Nanometer layered porous calcium hydroxide and preparation method and application thereof

Abstract

The application provides nano-layered porous calcium hydroxide and a preparation method and application thereof. The preparation method of the nano-layered porous calcium hydroxide is based on an alcohol solution method, and the process method is simple, efficient, economic and feasible; the equipment and instrument required are simple, and the digestion reaction can be quickly completed at room temperature without adding high-priced polymerization inhibitors and lye. The nano calcium hydroxide prepared by the application has a layered porous structure, the particle size reaches the nanometer scale, the size is uniform, the dispersibility is good, and the specific surface area can reach 40 m 2 / g or more. The prepared calcium hydroxide material can efficiently remove low-concentration SO2, is generally applicable to the dry desulfurization process of small and medium-sized enterprises, and can effectively reduce the investment and operation cost compared with other flue gas purification methods.

Description

Technical Field

[0001] This invention relates to the field of dry desulfurization technology, and in particular to a nano-layered porous calcium hydroxide, its preparation method, and its application. Background Technology

[0002] With increasingly stringent national environmental protection requirements, the need for emission reduction of acidic pollutants such as SO2 from biomass boilers and industries such as coking, metallurgy, and cement is becoming increasingly urgent. These industries are predominantly composed of small and medium-sized enterprises with relatively low SO2 and other acidic emissions. While conventional wet and semi-dry desulfurization methods can achieve efficient and stable desulfurization, their construction and operating costs are relatively high. In contrast, dry desulfurization processes are simpler, require less equipment investment, have shorter retrofitting cycles, generate no wastewater or waste residue during operation, eliminate corrosion and scaling problems, have low heat loss, and are economical and environmentally friendly, thus possessing significant market application potential.

[0003] Dry desulfurization processes typically use absorbents in powder, granular, or gaseous form. The principle primarily involves a chemical reaction on the surface of the adsorbent, converting SO2 in the flue gas into compounds, thereby removing SO2. Currently, commonly used dry desulfurization absorbents are sodium bicarbonate and calcium hydroxide. Sodium bicarbonate exhibits high desulfurization efficiency within a certain temperature range, but suffers from high cost and difficulty in treating and utilizing byproducts. While ordinary calcium-based absorbents produce relatively easy-to-treat byproducts, they also have drawbacks such as relatively low desulfurization efficiency and excessive dosage. Therefore, optimizing the preparation process of calcium-based absorbents and improving the specific surface area and desulfurization efficiency of calcium hydroxide materials are crucial for the promotion and application of dry desulfurization technology.

[0004] Existing technologies have limitations and shortcomings: Nanoscale calcium hydroxide materials exhibit high dispersibility and typically possess a high specific surface area, which is beneficial for increasing the gas-liquid contact area and improving desulfurization efficiency. Aqueous digestion is a conventional method for constructing calcium hydroxide materials. However, Ca(OH)₂ crystals are extremely polar, and during aqueous digestion, crystal particles easily grow, making it difficult to form nanoscale Ca(OH)₂ crystals. To reduce the Ca(OH)₂ crystal particle size, researchers have successively developed composite preparation methods such as microemulsion methods, hydrothermal methods, and microemulsion-hydrothermal methods. However, these methods still have drawbacks, such as large synthesized nanoparticle size and relatively low specific surface area (generally <15 μm). 2 / g), the product preparation steps are cumbersome.

[0005] Therefore, it is of great significance to develop a simple and low-cost method to synthesize Ca(OH)2 nanoparticles with small size and ideal morphology. Summary of the Invention

[0006] In view of this, the present invention provides a nano-layered porous calcium hydroxide, its preparation method and application, to solve or at least partially solve the defects existing in the prior art.

[0007] In a first aspect, the present invention provides a method for preparing nano-layered porous calcium hydroxide, comprising the following steps:

[0008] Quicklime was added to an alcohol solution for coating to obtain the first precursor slurry.

[0009] The first precursor slurry was added to water to carry out a digestion reaction, resulting in the second precursor slurry.

[0010] The second precursor slurry was subjected to solid-liquid separation, and the resulting solid was dried to obtain nano-layered porous calcium hydroxide.

