Experimental Determination of Direction and Order of Magnitude of Solubility Isotope Effects

Abstract The aim of the experimental investigations was (a) to give more detailed information about the direction (sign) and the order of magnitude of the solubility isotope effects (IE) of the corresponding species of methane, ethane, nitrogen, carbon dioxide and hydrogen in crude oil and (b) to decompose the isotope effects into their physicochemical parts and to quantify them. It is shown that the IE in crude oil are composed of four contributions: The experiments were carried out in a PVT apparatus. The measured isotope effects were fitted to the function which allows the calculation of the IE in the Henry coefficient ΔKi /Ki , (from C(1 − A)), the partial molar volumes Δvip/RT (from A ∗ B ∗ C) and the nonideal behaviour (ΔΦ i /Φ i - Δγ i /γ i ) in both phases. The results showed a large difference in direction and order of magnitude of the thermodynamic isotope effects, which are more significant in the case of hydrogen, methane and ethane. The pressure dependence of the D-IE was remarkably different...