Experimental and modeling investigations of the interfacial tension of three different diesel + nitrogen mixtures at high pressures and temperatures

Abstract

Interfacial tension (IFT) data are reported at temperatures up to 530 K and pressures up to 100 MPa for mixtures of N2 with a highly paraffinic diesel, an ultra-low sulfur diesel, and a highly aromatic diesel. The impact of composition on the IFT is determined by comparing data for each system at the same temperature and pressure calculated from a Tait-like relationship fit to the experimental data. The greatest differences in diesel + N2 IFT values are found near the normal boiling point (Tboil) of each diesel where lower molecular weight diesel components begin to dissolve in the N2-rich vapor phase. IFT data are modeled with density gradient theory (DGT) coupled with the perturbed-chain, statistical associating fluid theory equation of state (EoS). Diesel EoS parameters are calculated using three variations of a pseudo-component technique created from one group contribution (GC) method developed from high-pressure density data and from two other GC methods (S-GC and T-GC) developed from differing sets of pure component vapor pressure and saturated liquid density data. The IFT predictions significantly improve when the DGT influence parameter, cii, is allowed to vary with temperature. The DGT predictions with the B-GC method are in closest agreement with data at temperatures below Tboil, which is attributed to the more accurate representation of liquid phase densities. However, at temperatures above Tboil, where significant amounts of low molecular weight diesel components dissolve in the N2-rich vapor phase, DGT predictions with the S-GC and T-GC methods provide the closest agreement with IFT data.