CN115745732A - Method for preparing fluoromethane - Google Patents

Abstract

The invention discloses a method for preparing fluoromethane, which comprises the steps of taking methyl chloroformate and fluoride salt as raw materials, carrying out heating reflux reaction in a sulfone or ether solvent, absorbing the generated gas-phase product by an alkali solution, condensing at low temperature and collecting to obtain a fluoromethane product, and carrying out deep purification to obtain an electronic-grade fluoromethane product. The method adopts a one-step liquid phase method for synthesis, and has the characteristics of simple production process, cheap and easily-obtained raw materials, high reaction conversion rate, less gaseous by-products and small corrosion to equipment.

Description

Method for preparing fluoromethane

Technical Field

The invention relates to the field of fluorine-containing fine chemicals, and particularly relates to a method for preparing fluoromethane.

Background

Electronic gases are essential basic support source materials in the development of integrated circuits, optoelectronics, microelectronics, particularly very large scale integrated circuits, liquid crystal display devices, semiconductor light emitting devices, and semiconductor material fabrication processes, and are known as "blood" and "grain" in the electronics industry. The fluoromethane is a green and efficient electronic special gas, is used for etching semiconductors and electronic products, has good etching selectivity on silicide films, and can dissolve fluorine ions under a radio frequency field to carry out reactive ion etching. The fluoromethane has the lowest C/F ratio (1: 1) in the mainstream etching gas, has extremely high selectivity, and has larger requirements in the manufacturing process of Fin-FET,3D-NAND and DRAM semiconductor devices.

The preparation method of the fluoromethane mainly comprises the following steps:

1. gas-phase hydrodechlorination: using monofluoro-dichloromethane HCFC-21 or monofluoro-chloromethane HCFC-31 as raw material, and making them produce hydrodechlorination reaction with hydrogen under the action of catalyst (see document CN 104016829A).

The catalyst adopted by the process is expensive (supported Ni, pd, pt and Rh-based catalyst), low in selectivity and short in service life, and the product contains a large amount of corrosive gas and various halogen substituted products and is difficult to separate and purify. When HCFC-21 is used as starting material, the catalyst is 2% Pd/C, H at 250% ₂ HCFC-21=6/1 (mol/mol), HCFC-21 conversion was 62.5%, selectivity was 65.4%. With the ban of ozone depletion substances and greenhouse gases in the international society, HCFC-21 or HCFC-31, which is a raw material, is difficult to obtain.

2. Gas phase fluorination: methane chloride is used as a raw material and is subjected to halogen exchange reaction with hydrogen fluoride under the action of a metal fluoride salt catalyst (see documents CN100562510C, WO2006030677 and CN 106542959A).

The process has a conversion rate of less than 20%, and the gas product contains a large amount of corrosive gas and multiple by-product gases (such as HCl and HFCH) such as halogen substituted products ₃ Cl、CH ₂ FCl、CH ₄ 、C ₂ H ₄ Etc.) cause difficulty in separation and purification, severe corrosion of equipment, etc.

3. A methanol fluorination method: methanol is a raw material with low cost and wide sources, and the methanol is used as the raw material to react with hydrogen fluoride under the action of a metal fluoride salt catalyst to prepare the fluoromethane (see documents JP60115538 and JP 60115536).

The process adopts AlF ₃ Or CrF ₃ The catalyst can generate water with the same molar weight as the fluoromethane in the reaction process, the service life of the catalyst is greatly influenced, and equipment is seriously corroded.

Disclosure of Invention

In order to overcome the defects in the prior art, the invention aims to provide a method for preparing fluoromethane, which adopts a one-step liquid phase method for synthesis and has the characteristics of simple production process, cheap and easily-obtained raw materials, high reaction conversion rate, less gaseous byproducts and small corrosion to equipment.

The reactions that occur are as follows:

in order to realize the purpose of the invention, the technical scheme of the invention is as follows: methyl chloroformate and fluoride salt are used as raw materials, heating reflux reaction is carried out in sulfone or ether solvents, generated gas-phase products are absorbed by alkali solution, then low-temperature condensation is carried out, and fluoromethane products are collected and obtained, and electronic-grade fluoromethane products are obtained after deep purification.

