A method and product for preparing formate crystals using core-shell microcapsules

Abstract

This application relates to the field of functional crystalline material preparation and microfluidic application technology, specifically disclosing a method and product for preparing formate crystals using core-shell microcapsules, including the following steps: (1) dissolving a solid alkaline raw material in a formic acid solution to prepare reaction solution a; (2) separately conveying polymer solution A and polymer solution B with phase separation characteristics, and reaction solution a, so that they are mixed at the intersection of microchannels to prepare dispersed phase b, which is then introduced into the assembly zone for phase separation assembly to form core-shell microcapsules; (3) the core-shell microcapsules are crystallized in a continuous temperature-changing crystallization zone to form formate solid; (4) the formate solid is collected, washed and dried sequentially to obtain the target product; (5) the oil layer is continuously extracted and returned to the assembly zone for recycling. The formate crystals prepared in this application not only have a large particle size, but also exhibit good size uniformity and morphological repeatability, and have the advantages of high throughput, green environmental protection, and simple operation.

Description

Technical Field

[0001] This application relates to the field of functional crystalline material preparation and microfluidic application technology, specifically to a method for preparing formate crystals using core-shell microcapsules and formate products. Background Technology

[0002] Formates are a class of organic compounds, typically salts formed by the combination of formic acid (HCOOH) and metal ions. They are primarily used as animal feed additives, offering advantages such as safety, ease of use, high efficiency, and economy. Formates can effectively increase daily feed intake in livestock, promoting growth and development. Furthermore, they can regulate the acid-base environment of the animal's gastrointestinal tract, altering pH levels to inhibit the growth and reproduction of harmful bacteria, thereby reducing the incidence of gastrointestinal diseases and promoting the digestion and absorption of nutrients. Appropriate use of formates improves the utilization rate of nutrients in feed and enhances the quality of livestock products.

[0003] However, the traditional formate crystallization preparation process based on reaction vessels has many problems, such as low product purity, low crystallization yield, large batch-to-batch variability, uncontrollable crystal form, fragile crystals, and difficulty in preparing large-size crystals. Therefore, developing a method for large-scale preparation of high-purity and high-stability formate crystals is a major challenge. Summary of the Invention

[0004] The purpose of this application is to provide a method for controlled crystallization of formate using core-shell microcapsules. The formate products prepared by this method exhibit controllable crystal form and size, high consistency, and high purity. This method solves the problems of low purity and poor batch stability in traditional batch production, enabling low-energy, large-scale, continuous, and efficient production of formate. The application of the core-shell structure ensures a stable and closed nucleation and growth process for formate crystals. Furthermore, the limited crystal growth space allows for the formation of large formate crystals, making the final product less prone to deliquescence. Additionally, the collected oil layer can be completely recycled back into the system.

[0005] Therefore, one aspect of this application provides a method for preparing formate crystals using core-shell microcapsules, comprising the following steps:

[0006] (1) Add the solid alkaline raw material to the formic acid solution and stir until completely dissolved to prepare reaction solution a. Control the reaction temperature to 45-80℃.

[0007] (2) Polymer solution A, polymer solution B and reaction liquid a are respectively delivered by metering pump and mixed at the junction of microchannels to prepare dispersed phase b. After being sheared into droplets in oil phase C containing emulsifier, it enters the assembly zone for phase separation assembly to form core-shell microcapsules; wherein, polymer solution A and polymer solution B exhibit phase separation characteristics.

[0008] (3) The core-shell microcapsules are crystallized in a continuous temperature-changing crystallization zone to form formate solids. The continuous temperature-changing crystallization zone includes at least a first cooling zone, a second heating zone and a third cooling zone in a continuous cascade. The set temperature of the first cooling zone is 0-10℃, the set temperature of the second heating zone is 25-40℃, and the set temperature of the third cooling zone is 10-20℃.

[0009] (4) After the formate solid settles to the bottom of the collecting device, it is collected, washed and dried in sequence to obtain the target product;

[0010] (5) Continuously extract the upper oil layer in the collection device and transfer it to the storage device, and then circulate the oil layer back to the assembly area for recycling.

[0011] Optionally, in combination with any of the above aspects, in another implementation of this aspect, in step (1), the molar ratio of formic acid in the formic acid solution to the solid alkaline raw material is 1.2-4.5:1, and the mass concentration of the formic acid solution is 85%-100%.

[0012] Optionally, in conjunction with any of the above aspects, in another implementation of this aspect, in step (1), the solid alkaline raw material is selected from one or more of sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, sodium oxide, potassium oxide, sodium formate, and potassium formate.

