CA1099281A - Fat process - Google Patents

Abstract

Abstract of the Disclosure The separation of solid particulate matter from liquid material in which it is dispersed is improved by agglomerating the particles together by stirring to give homogeneous agitation. A smooth, preferably cylindrical stirrer is employed. In an important application fatty material such as fat or fatty acid mixtures in liquid phase, optionally dissolved in a solvent, is cooled to precipitate a fraction during homogeneous agitation to agglomerate the crystals as the precipitate. An unusually good filtration rate is possible, even with very heavy crops of crystals.

Description

cA.166 This inve~-tion relates to separating solid particulate ~atter fro~ ~atty ~a-terial, particularly ~a-tty acids and their esters, especially ~ats. More particularly the invention relates to fractionation processes applied to 5 such substancesO
~ he separation o~ solid particula-te matter ~rom liquid ~atty material in which it is d~spersed is effected in the course o~ reiining and fractionation operations. In the latter, selected fatty acids or glycerides in fats or glyceride oils may be precipitated as solid particles, usually by cooling and separated for exa~ple by filtration from others re~aining in.liquid phase~ someti~es dissolved in solvents~
In these operations the separation of the solid and liquid phases is o~ten slow; the precipitate on the ~or~ of particles may retain a high proportion of the liquid component o~ -the fatty ma-Serial by adsorption and drainage o~ liquid phase compone~ts ~ro~ it may be poor, even with centri~ugation, especially in recrystallisation operations. ~epeatedly ~ashing the solid matter to re~ove the liquid clinging to it may be necessary but takes up more time and is ex-travagant o~
solvent.
Although, there~ore, more complete separatio~ may be highly desirable, whether to improve the quality o~ $he solid phase or the yield o~ the liquid, it is in any case time-consuming and expensive and ~ay even be impracticalO

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cA.166 In the process o~ the present invention the particulate ~at-ter is converted to an aggregate form ~ore readily separated ~ro~ the liquid phase by draining~ the process co~prising subjecting ~atty material in liquid ~or~
containing the particulate ~atter dispersed -therein, -to ho~ogeneous agitation u~til a sùbstantial amount o~ the par-ticulates is aggregated, and separating the liquid ~atty ~aterial there~rom.

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Homogeneous agitatio~ occurs when the velocity gradie~t between any two particles in the migture adjacent radially to one a~lother is the same. Under the in~luence of the homogeneous agitatio~ the particles of the solid phase coalesce in agglomerates which are much more easily drained of adhere~t liquid pha~e in the subsequent separation ope~ations, lS Homogeneous agitation is preferably ef~ected by a , stirrer with a smooth pro~ile~ Turbulence in the ~atty material undergoing homogeneous agitation should be mint~ised.
~omogeneou~ agita~io~, giving streamline ~low is provided by a stirrer with a smooth and regular pro~ile, as by a cylindrical stirrer conce~tric with a~d rotating i-n a chamber contai~i.ng the fatty material 7 0~ a vertical, incli~ed or horizontal axis, ~ he radial dimensions of the stirrer are not critical, bùt s~all stirrers may be slower to affect aggregatio~, other . things being equalO Pre~erably the ~tirrer i9 from one-third to two~thirds the diameter o~ the agitation chamber, ~, cAo 166

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-particularly about hal~ its diame-ter, but it pre~erably extends substantially the full depth o~ the ~atty ~aterial in tbe chamber, to ens~re co~plete stirring. ~he depth i9 itself not critical in relatio~ to the radial dimensions, at least in batch operatio~s, but it is at any rate pre~erably at le~st as great as the radial width of the annulus of ~atty material enclosed between the walls of the -chamber and the stirrer, more particularly twice as deep or more. A partîcular ~eature o~ the inven~ion is that ~o auxiliary fluid is required to promote aggregation o~ the .
particles. . . ... .
The speed of the stirrer should pre~erably be as slow as is consiste~t with achieving the desired e~ect, pre~erably ~rom 1 to 200, especially 10 to 100 r9p.mO, pre~erably corresponding to a velocity gradien~ o~ from 1 -~o 250 m/min/m, e~pecially 10 to lOO.m/min/m. radially. Where the observed aggregatio~ is unduly slow to develop with a small stirrer, it is best to replace it with a bigger stirrer operated at the same or slower speeds, to obtain quicker aggregation~
The process is suitable ~or batchwise or conti~uous operation but in the latter event preferably the chamber is deep relative to the annulus width to provide several mixing stage~ in the annular zone con-taining the fatty material and combi~e good mixing with maximum contact between the liquid a~d solid material.

