Definition Kraft pulping is a chemical pulping process that separates lignin from cellulose fibers in lignocellulosic biomass through alkaline cooking with a mixture of sodium hydroxide and sodium sulfide, collectively known as white liquor

. The process operates at elevated temperatures (typically 150–170 °C) and pressures within sealed digesters, where hydroxide ions (OH⁻) and hydrosulfide ions (HS⁻) act as nucleophilic reagents that cleave lignin's ether and ester linkages, thereby solubilizing the lignin polymer into the cooking medium as black liquor

. The distinguishing feature of the kraft process, relative to other chemical pulping methods such as sulfite pulping, is the inclusion of sodium sulfide in the cooking liquor, which enhances delignification kinetics by generating more reactive polysulfide and hydrosulfide species that selectively attack lignin's β-O-4 aryl ether bonds while affording greater preservation of cellulose integrity

. The resulting pulp, termed kraft pulp or sulfate pulp, retains 45–55% of the original wood mass, with the remainder consisting of dissolved lignin, hemicelluloses, and degraded carbohydrates

. The term "kraft" derives from the German word for "strength," reflecting the superior mechanical properties of kraft pulp fibers compared to those produced by alternative pulping methods

. The process is characterized by a chemical recovery cycle in which inorganic cooking chemicals are regenerated from the spent black liquor through evaporation and combustion in a recovery boiler, enabling continuous operation and chemical reuse

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