Method for purifying aged landfill leachate by integrating separation and reaction

Abstract

The present application belongs to the field of environmental protection, and discloses a kind of old landfill leachate separation and reaction integrated purification method, landfill leachate is softened to remove calcium and magnesium ions in alkaline adjusting pool first, softened leachate is removed free ammonia and volatile organic pollutants by gas stripping tower;Gas stripping kettle liquid containing refractory organic pollutants and inorganic salt enters nanofiltration system, and the permeate obtained by nanofiltration system treatment has COD concentration ≤70mg / L and ammonia nitrogen concentration ≤5mg / L;Free ammonia, volatile organic pollutants and nanofiltration concentrated solution are purified by oxygen cracking to obtain inorganic small molecules such as carbon dioxide, water and nitrogen, and the TOC content of residual inorganic salt is less than 10mg / kg;There is no secondary pollution generation in the whole purification process, and the indexes of effluent water all reach the national standard of domestic waste landfill pollution control standard (GB16889-2008).

Description

TECHNICAL FIELD

[0001] The present application relates to a kind of old garbage leachate separation and reaction integrated purification method, belong to environmental protection field, it is applied to old domestic waste leachate processing. BACKGROUND

[0002] Old garbage leachate contains high concentration ammonia nitrogen, biodegradable organic matter, salt and a small amount of volatile organic pollutants, direct discharge will pollute natural water and soil, seriously endanger people's health.Patent CN115259546A discloses a kind of combined process based on "biology+multistage membrane", it is the typical process of old garbage leachate disposal, wherein biological treatment section is mainly aimed at ammonia nitrogen and small molecule organic pollutants, membrane treatment section is mainly separated biodegradable pollutants, specific process also exists difference according to water quality and quantity.

[0003] Ammonia nitrogen in old garbage leachate can be converted into harmless nitrogen to the environment except for the process disclosed in patent CN110357271B based on "nitrification-denitrification" treatment, stripping deamination method disclosed in patent CN212609575U can also effectively separate ammonia nitrogen in garbage leachate.However, the existing stripping deamination process needs to consume a large amount of steam, which has the disadvantages of high process energy consumption and operation cost.For old garbage leachate in some scenarios, patent CN213537454U discloses a DTRO membrane technology to replace the above-mentioned combined process to directly treat old garbage leachate, and the membrane effluent also meets the relevant discharge standards.

[0004] In fact, the content of biodegradable organic matter in old leachate is generally very low, so the biological treatment section in the combined process can only play a pretreatment role for the membrane process, and small molecule organic matter and ammonia nitrogen that cannot be separated by the membrane will be removed preferentially.As the main body of the combined process of old leachate, the membrane separation technology can achieve standard discharge of effluent, but inevitably produces a large amount of membrane concentrate which is directly recirculated into the landfill, and does not convert into harmless substances to the environment, resulting in persistent accumulation of difficult-to-degrade organic pollutants such as humic acid and various inorganic salts, and does not fundamentally degrade the difficult-to-degrade organic pollutants in the leachate.

[0005] Patent CN217627972U discloses a method for disposing membrane concentrate by multi-stage MVR technology, but such technology does not convert the difficult-to-degrade organic matter in the membrane concentrate into inorganic small molecules during the disposal of pollutants, and the pollutants remain in the evaporated solid waste, which finally needs to be sent to an incineration plant for high-temperature incineration disposal.Therefore, the "neck" problem of old garbage leachate treatment is the lack of concentrate reaction purification technology matched with membrane separation to completely convert the organic pollutants in the concentrate into harmless substances to the environment. SUMMARY

[0006] The present application aims at the problem of difficult purification of membrane concentrated liquid in the existing aging landfill leachate treatment technology, and provides an integrated separation-reaction aging landfill leachate comprehensive treatment method.

[0007] The purpose of the present application is achieved by the following technical solutions:

[0008] An aging landfill leachate separation and reaction integrated purification method, characterized in that landfill leachate is pumped into an alkaline adjusting tank, and after being stirred uniformly, the leachate is softened by adjusting to alkalinity with sodium hydroxide solution; calcium and magnesium precipitates formed in the softening process are deposited by gravity at the bottom of a precipitate tank to realize solid-liquid separation, and the softened leachate is subjected to removal of free ammonia and volatile organic pollutants by high-speed gas entrainment in a constant-temperature gas stripping tower; the gas stripping tower kettle liquid is treated by a nanofiltration system.

