U.S. patent application number 09/963001 was filed with the patent office on 2002-07-25 for use of alkyleneamines for enhancing lime mud dewatering.
Invention is credited to Croft, Alan P..
Application Number | 20020096271 09/963001 |
Document ID | / |
Family ID | 23417428 |
Filed Date | 2002-07-25 |
United States Patent
Application |
20020096271 |
Kind Code |
A1 |
Croft, Alan P. |
July 25, 2002 |
Use of alkyleneamines for enhancing lime mud dewatering
Abstract
A process for de-watering lime mud in a Krafft pulping process
is described. The process includes an improvement which comprises
adding an effective water-removal rate enhancing amount of an
alkyleneamine to the lime mud prior to filtration. The preferred
alkyleneamine is ethyleneamine, that is, an amine having at least
one --(CR2-CR2-NH--)-- unit wherein each R is independently is H or
an alkyl (straight-chain, branched, or cyclic) group of from about
1 to about 10 carbon atoms. Ethyleneamines include ethylenediamine,
diethylenetriamine, triethylenediamine, triethylenetetramine,
tetraethylenepentamine, piperazine, aminoethylpiperazine, and
ethyleneamine mixtures such as mixtures of ethyleneamine oligomers
having an average molecular weight of about 200-500.
Inventors: |
Croft, Alan P.; (Lake
Jackson, TX) |
Correspondence
Address: |
DRAGAN J. KARADZIC
2301 N. Brazosport Blvd. B-1211
FREEPORT
TX
77541-3257
US
|
Family ID: |
23417428 |
Appl. No.: |
09/963001 |
Filed: |
September 25, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09963001 |
Sep 25, 2001 |
|
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|
09360301 |
Jul 23, 1999 |
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Current U.S.
Class: |
162/30.1 ;
162/166; 162/169 |
Current CPC
Class: |
Y02P 40/40 20151101;
Y02P 40/44 20151101; D21C 11/0085 20130101; D21C 11/0078
20130101 |
Class at
Publication: |
162/30.1 ;
162/166; 162/169 |
International
Class: |
D21C 011/04; D21H
017/07; D21H 017/35 |
Claims
What is claimed is:
1. A composition from which lime suitable for treating green liquor
in a Krafft pulping process may be yielded, which composition
comprises: a) lime mud; b) water; and c) an alkyleneamine, present
in an effective amount for increasing the water removal rate of
said lime mud, when the lime mud is dried in a pre-coat filter.
2. The composition of claim 1 wherein the alkyleneamine is
ethyleneamine.
3. The composition of claim 2 wherein the ethyleneamine has at
least one --(CR2-CR2-NH--)-- unit.
4. The composition of claim 1 wherein the ethyleneamine has a
molecular weight of from about 50 to about 1000.
5. The composition of claim 2 wherein the ethyleneamine is selected
from the group consisting of: ethylenediamine, diethylenetriamine,
triethylenetetramine, tetraethylenepentamine, mixtures of
ethyleneamine oligomers having an average molecular weight of about
200-500, and mixtures thereof.
6. The composition of claim 5 wherein the ethylene is selected from
the group consisting of: ethylenediamine, tetraethylenepentamine,
and mixtures of ethyleneamine oligomers having an average molecular
weight of about 200-500.
7. The composition of claim 6 wherein the ethyleneamine is a
mixture of ethyleneamine oligomers having an average molecular
weight of about 200-500.
8. The composition of claim 1 wherein the ethyleneamine is present
in an amount of from about 10 to about 10,000 ppm based upon the
total composition.
9. The composition of claim 1 wherein the ethyleneamine is present
in an amount of from about 100 to about 5,000 ppm based upon the
total composition.
10. The composition of claim 1 wherein the ethyleneamine is present
in an amount of from about 500 to about 3,000 ppm based upon the
total composition.
Description
[0001] This invention relates to dewatering of a lime mud and
particularly to dewatering of lime mud in the chemicals recovery
cycle of a kraft pulping process.
[0002] Processes of preparing cellulosic pulps including kraft
pulping process are within the skill in the art for instance as
discussed in Casey, Pulp and Paper; Chemistry and Chemical
Technology, 3rd ed., vol. 1, (1980) especially pages 291-491 and
504-567. In chemical pulps, the wood or other cellulose source is
advantageously separated into pulp with the help of chemicals. Two
principal chemical pulping methods are in use: soda process and
kraft process. The soda process utilizes a strongly alkaline
solution of sodium hydroxide to digest wood chips. Kraft pulping
process utilizes sulfate materials (reduced to sulfites in the
furnace) and hydroxides. The kraft pulping process is widely used
these days for producing pulp for subsequent processing to produce
paper for instance as discussed in Gary A. Smook, "Handbook for
Pulp and Paper Technologists", Second Edition, Angus Wilde
Publications, pp. 74-83 and 133-162 (1992).
