Nano calcium hydroxide and preparation method thereof

Abstract

The present application provides a nano calcium hydroxide and a preparation method thereof, relating to the field of nanomaterial technology. The preparation method of the nano calcium hydroxide of the present application comprises: mixing a water-soluble calcium salt, an inhibitor and water to obtain a precursor solution; adding an alkali solution dropwise to the precursor solution and performing a hydrothermal reaction to obtain the nano calcium hydroxide; the inhibitor comprises a polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer. Nano calcium hydroxide with a porous structure inside the particles can be prepared using this preparation method, and the nano particles are highly active and have extremely strong adsorption activity for sulfur dioxide. When applied to cement kiln dry desulfurization, the desulfurization efficiency is high.

Description

Technical Field

[0001] The present application relates to the technical field of nanomaterials, and in particular to nano calcium hydroxide and a preparation method thereof. Background Art

[0002] Calcium hydroxide, commonly known as slaked lime or hydrated lime, is a chemical raw material with a wide range of applications in chemistry, medicine, food, industry, agriculture, and other fields. In particular, it can be used in industry as an environmental neutralizer, acidic wastewater and sewage treatment, and boiler flue gas desulfurization. To improve the performance of calcium hydroxide, increasing the specific surface area of ​​the particles and reducing their size is an effective approach.

[0003] To obtain nanoscale calcium hydroxide, scholars have invented many methods. These can be roughly divided into two categories: top-down method and bottom-up method. The former top-down method mainly adopts the form of crushing and grinding, but this method is time-consuming and energy-consuming, and the yield of nano calcium hydroxide is very low. The bottom-up method is to use chemical methods to obtain nanoscale calcium hydroxide particles through crystal growth. This method mainly includes aqueous solution method, alcohol solution method, microemulsion method, plasma metal method, ion resin exchange method, and calcium carbide and calcium metal method.

[0004] In the prior art, Piero Baglioni et al. pioneered the use of an aqueous solution method to synthesize calcium hydroxide particles and disperse them in an isopropanol solution. However, the calcium hydroxide particles synthesized by this method are large in size, cannot strictly be called nano-calcium hydroxide, and have poor stability. Barbara Salvadori et al. synthesized nano-calcium hydroxide using an alcohol solution method (i.e., adding ethylene glycol or propylene glycol to the precursor). By carefully controlling parameters such as the precursor molar ratio, reaction temperature, alcohol addition amount, and reaction time, they ultimately synthesized nano-calcium hydroxide particles with a size range of 30-150 nm. However, the surface of the nano-calcium hydroxide synthesized by this method easily adsorbs ethylene glycol or propylene glycol; in addition, this method is time-consuming, energy-intensive, and complex to operate. Alessio Nanni et al. synthesized 2-10 nm calcium hydroxide nanoparticles using a microemulsion method. However, the nano-calcium hydroxide synthesized by this method carbonizes too quickly, making it difficult to use for the adsorption of sulfur oxides and nitrogen oxides. The plasma metal method, invented by Tong Liu et al., is a method for synthesizing nano-calcium hydroxide. Although this method produces large quantities and is fast, it requires high equipment requirements and is expensive. People such as Giuliana Taglieri then adopt ion exchange resin method to synthesize regular hexagonal calcium hydroxide particles. Although the calcium hydroxide crystallinity synthesized by this method is good, particle size is larger (about 200nm), and needs to be purified, which is long consuming time. The calcium carbide method is a kind of nano calcium hydroxide synthetic method that people such as Carlos Rodriguez-Navarro have developed and realized industrialized production. This method is simple to operate and has low cost, but the shortcoming is that the synthetic calcium hydroxide particles are larger (about 150nm), poor stability, and need to be further purified, which is long consuming time. Another kind of synthetic method that has realized industrial production and is also the more popular nano calcium hydroxide is the calcium metal method. The advantage of this method is that nano calcium hydroxide can be synthesized in a large amount, and can have good stability, without the need for separation and purification, but the shortcoming is complicated operation (repeated temperature control is needed in the building-up process), and the particle is larger (about 200nm, energy consumption, time consumption, cost are relatively high).

