CN111644197A - Catalytic system for preparing aromatic hydrocarbon by low-temperature methane conversion, preparation method and application - Google Patents

Abstract

The invention discloses a catalytic system, preparation method and application of a low-temperature methane conversion to aromatic hydrocarbons. The catalytic system comprises: a molybdenum-based molecular sieve catalyst and a catalyst supported by iron oxide; the molybdenum-based molecular sieve catalyst and a catalyst supported by iron oxide The mass ratio of the catalyst is 1:1-10; wherein, the active component of the molybdenum-based molecular sieve catalyst is Mo, and the mass percentage content of the active component Mo in the molybdenum-based molecular sieve catalyst is 1%-10%; iron oxide is used as a carrier In the catalyst, the carrier Fe ₂ O ₃ is in powder form, and the mass percentage of iron oxide is 1%-10%. The catalytic system enables methane to be converted into high value-added aromatic hydrocarbon raw materials at a lower temperature, thereby improving the utilization value of methane. The generated product has good selectivity, the selectivity of aromatic hydrocarbons can reach 70%, the catalyst has good stability, and can be continuously reacted for 100 hours without deactivation.

Description

Catalytic system, preparation method and application of low temperature methane conversion to aromatic hydrocarbons

technical field

The present invention relates to the field of methane conversion reaction. More specifically, it relates to a catalytic system, preparation method and application of low-temperature methane conversion to aromatic hydrocarbons.

Background technique

After entering the 21st century, with the development of shale gas and marine "flammable ice", the reserves of natural gas are further enriched, and the reserves of methane, the main component of natural gas, have also increased significantly. Methane can further generate high value-added chemical products through catalytic reactions. Under the background of the depletion of global oil resources, the effective utilization of methane has attracted the attention of many scholars all over the world.

The methane conversion pathway is mainly divided into indirect method and direct method. In the indirect method, methane is reformed or partially oxidized at high temperature to produce a certain proportion of CO and H ₂ into a synthesis gas, and then the organic chemical raw materials we need are directly or indirectly produced from the synthesis gas under the action of a catalyst. The direct method refers to the direct conversion of methane into chemical products with high added value under the action of catalysts. The indirect process technology is complex and energy-intensive, while the direct process has lower energy consumption and higher methane utilization rate, so the direct conversion of methane has received extensive attention in recent years.

酸位上转化成苯和萘(Acs Catalysis,2017,7(3))。Bao等人将具有高催化活性的单中心低价铁原子嵌入到氧化硅或碳化硅晶格中，进而形成高温稳定的催化活性中心，使甲烷的单程转化率达48.1％，乙烯的选择性为48.4％，所有产物(乙烯、苯和萘)的选择性>99％(Science Foundation in China,2014,344,616-619)。这些方法虽然降低了甲烷转化温度，但催化剂制备以及反应条件很难实现工业化，而且反应过程中催化剂的积碳问题使得催化剂快速失活。Among the direct conversion of methane, anaerobic conversion has been widely studied due to its advantages of high atom utilization and environmental friendliness. The methane molecule has a regular tetrahedral structure composed of weakly polarized CH bonds, and has very stable chemical and thermodynamic properties. In the absence of a catalyst, it takes thousands of degrees of high temperature to break the CH bond of methane. In 1993, Wang et al. reported for the first time the anaerobic aromatization of methane at 973K over a Mo/HZSM-5 molecular sieve catalyst in a continuous flow mode, with a methane conversion rate of 7.2% and a benzene selectivity of 100%. It is an important milestone in the process, and many scientists have done a lot of research on it since then. Koerts et al. designed a two-step catalytic reaction system from methane to ethane, propane, butane and pentane from the reaction mechanism: the first step is the dissociation and adsorption of methane on transition metal catalysts to generate surface carbon species and hydrogen, The required temperature is about 400°C; the second step is hydrogenation of carbon species to generate small molecular alkanes, and the required temperature is about 100°C (Cheminform, 1993, 24(8): 101-114). Barrabes et al. found that transition metals can activate methane at lower temperatures (Appl.catal.B:Environ, 2009, 87:84-91). Vesna et al. studied the chemisorption of methane with Pt catalysts at low temperature (200-450 °C) in a fixed-bed reactor (Applied Catalysis A General, 2014, 488: 138-147). Duygu et al. found that Pt and PtSn catalysts supported on SiO ₂ and HZSM-5 can be used for methane conversion under non-oxidative conditions, adding Sn to Pt/SiO 2 can synthesize more active ethylene-forming catalysts, and prepare supported HZSM- 5 Pt and PtSn catalysts on zeolite, which can improve activity and selectivity to non-coke products, these catalysts operate through a bifunctional mechanism in which ethylene is first produced on highly dispersed PtSn nanoparticles and then in zeolite support.

It is converted into benzene and naphthalene in the acid position (Acs Catalysis, 2017, 7(3)). Bao et al. embedded a single-center low-valent iron atom with high catalytic activity into the lattice of silicon oxide or silicon carbide to form a high-temperature stable catalytic active center, resulting in a one-pass conversion of methane of 48.1% and a selectivity of ethylene as 48.4% with >99% selectivity for all products (ethylene, benzene and naphthalene) (Science Foundation in China, 2014, 344, 616-619). Although these methods reduce the methane conversion temperature, the catalyst preparation and reaction conditions are difficult to achieve industrialization, and the problem of carbon deposition of the catalyst during the reaction process makes the catalyst rapidly deactivate.

SUMMARY OF THE INVENTION

The first technical problem to be solved by the present invention is to provide a catalytic system for converting methane to aromatics at low temperature. The catalytic system enables methane to be converted into high value-added aromatic hydrocarbon raw materials at a lower temperature, thereby improving the utilization value of methane. The generated product has good selectivity, the selectivity of aromatic hydrocarbons can reach 70%, the catalyst has good stability, and can be continuously reacted for 100 hours without deactivation.

