Method, system and application of methane oxidative coupling to olefins

Abstract

The present invention relates to the field of catalysis and discloses a method, system, and application thereof for oxidative coupling of methane to olefins. The method comprises: (1) premixing methane, oxygen, and an inert gas, and heating the premixed mixed gas with water vapor; (2) contacting the heated mixed gas with a catalyst for a catalytic reaction; (3) contacting a gas product obtained by the catalytic reaction with an absorbent to absorb methane and water vapor in the gas product, and returning the material containing methane, water vapor, and absorbent to step (1) for regeneration to release methane and water vapor. By reducing the premixing time and extending the methane autoignition induction time, the residence time of methane in the reactor is increased, which can reduce the risk of explosion, increase the reaction time of methane, and improve the methane conversion rate.

Description

Technical Field

[0001] The present invention relates to the field of catalysis, and in particular to a method and system for preparing olefins through oxidative coupling of methane and applications thereof. Background Art

[0002] Methane, the main component of natural gas and rock gas, has the advantages of high calorific value, low pollution, and low price. With the scarcity of oil resources, the utilization of natural gas is expected to replace oil resources and become a source of new raw materials for the chemical industry.

[0003] Currently, the most mature process in natural gas chemical industry is the syngas process, which first oxidizes methane into carbon monoxide and hydrogen, and then synthesizes chemical products such as methanol, ammonia, dimethyl ether, and synthetic alcohols from the carbon monoxide and hydrogen. There are three main pathways for converting methane to syngas: steam reforming, carbon dioxide reforming, and partial oxidation. Because ethylene is an important chemical feedstock with high demand and output value, direct methane oxidation to olefins has attracted considerable attention from engineers. However, the methane oxidation reaction requires high temperatures and pressures, placing stringent requirements on the residence time of the methane and oxygen mixture in the reactor. This is primarily because the autoignition induction time of a methane-oxygen mixture is short under high temperatures and pressures. If the residence time of the mixture in the reactor is too long, exceeding the autoignition induction time, there is a risk of explosion.

[0004] In recent years, researchers have conducted extensive research on the methane-to-olefins process. After searching, CN107108401A discloses a method for producing ethylene and synthesis gas by combining methane oxidative coupling with methane dry reforming reaction. The specific process of this invention is to introduce a raw gas containing methane and oxygen into a methane oxidative coupling reactor, catalytically react methane and oxygen to produce CO, CO2, H2O and C2H4, etc. The gas after the reaction is cooled and separated by a separation unit to separate C2H4 to obtain a mixed gas mainly containing CH4, CO, CO2 and H2. The mixed gas is preheated and introduced into a dry reforming reactor to catalytically convert CO2 and CH4 into synthesis gas. This invention uses the heat generated by the oxidative coupling of methane to drive the endothermic dry reforming of the methane reaction. However, this method places the reaction process of methane oxidative coupling to ethylene and the reaction process of methane reforming to synthesis gas in the same reaction vessel. At the same time, it also supplements the segmented alternating distribution of catalytic materials and inert materials in the reactor. On the one hand, the reaction products are mixed together and difficult to separate. On the other hand, the changes in residence time and auto-ignition induction time are not taken into account, thus posing a risk of combustion and explosion.

[0005] CN102093157A provides a combined process for directly converting methane-containing feedstock into ethylene and simultaneously producing synthesis gas. This invention overcomes the limitations of previous direct methane-to-ethylene production methods, which focused on a single product. In addition to converting methane into ethylene at high yields, it also considers further utilization of methane, namely, converting it into synthesis gas at high yields. However, this invention utilizes a methane wet reforming process to produce synthesis gas, which consumes large amounts of water and heat, and wastes the reaction heat released by the oxidative coupling of methane. Furthermore, the risk of explosion of the methane mixture is not considered.

