Modified activated carbon for indoor formaldehyde adsorption and preparation method thereof

Abstract

The invention discloses modified activated carbon for indoor formaldehyde adsorption and a preparation method thereof. The method comprises the following steps: 1) preparing an amino acid solution; 2) dipping the activated carbon in an amino acid solution, carrying out ultrasonic oscillation for a certain time, and dipping for a preset time; 3) drying the impregnated activated carbon in a drying box; and 4) placing the dried activated carbon in a tubular furnace filled with shielding gas for high-temperature activation for 2-10 h. The high-temperature activation in the protective gas is beneficial to formation of micropores of the activated carbon, avoids the influence of air or oxygen on amino acid in the heating process, adsorbs the amino acid and derivatives thereof into the micropores formed by the activated carbon, greatly improves polarity modification of the activated carbon, increases effective oxygen-containing functional groups on the surface of the activated carbon, and improves the adsorption capacity of the activated carbon. The adsorption capacity of the activated carbon on formaldehyde polar molecules is enhanced, and the chemical adsorption effect on formaldehyde can be further promoted on the basis of physical adsorption of the activated carbon.

Description

Technical Field

[0001] The present disclosure relates to the technical field of air purification materials, and in particular to a modified activated carbon for indoor formaldehyde adsorption and a preparation method thereof. Background Art

[0002] Formaldehyde is a typical gaseous pollutant in indoor environments and is both teratogenic and carcinogenic. Exposure to high concentrations of formaldehyde can cause chest tightness, shortness of breath, nausea, vomiting, and even death. Long-term exposure to lower concentrations can cause chronic respiratory diseases, brain tumors, nasopharyngeal cancer, leukemia, and chromosomal abnormalities in newborns. Activated carbon has a well-developed porosity, numerous micropores and mesopores, and a large surface area, making it particularly suitable for the adsorption, separation, and purification of gaseous pollutants. It is an effective tool for the adsorption of harmful gases. However, relying solely on the physical adsorption capacity of activated carbon is very limited, and there is a risk of secondary contamination.

[0003] The existing chemical amino acid modification of activated carbon can effectively solve the above-mentioned problems. It relies on the dual means of physical adsorption and chemical efficient decomposition to treat formaldehyde gaseous pollutants, which can effectively avoid the risk of secondary pollution. However, the existing activated carbon modification method is to immerse the activated carbon in an amino acid solution and dry it at low temperature. Although it can improve the formaldehyde adsorption capacity to a certain extent, the amino acid molecules are mainly attached to the activated carbon surface through van der Waals forces at low temperatures. The binding force is weak and it is easily affected by environmental humidity or temperature changes and desorbed. The amino group (-NH2) or carboxyl group (-COOH) in the amino acid needs to form hydrogen bonds or covalent bonds (such as amide bonds) with the oxygen-containing functional groups (such as hydroxyl and carbonyl) on the surface of the activated carbon. Low-temperature drying is difficult to provide enough energy to drive such chemical reactions, resulting in a low chemical bonding ratio, which makes the formaldehyde adsorption capacity of the existing modified activated carbon not high. Summary of the Invention

[0004] In view of the problems existing in the prior art, the object of the present invention is to provide a modified activated carbon with improved formaldehyde adsorption capacity and a preparation method thereof.

[0005] To achieve the above object, the present invention provides a method for preparing modified activated carbon for indoor formaldehyde adsorption, comprising the following steps:

[0006] 1) Prepare amino acid solution;

[0007] 2) immersing the activated carbon in the amino acid solution and ultrasonically shaking it for a certain period of time, and then immersing it for a predetermined time;

[0008] 3) drying the impregnated activated carbon in a drying oven;

[0009] 4) Place the dried activated carbon in a tubular furnace with protective gas for high-temperature activation for 2 to 10 hours.

