Method for preparing methanol and its derivatives by photocatalytic methane and catalyst used therefor

Abstract

The present invention belongs to the field of chemical engineering, and particularly relates to a method for activating methane to produce methanol using a ruthenium-containing catalyst. The present invention discloses a preparation method of a ruthenium-loaded catalyst, which includes the following steps: pretreating activated carbon to obtain pretreated activated carbon as a carrier; loading noble metal ruthenium onto the carrier to obtain a ruthenium-loaded catalyst. The present invention also provides a method for photocatalytically preparing methanol / methanol derivatives from methane: including the following steps: putting the ruthenium-loaded catalyst into an autoclave, then adding a reaction solvent and an oxidant, first displacing the air in the autoclave with methane, and then continuing to introduce methane until the pressure reaches 0.5-2 MPa, and then sealing the autoclave, providing a light source by a short-arc xenon lamp, and reacting at room temperature to obtain methanol / methanol derivatives. The method for preparing methanol by the present invention has the characteristics of relatively simple process, mild conditions, and high yield.

Description

Technical Field

[0001] The present invention belongs to the field of chemical engineering, and particularly relates to a method for activating methane to methanol by using a ruthenium-containing catalyst. Background Art

[0002] With the continuous development of social economy, people are increasingly concerned about the effective utilization of energy. Methane, as the main component of resources such as natural gas and shale gas, has a huge stock in nature. Converting it into methanol with higher added value has become a topic of concern. Currently, the commonly used industrial production route is the indirect method. First, methane is converted into syngas (CO and H2), and then the syngas is further converted into methanol. This steam reforming scheme for indirectly synthesizing methanol needs to be carried out under high temperature and high pressure conditions, and its production cost and maintenance cost are relatively high. Therefore, developing a catalyst that can directly convert methane into methanol under mild conditions has broad application prospects.

[0003] Supported catalysts have the characteristics of high active sites and good selectivity. Richard reported a La-doped WO3 material, and methane was converted into methanol under ultraviolet light irradiation, but the conversion rate of methane was very low, only 10% (Photocatalytic conversion of methane). Hameed et al. prepared an Ag-modified WO3 material for the production of methanol from methane. The research shows that the addition of the noble metal element Ag can enhance the photon absorption ability and accelerate the generation rate of hydroxyl radicals, and the generation rate of methanol has been significantly improved (Photocatalytic conversion of methane into methanol: Performance of silver impregnated WO3). Ruthenium, as a member of the noble metals, has the advantages of good reaction activity and relatively low price, and has good activation effects in various activation reactions. Patent CN115212875A discloses a photocatalytic dry reforming of methane method with ruthenium doped on a porous titanium-silicon material. Compared with other noble metal-doped catalysts, the doped ruthenium metal has more active sites, and methane can be successfully converted into H2 and CO under irradiation with a 300W xenon lamp for 2 hours. However, the preparation process of this method's catalyst is relatively complex, and its catalytic activity for oxidizing methane to methanol is not yet clear. Patent CN112876338B discloses a method for preparing a ruthenium catalyst supported on ZrO2 and catalyzing methane to prepare methanol and formic acid in a liquid phase. The ruthenium is loaded on a ZrO2 support treated with sulfuric acid, and the product can be obtained by reacting at a lower temperature (<100°C) for a long time, but its reaction pressure is relatively high, and the effect is good at 5 Mpa, and the maximum yield is relatively low (<25 μmol).

[0004] In summary, the direct conversion of methane to methanol under mild conditions requires overcoming the relatively high C-H bond energy of methane. Common reaction routes have problems such as high reaction temperature and pressure, low conversion rate, and low reaction rate. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a mild and efficient method for preparing methanol and its derivatives by photocatalytic methane and the catalyst used.

