A method for continuously producing monofluoromethane and an apparatus therefor

Abstract

The application discloses a method and device for continuously and efficiently preparing monofluoromethane. Dimethyl carbonate is evaporated into a gas phase, and the gas phase is introduced into a reactor filled with a catalyst bed loaded with an alkali metal fluoride salt for reaction. The reaction temperature is 90-200 DEG C, the reaction pressure is 0.1-2.0 MPa, the residence time of the dimethyl carbonate steam flow in the bed is 1.0-180 s, and the effluent gas after reaction is subjected to alkali washing to obtain monofluoromethane. The monofluoromethane is separated and purified through a further adsorption rectification system to obtain electronic-grade monofluoromethane product. The method has the characteristics of high dimethyl carbonate conversion rate, high monofluoromethane yield, simple process, low raw material toxicity, easy separation and purification of the product, safety, high efficiency and suitability for continuous industrial production.

Description

TECHNICAL FIELD

[0001] The present application relates to a method for preparing monofluoromethane. BACKGROUND

[0002] Electronic gas is an indispensable basic supporting source material in the development of integrated circuits, optoelectronics, microelectronics, especially very large scale integrated circuits, liquid crystal display devices, semiconductor light emitting devices and semiconductor material manufacturing processes, and it is called the "blood" and "food" of the electronic industry. Monofluoromethane is a green and efficient electronic special gas used for etching of semiconductors and electronic products, and has good selectivity for etching of silicide thin films. Under radio frequency, monofluoromethane can dissolve fluorine ions and carry out reactive ion etching. Monofluoromethane has the lowest C / F ratio (1:1) among mainstream etching gases, and has extremely high selectivity. Due to the need for the development of advanced processes, the compound growth rate can reach more than 15% in the next five years.

[0003] At present, the preparation methods of monofluoromethane mainly include the following:

[0004] (1) Gas phase hydrogenation dechlorination method: taking monofluorodichloromethane or monofluoromonochloromethane as raw material, hydrogenation dechlorination reaction is carried out with hydrogen under the action of catalyst (CN104016829A).

[0005]

[0006] The defects of this process are that the catalyst is relatively expensive, the selectivity is low, the space-time yield of monofluoromethane is low, and with the prohibition of ozone-depleting substances and greenhouse gases by the international community, the raw materials HCFC-21 or HCFC-31 will be difficult to obtain.

[0007] (2) Gas phase fluorination method: taking monochloromethane as raw material, halogen exchange reaction is carried out with hydrogen fluoride under the action of metal fluorinated salt catalyst (CN100562510C).

[0008]

[0009] The defects of this process are low conversion rate, many gas phase by-products (HCl, HF, CH3Cl, CH2FCl, CH4, C2H4, etc.), difficult product separation and purification, and serious equipment corrosion.

[0010] (3) Methanol fluorination method: methanol is a low-cost and widely available raw material, and monofluoromethane is prepared by reacting methanol with hydrogen fluoride under the action of metal fluorinated salt catalyst (JP60115538, JP60115536).

[0011]

[0012] The method has the defects of low conversion rate, large amount of water generated during the reaction, which greatly affects the service life of the catalyst, and serious corrosion of the equipment.

[0013] (4) Methyl ester substitution method: dimethyl sulfate (US2016168060) or dimethyl carbonate (CN112898114) is used as raw material to react with alkali metal fluoride salt to prepare monofluoromethane, which has the advantages of simple process, less by-products, easy separation and purification to electronic grade, etc. The defect of this method is that dimethyl sulfate is a highly toxic compound with carcinogenic potential; dimethyl carbonate has lower toxicity, but the reactivity of fluoride salt in the liquid phase system is very poor, and the conversion rate is less than 30% after 48h of reaction. Moreover, a large amount of organic waste liquid is generated after the reaction due to the addition of a large amount of proton solvent as a phase transfer catalyst to promote the reaction. The process is a batch solid-liquid reaction in a reaction kettle, which takes a long time, has very low conversion rate and yield, and cannot realize continuous production, so it has little value in actual industrial production. SUMMARY

[0014] To overcome the defects of the prior art, the first object of the present application is to provide a method for continuously and efficiently preparing monofluoromethane, which has high conversion rate of dimethyl carbonate, high yield of monofluoromethane, simple process, low toxicity of raw materials, easy separation and purification of products, safety, high efficiency, and is suitable for continuous industrial production.

[0015] The second object of the present application is to provide a device used in the preparation method.

