CA1055656A - Bleach hydrolysis of cellulose with substantially reduced use of chlorine - Google Patents
Bleach hydrolysis of cellulose with substantially reduced use of chlorineInfo
- Publication number
- CA1055656A CA1055656A CA201,323A CA201323A CA1055656A CA 1055656 A CA1055656 A CA 1055656A CA 201323 A CA201323 A CA 201323A CA 1055656 A CA1055656 A CA 1055656A
- Authority
- CA
- Canada
- Prior art keywords
- pulp
- hydrolysis
- stage
- bleaching
- peroxide
- 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.)
- Expired
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
- D21C9/1057—Multistage, with compounds cited in more than one sub-group D21C9/10, D21C9/12, D21C9/16
Abstract
ABSTRACT OF THE DISCLOSURE
The present invention provides in a multistage process for fully bleaching a pulp, the improvement in which in the first stage of said bleaching process, the pulp is hydrolyzed with a strongly alkaline aqueous peroxide solution whereby a minimum of chlorine may be used in said process.
The present invention provides in a multistage process for fully bleaching a pulp, the improvement in which in the first stage of said bleaching process, the pulp is hydrolyzed with a strongly alkaline aqueous peroxide solution whereby a minimum of chlorine may be used in said process.
Description
~S5656 The present invention relates to the multis~age bleach-ing of pulps.
Pulps which are obtained by means of various hydrolyz-ing processes of an alkaline or acid kind still contain consid- ~
erable amounts of lignin, hemicelluloses and other si~ilar ~. . .
components, which must be removed by subsequent bleaching pro-cesses in order to obtain products having high whiteness, white-ness stability or specific serviclability, as for example, suit- :
ability for use in the viscose rayon process. sleaching chemi~
cals such as chlorine (C), chlorine dioxide (D), sodium or .~
calcium hypochlorite ~H) are used in a variety of stages with ~.
intermediate alkaline extractions (E). MGreover, it is known to use hydrogen peroxide and sodium peroxide and organic per-compounds (P) for bleaching pulps, ei~her in the rorm of single-stage bleaching or as the final stage in multistage bleaching particularly in order -to obtain good whiteness stability :i.e.
resistance to yellowing.
The full bleaching of pulps (whiteness degree of 88%
of MgO or better 90~ of MgO) requires one or several chlorina-tion stages and additional hypochlorite stages and selectively ;
also chlorine dioxide stages. Because of -these processes sub-stantial amounts of hydrochloric acid, or when neutralization ..
is effected, substantial amounts of sodium chloride get into the effluent water and thus into the main canal and into the waters which receive the effluent water. The multistage bleaching pro-cesses C/E/H, C/E/H/H, C/E/D/E/D, C/E/H/D/P, C/E/H/D/E/D and C/E/H/D/~ are given as examples of the bleaching processes used :
today. Thus, all these processes start with a chlorination stage and subsequent extraction stage.
In connection with above waste water problems and the loading of the main canal with salts and dissolved organic sub-stances bleaching sequences such as PDPDP or even P/PES/P/PES/P, ~ ' . : ' ' , : :':
, :'. ', ~ ' , , : , ~ ' ' where P is peroxide and PES is pex-acid which allow a major por-tion of the bleaching waste waters to be charged to cooking-liquor regeneration processes are disclosed in German Patent Applications Nos. P 22 19 504.6-45 and P 22 19 505.7-45 published - 15/11/1973 and 8/11/73 respectively.
The attempt to replace, in the sulphate pulping pro-cess, the chlorine treatr.lent by a treatment with molecular oxygen _l-is referred to. How~ver, the ~reatment must be carried out under pressure. Moreover, it is still open to question whether the losses in strength which are caused per se by the alkaline treat- ¦
ment with oxygen under pressure can be prevented by the addi-tions proposed in the literature such as magnesium carbonate or !`
magnes.ium oxide (German Published SpeciEication 2,:lO9,542, published September 16, 1971, Rowlandson, Tappi 5~, 962-967 (1971), No. 6).
However, this technology was used heretofore only tentatively on a large industrial scale and the fact that nothing is known about the feasability of applying it to sul-phite pulps constitutes a further limitation.
The present invention provides a multistage process for fully bleaching pulps which can be carried out in existing bleaching apparatus of a pulp mill with substantially lower ~¦
~ ~ .
amounts of chlorine than heretofore.
I It has now been discovered that pulps can be fully .
bleached in sevexal stages without the use of pressure when the bleaching sequence ~if required in co~,lbination with a slight partial chlorination) starts with a stronyly alkaline ~;
peroxide bleach hydrolysis.
This strongly alkaline peroxide bleaching stage (P) .
which simultaneously acts as a hydrolysis replaces the conven-tional acid chlorination with subsequent alkaline extraction stage, i.e., the stages C-E of these processes mentioned herein-L[D55656 1~ ~
before. This makes it possible to operate with substantia]ly . ~ -lower amounts of chlorine than heretofore.
As in the known bleaching processes, the bleaching : :~
effect '` ';
'' ~ .
, . . .
' ',, .
,:
'.
~" .
.
j .
~: .
, , '',' ' ' .:
;' ''.
.. .. .
~, .
, -:
.,, :
. ' , ... .
.- 30 .'''' ' ' .
