992

This article was writ-len for INFORM byJohn Bell and JosephZachwieja of AhaNobel Central Re-search in DobbsFerry, New York. I,deals wilh historicaland currenl develop-ment and applicationof cationic serfoc-

lonls in mineral processing, wood preservation, and as surfactantadjuvants for agricultural chemicals.

OLEOCHEMICALS

(-NH2) head group and predominanliylinear carbon chain with an even num-ber of carbon atoms (i.e., CIO,el2,C14, etc.). These molecules will ion-ize in water to liberate a long-chainfatty ion having a positive charge.This fauy cation will attach itself tominerals having a high concentrationof negative surface charges and pro-vide a hydrophobic surface that willpenni! flotation.

Another class of cationic surfactantis derived from petroleum con-stituents. This class is the etherumines and ether diarnines. derivedfrom alcohols. The result is an aminewith an oxygen atom in the chain,three carbons from the nitrogen. Thepresence of the oxygen atom (etherlinkage) imparts a hydrophilic charac-ter to the otherwise hydrophobicchain. This results in an amine withmore solubility and somewhat weakercollecting properties than a fattyamine. The ether amines are usuallyliquid products at room temperature.These surfactants have been used suc-cessfully as collectors in the reverseflotation of silica from iron oxides.

ApplicationsFroth flotation of industrial (non-metallic) minerals can be divided intothree main categories: (a) potash (sol-uble-salt) minerals. (b) insolubleoxides and silicates. and (c) semisolu-ble-salr minerals. The major industrialminerals and the correspondingcationic collector(s) used to separate

these minerals by flotation are foundin Table I. Examples of each of thethree main categories are describedbelow.

Potash. Potash is the general termused for various soluble salts of potas-sium, but more recently it has come tobe applied to potassium chloride.which is the largest source of potassi-om.

The most widely occurring potassi-um ores are: (a) sylvinite, a mixture ofsylvite (KCl) and halite (NaCI). (b)carnallite. a mixed potassium andmagnesium chloride (KCI • MgCI2 • 6H20) accompanied by NaCI, and (c)kainite, a mixture of potassium chlo-ride and magnesium sulfate (KCl •MgS04 • 3 H20). Of these ores, themajor source of potassium chloride issylvinite. and it is mined to a muchgreater extent because of its higherpotassium content. The major use ofpotassium is in fertilizer formulations.

Flotation of sylvite from a sylviniteore must be carried out by dispersingthe ground ore in a brine solution.which is saturated with respect to bothpotassium and sodium chloride.because it is extremely soluble inwater. In a typical example, sylviniterun of mine ore is first ground to -6mesh in an impact crusher. This ore isthen further ground in saturated brinesolution in a rod mill to approximately-14 mesh. The 14-mesh material isthen deslimed, which removes most ofthe slimes, and is then used as feed tothe flotation circuit. As a first stage.

Industrial uses of cationic surfactants

Cationic reagents have been usedin mineral processing since themid-1930s and are based upon

Iauy nitrogen derivatives. The initialcommercial development was cen-tered around a flotation collectorcapable of separating potassium chlo-ride from sodium chloride-potashflotation. The first commercial sale forAkzc Nobel. known then as Armourand Company. was realized in thesummer of 1940 to a potash producerin Carlsbad. New Mexico. for theflotation of potash. The success of thepotash flotation collector led to thedevelopment of other cationic mineralprocessing reagents. Flotation collec-tors for iron ore. phosphate. calciumcarbonate. silica sand. feldspar. andother silicates developed into a largecommercial business. Another areathat realized commercial success wasthe development and use of arnicak-ing/antidusting reagents for hygro-scopic sans. fertilizer mixes, and gran-ular fertilizers.

ChemistryThe application of cationic surfac-tants. i.e., fauy chemicals, to mineralprocessing has been promoted by theuse of fatty anunes. [Imine salts. andquaternary ammonium compounds.The fuuy nmines are derived fromfatty acids (obtained by splitting of thefats and oils) by reaction of the acidswith ammoniu to give fatty amides,followed by dehydration of the amidesto fatty nitrites and. finally, reductionof the nitriles with hydrogen at highpressure to give fatty amines. Thesefatty emtnes can be further derivatizedto give dinmines, quaternary amlnes.ethoxylated amines, propoxylatedamines. etc.

Fatty amines derived from naturaloils contain carbon chains with 8-24carbon atoms. Most flotation collec-tors are based on coconut oil (12-14carbon atoms) and tallow (16-18 car-bon atoms), but other products derivedfrom oleic acid (18 carbon atoms) orfish oils (20-24 carbon atoms) areavailable commercially.

Amines derived from natural fatsand oils have a hydrophilic amine

INFORM. Vol. 7. no. 9 (September 1996)

993

conditioning at high solids (60%)takes place with the addition of adepressant. such as guar. starch, orcarboxymethyl cellulose (CMC). todepress any slimes not removed in thedesliming stage. In the second stage. aprimary amine collector. which hasbeen neutralized with eitherhydrochloric acid or acetic acid, isadded as an aqueous dispersion withan extender oil al a dosage from 0.1-0.5 Ibllon of feed. This activates thesylvite component of the ore and northe halite, thus allowing selective sep-aration by notation. The notation iscarried out at 20-40% solids andoccurs fairly rapidly with the sylvitebeing collected in the froth layer.

Calcite. Calcite is present as theprincipal constituent of metamorphiclimestone and occurs in limestone as avein material. It is often associatedwith contaminants such as mica. sili-ca. and pyrite: many limestone orescontain 10-20% of these contami-nants. Cationic-reverse flotation isused to remove these contaminantsfrom the calcite. First. the ore isground to the optimum liberation size.If clay slimes are present, they aredepressed with a slimes depressantsuch as guar or starch. In general. thepH is not controlled and is usually inthe range 8-9. 'The mica and silicacontaminants are floated with either adiamine or quaternary amine collector(0.5-1.0 lb/ton of feed). Calcite isremoved as the tailings product fromthe Float cell. Flotation of calcite hasincreased recently to meet the demandfor white filler for the paper industry.The use of cationic-reverse Ilotarionhas the advantage thai little residualcollector remains in the calcite prod-uct, whereas direct fatty acid notation(anionic notation) of calcite gives aconcentrate coated with collector. Thiscollector-coated calcite is difficult touse in the paper industry.

Iron oxides. The taconites are ironore deposits consisting of dissemina-tions of iron oxides in silica. The ironoxide occurs as magnetite or as oxi-dized taconites. which are comprisedof hematite. limonite. goethite. andsome magnetite. Magnetite is concen-trated mainly by magnetic separation,while the oxidized taconites, whichare nonmagnetic. are concentrated by

Oassiflcations

Ocsliming

Causlic

S~hAmine

Condilioning

Rougher notalion Cleaner fiOl:ation

Final iron concentrate

!Scavenger cleaner

Tailings

Figure 1. SchematIc 01Ironoxide !lotatlon

then conditioned with caustic soda(pH II) and cornstarch, which isadded to depress the iron particles.After conditioning, an amine collec-tor. such as primary ether amine(0.1-0.2 lbllon of feed), is added justprior to the notation cells; this acu-vates the silica. which is then recov-ered by reverse flotation. Followingthis rougher flotation. the concentrate,which contains mainly silica, is sent toscavenger flotation; the middlingsproduct is recycled to the rougherfloat cells. The underflow from therougher flotation, which contains theconcentrated iron oxide, is then sent tocleaner notation to produce the finaliron concentrate.

Anticoking. Cationic chemicals areused to control caking of hygroscopicsalts such as fertilizers (potash andammonium nitrate). A secondary ben-efit of using cationic chemicals is thecontrol of dust caused by mixing. siz-ing. and transfer of fertilizer products.Caking results from absorption of

flotation. Fine grinding usually isrequired to liberate the minerals. par-ticularly in low-grade taconite ores.Most of these taconites are ground to80% -44 pm and some to 90% -25urn.

