WO2017075990A1 - Method for preparing superfine zinc oxide powder - Google Patents

Abstract

A method for preparing superfine zinc oxide powder. Crude particle zinc oxide or metal zinc is used as a raw material; an organic acid zinc salt solution is generated by means of organic acid dissolution; oxalic acid is added to generate zinc oxalate sediment; filtering is carried out to obtain zinc oxalate solid and organic acid; organic acid is used as a raw material for dissolving the crude particle zinc oxide or metal zinc in the next batch; and the zinc oxalate is calcined to obtain uniform-particle zinc oxide powder. In the method, no waste liquid or waste solids are discharged in the preparation process, and the average particle size of particles of obtained zinc oxide powder ranges from 30 nm to 200 nm in average and can be adjusted by means of the raw material proportion.

Description

Preparation method of ultrafine zinc oxide powder Technical field

The invention belongs to the field of preparation of ultrafine powder materials, and relates to a preparation method of environment-friendly ultrafine zinc oxide powder.

Background technique

Zinc oxide powder is a white powder with high refractive index, excellent thermal conductivity, antibacterial and anti-ultraviolet properties, and is widely used. In the fields of plastics, synthetic rubber, paints, papermaking, etc., zinc oxide is widely used as a covering agent and a coloring agent, commonly known as zinc white; in cosmetics sunscreen, zinc oxide acts as a sunscreen to block ultraviolet rays. Zinc oxide has excellent ambient temperature luminescence properties and is widely used in the semiconductor field, such as liquid crystal displays, thin film transistors, and light-emitting diodes. In the field of food and medicine, zinc oxide is used as a nutritional supplement, an antibacterial agent, and an astringent. Zinc oxide is also used as a component of the desulfurizer in the chemical industry.

The application of zinc oxide in the above various fields often has certain requirements on the distribution of particle size and particle size. For example, the application of zinc oxide in coatings generally uses micron-sized zinc oxide; as an antibacterial use, generally, the smaller the particle size, the better the antibacterial effect; and as a sunscreen, the particle size is generally required to be about 100 nm. The narrow distribution of the particle size distribution of zinc oxide products is more desirable because the narrow distribution imparts a more uniform performance to the particles.

Common zinc oxide production methods include direct method, indirect method and wet method.

The direct method is also called the "Wei's furnace" method, because it first appeared in the United States, also known as the "American law." Direct production of zinc oxide has the advantages of lower cost and high thermal efficiency. The zinc-containing raw material is reduced by carbonaceous material mainly composed of coal at 1000 to 1200 °C. The zinc vapor and CO contained in the combustion gas are introduced into the oxidation equipment to complete the oxidation reaction, and then passed through a heat exchanger, cooled, and then passed into a bag separator to collect the finished product. The zinc oxide produced by the direct method is a needle-like structure and is a micron industrial grade zinc oxide. The impurities in the direct process zinc oxide preparation process are not completely separated, the whiteness is not good, and the price on the market is also low.

The indirect method originated in France and is also known as the "French law." Industrially, the indirect method for producing ZnO is to first melt the zinc block at a high temperature and evaporate it into zinc vapor, thereby oxidizing to form ZnO. The purity of the product is related to the purity of the zinc block used.

Among the above two methods, the direct method has no impurity removal process, the purity of zinc oxide produced is not very high, and the particle size and distribution are not properly controlled; the indirect method uses high-purity zinc ingot as raw material to obtain high-purity zinc oxide. However, the particle size is generally on the order of micrometers, and the particle size distribution is also wide.

In order to improve the quality of zinc oxide, many methods have been used for improvement. Wet production of zinc oxide is a common method. The zinc oxide produced by this type of method has a large specific surface area, so it is also called active ZnO.

