Reactors with alumina coating on their inner surface and their preparation methods, and methods for producing C2 hydrocarbons by oxidative coupling of methane.

Abstract

This invention relates to the field of methane oxidative coupling to C2 hydrocarbons, and discloses a reactor with an inner surface coated with alumina, its preparation method, and a method for methane oxidative coupling to C2 hydrocarbons. The reactor includes an alloy reaction tube and an alumina film attached to the inner surface of the alloy reaction tube. The alumina film has a thickness of 1-10 μm and a coverage rate of more than 50% on the inner surface of the alloy reaction tube. The reactor also includes a catalyst filled within the cavity of the alloy reaction tube. The catalyst includes a support and at least one active component selected from Na, W, Mn, Y, and Sr supported on the support, wherein the support is selected from silica. In the reactor provided by this invention, the alumina film formed on the inner wall surface can effectively cover the iron element on the inner surface of the alloy tube, thereby reducing the formation of by-products during the methane oxidative coupling reaction. Combined with the specific catalyst filled in the reactor, the yield and selectivity of the product can be further improved.

Description

Technical Field

[0001] This invention relates to the field of methane oxidative coupling to produce C2 hydrocarbons, specifically to a reactor with alumina adhering to its inner surface, its preparation method, and a method for methane oxidative coupling to produce C2 hydrocarbons. Background Technology

[0002] In recent years, with continuous breakthroughs in natural gas exploration technologies such as shale gas and methane hydrate, a number of large and medium-sized gas fields have emerged, and proven reserves and production have grown rapidly. The proportion of natural gas in primary energy is gradually increasing, and natural gas chemical engineering is gradually becoming one of the development directions of the petrochemical industry. To reduce dependence on petroleum resources for olefin production, methane-based olefin production technology has become a research hotspot in recent years.

[0003] Since the methane oxidative coupling route was first proposed in 1982, over 30 years have passed, and numerous scientists have done extensive work to improve catalyst performance. However, because the methane oxidative coupling reaction is a high-temperature, strongly exothermic reaction, and considering the side reactions that occur during methane oxidation, the heat released in the entire reaction is substantial. Therefore, controlling the reaction temperature and removing the heat of reaction have become key challenges in the entire technology. Currently, most reaction processes use stainless steel or alloy reactors, but the use of stainless steel or alloy reactors in methane oxidative coupling reactions generally suffers from low product selectivity and low yield. Existing technologies reported on methane oxidative coupling are primarily carried out in quartz glass reactors, but the properties of quartz severely restrict its further scale-up production. Therefore, how to improve the mechanical strength of the reaction tube while avoiding the occurrence of side reactions in the methane oxidation reaction is an important problem that urgently needs to be solved. Summary of the Invention

[0004] The purpose of this invention is to overcome the technical problems existing in the prior art and to provide a reactor with alumina attached to its inner surface, a method for preparing the reactor, and a method for producing C2 hydrocarbons by oxidative coupling of methane.

[0005] To achieve the above objectives, the first aspect of the present invention provides a reactor with an alumina film attached to its inner surface. The reactor includes an alloy reaction tube and an alumina film attached to the inner surface of the alloy reaction tube, wherein the thickness of the alumina film is 1-10 μm and the coverage of the alumina film on the inner surface of the alloy reaction tube is greater than 50%.

[0006] The reactor further includes a catalyst filled in the cavity on the inner surface of the alloy reaction tube. The catalyst includes a support and at least one active component selected from Na, W, Mn, Y and Sr supported on the support, wherein the support is selected from silicon dioxide.

[0007] A second aspect of the present invention provides a method for preparing the aforementioned reactor, the method comprising the following steps:

[0008] (1) An aluminum oxide film is attached to the inner surface of the alloy reaction tube to obtain the reactor precursor;

[0009] (2) A catalyst section is filled in the reactor front body to obtain the reactor.

[0010] A third aspect of the present invention provides a method for producing C2 hydrocarbons by oxidative coupling of methane, the method comprising: introducing methane and oxygen into the aforementioned reactor to carry out an oxidative coupling reaction.