[0005] Although there have been many studies on the preparation of nano-scale calcium hydroxide, these processes are either too expensive, the nanoparticle size is too large, or the product has poor stability, low activity, and poor adsorption performance for sulfur oxides and nitrogen oxides. Therefore, it is necessary to find a low-cost, simple process for the production of nano-calcium hydroxide that has strong adsorption activity for sulfur dioxide. Summary of the Invention

[0006] The purpose of this application is to provide a nano calcium hydroxide and a preparation method thereof. By adding an inhibitor, the dispersibility of the nano calcium hydroxide is improved, the size of the nanoparticles is reduced, and the surface activity of the particles is increased, so that it has extremely strong adsorption activity for sulfur dioxide.

[0007] To achieve the above objectives, the technical solutions of this application are as follows:

[0008] The present application provides a method for preparing nano calcium hydroxide, comprising:

[0009] mixing a water-soluble calcium salt, a polymerization inhibitor, and water to obtain a precursor solution;

[0010] adding alkaline solution dropwise to the precursor solution and performing a hydrothermal reaction to obtain the nano calcium hydroxide;

[0011] The polymerization inhibitor includes a polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer.

[0012] Preferably, the preparation method satisfies at least one of the following conditions:

[0013] a. The water-soluble calcium salt comprises at least one of calcium chloride, calcium bicarbonate, calcium nitrate, calcium dihydrogen phosphate, calcium bromide and calcium iodide;

[0014] b. Ca in the precursor solution 2+ The concentration is 0.4mol / L-1mol / L;

[0015] c. The alkali solution comprises at least one of a sodium hydroxide solution and a potassium hydroxide solution;

[0016] d. OH in the alkali solution - The concentration is 1mol / L-2mol / L.

[0017] Preferably, the preparation method further satisfies at least one of the following conditions:

[0018] e. When the alkali solution is added dropwise, OH in the alkali solution - The amount of substance is Ca in the precursor solution 2+ 1.8-2.2 times the amount of substance;

[0019] f. The addition rate is 40mL / h-80mL / h;

[0020] g. The temperature of the hydrothermal reaction is 180°C-240°C and the time is 8h-14h.

[0021] Preferably, the process of adding the alkali solution dropwise to the precursor solution comprises: continuously stirring the precursor solution during the adding, and continuing stirring for 2 minutes to 5 minutes after the adding is completed to obtain a mixed solution.

[0022] Further preferably, the performing the hydrothermal reaction includes: placing the mixed solution in a reactor to perform the hydrothermal reaction.

[0023] Furthermore, after the hydrothermal reaction, the process further includes: cooling the reactor to room temperature, removing the supernatant, filtering, and washing to obtain a product.

[0024] Optionally, after obtaining the product, the method further comprises: adding a dispersant to the product, mixing evenly, and drying to obtain the nano calcium hydroxide.

[0025] Specifically, at least one of the following conditions is also met:

[0026] h. The dispersant comprises at least one of a polycarboxylate and cetyltrimethylammonium bromide;

[0027] i. The mass of the dispersant is 0.5%-0.8% of the mass of the water-soluble calcium salt;

[0028] j. The drying temperature is 50°C-80°C and the drying time is 8h-12h.

[0029] Preferably, the mass of the polymerization inhibitor is 0.1%-0.3% of the mass of the water-soluble calcium salt.

[0030] The present application also provides a nano calcium hydroxide, which is prepared using the above-mentioned preparation method; the particles of the nano calcium hydroxide contain a pore structure.

