Equilibrium calculations for
fatty acid calcium soaps in pulp
washing
Marianne Björklund Jansson and Rickard Wadsborn
2005
According to Innventia Confidentiality Policy this report is public since 2011-02-04
Equilibrium calculations for fatty
acid calcium soaps in pulp
washing
Marianne Björklund Jansson and Rickard Wadsborn
Report no.: STFI-Packforsk 140 | December 2005
Cluster: Chemical pulp, fibre line
Distribution restricted to: AGA, AssiDomän Cartonboard, Billerud, Borregaard, Eka
Chemicals, Holmen Iggesund Paperboard, Kemira, Korsnäs, Metsä-Botnia, Mondi
Packaging, M-real, Peterson & Søn, Stora Enso, Södra Cell, Voith
a report from STFI-Packforsk
According to Innventia Confidentiality Policy this report is public since 2011-02-04
According to STFI-Packforsk's Confidentiality Policy this report is assigned category 2
Equilibrium calculations
STFI-Packforsk report no. 140
Acknowledgements
This work has been performed within the Cluster research program of Chemical pulp fibre line, in the period 2004-2005.
According to Innventia Confidentiality Policy this report is public since 2011-02-04
According to STFI-Packforsk's Confidentiality Policy this report is assigned category 2
Equilibrium calculations
STFI-Packforsk report no. 140
Table of contents
Page
1
Summary .....................................................................................................1
2
Background.................................................................................................2
3
The reactions of calcium during pulping and washing ...........................3
4
5
3.1
Sources of calcium ....................................................................................... 3
3.2
Sources of carbonate ................................................................................... 3
3.3
Calcium bound to fibres and lignin ............................................................... 4
3.4
Calcium soaps of fatty and resin acids ......................................................... 4
Experimental ...............................................................................................8
4.1
Equilibrium calculations ................................................................................ 8
4.1.1
4.1.2
4.1.3
The calculation program ............................................................................................8
Components ..............................................................................................................8
Equilibrium constants.................................................................................................8
4.2
Chemical analysis of mill samples................................................................ 9
Results.......................................................................................................10
5.1
Composition of mill samples....................................................................... 10
5.2
Equilibrium calculations .............................................................................. 12
5.2.1
5.2.2
5.2.3
5.2.4
5.2.5
5.2.6
5.2.7
Guide to the diagrams .............................................................................................12
Influence of the solubility product of the calcium soaps. .........................................13
Influence of the carbonate concentration on the formation of calcium soaps .........17
Influence of the pulp consistency ............................................................................19
Calcium binding capacity of carboxyl groups in the fibres.......................................21
Influence of calcium concentration ..........................................................................22
Case “bleached pulp”...............................................................................................23
6
Discussion and conclusions ...................................................................26
7
References ................................................................................................28
8
Appendix A. Discription of mill samples ...............................................31
According to Innventia Confidentiality Policy this report is public since 2011-02-04
According to Innventia Confidentiality Policy this report is public since 2011-02-04
According to STFI-Packforsk's Confidentiality Policy this report is assigned category 2
Equilibrium calculations
STFI-Packforsk report no. 140
1 (32)
1 Summary
The influence of some parameters on the precipitation of calcium soaps during the
conditions of pulp washing and bleaching have been investigated, using a process
simulation program extended with a tool that handles chemical equilibrium calculations.
The aim of the calculations was to identify parameters where a small change in
concentration will influence the formation of calcium soaps. The calculated phase
diagrams illustrate how the precipitation of different calcium soaps is affected by e.g.
calcium and carbonate concentrations, and pH.
For the concentrations of the ingoing chemical components, data from three mills, all
producing hardwood kraft, was used. The mill samples, pulps and filtrates, were taken
from the washing stage after the oxygen stage and from the last washing stage in the
bleaching line.
A marked influence on the solubility product, pKs, for the different calcium soaps is seen.
Especially the formation of calcium soaps from the most prevailing, unsaturated fatty
acids, e.g. linoleic acid, seems extensively to be depending on the concentrations of
ingoing components, e.g. calcium and carbonate, and the pH. Resin acids, with a pKs for
the calcium soaps around 9, do not form calcium soaps at any of the tested conditions.
According to Innventia Confidentiality Policy this report is public since 2011-02-04
According to STFI-Packforsk's Confidentiality Policy this report is assigned category 2
Equilibrium calculations
STFI-Packforsk report no. 140
2 (32)
2 Background
Wood resin (pitch) often gives problems in the pulp production line e.g. by clogging wires
and screens. Further, pitch deposits formed on equipment during pulp screening and
bleaching often are the main source for dirt specks in the bleached pulp. The deposits
often consist of a combination of calcium soaps of fatty acids and calcium carbonate
mixed with other resin components and fibres (Ollandt 1979, Dorris et al, 1983). The
formation of calcium soaps will impair the washing of wood resin, both because the
formed calcium soaps are water insoluble and therefore will stick to the fibres and also
since the capacity for solubilization of the neutral pitch components will decline when the
concentration of soluble sodium soaps is decreased. The sodium soaps of fatty and resin
acids work as a detergent in the pulp washing and are able to solubilize the waterinsoluble neutral components, e.g. sterols, in the micelles formed.
Besides the concentrations of calcium and fatty acids the formation of calcium soaps
depends on a number of parameters. Among the most important are: pH, temperature,
ionic strength and the concentration of inorganic ions, such as carbonate and metal ions,
and the concentration of dissolved lignin. Further, both the amount of the wood resin itself
and its composition will have a major influence on the deposition of calcium soaps, due to
the complicated solubility behaviour of the resin components. Birch extractives normally
are more problematic depending on the higher percentage of neutral compounds. Further
birch resin contains a higher proportion of long chain, saturated fatty acids, forming more
insoluble calcium soaps, compared to spruce and pine.
In this report the influence of some of these parameters on the precipitation of calcium
soaps have been investigated, by calculations using a process simulation program
extended with a tool that handles chemical equilibrium calculations (Berggren et al 2003,
Gu 2004 a and b). The calculated phase diagrams illustrate how the precipitation of
different calcium soaps is affected by e.g. calcium and carbonate concentrations, and pH.
However, some effects such as solubilization and dispersion of resin components may not
be accounted for by the conducted simulations, and these effects were not considered.
The aim of the calculations was to identify parameters where a small change in
concentration will influence the formation of calcium soaps. Since the system is very
complex and it is not possible to take account for all factors, it has in this work not been
our intention to transfer the calculation directly to a specific mill situation.
According to Innventia Confidentiality Policy this report is public since 2011-02-04
According to STFI-Packforsk's Confidentiality Policy this report is assigned category 2
Equilibrium calculations
STFI-Packforsk report no. 140
3 (32)
3 The reactions of calcium during pulping and washing
3.1 Sources of calcium
The main part of the calcium coming into the pulp mill originates from the wood. Calcium
is, after potassium, the most common non-process element in wood and bark. Typical
concentrations in wood and bark are given in table 1. As seen, the calcium intake can be
increased significantly with poor debarking. Another source of calcium is the white
liquor. However, with a proper white liquor clarification this amount may be about 50
mg/kg pulp, which is less than 5 % of the amount entering the mill with the wood. During
periods with problems with the white liquor clarification the amount of calcium coming
with the white liquor may be substantial. Values up to 1900 mg/kg pulp have been
reported (Douek and Allen, 1980b).
