A nitrogen-doped biochar based on alkaline lignin, its low-temperature pyrolysis preparation method and application

Abstract

This invention belongs to the field of biochar materials technology, and discloses a nitrogen-doped biochar based on basic lignin, its low-temperature pyrolysis preparation method, and its application. The preparation method includes the following steps: pretreated material with basic lignin is mixed and ground with inorganic salts and urea, vacuum dried, calcined at low temperature, washed, and then dried by forced air to obtain nitrogen-doped biochar based on basic lignin. The biochar raw material of this invention is commercially available basic lignin, which is widely available, has a simple composition, and is low in cost. The nitrogen-doped biochar based on basic lignin can be obtained using a simple pyrolysis method. The preparation process is simple, has low temperature requirements, and the obtained biochar has a strong activation effect on persulfate, enabling rapid degradation of organic pollutants in water.

Description

Technical Field

[0001] This invention belongs to the field of biochar materials technology, and particularly relates to a nitrogen-doped biochar based on alkaline lignin, its low-temperature pyrolysis preparation method, and its application. Background Technology

[0002] With the rapid development of industry and agriculture in China, environmental problems have become increasingly complex. It has been reported that over 80% of water bodies are polluted to varying degrees, many with serious exceedances of organic pollutants. Due to the high toxicity and recalcitrant nature of these organic pollutants, traditional treatment methods (such as biological methods, adsorption, and extraction) often face problems such as low efficiency, high cost, and the generation of harmful byproducts during purification. In recent years, advanced oxidation technologies based on persulfate have attracted much attention. Compared to hydrogen peroxide, persulfate is more easily activated by external energy sources or catalysts, thus generating sulfate free radicals with longer survival times and stronger oxidizing power. Therefore, this technology is considered an effective approach to water pollution control. Furthermore, the persulfate catalytic reaction has relatively relaxed requirements for reaction conditions and can be activated through various methods (such as heat, ultrasound, transition metals, transition metal oxides, composite oxides, and carbon materials). Carbon materials, as a high-quality catalyst, have attracted considerable attention from researchers due to their good biocompatibility, wide availability, large specific surface area, acid and alkali resistance, and lack of metal leaching, making them promising for practical applications.

[0003] Biochar is a low-cost, readily available, and environmentally friendly alternative, and as a sustainable catalyst material, it has enormous potential and prospects. However, existing biochar materials are generally prepared using high-temperature pyrolysis as the synthesis method. Biochar catalysts prepared at low temperatures using pyrolysis methods have poor activation efficiency for persulfate, and there is an urgent need to find a low-temperature preparation method to overcome this obstacle. Summary of the Invention

[0004] In order to overcome the drawbacks and shortcomings of the existing technology, which requires high temperature conditions (700-1000℃) for the preparation of biochar catalysts and results in energy waste, and also to solve the problem that biochar catalysts are difficult to activate persulfate and have low efficiency in degrading pollutants, the primary objective of this invention is to provide a low-temperature pyrolysis preparation method for nitrogen-doped biochar based on alkaline lignin.

[0005] Another object of the present invention is to provide nitrogen-doped biochar based on alkaline lignin prepared by the above preparation method.

[0006] Another object of the present invention is to provide the application of the above-mentioned nitrogen-doped biochar based on basic lignin.

[0007] The objective of this invention is achieved through the following technical solution:

[0008] A low-temperature pyrolysis preparation method for nitrogen-doped biochar based on alkaline lignin includes the following steps: mixing and grinding the pretreated material with inorganic salts and urea, vacuum drying, low-temperature calcination, washing, and then drying with forced air to obtain nitrogen-doped biochar based on alkaline lignin.

[0009] The alkaline lignin is commercially available alkaline lignin.

[0010] The pretreatment is a pyrolysis treatment, specifically a pyrolysis treatment performed by heating to 350℃~400℃ at a heating rate of 5~15℃ / min and holding for 1~4 h.

[0011] The grinding was carried out in an agate mortar with added ethanol and water for 15-25 ml, wherein the volume ratio of ethanol to water was 3:2 and the total volume of ethanol and water was 10-15 ml.

[0012] The mass ratio of the alkaline lignin pretreated material, inorganic salts, and urea is (3-4):(20-25):(6-8); the inorganic salts are potassium chloride and sodium chloride in a mass ratio of 1:(1-2).