[0013] Optionally, in conjunction with any of the above aspects, in another implementation of this aspect, in step (2), polymer A in polymer solution A is selected from one or more of double-bonded gelatin, gelatin, hyperbranched polyethylene glycol, polyethylene glycol, poly(N-isopropylacrylamide), and polyvinylpyrrolidone, and the mass fraction of polymer A in polymer solution A is 2-20%, and the solvent is water; polymer B in polymer solution B is selected from one or more of dextran, hydroxypropyl dextran, polyvinyl alcohol, carboxymethyl cellulose, methyl cellulose, and polyacrylamide, and the mass fraction of polymer B in polymer solution B is 5-40%, and the solvent is water.

[0014] Optionally, in conjunction with any of the above aspects, in another implementation of this aspect, in step (2), the phase separation system composed of polymer A and polymer B may respectively adopt one of the following polymer combinations: double bond gelatin / gelatin and hyperbranched polyethylene glycol / polyethylene glycol / dextran; polyethylene glycol / hyperbranched polyethylene glycol and dextran / polyvinyl alcohol / polyvinylpyrrolidone; polyvinylpyrrolidone / polyvinyl alcohol and methylcellulose / hydroxypropyl dextran / dextran; methylcellulose and dextran / hydroxypropyl dextran; poly(N-isopropylacrylamide) and polyacrylamide / polyvinyl alcohol (in the above description, " / " means "or").

[0015] Optionally, in combination with any of the above aspects, in another implementation of this aspect, in step (2), the flow rate of the polymer solution A is 1-5 mL / min, the flow rate of the polymer solution B is 1-5 mL / min, and the flow rate of the reaction liquid a is 2-20 mL / min.

[0016] Optionally, in conjunction with any of the above aspects, in another implementation of this aspect, in step (2), the flow rate of the oil phase C is 10-50 mL / min, the oil phase in the oil phase C is selected from one or more of dimethyl silicone oil, phenyl silicone oil, fluorinated silicone oil, and methylphenyl silicone oil, the emulsifier is selected from at least one of Dow Corning 749, Span 80, Span 60, Tween, sodium dodecyl sulfate, and octadecyltrimethylammonium chloride, and the mass of the emulsifier is 2%-10% of the mass of the oil phase C.

[0017] Optionally, in combination with any of the above aspects, in another implementation of this aspect, in step (2), the shell thickness of the core-shell microcapsule is 50-200 μm and the core thickness is 10-800 μm.

[0018] Alternatively, in combination with any of the above aspects, in another implementation of this aspect, in step (2), the set temperature of the assembly area is 45-60°C.

[0019] Optionally, in conjunction with any of the above aspects, in another implementation of this aspect, the residence time of the reactants in the assembly zone is 1-5 min, the residence time in the first cooling zone is 1-5 min, the residence time in the second heating zone is 1-10 min, and the residence time in the third cooling zone is 2-10 min.

[0020] Optionally, in combination with any of the above aspects, in another implementation of this aspect, in step (5), the flow rate of extracting the upper oil layer is 5-50 mL / min, and the flow rate of the circulating return is 5-50 mL / min.

[0021] Another aspect of this application provides a formate crystal, which is prepared by the method according to any of the above aspects.

[0022] As described above, the method for controlled crystallization of formate using core-shell microcapsules provided in this application involves mixing a solid alkaline raw material with a formic acid solution to form a reaction solution a, which is then combined with polymer solutions A and B, which have phase separation characteristics, to form an aqueous system. This system is then sheared in an oil phase C and transported to an assembly zone for phase separation assembly to form core-shell microcapsules. Continuous crystallization is then performed in a continuously variable temperature crystallization zone to ultimately obtain the formate product. Specifically, in the assembly zone, polymer solutions A and B exhibit phase separation effects. For example, polymers may exhibit different charges in aqueous solutions, leading to interactions that drive phase separation; or, polymer molecules may contain hydrophobic groups, relying on hydrophilic-hydrophobic interactions to drive phase separation; or, at a certain concentration, the polymer's molecular chain entanglement and volume effect in solution may be enhanced, disrupting the solubility equilibrium. Based on the intermolecular interactions and / or thermodynamic instabilities of the two solutions, the droplets formed by the shearing of the oil phase after mixing the reaction solution will undergo phase separation again, forming a core-shell structure. Each core-shell microcapsule will be independently crystallized at varying temperatures as a single system unit in the crystallization process. This ensures that low molecular weight formate aggregates in the core, promotes the formation of formate supersaturation, and is more conducive to the subsequent crystallization process. At the same time, it can control the particle morphology of formate crystals with high precision.

