GAS CHROMATOGRAPHIC SEPARATION OF LOW MOLECULAR WEIGHT FLUOROCARBONS by Robert N. Bright and Richard A. Matula Fluid Dynamics Laboratory Department of Mechanical Engineering College of Engineering The University of Michigan Ann Arbor, Michigan This research has been sponsored by the Air Force Office of Scientific Research, Office of Aerospace Research, United States Air Force, under Grant AF-AFOSR-1144-67, and administered through the Office of Research Administration, The University of Michigan. Reproduction in whole or in part is permitted for any purpose of the United States Government.

GAS CHROMATOGRAPHIC SEPARATION OF LOW MOLECULAR WEIGHT FLUOROCARBONS Robert N. Bright Richard A. Matula ABSTRACT Application of gas-solid chromatography techniques to the separation of low molecular weight fluorocarbons incorporates a number of advantages over previous analysis techniques. These advantages include isothermal operation up to 200~C, elimination of substrate bleed, stability of the base line, minimum retention times and convenience. The relative retention volumes with respect to perfluoroethane of a number of low molecular weight fluorocarbons as a function of column support material and operating conditions are reported. The separation of a number of important species which are formed during the thermal oxidation of low molecular weight fluorocarbons are also discussed.

INTRODUCTION The qualitative and quantitative analysis of low molecular weight fluorocarbon mixtures has many applications including analysis of various fluorocarbon refrigerants, quality control of certain aerosol products and kinetic studies related to the thermal decomposition of fluorocarbons. Tatlow and co-workers (1-5) have employed gas chromatography techniques for the analysis and preparative separation of a number of perfluorinated and almost perfluorinated cyclohexanes, cyclohexenes and benzenes. Reed (6) has studied the chromatography of perfluoroalkanes, C5F12, C6F14 and C7F16 on a range of stationary phases. Serpinet (7) has considered the separation of a number of fluoro- and fluorochlorocarbons. Unfortunately the perfluorinated compounds were eluted rapidly and they were followed by compounds containing at least one other atom which were retained and resolved. Campbell and Gudzinowicz (8) have reported the separation of various fluorocarbons and sulfur-fluoride compounds. Green and Wachi (9) concluded that Kel-F oils were not completely satisfactory for the separation of fluorocarbons. The results of Green and Wachi (9) indicated that a number of low boiling point fluorocarbons could be separated by temperature programming a silica-gel column or by maintaining a Chromosorb W column employing CH2 -CHCO2CH2-(CF2CF2)3H (courtesy of E.I. duPont de Nemours and Co., Wilmington, Delaware) as the liquid substrate at 0~C. 2

Recently Drennan and Matula (10) have reported that carbon dioxide and carbonyl fluoride mixtures can be separated on a composite Porapak (Waters Associate, Inc.) column. The purpose of the present paper is to report the relative retention times of a number of low molecular weight fluorocarbons on Porapak columns, and to extend the use of Porapak columns for the analysis of the products of combustion of low molecular weight fluorocarbons. EXPERIMENTAL Apparatus and Reagents. An Aerograph model No. 202-B gas chromatograph employing a thermal conductivity detector was used for this study. Mixtures were introduced into the gas chromatograph through a gas sampling valve used in conjunction with a 2ml sample volume. The chromatograph was equipped with a linear temperature programmer which was capable of maintaining isothermal column operation in the temperature range 30 to 400~C. The fluorocarbons utilized in this study were obtained from a number of sources. The perfluoromethane (CF4), perfluoroethane (C2F6) and a mixture of cis- and trans- C 4F-2 were purchased from the Matheson Company, East Rutherford, New Jersey. The 2-trifluoromethylpropene (C4F10), perfluorobutane (C4F10), perfluorobutadiene -1,3 (C4F6), perfluorobutyne-2 (C4F6), perfluorocyclobutene (c-C4F.), perfluorocyclobutane (c-C4F8), perfluorocyclobutene (c-C4F6), perfluoropropane (C3F8), and perfluoropropene (C3F6) were purchased from Penninsular Chemresearch, Inc., Gainesville, Florida. The perfluoroethylene (C2F4) and carbonyl fluoride (CF20) were purchased from Columbia Organic 3