The second technical problem to be solved by the present invention is to provide a preparation method of a catalytic system for converting methane to aromatic hydrocarbons at a low temperature.

The third technical problem to be solved by the present invention is to provide the application of the above-mentioned catalytic system in the conversion of low temperature methane to aromatics.

In order to solve the above-mentioned first technical problem, the present invention adopts the following technical scheme:

A catalytic system for converting low temperature methane to aromatic hydrocarbons, comprising:

Molybdenum-based molecular sieve catalysts and catalysts supported by iron oxide;

The mass ratio of the molybdenum-based molecular sieve catalyst to the catalyst supported by iron oxide is 1:1-10;

Wherein, the active component of the molybdenum-based molecular sieve catalyst is Mo, and the mass percentage of the active component Mo in the molybdenum-based molecular sieve catalyst is 1%-10%;

In the catalyst using iron oxide as a carrier, the carrier Fe ₂ O ₃ is in powder form, and the mass percentage of iron oxide is 1%-10%.

Preferably, the molecular sieve in the molybdenum-based molecular sieve catalyst is selected from one or more of HZSM-5 molecular sieve, SAPO-34 molecular sieve, Hβ molecular sieve, MCM-41 molecular sieve, Q10 molecular sieve, and HY molecular sieve.

Preferably, the molar ratio of the silicon-alumina components of the molecular sieve is 20-150:1.

Preferably, in the iron oxide-supported catalyst, the active metal is Pt, Pd, Ru, Ni, Mn, Cu, Co, Zr, Mg, Cr, Zn, Ce, K, Al, Ag, Rh one or more.

In order to solve the above-mentioned second technical problem, the present invention adopts the following technical scheme:

A preparation method of a catalytic system for producing aromatic hydrocarbons from low-temperature methane conversion, comprising the steps of:

The molybdenum-based molecular sieve catalyst and the catalyst supported by iron oxide are prepared by the impregnation method. The two catalysts are fully ground according to the mass ratio of 1:1-10 until they are evenly mixed, and the obtained powder is granulated to obtain a low-temperature methane conversion to aromatics catalytic system.

Preferably, the preparation method of the catalytic system of the low-temperature methane conversion to aromatic hydrocarbons comprises the following specific steps:

1) calcining the molecular sieve carrier at 400-550°C for 2-12h;

2) Molybdenum-based molecular sieve catalyst was prepared by excess impregnation method. Mo precursor and molecular sieve carrier were weighed and dissolved in deionized water in proportion, stirred and evaporated to dryness at 55-65°C, and then dried at 115-125°C for 10-15h, 540 -560 ℃ roasting to obtain molybdenum-based molecular sieve catalyst;

3) Preparation of catalyst with iron oxide as carrier by excessive impregnation method: Weigh transition metal precursor and Fe ₂ O ₃ powder in proportion, dissolve in appropriate amount of ethylene glycol or deionized water, stir evenly, and dry at 120-150°C 10-15h, calcining at 380-420°C to obtain a catalyst supported by iron oxide;

4) The molybdenum-based molecular sieve catalyst and the catalyst supported by iron oxide are fully ground according to the mass ratio until they are evenly mixed, and the obtained powder is granulated to obtain a catalytic system for converting methane to aromatics at a low temperature.

Preferably, in step 1), the molecular sieve carrier is selected from one or more of HZSM-5 molecular sieve, SAPO-34 molecular sieve, Hβ molecular sieve, MCM-41 molecular sieve, Q10 molecular sieve, and HY molecular sieve.

Preferably, in step 2), the Mo precursor is ammonium molybdate tetrahydrate crystal; the amount of deionized water for dissolving the Mo precursor and the molecular sieve carrier is 2-6mL/g, and the calcination time is 2-12h.

Preferably, in step 3), the transition metal precursor is selected from chloroplatinic acid hexahydrate crystal, dinitrosodiammine platinum solution, palladium chloride powder, palladium nitrate solution, ruthenium nitrate solution, hexahydrate nickel nitrate crystal One or more of the above; the amount of ethylene glycol or deionized water for dissolving the transition metal precursor and Fe ₂ O ₃ powder is 0-1 mL/g, and the calcination time is 2-12 h.

Preferably, in step 4), the mass ratio of the molybdenum-based molecular sieve catalyst to the catalyst supported by iron oxide is 1:1-10.

In order to solve the above-mentioned third technical problem, the application of the catalytic system of a kind of low-temperature methane conversion to aromatic hydrocarbons of the present invention comprises the following concrete steps:

11) the reaction is carried out in a fixed-bed reactor, and the catalyst is placed in a quartz glass tube;

12) The catalyst is activated by introducing reducing gas, the activation temperature is 300-500°C, and the maintenance time is 1-10h;

13) Feed the raw material gas to react, the raw material gas is 90% methane gas (10% Ar is used as internal standard gas), the reaction temperature is 350-600 ° C, the reaction pressure is 0.01-0.5MPa, and the space velocity is 5000-20000mL/ g _cat h.

Preferably, in step 12), the reducing gas is one or more of hydrogen and synthesis gas.

Preferably, in step 13), an auxiliary agent is added in the reaction process, and the auxiliary agent is selected from one or more of benzene, toluene and xylene.

Any range recited herein includes the endpoints and any number between the endpoints and any sub-ranges formed by the endpoints or any number between the endpoints.

Unless otherwise specified, each raw material in the present invention can be obtained through commercial purchase, and the equipment used in the present invention can be performed with conventional equipment in the field or with reference to the prior art in the field.

Compared with the prior art, the present invention has the following beneficial effects:

The method can complete the conversion of methane at a low temperature of 350-600 DEG C, and the preparation method of the catalyst is simple, the operation is convenient, the selectivity of the generated product is good, the selectivity of aromatics exceeds 70%, the catalyst is stable, and the reaction can be continued for 100 hours. Not inactivated.

