SD4 33
U5-2.1q“,
THE VISCOSITY-TEMPERATURE-TOTAL SOLIDS
RELATIONSHIP OF SULFATE BLACK LIQUORS
October 1942
No. 81416
UNITED STATES DEPARTMENT OF AGRICULTURE
FOREST SERVICE
FOREST PRODUCTS LABORATORY
Madison, Wisconsin
In Cooperation with the University of Wisconsin
TEE VISCOSITY-TEMPERATURE-TOTAL SOLIDS RELATIONSHIP OF
SULFATE' BLACK LIQUORS
By
SIDNEY L. SCHWARTZ,
Assistant Engineer
SYNOPSIS
Sulfate black liquors increase in viscosity with increased concentration.
Above a totall solids concentration of 40 percent, the viscosities of the
liquors rise rapidly with increases in concentration, but are markedly decreased by increases in temperature. At concentrations of less than 40
percent the viscosities are, relatively sneaking, not much greater than that
of water, and the effect of temperature is relatively slight.
INTRODUCTION
In the evaporation step incident to recovery of chemicals from sulfate black
liquors, the liquors are usually concentrated in multiple-effect vacuum
evaporators to total-solids contents ranging from 55 to 6o percent. In
this evaporating process the flow of the liquor and the transfer of heat to
the liquor are two problems confronting both the equipment designer and the
operator. Since the viscosity of a liquid is an important factor (5) in
both of these considerations, the investigation reported here was undertaken
with the objective of measuring the viscosity changes which occur with
changes in temperature and concentration of several sulfate spent or black
liquors.
MATERIALS AND PROCEDURE
Three black liquor samples, designated as liquors A, B, and 0, were studied.
S ample A was a commercial sulfate black liquor secured from a "Wisconsin mill.
Sample B was a laboratory seMicommercial loblolly pine sulfate black liquor,
and sample C was a laboratory semicemmercial jack pine sulfate -black liquor.
As these black liquors resulted from various cooking conditions, they can
best be characterized by the„ data in table 1.
Mimeo, No. R1416
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Several samples of each were evaporated on a steam bath. Total solids of
these samples were determined and several batches of each liquor of various
total solids content were prepared from the concentrated liquor. In cases
where the concentrated samples were used prior to making more dilute solutions,
the total solids co:Aent of the samples so obtained was determined. In no
case was the concentration of a liquor carried beyond 60 percent of total
solids.,
The total solids were determined by means of a modification of the Method
described by 0-iffin (2): A sample of black liquor (20 to 50 cc. depending
on the approximate -..)Lcentrain of the liquor) was weighed, diluted to 500 cc.
with water in a -vo,Llaatri: rusk; . and mixed thoroughly. A 50-cc. aliquot
was run into a weich'd IOC 'mil: porcelain evaporating dish, evaporated, and
then dried for 16 hoars (Over night) at 105 u C.
The purpose of vary4.ng the size of the samples weighed out was to secure
comparable re g idral sarples. A liquor con:,aiming slightly less than 20 percent of total :.ol:Os will yield a residual sample that approximates 1 gram
:
when a 50-cc. weighed saml,e is taken. V
There is a tendency towards :polymerizationand carbonization of-the organic
material
black liquor which - occurs cn eva-po2atnfT, especially at high
.temppramrec., In ihe Dreoelice of alkali(6) . In reog y,it i_Jn of this fact a
ana usea as a
sample of liquor L was concentrated by vascout
control.
The relative viscosities of the black liquors"were-deterthined by means of
This was accomplished b5 measuring the time of efflux
an Engler vis ,..:Ometer
of 200 ec. of each liquor through the orifice of the instrument. The time
of efflux for 200 cc—of water at 20° C. th•cugh a standard orifice on the
Engler is,51 seconds (3). The relative vis-:o:,ity cf any liquid at ,any
temperature to that of water at 20° C. may bd comp:Lted by dividing its time
of efflux in secona': by 51. This is called the "Engler number" or "Engler
ratio," and all the viscosity data secured were so computed.
The absolute viscosity may be approximated from the following formula (3)
-i 71
for an apparatus of normal dimensions: (0.001435T _ 3.22/T)
where 1 = coefficient of viscosity in C.G.S. units.
T = time of effluxof'200 .
specific gravity a:t'the temperature in ,que-stion.
For this reason the specific gravities of the various liquors , at the various
temperatures encountered in this study were determined. A. sUitable temperature control apparatus for determining specific gravities at various temperatures was provided by inserting a porcelain disc in the viscometer pan upon
which to rest the small, 5- to 10-cc. pycnometers. Water in contact with
Mimeo. Do. R1416
-2--
the pycnometer in the viscometer pan was allowed to come to a equilibrium
with the temperature of the bath and kept there for 10 minutes. The
pycnometers, clean, dried, and desiccated, were weighed. The specific
gravity was determined relative to water at 20° C.
