KR101287974B1 - The preparation method of high-yield difluoromathane from cholorodifluoromethane using hydrodechlorination - Google Patents

Abstract

In the method for preparing difluoromethane of the present invention, a reaction preparation step for removing oxygen in a reactor including a metal supported catalyst having Pd supported on a porous catalyst carrier, and a mixture including hydrogen and liquefied chlorodifluoromethane in the reactor The reaction step of obtaining a reactant containing difluoromethane by hydrodechlorination on a supercritical fluid having a pressure in the reactor is 50 to 300 bar, the temperature in the reactor is 300 to 500 ℃, A cooling step of cooling, and a collecting step of collecting difluoromethane from the reactants. According to the method for producing difluoromethane, it is possible to increase the yield of difluoromethane, to increase the production by using a high temperature and high pressure reaction, it is possible to prevent the caulking of the catalyst. In addition, chlorodifluoromethane, which is known to destroy the ozone layer, may be recovered and used to convert it into reusable difluoromethane, thereby increasing its usefulness.

Description

The preparation method of high-yield difluoromathane from cholorodifluoromethane using hydrodechlorination}

The present invention relates to a method for producing difluoromethane, using the metal supported catalyst and chlorodifluoromethane supported Pd in a porous catalyst carrier on a high-temperature, high-pressure supercritical fluid to produce a high yield of difluoromethane Provide a way to.

Chloro floro carbon (CFC) is a colorless, odorless, non-toxic material that is thermally and chemically very stable and non-corrosive, and its use has increased rapidly with the development of the chemical industry since the 1960s.

In addition, it can be used in a wide range of applications such as refrigerants, propellants, blowing agents, cleaning agents, etc. come.

However, from the mid-1990s, CFCs have not been decomposed in the atmosphere, but have diffused into the stratosphere, destroying the ozone layer in the stratosphere and inducing global warming. Development is also desperately needed.

The treatment of CFCs can be divided into complete and partial decomposition methods, depending on the product treated.

The complete decomposition method is a method of completely decomposing and treating CFCs into harmless materials by using an incineration method or a plasma method. However, this method has problems in that it is possible to dispose of useful resources such as fluorine and to cause serious corrosion of the device by halogen compounds generated during decomposition. Therefore, a method of converting CFCs into substitutes and useful substances by using partial decomposition of CFCs has received much attention.

To convert CFCs into CFC substitutes using partial decomposition, CFCs can be converted to hydrochloroflorocarbons (HCFCs) or hydrofluorofluoro compounds (CFCs) using hydrodechlorination. , HFC).

On the other hand, HCFC has lower ozone depletion potential than CFC, but HCFC is also concerned about the destruction of ozone layer.

Accordingly, the ozone layer destruction index is zero because it does not contain chlorine, and the global warming potential (GWP) is low.

Meanwhile, as a method for preparing difluoromethane (CH ₂ F ₂ , HFC-32), which is a substance that can replace chlorodifluoromethane (CHF ₂ Cl, HCFC-22), dichloromethane There are a liquid phase method and a gas phase method prepared by adding hydrogen fluoride (HF) to (CH ₂ Cl ₂ ). In general, the reaction for synthesizing HFC-32 (CH ₂ F ₂ ) is mainly fluorination reaction by the addition of hydrogen fluoride (HF) to methylene chloride (CH ₂ Cl ₂ ) to proceed on the catalyst. .

However, in order to prepare HFC-32 (CH ₂ F ₂ ), which is a useful substance by using HCFC-22 (CHF ₂ Cl) which should be disposed of in the future, hydrodechlorination reaction to remove chlorine in the substance and add hydrogen Should proceed.

Conventional techniques for converting HCFC-22 (CHF ₂ Cl) into HFC-32 (CH ₂ F ₂ ) using as a raw material include a catalystless pyrolysis reaction and hydrodechlorination using an appropriate metal supported catalyst in the gas phase. However, the non-catalytic method requires a high reaction temperature of 700 ° C. or higher, low yield, and carbonization of the reactants, and thus, there is a disadvantage in that the flow of the tube of the reactor is blocked during the continuous reaction.

Hydrodehydrochlorination of HCFC-22 using a catalyst in the gas phase can produce HFC-32 at a reaction temperature of about 400 ° C., thereby preventing carbonization of the reactants and having a continuous reaction. .

In such gas phase, the dechlorination reaction using a catalyst mainly uses a metal-supported catalyst in which a Group VII transition metal is supported on a carrier. Among these catalysts, palladium (Pd) -supported catalysts are compared with other transition metals. Alternatively, it shows excellent performance in selectively removing chlorine atoms present in HCFC, and also has excellent catalytic activity.

