Carbon-based conditioner as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of sludge dewatering treatment, and particularly relates to a carbon-based conditioner as well as a preparation method and application thereof. The average particle size of the carbon-based conditioner is 15-45 nm, the specific surface area is 600-1000 m < 2 > / g, the porosity is 50-90%, and the average pore size is 10-60 nm; based on the mass of the carbon-based conditioner, the content of the graphite crystals is 50-75wt%; the specific average particle size, specific surface area and porosity of the carbon-based conditioner endow the carbon-based conditioner with excellent adsorption performance, and when the carbon-based conditioner is applied to the sludge electric dehydration technology, the carbon-based conditioner can adsorb EPS, relieve filter cloth blockage and improve the electric dehydration effect; the specific graphite crystal content of the carbon-based conditioner provides a large number of free electrons, the free electrons form a conductive channel in the carbon-based conditioner, and after an electric field is applied, the free electrons and anions and cations ionized from the sludge have a synergistic effect, so that the conductivity of the whole system is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of sludge dewatering treatment, and specifically relates to a carbon-based conditioning agent and a preparation method and application thereof. Background Art

[0002] As the end product of biological sewage treatment, sludge poses great challenges to its treatment due to its high water holding capacity (initial water content is generally higher than 95%) and complex chemical composition (such as extracellular polymers (EPS), colloids, heavy metals and pathogens).

[0003] The primary task of sludge treatment is to reduce the volume of sludge through solid-liquid separation to reduce transportation and treatment costs. In addition, although sludge has a high water content and low energy density, it is rich in organic matter and has biomass carbon sources, such as proteins, polysaccharides, and lipids. These characteristics make sludge a highly potential renewable energy resource. Therefore, how to effectively dehydrate sludge and improve its resource utilization value has become a key issue that needs to be urgently addressed in the current sludge treatment field.

[0004] As an emerging sludge dehydration method, sludge electric dehydration technology (e.g., electro-osmosis sludge dehydration technology) ionizes electrolytes in sludge into anions and cations, which move in a directional manner under the action of the electric field, aggregate and squeeze the structure of the sludge, squeeze out the internal water, and achieve efficient sludge dehydration. However, if the electrolyte content in the sludge is insufficient and the water content is too high, the water will be diluted, which will reduce the electrolyte concentration of the system and lead to a decrease in the conductivity of the system. In addition, during the sludge dehydration process, the extracellular polymers (EPS) in the sludge will dissolve and release, and migrate to the surface or internal pores of the filter medium along with the water, blocking the filtration channel, increasing the filtration resistance, and worsening the sludge dehydration effect. Summary of the invention

[0005] Therefore, the technical problem to be solved by the present invention is to overcome the defects that the electrical conductivity of the system in the existing sludge electric dehydration process is poor, and as the dehydration proceeds, the filter medium will become clogged, reducing the dehydration effect, and the moisture content of the sludge after final dehydration is still relatively high, thereby providing a carbon-based conditioner and its preparation method and application.

[0006] To this end, the present invention provides the following technical solutions: The first aspect of the present invention provides a carbon-based conditioning agent, wherein the average particle size of the carbon-based conditioning agent is 15-45nm, and the specific surface area is 600-1000m 2 / g, porosity of 50-90%, average pore size of 10-60nm; The content of graphite crystals is 50-75 wt % based on the mass of the carbon-based conditioning agent.

[0007] According to the present invention, the average particle size of the carbon-based conditioner is 15 - 20 nm, the specific surface area is 800 - 1000 m 2 / g, the porosity is 60 - 80%, and the average pore size is 10 - 30 nm; Based on the mass of the carbon-based conditioner, the content of graphite crystals is 50 - 70 wt%.

[0008] In the second aspect of the present invention, a preparation method of a carbon-based conditioner is provided. Among them, the preparation method includes the following steps: mixing biomass activated carbon and solid base, pyrolyzing in a gas atmosphere containing a carbon source gas that can be cracked to obtain a mixture, and pickling to obtain a carbon-based conditioner; wherein, the conditions of the pyrolysis include: heating to 800 - 1500 °C at a rate of 5 - 20 °C / min, and the time is 1 - 2 h.