The range of total :solids .coVered was from
temperature range was from 20" to 960 0.:
a3.5 percent to 59.7- percent. The
RESULTS AND DISCUSSION
The vi s cosity-temperature-specific gravity data for liquors.A, B, and at
various degrees of concentrations, are recorded in tables ,"2; 3, and 4, and
plotted graphically in figure I. The data show that the viscosity of black
liquors at 20° C. increased with higher concentrations. The increase in
viscosity was especially rapid for total-solids concentrations above 40 .
percent. The viscosities of the liquors above 40-peroent total solids were
markedly affected by increased temperature. ko concentrations-below 40-percent total solids the viscosities were, relatively ?p eaking, not much greater
than that of water, and the effect on viscosity , due to increase in temperature
was comparatively slight.- Moore (4)--reported a similar viscosity-temperaturetotal solids relationship for sulfite waste liquor obtained with a Stormer
viscometer.
The viscosity-temperature-total solids relationships of the three liquors
studied are characterized by the curves in figure 1.
Differences in the viscosities of the three liquors are apparent. The viscosity of liquor C above 43 percent of total solids was definitely higher
than the corresponding viscosities of the other two, as shown in-table 2.
The viscosity of liquor B for all degrees of concentration was comraratively
low at 20° C. Anomalous-'results are evident, however, and may be attributed
to errors in total solids determinations, irregularities in temperature
control, and changes in total solids resulting from the variations in time
necessary to bring the temperatures of the various solutions into equilibrium
with the temperature-control bath. The latter is an important factor at high
concentrations, for a slight change in total solids in a solution containing
approximately 60 percent of solids will bring about a marked change in viscosity.
It is difficult to attribute the individual viscosity characteristics to
individual characteristics of the liquors. Though differences in the free
alkali content, the heat value of the residue., and the ratio of ash to total
solids, as shown in table 1, existed in the original liquors, the trend of
these variations cannot be correlated with viscosity.
An attempt was made to duplicate results obtained for several concentrations
of liquor A. A sample was concentrated by evaporation on a-steam bath and,
upon being tested, showed a total solids content of 57.0 percent. This
sample was designated as sample No. 11, from which samples No. 12, 13, and 14,
corresponding to 54. g -, 51.0-, and 47.3-percent total solids were prepared.
Mimeo. No. 81416
-3-
Viscosities were determined and the results, as plotted in figure 1, did not
Correspond with previous results. Total solids determinations on all,samples
revealed that they did not check with the calculated values. Further tests
showed that variations of ± 1.0 percent in total solids could be obtained..
A4 these determinations were run in batches which included all the samples
in question, the variations may be definitely attributed to day-to-day
variations in the temperature of the drying oven, which was set for 105° C.
Temperatures as high as 108° C. were observed. Furthermore, the errors
Produced by the variations of temperature in the oven would be greater at
the higher concentrations because of the method of sampling.
Sample No. 4, liquor A (47.3-percent total solids), which was prepared_ by
vacuum distillation at 36° C., was found to have practically the same viscosity as sample No. 10, which was prepared from a concentrated steam-bath
Sample. Further rork on vacuum-distilled samples was discontinued because
prior work at the Laboratory indicated that the viscosity of sample Yo. 4
was in the range of viscosities of samples obtained by other means of evapfration (table 3). Furthermore, viscosity data made available to the Laboratory by Babcock-Wilcox and Company (table 4), determined by the Sayboltfurol viscometer, are not, though similar in character, comparable to the
data obtained. In view of the above considerations, further work on vacuumdistilled samples. does :lot apicedt.Warranted.
Moreover, in regard f6 technical Viscometers such as Saybolt, Savbolt-furol,
Engler, and others; Bingham (1) had little to recoMtend. They are inaccurate
and have many sources of error, , In the case of the tnglet when calibrated
with Water at 20 6 di% the kinetic-energy correction amounts to 90 percent
of energy expended% The viscosity in. this particular cast has but little
part in determining the rate of flow.
BIBLIOGRAPHY
(1)
Bingham, E. C. "Fluidity and Plasticity." 1st edition, 2a impression,
page 324 (1922)%
(2)
Griffin, R% C. "Technical Methods of Analysis." 2a edition, 2d impression, page 392 (1927).
(3)
Higgins, W. F. Jour, Soc. Chem. Ind., Vol; 32, page 572 (1913).
(4)
Moore, H. X% Trans-Am. Inst. of Chem. Eng., Vol: XV, part II, page 240.
(5)
Walker, tewis, and McAdams. "Principles of Chemical Engineering."
2d edition, pages 73 to 192 (July 1927).
(6)
"The Manufacture of Pulp and Paper." 3d edition% volume III, part 5;
page 99.
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comparable• degrees of concentration.
Liquor samples
A
C
:Temper-:Engler :Temper:Engler :Temper-:Engler
: ature :
ature :
ature
0 0.