Table 1. Calcium and magnesium in Swedish pine, spruce and birch wood and bark,
(Magnusson et al 1980).
Wood
Bark
Ca
mg/kg
Mg
mg/kg
Ca
mg/kg
Mg
mg/kg
Pine
620
170
5210
650
Spruce
770
95
4990
640
Birch
680
190
3020
490
The form in which calcium is present in the wood is not totally clear. Analysis across the
cross-section of a pine tree (Fossum et al 1972) shows that the concentration of calcium is
highest in the cambium. Further it is somewhat higher in the heartwood than in the
sapwood. It is also somewhat increased in parenchyma cells and resin canals. However,
resin and fatty acids are not believed to exist in the form of calcium soaps in the wood
where the pH is slightly acidic.
3.2 Sources of carbonate
During the cook a major part of the calcium in the wood will dissolve in the cooking
liquor. A part will also be precipitated as calcium carbonate (Hartler and Libert, 1973).
Carbonate ions are present in the white liquor and are also formed during the kraft cook,
mainly from decarboxylation of acids in the hemicellulose. According to Hartler and
Libert (1973) the concentration of carbonate in cooks with carbonate-free white liquor
may amount to about 20 mmol/l at the end of the cook. The carbonate content in industrial
white liquor is about 200 to 300 mmol/l. Hartler and Libert also determined the calcium
concentration in the liquor during the cook. The calcium concentration was highest when
carbonate-free white liquor was used and amounted then to about 1.5 mmol/l, which
According to Innventia Confidentiality Policy this report is public since 2011-02-04
According to STFI-Packforsk's Confidentiality Policy this report is assigned category 2
Equilibrium calculations
STFI-Packforsk report no. 140
4 (32)
corresponds to 60 mg/l. If all the calcium in the wood had been dissolved the
concentration would have been about 5 times as high. At the end of the cook the
concentration of calcium decreased to about 20 mg/l. Hartler and Libert drew the
conclusion that the decrease was due to precipitation of calcium carbonate. Calcium
hydroxide is normally not precipitated during kraft cooking.
Calculating with a logarithmic apparent solubility product of calcium carbonate of -7.3,
the maximum concentration of dissolved calcium in a liquor holding 20 mmol/l carbonate,
would only be 0.1 mg/l. The reason for the much higher concentrations actually observed
is that supersaturation of the liquor is necessary before calcium carbonate precipitates.
3.3 Calcium bound to fibres and lignin
Calcium and other divalent ions are bound much harder to the fibres than monovalent ions
such as sodium and potassium. This, in combination with the formation of CaCO3(s),
transfers a substantial part of the calcium ions present in the cook with the pulp into the
pulp bleaching. After the oxygen stage the amounts of calcium in the three birch pulps
used in this project were around 1500 mg/kg. Similar values have been reported in the
literature. The calcium is most probably present in the pulp as CaCO3(s) (Wadsborn et al
2005) or bound to the acidic groups of the fibres. Other parts of the calcium may be in the
form of calcium soaps of fatty acids, which are adhered to the fibres.
The precipitation of calcium soaps is also affected by the lignin concentration. This was
demonstrated by Douek and Allen (1980a) in a model experiment showing that the
precipitation of calcium oleate did not take place in the presence of Indulin, a commercial
kraft lignin. Whether this was an effect of the binding of calcium ions to the lignin, or by
a dispersion effect on formed calcium soaps is not known. However, some phenolic
structures such as cathecols are known to be strong complexing agents for metals
(Westervelt et al 1982; Werner et al 1998).
3.4 Calcium soaps of fatty and resin acids
Calcium soaps of fatty acids often constitute a major part of the wood resin deposits in the
washing and screening departments and a part of the fatty acids from the wood is
probably transported with the pulp to the bleaching stages in the form of calcium soaps.
Resin acids or resin acid soaps are in several investigations reported not to be present in
such deposits (Ollandt 1979, Dorris et al 1983). This difference is probably due to the
difference in solubility product for the soaps of resin acids as compared to fatty acids.
The pKs-values of the calcium soaps are of course critical in the calculations. A small
literature check on the variations of the solubility with ionic strength and temperature has
been done, but only limited data, especially for the temperature dependence, have been
found. Examples of solubilities of some calcium soaps are given in table 2. As seen, the
solubility increases with temperature and ionic strength, also illustrated in figure 1. The
According to Innventia Confidentiality Policy this report is public since 2011-02-04
According to STFI-Packforsk's Confidentiality Policy this report is assigned category 2
Equilibrium calculations
STFI-Packforsk report no. 140
5 (32)
solubility of the soaps is thus higher during the cook and decreases when the temperature
is decreased and the ionic strength lowered during the pulp washing.
One article from 2001 gives the pKs for calcium oleate at pH 9 and 67°C to 11.6
(Beneventi et al), which is lower than the values in figure 1. However, the wood resin
contains several different fatty acids, both with more and less soluble soaps compared to
oleic acid.
Also seen in table 2 is that the solubility of the calcium soaps decreases with increased
length of the fatty acid carbon chain and increases by the number of double bonds in the
chain. Long chain, saturated fatty acids can therefore be expected to comprise a higher
percentage of the deposited material than their percentage in the wood resin. Since the
unsaturated acids, linoleic, linolenic and oleic acids, are dominating in the wood resin
these may still constitute a substantial part of the deposits. The major fatty and resin acids
presents in pine, spruce and birch are shown in table 3.
Table 2. Solubility product, pKs, for some calcium soaps at two ionic strengths and two
temperatures.
(25 °C)
(50 °C)
(67 °C)
I = 1.0
I = 0.1
pH 9.0
11.9a)
11.3 a)
10.7 a)
Myristic (14:0)
14.5 a)
13.9 a)
13.5 a)
Palmitic (16:0)
17.1 a)
16.2 a)
Stearic (18:0)
19.7 b1)
Lignoceric (24:0)
27.1 b2)
Oleic (18:1)
14.9 a)
13.5 a)
11.6 c)
Linoleic (18:2)
14.2 a)
12.8 a)
10.1 c)
Acid
(no of carbons:double
bonds)
I = 0.1
Lauric (12:0)
14.8 c)
9.9 c)
Linolenic (18:3)
Abietic
9.0 d)
a) Irani and Callis; b1) Al Attar and Beck; b2) Calculated from Al Attar and Beck
c) Beneventi et al; d) Calculated from Pohle
According to Innventia Confidentiality Policy this report is public since 2011-02-04
According to STFI-Packforsk's Confidentiality Policy this report is assigned category 2
Equilibrium calculations
STFI-Packforsk report no. 140
6 (32)
17
Solubility product of Ca(Ol)2
25C
50C
60C
80C
T=25C, Exp
16
15
pKs
14
13
12
11
10
0
0,2
0,4
0,6
0,8
1
1,2
Ionic strength, mol/l
Figure 1. Influence of temperature and ionic strength on the solubility product of calcium
oleate, based on experimental data from Irani and Callis. The temperature dependence is
based on data for calcium myristate (-15.8 kcal/mol).