[0006] Since oxidative coupling is an exothermic reaction, it is easy to cause methane and oxygen to explode, resulting in casualties. However, the current existing technology does not take into account the risk of methane explosion in oxidative coupling reactors. Summary of the Invention

[0007] The purpose of the present invention is to overcome the problem of methane residence time in the reactor being too long and causing explosion in the prior art, and to provide a method, system and application of methane oxidative coupling to olefins.

[0008] The inventors of the present invention unexpectedly discovered during experiments that by premixing and heating methane, oxygen, water vapor and an inert gas before carrying out a catalytic reaction, the water vapor can effectively prevent the safety valve from releasing or exploding due to excessive temperature or pressure after the methane explodes during oxidative coupling. In addition, by utilizing an absorbent to absorb the water and unreacted methane produced in the catalytic reaction of oxidative coupling, and then returning the material containing methane, water vapor and absorbent to the premixing and heating step for regeneration to release methane and water vapor, the resource utilization of methane and water vapor can be achieved.

[0009] In order to achieve the above object, the present invention provides a method for preparing olefins by oxidative coupling of methane, which comprises:

[0010] (1) premixing methane, oxygen and inert gas, and heating the premixed gas with water vapor;

[0011] (2) contacting the heated mixed gas with a catalyst to perform a catalytic reaction;

[0012] (3) contacting the gas product obtained from the catalytic reaction with an absorbent to absorb methane and water vapor in the gas product, and returning the material containing methane, water vapor and absorbent to step (1) for regeneration to release methane and water vapor.

[0013] A second aspect of the present invention provides a system for producing olefins by oxidative coupling of methane, the system comprising:

[0014] a premixing device, the premixing device being provided with a methane inlet, an oxygen inlet, an inert gas inlet, a first absorbent inlet, a first absorbent outlet, a water vapor inlet, and a mixed gas outlet, the premixing device being capable of premixing the methane, oxygen, and inert gas introduced therein, and heating the premixed mixed gas by the water vapor introduced therein;

[0015] A reaction device, wherein the reaction device is filled with a catalyst and is provided with a mixed gas inlet and a gas product outlet, wherein the mixed gas outlet is connected to the mixed gas inlet to feed the heated mixed gas into the reaction device;

[0016] An absorption device is provided with a gas product inlet, an olefin outlet and a second absorbent outlet, wherein the gas product outlet is connected to the gas product inlet, and the second absorbent outlet is connected to the first absorbent inlet.

[0017] The present invention provides a system for producing olefins by oxidative coupling of methane, which includes a premixing device, a reaction device, and an absorption device. Methane, oxygen, and an inert gas in the premixing device are premixed and heated using water vapor before entering the reaction device for a catalytic reaction. A gas product obtained by the catalytic reaction contacts an absorbent in the absorption device to absorb methane and water vapor in the gas product. The material containing methane, water vapor, and the absorbent is returned to the premixing device for regeneration to release methane and water vapor. Through the above process, the recycling of methane and water vapor can be achieved, preventing the safety valve from discharging or explosion due to excessive temperature or excessive pressure after the oxidative coupling of methane. The reaction time of methane is increased by reducing the premixing time and extending the methane spontaneous combustion induction time, thereby improving the methane conversion rate.

[0018] The third aspect of the present invention provides use of the above system in preparing olefins. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 Schematic diagram of the system structure of methane oxidative coupling to olefins according to one embodiment of the present invention.

[0020] Description of Reference Numerals

[0021] 100 premixing device, 101 methane inlet, 102 oxygen inlet, 103 inert gas inlet, 104 first absorbent inlet, 105 first absorbent outlet, 106 mixed gas outlet, 107 water vapor inlet, 200 reaction device, 201 mixed gas inlet, 202 gas product outlet, 203 heat exchange equipment, 204 catalyst, 300 absorption device, 301 gas product inlet, 302 olefin outlet, 303 second absorbent outlet, 304 second absorbent inlet, 11 circulating coolant, 12 fresh absorbent. DETAILED DESCRIPTION

[0022] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to form one or more new numerical ranges, and these numerical ranges should be considered to be specifically disclosed in the present invention.

