Dear DWSIM Developers,

My name is Pedro Lucas Silva de Andrade, a Chemical Engineering undergraduate at Universidade Federal de Minas Gerais - UFMG, in Brazil. I am simulating the supercritical transesterification of vegetable oil with ethanol for the production of biodiesel, thus operating in high conditions of temperature and pressure.

After many trials, I observed that Peng-Robinson EoS fails to represent the dense, homogeneous supercritical phase confirmed in the literature. In DWSIM, it converges to a low-density vapor phase. I understand this is a theoretical limitation of a cubic EoS for a highly associative system containing ethanol and glycerol.

My plan is to migrate the thermodynamic modeling to PC-SAFT, which I know is available in the Advanced EOS Library and is theoretically appropriate. Before I begin the parameterization, I need to understand the software's internal behavior to ensure I interpret the results correctly.

For this I have some questions regarding the flash equilibrium solver, and its phase classification. When DWSIM calculates a single phase above the mixture's critical point, how does it report this phase in the property table? Does it use a specific 'Supercritical' designation, or does it simply default to 'Vapor' or 'Liquid' based on the density root found?

Moreover, is the correct parameterization of PC-SAFT (with association parameters and kᵢⱼ values) sufficient for the native solver to find the correct high-density root in this region? Or are advanced solver settings required to favor this solution?

Lastly, is the use of external solvers required for modeling this type of associative system at supercritical conditions, or are the native DWSIM solvers fully capable when paired with an appropriate model like PC-SAFT?

My goal is to ensure that when I implement the correct model, I am also interpreting the simulator's output correctly.

Thank you for any clarification on the simulator's internal logic under these conditions.

Best regards,

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Pedro Lucas Silva de Andrade
Chemical Engineering Undergraduate
Universidade Federal de Minas Gerais (UFMG)
(37) 99938-2804