A method for the preparation of a catalyst for the preparation of formaldehyde

Abstract

The application relates to a preparation method and application of a catalyst for preparing formaldehyde. The catalyst is prepared by a coprecipitation method, sodium sulfide inorganic matter and aromatic organic compounds are added, and an ultrasonic heating mode is adopted, so that the problem of deep oxidation reaction of the catalyst in the previous process method can be effectively solved, the activity and stability of the catalyst are improved, and the service life of the catalyst is prolonged.

Description

Technical Field

[0001] This invention relates to the field of catalyst preparation, and more specifically to a method for preparing a catalyst for the preparation of formaldehyde. Background Technology

[0002] Formaldehyde is an important basic organic chemical raw material, playing a crucial role in adjusting the future energy structure and developing the chemical industry. Currently, my country has become the world's largest producer and consumer of formaldehyde, with domestic demand exceeding 2800 × 10⁻⁶ tons by 2022. 4 ton.

[0003] Formaldehyde can be produced from raw materials such as methanol, dimethyl ether, and natural gas, with methanol-to-formaldehyde technology being the most widely used. The methanol-to-air oxidation method is further divided into the silver method and the iron-molybdenum method. Compared to the silver method, the iron-molybdenum method has a lower reaction temperature and higher formaldehyde concentration, offering advantages such as lower cost and higher yield. Currently, there are numerous publicly disclosed patents for formaldehyde production using iron-molybdenum catalysts.

[0004] For example, US4420421 describes the use of different raw materials, sodium molybdate, to achieve a methanol conversion rate of 93%–95% and a selectivity of 92%. Patent CN105457648B prepared a catalyst containing a large number of mesopores and a certain proportion of macropores through co-precipitation, which is beneficial to the mass and heat transfer of the catalyst and improves the catalyst activity. CN110893344B prepared an iron-molybdenum catalyst using metallic iron, organic acid and molybdic acid as raw materials through co-precipitation of by-product hydrogen. The catalyst achieved high-efficiency methanol conversion at 200–350℃, but its inlet methanol concentration was low and the actual formaldehyde space-time yield was low.

[0005] However, existing iron-molybdenum catalysts exhibit varying degrees of deactivation over time, affecting their activity and lifespan. The primary cause of deactivation is the loss of molybdenum, leading to reduced activity and accompanied by deep oxidation reactions that generate CO and CO2, thus decreasing catalyst selectivity. While existing technologies improve catalyst activity and selectivity by adding additives, they do not fundamentally address the catalyst lifespan issue. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing a catalyst for formaldehyde production. This method involves using ultrasonic heating to distort some of the octahedrons in the FeO6 octahedral lattice, creating octahedral defects and forming channels. Excess Mo at the interface between the Fe2(MoO4)3 and MoO3 phases forms MoO3, which embeds into the interstitial spaces of the Fe2(MoO4)3 catalyst lattice, leading to a certain degree of lattice distortion. Mo then enters the channels. 6+The combination of ions and oxygen vacancies on the defective octahedrons forms an octahedral structure, which increases the lattice defects of the catalyst and adjusts the cyclic oxidation and dispersibility of the catalyst surface, thus giving the catalyst better catalytic activity. At the same time, by introducing benzene / sodium acetate, the large π bond of the benzene ring forms a conjugated system with the catalyst octahedron. Secondly, sulfur can combine with some oxygen vacancies on the octahedrons, which to some extent inhibits the deep oxidation reaction of formaldehyde and improves the selectivity of the catalyst.

[0007] To solve the above technical problems and achieve the above-mentioned objectives, the present invention adopts the following technical solution:

[0008] A method for preparing a catalyst for the preparation of formaldehyde includes the following steps:

[0009] a) Add an aqueous solution containing molybdenum salt, sodium sulfide, iron-containing substances, cerium salt, nickel salt, and aromatic compounds to the reactor in a parallel stream and stir thoroughly.

[0010] b) Control the pH value between 1.0 and 3.0, preferably between 1.5 and 2.8, and control the temperature of the reactor between 50 and 100°C for co-precipitation;

[0011] c) After co-precipitation, the reaction solution is transferred to an ultrasonic generator for ultrasonic and heat treatment;

[0012] d) The ultrasonically treated reaction solution was aged at 50℃~100℃, then filtered and washed to obtain a filter cake;

[0013] e) Dry the filter cake;

[0014] f) The dried catalyst powder is shaped and calcined at 400℃~560℃ to obtain the shaped catalyst.

