Method for preparing nano calcium carbonate based on ceramic microchannel membrane reactor

Abstract

The invention relates to the technical field of nano material preparation and resource recycling, in particular to a method for preparing nano calcium carbonate based on a ceramic microchannel membrane reactor, which comprises the following steps: mixing carbide slag and an ammonium chloride solution for leaching reaction, and carrying out solid-liquid separation to obtain calcium-containing ore dissolving liquid; adding a compound additive into the calcium-containing ore dissolving liquid; pumping the mixed solution into an in-membrane channel of a ceramic microchannel membrane reactor, introducing CO2-containing gas from the outer side of a membrane of the ceramic microchannel membrane reactor, dispersing the gas through micropores in a membrane wall to form micro-nano bubbles, entering a liquid phase of the in-membrane channel, contacting the gas phase and the liquid phase in a cross-flow form, and carrying out carbonization reaction, generating slurry containing nano calcium carbonate; and carrying out gas-liquid separation on the slurry, collecting a solid product in a liquid phase, and washing and drying to obtain the nano calcium carbonate. According to the invention, the reaction rate and the mass transfer efficiency are improved, so that the fixation rate of CO2 and the conversion rate of calcium element in the carbide slag are improved, and the high uniformity of the product is guaranteed.

Description

Technical Field

[0001] This invention relates to the field of nanomaterial preparation and resource recycling technology, and in particular to a method for preparing nano-calcium carbonate based on a ceramic microchannel membrane reactor. Background Technology

[0002] Nano-calcium carbonate, as an important inorganic chemical raw material, boasts advantages such as wide availability, low cost, and stable chemical properties, and is widely used in various industrial fields including plastics, rubber, coatings, papermaking, pharmaceuticals, and food. After surface modification, nano-calcium carbonate exhibits good compatibility with polymer matrices. In plastics, it serves as a reinforcing skeleton to improve the mechanical properties and dimensional stability of products; in rubber, it acts as a reinforcement and improves processing performance; in coatings and inks, it enhances hiding power, gloss, and durability; in papermaking, it is used as a high-grade filler to improve paper quality; and in the biopharmaceutical field, it can be used in drug delivery systems. With the upgrading and development of related industries, the demand for nano-calcium carbonate is increasing, especially for nanoscale products with uniform particle size distribution and good dispersibility.

[0003] Currently, the mainstream methods for industrial preparation of nano-calcium carbonate include bubbling carbonation, spray carbonation, and centrifugal methods, all based on the gas-liquid reaction of calcium hydroxide suspension with carbon dioxide gas. Bubbling carbonation is widely used due to its simplicity and ease of operation; however, it suffers from limited gas-liquid contact area, low mass transfer efficiency, difficulty in precisely controlling nanoparticle nucleation and growth, leading to product agglomeration, batch-to-batch quality instability, and difficulty in achieving continuous production. Spray carbonation increases the gas-liquid interface through atomization, improving reaction efficiency to some extent, but suffers from complex equipment structure, high energy consumption, and nozzle clogging. Centrifugal methods utilize rotating packed beds to enhance mass transfer, which is beneficial for nanoparticle formation; however, the large equipment investment and high operating and maintenance costs limit its application in small- to medium-scale production.

[0004] In recent years, to improve the controllable preparation of nano-calcium carbonate, researchers have attempted to optimize gas-liquid dispersion and mass transfer behavior by improving reactor structure or mixing methods. For example, using stirring devices with specific structures to control bubble size and distribution enhances the gas-liquid interface, providing a more uniform reaction environment. Other studies have constructed bubble-liquid film reactors based on bubble-cap disc stirrers, dividing the reaction liquid into thin liquid films and uniformly dispersing bubbles to form a gas-liquid system with a high specific surface area, thereby accelerating the carbonization reaction rate. These explorations provide valuable directions for improving the preparation process of nano-calcium carbonate.

[0005] Meanwhile, under the background of resource recycling and low-carbon development, utilizing industrial solid waste as a calcium source to prepare high-value-added calcium carbonate products has become an important research direction. Calcium carbide slag is a large-volume alkaline solid waste generated during acetylene production, and its main component is calcium oxide, possessing the potential to serve as a raw material for calcium carbonate synthesis. Industrial flue gas contains a large amount of carbon dioxide, which can be fixed into carbonate products through mineralization reactions, achieving the resource utilization of greenhouse gases. Therefore, developing nano-calcium carbonate synthesis technology using calcium carbide slag as a calcium source and flue gas carbon dioxide as a carbon source is of great significance for promoting the coordinated development of high-value conversion of industrial solid waste and carbon emission reduction.

[0006] However, most existing reaction systems lack effective control over bubble size, resulting in low carbon dioxide dispersion and dissolution efficiency and direct emission of large amounts of unreacted CO2. This not only reduces carbon fixation efficiency but also weakens the process's carbon reduction potential. Furthermore, when using solid wastes such as carbide slag as a calcium source, their low reactivity and slow dissolution due to their solid suspension state make it difficult to achieve efficient calcium ion dissolution and homogeneous reaction using conventional mixing methods, leading to limited conversion rates. Even with pretreatment, problems such as incomplete leaching and impurities affecting product purity often persist.

[0007] More importantly, most current processes still employ a step-by-step approach of calcium source extraction and carbonization, resulting in lengthy processes and high energy consumption. This fails to achieve the synergistic effect of efficient calcium ion leaching from carbide slag, rapid CO2 mineralization, and controllable nanoparticle growth within the same reaction system. Furthermore, in complex systems involving ammonium salt leaching, the reaction solution often contains high concentrations of ammonium and chloride ions. Traditional reactor and membrane materials are susceptible to corrosion or clogging, exhibiting insufficient chemical stability and anti-fouling capabilities, thus hindering their long-term stable operation in real industrial environments.

