CN111423334B - Method for preparing cubic anhydrous betaine crystals - Google Patents

Abstract

A method for preparing cubic anhydrous betaine crystals; an over-boiling burst nucleation method is adopted. Adding anhydrous betaine powder into a crystallizer, adding a solvent into the crystallizer, heating to completely dissolve the powder, and enabling the temperature of the solution to reach the boiling point of a crystallization system; rapidly cooling, and when crystal nuclei are separated out from the crystallization system, adding a small amount of anhydrous betaine powder into the crystallizer again to promote the crystallization system to separate out the crystal nuclei in an explosive manner; continuously cooling the solution to room temperature; and (4) cooling to the end temperature, filtering and washing the crystals, and drying to obtain a cubic anhydrous betaine crystal product. The crystallization method controls the growth process of the crystal by controlling the explosive nucleation process and the cooling process in the cooling process, and the two important processes also form the crystallization method-the over-boiling explosive nucleation method in the application. The method thoroughly changes the flaky crystal habit of the anhydrous betaine crystal, has short operation time and high production efficiency, and is more favorable for industrial production.

Description

Method for preparing cubic anhydrous betaine crystals

Technical Field

The application relates to a crystallization method of betaine, in particular to a method for preparing cubic anhydrous betaine crystals.

Background

Betaine is a compound with quaternary ammonium inner salt or ammonium onium structure, and is a derivative of glycineHowever, betaine has the simplest molecular structure. The chemical name of the substance is trimethylamine ethylene lactone, namely three methyl groups respectively replace three hydrogen atoms on the nitrogen atom of glycine, and the molecular formula is C ₅ H ₁₁ NO ₂ Molecular weight 117.15, structural formula shown below

Betaine is a natural component, commonly exists in animals and plants, is an intermediate product for metabolism in animals, and plays an important role in the metabolic process. Betaine also has a cleansing effect, does not harm the skin, is very safe, is an excellent zwitterionic surfactant, and is therefore frequently used in cleansing skin care products. This substance was named betaine since it was first found in the process of extracting sucrose from beet. At present, betaine applied to industry is mostly obtained by taking trimethylamine and chloroacetic acid as raw materials through a synthesis method, has no obvious difference in molecular structure and application effect from natural betaine, has properties and functions consistent with those of the natural betaine, and is widely used as a food additive.

The betaine molecule is also a zwitterion, is very soluble in water at 20 ℃, and has a solubility in water of 160g/100g water. Betaine is also readily soluble in moderately polar solvents such as methanol and ethanol, and the solubility of betaine decreases with decreasing solvent polarity. Betaine is poorly soluble in non-polar solvents. Betaine also has strong moisture absorption capacity and is easy to deliquesce, and betaine particles exposed to air with high humidity can quickly absorb water vapor in the air to become liquid, so that strict moisture-proof measures are required in the storage and transportation processes of betaine.

The betaine molecule is neutral, has good thermal stability, and has decomposition temperature of about 290 deg.C. However, betaine is unstable in chemical properties and can be decomposed at normal temperature under certain conditions to release trimethylamine. This substance has a strong unpleasant amine smell and the decomposition reaction is accelerated under alkaline conditions.

Betaine crystals have a variety of crystal habits, and the shape of the crystals is a focus of attention in the process of preparing betaine crystals. The betaine is colorless transparent crystal particles, and has sweet scent of saccharide. Betaine crystals with different crystal habits can be obtained from different pure solvents, and crystals with different crystal habits can also be obtained from mixed solvents with different compositions. These crystals obtained from different solvents have macroscopically different shapes and microscopically different molecular arrangements and are therefore characterized and distinguished by means of X-ray diffraction.

The hydrate crystals of betaine obtained from aqueous solutions with different solvent compositions will have different crystal habits, mainly reflected in the shape of the crystals. The crystal obtained from pure water is a 12-face body with rectangular pyramids added at two ends, and the crystal particles look very full; the crystal obtained from the mixed solvent of methanol and water is similar to a cuboid, and the crystal particle is relatively full; the hexagonal prism-shaped crystal is obtained from a mixed solvent of ethanol and water, but the bottom surface of the crystal is hexagonal, the thickness is smaller, and the crystal is flat; the crystals obtained from the mixed solution of acetone and water are approximately cubic, the bottom surface is similar to a rhombus, but the bottom surface is more similar to a square, the thickness is very similar to the bottom edge, and the crystal particles are full. Although the various crystal hydrates have different shapes, the hydrate crystals of the betaine have the common property that the crystals are crystal clear, the crystal particles have excellent refractive properties similar to dew, and the crystals seem to contain certain moisture from the appearance.