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The inventio~ is o~ particular i~portance ~or fractional crystallisation of fatty acids and their esters, especially ~atsO These include glyceride oils which are normally liquidO Fractional crystallisation may be applied to re~ove i~purities or to separate particular ~rac-tions of the fatty ~aterial having desired ~elting characteristics and may be carried out in the presence or abse~ce o~ solvent for the *atty material, although the process is particularly valuable in so-called dry ~ractionation processes in the absence of a solve~t, whe~ substantially longer filtration times are incurred due to the high viscosity of the liquid oleine fraction. This may be separated by washing the crystals with an aqueous dispersion o~ a suitable surfactant as in the so-called Lanza process. Suitable solvents for iat fractionatio~ i~clude ace~one, he~ane or nitropropane and ~ethanol ior fatty acids, preierably containing a little water.
The amount of solvent may vary fro~ 5:1 to 1:2 by weight relative to the iatty materialO Other solvents known in the art may also be used.
Preferably the fractional crystallisation is e~iected in situ during ho~ogeneous agitation, the fa-tty ~aterial belng cooled ~rom a wholly liquid or dissolved condition until crystallisation oY the fraction to be separated i9 complete, at the same ti~e subjecting the ~aterial to homogeneous agitation. Apparatus ior the purpose pre~erably comprises a ~ .

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stirring cha~ber ~itted with a coaxial stirrer, both o~
s~ooth cylindrical shape and size as described, and cooling ~eans for cooling for contents o~ the cha~ber, pre~erably througll the walls o~ the cha~ber and o~ the stirrer. A
S lower li~it ~ay be necessary to the speed of rotation of the stirrer, in order to ensure adequate heat trans~er and avoid excessive deposition o~ crystal growth on the cooling surfaces, which ha~pers heat trans~er. In contrast to many ~or~s of crystallisation apparatus~ the stirrer should not scrape the walls o~ the cooling cha~ber. Such ~eans do not prouide ho~ogeneous agitation.
The cooling rate is also affected by the te~perature di~ferential betwèen the cooling sur~ace and the ~atty ~aterialO Large te~perature di~erentials pro~ote rapid cooling but with the ~or~ation o~ ~icro-crystalllne growth.
S~all te~perature di~ierentials~ o~ the other hand, produce larger crystals but much more slowly. Temperature differentials speci~ied in this speci~ication are ~easured to the centre o~ the liquid and are preferably below 10C
~easured radiallyO A te~perature di~ferential o~ ~ro~ 5 to 20 centigrade degrees, pre~erably 5 to 10 centigrade degree~, is pre~erably maintained between the coolant and the body o~
t~e liquid undergoing cooling, at leaæt until crystals appear.
~herea~ter a higher di~ferential can be provided, but preferably not exceeding 2S centigrade degrees, especially 10 to 20 centigrade degreesO