[0003] In this process, wood chips are cooked (digested) under
conditions of heat and pressure using "white liquor" containing
sodium hydroxide (NaOH) and sodium sulfide (Na.sub.2S) to release
cellulose fibers from other components such as lignin. After
digestion, fibers are commonly released under pressure into a tank
in a process referred to as blowing or blowdown. Then the pulp is
washed to remove spent chemicals, lignin and other organic
chemicals. The liquid removed from the pulp is referred to as
"black liquor" and contains about 25 percent dissolved solids. The
black liquor resulting from the washing stage is concentrated by
evaporation to a desired concentration and burned to reclaim the
inorganic chemicals and provide fuel value. The organic materials
are advantageously incinerated to yield an inorganic smelt of
sodium carbonate (lime mud) and sodium sulfide. The resulting
inorganic smelt is dissolved to form "green liquor". Clarified
green liquor is reacted with lime (CaO) in a slaker (causticizer).
This produces the white liquor (which is reused in the digestion
step) and lime mud. The lime mud is then recalcined in a heated
lime kiln to recover lime (CaO) which is used in a slaker.
[0004] An important step in the processing of lime mud is lime mud
dewatering. This is typically done using a suitable filtration
means such as vacuum drum filter. Typically, a rotary vacuum drum
filter is used for dewatering lime mud and washing it just prior to
its entrance into the lime kiln. Lime mud from storage is diluted
to 25-35 percent solids and pumped to the "precoat" filter. This
filter operates at 15-20 inches of vacuum (about 9 psia). The drum
is covered with a screen made of stainless steel or plastic fiber
(typically 150 mesh). A cake of lime mud builds up on the screen as
the drum turns, and a doctor blade is fixed at a distance of
3/8-5/8 inch (about 0.94-1.56 cm.) from the screen. Consequently, a
layer of lime mud remains on the screen continually and acts as the
filter medium for the lime mud. Thus the name "precoat" filter.
This "precoat" enhances the filter's ability to remove fine
particles during the filtration process. During the filtration, as
the lime mud builds up, the doctor blade removes it and the
dewatered lime mud falls onto a screw feeder which transports it to
the feed end of the kiln. Dewatered lime mud is typically about
65-75 percent solids. The temperature at the pre-coat filter is
important. Best results are seen with temperatures of about
70.degree. C., while cold temperatures can reduce filter capacity
by 10 percent or more.
[0005] However, many filters are not efficient and the use of
dewatering additives would be desirable to facilitate removal of
water from and improve filtration of the lime. The use of
dewatering additives in the lime mud processing would not only
improve filtration of lime mud but would also result in less energy
required for heating the lime kiln to convert lime mud to lime.
[0006] The main benefit of using lime mud dewatering additives
would be the reduction of the water content of lime mud exiting the
filter. Additional benefits may be any of the following: reduction
of fuel consumption in the lime kiln resulting in the energy
savings; reduction of formation of "rings" and "balls" in the kiln
(better water removal results in greater removal of the
water-soluble salts responsible for these formations in the kiln);
reduction of sulfur stack emissions from the process (much of
sulfur is present at this point in the process as sodium salts;
better dewatering results in more efficient sulfur removal);
increased lime mud filter runability (a drier filter cake results
in less plugging of the screw feed that transports dewatered lime
mud to the kiln resulting in lower maintenance and less needed
cleanup).
[0007] Thus, there is a clear need in the cellulosic pulp industry
for an additive which will enhance dewatering of lime mud.
[0008] It has now been discovered that the use of alkyleneamines
improves reduction of the water content of lime mud exiting the
filter and improves on one or more of the aforementioned
benefits.
SUMMARY OF THE INVENTION
[0009] The present invention concerns an improved process for
dewatering lime mud wherein the improvement comprises adding an
effective amount of an alkyleneamine to lime mud prior to
filtration.
[0010] In another aspect, the present invention concerns an
improvement in a kraft pulping process wherein lime mud is filtered
to remove excess of water, the improvement comprising the addition
of an effective amount of an alkyleneamine to lime mud prior to
filtration.
[0011] In yet another aspect, the present invention concerns a lime
mud dewatering composition comprising lime mud and an effective
amount of an alkyleneamine.
DETAILED DESCRIPTION OF THE INVENTION
[0012] This invention is applicable to any lime mud and
particularly to lime mud in the spent chemicals recovery cycle of
the kraft cellulosic pulping process.
[0013] The term alkyleneamine is used to mean an amine having at
least one alkyleneamine unit or repeating alkyleneamine units such
as, for example, ethyleneamine, propyleneamine, and butyleneamine.
