Method and apparatus for activated conversion of low-concentration methane

Abstract

The invention provides a method and equipment for activating and converting low-concentration methane. The method comprises the following steps: conveying an acid solution and oxygen-containing gas containing methane into a micro-mixer for mixing to obtain a gas-liquid two-phase flow; conveying the gas-liquid two-phase flow into a microreactor, and carrying out catalytic oxidation reaction under the action of metal copper to obtain a gas-liquid mixture; in addition, the temperature of the catalytic oxidation reaction is 50 DEG C or less. According to the method disclosed by the invention, high-efficiency low-concentration methane activation conversion can be realized at normal temperature and normal pressure, and the methane conversion rate can reach 93% or above.

Description

Technical Field

[0001] The invention belongs to the field of methane activation and conversion, and in particular relates to a method and equipment for activating and converting low-concentration methane. Background Art

[0002] Low-concentration methane (0.1% to 5%) mainly comes from natural gas, oil and coal mining, agricultural emissions and wastewater treatment. These widely distributed low-concentration methane are usually unable to be directly burned or lack effective catalytic methods to convert them into high-value-added products (such as methanol). They are often directly discharged into the atmosphere, which has a significant impact on the global climate. Methane is a typical greenhouse gas. The greenhouse effect of methane per unit mass is about 25 times that of carbon dioxide. Therefore, the effective collection, conversion and utilization of low-concentration methane is not only of great environmental significance for reducing greenhouse gas emissions, but also can improve energy efficiency and promote sustainable development. However, due to the high carbon-hydrogen bond energy (413 kJ / mol) and poor polarity in methane molecules, high-energy consumption and high-carbon emission equipment are usually required to provide extreme reaction conditions such as high temperature and high pressure to achieve efficient activation and conversion of low-concentration methane.

[0003] In addition, the current existing technology for low-concentration methane activation conversion technology research is mainly focused on the development and utilization of Pd-based catalysts such as precious metal catalysts (for example, see references 1 and 2), metal oxide catalysts (for example, see references 3 and 4) and single-atom catalysts (for example, see reference 5), as well as the research on Pd-based catalyst modification, but the preparation process of these catalysts is complicated, the cost is high, and they are easily deactivated under reaction conditions, which is difficult to meet large-scale production needs. At the same time, precious metal catalysts such as Pd are very expensive and natural resources are extremely scarce, which seriously restricts the industrial application and development of low-concentration methane activation conversion technology. Therefore, the key to low-concentration methane activation conversion technology is to find an efficient and low-cost catalyst and explore a methane catalytic oxidation system with mild reaction conditions, controllable reaction process, high methane conversion rate, and low catalyst preparation and reaction operation costs.

[0004] So far, the reaction systems for direct catalytic oxidation of methane mainly include liquid-phase catalytic oxidation systems and gas-phase catalytic oxidation systems. Compared with the gas-phase catalytic oxidation reaction system of methane with a higher activation temperature, the liquid-phase catalytic oxidation reaction of methane is carried out in a liquid medium, which can achieve direct contact between the reactants and the catalyst molecules. The solvation effect of the medium can enable the reaction to proceed under mild conditions, with a lower reaction temperature (usually below 200°C), significantly reducing energy consumption. At the same time, the extremely low solubility of methane in the aqueous phase system (about 0.001 mol / L at room temperature) will also lead to limited mass transfer of methane during the reaction, further hindering the efficient conversion and utilization of low-concentration methane. Therefore, the development of efficient, low-cost and stable catalysts and catalytic oxidation systems with excellent mass transfer, mild reaction conditions, controllable reaction process and high methane conversion rate to achieve efficient low-concentration methane activation and conversion processes still faces many problems and challenges.

[0005] References:

[0006] Cited literature 1: Tianyu Guo, Jianping Du, Jinping Li. The effects of ceriamorphology on the properties of Pd / ceria catalyst for catalytic oxidation oflow-concentration methane[J]. Journal of Materials Science, 2016, 51: 10917-10925.

[0007] Cited literature 2: Xuefei Weng, Hongjia Ren, Mingshu Chen, Huilin Wan. Effect of surface oxygen on the activation of methane on Palladium and Platinumsurfaces[J]. ACS Catalysis, 2014, 4(8): 2598-2604.