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The inventio~ may be applied to both edible and non-edible vegetable9 animal and marine ~ats, their ~rac-tions and hydrogenated and i~teresteri~ied derivatives and their constitue~t fatty acids, ior eæample tallow, palm, sun~lower, safflower, ground~ut, soyabean and lauric oils.
The inventio~ i9 use~ul ~or carrying out winterisation. ~his is a form o~ fractional crystallisation commonly applied to edible oils, for example palm or cottonseed oil, or soyabean oil which is slightly hydrogenated to improve its resistance`to deterioration in storage, which are intended for use as salad oils or frying oils, to prevent the onset of turbidity on standing at ambient temperatures, due to the fractional crystallisation of a higher-melting stearine fraction i~ the oi].. In winterisation processes the stearine is removed by filtration af-ter cooling the oil but substantial losses can be incurred in conventional winterisation processes ~or the reasons above stated, in the separation of the oleine and s-teari~e fractions and in any case a small amou~t o~ the stearine o~ten stubbornly remai~s in the oil, to crystallise out later in storage, unless the oil is cooled ~o much lower temperatures, with the loss of even more oil. The present invention provides an economic and e~i¢ient winterisa-tion process, incurring minimum oil losses and providing magimum ef~ectiveness.
The inve~tio~ is also effective for fractionating fatty material for the recovery of a substantial proportion .
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of higher-~lting solid fraction in a single fractionatio~, as ~uch as a quar-ter of the total weight of -the ~a~ty ~aterial. In co~ventional practice the solid ~raction com~only absorbs at least twice its own weight of the lower ~elting, liquid fraction. Solid fractions o~ above about a quarter of the total weight treated there~ore form slurriss, the separation of which into their constituent liquid and solid fractions is extre~ely difficult, whether by filtration of centrifugation. In accordance ~ith the present invention the crystals are aggregated together and retain a substantially lower portion of the liquid fraction.
Tbe process o~ the invention may be carried ou-t at temperatures for example ~ro~ -20C to 50C, te~peratures being limited only by the physical li~its o~ solvents, where these are used, aod the a~ount of solids to be re~oved, not more than 35% being preferred. Separation o~ the agglomerated solid ~atter may be, ~or exa~ple, by decantation or by gravitation or pressure filtration or by cen-trifugation.
The i~ve~tioc is of particular i~poxtance for the recovery of ~at fractions having desired attributes ~or use in the food industryO Ia the formulation of margarine fats for e~a~ple ble~ds are often prepared of fats obtained by fractionation procedures to meet desired physical or chemical characteristics~ ~he fats may for e~a~ple be required to meet specified melting characteri~tics, or a high poly-` cAol66 Z8~

unsaturated fatty acid content ~ay be required ~r dietarypurposes. Care~ul ~ractionation in accordance with the it~vention enables ~ats to be obtained to meet such require-~ents. In the confectionery industry also hard butters are S obtainable with the critical ~elting perfor~ance required o~
fats used for this purpose, by fractionation in accordance with the invention, particularly ~rom palm oil bu-t also fro~
other vegetable fats which may be hardened before or a~ter ~ractionation.

E~UhMPLE 1 A cylindrical crystalliser chamber ~itted with a dished base and a cover plate ~as also provided with a cylindrical rotor, ~ixed to a vertical rotor sha~t extending into the chamber~which was rotatable by motor means mounted above the plate and was supported in bearings located in the centre o~ the cover plate and the dished base o~ the chamber.
~ he chamber was approximately half as deep again as it was wide and the rotor, extending ~ubstantially the full depth o~ the chamber 9 half as wide as the chamber. The chamber itsel~ was fi-tted with an s~ternal cooling jacket in which aqueous ethylene glycol solution, cooled to a predetermined temperature, could be circulated.
Soyabea~ oil was lightly hydrogenated to an Iodine Value o~ 110 to 112 using a fresh, ~upported nickel catalyst.
~his improves the stability o~ the oil against oxidative , .

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deterioration but leads to cloudiness in the oil on standing, due to the crystallisation o~ a stearine fraction. ~his was removed fro~ the oil in accordance with the invention using the apparatus described~
After re~oving the catalyst th~ oil was cooled to 36C and charged to the crystalliser chamber. The agitator was rotated to give a velocity gradient of about 15 ~etres/
~inute/~e-tre in the liquid in the annulus. Aqueous ethyle~e glycol circulated in the cooling jacket ~as maintained to provide a temperature gradien-t o~ 20C/metre measured radially through the oil, to a measuring point midway between the walls of the vessel and the rotorD l~en the temperature reached 21C crystals appeared and the temperature di~ferential increased to 35C/metre u~til a 1~ ~inal temperature o~ 3C was reached. ~he oil was then filtered through a sta~dard vacuum ~ tration unit, yielding 74~ of an olei~e i~ 3 hours, by weight o~ the hydrogenated oil. The oleine remained clear a~ 0C ~or at least 5 hours.
On the other ha~d the hydrogenated whole oil deposited stearine crystal~ even o~ standing at 20C.
I~ a comparatîve trial using conventional ~ractionation methods incorporati~g an agitator i~ the vessel instead o~
the rotor stirrer a~d scraping attachments ~or removing crystalline material forming on -the walls of the vessel, . .

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conditions were adjusted to give a si~ilar filtration ti~e, but a yield o~ only 60% was obtained, The oleine product in both instances was suitable ~or use as a ~rying oil, re~alning clear i~ storage at ambient conditions.