But. When HFC-32 is prepared by hydrodechlorination of HCFC-22 in the gas phase using a Pd-based catalyst, the yield of HFC-32 is very low, less than 10%, and coking of the catalyst by reaction byproducts and There is a problem in that the activity of the catalyst is reduced by the generation of palladium carbide (PdC _x ) whose activity is weakened due to carbonization of the Pd catalyst.

An object of the present invention is to use hydrochloric dechlorination in supercritical fluid using chlorodifluoromethane (CHF ₂ Cl, HCFC-22) as a raw material and a palladium (Pd) catalyst supported on carbons having a high specific surface area. The reaction provides a high yield of difluoromethane (CH ₂ F ₂ , HCFC-23).

In order to achieve the above object, a method for preparing difluoromethane according to an embodiment of the present invention is a reaction preparation step for removing oxygen in a reactor containing a metal supported catalyst Pd-supported in a porous catalyst carrier, the reactor To a mixture containing hydrogen and liquefied chlorodifluoromethane, difluoromethane by hydrodechlorination over a supercritical fluid having a pressure in the reactor of 50 to 300 bar and a temperature of 300 to 500 ° C in the reactor. A reaction step of obtaining a reactant comprising a, a cooling step of cooling the reactant, and a collection step of collecting difluoromethane from the reactant.

The method for preparing difluoromethane further includes a catalyst activation step between the reaction preparation step and the reaction step, wherein the catalyst activation step injects hydrogen into the reactor, and the pressure in the reactor is 50 to 150 bar, The temperature in the reactor may be to include a step of activating the catalyst to 300 to 500 ℃.

The metal supported catalyst may be 0.5 to 20% by weight based on the total amount of Pd supported catalyst.

The porous catalyst carrier may be a carbon-based carrier.

In the catalyst activation step, the pressure and temperature in the reactor may be maintained for 30 minutes to 2 hours.

The method for preparing difluoromethane further includes an acidic material removing step of removing a reaction by-product including an acidic substance by passing through a neutralization reactor the reactant cooled in the cooling step between the cooling step and the collecting step. It may be.

In the reaction step, the mixture may include the hydrogen and the liquefied chlorodifluoromethane in a molar ratio of 10: 1 to 2: 1.

The cooling step may be performed by exchanging heat with water using a heat exchanger.

The neutralization reactor may be one containing sodium hydroxide (NaOH).

1 is a hydrodechlorination reaction of chlorodifluoromethane (CHF ₂ Cl, HCFC-22) in a supercritical fluid according to an embodiment of the present invention, difluoromethane (CH ₂ F ₂ , HCFC-23) It shows a system for obtaining.

Referring to FIG. 1, the hydrochlorination dechlorination reactor of chlorodifluoromethane (CHF ₂ Cl) is a high pressure reactor (10), high pressure hydrogen storage container (11), high pressure chlorodifluoromethane storage container (12), supply Mixer 20 for mixing of materials, electric heater 30 for supercritical fluid phase reaction, mass flow controller (MFC) 40, 41 for introducing feed material into high pressure reactor, reactants and Coolers (50, 51) for rapid cooling of the product, neutralization reactor (60) for removing generated acidic substances, pressure reducing valve (70) for flowing out the product at atmospheric pressure while maintaining the pressure inside the reactor, metal catalyst 80 may be included.

Hereinafter, a method for preparing difluoromethane of the present invention will be described with reference to FIG. 1.

The method for preparing difluoromethane of the present invention includes a reaction preparation step, a reaction step, a cooling step, and a collection step.

The method for preparing difluoromethane may further include a catalyst activation step between the reaction preparation step and the reaction step.

The method for producing difluoromethane is between the cooling step and the collection step. It may further comprise an acidic material removal step.

The reaction preparation step is a process of removing oxygen in the reactor containing the metal supported catalyst Pd is supported on the porous catalyst carrier. Removing the oxygen may include injecting hydrogen into the reactor.

The preparing of the reaction may include removing the oxygen in the high pressure reactor 10 by inserting the metal supported catalyst into the high pressure reactor 10 and injecting hydrogen gas into the reactor 10 at room temperature.

The metal supported catalyst is preferably a metal supported catalyst having Pd attached to the surface of the porous catalyst carrier. Porous catalyst carriers have a very large surface area because numerous pores are formed on the surface.

Application of the porous carbon-based carrier to the porous catalyst carrier is preferable in that it has a high surface area and stable properties from the corrosion reaction of HCl or HF, which is a material produced from hydrodechlorination.