[0009] The free ammonia, volatile organic pollutants and concentrated liquid in the nanofiltration system are converted into inorganic small molecules by a near-oxygen cracking catalytic reaction, so as to obtain inorganic Na / K mixed salt water resources free of organic pollutants.

[0010] In the above method, the pH of alkalinity is adjusted to 8-12, and the ammonia nitrogen concentration in the gas stripping tower kettle liquid after gas stripping treatment is ≤10 mg / L.

[0011] In the above method, the mass fraction of salt in the aging landfill leachate is 2-5.5%.

[0012] The COD concentration of the aging landfill leachate is 500-5800 mg / L, and the ammonia nitrogen concentration is 1300-2200 mg / L.

[0013] The hardness of the aging landfill leachate is 650-1800 mg / L.

[0014] In the above method, the packing in the gas stripping tower is one or two of Rasching ring, Pall ring, theta ring, ladder ring, corrugated plate packing, metal wire mesh corrugated packing and grid packing.

[0015] In the above method, the temperature range of the tower body of the gas stripping tower is 30-70℃, the gas-liquid ratio is 300-1500:1, and the high-speed gas is air with a gas speed of 50-280 m 3 / h.

[0016] In the above method, the recovery rate of the nanofiltration system is 75-95%, the working pressure is 0.5-2 MPa, and the separation membrane material in the nanofiltration system is polyamide fiber.

[0017] In the above method, the near-oxygen cracking catalyst is an acidic molecular sieve loaded with metal oxide, and the loading amount of the metal oxide is 10-35%.

[0018] In the method: the metal oxide is one or two of vanadium oxide, copper oxide, cerium oxide, manganese oxide, cobalt oxide; the acidic carrier is one of Y-type and β-type molecular sieve.

[0019] In the method: the temperature of the near-oxygen cracking reactor is 400-500 DEG C, and the space velocity is 0.5-5 h -1 .

[0020] In some more detailed technical solutions:

[0021] An aging landfill leachate separation and reaction integrated purification method, the purification method first pumps the landfill leachate into an alkaline adjusting tank, uniformly stirs, and then adjusts the landfill leachate to be alkaline by using a sodium hydroxide solution; calcium / magnesium ions form a precipitate under an alkaline condition, so that the purpose of softening the landfill leachate is achieved; the softened landfill leachate is pumped from the top of the tower into an air stripping tower provided with a filler; air is introduced into the air stripping tower from the bottom; under the action of the filler, the air in the tower and the leachate are fully contacted; free ammonia and a small amount of volatile organic pollutants are removed. The kettle liquid of the air stripping tower is pumped into a nanofiltration system by a high-pressure pump; the permeate obtained by treating the nanofiltration system reaches the discharge standard; the free ammonia, the volatile organic pollutants, and the nanofiltration concentrated liquid are introduced into a near-oxygen cracking reactor; under the action of a dual-function catalyst, all organic matters and free ammonia are directly converted into inorganic small molecules harmless to the environment; the catalyst is recovered after being washed with water and desalted; and inorganic Na / K mixed salt is obtained, which is used for resource utilization without organic pollutants. The purification method of the aging landfill leachate disclosed by the application specifically comprises the following steps:

[0022] Softening: the pH of the landfill leachate is adjusted to 8-12 in the adjusting tank, so that calcium / magnesium precipitates are deposited at the bottom of the adjusting tank; after solid-liquid separation, the softened landfill leachate is obtained.

[0023] Air stripping: the softened landfill leachate is introduced into a constant-temperature air stripping tower provided with a filler; under the entrainment of high-speed gas, free ammonia and volatile organic pollutants are removed; the ammonia nitrogen concentration in the kettle liquid of the air stripping tower is ≤10 mg / L.

[0024] Nanofiltration: the kettle liquid of the air stripping tower is separated from pollutants in the leachate by a nanofiltration system; the permeate obtained by treating the nanofiltration system has a COD concentration ≤70 mg / L and an ammonia nitrogen concentration ≤5 mg / L; meanwhile, nanofiltration concentrated liquid containing refractory organic matter and inorganic salt is generated and introduced into the next step.

