Process for converting alkanes to alkenes using plasma technology

Abstract

The present application relates to the field of energy conversion, and discloses a method for converting alkane into olefin by using plasma technology, which comprises: contacting alkane with active substances generated by plasma electric field and a catalyst to convert alkane into olefin, wherein the catalyst comprises a carrier and active components loaded on the carrier, the active components contain a first active component and a second active component, the first active component is at least one selected from non-noble metals of group VIII and metals of group IB, the second active component is at least one selected from noble metals of group VIII, the weight ratio of the first active component to the second active component is 1-200:1, and the dispersion degree of the active components in the catalyst is 10-60%. The method provided by the present application further improves the dispersion degree of the active components by adding organic acid in the catalyst preparation process, thereby improving the hydrogenation activity of the catalyst and the selectivity of olefin.

Description

Technical Field

[0001] This invention relates to the field of energy conversion, and more specifically to a method for converting alkanes into olefins using plasma technology. Background Technology

[0002] Traditional coal chemical processes for producing ethylene suffer from drawbacks such as high water and energy consumption during the coal gasification stage. Therefore, with the development of combustible ice and shale gas, natural gas resource utilization technology has become a hot topic, and the process of converting natural gas into ethylene has become a new direction for technological development.

[0003] Existing reactions for producing ethylene from natural gas are mainly carried out through anaerobic and aerobic coupling. However, aerobic coupling has harsh operating conditions and poses a risk of deflagration, making it difficult to industrialize. Although anaerobic coupling can produce hydrogen and high-value-added olefins, it has the drawback of producing a large number of byproducts and being unable to be directionally converted into the target olefin product.

[0004] Isoelectronic technology for methane conversion can be carried out at ambient temperature and pressure under relatively mild operating conditions, and has attracted widespread attention in recent years. However, there is currently no equipment in China that can achieve full-process industrial production. Although various research institutions in China have made initial progress in the research on using plasma technology to convert natural gas into alkynes and olefins, for example, CN109503310A discloses a method for producing acetylene and hydrogen from natural gas. This method uses a plasma pyrolysis reactor, and after thermal pyrolysis, carbon black, acetylene, and hydrogen are separated through a series of measures. CN1176051C discloses a method for directly converting methane or natural gas into C2 hydrocarbons. This method uses pulsed microwave enhanced conventional high-voltage filamentary plasma technology to directly convert methane or natural gas into ethylene and acetylene under ambient or even high pressure and reaction temperature not exceeding 600 degrees Celsius. However, this method also has problems such as impure product composition and the need to improve the selectivity for ethylene. Summary of the Invention

[0005] The purpose of this invention is to overcome the problems of poor olefin selectivity, complex product composition, and inability to achieve full-process industrial production in the plasma conversion of alkanes to olefins process of existing technologies. This invention provides a method for converting alkanes to olefins using plasma technology, which has the advantages of not requiring additional heat source activation of the catalyst and achieving high olefin selectivity.

[0006] To achieve the above objectives, the present invention provides a method for converting alkanes into olefins using plasma technology. The method includes: contacting plasma-state alkane with a catalyst to convert the alkane into an olefin. The catalyst includes a support and an active component supported on the support. The active component contains a first active component and a second active component. The first active component is selected from at least one non-noble metal of Group VIII and a metal of Group IB. The second active component is selected from at least one noble metal of Group VIII. The weight ratio of the first active component to the second active component, based on metal elements, is 1-200:1. The dispersion of the active component in the catalyst is 10-60%.

[0007] The above technical solution enables the industrial-scale production of alkanes to olefins using plasma technology, effectively and stably improving olefin selectivity. This invention, by adding organic acids during the loading process, effectively promotes the penetration of active components into the internal pores of the support, ensuring uniform loading on the support surface, thereby further improving the hydrogenation activity and olefin selectivity of the catalyst. Furthermore, this method is adaptable to changes in the composition of the reaction tail gas after natural gas (alkane) passes through plasma, mitigating problems such as uneven catalyst bed temperature caused by the reaction tail gas, and effectively and stably improving olefin selectivity. Detailed Implementation

[0008] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0009] 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.

