A sludge-based biochar and a preparation method and application thereof

Abstract

This invention discloses a sludge-based biochar, its preparation method, and its application, relating to the field of adsorption material technology. The invention first performs alkali activation treatment on municipal sludge, then oxidizes it with sodium periodate, and then mixes the oxidized sludge with aminated lignin for reaction. The resulting biochar precursor is then pyrolyzed, and finally, the pyrolyzed biochar is subjected to ultraviolet irradiation under heating. The prepared sludge-based activated carbon exhibits a significantly increased adsorption capacity for VOCs, which is beneficial for better recycling and utilization of municipal sludge.

Description

Technical Field

[0001] This invention relates to the field of adsorption materials technology, and in particular to a sludge-based biochar, its preparation method, and its application. Background Technology

[0002] Municipal sludge refers to the sludge produced by urban wastewater treatment plants. It is produced in large quantities and has high treatment costs. Traditional methods of disposal, such as landfill and incineration, pose a risk of secondary pollution. Biomass carbonization technology, as an emerging environmental protection technology, provides a new approach to the treatment of municipal sludge. Biomass carbonization technology involves the high-temperature pyrolysis of waste biomass (such as crop straw, waste wood chips, livestock manure, and waste fruit peels) under limited oxygen conditions to produce biochar. This avoids the release of CO pollution into the atmosphere from the combustion of biomass and achieves the resource utilization of solid waste, thus achieving the goal of treating waste with waste. Current research indicates that sludge-based biochar can be used to adsorb volatile organic compounds (VOCs), showing promising application prospects and research value. However, biochar materials prepared by direct carbonization of municipal sludge suffer from low porosity and a limited range of surface functional groups, resulting in limited adsorption capacity for VOCs, which requires further improvement. Summary of the Invention

[0003] Based on the technical problems existing in the background technology, the present invention proposes a sludge-based biochar, its preparation method and application.

[0004] The present invention proposes a method for preparing sludge-based biochar, comprising the following steps:

[0005] S1. Add potassium hydroxide to dewatered municipal sludge with a water content of 60%~80%, stir at 30~70℃ for 6~12h, then adjust the pH to 4~6, add sodium periodate, stir the reaction in the dark, then filter, wash and dry the obtained solid to obtain oxidized sludge.

[0006] S2. The oxidized sludge is mixed with an aqueous dispersion of aminated lignin, stirred and reacted, and then dried to obtain a biochar precursor.

[0007] S3. The biochar precursor is pyrolyzed under vacuum by introducing a protective gas, cooled, crushed, and sieved. The resulting powder is then subjected to ultraviolet irradiation under heating to obtain sludge-based biochar.

[0008] Preferably, the amount of potassium hydroxide used is 20% to 40% of the dry weight of the dewatered municipal sludge; and the amount of sodium periodate used is 10% to 20% of the dry weight of the dewatered municipal sludge.

[0009] Preferably, in S1, the temperature of the light-protected stirring reaction is 30~70℃, and the time is 2~6h.

[0010] Preferably, in S2, the temperature of the stirring reaction is 30~50℃ and the time is 2~5h; the mass ratio of oxidized sludge to aminated lignin is 1:0.05~0.15; and the solid content of the aqueous dispersion of aminated lignin is 1%~5%.

[0011] Preferably, the preparation method of the aminated lignin includes: adding lignin and polyamine to water, dispersing them evenly, then adjusting the pH to 10-11, adding a formaldehyde solution with a concentration of 35-40 wt%, stirring the mixture at 60-85°C for 2-8 hours after the addition is complete, cooling the mixture after the reaction is complete, adding isopropanol to the reaction solution for precipitation, filtering the mixture, washing the precipitate with isopropanol and drying it to obtain the final product.

[0012] Preferably, the mass ratio of lignin, polyamine and formaldehyde solution is 1:0.5~0.8:0.4~0.8; the polyamine is at least one selected from ethylenediamine, diethanolamine, diethylenetriamine and triethylenetetramine.

