ≤ X ≤38%. From the above results, it can be seen that when... X The particle size distribution is optimal when the particle size distribution is 35%.

[0098] when X When the content is 35%, according to the law of conservation of mass:

[0099] ;

[0100] To determine the crystal nucleus size after the uniform nucleation reaction, the above formula is used to calculate... It is approximately equal to 14.1nm.

[0101] The volume increment required for the secondary reaction (i.e., the reaction to complete the formation of uniform nuclei) is as follows:

[0102] ;

[0103] in, The target particle size D50 is 20nm. In the above calculation, the intermediate value of 20nm is taken.

[0104] Corresponding substance ratio:

[0105] ;

[0106] in, This indicates the amount of substance consumed by the Ca(OH)2 suspension in the supergravity reactor 3 to complete the homogeneous crystal nucleation reaction; This indicates the amount of substance remaining in the Ca(OH)2 suspension in the supergravity reactor 3 after the homogeneous crystal nucleation reaction is completed; / The ratio result can match the volume increment requirement of secondary growth (i.e., completing the uniform nucleation reaction). Therefore... X =35% is the optimal value.

[0107] Since the two are equal, it can be concluded that 14.1nm can be grown to 20nm through a secondary reaction.

[0108] In step S2, the rotational speed of the hypergravity reactor 3 is determined using equation (1-2). :

[0109] Equation (1-2);

[0110] in, β Indicates the supergravity factor; g Represents gravitational acceleration; This indicates the radius of the core reaction zone in the rotor packing region of the supergravity reactor 3; the core reaction zone is 1 / 3 of the inner circle of the rotor packing region; the outer diameter of the rotor packing region is 800 mm, and the inner diameter is 440 mm.

[0111] β The lower limit is determined using equations (1-3) and (1-4):

[0112] Equation (1-3);

[0113] Equation (1-4);

[0114] in, The mass transfer coefficient in the liquid phase; The specific surface area of ​​the gas and liquid phases;

[0115] Solving equations (1-3) and (1-4) simultaneously, we obtain 900≤ β ;

[0116] Considering energy consumption and economy, set β The theoretical upper limit value is β ≤1300; Experiments show that when βAfter reaching 1300, the effect on crystal nucleus size and dispersibility is minimal, but energy consumption increases dramatically.

[0117] according to β The lower limit and theoretical upper limit are used to determine the rotational speed using equation (1-2). The speed is 1800~2200 r / min.

[0118] In step S2, the pressure inside the hypergravity reactor 3 is determined by simultaneously using equations (1-5), (1-6), and (1-7). P The pressure is 0.30~0.45MPa.

[0119] Equation (1-5);

[0120] Equation (1-6);

[0121] Equation (1-7);

[0122] in, This indicates the mass transfer rate of CO2 within the hypergravity reactor 3. This represents the volumetric mass transfer coefficient within the hypergravity reactor 3; CO [2] indicates the solubility of CO2 within the hypergravity reactor 3; K H Represents the Henry's constant; c 0 represents the initial molar concentration of the Ca(OH)2 suspension in the supergravity reactor 3.

[0123] In step S1, the specific surface area of ​​the Ca(OH)2 suspension is determined using equation (1-8). S 比 The lower limit is not less than 85m 2 / kg:

[0124] Equation (1-8);

[0125] in, The value represents the dissolution rate constant of calcium hydroxide in the Ca(OH)₂ suspension within the hypergravity reactor 3, and is taken as 1.2 × 10⁻⁶. -5 m / s; This indicates the saturation concentration of the Ca(OH)2 suspension in the supergravity reactor 3, with a value of 0.185 mol / L. c The concentration of the reaction system within the hypergravity reactor 3 is 0.527 mol / L. This represents the solid mass of calcium hydroxide in the Ca(OH)2 suspension within the supergravity reactor 3, and is taken as 0.18 kg.

