A method for catalytic conversion of methane to ethylene under plasma conditions

Abstract

The application relates to the field of low-temperature plasma catalysis, in particular to a method for catalytically converting methane into ethylene under plasma conditions, which comprises the following steps: 1) preparation of a high-entropy alloy catalyst, the high-entropy alloy catalyst being expressed as Fe u Ni v V w Zr x Ag y Cu z ; 2) under plasma conditions, a mixed gas formed by methane and argon is subjected to plasma generation and catalytic reaction under the action of the high-entropy alloy catalyst; and a product containing ethylene is obtained. The application develops a method for catalytically converting methane into ethylene directly under mild conditions under the action of a high-entropy alloy catalyst and under plasma conditions, and the method can realize efficient conversion of methane.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of low-temperature plasma catalysis, and particularly relates to a method for catalyzing methane to be converted into ethylene under plasma conditions. BACKGROUND

[0002] Ethylene is an important chemical raw material, and its production is a symbol of the development level of a country's petroleum chemical industry. Methane non-oxygen conversion to ethylene is a chemical technology direction that has attracted much attention in recent years. Developing methane non-oxygen conversion to ethylene technology can reduce the dependence on petroleum resources while improving the sustainable production capacity of ethylene. Methane non-oxygen conversion to ethylene, i.e., methane direct cracking to ethylene, is a strong endothermic reaction that is extremely difficult to occur thermodynamically due to the extremely high chemical stability of methane. Traditional thermal catalysis requires an extremely high temperature, usually above 1500K, to produce ethylene. However, under such high temperature conditions, ethylene itself is also not stable, so methane tends to generate carbon and hydrogen.

[0003] The existing method for synthesizing ethylene from methane and argon reaction adopts thermal catalytic methane non-oxidative coupling technology. The disadvantages of this method are that it usually requires a high temperature of 500℃ or above, the methane conversion rate is low, the energy consumption is high, and the catalyst deactivates quickly. SUMMARY

[0004] The technical problem to be solved by the present application is to provide a method for catalyzing methane to be converted into ethylene under plasma conditions based on plasma technology.

[0005] To solve the above problems, the present application provides a method for catalyzing methane to be converted into ethylene under plasma conditions, comprising the following steps:

[0006] 1) Preparation of high-entropy alloy catalyst;

[0007] 2) Under plasma conditions, the mixed gas formed by methane and argon reacts under the action of the high-entropy alloy catalyst to generate plasma and catalyze the reaction; and a product containing ethylene is obtained.

[0008] As an improvement of the method for catalyzing methane to be converted into ethylene under plasma conditions of the present application, the specific steps are as follows:

[0009] 1) Preparation of high-entropy alloy catalyst, comprising the following steps:

[0010] S1, mix powdery iron, nickel, vanadium, zirconium, silver and copper powders in a molar ratio of (0.5-2):(0.5-2):(0.5-2):(0.5-2):(0.5-2):(0.5-2) as alloy raw material powder;

[0011] The alloy raw material powder is smelted into an alloy ingot under an inert gas atmosphere;

[0012] The smelting can be performed in a vacuum arc smelting furnace.

[0013] S2, annealing the alloy ingot, and then naturally cooling the alloy ingot to obtain an annealed alloy ingot;

[0014] The annealing temperature is 1000-1500 K, and the annealing time is 1-4 h (preferably 2 h).

[0015] Note: K = ℃ + 273.15.

[0016] S3, grinding the annealed alloy ingot under an inert gas (for example, argon) atmosphere (using a high-energy ball mill) to obtain alloy particles.

[0017] S4, using a nitric acid solution with a concentration of 0.2-1 mol / L as an etching solution to dealloy the alloy particles for 12-48 h; and then washing and drying to obtain a high-entropy alloy catalyst.

[0018] 2) The reaction device used comprises a cylindrical quartz medium shell with a cavity, the cavity of the quartz medium shell serving as a discharge gap; a high-voltage electrode is arranged close to the upper surface of the quartz medium shell, a high-voltage lead is electrically connected with the high-voltage electrode, a grounding electrode is arranged close to the lower surface of the quartz medium shell, and a grounding lead is electrically connected with the grounding electrode; a raw material inlet and a product outlet, both of which are connected with the cavity of the quartz medium shell, are arranged on the two opposite sides of the quartz medium shell.