[0010] This invention provides a method for converting alkanes into olefins using plasma technology. The method includes: contacting plasma-state alkane with a catalyst to convert the alkane into an olefin. The catalyst includes a support and an active component supported on the support. The active component contains a first active component and a second active component. The first active component is selected from at least one non-noble metal of Group VIII and a metal of Group IB. The second active component is selected from at least one noble metal of Group VIII. The weight ratio of the first active component to the second active component, based on metal elements, is 1-200:1. The dispersion of the active component in the catalyst is 10-60%.

[0011] Preferably, the dispersibility of the active component is 40-60%.

[0012] According to a preferred embodiment of the present invention, the weight ratio of the first active component to the second active component, based on metal elements, is 0.1-10:1. For example, it can be 0.5:1, 0.8:1, 1:1, 1.2:1, 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1, 4.5:1, 5:1, 5.5:1, 6:1, 6.5:1, 7:1, 7.5:1, 8:1, 8.5:1, 9:1, 9.5:1, 10:1, or any intermediate value between any two of the above ratios.

[0013] According to the present invention, preferably, the first active component is selected from at least one of Cu, Ag, Au, Ni and Fe.

[0014] According to the present invention, preferably, the second active component is selected from at least one of Pt, Rh, Pd and Ir.

[0015] According to a preferred embodiment of the present invention, the weight ratio of the first active component to the catalyst is 0.1-2:100, and the weight of the first active component is calculated in terms of metal elements. That is, in terms of elements, the first active component accounts for 0.1-2% by weight of the total weight of the catalyst. For example, it can be 0.1% by weight, 0.3% by weight, 0.5% by weight, 0.8% by weight, 1% by weight, 1.2% by weight, 1.5% by weight, 1.8% by weight, 2% by weight, or it can be an intermediate value between any two of the above values.

[0016] According to a preferred embodiment of the present invention, the molar ratio of L acid to Brønsted acid in the Ti oxide doped support is 0.1-50:1, preferably 1-20:1.

[0017] Preferably, the support is selected from at least one of Ti oxide-doped Al2O3, SiO2, MgO, and molecular sieves. The molecular sieve can be any molecular sieve in the art, such as ZSM-5 molecular sieve, SBA-13 molecular sieve, SAPO-34 molecular sieve, etc.

[0018] The carrier used in this invention can be any commercially available (or custom-made) carrier that meets the above conditions, or it can be synthesized by ourselves based on existing technology.

[0019] Specifically, the synthesis method of the support may include: dispersing a conventional oxide support (preferably at least one of Al2O3, SiO2, MgO, and molecular sieve) in an organic solvent (such as anhydrous ethanol), then adding a titanium precursor solution (such as tetrabutyl titanate) dropwise, and reacting at 150-200°C for 10-60 minutes. After the reaction is complete, the precipitate is collected, washed 1-5 times each with water and anhydrous ethanol, and dried in an oven at 75-90°C for 20-30 hours.

[0020] More specifically, the synthesis method of the support may include: adding a conventional oxide support to 20-100 mL of anhydrous ethanol and ultrasonically dispersing it for 1-3 hours, followed by dropwise addition of a titanium precursor. After stirring under magnetic stirring for 1-2 hours, the mixture is transferred to a 50-100 mL hydrothermal reactor (Teflon-lined), and then placed in a microwave digester and reacted at 150-200°C for 10-60 minutes. During the synthesis, the microwave power is 180-220 W × the number of reactors. After the reaction is complete, the precipitate is collected, washed 1-5 times each with water and anhydrous ethanol, and dried in an oven at 75-90°C for 20-30 hours. The "number of reactors" refers to the number of reactors contained in the hydrothermal reactor.

