Paper making and fiber liberation – Processes and products – Reclamation – salvage or reuse of materials
Patent
1997-01-08
1998-08-04
Silverman, Stanley S.
Paper making and fiber liberation
Processes and products
Reclamation, salvage or reuse of materials
162189, 210767, 204554, D21F 166
Patent
active
057888159
DESCRIPTION:
BRIEF SUMMARY
This application is a 371 of PCT/SE96/00595 filed on May 7, 1996.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a process for the production of paper in which an aqueous suspension of cellulose containing fibres is drained in the presence of a drainage or retention aid and white water is recirculated to the production process. More specifically, the invention relates to a process in which white water is subjected to electrodialysis before being returned to the process, thereby improving drainage and retention.
A wide variety of drainage and retention aids are known in the art. These additives are included in the papermaking stock in order to facilitate drainage and/or to increase adsorption of fine particles and additives onto the cellulose fibres so that they are retained with the fibres. The drainage and retention aids employed include natural and synthetic organic polymers, inorganic materials and many combinations thereof. Usually, oppositely charged materials are used. As examples of commonly used drainage and retention aids can be mentioned cationic starch in combination with colloidal silicic acid, such as for example disclosed in EP 41056, and synthetic cationic polymers in combination with bentonite, such as for example disclosed in EP 235893. These processes and systems have been commercialized under the trade names Compozil.TM. and Hydrocol.TM., respectively.
Drainage of papermaking stocks produces cellulose fibre containing sheets or web-like products and white water. The white water, or back water, normally contains non-retained fibre remnants, electrolytes, fillers, etc., and is usually recirculated, either completely or partially, in different flow circuits. In the primary circuit, normally, white water obtained in the sheet-forming zone of the wire section is recycled for stock dilution. The primary circuit is usually maintained as closed as possible. The secondary white water circuit, normally, comprises excess water from the wire section as well as suction, press and cleaning water. Fibres and fillers are usually removed from this type of circulating water whereupon the resulting clarified water is returned to the process, for example for chemical preparation, stock preparation and stock dilution.
Electrodialysis involves the transport of ions through ion-selective or ion-exchange membranes from one solution to another under the influence of an electrical potential. Electrodialysis is commonly used for desalination of brackish water for the production of potable water and table salt.
SUMMARY OF THE INVENTION
According to the present invention it has been found that it is possible to improve drainage and retention in the production of paper by subjecting white water that is to be recirculated to electrodialysis. More specifically, the present invention relates to a process for the production of paper which comprises mixing an aqueous phase comprising white water with cellulose containing fibres, and optional fillers, in a mixing stage to form an aqueous suspension, draining the suspension in the presence of a drainage or retention aid to form a fibre containing sheet or web and white water, recirculating at least part of the white water to the mixing stage wherein at least part of the white water is subjected to electrodialysis before the mixing stage.
DETAILED DESCRIPTION OF THE INVENTION
The present invention results in a considerably improved retention and dewatering in papermaking and makes it possible to enhance the efficiency of drainage or retention aids used. This means that the speed of the paper machine can be increased and that substantially lower dosages of drainage or retention aids can be used to give a corresponding effect, thereby leading to an improved papermaking process in terms of productivity, runnability, paper quality as well as waste reduction. With more efficient retention and dewatering also formation and strength of the paper can be improved.
The term "white water" used herein is meant to include any aqueous phase
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Nilsson Lennart
Norell Maria
Eka Chemicals AB
Fortuna Jos'e A.
Mancini Ralph J.
Morris Louis A.
Silverman Stanley S.
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