[0009] In the present invention, the biomass activated carbon is also dried before being mixed with the base. The drying is a conventional drying in the art. The drying temperature is 80 - 100 °C, and the drying time is adjusted according to the material size until the drying is complete; the dried biomass activated carbon does not contain moisture, which can avoid the evaporation of water into water vapor in a high-temperature environment, resulting in a change in the gas atmosphere, and further affecting the properties of the obtained carbon-based conditioner. In addition, water vapor combines with the base to form a corrosive solution, which will affect the service life of the tubular furnace.

[0010] In the present invention, the mixing is a conventional mixing in the art, and it is only necessary to mix evenly.

[0011] In the present invention, the solid base is a conventional base in the art. Typically and non-limitingly, the solid base includes at least one of solid potassium hydroxide and solid sodium hydroxide.

[0012] In the present invention, the biomass activated carbon and the solid base are placed in a porcelain boat and pyrolyzed in a tubular furnace. After pyrolysis, it is naturally cooled to room temperature to obtain a mixture.

[0013] According to the present invention, the carbon source gas that can be cracked includes at least one of alkanes, alkenes, alkynes, and carbon monoxide.

[0014] According to the present invention, the carbon source gas that can be cracked includes at least one of methane, ethylene, propyne, and carbon monoxide.

[0015] According to the present invention, the gas atmosphere further includes a protective gas, and the volume ratio of the carbon source gas that can be cracked to the protective gas is 1:3 - 10.

[0016] In the present invention, the protective gas is a conventional gas in the art. Typically and non-limitingly, it includes at least one of nitrogen and helium.

[0017] In the present invention, the flow rate of the gas for creating the gas atmosphere is 100 - 200 mL / min.

[0018] According to the present invention, the mass ratio of the biomass activated carbon to the solid base is 1:2 - 5.

[0019] According to the present invention, the biomass activated carbon includes at least one of coconut shell activated carbon and straw activated carbon.

[0020] According to the present invention, the mass ratio of the biomass activated carbon to the solid base is 1:4.5 - 5.

[0021] According to the present invention, the pyrolysis conditions include: a heating rate of 5 - 10 °C / min and a temperature of 900 - 1000 °C.

[0022] According to the present invention, the mixture is washed with water until neutral and then dried, pickled, washed with water until neutral after pickling, and then dried to obtain a carbon-based conditioner.

[0023] In the present invention, the mixture is washed with water until neutral and then dried, and then pickled. Washing to neutral can remove the residual alkaline substances on the surface, avoid a large amount of heat released by the reaction of the alkali existing on the surface of the mixture with the acid, and damage the structure of the carbon-based conditioner. It also avoids the salt impurities generated by acid-base neutralization from clogging the pores; pickling can further remove impurities, optimize the pore distribution, and improve the material purity. Washing the pickled product with water until neutral and then drying can remove the acid introduced during pickling, prevent the corrosion of the material by the acid, and ensure the stability of material storage and processing. The washing water is laboratory water (deionized water) for washing; drying is carried out in a vacuum dryer. The pickling includes immersing the mixture in the acid. The volume of the acid is not limited as long as it can completely cover the mixture. The immersion time is 1 - 3 h; stirring is also carried out during immersion to make the pickling more thorough; the acid includes nitric acid and / or sulfuric acid. Specifically, when used, it is prepared into an aqueous solution of the acid for use, and the concentration of the aqueous solution of the acid is 15 - 30 g / L; after immersion, solid-liquid separation (filtration) is carried out, and the solid is collected for post-treatment.

[0024] The third aspect of the present invention provides an application of the aforementioned carbon-based conditioner in sludge electro-dewatering.

[0025] The fourth aspect of the present invention provides an application of the carbon-based conditioner prepared by the aforementioned preparation method in sludge electro-dewatering.

