阅读说明：本技术 一种大颗粒球形硫酸钠晶体的制备方法 (Preparation method of large-particle spherical sodium sulfate crystal ) 是由 龚俊波 王烁 王显军 黄孟阳 汤伟伟 刘烨 陈明洋 张明宇 王静康 荀春 尹秋响 于 2020-05-12 设计创作，主要内容包括：本发明公开一种大颗粒球形硫酸钠晶体的制备方法。在35～50℃下,配置一定的浓度硫酸钠水溶液,溶质硫酸钠与水的质量比为0.2:1～0.45:1；在相同温度下,配置有机溶剂-架桥剂的混合溶剂,有机溶剂与水的质量比为1:1～3:1,架桥剂与溶质硫酸钠的体积比为0.5:1～1:1。随后,将硫酸钠水溶液以0.5～4％/min的速率滴加至有机溶剂-架桥剂的混合溶剂中以析出晶体,并持续搅拌。滴加完毕后,保持搅拌0.5～5h。过滤、洗涤、干燥,得到球形硫酸钠晶体。该方法制得的硫酸钠晶体球形度好,粒度大,平均粒度大于600微米；过滤性能好,流动性高,不易结块,有利于提高产品生产效率,减少运输、储存中的结块现象。(The invention discloses a preparation method of a large-particle spherical sodium sulfate crystal. Preparing a sodium sulfate aqueous solution with a certain concentration at the temperature of 35-50 ℃, wherein the mass ratio of solute sodium sulfate to water is 0.2: 1-0.45: 1; preparing a mixed solvent of an organic solvent and a bridging agent at the same temperature, wherein the mass ratio of the organic solvent to water is 1: 1-3: 1, and the volume ratio of the bridging agent to solute sodium sulfate is 0.5: 1-1: 1. And then, dropwise adding the sodium sulfate aqueous solution into the mixed solvent of the organic solvent and the bridging agent at the speed of 0.5-4%/min to precipitate crystals, and continuously stirring. And after the dropwise addition is finished, keeping stirring for 0.5-5 h. Filtering, washing and drying to obtain spherical sodium sulfate crystals. The sodium sulfate crystal prepared by the method has good sphericity and large granularity, and the average granularity is more than 600 microns; the filter has good filtering performance and high fluidity, is not easy to agglomerate, is beneficial to improving the production efficiency of products and reducing the agglomeration phenomenon in transportation and storage.)

1. A preparation method of large-particle spherical sodium sulfate crystals is characterized by comprising the following steps:

(1) preparing a sodium sulfate aqueous solution at 35-50 ℃;

(2) maintaining the temperature of the step (1), and preparing a mixed solvent of an organic solvent and a bridging agent;

(3) dropwise adding the sodium sulfate aqueous solution obtained in the step (1) into the mixed solvent obtained in the step (2) to precipitate crystals, and continuously stirring; after the dropwise addition is finished, stirring for 0.5-5 h;

(4) filtering, washing and drying to obtain large-particle spherical sodium sulfate crystals.

2. The method as set forth in claim 1, characterized in that the mass ratio of solute sodium sulfate to water in the step (1) is 0.2:1 to 0.45: 1.

3. The method as set forth in claim 1, wherein the organic solvent in the step (2) is one of methanol, ethanol, n-propanol or isopropanol.

4. The method as set forth in claim 1, wherein the bridging agent in step (2) is one of dichloromethane, n-hexane or cyclohexane.

5. The method according to claim 1, wherein the mass ratio of the organic solvent to the water is 1:1 to 3: 1.

6. The method of claim 1, wherein the volume ratio of the bridging agent to the solute sodium sulfate is 0.5:1 to 1: 1.

7. The method as set forth in claim 1, wherein the dropping rate of the aqueous solution of sodium sulfate in the step (3) is 0.5 to 4%/min.

8. The method as set forth in claim 1, characterized in that the washing in the step (4) is washing with ethanol of 70-95% by mass fraction.

9. The method as set forth in claim 1, wherein the drying in the step (4) is drying under normal pressure at a temperature of 40 to 70 ℃ for 6 to 24 hours.

Technical Field

The invention belongs to the technical field of chemical engineering industrial crystallization, and particularly relates to a preparation method of a large-particle spherical sodium sulfate crystal.

