A process for preparing straw biomass charcoal by thermochemical oxidation and application method thereof

Abstract

The application discloses a kind of straw biomass charcoal thermochemical oxidation preparation process and application method, comprising: cutting into small section, washing, drying, grinding, obtain straw powder;Straw powder carbonization obtains straw charcoal;Nitrogen, TiO2 and ZnO are incorporated into straw charcoal material, and obtain doped straw charcoal;Zero-valent iron is loaded in doped straw charcoal, solid-liquid separation and drying, heat treatment obtains straw biomass charcoal adsorption material.The elemental iron of the application is adsorbed and attached in straw charcoal, and the straw biomass charcoal adsorption material obtained has strong adsorption performance on heavy metal elements in wastewater, uses nitrogen-containing heterocyclic compound and nano TiO2 powder, nano ZnO powder as the dopant of straw charcoal, gives the ability of straw biomass charcoal to reduce and fix heavy metal elements, improves the utilization rate of straw biomass charcoal adsorption material to light, and improves the adsorption capacity of straw biomass charcoal adsorption material to heavy metal elements.

Description

Technical Field

[0001] This invention belongs to the field of biochar and pollution treatment technology. More specifically, this invention relates to a thermochemical oxidation preparation process and application method of straw biochar. Background Technology

[0002] Biochar is a carbon material prepared from biomass through pyrolysis or carbonization, characterized by high specific surface area, porosity, and stable structure. Due to its excellent adsorption performance and environmental friendliness, biochar has broad application prospects in the adsorption of heavy metal elements. As an adsorbent material, biochar can effectively adsorb heavy metal elements. Its adsorption mechanism mainly includes physical adsorption and chemical adsorption. Physical adsorption mainly relies on physical properties such as specific surface area and pore volume, while chemical adsorption relies on the interaction between surface functional groups and heavy metal elements. The adsorption effect of biochar on heavy metal elements is affected by various factors, such as the nature and concentration of the heavy metal element, the pH value of the solution, and the ionic strength. Furthermore, modification treatment of biochar can also improve its adsorption performance for specific heavy metal elements.

[0003] Although biochar shows great promise for adsorbing heavy metals from wastewater, several challenges remain. First, the adsorption capacity of biochar is limited by its physical properties, such as specific surface area and pore volume. Second, the concentration of heavy metals in wastewater varies considerably, and different wastewaters contain different concentrations of heavy metals. For wastewater with lower heavy metal concentrations, biochar materials need to possess stronger adsorption capabilities. Third, many heavy metal atoms in wastewater typically exist in high-valence states; for example, uranium often exists as uranyl ions. To adsorb high-valence uranium, hexavalent uranium needs to be reduced and fixed to a lower valence state. Therefore, endowing biochar materials with photocatalytic oxidation-reduction capabilities is essential. Summary of the Invention

[0004] One object of the present invention is to solve at least the above-mentioned problems and / or defects, and to provide at least the advantages described below.

[0005] To achieve these objectives and other advantages according to the present invention, a thermochemical oxidation process for preparing straw biochar is provided, comprising the following steps:

[0006] Step 1: Cut the straw into small pieces, wash, dry, and crush to obtain straw powder;

[0007] Step 2: Carbonize the straw powder to obtain straw charcoal;

[0008] Step 3: Add nitrogen, TiO2 and ZnO to the straw char material to obtain doped straw char.

[0009] Step 4: Load zero-valent iron onto the doped straw char, separate the solid and liquid phases, dry the material, and heat-treat it to obtain the straw biomass char adsorbent material.

[0010] Preferably, in step one, the straw is cut into small pieces of 2-10 cm in length, and the washing method includes washing it multiple times with deionized water, then soaking it in a 0.1 mol / L NaOH solution for 1-3 hours, filtering it, washing it multiple times with deionized water, drying it at 60-110℃ for 30-60 minutes, and crushing it into particles with a particle size of 1-500 μm.

[0011] Preferably, in step two, the specific method for carbonizing straw powder to obtain straw charcoal includes: evacuating the high-temperature furnace, placing the straw powder into the high-temperature furnace, introducing inert gas, setting a first heating program to raise the temperature to 500-800℃, holding for 1-3 hours, then setting a second heating program to raise the temperature to 800-1000℃, holding for 20-30 minutes, then setting a cooling program to lower the temperature to 200-400℃, holding for 1-3 hours, and finally cooling to room temperature to obtain straw charcoal.

