Modified activated carbon suitable for adsorbing dioxins and a method for preparing the same

Abstract

The application discloses a preparation method of modified activated carbon suitable for adsorbing dioxin, and comprises the following steps: adding alkali lignin and chitosan into an alkaline solution, uniformly mixing to obtain a first solution; adding activated carbon into the first solution, uniformly mixing to obtain a second solution; evaporating the second solution to obtain a first solid; activating the first solid at 750 DEG C to 850 DEG C for 1.5h to 3.5h to obtain a second solid; and performing acid pickling, water washing and drying on the second solid to obtain a finished product. The preparation method of the modified activated carbon suitable for adsorbing dioxin can realize nitrogen doping, and finally obtains the modified activated carbon with suitable porosity and surface area, and the adsorption performance of the modified activated carbon is suitable for testing dioxin.

Description

Technical Field

[0001] This invention relates to the field of activated carbon adsorption of dioxins, and more particularly to a modified activated carbon suitable for adsorbing dioxins and its preparation method. Background Technology

[0002] Dioxins are a class of tricyclic aromatic organic compounds containing various different structures. They are persistent organic pollutants with characteristics such as high toxicity, poor degradation, bioaccumulation, and long-distance transport. They are considered "one of the most dangerous chemical substances in the world" and "the poison of the century," posing a huge threat to human health and the ecological environment. They can cause effects such as "teratogenicity, carcinogenicity, and mutagenicity." Their main source is the combustion of chlorinated hydrocarbons.

[0003] Dioxin concentrations in pollution sources are low, and dioxin analysis is an ultra-trace analysis, with concentrations in samples reaching the ppt to ppq level. Furthermore, dioxin samples are complex in composition and contain numerous interfering substances. Currently, the internationally accepted method for dioxin analysis is isotope dilution high-resolution gas chromatography-high-resolution mass spectrometry. Samples with overly complex compositions and excessive interfering substances can severely contaminate the instrument, directly affecting the detection results. Therefore, before instrumental analysis, dioxin samples need to be purified and enriched. The degree of sample interference removal and dioxin enrichment is a key factor in obtaining accurate detection results. The effectiveness of dioxin purification and enrichment directly impacts the analytical results.

[0004] In existing technologies, the sample is first purified, then separated using an activated carbon enrichment column to obtain a pretreated dioxin solution. Finally, it undergoes high-precision purification and separation using GC or HPLC, and the detection results are obtained by MS. However, the activated carbon and silica gel used in current technologies have long relied on imports, resulting in high costs. Furthermore, most activated carbons sold on the market have high specific surface areas and numerous micropores, and the adsorption performance varies greatly among different types. Therefore, selecting a suitable activated carbon is crucial for the effective purification and separation of dioxins from pollution sources. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a method for preparing modified activated carbon suitable for adsorbing dioxins, which can achieve nitrogen doping and finally obtain modified activated carbon with suitable porosity and surface area, whose adsorption performance is suitable for testing dioxins.

[0006] The technical problem to be solved by the present invention is to provide a modified activated carbon suitable for adsorbing dioxins, which can achieve nitrogen doping, has suitable porosity and surface area, and is suitable for adsorbing dioxins.

[0007] To address the aforementioned technical problems, this invention provides a method for preparing modified activated carbon suitable for adsorbing dioxins, comprising the following steps:

[0008] Alkali lignin and chitosan are added to an alkaline solution and mixed thoroughly to obtain the first solution.

[0009] Activated carbon is added to the first solution and mixed thoroughly to obtain the second solution;

[0010] The second solution is evaporated to obtain the first solid, and the first solid is activated at 750℃~850℃ for 1.5h~3.5h to obtain the second solid.

[0011] The second solid is then acid-washed, water-washed, and dried to obtain the finished product.

[0012] In one embodiment, 2 to 7 parts of alkali lignin and 7 to 11 parts of chitosan are added to 100 to 180 parts of alkaline solution by weight, and the mixture is stirred evenly to obtain a first solution.

[0013] In one embodiment, 4 to 6 parts of alkali lignin and 8 to 9 parts of chitosan are added to 130 to 160 parts of alkaline solution by weight, and the mixture is stirred evenly to obtain a first solution.

[0014] In one embodiment, the alkaline solution is a potassium hydroxide solution, and the concentration of the potassium hydroxide solution is 0.8 g / mL to 1.2 g / mL.

[0015] In one embodiment, the ratio of the amount of alkali lignin added to the amount of chitosan added is 1:(1.5-2).

