CA1080408A - Oxidation of pulping liquor - Google Patents
Oxidation of pulping liquorInfo
- Publication number
- CA1080408A CA1080408A CA136,634A CA136634A CA1080408A CA 1080408 A CA1080408 A CA 1080408A CA 136634 A CA136634 A CA 136634A CA 1080408 A CA1080408 A CA 1080408A
- Authority
- CA
- Canada
- Prior art keywords
- liquor
- wood
- mixture
- white
- white liquor
- 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
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Classifications
-
- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
- D21C3/00—Pulping cellulose-containing materials
- D21C3/02—Pulping cellulose-containing materials with inorganic bases or alkaline reacting compounds, e.g. sulfate processes
- D21C3/022—Pulping cellulose-containing materials with inorganic bases or alkaline reacting compounds, e.g. sulfate processes in presence of S-containing compounds
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- Chemical & Material Sciences (AREA)
- Inorganic Chemistry (AREA)
- Paper (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
A mixture of black liquor and white liquor is oxidized in the presence of wood to be pulped, so as to form a polysulfide pulping liquor which acts immediately upon the wood. The process allows increased yields of pulp with lower sulfidity levels and, thus, lessened pollution.
A mixture of black liquor and white liquor is oxidized in the presence of wood to be pulped, so as to form a polysulfide pulping liquor which acts immediately upon the wood. The process allows increased yields of pulp with lower sulfidity levels and, thus, lessened pollution.
Description
Brief Summary o the Invention Variou~ process~s have been developed or pulping of wood employing alkali metal polysulfide as a primary pulping agent. For exaraple, a procQss for forming a poly~ulfide pulping li~auor is described and claimed in our U.S. Patenk ~o. 3,470,061, gra~ted septemb0r 30, 1969. In ~hat patent, various ~angan~se compounds are employed for oxidation of alkali mQtal sulfide to alk~li m~3tal polysulfide.
A ~urther proc~ss for forming polysul~ide pulping li~uors is described in Per .~ndreas Landmark U.S0 Patent No 3,216,887, granted ~iovember 9, 1965, where t~e polysul~idll3 i3 form~3d by t~le air olcidatioll of sodium sulfide in a mixture of white liquor and black li~uor. Sub~e~auent to ~ormatior~ of the polysulfide, the liquor contacts the w~od to be pulpedO Becau5e of this me~hod of operation, a sul~idity level of at least 40%
is neces~ary in order to obtain any significant yield illcrease and, b~c:ause o~ this, there are sigi~iicant sulfur lo~es. The sulfur losses provide a signi~ ant level oP pollution.
White liguor, recirculated ~rom wood impragnation, is treated so as to form polysul~ida according to Canadian patent No. 815, 432, i3sued on June 17, 196g to Domtar Limited. EiEic-i~cy lev~ls operating in accordance with thi~ patent are relati-re-ly low.
In accordance with the present invention, it ha~ been de~ermined that a mix~ure of black liquor and white liguor ~:an be oxidized to produce alkali metal polysulide, while the mixed li~uor is in ~he presence of ~he wDod to be pulpedO Operating in thi~ manner, the relativcly unstable poly3ulfide act~ upon the wsod in~ediately after ~ormationO TllU5, nol: only ara there i~proved pulping yields, but, in addition, a lower level o~
sulfidity can be e~ployed. q~hi9 lower sulfidity r~sults in significantly dec~reasqd amount~ of sulfur loss, w~ich significant~
ly reduces pollution problems.
Brief Description o~ ~he Draw ng In the ac~companying drawing, ths pulp yields obtained according to t~e pre~ent process are compared with those obtainQd according to a ~tandard ~aft process, at varying, co~parable lignin levels.
