A method for efficiently pyrolyzing and degrading perfluorinated compounds in sludge

Abstract

The present invention belongs to the field of environmental protection and pollutant treatment, and particularly relates to a method for promoting the biodegradation of organofluorine compounds in sludge. Based on smoldering technology, the present invention uses solid porous media to improve the smoldering efficiency, adsorbs a large amount of perfluorinated compound pollutants in sludge onto the solid porous media, and uses the heat transfer and energy storage type aminated solid porous media grafted with amino groups, which can not only provide continuous heat, produce a synergistic effect to make the smoldering self-sustaining time long, but also selectively adsorb perfluorinated compounds, break their carbon-fluorine bonds, and the defluorination rate of perfluorinated compounds is above 90%. This method does not require dehydration treatment of sludge, the required equipment is simple, and it is easy to realize automatic operation, enabling highly water-containing sludge with low calorific value containing perfluorinated compounds to be efficiently degraded by the method of smoldering.

Description

Technical Field

[0001] The present invention belongs to the field of environmental protection and pollutant treatment, specifically relates to the treatment of sludge, and particularly relates to a method for promoting the efficient degradation of perfluorinated compounds in sludge. Background Art

[0002] Perfluorinated compounds (PFCs), as surfactants, have been widely used in pesticides, cosmetics, adhesives, oils and lubricants, etc. Currently, PFCs can be detected in surface water, groundwater, sediments, sludge, soil, and organisms at all trophic levels in the food chain and in the human body worldwide.

[0003] Fluorine is a substance with very strong subversiveness, which makes the C-F bond highly polar. The C-F bond is the strongest among all known covalent bonds, with a bond energy of about 460 KJ / mol. In perfluorinated compounds, the three unpaired electrons of fluoride ions can form a protective shell, so perfluorinated compounds are very stable, and the C-F bond can even remain stable in 100% boiling sulfuric acid. Due to the hydrophobicity, high organic matter affinity, and difficult degradation characteristics of PFCs, PFCs entering the sewage treatment system are easily adsorbed and accumulated in sludge, and are extremely difficult to degrade and have a huge toxic effect in sludge. On the other hand, the sludge production in China is huge, and the moisture content is as high as 80%.

[0004] Currently, the use of adsorbents (such as granular or powdered activated carbon) in aqueous media seems to be the most common and effective treatment technology. The adsorbent removes and concentrates PFCs from the aqueous media for subsequent treatment. However, this treatment technology is limited to aqueous media and is not applicable to sludge or sediments that may be affected by PFCs. At present, the main methods for treating fluorine-containing sludge include landfill, incineration, resource utilization, etc. to achieve harmless treatment. Moreover, in various sludge disposal methods, the high moisture content of sludge is a major problem. In existing various reduction and resource utilization disposal methods, it is necessary to pre-dewater the sludge or perform special drying treatment. For example, the sludge is used for cement batching after the moisture content is reduced to less than 40% through a special dewatering device, which makes the sludge treatment process complex, energy-consuming, with a small treatment capacity and high treatment cost.

[0005] Chinese Patent with publication number CN104496141B discloses a method for promoting the biodegradation of perfluorinated compounds in sludge, which is based on the microbial anaerobic fermentation treatment technology of sludge and sediment. Through the treatment of sludge and sediment, the perfluorinated compounds can be degraded during the microbial anaerobic fermentation process. However, this method takes a relatively long time, is not easy to control the degradation rate, and is not suitable for treating a large amount of sludge.

[0006] Therefore, there is an increasing demand for a method of harmless disposal and resource utilization that does not require pre-dewatering or specialized drying of wet sludge, has no special requirement for the upper limit of sludge moisture content, can handle a large volume of sludge, and causes no secondary pollution. Additionally, there is a need for a method and system that can reduce or degrade perfluorinated compounds with high decomposition temperatures in solid porous media at a lower cost and in a simpler manner.

[0007] Smoldering disposal is a new direct combustion disposal technology for high-moisture and low-calorific-value organic solid wastes. Organic solid wastes that cannot directly and self-sustainably burn in a conventional combustion device can, after being mixed with a porous medium filler, achieve independent self-sustaining combustion under forced air supply with a small amount of external heat provided through smoldering technology. Therefore, how to use a smoldering disposal system in combination with a porous medium filler to achieve efficient degradation of fluorine-containing sludge is currently a research focus and difficulty. Summary of the Invention

[0008] To overcome the disadvantages and deficiencies in the prior art, the primary objective of the present invention is to provide a method for efficiently smoldering and degrading perfluorinated compounds in sludge. This method utilizes a solid porous medium capable of heat transfer and energy storage, and through smoldering technology, it can achieve independent self-sustaining combustion under forced air supply with a small amount of external heat provided, thereby realizing efficient degradation of fluorine-containing sludge.

[0009] First, a method for smoldering treatment of high-moisture sludge containing perfluorinated compounds is provided. The high-moisture sludge containing perfluorinated compounds is mixed with a small amount of auxiliary fuel and a large amount of solid porous medium filler to modify the low-calorific-value fluorine-containing sludge, enabling the low-calorific-value fluorine-containing sludge to be treated through the smoldering process. This expands the treatment methods for high-moisture sludge containing perfluorinated compounds, with a simple treatment method and good economic performance. The sludge is high-moisture sludge containing perfluorinated compounds, with a water content as high as 80%, and the content of perfluorinated compounds is 100 - 300 micrograms per 1 kilogram of dry sludge weight. The auxiliary fuel is one or a mixture of sawdust, rice husks, charcoal particles, or crushed straw.

