H2O-HCl (Pitzer)

DWSIM Plus

Available with a DWSIM Plus (Patreon) subscription.

H₂O–HCl electrolyte property package using the Extended Pitzer model. Valid range: 0–16 mol/kg HCl, 273–473 K (0–200 °C). The model accounts for: Complete dissociation of HCl in water (H⁺ + Cl⁻).Activity coefficients via extended Pitzer (β⁰, β¹, β², C^φ).Water activity via osmotic coefficient.VLE: water vapour pressure depression + HCl partial pressure. Inherits from BaseElectrolytePropertyPackage so the package participates in the DWSIMPlus electrolyte machinery: stream classification of cations/anions/salts, LastEquilibriumResult caching consumed by CorrosionAndScaling models, and the standard CalculateChemicalEquilibria abstract contract used by external speciation consumers.

DWSIM.Extensions.PropertyPackages.Electrolytes.PropertyPackages.HClPropertyPackage
Assembly DWSIM.Extensions.PropertyPackages.Electrolytes.dll · Object ← PropertyPackage ← ElectrolyteBasePropertyPackage ← BaseElectrolytePropertyPackage ← HClPropertyPackage
Name in the flowsheet H2O-HCl (Pitzer) · FluentAPI PropertyPackages.Plus.HCl

Scope

The package describes hydrochloric acid: water and hydrogen chloride (Hydrogen chloride), with HCl fully dissociated into H⁺ and Cl^- in the liquid. It is meant for refinery overhead condensates, HCl absorbers and strippers, acid concentration, and acidified chlor-alkali brines. Other ions in the stream (Na⁺, K⁺, SO₄^2-, ...) act as spectators that raise the ionic strength. Water takes its vapor pressure times the water activity, HCl its partial pressure over the solution, and other molecular compounds Henry's law or their vapor pressure.

Flash. Both partial pressures depend on the HCl molality of the liquid alone, so the K-values change steeply with the liquid composition. The package has its own flash: the unknown is the HCl fraction of the water plus HCl in the liquid, the vapor fraction follows from the water and HCl balances, and the other compounds split by their own K-values. Bubble and dew points are roots of their sums in temperature or in ln P; vapor fraction, enthalpy and entropy specifications are solved inside the region they fall in. Streams without water or without HCl use the default flash.

The mean activity coefficient is the binary Pitzer equation for a 1-1 electrolyte, ln γ_± = f^γ + m B^γ + m² C^γ, with b = 1.2, α₁ = 2.0 and the Debye-Hückel slope A_φ(298.15 K) = 0.3915. β⁰(T) and β¹(T) follow the high-temperature fit of Ruaya and Seward (1987); C^φ is zero in that fit. The water activity comes from the osmotic coefficient, and the pH is -log₁₀(m γ_±). The HCl partial pressure is p_HCl = K_H(T) m² γ_±², times a Poynting factor (partial molar volume of HCl 17.8 cm³/mol) above the saturation pressure of water (below 0.01 % at 1 atm, about 7 % at 100 bar). K_H is the inverse of the equilibrium constant of HCl(g) = H⁺ + Cl^-, from the NBS tables (Wagman et al., 1982: Δ_rG° = -35.93 kJ/mol, Δ_rH° = -74.85 kJ/mol) with a constant Δ_rC_p = -165.5 J/(mol·K); it is 0.0508 Pa·kg²/mol² at 25 °C. The liquid density gives HCl its apparent molar volume in water, φ_V(m, T), fitted to the densities of Perry's Table 2-57 (1 to 30 wt%, 0 to 100 °C, within 0.3 %).

Enthalpy. Dissolved HCl takes its apparent molar enthalpy on the ideal-gas reference of the vapor, H = Δ_solH^∞ + φ_L(m) + φ_Cp(m)(T - 298.15 K), with Δ_solH^∞ = -74.85 kJ/mol and φ_L from the NBS tables and φ_Cp from Parker (1965) at 25 °C; the liquid heat capacity carries the same φ_Cp. The integral heat of solution matches the NBS values within 0.001 kJ/mol from 0.01 to 18.5 mol/kg.