[0011] Preferably, in the method for preparing the nanolayered porous calcium hydroxide, the alcohol solution includes one or two of ethanol, n-butanol, and diethylene glycol.

[0012] Preferably, in the method for preparing the nanolayered porous calcium hydroxide, the alcohol solution comprises a mixture of ethanol and n-butanol, wherein the volume ratio of ethanol to n-butanol is (0.5-3.5):(0.5-3.5).

[0013] Alternatively, the alcohol solution comprises a mixture of ethanol and diethylene glycol, wherein the volume ratio of ethanol to diethylene glycol is (0.5–3.5):(0.5–3.5);

[0014] Alternatively, the alcohol solution may comprise a mixture of n-butanol and diethylene glycol, wherein the volume ratio of n-butanol to diethylene glycol is (0.5–3.5):(0.5–3.5).

[0015] Preferably, in the method for preparing the nanolayered porous calcium hydroxide, the concentration of quicklime in the first precursor slurry is 1-10 g / mL.

[0016] Preferably, in the preparation method of the nano-layered porous calcium hydroxide, quicklime is added to an alcohol solution for coating, and the coating time is 0.5 to 4 hours.

[0017] Preferably, in the method for preparing nano-layered porous calcium hydroxide, in the step of adding the first precursor slurry to water for digestion reaction, the mass of water is 1 to 5 times the mass of quicklime.

[0018] Preferably, in the preparation method of the nano-layered porous calcium hydroxide, in the step of adding the first precursor slurry to water for digestion reaction, the digestion reaction temperature is 40-80℃ and the time is 10-120min.

[0019] Preferably, the method for preparing the nanolayered porous calcium hydroxide involves solid-liquid separation of the second precursor slurry and drying of the resulting solid, wherein the drying temperature is 40–80°C and the drying time is 12–48 h.

[0020] Secondly, the present invention also provides a nano-layered porous calcium hydroxide, which is prepared by the preparation method described above.

[0021] Thirdly, the present invention also provides the application of the nano-layered porous calcium hydroxide prepared by the preparation method described above, or the nano-layered porous calcium hydroxide described above, as a desulfurization absorbent.

[0022] The method for preparing nano-layered porous calcium hydroxide of the present invention has the following advantages over the prior art:

[0023] 1. The preparation method of nano-layered porous calcium hydroxide of the present invention is based on the alcohol solution method. The process is simple, efficient, economical, and feasible. The equipment and instruments used are simple, and there is no need to add high-cost polymerization inhibitors or alkali solutions. The digestion reaction can be completed rapidly at room temperature. The nano-calcium hydroxide prepared by the present invention has a layered porous structure, with particle size reaching the nanoscale, uniform size, good dispersibility, and a specific surface area of ​​up to 40 m². 2 / g or more. The prepared calcium hydroxide material can efficiently remove low concentrations of SO2 and is widely applicable to dry desulfurization processes in small and medium-sized enterprises. Compared with other flue gas purification methods, it can effectively reduce investment and operating costs;

[0024] 2. The preparation method of nanolayered porous calcium hydroxide of the present invention uses ethanol, diethylene glycol, or a composite alcohol of ethanol and diethylene glycol to pretreat quicklime, which effectively improves the dry desulfurization efficiency of Ca(OH)2 material and significantly prolongs the penetration time of the desulfurizing agent. Among them, the pretreatment effect of ethanol and diethylene glycol composite alcohol is the best. The reason is that the pretreatment of quicklime with ethanol and diethylene glycol composite alcohol can generate a coating layer on the surface of quicklime, effectively reducing the digestion reaction rate and inhibiting the rapid growth of Ca(OH)2 crystals. By reducing the crystallinity of Ca(OH)2 material, more crystal structure defects are induced, promoting the absorption reaction of SO2. It induces Ca(OH)2 to form nanorods, nanolayers, and regular nanosheets and other nanomorphic structures, increases the specific surface area of ​​Ca(OH)2, and provides more reaction temperature for SO2 absorption reaction. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 The X-ray diffraction (XRD) patterns of the Ca(OH)2 materials prepared in Examples 1-3 and Comparative Example 1 of this invention are shown below.

