A method for preparing high specific surface area slaked lime by using low temperature plasma

Abstract

The application discloses a method for preparing high specific surface area slaked lime by using low temperature plasma, and the method comprises the following steps: dissolving carboxylic acid into water to obtain a carboxylic acid solution; spraying the carboxylic acid solution and quicklime powder into a low temperature plasma generator; and introducing the obtained solid powder into a gas-solid separator after irradiation of the low temperature plasma, so as to obtain a high specific surface area slaked lime product. The application solves the technical defects in the existing lime slaking process, and realizes the preparation of high specific surface area slaked lime by coupling the carboxylic acid reaction and the low temperature plasma irradiation. The application also provides a technical reference for the research and development of a new slaking device. The specific surface area of the slaked lime prepared by the application is up to 49.37 m 2 / g, which is higher than that of the same product on the market.

Description

Technical Field

[0001] This invention belongs to the field of value-added calcium-based material research and development, specifically involving a method for preparing high specific surface area slaked lime using low-temperature plasma. Background Technology

[0002] The traditional method of lime slaking involves reacting quicklime with water to produce slaked lime; this process is also known as lime "slaking" or "hydration." When quicklime is placed in water, it releases heat during the reaction, so the reaction temperature needs to be controlled to avoid overheating. The slaked lime water usually needs to be filtered and purified to remove impurities. The purified lime water can then be dried using methods such as centrifugation to obtain dry lime powder. The lime slaking process generates a significant amount of heat, therefore, it is crucial to control the reaction temperature to prevent overheating.

[0003] Compared to traditional slaked lime, high specific surface area slaked lime has a larger specific surface area, stronger adsorption performance, and better reactivity. Therefore, it can play a better role in practical applications and has important application value. Its main application areas include oil filtration, flue gas desulfurization, sewage treatment, and food additives.

[0004] However, it is difficult to prepare slaked lime with a high specific surface area using traditional lime slaking methods. The slaked lime particles prepared by traditional methods are relatively large, with low porosity between particles, which significantly limits their adsorption capacity and reactivity.

[0005] Therefore, new preparation technologies are needed to prepare slaked lime with high specific surface area. Exploring and developing slaked lime products with high specific surface area can not only overcome technological gaps in the industry but also provide a reference method for the preparation of similar high specific surface area materials. Summary of the Invention

[0006] Objective of the invention: The technical problem to be solved by the present invention is to provide a method for preparing high specific surface area slaked lime using low-temperature plasma.

[0007] Technical Solution: To solve the above-mentioned technical problems, the present invention provides a method for preparing high specific surface area slaked lime using low-temperature plasma, comprising the following steps:

[0008] (1) Dissolve the carboxyl acid in water to obtain a carboxyl acid solution;

[0009] (2) Inject carboxylic acid solution and quicklime powder into a low-temperature plasma generator. After low-temperature plasma irradiation, introduce it into a gas-solid separator. The solid powder obtained by separation is the high specific surface area slaked lime product.

[0010] The carboxylic acid mentioned in step (1) includes any one of acetic acid, oxalic acid, malic acid, tartaric acid, and citric acid.

[0011] In step (1), the concentration of the carboxylic acid solution is 0.02–0.2 mg / L.

[0012] In step (2), the mass ratio of carboxylic acid solution to quicklime powder is 1-2:100.

[0013] In step (2), the low-temperature plasma irradiation time is 5 to 55 minutes.

[0014] In step (2), the low-temperature plasma voltage is 5-75kV and the low-temperature plasma atmosphere is air or oxygen.

[0015] The present invention also includes high specific surface area slaked lime prepared by the method.

[0016] The surface area of ​​the slaked lime is 41.27–49.37 m². 2 / g.

