CN110606797A

CN110606797A - Preparation method of high-conversion-rate monofluoromethane

Info

Publication number: CN110606797A
Application number: CN201910536841.7A
Authority: CN
Inventors: 杜文东; 马建修; 王新鹏; 汤萍; 舒东永
Original assignee: Tianjin Lvling Gas Co Ltd; Greenwood Electronic Materials Tianjin Co Ltd
Current assignee: Tianjin Lvling Gas Co Ltd; Greenwood Electronic Materials Tianjin Co Ltd
Priority date: 2019-06-20
Filing date: 2019-06-20
Publication date: 2019-12-24

Abstract

The invention provides a preparation method of monofluoromethane with high conversion rate. A preparation method of monofluoromethane with high conversion rate comprises the following steps: carrying out deep dehydration treatment on the raw material gas, namely methane chloride; carrying out deep dehydration treatment on raw material gas hydrogen fluoride; carrying out deep dehydration treatment on the oxygen-containing gas; performing a fluorine-chlorine exchange reaction on methane chloride, hydrogen fluoride and oxygen-containing gas in a reactor under the condition of a catalyst to generate a semi-finished product; and the semi-finished product is subjected to primary purification and separation to obtain unreacted methane chloride and unreacted hydrogen fluoride, and the unreacted methane chloride and the unreacted hydrogen fluoride are returned to the reactor for recycling. According to the preparation method of the high-conversion-rate monofluoromethane, the carbon deposition prevention layer of silicon nitride or silicon phosphide is coated on the outer surface of the catalyst, and the oxygen-containing gas is introduced to carry out combustion reaction on the byproduct methane in time, so that a large amount of carbon deposition on the surface of the catalyst is avoided, the activity of the catalyst is obviously improved, and the conversion rate of the monofluoromethane is greatly improved.

Description

Preparation method of high-conversion-rate monofluoromethane

Technical Field

The invention relates to the fields of chemical engineering, separation engineering and electronic special gases, in particular to a preparation method of monofluoromethane with high conversion rate.

Background

Monofluoromethane (CH)₃F) Tetrahedron gas, nontoxic, colorless and tasteless at normal temperature and pressure, has been used mainly as a methylating agent in organic synthesis in the past, when transported under conditions of R-41, boiling point-78.2 deg.C, density 1.44 g/cm. Monofluoromethane is a green environmental gas (material greenhouse effect index GWP = 7) compared to carbon tetrafluoride, sulfur hexafluoride.

With the development of advanced processes of integrated circuits, the silicon nitride film in the shallow trench process has strong chemical inertness and is difficult to be accurately etched, and the process affects the yield of the integrated circuit manufacturing. In recent years, the mixture of high-purity electronic grade monofluoromethane, argon and oxygen is widely applied to etching of silicon nitride films, and has high selectivity. For example, the etched low-density silicon nitride film can be etched at 200 ℃ by high-purity electronic grade fluoromethane under the auxiliary enhancement action of plasma, so that the damage of high temperature to key elements of an integrated circuit is avoided. (reference: Japanese Journal of Applied Physics 2016, 55, 086502; Journal of Vacuum Science & Technology A, 2016, 34, 041301)

At present, two processes are mainly adopted for preparing the monofluoromethane, wherein one process is to prepare the monofluoromethane by using dichloromonofluoromethane as a raw material and carrying out hydrodechlorination reaction on the dichloromonofluoromethane and hydrogen through a catalyst, and the operation of the method is not easy to control. In the other method, methane chloride is used as a raw material, and fluorine and chlorine exchange is carried out by the action of a catalyst and hydrogen fluoride to prepare the methane fluoride. The second method is a safe and stable preparation technology with convenient operation, and the reaction equations are respectively as follows:

CH₃Cl + HF → CH₃f + HCl (catalyst)

The key to the above process is the preparation of the catalyst. A second method, CN106542959, discloses a fluorine-chlorine exchange catalyst, which is implemented by using trivalent chromium as an active metal and adding one catalyst promoter of tungsten, molybdenum, rhenium and ruthenium, and the fluorine-chlorine exchange catalyst disclosed in WO 2006/030677 is implemented by adding one catalyst promoter of indium, zinc, nickel, cobalt, magnesium and aluminum on the basis of trivalent chromium as an active metal. The crude monofluoromethane is obtained by the method, and the high purity requirement is met by separation operations such as rectification adsorption and the like. In the aspect of physicochemical basic research between monofluoromethane and impurity mixtures, the research is relatively rare, and only gas-liquid three-phase equilibrium data of monofluoromethane and carbon tetrafluoride exist. (J. chem. Thermodynmics 1998, 30,1271-

The practice shows that the existing fluorine-chlorine exchange process has some problems, such as simple reaction conditions, but methane is one of byproducts of the fluorine-chlorine exchange reaction, is easy to attach to the surface of the catalyst, causes carbon deposition on the pore channels, reduces the catalytic activity, and has the monofluoromethane conversion rate of only about 5%. In conclusion, the conventional method for producing monofluoromethane has low conversion rate and high cost.

Disclosure of Invention

In order to overcome the defects and shortcomings of the prior art, the invention aims to provide a preparation method of high-conversion-rate monofluoromethane, which adopts the monochloromethane and hydrogen fluoride as raw materials to prepare the monofluoromethane, coats a carbon deposition prevention layer of silicon nitride or silicon phosphide on the outer surface of a catalyst for reaction, and introduces oxygen-containing gas to carry out combustion reaction on byproduct methane in time, thereby avoiding a large amount of carbon deposition on the surface of the catalyst, obviously improving the activity of the catalyst and greatly improving the conversion rate of the monochloromethane.

The technical problem to be solved by the invention is realized by adopting the following technical scheme.

