borates kaj thomsen
TRANSCRIPT
Thermodynamic Modeling of the Solubility of Alkali and Earth Alkali Borates
Kaj Thomsen, Associate Professor
CERE, Center for Energy Resources Engineering
Department of Chemical and Biochemical Engineering
Technical University of Denmark
24-07-2012 Thermodynamic Modeling of the Solubility of Alkali and Earth Alkali Borates
2 DTU Chemical Engineering, Technical University of Denmark
Importance of borates
• Metabolizing effects – useful for controlling insects and bacteria
• Bleaching effects – useful in laundry detergents
• Buffering effects – widely used for controlling pH
• Dispersing effects – useful in paints, adhesives and cosmetics
• Vitrifying effects – modify the structure of glass, facilitate the production of LCD screens
• Inhibiting effects – forms a coating that protect metals from corrosion
• Flame-Proofing effects – useful as a flame retardant
• Neutron-Absorbing effects – useful in connection with certain hospital equipment and nuclear containment shields
• Micro nutrient for plants
• Glazing on ceramics
• Largest single use worldwide is as an ingredient in fiberglass
24-07-2012 Thermodynamic Modeling of the Solubility of Alkali and Earth Alkali Borates
3 DTU Chemical Engineering, Technical University of Denmark
Complexity of borates
• The chemical formulae for borates are often written in terms of the amounts of oxides:
Na2O B2O3 H2O Formula 1 Formula 2
1 1 1 Na2O•B2O3•H2O NaBO2•½H2O
1 1 4 Na2O•B2O3•4H2O NaBO2•2H2O
1 1 8 Na2O•B2O3•8H2O NaBO2•4H2O
1 2 Na2O•2B2O3 Na2B4O7
1 2 4 Na2O•2B2O3•4H2O Na2B4O7•4H2O
1 2 10 Na2O•2B2O3•10H2O Na2B4O7•10H2O
1 5 10 Na2O•5B2O3•10H2O NaB5O8•5H2O
2 1 1 2Na2O•B2O3•H2O NaBO2•NaOH
2 5 7 2Na2O•5B2O3•7H2O Na4B10O17•7H2O
2 9 11 2Na2O•9B2O3•11H2O Na4B18O29•11H2O
24-07-2012 Thermodynamic Modeling of the Solubility of Alkali and Earth Alkali Borates
4 DTU Chemical Engineering, Technical University of Denmark
Complexity of borates
• In this work, all borate species were expressed in terms of:
– H3BO3(aq), Boric acid
– B4O72-, Tetraborate ion
– BO2-, Metaborate ion
• B2O3 is considered to be a dehydrated form of Boric acid:
2H3BO3(aq) ↔ B2O3 + 3H2O
• B5O8- is formed when pH is raised:
5H3BO3(aq) + OH- ↔ B5O8- + 8H2O
• Tetraborate, B4O72- +is formed at slightly higher pH:
4H3BO3(aq) + 2OH- ↔ = B4O72- + 7H2O
• Metaborate, BO2- is formed when pH is increased more:
H3BO3(aq) +OH- ↔ BO2- + 2H2O
24-07-2012 Thermodynamic Modeling of the Solubility of Alkali and Earth Alkali Borates
5 DTU Chemical Engineering, Technical University of Denmark
Extended UNIQUAC model
• Not a new model but new parameters
– Original parameters were limited in terms of temperature, concentration, and pH
• Thermodynamic model for solutions containing electrolytes
– Debye-Hückel term for electrostatic interactions
– UNIQUAC term for short range interactions
– Soave-Redlich-Kwong term for gas phase fugacities
• The model is used for calculation of
– Speciation equilibrium
– Solid-liquid equilibrium
– Vapor liquid equilibrium
– Liquid-liquid equilibrium
– Thermal properties
24-07-2012 Thermodynamic Modeling of the Solubility of Alkali and Earth Alkali Borates
6 DTU Chemical Engineering, Technical University of Denmark
Extended UNIQUAC model
• Relative permittivity for pure water is used for all solutions
– The effect of other species on the chemical potentials in the solution is accounted for by interaction parameters