Detailed ways

In order to illustrate the present invention more clearly, the present invention will be further described below with reference to the preferred embodiments. Those skilled in the art should understand that the content specifically described below is illustrative rather than restrictive, and should not limit the protection scope of the present invention.

As one aspect of the present invention, a kind of catalytic system of low temperature methane conversion to aromatics, comprises:

Molybdenum-based molecular sieve catalysts and catalysts supported by iron oxide;

The mass ratio of the molybdenum-based molecular sieve catalyst to the catalyst supported by iron oxide is 1:1-10;

Wherein, the active component of the molybdenum-based molecular sieve catalyst is Mo, and the mass percentage content of the active component Mo in the molybdenum-based molecular sieve catalyst is 1% to 10%;

In the catalyst using iron oxide as a carrier, the carrier Fe ₂ O ₃ is in powder form, and the mass percentage of iron oxide is 1% to 10%.

In the present invention, the term "catalytic system" refers to the presence of a "catalyst" in the reactor as a whole, in the form of a mixture rather than a compound in the present invention.

In certain embodiments of the present invention, the molecular sieve in the platinum-based molecular sieve catalyst is selected from one or more of HZSM-5 molecular sieve, SAPO-34 molecular sieve, Hβ molecular sieve, MCM-41 molecular sieve, Q10 molecular sieve, and HY molecular sieve kind.

In certain embodiments of the present invention, the molar ratio of the silicon-alumina components of the molecular sieve is 20-150:1, and too low or too high acidity is not conducive to the formation of products during the reaction.

In some embodiments of the present invention, in the iron oxide-supported catalyst, the active metals are Pt, Pd, Ru, Ni, Mn, Cu, Co, Zr, Mg, Cr, Zn, Ce, K, One or more of Al, Ag, Rh.

As another aspect of the present invention, a kind of preparation method of the catalytic system of low temperature methane conversion to aromatics, comprises the steps:

The molybdenum-based molecular sieve catalyst and the catalyst supported by iron oxide are prepared by the impregnation method. The two catalysts are fully ground according to the mass ratio of 1:1-10 until they are evenly mixed, and the obtained powder is granulated to obtain a low-temperature methane conversion to aromatics catalytic system.

In certain embodiments of the present invention, the preparation method of the catalytic system for converting low temperature methane to aromatics comprises the following specific steps:

1) The molecular sieve carrier is calcined at 400-550 ℃ for 2-12 hours, so that the possible impurities on the molecular sieve can be effectively removed, so that it does not affect the judgment of the experimental results;

2) Molybdenum-based molecular sieve catalyst was prepared by excess impregnation method. Mo precursor and molecular sieve carrier were weighed and dissolved in deionized water in proportion, stirred and evaporated to dryness at 55-65°C, and then dried at 115-125°C for 10-15h, 540 Roasting at -560 °C to remove impurities that may exist in the catalyst preparation process and stabilize the catalyst structure to obtain a molybdenum-based molecular sieve catalyst;

3) Preparation of catalyst with iron oxide as carrier by excessive impregnation method: Weigh transition metal precursor and Fe ₂ O ₃ powder in proportion, dissolve in appropriate amount of ethylene glycol or deionized water, stir evenly, and dry at 120-150°C 10-15h, calcining at 380-420 ℃, to remove impurities that may exist in the catalyst preparation process, and to stabilize the catalyst structure to obtain a catalyst with iron oxide as a carrier;

4) The molybdenum-based molecular sieve catalyst and the catalyst supported by iron oxide are fully ground according to the mass ratio until they are evenly mixed, and the obtained powder is granulated to obtain a catalytic system for converting methane to aromatics at a low temperature.

In certain embodiments of the present invention, in step 1), the molecular sieve carrier is selected from one or more of HZSM-5 molecular sieve, SAPO-34 molecular sieve, Hβ molecular sieve, MCM-41 molecular sieve, Q10 molecular sieve, and HY molecular sieve kind.

In some embodiments of the present invention, in step 2), the Mo precursor is ammonium molybdate tetrahydrate crystal; the amount of deionized water for dissolving the Mo precursor and the molecular sieve carrier is 2-6 mL/g, and the calcination time is 2-6 mL/g. For 2 ~ 12h.

In some embodiments of the present invention, in step 3), the transition metal precursor is selected from the group consisting of chloroplatinic acid hexahydrate crystal, dinitrosodiammine platinum solution, palladium chloride powder, palladium nitrate solution, ruthenium nitrate solution, one or more of hexahydrate nickel nitrate crystals; the amount of ethylene glycol or deionized water for dissolving the transition metal precursor and Fe ₂ O ₃ powder is 0-1 mL/g, and the roasting time is 2-12 h.

In some embodiments of the present invention, in step 4), the mass ratio of the molybdenum-based molecular sieve catalyst to the catalyst supported by iron oxide is 1:1-10, and the ratio is too low to achieve aromatization. Too many highly acidic sites can easily lead to carbon deposition in the catalyst.

As another aspect of the present invention, the application of a kind of catalytic system of low-temperature methane conversion to aromatic hydrocarbons of the present invention comprises the following specific steps:

11) the reaction is carried out in a fixed-bed reactor, and the catalyst is placed in a quartz glass tube;

12) The catalyst is activated by introducing reducing gas. The activation temperature is 300-500 ° C. The catalyst cannot be fully reduced if the temperature is too low. When the temperature is too high, the catalytic reaction will easily lead to carbon deposition, which is not conducive to the subsequent reaction. 1-10h;

13) Feed the raw material gas to react, the raw material gas is 90% methane gas (10% Ar is used as internal standard gas), the reaction temperature is 350-600 ° C, the reaction pressure is 0.01-0.5MPa, and the space velocity is 5000-20000mL/ g _cat h, too low space velocity is not conducive to the progress of the reaction, and too high is not conducive to the control of the reaction.