The invention provides a preparation method of monofluoromethane with high conversion rate, which comprises the following steps:

and step S1: carrying out deep dehydration treatment on the raw material gas, namely methane chloride;

and step S2: carrying out deep dehydration treatment on raw material gas hydrogen fluoride;

and step S3: carrying out deep dehydration treatment on the oxygen-containing gas; the oxygen-containing gas is oxygen, air or mixed gas, and the mixed gas is formed by mixing oxygen and one of nitrogen or rare gas;

and step S4: performing a fluorine-chlorine exchange reaction on methane chloride, hydrogen fluoride and oxygen-containing gas in a reactor under the condition of a catalyst to generate a semi-finished product;

and step S5: and the semi-finished product is subjected to primary purification and separation to obtain unreacted methane chloride and unreacted hydrogen fluoride, and the unreacted methane chloride and the unreacted hydrogen fluoride are returned to the reactor for recycling.

Preferably, the outer surface of the catalyst is coated with silicon nitride or silicon phosphide as an anti-carbon deposition layer, the thickness of the anti-carbon deposition layer is 2 ~ 5mm, the surface opening rate is 50 ~ 80%, and the preparation process of the anti-carbon deposition layer comprises the steps of coating silicon nitride slurry or silicon phosphide slurry on the surface of the catalyst by adopting a surface shaking and sticking method, stirring for more than 2 hours, standing for more than 12 hours, and roasting for more than 4 hours at the temperature of 600 ~ 800 ℃.

Preferably, the nitrogen source is ammonia water or tetramethyl ammonium hydroxide, the silicon phosphide slurry is a mixture of a phosphorus source, sodium silicate and isopropanol, the phosphorus source is phosphoric acid or phosphorous acid, and the molar ratio of the nitrogen source or the phosphorus source, the sodium silicate and the isopropanol is (1.5 ~ 3): 1 (2.5 ~ 12).

Preferably, the catalyst takes a trivalent chromium compound as a catalyst active body, takes a silicon-aluminum microsphere as a carrier, takes indium, copper, zinc, nickel, cobalt, magnesium, tungsten, molybdenum, rhenium or ruthenium as a catalyst auxiliary agent, and adopts an impregnation method to load the catalyst active body and the catalyst auxiliary agent on the surface of the carrier.

Preferably, the content of the catalyst active body is 3 ~ 20 wt%, the content of the catalyst promoter is 0.1 ~ 2.0.0 wt%, and the rest is the carrier.

Preferably, the trivalent chromium compound is one of chromium oxide, chromium chloride, chromium nitrate or chromium hydroxide.

Preferably, the pore diameter of the silicon-aluminum microsphere is 4 ~ 10A, and the specific surface area is 400 ~ 1000 m²/m³The pore volume was 0.2 ~ 2.0.0 mL/g.

Preferably, the silica-alumina microspheres are alumina microspheres, zeolite molecular sieve microspheres or silica microspheres.

Preferably, the conditions of the fluorine-chlorine exchange reaction are that the reaction temperature is 150 ~ 400 ℃, the reaction pressure is 0.05 ~ 2.0.0 MPa, and the space velocity is 50 ~ 1000 h^-1The feed molar ratio of methyl chloride, hydrogen fluoride and oxygen-containing gas was 1 (4 ~ 10) to (0.1 ~ 0.3).

Preferably, the preliminary purification is performed by rectification, and the separated chloromethane and anhydrous hydrogen fluoride are collected in a buffer tank which is communicated with an inlet of the reactor.

The preparation method of the high-conversion-rate monofluoromethane has the beneficial effects that:

(1) the preparation method adopts the coating technology to coat the anti-carbon deposition layer of silicon nitride or silicon phosphide on the outer surface of the traditional catalyst, thereby avoiding a large amount of carbon deposition on the outer surface of the catalyst, effectively avoiding the carbon deposition and the activity reduction of a catalyst pore passage, and improving the conversion rate of the monofluoromethane.

(2) The preparation method of the invention introduces oxygen-containing gas to burn the byproduct methane in time, thereby avoiding the byproduct methane from attaching to the outer surface of the catalyst, effectively avoiding carbon deposition and activity reduction of catalyst pore channels, and improving the conversion rate of monofluoromethane; meanwhile, the byproduct methane is combusted in time, the separation difficulty of the monofluoromethane and impurities of a methane low separation system is reduced, and the subsequent separation and purification efficiency is obviously improved.

(3) The semi-finished product at the outlet of the reactor for fluorine-chlorine exchange is separated, and the unreacted raw materials are returned to the reactor for recycling, so that the utilization rate of the raw material gas is improved.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. The examples, in which specific conditions are not specified, were conducted under conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products available commercially.

Silicides are binary compounds of certain metals (e.g., lithium, calcium, magnesium, iron, chromium, etc.) and certain non-metals (e.g., boron, etc.) with silicon. The surface of the silicon nitride does not form chemical bonds with carbon, so that carbon can not be easily deposited on the surface of the silicide. The silicide is used for coating the surface of the catalyst, so that the condition that carbon is easily attached to the surface of the catalyst can be greatly improved. Wherein, the carbon deposition resistance of the catalyst after the silicon nitride and the silicon phosphide are coated is more excellent.

The present invention provides a high conversion ratio monofluoromethane and a method for preparing the same.