[0019] The high-entropy alloy catalyst is filled into the discharge gap (i.e., the discharge region is filled), and the air in the reaction device is first discharged; then a mixed gas formed by methane and argon is introduced into the discharge gap from the raw material inlet, and under the action of the high-entropy alloy catalyst and the plasma high-voltage electricity, plasma is generated and the reaction is catalyzed; and a product containing ethylene is obtained.

[0020] In the mixed gas, the volume content of methane is 10-50%.

[0021] Note: The product contains hydrogen in addition to ethylene.

[0022] Further improvement of the method for catalytically converting methane under plasma conditions to produce ethylene according to the application:

[0023] In step S1, the purity of iron, nickel, vanadium, zirconium, silver, and copper is all ≥ 99.95%.

[0024] Further improvement of the method for catalytically converting methane under plasma conditions to produce ethylene according to the application:

[0025] In the step S1, the alloy ingot is repeatedly melted for several times to ensure the uniformity of the components, and the number of melting times is 2-10 times;

[0026] In the step S3, the obtained alloy particles are ground to a particle size of 20-100 mu m.

[0027] As a further improvement of the method for catalyzing the methane anaerobic conversion to ethylene under plasma conditions of the application:

[0028] The voltage peak of the plasma high-voltage electricity is 12-18 kV, and the residence time of the methane and argon mixed gas in the discharge gap is 0.04-0.08 min.

[0029] The high-voltage power input frequency is 9 kHz, and the total flow is 100-180 mL / min.

[0030] The application realizes efficient catalysis of methane anaerobic conversion to ethylene under mild conditions. In order to avoid the problems existing in high temperature conditions, a low temperature plasma catalysis method is adopted to introduce high quality energy into the reaction system, so that it is a feasible way to convert methane to ethylene under mild conditions.

[0031] The beneficial effects of the application are:

[0032] 1. A method for directly converting methane to ethylene without oxygen is developed, which realizes efficient utilization of methane.

[0033] Note: Argon as an inert gas does not participate in the reaction, but only plays a role in diluting methane, improving reaction conversion rate, increasing electron density and enhancing reaction performance.

[0034] 2. The high-entropy alloy catalyst has high activity and high selectivity for target products.

[0035] 3. The plasma inputs high-quality energy into the reaction, which directly converts methane under mild conditions and avoids high temperature conditions.

[0036] In summary, the application develops a method for efficiently catalyzing methane anaerobic conversion to directly produce ethylene under mild conditions by combining plasma conditions and high-entropy alloy catalysts, which can realize efficient conversion of methane. BRIEF DESCRIPTION OF DRAWINGS

[0037] The specific embodiments of the application will be further described in detail below with reference to the accompanying drawings.

[0038] Figure 1 The schematic diagram of the plasma reactor device used in the application is shown in the figure. In the figure, 1 is a quartz medium, 2 is a high-voltage electrode, 3 is a grounding electrode, 4 is a discharge gap, 5 is a high-voltage wire, 6 is a grounding wire, 7 is a raw material inlet, and 8 is a product outlet. DETAILED DESCRIPTION

[0039] The application will be further described in connection with specific embodiments, but the scope of the application is not limited to this:

[0040] Device Example 1, a plasma reactor device:

[0041] A parallel-plate dielectric barrier discharge plasma reactor is used as a reaction device for catalytic methane aerobic conversion to ethylene under plasma conditions; the specific structure is as follows:

[0042] A cylindrical quartz dielectric shell 1 with a cavity inside, the upper surface and the lower surface of the quartz dielectric shell 1 are circular, and the upper surface and the lower surface are parallel to each other with a certain gap as the barrier medium. The gap between the upper surface and the lower surface forms a cavity as the discharge gap 4, which is also the catalyst filling area and gas passage.

