A method for recycling perfluorocarbon waste

Abstract

The present invention relates to the technical field of waste resource utilization, and in particular to a method for recycling perfluorocarbon waste. Perfluorocarbon waste is pre-treated, and then mixed with auxiliary materials at a mass ratio of 1:1-5 for perfluorocarbon waste: auxiliary materials to obtain a solid material to be treated; the solid material to be treated is mixed with cement raw material, and sintered at 1400-1500°C to obtain a clinker as a cement raw material; wherein the physical form of the perfluorocarbon waste is liquid or solid; and the auxiliary materials are selected from at least one of coal powder, quicklime powder, charcoal powder, slaked lime powder and cement clinker powder. The recycling method of the present invention can convert perfluorocarbon waste into primary minerals such as calcium fluoride as components in clinker, with low recycling cost and high efficiency.

Description

Technical Field

[0001] The invention relates to the technical field of waste resource utilization, and in particular to a method for recycling perfluorocarbon waste. Background Art

[0002] Perfluoroalkanes, also known as perfluorocarbons, are a class of compounds containing fully fluorinated carbon chains, in which all hydrogen atoms in their chemical structure are replaced by fluorine atoms, forming extremely stable carbon-fluorine bonds. Perfluoroalkanes are compounds that usually have low surface energy, high hydrophobicity and chemical stability, and are widely used in antifouling coatings, surface treatments and chemical reagents. However, the waste (perfluorocarbon waste) they produce is difficult to degrade, including waste electronic fluorination liquid, highly acidic fluorine tar cleaned from electrolytic cells, and residual tar in reactors produced during distillation. These wastes are mainly composed of carbon and fluorine elements, and contain no or small amounts of hydrogen, oxygen, nitrogen and sulfur components. At present, the supervision of the recycling of perfluorocarbon wastes is becoming increasingly stringent, and it is urgent to effectively recycle the difficult-to-decompose and difficult-to-use wastes produced during the production and use of perfluorocarbons.

[0003] In the prior art, the main methods for disposing perfluorocarbon wastes are catalytic oxidation and high-temperature incineration. Patent CN117732241A discloses a method for effectively decomposing fluorinated alkane substances, wherein the waste gas is introduced into an electric heater for heating, and after the heating is completed, the gas is introduced into a catalytic reactor, and a catalyst is added to catalytically oxidize the fluorinated waste gas to generate carbon dioxide, hydrogen fluoride and water. Although this method can recycle the gas containing fluorinated alkanes and produce non-toxic substances, it is not suitable for the recycling of non-gaseous perfluorocarbon wastes such as fluorine tar. Since perfluoroalkane compounds can only be completely decomposed into simple inorganic substances at temperatures above 1000°C, the main treatment method for liquid and solid perfluorocarbon wastes is high-temperature incineration. However, this treatment method will produce a large amount of fluorinated waste gas, such as hydrofluoric acid, which will corrode the equipment and require secondary treatment of the fluorinated acidic waste gas, increasing the investment cost. Moreover, since the total amount of waste generated during the production and use of perfluoroalkane compounds is not large, the mode of multiple small-scale treatment will lead to higher treatment costs. If they are piled up and treated at one time, corresponding containers and storage places will be required, which will also increase costs. Summary of the invention

[0004] In view of the technical problems in the prior art that liquid and solid perfluorocarbon wastes have great pollution and high cost when incinerated at high temperature, the present invention provides a method for recycling perfluorocarbon wastes, which converts perfluorocarbon wastes into natural primary minerals such as calcium fluoride and then applies them to the cement industry, thereby realizing the recycling of perfluorocarbon wastes without the need for secondary treatment.

[0005] The technical solution of the present invention is:

[0006] A method for recycling perfluorocarbon wastes, wherein the perfluorocarbon wastes are pre-treated, and then mixed with auxiliary materials at a mass ratio of 1:1-5 to obtain solid materials to be treated; the solid materials to be treated are mixed with cement raw materials, and sintered at 1400-1500°C to obtain clinker as a cement raw material;

[0007] Among them, the physical form of perfluorocarbon waste is liquid or solid;

[0008] The auxiliary material is selected from at least one of coal powder, quicklime powder, charcoal powder, slaked lime powder and cement clinker powder;

[0009] The amount of solid material to be treated is 0.15wt%-0.25wt% of the cement raw material.

