Coal bed gas low-temperature oxidation methanol molecular sieve imidazole skeleton material catalyst, and preparation method and application thereof

Abstract

The application discloses a kind of coal-bed gas low-temperature oxidation preparation methanol molecular sieve imidazole skeleton material catalyst and its preparation method and application, catalyst includes carrier and active component loaded on carrier, the carrier is the ZIF-8 molecular sieve imidazole skeleton material prepared with 2-methylimidazole as carbon source and nitrogen source, the active component is copper and noble metal, and noble metal is selected from any one or two or more mixtures of palladium, platinum, ruthenium.The application of catalyst in coal-bed gas partial oxidation preparation methanol, can achieve that methanol yield is as high as 18mmol·g cat ‑1 , methanol selectivity reaches 97%, service life is greater than or equal to 120h, meets the industrialization requirement of low concentration coal-bed gas partial oxidation preparation methanol, with good extensive industrialization prospect.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of coal-bed gas catalyst, in particular to a coal-bed gas low-temperature oxidation methanol synthesis zeolite imidazolate framework material catalyst, a preparation method and application thereof. BACKGROUND

[0002] Coal-bed gas refers to hydrocarbon gas stored in underground coal seams, is a kind of unconventional natural gas, as a new high-quality clean energy in recent decades, can be processed by low-temperature liquefaction or membrane separation technology to obtain methane. However, the coal-bed gas exploitation technology is still in the primary stage, the utilization rate of the exploited coal-bed gas is low, which brings great pressure to the environment, and the transportation cost is high, so the effective conversion into other chemicals is a suitable path for utilizing coal-bed gas.

[0003] Methanol is an important basic raw material and energy of chemical industry, and is an important medium connecting fossil energy and chemical production. The traditional industrial conversion route is mainly based on the indirect conversion of methane, that is, first converting methane into synthesis gas (CO and H2) through a steam reforming process, and then using Fischer-Tropsch synthesis to catalytically convert into liquid oxygen-containing substances or hydrocarbons at high temperature and high pressure. Since the synthesis gas route is an energy-intensive production process, how to directly convert methane into high-value chemicals such as methanol under mild reaction conditions will become a desirable and more economical alternative method. SUMMARY

[0004] The main purpose of the present application is to provide a coal-bed gas low-temperature oxidation methanol synthesis zeolite imidazolate framework material catalyst which can directly catalyze methane to generate methanol at a lower temperature, and has good selectivity and catalytic activity, and a preparation method and application thereof.

[0005] To achieve the above-mentioned purpose, the present application provides a coal-bed gas low-temperature oxidation methanol synthesis zeolite imidazolate framework material catalyst, which comprises a carrier and an active component loaded on the carrier, the carrier is a ZIF-8 zeolite imidazolate framework material prepared by taking 2-methyl imidazole as a carbon source and a nitrogen source, and the active component is copper and a noble metal, and the noble metal is selected from any one or a mixture of two or more of palladium, platinum and ruthenium.

[0006] Further, the content of copper is 3-7wt%, the content of noble metal is 3-6wt%, and the balance is the carrier.

[0007] Further, the preparation method of the ZIF-8 zeolite imidazolate framework material comprises the following steps: Zn(NO3)2·6H2O and 2-methyl imidazole are dissolved in a polar solvent respectively, mixed and stirred at room temperature, then washed and centrifuged with methanol, the obtained solid product is vacuum dried at 50-60℃ for 6-10h, and then ground and sieved to obtain the ZIF-8 zeolite imidazolate framework material.

[0008] Further, the mass ratio of Zn(NO3)2·6H2O and 2-methylimidazole is 9:10; the polar solvent is methanol, the volume ratio of methanol in which Zn(NO3)2·6H2O and 2-methylimidazole are dissolved is 17:10, and the concentration of the solution of Zn(NO3)2·6H2O dissolved in methanol is 32 g / L; and the vacuum pressure for vacuum drying is -0.2 bar.

[0009] The application further provides a preparation method of the coal-bed gas low-temperature oxidation methanol production molecular sieve imidazole skeleton material catalyst, which comprises the following steps: taking a copper precursor salt and a noble metal precursor salt, loading the copper and the noble metal on the ZIF-8 molecular sieve imidazole skeleton material by an impregnation method to obtain a catalyst precursor, and obtaining the coal-bed gas low-temperature oxidation methanol production molecular sieve imidazole skeleton material catalyst after calcination treatment of the catalyst precursor.