Options (package editor, saved in HClPP_Options):

Option	Default	Effect
UsePoyntingCorrection	on	Poynting factor on pHCl
UseHMWMixingRules	on	Harvie-Møller-Weare θ and ψ terms for HCl in NaCl, KCl and Na2SO4 brines; pairs without data fall back to the binary Pitzer value at the total ionic strength
TrackHClMonohydrate, TrackHClDihydrate, TrackHClTrihydrate	off	Solid HCl·nH2O below the peritectics at -15.4, -17.7 and -24.4 °C, from a Ksp = (γ±m)2awn anchored at the peritectic

Accuracy. Mean activity coefficient at 25 °C against Robinson and Stokes:

m (mol/kg)	0.1	0.5	1.0	3.0	6.0	10.0
γ±, model	0.794	0.755	0.804	1.280	3.040	10.65
γ±, Robinson and Stokes	0.796	0.757	0.809	1.316	3.22	10.4

The maximum-boiling azeotrope at 1 atm comes out at 18.9 wt% HCl and 107.75 °C, against 20.22 wt% and 108.58 °C measured. Bubble points at 1 atm against Perry's Tables 2-9 and 2-10:

wt% HCl	6	10	14	18	22	26	30
Tbubble, model (°C)	101.9	103.7	105.9	107.7	105.7	94.1	71.7
Tbubble, Perry (°C)	101.7	103.1	105.0	107.5	108.1	103.3	90.3

Limitations

• Well validated up to 6 mol/kg; 6 to 16 mol/kg is an extrapolation (about 5 %), and above 16 mol/kg the molality is clamped with a warning. Above 3 mol/kg keep the temperature below 100 °C.
• The Ruaya-Seward fit is validated for the binary to 350 °C; the package writes a warning outside 0 to 200 °C.
• Above about 22 wt% the bubble points fall below the measured ones (26 wt%: 94.1 against 103.3 °C).
• φ_Cp is held at its 25 °C value, so heats of solution far from 25 °C are extrapolated.
• A spectator salt lowers the water activity through the ionic strength only; with salt in the acid the vapor fraction jumps near the point where the liquid dries out, and specifications inside that jump stop with an error.
• The compound must be named Hydrogen chloride (or Hydrochloric acid, HCl); the hydrates are the compounds Hydrogen Chloride Monohydrate, Hydrogen Chloride Dihydrate and Hydrogen Chloride Trihydrate.

Example

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

Python

fs = (Flowsheet.Create("HClExample")
      .WithCompounds("Water", "Hydrogen chloride")
      .WithPropertyPackage(PropertyPackages.Plus.HCl))

kg_water = 1.0 / 0.018015          # mol of water in 1 kg
acids = {}
for m in (1.0, 6.0):               # mol of HCl per kg of water
    acids[m] = (fs.AddMaterialStream(f"HCl {m:g} mol/kg").At(Q.Celsius(25.0), Q.Bar(1.01325))
                .SetCompoundMolarFlow("Water", kg_water)
                .SetCompoundMolarFlow("Hydrogen chloride", m))

fs.Solve()

for m, acid in acids.items():
    liq = acid.Object.Phases[3]
    pH = liq.Properties.pH
    gamma_pm = 10.0 ** (-pH) / m       # pH = -log10(m gamma+-), HCl fully dissociated
    print(f"{m:g} mol/kg: pH = {pH:6.3f}, mean activity coefficient = {gamma_pm:.3f}")

# water partial pressure over the 1 mol/kg acid, from the liquid fugacity of water
liq = acids[1.0].Object.Phases[3]
w = liq.Compounds["Water"]
p_w = w.MoleFraction * w.FugacityCoeff * acids[1.0].Object.Phases[0].Properties.pressure
print(f"Water partial pressure over 1 mol/kg HCl = {p_w / 1000.0:.3f} kPa")

Output

1 mol/kg: pH =  0.095, mean activity coefficient = 0.804
6 mol/kg: pH = -1.261, mean activity coefficient = 3.040
Water partial pressure over 1 mol/kg HCl = 3.054 kPa

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 / Peng-Robinson EOS
Liquid fugacity	Pitzer Activity Coefficient + Vapor Pressure / Henry's Law
Vapor enthalpy, entropy, Cp/Cv	Ideal Gas / Lee-Kesler
Liquid enthalpy, entropy, Cp/Cv	Ideal Gas - Vaporization Enthalpy (no Pitzer excess term)
Vapor density	Ideal Gas / Peng-Robinson EOS
Liquid density	Water density correlation plus the molar volumes of the ions (with an ionic-strength term), from the electrolyte database; molecular solutes as pure liquids (HCl is a molecular solute here)
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: Nested_Loops_VLE.