Flotation of iron ores can beaccomplished by either direct orreverse flotation methods. In directnotation, iron oxide is floated usinganionic reagents such as petroleumsulfonates or fatty acids. Direct nota-tion sometimes results in the problemof the concentrate not making grade.Because of this, reverse flotation.using cationic collectors to float thesilica-containing gangue, is preferred.The reverse flotation of iron oxide(Figure I) essentially consists ofgrinding the ore to the optimum liber-ation size then sizing the ground pulp,after which cornstarch is added to thefinely ground pulp and the iron parti-cles are selectively flocculated. Nextthe iron panicles are deslimed of thefinely dispersed silica. The pulp is

INFORM. Vol. 7, no. 9 (September 1996)

994

Dosage

0.1-0.5 Ibltan0.1-5.0 lb/ton0.1-1.0 lbllonQ,I-O.51b/ton0.05--0.15 lbsron

OLEOCHEMICALS

Table 1Major industrIal minerals processed by cationic flolatlon

Industrialmineral Category

PotashPhosphateCalciteFeldspar/silica sand[ron oxides

Soluble saltSemisoluble saltSemisoluble saltInsoluble silicatesInsoluble oxides

moisture or moisture moving from thecore or center of a particle to the sur-face andlor a combination of both.Evaporation of this moisture withchanging atmospheric conditions canbring about bridging or fusionbetween adjacent particles which intum can lead to the loss of flow prop-erties. Other conditions besides mois-ture and atmospheric conditions playapart in contributing to the caking phe-nomena. These include chemicalmake-up, physical make-up, manufac-turing, and storage conditions, etc.

The degree of caking of hygroscop-ic salts, such as potash, is controlledby the judicious application of anti-caking conditioners. These condition-ers are typically primary amines andare applied to the potash at dosagesfrom 0.1-1.0 lblton as: (a) a nealproduct onto hot potash, (b) an aque-ous acid solution onto hOI potash, or(c) a mixture with a dedusting (hydro-carbon) oil onto ambient potash.These methods of application havebeen found to be effective in reducingthe tendency of potash crystals to cakeduring storage or transportation and toretain their free-flowing properties.

In conclusion, the successful bene-ficiation of industrial minerals, suchas potash, phosphate, calcite, feldspar,etc., relies on the use of cationic sur-factants. The "lion's" share of thesesurfacrants typically is used as cation-ic flotation collectors. These collec-tors consist of the following groups:fatty amines, amine salts, quaternaryammonium compounds. and etheramines. Cationic flotation efficiency isdependent upon several variables.among those are ore particle size, pulptemperature, slimes content, and waterchemistry. Cationic collectors offer anumber of advantages when compet-

Collector type

Primary aminesPrimary.ether nmtnesDiamines: quaternary aminesPrimary amines: diaminesEther amines: ether diamines

ing with anionic collectors in specificmineral separations: (a) there is rapidattachment of the collector to the min-erai surface resulting in sharp selectiv-ity, (b) the collectors function over awide range of pH, (c) the collectorspermit coarser feeds to be processed,and (d) the collectors are ideally suit-ed for reverse flotation to upgradeconcentrates. Other uses of cationicsurfactants include controlling cakingand dusting of hygroscopic salts andfertilizers.

Cationic surractants in woodpreservationUntil the mid to late 1980s, wood waspreserved against decay or deteriora-tion by a small number of standardpreservatives. Wood thai had to sur-vive in areas of severe decay hazards,such as utility poles that were placeddirectly in the ground. was pressuretreated with one of the big threepreservatives: creosote, pen-tachlorophenol in a heavy oil solution,or a solution of copper, chromium, andarsenate (CCA) salts. Wood that wasused in an application where the decayhazard was not so severe, such as exte-rior painted millwork, was treated withpentachlorophenol in a volatile solventformulation. Freshly cut lumber wassurface treated with sodium salts solu-tions of pentachlorophenol to preventthe growth of mold and staining fungiwhile the lumber was drying. Otherpreservatives did exist. Some of thesewere simple variations on the ones justmentioned, such as tetrachlorophenolor acidic copper chromate. Otherswere significantly different, such ascopper naphthenate or sodium tetrabo-rate. But these other preservatives onlyaccounted for a small portion of themarket.

But during the past two decades, ithas become increasing apparent thatthe widely used wood preservativeswould be coming under increasingenvironmental and regulatory pres-sure, due to concerns about toxicity,carcinogenicity, or heavy metal con-tent. Because of such pressures, theuse of some of these preservatives incertain applications has been restrict-ed. It is very possible that furtherrestrictions or bans on these preserva-tives may come about in the future.

Because of these potential regula-tory actions against pentachlorophe-nol, creosote, and CCA, there hasbeen a growing interest in other possi-ble preservatives. Long-chain alkylammonium compounds (AACs) areone class of compounds that havebeen the subject of increasing interestfor their potential as wood preserva-tives. Early research had examined theuse of both tertiary amine salts andquaternary ammonium compounds inthis application. Currently, the quater-naries are the compounds that are themost used as wood preservatives.

Quaternary ammonium compoundsare derivatives of ammonium saltswhere all four of the hydrogens havebeen replaced by organic groups.These compounds are thus cationic innature. For wood preservation, thecounteranion typically has been ahalide such as a chloride or bromide.

There are three types of quaternar-ies that are currently in use as woodpreservatives. The first type consistsof benzalkonium compounds (I),which have a single long-chain alkylgroup (usually mixtures of C 12 10CI8), a benzyl group, and two methylgroups on the nitrogen center. Thesecond type consists of the dialkylquaternaries, which have two methyl

INFORM, Vol. 7. no. 9 (September 1996)

995

groups and two long-chain alkylgroups. By far, the most commonlyused dialkyl compound is the didecylderivative (II), known as DDAC. Thethird type is the monoalkyl quaternarywith three methyls and a single alkylchain on the nitrogen. The monoalkylquaternaries have been less commonlyused than the other two types in woodpreservation applications. Typicallythe monoalkyl quaternaries have beenbased on cocoalkyJ (primarilyC12-C14) groups.

These compounds find a multitudeof uses as biocides and disinfectants.A number of different companies sup-ply these products for these markets.However, in the wood preservationmarket there are two major suppli-ers-Aha Nobel, which is based inThe Netherlands and Sweden, andLonza, which is based in Switzerland.Akzo Nobel supplies these productstypically under the Arquad tradenameand Lonza supplies them typicallyunder the Bardac rradename.

A major advantage that quaternar-ies have over other newer fungicidesthat are being evaluated as woodpreservatives, such as the uiazoles. isthat they often cost less than one tenthas much as the newer fungicides.

Wood decay, where the structure ofthe wood itself is destroyed, is primar-ily caused by fungi called basid-iomycetes. Mushrooms, whose famil-iar caps are fruiting bodies of thefungi, are members of this group.Other types of fungi, such as molds,can cause a surface deterioration ordiscoloration of wood which does notdestroy the structure of the wooditself. However, the growth of mold orstains indicate that the wood is in con-ditions that may lead to wood decay.

AACs show excellent biocidalactivity against wood-decaying basid-iomycetes in laboratory tests. Howev-er, AACs require the use of a co-bio-cide when they are used to preservewood that will be exposed to a severedecay hazard, such as wood that is inground contact. The use of AACsalone in wood is recommended onlyfor above-ground uses. At present, itis not clear why AACs are not effec-tive alone in wood that is in contactwith the ground. Some recent researchhas indicated that certain fungi. that

do not themselves decay wood, maybe able to biodegrade AACs in treatedwood. This then allows wood-rottingfungi to gain a foothold.

Recently a water-soluble combina-tion of copper salts and DDAC,referred to as ACQ, has been intro-duced in the United States by Chemi-cal Specialties Inc. (CSI). as a wood

Long-chain AACs, andin particular quaternaries,

are making upa growing portionof the market for

wood-preserving chemicals.

quaternaries mentioned above. This isin contrast to United States, whereDDAC predominates. These productsare often combinations of an AACwith other biocides.

In conclusion, long-chain AACs,and in particular quaternaries, aremaking up a growing portion of themarket for wood-preserving chemi-cals. The presently used compoundshave some weaknesses that preventthem from being used alone in certainapplications. However, producingproducts with multiple biocides is thedirection that most manufacturers ofwood preservatives are heading. Thus.because of their low cost and effec-tiveness, it is certain that the greatmajority of such products will beincluding an AAC as one component.