• The hydrogen ion is given fixed parameters, including interaction parameters with all other species
– The hydrogen ion is considered an anchor for the parameters
– The properties of all other species are determined relative to those of the hydrogen ion
• The temperature dependence of chemical potentials is determined by the Gibbs-Helmholtz equation:
0 0
2
/ln at constant pressure
d G RTd K H
dT dT RT
24-07-2012 Thermodynamic Modeling of the Solubility of Alkali and Earth Alkali Borates
7 DTU Chemical Engineering, Technical University of Denmark
Model parameters and standard state properties • Volume and surface area parameters for each species
– 6 parameters
• A binary interaction parameter for each pair of species
– 26 interaction parameters were used
– 5 of these have linear temperature dependency
• Values of the Gibbs energy of formation for ions is usually found in the NIST tables
• Values not found in the NIST tables were determined during parameter estimation:
– Enthalpy of formation of the tetraborate ion, B4O72-
– Gibbs energy of formation for 22 solid phases
– Enthalpy of formation for 20 solid phases
24-07-2012 Thermodynamic Modeling of the Solubility of Alkali and Earth Alkali Borates
8 DTU Chemical Engineering, Technical University of Denmark
Determination of parameters
• The adjustable parameters were determined using a modified Marquard routine from Harwell subroutine library and a Nelder-Mead simplex routine
• Parameter determination:
1. Core system consisting of H+, Li+,Na+, K+, Mg2+, Ca2+, OH-, Cl-, HCl, NO3
-, HNO3, SO42-, HSO4
- based on ca. 27000 experimental data points distributed on 23 binary and 87 ternary systems.
2. 3000 experimental data for borates in the above systems except HNO3 were used for
• Determining the 6+26 model parameters for the borate species
• Determining the 43 standard state properties for the various solid phases and the tetraborate ion
24-07-2012 Thermodynamic Modeling of the Solubility of Alkali and Earth Alkali Borates
9 DTU Chemical Engineering, Technical University of Denmark
Online experimental data bank - free
• Data bank for electrolyte solutions at http://www.cere.dtu.dk/Expertise/
• Over 150,000 experimental data on electronic form
• More than 350 solute species
• Types of data include:
– Activity/osmotic coefficient
– Enthalpy of mixing
– Heat capacity
– Degree of dissociation
– Gas solubility
– Enthalpy of absorption/evaporation
– Density
– Salt solubility (Solid-liquid equilibrium)
– Liquid-liquid equilibrium
– Vapor-liquid equilibrium
24-07-2012 Thermodynamic Modeling of the Solubility of Alkali and Earth Alkali Borates
10 DTU Chemical Engineering, Technical University of Denmark
-5
15
35
55
75
95
115
0 5 10 15 20 25 30
Tem
peratu
re °
C
Weight percent Na2B4O7
Horn and Van Wagener (1905)
Teeple (1929)
Blasdale and Slansky (1939)
Nies and Hulbert (1967)
Platford (1971)
Extended UNIQUAC model
Na2B4O7·10H2O Borax
Na2B4O7·4H2O Kernite
24-07-2012 Thermodynamic Modeling of the Solubility of Alkali and Earth Alkali Borates
11 DTU Chemical Engineering, Technical University of Denmark
0%
1%
2%
3%
4%
5%
6%
0% 10% 20% 30% 40%
wt
% H
3B
O3
wt % MgCl2
Extended UNIQUAC
Gode (1969)
H3BO3
MgCl2·6H2O
25°C
24-07-2012 Thermodynamic Modeling of the Solubility of Alkali and Earth Alkali Borates
12 DTU Chemical Engineering, Technical University of Denmark
0
10
20
30
40
50