[0016] In one embodiment, the ratio of the amount of activated carbon added to the amount of alkali lignin added is (6-10):1.

[0017] Preferably, the ratio of the amount of activated carbon added to the amount of alkali lignin added is (8-9):1.

[0018] In one embodiment, the second solid is washed with a hydrochloric acid solution with a mass concentration of 5% to 10% for 10 to 30 minutes during the pickling process.

[0019] In one embodiment, the second solid undergoes acid washing, water washing, and drying, wherein the drying conditions are: drying at 100℃~110℃ for 0.5h~2.5h under vacuum conditions.

[0020] Accordingly, the present invention also provides a modified activated carbon suitable for adsorbing dioxins, which is prepared by the above-described preparation method of modified activated carbon suitable for adsorbing dioxins.

[0021] Implementing this invention has the following beneficial effects:

[0022] This invention mixes activated carbon with an alkaline solution containing alkali lignin and chitosan, and then dries and activates it to obtain modified activated carbon with lignin-based activated carbon adhering to its surface. The introduction of chitosan enables the modified activated carbon to be successfully nitrogen-doped. The final modified activated carbon has suitable porosity and surface area, and its adsorption performance is suitable for testing dioxins. Attached Figure Description

[0023] Figure 1 This is a chromatogram of the dioxin test results in Example 1 of the present invention;

[0024] Figure 2 This is a chromatogram of the dioxin test results in Example 2 of the present invention;

[0025] Figure 3 This is a chromatogram of the dioxin test results in Example 3 of the present invention;

[0026] Figure 4 The chromatogram shows the dioxin test results of Comparative Example 1 of this invention.

[0027] Figure 5 This is a chromatogram of the dioxin test results of Comparative Example 2 of the present invention;

[0028] Figure 6 This is a chromatogram of the dioxin test results of Comparative Example 3 of the present invention. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be described in further detail below.

[0030] Unless otherwise stated or in case of contradiction, the terms or phrases used herein shall have the following meanings:

[0031] In this invention, "preferred" is merely a description of a more effective implementation method or embodiment, and should be understood as not constituting a limitation on the scope of protection of this invention.

[0032] In this invention, the technical features described in an open-ended manner include both closed-ended technical solutions composed of the listed features and open-ended technical solutions that include the listed features.

[0033] In this invention, numerical ranges are involved, and unless otherwise specified, they include the two endpoints of the numerical range.

[0034] To address the above problems, this invention provides a method for preparing modified activated carbon suitable for adsorbing dioxins, comprising the following steps:

[0035] S1. Add alkali lignin and chitosan to the alkaline solution, mix well to obtain the first solution;

[0036] In one embodiment, 2 to 7 parts of alkali lignin and 7 to 11 parts of chitosan are added to 100 to 180 parts of alkaline solution by weight, and the mixture is stirred evenly to obtain a first solution.

[0037] It should be noted that the pore structure of activated carbon consists of macropores (50–2000 nm), mesopores (2–50 nm), and micropores (less than 2 nm). These three types of pores are distributed in a dendritic pattern, with mesopores located on top of macropores, and micropores located on top of mesopores. Micropores typically provide the main adsorption sites. Increasing the micropore volume of activated carbon is beneficial for the adsorption of small molecules. However, if the mesopore volume is too small, the resistance to intramolecular diffusion increases, which is detrimental to the adsorption function of activated carbon.

[0038] This invention introduces lignin-based activated carbon onto the surface of activated carbon, thereby maximizing the increase of micropore adsorption points while maintaining mesopore volume, ultimately achieving a high dioxin adsorption capacity. However, excessive addition of alkali lignin will result in the final alkali lignin-based activated carbon depositing in most of the pores of the unmodified activated carbon, thus reducing the mesopore volume of the modified activated carbon and consequently decreasing the dioxin adsorption effect. Conversely, insufficient addition of alkali lignin will result in a small amount of alkali lignin-based activated carbon in the final modified activated carbon, failing to adequately increase the micropore volume and thus reducing the dioxin adsorption effect. Preferably, 4 to 6 parts by weight of alkali lignin and 8 to 9 parts by weight of chitosan are added to 130 to 160 parts of an alkaline solution, and the mixture is stirred thoroughly to obtain a first solution.

