Phase Transitions and Critical Properties of Binary Systems Consisting of Water, Alcohols, and Hydrocarbons

Abstract

Abstract By the method of constant volume piezometer values of p,T - and p,ρ,T-relations of binary homogeneous systems consist of water, alcohol (methanol, ethanol, 1-propanol) and hydrocarbon (n-pentane, n-hexane, n-heptane, n-octane) with the concentration of the second component x=0.2, 0.5, 0.8, 0.9 mole fraction were obtained at subcritical, nearcritical and supercritical regions of stare parameters. Using isochoric p-T break point technique the values of the phase transition parameters ps,ρs,Ts (lg⇄l and lg ⇄g l–liquid, g–gas) were determined. Using grapho-analytical method combining with the scaling behavior the critical parameters (pc,ρc,Tc) are evaluated. The dependence of pressure from temperature, density and composition along the phase coexistence curve is described by three parameter polynomial represented by expansion of the compressibility factor Zs=psVms/RTs=ps/RTsρms into a power series of density ω=ρs/ρc and temperature τ=Ts/Tc, and concentration x. Z s = p s / R T s ρ m s = 1 + ∑ i = 1 m ∑ j = 0 n ∑ k = 0 s a i j k ω i / τ j , p s = R T s ρ m s [ 1 + ∑ i = 1 m ∑ j = 0 n ∑ k = 0 s a i j k ω i / τ j ] . The average relative deviation of calculated values of pressure from experimental ones is varied 0.1–0.5 % depending on the studied system and its component composition. The dependence of temperature from density along the liquid↔gas phase coexistence curve is described by equations: far from critical points ρ l,g = ρ c (1±B0 τβ0 + B1 τβ1 ± B2 τβ2 + …), and in the symmetrical part of equilibrium curve (ρ l - ρ g )/2ρ c = B0 τβ0 + B2 τβ2 + B4 τβ4 + … Average relative error is 1.1-1.6%.