[0008] Reference 3: Tianyu Guo, Jianping Du, Jinting Wu, Shuang Wang, Jinping Li. Structure and kinetic investigations of surface-stepped CeO 2-supported Pdcatalysts for low-concentration methane oxidation[J].Chemical EngineeringJournal,2016,306:745-753.

[0009] Reference 4: CN108325525A

[0010] Cited literature 5: Pawan Kumar, Tareq A. Al-Attas, Jinguang Hu, Md. GolamKibria. Single atom catalysts for selective methane oxidation to oxygenates[J]. ACS Nano, 2022, 16(6):8557-8618. Summary of the invention

[0011] Problem that the invention aims to solve

[0012] In view of the problems existing in the prior art, such as high catalyst cost, harsh reaction conditions, high energy consumption, large mass transfer resistance, low conversion efficiency, etc., the present invention first provides a method for activating and converting low-concentration methane. The synthesis method is a full-process process for continuous conversion of micro-reactions based on a liquid-phase catalytic oxidation system, which can achieve safe and efficient conversion and utilization of low-concentration methane under normal temperature and pressure conditions.

[0013] Furthermore, the present invention also provides a device for implementing the method of activating and converting low-concentration methane. The device is simple and can ensure that the treatment method is carried out efficiently and orderly. The thermal risk of using the device is low and the production efficiency is high.

[0014] Solutions for solving problems

[0015] The present invention can solve the above technical problems by implementing the following technical solutions:

[0016] [1]. The present invention provides a method for activating and converting low-concentration methane, which comprises the following steps:

[0017] a) transporting an acidic solution and an oxygen-containing gas containing methane to a micromixer for mixing to obtain a gas-liquid two-phase flow;

[0018] b) transporting the gas-liquid two-phase flow to a microreactor and performing a catalytic oxidation reaction under the action of metallic copper to obtain a gas-liquid mixture;

[0019] Furthermore, the temperature of the catalytic oxidation reaction is below 50°C.

[0020] [2] The method according to [1], wherein:

[0021] In the acidic solution, the concentration of the acidic substance is 0.01 to 2 mol / L;

[0022] In the oxygen-containing gas containing methane, the concentration of methane is 0.1% to 5%, and the oxygen concentration of the oxygen-containing gas is 10 to 50%.

[0023] [3] The method according to [2], wherein:

[0024] The acidic substance includes one or more of sulfuric acid, perchloric acid, phosphoric acid, hydrochloric acid, hydrobromic acid and hydroiodic acid.

[0025] [4] A method according to any one of [1] to [3], wherein:

[0026] The volume flow ratio of the oxygen-containing gas containing methane to the acidic solution is (0.1-50):1.

[0027] [5] A method according to any one of [1] to [4], wherein:

[0028] The micro mixer is a microchannel mixer, a membrane dispersion mixer or a micro mesh mixer;

[0029] The microreactor is a coil-type microreactor, and the material of the coil-type microreactor is metallic copper; or the microreactor is a micro-packed bed reactor, and the filler in the micro-packed bed reactor is copper metal particles.

[0030] [6] A method according to any one of [1] to [5], wherein:

[0031] The channel diameter of the micro mixer is 0.1 to 2 mm;

[0032] The channel diameter of the microreactor is 0.2-10 mm.

[0033] [7] A method according to any one of [1] to [6], wherein:

[0034] The temperature in the micro mixer is 10 to 40° C., and the mixing time is 1 to 60 seconds;

[0035] The reaction temperature in the microreactor is 10-40° C., the reaction pressure is 0.8-1.2 atm, and the reaction time is 0.1-1.5 h.

[0036] [8] The method according to any one of [1] to [7], wherein the liquid component in the gas-liquid mixture includes methanol.

[0037] [9] The method according to any one of [1] to [8], wherein the method further comprises a step of performing gas-liquid separation on the gas-liquid mixture.

[0038]

[10] . Furthermore, the present invention also provides a device for implementing the method described in any one of [1] to [9] above, wherein the device comprises a micro-mixer and a micro-reactor connected in sequence;

[0039] Furthermore, the microreactor is made of copper or is filled with copper metal particles.

