(57a) Introduction to Rate Based Mass Transfer Models

Rate based mass transfer models are built on five key elements –

• Mass and energy balances around individual phases on a tray or in a packed segment
• Thermodynamic phase equilibrium

• Equilibrium across interfaces
• Kinetic effects on mass transfer rates
• Mass and heat transfer rate models for transport across interfaces.

In addition, the five key elements have interwoven relationships with chemical, physical, phase and transport properties based on the chemical species being used and the actual mass transfer hardware. In sharp contrast, an equilibrium stage model uses only mass and energy balances around an entire ideal stage plus thermodynamic phase equilibrium and use empirical correction factors to account for efficiencies and mass transfer hardware. For applications such as absorption, where the mass transfer efficiencies are poor (5-25%) equilibrium stage based models prove to be grossly non-predictive, while rate based models are mechanistic, and predictive. This presentation will focus on the characteristics of true mass transfer rate based models, contrast them with the ideal stages and introduce briefly the ProTreat ® process simulator.