CA2067750A1 - Chlorine dioxide pulp bleaching process using sequential chlorine addition - Google Patents
Chlorine dioxide pulp bleaching process using sequential chlorine additionInfo
- Publication number
- CA2067750A1 CA2067750A1 CA002067750A CA2067750A CA2067750A1 CA 2067750 A1 CA2067750 A1 CA 2067750A1 CA 002067750 A CA002067750 A CA 002067750A CA 2067750 A CA2067750 A CA 2067750A CA 2067750 A1 CA2067750 A1 CA 2067750A1
- Authority
- CA
- Canada
- Prior art keywords
- bleaching
- chlorine
- process according
- stage
- bleaching process
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
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
- D21C9/12—Bleaching ; Apparatus therefor with halogens or halogen-containing compounds
- D21C9/14—Bleaching ; Apparatus therefor with halogens or halogen-containing compounds with ClO2 or chlorites
- D21C9/142—Bleaching ; Apparatus therefor with halogens or halogen-containing compounds with ClO2 or chlorites with ClO2/Cl2 in a multistage process involving ClO2/Cl2 exclusively
Abstract
CHLORINE DIOXIDE PULP BLEACHING PROCESS USING
SEQUENTIAL CHLORINE ADDITION
ABSTRACT
A high-efficiency wood pulp bleaching process to produce wood pulps with high brightness and with high levels of chlorine substitution. The process comprises reacting chlorine and chlorine dioxide with wood pulp at a pH of about 7-10 for about 5-40 minutes. Next, the remaining chlorine is added and the mixture brought to a pH of 4 or less, where it is allowed to react for 30 or more minutes to complete the two-step high/low pH sequential chlorine addition bleaching process.
SEQUENTIAL CHLORINE ADDITION
ABSTRACT
A high-efficiency wood pulp bleaching process to produce wood pulps with high brightness and with high levels of chlorine substitution. The process comprises reacting chlorine and chlorine dioxide with wood pulp at a pH of about 7-10 for about 5-40 minutes. Next, the remaining chlorine is added and the mixture brought to a pH of 4 or less, where it is allowed to react for 30 or more minutes to complete the two-step high/low pH sequential chlorine addition bleaching process.
Description
2~750 r ~O gl/O~9lO PCT/US90/05826 - -1- ., Descri~n CHLORINE DIOXIDE PULP BLEACHING PROCESS USING `~`
SEQUENTIAL C~LORINE ADDITION
Technical Field The present.invention relates to the bleaching of pulp and more particularly to an improved proces~ for ~-~
bleaching wood pulp with chlorine dioxide and chlorine in a manner whereby the wood ~ulp is subjected to a two-step ~ :
high pH/low pH bleaching sta9O where!in chlorine dioxide and chlorine are used in tl-a first step and chlorine is used in the second step.
.
round ~rt.
~ As is well known in the wood pulp bleaching art, the ..
: main objectives of wood pulp bleaching are to increase the brightness oE the pulp and to make it suitable for the manufacture of printing and tissue grade papers by removal o~ modification of some of the constituents of . the unbleached pulp, including the lignin and its degradation products, resins, metal ions, non-cellulosic .
20 carbohydrate components, and various types o~ flecks. .~
', :~. ' "` .
,,, " ., .
.,., ..~ ,.:
'.: ~ ' '" ' ::
2~77~ :
-~WO91/05910 PCT/US90/05826 The bleaching of chemical wood pulp is normally carried out in multiple processing stages utilizing elemental chlorine, caustic soda, hypochlorites, oxygen, hydrogen - -peroxide, and chlorine dioxide. The number of stages required in a particular bleaching process is dependent upon the nature of the unbleached pulp as well as the end use to which the pulp will be put. A sul~ate or kraft pulp is today most typically bleached in a five-stage sequence which is designated as (CD)(EO)DED. In the 10 ~CD)~EO)DED designation, D denotes chlorine dioxide, C -denotes elemental chlorine, E denotes caustic extraction, .:
and 0 denotes oxygen gas. The multi--stage process in essence comprises a chlorination step (CD), a first oxidative extraction stage (EO), a ~irst bleaching stage ~Dl), a second caustic extraction stage (E2), and a second and final bleaching stage tD2~.
In the conventional (CD)(EO)DED multi~stage bleaching process, each o~ the two chlorine dioxide bleaching stages is carried out in a one-5tep process at a ~inal p~ of about 3.8 for three hours at 70 c~ntigrade. It is commonly known that p~l has an important bearing on brigh~ness and strength properties -as well as the clemical species present in the wood pulp mixture, and this particular pll has heretofore been considered optimal for eacll of the two chlorine dioxide bleaching stages in the (CD~(EO~DED sequence. It should . .
also be appreciated that although the (CD)(EO)DED
"'' `~
--. .
''.~`" ' ~ ~ " ' ' : . :
2~77~0 -WO91/0~910 PCT/US90/05826 sequence has been specifically addressed, the one-step chlorine dioxide bleaching stage can be used in any D-stage for mo~t other three, four, fivej or six-sta~e bleaching processes known to those familiar with the art of wood pulp bleaching.
Chlorine dioxide used at the mill site normally contains only about 10% chlGrine in the one-step chlorine dioxide bleaching stage pr~sently u~ed in the pulp and paper industry. Existing ~echnology does not allow for more than about 20% chlorine substitution without detrimentally affecting wood pulp quality. This is a s~gnific~nt concern in v~ew of the hi~h c06t of chlorlne dioxide in contrast to the relatively less expensive chlorlne. The present inv~ntion solves this well-known deficiency in state of the art chlorine dioxide bleaching by making it possible to perform higher levels of chlorine substitution through a two-step sequential addit$on of chlorine at controlled high/low pH levels durlng the ~hlorine dioxide bleaching proce6s. The advantages are a reduced use of chlorine dioxide and a slgniEicant reduction in chemical costs for the wood pulp bleachlng process.
`'', ' ~ -Disclosure of the Inve In accordance with the present invention, applicants 25 provide an improved process for bleaching wood pulp in ;
agueou9 suspencion using chlorine ùioxide and rhlorine in ~` ~ '' `'' "
,. ..
~W091/05910 2~77~0 PCTtUS90/OS826 a two-step high p~/low pH bleaching stage wherein -~
chlorine dioxide and chlorine are used in the first step ~-and chlorine is used in the second step. The chlorine dioxide and chlorine comprise between about 15-80%~`
chlorine on an available basis. The novel process comprises rirst subjecting the aqueous wood pulp suspens~on to a first bleaching step by mixing it with chlorine dioxide and chlorine and maintaining the mixture at a pB between about 7-lO for about 5-40 minutes. Next, ~;~
the mixture is subjected to a ~econd bleaching step by mixing it with the remaining chlorine and maintaining the -~
m~xture at a pH of 4 or less for at least 30 minutes.
This novel process can be used in any D stage of the (CD)(EO)DED bleaching sequ~nce a~ well as in any D
bleaching stage oE other three, four, five, ~ix, and seven-stage bleaching sequencesO ALl o~ the chlorine ~`
dioxide and approximately 0-40% of the chlorine charged are added initially in the first step of the bleaching process~ and th~ remainder of the chlorine is added at the second stage o~ the bleaching proce~s. The novel bleaching process provides for increasing chlorine substitution up to 60~ with nominal effect on wood pulp quality.