[0021] According to a preferred embodiment of the present invention, the catalyst has a specific surface area of ​​200-600 cm². 2 / g, the particle size of the active component in the catalyst is 5-8nm.

[0022] According to a preferred embodiment of the present invention, the method further includes the step of preparing the catalyst by loading the active component onto a support, wherein the loading of the active component onto the support includes: impregnating the support with an impregnation solution containing a precursor of the active component and an organic acid, followed by drying and calcination in sequence.

[0023] According to the present invention, the precursor of the active component includes a precursor of a first active component and a precursor of a second active component. The precursor of the first active component is selected from at least one precursor of a non-noble metal element from Group VIII and a precursor of a metal element from Group IB. The precursor of the second active component is selected from at least one precursor of a noble metal element from Group VIII.

[0024] According to a preferred embodiment of the present invention, the precursor of the active component may be a water-soluble salt of the corresponding metal element, such as nitrate, chloride, etc.

[0025] Preferably, the precursor of the first active component is selected from at least one of Cu(NO3)2, AgNO3, Ni(NO3)2 and Fe(NO3)3.

[0026] Preferably, the precursor of the second component is selected from at least one of H2PtCl6, HAuCl4, Rh(NO3)3, PdNO3 and iridium acetate.

[0027] There are no particular restrictions on the order of impregnation of the first and second active components; they can be carried out simultaneously or in a specific order.

[0028] There are no particular restrictions on the concentration of the precursor of the active component in the impregnation solution. The impregnation method can be either excess impregnation or equal volume impregnation.

[0029] In the method provided by this invention, the organic acid serves to promote better dispersion of the active component within the pores, thereby improving the dispersion of the active component. Therefore, there are no particular limitations on the concentration and amount of the organic acid, as long as it achieves the aforementioned effect. According to a preferred embodiment of this invention, the amount of organic acid added is 5-30% by weight of the total impregnation solution.

[0030] Preferably, the concentration of organic acid in the impregnation solution is 10-20% by weight.

[0031] In the method provided by this invention, there is no particular limitation on the type of organic acid, as long as it can achieve the aforementioned effect. Preferably, the organic acid is selected from C2-C8 organic acids, and more preferably from at least one of acetic acid, monochloroacetic acid, lactic acid, tartaric acid, and citric acid.

[0032] According to a preferred embodiment of the present invention, the impregnation is carried out in a one-step impregnation or a multi-step impregnation.

[0033] According to a preferred embodiment of the present invention, the one-step impregnation method includes immersing the carrier in an impregnation solution containing an active component precursor and an organic acid for 8-12 hours.

[0034] Preferably, the concentration of the precursor of the active component in the impregnation solution is 10-50% by weight.

[0035] According to a preferred embodiment of the present invention, the stepwise impregnation method may include:

[0036] (A) Immerse the carrier in an impregnation solution containing organic acid for 4-8 hours, filter and remove the impregnated carrier, then immerse it in an impregnation solution containing the precursor of the active component for 8-12 hours; or

[0037] (B) Immerse the carrier in an impregnation solution containing the precursor of the active component for 8-12 hours, and then add organic acid to it and continue impregnation for 4-8 hours.

[0038] In the stepwise impregnation method, the concentrations of organic acids and precursors of active components in the impregnation solution are as previously described and will not be repeated here.

[0039] According to the present invention, there are no particular limitations on the drying and calcining conditions, and any conventional drying and calcining conditions in the art can be used in the method described in the present invention.

[0040] According to a preferred embodiment of the present invention, the drying conditions include: a drying temperature of 100-120°C and a drying time of 8-12 hours.

[0041] According to the present invention, preferably, the drying can be carried out in a segmented drying manner.

[0042] According to a preferred embodiment of the present invention, the segmented drying method may employ the same drying method (e.g., oven drying, rotary evaporation drying, freeze drying, etc.) or may employ different drying methods respectively.

