(from German kraft, “strong”), chemical method for the production of wood pulp that employs a solution of caustic soda and sodium sulfide as the liquor in which the pulpwood is cooked in order to loosen the fibres. The kraft process differs from the sulfite process in that (1) the cooking liquor is alkaline and therefore is less corrosive to iron and steel, so that the digesters in which the process takes place need not be lined, and (2) the pulp produced is stronger than that produced by cooking with caustic soda alone. A further advantage of the kraft process is its capability of digesting pine chips; the resinous components dissolve in the alkaline liquor and can be recovered in the form of tall oil, a valuable by-product. Recovery of the sodium compounds is important in the economy of the kraft process.
Despite several attempts, no completely closed-loop kraft pulp mill has yet been built; that is, complete reuse of bleach effluents and complete recycling of water have not been achieved in production kraft mills. Under current technology, some process streams are recycled, and process streams that cannot be reused are subjected to advanced water treatment prior to discharge into the receiving environment. In this way, water pollution is kept to the minimum achievable by modern technology. Compare sulfite process.
Aspects of this topic are discussed in the following places at Britannica.
...except as fine, coarse, or bleached. Chemical pulps are classed as unbleached sulfite (strong and news grade), bleached sulfite (dissolving and paper grade), bleached and unbleached sulfate (kraft), and soda. “Semichemical” is a term applied to a process of cooking followed by mechanical treatment. Spruce, balsam fir, and hemlock are considered the best woods for sulfite and...
in papermaking: Chemical wood pulp )...a soda pulping recovery system. This substitution produced a cooking liquor that contained sodium sulfide along with caustic soda. Pulp so produced was stronger than soda pulp and was called “kraft” pulp, so named from the German and Swedish word for “strong.” The process has also been termed the sulfate process because of the use of sodium sulfate (salt cake) in the...
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(from German kraft, “strong”), chemical method for the production of wood pulp that employs a solution of caustic soda and sodium sulfide as the liquor in which the pulpwood is cooked in order to loosen the fibres. The kraft process differs from the sulfite process in that (1) the cooking liquor is alkaline and therefore is less corrosive to iron and steel, so that the digesters in which the process takes place need not be lined, and (2) the pulp produced is stronger than that produced by cooking with caustic soda alone. A further advantage of the kraft process is its capability of digesting pine chips; the resinous components dissolve in the alkaline liquor and can be recovered in the form of tall oil, a valuable by-product. Recovery of the sodium compounds is important in the economy of the kraft process.
Despite several attempts, no completely closed-loop kraft pulp mill has yet been built; that is, complete reuse of bleach effluents and complete recycling of water have not been achieved in production kraft mills. Under current technology, some process streams are recycled, and process streams that cannot be reused are subjected to advanced water treatment prior to discharge into the receiving environment. In this way, water pollution is kept to the minimum achievable by modern technology. Compare sulfite process.
Aspects of this topic are discussed in the following places at Britannica.
...except as fine, coarse, or bleached. Chemical pulps are classed as unbleached sulfite (strong and news grade), bleached sulfite (dissolving and paper grade), bleached and unbleached sulfate (kraft), and soda. “Semichemical” is a term applied to a process of cooking followed by mechanical treatment. Spruce, balsam fir, and hemlock are considered the best woods for sulfite and...
in papermaking: Chemical wood pulp )...a soda pulping recovery system. This...
Aspects of this topic are discussed in the following places at Britannica.
Turpentine oil is classified according to the way it is produced. Sulfate turpentine, used widely in the chemicals industry, is obtained as a by-product of the kraft, or sulfate, process of cooking wood pulp in the course of the manufacture of kraft paper. Wood turpentine is obtained by the steam distillation of dead, shredded bits of pine wood, while gum turpentine results from the...
Aspects of this topic are discussed in the following places at Britannica.
...Sulfate turpentine, used widely in the chemicals industry, is obtained as a by-product of the kraft, or sulfate, process of cooking wood pulp in the course of the manufacture of kraft paper. Wood turpentine is obtained by the steam distillation of dead, shredded bits of pine wood, while gum turpentine results from the distillation of the exudate of the living pine tree obtained by...
raw material for paper manufacture that contains vegetable, mineral, or man-made fibres. It forms a matted or felted sheet on a screen when moisture is removed.
Rags and other fibres, such as straw, grasses, and bark of the mitsumata and paper mulberry (kozo), have been used as paper pulp. Except for certain special papers (e.g., asbestos paper), nearly all papers are made of cellulosic (vegetable) fibres. The most abundant source of cellulose is the forest, though trees differ in the value of their fibre for making paper. The fibre of flax, cotton, jute, sisal, manila hemp, and the like usually comes to the paper industry as a secondary product, after serving other uses. Agricultural wastes—straw, corn stalks, bagasse (sugarcane waste), bamboo, and some other grasses—are used for making certain grades. Finally, one of the most important sources of pulp is the fibre recovered from old papers, rags, and cardboard boxes.
Wood pulps may be classified into two general groups, mechanical and chemical. Mechanical pulp, generally called groundwood, is usually produced by a mechanical grinding process and is not further classified except as fine, coarse, or bleached. Chemical pulps are classed as unbleached sulfite (strong and news grade), bleached sulfite (dissolving and paper grade), bleached and unbleached sulfate (kraft), and soda. “Semichemical” is a term applied to a process of cooking followed by mechanical treatment. Spruce, balsam fir, and hemlock are considered the best woods for sulfite and mechanical pulping; several varieties of pine are used for sulfate (kraft) pulping; hardwoods are pulped by all of the pulping processes. The chief European pulpwoods are Norway spruce, Scotch pine, and various hardwoods. See also kraft process; sulfite process.
Aspects of this topic are discussed in the following places at Britannica.
(from German kraft, “strong”), chemical method for the...
Aspects of this topic are discussed in the following places at Britannica.
...operation, wood chips are prepared and fed to the digesting equipment by methods previously described. The cooking vessels are still widely used as batch digesters. In the past 25 years, however, continuous digesters have been developed and are being widely adopted by the kraft industry. These huge cylindrical towers, more than 60 metres (200 feet) in height, have a number of zones or...
