Method for preparing formate crystal by using core-shell microcapsule and product

Abstract

The invention relates to the technical field of functional crystal material preparation and microfluidic application, and particularly discloses a method for preparing formate crystals by using core-shell microcapsules and a product, and the method comprises the following steps: (1) dissolving a solid alkaline raw material in a formic acid solution to prepare a reaction solution a; (2) respectively conveying a polymer solution A and a polymer solution B with phase separation characteristics and the reaction solution a to be mixed at the intersection of the microchannels to prepare a dispersed phase b, and then entering an assembly area to perform split-phase assembly to form a core-shell microcapsule; (3) crystallizing the core-shell microcapsule in a continuous variable-temperature crystallization region to form a formate solid; and (4) sequentially collecting, cleaning and drying the formate solid to obtain a target product. And (5) continuously extracting the oil layer, and refluxing to the assembly area for cyclic application. The formate crystal prepared by the invention not only has a larger particle size, but also shows good size uniformity and morphology repeatability, and has the advantages of high throughput, environmental friendliness, simplicity and convenience in operation and the like.

Description

Technical Field

[0001] This application relates to the technical field of the preparation of functional crystalline materials and microfluidic applications, and particularly relates to a method for preparing formate crystals using core-shell microcapsules and a formate product. Background Art

[0002] Formates are a class of organic compounds, usually salts formed by the combination of formic acid (HCOOH) and metal ions. They are mainly used as animal feed additives and have advantages such as safety, ease of use, high efficiency, and economy. Formates can effectively increase the daily food intake of livestock, which is beneficial to the growth and development of livestock. In addition, they can regulate the acid-base environment in the gastrointestinal tract of animals, change the pH value, inhibit the growth and reproduction of harmful bacteria in the gastrointestinal tract environment, thereby reducing the incidence of gastrointestinal diseases and promoting the digestion and absorption of nutrients. The 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 a reaction kettle has various problems such as low product purity, low crystallization yield, large batch differences, uncontrollable crystal form, fragile crystal grains, and difficulty in preparing large-particle-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 realizing controllable crystallization of formates using core-shell microcapsules. The formate product prepared by this method has characteristics such as controllable crystal form and crystal size, high consistency, and high purity, which can solve the problems of low formate purity and poor batch stability in traditional kettle production, and achieve low-energy consumption, large-scale continuous and efficient production of formates. The application of the core-shell structure not only ensures a stable and enclosed nucleation and growth process for formate crystals, but also realizes the formation of large-particle formate crystals due to the limitation of the crystal growth space, making the final product not easily deliquescent. In addition, the collected oil layer can be completely recycled back to the system for reuse.

[0005] To this end, in one aspect of this application, a method for preparing formate crystals using core-shell microcapsules is provided, including the following steps: (1) Add solid alkaline raw materials to a formic acid solution and stir until completely dissolved to prepare reaction solution a, and control the reaction temperature at 45 - 80°C; (2) Use metering pumps to separately transport polymer solution A, polymer solution B, and the reaction solution a to mix them at the intersection of microchannels to prepare a dispersed phase b, which is sheared into droplets in an oil phase C containing an emulsifier and then enters the assembly area for phase separation and assembly to form core-shell microcapsules; among them, polymer solution A and polymer solution B exhibit phase separation characteristics; (3) The core-shell microcapsules are crystallized through a continuous variable-temperature crystallization zone to form formate solids. Among them, the continuous variable-temperature crystallization zone at least includes a first cooling zone, a second heating zone, and a third cooling zone that are continuously cascaded. The set temperature of the first cooling zone is 0-10 °C, the set temperature of the second heating zone is 25-40 °C, and the set temperature of the third cooling zone is 10-20 °C; (4) After the formate solids sink to the bottom of the collection device, they are collected, washed, and dried in sequence to obtain the target product; (5) Continuously extract the upper oil layer in the collection device to transfer it to the liquid storage device, and then recycle the oil layer back to the assembly area for recycling.

[0006] Optionally, in combination with any of the above aspects, in another implementation manner of this aspect, in step (1), the molar ratio of formic acid to the solid basic raw material in the formic acid solution is 1.2-4.5:1, and the mass concentration of the formic acid solution is 85%-100%.

[0007] Optionally, in combination with any of the above aspects, in another implementation manner of this aspect, in step (1), the solid basic 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.

