KR100286118B1 - Method for preparing tetrafluoroethylene - Google Patents

Abstract

PURPOSE: Provided is a method for preparing tetrafluoroethylene, which can prepare ethylene tetrafluoride with a high yield by supplying calories requisite for pyrolysis reaction in a short time. CONSTITUTION: The method comprises the steps of (i) charging mineral particles of carbon component nonreactive with byproduct or gaseous reactant into reactor; (ii) supplying the gaseous reactant to the lower of the reactor so as to flow from the lower of the reactor to the top of the reactor, and forming a fluidized bed flowing the mineral particles; (iii) heating the fluidized bed to the temperature of 650-1,000 deg.C for the pyrolysis of the gaseous reactant; (iv) cooling the pyrolyzed product, and isolating and recovering the cooled product.

Description

Process for preparing ethylene tetrafluoride

The present invention relates to a method for producing tetrafluoroethylene (tetrafluoroethylene: CF ₂ = CF ₂ , hereinafter referred to as 'TFE') by pyrolyzing hydrogen fluoride hydrocarbon at high temperature at high speed. More specifically, the present invention relates to a method for preparing TFE by supplying the amount of heat required for a pyrolysis reaction within a short reaction time to pyrolyze fluorinated hydrocarbon fluoride including fluorine.

Polytetrafluoroethylene, which is most used industrially among fluorine resins, is produced through polymerization process using TFE as a monomer. In addition, TFE is the most important raw material of ethylene fluoride since it is used as a core basic raw material of other fluorine compounds or resins.

TFE for this purpose is usually prepared by thermal decomposition of fluorinated hydrocarbons containing fluorine at high temperature. In general, the molecular formula of the raw material of TFE is C _l H _m Cl _n F _o [where l, m, o = 1, 2, 3, ...; n = 0, 1, 2, ..], which is generally expressed as carbon number (l) <10, ratio of fluorine / hydrogen atom (o / m) and fluorine / carbon source The values of the ratio of embroidery (o / l) are usually one or more. Among them, chlorodifluoromethane (CHClF ₂ , hereinafter referred to as 'R22') or trifluoromethane (CHF ₃ ) is the most widely used commercially as a raw material of hydrocarbon fluoride for the production of TFE. Their pyrolysis scheme can be represented as follows:

2 CHClF _2- → CF ₂ = CF ₂ + 2 HCl

2 CHF _3- → CF ₂ = CF ₂ + 2 HF

Both of the pyrolysis reactions occur at high temperatures of 650 ~ 1,000 ° C., and there are many side reactions, and the produced TFE is continuously converted at high temperatures to produce various by-products. Therefore, a short reaction time is required to increase reaction selectivity. Therefore, in the present invention, the pyrolysis of R22, which is currently most used for TFE production, will be described as a TFE production method representing pyrolysis of hydrocarbon fluoride for TFE production.

As such, the high speed pyrolysis reaction at high temperature is a matter of how quickly the heat of reaction is efficiently supplied within a short reaction time. In the pyrolysis process of this characteristic, a tubular reactor has been mainly used commercially. According to Ullmann's Encyclopedia of Industrial Chemistry, Vol. A11, pp. 361, VCH, the conversion of these raw materials is less than 30% when heating the walls of metal or carbon tubular reactors and supplying R22 into them. And the TFE selectivity in the reaction product produced by the R22 conversion is below 83% level. As such, when the reactor is lengthened to increase the conversion rate (= converted R22 moles / number of supplied R22 moles) in the tubular reactor by supplying only R22, the selectivity of the TFE (= 2 x generated TFE is increased). As the number of moles / moles converted R22) becomes low, it is difficult to increase the TFE yield (= 2 x moles of generated TFE / number of supplied R22 moles) more than 20%, which is the product of conversion and selectivity. The root cause of this problem is that due to the limited heat transfer area of the reactor tube, the amount of heat required for R22 pyrolysis cannot be supplied within a limited reaction time, ie within the reactor residence time.

To solve this problem, German patent 1 073 475 (1958) has shown that incorporation of steam into the reaction can improve TFE selectivity by about 65%.