[0023] Furthermore, the formed core-shell microcapsules are fed into a continuous temperature-variable crystallization zone for crystallization. This scheme innovatively designs a continuous temperature-variable crystallization process for the reaction system in the core-shell microcapsules. Specifically, the continuous temperature-variable crystallization zone includes at least a first-stage cooling zone, a second-stage heating zone, and a third-stage cooling zone in a continuous cascade. The set temperature of the first-stage cooling zone is 0-10℃, the set temperature of the second-stage heating zone is 25-40℃, and the set temperature of the third-stage cooling zone is 10-20℃. The first low-temperature zone promotes the formation of crystal nuclei from the supersaturated reaction solution in the core-shell microcapsules, thereby precipitating formate crystals. The second heating zone dissolves some of the fine crystals precipitated from the formate, controls the formation of large crystals, and is conducive to the formation of crystal particles with uniform particle size. The third cooling zone allows the formate to reach a completely supersaturated state, accelerating crystal growth. Finally, the core-shell microcapsules sink to the bottom in the collection device due to gravity, resulting in large-particle formate crystals.

[0024] The reaction solution loaded within the core-shell microcapsule structure can respond to temperature changes. During continuous temperature variation, the core-shell structure can sequentially trigger different responses, such as a multi-stage crystallization process involving shell swelling, crystal growth, core enlargement, and crystal form stabilization. Furthermore, the physical barrier of the core-shell restricts the crystal growth direction, and combined with temperature changes, the porosity and swelling degree of the shell can be dynamically adjusted, guiding crystal growth along specific bulk crystal patterns. Temperature control can also regulate solvent evaporation rates and molecular diffusion, promoting the formation of a single crystal form and inhibiting the formation of non-target crystal forms. During temperature variation, sudden temperature changes can induce nucleation, while the confinement effect of the core-shell isolates the external environment, controlling the crystal growth rate and achieving high-yield, high-purity crystal synthesis. This prevents the core compound from degrading or oxidizing during crystallization, improving chemical and thermal stability. Continuous temperature-variable crystallization reduces energy waste through staged temperature control (e.g., low-temperature nucleation, high-temperature growth). The core-shell structure further reduces the required supersaturation through confinement effect, shortening the crystallization time; temperature changes can dynamically adjust the hydrophilicity and hydrophobicity of the shell (e.g., a temperature-sensitive shell is hydrophilic at low temperatures and hydrophobic at high temperatures), controlling the exchange of substances between the crystal and the outside world.

[0025] In addition, while ensuring controllable and continuous crystallization of formate crystals, the oil phase collected in the storage device can be directly recycled and reused, realizing the green and economical production of high-quality formate.

[0026] This application proposes a method for the controlled crystallization of formate using core-shell microcapsules. This method enables a continuous and stable formate crystallization process. A stable and controllable core-shell microcapsule structure is constructed using droplet microfluidics, encapsulating the formate precursor within the droplet core phase to form a reaction unit with an isolated reaction environment. Based on this, by precisely adjusting the external temperature, directional nucleation and controllable crystallization of formate within the capsule are achieved, thus overcoming the problems of wide particle size distribution and difficulty in control during traditional crystallization processes. The formate crystals prepared in this application not only have a large particle size but also exhibit good size uniformity and morphological reproducibility. This method has advantages such as high throughput, environmental friendliness, and ease of operation, and is suitable for the controllable synthesis of formate crystal materials, providing a new pathway for the precise manufacture of microstructured crystal materials.

[0027] Beneficial effects: Compared with the prior art, this application has the following significant advantages:

[0028] (1) In the assembly zone, due to the formation of microemulsion fluid, its specific surface area increases, and the mass and heat transfer is 2-3 orders of magnitude higher than that of the traditional batch crystallization process, resulting in higher crystallization efficiency. Furthermore, due to the polymer interface effect, phase separation begins to form a core-shell structure, which can strictly control the supersaturation.

[0029] (2) Crystallization in core-shell microcapsules has a narrower particle size distribution, resulting in high product consistency and enabling a stable crystallization process for materials. At the same time, the residence time is greatly shortened compared to batch crystallization, leading to high production efficiency.

[0030] (3) This application achieves crystal form control of formate by setting different temperature ranges in the crystallization zone, ensuring the generation of high-quality large-particle crystals and avoiding deliquescence.

[0031] (4) The crystals of formate can be simply filtered and cleaned. The post-processing is simple, the oil phase can be recycled and reused, and it is easy to scale up production.

[0032] The above summary provides a simplified overview of some concepts, which will be further described in detail in the following specific embodiments. The above summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to help determine the scope of the claimed subject matter. The claimed subject matter is not limited to embodiments that address any or all the shortcomings pointed out in the background art. Attached Figure Description

[0033] The accompanying drawings, incorporated in and forming part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application. To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, those skilled in the art can obtain other drawings based on these drawings without any creative effort. These drawings and textual descriptions are not intended to limit the scope of the concept of this application in any way, but rather to illustrate the concepts of this application to those skilled in the art by referring to specific embodiments.