[0039] Furthermore, the surface chemical properties of activated carbon are closely related to the adsorption and desorption of dioxins. To further improve the dioxin adsorption performance of activated carbon, this invention introduces chitosan into the first solution. During subsequent high-temperature activation, chitosan can introduce nitrogen doping into the modified activated carbon, further improving the adsorption efficiency of dioxins by the nitrogen-doped modified activated carbon. In one embodiment, the ratio of the amount of alkali lignin added to the amount of chitosan added is 1:(1.5-2). Excessive addition of chitosan will lead to excessive nitrogen doping, resulting in narrow pores that hinder the entry of adsorbed molecules into the interior of the activated carbon, thereby reducing the adsorption rate. Moreover, as the amount of chitosan added increases, the pores of the modified activated carbon become denser and smaller, and excessive micropore content is detrimental to dioxin adsorption.

[0040] In one embodiment, the alkaline solution is a potassium hydroxide solution with a concentration of 0.8 g / mL to 1.2 g / mL. Using a suitable alkaline solution facilitates thorough mixing of alkali lignin and chitosan with the subsequently added activated carbon. Furthermore, the alkaline solution has an etching effect, creating numerous uneven etching pits on the activated carbon surface. Using a suitable alkaline solution can generate a rich porous structure on the activated carbon surface, thereby improving the adsorption effect of dioxins.

[0041] S2. Add activated carbon to the first solution and mix well to obtain the second solution;

[0042] In one embodiment, the ratio of the amount of activated carbon to the amount of alkali lignin is (6-10):1. Excessive addition of alkali lignin will result in the final alkali lignin-based activated carbon being deposited in most of the pores of the unmodified activated carbon, thus reducing the mesopore volume of the modified activated carbon and consequently decreasing the dioxin adsorption effect. Conversely, insufficient addition of alkali lignin will result in a smaller amount of alkali lignin-based activated carbon in the final modified activated carbon, failing to adequately increase the micropore volume of the modified activated carbon and thus reducing the dioxin adsorption effect. Preferably, the ratio of the amount of activated carbon to the amount of alkali lignin is (8-9):1.

[0043] S3. The second solution is evaporated to obtain a first solid. The first solid is then activated at 750℃~850℃ for 1.5h~3.5h to obtain a second solid. During this process, the high temperature causes chemical changes in alkali lignin and chitosan, generating lignin-based activated carbon on the surface of unmodified activated carbon, and nitrogen is doped into the modified activated carbon. Preferably, the first solid is activated in a tube furnace at 750℃~850℃ for 1.5h~3.5h, with an inert gas introduced into the tube furnace to ensure activation.

[0044] S4. The second solid is acid-washed, water-washed, and dried to obtain the finished product.

[0045] In one embodiment, the second solid is washed with a hydrochloric acid solution with a mass concentration of 5-10 for 10-30 minutes during the acid washing process. In another embodiment, the second solid undergoes acid washing, water washing, and drying, wherein the drying conditions are: drying under vacuum at 100-110°C for 0.5-2.5 hours.

[0046] This invention mixes activated carbon with an alkaline solution containing alkali lignin and chitosan, and then dries and activates it to obtain modified activated carbon with lignin-based activated carbon adhering to its surface. The introduction of chitosan enables successful nitrogen doping of the modified activated carbon. The resulting modified activated carbon has suitable porosity and surface area, and its adsorption performance is suitable for the detection of dioxins. Accordingly, this invention also provides a modified activated carbon suitable for dioxin adsorption, which is prepared using the above-described method for preparing modified activated carbon suitable for dioxin adsorption.

[0047] The present invention is further illustrated below with specific embodiments:

[0048] Example 1

[0049] This embodiment provides a method for preparing modified activated carbon suitable for adsorbing dioxins, including the following steps: according to the weight, add 5 parts of alkali lignin and 7.5 parts of chitosan to 100 parts of potassium hydroxide solution with a concentration of 1g / mL, mix evenly to obtain a first solution;

[0050] Add 50 parts of activated carbon to the first solution and mix well to obtain the second solution;

[0051] The second solution was evaporated to obtain the first solid, and the first solid was activated by passing an inert gas at 800°C for 2 hours to obtain the second solid.

[0052] The second solid was washed with hydrochloric acid solution with a mass concentration of 8 for 15 min, washed with water, and dried at 105°C for 1.5 h to obtain the finished product.

[0053] Example 2

[0054] This embodiment provides a method for preparing modified activated carbon suitable for adsorbing dioxins, including the following steps: according to the weight, add 4 parts of alkali lignin and 8 parts of chitosan to 100 parts of potassium hydroxide solution with a concentration of 1g / mL, mix evenly to obtain a first solution;

[0055] Add 40 parts of activated carbon to the first solution and mix well to obtain the second solution;

[0056] The second solution was evaporated to obtain the first solid, and the first solid was activated by passing an inert gas at 800°C for 2 hours to obtain the second solid.

