Black liquor, kraft fractionation process

It is derived as a by-product from the Kraft (sulfate) process to make - paper pulp. Pinewood is the most common source. After separation of the pulp, the remaining black liquor is concentrated by evaporation, whereby the crude soap is salted out and collected. Acidulation with sulftiric acid and several refining steps gives crude tall oil. Production of one ton of paper pulp yields 30-40 kg of tall oil. Fractional steam-vacuum distillation (200-285 °C 13.3 kPa/lOOmm steam must be present to lower the b.p. and avoid decomposition) separates the oil from the pitch and low-boiling components. The oil is purified by additional fractionation procedures to separate the -+rosin and to produce various grades of purities of tall oil fatty acids (TOFA),... 

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