- 2a -depends on the kind of wood, i.er conifers (soft wood) or hard wood or annual plants, as well as on the manner in which the pulping process is carried out and thus on the degree of hydroly- `
sis .
The possible partial chlorination is necessary only when hard pulps, i.e., pulps rich in lignin and hemicellulose are bleached to whiteness contents of 90% of MgO. A partial chlorina-tion can be carried out either prior to the start of the actual bleaching operation, i.e., prior to the strongly alkaline peroxide stage, or the strongly alkaline peroxide stage is Eollowed by a partial chlorination and e~ctraction stage. ~pproximately one-flfth o the amount of chlorine used heretofore and approximately one-half of the amount of alkali used heretofore are required.
The amounts of chlorine used in these chlorination stages are only a fraction of the amounts normally used in the chlorination, as shown above. The peroxide stage is carried out ~;
with a large excess of alkali, as mentioned above. This partial chlorination can also be dispensed with the usual oxidation stages which follow the hydrolysis bleaching, such as hypochlorite, ;`
chlorine dioxide or peroxide, are efEected. This partial chlorina-tion may be omitted altogether when whiteness contents above 90%
of MgO are not required and when whiteness con-tents between 85 and i~
90% of ~gO are suficient. ~ -Bleaching with chlorine and alkali (C-E stage) dissolves out organic substances. Therefore, oxygen-consuming substances ',!~
and compounds having a high chlorine content get into the effluent water of the pulp mill,iwhereupon the waste water cannot be any ~
longer discharged into the main canals. ~ ~`
It is a known fact that bleaching waste waters which con-tain chlorine or chloride ions cause intense corrosion in theregenerative devices. The strongly alkaline bleach hydrolysis described permits the evaporation and concentrat:ion of the sub-.. . ~, .
stances dissolved out, their combustion and the regeneration of alkali in conventional apparatus. Moreover, the strongly alkaline peroxide treatment surprisingly showed that 85 to 90% of the sub-stances loading the waste waters are dissolved out in this stage and thus are not discharged into the main canal.
~ydrogen peroxide, sodium peroxide and other inorganic or organic peroxides or hydrogen peroxides, preferably hydrogen peroxide, sodium peroxide or t-butyl hydrogen peroxide or mixtures of these components in aqueous solutions are suitable as the per-compounds. Hydrogen peroxide and sodium peroxide are particularly suitable. The amount of peroxide used may be between 0.2 and 10%
by weight, preferably 0.6 to 6% by weight, computed as a 100%
hydrogen peroxide and relative to atro pulp (atro=absolutely dry).
Sodium hydroxide or even calcium hydroxide or ammonium hydroxide (N~13 or Ntl40~1) are preferably used as alkalis, i.e., alkali or alkaline earth hydroxides, required for the strongly alkaline peroxideic bleach hydrolysis described hereinbefore.
Said hydroxides are used in amounts from 2 to 15% by weight, pre-ferably from 4 to 8% by weight, computed as a 100% substance and ., .
relative to absolutely dry pulp.
The alkaline-peroxidic bleach hydrolysis is conventionally , carried out at temperatures ranging Erom 20C to the boiling point ; of the bleaching liquor.
,~.
~;- It is of course possible to carry out the bleaching operation under pressure, but the advantage obtained when using -the percompounds and the bleaching sequence mentioned hereinbefore lies particularly in the fact that the operation is at atmospheric ~, pressure, i.e., without the use of additional pressure and appara-tus.
As mentioned hereinbefore, the bleaching process is car-.. ...
ried out in existing bleacheries; the pulp consistencies prefer-ably are between 10 and 20%. By pulp consistency is meant percent ..... .
-- ~1 --.'":' ~ ', , ,~
',., ... . . ' . ~ . . ' :, . , r- ~L() 556 ~ I
; 7 by weight of pulp in the pulp suspension. However, it is also possible to carry out the strongly alkaline peroxidic stage at higher solids contents, i.e., up to 35%, using suitable technical aids, as for example, thick-pulp pumps, kneaders, and high- `
pressure filters.
he absence of sodium tetrasilicate, which is normally used in peroxidic bleaching stages, is a fu;rther advantage.
Conventional inorganic complexing agents or stabilizers, > -as for example, magnesium sulphate, or organic nitrogen- or phosphorus-containing complexing agents, as for example, ethylene ;~ -~diamine tetraacetic acid, diethylene triamine pentaacetic acid and nitrolo triacetic acid, can be used in the bleaching liquor.
It is also possible to use nitrogen-and phosphorus-free complex-ing agents. For example, polyoxy-carboxylic acids can be corres- ;~
pondingly used (German Published SpeciEications Nos. 1,904,940 published Aug. 6, 1970, 1,904,941 published August 6, 1970 and 1,942,556 published August 11, 1971. ~
The advance in the art oE the process according to the `;
- present invention lies in that pulps, including hard pulps, can be fully bleached in existing bleaching apparatus of the pulp . I .
, mills~ A further important advantagç lies in the recovery of ~
. .. . .
waste waters in which substances loading the main canal are dis-solved out in the first stage. The waste waters thus obtained can be evaporated and regenerated such that they are noncorrosive.
