UNIQUAC¶

UNIQUAC (Universal Quasi-Chemical) activity coefficient model for the liquid phase, with the r and q structural parameters of the compounds and binary parameters from the ChemSep databank, an ideal or Peng-Robinson vapor phase and vapor pressures from the compound correlations. For polar and hydrogen-bonding liquid mixtures, including partially miscible ones.

DWSIM.Thermodynamics.PropertyPackages.UNIQUACPropertyPackage
Assembly DWSIM.Thermodynamics.dll · Object ← PropertyPackage ← ActivityCoefficientPropertyPackage ← UNIQUACPropertyPackage
Name in the flowsheet UNIQUAC · FluentAPI PropertyPackages.UNIQUAC

Scope¶

An activity coefficient model for the liquid phase of polar, hydrogen-bonding and partially miscible mixtures at low to moderate pressure: water with alcohols, ketones or esters, heterogeneous azeotropes and decanters, extraction, and mixtures of molecules of very different size. The liquid fugacity is f_i^L = x_iγ_iP_i^sat times the Poynting factor, with the vapor pressure from the compound correlation; gases above their critical temperature dissolve by Henry's law.

UNIQUAC (Universal Quasi-Chemical) splits the excess Gibbs energy into two parts. The combinatorial part accounts for differences in size and shape through two pure-compound parameters, the relative volume r_i and the relative surface area q_i (coordination number z = 10). The residual part accounts for the interaction energies through two binary parameters per pair:

ln γ_i = ln γ_i^C + ln γ_i^R, τ_ij = exp[(-A_ij + B_ijT + C_ijT²)/(RT)]

with A in cal/mol, which is the classic τ_ij = exp[-(u_ij - u_jj)/RT] when B and C are zero. Only the residual part depends on temperature. UNIQUAC is also the basis of the UNIFAC group contribution method, which computes r, q and the interactions from functional groups.

Parameters. r and q of the compounds and the binary A₁₂, A₂₁, B and C come from the UNIQUAC tables of the ChemSep databank shipped with DWSIM. When a pair is missing and AutoEstimateMissingNRTLUNIQUACParameters is on (the default), the package estimates it from UNIFAC; a pair in which one compound boils below 200 K gets near-ideal values. The parameters can be edited in the package editor, fitted to VLE or LLE data with the Data Regression utility, or set from code with ConfigureUNIQUAC(c => c.WithBinary(c1, c2, a12, a21)), and are saved with the flowsheet.

Vapor phase and caloric properties. As in NRTL: ideal vapor by default with the Peng-Robinson vapor as an option (its k_ij saved as InteractionParameters_PR), enthalpy from the liquid heat capacity and the enthalpy of vaporization of the compounds by default, liquid densities from experimental data, Rackett or COSTALD. Analytical temperature and composition derivatives of ln γ_i are available to the flashes and the column solvers.

Limitations¶

Low to moderate pressure; for high pressure or gas-rich mixtures use an equation of state.
Parameters fitted to vapor-liquid data reproduce bubble points and vapor compositions, and may misplace the mutual solubilities of a liquid-liquid split. In the example (water and 1-butanol) the bubble temperature and the vapor match the measured heterogeneous azeotrope, while the butanol-rich liquid holds less water than measured. Fit the pair to LLE data when the liquid compositions matter.
Supercritical gases dissolve through Henry constants.

Example¶

This code runs on every build of this site, and the output below is what it printed.

Python

fs = (Flowsheet.Create("UNIQUACExample")
      .WithCompounds("Water", "1-butanol")
      .WithPropertyPackage(PropertyPackages.UNIQUAC))