[0008] Optionally, in combination with any of the above aspects, in another implementation manner of this aspect, in step (2), the polymer A in the polymer solution A is selected from one or more of double-bonded gelatin, gelatin, hyperbranched polyethylene glycol, polyethylene glycol, poly(N-isopropylacrylamide), and polyvinylpyrrolidone. The mass fraction of 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, methyl cellulose, and polyacrylamide. The mass fraction of polymer B in the polymer solution B is 5%-40%, and the solvent is water.

[0009] Optionally, in combination with any of the above aspects, in another implementation manner of this aspect, in step (2), the phase separation system composed of polymer A and polymer B can respectively adopt one of the following polymer combinations: double-bonded gelatin / gelatin and hyperbranched polyethylene glycol / polyethylene glycol / dextran; polyethylene glycol / hyperbranched polyethylene glycol and dextran / polyvinyl alcohol / polyvinylpyrrolidone; polyvinylpyrrolidone / polyvinyl alcohol and methyl cellulose / hydroxypropyl dextran / dextran; methyl cellulose and dextran / hydroxypropyl dextran; poly(N-isopropylacrylamide) and polyacrylamide / polyvinyl alcohol (the " / " in the above description means "or").

[0010] 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 solution a is 2-20 mL / min.

[0011] Optionally, in combination 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, Span80, Span60, Tween, sodium dodecyl sulfate, and octadecyltrimethylammonium chloride. The mass of the emulsifier is 2%-10% of the mass of the oil phase C.

[0012] Optionally, in combination with any of the above aspects, in another implementation of this aspect, in step (2), the shell layer thickness of the core-shell microcapsule is 50-200 μm, and the core layer thickness is 10-800 μm.

[0013] Optionally, 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.

[0014] Optionally, in combination with any of the above aspects, in another implementation of this aspect, the residence time of the reactants in the assembly area is 1-5 min, the residence time in the first cooling area is 1-5 min, the residence time in the second heating area is 1-10 min, and the residence time in the third cooling area is 2-10 min.

[0015] 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 reflux is 5-50 mL / min.

[0016] Another aspect of the present application provides a formate crystal, which is prepared by the method according to any of the above aspects.

[0017] As described above, the method for realizing controlled crystallization of formate using core-shell microcapsules provided in the present application is to form an aqueous phase system with a reaction solution a formed by mixing a solid alkaline raw material with a formic acid solution and a polymer solution A and a polymer solution B having phase separation characteristics, and then sheared in an oil phase C and transported to an assembly zone for phase separation assembly to form core-shell microcapsules, and then continuously crystallized through a continuous temperature-variable crystallization zone, and finally prepare a formate product. Specifically, in the assembly zone, because polymer solution A and polymer solution B have a phase separation effect, for example, polymers present different charges in aqueous solution, so that they interact to drive phase separation; or, polymer molecules contain hydrophobic groups, relying on hydrophilic and hydrophobic interactions to drive phase separation; or, a certain concentration of high polymer in the solution has enhanced molecular chain entanglement and volume effect, which will destroy the solubility balance. Based on the intermolecular interaction and / or thermodynamic instability of the two solutions, the mixed reaction solution will undergo phase separation again inside the droplets formed by shearing of the oil phase, forming a core-shell structure. Each core-shell microcapsule will be treated as a single system unit in the crystallization process and independently undergo variable temperature crystallization, which ensures that low molecular weight formate is aggregated in the core, promotes the formation of formate supersaturation, is more conducive to the subsequent crystallization process, and can control the particle morphology of formate crystals with high precision.

[0018] Furthermore, the formed core-shell microcapsules are sent to the continuous temperature-variable crystallization zone for crystallization. This solution 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 the first cooling zone, the second heating zone and the third cooling zone of the continuous cascade. The set temperature of the first cooling zone is 0-10°C, the set temperature of the second heating zone is 25-40°C, and the set temperature of the third cooling zone is 10-20°C. The first low-temperature zone promotes the supersaturated reaction liquid in the core-shell microcapsules to form crystal nuclei and precipitate formate crystals; the second heating zone dissolves part of the fine crystals precipitated by formate, controls the formation of large crystals, and is conducive to the formation of crystalline particles with uniform particle size; the third cooling zone makes the formate completely reach the supersaturated state, and the crystal growth is accelerated. Finally, the core-shell microcapsules sink to the bottom of the collection device due to gravity to obtain large-particle formate crystals.