Preferably, in step 12), the reducing gas is one or more of hydrogen and synthesis gas.

Preferably, in step 13), an auxiliary agent is added in the reaction process, and the auxiliary agent is selected from one or more of benzene, toluene and xylene.

Example 1

The preparation method of the catalytic system of low temperature methane conversion to produce aromatics, comprises the following steps:

Weigh 0.05g of _1Pt /Fe ₂ O ₃ and 0.15g of 6Mo/HZSM _- 5-36 catalyst respectively, and granulate the obtained powder after mixing evenly. : 6Mo/HZSM-5-36=1:3.

The above catalyst system was filled into a fixed-bed reactor, reduced at 400 °C for 3 h under a hydrogen atmosphere, and then heated to 550 °C for the reaction, the pressure was 0.1 MPa, the reaction gas was 10% Ar/CH ₄ , and the gas flow was 6.67 mL /min, the reaction space velocity was 8000mL/g _cat ·h. The reaction results are shown in Table 1.

Example 2

The preparation method of the catalytic system of low temperature methane conversion to produce aromatics, comprises the following steps:

Weigh 0.05g of _1Pt /Fe ₂ O ₃ and 0.25g of 6Mo/HZSM _- 5-36 catalyst respectively, and granulate the obtained powder after mixing evenly. : 6Mo/HZSM-5-36=1:5.

The above catalyst was filled into a fixed-bed reactor, and the catalyst was reduced at 400 °C for 3 h under a hydrogen atmosphere, and then heated to 550 °C to carry out the reaction, the pressure was 0.1 MPa, the reaction gas was 10% Ar/CH ₄ , and the gas flow was 6.67 mL /min, the reaction space velocity was 8000mL/g _cat ·h. The reaction results are shown in Table 1.

Example 3

The preparation method of the catalytic system of low temperature methane conversion to produce aromatics, comprises the following steps:

Weigh 0.05g of _1Pt /Fe ₂ O ₃ and 0.5g of 6Mo/HZSM _- 5-36 catalyst respectively, and granulate the obtained powder after mixing evenly. : 6Mo/HZSM-5-36=1:10.

The above catalyst was filled into a fixed-bed reactor, and the catalyst was reduced at 400 °C for 3 h under a hydrogen atmosphere, and then heated to 550 °C to carry out the reaction, the pressure was 0.1 MPa, the reaction gas was 10% Ar/CH ₄ , and the gas flow was 6.67 mL /min, the reaction space velocity was 8000mL/g _cat ·h. The reaction results are shown in Table 1.

Comparative Example 1

Weigh 0.5873 g of ammonium molybdate ((NH ₄ ) ₆ Mo ₇ O ₂₄ ·4H ₂ O) and dissolve it in 20 mL of deionized water. Weigh 5 g of HZSM-5 molecular sieve powder with a silicon-alumina ratio of 36 and pour it into the above solution. Stir on an electromagnetic stirrer at 60°C and evaporate to dryness. The obtained powder is placed in a porcelain dish and dried in an oven at 120°C for 12h. The obtained precursor is calcined at 550°C for 2h to obtain a molybdenum-based molecular sieve catalyst with a loading of 6wt%. Denoted as 6Mo/HZSM-5-36.

The above-mentioned catalyst was pressed and granulated under 10MPa, and the mesh number was 20-40 mesh. Weigh 0.05g of 6Mo/HZSM-5-36 and 0.25g of 20-40 mesh SiO ₂ and mix them uniformly and then fill them into a fixed-bed reactor. The catalyst is reduced at 400 °C for 3 h under a hydrogen atmosphere, and then heated to 550 °C. In the reaction, the pressure was 0.1 MPa, the reaction gas was 10% Ar/CH ₄ , the gas flow was 6.67 mL/min, and the reaction space velocity was 8000 mL/g _cat ·h. The reaction results are shown in Table 1.

Table 1

From the test results, it can be seen that when the mixing ratio of the two catalysts is changed, the reaction result changes obviously, and the mixing ratio of the two catalysts should be properly adjusted during the reaction. When the mixing ratio of the two catalysts is 1:5, the methane conversion rate is significantly improved, and the aromatics selectivity is greater than 70%, and the catalyst can be continuously reacted for 100 hours without deactivation. The methane conversion rate of the single 6Mo/HZSM-5 catalyst during the reaction is only 1.56, the aromatics selectivity is close to 33%, and the reaction can only run stably for 8 hours.

Example 4

The preparation method of the catalytic system of low temperature methane conversion to produce aromatics, comprises the following steps:

Weigh 0.05g of _1Pt /Fe ₂ O ₃ and 0.25g of 6Mo/HZSM _- 5-20 catalyst respectively, and granulate the obtained powder after mixing evenly. : 6Mo/HZSM-5-20=1:5.

The above catalyst was filled into a fixed-bed reactor, and the catalyst was reduced at 400 °C for 3 h under a hydrogen atmosphere, and then heated to 550 °C to carry out the reaction, the pressure was 0.1 MPa, the reaction gas was 10% Ar/CH ₄ , and the gas flow was 6.67 mL /min, the reaction space velocity was 8000mL/g _cat ·h. The reaction results are shown in Table 2.

Comparative Example 2

Weigh 0.5873 g of ammonium molybdate ((NH ₄ ) ₆ Mo ₇ O ₂₄ ·4H ₂ O) and dissolve it in 20 mL of deionized water. Weigh 5 g of HZSM-5 molecular sieve powder with a silicon-alumina ratio of 20 and pour it into the above solution. Stir on an electromagnetic stirrer at 60°C and evaporate to dryness. The obtained powder is placed in a porcelain dish and dried in an oven at 120°C for 12h. The obtained precursor is calcined at 550°C for 2h to obtain a molybdenum-based molecular sieve catalyst with a loading of 6wt%. Recorded as 6Mo/HZSM-5-20.