[0010] The objective of the present invention also lies in providing a solid porous medium filler to solve one or more technical problems existing in the prior art, and at least providing a beneficial option or creating conditions. The solid porous medium filler is a solid porous medium capable of heat transfer and energy storage, and is a heat transfer and energy storage type of aminated solid porous medium grafted with amine groups.

[0011] In order to solve the problems that during the smoldering process, the thermal conductivity of sludge is too low and a large amount of external heat is required to sustain combustion, and because the water content of sludge is relatively high, there is too little energy storage during the smoldering process and it cannot burn self-sustainedly independently, we prepared a solid porous medium capable of heat transfer and energy storage, which can not only improve the heat conduction during the smoldering process and enhance the smoldering efficiency, but also promote the problem that sludge in the entire smoldering system can continuously maintain energy, so that after a small amount of external energy is provided, the entire smoldering system can achieve uniform self-sustained combustion through the solid porous medium capable of heat transfer and energy storage. The preparation method of the solid porous medium capable of heat transfer and energy storage is specifically as follows:

[0012] S001, Take natural mica particles and heat them to 600 °C and keep them for 1 hour to obtain activated mica particles. Immerse the activated mica particles in a concentrated hydrochloric acid solution, stir for 2 - 3 hours, then filter, wash with deionized water at 70 °C until neutral, and evaporate to dryness at 70 °C. Add sodium dodecyl sulfate to it, raise the temperature to 80 °C, react for 2 - 3 hours, centrifuge the obtained solid, wash it with deionized water at 80 °C, and evaporate to dryness and grind it at 80 °C to obtain nano mica particles with increased micropores; among them, the mass ratio of activated mica flakes to sodium dodecyl sulfate is 2:1;

[0013] S002, Stir and heat high molecular weight polyvinyl alcohol and deionized water at 100 °C for 80 - 120 minutes until completely dissolved to obtain a polyvinyl alcohol solution, and the concentration of the polyvinyl alcohol solution is 3 - 6%;

[0014] S003, Add graphene oxide and nano mica particles to the polyvinyl alcohol solution, stir for 30 - 50 minutes to uniformly disperse the solid particles into the polyvinyl alcohol solution, fully react at 80 °C for 4 hours, dry the product at 20 °C, and pulverize and grind it to obtain a solid porous medium capable of heat transfer and energy storage;

[0015] Among them, the mass ratio of graphene oxide, nano mica particles and polyvinyl alcohol is 5 - 8:5 - 10:3 - 6;

[0016] A solid porous medium capable of heat transfer and energy storage and fluorine-containing sludge with a high water content are stirred evenly at a mass ratio of 5:100 - 150, and then auxiliary fuel is added and placed in a smoldering system for treatment. We found that after adding this solid porous medium capable of heat transfer and energy storage, the input of external energy required by the smoldering system is significantly reduced. However, after the sludge treatment, we found that the degradation rate of perfluorinated compounds in the sludge is only about 50%. Analyzing the reasons, mainly there is a large amount of graphene oxide in the solid porous medium capable of heat transfer and energy storage, and graphene oxide is prone to agglomeration in the smoldering system, so that the solid porous medium can only form self-sustained smoldering combustion around itself. This self-sustaining is unevenly dispersed and has no directional selectivity for perfluorinated compounds, which also makes it impossible to effectively degrade all perfluorinated compounds. Although the smoldering system is equipped with a stirring system by itself, the viscosity of the sludge itself results in low stirring efficiency and dead corners in stirring, making it difficult for the entire smoldering system to be in a completely uniform state. Especially when the external energy supply stops, stirring will not only cause energy loss, but also interfere with the energy accumulation during the smoldering process and cannot reach the high temperature required to destroy perfluorinated compounds.

[0017] Therefore, further, we modified graphene oxide so that it can be evenly dispersed in organic solutions or water and has directional selectivity for perfluorinated compounds. Then we improved the matrix it wraps, and finally prepared an amino-functionalized solid porous medium capable of heat transfer and energy storage. Among them, the polymer solution is not only the matrix of the solid porous medium, but also the main heat source for smoldering, and can assist the auxiliary fuel to make the entire smoldering process break through a high temperature of 800 °C. The preparation method of the amino-functionalized solid porous medium capable of heat transfer and energy storage is specifically as follows:

[0018] S101, Add hyperbranched polyamide-amine to an aqueous solution of graphene oxide, adjust it to be alkaline with a NaOH solution with a mass concentration of 0.05%, and then add 1-ethyl-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride, and stir and react at 60 - 80 °C for 10 - 15 hours, and then centrifuge, wash with water, and dry to obtain graphene oxide grafted with hyperbranched polyamide-amine;

[0019] The mass ratio of graphene oxide, 1-ethyl-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and hyperbranched polyamide-amine is 1:1:3 - 5;

[0020] Under alkaline catalytic conditions, the amino group in hyperbranched polyamide-amine undergoes a ring-opening reaction with the epoxy group on graphene oxide to obtain amino-modified graphene oxide, which can be stably dispersed in water or organic solvents;

[0021] Graphene oxide is a carbon framework material with a two-dimensional nanostructure. It can not only adsorb ions by itself but also serve as an excellent carrier for loading other substances. Hyperbranched polyamide-amine is a dendrimer with no toxicity and good biocompatibility. It has a large number of amine groups at its ends and is an ideal modifier. After modification, the surface of graphene oxide is enriched with positively charged amine groups, which are more likely to adsorb negatively charged perfluorinated compounds directionally.