D~tail~d De~cri tion of ~he Inv~ntion _ _ p _ ~ n accordance wi~h the present invention, wood chips are impregna~ed wi~h a miacture of white liquor and bla~:k lisluo~., Air, or anot~er oxygen bearing gas, i5 int~oduced into the li~uor in the digester, du:ring the impregnationr in ordsr to oxidize the alkali metal sulfi~e p~esent in the mixed liquors to alkali ~etal polysulfide. In th~ oxidation o~ alkali metal sulfide, not only is alkali metal polysulfide prod7lced, but~ additionally, sulfur, sulfites, and thios~lfate~ are produced. ~he ~ulfur coD~bines with a sulfid~ to yield t~e desired polysul~ide~ ~w-~0 ever, ~ecau~e o~ the instability o~ the polysulfid~J it ~ayreact with the sulfite to produce thiosulate. As the thio-sulfate is not effective in pulping, the result of thi~ reaction i~ los~ of e~f~ctiv~ pulping p~wer, ~o tha~ higher ~ulfur levels mu~ be maintained in.order to provide a given yield lev~l.
When thege higher sulfur levels are maintained, there is an increased loss of sulfur products to the atmosphere, m2aning increased pollution.
Aocording to t~e present process, w~ere th0 mixture of ~lack liquor and white liquor is oxi~ized, in the presens~e ~ o~
of wood to be pulped, the polysulide generated iæ i~mediately available to react with t~e wood. For thi~ reason, the poly-~ulfide is effectively employed before any ~ubstantial amount react~ with the sulfite, resulting in the ineffectual thio~ul-fate and loS5 of the yield improvement provided by the poly-sulfide~ ~hus, a given yield level can be obtained with a lower total sul~ur content.
~ he alkali me~al sul~ide employed i~, preferably, sodium sul~ide. This is the preferred material becau~e o~ i~5 signiicantly lowar cost and easier recovery.
In accordance with the present inven~ion, the sulfidity level of the mixed liquor need not be above 30%. ~he mixed liquor generally contains be~w~en 30 and 75% white liquor, with the remainder black liguor~ Pre~erably, betw~en 50 and 60%
white liquor is employed~ The black liguor which i9 used i3 the spent liquor from ~he dige~ting step, as is ~ormally obtained with Kraft processing.
It wa~ praviou~ly no~ed tha~ the afoæemen~ioned Landmark paten~ aid disclose an oxidation o~ a black liquor-white liquor mixture to form a polysulfide for pulping~ ~owever, as also indicated, the polysulfide is unstable and t~us react~ with the ~ulfit~ to form thiosulate, before the polysulfide can effectively b~ used. The prese~t pro~ess avoids this prc~blem, by carrying out the oxidation in the pres3nce o the wood chip, thus allowing for imrnediate utilization o~ the poly~ulfide and Fninimizing the formation of the in~ffectual thiosulfate.
~ s also indicated, the aforem~ntior~ed ~omtar Limi~ed pat~nt teaches the oxidation of white liquor, but thi~ oxidation i5 not carried out in the pres~nce c~f the wood chips. ~!he ~8C~4~
oxidation, according to Domtar, i~ carried out in a ressel 3eparate from tha chips, so that the inunediate reac~ion of the polysulfide with the w~od i~ not pos3ible and, therefore, a higher total ~ulur level i~ re~auired in order ~o obtain a given yield level, some of ths banefits o~ ~he polysulfide being lost.
~!he amount of oxygen bearing gas w~ich is erllployed, according ~o ~he process o$ the pre~ent invention, s~ould be suficient to oxidize a significant guantity o~ the sulfide pre~ent in the mixed liquor to polysulfide. Generally, ~ufficient polysul~id~s 10 is pxoduced tc significa~tly i~slprove the yield~ employing air in an am~unt o fro~ 200 to 2,000 standard cubic feet for each ton of pulp bei~g proces~ed. ~h~ gas being employed in this oxidation can b~ any havillg an oxygen conten~ of from 15 to lQ0%, ~ubstantially the remaind~r of the gas t~eam being made up o che~ica~ly inactive gases.
During impregnation of the wood, the temperature ~hould be maintained below 120C~ and, preerablyO th~ wnod chips are i~pregna~ed wi~h the ~ixed liquor at a tempera~ur~ of abo~t 90C. f~r about 45 min~te~ while maintaining the flow of the oxygen bearing gas. The ~low o~ oxygen bearing ga~ i~
th~ terminated and the tamperature of the contents are raised ~o n~r~al pulping temperatures of about 160 to 175C. in order to compl~te th~ pulping stage.