[0011] Compared with existing technologies, the reactor provided by this invention utilizes an inert film (alumina film) formed on the inner wall surface to effectively cover the iron content on the inner surface of the alloy tube, thereby reducing the formation of byproducts during the methane oxidative coupling reaction. Combined with a specific catalyst packed within the reactor, this further improves product yield and selectivity. Furthermore, the reactor preparation method (with an alumina film attached to the surface) provided by this invention is simple to operate, suitable not only for laboratory-scale reactions but also offering a new approach for selecting reactor materials in industrial-scale experiments. Detailed Implementation

[0012] The endpoints and any values ​​of the ranges 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 endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0013] The first aspect of the present invention provides a reactor with aluminum oxide attached to its inner surface. The reactor includes an alloy reaction tube and an aluminum oxide film attached to the inner surface of the alloy reaction tube, wherein the thickness of the aluminum oxide film is 1-10 μm and the coverage of the aluminum oxide film on the inner surface of the alloy reaction tube is greater than 50%.

[0014] The reactor further includes a catalyst filled in the cavity on the inner surface of the alloy reaction tube. The catalyst includes a support and at least one active component selected from Na, W, Mn, Y and Sr supported on the support, wherein the support is selected from silicon dioxide.

[0015] According to some embodiments of the present invention, the thickness of the alumina film can be 2-7 μm;

[0016] According to some embodiments of the present invention, the alumina film has a coverage of 80-90% on the inner surface of the alloy reaction tube.

[0017] In this invention, "coverage rate" refers to the effective area of ​​the alumina film covering the inner surface of the alloy reaction tube.

[0018] According to some embodiments of the present invention, the elemental composition of the alloy reaction tube material, by weight percentage, includes: 0-0.2 wt% C, 2-8 wt% Fe, 0-1 wt% Mn, 0-2 wt% Si, 14-23 wt% Cr, 8-10 wt% Mo, 55.8-76 wt% Ni, and 0-0.3 wt% sulfur and phosphorus.

[0019] According to some embodiments of the present invention, in the catalyst, relative to 100g of support, the content of Na is 1-5g, the content of W is 3-12g, the content of Mn is 3-25g, and the content of Y and / or Sr is 1-4g.

[0020] According to some embodiments of the present invention, in the catalyst, relative to 100g of support, the content of Na is 2-4g, the content of W is 3-10g, the content of Mn is 5-15g, and the content of Y and / or Sr is 1-2g.

[0021] In this invention, there are no particular limitations on the preparation method of the catalyst, as long as it meets the requirements of this invention. For example, it can be prepared by the following method: adding sodium and tungsten sources to deionized water, adding silica support, stirring for 1-4 hours, and drying at 100-120°C for 2-12 hours to obtain solid A; then dissolving manganese and / or yttrium and strontium sources in deionized water, adding solid A, stirring for 1-4 hours, and drying at 100-120°C for 2-12 hours to obtain solid B; then calcining solid B at 500-550°C for 4-5 hours, and then calcining at 850-880°C for 4-8 hours to obtain the catalyst of this invention. Preferably, the sodium source is sodium tungstate; the manganese source is preferably manganese nitrate; the yttrium source is preferably yttrium nitrate; and the strontium source is preferably strontium nitrate.

[0022] A second aspect of the present invention provides a method for preparing the aforementioned reactor, the method comprising the following steps:

[0023] (1) An aluminum oxide film is attached to the inner surface of the alloy reaction tube to obtain the reactor precursor;

[0024] (2) A catalyst section is filled in the reactor front body to obtain the reactor.

[0025] According to some embodiments of the present invention, in step (1), the method of attaching the alumina film can be: contacting the material to be coated with the inner surface of the alloy tube.

[0026] According to some embodiments of the present invention, the material to be coated may be an aluminum alkoxide organic compound, selected from aluminum sec-butoxide and / or aluminum isopropoxide, more preferably aluminum sec-butoxide.