[0010] Further, the copper precursor salt and the noble metal element precursor salt are respectively: copper acetylacetonate, palladium nitrate dihydrate, platinum acetylacetonate and ruthenium acetylacetonate.

[0011] Further, the impregnation loading process is as follows: the copper precursor salt, the noble metal precursor salt and the ZIF-8 molecular sieve imidazole skeleton material are added into methanol, stirred at room temperature for 6-8 hours, and then dried at a vacuum pressure of -0.2 bar and a temperature of 55-60 DEG C for 10-15 hours to obtain the catalyst precursor.

[0012] Further, the calcination treatment temperature is 400-500 DEG C, and the time is 2 hours.

[0013] The application further provides application of the catalyst in catalyzing coal-bed gas or a model thereof to produce methanol.

[0014] The application further provides a coal-bed gas low-temperature oxidation methanol production method, which comprises the following steps: taking coal-bed gas or a model thereof as a reaction raw material, adding the catalyst as claimed in any one of claims 1 to 4 to perform reaction, the raw material gas feed airspeed is 1000-4000 mL·h -1 ·g cat -1 , the air feed airspeed is 1500-3000 mL·h -1 ·g cat -1 , the water vapor feed airspeed is 3000-6000 mL·h -1 ·g cat -1 , the catalyst dosage is 300 mg-500 mg, and the reaction temperature is 180-280 DEG C.

[0015] Furthermore, the coalbed methane is a low-concentration coalbed methane with a methane volume concentration of less than 28%.

[0016] Imidazole framework-8 (ZIF-8), a typical organic molecular sieve, possesses a crystal structure bridged by zinc ions and methylimidazolium (MeIm) ligands, belonging to the metal-organic framework (MOF) materials. MOF materials are developed for catalytic reactions due to their unique crystal structure, modifiable pore structure, and high specific surface area. Transition metals and organic ligands, typically required elements in catalytic reactions, are used in their synthesis. Previous studies have shown that ZIF-8 crystals possess large cavity sizes, small connecting pore sizes, and high thermal / chemical stability, giving them superior performance compared to other MOF structures in applications such as gas adsorption. ZIF-8 also exhibits good thermal stability, and its structure can significantly influence product selectivity. Inspired by this, this invention attempts to modify the imidazole framework molecular sieve for the catalytic oxidation of methane to methanol, reducing raw material losses during catalyst preparation and improving methane conversion, methanol selectivity, and catalyst lifespan in the methanol production process.

[0017] In this invention, the copper active component exhibits good activity in the partial oxidation of methane to methanol from coalbed methane at low temperatures. The copper species, through strong interaction with the support, form polycopper active sites. On one hand, these sites can rapidly adsorb and activate methane, forming methyl radicals, which further adsorb onto the active sites to form methoxy groups, lowering the activation energy barrier. On the other hand, they can effectively inhibit the over-oxidation of hydroxyl radicals, thus preventing the formation of byproducts. The noble metal active component also plays a crucial role in the direct selective oxidation reaction of methane to methanol. Its loading onto carbon materials significantly improves the activation ability of methane and the selectivity of methanol. The carbon material, as a support, promotes the dispersion of active sites. The surface or internal pores and framework of the support can form highly active noble metal-rich nanoparticles with relatively large volumes, increasing the methanol yield.

[0018] The beneficial effects of this invention are reflected in:

[0019] 1. The imidazole molecular sieve catalyst of the present invention, used in the partial oxidation of coalbed methane to methanol, can achieve a methanol yield as high as 18 mmol·g. cat -1 With a methanol selectivity of 97% and a service life of ≥120h, it meets the industrial requirements for the partial oxidation of low-concentration coalbed methane to methanol and has good and broad industrial prospects.

[0020] 2. Compared with other metal catalysts, this invention utilizes a metal-organic framework material with high porosity, high surface area, high conductivity, and good ion exchange capacity as a support, and uses 2-methylimidazole as a carbon source and nitrogen source to synthesize carbon material catalysts, thereby reducing production costs.

[0021] 3. According to the active species structure inside the methane monooxygenase, the copper active component is doped into the molecular sieve imidazole skeleton material carrier skeleton to simulate the active structure in the biological enzyme, and the noble metal is used as the active component, and the catalytic effect is tested, so as to achieve high-efficiency catalytic activity in the field of low-concentration coal bed gas partial oxidation for preparing methanol. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 The XRD pattern of the ZIF-8 molecular sieve imidazole skeleton material carrier prepared in Example 1 of the present application. DETAILED DESCRIPTION

[0023] The present application will be further described and illustrated in detail below in combination with specific examples.