It is therefore an object of the present invention to pro~ide a more efficient wood pu1p b1eaching process.
~' .
'`' ' ~
:`. . '.
~WO91/05910 2 ~ ~ ~ 7 ~ ~ PCT/US90/0~826 It is another object of the present inverltion to increase chlorine substitution in the wood pulp bleaching process It is still another object of the present invention to reduce the chlorine dioxide requirements of tlle wood .
pulp bleaching process and to thereby reduce chemical costs.
It is yet another object of the present invention to allow for chlorine substitution in the D bleaching stage .
at a level greater than the conventionally accepted 20%
limit without a detrimental effect on wood pulp guality. .;
Description of the Drawings Some of the objects o~ the present invention having been stated, other objects will become evident as the lS description proc~eds, when taken in connection with the acco~panying drawings, ln which~
Fi~ure l is a graph of Dl brightness versus percent available chlorine on pulp as chlorine dioxide for one~
fitep D-stage ~leaching, conventional one-step chlorine~
chlorine dioxide mixture bleaching at maintain~d pl ,. ;~.
levels o~ 4 and 2 (as taught by the Rapson and Reeve ~ .
patents referenced herein), and the novel two-step ..
chlorine-chlorine dioxide method of the present invention ~ : :
- : :
~chlorine-chlorine dioxide mixtures contain 60% chlorine .;
`r,' ~ ~ ' . ., . "., .
',' ': ' , ' ," . ': .
',, ";.',',, ';, ' . '. ' ~ ' ' ' : . . ' .: ' ' .' ' ' ' ' . :. ' ' ' ~ '.. :' .:,' .. '' ' -~WO9l/05910 2 ~ ~ 7 7 ~ ~ PCT/US90/05826 :~ ' " "' .
on an aYailable chlorine basis, (CD)E kappa equals 5.1, :
and temper~ature is 70 centigrade); ~ -~
Figure 2 is a graph of D2 brightness versus D
charge for the subsequent bleaching of the pulps of .
Figure 1 through E2 and D2 stages tD2 charge of 0.3%
chlorine dioxide on pulp and temperature oP 70 centigrade);
Eigure 3 is a graph o~ the final D2 viscosity measurement6 for the pulps of E'igures 1 and 2 versus D
10 charge illustrating higher brightness and viscosity for .
the method of the invention when compared to conventional .-bleaching methods used in the Dl stage~
Figure 4 is a graph of Dl brightness versus D
charge ~percent available chlorine on pulp as chlorine 15 dioxide) for conventional one-step D stage bleaching and .
the method of the invention ((CD)hl is 60% chlorine, 40~ :
chlorine diox~de on an available basis and (CD)E kappa equals 5.2. Reaction temperatures are 70 centi~rade and ;~
50 cantigrade for (CD)hl and 70 centigrade for .
conventional D stage bleaching);
Figure 5 is a graph o~ D2 brightness versus D
charge (percent available chlorine on pulp as chlorine dioxide) for the pulps of Eigure 4 after E2 and D2 stage bleachin~ (D2 charge is O.~S C1O2 on pulp, and 25 temperature is 70 centigrade); -`' ~ ' ,.
''' " ' -WO91/05910 2 3 ~ 17 ~ ~ ~ PCT/US90/05~26 Figure 6 is a graph of Dl brightness versus charge (percent available chlorine on pulp as chlorine dioxide) for conventional one-step D stage ClO2 bleaching and the method of the invention ((CD)E kappa eguals 4.6, (CD)hl is 60% chlorine, 40% chlorine dioxide on an available basis, and temperature is 70 centigrade);
Figure 7 is a graph oP Dl and D2 brightness versus percent available chlorine on pulp as chlorine dioxide for conventional one-step D stage ClO2 bleaching and the lO novel two-step (CD)hl bleaching process of the present ~ :
invention wherein tCD) comprises 60% Cl2 and 40% ClO2 on An ~vallable basi~, temperature is 70 centlgraae, and (CD)E kappa equals 4.9;
Figure 8 is a graph of Dl brightne~s versu~ D
charge for conventional one-step D stage bleaching and the novel two-step (CD)hl bleaching process of the ~ -present invention at 70 centigrade for 3 hours with ; ::
5CD)E kappa equals 5.0 and wherein ~CD) is 60% Cl2 and 40% ClO2 on an available basis;
Figure 9 is a graph of D2 brightness versus D
charge or the pulps of Fi~ure 7 wherein the D2 charge i6 ';, -0.3% ClO2 on the pulp and temperature is 70 centigrade; ,;
and . .
Figure lO is a schematic representation o~ two ~ ~:
different process systems for a wood pulp bleaching plant which incorporate the chlorine dioxide with the ::
'.`' ~'~,' , ~" ~.''; "
_~o 91/0~9l0 2 0 6 7 7 ~ D p~T~Us9o/o5826 '~
~, .
sequential chlorine addition wood pulp bleaching process of ~he present inventionr ~est_Mode for Carr~_n~ Out the Invention It has preYiously been suggested in U.S. Patent No.
3,536,577 to Rapson to bleach wood pulp using an aqueous ~ ~
solution of chlorine dioxide and chlorine, treating the -wood pulp with alkali, and then treating the wood pulp ;
with chlorine dioxide. The process of Rapson provides for chlorine dioxide to constitute about 20-95% of the 10 total available chlorine of the solution in the first (CD) stage.
Also of interest, Canadian Patent No. 1,120,660 to Reeve discloses a bleachin~ sequence which~comprises subjecting the wood pulp to a ~irst bleach~ng step with a chlorine dioxide and chlorine solution and, after a period o~ ~ime from about 5 seCOnd~ to about 10 minutes, applying an aqueous chlorine solution to the pulp :
suspension in a second bleaching step which is allowed to , proceed for about 10-60 minutes. Reeve dificloses that 20 the first bleaching step is used usually effected at a ~:
pulp suspension pH of about 1-6, and the second bleaching ~ .:
step is usually effected at a pulp suspension pH of about 0.7-3.
Applicants' process provides for the use of -chlorine-chlorine dioxide bleaching in stages other than ,' :'.' '' ' . .
- wo gl/o~g~o 2 ~ ~ 7 ~ ~ ~ PCT/~S90/0~826 _g_ the ~ir~t (CD) stage, preferably the D stage designation ~n any 3-7 stage bleachinc3 saquence, whereas Rapson and Reeve both refer specifically to the fir~t (CD) stage of bleachlng.
With reference now to Figures 1-10 of the drawings, it ca~ be seen that applicants have improved upon the processes taught by Rapson and Reeve as well as upon the con~entional one-step bleaching stage used in the ;~ -majority of commercial bleaching mills. More .
10 specifically, applicants have invented a new and useful .
two-stage process for bleaching wood pulp slurries in a - :
chlorine-chlori~e dloxlde ~C12-~1O2) mlxture whlch gives ; :~
high~r brightness and pulp quality ~characterized by .
v~scosity) when compared to the conventional one-step :
15 C12~ClO2 mixture technology typically used today in i .
conventional bleaching mills. ~- :
Presently, wood pulp bleachinc~ with chlorine-chlorine dioxide mixtures 1~ typically carried out at 25 .:
centigrade - 60 centigrade in the fir~t stage of a ~CD)~EOlDED or (CD)(EO)D sequence. The consistency is usually around 3-5~, and bleaching times range from 15 minutes to 1 hour with an end pH of about 1.6-2.5 The ~:
application of conventional ~CD) bleaching procedures in thc D-staye of ~he above seyuences or in any other :
- 25 bleaching sequences has little commercial value due to the high viscosity loss (carboh~drate degradation) and poor brightness characteristics of the wood pulp. Thus, ~ , '` :": ' ,', ~. ~''. ' ', ' .
