Method for preparing methyl trifluoroacetate by photocatalytic oxidation of methane

Abstract

The present application belongs to the field of photocatalysis and methane oxidation, and particularly relates to a method for preparing methyl trifluoroacetate by photocatalytic oxidation of methane. The method is to catalytically oxidize methane to methyl trifluoroacetate in a mixed solvent composed of trifluoroacetic acid and hydrochloric acid, with an oxygen-containing gas as an oxidant, a phthalocyanine derivative as a catalyst, in the presence of a photosensitizer and under light conditions. The present application establishes an environmentally friendly and efficient method for catalytically oxidizing methane by selecting appropriate photosensitizers and catalysts, and realizes efficient catalytic oxidation of methane to prepare methyl trifluoroacetate. The present application is a new method for photocatalytic oxidation of methane with high selectivity, non-toxicity, greenness, safety and economy.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of photocatalysis and the field of methane oxidation, and particularly relates to a method for preparing methyl trifluoroacetate by photocatalytic oxidation of methane. BACKGROUND

[0002] The greenhouse effect caused by methane in the atmosphere is 26 times that of carbon dioxide. Reasonably and effectively utilizing methane has important influence on global energy utilization, environmental protection and circular economy. However, the methane molecule is very stable, and it requires as high as 104kcal / mol (435.14kJ / mol) of energy to open the first carbon-hydrogen bond. Therefore, at present, the methane conversion is mostly carried out in high-temperature and high-pressure environment, and is seriously polluting. Most of the generated methane is directly combusted for industrial production, residential life and gas power generation. Only about 10% of the methane is used for chemical production. Methane as a carbon source can be used to synthesize a variety of high-value 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, it is a win-win strategy to maximize the value of methane and reduce carbon emissions in the atmosphere by using methane more for chemical production rather than exothermic combustion.

[0003] Relatively speaking, the photocatalytic technology can realize the catalytic conversion of methane at low temperature by using light energy, thereby reducing the energy barrier of methane conversion. In 2005, Hu et al. (Y. Hu, S. Higashimoto, S. Takahashi, Y. Nagai, M. Anpo, Catal. Lett. 2005, 100, 35-37.) reported that the prepared V-MCM-41 catalyst selectively oxidized methane to methanol under the irradiation of ultraviolet light at room temperature. However, the methane conversion rate is low, nitrogen monoxide is seriously polluting to the environment, and the catalyst preparation is complicated. In 2014, Hameed et al. (M. A. Gondal, A. Hameed, Z. H. Yamani, A. Arfaj, Chem. Phys. Lett. 2004, 392, 372-377.) prepared Ag +WO3 catalyzes the selective photo-oxidation of methane to methanol. However, silver is expensive, and the catalyst is short-lived and easily deactivated, which is not suitable 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 TiO2 platinum nanoparticles and CuO to enable the photocatalytic oxidation 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 many shortcomings, such as low conversion rate and selectivity, and the use of noble metals in some systems cannot be avoided. Based on this, the present application proposes a method for selectively oxidizing methane to methyl trifluoroacetate under the condition of air as an oxidant, cheap nitrate as a photosensitizer, and phthalocyanine as a catalyst under light irradiation. It is a new method for photocatalytic oxidation of methane with high selectivity, non-toxicity, greenness, safety and economy. SUMMARY

[0004] The present application provides a method for photocatalytic oxidation of methane to methyl trifluoroacetate, which is carried out in a mixed solvent composed of trifluoroacetic acid and hydrochloric acid, using air as an oxidant, adding appropriate photosensitizer and catalyst, and catalytically oxidizing methane to methyl trifluoroacetate at room temperature. By selecting appropriate photosensitizer and catalyst, the present application establishes an environmentally friendly and efficient method for catalytic oxidation of methane selective reaction, and realizes the efficient catalytic oxidation of methane to prepare methyl trifluoroacetate.

