A method for producing monofluoromethane

Abstract

The present application relates to a preparation method of monofluoromethane, the preparation method comprises the following steps: (1) mixing halogenated methane, iodide and organic solvent, and reacting to obtain an organic solution of methyl iodide; the halogenated methane comprises liquid monochloromethane and / or monobromomethane; (2) mixing fluoride, a promoter and the organic solution of methyl iodide obtained in step (1), and reacting to generate gaseous product monofluoromethane. The preparation method provided by the present application does not require the use of a catalyst, and the organic solvent can be reused, thereby reducing production costs; the preparation method provided by the present application is simple to operate, the product quality is stable, the purity is high, and is suitable for continuous production.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of chemical synthesis and relates to a preparation method of monofluoromethane. BACKGROUND

[0002] Monofluoromethane, code HFC-41 or R41, is a colorless flammable gas with low room temperature effect potential value and zero ozone depletion potential value. In the integrated circuit manufacturing process, monofluoromethane is widely used as an etching gas for semiconductor fine processing.

[0003] The existing technology discloses a synthesis method of monofluoromethane, including dimethyl sulfate fluorination, chloromethane fluorination, fluorochloroalkane dechlorination, methanol fluorination and dimethyl ether fluorination.

[0004] For example, CN105408293A discloses a method for manufacturing fluorinated methane. The disclosed manufacturing method manufactures fluorinated methane by reacting dimethyl sulfate with at least one selected from hydrogen fluoride and fluoroacid salt or a metal fluoride salt as a fluorine compound in a liquid phase. When the fluorine compound contains hydrogen fluoride or fluoroacid salt, the reaction is carried out without a solvent or using a polar solvent as a solvent, and when the fluorine compound is a metal fluoride salt, the reaction is carried out using water as a solvent.

[0005] CN110283041A discloses a method for synthesizing monofluoromethane. The method is carried out in a fixed bed reactor. A catalyst is loaded in the fixed bed reactor. Monofluoromethane and HF are introduced into the fixed bed reactor to react to generate monofluoromethane. The catalyst comprises a catalyst carrier and metal Cr. The catalyst carrier is a fluorinated aluminum carrier doped with carbon. The metal Cr is doped or loaded on the catalyst carrier.

[0006] CN109824473A discloses a method for preparing monofluoromethane by using a Pd-M alloy supported catalyst. Metal M nanoparticles are first loaded on a carrier. Then, a Pd precursor aqueous solution is mixed and stirred to prepare monodispersed Pd atoms on the M metal through a displacement reaction. The Pd atoms are combined with the M metal to form a Pd-M alloy through calcination to obtain a monodispersed Pd-M alloy supported catalyst. When the catalyst is used to catalyze the hydrogenation dechlorination of chloromonofluoromethane to prepare monofluoromethane, the catalyst has high selectivity.

[0007] CN110204414A discloses a method for preparing monofluoromethane. Under the action of a composite fluorination catalyst, methanol and hydrogen fluoride undergo a gas phase fluorination reaction to generate monofluoromethane. The composite catalyst is composed of MnO2 and CrCl3 loaded on a mixture of activated carbon and AlF3.

[0008] In addition, besides the above-mentioned dimethyl sulfate fluorination method, chloromethane fluorination method, fluorochloroalkane dechlorination method and methanol fluorination method, the dimethyl ether fluorination method is that dimethyl ether and hydrogen fluoride are subjected to gas phase fluorination reaction to generate gaseous monofluoromethane and water in the presence of an aluminum fluoride catalyst.

[0009] The prior art monofluoromethane preparation method needs to use a catalyst, which inevitably causes the problem of catalyst carbon deposition and deactivation; moreover, the preparation process involves a gas-gas reaction, the conversion rate is low, and the raw material and product are difficult to separate. SUMMARY

[0010] The present application aims to provide a monofluoromethane preparation method, which has the characteristics of simple production process, cheap and easily available raw materials, no catalyst, high reaction conversion rate, less by-products and small corrosion to equipment.

[0011] To achieve the purpose of the present application, the following technical solutions are adopted:

[0012] The present application provides a monofluoromethane preparation method, which comprises the following steps:

[0013] (1) mixing halomethane, iodide and organic solvent to obtain an organic solution of methyl iodide;

[0014] The halomethane comprises liquid monochloromethane and / or monobromomethane;

[0015] (2) mixing fluoride, promoter and the organic solution of methyl iodide obtained in step (1) to generate gaseous product monofluoromethane.