[0013] In S1 and S2, the drying method is a conventional method, such as oven drying. Preferably, the drying temperature is 50~80℃ and the time is 5~12h.

[0014] Preferably, in step S3, the pyrolysis step is as follows: heating to 400-600°C at a heating rate of 1-5°C / min, and then holding at that temperature for 0.5-1h.

[0015] Preferably, in S3, the step of performing ultraviolet irradiation treatment under heating is as follows: the obtained powder is placed in a glass container, the glass container is placed on a hot plate with a temperature of 100℃~300℃, and irradiated with an ultraviolet lamp with a wavelength of 200~400nm and a power of 200~400W for 5~20h, and then cooled.

[0016] In this invention, the protective gas refers to one or more of nitrogen or inert gases (such as helium or argon).

[0017] The present invention also proposes a sludge-based biochar, which is prepared by the aforementioned preparation method.

[0018] The present invention also proposes the application of the sludge-based biochar in the adsorption and removal of VOCs.

[0019] The beneficial effects of this invention are as follows:

[0020] This invention first involves alkaline activation treatment of municipal sewage sludge, followed by oxidation with sodium periodate to remove impurities and introduce a large number of oxygen-containing groups such as aldehydes into the sludge, resulting in oxidized sludge. The oxidized sludge is then mixed with aminated lignin, and the resulting biochar precursor is pyrolyzed. The cross-linking effect between the aldehyde groups in the sludge and the amino groups in the lignin tightly binds the lignin to the sludge. On one hand, the lignin in the cross-linked structure effectively supports the pore morphology during high-temperature carbonization, preventing pore structure collapse and improving pore structure stability. Furthermore, the aldehyde groups and amino groups form... The cross-linked structure further optimizes the pore structure formed after carbonization, thereby improving the adsorption effect of biochar materials on VOCs. On the other hand, lignin and the sludge matrix can form a π-π conjugated system after carbonization, promoting the adsorption of aromatic VOCs such as toluene. Furthermore, the oxygen-containing groups in the sludge and the amino groups in the lignin can promote the adsorption of formaldehyde from VOCs by biochar. Finally, ultraviolet irradiation treatment of the pyrolysis-formed biochar can optimize the pore structure and introduce oxygen / nitrogen-containing functional groups, thereby further improving the adsorption effect on VOCs. The sludge-based activated carbon of this invention significantly improves the adsorption capacity of VOCs, which is beneficial for better recycling and utilization of municipal sludge. Detailed Implementation

[0021] The technical solution of the present invention will now be described in detail through specific embodiments.

[0022] Example 1

[0023] Preparation of sludge-based biochar:

[0024] S1. Add potassium hydroxide to dewatered municipal sludge with a moisture content of 75%, stir at 40℃ for 8 hours, then adjust the pH to 5.5, add sodium periodate, stir and react at 40℃ in the dark for 3 hours, then filter, wash the obtained solid with water, and dry at 60℃ for 6 hours to obtain oxidized sludge; wherein, the amount of potassium hydroxide is 30% of the dry weight of the dewatered municipal sludge; the amount of sodium periodate is 15% of the dry weight of the dewatered municipal sludge;

[0025] S2. After mixing the oxidized sludge with an aqueous dispersion of aminated lignin with a solid content of 2%, the mixture was stirred at 40°C for 3 hours and then dried at 60°C for 6 hours to obtain a biochar precursor; wherein the mass ratio of oxidized sludge to aminated lignin was 1:0.1.

[0026] S3. Nitrogen gas is introduced into the biochar precursor under vacuum, and the temperature is increased to 500℃ at a heating rate of 2℃ / min. The temperature is then maintained for 0.5h. After cooling, the precursor is pulverized and passed through a 200-mesh sieve. The resulting powder is then placed in a glass container and placed on a hot plate at 300℃. The container is then irradiated with a UV lamp with a wavelength of 200~400nm and a power of 300W for 16h. After cooling, sludge-based biochar is obtained.