Chemicals, Inc., Columbia, South Carolina. The iso-C4F8 used in this study was produced by pyrolyzing perfluoropropene at 700~C for 15 minutes in a Vycor reactor. Procedure. A number of variable length GSC columns were constructed by packing 1/4" O.D. copper tubing with 50/80 mesh Poropak (Waters Associate, Inc.). The separation capabilities of Types N, P, Q, R, S and T Poropak were studied. Before final instillation in the chromatograph, each of the columns was heated to 200~C and purged with helium (60 ml/min) for two hours. Prior to the analysis of the fluorocarbon combustion products, the column was conditioned by passing three 250 torr samples of CF20 through it. The retention volumes of all compounds were determined from the analysis of both pure compounds and fluorocarbon mixtures that had been prepared in the laboratory. The separations were obtained by operating the columns isothermally in the temperature range 75 to 175~C while maintaining a constant helium carrier gas flow rate of 60 ml/min. RESULTS AND DISCUSSION Fluorocarbon Analysis. The relative retention volumes of the various fluorocarbon compounds as a function of column material, length and temperature are listed in Tables 1-4. All of these results are based on a helium carrier gas flow rate of 60 ml/min. If the relative retention volume of a compound is not listed in the Tables the retention time was greater than 25 minutes, and a notation of n.a. implies that a compound was not tested. 4

Poropak Type P does not effectively separate the compounds of interest and hence results for this column are not listed. A ten foot column of Poropak Type T maintained at 150 C was found to be the most effective for the separation of a mixture containing air and a large number of low molecular weight fluorocarbons. A GSC chromatogram of a complex, gaseous fluorocarbon mixture obtained with the aid of a ten foot, Poropak Type T column is shown in Figure 1. The column temperature was maintained at 150 C and the separation was completed in approximately seventeen minutes. The perfluorocyclobutane and perfluorobutane were not resolved on this column. Fluorocarbon Combustion Products. The major equilibrium products associated with fluorocarbon combustion include 02, CF4, CO2, CF20 and C2F4. A GSC chromatogram of these compounds obtained with the aid of a six foot composite column consisting of two feet of 50/80 mesh Poropak type T followed by four feet of 50/80 mesh Poropak N is shown in Figure 2. The column temperature was maintained at 23~C and the helium carrier gas flow rate was 60 ml/min. ACKNOWLEDGEMENT This research was sponsored by the Air Force Office of Scientific Research, Office of Aerospace Research, United States Air Force, under Grant Number AF-AFOSR-1144-67. 5

REFERENCES 1. Evans, D., and Tatlow, J., J. Chem. Soc., 1184 (1955). 2. Godsell, J., Stacey, M., and Tatlow, J., Nature 178, 199 (1956). 3. Stephens, R. and Tatlow, J., Chem. and Ind. (London), 821 (1957). 4. Smith, R., and Tatlow, J., J. Chem. Soc. 2505 (1957). 5. Evans, D., and Tatlow, J., in "Vapour Phase Chromatography", Proceedings of the First Symposium, London, June, 1956, 256, Academic Press, New York (1957). 6. Reed, T.M., Anal. Chem., 30, 221 (1958). 7. Sperpinet, J., Chim. Anal., 41, 146 (1959). 8. Campbell, R. and Gudzinowicz, B., Anal. Chem., 33, No. 7 842 (1961). 9. Green, S., and Wachi, F., Anal. Chem., 35, No. 7, 928 (1963). 10. Drennan, G., and Matula, R., J. of Chrom. (in press). 6

TABLE 1 RELATIVE RETENTION VOLUMES OF SEVERAL FLUOROCARBONS ON PORAPAK TYPE T (C2F6 = 1.00) 6ft. at 100~C 6ft. at 150~C 6ft. at 175~C 10ft. at 150~ClOft. at 175~ C CompoundI tm(a) RRV (b) m RRV | m RRV tm RRV tm -.... -.......,. RRV -- Air CF4 CF4 C2F6 C2F4 C3F8 CF3-C=C-CF3 C3F6 c-C4F8 CF3-CF -CF2-CF3 trans-C 4F-2 cis-C4F8-2 c-C4 F6 CF2=CF-CF-=CF2 iso-C4F8 CF -C=CF C3 2 "3 a T I011 6.70 0.82 1.44 1.91 3.53 5.91 6.61 10.6 10.6 16.9 n.a. 18.0 22.3 n.a. 0.49 0.57 1.00 1.33 2.45 4.10 4.59 7.36 7.36 11.74 n.a. 12.50 15.49 n.a. 0.65 0.71 0.96 1.09 1.55 1.92 2.10 2.90 2.90 3.50 n.a. 3.95 4.55 n.a. 8.08 0.68 0.74 1.00 1.14 1.62 2.00 2.19 3.02 3.02 3.65 n.a. 4.12 4.74 n.a. 8.42 0.66 0.66 0.81 0.92 1.19 1.39 1.47 1.94 1.94 2.18 n.a. 2.44 2.73 0.82 0.82 1.00 1.14 1.47 1.72 1.82 2.39 2.39 2.69 n.a. 3.01 3.37 1.03 1.17 1.62 1.89 2.73 3.51 3.84 5.40 5.40 6.48 7.30 7.45 8.60 10.4 15.4 0.64 0.72 1.00 1.17 1.67 2.17 2.37 3.33 3.33 4.00 4.51 4.60 5.31 6.42 9.51 1.03 1.13 1.47 1.68 2.21 2.75 2.96 3.90 3.90 4.98 n.a. 5.02 5.63 0.70 0.77 1.00 1.14 1.50 1.87 2.01 2.65 2.65 3.39 n.a. 3.42 3.83 n.a. 6.29 n.a. 4.55 n.a. 5.62 n.a. 9.25 I - I -1 _ I -. - - - - - - - - - - - - - i~~~l __________ U I _________-_________ Helium Carrier Gas Flow Rate: 60 ml/min Column Material: 50/80 mesh (a) tm = retention time in minutes to peak (b) RRV = relative retention volume with respect to perfluoroFprp-e_ C oi4a e

