J. A. BROWNAND W. H. MEARS
960
Vol. 62
PHYSICAL PROPERTIES OF n-PERFLUOROBUTANE BY JAMESA. BROWN AND WHITNEY H. MEARS A Contribution of General Chemical Research Laboratory, Allied Chemical Corporation, Morristown, New Jersey Received April 8 , lD6S
A Martin-Houl equation of state has been obtained for n-perfluorobutane applicable to 800 p.s.i.a., 170" and to a molar volume of 0.38 I./g. mole. Vapor pressure and densities of liquid and saturated vapor were determined from -40 to 113.2", the measured critical temperature. From this information the rectilinear diameter line and the heats of vaporization have been computed.
Introduction For several years this Laboratory has conducted a program for investigating the physical properties of fluorine-containing molecules. As a part of this work, a Martin-Houl equation of state has been obtained for n-perfluorobutane while vapor pressure and liquid density data have been extended. Finally, heats of vaporization and the rectilinear diameter line have been computed. Material.-The n- erfluorobutane, prepared a t this Laboratory, was fist fractionated on a twenty-four bubble plate Oldershaw column and a center cut taken. Comparison of liquid and vapor infrared spectra and information from the vapor chromatograph indicated the presence of low boilers. These were removed from the sample by distillation in a vacuum jacketed column packed with Helipak, which possessed fifty theoretical plates. Distillation was continued until no variation was observed in the infrared spectrum of the vapor. The sample was then purged of non-condensable gases by freezing it in liquid nitrogen, pumping off any residual gas, closing off the cylinder and allowing it to reach room temperature. The process was repeated until no pressure was observed on a manometer upon cooling the sample in liquid nitrogen. The infrared curves of both liquid and vapor samples were checked between 625 and 5000 cm.-l on a Baird recording infrared spectrometer and were found to coincide throughout this frequency range within the error of the instrument. Data from the gas chromatograph showed less than 0.1 mole yo impurity. As will be shown subsequently, the critical temperature of this material agrees to within 0.1," with the literature value2 and its boiling point, -2.00 , is in good agreementowith that of Fowler,a -1.7 & 0.2" and of Simons,a -2.2 Accordingly, it is believed that the sample is of a purity of better than 99.8 mole %.
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Apparatus and Experimental Procedure The experimental techniques employed for obtaining vapor pressure and vapor density data were similar to those of earlier work,' except for certain refinements described here. The equipment was completely constructed with high pressure fittings and was equipped with a 1000 p.s.i. Heise gauge having 1 lb. subdivisions. This was calibrated under experimental conditions against a second Heise gauge which served as a secondary standard. The secondary standard was calibrated by an Ashcroft dead weight tester. For pressures below 1 atmosphere, the unit was connected t o a mercury manometer which had a precision of &0.3 mm. The volume of the equipment was obtained both by weighing its water content a t constant temperature, and by measurement of the density of a known quantity of CO2 under various pressures and temperatures with the application of the equation of state for CO2.6 The volume was found to be 1537.5 f 1.0 cc. at 25". Corrections were made for the expansion of this equipment with temperature. The unit was contained in an oil thermostat with a temperature fluctuation of