A primary advantage of the present p~ocess is that the formation of. polysulfide, with incr~a~ed yields~ can be carried ~u~ empl~ying pulping ~olu~ion having ~u~fidity levels no greate~ than 30%. Thu~, the white liquor employed con~ains between 5 and 60 grams per liter o~ sulfur, in all o~ its com-p~und and elemsntal forms. Preferably, the amount of sulfur ;~.
- 4 - ~
,,~ , ... . ..
contained in the whi~e liquor i~ be~ween 10 and 30 grams per liter~ e amoun~ of alkali contained in the pulping solu~ion i5 not critical, but should range from 15 to 400 grams per liter, as l~a20. More E~referably, the total alkali c~onten~ is from 70 to 120 gramsl per liter. The alkali i9 ~3nerally derived from the group consisting o:E ~odium hydroxide, sodium carbonate, and sodium ~ulf ide .
Paper p~oduced accordi~g to the proc:ess of tha pr~sen învention, compar~d with paper produced by the standard Kra~t process at eyuiv~lent Kappa numbsr~, doe.~ ~ot show any di:~erence with regard to bur~t or teæ strength. Th~re is a sligh~
increase in th~ luminous reflectance o~ tllese paper produat, ~rh0n ~:ompareld with lthe ~ra~t process using a black liquor re-cyde .
The irnprovements accomE~lished by the process o ~he pre~nt invention will be described in greater detail in th~3 following exam~ s. q~hese examples ~hould be con~idered as illu~trative onlyO and not as limiting in any way tha ~ull ~cope of the invention as ~overed in the append0d claims.
Exa~E~e 1 Two 20 lb. ch~rges (ov~n dry weigllt) of the sam~
batch of slash pine w~r~3 pulp~d according to this e~can~ple.
Ona ~3f t~e chargeY wa~ pulped according to a s~a~dard Kraft process, with black liguor recycle, ~ile the other batch wa~
pulped according to the present pro~ess where tlle mixed li~auor contained 55% white liquorl. In each case, the ~c)dium sulide level of the whi~e~ liquor wa~ 40 grams pe3r liter. A guantity of 5 cubic: feet of air per hour wa.~ introduced into the wood chip-mixed pulping liguor of th~ charge p~lped a~cording to -- S --the present invention during the 90 minute impregnation,~ while ~ !
maintaining ~he li~auor at a terap~ratur~ of 90C~ The dige~tion~
were oltherwise carried out under ~e ~ame condil~ion~ including ::
heating to 173Co~ after impregnation, over a perio~ of 30 minutes, and then holding the ~atarial at 173Co for 90 minute~.
T~e ~ctive alkali content of l:he wl~ite liguor er~ployed wa~ about 106 grams E~er liter, exE~re~sed as P~a20. ~rhe rç!~ults o~ pulping thes~ two batche:3 according ~o the proces~3es indicat0d ar~ ~hown be low in Tabla I:
q~able I
T~ of PxOcess ~Field ~%) Screerled 5rield (O ~CapE~a ~umber :~
Rraft Process 57.0 45O3 83.2 Oxidation of 5~ . 2 50 . 2 78 . 7 Liquor in the Pre~ence- of Wood Chips As can be seen from ~h~se resul~3, a ~3ignificantly improved yield ia; obtainea employing th~ oxidation p,roces~ of the p~e~ent invention, over a normal t~a~t proce-~, and thi~ increased yield i~; ob~ain2d wi~hou~ an increa~Q in ~he sulfur level of the liquor.
l~hus, ~he increasad yield~ come with no inereas~ in pollution.
Exampl~ 2 ~ rhe proce~ oiE ~he present invention was repeated, employing ~he same ~a~erials and conditions a~ noted in Exa~pl~3 :
1, but with certain proce~s variakion~. In particular, the mixed liglaor contain~ 60% white liquor and ~he air was introduced at a rate of 3 cubi~ fee~ per hour for a 45 minu~e impregna~ion period at 80C. Following dige~;tion, a yi~3ld o 57.,3% and a ~creen~d yield o 51.5% wexe realized at a Kappa number of 72.8. ~:
Thu~, the economic advan~age of ~he process of the pre~an~
invention, this advantage being obtained without an increase in pollution level, is agaln demonstrated.
