CA2373562A1 - Eop & ep process for bleaching of chemical pulp - Google Patents
Eop & ep process for bleaching of chemical pulp Download PDFInfo
- Publication number
- CA2373562A1 CA2373562A1 CA002373562A CA2373562A CA2373562A1 CA 2373562 A1 CA2373562 A1 CA 2373562A1 CA 002373562 A CA002373562 A CA 002373562A CA 2373562 A CA2373562 A CA 2373562A CA 2373562 A1 CA2373562 A1 CA 2373562A1
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- Prior art keywords
- chemical pulp
- bleaching solution
- bleached
- aqueous bleaching
- aqueous
- Prior art date
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Classifications
-
- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
- D21C9/00—After-treatment of cellulose pulp, e.g. of wood pulp, or cotton linters ; Treatment of dilute or dewatered pulp or process improvement taking place after obtaining the raw cellulosic material and not provided for elsewhere
- D21C9/10—Bleaching ; Apparatus therefor
- D21C9/147—Bleaching ; Apparatus therefor with oxygen or its allotropic modifications
-
- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
- D21C9/00—After-treatment of cellulose pulp, e.g. of wood pulp, or cotton linters ; Treatment of dilute or dewatered pulp or process improvement taking place after obtaining the raw cellulosic material and not provided for elsewhere
- D21C9/10—Bleaching ; Apparatus therefor
- D21C9/16—Bleaching ; Apparatus therefor with per compounds
- D21C9/163—Bleaching ; Apparatus therefor with per compounds with peroxides
Abstract
The subject process comprises providing chemical pulp and as E op, and/or E p aqueous bleaching solution. The E op aqueous bleaching solution comprises a peroxide compound, an oxygen-containing material, sodium hydroxide and magnesium hydroxide, in the absence of magnesium sulfate. Alternatively, the E
op aqueous chemical solution for bleaching chemical pulp comprises an E op aqueous bleaching solution consisting essentially of a peroxide compounds an oxygen-containing material, sodium hydroxide stud magnesium hydroxide.
In any case, the Chellean pulp is bleached with the E op aqueous bleaching solution to form a bleached chemical pulp. The E p aqueous bleaching solution comprises a peroxide compound, sodium hydroxide and magnesium hydroxide, in the absence of magnesium sulfate. Alternatively, the E p aqueous bleaching solution consists essentially of a peroxide compound, sodium hydroxide and magnesium hydroxide.
In any case, the chemical pulp is bleached with the E op, and/or E p aqueous bleaching solution to form a bleached chemical pulp as part of an overall chemical pulp bleaching sequence.
op aqueous chemical solution for bleaching chemical pulp comprises an E op aqueous bleaching solution consisting essentially of a peroxide compounds an oxygen-containing material, sodium hydroxide stud magnesium hydroxide.
In any case, the Chellean pulp is bleached with the E op aqueous bleaching solution to form a bleached chemical pulp. The E p aqueous bleaching solution comprises a peroxide compound, sodium hydroxide and magnesium hydroxide, in the absence of magnesium sulfate. Alternatively, the E p aqueous bleaching solution consists essentially of a peroxide compound, sodium hydroxide and magnesium hydroxide.
In any case, the chemical pulp is bleached with the E op, and/or E p aqueous bleaching solution to form a bleached chemical pulp as part of an overall chemical pulp bleaching sequence.
Description
Eon dt Ep PROCESS FOR BLEACHING OF CHEMICAL PULP
RELATED APPLICATION
This application claims priority from Provisional A.pplieation Serial Numbar 60/2? 1,987 filed on February 27, 2001.
BACKC3~ROUND OF THE INVENTION
Historically the treatment of wood chips to form a chemical pulp has been divided into two prOGO$5e5. The first process is pulping and the ascend process is 1.0 bleaching.
Pulping is the changigg of wood chips or othar wood particulate math to fibrous form. Chemical pulping includes partial removal of lignin and other materials associated with the wood.
Bleaching is the treatment of the partially delignifiod cellulosic fibers with chemicals to remove or slter the coloring matter associated therewith.
Bleaching brightens the fibers in order to reflect white light more truly.
Throughout the evolution of pulp bleaching, caustic soda (NaOH) has boon used as the primary alkali source in bleaching of chemical pulp. Caustic soda is a highly soluble alkali that readily provides an. optimum reaction pH and facilitates the dissolution of lignin from pulp in pulp bleaching. Since caustic soda is a strong base, carbohydrate degradation can occur resulting in a decrease in pulp viscosity and as increase in chemical oxygen demand (COD).
In conventional pulp bleaching, a D- E~-D-E,P-D bleaching saquence is often employed far brightening chemical pulp. E~ bleaching typically utilizes hydrogen pQroxide, oxygen, caustic soda cad magnesium sulfate as the bleaching chemicals. F,~ bleaching typically utilizes hydrogen peroxide ~d caustic soda s~s the bleaching chemicals. Conventional E~, and EP bleaching suffer tom the drawback of increased COD which is described above.
Accordingly, there is s need for a 8~ and Ep bleaching sequences which overcome the above-described drawbadG, SUMhfARY OF THE INVENTION
This ixrve~ion is directed to an E~, and an Ep process for bleaching chemical pulp which overcome drawbacks associated with conventional bleaching.
The subject process comprises providing a bleached chemical pulp produced by bleaching sequences in which E°p and/or the EP aqueous bleaching solutions employed therein include magnesium hydroxide in place of a substantial portion of the NaOH, and as a total replacement for any magnesium sulfate. The E°p aqueous bleaching solution can comprise a peroxide compound, an oxygen-containing materiel, sodium hydroxide and magnesium hydroxide, in the absence of magnesium sulfate. Attematiwely, the E~ aqueous chemical solution for bleaching chemical pulp can eomprisc an E~ aqueous bleaching solution consisting essentially of a peroxide compound, an oxygen-containing material, sodium hydroxide and magnesium hydroxide. In any case, chemical pulp is bleached with sa E~ aqueous bleaching solution to form an E°y bleached chemical pulp. The E~ aqueous bleaching solution of this invention can be employed in a D-E°P D-Ep-D bleaching sequence. The subject invention is also di~re,~ted to a bleaching sequence which includes the EP bleaching of chemical pulp. The F.~, aqueous bleaching solution can comprise a peroxide compound, sodium hydroxide and magnesium hydroxide, in the absence of magnesium sulfate. Stated another way, an Ep aqueous bleaching solution can be provided consisting essentially of a peroxide compound, sodium hydroxide and magnesium hydroxide. In certain bleaching sequences, for example, the ED aqueous bleaching solution of the subject invention can be provided for bleaching E~ bleached pulp to form an Ep bleached chemical pulp. The EP aqueous bleaching solution of this invention can also be employed in a D-E~ -D- Ep -D bleaching sequence.
In the E°P and/or Ep processes of the present invention, the amount of sodium hydroxide in the E°p and/or aqueous bleaching solution is preferably not more than about 8 % by weight, more preferably not more than about 5 % by weight, and most preferably not mass than about 3 % by weight, based on the O.D.
weight of said chemical pulp, Furthermore, the ratio of sodium hydroxide to magnesium hydroxide in said E~ aqueous bleaching solution ie not ttrore than about S:1 (based on an OH' molar ratio), prefierably not more than about 3:1 (based on an OFi' molar ratio), and most preferably not more than about 1:2 (based on an OH' molar ratio). As for the ratio of sodium hydroxide to magnesium hydroxide in said F,~, aqueous bleaching solution" it is not mono than about 1:1 (based oa an OH' molar ratio), preferably not more than about 1:3 (based on an OH' molar ratio). Most preferably about 100% magnesium hydroxide is employed without substantially any sodium hydroxide.
Both the E~ and P~, bleaching pmeassos of this invartioa preferably coatemplatos that the pulp viscosity of a final bleached chemical pulp is at least substantially the same as the pulp viscosity of a final bleached chemical pulp which is bleached with the same total amount of an E~ aqueous blaa~chiag solution comprising a peroxide compound, oxygen-eontainirtg material, sodium hydroxide, with or without magnesium sulfat~, is the absoacc of magnesium hydroxide, on the one hand, and/or an F,~ aqueous blaaehing solution comprising a peroxide compound and sodium hydroxide, with or without magnesium sulfate, in the absence of magnesium hydroxide, on the other hand. Pulp viscosity is measured in centipoises using the 0.5°~ CED viscosity test method described is TAPPI T-X30.
