The Kraft process (also known as Kraft pulping or sulfate process) is used in production of paper pulp and involves the use of caustic sodium hydroxide and sodium sulfide to extract the lignin from wood chips in large pressure vessels called digesters. Some digesters operate in a batch manner and some in a continuous process such as the Kamyr digester. International Paper Company Wood pulp is the most common material used to make paper. ... Look up caustic in Wiktionary, the free dictionary. ... Sodium hydroxide (NaOH), also known as lye or caustic soda or sodium hydrate, is a caustic metallic base. ... Sodium sulfide, or Na2S, is a water soluble chemical compound. ... Lignin (sometimes lignen) is a chemical compound (complex, highly cross-linked aromatic polymer) that is most commonly derived from wood and is an integral part of the cell walls of plants, especially in tracheids, xylem fibres and sclereids. ... A digester is a device used in papermaking which takes small wood chips, and cooks them for a number of hours, to soften them. ...

The spent, extracted pulping liquor, called black liquor, is concentrated by evaporation and burned in the recovery boiler to recover the inorganic chemicals for reuse in the pulping process. The recovery boiler also generates high pressure steam for the mill processes. The inorganic portion of the black liquor is used to regenerate the sodium hydroxide and sodium sulfide needed for pulping in a process called causticizing. It has been suggested that this article or section be merged into Kraft process. ... Recovery boiler is the part of Kraft process of pulping where chemicals for white liquor are recovered and reformed from black liquor. ...

In the case of softwood (conifer) pulping, a soaplike substance is collected from the liquor during evaporation. The soap is acidified to produce tall oil, a source of resin acids, fatty acids and other chemicals. Also turpentine originates from softwood. Despite being fairly hard, cedar is a softwood Softwood is the wood from conifers. ... SOAP (see below for name and origins) is a protocol for exchanging XML-based messages over computer networks, normally using HTTP/HTTPS. SOAP forms the foundation layer of the Web services stack, providing a basic messaging framework that more abstract layers can build on. ... Tall oil, also called liquid rosin or tallol, is a viscous yellow-black odorous liquid obtained as a byproduct of the Kraft process of wood pulp manufacture. ... This article needs to be wikified. ... In chemistry, especially biochemistry, a fatty acid is a carboxylic acid often with a long unbranched aliphatic tail (chain), which is either saturated or unsaturated. ... For the band, see Turpentine (band). ...

The high pressure steam, from the recovery boiler, is led to turbogenerators, reducing the steam pressure for the mill use and generating electricity. A modern kraft pulp mill is more than self-sufficient in its electrical generation and normally will provide a net flow of energy to the local electrical grid. Additionally: bark and wood residues are often fired in a separate power boiler to generate steam. Lightning strikes during a night-time thunderstorm. ...

The process name is derived from German kraft, meaning strength/power; both capitalized and lowercase names (Kraft process and kraft process) appear in the literature. It was developed by Carl Dahl in 1884 and now is used for about 80% of production volume of paper.

Kraft process differs from the sulfite process by using alkaline solution, which is less corrosive to the equipment. Sulfite process cannot process pulp from all wood species, for example from pine. Kraft process is also more efficient than the sulfite process. It produces stronger fiber, however the fiber is also rougher and darker that makes it somewhat more challenging to bleach. Commercial chlorine bleach To bleach something, is to remove or lighten its color, sometimes as a preliminary step in the process of dyeing; a bleach is a chemical that produces these effects, often via oxidation. ...

In a modern mill, brown pulp, (cellulose fibers containing residual lignin), following the cooking process is first washed to remove some of the dissolved organic material and then further delignified by an oxygen/alkali reaction and subsequently bleached with a combination of acidic (chlorine dioxide) and alkaline (sodium hydroxide) stages, reinforced with oxygen and/or hydrogen peroxide. Chlorine dioxide is a reddish-yellow gas which is one of several known oxides of chlorine. ... Sodium hydroxide (NaOH), also known as lye or caustic soda or sodium hydrate, is a caustic metallic base. ...

In the case of a plant designed to produce pulp to make brown sack paper or linerboard for boxes and packaging, the pulp does not always need to be bleached to a high brightness. In these cases, a higher yield of fiber from wood can be achieved.

Various byproducts containing hydrogen sulfide, methyl mercaptan, dimethyl sulfide, dimethyl disulfide, and other volatile sulfur compounds are the cause of the malodorous air emissions characteristic for pulp and paper mills utilizing the kraft process. Outside the modern mills the odour is perceivable only during disturbance situations, for example when shutting the mill down for maintenance break. The sulphur dioxide emissions of the kraft pulp mills are much lower than sulphur dioxide emissions from sulfite mills. Hydrogen sulfide (hydrogen sulphide in British English), H2S, is a colorless, toxic, flammable gas that is responsible for the foul odor of rotten eggs and flatulence. ... Methyl mercaptan (IUPAC name - methanethiol) is a colorless gas with a smell like rotten cabbage. ... Dimethyl sulfide causes that distinctive smell from your St. ... General Name, Symbol, Number sulfur, S, 16 Chemical series nonmetals Group, Period, Block 16, 3, p Appearance lemon yellow Standard atomic weight 32. ... International Paper Companys Kraft paper mill in Georgetown, South Carolina. ...

The process effluents are treated in a biological effluent treatment plant, which guarantees that the effluents are not toxic in the recipient.

External links

• US EPA article on Kraft pulping
• Reference Document on Best Available Techniques in Pulp and Paper Industry by European Commission, 2001