[0023] In one aspect, the present invention provides a method for preparing olefins by oxidative coupling of methane, comprising:

[0024] (1) premixing methane, oxygen and inert gas, and heating the premixed gas with water vapor;

[0025] (2) contacting the heated mixed gas with a catalyst to perform a catalytic reaction;

[0026] (3) contacting the gas product obtained from the catalytic reaction with an absorbent to absorb methane and water vapor in the gas product, and returning the material containing methane, water vapor and absorbent to step (1) for regeneration to release methane and water vapor.

[0027] In some embodiments of the present invention, in order to achieve energy reuse and thus reduce energy consumption, the method may further include: transporting the heat generated by the catalytic reaction to the heating step using water vapor as a heat carrier to heat the mixed gas.

[0028] In the present invention, the type of catalyst is not limited. A catalyst containing sodium tungstate and manganese oxide as active components and a silica carrier as support is preferred. For example, a weight percent Na2WO4 - b weight percent Mn / SiO2 can be used, where a is the weight percent of sodium tungstate calculated as W, ranging from 1 to 10, and b is the weight percent of manganese oxide calculated as Mn, ranging from 1 to 10.

[0029] According to a preferred embodiment of the present invention, the preparation method of the catalyst Na2WO4-Mn / SiO2 is as follows:

[0030] Na2WO4-Mn / SiO2 is prepared by the sol-gel method. Different dosages are calculated according to the composition of the catalyst. Under stirring conditions, Na2WO4, a manganese precursor, and a silicon source are mixed at 50-70°C, and then a solvent (for example, a volume ratio of ethanol to water of 1-2:1) and concentrated nitric acid are added. After reacting for 0.5-5 hours, the mixture is aged for 10-12 hours, dried at 110-120°C for 10-12 hours, calcined at 500-550°C for 3-4 hours, and then calcined at 800-850°C for 3-4 hours. The manganese precursor can be a water-soluble manganese salt. Preferably, the manganese precursor is manganese nitrate. The type of the silicon source is not limited. Preferably, the silicon source is ethyl orthosilicate.

[0031] In some embodiments of the present invention, in order to achieve recycling of the absorbent, the method further comprises: using the regenerated absorbent in step (3) to contact with the gas product to absorb methane and water vapor in the gas product.

[0032] In some embodiments of the present invention, to reduce the residence time of methane in the reactor and prevent explosion, preferably, the heating conditions are such that the temperature of the heated mixed gas is 100-350°C lower than the temperature of the catalytic reaction. More preferably, the heating conditions are such that the temperature of the heated mixed gas is 450-500°C.

[0033] In some embodiments of the present invention, the inert gas can be various existing gases or gas mixtures that do not react with raw materials and products. For example, it can be at least one of the zero-group element gas and nitrogen. From an economic point of view, the inert gas is preferably nitrogen.

[0034] In some embodiments of the present invention, the absorbent has the advantages of low saturated vapor pressure, low volatility, and the ability to absorb methane, and is preferably an ionic liquid. The anion of the ionic liquid has a structural formula as shown in Formula I, and the cation has a structural formula as shown in Formula II or Formula III:

[0035]

[0036] Wherein, in formula II, R1 and R2 are the same or different and are independently selected from hydrogen or a C1-C12 aliphatic hydrocarbon group, for example, methyl, ethyl, n-propyl or n-butyl.

[0037] In formula III, R1, R2, R3 and R4 are the same or different and are independently selected from hydrogen or a C1-C12 aliphatic group, for example, methyl, ethyl, n-propyl or n-butyl.

[0038] In some embodiments of the present invention, the absorbent is preferably at least one of 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, methyltributylphosphine bis(trifluoromethanesulfonyl)imide and 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide.