[0025] Near-oxygen cracking: free ammonia, volatile organic pollutants, and nanofiltration concentrated liquid are introduced into a near-oxygen cracking reactor. Under the action of a catalyst, refractory organic pollutants are converted into inorganic substances such as carbon dioxide, water, and nitrogen through cracking-oxidation consecutive reactions; free ammonia and volatile organic pollutants are converted into inorganic substances through catalytic oxidation reactions. Finally, Na / K mixed salt with a TOC content lower than 10 mg / kg is obtained; the catalyst is separated by water washing and reused.

[0026] The mass fraction of salt in the old landfill leachate is 2-5.5%, and the calcium and magnesium ions in the leachate are removed first to avoid the direct entry of the calcium and magnesium ions into the near-oxygen cracking to cause the deactivation of the catalyst.

[0027] In some more specific technical solutions: the near-oxygen cracking catalyst is prepared by an impregnation method, and the method comprises the following steps:

[0028] Step (1), the acid carrier calcined at a high temperature of 400-600 DEG C is soaked in an aqueous solution containing a metal oxide precursor metal chloride salt to obtain a mixed solution;

[0029] Step (2), the mixed solution in step (1) is dried to obtain a solid after the water is removed by a rotary evaporator, and the solid is heat-treated at a high temperature of 400-600 DEG C for 4-6 hours; the metal chloride salt is converted into a metal oxide after the heat treatment, and finally the near-oxygen cracking catalyst of the acid carrier loaded with the metal oxide is obtained.

[0030] The metal chloride salt is one or two of vanadium chloride, copper chloride dihydrate, cerium chloride heptahydrate, manganese chloride tetrahydrate and cobalt chloride hexahydrate.

[0031] The temperature of the near-oxygen cracking reactor is 400-500 DEG C, and the space velocity is 0.5-5 h -1 .

[0032] In the technical solution of the application: the pressure is a gauge pressure.

[0033] The beneficial effects of the application are embodied in:

[0034] The application adopts a separation-reaction integrated method of "softening-gas stripping-nanofiltration-near-oxygen cracking" to remove the refractory organic pollutants and ammonia nitrogen in the old landfill leachate, the COD of the purified water of the nanofiltration membrane is reduced to below 70 mg / L, and the ammonia nitrogen is reduced to below 5 mg / L; the non-methane total hydrocarbon concentration in the exhaust gas of the near-oxygen cracking reaction is reduced to 4.6 mg / m 3 The purified water meets the national standard of the Landfill Pollution Control Standard for Domestic Waste (GB 16889-2008), and can be directly discharged without further treatment and secondary pollution. DETAILED DESCRIPTION

[0035] Figure 1 The flow chart of the separation and reaction integrated purification method of the old landfill leachate of the application. DETAILED DESCRIPTION

[0036] The application is further described below through an implementation example, but the protection scope of the application is not limited thereto:

[0037] Example 1

[0038] The COD concentration of the landfill leachate to be treated is 990 mg / L, the ammonia nitrogen concentration is 1950 mg / L, the hardness is 1800 mg / L, and the salt content is 3.1%. As Figure 1 , 5.2 kg of saturated sodium hydroxide solution is added to 1000 kg of landfill leachate to adjust the pH of the leachate to 12, and calcium and magnesium ions form calcium and magnesium precipitates. After solid-liquid separation, the weight of the calcium and magnesium precipitates is 17 kg, and the mass fraction is 1.7% of the original leachate.

[0039] The softened leachate enters an air stripping tower composed of an air compressor, a packed tower, a water pump, and a heating device. The air velocity is 54 m 3 / h, the leachate feed flow rate is 0.18 m 3 / h, the gas-liquid ratio is 300, the packing in the air stripping tower is Raschig rings and Pall rings, and the tower body temperature is maintained at 50℃. The high-speed gas input by the air compressor enters the air stripping tower from the bottom, and the leachate transported by the water pump enters from the top. The gas and liquid phases in the air stripping tower are countercurrently contacted, and the gas carries the free ammonia and volatile organic pollutants in the leachate from bottom to top, while the liquid enters the air stripping tower from top to bottom. After the removal of free ammonia and volatile organic pollutants by air stripping, the leachate (ammonia nitrogen is 10 mg / L) is transported into a nanofiltration system with a working pressure of 2 MPa and a water recovery rate of 95%. The nanofiltration system uses polyamide separation membranes, which are purchased from Dow Chemical Company, USA, model NF270-400 (the same below). The COD concentration of the permeate obtained by the nanofiltration system is 70 mg / L, and the ammonia nitrogen concentration is 5 mg / L.

