Processing,,.

Removalof gums

andwaxes-

A •reviewThis article is by veronique Gibon andAlain Tirtiaux, of PractionnementTirtiaux, Pieurus, Belgium.

Crude oil•Mixer+- Acid + lye

•Holdingank•Heater•Centrlfugal separator+ +- Hot water

Heuer•Mixer•Centrlfugal separator,Fllure I. Americ~ (Ionl-mlx) method

Volume II • May 2000 • Inform

The refining of edible oils and fats can be operated accordingto rwo main routes: chemical refining and physical refining,each consisting of a series of operations conducted to removemainly gums, metals, pigments, hydroperoxides, waxes, andfree fatty acids.

The principal difference berween chemical and physicalrefining is how the free fatty acids are removed.

Degumming methodsChemical refining. In a chemical operation, the oil is clearedof gums and free Iarry adds during the neutralization step.

The "long-mix" technique (Figure 1) was developed basedon a long-rime/lew-temperature sequence especially designedto treat fresh North American soybean oil. Refining cotton-seed oil in the miscella State is also based 00 this type ofsequence.

The "short-mix" rechnique consists of a short contact timeat higher temperature (Figure 2). With this technique, condi-tioning of gums with phosphoric acid takes care of higher lev-els of nonhydratable pbospharides, fixed gossypol from cot-ronseed oil is more easily removed.

Crude 011•Heater+ +- Acid

Mixer•Holding tank+ +- Lye

Mixer•Holding tank•Centrifugal separator•{Heater+ +- Hot water (or lye)RE-REFINING(optional)

Mixer•Centrifugal separator]+ +- Hot water

Mixer•Centrifugal separator•Refiningor drying for stonlge

Fllur. 2. Standard (short-mix) f'leutraJiu.tion

S25

In a chemical refining, the heavyphase is a soapstcck, which normallyrequires further treatment.

Physical re(illil/g. If the physicalrefining option is chosen, most freeferry acids are carried through to (1

deodorizing unit. Operating ccndi-(ions (temperature, vacuum, andsteam) are carefully controlled inorder to allow the distillation andsteam stripping of the acids. A well-designed deodorizer operating at anacceptable efficiency will reduce theCOStS of the process. As distillationrequires a higher-temperature treat-ment, the oil must be carefullydegummed and bleached before enter-ing the deodorizing unit.

Water degumming (Figure 3) is thesimplest method for phosphatide reduc-rion; however, only the hydratablephosphatides can be removed by mixingthe oil with only water. This means thattypical gum contents after waterdegumming can still lie between 80 and200 parts per million (ppm) of phos-phorus, depending upon the type andthe qualiry of the crude oil.

With its Alcon process, the Lurgiorganization proposes a seed prepara-tion before solvent extraction; a crudeoil with a very low content of nonhy-dratable phosphatides results; as a con-sequence, Alcon-processed oil can bedegummed by water to residual phos-phorus levels of 10-20 ppm.

Crude oil~

Heuer+ ~ Acid

Mixer~

Holding tank+ ~ Hct water

Mixer~

Holding unk~

Centrifugal separ.ltol"~

Refining or drying for stor.lge

Crude oil~

Heater+ ~ Acid

Mixer~

Holding unk~

Bleaching

ba

Figun! 4. (a) Simple acid degummlnc; (b) dry deJUmminc

As the nonhydratable phosphntidesalso have to be removed, they must beactivated by different methods. At thepresent time, the preferred procedure isadd degumming [simple acid degum-ming, ultrafiltration (UF) degumming,special degumming, IMPAC (improvedacid) degumming, super/unidcgum-ming, top degumming], where the gumsare conditioned into a hydra table formleading to oil-insoluble metal salts andto phosphatides in their acidic state.

Oils with a low phosphatides con-rent, such as palm oil, palm kernel oil,coconut oil and animal fats, can bedegummed using the simple aciddegumming technique (Figure 4). Thehot crude oil (80-90"C) is thoroughlymixed with phosphoric or citric acid,followed by a reaction time of approxi-mately 5-20 minutes; 2-5% of water isthoroughly mixed with the oil before itis routed to a cenrrifuge separarcr,These oils can also be treated accordingto- a dry degumming sequence. In thiscase, the phospharides are simply add-treated and absorbed directly in thebleaching unit.