Specifically, the porous catalyst carrier may be any one selected from the group consisting of activated carbon, carbon aerogel, graphane, and combinations thereof. The porous catalyst carrier may be bulk, plate, It may be in the form of pellets, balls, powders.

The metal supported catalyst may be 0.5 to 20% by weight based on the total amount of Pd supported catalyst, and may be 1 to 10% by weight.

When the supported amount of the Pd of the metal supported catalyst is less than 0.5% by weight, the reaction yield may be low, and when the supported amount exceeds 20% by weight, there may be no benefit of the reaction by the catalyst.

The catalyst activation step is to inject hydrogen into the reactor, the pressure in the reactor is 50 to 150 bar, the temperature in the reactor to 300 to 500 ℃ step to activate the catalyst.

The catalyst activation step is made while injecting hydrogen introduced into the high pressure reactor (10) through a high pressure flow controller (MFC) 41 from the hydrogen storage vessel (11) through a mixer 20 at a constant flow rate to the high pressure reactor. Can be.

The flow rate of the hydrogen gas introduced into the reactor is not particularly limited, but is preferably 50 to 1500 ml / min. When the flow rate of hydrogen is less than 50 ml / min, the time for activating the metal supported catalyst may be long, and when the flow rate of hydrogen exceeds 1,500 ml / min, hydrogen may be consumed without gain.

In the catalyst activation step, the high-pressure reactor 10 is injected with the hydrogen gas, and heated with the electric heater 30 so that the temperature in the reactor 300 to 500 ℃ and the pressure in the reactor 50 to 150 bar and By raising the pressure, it can be maintained for 30 minutes to 2 hours, preferably for 30 minutes to 1 hour. In this case, the catalyst can be sufficiently activated.

When maintaining the inside of the reactor at the temperature and pressure, the inside of the reactor is maintained in a supercritical fluid state, that is, a high-density gas state in which no liquefaction occurs even when compressed, thereby increasing the efficiency of the reaction step.

The reaction step is to inject a mixture containing hydrogen and liquefied chlorodifluoromethane in the reactor, hydrodechlorine on a supercritical fluid of 50 to 300 bar pressure in the reactor, 300 to 500 ℃ temperature in the reactor The reaction yields a reactant comprising difluoromethane.

In the reaction step, when maintaining the temperature and pressure in the reactor in the above range, the reactants hydrogen (critical temperature = -240.2 ℃; critical pressure = 12.93 bar) and CHF ₂ Cl (critical temperature = 96.2 ℃; critical pressure = 49.36 bar), and the product CHF ₃ (critical temperature = 25.7 ° C; critical pressure = 48.16 bar), CH ₂ F ₂ (critical temperature = 78.45 ° C; critical pressure = 58.3 bar) and CH ₄ (critical temperature =-82.7 The critical pressure = 45.96 bar) can be effectively maintained by maintaining a supercritical fluid condition in which hydrodechlorination can be effected effectively.

The reaction step may include the step of mixing the liquefied chlorodifluoromethane (CHF ₂ Cl) and hydrogen gas in the mixer 20 and introduced into the high-pressure reactor 10 to react in a supercritical fluid. When the liquefied chlorodifluoromethane and the hydrogen gas are mixed and then introduced into the reactor, the yield of the reaction can be increased.

Specifically, the chlorodifluoromethane (CHF ₂ Cl) is discharged from the high pressure HCFC-22 storage container 12, liquefied through the cooler 50, and then the high pressure hydrogen before being introduced into the high pressure reactor (10) By mixing the hydrogen introduced into the mixer 20 from the storage vessel and the mixer 20, the yield can be increased when introduced into the catalyst layer in the future.

In the reaction step, the mixture may include the hydrogen and the liquefied chlorodifluoromethane in a molar ratio of 10: 1 to 2: 1.

When the molar ratio of hydrogen: chlorodifluoromethane is less than 2: 1, the amount of hydrogen reacted during hydrodechlorination may be small, so that the yield of difluoromethane (CH ₂ F ₂ ) may be lowered. If the molar ratio of: chlorodifluoromethane exceeds 10: 1, hydrogen may be consumed without gain, which may be undesirable from an economic point of view.

In the reaction step, the pressure in the reactor is 50 to 300 bar, it is suitable that the temperature in the reactor is 300 to 500 ℃.

If the pressure in the reactor is less than 50 bar, a supercritical fluid phase suitable for conducting an effective hydrodechlorination may not be formed, and if the pressure in the reactor exceeds 300 bar, the process cost may rise. have.