[0027] The preparation method of aminated lignin includes: adding lignin and diethylenetriamine to water and dispersing them evenly; then adjusting the pH to 10.5; adding a 37wt% formaldehyde solution dropwise; stirring the mixture at 80℃ for 5 hours after the addition is complete; cooling the mixture after the reaction is complete; adding isopropanol equivalent to 3 times the volume of the reaction solution to precipitate the lignin; filtering the precipitate; washing the precipitate with isopropanol; and drying the precipitate. The mass ratio of lignin, diethylenetriamine, and formaldehyde solution is 1:0.6:0.7.

[0028] Example 2

[0029] Preparation of sludge-based biochar:

[0030] S1. Add potassium hydroxide to dewatered municipal sludge with a moisture content of 60%, stir at 30°C for 6 hours, then adjust the pH to 4, add sodium periodate, stir and react at 30°C in the dark for 2 hours, then filter, wash the obtained solid with water, and dry at 60°C for 6 hours to obtain oxidized sludge; wherein, the amount of potassium hydroxide is 20% of the dry weight of the dewatered municipal sludge; and the amount of sodium periodate is 10% of the dry weight of the dewatered municipal sludge.

[0031] S2. After mixing the oxidized sludge with an aqueous dispersion of aminated lignin with a solid content of 1%, the mixture was stirred at 30°C for 2 hours and then dried at 60°C for 6 hours to obtain a biochar precursor; wherein the mass ratio of oxidized sludge to aminated lignin was 1:0.05.

[0032] S3. Nitrogen gas is introduced into the biochar precursor under vacuum, and the temperature is increased to 400℃ at a heating rate of 1℃ / min. The temperature is then maintained for 0.5h. After cooling, the precursor is pulverized and passed through a 200-mesh sieve. The resulting powder is then placed in a glass container and placed on a hot plate at 100℃. The container is then irradiated with a UV lamp with a wavelength of 200~400nm and a power of 200W for 5h. After cooling, sludge-based biochar is obtained.

[0033] The preparation method of amination lignin includes: adding lignin and triethylenetetramine to water, dispersing them evenly, adjusting the pH to 10, adding a 37wt% formaldehyde solution dropwise, stirring the mixture at 605℃ for 2 hours after the addition is complete, cooling the mixture after the reaction is complete, adding isopropanol equivalent to 3 times the volume of the reaction solution to precipitate the lignin, filtering the precipitate, washing it with isopropanol and drying it to obtain the lignin. The mass ratio of lignin, triethylenetetramine and formaldehyde solution is 1:0.5:0.4.

[0034] Example 3

[0035] Preparation of sludge-based biochar:

[0036] S1. Add potassium hydroxide to dewatered municipal sludge with a moisture content of 80%, stir at 70°C for 12 hours, then adjust the pH to 6, add sodium periodate, stir and react at 70°C in the dark for 6 hours, then filter, wash the obtained solid with water, and dry at 60°C for 6 hours to obtain oxidized sludge; wherein, the amount of potassium hydroxide is 40% of the dry weight of the dewatered municipal sludge; and the amount of sodium periodate is 20% of the dry weight of the dewatered municipal sludge.

[0037] S2. After mixing the oxidized sludge with an aqueous dispersion of aminated lignin with a solid content of 5%, the mixture was stirred at 50°C for 5 hours and then dried at 50°C for 5 hours to obtain a biochar precursor; wherein the mass ratio of oxidized sludge to aminated lignin was 1:0.15.

[0038] S3. Nitrogen gas is introduced into the biochar precursor under vacuum, and the temperature is increased to 600℃ at a heating rate of 5℃ / min. The temperature is then maintained for 1 hour. After cooling, the precursor is pulverized and passed through a 200-mesh sieve. The resulting powder is then placed in a glass container and placed on a hot plate at 200℃. The container is then irradiated with a UV lamp with a wavelength of 200~400nm and a power of 400W for 20 hours. After cooling, sludge-based biochar is obtained.

