Interactive Effects of API Gravity and Storage Geometry on Short-Term Volume Retention of Selected Polar and Nonpolar Organic Liquids

Abstract

The interactive effects of API gravity and storage geometry on the volume retention of selected polar and nonpolar organic liquids (ethanol, methanol, low-molecular-weight crude oil [LCO], and natural gas liquids [NGL]) were investigated in this study over 7 days of evaporative storage. The storage systems used for monitoring the process were shaped into five different geometries (horizontally cylindrical, vertically cylindrical, cuboidal, spherical, and conical), and the liquids used in this study were characterized by API gravity, dipole moment, standard enthalpy of vaporization, vapor pressure, and interfacial evaporation descriptors. The results showed that liquid retention was governed by a competitive interplay among volatility, cohesive intermolecular attraction, gas-phase mass transfer, and vessel geometry. The consistent poor retention of NGL was attributed to its high API gravity, low effective cohesive energy, and very high vapor pressure. At the same time, ethanol and LCO exhibited the highest retention due to their lower volatility and greater resistance to evaporation. The polar compounds showed that ethanol retained more volume than methanol. However, both compounds have a close range of API gravities and dipole moments, indicating that the enthalpy of vaporization and vapor pressure were more decisive than polarity alone. The role of geometry was enormous as the conical vessel had the highest cumulative retention, while the spherical vessel had the least. Therefore, short-term storage losses are controlled not by API gravity alone, but by the combined effects of thermodynamic properties and storage geometry, with clear implications for reducing evaporation losses and for storage design in the process industries.