The figure shows yield increases obtained employing the process of the present invention, when compared with standard Kraft pulping. As can be seen rom the figure, at Kappa numbers of ~rom 50 to 80, yield increases of ~rom 1 to 3% are obtained employing the process o~ the present invention. These yield increases are obtained without an increase in pollution level.
Mhile slash pine has been indicated as the wood pulped in the specific examples, various other wood species may also be used. In general, any wood pulpable according to a Kraft process can be pulped accord~bo the present invention, with improved yields~
The various streams in the pulping process according to the present invention are recoverecl by the same methods normally em~loyed in Kraft processing~ The sulfide level of the black liquor leaving the digester according to the present invention is no higher than that found in the blac]c liquor from a standard ~raft process. Thus, the present process provides a significant economic advantage over a standard ~raft process in that, while essentially the same equipment and processing are employed, increased yields are obtained.
The white liquor may be added to the wood to produce a white liquor-wood mixture in which the wood is impregnated with the white liquor, the black liquor then being added to the white liquor-wood mixture with the result that the wood is inevitably impregnated also with the black liquox. Thus, the impregnation of the wood is still with the white liquor and black liquor.
~8~40~3 The i.nvention has been described in detail with particular reference made to various prefexred embodiments thereof, but it will be understood that variations and modi-fications can be effected within the spirit and scope of the invention as described hereinabove and as defined in the appended claims.
~3 ~- - 8 -
A ~urther proc~ss for forming polysul~ide pulping li~uors is described in Per .~ndreas Landmark U.S0 Patent No 3,216,887, granted ~iovember 9, 1965, where t~e polysul~idll3 i3 form~3d by t~le air olcidatioll of sodium sulfide in a mixture of white liquor and black li~uor. Sub~e~auent to ~ormatior~ of the polysulfide, the liquor contacts the w~od to be pulpedO Becau5e of this me~hod of operation, a sul~idity level of at least 40%
is neces~ary in order to obtain any significant yield illcrease and, b~c:ause o~ this, there are sigi~iicant sulfur lo~es. The sulfur losses provide a signi~ ant level oP pollution.
White liguor, recirculated ~rom wood impragnation, is treated so as to form polysul~ida according to Canadian patent No. 815, 432, i3sued on June 17, 196g to Domtar Limited. EiEic-i~cy lev~ls operating in accordance with thi~ patent are relati-re-ly low.
In accordance with the present invention, it ha~ been de~ermined that a mix~ure of black liquor and white liguor ~:an be oxidized to produce alkali metal polysulide, while the mixed li~uor is in ~he presence of ~he wDod to be pulpedO Operating in thi~ manner, the relativcly unstable poly3ulfide act~ upon the wsod in~ediately after ~ormationO TllU5, nol: only ara there i~proved pulping yields, but, in addition, a lower level o~
sulfidity can be e~ployed. q~hi9 lower sulfidity r~sults in significantly dec~reasqd amount~ of sulfur loss, w~ich significant~
ly reduces pollution problems.
Brief Description o~ ~he Draw ng In the ac~companying drawing, ths pulp yields obtained according to t~e pre~ent process are compared with those obtainQd according to a ~tandard ~aft process, at varying, co~parable lignin levels.
D~tail~d De~cri tion of ~he Inv~ntion _ _ p _ ~ n accordance wi~h the present invention, wood chips are impregna~ed wi~h a miacture of white liquor and bla~:k lisluo~., Air, or anot~er oxygen bearing gas, i5 int~oduced into the li~uor in the digester, du:ring the impregnationr in ordsr to oxidize the alkali metal sulfi~e p~esent in the mixed liquors to alkali ~etal polysulfide. In th~ oxidation o~ alkali metal sulfide, not only is alkali metal polysulfide prod7lced, but~ additionally, sulfur, sulfites, and thios~lfate~ are produced. ~he ~ulfur coD~bines with a sulfid~ to yield t~e desired polysul~ide~ ~w-~0 ever, ~ecau~e o~ the instability o~ the polysulfid~J it ~ayreact with the sulfite to produce thiosulate. As the thio-sulfate is not effective in pulping, the result of thi~ reaction i~ los~ of e~f~ctiv~ pulping p~wer, ~o tha~ higher ~ulfur levels mu~ be maintained in.order to provide a given yield lev~l.
