Method for preparing activated carbon by mixing biomass with mariculture sediment and application thereof

Abstract

The application discloses a method for preparing activated carbon by mixing seawater breeding mud and biomass and application of the activated carbon. The preparation of the activated carbon comprises the following steps: desalination of seawater breeding mud to obtain low-salt mud particles; the low-salt mud particles are uniformly mixed with biomass powder at a ratio of 1:(3-5), pyrolysis and carbonization are carried out under a nitrogen atmosphere at 350-450 DEG C to obtain pre-carbonized biomass material; the pre-carbonized biomass material is uniformly mixed with an activating agent at a mass ratio of 1:(4-5), and mechanical chemical ball milling is carried out in a ball mill tank, then the ball-milled mixture is transferred to a tube furnace, high-temperature activation is carried out under a nitrogen atmosphere at 800-1000 DEG C to obtain activated carbon. The material has a hierarchical porous structure and a high specific surface area, can adsorb and remove various pollutants, especially has a high adsorption capacity for VOCs and CO2, can be mass-produced, has a low cost, is suitable for a wide temperature range, has a long service life and has a good application prospect.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of activated carbon preparation, and particularly relates to a method for preparing activated carbon by doping biomass into seawater breeding mud and application. BACKGROUND

[0002] In recent years, the seawater breeding industry in China has developed rapidly, and the seawater breeding output has ranked first in the world for many years, playing an important role in economic and social development. At present, the types of seawater breeding in Sanmen County mainly include pond breeding, factory breeding, open seawater breeding (tidal flat, net cage, raft, hanging cage and bottom seeding), etc. Intensive seawater breeding requires feeding a large amount of feed, and a considerable part of the feed cannot be eaten by fish, resulting in high concentrations of pollutants such as nitrogen, phosphorus and suspended solids in breeding tail water. In the pond breeding mode, residual feed, fertilizer, silt and animal manure will accumulate to form sludge, bringing a lot of pathogenic bacteria and viruses. In order to protect the breeding income, fishermen will clean the pond and disinfect it, and the sludge will be discharged into the sea with the breeding tail water through the gate, which will affect the nearshore water environment, even cause imbalance of the nearshore marine ecosystem, frequent red tide and disease breeding, and thus pose a threat to the nearshore marine environment quality and sustainable development and utilization of marine fishery resources. Therefore, it is urgent to efficiently treat seawater breeding pollution, and the treatment of seawater breeding pond sludge has become a public concern of environmental and ecological problems.

[0003] The seawater breeding sludge contains silt, shells, debris, a large amount of uneaten feed and fish excrement, contains a large amount of protein and other macromolecular substances, and due to the long-term accumulation of the sludge at the bottom of the breeding pond, the functional bacterial flora cannot fully denitrify and remove phosphorus, and the nitrogen and phosphorus contents are high, and the sludge also contains a foul odor. In addition, the inorganic chlorine salt content in the seawater breeding pond sludge is high. Inorganic chlorine salt not only reduces the quality of the resource product, but also damages the production process. However, there is no efficient and low-cost resource utilization method for seawater breeding sludge.

[0004] The abundant biomass is a typical energy resource in China, and a large amount of biological waste is produced every year. These biomasses include corn stalks and corn cobs, wheat and rice stalks, etc. left by agricultural planting; the physical or chemical activation method can be used to modify and activate the biochar, so as to greatly improve the pore structure, surface functional groups and other physical and chemical properties of the biochar, so that micropores and mesopores are formed on the surface of the biochar, the porosity is increased, and the specific surface area is effectively increased, thereby improving the adsorption capacity. The biochar is a high-potential biomass-based porous adsorption material due to its low cost, abundant raw material source and various modification and activation methods.

[0005] Based on this, the application develops a method for preparing activated carbon by doping biomass into seawater breeding sludge for waste resource utilization. SUMMARY

[0006] To address at least one of the aforementioned problems, this invention provides a method for preparing activated carbon by incorporating biomass into seawater aquaculture sediment and its application.

[0007] To achieve the above objectives, the present invention employs the following technical means:

[0008] A method for preparing activated carbon by mixing biomass with marine aquaculture sediment includes the following steps:

[0009] S1. After mud-water separation and screening, solid bottom mud is obtained from the mud-water slurry of the seawater aquaculture pond. The solid bottom mud is washed in a multi-stage water washing system with a liquid-solid ratio greater than 1:6 for 1 hour, and then the liquid and solid are separated. The separated bottom mud is dewatered by pressure filtration and then heat-dried at 80-120℃ to obtain low-salt bottom mud particles.

