High-activity calcium hydroxide and preparation method and application thereof

Abstract

The application discloses high-activity calcium hydroxide, a preparation method and application thereof, and belongs to the field of calcium hydroxide production technology. A certain amount of foaming agent azodicarbonamide, a proper amount of activator, and a proper amount of dispersing aids such as sodium hexametaphosphate and sodium pyrophosphate are added into quicklime, and then are fully mixed and uniformly mixed. The mixed material is mixed with water in a digester, the quicklime is reacted with the water, calcium hydroxide is generated, and a large amount of heat is generated at the same time. The material reaches the foaming agent decomposition temperature, a large amount of nitrogen gas released after decomposition of the foaming agent forms rich pores in the calcium hydroxide, and the dispersing aids can prevent calcium hydroxide particles from being aggregated. Finally, the high-activity calcium hydroxide product with high specific surface area is obtained, and can be used in a dry flue gas desulfurization process.

Description

Technical Field

[0001] This invention specifically relates to a highly active calcium hydroxide, its preparation method, and its application. Background Technology

[0002] The information disclosed in this background section is intended only to enhance some understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that the information constitutes prior art known to those skilled in the art.

[0003] Dry flue gas desulfurization is an important and efficient technology for removing acidic gases from flue gas, and it has been widely used in flue gas pollution control in various industrial sectors. When calcium hydroxide is used as a desulfurizing agent, it offers advantages such as low cost and a wide operating temperature range. Its quality should meet the requirements of the "HJ178 General Technical Specification for Flue Gas Desulfurization Engineering Using Circulating Fluidized Bed Method". The BET specific surface area, as an important performance indicator of calcium hydroxide desulfurizing agent, should meet the requirement of ≥18m². 2 The requirement of / g and the fact that calcium hydroxide with a higher specific surface area has better desulfurization performance make the preparation method of high specific surface area calcium hydroxide one of the important links in improving the efficiency of dry flue gas desulfurization, with significant market value and application prospects.

[0004] Most existing dry production processes for calcium hydroxide use mechanical stirring equipment to fully mix and digest a fixed amount of water and calcium oxide. This method has the disadvantages of low quicklime utilization and uneven particle size and underdeveloped pore structure of the calcium hydroxide produced, which cannot produce highly active calcium hydroxide that meets the requirements of dry flue gas desulfurization. Summary of the Invention

[0005] To address the problems in the background technology, this invention proposes a method for preparing highly active calcium hydroxide by adding an additive to quicklime, which generates a large amount of gas during its digestion process, thereby increasing the porosity of the product, calcium hydroxide. Azo-based organic foaming agents are insoluble in water and decompose upon heating, releasing a large amount of nitrogen gas. With the assistance of activators such as zinc oxide, stearates, and carbonates, their decomposition temperature can be flexibly adjusted.

[0006] A certain amount of foaming agent azodicarbonamide and an appropriate amount of activator are added to quicklime, along with appropriate amounts of dispersants such as sodium hexametaphosphate and sodium pyrophosphate. After thorough mixing, the quicklime is mixed with water in a digester. The quicklime reacts with the water to produce calcium hydroxide, generating a large amount of heat. The material reaches the decomposition temperature of the foaming agent, and the large amount of nitrogen released after decomposition forms abundant pores in the calcium hydroxide. The dispersant can prevent the calcium hydroxide particles from agglomerating, ultimately yielding a calcium hydroxide product with high specific surface area and high activity, which can be used in dry flue gas desulfurization processes.

[0007] The specific technical solution adopted in this invention is as follows:

[0008] In a first aspect of the present invention, a method for preparing highly active calcium hydroxide is provided, the method comprising the following steps:

[0009] After thoroughly mixing the set amounts of quicklime, azodicarbonamide, activator, and dispersant, the mixture is reacted with water to obtain highly active calcium hydroxide.

[0010] Preferably, the particle size of quicklime is 45-180 μm.