Krupp has developed the UF degum-ming (Figure 5) for vegetable oils for

which a conventional simple aciddegumming will not achieve a level of3-5 pprn of phosphorus as required forfinal steam-stripping refining. The oil isheated and mixed with acid for condi-tioning the gummy substances; aftercooling, a flocculating agent and, ifnecessary, soft water are dosed into theoil before it is moved into a retentiontank where the gums are coagulated.After this, the oil is heated and cen-trifuged, and eventually washed and

Crude oil~

Heater+ ~ Acid

Mixer~

Holding tank+ ~ Aocculating agent + water

Mixer~

Holding tank~

Heater~

Centrifugal separ.ltor~

Refining or drying for stor.r.ge

Crude oil~

Heater+ ~ Hot water

MIXer~

Centrifugal separator~

Refining or drying (or stor.lge

Ficun! l. Water decummlna FII'ln! 5. Ultrafiltration (UF) decumming

Volume I I • May 2000 • Inform

526

Crude oil+

Heater+ ... Acid (Speci ..! ilddltive)

Mixer+

Holding tank+ ... Lye: Hot water

Mixer

+Holding tank

+Heater

+Centrifugalse~n.tor

... +- Hot waterMixer

+Centrifugal separator

+RefinIng or drying for storage

Figure 6. Special degumming (Alfa-Lanl)

centrifuged again, before entering thebleaching unit.

Alfa-Laval's special degummingprocess (Figure 6), also called acidrefining, has been developed for high-phosphatide content oils, such as soy-bean, sunflower, and rapeseed. Thecrude oil is heated at 70°C and thegums are treated with phosphoric orcitric acid by mixing, followed by aretention time of approximately fiveminutes. A critical quantity of dilutecaustic soda is added to neutralize theacid. If the degree of neutralization isroc low, then the viscosity of the gumsis tOO high, leading to difficulties inthe centrifugal separator; if it is toohigh, portions of the free fatty acidsare transformed into soaps, leading tohigher losses due to emulsification.Water is then added to the neutralizedmixture, with 20 minutes required forthe total hydration of the gums, beforea second centrifugation. In case of

Volume I I • May 2000 • Inform

Processing

Crude oil+

Heater... +- Acid

Mixer+

Holding tank... +- l)'1i!

Crude on+

Heater... +- lecithin

Mixer... +- Acid

Mixer+

Holding lank

+Cooler

... +- Wa~rMixer

+Hydration tank

+Heater

+CenDifugal 5epanltOr

+COO"

... ... l)'1i!Holding and agglomeration a.nk

+Heater

+Centrifugal separatOr

+Refining or drying for stOrage

Figure 7. Superlunidegumming (Un1iever)

high-quality oilseeds, acid, dilutedcaustic soda, and water can be mixedwith the oil before the first centrifugalseparator, thereby saving investmentCOSts. In De Srner's IMPAC degum-ming, special additives are simplyadded before the citric acid and caus-tic soda in order to improve the wet-ting of the nonhvdraeablc phcs-pharides and hence their solubility inthe aqueous phase.

Unilever's superdegumming (Figure 7)is based on the fact that hydra table phos-pherides containing polar groups canform liquid crystals when they are put incontact with water at low temperature.The crude oil (sometimes treated withlecithin) is heated (75°q, thoroughlymixed with citric acid, and sent into a15-minute retention tank. The whole isthen cooled to 25°C and held for threehours after addition of warer, duringwhich the phosphatides develop theircrystalline form. After heating, the gums

Mixer

+Centrif'upl separator

... +- Wa~rMixer

+Holding tank

+Centrifugal separator

+Refining or drying for stOrage

Firure 8. Top derummlng (Vandemoortele)

are separated in a centrifugal separator.At this stage, the phosphorus content isonly 15-30 ppm, so the oil must under-go a second step before physical refining.The superdegummed oil is first cooled to40°C, treated with a small quantity ofdilute caustic soda, held for two hours,heated, and finally centrifuged. At theend of this combined super/unidegum-ming, the phosphorus content has fallenbelow 5 ppm, and the wax content islowered.