[0010] S2. Wash, dry and crush the biomass material to obtain biomass powder. Mix the low-salt bottom mud particles treated in S1 with the biomass powder in a ratio of 1: (3-5) and pyrolyze and carbonize at 350-450℃ under a nitrogen atmosphere to obtain pre-carbonized biomass material.

[0011] S3. The pre-carbonized biomass material obtained in S2 is mixed with the activator at a mass ratio of 1:(4-5) and placed in a ball mill jar for mechanochemical ball milling. Then the ball-milled mixture is transferred to a tube furnace and activated at a high temperature of 800-1000℃ under a nitrogen atmosphere to obtain activated carbon.

[0012] In some embodiments of the present invention, the biomass material is soybean straw or corn straw. In some embodiments of the present invention, preferably, the biomass material is soybean straw.

[0013] In some embodiments of the present invention, low-salt sediment particles and biomass powder are mixed in a ratio of 1:4, and the high-temperature activation temperature is preferably 900°C.

[0014] In some embodiments of the present invention, the multi-stage water washing wastewater after solid-liquid separation in step S1 is evaporated, concentrated, and crystallized to precipitate sodium chloride, and the condensate is returned to the multi-stage water washing system for reuse.

[0015] In some embodiments of the present invention, the activated carbon obtained in step S3 is washed in an acid solution, washed with distilled water until neutral, and dried to obtain the final activated carbon.

[0016] In some embodiments of the present invention, in steps S2 and S3, the nitrogen flow rate is 150-250 mL / min, and the pyrolysis time is 2-3 h.

[0017] In some embodiments of the present invention, in step S3, the activator is one or more of potassium bicarbonate, potassium chloride, potassium hydroxide, sodium thiosulfate, thiourea, melamine, urea, and zinc chloride.

[0018] In some embodiments of the present invention, in step S3, the activator is potassium bicarbonate and sodium thiosulfate; the mass ratio of potassium bicarbonate to sodium thiosulfate is (4-5):1.

[0019] In some embodiments of the present invention, preferably, biochar is mixed with potassium bicarbonate and sodium thiosulfate in a mass ratio of 3:10:4.

[0020] In some embodiments of the present invention, in step S3, the ball milling ball-to-material mass ratio is (5-30): 1, 400-800 r / min, and the ball milling time is 0.3-2 h.

[0021] In some embodiments of the present invention, the acid solution in step S4 is one of nitric acid solution, hydrochloric acid solution, and sulfuric acid solution, and the concentration of the acid solution is 0.5-1 mol / L.

[0022] A second aspect of the present invention provides activated carbon prepared according to the method described in the first aspect.

[0023] The present invention provides the application of biochar prepared by the method described in the first aspect in the adsorption of pollutants VOCs and CO2 in exhaust gas / flue gas, and further, in the adsorption and removal of chlorobenzene and toluene in flue gas.

[0024] Beneficial effects of the present invention

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] This invention employs a circulating water washing method to achieve efficient desalination of marine aquaculture pond sediment, directly removing inorganic chlorides to obtain low-salt sediment. Then, using the sediment and biomass as raw materials, biochar material is prepared through a low-temperature carbonization and high-temperature activation process. This material possesses a hierarchical porous structure and a high specific surface area, which is beneficial for gas adsorption and removal. The biomass-based char material prepared by this method can adsorb and remove various pollutants, especially VOCs and CO2, exhibiting high adsorption capacity. It can be mass-produced at low cost, has a wide applicable temperature range, and a long service life, demonstrating promising application prospects. Attached Figure Description

[0027] Figure 1 The image shown is a scanning electron microscope (SEM) image of the bottom mud of the aquaculture pond in Example 1;

[0028] Figure 2 The particle size analysis diagram of the bottom mud in the aquaculture pond in Example 1 is shown;

[0029] Figure 3 The graph shows the variation of chlorine content in sediment with different liquid-to-solid ratios in Example 1.

[0030] Figure 4 SEM comparison images of the activated carbon prepared in Examples 9 and 10 are shown; where (a) and (b) are AC-8; (c) and (d) are AC-9;

[0031] Figure 5 The saturated adsorption capacities of biochar materials for benzene, toluene, chlorobenzene, and CO2 in Examples 3, 9, and 10 are shown.

