CA2063591C - Environmentally improved process for bleaching lignocellulosic materials - Google Patents

Abstract

A process for delignifying and bleaching a lignocellulosic pulp without the use of elemental chlorine by partially delignifying the pulp to a K No. of about 10 or less and a viscosity of greater than about 13 cps; and further delignifying the partially delignified pulp with an effective amount of ozone for a sufficient time to obtain a substantially delignified pulp having a K No. of about 5 or less, a viscosity of greater than about 10, and a GE rightness of at least about 50 %. The substantially delignified pulp may be brightened by the addition of a bleaching agent such as chlorine dioxide or a peroxide to obtain a final product having a GE brightness of at least about 65 %, preferably abovt 70 % to as high as 90 %. Because of the absence of a elemental chlorine in this sequence, filtrate from all stages but the chlorine dioxide stage (if used) can be recovered without sewering. Major environmental improvements are thus achieved.

Description

2 0 6 3 ~ 91 PCT/US90/02823 ENVIRONMENTALLY IMPROVED PROCESS
FOR BLEACHING LIGNOCELLULOSIC MATERIALS

Field o~ th~ Invention This invention relates to a novel, _nvironmentally acceptable process ~or delig~i~ying and bleaching lignocellulosic pulp which does not reguire the use of ele~ental chlorine and which produces a pulp of accep~able strength. Use of this process also reduces the amount of 10 environme~tal pollutants.

Backgrou~d of the Invention Wood is comprised of two main components - a ~ibrsus 15 carbohydrate, i.e., c~llulosic portion, and a non-fibrous component. The polymeric ch~inc forming the ~ibrous cellulose portion of the wood are aligned with on~ another and form strong associated bonds with adjac~nt rh~;nc. The non-fibrous portion of the wood comprises a three-~; ?nRional polymeric 20 material ~ormed primarily of pheny:lpropane units, known as lignin. Part of ~he lignin is between the cellulosic fibers, bonding them into a solid ~a6s, although a substantial portion o~ the lignin is also distributed within the fibers themselves.
For use in paper ~aking proce~se~, wood ~U5~ first be 25 reduced to pulp. Pulp may b~ defined as wood fibers capable of . being slurried or suspended and then deposi~.ed upon a screen to form a sheet ~ 3 01 of paper . The methods employed to accomplish the pulping step usually involve eith~r physical or ch~mical treat~nent of the wood, or a combination of these two 30 treatments, to alter the wood's chemical form and to impart desired properties to the resultant product. There are thus two main types of pulping technigues ~ i . e ., m~chanical pulping and chemical pulping. In mechanical pulping, the wood is physically separated into individual fibers. In che~ical

3~ pulping, the wood chips are digested with chemical solutions to 2~i3~

4~ 2 PCS/US90/02823 solubilize a portion of the lignin and thus permit its removal.
The commonly utilized chemical pulping processes are broadly classified as: (l) the soda process, (2) the sulfite process, and (3) the Kraft proeess, with the latter process being most

5 commonly used and being capabl of a variety of well-known ~odifications as described below.
The soda proce~s is well known in the art. It employs sodium hydroxide (NaOH) as the activs reagent to break d~wn the lignin and to ~ssi~t in its removal. The sulfite 10 process is also well known in the art (see, e~g., Handbook for Pulp ~ Paper Technologists - Chapter 6: Sulfite Pulping (TAPPI, U.S.A.).
The Kraft process together with its numerous variations i~ the principle chemical process utilized in paper 1~ manufacturing. The ba~ic Kraft process, as described in the Handbook For Pulp and Paper TechnQlogists - Chapter 7: Xraft Pulping (TAPPI, U.S.A.), involvs~ digesting the wood chips in an aqueou~ solution of sodium hydroxide ~NaOH) and sodium sul~ide (Na2S). This process is highly effective in the ~a pulping of even difficult woods such as southern softwoods, as well as the other more readily pulped species of wood such as northern ha~ ods and s~twoods. The Rraft process likewise generally produces a relatively high-~trength pulp since its use results in a d1 ; ni shed attack on the cellulose component 25 o~ the wood.
The modified Kraft techniques can re~ult in even less degradation in the polymeric structure of the cellulosic fibers during pulping and therefore the strength lo~s in the resultant paper product is di ;nished as compared to that occurring with 30 the standard Kraft process. One modified Kra~t pulping process is known as "extended delignification'l, which is a broad term used in the art to encompass a variety of modified Xraft techniques, such as adding the pulping chemicals in a specific defined sequence, or at different locations within the digester 35 apparatus, or at different time periods, or with a removal and WO91/18145 - 2 0 ~ 1 PCT/US90/02823 reinjection o~ cooling liquors in a prescribed sequence, so as to more effectively remove a greater amount of lignin while r~ducing the severity o~ the pulping li~uor's chemical attack on the cellulosic fibers. Another modification of the Kraft process is the Kraft-AQ proces , wherein a small amount of anthraquinone i6 added to the Rra~t pulping liquor to accelerate deliynification while limiting the attack upon the cellulosic fibers which comprise the wood.
A variety of additional ~x*~n~e~ delignification techniques ar~ known in the art and include Kamyr Modified Continuous C~Qk;~g (MCC) as described by V.A. Kortelainen and E.A~ Backlund in TAPPI, vol. 68 (ll~, 70 (19853: Beloit Rapid Displacement Heating (RDH) as reported by R. S. Grant in TAPPI, vol. 66 (3), ~20 (1983); and Sunds Cold Blow Cooking as 15 re~orted by B. Pettersson and B. Ernerfeldt in Pulp and Paper, vol. 59 (ll), 90 (19~5).
Digestion o~ the wood by a Kraft or modified Kraft process results in the formation o~ ~ dark colored slurry of cellulose fibers known as "brown&tock". Th~ dark color of ~he 20 brownstock is attributable to the i'ack that not all of the lignin has been removed during dige~stion and has been che~ically modified in pulping to i-~oro chromophoric groups.
Thus, in order to lighten the color o~ the brownstock pulp, i.e., to make it suitable for u~e a5 printing and writing and 25 other white paper applicati~ns, it i6 necessAry to continue the r~moval of ~he r~aining lignin by the addition of delignifying material and by chemically converting any residual lignin into colorless compDunds by a process known as !'bleachin~" or ~brightening".
Prior to bleaching the pulp, however, the digested material is conventionally transferred to a separate blow tank after the chemical treatments involved in the pulping process are complsted. Within the blow tank, the pressure developed during the initial c,emical treatment of the lignocellulosic 3~ material is rsliev~d and the pulp ma~erial is separated into a 2 ~
WO 9~/18145 4 - P~/US9U/02823 f ibrous mass . The re~ulting f ibrous mass is then sub; ected to a series of washing steps to re3nove the combination of any residual chemicals and the soluble materials (such as the lignin) which were separated ~rom the fibrous ma~erials in the 5 pulping process. Frequently, the pulp al50 undergoes one or more screening step~ designed to separate out the larger portion~ of undefibered wood for special proces~;ing ~recooking, ?~l-~nical grinding, etc. ) .
The re~;idue olbtained ~rom the wa~hing proces6, 10 com~only ref~arred to as black liquor, is cs:llected, conc~ntrated, and then inciner~ted in an environm~antally safe manner in a recovery boiler. The technique for the collection, concentratic3rl and burning of the black liquor is conventional and is well known in the ~rt.
The d~lignification and bleaching processes are conducted on the washed f ibrous mass in a series of steps, using selected c:ombinations of chemical reactants. In the prior art, various colabinations of chemical treatment6 have been ~uggested. Furthermore, individual txeat~ent steps have ;!0 been rearranged in an Al -~ t; limit:Less number of combinations and permutatiorls. Th~refore, in order to simplify the explanation of the various bleaching processe~ and systems, the use of letter codes i6 conven~iona:Lly employed in combination to describe the particular chemic:a:l reactants @mployed and the 2~; sequence of the ~tep~ o~ the proce~s.
The letter code~ which will b~ used hereafter, wherP
appropriate, are as ~O11QWS:

C = Chlorination - Reaction with elemental chlorine in acidic medium.
, 30 E = Alkaline - Dissolution of reaction products Extraction with NaOH.
E = Oxidative - Dissolution of reaction produsts ~ Alkaline with NaOH and oxygen.
Extraction 2 0 6 ~ ~ 9 .1 D = Chlorine - Reaction with ClO in aci~ic Dioxide medium. 2 P = Peroxide - ~eaction with peroxides in alkaline ~ediu~.
o = Oxygen - Reaction with ~lemen~al oxygen in alkaline medium.
O - ~odi~ied - Uniform alkali treatment of low O~ygen to medium con~istency pulp ~ollowed by reaction o~ high consistency pulp with oxygen.
Z = Ozon~ - Reaction with ozone.
Zm = Mo~ified - Uniform reaction with ozone.
Ozone C/D - Admixtures of chlorine and chlorine dioxi~e.
H = Hypochlorite - Reaction with hypochlorite in an alk~lin~ solution.

0~ and Z~ are modified proce~se~ according to the pre~ent invention and are described further in the Detailed 20 Descripkion of the Invention.
It has been conventiunal for ~any years to deligni y and bleach wood pulp by using elem~sntal chlorine. Exemplifying the bleaching of lignocellulosic pulps are the processes disclosed in, for example, U.S. Pat. Nos. 1,957,937 to Campbell 25 st al., 2,g75,l69 to Cranford et al. and, 3,462,344 to Rindron et al.l and Handbook For Pulp and Pap~r Technologists - Chapter ll- Bleaching (ll.3) (TAPPI, USA).
How@Yer ~ although elemental chlorine has proven to be an ~fective bleachins agent, it i~ dif~icult to handle and 3~ potentially hazardous to both mill person~el and equipment.
For example, the effluents ~rom chlorine bleaching processe~
contain large r ~~ S of chlorides produced as the by-product of these processes. These chlorides readily corrode processing equipment, thus requiring use of c05tly materials in the 35 con~truction of ~uch mills. Further, the build-up of chlorides 2 ~

6 PCT/US90/02~23 within the mill precludes recycling th~ washer filtrate after a chlorination s~age in a closed system operation without employing recovery Rystems requiring extensive, and therefore exp~nsive, ~odifications. In addition, conc~rn about the 5 potential environmental effec~s of chlorinated organics in effluents, which the U.S. Environ~ental Protection Agency believes to be toxic to h -n~ and animals, has caused significant changes in govern~ent reguirements and permits for bleach mills which include standards that may be impos6ible to 10 meet with conventional bleaching or pollution control technology.
To avoid these disadvantages, the paper industry has attempted to reduce or eliminate the us~ of elemental chlorine and chlorine-containing compounds from multi-stage bleaching 15 processes for lignocellulosic pulps. Complicating these efforts is the requirement that high level~ of pulp brightness are required for many of the application~ for which such pulp is to be used.
ln this co~nection, ~fforts have be~n made to develop 20 a bleaching process in which chlorine-containing agents are replaced, for example, by oxygen for th~ purpose of bleaching the pulp. The use of oxygen does permit the recy ling of effluent from this stage ~or recovary a~d does p~rmit a substantial reduction in the A ~nL of elemental chlorine used.
25 A number of process~s for bleaching and delisnifying pulp with oxygen have been proposed, such a~ Richter U.S. Pat. 1,860,432, Grangaard et ~1. U.S. Pats. 2,926,114 and 3,024~158, Gaschke et al. U.S. Pat. 3,274,049, Meylan et al. U.S~ Pat. 3,384,533, Watanabe U.S. Pat. 3,251,730, Rerolle et al. U.S. Pat.
3D 3,423,282, Farley U.S. Pat. 3,661,699, ~ooi U.S~ Pat. 4,6l9,733 and P. Christensen in "Bleaching of Sulphat~ Pulps with Hydrogen Peroxide", Norsk 6kogindustri, 268-27l (1973).
Alkaline pretreatments of pulp prior to oxygen delignification are suggested by U.S. Pat. No. 4,806,203 to Elton.

2 ~
W091/18145 _7_ PCT/US90/02823 The us~ of oxygen, however, is not a çompletely satis~actory 501ution ~n ~he probleDs encountered with elemental chlorin~. Oxygen is not a~ selective a delignification agant a~ elemental chlorine, and the R No. of 5 the pulp, u~ing conventional o~ygen delignification methods, can be reduced only a li~ited amount until there i~ a disproportionate, i.e.; unacceptabl~l attack on the cellulosic fibers. Also, after oxygen delignification, the r~aining lignin has heretofore typically been re~oved by chlorine 10 bleaching method6 to obtain a ~ully-bleached pulp, but using much r~duced ~ S of chlorine. ~owever, even at such reduced chlorine concentrations, th~ corrosive chlorides would soon reach unacceptable concentration levels in a closed cycle operation.
To avoid the use of chlorin~ bleaching agents, the removal of ~uch 1~ 7 i ni ~ lignin with the use of ozone in the bleaching of chemical pulp has previously been attempted.
Although ozone may initially appear to be an ide~l material for bleaching lignoce1 lu106ic ma~erials, tha exceptional oxidative 20 properties of ozone and its r~lative high cost have heretofore li~ited the developm~nt of 6ati6~actory ozone bleaching processes ~or lignocellulosic materials, especially southern softwoods. ozone will readily react with lignin to effectively reduce the X No., but it will al~o, under most conditions, aggres~iYely attack the carbohydrate which compri~es the cellulo~ic fiber~ and ~ubstantially reduce the ~trengkh of the resulting pulp. Ozone, likewi~e, is extremely ~en~itive to proc~ss conditions sueh as pH with respect to its oxidative and chemical stability, and such changes can significantly alter 30 the reactivity of ozo~e with respect to the lignocellulo~ic materials.
Since ~round the turn of the century, when the delignifying capabiliti~s of o~one were first recognized, there has been substantial and continuous work by numerous persons in 35 the field to develop a commercially uitable method using ozone 2~3~1 WO91/18145 8 PC1'/US90/02823 in the bleaching of lignoc~llulosic ~aterials. Furthermore, numerous ar~icles and patents have been issued in this area and there have been reports of attempts ~t conducting ozone bleaching on a non-commercial pilot scale basis. For example, 5 U.S. Pat. 2,~66,~33 to BrAh~n~r et al., describes a bleaching process wher~in ozone is p~ed through a pulp ha~ing a moisture content (adjusted to an oven dry consistency) of between 25 and 55 pPr cent and a pH adjusted to th~ range of 4 to 7.
Other non-chlorine bleach s0quences are dsscribed by S. Xoth~nhPrg~ D. Robinson & Du John~onbaugh, NBleaching o~
Oxygen Pulps with Ozone", Tappi, 182 185 (l975) Z, ZEZ, ZP
and ZPa(Pa peroxyacetic acid~: and N. Soteland, "Bleaching of Chemical Pulps With Oxygen and Ozone", Pulp and Paper Magazine 15 ~~ Canada; Tl53-58 (1974) - OZEP, OP and ZP.
Also, V.S. Pat. No. 4,l96,043 to Singh discloses a multi~stage bleaching process which ~lso ~ttempts to eliminate the use of chlorine c~. ,ounds, and includes examples peci~ically directed to hardwood~. It is w~ll known to those 20 skilled in the art that hardwoods are easier to bleach than mo~t softwoods. This process is charact~rized by from one to three ozo~e bleaching stages and a final treat~ant with alkaline hyd~Gyen peroxide, each stage being separated by an alkalin~ extraction. One such s~uence may be described in the 25 c_ -n shorthand no~enclature of the paper industry as ZEZEP.
In accordance With t~is process, the effluent rrom each treatment stage may be collected and recycled ~or u6e in bleaching operation~, preferably at an earlier ~tage than that from which it was obtained. This patent also provides a so-3D call~d countercurrent e~fluent flow.
Despite all of the research conducted in this area,no commercially feasible process for the manufacture of ozone bleached lignocellulosic pulps, especially southern softwood, has heretofore been disclosed, and numerous failures have been 35 reported.

~ o ~

The present invention provides novel combinations of pulping and bleaching steps which overcome the problems encountered in ths prior art as discussed herein and which e~sentially eliminate the discharge of hlorinated organics and 5 minimizes col~r and BOD releases to produce a high grade bleached pulp in a co~mercially ~ea~ible ~anner.

Summary of the Invention Accordingly, it is a~ sbject o~ the pre~ent invenkion to provide a multi-stage process ~or deli~nifying and bleaching lignocellulosic pulp without the use of elemental chlorine bleaching agents to ~ubstantially r~duce or ~liminate pollution of the enYi~o -nt while optimizing he physical properties of 15 the pulp in an energy ef~icient, cost effective process. The present invention can work on virtually all wood spe~ies, including the diPficult-to-bleach southern U.S. softwoods.
The proc~s~ of the pre~ent invention is composed of ~hre~ or more ~tep~ with a number of possibl~ variations within 20 and betwe~n the step~. The~e ~tep~ can be described a~
follows:
A first step involves delignification of wood chip~
into a lignoc~llulo~ic pulp, using any one of ~everal chemical pulping proGesses, followed by a w~hi~g re~oYal of ~08~ o~ the 25 di~solved organics and cookiny ch~miaal~ for recycle and recovery. U~ually included is a ~creening of th2 pulp ~o remove bundles of fiber~ that have not been separated in pulping. This deligni~ication ~tep i5 con~ucted so tha~, for a southern U.S. ~oftwood, for example, pulp with a K No. in the 30 range of about 20-24 (target of 21), a cupriethylenediamine ("CED") viscosity in the range of about 21-28, and a GE
brightnes~ in the range of about 15-25 is typic~lly obtained.
For southern U.S. hardwood, pulp with a X NoO in the range of about 10-14 (target 12.5) and a CED viscosity of about 21-28 is 35 t~pically obtained.