[0022] S102, The high molecular weight polyether alcohol and N,N-dimethylformamide are stirred and heated at 80 °C for 80 - 120 minutes until a transparent liquid is obtained after complete dissolution; polylactic acid and ethanol are dissolved in a mass ratio of 1:2 and then added to the transparent liquid, and finally a high molecular weight solution is obtained; the mass ratio of polyether alcohol to N,N-dimethylformamide is 1:1; the mass ratio of polyether alcohol to polylactic acid is 1:1 - 2;

[0023] S103, The graphene oxide grafted with hyperbranched polyamide-amine and nano mica particles are added to the high molecular weight solution, and stirred for 30 - 50 minutes to uniformly disperse the solid particles into the composite high molecular weight solution. The reaction is carried out at 60 °C for 4 hours, and the product is dried at 20 °C and then crushed and ground to obtain an amino-functionalized solid porous medium capable of heat transfer and energy storage; the mass ratio of graphene oxide grafted with hyperbranched polyamide-amine, nano mica particles and polyether alcohol is 5 - 8:5 - 10:10 - 20;

[0024] The porous material not only provides a reaction area for smoldering combustion but also ensures that sufficient oxygen diffuses to the fuel surface for oxidation and exothermic reactions. Compared with flaming combustion, smoldering combustion propagates under oxygen-limited conditions. Therefore, the oxidation reaction rate is slower, and the corresponding reaction temperature and reaction rate are lower. However, this characteristic makes smoldering combustion more stable, and the continuously released heat can be continuously absorbed and stored by mica. When the external energy cannot be further increased or the external energy cannot be transmitted, the polymer in the composite high molecular weight solution can release a large amount of heat under high temperature, and the energy stored in mica can also be continuously released, enabling smoldering combustion to achieve self-sustenance using the energy of the fuel itself and to proceed uniformly and stably throughout the system, resulting in the accumulation of a large amount of heat energy, thus reaching a high temperature of 800 °C, which plays a role in destroying perfluorinated compounds, so that the entire system can efficiently degrade perfluorinated compounds in sludge.

[0025] During the smoldering process of polyether alcohol and polylactic acid, carbon-hydrogen bonds can break and release energy to maintain the combustion reaction. At the same time, polyether alcohol and polylactic acid have high molecular weights and long molecular chains. Under the action of high temperature, they use a solid porous medium that can transfer and store heat as a framework to connect the entire sludge system into a network structure and provide sufficient energy to support the combustion reaction. In particular, polyether alcohol can release a large amount of heat at high temperatures, which can promote the auxiliary fuel to reach a higher smoldering temperature, enabling the temperature to rise above 800°C during smoldering, generating a high temperature sufficient to destroy perfluorinated compounds; and no toxic gases such as nitrogen and sulfur are produced during the combustion process.

[0026] Furthermore, a method for efficiently degrading perfluorinated compounds in sludge by smoldering is provided, specifically as follows:

[0027] S201, Mix the high-water-content sludge containing perfluorinated compounds, auxiliary fuel, and a solid porous medium that can transfer and store heat evenly to obtain a mixture;

[0028] Among them, the mass ratio of the high-water-content sludge containing perfluorinated compounds, auxiliary fuel, and a solid porous medium that can transfer and store heat is 1000-1500:2-4:30-50;

[0029] S202, Put the mixture into a smoldering furnace, continuously heat the mixture at 220°C - 300°C at the bottom, and at the same time supply air from the bottom of the furnace upwards at a speed of 4.0 cm / s - 6.0 cm / s, stir until the mixture reaches 400°C - 500°C, the mixture starts self-sustaining smoldering combustion, stop heating, stop stirring, continue the reaction for 18 - 24 hours to obtain a degraded sludge mixture, and detect the mixture;

[0030] S203, Collect the waste gas generated from the mixture during smoldering combustion; finally, treat the above waste gas and the waste gas evaporated from the mixture.

[0031] S204, Sample and detect the degraded sludge mixture obtained in step S202. If the concentration of perfluoroalkane compounds detected does not exceed 50 ppt, the reaction ends; if it exceeds, continue to heat the bottom of the degraded sludge mixture in the smoldering furnace to 300°C, heat for 1 - 3 hours, supply air from the bottom of the furnace upwards at a speed of 4.0 cm / s - 6.0 cm / s, then stop heating, continue the reaction for 4 - 6 hours, re-detect. If it exceeds, repeat steps S204 and S203 until the concentration of perfluorinated compounds detected does not exceed 100 ppt.

[0032] The method can treat low calorific value fluorine-containing sludge with high water content, and solves the technical problem that the existing process cannot treat sludge with high water content. Through the aminated solid porous medium that can transfer heat and store energy, it has its own polymer combustible energy. After cutting off the external energy, it can quickly release a large amount of heat, and maintain self-sustaining combustion through the combustion of the polymer at high temperature. The graphene oxide grafted with hyperbranched polyamide-amine has a large number of amine groups on the surface, has a directional selection ability for free perfluorinated compounds in the sludge, and can destructively degrade perfluorinated compounds. The CF bond breakage rate is as high as more than 90%, achieving the effect of highly efficient degradation of perfluorinated compounds. Compared with the existing technology, it has the following beneficial effects:

[0033] 1) The present invention provides a method for treating fluorine-containing sludge by smoldering, wherein high-water-content sludge is uniformly mixed with auxiliary fuel and solid porous medium to obtain a mixture, which is then put into a smoldering furnace for smoldering combustion. By using a solid porous medium capable of heat transfer and energy storage, independent self-sustaining combustion can be achieved by forced air supply under the condition of providing a small amount of external heat through smoldering technology. The combustion energy provided by a high molecular polymer at a high temperature can be wrapped in the solid porous medium capable of heat transfer and energy storage to assist the auxiliary fuel to reach a high temperature of more than 800°C, thereby destructively degrading perfluorinated compounds, and the CF bond breakage rate thereof is as high as more than 90%.

