Journal of the Institute of Petroleum, Vol. 31, No. 264

V o l . 31. N o. 264. D e c e m b e r 1945.

CORRELATION OF CHEMICAL CONSTITUTION AND OXIDATION SUSCEPTIBILITY OF LUBRICAT­

ING OIL COMPONENTS.*

B y S. F r e d e r i c k K a p e e ,- ) - J o h n R . B o w m a n ,£ and

A l e x a n d e r L o w y . §

Abstract.

T h is p a p e r p re sen ts a s tu d y of th e influence of chem ical c o n s titu tio n on th e su sce p tib ility to o x id atio n of th e several g en eral ty p e s of co m p o n en ts in p e tro leu m lu b ric a tin g oils. A fra c tio n a tio n of a P e n n sy lv a n ia lu b ric atin g o il-stock h a s b een effected b y d istillatio n a n d e x tra c tio n . T h e p h y sical p ro p e rtie s of th e frac tio n s a n d th e ir chem ical c o n stitu tio n s as calcu la te d b y W a te rm a n ’s m e th o d a re re p o rte d . S elected frac tio n s w ere oxidized, a n d th e e x te n t of o x id atio n w as m ea su re d b y th e a c id ity developed a n d b y th e increase of viscosity.

S im ilar tr e a tm e n t w as th e n a p p lied to a different sto ck ; frac tio n s from th e tw o sto c k s gav e th e sam e b e h av io u r on o x id atio n .

F ro m th e collected d a ta , som e g en eralizatio n s h av e been m ad e concerning th e dependence of o x id atio n su sce p tib ility on chem ical co n stitu tio n .

In t r o d u c t i o n.

A l t h o u g h a g reat am ount of research has been done on th e oxidation of petroleum oils, m ost of it, of necessity, has been of em pirical nature.

Thus, it is generally believed th a t paraffinic oils form acidic oxidation products m ore readily th a n do more cyclic oils, while th e opposite is tru e with regard to sludge precipitation. Arom atic compounds, a t least in high concentrations, are easily oxidized, y et there are indications th a t natural traces of them m ay act as anti-oxidants. N early all th e broad knowledge of th is kind is purely qualitative in character.

The recent developm ent of highly efficient m ethods of fractionation and the establishm ent of correlations betw een physical properties and chemical constitution now enable th e p reparation and recognition of very hom o­

geneous fractions. The recording of findings concerning th e behaviour of such fractions on oxidation is th e principal object of this paper.

U nfortunately, no oxidation tests perm it clean-cut interpretation. The oxidation can be carried out under a great v ariety of conditions, and m any of its results can be m easured, b u t all indications are of functional ra th er th an basic significance. The tw o types of effects selected for investigation here, developm ent of non-volatile acidity and increase in viscosity, appeared to be th e m ost nearly fundam ental of th e simple changes to be recognized.

* A b s tra c te d from a th esis p re sen te d b y S. F re d e ric k K a p ff to th e G ra d u a te School of th e U n iv e rsity of P itts b u rg h in p a r tia l fulfilm ent of th e req u ire m en ts fo r th e P h.D . degree. (C o n trib u tio n N o. 566 from th e D e p a rtm e n t of C hem istry, U n iv e rsity of P itts b u rg h , a n d from th e M ellon I n s titu te of In d u s tria l R esearch.)

t D istilla tio n P ro d u c ts, In c ., R o ch ester, N .Y .

f S enior Fellow , M ultiple Fellow ship on P etro leu m , M ellon I n s titu te of In d u s tria l R esearch , P itts b u rg h , P a .

§ F o rm e rly P rofessor of C hem istry, U n iv e rsity of P i tts b u r g h ; died, D ecem ber 25,

1 9 1 1 . _ -

B o th alteratio n s concern th e oil molecule itself, n o t fragm ents broken off b y th e ac tio n ; th e first change m ay roughly be ta k e n as a m easure of a tta c k on th e side-chains, a n d th e second, even m ore roughly, as a n indica­

tio n of consequent condensation.

Fr a c t i o n a t i o n o f t h e Oi l s.

