Method for producing biochar for PFAS removal

Abstract

To provide a method for producing biochar for PFAS removal that enables environmentally friendly and sustainable production.SOLUTION: Biochar for PFAS removal is produced by drying a material derived from an aquatic plant of the genus Alternanthera or the genus Ludwigia and then carbonizing it at 350°C to 1000°C.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for producing biochar for removing PFAS. [Background technology]

[0002] Recently, perfluoroalkyl and polyfluoroalkyl compounds (hereinafter referred to as "PFAS") have been used in food packaging materials, textile products, fire foams, etc. due to their water- and oil-repellent properties, but they have raised concerns about their persistence in the environment and their tendency to accumulate in living organisms.

[0003] In particular, the use of perfluorooctane sulfonate (PFOS), perfluorooctanoic acid (PFOA), and perfluorohexane sulfonate (PFHxS), which are types of PFAS, has been restricted or eliminated internationally.

[0004] Technologies for adsorbing and removing such PFAS, particularly activated carbon that adsorbs and removes PFAS present in aqueous environments, are known (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 7427849 Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention aims to solve a technical problem that must be solved in order to provide an environmentally friendly and sustainable adsorbent that can replace conventional activated carbon for PFAS removal. [Means for solving the problem]

[0007] The inventors have discovered that biochar, obtained by carbonizing aquatic plants of the genus Polygonum or Polygonum, which have traditionally been incinerated, may be an alternative to activated carbon for removing PFAS.

[0008] To achieve the above object, the method for producing biochar for PFAS removal according to the present invention carbonizes a material derived from an aquatic plant of the genus Adonis or Polygonum.

[0009] According to this configuration, aquatic plants of the genus Polygonum or Polygonum, which have traditionally been incinerated, can be effectively utilized to obtain environmentally friendly and sustainable biochar for removing PFAS. [Effects of the Invention]

[0010] According to this invention, it is possible to obtain environmentally friendly and sustainable biochar for PFAS removal. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a flowchart showing the steps of a method for producing biochar for PFAS removal according to one embodiment of the present invention. [Figure 2] 1 is a table showing the results of an analysis of the basic properties of the adsorbents of Examples and Comparative Examples. [Figure 3] Graph showing the experimental results of a PFOS adsorption experiment. [Figure 4] Graph showing the experimental results of a PFOA adsorption experiment. [Figure 5] Graph showing experimental results of PFHxS adsorption experiments. [Figure 6] 1 is a table showing PFAS adsorption rates for Examples and Comparative Examples. DETAILED DESCRIPTION OF THE INVENTION

[0012] An embodiment of the present invention will be described with reference to the drawings. Note that, hereinafter, when referring to the number, numerical value, amount, range, etc. of components, unless otherwise specified or when it is clearly limited to a specific number in principle, the number is not limited to the specific number, and may be more or less than the specific number.

[0013] First, we will explain the material of the biochar for removing PFAS (hereinafter referred to as "biochar") obtained by the production method according to one embodiment of the present invention.

[0014] Biochar is made from materials derived from aquatic plants of the genus Polygonum or Polygonum genus, i.e., aquatic plants of the genus Polygonum or Polygonum genus themselves, or aquatic plants of the genus Polygonum or Polygonum genus that have been subjected to various treatments.

[0015] Aquatic plants of the genus Polygonum or Polygonum genus are perennial plants that can live both on land and in water. They have a strong reproductive ability and not only have a negative impact on aquatic ecosystems, but when they proliferate in rice paddies and waterways, they block the flow of water, hindering irrigation and agriculture, making them a problematic, noxious weed. After being eradicated, they are generally incinerated.

[0016] However, because aquatic plants contain a lot of water, incineration places a heavy burden on treatment facilities. Therefore, it is desirable to effectively utilize aquatic plants of the genus Azolla or Polygonum as a resource.

[0017] A flowchart showing the steps of a biochar production method is shown in Figure 1. The following describes an example of producing biochar from Azolla longus, a species of the Azolla genus. However, the biochar material may be any aquatic plant derived from the Azolla or Polygonum genus.

[0018] First, the long-legged weed that has been eradicated from rice paddies, waterways, etc. is dried (step S1).

[0019] The vine weed is dried until it reaches a moisture content suitable for carbonization, as described below. Methods for drying the vine weed include, for example, spreading it on a blue sheet and drying it in the sun, or using a dryer to dry it efficiently in a short time. Drying conditions for the dryer include, for example, setting the drying temperature to approximately 45°C and the drying time overnight. The drying temperature and drying time can be adjusted as appropriate depending on the variety and moisture content of the aquatic plant to be dried.