The common wet zinc oxide preparation process uses zinc sulfate ZnSO ₄ or zinc chloride ZnCl ₂ as raw materials, removes impurities, and adds sodium carbonate Na ₂ CO ₃ solution to form basic zinc carbonate Zn ₂ (OH) ₂ CO ₃ precipitate. After repeated rinsing and filtration, the impurity ions are removed, mainly to remove sulfate ions, chloride ions, sodium ions, etc., and the ionic strength of the water washing liquid is continuously decreased with the washing process, and is reduced to a certain degree, and then dried and baked at a high temperature. ZnO is obtained, and this method is also called sodium carbonate method. The purity of the zinc oxide powder obtained by the wet method depends not only on the zinc sulfate ZnSO ₄ or the zinc chloride ZnCl ₂ raw material but also on the degree of water washing. If the washing is not sufficient, sulfate or chloride ions and sodium ions will remain, which will eventually affect the quality of the zinc oxide product. In addition to the sodium carbonate precipitant, the wet method uses sodium bicarbonate, ammonium oxalate, urea, etc. The purpose of using these precipitants is mainly to control the precipitation reaction, thereby controlling the size and distribution of the final zinc oxide particle size. But no matter what precipitant is used, the washing in the process can't be avoided. The water washing process consumes a large amount of water, and the water consumption is 10-100 times of the weight of the product. It needs regeneration or recycling or treatment discharge. The electrolyte concentration, crystallization and treatment of the washing are very expensive and difficult to solve. The washing process is given to the wet chemical method. Brought a lot of trouble. Such a process produces a large amount of waste and consumes a large amount of energy, which does not conform to the concept of green and low carbon.

The Austrian patent (Ausp itzer Otto. Zinkoxyd: AT, 176207 [P]. 1953-09-25) reports a process for preparing basic zinc carbonate by reacting high-purity coarse-grained zinc oxide with carbon dioxide under hydrothermal conditions, and then The zinc oxide particles are obtained by calcination. That is, in an autoclave containing water and high-purity crude zinc oxide particles, carbon dioxide gas is introduced to maintain a certain temperature and pressure, and when the reaction proceeds to a certain content of zinc carbonate, the basic zinc carbonate is separated, and then dried and calcined. An active zinc oxide powder having a particle diameter of about 0.05 μm, a narrow particle size distribution, and high purity was obtained. The advantages and disadvantages of this method are obvious. The advantage is that no impurity ions are introduced, the purity of the product is high, and more importantly, the environmental pressure caused by the water washing process is avoided; the disadvantage is that it needs to be carried out under a higher pressure, equipment investment Large, inconvenient to operate, and then carbon dioxide gas as raw material, high purity carbon dioxide gas is not only inconvenient source, but also requires compression feed.

There are many research methods for the preparation of zinc oxide, such as solid phase grinding, microwave field radiant heating, high frequency induction heating, plasma heating, electron beam heating and laser heating, sputtering, and supergravity. , microemulsion method, etc., these methods are generally inconvenient to operate, not suitable for large-scale industrial production, only stay in the experimental stage.

Summary of the invention

The object of the present invention is to provide a method for preparing ultrafine zinc oxide powder, which is suitable for large-scale production, does not require a water washing process, has no liquid waste and solid waste discharge, and has a uniform particle size distribution and particle size. The size can be adjusted.

In order to achieve the above object, the present invention adopts the following technical scheme: adding coarse zinc oxide powder or metal zinc to an organic acid solution until the zinc oxide particles or metal zinc are completely dissolved as a transparent liquid, and then adding oxalic acid to form a precipitate and filtering. The precipitate and the filtrate are obtained, the precipitate is zinc oxalate, and the precipitate is dried at 80-300 ° C to obtain a white powder, which is dried. The generated gas phase partial condensation recovery is combined with the filtrate; the dried powder is calcined at a temperature of 400-600 ° C for 1-4 hours to obtain an ultrafine zinc oxide powder, and the combined filtrate is an organic acid solution, which is used repeatedly and used directly. The next batch dissolves the coarse zinc oxide particles or metallic zinc.

The organic acid of the present invention is added to dissolve crude zinc oxide or metallic zinc, and the organic acid may be selected from acetic acid, formic acid, benzoic acid, lactic acid, or the like, or a mixture thereof. The amount of organic acid added is based on an aqueous solution in which metal zinc or zinc oxide is completely converted into an organic zinc salt. Excess organic acid can accelerate the dissolution process, but too much excess is also unnecessary, so a suitable ratio is ZnO or Zn: organic Acid (molar ratio) = 1:2:3.