The preferred alkyleneamine is ethyleneamine, that is, an amine
having at least one ethyleneamine unit or repeating ethyleneamine
units. An ethyleneamine unit is --(CR.sub.2--CR.sub.2--NH--)--
where R is H or an alkyl (straight, branched or cyclic) group,
preferably H, but if alkyl of from about 1 to about 10 carbon
atoms. Ethyleneamines have at least two amine groups, which groups
are primary or secondary amine groups; tertiary amine groups are
optionally also present. Thus, ethyleneamines include
ethylenediamine (EDA), diethylenetriamine (DETA),
triethylenediamine (TEDA), triethylenetetramine (TETA),
tetraethylenepentamine (TEPA), piperazine (PIP),
aminoethylpiperazine (AEP), ethyleneamine mixtures such as mixtures
of ethyleneamine oligomers having an average molecular weight of
about 250-500 commercially available from The Dow Chemical Company
under the trade designation Ethyleneamine E-100 (E-100), and other
mixtures thereof. In the case of ethyleneamines having isomers, one
isomer or a mixture of isomers is suitably used in the practice of
the invention. It is preferred that the ethyleneamine be soluble in
the aqueous lime mud composition; therefore, the molecular weight
or average molecular weight in the case of a mixture of the
ethyleneamines is preferably sufficiently low to retain solubility
in the aqueous lime mud composition, preferably in lime mud water
slurry. More preferably, the molecular weight or average molecular
weight of the alkyleneamine is from about 50 to about 1000, more
preferably from about 100 to about 500, most preferably from about
200 to about 500. Among ethyleneamines, ethylenediamine,
diethylenetriamine, triethylenetetramine, tetraethylenepentamine,
and Ethyleneamine E-100 ethyleneamine oligomers mixtures are
preferred with ethylenediamine, diethylenetriamine,
triethylenetetramine, and tetraethylenepentamine more preferred and
Ethyleneamine E-100 ethyleneamine oligomers mixtures most
preferred.
[0014] Conditions of use are not critical to the invention.
However, dewatering is expected within the art to be more efficient
at elevated temperatures than at temperatures at or below room
temperature. Best dewatering results are seen with temperatures of
about 70.degree. C. to about 90.degree. C., while cold temperatures
can reduce filter capacity by 10 percent or more. A temperature of
about 77.degree. C. is conveniently used in dewatering of lime
mud.
[0015] The alkyleneamines are used in any amount effective to
enhance dewatering of lime mud. The concentration of the
alkyleneamines which has been found to be effective for enhancing
dewatering lime mud is typically in the range of from about 10 to
about 10,000, preferably from about 100 to about 5,000, most
preferably from about 500 to about 3,000, parts per million by
weight (ppm) based on the weight of lime mud composition.
[0016] The alkyleneamine is conveniently added to the lime mud
composition prior to the filtration thereof. Typically, the
alkyleneamine is added to lime mud coming out of storage or through
the water showers that are directed upon the filter cake on the
lime mud filter.
[0017] The use of alkyleneamine dewatering additive can increase
the percent of solids by 3-5 percent in the lime mud having solids
content above 70 percent and by more than 10 percent in the lime
mud having solids content of 60-65 percent.
[0018] The following examples are offered to illustrate but not
limit the invention. All ratios, percentages and parts are by
weight unless otherwise indicated.
EXAMPLES
[0019] The effectiveness of alkyleneamines to improve dewatering of
lime mud was evaluated in a lab scale test using the Baroid filter
press. In this small lab-scale press which is often used for
evaluation of dewatering processes, simple filtration occurs under
pressure. The pressure is maintained by using a regulated nitrogen
supply. A slurry to be filtered is prepared and added to the press,
which is then closed and pressurized. The volume of filtrate
collected during a set time period is noted as the filtration rate
for the slurry.
[0020] Lime mud slurries (30 percent solids) were prepared either
with or without an alkyleneamine incorporated. An initial slurry
was filtered in the Baroid filter press (at 10 psig pressure) to
produce a filter cake to act as a filter medium for subsequent
filtration of a second lime mud slurry. This is analogous to the
use of a precoat on the vacuum drum filter used in the kraft
process. The volume of filtrate collected over a 10 seconds test
period during the second filtration was used as a measure of
filtration rate. Multiple experimental replications were undertaken
to minimize the variation often noted when heterogeneous materials
(like lime mud slurries) are subjected to tests of this nature.