[0008] Therefore, there is an urgent need to develop a novel reaction process that can achieve efficient gas-liquid dispersion and mass transfer, accelerate reaction kinetics, precisely control product morphology and particle size, and adapt to complex systems with high ionic strength and high solid content, so as to promote the deep integration of green, low-carbon, and continuous preparation of nano-calcium carbonate with the resource utilization of industrial waste.

[0009] In view of this, the present invention is proposed. Summary of the Invention

[0010] The purpose of this invention is to provide a method for preparing nano-calcium carbonate based on a ceramic microchannel membrane reactor. This method improves the CO2 fixation rate and the calcium conversion rate in carbide slag by increasing the reaction rate and mass transfer efficiency, thus ensuring the high uniformity of the product.

[0011] The first aspect of this invention provides a method for preparing nano-calcium carbonate based on a ceramic microchannel membrane reactor, comprising the following steps: S1. Mix calcium carbide slag with ammonium chloride solution for leaching reaction. After solid-liquid separation, calcium-containing ore solution is obtained. S2. Add composite additives to calcium-containing molten mineral solution; S3. The mixture obtained in step S2 is pumped into the inner channel of the ceramic microchannel membrane reactor. At the same time, CO2-containing gas is introduced from the outside of the ceramic microchannel membrane reactor. The gas is dispersed through the micropores of the membrane wall to form micro-nano bubbles and then enters the liquid phase in the inner channel of the membrane. The gas and liquid phases contact each other in a cross-flow manner and carry out a carbonization reaction to generate a slurry containing nano-calcium carbonate. S4. The slurry obtained in step S3 is subjected to gas-liquid separation, and the solid product in the liquid phase is collected. After washing and drying, nano-calcium carbonate is obtained. The membrane module substrate of the ceramic microchannel membrane reactor is a porous ceramic material, and a hydrophobic and corrosion-resistant modified functional layer is formed on its membrane surface.

[0012] This invention achieves the synergistic conversion of industrial solid waste and waste gas by constructing an integrated process consisting of three functional modules: a calcium-containing leaching solution generated by a calcium carbide slag-ammonium chloride leaching system, a composite additive to regulate crystal growth, and a self-made special ceramic microchannel membrane module to achieve efficient gas-liquid contact.

[0013] Specifically, firstly, ammonium chloride solution is used to selectively leach calcium carbide slag to generate calcium-rich calcium carbide slag. 2+ The calcium-containing soluble mineral solution was then introduced into a specialized ceramic microchannel membrane reactor with acid and alkali resistance, superhydrophobicity, ammonia and chlorine resistance, and anti-scaling properties. The calcium-containing soluble mineral solution was introduced into the inner channels of the membrane reactor, while industrial carbon dioxide-containing flue gas was introduced into the outer channels. Through a cross-flow operation mode, the gas was cut into micro- and nano-sized bubbles on the membrane surface before entering the liquid phase, significantly increasing the gas-liquid interface. With the synergistic effect of composite additives, Ca... 2+ A rapid mineralization reaction occurs with CO2 to generate a slurry containing nano-sized calcium carbonate. The slurry undergoes gas-liquid separation, washing, pressure filtration, and drying to obtain a nano-sized product with a uniform particle size distribution. The entire process utilizes a cross-flow design in a ceramic microchannel membrane reactor to enhance mass transfer kinetics. Simultaneously, interface modification of the membrane material imparts acid and alkali resistance, superhydrophobicity, ammonia and chlorine resistance, and anti-fouling properties. The construction of numerous micro- and nano-structures further enhances its anti-fouling characteristics, significantly extending the membrane module's lifespan. Research indicates that by introducing a dedicated ceramic microchannel membrane reactor combined with unique composite additives, the carbonation reaction can be completed within tens of seconds, achieving a reaction efficiency dozens of times higher than that of traditional reactors.

[0014] Compared to existing technologies, this invention adopts a membrane reactor configuration with differentiated internal and external channel flow in its structural design. In terms of control, it achieves coupled regulation of gas-liquid cross-flow and microbubble dispersion. In terms of operational stability, it uses material modification to make it acid and alkali resistant, superhydrophobic, ammonia and chlorine resistant, and anti-scaling, ensuring long-term operating performance. In terms of ease of use, it simplifies the reaction process and reduces energy consumption. At the same time, it realizes the high-value conversion of calcium in carbide slag and the effective sequestration of industrial CO2, achieving the dual benefits of resource recycling and carbon emission reduction.

[0015] As a preferred embodiment of this technical solution, in step S2, the composite additive includes any two or three of the following: polyphosphate compounds, organic polymer compounds, and surfactants, wherein the mass ratio of the polyphosphate compound, the organic polymer compound, and the surfactant is (1-3):(1-5):(0.01-0.10). Preferably, the amount of the composite additive added is 0.5% to 4% of the solid mass in the calcium-containing molten mineral solution.

[0016] As a preferred embodiment of this technical solution, the polyphosphate compound includes any one or more of sodium pyrophosphate, sodium polyphosphate, and sodium hexametaphosphate. More preferably, the polyphosphates include any one or more of the following: sodium pyrophosphate, ammonium polyphosphate, sodium polyphosphate, sodium hexametaphosphate, magnesium ammonium phosphate, and polyphosphate-producing bacteria extract PolyP particles. The polyphosphates mainly act as primary crystallization control agents to chelate calcium ions, causing calcium carbonate crystal nuclei to be adsorbed on the surface of the microsoluble particles formed thereon, thus restricting their anisotropic growth.