[0026] The technical solution of the present invention has the following advantages: 1. The present invention provides a carbon-based conditioner, wherein the average particle size of the carbon-based conditioner is 15 - 45 nm, and the specific surface area is 600 - 1000 m 2 / g, with a porosity of 50 - 90% and an average pore size of 10 - 60 nm; based on the mass of the carbon-based conditioner, the content of graphite crystals is 50 - 75 wt%; the specific average particle size, specific surface area, and porosity of the carbon-based conditioner endow it with excellent adsorption performance. When applied to the sludge electro-dewatering technology, the carbon-based conditioner can adsorb EPS, relieve filter cloth blockage, and improve the electro-dewatering effect; the specific graphite crystal content of the carbon-based conditioner provides a large number of free electrons, which form a conductive channel inside the carbon-based conditioner. After applying an electric field, the free electrons and the anions and cations ionized from the sludge act synergistically to improve the conductivity of the whole system.

[0027] 2. The specific average particle size, specific surface area, porosity, and pore diameter of the carbon-based conditioner of the present invention can further accurately capture EPS, greatly improving the filtration efficiency; the specific graphite crystal content can further construct a denser and more efficient conductive channel.

[0028] 3. The present invention provides a preparation method of a carbon-based conditioner, wherein the preparation method includes the following steps: mixing biomass activated carbon and solid base, pyrolyzing in a gas atmosphere containing a carbon source gas that can be cracked to obtain a mixture, and pickling to obtain the carbon-based conditioner; wherein, the pyrolysis conditions include: heating up to 800 - 1500 °C at a rate of 5 - 20 °C / min for 1 - 2 h; when the biomass activated carbon and the solid base are mixed, the solid base can corrode the carbon skeleton to form a microporous or mesoporous structure, and can also provide an alkaline environment to promote the bonding of carbon atoms and the transformation to an ordered graphite structure to generate graphite crystals; the carbon source gas that can be cracked undergoes cracking under specific pyrolysis conditions and deposits on the surface and in the pores of the biomass activated carbon. Although it reduces the pore size to a certain extent, it can fill the structural defects of the pore walls of the biomass activated carbon, making the pore structure more perfect; pickling can remove impurities and optimize the pore structure, improving the material purity; and the preparation method of the present invention is simple, the raw materials are easy to obtain, the cost is low, and it can be widely promoted on a large scale.

[0029] 4. In the present invention, the carbon source gas that can be cracked and the protective gas are used together. Compared with only using the carbon source gas that can be cracked, the protective gas can slow down the cracking rate, prevent carbon deposition from being too fast and causing caking, further ensuring the stability of various parameters of the carbon-based conditioner. At the same time, using only the carbon source gas that can be cracked has the risk of explosion and fire. Introducing the protective gas can improve the safety of the system and also reduce the cost.

[0030] 5. The specific mass ratio of the biomass activated carbon and the solid base in the present invention can further adjust various parameters of the final carbon-based conditioner, improving the overall adsorption performance; and it can make more carbon atoms form graphite crystals at a specific temperature and make the arrangement of the graphite crystals more regular.

[0031] 6. In the present invention, under specific pyrolysis conditions, the bonding and rearrangement of carbon atoms can be further made more orderly, so that the average particle size, specific surface area, porosity and average pore diameter of the carbon-based conditioner can be further regulated, improving the adsorption performance; and due to the increased orderliness of carbon atoms, there are fewer lattice defects in the graphite crystal, improving the electrical conductivity.

[0032] 7. In the present invention, the mixture is washed with water until neutral and then dried, and then pickled. Washing to neutral can remove the residual alkaline substances on the surface, avoiding the large amount of heat released by the reaction of the alkali existing on the surface of the mixture with the acid used in pickling, which may damage the structure of the carbon-based conditioner, and also avoiding the blockage of pores by the salt impurities generated by acid-base neutralization; pickling can further remove impurities and optimize the pore distribution, improving the material purity. Washing the pickled product with water until neutral and then drying can remove the acid introduced in pickling, preventing the corrosion of the material by the acid and ensuring the stability of material storage and processing. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for the description of the specific embodiments or the prior art. Obviously, the following drawings are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0034] Figure 1 is the XRD pattern of the carbon-based conditioner of Example 1 and Comparative Example 1; Figure 2 is the XRD pattern of the carbon-based conditioner of Example 4 and Comparative Example 1. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0035] The following embodiments are provided to better further understand the present invention, which is not limited to the best embodiment, and does not limit the content and protection scope of the present invention. Any product identical or similar to the present invention obtained by anyone under the inspiration of the present invention or by combining the features of the present invention with other prior art features falls within the protection scope of the present invention.