[0019] The reaction solution loaded inside the core-shell microcapsule structure can respond to temperature changes. During the continuous temperature change process, the core-shell structure can trigger different responses in sequence, such as a multi-stage crystallization process of shell swelling - crystal growth - core layer enlargement - crystal form tending to be stable. In addition, the physical barrier of the core-shell restricts the crystal growth direction. Combining with the temperature change process, the porosity and swelling degree of the shell layer can be dynamically adjusted to guide the crystal to grow along a specific block crystal. The regulation of temperature can also regulate the solvent evaporation rate and molecular diffusion, promote the formation of a single crystal form, and inhibit the formation of non-target crystal forms. During the temperature change process, a sudden temperature change can induce nucleation, and the confinement effect of the core-shell can isolate the external environment, control the crystal growth rate, achieve high-yield and high-purity crystal synthesis, prevent the core compound from degrading or oxidizing during the crystallization process, and improve chemical stability and thermal stability. Continuous variable-temperature crystallization reduces energy waste through staged temperature regulation (such as low-temperature nucleation and high-temperature growth). The core-shell structure further reduces the required supersaturation through the confinement effect and shortens the crystallization time. The temperature change can dynamically adjust the hydrophilicity and hydrophobicity of the shell layer (such as a temperature-sensitive shell layer being hydrophilic at low temperature and hydrophobic at high temperature), and control the material exchange between the crystal and the outside world.

[0020] In addition, while ensuring the controllable crystal form and continuous crystallization of formate, the oil phase collected in the liquid storage device can be directly recycled, realizing the green economic production of the whole high-quality formate.

[0021] The method for realizing controllable crystallization of formate by using core-shell microcapsules proposed in this application can achieve a continuous and stable formate crystallization process. The liquid droplet microfluidics technology is used to construct a stable and controllable core-shell microcapsule structure, and the formate precursor is encapsulated in the liquid droplet core phase to form a reaction unit with an isolated reaction environment. On this basis, by precisely adjusting the external temperature, the directional nucleation and controllable crystallization of formate in the capsule are realized, thus breaking through the problems of wide particle size distribution and difficult control in the traditional crystallization process. The formate crystals prepared in this application not only have a larger particle size, but also show good size uniformity and morphology repeatability. This method has the advantages of high throughput, environmental friendliness, and simple operation, is suitable for the controllable synthesis of formate crystal materials, and provides a new path for the precise manufacturing of microstructured crystal materials.

[0022] Beneficial effects: Compared with the prior art, this application has the following remarkable advantages: (1) In the assembly area, due to the formation of the microemulsion fluid, its specific surface area increases, and the mass transfer and heat transfer are 2 - 3 orders of magnitude higher than those in the traditional batch crystallization process, with higher crystallization efficiency. And due to the polymer interface effect, phase separation begins to form a core-shell structure, which can strictly control the supersaturation. (2) Crystallization in the core-shell microcapsule has a narrow particle size distribution, high product consistency, can realize a stable crystallization process of materials, and at the same time, the residence time is greatly shortened compared with batch crystallization, with high production efficiency. (3) By setting different temperature ranges in the crystallization zone, the present application realizes the control of the crystal form of formate, ensures the generation of high-quality large granular crystals, and avoids deliquescence.

[0023] (4) The crystals of formate can be obtained by simple filtration and washing. The post-treatment process is simple, the oil phase can be recycled and reused, and it is easy to scale up production.

[0024] The above invention content is provided to introduce some concepts in a simplified form, which will be further described in detail in the following specific embodiments. The above invention content is neither intended to identify the key features or essential features of the claimed subject matter, nor is it intended to be used to help determine the scope of the claimed subject matter. The claimed subject matter of the present application is not limited to the embodiments that solve any or all of the disadvantages pointed out in the background art. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The drawings herein are incorporated into the specification and form a part of this specification, showing embodiments consistent with the present application, and are used together with the specification to explain the principles of the present application. In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, for those of ordinary skill in the art, other drawings can also be obtained based on these drawings without creative efforts. These drawings and the text description are not intended to limit the scope of the concept of the present application in any way, but to illustrate the concept of the present application to those skilled in the art by referring to specific embodiments.