[0040] The gas containing free ammonia and volatile organic pollutants and the nanofiltration concentrate enter an oxygen proximity cracking reactor with a working temperature of 500℃ and an air speed of 5 h -1 . The loading of the active component, cobalt oxide, is 10%. The salt in the oxygen proximity cracking reactor has a TOC content of 10 mg / kg after washing and recrystallization, and the main components are sodium salt and potassium salt. The catalyst separated by water washing is recycled. The non-methane total hydrocarbon of the purified gas in the oxygen proximity cracking reactor is 4.3 mg / m 3 .

[0041] The cobalt oxide / Y molecular sieve catalyst is prepared by impregnation method, including the following steps:

[0042] (1) 1 kg of Y molecular sieve is calcined at 400℃, then soaked in a 2L aqueous solution containing 99g of cobalt chloride hexahydrate;

[0043] (2) After removing water by a rotary evaporator, a solid is obtained by drying, and then heat treated at 600℃ for 4h. The cobalt chloride hexahydrate is converted to cobalt oxide after heat treatment, and finally an acidic carrier loaded with metal oxide catalyst: cobalt oxide / Y molecular sieve is obtained.

[0044] Example 2

[0045] The COD concentration of the landfill leachate to be treated was 500 mg / L, the ammonia nitrogen concentration was 2200 mg / L, the hardness was 650 mg / L, and the salt content was 5.5%. 1.8 kg of saturated sodium hydroxide solution was added to the conditioning tank containing 1000 kg of landfill leachate, and the pH of the leachate was adjusted to 8. The weight of the calcium and magnesium precipitate was 23 kg, and the mass fraction was 2.3% of the original leachate.

[0046] The softened leachate from the conditioning tank entered the constant-temperature countercurrent stripping tower, the air velocity was 270 m 3 / h, the leachate feed flow rate was 0.18 m 3 / h, the gas-liquid ratio was 1500, and the packing in the stripping tower was θ ring and ladder ring. The tower body temperature was maintained at 70°C. The tower kettle liquid with an ammonia nitrogen concentration of 2.0 mg / L was transported into the nanofiltration system with a working pressure of 0.5 MPa and a purified water recovery rate of 75% by a high-pressure pump. The permeate obtained by the nanofiltration system had a COD concentration of 45.3 mg / L and an ammonia nitrogen concentration of 1.7 mg / L.

[0047] The gas containing free ammonia and volatile organic pollutants and the nanofiltration concentrate were passed into the near-oxygen cracking reactor filled with vanadium oxide-copper oxide / Y molecular sieve catalyst, the working temperature was 400°C, the space velocity was 0.5 h -1 , the loading of vanadium oxide was 5%, the loading of copper oxide was 10%, and the total loading of the oxidation active component was 15%. Sodium salt and potassium salt with a TOC content of 7.6 mg / kg were obtained by near-oxygen cracking treatment, and the catalyst was separated by water washing and recycled for use. The non-methane total hydrocarbon of the purified gas from the near-oxygen cracking reactor was 2.3 mg / m 3 .

[0048] The vanadium oxide-copper oxide / Y molecular sieve catalyst was prepared by an impregnation method, including the following steps:

[0049] (1) 1 kg of Y molecular sieve was calcined at a high temperature of 600°C, and then soaked in a 5 L aqueous solution containing 45 g of vanadium chloride and 214 g of copper chloride dihydrate;

[0050] (2) After removing the water by a rotary evaporator, a solid was obtained by drying, and then heat-treated at a high temperature of 400°C for 6 h. After heat treatment, vanadium chloride was converted into vanadium oxide, and copper chloride dihydrate was converted into copper oxide. Finally, an acidic carrier loaded with metal oxide catalyst, vanadium oxide-copper oxide / Y molecular sieve, was obtained.

[0051] Example 3

[0052] The COD concentration of the landfill leachate to be treated was 5800 mg / L, the ammonia nitrogen concentration was 1300 mg / L, the hardness was 1320 mg / L, and the salt content was 2%.Figure 1 In 1000 kg of landfill leachate, 5.2 kg of saturated sodium hydroxide solution was added to adjust the pH of the leachate to 12, and the solid precipitate was separated, the weight of calcium and magnesium precipitate was 12 kg, and the mass fraction was 1.2% of the original leachate.

