U.S. patent application number 10/053408 was filed with the patent office on 2002-10-10 for kraft pulp yield by heat treatment of polysulphide liquors generated by oxidation.
Invention is credited to Dorris, Gilles Marcel, Hu, Thomas Qinxiong, Leclerc, Denys Francois, Page, Natalie, Uloth, Victor Charles, van Heek, Ronald Peter.
Application Number | 20020144794 10/053408 |
Document ID | / |
Family ID | 23002095 |
Filed Date | 2002-10-10 |
United States Patent
Application |
20020144794 |
Kind Code |
A1 |
van Heek, Ronald Peter ; et
al. |
October 10, 2002 |
Kraft pulp yield by heat treatment of polysulphide liquors
generated by oxidation
Abstract
Oxidized white liquor is heat treated to increase the
concentration of PS.sub.UV measured at 285 or 286 nm or PS.sub.VIS
measured at 416 nm and the PS.sub.UV/PS.sub.GR or
PS.sub.VIS/PS.sub.GR ratio, whereby the content of active
polysulphide in the total polysulphide is increased which active
polysulphide can be exploited to increase pulp yield in Kraft
pulping.
Inventors: |
van Heek, Ronald Peter;
(Prince George, CA) ; Dorris, Gilles Marcel;
(Vimont, CA) ; Uloth, Victor Charles; (Prince
George, CA) ; Page, Natalie; (Laval, CA) ; Hu,
Thomas Qinxiong; (Vancouver, CA) ; Leclerc, Denys
Francois; (Vancouver, CA) |
Correspondence
Address: |
OGILVY RENAULT
1981 MCGILL COLLEGE AVENUE
SUITE 1600
MONTREAL
QC
H3A2Y3
CA
|
Family ID: |
23002095 |
Appl. No.: |
10/053408 |
Filed: |
January 23, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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60263519 |
Jan 24, 2001 |
|
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Current U.S.
Class: |
162/30.11 |
Current CPC
Class: |
D21C 11/0057
20130101 |
Class at
Publication: |
162/30.11 |
International
Class: |
D21C 011/04 |
Claims
1. A method which comprises exposing an oxidized white liquor
produced by oxidizing a white liquor with oxygen containing gas in
the presence of lime mud, manganese dioxide or both, to a
controlled temperature effective to increase the concentration of
PS.sub.UV measured at 285 or 286 nm or PS.sub.VIS measured at 416
nm and the PS.sub.UV/PS.sub.GR or PS.sub.VIS/PS.sub.GR ratio of
polysulphide in the oxidized white liquor.
2. A method according to claim 1, wherein said temperature is
20.degree. C. to 95.degree. C. and said exposing is for a time up
to 72 hours.
3. A method according to claim 2, wherein said oxidized white
liquor is maintained at a temperature of 50.degree. C. to
90.degree. C. for 1 to 48 hours.
4. A method of increasing the concentration of PS.sub.UV measured
at 285 or 286 nm or PS.sub.VIS measured at 416 nm and the
PS.sub.UV/PS.sub.GR or PS.sub.VIS/PS.sub.GR ratio of a polysulphide
liquor generated by oxidation of white liquor in the presence of
lime mud, manganese dioxide or both, said method comprising heating
or cooling if necessary and then storing said polysulphide liquor
at a temperature between 20.degree. C. and 95.degree. C. for a time
of up to 72 hours.
5. A method according to claim 4, wherein said polysulphide liquor
is maintained at a temperature of 50.degree. C. to 90.degree. C.
for 1 to 48 hours.
6. A method of increasing the yield of pulp in Kraft pulping with a
white liquor containing polysulphide comprising: i) oxidizing a
white liquor with oxygen containing gas in the presence of lime
mud, manganese dioxide or both to produce an oxidized white liquor
containing polysulphide, ii) heating or cooling if necessary and
then storing said oxidized white liquor to increase the
concentration of PS.sub.UV measured at 285 or 286 nm or PS.sub.VIS
measured at 416 nm and the PS.sub.UV/PS.sub.GR or
PS.sub.VIS/PS.sub.GR ratio of polysulphide in the oxidized white
liquor, and in a subsequent step: iii) delignifying pulp with the
oxidized white liquor from step ii).
7. A method according to claim 6, wherein said oxidizing in step i)
is in the presence of lime mud and a catalytic amount of manganese
dioxide, and including a step of: separating said oxidized white
liquor produced in step i) from said lime mud and manganese dioxide
prior to said heating or cooling if necessary and storing in step
ii).
8. A method according to claim 7, wherein step ii) comprises
heating or cooling if necessary said oxidized white liquor to a
temperature of 20.degree. C. to 95.degree. C. for a time up to 72
hours.
9. A method according to claim 8, wherein said temperature is 50 to
90.degree. C. and said time is 1 to 48 hours.
10. A method according to claim 8, including prior to step i):
causticizing a green liquor with lime in the presence of manganese
dioxide to produce said white liquor and lime mud containing said
manganese dioxide.
11. A method of producing an oxidized white liquor containing
polysulphide comprising: i) oxidizing a white liquor with oxygen
containing gas in the presence of lime mud, manganese dioxide or
both to produce an oxidized white liquor containing polysulphide
and having a first PS.sub.UV concentration measured at 285 or 286
nm or PS.sub.VIS concentration measured at 416 nm or
PS.sub.UV/PS.sub.GR or PS.sub.VIS/PS.sub.GR ratio, and ii) heating
or cooling if necessary and then storing said oxidized white liquor
to produce an oxidized white liquor having a second PS.sub.UV
concentration measured at 285 or 286 nm or PS.sub.VIS concentration
measured at 416 nm or PS.sub.UV/PS.sub.GR or PS.sub.VIS/PS.sub.GR
ratio, wherein said second concentration or ratio is greater than
said first ratio.