According to Innventia Confidentiality Policy this report is public since 2011-02-04
According to STFI-Packforsk's Confidentiality Policy this report is assigned category 2
Equilibrium calculations
STFI-Packforsk report no. 140
7 (32)
Table 3. Example of fatty and resin acid composition in pine (Pinus sylvestris), spruce (Picea
abies) and birch (Betula pendula). Data for pine and spruce from Holmbom 1980.
Fatty acid
Saturated:
Palmitic (16:0)
17:0ai*
Stearic (18:0)
Lignoceric (24:0)
Other saturated**
Unsaturated:
11-18:1
Oleic 9-18:1)
Linoleic (9,12-18:2)
Linolenic (9,12,1518:3)
Pinolenic (5,9,12-18:3)
20:1
5,11,14-20:3
Other unsaturated**
Other minor < 0.2 % each
Sum
Resin acids
Pimaric
Sandaracopimaric
Isopimaric
Levopimaric
Palustric
Abietic
Neoabietic
Dehydroabietic
Other minor
Sum
Pine wood
(% of total fatty
acids)
Spruce wood
(% of total fatty
acids)
Birch wood 1)
(% of total fatty
acids)
1.0
0.8
<0.2
<0.2
0.9
3.6
3.0
0.6
<0.2
2.8
9.2
n.d.
4.9
8.1
5.3
0.5
35.3
40.5
0.8
10.6
<0.2
4.6
3.5
2.0
25.0
36.4
0.9
14.9
<0.2
3.4
4.6
n.a.
5.6
59.0
1.3
0
4.7
n.d.
n.d.
1.5
100
Pine wood
(% of total resin
acids)
8.1
1.6
3.5
30.0
15.1
15.8
11.1
14.4
0.4
100
2.8
100
Spruce wood
(% of total resin
acids)
6.2
6.4
13.3
16.2
13.5
11.2
10.2
22.6
0.4
100
1.9
100
Birch wood
* a.i. (ante-iso) = branched at the carbon atom n-2.
** < 1.0% each
1)
Compilation of data from different sources
Resin acids
not present
-
According to Innventia Confidentiality Policy this report is public since 2011-02-04
According to STFI-Packforsk's Confidentiality Policy this report is assigned category 2
Equilibrium calculations
STFI-Packforsk report no. 140
8 (32)
4 Experimental
4.1 Equilibrium calculations
4.1.1 The calculation program
Calculations testing the potential for formation of calcium soaps in model systems at
different conditions have been performed using the process simulation program
WinGEMS (Pacific Simulation) extended with a tool developed to calculate the
distribution of metals in the fibre line at equilibrium (Gu et al 2004a and b, Berggren et al
2003). The tool, called MeteQ, is based on SOLGASWATER (Eriksson 1979) and uses
any chemical equilibrium model predefined by the user. The formation constants of the
compounds are adjusted for variations in temperature and ionic strength according to the
Vant-Hoff and Davies equations, respectively. Details of the implementation and the
validation of the tool may be found elsewhere (Gu et al 2004a and b Berggren et al 2003).
4.1.2 Components
Most of the calculations have been done using the following components: H+ (= pH),
Ca2+, CO32 , resin components such as resin acids (RA) and fatty acids (FA) with different
pKs-values for formation of calcium soaps. The carboxyl groups in the fibres have also
been included. The fatty acids have been divided in two groups, FA1 and FA2 with
different pKs as described in 5.2.1 below.
4.1.3 Equilibrium constants
The following equilibrium reactions have been included:
Inorganic compounds
H2O → OH- + H+
-
H+ + CO32 → HCO3
-
-
2 H+ + CO32 → H2CO3 (aq)
dissolved carbonic acid
Ca2+ + H2O → CaOH+
Ca2+ + CO32 → CaCO3 (s)
-
precipitated calcium carbonate
-
precipitated calcium hydroxide
Ca2+ + 2 OH → Ca(OH)2 (s)
Organic compounds
-
H+ + FA → HOl (aq)
-
Ca2+ + 2 FA → CaOl (s)
-
H+ + FA → HOl (s)
dissolved undissociated acid
calcium soap
precipitated undissociated acid
Corresponding reactions for resin acids (RA)
Ca2+ + 2 pulp-COOH → (pulp-COO)2Ca
Ca bound to fibres
According to Innventia Confidentiality Policy this report is public since 2011-02-04
According to STFI-Packforsk's Confidentiality Policy this report is assigned category 2
Equilibrium calculations
STFI-Packforsk report no. 140
9 (32)
The equilibrium constants have been adjusted to a temperature of 70 C . Sodium has not
been used as a component, but the equilibrium constants have been adjusted as close as
possible to the estimated ionic strength in the different cases.
For water, carbonic acid, calcium hydroxide, calcium carbonate and carboxyl groups in
the pulp the constants estimated previously at STFI-Packforsk (Ulmgren 2003) have been
used.
For the fatty acids calcium soaps pKs-values from 12 to 20 has been used. For the resin
acids a pKs-value of 9.0 has been used.
4.2 Chemical analysis of mill samples
TOC was determined according to SS 028199.
Carbonate was determined as total inorganic carbon according to SCAN-N 32
Calcium
Pulp samples were ashed at 575 °C and dissolved in hydrochloric acid. The filtrates were
wet digested in a microwave oven with nitric acid and peroxide. Calcium was quantified
by ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectrometry)
Extractives
The pulp samples were extracted with acetone after acidification with acetic acid,
according to SCAN CM 49.
The filtrate samples were acidified to pH 3 and extracted with petroleum ether after
addition of acetone and methanol, according to (McMahon, 1980).
The silylated extracts were analysed by GC-MS (gas chromatography-mass spectrometry)
for quantification of individual compounds.
The sum of unsaturated fatty acids has been used for component FA1 (unsaturated fatty
acids). The main acids were palmitoleic, oleic, linoleic, and linolenic acid.
The sum of saturated fatty acids has been used for component FA2 (saturated fatty acids).
The main acids were palmitic, stearic, arachinic, and lignoceric acid.
The sum of individual resin acids has been used for the component RA (resin acids).
According to Innventia Confidentiality Policy this report is public since 2011-02-04
According to STFI-Packforsk's Confidentiality Policy this report is assigned category 2
Equilibrium calculations
STFI-Packforsk report no. 140
10 (32)
5 Results
5.1 Composition of mill samples
In order to acquire relevant indata for the simulations, samples from three different mills
(A, B and C) all producing bleached hardwood pulp were collected in the fall 2003. Both
pulps and filtrates were sampled at three different positions: after cooking, after oxygen
delignification and from fully bleached pulp. The content of extractives in the different
samples are shown in table 4. Mill A has a higher extract content after cooking, mainly
depending on the higher amount of tall oil added to the cooking, 1.6 % compared to 1.3
% in mill B and no addition in mill C. The degree of washing accomplished in the
sampling point “after oxygen stage” may also be different. Both the sodium content and
the pH in the oxygen stage filtrate are much higher in mill A compared to mill B and C.
