AU2005229652A1 - Peroxide/oxygen/alkali pulp bleaching - Google Patents

Description

01-NOI.J-2005 03:46 P j PPRK 64 9 3566990 P.03 01-NOU-2005 03:48 A J PARK 64 9 3566990 P.03 -1- Regulation 3.2

AUSTRALIA

PATENTS ACT, 1990 COMPLETE

SPECIFICATION

FOR A STANDARD

PATENT

ORIGINAL

Name of Applicant: CARTER HOLT HARVEY

LIMITED

Actual Inventors: THOMAS ALAN CLARK and ADRIAN

RICHARD

LYSAGHT

Address for service A J PARK, Level 11, 60 Marcus Clarke Street, Canberra

ACT

in Australia: 2601, Australia Invention Title: PEROXIDE/OXYGEN/ALKALI PULP BLEACHING The following statement is a full description of this invention, including the best method of performing it known to us.

COMS ID No: SBMI-01868505 Received by IP Australia: Time 14:00 Date 2005-11-01 01-NOV-2005 03:49 A J PRRK 01-OU-00503:9 PJ PRK64 9 3566990 P.04 -2- C The invention relates to pulp treatment Procedures intended to improve the brightness stbltNadcl taiity of products formed from the unblached pulp.

>0saiiyadclu tb Z For linerboard and other products produced from nbleached wood pulp such as pulp, colour and brightness can be key qualities in determining value to a customer, Manufacturers of packaging, who are primary users of linerboard, generally require a product of consistent brightness and colour.

Unbleached linerboard is generally produced from pulp having a high lignin content.

The higher the lignin content, the higher the yield. However, high lignin contaning pullps N 10 have a dark colour. Lighter coloured, lower lignin content unbleached pulp can be used for the top layer of linerboard sheets for packaging intended to have a reasonable quality printed o outer surface.

Colour stability can be a problem with linerboard and other products produced from unbleached pulp. The product may tend to darken under exposure to light, and in particular is ultraviolet light. The product colour also changes to become more red in shade. The darkening and reddening -process is referred to as "reversion!' and if significant is poorly regarded in the market.

In the manufacture of bleached pulp, it is known to use oxygen and alkali to delignify the pulp prior to bleaching. The process involves exposure of the pulp for a reasonably prolonged period, of generally an hour or more, to caustic conditions (an alkali charge in excess of with an oxygen charge of 10-20 kg/ton pulp, or more, at a temperature generally of the order of 95 0 C or more. Such oxygen delignification is used to reduce the Kappa number of the pulp generally by about 30 50%. The resulting pulp may then, be bleached to high brightness with conventional bleaching processes and with nearly complete removal of the lignin, to produce a product having high brightness and colour stability. In general, such an oxygen delignification process is considered not appropriate in the manufacture of unbleached linerboard, since it is desirable to maintain the pulp yield as high as possible, while achieving an acceptable linerboard brightness and colour.

Our Australian Patent No. 766612 relates to a procedure adapted to improve brightness stability and colour stability in products produced from a pulp without subsequent bleaching the process prior to the formtion of preferably linerboard).

The procedure of our aforementioned Patent Specification involved treating the unbleached kraft pulp from which the linerboard is to be produced at alkaline p11 (preferably 10.5 to 12) with oxygen or an oxygen containing gas (such as air) for a time insufficient to COMB ID No: SBMI-01868505 Received by IP Australia: Time (I-tm) 14:00 Date 2005-11-01 01-NOV-2005 03:49 A J PARK 01-NU--005 03:9 P1 Pl~(64 9 3566990 -3significantly reduce the lignin content yet to confer an end use advantage. The full Content of 0 the aforementioned Australian Patent is hereby included by way of reference.

In our Australian patent, in the final stages of the processing of kraft Pulp, we z disclosed that when washing was carried out substantially under anoxic conditions the 5 resulting pulp was brighter and more yellow than pulp produced when washed in the presence o of oxygen, yet linerboard products formed from this brighter pulp had poor brightness and colour stability with severe brightness and colour reversion upon exposure to light. It was this reversion that the patented process addressed and that the present invention can also address.

While in the preferred form of the process of our aforementioned patent the ci 10 alkali/oxygen treatment was carried out after washing of the pulp and prior to storage, the In treatment could be applied at different locations in any particular fibreline configuration. For o example, in a multi-washer fibreline the treatment of that invention could be applied before the last washer thereby enabling the added sodium hydroxide to be recovered in the final washer filtrate. The process was also stated as including a less than optimnal treatment configuration where the treatment with the oxygen or oxygen containing gas was before pulp washing which lead to loss of most of the oxygen by reaction with sulphide ion and dissolved lignixis in the weak black liquor.

The experimentation of our aforementioned patent referred to the Kappa number as a measure to reflect pulp yield. It was stated however that the measurement of actual lignin content indicates that the process of the invention may result in somne lignin being oxidised but not removed and thus a reduction in Kappa number of 10% corresponded with a reduction in lignin content of only about The colour of the linerboard was measured by the CIE optical parameters referred to as a* (a measure of redness) and b* (a measure of yellowness).

In addition I) was measured as a measure of brightness or lightness of a product. An alternative was to use ISO Brightness instead of L*K Colour reversion can be quantified by measuring ISO Brightness, a* and b* before and after exposure of a product such as paper or linerboard to strong ultraviolet light for a predetermined period. It is characterised by increasing redness and decreasing yellowness and brightness.

