U.S. patent number 3,607,083 [Application Number 04/877,745] was granted by the patent office on 1971-09-21 for analysis of kraft liquors.
This patent grant is currently assigned to Westvaco Corporation. Invention is credited to Anirudh K. Chowdhry.
United States Patent |
3,607,083 |
Chowdhry |
September 21, 1971 |
ANALYSIS OF KRAFT LIQUORS
Abstract
Kraft cooking liquors used in the pulping of wood are analyzed
for apparent causticity by utilizing conductivity measurements
taken before and after precipitation of the soluble carbonates in
the liquors. The differential conductivity determined correlates
directly with the apparent causticity of the cooking liquor.
Inventors: |
Chowdhry; Anirudh K. (Flushing,
NY) |
Assignee: |
Westvaco Corporation (New York,
NY)
|
Family
ID: |
25370627 |
Appl.
No.: |
04/877,745 |
Filed: |
November 18, 1969 |
Current U.S.
Class: |
436/150; 162/49;
422/78 |
Current CPC
Class: |
G01N
27/021 (20130101); G01N 33/343 (20130101) |
Current International
Class: |
G01N
27/02 (20060101); G01N 33/34 (20060101); G01n
027/26 () |
Field of
Search: |
;23/230,253 ;324/3B |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
R J. Burrock, Chem. Abstr. 55, 987od (1961).
|
Primary Examiner: Wolk; Morris O.
Assistant Examiner: Reese; R. M.
Claims
I claim:
1. The process of determining the apparent causticity of an
alkaline cooking liquor used in the pulping of wood which comprises
the steps of:
a. measuring the electrical conductivity of an alkaline cooking
liquor;
b. precipitating soluble carbonates from the cooking liquor;
c. and measuring the electrical conductivity of the cooking liquor
after the carbonates have precipitated,
the difference between the conductivity measurements of steps (a)
and (c) corresponding directly to the apparent causticity of the
cooking liquor.
2. The process of claim 1 wherein the soluble carbonates are
precipitated by the addition of barium chloride in solution to the
alkaline cooking liquor.
3. The process of claim 1 which includes, before step (a), the step
of cooling the cooking liquor to a temperature of about 25.degree.
C.
4. The process of determining the apparent causticity of a kraft
cooking liquor used in the pulping of wood, wherein the liquor
contains soluble carbonates, which comprises the steps of:
a. filtering suspended materials from a kraft cooking liquor;
b. passing the liquor through an electrical conductivity measuring
device;
c. measuring the electrical conductivity of the liquor for a first
time;
d. adding a solution of barium chloride to the liquid to
precipitate the soluble carbonates in the liquor;
e. filtering the precipitated carbonates from the liquor;
f. passing the liquor through an electrical conductivity measuring
device;
g. and measuring the electrical conductivity of the liquor for a
second time,
the difference between the conductivity measurements of steps (c)
and (g) corresponding directly to the apparent causticity of the
cooking liquor.
5. The process of claim 4 which includes, between steps (a) and (b)
the additional step of cooling the cooking liquor to a temperature
of about 25.degree. C.
Description
BRIEF SUMMARY OF THE INVENTION
This invention relates to alkaline cooling liquors used in the
manufacture of cellulosic pulp. More particularly, it relates to an
effective and timely process for determining the apparent
causticity of circulating kraft liquors which are used in the
pulping of wood.
As is well known, one general method of preparing pulp, from which
paper is made, is by cooking chips of wood in the presence of
chemicals. In chemical pulping, the object is to selectively remove
the lignious material in the wood chips and loosen cellulosic
fibers so that when the pulping digester is blown, the fibers may
be recovered. In the case of the kraft process, which is an
alkaline cooking process, the primary cooking chemicals are sodium
hydroxide and sodium sulfide, both of which are strong alkalies.
These chemicals are contained in the cooking liquor, which at
various stages of the kraft process is referred to as: white
liquor, that which is charged to the digesters and having a high
concentration of sodium hydroxide; black liquor, the spent liquor
from the digesters; and green liquor, having a high concentration
of sodium carbonate, prepared by dissolving recovered chemicals in
water and weak liquor, from which white liquor is made by
causticizing through the addition of lime.
