1. What is the UNIFAC Model?

The UNIFAC (UNIQUAC Functional-group Activity Coefficients) method is a group contribution method for predicting activity coefficients in non-ideal mixtures. It divides the activity coefficient into combinatorial (γ^C) and residual (γ^R) parts.

2. How Does the Calculator Work?

The calculator uses the UNIFAC equation:

Where:

• \( \gamma^C \) — Combinatorial part (accounts for molecular size/shape differences)
• \( \gamma^R \) — Residual part (accounts for group interactions)
• \( \gamma \) — Total activity coefficient (unitless)

Explanation: The model requires group interaction parameters between all functional groups in the mixture.

3. Importance of Activity Coefficients

Details: Activity coefficients are crucial for predicting vapor-liquid equilibrium, liquid-liquid equilibrium, and solubility in non-ideal mixtures.

4. Using the Calculator

Tips: Enter temperature in Kelvin, mole fraction (0-1), and component groups (e.g., CH3, CH2, OH, etc.). The calculator estimates γ based on group contributions.

5. Frequently Asked Questions (FAQ)

Q1: What are the limitations of UNIFAC?
A: UNIFAC may be less accurate for complex molecules, systems with strong hydrogen bonding, or near critical points.

Q2: How are group parameters determined?
A: Parameters are fitted to extensive experimental vapor-liquid equilibrium data for many binary systems.

Q3: What's the difference between UNIFAC and UNIQUAC?
A: UNIFAC is a group contribution version of UNIQUAC, which requires pure component parameters.

Q4: Can UNIFAC predict all mixture properties?
A: No, it's primarily for activity coefficients, though these can be used to calculate other properties.

Q5: Are there different UNIFAC versions?
A: Yes, including original UNIFAC, modified UNIFAC (Dortmund), and others with different parameter tables.