When thege higher sulfur levels are maintained, there is an increased loss of sulfur products to the atmosphere, m2aning increased pollution.
Aocording to t~e present process, w~ere th0 mixture of ~lack liquor and white liquor is oxi~ized, in the presens~e ~ o~
of wood to be pulped, the polysulide generated iæ i~mediately available to react with t~e wood. For thi~ reason, the poly-~ulfide is effectively employed before any ~ubstantial amount react~ with the sulfite, resulting in the ineffectual thio~ul-fate and loS5 of the yield improvement provided by the poly-sulfide~ ~hus, a given yield level can be obtained with a lower total sul~ur content.
~ he alkali me~al sul~ide employed i~, preferably, sodium sul~ide. This is the preferred material becau~e o~ i~5 signiicantly lowar cost and easier recovery.
In accordance with the present inven~ion, the sulfidity level of the mixed liquor need not be above 30%. ~he mixed liquor generally contains be~w~en 30 and 75% white liquor, with the remainder black liguor~ Pre~erably, betw~en 50 and 60%
white liquor is employed~ The black liguor which i9 used i3 the spent liquor from ~he dige~ting step, as is ~ormally obtained with Kraft processing.
It wa~ praviou~ly no~ed tha~ the afoæemen~ioned Landmark paten~ aid disclose an oxidation o~ a black liquor-white liquor mixture to form a polysulfide for pulping~ ~owever, as also indicated, the polysulfide is unstable and t~us react~ with the ~ulfit~ to form thiosulate, before the polysulfide can effectively b~ used. The prese~t pro~ess avoids this prc~blem, by carrying out the oxidation in the pres3nce o the wood chip, thus allowing for imrnediate utilization o~ the poly~ulfide and Fninimizing the formation of the in~ffectual thiosulfate.
~ s also indicated, the aforem~ntior~ed ~omtar Limi~ed pat~nt teaches the oxidation of white liquor, but thi~ oxidation i5 not carried out in the pres~nce c~f the wood chips. ~!he ~8C~4~
oxidation, according to Domtar, i~ carried out in a ressel 3eparate from tha chips, so that the inunediate reac~ion of the polysulfide with the w~od i~ not pos3ible and, therefore, a higher total ~ulur level i~ re~auired in order ~o obtain a given yield level, some of ths banefits o~ ~he polysulfide being lost.
~!he amount of oxygen bearing gas w~ich is erllployed, according ~o ~he process o$ the pre~ent invention, s~ould be suficient to oxidize a significant guantity o~ the sulfide pre~ent in the mixed liquor to polysulfide. Generally, ~ufficient polysul~id~s 10 is pxoduced tc significa~tly i~slprove the yield~ employing air in an am~unt o fro~ 200 to 2,000 standard cubic feet for each ton of pulp bei~g proces~ed. ~h~ gas being employed in this oxidation can b~ any havillg an oxygen conten~ of from 15 to lQ0%, ~ubstantially the remaind~r of the gas t~eam being made up o che~ica~ly inactive gases.
During impregnation of the wood, the temperature ~hould be maintained below 120C~ and, preerablyO th~ wnod chips are i~pregna~ed wi~h the ~ixed liquor at a tempera~ur~ of abo~t 90C. f~r about 45 min~te~ while maintaining the flow of the oxygen bearing gas. The ~low o~ oxygen bearing ga~ i~
th~ terminated and the tamperature of the contents are raised ~o n~r~al pulping temperatures of about 160 to 175C. in order to compl~te th~ pulping stage.