2~3~3:~
'WO91/18145 -10 PCT/US90/02823 Among, but not limited to, the efPective embodiments of thi~ first st@p are: -a. Kraft pulping using either a continuous or batch dige~tion stag~;
b. Continuous digestion kraft pulping with extended delignification using staged alkali addition and countercurrent final cooking;
c. Batch digestion kraft pulping with extended delignification using rapid liquor displacement 1~ and cold blowing techniques; or d. Rra~t-AQ pulping to achieve exte~ded delignification using either a continuous or batch dig~tion ~tage.
The extended delignificati4n techniques ~;~cu~sed in (b) and (c) abov~, may include, for example, the Xamyr ~CC, the Beloit RDH and Sunds Cold Blow Cooki n~ techniques described in the ba¢~o~l.d portlon of this specification. ~ep~n~ upon the type of lignocellulosic material used, the soda and sulfit~
processe~ mentionRd abov~ may be used.
2~ A secon~ ~tep of the process include~ an oxygen delignifica ion treatment to further remove lignin without an aocompanying sig~i~icant loss in cellulosic ~iber strength.
This would include a w~hing removal of the dissolved organics and alkali for r~cycle an~ recovery. Pulp screening is also 25 performed at ti~es after oxygen delignification.
During the oxygen deligni~ic~tion step, the K No. of the increa~ed consi~tency pulp is decreased by at least about 45% (for 0) to at lea~t about 60% (~or ~m) without signi~icantly damaging the cellulose coMponent of the pulp.
, 30 Also, the ratio of K No. to vi~co ity o~ the pulp is typically decrea~ed by at least 25%. For the ~oftwood pulp de~cribed above using ~m~ a K No. of about 7 to 10 and a viscosity of above about 13 i8 ~3~
WO 91/1814~ PCr/US90/02B23 easily achieved. For hardwQod pulp, a K No. of about 5 ~o 8 and a viscosity ~bove about 13 is achieved after the oxygen daligni~icatiorl ~tep.
~ ong, but not limited to, the possible e~bodiments to this step are:
a. C:onventiorlal oxygen delignific:atisan~ c:omprised of an alkalin~ oxygen treatment o~ the pulp at either low, mediu~a, or high pulp consistency (O);
or b. The preferred t hodi ~ t of an alkaline treatment at low to medium pulp consistenc:y, i . e., less than about 10% iby weight, followed by high pulp consistenc:y oxyyen treatment, i . e, . greater than about 20~ by weight (O~).
For pulp end U8~5 that do not require brightn~sse6 above about 3596 GEB (oflten referred to as ~e~ bleached pulp), it is possible to us~ pulp that ha~ been processed only through steE~ 2 directly in the paper~aking pro e~;50 A third 6tep of tha proc:le~a; incll~de. an acidic, 20 gas~ous ozone ble~ch;n~ treat~ent (Z or Zm~ under defined proc~s6 paraDle~er~ to provide a highly ~elective removal and bleaching of lignin with miniDIal degrad tion of' cellulo e.
Amonq the pro e~s paramet~r~ are c:hel~ting agen~s ~or metal ion control, p~ c:ontrol, pulp particle size control, pulp con~istency, ozone con~ntratic)n and ga~/pulp corltact control.
Prior to treat~ent with ozone, the chelating agent, for exa~ple oxalic acid, di~thyl~netri~ ine pentaacetic acid (nDTPA") or ethylene ~;r- inetetraacetic acid (~'E~TA") may be added to the pulp to substantially bind with ~etal ions contained therein.
30 ~urther, the pH of the pulp is preferably adjusted to a range o~ between about 1-4 prior to the third step. ~his may be accomplished by ~;ng to the pulp a ~uf~icient quantity of an acidic materi~l. Advantageously, the consistency of the pulp is increased to between about 35-45% by weight and the particle 2 ~ 9 ~
WO 9l/t814~ 12- PCI/US90/02823 size o~ the fiber flocs ar~ comminuted to a siz~ o~ about 5 mm or less prior to the ozone deligni~Eication ~;tep. Inclusled is a dissolved organic w~sh i ng stage îor racycle and recovery .
During the ozone step, the pulp is preferably 5 maintained at ambienl: temperature or at least at a pulp temperature of les6 than abs:~ut 120'F. The ozone may be provided by an ozone-c:ont~ ; nq gas which may comprise, ~or example, oxygen or air. When an ozone/oxygen mixtllre is used, the ozone ~or~nt.1ation i~ pre~erably between about 1 and 8 10 percent by voluDIe, wher~as ~or ozone/2lir mixtures, an ozone concentration of betw~en about 1 and 4 percent by volume is acceptable. Within the ozone reactor vess~l, the substantially deligni~ied pulp is advanced in a manner which subjects substantially all of the pulp particle~ to the ozone in a 1~, uniform fahion.
It has been found that pulps with K Nos. grez,ter than about 10 a~ter the fiec::ond tep are not suitable for this third step, becau~e of the sub~tantial amounts of ozone required to r~duce the K No. to the desired level, which typically results 20 in the properties OI the pulp being adver~:ely and deleteriously af~ected by exc~ssive ozone degradation of the cellulose fibers of the pulp. When pulp having a K No. of le~~s than 10 is ozonated, a lesser concentration o~ ozone is used, with only a in; ~1 amoun~ of c:ellulo~e degradation occurring. ~hs product 25 from this ozon~tion . ~tQp for either the starting southenl U . S;
softwood or ha~lwoo~ describ2cl above is a pulp having a K ~o.
o~ less than ahout 5 and generally in the ranqe o~ about 3 to 4 (tarq~t of 3.5), a vi~cosity of above about 10, and a GE
brightness o~ at lea~t 50% (typically about 54% or high~r for . 30 so~twood and 63% or higher for hardwood).
Among, but not limited to, the ef~ective embodiments Por this ~tep are:
a. Treatment oP the acidified pulp by countercurrent contact o~ ozone in an oxygen or air carrier gas; or WO 91/18145 2 036 3 ~ 9 ~ PCI/US90/02823 b . Treatment of the acidif ied pulp by cocurrent contact o~ ozone in an oxygen or air carrier gas.
An additional bleachiny ~ep may then be used to 5 bring the pulp to a desired fully bleached state, i.e., one having GE brighkness levels o~ about 70 to 95% using any number of possible, well reoognlzed bleaching and extrac~cion prsc~ses. ~ong, but not limited to, the effective embodimen'c-~ are:
a. A conventional extrac:lcion stage with wa~hing followe~ by a peroxide stage with washing;
(i.e., I:P);
b . Conventional alkali ex~rac:tion and w2~Fh i n~
~tages ~ollowed by a conventional chlorine dioxide stage with ws~l:hi~ (i.e. ~ ED~:
c. A conventional alkali extraction and washing ~tage îollowed by a conventional chlorine dioxide ~tage wîth wa~hin~, followsd by a repeat of the extraction and chlorine dioxide ~;tages ( i . e ., EDED); or d. An extraction stage, augmentad with either oxygen or oxygen ancl peroxide, followed by a conYentional chlorine dioxide ~tage: i.e., (E~)D
or (Eop) D-The extraction ~ta~e may co~pri~e, is~ a further emboA; -nt, combining the substantially delignified pulp with an effective amoun~c of an alkaline material in an aqueous alkaline solution for a predeteL i ne-l time and at a predetermined t0mperature correlated to the quantity of 30 alkaline material to solubilize a substantial portion of any lignin which remains in the pulp. Thereafter, a portion of the aqueous alkaline solution may be extracted to remove ~ubstantially all o~ the solubilized lignin therefrom.
Following the extraction stage, the substantially 3~ deligni~ied pulp may be treated in the additional bleaohing WO91/18145 -14- PCT/US~0/028~3 step to raise the GE brightness of the resul~ant pulp to at least about 70%. Preferred ~rightening agents include chlorine dioxide or a peroxide.
The (Eo)D~ (Eop)D or ED~D embodi~ents will achieve 5 the highest brightness level6. ~or the ED embodiment, ~he chlorine dioxide stage filtrate cannot, without traatment, be recycled for ch~mical recovery because of the presence of the inorganic chlorides. Since thia is the only required sewered filtrate from the proce~6, however, dramatic reductions in 10 ef~luent volu~e, color, COD, BOD, and chlorinated organics are achieved. Color of leGs than 2 pounds per ~on, BOD5 of less than 2 pounds per tcn and total organic chlorid (TOCl) of less than 2 and preferably leQs than o.~ can be achieved. It is also possible to treat the chlorine dioxide stage fil~rate with 15 a membrane ~iltration process which will allow essentially co~plete recycle. In the EP ~ ~o~;ment, no chlorinated materials are formed in the bleaching process and virtually all the liquid filtrates can be recycled and recovered, producing an al~ost e~luent-free process.

Brief Description o~ khe Drawing~

FIG. l is a block flow diagram of the preferred methods of this invention wherein a ~olid line represents pulp 2~ ~low and a broken line represgnts ef~luent flow;
FIG. 2 is a s~hl -tic representation of a preferred method of the invention;
FIG. 3 is a cros~-sectional drawing of a portion of an ozonation apparatus shown in Fig. ~, taken along line 3--3;
FIG. 3A is a cross-sectional drawing of a portion of a preferred ozonation apparatus shown in Fig. 2, taken along line 3--3; and FIG. 4 is a comparison of the recycle and waste streams for a variety of pulp treatment procesQes.

~3~
WO91/1~145 -15- PCT/U~90/02823 Detailed Description of the Invention The pre~ent invention relates to novel methods for delignifying and bleachin~ pulp while in1 izing the degree of attack upon the cellulosi~ portion of the wood, thus forming a product having acceptable strength properties ~vr the manufacture of paper and variou~ paper products. For convenience in underst~n~;ng the imp~o~ nt over the prior art o~fered with the u6e of the pree~ntly di~closed deligni~ication 10 and bleachin~ proces~, provided below are the d~finition~ of ce~eral param~ter~ involved in the variou6 ~tages in any delignification/bleaching proce s.

Ao General Definitions Throughout this spec~fication, the ~ollowing definitions will be used:
'~Consl~tency~ is defined as the r -un~ of pulp fiber in a slurry, expre~sed as a percentage of the tDtal weight of the oven dry fiber and water. It is someti~s also referred to 20 as pulp concen~ration. The consisl:ency of a pulp will depend upon operation of and the type of dewatering equipment us~d.
The following d~finitions are based on those found in Rydholm, Pulping.~l~c~se~, Interscience Publi~her , l~65, pages 862-863 and TAPPI ~IJno~L~ph No. 27, The Bleachin~ of Pulp, Rapson, Ed., 25 Tha ~echnical As~oci~tion of Pulp and Paper Industry, 1963, page~ 186-187.
I'Low consistency~ includes ranges up to 6%, usually between 3 and 5~. It is a s11spenRion that i~ le by an ordinary centrifugal pump and is obtainabl~ using deckers and 30 filters without press rolls.
"Medium consistency" is between about 6 and 20%.
Fifteen percent is a ~ividing point within the medium-consistency range. Below 15% the consistency can be obtained by filters. This is the consistency of the pulp mat leaving a 35 vacuum drum filter in the brownstock w~ch;ng system and the bleaching system. The consi~tency of a ~lurry from a washer, eithar a brownstock washer or a bleaching stage washer, is 9-15~. Above about 15%, pres6 xoll~ are needed for dewatering.
Rydholm states that the usual range for medi~m consistency i5 5 10-18%, while Rapson states it i6 9-~ 5~. The slurry is p, ,~hle by special ~achinery even though it is still a coherent liquid phase at higher temperatures and under some compressionO
"High con~istenGy" i~ above about 20% up to about 10 50~. Rydholm states that the usual range is 25-35% and Rapson states that the range is fro~ 20-35%. These consistancies are obtainable only by the use o~ presses. ~he li~uid phase i~
completely absorbed by the fibers, and the pulp can be pumped only very short distances.
1~ Further, in this specification "pulping" is used in its conventional sense to refer to a digestion of lignocellulosic ~at~rial to form brown~tock. Pulping would include, for example, Kra~t, the Kraft-A~ process and forms of extend~d delignification.
The term "modi~ied Kraft process9~ is used herein to include exten~ delignification and all other modified ~raft proce~ses with the exception of the Kraft-AQ proc~ss, since this process ha~ achieved a special ctatus and acceptance in the art and is ~eparately known by that na~e. Al~o, the oxygen X5 deligni~ication step following co~p:Letion of pulping will not ~e considered as an extended delignification: rather, we have ~ho~n to call it a first step o~ a delignification process for ble~ching or brightening the pulp.
Further, there are two principal typec O~
, 30 measurement~ to determine the completeness of the pulping or bleaching process, i.e., the "degree of delignification" and the "brightness" o~ the pulp. The degree of delignification is normally used in conn~ction with the pulping process and the early bleaching stages. It tends to be less precise when only 35 small amounts of lignin are present in the pulp, i.e., in the 2 ~
WO 91/1814~ 17 ~ PCr/US90/02823 later bleaching stages. The brightness ~actor is normally used in c~nnection with the bleaching process because it tends to be mor~3 precise when the pulp is lightly colored and its re~lectivity is high~
There ar~ many ~el:hods o~ mea uring the degr~e of deli~nification but ~o~t are variatione of the permanganate test. The nor~al pe~ n~te te~t provid~ a perm~nganate or "K No. 1- which is the - '- ?r o~ cubic centi~eterE; o~ tenth normal potal. 8ium per;~anganate ~;olution ~on~ .' by one gram o~
10 oven dried pulp under ~pec:i~ied condition~;. It i~ dete, i ne-l by TAPPI Standard Te~t T-2 l4 .
There are al~o a h~ ~er of ~nethods o~ measuring pulp brightness. Thi~ parameter i u~ually a ~easure o~
rsflectivity and it6 value i~ expr~ ed a~ a percent o~ 80~111e 15 scal~ tandard ~ethod is GE brightne6s which i8 expre~ ed a6 a p~rcentage of a ~; GE brightnes6 a~ detennined by TAPPI Standard Method TPD-103.
~ qoreover, where appropri~te, the letter code~
describ~d in the BackyLe~und Art eec:tion will be utilized to 20 designate the variou~ ~tages of pulp trQabnent throughout this ~t~iled De cr~ption of the Imrention.

B. The Process 8t~p~; of the Invention The value~ (i.e,, R No., vi~co~ity and GE brightness~
2~ obt~i~e~ by u~e of the pr~ent pulping, deligni~ication and bl~aching proce~, a~ s~t forth below, d~mon~trate the ability of thi~ proceY~ to enhance the degree of lignin removal from th~ pulp while ~inimizing the resultant d~gradation o~ the cellulose. After the oxyg~n delignification step, and prior to , ~o brightening, the pulp h~s been partially delignified to a K No.
of about 5 to lO, prePerably be~ n about 7 to lO ~or U.S.
softwoods and about 5 to 7 for U~S. h~rdwoods. This partially delignified pulp ha6 a viscosity of above about lG, generally more than 13 and pr~~erably, at least 14 (for ~o~twood pulp) or 35 15 (Por hardwood pulp). This partially delignified material 2~ ~7 ~.~

thus has good strength and suitable visco~ity ~o that it can with~tand the effects of ozone~ The partially delignified pulp is subjected to ozone to further delignify ~he pulp, thus reducing the X No. of the pulp to about 3 to 4 for both 5 softwoods and hardwood~ while increa~ing ~he GE brightness of the pulp to at least about 50-70%. For softwood pulp, a GE
brightness of about 5~% or higher is ~ypically achieved, while for hardwood pulp, values of about 63% or more are attained.
Thereafter, the brightnes6 of the pulp is further increa~ed by 10 an alkali extraction and an additional bleaching step using chlorine dioxide or peroxid~.
For convenience in understanding the present invention therefore, Fig. 1 set6 forth, in schematic form, the various stages utilized in pulping, delignifying and 15 brightening a pulp according to the invention. ~s illustrated in Fig. 1, the invention comprise6 a multi-staye process including the ~teps of:
(a) pulping the lignocellulosic material whereby the pulping chemicals may be recovered and reused in a ~n~eF well-known in the art;
(b) wA~hing the pulp to remove chemical residues from the pulping li~uor toge~her with residual lignin and usually including a screening of the pulp to remove fiber bundles that have not been separated during pulping;
tc) alkaline oxygen deligni~ication (i.e., O or ~m) of the pulp;
(d) wARhing the partially delignified pulp obtained in ~tep (c) above to remove dissolved organics from the oxygen treatment optionally, screening ~ay ~e done at this point, while also recycling at least a portion of the effluent from this step to a previous step;

2~3~

(e~ chelation and acidific~._ion oP the pulp to bind ~etal ions and to adju t the p~ to a preferred ~ç3v81;
(f) contacting the pulp with OZORe ~i.e., Z or Zm) ko furthar delignify and to partially bleach this material;
(g) w~hin~ the ozonated pulp, while recycling at lea~t a portion of th~ efPluent from this step to a previous step;
(h) cau~tic extraction to re~ove re idual lignin;
(i) w~8h~g the extract2d pulp while recycling at least a portion o~ the effluent to a pr~vious step;
(j) adding a ~econ~ bleachlng agent (i.e., D or P to t5 brighten and bleach the pulp~;
(k) wA~hing the bleached pulp to obtain a bleached product having a GE brightnQ~ of about 70-90%;
a~d (1) recycling at least a portion of the effluent ~ro~ the P bleaching stage to a previou step;
or ~ewQring the ePf:Luent ~rom the D bleaching ~tage or, a~ter a~y~ iate treatment, recycling this effluent to a previous step.