[0043] According to a preferred embodiment of the present invention, the drying can be carried out in the following segmented drying manner:

[0044] (1) First drying: Drying is carried out by rotary evaporation. The drying temperature is 50-100℃, preferably 70-90℃. The drying time is 1-5h, preferably 3-5h.

[0045] (2) Second drying: Drying is carried out by oven drying. The drying temperature is 100-150℃, preferably 100-120℃. The drying time is 5-10h, preferably 7-9h.

[0046] According to a preferred embodiment of the present invention, the calcination conditions include: a calcination temperature of 450-500°C and a calcination time of 2-6 hours.

[0047] According to a preferred embodiment of the present invention, the method further includes: pretreating the carrier before loading the active component onto the carrier to remove moisture and organic impurities that may be present in the carrier.

[0048] Preferably, the pretreatment includes drying and calcining the carrier to remove moisture and organic impurities.

[0049] More preferably, the pretreatment conditions include: drying temperature 100-120℃, drying time 8-12h, calcination temperature 450-500℃, heating rate 1-4℃, and calcination time 2-6h.

[0050] According to a preferred embodiment of the present invention, the active component exists in an oxidized state on the support (after preparation). During use, the active component exists in a reduced state (metallic form) on the support. Therefore, the method provided by the present invention further includes a step of reducing the catalyst to reduce the active component loaded on it before use. The reduction treatment can be carried out using any method existing in the art for reducing catalysts. For example, the catalyst can be placed in a reducing atmosphere (provided by a reducing gas, such as H2) for a period of time to reduce the active component therein.

[0051] According to a preferred embodiment of the present invention, the active substance generated by the plasma electric field through the alkane is produced under the action of the plasma source.

[0052] A plasma source is a device capable of breaking at least one CH bond in an alkane, facilitating the conversion of alkanes to alkenes. Common plasma sources include: nonthermal plasma (low-temperature plasma), corona discharge, dielectric barrier discharge, microwave discharge, and normal glow discharge. Adjusting the plasma source settings, such as frequency and voltage, can have different effects on the reaction. Specific energy consumption is an important parameter of a plasma source, representing the electrical energy extracted by the source to produce a unit amount of plasma-state alkane.

[0053] According to the present invention, the plasma source can be any plasma source commonly used in the art.

[0054] Preferably, the specific energy consumption of the plasma source is 5-100 kJ / L. The unit "kJ / L" represents the electrical energy (kJ) absorbed by the plasma source when converting a unit volume (L) of alkane into plasma-state alkane.

[0055] According to the present invention, the alkane may be C1-C60. 10 Alkanes.

[0056] Preferably, the alkane is at least one of C1-C5 alkanes, more preferably at least one of methane, ethane, propane, butane and pentane.

[0057] According to the present invention, the olefin may be C2-C 20 olefins.

[0058] Preferably, the olefin is at least one of C2-C4 olefins, more preferably at least one of ethylene, propylene, butadiene, isoprene, 1-butene and isobutene.

[0059] According to the present invention, there are no particular limitations on the contact conditions between the plasma-state alkane and the catalyst, and any conventional contact conditions in the art can be applied to the method provided by the present invention.

[0060] To further improve the selectivity of olefins, the contact conditions preferably include: a temperature of 25-35°C, a pressure of 0.05-0.25 MPa, and a time of more than 8 hours.

[0061] More preferably, the contact conditions include: temperature 25-30°C, pressure 0.08-0.15 MPa, and time 8-20 h.

[0062] According to a preferred embodiment of the present invention, the contact can be carried out in the presence of hydrogen gas for the purpose of accelerating the reaction.

[0063] More preferably, the volume ratio of hydrogen to alkane is 0-10:1, more preferably 1-5:1.

[0064] The present invention will be described in detail below through specific embodiments. It should be noted that the following embodiments are only used to further explain and illustrate the present invention, and are not intended to limit the present invention.