[0026] Figure 1 It is a schematic flow chart for preparing formate crystallization using core-shell microcapsules in Embodiment 1 of the present application; Figure 2 It is a particle size distribution diagram of the core and shell in the core-shell microcapsules in Embodiment 2 of the present application; Figure 3 It is the influence of different molar ratios of formic acid and sodium formate on the crystallization rate of disodium formate in Embodiment 3 of the present application; Figure 4 It is the influence of the flow rate ratio of the oil phase to the dispersion phase b on the crystallization rate in Embodiment 4 of the present application; Figure 5 It is the influence of the residence time of the core-shell microcapsules at variable temperatures in the second and third sections in the crystallization zone on the crystallization rate in Embodiment 5 of the present application; Figure 6 It is the comparison of the crystal forms of formate prepared by the traditional kettle method and the core-shell microcapsule method in Embodiment 6 of the present application; Figure 7 It is the XRD comparison spectrum of the granular formate product synthesized in Embodiment 6 of the present application, the standard formate crystal, and the acicular crystal formate crystal; Figure 8This is a dynamic change diagram of the core-shell microcapsules just entering the crystallization zone in Assembly Zone in Example 6 of this application. Detailed Description of the Invention

[0027] Here, exemplary embodiments will be described in detail, and examples thereof are shown in the drawings. When the following description refers to the drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this application. On the contrary, they are merely examples of devices and methods consistent with some aspects of this application as detailed in the appended claims.

[0028] It should be understood that the specific embodiments described herein are merely used to explain this application and are not used to limit the scope of rights of this application.

[0029] This application provides a method for preparing formate crystals using core-shell microcapsules, including the following steps: (1) Add solid alkaline raw materials to formic acid solution and stir until completely dissolved to prepare reaction solution a, and control the reaction temperature at 45 - 80 °C; (2) Use metering pumps to separately transport polymer solution A, polymer solution B, and the reaction solution a to mix them at the intersection of microchannels to prepare dispersed phase b. After being sheared into droplets in oil phase C containing emulsifier, enter the assembly zone for phase separation and assembly to form core-shell microcapsules; among them, polymer solution A and polymer solution B exhibit phase separation characteristics; (3) The core-shell microcapsules are crystallized through a continuous variable-temperature crystallization zone to form formate solids. Among them, the continuous variable-temperature crystallization zone at least includes a continuously cascaded first cooling zone, a second heating zone, and a third cooling zone. The set temperature of the first cooling zone is 0 - 10 °C, the set temperature of the second heating zone is 25 - 40 °C, and the set temperature of the third cooling zone is 10 - 20 °C; (4) After the formate solids sink to the bottom of the collection device, they are collected, washed, and dried in sequence to obtain the target product; (5) Continuously extract the upper oil layer in the collection device and transfer it to the storage device, and then recycle the oil layer back to the assembly zone for recycling.

[0030] The technical solution of this application will be further described below with reference to the drawings.

[0031] Example 1

[0032] The method for realizing controllable crystallization of formate using core-shell microcapsules is as Figure 1 shown. The specific preparation method is as follows: 1. Preparation of reaction solution a Under stirring conditions, solid sodium hydroxide raw material is completely dissolved in 85% formic acid solution to form reaction solution a. The molar ratio of formic acid to sodium hydroxide is controlled to be 1.2:1, and the reaction temperature is set at 60 °C.

[0033] 2. Preparation and crystallization of core-shell microcapsules Methyl silicone oil containing 2% Dow Corning 749 is used as the continuous phase, with a flow rate set at 20 mL / min. The flow rate of the dispersed phase reaction solution a is set at 4 mL / min, the flow rate of the 5% double-bond gelatin solution is set at 2 mL / min, and the flow rate of the 10% carboxymethyl cellulose solution is set at 2 mL / min. After meeting with the oil phase at the confluence, it is sheared into microspheres and introduced into the assembly area with a set temperature of 45 °C, where the residence time is 2 min. Then it passes through the cooling zone set at 10 °C, the heating zone set at 40 °C, and the cooling zone set at 10 °C in sequence. The residence time in the first cooling zone is 1 min, the residence time in the second heating zone is 5 min, and the residence time in the third cooling zone is 10 min.

[0034] 3. Collection of formate product and recycling of oil phase The whole crystallized core-shell microcapsules are collected in the collection device. The crystalline solid phase layer will settle quickly. After accumulating a certain amount of solid phase, sodium formate crystals are collected at the bottom of the kettle and filtered. After adding an oil phase demulsifier and ethanol for simple cleaning, they are placed in a vacuum drying oven at 50 °C to prepare the final product. In addition, the upper oil phase is collected in the liquid storage device at a pumping speed of 20 mL / min, and then the oil phase is refluxed to the reaction system at a flow rate of 20 mL / min to achieve re-circulation reaction.

