Paper making and fiber liberation – Processes of chemical liberation – recovery or purification... – With regeneration – reclamation – reuse – recycling or...
Patent
1996-04-11
1999-11-09
Alvo, Steven
Paper making and fiber liberation
Processes of chemical liberation, recovery or purification...
With regeneration, reclamation, reuse, recycling or...
162 40, 162 41, 162 65, 162 76, 162 78, 162 79, D21C 9153, D21C 916, D21C 1100
Patent
active
059806893
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a method of separating metal ions from pulps of lignocellulose-containing material. More particularly, the present invention relates to such methods in connection with the bleaching of such pulps with hydrogen peroxide or ozone, in which methods a main flow of pulp is treated with a chelating agent and washed prior to such bleaching.
BACKGROUND OF THE INVENTION
In present pulp mills, as well as those contemplated in the future, there are and will be liquid flows which are contaminated by various metal ions, which can disturb the bleaching reactions which take place during bleaching with hydrogen peroxide or ozone. These liquid flows occur, for example, during totally chlorine-free bleaching, so-called TCF-bleaching (TCF=Totally Chlorine Free), when the pulp is treated with chelating agents, such as EDTA or DTPA, in order to substantially reduce the metal ion content of the pulp prior to its bleaching with peroxide or ozone. This type of bleaching, in order to yield high ISO-brightness, requires that both the pulp and the process water be free or substantially free of certain metal ions since otherwise the charged hydrogen peroxide will effectively disintegrate to water and oxygen gas, and the charged ozone to oxygen gas, without having any simultaneous bleaching effect.
Particularly at those times when the pulp mill is closed, for example for environmental reasons, these liquids containing metal ions can be very difficult to deal with in order to prevent their contact with the bleaching step which would then deteriorate bleaching efficiency.
SUMMARY OF THE INVENTION
These and other objects have now been realized by the invention of a method of separating metal ions from a metal-ion and lignocellulose-containing material comprising treating the metal-ion and lignocellulose-containing material with a chelating agent in order to produce a flow of lignocellulose-containing material containing dissolved metal ions, washing the flow of lignocellulose-containing material containing the dissolved metal ions to produce a first washed flow of lignocellulose-containing material and a first liquid stream containing the metal ions, bleaching the first washed flow of lignocellulose-containing material with a bleaching agent selected from the group consisting of hydrogen peroxide and ozone so as to produce a flow of bleached lignocellulose-containing material, mixing the first liquid stream containing the metal ions with a second flow of lignocellulose-containing material so as to bind the metal ions to the second flow of lignocellulose-containing material, washing the second flow of lignocellulose-containing material to produce a second washed flow of lignocellulose-containing material and a second liquid stream substantially free of the metal ions, and washing the second wash flow of lignocellulose-containing material at a pH of less than about 3 to produce a third washed flow of lignocellulose-containing material in a third liquid stream containing the metal ions.
In accordance with one embodiment of the method of the present invention, the method includes separating the flow of bleached lignocellulose-containing material into a primary flow of bleached lignocellulose-containing material and a secondary flow of bleached lignocellulose-containing material, and the second flow of lignocellulose-containing material comprises the secondary flow of bleached lignocellulose-containing material.
In a preferred embodiment of the method of the present invention, the method includes combining the third washed flow of lignocellulose-containing material with the primary flow of bleached lignocellulose-containing material.
In accordance with another embodiment of the method of the present invention, the second flow of lignocellulose-containing material comprises the flow of bleached lignocellulose-containing material.
In accordance with another embodiment of the method of the present invention, the second flow of lignocellulose-containing material comprises a separate f
REFERENCES:
patent: 5415734 (1995-05-01), Backlund et al.
patent: 5462641 (1995-10-01), Bergvist et al.
Alvo Steven
Sunds Defibrator Industries AB
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