[0027] According to some embodiments of the present invention, the contact conditions may include: a temperature of 700-900°C, preferably 700-850°C; and a time of 5-10 hours, preferably 5-7 hours.

[0028] In this invention, the contact method can be: depositing the material to be coated as a deposition liquid on the inner surface of the alloy reaction tube.

[0029] In this invention, before the material to be coated comes into contact with the inner surface of the alloy reaction tube, the material to be coated is preheated at 70-150°C for 10-30 minutes.

[0030] According to some embodiments of the invention, the contact is carried out in the presence of air.

[0031] Preferably, the air flow rate is 300-1200 mL / min relative to the cross-sectional diameter of the alloy reaction tube, more preferably 500-900 mL / min.

[0032] The present invention does not impose a specific limitation on the amount of the material to be coated, as long as it meets the requirements of the present invention. Preferably, the amount of the material to be coated is such that the thickness of the alumina film attached to the inner surface of the alloy reaction tube is 1-10 μm, preferably 2-7 μm.

[0033] Preferably, the amount of material to be coated is such that the coverage of the alumina film on the inner surface of the alloy reaction tube is greater than or equal to 50%, and more preferably 80-90%.

[0034] According to some embodiments of the present invention, in step (2), the volume is 20 cm³ relative to the cavity volume. 3 The alloy reaction tube has a catalyst section with a loading amount of 0.15-0.6g, preferably 0.2-0.4g.

[0035] In this invention, there are no particular restrictions on the length, diameter of the cross-section, and thickness of the alloy tube (these can be selected according to actual needs), as long as they meet the requirements of this invention.

[0036] A third aspect of the present invention provides a method for producing C2 hydrocarbons by oxidative coupling of methane, the method comprising: introducing methane and oxygen into the aforementioned reactor to carry out an oxidative coupling reaction.

[0037] According to some embodiments of the present invention, prior to the oxidative coupling reaction, the reactor is further subjected to a filling process with an inert material.

[0038] According to some embodiments of the present invention, the filling process can be carried out by filling the catalyst section in the reactor with a first inert material section and a second inert material section, respectively.

[0039] According to some embodiments of the present invention, the cavity volume is 20 cm³. 3 The alloy reaction tube has a first inert material section with a filling amount of 10-30g, preferably 15-20g, and a second inert material section with a filling amount of 10-30g, preferably 20-25g.

[0040] According to some embodiments of the present invention, in the direction of the reaction stream, the length ratio of the first inert material segment, the second inert material segment and the catalyst segment can be 1:(1-1.5):(0.02-0.15), preferably 1:(1-1.3):(0.03-0.11).

[0041] According to some embodiments of the present invention, the inert materials filled in the first inert material segment and the second inert material segment are each independently selected from silicon dioxide and / or aluminum oxide.

[0042] According to some embodiments of the present invention, the conditions for the oxidative coupling reaction may include: a temperature of 700-900°C, preferably 750-850°C; a time of 0.2-15 h, preferably 0.5-8 h; and / or a gas hourly space velocity (GHSV) of 3000-30000 mL / (g·h), preferably 5000-25000 mL / (g·h) for the reaction of methane and oxygen.

[0043] According to some embodiments of the present invention, the amount of methane used may be 2-10 mol relative to 1 mol of oxygen.

[0044] The present invention will be described in detail below through embodiments.

[0045] Unless otherwise specified, all reagents used in the following examples and comparative examples are commercially available analytical grade reagents.

[0046] Preparation Example 1 (Preparation of Catalyst C1)

[0047] 7.7g of sodium tungstate was added to deionized water, followed by 100g of silica support. The mixture was stirred for 2 hours and dried at 120°C for 2 hours to obtain solid A. Then, 9.8g of manganese nitrate and 4.3g of yttrium nitrate were dissolved in deionized water, and solid A was added to the solution. The mixture was stirred for 2 hours and dried at 120°C for 2 hours to obtain solid B. Solid B was then calcined at 550°C for 4 hours, followed by calcination at 850°C for 6 hours to obtain catalyst C1 (1wt% Na-4.3wt% W-3wt% Mn-1wt% Y / SiO2).