[0011] Preferably, the activator is one or more of zinc oxide, stearate, and carbonate.

[0012] More preferably, the stearate is zinc stearate or lead stearate.

[0013] More preferably, the carbonate is sodium bicarbonate or ammonium bicarbonate.

[0014] Preferably, the dispersant is sodium hexametaphosphate and / or sodium pyrophosphate.

[0015] Preferably, the mass ratio of quicklime, azodicarbonamide, activator, dispersant and water is 100:(0.5-2):(0.2-2):(0.5-5):(40-100).

[0016] Preferably, the reaction temperature is 20-180℃ and the reaction time is 15-60 min.

[0017] In a second aspect of the invention, highly active calcium hydroxide prepared by the above method is provided.

[0018] The obtained highly active calcium hydroxide has uniform particle size, well-developed pore structure, and a specific surface area of ​​≥40 m². 2 / g, with a particle size of 18-120μm, a water content of ≤2%, a specific pore volume of 0.1-0.2ml / g, and an average pore size of 10-100nm.

[0019] In a third aspect of the invention, the application of the highly active calcium hydroxide in dry flue gas desulfurization is provided.

[0020] The highly active calcium hydroxide prepared by the above method can be sprayed into the flue gas duct in dry powder form, which can efficiently remove SO2 from the flue gas. By adjusting the injection rate of the highly active calcium hydroxide according to the SO2 content in the flue gas, the SO2 content of the treated flue gas can be controlled at 30 mg / m³. 3 The levels are below the required levels, which meets the air pollutant emission requirements of national and industry standards.

[0021] Compared with the related technologies known to the inventors, one of the technical solutions of the present invention has the following beneficial effects:

[0022] (1) Using an organic foaming agent that releases nitrogen gas after thermal decomposition can increase the specific surface area of ​​calcium hydroxide products.

[0023] (2) The activator of azo foaming agent can lower its decomposition temperature. With appropriate dosage, it can cause the material to decompose at an elevated temperature when quicklime reacts with water.

[0024] (3) The quicklime digestion adopts a dry process, which does not produce wastewater discharge and the production process is clean. Attached Figure Description

[0025] The accompanying drawings, which form part of this specification, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0026] Figure 1 This is a pore size distribution diagram of calcium hydroxide powder. Detailed Implementation

[0027] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0028] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments of the present invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, and / or combinations thereof.

[0029] To enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments.

[0030] Example 1

[0031] 1 kg of quicklime powder with a particle size of 120-180 μm was mixed evenly with 15 g of azodicarbonamide, 3.75 g of zinc oxide, 0.75 g of zinc stearate, and 10 g of sodium hexametaphosphate. The mixture was placed in a sealed container, and 480 g of deionized water at 25 °C was added by spraying under stirring. After reacting for 30 min, stirring was stopped. The reactants were allowed to stand for 3 hours, and then dried at 120 °C for 2 hours to obtain the calcium hydroxide product. The pore size distribution of the calcium hydroxide powder is as follows: Figure 1 As shown. Its specific surface area is analyzed to be 49.2 m². 2 / g, with a moisture content of 1.4%.

[0032] Example 2

[0033] 1 kg of quicklime powder with a particle size of 120-180 μm was mixed evenly with 15 g of azodicarbonamide, 5 g of lead stearate, 1.5 g of sodium bicarbonate, and 10 g of sodium hexametaphosphate. The mixture was placed in a sealed container, and 480 g of deionized water at 25 °C was added by spraying under stirring. After reacting for 30 min, stirring was stopped. The reactants were allowed to stand for 3 hours, and then dried at 120 °C for 2 hours to obtain the calcium hydroxide product. The pore size distribution of the calcium hydroxide powder is as follows: Figure 1 As shown. Its specific surface area is analyzed to be 42.6 m². 2 / g, with a moisture content of 1.8%.