25 1- Pulpinq The f$rst stage in the ~ethod of the present invention wherein procedure~ can be utilized which improve the ;- ~n~ of lignin ved from the lignocellulosic material while ini izing the A Un~ of degradation of the cellulose, is 30 in the pulping step. The particular pulping process used in the method of the invention is, to a larqe extent, dependent on the type of lignocellulosic material and, ~ore particularly, the type of wood which is used a~ a starting material.
Moreover, a~ illustrated in Fig. 1, the pulping liquor used in 3S c~emical pulping techniques ~ay be recovered and reused in a -20- 2~3~

manner well-known in the art. Thi~ ~tep is typically followed by wA.chi~g ~o remove mo6t of the di~olved organics an~ cooking chemicals for recycle and recovery, a~ w~ll as a screening stage in which the pulp is pas ed through a ~creening apparatus to remove bundles of fiber~ that have not been separated in pulpi~g.
The Kraft process i~ generally acceptable for u~e with all wood~ as co~pared t~ ~he oth2r noted proce~s~, as the final pulps obtained fro~ the Rraft proce~6 hav~ ~cceptable 1n phy~ical properties, although the brownstock pulp i5 also darker in color.
Depen~in~ upon the lignocellulosic starting material, the results obtained with conventional Kraft proces~e6 may be ~nh~naed by the use o~ extended deligni~icati.on techniques or the Kraft-AQ proGess~ ~oreover, these ~echniques are preferred for obt~;~ino the greate~t degr~e of reduction in ~ No. of the pulp without deleteriously affecting the ctrength and viscosity properties of the pulp.
When u~ing the Kraft-AQ technique, the amount of anthra~linone in the cookin~ liquor ~hould be an amount of at least about 0.01% by weight, ba~ed on the oven dried weight of the wood to be pulped, with ~ -L l~3 of ~ro~ about 0.02 to about O.1% generally b~ing pre~erred. The inclusion sf anthraquinone in the Kra~t pulping proces~ contr:ibutes signi~icantly to the ~ vdl oP the lignin without adver~ely affecting the desired s~rength characteris~ics o~ the r~m~ining cellulose. Also, the addition~l co~t ~or the Anthr~inone is partially offset by the saving~ in co~t of che~icals in the subsequent Zm~ E and D
or P 6tep8.
~lternatively, or perhaps even additively to Kraft-AQ, is the use of techniques for axtende~ delignification such as the Kamyr MCC, Beloit RDH and Sund~ Cold Blow Methods for batch dige~ters. These techniques also of~er the ability to ~5 2 ~ 9 ~
WO 91/1814~ -21- PCI/~IS90/02823 remove more o~ the liçjnin during pulping without adversely affeoting the desired ~trength charac:texi~tics of the remaining cellulose .

5 2. oxygen r~elignification The next ~tep in th~ ~ethod of the pre~ent imr~ntion concerns the portis:~n o~ ~he bl~aching proceE;s which pri~arily involv~s L~ dl 0~ the re~idual lignin fro~ the brownstock pulp being prvce~se~ . In the method of this invention I thi.s stage compri~es ~n oxygen deliga~ification step. The ~olid ~at~rial~ removed in this stage ar~ oxygenated ~Gaterial~ which can, like the black liquor, b~ collectad, concentrated, and then incineratad in an envi~o -ntally saf~ ronn~r in a conventional re-::overy boiler. At least a portion of the liquid 15 pha~3e i recycled as illu~trated in ~ig. l.
It has been found t,hat the oxygen deligni~ication 3tep ~arl ~e conducted in the manner which allows ~or the 1 of increased perc~antage6 of the remaining lignin irl the brownstock pulp without cau~ ng an ~ cc~ptable corresponding 20 decrease in the viseosity of the pulp. Broadly, the process which has been identified i5 practic:ed by treating the brownstock pulp ~rom th~ pulping proces~ at low to medium consi~tency, as de~cribed below, wi.th the require~ ~ unL of alkali nece~s~ry ror the oxygen delignification ~ep ~o as ~o ensure uni~o~m application of the alkali, and therea~ter rai~ing the consi~tency and deligni~ying a~ high consi~tencies.
Alth~t~h high con~i~tency delignification is preferred, low or mediu~ con~iste~cy oxygen delignificatisn techniques may be utilized in place of high conslstency delignification.
, 30 T~e high consistency o~ygen delignification step is pre~erably ~arrisd out in the pre~ence of an aqueous alkaline solution at a pulp con~i~te~cy o~ ~rom about ~5% to about 3~ .
and even more preferably, at about 27%. This improved process (~m) allows ~or the removal of at least 60~ of the residual 35 lignin ~ro~ the brownstock pulp, co~pared to the 45-50%

2 ~

removable with conventional oxygen delignification steps, without the hereto~ore expected undesirable decrease in the r~lative viscosity. Because of the unique process capabilities of this modified process, it clearly constitutes the preferred 5 oxygen prooess for use in the method of ~his invention.
T~e treat~ent step of the modiPied oxygen process (~m) comprise6 substantially uniformly co~bining wood pulp, preferably Kraft brown~tock pulp, with an aqueous alkaline solution while maint~;nin~ the CDn i6tency of the pulp at less ~O than about 10% and preferably less than about 5% by weight.
The aqueous alkalin~ solution i8 preferably present in an amount su~ficient to provide fro~ about 0.5% to about 4~ active alkali by weight after thicke~i ng based upon the oven dry pulp weight of the brownstock pulp, and even ~ore pref~rably about 15 2.5% active alkali by weight after thic-kPn1 n~ based upon the oven dry weight of the brow~stock pulp.
This step uniformly di~trlbutes th~ a~ueous alkaline solution throughout the low consistency brownstock and ensures that sub tantially all the brownstock fiber~ are axposed to a 2n uni~orm application of alkaline solution. Surprisingly, the brown tock pulp treated in this ~nn~r is not substantially delignified in the treat~ent step, but it is more effectively delignified in the s~bsequent high consistency oxygen delignification step than brownstock that is treated with 25 ~lkaline solutions at high consistincy according to the methods conventionally e~ployed. The localized inho~ogeneities in the distribution of alkali in conventional high consistency pulp are avoided, thus eliminating attendant non uni orm oxygen delignification.
3D Thi~ homogeneous distribution step thus preferably comprises uniformly combining the pulp with an aqueous alkaline solution for at least about l minute and preferably no more than about 15 minutes. It is believed that treatment times of less than about l minute will not generally provide 3~

WO 91/lB145 - -23- PCl/US90/02823 suffici~nt time to attain substantially uniform distribution, wherea~ treatment times in exc~; o~ about 15 minutes are not expected to produce ~ ;tantial further benef it .
Morl30ver, the preferred alkaline treatment of pulp 5 according l:o the pre~ant invention ~ay be c:arried out oYer a wide range of temper~ture conditions. According to a preferrod practic~, the treat~ent step i~ carried out at a temperature of from about roo~ tQmperature to about 150~F, with te~p2raturQ~ ranging 9~rom about 90~F to about 150~F
10 b~ing ~ven morç! preferred. Atmospheric pressure t~r elevated pre~;ure may b~2 employsd. Th~ treat~erlt step i~; completed when the aqueou6 alkalin~ solution i s~ 3tantially uniformly di~tributed throughout the low con~i6tency pulp. The amount of aqueou~ alkaline 801uti.0n preeent in th~ treatment step can 15 vary greatly accclrding to the particular process par~ eters of the d~ligrlification reaction. The amount of the alkaline solu'cion e~feetiv0 for the purpoce of the pres~nt irlvention will ~ep~rV9 primarily upon the ext~nt of delignification de~ired in ll:he oxygen ble~hi~ step and the strength of the a~ particular ~olution being u~e!d. The aqlleo~ alkaline solutions preferably u~c~d C~D~prise a sodila~ hydroxide ~Lolution having a c~ euLL~.tion o~ from abou~ 20 ~o about 120 g/l. Thi~; solution is ~ixed with the low s:onsl tency pulp, ~o that the overall mia~tur¢ ha a e~uncPntration of alkaline ~aterial of }: etween 25 about 6 . 5 and '. 3 . 5 g~l, and pre~erably ars:~und 9 g/l . Thus, for a 5 to 15 minute treat~nent of a 3 to S percent con~istency pulp at temperature~ between 120 to 1~0'~ at these concentrations of alkali~Qe ~aterial, a unifor~ distribution o~ E;uch alkaline rlate!rial is obt~ e~ throughout the pulp.
According to ~ preferred ~ ' i ?nt of the present inv~ntion, an aqueou~ sodium hydroxide solution is added to the low c:on~istency pulp in an amount suf. ici~nt to provide from about 15% to about 3096 by weight of sodium hydroxide based on dry pulp weight. Other alkaline source~ having an equivalent 3~

~3~
W~91/18145 -24- P~T/U~90/028~3 sodium hydroxide content, such as oxidized white liquor ~rom the conventional Kraft recovery and regeneration cycle, may also be employed.
Following the low ~on~i~tency caustic treatment step described above, th~ con~istency o~ the treated pulp is increasPd to greater than about 20%, pre~rably from about 25% to about 35%O Several methods are available and well known in the art for increasing the consistency of the pulp, such as pres~ing the wood pulp to remove li~uid therefrom.
ThereaPter, oxygen delignification is conducted on the high con istency pulp. Methods are availabl~e and well known in the art for dissolving gaseous oxygen into the liquid phase o~ high con~istency pulp to affect delignification ther~of. It i~ conte~plated that any of these well known ~ethods are adaptable for u~e according to the pre~en~ invention. It is preferred, however, that oxygen delignification according to th~e presant invention comprise ~ Lo~cing y~Reo11~ oxygen at about 80 to about lU0 psig into the liquid pha~e of the high consistency pulp while ~aintaining the temperature of the pulp between about 90~C
and l30~C. The average cont~ct tim6e between the high consi~tency pulp and the y~Meo~l~ o~rgen i8 preferably ~rom about 20 minutes to about 60 ~inut~e~s.
~y ~ollowing the pre~erred process according to the present invention, it is pos~ible to obtain a reduction in K No. for the pulp after the oxygen delignification step o~ at lea ~ about 60% with e~sentially no damage to the cellulose portion of the pulp. By comparison, conventional oxygen delignification c~n only achieve reductions in R No.
of about 50~ before degradation of cellulo~ occurs. Thus, the pre~ent preferred process l~neY~ectedly provides an increase of at least ~0% in deligni~ication compared to prior art delignification processes: i.e., from 50% to at lea~t about 60% reduction of the K No. for the inc~mi~
35 pulp. R~ductions of 70% and more can even be achieved with 2~6~
WO 91/~81~ -25- PCJ/US90/~2823 mini31al cellulos~3 degradation. The avoidance of deterioration of the celluloF~e c~ t o~ the pulp is evident by the ini ~1 change in ViE~::0~3ity oP pulp which is treated in acc:ordance with the presenk inverltiorl.
Upon ent~ring the oxygeJa deligni~icakion step, pulp K Id08. for the particular pulp range ~rom about 10-26 dep~n~ing upon the tyEe o~E wood (e.g., for }~raft pulping, about 10-14, target 12 ~ 5 for ha~ oo~ and about ~0-24, target 21, ~or soEL~ood~, while 2!lft~r oxygen delignifi-cation, the ~ No. i~ generally in the range of about 5-10.
A prscessing ~cheDIle Ior carrying out the ~thosl of the pr~sent invention is depicted in ~che~atic fonn in Fig.
2. The st~ps depicted therein repr~ent a preferred operating 8y tem that tends to D~aximize certairl benefit~ of 15 the pre~snt irlvention. Wood chip~3 2 are i~ ced into a dige~;ter 4 where th~s,~ are cookedl in a 1 iquor 8uch a~ a 1 iquor o~ ~odium hy-l~Gs~ide and sodi~ suli~ide. The cool~ n~ unit 4 produces a Kra~t bL~ ock ~ and a black liquor S co~taining khe reaction ~lo~u~~ o~ lignin ~olubilization. The 20 brownstock is treated in w~h;~ UllitS co~prising, pref~rably, blow tank 10 and washer 12 where residual liquor cont~i n~ in the pulp is re~oved. ~any method~ are available and well known in the art ~or wA~hin~ brown~tock, such as diffusion w~hin~ rotary pres~ur~ w~hin~ horizontal belt filtering, and dilution/~x~raction. These ~ethod~ are all within the scope o~ the present in~ention. Al~o, screening of brownRtock i~ often done sither before or after the w~h i n~ step~ in order to remove larger portion~ o~
undefibered wood for ~pecial proce~sing.
3~ Tha washed brownstock i~ introduced int~ a treatment unit 14 where it is treated with an alkaline solution and maintained at a consistency of less than about 10% and pre~erably less than about 5%. The proces~ of the present invention preferably include~ means for introducing 3~ make-up cau~tio 16 into the txeat~nt stage to maintain the ~ WO91/i8145 -26- ~,3~3d,~823 desired çaustic applica~ion l~vel. The trea~ed pulp 18 is forwarded to a thickening unit 20 where the consistency of the pulp is increa~ed, by pre6 ing for example, to at least about 20% by weight and preferably to about 25% to about 35%.
The liquid 22 removed ~rom the thickening unit 20 is preferably returned to washing unit 12 for further use. The high consistency "pressed" brownstock 24 produced in the thick~n; ng unit 20 i6 forwarded to the oxygen delignification reactor vessel 26 where it i8 contacted with gaseous oxygen 10 28. The delignified brown6tock 30 is preferably forwarded through blow tank 32 and then to a second w~h;~ unit 34 wherein the pulp is wa~hed with water to remove any di ~olved organics and to produce high quality, low color pulp 36. At least ~ portion o~ the ePfluent 38 from this washing step is 15 preferably returned to w~hing unit 12 for use therein. The effluent 13 ~rom washing unit 12 may be recycled alone or optionally with all or a portion of effluent 3 , to either the blow tank lO or ultimately black liquor line 6.
Additionally, the partially delignified pulp obtained after 20 oxygen deligni~ication may be scr~ened to remove fiber bundles from the pulp that have not separated ~or further treat~ent such as ~echanical grinding. From here, pulp 36 could be sent to ~ubsequent bleaching stages to produce a fully bleached product.
In a particularly preferrled method of the present invention as ~hown in Fig. 2, in order to sllrces~ully utilize ozone bleaching, Kraft pulping of the wood may be carried out, followed by the modified low-consixtency alkali treatment/high consi~tency oxygen delignification procedure (~m) described 3~ abov~. For softwoods, as noted above, this combination results in a pulp with a K No. of about 8 to 10, preferably 9, and a vi~cosity of greater than about 13 to 14. Alternatively, it is possibl~ to subject the wood to Kraft AQ pulping followed by a conventional oxygen deligni~ication step (i.~., 0, high 36 consistency alkaline tr~atment followed by high consistency WO 91/1~14~ -27- P~l/US90/02823 ox~gen d$~lignification) to achieve a pulp haYing ~imilar characteri~;tic~;O In plac:e of Xr~t ~52 pulpiny, it i8 ~lso possible to u~e ex~6~nde~ deligni~ication proc~e~, followad by a standard oxygen deligni~icaltion ~;tep to achieve pulp with the 5 desired propertie~ o u~e:Eul, ~lthou~h le 8 preferred due to incr~ased c:ost~ or pros~e~s stepE;, i~ th~3 combination o~
Rraft pulping with extencled delignifis::ation technlques such as ~Ramyr MCC, Beloit RDH or th~ Sunds Cold Blow Cook~n~ process, as de~cribed in th~ Bac3cground Art s~s:tion of this 10 spes::ification, followed by conYentional oxygen delignification.
Any of a wide variety o~ pulping and oxygen delignification staps c~n be used in combination as long as they achieve th~e above K No. and visc:o~ity values prior to the ozone step.
~; Corlventional Kraft pulpirlg ~ollowed by conventional oxygen delignification i~ gener~lly not acceptable in this inv~n~ion, excep1: for certain haL.h ood ~uch as~ asperl which are relativ~ly ~a3y to deligni~y and b:lQach, fs;ince ~or a giv~n wood speci~s the co~3ination oiE thQ~e collventional technigues 2~ norlDally require~ the u~e of th~ greatest amount of ozone in the o~onation step with concomitanl! greatex c:ellulose degradation .
By taE:e of the pre~ent invention, the ozone consumptiorl may be re~uçe~l by u~ing a number o~ al~ern~te 25 routes, such ~ standard kraf'c cookir~ followed by a loodified ~xy~ delignification ~tep (~~ or n~odi~ied kraft pulping with a~t~ de~ delignific:ation (such as ~amyr MCC, Beloit RDH or Sund~ Cold ~low) îollowed by a CCil~tel'l~ ional c~xygen d~ligni~ication step (o), or by Xra~t AQ coo3ci~y followed by a 3~ co~.ve~l.ional oxygen d~ligr~i~ication step (o) as disc~c~e~9 above. An ev~3n gr~ater reduction in ozone co~ ion will be achieved both with the use o~ modified Kraft pulping with ext~3nde~g deligni~ication (Kamyr 1!9CC, E~eloit R~H or Sunds Cold Blow) followed by a modi~ied ox~gen deli~nific:ation step (~m)~
35 or alternately when a Kra~t AQ coo~ proce~6 with extended deligni~ication (Kamyr MCC, ~eloit ~DH or Sund~ Cold Blow~ is ~6~
W091/1814~ -28- PCT/US90/02823 followed by a conventional oxygen delignification step (0)~
U~ing all of these techniques tog~ther in one proce~s, i.e., Rra~t AQ cooking modi~ied by ext~ A deligniPication (Kamyr MCC, Beloit RDH or Sunds Cold Blow), followed by a modi~ied oxygen delignification ~ep (0~), reduce6 the a~ount of ozone con~ even fur~her. R~duction in the a~ount o~ ozone consumed generally permit~ the Yi~cs~ity o~ the pulp to be maintained at acc~ptable levels.
The ~dvantages of u~lng ~he ~odified high consistency 10 oxygen delignification ble~ching tep (0~) describ~d above are clearly illustrated by co~parison of the K No6. and visco6ities obtained u~ing southern softwoods to related procecseE under oth~rwise substan~ially identical process conditions. U~ing a conventional Kraft pulping procedure and conv~ntional high 15 con~isten~y oxygen deli~nification bleachins, the resulting pulp5 obtained will typically have a R No. of about 12 to 14 and a visco~ity of about 15. Thi~ ~ No. i5 ~00 larg~ to permit later delignification using the ozon~ stage o~ the present invQntion. Ho~ever, the use of co~ventional Xraft pulping with 2~ the modi~ied high consistency oxyge!n ~leaching surprisingly results in a pulp having a K No. oi' le~s than about 9, while the visc06ity of the pulp is above about 12 to 14. Thi~
preforred pulp R No. p~rmitR utilization of the ozone delignification bleaching stage of the invention.