[0053] The softened leachate entered the constant-temperature countercurrent stripping tower, the air velocity was 162 m 3 / h, the leachate feed flow rate was 0.18 m 3 / h, the gas-liquid ratio was 900, the packing in the stripping tower was metal wire mesh corrugated packing, and the tower body temperature was maintained at 30℃. The leachate after removal of free ammonia and volatile organic pollutants (ammonia nitrogen was 5.1 mg / L) was transported into the nanofiltration system with a working pressure of 1.5 MPa and a purification water recovery rate of 85% by a high-pressure pump, and the permeate obtained by the nanofiltration system had a COD concentration of 54.8 mg / L and an ammonia nitrogen concentration of 4.1 mg / L.

[0054] The gas containing free ammonia and volatile organic pollutants and the nanofiltration concentrate were continuously introduced into the near-oxygen cracking reactor with a working temperature of 500℃ and an air speed of 4h -1 , and the near-oxygen cracking reactor was filled with manganese oxide-cerium oxide / β molecular sieve catalyst, the loading amount of manganese oxide was 15%, the loading amount of cerium oxide was 20%, the total loading amount of the oxidizing active component was 35%, and finally sodium salt and potassium salt with a TOC content of 5.5 mg / kg were obtained; the non-methane total hydrocarbon concentration of the purified gas in the near-oxygen cracking reactor was 4.6 mg / m 3 .

[0055] The manganese oxide-cerium oxide / β molecular sieve catalyst was prepared by an impregnation method, including the following steps:

[0056] (1) 1 kg of β molecular sieve was calcined at a high temperature of 600℃, and then soaked in a 5L aqueous solution containing 435 g of cerium chloride heptahydrate and 188 g of manganese chloride tetrahydrate;

[0057] (2) After removing water by a rotary evaporator, a solid was obtained by drying, and was heat-treated at a high temperature of 500℃ for 6h; after heat treatment, the cerium chloride heptahydrate was converted into cerium oxide, and the manganese chloride tetrahydrate was converted into manganese oxide, and finally an acidic carrier loaded metal oxide catalyst: cerium oxide-manganese oxide / Y molecular sieve was obtained.

[0058] Example 4

[0059] The gas containing free ammonia and volatile organic pollutants and the nanofiltration concentrate in the implementation case 3 were continuously introduced into the near-oxygen cracking reactor with a working temperature of 450℃ and an air speed of 3h -1, the oxygen cracking reactor filled with copper oxide / Y molecular sieve catalyst, the oxidation active component copper oxide load is 10%, after the oxygen cracking reactor runs for 300h, 50kg purified water is introduced into the reactor to wash out the salt in the oxygen cracking reactor, after washing, evaporation and recrystallization, sodium salt and potassium salt with TOC content of 5.2mg / kg are obtained, the catalyst is separated by water washing and recycled; the non-methane total hydrocarbon concentration of the purified gas in the oxygen cracking reactor is 2.6mg / m 3 .

[0060] The copper oxide / Y molecular sieve catalyst is prepared by impregnation method, including the following steps:

[0061] (1) 1kg Y molecular sieve is soaked in a 2L aqueous solution containing 214g copper chloride dihydrate after high-temperature calcination at 600℃;

[0062] (2) after removing water by a rotary evaporator, the solid is obtained by drying, and is heat-treated at a high temperature of 500℃ for 6h; after heat treatment, the copper chloride dihydrate is converted into copper oxide, and finally the acid carrier loaded metal oxide catalyst: copper oxide / Y molecular sieve is obtained.

[0063] Example 5

[0064] The catalyst separated by water washing in Example 4 is refilled, and the nanofiltration concentrated solution in Example 3 and the entraining gas of the gas stripping tower are continuously introduced, the working temperature is 450℃, and the space velocity is 3h -1 , the non-methane total hydrocarbon concentration of the purified gas in the oxygen cracking reactor is ≤4.6mg / m 3 , and the catalytic activity is not affected after the catalyst is washed by water.