The embodiment of the invention provides a preparation method of monofluoromethane with high conversion rate, which comprises the following steps:

the oxygen-containing gas contains oxygen components, and can burn the byproduct methane in the subsequent fluorine-chlorine exchange reaction, so that the byproduct methane is effectively prevented from being attached to the outer surface of the catalyst, the carbon deposition and the activity reduction of a catalyst pore passage are effectively avoided, and the conversion rate of monofluoromethane is improved; meanwhile, the byproduct methane is combusted in time, the separation difficulty of the monofluoromethane and impurities of a methane low separation system is reduced, and the subsequent separation and purification efficiency is obviously improved.

further, in the preferred embodiment of the invention, the outer surface of the catalyst is coated with silicon nitride or silicon phosphide as an anti-carbon deposition layer, the thickness of the anti-carbon deposition layer is 2 ~ 5mm, the surface opening rate is 50 ~ 80%, the preparation process of the anti-carbon deposition layer is that silicon nitride slurry or silicon phosphide slurry is coated on the surface of the catalyst by adopting a surface shaking and adhering method, then the mixture is stirred for more than 2 hours, kept stand for more than 12 hours and roasted for more than 4 hours at the temperature of 600 ~ 800 ℃, the anti-carbon deposition layer of silicon nitride or silicon phosphide is coated on the outer surface of the traditional catalyst by adopting a coating technology, so that a large amount of carbon deposition on the outer surface of the catalyst is avoided, the carbon deposition and the activity reduction of a catalyst pore passage are effectively avoided, the conversion rate of monofluoromethane is improved, the anti-carbon deposition layer is coated by adopting the surface shaking and adhering method, the operation of the method is simple.

Further, in the preferred embodiment of the invention, the silicon nitride slurry is a mixture of a nitrogen source, sodium silicate and isopropanol, the nitrogen source is ammonia water or tetramethylammonium hydroxide, the silicon phosphide slurry is a mixture of a phosphorus source, sodium silicate and isopropanol, the phosphorus source is phosphoric acid or phosphorous acid, the dosage ratio of the nitrogen source or the phosphorus source, the sodium silicate and the isopropanol is (1.5 ~ 3): 1, (2.5 ~ 12), the sodium silicate and the isopropanol are mixed with the nitrogen source or the phosphorus source according to a certain proportion to prepare the slurry, and the finally obtained carbon deposition prevention layer is uniform in thickness and good in carbon deposition prevention effect.

Further, in the preferred embodiment of the invention, the catalyst uses trivalent chromium compound as the active bulk of the catalyst, uses silica-alumina microspheres as the carrier, uses indium, copper, zinc, nickel, cobalt, magnesium, tungsten, molybdenum, rhenium or ruthenium as the catalyst promoter, and adopts the impregnation method to load the active bulk of the catalyst and the catalyst promoter on the surface of the carrier. The trivalent chromium compound is used as the active body of the catalyst, and the catalyst synthesized by using the silicon-aluminum microsphere as the carrier has excellent performance in the fluorine-chlorine exchange reaction. The impregnation method is simple to operate, and the catalyst active body and the catalyst auxiliary agent can be uniformly coated on the surface of the carrier.

Further, in the preferred embodiment of the present invention, the content of the catalyst active bulk is 3 ~ 20 wt%, the content of the catalyst promoter is 0.1 ~ 2.0.0 wt%, and the balance is the carrier, and when the content of the catalyst active bulk, the content of the catalyst promoter, and the content of the carrier are the above ratios, the performance of the prepared catalyst is excellent.

Further, in a preferred embodiment of the present invention, the trivalent chromium compound is one of chromium oxide, chromium chloride, chromium nitrate or chromium hydroxide. When the chromium compound is limited to be one of chromium oxide, chromium chloride, chromium nitrate or chromium hydroxide in the process of preparing the catalyst, the prepared catalyst has excellent performance.

Further, in the preferred embodiment of the present invention, the pore diameter of the silica-alumina microsphere is 4 ~ 10A, and the specific surface area is 400 ~ 1000 m²/m³The pore volume is 0.2 ~ 2.0.0 mL/g, the specific surface area is 400 ~ 1000 m when the pore diameter is 4 ~ 10A²/m³The pore volume was 0.2 ~ 2.0.0 mL/g, and the support had a larger pore diameter allowing the catalyst active material and the catalyst promoter to be supported on its surface while the support had a larger comparative area.

Further, in the preferred embodiment of the present invention, the silica-alumina microspheres are alumina microspheres, zeolite molecular sieve microspheres or silica microspheres. When the silicon-aluminum microspheres are alumina microspheres, zeolite molecular sieve microspheres or silica microspheres, the carrier is relatively stable, and the catalyst active substances and the catalyst auxiliary agents are more easily loaded on the silicon-aluminum microspheres.

Further, in the preferred embodiment of the present invention, the conditions of the fluorine-chlorine exchange reaction are that the reaction temperature is 150 ~ 400 ℃, the reaction pressure is 0.05 ~ 2.0.0 MPa, and the space velocity is 50 ~ 1000 h^-1The molar ratio of the chloromethane to the hydrogen fluoride to the oxygen-containing gas is 1 (4 ~ 10): (0.1 ~ 0.3.3). in the fluorine-chlorine exchange reaction, the reaction conditions are controlled such that the reaction temperature is 150 ~ 400 ℃, the reaction pressure is 0.05 ~ 2.0.0 MPa, and the space velocity is 50 ~ 1000 h and 1000 h^-1When the feeding molar ratio of the monochloromethane to the hydrogen fluoride to the oxygen-containing gas is 1 (4 ~ 10) to (0.1 ~ 0.3.3), the conversion rate, the reaction speed and the reaction cost of the monofluoromethane in the reaction can be considered, so that the two indexes are kept in a relatively high range, the energy consumption of the reaction is low, and the reaction cost is effectively controlled.

Further, in the preferred embodiment of the present invention, the preliminary purification is performed by rectification, and the separated monochloromethane and anhydrous hydrogen fluoride are collected in a buffer tank, which is connected to the inlet of the reactor. The chloromethane and the anhydrous hydrogen fluoride are separated and then returned to the reactor again to carry out fluorine-chlorine exchange reaction again, so that the utilization rate of the raw materials, namely the chloromethane and the hydrogen fluoride is effectively improved, and the raw materials are saved.

