Oil Extraction and Processing Questions and Answers

Answer: C

Correct answer: Hexane dissolves the oil and is discarded after a single pass

Hexane is recovered and recirculated continuously. The miscella is distilled to evaporate it, the vapour is condensed, and the solvent returns to the extractor; the meal is desolventised so that its hexane is recovered too.

Discarding it would be ruinous on three counts at once - cost, fire risk and emissions - which is why loss is measured in litres per tonne and kept below one. The other three statements are all true: countercurrent contact maintains the driving force, the miscella is distilled, and hexane is the usual commercial solvent.

Answer: D

Correct answer: Rolling the flakes thin enough to crumble

Thinner flakes help only up to a point. Once they crumble, the fines blind the percolation bed, the miscella will not drain through it, and extraction gets worse rather than better.

The practical floor is around 0.3 mm. The other three all help: dehulling enriches the feed and removes absorbent material, cooking thins the oil and ruptures cell structure, and countercurrent contact keeps a concentration difference at every stage so that even the last traces face nearly fresh solvent.

Answer: A

Correct answer: To increase the oil's iodine value

Refining removes impurities; it does not alter the fatty acid composition. Iodine value reflects the number of double bonds in the triglycerides, which is fixed by the seed, so no refining step raises it.

If anything the value falls slightly, since the high temperature of deodorisation can isomerise or degrade a little of the unsaturation. The other three are exactly what refining is for: free fatty acids, colour pigments and odour compounds are removed in neutralisation, bleaching and deodorisation respectively.

Answer: B

Correct answer: Inadvisable: such a seed drains poorly

At 45 per cent oil the flakes release so much liquid that the bed floods: the miscella cannot percolate, drainage stops and the extractor cannot work properly.

The route for such a seed is pre-press solvent extraction - press first to bring the oil down to 15 to 20 per cent, then extract the cake, reaching residuals below one per cent. Direct solvent extraction is right for low-oil seeds such as soybean at around 20 per cent, which is why the practice is not standard for all seeds.

Answer: C

Correct answer: It is carried out under high vacuum

Deodorisation runs at a few millibars absolute. The vacuum lowers the boiling points of the free fatty acids, aldehydes and ketones enough that stripping steam removes them at 240 to 260 degrees Celsius, a temperature the triglycerides survive.

At atmospheric pressure the temperature required would decompose the oil, darken it badly and generate trans isomers. The other two options name different steps: phospholipids are removed by degumming, and activated earth belongs to bleaching.

Answer: D

Correct answer: Allowing free fatty acids to rise before refining

Higher acidity means more soap formed, and neutral oil is lost both by saponification from the excess alkali and by entrainment in that soap. Refining loss therefore rises faster than the acidity itself.

The other three all reduce it. Prompt processing limits hydrolysis in the first place; careful control of alkali strength and excess limits the saponification of neutral oil; and physical refining of a high-acid oil avoids soap formation altogether, stripping the acids by distillation instead.

Answer: A

Correct answer: It is essentially free of oil

Cake retains 5 to 8 per cent oil, because compression cannot empty a cellular material - some oil stays in unbroken cells and some is held by capillary forces in the compressed mass.

That residual is precisely why the other statements are true: the cake is commonly solvent extracted afterwards to recover it, and what remains becomes a protein feed once the solvent has been driven off in a desolventiser-toaster. Only after solvent extraction is the material genuinely low in oil, below one per cent.

Answer: B

Correct answer: The seed's angle of repose

The angle of repose governs the slope of hoppers and chutes in the handling system, which every plant needs but which has nothing to do with extraction itself.

The other three go to the heart of the design. Flake bed permeability decides whether the miscella will percolate at all. Hexane's flash point sets the whole fire and electrical specification of the building. Miscella distillation duty sizes the evaporators, condensers and steam supply. Each of the three would change the plant fundamentally; the angle of repose changes a chute angle.

Answer: C

Correct answer: Its low speed keeps the oil cool

A ghani turns slowly, so little heat is generated by friction and the oil leaves at close to ambient temperature. That is the traditional method's one real technical advantage: minimal thermal damage, and natural flavour and colour retained.

Everything else weighs against it. Recovery is poor, at roughly 12 per cent oil left in the cake, so it recovers nothing like all the oil; it uses no solvent; and it takes whole or coarsely broken seed rather than flakes. It survives for cold-pressed speciality oils where the flavour commands the price.

Answer: D

Correct answer: Bleaching removes metals and peroxides first

Deodorisation works at 240 to 260 degrees Celsius, and at that temperature trace metals catalyse oxidation and residual peroxides decompose into coloured and odorous products. An oil that arrived unbleached would leave the deodoriser darker than it went in.

Bleaching earth adsorbs those metals and peroxides along with the colour pigments, so the oil enters the deodoriser in a state where heat does no harm. The order is fixed by that dependence, not by any equipment consideration - bleaching needs only a mild vacuum, and deodorisation adds no colour to a properly bleached oil.