[0016] The preparation method provided by the present application adopts a two-step liquid method, and no catalyst is used in the preparation process. In the first step, the organic solution of methyl iodide is generated, and the halide is precipitated out of the organic solution because it is difficult to dissolve in the organic solvent, thereby realizing the separation of the halide and the organic solution of methyl iodide. Then, the organic solution of methyl iodide is reacted with fluoride and promoter, and the preparation of monofluoromethane is completed when no gas is generated. The residual organic solution containing iodide can be recycled, thereby reducing the production cost.

[0017] Preferably, the iodide in step (1) comprises any one or a combination of at least two of sodium iodide, potassium iodide or aluminum iodide.

[0018] Preferably, the molar ratio of the iodide to the halomethane in step (1) is ≥1.1.

[0019] Preferably, the organic solvent in step (1) comprises any one or a combination of at least two of acetone, diethyl ether or anhydrous ethanol.

[0020] Preferably, the molar volume ratio of the halogenated methane to the organic solvent in step (1) is (1.9-2.1):1, and the unit of the molar volume ratio is mol / L.

[0021] Preferably, the temperature of the reaction in step (1) is 10-30℃.

[0022] Preferably, the time of the reaction in step (1) is ≥2h.

[0023] Preferably, the fluoride in step (2) comprises any one or a combination of at least two of sodium fluoride, potassium fluoride or aluminum fluoride.

[0024] Preferably, the cation in the fluoride in step (2) is the same as the cation of the iodide in step (1).

[0025] Preferably, the molar ratio of the halogenated methane to the fluoride is 1:(0.8-1.2).

[0026] Preferably, the promoter comprises 18-crown-6.

[0027] Preferably, the molar ratio of the halogenated methane to the promoter is 1:(0.09-0.1).

[0028] Preferably, the temperature of the reaction in step (2) is 10-40℃.

[0029] Preferably, the preparation method further comprises water washing, alkali washing and condensation recovery after obtaining the gaseous product monofluoromethane.

[0030] Preferably, the temperature of the condensation recovery is -196℃ to -80℃, preferably -120℃ to -100℃.

[0031] Preferably, the preparation method comprises the following steps:

[0032] (1) mixing a halogenated methane, an iodide and an organic solvent, and reacting at 10-30℃ for ≥2h to obtain an organic solution of methyl iodide;

[0033] The halogenated methane comprises monochloromethane and / or monobromomethane;

[0034] The iodide comprises any one or a combination of at least two of sodium iodide, potassium iodide or aluminum iodide;

[0035] The molar ratio of the iodide to the halogenated methane is ≥1.1;

[0036] The organic solvent comprises any one or a combination of at least two of acetone, diethyl ether or anhydrous ethanol;

[0037] The molar volume ratio of the halogenated methane and the organic solvent is (1.9-2.1):1, and the unit of the molar volume ratio is mol / L;

[0038] (2) mixing fluoride, promoter 18-crown-6 and the organic solution of iodomethane obtained in step (1) to react to generate gaseous product monofluoromethane at 10-40℃, and then performing water washing, alkali washing and condensation recovery to obtain monofluoromethane with a purity of ≥99%;

[0039] The fluoride includes any one or a combination of at least two of sodium fluoride, potassium fluoride or aluminum fluoride;

[0040] The cation in the fluoride is the same as that of the iodide;

[0041] The molar ratio of the halogenated methane and the fluoride is 1:(0.8-1.2);

[0042] The molar ratio of the halogenated methane and the promoter is 1:(0.09-0.1).

[0043] Compared with the prior art, the present application has the following beneficial effects:

[0044] The preparation method provided by the present application adopts a two-step liquid method, and no catalyst is used in the preparation process. In the first step of the reaction, the organic solution of iodomethane is generated, and the halide is precipitated out because it is difficult to dissolve in the organic solvent, so that the separation of the halide and the organic solution of iodomethane is realized. Then, the organic solution of iodomethane is reacted with fluoride and a promoter, and the preparation of monofluoromethane is completed when no gas is generated. The residual organic solution containing iodide can be recycled, thereby reducing the production cost. DETAILED DESCRIPTION

[0045] The technical solutions of the present application will be further described through specific embodiments. Those skilled in the art should understand that the embodiments are only used to help understand the present application, and should not be regarded as specific limitations on the present application.