In the method of the invention, the organic acid solution is substantially quantitatively recovered, and the entire preparation process does not produce waste water and solid waste.

The precipitating agent used in the present invention is oxalic acid with or without crystal water.

The ultrafine zinc oxide powder obtained by the method of the invention has a uniform particle size distribution and a controllable particle size. Applicants have found that the average particle size of the ultrafine zinc oxide product can be adjusted by adjusting the molar ratio of the added metal zinc or zinc oxide to oxalic acid to obtain ultrafine zinc oxide having an average particle diameter of 30-200 nm, preferably having a particle diameter of 50. -150nm. Adjusting the ratio of ZnO or Zn to oxalic acid (molar ratio) of 0.5-1.5:1, preferably 0.8-1.2:1, can obtain zinc oxide of the required particle size, and Table 1 lists the ratio of different ZnO or Zn to oxalic acid (molar) The average particle size of the zinc oxide particles.

Table 1

ZnO or Zn: oxalic acid (molar ratio)	Average particle size (unit: nm; deviation ± 5)
0.8	50
0.9	85
1.0	100
1.1	120
1.2	140

Advantageous Effects: The preparation method of the ultrafine zinc oxide powder of the invention has no waste liquid and no waste solid discharge in the process of preparing ultrafine zinc oxide, and the zinc oxide product has controllable particle size and uniform particle size distribution. The invention is suitable for large-scale industrial production, solves the problem of generating a large amount of waste water in the process of preparing ultrafine zinc oxide by the traditional precipitation method, and does not produce other solid waste, is environmentally friendly, and the obtained product has a controllable particle size, because Adding other additives, less impurities, can meet the needs of daily chemical, coating, rubber, electronics, absorbing materials and other fields.

The invention is described in detail below with reference to specific embodiments. The scope of the present invention is not limited to the specific embodiments, but is defined by the claims.

DRAWINGS

Figure 1 is a process flow diagram of the present invention.

Figure 2 is an electron micrograph of zinc oxide particles prepared in Example 1.

Fig. 3 is an electron micrograph of zinc oxide particles prepared by applying the filtrate in Example 1.

Figure 4 is an electron micrograph of zinc oxide particles prepared in Example 2.

Fig. 5 is an electron micrograph of zinc oxide particles prepared by applying the filtrate in Example 2.

Figure 6 is an electron micrograph of zinc oxide particles prepared in Example 3.

Fig. 7 is an electron micrograph of zinc oxide particles prepared by applying the filtrate in Example 3.

Figure 8 is an electron micrograph of zinc oxide particles prepared in Example 4.

Figure 9 is an electron micrograph of zinc oxide particles prepared after the filtrate was applied in Example 4.

Figure 10 is an electron micrograph of zinc oxide particles prepared in Example 5.

Figure 11 is an electron micrograph of zinc oxide particles prepared after the filtrate was applied in Example 5.

Figure 12 is an electron micrograph of zinc oxide particles prepared in Example 6.

Figure 13 is an electron micrograph of zinc oxide particles prepared after the filtrate was applied in Example 6.

Figure 14 is an electron micrograph of zinc oxide particles prepared in Example 7.

Figure 15 is an electron micrograph of zinc oxide particles prepared after the filtrate was applied in Example 7.

detailed description

The technical solutions of the present invention are further described in detail below by way of specific embodiments, but it is necessary to point out that the following examples are only for the description of the invention and are not intended to limit the scope of the invention.

Example 1

27.67 kg (340 mol) of coarse-grained zinc oxide powder was slowly added to 242.86 liters, and the concentration was 2.8 mol/L acetic acid solution (containing 680 mol of acetic acid). After stirring, the zinc oxide particles gradually dissolved completely into a transparent liquid, and then added 42.86 kg. Oxalic acid dihydrate (340 moles) was formed as a white precipitate which was filtered to give a precipitate cake and filtrate.

The precipitated cake was dried at 105 ° C to give a white powder. The white powder obtained by drying was calcined at a temperature of 500 to 600 ° C for 1.5 hours to obtain 27 kg of an average particle diameter of 100 nm of zinc oxide powder. The powder electron micrograph is shown in Figure 2.