To further improve this, British patent GB 960 309 (1962) proposed a method of pyrolysing a mixture of high temperature superheated steam in R22 and feeding it to a tubular reactor. According to this method, superheated steam of 800-1,000 ° C. (based on the inlet temperature of the reactor pyrolysis zone) must be supplied so that the temperature of the reaction gas exiting the pyrolysis zone of the tubular reactor can be 650-800 ° C.

The amount and temperature of the superheated steam not only heat the supplied R22 to the temperature range of the pyrolysis zone but also supply the reaction heat for the pyrolysis process, which is an endothermic reaction, so that the mixture of the reaction gas and steam is 650-800 ° C at the outlet of the reaction zone. It should be sufficient to provide all the heat to be kept in range. Therefore, in order to obtain a high reaction yield, the dilution rate of R22 by such superheated steam must be very high as suggested in the above patent. Therefore, in order to generate and procure a large amount of superheated steam at 800-1,000 ° C to be 10 times or more of the number of moles of R22, the installation of a large combustion furnace is essential and the burden of environmental problems due to the combustion of fuel is increased. Therefore, while supplying superheated steam to the tubular reactor, the wall surface of the reactor tube has been electrically heated to supply the amount of heat required for pyrolysis. Due to these constraints, even in commercial TFE manufacturing processes, it is common to operate at a level of 50-60% yield of TFE.

In addition, as described in the patent, the tubular reactor is more difficult to operate and control the reactor than in the case of isothermal reaction because of the adiabatic reaction characteristic that the temperature varies depending on the internal position.

On the other hand, to prevent further side reactions of the resulting TFE, the mixture of reaction product and excess steam must be quenched immediately at the outlet of the reaction zone. At this time, the heat capacity of the reaction mixture is large, and the burden of the quenching process is also increased.

In addition to these problems, there is also a problem in that the supply of superheated steam higher than the pyrolysis reaction temperature and the heating of the reactor tube wall generate and accumulate coke material at the inner wall of the tube or at the outlet of the reactor, thereby making continuous reactor operation impossible.

In order to solve the problems of the pyrolysis process by the tubular reactor that requires the use of superheated steam, US Patent 4,849,554 (1989) recently proposed a high frequency induction heating reactor. The reactor makes a large number of holes in the radial direction of the carbon-based heating element heated to 800-980 ° C. with electromagnetic induction coils so that the reaction gas can be pyrolyzed while passing through the holes. This method has the advantage of controlling the pyrolysis reaction closer to the isothermal reaction away from the adiabatic reaction using the superheated steam described above. However, the results of pyrolysis experiments exemplified in this patent have the disadvantage that the conversion rate of R22 is significantly lower than that of pyrolysis using superheated steam. Such a result can be sufficiently predicted considering that the heat of the heating element cannot be sufficiently supplied with the reaction gas in the short time passing through the heating element due to the limited heat transfer effect between the heating element and the reaction gas due to the limited heat transfer effect between the heating element and the reaction gas. .

As shown in the prior art, the production of TFE by pyrolysis of hydrocarbon fluoride requires a new method for preheating the reaction gas in a limited space and supplying the heat of reaction required for pyrolysis in a very short time. There is.

1 is an exemplary diagram for preparing ethylene tetrafluoride according to the present invention.

<Explanation of symbols for main parts of drawing>

1: solid particle 2: raw material gas

3: dilution gas 4: reaction gas mixture

6: heating means 7: raw material supply part

8 gas dispersing means 9 cooler

The inventors have focused on the fact that not only fast heat transfer is possible between a large number of heated particles and gas flows, but also that the surface area of the particles required for heat transfer is so large that a large amount of heat can be supplied to the gas around the particles within a limited space. The present invention has been achieved by experimentally confirming that TFE can be effectively produced by high-speed pyrolysis of hydrogen fluoride hydrocarbon at a high temperature.

Accordingly, the present invention, in the production of hydrogen tetrafluorohydrocarbons by the pyrolysis reaction using a hydrocarbon fluoride as a raw material, to fill the solid particles inside the reactor, so that the source gas flows through the solid particles to the top of the reactor After supplying the source gas into the reactor to form a fluidized bed for flowing the solid particles, and pyrolyzing the source gas by heating the fluidized bed to a temperature range of 650-1,000 ℃, the resulting product gas is cooled The present invention provides a method for producing ethylene tetrafluoride, which is characterized in that the separation and recovery are carried out.

