A method for preparing C2 hydrocarbons by chemical chain oxidative coupling of methane with water vapor co-feed

Abstract

The present invention provides a method for preparing C2 hydrocarbons by chemical chain oxidation coupling of methane with water vapor as co-feed. The method comprises the following steps: oxidation stage: oxidizing the catalyst under air atmosphere; purging stage: purging the oxidized catalyst with inert gas; reduction stage: making water vapor and methane co-feed contact with the purged catalyst to generate C2 hydrocarbons. The present invention utilizes the migration of lattice oxygen in the catalyst out of the surface at high temperature to form adsorbed oxygen species to oxidize methane. The adsorbed oxygen species replace oxygen, which hinders the deep contact between methane and oxygen, thereby reducing the occurrence of side reactions, and at the same time avoiding the explosion caused by direct mixing of methane and gaseous oxygen, and the reaction safety is higher.

Description

Technical Field

[0001] The invention belongs to the technical field of petrochemical industry and relates to a method for preparing carbon dihydrocarbons by chemical chain oxidation coupling of methane with water vapor as co-feed. Background Art

[0002] Methane is the main component of natural gas, accounting for about 80-90%. How to efficiently utilize methane is currently a recognized problem. Methane conversion has indirect conversion and direct conversion. Indirect conversion first converts methane into synthesis gas, and then the synthesis gas is used to produce liquid hydrocarbons or hydrocarbons through the Fischer-Tropsch process. However, due to the complex process, high energy consumption, high production cost, and large investment, this route has obvious limitations, which has prompted people to continuously explore more energy-efficient direct methane conversion technology. Since the first report of methane direct coupling with oxygen to synthesize C2 hydrocarbon products (i.e., oxidative coupling of methane, abbreviated as OCM) in 1982, it has attracted widespread attention from all over the world. In the traditional methane oxidative coupling process, free oxygen is used as an oxidant and is introduced into the reactor with methane in a certain ratio. Under high temperature conditions, methane is oxidized to methyl radicals on the catalyst surface. The generated methyl radicals undergo coupling reactions to generate ethane and then dehydrogenate to generate ethylene. During the reaction, due to the high activity of free oxygen, it will react with the intermediate products in the process, resulting in excessive oxidation of methane, resulting in low selectivity and yield of C2 hydrocarbons; and under high temperature conditions, free oxygen and methane are mixed, which poses a risk of explosion, greatly restricting its industrial development. Therefore, obtaining high C2 hydrocarbon selectivity at high conversion rate has become the focus of current research.

[0003] Chemical chain methane oxidative coupling (CL-OCM) uses metal oxides as oxygen carriers. The lattice oxygen of the oxygen carrier undergoes a coupling reaction with methane in the fuel reactor to generate C2 hydrocarbons. The reduced oxygen carrier is then oxidized in the air to replenish the lattice oxygen to achieve oxygen carrier regeneration. The reaction and regeneration of the oxygen carrier medium reduces the depth of contact between methane and oxygen, thereby reducing the occurrence of side reactions and improving the selectivity of the target product C2 hydrocarbons. Currently disclosed patents such as CN112295559A, CN109438159A, and CN113398947A prepare different oxygen carrier catalysts, and transfer oxygen atoms to supply oxygen for the reaction by reducing and oxidizing the lattice oxygen of the oxygen carrier.

[0004] In addition, the literature [Angew.Chem.Int.Edit.,2008,47,7689-7693] introduced water components into the OCM reaction and found that the OH· radicals produced by the reaction of water and gas-phase oxygen can effectively break the CH bonds in methane to produce methyl radicals. The methyl radicals can further generate ethane after gas-phase coupling, thereby effectively increasing the generation rate of C2 hydrocarbons. The literature [ACS Catal.2020,10,8751-8764] reported that in the presence of gas-phase oxygen, water converts diatomic adsorbed oxygen species on the catalyst surface into monoatomic adsorbed oxygen species, which can selectively convert methane into C2 hydrocarbons, thereby increasing the selectivity of C2 hydrocarbons. Regardless of the mechanism, the water component must coexist with gas-phase oxygen to improve the selectivity of C2 hydrocarbons. Therefore, in the CL-OCM without gas-phase oxygen feed reaction, whether water vapor can improve the selectivity of C2 hydrocarbons is often overlooked. Summary of the invention

[0005] In order to solve the above technical problems, the purpose of the present invention is to provide a method for preparing C2 hydrocarbons by chemical chain oxidative coupling of methane. The method can significantly improve the conversion of methane and inhibit the deep oxidation of products such as C2 hydrocarbons to COx by pre-oxidizing the catalyst and feeding water vapor and methane together, thereby obtaining a high C2 hydrocarbon yield.