[0040] Effects of the Invention

[0041] The present invention uses a metallic copper catalyst and a liquid-phase catalytic oxidation system and a micro-reaction process with a micro-mixer and a micro-reactor as the core to activate and convert low-concentration methane, which can fully ensure uniform mixing of materials, greatly enhance the gas-liquid two-phase mass transfer efficiency, and also improve the safety performance of the reaction.

[0042] The present invention uses metallic copper as a catalyst, which can combine oxygen and acidic solution to form a large number of active sites, thereby realizing a methane activation reaction under mild conditions (such as normal temperature and pressure), and the copper catalyst is stably and efficiently recycled, realizing a process of high-performance, long-term activation of low-concentration methane to prepare high-value-added chemical products (such as methanol), and the copper material is cheap and easy to obtain. Therefore, the method of the present invention has the advantages of simple operation, low energy consumption, low cost and easy scale-up.

[0043] Furthermore, the equipment for implementing the method for activating and converting low-concentration methane of the present invention can ensure that the treatment method is carried out efficiently and orderly, and the thermal risk of using the equipment is low and the production efficiency is high. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 A flow chart of an apparatus for implementing a method for activating and converting low-concentration methane according to the present invention is shown;

[0045] Figure 2 Another equipment flow chart of the method for implementing the activation and conversion of low-concentration methane of the present invention is shown;

[0046] Figure 3 The figure shows the results of measuring the methane conversion rate in Examples 1 to 5 of the present invention;

[0047] Figure 4 The figure shows the results of measuring the methane conversion rate in Examples 6 to 12 of the present invention;

[0048] Figure 5 The figure shows the results of measuring the methane conversion rate under different acid concentrations of the present invention;

[0049] Figure 6 The figure shows the test results of low-concentration methane conversion stability of the present invention. DETAILED DESCRIPTION

[0050] Various exemplary embodiments, features and aspects of the present invention will be described in detail below. The word "exemplary" used here means "used as an example, embodiment or illustrative". Any embodiment described here as "exemplary" is not necessarily interpreted as being superior or better than other embodiments.

[0051] In addition, in order to better illustrate the present invention, numerous specific details are provided in the following specific embodiments. It should be understood by those skilled in the art that the present invention can be implemented without certain specific details. In other examples, methods, means, equipment and steps well known to those skilled in the art are not described in detail in order to highlight the subject matter of the present invention.

[0052] Unless otherwise stated, the units used in this specification are all international standard units, and the numerical values ​​and numerical ranges appearing in the present invention should be understood to include the inevitable systematic errors in industrial production.

[0053] In this specification, the word "may" means both performing a certain process and not performing a certain process.

[0054] In this specification, the references to "some specific / preferred embodiments", "other specific / preferred embodiments", "embodiments", etc., mean that the specific elements (e.g., features, structures, properties and / or characteristics) described in connection with the embodiments are included in at least one embodiment described herein, and may or may not exist in other embodiments. In addition, it should be understood that the elements may be combined in various embodiments in any suitable manner.

[0055] In this specification, the numerical range expressed using "a numerical value A to a numerical value B" means a range including the endpoints numerical values ​​A and B.

[0056] In this specification, when "normal temperature" or "room temperature" is used, the temperature may be 10 to 40°C.

[0057] In this specification, when "normal pressure" is used, the pressure is 1 atm.

[0058] In this specification, unless otherwise specified, the word "multiple" in "multiple", "multiple", "plurality", etc. means a numerical value of 2 or more.

[0059] The present invention mainly provides a method for activating and converting low-concentration methane, which is mainly based on the following insights:

[0060] In the traditional low-concentration methane activation and conversion technology, high temperature (200°C to 600°C) or high pressure (5bar to 50bar) is usually required to activate or convert methane into high-value-added chemical products such as methanol, and the reaction process has high energy consumption and high carbon emissions. In addition, the traditional low-concentration methane activation and conversion technology generally uses precious metal catalysts, which have a complicated preparation process and high cost, are easily deactivated under reaction conditions, and are difficult to meet large-scale production needs. The present invention uses metallic copper as a catalyst, and the raw materials are cheap and easy to obtain. It is based on the full-process process of continuous conversion of micro-reactions of the liquid-phase catalytic oxidation system, has high reaction activity and selectivity, is easy to scale up, and realizes the catalytic oxidation of low-concentration methane at normal temperature and pressure to prepare high-value-added chemical products (such as methanol), avoiding the use of high-temperature and high-pressure equipment.