[0034] Example 3

[0035] 1 kg of quicklime powder with a particle size of 120-180 μm was mixed evenly with 15 g of azodicarbonamide, 3.5 g of ammonium bicarbonate, and 10 g of sodium hexametaphosphate. The mixture was placed in a sealed container, and 480 g of deionized water at 25 °C was added by spraying under stirring. After reacting for 30 min, stirring was stopped. The reactants were allowed to stand for 3 hours, and then dried at 120 °C for 2 hours to obtain the calcium hydroxide product. The pore size distribution of the calcium hydroxide powder is as follows: Figure 1 As shown. Its specific surface area is analyzed to be 42.5 m². 2 / g, with a moisture content of 1.2%.

[0036] Comparative Example 1

[0037] This invention investigated various foaming agents and found that only azodicarbonamide foaming agent can prepare highly active calcium hydroxide.

[0038] 1 kg of quicklime powder with a particle size of 120-180 μm was mixed evenly with 15 g of p-toluenesulfonyl hydrazine, 3.75 g of zinc oxide, 0.75 g of zinc stearate, and 10 g of sodium hexametaphosphate. The mixture was placed in a sealed container, and 480 g of deionized water at 25 °C was added by spraying under stirring. After reacting for 30 min, stirring was stopped. The reactants were allowed to stand for 3 hours and then dried at 120 °C for 2 hours to obtain the calcium hydroxide product. The pore size distribution of the calcium hydroxide powder is as follows: Figure 1 As shown. Its specific surface area is analyzed to be 23.2 m². 2 / g, with a moisture content of 1.2%. Compared with Example 1, the obtained product has a lower specific surface area, mainly because the gas generation rate of p-toluenesulfonyl hydrazine is slower and does not match the time of the quicklime digestion reaction process, thus a product with a high specific surface area cannot be obtained.

[0039] Comparative Example 2

[0040] 1 kg of quicklime powder with a particle size of 120-180 μm was mixed evenly with 15 g of azobisisobutyronitrile (AIBN), 3.75 g of zinc oxide, 0.75 g of zinc stearate, and 10 g of sodium hexametaphosphate. The mixture was placed in a sealed container, and 480 g of deionized water at 25 °C was added by spraying while stirring. After reacting for 30 min, stirring was stopped. The reactants were allowed to stand for 3 hours and then dried at 120 °C for 2 hours to obtain the calcium hydroxide product. The pore size distribution of the calcium hydroxide powder is shown in the figure. Figure 1 As shown. Its specific surface area is analyzed to be 20.5 m². 2 / g, with a water content of 1.0%. Compared with Example 1, the obtained product has a lower specific surface area, mainly because azobisisobutyronitrile is not very hydrophilic and is not fully compatible with quicklime and water during the quicklime digestion reaction. The produced gas cannot generate a large number of pores in the calcium hydroxide product, so a product with a high specific surface area cannot be obtained.

[0041] Comparative Example 3

[0042] This invention investigated activators in digestion reactions and found that only when azodicarbonamide is used as a foaming agent, zinc oxide, zinc stearate, lead stearate, sodium bicarbonate, etc. are used as activators, and sodium hexametaphosphate and / or sodium pyrophosphate are used as dispersants can a specific surface area ≥40m² be prepared. 2 / g of highly active calcium hydroxide.

[0043] Compared with Example 1, the difference is that 3.75g of zinc oxide and 0.75g of zinc stearate are replaced with 4.5g of ammonium sulfate.

[0044] The obtained product, calcium hydroxide powder, has the following pore size distribution: Figure 1 As shown. Its disadvantage is that its specific surface area is 27.4 m². 2 / g, which does not meet the standards for highly active calcium hydroxide products.

[0045] Comparative Example 4

[0046] Compared with Example 1, the difference is that sodium hexametaphosphate is replaced with sodium oleate.

[0047] The obtained product, calcium hydroxide powder, has the following pore size distribution: Figure 1 As shown. Its disadvantage is that its specific surface area is 26.1 m². 2 / g, which does not meet the standards for highly active calcium hydroxide products.