Betaines have not only a variety of crystal habits, but also a variety of solvates. Wherein the crystals obtained from a strongly polar solvent such as water are solvate crystals, and the crystals obtained from an aqueous solution are usually monohydrate; the crystals obtained from moderately polar solvents such as methanol or ethanol are usually anhydrous crystals. The hydrate crystals of betaine obtained from different solvents also have different thermal and chemical stability, wherein the chemical stability depends on the thermal stability. Betaine hydrate crystals themselves are relatively stable chemically but are poorly thermally stable. The crystal can be dehydrated after the temperature is increased in an environment with low humidity, the shape of the crystal after dehydration is not changed, and the crystal is white and is not transparent any more. Since water molecules are lost, the crystal at this time is microscopically porous, and chemical stability is also deteriorated. Due to the large specific surface area of the porous structure, gases such as oxygen and water vapor in the air which are easy to undergo chemical reaction enter the interior of the porous structure and are adsorbed on the inner surface, so that the betaine particles are deliquesced and emit trimethylamine smell. Therefore, the chemical properties of the betaine crystals before dehydration are relatively stable, but the chemical stability of the betaine granules after dehydration is reduced, i.e. the chemical stability is determined by the thermal stability. Since betaine hydrate crystals obtained in different solvents have different dehydration temperatures, these hydrate crystals also have different stabilities. Generally, the dehydration temperature of betaine hydrate crystals obtained from pure water is low, and water molecules can be removed when the temperature reaches 50 ℃; the dehydration temperature of betaine hydrate crystals obtained from a mixed solution of acetone and water is high, and water molecules can be removed only when the temperature is higher than 95 ℃.

In the process of preparing the anhydrous betaine crystal, the stability of the crystal is the guarantee of the product quality. Unlike betaine hydrate crystals, anhydrous betaine crystals do not contain crystal water inside, and therefore, the influence of crystal dehydration does not need to be considered. Meanwhile, as the anhydrous betaine crystal does not contain crystal water, the betaine molecules are arranged more closely on a microcosmic scale, so that the anhydrous betaine crystal and the betaine hydrate crystal have different thermal stability and chemical stability. Therefore, the anhydrous betaine crystals do not release off-flavors.

In the process of preparing anhydrous betaine crystals, the bulk density of the crystal product is an important factor to consider. The anhydrous betaine crystal is generally a plate-like crystal, and the bottom surface is a rhomboid which is approximately square, but the anhydrous betaine crystal is generally a plate-like crystal because of its thin thickness. These flaked crystals are detrimental to the flow of the crystal particles, resulting in a lower bulk density of the crystal particles, typically 0.5 to 0.6g/mL. The thin flaky crystal is easy to break, and broken crystal slices are mixed in crystal particles, so that the quality of a crystal product is seriously influenced. Therefore, it is a problem to be solved at present to improve the morphology of the crystal particles of anhydrous betaine so that the crystal particles have good fluidity, and the root cause of the problem is the plate-like crystal habit of the anhydrous betaine crystals.

In the preparation of anhydrous betaine crystals, the uniformity of the crystal particles is another important factor to consider. Because of the large size of the betaine crystals, the size is typically in the order of millimeters. The shape of each crystal is substantially fixed, but its size is not fixed, and the crystal particles always have a large size. In the same batch of anhydrous betaine crystal particles, the particle size of large size can reach several millimeters, while the particle size of small crystal particles is less than one millimeter, so that the particle sizes of the same batch of betaine crystal particles are distributed. It is always desirable that all crystal grains have the same size in the case of crystal sizes meeting the size requirement, but this is not done, so that the crystal grains in a certain size range have a smaller number of crystal grains, and the size distribution of the crystal grains is more concentrated, that is, the grain sizes are more uniform, as long as the size range is narrow enough and the number of crystal grains in the size range is large enough.

In the process for producing anhydrous betaine crystal particles, in addition to the desired uniformity in particle size in terms of particle size, it is often desirable to obtain crystal particles having a certain size range. Because larger crystal particles, although having a smaller specific surface area, also have a reduced dissolution rate; smaller crystal particles have a larger dissolution rate but absorb moisture easily due to a larger specific surface area. In all these cases, the size and the direction of the crystal grains are both advantageous and disadvantageous. In the actual production, both the advantages and the disadvantages are considered, and the granularity is regulated and controlled based on the requirements. Therefore, how to adjust the grain size of the crystals according to the requirement is also a practical problem to be solved.

After investigation of the market, two types of betaine are found on the market. One is derived from the dehydration of betaine hydrate crystals, which give off the odor of trimethylamine; the other is anhydrous betaine crystals obtained directly by crystallization, which do not release the odor of trimethylamine, and in contrast, give off sweet taste of light sugars. The latter crystal is shown in FIG. 1, and it can be seen that the crystal is a rhombohedral plate crystal, the rhombohedral shape of which resembles a square, and the ratio of the height of the crystal to one quarter of the circumference of the rhombohedral shape is less than 0.2. Through measurement, the bulk density of the crystal particles in the attached figure 1 is 0.7g/mL, and the mass ratio of the crystal particles with the particle size distribution of 20-60 meshes is 78.1wt%.