[0031] Beneficial effects of this application:

[0032] The preparation method of the present application is based on a hydrothermal method. The process is simple, efficient, and economically feasible. The equipment and instruments used are simple. By adding an inhibitor to the calcium salt solution, when the alkali solution is added dropwise to react to generate calcium hydroxide, the inhibitor can be adsorbed on the surface of the calcium hydroxide particles generated by the reaction, which can not only slow down the continued growth of the nanoparticles, but also improve the dispersibility of the nanoparticles. At the same time, by conducting a hydrothermal reaction in a reactor, nanoparticles with a porous structure, small particle size, high purity, and good dispersibility can be further obtained.

[0033] The nano calcium hydroxide prepared in the present application has a small particle size, and the nanoparticles have a porous structure and high activity, which makes it have extremely strong adsorption activity for sulfur dioxide, and thus has high desulfurization efficiency when applied to cement kiln dry desulfurization. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope of the present invention.

[0035] Figure 1 TEM image of nano sodium hydroxide prepared in Example 1;

[0036] Figure 2 This is a TEM image of the nano-sodium hydroxide prepared in Example 2;

[0037] Figure 3 This is a TEM image of the nano-sodium hydroxide prepared in Example 3;

[0038] Figure 4 This is a TEM image of the nano-sodium hydroxide prepared in Comparative Example 1. DETAILED DESCRIPTION

[0039] As used herein:

[0040] "Prepared from" is synonymous with "comprising." As used herein, the terms "comprising," "including," "having," "containing," or any other variations thereof, are intended to cover a non-exclusive inclusion. For example, a composition, process, method, article, or apparatus that comprises the listed elements is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such composition, process, method, article, or apparatus. The conjunction "consisting of" excludes any unspecified element, step, or component.

[0041] When an amount, concentration, or other value or parameter is expressed as a range, a preferred range, or a range defined by a series of upper preferred values ​​and lower preferred values, this should be understood as specifically disclosing all ranges formed by any pairing of any range upper limit or preferred value with any range lower limit or preferred value, regardless of whether the range is disclosed alone. For example, when a range of "1 to 5" is disclosed, the described range should be interpreted as including the range "1 to 4", "1 to 3", "1 to 2", "1 to 2 and 4 to 5", "1 to 3 and 5", etc. When a numerical range is described herein, unless otherwise stated, the range is intended to include its end values ​​and all integers and fractions within the range.

[0042] In these examples, parts and percentages are by mass unless otherwise indicated.

[0043] "Parts by mass" refers to the basic unit of measurement used to express the mass ratio of multiple components. One part can represent any unit of mass, such as 1g or 2.689g. If we say that the mass of component A is a parts and the mass of component B is b parts, this means the ratio of the mass of component A to the mass of component B is a:b. Alternatively, we could say that the mass of component A is aK and the mass of component B is bK (K is an arbitrary number representing a multiplication factor). It's important to note that, unlike parts by mass, the sum of the mass of all components is not limited to 100 parts.

[0044] "And / or" is used to indicate that one or both of the stated situations may occur, for example, A and / or B includes (A and B) and (A or B).

[0045] The present application provides a method for preparing nano calcium hydroxide, which specifically comprises:

[0046] S1: mixing a water-soluble calcium salt, a polymerization inhibitor and water to obtain a precursor solution;

[0047] S2: adding alkaline solution dropwise to the precursor solution and performing a hydrothermal reaction to obtain the nano calcium hydroxide.

[0048] The polymerization inhibitor in S1 includes a polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer.

[0049] It should be noted that the polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer is a nonionic surfactant that can be used as a template, structure-directing agent, and porogen to prepare nanomaterials with high specific surface area, thereby improving the adsorption capacity of nanomaterials. The addition of the triblock copolymer to the water-soluble calcium salt solution of the present application not only provides a porous structure in the prepared nano-calcium hydroxide particles, thereby increasing the adsorption capacity of the nanoparticles, but also acts as a polymerization inhibitor to further prevent the particle size growth of the nano-calcium hydroxide and improve the dispersibility between the particles.