[0006] To achieve the above object, the present invention provides a method for preparing C2 hydrocarbons by chemical chain oxidative coupling of methane with water vapor as co-feed, which comprises the following steps:

[0007] Oxidation stage: oxidizing the catalyst in an air atmosphere;

[0008] Purge stage: use inert gas to purge the oxidized catalyst;

[0009] Reduction stage: water vapor and methane are co-fed and contacted with the purged catalyst to produce carbon dihydrocarbons.

[0010] In the above method, during the oxidation stage, active oxygen species can be generated by oxidizing the catalyst with air. After the gaseous oxygen on the catalyst surface is purged with an inert gas, water vapor and methane are introduced to reduce the catalyst to a reduced state, consume the oxygen species, and generate products such as C2 hydrocarbons.

[0011] In the above method, preferably, the catalyst comprises a carrier and a metal active component supported on the carrier, the carrier comprises silicon dioxide and / or titanium dioxide, and the metal active component comprises sodium, tungsten and manganese.

[0012] In the above method, preferably, based on 100% by mass of the catalyst, the content of manganese is 3.0-11.0wt%, the content of sodium is 0.7-2.6wt%, and the content of tungsten is 3.1-10.6wt%. The remainder of the catalyst is the carrier.

[0013] In the above method, preferably, based on 100% by mass of the catalyst, the mass content of Mn is 3.0-11.0 wt%, and the mass content of Na2WO4 is 5.0-11.0 wt%.

[0014] In the above method, preferably, the method further comprises an oxidation regeneration stage: the catalyst that has passed the reduction stage is reacted with air for regeneration. The catalyst can be restored to the state before the reaction with methane through cyclic regeneration.

[0015] In the above method, preferably, in the reduction stage, water vapor, methane and inert gas are fed together, and based on the sum of the volumes of the three being 100%, the content of the water vapor is 5%-30%, the content of the methane is 40%, and the content of the inert gas is 30-55%.

[0016] In the above method, preferably, the inert gas is argon.

[0017] In the above method, preferably, in the reduction stage, water vapor, methane and argon are fed together, and the contents of the three are 30%, 40% and 30% respectively.

[0018] In the above method, preferably, the reaction temperature in each stage is 800-900°C, more preferably 800-875°C, further preferably 800-850°C.

[0019] In the above method, preferably, the reaction pressure in each stage is normal pressure.

[0020] In the above method, preferably, in the reduction stage, the flow rate of the co-fed gas is 30-100 mL / min.

[0021] The technical solution of the present invention can solve the technical problems of the occurrence of side reactions under high temperature conditions in the traditional methane oxidative coupling process for producing C2 hydrocarbons, and the deep oxidation of products such as ethylene into COx (CO and CO2), which leads to limited C2 hydrocarbon yield. It can significantly improve the conversion of methane and inhibit the deep oxidation of products such as C2 hydrocarbons into COx, thereby obtaining a high C2 hydrocarbon yield.

[0022] The Mn-Na-W / SiO2 catalyst provided in the preferred embodiment of the present invention can convert lattice oxygen into gas-phase oxygen at high temperature and adsorb on the catalyst surface to form adsorbed oxygen species. In the CL-OCM process with water vapor co-feed, after the introduction of water vapor, the water vapor can convert the gas-phase oxygen and adsorbed oxygen generated in situ by the catalyst into selective oxygen species, while avoiding the presence of a large amount of free gas-phase oxygen, reducing the deep oxidation of methane, and significantly improving the selectivity of C2 hydrocarbons.