A series o~ experiments was carried out by fractionating similar hardened soyabean oil, charged at 30C
in similar equipment~ co~prising a cha~ber 60 c~ dia~eter and 1 ~etre high, ~itted with a rotor stirrer 30 c~ diameter, The e~fect was observed on ~iltration speed and oleine yield o~ fractionation temperature and te~perature di~ferential which, however, re~ained coostant in each experime~t, in all of which the rotatiooal speed was 42 r.p.~. corresponding to a velocity gradient o~ 264 m/hour/~, ~he effect was also observed of "stabilisationl' by ~aintaining the cooled fat for 2 hours at the fractionation te~pera-ture.
From all the e~peri~ents an oleine was obtained which re~ained clear at 0C after 5 hours. Further particulars appear in the Table below.

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Coolin~ Conditions Ex~e_iment (hoursj Yield Filtration nO~l. Stabilisation F~nal ~r8m Oleine C time (hours) C 30_C

1 ~ 10 67.6 ~.2

3-4 la 2 12 65.7 4.0 2 ~ 10 ~ . 6 63.6 0~99 2a ~ 2 ) 8 60 8 0~68 3 6 - -1.5 7 61.3 0.63 Experi~ents 1 a-nd 2 demonstrate the marked decrease in filtration speed and considerable increase in oleine yield that ~ollow~ when ~t is reduced, ~or the same final temperature~
Co~parison o~ E~perime~ts 1 and la and again 2 and 2a surprisingly shows that a "stabilisation" period at the ~ractionation temperature i9 deleterious, contrary to conventional ~ractio~ation practice. Finally~ Experiment 3 also shows that a good oleine yield can be obtained, comparable with Experi~ent 2a9 even at the lower te~pera-ture o~ -1.5C, by ~ain-tai~ing a lower ~ t and avoiding a prolooged stabilisation te~peratureO

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~, cA.166 Palm oil (I.V. 53) was stirred at 100 r.p,m. in a cylindrical vessel twice as deep as wide, fitted wîth a cooling jacket and a coaxial cylindrical ~otor extending substantially the full depth of the oil, the dia~eter o~ khe rotor being half that of the vessel. Fro~ 50C the oil was cooled at 12C per hour to 28C~ at which te~perature it was ~aintained with continued stirring ~or 52 hours, when NMR
analysis o~ a sa~le showed 8% solids for~ed. The oil was filtered at the same te~perature, with a ~low rate of above 10 ~3/~2 per hour at a ~iltration pressure of 0.5 atmospheres.
~he ~iltrate was 80% o~ original pal~ oil, leaving a residue of 20~ retained by the filter, The Example was repeated in continuously operating equip~ent o~ the sa~e proportions, using a stirrer speed o~
40 r.p.~., 9% solids being reported and the ~iltrate again a~ounting to 80% of the original oil 9 with an Iodine Value of S7 and a ~iltratio~ rate of 6.5 ~ /~ per hour. Residence ti~e ~as 2 hours.
At a crystallisation te~perature of 1~C and a stirrer speed of 80 rOpOmO~ a yield o~ 45,~ liquid ~raction was recovered fro~ tlle continuous equip~ent, with an I ~Vo Of 63 ~ 2 to ~iltration rate of 0O5 ~3/~ per hour. This is a~
excellent recovery considering the heavy residue to be re~oved, Reside~ce ti~e was 5 hours.

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, cA.166 ~ Z 8 EXAMPL~ 4 Malaya~ pal~ oil ~raction ~I.V. 58.4), ob-tai~ed by dry fractionatio~ of palm oil, was ~ixed with ~our ti~es its .. -?
weight o~ aceto~e and ~ractiona~ed at 3C by cooling in the batch apparatus described i~ Exa~ple 3, ~rom 50C to 3C at the rate of 12C per hour with stirring at 300 r.p,~
After stirring ~or 3 hours at this te~perature ~iltration was rapid and the ~iltration residue was washed -~our ti~es, each ti~ewith 11 ti~es the weight o~ startiag oil, o~ acetone.
A~ter evaporating oi~ solvent a residue of 36% (I.V. 41~3) ~as obtained with a filtrate oil yield Of 64% (I.V. 68.5)~
based on the starting oil, Exa~ple 4 was repeated a-t -6C, cooling ~ro~ 30C
lS with 5 hours' stabilisatio~, using assolvent -a:n-equal a~ount by weight of hexane. A~ter washing the filtration residue twice, each time using an equal amount by weight o~ the starting oil oi hexane, and evapcrating o~f the solvent, a ~iltrate oil o~ 64.1% by weight o~ the starting oil wa~
recoverèd o~ I.V. 67.8 and a residue o~ 35,g/0 o~ I~Vo`43~2 EXA~LE 6 Tallow -fatty acids of I.V. 56 were dissolved in 12 ti~es their weight o~ a ~ixture o~ 92% ~ethanol with 8% water and fractionated in the apparatus described in Example 3, by .. . . . . . . . _ ... ... . . . . . . . . . . .

