Method for preparing methyl trifluoroacetate through photocatalytic oxidation of methane

Abstract

The invention belongs to the technical field of photocatalysis and the technical field of methane oxidation, and particularly relates to a method for preparing methyl trifluoroacetate through photocatalytic oxidation of methane. According to the method, in a mixed solvent composed of trifluoroacetic acid and hydrochloric acid, oxygen-containing gas is used as an oxidizing agent, a phthalocyanine derivative is used as a catalyst, and methane is catalytically oxidized into methyl trifluoroacetate in the presence of a photosensitizer and under the illumination condition. By selecting the proper photosensitizer and catalyst, the invention establishes an environment-friendly method for efficient catalytic oxidation of methane selective reaction, realizes efficient catalytic oxidation of methane to prepare methyl trifluoroacetate, and is a novel method for photocatalytic oxidation of methane with high selectivity, no toxicity, green, safety and economy.

Description

Technical Field

[0001] The invention belongs to the technical field of photocatalysis and methane oxidation, and in particular relates to a method for preparing methyl trifluoroacetate by photocatalytic oxidation of methane. Background Art

[0002] The greenhouse effect caused by methane in the atmosphere is 26 times that of carbon dioxide. The rational and effective use of methane has an important impact on global energy utilization, environmental protection and circular economy. However, methane molecules are very stable, and it takes up to 104kcal / mol (435.14kJ / mol) of energy to open the first carbon-hydrogen bond. Therefore, methane conversion is currently mostly carried out under high temperature and high pressure, and it is seriously polluting. Most of the methane produced is directly burned for industrial production, residents' lives and gas-fired power generation. Only about 10% of methane is used in chemical production. Methane, as a carbon source, can be used to synthesize a variety of high-value-added chemical products. At the same time, compared with other solid and liquid chemical raw materials, methane has the advantages of low water, ash and sulfide content. Therefore, using methane more for chemical production rather than exothermic combustion is a win-win strategy to maximize the value of methane and reduce carbon emissions in the atmosphere.

[0003] Relatively speaking, photocatalytic technology uses light energy to achieve catalytic conversion of methane at low temperatures, reducing the energy barrier for methane conversion. In 2005, Hu et al. (Y. Hu, S. Higashimoto, S. Takahashi, Y. Nagai, M. Anpo, Catal. Lett. 2005, 100, 35–37.) reported the preparation of V-MCM-41 catalyst, in which methane was selectively oxidized to methanol by nitric oxide under ultraviolet light at room temperature. However, the methane conversion rate is low, nitric oxide seriously pollutes the environment, and the catalyst preparation is cumbersome. In 2014, Hameed (M. A. Gondal, A. Hameed, Z. H. Amani, A. Arfaj, Chem. Phys. Lett. 2004, 392, 372–377.) et al. prepared Ag + Dip-dyed WO 3 Catalyze the selective photooxidation of methane to methanol. However, silver is expensive, and the catalyst has a short life and is easily deactivated, making it unsuitable for industrial production. In 2020, Li et al. (X. Li, J. Xie, H. Rao, C. Wang, J. Tang, Angew. Chem. Int. Ed. 2020, 59, 19702–19707; Angew. Chem. 2020, 132, 19870–19875.) used TiO 2Platinum nanoparticles and CuO enable photocatalytic oxidative coupling of methane in a flow system at room temperature and atmospheric pressure. However, its selectivity is only 60% and the catalyst preparation is expensive. At present, there has been some progress in the basic research of photocatalytic methane conversion, but there are still disadvantages such as extremely low conversion rate and selectivity, and some systems cannot avoid the use of precious metals. Based on this, the present invention proposes a method for selectively oxidizing methane to prepare methyl trifluoroacetate under light conditions at room temperature using air as an oxidant and cheap nitrates as photosensitizers, and phthalocyanine as a catalyst. It is a new method for photocatalytic oxidation of methane with high selectivity, non-toxicity, green, safety and economy. Summary of the invention

[0004] In order to solve the above technical problems, the present invention provides a method for preparing methyl trifluoroacetate by photocatalytic oxidation of methane, wherein the method is to catalytically oxidize methane to methyl trifluoroacetate in a mixed solvent consisting of trifluoroacetic acid and hydrochloric acid, with air as an oxidant, at room temperature, adding a suitable photosensitizer and a catalyst. By selecting a suitable photosensitizer and a catalyst, the present invention establishes an environmentally friendly method for the selective reaction of high-efficiency catalytic oxidation of methane, and realizes the preparation of methyl trifluoroacetate by high-efficiency catalytic oxidation of methane.