[0126] In step S1, the pretreatment includes first grinding the CaO raw material in a ball mill until the particle size is ≤10μm to obtain CaO powder; then, after digestion and impurity removal, refined lime milk is obtained, which is then sent to a dilution tank and water is added to adjust the concentration to obtain a Ca(OH)2 suspension with a mass concentration of 6.0%±0.3%; finally, a dispersant is added to the Ca(OH)2 suspension, and after stirring and mixing, the specific surface area is obtained. S 比 Not less than 85m 2 / kg of Ca(OH)2 suspension.

[0127] The digestion process is as follows:

[0128] Add CaO powder and deionized water at a mass ratio of 1:8 to a volume of 10m³. 3 In a digester equipped with stirring and jacketed temperature control, the mixture was reacted at 50±5℃ for 40 min to produce a Ca(OH)2 coarse lime slurry with a mass concentration of 8%.

[0129] The impurity removal steps are as follows:

[0130] The crude lime slurry of Ca(OH)2 was screened through a 150μm vibrating screen to remove large particulate impurities, and then filtered through a 0.5μm dynamic microfiltration membrane to obtain refined lime slurry.

[0131] The dispersant includes sodium polyacrylate, which is added at 0.4% of the mass of the Ca(OH)2 suspension.

[0132] In step S3, the first post-processing includes sequentially performing solid-liquid separation, washing to remove impurities, and drying and grading on the second reaction solution to obtain the ultrafine nano calcium carbonate.

[0133] The solid-liquid separation includes using a hydrocyclone separator (with a tangential velocity of 11-13 m / s) to perform hydrocyclone separation on the second reaction liquid to remove large agglomerates and obtain a first underflow; centrifuging the first underflow through a disc centrifuge to obtain a second underflow and a clear liquid; sending the second underflow into a belt filter press and dewatering it at 0.6-0.8 MPa to obtain a wet material with a moisture content of 32%-38%; and recovering the clear liquid as mother liquor to a dilution tank.

[0134] The washing and impurity removal process includes washing the wet material with deionized water in a three-stage countercurrent washing tank until the conductivity of the filtrate is ≤50μS / cm.

[0135] The drying and grading process involves first drying the washed and cleaned wet material using a vacuum dryer until the moisture content is <1%, and then grading and purifying it using an air classifier (±1nm accuracy); the purified powder is then packaged into finished products using a fully automatic packaging machine.

[0136] The second post-treatment includes absorbing the CO2 tail gas through a water scrubbing tower before discharging it in compliance with emission standards.

[0137] The core parameters and actual particle size (specifically, primary particle size) of the ultrafine nano-calcium carbonate with a target particle size D50 of 20 nm prepared in the examples are shown in Table 1. The actual particle size was measured as follows: the actual particle size was measured according to the GB / T 19590-2023 standard for the test of average particle size (TEM) in nano-calcium carbonate, with a 500 g sample taken for testing.

[0138] Table 1. Core parameters and actual particle size.

[0139]

[0140] As shown in Table 1, the core parameters employed in this invention ensure that the primary particle size D50 of the prepared nano-calcium carbonate meets the target design requirements, and that the particle size distribution is uniform. Specifically, the primary particle size core indicator D50 of the prepared product falls precisely within the target range of 20 nm, while D10 and D97 are also within the reasonable upper and lower limits of this range. The overall particle size distribution is concentrated, with no obviously abnormally large or small particles, fully demonstrating that the core parameter control system of this invention has reliable particle size control capabilities. From an application value perspective, this particle size specification meets the theoretical design expectations for the microstructure and properties of nano-calcium carbonate, satisfying the actual needs of downstream applications for material particle size consistency and dispersion, further verifying the scientific nature and practicality of the core parameter design of this invention.