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
ElectrolyteFlash_ReactionSetID	DefaultSet	Reaction set of the electrolyte flash of the base package; this package flashes with its own K-values and does not read it
ElectrolyteFlash_Tolerance	1E-07	Tolerance of the same base flash, not used by this package
ElectrolyteFlash_MaximumIterations	200	Iteration limit of the same base flash, not used by this package
IncludeExcessEnthalpy	false	Option of the electrolyte base class (off by default); this package supplies no excess enthalpy, so it has no effect
GenerateSolubilityReactions	false	Option of the electrolyte base class, not used by this package (its flash takes no reactions)
UseReactiveKvalues	false	Option of the electrolyte base class for the rigorous column, not used by this package (it always gives its own K-values)
HClPP_Options	5 UsePoyntingCorrection entries	The model options, UsePoyntingCorrection (default true), UseHMWMixingRules (true) and TrackHClMonohydrate, TrackHClDihydrate, TrackHClTrihydrate (false)

First UsePoyntingCorrection of HClPP_Options in the example

<UsePoyntingCorrection>true</UsePoyntingCorrection>

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

Element	Value
Type	82 characters
ComponentName	H2O-HCl (Pitzer)
ComponentDescription	76 characters
Tag	H2O-HCl (Pitzer)
UseHenryConstants	true
AutoEstimateMissingNRTLUNIQUACParameters	true
UseImmiscibleListForLiquid2InitialEstimates	true
SingleCompoundCheckThreshold	0.99999
OverrideKvalFugCoeff	false
OverrideEnthalpyCalculation	false
OverrideEntropyCalculation	false
LiquidDensityCalculationMode_Subcritical	Rackett_and_ExpData
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	LeeKesler
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

  ---

  • H\(_2\)O–HCl (Pitzer)
  • Aqueous-Phase pH and Ionic Strength
  • Vapour-Phase Fugacity Convention

• Used with

  ---

  • Absorption Column
  • Distillation Column
  • Neutralization Reactor

API members

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

Constructors

HClPropertyPackage()

C#VB.NET

public HClPropertyPackage()

Public Sub New()

HClPropertyPackage(bool)

Parameter	Type	Description
comode	Boolean

C#VB.NET

public HClPropertyPackage(bool comode)

Public Sub New(comode As Boolean)

Properties

FlashBase: The package's own flash, HClFlash: it solves the water-HCl tie line directly, which the steep composition dependence...

The package's own flash, HClFlash: it solves the water-HCl tie line directly, which the steep composition dependence of the K-values requires.

C#VB.NET

public override FlashAlgorithm FlashBase { get; }

Public Overrides ReadOnly Property FlashBase As FlashAlgorithm

ImplementsCrossPlatformEditor

C#VB.NET

public override bool ImplementsCrossPlatformEditor { get; }

Public Overrides ReadOnly Property ImplementsCrossPlatformEditor As Boolean

ShouldUseKvalueMethod3

C#VB.NET

public override bool ShouldUseKvalueMethod3 { get; }

Public Overrides ReadOnly Property ShouldUseKvalueMethod3 As Boolean

TrackHClDihydrate: Track HCl·2H₂O dihydrate saturation.

Track HCl·2H₂O dihydrate saturation. Default false; meaningful below 255 K.

C#VB.NET

public bool TrackHClDihydrate { get; set; }

Public Property TrackHClDihydrate As Boolean

TrackHClMonohydrate: Track HCl·H₂O hydrate saturation.

Track HCl·H₂O hydrate saturation. Default false. When enabled, the stream's solid-phase fugacity for HCl·H₂O is computed from HydrateKsp; only meaningful below 258 K where the monohydrate is the equilibrium phase.

C#VB.NET

public bool TrackHClMonohydrate { get; set; }

Public Property TrackHClMonohydrate As Boolean

TrackHClTrihydrate: Track HCl·3H₂O trihydrate saturation.

Track HCl·3H₂O trihydrate saturation. Default false; meaningful below 249 K.