[0016] To achieve the first object, the technical solution of the present application is: a method for continuously and efficiently preparing monofluoromethane, wherein dimethyl carbonate is evaporated into a gas phase, and the gas phase is introduced into a reactor filled with a catalyst bed loaded with an alkali metal fluoride salt for reaction. The reaction temperature is 90-200℃, the reaction pressure is 0.1-2.0MPa, the residence time of dimethyl carbonate vapor stream in the bed is 1.0-180s, and the effluent gas after reaction is washed with alkali to obtain monofluoromethane.

[0017] Further, the gas after alkali washing enters an adsorption rectification device for separation and purification to obtain high-purity electronic-grade monofluoromethane gas. The reaction formula is shown in (1):

[0018]

[0019] Further, a method for continuously and efficiently preparing monofluoromethane, comprising the following steps:

[0020] The dimethyl carbonate is continuously introduced into the evaporator for complete vaporization, and the vaporized dimethyl carbonate enters the reactor bed filled with the supported alkali metal fluoride catalyst, the bed temperature is controlled at 90-200°C, preferably 95-160°C; the pressure is 0.1-2.0 MPa, preferably 0.1-1.0 MPa; the residence time of dimethyl carbonate vapor in the bed is controlled at 1.0-180 s, preferably 5-60 s; the reaction mixture gas is washed with alkali to obtain monofluoromethane. The molar ratio of dimethyl carbonate vapor to alkali metal fluoride in the reactor is generally 1:1-20, preferably 1:2-10. In this method, the conversion rate of dimethyl carbonate can reach more than 82%, the yield of monofluoromethane is 74%-81%, and the content of monofluoromethane in the reaction mixture gas after alkali washing is more than 95%. The monofluoromethane obtained by this method is separated and purified by an adsorption rectification system to obtain electronic-grade monofluoromethane product.

[0021] The evaporator is used to realize the vaporization of dimethyl carbonate, and the temperature is generally controlled at 90-95°C, preferably 90-92°C, to ensure complete vaporization of dimethyl carbonate. The alkali washing is to remove acidic gases such as hydrogen fluoride and residual dimethyl carbonate that may be generated in the reaction.

[0022] The supported alkali metal fluoride catalyst refers to a catalyst prepared by loading alkali metal fluoride on a carrier, which is used to increase the contact area between alkali metal fluoride and dimethyl carbonate vapor at the micro level to improve the reaction conversion rate. The alkali metal fluoride can be one or more of potassium fluoride, cesium fluoride, sodium fluoride, etc., and potassium fluoride is preferred. The carrier can be one or more of calcium fluoride, aluminum fluoride, magnesium fluoride, etc., and calcium fluoride is preferred. The specific surface area of the carrier is preferably more than 10 m 2 / g.

[0023] The preparation method of the supported alkali metal fluoride catalyst is to load alkali metal fluoride on the carrier, and then dry and bake in a vacuum. The molar ratio of alkali metal fluoride to carrier is generally 1:1-10, preferably 1:2-5. The specific preparation method is as follows: according to the equal-volume impregnation method, the alkali metal fluoride is dissolved in water (or methanol) to prepare a solution, which is sprayed onto the carrier, and then the carrier loaded with alkali metal fluoride is placed in a vacuum oven for drying. The drying temperature is generally 60-150°C, preferably 80-120°C; the drying time is generally 1-5 h, preferably 1-2 h; then the temperature is increased to 150-260°C, preferably 160-200°C, for baking, and the baking time is 1-10 h, preferably 4-8 h. The vacuum degree of the oven is controlled at 0--0.1 MPa, preferably -0.08--0.1 MPa during drying and baking.

[0024] To achieve the second object, the application provides a device for continuously and efficiently preparing monofluoromethane, wherein carbon dioxide dimethyl ester storage tank 1, peristaltic pump 2, evaporator 3, gas flow meter 4, reactor 5 and alkali washing tower 6 are sequentially connected in the order of material flow; peristaltic pump 2 and gas flow meter 4 are both connected to the upper part of evaporator 3; gas flow meter 4 is connected to the upper part of reactor 5, and alkali washing tower 6 is connected to the lower part of reactor 5, and the inside of the reactor is provided with a supported alkali metal fluoride catalyst.

[0025] Carbon dioxide dimethyl ester in the carbon dioxide dimethyl ester storage tank is pumped into the evaporator by the peristaltic pump for vaporization, then measured by the flow meter and enters the reactor to react with the alkali metal fluoride to generate monofluoromethane; the reaction mixture gas from the reactor enters the adsorption rectification system after removing the acidic gas such as hydrogen fluoride and residual carbon dioxide dimethyl ester by alkali washing.