The content of the present invention will be described in detail with reference to FIG.

When a high-speed gas flows from the bottom of the particle layer made of the solid particles 1 to the upper direction, the particles flow. Such a fluidized bed has a characteristic that the surface area of particles is very large and the velocity of gas flowing around the particles is very high so that heat transfer can occur very quickly and sufficiently not only between particles but also between particles and gases. These reaction gases can contribute directly to the flow of particles in the fluidized bed because both the raw materials and reaction products, such as R22 and methane trifluoride, are gases, such as high temperature TFE production reactions.

In addition, it is also necessary to supply an additional diluent gas because it is difficult to simultaneously satisfy the operating conditions such as particle flow, heat transfer, reaction yield, etc., depending on the size of the particles or the volume of the fluidized bed. As the diluting gas, a gas that does not directly participate in the reaction, such as carbon dioxide, carbon monoxide, or nitrogen, an inert gas such as argon or helium, and steam may be used.

The source gas 2 and the dilution gas 3 may be supplied separately as shown in FIG. 1, but may be premixed and supplied into the fluidized bed in the form of a mixed gas. At this time, the raw material of the hydrocarbon fluoride 2 may be preheated to about 600-700 ° C., and the diluent gas 3 may be preheated and supplied to a required temperature in consideration of the heating load inside the reactor.

The reaction gas mixture 4 which has passed through the fluidized bed is passed to a separation and recovery process via a cooler 9 which is cooled by a coolant 10 such as cooling water or cooling oil. Such a cooler may be connected to the outside of the reactor, but may also be installed in an empty space above the fluidized bed as illustrated in FIG. 1 so that the reaction gas mixture passing through the fluidized bed continues unnecessarily additional reaction at high temperature, resulting in low TFE selectivity. Loss can be solved.

Inside the fluidized bed, the intermixing of the particles is smooth and the contact with the solid wall 5 constituting the fluidized bed is constantly repeated. Especially, the radiant heat transfer between the particles occurs spontaneously in the range of 650-1,000 ° C, the pyrolysis temperature of the hydrocarbon fluoride. . Thus, the heated particles can be easily reheated by suitable heating means 6 even if the heat is lost to the reaction gas flowing in the surroundings. As the means 6 for heating the fluid particles, an electric resistance heating method which can be installed outside the fluidized bed wall 5 or inside the fluidized bed, and a radiation heating method such as microwave or infrared light can be used.

The solid particles (1) used in the fluidized bed are inorganic materials such as carbonaceous particles that do not react with the reaction source gas (2) or reaction by-products such as hydrogen chloride (HCl) and hydrogen fluoride (HF), such as activated carbon.

Since the method for producing TFE according to the present invention utilizes a fluidized bed as a heat transfer medium, it is possible to supply sufficient amount of heat to the reaction gas, thereby easily increasing the conversion rate of hydrocarbon fluoride which is a raw material.

On the other hand, according to the present invention it is possible to improve the TFE selectivity through pyrolysis. To this end, by adjusting the height of the fluidized bed, the average residence time of the reaction gas in the fluidized bed can be lowered to 0.2 seconds or less, and unlike conventional tubular reactors, it is possible to easily supply the amount of heat required for the reaction despite the short reaction time. . In practice, various methods can be used to supply the amount of heat required for the reaction while shortening the reaction time in the fluidized bed. For example, as illustrated in FIG. 1, the reactive gas supply unit supplies diluent gas through the gas dispersing means 8 while dividing and supplying the reaction source gas containing hydrogen fluoride through the nozzle or tubular supply unit 7. The height of the outlet of (7) is higher than the diluent gas dispersing means 8, so that there is a method of restricting the region where the pyrolysis reaction occurs in the fluidized bed to the top of the fluidized bed.

Therefore, in the present invention, the dilution gas is also supplied into the fluidized bed through the dilution gas dispersing means installed at the bottom of the reactor, and at the same time, the gas containing the hydrocarbon fluoride is supplied at a position higher than the dilution gas dispersing means. It may be supplied into the fluidized bed through the installed gas supply means.