[0034] Figure 1 This is a schematic diagram of the process for preparing formate crystals using core-shell microcapsules in Example 1 of this application;

[0035] Figure 2 This is a particle size distribution diagram of the core-shell microcapsules in Example 2 of this application;

[0036] Figure 3 This illustrates the effect of different molar ratios of formic acid and sodium formate on the crystallization rate of sodium diformate in Example 3 of this application.

[0037] Figure 4 The effect of the flow rate ratio of oil phase to dispersed phase b on the crystallization rate in Example 4 of this application;

[0038] Figure 5 This illustrates the effect of the residence time of the core-shell microcapsules in the second and third temperature-controlled sections of the crystallization zone on the crystallization rate in Example 5 of this application.

[0039] Figure 6 This is a comparison of the crystal forms of formate prepared by the conventional batch process and the core-shell microcapsule method in Example 6 of this application;

[0040] Figure 7 The XRD comparison spectra of the particulate formate product synthesized in Example 6 of this application with standard formate crystals and needle-shaped formate crystals are shown.

[0041] Figure 8 This is a dynamic change diagram of the core-shell microcapsule in Example 6 of this application as it enters the crystallization zone from the assembly zone. Detailed Implementation

[0042] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numbers in different drawings denote the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this application. Rather, they are merely examples of apparatuses and methods consistent with some aspects of this application as detailed in the appended claims.

[0043] It should be understood that the specific embodiments described herein are merely illustrative of this application and are not intended to limit the scope of this application.

[0044] This application provides a method for preparing formate crystals using core-shell microcapsules, comprising the following steps:

[0045] (1) Add the solid alkaline raw material to the formic acid solution and stir until completely dissolved to prepare reaction solution a. Control the reaction temperature to 45-80℃.

[0046] (2) Polymer solution A, polymer solution B and reaction liquid a are respectively delivered by metering pump and mixed at the junction of microchannels to prepare dispersed phase b. After being sheared into droplets in oil phase C containing emulsifier, it enters the assembly zone for phase separation assembly to form core-shell microcapsules; wherein, polymer solution A and polymer solution B exhibit phase separation characteristics.

[0047] (3) The core-shell microcapsules are crystallized in a continuous temperature-changing crystallization zone to form formate solids. The continuous temperature-changing crystallization zone includes at least a first cooling zone, a second heating zone and a third cooling zone in a continuous cascade. The set temperature of the first cooling zone is 0-10℃, the set temperature of the second heating zone is 25-40℃, and the set temperature of the third cooling zone is 10-20℃.

[0048] (4) After the formate solid settles to the bottom of the collecting device, it is collected, washed and dried in sequence to obtain the target product;

[0049] (5) Continuously extract the upper oil layer in the collection device and transfer it to the storage device, and then circulate the oil layer back to the assembly area for recycling.

[0050] The technical solution of this application will be further described below with reference to the accompanying drawings.

[0051] Example 1

[0052] This is based on a method for controlled crystallization of formate using core-shell microcapsules, such as... Figure 1 As shown. The specific preparation method is as follows:

[0053] 1. Preparation of reaction solution a

[0054] Under stirring conditions, solid sodium hydroxide raw material was completely dissolved in 85% formic acid solution to form reaction solution a. The molar ratio of formic acid to sodium hydroxide was controlled at 1.2:1, and the reaction temperature was set at 60℃.

[0055] 2. Preparation and crystallization of core-shell microcapsules

[0056] Methyl silicone oil containing 2% Dow Corning 749 was used as the continuous phase, with a flow rate of 20 mL / min. The flow rate of the dispersed phase reaction solution a was set to 4 mL / min, the flow rate of the 5% double bond gelatin solution was set to 2 mL / min, and the flow rate of the 10% carboxymethyl cellulose solution was set to 2 mL / min. After merging with the oil phase at the junction, the mixture was sheared into microspheres and passed into an assembly zone with a temperature set to 45℃ for a residence time of 2 min. Then, the mixture was passed sequentially through a cooling zone set to 10℃, a heating zone set to 40℃, and a cooling zone set to 10℃. The residence time in the first cooling zone was 1 min, the residence time in the second heating zone was 5 min, and the residence time in the third cooling zone was 10 min.

[0057] 3. Collection of formate products and recycling of the oil phase.

[0058] The entire crystallized core-shell microcapsules are collected in a collection device, where the crystalline solid phase layer settles rapidly. After accumulating a certain amount of solid phase, sodium formate crystals are collected from the bottom of the vessel and filtered. After simple washing with an oil phase demulsifier and ethanol, the product is placed in a 50°C vacuum drying oven to prepare the final product. Meanwhile, the upper oil phase is collected in a storage device at a pumping rate of 20 mL / min, and then refluxed back into the reaction system at a flow rate of 20 mL / min to achieve a second cycle of the reaction.