[0039] The preparation method of amination lignin includes: adding lignin and ethylenediamine to water, dispersing them evenly, adjusting the pH to 11, adding a 37wt% formaldehyde solution dropwise, stirring the mixture at 85℃ for 8 hours after the addition is complete, cooling the mixture after the reaction is complete, adding isopropanol equivalent to 3 times the volume of the reaction solution to precipitate the lignin, filtering the precipitate, washing it with isopropanol and drying it to obtain the lignin. The mass ratio of lignin, ethylenediamine and formaldehyde solution is 1:0.8:0.8.

[0040] Comparative Example 1

[0041] Preparation of sludge-based biochar:

[0042] S1. Add potassium hydroxide to dewatered municipal sludge with a moisture content of 75%, stir at 40°C for 8 hours, then filter, wash the obtained solid with water, and dry at 60°C for 6 hours to obtain alkali-activated sludge; wherein, the amount of potassium hydroxide used is 30% of the dry weight of the dewatered municipal sludge;

[0043] S2. The alkali-activated sludge is purged with nitrogen under vacuum and heated to 500°C at a rate of 2°C / min. The temperature is then maintained for 0.5 hours. After cooling, the sludge is pulverized and passed through a 200-mesh sieve. The resulting powder is then placed in a glass container and placed on a hot plate at 300°C. The container is then irradiated with a 300W ultraviolet lamp with a wavelength of 200-400nm for 16 hours. After cooling, sludge-based biochar is obtained.

[0044] Comparative Example 2

[0045] Preparation of sludge-based biochar:

[0046] S1. Add potassium hydroxide to dewatered municipal sludge with a moisture content of 75%, stir at 40°C for 8 hours, then filter, wash the obtained solid with water, and dry at 60°C for 6 hours to obtain alkali-activated sludge; wherein, the amount of potassium hydroxide used is 30% of the dry weight of the dewatered municipal sludge;

[0047] S2. Alkali-activated sludge is mixed with an aqueous dispersion of lignin with a solid content of 2%, and stirred at 40°C for 3 hours. Then it is dried at 60°C for 6 hours to obtain a biochar precursor. The mass ratio of alkali-activated sludge to lignin is 1:0.1.

[0048] S3. Nitrogen gas is introduced into the biochar precursor under vacuum, and the temperature is increased to 500℃ at a heating rate of 2℃ / min. The temperature is then maintained for 0.5h. After cooling, the precursor is pulverized and passed through a 200-mesh sieve. The resulting powder is then placed in a glass container and placed on a hot plate at 300℃. The container is then irradiated with a UV lamp with a wavelength of 200~400nm and a power of 300W for 16h. After cooling, sludge-based biochar is obtained.

[0049] Comparative Example 3

[0050] Preparation of sludge-based biochar:

[0051] S1. Add potassium hydroxide to dewatered municipal sludge with a moisture content of 75%, stir at 40℃ for 8 hours, then adjust the pH to 5.5, add sodium periodate, stir and react at 40℃ in the dark for 3 hours, then filter, wash the obtained solid with water, and dry at 60℃ for 6 hours to obtain oxidized sludge; wherein, the amount of potassium hydroxide is 30% of the dry weight of the dewatered municipal sludge; the amount of sodium periodate is 15% of the dry weight of the dewatered municipal sludge;

[0052] S2. The oxidized sludge was mixed with an aqueous dispersion of lignin with a solid content of 2%, and stirred at 40°C for 3 hours. Then it was dried at 60°C for 6 hours to obtain a biochar precursor. The mass ratio of oxidized sludge to lignin was 1:0.1.

[0053] S3. Nitrogen gas is introduced into the biochar precursor under vacuum, and the temperature is increased to 500℃ at a heating rate of 2℃ / min. The temperature is then maintained for 0.5h. After cooling, the precursor is pulverized and passed through a 200-mesh sieve. The resulting powder is then placed in a glass container and placed on a hot plate at 300℃. The container is then irradiated with a UV lamp with a wavelength of 200~400nm and a power of 300W for 16h. After cooling, sludge-based biochar is obtained.