Vandemoortele, with some assistancefrom Westfalia, has patented a processcalled top degumming (Figure 8). Thecrude oil is heated at 90-105"C andintensively mixed with phosphoric acid;after a retention time of approximatelythree minutes, the phosphoric acid ispartially neutralized with dilute causticsoda and the components are separatedin a cenn-ifuge. In a second stage, hocwater is added and after a short resi-dence time, the separation takes place

Crude oil

+Heater

• ... Citric acIdMixer

.. e-, NaOHAgitated holding tank

.. ... EnzymeMixer•ReactOr

+Heater•Centrifugal separator•Refining or drying for storage

Figure 9. Enzymu: procelS (Lurgl)

on a special high g-force centrifugal sep~araror, Phosphorus levels lower than 5ppm characterize top-degumrned oil.

Besides acid degumming, Lurgi'sEnzymax process (Figure 9) consists inmixing the oil with citric acid and caus-tic soda to a buffered pH 5 into whichphospholipase is dispersed. The enzymeis given sufficient lime to catalyze theconversion of non hydra table pbos-phatides into oil-soluble lysophos-phatides, which are then removed bycentrifugation, yielding a degummed oillow in phosphorus .

............~Ia .-" ...""'.--pow In 0M0i0n~ct"'lliet.

527

Crude oil•Heater.. +- Chemicals + water

Mixer•Holding tank+

Centrifugal separator•Refining or drying for storage

a

P < SppmFe <O.lppm

Figure 10. (a) S.O.F.T. degumming (Tirtlaux); (b) flowsheet (or a S.O.F.T. degumming plant

b. ,

In the S.O.F.T. degumming (Figure10) system patented by Tirtiaux, the oilis heated (7S-8S"C) and mixed with awater solution (2-5%) containing awetting agent and a cornplexing mole-cule that is able to form a Strong chelatewith a series of ions, including magne-sium, calcium, and iron. The divalentcomponent of the water-insoluble, non-hydratable phosphatides can beremoved through the chelating action ofEDTA (ethylenediaminetetraaceticacid). Subsequent hydration of thephospharides for a period of 20 minutes

and centrifugation provide a degummedoil with a phosphatide conrenr lowerthan 5 ppm. The efficient removal «0.1ppm) of iron as an oil-insoluble com-plex with EDTA confers to thedegummed oils an improved oxidativestability and lowered risk of deteriora-tion of the refined oils. The main advan-tage of this process is its simplicity as itonly needs a special mixer (high-shear)and one centrifugal separator (self-cleaning). Phosphorus contents lowerthan 5 ppm can be anticipated for anycrude or water degummed oil contain-

To join, contact: AOCS, Membership ~, P.O. Boll 3489, CIwnpaign, IL 61826-3489 USA. I'ttone: 1-217·359-2344;fax: '.217·351_8091; E-mail: membershipthlocs.org.

Volume I I • May 2000 • Inform

Table ICharacteristics of different crude and water deaummed oils, S.O.F.T. degummed In pilot plant (phosphorus by AOCS Ca 11-55; calcium,magnesium, and Iron by ICP lpectrometry)

Oil PV FFA Phosphorus Calcium Magn~ium Iron'%1 (ppm) (ppm) (ppm) (ppm)

Water- Before 2.7 0.2 76 34 17 0.5degurnmed After 2.0 0.7 0.3 0.03soybean

Water- Before 12.5 1.1 128 " 35 I.'degummed After 2.' 0.1 0.02 0.04soybean

Water- Before L5 " " II L5degummed After 1.2 0.2 0.02 0.03rapeseed

Crude Before 1.7 88 27 " 1.5sunflower After I.' 0.5 02 0.04

Crud, Before 0.' m II. " 3.2soybean After 3 0.4 0.1 0.05

Crude Before 0.' 265 189 69 I.'rapeseed After I.' 0.2 0.1 O.oJ

Crude corn Before 2.5 321 3 40 2After 5 0.1 0.7 0.1

Crude palm Before 2.5 8 , 3 4After 0.7 0.2 0.04 0.05

Crude palm Before 7.3 5.0 16 13.2 48 '.3After 2.' 0.3 0.06 0.1

528

ing high or low levels of phospheridcs(Tables I and 2).

The simplicity of the system makes itpossible for the refiner ro switch fromalkali refining or from any otherdegumming process ro the present oneat very low COStS.

Nore that although membranetechniques for degumming oils havebeen tested successfully 3S laboratoryand pilot-plant scales, they have notbeen applied yet on a large industrialscale.