TABLE 2 RELATIVE RETENTION VOLUMES OF SEVERAL FLUOROCARBONS ON PORAPAK TYPE N (C2F6 = 1.00) 5ft. at 100~C 5ft.at 150~C 10ft. at 175~C Compound tm(a) RRV(b tm RRV m RRV Air 0.60 0.49 0.58 0.76 1.17 0.81 CF4 0.71 0.58 0.58 0.76 1.17 0.81 C2F6 1.22 1.00 0.76 1.00 1.44 1.00 C2F4 1.56 1.27 0.86 1.12 1.62 1.12 C3F8 2.87 2.35 1.19 1.57 2.03 1.41 CF3-C=C-CF3 4.62 3.79 1.48 1.95 2.35 1.63 C3F C3F6 4.99 4.09 1.57 2.07 2.95 2.05 c-C4F8 7.84 6.13 2.15 2.83 3.13 2.17 CF3-CF2-CF2CF3 8.44 6.92 2.24 2.93 3.13 2.17 trans-C4F8-2 12.53 10.27 2.56 3.37 3.46 2.40 cis-C4F8-2 n.a. n.a. n.a. n.a. 3.70 2.57 c-C4F6 12.53 10.27 2.83 3.72 3.90 2.71 CF2=CF-CF=CF2 16.2 13.28 3.29 4.33 4.35 3.02 iso-C4F 8 n.a. n.a. n.a. n.a. 4.65 3.23 CF -C=CF --- --- 5.90 7.76 7.32 5.08 CF3 2 c3 Helium Carrier Gas Flow Rate: 60 ml/min Column Material: 50/80 mesh (a) tm = retention time in minutes to peak (b) RRV = relative retention volume with respect to perfluoropepeo C Vh IU

TABLE 3 RELATIVE RETENTION VOLUMES OF SEVERAL FLUOROCARBONS ON PORAPAK TYPES R and S (C2F6 = 1.00) Type R Type R Type S Type S 6ft. at 100~C R 6ft. at 150 C S 6ft. at 100 C S 6ft. at 150~C t (a) (b) t tt Compound m RRV m RRV m RRV m RRV Air 0.85 0.57 0.86 0.80 0.80 0.57 0.75 0.75 CF4 0.95 0.64 0.86 0,80 0.90 0.64 0.80 0.80 C2F6 1.48 1.00 1.07 1.00 1.41 1.00 1.00 1.00 C2F4 1,86 1.26 1.17 1.10 1.71 1.21 1.10 1.12 C3F8 3.00 2.03 1.54 1.44 2.98 2.11 1.42 1.42 CF3 -C=C-CF3 |4.30 2.91 1.81 1.69 2.98 2.11 1.42 1.42 C3F6 4.33 2.93 1.80 1.68 4.19 2.97 1.70 1.70 CC4 F8 |6.88 4.65 2.39 2.23 6.90 4.89 2.30 2.30 CF3-CF2 -CF2-CF3 7.56 5.11 2.57 2.40 7.63 5.41 2.45 2.45 trans-C 4F-2 8.80 5.95 2.57 2.40 8.80 6.24 2.45 2.45 c-C4F6 c-C 4 6 9.62 6.50 2.87 2.68 9.98 7.08 2.70 2.70 CF 2=CF-CF=CF2 12.30 8.31 3.31 3.09 12.5 8.86 3.20 3.20 CF3- =CF-2 ---- 6.10 5.70 -. — ---- 15.69 5.69 (a) t = Retention time in minutes to peak (b) RRV = Relative retention volume with respect to Perfluorolpropone etha e Helium Carrier gas flow rate: 60 ml/min Column Material: 50/80 mesh

