CN108992965B - Continuous cooling crystallization preparation process and device for large particles of uniform sodium hypophosphite monohydrate - Google Patents
Continuous cooling crystallization preparation process and device for large particles of uniform sodium hypophosphite monohydrate Download PDFInfo
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Abstract
The invention discloses a continuous cooling crystallization preparation process and a continuous cooling crystallization preparation device for large uniform particles of sodium hypophosphite monohydrate. The process comprises the steps of transferring a raw material liquid to a continuous cooling crystallization device, starting stirring, a circulating pump, circulating cooling water and the like after the liquid level meets the requirement, slowly cooling, adding sodium hypophosphite monohydrate seed crystals when the temperature of the solution is in front of a crystallization point, continuously and slowly cooling until the temperature is reduced to a terminal temperature, taking the seed crystals as a mother liquid of continuous crystallization, continuously conveying the raw material liquid to the continuous cooling crystallization device, continuously conveying sodium hypophosphite monohydrate crystal slurry to a concentrated liquid transfer tank by a crystal slurry pump, controlling the crystal growth time, then carrying out centrifugal separation, washing and drying to obtain uniform sodium hypophosphite monohydrate particle products, and carrying out heat exchange by adopting an external circulation heat exchanger to maintain the temperature stability of a crystallization system. The method has the effects of continuously and stably preparing the large granular sodium hypophosphite monohydrate product, uniform particle size distribution and high product purity.
Description
Technical Field
The invention relates to the technical field of stability of continuous cooling crystallization operation of a solubility system, in particular to a preparation process and a device for continuous cooling crystallization of large particles of uniform sodium hypophosphite monohydrate.
Background
Sodium hypophosphite monohydrate, formula NaH2PO2·H2O, molecular weight 105.99, crystal density 1.388g/cm3It is easily soluble in water, glycerol and alcohol, and insoluble in diethyl ether, and the water solution is neutral. The solubility in water at 25 ℃ was 100g/100g water and the solubility at 100 ℃ was 667g/100g water.
Sodium hypophosphite is mainly used for chemical plating. The strong reducibility of the product is utilized to cause the surface of the workpiece to generate natural catalytic reduction reaction, and the surface of the workpiece is plated with nickel-phosphorus amorphous alloy. After the plating layer is formed, the surface hardware of the workpiece can reach more than HV850, the wear resistance is greatly improved, the chemical corrosion resistance is excellent because the plating layer is amorphous and has no pores, and the plating layer surface is glossy, so the plating layer can be plated on ornaments. It is suitable for plating metal with complex shape, especially for plating non-metal parts, and is convenient to use.
At present, the crystallization process of sodium hypophosphite monohydrate is to concentrate the treated feed liquid to 46-49 Be degrees, send the concentrated feed liquid into an intermittent crystallization kettle (a cooling jacket or a built-in cooling coil) for cooling crystallization, wherein a cooling medium is circulating cooling water, the crystallized sodium hypophosphite monohydrate is separated by a centrifuge to remove mother liquor, and then the crystallized sodium hypophosphite monohydrate is dried to obtain a finished product and packaged.
The heat exchange efficiency that the heat transfer interface scabs influences the later stage exists in traditional intermittent cooling crystallization process, secondly because the distribution broad of the difficult product crystal granularity that leads to of supersaturation degree control of intermittent cooling crystallization process, the product particle size distribution of certain chemical industry enterprise's sodium hypophosphite of monohydrate as follows:
| screen (mesh) | <20 | 20～30 | 30～40 | 40～60 | 60～80 | >80 |
| Mass fraction | 0.153 | 0.32 | 0.28 | 0.136 | 0.078 | 0.033 |
Compared with intermittent crystallization, the continuous crystallization process has the outstanding advantages of uniform product granularity, high stability, small occupied area of equipment, high automation control degree, high energy efficiency, low labor cost and the like, and is particularly suitable for large-scale production. The operation of a continuous crystallizer has several requirements: controlling the particle size distribution of the product meeting the requirements; the crystallizer has the highest production strength possible; the speed of the crystal scale is reduced as much as possible so as to prolong the normal operation period of the crystallizer; the stability of the crystallizer is maintained.
