Fat fractionation

Ali AhmadpourChemical Eng. Dept.Ferdowsi University of Mashhad

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Contents

Introduction Fractionation & Crystallization Dry fractionation Detergent fractionation Solvent fractionation

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Introduction Edible fats derived from animal, marine or plant sources, are

not available in edible form. Their recovery are usually through crushing (seed oils), cold

expression (seed oils) and churning (as in butter from dairy cream).

In some cases, the fats are processed further through degumming, bleaching, neutralization and alkali refining or physical refining, and finally deodorization.

Therefore, the fat would have undergone some form of separation during one or several stages of process, starting initially with filtration to remove impurities.

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Cont. A number of these edible fats are treated further, through

hydrogenation, interesterification and fractionation to improve their oxidative stability, nutritional and functional value and processing properties.

Hydrogenation and interesterification reactions are mostly followed by separation processes, to remove, for instance, nickel catalyst from the hardened fat.

Fractionation, however, is primarily a separation process, where fat is first nucleated and crystallized and then separated from the liquid phase using one of several techniques.

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Fat

Triacylgylceride or fat: three fatty acids attached to a glycerol backbone.

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Fatty acids Fatty acids are long chain hydrocarbons with a carboxyl group on one

end. They differ by number of carbons in the hydrocarbon region and

degree of saturation. The degree of saturation refers to the presence or absence of C=C

double bonds in the hydrocarbon region. Both stearic acid and oleic acid have 17 carbons in the hydrocarbon

region, but oleic acid has one C=C bond and is considered an unsaturated fatty acid while stearic acid has only C-C bonds and is considered a saturated fatty acid.

The presence of the C=C double bond gives the hydrocarbon region a distinct bend whereas the saturated fatty acid has a linear appearance.

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Fatty acids

Palmitic Acid (C 16:0):

Stearic Acid (C 18:0):

Oleic Acid (C 18:1):

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Fatty acids

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Fractionation Three major commercial processes are available for the

fractionation of fats. These combine the crystallization and separation processes: Dry fractionation: The crystallization stage can be either rapid

or slow and crystals are separated through direct filtration i.e. without the use of additives.

Detergent fractionation: Crystallization is generally rapid and an aqueous solution containing detergent is used to facilitate the separation of the crystals from olein (soft semi-fluid yellow fraction) by centrifugation.

Solvent fractionation: The crystallization is carried out in solvents followed by filtration. This process is not used widely due to its high operating costs except for the production of high value products such as cocoa butter replacer.

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Fractionation process

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Crystallization

Two steps in crystallization process:

Nucleation

Growth

PrimarySecondaryHomogeneousHeterogeneous

Nucleation

Nuclei Cluster Embryo Nucleus Crystal

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Cont. For a given reactor vessel with a fixed rate of agitation, the

cooling rate, determines final crystal composition:1) Rapid cooling rates results in high yields of crystals with low N20

values (solid fat index values at 20°C) due to entrapped olein.2) Moderate cooling rates promotes the development of crystals with

primarily high melting triacylglycerols and high N20 values, although the yields are reduced.

3) Slow cooling rates results in high yields of crystals, but the solid fraction reduce N20 values. This is due to the development of nuclei which allow growth of crystals comprising high and medium melting triacylglycerols.

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Crystal forms Crystals can exist in three main forms: α, β' and β in order of

increasing stabilities and melting points. A metastable α-form: rapid cooling, very small crystals. In general the oil crystallizes into the unstable α-form and then

rapidly transforms into the more stable β'-form, and much more slowly into the β-form.

β'-form: firm and uniform spherical size, easy to separate from the olein phase, about 0.1 mm in size.

β'-crystals are formed readily when the oil is free from crystal inhibitors such as gums, carbohydrates, soap, mineral acids and monoglycerides.

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Crystal forms

α Crystals – Unstable β' Crystals – Stable- large amounts of small air cells- Yields whiter, creamier product that is tender and has a smooth texture.(Soybean, Peanut, Corn, Safflower, Olive, Coconut, Lard, Cocoa butter)β Crystals – Most stable- small amounts of large air cells - Yields large clustered crystals with a waxy or grainy texture.(Cottonseed, Palm, Rapeseed, milkfat, Tallow, Modified lard)

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Dry Fractionation Two forms of dry fractionation used for the removal of waxes and

high melting triacylglycerols from liquid vegetable oils are: Dewaxing Winterization

Fats which contain a large proportion of higher melting triacylglycerols, are treated to full fractionation (typically 20-30% stearin and 70-80% olein).