[0017] As a preferred embodiment of this technical solution, the organic polymer compound includes any one or more of polyacrylic acid, polyethylene oxide, and chitosan; More preferably, the organic polymer includes any one or more of polyglutamic acid, polyvinyl chloride, polyacrylic acid, polyethylene oxide, and natural organic polymer starch and chitosan. The organic polymer mainly acts as a dispersant to prevent the aggregation of crystal nuclei in a long-term manner, allowing them to grow independently and hindering secondary crystallization.

[0018] Among them, for carboxyl-containing polymers, such as polyglutamic acid, polyvinyl chloride, and polyacrylic acid, crystallization is mainly controlled by the chemical adsorption and chelation of carboxyl groups; For polyhydroxy or polyether polymers, such as starch and polyethylene oxide, crystal growth kinetics are mainly affected by hydrogen bonding, steric hindrance, and control of solution viscosity. Chitosan can exert its effects through the interaction of amino groups and steric hindrance.

[0019] As a preferred embodiment of this technical solution, the surfactant includes any one or two of sodium dodecyl sulfate and polyoxyethylene sorbitan fatty acid ester.

[0020] More preferably, the surfactants include any one or more of the following: anionic sodium stearate, sodium dodecyl sulfate, sodium α-alkenyl sulfonate, rhamnolipid, sophorolipid; cationic octadecyltrimethylammonium chloride, benzalkonium chloride; and nonionic sorbitan fatty acid ester, polyoxyethylene sorbitan fatty acid ester. The surfactants mainly act as crystal form control agents to regulate the shape of each particle and change the surface properties of each particle, making the particles more uniform and more stable.

[0021] More preferably, the composite additive is a mixture of polyphosphates and organic polymers, or a mixture of polyphosphates and surfactants, or a mixture of polyphosphates, organic polymers, and surfactants.

[0022] More preferably, the composite additive is added in two parts. The first part (a mixture of polyphosphates and organic polymers) is added before entering the membrane channel of the primary membrane reactor, for example, it can be added in the storage tank containing calcium slurry. The second part (surfactant) is added before entering the membrane channel of the secondary membrane reactor, for example, it can be added in the primary gas-liquid separator.

[0023] After adjusting the pH of the calcium-containing mineral solution to 11-10, add the composite additive and stir thoroughly to dissolve. The phosphate (-PO4) groups on the polyphosphate molecular chains of the composite additive... 3- Polar functional groups (such as carboxyl, hydroxyl, amino, and ether bonds) on the molecular chains of calcium carbonate crystal nuclei can adsorb onto the surface of calcium carbonate crystal nuclei or inhibit the aggregation and excessive growth of crystal nuclei through steric hindrance, especially the {104} crystal face, inhibiting its preferential growth and thus limiting the anisotropic development of crystals; long alkyl chains (-CH4) in organic polymers can form steric hindrance in solution, hindering secondary crystallization and controlling the size of nanoparticles; amphoteric groups of surfactants can form an electric double layer on the particle surface, increasing the absolute value of the Zeta potential to above -30mV, enhancing electrostatic repulsion, significantly reducing van der Waals attraction between nanoparticles, and preventing aggregation.

[0024] Studies have shown that, through the synergistic effect of two or three of the above-mentioned additives, this invention can obtain nano-calcium carbonate particles with a particle size concentrated in the range of 50-100 nm, a narrow distribution, and a regular morphology, which significantly improves the uniformity and performance stability of the product.

[0025] As a preferred embodiment of this technical solution, in step S3, the carbonization reaction is carried out in a two-stage series ceramic microchannel membrane reactor system; Preferably, the mixture first enters the membrane channel of the primary membrane reactor, while CO2-containing gas is simultaneously introduced into the outer membrane of the primary membrane reactor to carry out a primary carbonization reaction, thereby initiating the nucleation process and avoiding instantaneous supersaturation that could cause nucleus explosion. After the primary carbonization reaction, the slurry is aged in a gas-liquid separator and then enters the membrane channel of the secondary membrane reactor. At the same time, CO2-containing gas is introduced into the outer membrane of the secondary membrane reactor to carry out the main carbonization reaction, so as to finely control the growth.

[0026] More preferably, each stage of the membrane reactor is equipped with an independent flow regulating valve, flow monitor, online pH monitoring probe, and pressure gauge. A primary gas-liquid separator is installed between the primary and secondary membrane reactors. After being stirred and aged in the gas-liquid separator, the material is fed into the secondary membrane reactor via a secondary feed pump, thus achieving segmented and precise control of the reaction process. This staged response design avoids explosive crystallization caused by local supersaturation, improving the controllability of product particle size and batch consistency.

[0027] This invention employs a two-stage membrane reactor series cross-flow reaction mechanism. The first stage initiates nucleation, while the second stage precisely controls crystal growth. It is also equipped with an independent flow rate adjustment and pH online monitoring feedback mechanism to avoid explosive crystallization caused by local supersaturation, thus achieving segmented and precise control of the particle size distribution of nano-calcium carbonate.

[0028] Therefore, this invention uses industrial solid waste carbide slag and industrial waste gas carbon dioxide as raw material sources, and realizes the high-value conversion of calcium and the solidification and storage of carbon through an integrated leaching-mineralization process. At the same time, it achieves the dual goals of recycling carbide slag resources and reducing CO2 emissions. The entire preparation process does not require high pressure and high temperature conditions, is easy to operate, has low energy consumption, and the gas-liquid separation after the reaction is simple and efficient, and has good potential for engineering scale-up and industrial application prospects.

[0029] As a preferred embodiment of this technical solution, the reaction process is controlled by online monitoring of pH value; Preferably, the pH of the slurry at the outlet of the primary membrane reactor is controlled between 9.2 and 9.8, and the pH of the slurry at the outlet of the secondary membrane reactor is controlled below 8.5, so as to ensure that the reaction is basically complete, the CO2 fixation rate is above 90%, and the reaction process is precisely controlled in stages.