This includes the effluent waters obtained in full bleaching of ; hard pulps. ~
The examples hereafter serve to illustrate the process ;
according to the invention. The percentages always are percent by weight, relative unbleached dry pulp. In all the tests tap ~`
water of 5 German hardness was used and the operations were carried out in batches of 100 to 500 g of pulp (dry weight) in enamelled containers. The pH values were measured at the start :, :
~ of the bleaching operation. After each stage the pulp was washed .. ,,: :,, . .;
.. :. _ 5 .
:, - ;, ~ ~ID$~
.
with tap water and after the last stage it was acidified with ;
sulphur dioxide. The whiteness degrees~luminance factors) were determined according to German standard methods (Zellscheming Merkblatter) with the Zeiss Elrepho whiteness degree meter (filter R46).
i: :
i~ Example 1 , A beech-rayon sulphite pulp (kappa number 9.6, whiteness degree unbleached 51.0% of MgO) which had been produced according to the calcium bisulphite process, was bleached in a four-stage sequence under the following conditions: -1st stage 1~3% of H2O2l+ 8% of NaOH, 12V,~O~`pulplconsils~enc~r65C,2h 2nd stage 0.36% of NaOCl 12% pulp consistency, 50C,l~h 3rd stage 0.13% of ClO2 14% pulp consistency, 65C,l~h 4th stage 0.57~/O of NaOCl 12% pulp consistency, 55C,2h Ater ~he fourth stage the pu;lp had a whiteness content of 93.3% of MgO. A slightly higher whiteness content of 94.~/O of , MgO could be obtained with the following sequence:
1st stage 1.3% of H2O2 - 8% of NaOH, 12% pulp consistency, 65C,2h , 2nd stage 0.13% of ClO2 14% pulp consistency, 65C,l~h --`
3rd stage 0.36% of NaOCl 12% pulp consistency, 50C,l~h ~th stage 0.57% of NaOCl 12% pulp consistency, 55C,2h The kappa number could be reduced from approximately 9.6 in the unbleached pulp to below 1. The lignin content decreased ~
; from 1.2% to 0.18%. ~ -`s The other chemical characteristic values such as hemi-'~; cellulose~d~cel~ ose~ R18 value, ash and methanol-benzene extract ; also correspond to conventional methods. More specifically, the pulp can be readily processed into viscose rayon. The loss of substance due to this bleaching process (P-H-D-H) is approximately 7.5% relative to unbleached beech-rayon pulp.
Example 2 A beech-paper sulphite pulp (kappa number 22.3, whiteness i.., ~ - 6 .':
degree unbleached 56.7% of MgO) was bleached in a four-stage . ; .
sequence under the following conditions:
1st stage 1.3% of H2O2 - 8.9% of NaOH, 12% pulp consistency, 65C,2h ~
2nd stage 0.5% of NaOCl 12% pulp consistency, 40C,l~h `;~ -3rd stage 0.22V/o of ClO2 l~/o pulp consistency, 65C,2h r~, 4th stage 0.17% of NaOCl 12% pulp consistency, 50C,2h The final whiteness content was 88.0% of MgO in this case.
If the amount of peroxide used in the first stage is in-creased to 2.6% of H2O2, then a whiteness degree of 91~4V/o of MgO
. . . ~
; 10 can be obtained with a total of only three stages (P-D-H).
.. ~,-.
1st stage 2.6% of H2O2 - 8.0% of NaOH, 12% pulp consistency, 65C,2h ~`
2nd stage 0.22% of C102 12% pulp consistency, 65C,2h 3rd stage 0.5% of NaOCl 14% pulp consistency, 45C,2h Example 3 In order to attain a maximum bleaching efEect on a beech-calcium bisulphite paper pulp (see Example 2) a weak chlorination stage is inserted prior to the strongly alkaline-peroxidic bleach hydrolysis.
. .
1st stage 0.5% of C12 4% pulp consistency, cold, ~h 2nd stage 1.3% of H2O 12% pulp consistency, 65C, 2h ~;~vj ~If `~2t 3rd stage 0.66% of NaOCl 12% pulp consistency, 50C, 2h ~, 4th stage 0.23% of ClO2 14% pulp consistency, 65C, l~h 5th stage 0.27% of NaOCl 12% pulp consistency, 52C, 2h ;
0.2% of NaQH
. .. .
~ ~fter this stage sequence a whiteness content of 95.4% ~;
", . .
of MgO was attained. The pulp yield was 93.2% relative totthe unbleached pulp. In the first two stages (CP) 87.1% oE the sub-s stances loading the waste waters were dissolved and were then pas-sed to a regeneration process. ;
,~ . . .
Example 4 :.. ,i.~ : .
A spruce paper pulp (kappa number 19.55, whiteness un-` bleached 50.2% of MgO) produced according to the calcium bisulphite ,~r . . ~:
.~ . ' '~"' ' ' ' . ~ , . . .
S5~
, ,,`.
process is bleached in a four-stage process according to the fol-lowing sequence:
1st stage 2.6% of H202 l~/o pulp consistency, 65C, 2h 8.0% of NaOH
2nd stage 0.2% of C102 12% pulp consistency, ~5-50Cg lh 3rd stage 0.3% of C102 14~/o pulp consistency, 57C, lh 4th stage 0.63% of NaOCl 12% pulp consistency, 43C, 2h `
By means of this bleaching process a whiteness content of 87.4% of MgO is attained.
