Thermodynamic Properties of Fluorochloromethanes Vapor Pressure of Three and -Ethanes
Fluorochloromet hanes and Trifluorotrichloroethane'
Vapor pressure measurements have been made on difluorochloromethane (CHCIFz), dichlorofluoromethane (CHCLF), trichlorofluoromethane (CC13F), and trifluorotrichloroethane (CClzF-CCIFz) at various pressures between 0.1 and 50 atmospheres. These data have been used to determine for each compound the constants of a vapor pressure equation of the form: loglop
A
+B +C
logla
T
A. F. BENNING .4ND R. C. -MCHARYESS Kinetic Chemicals, Inc., Wilmington, Del.
200-cc. capacity. The condensed difluorochloromethane was stored in steel cylinders fitted with brass needle valves since its vapor pressure at room temperature is too high to allow safe storage in glass. I n no case was there obtained in the first fractionation more than 2-3 per cent of material which had a boiling point detectably (0.05' C.) lower or higher than that of the main body of material. At no time in the second and third fractionations was there any detectable change in the boiling point of the product. I n the case of one compound the vapor pressure of samples from the first and last of the tubes filled with the fraction of highest quality were checked by an isoteniscope and found to be identical. These facts show that the final product obtained from the fractionations was of a constant quality as regards boiling point. This material of highest purity was used in the measurements of such properties as vapor pressure, vapor density, and critical temperature which require the ude of pure materials for accurate results. The first and last fourths of the final fractionation were employed in the measurement of liquid densities and C,/C,. The discarded portions of the second fractionation were used in the measurement of the heat capacities of the liquid and vapor. These additional properties are the subjects of reports to be published.
+ DT
The equations thus obtained have been used in the calculation of tables of thermodynamic properties for each compound.
S OUTLISED in the first paper of this series ( I ) , a comprehensive investigation of the physical properties of the above four compounds was carried out in order to provide the information necessary for the calculation of their thermodynamic properties. This paper covers in detail the experimental work and the results obtained in the work on one property of these compounds--rapor pressure. The vapor pressure measurements were made by a static method using specially designed glass isoteniscopes. Since all nonpolar compounds have similar vapor pressure curves, the number of temperatures a t which the vapor pressure measurements were made on each compound was limited to that which would accurately fix the position and slope of the vapor pressure curve over the desired range. To satisfy these requirements, it Tyas found necessary to make determinations a t pressures of approximately 0.3, 1, 3, 10, and 30 atmospheres on all four compounds and a t pressures of 0.1 and 4050 atmospheres on certain of them. These data were used to determine the constants of a vapor pressure equation for each compound.
A
Apparatus and Procedure All vapor pressure measurements were made with the aid of glass isoteniscopes each of which had a mercury-filled differential manometer for balancing the pressure in the measuring system against that of the liquid in the isoteniscope. The differential manometer on the isoteniscope used a t pressures of 1atmosphere or less and a t temperatures below 25" C. was outside of the bath. On the high-pressure isoteniscope it was in the bath and as close to the bulb of the instrument as possible. The latter isoteniscope was of very rugged glass construction with a wall thickness of 3 mm. The isoteniscopes were connected to the necessary auxiliary equipment such as buffer tanks, manometers or pressure gages, pressure or vacuum supply, and control valves by means of rubber or copper tubing. The high-pressure isoteniscope was connected to the copper tubing through a metal-to-glass seal. The instrument, including the metal-to-glass seal, was tested under hydrostatic pressures as high as 2000 pounds per square inch without failure. The compound in the isoteniscope was kept a t constant temperature by means of a bath of boiling liquid. At low
Purification of Materials The compounds under investigation were purified by fractionation a t atmospheric pressure in a 90-cm. silicon carbide packed lass column. The starting material in each case consiste of 11-14 kg. of the best grade of commercial product available. This material was fractionated three times; a high reflux ratio was used, and the first and last fourths of each fractionation were discarded. The middle cut of the last fractionation (about 1.5 kg.) was dried with PpOs, and the condensed vapor stored in sealed glass tubes of about
2
1
The first paper in this series appeared in 1939 ( I ) .