[0030] As a preferred embodiment of this technical solution, in the primary membrane reactor, the linear velocity of the mixture in the membrane channel is 2.0 × 10⁻⁶. -5 ~3.0×10 -5 The gas velocity in the membrane channel is 3.2 × 10 m / s. -4 ~3.7×10 -4 m / s; In a two-stage membrane reactor, the linear velocity of the slurry in the membrane channel is 1.0 × 10⁻⁶. -5 ~1.5×10 -5 The gas velocity in the membrane channel is 6.5 × 10 m / s. -4 ~7.0×10 -4 m / s.

[0031] More preferably, in continuous production, the primary feed pump and the secondary feed pump are coordinated and adjusted at a flow rate ratio of 1.5:1 to 2:1. After the material is induced to nucleate in the primary membrane reactor, it is stirred, aged and stabilized in the primary gas-liquid separator for 10 to 20 minutes before entering the secondary membrane reactor.

[0032] More preferably, the residence time of liquid in the primary membrane is controlled to be 30-40 seconds, and the residence time of liquid in the secondary membrane is controlled to be 70-80 seconds.

[0033] More preferably, the CO2 supply and liquid transport in the two-stage membrane reactor are adjusted synchronously to ensure that the reaction proceeds according to the preset rhythm. Specifically, the gas residence time in the first-stage membrane is controlled at 4.5~4.7 s, the gas residence time in the second-stage membrane is controlled at 2.2~2.4 s, and the gas-liquid flow rate ratio in the two-stage membrane reactor is controlled at 25:1~12.5:1 to form suitable shear force and turbulence intensity, thereby creating gradient-enhanced mass transfer conditions.

[0034] In the membrane reactor of this invention, a shear field is formed in the gas phase to drive cross-flow between the gas and liquid phases, and bubbles continuously dissolve in the liquid phase and participate in the reaction. Studies have shown that this cross-flow-microbubble coupling mechanism can increase the gas-liquid mass transfer coefficient to more than 10 times that of traditional bubble column reactors, and significantly shorten the total mineralization reaction time from the traditional 2-4 hours to less than 30 minutes. Furthermore, this staged response design can control local supersaturation, avoid non-uniform nucleation, and achieve a batch-to-batch particle size variation coefficient of less than 5%.

[0035] During the production process, a periodic acid washing program can be configured as needed, performing a gas-liquid backflushing weak acid cleaning once every 1000 hours of operation to maintain stable membrane flux and further improve operational convenience and long-term operational reliability.

[0036] In a preferred embodiment of this technical solution, in step S3, the inlet pressure of the CO2-containing gas is 0.2–0.3 MPa.

[0037] More preferably, the diameter of the micro-nano bubbles is 0.1 to 100 μm.

[0038] This invention employs a dedicated ceramic microchannel membrane reactor to cut carbon dioxide flue gas into micro- and nano-sized bubbles, significantly increasing the gas-liquid contact interface and greatly improving the gas-liquid mass transfer efficiency, thus solving the technical problem of low mass transfer efficiency in traditional reactors.

[0039] In a preferred embodiment of this technical solution, step S3, the method for preparing the hydrophobic and corrosion-resistant modified functional layer includes four steps: hydroxyl loading pretreatment, long-chain organic acid activation, silane coupling agent impregnation, and high-temperature curing. T1. Immerse the membrane module substrate in an alkaline solution (such as NaOH or KOH) for 10-20 hours to perform hydroxyl loading pretreatment and remove other surface impurities; T2. The membrane substrate treated in step T1 is reacted with C12-C18 long-chain fatty acids and fixed under gradient high temperature (80-120℃) to construct an organic molecular layer; wherein, the C12-C18 long-chain fatty acids include one or more of bio-based polyglutamic acid, lauric acid, myristic acid, palmitic acid and oleic acid. T3. Immerse the membrane substrate treated in step T2 in a silane coupling agent solution at a concentration of 0.1-0.2 mol / L for 20-28 hours to carry out the grafting reaction, and then cure it in a high-temperature drying oven at 100-150℃ or above for 3-6 hours. Repeat this process three times to construct a multi-layered micro / nano structure and hydrophobic molecular layer, and enhance the membrane material's tolerance to ammonium and chloride ions through covalent bonding. The silane coupling agent includes one or more of n-octyltriethoxysilane, hexyltrimethoxysilane, dichloromethyloctylsilane, and hexamethyldisilazane. During the reaction, the silane coupling agent molecule first undergoes hydrolysis to generate an intermediate containing silanol groups (-Si(OH)3). Subsequently, under heating conditions, these silanol groups undergo a dehydration condensation reaction with the hydroxyl groups (-OH) preloaded on the surface of the ceramic membrane matrix to form strong Si-O-Si or Si-OM (M represents metal atoms of the ceramic matrix such as Al), thereby chemically grafting the hydrophobic long-chain alkyl groups at the end of the silane coupling agent molecule onto the membrane surface.

[0040] T4. The membrane substrate treated in step T3 is dried at 120°C and then heated and fixed at 200°C for 2 hours to form a bifunctional interface layer with both hydrophobic group and micro / nano structure characteristics on the membrane surface.

[0041] As a preferred embodiment of this technical solution, the membrane module substrate is made of alumina composite silicon carbide material with an average pore size of 0.1 to 1.0 μm.

