Tall oil
Tall oil (from Swedish: tall = pine), also known as liquid rosin , is an oily mixture of substances which is the most important by-product in the production of pulp (more precisely: sulphate pulp , especially with pine wood ). It is a black and yellow liquid, which is composed mainly of fatty acids (about 42 to 55%) and resin acids (about 33 to 47%) as well as sterols and other substances. The composition varies greatly due to its origin from resinous woods. Despite its vegetable origin, it is not a vegetable oil .
Manufacturing
Tall oil is a by-product of the pulp industry; it contains the extract substances of the wood that are released during pulp boiling.
raw material
In addition to the main components, cellulose , hemicellulose and lignin , wood contains between 1 and 3 percent resins . A distinction is made between different types of resin: The resin contained in the so-called parenchymal cells consists of triglycerides , fatty acids, resin acids, sterols and sterol esters and is used to store nutrients. The resin present in the radial resin ducts, on the other hand, consists mainly of resin acids and terpenes and is used to close wounds in the event of damage to the tree bark.
The traditional method of extracting resin from trees by scratching the bark ( resins ) almost exclusively extracts the resin from the resin veins. In contrast, the sulphate process extracts all of the resin during pulp production, including the portion from the parenchymal cells. Accordingly, the resin from cellulose production contains not only resin acids but also fatty acids and sterols.
Procedure
During cellulose production , the resins are produced as soaps , the so-called tall soaps , in the black liquor and are deposited as such . In the first step, the crude tall oil is separated from these tall soaps as a black, viscous liquid by adding sulfuric acid . Depending on its origin, crude tall oil consists of 20 to 65 percent resin acids, 15 to 55 percent fatty acids and 5 to 30 percent unsaponifiable components. Crude tall oil can be extracted continuously or discontinuously; the yield is between 30 and 40 kg / t of pulp.
Further processing and use
Crude tall oil as such has only limited use, for example as an emulsifier additive . The products made from crude tall oil by fractionation are more industrially important, especially fatty acids and resin acids.
Fractionation
There are extractive and distillative processes for fractionation, but only the distillative process has prevailed. The demands on the distillation are high, especially since the products have a high boiling point and at the same time tend to decompose and polymerize. Furthermore, due to the acids and sulfur compounds it contains and the associated corrosiveness, the starting material places high demands on the materials for the distillation plants.
Distillation and refining
The untreated tall oil can be distilled to tall resin with a rosin content of 10 to 35 percent at temperatures between 200 and 285 ° C. Subsequent refining results in fractions of tall oil fatty acids with a rosin content of 1 to 10 percent. Typical tall oil fatty acid fractions contain about 1 to 3% saturated fatty acids and a very high proportion of unsaturated fatty acids. The proportion of linoleic acid and (little) linolenic acid is 45 to 65%, oleic acid is 25 to 45%.
Products: fatty acids
The products from tall oil distillation are used in a variety of ways in the processing industry; Tall oil fatty acids (TOFA) can usually be used for the same purposes as fatty acids from other sources. Among other things, they contain unsaturated fatty acids (e.g. oleic acid ) and are therefore an inexpensive source of fatty acids with a low boiling point. As an alternative to sebum fatty acids (from animal products), they are used in soaps . There are also applications in which tall oil fatty acids are unrivaled, for example in Europe a large proportion of these fatty acids are used as raw materials for coatings. Tall oil fatty acid contains only a small amount of linolenic acid , which prevents yellowing of white pigments (as occurs with fatty acids from other sources). Other products made from tall oil fatty acids are polyamide resins for the printing and adhesives industry and epoxy resins .
Products: Tall Harz
Tall resin ( colophony ) is also used in the same way as balsam resin . A significant part of tall resin goes into the production of paper sizing agents based on natural resin. The resin acids, after they have been reacted with fumaric acid or maleic anhydride according to the Diels-Alder addition reaction type, are converted into an approximately thirty percent dispersion by dispersing with sodium hydroxide solution and emulsifier. These dispersions are used in paper production to adjust the water absorption capacity of the paper. This improves the writability and printability of the paper.
Tall resin is also used for adhesives and printing inks. Another consumer is the rubber industry, where tall resins are used as emulsifiers in the manufacture of synthetic rubber . In addition, relatively small amounts are used in the manufacture of chewing gum. As an impregnation for wooden floors, it is also used in wood oils, as well as in wood stains. There are other applications in the field of construction chemistry, for example as an air-entraining agent in concrete. Tall pitch is increasingly being used as a substitute for bitumen or as an emulsifying additive in asphalt ; In contrast to bitumen, it does not contain any polycyclic aromatics. Tall pitch is also used for colored asphalt, grout, sealant, concrete emulsifier.
Individual evidence
- ↑ a b c d e Keyword "Tall Oil" In: Hans Zoebelein (Ed.): Dictionary of Renewable Resources. 2nd edition, Wiley-VCH, Weinheim and New York 1996, ISBN 3-527-30114-3 , p. 299.
- ↑ a b c d Entry Tall Oil at chemicalland21.com, accessed December 9, 2015.