Method for preparing methanol in one step using methane and carbon dioxide as raw materials

Abstract

The present invention provides a method for producing methanol in one step using methane and carbon dioxide as raw materials, comprising the following steps: introducing methane and carbon dioxide into a dielectric barrier discharge plasma reactor containing a catalyst, and synthesizing methanol in one step at 100-300°C; wherein the molar ratio of methane to carbon dioxide is 0.5-5; the residence time of the methane and carbon dioxide mixture in the plasma catalytic discharge space is 1-10 seconds; and the catalyst is a copper-based catalyst comprising a molecular sieve support with a silicon-aluminum ratio of 1-20 and an active component copper, wherein the copper content is 0.1%-70.0%, based on 100% by mass of the catalyst. This method uses a catalyst composed of a specific support and active component to convert methane and carbon dioxide into methanol in one step with high selectivity, solving the problems of multiple-step processes and low methanol selectivity in the reaction products faced by existing methane and carbon dioxide conversion technologies, improving the utilization value of the two greenhouse gases, and facilitating chemical production and use.

Description

Technical Field

[0001] The invention belongs to the technical field of methanol synthesis, and particularly relates to a method for preparing methanol using methane and carbon dioxide as raw materials. Background Art

[0002] Methane and carbon dioxide are major greenhouse gases in the atmosphere and are also potential "carbon resources." Turning these gases into valuable resources would not only alleviate the ecological and environmental challenges associated with greenhouse gas emissions but also enable the sustainable recycling of carbon resources. Therefore, research on the co-conversion of methane and carbon dioxide is of great significance to natural gas chemical industry, petrochemical industry, and environmental protection, and has attracted widespread attention from both academia and industry.

[0003] Producing methanol from methane and carbon dioxide is one of the ideal ways to utilize both. Methanol is an important chemical raw material, used as a gasoline additive, and can also be used to produce chemicals such as olefins and aromatics through processes such as MTO and MTP. Currently, conventional catalytic conversion of methane and carbon dioxide to methanol requires a two-step process under high temperature and high pressure, which is energy-intensive and complex. The first step is to reform methane and carbon dioxide at high temperature to produce synthesis gas (CH4 + CO2 → 2CO + 2H2, ΔH298K = 247 kJ / mol). The second step is to convert the resulting synthesis gas into methanol under high pressure (CO + 2H2 → CH3OH). In the first step, due to the extremely high thermodynamic stability of methane and carbon dioxide, the reforming process typically requires high temperatures of 1100-1200K. This high temperature is demanding on the equipment and can easily lead to carbon deposits, reducing carbon utilization. Furthermore, high temperatures can easily cause catalyst deactivation due to sintering and carbon deposition, reducing catalyst stability. In the second step, because the conversion of syngas to methanol involves a molecular weight reduction reaction, methanol synthesis requires high pressure conditions. This high pressure also places stringent requirements on the equipment, making practical operation difficult and energy-intensive. Clearly, the above two-step method for converting methane and carbon dioxide into methanol carries high operating, equipment, and maintenance costs.

[0004] Non-equilibrium plasma is a thermodynamic non-equilibrium system. Its outstanding feature is that the temperature of heavy particles is low, which can be as low as room temperature, but the temperature of free electrons is high (Te≈10 4 -10 5K≈1-10eV), these high-energy free electrons transfer energy to the reactant molecules by inelastic collisions, activating the reactant molecules into highly active species, thereby initiating chemical reactions. Non-equilibrium plasma is particularly effective in activating inert molecules, such as CO2, CH4, and N2. Due to the unique properties of non-equilibrium plasma, non-equilibrium plasma technology has been widely used in the low-temperature activation conversion of methane and carbon dioxide in recent years, which can alleviate the problem of catalyst deactivation due to high-temperature sintering to a certain extent. However, the main product of the reaction is synthesis gas (such as CN109867261A, CN109264671A, CN108408690A, KR1743954B1, KR2016077957A, CN104071747A, PT105078A1, CN1180058C, JP2002037601A, JP11322638A, JP11278802A). Only a few studies have found methanol production in addition to syngas.