Table 4. Extract content in the mill samples. Pulp samples were extracted with acetone
after acidification. The filtrates were extracted with PAM (petroleum
ether/acetone/methanol) after acidification
After cook
After oxygen
Bleached pulp
Pulp, g/kg
Filtrate, g/l
Pulp, g/kg
Filtrate, g/l
Pulp, g/kg
Filtrate, g/l
Mill A
78.5
2.1
6.8
2.9
0.7
0.01
Mill B
38
3.9
3.4
0.32
1.8
0.06
Mill C
32.3
1.7
8.8
0.97
2.7
0.006
In this report only the positions “after oxygen” and “bleached pulp” have been used for
the simulations. Some data describing the mill processes and the samples analysed are
given in Appendix A. The complete analytical results are reported in (Björklund Jansson,
2005).
The major part of the simulations has been performed for the case “oxygen stage” and the
pulp consistency 2 %. The concentrations used in these calculations are given in table 5.
Concentrations for the case “bleached pulp” and the pulp consistency 25 % are given in
Appendix A.
According to Innventia Confidentiality Policy this report is public since 2011-02-04
According to STFI-Packforsk's Confidentiality Policy this report is assigned category 2
Equilibrium calculations
STFI-Packforsk report no. 140
11 (32)
Table 5. Conditions and concentrations used for the case “after oxygen stage”,
pulp consistency 2 %.
Mill A
Mill B
Mill C
I, M
0.5
0.2
0.2
T, °C
70
70
70
Ca , mM
1.7
0.76
1.1
CO3 mM
189
61
66
FA1, mM
1.7
0,50
1.2
RA, mM
2.6
0.65
0.05
FA2, mM
0.82
0,27
0.6
pH
11.6
10.7
10.9
pulp*, mM
2.5
2.5
2.5
2+
The concentrations of carbonate and the pH-values in the filtrates from the three mills are
illustrated in figure 2. Mill A uses addition of carbon dioxide in the washing line. This is
most probably the reason for the substantially higher concentrations of carbonate ions in
the filtrates from mill A. Increased amounts of carbonate ions has earlier in laboratory
experiments been shown to improve the washing with regard to removal of extractives
(Back and Björklund Jansson, 1987). In this case, the carbon dioxide addition is used
mainly in order to improve the dewatering effect on the washers.
The higher pH in the filtrate from the bleached pulp in mill B compared to mill A and C is
caused by the differences in bleaching sequence, peroxide stage was used in mill B
compared to chlorine dioxide in mill A and mill C.
450
14
Carbonate mill A
400
12
Carbonate mill B
350
Carbonate mill C
10
pH mill A
250
8
200
6
pH mill B
pH
mmol/l
300
pH mill C
150
4
100
2
50
0
0
Filtrate pressed
from pulp after
cooking
Filtrate after
oxygen stage
Filtrate from last
washing stage
(bleached pulp)
Figure 2. pH, and carbonate concentration in the mill filtrates.
According to Innventia Confidentiality Policy this report is public since 2011-02-04
According to STFI-Packforsk's Confidentiality Policy this report is assigned category 2
Equilibrium calculations
STFI-Packforsk report no. 140
12 (32)
5.2 Equilibrium calculations
5.2.1 Guide to the diagrams
In order to make estimations of the distribution of metal ions at equilibrium, the number
of components in the system has to be defined and all the possible reactions of each
component described, using the equilibrium constants for the reactions during the present
conditions. Furthermore, the total concentrations for all the components, except the one
that is used as a master variable, have to be fixed. In these calculations we have mainly
used pH as the master variable, but in some diagrams also the carbonate concentration or
the calcium concentration has been used as the master variable. The pH was fixed in these
cases.
The components and equations used in this work are given in the experimental part (See
4.1).
In most simulations, three different acidic components have been used.
•
The first group (FA1) represents the unsaturated fatty acids, such as oleic, linoleic
and linolenic acids. The solubility product for the formation of calcium soaps for
these acids was varied between 11 and 15, in order to exemplify the influence of
the different pKs-values.
•
The second group (FA2) represents the saturated fatty acids, which form more
insoluble calcium soaps. In most calculations the pKs-value for this component
was set to 19.7. However, as seen in table 2, the pKs for some acids included in
this group is much higher.
•
The third group represents the resin acids (RA) and for this component a pKs for
formation of calcium soaps of 9.0 was used. (Value from Pohle, 9.6, adjusted to
higher ionic strength.)
In the calculations two different sets of conditions were used, representing concentrations
in the oxygen stage and in the bleached pulp. The concentrations from the analysis of the
samples from the three mills (A, B and C) were used as input data for the calculations.
Each given combination of input data in the form of concentrations will result in a set of
graphs, one for each component, showing the different forms in which this component is
present at different pH:s, if pH is the master variable.
The results are plotted as “fraction diagrams”. An example is given in figure 3, showing
the equilibrium diagrams from a simulation where the concentrations from the oxygen
stage in mill C have been used as input. As seen the fatty acid in the group FA1, here with
a pKs of 12, is partly present in the form of calcium soaps and partly as a free anions.
Further, the fraction diagram for calcium in this example shows that calcium, at pH:s
relevant to the pulp washing, is present both in the form of calcium carbonate and bound
to FA1 and FA2. At a pH above 13,3 calcium hydroxide is formed and the calcium soaps
According to Innventia Confidentiality Policy this report is public since 2011-02-04
According to STFI-Packforsk's Confidentiality Policy this report is assigned category 2
Equilibrium calculations
STFI-Packforsk report no. 140
13 (32)
of FA1 and the calcium carbonate are dissolved. However, the calcium soaps of FA2 are
still present.
Mill C, oxygen stage (2 %)
FA1 pKs 12
1,0
0,8
Fraction FA1
Free acid anion
Undissolved acid
0,6
0,4
Ca-soap
0,2
0,0
4
5
6
7
8
9
pH
10
11
12
13
14
Mill C, oxygen stage (2 %)
FA1 pKs 12
1
Ca2+
CaCO3
Ca(FA1)2
Ca2+
0,8
Fraction Ca
CaCO3
Ca(FA2)2
Capulp2+
CaOHCa(OH)2
0,6
0,4
Ca(FA2)2
0,2
Ca(FA1)2
0
2
4
6
8
10
12
14
pH
Figure 3. Equilibrium diagrams illustrating the different forms of one group of fatty acids
(FA1) with a pKs of 12 (top) and the different forms of Ca (bottom) as a function of pH in
mill C. See also figure 4 and 5 showing the fraction diagrams for RA (resin acids) and
FA2.