2o Also, the preferred E~, process generates a bleach oi~luent which has a COD which is less Than the COD of a bleach e~luont from an E~ process which esaploys an Eq, aqueous bleaching solution comprising the peroxide compound, oxygen-containing material, sodium hydroxide, with or without magnesium sulfate, in the absence of magnesium hydroxide_ More specifically, the COD of the bleach effluent produead wring the E.q, aqueous bleaching solution of the present invention is preferably at least about 5%, morn preferably at least about 8%, and most preferably at least about 10%, less than the COD geacratad by as E~ stage which uses an E~ aqueous bleaching solution comprising said peroxide compound, oxygen-containing material, sodium hydroxide, with or without n~gneaium sulfate, in the absence of:nagnosium hydroxide. COD is measured in mglL using a HACH test ldt.
Moreover, the bleached chemical pulp of x bleach aequenco containing the subject process preferably has a final ISO brightness (% ISO) of which is at least substantially the same as the dal ISO brightness (% ISO) of bleached chemical pulp which is bleached with the same bleach sequence but with as E~ aqueous bleaching solution comprising a peroxide compound, oxygen-containing nzsterial, sodium hydroxide, with or without magnesium sulfate, in the absence of magnesium hydroxide, on the ono hand, and/or an EP aqueous bleaching solution comprising a peroxide compound and sodium hydroxide, with or without magnesium sulfate, in the absence of magnesium hydroxide, on the other h~tad.
1 o ISO brightness is measured using the teat method deacribod in TAPPI ?-45Z.
The process of this invention also produces a bleached charnical pulp having a preferred wet zero span tensile strength which is at least substatltixlly the same as the wet zero span tensile strength of bleached chemical pulp which is bleached with the same total amount of an E~ aqueous bleaching solution comprising a peroxide compound, oxygen-containing material, sodium hydroxide, with or without magnesium sulfate, in the absence of magnesium hydroxide, on the ono hand, arul/or as Ep aqueous bleaching solutian comprising a pe~roxidc carnpound and sodium hydroxide, with or without magnesium sulfate, in the absence of magnesium hydroxide, on the other hand Wet zero spats tensile strength is measured in bn using a Pulmac wet zero-spars tensile apparxtus_ E~ and P~, bleaching are typically part of a broader overall ehecr~ical pulp bleaching sequmco_ Thus, there can be one or mono additional chemical pulp bleaching stages that occur prior to Fey, and F,~, bleaching, as well as one or more additional chemical pulp bleaching stages that occur aubsequcnt to F.ro,, and Ep bleaching. Usually, these additional chemical pulp bleaching stages are conducted employing oonvontional bleaching technology utilizing bleaching ch~aicaia such as CIOz, Oz, Cl= and peroxide.
The foregoing and other objects, features and advantages of the invention will become morn apparent from the detailed description of a preferred embodiment of the invention below which proceeds with reference to the accompanying drawings.
d DESCRIPTION OF THE Dn,A,W'>T1GS
FIG. 1 is a schematic diagrarrt comparing pulp brightness for various levels of bleaching solution in an E~, ble~ehing process.
FIC3, 2 is a schacnatic diagram comparing pulp viscosity for various levels of bleaching solution in an P,,~ bloacbing process.
FIG. 3 is a schematic diagratri comparing pulp wet tern-span tensile strength for various levels of bleaching solution in an E°,, bleaching process.
FIG. 4 is a sehomatic diagram tampering pulp COD for various levels of bleaching solution irr an E,~ blaaahing psocess.
DETAILED DESCRIPTION OF THE PRESENT INVENTION
As set forth in Tables I-III, an aqueous slurry containing magnesium hydroxide was employed as a partial substitution fnr caustic ands and a complete replacement for magnesium sulfate in the e~ctraction-oxygen-peroxide stage (E~,,) of the bleaching of northeast softwood kraft pulp. More specifically, laboratory experiments examined the bleachability of the pulp through a complete DBopDEpD
bleach aequance with complete replacement ofmagaesium Sulfate and partial substitution of NaOH on an OH' molar basis using CellGuard""OP (sec description of CellC~uard""OP below) in the F.q, stage. Three magnesium hydroxide substitution levels were evaluated in the E~, stage: 0°/a, 259°, and 30°/p of the OH' derived from CollGuard"~OP and the balance Srom NaOH.
In Table III, an aQucous slurry containing magnesium hydroxide was also employed as a partial substitution for caustic soda and a complete replaaoment for magnesium sulfate in the oactraction-peroxide stage (F.~) of the bleaching of northeast soRwood kraft pulp. More speciEcally, laboratory experiments examined the bleachsbility of the pulp through a complete D E"~ D F.,, I7 bleach sequence with complata raplacearent of magnesium sulfate and partial substitution of NaOH on an OH- molar basis using CellCiuard'~OP (see description of CcllC~uard~"OP below) is both the F.°,, and Bp stages. Four magnesium hydroxide c substitution levels were evaluated is the EP stage: 0%, 25%, SOor6, 7S% and 100'/0 of the OH' derived frtrm CallGuard"~OP and the balsaee, if nay, from NaOH.
Bleaching experiments for the ~ stage were performed in a 2-liter, medium consistency oxygen reactor equipped with a mixer. The oxygen reactor was treated with nitric acid to passivate the surface to avail contamination from metals. The Do, D,, F,p, and Dx stages were performed by traditional bag bleaching methods. The bmwnstock ktaR pulp to be bleached bad a kappa number of 29.2, a brightness of 26.9° ISO, and viscosity of 48.0 cps. This ktaR pulp was bleach~l under the conditions outlined in Tables I-III. Chemical doasges were based on the weight of oven-dried pulp. The oxporinaeatal procedure for oath stage is summarized as follows:
egg. Standard conditions as sot forth in Tables I-III wore employed for the Do stage. The kappa factor was adjusted with 2.44% C10= to reach the desired kappa number out of the Do stage. The pulp was then washed to pH 7.5.
E. After the Do stage, the pulp was exttact~d with a conventional F.~ stage which employed 1.7% NaOH sad 0.1 % MgSO,s. For comparison purposes in Tables I and II, bleaching experiments using CcllGuard"'OP as a replacement fo* MgS04 and as a partial substitute for NaOH were conducted, Caustic sale replacement was based on an OH' molar basis. For example, at 25%
substitution where 25% of the OH' comes 8rom Mg(OH)z, the respective alkali dosages used were 1.275% NaOH sad 0.31~o CellGuard'~"OP. Cax~atio soda contains 42.51 % by weight OH' ions while maguosium hydroxide contains 58.32°Yo by weight OH' ions, For the E°,, stage in Tables I-III, bleaching occurred at 138 kPa of 02 pressure for 20 minutes followed by bleaching at atmospheric pressure for the remaining 40 minutes.
Martin Marietta Magnesia Specialties, LLC is the maaufaaturer of CcllGuard~OP Magaesiium Hydroxide Slung for use in pulp bleaching. The CeIlGuard""OP Mag~nosium Hydroxide Slurry, which is produced $om a dolomitie limo and magnesium brine process, contains 62% by weight Mg(OIT)z solids suspended in water. The purity of the magnesium hydroxide is over 98% with low levels of transition motels. This product has a fine particle size (3 microns as toeasured by Micromeritics Sedigtaph 5100) which promotes high reactivity and excellent suspension stability.
I~1~3 Pulp Time Temp Pressure Chemical Stage Consistency(mm) (C) (kPa) % on O.D.
pulp a Do 12 45 60 -__ 2,44% Cl 0.5% HsOa 138 kPa of Oz 1.7/ NaOH
for or EoP 12 60 70 20 mur, then Mg(OH~/NaOH
arm 0.1 % MgS04 (for Contro:
onI
D 12 180 80 -- _ QZ
1.2% C1 EP 12 40 70 --~-- (1. I5% HaOs 0.5% NaOH
Dz I2 100 80 --- 0.6% CIOz DmF.~,~,~'I~T es I and I11-Standard conditions ware employed for the Dt-F.~-D= stages shown in Tables I and II. The pulp and filtrate following each bleaching stage were tested for I,SO brightness sad end pH, respectively. The pH
of the residual liquor was dettrrnined using a pH meter and appropriate buffer solutions to calibrate the pH meter. Pulp samples from the E~" D~, and D2 stages ZO were tested for viscosity and wet zero-span tensile strength. The respective filtrates were analyzed for chemical oxygen demand (COD).
After the Do stage and washing stop, the lcsppa number decre~aeed from 29.2 to 11.9. Pulp brightness iaCreased fi~ 26,9% ISO to 35.9% ISO.