This Example clearly shows that for obtaining whiteness degrees between 85 and 90% of MgO a chl-orination stage can be dispensed with even in hard spruce paper pulps. ~-For whiteness contents higher than 90% the Eollowing sequences with subsequent partial chlorination are suLtable:
1st stage 1.3% of H22 12% pulp consistency, 65C, 2h 6.0% o NaOH
2nd stage 1.3% of C12 4% pulp consistency, cold, ~h 3rd stage 1.2% of NaOH 12% pulp consistency, 60C, lh 4th stage 0.62% of NaOCl 12% pulp consistency, 50C, 2h 5th stage 0.34% of C102 14% pulp consistency, 70C, 2h , 6th stage 0.30% of NaCl 12% pulp consistency, 50C, 2h This whiteness content was 92.5% of MgO in this case.
,. ;
With a preceding partLal chlorination a whiteness content of 94.1% of MgO is attained.
;...................................................................... .
1st stage 1% o~ C12 4% pulp consistency, cold, ~h 2nd stage 1.3% of H22 12V/o pulp consistency, 65C, 2h 6% of NaOH
, 3rd stage 0.66% of NaOCl 12% pulp consistency, 50C, 2h 4th stage 0.30% of C102 1~% pulp consistency, 65C, l~h 5th stage 0.66% of NaOCl l~/o pulp consistency, 53C, 2h `; 0.2% of NaOH
The abo~e Examples show that the whiteness degree required for high bleaching of pulps can be attained by means of the bleach ` . ,'~' '' ' .
~ `~
hydrolysis of the present invention. The yield corresponded to the order known from conventional strongly chlorine-containing :
multistage bleaching processes. Moreover, since in the alkaline~
.. . .
peroxidic bleach hydrolysis 7/8 of the organic substances which . :~
can be dissolved out are no longer discharged~into the main canal but are fed to the regeneration process, the load on the waste :
water is substantially reduced.
: `
'; `,'`" " :'.
.''.
.
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,: . ' ' ' ' .: , :.
.
,, ' :
.
~ ~ .
,.;' ;. , . ~ .
~,. ~"''.
-' .
.'~ ., .
; .
' ::
: , ' ;........... , , ., , . ., , . ~
Pulps which are obtained by means of various hydrolyz-ing processes of an alkaline or acid kind still contain consid- ~
erable amounts of lignin, hemicelluloses and other si~ilar ~. . .
components, which must be removed by subsequent bleaching pro-cesses in order to obtain products having high whiteness, white-ness stability or specific serviclability, as for example, suit- :
ability for use in the viscose rayon process. sleaching chemi~
cals such as chlorine (C), chlorine dioxide (D), sodium or .~
calcium hypochlorite ~H) are used in a variety of stages with ~.
intermediate alkaline extractions (E). MGreover, it is known to use hydrogen peroxide and sodium peroxide and organic per-compounds (P) for bleaching pulps, ei~her in the rorm of single-stage bleaching or as the final stage in multistage bleaching particularly in order -to obtain good whiteness stability :i.e.
resistance to yellowing.
The full bleaching of pulps (whiteness degree of 88%
of MgO or better 90~ of MgO) requires one or several chlorina-tion stages and additional hypochlorite stages and selectively ;
also chlorine dioxide stages. Because of -these processes sub-stantial amounts of hydrochloric acid, or when neutralization ..
is effected, substantial amounts of sodium chloride get into the effluent water and thus into the main canal and into the waters which receive the effluent water. The multistage bleaching pro-cesses C/E/H, C/E/H/H, C/E/D/E/D, C/E/H/D/P, C/E/H/D/E/D and C/E/H/D/~ are given as examples of the bleaching processes used :
today. Thus, all these processes start with a chlorination stage and subsequent extraction stage.
In connection with above waste water problems and the loading of the main canal with salts and dissolved organic sub-stances bleaching sequences such as PDPDP or even P/PES/P/PES/P, ~ ' . : ' ' , : :':
, :'. ', ~ ' , , : , ~ ' ' where P is peroxide and PES is pex-acid which allow a major por-tion of the bleaching waste waters to be charged to cooking-liquor regeneration processes are disclosed in German Patent Applications Nos. P 22 19 504.6-45 and P 22 19 505.7-45 published - 15/11/1973 and 8/11/73 respectively.
The attempt to replace, in the sulphate pulping pro-cess, the chlorine treatr.lent by a treatment with molecular oxygen _l-is referred to. How~ver, the ~reatment must be carried out under pressure. Moreover, it is still open to question whether the losses in strength which are caused per se by the alkaline treat- ¦
ment with oxygen under pressure can be prevented by the addi-tions proposed in the literature such as magnesium carbonate or !`
magnes.ium oxide (German Published SpeciEication 2,:lO9,542, published September 16, 1971, Rowlandson, Tappi 5~, 962-967 (1971), No. 6).
However, this technology was used heretofore only tentatively on a large industrial scale and the fact that nothing is known about the feasability of applying it to sul-phite pulps constitutes a further limitation.
The present invention provides a multistage process for fully bleaching pulps which can be carried out in existing bleaching apparatus of a pulp mill with substantially lower ~¦
~ ~ .
amounts of chlorine than heretofore.