Surfaetants as adjuvants (01" agri-cultureModern agricultural practice reliesupon the responsible use of pesticidesto overcome the damaging effects ofdisease, insects, fungal growth, andcompeting weed species in order tomaximize crop yields and quality. Sur-factants are used in a variety of waysto improve the effectiveness of activepesticides and their formulations. Sur-factants are typically inert chemicalswith no pesticidal properties. In gener-al, the cost of surfactants is relativelylow compared to the cost of pesti-cides, but they often are able to givelarge improvements in the physicalproperties of pesticide formulations orlarge increases in the bioefficacy ofthese formulations; in the latter case asurfactant is said to act as an adjuvantand may function through improvedwetting of plant surfaces andlor byincreasing penetration rates of the pes-ticide into the plant.

A number of different companiessupply either anionic, nonionic, orcationic surfactants to the agricultureindustry for use as adjuvants. Anionicand nonionic surfactants have seen the"lion's share" of use as adjuvants.However, the cationic surfactants(fatty-nitrogen based), in particular.can offer superior adjuvancy withmany pesticides, through both in-for-mulation and tank-mix modes. Theseproducts can be used generally as for-mulation ingredients. emulsifiers, and

preservative for ground contact use.CSl's tests indicated that this formula-tion may nearly be as effective in pre-venting decay as CCA. CSl's originalformulation used ammonia hydroxideto solvate the copper sail during thetreatment process. CSI recently hasintroduced a new formulation thatuses short-chain amines to solvate thecopper, a change that has apparentlymade the process more popular withwood-treating companies.

It is in the market for products thatprevent sapstain and mold on freshlycut lumber, that AAC-based formula-tions have taken over and replacedolder products. The top-selling prod-uct in the United States and Canada isNP-l, which is a combination ofDDAC and a second biocide, 3-iodo-2-propynyl butylcarbamate. Thisproduct is manufactured by Kopcoat.A large portion of the rest of the anti-sapsrain market in Canada is filledwith other formulations containingDDAC. In Europe, Sinesto B. which isa combination of lrimethylcocoalky-lammonium chloride and ethylhex-anoate, has a major share of the mar-ket in a number of countries.

The European producers of woodpreservatives have been way ahead oftheir U.S. counterparts in introducingAAC-base products for treating woodthat will be used in above-groundapplications. Furthermore. the prod-ucts that have been introduced therecontain anyone of the three types of

INFORM. Vol. 7. no. 9 (September 1996)

9Q6

SOY PROTEINCONCENTRATESoy protein concentrate processing is a very

lucrative and exciting business. A business thatcan serve as your means to achieve steady and

generous profits and to end losses due tonegative "crushing margins."

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Ever since 1963, Hayes has been providing its expertise,engineering designs, equipment and complete plants to allthe leading soy protein concentrate manufacturers theworld over. Hayes' appropriate systems are in use in soyprotein concentrate plants in the United States, Denmark,The Netherlands, Israel, France and elsewhere.

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OLEOCHEMICALS

dispersing aids. In fact, certain pesti-cides, such as glyphosate, require theaddition of fatty nitrogen-based adju-vants in order to achieve effectiveweed control. and their formulationsrely upon the properties unique 10 thistype of surfactant.

Our firm recently has developed theAgHance range of surfactants as thenext generation adjuvant products. Asan example. one of the adjuvantsdeveloped in this program is a blend ofa patented. modified fatly-amine poly-mer with a sugar-based surfactant, andan added buffering agent (pH 4-6)which was developed specifically fortank mix applications. The sugar-basedsurfactant provides excellent spread-ing. wetting. and sticking properties.thus giving improved distribution ofthe spray droplet on the plant leaf. Incontrast. the amine polymer providesefficient penetration of the pesticidethrough the wax and cuticle layers intothe plant system. Hence. the actions ofthese two surtactanrs complement eachother. giving excellent overall resultswith both contact and systemic pesti-cides at low dosage rates.

Many active pesticides are regis-tered for use in worldwide agriculture,with new products entering the mar-ketplace on an ongoing basis. The rateof new product introduction is declin-ing because of the enormous costsinvolved in research, development,and registration of a new active mate-rial. These mounting costs have led \0an increasing market trend toward thereformulation of existing active pesti-cides. Surfactants have a vital role toplay in these reformulation activitiesand can greatly facilitate the develop-ment of mere environmentally friend-ly, solvent-free types of formulationincluding microemulsions, water-dis-persible granules, and water-solublepowders.

In conclusion, boosting the bioeffi-cacy of a pesticide through the use ofsurfactant adjuvants translates intotwo important real-world benefits by(a) allowing effective pest control tobe accomplished using lower doserates of active pesticides; namelyreduction in the pesticide loadimposed on the environment and (b)reducing costs to the farmer and thusto the consumer.

997

New fatty alcohol plant using fixed-bed reactorThe successful commissioning of thefatty alcohol plant at P.T. BatarnasMegah's production site in Indonesiamay well mark the beginning of a newera in fatty alcohol technology. Theplant, operating on a proprietary Lurgiprocess, is the second fatty alcoholplant built by that firm for SalimOlcochemicals. The new facility pro-duces top-quality fatty alcohols andglycerine while providing operatingflexibility and excellent economics.The process uses a fixed-bed reactorfor the hydrogenation of fatty acidmethyl ester derived from natural oilsand fats. In addition to saturated fattyalcohols. the plant also can produceunsaturated fatty alcohols.

Plant conceptOils with a high content of fatty acidsof chain lengths C12-18 are best suit-ed for conversion to Iauy alcoholsdestined for further processing intofeedstocks for detergent production,such as fatty alcohol ethoxylates andsulfates, due to their surface-activeproperties and biodegradability. Forthis reason, palm kernel oil andcoconut oil are the predominant rawmaterials for fany alcohol production,although other vegetable and animal

oils can be used for this application.Due to the operating flexibility

required to produce both saturatedfatty alcohols (60,000 tons a year) orunsaturated fatty alcohols (30,000tons a year) in the same plant, a pro-cess system based on the methyl esterroute was selected. All fatty alcoholplants previously built by our firm hadbeen based on the acid route (directhydrogenation of the fatty acid in aslurry reactor). A new fixed-bed pro-cess had to be developed as the con-vemional slurry process proved to beunsuitable for the production of high-quality unsaturated fatty alcohols.

The individual process unitsrequired for the overall plant are

Salim Oleochemicals fattyalcohol plant built by LurgiOf, Gas Chemie GmbH

shown in Figure I. Processes such aslransesterification and carbonyl con-version had to be newly developedand were implemented for the firsttime in this plant. In other cases, suchas, for example, hydrogen production,the existing processes were adaptedand enhanced.

The Batamas Megah plant consistsof the following individual plant units.In the front-end pre-treatment unit,crude oil is freed from gums, phos-phatides, and natural pigments beforebeing transferred to the deacidificationunit for the removal of free fatty acids.Apart from providing the acid-free oilrequired for subsequent transesterifi-calion, deacidification generates fatty

T1W artick was prrpamlfor INFORM by F. GlJn·lIer aM G. MalloA: ofL.r,i 01. GasC"e"';~GmbH. FranA:fllrtlM.a.""""Y-

F._ 8._

INFORM. Vol. 7. no. 9 (September 1996)

998

OLEOCHEMICALS

The crude fatty alcohol from thehydrogenation unit is separated intomarketable fractions in the fatly alco-hol fractionation/distillation unit. lnthe downstream carbonyl conversionstep, the fatty alcohol is rehydrogenat-ed for maximum reduction of the car-bonyl number. The co-product crudemethanol is distilled in a methanolrecovery unit to obtain pure methanolfor reuse as a reactant in the transes-terification process.

Apart from these process sections.the overall plant is equipped with allthe required equipment and facilities10 ensure self-sustained utility supply,e.g., electric power, steam, coolingwater, nitrogen, and air.