[0034] 2) The present invention modifies graphene oxide so that it can be evenly dispersed in organic solution or water and has directional selectivity for perfluorinated compounds. Then the matrix wrapped by it is improved so that it is not only the matrix of solid porous medium, but also the main heat source of smoldering. Finally, it is prepared into an aminated solid porous medium capable of heat transfer and energy storage. After the stirring is stopped during the smoldering process, it can be used as a skeleton. Under the action of high molecular polymer, the skeleton of this solid porous heat transfer material is used to connect the entire smoldering furnace to form a mesh structure. The graphene oxide grafted with hyperbranched polyamide-amine is used as a grid connection point to improve the thermal conductivity of the mixture in the smoldering furnace. Under the action of the energy released by the mica energy storage ball and the energy released by the combustion of the high molecular polymer, the heat released by itself can be quickly transferred to the surrounding sludge, which can effectively improve the thermal conductivity of the entire system, provide energy for the self-sustaining combustion of the smoldering system, and assist the auxiliary fuel to reach a high temperature that destroys the CF bond.

[0035] 3) The method for efficiently smoldering and degrading perfluorinated compounds in sludge provided by this application has a simple process flow, convenient operation, low energy consumption, good and stable treatment effect, is easy to realize industrial application, can treat low-calorie fluorine-containing sludge with high water content, and solves the technical problem that the existing processes cannot treat fluorine-containing sludge with high water content. The auxiliary fuel added to the low-calorie fluorine-containing sludge is agricultural and forestry waste such as sawdust and rice husks, and the addition amount is very small. Firstly, the price of agricultural and forestry waste is very cheap. Secondly, the amount of added agricultural and forestry waste is very small, and the economy is good. Description of the Drawings

[0036] Figure 1 , the degradation effect diagrams of perfluorinated compounds in sludge by efficient smoldering in Example 2 and 3, and Comparative Example 1;

[0037] Figure 2 , the schematic diagram of each temperature acquisition point in the smoldering furnace. Detailed Embodiments

[0038] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. In addition, it should be understood that after reading the content described in 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 by the appended claims of this application.

[0039] Example 1

[0040] A method for efficiently smoldering and degrading perfluorinated compounds in sludge. First, a solid porous medium capable of heat transfer and energy storage is prepared, specifically:

[0041] Take 20 parts of natural mica particles and heat them to 600 °C for 1 hour to obtain activated mica particles. Immerse the activated mica particles in a concentrated hydrochloric acid solution, stir for 3 hours, then filter, wash with deionized water at 70 °C until neutral, and evaporate to dryness at 70 °C. Add 10 parts of sodium dodecyl sulfate to it, raise the temperature to 80 °C, react for 3 hours, centrifuge the obtained solid, wash with deionized water at 80 °C, and evaporate to dryness and grind at 80 °C to obtain nano mica particles with increased micropores;

[0042] Stir and heat 5 parts of high molecular weight polyvinyl alcohol and 95 parts of deionized water at 100 °C for 80 - 120 minutes until completely dissolved to obtain a 5% polyvinyl alcohol solution;

[0043] Add 5 parts of graphene oxide and 10 parts of nano mica particles to 100 parts of 5% polyvinyl alcohol solution, stir for 50 minutes to uniformly disperse the solid particles into the polyvinyl alcohol solution, fully react at 80 °C for 4 hours, dry the product at 20 °C, and crush and grind to obtain a solid porous medium capable of heat transfer and energy storage;

[0044] Further, a method for efficiently smoldering and degrading perfluorinated compounds in sludge is provided, specifically as follows:

[0045] Mix 1000 parts of high-moisture sludge containing perfluorinated compounds evenly with 4 parts of charcoal particles and 50 parts of solid porous media capable of heat transfer and energy storage; among them, every 1 kg of dry sludge contains 200 micrograms of perfluorinated compounds.

[0046] Put the mixture into a smoldering furnace, continuously heat the bottom mixture at 220 °C, and at the same time supply air from the bottom of the furnace upward at a speed of 4.0 cm / s, stir until the mixture reaches 420 °C, the mixture starts self-sustaining smoldering combustion, stop heating, stop stirring, and continue the reaction for 24 hours to obtain the degraded sludge mixture. After the sample is purified by solid-phase extraction (SPE), the concentrations of PFOS and PFOA are detected by high-performance liquid chromatography-mass spectrometry (HPLC-MSMS).

[0047] Collect the waste gas generated from the mixture during smoldering combustion; finally, treat the above waste gas and the waste gas evaporated from the mixture.

[0048] The detected concentration of perfluoroalkane compounds is 52 micrograms of PFOS per 1 kg of dry sludge, that is, 42000 ppt, and 59 micrograms of PFOA, that is, 42000 ppt; extending the reaction time cannot continue to decrease.