[0005] Specifically, Chinese patent document CN108408690A discloses a method for producing high-quality synthesis gas from methane, carbon dioxide, and water. Its technical features include: first, water simultaneously generates oxygen and hydrogen at the anode and cathode of a water electrolysis cell, respectively. All or part of the generated oxygen mixes with methane and carbon dioxide, and the resulting gas mixture (O2 / CH4 / CO2) flows into a plasma catalytic reforming reactor to react and generate a reformed product gas. The resulting reformed product gas is mixed with hydrogen generated at the cathode of the water electrolysis cell to produce high-quality synthesis gas. Second, the plasma catalytic reforming reactor comprises two reaction units: a plasma reaction unit and a catalytic reaction unit. The plasma in the plasma reaction unit is generated by a sliding arc discharge between a high-voltage electrode and a grounded electrode. The characteristic of sliding arc discharge is that there is no dielectric layer between the high-voltage electrode and the grounded electrode, resulting in a single discharge region with a small effective discharge volume. Because the discharge current constantly moves between the two electrodes, disappears, and regenerates, it is impossible to fill the discharge region with a catalyst. Therefore, the so-called plasma catalysis is actually a two-stage combination of plasma and catalyst, with the catalyst located downstream of the arc discharge region, not within the discharge region. The catalyst filled in the catalytic reaction unit is a nickel-based, cobalt-based, or platinum-based methane reforming catalyst. A portion of the energy required by the catalytic reaction zone comes from the upstream plasma reaction zone unit, and the other portion is supplied by external heating of the reactor. Thirdly, the external heating temperature of the plasma catalytic reforming reactor is 700-850°C. The defects or deficiencies of this technical solution are: (1) for methane and carbon dioxide, the water introduced in this method is actually equivalent to the introduction of O2 and H2; firstly, the O2 generated by water electrolysis is introduced into the mixed gas of CH4 and CO2, which is equivalent to the introduction of First, an O2 oxidant is introduced. O2 can only activate and convert CH4, while O2 has a certain side effect on the conversion of CO2 (CH4+CO2→CO+H2, O2 can oxidize part of CO and H2 to produce CO2 and H2O); second, the mixing reaction of O2 and CH4 has strict requirements on the ratio of the two, which cannot exceed the explosion limit of the mixture of the two, otherwise the reaction process is prone to "explosion", posing a safety hazard; third, the H2 produced by water electrolysis is introduced into the reformed product gas (CO and H2) obtained in the previous step, which only plays a role in adjusting the ratio of CO and H2 in the reformed product. In contrast, the direct introduction of unelectrolyzed water into the CH4 and CO2 mixture can directly reform water and methane to produce synthesis gas (CH4+H2O→CO+H2), avoiding the above-mentioned safety hazards and excessive oxidation of the products CO and H2 to CO2 and H2O.(2) The plasma catalytic reforming reaction is actually composed of two reaction units, namely the sliding arc discharge plasma reaction unit and the downstream catalytic reaction unit. That is, the catalyst is located downstream of the sliding arc plasma reaction unit, not in the plasma reaction zone. This situation causes the short-lived, highly active species produced in the discharge zone to disappear upon reaching the catalyst surface and transform into low-energy neutral species. In other words, the catalyst cannot utilize the short-lived, highly active species produced by the discharge unit and can only utilize the low-energy, long-lived species produced by the upstream discharge unit, thereby reducing the synergistic ability between the catalyst and the plasma. (3) The external heating temperature of the plasma catalytic reforming reactor is 700-850°C, which requires high energy injection and high energy consumption. More importantly, such high temperatures can easily lead to catalyst sintering and deactivation, resulting in poor catalyst stability and short life. In particular, the precious metal "platinum-based methane reforming catalyst" mentioned in this patent disclosure is more susceptible to sintering and deactivation at high temperatures.

[0006] Journal of Physics: Conference Series, 2019, 1386, 012045 discloses the introduction of liquid water into a mixture of methane, carbon dioxide and helium to obtain a mixed gas, and the resulting mixed gas is converted into a liquid product in a plasma reaction system, and water has been shown to promote the formation of oxygen-containing compounds (methanol, ethanol, propanol, butanol, acetaldehyde, formic acid, acetic acid, propionic acid); the plasma involved is generated by dielectric barrier discharge, and the discharge area is filled with materials; the filling material includes one of the naturally occurring molecular sieves in Colombia, glass wool or magnesium oxide / aluminum oxide mixed areas, and the natural molecular sieve involved is composed of 70% heulandite, 25% plagioclase and 5% chlorite; the defects or shortcomings of this technical solution are: the liquid product obtained by the reaction has a complex composition and low selectivity, with the highest total selectivity being 9.8%, of which the methanol selectivity is only 5.9%.

[0007] "Journal of CO2 Utilization, 2020, 35, 79" discloses that liquid water is first used to soak catalysts such as Ca(OH)2, and then the catalyst is filled in a plasma catalytic methane and carbon dioxide reactor to study the effect of water on the reaction; the defects or shortcomings of this technical solution are: water promotes the conversion of methane to produce CO, but the promoting effect of water on the generation of oxygen-containing liquid products is extremely small. After the introduction of water, the total selectivity of oxygen-containing liquid products is only increased by 0.1%; the oxygen-containing liquid products obtained by the reaction have a complex composition, consisting of methanol, ethanol, formaldehyde, acetaldehyde and acetone, with a total selectivity of up to 6.7%, of which the methanol selectivity is only 1.2%.

[0008] "Applied Catalysis B: Environmental, 2020, 261, 118228" discloses a catalyst for plasma catalysis of carbon dioxide and methane to produce liquid products, which is characterized by: using non-equilibrium plasma and catalyst coupling to convert carbon dioxide and methane into liquid products in one step, the non-equilibrium plasma involved is generated by dielectric barrier discharge, and a compressed air gun is used to promptly remove the electric heat generated during the discharge process to achieve the purpose of generating liquid products; the catalyst involved includes a SiO2-loaded Fe or Co-loaded catalyst, the catalyst is prepared by an impregnation method, and the catalyst is reduced and pretreated with a H2 / N2 (5% / 95%) mixed gas at a high temperature of 600°C for 10 hours before use; the defects or shortcomings of this technical solution are: the total selectivity of the liquid product obtained by the reaction is low, with a maximum of 47.9%; compared with the Co / SiO2 catalyst, Fe / SiO2 is more conducive to the production of alcohols (methanol and ethanol), and the resulting methanol selectivity is as high as 31%.