The above-mentioned catalyst was compressed and granulated under 10 MPa, and the mesh number was 20-40 mesh. Weigh 0.05g of 6Mo/HZSM-5-20 and 0.25g of 20-40 mesh SiO ₂ and mix them uniformly and then fill them into a fixed-bed reactor. The catalyst is reduced at 400 °C for 3 h under a hydrogen atmosphere, and then heated to 550 °C. The reaction was carried out with a pressure of 0.1 MPa, a reaction gas of 10% Ar/CH ₄ , a gas flow of 6.67 mL/min, and a reaction space velocity of 8000 mL/g _cat ·h. The reaction results are shown in Table 2.

Table 2

It can be seen from the test results that when the silicon-alumina ratio of the molecular sieve is changed, the methane conversion rate and aromatics selectivity of the mixed catalyst are higher, and the catalyst can continuously react for 100 hours without deactivation. The methane conversion rate and aromatics selectivity of the single 6Mo/HZSM-5-20 catalyst during the reaction are both low, and the reaction can only run stably for 8 hours.

Example 5

The preparation method of the catalytic system of low temperature methane conversion to produce aromatics, comprises the following steps:

Weigh 0.05g of _1Pt /Fe ₂ O ₃ and 0.25g of 6Mo/HZSM _- 5-150 catalyst respectively, and granulate the obtained powder after mixing evenly. : 6Mo/HZSM-5-150=1:5.

The above catalyst was filled into a fixed-bed reactor, and the catalyst was reduced at 400 °C for 3 h under a hydrogen atmosphere, and then heated to 550 °C to carry out the reaction, the pressure was 0.1 MPa, the reaction gas was 10% Ar/CH ₄ , and the gas flow was 6.67 mL /min, the reaction space velocity was 8000mL/g _cat ·h. During the reaction, the methane conversion and aromatics selectivity were slightly lower than those in Example 4, but the catalyst could still continue to react for 100 hours without deactivation.

Example 6

The preparation method of the catalytic system of low temperature methane conversion to produce aromatics, comprises the following steps:

Weigh 0.05g of _1Pt /Fe ₂ O ₃ and 0.25g of 1Mo/HZSM _- 5-36 catalyst respectively, and granulate the obtained powder after mixing evenly. : 1Mo/HZSM-5-36=1:5.

The above catalyst was filled into a fixed-bed reactor, and the catalyst was reduced at 400 °C for 3 h under a hydrogen atmosphere, and then heated to 550 °C to carry out the reaction, the pressure was 0.1 MPa, the reaction gas was 10% Ar/CH ₄ , and the gas flow was 6.67 mL /min, the reaction space velocity was 8000mL/g _cat ·h. The reaction results are shown in Table 3.

Comparative Example 3

Weigh 0.0979 g of ammonium molybdate ((NH ₄ ) ₆ Mo ₇ O ₂₄ ·4H ₂ O) and dissolve it in 20 mL of deionized water. Weigh 5 g of HZSM-5 molecular sieve powder with a silicon-aluminum ratio of 36 and pour it into the above solution. Stirring on an electromagnetic stirrer at 60°C and evaporated to dryness, the obtained powder was placed in a porcelain dish and dried in an oven at 120°C for 12h. The obtained precursor was calcined at 550°C for 2h to obtain a molybdenum-based molecular sieve catalyst with a loading of 1wt%. Recorded as 1Mo/HZSM-5-36.

The above-mentioned catalyst was pressed and granulated under 10MPa, and the mesh number was 20-40 mesh. Weigh 0.05g of 1Mo/HZSM-5-36 and 0.25g of 20-40 mesh SiO ₂ and mix them uniformly and then fill them into a fixed-bed reactor. The catalyst is reduced at 400 °C for 3 h under a hydrogen atmosphere, and then heated to 550 °C. The reaction was carried out with a pressure of 0.1 MPa, a reaction gas of 10% Ar/CH ₄ , a gas flow of 6.67 mL/min, and a reaction space velocity of 8000 mL/g _cat ·h. The reaction results are shown in Table 3.

table 3

It can be seen from the test results that when the loading of Mo in the molecular sieve catalyst is changed, the methane conversion rate of the mixed catalyst is maintained at 4.04%, the aromatics selectivity is maintained at more than 70%, and the catalyst has a slight carbon deposition, which can be continuously reacted for 100h without loss. live. The methane conversion rate of the single 1Mo/HZSM-5-36 catalyst during the reaction is extremely low, the aromatics selectivity does not exceed 16%, and the reaction can only run stably for 8 hours.

Example 7

The preparation method of the catalytic system of low temperature methane conversion to produce aromatics, comprises the following steps:

Weigh 0.05g of _1Pt /Fe ₂ O ₃ and 0.25g of 10Mo/HZSM _- 5-36 catalyst respectively, and granulate the obtained powder after mixing evenly. : 10Mo/HZSM-5-36=1:5.

The above catalyst was filled into a fixed-bed reactor, and the catalyst was reduced at 400 °C for 3 h under a hydrogen atmosphere, and then heated to 550 °C to carry out the reaction, the pressure was 0.1 MPa, the reaction gas was 10% Ar/CH ₄ , and the gas flow was 6.67 mL /min, the reaction space velocity was 8000mL/g _cat ·h. From the reaction results, when the loading of Mo in the molecular sieve catalyst was increased, the methane conversion and aromatics selectivity decreased slightly compared with Example 6.

Example 8

The preparation method of the catalytic system of low temperature methane conversion to produce aromatics, comprises the following steps:

Weigh 0.05g of _1Pt /Fe ₂ O ₃ and 0.25g _of 6Mo/Hβ catalyst respectively, and granulate the obtained powder after mixing evenly. = 1:5.

