TABLE OF CONTENTS A phase is defined as that part of a system that is uniform in physical and chemical properties, homogeneous in composition, and separated from other coexisting phases by definite boundary surfaces. The most important phases occurring in petroleum production are the hydrocarbon liquid phase and the gas phase. Water is also commonly present as an additional liquid phase. These can coexist in equilibrium when the variables describing change in the entire system remain constant with time and position. The chief variables that determine the state of equilibrium are system temperature, system pressure, and composition.
The conditions under which these different phases can exist are a matter of considerable practical importance in designing surface separation facilities and developing compositional models. These types of calculations are based on the concept of equilibrium ratios.
A system that contains only one component is considered the simplest type of hydrocarbon system. The word component refers to the number of molecular or atomic species present in the substance. A single-component system is composed entirely of one kind of atom or molecule. We often use the word pure to describe a single-component system. The qualitative understanding of the relationship that exists between temperature T, pressure p, and volume V of pure components can provide an excellent basis for understanding the phase behavior of complex hydrocarbon mixtures.
Consider a closed evacuated container that has been partially filled with a pure component in the liquid state. The molecules of the liquid are in...