[0035] Example 2

[0036] The specific preparation method is as follows: 1. Preparation of reaction solution a Under stirring conditions, solid sodium carbonate raw material is completely dissolved in pure formic acid solution to form reaction solution a. The molar ratio of formic acid to sodium carbonate is controlled to be 2:1, and the reaction temperature is set at 45 °C.

[0037] 2. Preparation and crystallization of core-shell microcapsules Using phenyl silicone oil containing 2% Dow Corning 749 as the continuous phase, setting the flow rate to 50 mL / min, the flow rate of the dispersed phase reaction solution a to 10 mL / min, the flow rate of the 5% gelatin solution to 5 mL / min, and the flow rate of the 10% carboxymethyl cellulose solution to 5 mL / min. After converging with the oil phase at the intersection, it is sheared into microspheres, passed into the assembly area with a set temperature of 60 °C, and the residence time is 2 min. Then it passes through the cooling area set at 0 °C, the heating area set at 25 °C, and the cooling area set at 10 °C in sequence. The residence time in the first cooling area is 1 min, the residence time in the second heating area is 2 min, and the residence time in the third cooling area is 5 min.

[0038] 3. Collection of formate products and recycling of the oil phase Collect the entire crystallized core-shell microcapsules in the collection device. The crystalline solid phase layer will settle quickly. After accumulating a certain amount of solid phase, start collecting sodium formate crystals at the bottom of the kettle and filter them. After adding an oil phase demulsifier and ethanol for simple cleaning, put them into a vacuum drying oven at 50 °C to prepare the final product. In addition, the upper oil phase is collected in the liquid storage device at a pumping speed of 50 mL / min, and then the oil phase is refluxed to the reaction system at a flow rate of 50 mL / min to achieve re-circulation reaction.

[0039] The particle size distribution of the core-shell microcapsules prepared by droplet microfluidics technology is as Figure 2 shown. The particle sizes of the core layers containing sodium formate crystals are uniform and concentrated, mainly distributed around 80 μm. All the core layer crystallization regions are controllable, and there is no obvious demulsification phenomenon. The size distribution of the overall outer protective shell layer is also relatively concentrated, mostly with a thickness of 130 μm. The structure of this monodisperse core-shell microcapsule improves the structural stability of sodium formate crystallization and provides a protective barrier for the nucleation, growth, and maturation of crystals.

[0040] Example 3

[0041] The specific preparation method is as follows: 1. Preparation of reaction solution a Under stirring conditions, completely dissolve the solid raw material of sodium formate in 85% formic acid solution to form reaction solution a, control the molar ratio of formic acid to sodium formate to be 3:1, and set the reaction temperature to 55 °C.

[0042] 2. Preparation and crystallization of core-shell microcapsules Using fluorinated silicone oil containing 10% Span80 as the continuous phase, set the flow rate to 10 mL / min, the flow rate of the dispersed phase reaction solution a to 2 mL / min, the flow rate of the 10% polyethylene glycol solution to 1 mL / min, and the flow rate of the 40% dextran solution to 1 mL / min. After converging with the oil phase at the intersection, it is sheared into microspheres and introduced into the assembly area with a set temperature of 50 °C, with a residence time of 5 min. Then, it passes through the cooling area set at 0 °C, the heating area set at 40 °C, and the cooling area set at 10 °C in sequence. The residence time in the first-stage cooling area is 1 min, the residence time in the second-stage heating area is 2 min, and the residence time in the third-stage cooling area is 10 min.

[0043] 3. Collection of formate products and recycling of the oil phase Collect the entire crystallized core-shell microcapsules in the collection device. The crystalline solid phase layer will settle rapidly. After accumulating a certain amount of solid phase, start collecting sodium formate crystals at the bottom of the kettle and filter them. After adding an oil-phase demulsifier and ethanol for simple cleaning, place them in a vacuum drying oven at 50 °C to prepare the final product. In addition, the upper oil phase is collected in the liquid storage device at a pumping speed of 50 mL / min, and then the oil phase is refluxed to the reaction system at a flow rate of 10 mL / min to achieve re-circulation reaction.