5.2.2 Influence of the solubility product of the calcium soaps.
The most critical input value in the calculations is of course the solubility product (Ks) of
the fatty acid calcium soaps. Most values in the literature are given at room temperature
and low ionic strength. However some information about the influence of temperature and
ionic strength can be found in the literature, see table 2 above. From these values an
extrapolation has been made with the result that the pKs of calcium oleate decreases from
14.9 at I = 0.1 M and 25 °C to about 12.2 at I = 1.0 and 70 °C. Similarly the pKs of
According to Innventia Confidentiality Policy this report is public since 2011-02-04
According to STFI-Packforsk's Confidentiality Policy this report is assigned category 2
Equilibrium calculations
STFI-Packforsk report no. 140
14 (32)
linoleic acid, which is one of the most abundant fatty acids in wood, decreases from 14.2
to 11.5.
For this reason the calculations have been performed for different pKs-values, from 12 to
15 for the unsaturated acids (= FA1) and at 19.7 as an example of a saturated acid (FA2).
From the results it can be seen that acids with a pKs of 9, as used for the resin acids, or
below, do not form calcium soaps under any of the conditions used in the calculations.
This is in agreement with the experience from mill situations, where resin acids normally
are missing in deposits from the washing, screening and bleaching areas. A typical
diagram of the resin acids is shown in figure 4, taken from the same simulation conditions
as in figure 3. The undissociated resin acids, present at lower pH:s, have a higher
solubility than the fatty acids and are therefore also present in the form of dissolved,
undissociated acid.
Mill C, oxygen stage (2 %)
Resin acid pKs 9
1,0
Undissolved acid
0,8
Fraction RA
Free acid anion
0,6
0,4
Dissolved undissociated acid
0,2
0,0
4
5
6
7
8
9
pH
10
11
12
13
14
Figure 4. Typical example of equilibrium diagram for the resin acids. Same simulation as in
figure 3 and 5.
Further, the group FA2 (= fatty acids with a pKs of 19.7 or higher) were in the
calculations present only in the form of calcium soaps, regardless of the pH and the
carbonate concentration. A typical example is shown in figure 5. The fatty acids in group
FA2 are only present as calcium soaps at all pH:s above 5.8. Below pH 5.8 the fatty acids
FA2 are present in the undissociated form, with a very low solubility in water.
According to Innventia Confidentiality Policy this report is public since 2011-02-04
According to STFI-Packforsk's Confidentiality Policy this report is assigned category 2
Equilibrium calculations
STFI-Packforsk report no. 140
15 (32)
Mill C, oxygen stage (2 %)
FA2 pKs 19.7
1,0
Fraction FA2
0,8
Undissolved
acid
Ca-soap
0,6
0,4
0,2
0,0
4
5
6
7
8
9
pH
10
11
12
13
14
Figure 5. Typical example of equilibrium diagram for the saturated fatty acids (FA2).
Same simulation as in figure 3 and 4.
For the group FA1, (= the most prevailing acids, such as the unsaturated C18 acids, oleic,
linoleic and linolenic) the results show a more complicated picture. Some results, using
the concentrations in the oxygen stages in mill A and B, are shown in figure 6. The figure
illustrates the pH-interval where fatty acids soaps are formed using pKs-values between
12 and 13. For the acids in this group probably variations in the conditions during
washing will influence the precipitation of the soaps.
According to Innventia Confidentiality Policy this report is public since 2011-02-04
According to STFI-Packforsk's Confidentiality Policy this report is assigned category 2
Equilibrium calculations
STFI-Packforsk report no. 140
16 (32)
Mill A O2 (2 %)
1,0
pKs of 19.7
0,8
Fraction
pKs of 13
0,6
pKs of 12.5
0,4
0,2
pKs of 12
0,0
4
5
6
7
8
9
pH
10
11
12
13
14
Mill A O2 (2 %)
1,0
pKs of 12
Fraction
0,8
0,6
Lower carbonate conc.
90 mM
0,4
Actual carbonate conc.
189 mM
0,2
0,0
4
5
6
7
8
9
pH
10
11
12
13
14
Mill B O2 (2 %)
1,0
pKs of 19.7
0,8
Fraction
pKs of 13
0,6
0,4
pKs of 12.5
0,2
pKs of 12
0,0
4
5
6
7
8
9
pH
10
11
12
13
14
Figure 6. Partial equilibrium diagrams illustrating the pH-intervals for formation of calcium
soaps in mill A and mill B for fatty acids with four different pKs-values. The ordinate gives
the fraction of the fatty acid forming calcium soap. For mill A also a comparison with a
lowered carbonate concentration 90 instead of 189 mM, is shown. The carbonate
concentration in mill B was 61 mM.
According to Innventia Confidentiality Policy this report is public since 2011-02-04
According to STFI-Packforsk's Confidentiality Policy this report is assigned category 2
Equilibrium calculations
STFI-Packforsk report no. 140
17 (32)
5.2.3 Influence of the carbonate concentration on the formation of calcium
soaps
For the unsaturated acids in group FA1 there is also in some cases a marked influence of
the carbonate concentration. One example is shown in figure 7. In this case the pH has
been set to the value measured in each mill (Table 5) and the different forms of FA1
(unsaturated fatty acids) was estimated as functions of the carbonate concentration. As
seen the formation of calcium soaps was markedly affected by the carbonate
concentration.
The carbonate concentrations in figure 7 should be compared to the concentrations of
carbonate measured after the oxygen stage in mill A, using an addition of carbon dioxide
in the washing line, 193 mM, and the carbonate concentrations in mill B and C, in both
cases about 65 mM.
According to Innventia Confidentiality Policy this report is public since 2011-02-04
According to STFI-Packforsk's Confidentiality Policy this report is assigned category 2
Equilibrium calculations
STFI-Packforsk report no. 140
18 (32)
Mill A, oxygen stage (2 and 25 %)
FA1 pKs 12
1
0,9
25 %
2%
0,8
0,7
Fraction FA1
Free acid anion
0,6
0,5
0,4
Calcium soap
0,3
0,2
25 %
2%
0,1
0
0
50
100
150
200
250
300
Carbonate, mM
Mill B, oxygen stage (2 and 25 %)
FA1 pKs 12
1
0,9
Free acid anion
0,8
Fraction FA1
0,7
0,6
0,5
0,4
0,3
Calcium soap
0,2
0,1
0
0
50
100
150
200
250
300
Carbonate, mM
Mill C, oxygen stage (2 and 25 %)
FA1 pKs 12
1
0,9
0,8
2%
0,7
Free acid anion
25 %
Fraction
0,6
0,5
0,4
25 %
Calcium soap
2%
0,3
0,2
0,1
0
0
50
100
150
200
250
300
Carbonate, mM
Figure 7. Influence of carbonate in mill A, B and C. Fatty acid pKs = 12, Pulp conc. 2 and 25 %
Less influence of carbonate in mill B compared to mill A and C.