[0020] Before drying, it is preferable to trim the vines to a predetermined length (for example, about 15 cm), which allows the vines to dry smoothly and uniformly.

[0021] Next, the dried vine weed is carbonized (step S2).

[0022] Carbonization of Asarum is carried out by pyrolyzing Asarum under low-oxygen conditions using a pyrolysis furnace such as an electric muffle furnace. The carbonization conditions in the pyrolysis furnace are, for example, a carbonization temperature of 350°C to 1000°C and a carbonization time of approximately 1 to 4 hours. The carbonization temperature and time can be adjusted depending on the desired biochar properties (e.g., pH value, carbon content, total pore volume, specific surface area, average pore diameter, etc.). Plant roots are known to store nitrogen, and the inclusion of Asarum roots in the biochar material is thought to increase the nitrogen content of the biochar.

[0023] By carbonizing the alder weed in this way and then crushing and molding the biochar into a shape suitable for its intended use, it is expected to exhibit PFAS adsorption capacity roughly equivalent to that of conventional activated carbon.

[0024] Furthermore, by producing biochar from materials derived from aquatic plants of the genus Azolla or Polygonum, which have traditionally been incinerated, it is possible to obtain environmentally friendly and sustainable biochar. [Example]

[0025] Comparative experiments were conducted to evaluate the adsorption performance of two types of biochar obtained by the method for producing biochar for PFAS removal according to the present invention (hereinafter referred to as "Experimental Examples 1 and 2"), a coal-based activated carbon manufactured by Serachem Co., Ltd. (hereinafter referred to as "Comparative Example 1"), and a coconut shell activated carbon manufactured by Serachem Co., Ltd. (hereinafter referred to as "Comparative Example 2"). All of the particles in Experimental Examples 1 and 2 and Comparative Examples 1 and 2 were sieved to a particle size of 600 μm or less.

[0026] (1) Experimental method (1.1) Materials used Experimental Example 1 The vine weed was cut into pieces approximately 15 cm long and dried overnight in a dryer at 45°C. The dried vine weed was placed in an electric muffle furnace (FUW242PA, manufactured by Toyo Seisakusho Co., Ltd.) and carbonized at 600°C for 4 hours to obtain biochar 600BC.

[0027] Experimental Example 2 The vine weed was cut into pieces approximately 15 cm long and dried overnight in a dryer at 45°C. The dried vine weed was placed in an electric muffle furnace (FUW242PA, manufactured by Toyo Seisakusho Co., Ltd.) and carbonized at 900°C for 4 hours to obtain biochar 900BC.

[0028] (1.2) Test water The following two types of test water were prepared: River water collected in Japan (hereinafter referred to as "river water") For comparison, a mixed standard solution of three organic fluorine compounds, PFOA, PFOS, and PFHxS (2 μg / mL, for water quality testing, Fujifilm Wako Pure Chemical Corporation) was diluted with purified water to prepare 100 ng / L simulated PFAS-contaminated water (hereinafter referred to as "simulated water").

[0029] (1.3) Experimental Method Adsorption experiments were conducted in 10 test plots: eight plots in which four types of charcoal samples (Experimental Examples 1 and 2 and Comparative Examples 1 and 2) were added to two types of test water (simulated water and river water), and two test plots in which simulated water and river water were used as controls without any charcoal samples. 0.5 g of charcoal sample and 25 mL of test water were placed in a 50 mL methanol-washed polyester centrifuge tube to achieve a solid-liquid ratio of 1:50 (charcoal sample:test water). The tubes were shaken at 225 rpm for 63.5 hours using a shaker (Taitec Corporation, SR-2w). The adsorption experiments were conducted at room temperature (25 °C) in five replicates. After shaking, the tubes were centrifuged at 2,500 rpm for 20 minutes in a centrifuge (Kubota Manufacturing Co., Ltd., KN-70). The filtrates from the five replicates were then mixed to prepare a single analytical sample.