[0032] Figure 6 The diagram shows a comparison of the saturated adsorption capacity changes of the activated carbon prepared in Example 9 and commercial activated carbon for the cyclic adsorption of chlorobenzene, where (a) is AC-8 and (b) is commercial activated carbon AC. Detailed Implementation

[0033] The following examples are used to illustrate preferred embodiments of the invention. Those skilled in the art will understand that the techniques disclosed in the examples represent techniques discovered by the inventors that can be used to implement the invention, and therefore can be considered preferred embodiments for implementing the invention. However, those skilled in the art should understand from this specification that many modifications can be made to the specific embodiments disclosed herein, still yielding the same or similar results, without departing from the spirit or scope of the invention.

[0034] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains, and all materials disclosed herein and cited therein are incorporated herein by reference. Many equivalent techniques of specific embodiments of the invention described herein will be recognized or can be understood by ordinary experimentation by those skilled in the art. These equivalents will be included in the claims.

[0035] The technical solution of this application will be further described in detail below with reference to specific embodiments.

[0036] Example 1: Desalination of marine aquaculture sediment

[0037] The mud and water from the marine aquaculture pond are pumped into a primary mud-water separation system. The wastewater enters a primary wastewater storage tank, while the solid bottom mud enters a bottom mud storage tank. The bottom mud coming out of the bottom mud storage tank enters a screening machine to remove stones, shells, and other debris from the bottom mud of the aquaculture pond, resulting in screened bottom mud.

[0038] The screened bottom sludge enters a multi-stage washing system for desalination. After the washing wastewater becomes saturated, the solid-liquid separation process concentrates the wastewater to a certain concentration at 110℃, crystallizing out sodium chloride. The condensate is returned to the process system. The precipitated salt meets national standards, and the sodium chloride meets the quality requirements of Grade II refined industrial salt in GB / T5462-2003. It can be directly recycled or sold as a by-product, realizing the resource utilization of salt and yielding significant economic benefits.

[0039] The washed bottom sludge is mechanically dewatered using a filter press to minimize the sludge moisture content and fully utilize the mechanical dewatering process to reduce the volume of sludge. Thermal drying further reduces the sludge moisture content until granular sludge is formed.

[0040] (1) Determination of physical and chemical properties of seawater aquaculture pond bottom mud used in the experiment

[0041] The bottom mud of the marine aquaculture pond is dark brown, with high water content, a foul odor, a pH of 8.2, total phosphorus of 731 mg / kg, total nitrogen of 1260 mg / kg, organic carbon of 2.06%, and total salinity of 9.22 g / kg. The mud contains sand, shells, and shrimp and crab remains. A scanning electron microscope image of the pond bottom mud is shown below. Figure 1 As shown, particle size analysis is as follows Figure 2 As shown.

[0042] (2) Elemental analysis of bottom mud in marine aquaculture ponds

[0043] XRF analysis of the sediment revealed that the main chemical components Si, Al, Fe, Ca, K, Cl, Mg, Na, S, Ti, and P accounted for 39.1%, 14.0%, 13.8%, 10.6%, 6.61%, 5.27%, 2.98%, 2.51%, 1.70%, and 1.4% by mass, respectively. However, the contents of Cl, Na, and Fe were relatively high, and Cl and Na are hazardous elements that need to be removed.

[0044] (3) The washing time directly affects the dissolution and diffusion of salt. In order to explore the optimal washing desalination operation, we selected a liquid-solid ratio of 10 mL / g and investigated the effect of different washing times of 10 min, 20 min, 30 min, 1 h, 2 h and 3 h on the content of bottom sediment components. The results are shown in Table 1.

[0045] Table 1. Effects of different washing times on the composition of bottom mud in aquaculture ponds.

[0046]

[0047] The results showed that the elution rate of Cl was 89% after 1 hour of washing and 91% after 3 hours of washing; the elution rate of Na was 52% after 1 hour of washing and 60% after 3 hours of washing. Therefore, a washing time of 1 hour was determined to be the optimal washing time.

[0048] (4) Based on the optimal washing time of 1 hour, the effect of liquid-solid ratios of 1:1, 2:1, 4:1, 6:1, 8:1, and 10:1 on the chloride content in the sediment was investigated. The results are as follows: Figure 3 As shown.

[0049] The results showed that when the liquid-to-solid ratio was less than 4, the chlorine content in the washed sediment decreased sharply with the increase of the liquid-to-solid ratio. When the liquid-to-solid ratio was 6, the chlorine removal rate in the sediment was as high as 90% or more.