# 60 mol% water lies inside the miscibility gap: at its bubble point two liquids
# boil together with one vapor (vapor-liquid-liquid equilibrium)
feed = (fs.AddMaterialStream("Water + butanol")
        .WithPressure(Q.Bar(1.01325)).WithVaporFraction(0.0)
        .SetCompoundMolarFlow("Water", 0.6)
        .SetCompoundMolarFlow("1-butanol", 0.4))

fs.Solve()

s = feed.Object
vapor = s.Phases[2]
# the two liquid phases: the one with less water is the butanol-rich phase
liquids = sorted((s.Phases[3], s.Phases[4]), key=lambda p: p.Compounds["Water"].MoleFraction)
organic, aqueous = liquids
print(f"Bubble temperature   = {s.GetTemperature() - 273.15:.2f} C")
print(f"Water in vapor       = {vapor.Compounds['Water'].MoleFraction:.4f} (mole fraction), "
      f"{vapor.Compounds['Water'].MassFraction * 100:.1f} wt%")
print(f"Water in organic     = {organic.Compounds['Water'].MassFraction * 100:.1f} wt%")
print(f"Butanol in aqueous   = {aqueous.Compounds['1-butanol'].MassFraction * 100:.1f} wt%")
print(f"Aqueous phase        = {aqueous.Properties.molarfraction:.4f} of the liquid (mole fraction)")

Output

Bubble temperature   = 92.89 C
Water in vapor       = 0.7604 (mole fraction), 43.6 wt%
Water in organic     = 17.4 wt%
Butanol in aqueous   = 7.7 wt%
Aqueous phase        = 0.2636 of the liquid (mole fraction)

DWSIM 10.2.11.0, generated 2026-10-08.

Property methods¶

How the package calculates each property, as it reports it in PropertyMethodsInfo (the property package editor shows the same list).

Property	Method
Vapor fugacity	Ideal / PR EOS
Liquid fugacity	Activity Coefficient + Poynting + Vapor Pressure / Henry's Constant
Vapor enthalpy, entropy, Cp/Cv	Ideal / Lee-Kesler / Excess / Experimental
Liquid enthalpy, entropy, Cp/Cv	Ideal / Lee-Kesler / Excess / Experimental
Vapor density	Ideal / PR EOS
Liquid density	Experimental / Rackett / COSTALD
Vapor viscosity	Experimental / Lucas / Jossi-Stiel-Thodos
Liquid viscosity	Experimental / Letsou-Stiel
Vapor thermal conductivity	Experimental / Ely-Hanley
Liquid thermal conductivity	Experimental / Latini
Surface tension	Experimental / Brock-Bird
Solid density	Experimental Data / User-Defined
Solid enthalpy, entropy, Cp/Cv	Experimental Solid Cp / From Liquid Phase Enthalpy + Enthalpy of Fusion

Default flash algorithm: Universal.

Configuration saved with the flowsheet¶

The package writes its settings to the simulation file (SaveData) and reads them back on load (LoadData). The elements below are the ones this package adds to those of every property package, as written for the example.

Element	Content in the example	What it holds
`InteractionParameters_PR`	empty	k_ij of the Peng-Robinson equation used for the vapor phase when it is not ideal (`Value`), pairs of the flowsheet compounds
`InteractionParameters_UNIQUAC`	2 `InteractionParameter` entries (`Compound1`, `Compound2`, `ID1`, `ID2`, `A12`, `A21`, `B12`, `B21`, `C12`, `C21`)	UNIQUAC parameters of the pairs of the flowsheet compounds; τ_ij = exp[(-A_ij + B_ijT + C_ijT²)/(RT)] with A in cal/mol

First InteractionParameter of InteractionParameters_UNIQUAC in the example

<InteractionParameter Compound1="Water" Compound2="1-butanol" ID1="1921" ID2="1105" A12="548.2453" A21="89.0444" B12="0" B21="0" C12="0" C21="0" />

