(667g) Prediction of Phase Behavior of Strongly Associating Fluids By Explicit Consideration of Transitions in Local Fluid Structures

Accurate modeling of phase behavior of acetic acid has been of great interest both in academia and industry.  The challenge is to accurately describe the various local structures (hydrogen bonding configurations) and the transition in the distribution of local structures associated with phase transitions. In this work we use the PR+COSMOSAC EOS to predict the phase behaviors of fluids containing acetic acid. The PR+COSMOSAC EOS does not use any species dependent parameter and does not require input of experimental data. However to accurately model strongly associating fluids, it is necessary to identify the important local fluid structures such as the monomer, cyclic dimer, chain fragment of acetic acid and the cross dimer of acetic acid and alcohol. The transformations among these structures are considered by chemical reactions.  With the explicit inclusions of these associating structures the PR+COSMOSAC EOS is as accurate as the mod-UNIFAC+ Hayden-O’Connell EOS in describing the vapor liquid equilibrium of 19 binary mixtures (447 data points, temperature range from 293.15 to 426.39) is 6.49% (AARD-P%) in pressure and 2.22% (AAD-y%) in vapor composition, which is similar to those from the mod-UNIFAC+HOC 5.16% and 1.87%.  The root-mean square error in predicting liquid composition in liquid-liquid equilibrium of 5 binary systems (51 data points, temperature range from 289.15K to 337K) is found to be 0.091, which is more accurate than that from mod-UNIFAC, 0.173.  Our results show that the phase behavior of strongly associating systems can be predicted accurately by explicit consideration of the significant local fluid structures.