In this case, the residence time of the reaction gas is limited to a short time, but in the fluidized bed region lower than the outlet of the gas supply unit 7, a space for sufficiently heating the fluidized bed particles by the heating means 6 is provided. Then, in addition to the direct heating of the upper reaction zone by the heating means 6, it is possible to additionally supply the amount of heat consumed in the reaction zone by natural particle mixing or forced convection and radiant heat transfer between the reaction zone and the heating zone.

As described above, the fluidized bed heating method proposed in the present invention can supply heat required for pyrolysis even during a short average residence time of the reaction gas, thereby increasing the conversion rate of hydrocarbon fluoride and the selectivity of TFE, thereby producing a high yield of TFE. Provide the means to do it.

Hereinafter, although an Example is given and this invention is demonstrated in detail, the content of this invention is not limited to an Example.

Example 1

In order to practice the present invention, a fluidized bed reactor was installed inside a cylindrical vessel made of stainless steel. As a fluidized bed reactor, a fluidized bed was formed therein as follows using a quartz tube having an inner diameter of 45 mm and a height of 500 mm.

Activated charcoal with an average particle diameter of 0.34 mm was used as a flowing particle and the amount was 183 g. A gas dispersion plate was installed in the lower part of the fluidized bed, and in the middle of the distribution plate, an R22 supply nozzle used as a raw material gas for TFE production was installed and the height was adjusted so that the raw material gas was supplied at a desired height inside the fluidized bed. Diluent gas and source gas were supplied to the fluidized bed to allow particles to flow. 90% of the nitrogen used as the dilution gas was preheated to about 500 ° C., and then supplied through a gas dispersion plate, and the remaining 10% of the diluted gas and the source gas were supplied. Was premixed and preheated to 300 ° C. and then fed through a nozzle to flow the particles. At this time, the feed rates of the hydrocarbon fluoride raw material R22 and the dilution gas were 0.12 mol / min and 0.29 mol / min, respectively, so that the dilution rate (= molar ratio of the dilution gas to the raw material gas) was 2.4. The height of the nozzle was adjusted so that the average time of the source gas staying inside the fluidized bed above the nozzle, that is, the reaction time was 0.173 seconds.

The particles inside the fluidized bed were heated by feeding microwaves at a frequency of 2450 MHz through a waveguide connected to the stainless steel vessel. Insulation was filled between the vessel and the fluidized bed reactor to insulate the reactor. Inside the fluidized bed, the thermolysis reaction temperature was kept constant at 760 ° C (within ± 3 ° C) using five thermocouples.

The upper portion of the fluidized bed was provided with an expansion zone having an inner diameter of 120 mm and a height of 300 mm to cool the outer wall, and the reaction gas exiting the region was cooled while passing through a cooler. The reaction pressure was maintained at 1.1 atmospheres based on the pressure inside this extended zone. In order to know the reaction result, a part of the cooled reaction gas was removed from the fluidized bed reactor outlet and the components of the reaction product were analyzed by gas chromatography.

As a result of the continuous R22 pyrolysis reaction by the above heating method, as summarized in Table 1, the conversion rate of the converted R22 and the selectivity of TFE in the reaction product were 87.8% and 64.8%, respectively. = Conversion x selectivity) of 56.9%.

Example 2

TFE was prepared in the same manner as in Example 1, except for the following conditions. The average particle diameter and the filling amount of the fluidized particles were 0.67 mm and 170 g, respectively, and the feed rates of the source gas (R22) and the diluent gas (nitrogen) were 0.31 mol / min and 1.22 mol / min, respectively, so that the dilution rate was 3.9. . Moreover, the fluidized bed reactor was continuously operated so that reaction temperature and reaction time might be 780 degreeC and 0.073 second, respectively.

As a result of the R22 pyrolysis reaction by the fluidized bed heating method, as summarized in Table 1, the conversion rate of the converted R22 and the selectivity of TFE in the reaction product were 81.4% and 81.2%, respectively, and the yield of TFE was 66.1%. appear.

Example 3

Using the reactor used in Example 1, TFE was prepared in the same manner as in Example 2 except for the following conditions. The feed rates of nitrogen as source gas R22 and dilution gas were 0.06 mol / min and 1.22 mol / min, respectively, so that the dilution rate was 20.3. Moreover, the fluidized bed reactor was continuously operated so that reaction time might be 0.066 second.