[0006] To solve the above technical problem, the present invention provides a method for preparing a ruthenium-loaded catalyst (preparing a ruthenium-loaded catalyst by photodeposition method), which includes the following steps:

[0007] 1) Prepare activated carbon as a carrier:

[0008] Pre-treat the activated carbon to obtain pre-treated activated carbon as the carrier;

[0009] 2) Load noble metal ruthenium onto the carrier:

[0010] First, mix water and an organic solvent to form a mixed solvent, and the volume ratio of water to the organic solvent is 1-8:1;

[0011] Mix titanium dioxide and the pre-treated activated carbon obtained in step 1) according to a weight ratio of 1:(1±0.1) to obtain a mixed-treated carrier;

[0012] Disperse the mixed-treated carrier in the mixed solvent, and then add ruthenium metal salt and mix evenly. The weight ratio of ruthenium in the ruthenium metal salt to the mixed-treated carrier is 0.1-5% (that is, the loading amount of the active center ruthenium element is 0.1-5% by mass);

[0013] Then, carry out a stirring reaction (at room temperature) under light source irradiation for 6±2 h, so as to load ruthenium on the surface of the mixed-treated carrier. Freeze and solidify the reaction product, and then carry out vacuum freeze-drying to obtain a ruthenium-loaded catalyst (that is, a ruthenium metal photocatalyst supported on activated carbon).

[0014] Note: During the light source irradiation process, ruthenium metal salt will form metallic ruthenium; during the above light source irradiation process, the mixed-treated carrier does not react, so its weight remains unchanged.

[0015] As an improvement to the method for preparing the ruthenium-loaded catalyst of the present invention:

[0016] The ruthenium metal salt is ruthenium trichloride, ruthenium iodide, ruthenium acetate (preferably RuCl3·3H2O).

[0017] As a further improvement to the method for preparing the ruthenium-loaded catalyst of the present invention:

[0018] The weight ratio of ruthenium in the ruthenium metal salt to the carrier after mixing treatment is 1-5% (optimally 1%).

[0019] As a further improvement to the preparation method of the ruthenium-loaded catalyst of the present invention:

[0020] The organic solvent is ethylene glycol, ethanol, propanol, acetone, dioxane.

[0021] Generally: for every 50 mg of TiO2, 20-40 mL of the mixed solvent is used.

[0022] As a further improvement to the preparation method of the ruthenium-loaded catalyst of the present invention, step 1) is:

[0023] Add 1 g of activated carbon powder (activated carbon with a carbon content ≥ 90%) to 50 ± 2 mL of concentrated sulfuric acid (sulfuric acid solution with a mass concentration of 95-98%), stir evenly in an ice bath (stirring time is 2 ± 0.5 h); add 5 ± 0.5 g of potassium permanganate, then react at 30 ± 5 °C for 1 ± 0.1 h, then add 50 ± 5 mL of deionized water and heat up to 80 ± 10 °C to react for 2 ± 0.2 h. After the reaction ends and cools down to room temperature, add 50 ± 5 mL of deionized water and 5 ± 0.5 mL of hydrogen peroxide solution with a mass concentration of 28-32%; then perform suction filtration, and wash the solid obtained by suction filtration with deionized water (wash repeatedly until the pH reaches neutral); add water to the washed solid for ultrasonic dispersion (ultrasonic dispersion time is about 2 ± 0.5 h), and finally perform vacuum freeze-drying (freeze-drying time is about 10 ± 1 h) to obtain the pretreated activated carbon.

[0024] The present invention also simultaneously provides a method for photocatalytically preparing methanol / methanol derivatives from methane: using the ruthenium-loaded catalyst prepared by any of the above methods, including the following steps:

[0025] Put the ruthenium-loaded catalyst (ω% = 0.1-5%) into an autoclave (a 100 mL autoclave with a window), then add the reaction solvent and the oxidant. First, displace the air in the autoclave with methane, and then continue to introduce methane until the pressure reaches 0.5-2 MPa, then seal the autoclave. Provide a light source with a short-arc xenon lamp and react at room temperature for 4-16 hours; thus obtain methanol / methanol derivatives;

[0026] The dosage ratio of ruthenium catalyst to oxidant = 1 mg: 1-1.5 g.

[0027] As an improvement to the method for photocatalytically preparing methanol / methanol derivatives from methane of the present invention: for every 1-1.5 g of oxidant, 10 ± 2 mL of the reaction solvent is used.

[0028] As a further improvement of the method for photocatalytically preparing methanol / methanol derivatives from methane according to the present invention, the oxidant is: H2O2, K2S2O8, NaClO.

