Method for preparing activated carbon from mariculture bottom mud doped with biomass and application of activated carbon

Abstract

The invention discloses a method for preparing activated carbon from mariculture bottom mud doped with biomass and application. The preparation method of the activated carbon comprises the following steps: desalting the mariculture bottom mud to obtain low-salt bottom mud particles; uniformly mixing the low-salt sediment particles with biomass powder according to a ratio of 1: (3-5), and carrying out pyrolysis carbonization at 350-450 DEG C in a nitrogen atmosphere to obtain a pre-carbonized biomass material; and uniformly mixing the pre-carbonized biomass material and an activator according to a mass ratio of 1: (4-5), placing the mixture in a ball milling tank, carrying out mechanochemical ball milling, transferring the ball-milled mixture to a tubular furnace, and carrying out high-temperature activation at 800-1000 DEG C in a nitrogen atmosphere to obtain the activated carbon. The material has a hierarchical porous structure and a relatively high specific surface area, can adsorb and remove various pollutants, particularly has relatively high adsorption capacity for VOCs and CO2, can be produced in batches, is low in cost, wide in applicable temperature range and long in service life, and has a good application prospect.

Description

Technical Field

[0001] The invention belongs to the technical field of activated carbon preparation, and specifically relates to a method for preparing activated carbon by doping seawater aquaculture sludge with biomass and application thereof. Background Art

[0002] In recent years, my country's marine aquaculture industry has developed rapidly, and the output of marine aquaculture has ranked first in the world for many consecutive years, playing an important role in economic and social development. At present, the types of marine aquaculture in Sanmen County mainly include pond aquaculture, factory aquaculture, open marine aquaculture (tidal flats, cages, rafts, hanging cages and bottom seeding), etc. Intensive marine aquaculture requires feeding a large amount of bait, a considerable part of which cannot be eaten by fish, etc., resulting in high concentrations of pollutants such as nitrogen, phosphorus, and suspended solids in the aquaculture tailwater. Among them, the residual bait, fertilizer, silt, and animal feces in the pond aquaculture model will also accumulate to form silt, bringing many pathogenic bacteria and viruses. In order to ensure the income from aquaculture, fishermen will clean and disinfect the ponds, and discharge the bottom mud into the sea through the gates along with the aquaculture tailwater, which will affect the environment of the offshore waters and even cause the imbalance of the ecosystem in the offshore waters, frequent red tides, and the breeding of diseases, which will threaten the quality of the offshore marine environment and the sustainable development and utilization of marine fishery resources. Therefore, it is urgent to efficiently deal with marine aquaculture pollution, and the treatment of the bottom mud of marine aquaculture ponds has become an environmental and ecological issue of public concern.

[0003] Seawater aquaculture sediment contains sand, shells, debris, and complex composition. It contains a large amount of uneaten bait and fish excrement, and contains a large amount of high-molecular substances such as protein. At the same time, due to the long-term accumulation of sediment at the bottom of the aquaculture pond in an anaerobic state, the functional bacteria cannot fully remove nitrogen and phosphorus, and the nitrogen and phosphorus content is high, and it also contains a foul odor. In addition, the inorganic chloride content in the seawater aquaculture pond sediment is high, which will not only reduce the quality of its resource-based products but also destroy its production process. However, there is currently no efficient and low-cost resource method for seawater aquaculture sediment.

[0004] Biomass, which is rich in reserves, is a typical energy resource in my country. A large amount of biological waste is produced every year. These biomasses include corn stalks and corn cobs, wheat and rice straws, etc. left over from agricultural planting. Modification and activation of biochar by physical or chemical activation can greatly improve the pore structure, surface functional groups and other physical and chemical properties of biochar, forming micropores and mesopores on its surface. The porosity increases while the specific surface area also increases effectively, thereby improving the adsorption capacity. Biochar is a high-potential biomass-based porous adsorption material due to its low cost, abundant raw material sources, and diverse modification and activation methods.

[0005] Based on this, the present application develops a method for preparing activated carbon by doping seawater aquaculture mud with biomass for waste resource utilization. Summary of the invention

[0006] In order to solve at least one of the above problems, the present invention provides a method for preparing activated carbon by doping biomass with seawater aquaculture sediment and its application.