[0030] (2)Analysis items (2.1) Analysis of basic properties of adsorbents pH value The pH of the charcoal sample and test water was measured using a pH meter (LAQUA F-71, manufactured by Horiba, Ltd.). The pH of the charcoal sample was measured by mixing the charcoal sample and pure water at a solid-liquid ratio of 1:20 (charcoal sample:pure water), shaking the mixture for 1.5 hours using a shaker (NR-150, manufactured by Taitec Co., Ltd.), leaving it to stand for 30 minutes, and then measuring the adjusted eluate.

[0031] Carbon and nitrogen content The charcoal samples were measured using a CHN Coder (J Science Lab, CHN Coder JM10), and the carbon and nitrogen contents in the charcoal samples were calculated.

[0032] Total pore volume, specific surface area and average pore diameter To analyze the total pore volume, specific surface area, and average pore diameter of the biochar, the charcoal samples were measured with a physical adsorption analyzer (ASAP) (Micromeritics, ASAP 2020).

[0033] ·Functional group To compare the properties of activated carbon and biochar, the charcoal samples were measured using a Fourier transform infrared spectrophotometer (FT-IR) (Shimadzu Corporation, IRAffinity-1s) using attenuated total reflectance (ATR) to analyze the surface functional groups of the charcoal samples.

[0034] (2.2) PFAS adsorption amount Sample pretreatment PFOA, PFOS, and PFHxS were analyzed using solid-phase extraction-liquid chromatography-mass spectrometry. First, a 100 mL aliquot of sample was prepared. A mixed internal standard solution of three organofluorine compounds, PFOA, PFOS, and PFHxS (2 μg / mL for water quality testing, Fujifilm Wako Pure Chemical Corporation), was diluted with a methanol-water mixture and 50 μL of the prepared 2 ng / mL standard solution was added. The sample was then passed through a solid-phase column at a rate of approximately 20 mL / min for solid-phase extraction. The sample container was then rinsed with 10 mL of purified water, and the rinse solution was then passed through the solid-phase column. The column was then centrifuged at 3,000 rpm for 10 minutes to remove water. After dehydration, 5 mL of methanol was passed through the column, and the eluate was collected in a 10 mL stoppered test tube. The eluate was dried by blowing nitrogen gas through the eluate, and the volume was adjusted to 1 mL with a methanol-water mixture to prepare the test solution.

[0035] Liquid chromatograph mass spectrometer (LC / MS / MS) 20 μL of the test solution was injected into an LC / MS / MS (LC: AQUITY UPLC Hclass, manufactured by Nihon Waters Co., Ltd.; MS: TQ-s micro, manufactured by Nihon Waters Co., Ltd.). The mobile phase was an aqueous solution of ammonium acetate (10 mmol / L) and acetonitrile. The peak area of ​​the peak corresponding to the retention time was measured, and the ratio of the peak area of ​​each target substance to the standard substance was calculated. The concentration ratio of each target substance to the standard substance was then calculated from the calibration curve.

[0036] Calculating PFAS concentrations The concentration (ng / L) of each target substance in the sample was calculated using the following formula:

[0037]

number

[0038] (3) Experimental results (3.1) Basic characteristics of adsorbents The analysis results of the basic properties of the adsorbents of Comparative Examples 1 and 2 and Experimental Examples 1 and 2 are shown in Fig. 2. In Figs. 2 to 6, "ACW" corresponds to Comparative Example 1, "BCW" corresponds to Comparative Example 2, "600BC" corresponds to Example 1, and "900BC" corresponds to Example 2.

[0039] pH When the pH values ​​of Comparative Examples 1 and 2 were compared with those of Experimental Examples 1 and 2, the latter showed higher pH values. When Comparative Example 1 and Comparative Example 2 were compared, there was no significant difference in pH value, and when Experimental Example 1 and Experimental Example 2 were compared, the latter, which had a higher carbonization temperature, showed a higher pH value.

[0040] Carbon content The carbon content was higher in Comparative Examples 1 and 2 than in Experimental Examples 1 and 2, with Comparative Example 2 showing the highest carbon content. The carbon content in Experimental Examples 1 and 2 was about 70% of that in Comparative Examples 1 and 2, and no difference in carbon content was observed depending on the carbonization temperature.

[0041] ·Nitrogen content The nitrogen content was higher in Experimental Examples 1 and 2 than in Comparative Examples 1 and 2, with Experimental Example 1 showing the highest nitrogen content, approximately twice that of Experimental Example 2. Furthermore, Comparative Example 1 showed a higher nitrogen content than Comparative Example 2.