3. ~he Ozone Step ~ he next step in the ~ethod of thi~ invention is ozone deligni~ication and bleaching of the oxygen-delignified hrownstock pulp~ This ozonation takes place in an ozone . 30 reactor which is described below in detail and illustrated in Figs. 2, 3 and 3A. Prior to treatment o~ the pulp with the ozone, the pulp is conditioned so as to ensure the most effective ~elective delignification of the pulp and to ini~;ze the chemical attack of the ozone on the cellulo~e. The 35 incoming pulp 36 is directed into a ;~;n~ chest 40, where it 2 ~ 9 ~
WO 91~18145 29 PCI/US9û102823 i6 diluted to ~ low Cl:~S15i tency. An acid ~2 such a~ ~~ulfuric acid, formic acid, acetic elcid or the like, is added to the low consi~tency pulp to decreaE;e the p~ of ~he pulp in mixing chest 4 0 to the range of about 1 to 4 and pre~rably between 2 and 3 .
5 The plI is adju~ted a~ described above sin::e it is known that the r~lative effectivenes~ of ozone bleaching of pulp~; is ~ep~n~Pnt upon the pH of th~ pulp mixture. Lower pH values do not appear to hav~ any bene~icial eff'ect on the further proce~sing of the pulp, wh~rea~ inc:r~asing the pH to above 10 about 4 to 5 cau es ~ dec:rea~3~ in vi~c06ity and ~n irlcrea~e in o~one con~u~ption.
The alcic31ified pulp i~; treated with ch~l~ting agent 44 to complex any m~tal~ or ~etal ~alt~ which ~ay be pre~ent in the pulp. ThiE~ chel~ting ~tep i8 u~;ed to rendler such metals 15 non-reactive or harmles~; in the ozone reactor B0 that they will not cau~e breakdown c~ the ozune, thuE~ dec:rea~ing the e~iciency O:e the lignin removal and al80 r~ducing the vi~cosity o~ th~ cellulo~;e.
Ch~lating agerlt~ axe kno~n ~ se and include, for 20 example, polycarbe~xylat~s and polycarboxylat~ derivative!~3 such a~ the di-, tri-, and tetra-carboxylateE~, amide~a, and the like.
Preferred chelating agents for thi~ o~one trea~ent, for r~a~oT-~ of co~t and ~rici~ncy, inc,lude DrrPAf E~ nd oxalic acid. ~ ,~n~ of thes~ ch~31ating ~g~nts ranging Iro~ about 25 0.19~ to about 0~ 2S by weight o~ ov~n dry pulp are gerlerally effective, although addi~ional amoun~ may be n~ec~e~ when high metal ion concentration~ are pre~ent.
Th~ efP~ctivene~s of the ozone bleaching process i~
controlled by a n 'er of inter-related process par~DIeters, including th~ pH level and the - ~nt of metal E;alts in the pulp ~s di cus~ed above. Another very important parameter is the con~i~tency of the pulp dur~ ng the ozone bl~aching process .
The pulp which is to be bleached DIUst contain ~uPficient water 80 that the water exislts a~ a continuous phase through the 35 individual fiber~, that is, the fiber should be suPPiciently 2 ~
WO 91/1~14~ 30 ~r/US9~)/02823 saturated with water. ~he water in the fiber allows the transfer of the ozone from the gal4e~ ozone atmo6phere to both l:reat th~ outer surface of the fiber~, and pos6ibly more impor~antly, ~or the ozone to be tran~erred via the water 5 pha~;e to the less accessi~le interiox portion of the individual fibers and thereby proYide more complete removal of lignin from the ~ibers. ~he con6istency, on th~ oth~r hand, should not be so low that the ozone i~; diluted and tends to chemically break down rather than bleach the pulp.
The pre erred range of con~istency, especially for southern V.S. softwood, ha6 been ~ound to be betwe~n about 2~%
and about 50%, with the opti~oum result~3 being obtained at between about 38% and about 45%. Within the above rang2s, preferred re~ults are obtained as indicated by th~ relative 15 ~mount of deliç1nification, the relatively low amoun~ of degradation of the celluloee, and the noticeable increase in the brightnes~ of the tr ated pulp~.
The reaction ~emp6!ratllre at whic~ the ozon~ bleaching i8 cc~ cted ~ ~ likewise an important controlling factor in the 20 proce~s oî the pre~ent invention. The o one step can be effectively con cted at temperatures up to a certain critical temperature, at which the reaction cc ~nce6 to cause excessive degradation of the cellulose~ Thi~ critical t~mperature will vary ~ignificantly ~lep~n~lin~ upon the particular type of wood 25 employed to form the pulp and the hi~tory of the prior treatD~ent o~ the pulp. The -Y; 1~ temperature of the pulp ~iber at which the reaction ~hould be concluotl3d ~hould not ~Yce~ the temperature at which exc:essive degradation of the cellulo~e occurs, which with ~outhern U . S . softwoQd is a r; of about 120~F - 150~F.
The ozone gas whic:h is used in the bleaching process may be employed as a mixture of ozone with oxygen and/or an inert; ga~, or can be employed as a mixture of ozone with air.
The ~ nt of ozone whic:h can satisfactvrily be incorporated 35 into the treatment gases is limited by the stability of the ~3~
WO 91/18~45 ~3 l- pCr/lJ~0/02823 os:one in the gas ~ ure. Ozone ga~; mixtures which typically contain about 1-8% by weight of ozone in an ozone/oxygen ~ixtur~, or about l-496 ozone in an osone/air mixture, are suitable for uE~e in this irlverltion. The higher concentration 5 of ozone in the ozone ~a~ DliXture allows f or th~ u~e of relatively ~maller ~3ize rsactor6 and horter r~;~ction time to treat equivalen~ ount~ o~ pulp, ~:he,reby lessening the capital coE;t requlred for the equipment. l~owevs~r, ozone gas ~ixtures cont~;nin~ lower amount~3 Or o~one tend to be les~ exp~n ive to 10 prsduce and ~aay redue:e operating c05ts.
A further ccmtrolling ~actor i~ the relative weight of the ozone u~ed to bleach a given weight of the pulp. This amount is det~rmined, at l~ast in part~ by the amount o~ ligrlin which i~3 to be . ~~ : v ed during the o~one bleaching procs&s, t5 balanced again t khe relative r _ ullL Gf d~gradation of the cellulose which c:an be tolQrat~d during ozone bleaching. In accordance with the prefE3rred ~aethod of thi~ im~ention, an _I.L of ozone i8 u~ed wr...ch will r~act with about 50~ to 70%
of the lignin pre~enk in the pulp. The ~ntire a~ount of lignin 2n in the pulp i~ not removed in th~ ozone bl~aching ~tep as evi~ence~ by ~he K No. of about 3 to 4 obt~ine~ after this 8tQp, hecA-~e ~he ~~ence of all lignin in the reaction zone would result in the ozone reacting exce~lvely with ~he c~llu~o~e to ~ubstantially decrea~e the degr~e o~
2~ polym~riz~tion of ~he cellulose. In ~he preferred me~hod o~
khis invention, the r ~ of ozone added, based on the oven driQd ~eight of the pulp, ~ypically i~ about ~rom 0.2% to about l~ to reach th~ nin levels of a 3-4 K No. Higher amounts may be reguired if signi~icant quantiti~s of dissolved solids 3~ are pre~ent ir ~e ~ystem.
The i~ie of the reaction used for the ozone bleachin~
step i~ deter~ - d by the desired rate of completion of the ozone bleaching reaction as indicated by complete or ~ubstantially complete consumption oP the ozone which is 35 utilized. This time will vary depending upon the concentration ~ ~ ~ p~
WO 91/1~145 -32- PCI/IJS90/02823 of the ozone in the ozone gas mixture t with relatively more concentrated ozone ~ixtures reac~ing more quickly, and the relative amount of lignin which it ie dl~;ired ~o remove. The ti~ae required is preferably le86 than two minutes, but the 5 proc:edure may take substan ially longer depending on other reaction parameter l~n i~portant f~ature of the invention is that the pulp i~ bleac:had uniformly. This feature i8 obtained in part, by ~ tis~n of the pulp into di~cr~te ~loc partic::le~ of a 1~ si e which is of a sufficiently ~mall 1l; r -g er and of a suf f ici~ntly low bulk d~nRity o that the ozc~ne gas ~ixture will completely p~netrate a majority o~ the fiber flocs, i.e., which compri~e aggls:~erations of fiber~S. During c inution it .
is not fea~;ible to co~pletely eeparate the pulp fibers into t5 distins:t fiber~. In general, the fls:~c particles resulting from z: ; nution have a relatively coDIpacted c:entral core ~ . uunded by i~ plurality o~ outwardly extC~n~in~ fiber~. For purposes of this invention, the floc particle size i~ sletermined by mea~uring what was determined to be th~ ~mallest diameter of 2~ this relatively unfluf~'ed central core.
Bleachins7 unifor~ity is to a large extent also ~ep~n~nt on certain of the other process para~eters, but it has been Pound that if the floc par'cicle ize i8 limited to a ~aximum of 5m~, and preferably even le~ or example, 3mm--25 that uniPorm treat~ent o~ a sub~tantial majorlty of the~eparticles can readily be achieved, a~ evic~Pnce~l by observation of an insigni~is::ant number o~ darker ~ erbleached floc centers. Where the floc particl~ size waE~ greater than about 5~n, bleaching w~s non-uni~orm, as ~viden~ed by a majority of 30 darker unbleached flos~ enters. Therefore it is i~portant to achieve suf~icient c i n-ltion so that a miljority of the flocs lre below an average of about 5 ~ for uniform ozone treatment thereof.
A still further important process para~eter is that ~5 during the ozone bleaching process the particles to be bleached should be exposed to the ozone bleaching mixture by mixing so 20~3~9 as to allow acce~; of the s~zone ga~ D~iacture to all ~ rfa ::e~ of the floc:s and equ~l acco~ of the ozon~ ga6 mixtur~ to all f locs . Th~ mixing of the pulp in the ozone gas ~ixture gives superior results s~ith ra~ard to uni~ormity a~ compared to the 5 results obtained with a ~tatic ~ed of floc~; wherein ~ome of the ~loc~ are i~olated fro~ the ozone gas relative to other ~locs and ther¢by bl~hed l~ than oth~r fls~cs.
The movement of' th~ floc~ 80 a~ to eYpoE~e t~em to the ozone ga D~ixture cause~ uniform trQ~tDaent of the ~locl; with 1~ r~~~pect to each other. 'rhis treatment r¢~ults in the d~ired amourlt of lignin beins~ L~ ov~d uniformly frola the pulp w~thout ~Yr~ ive d~terioration o~ the cellulo8~ in th~ fib~r~; which c:ompri~e thQ ~Elocs. The c:ontrol of th~ ozone treatment in acs::ordance with this inverltion by u~;e of a controlled particle 15 size and by turbulenl: ~o~e~ent during ozone tr~at~ent has bean found to result in a f inal pulp typi ::ally having le~E~ than about a 5% variation in GE briyhtnes~, X No. an~ viscoE~ity. In Q ,~ on, if th6~ treat~ent i8 non-unifor~, al8 typically oc~ in ~tatie b~d reactor3 (th~t i~, reactor~ wherein th~
;!0 particles are not agitated during ozone treat~ent~, s~e portions of th~ bed are ~ 3tantial1ly over-ble~che~l whil~ other por1~ ns remain relatively unr~ct:ed because the flow o~E the ozone ga~: mixture through th~ ~3tatic bed reac:tor i~ not uniform.
Treating pulp at high con~istencies with ozone wi~hou~ p~ying particular at~ention to the comminution o~ the pulp ~ibers or ~o the proper contact between the individual f ibers and the reactant gas streaDI invariably results in a non-uni~orm ozon~ bl~aching OI the f ibers . The pre~ent 30 application desiqnates such a non~ orm ozone treatment with the letter ~-Z-i. The use o~ a modified ozone technique according to the present invention, as ~lt~cl~c~ed above, in which the f ibers are comminuted to a ~3ize of about 5 mm or less and are properly and uniformly contacte~ with the ozone gas 36 stream, ha~ been designated herein ' as 17Z,~

2 ~ 9 3.

WO 91/1814$ 34 PCI/US90/02823 Pulp exiting the ozone reac:tor ha~; a GE brightness of about at le~st 50 parcent and generally around 50 to 70 percent, with hardwood~; u~ually being a3: ov about 55 percent .
The pulp ( for h~l~ood~; or eoftwood~ al~o ha~; a g No . o~
5 between about 3 arld 4 (targ~ of 3 . 5), which i8 erltir~ly sati~~acto~ for pulp at thi~ ~tage of the proce~.
An apparatus which i~; e~;pecially uitable for ozone bleach; r~ in accordance with the pr~ nt invention i6 illustrated irt ~Fig6 . 2, 3 and 3A. A~ dlescribed ~bove , wa~hed 10 pulp 36 i~ directed to iYillg che~;t 40 wh~re it is treated with ~n a::id 42 and a ch~latlng agent 44~ The acidi:fied, chelated low-con~i~tency pulp 46 iE; introc~ into thicl~ni r~ unit 48 ~or r~a~oving C~ce~e liquid 50 froDI the pulp, ~uc:h a~; a twin roll press whereill the consistency of the pulp i~ raised to l:he desired level. At least a portion o~ this exces~ liq~id 50 may be recycled to mixing chest 40, with a L._ '' ini ng purtion being direc:ted to blow tarlk 32. The ree;ulting high cor~ tency pulp 52 i8 th~~n p;~Bec~ through screw Peeder 54 which act~ as a ga~
s~al for th~ ozone gas and thereafl:er through a ~ ting 20 unit 56, ~uch a~ a ~luf~r, where the pulp iR ~ uted to pulp fiber flocs 60 of a pre-detenDined size whic:h, as noted above, E~hould ~e~ ;ur~ akout 5 ~m or l~s in ~ize. The c:om3ninuted particles are then inL~ o.~ice~ into ~ dynaDIic ozone reaction ~ Pr 58 which, a~; illustrated, is a aomreyor 62 25 powered by motor 64. Conveyor 62 i5 specifically d~6igned for ~ri Yi ~ and ~ransporting the pulp particles 60 80 as to allow the entir~ ~ur~ace of the particle~ to h~c_ ? ~Toaecl to the ozone ga6 mixture 66 during ~Y~ ~t of the pulp. A~; furthe shown in Fig. 2, pulp fib~r flocs 60 after treat~ent are 3~ allowed to fall into dilution tank 68.
Fig. 3 i~ a cross-sectional view through ozone reactor 58 illustrating the arran~f2ment o~ the pulp particles 60 a~ they are carried through the reactor by conveyor ~2.

2 ~
WO 91/1$~45 3~ Pcr/us9o/o2823 FigO 3A i5 a crc~qs-sectional view of a preferred conveyor utilizing a paddle-like arrangemerlt to move the comminuted particles through reaction chA ~~r 5~.
The proce~s in Fig. 2 show~ the pulp being treated 5 with ozone cocurrerltly with the ozone-gas ~ixture.
P~lternately, however the portion of the pulp which ha~; been bleached to the greatest extent ~ay initially be contacted with the newly introduced ozone mi~ure cont~in~ng the ~;
amount of ozc)ne by pa~ing the ozone-Gorlt~ i nçl ga~; in a 10 direction countRr-current to the flow of pulp 60. The pulp ent~ring the reactor has the highe3t 1 ignin t:ontent and initially contac:ts the exiting, nearly exhausted ozone mixture, thereby providing the opti~num chance to con~ume ~rir1:ually all of the ozone. Thi~ i~ an e~ficient method for stripping ozone 15 from the ozone/oxygen or ozone/air mixtureO
When the ozone 66 i~; contacted with the pulp in a CO~1LL~n~_ ~nner, a~ sho~m in Fig. 2, the remaining spent ozone gas 70 can be re-::overed ~rom dilution tank S8. In tank 68, dilu~ion wa~er 72, w~ich also 8erv~6 as an ozone ga8 ~eal~ is 2n added to ~ ce the consi~tency of the pulp to a low level to facilitate ~ovesle1lt of the ble~che~ pulp 74 through the 81lhsequ~n~ proce8s ~iteps.
The ~pent ozone gas 70 f:ro~ dilution tank 68 i6 dir~c:ted to a carrier gas pr~treat,m~nt stage 7 6 where a carrier 25 ga~ 78 of oxygen or air is added. This mixture 80 is directed to ozone generator 82 where the appropriate amount of ozone is generated to obtain the desired concentration. The proper o~one/air mixture 65 i6 then direct~d to ozone reactor 58 for delignification and bleaching o~ the pulp.
After completion of the 020ne bleachin~ step, the substantially deli~nified pulp 74 is again thoroughly washed in wa~her 84 as show~ Ln Fig. 2 and at least a portion oP the water 86 which is recovered is recycled to w~h i ng unit 3~ of the process, thereby producing major environmental benefits 35 from the elimination of sewered liquid.

