What Is a Tall Oil?
Tall oil is a mixture of fatty acids, resin acids, and unsaponifiable substances produced as a byproduct of the pulp manufacturing process.
It appears as a dark brown viscous liquid. During pulp production, wood chips undergo processing and evaporation with an alkaline solution, resulting in the extraction of pulp (fiber). The concentrated liquid derived from this process, known as black liquor, yields tall oil.
The unrefined tall oil obtained from black liquor is termed crude tall oil, which can be further separated and refined into tall rosin and tall fatty acids through distillation in a distillation column. These refined products find industrial applications.
Uses of Tall Oils
Tall oil serves as an inexpensive fatty acid raw material widely utilized in various industries, notably in the manufacture of greases, industrial soaps, emulsifiers, paints, and printing inks. Tall oil fatty acids find application as paint resins, such as alkyd resins, and in the production of azelaic acid, oleic acid, and linoleic acid.
Additionally, it functions as a surfactant in fuel additives and detergents. Tall oil rosin serves as an emulsifier for synthetic rubber, various anti-slip agents, and paints for road surface markings.
It is also extensively employed as an adhesive agent in tapes, hot melt adhesives, and recycled paper processing agents, among other applications.
Properties of Tall Oils
Derived from pine wood, tall oil exhibits less susceptibility to seasonal changes compared to other plant-derived alternatives. Tall oil fatty acids predominantly comprise oleic acid and linoleic acid, with negligible amounts of stearic acid and palmitic acid.
It contains no polyunsaturated fatty acids beyond linolenic acid and minimal quantities of saturated fatty acids. Tall oil rosin primarily consists of resin acids, including abietic acid, dehydroabietic acid, neoabietic acid, parastatic acid, pimaric acid, and isopimaric acid.
Additional components present in tall oil include sesquiterpenes, terpene alcohols, phenolic substances, and low molecular weight fatty acids, while pitch comprises esters of fatty acids and resin acids, along with their polymerization products, oxides, sterols, and ligninous substances.
Types of Tall Oils
Tall oil is primarily produced in paper mills located in the United States, Canada, Russia, and China. As it is derived from wood, its composition ratio varies based on the pine species utilized.
In Japan, tall oil is mainly imported from North America and further refined into tall rosin. Crude tall oil serves as the raw material for tall oil fatty acids, tall oil fats (tall rosin), and other substances, which are separated into several types through distillation and refining processes for industrial applications.
Other Information on Tall Oils
1. Origin of Tall Oil
The term “tall” originates from the Swedish word for pine (tall). The composition of tall oil varies depending on the pine species used, such as slash pine, European red pine, and babyshoe pine.
2. Tall Oil Production Process
In kraft pulp mills, tall oil is produced as a byproduct through the following processes:
- Wood chips (pulpwood) are boiled and dissolved with chemicals like sodium hydroxide (caustic soda) (evaporation).
- Pulp (wood fiber) is separated from the resulting white liquid (a mixture of lignin, resin, and chemicals).
- The white liquor is concentrated to obtain black liquor.
- Sodium soap of the resin acids and fatty acids present in pine, dissolved in black liquor, is salted out during concentration, forming creamy suspended solids (skimmings).
- The skimmings are decomposed with acid to liberate crude tall oil.
The crude tall oil obtained is then distilled in a distillation column, yielding four fractions: tall oil fatty acids, tall oil fat (tall rosin), tall oil primary distillate, and pitch, which can be reprocessed into various bio-chemicals.