[0005] The above-mentioned object of the invention is achieved through the following scheme:

[0006] A method for preparing methyl trifluoroacetate by photocatalytic oxidation of methane, wherein methane is catalytically oxidized to methyl trifluoroacetate in a mixed solvent consisting of trifluoroacetic acid and hydrochloric acid, with an oxygen-containing gas as an oxidant and a phthalocyanine derivative as a catalyst, in the presence of a photosensitizer and under light conditions; the reaction chemical equation is:

[0007] CH 4 +O 2 →MTFA

[0008] The structural formula of phthalocyanine derivatives is shown below:

[0009]

[0010] In the formula, the metal element M of the phthalocyanine derivative is one of zinc, cobalt and manganese, and the substituents R are each independently selected from one of H, F, Cl, Br and nitro.

[0011] By adopting the above technical scheme, the present invention can make methane slightly soluble in a solvent, and hydrochloric acid reacts with photosensitizers such as sodium nitrite to produce nitrosyl chloride NOCl, and irradiating the gas phase part of methane with light to produce free radicals, which react with NOCl to generate methanol, and then methanol and trifluoroacetic acid generate methyl trifluoroacetate.

[0012] Preferably, the catalyst phthalocyanine derivative is selected from at least one of zinc phthalocyanine, cobalt phthalocyanine, perchloro zinc phthalocyanine, tetranitro zinc phthalocyanine, perfluoro zinc phthalocyanine, perchloro cobalt phthalocyanine, perfluoro cobalt phthalocyanine, tetrabromo cobalt phthalocyanine, tetranitro cobalt phthalocyanine, and perfluoro manganese phthalocyanine, and more preferably cobalt phthalocyanine. The structure of the phthalocyanine derivative is as follows:

[0013]

[0014]

[0015] Preferably, the catalyst is fed in such a manner that the molar ratio of catalyst to methane is (1-2):30; more preferably, it is 1.5:30.

[0016] Preferably, the photosensitizer is selected from at least one of benzophenone, anthraquinone compounds, nitrates, and nitrites; more preferably, it is selected from at least one of sodium nitrite, sodium nitrate, silver nitrate, and ferric nitrate, and more preferably, sodium nitrite. More preferably, the photosensitizer is added in an amount such that the molar ratio of the photosensitizer to methane is 1:10.

[0017] Preferably, the volume ratio of trifluoroacetic acid to hydrochloric acid is (5-1):1, more preferably 5:1. More preferably, the ratio of methane to mixed solvent is (3-30) ml of mixed solvent for 1 mmol of methane, more preferably 3 ml of mixed solvent for 1 mmol of methane.

[0018] Preferably, the oxygen-containing gas is air, and the volume ratio of methane to air is (2-1):(5-10), more preferably 1: 10. The oxygen-containing gas may also be oxygen, but oxygen is highly unsafe and needs to be used with caution.

[0019] Preferably, the illumination conditions are 356 nm and white light.

[0020] Preferably, the reaction time of the method is 12h-48h.

[0021] Preferably, the reaction of the method is carried out at room temperature, and the room temperature is preferably 15°C-40°C.

[0022] Compared with the prior art, the invention has the following beneficial effects: in the invention, in a mixed solvent consisting of trifluoroacetic acid and hydrochloric acid, air is used as an oxidant, and at room temperature, a suitable photosensitizer and a catalyst are added to catalytically oxidize methane to methyl trifluoroacetate. The invention establishes an environmentally friendly method for the selective reaction of high-efficiency catalytic oxidation of methane by selecting a suitable photosensitizer and a catalyst, realizes the preparation of methyl trifluoroacetate by high-efficiency catalytic oxidation of methane, and is a new method for photocatalytic oxidation of methane with high selectivity, non-toxicity, greenness, safety, and economy. DETAILED DESCRIPTION

[0023] In order to better clarify and understand the purpose, process scheme and advantages of the present invention, the technical scheme and implementation method of the present invention are further described clearly, completely and in detail through specific examples below. It should be noted that the embodiments described in the present invention are implemented on the premise of the technical scheme of the present invention, and detailed implementation methods and specific operation processes are given, but they are only part of the embodiments of the present invention, not all of the embodiments. The specific implementation methods described are limited to explaining and interpreting the present invention, and do not limit the present invention. Based on the embodiments in the present invention, all other implementation methods obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0024] The experimental methods and conditions used in the embodiments of the present invention are conventional methods and conventional conditions unless otherwise specified. The materials, reagents or instruments used in the embodiments, unless otherwise specified, can be obtained from commercial sources or prepared by conventional methods. The reaction conditions embodied in the content of the invention of the present invention can achieve the reaction and obtain the product of the expected effect. Due to space limitations, some embodiments are listed below to further illustrate the advantages of the technical solution of the present invention.