Background

Sodium sulfate (CAS: 7757-82-6), molecular formula Na₂SO₄Also called anhydrous sodium sulphate, is a basic inorganic chemical product. Sodium sulfate is an important raw material in the processes of synthesizing detergents, papermaking and manufacturing glass, is widely applied to the production of dyes, feeds and medical products, and is also a commonly used drying agent in a laboratory. In recent years, with the continuous upgrading and development of downstream industries, the market needs special anhydrous sodium sulphateThe demand is increasing day by day, and the large-particle sodium sulfate is favored by the market by virtue of the unique advantages of beautiful appearance, easy electrolysis, easy separation from mother liquor, convenient washing and the like. At present, sodium sulfate is mostly prepared by an evaporation or mechanical freezing method in industry, and the obtained product is generally a monoclinic or orthorhombic granular or short columnar crystal with a small particle size of 20-200 microns. The small-granularity sodium sulfate has low added value, is easy to form compact filter cakes in the filtering process, increases the operation difficulty and power consumption, reduces the production efficiency and easily causes the problem of dust pollution. In addition, sodium sulfate also has hygroscopicity, and after the sodium sulfate absorbs moisture, liquid bridges are formed at the positions where crystals are contacted with each other, and along with the change of environmental humidity, the liquid bridges are further converted into crystal bridges, so that the sodium sulfate crystals have the problems of easy agglomeration and agglomeration, and the quality of products is reduced. To sum up, the problems of the existing sodium sulfate products are as follows: the product has small granularity, difficult filtration and easy agglomeration.

The shape and granularity of the sodium sulfate crystal are improved, the powder performance of the crystal is improved, the problems can be effectively solved, and the added value of the sodium sulfate, which is a basic chemical product, can be increased. At present, much of the reported methods have been dedicated to increasing the particle size of sodium sulfate. For example, patent CN100545091C discloses a method for preparing large-particle sodium sulfate by reverse circulation technology, but the product d prepared by the method₅₀Only 0.234mm, the particle size increase is limited. The patent CN110217805A utilizes a seed crystal adding mode to prepare large-particle sodium sulfate, but the mode has difficulty in stably controlling the nucleation and growth of sodium sulfate, so that the product particle size distribution is not uniform, and the large-particle sodium sulfate product can be obtained only through primary cyclone separation, which increases the equipment cost and the production cost. Patent CN101007640A prepares large-particle sodium sulfate by adding solid surfactant, and the product with more than 40 meshes (425um) can reach 80 percent, but solid impurities are introduced in the production process, so that the quality of the product is reduced.

The above reported preparation methods all aim to increase the particle size of sodium sulfate, but it is difficult to obtain a large particle sodium sulfate product with uniform particle size without introducing solid impurities. Moreover, the problem of easy caking cannot be solved by simply increasing the granularity of the sodium sulfate.

Therefore, under the condition of not introducing solid impurities, the development of a preparation method of sodium sulfate which has large and uniform particle size, good fluidity and difficult caking is still the problem which is not solved by the prior art.

Disclosure of Invention

In order to solve the defects of the existing product, the invention provides a method for preparing large-particle spherical sodium sulfate crystals, the prepared sodium sulfate product has large granularity and good filtering performance, and no solid additive is introduced in the preparation process; meanwhile, the crystal has high sphericity and good fluidity, so the crystal has good anti-caking performance and has unique advantages in the processes of production, transportation and storage.

The technical scheme of the invention is as follows:

(1) preparing a sodium sulfate aqueous solution at 35-50 ℃;

(2) maintaining the temperature of the step (1), and preparing a mixed solvent of an organic solvent and a bridging agent;

(3) dropwise adding the sodium sulfate aqueous solution obtained in the step (1) into the mixed solvent obtained in the step (2) to precipitate crystals, and continuously stirring; after the dropwise addition is finished, stirring for 0.5-5 h;

(4) filtering, washing and drying to obtain the sodium sulfate spherical crystal.

In the sodium sulfate aqueous solution in the step (1), the mass ratio of solute sodium sulfate to water is 0.2: 1-0.45: 1.

The organic solvent in the step (2) is selected from one of methanol, ethanol, n-propanol or isopropanol, and the mass ratio of the organic solvent to water is 1: 1-3: 1.

The bridging agent in the step (2) is one of dichloromethane, n-hexane or cyclohexane, and the volume ratio of the bridging agent to solute sodium sulfate is 0.5: 1-1: 1.

And (3) the dropping speed of the sodium sulfate aqueous solution in the step (3) is 0.5-4%/min.

The washing in the step (4) is carried out by using ethanol with the mass fraction of 70-95%.

The drying in the step (4) is drying under normal pressure, the temperature is 40-70 ℃, and the drying time is 6-24 hours.

The sodium sulfate spherulite product prepared by the method has large granularity, the average granularity of the sodium sulfate spherulite product is larger than 600 microns, the fluidity is high, the angle of repose is 29-32 degrees, the residual solvent after filtration is 1.1-2.8 percent, the caking rate is 2.0-5.5 percent, and the sodium sulfate spherulite product has good filtration performance and caking resistance.