[0009] AngewandteChemie International Edition, 2017, 56, 13679, reports a method for producing high-value-added fuels and chemicals from carbon dioxide and methane using plasma catalysis. This method utilizes a non-equilibrium plasma, or a non-equilibrium plasma coupled with a catalyst, to convert carbon dioxide and methane into high-value-added fuels and chemicals in a single step at ambient temperature and pressure. The non-equilibrium plasma involved is generated by dielectric barrier discharge (DBD). This publication describes a novel DBD plasma reactor, specifically a wire-and-sleeve reactor with an inner cylinder serving as the reaction zone and an outer cylinder connected to circulating water. The circulating water serves the dual purpose of promptly removing discharge reaction heat to control the reaction temperature and also serves as a discharge ground electrode to produce liquid products. The central electrode is a stainless steel rod. The catalysts involved are Cu / γ-Al2O3, Au / γ-Al2O3 and Pt / γ-Al2O3; the defects or shortcomings of this technical solution are as follows: the liquid products obtained by the reaction are composed of acetic acid, methanol, ethanol, formaldehyde and acetone; the total selectivity of the liquid products is as high as 59.1%, with acetic acid as the main product; in addition, this public document mentions that filling the plasma reactor with Cu / γ-Al2O3, Au / γ-Al2O3 or Pt / γ-Al2O3 catalysts results in low methanol selectivity, and the highest methanol selectivity obtained is only 11.9%.

[0010] The Journal of CO2 Utilization, 2021, 52, 101675, reports a Ni-based catalyst for plasma-catalyzed conversion of carbon dioxide and methane to liquid products. This catalyst utilizes a nonequilibrium plasma coupled with a Ni catalyst to convert carbon dioxide and methane into liquid products in a single step. The nonequilibrium plasma is generated by nanosecond pulsed discharge, and the Ni-based catalyst is prepared by impregnation. This technical solution has several drawbacks: the resulting liquid product contains a complex alcohol composition, including methanol, ethanol, ethylene glycol, and propanol. While the NiAl-LDH / NF catalyst favors methanol production, the corresponding methanol selectivity is only 12.3% at its highest.

[0011] Energy Conversion and Management, 2019, 191, 93, reports a catalyst for plasma-catalyzed conversion of carbon dioxide and methane to liquid products. Its characteristics are: Under the condition of introducing Ar into the carbon dioxide and methane mixture, a non-equilibrium plasma coupled with a catalyst is used to convert carbon dioxide and methane into liquid products in a single step. The non-equilibrium plasma involved is generated by dielectric barrier discharge; the catalyst involved is a CZSM-5-supported Pt, Ag, Pd, Re, or Ir catalyst, all prepared by an impregnation method. The technical solution has defects or shortcomings: the total liquid product selectivity corresponding to the Pt / CZSM-5 catalyst is up to 60%, and the liquid products obtained in the reaction include formaldehyde, methanol, ethanol, and acetone, but the selectivity of each product is not given. Summary of the Invention

[0012] Because the chemical properties of methane and carbon dioxide are extremely stable, which contradicts the active chemical properties of methanol, the methanol production reaction from methane and carbon dioxide is limited by reaction kinetics at low temperatures and by reaction thermodynamics at high temperatures. In other words, low temperatures are not conducive to the activation and conversion of CH4 and CO2. While high temperatures are conducive to the activation of CH4 and CO2, they are not conducive to methanol production. This is because methanol is very likely to undergo deep reactions at high temperatures, converting into more stable byproducts such as CO and H2, or returning to the raw CH4 and CO2, resulting in low methanol selectivity.

[0013] In view of this, the present invention provides a method for preparing methanol in one step using methane and carbon dioxide as raw materials, converting methane and carbon dioxide into methanol in one step with high selectivity, solving the problems of multi-step processes and low methanol selectivity in reaction products faced by existing methane and carbon dioxide conversion technologies, improving the utilization value of the two major greenhouse gases, and facilitating chemical production and use.

[0014] To this end, the present invention provides the following technical solutions:

[0015] A method for preparing methanol in one step using methane and carbon dioxide as raw materials comprises the following steps:

[0016] Methanol is synthesized in one step by introducing methane and carbon dioxide into a dielectric barrier discharge plasma reactor containing a catalyst;

[0017] Wherein, the molar ratio of the methane to the carbon dioxide is 0.5 to 5, preferably 1 to 3;

[0018] The residence time of the mixed gas of methane and carbon dioxide in the plasma catalytic discharge space is 1 to 10 seconds, preferably 4 to 6 seconds;

[0019] The reaction temperature is 100-300°C, and the reaction temperature comes from the electric heat generated by plasma discharge;

[0020] The catalyst is a copper-based catalyst, comprising a carrier and an active component; the carrier is a molecular sieve with a silicon-aluminum ratio of 1 to 20, and the active component comprises copper;

[0021] Based on 100% of the mass of the catalyst, the copper content is 0.1% to 70.0%.