Whilst the method of our aforementioned patent was described wit particular reference to the manufacture of unbleached kraft linerboard, the invention was stated as being equally applicable to the manufacture of other paper grades in which unbleached krafl pulp is used The present invention also relates to a lcraft pulp treatment procedure useful (inter alia) in the manufacture of a linerboard or equivalent paper or paperboard products.

COMS ID No: SBMI-01 888505 Received by IP Australia: Time 14:00 Date 2005-11-01 1-NOU-2005 03:49 A J PARK 64 9 3566990 P.06 -4- SThe present invention seeks to improve the invention of our aforesaid Australian SPatent and that is one object of the present invention.

Another or alternate object is to enhance characteristics as to reversion resistance Sand/or brightness without reliance of a bleaching process yet reliant on oxygen or an oxygen containing gas and a source or sources of peroxygen species [preferably to synergistic S effect] in alkaline conditions, without reliance on a mechanical pulp and/or without treatment in the context of deliberate 02-delignification and Eop peroxide reinforced In oxygen-delignification) stages.

IND By way of example, see: S 10 US 4756798 which uses alkaline peroxide and oxygen in conjunction with t 'brightening a mechanical pulp, and 8 EP 0206560A2 which uses alkaline peroxygens and oxygen in conjunction with 02- Sdelignification of unbleached kraft pulp, and also the use of oxygen and peroxygens to reinforce the alkaline extraction (Eop) stage of bleaching of chlorine or chlorine dioxide bleached kraft pulps, The present invention is an alternative to these disclosed uses of alkali, oxygen and peroxygens in chemical pulp delignification and bleaching and in prolonged mechanical pulp brightening.

Another or alternate object is to enhance characteristics as to reversion resistance (preferably by brightening by below 3% ISO) without reliance of a bleaching process yet reliant on oxygen or an oxygen containing gas and a source or sources of peroxygen species [preferably to synergistic effect] in alkaline conditions, without reliance on a mechanical pulp, and/or without treatment in the context of deliberate substantial 02-delignification and Eop peroxide and oxygen reinforced alkaline extraction) stages.

The present invention is directed to all pulpable wood species inclusive of both softwood and hardwood species. Our preference is to softwoods such as conifers of the pine species Radiata). The process can be applied none the less to any high yield pulps (including semi-chemical pulps and mechanical pulps) irrespective of end use applications.

In one aspect the invention consists in a method of colour stabilisation of a high lignin pulp which involves subjecting a high lignin content pulp stream (preferably totally unbleached) to the presence of a peroxygen compound (or active metabolites thereof) under oxygen pressure and in alkaline conditions for a time less than one hour.

COMS ID No: SBMI-01868505 Received by IP Australia: Time 14:00 Date 2005-11-01 01-NOU-2005 03:50 A J PARK 64 9 3566990 P.077 Preferably the time is less than 30 minutes and more preferably less than 20 minutes.

Preferably the time is from 1 to 15 minutes, more preferably 3 to 10 minutes.

Preferably the time is a transit period in a pipeline and/or "retention" tube.

Preferably the pulp is brightened by the peroxygen compound by less than 3% ISO (more preferably less than 2% ISO).

In another aspect the invention is an improvement of the process of our aforementioned Australian Patent in its broadest aspects for kraft pulp processing [irrespective of pH claimed therein provided operated in alkaline conditions], the improvement being to provide less colour reversion of paper, linerboard, or the like to be formed from the high lignin pulp by the use of a peroxygen compound (preferably at least in part under oxygen pressure) as a brightening stage.

Preferably the brightening stage is in alkaline conditions e.g. substantially as herein described.

The increase in brightness is less than 10% ISO and preferably less than 5% ISO.

Preferably the increase in brightness is less than 3% ISO Preferably the increase in brightness is less than 2% ISO.

In another aspect the invention consists in a process for reducing colour reversion of a paper product to be made from high lignin pulp, the process involving subjecting a pulp that has been subjected to little (if any) delignification to both (serially and/or simultaneous) alkaline oxygenation, and peroxide brightening by less than 10% ISO, more preferably by less than ISO and usually by 3% ISO.

Preferably is performed at least in part under oxygenation and in alkaline conditions.

Preferably both and follow at least one wash of the pulp.

Preferably at least is performed at least in part in a pipeline and/or retention tube.

Preferably the oxygenation of is at a pressure of oxygen or an oxygen containing gas of from 1 to 20 bar, more preferably 1 to 10 bar, most preferably 1 to 5 bar.

Preferably the oxygenation of is at a pressure of oxygen or an oxygen containing gas of from 1 to 10 bar, more preferably 1 to 5 bar (yet optionally with storage to follow at less than 10 bar).

Preferably the oxygenation of and is simultaneous.

COMS ID No: SBMI-01868505 Received by IP Australia: Time 14:00 Date 2005-11-01 01-NOU-2005 03:50 A J PARK 01-OIJ-205 3:5 P3 RRK64 9 3566990 P.09 -6- In another aspect the invention consists in a mnethod of producing a Icraft Pulp (preferably of high lignin content and preferably unbleached) suitable for linerboard and/or other paper product manufacture which involves subjecting a high lignin content Z (preferably unbleached) pulp stream to brightening (preferably by less than 10% ISO, more preferably by less than 5% ISO and usually by below 3% ISO) in alkaline conditions with at least one peroxygen compound (preferably hydrogen peroxide), and (N oxygen and/or an oxygen containing gas in such a way as to leave the pulp wit a high lignin content.

ci In one aspect the invention consists in a method of producing a kraft pulp (preferably of high lignin content and preferably ubleached) suitable for linerboard and/or other paper product manufactue which involves subjecting a high lignin content (preferably unbleached) pulp stream to brightening in alkaline conditions with at least one peroxygen compound (preferably hydrogen peroxide), and oxygen and/or an oxygen containing gas in such a way as to leave the pulp with a high lignin content.