Wax content and cold stability,an updateThe quanritarive measurement of waxesin oil can be done by chromatographictechniques, but it is rime-consuming

Volume I I • May 2000 • Inform

Processing

The cold-test stability also dependsupon local requirements; for example,in cold countries, a 48-hour cold testat ooe is usually required, correspond-ing to a wax content of roughly 15ppm.

and for this reason many companieshave chosen to use the rurbidimerer(correctly calibrated) as a rapid andadequate method for wax content mea-surements. In cases when such equip-ment is nor available, the cold test isnormally used as reference: a dewaxedsunflower or corn oil remaining clearfor at least 24 hours at ooe correspondsroughly to a wax content below 50ppm. Nevertheless, it has been notedthat despite passing a 24-hour cold test,an oil may develop a haze after a fewdays of storage at room temperature ina clear bottle. This is probably due to aviscosity problem at aoc that delays thecrystallization of the waxes. For thisreason, some users prefer [0 perform thecold test of dewaxed sunflower at Ire.

Dewaxing VS.winterization"Dewaxing" and "winterization" areoften confused. "Dewaxing" consists inremoving waxes from the oil by usingone of the above-mentioned techniques."Winterization" is a term commonlyused ro describe the removal of any solidparticles rhat can cause cloudiness of theoil during storage. Such particles can bewaxes, polymerized oil, and even satu-rated triglycerides. If sarurared triglyc-erides are to be removed, [he term "frac-

Table 2W;ateMieaummed 5O)'bean 011,crude com, sunnower and palm oils, S.O.F.T. degummed In Industrial pl;ants (4 Tlhour) (phosphorus byAOCS Ca 12·55; calcium, magnesium,;and Iron by ICP $pectrometry).

Oil FFA Phosphorus Calcium Magnesium Iron(%1 (ppm) (ppm) (ppm) (ppm)

Crude Before I.S 40.5 18.4 5.' I.,sunflower Afler 4.1 0.2 0.1 ",0.1

Crude palm Before 3.0 9.1 7.7 1.1 1.7After 0.8 0.2 0.06 0.05

OilPhosphorus (ppm)Before treatment

Water degummed soybean(FFA: 0.5-1.0%)

Crude com(FFA: 1.9-2.5%)

rionarion" is more appropriate. At rimesthe full dewaxing process is divided intotwo parts: dcwaxing, which allowsreduction of the wax conreur to approx-imately 100-150 ppm (for example bycombined neurralization/dewaxing or bysuperlunidegumming), and winteriza-tion, which involves a polishing filtra-tion of a dewaxed oil. According to this,one could say that it is nor necessary towinterize a S.O.F.T. degummedJdewaxed oil.

DewaxingSeveral oils, mainly sunt1ower, corn, saf-flower, rice bran, grapeseed and olive-pomace oils, contain waxes that mustbe removed during the refining process.Dewaxing, which is a form of winreri-

Phosphorus (ppm)After treatmem

1028388

11682

120

5.05-'5-'3.17.84.3

330134887'68287

4.83-''.34.83.'

zarion, refers rc the removal of high-melting-point waxes that are responsi-ble for the turbidity of the oils whenexposed to storage conditions in thesupermarket or in the refrigerator.Waxes are long-chain fatry acid esters oflong-chain fany alcohols, which tosome extent crystallize under room tem-perature and certainly at refrigeratorremperarure, leading to the clouding ofthe oil. As 3 result, the appearance ofthe oil in transparent bonles is altered,

Filler aid+

'"

which reduces the marketability of theproduct.

In a typical conventional dewaxingmerhod (Figure I l}, the neutralized oilis cooled under constant agitation to atemperature of approximately 4°C, Aseeding material that also can act as fil-ter aid in the filtration operation(Kieselguhr, Perlite, or wood pulp) isoften added to improve the crystalliza-tion of the waxes. The oil is transferredto a maruraror; under weak agitation.