[0059] Example 2

[0060] The specific preparation method is as follows:

[0061] 1. Preparation of reaction solution a

[0062] Under stirring conditions, solid sodium carbonate is completely dissolved in pure formic acid solution to form reaction solution a. The molar ratio of formic acid to sodium carbonate is controlled at 2:1, and the reaction temperature is set at 45℃.

[0063] 2. Preparation and crystallization of core-shell microcapsules

[0064] Phenyl silicone oil containing 2% Dow Corning 749 was used as the continuous phase, with a flow rate of 50 mL / min. The flow rate of the dispersed phase reaction liquid a was set to 10 mL / min, the flow rate of the 5% gelatin solution was set to 5 mL / min, and the flow rate of the 10% carboxymethyl cellulose solution was set to 5 mL / min. After merging with the oil phase at the junction, the mixture was sheared into microspheres and passed into an assembly zone with a temperature set to 60℃ for a residence time of 2 min. Then, the mixture was passed sequentially through a cooling zone set to 0℃, a heating zone set to 25℃, and a cooling zone set to 10℃. The residence time in the first cooling zone was 1 min, the residence time in the second heating zone was 2 min, and the residence time in the third cooling zone was 5 min.

[0065] 3. Collection of formate products and recycling of the oil phase.

[0066] The entire crystallized core-shell microcapsules are collected in a collection device, where the crystalline solid phase layer settles rapidly. After accumulating a certain amount of solid phase, sodium diformate crystals are collected from the bottom of the vessel and filtered. After simple washing with an oil phase demulsifier and ethanol, the product is placed in a 50°C vacuum drying oven to prepare the final product. Meanwhile, the upper oil phase is collected in a storage device at a pumping rate of 50 mL / min, and then refluxed back into the reaction system at a flow rate of 50 mL / min to achieve a second cycle of the reaction.

[0067] The particle size distribution of core-shell microcapsules prepared using droplet microfluidics is as follows: Figure 2 As shown, the core layer containing sodium diformate crystals prepared has a uniform and concentrated particle size, mainly distributed around 80 μm. All core layer crystallization regions are controllable, with no obvious demulsification phenomenon. The overall outer protective shell size distribution is also relatively concentrated, mostly with a thickness of 130 μm. This monodisperse core-shell microcapsule structure improves the structural stability of sodium diformate crystals and provides a protective barrier for crystal nucleation, growth and maturation.

[0068] Example 3

[0069] The specific preparation method is as follows:

[0070] 1. Preparation of reaction solution a

[0071] Under stirring conditions, sodium formate solid raw material is completely dissolved in 85% formic acid solution to form reaction solution a. The molar ratio of formic acid to sodium formate is controlled at 3:1, and the reaction temperature is set at 55℃.

[0072] 2. Preparation and crystallization of core-shell microcapsules

[0073] Fluorinated silicone oil containing 10% Span80 was used as the continuous phase, with a flow rate of 10 mL / min. The flow rate of the dispersed phase reaction liquid a was set to 2 mL / min, the flow rate of the 10% polyethylene glycol solution was set to 1 mL / min, and the flow rate of the 40% dextran solution was set to 1 mL / min. After merging with the oil phase at the junction, the mixture was sheared into microspheres and passed into an assembly zone with a temperature set to 50℃ for 5 min. Then, the mixture was passed sequentially through a cooling zone set to 0℃, a heating zone set to 40℃, and a cooling zone set to 10℃. The residence time in the first cooling zone was 1 min, the residence time in the second heating zone was 2 min, and the residence time in the third cooling zone was 10 min.

[0074] 3. Collection of formate products and recycling of the oil phase.

[0075] The entire crystallized core-shell microcapsules are collected in a collection device, where the crystalline solid phase layer settles rapidly. After accumulating a certain amount of solid phase, sodium diformate crystals are collected from the bottom of the vessel and filtered. After simple washing with an oil phase demulsifier and ethanol, the product is placed in a 50°C vacuum drying oven to prepare the final product. Meanwhile, the upper oil phase is collected in a storage device at a pumping rate of 50 mL / min, and then refluxed back into the reaction system at a flow rate of 10 mL / min to achieve a second cycle of the reaction.