In one aspect the invention consists in a method of producing a kraft pulp (preferably of high lignin content and preferably unbleached) suitable for linerboard and/or other paper product manufacture which involves subjecting a high lignin content (preferably unbleached) pulp stream to brightening in alkaline conditions with at least one peroxygen compound (preferably hydrogen peroxide), and oxygen and/or an oxygen containing gas in such a way as to leave the pulp with a high lionn content.

In another aspect the invention consists in a method of producing a kraft pulp (preferably of high lignin content and preferably unbieached) suitable for linerboard and/or other paper product manufacture which involves subjecting a high lignin content (preferably unbleached) pulp stream to brightening in alkaline conditions with at least one peroxygen compound (preferably hydrogen peroxide), and oxygen and/or arn oxygen containing gas, COMS ID No: SBMI-01 868505 Received by P1 Australia: Time 14:00 Date 2005-11-01 01-NOU-2005 03:51 A J PARK 64 9 3566990 P.09 -7- 0 storing the resulting pulp without addition of oxygen and/or an oxygen containing gas under the action of any persistent and/or frther added peroxygen compound(s), and Z deriving the brightened kraft pulp of high lignin content from step S 5 In another aspect the invention consists in a method of producing a kraft pulp (preferably of high lignin content and preferably unbleached) suitable for linerboard and/or other paper product manufacture which involves S(a) subjecting a high lignin content (preferably unbleached) pulp stream to 0 brightening in alkaline conditions with S 10 at least one peroxygen compound (preferably hydrogen peroxide), and t oxygen and/or an oxygen containing gas, 8 storing the resulting pulp without addition of oxygen and/or an oxygen containing gas under the action of any persistent and/or further added peroxygen compound(s), and deriving the brightened kraft pulp of high lignin content from step In another aspect the invention consists in a method of producing a kraft pulp (preferably of high lignin content and preferably unbleached) suitable for linerboard and/or other paper product manufacture which involves subjecting a high lignin content (preferably unbleached) pulp stream to brightening in alkaline conditions with at least one peroxygen compound (preferably hydrogen peroxide), and oxygen and/or an oxygen containing gas, storing the resulting pulp without addition of oxygen and/or an oxygen containing gas under the action of any persistent and/or further added peroxygen compound(s), and deriving the brightened kraft pulp of high lignin content from step Optionally at least additive may be present and/or have been present for "peroxide stabilising" purposes.

In many brightening stages, using hydrogen peroxide, stabilisers are added.

Transition metals, especially manganese, catalyse the decomposition of peroxides. Different chemicals can be added to adsorb or sequester the transition metals magnesium sulphate, magnesium hydroxide, chelating agents such as EDTA or DPTA, and sodium silicate).

COMS ID No: SBMI-01868505 Received by IP Australia: Time 14:00 Date 2005-11-01 01-NOU-2005 03:51 P j PRRK 64 9 3566990 01-NOV-2005 03:51 A J PA::RK 64 9 3566990 P. -8- 0In preferred forms of the present invention the pulp stream has been subjected to at cleast one wash prior to being exposed to the brightening procedure with the peroxygen compound(s) and oxygen or oxygen containing gas.

Z Less preferred is any procedure where there is a commencement of the brightening with such materials prior to washing as such materials will be challenged for their use by additional content sulphide ions) beyond that being targeted to provide the favourable outcomes for a pulp stream to be used as, for example, a linerboard and of course the alkali In becomes less easily recoverable.

As used herein the term "high lignin content" in respect of the kraft pulp stream to be c,1 10 treated refers to pulp having a Kappa number greater than 0As used herein the term "and/or" means "and" or or where appropriate both.

oAs used herein the term following a noun means the singular and/or plural forms of that noun.

As used herein "unbleached", "bleaching", etc refers to chlorine, chlorine dioxide, or other such bleaching reagent treatments.

As used herein the term "peroxygen compound" refers to one or more peroxygen compound(s) capable of providing, analogously to hydrogen peroxide, a source of peroxide ions and/or active peroxygen.

As used herein the term "oxygen containing gas" can refer to air or other gas having an oxygen content.

Reference to "oxygen" includes within its ambit pure or impure oxygen gas it may have a water content and may have minor presences of other gases).

As used herein the term "adt' means air dried tonne of pulp.

As used herein the term "kraft pulp" refers to a non mechanical pulp (preferably as a slurry and/or almost dry). The pulp is preferably unbleached i.e. has not been subjected to any treatment with oxygen, chlorine or chlorine-dioxide or other bleaching chemicals.

Preferably the Kappa number of the starting pulp (post or pre wash) is that indicative of an unbleached pulp stream.

Preferably the pulp stream input is at a Kappa number above Preferably the Kappa number most preferably is in the range of 40 to 100, more preferably 50 to 90 and most preferably 60 to The Kappa numbers given are typical of a conifer such as a pinus species pinus radiata) but could also be that of other conifer species e.g. Douglas fir, Loblolly pine, Spruce, etc.