[0007] In order to achieve the above object, the present invention adopts the following technical means: A method for preparing activated carbon by doping biomass with seawater aquaculture sludge comprises the following steps: S1. After mud-water separation and screening, the mud water from the bottom of the seawater aquaculture pond is used to obtain solid sludge. The solid sludge enters the multi-stage washing system with a liquid-to-solid ratio greater than 1:6 and is washed for 1 hour before liquid-solid separation. The separated sludge is dehydrated by filter pressing and thermally dried at 80-120°C to obtain low-salt sludge particles. S2, washing, drying and crushing the biomass material to obtain biomass powder, mixing the low-salt sludge particles treated in S1 with the biomass powder in a ratio of 1: (3-5), pyrolyzing and carbonizing at 350-450° C. in a nitrogen atmosphere to obtain a pre-carbonized biomass material; S3. The pre-carbonized biomass material obtained in S2 is mixed evenly with the activator in a mass ratio of 1:(4-5), and the mixture is placed in a ball mill for mechanochemical ball milling. The ball mill mixture is then transferred to a tubular furnace for high-temperature activation at 800-1000°C under a nitrogen atmosphere to obtain activated carbon.

[0008] 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.

[0009] In some embodiments of the present invention, low-salt sludge particles and biomass powder are mixed in a ratio of 1:4, and the high-temperature activation temperature is preferably 900°C.

[0010] In some embodiments of the present invention, the multi-stage washing wastewater after solid-liquid separation in step S1 is evaporated, concentrated and crystallized to precipitate sodium chloride, and the condensed water is returned to the multi-stage washing system for reuse.

[0011] 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.

[0012] 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.

[0013] In some embodiments of the present invention, in step S3, the activating agent is one or more of potassium bicarbonate, potassium chloride, potassium hydroxide, sodium thiosulfate, thiourea, melamine, urea, and zinc chloride.

[0014] In some embodiments of the present invention, in step S3, the activating agents are potassium bicarbonate and sodium thiosulfate; the mass ratio of potassium bicarbonate to sodium thiosulfate is (4-5):1.

[0015] 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.

[0016] In some embodiments of the present invention, in step S3, the ball-to-material mass ratio (5-30) is: 1,400-800 r / min, and the ball-milling time is 0.3-2 h.

[0017] 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.

[0018] The second aspect of the present invention provides an activated carbon prepared according to the method described in the first aspect.

[0019] The present invention provides the use 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.

[0020] Beneficial effects of the present invention Compared with the prior art, the present invention has the following beneficial effects: The present invention adopts a circulating water washing method to achieve efficient desalination of the bottom mud of seawater aquaculture ponds, and can directly remove inorganic chloride salts in the bottom mud of seawater aquaculture ponds to obtain low-salt bottom mud; then the bottom mud and biomass are used as raw materials to prepare biomass carbon materials through a low-temperature carbonization and high-temperature activation method. This material has a hierarchical porous structure and a high specific surface area, which is conducive to the adsorption and removal of gases. The biomass-based carbon material prepared by the method of the present invention can adsorb and remove a variety of pollutants, especially VOCs and CO2, has a high adsorption capacity, can be mass-produced, has low cost, is applicable to a wide temperature range, has a long service life, and has good application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 The SEM image of the aquaculture pond sludge in Example 1 is shown; Figure 2 The particle size analysis diagram of the aquaculture pond mud in Example 1 is shown; Figure 3 The graph showing the change of chlorine content in the bottom mud at different liquid-to-solid ratios in Example 1 is shown; Figure 4 The SEM comparison images of the activated carbons prepared in Example 9 and Example 10 are shown; wherein (a) and (b) are AC-8; (c) and (d) are AC-9; Figure 5 The saturated adsorption capacity of benzene, toluene, chlorobenzene and CO2 by the biochar materials in Examples 3, 9 and 10 is shown; Figure 6 A comparison chart of the changes in saturated adsorption capacity of chlorobenzene cyclic adsorption of the activated carbon prepared in Example 9 and commercial activated carbon is shown, wherein (a) is AC-8; (b) is commercial activated carbon AC. DETAILED DESCRIPTION

[0022] The following examples are used to demonstrate preferred embodiments of the present invention. It will be appreciated by those skilled in the art that the techniques disclosed in the following examples represent techniques discovered by the inventors that can be used to implement the present invention and therefore can be considered as preferred embodiments of the present invention. However, it will be appreciated by those skilled in the art based on this specification that many modifications may be made to the specific embodiments disclosed herein and still achieve the same or similar results without departing from the spirit or scope of the present invention.