[0015] In the preparation method, in step a), the molybdenum salt includes one or more of ammonium polymolybdate, molybdenum trioxide, molybdic acid, and molybdenum disulfide, preferably ammonium polymolybdate;

[0016] The iron-containing substances include one or more of ferric chloride, ferric nitrate, iron oxide, and iron powder, preferably ferric chloride and / or ferric nitrate;

[0017] The cerium salt is preferably cerium nitrate, and the nickel salt is preferably nickel nitrate;

[0018] The aromatic compounds are sodium benzoate and sodium phenylacetate.

[0019] In step c), the frequency range of the ultrasonic waves used in the ultrasonic treatment is 30kHz to 50kHz, the heating temperature is controlled at 30 to 80℃, and the treatment time is 0.1 to 2h.

[0020] In step d), the aging time is 24–48 hours.

[0021] In step e), the filter cake is dried at 50℃~100℃ for 10~28 hours, and then dried at 100℃~150℃ for 15h~30h to obtain catalyst powder.

[0022] In step f), the roasting process lasts for 5–20 hours.

[0023] The forming methods include, but are not limited to, extrusion, tableting, and rolling; the shapes of the resulting formed catalysts include, but are not limited to, strips, cylinders, hollow cylinders, and spherical particles.

[0024] For example, a suitable extrusion molding method includes the following steps: adding a pore-forming agent and a binder to catalyst powder and then extruding it to obtain strip-shaped particles. The pore-forming agent is one or more of guar gum powder, cellulose, hydroxymethyl cellulose, and polyvinyl alcohol, and the amount of the pore-forming agent is 1% to 6% of the mass of the catalyst powder. The binder is one or more of water, glycerol, ethanol, graphite, stearic acid, magnesium stearate, and zinc stearate, preferably one or more of water, glycerol, graphite, and magnesium stearate, and the amount of the binder is 8% to 15% of the mass of the catalyst powder.

[0025] For example, a suitable tableting method includes the following steps: adding a pore-forming agent and a lubricant to the catalyst powder and then pressing it into tablets to obtain cylindrical or hollow cylindrical particles. The pore-forming agent is one or more of guar gum powder, cellulose, polyethylene, polypropylene, and polyvinyl chloride, preferably guar gum powder and / or cellulose, and the amount of the pore-forming agent is 1% to 5% of the catalyst powder mass. The lubricant is one or more of stearic acid, magnesium stearate, zinc stearate, and graphite, preferably one or more of magnesium stearate, zinc stearate, and graphite, and the amount of the lubricant is 0.1% to 1% of the catalyst powder mass.

[0026] For example, a suitable roll forming method includes the following steps: adding a pore-forming agent and a binder to catalyst powder, and then roll forming it with a spherical carrier. The pore-forming agent is one or more of guar gum powder, cellulose, polyvinyl alcohol, polyvinylpyrrolidone, starch, and pullulan, preferably one or more of guar gum powder, polyvinylpyrrolidone, and starch, and the amount of the pore-forming agent is 1% to 5% of the mass of the catalyst powder. The binder is one or more of water, ethanol, ethylene glycol, and glycerol, preferably one or more of water, ethanol, and glycerol, and the amount of the binder is 20% to 35% of the mass of the catalyst powder. The spherical carrier is preferably a porous alumina carrier with a diameter of 2.3 to 3.5 mm, and the amount used is 50% to 70% of the mass of the catalyst powder.

[0027] A catalyst for the preparation of formaldehyde, prepared by the above method, preferably wherein: the Mo / Fe molar ratio is 0.5–1.0:1; the S / Fe molar ratio is 0.1–2.0; the Ce / Fe molar ratio is 0.1–0.4; the Ni / Fe molar ratio is 0.1–0.5; and the aromatic compound / Fe molar ratio is 0.5–1.1.

[0028] A method for preparing aldehydes by alcohol oxidation, using the above-mentioned catalyst, wherein:

[0029] The reaction temperature is 320–420℃; the reaction pressure is 0.05–0.3 MPa absolute; and the gaseous feedstock volume hourly space velocity is 7000–12000 h⁻¹. -1 The gaseous raw materials include methanol, diluent gas, and O2, wherein the diluent gas is an inert gas, preferably N2. The molar ratio between the gases is 1:9 to 12:1 to 3.

