Thermal Properties of Hydrogen Fluoride from EOS +Association Model

Hydrogen fluoride (HF) has found a wide variety of uses in the chemical process industry. It is used as an alkylation catalyst in the making of high-octane fuel, it provides a fluoride ion source in the electrolytic production of aluminum, and it is also the fluorine source in fluorocarbon manufacture. Intrinsic to the successful design of separation and heat-transfer equipment utilizing HF is its accurate thermodynamic description. Extensive hydrogen bonding in HF makes popular equations of state such as Peng-Robinson ill-equipped to provide a useful model. Additionally, and more debilitating, is the scarcity of HF experimental data due to its extreme caustic nature. Recently, Lencka and Anderko (1993) proposed a thermodynamic model for HF which treats the chemical effects of the association reactions separately from the physical effects of the associated cluster interactions. This relatively simple model was used to study the heat of vaporization of HF from 233.15 K to its predicted critical point. Additionally, constant pressure and constant volume molar heat capacities are derived from the theory and compared to literature data. Other models for HF similar to the one studied in this article have appeared recently (Chai Kao et al., 1995; Twu et al., 1993; Economou and Peters, 1995). These models, while effective in their prediction of heat of vaporization, are much more demanding computationally than that proposed by Lencka and Anderko (1993). Its simplicity and effectiveness makes the latter model appealing as a focus for this present study.