According to Innventia Confidentiality Policy this report is public since 2011-02-04
According to STFI-Packforsk's Confidentiality Policy this report is assigned category 2
Equilibrium calculations
STFI-Packforsk report no. 140
19 (32)
5.2.4 Influence of the pulp consistency
Since the calculations in WinGEMS have been conducted for a set sample mass, e g per
kg wet pulp sample, it is needed to know the total concentration of each component in that
sample. In these calculations the total concentrations have been set using the values from
the analysis of samples from three different mills (A, B and C). Since some of the
components are mainly bound to the fibres, and other components are dissolved in the
liquor, the amount of a specified component will depend on the pulp consistency. Here we
have used two fibre concentrations, 2 % and 25 %. For soluble components, such as e.g.
pH and sodium, the pulp consistency will not affect the concentrations significantly.
However, for components that are present mainly in different insoluble forms, e g
calcium ions and saturated fatty acids (FA2), and of course the carboxyl groups in the
fibres, the pulp consistency chosen for the calculations will alter the total amount of that
component.
As an example, the different forms of two of the components, calcium and carbonate,- in
the position “oxygen stage in mill A” are shown in figures 8 and 9 for a pulp consistency
of 2 % and 25 % respectively.
The concentration of carbonate in all mill filtrates in the position “oxygen stage” is in all
three mills much higher than the calcium concentration. For this reason the major part of
carbonate is present in free form, as illustrated in figure 9. At the higher pulp consistency
also carbonate in the form of calcium carbonate is present. The situation is similar in mill
B and mill C.
According to Innventia Confidentiality Policy this report is public since 2011-02-04
According to STFI-Packforsk's Confidentiality Policy this report is assigned category 2
Equilibrium calculations
STFI-Packforsk report no. 140
20 (32)
Mill A, oxygen stage (2 %)
FA1 pKs 12
1
Ca2+
CaCO3
Fraction Ca
0,8
Ca2+
CaCO3
Ca(FA1)2
0,6
Ca(FA2)2
Capulp2+
CaOHCa(OH)2
0,4
Ca(FA2)2
0,2
Ca(FA1)2
0
2
4
6
8
10
12
14
pH
Mill A, oxygen stage (25 %)
FA1 pKs 12
1
Ca-pulp
CaCO3
Fraction Ca
0,8
Ca2+
CaCO3
Ca(FA1)2
0,6
Ca(FA2)2
Ca-pulp
CaOHCa(OH)2
0,4
Ca2+
0,2
Ca(FA2)2
0
2
4
6
8
10
12
14
pH
Figure 8. Equilibrium diagrams illustrating the different forms of calcium as a function of
pH in mill A at two different pulp consistencies, 2 (above) and 25 % (below).
According to Innventia Confidentiality Policy this report is public since 2011-02-04
According to STFI-Packforsk's Confidentiality Policy this report is assigned category 2
Equilibrium calculations
STFI-Packforsk report no. 140
21 (32)
Mill A, oxygen stage (2 %)
FA1 pKs 12
1
H2CO3
CO32-
HCO3-
Fraction carbonate
0,8
0,6
0,4
0,2
CaCO3
0
2
4
6
8
10
12
14
pH
Mill A, oxygen stage (25 %)
FA1 pKs 12
1
H2CO3
CO32-
HCO3-
Fraction carbonate
0,8
0,6
0,4
0,2
CaCO3
0
2
4
6
8
10
12
14
pH
Figure 9. Equilibrium diagrams illustrating the different forms of carbonate as a function
of pH in mill A at two different pulp consistencies, 2 (above) and 25 % (below).
5.2.5 Calcium binding capacity of carboxyl groups in the fibres
The carboxylic groups in the fibres, have been used as one component in the calculations,
since they may compete for the calcium ions. An amount of 126 mmol of carboxylic
groups per kg of pulp has been assumed (Athley and Ulmgren, 2001). Figure 10
illustrates the binding of calcium to these carboxylic groups in mill A and mill B in the
position “oxygen stage” at two different pulp consistencies. As seen, the carboxylic
groups are undissociated at low pH:s and in free form at high pH:s. At pH:s around 3 to 8
a part of the carboxylic groups are associated to calcium ions. The pH area for binding of
calcium to the fibres is somewhat larger at the higher pulp consistency of 25 %.
According to Innventia Confidentiality Policy this report is public since 2011-02-04
According to STFI-Packforsk's Confidentiality Policy this report is assigned category 2
Equilibrium calculations
STFI-Packforsk report no. 140
22 (32)
However, since most of these calculations have been made for pH:s above 8 the presence
of the fibres do not have any major influence on the precipitation of the calcium soaps of
fatty acids.
Mill A and B, oxygen stage (2%)
1
Fraction pulp
0,8
PulpHpulp
CaPulp
PulpHpulp
CaPulp
0,6
0,4
0,2
0
0
2
4
6
8
10
12
pH
Mill A and B, oxygen stage (25 %)
1
Fraction
0,8
PulpHpulp
CaPulp
PulpHpulp
CaPulp
0,6
0,4
0,2
0
0
2
4
6
8
10
12
pH
Figure 10. The different forms of the carboxyl groups in the fibres in the position “oxygen
stage” in mill A and B. Above at a pulp consistency of 2 %; below at a pulp consistency of
25 %. Mill A (open symbols) and mill B (filled symbols).
5.2.6 Influence of calcium concentration
One simulation has been done with the calcium concentration as a master variable. The
concentrations of ”mill B oxygen stage” have been used, that is a pH of 10.7 and a
carbonate concentration of 61 mM. The results are shown for FA2 (pKs = 19.7) in figure
11 and for FA1 in figure 12. In figure 12 also a simulation with a three-fold increase in
the concentration of the FA1 component is shown. The increased fatty acid concentration
gives a formation of calcium soaps.
According to Innventia Confidentiality Policy this report is public since 2011-02-04
According to STFI-Packforsk's Confidentiality Policy this report is assigned category 2
Equilibrium calculations
STFI-Packforsk report no. 140
23 (32)
Mill B, Oxygen stage (2 %)
FA2 pKs 19.7
1
0,9
Ca-soap
Fraction FA2
0,8
0,7
0,6
0,5
0,4
0,3
Free acid anion
0,2
0,1
0
0
1
2
3
Ca (mM)
Figure 11 Influence of the calcium concentration in mill B Fatty acid pKs = 19.7, Pulp
conc. 2 %. (pH 10.7, carbonate 61mM)
Mill B, Oxygen stage (2 %)
FA1 pKs 12
Mill B, Oxygen stage (2 %)
FA1 pKs 12
1
1
0,9
0,9
Free acid anion
0,8
Free acid anion
0,7
Fraction FA1
Fraction FA1
0,8
0,6
0,5
0,4
0,3
0,7
0,6
0,5
0,4
0,3
0,2
Ca-soap
0,2
Ca-soap
0,1
0,1
0
0
0
1
2
Ca (mM)
3
0
1
2
3
4
Ca (mM)
Figure 12 Influence of the calcium concentration in mill B Fatty acid pKs = 12.0.
Left: Actual concentration of FA1. Right: FA1 increased three times to 1.5 mM.
The calcium concentration in mill B was in the oxygen stage 0.8 mM.
5.2.7 Case “bleached pulp”
For the ECF bleached pulp in mill A and C the pH is 4.4 and 6.7 respectively. At these
pH:s also the carboxyl groups of the fibres will bind a part of the calcium ions, figure 13.