The features and properties of the present invention are described in further detail below with reference to examples.

Example 1

This example provides a method for preparing high conversion of monofluoromethane, which includes the following steps:

and step S1: 3A zeolite molecular sieve is used as adsorbent, and the adsorption temperature is controlled at 20 ℃, and the space velocity is controlled at 600 h^-1Carrying out deep dehydration treatment on the raw material gas, namely methane chloride; in this embodiment, the 3A zeolite molecular sieve is used as the adsorbent, and in other embodiments, zeolite molecular sieves such as 4A, 5A, and 13X, activated alumina, and silica gel may also be used as the adsorbent, all of which achieve the technical effects of this embodiment and are within the scope of this embodiment.

And step S2: sodium fluoride in metal fluoride is used as an adsorbent, the adsorption temperature is controlled to be 50 ℃, and the space velocity is controlled to be 600 h^-1Carrying out deep dehydration treatment on raw material gas hydrogen fluoride; in this embodiment, sodium fluoride is used as the adsorbent, and in other embodiments, metal fluorides such as potassium fluoride, calcium fluoride, aluminum fluoride, magnesium fluoride and the like may also be used as the adsorbent, all of which can achieve the technical effects of this embodiment and are within the protection scope of this embodiment.

And step S3: the 4A zeolite molecular sieve is adopted as an adsorbent, the adsorption temperature is controlled to be 50 ℃, and the space velocity is controlled to be 600 h^-1And carrying out deep dehydration treatment on the oxygen-containing gas. Wherein the oxygen-containing gas is oxygen; in this embodiment, the zeolite molecular sieve 4A is used as the adsorbent, and in other embodiments, zeolite molecular sieves such as 3A, 5A, and 13X, activated alumina, and silica gel may also be used as the adsorbent, all of which achieve the technical effects of this embodiment and are within the scope of this embodiment. In the present embodiment, the oxygen-containing gas is oxygen, and in other embodiments, the oxygen-containing gas may be air or a mixture of air and oxygen, wherein the mixture is formed by mixing oxygen and one of nitrogen or a rare gas, and the technical effects of the present embodiment can be achieved all in the following embodimentsThe scope of the present embodiment.

And step S4: introducing methyl chloride, hydrogen fluoride and oxygen-containing gas into a reactor provided with a catalyst at the feeding rates of 0.5mol/min, 3.5 mol/min and 0.1 mol/min respectively to perform fluorine-chlorine exchange reaction, and producing a semi-finished product. The reactor adopts a fixed bed reactor, and the reaction temperature in the reactor is controlled to be 275 ℃, the reaction pressure is controlled to be 1.0 MPa, and the space velocity is controlled to be 520 h^-1。

The catalyst takes a trivalent chromium compound as a catalyst active body, takes silicon-aluminum microspheres as a carrier, takes indium, copper, zinc, nickel, cobalt, magnesium, tungsten, molybdenum, rhenium or ruthenium as a catalyst auxiliary agent, and adopts an impregnation method to load the catalyst active body and the catalyst auxiliary agent on the surface of the carrier. The content of the catalyst active body is 11 wt%, the content of the catalyst auxiliary agent is 1.05 wt%, and the balance is the carrier. The aperture of the silicon-aluminum microsphere is 7A, and the specific surface area is 700 m²/m³The pore volume is 1.1 mL/g, it should be noted that, in this embodiment, the trivalent chromium compound is chromium oxide, and in other embodiments, the trivalent chromium compound may also be one of chromium chloride, chromium nitrate or chromium hydroxide, and all that can achieve the technical effects of this embodiment is within the protection scope of this embodiment. The silica-alumina microspheres in this embodiment may be alumina microspheres, zeolite molecular sieve microspheres, or silica microspheres.

The outer surface of the catalyst is coated with silicon phosphide as a carbon deposition prevention layer, the thickness of the carbon deposition prevention layer is 3.5mm, and the surface aperture ratio is 75%. The preparation process of the carbon deposition prevention layer comprises the following steps: coating the silicon phosphide slurry on the surface of the catalyst by adopting a surface shaking and sticking method, then stirring for 3 hours, standing for 14 hours, and roasting for 5 hours at the temperature of 700 ℃.

The technical effects of the present embodiment can be achieved by using phosphoric acid as a phosphorus source in the present embodiment, and phosphorous acid as a phosphorus source in other embodiments, and are within the protection range of the present embodiment, the molar ratio of the phosphorus source, the sodium silicate and the isopropanol in the present embodiment is 2.25: 1: 7.25, and the molar ratio of the phosphorus source, the sodium silicate and the isopropanol in other embodiments can be within the range of (1.5 ~ 3): 1 (2.5 ~ 12), and the technical effects of the present embodiment can be achieved, and are within the protection range of the present embodiment.

And step S5: after the semi-finished product is rectified and primarily purified, the separated methane chloride and anhydrous hydrogen fluoride are collected into a buffer tank. The buffer tank is communicated to the inlet of the reactor, and returns the unreacted methane chloride and the unreacted hydrogen fluoride to the reactor for recycling.

Example 2

And step S3: the 4A zeolite molecular sieve is adopted as an adsorbent, the adsorption temperature is controlled to be 50 ℃, and the space velocity is controlled to be 600 h^-1And carrying out deep dehydration treatment on the oxygen-containing gas. Wherein the oxygen-containing gas is oxygen; in this embodiment, the zeolite molecular sieve 4A is used as the adsorbent, and in other embodiments, zeolite molecular sieves such as 3A, 5A, and 13X, activated alumina, and silica gel may also be used as the adsorbent, all of which achieve the technical effects of this embodiment and are within the scope of this embodiment. In this embodiment, the oxygen-containing gas is oxygen, and in other embodiments, the oxygen-containing gas may be emptyOne of a gas and a mixed gas, wherein the mixed gas is formed by mixing one of nitrogen or a rare gas with oxygen, both technical effects of the present embodiment can be achieved, and both are within the protection scope of the present embodiment.

