Method for producing dry etching gas

Abstract

Provided is a method for producing fluoromethane and 3,3,3-trifluoro-2-(trifluoromethyl)propanoyl fluoride ((CF.sub.3).sub.2CHCOF), which are useful as dry etching gases etc., safely and inexpensively with high purity. According to the method in which 1,1,3,3,3-pentafluoro-2-trifluoromethylpropyl methyl ether is pyrolyzed in a gas phase in the presence of a catalyst, the desired fluoromethane and 3,3,3-trifluoro-2-(trifluoromethyl)propanoyl fluoride can be obtained with high selectivity and high conversion of the starting material by a simple process in which a pyrolysis reaction is performed in a gas phase using the inexpensive starting material.

Claims

1. A method for producing fluoromethane and 3,3,3-trifluoro-2-(trifluoromethyl)propanoyl fluoride, the method comprising pyrolyzing 1,1,3,3,3-pentafluoro-2-trifluoromethylpropyl methyl ether in a gas phase in the presence of a -alumina catalyst and/or silica alumina catalyst.

2. The method according to claim 1, wherein the 1,1,3,3,3-pentafluoro-2-trifluoromethylpropyl methyl ether used as a starting material is obtained by reacting perfluoroisobutylene and methanol.

3. The method according to claim 1, comprising the steps of: (1) reacting perfluoroisobutylene and methanol to obtain 1,1,3,3,3-pentafluoro-2-trifluoromethylpropyl methyl ether; and (2) pyrolyzing the 1,1,3,3,3-pentafluoro-2-trifluoromethylpropyl methyl ether obtained in step (1) in a gas phase in the presence of a catalyst to obtain fluoromethane and 3,3,3-trifluoro-2-(trifluoromethyl)propanoyl fluoride.

4. The method according to claim 1, wherein the catalyst has a pore volume of 0.5 ml/g or more.

5. The method according to claim 1, wherein the reaction temperature of the pyrolysis reaction is in the range of 100 to 400 C.

6. The method according to claim 1, wherein the pressure during the pyrolysis reaction is in the range of 0.05 to 1 MPa.

7. The method according to claim 1, further comprising, after obtaining the pyrolyzed product comprising fluoromethane and 3,3,3-trifluoro-2-(trifluoromethyl)propanoyl fluoride, the step of cooling the product to separate it into a low-boiling-point component comprising the fluoromethane and a high-boiling-point component comprising the 3,3,3-trifluoro-2-(trifluoromethyl)propanoyl fluoride.

8. The method according to claim 1, further comprising, after obtaining the pyrolyzed product comprising fluoromethane and 3,3,3-trifluoro-2-(trifluoromethyl)propanoyl fluoride, the step of bringing the product into contact with water or an aqueous alkaline solution to remove the 3,3,3-trifluoro-2-(trifluoromethyl)propanoyl fluoride.

9. The method according to claim 1, further comprising, after obtaining the pyrolyzed product comprising fluoromethane and 3,3,3-trifluoro-2-(trifluoromethyl)propanoyl fluoride, the step of subjecting the product to a distillation operation to obtain the 3,3,3-trifluoro-2-(trifluoromethyl)propanoyl fluoride as a column bottom component.

10. The method according to claim 1, further comprising, after obtaining the pyrolyzed product comprising fluoromethane and 3,3,3-trifluoro-2-(trifluoromethyl)propanoyl fluoride, the step of bringing the product into contact with an alcohol to remove the 3,3,3-trifluoro-2-(trifluoromethyl)propanoyl fluoride.

11. The method according to claim 10, wherein the alcohol is at least one member selected from the group consisting of methanol, ethanol, and propanol.

Description

DESCRIPTION OF EMBODIMENTS

(1) Hereinafter, the present invention is described in more detail with reference to Examples.

Examples 1 to 5

(2) -alumina (Al.sub.2O.sub.3) A (pore volume of 0.45 ml/g) (average particle size of 3 mm) that was not fluorinated was used as a catalyst. The catalyst was placed in a tubular Hastelloy reactor with an inner diameter of 15 mm and a length of 650 mm. The reactor was heated to 200 C., and 1,1,3,3,3-pentafluoro-2-trifluoromethylpropyl methyl ether, which is a starting material, was supplied to the reactor. Table 1 shows the contact time: W/F (g.Math.sec/cc), i.e., the ratio of the amount of the catalyst W (g) relative to the supply rate F (cc/sec) of the starting material.