The stability and the controllability are the key of a continuous crystallization system, the supersaturation is the core of the crystallization process, secondary processes such as the nucleation rate, the crystal growth rate, the aggregation and the like are closely related to the supersaturation,
however, the system has some special difficulties in the continuous crystallization process, which makes the continuous crystallization process of sodium hypophosphite monohydrate difficult to realize stability, and the product is far from batch crystallization products. From the macroscopic view, the reason is that the solubility of sodium hypophosphite in water is very high, so that the density of the raw material liquid is high, and when the density is 48Be degrees, the density reaches 1500kg/m3The density of the mother liquor after crystallization was about 1370kg/m3And the density of the sodium hypophosphite monohydrate crystals is 1388kg/m3The density difference between the two is extremely small, so that the particle sedimentation rate is very low, and a good grading effect cannot be realized for efficient continuous crystallizers such as DTB (draw texturing yarn), OSLO (open air crystallizer) and the like; ② the viscosity of the feed liquid is high, the crystal content in the crystallization mother liquid reaches more than 50 percent (1 m)3700kg of crystals can be generated by raw material liquid crystallization), the viscosity of the suspension crystal slurry can be greatly increased, the growth of the crystals is extremely unfavorable, a long crystal growth time is required on the premise of strictly controlling the number of crystal nuclei, if the nucleation control is not good, the crystal slurry can be deteriorated into milk-like slurry, the crystals can be difficult to grow (as shown in figure 1), and the high-viscosity crystallization is overAnd trace impurities are easily adsorbed on the surface of the crystal and are not easily washed clean, so that the purity of the product is influenced. The microscopic reason for the above phenomena is that sodium hypophosphite forms a strong hydrogen bonding effect with water molecules in an aqueous solution, and the hydrogen bonding effect leads to high solubility, and further leads to a macroscopic phenomenon of high solution density and high viscosity, and how to weaken the hydrogen bonding effect and reduce the viscosity is the key to realizing stable continuous crystallization.
The crystallization of sodium hypophosphite monohydrate in water solution belongs to a viscous physical property and slow-growth crystallization process, at present, no continuous crystallization related report exists in China, for a viscous substance crystallization system, a horizontal multi-chamber continuous crystallizer or a tower type continuous crystallizer and the like with low production efficiency are often adopted, the crystal growth retention time is often dozens of hours, and efficient continuous crystallizers such as DTB (draw texturing yarn), OSLO (open source air) and the like cannot be stably used.
Disclosure of Invention
In order to solve one or more of the problems, the invention provides a continuous cooling crystallization preparation process and a device for uniform sodium hypophosphite monohydrate large particles.
The continuous cooling crystallization preparation process of the uniform large particles of the sodium hypophosphite monohydrate comprises the following steps: adding the sodium hypophosphite solution into a concentrated solution tank, concentrating to form a concentrated solution at 85-95 ℃, and then adding a hydrogen bond weakening solvent in a certain proportion to form a raw material solution;
inputting a raw material liquid into a continuous cooling crystallization device through a first conveying pump, starting a stirring part, a circulating pump, circulating cooling water and the like of the continuous cooling crystallization device after the liquid level meets the requirement, slowly cooling at a cooling rate of 2-5 ℃/h, adding sodium hypophosphite monohydrate seed crystals when the temperature of the solution is 1-3 ℃ before a crystallization point, continuously and slowly cooling at a cooling rate of 3-8 ℃/h until the temperature is reduced to 40-45 ℃, and taking the solution as a mother liquid of continuous crystallization;
continuously conveying the raw material liquid to a continuous cooling crystallization device at a uniform speed by a first conveying pump, and continuously conveying the sodium hypophosphite monohydrate crystal slurry to a crystal slurry transfer tank by a crystal slurry pump, wherein the continuous cooling crystallization device adopts an external circulation tubular heat exchanger for heat exchange to maintain the temperature stability of a crystallization system, and the growth residence time of a macroscopic crystal in the continuous cooling crystallization device is controlled to be 2-8 h;
and continuously feeding the crystal mush treated by the crystal mush transfer tank into a centrifugal machine, and centrifugally separating, washing and drying the crystal mush by the centrifugal machine to obtain a uniform large-particle sodium hypophosphite monohydrate product.
In some embodiments, the concentrate has a Baume of 46-48Be DEG, and the solution density is 1420-3。
In some embodiments, the temperature of the concentrate is 90 ℃.
In some embodiments, the hydrogen bond weakening solvent is a non-aqueous solvent, and the hydrogen bond weakening solvent is one or more of methanol, ethanol, propanol, and isopropanol.
In some embodiments, the volume ratio of the hydrogen bond weakening solvent to the sodium hypophosphite solution is 1:3 to 1: 10.
In some embodiments, the residence time of the macro crystal growth in the continuous cooling crystallization device is 3-6 h.
In some embodiments, at the clear mother liquor discharge port of the crystal slurry transfer tank and the centrifugal mother liquor discharge port of the centrifugal machine, a part of the mother liquor returns to the concentrated liquid tank, a part of the mother liquor returns to the continuous cooling crystallization device to reduce the internal crystal slurry suspension density, and the crystal slurry suspension density is controlled to be 300-500 kg/m3And (4) crystal slurry.
