Oil Extraction and Processing Questions and Answers

Answer: C

Correct answer: Neutral oil is lost alongside the acid

The refining factor is total loss divided by the free acid present, and every row exceeds one - 1.83, 1.75, 1.67, 1.63. More is lost than the acid accounts for, and the surplus is neutral oil, saponified by excess alkali or entrained in the soapstock.

The first and fourth options are contradicted by the loss column, which plainly rises with acidity. The second misreads the trend: the factor falls as acidity rises, since the fixed component of the loss becomes a smaller share of a larger total - but it never approaches one.

Answer: D

Correct answer: Linseed, on its very high iodine value

Iodine value counts double bonds, and it is those that oxygen attacks. Linseed at 180 is far the most unsaturated of the four, which is why linseed oil dries to a film in air and is used as a paint vehicle rather than kept as a food oil.

Coconut at 9 is almost saturated and correspondingly stable, whatever its saponification value - that column reports mean chain length, not oxidisability, and coconut's 255 simply reflects its short chains. Palm's semi-solidity is a consequence of low unsaturation, not an independent reason.

Answer: A

Correct answer: 0.35 mm

Two columns must be satisfied at once. Extraction time falls steadily as the flake thins, from 62 minutes to 31, but bed drainage collapses below 0.35 mm.

At 0.25 mm and 0.18 mm the flakes break into fines that blind the bed, so the shorter times in the table could not be realised in practice - the miscella would not percolate. At 0.50 mm drainage is excellent but extraction takes half as long again. 0.35 mm keeps drainage good while taking most of the available reduction in time, which is what a compromise means.

Answer: B

Correct answer: Both A and R are true, and R is the correct explanation of A

Both are true and the reason is exactly why flaking is done. Rolling ruptures the oil-bearing cells, so the oil is no longer locked inside intact cell walls, and it reduces the thickness to a few tenths of a millimetre.

Solvent then has only a very short path to diffuse in, and dissolved oil a short path out, which is what allows residual oil below one per cent in a workable residence time. Note that flaking adds nothing and removes nothing - the oil content is unchanged, and it is accessibility alone that improves.

Answer: C

Correct answer: Both A and R are true, and R is the correct explanation of A

Both are true and the reason is the whole basis of the precautions. Commercial hexane has a flash point around minus 22 degrees Celsius and forms explosive mixtures with air over a wide range of concentrations.

Everything in the plant follows from that: electrical equipment is flameproof, the building is designed to vent an explosion, vapour is recovered rather than released, and hot work is tightly controlled. It is also why hexane loss per tonne is watched as a safety figure and not merely as a cost.

Answer: D

Correct answer: Both A and R are true, and R is the correct explanation of A

Both are true and the reason gives the order its logic. Phosphatides are surface-active: left in the oil they stabilise emulsions, so the soapstock will not separate cleanly in the centrifuge and neutral oil is carried away with it.

They also consume bleaching earth, foul heat-exchange surfaces and darken the oil during deodorisation. Removing them first therefore improves every later step, which is why degumming heads the refinery sequence. For physical refining it is more critical still, since there is no alkali stage to remove any that survive.

Answer: A

Correct answer: A is false but R is true

The reason is sound and it is precisely what defeats the assertion. Hydroperoxides are the primary products of oxidation, and they are unstable: as oxidation proceeds they decompose into aldehydes and ketones.

So a low peroxide value is ambiguous. It may mean a fresh oil that has not yet oxidised, or a badly deteriorated one whose peroxides have already broken down - the value rises, peaks and then falls. That is why peroxide value is read alongside anisidine value, which measures the secondary products and keeps rising, the two together giving the totox picture.

Answer: B

Correct answer: Both A and R are true, and R is the correct explanation of A

Both are true and the reason is the mechanism. A press works by squeezing, and squeezing cannot empty a cellular structure: some oil is held in unbroken cells and some by capillary forces in the compressed mass, leaving 5 to 8 per cent in the cake.

Solvent extraction does not have this limit, because it dissolves the oil rather than expelling it mechanically, and reaches below 1 per cent. The gap between the two figures is exactly what makes pre-press solvent extraction worthwhile for a high-oil seed.

Answer: C

Correct answer: Both A and R are true, and R is the correct explanation of A

Both are true and the reason explains the position. Deodorisation strips the volatile aldehydes, ketones and residual free fatty acids that carry flavour and odour, by steam distillation at a few millibars absolute.

It comes last because it removes the very compounds that earlier steps generate or leave behind, and because any impurity still present - a phosphatide, a trace metal - would be darkened by the temperature it uses. Doing it earlier would mean re-contaminating a finished oil, so the sequence is fixed by what each step leaves for the next.

Answer: D

Correct answer: A is false but R is true

The reason is correct and it refutes the assertion. Hulls carry almost no oil, so they dilute the feed; they occupy extractor volume that could hold oil-bearing material; and being absorbent, they retain oil during processing and carry it out in the meal.

Every one of those is an argument for dehulling before solvent extraction, not against it. Dehulling also raises the protein content of the meal, which is worth money in its own right. The assertion states the opposite of what the reason establishes.