[0029] As a further improvement of the method for photocatalytically preparing methanol / methanol derivatives from methane according to the present invention: the reaction solvent is: H2O, CF3COOH (trifluoroacetic acid), acetic acid.

[0030] In the catalytic activation method of methane of the present invention, a supported catalyst with transition metal ruthenium as the active center atom is developed to activate methane under mild conditions to prepare methanol / methanol derivatives. Under the reaction conditions of normal temperature and 0.5 - 2 MPa, methane is converted into methanol by light irradiation.

[0031] The reaction equation for photocatalytically preparing methanol from methane of the present invention is as follows:

[0032]

[0033] By comparing the characteristics of different reaction routes, the inventor established a technical development route for efficiently converting methane into methanol / methanol derivatives by directly using a ruthenium metal catalyst at normal temperature with methane and trifluoroacetic acid as raw materials and reaction solvents. One of the key technical difficulties lies in the development of an efficient single-atom catalyst.

[0034] The method for photocatalytically preparing methanol / methanol derivatives from methane of the present invention has the following technical advantages:

[0035] 1. The supported ruthenium catalyst prepared by the present invention has high activity, the preparation method is relatively simple, and the efficiency of activating methane to prepare methanol is high.

[0036] 2. During the formation of methanol, methane is used as the raw material, and the raw material source is wide. The reaction can be realized at room temperature under light irradiation, saving energy costs, and the production process is environmentally friendly.

[0037] 3. The method for preparing methanol by the present invention has the characteristics of relatively simple process, mild conditions, and high yield.

[0038] 4. Compared with CN112876338B, the present invention greatly reduces the catalyst dosage, reaction temperature and reaction pressure, but still has excellent reaction efficiency. Specific Embodiments

[0039] The present invention will be further described below in conjunction with specific embodiments, but the protection scope of the present invention is not limited thereto:

[0040] Activated carbon powder, activated carbon powder with a carbon content of ≥90% (screened through a 100-mesh sieve).

[0041] Catalyst Preparation Example 1: Preparation of Ruthenium-Loaded Activated Carbon Catalyst (1%) by Photodeposition Method

[0042] 1) Add 1 g of activated carbon powder to 48 mL of concentrated sulfuric acid (sulfuric acid solution with a mass concentration of 95%), stir in an ice bath (0 °C) for 2 h until evenly mixed; add 5 g of potassium permanganate, transfer it to a 30 °C water bath and mix for 1 h; add 50 mL of deionized water to the mixture and heat to 80 °C for 2 h. After the reaction is completed and cooled to room temperature, add 50 mL of deionized water and 5 mL of hydrogen peroxide solution (mass concentration of 30%); after filtration, the solid obtained by filtration is washed with deionized water (50 mL) multiple times until the pH is close to neutral; add 20 mL of water to the washed solid and perform ultrasonic dispersion (ultrasonic dispersion time is about 2 h), then place it in a vacuum freeze-drying oven and dry at -50 °C to -20 °C for 10 h (at this time, it has been dried to a constant weight) to obtain pretreated activated carbon.

[0043] 2) Mix water and ethylene glycol in a ratio of 8:1 (v / v) to obtain a mixed solvent;

[0044] Mix 50 mg of the pretreated activated carbon obtained in step 1) and 50 mg of TiO2 as the mixed treated support, disperse the mixed treated support in 30 ml of the mixed solvent, start stirring until the activated carbon and TiO2 are evenly dispersed to obtain a dispersion;

[0045] Add about 2.58 mg of RuCl3·3H2O (ruthenium content 1 mg) to the dispersion, then place it under light irradiation (using a 500 W spherical short-arc xenon lamp as the light source, the light source wavelength range is 300 - 1100 nm, and the light source is located 5 - 10 cm above the dispersion) and stir at room temperature for 6 h, then put it in the refrigerator (-20 °C) to freeze and solidify into a solid, and finally vacuum freeze-dry at -50 °C to -20 °C for 24 h (at this time, it has been dried to a constant weight) to obtain 101.0 mg of ruthenium-loaded activated carbon catalyst with a mass fraction of 1.0%.