COMS ID No: SBMI-01868505 Received by IP Australia: Time 14:00 Date 2005-11-01 01-NOV-2005 03:51 A J PARK 01-OU-00503:1 Pj PRK64 9 3566990 P.11 -9- The term "high lignin c-ontet in respect of the product post the treatment 'with the at least one peroxygeri comnpound in the Presence of oxygen and/or an oxygen containing gas, or post a storage step thereafter is preferably of a Kappa number no more than 10% less than that Kappa number of the pulp stream treated to brightening, Preferably the resultant Kappa number of the brightened kraft pulp is in the range of from 50 to 100, more preferably 60 to and most preferably 70 to Preferably the storage of the at least partly brightened pulp is at a pressure no greater tan 10 bar- Such storage if desired can be at ambient pressures as can the brightening treatment prior to such storage.

Preferably the brightening treatment is at a pressure no greater than 10 bar.

Preferably storage is at ambient pressure(s) yet the transit includes a pressurised stage (preferably a pressurised pipeline) e.g. at from I to 5 bar gauge pressure.

The brightening can be at PH conditions of from 8 to 13.

Preferably the alkaline conditions of the brightening is at an alkaline pH of from to 13.0.

More preferably the PH range most preferably to a target greater than 10.0 about 10.5) and preferably is to a range from 10.0 to 12.0 and most preferably from 10.5 to 11.0.

Preferably the alkaline conditions are maintained where appropriate by the addition of a source of hydroxide ions (for example caustic soda). For example 2 to 5 kg NaOH per tonne of air-dry pulp. other compatible alkalis include Mg(OH)2, and KOH.

Preferably at least some (most) of the black liquor alkali is passed to recover alkali NaOH) prior to the alkaline/peroxide/OZ treatment.

Preferably the PH is maintained with a charge or charges of alkali beyond tat which was present (and of which there can be some residue) prior to one or more washing steps.

Preferably the brightening treatment is performed after washing or partial washing of the pulp stream e.g. using one or more washers.

Preferably the brightening in the presence of both the at least one peroxygen compound and oxygen and/or an oxygen containing gas is for a period of time less than minutes. Preferably the period of time is less than 15 minutes. More preferably the period of time is less than 10 minutes. Most preferably the period of time is about 5 minutes or less.

Preferably the brightening step in alkaine conditions with at least one peroxygen compound and oxygen and/or an oxygen containing gas is at a temperature within the range of from 60 9 C to 100 0 C. Preferably the temnperature(s) is below 100 0 C. More preferably the temperature is from 80 0 C to 90 0 C and most preferably about 85 0

C.

COMB ID No: SBMI-01868505 Received by IP Australia: Time 14:00 Date 2005-11-01 01-NOU-20~5 03:52 R 3 PPRK 64 9 3566990 P.12 01-NOU-2005 03:52 A J PARK 64 9 3566990 P.12 Preferably the resultant wood pulp has a Kappa number in the range of 60 to Preferably the conditions of the brightening step of the present invention is such that the pulp pH(s), temperature(s), peroxygen compound amount(s) and oxygen availability(s), and time of treatment is such that the Kappa number of the pulp stream being brightened is not reduced by more than 10% (or the lignin content reduced by more than Preferably the conditions are such as to be insufficient to reduce the Kappa number by more than 5% (or the lignin content by more than Preferably the pH is maintained by adding an alkali charge (for example of caustic soda) to the pulp of less than 0.5% by dry weight of the pulp.

preferably a pH range of 10.0 12.0 arises from alkali addition generally of less than kg/adt pulp. Oxygen charged is preferably at about 2 kg/adt or less. Peroxide is preferably charged at generally less than 5 kg/adt.

Preferably where there is a treatment with the peroxygen compound and gaseous oxygen in transit to storage preferably the storage is in conditions where there is expected to be a persistent peroxygen compound availability (and, optionally, also some unvented gaseous oxygen).

Most preferably the peroxygen compound is hydrogen peroxide or a source of an equivalent peroxide.

The full content of our aforementioned Australian Patent Specification is here included as are the options discussed therein as to just where relative to washings and/or storage the alkali/oxygen treatment can be carried out. Likewise with the synergistic and/or improved procedures of the present invention.

In still a further aspect the present invention consists in a pulp derived from a method in accordance with any aspect of the present invention.

In yet a further aspect the present invention consists in a paper product manufactured from a pulp produced by a method in accordance with any aspect of the present invention. In yet a further aspect preferably said paper product is a linerboard.

In yet a further aspect the present invention consists in a linerboard produced by a method in accordance with an aspect of the present invention.

In yet a further aspect the present invention consists in a laminate formed from lignocellulosic material where at least one side of the laminate is of a linerboard produced by a method in accordance with the present invention.

In yet a further aspect the present invention consists in a linerboard derived from unbleached kraft pulp of the present invention.

COMS ID No: SBMI-01868505 Received by IP Australia: Time 14:00 Date 2005-11-01 01-NOU-2005 03:52 A J PRRK 01-OU-00503:2 PJ PRK64 9 3566990 P. 13 InIn still a firther aspect the Present invention consists in a laminate where One o exterior layer is of a linerboard of unbleached kraft pulp improved as to brightness and/or reversion resistance by a method in accordance with the present invention.