Table 2Product mix

Table 1Typical quality of refined glycerine

>99.8%<0.01%

<5 APHA<5APHA

0.2 meq/l 00 gnegative

<20 ppm<I ppm

<0.01 ppm<2 ppm

C6I1OC6C8CIOciz/rsCl2ll4CI2CI4CI6CI8

Fatty alcoholFatty alcoholFatty alcoholFatty alcoholFatty alcoholFatty alcoholFatty alcoholFatty alcoholFatty alcoholFatty alcohol

Glycerol concentrationMoistureColorHeat stabilitySap equivalentReducing substancesSulfate ashHeavy metalArsenicChloride

mixed or pure fractions. which areeither directly sold on the market orhydrogenated to fatty alcohol.

The hydrogen required for hydro-genation is generated in a productionunit, which uses a steam reformer anda pressure swing absorber to producehydrogen with a purity of over99.99%.

Hydrogenation of the fatty acidmethyl ester is accomplished in thefatty alcohol synthesis section using anewly developed fixed-bed reactorpacked with a catalyst in tablet form.

acid distillate as a co-product. Trans-esterification takes place on an alka-line catalyst with an excess ofmethanol, and crude fatty acid methylester plus crude glycerine is formed.

The glycerine is subjected to chem-ical pretreatment followed by evapora-tion and double distilluuon. A finalbleaching step yields pharmaceutical-grade glycerine of highest quality.Table I shows the quality of therefined glycerine from this process.

The crude fatty acid methyl ester isfractionated and distilled to obtain

InnovationsThe newly developed transesterifica-tion process is a novel and simplemethod of producing fatty acid methylester. Using a patented reaction con-trol concept. the oil is converted tofatty acid methyl ester at atmosphericpressure and a relatively low tempera-ture; conversion efficiencies of more

Peek Heat HotHeater Exch_ger Separator

Cold........... SbipperReact...

cw

CnKIe CrudeFatty Alcohol Methanol

Fatty AcidMethyI_

Hyd"""",

Figure 1. Processing route for fatty alcohol production

INFORM. Vol. 7. no. Q (September lQ96)

Crude Palm kernel Oil

--

Fatty AlcoholFractions

Fatty Acid Distillate

G""....

C6fI 0 Methyl8S~

Figure 2. Fatty alcohol production from fatty acid methyl eater

than 98.5% are achieved. Continuousreactor operation assures a uniformquality of the fany acid methyl esterand glycerine products.

The fatty alcohol synthesis unit,which forms the hub of the overallplant, likewise is based on a newlydeveloped process. Here, the fatty acidmethyl ester is hydrogenated to pro-duce fatty alcohol and methanol. Thedesign parameters for fixed-bedhydrogenation were established bypilot tests on various catalysts at ourresearch and development facility.Based on our experience in the con-struction of hydrogenation plants fornative oils (hardening), other naturalproducts (e.g.. sugars), and for petro-chemical applications, it was possibleto transfer the pilot test results directlyto commercial-scale conditions usinga scale-up factor of over 30,000.

Tbe new fatty alcohol syntbesis

unit (see Figure 2) is fed with distilledfatty acid methyl ester, which is pre-heated, together with makeup hydro-gen, before being admitted to the reac-tor. The reactor is charged with pre-heated hydrogen from the H2 recyclecircuit. The product discharging fromthe reactor consists primarily of thefatty alcohol formed, plus methanoland excess hydrogen.

The reactor discharge product iscooled using recycle hydrogen as acooling medium before the liquidfraction is separated in the hOI separa-tor. In the downstream stripper, thegreater part of the methanol is separnt-00.

The crude fatty alcohol is cooledand tben routed to an intermediatestorage tank from where it is fed to thefatty alcohol fractionation and distilla-tion unit. The recycle hydrogen dis-charging from the hot separator also is

cooled down, the condensate beingdirected to the stripper and thenreturned to the reactor via the H2 recy-cle compressor.

In tbe normal plant-operatingmode-production of saturated fanyalcohol-the peak heater is onlyrequired during the heating-up phase,i.e .• for start-up. As soon as normaloperating conditions are established,the reactor temperature is controlledsolely via the fatty acid methyl esterpreheater.

The reactor is designed as a single-wall pressure vessel made of bigh-alloy steel, which is resistant to pres-surized hydrogen.

The following reactor operatingparameters were empirically estab-lished for the hydrogenation of fattyacid methyl ester:

• Feed: CJ2/IS fatty acid methylester,

• Reaction temperature:208-2l5°C,

• Pressure: 240 to 260 bar.Chemical reaction of the methyl

ester with the hydrogen starts in theupper catalyst layer and can bechecked by means of the temperatureprofile across the reactor. In this way,the catalyst activity and its remainingservice life can be determined at anytime.

The fatty acid methyl ester flowsdownward through the catalyst pack-ing as trickle phase and forms fattyalcohol. In this connection, it is cru-cial that the entire catalyst is thor-oughly wetted in order to ensure com-plete reaction. The trickle bed reactoris not only the technology of choicefrom the point of view of reactioncontrol but also offers such benefits aslower capital COSI-through the small-er reactor dimensions-and reducedelectricity costs for the circulation ofthe recycle hydrogen.

For other reactor systems, forexample a gas-phase reactor, thesecosts are much higher because thehigh-boiling components (Ctz to CI8methyl ester or alcohol) have to bepresent in the gas phase. This can beachieved by dilution with largeamounts of hydrogen, but at theexpense of high hydrogen recyclerates. Hence, the end result will belarge-vessel heat exchangers and large

INFORM. Vol. 7. no. 9 (September 1996)

1000

fatty acids, the fatty acid route has tobe selected for the production plant. Insuch a case, direct hydrogenation ofthe fatty acid to fatty alcohol isaccomplished by the slurry reactorprocess. AI roughly identical capitaland operating costs, the fatty acidroute offers the following advantagesover the methyl ester route: no needfor methanol handling equipment, nointerruptions in operation for catalystreplacement. and the possibility ofusing feedstocks with a higher FFAcontent.

A 50,OOO-ton-per-year fatty alcoholproject of Lu Do & Lu Ym Oleochemi-eals Corporation, The Philippines, willbe based on this tried-and-tested fattyacid route. After this plant has gone onstream at the end of 1998, nine Lurgi-built fatty alcohol plants accounting fora total capacity of over 200,000 tons peryear of fatty alcohol will be in opera-tion worldwide, corresponding to amarket share of approximately 25%.

An interesting future possibility isthe combination of the two routes.This can accomplished by using con-ventional technologies for convertingoil to fatty acids. Part of the fatty acidproduct could be directly sold on themarket while the other part is furtherprocessed to a fatty acid/fatty alcoholester (wax ester) for conversion tofatty alcohol by the fixed-bed hydro-genation process. A new patented waxester route has been developed duringthe past few months and opens thedoor to a new approach with furtheradvantages in terms of flexibility andprocess economics. In connectionwith bioengineercd rapeseed with high"Iaurate" content, the new wax esterroute could lead to the production offatty alcohols in the detergents rangein countries without palm kernel orcoconut oil production but with a his-tory of high rapeseed oil production .•

OLEOCHEMICALS

Proceedings of the AOCSICSMANew Horizons Detergent Industry Conference

To receive ordering information, call toll-free 1-800-336-AOCS in U.S. and Canadaor 1-217-359-5401, ext. 128 or fax 1-217-351-8091.

Table 3Typical quality of final fatty alcohols

Acid valueSaponification valueIodine valueColorCarbonyl valueHeMoisturePure cuts

<0.02<0.2

0.02-0.05<5 APHA

<3 ppm0.2.....Q.3%

dl05%>99% purity

piping diameters as well as high elec-tricity costs for gas circulation. Incomparison, the trickle-phase reactorcan process a broad range of methylester feedstocks at consistently goodproduct quality. It lends itself to thehydrogenation of any methyl esterfractions derived from the standardoils and fats. The main fraction pro-cessed is certainly CI2/IS but alsoC121l6. Moreover, the trickle-phasereactor is suited to the hydrogenationof the C6/10 fraction, a feedstock forthe production of palm kernel oil orcoconut oil-derived low-chain alco-hols enjoying demand on the market.

Changes from one product to theother can be accomplished withoutany problems by simply optimizingthe reactor temperature within a smallrange. This underlines the great flexi-bility of the selected reactor system.