[0030] The catalyst is pretreated before use; preferably, the pretreatment includes the following steps: the catalyst is heated at a volume hourly space velocity (VHSV) of 5000–10000 h⁻¹. -1 In an air or O2 / N2 mixed gas atmosphere, the temperature is raised to 200–400°C at a heating rate of 1–20°C / min and held for 30–180 min, then subjected to a volume hourly space velocity (VHSV) of 2000–3500 h⁻¹. -1 Purge with N2 for 1–180 min.

[0031] The beneficial effects of this invention are as follows:

[0032] The catalyst manufactured using the method of this invention can effectively solve the problem of deep oxidation reaction of catalysts in previous processes, while improving the activity and stability of the catalyst and extending its lifespan. Detailed Implementation

[0033] The technical solution of the present invention will be further described below through examples, but it is not limited thereto.

[0034] Unless otherwise specified, all equipment and raw materials used in this invention are commercially available.

[0035] Example 1

[0036] 0.07 mol ammonium heptamolybdate (chemical formula: (NH4)6Mo7O2·4H2O), 1 mol ferric chloride hexahydrate (chemical formula: FeCl3·6H2O), 1 mol sodium sulfide (chemical formula: Na2S), 0.3 mol nickel nitrate (chemical formula: Ni(NO3)3), 0.1 mol cerium nitrate (chemical formula: Ce(NO3)3), and 0.8 mol sodium phenylacetate were dissolved in 1000 g of deionized water, stirred thoroughly, and then added to the reaction vessel. The solution temperature in the vessel was maintained at 90 °C, and the pH was adjusted to 2.0 for co-precipitation.

[0037] The reaction solution was ultrasonically treated (Merritek Technology, model UC-6200, 40kHz, 30℃) for 1.5 hours. After ultrasonication, it was kept at 90℃ and stirred for 28 hours for aging. The mixture was filtered and washed, and the filter cake was dried at 90℃ for 24 hours, followed by drying at 120℃ for 20 hours. After drying, a blocky solid was obtained, which was crushed to obtain particles of 30-60 mesh.

[0038] Take 50g of 30-60 mesh particles, add 2.5g of pore-forming agent guar gum powder and 0.5g of lubricant magnesium stearate, mix evenly, and form into hollow cylindrical particles using a tablet press. Calcine the formed particles at 420℃ for 5 hours to obtain the catalyst.

[0039] 25g of catalyst was loaded into a 50cm long reactor, with the reaction tube being a Ф25mm stainless steel tube. The catalyst pretreatment process was as follows: air was first introduced at a volume hourly space velocity (VHSV) of 8000h. -1 The reaction tube temperature was heated from room temperature to 250°C at a rate of 5°C / min and held for 120 min, then purged with nitrogen for 180 min at a volume hourly space velocity (VHSV) of 2000 h⁻¹. -1 .

[0040] After catalyst pretreatment, the mixture was subjected to a methanol:oxygen:nitrogen:water ratio of 1:1.3:10:0.13 (molar ratio) and a volume hourly space velocity of 10000 h⁻¹. -1 An oxidation reaction was carried out for 100 hours under standard conditions, at 380℃ and normal pressure. The selectivity for formaldehyde was 95.5%, and the conversion rate of methanol was 97.8%.

[0041] Example 2

[0042] 0.11 mol ammonium heptamolybdate (chemical formula: (NH4)6Mo7O2·4H2O), 1 mol ferric chloride hexahydrate (chemical formula: FeCl3·6H2O), 2 mol sodium sulfide (chemical formula: Na2S), 0.5 mol nickel nitrate (chemical formula: Ni(NO3)3), 0.2 mol cerium nitrate (chemical formula: Ce(NO3)3), and 1.1 mol sodium phenylacetate were dissolved in 1000 g of deionized water, stirred thoroughly, and added to the reaction vessel. The solution temperature in the vessel was maintained at 90℃, and the pH was adjusted to 2.0 for co-precipitation.