[0022] The copper content in the specific catalyst can be selected based on actual needs in combination with other factors, such as 0.5%, 1.0%, 5%, 8%, 15%, 35%, 45%, 40%, 55%, 60%, 65%, etc.

[0023] Optionally, the carrier is a molecular sieve with a silicon-aluminum ratio of 2 to 10.

[0024] Optionally, the reaction temperature is 150-250°C.

[0025] The dielectric barrier discharge plasma reactor of the present invention comprises three parts: an insulating medium, a high-voltage electrode and a low-voltage electrode. The insulating medium is placed between the high-voltage electrode and the low-voltage electrode, and a catalyst is filled in the non-equilibrium ion discharge space.

[0026] The present invention does not particularly limit the type of dielectric barrier discharge plasma reactor, and can be a dielectric barrier discharge reactor with a wire-tube electrode structure, a needle-plate electrode structure, a tube-plate electrode structure, a tube-tube electrode structure, or a plate-plate electrode structure. The discharge barrier dielectric layer is also not limited, and can be a glass layer, a quartz layer, a mica layer, or a plexiglass layer.

[0027] Optionally, based on 100% by mass of the catalyst, the copper content is 5.0% to 50.0%; preferably, the copper content is 5.0%-30%, such as 10%, 15%, 20%, 25%, etc.

[0028] Optionally, the catalyst further contains a modifier, and the modifier is selected from one or more of IA, IIA, VIIIB, IIB and lanthanide metals in the periodic table.

[0029] Optionally, the molar ratio of the copper to the modifier is 2-8.

[0030] Preferably, the modifier is selected from at least one of zinc, sodium, potassium, rubidium, cesium, lithium, beryllium, magnesium, calcium, strontium, barium, cerium, nickel, cobalt and iron.

[0031] The present invention is not particularly limited to the preparation method of the above-mentioned catalyst. Any commonly used preparation method in the prior art can be used to prepare the catalyst of the present invention. For example, the preparation method of the catalyst includes mixing the precursor of the active component (the precursor of the active component and the precursor of the modifier) ​​with the support or the support precursor, drying, and calcining.

[0032] The process of mixing the precursor of the active component with the carrier can adopt the impregnation method and the deposition precipitation method.

[0033] For example, the impregnation method can be used, wherein the carrier after calcination and impurity removal is mixed with the precursor solution of the active component, stirred at 20-80°C for 0.5-2h, separated, and the filter cake obtained after separation is dried at 100-120°C and finally calcined to obtain the catalyst.

[0034] For example, a sedimentation precipitation method can be used, in which the carrier after calcination and impurity removal is mixed with the precursor solution of the active component to obtain a mixed solution, and the precipitant solution is slowly added dropwise to the mixed solution while stirring. The mixture is separated, and the filter cake obtained by separation is dried at 100-120°C and finally hot-calcined to obtain the catalyst. The precipitant is recommended to be at least one of ammonia water, urea, sodium bicarbonate, sodium carbonate and sodium hydroxide.

[0035] The precursor of the active component copper in the catalyst of the present invention is preferably at least one of soluble copper salts such as nitrate, acetate, oxalate, sulfate, chloride, etc.

[0036] The precursor of the modifier in the catalyst of the present invention is preferably at least one of soluble salts such as nitrate, acetate, oxalate, sulfate, chloride, etc.

[0037] The present invention also does not limit the calcination form after drying during the catalyst preparation process, and can be thermal calcination. The thermal calcination atmosphere is usually oxygen or a mixture of oxygen and one of nitrogen, argon, and helium. The recommended thermal calcination temperature is 400-600°C, preferably 450-550°C; the recommended calcination time is 2-6 hours, preferably 3-4 hours.

[0038] Optionally, the dielectric barrier discharge plasma reactor further contains water vapor. When water vapor is added, the volume proportion of water vapor in the mixed gas of methane, carbon dioxide and water vapor is preferably 5% to 70%, more preferably 20% to 50%.

[0039] The present invention does not particularly limit the method of adding methane, carbon dioxide and water vapor. They can be added to the dielectric barrier discharge plasma reactor separately, or partly or completely mixed before adding to the dielectric barrier discharge plasma reactor.

[0040] The water vapor introduction method recommended by the present invention is to introduce water vapor into a mixture of methane and carbon dioxide by a bubbling method; the bubbling method is to pass the methane and carbon dioxide mixture through a bubbler filled with liquid water to obtain a mixture of methane, carbon dioxide and water vapor, and circulating water is passed between the inner and outer glass tubes of the bubbler. The saturated vapor pressure of the water vapor in the bubbler is controlled by the temperature of the circulating water, thereby regulating the volume ratio of water vapor in the mixture.

[0041] The present invention is characterized in that methane and carbon dioxide are reacted in one step to synthesize methanol. Preferably, methane, carbon dioxide and water vapor are mixed and reacted together in a plasma catalytic reactor to directly obtain a product containing high-concentration methanol.