[0076] like Figure 3As shown, under the same conditions, the effects of batch crystallization and core-shell microcapsule crystallization on the crystallization rate of sodium diformate were tested by controlling the molar ratio of formic acid to sodium formate to be 1, 1.5, 2, 2.5, 3, 3.5, 4, and 4.5. With the increase of the molar ratio of formic acid to sodium formate, the crystallization rate of both increased continuously. This is because excess formic acid and sodium formate associate through hydrogen bonds to form sodium diformate. The batch crystallization rate tended to stabilize in the latter half, while the crystallization rate of the core-shell microcapsule crystallization technology reached its highest level of 95% at a molar ratio of 3, and then gradually decreased. However, the crystallization rate shows that the core-shell microcapsule crystallization method is far superior to batch crystallization, with an overall crystallization rate at least 10% higher. In addition, ICP (inductively coupled plasma atomic emission spectrometry) tests were performed on the sodium diformate products obtained by batch crystallization and continuous crystallization by core-shell microcapsules, as shown in the table below. According to the chemical equation of sodium diformate, its theoretical sodium content is about 20.18%. Sodium diformate prepared by the core-shell microcapsule crystallization method has a sodium content of 21.1% as determined by ICP, while the sodium content measured by batch crystallization is about 28%. It is obvious that the product of batch crystallization contains a mixture of sodium diformate and sodium formate. The core-shell crystallization process can achieve stable and efficient preparation of sodium diformate crystals.

[0077]

[0078] Example 4

[0079] The specific preparation method is as follows:

[0080] 1. Preparation of reaction solution a

[0081] Under stirring conditions, potassium hydroxide solid raw material is completely dissolved in 85% formic acid solution to form reaction solution a. The molar ratio of formic acid to potassium hydroxide is controlled at 4.5:1, and the reaction temperature is set at 55℃.

[0082] 2. Preparation and crystallization of core-shell microcapsules

[0083] Methyl silicone oil containing 10% Span60 was used as the continuous phase, with a flow rate of 60 mL / min. The flow rate of the dispersed phase reaction liquid a was set to 20 mL / min, the flow rate of the 10% polyvinylpyrrolidone solution was set to 10 mL / min, and the flow rate of the 20% dextran solution was set to 10 mL / min. After merging with the oil phase at the junction, the mixture was sheared into microspheres and introduced into an assembly zone with a temperature set to 60℃ for a residence time of 5 min. Then, the mixture was sequentially passed through a cooling zone set to 0℃, a heating zone set to 25℃, and a cooling zone set to 10℃. The residence time in the first cooling zone was 2 min, the residence time in the second heating zone was 2 min, and the residence time in the third cooling zone was 5 min.

[0084] 3. Collection of formate products and recycling of the oil phase.

[0085] The entire crystallized core-shell microcapsules are collected in a collection device, where the crystalline solid phase layer settles rapidly. After accumulating a certain amount of solid phase, potassium diformate crystals are collected from the bottom of the vessel and filtered. After simple washing with an oil phase demulsifier and ethanol, the product is placed in a 50°C vacuum drying oven to prepare the final product. Meanwhile, the upper oil phase is collected in a storage device at a pumping rate of 50 mL / min, and then refluxed back into the reaction system at a flow rate of 20 mL / min to achieve a second cycle of the reaction.

[0086] Controlling other conditions, the effect of the flow rate ratio of the oil phase to the dispersed phase b on the crystallization rate of potassium diformate was investigated. Figure 4 As shown, the crystallization rate of potassium diformate gradually increases with the increase of the ratio of oil phase to dispersed phase b flow rate. This is because the increase of oil phase shears the mixed solution of dispersed phase b into micro-emulsions, resulting in an increase in specific surface area and enhanced mass and heat transfer. The crystallization rate reaches the highest of 92% when the flow rate ratio is 3.1. However, with the continuous increase of oil phase flow rate, the number of crystallization units in each micro-emulsion decreases. The influence of temperature and polymer phase separation assembly on micro-emulsion crystallization increases, making it easier to form fine crystals, which leads to a decrease in crystallization rate.

[0087] Example 5

[0088] The specific preparation method is as follows:

[0089] 1. Preparation of reaction solution a

[0090] Under stirring conditions, solid potassium carbonate raw material is completely dissolved in 85% formic acid solution to form reaction solution a. The molar ratio of formic acid to potassium carbonate is controlled at 2:1, and the reaction temperature is set at 60℃.

[0091] 2. Preparation and crystallization of core-shell microcapsules

[0092] Methylphenyl silicone oil containing 10% sodium dodecyl sulfate was used as the continuous phase, with a flow rate of 40 mL / min. The flow rate of the dispersed phase reaction liquid a was set to 20 mL / min, the flow rate of the 10% poly(N-isopropylacrylamide) solution was set to 10 mL / min, and the flow rate of the 20% polyacrylamide solution was set to 10 mL / min. After merging with the oil phase at the junction, the mixture was sheared into microspheres and introduced into an assembly zone with a temperature of 45°C for 5 min. Then, it was sequentially passed through a cooling zone set to 0°C, a heating zone set to 25°C, and a cooling zone set to 10°C. The residence time in the first cooling zone was 2 min, the residence time in the second heating zone was 2 min, and the residence time in the third cooling zone was 10 min.