[0043] The reaction solution was ultrasonically treated for 1.5 hours (Merritek Technology, model UC-6200, 40kHz, 30℃), and then aged at 90℃ for 28 hours with stirring after ultrasonication. The mixture was filtered and washed, and the filter cake was dried at 90℃ for 24 hours, followed by drying at 120℃ for 20 hours. After drying, a blocky solid was obtained, which was then crushed to obtain particles of 30–60 mesh.

[0044] Take 50g of 30-60 mesh particles, add 2.5g of pore-forming agent guar gum powder and 0.5g of lubricant magnesium stearate, mix evenly, and form into hollow cylindrical particles using a tablet press. Calcine the formed particles at 420℃ for 5 hours to obtain the catalyst.

[0045] 25g of catalyst was loaded into a 50cm long reactor, with the reaction tube being a Ф25mm stainless steel tube. The catalyst pretreatment process was as follows: air was first introduced at a volume hourly space velocity (VHSV) of 8000h. -1 The reaction tube temperature was heated from room temperature to 250°C at a rate of 5°C / min and held for 120 min, then purged with nitrogen for 180 min at a volume hourly space velocity (VHSV) of 3000 h⁻¹. -1 .

[0046] After catalyst pretreatment, the mixture was subjected to a methanol:oxygen:nitrogen:water ratio of 1:1.3:10:0.13 (molar ratio) and a volume hourly space velocity of 10000 h⁻¹. -1 An oxidation reaction was carried out for 100 hours under standard conditions, at 380℃ and normal pressure. The selectivity for formaldehyde was 95.0%, and the conversion rate of methanol was 98.8%.

[0047] Example 3

[0048] 0.14 mol ammonium heptamolybdate (chemical formula: (NH4)6Mo7O2·4H2O), 1 mol ferric chloride hexahydrate (chemical formula: FeCl3·6H2O), 0.1 mol sodium sulfide (chemical formula: Na2S), 0.1 mol nickel nitrate (chemical formula: Ni(NO3)3), 0.4 mol cerium nitrate (chemical formula: Ce(NO3)3), and 0.5 mol sodium phenylacetate were dissolved in 1000 g of deionized water, stirred thoroughly, and then added to the reaction vessel. The solution temperature in the vessel was maintained at 90℃, and the pH was adjusted to 2.0 for co-precipitation.

[0049] The reaction solution was ultrasonically treated for 1.5 hours (Merritek Technology, model UC-6200, 40kHz, 30℃), and then aged at 90℃ for 28 hours with stirring after ultrasonication. The mixture was filtered and washed, and the filter cake was dried at 90℃ for 24 hours, followed by drying at 120℃ for 20 hours. After drying, a blocky solid was obtained, which was then crushed to obtain particles of 30–60 mesh.

[0050] Take 50g of 30-60 mesh particles, add 2.5g of pore-forming agent guar gum powder and 0.5g of lubricant magnesium stearate, mix evenly, and form into hollow cylindrical particles using a tablet press. Calcine the formed particles at 420℃ for 5 hours to obtain the catalyst.

[0051] 25g of catalyst was loaded into a 50cm long reactor, with the reaction tube being a Ф25mm stainless steel tube. The catalyst pretreatment process was as follows: air was first introduced at a volume hourly space velocity (VHSV) of 8000h. -1 The reaction tube temperature was heated from room temperature to 250°C at a rate of 5°C / min and held for 120 min, then purged with nitrogen for 180 min at a volume hourly space velocity (VHSV) of 2000 h⁻¹. -1 .

[0052] After catalyst pretreatment, the mixture was subjected to a methanol:oxygen:nitrogen:water ratio of 1:1.3:10:0.13 (molar ratio) and a volume hourly space velocity of 10000 h⁻¹. -1 An oxidation reaction was carried out for 100 hours under standard conditions, at 380℃ and normal pressure. The selectivity for formaldehyde was 94.5%, and the conversion rate of methanol was 98.1%.