[0050] In an optional embodiment of the present application, the water-soluble calcium salt in S1 includes at least one of calcium chloride, calcium bicarbonate, calcium nitrate, calcium dihydrogen phosphate, calcium bromide and calcium iodide. More preferably, the water-soluble calcium salt is calcium chloride.

[0051] In an optional embodiment of the present application, the precursor solution in S1 contains Ca 2+ The concentration is 0.4mol / L-1mol / L, for example, it can be 0.4mol / L, 0.5mol / L, 0.6mol / L, 0.7mol / L, 0.8mol / L, 0.9mol / L, 1mol / L or any value between 0.4mol / L and 1mol / L.

[0052] In an optional embodiment of the present application, the mass of the polymerization inhibitor in S1 is 0.1%-0.3% of the mass of the water-soluble calcium salt, for example, it can be 0.1%, 0.2%, 0.3% or any value between 0.1% and 0.3%.

[0053] In an optional embodiment of the present application, the alkali solution in S2 includes at least one of a sodium hydroxide solution and a potassium hydroxide solution. More preferably, the alkali solution is a sodium hydroxide solution.

[0054] In an optional embodiment of the present application, the OH in the alkali solution in S2 - The concentration is 1mol / L-2mol / L, for example, it can be 1mol / L, 0.5mol / L, 1.2mol / L, 1.4mol / L, 1.6mol / L, 1.8mol / L, 2mol / L or any value between 1mol / L and 2mol / L.

[0055] In an optional embodiment of the present application, when the alkali solution is added dropwise in S2, the OH in the alkali solution - The amount of substance is the Ca in the water-soluble calcium salt solution 2+ 1.8-2.2 times, more preferably 2 times the amount of the substance.

[0056] In an optional embodiment of the present application, when the dripping is performed in S2, the dripping rate is 40mL / h-80mL / h, for example, it can be 40mL / h, 50mL / h, 60mL / h, 70mL / h, 80mL / h or any value between 40mL / h-80mL / h.

[0057] In an optional embodiment of the present application, the temperature required for the hydrothermal reaction in S2 is 180℃-240℃, for example, it can be 180℃, 190℃, 200℃, 210℃, 220℃, 230℃, 240℃ or any value between 180℃-240℃; the time is 8h-14h, for example, it can be 8h, 10h, 12h, 14h or any value between 8h-14h.

[0058] In an optional embodiment of the present application, the process of adding the alkali solution in S2 includes: continuously stirring the precursor solution in S1, and then adding the alkali solution to the continuously stirred precursor solution. After the addition is completed, stirring needs to be continued for 2 minutes to 5 minutes to obtain a mixed solution.

[0059] The continued stirring here is mainly to ensure that the reactants in the mixed solution are fully contacted and react to form an initial calcium hydroxide suspension.

[0060] In an optional embodiment of the present application, the process of performing the hydrothermal reaction in S2 includes: placing the mixed solution formed after the dropwise addition is completed in a reactor, and then performing the hydrothermal reaction.

[0061] When placing the mixed solution in the reactor, the mixed solution is placed in the reactor's polytetrafluoroethylene liner, which is then placed in a stainless steel outer sleeve. Finally, the reactor is sealed and placed in a forced air drying oven for reaction. Performing the hydrothermal reaction in the reactor can isolate the interference of external impurities. The polytetrafluoroethylene liner has stable performance and strong acid and alkali resistance, providing a stable environment for the hydrothermal reaction.

[0062] In an optional embodiment of the present application, after the hydrothermal reaction in S2 is completed, the process further includes: cooling the reactor to room temperature, removing the supernatant, filtering, and washing to obtain a product.

[0063] It should be noted that after removing the supernatant in the polytetrafluoroethylene liner, the product can be filtered by suction, and then washed multiple times with deionized water.

[0064] Furthermore, after obtaining the product, the method further comprises: adding a dispersant to the product, mixing evenly, and drying to obtain the nano calcium hydroxide.

[0065] In a preferred embodiment, the dispersant includes at least one of polycarboxylate and cetyltrimethylammonium bromide.

