In the alkaline pulping processes using resinous woods, the rosin and fatty acids in the wood are saponified and dissolved in the spent cooking or digestion liquor. As the black liquor is concentrated by evaporation, some of the organic acid soaps plus some unsaponifiable material become insoluble and may be skimmed from the surface of the liquor. Many alkaline pulp mills today have acidulation plants for converting these tall oil skimmings to crude tall oil; therefore, many mills market this product to chemical manufacturers.
The methods for analysis of the tall oil skimmings are contained in TAPPI T 635 “Analysis of Tall Oil Skimmings.” This procedure pertains to analysis of the crude “acidified” tall oil only. Operating variables in the acidulation process can affect the quality of the oil in various ways; therefore, these analytical tests are used by the producers as well as the consumers of crude tall oil to monitor its quality.