[0027] Figure 2 The images are scanning electron microscope (SEM) images of the Ca(OH)2 materials prepared in Examples 1-3 and Comparative Example 1 of this invention.

[0028] Figure 3 This is a transmission electron microscope (TEM) image of the Ca(OH)2 material prepared in Example 3 of the present invention;

[0029] Figure 4 The graph shows the change of SO2 concentration with reaction time during the desulfurization process of Ca(OH)2 materials prepared by different methods in Examples 1-3 and Comparative Example 1 of this invention.

[0030] Figure 5 The graph shows the change in SO2 removal efficiency with reaction time during the desulfurization process of Ca(OH)2 materials prepared by different methods in Examples 1-3 and Comparative Example 1 of this invention. Detailed Implementation

[0031] The technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0032] It should be noted that the order of description of the following embodiments is not intended to limit the preferred order of embodiments. Furthermore, in the description of this application, the term "comprising" means "including but not limited to". Various embodiments of the present invention may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a rigid limitation on the scope of the invention; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single digits within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Additionally, whenever a numerical range is indicated herein, it means including any referenced number (fraction or integer) within the indicated range.

[0033] This invention provides a method for preparing nano-layered porous calcium hydroxide, comprising the following steps:

[0034] S1. Quicklime is added to an alcohol solution for coating to obtain the first precursor slurry;

[0035] S2. The first precursor slurry is added to water to carry out a digestion reaction to obtain the second precursor slurry.

[0036] S3. The second precursor slurry is subjected to solid-liquid separation, and the resulting solid is dried to obtain nano-layered porous calcium hydroxide.

[0037] The method for preparing nano-layered porous calcium hydroxide of the present invention uses quicklime whose main component is calcium oxide (CaO). Quicklime is added to an alcohol solution for coating to obtain a first precursor slurry. The first precursor slurry is then added to water for a digestion reaction to obtain a second precursor slurry. The second precursor slurry undergoes solid-liquid separation, and the resulting solid is dried to obtain nano-layered porous calcium hydroxide. Specifically, the solid-liquid separation can be centrifugation. The method for preparing nano-layered porous calcium hydroxide of the present invention is based on an alcohol solution method. The process is simple, efficient, economical, and feasible. The equipment and instruments used are simple, requiring no high-valent polymerization inhibitors or alkali solutions. The digestion reaction can be completed rapidly at room temperature. The nano-calcium hydroxide prepared by the present invention exhibits a layered porous structure with nanoscale particle size, uniform size, good dispersibility, and a specific surface area of ​​up to 40 m². 2 The prepared calcium hydroxide material can efficiently remove low concentrations of SO2 and is widely applicable to dry desulfurization processes in small and medium-sized enterprises. Compared with other flue gas purification methods, it can effectively reduce investment and operating costs.

[0038] In some embodiments, the alcohol solution includes one or two of ethanol, n-butanol, and diethylene glycol.

[0039] In some embodiments, the alcohol solution comprises a mixture of ethanol and n-butanol, wherein the volume ratio of ethanol to n-butanol is (0.5–3.5):(0.5–3.5).

[0040] In some embodiments, the alcohol solution comprises a mixture of ethanol and diethylene glycol, wherein the volume ratio of ethanol to diethylene glycol is (0.5–3.5):(0.5–3.5).

[0041] In some embodiments, the alcohol solution comprises a mixture of n-butanol and diethylene glycol, wherein the volume ratio of n-butanol to diethylene glycol is (0.5–3.5):(0.5–3.5).