[0026] The evaporator can be selected from a reaction kettle, a falling film evaporator, a wiped film evaporator and a molecular distiller, and the wiped film evaporator is preferred; the reactor can be selected from a tubular reactor, a fixed bed reactor and a fluidized bed reactor, and the reactor is provided with a heating device for controlling the bed layer reaction temperature; the reactor pressure and residence time can be adjusted by adjusting the feeding speed of the peristaltic pump.

[0027] The method and device provided by the application can continuously, safely and efficiently prepare high-purity electronic-grade monofluoromethane gas, and have the following beneficial effects:

[0028] (1) The method uses the evaporator to vaporize the reactant carbon dioxide dimethyl ester, then the vaporized carbon dioxide dimethyl ester flows through the bed layer of the reactor at a certain speed to react with the active component alkali metal fluoride; compared with the liquid-solid reaction system which can only be carried out in a kettle reactor (which belongs to a batch reaction), the method is easier to realize continuous production.

[0029] (2) The method adopts the continuous feeding and discharging mode in the processes of carbon dioxide dimethyl ester vaporization and reaction with the alkali metal fluoride, and the residence time of the material in the evaporator and the reactor is relatively short, so that the instantaneous heating and the amount of the reactant are very small, and the safety of the reaction is higher.

[0030] (3) The method uses the equal-volume impregnation method to load the alkali metal fluoride onto a carrier with a large specific surface area to prepare a reaction catalyst, so that the alkali metal fluoride and the carbon dioxide dimethyl ester have a large contact area at the micro level, which is conducive to improving the conversion rate of the reaction system; compared with the liquid-solid reaction system, the solubility of the alkali metal fluoride in the liquid phase is extremely poor, so a large amount of proton solvent needs to be added as a phase transfer catalyst to promote the reaction, so the method is more efficient, convenient and economical. The conversion rate of the carbon dioxide dimethyl ester in the method can be more than 82%, and the yield of the monofluoromethane can be more than 74%.

[0031] (4) The method described in the present application does not require the use of solvents, no waste liquid is generated, a small amount of unreacted dimethyl carbonate vapor remaining in the reaction mixture gas can be absorbed by lye, no waste gas is generated, the supported alkali metal fluoride salt catalyst used in the reaction can be regenerated by hydrogen fluoride gas to achieve recycling, no waste solid is generated, and truly green pollution-free zero discharge is achieved. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 The figure is a schematic diagram of the device of the present application.

[0033] It includes: a dimethyl carbonate storage tank 1, a peristaltic pump 2, an evaporator 3, a gas flow meter 4, a reactor 5, an alkali washing tower 6, and an adsorption rectification system 7. DETAILED DESCRIPTION

[0034] The specific embodiments of the present application are described in detail below in conjunction with examples.

[0035] Example 1

[0036] Preparation of the supported alkali metal fluoride salt catalyst: potassium fluoride is selected as the reaction active component, calcium fluoride is selected as the carrier, and the potassium fluoride is dissolved in an appropriate amount of water to prepare a solution according to a molar ratio of potassium fluoride to calcium fluoride of 1:2 (the volume of the prepared solution is determined according to the requirements of the equal-volume impregnation method), the prepared solution is uniformly sprayed on the carrier calcium fluoride, and then the carrier is placed in a vacuum oven for drying, with a control temperature of 80°C and a pressure of -0.1 MPa, and dried for 4 h, and then baked at a temperature of 180°C for 8 h to obtain the reaction catalyst.

[0037] As shown in Figure 1 the preparation of monofluoromethane: a 316L stainless steel fixed-bed reactor is used as the reactor 5, a wiped-film evaporator is used as the evaporator 3, and the remaining devices are sequentially connected to form a continuous reaction device; the prepared supported potassium fluoride catalyst is loaded into the reactor 5, and stainless steel wire mesh is used to seal both ends of the reactor to prevent the reaction catalyst from entering the pipeline; the heating device of the evaporator 3 is turned on and the heating temperature is set to 92°C, the heating device of the reactor 5 is turned on and the heating temperature is set to 150°C, after the temperature is stable, the peristaltic pump 2 is turned on to continuously pump dimethyl carbonate into the evaporator 3 for vaporization, the vapor enters the reactor 5 to react with potassium fluoride, the pressure in the reactor 5 is controlled to be 0.5 MPa by adjusting the speed of the peristaltic pump 2, the residence time of the vapor in the reactor is 8 s, and the reaction gas is sampled and analyzed after flowing out of the alkali washing tower 6. The conversion rate of dimethyl carbonate is 83.3%, the yield of monofluoromethane is 76.5%, and the content of monofluoromethane after alkali washing of the reaction mixture gas is 96.5%.