[0048] Comparative Example 5

[0049] The difference from Example 1 is that the mass of azodicarbonamide is 22g and the mass of sodium hexametaphosphate is 55g. Everything else is the same as in Example 1.

[0050] The obtained product, calcium hydroxide powder, has the following pore size distribution: Figure 1 As shown. Its disadvantage is that its specific surface area is 25.3 m². 2 / g, which does not meet the standards for highly active calcium hydroxide products.

[0051] Application examples

[0052] The desulfurization performance of calcium hydroxide powders obtained in Examples 1-3 and Comparative Examples 1-5 was evaluated using a fixed-bed reactor. The fixed-bed reactor had an inner diameter of 12 mm and a length of 300 mm. The simulated flue gas composition was a mixture of SO2, CO2, O2, and N2, with an SO2 concentration of 500 ppmV, CO2 and O2 volume fractions of 10% and 5%, respectively, and the remainder being N2. The flue gas flow rate was 1000 mL / min, and the SO2 content at the reactor outlet was analyzed using an infrared gas analyzer. For all samples, the reactor loading was 30 mL. The time from the start of flue gas introduction to the SO2 content in the reactor outlet gas reaching 20 ppm was defined as the desulfurization breakthrough time of the corresponding adsorbent. The comparative results obtained from the evaluation are shown in the table below.

[0053] <![CDATA[Specific surface area / (m 2 / g)]]> 49.2 42.6 42.5 23.2 20.5 27.4 26.1 25.3 Penetration time / min 87.2 67.3 64.4 33.5 30.3 35.2 34.5 34.7

[0054] As can be seen from the data in the table, the active calcium hydroxide in Example 1 has the highest specific surface area and, as demonstrated by the evaluation experiment, also has the longest desulfurization breakthrough time. The specific surface area of ​​calcium hydroxide and its desulfurization performance are positively correlated.

[0055] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for preparing highly active calcium hydroxide, characterized in that, The method includes the following steps: After thoroughly mixing the set amounts of quicklime, azodicarbonamide, activator, and dispersant, it is reacted with water to obtain highly active calcium hydroxide. The activator is one or more of zinc oxide, stearate, and bicarbonate; The stearate is zinc stearate or lead stearate; the bicarbonate is sodium bicarbonate or ammonium bicarbonate.

2. The method for preparing highly active calcium hydroxide as described in claim 1, characterized in that, The particle size of quicklime is 45-180μm.

3. The method for preparing highly active calcium hydroxide as described in claim 1, characterized in that, The dispersant is sodium hexametaphosphate and / or sodium pyrophosphate.

4. The method for preparing highly active calcium hydroxide as described in claim 1, characterized in that, The ratio of quicklime, azodicarbonamide, activator, dispersant and water is 100:(0.5-2):(0.2-2):(0.5-5):(40-100).

5. The method for preparing highly active calcium hydroxide as described in claim 1, characterized in that, The reaction temperature is 20-180°C, and the reaction time is 15-60 min.

6. A highly active calcium hydroxide prepared by any one of claims 1 to 5.

7. The highly active calcium hydroxide as described in claim 6, characterized in that, The obtained highly active calcium hydroxide has a specific surface area of ​​≥40m². 2 / g, with a particle size of 18-120μm, a water content of ≤2%, a specific pore volume of 0.1-0.2ml / g, and an average pore size of 10-100nm.

8. The application of the highly active calcium hydroxide as described in claim 6 in dry flue gas desulfurization.

9. The application as described in claim 8, characterized in that, Highly active calcium hydroxide, sprayed as dry powder into the flue gas duct, can remove SO2 from the flue gas. The injection rate of highly active calcium hydroxide can be adjusted according to the SO2 content in the flue gas, and the SO2 content of the treated flue gas can be controlled at 30 mg / m³. 3 The indicators are as follows.

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