[0023] Compared with the existing oxidative coupling reaction technology, the present invention adopts the technical solution of pre-oxidizing the catalyst and introducing water vapor into the chemical chain methane oxidative coupling reaction, which has the following advantages:

[0024] (1) The present invention utilizes the migration of lattice oxygen in the catalyst to the surface at high temperature to form adsorbed oxygen species to oxidize methane. The adsorbed oxygen species replace oxygen, which hinders the deep contact between methane and oxygen, thereby reducing the occurrence of side reactions and avoiding the risk of explosion caused by direct mixing of methane and gaseous oxygen, making the reaction safer.

[0025] (2) In the method for co-feeding water vapor and methane provided by the present invention, water vapor can interact with oxygen species on the catalyst surface in the chemical chain methane oxidative coupling reaction, and generate monatomic oxygen (active oxygen species) and OH· free radicals under the condition that methane is not in direct contact with oxygen, thereby selectively converting CH4 into C2 hydrocarbons, thereby improving the selectivity and yield of C2 hydrocarbons. Compared with anhydrous, by optimizing different water vapor feed amounts, the C2 hydrocarbon selectivity can reach up to 81% at the same methane conversion rate; after optimizing different reaction temperatures, the C2 hydrocarbon yield is increased by 1 times, and the reaction performance is not reduced within 50 cycles. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 The reaction performance results provided for Example 1 and Comparative Example 1 are shown in FIG.

[0027] Figure 2 The reaction performance result diagram provided for Example 2 and Comparative Example 2.

[0028] Figure 3 The reaction performance result diagram provided for Example 3 and Comparative Example 3.

[0029] Figure 4 The reaction performance result diagram provided for Example 4 and Comparative Example 4.

[0030] Figure 5 The reaction performance result diagram provided for Example 5 and Comparative Example 5.

[0031] Figure 6 The 50-cycle reaction performance result diagram provided for Example 1 and Comparative Example 1. DETAILED DESCRIPTION

[0032] In order to have a clearer understanding of the technical features, purposes and beneficial effects of the present invention, the technical solution of the present invention is now described in detail below, but it should not be construed as limiting the applicable scope of the present invention.

[0033] Example 1

[0034] This embodiment provides a method for preparing C2 hydrocarbons by chemical chain oxidative coupling of methane, wherein the selected supported catalyst is prepared by the following steps:

[0035] (1) At room temperature, 1.0 g of SiO2 carrier and 0.3810 g of Mn(NO3)2·4H2O were dispersed in 10 mL of deionized water and stirred for 0.5 h to obtain a uniform mixture I. The mixture I was dried in an oven at 130°C for 5 h;

[0036] (2) Weigh 0.0508 g of Na2WO4·2H2O and dissolve it in 10 mL of deionized water. Stir for 0.5 h to obtain a uniform solution II.

[0037] (3) Dispersing the dried mixture I in solution II, stirring for 0.5 h to obtain a uniform mixture III, and drying the mixture III in an oven at 130 °C for 5 h;

[0038] (4) The dried product was ground into powder, and the temperature was raised to 800°C at a heating rate of 10°C / min in an air atmosphere in a muffle furnace and maintained for 8 h to obtain a supported catalyst 9Mn-5Na2WO4 / SiO2, which was marked as catalyst #1.

[0039] In the catalyst #1 provided in this embodiment, based on the mass of the catalyst being 100%, the mass content of Mn is 9.0 wt%, and the mass content of Na2WO4 is 5.0 wt%.

[0040] In this embodiment, catalyst 1# is applied to the reaction of producing C2 hydrocarbons by chemical chaining oxidative coupling of methane with steam as co-feed, which specifically includes:

[0041] 0.2g of 1# catalyst was weighed and placed in a quartz tube reaction tube, and heated under a helium atmosphere with a flow rate of 30mL / min. The reactor was heated to a target temperature of 800-875°C at a heating rate of 10°C / min. After stabilization for 15min, the helium was switched to 30mL / min air oxidation for 15min, and then switched to helium for purging, and then pulsed (frequency about once per minute) H2O / CH4 / Ar (water vapor volume fraction of 30%, methane volume fraction of 40%) mixed gas was introduced for reduction reaction, and after reduction, pulsed air was introduced for regeneration to complete the above cycle. The reaction results are shown in Table 1.