If the temperature in the reactor is less than 300 ℃, the effective hydrodechlorination may not proceed, the conversion of chlorodifluoromethane may be lowered. When the temperature in the reactor exceeds 500 ℃, hydrodechlorination may proceed excessively, the selectivity of difluoromethane can be lowered and the selectivity of methane can be high, the yield of the reaction may be lowered .

When the reaction is carried out while maintaining the temperature and pressure in the reactor, the conversion rate of chlorodifluoromethane may be increased, and the selectivity of difluoromethane of the product may be increased, and chlorodi may be reacted even for a long time. The conversion of fluoromethane and the yield of difluoromethane may hardly decrease.

The cooling step is a step of cooling the reactants passed through the reaction step. The cooling step may include a step of quenching the material flowing out of the high pressure reactor 10 through the heat exchanger 51.

The cooling step is a heat exchanger (51) for exchanging the heat of the reaction material flowing out from the high-pressure reactor (10) after the hydrodechlorination reaction in a supercritical fluid, the inner tube is wound in the form of a coil using heat below zero It can be done through.

The acidic material removing step is a step in which the reactant cooled in the cooling step passes a neutralization reactor to remove reaction by-products containing acidic material.

The acidic material removing step may include passing the cooled reactant through a neutralization reactor 60 to remove reaction by-products including acidic materials that may be included in the reactant.

Specifically, the reactant passed through the heat exchanger 51 may be passed through a neutralization reactor 60 containing basic sodium hydroxide (NaOH) to remove acidic substances that may have been generated during hydrodechlorination.

The collection step is a step of collecting difluoromethane from the reactant. The collecting step may include collecting the gaseous reactant in the collection vessel by passing the reactant through the pressure reducing valve 70.

The present invention proceeds the hydrodechlorination reaction using a catalyst in a supercritical fluid, it is possible to increase the yield of the reaction by using a high material transfer rate and a fast heat transfer rate which is an advantage of the supercritical fluid. In addition, it is possible to significantly reduce the decrease in catalyst activity due to mass transfer, thereby rapidly increasing the activity of the catalyst, and to prevent coking of the catalyst due to its dissolving power to organic materials.

In addition, the reaction on the supercritical fluid can facilitate the desorption of the HFC-32 product generated on the surface of the catalyst and can inhibit the hydrogenation of HFC-32 into methane, thereby increasing the selectivity of HFC-32. . Finally, the reaction in the supercritical fluid is a high-pressure compression reaction process, so even a small capacity reactor can be used to increase the yield.

The present invention recovers a chlorodifluoromethane (CHF ₂ Cl, HCFC-22) refrigerant, which is expected to be banned in the future due to a high ozone layer destruction index and a high global warming index, and reused as a raw material. (CH ₂ F ₂ , HFC-32), using a supercritical fluidized hydrochlorination reaction using a Pd-based catalyst in a much higher yield than the reaction in the gas phase, difluoromethane (CH ₂ F ₂ , HFC-32).

The method for producing difluoromethane of the present invention can increase the yield of difluoromethane, can increase the production by using a high temperature and high pressure reaction, it is possible to prevent the caulking of the catalyst. In addition, chlorodifluoromethane, which is known to destroy the ozone layer, may be recovered and used to convert it into reusable difluoromethane, thereby increasing its usefulness.

1 illustrates a system for obtaining difluoromethane by hydrodechlorination of chlorodifluoromethane (CHF ₂ Cl) in a supercritical fluid according to an embodiment of the present invention.
FIG. 2 shows a system for hydrodechlorination of chlorodifluoromethane (CHF ₂ Cl) in continuous atmospheric pressure.
3 is a graph showing the conversion of chlorodifluoromethane and the yield of difluoromethane, trifluoromethane, methane of Example 1.
4 is a graph showing the conversion of chlorodifluoromethane and the yield of difluoromethane, trifluoromethane, methane of Comparative Example 1.
5 is a graph showing the conversion of chlorodifluoromethane and the yield of difluoromethane, trifluoromethane, methane of Comparative Example 2.
Figure 6 is a graph showing the conversion of chlorodifluoromethane and the yield of difluoromethane, trifluoromethane, methane of Comparative Example 3.
7 is a graph showing the conversion of chlorodifluoromethane and the yield of difluoromethane, trifluoromethane, methane of Comparative Example 4.
FIG. 8 is an X-ray diffraction (XRD) analysis of the catalyst before and after hydrodechlorination of the catalyst loaded with 5% by weight of Pd on activated carbon used in Example 1 and Comparative Example 1; The result is.

Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily carry out the present invention. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.