[0042] This invention employs an alumina-silicon carbide composite porous matrix and a ceramic microchannel membrane module modified in multiple ways to enhance hydrophobicity, ammonia and chloride resistance, and anti-fouling properties. A micro-nano structure at the membrane interface is constructed through gradient covalent bonding and loaded with functional groups. This results in excellent chemical stability and corrosion resistance even in environments with high concentrations of ammonium and chloride ions, effectively inhibiting membrane pore blockage and material degradation, reducing capillary phenomena and mass transfer resistance in the membrane reactor, extending the continuous operating life of the membrane module to over 1000 hours, and improving the system's regenerability and operational stability.

[0043] In a preferred embodiment of this technical solution, in step S1, the concentration of the ammonium chloride solution is 0.1–1.0 mol / L, the leaching reaction temperature is 40–60°C, and the reaction time is 1–3 h.

[0044] The second aspect of the present invention provides a nano-calcium carbonate prepared according to the above method, wherein the particle size of the nano-calcium carbonate is concentrated in the range of 50 to 100 nm, the particle size variation coefficient between batches is less than 5%, and the product has high morphological regularity, which can meet the strict requirements for nanofillers in high-end coatings, plastic fillers and other fields.

[0045] The method for preparing nano-calcium carbonate based on a ceramic microchannel membrane reactor of the present invention has at least the following beneficial effects: 1. This invention integrates calcium carbide slag leaching, carbonization reaction, and product separation into a single process flow. Its integrated continuous process design fundamentally eliminates the intermittent operation mode of traditional batch reactors, providing a foundation for large-scale, automated continuous production. In the carbonization reaction stage, this invention uses a modified ceramic membrane microchannel membrane reactor and adopts a cross-flow contact mode of "liquid inside the membrane, gas outside the membrane." That is, firstly, when the gas passes through the micropores of the membrane wall, it is forcibly dispersed into micro- and nano-bubbles, increasing the gas-liquid contact interface area per unit volume by orders of magnitude compared to the traditional bubbling method. Secondly, the cross-flow mode generates continuous gas-liquid shear force within the membrane channel, effectively thinning the liquid membrane mass transfer boundary layer and promoting the renewal, merging, and redispersing of bubbles, thereby significantly improving the mass transfer coefficient of CO2 from the gas phase to the liquid phase. Therefore, the efficient mass transfer mechanism formed by the combined action of "micropore dispersion" and "cross-flow shearing" in this invention directly overcomes the inherent defects of existing technologies such as bubble carbonization, which rely on natural gas dispersion and have limited contact area, resulting in insufficient mass transfer driving force and slow reaction. The carbonization reaction rate is greatly improved, enabling the entire mineralization reaction process to be completed within tens of minutes, rather than the several hours required by traditional methods, thereby meeting the needs of rapid and continuous production. 2. The surface of the ceramic microchannel membrane reactor substrate used in this invention is formed with a hydrophobic and corrosion-resistant modified functional layer, ensuring that the core components of the ceramic microchannel membrane reactor can withstand high concentrations of ammonium ions (NH4+).+ ) and chloride ions (Cl - In complex feed liquid environments, this technology effectively prevents membrane pores from becoming clogged due to salt crystallization or corrosion products, and membrane materials from failing due to chemical erosion. It solves the problems of insufficient chemical stability and anti-interference capabilities of existing reactors and membrane materials in complex ionic environments, hindering long-term stable operation. This significantly reduces equipment maintenance frequency and costs, and improves the operational reliability and engineering application potential of the entire process system. In summary, this invention not only synergistically couples the two objectives of "high-value conversion of waste" and "carbon emission reduction", but also improves the CO2 fixation rate and the calcium conversion rate in carbide slag by increasing the reaction rate and mass transfer efficiency, ensuring the high uniformity of the product, and providing a practical and feasible technical path for the large-scale, high-value co-processing of industrial solid waste and waste gas. Attached Figure Description

[0046] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0047] Figure 1 This is a schematic diagram illustrating the construction principle of the hydrophobic and corrosion-resistant modified functional layer on the substrate surface of the membrane module of the present invention. Figure 2 These are the XRD test results of the membrane module before and after modification according to the present invention; Figure 3 These are the FTIR test results of the membrane module before and after modification according to the present invention; Figure 4 These are the surface contact angle test results of the membrane module before and after modification according to the present invention; Figure 5 These are scanning electron microscope (SEM) images of the membrane module before and after modification according to the present invention. Figure 6 This is a comparison diagram of the mineralization effect of the membrane module before and after modification according to the present invention; Figure 7 This is a long-term (1000 h) mineralization experiment of the modified membrane module of the present invention; Figure 8 This is a process route diagram for an embodiment of the present invention; Figure 9 This is a schematic diagram of the process system according to an embodiment of the present invention; Figure 10 These are TEM images of the products obtained in the embodiments of the present invention; Figure 11 This is a SEM image of the product obtained in an embodiment of the present invention. Detailed Implementation

[0048] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0049] It should be noted that the terminology used herein is for the purpose of describing particular implementations only and is not intended to limit the exemplary implementations according to this application. As used herein, the singular form includes the plural form unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this description, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0050] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. 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.