[0042] The method for preparing nanolayered porous calcium hydroxide of the present invention involves pretreating quicklime with ethanol, diethylene glycol, or a composite of ethanol and diethylene glycol. This effectively improves the dry desulfurization efficiency of Ca(OH)2 materials and significantly prolongs the penetration time of the desulfurizing agent. Among these methods, the pretreatment with the composite of ethanol and diethylene glycol yields the best results. This is because the pretreatment of quicklime with the composite of ethanol and diethylene glycol generates a coating layer on the surface of the quicklime, effectively reducing the digestion reaction rate and inhibiting the rapid growth of Ca(OH)2 crystals. By reducing the crystallinity of Ca(OH)2 materials, more crystal structure defects are induced, promoting the absorption reaction of SO2. Furthermore, the method induces the formation of nanorods, nanolayers, and regular nanosheets in Ca(OH)2, increasing the specific surface area of ​​Ca(OH)2 and providing more reaction temperature for the SO2 absorption reaction.

[0043] In some embodiments, the concentration of quicklime in the first precursor slurry is 1–10 g / mL.

[0044] In some embodiments, quicklime is added to an alcohol solution for coating, and the coating time is 0.5 to 4 hours.

[0045] In some embodiments, in the step of adding the first precursor slurry to water to carry out the digestion reaction, the mass of water is 1 to 5 times the mass of quicklime.

[0046] Specifically, the first precursor slurry is added to water, and the water used is deionized water.

[0047] In some embodiments, in the step of adding the first precursor slurry to water for digestion, the digestion temperature is 40–80°C and the time is 10–120 min.

[0048] In some embodiments, the second precursor slurry is subjected to solid-liquid separation, and the resulting solid is dried, wherein the drying temperature is 40–80°C and the drying time is 12–48 h.

[0049] Based on the same inventive concept, the present invention also provides a nano-layered porous calcium hydroxide, which is prepared by the above-described preparation method.

[0050] Based on the same inventive concept, the present invention also provides the application of nano-layered porous calcium hydroxide prepared by the above preparation method or the above-mentioned nano-layered porous calcium hydroxide as a desulfurization absorbent.

[0051] Specifically, the nano-layered porous calcium hydroxide of the present invention is suitable for dry desulfurization processes in small and medium-sized enterprises.

[0052] The following specific embodiments further illustrate the nano-layered porous calcium hydroxide of the present invention, its preparation method, and its applications. This section further illustrates the content of the present invention in conjunction with specific embodiments, but should not be construed as limiting the present invention. Unless otherwise specified, the technical means used in the embodiments are conventional means well known to those skilled in the art. Unless otherwise specified, the reagents, methods, and equipment used in the present invention are conventional reagents, methods, and equipment in the art.

[0053] Example 1

[0054] This application provides a method for preparing nano-layered porous calcium hydroxide, comprising the following steps:

[0055] S1. Add 10g of quicklime (i.e. CaO) to 4mL of ethanol and coat for 2h to obtain the first precursor slurry.

[0056] S2. Add 18 mL of deionized water to the first precursor slurry in S1 and digest it at 60 °C for 15 min to obtain the second precursor slurry.

[0057] S3. Centrifuge the second precursor slurry in S2 to separate the solid. Dry the obtained solid at 60°C for 30 hours to obtain nano-layered porous calcium hydroxide material.

[0058] Example 2

[0059] This application provides a method for preparing nano-layered porous calcium hydroxide, comprising the following steps:

[0060] S1. Add 10g of quicklime (i.e. CaO) to 4mL of diethylene glycol and coat for 2h to obtain the first precursor slurry.

[0061] S2. Add 18 mL of deionized water to the first precursor slurry in S1 and digest it at 60 °C for 15 min to obtain the second precursor slurry.

[0062] S3. Centrifuge the second precursor slurry in S2 to separate the solid. Dry the obtained solid at 60°C for 30 hours to obtain nano-layered porous calcium hydroxide material.

[0063] Example 3

[0064] This application provides a method for preparing nano-layered porous calcium hydroxide, comprising the following steps:

[0065] S1. Add 10g of quicklime (i.e., CaO) to 4mL of alcohol solution and coat for 2h to obtain the first precursor slurry; wherein the alcohol solution includes a mixture of ethanol and diethylene glycol, wherein the volume ratio of ethanol to diethylene glycol is 3.5:0.5.

[0066] S2. Add 18 mL of deionized water to the first precursor slurry in S1 and digest it at 60 °C for 15 min to obtain the second precursor slurry.