[0024] Unless otherwise specified, the raw materials used in the examples of the present application are commercially available or can be obtained by those skilled in the art; unless otherwise specified, the methods used in the examples of the present application are methods mastered by those skilled in the art.

[0025] Example 1

[0026] Preparation of coal bed gas low-temperature oxidation methanol molecular sieve imidazole skeleton material catalyst

[0027] The copper (Cu) content of the coal bed gas low-temperature oxidation methanol molecular sieve imidazole skeleton material catalyst prepared in this example is 3wt%, the palladium (Pd) content is 5wt%, and the balance is the molecular sieve imidazole skeleton material carrier. The preparation method is as follows:

[0028] (1) 3g of Zn(NO3)2·6H2O was dissolved in 90ml of methanol, then 3g of 2-methylimidazole was dissolved in another 50ml of methanol solution and injected into the above solution, and stirred at a speed of 300 revolutions per minute at room temperature for 10h. After repeated washing with methanol and centrifugation, the obtained solid product was placed in a vacuum pressure of-0.2bar and vacuum dried at 60℃ for 6h, and the obtained product was fully ground in a mortar and sieved (60 mesh, same below) to obtain a ZIF-8 molecular sieve imidazole skeleton material, i.e. a carrier.

[0029] (2) Take 0.005 g of copper acetylacetonate, 0.005 g of palladium nitrate dihydrate, and 0.2 g of ZIF-8 molecular sieve imidazole framework material, and place them in 20 ml of methanol. Stir at room temperature for 6 h, and then vacuum dry at -0.2 bar vacuum pressure and 55°C for 15 h to obtain a catalyst precursor. The catalyst precursor is ground in a mortar and sieved (60 mesh, same below) and then placed in a tube furnace and calcined at 400°C for 2 h under a reducing atmosphere (H2 / N2mixed gas, H2 / N2=10% / 90%, flow rate 60-80 ml / min) to obtain the coalbed methane low-temperature oxidation to methanol molecular sieve imidazole framework material catalyst, No. 1#.

[0030] Under the reaction conditions of a methane-nitrogen mixed gas with a methane volume concentration of 28%, a reaction temperature of 280°C, a reaction pressure of one atmosphere, a water vapor feed space velocity of 6000 mL·h -1 ·g cat -1 , a feed gas space velocity of 4000 mL·h -1 ·g cat -1 , an air feed space velocity of 2500 mL·h -1 ·g cat -1 , and a catalyst dosage of 500 mg, the catalyst was evaluated for catalytic activity, and the methanol yield was 20 mmol·g cat -1 , the methanol selectivity was 97%, and the service life was more than 120 h.

[0031] Example 2

[0032] Preparation of a coalbed methane low-temperature oxidation to methanol molecular sieve imidazole framework material catalyst

[0033] The coalbed methane low-temperature oxidation to methanol molecular sieve imidazole framework material catalyst prepared in this example has a copper (Cu) content of 7 wt%, a platinum (Pt) content of 3 wt%, and the balance is a molecular sieve imidazole framework material carrier. The preparation method is as follows:

[0034] (1) Weigh 2.5 g of Zn(NO3)2·6H2O and dissolve it in 75 ml of methanol. Then, 2.5 g of 2-methylimidazole is dissolved in another 40 ml of methanol solution and injected into the above solution. Stir at room temperature at a speed of 300 revolutions per minute for 12 h. Repeat the washing with methanol and centrifugation, and place the obtained solid product in a vacuum dryer at -0.2 bar vacuum pressure and 50°C for 8 h. The obtained product is ground in a mortar and sieved to obtain a ZIF-8 molecular sieve imidazole framework material, i.e., a carrier.

[0035] (2) Take 0.005 g of copper acetylacetonate, 0.005 g of platinum acetylacetonate, and 0.25 g of ZIF-8 molecular sieve imidazole framework material, and place them in 15 ml of methanol. Stir at room temperature for 6 h, and then vacuum dry at -0.2 bar vacuum pressure and 60°C for 12 h to obtain a catalyst precursor. The catalyst precursor is ground in a mortar and sieved, and then placed in a tube furnace and calcined at 400°C for 2 h under a reducing atmosphere (H2 / N2mixed gas, H2 / N2=10% / 90%, flow rate 60-80 ml / min) to obtain the coal-bed gas low-temperature oxidation methanol molecular sieve imidazole framework material catalyst, No. 2.