[0051] Example 1 This embodiment provides a method for constructing a hydrophobic and corrosion-resistant modified functional layer on the surface of a membrane module substrate, including the following steps: T1. The membrane module substrate with an average pore size of 0.5 μm, a porosity of 30%, and a substrate material of sintered alumina composite silicon carbide was placed in 4 mol / L NaOH / KOH and soaked at room temperature for 12 h to increase the surface hydroxyl density and provide active sites for subsequent coupling reactions. T2. Using chemical methods, C12-C18 long-chain fatty acids, including one or more of bio-based polyglutamic acid, lauric acid, myristic acid, palmitic acid, and oleic acid, are chemically loaded onto the membrane interface. The solvent used for the alkyl chain reaction is a mixture of ethanol and water (ethanol:water = 20:1, v / v). 0.1 mol / L acetic acid is added to adjust the pH to 4.5 during the reaction. The reaction is carried out at three gradients of 60 ℃, 70 ℃, and 80 ℃ for 12 h, respectively, to form micro-nano structures at different levels on the matrix surface. T3. Using the impregnation-heat fixation method, the film substrate treated in step T2 is placed in a silane coupling agent solution at 60-80℃ with a concentration of 0.1-0.2 mol / L for 24 hours, and then dried at 120℃ for 2 hours. This process is repeated three times. Finally, the silane molecules undergo a condensation reaction with the hydroxyl groups on the ceramic surface to form a dense covalently bonded hydrophobic layer. T4. The membrane substrate treated in step T3 is dried at 120°C and then heated and fixed at 200°C for 2 hours to form a bifunctional interface layer with both hydrophobic group and micro / nano structure characteristics on the membrane surface.

[0052] Figure 1 This is a schematic diagram illustrating the construction principle of the hydrophobic and corrosion-resistant modified functional layer on the substrate surface of the membrane module of the present invention. Figure 2 The XRD test results are for the surface of the membrane module before and after modification. Figure 3 The results are FTIR tests of the membrane module before and after modification. Figure 4 The results show the surface contact angle test results of the membrane module before and after modification; Figure 5 Scanning electron microscope (SEM) images of the membrane module surface before and after modification; Figure 6 This is a comparison chart of the mineralization effects of the membrane module before and after modification. Figure 7 Long-term (1000 h) mineralization experiment for modified membrane modules.

[0053] Depend on Figure 1-7 It can be seen that the area of ​​the C atom peak on the surface of the modified membrane module increases significantly. Figure 2 FTIR spectrum ( Figure 3 (Displayed at 1100 cm) -1 The presence of a strong Si-O-Si absorption band at the point indicates the successful construction of the organic functional layer; the thickness of this modified layer is approximately 200 nm, and the contact angle is greater than 110°. o ( Figure 4 ), and the surface exhibits a multi-layered micro-nano structure ( Figure 5 This modified layer exhibits excellent hydrophobic and antifouling properties, and it can resist NH4+. + The resulting alkaline swelling can also block Cl. - The lattice disruption caused by permeation ensures the long-term stable operation of the membrane module in a complex ionic environment. Experiments show that even after 1000 hours of continuous operation with a feed solution containing NH4+, the membrane module remains stable. + Concentration reached 2.44 mol / L, Cl - Under harsh conditions with a concentration of 2.44 mol / L, the membrane flux decline was less than 15%, with no obvious corrosion or cracking. The flux recovery rate after acid washing and regeneration reached 100%. Figure 6-7 ).

[0054] Therefore, this modification method and structural design not only change the hydrophilic groups on the surface of the membrane module substrate to hydrophobic groups through chemical methods to make it hydrophobic, but also effectively inhibit membrane pore blockage and chemical corrosion, and regenerate the membrane module after acid washing, extending the service life of the membrane module to more than 30 days of continuous operation without significant flux decline, thereby improving the stability and regenerativeness of the system.

[0055] Example 2 This embodiment provides a method for preparing nano-calcium carbonate based on a ceramic microchannel membrane reactor, including the following steps: S1. Mix industrial solid waste carbide slag with a 0.5 mol / L ammonium chloride solution according to NH4. + / Ca 2+ =2.0 was mixed in a leaching reactor and stirred for 2 hours in a 50 °C water bath to complete selective leaching. After filtration, a Ca-rich solution was obtained. 2+ The calcium-containing leaching solution contains calcium ions at concentrations of 0.7–0.9 mol / L. S2. Add composite additives (ammonium tripolyphosphate and chitosan) to the calcium-containing molten mineral solution at a concentration of 2% of the solid content to regulate the crystal nucleation and growth process. S3. After stirring the above mixture for 10 min, pump it into the membrane channel of the modified microporous ceramic membrane reactor at a flow rate of 2.0 × 10⁻⁶. -5 ~3.0×10 -5 The fluid flows at a linear velocity of m / s in the primary membrane channel, with a residence time of 35-37 s. The pH at the outlet of the primary membrane reactor is controlled at 9.2-9.8. The fluid then enters the primary gas-liquid separator, where an auxiliary agent (sodium stearate) is added at 0.01% of the solid content. After stirring and aging for 10-20 min, the fluid is then introduced at a velocity of 1.0 × 10⁻⁶ m / s. -5 ~1.5×10 -5 The gas flows at a linear velocity of m / s in the secondary membrane channel, with a residence time of 72-74 s. The pH at the outlet of the secondary membrane reactor is controlled below 8.5 before entering the secondary gas-liquid separator for solid-liquid separation. Simultaneously, CO2 gas (volume concentration ≥12%) from the industrial flue gas, after compression and purification, is injected in parallel into the porous membrane wall from the outside of the membranes in the primary and secondary membrane reactors at a pressure of 0.2-0.3 MPa. The residence time of the gas in the primary membrane is controlled at 4.5-4.7 s, and the flow rate is 3.2 × 10⁻⁶ m / s. -4 ~3.7×10 -4 It flows at a linear velocity of m / s in the first-stage membrane channel at a rate of 6.5 × 10⁻⁶ m / s. -4 ~7.0×10 -4 A linear velocity of m / s flows in the secondary membrane channel, and the gas residence time in the secondary membrane is controlled to be 2.2~2.4 s, forming a stable cross-flow shear gas-liquid two-phase environment; S4. The reacted slurry enters the gas-liquid separator. Unreacted gas is discharged from the top and recycled, while the liquid phase carries the generated nano-calcium carbonate particles into the subsequent pressure filtration, washing and drying processes.