Further, a method for preparing fluoromethane, comprising the steps of:

(1) Methyl chloroformate and fluoride salt are dissolved in sulfone or ether solvent and heated to reflux reaction to produce gas phase product containing fluoromethane and carbon dioxide. The reaction temperature is generally 80 to 200 ℃, preferably 120 to 200 ℃ according to the boiling point of the solvent; the reaction was terminated when no significant bubbles were generated.

(2) Introducing the gas-phase product into an absorption tower filled with an alkali solution for washing;

(3) And (4) freezing and collecting the washed gas-phase product at low temperature to obtain a crude fluoromethane product.

Selecting a variety with a higher boiling point from the sulfone or ether solvents in the step (1), wherein the variety is selected from but not limited to at least one of dimethyl sulfoxide, sulfolane, styrene sulfone and the like, or at least one of diethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether or methyl ether-terminated polyethylene glycol ether and the like, and sulfolane or tetraethylene glycol dimethyl ether is preferred; the fluoride salt is selected from at least one of lithium fluoride, sodium fluoride, potassium fluoride, cesium fluoride, tetramethylammonium fluoride or tetrabutylammonium fluoride, and the like, preferably sodium fluoride and potassium fluoride; the feeding mol ratio of the methyl chloroformate/fluoride salt/sulfone or ether solvent is generally 1: 1.05-5: 1-5, preferably 1: 1.05-2: 1-2.

The gas phase product in the step (2) mainly comprises fluoromethane, nitrogen, methane, carbon monoxide, carbon dioxide, a small amount of hydrogen chloride and hydrogen fluoride acid gas; the alkali solution refers to an aqueous solution of calcium hydroxide, sodium hydroxide, potassium hydroxide, sodium methoxide or sodium ethoxide, and the concentration of the alkali solution is generally 0.1-20 wt%, preferably 1-10 wt%. The alkali washing is to remove carbon dioxide and a small amount of acid gases such as hydrogen chloride, hydrogen fluoride and the like.

The low-temperature freezing collection temperature in the step (3) is-80 to-196 ℃, preferably-100 to-120 ℃, and the low-temperature refrigerant is liquid nitrogen.

Compared with the prior art, the method has the beneficial effects that: 1. the selected raw materials are all commercially available, and the methyl chloroformate, the fluoride salt and the reaction solvent are cheap and easy to obtain; 2. one-step liquid phase synthesis is adopted, and the process is simple; 3. less by-products, no moisture and less corrosion to equipment.

Detailed Description

The present invention will be described in further detail with reference to examples, but the present invention is not limited to the following examples.

Example 1

94.5g of methyl chloroformate, 84g of sodium fluoride and 120g of sulfolane are added into a 1L reaction kettle with a condensing reflux device, the mixture is heated to 160 ℃ for reflux reaction until no obvious bubbles are generated, a gas-phase product is washed by 20wt% of sodium hydroxide aqueous solution and is frozen and collected at-100 ℃ to obtain a fluoromethane product, the conversion rate of the methyl chloroformate is 95%, and the yield of the fluoromethane product is 68%.

Example 2

94.5g of methyl chloroformate, 104.4g of potassium fluoride and 444g of tetraethyleneglycol dimethyl ether are added into a 1L reaction kettle with a condensation reflux device, the reaction kettle is heated to 200 ℃ for reflux reaction until no obvious bubbles are generated, a gas-phase product is washed by 0.1wt% of calcium hydroxide aqueous solution, and then the gas-phase product is frozen and collected at-120 ℃ to obtain a fluoromethane product, wherein the conversion rate of the methyl chloroformate is 99%, and the yield of the fluoromethane is 65%.

Example 3

Adding 94.5g of methyl chloroformate, 151.9g of cesium fluoride and 327g of phenethyl sulfone into a 1L reaction kettle with a condensation reflux device, heating to 120 ℃, carrying out reflux reaction until no obvious bubbles are generated, washing a gas-phase product by using an ethanol solution of 15wt% sodium ethoxide, and freezing and collecting at-160 ℃ to obtain a fluoromethane product, wherein the conversion rate of the methyl chloroformate is 90%, and the yield of the fluoromethane is 60%.