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All vapor pressure measurements were made with a merOF DIFLUOROCHLOROMETHANE TABLEI. VAPORPRESSURE cury manometer or one of three high-grade Bourdon-type pressure gages having ranges of 0-60, 0-300, and 0-700 Loglo p = 25.1144 8.14181ogro T + 0.0051838 T pounds. The smallest scale divisions on the three gages (Where p atmospheres abs.; T = ' X. = C. + 273.10) were 1, 2, and 10 pounds, respectively, and all pressures were Obsvd. p Deviation Obsvd. p t Calcd. p (This Work) from Calod. (Other Work: estimated to the nearest tenth of the smallest scale division. c. Atm. Atm. % Atm. The pressures measured on each gage were such that it was +0.3 ...... 0.3456 0.3466 -61.26 possible to read them with an accuracy of 0.3 per cent or 1.0066 0.0 ...... -40.66 1.0064 4.197 $0.5 - 5.00 4.176 better. The pressure gages were calibrated both before and +22.6 9.726 ... 9:39.(4) after use with the aid of a dead-weight gage tester. Check 25.15 10.43 1Ij:ii -0.6 ...... 40.1 15.31 .... ... 14.87 (4) calibrations were found to agree within the limits of accuracy 50.3 19.48 .... ... 1 9 . 4 6 (4) 60.3 24.30 .... ... 2 4 . 0 8 (4) with which the gages could be read. All pressure measure71.5 30.67 .... ... 3 0 . 6 2 (4) ments were converted t o absolute pressures with the aid of a 75.90 33.46 33.27 -0.6 85.4 40.12 .... 39: 23'(4) standard mercury barometer. All barometer and manome92.60 45.75 45.92 +0:4 ...... ter readings were reduced to 0" C., sea level, and latitude 45'.
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7-
OF DICHLOROFLUOROMETHANE Calculation of Vapor Pressure Equation TABLE11. VAPORPRESSURE 2367 41 The vapor pressure data obtained experimentally for each 38.2974 - 13.0295 loglo T + 0.0071731 T Logip p of the four compounds investigated were used to calculate the Deviation constants of a vapor pressure equation of the form 1 Calod. p Obsvd. p from Calcd. c. Atm. Aim. % B loglo p = A C loglo T D1' -29.65 0.1681 0.1708 +1.6 T 0.0 -8.76 0.4765 0.4765 +8.92 1.000 1.000 0.0 Ordinarily the data obtained a t pressures of 0.3, 1, 10, and 43.93 3.280 3.293 +0.4 -0.4 82.85 9.043 9.007 30 atmospheres were used to set up four equations which were 139.08 27.36 27.35 0.0 48.30 +1.0 174.60 47.84 then solved simultaneously to determine the constants A , B , C, and D. The data a t other pressures were used to check and adjust this equation. The equations calculated as outlined above are not necestemperatures this bath liquid was contained in a 200-cc. sarily those shown in Tables I to IV. I n some cases it was unsilvered Dewar flask and heated electrically. When the found necessary to adjust the equations further (always keephigh-pressure isoteniscope was being used, the bath liquid was ing within the limits of experimental error) in order t o obtain kept in a large test tube 65 mm. 0. d. by 350 mm. long. I n so ones which would give the most consistent values when used far as possible, bath liquids were chosen which were nonin conjunction with the other data necessary for the calculaflammable. A condenser was mounted in the top of the bath tion and checking of the thermodynamic tables. These final and a thermometer extended into the bath liquid. If necesvapor pressure equations are shown in Tables I to IV. sary, the bath temperature could be varied by increasing or decreasing the pressure on the outlet of this condenser. The isoteniscopes were filled by condensing in them vapor OF TRICHLOROFLUOROMETHANE T.LBLE 111. VAPORPRESSURE from one of the 200-cc. glass storage tubes. The necessary precautions were taken to prevent contamination of the conLoglo p = 34.8838 - 11.7406 1000 T + 0.0064249 T densate by moisture or any other foreign material. I n most Deviation 1 Calod. p