Z The present invention, inter alia, provides o(i) an improvement to our patented process, since the peroxide further reduces the colour reversion of the pulp, ~fl(ii) a means of brightening the unbleached pulp; and (iii) a means of modifying the colour of the pulp to be more golden (less red and ci more yellow).

o to These are all useful outcomes for pulp intended for use in the top sheet of linerboard.

The process conditions are novel. The reaction only requires peroxide and oxygen (optimally under some pressure) for about 5 minutes. The usefulness of this is that a pressure vessel is not required, only a section of pipe or "retention tube" with about 5 minutes retention time even for optimal pressures.

The invention also therefore consists in plant adapted for the performance of a methiod of the present invention.

Preferably said plant is some adaption of, for example, an existing plant as depicted in Figure I i.e. so as to perform a process substantially as described with reference to Figure 2 and/or elsewhere in the present specification.

Preferably the exposure to pressurised oxygen and the peroxygen compound is in transit in a pipeline preferably downstream of a washer preferably so as to enable alkali recovery from the washer- The present invention therefore consists in plant with alkali recovery adapted for the performancee of the present inventioni.

The invention also consists in a process, pulp or linens produced by or using a process, and plant adapted to perform a process substantially as herein described (in any combination of preferred forms and/or parameters) with reference to Figure 2 and/or Figure 3 of the accompanying drawings.

Preferred forms of the present invention will now be described with reference to the accompanying drawings in which COMS ID No: SBMI-01868505 Received by IP Australia: lime 14:00 Date 2005-11-01 1-NO-2005 03:52 Af J PRK 64 9 3566990 P.14 -12- Figure 1 is a diagrammatic view of, for example, the existing plant layout at our Kinleith Plant showing diagrammatically from the log the pictorialised treatment processes through to the paper machine, 0 Figure 2 shows a schematic flow diagram showing a most preferred positioning of the brightening procedure of the present invention such that a minimum of plant change is o required to the plant layout as depicted in Figure 1, Figure 3 is a diagram of a preferred plant adaption and its flow inputs and sequences.

N- In the preferred form of the present invention the preferred process of the present IC invention involves the alkali conditions of washed pulp prior to pulp storage, and i 10 Figure 4 is a scatter plot of b* verses L for the nine experimental trials of Table 3.

^t Shown in the flow diagram of Figure 2 is the introduction of the caustic soda (sodium o hydroxide) and gaseous oxygen or air (shown as 02) and a peroxide compound (shown preferably as hydrogen peroxide).

1. It is best that the pulp is washed, so the chemicals are more efficient at degrading the colour-forming chemical groups in the pulp lignin.

2. At least 5 minutes retention time if preferred under conditions of high pressure a stock delivery line or retention tube from 2 to 5 bar gauge pressure], since the oxygen reacts more quickly under pressure. Additional retention time in the HD storage tower) is desirable for the peroxide to fully react, but oxygen gas need not be present at this stage. It is free to vent also.

3. In a multi-washer sequence two or more washers in series), the treatment could be applied between any two of the washers, providing there is enough retention time and the right temperature and pressure conditions.

4. The treatment could also be applied to unwashed stock, but the efficiency of the chemicals would be very poor. That is because the oxygen and peroxide would react preferentially with the dissolved lignin material and the sodium sulphide contained in the cooking liquor.

The treatment could also be applied after the HD (High Density) pulp storage tower, providing there is enough retention time in the delivery system to the paper machine.

However, such a configuration may not allow enough retention time for the peroxide to fully react.

One plant arrangement would have the oxygen injected into a pipeline between two pumps. The first pump, pumps the stock (plus oxygen, peroxide, and caustic) away from the COMS ID No: SBMI-01868505 Received by IP Australia: Time 14:00 Date 2005-11-01 01-NOV-2005 03:53 A J PARK 01-OU-00503:3 PJ PRK64 9 3566990 -13 o washer to the second, booster pump, which Pumps the pulp on to the storage tower. The c-i second pump preferably has a degassiog unit. Some entrained oxygen gas may still go with the stock into the storage tower. The storage toweripefabyontohetmseeo 0 z entrained gas would be free to vent off.

In these reactions involving oxygen, pressure is preferred to drive the reaction rate.

0 The oxygen preferably is only present under pressure during the first 5 or so minutes.

We have evaluated the effectiveness of alkaline hydrogen peroxide, as a means of increasing brightness and preventing colour reversion.

Exnmple 1 The plant arrangement was as shown in Figure 3. The pulp washer is the o displacement washer Alkai and hydrogen peroxide were added to the stand-pipe below the washer the stock was then pumped by a medium consistency (MC) pump (3) into the pipeline Oxygen gas was added after the MC pump. The treated stock was further pumped by a booster pump to the high density storage tower Samples of the treated pulp were taken from the base of the high density storage tower and tested for their optical properties of ISO Brightness, a* and It.

The charge of sodium hydroxide was I kg/adt, providing a stock P11 of about 11.4.

The charge of oxygen was 2 kgladt and peroxide was charged at either 0, 5, or 10 kg/adt. At each level of hydrogen peroxide, the treatment process was performned with the oxygen supply either on or off.

It was found that a combination of peroxide and oxygen gave a significant decrease in the extent of colour -reversion, as indicated in Tfable 1 by the change in e* reversion (after exposure to UV light). In addition, a marked increase in pulp brightness, up to 6% ISO with a 1% peroxide charge was also obtained. There was a marked synergy between oxygen and peroxide, the combination giving a larger brightness gain than when peroxide was applied without oxygen.

