Interfacial tension measurements of methane + propane binary and methane + propane + n-heptane ternary mixtures at low temperatures

Abstract

The interfacial tension (IFT) between a liquid and a gas is essential in the design of liquid-gas separators as it determines the size of liquid droplets which can become entrained in the gas phase. In liquefied natural gas (LNG) plants, the scrub column is designed to remove components heavier than propane. However, if this column is poorly designed, these heavier components can carry over in the top product and potentially cause a solids formation problem in the main cryogenic heat exchanger. Therefore, accurate measurements and predictions of IFT are required to ensure good separation of heavy components prior to the liquefaction of the natural gas. In this work, reference-quality IFT measurements of methane + propane binary mixtures and methane + propane + n-heptane ternary mixtures were conducted at low temperatures (204 to 230) K and pressures up to the mixtures’ critical points using the differential capillary rise method in a high-pressure visual sapphire cell. The combined standard absolute uncertainties of the measured IFT were between (0.04 and 0.96) mN·m−1. The absolute deviations of measured IFT from values predicted with a Parachor model were within 3 mN⋅m−1, while a Linear Gradient Theory model over predicts mixtures’ IFT by up to 5.2 mN⋅m−1. The reference-quality IFT experimental data provided by this work should facilitate improvements of prediction models and allow separators in LNG plants to be designed with more confidence.