The fractio n atio n of th e lubricating oil-stock followed, in an ab b reviated fashion, th e fractio n atio n of “ w ater-w hite oil ” b y R ossini a n d his co­

workers a t th e N atio n al B ureau of S tan d ard s, u n d er A .P .I. P ro ject No. 6.8 T he oil was first subjected to system atic fractional distillations, a n d th e distillate cuts, in tu rn , were subjected to fractio n al ex tractio n . The o u t­

come is a square a rra y of m an y fractions, a rran g ed in one direction by m olecular size (distillation) a n d in th e oth er b y m olecular ty p e (extraction).

D etails of th e a p p a ra tu s an d procedure follow.

Distillation.

As th e lightest com ponents of th e stock fra ctio n ated h a d m olecular weights of over 300, all distillations were perform ed u n d er high vacuum . Simple pot-stills were used up to a tem p e ra tu re of 300° C., corresponding to a molecular weight of ab o u t 500, an d beyond t h a t p o in t m olecular distillation was em ployed.

Pot-Stills. The ty p e of p o t-still em ployed is illu strated in Fig. 1; it is of all-glass construction a n d conventional design. The still-pot is a 1- litre spherical flask provided w ith filling an d vap o u r tu b es. T he former has a ground-glass stopper carrying a th erm o m eter well.

The p o t was h eated electrically b y ring-heaters b o lted on th e underside of a solid alum inium block, th e u p p er surface of th e la tte r being machined to fit th e bo tto m of th e pot. This arrangem ent gives v ery uniform heating to th e charge, reducing local a n d “ skin ” overheating. T he entire pot an d h eater assem bly was enclosed in a n a ir-b ath . T he fairly uniform te m p era tu re established in th is space p rev en ts condensation on th e upper p a rts of th e pot.

S trictly speaking, no rectifying colum n is provided in th e v ap o u r line;

a t th e pressures em ployed no appreciable enrichm ent can be o btained by an y ty p e of c o untercurrent contacting o f v ap o u r a n d reflux. T he vapour line, however, does carry th re e th in bulbs enclosed in a silvered evacuated jacket. This device serves m erely as a v ap o u r riser to sep arate th e con­

denser from th e h o t air b a th aro u n d th e p o t ; th e bulbs act to give sufficient m echanical flexibility to to lerate th e difference in expansion betw een the jack et an d th e colum n proper.

Above th e jack et th ere is an off-set to catch en tra in e d distilland. Of th e several devices stu d ied in th is lab o rato ry , th is one is b y far th e m ost satisfactory for suppressing e n tra in m en t in high-vacuum distillations.

The problem is im p o rta n t because th e vapour velocities are alw ays exceed­

ingly high, an d th e v apour te n d s to ca rry w ith it large am o u n ts of spray.

I n th e arrangem ent shown, th e large v apour velocity is used to ad v an ta g e, for th e sw iftly m oving droplets are th ro w n against th e walls of th e tu b e a t th e bend. Such an off-set, however, offers little resistance to th e flow of th e vapour its e lf; m ost other devices, such as baffles an d V igreux points, 454 K A P F F , B O W M A N , A N D L O W S ' : C H E M IC A L C O N S T IT U T IO N A N D

O X ID A T IO N S U S C E P T I B I L IT Y O F L U B R IC A T IN G O IL C O M P O N E N T S . 455 introduce large pressure drops a t high vapour velocities. The off-set is n o t o f convenient shape for jacketing, so it is provided w ith a light winding of nichrom e wire electrically h eated to m aintain it in approxim ately ad iab atic condition.

Fi g. 1.

H I G H V A C U U M P O T S T I L L .

The condenser is m erely a vertical air-cooled tube. Vapour rises in it, a n d th e condensate runs down th e inner surface to an annular trough.

F rom th e collecting trough th e distillate runs to th e receiver. T he receiver system has th ree stopcocks, so th a t th e receivers m ay be changed w ithout breaking th e vacuum or in terru p tin g th e distillation, a conven-

tio n al arrangem ent. A t th e to p of th e condenser a 1-litre bulb serves as a surge ta n k to m a in tain th e vacuum while a new e m p ty receiver is being e v a c u a te d ; a m anom eter indicates th e course of th is evacuation, revealing w hen th e receiver, th e still an d th e vacuum line m ay again be connected together.