[0036] For those steps or conditions not specified in the embodiments, the operations or conditions of the conventional experimental steps described in the literature in this field can be followed. For the reagents or instruments not specified by the manufacturer, they are all conventional reagent products that can be obtained through commercial purchase.

[0037] Coconut shell activated carbon: purchased from Jiangsu Pushida Environmental Protection Technology Co., Ltd.; named psd; The purity of solid potassium hydroxide is analytical pure; The concentration of the dilute nitric acid solution is 30 g / L; The water used in the examples and comparative examples was deionized water.

[0038] Example 1 This example provides a carbon-based conditioner, and the preparation method includes the following steps: The coconut shell activated carbon was dried at 100 °C. The dried coconut shell activated carbon and solid potassium hydroxide were evenly mixed in a porcelain boat according to a mass ratio of 1:2. The porcelain boat was placed in a tube furnace, and a mixed gas of methane and nitrogen was introduced, wherein the volume ratio of methane to nitrogen was 1:3, and the flow rate of the mixed gas was 100 mL / min; it was heated at a rate of 5 °C / min to 1000 °C for 1.5 h and then naturally cooled to room temperature to obtain a mixture; the mixture was washed with water until neutral, dried in a vacuum dryer for 12 h, the dried product was immersed in a dilute nitric acid solution and stirred for 1 h, the solid was collected after filtration by suction, washed with water until neutral, and dried in a vacuum dryer for 12 h to obtain the carbon-based conditioner.

[0039] Example 2 This example provides a carbon-based conditioner, and the preparation method includes the following steps: The coconut shell activated carbon was dried at 100 °C. The dried coconut shell activated carbon and solid sodium hydroxide were evenly mixed in a porcelain boat according to a mass ratio of 1:4. The porcelain boat was placed in a tube furnace, and a mixed gas of methane and nitrogen was introduced, wherein the volume ratio of methane to nitrogen was 1:5, and the flow rate of the mixed gas was 120 mL / min; it was heated at a rate of 10 °C / min to 1500 °C for 1.5 h and then naturally cooled to room temperature to obtain a mixture; the mixture was washed with water until neutral, dried in a vacuum dryer for 12 h, the dried product was immersed in a dilute nitric acid solution and stirred for 1 h, the solid was collected after filtration by suction, washed with water until neutral, and dried in a vacuum dryer for 12 h to obtain the carbon-based conditioner.

[0040] Example 3 This example provides a carbon-based conditioner, and the preparation method includes the following steps: In the same manner as in Example 1, the difference is that the pyrolysis conditions include: heating at a rate of 20 °C / min to 1500 °C for 1.5 h.

[0041] Example 4 This example provides a carbon-based conditioner, and the preparation method includes the following steps: In the same manner as in Example 2, the difference is that the mass ratio of coconut shell activated carbon to solid potassium hydroxide is 1:5.

[0042] Example 5 This example provides a carbon-based conditioner, and the preparation method includes the following steps: In the same manner as in Example 2, except that methane is replaced with an equal volume of ethylene.

[0043] Example 6 This example provides a carbon-based conditioner, and the preparation method includes the following steps: In the same manner as in Example 2, except that methane is replaced with an equal volume of acetylene.

[0044] Comparative Example 1 This comparative example provides a carbon-based conditioner, and the preparation method includes the following steps: In the same manner as in Example 1, except that solid potassium hydroxide is not added.

[0045] Comparative Example 2 This comparative example provides a carbon-based conditioner, and the preparation method includes the following steps: In the same manner as in Example 1, except that only nitrogen is introduced, and the volume of nitrogen is equal to the total volume of methane and nitrogen in Example 3.

[0046] Comparative Example 3 This comparative example provides a carbon-based conditioner, and the preparation method includes the following steps: In the same manner as in Example 1, except that the mixture is washed with water until neutral and dried in a dryer for 12 h to obtain the carbon-based conditioner.

[0047] Comparative Example 4 This comparative example provides a carbon-based conditioner, and the preparation method includes the following steps: In the same manner as in Example 3, except that the temperature is raised to 600 °C at a rate of 20 °C / min and heated for 1.5 h.