12. A method according to claim 11, wherein step ii) comprises
heating or cooling if necessary said oxidized white liquor to a
temperature of 20.degree. C. to 95.degree. C. and storing said
oxidized white liquor for a time up to 72 hours.
13. A method according to claim 12, wherein said temperature is 50
to 90.degree. C. and said time is 1 to 48 hours.
14. A method according to claim 13, including prior to step i):
causticizing a green liquor with lime in the presence of manganese
dioxide to produce said white liquor and lime mud containing said
manganese dioxide.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This Application claims priority under 35 U.S.C. 119(e) from
U.S. Provisional Application Ser. No. 60/263,519, filed Jan. 24,
2001.
BACKGROUND OF THE INVENTION
[0002] (i) Field of the Invention
[0003] The present invention relates to an improvement in any
process which generates polysulphide by the oxidation of white
liquor the invention also relates to a method of increasing the
yield of pulp in Kraft pulping with an oxidized white liquor.
[0004] (ii) Description of the Prior Art
[0005] In Kraft pulping operations, where the goal is to remove
lignin while retaining carbohydrates, yield is increased by
minimizing carbohydrate (i.e., cellulose and hemicellulose)
degradation. This degradation occurs through the "peeling" reaction
in which sugar units are sequentially removed from the reducing end
group of the polysaccharide chains. One way to prevent this
reaction is to convert aldehyde groups on the wood polysaccharides
to a form which is relatively inert to further "peeling". This
conversion is achieved by either oxidizing the aldehyde to its
corresponding carboxylic acid (Alfredsson et al., 1963), (Holton,
1977) or, alternatively, reducing it to its alcohol form (Hartler,
1959), (Pettersson et al., 1961). The two methods that are applied
in the pulp and paper industry involve the oxidation process and
use anthraquinone (Holton, 1977), or polysulphide (Clayton et al.,
1967), (Landmark et al., 1965), (Sanyer et al., 1964), (Teder,
1969), or both as oxidizing agents. Anthraquinone is a catalytic
additive while polysulphide is generated from white liquor by
oxidation of sodium sulfide in one of several processes (Dorris,
1992), (Smith et al., 1977).
SUMMARY OF THE INVENTION
[0006] It is an object of the present invention to increase the
concentration of PS.sub.UV measured at 285 or 286 nm or PS.sub.VIS
measured at 416 nm and the PS.sub.UV/PS.sub.GR or
PS.sub.VIS/PS.sub.GR ratio of polysulphide liquors generated by the
oxidation of white liquor without substantial loss of polysulphide
charge.
[0007] It is a further object of the present invention to increase
the yield of pulp from wood particles by cooking the wood particles
in a polysulphide liquor having a high concentration of PS.sub.UV
measured at 285 or 286 nm or PS.sub.VIS measured at 416 nm and the
PS.sub.UV/PS.sub.GR or PS.sub.VIS/PS.sub.GR ratio, generated by the
oxidation of white liquor.
[0008] It is a still further object of the invention to increase
the content of active polysulphide in a polysulphide liquor
generated by the oxidation of white liquor.
[0009] It is another object of the present invention to increase
the yield of pulp from wood particles by cooking wood particles in
a polysulphide liquor generated by the oxidation of white liquors
and which have been thermally treated.
[0010] In accordance with one aspect of the invention, there is
provided a method which comprises exposing an oxidized white liquor
to a temperature effective to increase the concentration of
PS.sub.UV measured at 285 or 286 nm or PS.sub.VIS measured at 416
nm and the PS.sub.UV/PS.sub.GR or PS.sub.VIS/PS.sub.GR ratio of
polysulphide in the oxidized white liquor.
[0011] In accordance with another aspect of the invention, there is
provided a method of increasing the concentration of PS.sub.UV
measured at 285 or 286 nm or PS.sub.VIS measured at 416 nm and the
PS.sub.UV/PS.sub.GR or PS.sub.VIS/PS.sub.GR ratio of a polysulphide
liquor, said method comprising heating or cooling if necessary and
then storing said liquor at a temperature between 20.degree. C. and
95.degree. C. for a time of up to 72 hours.
[0012] In accordance with yet another aspect of the invention,
there is provided a method of producing an oxidized white liquor
containing polysulphide comprising: oxidizing a white liquor to
produce an oxidized white liquor containing polysulphide and having
a first PS.sub.UV/PS.sub.GR or PS.sub.VIS/PS.sub.GR ratio, and heat
said oxidized white liquor to produce an oxidized white liquor
having a second PS.sub.UV/PS.sub.GR or PS.sub.VIS/PS.sub.GR ratio,
wherein said second ratio is greater than said first ratio.
[0013] In accordance with still another aspect of the invention,
there is provided a method of increasing the yield of pulp in Kraft
pulping with a white liquor containing polysulphide comprising:
oxidizing a white liquor to produce an oxidized white liquor
containing polysulphide, ii) heating or cooling if necessary and
then storing said oxidized white liquor to increase the
concentration of PS.sub.UV measured at 285 or 286 nm or PS.sub.VIS
measured at 416 nm and the PS.sub.UV/PS.sub.GR or
PS.sub.VIS/PS.sub.GR ratio of polysulphide in the oxidized white
liquor, and in a subsequent step: iii) delignifying pulp with the
oxidized white liquor from step ii).
[0014] The invention relates to the heat treatment of a
polysulphide liquor generated by the oxidation of white liquor.
This heat treatment is preferably at a temperature below 95.degree.
C., more preferably between 20.degree. C. and 95.degree. C., and
most preferably between 50 and 95.degree. C. for a time up to 72
hours, preferably 1 to 48 hours, more preferably 6 to 30 hours,
even more preferably 12 to 24 hours.