[0038] Example 2

[0039] Preparation of supported alkali metal fluoride salt catalyst: Potassium fluoride was selected as the reactive component and calcium fluoride as the carrier. Potassium fluoride was dissolved in an appropriate amount of water at a molar ratio of 1:6 to prepare a solution (the volume of the solution was determined according to the requirements of the equal volume impregnation method). The prepared solution was sprayed evenly onto the calcium fluoride carrier and then placed in a vacuum oven for drying. The temperature was controlled at 120℃ and the vacuum degree was -0.08MPa for 3 hours. Then, the temperature was raised to 220℃ and baked for 4 hours to obtain the reactive catalyst.

[0040] like Figure 1 As shown, the preparation of monofluoromethane: A 316L stainless steel fluidized bed reactor (reactor 5) and a falling film evaporator (evaporator 3) are connected in sequence with other devices to form a continuous reaction apparatus. The prepared supported potassium fluoride catalyst is loaded into reactor 5. The heating device of evaporator 3 is turned on and the heating temperature is set to 92℃. The heating device of reactor 5 is turned on and the heating temperature is set to 180℃. After the temperature stabilizes, peristaltic pump 2 is turned on to continuously pump dimethyl carbonate into evaporator 3 for vaporization. The vapor enters reactor 5 and reacts with potassium fluoride. The pressure inside reactor 5 is controlled to 0.2 MPa by adjusting the speed of peristaltic pump 2. The residence time of the vapor in the reactor is 60 s. The reaction gas is sampled and analyzed after flowing out of alkaline washing tower 6. The conversion rate of dimethyl carbonate is 89.2%, the yield of monofluoromethane is 82.5%, and the monofluoromethane content of the reaction mixture after alkaline washing is 96.8%.

[0041] Example 3

[0042] Preparation of supported alkali metal fluoride salt catalyst: Cesium fluoride was selected as the reactive component and calcium fluoride as the carrier. Cesium fluoride was dissolved in an appropriate amount of water to prepare a solution at a molar ratio of 1:10 (the volume of the solution was determined according to the requirements of the equal volume impregnation method). The prepared solution was sprayed evenly onto the calcium fluoride carrier and then placed in a vacuum oven for drying. The temperature was controlled at 120℃ and the vacuum degree was -0.1MPa for 2 hours. Then, the temperature was raised to 200℃ and baked for 6 hours to obtain the reactive catalyst.

[0043] Preparation of monofluoromethane: a nickel-made tubular reactor was used as reactor 5, a wiped-film evaporator was used as evaporator 3, and the rest of the devices were connected in sequence to form a continuous reaction device; the prepared supported cesium fluoride catalyst was loaded into reactor 5, and stainless steel wire mesh was used to seal both ends of the reactor to prevent the reaction catalyst from entering the pipeline; the heating device of evaporator 3 was turned on and the heating temperature was set to 92°C, the heating device of reactor 5 was turned on and the heating temperature was set to 100°C, after the temperature was stable, the peristaltic pump 2 was started to continuously pump dimethyl carbonate into the evaporator 3 for vaporization, the vapor entered the reactor 5 to react with cesium fluoride, the pressure in the reactor 5 was controlled to be 0.1 MPa by adjusting the speed of the peristaltic pump 2, the residence time of the vapor in the reactor was 180 s, and the reaction gas was sampled and analyzed after flowing out of the alkali washing tower 6. The conversion rate of dimethyl carbonate was 87.1%, the yield of monofluoromethane was 80.2%, and the content of monofluoromethane after alkali washing of the reaction mixture was 98%.

[0044] Example 4

[0045] Preparation of supported alkali metal fluoride catalyst: sodium fluoride was selected as the reaction active component, and aluminum fluoride was selected as the carrier. The sodium fluoride was dissolved in an appropriate amount of water to form a solution according to a molar ratio of sodium fluoride to aluminum fluoride of 1:4 (the volume of the solution was determined according to the requirements of the equal-volume impregnation method), the prepared solution was uniformly sprayed on the carrier sodium fluoride, and then the mixture was placed in a vacuum oven for drying, with a temperature control of 150°C and a vacuum degree of -0.1 MPa, and dried for 1 h, and then baked at 260°C for 4 h to obtain the reaction catalyst.