The filtrate was tested for acidity, and the addition of glacial acetic acid and water was added to form a 242.86 liter 2.8 mol/L acetic acid solution. The above process was repeated to obtain an average particle size of 27 nm of ultra-fine zinc oxide powder of 101 nm. The powder electron micrograph is shown in Figure 3.

Example 2

27.67 kg (340 mol) of coarse-grained zinc oxide powder was slowly added to 242.86 liters, and the concentration was 3.0 mol/L benzoic acid solution (containing 728.6 mol of benzoic acid). The zinc oxide particles were gradually dissolved completely into a transparent liquid under stirring, and then added to 42.86. Kilograms of oxalic acid dihydrate (340 moles) were formed with a white precipitate which was filtered to give a precipitate and filtrate.

The precipitated cake was dried at 105 ° C to give a white powder. The white powder obtained by drying was calcined at a temperature of 500 to 600 ° C for 2 hours to obtain 27.67 kg of an ultrafine powder of zinc oxide having an average particle diameter of 103 nm. The powder electron micrograph is shown in Figure 4.

The filtrate was tested for acidity, and the benzoic acid and water were added to form 242.86 liters of a 3.0 mol/L benzoic acid solution. The above process was repeated to obtain an average particle size of 98 nm zinc oxide ultrafine powder of 27.67 kg. The powder electron micrograph is shown in Figure 5.

Example 3

27.67 kg (340 mol) of coarse-grained zinc oxide powder was slowly added to 242.86 liters, the concentration was 3.36 mol / L acetic acid solution (containing 816 moles of acetic acid), and the zinc oxide particles gradually dissolved completely into a transparent liquid under stirring, and then added 38.57 kg. Oxalic acid dihydrate (306 moles) was formed as a white precipitate which was filtered to give a precipitate and filtrate.

The precipitated cake was dried at 105 ° C to give a white powder. The white powder obtained by drying was calcined at a temperature of 500 to 600 ° C for 4 hours to obtain 27 kg of an ultrafine powder of zinc oxide having an average particle diameter of 85 nm. The powder electron micrograph is shown in Figure 6.

The filtrate was tested for acidity, and acetic acid and water were added to form 242.86 liters of 2.8 mol/L acetic acid solution. The above process was repeated to obtain an average particle size of 87 nm zinc oxide ultrafine powder of 27 kg. The powder electron micrograph is shown in Figure 7.

Example 4

27.67 kg (340 mol) of coarse-grained zinc oxide powder was slowly added to 242.86 liters, and the concentration was 3.08 mol/L formic acid solution (containing 748 mol of formic acid). The zinc oxide particles were gradually dissolved completely into a transparent liquid under stirring, and then 47.15 kg was added. Oxalic acid dihydrate (374 moles) was formed as a white precipitate which was filtered to give a precipitate and filtrate.

The precipitated cake portion was dried at 105 ° C to obtain a white powder. The white powder obtained by drying was calcined at a temperature of 500 to 600 ° C for 2 hours to obtain 27 kg of an ultrafine powder of zinc oxide having an average particle diameter of 121 nm. The powder electron micrograph is shown in Figure 8.

The filtrate was tested for acidity, and the formic acid and water were added to form a 242.86 liter 2.8 mol/L concentrated formic acid solution. The above process was repeated to obtain an average particle size of 123 nm of ultrafine zinc oxide powder of 123 nm. The powder electron micrograph is shown in Figure 9.

Example 5

27.67 kg (340 mol) of coarse-grained zinc oxide powder was slowly added to 242.86 liters, and the concentration was 2.8 mol/L lactic acid solution (containing 680 mol of lactic acid). After stirring, the zinc oxide particles gradually dissolved completely into a transparent liquid, and then added 47.15 kg. Oxalic acid dihydrate (374 moles) was formed as a white precipitate which was filtered to give a precipitate and filtrate.

The precipitated cake portion was dried at 105 ° C to obtain a white powder. The white powder obtained by drying was calcined at a temperature of 500 to 600 ° C for 2 hours to obtain 27.67 kg of an ultrafine powder of zinc oxide having an average particle diameter of 141 nm. The powder electron micrograph is shown in Figure 10.