As production progresses, thesaponification value in the crude fattyalcohol will rise gradually. As soon asa sharp increase in the saponificationvalue occurs, the catalyst has to bereplaced. The variations are accept-able up to a defined range, since theonly consequence is a higher residuerate in the downstream fatty alcoholdistillation column. In operating prac-tice, a new breakthrough in very lowcatalyst consumption is beingachieved.

The alternative plant operatingmode permits the production of unset-urated fatty alcohols. These can bederived from various raw materialscontaining the corresponding unsatu-rated fany acid components such aspalm oil, palm kernel oil, tallow, ortallow olein. For the production ofunsaturated fatty alcohols, a secondhydrogenation reactor packed with aspecial catalyst has been provided.

The fatty alcohol fractionation/distillation unit downstream of thehydrogenation reactor yields the finalproduct spectrum shown in Table 2.Depending on the product specifica-tions to be met, various product cutsor pure cuts can be produced, includ-ing cuts with purities of 99% orhigher.

Table 3 shows the typical fattyalcohol qualities after carbonyl con-version. Mention should be made ofthe extremely low carbonyl levelattained by the newly developed unit.In this way, the market's ever morestringent quality specifications forfatty alcohol products can be met reli-ably. This performance is the result ofthe application and further develop-ment of the tried-and-tested hydro-genation technology.

OutlookDuring the commissioning period andsubsequent production, the new fattyalcohol plant demonstrated excellentglycerine quality, excellent quality ofthe CI2 to CIS alcohols, and extreme-ly low catalyst consumption.

The catalysts employed are readilyavailable on the market; the processcan be licensed without any restric-tions, because our finn has no produc-tion and marketing interests.

If, contrary to the above processroute, the low chains and additionalother fractions are to be marketed as

INFORM. Vol. 7. no. 9 (September 1996)

lOOl

Oxidative degradation of lubricating oilsAtmospheric oxygen causes mostorganic substances, including lubricat-ing oil, to undergo oxidation. Suchoxidation that occurs under relativelymild conditions is called autoxidation.Autoxidation of lubricating oils leadsto many undesirable changes in per-formance that cannot be avoidedentirely as long as the oils are used inan air environment. In order 10preventoxidative degradation of lubricatingoils. they are usually formulated witha variety of antioxidants. Molecularstructures of base oils of lubricatingoils also are very imponant to consid-er because they strongly influenceoxidative stability. Much research hasbeen directed 10 obtain synthetic-based oils whose molecular structuresare optimized for better oxidation sta-bility.

A wide variety of synthetic baseoils have been developed, Olcochem-leal-based synthetic oils, i.e .. estersof straight-chain carboxylic acidwith neopentylpolyols, are one of themost oxidatively stable base oils andcurrently arc used as high-tempera-ture lubricating oils such as Type IIjet engine oils, Optimization of thecomposition of petroleum-based oilsalso has received much attention.The composition of mineral-basedoils, i.c.. the relative distribution ofthe molecular types such as paraf-finic, naphthenic, and aromatichydrocarbons and certain sulfur andnitrogen-containing species, isknown to affect the oxidative stabili-ty of lubricating oils, This reviewpaper first explains the basic mecha-nisms of the autoxidation of hydro-carbons and its prevention in order tounderstand the process of oxidativedegradation of lubricating oils. Nextthis article introduces some recentinvestigations that have allowed theprediction of useful oxidation life oflubricating oils by applying kineticsof hydrocarbon autoxidation and itsprevention.

Mechanism of hydrocarbon autoxi-dation and its preventionAutoxidation of hydrocarbons. Autox-idation of hydrocarbons and oleo-

J.... T.""'" H.U1aIa ....

T1W aTtick was p"ptJRd by Jinichi IBtJl'WIii. TosJrio Yoshida, andHanunichi ~. C~1IIrD1T«IuaictJJ ~MQn:h UIboratory,Nippon Oil Co, Ud.. 8Chidori-dto. Naka-bl. yotohama, Kanogawa23/. Japan.

chemicals, including lubricating oils.is a radical chain process in whichfree radicals are reaction intermediates(1,2). Figure I includes six reactionsthat show the main elementary reac-tions involved in this process.

The first step for each chain reac-tion involves the production of a freeradical from a hydrocarbon molecule(Reaction I). Such "spontaneous"chain initiation is thought to be the

reaction between the hydrocarbonand the dissolved oxygen (3,4), butthe reaction is very slow and itsdetails are not clear, AI elevated tem-peratures (higher than 100°C), whichlubricating oils may encounter inservice, radical decomposition ofhydroperoxides (ROOH), formed inthe propagation reaction, becomesthe main initiation for the autoxida-tion (Reaction I'). Thus, once the

ReactionInitiationRH

_ R' Oenerencn of free radical (I)

Decomposition of bydropemxlde (t')RooH

{-on

RH+ .oR

_ R{)o+-QH

{H20

_ R' +ROH

PropagationR' + O2

ROO- + RH

_ R{)()o (2)

(3)_ ROOH+R'

Termination

2R'_ R-R

_ ROOR

_ ROOR (~kelOl'lC, akohoI) + O:!

(4)

(5)

(6)

R' + ROO-

2R{)()o

Agure 1, Initilltlon, profNIglltion, lind termination reactions

tNFORM.Vol. 7.00. 9 (September 1996)

1002

{aROOH has been formed, oxidationproceeds spontaneously and at anincreasingly faster rare. This is thereason the reaction is called autoxi-dation.

The radical R· reacts very quicklywith oxygen to form peroxyl radicalROO- which, in a subsequent muchslower step. attacks RH to formhydroperoxides and a new R- (propa-gation steps 2 and 3). The propagationsequence of Reactions 2 and 3 contin-ue in a chain reaction until finally thefree radicals (R- and R()()') form sta-ble inactive products through thebimolecular radical-radical termina-tion (Reactions 4. 5, and 6). In otherwords, each time one reaction is initi-aled, a large number of hydrocarbonmolecules may be oxidized intosoos.

The overall rates of hydrocarbonautoxidation depend on the rates ofthe initiations. propagation, and termi-nation reactions described above.Under ideal conditions, in which thereis enough supply of oxygen, the over-all rate of autoxidation is given byEquation I.

;/\RHI = ;/\°2]- d[ROOH) =dl dl dl

~[RH)Rill2(2k!) [I)

Overell rete of oxld.tlon wn.re RI. rate ofInltl.tlon. (M.-'): kp. rete ecnetent forprop41getlon (Reaction 3, M-''-'): kt. ratecon.tant for termination (Reaction 8,M-'.-')

At specified rates of chain initia-tion, the rate of hydrocarbon autoxi-dation is determined by the values ofkp and 2k,. The oxldizabitiry of thehydrocarbon is given by the ratiokrl(2k,) Itl. Ingold (I) and Howard (2)of the Naricnal Research Council ofCanada have measured the propaga-tion rate constant, kp' for a wide vari-ety of organic substrates. The valuesof kp at 30DC have been correlatedwith the strengths of the C-H bondsthat are broken. DIR-HJ (5). Twoempirical relations have beenderived. one for tertiary peroxyl radi-

OLEOCHEMICALS

oo-I

- CH(CH:z}mCH2 - -+-

OOH oo-I I

- CH(CH:z}mCH -

OOHI •

- CH(CH:z}mCH -

o OOHII I

-+- -C(CH1)mCH - +H(}O

o OOHII I

RCCH~HR'

o 0II II

-+- - RC OH + CHlCR'

Scheme 1, (a) Intramoleeullr hydrogen abstrKtlon reactions: (b) decom~sffion of e, 'f"hydroperoxyketones

cals (Equation 2) and one for sec-

log [.tp'.ROQ>per active hydrogen/(M·II·I») _

IS.4-0.2D(R-H»)

121

ondary peroxyl radicals (Equation3).

log [kp'.ROQ>per active hydrogen/(M·ls·I))_

16.4- O.2D(R-H)1

131

These equations hold extremelywell for hydrocarbons and reason-ably well for substrates containingbereroatoms, i.e .. esters and alky-lene glycols. The activation ener-gies and pre-exponential factors foroxidation of some hydrocarbons byt-butylperoxyl radical also havebeen measured. and the empiricalrelation (Equation 4) has beenderived.