[0057] The second solid was washed with hydrochloric acid solution with a mass concentration of 8 for 15 min, washed with water, and dried at 105°C for 1.5 h to obtain the finished product.

[0058] Example 3

[0059] This embodiment provides a method for preparing modified activated carbon suitable for adsorbing dioxins, including the following steps: according to the weight, add 7 parts of alkali lignin and 10.5 parts of chitosan to 100 parts of potassium hydroxide solution with a concentration of 1 g / mL, mix evenly to obtain a first solution;

[0060] Add 81 parts of activated carbon to the first solution and mix well to obtain the second solution;

[0061] The second solution was evaporated to obtain the first solid, and the first solid was activated by passing an inert gas at 800°C for 2 hours to obtain the second solid.

[0062] The second solid was washed with hydrochloric acid solution with a mass concentration of 8 for 15 min, washed with water, and dried at 105°C for 1.5 h to obtain the finished product.

[0063] Comparative Example 1

[0064] The difference between Comparative Example 1 and Example 1 is that, by weight, 7.5 parts of chitosan were added to 100 parts of a 1 g / mL potassium hydroxide solution, and the mixture was stirred thoroughly to obtain the first solution. All other steps were the same as in Example 1.

[0065] Comparative Example 2

[0066] The difference between this comparative example and Example 1 is that, by weight, 5 parts of alkali lignin were added to 100 parts of a 1 g / mL potassium hydroxide solution, and the mixture was stirred thoroughly to obtain the first solution. Everything else was the same as in Example 1.

[0067] Comparative Example 2

[0068] The difference between this comparative example and Example 1 is that, by weight, 5 parts of alkali lignin were added to 100 parts of a 1 g / mL potassium hydroxide solution, and the mixture was stirred thoroughly to obtain the first solution. Everything else was the same as in Example 1.

[0069] Comparative Example 3

[0070] The difference between this comparative example and Example 1 is that the first solution does not contain alkali lignin and chitosan. Everything else is the same as in Example 1.

[0071] Modified activated carbon suitable for dioxin adsorption, prepared in Examples 1-3 and Comparative Examples 1-3, were used as packing materials to obtain packed columns. Six standard samples containing 5 μL of EPA-1613-LCS were added to the top of the packed column. First, the column was eluted with hexane and a 1:1 mixture of hexane and dichloromethane to remove interfering components and achieve purification, thus meeting the detection conditions for high-resolution gas chromatography-high-resolution mass spectrometry. During the elution purification process, the packed column also adsorbed and enriched dioxin components. In the first step, the packed column was eluted with 120 mL of hexane solution at a rate of 1-2 seconds / drop, and the hexane eluent was collected to obtain the first eluent. In the second step, after the hexane elution was completed, the packed column was eluted again with 50 mL of a 1:1 mixture of hexane and dichloromethane, and the mixed eluent was collected to obtain the second eluent. After elution and purification, the dioxin-enriched components in the packed column are eluted with toluene. In the third step, after elution with the mixed solution, the packed column is eluted with 80 mL of toluene. The toluene eluent is collected to obtain the first eluent. To ensure that no dioxin components remain uneluted, the packed column is eluted again with 80 mL of toluene to obtain the second eluent. All collected eluents and elutions are concentrated to near dryness, then redissolved in n-hexane and transferred to a sample vial. 5 μL of EPA-1613-ISS standard is added, and the volume is adjusted to 30 mL with nonane. Finally, the sample is analyzed. The recoveries of 15 compounds are evaluated according to the recovery range specified in HJ77.4-2008 "Determination of Dioxins in Soil and Sediments by Isotope Dilution High-Resolution Gas Chromatography-High-Resolution Mass Spectrometry". The chromatogram results of the first eluent, which contains the most dioxins, are shown below. Figures 1-6 As shown in Table 1:

[0072] Table 1 shows the dioxin content of the first eluents obtained in Examples 1-3 and Comparative Examples 1-3.

[0073]

[0074] The recovery rates of 15 compounds were evaluated according to the range specified in HJ77.4-2008 "Determination of Dioxins in Soil and Sediments by Isotope Dilution High-Resolution Gas Chromatography-High-Resolution Mass Spectrometry". All test items were within the acceptable range, and the recovery rates of each item in Examples 1-3 were better than those in Comparative Examples 1-3.