With the development of chemical pulping processes has come the
realization that better control over a cooking process is needed in
order to obtain the most efficient use of the chemicals. The only
controls exercised over most processes pertain to maintaining
temperature and pressure over a period of time, and great reliance
is usually placed on the experience of the operators to achieve a
quality pulp. The need for monitoring a cooking liquor by quick and
effective means has been recognized, and to some extent, met with a
measure of success. It is, of course, possible to test in the
laboratory a sample of liquor for apparent causticity, but this
generally takes a half hour or more, and the time involved is much
too long to allow for efficient corrections in the causticity of
the liquor. Until the causticity of the liquor is corrected,
inactive sodium carbonate, a byproduct formed during the smelting
procedure of the well-known chemical recovery operation, is
recycled to the digesters.
Analyzers have been proposed for determining the apparent
alkalinity of a cooking liquor, but monitoring procedures proposed
to date have used modification of normal analytical techniques and
are therefore relatively slow by nature. In one proposed monitoring
system, conductivity measurements are made before and after the
liquor sample has been neutralized with carbon dioxide treatment,
with the differential conductivity said to be proportional to the
hydroxyl ion concentration of the liquor. This method is adequate
for analyzing liquors having low concentrations of sodium
hydroxide, as in black liquors, but when used to monitor a liquor
having a high hydroxyl ion concentration, such as white liquor, the
neutralizing time is prohibitively long for effective process
control purposes. In another proposed system, changes in effective
alkali are recorded as changes in percent light transmittance, the
measurement being taken after the sample has been treated and
passed through a cellulose membrane dialyzer.
The present invention is directed to a quick and effective method
of determining the apparent causticity of kraft cooking liquors,
regardless of the hydroxyl ion concentration of the liquor.
According to the present invention, the soluble carbonates are
quickly precipitated from the liquor by the addition of barium
chloride, and it has been found that the difference between the
conductivity of the liquor before and after the precipitation is
directly proportional to the apparent causticity of the liquor.
This property of the liquor can then be used to control necessary
chemical additions to the circulating liquor in order to maintain
an effective amount of cooking chemicals. Apparent causticity is
defined as the amount of sodium hydroxide as sodium oxide, divided
by the sum of the amounts of sodium hydroxide, sodium sulfide, and
sodium carbonate, all expressed as sodium oxide. Percent apparent
causticity can be expressed according to the following:
In practicing the present invention, a sample of kraft liquor is
preferably filtered to remove any suspended materials, such as pulp
particles and other debris likely to be found in cooking liquors.
The conductivity of the liquor is then determined by using a
standard conductivity cell. Barium chloride is then added to
immediately precipitate the sodium carbonate in the liquor. The
precipitated material is removed through filtering and the
conductivity of the liquid is again determined. The difference
between the conductivities before and after precipitation
surprisingly has been found to have a straight line relationship
with the apparent causticity of the liquor. The total time involved
in obtaining the differential conductivity measurement according to
the present invention need be no more than about 5 minutes.
Preferably the conductivity cell has a temperature compensator, as
is available on some commercial conductivity measuring units, so
that the temperature of the liquor has no influence on the
conductivity measurements. If a conductivity cell, having no means
for temperature compensation, is employed, the liquor is preferably
cooled to a predetermined temperature before the conductivity
measurements are made. The predetermined temperature is not
critical, and cooling the liquor to about 25.degree. C. has worked
satisfactorily.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be described with the aid of the following
drawings, in which:
FIG. 1 is a simplified diagrammatic flow sheet of the process of
this invention; and
FIG. 2 is a graph showing the relationship between the calculated
percent apparent causticity of various kraft cooking liquors and
differential conductivity measurements determined according to the
present process.
DETAILED DESCRIPTION
Kraft cooking liquor is taken from the circulating cooking liquor
of a kraft mill, as for example from the causticizer, passes
through conduit 10 and is pumped by pump 12 through conduit 14,
valve 16, to a self-cleaning filter 18 where fibers and other
debris are removed from the liquor. The liquor then passes through
conduit 20, cooling coil 22, where the temperature of the liquor is
cooled to a predetermined temperature, such as 25.degree. C., and
then through conduit 24 to conductivity cell unit 26. It is obvious
that if conductivity unit 26 is equipped with a temperature
compensator, the cooling coil 22 may be eliminated and the liquid
passed from filter 18 directly to conductivity unit 26. The
electrical conductivity of the liquor is measured in unit 26 and a
signal, corresponding to the value of the conductivity measurement,
is sent to analog computer 28 via circuit 30.