Table 1 Changes in brightness and a* reversion under different combinations of oxygen and hydrogen peroxide (Example 1) COMS ID Na:SBMI-01868505 Received by P1 Australia: Time 14:00 Date 2005-11-01 01-NO-20~5 03:53 A J PARK 64 9 3566990 P.16 14- 3.00 SUntreated Pulp 3 0 Pre-trial Reference 1 24.1 0.46 0.5% peroxide/no 02 26.3 2.2 1.41 peroxide/02 27.3 3.2 0.29 peroxide/no 02 27.2 3.1 0.72 1.00 peroxide/O 2 30.0 5.9 0.23 Post-trial Reference 2 24.1 0.54

ID

N Example 2 SThe plant arrangement was as shown in Figure 3 and the chemicals were added as o described in Example 1. The charge of sodium hydroxide was 1 kg/adt pulp and the charge of c 5 oxygen was 2 kg/adt pulp. The charge of hydrogen peroxide was either 0 or 3.4 kg/adt.

As shown in Table 2, the treatment, when peroxide was added, resulted in a decrease in the redness of the pulp and an increase in the yellowness while also increasing brightness.

Table 2 Optical properties for samples from Example 2, after forming brightness pads at pH and air-drying Chemical Charge Unreverted pulp (as produced) Trial Period 02

H

2 0 2 Brightness L* a* b* (kg/adt) (kg/adt) Standard 2 0 23.46 66.90 5.62 20.89 treatment Treatment with 2 3.4 25.69 70.60 3.81 23.49 Peroxide Example 3 The plant arrangement was as shown in Figure 3 and the chemicals were added as described in Example 1. The charge of sodium hydroxide was either 0.5 or 1.1 kg/adt pulp, the charge of oxygen was either 2 or 4 kg/adt pulp, and the charge of hydrogen peroxide was either 0, 3.3, or 6.6 kg/adt.

COMS ID No: SBMI-01868505 Received by IP Australia: Time 14:00 Date 2005-11-01 01-NOU-2005 03:53 A J PARK 64 9 3566990 P.17 As shown in Table 3, the treatment was conducted under a range of chemical charge Sconditions. The charge level of all three chemicals (NaOH, oxygen, and hydrogen peroxide) influenced the brightness and colour of the treated pulp. The greatest gain in Brightness and SL* was observed in Experiment H, with a NaOh charge of 0.5 kg/adt, an oxygen charge of 4 kg/adt and a peroxide charge of 6.6 kg/.adt. It is also noted that Experiments E H, at the Shigher oxygen charge, all produced pulps that were significantly more colour stable (after exposure to UV light).

Figure 4 gives a plot of L* against b* for all the experimental trials and shows that increasing N 10 Brightness and L* is accompanied by an increase in In other words, the pulp becomes S lighter and more yellow in colour.

(N

COMS ID No: SBMI-01868505 Received by IP Australia: Time 14:00 Date 2005-11-01 2005229652 01 Nov 2005 -16-

C

Ln 0 Table 3 Colour properties of treated pulp and the change in a and b after UV light exposure.

Change in a* and b* after Chemical Chare Conditions 0 tCal Pro erties of Treated Pul osu to UV i ht niialan inal z Sodium Oxygen Hydrogen Change Change Change Hydroxide Charge Peroxide ISO Cae hg hn L, a b

H

CExperiment Charge Charge Brightness L* in in in Iiia&ia HD H O6ID kat k dt _k2ladt 3 No 202 1 20 -0 2.1 8 39 211 363 -0.63 1.60 10.68 10.67 M A 1.1 2.0 3.3 24.83 69-9-3 3.75 3.00 3.25 -0.52 1.2 i -0 9.97 a 50 7.5 37 35 .2 -0.49 1.35 10.62 02 SC 0.5 2.0 3.3 25-24 -TO 42 S.77 2 90 425 -0.69 1.9 10-28 9.28 D0--26-3.6 2572 1.28 377 -Y3-76 -T-4 -7 38 TO 37 -6.07 E 1 4.0 3 24.75 3-92 397 '3 22 2.58 -0.22 04 .7 1 40 51 70.89 3.92 -4.-28 2.69 1.09 10.5 9.40 ~G 0.5 4.0 3.3 25.42 08 2. 25 .1 D2 .2 H 863.6 351 375 24.08 3.3j -0 1 106 9.71 7.80 SBrightriss pads were exposed to UV-B light for 30 millute-s and tken ro-tested, fbr an d V. Chauges are epressed as original value UV reverted value).

I.CD

0 6u

Claims (46)