[0075] Considering the possibility of incompletely eluted dioxin components in the packed column, all second eluents were further analyzed. The results showed no dioxin components detected in Comparative Examples 1-3, while O8CDD showed a 20% recovery rate in Examples 2 and 3, and no recovery rate in Example 1. These data indicate that Examples 1-3 have a stronger dioxin adsorption capacity than Comparative Examples 1-3. Furthermore, the analysis of the second eluent data suggests that Examples 2 and 3 have a stronger dioxin adsorption capacity than Example 1, requiring more toluene.

[0076] Since no dioxin components were detected in the comparative examples in the second eluent, to verify whether the dioxins in Comparative Examples 1 to 3 were lost during the elution process, all the first and second eluents were tested. The results were as follows: In the first eluent of Comparative Examples 1 to 3, O8CDD had a recovery rate of about 30%, 1,2,3,4,6,7,8-H7CDD and 1,2,3,4,7,8,9-H7CDF had a recovery rate of about 10%, and the remaining items also had a low recovery rate. In particular, in Comparative Example 3, 2,3,7,8-T4CDD had a recovery rate of about 40% and 2,3,7,8-T4CDF had a recovery rate of about 50%. These results indicate that the dioxins in Comparative Examples 1 to 3 were lost during the elution process. However, when the first rinsing solution in Examples 1 to 3 was tested, no dioxin component recovery rate was found, which indicates that the dioxins in Examples 1 to 3 were not lost during the rinsing process.

[0077] In summary, the test results of the first and second eluents indicate that the adsorption capacity of dioxins in Examples 1-3 is higher than that in Comparative Examples 1-3. The test results of the first eluent show that Comparative Examples 1-3 all experienced varying degrees of dioxin component loss during hexane elution, with Comparative Example 3 exhibiting the weakest adsorption capacity and significant loss of some dioxin components. In contrast, no dioxin loss occurred during the elution process in Examples 1-3. Considering both the adsorption capacity of the packed column for dioxin components and the elution rate during toluene elution, Examples 1-3 all demonstrate good dioxin adsorption capacity and good elution rate during toluene elution. Example 1, in particular, shows a better balance between adsorption capacity and elution rate, effectively adsorbing dioxin components during elution and achieving complete elution during toluene elution.

[0078] The above description is a preferred embodiment of the invention. It should be noted that, for those skilled in the art, several improvements and modifications can be made without departing from the principle of the invention, and these improvements and modifications are also considered to be within the scope of protection of the invention.

Claims

1. Use of a modified activated carbon in adsorbing dioxins, characterized in that, The preparation method of the modified activated carbon comprises the following steps: alkali lignin and chitosan are added into a basic solution, and a first solution is obtained after mixing uniformly; activated carbon is added into the first solution, and a second solution is obtained after mixing uniformly; the second solution is treated by evaporation to obtain a first solid, and the first solid is activated at 750-850 DEG C for 1.5-3.5 h to obtain a second solid; the second solid is washed with acid, washed with water and dried to obtain a finished product; the ratio of the added amount of alkali lignin to the added amount of chitosan is 1: (1.5-2); the ratio of the added amount of activated carbon to the added amount of alkali lignin is (6-10): 1; The pore structure of the activated carbon is composed of macropores with a pore size of 50-2000 nm, mesopores with a pore size of 2-50 nm and micropores with a pore size of less than 2 nm, and the three kinds of pores are distributed in a tree shape, the mesopores are distributed on the macropores, and the micropores are distributed on the mesopores.

2. The use of the modified activated carbon according to claim 1 in adsorbing dioxins, characterized in that, 2-7 parts of alkali lignin and 7-11 parts of chitosan are added into 100-180 parts of a basic solution according to weight parts, and a first solution is obtained after mixing uniformly.

3. The use of the modified activated carbon according to claim 2 in adsorbing dioxins, characterized in that, 4-6 parts of alkali lignin and 8-9 parts of chitosan are added into 130-160 parts of a basic solution according to weight parts, and a first solution is obtained after mixing uniformly.

4. The use of the modified activated carbon according to claim 1 in adsorbing dioxins, characterized in that, The basic solution is a potassium hydroxide solution, and the concentration of the potassium hydroxide solution is 0.8-1.2 g / mL.

5. The use of the modified activated carbon according to claim 1 in adsorbing dioxins, characterized in that, The second solid is washed with a hydrochloric acid solution with a mass concentration of 5-10% for 10-30 min.

6. The use of the modified activated carbon according to claim 1 in adsorbing dioxins, characterized in that, In the acid washing, water washing and drying of the second solid, the drying conditions are as follows: under vacuum conditions, drying at 100-110 DEG C for 0.5-2.5 h.

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