[0042] Total pore volume, specific surface area and average pore diameter Comparing the results of total pore volume, specific surface area, and average pore diameter between Experimental Examples 1 and 2, Experimental Example 2 showed a total pore volume value 15.3 times that of Experimental Example 1 and a specific surface area value 39.9 times that of Experimental Example 1, and Experimental Example 1 showed an average pore diameter value 2.61 times that of Experimental Example 2. In Comparative Example 2, the total pore volume and specific surface area were the largest compared to Experimental Examples 1 and 2, but the average pore diameter was the smallest.

[0043] ·Functional group FT-IR analysis was performed on Comparative Examples 1 and 2 and Experimental Examples 1 and 2 before and after the adsorption experiment. As a result, wavelength peaks were only observed in Experimental Examples 1 and 2, and carbon-hydrogen bonds and hydroxyl groups were confirmed in both Experimental Examples 1 and 2. Furthermore, carbonyl groups were confirmed only in Experimental Example 1. The FT-IR analysis results were the same before and after the adsorption experiment.

[0044] (3.2) PFAS adsorption experiment results PFOS The results of the PFOS adsorption experiments for Comparative Examples 1 and 2 and Experimental Examples 1 and 2 are shown in Figure 3. Comparative Example 1 adsorbed all of the PFOS detectable in the test water, both the simulated water and the river water. Comparative Example 2 adsorbed all of the PFOS detectable in the river water, but was unable to adsorb all of the PFOS in the simulated water (0.35 ng / L of linear PFOS, 0.06 ng / L of branched PFOS, and a total of 0.41 ng / L remained). Experimental Example 2 adsorbed all of the PFOS detectable in the test water, both the simulated water and the river water. Experimental Example 1 adsorbed all of the PFOS detectable in the river water, but was unable to adsorb all of the PFOS in the simulated water (0.18 ng / L of linear PFOS, 0.06 ng / L of branched PFOS, and a total of 0.24 ng / L remained).

[0045] PFOA The results of the PFOA adsorption experiments for Comparative Examples 1 and 2 and Experimental Examples 1 and 2 are shown in Figure 4. Comparative Examples 1 and 2 adsorbed all detectable PFOA in the river water, but were unable to adsorb all of the linear PFOA in the simulated water (0.08 ng / L remained in Comparative Example 1, and 0.20 ng / L remained in Comparative Example 2). Experimental Example 2 adsorbed all of the detectable PFOA in the test water, both in the simulated water and the river water. Experimental Example 1 was unable to adsorb all of the linear PFOA in the simulated water and the river water (2.58 ng / L remained in the simulated water, and 0.13 ng / L remained in the river water). PFHxS The results of the PFHxS adsorption experiments for Comparative Examples 1 and 2 and Experimental Examples 1 and 2 are shown in Figure 5. Comparative Example 1 adsorbed all detectable PFHxS in both the simulated water and the river water, whereas Comparative Example 2 adsorbed all detectable PFHxS in the river water but failed to adsorb all linear PFHxS in the simulated water (0.14 ng / L remained). Experimental Example 2 adsorbed all detectable PFHxS in both the simulated water and the river water, whereas Experimental Example 1 failed to adsorb all PFHxS in either the simulated water or the river water (2.17 ng / L of linear PFHxS and 0.60 ng / L of branched PFHxS remained in the simulated water, totaling 2.76 ng / L; and 0.17 ng / L of linear PFHxS and 0.08 ng / L of branched PFHxS remained in the river water, totaling 0.25 ng / L).

[0046] (4) Discussion (4.1) Basic characteristics of adsorbents pH The results of Experimental Example 2, which showed a higher pH value than Experimental Example 1, were compared with those of previous studies, and it was inferred that the higher the carbonization temperature when producing biochar, the more ash there will be in the biochar, and the higher the pH value.

[0047] Total carbon content It was confirmed that the total carbon amounts in Comparative Examples 1 and 2 and Experimental Examples 1 and 2 were equivalent to the total carbon amounts known from previous studies (total carbon amount of activated carbon: approximately 900 mg / g, total carbon amount of biochar: 400 to 700 mg / g).

[0048] ·Total nitrogen content It was confirmed that the total nitrogen amounts in Experiments 1 and 2 were both higher than the values ​​shown in previous studies. Plant roots can act as a nitrogen storage site, and Experiments 1 and 2 also contained a large amount of the roots of Coleus orbiculatus. This may have been the reason for the higher total nitrogen amounts in Experiments 1 and 2.