[0053] Comparative Example 1

[0054] 0.07 mol ammonium heptamolybdate (chemical formula (NH4)6Mo7O2·4H2O), 1 mol ferric chloride hexahydrate (chemical formula FeCl3·6H2O), 0.3 mol nickel nitrate (chemical formula Ni(NO3)3), and 0.1 mol cerium nitrate (chemical formula Ce(NO3)3) were dissolved in 1000 g of deionized water, stirred thoroughly, and then fed into a reaction vessel. The solution temperature in the vessel was maintained at 90℃, and the pH was adjusted to 2.0 for co-precipitation. The mixture was then aged at 90℃ with stirring for 28 h. After filtration and washing, the filter cake was dried at 90℃ for 24 h, and then dried at 120℃ for 20 h. The dried product was a blocky solid, which was crushed to obtain 30–60 mesh particles. 50 g of these 30–60 mesh particles were taken, and 2.5 g of pore-forming agent guar gum powder and 0.5 g of lubricant magnesium stearate were added. The mixture was thoroughly mixed and then pressed into hollow cylindrical particles using a tablet press. The shaped particles were calcined at 420℃ for 5 hours to obtain the catalyst.

[0055] The oxidation reaction was carried out for 100 hours using the same method as in Example 1. The selectivity for formaldehyde was 90.5%, and the conversion rate of methanol was 92.8%.

[0056] Comparative Example 2

[0057] 0.07 mol ammonium heptamolybdate (chemical formula: (NH4)6Mo7O2·4H2O), 1 mol ferric chloride hexahydrate (chemical formula: FeCl3·6H2O), 0.3 mol nickel nitrate (chemical formula: Ni(NO3)3), and 0.1 mol cerium nitrate (chemical formula: Ce(NO3)3) were dissolved in 1000 g of deionized water, stirred thoroughly, and then added to the reaction vessel. The solution temperature in the vessel was maintained at 90 °C, and the pH was adjusted to 2.0 to carry out co-precipitation.

[0058] The reaction solution was ultrasonically treated for 1.5 hours (Merritek Technology, model UC-6200, 40kHz, 30℃), and then aged at 90℃ for 28 hours with stirring after ultrasonication. The mixture was filtered and washed, and the filter cake was dried at 90℃ for 24 hours, followed by drying at 120℃ for 20 hours. After drying, a blocky solid was obtained, which was then crushed to obtain particles of 30–60 mesh.

[0059] Take 50g of 30-60 mesh particles, add 2.5g of pore-forming agent guar gum powder and 0.5g of lubricant magnesium stearate, mix evenly, and form into hollow cylindrical particles using a tablet press. Calcine the formed particles at 420℃ for 5 hours to obtain the catalyst.

[0060] The oxidation reaction was carried out for 100 hours using the same method as in Example 1. The selectivity for formaldehyde was 92.5%, and the conversion rate of methanol was 93.8%.

[0061] Comparative Example 3

[0062] 0.07 mol ammonium heptamolybdate (chemical formula (NH4)6Mo7O2·4H2O), 1 mol ferric chloride hexahydrate (chemical formula FeCl3·6H2O), 1 mol sodium sulfide (chemical formula Na2S), 0.3 mol nickel nitrate (chemical formula Ni(NO3)3), 0.1 mol cerium nitrate (chemical formula Ce(NO3)3), and 0.8 mol sodium phenylacetate were dissolved in 1000 g of deionized water, stirred thoroughly, and then fed into a reaction vessel. The solution temperature in the vessel was maintained at 90 °C, and the pH was adjusted to 2.0 for co-precipitation. The mixture was then aged at 90 °C with stirring for 28 h. After filtration and washing, the filter cake was dried at 90 °C for 24 h and then at 120 °C for 20 h. The dried product was a blocky solid, which was crushed to obtain particles of 30–60 mesh. Take 50g of 30-60 mesh particles, add 2.5g of pore-forming agent guar gum powder and 0.5g of lubricant magnesium stearate, mix evenly, and form into hollow cylindrical particles using a tablet press. Calcine the formed particles at 420℃ for 5 hours to obtain the catalyst.

[0063] The oxidation reaction was carried out for 100 hours using the same method as in Example 1. The selectivity for formaldehyde was 91.5%, and the conversion rate of methanol was 93.8%.

[0064] Comparative Example 4

[0065] 0.07 mol ammonium heptamolybdate (chemical formula: (NH4)6Mo7O2·4H2O), 1 mol ferric chloride hexahydrate (chemical formula: FeCl3·6H2O), 1 mol sodium sulfide (chemical formula: Na2S), 0.3 mol nickel nitrate (chemical formula: Ni(NO3)3), and 0.1 mol cerium nitrate (chemical formula: Ce(NO3)3) were dissolved in 1000 g of deionized water, stirred thoroughly, and then added to the reaction vessel. The solution temperature in the vessel was maintained at 90 °C, and the pH was adjusted to 2.0 to carry out co-precipitation.