[0046] Catalyst Preparation Example 2: Preparation of Ruthenium-Loaded Activated Carbon Catalyst (0.1%) by Photodeposition Method

[0047] 1) The same as step 1) in Catalyst Preparation Example 1;

[0048] 2) Change "about 2.58 mg of RuCl3·3H2O (ruthenium content 1 mg)" to "about 0.258 mg of RuCl3·3H2O (ruthenium content 0.1 mg)", and the rest is the same as step 2) in Catalyst Preparation Example 1; obtain 100.1 mg of ruthenium-loaded activated carbon catalyst with a mass fraction of 0.1%.

[0049] Catalyst Preparation Example 3: Preparation of Ruthenium-Loaded Activated Carbon Catalyst (3%) by Photodeposition Method

[0050] 1), the same as step 1) in Catalyst Preparation Example 1;

[0051] 2), change "about 2.58 mg RuCl3·3H2O (ruthenium content 1 mg)" to "about 14.29 mg ruthenium iodide (ruthenium content 3 mg)", and the rest is the same as step 2) in Catalyst Preparation Example 1; 103.0 mg of activated carbon supported ruthenium catalyst with a mass fraction of 3.0% is obtained.

[0052] Catalyst Preparation Example 4. Preparation of activated carbon supported ruthenium catalyst (5%) by photodeposition method

[0053] 1), the same as step 1) in Catalyst Preparation Example 1;

[0054] 2) Change "about 2.58 mg RuCl3·3H2O (ruthenium content 1 mg)" to "about 13.76 mg ruthenium acetate (ruthenium content 5 mg)", and the rest is the same as step 2) in Catalyst Preparation Example 1; 105.0 mg of activated carbon supported ruthenium catalyst with a mass fraction of 5.0% is obtained.

[0055] Example 1. A method for photocatalytically preparing methanol derivatives from methane, which sequentially performs the following steps:

[0056] 1), Add 1 mg of activated carbon supported ruthenium catalyst (1%) to a 100 mL autoclave with a window containing 10 mL of CF3COOH (trifluoroacetic acid), and add 1.35 g of K2S2O8. After sealing, replace the gas in the autoclave with methane; set the reaction temperature to room temperature (ambient temperature), and then continue to introduce methane until the pressure in the autoclave is 1 MPa (about 0.04 mol). Stir and react for 12 h under xenon lamp irradiation (using a 500 W xenon lamp for irradiation, the light source wavelength range is 300 - 1100 nm, and the xenon lamp is at a height of 5 - 10 cm above the autoclave window).

[0057] 2), After the reaction time set in step 1) arrives, cool the autoclave to -10 °C. After collecting the gas (methane) in the autoclave with an air bag, add 5 mL of toluene to the reaction kettle to extract the liquid phase reaction product. The product (toluene extract) is mainly methanol derivative (methyl trifluoroacetate) by GC detection, and a small amount of formaldehyde is generated. The results are shown in Table 1.

[0058] Example 2. A method for photocatalytically preparing methanol from methane, which sequentially performs the following steps:

[0059] 1), Add 1 mg of ruthenium catalyst supported on activated carbon (0.1%) to a 100 mL autoclave with a viewing window containing 10 mL of H2O, and add 1 mL of hydrogen peroxide (mass concentration 30%). After sealing, introduce methane to displace the gas in the autoclave. Set the reaction temperature at room temperature, and then continue to introduce methane until the pressure in the autoclave reaches 0.5 MPa (about 0.02 mol). Stir and react for 16 h under xenon lamp irradiation.

[0060] 2), Identical to step 2) of Example 1. The product was detected by GC and mainly consisted of methanol with a small amount of formaldehyde generated. The results are shown in Table 1.

[0061] Example 3. A method for photocatalytically preparing methanol derivatives from methane, which comprises the following steps in sequence:

[0062] 1), Add 1 mg of ruthenium catalyst supported on activated carbon (3%) to a 100 mL autoclave with a viewing window containing 10 mL of acetic acid CH3COOH, and add 1 mL of hydrogen peroxide (mass concentration 30%). After sealing, introduce methane to displace the gas in the autoclave. Set the reaction temperature at room temperature, and then continue to introduce methane until the pressure in the autoclave reaches 1 MPa. Stir and react for 12 h under xenon lamp irradiation.