Ep'·ROQ>flkcallmol)J = O.SS(D(R-HJ - 62..5)

141

These empirical equations per-mit the calculation of the rate con-stants for chain propagation in theautoxidation of many organic sub-strates at a wide range of tempera-tures.

(b1

Oxidation of polyol ester syntheticlubricating oilsKinetics and mechanism of hydrocar-bon autoxidation at elevated tempera-tures. As described previously, differ-ences in the rate of oxidation hydro-carbons having different structurescan be roughly estimated from Equa-tions 1-4 even at high temperature.However. no information is given as totheir kinetics and mechanism of for-mation or the important oxidationproducts such as carboxylic acids,ketones, and alcohoJs, etc., that lead tothe deterioration of various kinds orlubricant performance (6).

At high temperatures, thehydroperoxides, ROOH, formed in thepropagation reaction. no longer existas stable compounds. They undergoradical decomposition and yield verycomplex mixtures of carboxylic acids.ketones, and alcohols. Furthermore,the occurrence of chain-branchingreactions yielding free radicals leads10 autocatalysis at low conversionsand also increases the oxidation rate toa point where it is difficult to maintainoxygen saturation in the liquid. Con-sequently the rates of reactionsbecome controlled by the rate of oxy-gen mass transfers, and kinetic inter-pretation or the results of such experi-ments become meaningless.

Excellent research on the autoxida-tion of kinetics or hydrocarbons at ele-vated temperature was accomplishedby Jensen et ai. (7.8) or Ford MotorCompany. The main problem of theinsufficient oxygen supply to the liq-uid was solved by devising and utiliz-

INFORM. Vol. 7. no. 9 (September 1996)

1003

ROO- + A" _ Inactive productS (8)

sent PAN and the aminyl radical400

-C,

300." • n·Ct,:§.•l!·c

200&0

.2~ • n-C1~.s

100

• n-C,

0I 2 3 4

lo1IN3[RH]M-1

Agure 2.. InhibiUon period. from the phenykJ-n.lphthylamlne-lnhlbited .utOltldation of.Itrliight~n pentMrythrtto/ .Ikllno.tn at 232"C Q.' reactivity parameter, 1INalRHJ

ing an ingenious stirred-now microre-actor. Using hexadecane as a modelhydrocarbon and analyzing the oxida-tion process in detail, the formationmechanisms of carboxylic acids,ketones, and alcohols formed in thehexadecane autoxidation at elevatedtemperature was first kinetically eluci-dated. The major points in the reactionmechanisms are shown in Scheme 1.

The intramolecular hydrogenabstraction reaction has been recog-nized in branched hydrocarbons withtertiary hydrogen atoms (polypropy-lene, for instance), but it was clearlyconfirmed in n-alkane for the firsttime. Polyfunctional products (di- ortrihydroperoxides), in addition to thehydroperoxy-ketones, are formed bythe intramolecular hydrogen abstrac-tion reactions even in the very earlystages of the reaction (in the range of0.1-2.3 mol% conversions), The dis-tributions of the difunctional productsobtained in this study was in completeaccord with the results reported inhydrocarbon oxidation studies in thegas phase at 400-500°C. Thus it wasfirst verified that essentially the samereaction as in the gas phase alsooccurred in the liquid phase,

Theoretical calculation of oxida-lion life of polyo/ ester lubricating

R()()o + AH ----+ ROOH + A- (7)

derived from PAN, respectively, Theradical A- generated above is suffi-ciently stable to undergo the radical-radical reaction shown in Reaction 8,

oils. Based on the results of thekinetic and mechanistic studiesdescribed previously, Korcek and co-workers (9-11) conducted the kineticstudy of the oxidative degradationand its prevention for polyol esterslubricating oils. The polyol esters,which are trimethylolpropane or pen-taerythritol esters of straight-chaincarboxylic acids, are generally usedas base oils for Type II jet engineoils. Figure 2 shows the oxidationlife of polyol esters inhibited withphenyl-a-naphthylamine (PAN), oneof the most effective chain-breakingantioxidants for high-temperaturelubricating oils. Oxidation test wascarried out at a very high tempera-tures of 23rC. Induction periods,the elapsed limes until rapid oxygenuptake occurred, were regarded asthe oxidation life of the polyolesters.

The free radical chain reaction inthe autoxidation of hydrocarbons andoleochemicals, such as esters, wasinhibited quite effectively in the pres-ence of a small amount of chain-breaking antioxidants such as PAN(12,13). PAN provides a hydrogenatom to the peroxyl radical andbecomes a fairly stable aminyl radical(Reaction 7), where AH and A- repre-

11N3(RH} on the horizontal axis ofFigure 2 was introduced as a reactivityparameter by Korcek et at. N3 is thenumber of hydrogen atoms in amolecule of the esters which areabstractable by the peroxyl radicals.As is seen from Figure 2, the longerthe alkyl chain of the straight-chaincarboxylic acids, the shorter the oxi-dation life of the polyol esters. Theimportant point is that the oxidationlife is even shorter than that estimatedfrom the reactivity parameter. Korceket al. postulated that this was a resultof the ease of intramolecular hydrogenabstractions reactions. It was foundthat the rate of the intramolecularabstraction is 5-8 limes faster thanthat of intermolecular hydrogenabstraction in the model system ofhexadecane and about 20 times fasterthan in the pentaerythritol esters(9,11). Consequently, the easier thehydrogen abstraction reaction (easierin long-chain carboxylic acids), theeasier is the oxidation, which leads tothe short oxidation life. It should benoted that the rates of oxidation ofpolyol esters at high temperature aremuch smaller than those of hydrocar-bon synthetic oils such as poly--ole fins, even in the longer alkylchain carboxylic acid esters (smalleroxidizability, see Equation I). This isthe reason why polyol esters currentlyare used as the base oils of Type IIjetengine oils exclusively.

Taking into account the intramolec-ular hydrogen abstraction reaction, theoxidation life of the polyol esters inthe presence of PAN was theoreticallycalculated by the numerical integra-tion with a computer as the timeelapsed until PAN was consumed

tNfORM.Vol. 7. no. 9 (September 1996)

1004

OlEOCHEMICALS

20~

~ SIC" "0.85

;l 16~0

1 12E,

"g00• 8~S~~• 4e SIC ..." 0.15g

~ 04 8 12 16

rc, + 5) x ~~ moI'J>

Allure 3. Correlation betwMn oxidation lime to reach the oxygen consumption 01 0.4moll\... and (:ompolltion parameler (eA + 51 II: CplCN

completely. The calculated valueagreed very well with the experimen-tal value, indicating that the complexoxidative degradation of lubricatingoil at high temperatures can be esti-mated accurately from kinetics andmechanism of hydrocarbon antioxi-dants.

Oxidation of turbine oils formulatedwith mineral-based oils and antioxi-dantsRelation between tile base oil com-position of lubricating oils and theoxidative stability: oxidation of min-eral-based oil without autaxidarus.Petroleum-based, mineral-based oilsare extremely complex mixtureswhich contain major proportions ofhydrocarbons and minor proportionsof sulfur, nitrogen, and oxygen-con-taining organic compounds. Thehydrocarbon components can beclassified into three general types:straight and branched-chain paraf-finic compounds, alkylated poly-cyclic, and fused-ring saturatedhydrocarbons. collectively known asnaphthenes. and alkylated andcycloalkylated mono- and polynucle-ar aromatics.