A re -e n tra n t tu b e in th e surge-bulb serves as a t r a p ; it m ay be filled w ith a d ry ice-acetone m ix tu re during runs, b u t th is p reca u tio n is scarcely necessary.

The vacuum was n o t controlled, b u t was m erely th e b est t h a t th e pum p used could p ro d u c e ; it ran g ed betw een OT a n d 0-01 m m . H g.

L ittle need be said ab o u t th e o peration o f th e p o t-stills o th er th a n th e m ention of a few precautions, principally th e necessity of low -tem perature degassing. A fter regreasing all stopcocks a n d charging, th e p o t m ay be h eated rap id ly u p to ab o u t 100° C., b u t m u st be held a t th is tem p eratu re under vacuum u n til all bubbling ceases. As is well know n, oils dissolve large am o u n ts of air. This air is released ra th e r slowly even a t high vacuum an d high te m p eratu re, a n d unless it is com pletely rem oved before th e high distillation tem p eratu res are reached, o xidation m ay occur to a serious e x te n t. Incom plete degassing has freq u en tly been observed to yield d istin ctly coloured distillates from w ater-w hite distillands.

The h e a t in p u t to th e stills was reg u lated to give a d istillatio n ra te of a b o u t 5 m l./m in. Some tria l ru n s on relativ ely w ide cuts show ed th a t, at least as far as viscosity is concerned, th e separations o b tain ed are not d ependent on d istillatio n ra te in th is region.

A t no tim e was th e p o t tem p e ra tu re allowed to exceed 300° C. Trial ru n s on several oils of varied ty p es d em o n stra ted t h a t none underw ent pyrolysis (as in dicated by gas form ation) a t th is te m p e ra tu re, b u t th a t m any did ap p ear to break dow n a t slightly higher te m p e ra tu res. Oils of high sulphur co n ten t presen t a n exception, some of th e m producing gas at m uch lower tem peratures.

T est of th e rm a l stab ility is easily m ade by closing th e stopcock in the m ain vacuum line during a distillation. I f a n appreciable a m o u n t of gas is being evolved, it collects in th e surge-bulb, increases th e pressure, and quickly stops th e d is tilla tio n ; below pyrolysis tem p e ra tu res distillatio n will continue alm ost indefinitely w ith o u t pum ping.

A w ord ab o u t te m p e ratu re m easurem ent a n d its significance in high vacuum distillation m ay be in place here. T he th erm o m eter in th e p o t of such a still is used only to indicate th e a tta in m e n t of a safe m axim um tem p e ratu re, and, therefore, w hen th e d istillatio n should be stopped.

These tem p eratu res are definitely n o t re p ro d u c ib le ; th e y will frequently differ as m uch as 15° C. for successive ru n s on th e sam e m aterial w ith th e same percentage ta k e n overhead, a consequence of su perheating, which is always present to a large e x te n t in v acu u m pot-stills. T he am o u n t of superheat depends critically on th e d istillatio n r a te a n d th e p re s s u re ; it cannot be reduced to even a sm all value, a n d th e m ost accu rate control of pressure an d h e a t in p u t will n o t hold it ap p ro x im a tely co n sta n t or reproducible.

N o effort was m ade to m easure vapour tem p era tu res. H ere, of course, superheating does n o t interfere, b u t, on th e o th er h an d , ra d ia tio n is a p t to be so large th a t equilibrium is n o t achieved, a n d pressure effects are still as 456 K A P F F , B O W M A N , A N D L O W Y I C H E M IC A L C O N S T IT U T IO N A N D

large as for liquid tem peratures. Consequently vapour tem peratures were considered to be of no significance.

E xperience has shown th a t an operator can ru n th ree of these stills sim ultaneously.