In some embodiments, the slurry has a suspension density of 400 to 500kg/m3And (4) crystal slurry.
In some embodiments, the particle size of the sodium hypophosphite monohydrate seed crystal is about 0.1-0.3 mm, and the addition amount is 5-20 per mill.
The invention provides a high-efficiency, stable and continuous cooling crystallization process technology for uniform large particles of sodium hypophosphite monohydrate, and compared with the prior art, the invention has the following beneficial effects: firstly, the process is suitable for a viscous material system with slow crystal growth, and granular sodium hypophosphite monohydrate crystals (10-40 meshes of crystals are more than 90%) with the granularity of 0.6-1.2 mm and uniform granularity distribution are prepared. Compared with the prior art and the invention patent, the method has the advantages of stable process, no milk-like phenomenon, high product purity, monodispersity, good fluidity, no caking in the process of storage and transportation and the like.
According to one aspect of the invention, the continuous cooling crystallization preparation device for large uniform particles of sodium hypophosphite monohydrate comprises a concentrated solution tank, a flow regulating valve, a first delivery pump, a continuous cooling crystallization device, a crystal slurry pump, a crystal slurry transfer tank and a centrifuge,
the concentrated liquid tank, the flow regulating valve and the inlet of the first delivery pump are connected in turn through pipelines,
the outlet of the first delivery pump is communicated with the feed inlet of the continuous cooling crystallization device through a pipeline, the discharge port of the continuous cooling crystallization device is communicated with the inlet of the crystal slurry pump through a pipeline, the outlet of the crystal slurry pump is communicated with the upper end of the crystal slurry transfer tank through a pipeline, the crystal slurry discharge port of the crystal slurry transfer tank is communicated with a centrifuge, and the product discharge port of the centrifuge is used for obtaining a large granular sodium hypophosphite monohydrate product,
the clear mother liquor discharge port of the crystal slurry transfer tank is communicated with the centrifugal mother liquor discharge port of the centrifugal machine through a pipeline, one part of the clear mother liquor is returned to the continuous cooling crystallization device through the pipeline, and the other part of the clear mother liquor is returned to the concentrated liquid tank.
The continuous cooling crystallization device is a DTB continuous cooling crystallization device or an OSLO continuous cooling crystallization device. Compared with the prior art, the invention has the beneficial effects that: the invention has the advantages of simple structure, convenient operation, easy realization of automatic control and the like.
Drawings
FIG. 1 is a photograph of a prior art milk-like slurry;
FIG. 2 is a schematic flow chart of a continuous cooling crystallization process for preparing particles of sodium hypophosphite monohydrate according to an embodiment of the present invention;
FIG. 3 is a photograph of a sodium hypophosphite monohydrate product as prepared in example 1 of the present invention;
FIG. 4 is a photograph of a sodium hypophosphite monohydrate product as prepared in example 2 of the present invention;
FIG. 5 is a photograph of a sodium hypophosphite monohydrate product as prepared in example 3 of the present invention;
table 1 shows the particle size distribution data (sieved) of the sodium hypophosphite monohydrate product prepared in inventive example 1;
table 2 shows the particle size distribution data (sieved) of the sodium hypophosphite monohydrate product prepared in inventive example 2;
table 3 shows the particle size distribution data (sieved) of the sodium hypophosphite monohydrate product prepared in inventive example 3.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings and specific embodiments.
Example 1
Adding the sodium hypophosphite solution into a concentrated solution tank 1, concentrating to form a concentrated solution, wherein the temperature of the concentrated solution is 90 ℃, the concentration of the concentrated solution is 48Be degrees (Baume degree), and the solution density of the concentrated solution is 1500kg/m3，
The solvent (ethanol) for weakening hydrogen bonds is mixed according to the volume ratio of 1:4 (V)Solvent(s)：VSodium hypophosphite solution) Adding the concentrated solution to form a raw material solution;
inputting the raw material liquid into a continuous cooling crystallization device 4 through a first conveying pump 3, starting a stirring paddle 41, an external circulating pump 42 and circulating water when the liquid level meets the requirement, slowly cooling at a cooling rate of 4 ℃/h, adding sodium hypophosphite monohydrate crystal seeds with the granularity of 0.25mm (60-65 meshes) when the temperature of the solution reaches 80 ℃ (about 2 ℃ higher than the crystallization point), continuously cooling at a cooling rate of 5 ℃/h until the temperature is reduced to 45 ℃ to form mother liquid;
continuously conveying the raw material liquid to a continuous cooling crystallization device 4 by using a first conveying pump 3, continuously conveying sodium hypophosphite monohydrate crystal slurry to a crystal slurry transfer tank 6 by using a crystal slurry pump 5, controlling the growth time of macro crystals of the continuous cooling crystallization device 4 to be 4h, then centrifugally separating, washing and drying by using a centrifugal machine 7 to obtain uniform sodium hypophosphite monohydrate particle products, returning a part of mother liquid to a concentrated liquid tank 1, returning a part of centrifugal mother liquid to the continuous cooling crystallization device 4 to reduce the suspension density of the crystal slurry, and controlling the suspension density of the crystal slurry to be 450kg/m3And (3) carrying out heat exchange on the crystal slurry and the continuous cooling crystallization device by adopting an external circulation tube type heat exchanger so as to maintain the temperature stability of a crystallization system.