[0023] 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 the invention belongs, and the materials cited herein and those cited by them are incorporated by reference. Those skilled in the art will recognize or will learn through routine experimentation that there are many equivalents to the specific embodiments of the invention described herein. Such equivalents are intended to be encompassed by the claims.

[0024] The technical solution of the present application is further described in detail below in conjunction with specific implementation methods.

[0025] Example 1 Desalination of seawater aquaculture sludge The muddy water from the seawater aquaculture pond is pumped into the primary mud-water separation system, the wastewater enters the primary wastewater storage tank, the solid sludge enters the sludge storage tank, and the sludge coming out of the sludge storage tank enters the screening machine to remove stones, shells, etc. from the aquaculture pond sludge to obtain the screened sludge.

[0026] The sludge after screening enters the multi-stage washing system for multi-stage washing and desalination. After the washing wastewater is saturated, the washing wastewater obtained by solid-liquid separation is evaporated and concentrated to a certain concentration at a temperature of 110°C to crystallize sodium chloride, and the condensed water returns to the process system. The precipitated salt meets the national standard, and the sodium chloride meets the national standard GB / T5462-2003, the quality requirements of the second level of refined industrial salt, which can be directly recycled or sold as a by-product, realizing the resource utilization of salts, which will have great economic benefits.

[0027] The washed sludge is dehydrated mechanically through a filter press to minimize the moisture content of the sludge, give full play to the process performance of mechanical dehydration, and achieve sludge reduction; thermal drying further reduces the moisture content of the sludge until granular sludge is formed.

[0028] (1) Determination of physical and chemical properties of the sediment from the seawater aquaculture pond used in the experiment The bottom mud of the seawater aquaculture pond is dark brown, with high water content, foul odor, pH value of 8.2, total phosphorus of 731 mg / kg, total nitrogen of 1260 mg / kg, organic carbon of 2.06%, and total salt content of 9.22 g / Kg. The bottom mud contains sand, shells, shrimp and crab remains, etc. Figure 1 As shown, the particle size analysis Figure 2 shown.

[0029] (2) Elemental analysis of marine aquaculture pond mud XRF composition analysis of the sludge showed that the mass percentages of the main chemical components of the sludge, Si, Al, Fe, Ca, K, Cl, Mg, Na, S, Ti, and P, were 39.1%, 14.0%, 13.8%, 10.6%, 6.61%, 5.27%, 2.98%, 2.51%, 1.70%, and 1.4%, respectively. However, the contents of Cl, Na, and Fe were relatively high, and Cl and Na are hazardous elements that need to be removed.

[0030] (3) The washing time directly affects the dissolution and diffusion of salt. In order to explore the optimal water-washing desalination operation, we selected a liquid-to-solid ratio of 10 mL / g and investigated the changes in the content of sediment components at different washing times of 10 min, 20 min, 30 min, 1 h, 2 h, and 3 h. The results are shown in Table 1.

[0031] Table 1 Effect of different washing times on the content of sediment components in aquaculture pond sediment

[0032] The results showed that the elution rate of Cl was 89% after 1 hour of water washing and 91% after 3 hours of water washing; the elution rate of Na was 52% after 1 hour of water washing and 60% after 3 hours of water washing. Therefore, 1 hour of water washing was determined to be the optimal water washing time.

[0033] (4) Based on the optimal washing time of 1h, the influence of the chloride content in the sediment under the conditions of liquid-to-solid ratio of 1:1, 2:1, 4:1, 6:1, 8:1, and 10:1 was investigated. The results are as follows: Figure 3 shown.

[0034] The results showed that when the liquid-solid ratio was less than 4, the chlorine content in the sludge after washing dropped sharply as the liquid-solid ratio increased. When the liquid-solid ratio was 6, the removal rate of chlorine in the sludge was as high as over 90%.

