DRY FRACTIONATION.doc

DRY FRACTIONAT FRAC TIONATION ION 1. Historical perspective In edible oil processing, a fractionation process consists consists of a controlled cooling of the oil, thereby inducing a partial, or ‘fractional’, crystallization. The remaining liquid (olein) is then separated from the solid fraction (stearin) by means of a filtration or centrifugation.

This kind of fract fractionat ionation ion process has been applied for almos almostt !" year years. s. In most literature literature,, Hippolyte Mège-Mouriès is credited #ith the in$ention of %a patented method to produce certain fats of animal origin&. In fact, he concocted the production of a sort of margarine fat, by separating a liquid fraction from ordinary tallo# tal lo# aft after er gen gentle tle coo coolin ling. g. 'ut #it #ith h only temperat temperature ure dif differ ferenc ence e as the dri dri$in $ing g for force, ce, a fra fracti ctiona onall crystallization crystallizat ion of a fat is a perfectly natural, spontaneous phenomenon. o it #as also obser$ed that in palm (kernel) oil har$ested in tropical regions, small crystals #ould appear upon cooling and form a crystal suspension in the #ooden barrels during shipping to chillier estern *urope. These slightly denser solids e$entually settled, and such fractions could effecti$ely replace hardened fats in margarines +. In a more e$ocati$e t#ist, #e could therefore consider these #ooden shipping drums the $ery first oil crystallizers crystallizers,, #ith  -ust the peaceful ocean #a$es pro$iding the necessary agitation to keep the mi in suspension. /oreo$er, the natural fractional crystallization of fats #hen mildly cooled is echoed in the term ‘#interization’, referring to the habit of lea$ing large oil tanks quiescent in #intertime to induce some mild crystallization and obtain a liquid fraction #ith impro$ed cold stability, in an economic fashion +0.

1espite the apparent spontaneity of the process itself, it took until the years 23" for the fractionation industry (and technology) to boom, #hen the production of palm oil in outh4*ast 5sia hea$ily increased and eport taes on processed palm oil #ere reduced. 5t that time ho#e$er, the boundaries of the technology #ere mainly determined by the phase separation. In the early stages of fractionation technology, the olein and stearin fractions of oils and fats had to be separated by settling, using only the force of gra$ity to bring about a separation bet#een the hea$ier solid phase and the lighter liquid phase, #hich left the settled solid phase containing large quantities of entrained (trapped) liquid oil, almost certainly more than 6!7 +8. In the lastt dec las decade ades, s, the con contin tinuou uous s de$ de$elo elopme pment nt of sep separa aratio tion n tec techni hnique ques, s, fro from m $ac $acuum uum bel beltt fil filtra tratio tion n to centrifuges and membrane press filters, has put fractionation on the map as a $ersatile and economic modification technique. 5lthough some specific techniques relying on use of detergents are still applied for  $ery particular production, actually only t#o main fractionation technologies are used in the 0st century’s edible oil industry9

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Dry ractio!atio!, also kno#n as crystallization from the melt, is fractional crystallization in its most simple form, and the economy of the technology allo#s it to be used for production of commodity fats. 1ry fractionation has long been regarded as an unpredictable, tedious and labor4intensi$e process. :o#e$er, the relati$ely cheap dry fractionation technique has e$ol$ed to the modification technology of the 0st century +;, as #ithout additi$es, polluting effluents or post4refining in$ol$ed, the sustainability and safety of the process is second to none.

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"olve!t ractio!atio!, already patented in the 2!"’s, in$ol$es the use of heane or acetone to let the high4melting components crystallize in a $ery lo#4$iscous organic sol$ent. This can be helpful #ith respect to the selecti$ity of the reaction, but mainly offers ad$antages in the field of phase separation9 much purer solid fractions can be obtained, e$en #ith a $acuum filtration. 'eing a more epensi$e process, it is less common than dry fractionation and only comes into the picture #hen a $ery high added $alue of (at least one of) the resulting fractions makes up for the high cost.

In this contribution, the emphasis is on dry fractionation technology.

#. T$e Crystalli%atio! "tage &ri!cipal co!cepts

 5 controlled crystallization of the melt is the backbone of any dry fractionation process, and the success of  this process relies principally on the phase beha$ior of the constituent triglyceridess. Therefore it is probably useful to dedicate some #ords to that part of the physical chemistry of fats and oils that lies at the basis of  the fractionation technology.

If anything is clear from bro#sing through the Lipid Library , it is the fact that a natural oil is a $ery comple miture of different triglycerides (not to mention diglycerides, free fatty acids, phospholipids, sterols, and uncountable other minor constituents). The mi of triglycerides does ha$e a repercussion on the melting beha$ior of a fat9 it does not ehibit a sharp melting point, but often displays a steady softening (or  increasing liquid content) #ith increasing temperature, until it is completely liquid. The position and #idth of  this melting range on a temperature scale is determined by the type of constituting triglycerides and compositional heterogeneity of the oil9

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The type of the triglycerides9 in a $ery simple approach, the longer the fatty acid moieties, the larger  the total molecule and consequently, the more energy (i.e. higher temperature) #ill be required to con$ert such triglycerides from a solid to a liquid ‘state’. 5 double bond in the carbon chain decreases the melting point dramatically, ho#e$er, and this is #hy oils containing a high proportion of unsaturated fatty acids are generally liquid.

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The broader the spectrum of triglycerides present in the oil, the broader the melting range. ome of  the triglycerides #ill only solidify (or melt) at !