As seen in figures 14 and 15 about 50 % of the calcium is bound to the pulp. The rest of
the calcium is free calcium ions at lower pH:s, such as in the chlorine dioxide stages in
mill A and C. In mill B that has TCF bleaching, and a pH of 10.7, a part of the calcium is
still bound as calcium carbonate. At the conditions of the bleached pulp the FA2 are still
bound as Calcium soaps, but the FA1 are in the calculations in the free form. The main
According to Innventia Confidentiality Policy this report is public since 2011-02-04
According to STFI-Packforsk's Confidentiality Policy this report is assigned category 2
Equilibrium calculations
STFI-Packforsk report no. 140
24 (32)
reason for this is that the concentration is very low. If the concentration of FA1 is
increased about 30 times a part of the unsaturated acids will form calcium soaps.
Mill A, B and C Bleached pulp, 2%
1
B
A
Fraction pulp
0,8
C
sodium form
undissociateded
0,6
0,4
calcium form
C
0,2
A
B
0
0
2
4
6
pH
8
10
12
Figure 13. The form of the carboxylic groups in the fibres as a function of pH in the mills
A, B and C. Conditions bleached pulp.
Mill B, Bleached pulp 2%
1
-
2+
Fraction calcium
CaCO3
Ca
0,8
0,6
CaOH
Ca-pulp
0,4
Ca(FA2)2
0,2
0
0
2
4
6
8
10
12
pH
Figure 14. Equilibrium diagram illustrating the different forms of Ca in the bleached pulp in
mill B.
According to Innventia Confidentiality Policy this report is public since 2011-02-04
According to STFI-Packforsk's Confidentiality Policy this report is assigned category 2
Equilibrium calculations
STFI-Packforsk report no. 140
25 (32)
Mill A and C, Bleached pulp 2%
1
-
CaOH
Fraction calcium
0,8
CaCO3 (mill C)
0,6
Ca-pulp
0,4
Ca2+
0,2
Ca(FA2)2
0
0
2
4
6
8
10
12
pH
Figure 15. Equilibrium diagrams illustrating the different forms of Ca in mill A and C as
a function of pH.
The reason for no formation of calcium carbonate in mill A even at higher pH-values and
the low formation in mill C is an “artefact” depending on the input data. The input data
for the bleached pulp is the carbonate content in the bleached pulp measured at the actual
pH, which was 4.4, 6.7 and 10.5 in mill A, B and C respectively. For the simulations it
might be better to use the carbonate content at a higher pH and this will be tested in future
simulations.
According to Innventia Confidentiality Policy this report is public since 2011-02-04
According to STFI-Packforsk's Confidentiality Policy this report is assigned category 2
Equilibrium calculations
STFI-Packforsk report no. 140
26 (32)
6 Discussion and conclusions
All the three mills used in the simulations produce hardwood kraft pulp. The extract
content of the bleached pulp was 0.7 mg/kg in mill A, 1.8 mg/kg in mill B and 2.7 mg/kg
in mill C. However, there are several differences between the mills that may affect the
deresination of the pulp. E.g. addition of tall oil in the cooking was used in mill A (1.6
%) and mill B (1.3 %), but not in mill C. Further, mill A adds carbon dioxide after the
oxygen stage, which increases the carbonate concentration in the filtrates. The results
from analysis of the samples in the three mills and the washing efficiency are discussed
also in (Björklund Jansson, 2005).
The aim of the simulations presented in this report has at this stage primarily been to
identify parameters, where a small change in concentrations will influence the formation
of calcium soaps, and not to simulate the degree of deresination. Formation of calcium
soaps in pulp washing is detrimental both since the soaps themselves are very sticky and
difficult to wash out and also because the formation of calcium soaps reduces the amount
of soluble sodium soaps. The sodium soaps will act as a detergent in pulp washing by
solubilizing otherwise insoluble wood extractives, such as e.g. sterols and steryl esters, in
micelles. This is the reason for the positive effect of the tall oil addition.
A crucial value for the formation of calcium soaps is of course the solubility product, Ks,
for the soaps. In the present study it was shown that saturated fatty acids, with a pKs of 19
or higher, will form calcium soaps during most of the tested conditions. On the other
hand, the formation of calcium soaps from the most prevailing unsaturated fatty acids, e.g.
linoleic acid, seems to be depending on the concentrations of the ingoing compounds, e.g.
calcium and carbonate, and the pH. This means that the formation of these soaps may be
possible to prevent by changing these variables. Resin acids with a pKs of the calcium
soaps of around 9, do not form calcium soaps at any of the tested conditions. The effect of
other cations, especially magnesium and manganese, would be possible to include in the
simulations, but have not been included in this study.
At oxygen stage conditions a varying amount of carbonate seems to influence the
formation of calcium soaps. Thus, the addition of carbon dioxide in mill A may be one of
the factors contributing to the, for a birch pulp, very low extract content in the bleached
pulp from this mill. The simulations also show that the formation of calcium soaps is
more affected by the carbonate concentration at a higher pulp consistency.
The variation in the carbonate concentration has so far been tested only at the actual pH
measured in the filtrates from the three mills. In future simulations it would be of interest
to study the effect of an increase in carbonate concentration, on the formation of Casoaps, at different pH-values. Further, any formation of complexes between dissolved
lignin and calcium ions has not been accounted for, due to the lack of complexing
constants.
Another aspect that has so far not been addressed is the dynamics of the system. If
calcium soaps are formed at some stage, how quickly will they dissolve when the
According to Innventia Confidentiality Policy this report is public since 2011-02-04
According to STFI-Packforsk's Confidentiality Policy this report is assigned category 2
Equilibrium calculations
STFI-Packforsk report no. 140
27 (32)
conditions change as e.g. during the dilutions and concentrations done in each washing
stage?
According to Innventia Confidentiality Policy this report is public since 2011-02-04
According to STFI-Packforsk's Confidentiality Policy this report is assigned category 2
Equilibrium calculations
STFI-Packforsk report no. 140
28 (32)
7 References
Athley K, Ulmgren P (2001)
Acid-base properties of oxygen-delignified kraft pulps
Nordic Pulp Paper Res 16:3, 195
Al Attar A and Beck W H (1970)
Thermodynamic solubility products of long-chain normal fatty acids and their alkaline
earth and lanthanum salts in water
J Electroanal. Chem 27 p.59
Back, E.L and Björklund Jansson M:
Harzkomponenten im Holz und Auswaschung derselben nach einer Sulfatkochung
Wochenblatt für Papierfabrikation (1987) No 8, p.339
Berggren R, Lindgren K, Sarman S, Samuelsson Å
Apparent solubility of sparingly soluble salts in the fiber line- validation of equilibrium
calculations in WinGEMS
STFI Report CHEM 106 (2003)
Beneventi D, Carre B, Gandini A (2001)
Precipitation and solubility of calcium soaps in basic aqueous media
J Colloid Interface Sci 237, 142
Björklund Jansson M (2005)
Birch extractives in kraft pulp washing
STFI-Packforsk report no. 141
Douek M and Allen L (1980a)
Calcium soap deposition in kraft mill brownstock systems
Pulp Paper Canada 81:11 T318
Douek M and Allen L (1980b)
The distribution of calcium in kraft mill brownstock systems
Svensk Papperstid. 83:15, 425
Dorris GM, Douek M, Allen LH (1983)
Analysis of metal soaps in kraft mill brownstock pitch deposits
J Pulp Paper Sci 9:1,TR1
Eriksson G (1979)
An algorithm for the computation of aqueous multicomponent, multiphase equilibria.