The above catalyst was filled into a fixed-bed reactor, and the catalyst was reduced at 400 °C for 3 h under a hydrogen atmosphere, and then heated to 550 °C to carry out the reaction, the pressure was 0.1 MPa, the reaction gas was 10% Ar/CH ₄ , and the gas flow was 6.67 mL /min, the reaction space velocity was 8000mL/g _cat ·h. The reaction results are shown in Table 4.

Comparative Example 4

Weigh 0.5873 g of ammonium molybdate ((NH ₄ ) ₆ Mo ₇ O ₂₄ ·4H ₂ O) and dissolve it in 20 mL of deionized water. Weigh 5 g of Hβ molecular sieve powder and pour it into the above solution. After drying, the obtained powder was placed in a porcelain dish and dried in an oven at 120°C for 12h. The obtained precursor was calcined at 550°C for 2h to obtain a molybdenum-based molecular sieve catalyst with a loading of 6wt%, denoted as 6Mo/Hβ.

The above-mentioned catalyst was compressed and granulated under 10 MPa, and the mesh number was 20-40 mesh. Weigh 0.05g of 6Mo/Hβ and 0.25g of 20-40 mesh SiO ₂ and mix them evenly, and then fill them into a fixed-bed reactor. The catalyst is reduced at 400 °C for 3 h under a hydrogen atmosphere, and then heated to 550 °C for the reaction. is 0.1 MPa, the reaction gas is 10% Ar/CH ₄ , the gas flow rate is 6.67 mL/min, and the reaction space velocity is 8000 mL/g _cat ·h. The reaction results are shown in Table 4.

Table 4

It can be seen from the test results that when the type of molecular sieve in the molecular sieve catalyst is changed, the methane conversion rate of the mixed catalyst is maintained at 3.73%, the aromatics selectivity is maintained at more than 50%, the catalyst has a slight carbon deposit, and can be continuously reacted for 100h without deactivation . The methane conversion rate of the single 6Mo/Hβ catalyst during the reaction is extremely low, the aromatics selectivity is close to no more than 16%, and the reaction can only run stably for 8 hours.

Example 9

The preparation method of the catalytic system of low temperature methane conversion to produce aromatics, comprises the following steps:

Weigh 0.05g of _1Pt /Fe ₂ O ₃ and 0.25g _of 6Mo/SAPO-34 catalyst respectively, and granulate the obtained powder after mixing evenly. /SAPO-34=1:5.

The above catalyst was filled into a fixed-bed reactor, and the catalyst was reduced at 400 °C for 3 h under a hydrogen atmosphere, and then heated to 550 °C to carry out the reaction, the pressure was 0.1 MPa, the reaction gas was 10% Ar/CH ₄ , and the gas flow was 6.67 mL /min, the reaction space velocity was 8000mL/g _cat ·h. Judging from the reaction results, when SAPO-34 molecular sieve was used as the carrier of the molecular sieve catalyst, the methane conversion rate was low, but the catalyst could still maintain the reaction for 100h without deactivation.

Example 10

The preparation method of the catalytic system of low temperature methane conversion to produce aromatics, comprises the following steps:

Weigh 0.05g of _1Pd /Fe ₂ O ₃ and 0.25g of 6Mo/HZSM _- 5-36 catalyst respectively, and granulate the obtained powder after mixing evenly. : 6Mo/HZSM-5-36=1:5.

The above catalyst was filled into a fixed-bed reactor, and the catalyst was reduced at 400 °C for 3 h under a hydrogen atmosphere, and then heated to 550 °C to carry out the reaction, the pressure was 0.1 MPa, the reaction gas was 10% Ar/CH ₄ , and the gas flow was 6.67 mL /min, the reaction space velocity was 8000mL/g _cat ·h. The reaction results are shown in Table 5.

Example 11

Weigh 0.05g of _1Pd /Fe ₂ O ₃ and 0.25g of 6Mo/HZSM _- 5-36 catalyst respectively, and granulate the obtained powder after mixing evenly. : 6Mo/HZSM-5-36=1:5.

The above catalyst was filled into a fixed bed reactor, the catalyst was reduced at 400 °C for 1 h under a hydrogen atmosphere, and then heated to 550 °C for reaction, the pressure was 0.1 MPa, the reaction gas was 10% Ar/CH ₄ , and the gas flow was the gas flow was 6.67 mL/min, and the reaction space velocity was 8000 mL/g _cat h. The reaction results are shown in Table 5.

table 5

It can be seen from the test results that when the reduction time of the mixed catalyst is changed, reducing the reduction time can effectively reduce the carbon deposition of the catalyst, the aromatics selectivity is maintained at more than 70%, and the two reactions can be continuously reacted for 100 hours without deactivation.

Example 12

The preparation method of the catalytic system of low temperature methane conversion to produce aromatics, comprises the following steps:

Weigh 0.05g of 3Ru/Fe ₂ O ₃ and 0.25g _of 6Mo/HZSM _- 5-36 catalyst respectively, and granulate the obtained powder after mixing evenly. : 6Mo/HZSM-5-36=1:5.

The above catalyst was filled into a fixed-bed reactor, and the catalyst was reduced at 400 °C for 3 h under a hydrogen atmosphere, and then heated to 550 °C to carry out the reaction, the pressure was 0.1 MPa, the reaction gas was 10% Ar/CH ₄ , and the gas flow was 6.67 mL /min, the reaction space velocity was 8000mL/g _cat ·h. The reaction results are shown in Table 6.

Comparative Example 5

Weigh 3.0927 g of ruthenium nitrosyl nitrate solution (HN ₄ O ₁₀ Ru) in a porcelain dish, weigh 3 g of Fe ₂ O ₃ powder and pour it into the above solution, stir until it is evenly mixed and evaporate to dryness into a paste, place it at 150 After drying in a ℃ oven for 12 h, an iron-based catalyst with a loading of 3 wt% can be obtained, which is denoted as 3Ru/Fe ₂ O ₃ .