Molecular Still. The m olecular still used (Fig. 2) was of th e conventional

O X ID A T IO N S U S C E P T I B I L IT Y O F L U B R IC A T IN G O IL C O M P O N E N T S . 457

M OLECTJLAJR s t i l l.

concentric tu b e , flowing film ty p e ; th e rad ial clearance betw een th e evaporator (inner tube) and th e condenser (outer tube) was 1-0 c m .; th e evaporator was 100 cm. long and 2-5 cm. o.d.

P erhaps th e only novel feature of th is still was th e m ethod of heating th e evaporator w ith m ercury vapour. The inside of th e tu b e com m unicated w ith a welded steel boiler by a K ovar glass-m etal seal. A side arm on th e boiler led th ro u g h a rubber hose to an evacuated levelling bulb, and another

side arm carrying a U -shaped tra p connected th e system w ith th e vacuum line. The levelling bulb contained electric co n tacts for controlling th e h e a t in p u t to th e boiler th ro u g h a relay.

I n operation th e entire a p p a ra tu s was first evacuated. T hen th e h eat was tu rn e d on th e m ercury boiler. Soon a fter th e m ercury s ta rte d to vaporize, sufficient liquid condensed to fill th e tr a p of th e glass side arm , sealing off th e whole m ercury system from th e re st of th e a p p a ra tu s. As heating was continued, th e v apour pressure of th e m ercury increased, forcing liquid m ercury up in to th e glass side arm , w hich served for te m ­ p era tu re indication, a n d also in to th e levelling bulb, w hich provided te m ­ p era tu re control. T he tem p e ra tu re was easily set a t a n y desired value by changing th e height of th e levelling bulb.

Degassing was accom plished b y ra d ia n t h eaters w ith reflectors (not shown in th e figure) directed on th e charge-bulb a t th e to p of th e ap p aratu s.

E xperience has in d icated t h a t satisfacto ry rem oval of air can best be achieved b y m aintaining a te m p eratu re of ab o u t 100° C. overnight under high vacuum .

Two additional bulbs, identical w ith th e charge-bulb as illu strated , were used as receivers. T he arran g em en t o f stopcocks th ereo n enabled suc­

cessive distillations on a single b a tch w ith o u t breaking th e vacuum over th e oil. A fter a charge h a d been placed in th e to p bulb a n d degassed, and th e ru n m ade, th e residuum receiver an d th e charge-bulb were interchanged, w ith all stopcocks closed, a n d an o th er pass could be accom plished w ithout fu rth e r degassing.

T he am o u n t of distillate rem oved on a single pass depends, o f course, on th e te m p eratu re an d th e flow ra te as well as on th e n a tu re of th e charge.

Conditions for producing a cu t of desired volum e were found b y trial.

U sually th e tem p era tu re could be set ra th e r closely b y approxim ation, an d fine ad ju stm e n t could be m ade b y changing th e flow ra te as th e first few m illilitres ra n th ro u g h . D rop-counting tip s w ere pro v id ed on the lines to th e tw o receivers, an d b y w atching th em th e distillate : residuum ra tio could be determ ined quickly.

The distilland th ro u g h o u t ra te was usually set a t ab o u t 100 ml. p er hour, b u t th is ra te could be doubled for th e lig h test fractions or h alv ed for the heaviest ones.

D istillation Procedure.— F o u r cycles of system atic fractio n a l distillation were applied to th e stocks. Twelve litres of stock oil was used in each case.

T he 12 litres of stock was distilled in several batches to give fifteen app ro x im ately equal d istillate cuts, an d corresponding cuts were com bined.

T he fifteen p rim ary fractions so o b tain ed were in tu r n distilled in to ab o u t te n cuts each, for w hich viscosities were determ ined a t 100° F . A fter re ­ arranging these secondary fractions in order of ascending viscosity, th e y were com bined to give a new set of fifteen p rim ary fractio n s of ap p ro x i­

m a tely equal volum e. This cycle was rep eated four tim es ; th u s th e fifteen large p rim a ry fractions were distilled to afford te n sm all secondary fractions each, an d th e la tte r were th e n blended back, on a viscosity basis, to again give p rim ary fractions ; afte r four such cycles th e overlap of properties am ong th e fractions was practically nil, except for th e tw o lig h test ones.

