Preparation method of nano calcium hydroxide with controllable particle size

Abstract

The invention discloses a preparation method of nano calcium hydroxide with controllable particle size, which comprises the following steps: (1) crushing calcium oxide to obtain calcium oxide powder with the maximum particle size of not more than 5mm; (2) carrying out ball milling on the calcium oxide powder or a mixture of the calcium oxide powder and a grinding aid to obtain calcium oxide ultrafine powder with the average particle size of not more than 50 microns; (3) uniformly mixing the calcium oxide ultrafine powder with a liquid dispersant to obtain calcium oxide sticky slurry or calcium oxide emulsion; (4) adding water into the calcium oxide sticky slurry or the calcium oxide emulsion, stirring, and digesting calcium oxide to obtain calcium hydroxide; and (5) drying and separating the calcium hydroxide to obtain the nano calcium hydroxide. The preparation method is low in cost, simple in preparation and controllable in particle size.

Description

Technical Field

[0001] The invention relates to a method for preparing a nano inorganic compound, in particular to a method for preparing nano calcium hydroxide with controllable particle size. Background Art

[0002] Calcium hydroxide is a common inorganic compound, widely used in various industrial and environmental protection fields. Industrial calcium hydroxide is usually obtained by the reaction of calcium oxide and water, and appears as a white powder. After dissolving in water, the solution formed is strongly alkaline, and it is one of the cheapest alkaline substances in the industrial field. Based on the chemical properties of calcium hydroxide, it has broad application prospects in cultural relics protection and flue gas desulfurization.

[0003] In the field of environmental protection, the research on the use of calcium hydroxide for flue gas desulfurization began in the United States in the 1970s. With the improvement of environmental protection awareness and the rise of environmental protection movements in various industries, the application demand of using cheap alkaline sources to absorb sulfides emitted in flue gas has emerged. However, the particle size of calcium hydroxide obtained by digestion of calcium oxide and water is 10-50μm, and the reaction activity is poor. When used in flue gas desulfurization, the reaction efficiency is low. Reducing the particle size of calcium hydroxide, increasing porosity, and increasing specific surface area and reaction activity are important methods to achieve low-cost flue gas desulfurization. In order to control air pollution, the country has formulated a series of environmental emission standards, such as GB 16171-2012, GB13271-2014 and GB41618-2022, etc., to limit sulfur dioxide emissions in industries such as boilers, coking, lime, calcium carbide and coal-fired power generation, and supervise enterprises through online environmental protection equipment to strictly implement the above standards. At present, environmental protection costs are an important part of the production costs of industrial enterprises, making cheap desulfurization a huge potential market in China. Generally speaking, the specific surface area of ​​calcium hydroxide obtained by ordinary digestion is 5m 2 / g to 8m 2 / g, further reducing the particle size of calcium hydroxide, when its particle size is reduced to below 500nm, with the increase of porosity, the specific surface area can reach 35m 2 / g or more, through dry desulfurization, its removal rate of sulfur dioxide can reach more than 90%, meeting the domestic flue gas desulfurization standards. Due to its good adsorption effect, nano calcium hydroxide can also be used in water pollution treatment, waste incineration power generation and other industries. Nano calcium hydroxide can also be used as an additive in high-performance photovoltaic glass, insulating rubber, cultural relics restoration and other fields.

[0004] Existing nano calcium hydroxide and high specific surface area calcium hydroxide are usually produced by wet method, that is, calcium oxide is dissolved in excess water, and the crystal growth of calcium hydroxide is controlled by surfactant and calcium hydroxide crystal growth retardant, so as to prepare nano calcium hydroxide. In this method, excessive water makes it difficult to dry the product, and the size of the prepared calcium hydroxide is difficult to control.

[0005] From the above background, it can be seen that developing a nano calcium hydroxide production process that can control particle size can meet subsequent different application needs and has far-reaching social and commercial value. Summary of the invention

[0006] The technical problem to be solved by the present invention is to provide a method for preparing nano calcium hydroxide with controllable particle size. The preparation method is simple, and the size of the obtained nano calcium hydroxide is small and controllable.