[0013] The low-temperature calcination is carried out in an argon protective atmosphere at a flow rate of 40-80 mL / min, with the temperature increased to 400-500℃ at a heating rate of 1-10℃ / min and held for 1-4 h.

[0014] The vacuum drying is carried out at a temperature of 80℃ for 2 to 12 hours; the washing is carried out by washing the material three times with ultrapure water, using 20 to 50 ml of ultrapure water each time; the forced-air drying is carried out at a temperature of 60℃ to 80℃ for 8 to 12 hours.

[0015] A nitrogen-doped biochar based on alkaline lignin prepared by the above-described preparation method.

[0016] The above-mentioned application of nitrogen-doped biochar based on alkaline lignin in the removal of organic pollutants from wastewater is carried out according to the following operating steps: under stirring conditions, nitrogen-doped biochar based on alkaline lignin and persulfate are added sequentially to the wastewater to react and remove organic pollutants; the mass ratio of nitrogen-doped biochar based on alkaline lignin, persulfate and organic pollutants is (0.1-2):(0.1-2):(0.01-0.05); the stirring is carried out at a temperature of 21-30℃ and a speed of 250-400 rpm for 20 min to 2 h.

[0017] The mass ratio of nitrogen-doped biochar based on alkaline lignin, persulfate, and organic pollutants is 0.05:0.03:0.05. Under this selection, the removal effect of organic pollutants is optimal. The stirring time is 30 min to 1 h, and the temperature is 25 °C.

[0018] The pH values ​​of the wastewater were 3.56, 4.58, 10.11 and 11.65, respectively. The efficiency of nitrogen-doped biochar based on alkaline lignin in degrading pollutants in the water was almost unaffected by the pH value of the water body.

[0019] The persulfate is a permonosulfate.

[0020] In this invention, nitrogen-doped biochar based on alkaline lignin achieves a 100% removal rate of organic pollutants by activating persulfate. The nitrogen-doped biochar based on alkaline lignin can be repeatedly tested; after three reactions, the removal rate of organic pollutants still reaches over 95%, and it is largely unaffected by most inorganic anions in the water. Specifically, by adding common inorganic anions found in the environment to the wastewater and repeating the steps of activating persulfate with nitrogen-doped biochar based on alkaline lignin to remove organic pollutants, the efficiency of this biochar in activating persulfate to remove organic pollutants remains above 80%. This biochar possesses good cycle stability and anti-interference properties, not only saving economic costs in wastewater treatment but also allowing its application in high-salinity wastewater systems to degrade organic pollutants.

[0021] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0022] (1) Compared with cumbersome mechanical ball milling, multi-step processing and high-temperature calcination, the present invention prepares nitrogen-doped biochar based on alkaline lignin with high efficiency activation of persulfate in one step by simply mixing and grinding and then calcining at low temperature. The preparation of this biochar is simple, has low requirements for equipment and pyrolysis temperature, has a wide range of raw material sources, clear and stable composition, low cost, and avoids secondary pollution to the environment. The biochar obtained has high activation efficiency of persulfate, good cycle stability of the material, and excellent resistance to aquatic environment.

[0023] (2) Based on the specific experimental data, the nitrogen-doped biochar based on alkaline lignin of this invention has a degradation efficiency of up to 100% for organic pollutants in the application of activating persulfate to remove organic pollutants in water, which shows that it has a good application prospect in the field of water pollution treatment. Attached Figure Description

[0024] Figure 1 The graph shows the degradation efficiency of paracetamol by nitrogen-doped biochar materials based on alkaline lignin prepared in Examples 1 and 2.

[0025] Figure 2 The graph shows the degradation efficiency of AL@NX prepared in Example 1 on paracetamol at different PMS concentrations.

[0026] Figure 3 The graph shows the degradation efficiency of AL@NX prepared in Example 1 on paracetamol at different material concentrations.

[0027] Figure 4 The graph shows the degradation efficiency of AL@NX cyclically degrading paracetamol prepared in Example 1.

[0028] Figure 5 The degradation efficiency of AL@NX prepared in Example 1 on paracetamol under anionic and humic acid conditions is shown in the figure.