[0048] Preparation Example 2 (Preparation of Catalyst C2)

[0049] 38.5g of sodium tungstate was added to deionized water, followed by 100g of silica support. The mixture was stirred for 4 hours and dried at 100℃ for 6 hours to obtain solid A. Then, 39.2g of manganese nitrate and 9.6g of strontium nitrate were dissolved in deionized water, and solid A was added to the solution. The mixture was stirred for 4 hours and dried at 100℃ for 6 hours to obtain solid B. Solid B was then calcined at 500℃ for 5 hours, followed by calcination at 880℃ for another 4 hours to obtain catalyst C2 (5wt% Na-21.5wt% W-12wt% Mn-4wt% Sr / SiO2).

[0050] Preparation Example 3 (Preparation of Catalyst C3)

[0051] 23g of sodium tungstate was added to deionized water, followed by 100g of silica support. The mixture was stirred for 2 hours and dried at 100℃ for 12 hours to obtain solid A. Then, 29.5g of manganese nitrate and 4.8g of strontium nitrate were dissolved in deionized water, and solid A was added to the solution. The mixture was stirred for 2 hours and dried at 100℃ for 12 hours to obtain solid B. Solid B was then calcined at 520℃ for 4 hours, followed by calcination at 860℃ for another 8 hours to obtain catalyst C3 (3wt% Na-13wt% W-9wt% Mn-2wt% Sr / SiO2).

[0052] Preparation Example 4 (Preparation of Catalyst C4)

[0053] 77g of sodium tungstate was added to deionized water, followed by 100g of silica support. The mixture was stirred for 2 hours and dried at 120°C for 2 hours to obtain solid A. Then, 3.3g of manganese nitrate and 14.5g of strontium nitrate were dissolved in deionized water, and solid A was added to the solution. The mixture was stirred for 2 hours and dried at 120°C for 2 hours to obtain solid B. Solid B was then calcined at 550°C for 4 hours, followed by calcination at 850°C for 6 hours to obtain catalyst C4 (10wt% Na-43wt% W-1wt% Mn-6wt% Sr / SiO2).

[0054] Preparation Example 5 (Preparation of Catalyst C5)

[0055] 23g of sodium tungstate was added to deionized water, followed by 100g of alumina support. The mixture was stirred for 2 hours and dried at 120℃ for 2 hours to obtain solid A. Solid A was then calcined at 550℃ for 4 hours, followed by calcination at 850℃ for 6 hours to obtain catalyst C5 (3wt% Na-13wt% W / Al2O3).

[0056] Example 1

[0057] The alloy reaction tube material used in this embodiment has the following composition: 16 wt% chromium, 64 wt% nickel, 1 wt% manganese, 1 wt% silicon, 0.1 wt% carbon, 10 wt% molybdenum, 0.1 wt% sulfur, 0.2 wt% phosphorus and 7.6 wt% iron.

[0058] (1) After heating an alloy reaction tube with a length of 500 mm, a cross-sectional diameter of 10 mm (outer diameter) and a thickness of 1 mm to 700 °C and holding it at that temperature for 20 min; 80 g of sec-butoxide aluminum deposition solution was preheated at 80 °C for 20 min, and air was introduced into the deposition solution at 700 °C, with the air flow rate controlled at 900 mL / min; the sec-butoxide aluminum was carried into the reaction tube by the air and deposited for 5 h (there was residual solution after deposition) to obtain the reactor precursor; wherein, the thickness of the alumina film was 2 μm, and the coverage of the alumina film on the inner surface of the alloy reaction tube was 90%;

[0059] (2) 0.2g of catalyst C1 (1wt% Na-4.3wt% W-3wt% Mn-1wt% Y / SiO2) is filled into the reactor prebody prepared in step (1); reactor S1 with alumina attached to its inner surface is obtained.

