Aspen Plus Thermodynamic Method Selection Guide v3.2

The guide is structured around decision logic rooted in molecular interactions and phase equilibrium fundamentals. It categorizes systems by key attributes—including presence of electrolytes, supercritical components, highly polar or associating compounds (e.g., alcohols, acids), and azeotrope-forming mixtures—and prescribes models based on empirical validation and extensive benchmarking against experimental data (e.g., VLE, LLE, and PVT). Each recommended method (e.g., NRTL-RK, UNIFAC-Dortmund + PR, eNRTL for electrolytes) is accompanied by applicability limits, parameter availability (built-in vs. user-defined), and guidance on required property databanks (e.g., DECHEMA, NIST). A core principle is the 'hierarchy of fidelity': simpler models (e.g., Wilson) are recommended for preliminary design when robustness outweighs precision, while advanced models (e.g., CPA, SAFT-VR) are reserved for highly associating or complex systems where standard models fail. The guide also emphasizes workflow integration—highlighting when to use property estimation tools (e.g., UNIFAC), how to handle missing binary parameters, and strategies for model validation using sensitivity analysis and experimental tie-line matching.