The effects of CcllGuard"~"OP substitution in the P~ stage on each of the pulp 15 parameters were measured. Table II contains a summary of results for each bleaching test performed.
FIG. 1 compares pulp brightness for the various levels of CellGusrd~"OP
substitution in tire E~ stage. The data shows the increasing trend is brightness with each subsequent bleaching stage for all substitution cases. The control 20 sample, which employed 100°i6 4H' from NaOH (or 4°Yo OH' from C~llGuard"'~OP) and MgSO,, yielded as increase in brightness from 62.1 % ISO after the E°P stage to a final pulp brightness of 90.8% ISO after the D2 stage.
At 25% substitution with CellGuard""OP in the E~ stage, brightness slier this bleaching step (60.1% ISO) was lowar than the control. However, equivalent final pulp brightness after the Da stage resulted in 90.5% ISO at the same C10= and HZOZ charge in the Dl and EP stages respectively ats the control sample.
At 50% substitution with CollC~ruatd~"OP, Figure 1 shows that the brightness after the Pte,,, stage was 59.7% ISO. Even with the use of a mild alkali in the extraction stage which lowers the bleaching pH to 10.1 for 25°!° substitution and 9.3 for 50% substitution, comparable final brightness was achieved as eridence by the final 89.9% ISO brightness result after the Da stage.
At the end of the E~,, stage, the control sartnpIe yielded a pulp viscosity of 27.8 cps. As shown in FIG. 2, both the 25% and SO% substitution runs with CellGuard"'OP produced higher viscosity results of 28.6 cps and 29,3 cps respectively after the E~ stage. These results indicate that CellGusrd'7"OP
servos a dual role as a peroxide activator and cellulose pmtoctor. In a conventional E~
system where NaOH and MgS04 are utilized, CellGuard"~OP Mg(OH)2 can reduce the NaOH consumption and eliminate MgS04. As soon in FIG. 2, the control sample's final viscosity was 16.5 cps, the 25% and 50% substitution samples with CellGuard~OP produced pulps with respcctivo viscosities of 17.5 cps and 18_6 cps. By utilizing CellGuard"'OP Magnesium Hydroxide in the E%, stage, a one to two point increaso in pulp viscosity over the conventional E°,, stage was achieved.
Fiber strength was maintained in both CollGuard~OP substitution cases as shown in Figure 3. Wet zero-spas tensile strength for all cases ranged from 10.9 -11.0 km for the E~ stage, 10.2 - 10.6 for the D~ stage, and 10.3 - 10.4 inn for the DZ stage.
High chomical oxygen demand (COD) is gonorated in the E~ stage where the most of the extraction occurs (ace FIG. 4). Partially substituting the NaOH
charge with a weak alkali such as Mg(OH)2 reduces the organic loading in the effluent from the E~, stage. 'The highcFr substitution rate with CellGuard~OP
yielded a noticeable ~da~otion itt COD whoa cared to tho control aa:aple. Then control sample generated 4635 mgt COD vatsus 4105 mg/L COD for the 50%
substitution cast, which roprosenta an 11% roduction. Lower COD loading can contribute to reduced e~'tuent treatment costs dowaatream.
By employing partial substitution of CellGuard'~OP Magnesium Hydsoxide Slurry for eausdc soda and eliminating magnesium sulfate in the Eop stage, a strong alkali is present to facilitate lignin removal while a mild allca~lii is added to promote peroxide bleaching arid eelluloac protecdon. CallGuard~'"OP can replace up to 50% of the caustic soda requirement in the Eq, stage producing final pulp from the Da stage with similar brightness, permanganate number, and wet aem-span tensile strength a: pulp bleached with a 100% caustic soda charge.
At 50% substitution of caustic soda, the use of Cdlt~luard~OP improves the pulp viscosity by 12% and reduces the COD after the E~, stage; by 1 I %. Since only 0.73 kg of magneaiurn hydroxide provides the equivalent amount of hydroxyl ions as 1 kg of caustic soda, Ce11C3uard~"OP reduces bleaching costs in many cases.
At no added cost beyond the amount required for caustic soda replacement, Cell(~uard'~"OP also elitniaates the steed for magnesium sulfate for i~ther reduction in chmaical costs_ RESULTS OF PARTIAL SUBS'ITTUZTON OF
CAUSTIC SODw vViT~i MAaIvtESItJM HYDROXIDE SLURRY
IN THE EOP STA(i8 Og A DEopDEpD BLEACH SEQUENCE
..
Star Chemical Timo Tamp PressureEnd ~ $ COD
,...
a (r6 on (~) (~ (I~'a)pfY ~ ~ ~ ~ ~, (~) pulp) ' Brown- , ; 26 48 (~~ 5 9 0 ~ 12 ' . . .
stock , ; ~ .
. ~; .
.. ' 7.4 0.22 kf 45 ~0 2.3Z 35.9 ' (11.9 as D Stage D (2.44% , ~.
C10~ kappa) 0.5~6 FIz02 138 kPa Oa 1.7% NaOH for ~ 70 ,20 11.3 62.1 27.8 3.1 10.9 4635 Eop 0.1 % MBS04 ~jn,~
thaa 0~~ Mg(OH)i Coatrol N
OH +
a M~SO~ 1.2% CIOs 180 80 2.3 80.2 21.4 1.1 10.2 1352 D
0. I S~b 40 70 ~ 11.4 86.0 Hi0=
E 0.5 % NaOH
0.6% CIO= 100 80 ~ 3.3 90.8 16.5 O.B 10.3 176 D
0.5% H=Os Id?a pr 1.275/b fpr NaOH
60 70 20 10.1 60.1 28.6 3.4 I0.8 4555 Eop 0.31~o min, then 25% MB(OH)z a~
Substirution _ CellGuard'~ 1.2% CIOa 180 80 . ' 2.3 78.9 22.1 1.3 10.3 1326 .
in Eop D, 0.15% Ii=O=~ 70 ~' 11 85 ' . .
4 3 ' E 0.5 9~o . . . ' ' . ' . ..
NaOH ' D 0.6% C10~ 100 80 '' 3.3 90.5 17.5 0.6 10.2 ' 0.5% I~ZOz kPa 0.85% NaOH
~ 70 20 9.3 59.7 29.3 3.5 11.0 4105 Eop 0.62% min, ~a MB(O~t 50% a~
S
b rit ti u , s on u CellGuard'"D 1.2% CIOz 180 80 : 2.3 76.3 22.0 1.4 10.6 1420 i E
op n 0.15% Hl0=
40 70 ' 3 83 B 0.5% NaOH . . .
D 0.6% CIOi 100 80 . 3.2 89.9 18.6 0.7 10.4 184 ' % on oven-dried pulp = After waahiag, pH was 7.5 All experimaata wore conducted at 12% pulp consistency.
B°P -DZ-E~DZS~ag, ~ ('Tabl~IIn-Standard conditions were employed for the D~ and DZ stages of bleaching processes shown in Table III. In the experiments involving substitution of magnesium hydroxide for NaOlI in the Ep stage, magatsium hydroxide was substituted for all of the magaeaium sulfate sad a portion of the NaOH (25%, 50%, 75% or 100%). The E~ atagc employed a 50%
substitution of magnesium hydroxide for NaOH, and 100% substitution for all of the magnesium sulfate, in all the bleaching experiments. The pulp and filtrate following each bleaching stage were tested for IS4 brightness and end pH, respectively. The pH of the residual liquor was detenainod using a pH motor and appropriate buffer solutions to calibrate the pH meter. Pulp samplas from the Eq,, D~, and DZ stages were also tested for viscosity and K#. As seen in Table IIi, the ~rLal ISO brightness, viscosity and K# of the bleached chemical pulp of the process of the present ~invontion is comparable or greater than the the final ISO
brightness, viscosity and K# of bleached chemical pulp which is bleached with the same total amount of an F.~, aqueous bleaching solution comprising said paroxide compound and sodium hydroxide, but in the absence of magneaium hydroxide.
Table III. RESULTS OF SUBS~TT~J'TION OF CAUSTIC SODA
AND MAC~NESIIJM SULFATE WITH MAC3NESIUM
HYDROXIDE SLURRY
In E~ and Ep Stages of a DES DEpD Bleach Sequence StaOe C~tmital Tlms T >cure Kappa KB !SO Vit-e,~ (rp(p)$ (pd~ 25 Brl=bt eaa-m!
aea~ ity Ye ep BS $rpWI~t~Ck 30.4 Z6.1 51.9 D
After W,flblp/~
O 13.7 8.6 34.3 48.Z
Z2kf ~, ~,5 pD D .
