(741e) A Modified PC-SAFT Equation of State for Water Which Includes an Association Dependent Hard Sphere Diameter

Application of the SAFT class of equations of state to systems of commercial interest is often challenged by the inaccuracy SAFT in the description of pure water properties. SAFT approaches typically predict liquid water densities at ambient conditions which are several percent in error. In addition, SAFT approaches substantially underpredict (~15%) the heat capacity of liquid water at ambient conditions. The liquid density error is exacerbated by the fact that pure water streams are often defined volumetrically, meaning the density must be used to convert to a mass or molar flowrate within the process simulation. If the density error is 5%, the error in mass flowrate calculated from the volumetric flowrate will also be 5%. Further, a 15% error in heat capacity can result in substantial errors in energy balances within process simulations. This limits the applicability of SAFT based approaches to many processes of commercial interest. We address this issue by introduction of an association dependent hard sphere diameter within the PC-SAFT equation of state. The new approach is demonstrated to be a step change in accuracy for the representation of pure water properties as compared to standard PC-SAFT applications. Extension of the approach to mixtures is discussed.