[0017] Reaction Mechanism: This invention simultaneously sprays in an aqueous solution of carboxylic acid and quicklime. The aqueous solution of carboxylic acid reacts with the quicklime to simultaneously generate a blend of calcium carboxylate and slaked lime. The calcium carboxylate is mixed in with the slaked lime, and its formation corrodes the surface of the slaked lime particles. During low-temperature plasma irradiation, oxygen and water vapor in the air, as well as water in the sprayed carboxylic acid solution, ionize and dissociate in the discharge channel, generating oxygen free radicals and hydroxyl free radicals. The generated oxygen free radicals and hydroxyl free radicals not only directly etch the surface of the slaked lime particles, but also react with calcium carboxylate, causing it to revert to calcium hydroxide and release carbon dioxide gas and water vapor. The conversion of calcium carboxylate to calcium hydroxide and the release of carbon dioxide both contribute to further increasing the specific surface area of ​​the slaked lime, and the released water vapor participates in the reaction in a recycling manner.

[0018] Beneficial Effects: Compared with existing technologies, this invention has the following advantages: This invention solves the technical defects in existing lime digestion processes by achieving the preparation of high specific surface area slaked lime through a coupled carboxylic acid reaction and low-temperature plasma irradiation. The content of this invention can also provide technical reference for the development of novel digestion equipment. The slaked lime prepared by this invention has a maximum specific surface area of ​​49.37 m². 2 / g, higher than similar products currently sold on the market. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the low-temperature plasma generator and material injection used in this invention;

[0020] Figure 2 This is a flowchart of the preparation method of the present invention. Detailed Implementation

[0021] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0022] Example 1: Effect of carboxylic acid solution concentration on the specific surface area of ​​the prepared high specific surface area slaked lime

[0023] Carboxylic acid was dissolved in water to prepare carboxylic acid solutions with concentrations of 0.005 mg / L, 0.01 mg / L, 0.015 mg / L, 0.02 mg / L, 0.11 mg / L, 0.2 mg / L, 0.225 mg / L, 0.25 mg / L, and 0.275 mg / L, respectively, where the carboxylic acid was acetic acid. The carboxylic acid solution and quicklime powder were injected into a low-temperature plasma generator at a mass ratio of 1:100. After irradiation with low-temperature plasma for 5 minutes, the mixture was introduced into a gas-solid separator. The separated solid powder was the high specific surface area slaked lime product. The low-temperature plasma voltage was 5 kV, and the atmosphere was air.

[0024] Specific surface area detection of slaked lime: The specific surface area of ​​slaked lime was detected and determined in accordance with the standard GB / T19587-2017 "Determination of specific surface area of ​​solid substances by gas adsorption BET method".

[0025] The test results of the embodiments of the present invention are shown in Table 1.

[0026] Table 1. Effect of carboxyl acid solution concentration on the specific surface area of ​​the prepared high specific surface area slaked lime.

[0027] 0.005 mg / L 27.52 ±0.2％ 0.01 mg / L 31.48 ±0.1％ 0.015 mg / L 36.92 ±0.1％ 0.02 mg / L 41.27 ±0.1％ 0.11 mg / L 43.85 ±0.1％ 0.2 mg / L 44.06 ±0.1％ 0.225 mg / L 41.05 ±0.1％ 0.25 mg / L 38.71 ±0.1％ 0.275 mg / L 34.34 ±0.1％

[0028] As shown in Table 1, when the concentration of the carboxylic acid solution is less than 0.02 mg / L (e.g., 0.015 mg / L, 0.01 mg / L, 0.005 mg / L, and even lower values ​​not listed in Table 1), the low concentration of the carboxylic acid solution leads to insufficient reaction between the carboxylic acid aqueous solution and quicklime, resulting in a reduction in the formation of calcium carboxylate and hydrated lime blends. Consequently, the specific surface area of ​​the prepared high specific surface area hydrated lime decreases significantly with decreasing carboxylic acid solution concentration. When the carboxylic acid solution concentration is equal to 0.02–0.2 mg / L (e.g., 0.02 mg / L, 0.11 mg / L, and 0.2 mg / L in Table 1), and carboxylic acid aqueous solution and quicklime are sprayed simultaneously, the carboxylic acid aqueous solution reacts with the quicklime, simultaneously forming calcium carboxylate and hydrated lime blends. The calcium carboxylate mixed in with the hydrated lime corrodes the surface of the hydrated lime particles. Ultimately, the specific surface area of ​​the prepared high specific surface area hydrated lime was all greater than 41 m². 2 / g. When the concentration of the carboxylic acid solution is greater than 0.2 mg / L (as shown in Table 1, carboxylic acid solution concentrations = 0.225 mg / L, 0.25 mg / L, 0.275 mg / L, and higher values ​​not listed in Table 1), the concentration of the carboxylic acid solution is too high. This reduces the efficiency of calcium hydroxide conversion and the release of carbon dioxide and water vapor during plasma irradiation, leading to a significant decrease in the specific surface area of ​​the prepared high-specific-surface-area slaked lime with further increases in carboxylic acid solution concentration. Overall, considering both benefits and costs, a carboxylic acid solution concentration of 0.02–0.2 mg / L is most favorable for increasing the specific surface area of ​​the prepared slaked lime.