[0012] Preferably, the high-temperature furnace is evacuated to a vacuum level of 1.2 × 10⁻⁶. -3 ~3.6×10 -2 Pa, the inert gas introduced is argon or helium, the first heating program is 2 to 20 °C / min, the second heating program is 10 to 20 °C / min, and the cooling program is 5 to 10 °C / min.

[0013] Preferably, in step three, the method of incorporating nitrogen, TiO2, and ZnO into the straw charcoal material includes:

[0014] S31. Mix nicotinic acid, imidazole, and 2,3-pyridinedicarboxylic acid in a mass ratio of 2:1:1, grind them to a particle size of 100-500 mesh, and obtain a nitrogen-containing mixture powder; then add the nitrogen-containing mixture powder to a 0.5 mol / L sodium carbonate solution and soak for 2-12 hours.

[0015] S32. Dry the soaked nitrogen-containing mixture powder and mix it with straw charcoal, nano TiO2 powder with a particle size of 10-100nm and ZnO powder with a particle size of 10-200nm to obtain mixture A;

[0016] S33. Mixture A is placed in a quartz glass tube and subjected to heat treatment at a temperature of 150–180°C for 1–3 hours to obtain doped straw char.

[0017] Preferably, in step S32, the mass ratio of straw charcoal, nitrogen-containing mixed powder, and nano-TiO2 powder is 30–100:5–10:2–5:1–10.

[0018] Preferably, in step four, the method of loading zero-valent iron onto the doped straw charcoal includes:

[0019] The doped straw char was immersed in a ferrous chloride solution, a reducing agent was added to the ferrous chloride solution, and after stirring, it was allowed to stand for 1 to 12 hours. The zero-valent iron reduced by the reducing agent adhered to the doped straw char. After solid-liquid separation and drying, the straw biochar adsorbent material was obtained.

[0020] Preferably, the concentration of the ferrous chloride solution is 0.05–0.1 mol / L, and the volume-to-mass ratio of the ferrous chloride solution to the doped straw charcoal is 500–2500 mL: 50–250 g; the reducing agent is one of hydrazine hydrate, hydroxylamine, or sodium borohydride, and the molar amount of the reducing agent is 1–3 times the molar amount of ferrous chloride.

[0021] An application of thermochemically oxidized straw biochar, which is used to adsorb heavy metals in wastewater.

[0022] The present invention has at least the following beneficial effects:

[0023] This invention uses straw char obtained from straw carbonization and elemental iron attached to straw char as the main raw materials. By utilizing the porous and large specific surface area characteristics of straw char, the reduced elemental iron is adsorbed and attached to the straw char, realizing the organic combination of iron and straw char. The resulting iron-straw char has strong adsorption performance, which enables it to effectively adsorb and fix heavy metal elements (uranium) in wastewater.

[0024] This invention provides a thermochemical oxidation process for preparing straw biochar. Utilizing the porous and large specific surface area characteristics of the carbonized straw char, nitrogen-containing heterocyclic compounds, nano-TiO2 powder, and nano-ZnO powder are used as dopants in the straw char. This process endows the straw biochar adsorbent material with the ability to photocatalytically reduce heavy metal elements, building upon its existing adsorption capacity for heavy metals. Specifically, the nano-TiO2 powder is primarily used for utilizing ultraviolet light; when TiO2 is irradiated with ultraviolet light, electron-hole pairs are generated on its surface. Yes, these electrons and holes have reducing power, which can reduce heavy metal elements electrostatically adsorbed on the TiO2 surface to low or zero valence states, thereby removing heavy metal ions. ZnO has a wider band gap than TiO2 and is mainly used to catalytically reduce heavy metal elements using visible light. By simultaneously incorporating nano-TiO2 powder and nano-ZnO powder, broadband coverage of ultraviolet and visible light is achieved, improving the light utilization rate of straw biochar adsorbent materials and enhancing their catalytic reduction ability for heavy metal elements.

[0025] Other advantages, objectives and features of the present invention will become apparent in part from the following description, and in part from those skilled in the art through study and practice of the invention. Detailed Implementation

[0026] The present invention will now be described in further detail so that those skilled in the art can implement it based on the description.

[0027] It should be understood that terms such as “having,” “comprising,” and “including” as used herein do not exclude the presence or addition of one or more other elements or combinations thereof.

[0028] Example 1

[0029] This embodiment provides a thermochemical oxidation process for preparing straw biochar, including the following steps:

[0030] Step 1: Cut 1000g of straw into 2-10cm long pieces, wash with deionized water 5 times, then soak in 0.1mol / L NaOH solution for 1 hour, filter and wash with deionized water 3 times; dry at 80℃ for 30 minutes; the particle size of the pulverized straw is 20-100μm to obtain straw powder.