[0029] Figure 6 The graph shows the degradation efficiency of AL@NX prepared in Example 1 for paracetamol under different water conditions.

[0030] Figure 7 The graph shows the degradation efficiency of AL@NX prepared in Example 1 on paracetamol at different pH values.

[0031] Figure 8 Scanning electron microscope images of the materials prepared for Examples 1 and 2 (a.AL@NX b.AL@N c.AL@X d.AL@BC).

[0032] Figure 9 Raman spectroscopy results for the materials prepared in Examples 1 and 2. Detailed Implementation

[0033] The present invention will be further described in detail below with reference to the embodiments and accompanying drawings, but the embodiments of the present invention are not limited thereto.

[0034] Example 1

[0035] This embodiment describes the low-temperature pyrolysis preparation of nitrogen-doped biochar based on basic lignin. The specific steps are as follows:

[0036] (1) Purchase commercially available alkaline lignin. First, place an appropriate amount of alkaline lignin in a tube furnace and purge with argon gas for 20 to 40 minutes at a flow rate of 80 to 100 ml / min to ensure that the air in the tube furnace is completely replaced by the protective gas. Then, set the heating program with a heating rate of 5°C / min, and heat from 25°C to 400°C. Hold for 1 to 2 hours to obtain a black powder. Place the black powder in a mortar and grind for 10 to 20 minutes. Pass through a 150-mesh sieve to obtain an alkaline lignin biochar precursor.

[0037] (2) Mix the alkaline lignin precursor, urea and inorganic salt in a mass ratio of 3:6:20, place them in an agate mortar, add 3 ml of anhydrous ethanol and 2 ml of ultrapure water respectively, grind for 10-15 min, place the resulting mixture in a drying oven, set the temperature to 80℃, and dry for 12 h to obtain a gray mixture. Place the gray mixture in a mortar and grind for 10-20 min until the gray mixture changes from a block to a gray powder.

[0038] (3) The gray powder was placed in a quartz boat and put into a tube furnace. Argon gas was first passed through for 20 minutes at a flow rate of 100 ml / min to ensure that the air in the tube furnace was completely replaced by the protective gas (argon). Then, the heating program was set with a heating rate of 1℃ / min, from 25℃ to 500℃. After cooling for 4 hours, a black and white mixture was obtained (the black powder was the material and the white powder was the salt). The mixture was washed three times with ultrapure water. The material and salt were separated by taking advantage of the fact that salts are easily soluble in water. The mixture was filtered through a 0.45-micron filter membrane, leaving the black powder. The powder was then placed in a drying oven at a temperature of 80℃ for 12 hours to obtain nitrogen-doped biochar based on alkaline lignin, named AL@NX.

[0039] Example 2

[0040] This embodiment is an investigation and test of key factors in biochar preparation.

[0041] (1) After repeating step (1) of Example 1, the obtained alkaline lignin biochar precursor was added to an agate mortar, and 3 ml of anhydrous ethanol and 2 ml of ultrapure water were added respectively. The mixture was ground for 10-15 min. The resulting mixture was placed in a drying oven with the temperature set at 80°C and the drying time set at 12 h to obtain a black powder. Then, step (3) of Example 1 was repeated to obtain the original biochar, which was named AL@BC.

[0042] (2) After repeating step (1) of Example 1, the obtained alkaline lignin biochar precursor and urea were added to an agate mortar, and 3 ml of anhydrous ethanol and 2 ml of ultrapure water were added respectively. The mixture was ground for 10-15 min. The resulting mixture was placed in a drying oven with the temperature set at 80°C and the drying time set at 12 h to obtain a dark gray mixture. Then, step (3) of Example 1 was repeated to obtain biochar that was not prepared by the molten salt assisted method, named AL@N.

[0043] (3) After repeating step (1) of Example 1, the obtained alkaline lignin biochar precursor and inorganic salt were added to an agate mortar, and 3 ml of anhydrous ethanol and 2 ml of ultrapure water were added respectively. The mixture was ground for 10-15 min. The resulting mixture was placed in a drying oven with the temperature set at 80°C and the drying time set at 12 h to obtain a dark gray mixture. Then, step (3) of Example 1 was repeated to obtain biochar prepared without the addition of nitrogen source, which was named AL@X.