[0029] Example 2: Effect of Low-Temperature Plasma Irradiation Time on the Specific Surface Area of ​​the Prepared High Specific Surface Area Slaked Lime

[0030] Carboxylic acid was dissolved in water to prepare a 0.2 mg / L carboxylic acid solution, wherein the carboxylic acid was oxalic acid. The carboxylic acid solution and quicklime powder were injected into a low-temperature plasma generator at a mass ratio of 1.5:100. After irradiation with low-temperature plasma for 2.5 minutes, 3 minutes, 4 minutes, 5 minutes, 30 minutes, 55 minutes, 60 minutes, 65 minutes, and 70 minutes, the solution was introduced into a gas-solid separator. The resulting solid powder was the high specific surface area slaked lime product. The low-temperature plasma voltage was 40 kV, and the atmosphere was oxygen.

[0031] The specific surface area of ​​hydrated lime was tested in the same manner as in Example 1. The test results of the present invention are shown in Table 2.

[0032] Table 2. Effect of low-temperature plasma irradiation time on the specific surface area of ​​the prepared high specific surface area hydrated lime.

[0033] 2.5 minutes 29.68 ±0.2％ 3 minutes 34.27 ±0.1％ 4 minutes 39.85 ±0.1％ 5 minutes 44.21 ±0.1％ 30 minutes 45.46 ±0.1％ 55 minutes 47.12 ±0.1％ 60 minutes 44.05 ±0.1％ 65 minutes 41.89 ±0.2％ 70 minutes 37.63 ±0.1％

[0034] As shown in Table 2, when the low-temperature plasma irradiation time is less than 5 minutes (as shown in Table 2, low-temperature plasma irradiation time = 4 minutes, 3 minutes, 2.5 minutes, and even lower values ​​not listed in Table 2), the shorter irradiation time reduces the etching efficiency of the slaked lime surface and the decomposition efficiency of calcium carboxylate, resulting in a significant decrease in the specific surface area of ​​the prepared high specific surface area slaked lime as the low-temperature plasma irradiation time decreases. When the low-temperature plasma irradiation time is equal to 5–55 minutes (as shown in Table 2, low-temperature plasma irradiation time = 5 minutes, 30 minutes, and 55 minutes), during the low-temperature plasma irradiation process, oxygen and water vapor in the air, as well as water in the injected carboxylate solution, undergo ionization and dissociation in the discharge channel, generating oxygen free radicals and hydroxyl free radicals. The generated oxygen free radicals and hydroxyl free radicals not only directly etch the surface of the slaked lime particles, but also react with calcium carboxylate, causing it to revert to calcium hydroxide and release carbon dioxide gas and water vapor. The conversion of calcium carboxylate to calcium hydroxide and the release of carbon dioxide both contribute to further increasing the specific surface area of ​​the slaked lime, and the released water vapor participates in the reaction in a recycling manner. Ultimately, the specific surface area of ​​the prepared high specific surface area hydrated lime was all greater than 44 m². 2 / g. When the low-temperature plasma irradiation time exceeds 55 minutes (as shown in Table 2, low-temperature plasma irradiation time = 60 minutes, 65 minutes, 70 minutes, and higher values ​​not listed in Table 2), the excessively long irradiation time leads to over-burning of the material and sealing of the particle structure, resulting in a significant decrease in the specific surface area of ​​the prepared high-specific-surface-area slaked lime as the low-temperature plasma irradiation time further increases. Overall, considering both benefits and costs, a low-temperature plasma irradiation time of 5–55 minutes is most conducive to improving the specific surface area of ​​the prepared slaked lime.