The catalyst takes a trivalent chromium compound as a catalyst active body, takes silicon-aluminum microspheres as a carrier, takes indium, copper, zinc, nickel, cobalt, magnesium, tungsten, molybdenum, rhenium or ruthenium as a catalyst auxiliary agent, and adopts an impregnation method to load the catalyst active body and the catalyst auxiliary agent on the surface of the carrier. The content of the catalyst active body is 11 wt%, the content of the catalyst auxiliary agent is 1.05 wt%, and the balance is the carrier. The aperture of the silicon-aluminum microsphere is 7A, and the specific surface area is 700 m²/m³The pore volume was 1.1 mL/g. It should be noted that, in this embodiment, the trivalent chromium compound is chromium oxide, and in other embodiments, the trivalent chromium compound may also be one of chromium chloride, chromium nitrate, or chromium hydroxide, and all of the technical effects of this embodiment can be achieved are within the scope of protection of this embodiment. The silica-alumina microspheres in this embodiment may be alumina microspheres, zeolite molecular sieve microspheres, or silica microspheres.

The outer surface of the catalyst is coated with silicon nitride as a carbon deposition prevention layer, the thickness of the carbon deposition prevention layer is 3.5mm, and the surface aperture ratio is 75%. The preparation process of the carbon deposition prevention layer comprises the following steps: coating the silicon nitride slurry on the surface of the catalyst by adopting a surface shaking and sticking method, then stirring for 3 hours, standing for 14 hours, and roasting for 5 hours at the temperature of 700 ℃.

The silicon nitride slurry is a mixture of 2.25mol of ammonia water, 1mol of sodium silicate and 7.25mol of isopropanol, in the present embodiment, the nitrogen source is ammonia water, in other embodiments, the nitrogen source can also be tetramethylammonium hydroxide, and the technical effects of the present embodiment can be achieved, and also within the protection range of the present embodiment, in the present embodiment, the molar ratio of the nitrogen source, the sodium silicate and the isopropanol is 2.25: 1: 7.25, in other embodiments, the molar ratio of the nitrogen source, the sodium silicate and the isopropanol can be within the range of (1.5 ~ 3: 1: 2.5 ~ 12), and the technical effects of the present embodiment can be achieved, and are within the protection range of the present embodiment.

Example 3

and step S1: zeolite molecular sieve silica gel is used as adsorbent, and the adsorption temperature is controlled to be-30 ℃, and the space velocity is controlled to be 1000 h^-1Carrying out deep dehydration treatment on the raw material gas, namely methane chloride; in this embodiment, silica gel is used as the adsorbent, and in other embodiments, zeolite molecular sieves such as 3A, 4A, 5A, 13X, activated alumina, etc. may also be used as the adsorbent, all of which achieve the technical effects of this embodiment and are within the scope of this embodiment.

And step S2: magnesium fluoride in metal fluoride is used as an adsorbent, the adsorption temperature is controlled to be 70 ℃, and the space velocity is controlled to be 200h^-1Carrying out deep dehydration treatment on raw material gas hydrogen fluoride; in this embodiment, magnesium fluoride is used as the adsorbent, and in other embodiments, metal fluorides such as sodium fluoride, potassium fluoride, calcium fluoride, and aluminum fluoride may also be used as the adsorbent, all of which achieve the technical effects of this embodiment and are within the scope of this embodiment.

And step S3: zeolite molecular sieve 13X is used as adsorbent, and the adsorption temperature is controlled at 70 ℃, and the space velocity is controlled at 200h^-1And carrying out deep dehydration treatment on the oxygen-containing gas. Wherein the oxygen-containing gas is air; in this embodiment, zeolite molecular sieve 13X is used as the adsorbent, and in other embodiments, zeolite molecular sieves such as 3A, 4A, and 5A, activated alumina, and silica gel can be used as the adsorbent, which can achieve the technical effects of this embodimentAre within the scope of the present embodiment. In the present embodiment, the oxygen-containing gas is air, and in other embodiments, the oxygen-containing gas may also be oxygen or one of mixed gases, wherein the mixed gas is formed by mixing one of nitrogen or rare gas with oxygen, both technical effects of the present embodiment can be achieved, and all of them are within the protection scope of the present embodiment.

And step S4: methyl chloride, hydrogen fluoride and an oxygen-containing gas are mixed at a ratio of 0.5mol/min to 2 mol/min: feeding the mixture into a reactor provided with a catalyst at a feeding rate of 0.15 mol/min for fluorine-chlorine exchange reaction, and producing a semi-finished product. The reactor adopts a fixed bed reactor, and the reaction temperature in the reactor is controlled to be 150 ℃, the reaction pressure is controlled to be 2.0 MPa, and the airspeed is controlled to be 50 h^-1。

The catalyst takes a trivalent chromium compound as a catalyst active body, takes silicon-aluminum microspheres as a carrier, takes indium, copper, zinc, nickel, cobalt, magnesium, tungsten, molybdenum, rhenium or ruthenium as a catalyst auxiliary agent, and adopts an impregnation method to load the catalyst active body and the catalyst auxiliary agent on the surface of the carrier. The content of the catalyst active body is 3wt%, the content of the catalyst auxiliary agent is 2.0 wt%, and the balance is the carrier. Wherein the trivalent chromium compound is one of chromium oxide, chromium chloride, chromium nitrate or chromium hydroxide; the aperture of the silicon-aluminum microsphere is 4A, and the specific surface area is 1000 m²/m³The pore volume is 0.2mL/g, and the silicon-aluminum microsphere is an alumina microsphere, a zeolite molecular sieve microsphere or a silicon dioxide microsphere.