I It has now been discovered that pulps can be fully .
bleached in sevexal stages without the use of pressure when the bleaching sequence ~if required in co~,lbination with a slight partial chlorination) starts with a stronyly alkaline ~;
peroxide bleach hydrolysis.
This strongly alkaline peroxide bleaching stage (P) .
which simultaneously acts as a hydrolysis replaces the conven-tional acid chlorination with subsequent alkaline extraction stage, i.e., the stages C-E of these processes mentioned herein-L[D55656 1~ ~
before. This makes it possible to operate with substantia]ly . ~ -lower amounts of chlorine than heretofore.
As in the known bleaching processes, the bleaching : :~
effect '` ';
'' ~ .
, . . .
' ',, .
,:
'.
~" .
.
j .
~: .
, , '',' ' ' .:
;' ''.
.. .. .
~, .
, -:
.,, :
. ' , ... .
.- 30 .'''' ' ' .
- 2a -depends on the kind of wood, i.er conifers (soft wood) or hard wood or annual plants, as well as on the manner in which the pulping process is carried out and thus on the degree of hydroly- `
sis .
The possible partial chlorination is necessary only when hard pulps, i.e., pulps rich in lignin and hemicellulose are bleached to whiteness contents of 90% of MgO. A partial chlorina-tion can be carried out either prior to the start of the actual bleaching operation, i.e., prior to the strongly alkaline peroxide stage, or the strongly alkaline peroxide stage is Eollowed by a partial chlorination and e~ctraction stage. ~pproximately one-flfth o the amount of chlorine used heretofore and approximately one-half of the amount of alkali used heretofore are required.
The amounts of chlorine used in these chlorination stages are only a fraction of the amounts normally used in the chlorination, as shown above. The peroxide stage is carried out ~;
with a large excess of alkali, as mentioned above. This partial chlorination can also be dispensed with the usual oxidation stages which follow the hydrolysis bleaching, such as hypochlorite, ;`
chlorine dioxide or peroxide, are efEected. This partial chlorina-tion may be omitted altogether when whiteness contents above 90%
of MgO are not required and when whiteness con-tents between 85 and i~
90% of ~gO are suficient. ~ -Bleaching with chlorine and alkali (C-E stage) dissolves out organic substances. Therefore, oxygen-consuming substances ',!~
and compounds having a high chlorine content get into the effluent water of the pulp mill,iwhereupon the waste water cannot be any ~
longer discharged into the main canals. ~ ~`
It is a known fact that bleaching waste waters which con-tain chlorine or chloride ions cause intense corrosion in theregenerative devices. The strongly alkaline bleach hydrolysis described permits the evaporation and concentrat:ion of the sub-.. . ~, .
stances dissolved out, their combustion and the regeneration of alkali in conventional apparatus. Moreover, the strongly alkaline peroxide treatment surprisingly showed that 85 to 90% of the sub-stances loading the waste waters are dissolved out in this stage and thus are not discharged into the main canal.
~ydrogen peroxide, sodium peroxide and other inorganic or organic peroxides or hydrogen peroxides, preferably hydrogen peroxide, sodium peroxide or t-butyl hydrogen peroxide or mixtures of these components in aqueous solutions are suitable as the per-compounds. Hydrogen peroxide and sodium peroxide are particularly suitable. The amount of peroxide used may be between 0.2 and 10%
by weight, preferably 0.6 to 6% by weight, computed as a 100%
hydrogen peroxide and relative to atro pulp (atro=absolutely dry).
Sodium hydroxide or even calcium hydroxide or ammonium hydroxide (N~13 or Ntl40~1) are preferably used as alkalis, i.e., alkali or alkaline earth hydroxides, required for the strongly alkaline peroxideic bleach hydrolysis described hereinbefore.
Said hydroxides are used in amounts from 2 to 15% by weight, pre-ferably from 4 to 8% by weight, computed as a 100% substance and ., .
relative to absolutely dry pulp.
The alkaline-peroxidic bleach hydrolysis is conventionally , carried out at temperatures ranging Erom 20C to the boiling point ; of the bleaching liquor.
,~.
~;- It is of course possible to carry out the bleaching operation under pressure, but the advantage obtained when using -the percompounds and the bleaching sequence mentioned hereinbefore lies particularly in the fact that the operation is at atmospheric ~, pressure, i.e., without the use of additional pressure and appara-tus.
As mentioned hereinbefore, the bleaching process is car-.. ...
ried out in existing bleacheries; the pulp consistencies prefer-ably are between 10 and 20%. By pulp consistency is meant percent ..... .
-- ~1 --.'":' ~ ', , ,~
',., ... . . ' . ~ . . ' :, . , r- ~L() 556 ~ I
; 7 by weight of pulp in the pulp suspension. However, it is also possible to carry out the strongly alkaline peroxidic stage at higher solids contents, i.e., up to 35%, using suitable technical aids, as for example, thick-pulp pumps, kneaders, and high- `
pressure filters.
he absence of sodium tetrasilicate, which is normally used in peroxidic bleaching stages, is a fu;rther advantage.
Conventional inorganic complexing agents or stabilizers, > -as for example, magnesium sulphate, or organic nitrogen- or phosphorus-containing complexing agents, as for example, ethylene ;~ -~diamine tetraacetic acid, diethylene triamine pentaacetic acid and nitrolo triacetic acid, can be used in the bleaching liquor.