< Example  1>

Supercritical HCFC On -22 Pd Of activated carbon Chlorodifluoromethane using CHF ₂ Cl )of Hydrodechlorination

1 illustrates a system for obtaining difluoromethane by hydrodechlorination of chlorodifluoromethane (CHF ₂ Cl) in a supercritical fluid according to an embodiment of the present invention. Hereinafter, Embodiment 1 will be described with reference to FIG. 1.

2.0 g of 5% by weight of Pd / activated carbon is added to the central portion of the high temperature high pressure reactor (10) with a metal supported catalyst, and at a temperature of 750 ml / min at room temperature to remove oxygen in the high temperature high pressure reactor (10). Hydrogen was injected for 10 minutes.

After removing the oxygen in the high temperature high pressure reactor (10), hydrogen is continuously injected at a flow rate of 750 ml / min to reduce the catalyst and the internal temperature of the high temperature high pressure reactor is 400 ℃, the pressure of the high temperature high pressure reactor Was raised to 100 bar and the catalyst was activated (reduced) for 1 hour.

Hydrogen and chlorodifluoromethane liquefied using a cooler (40) were introduced into the mixer, mixed well, and then introduced into a high temperature high pressure reactor (10). At this time, the flow rate of chlorodifluoromethane introduced into the mixer 20 was set to 150 ml / min, and the molar ratio of hydrogen: chlorodifluoromethane was adjusted to 5: 1 to be introduced into the high temperature high pressure reactor 10. The internal temperature of the high temperature high pressure reactor 10 was kept constant at 400 ° C.

The reactant flowing out of the high temperature and high pressure reactor (10) was quenched by passing through a heat exchanger (40) which wound the inner tube in the form of a coil and exchanges heat with subzero water. The reactant passed through the heat exchanger 40 removes acidic substances, which may have been produced through the neutralization reactor 51 containing sodium hydroxide (NaOH), and then passes through the pressure reducing valve 70 to collect the gas sample collection vessel. Collected on.

The collected reactants were analyzed by gas chromatography, and the results are shown in FIG. 3.

< Comparative example  1>

On atmospheric pressure Pd Of activated carbon Using Chlorodifluoromethane (CHF ₂ Cl) Hydrodechlorination

FIG. 2 shows a hydrodechlorination system of chlorodifluoromethane (CHF ₂ Cl) in continuous atmospheric pressure. Referring to FIG. 2, the hydrodechlorination system is an atmospheric pressure reactor 10, a high pressure hydrogen storage container 11, a chlorodifluoromethane storage container 12, an electric heater 20 for high temperature reaction, and a supply. High pressure flow controllers (MFCs) 30 and 31 for introducing water into the high pressure reactor, coolers 40 for rapid cooling of product materials, neutralization reactors 50 for removing generated acidic substances, and metal catalysts (80). ). Hereinafter, Comparative Example 2 will be described with reference to FIG. 2.

In order to remove oxygen in the atmospheric pressure reactor 10, 2.0 g of activated carbon having a specific surface area of 600 m ² / g loaded with 5% by weight of Pd with a metal supported catalyst was put in the center portion of the atmospheric pressure reactor 10. And hydrogen was injected for 10 minutes at a flow rate of 750 ml / min at room temperature.

In order to activate the metal supported catalyst, while continuously injecting hydrogen gas at a flow rate of 750 ml / min, the temperature of the atmospheric pressure reactor 10 was raised to 400 ° C. using an electric heater 20, and the catalyst was heated for 1 hour. Reduced (activated).

After activating the catalyst, the chlorodifluoromethane gas was introduced into the atmospheric reactor 10 at a flow rate of 150 ml / min, and the hydrogen: chlorodifluoromethane molar ratio was adjusted to 5: 1, followed by hydrodechlorination. Proceeded.

At this time, the hydrogen and the chlorodifluoromethane were introduced and mixed at right angles to the cross-shaped joint pipe of stainless steel (SS316), and the K-thermocouple was installed on the upper portion of the catalyst of the atmospheric pressure reactor (10) for the reactor ( 10) The internal temperature was measured.

In order to prevent corrosion and scale, the atmospheric pressure reactor 10 used an Inconel 625 material having strong heat resistance and acid resistance, and connected to a thermocouple outside of the atmospheric pressure reactor 10, the center of the atmospheric pressure reactor 10 and The temperature was measured at each of the two places in the upper bottom.

The reactant flowing out of the atmospheric pressure reactor (10) was quenched through the air-cooled heat exchanger (40), and 900 mL of the exhaust material passed through the heat exchanger (40) for removal of acidic substances that may be generated during the high temperature reaction. After passing through the neutralization reactor (50), and passed through a silica gel tube for water removal was collected in the gas sample collection vessel.