[0039] In some embodiments of the present invention, the volume flow ratio of the methane to the oxygen is preferably 1:0.25-4. The volume flow ratio of the water vapor to the inert gas is preferably 1-5:1. After the water vapor is introduced into the mixed gas, the volume percentage of the methane is preferably 20-80% by volume. In some embodiments of the present invention, the conditions for the catalytic reaction include: the catalytic reaction temperature is preferably 600-850°C. The catalytic reaction pressure is preferably 0.5-5 MPa. The reaction gas hourly space velocity based on methane and oxygen is preferably 100-200 mL / (g·h). The catalytic reaction reaction time is preferably 80-100 ms.

[0040] In some embodiments of the present invention, the absorption conditions include: the absorption temperature is preferably 50-100° C., more preferably 55-80° C. The absorption pressure is preferably 1-5 MPa, more preferably 1-2 MPa.

[0041] In the present invention, residence time refers to the time it takes for a fluid element to travel from the inlet to the outlet of the reactor.

[0042] In the present invention, the auto-ignition induction time refers to the time after the combustible gas is mixed with oxygen, and even if the temperature exceeds the auto-ignition point, it will not burn immediately, but will burn after a period of time. This period of time is called the auto-ignition induction time and is one of the important parameters of the fuel.

[0043] A second aspect of the present invention provides a system for producing olefins by oxidative coupling of methane, the system comprising:

[0044] a premixing device, the premixing device being provided with a methane inlet, an oxygen inlet, an inert gas inlet, a first absorbent inlet, a first absorbent outlet, a water vapor inlet, and a mixed gas outlet, the premixing device being capable of premixing the methane, oxygen, and inert gas introduced therein, and heating the premixed mixed gas by the water vapor introduced therein;

[0045] A reaction device, wherein the reaction device is filled with a catalyst and is provided with a mixed gas inlet and a gas product outlet, wherein the mixed gas outlet is connected to the mixed gas inlet to feed the heated mixed gas into the reaction device;

[0046] An absorption device is provided with a gas product inlet, an olefin outlet and a second absorbent outlet, wherein the gas product outlet is connected to the gas product inlet, and the second absorbent outlet is connected to the first absorbent inlet.

[0047] In some embodiments of the present invention, in order to achieve energy reuse and thus reduce energy consumption, the reaction device is further provided with a heat exchange device, which can transport the heat generated in the reaction device to the premixing device using water vapor as a heat carrier.

[0048] In the present invention, the specific structure of the heat exchange device is not limited. It can be a coil or a serpentine arranged around the inner wall of the reaction device, as long as it can transport the heat in the reaction device to the premixing device using water vapor as the heat carrier.

[0049] In some embodiments of the present invention, in order to achieve recycling of the absorbent, the absorption device is further provided with a second absorbent inlet, wherein the second absorbent inlet is connected to the first absorbent outlet.

[0050] In the present invention, the second absorbent inlet can be used to input fresh absorbent or absorbent recycled from the premixing device into the absorption device.

[0051] In some embodiments of the present invention, the inert gas is preferably at least one of a Group 0 element gas and nitrogen.

[0052] In some embodiments of the present invention, the method for oxidative coupling of methane to olefins is carried out in the above system.

