On the issue of balancing binary interaction parameters
Thread Content
There is an existing organic mixture, mainly composed of ethyl acetate, isopropanol, and water. Currently, the gas feed is compressed by a compressor and then sent to a heat exchanger for condensation. I’m confused as to whether the binary interaction parameter for ethyl acetate and water should use LLE or VLE; I’d appreciate some guidance from experts
When dealing with the condensation of a mixture of ethyl acetate and water, the Vapor-Liquid Equilibrium (VLE) model should be utilized. Because your scenario involves a gaseous mixture being compressed and condensed, the main focus is on the process of gas turning into liquid. LLE (liquid-liquid equilibrium) is primarily used to analyze the interactions between two or more liquid components, and it is not applicable to gas-to-liquid conversion processes. Therefore, in this case, VLE data and models should be used for calculations and design. .
Simulating such compression and condensation cooling processes only requires VLE calculations. If downstream processes include modules such as decanters (which separate the oil phase from the water phase in a mixed-phase liquid) that involve calculations related to liquid-liquid equilibrium, then the VLLE method must be employed. Furthermore, acetate ethyl ester, isopropanol, and water form azeotropes with each other in pairs; it is necessary to check whether the chosen thermodynamic method can accurately represent the phase equilibrium properties of these three pairs of azeotropic systems.
The VLLE method refers to property calculation methods such as NRTL and UNIQUAC that can utilize VLLE, or does it refer to binary interaction parameters? There is no concept of VLLE for binary interaction parameters
When adding a thermodynamic method to the modeling, if that method is applicable not only to VLE but also to VLLE, an “VLE/VLLE Options” option will appear in the menu for defining the thermodynamic method, thereby allowing users to specify whether it should be used for VLE calculations or VLLE calculations. The binary interaction parameters are used for the calculation of the phase equilibrium constant K; information such as the binary interaction parameters of the LLE component can be viewed in the LLE option of the K-value method only after this method is defined as VLLE. When it comes to phase equilibrium calculations, the set of thermodynamic methods first refers to the methods for determining the phase equilibrium constant K; as for specific property values such as the enthalpy and density of gas and liquid phases, the method set provides default methods for each of them. If users have sufficient actual data to show that the calculation results of a certain default method exhibit large deviations, they can replace that default method with another more suitable one. For example, for certain aromatic systems, using COSTALD or API for the liquid phase density may be more accurate than the default method.
It seems that in Aspen, there is no VLE/VLLE option when defining property methods; this option seems to be available only in PROII. So how should one define it in Aspen?
Aspen defines key components in the two liquid phases in Properties/Prop-Sets, etc.