[0015] In one preferred embodiment of the invention, there is
provided a method which comprises exposing an oxidized white liquor
produced by oxidation of white liquor in the presence of lime mud,
or MnO.sub.2 or both lime and MnO.sub.2 to a temperature effective
to increase the concentration of PS.sub.UV measured at 285 or 286
nm or PS.sub.VIS measured at 416 nm and the PS.sub.UV/PS.sub.GR or
PS.sub.VIS/PS.sub.GR ratio of polysulphide in the oxidized white
liquor. Preferably the temperature, in this latter preferred
embodiment, is below 95.degree. C. and the period of exposure is
for a time up to 72 hours; more preferably the temperature is
between 50.degree. C. and 95.degree. C., for an exposure time up to
48 hours.
[0016] In another preferred embodiment of the invention, there is
provided a method of increasing the PS.sub.UV/PS.sub.GR or
PS.sub.VIS/PS.sub.GR ratio of a polysulphide liquor generated by
oxidation of white liquor in the presence of lime mud or MnO.sub.2
or both lime mud and MnO.sub.2;which method comprises heat treating
the oxidized white liquor at a temperature between 50.degree. C.
and 95.degree. C. for a time of up to 72 hours, and preferably up
to 48 hours.
[0017] In still another preferred embodiment of the invention,
there is provided a method of increasing the yield of pulp in Kraft
pulping with a white liquor containing polysulphide comprising: i)
oxidizing a white liquor in the presence of lime mud, MnO.sub.2 or
both lime mud and MnO.sub.2 to produce an oxidized white liquor
containing polysulphide, ii) heat treating the oxidized white
liquor to increase the concentration of PS.sub.UV measured at 285
or 286 nm or PS.sub.VIS measured at 416 nm and the
PS.sub.UV/PS.sub.GR or PS.sub.VIS/PS.sub.GR ratio of polysulphide
in the oxidized white liquor, and iii) cooking wood chips with the
oxidized white liquor from step ii) to produce pulp.
BRIEF DESCRIPTION OF DRAWINGS
[0018] FIG. 1 illustrates graphically the yield benefit in pulp
delignification with increase in PS.sub.UV/PS.sub.GR ratio;
[0019] FIG. 2 illustrates graphically the relationship between
polysulphide decomposition and temperature; and
[0020] FIGS. 3 and 4 show the relationship between pulp yield and
permanganate number for polysulphide liquors of the invention at
different temperatures; and conventional white liquors for
different pulps.
DETAILED DESCRIPTION OF THE INVENTION
[0021] i) Oxidized White Liquor
[0022] The oxidized white liquor in this invention is one produced
by oxidizing sodium sulphide in the white liquor to sodium
polysulphide.
[0023] The invention is not confined to any particular oxidation
procedure for producing the polysulphide or oxidized white liquor.
The invention thus extends to oxidized white liquors in which the
oxidation is carried out with oxygen or oxygen-containing gases
such as air, in the presence of a catalyst, for example,
wet-proofed activated carbon in the MOXY (trademark of The Mead
Corporation) process; lime mud in the PAPRILOX (trademark of Pulp
and Paper Research Institute of Canada) process, lime mud spiked
with manganese dioxide; or with oxygen or oxygen containing gas in
the presence of a metal oxide, such as oxides of manganese, iron,
cobalt, zinc, aluminum, nickel or chromium, which metal oxide
functions as a catalyst for polysulphide formation.
[0024] An especially preferred or advantageous oxidized white
liquor for use in the invention is that produced by oxidation of a
white liquor produced by causticizing green liquor and containing
the lime mud generated in the causticization process.
[0025] Green liquor is produced from the smelt derived from black
liquor in chemical recovery of a conventional Kraft liquor cycle.
The green liquor comprises sodium carbonate and sodium sulphide and
the causticization involves addition of lime, calcium oxide, to the
green liquid. The lime reacts with the sodium carbonate to produce
sodium hydroxide with precipitation of insoluble calcium carbonate.
The suspended solids comprising the calcium carbonate, unreacted
calcium oxide and other insoluble solids present in the smelt, is
referred to as lime mud.
[0026] This lime mud is thus a by-product of the white liquor
formation.
[0027] The white liquor suspension containing lime mud, can be
employed directly in the production of the oxidized white liquor,
as outlined in U.S. Pat. No. 5,082,526 incorporated herein by
reference. Especially advantageously, a catalytic amount of
manganese dioxide is added to the white liquor suspension to
further enhance the oxidation. Suitable catalytic amounts of
manganese dioxide comprise 0.1 to 2.0 g/l of a white liquor.
[0028] In such case, the resulting oxidized white liquor contains
the lime mud and, where applicable, the added manganese dioxide
catalyst, as suspended solids.
[0029] ii. Heat Treatment
[0030] The process of this invention for increasing the
concentration of PS.sub.UV measured at 285 or 286 nm or PS.sub.VIS
measured at 416 nm and the PS.sub.UV/PS.sub.GR or
PS.sub.VIS/PS.sub.GR ratio of polysulphide liquors generated by the
oxidation of white liquor is a process in which the polysulphide
liquor is heat treated within a range of temperatures and times
without substantial loss of polysulphide charge.
[0031] Increasing the concentration of PS.sub.UV measured at 285 or
286 nm or PS.sub.VIS measured at 416 nm and the PS.sub.UV/PS.sub.GR
or PS.sub.VIS/PS.sub.GR ratio increases the active polysulphide
content in the liquor. The oxidized white liquor is separated from
the oxidation catalysts such as lime mud and manganese oxide prior
to the heat treatment.