[0010] The reaction equation is as follows:

[0011] 2C n F m + mCaO + (2n-m / 2)O 2 →2nCO 2 +mCaF 2 ;

[0012] 6C n F m +mAl 2 O 3 + (6n-3 / 2m)O 2 →6nCO 2 +2mAlF 3 ;

[0013] C n F m Refers to perfluorocarbon waste, which is not a single substance, and its chemical composition is not fixed. n and m are coefficients; CaO, Al 2 O 3 It is a component in cement raw material.

[0014] Furthermore, liquid perfluorocarbon wastes include waste electronic fluorination liquid, fluorine tar cleaned out of the electrolytic cell during the perfluorocarbon production process, residual tar in the reactor during the perfluorocarbon distillation process, fluorine oil used in molding machines, and artificial blood products with carbon and fluorine as the main components.

[0015] Furthermore, the waste electronic fluorination liquid includes waste FC-3283 electronic fluorination liquid, FC-43 electronic fluorination liquid, and perfluorobutylsulfonyl fluoride; the fluorine tar cleaned out of the electrolytic cell during the perfluorocarbon production process includes the fluorine tar produced during the electrolysis of perfluorotripropylamine; and artificial blood products include products containing perfluorodecalin, perfluorooctane bromide and / or perfluorotriethylamine.

[0016] Furthermore, solid perfluorocarbon wastes include waste perfluoropolymer products.

[0017] Furthermore, the discarded perfluorinated polymer products include polytetrafluoroethylene fillers, polytetrafluoroethylene coatings, and fluorinated surfactants.

[0018] Further, the specific steps are as follows:

[0019] (1) adding liquid perfluorocarbon waste to ice water in portions, stirring and filtering to obtain a mixed liquid; filtering the mixed liquid to obtain a filtrate and a solid filter residue; washing the solid filter residue with water to obtain a washed solid filter residue and a washing liquid;

[0020] (2) After the eluent and the filtrate are combined, activated carbon is added, stirred evenly, and filtered to obtain an activated carbon-solid mixture and a fluorine-containing aqueous solution;

[0021] (3) Adding the washed solid filter residue, activated carbon-solid mixture and slaked lime powder into a mixer, mixing and stirring to obtain a solid material to be treated;

[0022] (4) The solid material to be treated is mixed into cement raw material and sintered in a decomposition furnace at 1400-1500°C to obtain clinker which is the raw material of cement.

[0023] Furthermore, the mass ratio of liquid perfluorocarbon waste to ice water is 1:1; the mass ratio of liquid perfluorocarbon waste to activated carbon is 5:1; and the mass ratio of solid filter residue after elution: activated carbon-solid mixture and slaked lime powder is 2:3:21.

[0024] Further, the specific steps are as follows:

[0025] (1) The solid perfluorocarbon waste is crushed in a crusher, and then mixed with cement clinker powder to obtain a mixed solid material to be treated;

[0026] (2) The solid material to be treated is uniformly mixed into the cement raw material and sintered in a decomposition furnace at 1400-1500°C to obtain clinker as the cement raw material.

[0027] Furthermore, the particle size of the solid perfluorocarbon waste after crushing is 0.1-3 mm; the particle size of the cement clinker powder is 10-50 mm.

[0028] The beneficial effects of the present invention are:

[0029] The recycling method used in the present invention can achieve efficient recycling of non-gaseous perfluorocarbon waste. It is simply pre-treated and mixed with auxiliary materials, and then a small amount is added to the cement raw material and sintered at a high temperature of 1400-1500°C. It can completely decompose the perfluorocarbon waste without generating fluorine-containing acidic waste gas that corrodes the equipment. The generated calcium fluoride, aluminum fluoride and other substances are components that are difficult to dissolve in water. As non-main components of clinker, they do not affect the performance and quality of cement clinker. In particular, the recycling method provided by the present invention can consume the difficult-to-dispose fluorotar products through the huge production capacity of cement, and has the advantages of low cost and high disposal efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0031] Figure 1 This is a process flow chart for the recovery and utilization of fluorine tar in Example 1.