[0042] Compared with the prior art, the advantages of the technical solution of the present invention are:

[0043] The inventors have discovered that the catalyst used in the present method, which contains copper as the primary active component and a molecular sieve with a low silicon-to-aluminum ratio as a support, can further enhance methanol selectivity in the product of the plasma-catalyzed reaction of carbon dioxide and methane. Copper-based catalysts, particularly molecular sieves with a copper-to-silicon-to-aluminum ratio of 1 to 20, significantly enhance methanol selectivity in the product. Copper-to-silicon-to-aluminum molecular sieves with a silicon-to-aluminum ratio greater than 20 (such as HZSM-5 with a silicon-to-aluminum ratio of 30 and S-1 with an infinite silicon-to-aluminum ratio) promote carbon monoxide production. Given that the acid site density of low-silicon-to-aluminum molecular sieves is much greater than that of high-silicon-to-aluminum molecular sieves, it is speculated that the acidity of the molecular sieve is the primary factor affecting catalyst activity. Furthermore, when using a low-silicon-to-aluminum molecular sieve as the catalyst support, high methanol selectivity is maintained across a wide copper content range of 0.1-70 wt%. It is speculated that crystalline copper oxide nanoparticles may be the catalytically active sites for methanol production. Comprehensive analysis reveals that the synergistic effect of the crystalline copper oxide nanoparticles and the acid sites may be the primary reason for the high methanol selectivity of the copper-based low-silicon-to-aluminum molecular sieve composite catalyst.

[0044] 2. The inventors have unexpectedly discovered through research that the introduction of water vapor under mild conditions can further improve the selectivity of methanol. The reason for this is that water vapor plays the following two main roles in the reaction process: On the one hand, water vapor can act as an extractant to protect the target product, methanol. By utilizing the property of methanol being highly soluble in water, water vapor can be used to desorb methanol from the catalyst surface in a timely manner, preventing methanol from further reacting on the catalyst surface to produce by-products such as CO, thereby improving the selectivity of methanol; on the other hand, water vapor can promote the oxidation of methane to produce alcohols, and water molecules in the plasma region may produce OH species. The OH species can not only promote the dissociation of CH4 to produce CH3 species, but also directly react with CH3 to produce methanol, thereby improving the selectivity of methanol.

[0045] 3. The method provided by the present invention for producing methanol in one step using methane and carbon dioxide as raw materials can significantly improve the selectivity of the target product methanol in the reaction products through the synergistic effect of a catalyst of a specific composition and non-equilibrium plasma. The obtained methanol selectivity performance reaches more than 65%, which is much higher than the best result in the current public literature. It solves the problems of multi-step processes and low methanol selectivity in the reaction products faced by existing methane and carbon dioxide conversion technologies, improves the utilization value of the two major greenhouse gases, and is beneficial to chemical production and use. DETAILED DESCRIPTION

[0046] The present invention is described in detail below by way of examples. It is necessary to point out that the following examples are only used to further illustrate the present invention and are not to be construed as limiting the scope of protection of the present invention. Those skilled in the art may make some non-essential improvements and adjustments to the present invention based on the above disclosure.

[0047] If no specific experimental steps or conditions are specified in the Examples and Comparative Examples, the conventional experimental steps or conditions described in the literature in the field can be used. If the manufacturer of the reagents or instruments is not specified, they are all commercially available conventional reagents.

[0048] The plasma catalytic reactors used below are all dielectric barrier discharge quartz reactors; the purity of methane and carbon dioxide gases is 99%. Water vapor is obtained by passing a mixture of methane and carbon dioxide through a bubbler filled with liquid water. Circulating water at a certain temperature is passed between the inner and outer glass tubes of the bubbler. This circulating water is used to control the saturated vapor pressure of the water vapor in the bubbler, thereby obtaining a mixed gas containing different water vapor concentrations.

[0049] Conventional non-equilibrium plasma discharge frequencies (e.g., 6-20 kHz) and discharge gaps (e.g., 1-5 mm) are sufficient for implementing the technical solution of this invention. For ease of comparison, the discharge frequency of the non-equilibrium plasma described below is 9.0 kHz, and the discharge gap is 3 mm. A copper-based catalyst is packed into the reactor's discharge zone; the reaction temperature is generated by the electric heat generated by the non-equilibrium plasma discharge. The mixed gas flows through the plasma catalytic reaction discharge zone, and the reaction products flow through a cold trap (a mixture of liquid nitrogen and isopropyl alcohol) to separate into gas and liquid phases. The gas phase is analyzed by online Shimadzu chromatography, and the liquid phase products are collected and analyzed by a Shimadzu GC-2014 chromatograph.

[0050] Example 1

[0051] Catalyst preparation: 13X zeolite with a silicon-aluminum molar ratio of 10 was first calcined at 400°C for 5 hours to remove impurities, and the obtained 13X powder was retained for later use; the copper precursor Cu(NO3)2·3H2O was dissolved in deionized water to obtain a copper nitrate solution, and then the above 13X powder was added to the copper nitrate solution under stirring conditions and stirred for 2 hours. The mixture was filtered, and the filter cake was dried at 120°C overnight and calcined in air at 540°C for 3 hours to obtain a theoretical 0.1wt% Cu / 13X catalyst.

[0052] One-step production of methanol using methane and carbon dioxide as raw materials:

[0053] Utilizing the synergistic effect of the prepared 0.1% Cu / 13X and non-equilibrium plasma, the plasma catalytic reaction temperature was 150° C., the molar ratio of methane to carbon dioxide was 1:1, and the residence time of the mixed gas in the plasma catalytic discharge space was 5 s.