[0032] In particularly advantageous embodiments, the liquors
generated by the oxidation of white liquor in the presence of
MnO.sub.2'lime mud or both MnO.sub.2 and lime mud are heat treated
at a temperature below 95.degree. C. for a time up to 72 hours to
increase the concentration of PS.sub.UV measured at 285 or 286 nm
or PS.sub.VIS measured at 416 nm and the PS.sub.UV/PS.sub.GR or
PS.sub.VIS/PS.sub.GR ratio.
[0033] The temperature of the polysulphide liquor for the heat
treatment can be adjusted using a heat exchanger. The temperature
of the polysulphide liquor can also be adjusted by evaporative
cooling with an oxygen-containing gas. Normal practice is to remove
the heat generated by the reactions between sodium sulphide and
oxygen, to prevent the oxidized liquor temperature from rising to
or above the liquor boiling point (Uloth et al., 1997, Tench et
al., 1999). Storage may be provided by existing tankage provided
both for liquor clarification and flow buffering or by new tankage.
The target storage temperature and storage time can be optimized to
ensure that the maximum charge of active polysulphide in the
polysulphide liquor, is delivered to the pulp digester.
[0034] The heat treatment is preferably carried out by maintaining
the oxidized liquor at a temperature of 50.degree. C. to 90.degree.
C. for a time of 1 to 48 hours.
[0035] iii) Polysulphide PS.sub.UV/PS.sub.GR or
PS.sub.VIS/PS.sub.GR Ratio
[0036] Polysulphide can be generated from sodium sulphide in a
white liquor by various methods including the direct addition of
sulphur to the white liquor. However, this method cannot be used
industrially without a bleed of sulphur from the Kraft recovery
cycle, which is expensive to provide. Having different methods of
polysulphide generation, however, allows comparisons of the form of
the polysulphide that is generated by each of the different
methods. These comparisons have shown that there are differences in
what is measured as polysulphide when polysulphide liquor is
generated by the direct addition of sulphur to the white liquor and
when it is generated by the oxidation of white liquor.
[0037] Polysulphide can be measured in many ways but two of the
most simple and effective are measurement by gravimetry (PS.sub.GR)
and by UV or VIS absorption (PS.sub.UV or PS.sub.VIS). The two
methods can be used to give a PS.sub.UV/PS.sub.GR or
PS.sub.VIS/PS.sub.GR ratio. Polysulphide generated by direct
sulphur addition has a PS.sub.UV/PS.sub.GR or PS.sub.VIS/PS.sub.GR
ratio very close to 1, but polysulphide generated by oxidation of
white liquor has a ratio that varies depending on the way that it
has been made.
[0038] The differences in the form of polysulphide in the white
liquor change the degree to which the yield of pulp is increased by
the application of a given polysulphide charge. Polysulphide
liquors that have a PS.sub.UV/PS.sub.GR or PS.sub.VIS/PS.sub.GR
ratio of 1 deliver the full yield expected from the application of
a given polysulphide charge in the Kraft pulping process. In such
polysulphide liquors, the polysulphide content may thus be
considered to be active polysulphide i.e. polysulphide which
oxidizes aldehyde groups on wood polysaccharides to inhibit
carbohydrate degradation during delignification of pulp.
[0039] Oxidized liquors that have lower ratios are found to deliver
diminishing amounts of the expected yield (FIG. 1).
[0040] The lower the PS.sub.UV/PS.sub.GR or PS.sub.VIS/PS.sub.GR
ratio, the lower is the content of active polysulphide in the
polysulphide of the liquor, and conversely, the higher is the
content of inactive polysulphide.
[0041] It is therefore desirable in industrial application that the
concentration of PS.sub.UV measured at 285 or 286 nm or PS.sub.VIS
measured at 416 nm and the PS.sub.UV/PS.sub.GR or
PS.sub.VIS/PS.sub.GR ratio of the polysulphide liquor be as high as
possible, or as close to 1 as possible.
[0042] The heat treatment of the invention does result in some loss
in the total polysulphide content, determined as both active and
inactive. The loss depends on the treatment temperature and
time.
[0043] It will be recognized that the heat treatment parameters are
desirably selected to establish a satisfactory content of active
polysulphide for the protective oxidation of the carbohydrate
aldehyde groups. As such, a balance is to be achieved between
PS.sub.UV/PS.sub.GR or PS.sub.VIS/PS.sub.GR ratio and the actual
concentration of active polysulphide. A PS.sub.UV/PS.sub.GR or
PS.sub.VIS/PS.sub.GR ratio close to 1 will not be beneficial if the
heat treatment has decreased the total polysulphide content to a
level where the active polysulphide content is inadequate for the
protective oxidation reaction.
[0044] On the other hand, a low PS.sub.UV/PS.sub.GR or
PS.sub.VIS/PS.sub.GR ratio will be beneficial where the total
polysulphide content remains high such that the ratio signifies an
adequate active polysulphide content for the protective oxidation
reaction.
[0045] In general, an active polysulphide concentration of at least
4 g/l, and preferably at least 6 g/l, in the oxidized white liquor,
is required for effective oxidation of the carbohydrate aldehyde
groups in the wood chips.
[0046] The PS.sub.UV can be measured at, for example, at 285 nm,
286 nm or a 416 nm wavelength.
[0047] Experimental
[0048] The liquors used to generate the results in FIG. 1 were
obtained as follows. White liquors of varying concentrations and
compositions (800 mL; preheated to 70.degree. C. in a microwave
oven) were brought to 90.degree. C. (in an oil bath) in a stainless
steel reactor (1 L) equipped with a condenser (5.degree. C.) and
ports for adding gas and MnO.sub.2 and for withdrawing samples.
