Modified biochar and preparation method thereof

Abstract

The invention belongs to the technical field of wastewater treatment, and particularly relates to modified biochar and a preparation method thereof. The method comprises the following steps: weighing raw materials: ZnCl2 and soy sauce residue biomass; wherein the mass ratio of the ZnCl2 to the soy sauce residue biomass is m: 1, and the value of m is 0.25-1; the preparation method comprises the following steps: dissolving ZnCl2 in a certain amount of deionized water, and adding ground, washed and dried soy sauce residue biomass to obtain a solution A; the solution A is stirred for 10-14 h and then dried, and a mixture B is obtained; high-temperature pyrolysis: placing the mixture B in high-temperature pyrolysis equipment, heating to a preset calcination temperature at a rate of 4-6 DEG C / min in an N2 atmosphere, and lasting for 80-100 min to obtain a sample C; and sequentially cooling, washing and drying the sample C to obtain the modified biochar n-mZnBC. The prepared zinc chloride-doped sauce residue biochar has a good adsorption removal effect on 4-CP and Cr (VI), has low cost and high performance, and lays a theoretical foundation for practical application scenarios such as industrial wastewater in the future.

Description

Technical Field

[0001] The present application belongs to the technical field of wastewater treatment, and in particular relates to a modified biochar and a preparation method thereof. Background Art

[0002] Physical adsorption has become the first choice due to its green, environmentally friendly and efficient performance advantages, but ordinary adsorbents are difficult to use on a large scale due to their high cost and poor effect. Biochar has attracted more and more attention from domestic and foreign scientific researchers due to its low cost, green and pollution-free advantages.

[0003] Soy sauce has become an indispensable part of the dining table as a food seasoning that enhances the flavor. According to surveys, soy sauce residue itself is rich in resources and contains a large amount of key ingredients such as protein, fat, dietary fiber and soy isoflavones, but this high-potential biomass has not been taken seriously. Therefore, it is imperative to find a way to utilize soy sauce residue. At present, the most typical organic pollutants in natural water bodies are chlorophenols, and Cr(VI) is the most common heavy metal pollution in water bodies. Therefore, based on the current background conditions, this program focuses on finding a new multifunctional adsorbent material to effectively remove typical pollutants in water bodies.

[0004] Based on this, the present application proposes a modified biochar and a preparation method thereof. Summary of the invention

[0005] In view of this, the embodiments of the present application provide a modified biochar and a preparation method thereof, which are used to effectively remove typical pollutants in water bodies.

[0006] The present application embodiment adopts the following technical solutions:

[0007] The present invention provides a method for preparing modified biochar, which comprises the following steps:

[0008] Weigh the raw materials: ZnCl2 and soy sauce residue biomass; wherein the mass ratio of ZnCl2 to soy sauce residue biomass is m:1, and m is 0.25-1;

[0009] Dissolve ZnCl2 in a certain amount of deionized water, and add the ground, washed and dried soy sauce residue biomass to obtain solution A;

[0010] The solution A is stirred, and after stirring for 10-14 hours, the mixture is dried to obtain a mixture B;

[0011] High temperature pyrolysis: Place mixture B in a high temperature pyrolysis device, heat it to a preset calcination temperature at a rate of 4-6°C / min under a N2 atmosphere for 80-100 min to obtain sample C;

[0012] Sample C was cooled, washed and dried in sequence to obtain modified biochar n-mZnBC; wherein n is the preset calcination temperature of the high-temperature pyrolysis process, and m is the mass ratio of ZnCl2 to the mass of soy sauce residue biomass.

[0013] In a specific embodiment, m is 0.25, 0.5, 0.75 or 1.

[0014] In a specific embodiment, in the step of stirring solution A, the mixture B is obtained by drying after stirring for 12 hours.

[0015] In a specific embodiment, in the high temperature pyrolysis step, the tubular furnace is heated to a preset calcination temperature at a rate of 5° C. / min under a N 2 atmosphere.

[0016] In a specific embodiment, the preset calcination temperature is 500°C, 600°C, 700°C or 800°C.

[0017] In a specific embodiment, in the high temperature pyrolysis step, the duration of the high temperature pyrolysis is 90 minutes.