_~WO91/05910 2 ~ ~ 7 7 ~ ~ PCT/US90/0~826 existing ~CD) technology is typically only used as a first stage or pre-bleaching stage in the multi-stage bleaching process on wood pulp. Although others have proposed chlorine-chlorine dioxide bleaching in either one or two-step stages, such as disclosed in the Rapson and Reeve patents discussed above, it can be seen in Figures 1, 2 and 3 of the drawings that the novel two- ~
step chlorine-chlorine dioxide bleaching process of the .-present invention provides surprisingly and une~pectedly 10 better brightness and viscosity than has heretofore been . . ~ ;
achieved.
.. .,~. ..
In order to increa~e the effectivene~s of chlorine- .
chlorine dioxide bleaching of wood pulp, applicants have .~
discovered a new two-step chlorine-chlorine dioxide .
process which includes the following steps:
1. Pulp slurry is reacted with a chlorine and chlorine dioxide mlxture for about 5-40 minutes at a pH
of about 7-10. Normally, caustic is also mixed with the ~ ..
pulp slu~ry, and the caustic most suitably comprise -~
20 sodium hydroxide. The reaction temperature is between : :
about 40-80 centigrade, most suitahly about 70 .
centigrade, and the optimal pll during the first bleaching step is between about B-9.5; and ..
2. After the ~irst bleaching step, the remaining 25 chlorine is added ~o the pulp mixture, and the pH is ;~
maintained at 4 or less, most suitably a pH of about 2- :
' '.
~WO91/0~91~ PCT/US90/05826 2~677~
3.5 for at least 30 minutes, preferably about 30 minutes - 2.5 hours. The reaction temperature is between about ~ : -40-~0 centigrade, most suitably 70 centigrade.
Pulp con~istency fo~ both stepfi ifi between about 10 13.5% w$th the final consistency of the mixture after the ~ -~
second step at most suitably about 10%. The chlorine . . .
dioxide and chlorine used in the bleaching proce~s . ~ ;
comprise between about 15-80% chlorine on an available basis, and preferably all of the chlorine dioxide and 10 one-third of the chlorine are added at the first step, ~
and the remaining two-thirds of the chlorine are added at : :
the se~ond bleaching step. It should be appreclated that to calculate total charge such as percent chlorine on ~ :
pulp, the formula C102 ~ 2.63 C12 i8 used. For example, ..
if a 1% C102 charge is placed on wood pulp, it is equivalent to 2.63% available chlorine on the wood pulp.
Thus, lf one charges 1% available C102 on wood pulp, ~here is actually charged 2.63~ available chlorine of which 40% is C102 and 60~ is C12.
The new two-step process developed by applicants has . .;: .
been used to bleach pulp in the Dl stage of a (CD)(EO)DED
sequence with chlorine-chlorine dioxide mixtures of up to 60% of the chemical charged as chlorine on an available - :
basi~ with brightness and viscosity characteristics 25 comparable to a conventional chlorine-chlorine dioxide ~- :
stage (~ee Figures 1, 2 and ~-9). .~ .
.
.. .
. ., ~ ,..~ . .
: ' :, ;
W~91/05910 P~T/US90/05826 2~67~
Applicants' process is particularly attractive since ~-the new two-step chlorine-chlorine dioxide bleaching process allows for substituting chlorine for chlorine dioxide and thus results in substantial chemical cost reduction ~ince chlorine is a significantly less -expensive chemical. With the use of the novel two-step bleaching process of the present invention, it i8 now commercially possible to bleach wood pulp to a comparable ~
brightness as can be achieved in conventional one-step --lo chlorine aioxide bleaching ~t a significantly reduced commercial cost due to savings achieved by substituting -`
cheaper chlorine for more expensive chlorine dioxide in the wood pulp bleaching process.
Method of the Invention To prove the efficacy oE the new process generally described above, detailed bleaching experiments were carried out by applicants on souther~ pine k~aft pulp.
.: . . .
The furnish was obtained from the decker before the . . .
bleach plant, and to insure maximum mixing ~CD) stage ; ;
bleaching was done in plastic Nalgene bottles which rolled on a ball-mill type apparatus for the full ~-reaction time. All other bleaching stages were carried out in sealed polyester ba9s which were kneaded at ~ -various times throughout the bleach to insure proper 25 mixing. `~
': ~
~. ...,~j, .
''`.
~o g~to~gl~ 2 ~ ~ ~ 7 ~ ~ PCT/US90/05826 :
Proces~ing parameters used by applicants for the multiple bleachiny stages are listed in Table 1 below.
Chlorination stage charges were varied to achieve target ~`
(CD)E kappa numbers, and ail charges are on OD brownstock -pulp. Optimum high/low pH values are 8-9.5 and 2-3.5 respectively. Large batches of (CD3E pulp were made and - -then divided into individual DED and (CD)hlED runs or compari~on. All comparisons were made on pulps from the same (CD)E batch, and all water used in bleaching and . , . :
washing was distilled. Chlorine dioxide solutions used in testing were generated on site by acidifying sodium chlorite solution and absorbing the ClO2 gas in cold ` -distilled water.
:: ' Proces6ing parameters Eor the bleachin~ experiments and the analytical methods used in the experiments are as ~ollows~
... . .
,.. ,,.:' '': ' " ~, .~
" ' . . !; ` ', ''. ' . `
"; "'~ ,' .''; :
''' "'".
','; '' -. ~'' ' .
~wo glto~glo 2 ~ ~ ~ 7 ~ ~ PCr~USgO/05826 -14- ~ .
c~ r o ~r u~ ~ :' .:
~ V . . i:
. .., U~
.~ o o U~ o o o o . , ~ o o o o o o o o '' `:, `
a~ I` I` ~` I`I` I~ o :` .: ..
E3 I I I O ' `
E~ p, ,~
,1 ' ~o ;
m O ~
a~ u ~ I 07 0 0~ ~ . ' O O O C; O O O O
D~
_I p, o : ~c ~ Q'.a ~o ~ ~
u al -1 c o ~1 ~ a t~l N ~ 3 ~
.C . ~ ~ ~ ~ ~ h ~ 1~11`
u I ~1 o o ~ u~ la ~ o ~
a~ O ~ ~`
~t ~ c~ o ~ ~ .a ~ ~a ~ " ,~ ` `' ::' U L- U ~ ~
c ~ o O b C Z E~ Z ~ ~ .
tn a .
:
/ ' : . ' I` ' ' . ~:
--~W091/0~9iO 2 ~ ~ ~ 7 ~ ~ P~T/US90/~5826 ,, Thus, applicants' method provides for mixing chlorine, chlorine dioxide and caustic with an agueou ` `; -wood pulp slurry for about 5-15 minutes at a pH of about : .: . .
7-10. The optimum pH is between about 8-9.5 for best viscosity, and consistency is between about 10-13.5%.