Obsvd. p from Calcd. cases fresh samples were used for each vapor pressure deterc. Atm. Atm. % mination. I n the few cases where two determinations were 0.0930 +0.5 -29.65 0.0925 made on one sample, the one a t the higher temperature and 0.3972 +o. 1 +0.01 0.3967 1.009 -0.2 24.02 1.011 pressure was always made first. After the bulb of the iso3.211 +0.6 61.15 3.193 12.12 0.2 119.62 12.14 teniscope had been filled with a sample of the compound under 33.67 -0.4 180.67 33.81 investigation, the regular procedure was to bring the bath up 42.18 +0.7 195.65 41.87 to the desired constant temperature and make pressure readings after two, three, and four fifths of the liquid in the bulb OF TRIFLUOROTRICHLOROETHAN T-LBLE IV. VAPORPRESSURE had been boiled out past the differential mercury manomeLogio p = 29.5335 240:10 9.2635 logla T + 0.0036970 T ter. Several readings were made a t each stage of the Obsvd. p Deviation Obsvd. P boiling out to ensure the establishment of complete temperat Calcd. p (This Work) from Celod. (Other Work) ture equilibrium. All vapor pressure measurements after c. Atm. Atm. % Atm. either three or four fifths of the liquid had been boiled out 0.0311 (9) ..... 0.0361 -25.48 0.0996 $4: 4 0,0953 -8.40 agreed within the limits of accuracy with which the pressures 0 : io3s'(3) ..... ... 0,1020 -7.10 0.1438 ( 6 ) ... 0.1459 ..... could be read. I n most cases the readings a t all three stages 0.0 0.3575 ( 3 ) 0 , 3 5 5 0 . . . . . . . . t19.75 agreed. The bath liquid was boiled sufficiently vigorously to 0.3586 ( 6 ) ..... ... 0,3587 20.0 0 . 0 0 . 3 6 1 6 0.3615 2 0 . 1 9 prevent variations of more than 0.04' C. from the average o :+5i4'(9) ... 0.7832 ..... 39.31 0,7739 (6) 0.7718 bath temperature. ... 40.0 i : boo -0.2 ...... 1.002 47.57 Mercury thermometers were used for all temperature meas1 . 5 3 3 (9) ... 1.546 ..... 61.16 2 . 563 (9) . . . . . 2 . 5 9 1 7 9 . 2 5 urements above -30' C. The thermometers were calibrated $0: 2 ...... 2.891 2 . 885 83.30 -0.1 ...... 8.088 by comparison with a platinum resistance thermometer which 8.098 128.70 ...... 32.24 +7.0 30.12 210.62 had been calibrated by the National Bureau of Standards. The calibrations were carried out in the same bath of boiling liquid and under conditions identical with those under which Results the particular vapor pressure measurement was made. All The vapor pressure data obtained experimentally for the temperatures were read or estimated to the nearest 0.01" C. four fluids with the apparatus and procedure outlined above Temperatures below -30' C. were measured directly with are shown in Tables I t o IV. The corresponding calculated the platinum resistance thermometer.
+
+ +
Q
2F
E
~~
+
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points have been corrected to the standard pressure of 760 OF FLUOROCHLORO HYDROCARBONSmm., using the values of d t / d p calculated from the vapor TABLEV. BOILINGPOINTS AT A PRESSURE OF 760 MM. pressure equations and shown in column 4. Other boiling Obsvd. B. P. Calcd. d t / d p at Obsvd. B . P. points which have been reported for these compounds are Compound (This Work)a,b EL P. B. P. (Other Work) also shown in Table V. e. C. C./Mm. c. CHClF? -40.80 -40.80 0.028 -40.8 t o -40.6 (S), -39.8 (9) Literature Cited CHC1.F 8.92 8.92 0.034 8.9 to 9.0 (6).13.5 t o _ ~ .~ ~ _ 15.5 (21, 14.5 ( I f ) (1) Benning, A. F., and McHarness, R. C., ISD.ENG.CHEM.,31, 24 (8),24.9(10) 23.71 0.037 CClsF 23.77 912-16 (1939). 0.039 47 2 5 C (6) 47 3 b (SI, 47.52 47.57 CChF-CClF2 47.4 (12j, 4f.68 (91, ( 2 ) Booth, H. S., and Bixby, E. M., Ibid., 24, 637-41 (1932). 0
47.7 ~... f7) \ ,
Q
b c
From va or pressure data Correctefto 760 mm. by &ing the d t / d p ratio given in column 4. Extrapolated t o 760 mm. b y the authors.