[0044] As Figure 3 shown, under the same conditions, by controlling the molar ratio of formic acid to sodium formate to 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, the effects of kettle crystallization and core-shell microcapsule crystallization on the crystallization rate of sodium formate were tested. As the molar ratio of formic acid to sodium formate increases, the crystallization rates of both continue to increase. This is the result of the formation of sodium formate by the hydrogen bond association of excess formic acid and sodium formate. The kettle crystallization rate tends to be stable in the second half. The crystallization rate of the core-shell microcapsule crystallization technology reaches the highest 95% at a molar ratio of 3, and then gradually decreases. However, it can be seen from the crystallization rate that the core-shell microcapsule crystallization method is far superior to kettle crystallization, and the overall crystallization rate is at least 10% higher than that of kettle crystallization. In addition, ICP tests (inductively coupled plasma emission spectrometer) were performed on the sodium formate products of kettle crystallization and core-shell microcapsule continuous crystallization, as shown in the following table. According to the chemical equation of sodium formate, the theoretical sodium element content is about 20.18%. For the sodium formate prepared by the core-shell microcapsule crystallization method, the sodium element content measured by ICP quantification is 21.1%, while the sodium element content measured by kettle crystallization is about 28%. Obviously, the product of kettle crystallization contains a mixture of sodium formate and formic acid. The stable and efficient preparation of sodium formate crystals can be achieved by using this core-shell crystallization process.

[0045]

[0046] Example 4 The specific preparation method is as follows: 1. Preparation of reaction solution a Under stirring conditions, solid potassium hydroxide 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 to be 4.5:1, and the reaction temperature is set at 55 °C.

[0047] 2. Preparation and crystallization of core-shell microcapsules Methyl silicone oil containing 10% Span60 is used as the continuous phase, with a flow rate set at 60 mL / min. The flow rate of the dispersed phase reaction solution a is set at 20 mL / min, the flow rate of 10% polyvinylpyrrolidone solution is set at 10 mL / min, and the flow rate of 20% dextran solution is set at 10 mL / min. After converging with the oil phase at the intersection, it is sheared into microspheres, passed into the assembly area with a set temperature of 60 °C, and the residence time is 5 min. Then it passes through the cooling area set at 0 °C, the heating area set at 25 °C, and the cooling area set at 10 °C in sequence. The residence time in the first-stage cooling area is 2 min, the residence time in the second-stage heating area is 2 min, and the residence time in the third-stage cooling area is 5 min.

[0048] 3. Collection of formate product and recycling of oil phase The whole crystallized core-shell microcapsules are collected in the collection device. The crystalline solid phase layer will settle rapidly. After a certain amount of solid phase has accumulated, potassium diformate crystals are collected at the bottom of the kettle and filtered. After simple washing with an oil phase demulsifier and ethanol, they are placed in a vacuum drying oven at 50 °C to prepare the final product. In addition, the upper oil phase is collected in the liquid storage device at a pumping speed of 50 mL / min, and then the oil phase is refluxed to the reaction system at a flow rate of 20 mL / min to achieve re-circulation reaction.

[0049] With other conditions unchanged, the influence of the flow rate ratio of the oil phase to the dispersed phase b on the crystallization rate of potassium diformate was investigated. As Figure 4 shown, as the ratio of the flow rate of the oil phase to the dispersed phase b increases, the crystallization rate of potassium diformate gradually increases. This is because the increase in the oil phase shears the mixed solution of the dispersed phase b into tiny emulsions, resulting in an increase in specific surface area and enhanced mass transfer and heat transfer. The crystallization rate reaches the highest 92% when the flow rate ratio is 3.1. However, with the continuous increase in the oil phase flow rate, the number of crystallization units in each tiny emulsion will decrease, and the influence of temperature and polymer phase separation assembly on the crystallization of tiny emulsions will increase, making it easier to form fine crystals, resulting in a decrease in the crystallization rate.

[0050] Example 5

[0051] The specific preparation method is as follows: 1. Preparation of reaction solution a 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 to be 2:1, and the reaction temperature is set at 60 °C.