[0031] Step 2: Evacuate the high-temperature furnace to a vacuum level of 2.5 × 10⁻⁶. -3Pa, put straw powder into a high-temperature furnace and introduce argon gas. Set the heating program to 5℃ / min to raise the temperature to 600℃ and hold for 1 hour. Then set the heating program to 10℃ / min to raise the temperature to 800℃ and hold for 20 minutes. Then set the cooling program to 5℃ / min to lower the temperature to 200℃ and hold for 1 hour. After cooling to room temperature, straw charcoal is obtained.

[0032] Step 3: Add nitrogen, TiO2, and ZnO to 500g of straw charcoal material to obtain doped straw charcoal, specifically including:

[0033] S31. Mix 40g nicotinic acid, 20g imidazole, and 20g 2,3-pyridinedicarboxylic acid, and grind them to a particle size of 100-500 mesh to obtain a nitrogen-containing mixture powder; then add the nitrogen-containing mixture powder to 500mL of 0.5mol / L sodium carbonate solution and soak for 6h.

[0034] S32. Dry the soaked nitrogen-containing mixture powder, weigh 50g of the dried nitrogen-containing mixture powder and mix it with 500g of straw charcoal, 20g of nano TiO2 powder with a particle size of 10-100nm and 10g of ZnO powder with a particle size of 10-200nm to obtain mixture A.

[0035] S33. Mixture A is placed in a quartz glass tube and subjected to heat treatment at a temperature of 150°C for 1 hour to obtain doped straw char.

[0036] Step 4: Immerse the doped straw char in 1000 mL of 0.1 mol / L ferrous chloride solution, add 0.2 mol sodium borohydride to the ferrous chloride solution, stir, and let stand for 2 hours. The zero-valent iron reduced by sodium borohydride adheres to the doped straw char. After solid-liquid separation and drying, obtain straw biomass char adsorbent material. After solid-liquid separation and drying, heat treatment is performed to obtain straw biomass char adsorbent material.

[0037] Example 2

[0038] This embodiment provides a thermochemical oxidation process for preparing straw biochar, including the following steps:

[0039] Step 1: Cut 1000g of straw into 2-10cm long pieces, wash with deionized water 5 times, then soak in 0.1mol / L NaOH solution for 2h, filter and wash with deionized water 3 times; dry at 90℃ for 50min; the particle size of the pulverized straw is 200-300μm to obtain straw powder.

[0040] Step 2: Evacuate the high-temperature furnace to 3.0 × 10⁻⁶. -3Pa, put straw powder into a high-temperature furnace and introduce argon gas. Set the heating program at 15℃ / min to raise the temperature to 700℃ and hold for 2 hours. Then set the heating program at 10℃ / min to raise the temperature to 900℃ and hold for 25 minutes. Then set the cooling program at 10℃ / min to lower the temperature to 300℃ and hold for 2 hours. After cooling to room temperature, straw charcoal is obtained.

[0041] Step 3: Add nitrogen, TiO2, and ZnO to 500g of straw charcoal material to obtain doped straw charcoal, specifically including:

[0042] S31. Mix 80g of nicotinic acid, 40g of imidazole, and 40g of 2,3-pyridinedicarboxylic acid, and grind them to a particle size of 100-500 mesh to obtain a nitrogen-containing mixture powder; then add the nitrogen-containing mixture powder to a 0.5mol / L sodium carbonate solution and soak for 8 hours.

[0043] S32. Dry the soaked nitrogen-containing mixture powder, and weigh 80g of nitrogen-containing mixture powder and mix it with straw charcoal, 30g of nano TiO2 powder with a particle size of 10-100nm and 30g of ZnO powder with a particle size of 10-200nm to obtain mixture A;

[0044] S33. Mixture A is placed in a quartz glass tube and subjected to heat treatment at a temperature of 160℃ for 2 hours to obtain doped straw char.

[0045] Step 4: Immerse the doped straw char in 1000 mL of 0.1 mol / L ferrous chloride solution, add 0.2 mol sodium borohydride to the ferrous chloride solution, stir, and let stand for 5 h. The zero-valent iron reduced by sodium borohydride adheres to the doped straw char. After solid-liquid separation and drying, obtain straw biomass char adsorbent material. After solid-liquid separation and drying, heat treatment is performed to obtain straw biomass char adsorbent material.

[0046] Example 3

[0047] This embodiment provides a thermochemical oxidation process for preparing straw biochar, including the following steps:

[0048] Step 1: Cut 1000g of straw into 2-10cm long pieces, wash with deionized water 5 times, then soak in 0.1mol / L NaOH solution for 3h, filter and wash with deionized water several times; dry at 110℃ for 30min; the particle size of the pulverized straw is 1-500μm, and straw powder is obtained.