It is also possible to use nitrogen-and phosphorus-free complex-ing agents. For example, polyoxy-carboxylic acids can be corres- ;~
pondingly used (German Published SpeciEications Nos. 1,904,940 published Aug. 6, 1970, 1,904,941 published August 6, 1970 and 1,942,556 published August 11, 1971. ~
The advance in the art oE the process according to the `;
- present invention lies in that pulps, including hard pulps, can be fully bleached in existing bleaching apparatus of the pulp . I .
, mills~ A further important advantagç lies in the recovery of ~
. .. . .
waste waters in which substances loading the main canal are dis-solved out in the first stage. The waste waters thus obtained can be evaporated and regenerated such that they are noncorrosive.
This includes the effluent waters obtained in full bleaching of ; hard pulps. ~
The examples hereafter serve to illustrate the process ;
according to the invention. The percentages always are percent by weight, relative unbleached dry pulp. In all the tests tap ~`
water of 5 German hardness was used and the operations were carried out in batches of 100 to 500 g of pulp (dry weight) in enamelled containers. The pH values were measured at the start :, :
~ of the bleaching operation. After each stage the pulp was washed .. ,,: :,, . .;
.. :. _ 5 .
:, - ;, ~ ~ID$~
.
with tap water and after the last stage it was acidified with ;
sulphur dioxide. The whiteness degrees~luminance factors) were determined according to German standard methods (Zellscheming Merkblatter) with the Zeiss Elrepho whiteness degree meter (filter R46).
i: :
i~ Example 1 , A beech-rayon sulphite pulp (kappa number 9.6, whiteness degree unbleached 51.0% of MgO) which had been produced according to the calcium bisulphite process, was bleached in a four-stage sequence under the following conditions: -1st stage 1~3% of H2O2l+ 8% of NaOH, 12V,~O~`pulplconsils~enc~r65C,2h 2nd stage 0.36% of NaOCl 12% pulp consistency, 50C,l~h 3rd stage 0.13% of ClO2 14% pulp consistency, 65C,l~h 4th stage 0.57~/O of NaOCl 12% pulp consistency, 55C,2h Ater ~he fourth stage the pu;lp had a whiteness content of 93.3% of MgO. A slightly higher whiteness content of 94.~/O of , MgO could be obtained with the following sequence:
1st stage 1.3% of H2O2 - 8% of NaOH, 12% pulp consistency, 65C,2h , 2nd stage 0.13% of ClO2 14% pulp consistency, 65C,l~h --`
3rd stage 0.36% of NaOCl 12% pulp consistency, 50C,l~h ~th stage 0.57% of NaOCl 12% pulp consistency, 55C,2h The kappa number could be reduced from approximately 9.6 in the unbleached pulp to below 1. The lignin content decreased ~
; from 1.2% to 0.18%. ~ -`s The other chemical characteristic values such as hemi-'~; cellulose~d~cel~ ose~ R18 value, ash and methanol-benzene extract ; also correspond to conventional methods. More specifically, the pulp can be readily processed into viscose rayon. The loss of substance due to this bleaching process (P-H-D-H) is approximately 7.5% relative to unbleached beech-rayon pulp.
Example 2 A beech-paper sulphite pulp (kappa number 22.3, whiteness i.., ~ - 6 .':
degree unbleached 56.7% of MgO) was bleached in a four-stage . ; .
sequence under the following conditions:
1st stage 1.3% of H2O2 - 8.9% of NaOH, 12% pulp consistency, 65C,2h ~
2nd stage 0.5% of NaOCl 12% pulp consistency, 40C,l~h `;~ -3rd stage 0.22V/o of ClO2 l~/o pulp consistency, 65C,2h r~, 4th stage 0.17% of NaOCl 12% pulp consistency, 50C,2h The final whiteness content was 88.0% of MgO in this case.
If the amount of peroxide used in the first stage is in-creased to 2.6% of H2O2, then a whiteness degree of 91~4V/o of MgO
. . . ~
; 10 can be obtained with a total of only three stages (P-D-H).
.. ~,-.
1st stage 2.6% of H2O2 - 8.0% of NaOH, 12% pulp consistency, 65C,2h ~`
2nd stage 0.22% of C102 12% pulp consistency, 65C,2h 3rd stage 0.5% of NaOCl 14% pulp consistency, 45C,2h Example 3 In order to attain a maximum bleaching efEect on a beech-calcium bisulphite paper pulp (see Example 2) a weak chlorination stage is inserted prior to the strongly alkaline-peroxidic bleach hydrolysis.
. .
1st stage 0.5% of C12 4% pulp consistency, cold, ~h 2nd stage 1.3% of H2O 12% pulp consistency, 65C, 2h ~;~vj ~If `~2t 3rd stage 0.66% of NaOCl 12% pulp consistency, 50C, 2h ~, 4th stage 0.23% of ClO2 14% pulp consistency, 65C, l~h 5th stage 0.27% of NaOCl 12% pulp consistency, 52C, 2h ;
0.2% of NaQH
. .. .
~ ~fter this stage sequence a whiteness content of 95.4% ~;
", . .
of MgO was attained. The pulp yield was 93.2% relative totthe unbleached pulp. In the first two stages (CP) 87.1% oE the sub-s stances loading the waste waters were dissolved and were then pas-sed to a regeneration process. ;
,~ . . .