The review of the literature shows that no paper or patent is available to research and control the bulk density of the anhydrous betaine crystals, and the shape of the crystals is not deeply researched. Only three patents discussing the particle size distribution of crystal particles, namely EP 2292571 A2, US 6821339 B2 and US 20030131784 A1, describe methods for regulating the particle size of crystal particles. In these patents, the size of the crystal particles is controlled by feeding seeds, which are prepared in a separate process. The crystal particles obtained by crystallization using the methods of these patents have a particle size in the range of 0.25 to 1mm, and no discussion is given in the patents about the bulk density and crystal habit of the crystal particles.

As can be seen from the above practical problems such as the properties and requirements of betaine crystals, the stability of anhydrous betaine crystals is higher than that of betaine hydrates, so the scheme for preparing anhydrous betaine crystals is superior to that for preparing betaine hydrate crystals. However, the existing method for preparing anhydrous betaine still has technical problems to be solved, and how to improve the bulk density of anhydrous betaine crystals and concentrate the particle size distribution is a difficult problem at present.

Disclosure of Invention

The crystallization method in the present application is proposed in view of the above practical circumstances and problems. The anhydrous betaine crystal particles prepared by the method not only have high bulk density, but also have concentrated particle size distribution. The application not only provides a complete crystallization method from anhydrous betaine powder to anhydrous betaine crystal particles, but also summarizes a new crystallization method, namely an over-boiling burst nucleation method through a large number of practices.

The crystallization method in the application adopts an over-boiling explosion nucleation method, and crystal nuclei with uniform particle sizes are formed in a solution by controlling the nucleation process in the crystallization process; and then controlling the temperature reduction process to ensure that the crystal particles grow well, thereby completing the preparation process of the anhydrous betaine crystal particles.

Over-boiling burst nucleation

In the case of the over-boiling explosion nucleation method, "over-boiling" means that the temperature of the solution exceeds the boiling point of the solvent in order to form cubic crystal nuclei; "explosion" means the formation of a large number of crystal nuclei in a short time, with the aim of forming crystal nuclei having a uniform particle size. The principle of the method can be explained by the solubility curve in FIG. 2. In FIG. 2, the horizontal axis represents the temperature of the solution, the vertical axis represents the betaine concentration in the solution, and each point on the solubility curve in the graph represents the betaine concentration after the solution at that temperature reaches equilibrium. In FIG. 2, the state at point A represents the state of the solution at the moment of adding the solvent, at which the temperature of the solution is room temperature, and since betaine has not been dissolved yet, the betaine concentration in the solution is 0. With the temperature of the solution rising, betaine is gradually dissolved in the solution, and the state of the solution gradually moves from point a to point B. Point B represents the solution state at which the solution temperature reached the highest during the warming dissolution, at which point the betaine concentration in the solution reached the maximum and exceeded the equilibrium concentration at that temperature. During the process of reducing the temperature of the solution, the difference between the concentration of the solution and the equilibrium concentration is increased, the supersaturation degree of the solution is increased, but crystal nuclei cannot be immediately separated out from the solution. The betaine concentration in the solution was constant, and the state of the solution gradually shifted from point B to point C. The point C represents the critical state of the solution crystallization, and is the critical point of the solution crystallization, and the difference between the betaine concentration and the equilibrium concentration in the solution reaches the maximum at this time, and crystal nuclei begin to precipitate in the solution.

In the process of changing the state of the solution from point B to point C, it is a conventional practice to add seed crystals to the solution. The purpose of putting the seed crystal is to ensure that the seed crystal particles absorb supersaturated solute and reduce the supersaturation degree of the solution, thereby avoiding the problem of smaller crystal granularity caused by explosive precipitation of crystal nuclei in the solution and obtaining a crystal product with larger granularity. The added seed crystal is fine crystal particles which are sieved, have small particle size and relatively uniform particle size, and are helpful for obtaining crystal products with uniform particle size. However, the preparation of the seed crystal requires a separate process to be completed, which still requires time and labor.

According to the principle of the seed crystal, and the characteristics of the betaine crystallization process, the applicant controls the crystal quantity and the particle size in the solution from the crystallization point of view, namely, the process of forming crystal nuclei in the solution replaces the preparation process of the seed crystal. After the solution reaches the point C, the temperature is further reduced, and the solution is divided into two cases, wherein one case is that crystal nuclei are immediately precipitated in the solution in an explosive manner, and the other case is that only a small amount of crystal nuclei are precipitated. In the former case, the solution is subjected to explosive nucleation, the betaine concentration in the solution is rapidly decreased, and the state of the solution gradually shifts from the point C to the point D. The D point represents the state of the solution when the temperature of the solution is reduced to room temperature, but the solution does not reach the equilibrium, and the concentration of the betaine in the solution is higher than the equilibrium concentration. In the process of keeping the temperature at room temperature, the temperature of the solution is not changed, the concentration of the betaine in the solution is gradually reduced, and the state of the solution gradually moves from the point D to the point E. Point E represents the state of the solution at room temperature at which the solution reaches equilibrium, when the betaine concentration in the solution equals the equilibrium concentration. During the process of moving the point C state to the point D state, new crystal nuclei continue to be formed in the solution for a short period of time, the formed crystal nuclei have the capacity of absorbing the solute, and the process of forming the crystal nuclei is finished when the rate of absorbing the solute by the crystal nuclei is equal to the rate of precipitating the solute by the solution. Because the time difference of the crystal nucleus formation is short, the granularity of the crystal product is uniform. In the latter case, because the number of crystal nuclei in the solution is small, the crystal nuclei can also be precipitated in the solution in a burst manner in the subsequent cooling process, i.e., the process of precipitating the crystal nuclei in a burst manner is delayed, and the time of forming the crystal nuclei is prolonged. Due to the large difference in the time of formation of the crystal nuclei, the particle size of the crystal product also becomes non-uniform.