Neutralized oil .... I Cooler ~ I Crystallizer I.... I Filter I -+ Dewaxed 011

FI,ure I I. Conventional dewu.ina

Volume I I • May 2000 • Inform

Diluted caustic soda•Oilout of first centrifuge..... I Huter I..... I Mixer 1.. I Cooler I

Cold water•.....ICrystalHzers I -+ IHuter I.. ICentrifugal separator I

Processing

5lO

Hot water•I Mixer I -+ ICentrifugal sepmrorl -+ Neutrarll:edidewued oil

Flaul"e 11. [)ewaxinlU an extension of the neutnllz.ation step

.. I Heater I

When the growth of the wax crystals iscompleted (4-16 hours), the oil is trans-ferred to the filtration unit (after mildheating at a maximum temperarure of15°C) where the separation takes placeon pressure-leaf filters. This method isstill widely used for oils with a wax con-tent of less than 500 ppm, which ismore or less an upper limit, as filtrationproblems can occur at greater wax con-tents. Another dewaxing system thathas been proven effective is to use sim-ple rapid cooling and filtration of the oilwithout using any marurator.

The dewaxing of high-wax contentoils is generally integrated as an exten-sion of the neutralization step (Figure12) of chemical refining (Figure 2). Theoil is heated to 85-90°C, and a small

Acid•Crude oil -+ Mixer

Caustic soda•-e IMixer I ..... I Crystallizer I .. Heater I

quantity of acid is added; the retentiontime is approximately three [Q five min-utes without agitation. High-tempera-ture caustic soda is dosed [Q neutralizethe free fatty acids (and the acid itself);a rerenrion time of five minutes isrequired before centrifugation. Down-stream of this step, diluted caustic sodais dosed to reach a higher level of soaps(at least 2,500 ppm), which are used asagglomerating agents of the waxes. Thewhole is then cooled to approximately5°C before entering a series of crysral-lizers. At the end of this, cold water isadded and then removed with the crys-tallized waxes and soaps in a secondcentrifugation, after heating at 15"C toreduce the viscosity. Final washing isperformed either at 90-95°C or at low

-+ I Holding tank I -+ I Cooler I

Hot water•.. ICentrifuel separatOr! .. I Heater I _ I Mixer I_ [ Centrifuplseparatorl .. Neutn.liudldewaxed oil

Volume 11 • May 2000 • Inform

FiJUI"e Il. Cold nlftnln,

Neuu.lized. or bleached or decdortzed oil ..... I Cooler IFilter aid

+I Crystallizer I ..... ..... Dewaxed 011Filter

Flaure 14. Polishing filtration

temperature before the oil goes [Q thebleaching section. Depending upon thecold test requirements, a polishing fil-tration can be recommended.

Cold refining (Figure 13) is an alter-native for oils with low acidity; other-wise, the oil losses would be tOO high.After dosing with a small quantity ofacid for a short time, the oil is cooled.Caustic soda is then added to neutralizethe free fatty acids, and the whole issent to crysrallizers, to allow wax crys-tals to grow. After several hours, themass is centrifuged, and the dewaxed oilis washed at high temperature and cen-trifuged again.

Polishing filtration (Figure 14) isgenerally carried out before or afterbleaching and, less frequently, afterdeodorizing. In the latter case, the oil iscooled to 12-1S"C and kept 10-12

hours without agitation. Filtration isdone after the addition of filter aid.Even if this procedure is economicallyinteresting (because the oil, in any case,has to be cooled at the coder of thedeodorizer for storage), some problemsof increases in peroxide or of polymer-ization products during the deodorizingof any nondewaxed oil can be encoun-tered. Polishing filtration between thebleaching and deodorizing steps is noteconomical from an energy point ofview. The main interest lies, however, inthe use of dried oil, which prevents anyproblems during filtration, and in thefact that oil entering the deodorizingunit is free from waxes. To polish beforebleaching would be economically ideal,at the point where the remaining waxcrystals are still in the oil as solids, thatis, after the second centrifugation (or

5~m

531

the third one if washing is performed).The only problem lies in the 0.4--0.5%moisture in the oil, requiring specialattention during the filtration.

When a choice has to be madeberween physical and chemical refiningfor the treatment of oils with high waxcontents, the question of the efficiencyof the dewaxing is often brought up forconsideration. Up to now, a slightlymodified super/unidegumming was theonly possible way (0 reduce the waxcontent while degumming. During thehydration of the phosphatides at lowtemperature (25°q (Figure 7), pan ofthe waxes also crystallize and can beremoved together with the gums. If thistemperature is lowered to SoC. partialwinterization can be achieved.Polishing filtration is nevertheless nec-essary to reach strict cold-stabilityrequirements.

