Tall oil

Key takeaways

Tall oil belongs to chemistry; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Tall oil to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Tall oil from memory before moving on to harder problems.

Reference excerpt

Tall oil, also called liquid rosin or tallol, is a viscous yellow-black odorous liquid obtained as a by-product of the kraft process of wood pulp manufacture when pulping mainly coniferous trees. The name originated as an anglicization of the Swedish tallolja ('pine oil'). Tall oil is the third largest chemical by-product in a kraft mill after lignin and hemicellulose. The kraft process yields in the range of 30–50 kg of crude tall oil per ton pulp. If not used internally, sales of tall oil can contribute up to 1.0–1.5% of the mill's revenue.

Manufacturing

In the kraft process, high alkalinity and temperature convert the esters and carboxylic acids in rosin into soluble sodium soaps of lignin, rosin, and fatty acids. The spent cooking liquor is called weak black liquor and is about 15% dry content. The black liquor is concentrated in a multiple effect evaporator and after the first stage the black liquor is about 20–30% solids. At this stage it is called intermediate liquor. Normally the soaps start to float in the storage tank for the weak or intermediate liquors and are skimmed off and collected. A good soap skimming operation reduces the soap content of the black liquor down to 0.2–0.4% w/w of the dry residue. The collected soap is called raw rosin soap or rosinate. The raw rosin soap is then allowed to settle or is centrifuged to release as much of the entrained black liquor as possible. The soap goes then to the acidulator where it is heated and acidified with sulfuric acid to produce crude tall oil (CTO). The soap skimming and acidulator operation can be improved by addition of flocculants. A flocculant will shorten the separation time and give a cleaner soap with lower viscosity. This makes the acidulator run more smoothly as well. Most pines give a soap yield of 5–25 kg/ton pulp, while Scots pine gives 20–50 kg/ton. Scots pine grown in northern Scandinavia give a yield of even more than 50 kg/ton. Globally about 2 mill ton/year of CTO are refined.

Composition

The composition of crude tall oil depends on the type of wood 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 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%), other sterols, and other alkyl hydrocarbon derivatives. Fractional distillation of the crude tall oil produces pitch, tall oil rosin with a high purity in abietic acid, Tall Oil Fatty Acid (TOFA) consisting of non-saturated acids (mainly oleic acid and linoleic acid), and Distilled Tall Oil (DTO) consisting of a mix of heavier fatty acids and abietic acid.

Applications Historically, CTO was primarily refined into four different fractions:

Pitch Tall oil rosin (TOR) Tall oil fatty acid (TOFA) Distilled tall oil (DTO) Pitch was historically prized as a natural adhesive, waterproof sealant, and in some traditional medicine, and is still used for some of these purposes It is also used as a binder in cement, an adhesive, and an emulsifier for asphalt.. TOR is used as a component of adhesives, rubbers, and inks, and as an emulsifier. TOFA is a low-cost and vegan alternative to tallow fatty acids for production of soaps and lubricants. When esterified with pentaerythritol, it is used as a compound of adhesives and oil-based varnishes. When TOFA is dimerized to dimer acid it is used for making polyamide and epoxy resin. DTO is used for making alkyd resins, which improve the hardness, drying time, and water resistance of paints and varnishes. In addition to being the source of these fractions, CTO is also used as an advanced feedstock for biofuels like hydrotreated vegetable oil (HVO)/renewable diesel and sustainable aviation fuels (SAF). As the preference for biofuels has increased, so has demand for CTO for this use. From 2008 to 2019 demand for CTO as a biofuel feedstock increased 60%. Given that CTO is a byproduct of the kraft pulping process and paper and paperboard production is on the decline (having peaked in 1999 and dropped 24% since), CTO is in increasingly short supply for all uses. In some regions CTO demand now exceeds supply. This has constrained the supply of CTO available for fractioning, leading to the development of synthetic alternatives. These include R-6000 (a soy-based alternative developed specifically for metalworking fluid formulations) and TruFA (derived from seed and vegetable oils in different formulations to suit a range of industrial and agricultural processes). These alternatives tend to come from plant sources with much shorter growing cycles than traditional tall oil, and require less energy-intensive processing.

References

Worked examples

Example 1 — a first encounter with Tall oil

Start with the simplest possible case. Write down what Tall oil claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In chemistry, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Tall oil before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Tall oil ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Tall oil

In research: Tall oil appears in chemistry research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Tall oil in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Tall oil is common in secondary-school and first-year university syllabi. It links to neighbouring topics Fatty acids, Papermaking, Renewable resources, so understanding it makes those chapters shorter.
In everyday life: Look for Tall oil outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

How to study Tall oil in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Tall oil means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Tall oil out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Tall oil in simple terms?

Tall oil, also called liquid rosin or tallol, is a viscous yellow-black odorous liquid obtained as a by-product of the kraft process of wood pulp manufacture when pulping mainly coniferous trees. The name originated as an anglicization of the Swedish tallolja ('pine oil').

Why does Tall oil matter?

Because it connects several chemistry ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Tall oil?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Tall oil.