[0141] Furthermore, the particle size distribution of nano-calcium carbonate prepared by existing high-gravity methods is relatively wide, making it difficult to prepare ultrafine nano-calcium carbonate with a target particle size D50 of 20 nm as described in the embodiments of this invention. Specifically:

[0142] See existing literature (Chen Jianfeng, Chu Guangwen, Zou Haikui. Hypergravity Reaction Engineering [M]. Chemical Industry Press: 2020: 255.), which discloses a comparison diagram of nano-calcium carbonate prepared by hypergravity method and ordinary carbonation method in "Chapter 8 Hypergravity Reaction Crystallization and Industrial Application" (page 255), specifically Figure 8-11(c) (i.e., in this embodiment). Figure 2 The particle size distribution of nano-calcium carbonate prepared by the centrifugal method. Figure 2The results show that the particle size of nano-calcium carbonate is mainly concentrated in the range of 15-40 nm; among them, the particle frequency is highest at around 28 nm, approaching 45%; a secondary peak exists at around 25 nm, with a frequency exceeding 20%; and the frequency is approximately 10% at around 33 nm. The frequency is relatively low when the particle size is less than 15 nm or greater than 40 nm. Therefore, from... Figure 2 As can be seen from the existing literature, the average particle size of the nano-calcium carbonate prepared by the supergravity method is about 25-30 nm, and the particle size distribution range is relatively wide, making it difficult to prepare the ultrafine nano-calcium carbonate with a target particle size D50 of 20 nm as described in the embodiments of the present invention.

[0143] The above description is merely a preferred embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural transformations made using the contents of the present invention's specification and drawings under the inventive concept of the present invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. A continuous production method of ultra-micro nano calcium carbonate, characterized in that, The application relates to a method for preparing ultra-micro nano calcium carbonate. Step S1, the CaO raw material is pretreated to obtain a Ca(OH)2 suspension with a mass concentration of 6.0%±0.3% and a specific surface area of 300-400 m2 / g S 比 not less than 85 m 2 / kg of Ca(OH)2 suspension; The method comprises the following steps: Specifically, the Ca(OH)2 suspension is stored in a storage tank, and the CO2 gas is stored in a gas storage tank; the Ca(OH)2 suspension is fed into a top feeding port of the supergravity reactor by using a feeding assembly, and the feeding flow rate of the Ca(OH)2 suspension is controlled to be 4-6 m3 / h; the CO2 gas is fed into a bottom feeding port of the supergravity reactor by using a first gas feeding assembly, and the feeding flow rate of the CO2 gas is controlled to be 300-400 Nm3 / h, and the feeding gas pressure is 0.6-1.0 MPa; the rotating speed of the supergravity reactor is controlled to be 1800-2200 r / min, the pressure in the supergravity reactor is controlled to be 0.30-0.45 MPa, and the reaction temperature in the supergravity reactor is controlled to be 20±2℃; the residence time of the reaction system formed by the convection of the Ca(OH)2 suspension and the CO2 gas in the supergravity reactor is 5-7 s, and the uniform crystal nucleus generation reaction is completed to obtain a first reaction liquid; wherein the Ca(OH)2 in the Ca(OH)2 suspension has a conversion rate of 30%-42% after the uniform crystal nucleus generation reaction is completed. 3 3 P t 2+ X ​​​​​​​ The first reaction solution is conveyed to the pipeline reactor, and the conveying flow rate is controlled at 0.27~0.62m / s; CO2 gas is introduced into the pipeline reactor using a second air inlet assembly, and the pressure inside the pipeline reactor is controlled. The pressure is 0.2~0.3 MPa; the reaction temperature inside the pipeline reactor is controlled at 20±2℃; the residence time of the first reaction liquid and CO2 gas inside the pipeline reactor is... The uniform crystal nucleus growth reaction is completed in 105~130s, yielding the second reaction solution; S2, continuously reacting the Ca(OH)2 suspension by using an ultra-micro nano calcium carbonate continuous production device; 2. The continuous production process of ultrafine nanometer calcium carbonate according to claim 1, characterized in that, S3, obtaining the ultra-micro nano calcium carbonate with a target particle size D50 of 15-20 nm by performing first post-treatment on the second reaction liquid; and performing second post-treatment on the CO2 tail gas discharged from the hypergravity reactor and the pipeline reactor and then discharging the CO2 tail gas. The ultra-micro nano calcium carbonate continuous production device comprises a storage tank, a gas storage tank, a hypergravity reactor, a pipeline reactor, a stirring part, a first pressure sensor, a temperature sensor and a second pressure sensor. The storage tank is communicated with the top feeding port of the hypergravity reactor through a feeding assembly. The gas storage tank is communicated with the bottom gas inlet of the hypergravity reactor through a first gas inlet assembly. The gas storage tank is communicated with the material inlet of the pipeline reactor through a second gas inlet assembly. The material outlet of the hypergravity reactor is communicated with the material inlet of the pipeline reactor. The stirring end of the stirring part is arranged in the storage tank, and the end far away from the stirring end is arranged outside the storage tank and connected with a driving part. The first pressure sensor and the temperature sensor are arranged in the hypergravity reactor.