[0065] Unless otherwise specified, all chemicals used in the following examples were purchased from reputable chemical reagent suppliers and were of analytical grade. The Al2O3, SBA-13, SiO2, MgO supports, and ZSM-5 molecular sieve used in the preparation of the Ti oxide doping support were all purchased from Sinopharm Reagent Company.

[0066] The Ti oxide doped support preparation method used in the following examples is as follows:

[0067] 10 g of a conventional oxide support was ultrasonically dispersed in 60 mL of anhydrous ethanol for 2 hours. Then, 40 g of tetrabutyl titanate was added dropwise. After stirring magnetically for 1 hour, the mixture was transferred to a 100 mL Teflon-lined hydrothermal reactor. The reactor was then placed in a microwave digester and reacted at 200 °C for 60 minutes. The microwave power during the synthesis was 200 W. After the reaction was complete, the precipitate was collected, washed three times each with water and anhydrous ethanol, and dried in an oven at 80 °C for 24 hours.

[0068] The surface L acid to Brønsted acid molar ratios of the TiO2-Al2O3 support, TiO2-SBA-13 support, TiO2-SiO2 support, TiO2-MgO support, and TiO2-ZSM-5 support prepared by the above methods were found to be 17.5:1, 7.7:1, 3.6:1, 1.2:1, and 5.5:1, respectively.

[0069] In the following examples, the particle size of the active component in the catalyst was tested using the CO pulse adsorption method. The specific conditions were as follows: 1 g of catalyst was placed in a U-tube, argon gas was introduced, and the temperature was raised to 350°C and maintained for 1 hour to remove moisture and impurities. The temperature was then lowered to room temperature, hydrogen gas was introduced, and the temperature was raised again to 350°C and maintained for 2 hours to reduce the catalyst. The temperature was then lowered to 50°C, and He gas was introduced to purge for 30 minutes to remove physically adsorbed H2. After the baseline stabilized, a fixed volume of CO was intermittently injected into the sample tube until adsorption saturation was reached, and the CO adsorption capacity was calculated.

[0070] Method for calculating the dispersion of active components in catalysts: The particle size of active components in catalysts is tested using the CO pulse adsorption method. Specific conditions are as follows: 1g of catalyst is placed in a U-tube, argon gas is introduced, and the temperature is raised to 350℃ and maintained for 1 hour to remove moisture and impurities. The temperature is then lowered to room temperature, hydrogen gas is introduced, and the temperature is raised again to 350℃ and maintained for 2 hours to reduce the catalyst. The temperature is then lowered to 50℃, and He gas is introduced to purge for 30 minutes to remove physically adsorbed H2. After baseline stabilization, a fixed volume of CO is intermittently injected into the sample tube until adsorption saturation is reached. The CO adsorption amount is calculated, and adsorption is performed according to a 1:1 atomic ratio of CO to active components to obtain the number of atoms of the active component on the catalyst surface.

[0071] Dispersion = (Number of atoms of active component on catalyst surface / Total number of atoms of supported active component) * 100%

[0072] Example 1

[0073] Palladium nitrate was dissolved in deionized water to form a palladium nitrate solution (palladium content 18 wt%), and copper nitrate was dissolved in deionized water to form a copper nitrate solution (copper content 30 wt%). The mixing ratio of the palladium nitrate solution and the copper nitrate solution was such that the palladium loading accounted for 0.5 wt% of the catalyst mass, and the copper loading accounted for 1 wt% of the catalyst mass. Acetic acid was added to make the concentration of acetic acid in the mixed solution 15 wt%, and an impregnation solution was obtained. Using a TiO2-Al2O3 support, the support was immersed in the impregnation solution for 12 h using an excess impregnation method. It was then dried in a rotary evaporator at 80 °C for 4 h, and then further dried in an oven at 120 °C for 8 h. Finally, it was calcined in a muffle furnace at 450 °C for 5 h to obtain catalyst 1, the chemical composition of which is shown in Table 1.