In this example, the form of the sodium hypophosphite monohydrate product is shown in fig. 3, and the particle size distribution data of the sodium hypophosphite monohydrate product is detailed in table 1, wherein the average particle size is 0.95mm, and the content of 10-40 mesh crystals is 92.5%.
Example 2
Adding the sodium hypophosphite solution into a concentrated solution tank 1, concentrating to form a concentrated solution, wherein the temperature of the concentrated solution is 90 ℃, the concentration of the concentrated solution is 47Be degrees (Baume degree), and the solution density of the concentrated solution is 1460kg/m3，
The solvent (methanol) for weakening hydrogen bonds is mixed according to the volume ratio of 1:9 (V)Solvent(s)：VSodium hypophosphite solution) Adding the concentrated solution to form a raw material solution;
inputting the raw material liquid into a continuous cooling crystallization device 4 through a first conveying pump 3, starting a stirring paddle 41, an external circulating pump 42 and circulating water when the liquid level meets the requirement, slowly cooling at a cooling rate of 4 ℃/h, adding sodium hypophosphite monohydrate crystal seeds with the granularity of 0.25mm (60-65 meshes) when the temperature of the solution reaches 80 ℃ (about 2 ℃ higher than the crystallization point), continuously cooling at a cooling rate of 4 ℃/h until the temperature is reduced to 45 ℃ to form mother liquid;
continuously conveying the raw material liquid to a continuous cooling crystallization device 4 by using a first conveying pump 3, continuously conveying sodium hypophosphite monohydrate crystal slurry to a crystal slurry transfer tank 6 by using a crystal slurry pump 5, controlling the crystal growth time of the continuous cooling crystallization device 4 to be 3h, then centrifugally separating, washing and drying by using a centrifugal machine 7 to obtain a uniform sodium hypophosphite monohydrate particle product, returning a part of mother liquid to a concentrated liquid tank 1, returning a part of centrifugal mother liquid to the continuous cooling crystallization device 4 to reduce the suspension density of the crystal slurry, and controlling the suspension density of the crystal slurry to be 500kg/m3The crystal slurry continuous cooling crystallization device 4 adopts an external circulation tube type heat exchanger for heat exchange so as to maintain the temperature of the crystallization system to be stable.
In this example, the form of the sodium hypophosphite monohydrate product is shown in fig. 4, the particle size distribution data of the sodium hypophosphite monohydrate product is detailed in table 2, the average particle size of the sodium hypophosphite monohydrate product is 0.9mm, and the content of 10-40 mesh crystals is 91.3%.
Example 3
Adding the sodium hypophosphite solution into a concentrated solution tank 1, concentrating to form a concentrated solution, wherein the temperature of the concentrated solution is 90 ℃, the concentration of the concentrated solution is 46Be degrees (Baume degree), and the solution density of the concentrated solution is 1420kg/m3，
The hydrogen bond weakening solvent (isopropanol) is mixed according to the volume ratio of 1:3 (V)Solvent(s)：VSodium hypophosphite solution) Adding the concentrated solution to form a raw material solution;
inputting the raw material liquid into a continuous cooling crystallization device 4 through a first conveying pump 3, starting a stirring paddle 41, an external circulating pump 42 and circulating water when the liquid level meets the requirement, slowly cooling at a cooling rate of 5 ℃/h, adding sodium hypophosphite monohydrate crystal seeds with the granularity of 0.25mm (60-65 meshes) when the temperature of the solution reaches 80 ℃ (about 2 ℃ higher than the crystallization point), continuously cooling at a cooling rate of 5 ℃/h until the temperature is reduced to 45 ℃ to form mother liquid;
continuously conveying the raw material liquid to a continuous cooling crystallization device 4 by using a first conveying pump 3, continuously conveying sodium hypophosphite monohydrate crystal slurry to a crystal slurry transfer tank 6 by using a crystal slurry pump 5, controlling the crystal growth time of the continuous cooling crystallization device 4 to be 6h, then centrifugally separating, washing and drying by using a centrifugal machine 7 to obtain a uniform sodium hypophosphite monohydrate particle product, returning a part of mother liquid to a concentrated liquid tank 1, returning a part of centrifugal mother liquid to the continuous cooling crystallization device 4 to reduce the suspension density of the crystal slurry, and controlling the suspension density of the crystal slurry to be 400kg/m3The crystal slurry continuous cooling crystallization device 4 adopts an external circulation tube type heat exchanger for heat exchange so as to maintain the temperature of the crystallization system to be stable.
