COMPRESSIBILITY FACTORS OF PROPANE-METHANE MIXTURES IN THE TEMPERATURE-RANGE FROM 0 TO 50-DEGREES-C DETERMINED WITH AN AUTOMATED EXPANSION APPARATUS

An automated expansion apparatus has been set up which can be used for PVT measurements on gases front 0 to 50 degrees C at pressures from 2 to 6 MPa. It consists of two chambers connected by an expansion valve . The ratio of the two volumes is 1:54. The measurements along one iso therm, which take 20 h, can be performed routinely and without operato r attendance. The relative uncertainty of the compressibility factor i s estimated to be 1,0 . 10(-3). ln this work the compressibility facto rs of binary mixtures of methane and propane were determined on high-g rade gas, the mole fractions of propane being 0,01; 0,03; and 0,05. Fi ve isotherms were measured for each of the mixtures. Data from the lit erature for the virial coefficients of the pure substances were used t o establish a virial equation of state which approximates the measured compressibility factors with a relative standard deviation of 0,5 . 1 0(-3). This is substantially smaller than the uncertainty. The interac tion virial coefficients were calculated front this equation of stare. The results obtained are in good agreement with other available data.