[0050] Example 2: Preparation of Activated Carbon AC-1

[0051] (1) Mix the washed bottom mud and soybean straw at a mud-to-straw mass ratio of 1:4 and stir thoroughly;

[0052] (2) Under a nitrogen atmosphere, pyrolysis carbonization was carried out at 400℃ for 2 hours, with a nitrogen flow rate of 200 ml / min, to obtain pre-carbonized material;

[0053] (3) The obtained biochar was mixed with potassium chloride and sodium thiosulfate in a mass ratio of 3:10:4 and placed in a ball mill jar for mechanical and chemical ball milling at a speed of 500 r / min for 0.5 h. Then the ball-milled mixture was transferred to a tube furnace and activated at 800 °C under a nitrogen atmosphere for 2 h with a nitrogen flow rate of 200 ml / min to obtain activated carbon.

[0054] (4) The obtained activated carbon is washed in 1 mol / L hydrochloric acid solution, then washed with distilled water until neutral, and the collected material is dried overnight to obtain the final biochar material, labeled as AC-1.

[0055] Example 3: Preparation of Activated Carbon AC-2

[0056] The steps are the same as in Example 2, except that in step (1), the original bottom mud and soybean straw are mixed and ground to obtain a material labeled AC-2.

[0057] Example 4: Preparation of Activated Carbon AC-3

[0058] The steps are the same as in Example 2, except that the ratio of the washed bottom mud to soybean straw in step (1) is 1:1, and the resulting material is labeled AC-3.

[0059] Example 5: Preparation of Activated Carbon AC-4

[0060] The steps are the same as in Example 2, except that the ratio of the washed bottom mud to soybean straw in step (1) is 1:3, and the resulting material is labeled AC-4.

[0061] Example 6: Preparation of Activated Carbon AC-5

[0062] The steps are the same as in Example 2, except that the ratio of the washed bottom mud to soybean straw in step (1) is 1:5, and the resulting material is marked as AC-5.

[0063] Example 7 Preparation of Activated Carbon AC-6

[0064] The steps are the same as in Example 2, except that the activation temperature in step (3) is 900°C, and the resulting material is marked as AC-6.

[0065] Example 8: Preparation of Activated Carbon AC-7

[0066] The steps are the same as in Example 2, except that the activation temperature in step (3) is 1000℃, and the material is marked as AC-7.

[0067] Example 9: Preparation of Activated Carbon AC-8

[0068] The steps are the same as in Example 2, except that in step (3), biochar, potassium bicarbonate, and sodium thiosulfate are mixed evenly in a mass ratio of 3:10:4 and the activation temperature is 900℃, and the resulting material is marked as AC-8.

[0069] Example 10 Preparation of Activated Carbon AC-9

[0070] The steps are the same as in Example 2, except that the biomass in step (1) is corn straw, and the resulting material is labeled AC-9.

[0071] Performance Comparison

[0072] (1) We compared the activated carbon materials prepared in Examples 2 to 10 with commercial activated carbon (Xinhui activated carbon, ZZ-40). The pore structure parameters of the materials calculated by nitrogen adsorption-desorption isotherms are shown in Table 2: specific surface area, pore diameter and pore volume.

[0073] Table 2. Specific surface area, pore size, and pore volume parameters of the activated carbon obtained in Examples 2-10 and commercial activated carbon.

[0074]

[0075] The results showed that, compared with AC-1, the biochar material (AC-2) made from unwashed sediment mixed with soybean straw had a smaller specific surface area, larger pore size, and smaller micropores. Compared with activation temperatures of 800℃ (AC-1) and 1000℃ (AC-7), the activated carbon at an activation temperature of 900℃ (AC-6) had a larger specific surface area, smaller pore size, and more micropores. Compared with AC-1, the use of potassium bicarbonate and sodium thiosulfate as activators could better regulate the structure of the biochar material, and AC-6 had a hierarchical porous biochar with a larger specific surface area and pore volume.

[0076] (2) Compare the SEM images of AC-8 and AC-9, such as Figure 4 As shown.

[0077] The results showed that AC-9 prepared by mixing corn straw with sediment exhibited a dense carbon layer structure, and it was difficult to observe a multi-level pore structure. Most of the pores were micropores, lacking the interweaving of mesopores and macropores. AC-8 prepared by mixing soybean straw with sediment had abundant multi-level pores and a higher level of specific surface area and pore volume.

[0078] (3) Investigation on the adsorption performance of materials AC-2, AC-8, and AC-9 for benzene, toluene, chlorobenzene, and CO2

[0079] The experimental system employed fixed-bed adsorption to test the dynamic VOCs adsorption performance of the material. Nitrogen was used as the carrier gas, with a total gas flow rate of 200 mL / min. The concentrations of benzene, toluene, and chlorobenzene were approximately 500 ppm, and the CO2 concentration was 1000 ppm. The amount of biochar material used was 0.05 g, and the adsorption bed thickness was approximately 5 mm. The adsorption environment was controlled at 303 K within a quartz tube with an inner diameter of 8 mm. The adsorption capacity of the biomass-based porous char was as follows: Figure 5 As shown.