1. 01-NOU-2005 03:54 A J PARK 01-tJU200 0354 J PRK64 9 3566990 P.19
2. 17- THE CLAIMS DEFINING THE INVENTION ARIE AS FOLLOWS: 1 A method of colour stabilisationi of a high lignin pulp which involves subjecting a high lignin content pulp stream to the presence of a peroxygen compound (or active mnetabolites thereof) under oxygen pressure and in alkaline conditions for a time less than one hour. 2. A method of claim I wherein the pulp stream is unbicached. 3. A method of claim I or 2 wherein the time is less than 30 minutes. 4, A method of any one of the preceding claims wherein the time less than 20 minutes. 5. A method of any one of the preceding claims wherein the time is from 1 to miinutes, 6. A method of any one of the preceding claims wherein the time is from 3 to minutes. 7. A method of any one of the preceding claims wherein the time is a transit period in a 1s pipeline and/or "retention"' tube. 8. A method of any one of the preceding claims wherein the pulp is brightened by at least one peroxygen compound by less than 10% ISO. 9. A method of claim 8 wherein the brightening is by less than 5% ISO. A method of any one of the preceding claims wherein the pulp is brightened by at least one peroxygen compound by less than 3% ISO. 11. A method of any one of the preceding claims wherein the pulp is brightened by less than 2% ISO. 12. A method of any one of the preceding claims wherein the pulp stream input is at a Kappa number above 13. A method of claim 12 wherein the Kappa number most is in the range of 40 to 100. 14. A method of claim 13 wherein the Kappa number is in the range of 50 to A method of claim 14 wherein the Kappa number is in the range of 60 to $0. 16 A process for reducing colour reversion of a paper product to be made from high lignin pulp, the process involving subjecting a pulp that has been subjected to little (if any) delignification to both (serially and/or simultaneous) alkaline oxygenation, and peroxide brightening by less than 10% ISO. 17. A process of claim 16 wherein the peroxide brightening is by less than 5% ISO, COMS ID No: SBMI-01868505 Received by IP Australia: Time 14:00 Date 2005-11-01 01-NOU-2005 03:54 A J PARK 64 9 3566990 0
3. 18. A process Of claim 17 wherein the peroxide brightening is by less th= 3% ISO. o
4. 19. A process of any one of claims 16 to 18 wherein is Performed at least in Part under oxygenation and in alkaline conditions. A process of any one of claims 16 to 19 wherein both and follow at least one wash of the pulp. o21. A process of any one of claims 16 to 20 wherein at least is performed at least in part in a pipeline and/or retention tube. In22. A process of any one of claims 16 to 21 wherein the oxygenation of is at a pressure of oxygen or an oxygen containing gas of from I to 20 bar. ci 10 23. A process of claim 22 wherein the pressure is from I to 10 bar. tn24. A process of claim 23 wherein the pressure is from I to 5 bar. A process of claim 19 wherein the oxygenation of is at a pressure of oxygen or an oxygen containing gas of from 1 to 10 bar.
5. 26. A process of claim 25 wherein the oxygenation pressure of is from 1 to 5 bar.
6. 27. A process of claim 25 with storage to follow at less than 10 bar.
7. 28. A process of any one of claims 19 and 25 to 28 wherein the oxygenation of and is simultaneous.
8. 29. A method of producing a kraft pulp suitable for linerboard and/or other paper product manufacture which involves subjecting a high lignin content pulp strewm to brightening in alkaline conditions with at least one peroxygen compound, and oxygen and/or an oxygen containing gas in such a way as to leave the pulp with a high lignin content. A method of claim 29 wherein the pulp is of Kappa number in the range 40 to 100.
9. 31. A method of claim 29 or 30 wherein the pulp is unbleached.
10. 32. A method of any one of claims 29 to 31 wherein the brightening is by less than ISO.
11. 33. A method of claim 32 wherein the brightening is by less than 5% IMO
12. 34. A method of claim 33 wherein the brightening is by less than 3% ISO.
13. 35. A method of producing a kraft pulp suitable for linerboard and/or other paper product manufacture which involves subjecting an at least substantially unbleached pulp stream of Kappa number above 25 to brightening in alkaline conditions with COMB ID No: SSMI-01868505 Received by IP Australia: Time 14:00 Date 2005-11-01 01-NOU-2005 03:54 A J PARK 01-OU-00503:4 PJ PRK64 9 3566990 P.21 -19- o at least one peroxygcfl compound, and oxygen and/or an oxygen containing gas o in such a way as to leave the pulp with a Kappa nwnber above
14. 36. A meteod of claim 35 wherein a or the peroxygen compound is hydrogen peroxide.
15. 37. A method of producing a Icraft pulp suitable for linerboard and/or other paper product manufacture which involves subjecting an at least substantially unbleached pulp stream of Kappa number above 25 to brightening in alkaline conditions simultaneously with at least one peroxygen compound, and IC) oxygen and/or an oxygen containing gas ci 10 in such a way as to leave the pulp with a Kappa number above 25 which is not more than below the Kappa number prior to brightening.
16. 38. A method of producing a kruft pulp suitable for linerboard and/or other paper product manufacture which involves subjecting a high lignin content pulp stream to brightening in alkaline conditions with at least one peroxygell compound, and oxygen and/or an oxygen containing gas, storing the resulting pulp without addition of oxygen and/or an oxygen containing gas under the action of any persistent and/or further added peroxygen compound(s), and deriving the brightened kraft pulp of high lignin content fromn step
17. 39. A method of claim 3 8 wherein the pulp prior to is unbleached. A method of claim 39 wherein the or a compound of is hydrogen peroxide