[0074] Example 2

[0075] Palladium nitrate is dissolved in deionized water to form a palladium nitrate solution (palladium content is 18 wt%), and silver nitrate is dissolved in deionized water to form a silver nitrate solution (silver content is 30 wt%). The mixing ratio of the palladium nitrate solution and the silver nitrate solution is such that the palladium loading accounts for 0.5 wt% of the catalyst mass and the silver loading accounts for 1 wt% of the catalyst mass, thus forming an active component impregnation solution.

[0076] The TiO2-Al2O3 support was first impregnated with a 15% by weight acetic acid solution for 5 hours using an excess impregnation method. The impregnated support was then filtered out and impregnated in the active component impregnation solution for 12 hours using the excess impregnation method. It was then dried in a rotary evaporator at 80°C for 4 hours, followed by further drying in an oven at 120°C for 8 hours. Finally, it was calcined in a muffle furnace at 450°C for 5 hours to obtain catalyst 2, the chemical composition of which is shown in Table 1.

[0077] Example 3

[0078] Palladium nitrate was dissolved in deionized water to form a palladium nitrate solution (palladium content 18 wt%), and nickel nitrate was dissolved in deionized water to form a nickel nitrate solution (nickel content 30 wt%). The mixing ratio of the palladium nitrate solution and the nickel nitrate solution was such that the palladium loading accounted for 0.5 wt% of the catalyst mass, and the nickel loading accounted for 1 wt% of the catalyst mass. Tartaric acid was added to make the concentration of tartaric acid in the mixed solution 15 wt%, and an impregnation solution was obtained. Using a TiO2-Al2O3 support, the support was immersed in the impregnation solution for 12 h using an excess impregnation method. It was then dried in a rotary evaporator at 80 °C for 4 h, and then further dried in an oven at 120 °C for 8 h. Finally, it was calcined in a muffle furnace at 450 °C for 5 h to obtain catalyst 3, the chemical composition of which is shown in Table 1.

[0079] Example 4

[0080] The method described in Example 1 is used, except that the following impregnation method is employed:

[0081] The carrier was first impregnated in the active component impregnation solution for 12 hours, and then acetic acid was added to bring the concentration of acetic acid in the impregnation solution to 15% by weight. Impregnation continued for another 5 hours, followed by drying and calcination using the method and conditions described in Example 1. Catalyst 4 was obtained. Its chemical composition is shown in Table 1.

[0082] Example 5

[0083] The method described in Example 1 was used, except that Rh was used as the second active component and MgO-TiO2 support was used. All other steps and conditions were the same as in Example 1. Catalyst 5 was obtained, and its chemical composition is shown in Table 1.

[0084] Example 6

[0085] The method described in Example 1 was used, except that Fe was used as the first active component and TiO2-ZSM-5 support was used. All other steps and conditions were the same as in Example 1. Catalyst 6 was obtained, and its chemical composition is shown in Table 1.

[0086] Example 7

[0087] The method described in Example 1 was used, except that Ir and Au were used as the first and second active components, respectively, and the support was replaced with Al2O3. All other steps and conditions were the same as in Example 1. Catalyst 7 was obtained, and its chemical composition is shown in Table 1.

[0088] Example 8

[0089] The method described in Example 2 was used, except that the support was replaced with TiO2. All other steps and conditions were the same as in Example 2. Catalyst 8 was obtained, and its chemical composition is shown in Table 1.

[0090] Comparative Example 1

[0091] The method described in Example 1 was used, except that the impregnation solution did not contain copper nitrate and the support was replaced with TiO2-SBA-13. All other steps and conditions were the same as in Example 1. Catalyst D1 was obtained, and its chemical composition is shown in Table 1.