[0035] Example 3: Effect of Low-Temperature Plasma Application Voltage on the Specific Surface Area of ​​the Prepared High Specific Surface Area Slaked Lime

[0036] Carboxylic acid was dissolved in water to prepare a 0.2 mg / L carboxylic acid solution, wherein the carboxylic acid was malic acid. The carboxylic acid solution and quicklime powder were injected into a low-temperature plasma generator at a mass ratio of 2:100. After irradiation with low-temperature plasma for 55 minutes, the solution was introduced into a gas-solid separator. The separated solid powder was the high specific surface area slaked lime product. The low-temperature plasma application voltages were 2.5 kV, 3 kV, 4 kV, 5 kV, 40 kV, 75 kV, 77.5 kV, 80 kV, and 82.5 kV, and the low-temperature plasma atmosphere was air.

[0037] The specific surface area of ​​hydrated lime was tested in the same manner as in Example 1. The test results of the present invention are shown in Table 3.

[0038] Table 3. Effect of low-temperature plasma voltage on the specific surface area of ​​the prepared high specific surface area hydrated lime.

[0039] 2.5kV 34.75 ±0.1％ 3kV 38.24 ±0.1％ 4kV 42.89 ±0.1％ 5kV 47.46 ±0.1％ 40kV 48.09 ±0.1％ 75kV 49.37 ±0.1％ 77.5kV 46.92 ±0.2％ 80kV 42.78 ±0.2％ 82.5kV 37.61 ±0.1％

[0040] As shown in Table 3, when the low-temperature plasma voltage is less than 5 kV (as shown in Table 3, low-temperature plasma voltage = 4 kV, 3 kV, 2.5 kV and even lower values ​​not listed in Table 3), the low-temperature plasma voltage is relatively small, resulting in reduced etching efficiency and calcium carboxylate decomposition efficiency on the slaked lime surface. Consequently, the specific surface area of ​​the prepared high specific surface area slaked lime decreases significantly with decreasing low-temperature plasma voltage. When the low-temperature plasma voltage is equal to 5–75 kV (as shown in Table 3, low-temperature plasma voltage = 5 kV, 40 kV, 75 kV), during low-temperature plasma irradiation, oxygen and water vapor in the air, as well as water in the injected carboxylate solution, undergo ionization and dissociation in the discharge channel, generating oxygen free radicals and hydroxyl free radicals. The generated oxygen and hydroxyl radicals not only directly etch the surface of the slaked lime particles, but also react with calcium carboxylate, converting it back into calcium hydroxide and releasing carbon dioxide and water vapor. The conversion of calcium carboxylate to calcium hydroxide and the release of carbon dioxide both contribute to further increasing the specific surface area of ​​the slaked lime, while the released water vapor participates in the reaction. Ultimately, the prepared high specific surface area slaked lime has a specific surface area greater than 47 m². 2 / g. When the low-temperature plasma voltage exceeds 75kV (as shown in Table 3, low-temperature plasma irradiation time = 77.5kV, 80kV, 82.5kV and higher values ​​not listed in Table 3), the excessively high low-temperature plasma voltage leads to over-burning of the material and sealing of the particle structure, resulting in a significant decrease in the specific surface area of ​​the prepared high-specific-surface-area slaked lime as the low-temperature plasma voltage further increases. Overall, considering both benefits and costs, a low-temperature plasma voltage of 5–75kV is most favorable for increasing the specific surface area of ​​the prepared slaked lime.

[0041] Example 4: Effect of carboxylic acid type on the specific surface area of ​​the prepared high specific surface area slaked lime

[0042] A carboxylic acid solution with a concentration of 0.2 mg / L was prepared by dissolving a carboxylic acid in water. The carboxylic acid could be any one of acetic acid, oxalic acid, malic acid, tartaric acid, or citric acid. The carboxylic acid solution and quicklime powder were injected into a low-temperature plasma generator at a mass ratio of 2:100. After irradiation with low-temperature plasma for 55 minutes, the solution was introduced into a gas-solid separator. The resulting solid powder was the high specific surface area slaked lime product. The low-temperature plasma voltage was 75 kV, and the atmosphere was oxygen.