[0067] S3. Centrifuge the second precursor slurry in S2 to separate the solid. Dry the obtained solid at 60°C for 30 hours to obtain nano-layered porous calcium hydroxide material.

[0068] Comparative Example 1

[0069] This comparative example provides a method for preparing calcium hydroxide, comprising the following steps:

[0070] S1. Add 10g of quicklime (i.e. CaO) to 18mL of deionized water and digest it at 60℃ for 15min to obtain the precursor slurry.

[0071] S1. Centrifuge the precursor slurry in S1 to separate the solid. Dry the solid at 60°C for 30 hours to obtain calcium hydroxide material.

[0072] Performance testing

[0073] The Ca(OH)₂ materials prepared in Examples 1-3 and Comparative Example 1 were characterized by X-ray diffraction (XRD). The characterization results are as follows: Figure 1 As shown. Figure 1 In the examples, (a) is Example 1, (b) is Example 2, (c) is Example 3, and (d) is Comparative Example 1.

[0074] Will Figure 1Comparing curves (a), (b), (c), and (d), it can be seen that the Ca(OH)₂ produced in Comparative Example 1, without the addition of alcohol or a complex alcohol solution, has the highest crystallinity, indicating the formation of large-scale aggregated Ca(OH)₂. Examples 1-3 pretreated quicklime in ethanol, diethylene glycol, or a complex alcohol solution of ethanol and diethylene glycol, which to varying degrees inhibited the particle aggregation of Ca(OH)₂ during growth, thus facilitating the construction of Ca(OH)₂ nanomaterials. The pretreatment with diethylene glycol, ethanol, or a complex alcohol solution of diethylene glycol showed the best effect.

[0075] The Ca(OH)₂ materials prepared in Examples 1-3 and Comparative Example 1 were characterized by scanning electron microscopy (SEM). The characterization results are as follows: Figure 2 As shown. Figure 2 In the examples, (a) is Example 1, (b) is Example 2, (c) is Example 3, and (d) is Comparative Example 1.

[0076] Will Figure 2 A comparison of (a), (b), (c), and (d) shows that in Comparative Example 1, without the addition of alcohol or a complex alcohol solution, the generated Ca(OH)₂ particles are uneven in size, with large-scale aggregated Ca(OH)₂ particles forming. In Example 1, coating quicklime in an ethanol solution before the digestion reaction effectively inhibits the aggregation of Ca(OH)₂, which is beneficial for constructing Ca(OH)₂ nanomaterials. The resulting Ca(OH)₂ material exhibits a nanorod-like structure with a size of approximately 20 nm × 100 nm. In Example 2, coating quicklime in a diethylene glycol solution before the digestion reaction, and the diethylene glycol pretreatment, facilitates the formation of nano-thin layered materials of Ca(OH)₂, which is beneficial for increasing the specific surface area of ​​the Ca(OH)₂ material. In Example 3, quicklime was coated in a composite alcohol solution of ethanol and diethylene glycol, and then subjected to a digestion reaction. After pretreatment with the composite alcohol of ethanol and diethylene glycol, the prepared Ca(OH)2 material integrated the advantages of ethanol pretreatment and diethylene glycol pretreatment, forming a nanosheet material with regular morphology and uniform size.

[0077] The Ca(OH)₂ material prepared in Example 3 was characterized by transmission electron microscopy (TEM), and the characterization results are as follows: Figure 3 As shown.

[0078] from Figure 3 As can be seen, the Ca(OH)2 material prepared in Example 3 has a regular pore structure, which is beneficial to providing sufficient reaction sites for SO2 and promoting the improvement of dry desulfurization efficiency.

[0079] The Ca(OH)₂ materials prepared in Examples 1-3 and Comparative Example 1 were characterized by nitrogen adsorption-desorption, and their specific surface areas were compared. The specific surface areas of the Ca(OH)₂ obtained in Examples 1-3 and Comparative Example 1 were 14.5 m² / s². 2 / g, 27.5m² / g, 25.7m 2 / g, 13.3g / m 2 This indicates that the addition of alcohol solution helps to inhibit Ca(OH)2 aggregation and increase the specific surface area of ​​the material. The effect is more obvious when diethylene glycol, ethanol and diethylene glycol complex alcohol are added.