The collected reactants were analyzed by gas chromatography and the results are shown in FIG. 4.

< Comparative example  2>

Supercritical HCFC On -22 Pd / γ- Al2O3 Using Chlorodifluoromethane (CHF ₂ Cl) Hydrodechlorination

The same method as in Example 1, except that the metal supported catalyst introduced into the high-temperature high-pressure reactor is a catalyst in which 5% by weight of Pd is supported on γ-Al ₂ O ₃ having a surface area of 160 m ² / g. Hydrochlorination of chlorodifluoromethane (CHF ₂ Cl) over supercritical HCFC-22 was carried out to give a reaction product containing difluoromethane.

The obtained reactant was analyzed by gas chromatography and the results are shown in FIG. 5.

< Comparative example  3>

Supercritical HCFC On -22 Ni Of activated carbon Chlorodifluoromethane using CHF ₂ Cl )of Hydrodechlorination

In the same manner as in Example 1, except that the metal supported catalyst introduced into the high temperature high pressure reactor 10 is a catalyst in which 20 wt% of Ni is supported on activated carbon having a surface area of 600 m ² / g. Hydrodechlorination of chlorodifluoromethane (CHF ₂ Cl) over critical HCFC-22 was carried out to obtain a reaction comprising difluoromethane.

The obtained reactant was analyzed by gas chromatography and the results are shown in FIG. 6.

< Comparative example  4>

Supercritical HCFC On -22 Ni Of SiO ₂ - Al ₂ O ₃ Using Chlorodifluoromethane (CHF ₂ Cl) Hydrodechlorination

Example 1 except that the metal supported catalyst introduced into the high temperature high pressure reactor 10 is a catalyst in which 58 wt% of Ni is supported on SiO ₂ -Al ₂ O ₃ having a surface area of 250 m ² / g. In the same manner, hydrodechlorination of chlorodifluoromethane (CHF ₂ Cl) on supercritical HCFC-22 was carried out to obtain a reaction comprising difluoromethane.

The obtained reactant was analyzed by gas chromatography and the results are shown in FIG. 7.

< Experimental Example  1>

Example  1 and Comparative example  1 of Of chlorofluoromethane  Conversion rate and Difluoromethane  Yield comparison

In order to compare the conversion rate and the product yield of the hydrodechlorination reaction of chlorofluoromethane on the supercritical HCFC-22 according to the present invention with the results of the atmospheric pressure, the experimental conditions are as shown in Table 1 below. 1 and Comparative Example 1 was carried out for 7 hours continuously and the results are shown in FIGS. 3 and 4. Experimental results of hydrodechlorination of chlorofluoromethane carried out continuously for 7 hours were as follows.

Experimental variable Example 1 Comparative Example 1 pressure 100 bar 1 bar Temperature 400 ° C 400 ° C catalyst 5 wt% Pd / activated carbon 5 wt% Pd / activated carbon Flow rate of chlorofluoromethane 150 ml / min 150 ml / min Hydrogen flow rate 750 ml / min 750 ml / min

3 is a graph showing the conversion of chlorodifluoromethane and the yield of difluoromethane, trifluoromethane, methane of Example 1, Figure 4 is a conversion rate of chlorodifluoromethane of Comparative Example 1 Graph showing the yield of difluoromethane, trifluoromethane, methane.

3 and 4, in the case of hydrodechlorination using 5% by weight of Pd / activated carbon in the supercritical HCFC-22 of Example 1, the conversion rate of HCFC-22 is 95%. It was very high and the yield of HFC-32 was also very high (85%). In addition, the yield of the side reaction trifluoromethane (CHF ₃ , HFCF-23) was very low, less than 2%, the yield of methane was also very low (10%).

In Comparative Example 1, when hydrodechlorination was carried out at the same reaction temperature using the same catalyst in gas phase HCFC-22, the conversion rate of HCFC-22 was very low (2 to 3%), and the yield of HFC-32 was 1 It was found to be very low (2% to 2%), so that the hydrodechlorination reaction in the gas phase was almost in progress.

Experimental Example 1 shows that the conversion rate of HCFC-22 and the yield of HFC-32 in the supercritical HCFC-22 reaction are superior to the reaction in the atmospheric pressure.

< Experimental Example  2>

Example  1 and Comparative example  2 of Of chlorofluoromethane  Conversion rate and Difluoromethane  Yield comparison

To determine the effect of varying catalyst on supercritical HCFC-22, the conversion of chlorofluoromethane (CHF ₂ Cl, HCFC-22) and the yield of difluoromethane (CH ₂ F ₂ , HFC-32) After performing the hydrodechlorination of Example 1 and Comparative Example 2 continuously in the experimental conditions as shown in Table 2, the results are shown in Figures 3 and 5.