[0049] Example 2

[0050] A method for efficiently smoldering and degrading perfluorinated compounds in sludge. First, prepare an amino-functionalized solid porous medium capable of heat transfer and energy storage, specifically as follows:

[0051] Take 20 parts of natural mica particles, heat them to 600 °C, and keep them for 1 hour to obtain activated mica particles. Immerse the activated mica particles in a concentrated hydrochloric acid solution, stir for 3 hours, then filter, wash with deionized water at 70 °C until neutral, and evaporate to dryness at 70 °C. Add 10 parts of sodium dodecyl sulfate to it, raise the temperature to 80 °C, react for 3 hours, centrifuge the obtained solid, wash with deionized water at 80 °C, and evaporate to dryness and grind at 80 °C to obtain nano mica particles with increased micropores;

[0052] Disperse 10 parts of graphene oxide in 90 parts of deionized water to obtain a graphene oxide solution, then add 30 parts of hyperbranched polyamide-amine, adjust it to be alkaline with a 0.05% NaOH solution by mass concentration, and then add 10 parts of 1-ethyl-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride, stir and react at 80 °C for 15 hours, centrifuge, wash with water, and dry to obtain graphene oxide grafted with hyperbranched polyamide-amine;

[0053] 10 parts of high molecular polyether alcohol and 10 parts of N,N-dimethylamide are stirred and heated at 80 °C for 120 minutes until completely dissolved into a transparent liquid; 10 parts of polylactic acid and 20 parts of ethanol are dissolved and then added to the transparent liquid, and after stirring evenly, a high molecular solution is finally obtained;

[0054] Graphene oxide grafted with 5 parts of hyperbranched polyamide-amine and 10 parts of nano mica particles are added to 50 parts of the high molecular solution, stirred for 50 minutes to uniformly disperse the solid particles into the composite high molecular solution, and fully reacted at 60 °C for 4 hours. The product is dried at 20 °C, pulverized and ground to obtain an amino-functionalized solid porous medium capable of heat transfer and energy storage;

[0055] 1000 parts of high water content sludge containing perfluorinated compounds, 4 parts of charcoal particles and 50 parts of the solid porous medium capable of heat transfer and energy storage are mixed evenly to obtain a mixture; each 1 kg of dry sludge in the high water content sludge contains 200 micrograms of perfluorinated compounds.

[0056] The mixture is put into a smoldering furnace, and the bottom mixture is continuously heated at 220 °C. At the same time, air is supplied from the bottom of the furnace upward at a speed of 4.0 cm / s, and stirred until the mixture reaches 420 °C. The mixture starts self-sustained smoldering combustion, heating is stopped, stirring is stopped, and the reaction continues for 24 hours to obtain a degraded sludge mixture, and the mixture is detected;

[0057] The waste gas generated from the mixture during the smoldering combustion is collected; finally, the above waste gas and the waste gas evaporated from the mixture are treated.

[0058] The obtained degraded sludge mixture is detected and contains 0.01 micrograms of PFOS, that is, 10 ppt, and 0.05 micrograms of PFOA, that is, 50 ppt.

[0059] Example 3

[0060] A method for efficiently smoldering and degrading perfluorinated compounds in sludge. First, an amino-functionalized solid porous medium capable of heat transfer and energy storage is prepared, specifically:

[0061] Take 20 parts of natural mica particles, heat them to 600 °C and keep for 1 hour to obtain activated mica particles. The activated mica particles are soaked and stirred in a concentrated hydrochloric acid solution for 2 hours and then filtered, washed with deionized water at 70 °C until neutral, and evaporated to dryness at 70 °C. 10 parts of sodium dodecyl sulfonate are added to it, heated to 80 °C, reacted for 3 hours, and the solid obtained by centrifugation is washed with deionized water at 80 °C and evaporated to dryness and ground at 80 °C to obtain nano mica particles with increased micropores;

[0062] Disperse 10 parts of graphene oxide in 90 parts of deionized water to obtain a graphene oxide solution. Then add 50 parts of hyperbranched polyamide-amine, adjust it to be alkaline with a NaOH solution with a mass concentration of 0.05%, and then add 10 parts of 1-ethyl-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride. Stir and react at 80 °C for 15 hours, centrifuge, wash with water, and dry to obtain graphene oxide grafted with hyperbranched polyamide-amine;

[0063] Stir and heat 20 parts of high molecular polyether alcohol and 20 parts of N,N-dimethylformamide at 80 °C for 120 minutes until a transparent liquid is obtained after complete dissolution; dissolve 10 parts of polylactic acid and 20 parts of ethanol and then add them to the transparent liquid, stir evenly to finally obtain a high molecular solution;

[0064] Add 8 parts of graphene oxide grafted with 8 parts of hyperbranched polyamide-amine and 8 parts of nano mica particles to 50 parts of the high molecular solution, stir for 50 minutes to uniformly disperse the solid particles into the composite high molecular solution, fully react at 60 °C for 4 hours, dry the product at 20 °C, and pulverize and grind to obtain an amino-functionalized solid porous medium with heat transfer and energy storage capabilities;

[0065] Mix 1500 parts of high water content sludge containing perfluorinated compounds, 4 parts of charcoal particles, and 40 parts of the solid porous medium with heat transfer and energy storage capabilities to obtain a mixture; among them, each 1 kg of dry sludge in the high water content sludge contains 200 micrograms of perfluorinated compounds.