[0063] 2), Identical to step 2) of Example 1. The product was detected by GC and mainly consisted of methanol derivatives (ethyl acetate) with a small amount of formaldehyde generated. The results are shown in Table 1.

[0064] Example 4. A method for photocatalytically preparing methanol derivatives from methane, which comprises the following steps in sequence:

[0065] 1), Add 1 mg of ruthenium catalyst supported on activated carbon (3%) to a 100 mL autoclave containing 10 mL of CF3COOH, and add about 1 mL of NaClO solution (containing 1.25 g of NaClO). After sealing, introduce methane to displace the gas in the autoclave. Set the reaction temperature at room temperature, and then continue to introduce methane until the pressure in the autoclave reaches 1 MPa. Stir and react for 8 h under xenon lamp irradiation.

[0066] 2), Identical to step 2) of Example 1. The product was detected by GC and mainly consisted of methanol derivatives (methyl trifluoroacetate) with a small amount of formaldehyde generated. The results are shown in Table 1.

[0067] Example 5. A method for photocatalytically preparing methanol derivatives from methane, which comprises the following steps in sequence:

[0068] 1), 1 mg of ruthenium-loaded catalyst (5%) was added to a 100 mL autoclave containing 10 mL of acetic acid, and 1 mL of hydrogen peroxide (mass concentration 30%) was added. After sealing, methane was introduced to displace the gas in the autoclave; the reaction temperature was set at room temperature, and then methane was continuously introduced until the pressure in the autoclave reached 2 MPa. The reaction was stirred under xenon lamp irradiation for 4 h.

[0069] 2), The same as step 2) of Example 1. The product was detected by GC, and the main product was methanol derivative (ethyl acetate), with a small amount of formaldehyde generated. The results are shown in Table 1.

[0070] Table 1

[0071]

[0072] The calculation formula for selectivity is

[0073]

[0074] Taking Example 1 as an example, the target product refers to methanol derivative (methyl trifluoroacetate), and the total generated products refer to methanol derivative and formaldehyde.

[0075] The calculation formula for yield is

[0076]

[0077] Comparative Example 1: The mixed solvent in step 2) of Catalyst Preparation Example 1 was changed as shown in Table 2, and the total volume of the mixed solvent remained unchanged. The rest was the same as Catalyst Preparation Example 1.

[0078] The obtained catalyst was used to replace the ruthenium catalyst in Example 1, and the other conditions were the same as those in Example 1. The selectivity results were not much different from those in Example 1, and the yield results are shown in Table 2.

[0079] Table 2

[0080] Mixed solvent (v / v) <![CDATA[Yield (μmol·h -1 ·g -1 Cat )]]> Example 1 Water: Ethylene glycol = 8:1 6.4 Comparative Example 1 Water: Ethylene glycol = 5:1 4.3 Water: Ethylene glycol = 1:1 3.6 Water: Ethanol = 8:1 4.9 Water: Propanol = 8:1 5.1 Water: Acetone = 8:1 3.3 Water: Dioxane = 8:1 4.2

[0081] Comparative Example 2: The activated carbon in step 1) of Catalyst Preparation Example 1 was changed to graphene / carbon powder, that is, graphene and carbon powder were pretreated separately to obtain pretreated graphene and pretreated carbon powder; "pretreated graphene / pretreated carbon powder" was used to replace "pretreated activated carbon", and the rest was the same as Catalyst Preparation Example 1.

[0082] The obtained catalyst was used to replace the ruthenium catalyst in Example 1, and the other conditions were the same as those in Example 1. The results are shown in Table 3.

[0083] Table 3

[0084] Carrier Selectivity (%) <![CDATA[Yield (μmol·h -1 ·g -1 Cat )]]> Example 1 Activated carbon 89％ 6.4 Comparative Example 2 Graphene 62％ 2.7 Carbon powder 56％ 1.3

[0085] Comparative Example 3: The TiO2 in step 2) of Catalyst Preparation Example 1 is replaced with SiO2, and the rest is the same as Catalyst Preparation Example 1.

[0086] The obtained catalyst was used to replace the ruthenium catalyst in Example 1, and the other conditions were the same as those in Example 1. No methanol derivatives were detected after the reaction.