Experimental variable Example 1 Comparative Example 2 pressure 100 bar 100 bar Temperature 400 ° C 400 ° C catalyst 5 wt% Pd / activated carbon 5 wt% Pd / γ-Al ₂ O ₃ Flow rate of chlorofluoromethane 150 ml / min 150 ml / min Hydrogen flow rate 750 ml / min 750 ml / min

5 is a graph showing the conversion of chlorodifluoromethane and the yield of difluoromethane, trifluoromethane, methane of Comparative Example 2.

3 and 5, hydrodechlorination was carried out under the same conditions as in Example 1 using a catalyst in which 5% by weight of Pd was supported on γ-Al ₂ O ₃ in Comparative Example 2. The conversion rate of HCFC-22 was very high at 100%. However, the yield of HFC-32 to be prepared was very low, less than 2%, and the yield of reaction by-product methane was very high, 95%. Therefore, when using 5% by weight of Pd / γ-Al ₂ O _{3 It} was found that methane is formed as the main product.

< Experimental Example  3>

Example  1 and Comparative example  3 of Of chlorofluoromethane  Conversion rate and Difluoromethane  Yield comparison

Experiment to determine the effect of conversion of chlorofluoromethane (CHF ₂ Cl, HCFC-22) and yield of difluoromethane (CH ₂ F ₂ , HFC-32) with varying catalyst on supercritical HCFC-22 Example 1 and Comparative Example 2 as shown in Table 3 after the conditions were performed for 7 hours in succession, the results are shown in Figures 3 and 6. Experimental results of hydrodechlorination of chlorofluoromethane carried out for 7 hours continuously were as follows.

Experimental variable Example 1 Comparative Example 3 pressure 100 bar 100 bar Temperature 400 ° C 400 ° C catalyst 5 wt% Pd / activated carbon 20 wt% Ni / activated carbon Flow rate of chlorofluoromethane 150 ml / min 150 ml / min Hydrogen flow rate 750 ml / min 750 ml / min

Figure 6 is a graph showing the conversion of chlorodifluoromethane and the yield of difluoromethane, trifluoromethane, methane of Comparative Example 3.

Referring to FIGS. 3 and 6, in the case of performing hydrodechlorination under the same conditions as in Example 1 using a catalyst having 20 wt% of Ni supported on activated carbon in Comparative Example 3, HCFC-22 The initial conversion of was very high at 90%, and the initial yield of HFC-32 was about 30%.

However, as the reaction progressed, the activity of hydrodechlorination of the Ni / activated carbon catalyst was weakened. After 7 hours, the conversion rate of HCFC-22 was reduced to 15%, and the HFC-32 yield was 10%. Decreased.

As a result, the catalyst having 20 wt% Ni supported on carbon applied in Comparative Example 3 had a low conversion rate of HCFC-22 under the same reaction conditions when 5 wt% compared to a catalyst supported on Pd activated carbon, and HFC It was confirmed that the yield of -32 was also low.

< Experimental Example  4>

Example  1 and Comparative example  4 of Of chlorofluoromethane  Conversion rate and Difluoromethane  Yield comparison

Experiment to determine the effect of conversion of chlorofluoromethane (CHF ₂ Cl, HCFC-22) and yield of difluoromethane (CH ₂ F ₂ , HFC-32) with varying catalyst on supercritical HCFC-22 Example 1 and Comparative Example 4 as shown in Table 4 after the conditions were performed for 7 hours in succession, the results are shown in Figures 3 and 7. Experimental results of hydrodechlorination of chlorofluoromethane carried out for 7 hours continuously were as follows.

Experimental variable Example 1 Comparative Example 4 pressure 100 bar 100 bar Temperature 400 ° C 400 ° C catalyst 5 wt% Pd / activated carbon 58 wt% Ni / SiO ₂ -Al ₂ O ₃ Flow rate of chlorofluoromethane 150 ml / min 150 ml / min Hydrogen flow rate 750 ml / min 750 ml / min

7 is a graph showing the conversion of chlorodifluoromethane and the yield of difluoromethane, trifluoromethane, methane of Comparative Example 4.

3 and 7, hydrodechlorination was carried out under the same conditions as in Example 1 using a catalyst in which 58 wt% of Ni was supported on SiO ₂ -Al ₂ O ₃ in Comparative Example 3. When proceeded for a time, the conversion of HCFC-22 was maintained at 40%, the yield of HFCF-32 was between 35-40%.