TABLE 4 RELATIVE RETENTION VOLUMES OF SEVERAL FLUOROCARBONS ON PROAPAK TYPE Q (C2F6 - 1.00 Type Q Q 6 ft at 100~C Type Q Q 6ft. at 150~C 0 Compound | t RRV t RRV Compound m m Air 0.79 0.52 0.83 0.75 CF4 0.90 0.60 0.85 0.77 C2Fg 1.51 1.00 1.11 1.00 264 C2F 1.74 1.15 1.22 1.10 C3F8 3.32 2.20 1.56 1.51 38 CF3-C=C-CF3 4.55 3.01 1.80 1.73 C3F 6 4.20 2.78 1.95 1.76 c-C4F8 7.49 4.96 2.81 2.53 CF3 —CF2-CFCF n.a. n.a. n.a. n.a. t CF2-CF2 - c | 2 -.3 trans-C4F -2 n.a. n.a. n.a. n.a. c -C6F. n.a. n.a. n.a. n.a. CF2=CF-CF=CF2 na. n.a. n.a. n.a. CF3- CF 2 na. n.a. n.a. n.a. CF 3 c ICF2 ____ -J (a) tm = Retention time in minutes m to peak Helium Carrier Gas flow rate: 60 ml/min Column Material: 50/80 mesh (b) RRV = Relative retention volume with respect to Perfluoropreope e-+kcav e

CF4 LLU U) z 0 0 -U) LU cr aLd 0 a: IrJ 0 0 LUJ W: C c-C4F iso-C4F 2 C F CF3CCF2 0 2 4 6 MINUTES 10 12 14 16 18 FIG. I GAS-SOLID CHROMATOGRAM of FLUOROCARBONS

CF 0 3 6 9 12 15 18 TIME, MIN FIG.2 TYPICAL CHROMATOGRAM OF C2F4 OXI DATION PRODUCTS

Unclassified Secruritv Classification I JkluY~i %k, bs abIlII~ ia &Jl DOCUMENT CONTROL DATA R & D (Security classification of title, body of abstract and indexing annotation must be entered when the overall report Is classified) 1. ORIGINATING ACTIVITY (Corporate author) 2a. REPORT SECURITY CLASSIFICATION The University of Michigan Unclassified Department of Mechanical Engineering 2b. GROUP Ann Arbor, Michigan 3. REPORT TITLE GAS CHROMATOGRAPHIC SEPARATION OF LOW MOLECULAR WEIGHT FLUOROCARBONS 4. DESCRIPTIVE NOTES (Type of report and inclusive dates) 5. AU THOR(S) (First name, middle initial, last name) Robert N. Bright and Richard A. Matula 6. REPORT DATE 7a. TOTAL NO. OF PAGES 7b. NO. OF REFS March, 1968 12 10 Ba. CONTRACT OR GRANT NO. 9a. ORIGINATOR'S REPORT NUMBER(S) AF-AFOSR-1144-67 Fluid Dynamics Laboratory b. PROJECT NO. Publication No. 68-3 c. 9750-02 9b. OTHER REPORT NO(S) (Any other numbers that may be assigned this report) d. 10. DISTRIBUTION STATEMENT 1I. SUPPLEMENTARY NOTES 12. SPONSORING MILITARY ACTIVITY Air Force Office of Scientific Research (SREP) Tech, other 1400 Wilson Boulevard 1,~~~~~~~__________Arlington, Virgnia 2220_ 13. ABSTRAC T Application of gas-solid chromatography techniques to the separation of low molecular weight fluorocarbons incorporates a number of advantages over previous analysis techniques. These advantages include isothermal operation up to 200~C, elimination of substrate bleed, stability of the base line, minimum retention times and convenience. The relative retention volumes with respect to perfluoroethane of a number of low molecular weight fluorocarbons as a function of column support material and operating conditions are reported. The separation of a number of important species which are formed during the thermal oxidation of low molecular weight fluorocarbons are also discussed. -- DD FOF 14 73 DD INOV 651473 Unclassified. Securityv Classtication

TTn,-l1. C o f ifIed SecUritv Classification ~1 ~~~~~4 | 1 LLINK A LINK B LINK C KEY WORDS 1 ' RO L E WT ROL E W T O L E W T I Carbonyl Fluoride Carbon Dioxide Fluorocarbons Gas Chromatography I MA I..i I I..j -I 1I l Lmm_ - Amm TTncl assified Se( urltv Clo""Ifica"I''ll