White liquor
Encyclopedia
White liquor is a strongly alkaline solution used in the first stage of the Kraft process
in which lignin
and hemicellulose
are separated from the cellulose fiber
in Kraft process
for the production of pulp
. It is called white liquor due to the white opaque colour.
in water and is the active component in Kraft pulping. White liquor also contains minor amounts of sodium carbonate
, sodium sulfate
, sodium thiosulfate
, sodium chloride
, calcium carbonate
and other accumulated salts and non-process elements. These additional components are considered inert in the Kraft process, except sodium carbonate that contributes to a lesser extent.
The chemical composition and properties of the white liquor are calculated as total alkali, active alkali, effective alkali, sulfidity, causticity and reduction.
.
Kraft process
The kraft process describes a technology for conversion of wood into wood pulp consisting of almost pure cellulose fibers...
in which lignin
Lignin
Lignin or lignen is a complex chemical compound most commonly derived from wood, and an integral part of the secondary cell walls of plants and some algae. The term was introduced in 1819 by de Candolle and is derived from the Latin word lignum, meaning wood...
and hemicellulose
Hemicellulose
A hemicellulose is any of several heteropolymers , such as arabinoxylans, present along with cellulose in almost all plant cell walls. While cellulose is crystalline, strong, and resistant to hydrolysis, hemicellulose has a random, amorphous structure with little strength...
are separated from the cellulose fiber
Cellulose fiber
Cellulose fibers are fibres of cellulose from any source, either natural or manufactured.-Textile:In the textile industry regenerated cellulose is used as fibers such as rayon, . Cellulose fibers are manufactured from dissolving pulp...
in Kraft process
Kraft process
The kraft process describes a technology for conversion of wood into wood pulp consisting of almost pure cellulose fibers...
for the production of pulp
Pulp (paper)
Pulp is a lignocellulosic fibrous material prepared by chemically or mechanically separating cellulose fibres from wood, fibre crops or waste paper. Wood pulp is the most common raw material in papermaking.-History:...
. It is called white liquor due to the white opaque colour.
Composition
White liquor consists mainly of sodium hydroxide and sodium sulfideSodium sulfide
Sodium sulfide is the name used to refer to the chemical compound Na2S, but more commonly it refers to the hydrate Na2S·9H2O. Both are colorless water-soluble salts that give strongly alkaline solutions...
in water and is the active component in Kraft pulping. White liquor also contains minor amounts of sodium carbonate
Sodium carbonate
Sodium carbonate , Na2CO3 is a sodium salt of carbonic acid. It most commonly occurs as a crystalline heptahydrate, which readily effloresces to form a white powder, the monohydrate. Sodium carbonate is domestically well-known for its everyday use as a water softener. It can be extracted from the...
, sodium sulfate
Sodium sulfate
Sodium sulfate is the sodium salt of sulfuric acid. When anhydrous, it is a white crystalline solid of formula Na2SO4 known as the mineral thenardite; the decahydrate Na2SO4·10H2O has been known as Glauber's salt or, historically, sal mirabilis since the 17th century. Another solid is the...
, sodium thiosulfate
Sodium thiosulfate
Sodium thiosulfate , also spelled sodium thiosulphate, is a colorless crystalline compound that is more familiar as the pentahydrate, Na2S2O3•5H2O, an efflorescent, monoclinic crystalline substance also called sodium hyposulfite or “hypo.”...
, sodium chloride
Sodium chloride
Sodium chloride, also known as salt, common salt, table salt or halite, is an inorganic compound with the formula NaCl. Sodium chloride is the salt most responsible for the salinity of the ocean and of the extracellular fluid of many multicellular organisms...
, calcium carbonate
Calcium carbonate
Calcium carbonate is a chemical compound with the formula CaCO3. It is a common substance found in rocks in all parts of the world, and is the main component of shells of marine organisms, snails, coal balls, pearls, and eggshells. Calcium carbonate is the active ingredient in agricultural lime,...
and other accumulated salts and non-process elements. These additional components are considered inert in the Kraft process, except sodium carbonate that contributes to a lesser extent.
The chemical composition and properties of the white liquor are calculated as total alkali, active alkali, effective alkali, sulfidity, causticity and reduction.
| Total alkali | All Na- compounds | |
| 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 is a mixture of white liquor, water from the wood chips, condensed steam and black liquorBlack liquor
Black liquor is the spent cooking liquor from the kraft process when digesting pulpwood into paper pulp removing lignin, hemicelluloses and other extractives from the wood to free the cellulose fibers....
.