The filtrate was tested for acidity, and the lactic acid and water were added to form 242.86 liters of 2.8 mol/L lactic acid solution. The above process was repeated to obtain an average particle size of 137 nm zinc oxide ultrafine powder of 27.67 kg. The powder electron micrograph is shown in Figure 11.

Example 6

27.67 kg (340 mol) of coarse-grained zinc oxide powder was slowly added to 242.86 liters, and the concentration was 3.052 mol/L acetic acid solution (containing 741.2 mol of acetic acid). After stirring, the zinc oxide particles gradually dissolved completely into a transparent liquid, and then added 34.29 kg. Oxalic acid dihydrate (272 moles) was formed as a white precipitate which was filtered to give a precipitate and filtrate.

The precipitated cake portion was dried at 105 ° C to obtain a white powder. The white powder obtained by drying was calcined at a temperature of 500 to 600 ° C for 1 hour to obtain 27.67 kg of an ultrafine powder of zinc oxide having an average particle diameter of 55 nm. The powder electron micrograph is shown in Figure 12.

The filtrate was tested for acidity, and the addition of glacial acetic acid and water was added to form a 242.86 liter 2.8 mol/L acetic acid solution. The above process was repeated to obtain an average particle size of 57 nm zinc oxide ultrafine powder of 27.67 kg. The powder electron micrograph is shown in Figure 13.

Example 7

22.23 kg (340 mol) of zinc powder was slowly added to 242.86 liters, the concentration of 4.2mol / L formic acid and benzoic acid mixed solution (containing 510 moles of formic acid, 510 moles of benzoic acid), the zinc oxide particles gradually dissolved completely into a transparent liquid. Further, 47.15 kg of oxalic acid dihydrate (374 mol) was added, and a white precipitate formed, which was filtered to obtain a precipitate and a filtrate.

The precipitated cake was dried at 105 ° C to give a white powder. The white powder obtained by drying was calcined at a temperature of 500 to 600 ° C for 4 hours to obtain 27 kg of an ultrafine powder of zinc oxide having an average particle diameter of 116 nm. The powder electron micrograph is shown in Figure 14.

The filtrate was tested for acidity, and the formic acid and water were added to form a 242.86 liter 2.8 mol/L concentrated formic acid solution. The above process was repeated to obtain an average particle size of 117 nm zinc oxide ultrafine powder of 27 kg. The powder electron micrograph is shown in Figure 15.

Claims (8)

1. A method for preparing ultrafine zinc oxide powder, characterized in that coarse zinc oxide powder or metal zinc is added to an organic acid solution to form an organic zinc salt solution, and then oxalic acid is added to form a white precipitate, which is filtered to obtain a precipitate and The filtrate; the precipitate is zinc oxalate, and the precipitate is dried and calcined to obtain ultrafine zinc oxide powder; the filtrate is an organic acid solution and is repeatedly used.
2. The method for preparing ultrafine zinc oxide powder according to claim 1, wherein the drying temperature is 80-300 ° C, and the condensable gas produced by drying is condensed and recovered and combined into an organic acid solution.
3. The method for producing an ultrafine zinc oxide powder according to claim 1, wherein the calcination temperature is 400 to 600 ° C for a period of 1 to 4 hours.
4. The method for producing an ultrafine zinc oxide powder according to claim 1, wherein the organic acid is one or more selected from the group consisting of acetic acid, formic acid, benzoic acid, and lactic acid.
5. The method for preparing ultrafine zinc oxide powder according to claim 1, wherein the organic acid is used in a ratio of a molar ratio of zinc oxide or zinc to an organic acid of 1:2 to 1: 3.
6. The method for producing ultrafine zinc oxide powder according to claim 1, wherein the oxalic acid is added in a molar ratio of zinc oxide or zinc to oxalic acid of from 0.5 to 1.5:1.
7. The method for producing an ultrafine zinc oxide powder according to claim 6, wherein the coarse particle zinc oxide or the molar ratio of zinc to oxalic acid is from 0.8 to 1.2:1.
8. The method for preparing an ultrafine zinc oxide powder according to claim 1, wherein the ultrafine zinc oxide powder particles prepared by the method have an average particle diameter ranging from 30 nm to 200 nm.

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