Temperature is between about 40-80 centigrade. ~or the -~
second step in applicants' novel process, chlorine is then added to the pulp slurry which results in a decrease ln p~ to about 2-3.5. Reaction time is between about 30 ~ -10 minutes to 2.5 hours, reaction temperature is between -~
about 40-80 centigrade, and the final consistency of th~
wood pulp is about 10%.
Best brightness and viscosity have been found when all of the chlorine dioxide and one-third of the chlorine to be charged are added in the fir~;t step of the novel bleaching proceæs. The other two-l:hirds of the chlorine are added at the second step and allowed to react for 1-2 hours at 70 centigrade or 1.5 or more hours at 50 centigrade. Temperature and time dependents for effici~nt chemical consumption and optimum pulp brightness are important, and 5uitable combinations can be developed according to the needs of any given wood pulp bleaching mill.
Although applicants have disclosed the application . .
of the two-step chlorine-chlorine dioxide bleaching stage to the Dl stage of a (CD)(r'O)DED sequence, it should be appreciated that the process can be used ln any D or lCD) ; ~
:' :
. , ' ~ `
.
WO91/05910 2 ~ ~ ~ 7 ~ ~ PCT~S90/05826 stage in any three, four, five, ~ix or seven-stage bleaching sequence. Also, although applicants disclose the addition of the remaining chlorine to the pulp in the second 8tep of the new process, additional chlorine ~ -dioxide can also be added at this time to the pulp mixture. -~`
.
Process Apparatus The two-step high/low p~ bleaching process can be implemented in both a new plant or an existing pulp `-bleaching plant. The optimum design schematic is shown ln Flgur~ 10, where C1O2 and caustic are added to the first mixer. The pulp flows into a J or U tube (Figure lOA) or upflow tower (Figure lOB) with a retention time o~ ~pproximately 5~40 minutes. A second mixer i~
provided to mix chlorine with the pulp for the second step of the process. The pulp can then be discharged directly to a down~low tower. The retention time in the downElow tower is 2 or more hours and most fiuitably between 2.5-3.9 hours. In an existing bleach plant the ~implest method for implementing the two-step high/low pH
bleaching process technolo9y would be to install a mixer ` ~-on the discharge from the upflow leg of the tower to the downflow leg of the tower.
It will be understood that various details of the invention may be changed without departing from the scope of the invention. Furthermore, the foregoing description , ~VO91/05910 2 ~ ~ ~ 7 ~ O PCT/US90/05826 -~
-, : , . :
i~ for the purpose of illustration only, and not for the :: ~
purpose of limitation--the invention being defined by the ~ ~:
claims. ;~
,~
' ' ~,, ' .
.... .
....
"'. . ..
. ~ ... .
.'"~`'.'' ..
'` - ,'~:, ' : . . :
.
, :
'`'' . ', : ~
;.. : , 3'.: '.`
:'.,., ,` :, ":
'''i'' `',` ` : ' ~:',,~,'''.".. '.;
;'-':, ', ' :
~':' , .'.'.' ' ' ~, . . :. ..
~.:' : '. : ~
; '.~ , '.
,''; ~'" .~,' ' ','''''',',,'
SEQUENTIAL C~LORINE ADDITION
Technical Field The present.invention relates to the bleaching of pulp and more particularly to an improved proces~ for ~-~
bleaching wood pulp with chlorine dioxide and chlorine in a manner whereby the wood ~ulp is subjected to a two-step ~ :
high pH/low pH bleaching sta9O where!in chlorine dioxide and chlorine are used in tl-a first step and chlorine is used in the second step.
.
round ~rt.
~ As is well known in the wood pulp bleaching art, the ..
: main objectives of wood pulp bleaching are to increase the brightness oE the pulp and to make it suitable for the manufacture of printing and tissue grade papers by removal o~ modification of some of the constituents of . the unbleached pulp, including the lignin and its degradation products, resins, metal ions, non-cellulosic .
20 carbohydrate components, and various types o~ flecks. .~
', :~. ' "` .
,,, " ., .
.,., ..~ ,.:
'.: ~ ' '" ' ::
2~77~ :
-~WO91/05910 PCT/US90/05826 The bleaching of chemical wood pulp is normally carried out in multiple processing stages utilizing elemental chlorine, caustic soda, hypochlorites, oxygen, hydrogen - -peroxide, and chlorine dioxide. The number of stages required in a particular bleaching process is dependent upon the nature of the unbleached pulp as well as the end use to which the pulp will be put. A sul~ate or kraft pulp is today most typically bleached in a five-stage sequence which is designated as (CD)(EO)DED. In the 10 ~CD)~EO)DED designation, D denotes chlorine dioxide, C -denotes elemental chlorine, E denotes caustic extraction, .:
and 0 denotes oxygen gas. The multi--stage process in essence comprises a chlorination step (CD), a first oxidative extraction stage (EO), a ~irst bleaching stage ~Dl), a second caustic extraction stage (E2), and a second and final bleaching stage tD2~.
In the conventional (CD)(EO)DED multi~stage bleaching process, each o~ the two chlorine dioxide bleaching stages is carried out in a one-5tep process at a ~inal p~ of about 3.8 for three hours at 70 c~ntigrade. It is commonly known that p~l has an important bearing on brigh~ness and strength properties -as well as the clemical species present in the wood pulp mixture, and this particular pll has heretofore been considered optimal for eacll of the two chlorine dioxide bleaching stages in the (CD~(EO~DED sequence. It should . .
also be appreciated that although the (CD)(EO)DED
"'' `~
--. .
''.~`" ' ~ ~ " ' ' : . :
2~77~0 -WO91/0~910 PCT/US90/05826 sequence has been specifically addressed, the one-step chlorine dioxide bleaching stage can be used in any D-stage for mo~t other three, four, fivej or six-sta~e bleaching processes known to those familiar with the art of wood pulp bleaching.
Chlorine dioxide used at the mill site normally contains only about 10% chlGrine in the one-step chlorine dioxide bleaching stage pr~sently u~ed in the pulp and paper industry. Existing ~echnology does not allow for more than about 20% chlorine substitution without detrimentally affecting wood pulp quality. This is a s~gnific~nt concern in v~ew of the hi~h c06t of chlorlne dioxide in contrast to the relatively less expensive chlorlne. The present inv~ntion solves this well-known deficiency in state of the art chlorine dioxide bleaching by making it possible to perform higher levels of chlorine substitution through a two-step sequential addit$on of chlorine at controlled high/low pH levels durlng the ~hlorine dioxide bleaching proce6s. The advantages are a reduced use of chlorine dioxide and a slgniEicant reduction in chemical costs for the wood pulp bleachlng process.
`'', ' ~ -Disclosure of the Inve In accordance with the present invention, applicants 25 provide an improved process for bleaching wood pulp in ;
agueou9 suspencion using chlorine ùioxide and rhlorine in ~` ~ '' `'' "
,. ..