The pot-stills were applicable for slightly over h a lf of th e distillations.

458 K A P F F , B O W M A N , A N D L O W Y : C H E M IC A L (JUJN s i n u n u n . 1 <'

U A H 9A T IO N S U S C E P T I B I L IT Y O F L U B R IC A T IN G O IL C O M P O N E N T S . 459 I n each instance, as m entioned, th e distillation was tran sferred to th e molecular still, where th e tem p era tu re reached 300° C. The residue from th e pot-stills, hoiling ab o u t 300° C., sta rte d distilling rapidly in th e m ole­

cular still a t 175° C .; and tak in g th e tem p eratu re up to 300° C. in th a t still left only a few per cent, as residuum , which was

n o t fu rth e r tre a te d or exam ined.

Solvent Extraction.

The ex tracto rs, of w hich tw o were b uilt, are illustrated in Fig. 3. They difFer principally from conventional models 3 h v being lo n g e r; th e length of th e colum ns proper was 100 feet. A fter difficulty had been experienced from bum ping, a side tu b e was sealed in to th e upper p a rt ju s t below th e boiler, through w hich a slow, fine stream of dry carbon dioxide was bubbled.

I n operation, th e solvent was boiled off a t th e top, and, a fter condensation, was allowed to rise through th e charge in th e reservoir a t th e bottom . As th is fresh solvent dissolves some of th e oil, it rises again th ro u g h th e column to th e boiler. R e­

moval of th e solvent th e re causes precipitation of dissolved oil as a fine emulsion, an d th e precip itated droplets th e n fall down th e column, countercurrent to th e fresh ex tra c t phase.

Use of ap p a ra tu s of th is ty p e considerably lim its the choice of solvent. I n addition to being low- boiling, th e solvent m ust have a lower density th a n the oil, or, m ore strictly, it m u st form system s w ith th e oil in w hich th e e x tra c t phase always has a lower density th a n th e raffinate phase, even after processing th ro u g h m any effective tran sfer units.

This requirem ent is stringent, because highly arom atic oils m ay yield ex tra cts of relatively high density.

Acetone was selected as th e basic solvent. I t has nearly ideal properties for ex trac tio n of th e in te r­

m ediate distillate fractions. A pparently no one unm ixed solvent exists w hich is suitable for all th e varied close cuts which were stu d ied ; th e lightest cuts were alm ost w holly miscible w ith acetone, a n d th e heaviest alm ost insoluble. Solvent modifiers were therefore em ployed to produce m ixed solvents.

Fi g. 3 . S O L V E N T E X T R A C T O R .

A nhydrous m ethanol was found to be excellent for reducing solubility, an d a hexane cu t equally good for increasing it. The la tte r was a 5-25 per cent, fraction of a commercial hexane, rich in 2 : 3-dim ethylbutane. The th ree solvents boil a t n early th e same tem perature, and even te n d to form azeotropes boiling only slightly lower, so th a t little change in com position is induced b y th e simple distillation w hich rem oves solvent from th e boiler.

T hus, for th e lightest distillate th e solvent used was pure m ethanol;

for th e succeeding cuts acetone was in troduced in increasing a m o u n ts ; for th e six th th ro u g h th e te n th pure acetone was em ployed. F in ally , for fractio n eleven, 3 per cent, of th e hexane cu t was added, a n d for th e fifteenth fractio n a 15 per cent, ad d itio n was necessary.

The g reat length of th e ex tracto rs m ade th e m v ery efficient, b u t a con­

siderable tim e was required for th em to reach equilibrium , as found by a semi-micro aniline-point d eterm ination. A stea d y sta te was assum ed to p revail tw enty-four hours afte r th e aniline p o in t of th e solvent-free ex tra c t failed to fall m ore th a n 0-5° C. in tw en ty -fo u r hours. This period was alw ays several days, often te n days a t th e extrem e of th e series.

A fter equilibrium h a d been a tta in e d , th e entire contents of th e boiler were rem oved an d th e solvent was strip p ed from it w ith a sm all continuous tube-still.

