Chlorine-free bleaching with short sequence and filtrate recirculation
CA 2134730 C · Owner: Ahlstrom Machinery Oy · Inventors: Henricson, Kaj; Pikka, Olavi; Stromberg, Bertil
Overview
Its claims, description and drawings are in the Canadian Patents Database.
Open the CIPO recordAbstract From the Canadian patent
A method of total chlorine-free bleaching to a brightness of ISO 82-90 uses an acid stage and a superatmospheric pressure peroxide stage. The acid stage (which may be the only acid stage) may comprise a Q stage or a Z (ozone) stage, in which metals in the pulp are freed from pulp fibers and become dissolved in the surrounding liquid. The pulp is then subjected to fractional washing to produce at least two wash filtrates the first filtrate, having over 50% of the dissolved metals from the pulp. The first filtrate is ultimately returned (e.g. through brown stock washing) to the black liquor recovery system of the pulp mill so that the metals precipitate on organics in the black liquor …
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Listed from its CIPO record in Patent Yard's archive of Canadian patents past their term. Its claims, description and drawings are in the CIPO record and on Google Patents, and the Claude kit works from them.
Why it's free to use
- Filed October 31, 1994 and granted December 30, 2003. A Canadian patent filed from October 1, 1989 lasts 20 years from filing, so its term ended October 31, 2014.
- A certificate of supplementary protection adds at most two years for a drug, so even that would have ended by October 31, 2016.
- We check Canadian rights only. A patent in its family in another country could still be in force: check its family on Google Patents.
Timeline
Timeline From CIPO dates
Sources & verification
Official CIPO records
Everything on this page comes from the CIPO record linked above. Contains information licensed under the Open Government Licence – Canada.