As a result of the R22 pyrolysis reaction by the fluidized bed heating method, as summarized in Table 1, the conversion rate of the converted R22 and the selectivity of TFE in the reaction product were 89.5% and 87.2%, respectively, and the yield of TFE was 78.0%. appear.

Example 4

Using the reactor used in Example 1, TFE was prepared in the same manner as in Example 3 except for the following conditions. The fluidized bed reactor was run continuously so that the reaction temperature and reaction time were 840 ° C. and 0.062 seconds, respectively.

As a result of the R22 pyrolysis reaction by the fluidized bed heating method, as summarized in Table 1, the conversion rate of the converted R22 and the selectivity of TFE in the reaction product were 93.3% and 68.0%, respectively, and the yield of TFE was 63.4%. appear.

Example 5

TFE was prepared in the same manner as in Example 1, except for the following conditions. The average particle diameter and the filling amount of the fluidized particles were 1.09 mm and 162 g, respectively, and the dilution ratio was 26.4 with the feed rates of nitrogen as the source gas (R22) and the diluent gas being 0.12 mol / min and 3.17 mol / min, respectively. Moreover, the fluidized bed reactor was continuously operated so that reaction temperature and reaction time might be 870 degreeC and 0.030 second, respectively.

As a result of the R22 pyrolysis reaction by the fluidized bed heating method, as summarized in Table 1, the conversion rate of converted R22 and the selectivity of TFE in the reaction product were 95.2% and 89.6%, respectively, and the yield of TFE was 85.3%. appear.

Example 6

Using the reactor used in Example 1, TFE was prepared in the same manner as in Example 5 except for the following conditions. Carbon dioxide (CO ₂ ) was used as the diluent gas instead of nitrogen. The feed rates of the source gas R22 and the dilution gas CO ₂ were 0.12 mol / min and 2.82 mol / min, respectively, so that the dilution rate was 23.5. Moreover, the fluidized bed reactor was continuously operated so that reaction time and reaction pressure might be 0.078 second and 2.1 atmospheres, respectively.

As a result of the R22 pyrolysis reaction by the fluidized bed heating method, as summarized in Table 2, the conversion rate of the converted R22 and the selectivity of TFE in the reaction product were 97.8% and 79.2%, respectively, and the yield of TFE was 77.4%. appear.

Example 7

Using the reactor used in Example 1, TFE was prepared in the same manner as in Example 5 except for the following conditions. Instead of nitrogen, helium (He), an inert gas, was used as the diluent gas. The feed rates of the source gas R22 and the dilution gas He were 0.12 mol / min and 2.50 mol / min, respectively, so that the dilution rate was 20.8. Moreover, the fluidized bed reactor was continuously operated so that reaction time might be 0.043 second.

As a result of the R22 pyrolysis reaction by the fluidized bed heating method, as summarized in Table 2, the conversion rate of R22 and the selectivity of TFE in the reaction product were 96.7% and 87.2%, respectively. Appeared.

Example 8

Using the reactor used in Example 1, TFE was prepared in the same manner as in Example 5 except for the following conditions. Only 81 g of 50% of Flow Example 5 with an average particle diameter of 1.09 mm was charged. Superheated steam at 500 ° C. was used as the diluent gas in place of nitrogen. Moreover, the dilution rate was set to 14.2 by supplying steam of 1.7 mol / min as diluent gas. On the other hand, the fluidized bed reactor was continuously operated so that the reaction time was 0.048 second.

As a result of the R22 pyrolysis reaction by the fluidized bed heating method, as summarized in Table 2, the conversion rate of the converted R22 and the selectivity of TFE in the reaction product were 97.2% and 84.3%, respectively, and the yield of TFE was 81.9%. appear.

Example 9

Using the reactor used in Example 1, TFE was prepared in the same manner as in Example 5 except for the following conditions. As source gas, methane trifluoride (CHF ₃ ) was supplied instead of R 22. Moreover, the fluidized bed reactor was continuously operated so that reaction temperature and reaction time might be 800 degreeC and 0.048 second, respectively.

As a result of the R22 pyrolysis reaction by the fluidized bed heating method, as summarized in Table 2, the conversion rate of the converted R22 and the selectivity of TFE in the reaction product were 92.3% and 87.5%, respectively, and the yield of TFE was 80.9%. appear.