[0060] Example 2

[0061] The alloy reaction tube material used in this embodiment has the following composition: 23wt% chromium, 60wt% nickel, 0.5wt% manganese, 0.5wt% silicon, 0.2wt% carbon, 8wt% molybdenum, 0.2wt% sulfur, 0.1wt% phosphorus and 7.5wt% iron.

[0062] (1) The alloy reaction tube with a length of 500 mm, a cross-sectional diameter of 10 mm (outer diameter), and a thickness of 1.5 mm was heated to 850 °C and held at that temperature for 20 min; 75 g of aluminum sec-butoxide deposition solution was preheated at 130 °C for 10 min, and air was introduced into the deposition solution at 850 °C, with the air flow rate controlled at 500 mL / min; aluminum isopropoxide was carried into the alloy reaction tube by the air and deposited for 9 h (there was residual solution after deposition) to obtain the reactor precursor; wherein, the thickness of the alumina film was 6.5 μm, and the coverage of the alumina film on the inner surface of the alloy reaction tube was 80%;

[0063] (2) 0.2g of catalyst C2 (5wt% Na-21.5wt% W-12wt% Mn-4wt% Sr / SiO2) was filled into the reactor prebody prepared in step (1); reactor S2 with alumina attached to its inner surface was obtained.

[0064] Example 3

[0065] The alloy reaction tube material used in this embodiment has the following composition: 15wt% chromium, 68wt% nickel, 0.2wt% manganese, 2wt% silicon, 0.2wt% carbon, 9wt% molybdenum, 0.2wt% sulfur, 0.1wt% phosphorus and 5.3wt% iron.

[0066] (1) After heating an alloy reaction tube with a length of 500 mm, a cross-sectional diameter of 10 mm (outer diameter) and a thickness of 1 mm to 800 °C and holding it at that temperature for 20 min; 78 g of aluminum sec-butoxide deposition solution was preheated at 100 °C for 20 min, and air was introduced into the deposition solution at 800 °C, with the air flow rate controlled at 700 mL / min; aluminum sec-butoxide was carried into the alloy reaction tube by the air and deposited for 6 h (there was residual solution after deposition) to obtain the reactor precursor; wherein, the thickness of the alumina film was 5 μm, and the coverage of the alumina film on the inner surface of the alloy reaction tube was 85%;

[0067] (2) 0.2g of catalyst C3 (3wt% Na-13wt% W-9wt% Mn-2wt% Sr / SiO2) was filled into the reactor prebody prepared in step (1); reactor S3 with alumina attached to its inner surface was obtained.

[0068] Examples 4-6

[0069] The process was carried out in accordance with Example 1, except that Examples 4-6 changed one or more parameters, such as the contact temperature or time in step (1), the air flow rate, the type or amount of aluminum source, and the composition or filling amount of the catalyst in step (2), as shown in Table 1. Reactors S4-S6 with alumina adhering to their inner surfaces were finally obtained.

[0070] Comparative Example 1

[0071] The process was carried out in accordance with Example 1, except that no alumina film was attached to the inner surface of the alloy reaction tube, as detailed in Table 1. Reactor D1 was obtained.

[0072] Comparative Example 2

[0073] The process was carried out in accordance with Example 1, except that the deposition time of aluminum sec-butoxide on the inner surface of the alloy reaction tube was changed to 0.5 h. Ultimately, the thickness of the alumina film was 0.2 μm, and the coverage of the alumina film on the inner surface of the alloy reaction tube was 50%, as detailed in Table 1. Reactor D2 was thus obtained.

[0074] Comparative Example 3

[0075] The procedure was carried out as in Example 1, except that the catalyst composition was changed to C5 (3wt% Na-13wt% W / Al2O3), as detailed in Table 1. Reactor D3 was obtained.

[0076] Comparative Example 4

[0077] The process was carried out in the same manner as Comparative Example 1, except that the catalyst composition was changed to C5. Reactor D4 was obtained.