[0035] Example 2 Preparation of activated carbon AC-1 (1) Mix the washed sludge and soybean straw in a mud-to-stalk mass ratio of 1:4 and stir thoroughly; (2) In a nitrogen atmosphere, pyrolysis carbonization was performed at 400 °C for 2 h and a nitrogen flow rate of 200 ml / min to obtain a pre-carbonized material; (3) The obtained biochar was mixed with potassium chloride and sodium thiosulfate as an activator in a mass ratio of 3:10:4 and placed in a ball mill for mechanochemical ball milling at a speed of 500 r / min for 0.5 h. The ball milled mixture was then transferred to a tubular furnace for high-temperature activation at 800 °C under a nitrogen atmosphere for 2 h at a nitrogen flow rate of 200 ml / min to obtain activated carbon. (4) The obtained activated carbon was washed in a 1 mol / L hydrochloric acid solution and then washed with distilled water until neutral. The collected material was dried overnight to obtain the final biochar material, which was labeled as AC-1.

[0036] Example 3 Preparation of activated carbon AC-2 The steps are the same as those in Example 2, except that in step (1), the original sludge is mixed with soybean straw and ground to obtain a material labeled AC-2.

[0037] Example 4 Preparation of activated carbon AC-3 The steps are the same as those in Example 2, except that in step (1), the ratio of washed sludge to soybean straw is 1:1, and the obtained material is marked as AC-3.

[0038] Example 5 Preparation of activated carbon AC-4 The steps are the same as those in Example 2, except that in step (1), the ratio of washed sludge to soybean straw is 1:3, and the obtained material is marked as AC-4.

[0039] Example 6 Preparation of activated carbon AC-5 The steps are the same as those in Example 2, except that in step (1), the ratio of washed sludge to soybean straw is 1:5, and the obtained material is marked as AC-5.

[0040] Example 7 Preparation of activated carbon AC-6 The steps are the same as those in Example 2, except that the activation temperature in step (3) is 900° C., and the obtained material is labeled AC-6.

[0041] Example 8 Preparation of activated carbon AC-7 The steps are the same as those in Example 2, except that the activation temperature in step (3) is 1000° C., and the obtained material is labeled AC-7.

[0042] Example 9 Preparation of activated carbon AC-8 The steps are the same as those in Example 2, except that: in step (3), the biochar is evenly mixed with potassium bicarbonate and sodium thiosulfate in a mass ratio of 3:10:4, the activation temperature is 900°C, and the obtained material is marked as AC-8.

[0043] Example 10 Preparation of activated carbon AC-9 The steps are the same as those in Example 2, except that the biomass in step (1) is corn stalks, and the obtained material is labeled AC-9.

[0044] Performance Comparison (1) We compared the activated carbon materials prepared in Examples 2 to 10 with commercial activated carbon (Xinhui activated carbon, ZZ-40), and the pore structure parameters of the materials calculated by nitrogen adsorption-desorption isotherms: specific surface area, pore diameter, and pore volume parameters are shown in Table 2.

[0045] Table 2 Specific surface area, pore size, and pore volume parameters of the activated carbon obtained in Example 2-10 and commercial activated carbon

[0046] The results showed that compared with AC-1, the biochar material (AC-2) made from unwashed sludge mixed with soybean straw had a smaller specific surface area, larger pore size, and very small micropores; compared with activation temperatures of 800℃ (AC-1) and 1000℃ (AC-7), when the activation temperature was 900℃ (AC-6), the activated carbon had a larger specific surface area, smaller pore size, and more micropores; compared with AC-1, the use of activating agents potassium bicarbonate and sodium thiosulfate could better regulate the structure of the biochar material, and AC-6 had a multi-level porous biochar with a larger specific surface area and pore volume.

[0047] (2) Compare the SEM of AC-8 and AC-9, such as Figure 4 shown.

[0048] The results showed that AC-9 made from sediment mixed with corn straw exhibited a dense carbon layer structure, and it was difficult to observe a multi-level pore structure. Most of the pores were micropores, and there was a lack of interlacing of mesopores and macropores. AC-8 made from sediment mixed with soybean straw had abundant multi-level pores and a higher level of specific surface area and pore volume.