2 ~
W~ 91/1~145 PCr/US9O/02~23 The bleached low consi~tency pulp 7~ after ozonation will have a reduced amount of lignin, and ~h~refore, a lower X
No. and an acceptable visco~;ity. The ¢xact values fox the ~
No. ancl the viscosity which are obtained are dependent upon the ~; partic:ular processing to which the pulp has been subjected.
For example, a southern U. S . Eloftwood pulp which is pulp¢d with a conventional Kraft method, initially delignified by modified high consi~tency oxygen delignificatioll (~m) ~ and subsequently îurther delignified with ozc~e, pre,ferably by a modi~ied 1~ uniform ozone treatment (Z~) ~ will typically have a K No. of about 3-4 and a vi~cosity of about lO . Southern U . S O softwood pulp which is subjec:ted ~o Kraft AQ pulping and then to modified high consistency oxygen hleaching (~m) and modified uniform ozone treatment (Zm) will typically have a K No. o~
15 about 2 and a viscosity of greater than aboul: 12.
The resulting pulp 74 will be noticeably brighter than the starting pulp. For ~xa~aple, ~;outhern ~oftwood, aft~r the pulping proce~s, has a GE brightn~ss of about 15% to 259c;
after the oxygen bleac:hing proce~, a GE brightne s of about 2C~ 2596 to 45%; and after the ozone bleaching proce~s, a GE
brightness o~ about 50% to 70%.

4. Alkaline Extraction The washed pulp 88 fro~ the ozone stage is then 25 combined with a sufficient amount of alkaline material so in extractioll ve~;sel 92 to e~fect ex~rackion. Thus, pulp 88 is subjected to an aqueous alkaline solution for a predetermined ti~De and at a predetermined temperature c :>rrelated to the quantity of alkaline material to solubilize a substantial 30 portion of any lignin which Ll - in~ in the pulp, in ve~;sel 92 .
This extraction process al50 increafies the brightness of the pulp, typically by about 2 GE brightness points. Thereafter, the alkali treatsd pulp 94 is directed to washing unit 96, the aqueous alkaline solution is washed from the pulp ~o as to 35 remove substantially all of the solubilized lignin from the 2~3~ ~
WO91/18145 37 PCT/US9~/02823 pulp, thus forming a sub6tantially lignin-free pulp. This step is well known to those skilled in the art and no further comment is ~1e~ -~ necess~ry h~re. The examples illustrate the pre~erred extraction param~ters ~or this step of ~he process.
5 At least a portion of the alkaline ~olution 98 which is recover~d i~ recycled to wa~hin~ unit 84. ~gain, ~ajor environmental benefit~ are achieved from the eli~ination of sewering o~ thi~ solution.
In ~o~ c~se6, particularly where higher final 10 brightn~s~es are targeted, the extraction step ~an be augmented by incorporating an oxygen treatment within the caustic extraction step ~Eo)~ This alternative, ~lso well known to tho~e ~killed in the art, require6 no further c~ -nt here.

15 5. Additional Bleaching Staqes For most paper~aking purposes, a final brightness in the range o~ 50 to 65 is un~atisfa tory. Accordin~ly, in order to further rai~e the GE brightne~s to the ~ore desirable rang oP about 70 t~ 95~, the pulp i8 subjected to brightening 20 bleaching, which is prim~rily int~n~d to convert the chl~ oph~rir groups on the lignin remaining in the pulp into a c~lorle~s state.
Aft~r extracting and rew:~hin~ the pulp, the brighteni~g blaaching of the o~one-bleached and extracted pulp 25 can be performed u~ing a variety o~ ~aterial~. As illustrated in Fig. 2, the washed pulp lO0 is combined with the chosen bleaching agent 102 in bleaching vess~l 104. The preferr~d bleaching agent is chlorine dioxide or peroxide. After bleaching, the pulp 106 is washed with watex ll~ in washing , 3~ unit 108 and the effluent is either recycled llO or sewered 112. When recycled, at least a portion of wash water stream llO is directed to washia~ unit 96. The resultant bleached pulp 116 may then be collected and used in a variety o~
application~.

~3~3~
WO91/1814~ -38- PCT/US90/02823 One of the principal materials which ha~ h~retofore b~en u~ed, and which is generally highly effective, is chlorine dioxide (D) (see Fig. l). In accordance with the invention, an appropriate amoun~ of chlorine dioxide enables high-strength 5 p~lp6 having a GE brightnes~ value greater than about ~o% to be obtained. Since the pulp~ entering the chlorine dioxide stage are relatively low in lignin, the chlorine dioxide brightening bleaching can be carried out in the pre ence of only from about O.25% to about 1% of chlorin~ dioxide based on the oven dry 10 weight of the pulp.
The chlorine dioxide which i~ utilized in the brighteniny proce s ~hould preferably be prepared by a process which i~ free ~rom elemental chlorine. Alternatively, however, and less preferably, chlorine dioxlde which doe6 contain a 15 minor A - ~nt of elemental chlorine can be used without any 6ubstantial increase in the relative A -un~ of undesirable pollut~nt~ because of the relatively low amount of lignin present in the ozone-bleached pulp~ The effluent from the final bleaching ~tep of thi~ invQntion when u~ing chlorine 20 dioxide i~ exceptio~ally low and can be discharged ~afely 35 shown in Fig. 2.
If ~ewering of th~ efflulant fro~ the final chlorine dioxide bleaching ~tep is unacceptable t the stream can, however, be further purified by being treated with a ~embrane 25 ~iltration process such ~s reverse osmosis. This technique provide~ a clean filtrate that can be recycled back to previous bl¢aching stages for further use. Thi~ has the benefit of reducing Presh water usage. ~oreover, the concentrated chloride stream6 that result from the me~brane filtration are D relatively low in volu~e.
There ~ay be some cases when extremely high pulp brigh~ness~fi are desired, for example, 92-95% GEB, wher~
additional stages of bleaching may be required. An additional extraction and chlorine dioxide treatment would be a common 3S choice, thereby creating a OmZmEDED bleach sequence.

2 ~
WO91/18145 _39_ PCT/US90/02823 Instead of using cAlorine dioxide for final brighkening, tbe brightening bleachinq may be conducted with hydrogen p~roxide, as also shown in Fig. 1. Thi~ technique provides a co~pl~tely chlorine~free bleaching cycle (such as an 5 O~ZmEP sequence), wherein no chlorinated ~aterials are foxmed in the bleaching proce3s and the liquid extraction product c~n be readily recycled without the n~ce~ity for cumbersome ~iltration techniques. When utilizing peroxide~ a6 the bleaching agent, however, the K No. of the pulp from either 10 so~twood or hardwood should be reduced to a level of about 6 prior to the ozonation step in ord~r to obtain, as a ~inal product following the peroxide bl~aching stage, a pulp of acreptable brightness, i.e., a GE Brightne s of gr~ater than about 80%, ~ince peroxide i~ not a~ e~fective at bleaching as 15 is chlorine dioxide. Where a completely chlorine/chlorine dioxide~free process i~ de6ired, howev~r, peroxide provides acceptable re~ults.
Typical peroxide bxightening agents and their use in this ~tep are conventional, and one ~killed in the art would 2~ know the appropriate ~onc~ntration, type~ and u~e o~ 3ueh peroxide agents. Hydrogen peroxide i~ preferred.
The washed, further brightened pulp ha a GE
brightnes~ of between about 70 and 95%, and preferably between about 80 and 95~. Also, the phy~ical propertie~ of this pulp are co~ensurat with those obtainable by pulp produced by co~,ven~io~al CEDED or OC/DED proces~es.

6. W~hin~ Effluent Recycle In any pulp process, filtrate management is an 30 important factor in the overall econo~y or cost of operation of the process. The water which i~ used in the process requires both acces~ to a suitable ource and treatment of the effluent prior to ~isch~rge.

~S3~
WO91/18145 40 PCT/~S90/02823 In an effor~ to reduce the water demand of the process, it i6 desirable to recycle a6 ~u¢h of th~ effluQnt as possible. ~his practice cannot be u~ed with processes utilizing chlorine or multiple s~ep~ of chlorine dioxide, since 5 the effluents produced by these proc~ contain large amounts of chlorides produced by the by-products of such chemicals.
Thus, recycling the e effluents cau~es a build-up of chlorides which, in tuxn, cause6 ~ither corrosion of proce~sing equipment or t~e use of eYr~ive ~aterial~ af con~truction. In 10 addition, such recycled ef~luent re~uire substantial treatment before these effluents can be ~ch~rged from the mill, thus requiri~g ~urther expenditures for aquipment and treatment chemicals.
A~ illustrated in Fiy. 4, use o~ either the 1~ conventio~al CEDED process or the OC~DED technique results in a significant di~pos~l problem with regard to the e~fluents produced from the w~hin~ steps due to the high leYels of chloride r~ont~ini~q ~ ~unds found therein. A~ noted above, the~e strea~s cannot be recycled, and are preferably treated 20 before ~is~h~rge into the environment. Recycling of effluent could be u ed to decrease the a -_n~ of water used, but then the proce s e~uipment m~y be ~ubject to increased corrosion rates due to the increased chloride level in the re~ycled e~fluent.
In contra~t, howev~r, use of the Om~mED proce6s of the invention result~ in formation of only a inir 1 amount of chlorinated material in the wash water, which water can be ~aPely ~ rged, i.e.l sewered, within mo~t environmental protection standards. Alternately, this effluent ~ay be 30 treated by reverse ssmosis to provide an even cleaner filtrate that may be recycled to previous bleaching ~tages as shown for further use without the build-up of chlorides. When a D
bleaching ~tage is desired, steps may be taken to reduce the demand for chlorine dioxide. An Eo step may allow the pulp to WO91/181~5 2 ~ ~ 3 5 9 ~ PCT/US90/02823 achieve greater lev~ls of brightne~s ~lthough additional expense is incurred by the use o~ additional sodium hydroxide and oxyg~n in this step. ~l o, there are Xnown industry procedures for preparing shlorine dioxide whereby r~sidual 5 chlorine levels are in;~ized (e.gO, the R8 proc~ss vs. the R3 proce~s). The~e reduced chlorina lev~l chemical~ are pr~ferred for use in the D stage to reduce the chloride levels of th~
wash water e~lu~nt.
In~tead o~ O~ZmED, one ~ay use the OmZmEP process of 10 the inven~ion to obtain additional subRtantial advantage over the prior art in that no chlorinated co~pounds whatsoever are produced. Thi~ enables all of the efflu~nt to be r2cycled without experiencing the proble~s of chloride build-up in the proces wash water streams.
Accordingly, the proces6 of the present inv~ntion achieve~ sub3tantial advantages with respect to reductions in effluent volume, color, COD, BOD and chlorinated organics.
MoreoYer, since the effluent used in the wA~hin~ steps contains significan~ly reduced chloride levels comp~red to prior art 20 processes which utilize chlorine, t:he wA~h;~ unit vents will not be c~rrying chlorina~ed organic ~ unds or gases which require tr~at~ent prior to ~i~ch~s~.

EXAMPLES

The scope of the invention is further described i~
conn~ction with the follcwinq examples which are set forth for purposes of illustration only and which are not to be con trued as limiting the scope of the invention in any 30 manner. Unle6s otherwise indicated, all che~ical percentages are calculated on the basis of the weight of oven dried (OD) fiber. Also, o~e skilled in the art would understdnd that the target brightness values do not need to be precisely achieved, ae GEB value of plu5 or minus 2% ~rom the 2~3~
W091/1~145 ~2 PCT/US90/~23 target are acceptabl~. In all the examples having a D stage, except Example ll, ~n R-3 type of chlorine dioxid~ solution, known to contain a 6:l ratio of dioxide to elemental chlorine, was u~ed.

EX~MPL2 1 (Compara~ive) Loblolly pine chipfi were lab batch cooked according to the conditions in Table I to produce a ~onventional kra~t pulp. The resulting pulp had a ~ No. of 22.6 and a visco~ity of 27.l cps. The kraft pulp wa then subjected to cQnventional oxygen treatment (Tables II and V) fo7lowed by bleaching to a final target brightness of 83 GEB using both a convantional OC/DED sequence (Table III) and an OZmED
blea~h; nq ~equence (Tables IV and V). The ozone bleaching stage was run at 35% consi~t~ncy with an ozone application of 0.~1%.

2~

. 30 2 ~
WO 91/18145 43 PCr/lJS90/û2823 TABLE I
LOE~LOLLY PINE }~FT PULPING CONDITIONS
CONDITION/STEP PARAIIETER

PREST}31~M TIME (minO ) 2 . 5 TIME TO ~ 175~C 1 hour TIklE ~T ~ ;KATURE - 175~C 1 hour LI~2UOR:WOOD ratio 4: l SULFIDITY (%~ 25.8 ACTIVE ATX~T.T ( % ) 17 . 4 % AA FRC~M BI~CR LIQU~R FIT.l'.~CK O . ~3 K NO. 22 . 6 VISCOSITY (ep~) 27.1 TABLE II
PINE rypIcAL cor~v~ oNAL O STAGE R~.FAC~TNG CONDITIONS
PULP
PRESSURE CONSISTENCY
(PSIG) 9~ C13ENICAL ~ TEMP ~~C) (%) 2 . 5 NaOH 10 . 2 110 27*
0.1 MgS04 * both for alkali addition ~nd oxygen deligTlification . 30 2~3~
WO 91/18145 _44_ PCl'/US9~/02~23 TABIE I I I
PINE TYPICAIJ C/DED Bhl~CHING Ct)NDITIONS
STEPCHEMICAL pH TEMP PU~
( % ) ( ~ C ~ CONS I STENCY
(%) C/D3 . 6 Cl2 l . 8 50 3 .15 0. 6 ~l~2 E1.5 NaOH 11.5 70 12 - 10 D0 . 3 ClO2 4 O 2 60 12 TABLE IV
PINE TYPICAL ACIDIFICATION CONDITIONS
STEP % CHE~ICAL pH TE~P PUI P
~C) CONSIS~E~CY
(%~
Acidification to pH 2 2 22 3-4 (H S0 ) 2 d, Chelation 0s ll 2 22 3-4 ( oxal ic acid ) S~EP CHEMII::AL pH ThMP. PULP
(%) (~C) CONSISTENCY
(%) Z (Ozone) 0 . 2 to î 2 to 4 22 35-45 E 1.5 NaOH 11.5 70 12 D l . 0 Cl02 4 . 2 60 12 As shown in Table VI and VII ~low, OZmED bleaching under the~e c:orldiltions produced a pulp ha~ing acceptable strenyth properties compared to an 83% GE target brightnes~ OC/DED
basel ine pulp . Under these condition~, the OZmED pulp had 5 marginal viscosity of ~ . 7 cp~. The E;trength proper~ies were measured on an OZmED pulp where the final D-stage application was 2 . 5% . Target brightness was reached only with an excessive chlorin~ dioxide charge. The OZ~E pulps response to chlorine dioxide treatment shows that higher briyhtness can 10 only be achieYed by signif icantly in~reasing the ozone application, which then cause significant viscosity and strength loss of the pulp.
TABLE VI
PINE ~RAFT OC/DED A21D KRAFr OZ~ED PROPERTIES COMPARISON
OC/DED OZ~nED
CSE* TEAR ~F.AKT~G CSF* TEAR P~F~AKTNG
FACTOR LENGTH FACTOR LENGTH

646 205 6 . s4 659228 5 . 85 508 142 8 . 46 492147 8 . 49 351 145 8 . 81 334126 8 . 50 178 129 8.43 197121 8.54 * Cnn~ n Starldard Freeness , 30 2 9 6 3 ~ ~ 1 W O 91/18145 ~6 PCT/US90/02823 TABLE VII
PINE KRAFT OZ ED BRIGHTNESS RESPONSE

ClO2 (~) O 1.3 1.5 1.7 l.9 2.2 2.52.8 Brlght- 48.0 61.3 76.l 79.4 81.0 81.8 83.9 83.9 ness (GEB ~) EX~MPLE 2 A kra~t/AQ brownstock was prepared in a laboratory batch digester fro~ loblolly pine chip6 as described in Tabl~ VIII.
The K No. o~ the re~ulting brownstock was 18.3 and the Vi~coSlty was 20.6 cps. The ~r~ft/AQ pulping conditions pro~~ce~ a pulp having a significantly lower lignin content than in Example 1 as evi~enced by the K No., without unacc~ptable deterioration of pulp strength as evidencsd by the viscosity.

W~ 9~/181~5 ~L7 ~/US90/~823 ThBl;E3 VI I I
IJOBLOLLY PINE ~FT/AQ PULPING C'ONDITIC~NS

CONDITIOM~STEP PA~ETER

PXEST:ESAM TIME (min. ) 2 . 5 TI~E TO 1~l~ 175~C 1 hour TI~E AT lhr.~;~A~ruRE - 175~C 1 hour I.IQUOR:WOOD ratio 4 :1 SUL~IDITY (%~ 25 . 3 ACTIVE .I'~T.l~T.T ( 96 ~ 113 . O
% AA FROM BL~C~C LIQUOR FILLB.~r~ o . 43 AQ - % ON woola 0 . 025 K NO. lE~ . 3 VISC:O~ITY 20. 6 21) The Kraft~AQ bro6~tock was then subj ected to further bleaching using the conventional OC/DED E~e~auence and the OZmED sequence as ghown in Tables II, III, IV and V to a 25 t2rget brightness of 83% GEB. U~;e of the Kra~t AQ pulping technology achieved t~e goal of producing a starting pulp with a low K No., havlng acceptable viscosity properties, for the ozone bleaching ~equenc:e. The ozone bleaching stage was run at 35% consistency with an o~one application of o. 35% and 30 1. 69~ C:102 was used in the f inal D stage to reach target brightnes~ .