A few tria l te sts showed th a t, w ith m aterials such as th e final distillates from th e stocks exam ined, th e overlap of properties for successive ex tra c t fractions was nil. This tria l was m ade b y a sim ple e x tractio n , in a sep arato ry funnel, of tw o successive e x tra c t fractions. T he am o u n ts of solvent were so chosen th a t th e raffinate phase of th e first a n d th e e x tract phase of th e second fractio n were v ery sm all portions of th e whole. The aniline points of these “ in itial ” e x tra c t an d raffinate oils p roved to be identical, proving th a t, u n d er th e conditions em ployed, th e efficiency of the e x tracto rs was lim ited only b y th e size o f th e fractions. Since th e com­

positions of th e cuts produced b y one pass th ro u g h th e e x tra c to r were n early m u tu ally exclusive, no successive fra ctio n atio n was required, as had been necessary in th e case of th e distillatio n separations.

E ach of th e final distillate fractions, therefore, was passed th ro u g h an ex tra c to r once, an d was so divided in to ab o u t te n fractions of n early equal volum e. These e x tra cts were th e principal m aterials stu d ied w ith respect to physical properties, chem ical c o n stitution, an d o x id atio n characteristics;

each of th e tw o stocks yielded ab o u t 150 such final e x tra c t fractions.

Physical Properties.

The usual physical properties were determ ined on a n u m b er of th e final e x tra c t fractions, em phasis being placed on those know n a t th e tim e th a t th e w ork was done to be specifically correlated w ith chem ical constitution.

Several series of “ key fractions ” were selected for intensive stu d y in this re sp ect; th e y were chosen a t th e tw o ends a n d th e m iddle of b o th the distillation an d th e ex tractio n sequences, respectively.

Methods. Because th e final fractions were sm all in am o u n t, only a few cubic centim etres, semi-micro te sts were devised for th e d eterm in atio n of th eir physical properties. D escriptions o f th e m ethods for viscosity 1 an d m olecular w e ig h t5 have alread y been p u b lish e d ; densities and refractive indices were m easured by conventional procedures. Aniline points were determ ined on 0-50-ml. sam ples, th e volum es being obtained indirectly b y weighing, th e den sity having previously been determ ined.

Data. The physical p ro p e rty d a ta for th e final e x tra c t fractio n s of th e principal stock stu d ied are given in Table I.

In th e code of n o ta tio n , th e first num ber is th e ordinal num b er of th e d istilla te ; u n e x tra c te d distillates have only th is sym bol. The e x tra c ts carry a second num ber, sep arated by a hyphen, which is th e ordinal num ber 460 K A P F E , B O W M A N , A N D L O W Y . ____________

TableI. Physical Properties of the LongResiduum Stockand itsFractions.

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(MC<JCOCOCOeOCOCOCOCOCOCO ¹¹

a Oo

«5

N N O H O N ^ iO H H O T ff C O O O C O

oo cb csi o 03 th cb ib 03 o cb r* <b o> I OCOOJOiOOOOOOOHHHHH I

O3Ot>I>00r-IC0l0rHe0U0-*^

II II I IS 1 IS I

a coiococoocot^THi-KMT^coiouri(Mr^eo <003Tf<i003r-IC0CC>03'<i<,-l<MTt<00C0C3O 03ONNN00C0 00M03OOOOHH1# C00000C0C00000C00000O3O3O3O3O3O3O3

O O O O O O O O O O O O O O O O O O O O O O O O O O O O O

I II II IS MS I

^ ^ ^ ^ 03 r-( cq CO-H O ^ HNCO^mcOt-OOOHHpH

£ ./? T T T ^ hhhhhhhhhhhh

1-3 h3 h3 h3 t-3 1-3 Hi 1-3 H-3 1-3 Hi t-3 h3 i-3 h3 t-3 1-3 k! >-3 1-3 t-3 h3 h3 h3 h3 H-3 i-3 1-3 1-3 h3 1-3 1-3 >-3 1-3 h3 1-3 h3 t-3 1-3 1-3

TableI—continued. Watermananalysis: ^ C atoms/molecule. g Paraffin.