During the rise to temperature, the liquor was stirred mechanically
(600 rpm; Eurostar Power Digi-Visc-trademark) under a nitrogen flow
(50 mL/min; 2 .mu.m stainless steel sparger (Supelco-trademark)).
The impeller type used was a Rushton disk turbine with 6 flat
blades (48 mm diameter). Finely powdered MnO.sub.2 (1 g/L; Brickox
6807-trademark of Prince Manufacturing Company) was added to the
reactor when the liquor reached 90.degree. C. PS.sub.OWL was
generated by bubbling air (450 mL/min) into the liquor at a
constant stirring rate of 1000 rpm. The generation of polysulphide
was monitored with a UV spectrometer at 286 nm (HP Vectra
QS/165-trademark; 1 mm path-length cells; oxygen-free NaOH (1N)
used for dilution and blanks). An absorptivity of 43.48
Lg.sup.-1cm.sup.-1 was used to calculate the concentration of
PS.sub.UV. Samples were removed from the reactor using a plastic
syringe, immediately filtered on a ceramic Buchner funnel, and
stored in polyethylene containers under argon prior to their
analysis. The stainless steel sparger was cleaned with HCl (3 N)
prior to subsequent use. The PS.sub.GR charge used in all the
pulping experiments was 1.58% on wood (oven dried basis).
[0049] The PS.sub.UV measurement for the ratios shown in FIG. 1
were obtained at 286 nm, a wavelength at which all polysulphide
species absorb with the same absorptivity. The PS measurement,
however, could also have been made at 416 nm with a similar
relationship between PS.sub.UV/PS.sub.GR or PS.sub.VIS/PS.sub.GR
ratio and yield being found.
[0050] FIG. 2 presents the % decomposition of polysulphide
determined by gravimetry and by UV spectrophotometry (286 nm) of a
typical liquor produced by catalytic oxidation with manganese
dioxide as it is heated at 1.8.degree. C. per minute; this
corresponds to the conventional rise to temperature used in Kraft
cooking of 90 min to 170.degree. C. It is very clear from this
figure that, at temperatures above 100.degree. C., polysulphide
decomposes rapidly.
[0051] Similar results can be generated by using liquors that are
produced by oxidizing white liquor with air in the presence of a
wet-proofed activated carbon catalyst. At the industrial scale,
this is done in a single oxidation step with compressed air blown
into a fixed bed of the carbon black catalyst. Smith and Sanders
(U.S. Pat. No. 4,024,229) have presented some details on the
production of PTFE-coated catalyst. Industrially the MOXY
(trademark of The Mead Corporation) and Chiyoda processes both use
carbon as the oxidation catalyst These liquors also produce liquors
that have PS.sub.UV/PS.sub.GR ratios of less than 1 and which can
be improved by the heat treatment of the invention. Heat treatment
increases the concentration of PS.sub.UV measured at 285 or 286 nm
or PS.sub.VIS measured at 416 nm and the PS.sub.UV/PS.sub.GR or
PS.sub.VIS/PS.sub.GR ratio of these liquors and therefore, the
fibre yield when using them for pulping.
EXAMPLES
Example 1
[0052] Oxidized white liquor was produced by causticizing 0.75 L of
green liquor with 45 g reburned lime, spiked with 0.6 g MnO.sub.2.
The manganese content of clarified green liquor samples is
typically 0.3 to 6.0 mg/L. The amount of manganese added in the
MnO.sub.2 in this example (504 mg/L) is about a hundred times that
normally found in green liquor. After 100 min causticizing time at
90.degree. C., oxygen was sparged into the causticized slurry at a
rate of 0.1 L/min for 30 min. After oxidation, the resulting
CaCO.sub.3 lime mud with added MnO.sub.2, was separated from the
oxidized white liquor. Samples of the clarified white liquor were
then stored in a thermostated bath held at a desired temperature.
At regular time intervals, small samples of liquor were withdrawn
for determination of polysulphide concentration by UV spectrometry
(PS.sub.UV) and by gravimetry (PS.sub.GR).
[0053] Example 1 illustrates the increase in the
PS.sub.UV/PS.sub.GR ratio when a freshly oxidized white liquor is
treated at 73.degree. C. for up to 48 hours.
[0054] Table I shows that by heat treatment at 73.degree. C. for 48
hours, the PS.sub.UV/PS.sub.GR ratio was changed from 0.45 to 0.86
while the polysulphide concentration (PS.sub.GR) was only decreased
from 9.3 g/L to 7.1 g/L. Over 48 hours at 73 C, the PS.sub.UV
concentration increased by 44%, from 4.23 to 6.08 gpl as sulphur.
As can be seen from FIG. 1, such an increase in ratio will allow
the yield increase from a given concentration of polysulphide to be
increased from zero to almost the full potential of that
concentration.
1TABLE 1 Stability at 73.degree. C. PS PS concentration
concentration Sample 286 (UV) (gravimetry) PS.sub.UV/PS.sub.GR Time
(h) abs g/L g/L) Ratio 0 0.73 4.23 9.34 0.45 1 0.78 4.54 8.12 0.56
2 0.81 4.71 8.36 0.56 3 0.85 4.92 8.30 0.59 20 1.05 6.08 7.06 0.86
24 1.06 6.13 7.60 0.81 48 1.05 6.08 7.10 0.86
Example 2
[0055] Example 2 illustrates the change in the ratio when the same
liquor is heat treated at 95.degree. C. At this temperature the
activation of the liquor, as measured by the change in ratio, is
very rapid. Within an hour the ratio has increased to a useful
0.74. Long times of treatment (>3 hours) are less useful at this
temperature because of the increasing loss of polysulphide
concentration measured either by UV spectrometry or gravimetry.