Alkylated and particularlycycloalkylated aromatics are oxidizedmuch more readily than saturated

hydrocarbons since they have benzylicC-H bonds, which are ca. 10 kcallmolweaker than alkane C-H bonds (seeabove). In refining, therefore, undesir-able aromatic, sulfur, nitrogen. andoxygen compounds are partiallyremoved, leaving the desirablealiphatic and naphthenic portion 10 berecovered as the final products. How-ever, extensive investigation of theoxidation of lubricating oils in thetemperature range l40-200°C haveshown that not all of the aromatic andsulfur compounds are undesirable(14). Thus, the best oxidation stabilityof base oils is obtained when aromaticand sulfur compounds are present inthe oil in optional concentrations inagreement with Von Fuchs' concept of

"optimal aromaticity" (15).Korcek and Jensen (14) evaluated

the relative oxidation stability of vari-ous base oils at 180°C and found thebest correlation between oxidationstability and composition of base oilsby introducing the compositionparameters (CA + S) X CplCN andSICA' CA' Cpo and CN are the molepercent carbon contents in the aromat-ic structure, paraffinic chains. andnaphthenic rings. respectively. S is themole percent sulfur content. The max-imum on the correlation curves foroils of a given SICA ratio determinesthe optimal composition defined byparameter (CA + S) X CplCN. Asdepicted in Figure 3, the desired baseoil composition, expressed by theparameter (CA + S) X CplCN for oilswith the ratio SICA - 0.35 was deter-mined to be between 5 and 8 molepercent and for high sulfur-containingoils (SICA - 0.8--0.9) between 6 andII mole percent. The "optimal" oxida-tion resistance for the base oils con-taining both aromatics and sulfurcompounds has been explained interms of peroxide-decomposing abili-ty of sulfur compound that wouldyield phenolic antioxidants from aro-matic hydroperoxides formed fromaromatic hydrocarbons (Scheme 2).

It was suggested that it was inadvis-able to use over-refined base stockswith (CA + S) x CplCN < 5 because oftheir tendency to "break down" veryrapidly (see discussion below, howev-er). It also was found that base oil con-taining less than optimal amounts ofaromatics and sulfur were sensitive tothe relative content of paraffinic andnaphthenic components in the saturatedhydrocarbon portion of the base oils.

OOH

©D

INFORM. VOl. 7, J"IO. 9 (September 1996)

Sc...... ,

OOH

©D

00 ~0~'~ __ ....::J.::.O -.:'::' ...;2.02-'00 r

Monoaromatics

oL-----,----'oc----,-,----wJ

tj

'j(](] \

1,(Xl) '" rSOIl

Concentration. mass 'l>

AgullI 4. Inhibition periods .rom the dl·tert-butyl p-cresollnhibited autoxidation 01hexadeeane blended with mono- and dlarornatlc traction.lrom minerai 011at 115"C

Relation between the base oil com-position of lubricating oils and theoxidative stability: oxidation of for-mulated lubricating oils. Today'slubricating oils depend greatly on var-ious additives. In particular, engineoils usually are formulated with vis-cosity modifiers for viscosity and vis-cosity index, pour point depressantsfor pour point, detergents and disper-sants for engine cleanliness, antiwearagents for wear prevention, antioxi-dants for long life, and so on. Conse-quently, the oxidative stability ofengine oils depends not only on baseoil compositions and types of antioxi-dants, but also on other additives andit becomes extremely difficult to pre-dict the oxidation stability of engineoils from the theoretical studies asdescribed above.

In contrast to the very complex oxi-dation behavior of engine oils, indus-trial circulating oils such as turbine--~--~----------~--~----~-,

oils exhibit much simpler oxidationbehavior because of low additive treat-ments and simple laboratory qualifica-tion tests associated with them. Achain-breaking, hindered phenolantioxidant is sometimes the onlyadditive for turbine oils. At the sametime, effectiveness of the hinderedphenols is strongly affected by thebase oil composition.

Nearly 30 years ago, Korcek et al.(16) revealed that base oils havingthe optimal amount of aromatics andsulfur compounds exhibit the longestoxidation life when a hindered phe-nol was added because of their goodinherent oxidation stability. However,with regard to the effectiveness of theantioxidants, such base oils respond-ed poorly to added antioxidants.Instead, base oils having smallamounts of aromatics and sulfurcompounds, though they are oxidizedreadily in the absence of antioxi-

dants, responded very well to addedantioxidants.

Recent long-life turbine oils aremanufactured from highly refinedbase stocks with a small amount ofhindered phenol antioxidants. Suchhighly refined base stocks, usuallyobtained by hydrotreating processes,are composed of saturates mostly,along with a small portion ofmonoaromatics (3-8%). The amountof polynuclear aromatics and sulfurcompounds, which act as antioxidants,and nitrogen heterocyclics, which actas prooxidants, are negligible in suchbase stocks. It has been shown that insuch highly refined base stocks theamount of monoaromauc hydrocar-bons, which are oxidized much morereadily than saturated hydrocarbons, isa key factor in detennining the oxida-tive stability of turbine oils (17,18).As shown in Figure 4, the addition ofa monoarornauc hydrocarbon reactionseparated from a mineral base oilmonotonically reduces the inhibitedoxidation life of hexadecane, a modelhydrocarbons for saturates (18). Fig-ure 4 also shows that, in contrast tothe monoaromatic hydrocarbon frac-tion, the additional of small amountsof diaromutic hydrocarbon fractionincreases the inhibited oxidation lifeof hexadecane. The inhibition of hcx-adecane autoxidation by the diarornat-ic hydrocarbons has been attributed tothe ability of the naphthalene ring toadd chain-carrying peroxyl radicals soas to produce resonance-stabilized,relatively unreactive benzocycJohexdi-enyl radicals (19,20). Thus, the naph-thalene ring acts as a chain-stoppingantioxidant for lubricating oils. Wehave confirmed that alkyl naphthalenesynthetic lubricating oils showremarkable oxidative stability, butdetails are not described in this article(21).

Among monoaromatic hydrocar-

Dynamic Properties of Interfacesand Association StructuresY.K.PiMa; and D.O. Shah, Ed~ors

To receive ordering information, call toll-free 1-800-336-AOCS in U.S. and Canadaor 1-217-359-5401, ext. 128 or fax 1-217-351-8091.

1005

1006

(9)

OLEOCHEMICALS

0.2Q 0.40

~ O.IS 0.30 !?• >0:

0.20i==to0.10+

i.' ~= [Q

0.05 0.10

O~------~----~~========-==---.J_O10 +"

Time. h

Figure 5. DIrect oxkl'tion of dl·'arl-butyl p-eresol (OBPC) in blphenyl-dlphenyl ethermhrture at lSO"C under 1.02 MP1I 0,

Figure 6. Calculated consumption ol.ntioxlo.nWln the model oil' Mving different~lIn content In~.te (.)and __ (b)..me. units

bons, naphtheno-aromatics werefound to be responsible for reducingthe oxidation life. i.e .. acceleratingantioxidant consumption. Alkylben-zenes. which had virtually no effect onreducing the oxidative stability,behaved similarly as stable, saturatedhydrocarbons. Consequently, we pre-viously have shown that the oxidationbehavior of turbine oils in laboratoryoxidation texts could be reproducedusing a mixture of hexadecane andtetralin containing di-re-r-butyl p-cresol (DBPC). the most commonlyused hindered phenol antioxidant forturbine oils. Two pure hydrocarbons,hexadecane and tetralin, are regardedas models of saturated hydrocarbonand naphthcno-aromatics in base oils,respectively.

Kinetic analysis for tile turbine oiloxidation via computer modeling. Wehave achieved computer simulationof the inhibited oxidation of modelhydrocarbon systems representingturbine oils of different composition,hexadecaneltetralin mixtures contain-ing DBPC, using the kinetic andmechanistic information obtainedfrom fundamental hydrocarbonautoxidation and inhibition studies(22). The computer simulation givesa very satisfactory agreementbetween calculated and measured

oxidation lives in the model oxida-tion system at IISoC without metalcatalysts, only when a direct oxida-tion reaction of DBPC is taken intoaccount (Reaction 9). Measurements

400.1000

occur under the condition of laborato-ry oxidation tests or actual service inpower plants (23). The simulationgives a very satisfactory agreementbetween calculated and measured oxi-dation lives. and shows that the directoxidation of DBPC is also the impor-tant process of DBPC consumptionunder these conditions. The impor-tance of the direct oxidation of DBPCdepends both on the tetralin content inthe model oils (i.e., base oil composi-tion) and on the severity of oxidationtests or operating conditions. The sim-ulation predicts that in moderatelyoperated turbine units the rate ofDBPC consumption is almost thesame regardless of the base oil com-positions, while the base oil composi-tion becomes an important factor indetermining the consumption rate inthe service units which are operatedunder severe conditions. such as existin the high-temperature regions (Fig-ure 6). Thus, under severe conditions,the presence of aromatic componentsin base oil could surely shorten theuseful oxidative life of turbine oil.