[0046] An embodiment of the present application provides a preparation method of monofluoromethane, which comprises the following steps:

[0047] (1) mixing halogenated methane, iodide and organic solvent to obtain an organic solution of iodomethane;

[0048] The halogenated methane includes liquid monochloromethane and / or monobromomethane;

[0049] (2) mixing fluoride, promoter and the organic solution of iodomethane obtained in step (1) to react to generate gaseous product monofluoromethane.

[0050] The preparation method provided by the present application is carried out by two-step liquid method, and no catalyst is needed in the preparation process. In the first step, iodomethane is generated in an organic solution, and halide is precipitated out because it is difficult to dissolve in the organic solvent, so the separation of halide and iodomethane organic solution is realized. Then, the iodomethane organic solution is reacted with fluoride and a promoter, and the reaction is completed when no gas is generated, so that monofluoromethane is prepared. The residual iodide-containing organic solution can be recycled, thereby reducing the production cost.

[0051] The reaction in the preparation method is carried out under stirring, and the specific parameters of stirring are not limited in the present application, as long as the reactants can be fully mixed.

[0052] In some embodiments, the iodide in step (1) includes any one or a combination of at least two of sodium iodide, potassium iodide or aluminum iodide, and typical but non-limiting combinations include a combination of sodium iodide and potassium iodide, a combination of potassium iodide and aluminum iodide, a combination of sodium iodide and aluminum iodide, or a combination of sodium iodide, potassium iodide and aluminum iodide.

[0053] In some embodiments, in order to fully react the halomethane, the molar ratio of the iodide to the halomethane in step (1) is ≥1.1, which can be 1.1, 1.12, 1.15, 1.18 or 1.2, but is not limited to the listed values, and other values not listed in the value range are also applicable.

[0054] The organic solvent used in the present application is an organic solvent in which iodine salt is easily soluble, and chloro salt and bromo salt are difficult to dissolve.

[0055] In some embodiments, the organic solvent in step (1) includes any one or a combination of at least two of acetone, diethyl ether or anhydrous ethanol, and typical but non-limiting combinations include a combination of acetone and diethyl ether, a combination of acetone and anhydrous ethanol, a combination of diethyl ether and anhydrous ethanol, or a combination of acetone, diethyl ether and anhydrous ethanol.

[0056] In some embodiments, the molar volume ratio in step (1) is (1.9-2.1):1, which can be 1.9:1, 2:1 or 2.1:1, but is not limited to the listed values, and other values not listed in the value range are also applicable, and the unit of the molar volume ratio is mol / L.

[0057] The reaction in step (1) of the present application can be carried out at room temperature.

[0058] In some embodiments, the temperature of the reaction in step (1) is 10-30℃, which can be 10℃, 15℃, 20℃, 25℃ or 30℃, but is not limited to the listed values, and other values not listed in the value range are also applicable.

[0059] In certain embodiments, the reaction of step (1) is carried out for a period of time of > 2 h, for example, it can be 2 h, 2.5 h, 3 h, 3.5 h, 4 h, or 5 h, but is not limited to the listed values, and other values not listed in the range are also applicable.

[0060] In certain embodiments, the fluoride of step (2) comprises any one or a combination of at least two of sodium fluoride, potassium fluoride, or aluminum fluoride, for example, it can be a combination of sodium fluoride and potassium fluoride, a combination of potassium fluoride and aluminum fluoride, a combination of sodium fluoride and aluminum fluoride, or a combination of sodium fluoride, potassium fluoride, and aluminum fluoride.

[0061] In certain embodiments, the cation in the fluoride of step (2) is the same as the cation of the iodide of step (1).

[0062] In certain embodiments, the molar ratio of the halomethane to the fluoride is 1: (0.8-1.2), for example, it can be 1:0.8, 1:0.9, 1:1, 1:1.1, or 1:1.2, but is not limited to the listed values, and other values not listed in the range are also applicable.

[0063] In certain embodiments, the promoter comprises 18-crown-6.

[0064] In certain embodiments, the molar ratio of the halomethane to the promoter is 1: (0.09-0.1), for example, it can be 1:0.09, 1:0.092, 1:0.095, 1:0.098, or 1:0.1, but is not limited to the listed values, and other values not listed in the range are also applicable.

[0065] The reaction in step (2) of the present application can be carried out at room temperature.