[0007] In order to solve the above technical problems, the present invention discloses a method for preparing nano calcium hydroxide with controllable particle size, which comprises the following steps:

[0008] (1) crushing calcium oxide to obtain calcium oxide powder with a maximum particle size not exceeding 5 mm;

[0009] (2) ball milling the calcium oxide powder or the mixture of the calcium oxide powder and the grinding aid to obtain ultrafine calcium oxide powder with an average particle size not exceeding 50 μm; in this step, when no grinding aid is added or a small amount of grinding aid is added, it is dry ball milling, and when more grinding aid is added, it is wet ball milling; in this step, the calcium oxide powder particles are reduced in size by collision and friction of the microspheres, and the effect is better in wet ball milling;

[0010] (3) The ultrafine calcium oxide powder is mixed with a liquid dispersant to obtain a viscous calcium oxide slurry or a calcium oxide emulsion; the liquid dispersant helps to further reduce the particle size of the ultrafine calcium oxide powder and makes the subsequent digestion reaction more moderate and more complete (if the ultrafine calcium oxide powder is directly digested with water, the reaction will be too violent);

[0011] (4) adding water to the calcium oxide viscous slurry or calcium oxide emulsion, stirring, and digesting the calcium oxide to obtain calcium hydroxide;

[0012] (5) Drying and separating the calcium hydroxide to obtain nano calcium hydroxide.

[0013] Furthermore, in step (2), the grinding aid is a volatile alcohol organic substance or an alcohol amine organic substance or a mixture of volatile alcohol organic substances and alcohol amine organic substances; in step (3), the liquid dispersant used is a volatile alcohol organic substance or an alcohol amine organic substance or a mixture of volatile alcohol substances and alcohol amine organic substances.

[0014] Furthermore, in step (2), the weight of the grinding aid added is 0% to 100% of the weight of the calcium oxide powder; in step (3), the weight of the liquid dispersant used is at least 5% of the weight of the calcium oxide powder. If the amount of liquid dispersant is too small, stirring is impossible. In order to control costs, it is generally not more than 100%.

[0015] When the amount of liquid dispersant used is small, the liquid dispersant and water can be mixed first, and then mixed with the ultrafine calcium oxide powder for digestion reaction, but the controllability is not as good as first mixing the ultrafine calcium oxide powder with the liquid dispersant and then adding water for digestion reaction.

[0016] Furthermore, the volatile alcohol organic matter is one or a mixture of two or more of methanol, ethanol or propanol, and the alcohol amine organic matter is one or a mixture of two or more of methanolamine, ethanolamine (including monoethanolamine, diethanolamine and triethanolamine).

[0017] Furthermore, the grinding aid and liquid dispersant used are of the same component, for example, both the grinding aid and the liquid dispersant are ethanol, or both the grinding aid and the liquid dispersant are a mixture of ethanol and triethylamine, which can reduce costs to a certain extent compared to when the two are of different components.

[0018] Furthermore, the total weight of the alcohol amine organic matter used in the liquid dispersant and the grinding aid is 0% to 10% of the weight of the calcium oxide powder.

[0019] Furthermore, the solid microspheres used in the ball milling in step (2) are inorganic microspheres that do not react with calcium oxide and have a harderness than calcium oxide, and the particle size is between 5 μm and 5 cm.

[0020] Furthermore, the inorganic microspheres are one or a mixture of two or more of silica microspheres, zirconium oxide microspheres, diamond microspheres, silicon carbide microspheres, metal microspheres, and ceramic microspheres.

[0021] Furthermore, in step (4), the weight of water added is 35% to 150% of the weight of the calcium oxide powder.

[0022] Furthermore, in step (1), the effective calcium content by weight of the calcium oxide used is greater than 90%, and the magnesium content by weight is less than 5%; in step (2), the increase in ball milling time can significantly reduce the diameter of the calcium oxide powder particles. In order to make the ball milling produce a significant effect, the ball milling time is at least 0.1h; in step (3), the calcium oxide ultrafine powder and the liquid dispersant are uniformly mixed by stirring in a closed container; in step (5), the calcium hydroxide is heated and dried or vacuum dried in a closed container, preferably heated and dried at 100°C to 200°C, to remove water and grinding aids and liquid dispersants with low melting points, and then the microspheres with relatively large particles are first screened out by screening (the mesh size of the sieve is selected according to the size of the microsphere particles, and generally a sieve with a mesh size greater than 16 is selected), and then a cyclone powder separator is used for powder separation to separate nano calcium hydroxide and microspheres with small particles. This step can also be directly carried out by a cyclone powder separator for powder separation.