[0018] In a specific embodiment, the washing step for sample C includes: rinsing with ethanol and deionized water alternately for multiple times.

[0019] The present application provides a modified biochar, which is n-mZnBC prepared by the method described in any one of claims 1 to 7.

[0020] The modified biochar provided in this application is used to remove 4-CP and hexavalent chromium in water.

[0021] At least one of the above technical solutions adopted in the embodiments of the present application can achieve the following beneficial effects: The solution of the present application uses soy sauce residue as raw material, and a new type of modified biochar (n-mZnBC) is prepared by a one-step impregnation method under a preset calcination temperature condition, and is used to adsorb tetrachlorophenol (4-CP). The results show that compared with the original biochar, n-mZnBC is a high-quality mesoporous adsorbent (4nm) with developed porosity (SBET=556.070m2 / g, Pore volume=0.97995cm3 / g), strong defect structure and rich surface functional groups (-OH, -C=O / -NH, -CH2). The maximum saturated adsorption capacity of 4-CP tetrachlorophenol is as high as 113.230mg / g, far exceeding the previous reports. Its main adsorption mechanism includes hydrogen bonding, π-π interaction, pore filling and electrostatic attraction and other chemical interactions as the dominant adsorption of 4-CP. In addition, it was found that ZnCl2 can promote the dehydration and rapid carbonization of biomass, reduce the production of toxic gases in tar (amines, ketones, benzene, etc.), and improve safety while ensuring effectiveness. The biochar prepared by the institute has low cost and high performance, laying a theoretical foundation for practical application scenarios such as industrial wastewater in the future. Moreover, soy sauce residue biochar is a very potential adsorbent, which has opened up new theoretical ideas for the use of waste biomass in water body remediation, and the zinc chloride-doped soy sauce residue biochar prepared in this application has good adsorption and removal effects on both 4-CP and Cr(VI). BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The drawings described herein are used to provide a further understanding of the present application and constitute a part of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0023] Figure 1 is a flow chart of a method for preparing modified biochar in an embodiment of the present application;

[0024] Figure 2 This is the SEM image of the original soybean residue biochar;

[0025] Figure 3 This is a SEM image of modified soy sauce residue biochar (the mass ratio of ZnCl2 to soy sauce residue biomass is 0.25);

[0026] Figure 4 This is a SEM image of modified soy sauce residue biochar (the mass ratio of ZnCl2 to soy sauce residue biomass is 0.5);

[0027] Figure 5 This is a SEM image of modified soy sauce residue biochar (the mass ratio of ZnCl2 to soy sauce residue biomass is 0.75);

[0028] Figure 6 This is a SEM image of modified soy sauce residue biochar (the mass ratio of ZnCl2 to soy sauce residue biomass is 1);

[0029] Figure 7 This is the SEM image of the modified soy sauce residue biochar after washing with deionized water (the mass ratio of ZnCl2 to soy sauce residue biomass is 0.5). DETAILED DESCRIPTION

[0030] As a byproduct of soy sauce production, soy sauce residue has a large output but a very low utilization rate. Soy sauce residue biomass contains a large amount of crude protein, oil and other trace elements. After reasonable utilization, the concept of waste treatment can be realized. In previous reports, there is little research on the soy sauce residue biochar system. On the other hand, ZnCl2, as a transition metal salt, is often used as a pore expander for biochar. Researchers have found that it can promote the formation of solid carbon and condensable products, and can also remove the formation of tar, ash and non-volatile substances. In the rapid pyrolysis of biochar, it was found that ZnCl2 can also inhibit the formation of most phenolic monomers in tar. Its ZnCl2 promotes the carbonization and aromatization of carbon, thereby inhibiting the decomposition of biomass. Therefore, ZnCl2-modified biochar has a good removal ability for aromatic organic pollutants. However, in the past, the direction of adsorbents was mainly focused on the simple level of pore structure and removal efficiency, and there was little research on tar and gas byproducts during the preparation process. However, the different components retained in the raw materials after carbonization and the mechanism of 4-CP removal during the adsorption of 4-CP by soy sauce residue modified biochar have not been explored.

