Paper making and fiber liberation – Processes of chemical liberation – recovery or purification... – Treatment with particular chemical
Reexamination Certificate
2000-11-28
2003-09-02
Alvo, Steve (Department: 1731)
Paper making and fiber liberation
Processes of chemical liberation, recovery or purification...
Treatment with particular chemical
C162S082000, C435S277000, C435S278000
Reexamination Certificate
active
06613192
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a method for producing paper pulp for use in the making of paper.
BACKGROUND OF THE INVENTION
In the manufacture of paper from wood, the wood is first converted to pulp. Pulping involves treating wood to separate the cellulose fibers. Pulping processes are divided into two broad classes: chemical pulping and mechanical pulping. Chemical pulping involves the use of chemicals to solubilize the lignin in the wood cell wall and to release cellulose fibers. Lignin is a natural glue-like material that holds the wood cell wall together. Chemical pulping is a low yield process (about 50%) with significant waste treatment and chemical recycling costs; however, the pulp produced has extremely high strength properties. Mechanical pulping involves the use of mechanical force to separate cellulose fibers. Mechanical processes are high yield (up to 95%) but give paper with lower strength properties, high color reversion and low brightness. Thus, currently available pulping processes offer a spectrum of pulp properties ranging from high yield, low strength mechanical pulps to low yield, high strength chemical pulp. A mixture of chemical pulp and mechanical pulp is used in many paper production processes to exploit these differences.
It has been suggested that biological systems can be also used to assist in the pulping of the wood. Attempts to improve primary pulp production processes by using isolated ligninolytic enzymes have so far been inhibited by the complex chemistry of the ligninolytic enzyme system, low yields in enzyme production and the ultrastructure of wood itself. White rot fungi, however, have great potential for this application. These fungi not only produce the whole set of enzymes necessary for lignin degradation but also act as a transport system for these enzymes by bringing them into the depth of wood chips and create the physiological conditions necessary for enzymatic reactions. Some of the white rot fungi are relatively selective for lignin and in that way their action mimic that of chemical pulping agents. It is these selective lignin degrading fungi which are useful for biopulping.
The use of white rot fungi for the biological delignification of wood was first studied at the West Virginia Pulp and Paper Company (now Westvaco) in the 1950s (Lawson and Still, 1957). In the 1970s Eriksson and coworkers at STFI demonstrated that fungal treatment could result in significant energy savings for mechanical pulping (U.S. Pat. No. 3,962,033, 1976; Ander and Eriksson, 1975; Eriksson and Vallander, 1982). Two sequential biopulping consortia comprised of the USDA Forest Products Laboratory (FPL), the Universities of Wisconsin and Minnesota, and 22 pulp and paper and allied companies have established the techno-economic feasibility of biopulping in connection with mechanical refining (Akhtar et al., 1992a,b, 1993, Blanchette et al., 1984, 1988, Leatham et al., 1989, 1990a,b, 1990, Myers et al., 1988). Four U.S. patents have been granted to the Wisconsin Alumni Research Foundation (WARF) (U.S. Pat. Nos. 5,055,159,1991; 5,460,697, 1994; PCT Int. Appl. WO9605362 A 1 February 1996, U.S. patent Ser. No. 08/801,704 now U.S. Pat. No. 5,750,005, File No. 960296.94339).
The effect of fungal pretreatment on chemical pulp production has been investigated to a much lesser extent. On biosulfite pulping, some work has been done in Austria and at FPL, U.S.A. However, detailed studies have not been carried out. Messner et al. (1992) reported ~30% reduction in kappa number in 2 weeks in case of birch and spruce. The brightness of the unbleached pulp increased by 4 ISO points. However, the strength properties deteriorated. Scott et al. (1996) reported about 48 and 21% reduction in kappa number (residual lignin in pulp) in 2 weeks with
Ceriporiopsis subvermispora
strains CZ-3 and SS-3 respectively during calcium acid sulfite pulping. However, the effect of fungal treatment on brightness and strength properties of the pulp were not examined. Also, the bleaching response of the fungal-treated pulp was not seen.
On biokraft pulping, some work has been done at FPL, U.S.A. and other laboratories on pine, aspen and red oak. Wolfaardt et al. (1993, 1996) reported about 18% reduction in kappa number at mill conditions, when pine wood was treated with white rot fungi. However, under all the tested conditions, yield and viscosity was lower and the alkali consumption was higher. Oriaran et al. (1990) reported that glucose supplemented aspen chips pretreated with white rot fungi led to kappa number reduction of 3 and 9% in 20 and 30 days respectively. A marked decrease in beating time was observed only after an incubation period of 30 days, while in the same period the water retention value increased from 102% to 137% and the fines also increased. However, the brightness of unbleached pulp decreased drastically by 62%. Tensile strength increased by 21% after 30 days, while the tear index decreased. Results obtained with red oak were similar to those obtained with aspen (Oriaran, 1991; Lobosky, 1991). A systematic literature survey has shown that no work has been done on biokraft pulping of eucalyptus. To the best of our knowledge, this is the first report where positive results on biokraft pulping have been obtained.
The present invention deals with a method for biokraft pulping of eucalyptus. It involves partial degradation/modification of eucalyptus wood with white rot fungi followed by kraft pulping of the treated wood. It has been found that pretreatment with white rot fungi improves chemical pulping efficiency and pulp properties (brightness and strength). Treated wood chips could be pulped in a shorter cooking time or could alternatively be used to produce pulp using lower active alkali charge or sulfidity. The bleached biopulps are easier to refine than the reference pulp.
SUMMARY OF THE INVENTION
An object of this invention is to provide a novel method for producing paper pulp for use in the making of paper by fungal treatment.
Another object of this invention is to provide a method for producing paper pulp for use in the making of paper which avoids or reduces the nutrient requirements during fungal treatment of wood chips.
Still another object of this invention is to provide a method for producing paper pulp for use in the making of paper which requires less amount of chemicals in comparison to conventional kraft pulping and consequently reduced effluents.
It is another object of the present invention to provide a method for producing paper pulp for use in the making of paper having higher strength.
Yet another object of the present invention is to provide a method for producing paper pulp for use in the making of paper and wherein the cooking time is reduced.
Other objects and advantages of the present invention will be more apparent from the ensuing description.
According to this invention there is provided a method for producing pulp from eucalyptus pulp for use in the making of paper comprising in the steps of:
a) inoculating eucalyptus wood chips with white rot fungi;
b) incubating the wood chips so as to cause a propagation of the fungus through the wood chips and allow the fungus to modify lignin; and
c) pulping of the degraded wood chips by a known kraft process;
In another embodiment, the foregoing steps are augmented by the further step of bleaching the kraft pulp by conventional bleaching processes. It will be further recognized that the eucalyptus chips biotreated by the metabolic activity of the white rot fungi during incubation are themselves a commodity of commerce which may be utilized directly in a kraft process, or transported to another location for kraft pulping at a time remote from the initial big treatment step.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The present invention deals with the biological pretreatment of wood chips for making of chemical pulp, for manufacture of paper. It has been particularly found that through the use of white rot fungi and the maintenance of suitable conditions during the treatment of woo
Akhtar Masood
Bajpai Pramod K.
Bajpai Pratima
Alvo Steve
Biopulping International, Inc.
Frenchick Grady J.
Michael & Best & Friedrich LLP
Peterson Jeffrey D.
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