kraft process

Chem. See sulfate process.

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Chemical method for producing wood pulp using caustic soda and sodium sulfide as the liquor in which the pulpwood is cooked to loosen the fibres.

The process (from German kraft, "strong") produces particularly strong and durable paper; another advantage is its capability of digesting pine chips; resins dissolve in the alkaline liquor and are recovered as tall oil, a valuable by-product. Recovery of sodium compounds is important in the economy of the process. In modern kraft mills, operations are completely contained; waste streams are recycled and reused, eliminating water pollution.

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▪ papermaking

      (from German kraft, “strong”), chemical method for the production of wood pulp (paper 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.

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