[0054] Reaction results: methanol selectivity 65.2%, CH4 conversion rate 25.2%, CO2 conversion rate 18.6%.

[0055] Example 2

[0056] The preparation method of the catalyst in this example is similar to that in Example 1, the only difference being the content of the active component copper. The theoretical content of copper in the catalyst prepared in this example is 5 wt%.

[0057] One-step production of methanol using methane and carbon dioxide as raw materials: Same as Example 1

[0058] Reaction results: methanol selectivity 70.8%, CH4 conversion rate 26.0%, CO2 conversion rate 19.5%.

[0059] Example 3

[0060] The preparation method of the catalyst in this example is similar to that in Example 1, the only difference being the content of the active component copper. The theoretical content of copper in the catalyst prepared in this example is 30 wt%.

[0061] One-step production of methanol using methane and carbon dioxide as raw materials: Same as Example 1

[0062] Reaction results: methanol selectivity 72.0%, CH4 conversion rate 30.5%, CO2 conversion rate 25.0%.

[0063] Example 4

[0064] The preparation method of the catalyst in this example is similar to that in Example 1, the only difference being the content of the active component copper. The theoretical content of copper in the catalyst prepared in this example is 50 wt%.

[0065] One-step production of methanol using methane and carbon dioxide as raw materials: Same as Example 1

[0066] Reaction results: methanol selectivity 67.8%, CH4 conversion rate 29.5%, CO2 conversion rate 23.6%.

[0067] Example 5

[0068] The preparation method of the catalyst in this example is similar to that in Example 1, the only difference being the content of the active component copper. The theoretical content of copper in the catalyst prepared in this example is 70 wt%.

[0069] One-step production of methanol using methane and carbon dioxide as raw materials: Same as Example 1

[0070] Reaction results: methanol selectivity 65.3%, CH4 conversion rate 25.1%, CO2 conversion rate 21.7%.

[0071] Example 6

[0072] The preparation method of the catalyst in this embodiment is similar to that in Example 1, with the only difference being the carrier. In this embodiment, 13X zeolite with a silicon-aluminum molar ratio of 2 is used.

[0073] One-step production of methanol using methane and carbon dioxide as raw materials: Same as Example 1

[0074] Reaction results: methanol selectivity 71.3%, CH4 conversion rate 24.0%, CO2 conversion rate 16.9%.

[0075] Example 7

[0076] The preparation method of the catalyst in this embodiment is similar to that in Example 1, with the only difference being the carrier. In this embodiment, 13X zeolite with a silicon-aluminum molar ratio of 20 is used.

[0077] One-step production of methanol using methane and carbon dioxide as raw materials: Same as Example 1

[0078] Reaction results: methanol selectivity 65.0%, CH4 conversion rate 28.4%, CO2 conversion rate 20.3%.

[0079] Example 8

[0080] The preparation method of the catalyst in this embodiment is similar to that in Example 6, with the only difference being the carrier. In this embodiment, Y zeolite with a silicon-aluminum molar ratio of 2 is used.

[0081] One-step production of methanol using methane and carbon dioxide as raw materials: Same as Example 1

[0082] Reaction results: methanol selectivity 68.5%, CH4 conversion rate 26.0%, CO2 conversion rate 19.3%.

[0083] Example 9

[0084] Preparation of catalyst: The preparation method of the catalyst in this example is similar to that in Example 2, except that the active component solution is different. In this example, the copper precursor Cu(NO3)2·3H2O and zinc nitrate are dissolved in deionized water to obtain a mixed solution to obtain a CuZnOx / 13X catalyst with a theoretical copper content of 5 wt% and a molar ratio of copper to zinc of 2:1.

[0085] One-step production of methanol using methane and carbon dioxide as raw materials:

[0086] Similar to Example 2, the only difference is that: in this example, the synergistic effect of the above-mentioned catalyst and non-equilibrium plasma is utilized, the plasma catalytic reaction temperature is 200°C, the molar ratio of methane to carbon dioxide is 3:1, and the residence time of the mixed gas in the plasma catalytic discharge space is 10s.

[0087] Reaction results: methanol selectivity 75.3%, CH4 conversion rate 45.4%, CO2 conversion rate 36.2%.

[0088] Example 10

[0089] Preparation of catalyst: The preparation method of the catalyst in this embodiment is similar to that in Example 2, except that the active component solution is different. In this embodiment, the copper precursor Cu(NO3)2·3H2O and sodium nitrate are dissolved in deionized water to obtain a mixed solution to obtain a CuNaOx / 13X catalyst with a theoretical copper content of 5wt% and a molar ratio of copper to sodium of 5:1.

[0090] One-step production of methanol using methane and carbon dioxide as raw materials:

[0091] Similar to Example 2, the only difference is that: in this example, the synergistic effect of the above-mentioned catalyst and non-equilibrium plasma is utilized, the plasma catalytic reaction temperature is 200°C, the molar ratio of methane to carbon dioxide is 5:1, and the residence time of the mixed gas in the plasma catalytic discharge space is 1 s.