~W091/05910 2~77~0 PCTtUS90/OS826 a two-step high p~/low pH bleaching stage wherein -~
chlorine dioxide and chlorine are used in the first step ~-and chlorine is used in the second step. The chlorine dioxide and chlorine comprise between about 15-80%~`
chlorine on an available basis. The novel process comprises rirst subjecting the aqueous wood pulp suspens~on to a first bleaching step by mixing it with chlorine dioxide and chlorine and maintaining the mixture at a pB between about 7-lO for about 5-40 minutes. Next, ~;~
the mixture is subjected to a ~econd bleaching step by mixing it with the remaining chlorine and maintaining the -~
m~xture at a pH of 4 or less for at least 30 minutes.
This novel process can be used in any D stage of the (CD)(EO)DED bleaching sequ~nce a~ well as in any D
bleaching stage oE other three, four, five, ~ix, and seven-stage bleaching sequencesO ALl o~ the chlorine ~`
dioxide and approximately 0-40% of the chlorine charged are added initially in the first step of the bleaching process~ and th~ remainder of the chlorine is added at the second stage o~ the bleaching proce~s. The novel bleaching process provides for increasing chlorine substitution up to 60~ with nominal effect on wood pulp quality.
It is therefore an object of the present invention to pro~ide a more efficient wood pu1p b1eaching process.
~' .
'`' ' ~
:`. . '.
~WO91/05910 2 ~ ~ ~ 7 ~ ~ PCT/US90/0~826 It is another object of the present inverltion to increase chlorine substitution in the wood pulp bleaching process It is still another object of the present invention to reduce the chlorine dioxide requirements of tlle wood .
pulp bleaching process and to thereby reduce chemical costs.
It is yet another object of the present invention to allow for chlorine substitution in the D bleaching stage .
at a level greater than the conventionally accepted 20%
limit without a detrimental effect on wood pulp guality. .;
Description of the Drawings Some of the objects o~ the present invention having been stated, other objects will become evident as the lS description proc~eds, when taken in connection with the acco~panying drawings, ln which~
Fi~ure l is a graph of Dl brightness versus percent available chlorine on pulp as chlorine dioxide for one~
fitep D-stage ~leaching, conventional one-step chlorine~
chlorine dioxide mixture bleaching at maintain~d pl ,. ;~.
levels o~ 4 and 2 (as taught by the Rapson and Reeve ~ .
patents referenced herein), and the novel two-step ..
chlorine-chlorine dioxide method of the present invention ~ : :
- : :
~chlorine-chlorine dioxide mixtures contain 60% chlorine .;
`r,' ~ ~ ' . ., . "., .
',' ': ' , ' ," . ': .
',, ";.',',, ';, ' . '. ' ~ ' ' ' : . . ' .: ' ' .' ' ' ' ' . :. ' ' ' ~ '.. :' .:,' .. '' ' -~WO9l/05910 2 ~ ~ 7 7 ~ ~ PCT/US90/05826 :~ ' " "' .
on an aYailable chlorine basis, (CD)E kappa equals 5.1, :
and temper~ature is 70 centigrade); ~ -~
Figure 2 is a graph of D2 brightness versus D
charge for the subsequent bleaching of the pulps of .
Figure 1 through E2 and D2 stages tD2 charge of 0.3%
chlorine dioxide on pulp and temperature oP 70 centigrade);
Eigure 3 is a graph o~ the final D2 viscosity measurement6 for the pulps of E'igures 1 and 2 versus D
10 charge illustrating higher brightness and viscosity for .
the method of the invention when compared to conventional .-bleaching methods used in the Dl stage~
Figure 4 is a graph of Dl brightness versus D
charge ~percent available chlorine on pulp as chlorine 15 dioxide) for conventional one-step D stage bleaching and .
the method of the invention ((CD)hl is 60% chlorine, 40~ :
chlorine diox~de on an available basis and (CD)E kappa equals 5.2. Reaction temperatures are 70 centi~rade and ;~
50 cantigrade for (CD)hl and 70 centigrade for .
conventional D stage bleaching);
Figure 5 is a graph o~ D2 brightness versus D
charge (percent available chlorine on pulp as chlorine dioxide) for the pulps of Eigure 4 after E2 and D2 stage bleachin~ (D2 charge is O.~S C1O2 on pulp, and 25 temperature is 70 centigrade); -`' ~ ' ,.
''' " ' -WO91/05910 2 3 ~ 17 ~ ~ ~ PCT/US90/05~26 Figure 6 is a graph of Dl brightness versus charge (percent available chlorine on pulp as chlorine dioxide) for conventional one-step D stage ClO2 bleaching and the method of the invention ((CD)E kappa eguals 4.6, (CD)hl is 60% chlorine, 40% chlorine dioxide on an available basis, and temperature is 70 centigrade);
Figure 7 is a graph oP Dl and D2 brightness versus percent available chlorine on pulp as chlorine dioxide for conventional one-step D stage ClO2 bleaching and the lO novel two-step (CD)hl bleaching process of the present ~ :
invention wherein tCD) comprises 60% Cl2 and 40% ClO2 on An ~vallable basi~, temperature is 70 centlgraae, and (CD)E kappa equals 4.9;
Figure 8 is a graph of Dl brightne~s versu~ D
charge for conventional one-step D stage bleaching and the novel two-step (CD)hl bleaching process of the ~ -present invention at 70 centigrade for 3 hours with ; ::
5CD)E kappa equals 5.0 and wherein ~CD) is 60% Cl2 and 40% ClO2 on an available basis;
Figure 9 is a graph of D2 brightness versus D
charge or the pulps of Fi~ure 7 wherein the D2 charge i6 ';, -0.3% ClO2 on the pulp and temperature is 70 centigrade; ,;
and . .
Figure lO is a schematic representation o~ two ~ ~:
different process systems for a wood pulp bleaching plant which incorporate the chlorine dioxide with the ::
'.`' ~'~,' , ~" ~.''; "
_~o 91/0~9l0 2 0 6 7 7 ~ D p~T~Us9o/o5826 '~
~, .
sequential chlorine addition wood pulp bleaching process of ~he present inventionr ~est_Mode for Carr~_n~ Out the Invention It has preYiously been suggested in U.S. Patent No.
3,536,577 to Rapson to bleach wood pulp using an aqueous ~ ~
solution of chlorine dioxide and chlorine, treating the -wood pulp with alkali, and then treating the wood pulp ;
with chlorine dioxide. The process of Rapson provides for chlorine dioxide to constitute about 20-95% of the 10 total available chlorine of the solution in the first (CD) stage.
Also of interest, Canadian Patent No. 1,120,660 to Reeve discloses a bleachin~ sequence which~comprises subjecting the wood pulp to a ~irst bleach~ng step with a chlorine dioxide and chlorine solution and, after a period o~ ~ime from about 5 seCOnd~ to about 10 minutes, applying an aqueous chlorine solution to the pulp :
suspension in a second bleaching step which is allowed to , proceed for about 10-60 minutes. Reeve dificloses that 20 the first bleaching step is used usually effected at a ~:
pulp suspension pH of about 1-6, and the second bleaching ~ .:
step is usually effected at a pulp suspension pH of about 0.7-3.
Applicants' process provides for the use of -chlorine-chlorine dioxide bleaching in stages other than ,' :'.' '' ' . .
- wo gl/o~g~o 2 ~ ~ 7 ~ ~ ~ PCT/~S90/0~826 _g_ the ~ir~t (CD) stage, preferably the D stage designation ~n any 3-7 stage bleachinc3 saquence, whereas Rapson and Reeve both refer specifically to the fir~t (CD) stage of bleachlng.