Settings common to every property package, as saved for the example

Element	Value
`Type`	`DWSIM.Thermodynamics.PropertyPackages.UNIQUACPropertyPackage`
`ComponentName`	`UNIQUAC`
`ComponentDescription`
`Tag`	`UNIQUAC`
`UseHenryConstants`	`true`
`AutoEstimateMissingNRTLUNIQUACParameters`	`true`
`UseImmiscibleListForLiquid2InitialEstimates`	`true`
`SingleCompoundCheckThreshold`	`0.99999`
`OverrideKvalFugCoeff`	`false`
`OverrideEnthalpyCalculation`	`false`
`OverrideEntropyCalculation`	`false`
`LiquidDensityCalculationMode_Subcritical`	`COSTALD`
`LiquidDensityCalculationMode_Supercritical`	`Rackett_and_ExpData`
`LiquidDensity_CorrectExpDataForPressure`	`true`
`LiquidDensity_UsePenelouxVolumeTranslation`	`true`
`LiquidViscosityCalculationMode_Subcritical`	`ExpData`
`LiquidViscosityCalculationMode_Supercritical`	`Letsou_Stiel`
`LiquidViscosity_CorrectExpDataForPressure`	`true`
`LiquidViscosity_MixingRule`	`MoleAverage`
`VaporPhaseFugacityCalculationMode`	`Ideal`
`SolidPhaseFugacityCalculationMethod`	`FromLiquidFugacity`
`SolidPhaseFugacity_UseIdealLiquidPhaseFugacity`	`false`
`SolidPhaseEnthalpy_UsesCp`	`false`
`EnthalpyEntropyCpCvCalculationMode`	`ExpData`
`LiquidEnthalpyEntropyCpCvCalculationMode_EOS`	`EOS`
`LiquidFugacity_UsePoyntingCorrectionFactor`	`true`
`ActivityCoefficientModels_IgnoreMissingInteractionParameters`	`false`
`IgnoreVaporFractionLimit`	`false`
`IgnoreSalinityLimit`	`false`
`CalculateAdditionalMaterialStreamProperties`	`true`
`FlashCalculationApproach`	`NestedLoops`
`DisplayMissingCompoundPropertiesWarning`	`false`
`ForcedSolids`	`[]`
`PropertyOverrides`	`{}`
`FlashSettings`	36 `Setting` entries

Learn more¶

User guide
Used with

API members¶

Public members declared by this class. Inherited members are documented on the base classes.

Constructors¶

UNIQUACPropertyPackage()

C#VB.NET

public UNIQUACPropertyPackage()

Public Sub New()

UNIQUACPropertyPackage(bool)

Parameter	Type	Description
`comode`	`Boolean`

C#VB.NET

public UNIQUACPropertyPackage(bool comode)

Public Sub New(comode As Boolean)

Properties¶

DisplayDescription

C#VB.NET

public override string DisplayDescription { get; }

Public Overrides ReadOnly Property DisplayDescription As String

DisplayName

C#VB.NET

public override string DisplayName { get; }

Public Overrides ReadOnly Property DisplayName As String

m_uni

C#VB.NET

public UNIQUAC m_uni { get; set; }

Public Property m_uni As UNIQUAC

Popular

C#VB.NET

public override bool Popular { get; }

Public Overrides ReadOnly Property Popular As Boolean

Methods¶

CheckMissingInteractionParameters(double[])

Parameter	Type	Description
`Vx`	`Double[]`

C#VB.NET

public override bool CheckMissingInteractionParameters(double[] Vx)

Public Overrides Function CheckMissingInteractionParameters(Vx As Double()) As Boolean

DisplayEditingForm()

C#VB.NET

public override void DisplayEditingForm()

Public Overrides Sub DisplayEditingForm()

EstimateMissingInteractionParameters(bool)

Parameter	Type	Description
`verbose`	`Boolean`

C#VB.NET

public void EstimateMissingInteractionParameters(bool verbose)

Public Sub EstimateMissingInteractionParameters(verbose As Boolean)

GetEditingForm(): Returns the binary interaction parameter editor of this package.

Returns the binary interaction parameter editor of this package.

C#VB.NET

public override object GetEditingForm()

Public Overrides Function GetEditingForm() As Object

GetModel()

C#VB.NET

public override object GetModel()

Public Overrides Function GetModel() As Object

RET_VQ()

C#VB.NET

public object RET_VQ()

Public Function RET_VQ() As Object

RET_VR()

C#VB.NET

public object RET_VR()

Public Function RET_VR() As Object

RunPostMaterialStreamSetRoutine()

C#VB.NET

public override void RunPostMaterialStreamSetRoutine()

Public Overrides Sub RunPostMaterialStreamSetRoutine()

Fields¶

ClassId

C#VB.NET

public const string ClassId = "5265F953-8825-4a80-9112-A3B68C329E4C"

Public Const ClassId As String = "5265F953-8825-4a80-9112-A3B68C329E4C"