[0010] Furthermore, step 4) placing the dried activated carbon in a tubular furnace filled with protective gas for high-temperature activation comprises:

[0011] The temperature in the tube furnace was raised from room temperature to 105 °C for the first step of heating;

[0012] The temperature in the tube furnace is raised to 150-180°C and calcined for 1-2 hours for the second stage of heating;

[0013] The temperature in the tube furnace is raised to 180-220° C. and calcined for 2 hours for the third stage of heating, and argon is introduced into the tube furnace at the same time for high-temperature activation.

[0014] Furthermore, the ventilation rate of the protective gas into the tubular furnace is 0.1 to 0.8 L / min.

[0015] Further, step 1) preparing the amino acid solution includes:

[0016] 2 to 50 parts by mass of amino acids or amino acid derivatives are stirred in 100 parts by mass of water at room temperature to prepare an amino acid solution with a mass fraction of 2% to 50% or ultrasonically dissolved for 2 to 20 minutes.

[0017] Furthermore, the amino acid types include one or more of alanine, glycine, glutamic acid, glutamine, leucine, isoleucine, cysteine, lysine, arginine, valine, tryptophan and chemically modified amino acid derivatives.

[0018] Furthermore, in step 2), the volume ratio of activated carbon to amino acid solution is 1:1.5-3.

[0019] Furthermore, in step 2), the ultrasonic oscillation time is 0.5-1 h, and the immersion time is 4-24 h.

[0020] Furthermore, in step 3), the temperature of the drying box is 100-150° C., and the drying time is 2-10 hours.

[0021] Furthermore, the modified activated carbon after high-temperature activation is naturally cooled to room temperature and stored in a sealed bag.

[0022] Another aspect of the present invention provides a modified activated carbon for indoor formaldehyde adsorption, which is prepared using the above-mentioned preparation method.

[0023] The present invention facilitates the formation of activated carbon micropores by performing high-temperature activation in a protective atmosphere, while avoiding the influence of air or oxygen on amino acids during the heating process, adsorbing amino acids and their derivatives into the micropores formed by the activated carbon, greatly improving the polarity modification of the activated carbon, increasing the effective oxygen-containing functional groups on the surface of the activated carbon, and enhancing the adsorption capacity of the activated carbon for formaldehyde polar molecules. On the basis of the physical adsorption of the activated carbon, the chemical adsorption of formaldehyde can be further promoted, so that the initial adsorption rate of the modified activated carbon for formaldehyde is greatly improved compared with the activated carbon before modification.

[0024] It is to be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0026] Figure 1 Schematic diagram of the unit formaldehyde adsorption capacity of the embodiment of the present invention and the conventional activated carbon;

[0027] Figure 2 FIG. 4 is a schematic diagram of formaldehyde removal rate according to an embodiment of the present invention. DETAILED DESCRIPTION

[0028] Example embodiments will now be described more fully with reference to the accompanying drawings. However, example embodiments can be embodied in many forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete and will fully convey the concepts of the example embodiments to those skilled in the art. Like reference numerals in the drawings represent like or similar parts, and thus repetitive description thereof will be omitted.

[0029] In addition, the described features, structures or characteristics may be combined in any suitable manner in one or more embodiments. In the following description, many specific details are provided to provide a full understanding of the embodiments of the present disclosure. However, those skilled in the art will appreciate that the technical solutions of the present disclosure can be practiced without one or more of the specific details, or other methods, components, materials, devices, steps, etc. can be adopted. In other cases, well-known structures, methods, devices, implementations, materials or operations are not shown or described in detail to avoid obscuring various aspects of the present disclosure.

[0030] Example 1

[0031] (1) Weigh 15 g of cysteine ​​and add it to a certain amount of water. Stir and sonicate for 5 minutes to completely dissolve it to prepare a 15% cysteine ​​solution.

[0032] (2) 60 g of 2 mm coal-based columnar activated carbon was placed in 200 mL of 15% cysteine ​​solution and immersed for 24 h. After completion, the immersed solution was filtered on a filter and allowed to stand for a period of time.