In order to obtain crystal particles having a relatively uniform particle size, it is necessary to shorten the nucleation period. Therefore, the first of the above nucleation processes is preferable, that is, it is necessary to precipitate the crystal nuclei explosively in the solution. In order to make the crystal product more uniform, the time of explosive crystal nucleus precipitation process needs to be shortened, and at the moment, the supersaturation degree of the solution in the C point state needs to be increased; in order to increase the supersaturation degree of the solution in the C-point state, the difference between the dissolved amount of betaine and the equilibrium concentration in the C-point state solution may be increased. However, to increase the difference between the dissolution amount and the equilibrium concentration of the solution at the point C, the state of the solution at the point C may be moved leftward or upward in the figure. The core of the over-boiling burst nucleation method lies in the control of the solution in the C point state, and the control method of the crystallization method for the C point accelerates the cooling rate of the 'B → C' process, so that the C point moves leftwards in the figure, the difference value between the solution concentration and the equilibrium concentration is increased, and the supersaturation degree of the solution is increased; or when the solution state reaches a crystallization critical point, adding anhydrous betaine powder into the solution, wherein the betaine concentration in the solution is increased suddenly, the point C moves upwards in the figure, the difference between the solution concentration and the equilibrium concentration is increased, and the supersaturation degree of the solution is also increased. Thus, the crystallization process can be completed instantly, the precipitated crystal nuclei have basically consistent sizes, and finally the crystal product with more concentrated particle size distribution can be obtained.

For the above crystallization process, the solution temperature of the process is above the boiling point of the solvent. For the anhydrous betaine crystals with flaky crystal habit, cubic crystal nuclei are favorably formed at higher temperature, and finally the cubic crystals are obtained, so that the formation of flaky crystals is avoided. Compared with the conventional cooling crystallization method, the cooling crystallization method does not need to prepare seed crystals, and the obtained anhydrous betaine crystal product is cubic. Because the cubic crystals have better fluidity, the bulk density of the crystal product is greatly improved compared with the conventional crystallization method, and the particle size distribution is more concentrated, so that the quality of the anhydrous betaine crystal product is greatly improved.

The process of nucleation by an overboiling explosion requires the following two steps:

1) Adding anhydrous betaine powder into a crystallizer, adding a solvent into the crystallizer, heating to completely dissolve the powder, and enabling the temperature of the solution to reach the boiling point of a crystallization system;

2) Rapidly cooling, and when crystal nuclei are separated out from the crystallization system, adding a small amount of anhydrous betaine powder into the crystallizer again to promote the crystal system to explode and nucleate to separate out the crystal nuclei; continuously cooling the solution to room temperature; and (4) cooling to the end temperature, filtering and washing the crystal, and drying to obtain a qualified anhydrous betaine crystal product.

The specific operating conditions of the above two steps

In the step 1), the used solvent is pure methanol or ethanol, a mixed solvent of methanol and ethanol, or a mixed solvent of methanol or ethanol and water; in a mixed solvent of methanol and water, the mass fraction of the water cannot reach 15wt%; in the mixed solvent of ethanol and water, the mass fraction of water cannot reach 10wt%.

In the step 1), the mass ratio of the anhydrous betaine powder to the methanol or methanol aqueous solution is 0.7-1.2, and the mass ratio of the anhydrous betaine powder to the ethanol or ethanol aqueous solution is 0.2-0.5.

In the step 1), when methanol or methanol-water solution is adopted as a solvent, the dissolving temperature range is 72-76 ℃; when ethanol or ethanol-water solution is used as a solvent, the dissolving temperature is 78-82 ℃; the temperature rise rate ranges from 5 to 7 ℃/min.

In the step 2), the rapid cooling rate range before the explosion nucleation process is 0.3-0.5 ℃/min, the dosage of the anhydrous betaine powder added again in the solution is not more than 0.01g/g solvent, and the solution temperature range in the explosion nucleation process is 70-82 ℃.

In the step 2), the temperature reduction rate range after the explosion nucleation process is 0.05-0.5 ℃/min, and the temperature reduction end point temperature range is 20-25 ℃.

