Paper making and fiber liberation – Processes of chemical liberation – recovery or purification... – Gas – vapor or mist contact
Reexamination Certificate
1996-11-22
2002-06-04
Alvo, Steve (Department: 1731)
Paper making and fiber liberation
Processes of chemical liberation, recovery or purification...
Gas, vapor or mist contact
C162S067000, C162S076000, C162S078000, C162S082000, C162S087000, C162S080000
Reexamination Certificate
active
06398908
ABSTRACT:
BACKGROUND OF THE INVENTION
In the production of chemical pulp of high brightness, wood chips are first cooked to separate the cellulose fibers. Part of the lignin holding the fibers together is thus degraded and modified, such that it can be removed by subsequent washing. However, in order to obtain sufficient brightness, more lignin has to be removed, together with brightness-impairing (chromophoric) groups. This is frequently effected by delignification with oxygen, followed by bleaching in several stages.
For environmental reasons, it has become increasingly common to treat chemical pulp with chlorine-free bleaching agents already in the first bleaching steps. The big advantage is the drastic reduction in the discharges of chlorinated organic substances detrimental to the environment, owing to the combined effect of a smaller amount of chlorine-containing bleaching agents and lower content of lignin, which is the organic substance primarily reacting with the chlorine.
It is known to use chlorine-free bleaching agents, such as hydrogen peroxide, peracetic acid or ozone, already in the prebleaching. However, the delignification and consumption of the bleaching agent become less effective than with chlorine-containing bleaching agents, unless the pulp is pretreated. Thus, a hydrogen peroxide treatment in an alkaline environment is disturbed by the presence in the pulp of ions of certain metals, such as Mn, Cu and Fe. These metal ions cause degradation of hydrogen peroxide, thereby reducing the efficiency of the peroxide treatment and increasing the consumption of peroxide. According to CA 1,206,704, this can be counteracted by pretreating the pulp with an acid, such as sulfuric acid or nitric acid, whereby the concentration of all types of metal ions is reduced. However, by this treatment also metal ions, for example Mg, which are advantageous to the peroxide treatment disappear, which ions stabilize the peroxide and increase the selectivity of the peroxide.
CA 575,636 discloses the addition of magnesium sulphate to stabilize alkaline peroxide solutions. However, the addition is made directly to the bleaching liquor and in an alkaline environment insoluble magnesium hydroxide precipitates. Furthermore, U.S. Pat. No. 4,222,819 discloses the addition of magnesium ions to acidic peroxide solutions, but also in this case the addition is made directly to the bleaching liquor. None of the related methods makes possible diffusion of the magnesium ions into the pulp to such an extent that a pulp of high brightness and strength can be obtained.
SUMMARY OF THE INVENTION
The present invention relates to a process for delignification and bleaching of chemically digested lignocellulose-containing pulp. In a first embodiment, the pulp is acid treated at a pH of between about 1 and about 6, whereupon a water-soluble compound containing an alkaline earth metal is added at a pH of between about 1 and about 7 before the pulp is treated with a chlorine-free bleaching agent. The initial acidic treatment removes the trace metals of the pulp, whereas the subsequent addition of alkaline earth metal ions in aqueous solution returns the ions to the positions in the pulp where they have a particularly beneficial effect on the preservation of the cellulose chains and, consequently, on the viscosity, as well as on the consumption of bleaching agent in the subsequent bleaching step. In a second embodiment, the acid treatment step and the alkaline earth metal treatment steps are combined. The presence of the alkaline earth metal ions during the acid treatment results in a substantial portion of the original alkaline earth metal to be retained in the pulp.
After the treatment according to the invention, the pulp may be finally bleached to the desired brightness, suitably with a chlorine-free bleaching agent, such as ozone, to completely avoid formation and discharge of AOX. The final bleaching step is preferably carried out in the presence of an alkaline earth metal ion such as magnesium, calcium or barium.