A primary advantage of the present p~ocess is that the formation of. polysulfide, with incr~a~ed yields~ can be carried ~u~ empl~ying pulping ~olu~ion having ~u~fidity levels no greate~ than 30%. Thu~, the white liquor employed con~ains between 5 and 60 grams per liter o~ sulfur, in all o~ its com-p~und and elemsntal forms. Preferably, the amount of sulfur ;~.
- 4 - ~
,,~ , ... . ..
contained in the whi~e liquor i~ be~ween 10 and 30 grams per liter~ e amoun~ of alkali contained in the pulping solu~ion i5 not critical, but should range from 15 to 400 grams per liter, as l~a20. More E~referably, the total alkali c~onten~ is from 70 to 120 gramsl per liter. The alkali i9 ~3nerally derived from the group consisting o:E ~odium hydroxide, sodium carbonate, and sodium ~ulf ide .
Paper p~oduced accordi~g to the proc:ess of tha pr~sen învention, compar~d with paper produced by the standard Kra~t process at eyuiv~lent Kappa numbsr~, doe.~ ~ot show any di:~erence with regard to bur~t or teæ strength. Th~re is a sligh~
increase in th~ luminous reflectance o~ tllese paper produat, ~rh0n ~:ompareld with lthe ~ra~t process using a black liquor re-cyde .
The irnprovements accomE~lished by the process o ~he pre~nt invention will be described in greater detail in th~3 following exam~ s. q~hese examples ~hould be con~idered as illu~trative onlyO and not as limiting in any way tha ~ull ~cope of the invention as ~overed in the append0d claims.
Exa~E~e 1 Two 20 lb. ch~rges (ov~n dry weigllt) of the sam~
batch of slash pine w~r~3 pulp~d according to this e~can~ple.
Ona ~3f t~e chargeY wa~ pulped according to a s~a~dard Kraft process, with black liguor recycle, ~ile the other batch wa~
pulped according to the present pro~ess where tlle mixed li~auor contained 55% white liquorl. In each case, the ~c)dium sulide level of the whi~e~ liquor wa~ 40 grams pe3r liter. A guantity of 5 cubic: feet of air per hour wa.~ introduced into the wood chip-mixed pulping liguor of th~ charge p~lped a~cording to -- S --the present invention during the 90 minute impregnation,~ while ~ !
maintaining ~he li~auor at a terap~ratur~ of 90C~ The dige~tion~
were oltherwise carried out under ~e ~ame condil~ion~ including ::
heating to 173Co~ after impregnation, over a perio~ of 30 minutes, and then holding the ~atarial at 173Co for 90 minute~.
T~e ~ctive alkali content of l:he wl~ite liguor er~ployed wa~ about 106 grams E~er liter, exE~re~sed as P~a20. ~rhe rç!~ults o~ pulping thes~ two batche:3 according ~o the proces~3es indicat0d ar~ ~hown be low in Tabla I:
q~able I
T~ of PxOcess ~Field ~%) Screerled 5rield (O ~CapE~a ~umber :~
Rraft Process 57.0 45O3 83.2 Oxidation of 5~ . 2 50 . 2 78 . 7 Liquor in the Pre~ence- of Wood Chips As can be seen from ~h~se resul~3, a ~3ignificantly improved yield ia; obtainea employing th~ oxidation p,roces~ of the p~e~ent invention, over a normal t~a~t proce-~, and thi~ increased yield i~; ob~ain2d wi~hou~ an increa~Q in ~he sulfur level of the liquor.
l~hus, ~he increasad yield~ come with no inereas~ in pollution.
Exampl~ 2 ~ rhe proce~ oiE ~he present invention was repeated, employing ~he same ~a~erials and conditions a~ noted in Exa~pl~3 :
1, but with certain proce~s variakion~. In particular, the mixed liglaor contain~ 60% white liquor and ~he air was introduced at a rate of 3 cubi~ fee~ per hour for a 45 minu~e impregna~ion period at 80C. Following dige~;tion, a yi~3ld o 57.,3% and a ~creen~d yield o 51.5% wexe realized at a Kappa number of 72.8. ~:
Thu~, the economic advan~age of ~he process of the pre~an~
invention, this advantage being obtained without an increase in pollution level, is agaln demonstrated.