[0044] AL@NX, AL@N, AL@X and AL@BC prepared in Examples 1 and 2 were added to a 50 ppm paracetamol solution, respectively. Persulfate (PMS) was also added to ensure that the material concentration in the system was 0.1 g / L and the PMS concentration was 1 mM. The reaction was carried out under room temperature and pressure with magnetic stirring for 30 min.

[0045] Take 0.5 mL of the PMS-treated water sample, add 0.5 mL of ethanol, and determine the acetaminophen concentration by high-performance liquid chromatography. Figure 1 As shown, the removal rates of paracetamol by AL@NX, AL@N, AL@X, and AL@BC were 100%, 95.7%, 11.8%, and 7.5%, respectively. However, the degradation rate of the AL@N system was much lower than that of the AL@NX system. Example 2 shows that nitrogen sources and molten salts can effectively improve the removal efficiency of paracetamol by biochar.

[0046] Example 3

[0047] This embodiment is a test of the performance of nitrogen-doped biochar based on alkaline lignin provided in Example 1 in reducing paracetamol under different persulfate concentrations.

[0048] AL@NX prepared in Example 1 was added to a 50 ppm paracetamol solution, along with persulfate (PMS) to ensure that the concentration of AL@NX in the system was 0.1 g / L and the concentration of PMS was 0.25 mM, 0.5 mM, 1.00 mM and 2.00 mM. The mixture was then magnetically stirred at room temperature and pressure for 30 min.

[0049] Take 0.5 mL of the PMS-treated water sample, add 0.5 mL of methanol, and determine the paracetamol concentration by high-performance liquid chromatography. Figure 2 As shown, a PMS concentration of 1.00 mM is the most suitable concentration for the reaction system.

[0050] Example 4

[0051] This embodiment is a test of the performance of nitrogen-doped biochar based on alkaline lignin in reducing paracetamol under different material concentrations, as provided in Example 1.

[0052] The AL@NX prepared in Example 1 was added to a 50 ppm paracetamol solution, along with persulfate (PMS) to ensure that the concentrations of AL@NX in the system were 0.05 g / L, 0.075 g / L, 0.100 g / L and 0.200 g / L, and the concentration of PMS was 1 mM. The reaction was carried out under room temperature and pressure with magnetic stirring for 30 min.

[0053] Take 0.5 mL of the PMS-treated water sample, add 0.5 mL of methanol, and determine the paracetamol concentration by high-performance liquid chromatography. Figure 3 As shown, a material concentration of 0.100 g / L is the most suitable concentration for the reaction system.

[0054] Example 5

[0055] This embodiment is a test of the cyclic stability of the nitrogen-doped biochar activated by alkaline lignin for the persulfate degradation of paracetamol provided in Example 1.

[0056] The AL@NX used in Example 2 was filtered through a 0.45-micron filter membrane, washed three times with ultrapure water, placed in a drying oven at 80°C for 12 hours, and then removed. The PMS treatment step of Example 2 was repeated. 0.5 mL of the PMS-treated water sample was taken, and 0.5 mL of methanol was added. The concentration of paracetamol was determined by high-performance liquid chromatography. Figure 4 As shown, after three experiments, the removal rate of acetaminophen by biochar-activated persulfate remained as high as 95%.

[0057] Example 6

[0058] This embodiment is a test of the interference resistance of the material provided in Example 1, which is nitrogen-doped biochar activated by alkaline lignin to degrade paracetamol using persulfate.

[0059] 1) Add 10 mol / L Cl to a 50 ppm paracetamol solution. - HCO3 - H2PO4 - Add 20 mg / L of humic acid (HA), then add the biochar prepared in Example 1, along with persulfate, to ensure that the AL@NX concentration in the system is 0.1 g / L and the PMS concentration is 1 mM. Stir the reaction magnetically at room temperature and pressure for 30 min.

[0060] Take 0.5 mL of the PMS-treated water sample, add 0.5 mL of methanol, and determine the paracetamol concentration by high-performance liquid chromatography. Figure 5 As shown, biochar activation had almost no impact on the removal rate of paracetamol by persulfate, while HCO3 was the most affected. -The removal rate of paracetamol also reached over 70%.

