Biomedical Engineering Reference
In-Depth Information
Table7.3
CalculatedandmeasuredpK
a
,pK
w
andapparentpK
a
valuesforsimplephenolic
substances,waterandKLsamples.
Sample
pK values
20
◦
C
50
◦
C
70
◦
C
125
◦
C
175
◦
C
Phenol
†
9.97
9.62
9.47
-
-
Phenol
∗
9.92
9.59
-
-
-
2-hydroxymethylphenol
∗
9.91
9.53
-
-
-
10
.
25
56
9.94
‡
9.74
‡
9.32
‡
9.03
‡
Coniferyl alcohol
Indulin AT, 0.01 M NaCl
†
10.6
10.2
10.0
-
-
Indulin AT, 0.1 M NaCl
†
10.4
10.1
9.8
-
-
Indulin AT, 0.01 M NaCl
‡
10.54
10.31
10.07
-
-
Indulin AT, 0.1 M NaCl
‡
10.47
10.25
10.00
-
-
Lignin, 8 kDa
‡
10.73
10.43
10.25
9.87
9.64
∗
Zavitsas 1967
†
experimentally obtained
‡
calculated
k
water
= d(
−
ln K
w
)/d(1/T)
30
k
coniferyl alc.
< k
water
20
k
HAc
< 0
10
2.4
2.8
3.2
T
−
1
×
10
3
(K
−
1
)
Figure7.3
Van'tHoff plots for (
•
)water, (
◦
) coniferyl alcohol and (
) aceticacid. As long
as the slope of the water curve (
k
water
=
H
water
/
R
) is the steepest, a net decrease in the
dissociationwill appear at temperature elevation. If
k
i
<
0, the pK
a
valuewill increase by
increasingtemperature.
Woerner and McCarthy 1988, Rudatin
et al
. 1989, Norgren
et al
. 2001ab, Norgren
et al
.
2002). For decades it has been known that in presence of high concentrations of monova-
lent metal ion salts at pH neutral conditions, KL starts to coagulate and finally precipitate
(Junker 1941). Moreover, by elevating the temperature in alkaline KL solutions the disso-
ciation of phenolic groups decreases, sometimes to levels below the threshold of solvency
(Norgren and Lindstrom 2000b, Norgren
et al
. 2001b). From the work of Lindstr om
(1980) it was found that colloidal KL, in conformity with other colloids, exhibits a
strongly marked critical coagulation concentration of added electrolytes (CCC). More
recent, Norgren
et al
. (2001b) showed that the experimentally observed phase behaviour
of colloidal KL can be described reasonably well by a theoretical approach derived from
the DLVO-theory.
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