[0093] 3. Collection of formate products and recycling of the oil phase.

[0094] The entire crystallized core-shell microcapsules are collected in a collection device, where the crystalline solid phase layer settles rapidly. After accumulating a certain amount of solid phase, potassium formate crystals are collected from the bottom of the vessel and filtered. After simple washing with an oil phase demulsifier and ethanol, the product is placed in a 50°C vacuum drying oven to prepare the final product. Meanwhile, the upper oil phase is collected in a storage device at a pumping rate of 50 mL / min, and then refluxed back into the reaction system at a flow rate of 40 mL / min to achieve a second cycle of the reaction.

[0095] Under the same conditions, the set temperature of the first cooling zone was controlled, and the residence time was ensured to be 2 minutes. The effects of the residence time in the latter two variable temperature zones on the crystallization rate of potassium formate were compared. Figure 5 As shown, the crystallization rate increases linearly with the increase of the initial residence time ratio. This is because when the hot fluid cools, the solubility of the solute in reaction solution a gradually decreases, and the solution reaches supersaturation. At this point, crystals begin to grow gradually, forming unit cells. After the unit cells accumulate, crystals are formed. When the residence time ratio is 1.5, the crystallization rate of potassium formate can reach 91%. However, continuously increasing the residence time in the second heating zone will cause all crystals to dissolve, affecting the final degree of crystallization. It is worth noting that the hot fluid brought from the assembly zone should not be allowed to crystallize completely at low temperatures. Although rapid cooling can quickly supersaturate and precipitate solids, the crystals do not have a slow growth process, which will seriously affect the crystal form and other properties, ultimately affecting the quality of the product.

[0096] Example 6

[0097] The specific preparation method is as follows:

[0098] 1. Preparation of reaction solution a

[0099] Under stirring conditions, sodium oxide solid raw material is completely dissolved in 85% formic acid solution to form reaction solution a. The molar ratio of formic acid to sodium oxide is controlled at 1.2:1, and the reaction temperature is set at 60℃.

[0100] 2. Preparation and crystallization of core-shell microcapsules

[0101] Methyl silicone oil containing 10% Dow Corning 749 was used as the continuous phase, with a flow rate of 20 mL / min. The flow rate of the dispersed phase reaction solution a was set to 5 mL / min, the flow rate of the 10% double bond gelatin solution was set to 10 mL / min, and the flow rate of the 20% carboxymethyl cellulose solution was set to 5 mL / min. After merging with the oil phase at the junction, the mixture was sheared into microspheres and passed into an assembly zone with a temperature set to 45℃ for a residence time of 5 min. Then, the mixture was passed sequentially through a cooling zone set to 0℃, a heating zone set to 25℃, and a cooling zone set to 10℃. The residence time in the first cooling zone was 2 min, the residence time in the second heating zone was 2 min, and the residence time in the third cooling zone was 10 min.

[0102] 3. Collection of formate products and recycling of the oil phase.

[0103] The entire crystallized core-shell microcapsules are collected in a collection device, where the crystalline solid phase layer settles rapidly. After accumulating a certain amount of solid phase, sodium diformate crystals are collected from the bottom of the vessel and filtered. After simple washing with silicone oil demulsifier and ethanol, the product is placed in a 50°C vacuum drying oven to prepare the final product. Meanwhile, the upper oil phase is collected in a storage device at a pumping rate of 50 mL / min, and then refluxed back into the reaction system at a flow rate of 50 mL / min to achieve a second cycle of the reaction.

[0104] like Figure 6 As shown, the crystal structure prepared using microfluidic technology in this embodiment exhibits an aggregated bulk crystal structure, while the crystal structure prepared using a traditional batch reactor is needle-like. Furthermore, using single-crystal XRD diffraction technology, a standard XRD pattern was directly derived based on the structural formula of sodium diformate, and compared with the prepared bulk and needle-like crystal structures using XRD (e.g., ...). Figure 7 As shown in the figure, the bulk crystal form prepared by the core-shell microcapsule crystallization technology is the final target product of sodium diformate crystals, demonstrating the advantage of the crystallization technology in this application in terms of crystal form selection. Furthermore, the changes in the droplets sheared by the oil phase in the assembly and crystallization regions can be observed during the reaction process, such as... Figure 8 As shown, the droplet in the assembly zone will slowly separate from the homogeneous droplet at the front end into a core-shell structure. At this time, the core liquid is in a homogeneous state. When it enters the first cooling zone of the crystallization zone, its core will become wrinkled. This also proves that its internal core layer is formate and will form a crystal structure.

[0105] The sequence numbers of the embodiments in this application are for descriptive purposes only and do not represent the superiority or inferiority of the embodiments.