[0080] The results showed that the adsorption characteristics of porous char doped with soybean straw (AC-8) and corn straw (AC-9) differed for organic pollutants and CO2. The adsorption capacity of soybean straw-based (AC-8) biochar doped with sediment for organic pollutants and CO2 was significantly higher than that of corn straw-based (AC-9) porous char, with the adsorption capacity decreasing in the order of AC-8 > AC-9 > AC-2. The original sediment char doped with biochar had the lowest adsorption capacity for organic pollutants and CO2. After washing, the sediment-doped biochar exhibited a stronger adsorption process because the hierarchical porous structure of the porous char reduced internal diffusion resistance.

[0081] (4) Investigation on the regeneration performance of material AC-8

[0082] The biochar material was regenerated using thermal desorption. The desorption-regeneration experiment temperature was 300℃, and the nitrogen flow rate was 100 mL / min. The biochar was purged until no VOCs were detected at the outlet. The regenerated carbon material was used for chlorobenzene adsorption experiments, and the saturated adsorption capacity of chlorobenzene was measured after 1, 2, and 3 adsorption-desorption cycles. The saturated adsorption capacity of AC-8 and commercial activated carbon AC for chlorobenzene was compared as follows: Figure 6 As shown.

[0083] The results showed that after three adsorption-desorption cycles, the saturated adsorption capacity of AC-8 for chlorobenzene decreased by less than 10%, while the saturated adsorption capacity of AC for chlorobenzene decreased by more than 20% after three adsorption-desorption cycles. This indicates that the regeneration performance of hierarchical porous biochar is much higher than that of commercial activated carbon AC (Xinhui activated carbon, ZZ-40).

[0084] All documents mentioned in this invention are incorporated herein by reference as if each document were individually incorporated by reference. Furthermore, it should be understood that after reading the foregoing teachings of this invention, those skilled in the art can make various alterations or modifications to this invention, and these equivalent forms also fall within the scope defined by this application.

Claims

1. A method for preparing activated carbon by mixing biomass with seawater aquaculture sediment, characterized in that, Includes the following steps: S1. After mud-water separation and screening, solid bottom mud is obtained from the mud-water slurry of the seawater aquaculture pond. The solid bottom mud is washed in a multi-stage water washing system with a liquid-solid ratio greater than 1:6 for 1 hour, and then the liquid and solid are separated. The separated bottom mud is dewatered by pressure filtration and then heat-dried at 80-120℃ to obtain low-salt bottom mud particles. S2. Wash, dry and crush soybean straw to obtain soybean straw powder. Mix the low-salt bottom mud particles obtained from S1 with soybean straw powder in a ratio of 1: (3-5). Pyrolyze and carbonize the mixture at 350-450℃ under a nitrogen atmosphere to obtain pre-carbonized straw material. S3. Mix the pre-carbonized straw material obtained in S2 with the activator at a mass ratio of 1:(4-5), place it in a ball mill jar for mechanochemical ball milling, transfer the ball-milled mixture to a tube furnace, and activate it at a high temperature of 800-1000℃ under a nitrogen atmosphere to obtain activated carbon. S4. The activated carbon obtained in step S3 is washed in an acid solution, washed with distilled water until neutral, and dried to obtain the final activated carbon. The activator is potassium bicarbonate and sodium thiosulfate; the mass ratio of potassium bicarbonate to sodium thiosulfate is (4-5):

1.

2. The method according to claim 1, characterized in that, In step S1, the multi-stage washing wastewater after solid-liquid separation is evaporated, concentrated, and crystallized to precipitate sodium chloride, and the condensate is returned to the multi-stage washing system for reuse.

3. The method according to claim 1, characterized in that, In steps S2 and S3, the nitrogen flow rate is 150-250 mL / min, and the pyrolysis time is 2-3 h.

4. The method according to claim 1, characterized in that: In step S3, the ball-to-material mass ratio is (5-30): 1, 400-800 r / min, and the ball milling time is 0.3-2 h.

5. The method according to claim 1, characterized in that: In step S3, the acid solution is one of nitric acid solution, hydrochloric acid solution, or sulfuric acid solution, and the concentration of the acid solution is 0.5-1 mol / L.

6. An activated carbon, characterized in that: It is prepared by the method described in any one of claims 1-5.

7. The application of activated carbon prepared by the method according to any one of claims 1-5 in the adsorption and removal of pollutants VOCs and CO2 in exhaust gas / flue gas.

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