[0042] Table 1 Reaction results of methane chemical chaining oxidative coupling to produce C2 hydrocarbons with steam co-feed (1#)

[0043] Temperature / ℃ Methane conversion rate / % <![CDATA[C2 hydrocarbon selectivity / %]]> <![CDATA[C2 hydrocarbon yield / %]]> 800 9.1 78.4 7.1 825 16.6 80.8 13.4 850 24.0 76.0 18.2 875 32.3 66.5 21.5

[0044] Comparative Example 1

[0045] In this comparative example, catalyst 1# is applied to the reaction of producing C2 hydrocarbons by chemical chaining oxidative coupling of methane. The difference between this method and the method of producing C2 hydrocarbons by chemical chaining oxidative coupling of methane with water vapor co-feed provided in Example 1 is that a CH4 / Ar (methane volume fraction is 40%) mixed gas is introduced in the reduction stage to cause a reduction reaction, and water vapor is not introduced. The rest is the same as Example 1. The reaction results are shown in Table 2.

[0046] Table 2 Reaction results of methane chemical chaining oxidative coupling to produce C2 hydrocarbons (1#)

[0047] Temperature / ℃ Methane conversion rate / % <![CDATA[C2 hydrocarbon selectivity / %]]> <![CDATA[C2 hydrocarbon yield / %]]> 800 5.6 64.3 3.6 825 8.2 71.3 5.8 850 14.1 74.1 10.4 875 25.7 62.7 16.1

[0048] The conversion rate of methane, C2 hydrocarbon selectivity and yield of catalyst 1# under the two methods of Example 1 and Comparative Example 1 are as follows: Figure 1 It can be seen from Table 1 and Table 2 that the chemical chaining oxidative coupling of methane to produce C2 hydrocarbons with steam as co-feed in Example 1 of the present invention has a better reaction effect, while in the reaction without steam as co-feed, the selectivity and yield of C2 hydrocarbons are relatively low.

[0049] The 50-cycle reaction performance results provided in Example 1 and Comparative Example 1 are as follows: Figure 6 As shown. Figure 6 It can be seen that the reaction performance of Example 1 did not decrease within 50 cycles.

[0050] Example 2

[0051] This embodiment provides a method for preparing C2 hydrocarbons by chemical chain oxidative coupling of methane, wherein the supported catalyst used is different from that in Example 1 in terms of the Mn content of the component. The specific preparation steps are as follows:

[0052] (1) At room temperature, 1.0 g of SiO2 carrier and 0.4656 g of Mn(NO3)2·4H2O were dispersed in 10 mL of deionized water and stirred for 0.5 h to obtain a uniform mixture I. The mixture I was dried in an oven at 130°C for 5 h;

[0053] (2) Weigh 0.0508 g of Na2WO4·2H2O and dissolve it in 10 mL of deionized water. Stir for 0.5 h to obtain a uniform solution II.

[0054] (3) Dispersing the dried mixture I in solution II, stirring for 0.5 h to obtain a uniform mixture III, and drying the mixture III in an oven at 130 °C for 5 h;

[0055] (4) The dried product was ground into powder, and the temperature was raised to 800°C at a heating rate of 10°C / min in an air atmosphere in a muffle furnace and maintained for 8 h to obtain a supported catalyst 11Mn-5Na2WO4 / SiO2, which was marked as catalyst #2.

[0056] In the 2# catalyst provided in this embodiment, based on the mass of the catalyst being 100%, the mass content of Mn is 11.0wt%, and the mass content of Na2WO4 is 5.0wt%.

[0057] In this embodiment, catalyst 2# is applied to the reaction of producing C2 hydrocarbons by chemical chaining oxidative coupling of methane with steam as co-feed, which specifically includes:

[0058] Weigh 0.2g of 2# catalyst and place it in a quartz tube reaction tube. Heat up in a helium atmosphere with a flow rate of 30mL / min. The reactor is heated to a target temperature of 800-875°C at a heating rate of 10°C / min. After stabilization for 15min, the helium is switched to 30mL / min air oxidation for 15min, then switched to helium for purging, and then pulsed into a H2O / CH4 / Ar (water vapor volume fraction of 30%, methane volume fraction of 40%) mixed gas for reduction reaction. After reduction, pulsed into air for regeneration to complete the above cycle. The reaction results are shown in Table 3.