W A P F F , B O WM A N , A N D L O W Y : U J i J i i i v i i U A i j oua o x j-v/j-i — ■ —

^ l | l l l l ' ^ | l ,9 | i l OS - . ° - I I | I | ° ? I I I 'T* |

« l !■1 1 M § l i l a I i l s s î s s â à à s à ' 1 1 U s ' p ' s 1 1 ' 1 1 ' « 1 1 1 § 1

Naphthene.

o i i1 1 i f i i m i m ^ | s s" s s 2 S 3 1 1 1 1 1 s m i s | m i l i u m

Aromatic.

S i i l 1 I S l i 1 1 : 1 1 l ^ l l l S I l o l 1 1 I I I S 1 1 l o i 1 1 1 1 1 1 1 1 I S 1

tH rH

V.G.C.

tH 0 0 «O H O N H O O O ' ^ I O O J H C O ’# ir t 0 0 CO IO CO

i0 i | | | | | 0 > | | | I > | C O ^ f f i U Î O T O O O O O O O i - N \ a 1 1 1 1 C i I 1 1 £ - I W I 1 1 1 C l 1 1 | N | 9 1 1 1 |: | 1 ?9 < » c» c » c o c » t ;. i > i > t ;. t r o s | J | I l | J | *> | <? I I 1 1 ^ 1 1 | *> [

ô © © 6 6 6 0 6 6 6 6 6 0 0 6 © 0 0 0 0 0

K.V.I.

O S , , , , , . T H . , . C D , I- O C O T t H H C O O O O iO t X M O O (O , 1 1 1 H , , 1 ^ 1 <0 1 . , . 0 0 . , , TH , s i 1 1 1 1 I s l 1 I s l 3 S 3 ' * ' o œ a > ° 5 S S Ï J S s 1 1 1 1 s 1 1 1 s 1 s 1 . 1 1 1 s M 1 H 1

1 + I I 1 + 1 1 +

Retractive Index. 00 (M 00 (M rH T-i 0 0 uO CO rfi rH CO O O N N N O N t ^ N N i O M O M O O N i O C - O O N O O i f l ^ O N O O O I O C O N O N C O O H C O O N O N O t ^ c O ^ M u O © O O C O C O » O C O tH C5 I> © c q © T * c O C5 -'i<CO© C5 GOCO N »0 C0 O 0 5 C0 t ' N ® C 0 t0 !0 « 0 I> «O 00 O OS 00 I> I> CD CO CO © N r f H O l O O M > N O O O O C d O G O N N N N C O O O i o lO IO UO rt< tJ< rti rti Tti i a U0 t o IO rti tJi hH t * »fl vO irt rh ^ tH iO © »O tH tH tM tH tH Th Tt<

H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H

Viscosity. 210° F.

00 CO CO O O O r-T ti-rH T tiiO O O O O C O C O C O »H CO h * rH 00

os 1 I I I | 1 00 1 1 l ^ l O O O C O O C O C X D iO O q O O S O S O 00 1 I I I CO I 1 | SO 1 i o I | 1 I o s I | | LfS I CO 1 1 1 1 1 1 ^ 1 1 1 tH 1 Ô Ô Ô t > c Ô i Ô » Ô i Ô i Ô T Î i T t i i b GS 1 1 1 I c ö l 1 l » Ö l OS 1 1 1 1 CO 1 1 1 © 1

rH N H H C0 CO

I=î oo tH

tH CO OS Tti CO Tti HO o CO I> CO Os C0

Tti r * CO O CO 1H IO C0 C0 »O CO 1^ OS CO o CO

» o | | l | ( | c b | | | c s i | c o i o c o r ^ c b r H i H c ô ô i ^ c ô c b o 1 1 1 1 cô 1 1 1 co 1 o s I I I I ô I I I 6 I

^ • • • • • • c o l l l c o l C O I> T-iO O iO TfiC O C O C O C O C O C O o 1 1 1 * 1 1 1 CO 1 t—< ■1 1 * »O 1 1 1 •'i1 i