Example 10

Using the reactor used in Example 1, TFE was prepared in the same manner as in Example 8 except for the following conditions. R22 and methane trifluoride (CHF ₃ ) were mixed at a molar ratio of 1: 1 as source gas, and the reaction time was supplied at a rate of 0.12 mol / min so that the reaction time was 0.037 seconds.

As a result of the R22 pyrolysis reaction by the fluidized bed heating method, as summarized in Table 2, the conversion rate of converted R22 and the selectivity of TFE in the reaction product were 95.8% and 86.7%, respectively, and the yield of TFE was 83.1%. appear.

As described above, the method of the present invention is much more effective than the conventional method in producing the TFE by pyrolysis of the reaction gas containing hydrocarbon fluoride. The main effects are as follows.

First, the present invention uses a fluidized bed of solid particles as a heat transfer means for supplying the amount of heat required for pyrolysis of hydrocarbon fluoride, thereby providing a means for obtaining a high yield of TFE due to its large heat transfer effect.

Secondly, according to the present invention, the conversion rate of hydrocarbon fluoride or the TFE selectivity in the reaction product can be easily adjusted according to the configuration of the fluidized bed, and the wide selection range of operating conditions allows the reactor to be manufactured economically and the optimization of the operating conditions is easy. Do.

Third, the present invention does not presuppose the supply of the superheated steam of 800 ~ 1,000 ℃ used in the conventional method allows to eliminate the process equipment necessary to generate, supply, recover and circulate a large amount of superheated steam. In addition, the burden on the pollution problem caused by such a process is also reduced according to the present invention. In addition, since a large amount of superheated steam is not used, the burden of the quenching process at the reactor outlet is greatly reduced.

Fourth, according to the reactor heating method according to the present invention, isothermal pyrolysis reaction is possible due to the smooth heat transfer effect in the fluidized bed. As a result, an unnecessary unnecessarily higher section is not generated at the reactor inner wall, the fluid particles, or the reactor outlet, so that coke generation and accumulation problems occurring at a higher temperature are significantly reduced than in the conventional adiabatic reaction system. This advantage allows the reactor operation to continue continuously.

Claims (8)

In the production of tetrafluorohydrocarbons by pyrolysis reaction using hydrocarbon fluoride as a raw material, the inside of the reactor is filled with inorganic particles of carbon components which do not react with the reaction source gas or reaction by-products, and flows from the bottom of the reactor to the top. Supplying a source gas to the bottom of the reactor to form a fluidized bed for flowing the inorganic particles, and pyrolyzing the source gas by heating the fluidized bed to a temperature range of 650-1,000 ° C., and then cooling the resulting product gas. Next, the method for producing ethylene tetrafluoride, characterized in that the separation and recovery. The method for producing ethylene tetrafluoride according to claim 1, wherein the hydrogen fluoride hydrocarbon is dichloromethane chloride, methane trifluoride, or a mixture thereof. The method of claim 1, wherein at least one diluent gas selected from the group consisting of carbon dioxide, carbon monoxide, nitrogen, argon, helium and steam is supplied to the fluidized bed in addition to the hydrocarbon fluoride. . The method of claim 1, wherein the height of the fluidized bed is adjusted such that the average residence time of the hydrocarbon fluoride staying in the fluidized bed is shorter than about 0.2 seconds. The method for producing ethylene tetrafluoride according to claim 1, wherein the heating means of the fluidized bed is at least one selected from the group consisting of electric resistance heating, microwave heating and infrared heating. The method for producing ethylene tetrafluoride according to claim 3, wherein the fluidized bed comprises a heating region in which only the diluent gas flows and a reaction region in which a gas containing the hydrocarbon fluoride flows. The dilution gas is supplied into the fluidized bed through the dilution gas dispersing means installed in the lower part of the reactor, and at the same time, the gas containing the hydrocarbon fluoride is supplied at a position higher than the dilution gas dispersing means. A method for producing ethylene tetrafluoride, characterized in that for feeding into the fluidized bed through the gas supply means installed. The method for producing ethylene tetrafluoride according to claim 1, wherein the inorganic particles of the carbon component which do not react with the reaction source gas or the reaction by-product are activated carbon.