3. The continuous production process of ultrafine nanometer calcium carbonate according to claim 2, characterized in that, The second pressure sensor is arranged in the pipeline reactor.

4. The continuous production method of ultrafine nanometer calcium carbonate according to claim 3, characterized in that, The pipeline reactor is an integrally-formed continuous S-shaped curved pipeline structure; the inner diameter of the pipeline reactor is 80-125 mm, and the length is 30-50 m. A gas-liquid separator is further arranged; the feeding end of the gas-liquid separator is communicated with the material outlet of the hypergravity reactor, and the discharging end of the gas-liquid separator is communicated with the material inlet of the pipeline reactor through a discharging assembly. The discharging assembly comprises a discharging pipeline and a discharging pump; the two ends of the discharging pipeline are respectively communicated with the gas-liquid separator and the material inlet of the pipeline reactor; and the discharging pump is arranged on the discharging pipeline. A pH meter is arranged on the pipeline between the gas-liquid separator and the hypergravity reactor. The feeding assembly comprises a feeding pipeline and a feeding pump; the two ends of the feeding pipeline are respectively communicated with the storage tank and the top feeding port of the hypergravity reactor; and the feeding pump is arranged on the feeding pipeline. The first gas inlet assembly comprises a first gas inlet pipeline, a first flow meter and a first adjusting valve; the two ends of the first gas inlet pipeline are respectively communicated with the gas storage tank and the bottom gas inlet of the hypergravity reactor; and the first flow meter and the first adjusting valve are arranged on the first gas inlet pipeline.

5. The continuous production process of ultrafine nanometer calcium carbonate according to claim 4, characterized in that, In the step S2, according to the heat balance equation, the Ca in the Ca(OH)2 suspension is determined by formula (1-1) 2+ Conversion rate after completion of the uniform nucleus generation reaction X : Formula (1-1); wherein The second gas inlet assembly comprises a second gas inlet pipeline, a second flow meter and a second adjusting valve; the two ends of the second gas inlet pipeline are respectively communicated with the gas storage tank and the material inlet of the pipeline reactor; and the second flow meter and the second adjusting valve are arranged on the second gas inlet pipeline. represents the density of the Ca(OH)2 suspension in the high gravity reactor; c p represents the specific heat capacity of the Ca(OH)2 suspension in the high gravity reactor; represents the flow rate of the Ca(OH)2 suspension in the high gravity reactor; The dispersant comprises sodium polyacrylate, and the adding amount of the sodium polyacrylate is 0.2%-0.6% of the mass of the Ca(OH)2 suspension. T represents the temperature increase value of the reaction system generated by the reaction of the Ca(OH)2 suspension with CO2 gas to produce calcium carbonate in the high gravity reactor, and In step S3, the first post-treatment comprises sequentially performing solid-liquid separation, impurity removal by washing and drying classification on the second reaction liquid, so as to obtain the ultra-micro nano calcium carbonate. ≤ 1.2 K; n a represents the molar flow rate of the Ca(OH)2 suspension in the high gravity reactor; ​ represents the absolute value of the enthalpy value of the reaction of the Ca(OH)2 suspension with CO2 gas to produce calcium carbonate in the high gravity reactor; from formula (1-1) and ​ ≤ 1.2 K, the conversion rate is determined X The upper limit value of the conversion rate is not higher than 42%. To control the standard deviation of the primary crystal nucleus particle diameter in the first reaction solution after the completion of the uniform crystal nucleus generation reaction ​ ≤ 2 nm, the lower limit value of the conversion rate X is not less than 30%.