[0056] Figure 8 This is a process flow diagram for this embodiment; Figure 9 This is a schematic diagram of the process system in this embodiment; Figure 10This is a TEM image of the product obtained in this embodiment; Figure 11 This is a SEM image of the product obtained in this embodiment.

[0057] Depend on Figure 10-11 It can be seen that the particle size of the product obtained in this embodiment is concentrated in the range of 50~70 nm, with a spherical morphology and uniform distribution.

[0058] Example 3 This embodiment aims to illustrate the regulatory effect of the specific composition and ratio of composite additives on the performance of nano-calcium carbonate products.

[0059] This embodiment is basically the same as Embodiment 2, except that: this embodiment sets up 5 different composite additive formulations (AEs), the composition and mass of which are shown in Table 1, and the addition amount of each is 2% of the solid content; in addition, this embodiment uses a single-stage modified ceramic microchannel membrane reactor, and the linear velocity of the fixed liquid is 2.5 × 10⁻⁶. -5 The carbonization reaction takes place at a pressure of 0.25 MPa and a speed of m / s.

[0060] Table 1. Compound Additive Formulation

[0061] Table 2 Comparison of product performance obtained from different compound additive formulations

[0062] As shown in Table 1-2, the particle size of calcium carbonate particles can be controlled within 50-100 nm by this composite additive formulation, which meets the particle size standard of nano calcium carbonate.

[0063] Example 4 This embodiment aims to study the precise regulation of reaction process and product consistency by a two-stage tandem microporous ceramic membrane reactor and online pH control.

[0064] This embodiment is basically the same as Embodiment 2, except that: in this embodiment, the outlet pH of the first-stage membrane reactor is precisely controlled to be 9.5±0.1 and the outlet pH of the second-stage membrane reactor is 8.2±0.1, while other flow rate and pressure parameters are the same as in Embodiment 2.

[0065] Five batches were run consecutively, and the particle size of the product obtained in each batch was analyzed. The results are shown in Table 3.

[0066] Table 3 Particle size of different batches of products

[0067] As shown in Table 3, through precise pH segmentation control, the reaction endpoints of each batch are stable, and the particle size and distribution of the products are highly consistent (with a small coefficient of variation), further demonstrating the effectiveness of the graded control strategy of this invention, while achieving the goals of "controllable products" and "stable batch quality".

[0068] Example 5 This embodiment represents the optimal process integration of the present invention.

[0069] The formulation of the composite additive in this embodiment is: ammonium tripolyphosphate, chitosan, and sodium stearate, in a mass ratio of 2:1:0.01; the mixture is prepared at a concentration of 2.75 × 10⁻⁶. -5 The fluid flows at a linear velocity of m / s in the primary membrane channel, with a residence time of 36.4 s. The pH at the outlet of the primary membrane reactor is controlled at 9.5. After stirring and aging in the primary gas-liquid separator for 15 min, the fluid is then introduced at a velocity of 1.38 × 10⁻⁶ m / s. -5 The gas flows at a linear velocity of m / s in the secondary membrane channel, with a residence time of 72.8 s. The pH at the outlet of the secondary membrane reactor is controlled below 8.2 before entering the secondary gas-liquid separator for solid-liquid separation. CO2 gas is injected in parallel into the porous membrane wall from the outside of the membranes of the primary and secondary membrane reactors at a pressure of 0.3 MPa. The CO2 gas has a flow rate of 3.44 × 10⁻⁶ m / s. -4 It flows in the first-stage membrane channel at a linear velocity of m / s, with a velocity of 6.89 × 10⁻⁶ m / s. -4 The gas flows at a linear velocity of m / s in the secondary membrane channel. The residence time of the gas in the primary membrane is controlled to be 4.6 s, and the residence time of the gas in the secondary membrane is controlled to be 2.3 s.

[0070] In this embodiment, the total process time from feeding to complete carbonization is less than 30 minutes; according to tail gas analysis, the CO2 recycling fixation rate can reach 91.79%, and the calcium conversion rate can reach 52.70%; the product particle size is 50-100 nm, and the distribution is uniform.

[0071] In this embodiment, after 1000 hours of continuous operation, the membrane flux decay was less than 15%, and there was no obvious corrosion or cracking. Furthermore, the particle size of the obtained product could still be maintained at 50-100 nm.

[0072] Compare with Example 1 This comparative example is basically the same as Example 5, except that: this comparative example uses a single-stage microporous ceramic membrane reactor, the total liquid residence time is similar to the sum of the two stages in Example 5, which is about 110 s, and the total CO2 flux is the same. The results are shown in Table 4.

[0073] Table 4. Influence of microporous ceramic membrane reactor structure on product quality

[0074] As shown in Table 4, compared with Control Example 1, the product obtained in Example 5 has a more concentrated particle size distribution, higher morphological regularity, and a smaller batch-to-batch particle size variation coefficient. This further demonstrates that the two-stage tandem design of the present invention, by creating a "nucleation zone" and a "growth zone," effectively avoids "explosive nucleation" and uncontrolled crystal growth caused by instantaneously high supersaturation in a single-stage reactor, thereby significantly improving the uniformity of particle size distribution and batch repeatability of the product.

[0075] Compare with Example 2 This comparative example aims to study the synergistic effect of composite additives and two-stage membrane reactors.

[0076] This comparative example is basically the same as Example 5, except that: this comparative example sets up 5 different combinations (Ⅰ-Ⅴ), the specific combinations are shown in Table 5, and the quality of the products obtained by different combination processes is shown in Table 6.

[0077] Table 5 Combination Methods

[0078] Table 6. Mass of products obtained from different combined processes

[0079] As shown in Tables 5-6, combining the two-stage reactor with the composite additives resulted in significantly better performance in terms of reaction rate, product particle size, distribution uniformity, and morphology than when any one part was used alone.