[0080] The Ca(OH)₂ materials prepared in Examples 1-3 and Comparative Example 1 were tested for dry desulfurization performance. The test results are as follows: Figures 4-5 As shown. Specifically, the reaction conditions during the test were: SO2 concentration of 1000 ppm, O2 volume concentration of 4 vol.%, N2 as the balance gas, simulated flue gas flow rate of 200 mL / min, Ca(OH)2 desulfurizing agent loading of 0.3 g, and simulated flue gas space velocity of 26000 h⁻¹. -1 The reaction temperature was 350℃. The SO2 concentration after dry desulfurization was detected by a flue gas analyzer, the desulfurization efficiency was calculated, and the desulfurization performance of the Ca(OH)2 desulfurizing agent was evaluated by the SO2 breakthrough time.

[0081] Desulfurization efficiency = (SO2 inlet concentration – SO2 outlet concentration) / SO2 inlet concentration × 100%;

[0082] SO2 breakthrough time is the time taken when the desulfurization efficiency is below 70%.

[0083] Specifically, Figure 4 The change of SO2 outlet concentration in the dry desulfurization unit with reaction time for Ca(OH)2 materials prepared by different methods during the desulfurization process; Figure 5 The SO2 removal efficiency of Ca(OH)2 materials prepared by different methods varies with reaction time during the desulfurization process.

[0084] from Figures 4-5As can be seen from the results, the dry desulfurization performance of the Ca(OH)2 materials prepared in Examples 1-3 and Comparative Example 1 shows that pretreatment of quicklime with ethanol, diethylene glycol, or a combination of ethanol and diethylene glycol effectively improves the dry desulfurization efficiency of the Ca(OH)2 materials and significantly prolongs the penetration time of the desulfurizing agent. Among these, the pretreatment with the combination of ethanol and diethylene glycol has the best effect. The reason for this is that pretreatment of quicklime with ethanol and diethylene glycol can generate a coating layer on the surface of quicklime, effectively reducing the digestion reaction rate and inhibiting the rapid growth of Ca(OH)2 crystals. By reducing the crystallinity of Ca(OH)2 materials, more crystal structure defects are induced, promoting the absorption reaction of SO2. Furthermore, it induces the formation of nanorods, nanolayers, and regular nanosheets in Ca(OH)2, increasing the specific surface area of ​​Ca(OH)2 and providing more reaction temperature for the SO2 absorption reaction.

[0085] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing nanolayered porous calcium hydroxide, characterized by, The method comprises the following steps: adding quicklime into an alcohol solution for coating to obtain a first precursor slurry; adding the first precursor slurry into water for digestion reaction to obtain a second precursor slurry; performing solid-liquid separation on the second precursor slurry, and drying the obtained solid to obtain the nano-layered porous calcium hydroxide; the alcohol solution comprises a mixture of ethanol and diethylene glycol, wherein the volume ratio of the ethanol and diethylene glycol is 3.5:0.5; the concentration of the quicklime in the first precursor slurry is 1-10 g / mL; the coating time of adding the quicklime into the alcohol solution for coating is 0.5-4 h; in the step of adding the first precursor slurry into water for digestion reaction, the mass of water is 1-5 times the mass of the quicklime; in the step of adding the first precursor slurry into water for digestion reaction, the digestion reaction is performed at a temperature of 40-80 ℃ for 10-120 min.

2. The method for preparing nano-layered porous calcium hydroxide as described in claim 1, characterized in that, performing solid-liquid separation on the second precursor slurry, and drying the obtained solid, wherein the drying temperature is 40-80 ℃, and the drying time is 12-48 h.

3. Nanolayered porous calcium hydroxide characterized in that, The nano-layered porous calcium hydroxide is prepared by the preparation method as claimed in any one of claims 1-2.

4. Application of the nano-layered porous calcium hydroxide prepared by the preparation method as claimed in any one of claims 1-2 or the nano-layered porous calcium hydroxide as claimed in claim 3 as a desulfurization absorbent.

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