Activity coefficients of hydrocarbons C₄to C₈in n-octadecane at 35°C. Gas-chromatographic investigation

Abstract

Activity coefficients at effectively infinite dilution yF3 of various hydrocarbons in n-octadecane at 35°C have been derived from gas-liquid chromatographic retention volume data extrapolated to zero gas pressure. The carrier gas was in most cases nitrogen, or occasionally argon; but three n-alk-1-enes were examined with hydrogen, nitrogen and argon to give a consistency check; the log yF3 values from the three carrier gases agree within 0-002. " Mixed " second virial coefficients B1 have been calculated for every hydrocarbonScarrier gas system. The activity coefficients are discussed in terms of the separability of the configurational (entropy of mixing) part and the interactional (energy of mixing) part. The energy of mixing part is analyzed in terms of the Hildebrand-Scatchard solubility parameter; the alkane systems are analyzed also by considering different types of contact points; and finally thc n-alkane systems are re-analyzed in terms of interactions between " end groups " and " middle groups ". The last analysis is marginally the most successful. The mixed second virial coefficients arecompared with the values predicted by the principle of corresponding states, using the Hudson-McCoubrey combining rule to estimate the mixed pseudo-critical temperatures, together with the McGlashan-Potter reduced equation of state. The agreement is in most cases within the experimental uncertainty. Other combining rules are less successful.

The excess molar enthalpy and cross-term second virial coefficients of (nitrogen + propane) and (nitrogen + butane) fromT= 241.2 to 393.4 K)

“…(13) Figure 3 shows these values to be about half as big as expected. Cross-term second virial coefficients obtained by Cruickshank et al (14)(15)(16) from chromatographic measurements are in good agreement with the curve shown in figure 3. Values of B 12 obtained by Cruickshank et al using this technique are generally reliable, and while the errors on the measurements are not as small as those on the measurements derived from our H E m values, the good agreement with our results is reassuring.…”

The determination of activity coefficients of alkenes, alkynes, and cycloalkanes at infinite dilution with the polar solvent tetrahydrothiophene-1,1-dioxide (sulpholane) using a g.l.c. technique atT=303.15 K andT=313.15 K

“…The experimental error in g a 13 is estimated to be better than 3 per cent and is not dissimilar to the estimated error established by the Bristol group. (15) This is based on our estimation of the experimental error in the flow rate measurements and retention time measurements which are 1·10 35 and 51). This reflects the association between alkynes and sulpholane and also the dissociation of the sulpholane on mixing.…”

Averaging the pressure and flow rate of the carrier gas in a gas chromatographic column

“…For traditional gas chromatography, i.e., at moderate pressures and pressure drops and Pi >Po, it is common to apply the "classical" factor j 23 , without appreciating the specificity of the different compressibility correction factors outlined above. Equations that incorporate ]'2 and even j4 have been suggested for chromatography with a non-ideal carrier gas, especially at elevated pressurs and flow rates [8,9]. It is remarkable, that all the compressibility correction factors approach unity on reducing the pressure drop in the column to zero, i.e., at pi/Po --~ 1 or, which is the same, at Pi-Po = Ap---> 0.…”