In the step 2), the washing process may be first washing with absolute ethanol or a mixed solvent of acetone and methanol, where the mass fraction of acetone in the mixed solvent is in the range of 50 to 60wt%, and then washing with acetone.

In the step 2), the washed crystal can be dried by adopting a vacuum-pumping mode at room temperature and then dried by adopting a forced air drying mode at the temperature of 50-105 ℃.

The crystal particles obtained by the method of the present application are shown in fig. 3 and fig. 4, respectively. As can be seen from the figure, the obtained crystal particles are colorless and transparent and are cubic, four sides of the rhombus at the bottom edge are almost equal, the acute angle inside the rhombus is 83.5 degrees +/-0.5 degrees, the obtuse angle is 96.5 degrees +/-0.5 degrees, the height of the cube is vertical to the bottom surface, and the ratio of the height of the crystal to one fourth of the circumference of the rhombus ranges from 0.21 to 1.00; the bulk density range of the obtained crystal particles is 0.701-0.780 g/mL, and the mass ratio range of the crystal particles with the particle size distribution of 20-60 meshes (the particle size is 0.25-0.84 mm) is 80.0-98.9 wt%; the test condition of X-ray powder diffraction is Cu Ka/40 kV/100mA, the range of 2 theta angles of diffraction is 2-60 degrees, the diffraction rate is 8 degrees/min, crystal particles are not ground, the 2 theta angles of characteristic diffraction peaks with relative intensity of more than 20 percent are respectively 12 degrees +/-0.5 degrees, 19.4 degrees +/-0.5 degrees, 24.5 degrees +/-0.5 degrees, 37 degrees +/-0.5 degrees and 50 degrees +/-0.5 degrees, and the spectrum of XRD is shown in figure 5. The comparison of the crystal particles of anhydrous betaine obtained by the crystallization method of the present application with those of commercially available anhydrous betaine is shown in Table 1

TABLE 1 comparison of commercially available Anhydrous betaine Crystal particles to Anhydrous betaine Crystal particles in the present application

As can be seen from the bulk density and particle size distribution in Table 1, the anhydrous betaine crystal particles prepared by the crystallization method in the present application are superior to the commercially available anhydrous betaine crystal particles even under conservative conditions.

In summary, the crystallization method of the present application controls the growth process of the crystal by controlling the explosive nucleation process and the cooling process in the cooling process, and these two important processes also constitute the crystallization method-the overboiling explosive nucleation method in the present application. The anhydrous betaine crystal particles obtained by the crystallization method are cubic, the flaky crystal habit of the anhydrous betaine crystal is thoroughly changed, and the bulk density of the crystal particles is remarkably improved; the crystallization method can also adjust the particle size and the distribution thereof according to the requirements, can ensure that the particle size of the crystal particles obtained by crystallization is in the required particle size range, and the particle size distribution is more concentrated; the crystallization method does not need seed crystals, thereby saving the preparation process of the seed crystals and simplifying the crystallization process; finally, the crystallization method has short operation time and high production efficiency, thereby being more beneficial to industrial production.

Drawings

FIG. 1 SEM photograph of commercially available anhydrous betaine crystals

FIG. 2 is a graph showing the change of the dissolution amount of a solution during a temperature-reducing crystallization process

FIG. 3 SEM image of anhydrous betaine crystal particles obtained by the crystallization method of the present application

FIG. 4 is a diagram of the crystal particles of anhydrous betaine obtained by the crystallization method of the present application

FIG. 5 XRD pattern of anhydrous betaine crystal particles obtained by the crystallization method of the present application

Wherein: a-instantaneous solution state after addition of solvent; b-solution state when the temperature of the solution rises to the maximum; c-the solution state of the crystallization critical point; d, solution state at the end of temperature reduction; e-state of solution after equilibration at room temperature.

Detailed Description

The present invention is further illustrated by the following examples, which should not be construed as limiting the invention thereto.

Example 1

To the crystallizer were added 91.9g of anhydrous betaine powder and 118g of anhydrous methanol, the ratio of anhydrous betaine powder to solvent was 0.78. Setting the stirring speed at 400r/min, heating at a heating rate of 7 ℃/min to dissolve the powder, and raising the temperature of the solution to 72.3 ℃ to reach the boiling point of a crystallization system.

Rapidly cooling, wherein the cooling rate is 0.3 ℃/min, when the temperature of the solution is reduced to 71.9 ℃, crystal nuclei begin to be separated out, anhydrous betaine powder is not added, namely the adding amount is 0g/g of solvent, the crystal nuclei are separated out in the solution in an explosive manner, and then, the temperature is continuously reduced to the room temperature at the cooling rate of 0.05 ℃/min.