The above-mentioned catalyst was pressed and granulated under 10MPa, and the mesh number was 20-40 mesh. Weigh 0.05g of 3Ru/Fe ₂ O ₃ and 0.25 g of SiO ₂ with a mesh number of 20-40, and mix them uniformly and then fill them into a fixed-bed reactor. In the reaction, the pressure was 0.1 MPa, the reaction gas was 10% Ar/CH ₄ , the gas flow was 6.67 mL/min, and the reaction space velocity was 8000 mL/g _cat ·h. The reaction results are shown in Table 6.

Table 6

From the test results, it can be concluded that the iron-based catalyst alone has a very low conversion rate of methane and basically no aromatic hydrocarbons are generated during the reaction. The conversion rate of the mixed catalyst was maintained at 7.08%, and the aromatics selectivity was over 70%, and the catalyst was maintained for 100 hours without deactivation.

Example 13

The preparation method of the catalytic system of low temperature methane conversion to produce aromatics, comprises the following steps:

Weigh 0.05g of 10Ni/Fe ₂ O ₃ and 0.25g _of 6Mo/HZSM _- 5-36 catalyst respectively, and granulate the obtained powder after mixing evenly. : 6Mo/HZSM-5-36=1:5.

The above catalyst was filled into a fixed bed reactor, the catalyst was reduced at 400°C for 10h in a hydrogen atmosphere, and then heated to 550°C for the reaction, the pressure was 0.1MPa, the reaction gas was 10% Ar/CH ₄ , and the gas flow was 6.67ml /min, the reaction space velocity is 8000ml/g _cat ·h. The reaction results are shown in Table 7.

Example 14

Weigh 0.05g of 10Ni/Fe ₂ O ₃ and 0.25g _of 6Mo/HZSM _- 5-36 catalyst respectively, and granulate the obtained powder after mixing evenly. : 6Mo/HZSM-5-36=1:5.

The above catalyst was filled into a fixed-bed reactor, and the catalyst was reduced at 400 °C for 10 h in a hydrogen atmosphere, and then heated to 550 °C for reaction, the pressure was 0.1 MPa, the reaction gas was 10% Ar/CH ₄ , and the gas flow was 16.67 ml /min, the reaction space velocity is 20000ml/g _cat ·h. The reaction results are shown in Table 7.

Table 7

From the test results, it can be concluded that increasing the space velocity can slightly improve the conversion rate of the catalyst, the aromatics selectivity of the Ni metal catalyst is slightly lower than that of the Pt metal catalyst during the reaction process, and the catalyst can maintain the reaction for 100h without deactivation.

Example 15

The preparation method of the catalytic system of low temperature methane conversion to produce aromatics, comprises the following steps:

Weigh 0.05g of _1Pt /Fe ₂ O ₃ and 0.05g of 6Mo/HZSM _- 5-36 catalyst respectively, and granulate the obtained powder after mixing evenly. : 6Mo/HZSM-5-36=1:1.

The above catalyst was filled into a fixed-bed reactor, and the catalyst was reduced at 300 °C for 3 hours in a synthesis gas atmosphere, and then heated to 550 °C for the reaction, the pressure was 0.1 MPa, the reaction gas was 10% Ar/CH ₄ , and the gas flow was 6.67 mL/min, and the reaction space velocity was 8000 mL/g _cat h. From the reaction results, it can be concluded that reducing the reduction temperature, the conversion rate of the catalyst decreases, but the catalyst can still maintain the reaction for 100h without deactivation.

Example 16

The preparation method of the catalytic system of low temperature methane conversion to produce aromatics, comprises the following steps:

Weigh 0.05g of _1Pt /Fe ₂ O ₃ and 0.05g of 6Mo/HZSM _- 5-36 catalyst respectively, and granulate the obtained powder after mixing evenly. : 6Mo/HZSM-5-36=1:1.

The above catalyst was filled into a fixed-bed reactor, and the catalyst was reduced at 500 °C for 3 hours in a synthesis gas atmosphere, and then heated to 550 °C for the reaction, the pressure was 0.1 MPa, the reaction gas was 10% Ar/CH ₄ , and the gas flow was 6.67 mL/min, and the reaction space velocity was 8000 mL/g _cat h. From the reaction results, it can be concluded that when the reduction temperature is increased, the conversion rate of the catalyst is appropriately increased, the selectivity of aromatics is better, and the catalyst can maintain the reaction for 100h without deactivation.

Example 17

Weigh 0.05g of _1Pt /Fe ₂ O ₃ and 0.25g of 6Mo/HZSM _- 5-36 catalyst respectively, and granulate the obtained powder after mixing evenly. : 6Mo/HZSM-5-36=1:5.

The above catalyst was filled into a fixed bed reactor, the catalyst was reduced at 400 °C for 3 hours under a hydrogen atmosphere, and then the temperature was raised to 550 °C for the reaction. During the reaction, toluene steam was introduced, the reaction pressure was 0.1 MPa, and the reaction gas was 10% Ar /CH ₄ , the gas flow rate was 6.67 mL/min, and the reaction space velocity was 8000 mL/g _cat ·h. The reaction results are shown in Table 13.

Example 18

Weigh 0.05g of _1Pt /Fe ₂ O ₃ and 0.25g of 6Mo/HZSM _- 5-36 catalyst respectively, and granulate the obtained powder after mixing evenly. : 6Mo/HZSM-5-36=1:5.