[0106] In this application, the same or similar terms, concepts, technical solutions and / or application scenario descriptions are generally described in detail only when they appear for the first time. When they appear again, they are generally not repeated for the sake of brevity. When understanding the technical solutions and other contents of this application, the same or similar terms, concepts, technical solutions and / or application scenario descriptions that are not described in detail later can be referred to their previous relevant detailed descriptions.

[0107] In this application, the descriptions of the various embodiments have different focuses. For parts that are not described in detail or recorded in a certain embodiment, please refer to the relevant descriptions of other embodiments.

[0108] The technical features of the present application can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of the present application.

[0109] The above are merely preferred embodiments of this application and do not limit the patent scope of this application. Any equivalent structural or procedural transformations made using the content of this application's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of this application.

Claims

1. A method for preparing formate salt crystals using core-shell microcapsules, characterized by, The method comprises the following steps: (1) adding solid alkaline raw materials into formic acid solution to stir until completely dissolved to prepare reaction liquid a, and controlling the reaction temperature to be 45-80℃; (2) using a metering pump to respectively deliver polymer solution A, polymer solution B and the reaction liquid a to mix at the intersection of the microchannel to prepare the dispersed phase b, which is sheared into droplets in the oil phase C containing an emulsifier and then enters the assembly area to perform phase separation assembly to form core-shell microcapsules; wherein the polymer A in the polymer solution A is selected from one or more of double-bond gelatin, gelatin, hyperbranched polyethylene glycol and polyethylene glycol, the mass fraction of the polymer A in the polymer solution A is 2-20%, and the solvent is water; the polymer B in the polymer solution B is selected from one or more of dextran, hydroxypropyl dextran, polyvinyl alcohol, carboxymethyl cellulose and methyl cellulose, the mass fraction of the polymer B in the polymer solution B is 5-40%, and the solvent is water; the polymer solution A and the polymer solution B exhibit phase separation characteristics; (3) the core-shell microcapsules are subjected to crystallization in a continuous variable-temperature crystallization area to form formate solid, wherein the continuous variable-temperature crystallization area at least comprises a first-stage temperature-decreasing area, a second-stage temperature-increasing area and a third-stage temperature-decreasing area connected in series, the set temperature of the first-stage temperature-decreasing area is 0-10℃, the set temperature of the second-stage temperature-increasing area is 25-40℃, and the set temperature of the third-stage temperature-decreasing area is 10-20℃; the temperature change process can dynamically adjust the porosity and swelling degree of the shell layer of the core-shell microcapsules, reduce the supersaturation required for crystallization, and guide the crystal to grow along a specific block crystal; (4) after the formate solid sinks to the bottom of the collection device, it is sequentially collected, washed and dried to obtain a target product; (5) continuously extracting the upper oil layer in the collection device to transfer it to a liquid storage device, and then circulating the oil layer back to the assembly area for recycling.

2. The method of claim 1, wherein, In step (1), the molar ratio of formic acid in the formic acid solution to the solid alkaline raw material is 1.2-4.5:1, and the mass concentration of the formic acid solution is 85%-100%.

3. The method according to claim 1 or 2, characterized in that, In step (1), the solid alkaline raw material is selected from one or more of sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, sodium oxide, potassium oxide, sodium formate and potassium formate.

4. The method of claim 1, wherein, In step (2), the flow rate of the polymer solution A is 1-5 mL / min, the flow rate of the polymer solution B is 1-5 mL / min, and the flow rate of the reaction liquid a is 2-20 mL / min.

5. The method according to claim 1 or 4, characterized in that, In step (2), the flow rate of the oil phase C is 10-50 mL / min, the oil phase in the oil phase C is selected from one or more of dimethyl silicone oil, phenyl silicone oil, fluorinated silicone oil and methyl phenyl silicone oil, the emulsifier is selected from at least one of Dow Corning 749, Span 80, Span 60, Tween, sodium dodecyl sulfate and octadecyl trimethyl ammonium chloride, and the mass of the emulsifier is 2%-10% of the mass of the oil phase C.

6. The method of claim 1, wherein, In step (2), the shell layer thickness of the core-shell microcapsules is 50-200 μm, and the core layer thickness is 10-800 μm.

7. The method of claim 1, wherein, In step (2), the temperature of the assembly zone is 45-60℃.

8. The method according to claim 1 or 7, characterized in that, The residence time of the reactants in the assembly zone is 1-5 min, in the first temperature decreasing zone is 1-5 min, in the second temperature increasing zone is 1-10 min, and in the third temperature decreasing zone is 2-10 min.

9. The method of claim 1, wherein, In step (5), the flow rate of the upper oil layer is 5-50 mL / min, and the flow rate of the circulating reflux is 5-50 mL / min.

Images