[0061] 2) Replace the ultrapure water in the 50ppm paracetamol solution prepared in step 1) with lake water and tap water, add the biochar provided in Example 1, and add persulfate to ensure that the AL@NX concentration in the system is 0.1g / L and the PMS concentration is 1mM. Stir the reaction magnetically for 30min at room temperature and pressure.

[0062] Take 0.5 mL of the PMS-treated water sample, add 0.5 mL of methanol, and determine the paracetamol concentration by high-performance liquid chromatography. Figure 6 As shown, the removal rate of acetaminophen by biochar-activated persulfate was almost unaffected by different aquatic environments, reaching 100%.

[0063] Example 7

[0064] The pH of the paracetamol solution was adjusted using sodium hydroxide and hydrochloric acid solutions (pH values ​​were 3.56, 4.58, 10.11 and 11.65, respectively). Then, 0.1 g / L of AL@NX prepared in Example 1 and 1 mM of PMS were added to the 50 ppm paracetamol solution and the mixture was magnetically stirred for 30 min at room temperature and pressure.

[0065] Take 0.5 mL of the PMS-treated water sample, add 0.5 mL of methanol, and determine the paracetamol concentration by high-performance liquid chromatography. Figure 7 As shown, the removal rate of acetaminophen by biochar-activated persulfate was almost unaffected by pH, reaching over 95%.

[0066] Example 8

[0067] The biochar prepared in Examples 1 and 2 above was subjected to scanning electron microscopy morphology testing and Raman spectroscopy. The test results are analyzed as follows: Figure 8 and Figure 9 Compared to synthesis methods that do not incorporate nitrogen sources and molten salts, alkaline lignin biochar prepared using urea and molten salts has a more disordered carbon structure, providing more active sites for activating persulfate.

[0068] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for preparing nitrogen-doped biochar based on basic lignin by low-temperature pyrolysis, characterized in that... The process includes the following steps: mixing and grinding the pretreated material with basic lignin, inorganic salts, and urea, vacuum drying, low-temperature calcination, washing, and then drying with forced air to obtain nitrogen-doped biochar based on basic lignin. The pretreatment is a pyrolysis treatment, specifically a pyrolysis treatment performed by heating to 350 ℃~400 ℃ at a heating rate of 5~15 ℃ / min and holding for 1~4 h. The mass ratio of the alkaline lignin pretreated material, inorganic salts, and urea is (3~4):(20~25):(6~8); the inorganic salt components are potassium chloride and sodium chloride in a mass ratio of 1:(1~2). The low-temperature calcination is carried out in an argon protective atmosphere at a flow rate of 40-80 mL / min, with the temperature increased to 400-500 °C at a heating rate of 1-10 °C / min and held for 1-4 h.

2. The preparation method according to claim 1, characterized in that: The alkaline lignin is commercially available alkaline lignin.

3. The preparation method according to claim 1, characterized in that: The grinding was carried out in an agate mortar with added ethanol and water for 15-25 minutes, wherein the volume ratio of ethanol to water was 3:2 and the total volume of ethanol and water was 10-15 ml.

4. The preparation method according to claim 1, characterized in that: The vacuum drying is carried out at a temperature of 80 ℃ for 2~12 h; the washing is carried out by washing the material three times with ultrapure water, using 20~50 ml of ultrapure water each time; the forced air drying is carried out at a temperature of 60 ℃~80 ℃ for 8 h~12 h.

5. A nitrogen-doped biochar based on alkaline lignin prepared by the preparation method according to any one of claims 1 to 4.

6. The application of nitrogen-doped biochar based on alkaline lignin according to claim 5 in the removal of organic pollutants from wastewater, characterized in that: The application is carried out according to the following steps: Under stirring conditions, nitrogen-doped biochar based on alkaline lignin and persulfate are added sequentially to the wastewater to react and remove organic pollutants; the mass ratio of nitrogen-doped biochar based on alkaline lignin, persulfate and organic pollutants is (0.1~2):(0.1~2):(0.01~0.05); the stirring is carried out at a temperature of 21~30℃ and a speed of 250~400 rpm for 20 min~2 h.

7. The application according to claim 6, characterized in that: The mass ratio of nitrogen-doped biochar based on alkaline lignin, persulfate, and organic pollutants is 0.05:0.03:0.05; the stirring time is 30 min to 1 h, and the temperature is 25 °C.

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