[0061] <First aspect>

[0062] In a first aspect of the present invention, a method for activating and converting low-concentration methane is provided, the method comprising the following steps:

[0063] a) transporting an acidic solution and an oxygen-containing gas containing methane to a micromixer for mixing to obtain a gas-liquid two-phase flow;

[0064] b) transporting the gas-liquid two-phase flow to a microreactor and performing a catalytic oxidation reaction under the action of metallic copper to obtain a gas-liquid mixture;

[0065] Furthermore, the temperature of the catalytic oxidation reaction is below 50°C.

[0066] Step a)

[0067] This step is a step of mixing the reaction raw materials, i.e., the acidic solution and the oxygen-containing gas containing methane, in a micro mixer. By using a micro mixer for the above mixing, the raw materials can be fully mixed. Specifically, a pump (e.g., a horizontal flow pump, a diaphragm pump, a magnetic pump, a centrifugal pump, etc.) or a gas mass flow controller can be used to pass the raw materials into the micro mixer.

[0068] In some specific embodiments, in the acidic solution, the concentration of the acidic substance is 0.01-2 mol / L, preferably 0.3-1 mol / L, for example, it can be 0.05 mol / L, 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 1 mol / L, 1.2 mol / L, 1.4 mol / L, 1.6 mol / L, 1.8 mol / L, 1.9 mol / L, etc.

[0069] In some specific embodiments, the concentration of methane in the oxygen-containing gas containing methane is 0.1% to 5%, preferably 0.5 to 5%, for example, it can be 0.3%, 0.5%, 1%, 2%, 2.5%, 3%, 4%, 5%, etc.; specifically, the methane concentration in the present invention refers to the volume concentration.

[0070] In some specific embodiments, the oxygen concentration in the oxygen-containing gas is 10-50%, preferably 15-30%, for example, 15%, 20%, 21%, 25%, 30%, 35%, 40%, 45%, etc. When the oxygen concentration in the oxygen-containing gas is within the above range, the oxidation reaction can be effectively carried out. Specifically, the oxygen concentration in the present invention refers to the volume concentration.

[0071] In some specific embodiments, the volume flow ratio of the oxygen-containing gas containing methane to the acidic solution is (0.1-50):1, preferably (0.25-40):1, for example, it can be 1:4, 1:3, 1:2, 1:1, 2:1, 2.5:1, 10:3, 5:1, 10:1, 15:1, 20:1, 25:1, 30:1, 35:1, 40:1, 45:1, 50:1, etc.; by making the volume flow ratio of the oxygen-containing gas containing methane to the acidic solution within the above range, methane can be fully converted and the conversion rate can be adjusted.

[0072] Furthermore, by adjusting the amount of the inlet liquid in the micro mixer, the volume flow ratio of the oxygen-containing gas containing methane to the acidic solution is (0.1-50):1.

[0073] Specifically, in the present invention, the solvent for dissolving the acidic substance is not particularly limited, and can be any feasible polar solvent in the art, preferably water.

[0074] Furthermore, the present invention does not specifically limit the acidic substance, and it may be a commonly used strong acidic substance in the art, such as sulfuric acid, perchloric acid, phosphoric acid, hydrochloric acid, hydrobromic acid or hydroiodic acid, preferably sulfuric acid.

[0075] Specifically, the present invention has no particular limitation on the type of oxygen-containing gas, and examples thereof include air, or air diluted with an inert gas such as nitrogen, argon or helium. Oxygen-containing air prepared by adding pure oxygen to air may also be used.

[0076] The present invention has no particular limitation on the micromixer used in step a), which can be any micromixer known in the art that is suitable for gas-liquid mixing, such as a microchannel mixer, a membrane dispersion mixer or a micromesh mixer, etc. In a preferred embodiment, the micromixer is a microchannel mixer.