[0066] It should be noted that the product after washing may agglomerate due to the lack of surfactant groups. This application further adds a dispersant to reduce the agglomeration of nanoparticles. Among them, polycarboxylate is a high-performance superplasticizer that can be used to disperse the material slurry; cetyltrimethylammonium bromide is a quaternary ammonium surfactant with hygroscopicity, which can also ensure the stability of nano calcium hydroxide.

[0067] In a preferred embodiment, the mass of the dispersant is 0.5%-0.8% of the mass of the water-soluble calcium salt, for example, it can be 0.5%, 0.6%, 0.7%, 0.8% or any value between 0.5% and 0.8%.

[0068] In a preferred embodiment, the material after the dispersant and the product are evenly mixed is dried, and the required temperature is 50°C-80°C, for example, it can be 50°C, 60°C, 70°C, 80°C or any value between 50°C and 80°C; the time is 8h-12h, for example, it can be 8h, 9h, 10h, 11h, 12h or any value between 8h-12h.

[0069] The present application also provides a nano-sodium hydroxide, which is prepared using the above-mentioned preparation method. The prepared nano-sodium hydroxide particles contain a porous structure.

[0070] The embodiments of the present invention will be described in detail below with reference to specific examples, but those skilled in the art will appreciate that the following examples are intended only to illustrate the present invention and should not be construed as limiting the scope of the present invention. Where specific conditions are not specified in the examples, the methods were performed according to conventional conditions or the conditions recommended by the manufacturer. Where the manufacturers of the reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0071] Example 1

[0072] The nano sodium hydroxide of the present embodiment, the specific preparation method comprises:

[0073] (1) Dissolve 2.22 g of anhydrous calcium chloride in 20 ml of deionized water (Solution A). Weigh 1.6 g of sodium hydroxide in 20 ml of deionized water (Solution B).

[0074] (2) Add the polymerization inhibitor polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer (the mass of which is 0.3% of the mass of anhydrous calcium chloride) to solution A, stir thoroughly, continue stirring after dissolution, and add solution B dropwise thereto while stirring at a dropping rate of 40 mL / h.

[0075] (3) After the addition is completed, the mixture is stirred and reacted for 2 minutes, and then the solution is transferred into the polytetrafluoroethylene liner of the autoclave. The inner sleeve is placed in the stainless steel outer sleeve. The autoclave is sealed and maintained at 200°C in a forced air drying oven for 14 hours.

[0076] (4) Finally, the product was cooled naturally to room temperature, the supernatant was discarded and filtered, and the product was washed several times with deionized water.

[0077] (5) Add polycarboxylate (the mass of which is 0.6% of the mass of anhydrous calcium chloride) to the washed product, mix and stir evenly, and then dry in a vacuum drying oven at 60° C. for 10 hours to obtain a nano-scale calcium hydroxide product.

[0078] Example 2

[0079] The specific preparation method of the nano sodium hydroxide of this embodiment is the same as that of Example 1, except that in step (1), anhydrous calcium chloride is dissolved in 35 ml of deionized water, and sodium hydroxide is dissolved in 30 ml of deionized water; and in step (2), the mass of the inhibitor is 0.2% of the mass of the anhydrous calcium chloride.

[0080] Example 3

[0081] The specific preparation method of the nano sodium hydroxide of this embodiment is the same as that of Example 1, except that in step (1), anhydrous calcium chloride is dissolved in 50 ml of deionized water, and sodium hydroxide is dissolved in 40 ml of deionized water; and in step (2), the mass of the inhibitor is 0.1% of the mass of the anhydrous calcium chloride.

[0082] Comparative Example 1

[0083] The same as Example 1, except that in step (2), no polymerization inhibitor was added to solution A, but solution B was directly added dropwise.