[0036] In a methane-nitrogen mixed gas with a methane volume concentration of 20%, the reaction temperature was 240°C, the reaction pressure was one atmosphere, the water vapor feed space velocity was 3000 mL·h -1 ·g cat -1 The feed space velocity of the raw gas was 2000 mL·h -1 ·g cat -1 The feed space velocity of the air was 2000 mL·h -1 ·g cat -1 The catalyst dosage was 500 mg, and the methanol yield was 19 mmol·g cat -1 The methanol selectivity was 95%, and the service life was more than 120 h.

[0037] Example 3

[0038] Preparation of a coal-bed gas low-temperature oxidation methanol molecular sieve imidazole framework material catalyst

[0039] The coal-bed gas low-temperature oxidation methanol molecular sieve imidazole framework material catalyst prepared in this example has a copper (Cu) content of 5 wt%, a ruthenium (Ru) content of 6 wt%, and the balance is a molecular sieve imidazole framework material carrier. The preparation method is as follows:

[0040] (1) Weigh 2.7 g of Zn(NO3)2·6H2O and dissolve it in 85 ml of methanol. Then, 3 g of 2-methylimidazole is dissolved in another 45 ml of methanol solution and injected into the above solution. Stir at room temperature at a speed of 300 revolutions per minute for 8 h. Repeat the washing with methanol and centrifugation, and place the obtained solid product in a vacuum dryer at -0.2 bar vacuum pressure and 55°C for 10 h. The obtained product is ground in a mortar and sieved to obtain a ZIF-8 molecular sieve imidazole framework material, i.e., a carrier.

[0041] (2) Weigh 0.005g of copper acetylacetone, 0.005g of ruthenium acetylacetone, and 0.2g of ZIF-8 molecular sieve imidazole framework material and place them in 15ml of methanol. Stir at room temperature for 6h, and then vacuum dry at -0.2bar vacuum pressure and 60℃ for 12h to obtain the catalyst precursor. The catalyst precursor is thoroughly ground and sieved in a mortar and then placed in a tubular calcination furnace and calcined at 400℃ for 2h under a reducing atmosphere (H2 / N2 mixed gas, H2 / N2=10% / 90%, flow rate 60~80ml / min) to obtain the catalyst of the molecular sieve imidazole framework material for low-temperature oxidation of coalbed methane to methanol, numbered 3#.

[0042] The reaction was carried out in a methane-nitrogen mixture with a methane volume concentration of 24%, at a temperature of 260°C, a pressure of one atmosphere, and a steam feed space velocity of 5000 mL·h. -1 ·g cat -1 The feed gas space velocity is 3000 mL·h -1 ·g cat -1 The air feed space velocity is 3000 mL·h -1 ·g cat -1 The catalytic activity of the catalyst was evaluated under reaction conditions with a catalyst dosage of 400 mg, and the methanol yield was 18 mmol·g. cat -1 It has a methanol selectivity of 96% and a service life of over 120 hours.

[0043] Example 4

[0044] Structural determination of the carrier

[0045] The crystal structure of the support prepared in Example 1 was analyzed by X-ray diffraction, and the results are as follows: Figure 1 As shown:

[0046] X-ray diffraction data showed that the ZIF-8 support has a graphite-like structure. A graphite-like diffraction peak appeared at 2θ = 26.542°, corresponding to the (002) plane of C, which is a typical characteristic diffraction peak of the molecular sieve imidazole framework material ZIF-8. In addition, a slight characteristic diffraction peak appeared at 2θ = 44.517°, corresponding to the (101) plane of C, indicating that the support has been successfully synthesized.

[0047] Example 5

[0048] Test on the effect of precious metals on catalyst performance

[0049] A control catalyst having a copper (Cu) active component content of 5 wt% and the balance of a molecular sieve imidazole framework material support was prepared according to the same preparation method as in Example 3, except that the active component ruthenium was omitted.

[0050] The control catalyst was evaluated for catalytic activity according to the same evaluation method as in Example 3, and the results were a methanol yield of 10 μmol·g cat -1 -1·h-1, a methanol selectivity of 40%, and a service life of more than 110 h. It can be seen that in the case of the active component being only copper and not containing a noble metal, the catalytic performance of the catalyst is greatly reduced.

[0051] Example 6

[0052] Test of the effect of different reaction conditions on the catalytic reaction of coal bed gas

[0053] The catalyst prepared in the above examples was placed in a fixed bed reactor, and Huainan coal bed gas (composition: CH4 content 28%, CO2 content 1.5%, N2 content 68.9%, heavy hydrocarbon gas (C 2+ ) content 1.6%) was used as the reaction raw material, different reaction conditions were set for the coal bed gas low-temperature oxidation reaction to produce methanol, and the conversion effect of the coal bed gas was tested. The specific reaction conditions and results are shown in Table 1.