2 ~
WO 91/1814~ -48- P~/US90/02~23 As shown in Tables IX and X below, the optical properties a~ measured by brightr~es~ respon~;e in the f inal chlorine dioxide ~tagf~ w~re i~proved and ~rength prvperties wer~ acceptable c:ompared to the OC/DED baseline.

TABLE IX
PINE K~AFT/AQ OC/DE~ AND 0~ ED PROPERTIES COMPARISON

10OC/DED OZmED
TEAR BREAKING TEAR BREAKING
CSF FACTOR LENG~H CSF FACTOR LEN5TH
658 194 6.02 650 194 6.2g 16 524 139 8.14 497 159 7.83 352 128 8.92 334 130 8.34 190 119 8.74 211 121 8.59 TABLE X
PINE KRAFT/AQ OZ ED BRIGHTNESS RESPONSE

25C102 (~) O 0.3 1.2 1.6 2.0 2.4 Brightness ~GEB~) 52.9 76.8 80.7 83.2 83.4 83.8 2 ~ 6 ~
W091/181~ ~9 PCT/US9~/02823 EX~MPLE 3 (Comparative) A pine Kraft brownstock having a K No. of about 24 was pressed to a consistency of about 30-36~ by weight to produce a high con~istency ~t. The m t of brownsto k was sprayed with a 10% sodium hydroxide solution in an amount su~ficient to produc~ approximately 2.5 weight percent ~odium hydroxide based on pulp dry weight. Dilution water was added in an sufficient to adjust the brown~tock mat to about 27%
~~ consistency. The high consist~ncy brownstock mat was then subjected to o~yg~n delignification using the following conditions: llO~C, 30 minutes, 80 psig ~2 Pine Kraft brownstock of Example 3 was introduced into a treatment ve~s~l along with a su~ficient volume of lO~ NaOH
solution to effect a 30% ~aOH addition bas~d on oven-dried pulp. Sufficient dilution water was added to obtain a brownstock consistency of about 3S by w~ight in the treatment ve~sel. The brownstock and the aqueous sodium hydroxide solution were uniformly mixed at room te~pera~ure by a ribbon mixer ~or about 15 minuteA. The tr2ated brown tock was then pressed to a consistency of about 27% by weight. After pre~sing, the sodium hydroxide on the ~iber equaled abou~
~.5% as in Example 3. The treated brownstock was ~hen deligni~ied according to the oxygen delig~i~ication proce~ure d~scribed in Example 3. A comparison is shown in Table XI.

~3~
WO~ gl45 50 PCT/US90/02823 TABLE XI

COMPARISON OF OXYGE~ STAGE BT~uT~G RESULTS

EXAMPLE 3(0) EXAMPL~ 4(0~) R No. 13 9 Visco~i~y (cps) 14.8 14.0 1~ As c~n be seen from a comparison of Examples 3 and 4, a pre~erred method o~ the present i~vention of u$ing a low consistency alkali addition followed by a high con~istency oxygen treat~ent (O~) produced a bleached brownstock having qreater delignification (lower K No.) than the prior art methods, without any sub~tantial chan~e in strength properties.
As a result of the lower X No. pulp produced by this process, subsequent bleaching step6 can be adjust~d to accommodate the higher brightness, lower lignin cont~inin~
2~ pulp. Thus, the bleaching stage8 for such pulp require less bleaching agent or shorter bleaching ti~es than ~or pulp which is not treated according to the pr~sent invention.

E~AMPLE 5:
Z5 Pulp produced ~rom pine in accordance with the ~m process of Example 4 of the pre~ent invention is comp~red to that produced conventionally (O) (i.e., with no low con~istency alkaline tre~t~enk step). Th~ av~rage caustic dosage ~or high consistency oxygen deligni~ication of 30 brownstock pulp was ~ound to be 45 pounds per oven dri~d ton (lb/t) or 2.3%. At that level, the average reduction in X
No. across the oxygen deligni~ication reactor was 10 units.
For the same level of caustic applied to pulp according to a WO91/18145 2 016 3 ~ 9 1 PCTtU590/02823 preferred treatment step, an average K No. drop during delignification was found to be 13 units: a 30% improvement compared to the conventional proce~s.
This advantage in delignificztion ~electivity can also b~ shown by a compari~ion of pulp visc06ity. The av~rage K No. and vi~c06ity for conventional pulp was 12.l and 14.4 cps, re~pectively. For the preferred treatment process of the invention, the average X No. at essentially the same vis~osity (l4.0 cp~) wa~ 8.3.
Deligni f ication ~electivity can also b2 e~pr~ ed as the change ln vi8c08ity versu~ the ch~n~ in K No.
between brown~tock and the correcpon~i~g treated pulpso Oxygen delignification selectivity decreases rath~r rapidly when the change in K No. begins to exce~d lO K No. units.
The d~crea e in selectivity is observed a~ a rapid incxease in the change in vi6cosity for a given change in K No. As an exa~ple, for a Çh~n~e in X No. o~ 12 units, the corresponding change in ~i cosity i~ expected to be 12 to 13 Cp8. By contra~t, for the same ch~n7~ in ~ No. (12) 2~ obtained by delignified pulps which have been kreated u~ing the prePerred ~ethod, the change in viscosity wa~ found to be about 6 cps. The change in vi8c06ity per change in X No.
app~ars to be consta~t up to ~ 16 to 17 K No. unit change for pulp obtained u~ing the pref~rred trea~ment proc~ss of the invention. The re~ults are shown in Table XII.

WO91/18145 52 PCTiUS90/02823 ~ABLE XII

PINE KRAFT PU~P PROPERTY COMPARISON
Conv~ntional Modified oxygen Oxygen Treatment (O) Treatment (O ) Unbleached Pulp X No. 21.9 20.5 10 Viscosity (cps~ 21.5 20.5 Ratio of K No./ l.02 l.0 ~isco~ity Q~ygen Deli~ni~ication Stage Pulp R No. 12.1 8.3 Viscosity (cps~ 14.4 l~.~
Ratio of X No./ 0.84 0.59 Viscosity Cau~tic, lb~t 39.4 46.0 Delignification (%) 44.7 59.5 EXAMP~E 6 A southern pine pulp was pro~uce~ in an operating 600 TPD ~ine paper ~ill using the modi~ied oxygen delignification process (o~) having the conditions of Table II in combination with the uni~orm alkali treatment a~ described in Examples 4 and ~ and the condition~ as ~hown in Table XIII
below. The O-~tage pulp produced by thi~ novel method had 30 th~ properties neeAe~ to stlcces~fully co~plete the bleaching process using ozone, as described in the embodiment of this invention. The oxygen stage pulp had a R No. of 7.9 (compared to a typical conventional O-stage X No. of about 12). Viscosity of the delignified pulp was 15 cps and was 35 not significantly reduced by the high degree of 2B~3~i91 deligniIication obtained by ~he l~e of th~ modified ~ vgen proce6s. This pulp ~-ould then be further bleached with ozone, utilizing any o~ the mamerous process emb~di ?nts desc:ribl3d herein to produce a pulp having acs::eptable *inal S strength anà optical propertie~.
C/DED bleaching of this pulp waE~ completed in the laboratory~ ~~ described in Table XIY, to provide a bas~line for comparison of properties.

t 0 TABI.E XI I I
TYPICAL ~ODIFIED OXYGEN (O ~ STAGE CONDITIONS
STEP % CHEMICAL pR TEMP PULP
IJSED ON OD ( ~~::) CONSISTEMCY
FIEiERS ( % ) 15 Treatmerlt 30% -- 2~ 3 4 (Nat)H) oxygen (~2 ) 80 psig l0 . 2 ll0 27 (MgSO4 ) o . l TABLE XIV
PINE KRAFT C/DED BLEACHING CONDITIONS
STEP CHEMI CALpH TEMP . PULP
( 9c ) ( ~C~ CONSISTENCY
(%) C/D 2 . 4 Cl2l. 8 50 3 .15 0 . 4 ClO2 30 E l . 05 NaOH ll . 5 70 12 D 0 . 23 Cl02 4 . 2 60 12 WO91/1814~ 43 ~ 9 ~ PCT/US90/02823 The ozone bleaching stage was carried out in a pilot plant reactor as shown in Fig. 2. Condition~ of operation of the pilot plant reactor are shown in Table XV.

TABLE XV
PILOT PLANT REACTOR TYPICAL OPERATING CONDITIONS

OPERATING PARAMETER VALUE OR CONDITION
Gas ~nd pulp ~1~ws Cocurrent Operating rate 6.5 OD TPD*
Gas flow rate 58 scf~
Pulp consisten~y 42 Ozon~ applic~tion (Note: 1.18 increa~ed ozone amount u~ed due to pulp containlng dissolved solids that consu~e ozone) Pulp residence time 1 ~i~ute Zm stage K No. 3.9 Z~ stage ~iscosity 11.8 ~ps Zm stag~ brightness 55% GEB

* oven dried tons per day The ozone bleached pulp generated in th~ pilot plant reactor was then treated in extraction and chlorine dioxide ~tages in the laboratory, as described in Table V above, to 30 produce a final bleached pulp product at target brightness.
A final D stage charg~ of only l.O % ClO2 was used on the fiber.

WO 91/1~1~5 _55_ PCI/US90/02823 The strenql:h and optical propertie~ o:E the ozon~
bleached pulp were acceptable comp~red to the conventional OC/DED baseline and the rasult6 o~ the comparitSon are shown in Tables XV~ and XVII below.

TABLE XVI
PINE O C/DED ~nd O Z ED P~OPE~TIES CONPARISON
O C/DED O Z ED
m m s~

GSFTEAR ~ ART~G CSF TEAR R~F.AKTNG
FACTOR LENGTH FACTOR LENG~H

15 656147 6 . 80 659 177 5 . 57 511 113 8 . 00 510 146 6 . 93 335 96 8 . 69 367 111 7 . 90 217 101 8 . 69 17~ 100 8 . 20 2~
TA~IE XVII
Plne_Om2 ED 13RI~ N~-~S }~:SPONSE

C1~2 (%) O 0.5 1.0 Brightness (GEB9~) 55 . 070. 0 84 . 2 , ~0 WO91/t8145 -56- PCT/U~9~/02823 To further exemplify the utility and range of applicability of the procsss of this inv~ntion, a southern hardwood fiber, from ~ixed hardwood co~prising predominantly gum and oak, wa~ bleached with ozone in ~he pilot plant described in Example Ç a~ove. ~ conventional oxyg~n stage pulp produced in the 600 TPD mill was treated with ozone in the pilot plant reactor. The oxygen stage pulp had a K No.
of 5.7 and a viscosity oP l4.l.
A portion of the 0 stage pulp was final bleached by the conventional C/DED sequence in ~he laboratory to provide a baselinD for comparison. The C/DED conditions are shown in Table XVIII.

TABLE XVIII
~UDWOOD TYPICAL C/DED BT.F.A~uTNG CONDITIO~S
STEP CHEMICAL pH T ~ . PULP
(4) (~C) CO~SISTENCY
(%) C/D 1.61 C12 1.8 50 j.15 0.26 C102 E 1.0 NaOH 11.9 70 12 25 D 0.35 C102 4.2 60 12 ~he ozone reactor treatment conditions are shown in T~ble XIX. The pilot plant Zm staye pulp was th~n ~in~l bleached by conventional E and D stages as ~hown in Table XX
to a target brightness. A D-stage C102 charge of only 0.35%

was used on OD fiber. Strength and brightness properties were acceptable compared to the baseline as shown in Tables XXI and XXIIo W ~ 91/18145 _~7_ PCT/US9~/02~3 TABLE XIX
HARDWOOD PILOT PLANT REACTOR OPERATING CONDITIONS
5 OPERATING PARAHETER VAL~E OR CONDITIOM
Gas and pulp flows Cocurrent Operatin~ rate 9 OD TPD
Gas flow rate 60 scfm 10 Pulp consistency 36 Ozone applic~tion (Note: 0.86 increased ozone a~ount used due to pulp contalning dissolved solids that consume ozone) 15 Pulp residence ti~e l minute Z stage R No. 2.5 Z stage viscosity ll.9 Z stage brightness 63% GEB

TABLE XX
ED $YPICAL R~F.AOUTNG CONDITIONS USED ON OZ ~ARD~OOD PULP
STEP ~HEMICALpH TEMP. PULP
~) (DC) CONSISTENCY

E l.O NaOH 12.0 70 12 D 0.35 ClO24.36 60 12 WO91/18145 5~ PC~/VS90/02823 TABLE XXI
~WOOD OC/DED oND OZ ED PROP~RTIES COMPARISON
ul OC~DED OZm~D
5 CSF T ~ ~R~AKT~G CSF T ~ BR~KING
FACTOR LENGTH FACTOR ~ GTH
526 89.9 ~.41 515 88.3 4.52 399 87.2 5.71 419 82.0 5.65 262 79.5 6.26 293 70.5 6.56 208 72.0 6.46 ~87 64.3 6.87 TABLE XXII
16 ~U~WOOD OZ ED BRIGHTNESS RESPONSE
~u Cl~2 (%) O 0.35 Bri~htne s (GEB~) 64.0 84.4 EXAMPLE 8:
Co~parison tests similar to Example 5 were carried out for laboratory prod~ce~ ~raft ha.Ld~ood pulp, from mixed hardwood comprising predominantly gum and oak. Again, it was found that a signi~ican~ly larger K No. ~rop across the o~ygen delignification reactor u~ing the modified oxygen proce s (O~) is achi~ved compared to conventional oxygen processing (O). The average caustic dosage for hardwood was 27 lb/t, or l.4%. This produced a K No. drop of about 5 units during the oxygen step. For the same level of Cal!StiC
utilized according to the modified oxygen process of the present invention, an average K No. drop of about 7.3 units was obtained, an increase of almost 50%.
3~

2 ~

This advantage in delignification ~electivity can also be shown by comparing pulp vi~cosity. ~he average hardwood K
No. and vi~co~ity were found to be 7.6 and 16 cps, respectively~ For the invention, a K N5. of 6 and a viscosity of 17.7 was obtAined~ Al~o, the K No. at the same visco~ity a~ the non-treated pulp (16 cps), wa~ found to be 5.8.
Delignification ~eleckivity can al~o be expressed in term~ of the change in Yi~Cosity ver~u~ the çhAn~e in K No.
betw~en brownstock and the correspo~ding modi~ied oxygen treat~d pulp~. In co~paring pulp8 which ar~ conventionally o~yg~n treated with tho~e o~ the invention, th~re i a ~reater de~rease in delignification electivi~y for increased degrees o~ delignific~tion. For a change in K No. of 4 unit~ the average change in viscosity wa~ 4 cps ~or pulps produced by the conventional proc~s~. By contrast, the change in X No. for the ~ame change in vi8c05ity for pulp5 produced by the ~odified oxygen method wa~ 7 unitsO
Expre~ed in ter~6 of a delignification selectivity ratio, the R~lectivity for the ~odified ~ethod wa~ l.8 K No./cps and khat ~or the conv~ntional procs~s wa~ l K No./cps, an incr~se of 80%. Results are ~hown in Table XXIII.

, 30 2 ~
WO 9t/1~145 -60 - PCr/US90/028~3 TABLE XXI I I

PULP PROPERTY COMEARISON
(HARDWOOD~
5Cs:>nventional oxyg~n Modif ied Oxygen U;~leas:hed Pulp Treatment (O) TreatD~ent (O ) K No. 12.3 ï3.0 Visc~sity (cp~)21 ~ 6 23 . 4 Ra~io of K No./ ~ ' 57 0 . 56 Viscosity O~cygen DeligniiEication Stage Pulp K No. 7.6 600 i Visc08ity. (Cp8) 16.~ 17.7 Ratio of K No./ 0 . 47 0 . 33 Vi~ o~ity Caustic, lb/t 27 . 6 26. 4 Delignii~ication (%) 38 . 0 54 . O

EX~MPL~: 9 A series oP experimPnts were carxied out in 'che pilot plant r~actor using pulp ~rom a 600 TPD f ine paper mill with 25 a conventional oxygen deligni~ication stage (O). These experiDI~nts were p~rformed to illu~trate the ~ff~c:t of pH on the ozone ble~h ~ ng proces~ using southern hardwood~ .
Reactor operating conditions were held constant at the conditioTIs shown in Table XXIV with the pH of the ozone stage being the only variable.