[0092] Comparative Example 2

[0093] The method described in Example 2 was used, except that the impregnation solution did not contain palladium nitrate and the support was replaced with TiO2-MgO. All other steps and conditions were the same as in Example 2. Catalyst D2 was obtained, and its chemical composition is shown in Table 1.

[0094] Comparative Example 3

[0095] The method described in Example 1 was used, except that palladium nitrate was replaced with ferric nitrate, and the amount was such that the Fe loading was 1% by weight. All other steps and conditions were the same as in Example 1. Catalyst D3 was obtained, and its chemical composition is shown in Table 1.

[0096] Comparative Example 4

[0097] The method described in Example 7 was used, except that acetic acid was not added to the impregnation solution. All other steps and conditions were the same as in Example 1. Catalyst D4 was obtained, and its chemical composition is shown in Table 1.

[0098] Comparative Example 5

[0099] The method described in Example 1 was used, except that acetic acid was not added to the impregnation solution; all other steps and conditions were the same as in Example 1. Catalyst D5 was obtained, and its chemical composition is shown in Table 1.

[0100] Table 1 Catalyst Characteristics

[0101]

[0102]

[0103] *Calculated based on the total weight of the active component (by element) and the carrier being 100% by weight.

[0104] **This refers to the molar ratio of Livic acid to Beta acid in the catalyst.

[0105] Test Example 1

[0106] More than 30g of the catalysts prepared in the examples and comparative examples were placed in a 1L plasma reactor (methane with a specific power consumption of 40kJ / L). The reaction was carried out at 25°C and 0.15MPa under the conditions of 0.5L / min methane, 1.5L / min hydrogen, 120W, and 120W. A control group experiment was also set up: the reaction was carried out directly under the above conditions without the addition of catalyst. The methane conversion rate and hydrocarbon selectivity in the products were detected and calculated according to the following method. The results are detailed in Table 2.

[0107] The reaction products were measured by gas chromatography. Based on the measurement results, the conversion rate of methane and the selectivity of hydrocarbons were calculated using the carbon balance method according to the following formula:

[0108]

[0109]

[0110]

[0111]

[0112]

[0113] S C3+ =S C3 +S C4 +S C5 +S C6

[0114] In the formula, X CH4 S represents the conversion rate of methane. C2H4 S represents ethylene selectivity. C2H2 S indicates acetylene selectivity. C2H6 S represents ethane selectivity. C3+ C represents 3+ Selectivity, N CH4，in Indicates the molar amount of imported methane, N CH4，out N represents the molar amount of methane exported. C2H4，out N represents the molar quantity of exported ethylene. C2H2，out Indicates the molar amount of acetylene exported, N Cn，out This represents the molar quantity of the product with n carbon atoms exported.

[0115] Table 2 Comparison of reaction results

[0116] catalyst Methane conversion rate % Acetylene selectivity % Ethylene selectivity % Ethane selectivity % <![CDATA[C 3+ Selectivity % 1 12.4 0 90.5 8.2 1.3 2 15.6 0 87.6 5.2 7.2 3 13.5 0 86.3 10.3 3.4 4 14.7 2.3 83.4 5.4 8.9 5 14.5 10.5 73.3 11.7 4.5 6 13.8 0 89.8 2.8 7.3 7 12.5 3.5 84.4 6.7 5.4 8 14.1 0 80.4 9.1 10.5 D1 14.9 0 44.5 45.8 9.7 D2 13.6 54.1 32.5 1.3 12.1 D3 14.2 43.2 34.7 2.1 20.0 D4 13.8 6.4 78.1 10.4 5.1 D5 12.3 0 87.5 9.2 3.3 control group 13.8 75.1 15.3 5.2 4.4

[0117] Further test results show that when catalysts 1-6 are used for the reaction, the temperature of the catalyst bed after plasma is relatively stable, with the temperature at the edge of the bed being about 100±10℃ and the temperature at the center of the bed being about 250±10℃.