[0084] The calcium hydroxide particles prepared in Examples 1-3 and Comparative Example 1 were subjected to TEM characterization tests. Figure 1 、 Figure 2 、 Figure 3 、 Figure 4 As shown. Figure 1-Figure 3 The results show that the particle size of the prepared nano calcium hydroxide particles is between 50nm and 120nm. The addition of the inhibitor can effectively slow down the continued growth of the nano particles and improve the dispersibility of the nano particles. Figure 1 and Figure 4 By comparing the results of Example 1 with those of Example 1, it can be seen that after adding the polymerization inhibitor, the prepared particles have obvious pore structure and are more dispersed, while in Comparative Example 1, no polymerization inhibitor is added, the prepared particles have no pore structure and the agglomeration between the particles is more serious.

[0085] In addition, the calcium hydroxide granules prepared in Examples 1-3 and Comparative Example 1 were also tested for desulfurization. Specifically, a 100 kg sample of calcium hydroxide granule powder was delivered to the outlet of a high-temperature blower on a cement production line and mixed with the flue gas. The desulfurization effect was evaluated by parameters such as the reduction of sulfur dioxide emissions to a minimum and the reaction time. The final test results are shown in Table 1.

[0086] Table 1 Desulfurization test results of calcium hydroxide prepared in Examples 1-3 and Comparative Example 1

[0087]

[0088] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

[0089] Furthermore, those skilled in the art will appreciate that although some embodiments herein include certain features included in other embodiments but not others, combinations of features from different embodiments are intended to be within the scope of the present invention and to form different embodiments. For example, any of the above-described claimed embodiments may be used in any combination. The information disclosed in this background section is intended solely to enhance understanding of the overall background of the present invention and should not be construed as an admission or any form of implication that such information constitutes prior art known to those skilled in the art.

Claims

1. A method for preparing nano calcium hydroxide, characterized in that, include: mixing a water-soluble calcium salt, a polymerization inhibitor, and water to obtain a precursor solution; adding an alkaline solution dropwise to the precursor solution and performing a hydrothermal reaction; The step of adding the alkali solution dropwise to the precursor solution comprises: continuously stirring the precursor solution during the adding step, and continuing stirring for 2 minutes to 5 minutes after the adding step is completed to obtain a mixed solution; The hydrothermal reaction comprises: placing the mixed solution in a reactor to carry out the hydrothermal reaction; The polymerization inhibitor includes a polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer; After the hydrothermal reaction, the process further comprises: cooling the reactor to room temperature, removing the supernatant, filtering, and washing to obtain a product; After obtaining the product, the method further comprises: adding a dispersant to the product, mixing evenly, and drying to obtain the nano calcium hydroxide; The dispersant includes at least one of polycarboxylate and cetyltrimethylammonium bromide; The mass of the polymerization inhibitor is 0.1%-0.3% of the mass of the water-soluble calcium salt.

2. The preparation method according to claim 1, wherein At least one of the following conditions is met: a. The water-soluble calcium salt comprises at least one of calcium chloride, calcium bicarbonate, calcium nitrate, calcium dihydrogen phosphate, calcium bromide and calcium iodide; b. Ca in the precursor solution 2+ The concentration is 0.4mol / L-1mol / L; c. The alkali solution comprises at least one of a sodium hydroxide solution and a potassium hydroxide solution; d. OH in the alkali solution - The concentration is 1mol / L-2mol / L.

3. The preparation method according to claim 1, wherein At least one of the following conditions is also met: e. When the alkali solution is added dropwise, OH in the alkali solution - The amount of substance is Ca in the precursor solution 2+ 1.8-2.2 times the amount of substance; f. The addition rate is 40mL / h-80mL / h; g. The temperature of the hydrothermal reaction is 180°C-240°C and the time is 8h-14h.

4. The preparation method according to any one of claims 1 to 3, wherein At least one of the following conditions is met: i. The mass of the dispersant is 0.5%-0.8% of the mass of the water-soluble calcium salt; j. The drying temperature is 50°C-80°C and the drying time is 8h-12h.

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