Total solids ....Percent :
:Number : °C. :Number :
20
:
Total solids ....Percent :
i
V
:
20
. : .90
:
20
: 90
Total solids ....Percent :
:
:
20
:
90
1
.9g : 90
:
35,0
.
20
90
20
90
: 10.04. 20
: 1.39: 90
20
90
1.31 :
2.00 :
1.0 g :
20
90
:
40
90
Total solids ....Percent :
:
: 33. go : 40
: 2.77 • 90
: 16.94 : • .3.92
59.5
Total solids ....Percent :
6o
96
: 7.30
1.41
:
49.6
: 36.40
: 1.90
: 15.14 : 20
: 1.65: 90
-
: 25.20 :
1. g 2 :
:
53.9
: 15.63 : 4o
: 2.32 : 90
: 33.0o
: 3.37
5s.5
57.4
6o
2.41
1.0g
43.2
: 5.1 g : 20
: 1.33: 90
54. g53.4
Total Solids ....Percent :
:
:
20
90
52.2
: 47.70.
1.77 :
:
1.51
.9g
35:0 .
50.0
: 25.90 : 20
: 1.67: 90
52.3
:
:
45.0
.
51.0
Total solids ....Percent :
Mimeo. No. R1416
20
.96
2.12 :
1.10 :
:
:
47.3
Total solids ....Percent :
1.29 :
:
37,5
25.0
25.0
24.9
90
0 0. :Num►ber
6o
95
: 12.39 :
: 3.02 :
:
:
: 40.30 :
: 4.22 :
:
: 6o
: 95
:
---
59.7
: 29.90
: 6.og
Table 3.--Viscosity, temperature, density relationship for sulfate black
liquor available a Labortary'prVor to January 1, 1938.
•
Total
solids
Temperature
•• Percent . :
Specific
gravity :
00... .
.:
:
52
70
24
: 1
3 6
:
51
70
90
:
:
:
31
58
:
•:
:
6o
Engler
Seconds
Number
1.02 :. : r.96.....3
:
:
48
47
.94
1.1110
1.1030
56
1.12
49
1.0935
48
.98
.96
1.0835
47
,94
1.1670
1.1535
1.1475
1.1375
7o
56
52.5
49
:
:
:
1.40
1.12
1.05
.98
_s3
58
71
1.2180
1.2055
276
109
5,52
2.18
1.1990
89
1.1900
87
72
1.74
1.46
59
1.2580
1.2520
1.2430
1,120
653
272
71
90
Mimeo. No. R1416
:
'Time of
efflux for
200 cc.
51
1.0560
1.0500
1.0400
34
. 70
90"
48
•
:
:
40
].
.
:
:
:
22.40
13.10
5.44
Table 4.--Evaluation of data from Babcock and Wilcox Com,mny T s viscosity,
temperature charts for sulfate black liquor.'
Total solids
Temperature
Percent
°C.
23.8
23.8
23.8
23.8
23.8
43.8
43.8
43.5
43,8
43.8
I
:
.
:
Engler
Saybolt furol
Number
Number
37,8
48.9
6o.o
71,1
82.2
9.0
8.o
7.3
7.0
7.0
37.8
48,9
60.0
71.1
g2.2
20.0
16.0
13.0
11.5
10.0
2.5
2.3
2.1
2.1
2.1
.2
4.2
3.5
3.1
2.g
53.8
53.8
53.8
53.8
53.8
:
:
:
:
65.6
71.1
76.7
82.2
93.3
72.0
56.o
43.0
33.0
27.o
:
19.0
14.5
11.0
8.5
. 7.o
63.8
63,8
63.8
63.8
.
:
:
:
52.2
87.8
93.3
98.9
350.0
230.0
16o.o
110.0
..
100.0
60.0
41.o
PS.0
98.9
98.9
98.9
98.9
98.9
98.9
6.8
7.0
S.0
9.5
25.0
110.0
14.0
23.5
3.8
3.8
53.5
63.8
1
:
:
:
2.0
2.1
2.3
2.6
6.g
20.0
Conversion of Saybolt furol values to Engler values made accordirtI . to
chart by H. G. Nevitt, Chem. and Met. Eng. June 23, 1920.
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MEMEMOgi
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I I SAMPLE C
EXPERIMENTAL (JACK FINE) SULFATE BLA CK LIQUOR I
Ma EMI
MEM=
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a
MEM'
MEMIrt,
,mkrima ''
/0
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20 30 40 50 60 70
80
90 /00
TEMPERATURE (DEGREES CENT/GRADE)
25 30 35
40 45 50 55 60
TOTAL SOLIDS (PERCENT)
FIG. 1
VISCOS/ TY-TEMPERATURE-TOTAL SOL/DS RELATIONSHIP
FOR. THREE KRAFT BLACK LIQUORS
Z M 35152 w