We also have conducted productanalyses of the turbine oils used inactual power plants under variousoperating conditions in order to clarifythe consumption mechanisms ofDBPC during use (24). Detailed anal-ysis of DBPC deterioration productsfrom used turbine oils shows that themajor deterioration product of DBPCis 4.4'-dihydroxyl 3,5,3',S'-tetra-ler,-butyl dibenzil (bisphenol, TBBP). Theformation of the bisphenol has beenadequately accounted for by the directoxidation of DB PC, which gives a

0.02 .------- --,

o~+ AH ---+ lnsctive prodUCt5

of DBPC consumption in nonoxidiz-able substrate prove that the DBPCconsumption actually occurs underthe oxidation condition (Figure 5).

We have extended the computersimulation study to the oxidation orthe hexadecaneltetralin model oils that

0.02

~• 0.01

":".0

(.)

30 40 50 60"000TIme.h

INFORM. Vol. 7. no. 9 (September 1996)

200 300

TIme.h

OH o-v + 0, - V + HO<>-CH, CH,

0

o- V OH 0

V - V + V2 - H,C °n-I ICH, CH, CH, CH2

0

V - + (HO-O-c+ + +(oPc+CH2

Scheme'

strong support for the conclusion thatdirect oxidation is the main process ofDBPe consumption in service(Scheme 3), The product analysis alsodiscloses that DBPe is consumedlargely by physical processes resultingfrom evaporation and other phenome-na.

Future trends or synthetic and min-erai-based oilsAs described throughout this article.esters of straight-chain carboxylicacids with neopcntylpolyols are cur-rently used as base oils for Type IIlubricating oils for aircraft gas turbineengines. Lubricating oils Formulatedfrom these base oils are more thermal-ly and oxidatively stable than Type Ilubricating oils which are based ondibasic acid esters. Lubricating oils ofeven greater stability than Type (( oilsare required for advanced aircraftengines, such as those equipped forsupersonic transports. and for ceramicgas turbine engines for automobiles.Therefore, the search for syntheticbase oils that are more thennally andoxidatively stable than Type 1.1 polyolester oils will be continued as animportant research subject. It shouldbe noted that these advanced syntheticoils must have bcuer viscosity-tern-perature characteristics. such as low-

temperature ff uidity. and be lessexpensive than Type III synthetic oils.such as polyphenyl esters and fluorinecompounds.

From the economical point of viewand worldwide availability,petroleum-based, mineral-based oilsshould remain to be widely used. Aspointed out in this article, eliminationof small amounts of "polar com-pound," such as sulfur and nitrogenheterocyclics from mineral-based oilssignificantly enhance the oxidativestability of formulated lubricatingoils. This currently is done by severehydrccracking processes. The severehydrccracking processes also yieldhighly paraffinic, very high viscosityindex: (VHVl) base oils. The VHVIbase oil, sometimes called "noncon-ventional base oil," gives excellentoxidative stability to a great variety offormulated lubricating oils. particu-larly industrial lubricating oils suchas turbine oils. The excellent oxida-tive stability of the VHVI base oil isattributed not only to the total elimi-nation of sulfur and nitrogen hetero-cyclics but also the hydrocarbon-typedistribution, i.e .. smaller amount ofaromatic hydrocarbons and higheramount of isoparaffins. It already hasbeen clarified that this hydrocarbon-type distribution highly favors the vis-

cosny-tcmperature characteristics.The optimization of the hydrocarbon-type distribution in the heterocyclics-free. nonconvenuonal base oil also isan important research subject fordesigning future high-performancebase oils.

ReferencesI. Ingold, K.U .• Peroxyl Radicals,

Accounts Chern. Res. 2: 1-7(1%9).

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3. Denisov, E.T.• Formation of FreeRadicals in the System RH + O2,Part I.Tetralin. Cycjohexanol andCyclohexanone, Kinetika iKatali4,53-59 (1965).

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5. Korcek. S., J.H.B. Chenier, J.A.Howard and K.U. Ingold, Abso-lute Rate Constants for Hydrocar-bon Autoxidation XXI, Activa-tion Energies for Propagation andthe Correlation of PropagationRate Constants with Carbon-Hydrogen Bond Strengths,Caned. J. Chem. 50:2285-2297( 1972).

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7. Jensen. R.K., S. Korcek , L.R.Mahoney and M. Zinbc, Liquid-Phase Autoxidation of OrganicCompounds at ElevatedTemperatures, I, The StirredFlow Reactor Technique andAnalysis of Primary Productsfrom u-Hexadecane Autoxidationat 120-18O"C, J. Am. Chem. Soc.101:7574-7584 (1979).

8. Jensen. R.K .. S. Korcek , L.R.Mahoney and M. Zinbo, Liquid-Phase Autoxidation of OrganicCompounds at Elevated Tempera-tures, 2, Kinetics and Mechanismsof the Formation of Cleavage Prod-ucts in n-Hexadecane Autoxida-

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tion, Ibid. 103:1742-1749 (1981),9. Hamilton, E.1. Jr., S. Korcek,

L.R. Mahoney and M. Zinbo,Kinetics and Mechanisms of theAutoxidation of PentaerythritolTetrahcptanoatc at 180-220DC.1111.J. CIIt:",. Killer. 12:577-603(1980).

10. Mahoney, L.R., S. Korcck, J.M.Norbeck and R.K. Jensen, Effectsof Structure on the Thcrmoxida-live Stability of Synthetic EsterLubricants. Theory and PredictiveMethod Development, ACSPreprint Div. Petrol. Chem.27,350-361 (1982).

1I. Jensen. R.K., S. Korcck and M.Zinbo, Oxidation and Inhibitionof Pcntaerythritol Esters, J. S)'nth.Lubt: /(2)091-105 (1984).

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(1975).15. Von Fuchs, G.H., and H. Dia-

mond, Oxidation Characteristicsof Lubricating Oils, Ind. Eng.Chern.34:927-937 (1942).

16. Korcek, S., J. Baxa and V. Vesely,The Oxidation Stability of Lubri-cating Oils. VnJ, The OxidationStability of Sulfur ContainingLubricating Oils in the Presenceof 2,6-Di-tert-butyl-4-methylphe-nol, Erdol Kohle 2/:462-468(1968).

17. Murray, D.W.. J.M. MacDonald,A.M. White and P.G. Wright, ANew Concept of Lubricant BaseOil Quality, Proc. 11th World.Pet. Congr: 4:447-461 (1984).

18. Yoshida, T., and H. Watanabe.Effects of Chemical Compositionon Oxidation Stability of Inhibit-ed Lubricating Oils, Part I,Oxida-tion Characteristics of Chro-matographed Fraction of Lubri-cating Oils, Bull. Japan Pet. ItISt.23(5)303-309 (1980).

19. Igarashi, J., 1. Lusztyk and K.U.Ingold, Autoxidation of Alkyl-naphthalenes, I, Self-inhibitionDuring the Autoxidation of 1- and2-Methylnaphthalenes Puts aLimit on the Maximum PossibleKinetic Chain Length. J. Am.

Chem. Soc. 114:7719-7726(1992).

20. Igarashi, J., R.K. Jensen, J.Lustzyk, S. Kcr cek and K.U.Ingold, Autoxidation of Alkyl-naphthalenes, 2. Inhibition of theAutoxidation of Hexadecane at160°C, Ibid. 114:7727-7736(1992).

21. Takashima, H., Development ofLong Drain Rotary Air Compres-sor Lubricants, Proc. of Japantnt, Tribal. Confr. Yokohama1005 (in press).

22. Igarashi. J., and T. Yoshida, Com-puter Simulation of Turbine OilOxidation, I, Consumption of aHindered Phenol Antioxidant inModel Hydrocarbon Systems at115°C, Lubrication Science7(1),3-23 (1994).

23. Igarashi, J., and T. Yoshida. Com-puter Simulation of Turbine OilOxidation, 2, Consumption of aHindered Phenol Antioxidant inLaboratory Oxidation Tests andin Service, Ibid. 7(2):107-131(1995).

24. Yoshida, T., and J. Igarashi, Con-sumption of Antioxidants of Tur-bine Oil in Service Unit, Tribol-og)' Transactions 34:51-58(1991). •

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