[0033] (3) Place the wet activated carbon on the filter in an oven at 100°C for 4 hours;

[0034] (4) The dried activated carbon was placed in a tubular furnace for high-temperature activation. The temperature was first raised from room temperature to 105°C, then raised to 150°C and calcined for 1 to 2 hours, and then gradually raised to 200°C and calcined for 2 hours. The entire process was simultaneously carried out in an argon protective gas flow with a ventilation rate of 0.6 L / min. After naturally cooling to room temperature, the final modified formaldehyde-removing activated carbon was obtained, which was recorded as modified coal-based activated carbon A.

[0035] Example 2

[0036] (1) Compared with Example 1, the difference is that the cysteine ​​in step (1) is replaced by lysine, and the mass fraction is prepared to be 10%.

[0037] (2) 80 g of 2 mm coal-based columnar activated carbon was placed in 200 mL of 10% lysine solution and soaked for 16 h. After completion, the impregnation solution was filtered on a filter and allowed to stand for a period of time.

[0038] (3) Place the wet activated carbon on the filter in an oven at 110°C for 4 hours;

[0039] (4) The dried activated carbon was placed in a tube furnace for high-temperature activation. The temperature was first raised from room temperature to 105°C, then raised to 180°C for calcination for 2h, and then gradually raised to 220°C for calcination for 2h. The staged temperature increase can gently activate the modified activated carbon. Compared with direct exposure to a fixed high temperature, the staged temperature increase provides a more gentle and controllable activation process. The initial lower temperature avoids the deactivation of the modified group that may occur at too high a temperature (such as amine oxidation, decomposition or sintering). The subsequent gradual temperature increase to a specific stage is then introduced to a higher temperature, reducing the risk of modifier failure or carbon structure damage due to local overheating. The entire process was simultaneously activated at high temperature in an argon protective gas flow with a ventilation rate of 0.8L / min. After natural cooling to room temperature, the final modified formaldehyde-removing activated carbon was obtained, which was recorded as modified coal-based activated carbon B.

[0040] Example 3

[0041] Compared with Example 1, the difference is that the 15% by mass cysteine ​​solution in step (1) is replaced by a 30% by mass glycine solution, and the prepared cysteine-modified activated carbon is recorded as modified coal-based activated carbon C.

[0042] Example 4

[0043] Compared with Example 1, the difference is that the 15% by mass cysteine ​​solution in step (1) is replaced by a 30% by mass cysteine ​​solution, and the prepared cysteine-modified activated carbon is recorded as modified coal-based activated carbon D.

[0044] Example 5

[0045] Compared with Example 1, the difference is that the cysteine ​​solution in Example 1 is replaced by the same volume of deionized water for soaking, and the activated carbon prepared is recorded as coal-based activated carbon E.

[0046] Example 6

[0047] Compared with Example 1, the difference is that the operation of step (3) is modified, and the wet activated carbon on the filter is placed in an oven with an oven temperature of 60°C and a drying time of 12 hours; the prepared cysteine-modified activated carbon is recorded as modified coal-based activated carbon F.

[0048] Example 7

[0049] Compared with Example 1, the difference is that the operation of step (4) is modified, and the dried activated carbon is placed in a tubular furnace for high-temperature activation, first heated from room temperature to 105°C, then heated to 140°C and calcined for 3h, and then gradually heated to 180°C and calcined for 2h. The whole process is simultaneously activated at high temperature in an argon protective gas flow with a ventilation rate of 0.8L / min. After naturally cooling to room temperature, the final modified formaldehyde-removing activated carbon is obtained, which is recorded as modified coal-based activated carbon G.

[0050] Example 8

[0051] Compared with Example 1, the difference is that the operation of step (4) is modified, and the dried activated carbon is placed in a tubular furnace for high-temperature activation, first heated from room temperature to 105°C, then heated to 150°C and calcined for 1 to 2 hours, and then gradually heated to 200°C and calcined for 2 hours. The entire process is not high-temperature activated in an argon protective gas flow. After naturally cooling to room temperature, the final modified formaldehyde-removing activated carbon is obtained, which is recorded as modified coal-based activated carbon H.