(3) The outlet gas from the reaction tube was analyzed using gas chromatography. Table 1 shows the analysis results. The numerical values shown in Table 1 are the component proportions (mol %) determined by multiplying the area ratio of each peak obtained by the gas chromatography by a coefficient for correcting a sensitivity to each gas.

(4) The terms described in Table 1 represent the following compounds.

(5) CH.sub.3F: fluoromethane

(6) C.sub.3H.sub.6: propene

(7) HFC-1225zc: CF.sub.2CHCF.sub.3

(8) HFC-236fa: CF.sub.3CH.sub.2CF.sub.3

(9) OIME: 1,1,3,3,3-pentafluoro-2-trifluoromethylpropyl methyl ether

(10) Fluoride: 3,3,3-trifluoro-2-(trifluoromethyl)propanoyl fluoride

(11) TABLE-US-00001 TABLE 1 Yield Yield Contact Conver- Analysis results (%) of of Time sion HFC- HFC- CH.sub.3F Fluoride Ex. W/F (%) CH.sub.3F C.sub.3H.sub.6 1225zc 236fa OIME Fluoride Others (%) (%) 1 1 95.2 50.0 0.03 0 0.05 2.4 45.7 1.8 99 91 2 3 99.6 48.8 0 0.7 0.03 0.2 49.9 0.4 98 99 3 5 100 47.9 0.05 0.4 0.08 0 51.3 1.6 97 99 4 10 100 49.7 0.03 0.6 0.05 0 49.5 0.1 99 99 5 15 96.6 48.7 0 1.1 0.15 1.7 48.4 0 97 97

(12) The low-boiling-point component containing CH.sub.3F and the high-boiling-point component containing fluoride were separately analyzed. The analysis results in Table 1 show the ratio, expressed as a percentage, of each of them to all of the components.

(13) As is clear from the above results, the two desired compounds, i.e., fluoromethane (CH.sub.3F) and 3,3,3-trifluoro-2-(trifluoromethyl)propanoyl fluoride ((CF.sub.3).sub.2CHCOF), can be obtained as main components by a pyrolysis reaction of 1,1,3,3,3-pentafluoro-2-trifluoromethylpropyl methyl ether. The yields of these compounds were both 91% or more, and impurities were suppressed to 0.8% to 2.1%.

Example 6

(14) The gas obtained after the pyrolysis in Example 4 was passed through a 5 wt % KOH aqueous solution, so that CH.sub.3F accounted for 99.5% of the gas component. This result confirms that 3,3,3-trifluoro-2-(trifluoromethyl)propanoyl fluoride can be separated and removed by bringing the produced gas after pyrolysis into contact with an aqueous alkaline solution. Further, the gas obtained after the separation was cooled, collected, and subjected to rectification, thereby obtaining CH.sub.3F with a purity of 99.99%.

Example 7

(15) Under the same conditions as those of Examples 1 to 5, the reactor was heated to 150 C., and 1,1,3,3,3-pentafluoro-2-trifluoromethylpropyl methyl ether, which is a starting material, was supplied to the reactor.

Example 8

(16) Under the same conditions as those of Examples 1 to 5, the reactor was heated to 250 C., and 1,1,3,3,3-pentafluoro-2-trifluoromethylpropyl methyl ether, which is a starting material, was supplied to the reactor.

(17) Table 2 below shows the results obtained by analyzing the outlet gas from the reactor using gas chromatography.

(18) TABLE-US-00002 TABLE 2 Yield Yield Contact Conver- Analysis results (%) of of Time sion HFC- HFC- CH.sub.3F Fluoride Ex. W/F (%) CH.sub.3F C.sub.3H.sub.6 1225zc 236fa OIME Fluoride Others (%) (%) 7 10 99.8 46.5 0 1.32 0.05 0.1 50 2.0 93 100 8 10 96 48 0.4 0.8 0.3 1.9 45.1 3.5 92 87

(19) As is clear from the above results, when the temperature of the pyrolysis was 150 C. (Example 7), the conversion was nearly 100%, and the yield of the product was high. When the temperature of the pyrolysis was 250 C. (Example 8), the conversion slightly decreased, but the yield of CH.sub.3F was maintained at a high value of 92%.