[0049] Step 2: Evacuate the high-temperature furnace to 3.6 × 10⁻⁶. -2Pa, put straw powder into a high-temperature furnace and introduce argon gas. Set the heating program to 20℃ / min to raise the temperature to 800℃ and hold for 3 hours. Then set the heating program to 20℃ / min to raise the temperature to 1000℃ and hold for 30 minutes. Then set the cooling program to 10℃ / min to lower the temperature to 400℃ and hold for 3 hours. After cooling to room temperature, straw charcoal is obtained.

[0050] Step 3: Add nitrogen, TiO2, and ZnO to 500g of straw charcoal material to obtain doped straw charcoal, specifically including:

[0051] S31. Mix 80g nicotinic acid, 40g imidazole, and 40g 2,3-pyridinedicarboxylic acid, and grind them to a particle size of 100-500 mesh to obtain a nitrogen-containing mixture powder; then add the nitrogen-containing mixture powder to 500mL of 0.5mol / L sodium carbonate solution and soak for 12h.

[0052] S32. Dry the soaked nitrogen-containing mixture powder, weigh 100g of the dried nitrogen-containing mixture powder and mix it with 500g of straw charcoal, 50g of nano TiO2 powder with a particle size of 10-100nm and 100g of ZnO powder with a particle size of 10-200nm to obtain mixture A.

[0053] S33. Mixture A is placed in a quartz glass tube and subjected to heat treatment at a temperature of 180°C for 3 hours to obtain doped straw char.

[0054] Step 4: Immerse the doped straw char in 2000 mL of 0.1 mol / L ferrous chloride solution, add 0.4 mol sodium borohydride to the ferrous chloride solution, stir, and let stand for 12 h. The zero-valent iron reduced by sodium borohydride adheres to the doped straw char. After solid-liquid separation and drying, obtain straw biomass char adsorbent material. After solid-liquid separation and drying, heat treatment is performed to obtain straw biomass char adsorbent material.

[0055] Comparative Example 1

[0056] This comparative example provides a thermochemical oxidation preparation process for straw biochar. The difference from Example 3 is that in step three, 500g of straw char is mixed with 100g of dried nitrogen-containing mixture powder (50g nicotinic acid, 50g imidazole, 50g 2,3-pyridinedicarboxylic acid) and 100g of nano-TiO2 powder with a particle size of 10-100nm. Nano-ZnO powder is not added. The rest of the method is the same as in Example 3.

[0057] Comparative Example 2

[0058] This comparative example provides a thermochemical oxidation preparation process for straw biochar. The difference between this process and Example 3 is that in step three, 500g of straw char is mixed with 100g of dried nitrogen-containing mixture powder (50g nicotinic acid, 50g imidazole, and 50g 2,3-pyridinedicarboxylic acid), and no nano TiO2 powder or nano ZnO powder is added. The rest of the process is the same as in Example 3.

[0059] Comparative Example 3

[0060] This comparative example provides a thermochemical oxidation preparation process for straw biochar. The difference between this process and Example 3 is that in step three, 500g of straw char is mixed with 100g of dried nitrogen-containing mixture powder (50g nicotinic acid, 50g imidazole, 50g 2,3-pyridinedicarboxylic acid) and 100g of nano ZnO powder with a particle size of 10-200nm. Nano TiO2 powder is not added. The rest of the method is the same as in Example 3.

[0061] Comparative Example 4

[0062] This comparative example provides a thermochemical oxidation preparation process for straw biochar. The difference between this process and Example 3 is that step four, which involves loading zero-valent iron onto the doped straw char, is not performed. The rest of the process is the same as in Example 3.

[0063] To determine the adsorption capacity of the straw biochar adsorbent materials prepared in Examples 1-3 and Comparative Examples 1-4 for uranium in wastewater, the following adsorption experiments were designed: 0.005 g of straw biochar prepared in Examples 1-3 and Comparative Examples 1-3 were weighed and added to 20 mL of uranium-containing solution with an initial uranium concentration of 80 mg / L. The solution pH was 7. The solution was magnetically stirred at 250 r / min for 4 h until adsorption equilibrium was reached. During the adsorption process, a light intensity of 1600 lux was set for each group. After adsorption equilibrium was reached, solid-liquid separation was performed using a microporous filter membrane, and the U(VI) concentration in the supernatant was measured at 651.8 nm using the azoarsine method III.