[0032] Figure 2 It is the ion chromatogram of free fluorine content in the clinker of Example 1.

[0033] Figure 3 This is the ion chromatogram of the total fluorine content after diluting the clinker in Example 1.

[0034] Figure 4 This is a process flow chart for recycling polytetrafluoroethylene filler in Example 2.

[0035] Figure 5 This is the ion chromatogram of the free fluorine content in the clinker of Example 2.

[0036] Figure 6 This is the ion chromatogram of the total fluorine content after diluting the clinker in Example 2.

[0037] Figure 7 Schematic diagram of the experimental device of comparative example 1.

[0038] Figure 8 This is the ion chromatogram of the total fluoride content after diluting the water sample in Example 1.

[0039] In the figure, 1-combustion container, 2-suction hood, 3-connecting pipe, 4-water absorption tank, 5-plastic filler, 6-ventilation pipe, 7-exhaust sampling air bag. DETAILED DESCRIPTION

[0040] In order to enable those skilled in the art to better understand the technical solutions in the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0041] Example 1

[0042] A method for recycling perfluorocarbon waste, in this embodiment, the perfluorocarbon waste is fluorine tar produced by electrolysis of perfluorotripropylamine, the main components of which are liquid fluorine-containing polymer and hydrogen fluoride;

[0043] See the process flow chart Figure 1 , the specific steps are as follows:

[0044] (1) placing 100 kg of ice water in a stirred reactor, slowly adding 100 kg of fluorine tar, stirring, and obtaining a black mixed liquid; filtering the black mixed liquid using medium-speed filter paper to obtain a black filtrate and a black solid residue; eluting the black solid residue twice with 2 kg of water to obtain a black solid and an eluent;

[0045] (2) After the eluent and the black filtrate are combined, 20 kg of activated carbon is added, stirred evenly, and filtered to obtain an activated carbon-black solid mixture and a light yellow hydrogen fluoride aqueous solution;

[0046] After testing, the acidity of the hydrogen fluoride aqueous solution is 17%, and the evaporation residue (the proportion of the solid residue remaining after the solution is evaporated to dryness to the total mass) is 0.1%, which can be recycled as a by-product or sold externally;

[0047] (3) Add 40 kg of black solid, 60 kg of activated carbon-black solid mixture and 420 kg of slaked lime powder (calcium hydroxide, particle size of 10-50 mm) into a mixer, mix and stir to obtain a solid material to be treated, and no obvious heat is released during the stirring process;

[0048] (4) Weigh 420 kg of solid material to be treated and mix it into 200 tons of cement raw material (mixing ratio is 0.21%) through the cement rotary kiln hazardous waste disposal mixing system, and sinter it in a decomposition furnace at 1500°C to obtain clinker as cement raw material.

[0049] Clinker fluorine content detection:

[0050] Take 10g of clinker and mix it with deionized water of the same mass, stir it and filter it. The filtrate is tested by ion chromatography. The free fluorine content in the clinker is 0.97ppm. The ion chromatogram is shown in Figure 2, ion chromatography data are shown in Table 1; 10g of clinker was mixed with an equal mass of concentrated sulfuric acid, diluted 40 times with deionized water, filtered, and the filtrate was tested by ion chromatography. The total fluorine content (free fluorine content and fluorine content fixed in the clinker) after dilution was 7.66ppm, and the ion chromatogram is shown in Figure 3 The ion chromatography data are shown in Table 2. The total fluorine content in the clinker is 306.4ppm, and the fluorine solidification rate in the clinker is 99.68%. The fluorine solidification rate is high, and the fluorine tar recovery effect is good.

[0051] Since the fluorine element in the prepared clinker all comes from fluorine tar, the fluorine content in the used fluorine tar is calculated to be 76%, which falls within the range of fluorine content in perfluorocarbon wastes known in the technical field (40%-80%).