The lack of any easy solution to degum-ming and dewaxing of oils with a highwax content has pushed development of anew concept that is mainly based on amodification of the S.O.ET. degumming,giving rise to the S.O.ET. degumming!dewaxing process (Figure 15).

P < 5ppmFe < O.lppm

Flsure 15. Flow sheet of ~ 5.0. F.T. .JUmmina/dewaxlnl plant

Volume I I • M;ay 2000 • Inform

SJ2

Processing

Table 1Char.u:terlstlu of S.O.F,T.degummedldewued com and sunflower oils In pilot plant (pholphorus by AOeS Ca 12·55;a.lcium, magne.sium,and Iron by ICP lpe«rometry)

Oil PV FFA P C. M. F. Cold(%) (ppm) (ppm) (ppm) (ppm) Test (h)

O·C ra-eRoom temp.

C~ .' 3.6 1.7 ) 11.7 U 47.5 2.0

A' 3.35 0.1 0." 0.1 >.,. >72>5,""

c~ a 2.5 310.8 3.0 <0.' I..A '.6 0.1 0.1 0.1 >.,. >72

>5,"",",- e 21 1.2 58.8 .., 227 0.7

A 1.6 0.1 0.01 0.03 >.,. >72>5,""

e 32 I.' Sl.6 20.7 14.5 0.'A 2.2 02 0.06 0.03 >.. >72

>5 '""

'"""- • " >0 61.3 2l.5 1<4.6 0.'A U 0.2 0." 0.03 >.,. >72

>S days

Sunflower e 0.92 <0.6 20.2 6.1 I.lA U 0.1 O.OS 0.05 >.,. >72

>5,""Sunflower e 1.00 34.3 18.3 5.' I.'

A I.. 0.2 0." O.OS >." >72>5,""

SunflO'M!r e 0.64 179.2 28.8 31.2 '.3A U 0.1 0.1 0.1 >.. >72

>5,""Sunflower a 0.87 187.8 36,8 38.6 1.6

A 2.' 02 0.1 0.05 >.. >72>$ days

Q Before treatment: b Afttr treatment

After [he oil is heated (75-SSoq andmixed with the water solution contain-ing the wetting agent and EDTA, [heemulsion is cooled to 6-S"C and senr to

a weakly agitated marurutor (8-10hours), where growth of the wax crys-tals occurs. The oil is then heated atlS"C to reduce the viscosity before thesubsequent separation in a centrifugalseparator. As small amounts of soapsare produced during the degummingprocess, washing is not necessary, which

Volume I I • Ma~2000 . Inform

permits a saving in equipment. Oilloss-es during the centrifugation at low tem-perature are very low.

During the degumming, the hydratedphosphatides are preferentially located atthe oiVwater interface. The growth of thewaxes therefore takes place in the midstof a degummed oil. It is indeed wellknown that phospharides strongly delayor inhibit the crystallization of thewaxes. Crystallization in a mediumwhere phosphaeides are already

"trapped" at the oil/water interface istherefore improved. As a consequence,the degummed/dewaxed, bleached anddeodorized/deacidified oil has a cold testof 48 hours minimum at O°C, and fur-ther polishing filtration is not necessary.

Finally, as the combined degum-mingldewaxing occurs before bleachingand deodorizing, the risk of peroxideformation as found in conventionalmethods of deodorization followed bydewaxing is reduced.

60c 500

~ 401=• 30Ed 20d

~c 1020

0

y '" 1.2802x - 0.6005R2 '" 0.9903

10 20Ions (ppm) -ICP

30

Figure 16. Correlation between titration ..nd sp<ectJ'Ometic method (ICP) for th" determl.nation of Ion content (calcium, m~nesium.;and iron) of oils

Physicit.lly refined sunflowerand corn oilsThe combined S.O.F.T. degumming!dewnxing technique was first developedall a pilot scale with different qualitiesof sunflower and corn oils. The oil isheared at 75-85°C, thoroughly mixedwith a water solution containing wet-ting agent and EDTA, cooled co 6"C,and held for eight hours in a maruraror,Afrer heating at ISoC, the oil is separat-ed by centrifugation from the watersolution containing gums and waxes.