Example 4 :.. ,i.~ : .
A spruce paper pulp (kappa number 19.55, whiteness un-` bleached 50.2% of MgO) produced according to the calcium bisulphite ,~r . . ~:
.~ . ' '~"' ' ' ' . ~ , . . .
S5~
, ,,`.
process is bleached in a four-stage process according to the fol-lowing sequence:
1st stage 2.6% of H202 l~/o pulp consistency, 65C, 2h 8.0% of NaOH
2nd stage 0.2% of C102 12% pulp consistency, ~5-50Cg lh 3rd stage 0.3% of C102 14~/o pulp consistency, 57C, lh 4th stage 0.63% of NaOCl 12% pulp consistency, 43C, 2h `
By means of this bleaching process a whiteness content of 87.4% of MgO is attained.
This Example clearly shows that for obtaining whiteness degrees between 85 and 90% of MgO a chl-orination stage can be dispensed with even in hard spruce paper pulps. ~-For whiteness contents higher than 90% the Eollowing sequences with subsequent partial chlorination are suLtable:
1st stage 1.3% of H22 12% pulp consistency, 65C, 2h 6.0% o NaOH
2nd stage 1.3% of C12 4% pulp consistency, cold, ~h 3rd stage 1.2% of NaOH 12% pulp consistency, 60C, lh 4th stage 0.62% of NaOCl 12% pulp consistency, 50C, 2h 5th stage 0.34% of C102 14% pulp consistency, 70C, 2h , 6th stage 0.30% of NaCl 12% pulp consistency, 50C, 2h This whiteness content was 92.5% of MgO in this case.
,. ;
With a preceding partLal chlorination a whiteness content of 94.1% of MgO is attained.
;...................................................................... .
1st stage 1% o~ C12 4% pulp consistency, cold, ~h 2nd stage 1.3% of H22 12V/o pulp consistency, 65C, 2h 6% of NaOH
, 3rd stage 0.66% of NaOCl 12% pulp consistency, 50C, 2h 4th stage 0.30% of C102 1~% pulp consistency, 65C, l~h 5th stage 0.66% of NaOCl l~/o pulp consistency, 53C, 2h `; 0.2% of NaOH
The abo~e Examples show that the whiteness degree required for high bleaching of pulps can be attained by means of the bleach ` . ,'~' '' ' .
~ `~
hydrolysis of the present invention. The yield corresponded to the order known from conventional strongly chlorine-containing :
multistage bleaching processes. Moreover, since in the alkaline~
.. . .
peroxidic bleach hydrolysis 7/8 of the organic substances which . :~
can be dissolved out are no longer discharged~into the main canal but are fed to the regeneration process, the load on the waste :
water is substantially reduced.
: `
'; `,'`" " :'.
.''.
.
: ':
,: . ' ' ' ' .: , :.
.
,, ' :
.
~ ~ .
,.;' ;. , . ~ .
~,. ~"''.
-' .
.'~ ., .
; .
' ::
: , ' ;........... , , ., , . ., , . ~
Claims (13)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. In a multistage process for fully bleaching a pulp in which the pulp is bleached in a plurality of stages by treat-ment with chlorine containing compounds selected from hypochlor-ite and chlorine dioxide, the improvement in which in a stage of said bleaching process, prior to said bleaching stages with said chlorine containing compounds, the pulp having a consistency not above 35% is hydrolyzed with an alkaline aqueous peroxide solu-tion, the amount of peroxide in said hydrolysis stage being from 0.2 to 10% by weight computed for a 100% hydrogen peroxide and relative to absolutely dry pulp, the amount of alkali in said hydrolysis stage being from 2 to 15% by weight, computed for a 100% substance, relative to absolutely dry pulp, the hydrolysis being carried out at a temperature ranging from 20°C to the boiling point of the bleaching liquor.
2. A process as claimed in claim l, in which the hydrolysis is effected in said hydrolysis stage under atmospheric pressure.
3. A process as claimed in claim 1, in which prior or subsequent to said hydrolysis said pulp which is a hard pulp.
is subjected to a partial chlorination.
is subjected to a partial chlorination.
4. A process as claimed in claim 1, 2 or 3 in which the amount of peroxide is from 0.6 to 6% by weight computed for a 100% hydrogen peroxide and relative to absolutely dry pulp.
5. A process as claimed in claim 1, 2 or 3, in which the amount of alkali in said hydrolysis stage if from 4 to 8% by weight, computed for 100% substance and relative to absolutely dry pulp.
6. A process as claimed in claim 3, in which the hydrolysis is at atmospheric pressure.
7. A process according to claim l, 2 or 3, in which hydrolysis is carried out on pulps having consistencies from 5 to 35%.
8. A process as claimed in claim 1, 2 or 3, in which the hydrolysis is carried out on pulps having consistencies from 10% to 20%.
9. A process according to claim 1, 2 or 3, in which the pulp is a hard pulp and in which the alkaline-peroxidic bleach hydrolysis is preceded by a partial chlorination.
10. A process according to claim 1, 2 or 3, in which the pulp is a hard pulp and which the alkaline-peroxidic bleach hydrolysis is followed by a weak partial chlorination and extrac-tion stage.
11. A process according to claim 1, 2 or 3, in which the bleaching liquors and the bleach waste liquors obtained from said hydrolysis stage are passed directly to a regeneration stage.