[0052] Comparative Example 1

[0053] Coal-based activated carbon that has not undergone chemical modification is recorded as unmodified coal-based activated carbon O.

[0054] Comparative Example 2

[0055] Compared with Example 1, the difference is that the operation of step (4) is omitted, and the prepared cysteine-modified activated carbon is recorded as modified coal-based activated carbon I.

[0056] This method primarily tests activated carbon's CTC value, formaldehyde removal rate, and formaldehyde adsorption capacity. The formaldehyde volatilization gas used is a mixture of commercially available formaldehyde solution and pure water in a 1:2 volume ratio. Air from a compressed air tank is then blown above the mixture to a constant concentration of formaldehyde. The formaldehyde flow rate is controlled by a gas mass flowmeter.

[0057] The coal-based columnar activated carbon samples provided in Examples 1-8 and Comparative Examples 1-2 were filled in an absorption bed to purify formaldehyde. The CTC value and initial formaldehyde removal rate were used as the main physical and chemical indicators for observation. The experimental results are shown in Table 1. CTC value test method: GB / T7702.13-1997 "Test method for coal-based granular activated carbon - Determination of carbon tetrachloride adsorption rate" was cited. The formaldehyde dynamic adsorption performance of the modified formaldehyde-removing activated carbon was tested, and the formaldehyde removal rate was calculated according to the following formula: Formaldehyde removal rate (%) = [initial concentration (ppm) - tail gas concentration (ppm)] / initial concentration (ppm) * 100.

[0058] Table 1

[0059]

[0060]

[0061] Comparison of the final formaldehyde unit adsorption capacity of coal-based activated carbon A, B, C, D, E, F, G, H, O, and I. The test results are shown in Figure 1 The unit adsorption capacity refers to the mass (in mg) of formaldehyde that can be adsorbed by each gram (g) of activated carbon under test conditions, and is calculated according to the following formula.

[0062] Unit adsorption capacity = [mass of adsorption saturated activated carbon - mass of activated carbon before adsorption] / mass of activated carbon before adsorption

[0063] from Figure 1 As can be seen from the figure, all samples have a certain absorption capacity for formaldehyde pollutants. Coal-based activated carbon O, being unmodified, has the worst formaldehyde adsorption, with a very low specific adsorption capacity. Coal-based activated carbon E, washed with deionized water, shows a slight improvement compared to coal-based activated carbon O because the water wash reduces the ash content in the activated carbon pores. Coal-based activated carbons A, B, and F, modified and activated with amino acids, exhibit significantly improved performance, with high specific adsorption capacities exceeding 100 mg / g.

[0064] The test data of the purification chamber of coal-based activated carbon B is shown in Table 2, and the curve of formaldehyde removal rate changing with time is shown in Figure 2Take 20g of coal-based activated carbon B and place it on the purifier tooling, then inside the purification chamber. The initial formaldehyde concentration in the chamber is 1.13ppm. Record the concentration over time, recording it every 5 minutes. The formaldehyde removal rate can be calculated based on the formaldehyde concentration at the corresponding time point and the initial concentration. Calculate the removal rate using the following formula.

[0065] Removal rate (%) = [initial concentration (ppm) - formaldehyde concentration (ppm)] / initial concentration (ppm) * 100

[0066] Table 2

[0067]

[0068] Through Table 2 and Figure 2 It can be seen that the modified activated carbon B in Example 2 of the present invention can reduce the formaldehyde concentration in the purification cabin to a safe concentration in 25 minutes and can achieve a formaldehyde removal rate of 98% in 30 minutes, and has a significant effect on adsorbing formaldehyde. This technical method is suitable for the modification of activated carbon for air purification.