[0066] Put the mixture into a smoldering furnace, continuously heat the bottom mixture at 220 °C, and at the same time supply air from the bottom of the furnace upward at a speed of 4.0 cm / s, stir until the mixture reaches 450 °C, the mixture starts self-sustained smoldering combustion, stop heating, stop stirring, and continue to react for 24 hours to obtain a degraded sludge mixture, and detect the mixture;

[0067] Collect the waste gas generated from the mixture during the smoldering combustion process; finally treat the above waste gas and the waste gas evaporated from the mixture.

[0068] Detect the obtained degraded sludge mixture, which contains 0.02 micrograms (i.e., 20 ppt) of PFOS and 0.04 micrograms (i.e., 40 ppt) of PFOA.

[0069] Example 4

[0070] A method for efficiently degrading perfluorinated compounds in sludge by smoldering. First, prepare an amino-functionalized solid porous medium with heat transfer and energy storage capabilities, specifically:

[0071] Take 20 portions of natural mica particles, heat them to 600 °C and keep for 1 hour to obtain activated mica particles. Immerse the activated mica particles in a concentrated hydrochloric acid solution, stir for 2 hours, then filter, wash with deionized water at 70 °C until neutral, and evaporate to dryness at 70 °C. Add 10 portions of sodium dodecyl sulfate to it, raise the temperature to 80 °C, react for 3 hours, centrifuge the resulting solid, wash with deionized water at 80 °C, and evaporate to dryness and grind at 80 °C to obtain nano mica particles with enlarged micropores;

[0072] Disperse 10 portions of graphene oxide in 90 portions of deionized water to obtain a graphene oxide solution. Then add 40 portions of hyperbranched polyamide-amine, adjust to alkaline with a NaOH solution with a mass concentration of 0.05%, and then add 10 portions of 1-ethyl-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride. Stir and react at 80 °C for 15 hours, centrifuge, wash with water, and dry to obtain graphene oxide grafted with hyperbranched polyamide-amine;

[0073] Stir and heat 20 portions of high molecular polyether alcohol and 20 portions of N,N-dimethylformamide at 80 °C for 120 minutes until completely dissolved to obtain a transparent liquid; dissolve 10 portions of polylactic acid and 20 portions of ethanol and add them to the transparent liquid, stir evenly to finally obtain a high molecular solution;

[0074] Add graphene oxide grafted with 8 portions of hyperbranched polyamide-amine and 10 portions of nano mica particles to 50 portions of the high molecular solution, stir for 30 - 50 minutes to uniformly disperse the solid particles into the composite high molecular solution, fully react at 60 °C for 4 hours, dry the product at 20 °C, and crush and grind to obtain an amino-functionalized solid porous medium capable of heat transfer and energy storage;

[0075] Mix 1200 portions of high water-content sludge containing perfluorinated compounds, 2 portions of charcoal particles, and 30 portions of the solid porous medium capable of heat transfer and energy storage evenly to obtain a mixture; among them, each 1 kg of dry sludge in the high water-content sludge contains 200 micrograms of perfluorinated compounds.

[0076] Put the mixture into a smoldering furnace, continuously heat the bottom mixture at 220 °C, and at the same time supply air from the bottom of the furnace upward at a speed of 4.0 cm / s, stir until the mixture reaches 450 °C, the mixture starts self-sustained smoldering combustion, stop heating, stop stirring, and continue to react for 24 hours to obtain a degraded sludge mixture, and detect the mixture;

[0077] Collect the waste gas generated from the mixture during the smoldering combustion; finally treat the above waste gas and the waste gas evaporated from the mixture.

[0078] Detect the obtained degraded sludge mixture, which contains 0.01 microgram (i.e., 10 ppt) of PFOS and 0.06 microgram (i.e., 60 ppt) of PFOA.

[0079] Comparative Example 1: Without using a polymer solution as the matrix, an equal amount of graphene oxide and nano-mica particles of hyperbranched polyamide-amine were directly used as the solid porous medium, and the others were the same as in Example 2;

[0080] Comparative Example 2: Without using a polymer solution as the matrix, an equal amount of graphene oxide and natural mica particles were directly used as the solid porous medium, and the others were the same as in Example 2;

[0081] Comparative Example 3: The solid porous medium used was ordinary sand of the same particle size, and stirring was not stopped during the smoldering process, and the others were the same as in Example 2;

[0082] Comparative Example 4: The solid porous medium used was ordinary sand of the same particle size, and stirring was stopped during the smoldering process, and the others were the same as in Example 2;

[0083] Comparison data of test effects

[0084] 1. Monitoring records of each temperature point of the smoldering furnace

[0085] When heating and stirring were stopped, the temperature of different parts inside the smoldering furnace was measured and monitored. A multi-point temperature measurement system inside the smoldering furnace based on wireless data transmission was used. This system used a single-chip microcomputer as the controller component and was externally equipped with temperature sensors. According to the experiment, the settings of each acquisition point from A to E were carried out as follows Figure 1 and the temperature of each point was recorded, as shown in Table 1;

[0086] It can be seen from Table 1 that in Examples 2-4, because a heat transfer and energy storage type amino-functionalized solid porous medium grafted with a polymer material was introduced, when the smoldering furnace did not provide an external heat source, the temperature at each acquisition point fluctuated little with time. After 8 hours, it basically remained between 800 and 1000 °C, and the temperature changed with time, first slightly increasing and then decreasing. This was mainly because after the external heat source stopped heating, the heat at the bottom had not been completely absorbed. The network structure formed with the solid porous medium as the skeleton and the polymer as the vein allowed the heat to be quickly conducted and dissipated, and the temperature continued to rise. As the heat dissipated, the heat inside the smoldering furnace was continuously transferred, and the temperature difference was continuously leveled, causing the temperature to slightly decrease. When no external heat source provided heat, the mica began to release the stored heat. At the same time, under the action of high temperature, the carbon-hydrogen bonds of the polymer continuously broke, releasing a large amount of heat, which allowed the temperature to continue to rise, forming a balance. In Comparative Example 2, because a heat transfer and energy storage type amino-functionalized solid porous medium was not introduced and no polymer was used to improve the heat source, the heat in the smoldering furnace could not be effectively transferred to all positions of the smoldering furnace in time. After the external heat source stopped providing energy, the temperature inside the furnace dropped sharply, and it could not provide the energy to maintain self-sustained combustion.