2TABLE 2 Stability at 95.degree. C. PS con- PS con- concentration
concentration Sample 286 (UV) (gravimetry) PS.sub.UV/PS.sub.GR Time
(h) abs g/L g/L Ratio 0 0.73 4.23 9.34 0.45 1 0.80 4.65 6.32 0.74 2
0.83 4.81 5.86 0.82 3 0.85 4.91 5.36 0.92 20 0.71 4.11 5.00 0.82 24
0.70 4.07 5.30 0.77 48 0.57 3.31 4.20 0.79
Example 3
[0056] Example 3 illustrates the change in the ratio and
polysulphide concentration at an intermediate temperature of
85.degree. C. At this temperature, it takes between 2 and 3 hours
for the activation of the liquor. Again longer times of treatment
are less useful because of the increasing loss of polysulphide
charge.
3TABLE 3 Stability at 85.degree. C. PS con- PS con- concentration
concentration Sample 286 (UV) (gravimetry) PS.sub.UV/PS.sub.GR Time
(h) abs g/L g/L Ratio 0 0.78 4.52 9.78 0.46 0.83 0.82 4.74 8.08
0.59 2 0.83 4.80 6.98 0.69 3 0.89 5.14 6.32 0.81 4 0.86 4.99 6.16
0.81 10 0.73 4.22 5.18 0.81 22 0.74 4.28 4.66 0.92 26 0.66 3.85
4.28 0.90 50.42 0.53 3.05 3.70 0.82
Example 4
[0057] Example 4 illustrates the change in the ratio and
polysulphide charge at 78.degree. C. but with the liquor having
been pre-activated over 4 days at ambient temperature. The ambient
temperature treatment increased the ratio from 0.46 to 0.55 without
any loss of polysulphide concentration.
4TABLE 4 Stability at 78.degree. C. PS con- PS con- concentration
concentration Sample 286 (UV) (gravimetry) PS.sub.UV/PS.sub.GR Time
(h) abs g/L g/L Ratio 0 0.92 5.33 9.62 0.55 0.83 0.87 5.02 8.86
0.57 2.5 0.87 5.05 7.86 0.64 3.5 0.87 5.02 7.78 0.65 4.5 0.88 5.08
6.56 0.77 10 0.83 4.80 6.04 0.79 24 0.84 4.84 5.34 0.91 48 0.59
3.43 5.00 0.69
Example 5
[0058] Oxidized white liquor was produced by causticizing 0.75 L of
green liquor with 53 g reburned lime, spiked with 1.5 g MnO.sub.2.
After 60 min causticizing time at 95.degree. C., air was sparged
into the causticized slurry at a rate of 0.55 L/min for 58 min.
After oxidation, the resulting CaCO.sub.3 lime mud with added
MnO.sub.2, was separated from the oxidized white liquor. Samples of
the clarified white liquor were then stored in a thermostated bath
held at a desired temperature. At regular time intervals, small
samples of liquor were withdrawn for determination of polysulphide
concentration by UV spectrometry (PS.sub.UV) and by gravimetry
(PS.sub.GRAV).
[0059] Example 5 illustrates the increase in the concentration of
PS.sub.UV measured at 285 or 286 nm and PS.sub.VIS measured at 416
nm and the PS.sub.UV/PS.sub.GR and PS.sub.VIS/PS.sub.GR ratio when
a freshly oxidized white liquor is treated at 60.degree. C. for up
to 20 hours.
[0060] The data in the table in this example shows that by heat
treatment at 60.degree. C. for 20 hours, the PS.sub.UV/PS.sub.GR or
PS.sub.285/PS.sub.GR ratio was changed from 0.44 to 0.60, and the
PS.sub.VIS/PS.sub.GR or PS.sub.416/PS.sub.GR ratio increased from
0.18 to 0.40, while the gravimetric polysulphide concentration was
only decreased from 8.4 g/L to 7.5 g/L. The PS.sub.416
concentration in the oxidized liquor doubled from 1.5 to 3.0 gpl
(as sulphur) during the 20 hours of storage at 60 C. As can be seen
from FIG. 1, such an increase in the PS.sub.UV/PS.sub.GR or
PS.sub.285/PS.sub.GR ratio will allow the yield increase from a
given concentration of polysulphide to be increased from zero to
approximately a third of the full potential of that
concentration.
5TABLE 5 Stability at 60.degree. C. PS con- PS con- PS con-
concentrat- concentrat- UV Vis Sample concentrat- ion (UV ion (Vis
285/ 416/ Time ion (gravi- 285) 416) Grav Grav (h) metry) g/L) g/L
g/L) ratio ratio 0 8.4 3.7 1.5 0.44 0.18 1 8.3 3.8 1.6 0.46 0.19 3
8.1 3.8 1.8 0.47 0.22 16 7.9 4.3 2.7 0.54 0.34 20 7.5 4.5 3.0 0.60
0.40
Example 6
[0061] Example 6 illustrates the change in the ratio when the same
liquor is heat treated at 80.degree. C. At this temperature the
activation of the liquor, as measured by the change in ratio, is
more rapid. Within 16 hours the ratio has increased to a useful
89.
[0062] The data in the table in this example shows that by heat
treatment at 80.degree. C. for 20 hours, the PS.sub.UV/PS.sub.GR or
PS.sub.285/PS.sub.GR ratio was changed from 0.44 to 0.93, and the
PS.sub.VIS/PS.sub.GR or PS.sub.416/PS.sub.GR ratio increased from
0.18 to 0.86, while the gravimetric polysulphide concentration was
decreased from 8.4 g/L to 4.6 g/L. As can be seen from FIG. 1, such
an increase in PS.sub.UV/PS.sub.GR or PS.sub.285/PS.sub.GR ratio
will allow the yield increase from a given concentration of
polysulphide to by increased from zero to almost the full potential
of that concentration.