[0077] According to the present invention, the micromixer can be obtained by adjusting the micromixer in the prior art, and the adjustment includes adjusting the microchannel equivalent diameter and / or microchannel volume. In some specific embodiments, the channel diameter of the micromixer is 0.1 to 2 mm, preferably 0.4 to 1.2 mm, for example, 0.5 mm, 0.8 mm, 1 mm, etc.

[0078] In some specific embodiments, the temperature in the micro mixer is 10-40°C, for example, 10°C, 15°C, 20°C, 25°C, 30°C, 35°C, 40°C, etc. By controlling the temperature in the micro mixer at 10-40°C, the reaction rate and the conversion rate of methane can be increased, and the reaction heat can be removed in time. The mixing time in the micro mixer is 1-60s, for example, 1s, 3s, 5s, 10s, 15s, 20s, 25s, 30s, 35s, 40s, 45s, 50s, 55s, etc.; by setting the mixing time to 1-60s, sufficient mixing can be ensured while taking into account the conversion efficiency.

[0079] Step b)

[0080] This step is a step of subjecting methane and oxygen to a catalytic oxidation reaction under a metallic copper catalyst and acidic conditions to generate carbon dioxide and methanol.

[0081] This step is carried out in a microreactor, and the present invention has no particular limitation on the microreactor, which can be any microreactor known in the art suitable for gas-liquid phase reaction, such as a coiled tube microreactor, a micro packed bed reactor or a microchannel reactor, etc. In some preferred embodiments, the microreactor is a coiled tube microreactor or a micro packed bed reactor. According to the present invention, the microreactor can be obtained by adjusting the microreactor in the prior art, and the adjustment includes adjusting the microchannel equivalent diameter and / or the microchannel volume.

[0082] In some specific embodiments, when the microreactor is a coil-type microreactor, the length of the coil-type microreactor is 0.5 to 5 m; the material of the microreactor is metallic copper. In some preferred embodiments, the content of metallic copper in the microreactor can be more than 50% by mass, more than 80% by mass, or all metallic copper.

[0083] In some specific embodiments, when the microreactor is a micro-packed bed reactor, the length of the micro-packed bed reactor is 5 to 40 cm; the material of the microreactor is acid-resistant materials such as glass, fluororubber hose or polymethyl methacrylate (PMMA, also known as organic glass), and the filler of the microreactor is copper metal particles. In some preferred embodiments, the particle size of the copper metal particles is 10 to 1000 μm, and the filling porosity of the filler (the percentage of the void volume between particles to the loose volume of the granular material in the stacked state) is 20% to 70%.

[0084] In some specific embodiments, the channel diameter of the microreactor is 0.2-10 mm, preferably 0.3-5 mm, for example, 0.4 mm, 1 mm, 2 mm, etc.

[0085] In some specific embodiments, the temperature in the microreactor is below 50°C, preferably 10-40°C, for example, 10°C, 15°C, 20°C, 25°C, 30°C, 35°C, 40°C, etc.; by controlling the temperature in the microreactor at 10-40°C, the reaction rate and the conversion rate of methane can be increased. The reaction pressure in the microreactor is 0.8-1.2atm, for example, 0.8atm, 0.9atm, 1.0atm, 1.1atm, 1.2atm, etc.; the reaction time in the microreactor is 0.1-1.5h, for example, 0.2h, 0.3h, 0.4h, 0.5h, 0.6h, 0.7h, 0.8h, 0.9h, 1h, 1.2h, 1.4h, 1.5h, etc.; by controlling the reaction pressure and reaction time in the microreactor within the above range, the equipment size and investment can be reduced while ensuring the reaction rate and methane conversion rate.

[0086] In some specific embodiments, the method further comprises separating the gas phase and the liquid phase of the gas-liquid mixture, with the gas phase in the upper layer and the liquid phase product in the lower layer. The separation can be performed by any means known in the art. In some specific embodiments, the gas-liquid mixture is passed into a gas-liquid separator for gas-liquid separation, exhaust gas is discharged from the upper part of the gas-liquid separator, and the product is drawn from the lower part of the gas-liquid separator. In some specific embodiments, the main component in the liquid phase product includes methanol.