[0066] In certain embodiments, the reaction of step (2) is carried out at a temperature of 10-40℃, for example, it can be 10℃, 15℃, 20℃, 25℃, 30℃, 35℃, or 40℃, but is not limited to the listed values, and other values not listed in the range are also applicable.

[0067] The composition of the gaseous product monofluoromethane obtained in step (2) of the present application comprises monofluoromethane, nitrogen, methane, carbon monoxide, carbon dioxide, and a small amount of acidic gases such as hydrogen chloride and hydrogen fluoride, and in certain embodiments, in order to obtain monofluoromethane with a purity of ≥ 99%, the preparation method further comprises water washing, alkali washing, and condensation recovery after obtaining the gaseous product monofluoromethane.

[0068] The present application can remove carbon dioxide, hydrogen chloride and hydrogen fluoride in gaseous product monofluoromethane by alkali washing. For example, the alkali washing uses alkali solution with concentration of 0.1-20wt%, such as 0.1wt%, 0.5wt%, 1wt%, 5wt%, 10wt%, 15wt% or 20wt%, but not limited to the listed values, other values in the range are also applicable, preferably 1-10wt%.

[0069] For example, the alkali washing uses alkali solution including any one or combination of at least two of calcium hydroxide aqueous solution, sodium hydroxide aqueous solution, potassium hydroxide aqueous solution, sodium methoxide methanol solution or sodium ethoxide ethanol solution.

[0070] In some embodiments, the condensation recovery temperature is -196℃ to -80℃, such as -196℃, -180℃, -160℃, -150℃, -120℃, -100℃ or -80℃, but not limited to the listed values, other values in the range are also applicable.

[0071] In some embodiments, the preparation method comprises the following steps:

[0072] (1) mixing halomethane, iodide and organic solvent, reacting at 10-30℃ for ≥2h to obtain iodomethane organic solution;

[0073] The halomethane includes monochloromethane and / or monobromomethane;

[0074] The iodide includes any one or combination of at least two of sodium iodide, potassium iodide or aluminum iodide;

[0075] The molar ratio of iodide to halomethane is ≥1.1;

[0076] The organic solvent includes any one or combination of at least two of acetone, diethyl ether or anhydrous ethanol;

[0077] The molar volume ratio of halomethane to organic solvent is (1.9-2.1):1, and the unit of the molar volume ratio is mol / L;

[0078] (2) mixing fluoride, promoter 18-crown-6 and iodomethane organic solution obtained in step (1), reacting at 10-40℃ to generate gaseous product monofluoromethane, then performing water washing, alkali washing and condensation recovery to obtain monofluoromethane with purity ≥99%;

[0079] The fluoride includes any one or combination of at least two of sodium fluoride, potassium fluoride or aluminum fluoride;

[0080] The cation in the fluoride is the same as that in the iodide;

[0081] the molar ratio of the halomethane to the fluoride is 1: (0.8-1.2);

[0082] the molar ratio of the halomethane to the promoter is 1: (0.09-0.1).

[0083] Example 1

[0084] The present example provides a method for preparing monofluoromethane, which comprises the following steps:

[0085] (1) mixing halomethane, iodide and organic solvent, under stirring condition, reacting at 15℃ under normal pressure for 3h, the produced sodium chloride is difficult to dissolve in acetone and precipitates, obtaining an organic solution of iodomethane;

[0086] the halomethane is monochloromethane;

[0087] the iodide is sodium iodide;

[0088] the molar ratio of the iodide to the halomethane is 1.1;

[0089] the organic solvent is acetone;

[0090] the molar volume ratio of the halomethane to the organic solvent is 2:1, and the unit of the molar volume ratio is mol / L;

[0091] (2) mixing fluoride, promoter 18-crown-6 and the organic solution of iodomethane obtained in step (1), under stirring condition at 20℃ under normal pressure until no obvious bubbles are generated, generating gaseous product monofluoromethane, then performing water washing, 20wt% sodium hydroxide aqueous solution washing and condensation recovery at -100℃, obtaining monofluoromethane with purity ≥99%;

[0092] the residual organic solution containing iodide after the reaction can be recycled;

[0093] the fluoride is sodium fluoride;

[0094] the molar ratio of the halomethane to the fluoride is 1:1;

[0095] the molar ratio of the halomethane to the promoter is 1:0.095.

