New molecular models for hydrogen fluoride, refrigerants and their mixtures
Advancing the chemical engineering fundamentals
Thermodynamics: Developments with SAFT EOS (T2-1c)
Keywords: molecular model, SAFT-VR, refrigerants
Michaela Pollock, C. Adjiman, A. Galindo, G. Jackson
ABSTRACT
As a result of the depletion of the ozone layer and the banning of chlorofluorocarbons (CFCs) from use as refrigerants, there has been great interest in accurately predicting phase equilibrium of replacement refrigerants and their mixtures with hydrogen fluoride (HF). HF is used in the production of replacement refrigerants by reaction with the original CFCs. Accurate prediction of phase equilibrium is required for process design and simulation. This is of industrial significance since a large proportion of capital and energy costs are related to separation processes, many of which are driven by phase equilibrium. The Statistical Associating Fluid Theory with potentials of Variable Range (SAFT-VR) is used to describe the phase behaviour of these highly polar systems. Pure component models for HF and a variety of refrigerants have been developed by optimising to pure component vapour pressures and liquid densities. Binary mixture data is used to further discriminate between different pure component models. A difficulty in using SAFT-VR to model refrigerants is in determining a physically meaningful and consistent value for the non-sphericity of the molecule. In this work the non-sphericity is determined from quantum mechanical analysis. Asymmetric association models have been developed for the highly non-ideal and azeotropic mixtures HF + H2O and HF + R134a (1,1,1,2-tetrafluoroethane). Binary interaction parameters are obtained from parameter estimation to isothermal and isobaric vapour liquid equilibrium (VLE) data over a wide temperature and pressure range. Another parameter estimation procedure, which models experimental set-up, is being developed so that SAFT-VR mixture parameters can be optimised to direct measurements instead of correlated or manipulated data.
Presented Tuesday 18, 08:45 to 09:05, in session Thermodynamics: Developments with SAFT EOS (T2-1c).