With reference now to Figures 1-10 of the drawings, it ca~ be seen that applicants have improved upon the processes taught by Rapson and Reeve as well as upon the con~entional one-step bleaching stage used in the ;~ -majority of commercial bleaching mills. More .
10 specifically, applicants have invented a new and useful .
two-stage process for bleaching wood pulp slurries in a - :
chlorine-chlori~e dloxlde ~C12-~1O2) mlxture whlch gives ; :~
high~r brightness and pulp quality ~characterized by .
v~scosity) when compared to the conventional one-step :
15 C12~ClO2 mixture technology typically used today in i .
conventional bleaching mills. ~- :
Presently, wood pulp bleachinc~ with chlorine-chlorine dioxide mixtures 1~ typically carried out at 25 .:
centigrade - 60 centigrade in the fir~t stage of a ~CD)~EOlDED or (CD)(EO)D sequence. The consistency is usually around 3-5~, and bleaching times range from 15 minutes to 1 hour with an end pH of about 1.6-2.5 The ~:
application of conventional ~CD) bleaching procedures in thc D-staye of ~he above seyuences or in any other :
- 25 bleaching sequences has little commercial value due to the high viscosity loss (carboh~drate degradation) and poor brightness characteristics of the wood pulp. Thus, ~ , '` :": ' ,', ~. ~''. ' ', ' .
_~WO91/05910 2 ~ ~ 7 7 ~ ~ PCT/US90/0~826 existing ~CD) technology is typically only used as a first stage or pre-bleaching stage in the multi-stage bleaching process on wood pulp. Although others have proposed chlorine-chlorine dioxide bleaching in either one or two-step stages, such as disclosed in the Rapson and Reeve patents discussed above, it can be seen in Figures 1, 2 and 3 of the drawings that the novel two- ~
step chlorine-chlorine dioxide bleaching process of the .-present invention provides surprisingly and une~pectedly 10 better brightness and viscosity than has heretofore been . . ~ ;
achieved.
.. .,~. ..
In order to increa~e the effectivene~s of chlorine- .
chlorine dioxide bleaching of wood pulp, applicants have .~
discovered a new two-step chlorine-chlorine dioxide .
process which includes the following steps:
1. Pulp slurry is reacted with a chlorine and chlorine dioxide mlxture for about 5-40 minutes at a pH
of about 7-10. Normally, caustic is also mixed with the ~ ..
pulp slu~ry, and the caustic most suitably comprise -~
20 sodium hydroxide. The reaction temperature is between : :
about 40-80 centigrade, most suitahly about 70 .
centigrade, and the optimal pll during the first bleaching step is between about B-9.5; and ..
2. After the ~irst bleaching step, the remaining 25 chlorine is added ~o the pulp mixture, and the pH is ;~
maintained at 4 or less, most suitably a pH of about 2- :
' '.
~WO91/0~91~ PCT/US90/05826 2~677~
3.5 for at least 30 minutes, preferably about 30 minutes - 2.5 hours. The reaction temperature is between about ~ : -40-~0 centigrade, most suitably 70 centigrade.
Pulp con~istency fo~ both stepfi ifi between about 10 13.5% w$th the final consistency of the mixture after the ~ -~
second step at most suitably about 10%. The chlorine . . .
dioxide and chlorine used in the bleaching proce~s . ~ ;
comprise between about 15-80% chlorine on an available basis, and preferably all of the chlorine dioxide and 10 one-third of the chlorine are added at the first step, ~
and the remaining two-thirds of the chlorine are added at : :
the se~ond bleaching step. It should be appreclated that to calculate total charge such as percent chlorine on ~ :
pulp, the formula C102 ~ 2.63 C12 i8 used. For example, ..
if a 1% C102 charge is placed on wood pulp, it is equivalent to 2.63% available chlorine on the wood pulp.
Thus, lf one charges 1% available C102 on wood pulp, ~here is actually charged 2.63~ available chlorine of which 40% is C102 and 60~ is C12.
The new two-step process developed by applicants has . .;: .
been used to bleach pulp in the Dl stage of a (CD)(EO)DED
sequence with chlorine-chlorine dioxide mixtures of up to 60% of the chemical charged as chlorine on an available - :
basi~ with brightness and viscosity characteristics 25 comparable to a conventional chlorine-chlorine dioxide ~- :
stage (~ee Figures 1, 2 and ~-9). .~ .
.
.. .
. ., ~ ,..~ . .
: ' :, ;
W~91/05910 P~T/US90/05826 2~67~
Applicants' process is particularly attractive since ~-the new two-step chlorine-chlorine dioxide bleaching process allows for substituting chlorine for chlorine dioxide and thus results in substantial chemical cost reduction ~ince chlorine is a significantly less -expensive chemical. With the use of the novel two-step bleaching process of the present invention, it i8 now commercially possible to bleach wood pulp to a comparable ~
brightness as can be achieved in conventional one-step --lo chlorine aioxide bleaching ~t a significantly reduced commercial cost due to savings achieved by substituting -`
cheaper chlorine for more expensive chlorine dioxide in the wood pulp bleaching process.
Method of the Invention To prove the efficacy oE the new process generally described above, detailed bleaching experiments were carried out by applicants on souther~ pine k~aft pulp.
.: . . .
The furnish was obtained from the decker before the . . .
bleach plant, and to insure maximum mixing ~CD) stage ; ;
bleaching was done in plastic Nalgene bottles which rolled on a ball-mill type apparatus for the full ~-reaction time. All other bleaching stages were carried out in sealed polyester ba9s which were kneaded at ~ -various times throughout the bleach to insure proper 25 mixing. `~
': ~
~. ...,~j, .
''`.
~o g~to~gl~ 2 ~ ~ ~ 7 ~ ~ PCT/US90/05826 :
Proces~ing parameters used by applicants for the multiple bleachiny stages are listed in Table 1 below.
Chlorination stage charges were varied to achieve target ~`
(CD)E kappa numbers, and ail charges are on OD brownstock -pulp. Optimum high/low pH values are 8-9.5 and 2-3.5 respectively. Large batches of (CD3E pulp were made and - -then divided into individual DED and (CD)hlED runs or compari~on. All comparisons were made on pulps from the same (CD)E batch, and all water used in bleaching and . , . :
washing was distilled. Chlorine dioxide solutions used in testing were generated on site by acidifying sodium chlorite solution and absorbing the ClO2 gas in cold ` -distilled water.
:: ' Proces6ing parameters Eor the bleachin~ experiments and the analytical methods used in the experiments are as ~ollows~
... . .
,.. ,,.:' '': ' " ~, .~
" ' . . !; ` ', ''. ' . `
"; "'~ ,' .''; :
''' "'".
','; '' -. ~'' ' .
~wo glto~glo 2 ~ ~ ~ 7 ~ ~ PCr~USgO/05826 -14- ~ .
c~ r o ~r u~ ~ :' .:
~ V . . i:
. .., U~
.~ o o U~ o o o o . , ~ o o o o o o o o '' `:, `
a~ I` I` ~` I`I` I~ o :` .: ..