[0069] The activation temperature provided by the present invention does not affect the structural changes and properties of the added amino acids, and when the argon protective gas is introduced, there is no air or oxygen, which reduces the possible effects of air or oxygen on the amino acids under elevated temperatures. The choice of temperature is also very important. At about 200°C, the high-temperature argon protective gas flow helps the micropores of the activated carbon to begin to form. The formation of micropores is mainly due to the rearrangement of carbon atoms inside the carbon material at high temperatures, which causes some carbon atoms to be removed, thereby forming tiny pores. The formation of micropores is a key step in the activated carbon activation process because micropores are the main source of the activated carbon's ability to adsorb formaldehyde. Too high a temperature may reach the melting point of the amino acid, causing the solid amino acid to melt into a liquid, so the stage-by-stage heating will also affect the amount of amino acids and their derivatives attached to the micropores in the activated carbon, thereby affecting the adsorption efficiency of the modified activated carbon to formaldehyde.

[0070] Other embodiments of the present disclosure will readily occur to those skilled in the art after considering the specification and practicing the invention disclosed herein. This application is intended to cover any variations, uses, or adaptations of the present disclosure that follow from the general principles of the present disclosure and include common knowledge or customary techniques in the art not disclosed herein. The description and examples are to be considered as exemplary only, with the true scope and spirit of the present disclosure being indicated by the claims.

[0071] It should be understood that the present disclosure is not limited to the exact structures that have been described above and shown in the drawings, and that various modifications and changes can be made without departing from the scope thereof. The scope of the present disclosure is limited only by the appended claims.

Claims

1. A method for preparing modified activated carbon for indoor formaldehyde adsorption, characterized in that: The steps include: 1) Prepare amino acid solution; 2) immersing the activated carbon in the amino acid solution and ultrasonically shaking it for a certain period of time, and then immersing it for a predetermined time; 3) drying the impregnated activated carbon in a drying oven; 4) Place the dried activated carbon in a tubular furnace with protective gas for high-temperature activation for 2 to 10 hours.

2. The preparation method according to claim 1, wherein Step 4) placing the dried activated carbon in a tubular furnace filled with protective gas for high-temperature activation includes: The temperature in the tube furnace was raised from room temperature to 105 °C for the first step of heating; The temperature in the tube furnace is raised to 150-180°C and calcined for 1-2 hours for the second stage of heating; The temperature in the tube furnace is raised to 180-220° C. and calcined for 2 hours for the third stage of heating, and argon is introduced into the tube furnace at the same time for high-temperature activation.

3. The preparation method according to claim 1 or 2, wherein The ventilation rate of the protective gas in the tubular furnace is 0.1 to 0.8 L / min.

4. The preparation method according to claim 1, wherein Step 1) preparing the amino acid solution comprises: 2 to 50 parts by mass of amino acids or amino acid derivatives are stirred in 100 parts by mass of water at room temperature to prepare an amino acid solution with a mass fraction of 2% to 50% or ultrasonically dissolved for 2 to 20 minutes.

5. The preparation method according to claim 4, wherein The amino acid types include one or more of alanine, glycine, glutamic acid, glutamine, leucine, isoleucine, cysteine, lysine, arginine, valine, tryptophan and chemically modified amino acid derivatives.

6. The preparation method according to claim 1, wherein In step 2), the volume ratio of activated carbon to amino acid solution is 1:1.5-3.

7. The preparation method according to claim 1, wherein In step 2), the ultrasonic oscillation time is 0.5-1 h, and the immersion time is 4-24 h.

8. The preparation method according to claim 1, wherein In step 3), the temperature of the drying box is 100-150° C., and the drying time is 2-10 hours.

9. The preparation method according to claim 1, wherein The modified activated carbon after high-temperature activation is naturally cooled to room temperature and stored in a sealed bag.

10. A modified activated carbon for formaldehyde adsorption, characterized in that: The method is as described in any one of claims 1 to 9.

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