[0118] 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. To avoid unnecessary repetition, the present invention will not describe all possible combinations separately. However, these simple modifications and combinations should also be considered as part of the content disclosed in this invention and are all within the protection scope of this invention.

Claims

1. A method for converting alkanes into olefins using plasma technology, characterized in that, The method includes: contacting plasma-state alkane with a catalyst to convert the alkane into an olefin, wherein the catalyst includes a support and an active component supported on the support, wherein the support is selected from at least one of Ti oxide-doped Al2O3 and molecular sieves; the active component contains a first active component and a second active component, wherein the first active component is selected from at least one of Cu, Ag, Ni and Fe, and the second active component is selected from Pd, and the weight ratio of the first active component to the second active component is 1-10:1 based on metal elements, and the dispersion of the active component in the catalyst is 40-60%, and the dispersion is calculated as: (number of active component atoms on the catalyst surface / total number of active component atoms supported) * 100%. The method further includes the step of preparing the catalyst by loading the active component onto a support, wherein the loading of the active component onto the support includes: impregnating the support with an impregnation solution containing a precursor of the active component and an organic acid, and then sequentially drying and calcining.

2. The method according to claim 1, wherein, The weight ratio of the first active component to the carrier is 0.1-2:100, and the weight of the first active component is calculated in terms of metal elements.

3. The method according to claim 1, wherein, The molar ratio of L acid to Brønsted acid in the carrier is 0.1-50:

1.

4. The method according to claim 3, wherein, The molar ratio of L acid to Brønsted acid in the carrier is 1-20:

1.

5. The method according to claim 1, wherein, The catalyst has a specific surface area of ​​200-600 cm². 2 / g, the particle size of the active component is 5-8nm.

6. The method according to claim 1, wherein, The amount of organic acid used is 5-30% by weight of the total amount of impregnation solution.

7. The method according to claim 6, wherein, The concentration of organic acid in the impregnation solution is 10-20% by weight.

8. The method according to claim 6 or 7, wherein, The organic acid is selected from C2-C8 organic acids.

9. The method according to claim 1, wherein, The organic acid is selected from at least one of acetic acid, monochloroacetic acid, lactic acid, tartaric acid, and citric acid.

10. The method according to claim 1, wherein, The impregnation is carried out in one step or in multiple steps.

11. The method according to claim 10, wherein, The impregnation method includes immersing the carrier in an impregnation solution containing an active component precursor and an organic acid for 8-12 hours.

12. The method according to claim 10, wherein, The stepwise impregnation method includes: (A) Immerse the carrier in an impregnation solution containing organic acid for 4-8 hours, filter and remove the impregnated carrier, and then immerse it in an impregnation solution containing the precursor of the active component for 8-12 hours; or (B) Immerse the carrier in an impregnation solution containing the precursor of the active component for 8-12 hours, and then add organic acid to it and continue impregnation for 4-8 hours.

13. The method according to claim 1, wherein, The drying conditions include: a drying temperature of 100-120℃ and a drying time of 8-12 hours; And / or, the calcination conditions include: a calcination temperature of 450-500℃ and a calcination time of 2-6h.

14. The method according to claim 1, wherein, The method further includes pretreating the carrier before loading the active component onto it to remove any moisture and organic impurities that may be present in the carrier.

15. The method according to claim 1, wherein, Alkanes in plasma state are produced under the action of a plasma source.

16. The method according to claim 15, wherein, The specific power consumption of the plasma source is 5-100 kJ / L.

17. The method according to claim 1, wherein, The alkane is C1-C 10 At least one of the alkanes.

18. The method according to claim 1, wherein, The olefin is C2-C. 20 At least one of the olefins.

19. The method according to claim 1, wherein, The contact conditions include: temperature 20-35℃, pressure 0.05-0.25MPa, and time 8 hours or more.

20. The method according to claim 19, wherein, The contact is carried out in the presence of hydrogen gas, with a volume ratio of hydrogen to alkane of 0-10:1.

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