The outer surface of the catalyst is coated with silicon nitride as a carbon deposition prevention layer, the thickness of the carbon deposition prevention layer is 2mm, the surface aperture ratio is 80%, and the preparation process of the carbon deposition prevention layer comprises the following steps: coating the silicon nitride slurry on the surface of the catalyst by adopting a surface shaking and sticking method, then stirring for 2 hours, standing for 13 hours, and roasting for 4 hours at the temperature of 600 ℃.

The silicon nitride slurry is a mixture of 1.5mol of tetramethylammonium hydroxide, 1mol of sodium silicate and 12mol of isopropanol, in this embodiment, the nitrogen source is tetramethylammonium hydroxide, in other embodiments, the nitrogen source can also be ammonia water, and the technical effects of this embodiment can be achieved, and also within the protection scope of this embodiment, in this embodiment, the molar ratio of the nitrogen source, sodium silicate and isopropanol is 1.5: 1: 12, in other embodiments, the molar ratio of the nitrogen source, sodium silicate and isopropanol can be within the range of (1.5 ~ 3): 1 (2.5 ~ 12), and the technical effects of this embodiment can be achieved, and are all within the protection scope of this embodiment.

Example 4

and step S1: active alumina is adopted as an adsorbent, the adsorption temperature is controlled to be 70 ℃, and the space velocity is controlled to be 200h^-1Carrying out deep dehydration treatment on the raw material gas, namely methane chloride; in this embodiment, activated alumina is used as the adsorbent, and in other embodiments, zeolite molecular sieves such as 3A, 4A, 5A, 13X, silica gel, etc. may also be used as the adsorbent, all of which achieve the technical effects of this embodiment and are within the scope of this embodiment.

And step S2: calcium fluoride in metal fluoride is used as an adsorbent, the adsorption temperature is controlled to be-30 ℃, and the space velocity is controlled to be 1000 h^-1Carrying out deep dehydration treatment on raw material gas hydrogen fluoride; in this embodiment, calcium fluoride is used as the adsorbent, and in other embodiments, metal fluorides such as sodium fluoride, potassium fluoride, aluminum fluoride, magnesium fluoride and the like may also be used as the adsorbent, all of which achieve the technical effects of this embodiment and are within the protection scope of this embodiment.

And step S3: activated alumina is used as adsorbent, such as 3A, 4A, 5A, 13X, activated alumina, silica gel, etc. The adsorption temperature is controlled to be-30 ℃ and the space velocity is controlled to be 1000 h^-1And carrying out deep dehydration treatment on the oxygen-containing gas. Wherein the oxygen-containing gas is a mixed gas, and the mixed gas is formed by mixing one of nitrogen or rare gas with oxygen. In this embodiment, activated alumina is used as the adsorbent, and in other embodiments, zeolite such as 3A, 4A, 5A, 13X, silica gel, etc. may be usedThe sub-sieve is an adsorbent, and can achieve the technical effects of the embodiment, and is within the protection range of the embodiment. In this embodiment, the oxygen-containing gas is a mixed gas, and in other embodiments, the oxygen-containing gas may also be one of oxygen and air, both of which can achieve the technical effects of this embodiment, and are within the protection scope of this embodiment.

And step S4: methyl chloride, hydrogen fluoride and an oxygen-containing gas are mixed at a ratio of 0.5mol/min to 5mol/min: feeding the mixture into a reactor provided with a catalyst at a feeding rate of 0.05mol/min for fluorine-chlorine exchange reaction, and producing a semi-finished product. The reaction temperature in the reactor is controlled to be 400 ℃, the reaction pressure is 0.05 MPa, and the space velocity is 1000 h^-1。

The catalyst takes a trivalent chromium compound as a catalyst active body, takes silicon-aluminum microspheres as a carrier, takes indium, copper, zinc, nickel, cobalt, magnesium, tungsten, molybdenum, rhenium or ruthenium as a catalyst auxiliary agent, and adopts an impregnation method to load the catalyst active body and the catalyst auxiliary agent on the surface of the carrier. The content of the catalyst active body is 20 wt%, the content of the catalyst auxiliary agent is 0.1wt%, and the balance is the carrier. Wherein the trivalent chromium compound is one of chromium oxide, chromium chloride, chromium nitrate or chromium hydroxide; the aperture of the silicon-aluminum microsphere is 10A, and the specific surface area is 400m²/m³The pore volume is 2.0 mL/g, and the silicon-aluminum microsphere is an alumina microsphere, a zeolite molecular sieve microsphere or a silicon dioxide microsphere.

The outer surface of the catalyst is coated with silicon phosphide as a carbon deposition prevention layer, the thickness of the carbon deposition prevention layer is 5mm, the surface aperture ratio is 50%, and the preparation process of the carbon deposition prevention layer comprises the following steps: and coating the silicon phosphide slurry on the surface of the catalyst by adopting a spray coating method, stirring for 4 hours, standing for 15 hours, and roasting for 7 hours at the temperature of 800 ℃.

Example 5

And step S2: sodium fluoride in metal fluoride is used as an adsorbent, the adsorption temperature is controlled to be 0 ℃, and the space velocity is controlled to be 600 h^-1Carrying out deep dehydration treatment on raw material gas hydrogen fluoride; in this embodiment, sodium fluoride is used as the adsorbent, and in other embodiments, metal fluorides such as potassium fluoride, calcium fluoride, aluminum fluoride, magnesium fluoride and the like may also be used as the adsorbent, all of which can achieve the technical effects of this embodiment and are within the protection scope of this embodiment.