[0049] Total pore volume, specific surface area and average pore diameter The measurement results for Comparative Example 2 were comparable to those of previous studies, suggesting that activated carbon produced by steam activation also possesses the characteristic of having a smaller average pore diameter compared to activated carbon produced by chemicals. Comparing the measurement results for Comparative Examples 1 and 2, a tendency was observed for the total pore volume and specific surface area to increase with increasing carbonization temperature. This result is consistent with previous studies, and the total pore volume and specific surface area of ​​Experimental Example 2 are considered to be higher than those of previous studies for biochar derived from plant materials. Furthermore, the average pore diameter decreased with increasing carbonization temperature. Based on previous studies, this result suggests that micropores were formed due to the release of volatile substances contained in biochar as the pyrolysis temperature increased. (4.2) Adsorption experiment Figure 6 shows the calculated adsorption rates for Comparative Examples 1 and 2 and Experimental Examples 1 and 2. Figure 6 shows that both Comparative Examples 1 and 2 achieved adsorption rates of over 99%. Previous studies have evaluated the adsorption capacity of activated carbon for PFAS, and similar results were obtained in this experiment. Experimental Example 2 demonstrated a PFAS adsorption capacity equivalent to that of activated carbon. Experimental Example 1 demonstrated lower results for branched-chain PFOA and branched-chain PFHxS compared to activated carbon and Comparative Example 2, but demonstrated sufficient adsorption capacity with adsorption rates of over 95% for all PFOS, all PFOA, and all PFHxS. Furthermore, Experimental Example 1 appeared to exhibit the highest adsorption rate for PFOS among PFOS, PFOA, and PFHxS. Contrary to expectations, the PFAS concentration in the river water was lower than in the simulated water, so no significant differences were observed between the river water (containing impurities other than PFAS) and the simulated water (containing no impurities other than PFAS).

[0050] Regarding the mechanism of PFAS adsorption, the results of FT-IR analysis showed that no wavelengths indicating functional groups were confirmed in Comparative Examples 1 and 2, and that there was no change in the wavelengths indicating functional groups before and after the adsorption experiments in Experimental Examples 1 and 2. This suggests that physical adsorption of PFAS occurs on activated carbon and biochar, rather than chemical adsorption by functional groups.

[0051] The ASAP measurement results confirmed high total pore volume and specific surface area values ​​in Comparative Example 2 and Experimental Example 2, which had adsorption rates of over 99%, suggesting that the total pore volume and specific surface area are related to PFAS adsorption. However, in Experimental Example 1, despite low total pore volume and specific surface area values, an adsorption rate of over 95% was obtained. This is thought to be related to the fact that the largest average pore diameter was obtained at 600BC, suggesting that alder weed-derived biochar may be an adsorbent with excellent adsorption properties for PFAS over a wide range of carbonization temperatures.

[0052] (5) Summary In this experiment, adsorption experiments were conducted to evaluate the adsorption and removal performance of PFAS from water using biochar derived from Aspergillus orbiculatus. Both Experiments 1 and 2 suggested an adsorption rate of over 95% for PFAS. In particular, Experiment 2 confirmed that the adsorption capacity was at the same level as activated carbon.

[0053] The present invention can be modified in various ways without departing from the spirit of the present invention, and it goes without saying that the present invention also covers such modifications.

[0054] For example, instead of the carbonization process using a carbonization furnace such as the muffle furnace described above, hydrothermal carbonization can be used, in which a reaction proceeds using water as a catalyst under anaerobic conditions and high temperature and pressure (e.g., 150°C to 400°C). Unlike carbonization processes using a muffle furnace, hydrothermal carbonization does not require the material to be dried beforehand because carbonization of the material proceeds in a wet state. After drying, the hydrothermal carbonized material is crushed and molded into a shape suitable for its intended use.

[0055] Furthermore, the present invention can be applied not only to adsorbents that adsorb and remove PFAS present in the aquatic environment, but also to soil improvement materials that are buried in agricultural soil, etc.

Claims

1. A method for producing biochar for removing PFAS, comprising carbonizing a material derived from an aquatic plant of the genus Polygonum or Polygonum.

2. 2. The method for producing biochar for removing PFAS according to claim 1, wherein the material is dried and then carbonized at 350°C to 1000°C.

3. The method for producing biochar for removing PFAS according to claim 1, characterized in that the material is hydrothermally carbonized at 150°C to 400°C.

Images