C#VB.NET

public bool TrackHClTrihydrate { get; set; }

Public Property TrackHClTrihydrate As Boolean

UseHMWMixingRules: Apply the Harvie–Møller–Weare 1984 mixing rules (cation–cation θ and triplet ψ) when spectator electrolytes are...

Apply the Harvie–Møller–Weare 1984 mixing rules (cation–cation θ and triplet ψ) when spectator electrolytes are present in the stream. Default true. Disable to fall back to the binary-Pitzer- with-I_total approximation (faster, marginally less accurate for HCl in NaCl/Na₂SO₄/etc. brines).

C#VB.NET

public bool UseHMWMixingRules { get; set; }

Public Property UseHMWMixingRules As Boolean

UsePoyntingCorrection: Apply the Poynting correction p_HCl(P) = p* · exp(V̄·(P-P_sat)/RT) to the HCl partial pressure when the system...

Apply the Poynting correction p_HCl(P) = p* · exp(V̄·(P-P_sat)/RT) to the HCl partial pressure when the system pressure exceeds water saturation. Default true. Disable to recover the bare Henry-law prediction (slightly faster, only relevant near 1 atm).

C#VB.NET

public bool UsePoyntingCorrection { get; set; }

Public Property UsePoyntingCorrection As Boolean

Methods

AUX_LIQDENS(double, double, double, int, bool): Liquid density [kg/m3].

Liquid density [kg/m3]. The electrolyte base adds a molecular solute's volume as a pure liquid, which for HCl (a gas above 188 K) is its liquid volume at the normal boiling point, about 30 cm3/mol against an apparent molar volume of 18-20 cm3/mol in water: 1 mol/kg acid at 25 C came out at 1002 kg/m3. Here HCl takes its apparent molar volume (ApparentMolarVolume) and the rest of the liquid keeps the base's volume.

Parameter	Type	Description
T	Double
P	Double
Pvp	Double
phaseid	Int32
FORCE_EOS	Boolean

C#VB.NET

public override double AUX_LIQDENS(double T, double P = 0, double Pvp = 0, int phaseid = 3, bool FORCE_EOS = false)

Public Overrides Function AUX_LIQDENS(T As Double, P As Double = 0, Pvp As Double = 0, phaseid As Integer = 3, FORCE_EOS As Boolean = False) As Double

CalculateChemicalEquilibria(double, double)

Parameter	Type	Description
T	Double
P	Double

C#VB.NET

public override EquilibriumResult CalculateChemicalEquilibria(double T, double P)

Public Overrides Function CalculateChemicalEquilibria(T As Double, P As Double) As EquilibriumResult

CalculateChemicalEquilibria(double, double, double[])

Parameter	Type	Description
T	Double
P	Double
x	Double[]

C#VB.NET

public override EquilibriumResult CalculateChemicalEquilibria(double T, double P, double[] x)

Public Overrides Function CalculateChemicalEquilibria(T As Double, P As Double, x As Double()) As EquilibriumResult

Clone()

C#VB.NET

public override PropertyPackage Clone()

Public Overrides Function Clone() As PropertyPackage

DisplayEditingForm()

C#VB.NET

public override void DisplayEditingForm()

Public Overrides Sub DisplayEditingForm()

DW_CalcEnthalpy(Array, double, double, State): Liquid enthalpy [kJ/kg].

Liquid enthalpy [kJ/kg]. The base puts every compound on its ideal gas enthalpy less its heat of vaporisation, which for HCl is the 9 kJ/mol of the pure liquid. Here dissolved HCl takes its apparent molar enthalpy (ApparentMolarEnthalpy): the integral heat of solution of HCl(g) in water, -74.85 kJ/mol at infinite dilution and less exothermic as the acid gets stronger, on the same ideal gas reference as the vapour. Water and the other compounds keep the base enthalpy.

Parameter	Type	Description
Vx0	Array
T	Double
P	Double
st	State

C#VB.NET

public override double DW_CalcEnthalpy(Array Vx0, double T, double P, State st)

Public Overrides Function DW_CalcEnthalpy(Vx0 As Array, T As Double, P As Double, st As State) As Double

DW_CalcEntropy(Array, double, double, State): Liquid entropy [kJ/(kg K)].

Liquid entropy [kJ/(kg K)]. The base liquid entropy of a compound is its ideal gas entropy less its heat of vaporisation over T; dissolved HCl takes its heat of solution over T in place of that, the same term the enthalpy changes divided by T.