[0087] It can also be seen from the temperature change record table of each temperature acquisition point A - F extracted from Table 1 that the temperature changes at each temperature point in Examples 2 - 3 are not significant, and the temperatures at all sampling points in the entire smoldering furnace are very stable. For Comparative Examples 2 - 3, due to the slow heat transfer of the water - containing sludge, the sampling points near the bottom of the smoldering furnace all showed the phenomenon that the temperature rose rapidly and then dropped rapidly to varying degrees. In Example 1, because there is less polymer material, a large amount of heat cannot be generated to assist all regions to reach a high temperature. Due to the aggregation of graphene oxide, the temperature distribution is uneven, and the temperature in the region with more graphene oxide rises faster. In Comparative Example 2, due to the aggregation of graphene oxide, local high temperatures occurred, and because there are fewer energy - generating points, high temperatures cannot be continuously generated. Although slow self - sustaining smoldering can be maintained, the temperature point for perfluorinated compound degradation cannot be reached. In Comparative Example 2, because there are even fewer available energy sources and the natural mica has little energy storage effect, the energy supply of the entire system is insufficient, the temperature cannot continue to rise, and the temperature differences at each sampling point are large. In Comparative Examples 3 and 4, because there are fewer heat sources and no materials can store energy, after stopping heating, only local areas can continue to absorb heat to generate the energy for self - sustaining combustion and maintain smoldering for 2 - 3 hours, and then the temperature will drop linearly to end the entire reaction.

[0088] Table 1, Temperature Record Table of Each Temperature Acquisition Point (°C)

[0089]

[0090] 2. Measurement of the Thermal Conductivity of the Mixture

[0091] In the study of the variation of the temperature field with time in a smoldering furnace, the thermophysical parameters are of great significance. Since the smoldering furnace itself is a dynamic equilibrium system, affected by temperature, heat source and materials, the mixture can be regarded as a porous semi-fluid medium. The size of the pores is a relative concept and has a significant impact on the heat transfer process of the porous medium. If the pores are filled with air, the thermal conductivity will be low, while if the pores are filled with liquid or a solid with high thermal conductivity, the thermal conductivity will be high. The higher the thermal conductivity, the faster the heat transfer, and the problem of rapid heat accumulation can be solved. The thermal conductivity of each sampling point when heating stops is measured with a YBF-3 thermal conductivity measuring instrument, as shown in Table 2. It can be seen from Table 2 that the thermal conductivities of each sampling point in Examples 2-4 are not very different, and the thermal conductivities are significantly higher than those of Comparative Examples 1-4. This is because first, there is a heat transfer and energy storage type of solid porous medium in Examples 2-4. There is graphene oxide with high thermal conductivity in the solid porous medium. When the graphene oxide grafted with hyperbranched polyamide-amine is filled in the pores, a grid skeleton is formed in the mixture, connecting the entire smoldering furnace into a large network system, greatly improving its heat conduction system, and thus accelerating heat transfer. In Example 1, because the graphene oxide was not modified and was unevenly dispersed in the system, the data of each sampling point differed greatly. In Comparative Example 1, there is no polymer, and the pores are occupied by water; in Comparative Example 2, a solid porous medium grafted with amine-based heat transfer and energy storage is not introduced, and the solid medium used is ordinary graphene oxide and ordinary mica. Ordinary mica is easy to absorb water, so it has no effect on improving the thermal conductivity. In Comparative Examples 3-4, ordinary sand is used, and the thermal conductivity cannot be significantly improved. The difference is that stirring is added in Comparative Example 3, so the heat transfer coefficients of each sampling point are about the same. In Comparative Example 4, because there is no stirring, the differences in each collection are relatively large. Therefore, Examples 2-4 can significantly improve the heat transfer efficiency compared with Comparative Examples 1-4, and continuously provide heat source for the smoldering furnace to keep it at a high temperature above 800 °C, accelerating the spread of heat, and at the same time promoting the degradation rate of perfluorinated compounds.

[0092] Table 2 Thermal Conductivity of Each Sampling Point in the Smoldering Furnace (W / m·K)

[0093]