When the temperature of the solution is reduced to 20 ℃, filtering is carried out, then the crystal is washed by acetone-methanol solution with the acetone mass fraction of 60wt%, and then the crystal is washed by acetone, and the washing process needs to be completed quickly. The washed crystals were then quickly dried in a forced air oven at 50 ℃ for 24h. The ratio of the height of the obtained anhydrous betaine crystal to one fourth of the circumference of a rhombus at the bottom edge ranges from 0.51 to 0.72, the bulk density of the crystal product is 0.71g/mL, and the mass proportion of crystal particles with the particle size distribution of 20-60 meshes is 86.7wt%.

Example 2

91.9g of anhydrous betaine powder and 118g of methanol were added to the crystallizer, and the mass ratio of the anhydrous betaine powder to the solvent was 0.78. Setting the stirring speed at 400r/min, heating at a heating rate of 6 ℃/min to dissolve the powder, and raising the temperature of the solution to 72.4 ℃ to reach the boiling point of a crystallization system.

And (3) rapidly cooling, wherein the cooling rate is 0.5 ℃/min, when the temperature of the solution is reduced to 72 ℃, crystal nuclei begin to precipitate, 1g of anhydrous betaine powder is added into the solution, namely the adding amount is 0.008g/g of solvent, the crystal nuclei are immediately precipitated in an explosive manner in the solution, and then the temperature is continuously reduced to the room temperature at the cooling rate of 0.05 ℃/min.

When the temperature of the solution is reduced to 20 ℃, filtering is carried out, then the crystal is quickly washed by acetone-methanol solution with acetone mass fraction of 60wt%, and then the crystal is immediately washed by acetone. The washed crystals were quickly dried in a forced air drying cabinet at 50 ℃ for 24h. The ratio of the height of the obtained crystal to one fourth of the circumference of a rhombus at the bottom edge is 0.62-0.81, the bulk density of the crystal product is 0.76g/mL, and the mass proportion of crystal particles with the particle size distribution of 20-60 meshes is 93.3wt%.

Embodiment 3

92.5g of anhydrous betaine powder and 118g of methanol were added to the crystallizer, and the mass ratio of the anhydrous betaine powder to the solvent was 0.78. Setting the stirring speed at 400r/min, heating at a heating rate of 5 ℃/min to dissolve the powder, and raising the temperature of the solution to 73.2 ℃ to reach the boiling point of a crystallization system.

And (3) rapidly cooling, wherein the cooling rate is 0.5 ℃/min, when the temperature of the solution is reduced to 73 ℃, crystal nuclei begin to precipitate, 0.5g of anhydrous betaine powder is added into the solution, namely the adding amount is 0.004g/g of solvent, the crystal nuclei are immediately precipitated in an explosive manner in the solution, and then the temperature is continuously reduced to room temperature at the cooling rate of 0.05 ℃/min.

When the temperature is reduced to 20 ℃, filtering is carried out, then the crystal is quickly washed by acetone-methanol solution with acetone mass fraction of 60wt%, and then the crystal is immediately washed by acetone. The washed crystals were quickly dried in a forced air oven at 50 ℃ for 24h. The ratio of the height of the obtained crystal to one fourth of the circumference of the rhombus at the bottom edge ranges from 0.65 to 0.79, the bulk density of the crystal product is 0.72g/mL, and the mass proportion of crystal particles with the particle size distribution of 20 to 60 meshes is 97.8wt%.

Example 4

Adding 111.2g of anhydrous betaine powder, 10g of water and 90g of methanol into a crystallizer, wherein the mass fraction of water in a solvent system is 10wt%, and the mass ratio of the anhydrous betaine powder to the solvent is 1.1. Setting the stirring speed at 400r/min, and heating to 72 ℃ at the heating rate of 7 ℃/min to dissolve the powder, wherein the boiling point of the powder is close to that of a crystallization system.

Rapidly cooling, wherein the cooling rate is 0.3 ℃/min, when the temperature of the solution is reduced to 70.4 ℃, crystal nuclei begin to be separated out, anhydrous betaine powder is not added, namely the adding amount is 0g/g, the crystal nuclei are separated out in the solution in an explosive manner, and then the temperature is continuously cooled to the room temperature at the cooling rate of 0.5 ℃/min.

When the temperature is reduced to 20 ℃, filtering is carried out, then acetone-methanol solution with acetone mass fraction of 60wt% is used for washing the crystal, and then acetone is used for washing the crystal immediately. The washed crystals were quickly dried in a forced air drying cabinet at 50 ℃ for 24h. The ratio of the height of the obtained crystal to one fourth of the circumference of the rhombus at the bottom edge ranges from 0.83 to 1.00, the bulk density of the crystal product is 0.72g/mL, and the mass proportion of crystal particles with the particle size distribution of 20 to 60 meshes is 89.7wt%.

Example 5

Adding 112.5g of anhydrous betaine powder, 10g of water and 90g of methanol into a crystallizer, wherein the mass fraction of water in a solvent system is 10wt%, and the mass ratio of the anhydrous betaine powder to the solvent is 1.1. Setting the stirring speed at 400r/min, and heating at a heating rate of 7 ℃/min to dissolve the powder to reach the boiling point of the crystallization system.