[0023] The microspheres are mixed microspheres of different particle sizes in the range of 5 μm to 5 cm. In step (4), after adding water and stirring, the microspheres of different particle sizes will be separated into layers, and the particles and the heavy particles will sink to the bottom, thereby separating a part. In step (5), the microspheres with small particles and light weight and the silicon dioxide brought by the calcium oxide raw material are separated in this step through screening and cyclone powder separator.

[0024] The main principle of the present invention is to reduce the size of calcium oxide particles by ball milling so that the average particle size does not exceed 50 μm. When the calcium oxide particles are dispersed in an organic solvent as a liquid dispersant to form a viscous slurry or emulsion, the reaction with water is highly controllable. In addition, when the calcium oxide ultrafine powder dispersed in the organic solvent reacts with water to generate calcium hydroxide, the calcium oxide particles will further crack into finer calcium hydroxide particles due to volume expansion. Through the grinding time, the selection of grinding aids, and the selection of liquid dispersants, the average size of the generated calcium hydroxide nanoparticles can be controlled to a certain extent between 50nm and 800nm.

[0025] The present invention has the following advantages:

[0026] (1) The present invention uses a method for preparing nano calcium hydroxide by ball milling. The preparation method is simple, and the crushing, ball milling and stirring processes are all suitable for large-scale commercial production and have great commercial value.

[0027] (2) The present invention can control the size of the prepared calcium hydroxide nanoparticles. According to the particle size reduction control principle, the particle size of the generated calcium hydroxide ultrafine powder can be regulated by selecting a grinding aid, controlling the size of solid microspheres, and regulating the amount of liquid dispersant added, thereby obtaining nano calcium hydroxide with an average particle size of 50 nm to 800 nm.

[0028] (3) The method disclosed in the present invention has a wide range of applications. According to the different requirements for different nano calcium hydroxide particle sizes in different application fields, the production parameters can be flexibly adjusted to meet market demand.

[0029] In summary, compared with the existing calcium hydroxide nanoparticle preparation technology, the present invention not only has significant technical progress, but also has huge commercial value. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 is a flow chart of the preparation process of the present invention;

[0031] Figure 2 This is a scanning electron microscope image of nano calcium hydroxide obtained in Example 1 of the present invention;

[0032] Figure 3 This is a scanning electron microscope image of the nano calcium hydroxide obtained in Example 2 of the present invention. DETAILED DESCRIPTION

[0033] The present invention is further explained below in conjunction with the examples. The following examples are only used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0034] The experimental operation process of the present invention is as follows Figure 1 shown.

[0035] Example 1

[0036] (1) Take 10 kg of calcium oxide, and the test results show that its effective calcium content reaches 93.1%, the magnesium content is 2.4%, and the average particle size is about 10 cm. After crushing by a pulverizer, calcium oxide powder with a maximum particle diameter of less than 5 mm is obtained.

[0037] (2) A mixture of 5 mm zirconium oxide balls and 50 μm silicon dioxide microspheres was ball milled, with a weight ratio of calcium oxide powder to grinding microspheres of 1:0.5 (ball milling time of 5 h) to obtain calcium oxide ultrafine powder. Scanning electron microscopy showed that the average particle size of the calcium oxide ultrafine powder was reduced to 5 μm.

[0038] (3) adding 15% anhydrous ethanol and mixing with ultrafine calcium oxide powder to obtain a viscous slurry;

[0039] (4) Then, the mixture is mixed with water accounting for 38% by weight of the calcium oxide powder obtained in step (1) and stirred. After the reaction is completed, the obtained powder is dried at 150° C., and then the microspheres and other impurities used in the ball mill are separated by a cyclone powder separator to obtain nano calcium hydroxide. The obtained nano calcium hydroxide is characterized by a scanning electron microscope. At the lowest cost, the average size of the obtained calcium hydroxide is about 700 nm. Figure 2As shown, the measured specific surface area is 35.6m 2 / g.

[0040] Embodiment 2:

[0041] (1) Take 5 kg of calcium oxide, and the test results show that its effective calcium content reaches 96.7%, the magnesium content is 1.1%, and the average particle size is about 10 cm. After crushing by a pulverizer, calcium oxide powder with a maximum particle diameter of less than 5 mm is obtained.