WO 91/18145 2 ~ ~1'3 ~ ~ PCI/US90/02823 TABLE XXIV
~IARDWOOD PILOT PLANT REACTOR TY~ICAL OPERATING CONDITIONS
OPERATING PARAM~TER VAlUE OR CONDITION

Gas ~nd pulp flows C~cu~rent Operating rat~ 9 OD TPD
Gas flow r~te 40 scfm lO Pulp c~nsi~tency 40%
Ozone applic~tion (Note: 15t increased ozone ~ount used due to pulp containing dlssolved qollds ths~ consume ozone) P~Llp residence tim~ 1 minute ~5 As can be ~een from T2~ble XXV below, the effect of pH on the ozone b1~achir~g process is ~ignificant with lower pH
benef icially i~proving the ~electivity of the blaa ::hing 20 proc:e~;s, TABLE aD~V
EFFECT OF pH ON HARDWOODS
;25 PARA~IET~ pH 5 pH 4 pH 3 pH 2 C~L~IGE IN K NO. ACROSS THE -2.79 -3.17 -3.16 -3.67 Zm STA~E
CHANGE IN BRIGHl~ESS +12.1 -~15.0 +11.7 ~17.4 ACROSS THE Zm STAGE (GEB) 3~ CHANGE IN VISCOSITY ACROSS -6.0 -7.1 -4.9 -4.4 THE Zm STAGE ( cp~ ) WO91tl814~ -62- PCT/US90/02823 EX~PLE 10 A number of comparative propertias are of interest to illustrate the bene~icial e~fects of producing fully blea~hed pulps using the OZ~ED proce~ ypical operatlng data and effluent ~ ?nts were collected ~rom operating mills using the CE~ED and OC/DED bleaching sequ~nces on Southern pine. These propertie~ were co~pared to tho~e of ef~luents pro~uce~ by the OZ~ED sequence, u~ing the OZ~ED pulp and effluent prepared in Example lo For the conv~ntional CEDED
sequence see Table XXVI, for the conventional OC/DED seguence see Tables II and III above and for the oZ E~ ~equence ee Tables IV and V ~bove. It sho~ld be noted that the CE~ED
~equence e~luent is the combined C, El, Dl, E2 and D2 effluentO The OC/DED efflu~nt is th~ C/D, E and D combined effluent anA the OZmED effluent i6 the D stage ePfluent, each repre~enting the several effluent properties. A~ shown in Table XXVII below, the ozone ble~hi n~ ~equenc~ sub~tantially re~u~ the environmental i~pact of th~ effluent from the ble~in~ proce~6. To d~t~ ;ne color, EPA method 110.2 was u8ed. From this data, it can be ~een that the present invention proYide~ a ~ischArge effluent having a color of no greater than about 2 pound per ton, a BOD5 value of no greater than about 2 pounds per ton and an amount of total organie chloride of no greater than about ~ and pre~erably le~s than about 0.8.

, 30 2 ~
WO 91/18145 63 P~r/lJS90tO2823 TABLE X~{VI
PINE CEDED sT.~.A~}lT~G CONDITIONS
STEP CHE~lICAL pH TENP. PULP
( ~ ) ( ~ C ) CONS I STE:NCY
(%) C 5 . 3 C12 4 . 10 40 3 . 15 E 3 . 25 N~ON 11. 3 70 12 E 0. 6 N~OH 11. 670 12 D 0.12 C102 3 60 12 TABLE XXVX I
COMPARISON OF CEDED, OC/DED AND OZ~ED BLEACHIN(:
PARAMF.TF.R CEDED OC/Dl:D OZ~ED
BOD5 ~lbs/t~n) 34 21 Col~r (lbs/ton) 367 83 les~ than 1 20 TOCl ( lbs/ton) 7 4 0 . 8 E~L~MPI E 11 Southern pine kraft pulp was bl~ached using three 2S modifi¢ation~ of the basic OZED ~Isquence. In the first ~laquence (02~ED), 1~he pulp was bleas:hed as in Tables IV and V
with conventional oxygen, Dodified ozone, caustic extraction and chloride dioxide as produ~ed in the R-3 sequence with a ClO2/Cl2 ratio of 6: l. In the second sequence, the modified 30 oxygen process (ODI) was utilized and again the final stage u6ed an R-3 ~ype of chlorine dioxide. In the third sequ~nce, the modified oxygen process (~m) was used ons:e again, and an WO 91/18145 --64- PCr/US90/02823 R-8 chlorine dioxide solution was employed with 95: l ratio in thi3 ~inal s~age. Table XXVIII d~mon3trates the positive envi - ~~ ~ntal impact o~fered with the use o~ ~he modified oxyg~n proces. (~m). ~he R-8 bleach liquor also hadl a 5 positive e~fect.

TA1 Sl,E X~nlI I I
EFlFLUEN~ E ROM E~T~A~~TT~G OF
PINE RRAP~ PULPS
1~
Sequence Q~ED 0,i7'i ~n ni 7,jl~n RatiO C1~2/Cl2 6: :L 6 :1 95 :1 in Last Stage TOCl, lb/torl 0.8 0.3 0.2 Southern loblolly pine pulp wer~ prepar~d by the kraft and kra~t/AQ pulping proce~e~ a6 de~cribed in Tables I and 20 VIII a~ove. The~;e pulps were furt.her ~;ubjected to conventiollal and modified oxyg~n delignification as described in Examples 4 and 5 to 2~how the ef'fect of co~bining these process~s (for exten~in~J delignifi.ca~ion with mi~ impact on pulp strength) on the ozone bleachinq sequence. As can 25 readily be se~n from Table XXIX, t:hese processes produc:e an ~dditive effect. Extremely low 0mZmE K Nos. can be reached with little impact on final visco~:ity~ Conver~ely, the amount of ozone neede~l to reas:h a target 0 Z E K No. of about 3.5 for the previously described ozone bleaching process c:an be 30 sub~tantially reduced. In addition, the additive effect produce~ a southern pine pulp that can be fully bleached by an O Z EP process where a very low o Z E K No. is required for a m m m m functional p~roxide stage.

~3~9~
W O 91/1~145 ~65- PCT/US90/02823 TABLE XXIX
ADDITIVE EFFECTS OF KRAFT/AQ AND MODIFIED OXYGEN (O~) PINE PULPS
PARAMETER KRAFT + O KRAFT/AQ + KRAFT/AQ
(Prior Art) O O
m OZONE APPLICATION OF
O.5% TO EACH CASE
K No. S.2 3.4 1.8 10 VISCOSITY (cps) 12.1 11 l0.1 PROPERTIES AND OZONE
APPLICATION AT
TARGET K No. of 3.5 Ozone (~) 1.0 0.5 0.29 VISCOSITY (cp~) 8.9 ll 1l.8 Example 13 Southern softwood, i.e., loblolly pine, wa~ bleached to target brightness of 83 GEB u~ing the conventional CEDED
Baquence a8 E~hown in Table XXVI, using the conventional OC/DED
~eq~ ce as shown in TableE; II and III above and using the OZmED sequenc~ as shown in Tables IV and Y above. Wood based 25 dirt wa~ refined and added to the OZDiED starting bro~mstocX at a level of O . 75% by w~ight to examine the ability of this ~equenc~ to re~ove dirt compared to CEDED and OC/DED bleaching.
Dirt propertie6 of the three sequ!ences, measured as Effective Black Area, bark and shives, were equivalent.

, 30 Example 14 Thi;, example illustrates the range of applic:ability of the ozone bleaching process of the invention. Bleached pulps can be produced over a wide range of product brigh~ne~ses, 35 utilizing appropriate combinations o~ ozone and chlorine 2 0 ~
WO 91/1~14~ -66- PC~/V~ X23 dioxide charges l:o minimize environm~ntal i~npact~ and operating co~t~ 8 6hown in T~ble XXX below, product~; having briyhtnes~
from above 65% GEB can be pro~luce~l by various combination~ of ozone and chlorine dioxide whila r~taining rea60nable str ngth 5 propertie~.

TABLE X~
OZI~ED R~ FAf:UTNG CONDITIONS

10 ST~P CHEMICAL pH TEMP. TIME PULP GEB K NO. VISCOSITY*
C) (mln. ) CON. (&) (40~1) (cps. ) (4) O [ Conditlons giv~n in Table XIII ] 40 8 . 5 12 . 5 Z O . 43 2 22 1 . 5 ~3 50 - - 10 15 ~ 1 . 5 11 . 5 70 ~0 1~ - - - - 9 . 8 D O . 5 4to5 70 180 12 65 - - 9 . 6 0.7 70 9.6 * Viscos1ty ~lu~8 ~fter the 0 st~ge ~re lnterpol~t~d Y~lues b~ed on est~bllshed data.

~ ile it is appar~nt that the inv~ntion herein disclosed i5 well calculatad to fulfill the objective~ stated above, it will be appreciat~d that numerou~: ~odification~; and .~ oA; -nts 25 ~nay be d~vi~ied by those ~killsd in the art, and it i~ intended that the ~rpen~e~ claims cover all such modifications and i ~nt~; a8 fall within the ~rue spirit and ~cope of the pre~ent inv~ntion.

, 3

Claims (125)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A process for the manufacture of a bleached pulp having a certain GE brightness and a certain strength as indicated by a certain viscosity which comprises:
chemically digesting a lignocellulosic material to provide a pulp;
oxygen delignifying the pulp to remove a substantial portion of the lignin;
the combination of the chemical digesting and oxygen delignifying steps being selected to provide an intermediate pulp containing a specified amount of lignin and having a specified viscosity; and ozone delignifying the intermediate pulp by adjusting the consistency and pH of the intermediate pulp to predetermined values, comminuting the intermediate pulp into discrete particles of a size having a sufficiently small diameter and a sufficiently low density to facilitate substantially complete penetration of a majority of the particles by ozone, and bleaching the particles with ozone in an amount sufficient to remove a substantial portion, but not all, of the lignin by intimately contacting and mixing the discrete particles with the ozone for a sufficient time and at a temperature sufficient to obtain substantially uniform delignification and bleaching throughout a majority of the particles to form a bleached pulp;
wherein the specified amount of lignin of the intermediate pulp is such that, after ozone delignification, the bleached pulp attains the certain GE brightness, and wherein the specified viscosity of the intermediate pulp is sufficiently high to compensate for viscosity decreases during ozone delignification, thus permitting the bleached pulp to attain the certain strength.

2. The process of claim 1 wherein the pulp particles have a size of less than about 5mm.

3. The process of claim 1 or 2 which comprises chemically digesting the lignocellulosic material by Kraft pulping, Kraft AQ pulping or extended delignification.

4. The process according to claim 1 wherein the oxygen delignification step comprises forming a low to medium consistency pulp; treating the low to medium consistency pulp with an aqueous solution of an alkaline material for a predetermined time and at a predetermined temperature relative to the quantity of the alkaline material to substantially uniformly distribute the alkaline material throughout the low to medium consistency pulp; raising the consistency of the pulp to a high consistency; and subjecting the resulting high consistency pulp to high consistency oxygen delignification to obtain the intermediate pulp.

5. The process of claim 1 wherein the certain GE
brightness is at least about 50%, the certain viscosity at the certain strength is greater than about 10 cps, and wherein the specified amount of lignin is indicated by an intermediate pulp K No. of about 10 or less and the specified viscosity is greater than about 13 cps.

6. The process of claim 1 wherein the lignocellulosic material is a softwood, the certain GE
brightness is at least about 50%, the certain viscosity at the certain strength is greater than about 10 cps, and wherein the specified amount of lignin is indicated by an intermediate pulp K No. of about 7-10 and the specified viscosity is greater than about 13 cps.

7. The process of claim 1 wherein the lignocellulosic material is a hardwood, the certain GE
brightness is at least about 55%, the certain viscosity at the certain strength is greater than about 10 cps, and wherein the specified amount of lignin is indicated by an intermediate pulp K No. of about 5-8 and the specified viscosity is greater than about 13 cps.

8. The process of claim 5, 6 or 7 wherein the amount of lignin contained in the pulp after ozone delignification is indicated by a bleached pulp K No. of about 3 to 4.

9. The process of claim 1 which further comprises bleaching the pulp after ozone delignification with a brightening agent to increase the GE brightness of the bleached pulp.

10. The process of claim 9 which further comprises combining the bleached pulp with an effective amount of alkaline material in an alkaline aqueous solution at a predetermined temperature, correlated to the amount of alkaline material combined, to solubilize a substantial portion of any lignin remaining in the bleached pulp; and thereafter extracting a portion of the aqueous alkaline solution so as to remove substantially all of the solubilized lignin therefrom and form an extracted pulp prior to bleaching with the brightening agent.

11. The method of claim 9 wherein the brightening agent is chlorine dioxide or a peroxide.

12. A process for delignifying and bleaching a lignocellulosic material to a pulp having a certain GE
brightness and a certain strength as indicated by a certain viscosity, which comprises:

digesting a lignocellulosic material to form a pulp having first K No. and first viscosity value;
delignifying said pulp with oxygen to form a partially delignified pulp having a second K No. lower than said first K No., and which is sufficient to enable the partially delignified pulp to be further delignified with ozone while maintaining viscosity at a level such that cellulose components of said partially delignified pulp have not been significantly chemically degraded by the oxygen delignification; and further delignifying the partially delignified pulp by applying thereto a sufficient amount of ozone for a sufficient time correlated to the amount of ozone applied to said partially delignified pulp to obtain a substantially delignified pulp having a third K No. significantly reduced below said second K No. of said partially delignified pulp and a GE brightness value substantially above that of the partially delignified pulp while maintaining viscosity and without agressively chemically attacking cellulose components of the pulp to avoid substantially reducing the strength of the pulp.

13. The process of claim 12 wherein the partially delignified pulp contains an amount of lignin which, after ozone delignification, permits the pulp to attain the certain GE brightness, and also has a viscosity which is sufficiently high to compensate for viscosity decreases during ozone delignification, thus permitting the substantially delignified pulp to attain the certain strength.

14. The process of claim 12 which further comprises combining the substantially delignified pulp with an effective amount of alkaline material in an alkaline aqueous solution at a predetermined temperature, correlated to the amount of alkaline material combined, to solubilize a substantial portion of any lignin remaining in the substantially delignified pulp;

and thereafter extracting a portion of the aqueous alkaline solution so as to remove substantially all of the solubilized lignin therefrom and form a substantially lignin-free pulp.

15. The process of claim 14 which further comprises bleaching the substantially lignin-free pulp to a brightness value which is substantially higher than that of the substantially delignified pulp.

16. The process of claim 12 wherein the viscosity of said partially delignified pulp is maintained at greater than about 13 cps.

17. The process of claim 16 wherein said partially delignified pulp is maintained at a viscosity decrease of about 30% or less of said first value.

18. The process of claim 12 wherein said lignocellulosic material is a hardwood.

19. The process of claim 18 wherein said first K No.
is between about 10-14.

20. The process of claim 18 wherein said first viscosity value is between about 21-28 cps.

21. The process of claim 18 wherein said second K
No. is between about 5-8.

22. The process of claim 21 wherein said third K No.
is less than about 5.

23. The process of claim 12 wherein said lignocellulosic material is a softwood.

24. The process of claim 23 wherein said first K No.
is between about 20-24.

25. The process of claim 23 wherein said second K
No. is between about 7-10.

26. The process of claim 12 wherein the oxygen delignification treatment is carried out on pulp of medium consistency.

27. The process of claim 12 wherein the partial delignification step further comprises:
treating said pulp with a quantity of alkaline material in an aqueous alkaline solution for a predetermined time and at a predetermined temperature correlated to the quantity of alkaline material to substantially complete a substantially uniform distribution of the alkaline material throughout the pulp;
increasing the consistency of the pulp after the completion of the treating step; and subjecting the increased consistency alkaline material containing pulp to high consistency oxygen delignification to obtain a partially delignified pulp.

28. The process of claim 12 wherein the viscosity of said substantially delignified pulp is maintained at greater than about 10 cps.

29. The process of claim 28 wherein said substantially delignified pulp is maintained at a viscosity decrease of about 30% or less of the viscosity of said partially delignified pulp.

30. The process of claim 12 wherein the further delignifying step additionally comprises:

increasing the consistency of said partially delignified pulp;
comminuting said increased consistency pulp to a predetermined particle size; and uniformly contacting said comminuted pulp with said effective amount of ozone as the pulp is advanced through the process.

31. The process of claim 30 wherein the particle size of said increased consistency pulp is comminuted to one that facilitates uniform contact with ozone without causing significant degradation of the cellulose components of the pulp.

32. The process of claim 31 wherein the pulp is comminuted to about 5 mm and advanced through the process in a manner to avoid a non-uniform application of the ozone to the pulp.

33. The process of claim 32 wherein the comminuted pulp is advanced cocurrently with the ozone.

34. The process of claim 32 wherein the comminuted pulp is advanced countercurrently to the ozone.

35. The process of claim 15 wherein the substantially lignin free pulp is bleached with chlorine dioxide.

36. The process of claim 15 wherein the substantially lignin free pulp is bleached with a peroxide.

37. The process of claim 35 or 36 wherein the bleaching step raises the GE brightness of said substantially lignin free pulp to at least about 70%.

38. The process of claim 35 or 36 wherein the bleaching step raises the GE brightness of said substantially lignin free pulp to at least about 80%.

39. The process of claim 35 or 36 wherein the bleaching step raises the GE brightness of said substantially lignin free pulp to at least about 90%.

40. A process for delignifying and bleaching lignocellulosic material which comprises:
partially delignifying lignocellulosic material to form a pulp having a K No. of about 10 or less and a viscosity of greater than about 13 cps; and further delignifying said pulp with an effective amount of ozone for a sufficient time to obtain a substantially delignified pulp having a K No. of about 5 or less, a viscosity of greater than about 10 and a GE brightness of at least about 50%.

41. The process of claim 40 wherein the lignocellulosic material is a softwood and is partially delignified to a pulp having a K No. of about 7 to 10 and a viscosity of above about 13 before further delignification with ozone.

42. The process of claim 41 wherein the softwood pulp has a K No. of about 3 to 4, a viscosity of above about 10 and a GE brightness of at least about 50% after said further delignification with ozone.

43. The process of claim 40 wherein the lignocellulosic material is a hardwood and is partially delignified to a pulp having a K No. of about 5 to 8 and a viscosity of above about 13 before further delignification with ozone.

44. The process of claim 43 wherein the hardwood pulp has a K No. of about 3 to 4, a viscosity of above about 10, and a GE brightness of at least about 55% after further delignification with ozone.

45. The process of claim 40 which further comprises:
combining the substantially delignified pulp with an effective amount of alkaline material in an aqueous alkaline solution for a predetermined time and at a predetermined temperature correlated to the quantity of alkaline material to solubilize a substantial portion of any lignin which remains in the pulp, and thereafter extracting a portion of the aqueous alkaline solution so as to remove substantially all of the solubilized lignin therefrom and form a substantially lignin-free pulp.