[0078] In Table 1, “thickness” refers to the thickness of the alumina film attached to the inner surface of the alloy reaction tube, which was measured by scanning electron microscopy (FEI XL-30 field emission environmental scanning electron microscope, USA); “coverage” refers to the coverage of the alumina film on the inner surface of the alloy reaction tube, which was measured by scanning electron microscopy (FEI XL-30 field emission environmental scanning electron microscope, USA).

[0079] Table 1

[0080]

[0081] The methane oxidative coupling reaction was evaluated using reactors (S1-S6, D1-D4) obtained in the above examples and comparative examples.

[0082] Test Example 1

[0083] The reactor prepared in Example 1 was used for the oxidative coupling of methane to C2 hydrocarbons. The reaction was carried out in a continuous flow fixed bed. Inert material, quartz sand, was loaded at both ends of the catalyst in the tube. The loading amount of inert material was 45 g. The length ratio of the first inert material section, the second inert material section and the catalyst section was 1:1.25:0.05. The reaction pressure was the pressure generated by the raw materials themselves. The reaction temperature was 800 °C. The alkane-oxygen ratio (molar ratio of methane to oxygen) was 2.2. The gas hourly space velocity (GHSV) of the reaction, calculated based on methane and oxygen, was 5000 mL / (g·h). After 1 hour of reaction, the performance evaluation results of the oxidative coupling of methane to ethylene are listed in Table 2.

[0084] Test Example 2

[0085] The reactor prepared in Example 1 was used for the oxidative coupling of methane to C2 hydrocarbons. The reaction was carried out in a continuous flow fixed bed. The catalyst in the tube was loaded with alumina as an inert material at both ends. The loading amount of the inert material was 35g. The length ratio of the first inert material section, the second inert material section and the catalyst section was 1:1.3:0.03. The reaction pressure was the pressure generated by the raw materials themselves. The reaction temperature was 830℃. The alkane-to-oxygen ratio was 4. The gas hourly space velocity (GHSV) of the reaction, calculated as methane and oxygen, was 25000mL / (g·h). After 1 hour of reaction, the performance evaluation results of the oxidative coupling of methane to ethylene are listed in Table 2.

[0086] Test Example 3

[0087] The reactor prepared in Example 1 was used for the oxidative coupling of methane to C2 hydrocarbons. The reaction was carried out in a continuous flow fixed bed. Inert materials, namely quartz sand, were loaded at both ends of the catalyst in the tube. The loading amount of inert material was 40 g. The length ratio of the first inert material section, the second inert material section and the catalyst section was 1:1:0.04. The reaction pressure was the pressure generated by the raw materials themselves. The reaction temperature was 780 °C. The alkane-to-oxygen ratio was 3. The gas hourly space velocity (GHSV) of the reaction, calculated as methane and oxygen, was 15000 mL / (g·h). After 1 hour of reaction, the performance evaluation results of the oxidative coupling of methane to ethylene are listed in Table 2.

[0088] Test Case 4-6 and Comparative Test Case 1-4

[0089] The test was conducted in the same manner as in Test Example 1, except that S1 was replaced by S4-S6 and D1-D4 respectively. The performance test results are shown in Table 2.

[0090] Comparative Test Example 5

[0091] The method was similar to that in Test Example 3, except that a quartz reactor was used and a C1 catalyst was employed for the oxidative coupling of methane to C2 hydrocarbons. The reaction performance evaluation is shown in Table 2.

[0092] Comparative Test Case 6

[0093] The method was similar to that in Test Example 3, except that a quartz reactor was used and a C5 catalyst was employed for the oxidative coupling of methane to C2 hydrocarbons. The reaction performance evaluation is shown in Table 2.

[0094] The reaction product components obtained from the test examples and control test examples were analyzed using a gas chromatograph (Gas Chromatograph, Model 7890A) purchased from Agilent Technologies. The products were determined using a dual-detection-channel, three-valve, four-column system, with the FID detector connected to an alumina column for analyzing CH4, C2H6, C2H4, C3H8, C3H6, and C4H. 10 C4H8, C n H m The TCD detector is mainly used to detect CO, CO2, N2, O2, and CH4.