In this example, the form of the sodium hypophosphite monohydrate product is shown in fig. 5, the particle size distribution data of the sodium hypophosphite monohydrate product is detailed in table 3, the average particle size of the sodium hypophosphite monohydrate product is 0.85mm, and the content of 10-40 mesh crystals is 90.5%.
What has been described above are merely some embodiments of the present invention. It will be apparent to those skilled in the art that various changes and modifications can be made without departing from the inventive concept thereof, and these changes and modifications can be made without departing from the spirit and scope of the invention.
Claims (4)
1. A continuous cooling crystallization preparation process of uniform sodium hypophosphite monohydrate large particles is characterized by comprising the following steps:
adding the sodium hypophosphite solution into a concentrated solution tank (1), concentrating to form a concentrated solution at 85-95 ℃, wherein the Baume degree of the concentrated solution is 46-48Be DEG, and the solution density is 1420-3(ii) a Then adding a hydrogen bond weakening solvent in a certain proportion to form a raw material solution, wherein the volume ratio of the hydrogen bond weakening solvent to the sodium hypophosphite solution is 1: 3-1: 10; the hydrogen bond weakening solvent is one or more of methanol, ethanol, propanol and isopropanol;
inputting the raw material liquid into a continuous cooling crystallization device (4) through a first conveying pump (3), starting a stirring part (41), a circulating pump (42) and circulating cooling water of the continuous cooling crystallization device (4) after the liquid level meets the requirement, slowly cooling at the speed of 2-5 ℃/h, and adding sodium hypophosphite monohydrate seed crystals when the temperature of the solution is 1-3 ℃ before the crystallization point, wherein the particle size of the sodium hypophosphite monohydrate seed crystals is 0.1-0.3 mm, and the addition amount is 5-20 per thousand; continuously and slowly cooling at the cooling rate of 3-8 ℃/h until the temperature is reduced to 40-45 ℃ to be used as mother liquor for continuous crystallization;
the first conveying pump (3) continuously conveys the raw material liquid to the continuous cooling crystallization device (4) at a uniform speed, the crystal slurry pump (5) continuously conveys the sodium hypophosphite monohydrate crystal slurry to the crystal slurry transfer tank (6), wherein the continuous cooling crystallization device (4) adopts an external circulation tubular heat exchanger to carry out heat exchange so as to maintain the temperature stability of a crystallization system, and the growth residence time of macro crystals in the continuous cooling crystallization device (4) is controlled to be 2-8 h;
the crystal mush treated by the crystal mush transfer tank (6) continuously enters a centrifugal machine (7), and the crystal mush is centrifugally separated, washed and dried by the centrifugal machine (7) to obtain a uniform large-particle sodium hypophosphite monohydrate product;
a part of mother liquor returns to the concentrated liquid tank (1) and the other part of mother liquor returns to the clear mother liquor discharge port of the crystal slurry transfer tank (6) and the centrifugal mother liquor discharge port of the centrifugal machine (7)The mother liquor is returned to the continuous cooling crystallization device (4) to reduce the suspension density of the internal crystal mush, and the suspension density of the crystal mush is controlled to be 300-500 kg/m3And (4) crystal slurry.
2. The continuous cooling crystallization preparation process of uniform sodium hypophosphite monohydrate large particles as claimed in claim 1, characterized in that the temperature of the concentrated solution is 90 ℃.
3. The continuous cooling crystallization preparation process of uniform sodium hypophosphite monohydrate with large particles as claimed in claim 1, characterized in that, in the continuous cooling crystallization device (4), the residence time of the macro crystal growth is 3-6 h.
4. The continuous cooling crystallization preparation process of uniform sodium hypophosphite monohydrate large particles as claimed in claim 1, wherein the suspension density of the crystal slurry is 400-500 kg/m3And (4) crystal slurry.
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