And (3) rapidly cooling, wherein the cooling rate is 0.5 ℃/min, when the temperature of the solution is reduced to 72.5 ℃, crystal nuclei begin to precipitate, 0.5g of anhydrous betaine powder is added into the solution, namely the adding amount is 0.005g/g of solvent, the crystal nuclei are immediately precipitated in an explosive manner in the solution, and then the temperature is continuously reduced to room temperature at the cooling rate of 0.1 ℃/min.

When the temperature is reduced to 20 ℃, filtering is carried out, then acetone-methanol solution with acetone mass fraction of 60wt% is used for washing the crystal, and then acetone is used for washing the crystal immediately. The washed crystals were quickly dried in a forced air drying cabinet at 50 ℃ for 24h. The ratio of the height of the obtained crystal to one fourth of the circumference of the rhombus at the bottom edge ranges from 0.84 to 1.00, the bulk density of the crystal product is 0.79g/mL, and the mass proportion of crystal particles with the particle size distribution of 20 to 60 meshes is 95.7wt%.

Example 6

Adding 96.3g of anhydrous betaine powder, 5g of water and 95g of methanol into a crystallizer, wherein the water content of a solvent system is 5wt%, and the mass ratio of the anhydrous betaine powder to the solvent is 0.96. Setting the stirring speed at 400r/min, and heating at a heating rate of 7 ℃/min to dissolve the powder to reach the boiling point of a crystallization system.

Rapidly cooling at a cooling rate of 0.5 ℃/min, when the temperature of the solution is reduced to 72.3 ℃, starting to precipitate crystal nuclei, adding 0.4g of anhydrous betaine powder into the solution, namely adding 0.004g/g of solvent, immediately precipitating the crystal nuclei in an explosive manner in the solution, and then continuously cooling to room temperature at a cooling rate of 0.3 ℃/min.

When the temperature is reduced to 20 ℃, filtering is carried out, then acetone-methanol solution with acetone mass fraction of 60wt% is used for washing the crystal, and then acetone is used for washing the crystal immediately. The washed crystals were quickly dried in a forced air drying cabinet at 50 ℃ for 24h. The ratio of the height of the obtained crystal to one fourth of the circumference of the rhombus at the bottom edge ranges from 0.82 to 0.96, the bulk density of the crystal product is 0.73g/mL, and the mass proportion of crystal particles with the particle size distribution of 20 to 60 meshes is 91.4wt%.

Example 7

27.2g of anhydrous betaine powder and 120.1g of anhydrous ethanol were added to the crystallizer, and the mass ratio of the anhydrous betaine powder to the solvent was 0.2. Setting the stirring speed at 400r/min, and heating to 78 deg.C at a heating rate of 7 deg.C/min to dissolve the powder and approach the boiling point temperature of the crystallization system.

And (3) rapidly cooling, wherein the cooling rate is 0.5 ℃/min, when the temperature of the solution is reduced to 75 ℃, crystal nuclei begin to precipitate, anhydrous betaine powder is not added into the solution, namely the adding amount is 0g/g, the crystal nuclei are precipitated in the solution in an explosive manner, and then the temperature is continuously cooled to room temperature at the cooling rate of 0.05 ℃/min.

When the temperature of the solution is reduced to 20 ℃, the solution is filtered, washed by absolute ethyl alcohol and then acetone, and the washing process needs to be completed quickly. The washed crystals were then quickly dried in a forced air drying cabinet at 50 ℃ for 24h. The ratio of the height of the obtained anhydrous betaine crystal to one fourth of the circumference of a rhombus at the bottom edge is 0.91-1.00, the bulk density of the crystal product is 0.77g/mL, and the mass proportion of crystal particles with the particle size distribution of 20-60 meshes is 99.0wt%.

Example 8

61g of anhydrous betaine powder and 240g of anhydrous ethanol were added to the crystallizer, and the mass ratio of the anhydrous betaine powder to the solvent was 0.25. Setting the stirring speed to 350r/min, and heating at a heating rate of 6 ℃/min to dissolve the powder to reach the boiling point temperature of a crystallization system.

And (3) rapidly cooling, wherein the cooling rate is 0.5 ℃/min, when the temperature of the solution is reduced to 79.8 ℃, crystal nuclei begin to precipitate, 0.1g of anhydrous betaine powder is added into the solution, namely the adding amount is 0.0004g/g of solvent, the crystal nuclei are immediately precipitated in a bursting manner in the solution, and then the temperature is continuously reduced to room temperature at the cooling rate of 0.05 ℃/min.

When the temperature of the solution is reduced to 20 ℃, the solution is filtered, washed by absolute ethyl alcohol and then acetone, and the washing process needs to be completed quickly. The washed crystals were then quickly dried in a forced air oven at 50 ℃ for 24h. The ratio of the height of the obtained anhydrous betaine crystal to one fourth of the circumference of a rhombus at the bottom edge is 0.90-1.00, the bulk density of the crystal product is 0.76g/mL, and the mass proportion of crystal particles with the particle size distribution of 20-60 meshes is 99.1wt%.