E3 I I I O ' `
E~ p, ,~
,1 ' ~o ;
m O ~
a~ u ~ I 07 0 0~ ~ . ' O O O C; O O O O
D~
_I p, o : ~c ~ Q'.a ~o ~ ~
u al -1 c o ~1 ~ a t~l N ~ 3 ~
.C . ~ ~ ~ ~ ~ h ~ 1~11`
u I ~1 o o ~ u~ la ~ o ~
a~ O ~ ~`
~t ~ c~ o ~ ~ .a ~ ~a ~ " ,~ ` `' ::' U L- U ~ ~
c ~ o O b C Z E~ Z ~ ~ .
tn a .
:
/ ' : . ' I` ' ' . ~:
--~W091/0~9iO 2 ~ ~ ~ 7 ~ ~ P~T/US90/~5826 ,, Thus, applicants' method provides for mixing chlorine, chlorine dioxide and caustic with an agueou ` `; -wood pulp slurry for about 5-15 minutes at a pH of about : .: . .
7-10. The optimum pH is between about 8-9.5 for best viscosity, and consistency is between about 10-13.5%.
Temperature is between about 40-80 centigrade. ~or the -~
second step in applicants' novel process, chlorine is then added to the pulp slurry which results in a decrease ln p~ to about 2-3.5. Reaction time is between about 30 ~ -10 minutes to 2.5 hours, reaction temperature is between -~
about 40-80 centigrade, and the final consistency of th~
wood pulp is about 10%.
Best brightness and viscosity have been found when all of the chlorine dioxide and one-third of the chlorine to be charged are added in the fir~;t step of the novel bleaching proceæs. The other two-l:hirds of the chlorine are added at the second step and allowed to react for 1-2 hours at 70 centigrade or 1.5 or more hours at 50 centigrade. Temperature and time dependents for effici~nt chemical consumption and optimum pulp brightness are important, and 5uitable combinations can be developed according to the needs of any given wood pulp bleaching mill.
Although applicants have disclosed the application . .
of the two-step chlorine-chlorine dioxide bleaching stage to the Dl stage of a (CD)(r'O)DED sequence, it should be appreciated that the process can be used ln any D or lCD) ; ~
:' :
. , ' ~ `
.
WO91/05910 2 ~ ~ ~ 7 ~ ~ PCT~S90/05826 stage in any three, four, five, ~ix or seven-stage bleaching sequence. Also, although applicants disclose the addition of the remaining chlorine to the pulp in the second 8tep of the new process, additional chlorine ~ -dioxide can also be added at this time to the pulp mixture. -~`
.
Process Apparatus The two-step high/low p~ bleaching process can be implemented in both a new plant or an existing pulp `-bleaching plant. The optimum design schematic is shown ln Flgur~ 10, where C1O2 and caustic are added to the first mixer. The pulp flows into a J or U tube (Figure lOA) or upflow tower (Figure lOB) with a retention time o~ ~pproximately 5~40 minutes. A second mixer i~
provided to mix chlorine with the pulp for the second step of the process. The pulp can then be discharged directly to a down~low tower. The retention time in the downElow tower is 2 or more hours and most fiuitably between 2.5-3.9 hours. In an existing bleach plant the ~implest method for implementing the two-step high/low pH
bleaching process technolo9y would be to install a mixer ` ~-on the discharge from the upflow leg of the tower to the downflow leg of the tower.
It will be understood that various details of the invention may be changed without departing from the scope of the invention. Furthermore, the foregoing description , ~VO91/05910 2 ~ ~ ~ 7 ~ O PCT/US90/05826 -~
-, : , . :
i~ for the purpose of illustration only, and not for the :: ~
purpose of limitation--the invention being defined by the ~ ~:
claims. ;~
,~
' ' ~,, ' .
.... .
....
"'. . ..
. ~ ... .
.'"~`'.'' ..
'` - ,'~:, ' : . . :
.
, :
'`'' . ', : ~
;.. : , 3'.: '.`
:'.,., ,` :, ":
'''i'' `',` ` : ' ~:',,~,'''.".. '.;
;'-':, ', ' :
~':' , .'.'.' ' ' ~, . . :. ..
~.:' : '. : ~
; '.~ , '.
,''; ~'" .~,' ' ','''''',',,'
Claims (25)
[received by the International Bureau on 4 April 1991 (04.04.91);
original claims 1,14-17 and 21-23 cancelled;
original claims 2,4-6,8-10,12,18-20 amended; new claims 24 and 25 added; other claims unchanged (6 pages)]
1. (Cancel)
2. A bleaching process according to claim 24 wherein caustic is also mixed with said aqueous wood pulp suspension during said first bleaching step.
3. A bleaching process according to claim 2 wherein said caustic comprises sodium hydroxide.
4. A bleaching process according to claim 24 wherein the pH of the mixture at the end of said first bleaching step is between about 8.0-9.5.
5. A bleaching process according to claim 24 wherein said first step reaction time is about 5-15 minutes.
6. A bleaching process according to claim 24 wherein the temperature during said first bleaching step is between about 40-80° centigrade.
7. A bleaching process according to claim 6 wherein the temperature during said first bleaching step is about 70° centigrade.
8. A bleaching process according to claim 24 wherein the pH of the mixture at the end of said second bleaching step is about 2.0-3.5.
9. A bleaching process according to claim 24 wherein said second step reaction time is about 30-150 minutes.
10. A bleaching process according to claim 24 wherein the temperature during said second bleaching step is between about 40-80° centigrade.
11. A bleaching process according to claim 10 wherein the temperature during said second bleaching step is about 70° centigrade.
12. A bleaching process according to claim 24 wherein consistency of the mixture during the first bleaching step and the second bleaching step is between about 10.0-13.5.
13. A bleaching process according to claim 12 wherein the final consistency of the mixture after the second bleaching step is about 10%.
14. (Cancel)
15. (Cancel)
16. (Cancel)
17. (Cancel) WO 91/??910 PCT/US90/05826
18. A bleaching process according to claim 25 wherein said caustic comprises sodium hydroxide.
19. A bleaching process according to claim 25 wherein consistency during the first bleaching step and the second bleaching step is between about 10.0-13.5.
20. A bleaching process according to claim 25 wherein the final consistency of the mixture after the second bleaching step is about 10%.
21. (Cancel)
22. (Cancel)
23. (Cancel)
24. A bleaching process for bleaching wood pulp in the D1 and/or D2 bleaching stage in an aqueous suspension using chlorine dioxide and chlorine wherein aid chlorine dioxide and chlorine comprise between 15-80% chlorine on an available basis, said bleaching process providing for high brightness and viscosity and high chlorine substitution, comprising the steps of:
subjecting said aqueous wood pulp suspension to a first bleaching step during said D1 and/or D2 bleaching stage by mixing it with chlorine dioxide and chlorine and an alkali for about 5-40 minutes so that the pH at the end of said first bleaching step is between about 7.0-10.0;
and subjecting said mixture to a second bleaching step during said D1 and/or D2 bleaching stage by mixing it with chlorine and allowing the mixture to react for at least 30 minutes 60 that the pH
at the end of said second bleaching step is 4.0 or less.
subjecting said aqueous wood pulp suspension to a first bleaching step during said D1 and/or D2 bleaching stage by mixing it with chlorine dioxide and chlorine and an alkali for about 5-40 minutes so that the pH at the end of said first bleaching step is between about 7.0-10.0;
and subjecting said mixture to a second bleaching step during said D1 and/or D2 bleaching stage by mixing it with chlorine and allowing the mixture to react for at least 30 minutes 60 that the pH
at the end of said second bleaching step is 4.0 or less.