And step S3: the 4A zeolite molecular sieve is used as an adsorbent, and the adsorption temperature is controlled to be 20 ℃. Space velocity of 600 h^-1And carrying out deep dehydration treatment on the oxygen-containing gas. Wherein the oxygen-containing gas is oxygen; in this embodiment, the zeolite molecular sieve 4A is used as the adsorbent, and in other embodiments, zeolite molecular sieves such as 3A, 5A, and 13X, activated alumina, and silica gel may also be used as the adsorbent, all of which achieve the technical effects of this embodiment and are within the scope of this embodiment. In this embodiment the oxygen-containing gas is oxygen, in other embodimentsThe oxygen-containing gas may be air or a mixture of air and oxygen, wherein the mixture is formed by mixing one of nitrogen or rare gas with oxygen, and the technical effects of the present embodiment can be achieved, all of which are within the protection scope of the present embodiment.

And step S4: introducing methyl chloride, hydrogen fluoride and oxygen-containing gas into a reactor provided with a catalyst at the feeding rates of 0.5mol/min, 3.5 mol/min and 0.1 mol/min respectively to perform fluorine-chlorine exchange reaction, and producing a semi-finished product. The reactor adopts a fixed bed reactor, and the reaction temperature in the reactor is controlled to be 275 ℃, the reaction pressure is controlled to be 0.05 MPa, and the space velocity is controlled to be 520 h^-1。

The catalyst takes a trivalent chromium compound as a catalyst active body, takes silicon-aluminum microspheres as a carrier, takes indium, copper, zinc, nickel, cobalt, magnesium, tungsten, molybdenum, rhenium or ruthenium as a catalyst auxiliary agent, and adopts an impregnation method to load the catalyst active body and the catalyst auxiliary agent on the surface of the carrier. The content of the catalyst active body is 15 wt%, the content of the catalyst auxiliary agent is 1.05 wt%, and the balance is the carrier. The aperture of the silicon-aluminum microsphere is 7A, and the specific surface area is 700 m²/m³The pore volume was 1.1 mL/g. It should be noted that, in this embodiment, the trivalent chromium compound is chromium oxide, and in other embodiments, the trivalent chromium compound may also be one of chromium chloride, chromium nitrate, or chromium hydroxide, and all of the technical effects of this embodiment can be achieved are within the scope of protection of this embodiment. The silica-alumina microspheres in this embodiment may be alumina microspheres, zeolite molecular sieve microspheres, or silica microspheres.

Comparative example 1

The main differences between this comparative example 1 and example 5 are: in step S4, the carbon deposit preventive layer is not coated on the surface of the catalyst.

Comparative example 2

The main differences between this comparative example 2 and example 5 are: in the step S4, the surface of the catalyst is not coated with the carbon deposit prevention layer, and the step S5 is: the semi-finished product is primarily purified and separated to obtain a finished product.

Comparative example 3

The main differences between this comparative example 3 and example 5 are: comparative example 2 did not have the step of S3.

Comparative example 4

The main differences between this comparative example 4 and example 5 are: the step of S5 is: the semi-finished product is primarily purified and separated to obtain a finished product.

Test example 1

The experimental example used to illustrate the evaluation method of the purity of monofluoromethane the content of oxygen + argon, nitrogen, carbon monoxide, carbon dioxide and other fluorocarbons in monofluoromethane synthesized in example 1 ~ 5 and comparative example 1 ~ 4 was determined by the cut sample injection method specified in GB/T28726 using the equipment agilent 7820. the content of water in monofluoromethane synthesized in example 1 ~ 5 and comparative example 1 ~ 4 was determined by the cavity ring-down spectroscopy in GB/T5832.3 using a cavity ring-down spectroscopy system (Tiger optics cavity ring-down water analyzer Halo-LP).

Pre-separation column, 316L stainless steel column with length of about 2m and inner diameter of 2mm, and Porapak Q (high molecular polymer) with particle size of 0.18mm ~ 0.25.25 mm.

The chromatographic column I is a 316L stainless steel column with the length of about 2m and the inner diameter of 2mm, and is filled with a 5A molecular sieve with the particle size of 0.18mm ~ 0.25mm and is used for analyzing oxygen, argon, nitrogen and carbon monoxide components.

Chromatographic column II, 316L stainless steel column with length of about 2m and inner diameter of 2mm, which is filled with Porapak Q (high molecular polymer) with particle size of 0.18mm ~ 0.25.25 mm for analyzing carbon dioxide and other fluorocarbon components.

Standard samples: the component content is about 90% by volume, and the balance gas is helium.

The monofluoromethane purity calculation formula:

A=100-（A1+ A2+ A3+ A4+ A5+ A6+）*10^-4

in the formula:

a: purity of monofluoromethane (volume fraction), 10^-2；

A1: oxygen + argon content (volume fraction), 10^-6；

A2: nitrogen content (volume fraction), 10^-6；

A3: carbon monoxide content (volume fraction), 10^-6；

A4: carbon dioxide content (volume fraction), 10^-6；

A5: content (volume fraction) of other fluorocarbons, 10^-6；

A6: water content (volume fraction), 10^-6。

Test example 2

The present test example was conducted to describe the evaluation method of the conversion rate of methyl chloride and to measure the content of methyl chloride in the raw material neutralized product of example 1 ~ 5 and comparative example 1 ~ 3 by gas chromatography using a gas chromatograph, and to calculate the conversion rate of methyl chloride, specifically, 100. mu.L of syringe specification, 50. mu.L of microinjector, 2m long and 4mm inner diameter of chromatographic column, stainless steel column, dinonyl phthalate 102 support = 15: 100, column temperature 45 ℃, detection chamber temperature 90 ℃ and vaporization chamber temperature 100 ℃ and carrier gas (nitrogen gas) 34 mL/min.