18. 41. A method of producing a kraft pulp of Kappa number above 25 suitable for linerboard and/or other paper product manufacture which involves subjecting a high lignin content pulp stream to brightening in alkaline conditions with at least one peroxygen compound, and oxygen and/or an oxygen containing gas, storing the resulting pulp without addition of oxygen and/or an oxygen containing gas under the action of any persistent and/or further added peroxygen compound(s), and COMS ID No: SBMI-01868505 Received by IP Australia: Time 14:00 Date 2005-11-01 01-NOV-2005 03:55 A J PARK 64 9 3566990 P.22 deriving the brightened kraft pulp of high lignin content from step the obrightening being less than 10% ISO.
19. 42. A method Of claim 41 wherein the brightening is by less than 5% ISO,
20. 43. A method of claim 42 wherein the brightening is by less then 3% ISO. 5 44. A method or process of any one of the preceding claims wherein the alkaline oconditions of the brightening is at an alkaline pH of from 10.5 to 13.0. A method or process of claim 42 wherein the pH range is from 10.5 to 12.0.
21. 46. A method or process of claim 43 wherein the pH range is from 11.0 to 11.5.
22. 47. A method or process of any one of claims 44 to 47 wherein the alkaline conditions C' 10 are maintained by the addition of a source of hydroxide ions.
23. 48. A method or process of any one of the preceding claims wherein at least some of the o black liquor alkali is passed to recover alkali prior to the alkaline/peroxide/C2 treatment.
24. 49. A method or process of any one of the preceding claims wherein the brightening step in alkaline conditions with at least one peroxygen compound and oxygen and/or an oxygen containing gas is at a temperature within the range of from 60 0 C to 100C. A method or process of claim 49 wherein the temperature(s) is below 100C.
25. 51. A method or process of claim 49 wherein the temperature is from 80 0 C to 90 0 C.
26. 52. A method or process of claim 50 wherein the temperature is about 85 0 C.
27. 53. A method or process of any one of the preceding claims wherein the resultant wood pulp has a Kappa number in the range of 60 to
28. 54. A method or process of any one of the preceding claims the conditions of the brightening step of the present invention is such that the pulp pH(s), temperature(s), peroxygen compound amount(s) and oxygen availability(s), and time of treatment is such that the Kappa number of the pulp stream being brightened is not reduced by more than 10% or the lignin content reduced by more than 6%. A method or process of claim 54 wherein the conditions are such as to be insufficient to reduce the Kappa number by more than 5% or the lignin content by more than 3%.
29. 56. A method or process of any one of the preceding claims wherein the alkaline pH is maintained by adding caustic soda or equivalent charge to the pulp by weight of less than 0.5% by dry weight of the pulp.
30. 57. A method or process of any one of the preceding claims the alkaline conditions is a pH in a pH range of 10.5 12.0 that arises from alkali addition of less than 5 kg/adt pulp.
31. 58. A method or process of any one of the preceding claims wherein oxygen charged is at about 2 kgladt or less. COMS ID No: SBMI-01868505 Received by IP Australia: Time 14:00 Date 2005-11-01 01-NOU-2005 03:55 A J PARK 64 9 3566990 P.23 -21- S59. A method or process of any one of the preceding claims wherein peroxide is O preferably charged at generally less than 5 kg/adt. A method or process of any one of the preceding claims where there is a treatment O with a or the said peroxygen compound and gaseous oxygen in transit to storage.
32. 61. A method or process of claim 60 wherein the storage is in conditions where there is Sexpected to be a persistent peroxygen compound availability (and, optionally, also some unvented gaseous oxygen).
33. 62. A process as disclosed and claimed in Australian Patent No. 766612 in its Sbroadest aspects for kraft pulp processing [irrespective of pH claimed therein provided S 10 operated in alkaline conditions], improved to provide less colour reversion of paper, 0 linerboard, or the like to be formed from the high lignin pulp by the use of a peroxygen 0 compound as a brightening stage.
34. 63. A process of claim 62 wherein the use of a peroxygen compound is at least in part under oxygen pressure.
35. 64. A process of claim 62 or 63 wherein the brightening stage is in alkaline conditions. A process of any one of claims 62 to 64 wherein the increase in brightness is by less than 10% ISO.
36. 66. A process of claim 65 wherein the increase is by less than 5% ISO.
37. 67. A process of claim 66 wherein the increase is by less than 3% ISO.
38. 68. A process of claim 67 wherein the increase is by less than 2% ISO.
39. 69. A process substantially as herein described (in any combination of preferred forms and/or parameters) with reference to Figure 2 and/or Figure 3 of the accompanying drawings. A pulp derived from a method or process of any one of the preceding claims.
40. 71. A paper product manufactured from a pulp of claim
41. 72. A linerboard produced from a pulp of claim
42. 73. A laminate formed from lignocellulosic material where at least one side of the laminate is of a linerboard of claim 72.
43. 74. A laminate where one exterior layer is of a linerboard of unbleached kraft pulp improved as to brightness and/or reversion resistance by a method or process in accordance with any one of claims 1 to 69. Plant adapted for the performance of a method or process of any one of claims 1 to 69.
44. 76. Plant of claim 73 which is an adaption of a plant as depicted in Figure 1. COMS ID No: SBMI-01868505 Received by IP Australia: Time 14:00 Date 2005-11-01 01-NODU-2005 03:56 A J PARK 64 9 3566990 P.24 -22- 0
45. 77. A plant of claim 76 adapted to perform a process substantially as described with O reference to Figure 2. >78. Plant of any one of claims 75 to 77 wherein there is to be exposure to pressurised Z oxygen and the peroxygen compound is in transit in a pipeline downstream of a washer to enable alkali recovery from the washer.
46. 79. Plant with alkali recovery adapted for the performance of a method or process of any c one of claims 1 to 69. SDATED THIS DAY OF )~oeA Acro n AJ PARK PER ORTIAPClf ci, AGENTS FOR THE APPLICANT COMS ID No: SBMI-01868505 Received by IP Australia: Time 14:00 Date 2005-11-01