[0064] The adsorption capacity q of straw biochar for uranium e The formula for calculating (mg / g) is:

[0065]

[0066] Where C0 is the initial U(VI) concentration (mg / L) of the uranium-containing solution, C e To determine the adsorption equilibrium concentration of U(VI) (mg / L), where V is the volume of the uranium-containing solution (mL) and m is the mass of added straw biochar (g), the measurement results are summarized in the table below:

[0067]

[0068] As can be seen from the table above, the straw biochar prepared by the thermochemical oxidation process of straw biochar provided by the present invention in Examples 1-3 all have an adsorption capacity of more than 158 mg / g for uranium in uranium-containing wastewater, which is significantly better than the adsorption effect of the materials prepared in Comparative Examples 1-4.

[0069] The number of devices and processing scale described herein are for the purpose of simplifying the description of the invention. Applications, modifications, and variations of the invention will be readily apparent to those skilled in the art.

[0070] Although embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. They can be applied to various fields suitable for the present invention. For those skilled in the art, other modifications can be easily made. Therefore, without departing from the general concept defined by the claims and their equivalents, the present invention is not limited to the specific details and examples shown and described herein.

Claims

1. An application of straw biochar, characterized in that, The straw biochar is used to adsorb the heavy metal uranium from wastewater; The thermochemical oxidation process for preparing straw biochar includes the following steps: Step 1: Cut the straw into small pieces, wash, dry, and crush to obtain straw powder; Step 2: Carbonize the straw powder to obtain straw charcoal; Step 3: Incorporate nitrogen, TiO2, and ZnO into the straw charcoal material to obtain doped straw charcoal; methods for incorporating nitrogen, TiO2, and ZnO into the straw charcoal material include: S31. Mix nicotinic acid, imidazole, and 2,3-pyridinedicarboxylic acid in a mass ratio of 2:1:1, grind them to a particle size of 100-500 mesh, and obtain a nitrogen-containing mixture powder; then add the nitrogen-containing mixture powder to a 0.5 mol / L sodium carbonate solution and soak for 2-12 hours. S32. Dry the soaked nitrogen-containing mixture powder and mix it with straw charcoal, nano TiO2 powder with a particle size of 10~100nm and ZnO powder with a particle size of 10~200nm to obtain mixture A; S33. Mixture A is placed in a quartz glass tube and subjected to heat treatment at a temperature of 150~180℃ for 1~3h to obtain doped straw char. Step 4: Loading zero-valent iron into the doped straw charcoal, including: The doped straw char was immersed in a ferrous chloride solution, a reducing agent was added to the ferrous chloride solution, and after stirring, it was allowed to stand for 1 to 12 hours. The zero-valent iron reduced by the reducing agent adhered to the doped straw char. After solid-liquid separation, drying, and heat treatment, the straw biochar adsorbent material was obtained.

2. The application of straw biochar as described in claim 1, characterized in that, In step one, the straw is cut into small sections of 2-10cm in length. The washing method includes washing it multiple times with deionized water, then soaking it in a 0.1mol / L NaOH solution for 1-3 hours, filtering it, and washing it multiple times with deionized water. It is then dried at 60-110℃ for 30-60 minutes. The particle size of the pulverized straw is 1-500μm.

3. The application of straw biochar as described in claim 1, characterized in that, In step two, the specific method for carbonizing straw powder to obtain straw charcoal includes: evacuating the high-temperature furnace, placing the straw powder into the high-temperature furnace, and introducing inert gas; setting a first heating program to raise the temperature to 500~800℃ and holding it for 1~3 hours; then setting a second heating program to raise the temperature to 800~1000℃ and holding it for 20~30 minutes; subsequently setting a cooling program to lower the temperature to 200~400℃ and holding it for 1~3 hours; and finally cooling to room temperature to obtain straw charcoal.

4. The application of straw biochar as described in claim 3, characterized in that, The high-temperature furnace was evacuated to a vacuum level of 1.2 × 10⁻⁶. -3 ~3.6×10 -2 Pa, the inert gas introduced is argon or helium, the first heating program is 2~20℃ / min, the second heating program is 10~20℃ / min, and the cooling program is 5~10℃ / min.

5. The application of straw biochar as described in claim 1, characterized in that, The concentration of the ferrous chloride solution is 0.05~0.1mol / L, and the volume-to-mass ratio of the ferrous chloride solution to the doped straw charcoal is 500~2500mL:50~250g; the reducing agent is one of hydrazine hydrate, hydroxylamine or sodium borohydride, and the molar amount of the reducing agent is 1~3 times the molar amount of ferrous chloride.

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