[0025] Example 1

[0026] CH 4 +O 2 →MTFA

[0027] Methane and air were premixed by volume (1:5). Sodium nitrite (2.2 mg, 30 μmol) and catalyst cat. (15 μmol) were added to a 40 ml Shrek tube and a tetrafluoroethylene stirrer was added. The side tube was sealed with a rubber septum, vacuumed, and backfilled with mixed gas three times (40 mL mixed gas, containing 0.3 mmol methane and 0.3 mmol oxygen). Hydrochloric acid (12 mol / L aqueous solution, 0.2 mL, 2 mmol) and trifluoroacetic acid (0.8 mL, 10.77 mmol) were then added in sequence. The reaction bottle was sealed with a Teflon-lined bottle cap and stirred at 25 ° C for 12 hours under 40W365 nm lamp irradiation. After the reaction was completed, post-treatment was performed, and 2 ml of deuterated chloroform was used for extraction. The lower organic phase was removed and dried with anhydrous sodium sulfate. After filtering, the filtrate was taken and the product methyl trifluoroacetate MTFA was detected by hydrogen nuclear magnetic resonance spectrum. The post-treatment operation steps of this embodiment are applicable to other embodiments. According to the data in the table, the best overall effect in terms of selectivity and yield is achieved when the catalyst is a phthalocyanine catalyst, and the best effect is achieved when the catalyst is cobalt phthalocyanine.

[0028] Table 1. Effects of different catalysts on the reaction

[0029]

[0030] Example 2

[0031] Methane and air (1:5) were premixed. Photosensitizer (30 μmol) and catalyst cobalt phthalocyanine (15 μmol, 8.6 mg) were added to a 40 ml Shrek tube and a tetrafluoroethylene stirrer was added. The side tube was sealed with a rubber septum, vacuumized, and backfilled with mixed gas three times (40 mL mixed gas, containing 0.3 mmol methane and 0.3 mmol oxygen). Hydrochloric acid (12 mol / L aqueous solution, 0.2 mL, 2 mmol) and trifluoroacetic acid (0.8 mL, 10.77 mmol) were then added in sequence. The reaction bottle was sealed with a Teflon-lined bottle cap and stirred at 25 ° C for 12 hours under 40W365 nm lamp irradiation. After the reaction was completed, the product MTFA was detected by hydrogen nuclear magnetic resonance spectrum. The post-processing operation steps of this embodiment are applicable to other embodiments. According to the data shown in the table, the best overall effect is that the photosensitizer is sodium nitrite.

[0032] Table 2. Effects of different photosensitizers on the reaction

[0033]

[0034]

[0035] Example 3

[0036] Methane and air (1:5) were premixed. Sodium nitrite (2.2 mg, 30 μmol), phthalate

[0037] Cobalt cyanine (8.6mg, 0.015mmol) was added to a 40ml Shrek tube and a tetrafluoro stirrer was added. The side tube was sealed with rubber, vacuumized, and backfilled with mixed gas three times (40mL mixed gas, containing 0.3mmol methane and 0.3mmol oxygen). Then hydrochloric acid and trifluoroacetic acid (hydrochloric acid concentration was 12mol / L, and the total volume of hydrochloric acid and trifluoroacetic acid was 1ml, and the specific volume ratio was shown in Table 3). The reaction bottle was sealed with a Teflon-lined bottle cap and stirred at 25°C for 12 hours under 40W 365nm lamp irradiation. After the reaction was completed, the product MTFA was obtained by hydrogen nuclear magnetic resonance spectrum. The post-processing operation steps of this embodiment are applicable to other embodiments. According to the data in the table, the conversion rate and yield of methane will increase when the volume of trifluoroacetic acid is large, but the selectivity will decrease when it rises to a point, so the optimal volume ratio is 4:1 for trifluoroacetic acid to hydrochloric acid.

[0038] Table 3. Effect of the volume ratio of trifluoroacetic acid to hydrochloric acid on the reaction

[0039]

[0040] Example 4

[0041] Methane and air are premixed. Sodium nitrite (2.2mg, 30μmol) and cobalt phthalocyanine (8.6mg, 0.015mmol) are added to a 40ml Shrek tube and a tetrafluoro stirrer is added. The side tube is sealed with a rubber septum, evacuated, and the mixed gas is backfilled three times (40mL mixed gas). Then hydrochloric acid (12mol / L aqueous solution, 0.2mL, 2mmol) and trifluoroacetic acid (0.8mL, 10.77mmol) are added in sequence. The reaction bottle is sealed with a Teflon-lined bottle cap and reacted at 25°C under irradiation with a 40W 365nm lamp. After the reaction is completed, the product MTFA is detected by hydrogen nuclear magnetic resonance spectrum. The post-processing operation steps of this embodiment are applicable to other embodiments. According to the data shown in the table, the volume ratio of methane and air with the best effect is 1:5 in terms of selectivity and yield.