[0005] The above object of the application is achieved by the following scheme:

[0006] A method for photocatalytic oxidation of methane to methyl trifluoroacetate, which is carried out in a mixed solvent composed of trifluoroacetic acid and hydrochloric acid, using air as an oxidant, adding appropriate photosensitizer and catalyst, and catalytically oxidizing methane to methyl trifluoroacetate at room temperature. By selecting appropriate photosensitizer and catalyst, the present application establishes an environmentally friendly and efficient method for catalytic oxidation of methane selective reaction, and realizes the efficient catalytic oxidation of methane to prepare methyl trifluoroacetate.

[0007] CH4+O2→MTFA

[0008] The structural formula of the phthalocyanine derivative is as follows:

[0009]

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

[0011] The application can make methane slightly soluble in the solvent, and the photosensitizer such as hydrochloric acid and sodium nitrite can react to produce nitrosyl chloride NOCl, the irradiation of light on the gaseous methane can produce free radicals to react with NOCl to produce methanol, and then the methanol and trifluoroacetic acid can produce methyl trifluoroacetate.

[0012] Preferably, the catalyst phthalocyanine derivative is at least one of zinc phthalocyanine, cobalt phthalocyanine, zinc per-chloro phthalocyanine, zinc tetranitro phthalocyanine, zinc per-fluoro phthalocyanine, cobalt per-chloro phthalocyanine, cobalt per-fluoro phthalocyanine, cobalt tetra-bromo phthalocyanine, cobalt tetranitro phthalocyanine, and manganese per-fluoro phthalocyanine, and more preferably, the catalyst is cobalt phthalocyanine.

[0013]

[0014]

[0015] Preferably, the feeding amount of the catalyst is a molar ratio of catalyst to methane of (1-2):30, and more preferably, the molar ratio is 1.5:30.

[0016] Preferably, the photosensitizer is at least one of benzophenone, anthraquinone, nitrate, and nitrite, and more preferably, the photosensitizer is at least one of sodium nitrite, sodium nitrate, silver nitrate, and iron nitrate, and more preferably, the photosensitizer is sodium nitrite. More preferably, the feeding amount of the photosensitizer is a molar ratio of photosensitizer to methane of 1:10.

[0017] Preferably, the volume ratio of trifluoroacetic acid to hydrochloric acid is (5-1):1, and more preferably, the volume ratio is 5:1. More preferably, the ratio of methane to the mixed solvent is (3-30) ml of mixed solvent per 1 mmol of methane, and more preferably, the ratio is 3 ml of mixed solvent per 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), and more preferably, the volume ratio is 1:10. The oxygen-containing gas can also be oxygen, but the use of oxygen is not safe and needs to be cautious.

[0019] Preferably, the light irradiation condition is 356 nm and white light.

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

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

[0022] Compared with the prior art, the beneficial effects of the present application are that the present application catalytically oxidizes methane to methyl trifluoroacetate in a mixed solvent composed of trifluoroacetic acid and hydrochloric acid, with air as the oxidant, at room temperature, by adding appropriate photosensitizer and catalyst. The present application establishes an environmentally friendly and efficient method for catalytically oxidizing methane selectively by selecting appropriate photosensitizer and catalyst, and realizes the preparation of methyl trifluoroacetate by high-efficiency catalytic oxidation of methane, which is a new method for photo-catalytic 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 application, the technical scheme and implementation manner of the present application are further described, clarified, completed and detailed in the following specific examples. It should be known that the described examples of the present application are implemented on the premise of the technical scheme of the present application, and give detailed implementation manners and specific operation processes, but only a part of the examples of the present application, not all the examples. The described specific implementation manners are limited to the description and explanation of the present application, and do not limit the present application. Based on the examples in the present application, all other implementation manners obtained by those skilled in the art without creative labor belong to the protection scope of the present application.

