Editing Kraft process (section)

===Cooking===
The wood chips are then cooked in pressurized digesters. Some digesters operate in a batch manner and some in a continuous process. Digesters producing 1,000 tonnes or more of pulp per day are common, with the largest producing more than 3,500 tonnes per day.<ref name="epa">{{cite web |url = https://nepis.epa.gov/Exe/ZyPURL.cgi?Dockey=9100PTP2.txt |title=Pollution Prevention Technologies for the Bleached Kraft Segment of the U.S. Pulp and Paper Industry|access-date=2022-02-06 |last=Woodman |first=Jocelyn |year=1993 |publisher=U.S. Environmental Protection Agency|page = 66}}</ref> Typically, delignification requires around two hours<ref>{{cite web
|url=http://biorefinery.utk.edu/technical_reviews/Basics%20of%20Kraft%20Pulping.pdf
|title=Basics of Kraft Pulping
|publisher=University of Tennessee Knoxville - Department of Chemical and Biomolecular Engineering
|access-date=2021-10-23
|archive-date=2021-10-23
|archive-url=https://web.archive.org/web/20211023194838/http://biorefinery.utk.edu/technical_reviews/Basics%20of%20Kraft%20Pulping.pdf
|url-status=dead
}}</ref> at {{convert|170|to|176|°C|°F}}. Under digesting conditions, lignin and [[hemicellulose]] degrade to give fragments that are soluble in the strongly basic liquid. The solid pulp (about 50% by weight of the dry wood chips) is collected and washed. At this point the pulp is known as ''brown stock'' because of its color. The combined liquids, known as [[black liquor]] (because of its color), contain lignin fragments, [[carbohydrate]]s from the breakdown of hemicellulose, [[sodium carbonate]], [[sodium sulfate]] and other inorganic salts.

[[Image:KraftEq.png|250px|thumb|right|net reaction in depolymerization of lignin by SH<sup>−</sup> (Ar = [[aromaticity|aryl]], R = [[alkyl]] groups).]]
One of the main chemical reactions that underpin the kraft process is the scission of ether bonds by the [[nucleophilic]] [[sulfide]] (S<sup>2−</sup>) or [[bisulfide]] (HS<sup>−</sup>) ions.<ref name="eero"/>