Reading the concentration C of methane chloride in the feed gas₀（mg/m³) And the concentration C of monochloromethane in the product₁（mg/m³）。

Conversion of monochloromethane Z = (C)₀- C₁）/ C₀*100%。

The results of test example 1 and test example 2 are shown in Table 1 below

TABLE 1 conversion of monochloromethane in the monofluoromethane process and volume percent monofluoromethane in the product prepared in example 1 ~ 5 and comparative example 1 ~ 4

From example 1 ~ 5 in Table 1, the purity of the monofluoromethane prepared by the present invention was as high as 80%, and the conversion of monochloromethane could reach 80% or more, even though the monochloromethane reacted in comparative example 4 and the unreacted hydrogen fluoride were not returned to the reactor for recycling, the conversion of the obtained monochloromethane was 25% and much higher than that of the conventional monochloromethane (refer to comparative example 2, and the conversion of the conventional monochloromethane was 15% or less), and at the same time, it was found by comparing comparative example 1 with example 5 that the application of the carbon block layer on the surface of the catalyst would have a great influence on the performance of the catalyst, because the conventional catalyst was easily deposited with carbon, and the conversion of the entire reaction was severely affected.

In conclusion, the invention provides a preparation method of monofluoromethane with high conversion rate. Firstly, the method adopts a coating technology to coat the anti-carbon deposition layer of silicon nitride or silicon phosphide on the outer surface of the traditional catalyst, thereby avoiding a large amount of carbon deposition on the outer surface of the catalyst, effectively avoiding the carbon deposition and the activity reduction of a catalyst pore passage, and improving the conversion rate of monofluoromethane. Secondly, oxygen-containing gas is introduced in the preparation process to timely combust the byproduct methane, so that the byproduct methane is prevented from being attached to the outer surface of the catalyst, thereby effectively preventing carbon deposition and activity reduction of catalyst pore channels and improving the conversion rate of monofluoromethane; meanwhile, the byproduct methane is combusted in time, the separation difficulty of the monofluoromethane and impurities of a methane low separation system is reduced, and the subsequent separation and purification efficiency is obviously improved. And thirdly, separating the semi-finished product at the outlet of the reactor for fluorine-chlorine exchange, and returning the unreacted raw materials to the reactor for recycling, so that the utilization rate of the raw material gas is improved.

The embodiments described above are some, but not all embodiments of the invention. The detailed description of the embodiments of the present invention is not intended to limit the scope of the invention as claimed, but is merely representative of selected embodiments of the invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Claims

1. A preparation method of monofluoromethane with high conversion rate is characterized by comprising the following steps:

and step S3: carrying out deep dehydration treatment on the oxygen-containing gas; the oxygen-containing gas is oxygen, air or a mixed gas, and the mixed gas is formed by mixing oxygen and one of nitrogen or rare gas;

and step S4: performing fluorine-chlorine exchange reaction on the methane chloride, the hydrogen fluoride and the oxygen-containing gas in a reactor under the condition of a catalyst to generate a semi-finished product;

2. The method for preparing monofluoromethane with high conversion rate according to claim 1, wherein in the step S4, the outer surface of the catalyst is coated with silicon nitride or silicon phosphide as a carbon deposition prevention layer, the thickness of the carbon deposition prevention layer is 2 ~ 5mm, the surface opening rate is 50 ~ 80%, and the carbon deposition prevention layer is prepared by coating silicon nitride slurry or silicon phosphide slurry on the surface of the catalyst by a surface shaking and adhering method, stirring for more than 2 hours, standing for more than 12 hours, and roasting at 600 ~ 800 ℃ for more than 4 hours.

3. The method for preparing high-conversion-rate monofluoromethane according to claim 2, wherein in the step S4, the silicon nitride slurry is a mixture of a nitrogen source, sodium silicate and isopropyl alcohol, the nitrogen source is ammonia water or tetramethylammonium hydroxide, the silicon phosphide slurry is a mixture of a phosphorus source, sodium silicate and isopropyl alcohol, the phosphorus source is phosphoric acid or phosphorous acid, and the molar ratio of the nitrogen source or the phosphorus source, the sodium silicate and the isopropyl alcohol is (1.5 ~ 3): 1 (2.5 ~ 12).

4. The method of claim 1, wherein in step S4, the catalyst comprises trivalent chromium compound as a catalyst active entity, silica-alumina microspheres as a carrier, and indium, copper, zinc, nickel, cobalt, magnesium, tungsten, molybdenum, rhenium, or ruthenium as a catalyst promoter, and the catalyst active entity and the catalyst promoter are loaded on the surface of the carrier by an impregnation method.

5. The method of claim 4, wherein the catalyst active material is 3 ~ 20 wt%, the catalyst promoter is 0.1 ~ 2.0.0 wt%, and the balance is a carrier.

6. The method of claim 5, wherein the trivalent chromium compound is one of chromium oxide, chromium chloride, chromium nitrate, and chromium hydroxide.

7. The method of claim 4, wherein the silica-alumina microspheres have a pore size of 4 ~ 10A and a specific surface area of 400 ~ 1000 m²/m³The pore volume was 0.2 ~ 2.0.0 mL/g.

8. The method of claim 7, wherein the silica-alumina microspheres are alumina microspheres, zeolite molecular sieve microspheres, or silica microspheres.

9. The process of claim 1, wherein in the step S4, the conditions of the fluorine-chlorine exchange reaction are reaction temperature 150 ~ 400 ℃, reaction pressure 0.05 ~ 2.0 MPa, and space velocity 50 ~ 1000 h^-1The feed molar ratio of the methyl chloride, the hydrogen fluoride and the oxygen-containing gas is 1 (4 ~ 10) to (0.1 ~ 0.3.3).

10. The method of claim 9, wherein in step S5, the preliminary purification is performed by distillation, and the separated methyl chloride and anhydrous hydrogen fluoride are collected in a buffer tank connected to the inlet of the reactor.