6TABLE 6 Stability at 80.degree. C. PS con- PS con- PS con-
concentrat- concentrat- UV Vis Sample concentrat- ion (UV ion (Vis
285/ 416/ Time ion (gravi- 285) 416) Grav Grav (h) metry) g/L) g/L
g/L) ratio ratio 0 8.4 3.7 1.5 0.44 0.18 1 7.7 3.8 1.9 0.49 0.25 3
6.6 4.0 2.6 0.60 0.39 16 4.8 4.3 3.9 0.89 0.81 20 4.6 4.3 4.0 0.93
0.86
Example 7
[0063] Example 7 illustrates the change in the ratio when a similar
liquor is heat treated at 70.degree. C. At this temperature the
activation of the liquor, as measured by the change in ratio, is
less rapid than at 80.degree. C., but more rapid than 60.degree. C.
Within 20 hours, the PS.sub.UV/PS.sub.GR or PS.sub.285/PS.sub.GR
ratio has increased to a useful 0.72 and the PS.sub.UV/PS.sub.GR or
PS.sub.416/PS.sub.GR ratio increased from 0.21 to 0.57. Through 20
hours of heat treatment at 70 C, the PS.sub.416 concentration was
more than doubled from 1.8 to 3.8 gpl (as sulphur).
7TABLE 7 Stability at 70.degree. C. PS con- PS con- PS con- Sample
centration centration centration UV Vis Time (gravimetry) (UV 285)
(Vis 416) 285/Grav 416/Grav (h) g/L g/L g/L ratio ratio 0 8.5 4.0
1.8 0.47 0.21 1 8.7 4.0 1.8 0.46 0.21 3 8.5 4.1 2.2 0.48 0.26 5 8.0
4.2 2.3 0.52 0.29 16 6.6 4.7 3.5 0.71 0.53 20 6.7 4.8 3.8 0.72
0.57
Example 8
[0064] Example 8 illustrates the change in the ratio when the same
liquor is heat treated at 90.degree. C. At this temperature, the
activation of the liquor, as measured by the change in ratio, is
very rapid. Within 5 hours, the PS.sub.UV/PS.sub.GR or
PS.sub.UV/PS.sub.GRAV ratio has increased to a useful 0.84, and the
PS.sub.VIS/PS.sub.GR or PS.sub.416/PS.sub.GR ratio increased from
0.21 to 0.74, while the gravimetric polysulphide concentration was
decreased from 8.5 g/L to 4.3 g/L. Longer times at this temperature
resulted in a lower PS.sub.GR, PS.sub.UV and PS.sub.VIS
concentrations with only a small gain in the ratios.
8TABLE 8 Stability at 90.degree. C. PS con- PS con- PS con- Sample
centration centration centration UV Vis Time (gravimetry) (UV 285)
(Vis 416) 285/Grav 416/Grav (h) g/L g/L g/L ratio ratio 0 8.5 4.0
1.8 0.47 0.21 1 6.9 3.7 2.2 0.53 0.31 3 4.8 3.6 2.9 0.74 0.61 5 4.3
3.6 3.2 0.84 0.74 16 3.8 3.3 3.1 0.86 0.80 20 3.6 3.3 3.1 0.91
0.84
EXAMPLE 9
[0065] Unclarified mill white liquor containing 100 g/L of lime mud
was oxidized with air in the presence of 2.0 g/L MnO.sub.2 at
85-90.degree. C. for 60 minutes, cooled quickly to room temperature
(20.degree. C.) using a water bath and filtered to remove the lime
mud and to give a clarified oxidized white liquor. One portion of
the oxidized white liquor was treated at 70.degree. C. for 20
hours. Another portion was stored at room temperature (20.degree.
C.) for 20 hours. The polysulphide concentrations in these two
oxidized white liquors were determined by gravimetry to be
PS.sub.GR=6.4 g/L and 7.7 g/L, respectively, and by UV to be
PS.sub.UV=5.1 g/L and 3.8 g/L, respectively. The
PS.sub.UV/PS.sub.GR of the oxidized white liquor treated at
70.degree. C. for 20 hours (OWL-70.degree. C.) was thus 0.80 and
the PS.sub.UV/PS.sub.GR of the oxidized white liquor stored at
20.degree. C. for 20 hours (OWL-20.degree. C.) was 0.49. The same
amounts of these two oxidized white liquors were then used for the
pulping of mixed softwood chips (50/50 black spruce and pine) in a
micro-digester using 50 g (OD weight) of the wood chips in each of
four stainless steel laboratory bombs. A control Kraft cook using
the white liquor (WL) was also carried out. The liquor to wood
ratio and the maximum cooking temperature were 4.5 to 1 and
170.degree. C., respectively. The PS.sub.GR charges were 1.3 and
1.5% (on wood) for the cook using OWL-70.degree. C. and the cook
using OWL-20.degree. C., respectively. Each bomb was cooked to a
certain H-factor. Upon completion of each cook, the pulp from each
bomb was well washed and screened through a laboratory flat screen
plate (0.2 mm or 0.008" slot). The screened pulp yields were
measured by weighing the oven-dried screened pulps and the
permanganate numbers determined according to PAPTAC, Standard G.
17H. FIG. 3 shows that the PS cook using the heat-treated oxidized
white liquor (OWL-70.degree. C.) at a ratio of
PS.sub.UV/PS.sub.GR=0.80 gives a higher yield gain over the Kraft
reference than the cook using oxidized white liquor without the
heat treatment (OWL-20.degree. C.) at a ratio of
PS.sub.UV/PS.sub.GR=0.49.