[0031] Based on the above considerations, the present application proposes a method for preparing modified biochar. In order to make the purpose, technical scheme and advantages of the present application clearer, the technical scheme of the present application will be clearly and completely described in combination with the specific embodiments of the present application and the corresponding drawings. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0032] like Figure 1 As shown, the method of the present application comprises the following steps:

[0033] S110, weighing raw materials: ZnCl2 and soy sauce residue biomass; wherein the mass ratio of ZnCl2 to the soy sauce residue biomass is m:1, and m is 0.25 to 1;

[0034] S120, dissolving ZnCl2 in a certain amount of deionized water, and adding the ground, washed and dried soy sauce residue biomass to obtain solution A;

[0035] S130, stirring solution A, and drying after stirring for 10-14 hours to obtain mixture B;

[0036] S140, high temperature pyrolysis: placing mixture B in a high temperature pyrolysis device, heating to a preset calcination temperature at a rate of 4-6°C / min under a N2 atmosphere for 80-100 min, to obtain sample C;

[0037] S150. Cool, wash and dry sample C in sequence to obtain modified biochar n-mZnBC; wherein n is the preset calcination temperature of the high-temperature pyrolysis process, and m is the mass ratio of ZnCl2 to the mass of soy sauce residue biomass.

[0038] In the above steps, ZnCl2, as a metal modifier, can promote certain H and O elements in the material to be converted into water vapor volatilization under high temperature conditions, and the high temperature environment accelerates the cross-linking of polymers into carbon. And ZnCl2 can suppress the generation of toxic substances in the biomass carbonization process, and increase the output of amino compounds, making biochar safer and more effective in practical applications. As a by-product of soy sauce production, soy sauce residues have huge output, and with the improvement of product grade, soy sauce residues by-products with higher utilization value are also produced. However, the development and utilization rate of soy sauce residues are not high at present. If they are not properly handled, they will cause great pollution to the environment and waste precious resources. If these industrial wastes can be converted into high-efficiency environmental management materials, it will be of great significance to promote the resource utilization of industrial wastes in my country and green sustainable development. This application uses soy sauce residues as biomass raw materials, and synthesizes ZnCl2 modified biochar by high-temperature pyrolysis by impregnation method.

[0039] In step S110, the mass ratio of ZnCl2 to the mass ratio of soy sauce residue biomass can be 0.25:1, 0.5:1, 0.75:1, 1:1. In step S120, the amount of deionized water is not specifically limited, that is, at least the amount of ZnCl2 and soy sauce residue biomass dissolved is reached. As an example, the amount of deionized water can be 10-15 times the mass of the soy sauce residue biomass. In step S130, the stirring time is preferably 12h. In step S140, under N2 atmosphere, the heating rate is preferably 5°C / min, the preset calcination temperature can be 500°C, 600°C, 700°C or 800°C, and the duration of high temperature pyrolysis is preferably 90min. In step S150, the washing of sample C can be performed by multiple alternating rinses with ethanol and deionized water.

[0040] The preparation method of the present application is further described in detail below in conjunction with a specific embodiment, and the structural characterization analysis of the prepared n-mZnBC is performed.

[0041] First, 2g of ZnCl2 was dissolved in 50ml of deionized water, and then 4g of soy sauce residue biomass that had been ground, washed and dried was added to obtain solution A. The mass ratio of ZnCl2 to soy sauce residue biomass was 0.5:1. After stirring solution A for 12h, it was dried to obtain mixture B. Then, mixture B was placed in a tube furnace and heated to 800℃ at a rate of 5℃ / min under N2 atmosphere, and pyrolysis was continued for 90min to obtain sample C. After sample C was cooled, it was alternately rinsed with ethanol and deionized water several times, and then dried to obtain 800-0.5ZnBC.

[0042] According to the above preparation method, under the premise that other conditions remain unchanged, 1g, 3g and 4g ZnCl2 are weighed respectively to prepare 800-0.25ZnBC, 800-0.75ZnBC and 800-1ZnBC. Similarly, under the premise that other conditions remain unchanged, changing the preset calcination temperature can obtain n-mZnBC with different calcination temperatures and different mass ratios of ZnCl2 and soy sauce residue biomass.