[0042] (2) A mixture of anhydrous ethanol and triethanolamine accounting for 20% and 10% of the weight of the calcium oxide powder respectively was added as a grinding aid, and a mixture of 3 mm zirconium oxide balls and 20 μm silicon dioxide microspheres was selected for ball milling, with a powder-to-ball ratio of 1:1 and a ball milling time of 20 h to obtain ultrafine calcium oxide powder. Scanning electron microscopy showed that the average calcium oxide particle size was reduced to 1 μm at this time.

[0043] (3) adding anhydrous ethanol accounting for 60% by weight of the ultrafine calcium oxide powder, and mixing with the ultrafine calcium oxide powder to obtain a calcium oxide emulsion.

[0044] (4) Then, the mixture is mixed with water accounting for 45% of the weight of the calcium oxide powder and stirred. After the reaction is completed, the obtained powder is dried at 150°C and then selected by a cyclone powder separator to separate the microspheres used in the ball mill and other impurities to obtain nano calcium hydroxide. The obtained nano calcium hydroxide is characterized by a scanning electron microscope. Under the optimal conditions, the average size of the obtained calcium hydroxide is about 100 nm. Figure 3 As shown, the measured specific surface area is 75.1m 2 / g.

Claims

1. A method for preparing nano calcium hydroxide with controllable particle size, characterized in that: The method comprises the following steps, (1) crushing calcium oxide to obtain calcium oxide powder with a maximum particle size not exceeding 5 mm; (2) ball milling the calcium oxide powder or the mixture of the calcium oxide powder and the grinding aid to obtain an ultrafine calcium oxide powder having an average particle size not exceeding 50 μm; (3) mixing the ultrafine calcium oxide powder and the liquid dispersant uniformly to obtain a calcium oxide viscous slurry or a calcium oxide emulsion; (4) adding water to the calcium oxide viscous slurry or calcium oxide emulsion, stirring, and digesting the calcium oxide to obtain calcium hydroxide; (5) Drying and separating the calcium hydroxide to obtain nano calcium hydroxide.

2. The preparation method according to claim 1, characterized in that: In step (2), the grinding aid is a volatile alcohol organic substance or an alcohol amine organic substance or a mixture of volatile alcohol organic substances and alcohol amine organic substances; in step (3), the liquid dispersant used is a volatile alcohol organic substance or an alcohol amine organic substance or a mixture of volatile alcohol organic substances and alcohol amine organic substances.

3. The preparation method according to claim 1 or 2, characterized in that: In step (2), the weight of the grinding aid added is 0% to 100% of the weight of the calcium oxide powder; in step (3), the weight amount of the liquid dispersant used is at least 5% of the weight of the calcium oxide powder.

4. The preparation method according to claim 2, characterized in that: The volatile alcohol organic matter is one of methanol, ethanol or propanol or a mixture of two or more thereof, and the alcohol amine organic matter is one of methyl alcohol amine and ethyl alcohol amine or a mixture of two or more thereof.

5. The preparation method according to claim 2 or 4, characterized in that: The grinding aid and liquid dispersant used are the same components.

6. The preparation method according to claim 2 or 4, characterized in that: The total weight of the alcohol amine organic matter used in the liquid dispersant and the grinding aid is 0% to 10% of the weight of the calcium oxide powder.

7. The preparation method according to claim 1, characterized in that: The solid microspheres used in the ball milling in step (2) are inorganic microspheres that do not react with calcium oxide and have a harderness than calcium oxide, and the particle size is between 5 μm and 5 cm.

8. The preparation method according to claim 7, characterized in that: The inorganic microspheres are one or a mixture of two or more of silicon dioxide microspheres, zirconium oxide microspheres, diamond microspheres, silicon carbide microspheres, metal microspheres and ceramic microspheres.

9. The preparation method according to claim 1, characterized in that: In step (4), the weight of water added is 35% to 150% of the weight of the calcium oxide powder.

10. The preparation method according to claim 1, characterized in that: In step (1), the effective calcium content by weight of the calcium oxide used is greater than 90%, and the magnesium content by weight is less than 5%; in step (3), the ultrafine calcium oxide powder and the liquid dispersant are uniformly mixed by stirring in a closed container; in step (5), the calcium hydroxide is dried by heating or vacuum drying in a closed container, and then the nano calcium hydroxide and microspheres are separated.

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