[0049] (3) Study on the adsorption performance of materials AC-2, AC-8 and AC-9 for benzene, toluene, chlorobenzene and CO2 The experimental system uses fixed bed adsorption to test the dynamic adsorption performance of VOCs on the material. Nitrogen is used as the carrier gas. The total flow rate of the adsorption experiment gas is 200 mL / min. The concentrations of benzene, toluene, and chlorobenzene are all about 500 ppm, the CO2 concentration is 1000 ppm, the amount of biomass carbon material is 0.05 g, the thickness of the adsorption bed is about 5 mm, and the adsorption environment temperature is controlled at 303 K in a quartz tube with an inner diameter of 8 mm. The adsorption capacity of biomass-based porous carbon is as follows: Figure 5 shown.

[0050] The results show that the adsorption characteristics of organic pollutants and CO2 by the porous carbons doped with soybean straw (AC-8) and corn straw (AC-9) are different. The adsorption capacity of organic pollutants and CO2 by the porous carbons doped with soybean straw (AC-8) is significantly higher than that by the porous carbons doped with corn straw (AC-9). The adsorption capacity is AC-8>AC-9>AC-2. The adsorption capacity of organic pollutants and CO2 by the biochars doped with the original peat is the lowest. The biochars doped with the washed sediments have a stronger adsorption process because the hierarchical porous structure of the porous carbon reduces the internal diffusion resistance.

[0051] (4) Study on the regeneration performance of material AC-8 The biochar material after the reaction was regenerated by thermal desorption. The desorption regeneration experiment temperature was 300℃ and the nitrogen flow rate was 100 mL / min. The biochar after the reaction was purged until no VOCs were detected at the outlet. The regenerated carbon material was used for the adsorption of chlorobenzene experiment, and the saturated adsorption capacity of chlorobenzene after 1, 2 and 3 adsorption and desorption cycles was measured. Comparison of the saturated adsorption capacity of chlorobenzene by AC-8 and commercial activated carbon AC Figure 6 shown.

[0052] The results showed that after three adsorption and desorption cycles, the saturated adsorption capacity of chlorobenzene of AC-8 decreased by less than 10%, while the saturated adsorption capacity of chlorobenzene of AC decreased by more than 20% after three adsorption and desorption cycles. It can be seen that the regeneration performance of multi-pore biochar is much higher than that of commercial activated carbon AC (Xinhui activated carbon, ZZ-40).

[0053] All documents mentioned in the present invention are cited as references in this application, just as each document is cited as references separately. In addition, it should be understood that after reading the above teachings of the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined in the present application.

Claims

1. A method for preparing activated carbon by doping biomass with seawater aquaculture sludge, characterized in that: The steps include: S1. After mud-water separation and screening, the mud water from the bottom of the seawater aquaculture pond is used to obtain solid sludge. The solid sludge enters the multi-stage washing system with a liquid-to-solid ratio greater than 1:6 and is washed for 1 hour before liquid-solid separation. The separated sludge is dehydrated by filter pressing and thermally dried at 80-120°C to obtain low-salt sludge particles. S2, washing, drying and crushing the biomass material to obtain biomass powder, mixing the low-salt sludge particles obtained by the treatment in S1 with the biomass powder in a ratio of 1: (3-5), pyrolyzing and carbonizing at 350-450° C. in a nitrogen atmosphere to obtain a pre-carbonized biomass material; S3. The pre-carbonized biomass material obtained in S2 is uniformly mixed with the activator in a mass ratio of 1:(4-5), placed in a ball mill for mechanochemical ball milling, and the ball milled mixture is transferred to a tubular furnace for high-temperature activation at 800-1000°C under a nitrogen atmosphere to obtain activated carbon.

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 condensed water returns to the multi-stage washing system for reuse.

3. The method according to claim 1, characterized in that 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.

4. 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.

5. The method according to claim 1, characterized in that: In step S3, the activator is one or more of potassium bicarbonate, potassium chloride, potassium hydroxide, sodium thiosulfate, thiourea, melamine, urea, and zinc chloride.

6. The method according to claim 1, characterized in that: In step S3, the activating agents are potassium bicarbonate and sodium thiosulfate; the mass ratio of potassium bicarbonate to sodium thiosulfate is (4-5):

1.

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

8. The method according to claim 3, characterized in that: In step S4, the acid solution 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.

9. An activated carbon, characterized in that: The method is prepared by any one of claims 1 to 8.

10. Use of the biochar prepared by the method according to any one of claims 1 to 8 in the adsorption and removal of pollutants VOCs and CO2 in exhaust gas / flue gas.

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