.54% CIO
g O.s'l,H=O= 60 70 138Kpa 3.5 61.6 41.9 I00% OH- 1.7% NaO~i CONTROL trem lr,o7~to.t~ Mgso, NaOH + o/. wtg (OHh thoa avn MgS04 Sequence Di 1.2%QO~ t80 80 1.3 79.6 Z9.s E & E sta es ~ 70 86.4 g s OH only Eo0rl, OH 0,4896 aOH
N
from NaOH 0% Mg (OH)s DZ 0.6/ CI 100 80 0.6 90.7 22.0 B 0.5/.H=Oz 60 70 1381Cpa 4.0 34.9 42.6 50~ OH 0.85% NaOH pf Z
from Me(Oli~0.6T% Mp min.
(OHj=
Substitution den arm Scquence 1.2% C10= 180 80 1.6 74.9 32.9 op 50%
0.15%H=0= 40 '~0 StrbStltatl0nBv Coptrol 0.48% NaOH
o% M~ (off:
Ep v~ysn~
Snbstitvtian DZ 0.6% C10= 100 s0 0.7 90.3 24.6 l2 Ro 0.15'yG~i~Oa40 70 83.d =3% O~ 0.36iG NWH
prom M8(OI~Lh0.0915 M8 (0F1), DZ 0.6lfi CID, 100 80 0.'7 90.2 ?4.d E
O.15YHiOi 40 70 3.1 s0% OH- 0.?4% NaOH
from M8(OH~0.18% Mg (OHM
ps 0.6% CIO= 100 80 0.8 89.9 25.2 Coot-ME(UH)= ~ o.is~x~ 40 ~o e~.s ~~~ oe-Subatitutionfrom Maoab o ~ ~ (o ~
sequence Hh ~' P D= 0.6% CIO, 100 80 89.5 25.3 50%
Substitution~ o.isx~to, 40 ~o ~8.s 1006 OH- 09~, Na013 E prom o 0.3s% Ma p (OH)=
Varying Sll~lat~ttlt~4n 0.6IG CIO, 100 SO 0.8 88.6 7R.0
RELATED APPLICATION
This application claims priority from Provisional A.pplieation Serial Numbar 60/2? 1,987 filed on February 27, 2001.
BACKC3~ROUND OF THE INVENTION
Historically the treatment of wood chips to form a chemical pulp has been divided into two prOGO$5e5. The first process is pulping and the ascend process is 1.0 bleaching.
Pulping is the changigg of wood chips or othar wood particulate math to fibrous form. Chemical pulping includes partial removal of lignin and other materials associated with the wood.
Bleaching is the treatment of the partially delignifiod cellulosic fibers with chemicals to remove or slter the coloring matter associated therewith.
Bleaching brightens the fibers in order to reflect white light more truly.
Throughout the evolution of pulp bleaching, caustic soda (NaOH) has boon used as the primary alkali source in bleaching of chemical pulp. Caustic soda is a highly soluble alkali that readily provides an. optimum reaction pH and facilitates the dissolution of lignin from pulp in pulp bleaching. Since caustic soda is a strong base, carbohydrate degradation can occur resulting in a decrease in pulp viscosity and as increase in chemical oxygen demand (COD).
In conventional pulp bleaching, a D- E~-D-E,P-D bleaching saquence is often employed far brightening chemical pulp. E~ bleaching typically utilizes hydrogen pQroxide, oxygen, caustic soda cad magnesium sulfate as the bleaching chemicals. F,~ bleaching typically utilizes hydrogen peroxide ~d caustic soda s~s the bleaching chemicals. Conventional E~, and EP bleaching suffer tom the drawback of increased COD which is described above.
Accordingly, there is s need for a 8~ and Ep bleaching sequences which overcome the above-described drawbadG, SUMhfARY OF THE INVENTION
This ixrve~ion is directed to an E~, and an Ep process for bleaching chemical pulp which overcome drawbacks associated with conventional bleaching.
The subject process comprises providing a bleached chemical pulp produced by bleaching sequences in which E°p and/or the EP aqueous bleaching solutions employed therein include magnesium hydroxide in place of a substantial portion of the NaOH, and as a total replacement for any magnesium sulfate. The E°p aqueous bleaching solution can comprise a peroxide compound, an oxygen-containing materiel, sodium hydroxide and magnesium hydroxide, in the absence of magnesium sulfate. Attematiwely, the E~ aqueous chemical solution for bleaching chemical pulp can eomprisc an E~ aqueous bleaching solution consisting essentially of a peroxide compound, an oxygen-containing material, sodium hydroxide and magnesium hydroxide. In any case, chemical pulp is bleached with sa E~ aqueous bleaching solution to form an E°y bleached chemical pulp. The E~ aqueous bleaching solution of this invention can be employed in a D-E°P D-Ep-D bleaching sequence. The subject invention is also di~re,~ted to a bleaching sequence which includes the EP bleaching of chemical pulp. The F.~, aqueous bleaching solution can comprise a peroxide compound, sodium hydroxide and magnesium hydroxide, in the absence of magnesium sulfate. Stated another way, an Ep aqueous bleaching solution can be provided consisting essentially of a peroxide compound, sodium hydroxide and magnesium hydroxide. In certain bleaching sequences, for example, the ED aqueous bleaching solution of the subject invention can be provided for bleaching E~ bleached pulp to form an Ep bleached chemical pulp. The EP aqueous bleaching solution of this invention can also be employed in a D-E~ -D- Ep -D bleaching sequence.
In the E°P and/or Ep processes of the present invention, the amount of sodium hydroxide in the E°p and/or aqueous bleaching solution is preferably not more than about 8 % by weight, more preferably not more than about 5 % by weight, and most preferably not mass than about 3 % by weight, based on the O.D.
weight of said chemical pulp, Furthermore, the ratio of sodium hydroxide to magnesium hydroxide in said E~ aqueous bleaching solution ie not ttrore than about S:1 (based on an OH' molar ratio), prefierably not more than about 3:1 (based on an OFi' molar ratio), and most preferably not more than about 1:2 (based on an OH' molar ratio). As for the ratio of sodium hydroxide to magnesium hydroxide in said F,~, aqueous bleaching solution" it is not mono than about 1:1 (based oa an OH' molar ratio), preferably not more than about 1:3 (based on an OH' molar ratio). Most preferably about 100% magnesium hydroxide is employed without substantially any sodium hydroxide.
Both the E~ and P~, bleaching pmeassos of this invartioa preferably coatemplatos that the pulp viscosity of a final bleached chemical pulp is at least substantially the same as the pulp viscosity of a final bleached chemical pulp which is bleached with the same total amount of an E~ aqueous blaa~chiag solution comprising a peroxide compound, oxygen-eontainirtg material, sodium hydroxide, with or without magnesium sulfat~, is the absoacc of magnesium hydroxide, on the one hand, and/or an F,~ aqueous blaaehing solution comprising a peroxide compound and sodium hydroxide, with or without magnesium sulfate, in the absence of magnesium hydroxide, on the other hand. Pulp viscosity is measured in centipoises using the 0.5°~ CED viscosity test method described is TAPPI T-X30.
2o Also, the preferred E~, process generates a bleach oi~luent which has a COD which is less Than the COD of a bleach e~luont from an E~ process which esaploys an Eq, aqueous bleaching solution comprising the peroxide compound, oxygen-containing material, sodium hydroxide, with or without magnesium sulfate, in the absence of magnesium hydroxide_ More specifically, the COD of the bleach effluent produead wring the E.q, aqueous bleaching solution of the present invention is preferably at least about 5%, morn preferably at least about 8%, and most preferably at least about 10%, less than the COD geacratad by as E~ stage which uses an E~ aqueous bleaching solution comprising said peroxide compound, oxygen-containing material, sodium hydroxide, with or without n~gneaium sulfate, in the absence of:nagnosium hydroxide. COD is measured in mglL using a HACH test ldt.
Moreover, the bleached chemical pulp of x bleach aequenco containing the subject process preferably has a final ISO brightness (% ISO) of which is at least substantially the same as the dal ISO brightness (% ISO) of bleached chemical pulp which is bleached with the same bleach sequence but with as E~ aqueous bleaching solution comprising a peroxide compound, oxygen-containing nzsterial, sodium hydroxide, with or without magnesium sulfate, in the absence of magnesium hydroxide, on the ono hand, and/or an EP aqueous bleaching solution comprising a peroxide compound and sodium hydroxide, with or without magnesium sulfate, in the absence of magnesium hydroxide, on the other h~tad.
1 o ISO brightness is measured using the teat method deacribod in TAPPI ?-45Z.