Examples 9 to 11

(20) -alumina (Example 9), TiO.sub.2 (Example 10), or CrO.sub.2 (Example 11) was used as a catalyst. Under the same conditions as those of Examples 1 to 5, the reactor was heated to 150 C., and 1,1,3,3,3-pentafluoro-2-trifluoromethylpropyl methyl ether, which is a starting material, was supplied to the reactor.

(21) TABLE-US-00003 TABLE 3 Yield Yield Contact Conver- Selectivity (%) of of Time sion HFC- HFC- CH.sub.3F Fluoride Ex. W/F (%) CH.sub.3F C.sub.3H.sub.6 1225zc 236fa Fluoride Others (%) (%) 9 5 77 49.7 0 0.1 0 49.6 0.6 77 76 10 5 100 49.4 0 0 0 50 0.6 99 100 11 5 74 49.3 0 0.1 0 49.7 0.9 73 74

(22) The selectivity in Table 3 shows the proportions, expressed in percentages, of the reaction product excluding unreacted OIME.

(23) When -alumina (Example 9) or CrO.sub.2 (Example 11) was used, the conversion decreased, but the selectivity of CH.sub.3F and fluoride was high. Since the selectivity is high, CH.sub.3F and fluoride can be obtained with high yields if the unreacted starting material is returned to the reactor.

Examples 12 to 17

(24) Under the same conditions as those of Examples 1 to 5, the reactor was heated to 200 C. 1,1,3,3,3-pentafluoro-2-trifluoromethylpropyl methyl ether in an amount of 15 cc/min, which is a starting material, was mixed with nitrogen in an amount of 15 cc/min, and the mixture was supplied to the reactor. A catalyst that was not fluorinated and had a different pore volume, i.e., -alumina (Al.sub.2O.sub.3) B (pore volume of 0.38 ml/g), C (pore volume of 0.43 ml/g), or D (pore volume of 0.64 ml/g) was used. -alumina B, C, and D had an average particle size of 3 mm. Table 4 shows the results of Example 12 obtained when a reaction was performed using B, the results of Example 13 obtained when a reaction was performed using C, and the results of Example 14 obtained when a reaction was performed using D. When C and D, which had larger pore volumes, were used, the yields of CH.sub.3F and fluoride were 99%.

(25) Further, these reactions were continuously carried out for 100 hours. The results of Example 15 were obtained using B in the reaction for 100 hours, the results of Example 16 were obtained using C in the reaction for 100 hours, and the results of Example 17 were obtained using D in the reaction for 100 hours.

(26) As shown in Examples 15 to 17, the larger the pore volume, the smaller the decrease in the conversion and selectivity regarding CH.sub.3F and fluoride, and the longer the catalyst can be used even without regeneration.

(27) TABLE-US-00004 TABLE 4 Yield Yield Contact Conver- Selectivity (%) of of Time sion HFC- HFC- CH.sub.3F Fluoride Ex. W/F (%) CH.sub.3F C.sub.3H.sub.6 1225zc 236fa Fluoride Others (%) (%) 12 5 96.0 49.8 0 0.2 0 49.6 0.4 96 95 13 5 99.8 49.9 0 0.1 0 49.9 0.1 99 99 14 5 99.9 49.8 0 0.1 0 49.9 0.1 99 99 15 5 54 48.1 0 0.5 0 47.7 3.7 52 52 16 5 73 49.9 0 0.1 0 49.9 0.1 73 73 17 5 90 49.7 0 0 0 49.7 0.6 89 89

Examples 18 to 20

(28) Under the same conditions as those of Examples 1 to 5, the reactor was heated to 150 C., and 1,1,3,3,3-pentafluoro-2-trifluoromethylpropyl methyl ether, which is a starting material, was supplied to the reactor. As a catalyst, -alumina (Al.sub.2O.sub.3) D (pore volume of 0.64 ml/g) (average particle size of 3 mm) that was not fluorinated was used.