When the above conductivity measurement is completed, valve 32 is
opened and the liquor passes from unit 26 to vessel 34 by way of
conduit 36. Simultaneously, a barium chloride solution (preferably
about 10 percent by weight) is metered from supply tank 38, passing
through valve 40 and conduit 42. The barium chloride solution is
supplied to vessel 34 in an amount about equal to that of the
liquor, on a volume basis. The soluble carbonates, especially
sodium carbonate, immediately precipitate from the liquor which is
then passed to self-cleaning filter 44 by means of pump 46, conduit
48, and valve 50. The precipitated materials are removed from the
liquor by filter 44, and the liquor then passes into conductivity
cell unit 26 by means of conduit 52. The electrical conductivity of
the liquor is measured again and a second signal is sent via
circuit 30 to analog computer 28 which performs, in known manner, a
subtraction of the two conductivity measurements. The differential
conductivity is transmitted through line 54 to recorder 56 to
provide a reading of the differential conductivity. When the
differential conductivity determination is complete, the liquor is
drained from the unit 26 by means of valve 58 and line 60.
To those skilled in the art, it will be readily apparent that
analog computer 28 controls the various valve openings and closings
by means of circuits 62, 64, 66, 68 and 70. Further, as will be
understood, the conductivity cell unit 26 is standard and well
known to those skilled in the art and may comprise, for example, a
Beckman conductivity bridge arrangement, Model No. RD-16B2,
including a Pyrex dip conductivity cell, Beckman Model No.
CELBB1.
It is to be understood that FIG. 1 is diagrammatic of a flow
pattern that may be utilized in practicing the present invention.
Various changes may be made in the flow path. For example, filter
44 can be eliminated by routing conduit 48 back to filter 18.
Obviously, the system is subject to other changes, as recognized by
those skilled in the art.
The differential conductivity of a kraft cooking liquor, as
determined according to the present process, has a straight line
relationship with the apparent causticity of the liquor. Various
samples of green and white kraft liquors were tested in the
laboratory by a known analytical procedure for apparent causticity.
This procedure involved dilution of a 5 ml. sample of liquor with
water to 25 ml. The diluted liquor was then titrated with 0.322261
N HC1 to the phenolphthalein endpoint (A) and to the methyl orange
endpoint (B). From the amounts of HC1 used for the two endpoints A
and B, the apparent causticity was calculated as follows:
Percent apparent causticity =A-(B-A)/B .times.100 The following
data was obtained from the known analytical procedure for several
kraft liquor samples:
---------------------------------------------------------------------------
Liquor No. Percent Apparent Causticity
__________________________________________________________________________
1 69.5 2 73.7 3 74.4 4 74.0 5 74.8 6 75.8 7 78.3 8 81.3
__________________________________________________________________________
Differential conductivity measurements were determined for the
above liquors according to the process of the present invention.
Conductivity measurements were made after the samples were quickly
cooled to about 25.degree. C. The complete process took only about
4 minutes. The differential conductivities were as follows:
---------------------------------------------------------------------------
Differential Conductivity Liquor No. (mho/cm.)
__________________________________________________________________________
1 135.0 2 140.0 3 145.0 4 144.0 5 146.0 6 147.0 7 153.5 8 161.0
__________________________________________________________________________
A plot of the differential conductivities of liquors 1-8 against
the calculated apparent causticities of the liquors obtained from
the known analytical procedure is shown in FIG. 2.
From the above, it can be seen that the apparent causticity of
kraft cooking liquors can be determined quickly and accurately
according to the process of this invention. The speed of the
process allows for timely corrections to be made in a kraft liquor
so as to obtain the most efficient use of the kraft process and
cooking chemicals.
It is obvious that variations may be made in the process of this
invention without departing from the spirit and scope thereof.
* * * * *