[0042] Table 4. Effect of the volume ratio of methane and air on the reaction

[0043]

[0044] Example 5

[0045] Methane and air (1:5) were premixed. Sodium nitrite (2.2 mg, 30 μmol) and cobalt phthalocyanine (8.6 mg, 0.015 mmol) were added to a 40 ml Shrek tube and a tetrafluoroethylene stirring rod was added. The side tube was sealed with a rubber septum, evacuated, and backfilled with mixed gas three times (40 mL of mixed gas, containing 0.3 mmol of methane and 0.3 mmol of oxygen). Hydrochloric acid (12 M aqueous solution, 0.2 mL, 2 mmol) and trifluoroacetic acid (0.8 mL, 10.77 mmol) were then added in sequence. The reaction bottle was sealed with a Teflon-lined bottle cap and reacted at 25 ° C under irradiation with a 40W 365 nm lamp. After the reaction was completed, the product MTFA was detected by hydrogen nuclear magnetic resonance spectroscopy. The post-processing operation steps of this embodiment are applicable to other embodiments.

[0046] Table 5. Effects of different reaction times on the reaction

[0047]

[0048] The above-described embodiments are only preferred solutions of the present invention and are not intended to limit the present invention in any form. Other variations and modifications are possible without exceeding the technical solutions described in the claims.

Claims

1. A method for preparing methyl trifluoroacetate by photocatalytic oxidation of methane, characterized in that: The method is to catalytically oxidize methane into methyl trifluoroacetate in a mixed solvent consisting of trifluoroacetic acid and hydrochloric acid, using oxygen-containing gas as an oxidant and a phthalocyanine derivative as a catalyst in the presence of a photosensitizer and under light conditions; the reaction chemical equation is: CH4+·O2→MTFA The structural formula of phthalocyanine derivatives is shown below: In the formula, the metal element M of the phthalocyanine derivative is one of zinc, cobalt and manganese, and the substituents R are each independently selected from one of H, F, Cl, Br and nitro.

2. The method for preparing methyl trifluoroacetate by photocatalytic oxidation of methane according to claim 1, characterized in that: The catalyst phthalocyanine derivative is selected from at least one of zinc phthalocyanine, cobalt phthalocyanine, perchloro zinc phthalocyanine, tetranitro zinc phthalocyanine, perfluoro zinc phthalocyanine, perchloro cobalt phthalocyanine, perfluoro cobalt phthalocyanine, tetrabromo cobalt phthalocyanine, tetranitro cobalt phthalocyanine and perfluoro manganese phthalocyanine.

3. The method for preparing methyl trifluoroacetate by photocatalytic oxidation of methane according to claim 1, characterized in that: The catalyst is fed in an amount such that the molar ratio of the catalyst to methane is (1-2):

30.

4. The method for preparing methyl trifluoroacetate by photocatalytic oxidation of methane according to claim 1, characterized in that: The photosensitizer is selected from at least one of nitrate and nitrite, and the feeding amount of the photosensitizer is such that the molar ratio of the photosensitizer to methane is 1:

10.

5. The method for preparing methyl trifluoroacetate by photocatalytic oxidation of methane according to claim 4, characterized in that: The photosensitizer is selected from at least one of sodium nitrite, sodium nitrate, silver nitrate and ferric nitrate.

6. The method for preparing methyl trifluoroacetate by photocatalytic oxidation of methane according to claim 1, characterized in that: The volume ratio of trifluoroacetic acid to hydrochloric acid is (5-1):1, and the ratio of methane to mixed solvent is (3-30) ml of mixed solvent for 1 mmol of methane.

7. The method for preparing methyl trifluoroacetate by photocatalytic oxidation of methane according to claim 1, characterized in that: The oxygen-containing gas is air, and the volume ratio of methane to air is (2-1):(5-10).

8. The method for preparing methyl trifluoroacetate by photocatalytic oxidation of methane according to claim 1, characterized in that: The illumination conditions are 365nm and white light.

9. The method for preparing methyl trifluoroacetate by photocatalytic oxidation of methane according to claim 1, characterized in that: The reaction time of the method is 12h-48h.

10. The method for preparing methyl trifluoroacetate by photocatalytic oxidation of methane according to claim 1, characterized in that: The reaction of the method is carried out at room temperature.

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