(29) The results of Example 18 were obtained when a reaction was continuously carried out for 370 hours. The conversion regarding CH.sub.3F and fluoride decreased, but the selectivity remained high. The results of Example 19 were obtained when a reaction was performed in the same manner as in Example 17 except that W/F was changed from 5 (g.Math.sec/cc) to 10 (g.Math.sec/cc). The conversion was restored by increasing W/F, showing 98%.

(30) Then, the catalyst was removed, and composition analysis of the surface thereof was performed by XPS (ESCA). The composition of the outermost surface was as follows: 25 wt % of fluorine, 8 wt % of carbon, 26 wt % of oxygen, and 41 wt % of aluminum.

(31) The results of Example 20 were obtained when a reaction was continuously carried out at W/F=30 (g.Math.sec/cc) for 700 hours. The conversion and selectivity regarding CH.sub.3F and fluoride remained high. When W/F was increased and 1,1,3,3,3-pentafluoro-2-trifluoromethylpropyl methyl ether was sufficiently contacted with the catalyst, the conversion and selectivity were high even if the reaction was performed for a long period of time.

(32) TABLE-US-00005 TABLE 5 Yield Yield Contact Conver- Selectivity (%) of of Time sion HFC- HFC- CH.sub.3F Fluoride Ex. W/F (%) CH.sub.3F C.sub.3H.sub.6 1225zc 236fa Fluoride Others (%) (%) 18 5 59 49.8 0 0.1 0 49.3 0.8 59 58 19 10 98.0 48.8 0 1.1 0.1 49.9 0.1 96 98 20 30 96.7 49.8 0 0 0 49.9 0.3 96 97

Examples 21 and 22

(33) Under the same conditions as those of Examples 1 to 5, the reactor was heated to 150 C., and 1,1,3,3,3-pentafluoro-2-trifluoromethylpropyl methyl ether, which is a starting material, was supplied to the reactor.

(34) As a catalyst, silica alumina A (SiO.sub.2/Al.sub.2O.sub.3=68 wt %/26 wt %) or silica alumina A (SiO.sub.2/Al.sub.2O.sub.3=83 wt %/13 wt %) was used. The conversion and selectivity regarding CH.sub.3F and fluoride were high.

Example 23

(35) 3.6 g of -alumina (Al.sub.2O.sub.3) D (pore volume of 0.64 ml/g) (average particle size of 3 mm) that was not fluorinated was placed in a tubular Hastelloy reactor with an inner diameter of 15 mm and a length of 650 mm. The reactor was heated to 350 C. while nitrogen was supplied in an amount of 50 cc/min. Trifluoromethane was then supplied thereto in an amount of 50 cc/min, and the mixed gas of nitrogen and trifluoromethane was allowed to flow at a trifluoromethane concentration of 50 vol % for 30 minutes to fluorinate the -alumina. Composition analysis of the surface of the catalyst was performed by XPS (ESCA). The composition of the outermost surface was as follows: 25 wt % of fluorine, 5 wt % of carbon, 29 wt % of oxygen, and 41 wt % of aluminum. Using the thus-obtained fluorinated -alumina catalyst, the reactor was heated to 150 C., and 1,1,3,3,3-pentafluoro-2-trifluoromethylpropyl methyl ether, which is a starting material, was supplied to the reactor.

(36) The conversion was 100%, and the yield of CH.sub.3F and the yield of fluoride were 96% and 100%, respectively.

(37) TABLE-US-00006 TABLE 6 Yield Yield Contact Conver- Selectivity (%) of of Time sion HFC- HFC- CH.sub.3F Fluoride Ex. W/F (%) CH.sub.3F C.sub.3H.sub.6 1225zc 236fa Fluoride Others (%) (%) 21 5 100 49.3 0 0.6 0 49.9 0.1 98 99 22 5 97.1 49.8 0 0.2 0 47.3 0.1 99 94 23 2 100 48.1 0 1.4 0.1 50 0.4 96 100