Example 9

31.2g of anhydrous betaine powder and 120g of anhydrous ethanol were added to the crystallizer, and the mass ratio of the anhydrous betaine powder to the solvent was 0.26. Setting the stirring speed at 400r/min, and heating at a heating rate of 5 ℃/min to dissolve the powder to reach the boiling temperature of the crystallization system.

And (3) rapidly cooling, wherein the cooling rate is 0.5 ℃/min, when the temperature of the solution is reduced to 80.2 ℃, crystal nuclei begin to precipitate, 1.1g of anhydrous betaine powder is added into the solution, namely the adding amount of the solvent is 0.009g/g, the crystal nuclei are immediately precipitated in a bursting manner in the solution, and then the temperature is continuously reduced to the room temperature at the cooling rate of 0.05 ℃/min.

When the temperature of the solution is reduced to 20 ℃, the solution is filtered, washed by absolute ethyl alcohol and then acetone, and the washing process needs to be completed quickly. The washed crystals were then quickly dried in a forced air oven at 50 ℃ for 24h. The ratio of the height of the obtained anhydrous betaine crystal to one fourth of the circumference of a rhombus at the bottom edge is 0.93-1.00, the bulk density of the crystal product is 0.78g/mL, and the mass proportion of crystal particles with the particle size distribution of 20-60 meshes is 99.3wt%.

Example 10

79.5g of anhydrous betaine powder, 5g of water and 240g of anhydrous ethanol are added into a crystallizer, the mass fraction of water in a solvent system is 2wt%, and the mass ratio of the anhydrous betaine powder to the solvent is 0.32. Setting the stirring speed to 350r/min, and heating at a heating rate of 5 ℃/min to dissolve the powder to reach the boiling point temperature of a crystallization system.

And (3) rapidly cooling, wherein the cooling rate is 0.5 ℃/min, when the solution is cooled to 80.2 ℃, crystal nuclei begin to precipitate, 1.5g of anhydrous betaine powder is added into the solution, namely the adding amount is 0.006g/g of solvent, the crystal nuclei are immediately precipitated in an explosive manner in the solution, and then the solution is continuously cooled to room temperature at the cooling rate of 0.1 ℃/min.

When the temperature of the solution is reduced to 20 ℃, the solution is filtered, washed by absolute ethyl alcohol and then acetone, and the washing process needs to be completed quickly. The washed crystals were then quickly dried in a forced air drying cabinet at 50 ℃ for 24h. The ratio of the height of the obtained anhydrous betaine crystal to one fourth of the circumference of a rhombus at the bottom edge is 0.91-0.99, the bulk density of the crystal product is 0.75g/mL, and the mass proportion of crystal particles with the particle size distribution of 20-60 meshes is 99.2wt%.

While the methods and techniques of the present invention have been described in terms of preferred embodiments, it will be apparent to those of skill in the art that variations and modifications of the methods and techniques described herein may be practiced without departing from the spirit and scope of the invention. It is expressly intended that all such similar substitutes and modifications apparent to those skilled in the art are deemed to be within the spirit, scope and content of the invention.

Claims (4)

1. A method for preparing cubic anhydrous betaine crystals is characterized by adopting an over-boiling burst nucleation method, and comprises the following steps:

1) Adding anhydrous betaine powder into a crystallizer, adding pure methanol or ethanol, or a mixed solvent of methanol and ethanol, or a mixed solvent of methanol or ethanol and water into the crystallizer, heating at the speed of 5-7 ℃/min to completely dissolve the powder, and enabling the temperature of the solution to reach the boiling point of a crystallization system; when methanol or methanol water solution is adopted as a solvent, the dissolving temperature range is 72-76 ℃; when ethanol or ethanol water solution is used as a solvent, the dissolving temperature range is 78-82 ℃;

2) Cooling at the speed of 0.3-0.5 ℃/min, when crystal nuclei are separated out in a crystallization system, adding anhydrous betaine powder into the crystallizer again to promote the crystal nuclei to be separated out by the crystal system in a bursting way at the temperature of 70-82 ℃; continuously reducing the temperature of the solution to 20-25 ℃ at the speed of 0.05-0.5 ℃/min; and (4) cooling to the end temperature, filtering and washing the crystal, and drying to obtain a qualified anhydrous betaine crystal product.

2. The method as set forth in claim 1, characterized in that in the step 1), the mass fraction of water in the mixed solvent of methanol and water is not up to 15wt%; in the mixed solvent of ethanol and water, the mass fraction of water cannot reach 10wt%.

3. The method as set forth in claim 1, wherein in the step 1), the ratio of the mass of the anhydrous betaine powder to the mass of the methanol or the aqueous methanol solution is in the range of 0.7 to 1.2.

4. The method according to claim 1, wherein in step 2), the amount of the added anhydrous betaine powder in the solution is not more than 0.01g/g solvent.

Images