[0053] According to a preferred embodiment of the present invention, Figure 1Methane, oxygen, and inert gas are introduced into the premixing device 100 through the methane inlet 101, the oxygen inlet 102, and the inert gas inlet 103, respectively, for premixing. Water vapor is discharged from the heat exchange device 203 and introduced into the premixing device 100 through the water vapor inlet 107 to heat the mixed gas. The heated mixed gas is discharged from the mixed gas outlet 106 and then enters the reaction device 200 through the mixed gas inlet 201, where it contacts the catalyst 204 for a catalytic reaction. The gas product obtained by the catalytic reaction enters the absorption device 300 through the gas product inlet 301, where it contacts the absorbent to absorb the methane and water vapor in the gas product. The separated olefin product is discharged from the absorption device 300 through the olefin outlet 302, and the material containing methane, water vapor, and absorbent is discharged from the absorption device 300 through the second absorbent outlet 303 and returns to the premixing device 100 through the first absorbent inlet 104 for regeneration to release methane and water vapor. In addition, the reaction device 200 is also provided with a heat exchange device 203, into which high-pressure steam (temperature 400-550°C, pressure 11.8-14.7 MPa) is introduced. This high-pressure steam can heat the reaction device, extract the heat generated in the reaction device 200, and transfer it to the high-pressure steam in the heat exchange device. After the steam is discharged from the heat exchange device 203, it is transported to the premixing device 100 through the steam inlet 107, thereby heating the mixed gas in the premixing device 100. The absorption device 300 is also provided with a second absorbent inlet 304. After the methane and water vapor are released, the absorbent is discharged from the premixing device 100 through the second absorbent inlet 304 and circulated to the absorption device 300 through the second absorbent inlet 304. Among them, fresh absorbent 12 or absorbent 11 recycled from the premixing device can be introduced into the absorption device 300 through the second absorbent inlet 304.

[0054] In this invention, the inert gas serves to prolong the methane-oxygen autoignition induction time, while the introduction of water vapor prevents the occurrence of methane explosions during oxidative coupling, which could lead to safety valve release or explosions due to excessive temperatures or pressures. This extended autoignition induction time also increases the methane's residence time in the catalyst bed, further increasing the reaction time and boosting the methane conversion rate.

[0055] In the present invention, the catalyst bed height can be set according to the feed rate, reaction temperature and pressure, and residence time. The setting principle is that the residence time of the methane-oxygen mixture is less than the autoignition induction time at the temperature and pressure.

[0056] The third aspect of the present invention provides use of the above system in preparing olefins.

[0057] In the present invention, the unit "mL / (g·h)" refers to the total amount of methane and oxygen gas (mL) used per 1 g of the catalyst in 1 hour.

[0058] In the present invention, pressure refers to gauge pressure.

[0059] In the present invention, C2 refers to at least one of ethylene, ethane and acetylene.

[0060] The present invention will be described in detail below through examples. In the examples and comparative examples, all reagents used were commercially available analytically pure reagents.

[0061] Preparation Example 1

[0062] Preparation of catalyst 5 wt% Na2WO4-2 wt% Mn / SiO2

[0063] Measure 100 mL of ethyl orthosilicate, heat it to 60°C in an oil bath with stirring, add 5 g of Na2WO4 and 2 g of Mn(NO3)2 to the above-mentioned ethyl orthosilicate respectively, then add 20 mL of ethanol (so that the volume ratio of ethanol to water is 2:1) and 10 mL of 20 (volume)% concentrated nitric acid, react for 2 hours, continue aging for 12 hours, then dry at 120°C for 12 hours, calcine at 550°C for 4 hours, and then calcine at 850°C for 4 hours.