[0043] Furthermore, the microstructure of the soybean residue biochar was analyzed using a scanning electron microscope. Figure 2-7 As shown, the microstructure is compared at the same calcination temperature.

[0044] Figure 2 This is the SEM image of the original soybean residue biochar. The biochar morphology shows the irregular layered structure unique to soybean residue biomass, with a smooth surface, very few pores and a disordered shape. Figure 3 The ZnCl2-modified soy sauce residue biochar with a doping mass ratio of 0.25 was prepared. The changes compared with the original biochar could be clearly distinguished. A pore-like structure appeared on the surface with a small amount of nanoparticles around it, which successfully proved the successful doping of ZnCl2.

[0045] When the doping ratio of ZnCl2 increases by 0.5, Figure 4 As shown in the figure, the modified biochar has orderly and tight "honeycomb channels". ZnCl2 undergoes dehydration and condensation reaction with the biomass surface, resulting in complete consumption of nanoparticles, which helps the formation of biochar channels, provides a larger specific surface area and abundant micropores, and increases the adsorption sites of biochar materials. After washing with deionized water, the impurities on the biochar surface are reduced, and the pores are smooth and regularly arranged (such as Figure 7 The adsorption performance of pollutants is further improved.

[0046] When the doping ratio of ZnCl2 increases to 0.75, Figure 5 As shown in the figure, it can be seen that the pores on the surface of biochar are neatly arranged but partially damaged; when the doping ratio of ZnCl2 is continued to increase to 1.00, as shown in the figure, Figure 6 As shown in the figure, the pore walls on the surface of biochar are thick and the pores are blocked, indicating that excessive ZnCl2 will cause the structural function of biochar to degenerate, the pores to collapse, and affect the adsorption of pollutants.

[0047] The elemental composition and particle distribution of ZnCl2-modified soy sauce residue biochar were further studied. Five elements including C, N, O, Cl and Zn were detected on ZnCl2-modified biochar. The atomic distribution was uniform, and the number was close to the value of EDS monitoring analysis. The successful loading of Zn also confirmed the correct analysis of the previous SEM. Further spectral analysis showed that the main elements on the surface of ZnBC were C and O. Since the low-salt solid of soy sauce residue is mainly composed of soybeans, wheat flour, etc., the fermented soy sauce (salt concentration 6% to 8%, water content 50% to 58%) is rich in crude protein, oil, soybean isoflavones, rich trace elements (Ca, Fe, Zn, Cu, Mn, Mg) and vitamins, etc., confirming the presence of trace elements such as Fe, Ca, Na, and Cl.

[0048] It is worth mentioning that in previous reports, the doping of ZnCl2 would reduce the content of H and O elements in the original biochar. This is because in the synthesis of the impregnation method, zinc chloride will play a role in the decomposition of the cellulose of the sauce residue biomass, and promote the dehydrogenation and deoxygenation of the biochar through high-temperature pyrolysis, so that it evaporates and detaches with gases such as water vapor and H2. However, the doping of ZnCl2 in this study changed the previous conclusions. With the gradual increase of the doping ratio, the O element gradually increased from 35.12% to 70.95 (1.0ZnBC).

[0049] The researchers further analyzed the specific surface area and pore characteristics of ZnCl2-doped soybean residue biochar. The study showed that high temperature can make the modified soybean residue biochar have a larger specific surface area, and with the increase of ZnCl2 doping ratio, the specific surface area of ​​biochar shows a trend of first increasing and then decreasing, and the average pore size of modified biochar is smaller than that of original biochar. The specific surface area of ​​original biochar is only 15.298m2g-1, and the specific surface area of ​​carbon materials is greatly increased by doping with ZnCl2. When the preparation temperature reaches 800℃ and above, ZnBC can have a very large specific surface area. Among them, the specific surface area of ​​800-0.5ZnBC reaches 556.070m2g-1, which is nearly 37 times larger than that of original biochar, and the average pore size is reduced to 1.8546nm, indicating that the mesoporous pore size is opened again to form more microporous structures. The specific surface area of ​​800-0.75ZnBC (376.378m2g-1) is slightly lower than that of the former, but the average pore size (2.3868nm) is larger. The large number of mesopores may enhance the contact between biochar and pollutants, and serve as an ion transport channel to help remove pollutants.