[0021] Lime Mud Slurry (30 Percent Solids) Preparation:
[0022] Lime mud (46.74 g., 80.23 percent solids) was weighed into a
tared 250 ml. beaker containing a 6 inch glass stirring rod. If no
alkyleneamine was to be added (comparative example), deionized
water was added to achieve a total net weight of 125.0 g (exclusive
of the weight of the beaker and stirring rod). The glass stirring
rod was used to stir the mixture until uniform. If an alkyleneamine
was to be added (examples of the invention), deionized water was
added until the net weight about 80 g was reached and the mixture
was stirred with the stirring rod. The addition was followed by the
addition of the desired quantity of an alkyleneamine as a 10
percent aqueous solution (for example, a 2000 ppm addition level,
based on lime mud solids, required adding 0.75 ml. of a 10 percent
solution of the alkyleneamine). Finally, deionized water was added
until a total net weight of 125.0 g was achieved. The mixture is
then stirred using the glass stirring rod until uniform.
[0023] The Baroid Press Initial Assembly and Loading:
[0024] The filter press was assembled with the body of the filter
press placed so that its bottom (the open face with two small holes
in the rim) was facing up. A 325 mesh screen, with the flat side
down, was inserted into the body of the press on top of the O-ring.
An O-ring was placed on the bottom cap. The bottom cap was inserted
into the body of the filter press and the set screws tightened
using an allen wrench. Then the bottom outlet valve was inserted
into the bottom cap and closed. Now the filter press body was
inverted and placed in a ring stand clamp. While stirring, the lime
mud mixture was poured into the filter press, using a small rubber
spatula to remove any residual lime mud from the sides of the
beaker. A 325 mesh screen and the top cap of the filter press were
installed using the same method previously used for the bottom cap.
Then the top outlet valve was inserted into the top cap and
closed.
[0025] Initial filtration was conducted as follows: A regulated
nitrogen line was attached on the top inlet valve on the body of
the filter press. The nitrogen pressure was set to 10 psig, but the
nitrogen supply valve to the nitrogen line was closed. The top
inlet valve on the filter press was then opened. A 500 ml.
disposable beaker was placed under the bottom outlet valve, and the
bottom outlet valve opened. At this point, the nitrogen supply
valve was opened, causing the filtrate to leave the filter press
and be collected in disposable beaker. After the flow through the
press was no longer steady, a timer is started and the nitrogen
flow through the filter press continued for additional 5 minutes to
ensure the initial mat is formed. At this point the nitrogen supply
valve, and the bottom outlet valves were closed
[0026] Baroid Filter Press Second Assembly and Loading:
[0027] The top cap of the filter press and screen were removed.
While stirring, a second lime mud slurry was poured into the filter
press, on top of the filter cake already present. A small rubber
spatula was again used to remove any residual lime mud from the
sides of the beaker. The top cap and screen were reinstalled using
the same method as described above. Then the top inlet valve was
inserted into the top cap and closed. A regulated nitrogen line was
attached on the top inlet valve on the body of the filter press,
taking care to ensure that the nitrogen pressure was set to 10
psig, but that the nitrogen supply valve to nitrogen line was
closed. The top inlet valve on the filter press was then opened and
a 25 ml. graduate cylinder placed under the bottom outlet valve. At
this point, the bottom outlet valve and the nitrogen supply valve
were simultaneously opened and a 10 second timer started, causing
the filtrate to leave the filter press and be collected in the
graduated cylinder during the 10 seconds collection period. The
nitrogen supply valve, the top inlet valve, and the bottom outlet
valves were closed. Finally, the volume of filtrate collected was
recorded.
[0028] Multiple dewatering tests were conducted at ambient
temperature both with lime mud slurry containing no ethyleneamine
and each lime mud slurry containing an ethyleneamine. The results
are provided in Table 1 below wherein the volumes of filtrate
collected during the 10 second test period (given as the average
value of tests run), together with the calculated percent
improvement in dewatering rates, are given.
1TABLE 1 Effectiveness of Various Alkyleneamines as Lime Mud
Dewatering Additives Additive Filtrate Concentration Volume Percent
Example Additive (ppm) (ml) Improvement C-1 None 0 11.6 0 1 EDA
2000 12.1 6.9 2 DETA 2000 11.7 0.9 3 TETA 2000 11.9 2.6 4 TEPA 2000
12.2 5.2 5 E-100 1000 12.7 9.5 6 E-100 1500 12.2 5.2 7 E-100 2000
14.0 20.7 8 E-100 2500 12.9 11.2 Note: C-1 is not an example of the
present invention
[0029] As can be seen from the data provided in Table 1, all tested
ethyleneamines improved lime mud dewatering. E-100 demonstrated to
be the most effective in dewatering lime mud since it improved
dewatering 20.7 percent at 2000 ppm and 11.2 percent at 2500 ppm
dose levels. In general there is some trend toward increased
dewatering performance with increasing molecular weight of the
homologs in the ethyleneamine series. However, no clear
relationship of alkyleneamine concentration to percent improvement
of lime mud dewatering can be elucidated. Although it appears that
2000 ppm additive level is optimal for use at ambient temperature,
another amount of an ethyleneamine may be optimal at an elevated
temperature.
* * * * *