[0048] Comparative Example 5 This comparative example provides a carbon-based conditioner, and the preparation method includes the following steps: In the same manner as in Example 3, except that the temperature is raised to 1800 °C at a rate of 20 °C / min and heated for 1.5 h.

[0049] Test Example Test of average particle size The particle size is obtained by detection with a transmission electron microscope (measured by the TEM scale), and the average value is taken after testing 3 times to obtain the average particle size.

[0050] Test of specific surface area Dynamic nitrogen adsorption specific surface area analyzer is used for flow adsorption to measure the specific surface area. The specific method is to adjust the nitrogen pressure to 1.5 kg·cm -2 , adjust the carrier gas flow rate v1 = 5 mL·min -1 (clean the pipeline), v2 = 15 mL·min-1 (Flow rate during formal test), stabilize the relative pressure of methanol (p / p0) at 0.25; weigh the mass of the carbon-based conditioner in the examples and comparative examples, introduce methane steam until the change in sample mass ≤ 0.5 mg, and calculate the adsorption capacity according to the BET formula.

[0051] Porosity Determination was carried out using a Micromeritics Autopore IV 9500 full-automatic mercury intrusion porosimeter.

[0052] Test of average pore size The test method for average pore size adopts the nitrogen adsorption capacity method and is calculated according to the BJH calculation method (see Petrochemical Analysis Methods (RIPP Test Methods), RIPP151-90, published by Science Press in 1990).

[0053] Test of graphite crystal content XRD test was carried out using an X'Pert PRO MPD instrument. First, determine the interlayer spacing d of the graphite (002) crystal plane. 002 Then substitute it into the Mering-Maire formula for calculation: ; In the formula: G is the graphite crystal content, wt%; 0.3440 is the interlayer spacing of non-graphitized carbon, nm; 0.3354 is the interlayer spacing of ideal graphite crystals, which is also 1 / 2 of the lattice constant of the c-axis of hexagonal graphite, nm; d 002 is the interlayer spacing of the (002) crystal plane of the carbon material, nm.

[0054] The test results are shown in Table 1; Table 1 Performance parameters of carbon-based conditioner

[0055] Sludge electroosmotic dewatering process Take 100 mL of sludge (collected from Xiaohongmen Sewage Treatment Plant of Beijing Drainage Group, with a water content of 97%) in a beaker, add a carbon-based conditioner. Based on the dry weight of the sludge, the content of the carbon-based conditioner is 10 wt%. Place the beaker, start the magnetic stirring device, and stir at 900 r·min -1 After stirring for 20 min, let it stand. Put the conditioned sludge into a cylindrical piston filter chamber for electroosmotic sludge dewatering test, collect the cake and the cathode and anode filtrates. The mechanical pressure used in the test is 0.5 MPa, the voltage is 55 V, the time is 1 h, and the current changes continuously during the test.

[0056] Test of resistivity The resistivity of the carbon-based conditioner was detected using the four-probe method. The four probes were gently pressed onto the surface of the sample at equal intervals (usually 1 mm), a constant current (50 mA) was output by the current source, the voltage value (V) was recorded, and then the resistivity was calculated using the following formula: ; s is the distance between the probes.

[0057] Testing of the average dehydration rate of the cathode Instantaneous dehydration rate testing method: During the i-th time interval Δti (Δt i =t i -t i-1 , t i and t i-1 are the times recorded for the i-th and (i - 1)-th times respectively), the corresponding cumulative water output masses are g1 and g i-1 , then the water output mass Δg during this time interval i =g i -g i-1 , instantaneous dehydration rate calculation formula: ; Cathode average dehydration rate calculation formula: ; In the formula: V A is the cathode average dehydration rate; V i is the instantaneous dehydration rate; n is the number of data acquisitions.

[0058] Testing of the water content of the sludge after electro-dehydration treatment Record the weight of the sludge after electro-dehydration treatment as the initial weight. Then, place the sludge after electro-dehydration treatment in an oven and heat it at 80 °C for 5 h. After drying, cool it to room temperature and record the weight of the solid as the dry weight; then calculate using the following formula: .