The process of this invention also produces a bleached charnical pulp having a preferred wet zero span tensile strength which is at least substatltixlly the same as the wet zero span tensile strength of bleached chemical pulp which is bleached with the same total amount of an E~ aqueous bleaching solution comprising a peroxide compound, oxygen-containing material, sodium hydroxide, with or without magnesium sulfate, in the absence of magnesium hydroxide, on the ono hand, arul/or as Ep aqueous bleaching solutian comprising a pe~roxidc carnpound and sodium hydroxide, with or without magnesium sulfate, in the absence of magnesium hydroxide, on the other hand Wet zero spats tensile strength is measured in bn using a Pulmac wet zero-spars tensile apparxtus_ E~ and P~, bleaching are typically part of a broader overall ehecr~ical pulp bleaching sequmco_ Thus, there can be one or mono additional chemical pulp bleaching stages that occur prior to Fey, and F,~, bleaching, as well as one or more additional chemical pulp bleaching stages that occur aubsequcnt to F.ro,, and Ep bleaching. Usually, these additional chemical pulp bleaching stages are conducted employing oonvontional bleaching technology utilizing bleaching ch~aicaia such as CIOz, Oz, Cl= and peroxide.
The foregoing and other objects, features and advantages of the invention will become morn apparent from the detailed description of a preferred embodiment of the invention below which proceeds with reference to the accompanying drawings.
d DESCRIPTION OF THE Dn,A,W'>T1GS
FIG. 1 is a schematic diagrarrt comparing pulp brightness for various levels of bleaching solution in an E~, ble~ehing process.
FIC3, 2 is a schacnatic diagram comparing pulp viscosity for various levels of bleaching solution in an P,,~ bloacbing process.
FIG. 3 is a schematic diagratri comparing pulp wet tern-span tensile strength for various levels of bleaching solution in an E°,, bleaching process.
FIG. 4 is a sehomatic diagram tampering pulp COD for various levels of bleaching solution irr an E,~ blaaahing psocess.
DETAILED DESCRIPTION OF THE PRESENT INVENTION
As set forth in Tables I-III, an aqueous slurry containing magnesium hydroxide was employed as a partial substitution fnr caustic ands and a complete replacement for magnesium sulfate in the e~ctraction-oxygen-peroxide stage (E~,,) of the bleaching of northeast softwood kraft pulp. More specifically, laboratory experiments examined the bleachability of the pulp through a complete DBopDEpD
bleach aequance with complete replacement ofmagaesium Sulfate and partial substitution of NaOH on an OH' molar basis using CellGuard""OP (sec description of CellC~uard""OP below) in the F.q, stage. Three magnesium hydroxide substitution levels were evaluated in the E~, stage: 0°/a, 259°, and 30°/p of the OH' derived from CollGuard"~OP and the balance Srom NaOH.
In Table III, an aQucous slurry containing magnesium hydroxide was also employed as a partial substitution for caustic soda and a complete replaaoment for magnesium sulfate in the oactraction-peroxide stage (F.~) of the bleaching of northeast soRwood kraft pulp. More speciEcally, laboratory experiments examined the bleachsbility of the pulp through a complete D E"~ D F.,, I7 bleach sequence with complata raplacearent of magnesium sulfate and partial substitution of NaOH on an OH- molar basis using CellCiuard'~OP (see description of CcllC~uard~"OP below) is both the F.°,, and Bp stages. Four magnesium hydroxide c substitution levels were evaluated is the EP stage: 0%, 25%, SOor6, 7S% and 100'/0 of the OH' derived frtrm CallGuard"~OP and the balsaee, if nay, from NaOH.
Bleaching experiments for the ~ stage were performed in a 2-liter, medium consistency oxygen reactor equipped with a mixer. The oxygen reactor was treated with nitric acid to passivate the surface to avail contamination from metals. The Do, D,, F,p, and Dx stages were performed by traditional bag bleaching methods. The bmwnstock ktaR pulp to be bleached bad a kappa number of 29.2, a brightness of 26.9° ISO, and viscosity of 48.0 cps. This ktaR pulp was bleach~l under the conditions outlined in Tables I-III. Chemical doasges were based on the weight of oven-dried pulp. The oxporinaeatal procedure for oath stage is summarized as follows:
egg. Standard conditions as sot forth in Tables I-III wore employed for the Do stage. The kappa factor was adjusted with 2.44% C10= to reach the desired kappa number out of the Do stage. The pulp was then washed to pH 7.5.
E. After the Do stage, the pulp was exttact~d with a conventional F.~ stage which employed 1.7% NaOH sad 0.1 % MgSO,s. For comparison purposes in Tables I and II, bleaching experiments using CcllGuard"'OP as a replacement fo* MgS04 and as a partial substitute for NaOH were conducted, Caustic sale replacement was based on an OH' molar basis. For example, at 25%
substitution where 25% of the OH' comes 8rom Mg(OH)z, the respective alkali dosages used were 1.275% NaOH sad 0.31~o CellGuard'~"OP. Cax~atio soda contains 42.51 % by weight OH' ions while maguosium hydroxide contains 58.32°Yo by weight OH' ions, For the E°,, stage in Tables I-III, bleaching occurred at 138 kPa of 02 pressure for 20 minutes followed by bleaching at atmospheric pressure for the remaining 40 minutes.
Martin Marietta Magnesia Specialties, LLC is the maaufaaturer of CcllGuard~OP Magaesiium Hydroxide Slung for use in pulp bleaching. The CeIlGuard""OP Mag~nosium Hydroxide Slurry, which is produced $om a dolomitie limo and magnesium brine process, contains 62% by weight Mg(OIT)z solids suspended in water. The purity of the magnesium hydroxide is over 98% with low levels of transition motels. This product has a fine particle size (3 microns as toeasured by Micromeritics Sedigtaph 5100) which promotes high reactivity and excellent suspension stability.
I~1~3 Pulp Time Temp Pressure Chemical Stage Consistency(mm) (C) (kPa) % on O.D.
pulp a Do 12 45 60 -__ 2,44% Cl 0.5% HsOa 138 kPa of Oz 1.7/ NaOH
for or EoP 12 60 70 20 mur, then Mg(OH~/NaOH
arm 0.1 % MgS04 (for Contro:
onI
D 12 180 80 -- _ QZ
1.2% C1 EP 12 40 70 --~-- (1. I5% HaOs 0.5% NaOH
Dz I2 100 80 --- 0.6% CIOz DmF.~,~,~'I~T es I and I11-Standard conditions ware employed for the Dt-F.~-D= stages shown in Tables I and II. The pulp and filtrate following each bleaching stage were tested for I,SO brightness sad end pH, respectively. The pH
of the residual liquor was dettrrnined using a pH meter and appropriate buffer solutions to calibrate the pH meter. Pulp samples from the E~" D~, and D2 stages ZO were tested for viscosity and wet zero-span tensile strength. The respective filtrates were analyzed for chemical oxygen demand (COD).
After the Do stage and washing stop, the lcsppa number decre~aeed from 29.2 to 11.9. Pulp brightness iaCreased fi~ 26,9% ISO to 35.9% ISO.
The effects of CcllGuard"~"OP substitution in the P~ stage on each of the pulp 15 parameters were measured. Table II contains a summary of results for each bleaching test performed.
FIG. 1 compares pulp brightness for the various levels of CellGusrd~"OP
substitution in tire E~ stage. The data shows the increasing trend is brightness with each subsequent bleaching stage for all substitution cases. The control 20 sample, which employed 100°i6 4H' from NaOH (or 4°Yo OH' from C~llGuard"'~OP) and MgSO,, yielded as increase in brightness from 62.1 % ISO after the E°P stage to a final pulp brightness of 90.8% ISO after the D2 stage.
At 25% substitution with CellGuard""OP in the E~ stage, brightness slier this bleaching step (60.1% ISO) was lowar than the control. However, equivalent final pulp brightness after the Da stage resulted in 90.5% ISO at the same C10= and HZOZ charge in the Dl and EP stages respectively ats the control sample.
At 50% substitution with CollC~ruatd~"OP, Figure 1 shows that the brightness after the Pte,,, stage was 59.7% ISO. Even with the use of a mild alkali in the extraction stage which lowers the bleaching pH to 10.1 for 25°!° substitution and 9.3 for 50% substitution, comparable final brightness was achieved as eridence by the final 89.9% ISO brightness result after the Da stage.