25. A bleaching process for bleaching wood pulp in the D1 and/or D2 bleaching stage in an aqueous suspension using chlorine dioxide and chlorine wherein said chlorine dioxide and chlorine comprise about 15-80% chlorine on an available basis, said bleaching process providing for high brightness and viscosity and high chlorine substitutions comprising the steps of:
subjecting said aqueous wood pulp suspension to a first bleaching step during said D1 and/or D2 bleaching stage by mixing it with chlorine dioxide and chlorine and an alkali for about 5-15 minutes at a temperature of about 40-80°C so that the pH at the end of said first bleaching step is between about 8.0-9.5; and subjecting said mixture to a second bleaching step during said D1 and/or D2 bleaching stage by mixing it with chlorine and allowing the mixture to react for 2.0-3.5-hours at a temperature of about 40-80°C 80 that the pH at the end of said second bleaching step is between about 2.0-3.5.
subjecting said aqueous wood pulp suspension to a first bleaching step during said D1 and/or D2 bleaching stage by mixing it with chlorine dioxide and chlorine and an alkali for about 5-15 minutes at a temperature of about 40-80°C so that the pH at the end of said first bleaching step is between about 8.0-9.5; and subjecting said mixture to a second bleaching step during said D1 and/or D2 bleaching stage by mixing it with chlorine and allowing the mixture to react for 2.0-3.5-hours at a temperature of about 40-80°C 80 that the pH at the end of said second bleaching step is between about 2.0-3.5.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US42408689A | 1989-10-19 | 1989-10-19 | |
| US424,086 | 1989-10-19 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2067750A1 true CA2067750A1 (en) | 1991-04-20 |
Family
ID=23681388
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002067750A Abandoned CA2067750A1 (en) | 1989-10-19 | 1990-10-17 | Chlorine dioxide pulp bleaching process using sequential chlorine addition |
Country Status (7)
| Country | Link |
|---|---|
| EP (1) | EP0496827A1 (en) |
| CN (1) | CN1051951A (en) |
| AU (1) | AU6730390A (en) |
| CA (1) | CA2067750A1 (en) |
| PL (1) | PL287416A1 (en) |
| WO (1) | WO1991005910A1 (en) |
| ZA (1) | ZA908340B (en) |
Families Citing this family (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5850026A (en) | 1996-07-03 | 1998-12-15 | Cargill, Incorporated | Canola oil having increased oleic acid and decreased linolenic acid content |
| CN1100177C (en) * | 2000-07-20 | 2003-01-29 | 华南理工大学 | High-temp ClO2 bleaching method of sulfated wood pulp |
| SE532370C2 (en) * | 2008-02-28 | 2009-12-29 | Metso Paper Inc | Method of bleaching a pulp |
| US9057156B2 (en) | 2010-12-22 | 2015-06-16 | Skzo Nobel Chemicals International B.V. | Process for improving chlorine dioxide bleaching of pulp |
| CA2898417C (en) | 2013-02-08 | 2021-07-27 | Arthur J. Nonni | Softwood kraft fiber having an improved .alpha.-cellulose content and its use in the production of chemical cellulose products |
| FR3062138B1 (en) * | 2017-01-23 | 2019-06-07 | Centre Technique De L'industrie Des Papiers, Cartons Et Celluloses | PROCESS FOR WHITENING A PAPER PULP |
| CN106958161B (en) * | 2017-03-13 | 2018-06-01 | 广西大学 | A kind of paper pulp high temperature ClO 2 bleaching section exhaust heat recovering method |
Family Cites Families (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3433702A (en) * | 1965-06-28 | 1969-03-18 | Hooker Chemical Corp | Woodpulp bleaching process |
| FR2432574A1 (en) * | 1978-08-01 | 1980-02-29 | Europeen Cellulose | PROCESS FOR BLEACHING PAPER PULP |
-
1990
- 1990-10-17 EP EP90916973A patent/EP0496827A1/en active Pending
- 1990-10-17 WO PCT/US1990/005826 patent/WO1991005910A1/en not_active Application Discontinuation
- 1990-10-17 AU AU67303/90A patent/AU6730390A/en not_active Abandoned
- 1990-10-17 CA CA002067750A patent/CA2067750A1/en not_active Abandoned
- 1990-10-18 ZA ZA908340A patent/ZA908340B/en unknown
- 1990-10-19 CN CN90109214A patent/CN1051951A/en active Pending
- 1990-10-19 PL PL28741690A patent/PL287416A1/en unknown
Also Published As
| Publication number | Publication date |
|---|---|
| PL287416A1 (en) | 1991-08-12 |
| EP0496827A1 (en) | 1992-08-05 |
| ZA908340B (en) | 1991-08-28 |
| AU6730390A (en) | 1991-05-16 |
| WO1991005910A1 (en) | 1991-05-02 |
| CN1051951A (en) | 1991-06-05 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| US5310458A (en) | Process for bleaching lignocellulose-containing pulps | |
| CA1119360A (en) | Method for bleaching oxygen delignified cellulose-containing pulp with ozone | |
| EP0512590B1 (en) | Process for bleaching of lignocellulose-containing material | |
| EP0511695B1 (en) | Process for bleaching of lignocellulose-containing pulp | |
| US4626319A (en) | Process for the delignification and acid bleaching of cellulose with oxygen and hydrogen peroxide | |
| CA2040871C (en) | Process for bleaching of lignocellulose-containing material | |
| CN110552226B (en) | Method for producing bleached pulp | |
| US3020197A (en) | Method for production of high brightness high strength wood pulps | |
| CA2067750A1 (en) | Chlorine dioxide pulp bleaching process using sequential chlorine addition | |
| US3884752A (en) | Single vessel wood pulp bleaching with chlorine dioxide followed by sodium hypochlorite or alkaline extraction | |
| US5268075A (en) | High efficiency two-step, high-low pH chlorine dioxide pulp bleaching process | |
| CA1251903A (en) | Alkaline-peroxide-oxygen treatment of unbleached and chlorinated chemical pulps | |
| EP0496782B1 (en) | High efficiency chlorine dioxide pulp bleaching process | |
| US2527563A (en) | Method of bleaching semichemical pulps | |
| US4657633A (en) | Delignification and bleaching of a cellulose pulp with an alkalioxygen-hypochlorite single stage sequential extraction | |
| US2741536A (en) | Available chlorine multi-stage bleaching of sulfite pulp | |
| WO1991012366A1 (en) | Bleaching of paper pulp | |
| EP0702735B1 (en) | Method of bleaching pulp without using chlorine chemicals | |
| AU675291B2 (en) | Method for chlorine-free bleaching of pulp with acetic acid as acidifying agent | |
| EP0553649A1 (en) | Process for delignifying a cellulose pulp | |
| US2178649A (en) | Process for bleaching wood pulp | |
| US5030324A (en) | Sequential bleaching procedure using chlorine and chlorine dioxide in a first chlorination stage of a multistage bleaching process | |
| AU642652B2 (en) | Bleaching of lignocellulosic pulp | |
| AU642971B2 (en) | Bleaching of paper pulp | |
| KR850001507B1 (en) | Process for the production of chemical paper pulp and pulp this prepared |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| FZDE | Dead |