[0094] 3. Removal Efficiency of Perfluorinated Compounds

[0095] Take three equal amounts of the degraded sludge mixture samples obtained in Examples 1-4 and Comparative Examples 1-4. For two of them, extract with methanol with a volume twice that of the sample, and then measure the remaining PFOA content and PFOS content by high performance liquid chromatography (HPLC). For the remaining one, filter it and measure the generated F ion content by ion chromatography (IC). Calculate the degradation rate and defluorination rate accordingly, as shown in Table 3. It can be seen from Table 3 that the degradation rate and defluorination rate of Examples 2-4 are significantly higher than those of Comparative Examples 1-4. This is because the heat transfer and energy storage type aminated solid porous medium grafted with amino groups provided in Examples 2-4 can selectively adsorb perfluorinated compounds. After adsorbing perfluorinated compounds, through the high molecular polymer it contains, the self-sustained smoldering combustion process can generate a temperature that can break perfluorinated compounds, and more synergistically assist the fuel to reach the temperature for perfluorinated compound degradation, and can reach a high temperature above 800 °C, causing the C-F bond to be completely broken. Although Example 1 can have self-sustained smoldering for a relatively long time, the high temperature time is short, so the degradation efficiency is not high. For Comparative Examples 1-4, the energy supply for self-sustained smoldering is small and cannot sustain smoldering, resulting in poor removal efficiency and even more inability to generate high temperature to break the C-F bond. From Figure 1 It can also be clearly seen that the removal efficiency of Examples 2 and 3 is significantly higher than that of Comparative Example 1.

[0096] Table 3 Removal rate of perfluorinated compounds

[0097]

[0098] The above is only used to illustrate the technical solution of the present invention and not to limit it. Any equivalent modifications and changes made by those of ordinary skill in the art to the technical solution of the present invention still fall within the scope covered by the present invention as long as they do not depart from the overall concept of the present invention.

Claims

1. A method for efficiently degrading perfluorinated compounds in sludge by smoldering combustion, characterized in that, The method described is a method of smoldering combustion in a smoldering furnace by mixing sludge, auxiliary fuel, and solid porous medium evenly to degrade and remove perfluorinated compounds; Among them, the sludge is high-moisture sludge containing perfluorinated compounds, and the content of perfluorinated compounds is 100-300 micrograms per 1 kg of dry sludge weight; the auxiliary fuel is one or a mixture of sawdust, rice husks, charcoal particles, or crushed straw; The solid porous medium is an amino-functionalized solid porous medium with heat transfer and energy storage ability grafted from a solid porous medium capable of heat transfer and energy storage; specifically: S101, Add hyperbranched polyamide-amine to an aqueous solution of graphene oxide, adjust it to be alkaline with a 0.05% NaOH solution by mass concentration, then add 1-ethyl-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride, and stir and react at 60-80 °C for 20-24 hours, centrifuge, wash with water, and dry to obtain graphene oxide grafted with hyperbranched polyamide-amine; S102, Stir and heat polyether alcohol and N,N-dimethylformamide at 80 °C for 80-120 minutes until it completely dissolves into a transparent liquid; dissolve polylactic acid and ethanol in a mass ratio of 1:2 and add it to the transparent liquid to finally obtain a polymer solution; S103, Add graphene oxide grafted with hyperbranched polyamide-amine and nano-mica particles to the polymer solution, stir for 30-50 minutes to evenly disperse the solid particles into the composite polymer solution, fully react at 80 °C for 4 hours, dry the product at 20 °C, and pulverize and grind to obtain an amino-functionalized solid porous medium with heat transfer and energy storage ability; Among them, the mass ratio of high-moisture sludge containing perfluorinated compounds, auxiliary fuel, and solid porous medium capable of heat transfer and energy storage is 1000-1500:2-4:30-50.

2. The method for efficiently degrading perfluorinated compounds in sludge by smoldering according to claim 1, characterized in that, The mass ratio of graphene oxide, 1-ethyl-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride, and hyperbranched polyamide-amine is 1:1:3-5; The mass ratio of polyether alcohol and N,N-dimethylformamide is 1:1; the mass ratio of polylactic acid and polyether alcohol is 1:1-2.

3. The method for efficiently anaerobically burning and degrading perfluorinated compounds in sludge according to claim 1, wherein A method for efficiently smoldering and degrading perfluorinated compounds in sludge, specifically: S201, Mix high-moisture sludge containing perfluorinated compounds, auxiliary fuel, and solid porous medium capable of heat transfer and energy storage evenly to obtain a mixture; S202, Put the mixture into a smoldering furnace, continuously heat the mixture at 220 °C - 300 °C at the bottom of the smoldering furnace, and at the same time supply air from the bottom of the furnace upward at a speed of 4.0 cm / s - 6.0 cm / s, stir until the mixture reaches 400 °C - 500 °C, the mixture starts self-sustaining smoldering combustion, stop heating, stop stirring, and continue to react for 18-24 hours to obtain a degraded sludge mixture, and detect the degraded sludge mixture; S203, Collect the waste gas generated from the mixture during smoldering combustion; finally treat the above waste gas and the waste gas evaporated from the mixture; S204, Sample and detect the degraded sludge mixture obtained in step S202. If the concentration of perfluoroalkyl compounds detected does not exceed 50 ppt, the reaction ends; if it exceeds, continue to heat the degraded sludge mixture to 300 °C at the bottom of the smoldering furnace, heat for 1 to 3 hours, supply air from the bottom of the furnace upward at a speed of 4.0 cm / s to 6.0 cm / s, then stop heating, continue the reaction for 4 to 6 hours, and re-detect. If it exceeds, repeat steps S203 and S204 until the concentration of perfluorinated compounds detected does not exceed 100 ppt.

4. The method for efficiently anoxically combusting and degrading perfluorinated compounds in sludge according to claim 1, wherein Perfluorinated compounds include perfluorooctanoic acid and perfluorooctane sulfonic acid.

5. The method for efficiently anoxically combusting and degrading perfluorinated compounds in sludge according to claim 1, wherein The particle size of the auxiliary fuel is less than or equal to 0.05 mm, and the average particle size of the solid porous medium is less than or equal to 0.5 mm.

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