[0087] Specifically, the present invention has no particular limitation on the gas-liquid separator, which can be any gas-liquid separator known in the art that is suitable for gas-liquid phase separation, such as a gas-liquid separation tank, a membrane phase separator, and the like.

[0088] Through the implementation of the above method, the methane conversion rate of the present invention can be above 93%, and the methanol selectivity can be above 7%.

[0089] <Second Aspect>

[0090] The second aspect of the present invention provides a device for implementing the synthesis method described in the first aspect, which includes a micro-mixer and a micro-reactor connected in sequence; and the micro-reactor is made of metallic copper or is filled with copper metal particles.

[0091] In some specific embodiments, the microreactor is further connected to a gas-liquid separator.

[0092] By using the device of the present invention, it can be ensured that the activation conversion of low-concentration methane of the present invention is carried out efficiently and orderly at normal temperature and pressure, and the thermal risk of using the device is low and the conversion efficiency is high.

[0093] Example

[0094] The embodiments of the present invention will be described in detail below in conjunction with the examples, but those skilled in the art will appreciate that the following examples are only used to illustrate the present invention and should not be considered to limit the scope of the present invention. If no specific conditions are specified in the examples, they are carried out according to normal conditions or the conditions recommended by the manufacturer. If the manufacturer is not specified for the reagents or instruments used, they are all conventional products that can be obtained commercially.

[0095] In the following embodiments, the conversion rate of methane is calculated as follows:

[0096] Methane conversion rate (mol%) = product mole number / methane feed mole number × 100%

[0097] In the following embodiments, the selectivity of methanol is calculated as follows:

[0098] Methanol selectivity (mol%) = moles of methanol produced / moles of product × 100%

[0099] Among them, the number of moles of product = the number of moles of methanol generated + the number of moles of carbon dioxide generated + the number of moles of by-products such as ethane generated The parameters of the micro-reactor used in the following examples are as follows:

[0100] (1) In accordance with Figure 1 Example

[0101] The micro mixer is a T-type micro three-way mixer made of pure titanium with a channel diameter of 1 mm.

[0102] The microreactor is a micro-packed bed reactor made of acid-resistant materials such as glass, fluororubber hose, PMMA, etc., with an inner diameter of 2 mm and a length of 20 cm (100 μm copper metal particles are used as fillers, which are filled into the pipe until it is full, with a porosity of 60%).

[0103] (2) In accordance with Figure 2 Example

[0104] The micro mixer is a T-type micro three-way mixer made of pure titanium with a channel diameter of 0.5 mm.

[0105] The microreactor is a coil-type microreactor made of copper, with an inner diameter of 0.4 mm and a length of 3 m.

[0106] The methane conversion described in the following examples was measured by gas chromatography; the methanol selectivity described in the following examples was measured by nuclear magnetic resonance (NMR).

[0107] Embodiment 1:

[0108] like Figure 1 As shown, 5% methane + 20% oxygen + 75% inert gas nitrogen is used as a low-concentration methane and oxygen mixed gas, and 0.5 mol / L sulfuric acid is used as an acidic solution. The low-concentration methane and oxygen mixed gas and the acidic solution are respectively transported to the micromixer by a horizontal flow pump for gas-liquid mixing. The mixer temperature is 25°C, the mixing time is 30s, the low-concentration methane and oxygen mixed gas flow rate is 5mL / min, and the acidic solution flow rate is 1mL / min. The mixed gas-liquid two-phase flow enters the microreactor for catalytic oxidation reaction. The reaction temperature is 25°C and the reaction pressure is 1.0atm. The products (liquid products and gas products) obtained at the outlet of the microreactor are collected at a reaction time of 1h, and the products are analyzed. It can be seen from the analysis that the liquid products are mainly methanol and water, and the gas products are mainly carbon dioxide and a small amount of unreacted methane.

[0109] Gas product reaction equation:

[0110]

[0111] Liquid product reaction equation:

[0112]

[0113] Embodiment 2:

[0114] Compared with Example 1, the difference is that the flow rate of the acidic solution is 5 mL / min.