[0054] Comparative Example 4

[0055] Preparation of sludge-based biochar:

[0056] S1. Add potassium hydroxide to dewatered municipal sludge with a moisture content of 75%, stir at 40°C for 8 hours, then filter, wash the obtained solid with water, and dry at 60°C for 6 hours to obtain alkali-activated sludge; wherein, the amount of potassium hydroxide used is 30% of the dry weight of the dewatered municipal sludge;

[0057] S2. Alkali-activated sludge is mixed with an aqueous dispersion of aminated lignin with a solid content of 2%, and stirred at 40°C for 3 hours. Then it is dried at 60°C for 6 hours to obtain a biochar precursor. The mass ratio of alkali-activated sludge to aminated lignin is 1:0.1.

[0058] S3. Nitrogen gas is introduced into the biochar precursor under vacuum, and the temperature is increased to 500℃ at a heating rate of 2℃ / min. The temperature is then maintained for 0.5h. After cooling, the precursor is pulverized and passed through a 200-mesh sieve. The resulting powder is then placed in a glass container and placed on a hot plate at 300℃. The container is then irradiated with a UV lamp with a wavelength of 200~400nm and a power of 300W for 16h. After cooling, sludge-based biochar is obtained.

[0059] The preparation method of aminated lignin includes: adding lignin and diethylenetriamine to water and dispersing them evenly; then adjusting the pH to 10.5; adding a 37wt% formaldehyde solution dropwise; stirring the mixture at 80℃ for 5 hours after the addition is complete; cooling the mixture after the reaction is complete; adding isopropanol equivalent to 3 times the volume of the reaction solution to precipitate the lignin; filtering the precipitate; washing the precipitate with isopropanol; and drying the precipitate. The mass ratio of lignin, diethylenetriamine, and formaldehyde solution is 1:0.6:0.7.

[0060] Test case

[0061] VOCs adsorption experiments were conducted on the sludge-based activated carbon prepared in Example 1 and Comparative Examples 1-4, respectively. The experimental method followed the national standard "Bamboo Charcoal for Air Purification" (GBT 26900-2011). Multi-component static adsorption of mixed TVOCs (formaldehyde, benzene, toluene, and xylene) was performed (formaldehyde, benzene, toluene, and xylene were analytical grade). 4 ml of formaldehyde solution was added, and 5 ml of analytical grade solutions were added to each of the benzene, toluene, and xylene solutions. 1 g of dried sample (accurate to 0.1 mg) was weighed and placed in a pre-weighed weighing bottle. The weighing bottle containing the analytical grade solution was then placed at the designated position at the bottom of the adsorption apparatus. The amount of VOCs volatilized should be greater than the amount of sample adsorbed. Simultaneously, the weighing bottle containing the sample was placed on the grid of the adsorption apparatus, and the apparatus was placed in a 20°C climate chamber for constant temperature adsorption for 24 hours. The adsorption capacity was then measured. The results are shown in Table 1.

[0062] Table 1

[0063] Test Project Example 1 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 TVOCs (benzene, toluene, xylene, formaldehyde) adsorption capacity (mg / g) 623 449 462 513 498