Example 10
[0066] Unclarified mill white liquor containing 100 g/L of lime mud
was oxidized with air in the presence of 2.0 g/L MnO.sub.2 at
85-90.degree. C. for 60 minutes, cooled quickly to room temperature
(20.degree. C.) using a water-bath and filtered to remove the lime
mud and to give a clarified oxidized white liquor. One portion of
the oxidized white liquor was treated at 70.degree. C. for 20
hours. Another portion was stored at room temperature (20.degree.
C.) for 20 hours. The polysulphide concentrations in these two
oxidized white liquors were determined by gravimetry to be
PS.sub.GR=6.0 g/L and 7.6 g/L respectively. The same amounts of
these two oxidized white liquors were then used for the pulping of
maple chips in a micro-digester using 50 g (OD weight) of the wood
chips in each of four stainless steel laboratory bombs. A control
Kraft cook using the white liquor (WL) was also carried out. The
liquor to wood ratio and the maximum cooking temperature were 4.0
to 1 and 165.degree. C., respectively. The PS.sub.GR charges were
1.1 and 1.4% (on wood) for the cook using OWL-70.degree. C. and the
cook using OWL-20.degree. C., respectively. Each bomb was cooked to
a certain H-factor. Upon completion of each cook, the pulp from
each bomb was well washed and screened through a laboratory flat
screen plate (0.2 mm or 0.008" slot). The screened pulp yields were
measured by weighing the oven-dried screened pulps and the
permanganate numbers determined according to PAPTAC, Standard G.
17H. FIG. 4 shows that the PS cook using the heat-treated oxidized
white liquor (OWL-70.degree. C.) again gives a higher yield gain
over the Kraft reference than the cook using oxidized white liquor
without the heat treatment (OWL-20.degree. C.).
Example 11
[0067] This example (through FIG. 5) summarizes the optimum storage
time needed to maximize the PS.sub.UV content of a polysulphide
liquor generated by the oxidation of white liquor. The active
polysulphide concentration (PS.sub.416) at a given storage time is
described by the curve which increases with time. The temperature
at which the liquor is held in storage is described by the curve
that decreases with time. FIG. 3 shows that, at the lowest
temperature evaluated (60.degree. C.), a storage time of 60 hours
is needed to produce 6 g/L of active polysulphide from a liquor
initially having a PS.sub.GR concentration of 8.5 g/L. At the
highest temperature evaluated (103.degree. C.) a storage time of 2
hours is needed to produce 2.3 g/L of active polysulphide from the
same liquor.
Example 12
[0068] In this example, a polysulphide liquor was made with
MnO.sub.2 but without lime mud. A synthetic white liquor was
prepared from sodium hydroxide and sodium sulphide. A sample (750
mL) of this white liquor was oxidized using air at 450 ml/min with
0.4 grams of a commercial grade MnO.sub.2 (0.53 g/L MnO.sub.2). The
composition of the synthetic white liquor and the product oxidized
liquor are illustrated in Table 9. Table 10 shows that heat
treatment at 77.degree. C. for 16.5 hours of this type of oxidized
liquor is effective in increasing the PS.sub.UV/P.sub.GR ratio from
0.46 to 0.97 and increasing the PS.sub.416 concentration in the
oxidized liquor from 1.4 to 3.3 gpl (as sulphur).
9TABLE 9 Composition of liquors used in this example. Synthetic
White 60 minutes Liquor Oxidation Na.sub.2S, g/L as S 18.11 11.16
PS, g/L as S 0.24 7.14 % Selectivity n/a 99
[0069]
10TABLE 10 Effect of thermal treatment (storage at 77 C. for 16.5
hours) with a polysulphide liquor generated with MnO.sub.2 in the
absence of lime mud. UV 285 nm 416 nm Gravimetric 285/grav PS, g/L
S PS, g/L S PS, g/L S ratio Before Thermal 3.3 1.4 7.14 0.46
treatment After Thermal 3.6 3.3 3.65 0.97 treatment
Example 13
[0070] In this example, a polysulphide liquor was made with a
wet-proofed activated carbon catalyst. Wet proofing was done by
spraying a dry film lubricant (TFE in Freon-trademark) on activated
carbon (50-200 mesh from Fisher Scientific Co. Ltd.). The resulting
paste was dried in the fume hood under a flow of nitrogen.
[0071] Table 11 shows that heat treatment at 65.degree. C., or
aging at 25.degree. C., over 60 hours of this type of oxidized
liquor increases the active polysulphide from 2.15 g/L to 4.55-5.68
g/L.
[0072] The oxidation was done at room temperature by adding 5 g of
wet-proofed carbon to about 300 mL of artificial white liquor
pre-heated to 85.degree. C. in a 500 mL beaker. Oxidation was done
for about 15 h by letting air diffuse through the floating carbon
into the white liquor. Samples of the oxidized liquor were then
analyzed by gravimetry and by UV spectrophotometry, just after
production (fresh) and then after storage for 60 h at 25.degree. C.
Another aliquot of the fresh oxidized liquor was also stored at
65.degree. C. for 60 h and then analyzed again.
[0073] The effect of liquor aging on the change in active
(PS.sup.act), inactive (PS.sup.inact) and total (PS.sup.tot)
concentrations of polysulphides is presented in Table 11.
11TABLE 11 Effect of thermal treatment with a polysulphide liquor
generated using a wet-proofed activated carbon catalyst PS
concentrations (g/L, as S) MOXY-type liquor PS.sup.act PS.sup.inact
PS.sup.tot Fresh 2.15 10.39 12.54 Aged 60 h at 25.degree. C. 4.55
3.07 7.62 Aged 60 h at 65.degree. C. 5.68 3.58 9.20
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* * * * *