[0095] The calculation methods for methane conversion rate, etc., are as follows:

[0096] Methane conversion rate = Amount of methane consumed in the reaction / Initial amount of methane × 100%

[0097] Ethylene selectivity = Amount of methane consumed to produce ethylene / Total methane consumption × 100%

[0098] Ethane selectivity = Amount of methane consumed to produce ethane / Total methane consumption × 100%

[0099] C2 hydrocarbon selectivity = ethane selectivity + ethylene selectivity

[0100] CO x (CO + CO2) selectivity = (Amount of methane consumed by the combined generation of CO and CO2) / (Total methane consumption) × 100%

[0101] C2 hydrocarbon yield = methane conversion rate × (ethane selectivity + ethylene selectivity)

[0102] Table 2

[0103]

[0104]

[0105] As can be seen from the test results in Table 2, compared with Comparative Test Example 1, Test Examples 1-6 showed higher selectivity for C2 hydrocarbons, higher yield of C2 hydrocarbons, and higher CO content. x The relatively low selectivity indicates that the reactor and method of this invention suppresses deep oxidation of methane and reduces side reactions during the oxidative coupling of methane to prepare C2 hydrocarbons. Compared to Comparative Test Example 2, Test Examples 1-6 show higher C2 hydrocarbon selectivity, higher C2 hydrocarbon yield, and higher CO2 content. x The relatively low selectivity indicates that only when the thickness of the alumina film attached to the inner surface of the alloy reaction tube is within the range of this invention (i.e., 1-10 μm), the catalyst of this invention results in fewer side reactions and a higher yield of C2 hydrocarbons during the oxidative coupling of methane. Compared to comparative test examples 3, 4, and 6, test examples 1-6 exhibit higher C2 hydrocarbon selectivity and yield, demonstrating that only by employing the technical solution of this invention with specific catalysts can superior catalytic effects be obtained.

[0106] Compared to Comparative Test Example 5, Test Example 3 shows little difference in the data in Table 2. However, the quartz tube used in Comparative Test Example 5 is fragile and would severely limit its further scale-up production. In contrast, the alloy reaction tube used in Test Example 3 is robust, has a long service life, and good thermal insulation properties, making it easy to use on a large scale.

[0107] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for the oxidative coupling of methane to produce C2 hydrocarbons, characterized in that, The method includes: (1) An alumina film is attached to the inner surface of the alloy reaction tube to obtain the reactor precursor; (2) A catalyst section is filled in the inlet of the reactor to obtain the reactor; (3) Methane and oxygen are introduced into a reactor with alumina adhering to its inner surface to carry out an oxidative coupling reaction; The reactor includes an alloy reaction tube and an alumina film attached to the inner surface of the alloy reaction tube. The alumina film has a thickness of 1-10µm and a coverage of more than 50% on the inner surface of the alloy reaction tube. The catalyst in the catalyst section includes a support and at least one active component selected from Na, W, Mn, Y and Sr supported on the support, wherein the support is selected from silica. In step (1), the method of attaching the alumina film is to bring the material to be coated into contact with the inner surface of the alloy reaction tube. The material to be coated is an aluminum alkoxide organic compound; The contact conditions include: a temperature of 700-900℃ and a time of 5-10 hours. The contact takes place in the presence of air.

2. The method according to claim 1, wherein, The thickness of the alumina film is 2-7µm.

3. The method according to claim 1, wherein, The alumina film has a coverage rate of 80-90% on the inner surface of the alloy reaction tube.

4. The method according to claim 1, wherein, The elemental composition of the alloy reaction tube material, by weight percentage, includes: 0-0.2 wt% C, 2-8 wt% Fe, 0-1 wt% Mn, 0-2 wt% Si, 14-23 wt% Cr, 8-10 wt% Mo, 55.8-76 wt% Ni, and 0-0.3 wt% sulfur and phosphorus.