REFERENCES:
patent: 2687943 (1954-08-01), Pete
patent: 3507744 (1970-04-01), Grangaard
patent: 3652385 (1972-03-01), Noreus et al.
patent: 3865685 (1975-02-01), Hebbel et al.
patent: 4222819 (1980-09-01), Fossum et al.
patent: 4619733 (1986-10-01), Kooi
patent: 4731161 (1988-03-01), Ehrhardt
patent: 4732650 (1988-03-01), Michalowski et al.
patent: 4834837 (1989-05-01), Loquenz et al.
patent: 4859283 (1989-08-01), Jayawant
patent: 5034096 (1991-07-01), Hammer et al.
patent: 5143581 (1992-09-01), Devic
patent: A-26798/88 (1989-08-01), None
patent: 575636 (1959-05-01), None
patent: 1122358 (1982-04-01), None
patent: 1206704 (1986-07-01), None
patent: 0 402 335 (1990-12-01), None
patent: 0415149 (1991-03-01), None
patent: 0 511 695 (1992-11-01), None
patent: 75-137933 (1975-11-01), None
patent: 51-102103 (1976-09-01), None
patent: 52-63402 (1977-05-01), None
patent: 53-143704 (1978-12-01), None
patent: 54-55606 (1979-05-01), None
patent: 55-158394 (1980-12-01), None
patent: 57-21590 (1982-02-01), None
patent: 58-132190 (1983-08-01), None
patent: 2-145884 (1990-06-01), None
patent: 3-64589 (1991-03-01), None
patent: 79/00637 (1979-09-01), None
Liebergott et al, “Bleaching of Softwood Kraft Pulp Without Chlorine Compounds”, Tappi, Aug. 1984.*
English abstract of European Patent application No. EP 0 578 304.
Abstract for Japanese application No. 54055606.
R. P. Singh, Tappi Press, 3rd Ed., 1979, pp. 164-165 & 177-178, The Bleaching of Pulp.
JP-3064589, Derwent Publications Ltd., London, GB; Mitsubishi Gas Chem KK, Mar. 19, 1991.
Ruhanen et al, “First Stage Bleaching of Softwood Kraft Pulp With Peroxide, Instead of Chlorine”, Tappi, J., Sep. 1982, p. 107-110.
J. P. Casey, “Pulp and Paper Chemistry and Chemical Technology”, 3rd Edition, vol. 1, p. 651, 1980, John Wiley & Sons, New York, NY.
Lachenal et al., “Improvement of Ozone Prebleaching of Kraft Pulps”, J. of Pulp and Paper Science, vol. 12, No. 2, Mar. 1986, p. J50-J53.
“Production of Bleached Chemical Pulp in the Future”, vol. 3, Bleachability & Chlorine Free Bleaching of Sulfite Pulps Mill Experiences, SPCI, Sweden, Jun. 11, 1991.
J.L. Colodette et al., “Factors Affecting Hydrogen Peroxide Stability in the Brightening of Mechanical and Chemimechanical Pulps”, J. of Pulp and Paper Science, vol. 15, No. 2, Mar. 1989, p. J45-J50.
A.F. Gilbert et al., Mechanism of Magnesium Retardation of Cellulose Degradation During Oxygen Bleaching, Tappi, Jun. 1973, vol. 56, No. 6, p. 95-99.
Abstract of Japanese application Nos. 52063402 and 75137933.
English translation of Japanese application No. 75137933.
Abstract of Japanese application No. 51102103.
Abstract of Japanese application No. 58132190.
Abstract of Japanese application No. 3064589.
Abstract of Japanese application No. 2145884.
Abstract of Japanese application No. 55158394.
Abstract of Japanese application No. 57021590.
Andersson Lennart
Basta Jiri
Hermansson Wenche Elisabeth
Holtinger Lillemor
Linsten Magnus
Alvo Steve
Burns Doane Swecker & Mathis L.L.P.
Eka Nobel AB
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