[0024] The experimental methods and conditions used in the examples of the present application are conventional methods and conventional conditions, and the materials, reagents or instruments used in the examples are commercially available or prepared by conventional methods, unless otherwise specified. The reaction conditions embodied in the inventive content of the present application can realize the described reactions and obtain the expected effect products. Due to the limitation of the length, the following part of the examples are listed to further illustrate the advantages of the technical scheme of the present application.

[0025] Example 1

[0026] CH4+O2→MTFA

[0027] Methane and air were premixed in a volume ratio of 1 :5. Sodium nitrite (2.2 mg, 30 μmol), catalyst cat. (15 μmol) were added to a 40 ml Schlenk tube, a Teflon stir bar was added. The side arm was sealed with a rubber septum, evacuated, and backfilled with the gas mixture three times (40 mL of the gas mixture containing 0.3 mmol methane and 0.3 mmol oxygen). Then hydrochloric acid (12 mol / L aqueous solution, 0.2 mL, 2 mmol), trifluoroacetic acid (0.8 mL, 10.77 mmol) were added in sequence. The reaction vessel was sealed with a Teflon-lined cap, and stirred at 25 °C under irradiation of a 40 W 365 nm lamp for 12 h. After the reaction was completed, the work-up was performed, and the product methyl trifluoroacetate MTFA was detected by proton nuclear magnetic resonance spectroscopy. The work-up procedure of this example is applicable to the other examples. According to the selectivity and yield shown in the table, the best effect is obtained when the catalyst is a phthalocyanine, and the best effect is obtained when the catalyst is cobalt phthalocyanine.

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

[0029]

[0030] Example 2

[0031] Methane and air were premixed in a volume ratio of 1 :5. Sodium nitrite (2.2 mg, 30 μmol), catalyst cat. (15 μmol) were added to a 40 ml Schlenk tube, a Teflon stir bar was added. The side arm was sealed with a rubber septum, evacuated, and backfilled with the gas mixture three times (40 mL of the gas mixture containing 0.3 mmol methane and 0.3 mmol oxygen). Then hydrochloric acid (12 mol / L aqueous solution, 0.2 mL, 2 mmol), trifluoroacetic acid (0.8 mL, 10.77 mmol) were added in sequence. The reaction vessel was sealed with a Teflon-lined cap, and stirred at 25 °C under irradiation of a 40 W 365 nm lamp for 12 h. After the reaction was completed, the work-up was performed, and the product methyl trifluoroacetate MTFA was detected by proton nuclear magnetic resonance spectroscopy. The work-up procedure of this example is applicable to the other examples. According to the selectivity and yield shown in the table, the best effect is obtained when the catalyst is a phthalocyanine, and the best effect is obtained when the catalyst is cobalt phthalocyanine.

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

[0033]

[0034]

[0035] Example 3

[0036] Methane and air were premixed in a volume ratio of 1 :5. Sodium nitrite (2.2 mg, 30 μmol), phthalocyanine cobalt (15 μmol, 8.6 mg) were added to a 40 ml Schlenk tube, a Teflon stir bar was added. The side arm was sealed with a rubber septum, evacuated, and backfilled with the gas mixture three times (40 mL of the gas mixture containing 0.3 mmol methane and 0.3 mmol oxygen). Then hydrochloric acid (12 mol / L aqueous solution, 0.2 mL, 2 mmol), trifluoroacetic acid (0.8 mL, 10.77 mmol) were added in sequence. The reaction vessel was sealed with a Teflon-lined cap, and stirred at 25 °C under irradiation of a 40 W 365 nm lamp for 12 h. After the reaction was completed, the product MTFA was detected by proton nuclear magnetic resonance spectroscopy. The work-up procedure of this example is applicable to the other examples. According to the selectivity and yield shown in the table, the best effect is obtained when the photosensitizer is sodium nitrite.

