Composition
See also: Resin acidThe composition of crude tall oil varies a lot, depending on the wood furnish used. A common quality measure for tall oil is acid number. With pure pines it is possible to have acid numbers in the range 160 - 165, while mills using a mix of softwoods and hardwoods in the furnish might give acid numbers in the range of 125 - 135.
Normally crude tall oil contains rosins (which contains resin acids (mainly abietic acid and its isomers), fatty acids (mainly palmitic acid, oleic acid and linoleic acid) and fatty alcohols), unsaponifiable sterols (5-10%), some sterols, and other alkyl hydrocarbon derivates.
By fractional distillation tall oil rosin is obtained, with rosin content reduced to 10-35%. By further reduction of the rosin content to 1-10%, tall oil fatty acid (TOFA) can be obtained, which is cheap, consists mostly of oleic acid, and is a source of volatile fatty acids.
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