[0059] Testing of the EPS content In this experiment, the filtrates from the anode and cathode were collected. The filtrates were passed through a 0.45-μm filter membrane, and the resulting solution was the dissolved organic matter (DOM) in the sludge, which was EPS. The DOM was measured using a Torch combustion auto-sampler analyzer (Teledyne Tekmar, USA).

[0060] The test results are shown in Table 2; Table 2 Parameter indicators and performance parameters of the products obtained during the sludge electro-dehydration technology

[0061] Figure 1 are the XRD patterns of the carbon-based conditioners of Example 1 and Comparative Example 1. From Figure 1It can be seen from [description] that in Example 1 compared with Comparative Example 1, characteristic diffraction peaks of graphite crystals can be seen in Example 1; Figure 2 is the XRD pattern of the carbon-based conditioner of Example 4 and Comparative Example 1. From Figure 2 it can be seen that in Example 4 compared with Comparative Example 1, characteristic diffraction peaks of graphite crystals can be seen in Example 4 and the peak value is higher than that in Example 1. There are two peaks at 26.4 and 43.8 in the XRD curves of Example 1 and Example 4, corresponding to the (002) peak and (100) peak of carbon respectively, indicating the appearance of graphite crystals in the modified coconut shell charcoal; the peak intensity of the graphite crystals in Example 4 is higher, proving that the mass ratio of coconut shell activated carbon and solid potassium hydroxide can further promote the formation of graphite crystals in coconut shell charcoal.

[0062] Obviously, the above examples are only for clear illustration and not a limitation of the implementation manner. For those of ordinary skill in the art, other different forms of changes or variations can be made on the basis of the above description. It is not necessary and impossible to list all implementation manners here. And the obvious changes or variations derived therefrom are still within the protection scope of the present invention.

Claims

1. A carbon-based conditioner, characterized in that, The average particle size of the carbon-based conditioner is 15-45 nm, the specific surface area is 600-1000 m 2 / g, the porosity is 50-90%, and the average pore size is 10-60 nm; Based on the mass of the carbon-based conditioner, the content of graphite crystals is 50 - 75 wt%.

2. The carbon-based conditioner according to claim 1, wherein The average particle size of the carbon-based conditioner is 15 - 20 nm, the specific surface area is 800 - 1000 m 2 / g, the porosity is 60 - 80%, and the average pore size is 10 - 30 nm; Based on the mass of the carbon-based conditioner, the content of graphite crystals is 50 - 70 wt%.

3. A preparation method of a carbon-based conditioner, characterized in that, The preparation method includes the following steps: Mix biomass activated carbon and solid base, pyrolyze in a gas atmosphere containing a gas with a cleavable carbon source to obtain a mixture, and perform pickling to obtain a carbon-based conditioner; Among them, the conditions for the pyrolysis include: heating up to 800 - 1500 °C at a rate of 5 - 20 °C / min for 1 - 2 h.

4. The preparation method according to claim 3, wherein, The gas containing a cleavable carbon source includes at least one of alkanes, alkenes, alkynes, and carbon monoxide.

5. The preparation method according to claim 3 or 4, characterized in that, The gas containing a cleavable carbon source includes at least one of methane, ethylene, propyne, and carbon monoxide; And / or, the gas atmosphere further includes a protective gas, and the volume ratio of the gas containing a cleavable carbon source to the protective gas is 1:3 - 10.

6. The preparation method according to claim 3, characterized in that, The mass ratio of the biomass activated carbon to the solid base is 1:2 - 5; And / or, the biomass activated carbon includes at least one of coconut shell activated carbon and straw activated carbon.

7. The preparation method according to claim 6, wherein The mass ratio of the biomass activated carbon to the solid base is 1:4.5 - 5.

8. The preparation method according to claim 3, characterized in that, The conditions for the pyrolysis include: the heating rate is 5 - 10 °C / min and the temperature is 900 - 1000 °C; And / or, wash the mixture with water until neutral and then dry, perform pickling, wash the pickled product with water until neutral and then dry to obtain a carbon-based conditioner.

9. Application of the carbon-based conditioner according to claim 1 or 2 in sludge electro-dewatering.

10. Application of the carbon-based conditioner prepared by the preparation method according to any one of claims 3 - 8 in sludge electro-dewatering.

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