[0043] The specific surface area of ​​hydrated lime was tested in the same manner as in Example 1. The test results of the present invention are shown in Table 4.

[0044] Table 4. Effect of carboxyl acid type on the specific surface area of ​​the prepared high specific surface area slaked lime.

[0045] Acetic acid 49.16 ±0.1％ oxalic acid 48.53 ±0.1％ malic acid 49.47 ±0.1％ tartaric acid 48.62 ±0.1％ Citric acid 49.04 ±0.1％

[0046] As shown in Table 4, when the carboxylic acid is any one of acetic acid, oxalic acid, malic acid, tartaric acid, or citric acid, there is no significant difference in the specific surface area of ​​the obtained slaked lime.

[0047] The effect of different processes on the specific surface area of ​​the prepared high specific surface area hydrated lime.

[0048] The process of this invention involves dissolving a carboxylic acid in water to prepare a 0.2 mg / L carboxylic acid solution, wherein the carboxylic acid is acetic acid. The carboxylic acid solution and quicklime powder are injected into a low-temperature plasma generator at a mass ratio of 2:100. After irradiation with low-temperature plasma for 55 minutes, the solution is introduced into a gas-solid separator. The resulting solid powder is the high specific surface area slaked lime product. The low-temperature plasma voltage is 75 kV, and the low-temperature plasma atmosphere is oxygen.

[0049] Comparative Process 1: Water and quicklime powder are added to a low-temperature plasma generator at a mass ratio of 2:100. After irradiation with low-temperature plasma for 55 minutes, the mixture is introduced into a gas-solid separator. The resulting solid powder is the high specific surface area scavenger.

[0050] The lime product is produced using a low-temperature plasma with a voltage of 75kV and an oxygen atmosphere.

[0051] Comparative Process 2: Dissolve carboxylic acid in water to prepare a 0.2 mg / L carboxylic acid solution, wherein the carboxylic acid is acetic acid. Spray the carboxylic acid solution and quicklime powder into a sealed container at a mass ratio of 2:100, mix for 55 minutes, and then introduce the mixture into a gas-solid separator. The solid powder obtained after separation is the high specific surface area slaked lime product.

[0052] The specific surface area of ​​hydrated lime was tested in the same manner as in Example 1. The test results of the present invention are shown in Table 5.

[0053] Table 5. Effects of different processes on the specific surface area of ​​the prepared high specific surface area hydrated lime.

[0054] The process of this invention 49.16 ±0.1％ Comparison Process 1 24.69 ±0.1％ Comparison Process 2 21.75 ±0.1％

[0055] As can be seen from Table 5, the specific surface area of ​​slaked lime achieved by the process of the present invention is significantly higher than that of slaked lime prepared by comparative process 1 and comparative process 2.

Claims

1. A method for preparing high specific surface area slaked lime using low-temperature plasma, characterized in that, Includes the following steps: (1) Dissolve the carboxylic acid in water to obtain a carboxylic acid solution; (2) Inject carboxylic acid solution and quicklime powder into the low-temperature plasma generator. After low-temperature plasma irradiation, introduce it into the gas-solid separator. The solid powder obtained by separation is the high specific surface area slaked lime product. The carboxylic acid mentioned in step (1) includes any one of acetic acid, oxalic acid, malic acid, tartaric acid, and citric acid. The concentration of the carboxylic acid solution in step (1) is 0.02~0.2 mg / L. The mass ratio of the carboxylic acid solution to quicklime powder in step (2) is 1~2:

100. The low-temperature plasma irradiation time in step (2) is 5~55 minutes. The low-temperature plasma voltage in step (2) is 5~75 kV. The low-temperature plasma atmosphere is air or oxygen.

2. The high specific surface area slaked lime prepared by the method of claim 1.

3. The high specific surface area slaked lime according to claim 2, characterized in that, The surface area of ​​the slaked lime is 41.27~49.37m². 2 / g.

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