Tall oil, its chemistries and applications
- Tall oil, which is derived from sustainable and renewable sources of fatty acids and resins, has been produced commercially since the 1930s.
- Tall oil offers unique properties and a wide range of applications.
- The pine chemical industry has a big impact on the global economy and is evolving to find new applications.
Tall oil is a unique type of “oil” with properties that differ from those of common edible vegetable oils, such as canola, coconut, corn, olive, palm, peanut, safflower, sesame, soybean and sunflower, as well as non-edible vegetable oils such as linseed oil and castor oil. The term “tall oil” comes from the Swedish word for pine oil: “Tallolja.” The term was anglicized to distinguish it from the essential oil that is produced from the steam-distillation of pine stumps, needles, twigs, and cones, and is referred to in English as pine oil.
Pine wood contains five major components, namely cellulose, hemicellulose, lignin, tall oil, and turpentine (Fig. 1). While cellulose fibers are mainly used for papermaking, the remaining components are considered to be by-products.
FIG. 1. Composition of a pine tree
For many years, tall oil was treated as waste or burned as fuel. Tall oil products were not made on a commercial scale until the 1930s, when the invention of the recovery boiler enabled recovery and reuse of organic chemicals in the Kraft wood-pulping process that separates tall oil from wood chips. (Fig. 2).
FIG. 2. Flow diagram of a typical kraft pulping process
In the Kraft process, after the pine chips are digested and filtered, the filtrate, called “black liquor,” is fed to an evaporator and skim tank for soap making. The soap is then acidulated to make crude tall oil (CTO). The CTO is then further fractionated at the refinery to get tall oil heads, tall oil fatty acids (TOFA), distilled tall oil fatty acids (DTO), tall oil rosin (TOR), and tall oil pitch (TOP) (Fig. 3).
FIG.3. Components in tall oil fractionation
The most important components in CTO are tall oil fatty acids (TOFA) and rosin acids (TOR). Unlike most vegetable oils and animal fats, tall oil is not produced as triglycerides but as straight fatty acids. Nevertheless, tall oil is considered to be from a renewable resource, just like vegetable oils. With about 3% of total weight in pine wood chips, crude tall oil(CTO) is valued at $243 million in world exports, contributing to global revenues of $10 billion for the pine chemical industry (“Global impact of the modern pine chemical industry,” Pine Chemical Association, 2016, “https://pinechemicals.site-ym.com/news/292194/GLOBAL-IMPACT-OF-THE-MODERN-PINE-CHEMICAL-INDUSTRY.htm).
Tall oil compositions
With a composition similar to that of vegetable oils, TOFA is a mixture of fatty acids with various chain lengths and saturations. The most common components are oleic acid, linoleic acid, linolenic acid, palmitic acid, and stearic acid. The carbon chain distribution of tall oil is similar to that of sunflower and soybean oil, which have a higher prevalence of longer chains (C16 and higher) than coconut and palm kernel oil do. A unique property of TOFA is that it contains various amount of rosin (represented here are abietic and pimaric acid). The presence of rosin creates physical properties that could not be obtained from vegetable and animal fats. For example, it reduces the bioactivity of TOFA in downstream formulations, particularly in metalworking fluid and Household, Industrial, and Institutional (HI&I) products.
FIG. 4. The molecular structures of two rosins found in tall oil fatty acids
In addition to TOFA and rosin, there are other often-ignored components of tall oil processing—unsaponifiables. These are neutral compounds that do not have carboxylic functional groups and thus do not readily form soap when they react with caustic. The main components of unsaponifiables are hydrocarbons, alcohols, and sterols. Although such compounds appear in all five fractions of tall oil distillation, they are more dominant in tall oil heads and pitch. The extraction of sterols makes the unsaponifiables portion of tall oil more commercially attractive.
Chemistries and applications
Derivatization of TOFA and rosin leads to their salts, esters, and resins. While C36 dimer acids and C-21 diacids are unique to TOFA, pitch can also be used to extract sterols for medical and fuel applications.