At the end of the E~,, stage, the control sartnpIe yielded a pulp viscosity of 27.8 cps. As shown in FIG. 2, both the 25% and SO% substitution runs with CellGuard"'OP produced higher viscosity results of 28.6 cps and 29,3 cps respectively after the E~ stage. These results indicate that CellGusrd'7"OP
servos a dual role as a peroxide activator and cellulose pmtoctor. In a conventional E~
system where NaOH and MgS04 are utilized, CellGuard"~OP Mg(OH)2 can reduce the NaOH consumption and eliminate MgS04. As soon in FIG. 2, the control sample's final viscosity was 16.5 cps, the 25% and 50% substitution samples with CellGuard~OP produced pulps with respcctivo viscosities of 17.5 cps and 18_6 cps. By utilizing CellGuard"'OP Magnesium Hydroxide in the E%, stage, a one to two point increaso in pulp viscosity over the conventional E°,, stage was achieved.
Fiber strength was maintained in both CollGuard~OP substitution cases as shown in Figure 3. Wet zero-spas tensile strength for all cases ranged from 10.9 -11.0 km for the E~ stage, 10.2 - 10.6 for the D~ stage, and 10.3 - 10.4 inn for the DZ stage.
High chomical oxygen demand (COD) is gonorated in the E~ stage where the most of the extraction occurs (ace FIG. 4). Partially substituting the NaOH
charge with a weak alkali such as Mg(OH)2 reduces the organic loading in the effluent from the E~, stage. 'The highcFr substitution rate with CellGuard~OP
yielded a noticeable ~da~otion itt COD whoa cared to tho control aa:aple. Then control sample generated 4635 mgt COD vatsus 4105 mg/L COD for the 50%
substitution cast, which roprosenta an 11% roduction. Lower COD loading can contribute to reduced e~'tuent treatment costs dowaatream.
By employing partial substitution of CellGuard'~OP Magnesium Hydsoxide Slurry for eausdc soda and eliminating magnesium sulfate in the Eop stage, a strong alkali is present to facilitate lignin removal while a mild allca~lii is added to promote peroxide bleaching arid eelluloac protecdon. CallGuard~'"OP can replace up to 50% of the caustic soda requirement in the Eq, stage producing final pulp from the Da stage with similar brightness, permanganate number, and wet aem-span tensile strength a: pulp bleached with a 100% caustic soda charge.
At 50% substitution of caustic soda, the use of Cdlt~luard~OP improves the pulp viscosity by 12% and reduces the COD after the E~, stage; by 1 I %. Since only 0.73 kg of magneaiurn hydroxide provides the equivalent amount of hydroxyl ions as 1 kg of caustic soda, Ce11C3uard~"OP reduces bleaching costs in many cases.
At no added cost beyond the amount required for caustic soda replacement, Cell(~uard'~"OP also elitniaates the steed for magnesium sulfate for i~ther reduction in chmaical costs_ RESULTS OF PARTIAL SUBS'ITTUZTON OF
CAUSTIC SODw vViT~i MAaIvtESItJM HYDROXIDE SLURRY
IN THE EOP STA(i8 Og A DEopDEpD BLEACH SEQUENCE
..
Star Chemical Timo Tamp PressureEnd ~ $ COD
,...
a (r6 on (~) (~ (I~'a)pfY ~ ~ ~ ~ ~, (~) pulp) ' Brown- , ; 26 48 (~~ 5 9 0 ~ 12 ' . . .
stock , ; ~ .
. ~; .
.. ' 7.4 0.22 kf 45 ~0 2.3Z 35.9 ' (11.9 as D Stage D (2.44% , ~.
C10~ kappa) 0.5~6 FIz02 138 kPa Oa 1.7% NaOH for ~ 70 ,20 11.3 62.1 27.8 3.1 10.9 4635 Eop 0.1 % MBS04 ~jn,~
thaa 0~~ Mg(OH)i Coatrol N
OH +
a M~SO~ 1.2% CIOs 180 80 2.3 80.2 21.4 1.1 10.2 1352 D
0. I S~b 40 70 ~ 11.4 86.0 Hi0=
E 0.5 % NaOH
0.6% CIO= 100 80 ~ 3.3 90.8 16.5 O.B 10.3 176 D
0.5% H=Os Id?a pr 1.275/b fpr NaOH
60 70 20 10.1 60.1 28.6 3.4 I0.8 4555 Eop 0.31~o min, then 25% MB(OH)z a~
Substirution _ CellGuard'~ 1.2% CIOa 180 80 . ' 2.3 78.9 22.1 1.3 10.3 1326 .
in Eop D, 0.15% Ii=O=~ 70 ~' 11 85 ' . .
4 3 ' E 0.5 9~o . . . ' ' . ' . ..
NaOH ' D 0.6% C10~ 100 80 '' 3.3 90.5 17.5 0.6 10.2 ' 0.5% I~ZOz kPa 0.85% NaOH
~ 70 20 9.3 59.7 29.3 3.5 11.0 4105 Eop 0.62% min, ~a MB(O~t 50% a~
S
b rit ti u , s on u CellGuard'"D 1.2% CIOz 180 80 : 2.3 76.3 22.0 1.4 10.6 1420 i E
op n 0.15% Hl0=
40 70 ' 3 83 B 0.5% NaOH . . .
D 0.6% CIOi 100 80 . 3.2 89.9 18.6 0.7 10.4 184 ' % on oven-dried pulp = After waahiag, pH was 7.5 All experimaata wore conducted at 12% pulp consistency.
B°P -DZ-E~DZS~ag, ~ ('Tabl~IIn-Standard conditions were employed for the D~ and DZ stages of bleaching processes shown in Table III. In the experiments involving substitution of magnesium hydroxide for NaOlI in the Ep stage, magatsium hydroxide was substituted for all of the magaeaium sulfate sad a portion of the NaOH (25%, 50%, 75% or 100%). The E~ atagc employed a 50%
substitution of magnesium hydroxide for NaOH, and 100% substitution for all of the magnesium sulfate, in all the bleaching experiments. The pulp and filtrate following each bleaching stage were tested for IS4 brightness and end pH, respectively. The pH of the residual liquor was detenainod using a pH motor and appropriate buffer solutions to calibrate the pH meter. Pulp samplas from the Eq,, D~, and DZ stages were also tested for viscosity and K#. As seen in Table IIi, the ~rLal ISO brightness, viscosity and K# of the bleached chemical pulp of the process of the present ~invontion is comparable or greater than the the final ISO
brightness, viscosity and K# of bleached chemical pulp which is bleached with the same total amount of an F.~, aqueous bleaching solution comprising said paroxide compound and sodium hydroxide, but in the absence of magneaium hydroxide.
Table III. RESULTS OF SUBS~TT~J'TION OF CAUSTIC SODA
AND MAC~NESIIJM SULFATE WITH MAC3NESIUM
HYDROXIDE SLURRY
In E~ and Ep Stages of a DES DEpD Bleach Sequence StaOe C~tmital Tlms T >cure Kappa KB !SO Vit-e,~ (rp(p)$ (pd~ 25 Brl=bt eaa-m!
aea~ ity Ye ep BS $rpWI~t~Ck 30.4 Z6.1 51.9 D
After W,flblp/~
O 13.7 8.6 34.3 48.Z
Z2kf ~, ~,5 pD D .
.54% CIO
g O.s'l,H=O= 60 70 138Kpa 3.5 61.6 41.9 I00% OH- 1.7% NaO~i CONTROL trem lr,o7~to.t~ Mgso, NaOH + o/. wtg (OHh thoa avn MgS04 Sequence Di 1.2%QO~ t80 80 1.3 79.6 Z9.s E & E sta es ~ 70 86.4 g s OH only Eo0rl, OH 0,4896 aOH
N
from NaOH 0% Mg (OH)s DZ 0.6/ CI 100 80 0.6 90.7 22.0 B 0.5/.H=Oz 60 70 1381Cpa 4.0 34.9 42.6 50~ OH 0.85% NaOH pf Z
from Me(Oli~0.6T% Mp min.