[0046] Preparation of monofluoromethane: a 316L stainless steel fixed-bed reactor was used as reactor 5, a wiped-film evaporator was used as evaporator 3, and the rest of the devices were connected in sequence to form a continuous reaction device; the prepared supported sodium fluoride catalyst was loaded into the special 316L stainless steel fixed-bed reactor 5, and stainless steel wire mesh was used to seal both ends of the reactor to prevent the reaction catalyst from entering the pipeline; the heating device of evaporator 3 was turned on and the heating temperature was set to 92°C, the heating device of reactor 5 was turned on and the heating temperature was set to 200°C, after the temperature was stable, the peristaltic pump 2 was started to continuously pump dimethyl carbonate into the evaporator 3 for vaporization, the vapor entered the reactor 5 to react with sodium fluoride, the pressure in the reactor 5 was controlled to be 1.0 MPa by adjusting the speed of the peristaltic pump 2, the residence time of the vapor in the reactor was 30 s, and the reaction gas was sampled and analyzed after flowing out of the alkali washing tower 6. The conversion rate of dimethyl carbonate was 82.7%, the yield of monofluoromethane was 74.8%, and the content of monofluoromethane after alkali washing of the reaction mixture was 95.1%.

[0047] Comparative Example

[0048] Preparation of monofluoromethane: Take a 250 mL three-necked flask, build a condensation reflux reaction device, respectively, take dimethyl carbonate 3.7 g, cesium fluoride 13.7 g, tetraethylene glycol dimethyl ether 100 g, and sequentially add them to the three-necked flask, start stirring, start oil bath heating, set the oil bath temperature to 140℃, and collect the product in a gas bag. Stop heating after 48 hours of reaction and take a sample for analysis. In this method, the conversion rate of dimethyl carbonate is 26.25%, and the yield of monofluoromethane is 22.33%.

Claims

1. A method for continuously preparing monofluoromethane, dimethyl carbonate is evaporated into a gas phase, the gas phase is introduced into a reactor filled with a catalyst bed loaded with an alkali metal fluoride salt, the reaction temperature is 90-200℃, the reaction pressure is 0.1-2.0 MPa, the residence time of the dimethyl carbonate vapor stream in the bed is 1.0-180 s, and the effluent gas after the reaction is washed with alkali to obtain monofluoromethane. The catalyst loaded with an alkali metal fluoride salt refers to a catalyst prepared by loading an alkali metal fluoride salt on a carrier, the alkali metal fluoride salt is one or more of potassium fluoride, cesium fluoride and sodium fluoride, and the carrier is one or more of calcium fluoride, aluminum fluoride and magnesium fluoride. The catalyst loaded with an alkali metal fluoride salt is prepared by loading an alkali metal fluoride salt on a carrier, vacuum drying and baking, the molar ratio of the alkali metal fluoride salt to the carrier is 1:1-10. According to an equal-volume impregnation method, the alkali metal fluoride salt is dissolved in water or methanol to prepare a solution, which is sprayed onto the carrier, and then the carrier loaded with the alkali metal fluoride salt is dried in a vacuum oven, the drying temperature is 60-150℃, the drying time is 1-5 h, and then the temperature is increased to 150-260℃ for baking, the baking time is 1-10 h, and the vacuum degree of the oven is controlled to be 0- -0.1 MPa during drying and baking.

2. The method of claim 1, wherein The method comprises the following steps: Dimethyl carbonate is continuously introduced into an evaporator for complete vaporization, the vaporized dimethyl carbonate enters a reactor bed filled with a supported alkali metal fluoride salt catalyst, the bed temperature is 95-160℃, the pressure is 0.1-1.0 MPa, and the residence time of the dimethyl carbonate vapor stream in the bed is 5-60 s, and the reaction mixture gas is washed with alkali to obtain monofluoromethane.

3. The method of claim 1, wherein Monofluoromethane is separated and purified by a further adsorption rectification system to obtain electronic-grade monofluoromethane product.

4. The method of claim 1, wherein The alkali metal fluoride salt is potassium fluoride; the carrier is calcium fluoride, and the specific surface area of the carrier is greater than or equal to 10 m 2 / g.

5. Apparatus for use in a method as claimed in any one of claims 1 to 4, characterised in that A dimethyl carbonate storage tank (1), a peristaltic pump (2), an evaporator (3), a gas flow meter (4), a reactor (5) and an alkali washing tower (6) are sequentially connected; the peristaltic pump (2) and the gas flow meter (4) are both connected to the upper part of the evaporator (3); the gas flow meter (4) is connected to the upper part of the reactor (5), the alkali washing tower (6) is connected to the lower part of the reactor (5), and the reactor is internally filled with a supported alkali metal fluoride salt catalyst; the upper part of the alkali washing tower (6) is connected to an adsorption rectification system (7); the evaporator is selected from a reaction kettle, a falling film evaporator, a wiped film evaporator or a molecular still; the reactor is a tubular reactor, a fixed bed reactor or a fluidized bed reactor, and the reactor is provided with a heating device.

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