[0059] Table 3 Reaction results of methane chemical chaining oxidative coupling to produce C2 hydrocarbons with steam co-feed (2#)

[0060] Temperature / ℃ Methane conversion rate / % <![CDATA[C2 hydrocarbon selectivity / %]]> <![CDATA[C2 hydrocarbon yield / %]]> 800 8.2 80.0 6.6 825 15.2 81.3 12.4 850 22.1 79.2 17.3 875 23.8 73.1 17.4

[0061] Comparative Example 2

[0062] In this comparative example, catalyst 2# is applied to the reaction of producing C2 hydrocarbons by chemical chaining oxidative coupling of methane. The difference between this method and the method of producing C2 hydrocarbons by chemical chaining oxidative coupling of methane with water vapor co-feed provided in Example 2 is that a CH4 / Ar (methane volume fraction is 40%) mixed gas is introduced in the reduction stage to cause a reduction reaction, and water vapor is not introduced. The rest is the same as Example 2. The reaction results are shown in Table 4.

[0063] Table 4 Reaction results of methane chemical chaining oxidative coupling to produce C2 hydrocarbons (2#)

[0064]

[0065]

[0066] The conversion rate of methane, C2 hydrocarbon selectivity and yield of catalyst 2# under the two methods of Example 2 and Comparative Example 2 are compared. Figure 2 It can be seen from Tables 3 and 4 that the chemical chaining oxidative coupling of methane to produce C2 hydrocarbons with steam as co-feed in Example 2 of the present invention has a better reaction effect, while in the reaction without steam as co-feed, the selectivity and yield of C2 hydrocarbons are relatively low.

[0067] Example 3

[0068] This embodiment provides a method for preparing C2 hydrocarbons by chemical chain oxidative coupling of methane, wherein the supported catalyst used is different from that in Example 1 in that the contents of components Mn, W, and Na are different. The specific preparation steps are as follows:

[0069] (1) At room temperature, 1.0 g of SiO2 carrier and 0.2962 g of Mn(NO3)2·4H2O were dispersed in 10 mL of deionized water and stirred for 0.5 h to obtain a uniform mixture I. The mixture I was dried in an oven at 130°C for 5 h;

[0070] (2) Weigh 0.1158 g of Na2WO4·2H2O and dissolve it in 10 mL of deionized water. Stir for 0.5 h to obtain a uniform solution II.

[0071] (3) Dispersing the dried mixture I in solution II, stirring for 0.5 h to obtain a uniform mixture III, and drying the mixture III in an oven at 130 °C for 5 h;

[0072] (4) The dried product was ground into powder, and the temperature was raised to 800°C at a heating rate of 10°C / min in an air atmosphere in a muffle furnace and maintained for 8 h to obtain a supported catalyst 7Mn-11Na2WO4 / SiO2, which was marked as catalyst #3.

[0073] In the 3# catalyst provided in this embodiment, based on the mass of the catalyst being 100%, the mass content of Mn is 7.0wt%, and the mass content of Na2WO4 is 11.0wt%.

[0074] In this embodiment, catalyst 3# is applied to the reaction of producing C2 hydrocarbons by chemical chaining oxidative coupling of methane with steam as co-feed, which specifically includes:

[0075] Weigh 0.2g of 3# catalyst and place it in a quartz tube reaction tube. Heat up in a helium atmosphere with a flow rate of 30mL / min. The reactor is heated to a target temperature of 800-875°C at a heating rate of 10°C / min. After stabilization for 15min, the helium is switched to 30mL / min air oxidation for 15min, then switched to helium for purging, and then pulsed into a H2O / CH4 / Ar (water vapor volume fraction of 30%, methane volume fraction of 40%) mixed gas for reduction reaction. After reduction, pulsed into air for regeneration to complete the above cycle. The reaction results are shown in Table 5.