5. The method according to claim 1, wherein, In the catalyst, relative to 100g of support, the content of Na is 1-5g, the content of W is 3-12g, the content of Mn is 3-25g, and the content of Y and / or Sr is 1-4g.

6. The method according to claim 5, wherein, In the catalyst, relative to 100g of support, the content of Na is 2-4g, the content of W is 3-10g, the content of Mn is 5-15g, and the content of Y and / or Sr is 1-2g.

7. The method according to claim 1, wherein, The material to be coated is selected from aluminum sec-butoxide and / or aluminum isopropoxide.

8. The method according to claim 7, wherein, The material to be coated is aluminum sec-butoxide.

9. The method according to claim 1, wherein, The contact conditions include: a temperature of 700-850℃ and a time of 5-7 hours.

10. The method according to claim 1, wherein, The air flow rate is 300-1200 mL / min relative to the cross-sectional diameter of the alloy reaction tube, which is 10 mm.

11. The method according to claim 10, wherein, The air flow rate is 500-900 mL / min relative to the cross-sectional diameter of the alloy reaction tube, which is 10 mm.

12. The method according to claim 1, wherein, The amount of material to be coated is such that the thickness of the alumina film attached to the inner surface of the alloy reaction tube is 1-10µm; the amount of material to be coated is such that the coverage of the alumina film on the inner surface of the alloy reaction tube is greater than or equal to 50%.

13. The method according to claim 12, wherein, The amount of material to be coated results in an alumina film thickness of 2-7µm adhering to the inner surface of the alloy reaction tube; the amount of material to be coated results in an alumina film coverage of 80-90% on the inner surface of the alloy reaction tube.

14. The method according to claim 1, wherein, In step (2), the volume of the cavity is 20 cm³. 3 The alloy reaction tube has a catalyst section with a loading amount of 0.15-0.6g.

15. The method according to claim 14, wherein, In step (2), the volume of the cavity is 20 cm³. 3 The alloy reaction tube has a catalyst section with a loading amount of 0.2-0.4g.

16. The method according to claim 1, wherein, Prior to the oxidative coupling reaction, the reactor is filled with inert material.

17. The method according to claim 16, wherein, The filling process is as follows: a first inert material segment and a second inert material segment are respectively filled at both ends of the catalyst segment in the reactor.

18. The method according to claim 17, wherein, The cavity volume is 20cm 3 The alloy reaction tube has a first inert material section with a filling amount of 10-30g and a second inert material section with a filling amount of 10-30g.

19. The method according to claim 18, wherein, The cavity volume is 20cm 3 The alloy reaction tube has a first inert material section with a filling amount of 15-20g and a second inert material section with a filling amount of 20-25g.

20. The method of claim 17, wherein, In the direction of the reaction stream, the length ratio of the first inert material segment, the second inert material segment, and the catalyst segment is 1:(1-1.5):(0.02-0.15).

21. The method according to claim 20, wherein, In the direction of the reaction stream, the length ratio of the first inert material segment, the second inert material segment, and the catalyst segment is 1:(1-1.3):(0.03-0.11).

22. The method according to claim 17, wherein, The inert materials filled in the first and second inert material segments are each independently selected from silicon dioxide and / or aluminum oxide.

23. The method according to claim 1, wherein, The conditions for the oxidative coupling reaction include: a temperature of 700-900℃ and a time of 0.2-15h.

24. The method according to claim 23, wherein, The conditions for the oxidative coupling reaction include: a temperature of 750-850℃ and a time of 0.5-8h.

25. The method according to claim 1, wherein, The gas hourly space velocity (HSV) for the reaction of methane and oxygen is 3000-30000 mL / (g·h).

26. The method of claim 25, wherein, The gas hourly space velocity (HSV) for the reaction of methane and oxygen is 5000-25000 mL / (g·h).

27. The method according to claim 1, wherein, The amount of methane used is 2-10 mol relative to 1 mol of oxygen.

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