Analytica Chimica Acta 112(1979), 375-382
According to Innventia Confidentiality Policy this report is public since 2011-02-04
According to STFI-Packforsk's Confidentiality Policy this report is assigned category 2
Equilibrium calculations
STFI-Packforsk report no. 140
29 (32)
Fossum T, Hartler N, Libert J (1972)
The inorganic content of wood
Svensk Papperstid. 75(4)307
Gu Y, Edwards L
Prediction of metals distribution in mill processes, Part 2: Fiber line metals profiles
Tappi J 3(2004):2, 13-20
Gu Y, Malmberg B, Edwards L
Prediction of metals distribution in mill processes, Part 1: Metals equilibrium model
Tappi J 3(2004):1, 26-32
Hartler N, Libert J (1973)
The behaviour of certain inorganic ions in the wood/white liquor system
Svensk Papperstid. 76:12, 454
Holmbom, B (1978)
Constituents of tall oil
Dissertation, Åbo Academy
Irani R R, Callis C F (1960)
Metal complexing by phosphorus compounds. II. Solubilities of calcium soaps and linear
carboxylic acids
J. Physical Chem 64(1960)1741
Magnusson H, Mörk K, Warnqvist B (1980)
Processfrämmande ämnen i sulfatmassafabriken
SCAN-Forsk-rapport nr 224
McMahon D H (1980)
Analysis of low levels of fatty and resin acids in kraft mill process streams
Tappi 63:9, 101
Ollandt (1979)
Harts i björksulfatamssaprocess
Diplomarbete, Åbo akademi
Pohle W D
Solubilities of calcium soaps of gum rosin, rosin acids and fatty acids
Oil&Soap 18(1941)244
According to Innventia Confidentiality Policy this report is public since 2011-02-04
According to STFI-Packforsk's Confidentiality Policy this report is assigned category 2
Equilibrium calculations
STFI-Packforsk report no. 140
30 (32)
Ulmgren P
Solubility of slightly soluble compounds in bleach plant filtrates - a summary.
STFI Report CHEM 88 (2003)
Wadsborn R, Samuelsson Å, Rådeström R, Edebo A, Lendrup H, Hedlund-Björnwall T,
Metal profiles in the bleach plant: modelling and mill validation
International Pulp Bleaching Conference, Stockholm, 2005.
Werner JA, Ragauskas AJ, Jiang JE (1998)
Evaluation of the intrinsic metal binding capacity of kraft black liquor lignins
Tappi Pulping Conf, Proceedings vol III, 1145
Westervelt HH, Frederick WJ, Malcolm EW, Easty DB (1982)
New evidence concerning the role of black liquor organics in the calcium carbonate scale
formation
Tappi, 65:5, 179
According to Innventia Confidentiality Policy this report is public since 2011-02-04
According to STFI-Packforsk's Confidentiality Policy this report is assigned category 2
Equilibrium calculations
STFI-Packforsk report no. 140
31 (32)
8 Appendix A. Description of mill samples
Table A1. Process data for mill A, B and C.
Mill A
Mill B
Wood mix
Birch ca 100 %
Birch/aspen 90/10
Tall oil
1.6 %
1.3 %
Carbon dioxide
yes
no
Bleaching sequence
ECF
TCF
O-O-D-E-D-D (OO)-Q-OP-PAAQ-PO
Kappa number:
- after cooking
17
16
- after oxygen
11
9
- bleached pulp
0
4.5
Table A2. Sampling positions in the mills
Sampling position Pulp samples
1. After cooking
The pulp was taken from the blow
line and pressed warm to a dry
content > 25 %.
Mill A
Mill B
Mill C
Pulp dry content
24.5
31.2
38.9
2. After oxygen
Pulp from washing stage after
oxygen delignification
Mill A
Mill B
Mill C
Equipment
Press
Press
Press
Pulp consistency
30.8
27.1
3. Bleached pulp
Pulp from last washing stage
Mill C
Birch/aspen 70/30
None
no
ECF
O-D-EOP-D-D
19.9
11.1
0.3
Filtrate samples
The filtrate from the
pressing of pulp 1
Filtrate from press
corresponding to pulp 2
21.7
Mill A
Mill B
Mill C
Equipment
Filter
Press
Press
Pulp consistency
10.9
21.1
27.1
Filtrate from press/filter
corresponding to pulp 3
According to Innventia Confidentiality Policy this report is public since 2011-02-04
According to STFI-Packforsk's Confidentiality Policy this report is assigned category 2
Equilibrium calculations
STFI-Packforsk report no. 140
32 (32)
Table A3. Concentrations used for simulations in position ”after oxygen stage” for two pulp
concentrations.
Mill A
Mill B
Mill C
25 %
2%
25 %
2%
25 %
2%
I, M
0.5
0.5
0.2
0.2
0.2
0.2
Ca2+, mM
9.2
1.7
8.5
0.8
9.6
1.1
CO3, mM
151
190
53.3
61.46
57
65
FA1, mM
1.4
1.7
0.4
0.5
1.1
1.2
RA, mM
0.6
2.6
0.02
0.7
0.0
0.1
FA2, mM
0.6
0.8
0.42
0.3
0.6
0.6
pH
11.6
11.6
10.7
10.7
10.9
10.9
pulp*, mM
31.5
2.5
31.5
2.5
31.5
2.5
Table A4. Concentrations used for simulations in position ”bleached pulp”
Mill A
Mill B
Mill C
25 %
2%
25 %
2%
25 %
2%
I, M
0.01
0.01
0.01
0.01
0.01
0.01
Ca2+, mM
1.0
0.2
4.0
0.4
4.7
0.55
CO3, mM
0
0
6.4
4.5
3.8
0.5
FA1, mM
0.040
0.0032
0.035
0.003
0.010
0.0008
FA2, mM
0.040
0.0204
0.19
0.1012
0.119
0.0164
RA, mM
0.000
0.0000
0.000
0.0000
0
0
pH
4.4
4.4
10.7
10.7
6.7
6.7
pulp*, mM
31.5
2.5
31.5
2.5
31.5
2.5
* Carboxylic groups in the pulp
According to Innventia Confidentiality Policy this report is public since 2011-02-04
STFI-Packforsk AB
Visit Drottning Kristinas väg 61 | Mail Box 5604, 114 86 Stockholm, Sweden
Tel +46 8676 70 00 | Fax +46 8411 55 18 | www.stfi-packforsk.se | info@stfi.se
VAT no. SE556603110901