[0076] Table 5 Reaction results of methane chemical chaining oxidative coupling to C2 hydrocarbons with steam co-feed (3#)

[0077]

[0078]

[0079] Comparative Example 3

[0080] In this comparative example, catalyst 3# is applied to the reaction of producing C2 hydrocarbons by chemical chaining oxidative coupling of methane. The difference between this method and the method of producing C2 hydrocarbons by chemical chaining oxidative coupling of methane with water vapor co-feed provided in Example 3 is that a CH4 / Ar (methane volume fraction is 40%) mixed gas is introduced in the reduction stage to cause a reduction reaction, and water vapor is not introduced. The rest is the same as Example 3. The reaction results are shown in Table 6.

[0081] Table 6 Reaction results of methane chemical chaining oxidative coupling to produce C2 hydrocarbons (3#)

[0082] Temperature / ℃ Methane conversion rate / % <![CDATA[C2 hydrocarbon selectivity / %]]> <![CDATA[C2 hydrocarbon yield / %]]> 800 5.8 61.8 3.6 825 8.4 66.8 5.6 850 13.4 70.6 9.4 875 22.7 67.3 15.3

[0083] The conversion rate of methane, C2 hydrocarbon selectivity and yield of catalyst 3# under the two methods of Example 3 and Comparative Example 3 are compared. Figure 3 It can be seen from Tables 5 and 6 that the chemical chaining oxidative coupling of methane to produce C2 hydrocarbons with steam as co-feed in Example 3 of the present invention has a better reaction effect, while in the reaction without steam as co-feed, the selectivity and yield of C2 hydrocarbons are relatively low.

[0084] Example 4

[0085] This embodiment provides a method for preparing C2 hydrocarbons by chemical chain oxidative coupling of methane, wherein the supported catalyst used is different from that in Example 1 in terms of the Mn content of the component. The specific preparation steps are as follows:

[0086] (1) At room temperature, 1.0 g of SiO2 carrier and 0.1297 g of Mn(NO3)2·4H2O were dispersed in 10 mL of deionized water and stirred for 0.5 h to obtain a uniform mixture I. The mixture I was dried in an oven at 130°C for 5 h;

[0087] (2) Weigh 0.0508 g of Na2WO4·2H2O and dissolve it in 10 mL of deionized water. Stir for 0.5 h to obtain a uniform solution II.

[0088] (3) Dispersing the dried mixture I in solution II, stirring for 0.5 h to obtain a uniform mixture III, and drying the mixture III in an oven at 130 °C for 5 h;

[0089] (4) The dried product was ground into powder, and the temperature was raised to 800°C at a heating rate of 10°C / min in an air atmosphere in a muffle furnace and maintained for 8 h to obtain a supported catalyst 3Mn-5Na2WO4 / SiO2, which was marked as catalyst #4.

[0090] In the 4# catalyst provided in this embodiment, based on the mass of the catalyst being 100%, the mass content of Mn is 3.0wt%, and the mass content of Na2WO4 is 5.0wt%.

[0091] In this embodiment, catalyst 4# is applied to the reaction of producing C2 hydrocarbons by chemical chaining oxidative coupling of methane with steam as co-feed, which specifically includes:

[0092] Weigh 0.2g of 4# catalyst and place it in a quartz tube reaction tube. Heat up in a helium atmosphere with a flow rate of 30mL / min. The reactor is heated to the target temperature of 800-875℃ at a heating rate of 10℃ / min. After stabilization for 15min, the helium is switched to 30mL / min air oxidation for 15min, then switched to helium for purging, and then pulsed into H2O / CH4 / Ar (water vapor volume fraction of 30%, methane volume fraction of 40%) mixed gas for reduction reaction. After reduction, pulsed into air for regeneration to complete the above cycle. The reaction results are shown in Table 7.