[0096] Example 2

[0097] The present example provides a method for preparing monofluoromethane, which comprises the following steps:

[0098] (1) mixing halomethane, iodide and organic solvent, under stirring condition, reacting at 10℃ under normal pressure for 4h, the produced sodium chloride is difficult to dissolve in acetone and precipitates, obtaining an organic solution of iodomethane;

[0099] the halomethane is chloromethane;

[0100] the iodide is sodium iodide;

[0101] the molar ratio of the iodide to the halomethane is 1.1;

[0102] the organic solvent is acetone;

[0103] the molar volume ratio of the halomethane to the organic solvent is 1.9:1, the unit of the molar volume ratio being mol / L;

[0104] (2) mixing the organic solution of the fluoride, the promoter 18-crown-6 and the iodomethane obtained in step (1), and reacting at 10°C under normal pressure and stirring until no obvious bubbles are generated, to produce gaseous product monofluoromethane, and then performing water washing, 20wt% sodium hydroxide aqueous solution washing and condensation recovery at -196°C to obtain monofluoromethane with purity ≥99%;

[0105] the organic solution containing the iodide remaining from the reaction can be recycled;

[0106] the fluoride is sodium fluoride;

[0107] the molar ratio of the halomethane to the fluoride is 1:0.8;

[0108] the molar ratio of the halomethane to the promoter is 1:0.09.

[0109] Example 3

[0110] The present example provides a method for preparing monofluoromethane, the method comprising the following steps:

[0111] (1) mixing the halomethane, the iodide and the organic solvent, and reacting at 30°C under normal pressure and stirring for 2h, so that the produced sodium chloride is precipitated out of the acetone and an organic solution of iodomethane is obtained;

[0112] the halomethane is chloromethane;

[0113] the iodide is sodium iodide;

[0114] the molar ratio of the iodide to the halomethane is 1.1;

[0115] the organic solvent is acetone;

[0116] the molar volume ratio of the halomethane to the organic solvent is 2.1:1, the unit of the molar volume ratio being mol / L;

[0117] (2) mixing fluoride, promoter 18-crown-6 and the organic solution of iodomethane obtained in step (1), and stirring at 40°C under normal pressure until no obvious bubbles are generated to form gaseous product monofluoromethane, then washing with water, 20wt% sodium hydroxide aqueous solution and recovering at -80°C to obtain monofluoromethane with purity ≥99%;

[0118] The iodide-containing organic solution left over from the reaction can be recycled;

[0119] The fluoride is sodium fluoride;

[0120] The molar ratio of halomethane to fluoride is 1:1.2;

[0121] The molar ratio of halomethane to promoter is 1:0.1.

[0122] Example 4

[0123] This example provides a method for preparing monofluoromethane, wherein the organic solvent acetone is replaced by an equal volume of diethyl ether, and the rest is the same as in Example 1.

[0124] Example 5

[0125] This example provides a method for preparing monofluoromethane, wherein the organic solvent acetone is replaced by an equal volume of anhydrous ethanol, and the rest is the same as in Example 1.

[0126] Example 6

[0127] This example provides a method for preparing monofluoromethane, wherein the iodide is replaced by potassium iodide at an equal molar amount, and the fluoride is replaced by potassium fluoride at an equal molar amount, and the rest is the same as in Example 1.

[0128] Example 7

[0129] This example provides a method for preparing monofluoromethane, wherein the iodide is replaced by aluminum iodide at an equal molar amount, and the fluoride is replaced by aluminum fluoride at an equal molar amount, and the rest is the same as in Example 1.

[0130] Example 8

[0131] This example provides a method for preparing monofluoromethane, wherein the monochloromethane is replaced by monobromomethane at an equal molar amount, and the rest is the same as in Example 1.

[0132] Example 9

[0133] This example provides a method for preparing monofluoromethane, wherein the molar ratio of halomethane to promoter is 1:0.08, and the rest is the same as in Example 1.

[0134] Example 10

[0135] The embodiment provides a preparation method of monofluoromethane, and the preparation method is the same as that of the embodiment 1 except that the molar ratio of halogenated methane to promoter is 1:0.12.

[0136] Performance characterization

[0137] The purity of monofluoromethane, the conversion rate of monochloromethane and the yield of monofluoromethane obtained in the embodiments 1-10 are determined, and the obtained results are shown in Table 1, wherein:

[0138] The calculation method of the purity of monofluoromethane is that the purity of monofluoromethane is measured by using gas chromatography;

[0139] The calculation method of the yield of monofluoromethane is that (measured content / theoretical total amount of synthesis) × 100 %;

[0140] The calculation method of the conversion rate of monochloromethane is that (actual consumption amount / total amount of monochloromethane used) × 100 %.