Parameter	Type	Description
Vx0	Array
T	Double
P	Double
st	State

C#VB.NET

public override double DW_CalcEntropy(Array Vx0, double T, double P, State st)

Public Overrides Function DW_CalcEntropy(Vx0 As Array, T As Double, P As Double, st As State) As Double

DW_CalcEquilibrium(FlashSpec, FlashSpec)

Parameter	Type	Description
spec1	FlashSpec
spec2	FlashSpec

C#VB.NET

public override void DW_CalcEquilibrium(FlashSpec spec1, FlashSpec spec2)

Public Overrides Sub DW_CalcEquilibrium(spec1 As FlashSpec, spec2 As FlashSpec)

DW_CalcFugCoeff(Array, double, double, State): Calculates fugacity coefficients for the specified composition at the specified conditions.

Calculates fugacity coefficients for the specified composition at the specified conditions.

Parameter	Type	Description
Vx	Array	Vector of doubles containing the molar composition of the mixture.
T	Double	Temperature in K
P	Double	Pressure in Pa
st	State	Mixture state (Liquid or Vapor)

C#VB.NET

public override double[] DW_CalcFugCoeff(Array Vx, double T, double P, State st)

Public Overrides Function DW_CalcFugCoeff(Vx As Array, T As Double, P As Double, st As State) As Double()

DW_CalcKvalue3(double[], double[], double, double): Calculates K-values of components in a mixture.

Calculates K-values of components in a mixture.

Parameter	Type	Description
Vnx	Double[]	Vector of doubles containing the molar flows of the liquid phase.
Vny	Double[]	Vector of doubles containing the molar flows of the vapor phase.
T	Double	Temperature of the system.
P	Double	Pressure of the system.

C#VB.NET

public override double[] DW_CalcKvalue3(double[] Vnx, double[] Vny, double T, double P)

Public Overrides Function DW_CalcKvalue3(Vnx As Double(), Vny As Double(), T As Double, P As Double) As Double()

DW_CalcPhaseProps(Phase)

Parameter	Type	Description
Phase	Phase

C#VB.NET

public override void DW_CalcPhaseProps(Phase Phase)

Public Overrides Sub DW_CalcPhaseProps(Phase As Phase)

DW_CalcProp(string, Phase): Provides a wrapper function for CAPE-OPEN CalcProp/CalcSingleProp functions.

Provides a wrapper function for CAPE-OPEN CalcProp/CalcSingleProp functions.

Parameter	Type	Description
property	String	The property to be calculated.
phase	Phase	The phase where the property must be calculated for.

C#VB.NET

public override void DW_CalcProp(string property, Phase phase)

Public Overrides Sub DW_CalcProp([property] As String, phase As Phase)

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

LoadData(List<XElement>): Reads the three calculation options back.

Reads the three calculation options back. A file saved before they were persisted has no such elements, and the options then keep their defaults (off).

Parameter	Type	Description
data	List<XElement>

C#VB.NET

public override bool LoadData(List<XElement> data)

Public Overrides Function LoadData(data As List(Of XElement)) As Boolean

PopulateCrossPlatformEditor(object): The Avalonia editor; see AvaloniaPackageEditors.

The Avalonia editor; see AvaloniaPackageEditors.

Parameter	Type	Description
container	Object

C#VB.NET

public override void PopulateCrossPlatformEditor(object container)

Public Overrides Sub PopulateCrossPlatformEditor(container As Object)

ReturnInstance(string)

Parameter	Type	Description
typename	String

C#VB.NET

public override object ReturnInstance(string typename)

Public Overrides Function ReturnInstance(typename As String) As Object

RunPostMaterialStreamSetRoutine()

C#VB.NET

public override void RunPostMaterialStreamSetRoutine()

Public Overrides Sub RunPostMaterialStreamSetRoutine()

SaveData(): Writes IncludeExcessEnthalpy, GenerateSolubilityReactions and UseReactiveKvalues after the data the base package...

Writes IncludeExcessEnthalpy, GenerateSolubilityReactions and UseReactiveKvalues after the data the base package saves, so the three options travel with the flowsheet file and with Clone.

C#VB.NET

public override List<XElement> SaveData()

Public Overrides Function SaveData() As List(Of XElement)