The processes are generally referred to by the filtration system (not crystallization) selected. Three major filtration routes are:a) Flat-bed vacuum band filter;b) Rotary drum vacuum filter;c) Membrane, positive pressure filter.

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Crystallization

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Flat-bed continuous filter (Florentine)

67-72% olein

Vacuum: 50-200 mbar

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Flat-bed filter

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Vacuband batch filter

76-80% olein

P= 3.3 bar

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Fat fractionation using Vacuband filtration

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Fat characteristics

Iodine value: is a measure of unsaturation.

Drop point: is a measure of melting point of oil.

Cloud point: is a measure of unsaturation.

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Type of OilMelting Range (°C) Iodine

numberOil / FatSunflower oil -18 125 to 135Olive oil -12 77 to 94Soybean oil -12 125 to 140Cotton seed oil 0 100 to 115Corn oil -5 115 to 124Coconut oil 20 to 24 8 to 10Palm kernel oil 20 to 26 12 to 18Palm oil 30 to 38 44 to 58Palm oleine 20 to 25 85 to 95Palm stearine 35 to 40 20 to 45Tallow 35 to 40 50 to 60Lard 32 to 36 60 to 70

Oil characteristics

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Rotary drum vacuum filter

70% olein

0.1-0.25 rpm

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Cont.

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Cont.

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Rotary Drum Vacuum Filter

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Fractionation

Filter-press in frontof a 16 tons crystallizer 2 x 16 tons crystallizers

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Tirtiaux Florentine filter usedfor cryo-fractionation

Filter-press plate after filtration

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Filter-press

Cakes being melted after filtration (filter-press)

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Filter press

Low pressure: 0.1-5 bar80% olein

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Filter Press - Typical arrangement

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Typical filter press operation

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Belt Filter Press

High pressure: 50 bar82% olein

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Comparative fractionation of palm oil using (a) a membrane filter press, and (b) a vacuum filter

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Detergent Fractionation

The process involves crystallization of the oil and separation of fractions aided by a water containing an aqueous detergent (sodium lauryl sulphate) and an electrolyte (magnesium sulphate or sodium sulphate).

The electrolyte facilitates the agglomeration of the oil droplets formed during the mixing process.

The detergent helps in fractionation as it wets the stearin crystals and displaces entrained olein.

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Cont.

The lower density olein can be separated from the stearin-detergent mixture of higher density by centrifuging.

The trace of detergent in olein can be removed by washing.

The heavier phase is heated to melt stearin and then centrifuge to separate it from detergent.

Maximum possible yield of >85%.

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Cont.

The critical factor determining the yield is the amount of olein remaining in the stearin suspension as droplets.

Important process considerations: Crystallization conditions,

Amount of surfactant,

Electrolyte concentration,

Weight ratio of detergent solution to partially crystallized fat,

Viscosity of the dispersion.

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Lipofrac fractionation process

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Solvent Fractionation

Solvent fractionation is a process involving the crystallization of a desired fraction from a mixture of triglycerides dissolved in a suitable solvent.

Fraction may be selectively crystallized at different temperatures after which they are separated and the solvent removed.

The two common solvents used are hexane (non-polar) and acetone (polar).

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Cont.

Solvent to oil ratio of 1:1 to 3:1 is normally used.

Cooling is done by chilled water, or if very low temperatures are desired, brine.

The olein/stearin fractions are separated by a process of filtration.

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Cont. Advantages:

Fractional crystallization is more efficient in the presence of solvents,

Improved yield of olein and stearin purity, Reduced processing time.

Disadvantages: The relative high cost of initial capital investment, High operational costs involved (energy requirements,

solvent loss (3-10 kg/tonne), and additional cost of cooling for the oil and entire quantity of solvent.

Flavor problems from solvent residues in the products make solvent fractionation of milk fat impracticable.

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Schematic diagram of solvent fractionation