[0052] 2. Preparation and crystallization of core-shell microcapsules Methylphenyl silicone oil containing 10% sodium dodecyl sulfate is used as the continuous phase, with a flow rate set at 40 mL / min. The flow rate of the dispersed phase reaction solution a is set at 20 mL / min, the flow rate of 10% poly(N-isopropylacrylamide) solution is set at 10 mL / min, and the flow rate of 20% polyacrylamide solution is set at 10 mL / min. After converging with the oil phase at the junction, it is sheared into microspheres and introduced into an assembly area with a set temperature of 45 °C, with a residence time of 5 min. Then it passes through a cooling zone set at 0 °C, a heating zone set at 25 °C, and a cooling zone set at 10 °C in sequence. The residence time in the first-stage cooling zone is 2 min, the residence time in the second-stage heating zone is 2 min, and the residence time in the third-stage cooling zone is 10 min.

[0053] 3. Collection of formate product and recycling of oil phase The entire crystallized core-shell microcapsules are collected in a collection device. The crystalline solid phase layer will settle rapidly. After accumulating a certain amount of solid phase, potassium formate crystals are collected at the bottom of the kettle and filtered. After simple washing with an oil-phase demulsifier and ethanol, they are placed in a vacuum drying oven at 50 °C to prepare the final product. In addition, the upper-layer oil phase is collected in a liquid storage device at a pumping speed of 50 mL / min, and then the oil phase is refluxed to the reaction system at a flow rate of 40 mL / min to achieve re-circulation reaction.

[0054] Under the same conditions, by controlling the set temperature of the first-stage cooling zone to ensure a residence time of 2 min, the influence of the residence time in the latter two variable-temperature zones on the crystallization rate of potassium formate was compared. As Figure 5 shown, as the initial residence time ratio increases, the crystallization rate rises linearly. This is because when the hot fluid encounters cold, the solubility of the solute inside reaction solution a gradually decreases, and the solution becomes supersaturated. At this time, crystals begin to grow gradually, forming unit cells, and the unit cells are enriched to form crystals. 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-stage heating zone will cause all the crystals to start dissolving, which will affect the final crystallization degree. It should be noted that the hot fluid brought from the assembly area cannot be completely crystallized at low temperature. 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 of the crystals, ultimately affecting the quality of the product.

[0055] Example 6

[0056] The specific preparation method is as follows: 1. Preparation of reaction solution a Under stirring conditions, the solid raw material of sodium oxide is completely dissolved in an 85% formic acid solution to form reaction solution a. The molar ratio of formic acid to sodium oxide is controlled to be 1.2:1, and the reaction temperature is set at 60 °C.

[0057] 2. Preparation and crystallization of core-shell microcapsules The methyl silicone oil containing 10% Dow Corning 749 is used as the continuous phase, with a flow rate set at 20 mL / min. The flow rate of the dispersed phase reaction solution a is set at 5 mL / min, the flow rate of the 10% double-bond gelatin solution is set at 10 mL / min, and the flow rate of the 20% carboxymethyl cellulose solution is set at 5 mL / min. After converging with the oil phase at the intersection, it is sheared into microspheres, passed into an assembly area with a set temperature of 45 °C, and the residence time is 5 min. Then it passes through a cooling area set at 0 °C, a heating area set at 25 °C, and a cooling area set at 10 °C in sequence. The residence time in the first cooling area is 2 min, the residence time in the second heating area is 2 min, and the residence time in the third cooling area is 10 min.

[0058] 3. Collection of formate products and recycling of the oil phase The entire crystallized core-shell microcapsules are collected in a collection device. The crystalline solid phase layer will settle quickly. After accumulating a certain amount of solid phase, the sodium formate crystals are collected at the bottom of the kettle and filtered. After adding a silicone oil demulsifier and ethanol for simple cleaning, they are placed in a vacuum drying oven at 50 °C to prepare the final product. In addition, the upper oil phase is collected in a liquid storage device at a pumping speed of 50 mL / min, and then the oil phase is refluxed to the reaction system at a flow rate of 50 mL / min to achieve re-circulation reaction.

[0059] As Figure 6 shown, in this embodiment, the crystal structure prepared by using the microfluidic technology presents an aggregated block crystal form, while the crystal structure prepared by the traditional kettle method is needle-shaped. Further, using the single crystal XRD diffraction technology, the standard XRD spectrum is directly derived based on the structural formula of sodium formate, and compared with the XRD of the prepared block crystals and needle-shaped crystal structures (as Figure 7 shown), which verifies that the block crystal form prepared by the core-shell microcapsule crystallization technology is the final desired sodium formate crystal target product, demonstrating the advantage of the crystallization technology in this application in crystal form selection. In addition, during the reaction process, the changes of the droplets sheared by the oil phase in the assembly area and the crystallization area can also be observed, as Figure 8As shown, in the assembly area, the droplet slowly separates from the homogeneous droplet at the front end and becomes a core-shell structure. At this time, the inner core liquid is in a homogeneous state. When it enters the first cooling zone of the crystallization area, its inner core will become wrinkled, which also proves indirectly that the inner core layer is formate and will form a crystal structure.