(OHj=
Substitution den arm Scquence 1.2% C10= 180 80 1.6 74.9 32.9 op 50%
0.15%H=0= 40 '~0 StrbStltatl0nBv Coptrol 0.48% NaOH
o% M~ (off:
Ep v~ysn~
Snbstitvtian DZ 0.6% C10= 100 s0 0.7 90.3 24.6 l2 Ro 0.15'yG~i~Oa40 70 83.d =3% O~ 0.36iG NWH
prom M8(OI~Lh0.0915 M8 (0F1), DZ 0.6lfi CID, 100 80 0.'7 90.2 ?4.d E
O.15YHiOi 40 70 3.1 s0% OH- 0.?4% NaOH
from M8(OH~0.18% Mg (OHM
ps 0.6% CIO= 100 80 0.8 89.9 25.2 Coot-ME(UH)= ~ o.is~x~ 40 ~o e~.s ~~~ oe-Subatitutionfrom Maoab o ~ ~ (o ~
sequence Hh ~' P D= 0.6% CIO, 100 80 89.5 25.3 50%
Substitution~ o.isx~to, 40 ~o ~8.s 1006 OH- 09~, Na013 E prom o 0.3s% Ma p (OH)=
Varying Sll~lat~ttlt~4n 0.6IG CIO, 100 SO 0.8 88.6 7R.0
Claims (35)
1. An E op process for bleaching chemical pulp, which comprises:
providing said chemical pulp;
providing an E op aqueous bleaching solution comprising a peroxide compound, as oxygen-containing material, sodium hydroxide and magnesium hydroxide, in the absence of magnesium sulfate; and bleaching said chemical pulp with said E op aqueous bleaching solution to form E op bleached chemical pulp.
providing said chemical pulp;
providing an E op aqueous bleaching solution comprising a peroxide compound, as oxygen-containing material, sodium hydroxide and magnesium hydroxide, in the absence of magnesium sulfate; and bleaching said chemical pulp with said E op aqueous bleaching solution to form E op bleached chemical pulp.
2. The process of claim 1, wherein the amount of sodium hydroxide in said E op aqueous bleaching solution is at not morn than about 8 % by weight, based on the O.D. weight of said E op chemical pulp.
3. The process of claim 1, wherein the ratio of sodium hydroxide to magnesium hydroxide in said E op aqueous bleaching solution is not more than about 5:1 (based on an OH- molar ratio).
4. The process of claim 1, wherein the pulp viscosity of a final bleached chemical pulp is at least substantially the same as the final pulp viscosity of bleached chemical pulp which is bleached with the same total amount of as E
op aqueous bleaching solution comprising said peroxide compound, an oxygen-containing material, sodium hydroxide, with or without magnesium sulfate, in the absence of magnesium hydroxide.
op aqueous bleaching solution comprising said peroxide compound, an oxygen-containing material, sodium hydroxide, with or without magnesium sulfate, in the absence of magnesium hydroxide.
5. The process of claim 1, wherein the final pulp brightness of said E op bleached chemical pulp produced from the E op bleached chemical pulp is at least substantially the same as the final pulp brightness of bleached chemical pulp which is bleached with same bleach sequence containing the same total amount of as E
op, aqueous bleaching solution comprising said peroxide compound, an oxygen-containing material, sodium hydroxide, with or without magnesium sulfate, in the absence of magnesium hydroxide.
op, aqueous bleaching solution comprising said peroxide compound, an oxygen-containing material, sodium hydroxide, with or without magnesium sulfate, in the absence of magnesium hydroxide.
6. The process of claim 1, wherein the COD of bleach effluent from an E op stage using said E op, aqueous bleaching solution is less than the COD
of bleach effluent from an E op stage which uses the same total amount of an E op aqueous bleaching solution comprising said peroxide, an oxygen-containing material compound, sodium hydroxide, with or without magnesium sulfate, in the absence of magnesium hydroxide.
of bleach effluent from an E op stage which uses the same total amount of an E op aqueous bleaching solution comprising said peroxide, an oxygen-containing material compound, sodium hydroxide, with or without magnesium sulfate, in the absence of magnesium hydroxide.
7. The process of claim 1, which further include the step of providing an E p aqueous bleaching solution comprising a peroxide compound, sodium hydroxide and magnesium hydroxide, in the absence of magnesium sulfate; and bleaching said E op bleached chemical pulp with said E p aqueous bleaching solution to form E p bleached chemical pulp.
8. The process of claim 1, which further includes the step of providing an E p aqueous bleaching solution consisting essentially of a peroxide compound, sodium hydroxide and magnesium hydroxide; and bleaching said E op, bleached chemical pulp with said E p aqueous bleaching solution to form E p bleached chemical pulp.
9. The process of claim 1, wherein the wet zero span tensile strength of said E op bleached chemical pulp is at least substantially the same as the wet zero span tensile strength of bleached chemical pulp which is bleached with the same total amount of an E op aqueous bleaching solution comprising said peroxide compound, an oxygen containing material, sodium hydroxide, with or without magnesium sulfate, in the absence of magnesium hydroxide.
10. The process of claim 1, wherein the COD in the bleach effluent of said bleached E op chemical pulp is at least about 5 % less than the COD in beach effluent of said bleached chemical pulp which is bleached with the same total amount of an E op aqueous bleaching solution comprising said peroxide compound, an oxygen-containing material, sodium hydroxide, with or without magnesium sulfate, in the absence of magnesium hydroxide.
11. An E op process for bleaching chemical pulp, which comprises:
providing said chemical pulp;
providing an E op aqueous bleaching solution consisting essentially of a peroxide compound, an oxygen-containing material, sodium hydroxide and magnesium hydroxide; and bleaching said chemical pulp with said E op aqueous bleaching solution to form said bleached chemical pulp.
providing said chemical pulp;
providing an E op aqueous bleaching solution consisting essentially of a peroxide compound, an oxygen-containing material, sodium hydroxide and magnesium hydroxide; and bleaching said chemical pulp with said E op aqueous bleaching solution to form said bleached chemical pulp.
12. The process of claim 11, wherein the amount of sodium hydroxide in said E op aqueous bleaching solution is at not more than about 8 % by weight, based on the O.D. weight of said E op chemical pulp.
13. The process of claim 11, wherein the ratio of sodium hydroxide to magnesium hydroxide in said E op aqueous bleaching solution is not more than about 5;1 (based on an OH- molar ratio).
14. The process of claim 11, wherein the pulp viscosity of a final bleached chemical pulp produced from the E op bleached chemical pulp is at least substantially the same as the final pulp viscosity of bleached chemical pulp which is bleached with the same total amount of an E op aqueous bleaching solution comprising said peroxide compound, as oxygen-containing material sodium hydroxide, with or without magnesium sulfate, is the absence of magnesium hydroxide.
15. The process of claim 11, wherein the final pulp brightness of said E op bleached chemical pulp is at least substantially the same as the final pulp brightness of bleached chemical pulp which is bleached with same bleach sequence containing the same total amount of an E op aqueous bleaching solution comprising said peroxide compound, an oxygen-containing material, sodium hydroxide, with or without magnesium sulfate, in the absence of magnesium hydroxide.
16. The process of claim 11, wherein the COD of bleach effluent front an E op stage using said E op aqueous bleaching solution is loss than the COD
of bleach effluent from an E op stage which uses the same total amount of an E op aqueous bleaching solution comprising said peroxide, an oxygen-containing material compound, sodium hydroxide, with or without magnesium sulfate, in the absence of magnesium hydroxide.
of bleach effluent from an E op stage which uses the same total amount of an E op aqueous bleaching solution comprising said peroxide, an oxygen-containing material compound, sodium hydroxide, with or without magnesium sulfate, in the absence of magnesium hydroxide.
17, The process of claim 11, which further includes the step of providing an E p aqueous bleaching solution comprising a peroxide compound, sodium hydroxide and magnesium hydroxide, in the absence of magnesium sulfate; end bleaching said E op bleached chemical pulp with said E p aqueous bleaching solution to form E p bleached chemical pulp.
18. The process of claim 11, which further includes the step of providing an E p aqueous bleaching solution consisting essentially of a peroxide compound, sodium hydroxide and magnesium hydroxide; and bleaching said E op bleached chemical pulp with said E p aqueous bleaching solution to form E p bleached chemical pulp.
19. The process of claim 11, wherein the wet zero span tensile strength of said E op bleached chemical pulp is at least substantially the same as the wet zero span tensile strength of bleached chemical pulp which is bleached with the same total amount of an E op aqueous bleaching solution comprising said peroxide compound, an oxygen-containing material, sodium hydroxide, with or without magnesium sulfate, in the absence of magnesium hydroxide.
20. The process of claim 11, wherein the COD in the bleach effluent of said bleached E op chemical pulp is at least about 5 % less than the COD in beach effluent of said bleached chemical pulp which is bleached with the same total amount of as E op aqueous bleaching solution comprising said peroxide compound, an oxygen-containing material, sodium hydroxide, with or without magnesium sulfate, in the absence of magnesium hydroxide.
21. An E op aqueous chemical solution for bleaching chemical pulp, which comprises an E op aqueous bleaching solution consisting essentially of a peroxide compound, as oxygen-containing material, sodium hydroxide and magnesium hydroxide.