Such dcgummedldewaxed oils arecharacterized by low levels of phospho-rus (P < 5 ppm), as well as cold-stabili-ty characteristics of completelydewaxed oils (Table 3). Moreover, inevery case, the iron content is extremelylow, giving the degummedldewaxed oilvery good oxidative stability. It is obvi-ous that the analysis of phosphorus isnot representative of the quality of theoil in terms of nonhydratable phos-pharides. As the lack of hydrarabihry ofthe phosphatides is mainly due to their

complexation with calcium, magne-sium, and iron, the quantity of thesecations can be directly linked to thecontent in nonhydrarable phosphatides.This information is important to opti-mize the process in terms of reagentconsumption. For this reason, a rapid

SJ3

40

and reliable method for determining thecontent of inorganic ions in the oil hasbeen developed. This method, based onextraction followed by cicraricn, hasbeen successfully correlated to the spec-troscopic results obtained from ion coreplasma inductively coupled plasma(ICP) spectrometry (Figure 16).

This degummingldewaxing processhas been developed in a refinery runningat a capacity of four rnerric rons per hourfor sunflower and corn oils. The short-mix process has been slightly modified ina S.O.ET. degurruningfdewaxing plant. Ahigh-shear mixer was installed to mix oiland water, and the water-in-oil emulsionsent to one existing crystallizer; aftereight hours at 6°C, the mixture waspumped, after heating at 15DC, to thecentrifugal separator; where the oil wassampled. The analysis of the continuousprocess for a specific batch of sunfloweroil is presented in Table 4. Thedegummedldewaxed oil described wasthen bleached and deodorized/deacidi-fied in a physical refining process. Thecharacteristics of the fully refined oil aredescribed in Table 5.

Table ..Characteristics of sunflower oil, before &nd after S.O.F.T. degurnrnlngidewaxinJ In anindustrial plant at -4 Tlhour

Sunflower oil

Acidity (%)Peroxide value (meq!kg)TotoxPhosphorus (ppm)Ions (ppm)Waxes (ppm)Soap (ppm)Cold rest (hours):we12"<:Room temperature

1.53.7'.1

40.525.6D

800

Q By ICP spectrometry

S.O.F.T.degummedJ

dewaxedoil

1.1

<1

20

>48>72..5 days

Volume I I • May 2000 • Infarm

".Processing

SODbleached(SODB)

TaiMe 5Characteristics or. refined lU""_r oil,with S.O.F.T.decummin&!dewaxln,u preueaanent in UI industrial plant at. metric toni perhour

feed oil

AcidiTY ('Yo) 1.5

Phosphorus (ppm) 40.5

Calcium 18.4(ppm)"

Magnesium S.,(ppm)"

Iron (ppm)" I.,PV (meqlkg) 3.7

Lovibcnd IRl30Y(1")

Waxes (ppm) 800

Cold tor(hours)

a By ICP spectrormuy.

As the process is performed underacidic conditions (pH 5), there is nosaponification of the feed oil; the slightreduction of the oil acidity is only dueto a side reaction of the unbalanced[EDTA-Ca++IMg++] complex with thefree fatty acids. EDTA can be found asits full acidic form (H4EDTA) or in adissociate form (H~EDTA-. H2EDTA--.HEDTA3-, EDTA -J depending uponthe pH conditions. The doubled dissoci-ated form H2EDTA-- is stable in mod-erate acidic media (pH 3-6), giving riseto the following reaction:

Volume I I • May 2000 • Inform

S.O.F.T.d""""",,,,,

dewaxed(SDD)

1.1

3.4

0.2

0.2

<0.1

4.3 R/40Y(5"114)

H2EDTA- + 2 Na+ +phosphatide-Ca ++IMg++--+[EDTA-Ca++IMg++ l" +2 Na" + 2H+ + phosphatide

The unbalanced IEDTA-Ca++IMg++j-- complex probablyremoves any free fatty acids as insolublesoaps.

A conventional dewaxing processaccompanied by the neutralizing stepused in a caustic refining plant gives riseto several problems:

SDDBdeodorized

(fully refined)

<0.05

0.7RJIOYl5' 1/4)

O.4RJ~ts- 1/4)

>48 at O"C>72 at 12"C> 5 days at room temp.

• The addition of dilute causticsoda after the first centrifugationincreases the soap content to 2,500ppm, with a risk of neutral oil lossesby saponification of the t riglyc-erides.