[0060] The serial numbers of the embodiments of the present application are only for description and do not represent the advantages or disadvantages of the embodiments.

[0061] In the present application, for the description of the same or similar term concepts, technical solutions, and / or application scenarios, generally only the first occurrence is described in detail. When it appears repeatedly later, for the sake of brevity, it is generally not described again. When understanding the technical solutions and other contents of the present application, for the same or similar term concepts, technical solutions, and / or application scenarios that are not described in detail later, reference can be made to the relevant detailed descriptions before.

[0062] In the present application, the descriptions of the various embodiments have their own emphases. For the parts not described or recorded in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0063] The technical features of the technical solutions of the present application can be combined arbitrarily. For the sake of concise description, not all possible combinations of the technical features in the above embodiments are described. However, as long as the combination of these technical features does not conflict, it should be considered as within the scope recorded in the present application.

[0064] The above are only the preferred embodiments of the present application, and do not limit the patent scope of the present application accordingly. Any equivalent structure or equivalent process transformation made by using the content of the specification and drawings of the present application, or directly or indirectly applied in other related technical fields, shall be included in the patent protection scope of the present application by the same token.

Claims

1. A method for preparing formate crystals using core-shell microcapsules, characterized in that, It includes the following steps: (1) Add the solid alkaline raw material into the formic acid solution and stir until completely dissolved to prepare reaction solution a, and control the reaction temperature at 45 - 80 °C; (2) Use metering pumps to respectively transport polymer solution A, polymer solution B and the reaction solution a to mix them at the intersection of the microchannels to prepare the dispersed phase b. After being sheared into droplets in the oil phase C containing an emulsifier, it enters the assembly area for phase separation and assembly to form core - shell microcapsules; among them, phase separation characteristics are exhibited between polymer solution A and polymer solution B; (3) The core - shell microcapsules are crystallized through a continuous variable - temperature crystallization zone to form formate solids. Among them, the continuous variable - temperature crystallization zone at least includes a continuously cascaded first cooling zone, a second heating zone and a third cooling zone. The set temperature of the first cooling zone is 0 - 10 °C, the set temperature of the second heating zone is 25 - 40 °C, and the set temperature of the third cooling zone is 10 - 20 °C; (4) After the formate solids sink to the bottom of the collection device, they are collected, washed and dried in sequence to obtain the target product; (5) Continuously extract the upper oil layer in the collection device and transfer it to the liquid storage device, and then recycle the oil layer back to the assembly area for recycling.

2. The method according to 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, potassium formate.

4. The method according to claim 1, wherein In step (2), the polymer A in the polymer solution A is selected from one or more of double - bond gelatin, gelatin, hyperbranched polyethylene glycol, polyethylene glycol, poly(N - isopropylacrylamide), polyvinylpyrrolidone. The mass fraction of 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, methyl cellulose, polyacrylamide. The mass fraction of polymer B in the polymer solution B is 5% - 40%, and the solvent is water.

5. The method according to claim 1, characterized in that, 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 solution a is 2 - 20 mL / min.

6. The method according to claim 1 or 5, 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, methylphenyl silicone oil. The emulsifier is selected from at least one of Dow Corning 749, Span80, Span60, Tween, sodium dodecyl sulfate, octadecyl trimethyl ammonium chloride. The mass of the emulsifier is 2% - 10% of the mass of the oil phase C.

7. The method according to 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.

8. The method according to claim 1, characterized in that, In step (2), the set temperature of the assembly area is 45 - 60 °C.

9. The method according to claim 1 or 8, characterized in that, 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.

10. The method according to claim 1, characterized in that In step (5), the flow rate for extracting the upper oil layer is 5 - 50 mL / min, and the flow rate for circulating and refluxing is 5 - 50 mL / min.

11. A formate crystallization, characterized in that, It is prepared by the method according to any one of claims 1 - 10.

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