Crude tall oil is obtained at decomposition of crude sulphate soap which is a by-product of cellulose producing at sulphate cooking.

The wood consists of cellulose and lignin – polyphenol compound in the form of fatty and resin acid esters. Besides, in wood are represented terpenes, phytosterols, terpene alcohols, free fatty and resin acids, and other compounds. At sulphate cooking (Kraft process) wood is being processed by white liquor (solution of caustic soda and sodium sulphide mixture) at a temperature 130 – 180°C. This results in disintegration of lignin linking and it passes into soluble state. Concurrently there takes place a hydrolysis of ester cross-links between lignin and fatty and resin acids residue, and also dissolution of free fatty and resin acids in cooking liquor in the form of sodium salts.

The obtained lignin mixture is settled in tanks. At that, sodium salts of fatty and resin acids plus unsaponifable matters, phytosterols, esters and other compounds having lesser density than the density of lignin solution in cooking liquor, are accumulated in the form of a layer in the upper part of the tank.

This layer called “crude sulphate soap” is separated from the main mass of cooking liquor that goes for regeneration of reagents. Crude sulphate soap is subjected to decomposition by sulphuric acid in reactors on batch or continuous scheme, and thus is obtained the crude tall oil. Composition and properties of crude tall oil are defined primarily by composition and properties of wood that goes for cooking.

The grades of crude tall oil under TU13-0281078-119-89 differ depending on wood species: softwood – first and second grade, mixed (softwood and hardwood) – first and second grade, and hardwood crude tall oil. The output of crude tall oil depends on content and specie of wood used in cooking process, and amounts up to 25 – 30 kg in 1t cellulose on an average.