Measurements of HmE and VmE for ( n-butane + sulphur hexafluoride) in the supercritical region at the pressure 6.00 MPa

Abstract

A flow mixing calorimeter followed by a vibrating-tube densimeter has been used to measure excess molar enthalpies H m E and excess molar volumes V m E of { xC 4H 10+(1− x)SF 6}. Measurements over a range of mole fractions x have been made in the supercritical region at the pressure p=6.00 MPa and at seven temperatures in the range T=311.25 K to T=425.55 K. The H m E( x) measurements at T=351.35 K were found to exhibit an unusual double maximum. Measurements at all temperatures are compared with the Patel–Teja equation of state with the parameters determined by solving a cubic equation as recommended, and also with parameters determined by the method suggested by Valderamma and Cisternas who proposed equations which are a function of the critical compression factor. The overall fit to the H m E and V m E measurements obtained using Valderamma and Cisternas equations was found to be better than that obtained using the parameters according to the method suggested by Patel and Teja.