[0080] In summary, this invention not only synergistically couples the two objectives of "high-value conversion of waste" and "carbon emission reduction," but also improves the CO2 fixation rate and the calcium conversion rate in carbide slag by increasing the reaction rate and mass transfer efficiency, ensuring high product uniformity. This provides a practical and feasible technical path for the large-scale, high-value co-processing of industrial solid waste and waste gas. Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing nano-calcium carbonate based on a ceramic microchannel membrane reactor, characterized in that, Includes the following steps: S1. Mix calcium carbide slag with ammonium chloride solution for leaching reaction. After solid-liquid separation, calcium-containing ore solution is obtained. S2. Add composite additives to calcium-containing molten mineral solution; S3. The mixture obtained in step S2 is pumped into the inner channel of the ceramic microchannel membrane reactor. At the same time, CO2-containing gas is introduced from the outside of the ceramic microchannel membrane reactor. The gas is dispersed through the micropores of the membrane wall to form micro-nano bubbles and then enters the liquid phase in the inner channel of the membrane. The gas and liquid phases contact each other in a cross-flow manner and carry out a carbonization reaction to generate a slurry containing nano-calcium carbonate. S4. The slurry obtained in step S3 is subjected to gas-liquid separation, and the solid product in the liquid phase is collected. After washing and drying, nano-calcium carbonate is obtained. The membrane module substrate of the ceramic microchannel membrane reactor is a porous ceramic material, and a hydrophobic and corrosion-resistant modified functional layer is formed on its membrane surface.

2. The method for preparing nano-calcium carbonate based on a ceramic microchannel membrane reactor according to claim 1, characterized in that, In step S2, the composite additive includes any two or three of polyphosphate compounds, organic polymer compounds, and surfactants, wherein the mass ratio of the polyphosphate compound, the organic polymer compound, and the surfactant is (1-3):(1-5):(0.01-0.10); Preferably, the amount of the composite additive added is 0.5% to 4% of the solid mass in the calcium-containing molten mineral solution.

3. The method for preparing nano-calcium carbonate based on a ceramic microchannel membrane reactor according to claim 2, characterized in that, The polyphosphate compound includes any one or more of sodium pyrophosphate, sodium polyphosphate, and sodium hexametaphosphate; The organic polymeric compounds include any one or more of polyacrylic acid, polyethylene oxide, polyglutamic acid, and chitosan; The surfactant includes any one or both of sodium dodecyl sulfate and polyoxyethylene sorbitan fatty acid ester.

4. The method for preparing nano-calcium carbonate based on a ceramic microchannel membrane reactor according to claim 1, characterized in that, In step S3, the carbonization reaction is carried out in a two-stage series ceramic microchannel membrane reactor system; Preferably, the mixture first enters the membrane channel of the primary membrane reactor, while CO2-containing gas is simultaneously introduced into the outer membrane of the primary membrane reactor to carry out the primary carbonization reaction. After the primary carbonization reaction, the slurry is aged in a gas-liquid separator and then enters the membrane channel of the secondary membrane reactor. At the same time, CO2-containing gas is introduced into the outer membrane of the secondary membrane reactor to carry out the main carbonization reaction.

5. The method for preparing nano-calcium carbonate based on a ceramic microchannel membrane reactor according to claim 4, characterized in that, The reaction process is controlled by online pH monitoring; Preferably, the pH of the slurry at the outlet of the primary membrane reactor is controlled between 9.2 and 9.8, and the pH of the slurry at the outlet of the secondary membrane reactor is controlled below 8.

5.

6. The method for preparing nano-calcium carbonate based on a ceramic microchannel membrane reactor according to claim 4 or 5, characterized in that, In a single-stage membrane reactor, the linear velocity of the mixture in the membrane channel is 2.0 × 10⁻⁶. -5 ~3.0×10 -5 The gas velocity in the membrane channel is 3.2 × 10 m / s. -4 ~3.7×10 -4 m / s; In a two-stage membrane reactor, the linear velocity of the slurry in the membrane channel is 1.0 × 10⁻⁶. -5 ~1.5×10 -5 The gas velocity in the membrane channel is 6.5 × 10 m / s. -4 ~7.0×10 -4 m / s.

7. The method for preparing nano-calcium carbonate based on a ceramic microchannel membrane reactor according to claim 1, characterized in that, In step S3, the pressure of the CO2-containing gas introduced is 0.2–0.3 MPa; Preferably, the diameter of the micro-nano bubbles is 0.1 to 100 μm.

8. The method for preparing nano-calcium carbonate based on a ceramic microchannel membrane reactor according to claim 1, characterized in that, In step S3, the method for preparing the hydrophobic and corrosion-resistant modified functional layer includes: T1. Immerse the membrane module substrate in an alkaline solution for hydroxyl loading pretreatment; T2. The membrane substrate treated in step T1 is reacted with C12-C18 long-chain fatty acids to construct an organic molecular layer. T3. The membrane substrate treated in step T2 is immersed in a silane coupling agent solution to carry out the grafting reaction. T4. The membrane substrate treated in step T3 is dried and heated to fix it in sequence, forming a hydrophobic and corrosion-resistant modified functional layer on the membrane surface.

9. The method for preparing nano-calcium carbonate based on a ceramic microchannel membrane reactor according to claim 1, characterized in that, The membrane module substrate is made of alumina composite silicon carbide material with an average pore size of 0.1 to 1.0 μm.

10. The method for preparing nano-calcium carbonate based on a ceramic microchannel membrane reactor according to claim 1, characterized in that, In step S1, the concentration of the ammonium chloride solution is 0.1–1.0 mol / L, the leaching reaction temperature is 40–60°C, and the reaction time is 1–3 h.

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