White liquor

White liquor is a strongly alkaline solution composed mainly of sodium hydroxide and sodium sulfide.[1] It is used in the first stage of the Kraft process in which lignin and hemicellulose are separated from cellulose fiber for the production of pulp.[1] The white liquor breaks the chemical bonds between lignin and cellulose substructures in wood materials. It is referred to as white liquor because of its white, opaque color.

Composition

White liquor consists mainly of sodium hydroxide and sodium sulfide in water, and is the active component in Kraft pulping.[1] White liquor also contains minor amounts of sodium carbonate, sodium sulfate, sodium thiosulfate, sodium chloride, and calcium carbonate, and other accumulated salts and non-process elements. These additional components are considered inert in the Kraft process—except for sodium carbonate, which contributes to a lesser extent.

The chemical characteristics of the white liquor, deriving from its properties, are described by the parameters total alkali, active alkali, effective alkali, sulfidity, causticity, and reduction.

Parameter Defining analytical value Units, citation
Total alkali All Na+ compounds [units unstated]
Active alkali (AA) NaOH + Na2S g NaOH equivalents, or % on dry wood
Effective alkali (EA) NaOH + ½ Na2S g NaOH equivalents, or % on dry wood{
Sulfidity Na2S / AA %
Causticity NaOH / (NaOH + Na2CO3) %
Reduction Na2S / (Na2S + Na2SO4) %

Application

The Kraft cooking liquor (white) is used to extract the lignin and break down the cellulose composition of wood chips into usable pulp. The white (cooking) liquor becomes weak black liquor and is sent to the recovery process.

See also

Further reading

  • Young, Raymond A.; Kundrot, Robert & Tillman, David A. (2003). "Pulp and Paper". In Meyers, Robert A. (ed.). Encyclopedia of Physical Science and Technology (3rd ed.). Academic Press. pp. 249–265. doi:10.1016/B0-12-227410-5/00619-0. ISBN 9780122274107. Retrieved June 21, 2026.{{cite book}}: CS1 maint: multiple names: authors list (link)

References

  1. 1 2 3 Gullichsen, Johan; Fogelholm, Carl-Johan (2000). "6A. Chemical Pulping". Papermaking Science and Technology. Tappi Press. pp. 41–42. ISBN 952-5216-06-3.
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