[0066] The reaction solution was ultrasonically treated for 1.5 hours (Merritek Technology, model UC-6200, 40kHz, 30℃), and then aged at 90℃ for 28 hours with stirring after ultrasonication. The mixture was filtered and washed, and the filter cake was dried at 90℃ for 24 hours, followed by drying at 120℃ for 20 hours. After drying, a blocky solid was obtained, which was then crushed to obtain particles of 30–60 mesh.

[0067] Take 50g of 30-60 mesh particles, add 2.5g of pore-forming agent guar gum powder and 0.5g of lubricant magnesium stearate, mix evenly, and form into hollow cylindrical particles using a tablet press. Calcine the formed particles at 420℃ for 5 hours to obtain the catalyst.

[0068] The oxidation reaction was carried out for 100 hours using the same method as in Example 1. The selectivity for formaldehyde was 92.1%, and the conversion rate of methanol was 93.6%.

[0069] A comparison of Example 1 and Comparative Examples 1, 2, 3, and 4 shows that by adding sodium sulfide inorganic matter and aromatic organic compounds and using ultrasonic heating, the problem of deep oxidation reaction of catalysts in previous processes can be effectively solved, while improving the activity and stability of the catalyst and extending its lifespan.

Claims

1. A method for preparing a catalyst for preparing formaldehyde, comprising the following steps: a) preparing a reaction solution by mixing a molybdenum salt, an iron-containing substance, a cerium salt, a nickel salt, and an aromatic compound; b) controlling the reaction conditions to co-precipitate; c) treating the reaction solution after co-precipitation by ultrasonic and heating; d) aging the reaction solution after ultrasonic treatment, then filtering and washing to obtain a filter cake; e) drying the filter cake; f) performing a molding treatment, and calcining to obtain a shaped catalyst; wherein: the aromatic compound is sodium benzoate or sodium phenylacetate; the molar ratio of Mo / Fe is 0.5-1.0:1; the molar ratio of S / Fe is 0.1-2.0; the molar ratio of Ce / Fe is 0.1-0.4; the molar ratio of Ni / Fe is 0.1-0.5; and the molar ratio of aromatic compound / Fe is 0.5-1.

1. a) adding a water solution containing molybdenum salt, sodium sulfide, iron-containing substance, cerium salt, nickel salt, aromatic compound into a reaction kettle for sufficient stirring; wherein, 2. The method according to claim 1, wherein in step a), the molybdenum salt comprises one or more of ammonium polymolybdate, molybdenum trioxide, molybdic acid, and molybdenum disulfide; the iron-containing substance comprises one or more of ferric chloride, ferric nitrate, iron oxide, and iron powder; the cerium salt is cerium nitrate, and the nickel salt is nickel nitrate.

3. The method according to claim 1, wherein in step b), the pH value is 1.0-3.0, and the temperature is 50-100°C.

4. The method according to claim 1, wherein in step c), the ultrasonic frequency range for ultrasonic treatment is 30-50 kHz, the heating temperature is 30-80°C, and the treatment time is 0.1-2 h.

5. The method according to claim 1, wherein in step d), the aging is performed at 50-100°C for 24-48 h.

6. The method according to claim 1, wherein in step e), the filter cake is dried at 50-100°C for 10-28 h, and then dried at 100-150°C for 15-30 h to obtain a catalyst powder.

7. The method according to claim 1, wherein in step f), the calcining is performed at 400-560°C for 5-20 h.

8. A catalyst for preparing formaldehyde obtained by the method according to any one of claims 1-7.

9. A method for preparing an aldehyde by alcohol oxidation, using the catalyst obtained by the method according to any one of claims 1-7 or the catalyst according to claim 8, wherein: the dilution gas is N2; the molar ratio of methanol, dilution gas, and O2 is 1:9-12:1-3. ​ ​ ​ ​ ​ ​ ​ ​ ​ The reaction temperature is 320-420℃, the reaction pressure is 0.05-0.3 MPa, and the volume space velocity of the gaseous raw material is 7000-12000 h -1 , wherein the gaseous raw material comprises methanol, dilution gas and O2.

10. The method of claim 9, wherein, ​ 11. The method of claim 9, wherein, ​