[0050] The present application also provides a modified biochar, which is n-mZnBC prepared by the above steps and is mainly used for removing 4-CP and hexavalent chromium in water.

[0051] Specifically, the researchers analyzed and studied the adsorption mechanism of 4-CP by the modified biochar provided in this application, and summarized it as follows: The soybean residue biochar modified by ZnCl2 doping has a large specific surface area and a good pore structure, and can adsorb 4-CP on the surface and in the pores of the biochar for pore filling. pH affects the charge properties of ZnBC and the morphology of 4-CP. The surface functional groups of ZnBC and 4-CP can attract each other through electrostatic effects. When the pH increases, the π-π interaction between 4-CP and biochar will weaken. Through the XPS analysis of the modified biochar after adsorption of 4-CP, it can be concluded that there is a "Lewis acid-base interaction" between 4-CP and pyridine N, and it will have a π-π interaction with pyridine N and pyrrole N. In summary, the possible mechanisms for the adsorption of 4-CP by soybean residue modified biochar include: pore filling mechanism, electrostatic attraction, π-π interaction and Lewis acid-base interaction.

[0052] The researchers analyzed and studied the mechanism of action of the modified biochar provided in this application on the removal of Cr(VI), and summarized it as follows: the soybean residue biochar modified by ZnCl2 doping has a large specific surface area and good porosity, which is conducive to the physical diffusion and adsorption of Cr(VI) ions by biochar; electrostatic action plays an important role in removing Cr(VI) mainly in the form of negatively charged ions; the adsorbed Cr(VI) then undergoes redox reaction and is reduced to Cr(III), and the N and O functional groups can provide electrons for the reduction of Cr(VI); finally, part of Cr(III) is complexed with C=O and fixed to the modified biochar. In summary, the mechanism of Cr(VI) removal by soybean residue modified biochar includes: pore filling mechanism, electrostatic action, reduction action and complexation.

[0053] It can be seen that soy sauce residue biochar is a very potential adsorbent, which opens up new theoretical ideas for the utilization of waste biomass in water body remediation.

[0054] The zinc chloride-doped sauce residue biochar prepared in this application has a good adsorption and removal effect on both 4-CP and Cr(VI). The specific conclusions are as follows:

[0055] (1) The removal of Cr(VI) by modified soy residue biochar under different preparation conditions was investigated. It was found that the preparation temperature was positively correlated with the removal rate of ZnBC for Cr(VI). The removal rate of the original biochar for Cr(VI) was only 22.28%. The removal efficiency increased significantly after modification with ZnCl2. The removal rate first increased and then decreased with the increase of ZnCl2 doping ratio. The removal effect of 800-0.75ZnBC on Cr(VI) was the best, and the removal rate could reach 99.16% at 120min. The removal rate of Cr(VI) by modified biochar showed a trend of gradually decreasing with the increase of solution pH. The removal efficiency was still 99.16% at pH=3, and the Zeta potential of ZnBC was zero at pH=3.9. The coexisting cations and anions will have different degrees of influence on the removal of Cr(VI). The influence of anions is slightly greater than that of cations, but the overall influence is small.

[0056] Through fitting of different kinetic models, the results show that the removal process of ZnBC for Cr(VI) is divided into three diffusion stages, the adsorption mechanism is relatively complex, and internal diffusion is not the only rate-controlling step; the removal process is a combination of physical adsorption and chemical adsorption, with chemical adsorption as the dominant process. By fitting the experimental data with Langmuir and Freundlich models, it is proved that the removal process is a chemical adsorption process with both monolayer adsorption and multilayer adsorption. The adsorption process proceeds in a direction that is favorable to the reaction. The maximum saturated adsorption capacity of ZnBC for Cr(VI) reaches 82.1180 mg / g. The fitting parameters of the Freundlich model indicate that the surface of ZnBC is uneven and the affinity and interaction between biochar and Cr(VI) are extremely strong during the removal process, and the adsorption reaction is easy to occur. The fitting parameters of the Redlich-Peterson model indicate that the removal process is more inclined to the Freundlich model. With the increase of the number of desorption times, the removal rate of ZnBC for Cr(VI) shows a downward trend. When repeated twice, the removal efficiency can still reach 67.35%. In the process of biochar removing Cr(VI), the maximum leaching amount of zinc ions did not exceed 0.5 mg / L after 120 min of reaction, and the impact on the environment was minimal.