However, the yield of the side reaction material methane is very high (20-25%), so that in the Comparative Example 4, the catalyst in which 58% by weight of Ni is supported on SiO ₂ -Al ₂ O ₃ is 5% by weight of Pd on activated carbon. Compared with the supported catalyst, it was confirmed that the conversion rate of HCFC-22 was low and the yield of HFC-32 was low under the same reaction conditions.

As can be seen from the above results, when Pd converts HCFC-22 into HFC-32 on supercritical HCFC-22 by hydrodechlorination using a catalyst supported on a carbon-based support, HFC at a yield higher than 85% It was confirmed that -32 could be prepared, and it was confirmed that the conversion and yield hardly decreased even after long-term reaction.

<Evaluation of Activity of Catalyst>

FIG. 8 shows 5 wt% Pd / activated carbon before activation, 5 wt% Pd / activated carbon after activation, and 5 wt% Pd / activated carbon after hydrodechlorination on supercritical HCFC-22 in Example 1 And XRD analysis of 5 wt% Pd / activated carbon catalyst after hydrodechlorination on an atmospheric pressure in Comparative Example 1.

Referring to FIG. 8, it can be seen that a large amount of carbide (PdCx) is present in metal Pd atoms of 5% by weight of Pd / activated carbon before activation. Such carbide (PdCx) is not catalytically active, it is preferable to convert to a metal Pd by reducing in a hydrogen atmosphere before the reaction. As a result of activating the catalyst by reducing the catalyst for 1 hour after raising the temperature to 400 ° C. and the pressure to 100 bar in Example 1, it was confirmed that the amount of carbide (PdCx) was reduced to less than half.

On the other hand, the amount of PdCx does not increase in the XRD analysis result of performing hydrodechlorination on the supercritical HCFC-22 in Example 1, whereas the hydrogenation dechlorination on the atmospheric pressure in Comparative Example 1 is performed. XRD analysis showed that the amount of PdCx increased by about 50%. It is believed that this result is that since the Pd lattice on supercritical HCFC-22 is not easily poisoned with PdCx, the reactivity of the supercritical reaction can be maintained much higher than the gas phase reaction.

Although the preferred embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements of those skilled in the art using the basic concepts of the present invention defined in the following claims are also provided. It belongs to the scope of right.

<Description of the code of FIG. 1>
10: high pressure reactor 11, 12: high pressure storage container
20: mixer 30: electric heater
40, 41: high pressure flow controller 50, 51: cooler (heat exchanger)
60: neutralization reactor 70: pressure reducing valve
80: metal catalyst
<Description of the code of FIG. 2>
10: atmospheric reactor 11, 12: high pressure storage container
20: electric heater 30, 31: flow meter
40: cooler (heat exchanger) 50: neutralization reactor
60: metal catalyst

Claims (9)

A reaction preparation step of removing oxygen in a reactor including a metal supported catalyst having Pd supported thereon,
Injecting a mixture containing hydrogen and liquefied chlorodifluoromethane into the reactor, difluorinated by hydrodechlorination over a supercritical fluid having a pressure in the reactor of 50 to 300 bar, a temperature of 300 to 500 ℃ in the reactor A reaction step of obtaining a reactant including romethane,
A cooling step of cooling the reactant, and
Collection step of collecting difluoromethane from the reaction
Method for producing difluoromethane comprising a. The method of claim 1,
Further comprising a catalyst activation step between the reaction preparation step and the reaction step,
The catalyst activation step is to inject hydrogen into the reactor, the pressure in the reactor is 50 to 150 bar, the temperature in the reactor to 300 to 500 ℃ a method for producing a difluoromethane comprising the step of activating the catalyst. . The method of claim 1,
The metal supported catalyst is a method for producing difluoromethane, wherein the amount of Pd supported is 0.5 to 20% by weight based on the entire metal supported catalyst. The method of claim 1,
The porous catalyst carrier is a method for producing difluoromethane that is a carbon-based carrier. The method of claim 2,
In the catalyst activation step, the pressure and temperature in the reactor, it is maintained for 30 minutes to 2 hours. The method of claim 1,
Between the cooling step and the collection step, the reactant cooled in the cooling step further comprises an acidic material removing step of removing the reaction by-products containing acidic material through the neutralization reactor. The method of claim 1,
The method of preparing a difluoromethane in the reaction step comprises the hydrogen and the liquefied chlorodifluoromethane in a molar ratio of 10: 1 to 2: 1. The method of claim 1,
The cooling step is a method of producing difluoromethane is carried out by exchanging heat with water using a heat exchanger. The method according to claim 6,
The neutralization reactor is a method for producing difluoromethane containing sodium hydroxide (NaOH).

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