The figure shows yield increases obtained employing the process of the present invention, when compared with standard Kraft pulping. As can be seen rom the figure, at Kappa numbers of ~rom 50 to 80, yield increases of ~rom 1 to 3% are obtained employing the process o~ the present invention. These yield increases are obtained without an increase in pollution level.
Mhile slash pine has been indicated as the wood pulped in the specific examples, various other wood species may also be used. In general, any wood pulpable according to a Kraft process can be pulped accord~bo the present invention, with improved yields~
The various streams in the pulping process according to the present invention are recoverecl by the same methods normally em~loyed in Kraft processing~ The sulfide level of the black liquor leaving the digester according to the present invention is no higher than that found in the blac]c liquor from a standard ~raft process. Thus, the present process provides a significant economic advantage over a standard ~raft process in that, while essentially the same equipment and processing are employed, increased yields are obtained.
The white liquor may be added to the wood to produce a white liquor-wood mixture in which the wood is impregnated with the white liquor, the black liquor then being added to the white liquor-wood mixture with the result that the wood is inevitably impregnated also with the black liquox. Thus, the impregnation of the wood is still with the white liquor and black liquor.
~8~40~3 The i.nvention has been described in detail with particular reference made to various prefexred embodiments thereof, but it will be understood that variations and modi-fications can be effected within the spirit and scope of the invention as described hereinabove and as defined in the appended claims.
~3 ~- - 8 -
Claims (8)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A process for the ppolysulfide pulping of wood comprising:
(a) impregnating the wood to be pulped by adding to the wood a quantity of white liquor containing sulfide with 5 to 60 grams per liter total sulfur to produce a white liquor-wood mixture, and adding to said white liquor-wood mixture a quantity of black liquor to produce a mixture of white liquor, black liquor and wood with the wood being impregnated by the white liquor and black liquor;
(b) introducing an oxygen bearing gas to said mixture of white liquor, black liquor and wood during the impregnation of the wood by the white liquor and black liquor for about 45 to 90 minutes at a temperature below 120°C, so as to oxidize the sulfide contained in the white liquor - black liquor mixture to polysulfide, while the mixture is in contact with the wood to be pulped; and (c) digesting the wood in said oxidized white liquor -black liquor mixture at a temperature of about 160 to 175°C.
(a) impregnating the wood to be pulped by adding to the wood a quantity of white liquor containing sulfide with 5 to 60 grams per liter total sulfur to produce a white liquor-wood mixture, and adding to said white liquor-wood mixture a quantity of black liquor to produce a mixture of white liquor, black liquor and wood with the wood being impregnated by the white liquor and black liquor;
(b) introducing an oxygen bearing gas to said mixture of white liquor, black liquor and wood during the impregnation of the wood by the white liquor and black liquor for about 45 to 90 minutes at a temperature below 120°C, so as to oxidize the sulfide contained in the white liquor - black liquor mixture to polysulfide, while the mixture is in contact with the wood to be pulped; and (c) digesting the wood in said oxidized white liquor -black liquor mixture at a temperature of about 160 to 175°C.
2. The process of claim 1 wherein said oxygen bearing gas contains from 15 to 100% oxygen.
3. The process of claim 1 wherein the white liquor consti-tues from 30 to 75% of the white 1 liquor-black liquor mixture.
4. The process of claim 3 wherein the white liquor consti-tues from about 50 to 60% of the white liquor-black liquor mixture.
5. A process for pulping wood employing polysulfide as the major pulping agent comprising:
(a) impregnating the wood to be pulped with a mixture of white liquor and black liquor, the white liquor containing sulphide with 5 to 60 grams per liter total sulfur;
(b) introducing an oxygen bearing gas into said white liquor-black liquor-wood mixture, during the impregnation of the wood, for about 45 to 90 minutes at a temperature below 120 C., so as to oxidize the sulfide values present in the mixture to polysulfide;
(c) digesting said wood in said oxidized white liquor-black liquor mixture at a temperature of about 160 to 175 C.