Current applications of TOFA include adhesive, inks surfactants, painting and coatings, mining, and metalworking. Rosin is used in many applications, including adhesives, inks, tires, chewing gums, varnishes, electronics, papermaking, coating, and roadmaking.
Esters are one of the most common derivatives of TOFA due to the esterification of polyols (glycerol, pentaerythritol, and trimethylolpropane), short chain alcohols, and ethoxylates. Alkyd resins are a major application of TOFA esters. Short-chain alcohol esters have been used in biodiesel, synthetic lubricants. and as surfactants. An example of a new product based on C-21 diacids is Altalub 5300, which has shown promise in lubricant applications (“Performance lubricity additive for metalworking fluids,” Tribology & Lubrication Technology 72: 76, 2016). TOFA amides are also being produced; applications include asphalt additives and mud drilling in oilfields.
TOFA in the forms of DTO, heads, and CTO or their mixtures, have been used as anionic collectors in mineral flotation. The presence of rosin acids in TOFA can sometimes help to improve the froth property of the collectors. In addition, TOFA amidoamines can also be used as cationic collectors in phosphate ore flotation (McSweeney, E., et al., 1987).
The Diels-Alder reaction is a very commonly practiced reaction for both TOFA and rosin derivatization. For example, maleic anhydride would be used as a reactant with a conjugated portion of TOFA (conjugated linoleic acid) or rosin (abietic-type acids). Another common reaction in tall oil derivatization is disproportionation—an isomerization reaction of TOFA or rosin under heat, usually with a catalyst. In TOFA, iodine has been used to catalyze disproportionation, thus converting non-conjugated linoleic acid to conjugated linoleic acid, and eventually to oleic acid. Similarly, rosin can be disproportionated from its conjugated diene components, such as abietic and palustric acid, to its aromatic form as dehydroabietic acid, which is widely used in the rubber industry. Diene portions of rosin can be utilized for a Diels Alder reaction with maleic acid or anhydrides—or fumaric acids—to make tricarboxylic acids and further derivatizations for ink and adhesive applications.
New potential applications
In addition to traditional applications in rubber, adhesive and inks, new applications of tall oil products have been developed.
Novel applications were recently discovered by making ionic liquids based on TOFA and rosin (Klejdsz, T., et.al., 2016).
In addition, new potential applications for rosin-based chemistry related to flame retardants have been explored (Zhang, M., et al., 2015, and Lei, et al., 2015). TOFA and rosin have also been explored as renewable hydrocarbon sources (Jenab, E., et al., 2014).
Despite of its long history, the tall oil industry continues to evolve. As people pay more and more attention to green chemistry and sustainability, tall oil offers alternative raw materials and products to both petroleum oil and other natural oils.
- Pine Chemical Association, “Global impact of the modern pine chemical industry, 2016, https://pinechemicals.site-ym.com/news/292194/GLOBAL-IMPACT-OF-THE-MODERN-PINE-CHEMICAL-INDUSTRY.htm
- McSweeney, E., H. Arlt, and L. Russell, “Tall Oil and Its Uses: II,” Pulp Chemical Association, Atlanta, GA, 1987
- Ingevity New Product, “Performance lubricity additive for metalworking fluids,” Tribology & Lubrication Technology 72: 76, 2016
- Klejdsz, T., et.al., “Biobased ionic liquids with abietate anion,” ACS Sustainable Chemistry & Engineering 4: 6543, 2016
- Wang, B., “Ionic liquids based on naturally derived fatty acids and rosin,” 2017, patent pending
- Jenab, E., P. Mussone, G. Nam, and D. Bressler, “Production of renewable hydrocarbons from thermal conversion of abietic acid and tall oil fatty acids,” Energy Fuels 28: 6988–6994, 2014 Zhang, M., Z. Luo, J. Zhang, S. Chen, and Y. Zhou, “Effects of a novel phosphorus–nitrogen flame retardant on rosin-based rigid polyurethane foams,” Polymer Degradation and Stability 120: 427–434, 2015
- Lei, G., S. Xu, and L. Weng, (2015) “Halogen-free rosin-based flame retardant and preparation method thereof,” CN104558019A, 2015