[0052] Table 1 Ion chromatography data of free fluorine content in clinker

[0053]

[0054] Table 2 Ion chromatography data of total fluorine content after dilution of clinker

[0055]

[0056] Example 2

[0057] A method for recycling perfluorocarbon waste, in this embodiment, the perfluorocarbon waste is polytetrafluoroethylene filler;

[0058] See the process flow chart Figure 4 , the specific steps are as follows:

[0059] (1) 100 kg of polytetrafluoroethylene filler is put into a grinder to be crushed into particles of 0.1-3 mm, and then mixed with 200 kg of cement clinker powder (particle size of 10-50 mm) to obtain a mixed solid material to be treated;

[0060] (2) 300 kg of solid material to be treated is evenly mixed into 200 tons of cement raw material (the mixing ratio is 0.15%) through the cement rotary kiln hazardous waste disposal mixing system. After sintering in a decomposition furnace at 1400°C, the structure is destroyed to generate calcium fluoride, and clinker, which is the raw material for cement, is obtained.

[0061] Clinker fluorine content detection:

[0062] Take 10g of clinker and mix it with deionized water of equal mass, stir it and filter it. The filtrate is tested by ion chromatography. The free fluorine content in the clinker is 0.8148ppm. The ion chromatogram is shown in Figure 5, ion chromatogram data are shown in Table 3; 10g of clinker was mixed with an equal mass of concentrated sulfuric acid, diluted 40 times with deionized water, filtered, and the filtrate was tested by ion chromatography. The total fluorine content after dilution was 7.791ppm. The ion chromatogram is shown in Figure 6 The ion chromatography data are shown in Table 4. The total fluorine content in the clinker is 311.64 ppm, and the fluorine curing rate in the clinker is 99.74%. The fluorine curing rate is high, and the recycling effect of polytetrafluoroethylene filler is good.

[0063] Since the fluorine elements in the prepared clinker all come from the polytetrafluoroethylene filler, the fluorine content in the polytetrafluoroethylene filler used is calculated to be 62.2%, which falls within the range of fluorine content in perfluorocarbon wastes (40%-80%) known in the technical field.

[0064] Table 3 Ion chromatography data of free fluorine content in clinker

[0065]

[0066] Table 4 Ion chromatography data of total fluorine content after dilution of clinker

[0067]

[0068] Comparative Example 1

[0069] A method for recycling perfluorocarbon waste, using an experimental simulation of high-temperature incineration to dispose of perfluorocarbon waste. The design of the experimental device is shown in Figure 7 , the specific design and operation process are as follows:

[0070] A combustion container 1 with two ends welded and a central opening on the side is prepared using a DN100 steel pipe. An air suction hood 2 equipped with an air suction device is placed above the central opening. The air suction hood 2 is connected to a connecting pipe 3. The other end of the connecting pipe 3 extends from the top of the tank into the water inside the water absorption tank 4. The mass of the water is 200 kg. Plastic fillers 5 for distributing the gas are evenly dispersed in the water. A ventilation pipe 6 is also connected to the top of the water absorption tank 4. The air inlet end of the ventilation pipe 6 extends from the top of the tank into the water absorption tank 4 and is above the water surface. The air outlet end of the ventilation pipe 6 is connected to an exhaust gas sampling air bag 7. Along the gas flow direction, branches and valves are sequentially arranged on the ventilation pipe 6.

[0071] The combustion container 1 is filled with 200g of fluorine tar (fluorine tar produced by electrolysis of perfluorotripropylamine from the same batch as in Example 1). The acetylene flame elbow penetrates into the combustion container 1 to slowly burn the fluorine tar. During this process, a large amount of black smoke is generated. Under the power of the suction device, the black smoke is concentrated from the suction hood 2 into the connecting pipe 3, and then enters the water absorption tank 4 for water washing, and then enters the exhaust gas sampling air bag 7 through the ventilation pipe 6. When the sampling is completed, the valve is closed, and the remaining gas that has not been sampled and collected is discharged from the branch on the ventilation pipe 6 and then enters the exhaust gas recovery system for disposal, and finally discharged into the air.

[0072] During the washing process, a small amount of oil was found floating on the water surface and a small amount of black carbonaceous sediment was found under the water surface. The water sample was taken with an absorption tube, filtered through a 0.22um PTFE membrane filter, and diluted 40 times. After ion chromatography, the total fluorine content in the diluted water sample was 8.655ppm. The ion chromatogram is shown in Figure 8 The ion chromatography data are shown in Table 5. The total amount of fluorine absorbed and fixed in water is 69.2 g, and the fluorine curing rate in water is 34.6%, which is much smaller than the fluorine curing rate of 99.68% in Example 1.