[0092] Reaction results: methanol selectivity 78.2%, CH4 conversion rate 27.0%, CO2 conversion rate 21.3%.

[0093] Example 11

[0094] Preparation of catalyst: The preparation method of the catalyst in this embodiment is similar to that in Example 2, except that the active component solution is different. In this embodiment, the copper precursor Cu(NO3)2·3H2O and calcium nitrate are dissolved in deionized water to obtain a mixed solution to obtain a CuCaOx / 13X catalyst with a theoretical copper content of 5wt% and a molar ratio of copper to calcium of 8:1.

[0095] One-step production of methanol using methane and carbon dioxide as raw materials:

[0096] Similar to Example 2, the only difference is that this example utilizes the synergistic effect of the above catalyst and non-equilibrium plasma, the plasma catalytic reaction temperature is 200° C., and the molar ratio of methane to carbon dioxide is 1:2.

[0097] Reaction results: methanol selectivity 73.2%, CH4 conversion rate 35.6%, CO2 conversion rate 18.6%.

[0098] Example 12

[0099] Preparation of catalyst: The preparation method of the catalyst in this embodiment is similar to that in Example 2, except that the active component solution is different. In this embodiment, the copper precursor Cu(NO3)2·3H2O and nickel nitrate are dissolved in deionized water to obtain a mixed solution to obtain a CuNiOx / 13X catalyst with a theoretical copper content of 5wt% and a molar ratio of copper to nickel of 8:1.

[0100] One-step production of methanol using methane and carbon dioxide as raw materials:

[0101] Similar to Example 2, the only difference is that this example utilizes the synergistic effect of the above catalyst and non-equilibrium plasma, the plasma catalytic reaction temperature is 300° C., and the molar ratio of methane to carbon dioxide is 5:1.

[0102] Reaction results: methanol selectivity 68.8%, CH4 conversion rate 25.0%, CO2 conversion rate 46.3%.

[0103] Example 13

[0104] Preparation of catalyst: The preparation method of the catalyst in this embodiment is the same as that in Example 9

[0105] One-step production of methanol using methane and carbon dioxide as raw materials:

[0106] Similar to Example 9, the only difference is that water vapor is introduced into the plasma catalytic reaction system, and the volume ratio of water vapor to the mixed gas of methane, carbon dioxide and water vapor is 5%.

[0107] Reaction results: methanol selectivity 78.0%, CH4 conversion rate 47.1%, CO2 conversion rate 26.5%.

[0108] Example 14

[0109] Preparation of catalyst: The preparation method of the catalyst in this embodiment is the same as that in Example 9

[0110] One-step production of methanol using methane and carbon dioxide as raw materials:

[0111] Similar to Example 9, the only difference is that water vapor is introduced into the plasma catalytic reaction system, and the volume ratio of water vapor to the mixed gas of methane, carbon dioxide and water vapor is 20%.

[0112] Reaction results: methanol selectivity 80.5%, CH4 conversion rate 48.9%, CO2 conversion rate 25.0%.

[0113] Example 15

[0114] Preparation of catalyst: The preparation method of the catalyst in this embodiment is the same as that in Example 9

[0115] One-step production of methanol using methane and carbon dioxide as raw materials:

[0116] Similar to Example 9, the only difference is that water vapor is introduced into the plasma catalytic reaction system, and the volume ratio of water vapor to the mixed gas of methane, carbon dioxide and water vapor is 50%.

[0117] Reaction results: methanol selectivity 84.4%, CH4 conversion rate 40.9%, CO2 conversion rate 23.6%.

[0118] Example 16

[0119] Preparation of catalyst: The preparation method of the catalyst in this embodiment is the same as that in Example 9

[0120] One-step production of methanol using methane and carbon dioxide as raw materials:

[0121] Similar to Example 9, the only difference is that water vapor is introduced into the plasma catalytic reaction system, and the volume ratio of water vapor to the mixed gas of methane, carbon dioxide and water vapor is 70%.

[0122] Reaction results: methanol selectivity 78.3%, CH4 conversion rate 39.0%, CO2 conversion rate 20.0%.

[0123] Comparative Example 1

[0124] The preparation method of the catalyst in this comparative example is similar to that of Example 3, the only difference being the content of the active component copper. The copper content in the catalyst prepared in this comparative example is 90 wt%.

[0125] One-step production of methanol using methane and carbon dioxide as raw materials: Same as Example 1

[0126] Reaction results: methanol selectivity 25.0%, CH4 conversion rate 35.7%, CO2 conversion rate 26.2%.

[0127] Comparative Example 2

[0128] The preparation method of the catalyst in this comparative example is similar to that in Example 3, with the only difference being the carrier. In this comparative example, HZSM-5 zeolite with a silicon-aluminum molar ratio of 30 is used.

[0129] One-step production of methanol using methane and carbon dioxide as raw materials: Same as Example 1

[0130] Reaction results: methanol selectivity 38.2%, CH4 conversion rate 31.0%, CO2 conversion rate 25.3%.

[0131] Comparative Example 3

[0132] The preparation method of the catalyst in this comparative example is similar to that in Example 7, with the only difference being the carrier. In this comparative example, S-1 zeolite having an infinite silicon-aluminum molar ratio is used.