[0093] Table 7 Reaction results of methane chemical chaining oxidative coupling to produce C2 hydrocarbons with steam co-feed (4#)

[0094] Temperature / ℃ Methane conversion rate / % <![CDATA[C2 hydrocarbon selectivity / %]]> <![CDATA[C2 hydrocarbon yield / %]]> 800 6.6 77.3 5.1 825 9.3 80.8 7.5 850 13.5 78.6 10.6 875 13.3 77.3 10.2

[0095] Comparative Example 4

[0096] In this comparative example, catalyst 4# is applied to the reaction of producing C2 hydrocarbons by chemical chaining oxidative coupling of methane. The difference between this method and the method of producing C2 hydrocarbons by chemical chaining oxidative coupling of methane with water vapor co-feed provided in Example 4 is that a CH4 / Ar (methane volume fraction is 40%) mixed gas is introduced in the reduction stage to cause a reduction reaction, and water vapor is not introduced. The rest is the same as Example 4. The reaction results are shown in Table 8.

[0097] Table 8 Reaction results of methane chemical chaining oxidative coupling to produce C2 hydrocarbons (4#)

[0098] Temperature / ℃ Methane conversion rate / % <![CDATA[C2 hydrocarbon selectivity / %]]> <![CDATA[C2 hydrocarbon yield / %]]> 800 4.0 68.7 2.8 825 5.0 70.2 3.5 850 7.1 73.0 5.1 875 8.6 70.9 6.1

[0099] The conversion rate of methane, C2 hydrocarbon selectivity and yield of catalyst 4# under the two methods of Example 4 and Comparative Example 4 are compared. Figure 4 It can be seen from Tables 7 and 8 that the chemical chaining oxidative coupling of methane to produce C2 hydrocarbons with steam co-feed in Example 4 of the present invention has a better reaction effect, while in the reaction without steam co-feed, the selectivity and yield of C2 hydrocarbons are relatively low.

[0100] Example 5

[0101] This embodiment provides a method for preparing carbon dihydrocarbons by chemical chain oxidative coupling of methane, wherein the supported catalyst used is different from that in Example 1 in that the carrier TiO2 and the content of Mn in the component are different. The specific preparation steps are as follows:

[0102] (1) At room temperature, 1.0 g of TiO2 carrier and 0.1297 g of Mn(NO3)2·4H2O were dispersed in 10 mL of deionized water and stirred for 0.5 h to obtain a uniform mixture I. The mixture I was dried in an oven at 130 °C for 5 h;

[0103] (2) Weigh 0.0508 g of Na2WO4·2H2O and dissolve it in 10 mL of deionized water. Stir for 0.5 h to obtain a uniform solution II.

[0104] (3) Dispersing the dried mixture I in solution II, stirring for 0.5 h to obtain a uniform mixture III, and drying the mixture III in an oven at 130 °C for 5 h;

[0105] (4) The dried product was ground into powder, and the temperature was raised to 800°C at a heating rate of 10°C / min in an air atmosphere in a muffle furnace and maintained for 8 h to obtain a supported catalyst 3Mn-5Na2WO4 / TiO2, which was marked as catalyst #5.

[0106] In the 5# catalyst provided in this embodiment, based on the mass of the catalyst being 100%, the mass content of Mn is 3.0wt%, and the mass content of Na2WO4 is 5.0wt%.

[0107] In this embodiment, catalyst 5# is applied to the reaction of producing C2 hydrocarbons by chemical chaining oxidative coupling of methane with steam as co-feed, which specifically includes:

[0108] Weigh 0.2g 5# catalyst and place it in a quartz tube reaction tube. Heat up under a flow rate of 30mL / min helium atmosphere. The reaction furnace is heated to a target temperature of 800-875°C at a heating rate of 10°C / min. After stabilizing for 15min, the helium is switched to 30mL / min air oxidation for 15min, then switched to helium for purging, and then pulsed into H2O / CH4 / Ar (water vapor volume fraction is 30%, methane volume fraction is 40%) mixed gas for reduction reaction. After reduction, pulsed into air regeneration to complete the above-mentioned cycle. This embodiment needs to use TiO2 as a carrier catalyst, so the reaction results are slightly different from those of Example 1-4. The reaction results are shown in Table 9.

