Species Table - Liquid Properties

From SysCAD Documentation
Jump to navigation Jump to search

Navigation: User Guide ➔ Species Table ➔ Liquid Properties

Main Editing User Species Database Species Database Data Table - Theory and Equations Viewing Properties
Species Database Editing User
Species Database
Importing data into Species Database Species Table Heat of Formation
and Entropy
Density Specific Heat
(Cp)
Phase Change
(solubility)
BPE &
Acid/Base
Ka/b
Vapour
Properties
Transport
Properties
Viewing
Species Properties
Species Properties Reports

Latest SysCAD Version: 25 February 2021 - SysCAD 9.3 Build 138.28098


Introduction

The two fields, Boiling Point Elevation (BPE) and the Disassociation constants (Ka/b), are only relevant for liquid species and hence they will not be visible for Solid or Gas species.

Both fields are optional, but will improve the quality of the solution results if they are completed.

Boiling Point Elevation

This field is optional.

The Boiling Point Elevation (BPE) is calculated for aqueous solutions using the following equation1:

[math] BPE = Kb*\sum(m*i) \,[/math]

where

[math]Kb[/math] is the Molal Boiling point elevation constant, or sometimes called the Ebullioscopic Constant.
For water Kb = 0.512°C/m
[math]m[/math] is the molality of each aqueous species - moles/kg water.
[math]i[/math] is the van't Hoff constant for each aqueous species.

Notes:

  1. The user may enter a van't Hoff Constant for each aqueous species in the Species Database. SysCAD will then use these values, together with the above equation to calculate the BPE for each stream when using the Standard Species Model and if van't Hoff is selected in PlantModel as the BPE Method in a project.
  2. The van't Hoff factor is a measure of the dissociation of the aqueous species in water. If the user cannot find a value for the van't Hoff factor in their references then the following approximations may be acceptable:
    • For relatively soluble species, then the van't Hoff Factor = number of ions in the species, e.g. i(BeCl2) = 3, i(MnSO4) = 2
    • For relatively insoluble species, then the van't Hoff Factor = 1, e.g. i(BaSO3) = 1

See Boiling Point Elevation for a general discussion on this topic.

The BPE value may then be used in vapour liquid equilibrium calculations, please see Vapour Liquid Equilibrium (VLE) for more information.

Example

For the following case:

Species
Mass (kg)
Moles (g moles)
Molality
van't Hoff Factor (i)
Fe2[SO4]3(aq) 10 25.01 0.025 4.4
MgSO4(aq) 15 124.6 0.125 1.21
NaCl(aq) 5 85.55 0.086 1.68
H2O(l) 1000 55508 - -
[math] BPE = 0.512*(0.025*4.4 + 0.125*1.21 + 0.086*1.68)[/math]
[math] BPE = 0.207[/math]°C

Reference

  1. Silderberg, M.S. “Chemistry - The Molecular Nature of Matter and Change”, 3rd Edition, 2003, pp508-509.

(Acid / Base) Dissociation (Ka/b)

This field is optional.

If the user requires a component to be included as an acid or base in the acidity, or pH, calculations, then this field must have the required acid or base dissociation constant. A number of 'standard' acids and bases are included in the default database with their associated dissociation constants. See Acidity Calculations for more information.

The acid/base dissociation constant is the equilibrium constant for the dissociation reaction of the particular acid or base in water:

For the equation [math] AB \rightleftharpoons A^+ + B^- [/math], the dissociation constant, K (Ka for acid, Kb for bases), is calculated as:

[math]K = \cfrac{[A ] [ B]}{[AB]} [/math]

where [AB] = concentration of the acid/base in mol/L in water

The form of the variable is:

ACIDS BASES

Ka(Ka1, Ka2, Ka3)

where

Ka1 - required
Ka2 - optional (only relevant for diprotic and triprotic acids)
Ka3 - optional (only relevant for triprotic acids)

Notes:

  1. For Ka ≥ 10, SysCAD assumes total dissociation.
  2. All Ka values MUST be positive values.

Kb(Kb1)

where

Kb1 - required

Notes:

  1. For Kb ≥ 1, SysCAD assumes total dissociation.
  2. Kb MUST be a positive value.

Examples: (with corresponding dissociation reactions)

Species Ka/Kb NOTES Dissociation Reactions
Hydrofluoric Acid (HF) Ka(6.8e-4) (a monoprotic acid) [math] (HF \rightleftharpoons H^+ + F^- )[/math]
Phosphoric Acid (H3PO4) Ka(7.2e-3, 6.3e-7, 4.2e-13) (a triprotic acid) [math] (H_3PO_4 \rightleftharpoons H^+ + H2PO4^-\rightleftharpoons H^+ + HPO4^{2-}\rightleftharpoons H^+ + PO4^{3-})[/math]
Sodium Hydroxide (NaOH) Kb(1) [math] (NaOH \rightleftharpoons Na^+ + OH^- )[/math]