6. The continuous production process of ultrafine nanometer calcium carbonate according to claim 5, characterized in that, In the step S2, the rotation speed of the high gravity reactor is determined by using the formula (1-2) : Formula (1-2); wherein, β represents the hypergravity factor; g represents the acceleration of gravity; represents the core reaction zone radius of the rotor packing zone in the hypergravity reactor; β The lower limit value of the range is determined using formula (1-3) and formula (1-4): Equation (1-3); Equation (1-4); wherein, is the liquid phase mass transfer coefficient; is the gas-liquid specific surface area; From the simultaneous equations of formula (1-3) and formula (1-4), it is obtained that 900≤ β ; β the theoretical upper limit value of β ≤ 1300; According to β the lower limit value and the theoretical upper limit value, the rotational speed n is 1800~2200r / min.

7. The continuous production process of ultrafine nanometer calcium carbonate according to claim 6, characterized in that, In the step S2, the pressure in the supergravity reactor is determined by using formula (1-5), formula (1-6) and formula (1-7) simultaneously P 0.30~0.45MPa: Formula (1-5); Equation (1-6); Formula (1-7); wherein, represents the mass transfer rate of CO2 within the high gravity reactor; represents the volumetric mass transfer coefficient within the high gravity reactor; ​ 2] represents the CO2 solubility within the high gravity reactor; K H represents the Henry's constant; c 0 represents the initial molar concentration of Ca(OH)2 suspension within the high gravity reactor.

8. The continuous production process of ultrafine nanometer calcium carbonate according to claim 7, characterized in that, In the step S1, the specific surface area of the Ca(OH)2 suspension is determined using formula (1-8) S 比 The lower limit value of the specific surface area is not less than 85 m2 / g 2 / kg: Formula (1-8); wherein, represents the dissolution rate constant of calcium hydroxide in the Ca(OH)2 suspension within the high gravity reactor; represents the saturation concentration of the Ca(OH)2 suspension within the high gravity reactor; c represents the concentration of the reaction system within the high gravity reactor; represents the solid phase mass of calcium hydroxide in the Ca(OH)2 suspension within the high gravity reactor.

9. The continuous production process of ultrafine nanometer calcium carbonate according to claim 8, characterized in that, In step S1, the pre-treatment comprises first grinding the CaO raw material to a particle size of ≤10 μm, then obtaining refined lime milk by digestion and impurity removal, then adding water to adjust the mass concentration of the Ca(OH)2 suspension to 6.0%±0.3%, and finally adding a dispersing agent to the Ca(OH)2 suspension, and after stirring and mixing, obtaining a Ca(OH)2 suspension with a specific surface area of 3000-4000 m2 / g S 比 not less than 85 m 2 / kg of Ca(OH)2 suspension; ​ ​ The solid-liquid separation comprises: performing cyclone separation treatment on the second reaction liquid to obtain a first underflow; performing centrifugal separation on the first underflow to obtain a second underflow; and dehydrating the second underflow at 0.6-0.8 MPa to obtain wet material with a water content of 32%-38%; The washing and impurity removal comprises: washing the wet material to obtain a filtrate with an electrical conductivity of ≤50 μS / cm; The drying and grading comprises: drying the wet material after the washing and impurity removal to a water content of <1%, and then grading and purifying; The second post-treatment comprises: performing water washing tower absorption on the CO2 tail gas to achieve standard emission.

10. An ultrafine nanometer calcium carbonate product, characterized in that, The ultra-micro nanometer calcium carbonate is prepared by the continuous production method of claim 9.

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