[0043] The two sides of the quartz dielectric shell 1 are respectively provided with a quartz branch pipe connected with the discharge gap 4, respectively as the raw material inlet 7 (gas raw material inlet) and the product outlet 8, that is, the raw material inlet 7, the product outlet 8, and the axis of the quartz dielectric shell 1 coincide.

[0044] A copper electrode is arranged close to the upper surface of the quartz dielectric shell 1 as a high-voltage electrode 2, and a high-voltage wire 5 is electrically connected with the high-voltage electrode 2; the distance between the high-voltage electrode 2 and the upper surface of the quartz dielectric shell 1 is ≤0.05 mm, thereby ensuring the close effect.

[0045] A copper electrode is arranged close to the lower surface of the quartz dielectric shell 1 as a grounding electrode 3, and a grounding wire 6 is electrically connected with the grounding electrode 3; the distance between the grounding electrode 3 and the lower surface of the quartz dielectric shell 1 is ≤0.05 mm, thereby ensuring the close effect.

[0046] Catalyst fillings are arranged in the discharge gap 4, thereby cooperating with plasma catalytic reaction during discharge.

[0047] A plasma high-voltage power supply is used to provide high-voltage alternating current with adjustable frequency and voltage peak value.

[0048] In actual use:

[0049] After the high-voltage wire 5 is connected to high-voltage, the high-voltage electrode 2 discharges to the grounding electrode 3, and the quartz dielectric 1 is used as dielectric material. A plasma high-voltage power supply is used to provide high-voltage alternating current with adjustable frequency and voltage peak value.

[0050] Specifically:

[0051] The wall thickness of the upper surface and the lower surface of the quartz dielectric shell 1 is 1mm~3mm, and the diameter is 30~100mm.

[0052] The high-voltage electrode 2 and the grounding electrode 3 are cylindrical and made of copper; the thickness is 10-30 mm, and the diameter is 20-80 mm, that is, the diameter of the high-voltage electrode 2 and the grounding electrode 3 is slightly smaller than the upper surface and the lower surface of the quartz dielectric shell 1.

[0053] The high-voltage electrode 2 is connected to the high-voltage power supply through a high-voltage wire 5, and the grounding electrode 3 is grounded through a grounding wire 6.

[0054] The plasma high-voltage power supply can generate stable alternating current with a voltage peak of 0-30 kV and a frequency of 1 kHz-50 kHz. The width of the discharge gap 4 (that is, the distance between the upper surface and the lower surface of the quartz dielectric shell 1) is 1.5-11 mm, and the discharge area is the common coverage area of the high-voltage electrode 2 and the grounding electrode 3, which is 300 mm 2 -4800 mm 2 , and the catalyst filling area is the discharge gap 4.

[0055] The raw gas is a mixture of methane and argon, and the proportion of methane is 10%-50%; the raw gas flow is 100-180 mL / min.

[0056] Catalyst preparation example 1: preparation of high-entropy alloy catalyst:

[0057] This scheme prepares a high-entropy alloy containing elements such as iron, nickel, vanadium, zirconium, silver, and copper, which is used to catalyze the oxygen-free conversion of methane to ethylene under plasma conditions.

[0058] The main steps are as follows:

[0059] S1, weigh the high-purity (purity ≥ 99.95%) iron, nickel, vanadium, zirconium, silver, and copper powders in the form of powder according to the molar ratio of (0.5-2):(0.5-2):(0.5-2):(0.5-2):(0.5-2):(0.5-2), and mix them thoroughly as alloy raw powder;

[0060] Put the alloy raw powder into a vacuum arc melting furnace, and melt it into an alloy ingot in an inert gas (such as argon) atmosphere; repeatedly melt the alloy ingot for 2-10 times to ensure uniform alloy composition.

[0061] S2, anneal the alloy ingot, and then cool it naturally to obtain an annealed alloy ingot;

[0062] The annealing temperature is 1000-1500 K, and the annealing time is 1-4 h.