[0064] Example 1

[0065] Methane, oxygen, and inert gas were introduced into the buffer tank 100 through the methane inlet 101, oxygen inlet 102, and inert gas inlet 103, respectively, for premixing. The methane feed rate was 100 L / h, the oxygen feed rate was 50 L / h, and the inert gas feed rate was 150 L / h. Water vapor was discharged from the coil 203 and introduced into the premixing device 100 through the water vapor inlet 107 to heat the mixed gas. The water vapor feed rate was 200 L / h, and the volume percentage of methane was 20%. The heated mixed gas had a temperature of 500°C. The heated mixed gas was discharged from the mixed gas outlet 106 and then entered the reaction device 200 through the mixed gas inlet 201. It then contacted the catalyst 204 for a catalytic reaction. The catalyst was the catalyst obtained in Preparation Example 1, with a catalyst loading of 10 g and a loading height of 0.5 m. The catalytic reaction temperature was 750°C. The pressure is 0.5 MPa, the hourly space velocity of the reaction gas, calculated based on methane and oxygen, is 150 mL / (g·h), the reaction time is 80 ms, and the residence time of the premixed gas in the catalyst bed is 100 ms. The gaseous product resulting from the catalytic reaction enters the absorption device 300 through the gaseous product inlet 301, where it comes into contact with the absorbent 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt to absorb the methane and water vapor in the gaseous product. The absorption temperature is 40°C and the pressure is 1 MPa. The separated olefin product exits the absorption device 300 through the olefin outlet 302, and the material containing methane, water vapor, and absorbent exits the absorption device 300 through the second absorbent outlet 303 and returns to the premixing device 100 through the first absorbent inlet 104 for regeneration to release methane and water vapor. In addition, high-pressure steam (temperature of 500°C, pressure of 14.5 MPa) is introduced into the heat exchanger 203. This high-pressure steam can heat the reaction unit and transfer the heat generated in the reaction unit 200 to the high-pressure steam in the heat exchanger. After the steam is discharged from the heat exchanger 203, it is transported to the premixing unit 100 through the steam inlet 107, thereby heating the mixed gas in the premixing unit 100. The absorption unit 300 is also provided with a second absorbent inlet 304. The absorbent containing the released methane and water vapor is discharged from the premixing unit 100 through the second absorbent inlet 304 and circulated to the absorption unit 300 through the second absorbent inlet 304. After the reaction is completed, the reaction product is collected from the olefin outlet 302.

[0066] Example 2

[0067] The reaction of oxidative coupling of methane to olefins was carried out according to the method of Example 1, except that the absorbent was methyltributylphosphine bis(trifluoromethanesulfonyl)imide salt.

[0068] Example 3

[0069] The reaction of oxidative coupling of methane to olefins was carried out according to the method of Example 1, except that the absorbent was 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide.

[0070] Example 4

[0071] The reaction of oxidative coupling of methane to olefins was carried out according to the method of Example 1, except that the feed flow rate of methane was 150 L / h and the feed flow rate of oxygen was 50 L / h.

[0072] Example 5

[0073] The reaction of oxidative coupling of methane to olefins was carried out according to the method of Example 1, except that the feed flow rate of methane was 200 L / h and the feed flow rate of oxygen was 50 L / h.

[0074] Example 6

[0075] The reaction of oxidative coupling of methane to olefins was carried out according to the method of Example 1, except that the temperature of the heated mixed gas was 450°C.

[0076] Example 7

[0077] The reaction of oxidative coupling of methane to olefins was carried out according to the method of Example 1, except that the temperature of the heated mixed gas was 475°C.

[0078] Example 8

[0079] The reaction of oxidative coupling of methane to olefins was carried out according to the method of Example 1, except that the temperature of the catalytic reaction was 800° C. and the pressure was 3.5 MPa.

[0080] Example 9

[0081] The reaction of oxidative coupling of methane to olefins was carried out according to the method of Example 1, except that the catalytic reaction temperature was 850° C. and the pressure was 5 MPa.

[0082] Example 10

[0083] The reaction of oxidative coupling of methane to olefins was carried out according to the method of Example 1, except that the absorbent was an imidazole ionic liquid, namely 1-ethyl, 3-methylimidazole hydrochloride.

[0084] Example 11

[0085] The reaction of oxidative coupling of methane to olefins was carried out according to the method of Example 1, except that the temperature of the heated mixed gas was 300°C.

[0086] Comparative Example 1

[0087] The reaction of oxidative coupling of methane to olefins was carried out according to the method of Example 1, except that no premixing device was set for premixing. If the residence time of the reaction mixture in the reactor (600 ms) was greater than its autoignition induction time (within 500 ms), combustion and explosion occurred.