• The high soap content has a neg-ative effect on the neutral oil lossesduring the separation at low tempera-ture.

• A final washing at high tempera-ture is performed because the soap con-tent in the oil after the second centrifugeis still above 600 ppm; three centrifugal

separators are therefore necessary insuch dewaxing plants.

• A polishing filtration is necessaryto achieve strict cold-stability require-ments.

In the S.O.F.T. degummingldewax-ing, there is no risk of saponification ofthe neutral oil, the soap content in theoil is very low, and only one centrifugalseparator is necessary. In the model ofwater-in-oil emulsion, the growth of thewaxes takes place in an alreadydegummed oil. As a consequence, thismechanism is greatly improved, andgood cold rests are achieved withoutrequiring any polishing filtration. Highand low levels of waxes can be easilyremoved before bleaching or drying ifthe oil has to be stored.

ConclusionsUp to now, the physical refining of wax-containing oils, such as sunflower oil orcom oil, was possible by the convention-al method, using pressure leaf filters forthe separation of the low-temperaturecrystalliz.ed waxes. This method can,however, be problematic when there is ahigh wax content. The superlunidegum-ming with the hydration step performedat low temperature is another possibility,but in this case, polishing filtration is stillrequired depending upon the cold-reststability requirements.

The main interest in the combineddegummingldewaxing is its simplicity,as only one high-shear mixer, low-tern-perature residence tanks, and a self-cleaning centrifugal separator (as wellas heat-exchangers) are necessary toachieve very strict cold stability require-ments. Compared with dewaxing

accompanied by the neutralization stepof caustic refining, the neutral oil lossesdue to soap formation are low with thenew procedure. For all those reasons,(he combined degummingldewaxingused in the pretreatment of physicallyrefined oils appears to be a very promis-ing approach.

BibliographyBailey's Industrial Oil and Fat Products

(Fifth Edition), Volume 2, edited byY.H. Hui, John Wiley & Sons Inc.,New York, New York, 1996.

Degumming and Neutraliuztion of Fatsand Oils, Alfa-Laval Separator AB,Industrial Separation Division,Tumba, Sweden, 1998.

Processing Lines for the Edible OilIndustry, GEA MechanicalSeparation Division, WestfaliaSeparator AG, Oelde, Germany,1998.

Update on Filtration in the ProcessingSteps of Edible Vegetable Oils,LF.C.·Lochem B.V., Lochem, TheNetherlands, 1998.

UFDegumming, Krupp Maschinen-rech-nik GmbH, Hamburg, Germany,1997.

Dijkstra, A.J.. Degumming, Refining,Washing, and Drying Fats and Oils,in Proceedings of the WorldConference on Oilseed Tech"ologyand Utilization, edited by T.H.Applewhite, AOeS Press,Champaign, illinois, 1992, pp.138-151.

Sl5

Buchold, H., Enzymax, a State of theArt Degumming Process and ItsApplications in the Oil Industry,Lurgi 01 - Gas - Chemie GmbH,Frankfurt am Main, Germany,1995.

Deffense, E., S.O.F.T. Degumming, inOils-Fats-Lipids, Proceedings ofthe 21st World Congress of theInternational Society for FatResearch (Volume 1), P.]. Barnes &Associates, Bridgwater, England,1996, pp. 125-128.

Gibon, V., and A. Tirtiaux, S.O.F.T.degumming: The simple route tophysical refining of soft oils,Malaysian Oil Sci. Technoi.7(2),48-54 (1998).

Gibon, V., and A. Tirriaux, EI procesode desgomado S.O.F.T., AceitesGraws 32:446-452 (1998).

Gibon, v., and A. Tirtiaux, Un RaffinageS.O.F.T., Oliaginellx Corps GrasLipides 5:371-377 (1998).

S.O.F.T. degumming, a process for themill, in Proceedings of the 1999PIPOC Conference, EmergingTedmofogies and Opportunities inthe Next Milfem,;um-Chem;stryand Tec.hnology,Palm Oil ResearchInstitute of Malaysia, KualaLumpur, Malaysia, 1999.

Determinacion of ion content in oil,Procedure SDOO1 (internal docu-mentation), FractionnementTirtiaux, FJeurus, Belgium, 1998.D

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