12. A process as claimed in claim 1, 2 or 3, in which the peroxide is hydrogen peroxide, sodium peroxide or t-butyl hydrogen peroxide or a mixture thereof.
13. A process as claimed in claim 1, 2 or 3, in which the alkali is sodium hydroxide, calcium hydroxide or ammonium hydroxide.
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE2327900A DE2327900C3 (en) | 1973-06-01 | 1973-06-01 | Bleaching of cellulose with considerably reduced use of chlorine |
| ZA757622A ZA757622B (en) | 1973-06-01 | 1975-12-04 | Bleaching process for wood pulp with the use of considerably reduced amounts of chlorine |
| CH1587875A CH618487A5 (en) | 1973-06-01 | 1975-12-05 | Multiple-stage process for the low-chlorine complete bleaching of wood pulp |
| FR7628206A FR2364999A1 (en) | 1973-06-01 | 1976-09-20 | Bleaching of cellulose pulps with reduced chlorine use - involving an initial degradation stage using strongly alkaline peroxide |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1055656A true CA1055656A (en) | 1979-06-05 |
Family
ID=27429620
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA201,323A Expired CA1055656A (en) | 1973-06-01 | 1974-05-31 | Bleach hydrolysis of cellulose with substantially reduced use of chlorine |
Country Status (9)
| Country | Link |
|---|---|
| AT (1) | AT334732B (en) |
| BE (1) | BE836358A (en) |
| CA (1) | CA1055656A (en) |
| CH (1) | CH618487A5 (en) |
| DE (1) | DE2327900C3 (en) |
| FI (1) | FI62361C (en) |
| FR (1) | FR2364999A1 (en) |
| SE (1) | SE415674B (en) |
| ZA (1) | ZA757622B (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2014106222A2 (en) * | 2012-12-31 | 2014-07-03 | Api Intellectual Property Holdings, Llc | Biomass fractionation processes employing sulfur dioxide |
Families Citing this family (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE2327900C3 (en) * | 1973-06-01 | 1985-02-07 | Degussa Ag, 6000 Frankfurt | Bleaching of cellulose with considerably reduced use of chlorine |
| DE2538673C2 (en) * | 1975-08-30 | 1986-01-16 | Degussa Ag, 6000 Frankfurt | Bleaching of cellulose with considerably reduced use of chlorine |
| BE869153A (en) * | 1977-07-29 | 1979-01-22 | Ugine Kuhlmann | PROCESS FOR THE MANUFACTURE OF CHEMICAL PAPER PULP |
| DE2841013C2 (en) * | 1978-09-21 | 1984-06-07 | Degussa Ag, 6000 Frankfurt | Process for full bleaching of pulp |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US2527563A (en) * | 1947-08-13 | 1950-10-31 | Buffalo Electro Chem Co | Method of bleaching semichemical pulps |
| FR1118216A (en) * | 1954-02-02 | 1956-06-01 | I Ab | Half-cellulose bleaching process |
| DE2327900C3 (en) * | 1973-06-01 | 1985-02-07 | Degussa Ag, 6000 Frankfurt | Bleaching of cellulose with considerably reduced use of chlorine |
-
1973
- 1973-06-01 DE DE2327900A patent/DE2327900C3/en not_active Expired
-
1974
- 1974-04-30 FI FI1326/74A patent/FI62361C/en active
- 1974-05-31 SE SE7407273A patent/SE415674B/en not_active IP Right Cessation
- 1974-05-31 AT AT452974A patent/AT334732B/en not_active IP Right Cessation
- 1974-05-31 CA CA201,323A patent/CA1055656A/en not_active Expired
-
1975
- 1975-12-04 ZA ZA757622A patent/ZA757622B/en unknown
- 1975-12-05 BE BE6045281A patent/BE836358A/en not_active IP Right Cessation
- 1975-12-05 CH CH1587875A patent/CH618487A5/en not_active IP Right Cessation
-
1976
- 1976-09-20 FR FR7628206A patent/FR2364999A1/en active Granted
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2014106222A2 (en) * | 2012-12-31 | 2014-07-03 | Api Intellectual Property Holdings, Llc | Biomass fractionation processes employing sulfur dioxide |
| WO2014106222A3 (en) * | 2012-12-31 | 2014-07-31 | Api Intellectual Property Holdings, Llc | Biomass fractionation processes employing sulfur dioxide |
Also Published As
| Publication number | Publication date |
|---|---|
| FI62361C (en) | 1982-12-10 |
| FR2364999A1 (en) | 1978-04-14 |
| DE2327900A1 (en) | 1975-01-02 |
| FR2364999B1 (en) | 1979-01-12 |
| BE836358A (en) | 1976-04-01 |
| DE2327900C3 (en) | 1985-02-07 |
| AT334732B (en) | 1976-02-10 |
| DE2327900B2 (en) | 1978-08-03 |
| SE7407273L (en) | 1974-12-02 |
| ZA757622B (en) | 1976-11-24 |
| SE415674B (en) | 1980-10-20 |
| ATA452974A (en) | 1976-05-15 |
| FI62361B (en) | 1982-08-31 |
| FI132674A (en) | 1974-12-02 |
| CH618487A5 (en) | 1980-07-31 |
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