Example 4

94.5g of methyl chloroformate, 274.6g of tetrabutylammonium fluoride and 480g of diethylene glycol dimethyl ether are added into a 1L reaction kettle with a condensation reflux device, the mixture is heated to 80 ℃ for reflux reaction until no obvious bubbles are generated, a gas-phase product is washed by 10wt% of potassium hydroxide aqueous solution, and then the gas-phase product is frozen and collected at-80 ℃ to obtain a fluoromethane product, wherein the conversion rate of the methyl chloroformate is 87%, and the yield of the fluoromethane is 34%.

Example 5

Adding 23.6g of methyl chloroformate, 32.5g of lithium fluoride and 500g of methyl ether-terminated polyethylene glycol ether into a 1L reaction kettle with a condensation reflux device, heating to 180 ℃, carrying out reflux reaction until no obvious bubbles are generated, washing a gas-phase product by using 10wt% of sodium methoxide methanol solution, and freezing and collecting at-140 ℃ to obtain a fluoromethane product, wherein the conversion rate of the methyl chloroformate is 90%, and the yield of the fluoromethane is 25%.

Example 6

Adding 94.5g of methyl chloroformate, 139.5g of tetramethylammonium fluoride and 335g of dimethyl sulfoxide into a 1L reaction kettle with a condensation reflux device, heating to 100 ℃ for reflux reaction, washing a gas-phase product by using 20wt% of potassium hydroxide aqueous solution, and freezing at-180 ℃ to collect a fluoromethane product, wherein the conversion rate of the methyl chloroformate is 88% and the yield of the fluoromethane is 50%.

Claims (10)

1. A method for preparing fluoromethane is characterized in that methyl chloroformate and fluoride salt are used as raw materials, heating reflux reaction is carried out in sulfone or ether solvents, generated gas phase products are absorbed by alkali solution, then low-temperature condensation is carried out, fluoromethane products are obtained, and electronic-grade fluoromethane products are obtained after deep purification.

2. The method of claim 1, comprising the steps of:

(1) Dissolving methyl chloroformate and fluoride salt in sulfone or ether solvent, heating and refluxing for reaction to generate a gas-phase product containing fluoromethane and carbon dioxide;

(2) Introducing the gas-phase product into an absorption tower filled with an alkali solution for washing;

(3) And (4) freezing and collecting the washed gas-phase product at low temperature to obtain a crude fluoromethane product.

3. The method as set forth in claim 1, wherein the reaction temperature in the step (1) is 80 to 200 ℃; the reaction was terminated when no significant bubbles were generated.

4. The process as set forth in claim 1, characterized in that the sulfone or ether solvent of step (1) is selected from at least one of dimethyl sulfoxide, sulfolane, phenylethanesulfone or at least one of diethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether or methyl ether terminated polyethylene glycol ether; the fluoride salt is at least one of lithium fluoride, sodium fluoride, potassium fluoride, cesium fluoride, tetramethylammonium fluoride or tetrabutylammonium fluoride.

5. The process as set forth in claim 1, characterized in that the sulfone or ether solvent of step (1) is selected from sulfolane or tetraglyme; the fluoride salt is selected from sodium fluoride or potassium fluoride.

6. The method as set forth in claim 1, characterized in that the molar ratio of methyl chloroformate/fluoride salt/sulfone or ether solvent is 1: 1.05-5: 1-5.

7. The method as set forth in claim 1, characterized in that the molar ratio of methyl chloroformate/fluoride salt/sulfone or ether solvent is 1: 1.05-2: 1-2.

8. The method of claim 1, wherein the alkali solution in step (2) is calcium hydroxide, sodium hydroxide or potassium hydroxide, sodium methoxide in methanol, or sodium ethoxide in absolute ethanol.

9. The method as set forth in claim 1, wherein the alkali solution has a concentration of 0.1wt% to 20wt%.

10. The method as claimed in claim 1, wherein the cryo-collection temperature in step (3) is-80 to-196 ℃, and the cryogenic refrigerant is liquid nitrogen.