[0063] S3, under the atmosphere of inert gas (such as argon), the alloy ingot after annealing treatment is grinded by a high-energy ball mill until the particle size of the obtained alloy particles is 20-100 μm;

[0064] S4, the alloy particles are dealloyed by using a nitric acid solution with a concentration of 0.1-2 mol / L as an etching liquid for 12-48 h; and then washed and dried to obtain a high-entropy alloy catalyst;

[0065] The high-entropy alloy catalyst is represented as Fe u Ni v V w Zr x Ag y Cu z , u, v, w, x, y, z are the molar ratios of Fe, Ni, V, Zr, Ag, Cu respectively; u:v:w:x:y:z=(0.5-2):(0.5-2):(0.5-2):(0.5-2):(0.5-2):(0.5-2).

[0066] Example 1: a method for catalyzing the aerobic conversion of methane to ethylene under plasma conditions

[0067] I. using a plasma reactor device as described in device example 1

[0068] The upper surface and the lower surface of the quartz medium shell 1 are both provided with a wall thickness of 2 mm and a diameter of 80 mm; the high-voltage electrode 2 and the grounding electrode 3 are both provided with a thickness of 20 mm and a diameter of 60 mm, and the upper and lower directions of the high-voltage electrode 2 and the grounding electrode 3 coincide with each other (the coverage areas of the high-voltage electrode 2 and the grounding electrode 3 relative to the quartz medium shell 1 coincide with each other), so the coverage area is about 2800 mm 2 . The spacing between the upper surface and the lower surface of the quartz medium shell 1 is 3 mm, that is, the width of the discharge gap 4 is 3 mm.

[0069] II. using the FeNiVZrAgCu (the molar amount of each metal is the same, that is, u, v, w, x, y, z=1) high-entropy alloy catalyst prepared in catalyst preparation example 1. High-purity iron, nickel, vanadium, zirconium, silver and copper powders (the purity of each is greater than 99.95%) are weighed according to the atomic proportion to obtain 30 g of mixed metal powder, which is mixed and then put into a vacuum arc melting furnace to be melted (the temperature is about 2000 ℃) into an alloy ingot under an argon atmosphere; the alloy ingot is naturally cooled and repeatedly melted for 5 times; then annealed at 1373 K for 2 h and naturally cooled; grinded and high-energy ball milled, and the particles with a particle size of 30-60 μm are screened; dealloyed by using 1 mol / L nitric acid for 24 h, and then washed and dried (water washing is performed until the washing liquid is neutral, and drying is performed at 120 ℃ until the weight is constant) to obtain the required high-entropy alloy catalyst (hereinafter referred to as catalyst).

[0070] III. During the reaction, the reactor is assembled, the catalyst fills the discharge gap 4 (i.e., fills the discharge area), nitrogen is continuously introduced through the raw material inlet 7 (gas raw material inlet) for 30 min, and the air in the discharge gap 4 is discharged from the product outlet 8; thereby realizing the discharge of air in the reactor; methane and argon are introduced at a volume flow rate of 1:9, and the total flow rate is 100 mL / min (the residence time of the mixed gas of methane and argon in the discharge gap 4 is 0.08 min); the high-voltage power supply inputs an alternating current with a frequency of 9 kHz and a peak voltage of 12 kV, plasma is generated, and catalytic reaction is carried out;

[0071] The catalytic reaction formula is:

[0072] The product is detected by gas chromatography-mass spectrometry. The separation of ethylene and hydrogen is a conventional technology in the industry, for example, ethylene and hydrogen can be separated by conventional pressure swing adsorption.

[0073] Example 2 series:

[0074] Compared with Example 1, the molar ratio of iron in the alloy is changed, that is, u is changed, and other operations are equivalent to Example 1, to obtain Example 2 series. The process parameters and reaction results are compared with those of Example 1, and see Table 1.

[0075] Table 1

[0076]

[0077] Example 3 series:

[0078] Compared with Example 1, the molar ratio of nickel in the alloy is changed, that is, v is changed, and other operations are equivalent to Example 1, to obtain Example 3 series. The process parameters and reaction results are compared with those of Example 1, and see Table 2.