[0065] Comparative Example 1

[0066] The landfill leachate to be treated is the same as in Example 1, and the landfill leachate sample is disposed by the process of aerobic nitrification-anoxic denitrification biochemical treatment and nanofiltration membrane separation. The daily treatment is 2 tons of leachate. After the aerobic nitrification-anoxic denitrification treatment, the ammonia nitrogen concentration of the leachate is reduced from 1950mg / L to 19.8mg / L, and the COD concentration is reduced from 990mg / L to 850mg / L; the leachate after biochemical treatment is treated by nanofiltration membrane, and the purified water COD is ≤100mg / L, reaching the landfill pollution control standard (GB16889-2008); however, the treatment process produces secondary pollution membrane concentrate, and the daily production reaches more than 600kg; the daily production of secondary pollution biochemical sludge in the anoxic denitrification process reaches more than 20kg. The treatment difficulty of secondary pollution will be much higher than that of the original landfill leachate.

[0067] Comparative Example 2

[0068] The landfill leachate to be treated is the same as in Example 1, and the leachate sample is disposed of by using the aerobic nitrification-anoxic denitrification biochemical treatment in series with the nanofiltration membrane separation and the mechanical vapor recompression (MVR) process, with a daily treatment of 2 tons of leachate. The mechanical vapor recompression (MVR) process is mainly used to treat the membrane concentrated liquid generated in the membrane separation stage; after the concentrated liquid is evaporated by the MVR process, the organic matter concentration in the water vapor generated in the evaporation process is ≤50 mg / m 3 ; During the operation of the device, due to the precipitation of calcium and magnesium ions, serious scaling phenomenon occurs in the MVR evaporator, and the thermal efficiency of the device decreases. After evaporation treatment, there are still more than 50 kg of MVR evaporation residual liquid in the concentrated liquid, which is also a kind of secondary pollution that is difficult to treat, and the above process still cannot achieve the ideal effect of full purification of the leachate.

Claims

1. A method for purifying aged refuse leachate by integrating separation and reaction, characterized in that The landfill leachate is pumped into the alkaline adjusting tank, stirred uniformly, and then softened by sodium hydroxide solution; the calcium and magnesium precipitates formed in the softening process are deposited at the bottom of the precipitate tank by gravity to realize solid-liquid separation, and the softened leachate is subjected to stripping by high-speed gas to remove free ammonia and volatile organic pollutants in the constant-temperature stripping tower; the kettle liquid in the stripping tower is treated by the nanofiltration system; The free ammonia, volatile organic pollutants, and concentrated liquid in the nanofiltration system are converted into inorganic small molecules by the catalytic reaction of the near-oxygen cracking, so as to obtain inorganic sodium / potassium mixed salt water resources without organic pollutants; The tower body temperature of the gas stripping tower ranges from 30 to 70 ℃, the gas-liquid ratio is 300-1500:1, the high-speed gas is air, and the gas speed is 50-280 m 3 / h. The recovery rate of the nanofiltration system is 75-95%, the working pressure is 0.5-2 MPa, and the separation membrane material in the nanofiltration system is polyamide fiber.

2. The method according to claim 1, characterized in that The method comprises the following steps: The pH of the alkaline is adjusted to 8-12, and the ammonia nitrogen concentration in the kettle liquid in the stripping tower after the stripping treatment is ≤10 mg / L.

3. The method according to claim 1 or 2, characterized in that The mass fraction of salt in the old landfill leachate is 2-5.5%; The COD concentration in the old landfill leachate is 500-5800 mg / L, and the ammonia nitrogen concentration is 1300-2200 mg / L; The hardness of the old landfill leachate is 650-1800 mg / L.

4. The method according to claim 1, wherein the method is characterized by The packing in the stripping tower is one or two of Raschig rings, Pall rings, theta rings, stepped rings, corrugated plate packings, wire mesh corrugated packings, and grid packings.

5. The method according to claim 1, wherein the method is characterized by The near-oxygen cracking catalyst is an acidic molecular sieve loaded with metal oxides, and the loading amount of the metal oxides is 10-35%.

6. The method according to claim 5, wherein the method is characterized by The metal oxide is one or two of vanadium oxide, copper oxide, cerium oxide, manganese oxide, and cobalt oxide; the acidic molecular sieve is Y-type. β One type of molecular sieve.

7. The method according to claim 1 or 2, wherein the method is characterized by The temperature of the oxygen cracking reactor is 400-500 ℃, and the space velocity is 0.5-5 h -1 .

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