[0115] Embodiment 3:

[0116] Compared with Example 1, the difference is that the flow rate of the acidic solution is 10 mL / min.

[0117] Embodiment 4:

[0118] Compared with Example 1, the difference is that the flow rate of the acidic solution is 15 mL / min.

[0119] Embodiment 5:

[0120] Compared with Example 1, the difference is that the flow rate of the acidic solution is 20 mL / min.

[0121] Embodiment 6:

[0122] like Figure 2 As shown, 0.5 mol / L sulfuric acid is introduced into the copper tube in advance, with a flow rate of 0.5 mL / min and a duration of 40 min to wash away the native oxide inside the copper tube. A volume fraction of 5% methane + 20% oxygen + 75% inert gas nitrogen is used as a low-concentration methane and oxygen mixed gas, and 0.5 mol / L sulfuric acid is used as an acidic solution. The low-concentration methane and oxygen mixed gas and the acidic solution are respectively transported to the micromixer by a horizontal flow pump for gas-liquid mixing. The mixer temperature is 25 ° C, the mixing time is 30 s, the low-concentration methane and oxygen mixed gas flow rate is 2 mL / min, and the acidic solution flow rate is 0.1 mL / min. The mixed gas-liquid two-phase flow enters the microreactor for catalytic oxidation reaction, the reaction temperature is 25 ° C, and the reaction pressure is 1.0 atm. The products (liquid products and gas products) obtained at the outlet of the microreactor are collected at a reaction time of 1 h, and the products are analyzed.

[0123] Embodiment 7:

[0124] Compared with Example 6, the difference is that the flow rate of the acidic solution is 0.05 mL / min.

[0125] Embodiment 8:

[0126] Compared with Example 6, the difference is that the flow rate of the acidic solution is 0.2 mL / min.

[0127] Embodiment 9:

[0128] Compared with Example 6, the difference is that the flow rate of the acidic solution is 0.4 mL / min.

[0129] Embodiment 10:

[0130] Compared with Example 6, the difference is that the flow rate of the acidic solution is 0.6 mL / min.

[0131] Embodiment 11:

[0132] Compared with Example 6, the difference is that the flow rate of the acidic solution is 0.8 mL / min.

[0133] Embodiment 12:

[0134] Compared with Example 6, the difference is that the flow rate of the acidic solution is 1.0 mL / min.

[0135] Embodiment 13:

[0136] Compared with Example 6, the difference is that: 2.5% methane+20% oxygen+77.5% inert gas nitrogen by volume is used as the low-concentration methane and oxygen mixed gas.

[0137] Embodiment 14:

[0138] Compared with Example 6, the difference is that the concentration of the acidic solution is 0.1 mol / L.

[0139] Embodiment 15:

[0140] Compared with Example 6, the difference is that the concentration of the acidic solution is 0.3 mol / L.

[0141] Embodiment 16:

[0142] Compared with Example 6, the difference is that the concentration of the acidic solution is 0.7 mol / L.

[0143] Comparative Example 1:

[0144] Compared with Example 6, the difference is that the 0.5 mol / L sulfuric acid solution is replaced by 0.5 mol / L Na 2 SO 4 Solution.

[0145] Test example:

[0146] 1. The methane conversion rate and methanol selectivity of Examples 1 to 16 and Comparative Example 1 were measured. The results are shown in Tables 1 and Figure 2 to Figure 5 shown.

[0147] Table 1:

[0148] Group Gas-liquid flow volume ratio (gas / acidic liquid) Methane conversion rate (%) Methanol selectivity (%) Example 1 5:1 88.60 3.98 Example 2 1:1 92.79 4.87 Example 3 1:2 81.95 3.16 Example 4 1:3 75.06 2.44 Example 5 1:4 70.52 1.49 Example 6 20:1 93.88 7.08 Example 7 40:1 91.60 6.52 Example 8 10:1 87.27 6.27 Example 9 5:1 83.75 5.47 Example 10 10:3 80.15 4.25 Embodiment 11 2.5:1 76.48 3.13 Example 12 2:1 71.45 2.66 Example 13 20:1 89.65 -- Embodiment 14 20:1 11.85 -- Embodiment 15 20:1 60.47 -- Example 16 20:1 94.22 -- Comparative Example 1 1:0 0 --

