Sorption of long chain normal paraffins in molecular sieves

Recent studies in these laboratories of the sorption of n-paraffins (in the C4—C20 range) in specially treated 5A molecular sieves have revealed that both temperature and molecular weight have somewhat unexpected effects on the isotherms determined by a McBain spring balance method (at 300–400°). The results do not agree with predictions in the literature that, with increasing carbon number, the isosteric heats of sorption should rise at a constant rate. Above C10, − ΔH decreases, temperature dependence becoming almost zero in the region C15—C20. The results are compared with the limited amount of published data, and discussed in terms of the configuration of the sorbed molecules, and of unusual entropy effects. The deductions are supported by some measurements, also reported, for the sorption of nC8—nC17 in 13X sieves.