[0088] Comparative Example 2

[0089] The oxidative coupling of methane to olefins was carried out according to the method of Example 1, except that no N2 was added.

[0090] Test Example 1

[0091] The components of the reaction products obtained in the examples and comparative examples were detected on a gas chromatograph model 7890A purchased from Agilent. The products were determined using a dual detection channel three-valve four-column system, in which the FID detector was connected to an alumina column for the analysis of CH4, C2H6, C2H4, C3H8, C3H6, C4H 10 、C4H8、C n H m And other components, TCD detector is mainly used to detect CO, CO2, N2, O2, CH4.

[0092] The calculation method of methane conversion rate is as follows:

[0093] Methane conversion rate = amount of methane consumed in the reaction / initial amount of methane × 100%

[0094] C2 selectivity = amount of methane consumed by generated C2 / total methane consumption × 100%

[0095] Ethylene yield = methane conversion × ethylene selectivity × 100%

[0096] Table 1

[0097]

[0098]

[0099] Note: “-” indicates that explosion occurred in Comparative Example 1 and no corresponding data was obtained.

[0100] It can be seen from the results in Table 1 that Examples 1-11 adopt the method of the present invention to carry out methane oxidative coupling to olefins, and the obtained methane conversion rate, C2 selectivity, and ethylene yield are all high, and no explosion occurs. However, in Comparative Example 1, no premixing device is provided, and the residence time is greater than the autoignition induction time, and the reaction system exhibits explosion. In Comparative Example 2, no N2 is added, and the methane conversion rate, C2 selectivity, and ethylene yield obtained by the reaction are all low.

[0101] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, various simple variations of the technical solution of the present invention may be made, including combining the various technical features in any other appropriate manner. These simple variations and combinations should also be regarded as disclosed in the present invention and fall within the scope of protection of the present invention.

Claims

1. A method for preparing olefins by oxidative coupling of methane, characterized in that: The method includes: (1) premixing methane, oxygen and inert gas, and heating the premixed gas with water vapor; (2) contacting the heated mixed gas with a catalyst to perform a catalytic reaction; (3) contacting the gas product obtained by the catalytic reaction with an absorbent to absorb methane and water vapor in the gas product, and returning the material containing methane, water vapor and absorbent to step (1) for regeneration to release methane and water vapor; The heating conditions are such that the temperature of the heated mixed gas is 100-350° C. lower than the temperature of the catalytic reaction; Wherein, the absorbent is methyltributylphosphine bis(trifluoromethanesulfonyl)imide salt and / or 1-ethyl-3-methylimidazole hydrochloric acid; Wherein, after water vapor is introduced into the mixed gas, the volume percentage of methane is 20-80 volume %.

2. The method according to claim 1, wherein The method further includes: transferring heat generated by the catalytic reaction to the heating step to heat the mixed gas; And / or, the method further comprises: using the regenerated absorbent in step (3) to contact with the gas product to absorb methane and water vapor in the gas product.

3. The method according to claim 1 or 2, wherein: The heating conditions are such that the temperature of the heated mixed gas is 450-500°C.

4. The method according to claim 1 or 2, wherein: The inert gas is at least one of a Group 0 element gas and nitrogen.

5. The method according to claim 3, wherein The inert gas is at least one of a Group 0 element gas and nitrogen.

6. The method according to claim 1, wherein The volume flow ratio of the methane to the oxygen is 1:0.25-4.

7. The method according to claim 1 or 2, wherein: The conditions of the catalytic reaction include: temperature of 600-850°C, pressure of 0.5-5 MPa, reaction gas hourly space velocity of 100-200 mL / (g·h) based on methane and oxygen, and reaction time of 80-100 ms; And / or, the absorption conditions include: temperature of 50-100° C. and pressure of 1-5 MPa.

8. The method according to claim 7, wherein: The absorption conditions include: temperature of 55-80° C. and pressure of 1-2 MPa.

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