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
mo
l H
2O
/(m
ol
Na
2O
+B
2O
3)
Na2O/(Na2O+B2O3) molar ratio
Extended UNIQUAC
Nies and Hulbert (1967)
Sborgi and Mecacci (1916)
60°C
H3BO3
Sassolite
NaB5O8·5H2O Sborgite
Na2B4O7·10H2O Borax
NaBO2·4H2O NaBO2·½H2O
NaOH·H2O
Na4B10O17·7H2O Excurrite
2Na2O·B2O3·H2O
NaBO2·2H2O
24-07-2012 Thermodynamic Modeling of the Solubility of Alkali and Earth Alkali Borates
13 DTU Chemical Engineering, Technical University of Denmark
0
10
20
30
40
50
60
70
80
0 0.2 0.4 0.6 0.8 1
H2O
/(K
2O
+B
2O
3) m
ol
basis
K2O/(K2O+B2O3) mol basis
Carpeni (1955)
Extended UNIQUAC
45°C H3BO3 KB5O8·4H2O
K2B4O7·4H2O
KBO2·H2O KOH·H2O
24-07-2012 Thermodynamic Modeling of the Solubility of Alkali and Earth Alkali Borates
14 DTU Chemical Engineering, Technical University of Denmark
0
50
100
150
200
250
300
350
400
450
500
0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2
H2O
/(M
gO
+B
2O
3 m
ol
ba
sis)
MgO/(MgO+B2O3) mol basis
D'Ans and Behrent (1957)
Extended UNIQUAC
83°C
H3BO3
MgO·3B2O3·7.5H2O
MgB2O4·3H2O
24-07-2012 Thermodynamic Modeling of the Solubility of Alkali and Earth Alkali Borates
15 DTU Chemical Engineering, Technical University of Denmark
0
500
1000
1500
2000
2500
0 0.2 0.4 0.6 0.8 1
H2O
/(C
aO
+B
2O
3)
mo
l b
asi
s
CaO/(CaO+B2O3) mol basis
Sborgi (1913)
Extended UNIQUAC
30°C
Ca(OH)2
CaB2O4·6H2O
2CaO·3B2O3·13H2O Inyoite
CaO·3B2O3·4H2O H3BO3
24-07-2012 Thermodynamic Modeling of the Solubility of Alkali and Earth Alkali Borates
16 DTU Chemical Engineering, Technical University of Denmark
0
0.5
1
1.5
2
2.5
3
3.5
0 10 20 30 40 50
Li 2
B4O
7
LiCl
T= 25.0°C
Extended UNIQUAC modelLepeshkov et al. (1963)Skvortsov et al. (1981)
Li2B4O7·3H2O
LiCl·H2O
24-07-2012 Thermodynamic Modeling of the Solubility of Alkali and Earth Alkali Borates
17 DTU Chemical Engineering, Technical University of Denmark
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
1.00
0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00
Li+
C
ation C
harg
e fra
ction
K+
SO42- Anion charge fraction B4O7
2-
T= 14.9°C
Sang et al. (2004)Sang et al. (2006) -metastableZeng et al. (2005)Zeng et al. (2007)Extended UNIQUAC model
Li2SO4·K2SO4
K2SO4
Li2SO4·H2O
K2B4O7·4H2O
Li2B4O7·3H2O
24-07-2012 Thermodynamic Modeling of the Solubility of Alkali and Earth Alkali Borates
18 DTU Chemical Engineering, Technical University of Denmark
Conclusion
• The complex system of alkali and earth alkali borates could be modeled using a relatively simple model with only a few parameters
• The system was modeled considering only three aqueous species H3BO3(aq), B4O7
2-, BO2-
• Can the modeling be improved by including B5O8- ?
• Most of the model parameters were not temperature dependent
• Many experimental solubility data are conflicting – better solubility data are needed!
• Meta stability is an issue in this system
Thank you very much for your attention
24-07-2012 Thermodynamic Modeling of the Solubility of Alkali and Earth Alkali Borates
20 DTU Chemical Engineering, Technical University of Denmark
Model implementation
• The model is implemented in a dynamic link library (DLL-file)
– Multi-phase flash algorithm
– The program can be called from programs that have a Visual Basic interface such as Microsoft Excel
– Simulations can be carried out directly in Excel
– The excel sheet can be used as an interface to Aspen Plus®
– The model can be implemented as a user model in Aspen Plus®