(a) impregnating the wood to be pulped with a mixture of white liquor and black liquor, the white liquor containing sulphide with 5 to 60 grams per liter total sulfur;
(b) introducing an oxygen bearing gas into said white liquor-black liquor-wood mixture, during the impregnation of the wood, for about 45 to 90 minutes at a temperature below 120 C., so as to oxidize the sulfide values present in the mixture to polysulfide;
(c) digesting said wood in said oxidized white liquor-black liquor mixture at a temperature of about 160 to 175 C.
6. The process of claim 5 wherein the white liquor constitutes from 30 to 75% of the white liquor-black liquor mixture.
7. The process of claim 6 wherein the white liquor constitutes from about 50 to 60% of the white liquor-black liquor mixture.
8. Alkaline pulping process, in which wood is subjected to heat and pressure with an alkaline cooking liquor, and in which the hemicelluloses of the wood are stabilized against the alkali by means of polysulphides, characterized by the fact that the wood is pretreated with a mixture of white liquor and black liquor containing alkali metal sulphide at 90-120°C which, while the mixture of white liquor and black liquor is in contact with the wood, is oxidized with an oxygen-containing gas and thereafter brought to cooking temperature.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US13032071A | 1971-04-01 | 1971-04-01 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1080408A true CA1080408A (en) | 1980-07-01 |
Family
ID=22444133
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA136,634A Expired CA1080408A (en) | 1971-04-01 | 1972-03-27 | Oxidation of pulping liquor |
Country Status (5)
| Country | Link |
|---|---|
| US (1) | US3723242A (en) |
| JP (1) | JPS5027082B1 (en) |
| CA (1) | CA1080408A (en) |
| FI (1) | FI55362C (en) |
| SE (1) | SE381691B (en) |
Families Citing this family (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3874991A (en) * | 1968-08-23 | 1975-04-01 | Westvaco Corp | Polysulfide impregnation of lignocellulosic materials in a continuous digester |
| AU473185B2 (en) * | 1973-07-25 | 1976-06-17 | Mooch Domsjo Aktiebolag | A method for producing oxidized white liquor |
| US4098639A (en) * | 1975-06-17 | 1978-07-04 | Mo Och Domsjo Aktiebolag | Process for reducing the requirement of fresh chemicals without increasing emissions in the pulping of cellulosic material |
| SE8106203L (en) * | 1981-10-21 | 1983-04-22 | Nils V Mannbro | SET FOR POLYSULPHIDE TREATMENT OF LIGNOCELLULOSAMATERIAL FOR ALKALIC PREPARATION |
| JPS5986131U (en) * | 1982-11-30 | 1984-06-11 | 昭和アルミニウム株式会社 | portable container |
| JPS62247812A (en) * | 1986-04-18 | 1987-10-28 | Chiyoda Chem Eng & Constr Co Ltd | Pressure-type upward flow deep bed filtration method and filter used in said method |
| SE468053B (en) * | 1988-12-20 | 1992-10-26 | Kamyr Ab | SET ON CONTINUOUS DISSOLUTION COOKING OF CELLULOSIC FIBER MATERIAL |
| US5192396A (en) * | 1988-12-20 | 1993-03-09 | Kamyr Ab | Process for the continuous digestion of cellulosic fiber material |
-
1971
- 1971-04-01 US US00130320A patent/US3723242A/en not_active Expired - Lifetime
-
1972
- 1972-03-27 CA CA136,634A patent/CA1080408A/en not_active Expired
- 1972-03-28 SE SE7203993A patent/SE381691B/en unknown
- 1972-03-29 FI FI885/72A patent/FI55362C/en active
- 1972-03-31 JP JP47031847A patent/JPS5027082B1/ja active Pending
Also Published As
| Publication number | Publication date |
|---|---|
| JPS5027082B1 (en) | 1975-09-05 |
| US3723242A (en) | 1973-03-27 |
| SE381691B (en) | 1975-12-15 |
| FI55362B (en) | 1979-03-30 |
| FI55362C (en) | 1979-07-10 |
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