[0109] Table 9 Reaction results of methane chemical chaining oxidative coupling to produce C2 hydrocarbons with steam co-feed (5#)

[0110] Temperature / ℃ Methane conversion rate / % <![CDATA[Selectivity of C2 hydrocarbons / %]]> <![CDATA[C2 hydrocarbon yield / %]]> 800 4.2 58.0 2.7 825 6.6 65.3 4.3 850 8.8 74.4 6.5 875 10.1 77.3 7.8

[0111] Comparative Example 5

[0112] In this comparative example, catalyst 5# is applied to the reaction of producing C2 hydrocarbons by chemical chaining oxidative coupling of methane. The difference between this method and the method of producing C2 hydrocarbons by chemical chaining oxidative coupling of methane with water vapor co-feed provided in Example 5 is that a CH4 / Ar (methane volume fraction is 40%) mixed gas is introduced in the reduction stage to cause a reduction reaction, and water vapor is not introduced. The rest is the same as Example 5. The reaction results are shown in Table 10.

[0113] Table 10 Reaction results of methane chemical chaining oxidative coupling to produce C2 hydrocarbons (5#)

[0114] Temperature / ℃ Methane conversion rate / % <![CDATA[C2 hydrocarbon selectivity / %]]> <![CDATA[C2 hydrocarbon yield / %]]> 800 3.2 37.8 1.2 825 4.2 46.8 1.9 850 4.8 59.5 2.9 875 6.4 64.4 4.1

[0115] The conversion rate of methane, C2 hydrocarbon selectivity and yield of catalyst 5# under the two methods of Example 5 and Comparative Example 5 are compared. Figure 5 It can be seen from Tables 9 and 10 that the chemical chaining oxidative coupling of methane to produce C2 hydrocarbons with steam co-feed in Example 5 of the present invention has a better reaction effect, while in the reaction without steam co-feed, the selectivity and yield of C2 hydrocarbons are relatively low.

Claims

1. A method for preparing C2 hydrocarbons by chemical chain oxidative coupling of methane with water vapor as co-feed, comprising the following steps: Oxidation stage: In an air atmosphere, the catalyst is oxidized to generate active oxygen species; Purging stage: using inert gas to purge the oxidized catalyst; Reduction stage: water vapor and methane are fed together to contact the purged catalyst, reducing the catalyst to a reduced state and consuming active oxygen species to generate carbon dihydrocarbons; The water vapor interacts with oxygen species on the catalyst surface, generating single atomic oxygen and OH· free radicals to selectively convert methane into dihydrocarbons without direct contact between methane and oxygen. The catalyst comprises a carrier and a metal active component supported on the carrier, wherein the carrier comprises silicon dioxide and / or titanium dioxide, and the metal active component comprises sodium, tungsten and manganese; In the reduction stage, water vapor, methane and inert gas are fed together. Taking the sum of the volumes of the three as 100%, the content of the water vapor is 5%-30%, the content of the methane is 40%, and the content of the inert gas is 30-55%.

2. The method according to claim 1, wherein: Based on 100% of the mass of the catalyst, the content of manganese element is 3.0-11.0wt%, the content of sodium element is 0.7-2.6wt%, and the content of tungsten element is 3.1-10.6wt%.

3. The method according to claim 2, wherein: Based on 100% of the mass of the catalyst, the mass content of Mn is 3.0-11.0 wt%, and the mass content of Na2WO4 is 5.0-11.0 wt%.

4. The method according to claim 1, wherein: The method also includes an oxidation regeneration stage: regenerating the catalyst after the reduction stage by reacting it with air.

5. The method according to claim 1, wherein: The inert gas is argon.

6. The method according to claim 5, wherein: In the reduction stage, water vapor, methane and argon are fed together, and the contents of the three are 30%, 40% and 30% respectively.

7. The method according to claim 1, wherein: The reaction temperature in each stage is 800-900°C.

8. The method according to claim 7, wherein: The reaction temperature in each stage is 800-875°C.

9. The method according to claim 7, wherein: The reaction temperature in each stage is 800-850°C.

10. The method according to claim 1, wherein: The reaction pressure in each stage is normal pressure.

11. The method according to claim 1, wherein: In the reduction stage, the flow rate of the co-feed gas was 30-100 mL / min.

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