[0073] The exhaust gas collected in the exhaust sampling bag 7 was tested by GC-MS gas chromatograph-mass spectrometer. After qualitative analysis, the testers found the presence of small molecular gases such as carbon tetrafluoride, hexafluoroethane and octafluoropropane after fracture. This also proved that the high-temperature incineration method cannot efficiently fix the fluorine element due to the lack of good fluorine fixers, and the fluorine element still exists in the gas after water washing.

[0074] Comparative Example 1 shows that fluorine tar will produce a large amount of fluorine-containing waste gas after high-temperature incineration treatment. Water washing does not achieve effective solidification, and the water after washing needs to be treated secondary, which increases the cost. At the same time, the fluorine-containing gas that has not been effectively solidified contains incompletely decomposed fluorocarbon small molecular fragments, and it is necessary to add a tail gas recovery device. It can only be discharged into the air after purification to meet the standards, which further increases the disposal cost.

[0075] Table 5 Ion chromatography data of total fluoride content after dilution of water samples

[0076]

[0077] Although the present invention has been described in detail with reference to the accompanying drawings and in combination with the preferred embodiments, the present invention is not limited thereto. Without departing from the spirit and essence of the present invention, a person of ordinary skill in the art may make various equivalent modifications or substitutions to the embodiments of the present invention, and these modifications or substitutions shall be within the scope of the present invention. Any person of ordinary skill in the art may easily think of changes or substitutions within the technical scope disclosed by the present invention, and these shall be within the scope of protection of the present invention.

Claims

1. A method for recycling perfluorocarbon waste, characterized in that: The perfluorocarbon waste is pre-treated, and then mixed with auxiliary materials at a mass ratio of 1:1-5 to obtain a solid material to be treated; the solid material to be treated is mixed with cement raw materials, and sintered at 1400-1500° C. to obtain a clinker as a cement raw material; Among them, the physical form of perfluorocarbon waste is liquid; The auxiliary material is selected from at least one of coal powder, quicklime powder, charcoal powder, slaked lime powder and cement clinker powder; The amount of solid material to be treated is 0.15wt%-0.25wt% of the cement raw material; Liquid perfluorocarbon waste includes fluorine tar removed from the electrolytic cell during the perfluorocarbon production process. The specific steps are as follows: (1) adding liquid perfluorocarbon waste to ice water in portions, stirring and filtering to obtain a mixed liquid; filtering the mixed liquid to obtain a filtrate and a solid filter residue; washing the solid filter residue with water to obtain a washed solid filter residue and a washing liquid; (2) After the eluent and the filtrate are combined, activated carbon is added, stirred evenly, and filtered to obtain an activated carbon-solid mixture and a fluorine-containing aqueous solution; (3) Adding the washed solid filter residue, activated carbon-solid mixture and slaked lime powder into a mixer, mixing and stirring to obtain a solid material to be treated; (4) The solid material to be treated is mixed into cement raw material and sintered in a decomposition furnace at 1400-1500°C to obtain clinker which is the raw material of cement.

2. A method for recycling perfluorocarbon waste according to claim 1, characterized in that: The fluorine tar cleaned out of the electrolytic cell during the production of perfluorocarbons includes the fluorine tar produced during the electrolysis of perfluorotripropylamine.

3. A method for recycling perfluorocarbon waste according to claim 1, characterized in that: Liquid perfluorocarbon wastes also include waste electronic fluorination liquids, residual tar from reactors during the perfluorocarbon distillation process, fluorinated oil used in molding machines, and artificial blood products containing perfluorodecalin, perfluorooctane bromide and / or perfluorotriethylamine.

4. A method for recycling perfluorocarbon waste according to claim 3, characterized in that: Waste electronic fluoride liquid includes waste FC-3283 electronic fluoride liquid, FC-43 electronic fluoride liquid, and perfluorobutylsulfonyl fluoride.

Images