Interfacial tension between water and non-polar fluids up to 473 K and 2800 bar

TLDR: In this paper, the Pendant Drop or standing bubble is applied to measure interfacial tension between water and nonpolar fluids to high temperatures and pressures, and a high pressure cell with two sapphire windows and auxiliary equipment with several feed autoclaves is described.

Abstract: The method of the Pendant Drop or Standing Bubble is applied to measure interfacial tensions between water and nonpolar fluids to high temperatures and pressures. The high pressure cell with two sapphire windows and the auxiliary equipment with several feed autoclaves is described. The shapes and sizes (about 2 mm) of drops and bubbles are recorded with microscope and video camera. A digital image processing procedure was developed which permits fast, objective and precise determination of the contour parameters. The six gases helium, neon, argon, nitrogen, methane, and propane have been investigated to 473 K (with nitrogen to 573 K) and (in part) to 2800 bar. Gas densities came close to liquid density values. For comparison, water plus liquid n-hexane, n-decane, and toluene was investigated to 473 K and 3000 bar. For these liquid hydrocarbons, the interfacial tension γ always increases with pressure. At 373 K for water-n-hexane γ is 41.8 mN/m at 100 bar and 47.3 mN/m at 2600 bar, respectively. In the water-gas systems γ decreases with pressure and passes through a flat minimum around 1000 bar. For water-nitrogen at 373 K γ = 52.5, 46.5 and 48.3 mN/m at 200, 1400 and 2800 bar. Only with water-helium γ increases continuously with pressure.