22. The E op aqueous bleaching solution of claim 21, wherein the amount of sodium hydroxide in said E op aqueous bleaching solution is at not more than about 8% by weight, based on the O.D. weight of said chemical pulp.
23. The E op aqueous bleaching solution of claim 21, wherein the ratio of sodium hydroxide to magnesium hydroxide in said E op aqueous bleaching solution is not more than about 5:1 (based on an OH- molar ratio).
24. The E op aqueous bleaching solution of claim 21, wherein the pulp viscosity of the final chemical pulp produced using said E op aqueous bleaching solution is at least substantially the same as the pulp viscosity of final bleached chemical pulp which is bleached with the same total amount of an E op aqueous bleaching solution comprising said peroxide, an oxygen-containing material compound, sodium hydroxide, with or without magnesium sulfate, in the absence of magnesium hydroxide.
25. The E op aqueous bleaching solution of claim 21, wherein the pulp brightness of E op bleached chemical pulp produced using said E op aqueous bleaching solution is at least substantially the same as the pulp final brightness of bleached chemical pulp which is bleached with a bleaching sequence containing the same total amount of an E op aqueous bleaching solution comprising said peroxide, an oxygen containing compound, sodium hydroxide, with or without magnesium sulfate, in the absence of magnesium hydroxide.
26. The E op aqueous bleaching solution of claim 21, wherein the COD
of bleach effluent produced using said E op aqueous bleaching solution is less than the COD of bleach effluent which is produced by the same total amount of an E
op aqueous bleaching solution comprising said peroxide compound, an oxygen-containing material, sodium hydroxide, with or without magnesium sulfate, in the absence of magnesium hydroxide.
of bleach effluent produced using said E op aqueous bleaching solution is less than the COD of bleach effluent which is produced by the same total amount of an E
op aqueous bleaching solution comprising said peroxide compound, an oxygen-containing material, sodium hydroxide, with or without magnesium sulfate, in the absence of magnesium hydroxide.
27. The E op aqueous bleaching solution of claim 21, wherein the ratio of sodium hydroxide to magnesium hydroxide in said E op aqueous bleaching solution is not more than about 3:1 (based on an OH- molar ratio).
28. The E op aqueous bleaching solution of claim 21, wherein the ratio of sodium hydroxide to magnesium hydroxide in said E op aqueous bleaching solution is not more than about 1;2 (based on an OH- molar ratio).
29. The E op aqueous bleaching solution of claim 21, wherein the wet zero span tensile strength of E op bleached chemical pulp produced using said E op aqueous bleaching solution is at least substantially the same as the wet zero span tensile strength of bleached chemical pulp which is bleached with the same total amount of an E op aqueous bleaching solution comprising said peroxide compound, an oxygen-containing material, sodium hydroxide, with or without magnesium sulfate, is the absence of magnesium hydroxide.
30. The E op aqueous bleaching solution of claim 21, wherein COD in the bleach effluent of said bleached E op chemical pulp is at least about 5 %
less than the COD in the bleach effluent of said bleached chemical pulp which is bleached with the same total amount of an E op aqueous bleaching solution comprising said peroxide compound, an oxygen-containing material, sodium hydroxide, with or without magnesium sulfate, in the absence of magnesium hydroxide.
less than the COD in the bleach effluent of said bleached chemical pulp which is bleached with the same total amount of an E op aqueous bleaching solution comprising said peroxide compound, an oxygen-containing material, sodium hydroxide, with or without magnesium sulfate, in the absence of magnesium hydroxide.
31. An E op process for bleaching chemical pulp, which comprises:
providing said chemical pulp:
providing en E p aqueous bleaching solution comprising a peroxide compound, sodium hydroxide and magnesium hydroxide, in the absence of magnesium sulfate; and bleaching said chemical pulp with said E op aqueous bleaching solution to form said bleached chemical pulp.
providing said chemical pulp:
providing en E p aqueous bleaching solution comprising a peroxide compound, sodium hydroxide and magnesium hydroxide, in the absence of magnesium sulfate; and bleaching said chemical pulp with said E op aqueous bleaching solution to form said bleached chemical pulp.
32. An E op process for bleaching chemical pulp, which comprises:
providing said chemical pulp;
providing an E op aqueous bleaching solution consisting essentially of a peroxide compound, sodium hydroxide and magnesium hydroxide; and bleaching said chemical pulp with said E op aqueous bleaching solution to form said bleached chemical pulp.
providing said chemical pulp;
providing an E op aqueous bleaching solution consisting essentially of a peroxide compound, sodium hydroxide and magnesium hydroxide; and bleaching said chemical pulp with said E op aqueous bleaching solution to form said bleached chemical pulp.
33. An E p aqueous chemical solution for bleaching chemical pulp, which comprises an E p aqueous bleaching solution consisting essentially of a peroxide compound, sodium hydroxide and magnesium hydroxide.
34. A process for bleaching chemical pulp, which comprises:
providing said chemical pulp;
providing an E op aqueous bleaching solution;
bleaching said chemical pulp with said E op aqueous bleaching solution to form E op bleached chemical pulp;
providing an E p aqueous bleaching solution comprising a peroxide compound, sodium hydroxide and magnesium hydroxide, in the absence of magnesium sulfate; and bleaching said E op bleached chemical pulp with said E p aqueous blenching solution to form E p bleached chemical pulp.
providing said chemical pulp;
providing an E op aqueous bleaching solution;
bleaching said chemical pulp with said E op aqueous bleaching solution to form E op bleached chemical pulp;
providing an E p aqueous bleaching solution comprising a peroxide compound, sodium hydroxide and magnesium hydroxide, in the absence of magnesium sulfate; and bleaching said E op bleached chemical pulp with said E p aqueous blenching solution to form E p bleached chemical pulp.
35. A process for bleaching chemical pulp, which comprises:
providing said chemical pulp;
providing an an E op aqueous bleaching solution;
bleaching said chemical pulp with said E op aqueous bleaching solution to form E op bleached chemical pulp;
providing an E p aqueous bleaching solution consisting essentially of a peroxide compound, sodium hydroxide and magnesium hydroxide; and bleaching said E op bleached chemical pulp with said E p aqueous bleaching solution to form E p bleached chemical pulp.
providing said chemical pulp;
providing an an E op aqueous bleaching solution;
bleaching said chemical pulp with said E op aqueous bleaching solution to form E op bleached chemical pulp;
providing an E p aqueous bleaching solution consisting essentially of a peroxide compound, sodium hydroxide and magnesium hydroxide; and bleaching said E op bleached chemical pulp with said E p aqueous bleaching solution to form E p bleached chemical pulp.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US27198701P | 2001-02-27 | 2001-02-27 | |
| US60/271,987 | 2001-02-27 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2373562A1 true CA2373562A1 (en) | 2002-08-27 |
Family
ID=23037929
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002373562A Abandoned CA2373562A1 (en) | 2001-02-27 | 2002-02-27 | Eop & ep process for bleaching of chemical pulp |
Country Status (2)
| Country | Link |
|---|---|
| US (1) | US20030024664A1 (en) |
| CA (1) | CA2373562A1 (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2009117818A1 (en) * | 2008-03-25 | 2009-10-01 | University Of New Brunswick | Process of chlorine dioxide bleaching of chemical pulps using magnesium hydroxide or magnesium oxide |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| SE363138B (en) * | 1968-06-13 | 1974-01-07 | Air Liquide Sa Etude Exploit P | |
| US4568420B1 (en) * | 1984-12-03 | 1999-03-02 | Int Paper Co | Multi-stage bleaching process including an enhanced oxidative extraction stage |
| FR2582692B1 (en) * | 1985-05-29 | 1987-12-11 | Atochem | TREATMENT OF CHEMICAL PAPER PULP WITH HYDROGEN PEROXIDE FOR BLEACHING |
-
2002
- 2002-02-27 CA CA002373562A patent/CA2373562A1/en not_active Abandoned
- 2002-02-27 US US10/086,191 patent/US20030024664A1/en not_active Abandoned
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2009117818A1 (en) * | 2008-03-25 | 2009-10-01 | University Of New Brunswick | Process of chlorine dioxide bleaching of chemical pulps using magnesium hydroxide or magnesium oxide |
Also Published As
| Publication number | Publication date |
|---|---|
| US20030024664A1 (en) | 2003-02-06 |
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| Date | Code | Title | Description |
|---|---|---|---|
| EEER | Examination request | ||
| FZDE | Discontinued |