[0087] Comparative Example 4: In step 2) of Catalyst Preparation Example 1, the "mixed treated carrier obtained by mixing pretreated activated carbon and TiO2" is replaced with "100 mg ZrO2 carrier", and the rest is the same as Catalyst Preparation Example 1.

[0088] The obtained catalyst was used to replace the ruthenium catalyst in Example 1, and the other conditions were the same as those in Example 1.

[0089] The results were as follows: the selectivity was about 68% and the yield was about 3.5 μmol·h -1 ·g -1 Cat .

[0090] Finally, it should be noted that the above examples are only some specific embodiments of the present invention. Obviously, the present invention is not limited to the above embodiments, and there are many variations. All variations that can be directly derived or associated with the content disclosed by a person skilled in the art should be considered as the protection scope of the present invention.

Claims

1. A method for preparing methanol / methanol derivatives by photocatalytic methane, characterized in that: Using a ruthenium-loaded catalyst, including the following steps: Put the ruthenium-loaded catalyst into an autoclave, then add a reaction solvent and an oxidant. First, displace the air in the autoclave with methane, and then continue to introduce methane until the pressure reaches 0.5 - 2 MPa, and then seal the autoclave. Provide light source by a short-arc xenon lamp, react at room temperature for 4 - 16 hours; thereby obtaining methanol / methanol derivatives; The dosage ratio of ruthenium-loaded catalyst to oxidant = 1 mg:1 - 1.5 g; The reaction solvent is: H2O, CF3COOH or acetic acid; The preparation method of the ruthenium-loaded catalyst includes the following steps: 1), Prepare activated carbon as a carrier: Pretreat the activated carbon: Add 1 g of activated carbon powder to 50 ± 2 mL of concentrated sulfuric acid, stir evenly in an ice bath; add 5 ± 0.5 g of potassium permanganate, then react at 30 ± 5 °C for 1 ± 0.1 h, then add 50 ± 5 mL of deionized water and heat up to 80 ± 10 °C to react for 2 ± 0.2 h. After the reaction ends and cools down to room temperature, add 50 ± 5 mL of deionized water and add 5 ± 0.5 mL of hydrogen peroxide solution with a mass concentration of 28 - 32%; then perform suction filtration, and wash the solid obtained by suction filtration with deionized water; add water to the washed solid for ultrasonic dispersion, and finally vacuum freeze-dry to obtain the pretreated activated carbon as a carrier; 2), Load the noble metal ruthenium onto the mixed-treated carrier: First, mix water and an organic solvent to form a mixed solvent, and the volume ratio of water to the organic solvent is 1 - 8:

1. The organic solvent is ethylene glycol, ethanol, propanol, acetone or dioxane; Mix titanium dioxide and the pretreated activated carbon obtained in step 1) according to a weight ratio of 1:(1 ± 0.1) to obtain a mixed-treated carrier; Disperse the mixed-treated carrier in the mixed solvent, and then add ruthenium metal salt and mix evenly. The weight ratio of ruthenium in the ruthenium metal salt to the mixed-treated carrier is 0.1 - 5%; Then carry out a stirring reaction under light source irradiation for 6 ± 2 h, thereby loading ruthenium on the surface of the mixed-treated carrier, freeze-curing the reaction product, and then vacuum freeze-dry to obtain the ruthenium-loaded catalyst.

2. The method for photocatalytic preparation of methanol / methanol derivatives from methane according to claim 1, characterized in that: The ruthenium metal salt is ruthenium trichloride, ruthenium iodide or ruthenium acetate.

3. The method for photocatalytic preparation of methanol / methanol derivatives from methane according to claim 2, characterized in that: The weight ratio of ruthenium in the ruthenium metal salt to the mixed-treated carrier is 1 - 5%.

4. The method for preparing methanol / methanol derivatives by photocatalytic methane according to claim 3, characterized in that: For every 1 - 1.5 g of oxidant, 10 ± 2 mL of reaction solvent is used.

5. The method for photocatalytic preparation of methanol / methanol derivatives from methane according to claim 4, characterized in that: The oxidant is: H2O2, K2S2O8 or NaClO.

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