[0149] 2. Low concentration methane conversion stability test

[0150] like Figure 2 As shown, 5% methane + 20% oxygen + 75% inert gas nitrogen with a volume fraction is used as a low-concentration methane and oxygen mixed gas, and 0.5 mol / L sulfuric acid is used as an acidic solution. The low-concentration methane and oxygen mixed gas and the acidic solution are respectively transported to the micromixer by a horizontal flow pump for gas-liquid mixing. The mixer temperature is 25°C, the mixing time is 30s, the low-concentration methane and oxygen mixed gas flow rate is 2mL / min, and the acidic solution flow rate is 0.1mL / min. The mixed gas-liquid two-phase flow enters the microreactor for catalytic oxidation reaction. The reactor temperature is 25°C and the pressure is 1.0atm. The products (liquid products and gas products) obtained at the outlet of the microreactor are collected at reaction times of 2h, 4h, 6h, 8h, 10h, and 12h, and the methane conversion rate is measured. The results are shown in Tables 2 and Figure 6 shown.

[0151] Table 2:

[0152] Reaction time (h) Methane conversion rate (%) 2 91.41 4 92.16 6 93.85 8 92.89 10 94.46 12 95.59

[0153] It should be noted that, although the technical solution of the present invention is introduced with specific examples, those skilled in the art will appreciate that the present invention should not be limited thereto.

[0154] The embodiments of the present invention have been described above, and the above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The selection of terms used herein is intended to best explain the principles of the embodiments, practical applications, or technical improvements in the market, or to enable other persons of ordinary skill in the art to understand the embodiments disclosed herein.

Claims

1. A method for activating and converting low-concentration methane, characterized in that: The following steps are involved: a) transporting an acidic solution and an oxygen-containing gas containing methane to a micromixer for mixing to obtain a gas-liquid two-phase flow; b) transporting the gas-liquid two-phase flow to a microreactor and performing a catalytic oxidation reaction under the action of metallic copper to obtain a gas-liquid mixture; Furthermore, the temperature of the catalytic oxidation reaction is below 50°C.

2. The method according to claim 1, characterized in that In the acidic solution, the concentration of the acidic substance is 0.01 to 2 mol / L; In the oxygen-containing gas containing methane, the concentration of methane is 0.1% to 5%, and the oxygen concentration of the oxygen-containing gas is 10 to 50%.

3. The method according to claim 2, characterized in that The acidic substance includes one or more of sulfuric acid, perchloric acid, phosphoric acid, hydrochloric acid, hydrobromic acid and hydroiodic acid.

4. The method according to any one of claims 1 to 3, characterized in that: The volume flow ratio of the oxygen-containing gas containing methane to the acidic solution is (0.1-50):

1.

5. The method according to any one of claims 1 to 4, characterized in that: The micro mixer is a microchannel mixer, a membrane dispersion mixer or a micro mesh mixer; The microreactor is a coil-type microreactor, and the material of the coil-type microreactor is metallic copper; or the microreactor is a micro-packed bed reactor, and the filler in the micro-packed bed reactor is copper metal particles.

6. The method according to any one of claims 1 to 5, characterized in that: The channel diameter of the micro mixer is 0.1 to 2 mm; The channel diameter of the microreactor is 0.2-10 mm.

7. The method according to any one of claims 1 to 6, characterized in that: The temperature in the micro mixer is 10 to 40° C., and the mixing time is 1 to 60 seconds; The reaction temperature in the microreactor is 10-40° C., the reaction pressure is 0.8-1.2 atm, and the reaction time is 0.1-1.5 h.

8. The method according to any one of claims 1 to 7, characterized in that: The liquid component in the gas-liquid mixture includes methanol.

9. The method according to any one of claims 1 to 8, characterized in that: The method further comprises the step of performing gas-liquid separation on the gas-liquid mixture.

10. A device for implementing the method according to any one of claims 1 to 9, characterized in that: The device comprises a micro mixer and a micro reactor connected in sequence; Furthermore, the microreactor is made of copper or is filled with copper metal particles.

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