[0079] Table 2

[0080]

[0081] Example 4 series:

[0082] Compared with Example 1, the molar ratio of vanadium in the alloy is changed, that is, w is changed, and other operations are equivalent to Example 1, to obtain Example 4 series. The process parameters and reaction results are compared with those of Example 1, and see Table 3.

[0083] Table 3

[0084]

[0085] Example 5 series:

[0086] The molar ratio of zirconium in the alloy, i.e. x, is changed relative to Example 1, and other operations are equivalent to those of Example 1 to obtain the Example 5 series. The process parameters and reaction results are compared with those of Example 1, and see Table 4.

[0087] Table 4

[0088]

[0089] Example 6 series:

[0090] The molar ratio of silver in the alloy, i.e. y, is changed relative to Example 1, and other operations are equivalent to those of Example 1 to obtain the Example 6 series. The process parameters and reaction results are compared with those of Example 1, and see Table 5.

[0091] Table 5

[0092]

[0093] Example 7 series:

[0094] The molar ratio of copper in the alloy, i.e. z, is changed relative to Example 1, and other operations are equivalent to those of Example 1 to obtain the Example 7 series. The process parameters and reaction results are compared with those of Example 1, and see Table 6.

[0095] Table 6

[0096]

[0097] Example 8 series:

[0098] The annealing temperature is changed relative to Example 1, and other operations are equivalent to those of Example 1 to obtain the Example 8 series. The process parameters and reaction results are compared with those of Example 1, and see Table 7.

[0099] Table 7

[0100]

[0101] Example 9 series:

[0102] The number of melting is changed relative to Example 1, and other operations are equivalent to those of Example 1 to obtain the Example 9 series. The process parameters and reaction results are compared with those of Example 1, and see Table 8.

[0103] Table 8

[0104]

[0105] Example 10 series:

[0106] The concentration of nitric acid was changed relative to Example 1, and other operations were equivalent to those of Example 1 to obtain the Example 10 series. The process parameters and reaction results are compared with those of Example 1 in Table 9.

[0107] Table 9

[0108]

[0109] Example 11 series:

[0110] The proportion of methane in the raw gas was changed relative to Example 1, and the flow rate of the mixed gas was kept unchanged; other operations were equivalent to those of Example 1 to obtain the Example 11 series. The process parameters and reaction results are compared with those of Example 1 in Table 10.

[0111] Table 10

[0112]

[0113] Example 12 series:

[0114] The peak-to-peak voltage (2 times the peak voltage) was changed relative to Example 1, and other operations were equivalent to those of Example 1 to obtain the Example 12 series. The process parameters and reaction results are compared with those of Example 1 in Table 11.

[0115] Table 11

[0116]

[0117] Example 13 series:

[0118] The flow rate of the methane-argon mixed gas was changed relative to Example 1, and the residence time of the mixed gas in the discharge gap 4 was changed accordingly; other operations were equivalent to those of Example 1 to obtain the Example 13 series. The process parameters and reaction results are compared with those of Example 1 in Table 12.

[0119] Table 12

[0120]

[0121] Comparative Example 1-1, the amount of Fe in Example 1 was changed to 0, i.e., u in Example 1 was changed to 0, and the rest was equivalent to Example 1. The results are as follows in Table 13.

[0122] Comparative Example 1-2, the amount of Ni in Example 1 was changed to 0, i.e., v in Example 1 was changed to 0, and the rest was equivalent to Example 1. The results are as follows in Table 13.

[0123] Comparative Example 1-3, the amount of V in Example 1 was changed to 0, i.e., w in Example 1 was changed to 0, and the rest was equivalent to Example 1. The results are as follows in Table 13.

[0124] Comparative Example 1-4, the amount of Zr in Example 1 was changed to 0, i.e. x in Example 1 was changed to 0, and the rest was identical to Example 1. The results obtained are shown in Table 13 below.

[0125] Comparative Example 1-5, the amount of Ag in Example 1 was changed to 0, i.e. y in Example 1 was changed to 0, and the rest was identical to Example 1. The results obtained are shown in Table 13 below.

