The operational limits for temperature, pressure, and composition in OLI software are determined by the selected thermodynamic framework. OLI provides three frameworks, each tailored to different application needs:
- MSE (Mixed Solvent Electrolyte) – Default framework since version 11.5
- MSE-SRK (MSE integrated with Soave–Redlich–Kwong Equation of State)
- AQ (Aqueous Model) – Legacy framework with narrower applicability
MSE Framework
The MSE framework offers the most extensive range of thermodynamic coverage, supporting highly non-ideal systems including concentrated electrolytes and mixed solvents. Its key operational limits are:
- Temperature: Up to \( 0.9 \cdot T_{\text{critical}} \) (90% of the system’s critical temperature). For water-rich systems, this corresponds to around 340 °C.
- Pressure: Up to 1500 atmospheres
- Ionic Strength: No limit
- Total Dissolved Solids (TDS): No limit
- Concentration: From infinite dilution to fused salt levels
MSE-SRK Framework
The MSE-SRK framework maintains compatibility with the MSE model in the water-rich liquid phase but is designed for scenarios where vapor-liquid equilibrium in hydrocarbon systems becomes significant. It is particularly useful in systems containing acid gases like CO2 and H2S in combination with light hydrocarbons (C1–C7), especially at elevated pressures.
- Water-rich liquid phase: Same ranges as the MSE framework
- Non-water-rich phases (e.g., CO2/H2S-rich gas or hydrocarbon mixtures): Valid at pressures of up to at least 1500 atm
For detailed information on phase behavior and supported chemistries, refer to the dedicated MSE-SRK documentation.
AQ Framework
The AQ (Aqueous) framework represents OLI’s earlier thermodynamic model, primarily suited for low to moderate ionic strength systems. While still supported, its applicability is more limited:
- Temperature: 0 °C to 300 °C
- Pressure: Up to 1500 atmospheres
- Ionic Strength: Valid up to 30 mol/kg H2O
For more information regarding when to use MSE or AQ, refer this this article.