[0054] Table 1

[0055]

[0056] It can be seen from the results that the reaction process of the catalyst of the present application for catalyzing the coal bed gas to produce methanol cannot be absent of air and water vapor, and it is inferred that the catalytic mechanism of the catalyst of the present application is that the methane is activated by the oxygen molecules on the metal active sites, breaks a C-H bond to generate a methyl group, the water introduced breaks an O-H bond to generate a hydroxyl group in a high-temperature steam state, the methyl group combines with the hydroxyl group to generate methanol, and finally the methanol product is removed from the surface of the catalyst. The overall reaction process conforms to the free radical mechanism.

[0057] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. The use of a coal-bed gas low-temperature oxidation methanol synthesis catalyst of a molecular sieve imidazole framework material in catalyzing the low-temperature oxidation of coal-bed gas or a model thereof to produce methanol, characterized in that, The catalyst comprises a carrier and an active component supported on the carrier, the carrier is ZIF-8 molecular sieve imidazole framework material prepared by taking 2-methyl imidazole as carbon source and nitrogen source, and the active component is copper and noble metal, and the noble metal is selected from any one or a mixture of two or more of palladium, platinum and ruthenium; The preparation method of the ZIF-8 molecular sieve imidazole framework material comprises the following steps: Zn(NO3)2·6H2O and 2-methyl imidazole are respectively dissolved in a polar solvent, mixed and stirred at room temperature, then washed with methanol and centrifuged, the obtained solid product is vacuum dried at 50-60℃ for 6-10h, and then grinded and sieved to obtain the ZIF-8 molecular sieve imidazole framework material; The loading method of the active component comprises the following steps: taking a precursor salt of copper and a precursor salt of noble metal, and loading the copper and the noble metal on the ZIF-8 molecular sieve imidazole framework material by impregnation to obtain a catalyst precursor, and the catalyst precursor is subjected to calcination treatment, the calcination treatment is carried out under a reducing atmosphere, the calcination treatment temperature is 400-500℃, and the time is 2h, to obtain the coal bed gas low-temperature oxidation methanol molecular sieve imidazole framework material catalyst. The application uses coal bed gas or its model substance as reaction raw material, adds the catalyst to react, the raw material gas feed air speed is 1000-4000 mL•h -1 •g cat -1 , the air feed air speed is 1500-3000 mL•h -1 •g cat -1 -1 •g cat -1 , the catalyst dosage is 300 mg-500 mg, and the reaction temperature is 180-280 ℃.​ 2. The use of a coal bed gas low temperature oxidation to methanol molecular sieve imidazolate framework material catalyst according to claim 1 in the catalysis of coal bed gas or a model thereof low temperature oxidation to methanol, characterized in that, In the catalyst, the content of copper is 3-7wt%, the content of noble metal is 3-6wt%, and the rest is the carrier.

3. The use of a coal bed gas low temperature oxidation to methanol molecular sieve imidazolate framework material catalyst according to claim 1 in the catalysis of coal bed gas or a model thereof low temperature oxidation to methanol, characterized in that, The mass ratio of Zn(NO3)2·6H2O to 2-methyl imidazole is 9:10, the polar solvent is methanol, the volume ratio of methanol in which Zn(NO3)2·6H2O and 2-methyl imidazole are respectively dissolved is 17:10, the concentration of the solution formed by dissolving Zn(NO3)2·6H2O in methanol is 32g / L, and the vacuum pressure of vacuum drying is-0.2bar.

4. The use of a coal bed gas low temperature oxidation to methanol molecular sieve imidazolate framework material catalyst according to claim 1 in the catalysis of coal bed gas or a model thereof low temperature oxidation to methanol, characterized in that, The impregnation loading process is: the copper precursor salt, noble metal precursor salt, ZIF-8 molecular sieve imidazole skeleton material are added into methanol, stirred at room temperature for 6-8h, then dried at-0.2bar vacuum pressure, 55-60 o C conditions for 10-15h to obtain the catalyst precursor.

5. The use of a coal bed gas low temperature oxidation to methanol molecular sieve imidazolate framework material catalyst according to claim 1 in the catalysis of coal bed gas or a model thereof low temperature oxidation to methanol, characterized in that, The coal bed gas is low-concentration coal bed gas with a methane volume concentration of less than 28%.

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