Vapor Pressure Predictions of the Sanchez-Lacombe Equation
Dr. Michael Misovich, Hope College
This research involved the study of the Sanchez-Lacombe (S-L) Ising (lattice) fluid equation of state (EOS). Chemical engineers use EOS to estimate vapor-liquid equilibrium properties such as vapor pressure for process analysis and simulation. A Maple 13® computer program generated vapor pressures from the S-L equation as a function of temperature for ranges of equation parameters. Characteristic temperature T*, characteristic pressure P*, and size parameter r were varied. These characteristic parameters differ numerically from the critical parameters used in most EOS; however, changing the characteristic parameters had no effect on the dimensionless relationship between vapor pressure and temperature expressed as reduced variables by dividing by critical constants. The size parameter r did affect the dimensionless relationship of vapor pressure to temperature. This was quantified by a quadratic relationship between r and the acentric factor ω used in standard corresponding states models and some common equations of state. Work continues to compare S-L vapor pressures to those predicted by cubic equations of state like Soave-Redlich-Kwong and Peng-Robinson and to produce a generalized Antoine vapor pressure relationship for S-L.
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