46. The process of claim 45 wherein said extracting step raises the brightness of the pulp by about 2%.

47. The process of claim 45 which further comprises bleaching the substantially lignin-free pulp with one of chlorine dioxide or a peroxide to raise the GE brightness to at least about 70%.

48. The process of claim 47 wherein the GE
brightness is raised to at least about 80%.

49. The process of claim 47 wherein the GE
brightness is raised to at least about 90%.

50. The process of claim 45 wherein the lignocellulosic material is partially delignified by an oxygen delignification treatment.

51. The process of claim 50 wherein the oxygen delignification treatment is carried out on pulp of medium consistency.

52. The process of claim 45 wherein the lignocellulosic material is partially delignified by:
forming a pulp having a relatively low consistency of less than 10% by weight;
treating the low consistency pulp with a quantity of alkaline material in an aqueous alkaline solution for a predetermined time and at a predetermined temperature correlated to the quantity of alkaline material to substantially complete a substantially uniform distribution of the alkaline material throughout the pulp;
increasing the consistency of the pulp to at least about 20% by weight after completion of the treating step; and subjecting the increased consistency alkaline material containing pulp to high consistency oxygen delignification to obtain a partially delignified pulp having a K No. of about 9 or less and a viscosity of about 13 or higher.

53. A process for delignifying and bleaching lignocellulosic material which comprises:
partially delignifying a lignocellulosic material to form a pulp;
reducing the consistency of the pulp to a low consistency of less than 10% by weight;
treating the low consistency pulp with a quantity of alkaline material in a aqueous alkaline solution for a predetermined time and at a predetermined temperature correlated to the quantity of alkaline material to substantially complete a substantially uniform distribution of the alkaline material throughout the pulp;
increasing the consistency of the pulp to at least about 20% by weight after completion of the treating step;

subjecting the increased consistency alkaline material containing pulp to high consistency oxygen delignification to obtain a partially delignified pulp having a K No. of about 9 or less and a viscosity of greater than about 13 cps;
further delignifying said partially delignified pulp with an effective amount of ozone for a sufficient time to obtain a substantially delignified pulp having a K No. of about 5 or less, a viscosity of greater than about 10 and a GE
brightness of at least about 50%;
combining the substantially delignified pulp with an effective amount of alkaline material in a aqueous alkaline solution for a predetermined time and at a predetermined temperature correlated to the quantity of alkaline material to solubilize a substantial portion of any lignin which remains in the pulp;
extracting a portion of aqueous alkaline solution so as to remove substantially all of the solubilized lignin therefrom and form substantially lignin-free pulp; and bleaching the substantially lignin-free pulp to raise the GE brightness thereof to at least about 70%.

54. The process of claim 53 wherein the GE
brightness is raised to at least about 80%.

55. The process of claim 53 wherein the GE
brightness is raised to at least about 90%.

56. The process of claim 53 wherein the lignocellulosic material is a softwood and is partially delignified to a K No. of about 8 to 9 and a viscosity of greater than about 14 before further delignification with ozone.

57. The process of claim 56 wherein the softwood pulp has a K No. of between about 3 to 4, a viscosity of above about 10, and a GE brightness of at least about 54% after said further delignification with ozone.

58. The process of claim 53 wherein the lignocellulosic material is a hardwood and is partially delignified to a K No. of about 6 to 7 and a viscosity of above about 15 before said further delignification with ozone.

59. The process of claim 58 wherein the hardwood pulp has a K No. of between about 3 to 4, a viscosity of above about 10, and a GE brightness of at least about 63% after said further delignification with ozone.

60. The process of claim 53 wherein the partially delignified lignocellulosic material is obtained by Kraft pulping, Kraft-AQ pulping or extended delignification of a lignocellulosic material.

61. The process of claim 53 which comprises decreasing the K No. of the increased consistency pulp by at least about 60% during the oxygen delignification step without significantly damaging the cellulose components of the pulp.

62. The process of claim 53 wherein the pulp is subjected to the high consistency oxygen delignification without substantially changing the viscosity of the pulp.

63. The process of claim 53 which comprises decreasing the ratio of K No. to viscosity of the pulp during the oxygen delignification step by at least 25%.

64. The process of claim 53 wherein the consistency of the pulp which is treated with the aqueous alkaline solution prior to oxygen delignification ranges between about 1 and 4.5%
by weight.

65. The process of claim 53 wherein the consistency of the pulp is increased to between about 25 and 35% by weight prior to the oxygen delignification step.

66. The process of claim 53 wherein the amount of alkaline material distributed throughout the low consistency pulp prior to oxygen delignification ranges from about 15 to 30% by weight based on the dry weight of the pulp.

67. The process of claim 66 wherein the aqueous alkaline solution has a concentration of alkaline material of between about 20 and 120 g/l, so that the concentration of alkaline material in the low consistency pulp ranges from about 6.5 to 13 g/l.

68. The process of claim 53 wherein the alkaline treating step is conducted for a time of between about 1 and 15 minutes at a temperature of between about 90 and 150°F.

69. The process of claim 53 wherein the initially formed pulp is brownstock pulp and further wherein at least a portion of the liquid obtained from the alkaline solution during the pulp consistency increasing step is recycled to the alkaline treating step.

70. A process for delignifying and bleaching a lignocellulosic material which comprises:
forming a brownstock pulp having a K No. of from about 10-24 by Kraft pulping, Kraft-AQ pulping or extended delignification of a lignocellulosic material;

decreasing the consistency of said pulp to about 1 to 4.5% by weight;
treating the decreased consistency pulp with a quantity of alkaline material in an aqueous alkaline solution having a concentration of alkaline material of between about 20 and 120 g/l, for a time of between about 1 and 15 minutes and at a temperature of between about 90 and 150°F such that the concentration of alkaline material in the decreased consistency pulp during this treating step ranges from about 6.5 to 13 g/l, so as to substantially complete a substantially uniform distribution of the alkaline material throughout the pulp;
increasing the consistency of the alkaline treated pulp to between about 25 to 35% by weight;
subjecting the increased consistency pulp to high consistency oxygen delignification without substantially changing the viscosity of the pulp to form a partially delignified pulp having a K No. of about 10 or less and a viscosity of greater than about 13, wherein the ratio of K No.
to viscosity of said pulp is decreased by at least about 25%
during oxygen delignification;
further delignifying said oxygen delignified pulp with an effective amount of ozone for a sufficient time to obtain a substantially delignified pulp having a K No. of about 5 or less, a viscosity of greater than about 10 and a GE
brightness of at least about 50%;
combining the substantially delignified pulp with an effective amount of alkaline material in an aqueous alkaline solution for a predetermined time and at a predetermined temperature correlated to the quantity of alkaline material to solubilize a substantial portion of any lignin which remains in the pulp;
extracting a portion of aqueous alkaline solution so as to remove substantially all of the solubilized lignin therefrom and form a substantially lignin-free pulp; and bleaching the substantially lignin-free pulp to raise the GE brightness thereof to at least about 70%.

71. The process of claim 70 wherein the GE
brightness is raised to at least about 80%.

72. The process of claim 70 wherein the GE
brightness is raised to at least about 90%.

73. The process of claim 70 which comprises decreasing the K No. of the increased consistency pulp by at least about 60% during the oxygen delignification step without significantly damaging the cellulose components of the pulp.

74. The process of claim 70 wherein the substantially lignin-free pulp is bleached with chlorine dioxide or a peroxide.

75. The process of claim 74 wherein the peroxide is hydrogen peroxide.

76. The process of claim 7 n which further comprises adding a chelating agent to said pulp prior to ozone delignification to render metal ions substantially non-reactive to ozone.

77. The process of claim 76 wherein the chelating agent is DTPA, EDTA or oxalic acid.

78. The process of claim 70 which further comprises adjusting the pH of the pulp to a range of about 1 to 4 by adding to the pulp a sufficient quantity of an acidic material prior to ozone delignification.

73. The process of claim 70 which further comprises increasing the consistency of the pulp to between about 25-50%
by weight prior to ozone delignification.

80. The process of claim 79 wherein the consistency of the pulp is increased to between about 35-45% by weight prior to ozone delignification.

81. The process of claim 70 which comprises comminuting said pulp to a diameter of less than about 5 mm after oxygen delignification and prior to ozone delignification.

82. The process of claim 70 which further comprises maintaining the pulp at a temperature of less than about 120°F
during ozone delignification.

83. The process of claim 70 wherein the ozone is provided by a mixture comprising ozone and oxygen.

84. The process of claim 83 wherein the ozone concentration in the mixture is between about 1 and 8 percent by volume.

85. The process of claim 70 wherein the ozone is provided by a mixture of ozone and air.

86. The process of claim 85 wherein the ozone concentration is between about 1 and 4 percent by volume.

87. The process of claim 70 which comprises advancing the partially delignified pulp during the ozone delignification step in a manner which subjects substantially all the pulp to ozone.

88. The process of claim 87 which comprises introducing the ozone countercurrently to the advancing pulp.

89. The process of claim 87 which comprises introducing the ozone cocurrently with the advancing pulp.

90. A process for delignifying and bleaching a lignocellulosic material which comprises:
partially delignifying a liynocellulosic material by pulping to form a pulp and delignifying said pulp with oxygen to form a partially delignified pulp having a K No.
of about 10 or less and a viscosity of greater than about 13 cps;
adding a chelating agent to said pulp to render metal ions therein substantially non-reactive to ozone;
adjusting the pH of said pulp to a range of about 1 and 4 by adding a sufficient quantity of an acidic material thereto;
increasing the consistency of said pulp to between about 25 and 50%;
comminuting said increased consistency pulp to a diameter of less than about 5 mm;
further delignifying said increased consistency pulp with an effective amount of ozone for a sufficient time by advancing the comminuted pulp in a manner which subjects substantially all the pulp to the ozone to obtain a substantially delignified pulp having a K No. of about 5 or less, a viscosity of greater than about 10 and a GE
brightness of at least about 50%;
combining the substantially delignified pulp with an effective amount of alkaline material in an aqueous alkaline solution for a predetermined time and at a predetermined temperature correlated to the quantity of alkaline material to solubilize a substantial portion of any lignin which remains in the pulp;

extracting a portion of aqueous alkaline solution so as to remove substantially all of the solubilized lignin therefrom and form a substantially lignin-free pulp; and bleaching the substantially lignin-free pulp with chlorine dioxide to raise the GE brightness thereof to at least about 70%.

91. The process of claim 90 wherein the GE
brightness is raised to at least about 80%.

92. The process of claim 90 wherein the GE
brightness is raised to at least about 90%.

93. The process of claim 90 wherein the pulping step comprises Kraft pulping and the oxygen delignification step decreases the K No. of the pulp by at least about 60%
without significantly damaging the cellulose components of the pulp or without substantially changing the viscosity of the pulp.

94. The process of claim 93 wherein the pulping step comprises Kraft AQ pulping.

95. The process of claim 94 wherein the oxygen delignification step decreases the K No. of the pulp by at least about 60% without significantly damaging the cellulose components of the pulp or without substantially changing the viscosity of the pulp.

96. The process of claim 90 wherein the pulping step comprises the combination of Kraft AQ pulping and extended delignification, and the oxygen delignification step decreases the K No. of the pulp by at least about 60%

without significantly damaging the cellulose components of the pulp or without substantially changing the viscosity of the pulp.

97. The process of claim 90 wherein during ozone delignification the pulp is advanced in a manner so that the pulp is maintained at a temperature of less than about 120°F.

98. The process of claim 90 wherein the chelating agent and acid are added to said pulp in a mixing chest.

99. The process of claim 98 wherein at least a portion of the liquid separated from the pulp during the consistency increasing step is recycled to the mixing chest.

100. The process of claim 98 wherein the pulp is advanced cocurrently with the ozone.

101. The process of claim 98 wherein the pulp is advanced countercurrently with the ozone.

102. A process for delignifying and bleaching a lignocellulosic material which comprises:
partially delignifying a lignocellulosic material by pulping to form a pulp and delignifying said pulp with oxygen to form a partially delignified pulp having a K No.
of about 10 or less and a viscosity of greater than about 13 cps;
adding a chelating agent to said pulp to render metal ions therein substantially non-reactive to ozone, adjusting the pH of said pulp to a range of about 1 and 4 by adding a sufficient quantity of an acidic material thereto;

increasing the consistency of said pulp to between about 25 and 50%;
comminuting said increased consistency pulp to a diameter of less than about 5 mm;
further delignifying said increased consistency pulp with an effective amount of ozone for a sufficient time to obtain a substantially delignified pulp having a K No. of about 5 or less, a viscosity of greater than about 10 and a GE brightness of at least about 50%;
combining the substantially delignified pulp with an effective amount of alkaline material in an aqueous alkaline solution for a predetermined time and at a predetermined temperature correlated to the quantity of alkaline material to solubilize a substantial portion of any lignin which remains in the pulp;
extracting a portion of aqueous alkaline solution so as to remove substantially all of the solubilized lignin therefrom and form a substantially lignin-free pulp; and bleaching the substantially lignin-free pulp with a peroxide to raise the GE brightness thereof to at least about 70%.

103. The process of claim 102 wherein the GE
brightness is raised to at least about 80%.

104. The process of claim 102 wherein the GE
brightness is raised to at least about 90%.

105. The process of claim 102 wherein the pulping step comprises Kraft pulping and the oxygen delignification step decreases the K No. of the pulp by at least about 60%
without siynificantly damaging the cellulose components of the pulp or without substantially changing the viscosity of the pulp.

106. The process of claim 102 wherein the pulping step comprises Kraft AQ pulping.

107. The process of claim 106 wherein the oxygen delignification step decreases the K No. of the pulp by at least about 60% without significantly damaging the cellulose components of the pulp or without substantially changing the viscosity of the pulp.

108. The process of claim 102 wherein the pulping step comprises the combination of Kraft AQ pulping and extended delignification, and the oxygen delignification step decreases the K No. of the pulp by at least about 60%
without significantly damaging the cellulose components of the pulp or without substantially changing the viscosity of the pulp.

109. The process of claim 99 or 102 wherein the ozone delignification reduces the R No. of the pulp by at least 50%.

110. The process of claim 90 or 102 wherein the bleaching step raises the GE brightness of the pulp by at least 50%.

111. The process of claim 10 wherein the GE
brightness of the pulp is increased to at least 83%.

112. A process for delignifying and bleaching a lignocellulosic material which comprises:

partially delignifying a lignocellulosic material by pulping to form a pulp, washing said pulp, and delignifying said pulp with oxygen to form a partially delignified pulp having a K No. of about 10 or less and a viscosity of greater than about 13 cps;
washing the partially delignified pulp;
further delignifying said partially delignified pulp with an effective amount of ozone for a sufficient time to obtain a substantially delignified pulp having a K No. of about 5 or less, a viscosity of greater than about 10 and a GE brightness of at least about 50%;
washing the substantially delignified pulp;
combining the substantially delignified pulp with an effective amount of alkaline material in an aqueous alkaline solution for a predetermined time and at a predetermined temperature correlated to the quantity of alkaline material to solubilize a substantial portion of any lignin which remains in the pulp;
extracting a portion of the aqueous alkaline solution so as to remove substantially all of the solubilized lignin therefrom and form a substantially lignin-free pulp;
washing the substantially lignin-free pulp;
bleaching the substantially lignin-free pulp with one of chlorine dioxide or a peroxide to raise the GE
brightness thereof to at least about 70%; and washing the bleached pulp.

113. The process of claim 112 wherein the GE
brightness is raised to at least about 80%.

114. The process of claim 112 wherein the GE
brightness is raised to at least about 90%.

115. The process of claim 112 wherein the bleached pulp washing step comprises washing said pulp with fresh water, and separating the pulp from the resulting wash water effluent.

116. The process of claim 112 wherein the bleaching step utilizes chlorine dioxide and the bleached pulp wash water effluent is discharged.

117. The process of claim 112 wherein the bleaching step utilizes chlorine dioxide and the bleached pulp wash water effluent is treated by reverse osmosis to form a treated filtrate and at least a portion of said treated filtrate is then directed to the substantially lignin-free pulp washing step.

118. The process of claim 112 wherein the bleaching step utilizes a peroxide and at least a portion of the bleached pulp is recycled to the step wherein the substantially lignin-free pulp is washed.

119. The process of claim 117 or 118 wherein the substantially lignin-free pulp washing step comprises washing said pulp with bleached pulp wash water, separating the pulp from the resulting wash water and directing at least a portion of said wash water to the substantially delignified pulp washing step.

120. The process of claim 119 wherein the substantially delignified pulp washing step comprises washing said pulp with the substantially lignin-free pulp wash water, separating the pulp from the resulting wash water and directing at least a portion of said wash water to the partially delignified pulp washing step.

121. The process of claim 120 wherein the partially delignified pulp washing step comprises washing said pulp with substantially delignified pulp wash water, separating the pulp from the resulting wash water and directing at least a portion of said wash water to the pulp washing step.

122. The process of claim 121 wherein the pulp washing step comprises washing said pulp with partially delignified pulp wash water, separating the pulp from the resulting wash water, and collecting and concentrating said wash water prior to incineration in a recovery boiler.

123. The process of claim 112 or 122 wherein the bleaching step utilizes chlorine dioxide having a minimum chlorine content.

124. The process of claim 112 or 122 wherein the water demand for the washing steps is substantially reduced compared to conventional CEDED or OC/DED processes.

125. The process of claim 116 wherein the discharge effluent has a color of no greater than about 2 pounds per ton, a BOD5 value of no greater than about 2 pounds per ton and an amount of total organic chlorides of no greater than about 2.