[0057] (2) XPS analysis of the modified biochar before and after Cr(VI) removal was performed, and the C1s, O 1s, N1s and Cr 2p peaks were fitted separately. It was found that Cr(VI) underwent redox reaction and was reduced to Cr(Ⅲ) during the removal process, and part of Cr(Ⅲ) was fixed in the modified biochar. The concentration of Cr(Ⅲ) in the solution after the reaction was detected to be 3.86 mg / L. Various N and O functional groups can reduce Cr(VI) and complex with the generated Cr(Ⅲ), which enhances the removal performance of modified soybean residue biochar for Cr(VI). Based on the experimental and analytical data, the main mechanism of Cr(VI) removal by soybean residue modified biochar was obtained, including pore filling mechanism, electrostatic effect, reduction and complexation.

[0058] (3) The adsorption performance of ZnBC in the mixed organic-inorganic pollution system was investigated. In the mixed pollutants of 4-CP and Cr(VI), the adsorption capacity of ZnBC for Cr(VI) decreased by 6.18%, and the adsorption capacity of ZnBC for 4-CP decreased by 17.88%, indicating that 4-CP and Cr(VI) would produce competitive adsorption, and the adsorption of 4-CP was greatly affected by the mixed pollution system.

[0059] The above describes specific embodiments of this specification, and other embodiments are within the scope of the appended claims. In some cases, the actions or steps described in the claims can be performed in an order different from that in the embodiments and still achieve the desired results. The same and similar parts between the various embodiments in this specification can be referenced to each other, and each embodiment focuses on the differences from other embodiments.

[0060] The above is only an embodiment of this specification and is not intended to limit the present application. For those skilled in the art, the present application may have various changes and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application should be included in the scope of the claims of the present application.

Claims

1. A method for preparing modified biochar, characterized in that: The method comprises the following steps: Weigh the raw materials: ZnCl2 and soy sauce residue biomass; wherein the mass ratio of ZnCl2 to soy sauce residue biomass is m:1, and m is 0.25-1; Dissolve ZnCl2 in a certain amount of deionized water, and add the ground, washed and dried soy sauce residue biomass to obtain solution A; The solution A is stirred, and after stirring for 10-14 hours, the mixture is dried to obtain a mixture B; High temperature pyrolysis: Place mixture B in a high temperature pyrolysis device, heat it to a preset calcination temperature at a rate of 4-6°C / min under a N2 atmosphere for 80-100 min to obtain sample C; Sample C was cooled, washed and dried in sequence to obtain modified biochar n-mZnBC; wherein n is the preset calcination temperature of the high-temperature pyrolysis process, and m is the mass ratio of ZnCl2 to the mass of soy sauce residue biomass.

2. The method according to claim 1, characterized in that The value of m is 0.25, 0.5, 0.75 or 1.

3. The method according to claim 1, characterized in that In the step of stirring solution A, the mixture B is obtained by drying after stirring for 12 hours.

4. The method according to claim 1, characterized in that In the high-temperature pyrolysis step, the tube furnace was heated to a preset calcination temperature at a rate of 5°C / min under a N2 atmosphere.

5. The method according to claim 1, characterized in that The preset calcination temperature is 500°C, 600°C, 700°C or 800°C.

6. The method according to claim 1, characterized in that In the high temperature pyrolysis step, the duration of the high temperature pyrolysis is 90 minutes.

7. The method according to claim 1, characterized in that The washing steps for sample C included multiple alternating rinses with ethanol and deionized water.

8. A modified biochar, characterized in that: The modified biochar is n-mZnBC prepared by the method described in any one of claims 1 to 7.

9. The modified biochar according to claim 8, characterized in that The modified biochar is used to remove 4-CP and hexavalent chromium in water.

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