The above catalyst was filled into a fixed bed reactor, the catalyst was reduced at 400 °C for 3 hours under a hydrogen atmosphere, and then the temperature was raised to 550 °C for the reaction. During the reaction, toluene steam was introduced, the reaction pressure was 0.1 MPa, and the reaction gas was 10% Ar /CH ₄ , the gas flow rate was 6.67 mL/min, and the reaction space velocity was 5000 mL/g _cat ·h. The reaction results are shown in Table 13.

Table 13

It can be concluded from the test results that when the reaction space velocity decreases, the catalyst conversion rate decreases slightly. In the reaction process, after adding the auxiliary agent, the aromatics selectivity of the catalyst is greater than 70%, and the catalyst can maintain the reaction for 100 hours without deactivation.

Obviously, the above-mentioned embodiments of the present invention are only examples for clearly illustrating the present invention, rather than limiting the embodiments of the present invention. For those of ordinary skill in the art, changes or modifications in other different forms can also be made on the basis of the above description. Not all implementations can be exhaustive here. Any obvious changes or changes derived from the technical solutions of the present invention are still within the protection scope of the present invention.

Claims (10)

1. the catalytic system of low-temperature methane conversion to produce aromatics, is characterized in that, comprises: Molybdenum-based molecular sieve catalysts and catalysts supported by iron oxide; The mass ratio of the molybdenum-based molecular sieve catalyst to the catalyst supported by iron oxide is 1:1-10; Wherein, the active component of the molybdenum-based molecular sieve catalyst is Mo, and the mass percentage of the active component Mo in the molybdenum-based molecular sieve catalyst is 1%-10%; In the catalyst using iron oxide as a carrier, the carrier Fe ₂ O ₃ is in powder form, and the mass percentage of iron oxide is 1%-10%. 2. catalytic system according to claim 1 is characterized in that: molecular sieve in described molybdenum-based molecular sieve catalyst is selected from HZSM-5 molecular sieve, SAPO-34 molecular sieve, Hβ molecular sieve, MCM-41 molecular sieve, Q10 molecular sieve, HY molecular sieve one or more of. 3. The catalytic system according to claim 1, wherein the molar ratio of the silicon-aluminum component of the molecular sieve is 20-150:1. 4. The catalytic system according to claim 1 is characterized in that: in the catalyst with iron oxide as carrier, the active metals are Pt, Pd, Ru, Ni, Mn, Cu, Co, Zr, Mg, Cr, Zn , one or more of Ce, K, Al, Ag, Rh. 5. the preparation method of catalytic system as described in any one of claim 1-4, is characterized in that, comprises the steps: The molybdenum-based molecular sieve catalyst and the catalyst supported by iron oxide are prepared by the impregnation method. The two catalysts are fully ground according to the mass ratio of 1:1-10 until they are evenly mixed, and the obtained powder is granulated to obtain a low-temperature methane conversion to aromatics catalytic system. 6. the preparation method of catalytic system according to claim 5, is characterized in that, comprises following concrete steps: 1) calcining the molecular sieve carrier at 400-550°C for 2-12h; 2) using excess impregnation method to prepare molybdenum-based molecular sieve catalyst: Weigh the Mo precursor and molecular sieve carrier in deionized water in proportion, stir and evaporate to dryness at 55-65 °C, then dry at 115-125 °C for 10-15 h, and calcinate at 540-560 °C to obtain a molybdenum-based molecular sieve catalyst; 3) adopt the excessive impregnation method to prepare the catalyst with iron oxide as carrier: Weigh the transition metal precursor and Fe ₂ O ₃ powder in proportion to dissolve in an appropriate amount of ethylene glycol or deionized water, stir evenly, dry at 120-150°C for 10-15h, and roast at 380-420°C to obtain iron oxide as a supported catalyst; 4) The molybdenum-based molecular sieve catalyst and the catalyst supported by iron oxide are fully ground according to the mass ratio until they are evenly mixed, and the obtained powder is granulated to obtain a catalytic system for converting methane to aromatics at a low temperature. 7. preparation method according to claim 6 is characterized in that: in step 1), described molecular sieve carrier is selected from HZSM-5 molecular sieve, SAPO-34 molecular sieve, Hβ molecular sieve, MCM-41 molecular sieve, Q10 molecular sieve, HY molecular sieve one or more of; Preferably, in step 2), the Mo precursor is ammonium molybdate tetrahydrate crystal; the amount of deionized water for dissolving the Mo precursor and the molecular sieve carrier is 2-6mL/g, and the calcination time is 2-12h. 8. preparation method according to claim 6, is characterized in that: in step 3), described transition metal precursor is selected from chloroplatinic acid hexahydrate crystal, dinitrosodiamine platinum solution, palladium chloride powder, Palladium nitrate solution, ruthenium nitrate solution, one or more in hexahydrate nickel nitrate crystal; The amount of ethylene glycol or deionized water that dissolves transition metal precursor and Fe ₂ O ₃ powder is 0-1mL/g, roasting The time is 2-12h; Preferably, in step 4), the mass ratio of the molybdenum-based molecular sieve catalyst to the catalyst supported by iron oxide is 1:1-10. 9. the application of the catalytic system of low temperature methane conversion to aromatics as described in any one of claim 1-4, is characterized in that, comprises following concrete steps: 11) the reaction is carried out in a fixed-bed reactor, and the catalyst is placed in a quartz glass tube; 12) The catalyst is activated by introducing reducing gas, the activation temperature is 300-500°C, and the maintenance time is 1-10h; 13) Feed the raw material gas to react, the raw material gas is 90% methane gas (10% Ar is used as internal standard gas), the reaction temperature is 350-600 ° C, the reaction pressure is 0.01-0.5MPa, and the space velocity is 5000-20000mL/ g _cat h. 10. The application according to claim 9, wherein: in step 12), the reducing gas is one or more of hydrogen and synthesis gas; Preferably, in step 13), an auxiliary agent is added in the reaction process, and the auxiliary agent is selected from one or more of benzene, toluene and xylene.