[0141] Table 1

[0142] Monofluoromethane purity (wt%) Monofluoromethane yield (%) Monochloromethane conversion (%) Example 1 99.3 71 98 Example 2 99.3 72 98 Example 3 99.3 67 97 Example 4 99.1 67 97 Example 5 99.2 63 96 Example 6 99.3 70 98 Example 7 99.3 70 98 Example 8 99.5 72 99 Example 9 99.3 68 95 Example 10 99.2 67 98

[0143] In conclusion, the preparation method provided by the embodiment is carried out by using two-step liquid method, and no catalyst is used in the preparation process. In the first step of the reaction, iodomethane is generated in an organic solution, and halide is precipitated out because it is difficult to dissolve in the organic solvent, so that the separation of halide and the iodomethane organic solution is realized. Then, the iodomethane organic solution is reacted with fluoride and promoter, and the preparation of monofluoromethane is completed when no gas is generated, and the residual organic solution containing iodide can be recycled, thereby reducing the production cost.

[0144] The above merely provides a specific implementation of the present application, but the protection scope of the present application is not limited to this. It should be understood by those skilled in the art that any change or replacement within the technical scope disclosed by the present application can be easily thought out by those skilled in the art, and all of these fall within the protection scope and disclosure scope of the present application.

Claims

1. A process for the production of monofluoromethane, characterized in that, The preparation method comprises the following steps: (1) mixing halomethane, iodide and organic solvent to obtain an organic solution of methyl iodide by reaction; The halomethane comprises liquid monochloromethane and / or monobromomethane; the iodide is aluminum iodide; the reaction temperature in step (1) is 10-30°C; (2) mixing fluoride, promoter and the organic solution of methyl iodide obtained in step (1) to generate gaseous product monofluoromethane by reaction; the molar ratio of the halomethane to the promoter is 1:(0.09-0.1); the fluoride is aluminum fluoride; the promoter is 18-crown-6; the reaction temperature in step (2) is 10-40°C.

2. The production method according to claim 1, characterized by, The molar ratio of the iodide to the halomethane in step (1) is greater than or equal to 1.

1.

3. The production method according to claim 1, characterized by, The organic solvent in step (1) comprises any one or a combination of at least two of acetone, diethyl ether or anhydrous ethanol.

4. The method of claim 1, wherein, The molar volume ratio of the halomethane to the organic solvent in step (1) is (1.9-2.1):1, and the unit of the molar volume ratio is mol / L.

5. The preparation method according to claim 1, characterized in that, The reaction time in step (1) is greater than or equal to 2h.

6. The method of claim 1, wherein, The molar ratio of the halomethane to the fluoride is 1:(0.8-1.2).

7. The preparation method according to claim 1, characterized in that, The preparation method further comprises water washing, alkali washing and condensation recovery after the gaseous product monofluoromethane is obtained.

8. The method of claim 7, wherein, The temperature of the condensation recovery is -196°C to -80°C.

9. The production method according to claim 8, characterized by, The temperature of the condensation recovery is -120°C to -100°C.

10. The method of claim 1, wherein, The preparation method comprises the following steps: (1) mixing halomethane, iodide and organic solvent to obtain an organic solution of methyl iodide by reaction for greater than or equal to 2h at 10-30°C; The halomethane comprises monochloromethane and / or monobromomethane; The iodide is aluminum iodide; The molar ratio of the iodide to the halomethane is greater than or equal to 1.1; The organic solvent comprises any one or a combination of at least two of acetone, diethyl ether or anhydrous ethanol; The molar volume ratio of the halomethane to the organic solvent is (1.9-2.1):1, and the unit of the molar volume ratio is mol / L; (2) mixing fluoride, promoter 18-crown-6 and the organic solution of methyl iodide obtained in step (1) to generate gaseous product monofluoromethane by reaction at 10-40°C, and then performing water washing, alkali washing and condensation recovery to obtain monofluoromethane with a purity of greater than or equal to 99%; The fluoride is aluminum fluoride; The molar ratio of the halomethane to the fluoride is 1:(0.8-1.2); The molar ratio of the halomethane to the promoter is 1:(0.09-0.1).