The invention provides a preparation method of large-particle spherical sodium sulfate crystals, which has the creativity that:

1. the sodium sulfate product with high sphericity is prepared. In the spherical crystallization technology, the selection of a solvent system, the adding sequence and the adding proportion among different solvents and the like are all key parameters influencing the performance of products, and scientific researchers need to develop targeted design according to professional knowledge and the chemical properties and particle properties of target products. If the good solvent, the anti-solvent and the bridging agent are selected blindly according to the past experience, or the operation parameters such as the addition sequence of each solvent are set arbitrarily, the target product deviates from the balling condition in the crystallization process, and the balling is difficult. According to the invention, a good solvent, an anti-solvent and a bridging agent are reasonably selected according to ternary phase diagrams of solvent systems at different temperatures, a proper crystallization temperature is selected according to the characteristics of a sodium sulfate elution crystallization process, the addition sequence and proportion of the solvents are adjusted, and finally the preparation of a spherical product is realized.

2. The prepared spherical sodium sulfate crystal has large granularity, and the average granularity is more than 600 microns. During the spherical crystallization, the bridging agent provides adhesion between the coalesced particles, and the mechanical agitation provides shear force. If the adhesive force is too small, the particles are not sufficiently agglomerated, and the final product is insufficiently balled; excessive adhesion causes severe agglomeration and the final product tends to form large lumps. The adhesion and shear forces required for spheronization are in specific ranges for different crystalline systems. The invention reasonably adjusts the dosage of the bridging agent according to the characteristics of the sodium sulfate crystallization system, increases the adhesive force in a certain range to prepare large-particle spherical products and improves the added value of the products.

3. The large-particle spherical sodium sulfate crystal prepared by the invention has good filtering performance. The filtration performance is evaluated according to the solvent residue rate after filtration, and the measurement method comprises the steps of weighing 30.0g of sodium sulfate, placing the sodium sulfate in 100.0mL of absolute ethyl alcohol, filtering for 90s under the vacuum degree of-0.06 MPa, weighing a filter cake, drying the filter cake under the conditions of normal pressure and 50 ℃ until the mass of the filter cake is unchanged, weighing the dried filter cake, and calculating the solvent residue rate. The expression is as follows:

wherein a is the residual rate of the solvent, m₁Mass of filter cake before drying, m₂Is the mass of the dried filter cake.

The solvent residue ratio of the large spherical sodium sulfate crystals of the present invention was 1.1 to 2.8%, while that of the commercially available bulk sodium sulfate crystals of conventional particle size (average particle size of 140 μm) was 8.5%, and that of the large bulk sodium sulfate crystals of comparative example (average particle size of 380 μm, prepared according to patent CN 101007640A) was 4.0%.

4. The invention improves the anti-caking property of the sodium sulfate crystal. The angle of repose of the large-particle spherical sodium sulfate crystals of the present invention was 29 to 32 °, and the angle of repose of the large-particle bulk sodium sulfate crystals of the conventional commercially available sodium sulfate crystals and those of the comparative examples were 38 °. The improvement of fluidity ensures that fixed contact points are not easy to form among crystals, and meanwhile, the sodium sulfate crystals are prepared into spherical shapes, so that the contact area among particles can be effectively reduced, the formation of crystal bridges among the crystals after moisture absorption is reduced, and the anti-caking performance is improved by the synergistic effect of the two. The anti-caking performance is evaluated according to the caking rate, and the measurement method comprises the steps of weighing 10.0g of sodium sulfate, paving the sodium sulfate in a surface dish, uniformly spraying 0.5mL of deionized water, and drying the sodium sulfate in a drying oven with the humidity of 50% and the temperature of 25 ℃ until the mass of the sodium sulfate is unchanged. The dried crystals are sieved by a sieve with a specific mesh number (5 meshes, 4000 micrometers), the crystals which do not pass through the sieve holes are the agglomerated crystals, and the expression of the agglomeration rate is as follows:

wherein b is the caking rate, m₃Mass of agglomerated crystals, m₄Is the total crystal mass.

The caking rate of the large-particle spherical sodium sulfate crystal of the invention was 2.0% to 5.5%, the caking rate of the commercially available bulk sodium sulfate crystal of conventional particle size was 48.0%, and the caking rate of the large-particle bulk sodium sulfate crystal in the comparative example was 46.2%.

Drawings

FIG. 1: photographs of large-particle spherical sodium sulfate crystals of the present application.

FIG. 2: the optical microscope photograph of the large-particle spherical sodium sulfate crystal of the present application.

FIG. 3: scanning electron microscope photographs of large-particle spherical sodium sulfate crystals of the present application.

FIG. 4: light microscope photographs of commercially available bulk sodium sulfate crystals of conventional particle size.

FIG. 5: light microscope photograph of large granular sodium sulfate crystals in bulk in comparative example.

Detailed Description