values and the equations from which they are derived are given, together with the deviation of the observed from the calculated values. The range of each equation is indicated by the magnitude of the deviations. Other vapor pressure measurements which have been made on these compounds and reported in the literature are also shown. Table V gives the calculated and observed boiling point of each compound. Where necessary the observed boiling
(3) Booth, H. S., Mong, W. L., and Burohfield, P. E., Ibid., 24,
328-31 (1932). (4) Booth, H. S., and Swinehart, C. F., J . Am. Chem. SOC.,57, 1337-42 (1935). (5) Henne, A. L., Ibid., 59, 1400-1 (1937). (6) Hovorka, F., and Geiger, F. E., Ibid., 55, 4759-61 (1933). (7) Locke, E. G., Brode, W. R., and Henne, A. L., Ibid., 56, 1726-8 (1934). (8) Midgley, T., Jr., and Henne, A. L., IND..ENO. CHEM.,22, 542-5 (1930). (9) Riedel, L., 2. ges. K d l t e - I d . , 45, 221-5 (1938) (10) Swarts, F., Be?., 26 Ref.,291-2 (1893). (11) Ibid., 26 Ref.,781-2 (1893). (12) Swarts, F., J. chim. phys., 28, 622-50 (1931). ,
I
COBTRIBUTION 3 from Kinetic Chemicals, Inc.
Naphthenic Acids from Gulf Coast Petroleum The naphthenic acids present in the lubricating oil portion of a Gulf Coast petroleum have a molecular weight range of about 220-440, corresponding to 1 4 2 9 carbon atoms per molecule. The hydrogen deficiency below the fatty acid series (C,H2,02) is 6 1 0 atoms per molecule. This is not due to simple unsaturation but to naphthenic rings with possible admixture with aromatic rings. If aromatic acids are absent, at least five naphthene ring closures are indicated in some of these acids. The acids are at least substantially monobasic.
HE term "naphthenic acids" describes the cyclic carboxylic acids occurring in and obtained from petroleum. Until recently commercial naphthenic acids have been extracted only from the kerosene and gas oil fractions; therefore their boiling points are within the range of these materials. These acids have an average molecular weight of the order of 200. Only recently have the naphthenic acids extracted from the lubricating oil fractions of petroleum become commercially available. These heavier acids from the higher boiling fractions obviously have higher molecular weights. Although a considerable amount of work has been done on the constitution of naphthenic acids, the experiments have centered mainly about the lighter acids, and comparatively little is known about the acids of high molecular weight.
T
COMPOSITION OF HIGHER BOILING ACIDS ROY W. HARKNESS .4ND JOHANNES H. BRUUN Sun Oil Company, Norwood, Penna. Thus in the early history of the study of these substances the names of Aschan ( 2 ) , Markownikoff (11), Zelinsky (14, 15), and Komppa ( 8 ) appear. The work of these investigators in general indicated that a 5-carbon ring predominated in the nucleus of the low-molecular-weight acids. Within recent years the investigations of von Braun (3, 4) have been outstanding because of their thoroughness. He succeeded in isolating the first homogeneous naphthenic acid from petroleum (6). It was found to be 3,3,4trimethylcyclopentylacetic acid H CH, having a molecular weight of 170 HsC--b--CCH3 I and the accompanying structural formula. The structure was H2-b AH2 established by degradation of the acids to ketones from which a pure \&,H2COOH individual ketone of known comH position was isolated. The existence of homologous acids differing only in the number of methylene groups adjacent to the carboxyl group was proved. With regard to acids of higher molecular weight yon Braun (4)states that they are of two types, monocyclic CnH2, - 201 and bicyclic CnHzn- 402.The monocyclic type comprises in general the acids of 8 to 12 carbon atoms. The bicyclic acids contain from 13 to as high as 23 carbon atoms per molecule.