[0037] Cobalt phthalocyanine (8.6 mg, 0.015 mmol) was added to a 40 ml Schlenk tube, and a Teflon stir bar was added. The side arm was sealed with a rubber septum, and the tube was 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 and trifluoroacetic acid were then added in sequence (hydrochloric acid concentration of 12 mol / L, total volume of hydrochloric acid and trifluoroacetic acid of 1 mL, specific volume ratio see Table 3). The reaction bottle was sealed with a Teflon-lined bottle cap, and was stirred at 25°C under irradiation of a 40W 365 nm lamp for 12 hours. After the reaction was completed, the product MTFA was detected by nuclear magnetic resonance hydrogen spectrum. The post-processing operation steps of this example are applicable to other examples. According to the data in the table, when the volume of trifluoroacetic acid is large, the conversion rate and yield of methane increase, but when it rises to a certain point, the selectivity decreases, so the optimal volume ratio is 4:1 for trifluoroacetic acid to hydrochloric acid.

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

[0039]

[0040] Example 4

[0041] Methane and air were pre-mixed. Sodium nitrite (2.2 mg, 30 μmol), cobalt phthalocyanine (8.6 mg, 0.015 mmol) were added to a 40 ml Schlenk tube, and a Teflon stir bar was added. The side arm was sealed with a rubber septum, and the tube was evacuated and backfilled with mixed gas three times (40 mL of mixed gas). 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 was reacted at 25°C under irradiation of a 40W 365 nm lamp. After the reaction was completed, the product MTFA was detected by nuclear magnetic resonance hydrogen spectrum. The post-processing operation steps of this example are applicable to other examples. According to the data in the table, the best volume ratio of methane to air in terms of selectivity and yield is 1:5.

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

[0043]

[0044] Example 5

[0045] Methane and air (1 :5) were premixed. Sodium nitrite (2.2 mg, 30 μmol), cobalt phthalocyanine (8.6 mg, 0.015 mmol) were added to a 40 ml Schlenk tube, and a Teflon stir bar was added. The side arm was sealed with a rubber septum, evacuated, and backfilled with the gas mixture three times (40 mL of the gas mixture 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 sequentially. The reaction vessel was sealed with a Teflon-lined cap and irradiated at 25 °C under a 40 W 365 nm lamp. After the reaction was complete, the product MTFA was detected by proton nuclear magnetic resonance spectroscopy. The work-up procedure of this example is applicable to the other examples.

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

[0047]

[0048] The above examples are only the preferred schemes of the present application, and do not limit the present application in any form. Other variants and modifications can be made without departing from the technical solutions recited in the claims.

Claims

1. A method for preparing methyl trifluoroacetate by photocatalytic oxidation of methane, characterized in that, The method involves the catalytic oxidation of methane to methyl trifluoroacetate in a mixed solvent of trifluoroacetic acid and hydrochloric acid, using an oxygen-containing gas as the oxidant and a phthalocyanine derivative as the catalyst, in the presence of a photosensitizer and under light irradiation. The chemical equation for the reaction is as follows: ， The catalyst phthalocyanine derivative is selected from at least one of zinc phthalocyanine, cobalt phthalocyanine, perchloro zinc phthalocyanine, tetranitro zinc phthalocyanine, perfluorinated zinc phthalocyanine, perchloro cobalt phthalocyanine, perfluorinated cobalt phthalocyanine, tetrabromo cobalt phthalocyanine, tetranitro cobalt phthalocyanine, and perfluorinated manganese phthalocyanine. The catalyst feed amount is such that the molar ratio of catalyst to methane is (1-2):30; The photosensitizer is selected from at least one of sodium nitrite, sodium nitrate, silver nitrate, and ferric nitrate, and the amount of photosensitizer added is such that the molar ratio of photosensitizer to methane is 1:

10. The volume ratio of trifluoroacetic acid to hydrochloric acid is (5-3):1; The illumination conditions described are 365nm lamp illumination.

2. The method for preparing methyl trifluoroacetate by photocatalytic oxidation of methane according to claim 1, characterized in that, The ratio of methane to mixed solvent is 1 mmol of methane requires (3-30) ml of mixed solvent.

3. 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).

4. 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.

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

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