[0133] One-step production of methanol using methane and carbon dioxide as raw materials: Same as Example 1

[0134] Reaction results: methanol selectivity 15.2%, CH4 conversion rate 34.6%, CO2 conversion rate 28.5%.

[0135] Comparative Example 4

[0136] According to the public document "Journal of Physics: Conference Series, 2019, 1386, 012045", the discharge reactor is made of quartz (inner diameter 4 mm, outer diameter 6 mm), and a stainless steel electrode (1.0 mm) is placed inside and connected to the high voltage generation system; the quartz tube is covered with copper tape (50 mm long, 25 mm wide, 25 μm thick, advanced tape-AT5260) as a ground electrode; the total gas rate of the raw gas is 40 ml / min (the gas rate is controlled by MFC Bronkhorst Brand); helium is introduced into the raw gas as a diluent (30 ml / min), and the methane and carbon dioxide flow rates are 7 ml / min and 3 ml / min, respectively; ultrapure water is introduced into the reaction system, and the water flow rate is controlled to 0.02 ml / min by a peristaltic pump (Metrohm, model 765); natural molecular sieve material (composed of 70% zeolite and 25% plagioclase) is filled in the plasma reactor, and CH4 and CO2 reforming reactions are carried out at room temperature and normal pressure.

[0137] Reaction results: methanol selectivity 5.9%, CH4 conversion rate 11.9%, CO2 conversion rate 5.2%.

[0138] Data Analysis: The performance data from the above examples and comparative examples demonstrate that the catalyst significantly impacts methanol selectivity in the product of the plasma-catalyzed methane and carbon dioxide conversion reaction. Copper-based catalysts, particularly molecular sieve composites with a copper to silicon-aluminum ratio of 1 to 20, significantly enhance methanol selectivity in the product. Molecular sieve composites with a copper to silicon-aluminum ratio greater than 20 promote carbon monoxide production. Given that the acid site density of low-silicon-aluminum molecular sieves is much greater than that of high-silicon-aluminum molecular sieves, it is speculated that the acid properties of the molecular sieve are the primary factor affecting catalyst activity. Furthermore, when using low-silicon-aluminum molecular sieves as catalyst supports, high methanol selectivity is maintained across a wide copper content range of 0.1-70 wt%, suggesting that crystalline copper oxide nanoparticles may be the catalytically active sites for methanol production. Comprehensive analysis reveals that the synergistic effect of crystalline copper oxide nanoparticles and acid sites may be the primary reason for the high methanol selectivity of the copper-based low-silicon-aluminum molecular sieve composite catalyst.

[0139] In addition, the introduction of water vapor into the plasma catalytic reaction system can further improve the selectivity of methanol. The reason for this is that water vapor plays the following two main roles in the reaction process: On the one hand, water vapor can act as an extractant to protect the target product methanol. By taking advantage of the fact that methanol is highly soluble in water, water vapor can be used to decompose methanol from the catalyst surface in a timely manner, preventing methanol from further reacting on the catalyst surface to produce by-products such as CO, thereby improving the selectivity of methanol; on the other hand, water vapor can promote the oxidation of methane to produce alcohols, and water molecules may produce OH species in the plasma region. This OH species can not only promote the dissociation of CH4 to produce CH3 species, but also directly react with CH3 to produce methanol, thereby improving the selectivity of methanol.

[0140] Of course, the present invention may have many other embodiments. Without departing from the spirit and essence of the present invention, those skilled in the art may make various corresponding changes and modifications based on the present invention, but these corresponding changes and modifications should all fall within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing methanol in one step using methane and carbon dioxide as raw materials, characterized in that: The steps include: Methanol is synthesized in one step by introducing methane and carbon dioxide into a dielectric barrier discharge plasma reactor containing a catalyst; Wherein, the molar ratio of the methane to the carbon dioxide is 0.5 to 5; The residence time of the methane and carbon dioxide mixture in the plasma catalytic discharge space is 1 to 10 seconds; The reaction temperature is 100~300℃; The catalyst is a copper-based catalyst, comprising a carrier and an active component; the carrier is a molecular sieve with a silicon-aluminum ratio of 1 to 20, and the active component comprises copper; Based on 100% by mass of the catalyst, the copper content is 0.1% to 70.0%.

2. The method according to claim 1, wherein The carrier is a molecular sieve with a silicon-aluminum ratio of 2 to 10.

3. The method according to claim 1, wherein Based on 100% by mass of the catalyst, the copper content is 5% to 50.0%.

4. The method according to claim 3, wherein Based on 100% by mass of the catalyst, the copper content is 5.0% to 30.0%.

5. The method according to claim 1, wherein The reaction temperature is 150-250 o C.

6. The method according to claim 1, wherein The catalyst further contains a modifier, which is selected from one or more of the metals of IA, IIA, VIIIB, IIB and lanthanide series in the periodic table.

7. The method according to claim 6, wherein The molar ratio of the copper to the modifier is 2 to 8.

8. The method according to claim 1, wherein The dielectric barrier discharge plasma reactor also contains water vapor.

9. The method according to claim 8, wherein The volume of the water vapor accounts for 5%-70% of the mixed gas of methane, carbon dioxide and water vapor.