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cooling from 30C to -7C at a cooling rate OI 18C per hour with stirri~glat 200 r.p.m. and immediately thereafter filtered of~ as be~ore and washed twice with the same solvent, eaoh -time with 88% of the original weight of acidO
S After evaporati~g of the solvent a filtrate of I.V. 95.2 in 56.1% yield was recovered together with 43.9% ~iltration residue of IoVo 508~ obtained as a free-flowing granular material 92% o~ the par-ticles of which had a diameter about 0.5 mm.

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Claims (18)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A process for fractionating fatty material comprising cooling said fatty material from a wholly liquid condition, in a cooling zone defined between the inner walls of a chamber and a stirrer having a smooth profile mounted in said chamber, to a temperature at which partial crystal-lization of said fatty material takes place while agglomera-tion of crystals resulting from homogeneous agitation occurs in said cooling zone; and separating agglomerated fat cry-stals thus formed from the remaining liquid fatty material.

2. Process according to Claim 1, in which homoge-neous agitation is provided in a chamber containing the fatty material by a cylindrical stirrer concentric therewith.

3. Process according to Claim 2, in which the chamber is cylindrical and its diameter is 1 and 1/2 to 3 times the diameter of the stirrer.

4. Process according to Claim 3, in which the chamber is at least as deep as the radial width of the fatty material enclosed in the chamber between the walls thereof, and the stirrer.

5. Process according to Claim 2, in which the stirrer is rotated at a speed providing a velocity gradient from 1 to 250 m/minute/m radially.

6. Process according to Claim 5, in which the velocity gradient is from 10 to 100 m/minute/m radially.

7. Process according to Claim 2, in which the stirrer is rotated at a speed from 10 to 100 r.p.m.

8. Process according to Claim 1, in which the agglomerated fat cyrstals comprise components of the fatty material which are selectively precipitated while the fatty material is subjected to homogeneous agitation.

9. Process according to Claim 8, in which a tem-perature differential below 10°C. measured radially is applied to cool the fatty material.

10. Process according to Claim 9, in which the fatty material is maintained at constant temperature after cooling to stabilize the precipitate.

11. Process according to Claim 8, in which from 5 to 35 wt % of the fatty material is precipitated.

12. Process according to Claim 1, in which the fatty material comprises fat.

13. Process according to Claim 12, in which the fat comprises palm oil or a fraction thereof.

14. Process according to Claim 12, in which the fat comprises soyabean oil.

15. Process according to Claim 1, in which a sol-vent for the fatty material is present.

16. Process according to Claim 15, in which the solvent is selected from the group consisting of hexane, acetone and nitropropane.

17. Process according to Claim 15, in which the amount of solvent present is from 1/2 to 5 parts by weight of the fatty material.

18. Process for fractionating fatty material selected from mixtures of fatty acids and their triglycerides comprising the steps of (a) retaining the fatty material in wholly liquid condition in an annular space defined between the walls of a cylindrical chamber and a cylindrical stirrer coaxial there-with and spaced therefrom which extends into the chamber, the stirrer having a diameter from 1/3 to 2/3 that of the chamber and the quantity of fatty material being such that the depth of the liquid in the chamber is at least twice the radial width of said annular space;
(b) cooling the fatty material through the sur-faces in contact therewith to a temperature from -20°C. to 50°C. at which a proportion not exceeding 35 wt % is preci-pitated from the mother liquor fatty material in the form of solid particulate matter while simultaneously rotating the stirrer at a speed at which homogeneous agitation takes place;
(c) continuing the homogeneous agitation to agglo-merate the particulate matter; and (d) separating the agglomerated particulate matter from the mother liquor.