[0126] Comparative Example 1-6, the amount of Cu in Example 1 was changed to 0, i.e. z in Example 1 was changed to 0, and the rest was identical to Example 1. The results obtained are shown in Table 13 below.

[0127] Comparative Example 2-1, the number of melting in Example 1 was changed to 1, and the rest was identical to Example 1. The results obtained are shown in Table 13 below.

[0128] Comparative Example 2-2, the annealing treatment in Example 1 was cancelled, and the rest was identical to Example 1. The results obtained are shown in Table 13 below.

[0129] Comparative Example 3-1, the catalyst in Example 1 was changed to quartz sand, and the rest was identical to Example 1. The results obtained are shown in Table 13 below.

[0130] Comparative Example 3-2, the catalyst in Example 1 was changed to none, and the rest was identical to Example 1. The results obtained are shown in Table 13 below.

[0131] Table 13

[0132]

[0133] Finally, it should also be noted that the above only lists several specific embodiments of the present application. Obviously, the present application is not limited to the above embodiments, and there can be many variations. All variations that can be directly derived or thought of by those of ordinary skill in the art from the disclosure of the present application should be considered within the scope of the present application.

Claims

1. Process for the catalytic, methane, anaerobic conversion into ethylene under plasma conditions, characterized in that The following steps are sequentially performed: 1) Preparation of high-entropy alloy catalyst, comprising the following steps: S1, mixing powdery iron, nickel, vanadium, zirconium, silver and copper powders in a molar ratio of (0.5-2):(0.5-2):(0.5-2):(0.5-2):(0.5-2):(0.5-2) as alloy raw material powder; The alloy raw material powder is melted into an alloy ingot under an inert gas atmosphere; S2, annealing the alloy ingot and then naturally cooling it to obtain an annealed alloy ingot; The annealing temperature is 1000-1500K, and the annealing time is 1-4h; S3, grinding the annealed alloy ingot under an inert gas atmosphere to obtain alloy particles; S4, using a nitric acid solution with a concentration of 0.2-1mol / L as an etching solution to dealloy the alloy particles for 12-48h; then washing and drying to obtain a high-entropy alloy catalyst; 2) The reaction device comprises a cylindrical quartz medium shell (1) with a cavity, the cavity of the quartz medium shell (1) serving as a discharge gap (4); a high-voltage electrode (2) is arranged close to the upper surface of the quartz medium shell (1), a high-voltage lead (5) is electrically connected to the high-voltage electrode (2), a grounding electrode (3) is arranged close to the lower surface of the quartz medium shell (1), and a grounding lead (6) is electrically connected to the grounding electrode (3); a raw material inlet (7) and a product outlet (8) are arranged on the two opposite sides of the quartz medium shell (1) and are in communication with the cavity of the quartz medium shell (1); The high-entropy alloy catalyst is filled into the discharge gap (4), and the air in the reaction device is first discharged; then a mixed gas of methane and argon is introduced into the discharge gap (4) from the raw material inlet (7), and under the action of the high-entropy alloy catalyst and the plasma high-voltage electricity, plasma is generated and the reaction is catalyzed; a product containing ethylene is obtained; In the mixed gas, the volume content of methane is 10-50%.

2. The method for catalytically converting methane into ethylene under plasma conditions according to claim 1, characterized in that: In step S1, the purity of iron, nickel, vanadium, zirconium, silver and copper is ≥99.95%.

3. The method for catalytically converting methane into ethylene under plasma conditions according to claim 2, characterized in that: In step S1, the alloy ingot is repeatedly melted multiple times to ensure uniform composition; the number of melting times is 2-10.

4. The method for catalytically converting methane into ethylene under plasma conditions according to claim 3, characterized in that: In step S3, the alloy particles are ground to a particle size of 20-100μm.

5. The method for catalytically converting methane into ethylene under plasma conditions according to any one of claims 1-4, characterized in that: The voltage peak value of the plasma high-voltage electricity is 12-18kV, and the residence time of the mixed gas of methane and argon in the discharge gap (4) is 0.04-0.08min.

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