The use of gas-liquid chromatography to determine activity coefficients and second virial coefficients of mixtures II. Experimental studies on hydrocarbon solutes

Abstract

This paper describes apparatus of a new design for measuring accurately gas-liquid retention volumes in packed columns under carrier gas pressures up to 25 atm. It includes a high pressure soap-film flowmeter, a high pressure vapour phase sample injection system and a pressure control system at the column outlet which enables a flame-ionization detector to be operated at atmospheric pressure. Results are reported for a series of hydrocarbon solutes in three different stationary liquids (squalane, dinonylphthalate and n -hexadecane), with nitrogen, hydrogen and argon as carrier gases. Solute activity coefficients at infinite dilution in the stationary liquids, and second virial coefficients ( B 12 ) for the solute + carrier gas mixtures have been obtained by analysing the retention volume data by the procedure established in part I. The activity coefficients are compared with values obtained from static vapour pressure measurements made by two widely different methods, and the agreement is satisfactory in both cases. The second virial coefficients ( B 12 ) are compared with those values predicted by the principle of corresponding states via the reduced equation of state of McGlashan & Potter (1962). The B 12 values given by using the ‘geometric mean’ combining rule for the mixed critical temperature in the reduced equation of state differ from our experimental values by as much as 75 cm 3 /mole. Using the combining rule of Hudson & McCoubrey (1960) or that of Munn (1961), both of which take account of differences in molal volume and ionization potential between the two components, however, gives B 12 values which agree with our experimental values.