[0064] As shown in Table 1, the biochar prepared in Example 1 showed a significant improvement in VOCs adsorption capacity compared to the biochar prepared in Comparative Example 1, which was obtained by simply activating and removing impurities from the sludge with alkali, followed by pyrolysis and ultraviolet irradiation. Comparative Example 2, compared to Comparative Example 1, only added unmodified lignin to the raw material, resulting in no significant improvement in VOCs adsorption. Comparative Example 3, compared to Comparative Example 1, not only added unmodified lignin to the raw material but also oxidized the sludge. Although the oxidation of the sludge introduced more oxygen-containing groups, which is beneficial for further improving the VOCs adsorption performance of the biochar, the adsorption effect was still far inferior to that of Example 1. Comparative Example 4, compared to Comparative Example 1, added aminated modified lignin to the raw material. Although the VOCs adsorption performance was improved compared to Comparative Example 2 (which added unmodified lignin), this was because amination introduced amino groups, which are beneficial for formaldehyde adsorption. Furthermore, amino groups can undergo weak cross-linking with some carboxyl groups and other oxygen-containing groups in the sludge itself, which can stabilize the pore structure to some extent. However, the improvement in VOCs adsorption performance was still significantly less than that of Example 1. In summary, this invention reacts oxidized sludge with aminated lignin to obtain a biochar precursor. Utilizing the cross-linking effect between aldehyde groups in the sludge and amino groups in the lignin, the cross-linked lignin effectively supports the pore structure, and the cross-linked structure formed by the aldehyde and amino groups further optimizes the pore structure after carbonization. Furthermore, the lignin and sludge matrix form a π-π conjugated system after carbonization, promoting the adsorption of aromatic VOCs such as toluene. Additionally, the oxygen-containing groups in the sludge and the amino groups in the lignin promote the adsorption of formaldehyde from VOCs by the biochar, thereby significantly improving the adsorption performance of biochar for VOCs.

[0065] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing sludge-based biochar for adsorbing and removing VOCs, characterized in that, Includes the following steps: S1. Add potassium hydroxide to dewatered municipal sludge with a water content of 60%~80%, stir at 30~70℃ for 6~12h, then adjust the pH to 4~6, add sodium periodate, stir the reaction in the dark, then filter, wash and dry the obtained solid to obtain oxidized sludge. S2. The oxidized sludge is mixed with an aqueous dispersion of aminated lignin, stirred and reacted, and then dried to obtain a biochar precursor. S3. The biochar precursor is pyrolyzed under a protective atmosphere, cooled, pulverized, and sieved. The resulting powder is then subjected to ultraviolet irradiation under heating to obtain sludge-based biochar.

2. The preparation method according to claim 1, characterized in that, The amount of potassium hydroxide used is 20% to 40% of the dry weight of the dewatered municipal sludge; the amount of sodium periodate used is 10% to 20% of the dry weight of the dewatered municipal sludge.

3. The preparation method according to claim 1, characterized in that, In S1, the temperature of the light-protected stirring reaction is 30~70℃, and the time is 2~6h.

4. The preparation method according to claim 1, characterized in that, In S2, the temperature of the stirring reaction is 30~50℃ and the time is 2~5h; the mass ratio of oxidized sludge to aminated lignin is 1:0.05~0.15; and the solid content of the aqueous dispersion of aminated lignin is 1%~5%.

5. The preparation method according to claim 1, characterized in that, The preparation method of the amination lignin includes: adding lignin and polyamine to water, dispersing them evenly, then adjusting the pH to 10-11, adding a formaldehyde solution with a concentration of 35-40 wt%, stirring the reaction at 60-85℃ for 2-8 hours after the addition is complete, cooling the reaction solution, adding isopropanol to the reaction solution for precipitation, filtering, washing the precipitate with isopropanol and drying it to obtain the final product.

6. The preparation method according to claim 5, characterized in that, The mass ratio of lignin, polyamine, and formaldehyde solution is 1:0.5~0.8:0.4~0.8; the polyamine is at least one of ethylenediamine, diethanolamine, diethylenetriamine, and triethylenetetramine.

7. The preparation method according to claim 1, characterized in that, In S3, the pyrolysis step is as follows: the temperature is increased to 400-600℃ at a heating rate of 1-5℃ / min, and then held at that temperature for 0.5-1h.

8. The preparation method according to claim 1, characterized in that, In S3, the step of performing ultraviolet irradiation treatment under heating is as follows: the obtained powder is placed in a glass container, the glass container is placed on an electric heating plate with a temperature of 100℃~300℃, and irradiated with an ultraviolet lamp with a wavelength of 200~400nm and a power of 200~400W for 5~20h, and then cooled.

9. A sludge-based biochar, characterized in that, It is prepared by the preparation method according to any one of claims 1 to 8.

10. The application of the sludge-based biochar according to claim 9 in the adsorption and removal of VOCs.