O CO CO © HO

CO CO CO

Mol.wt. rQ

CO . i i i . i Oi i i Oi © © t> © rH C O C O t> O O O O C O O O 1> , , , , CO , , I OS . CO , I i I 5® ! | | 5 ! | s i I I § 1; j | g 1 1 1 3 1 g I I 1 1 5 I I 1 5 1 g I I 1 1 g I I 1 “ 1

Aniline point, ° C. b - ï> H0 «O CO ^ 00 u0 o s CD r * CO -«dH 00 O CO o lO co

t i i i l i i è l i l â i I i g è æ è à é s s s s i l s i i ê i l l à i l l â i i â i i i â i

1 1—1 r—l H H H r H H H H ,—1 i—1 r—1 rH

à r i p < © |©

' 02 «O IcO

H0 CO Tti os 00 co tH CO O CO T * HO C0 O C0 CO OS r+i - ü OS

® i H , , , CO , I ' - ^ O O H C O C S H I O O S I O H rH . . , CO . , I> , (M , . , , ^ . . , C0 .

O CO ^ o 00 rti tH 0 5 1> co CO hO Tft rH CO r * OS CO ^

o 1 1 1 1 1 1 co 1 1 l o o l o o s o s o s o o o o o o c o o o o o o o o o © 1 1 1 I c o l 1 l o o l © 1 1 1 l oo 1 1 I c o l

tH Ô © r H © © © © © © © © © © © rH © © © © ©

Oil. LR3-1 1S3-2 LE.3-3 LR3-4 LK3-5 LR3-6 LR3-7 LR3-8 LR3-9 LR3-10. LR3-11. LR3-12. LR3-R LR1-1 1R4-2 LR4-3 LR4-4 1R4-5 LR4-6 LT4-7 LR4-8 LR4-9 LR4-10. LR4-11. LR4-R LR5-1 LR5-2 LR5-3 LR5-4 LR5-5 LR5-6 LR5-7 LR5-8 LR5-9 LR5-10. LR5-R. LR6-1 LR6-2 LR6-3 LR6-4 LR6-5 LR6-6 LR6-7 LR6-8 LR6-9 LR6-10. LR6-R

! I I I I I ś I I l ~ l i I I I f e l I I I I I I i I I Ś I

. M 2 X O O

11 I I I I S! I H i IS cooco

i2 X ¿ ¿ Ñ

I I

1 ! ? I ! I ? I S I I I 1 ? I I I I ç I I i Cł i i i X i Ci -Jr OJ © C5

I 1 I I I i 9 XXI I N

ô ô 66Ô 666

I 11: B l I I i l l 1 1 I s i i l I 1 = 1 I 1=1

x ^ ® N O O c « - o o c 5 O Î 1 5 X X N N N N N C O

© X — © r c;c;î! Ci

N - î l r î l N X i i î 'T N T : ' _ M i ü P i X C O N C C C N N O ' T O ' - T r C C l K - X O C ' i M x l:n o~x x x m ' N m -

ÿ C N N ^ D 7 - N t - X - I - r — © X ® i î S û - i ’î ’i

1 1 1 i.si i î s i ¿ i i i i s i 1 1 1: i 2 i 1 1: - r N ù - C M©©

I l l g l l i l g l 111 I I I l à I I l à I I g a üX 15- I X O T- © — ©

© O X —i-<

i l II I I t l I ^ O û û ô ûCi — ~3©C~t'-

S3 2 o

< - 1 1

«cqoir^©

I © t > Ñ ¿ 3 Ó l C X O - -

: 1 I 11 I Ü I I I

xO 'î- n o

— © - r - r X r~

— C N C X t »

0999x1

- 6 6 6 6 6

-r-'v-r^^frx-o-TTT N I— t— t~* t~- N L» I- t- L— t'“ t-

m m m r n m ñ ñ

TableI—continued. —----------------------rfx Watermananalysis : C atoms/molecule. m 1 Paraffin. fejr , B O W M A N , A N D L O W Y C H E M IC A L C O N S T IT U Xxuih

2 * * 211

111

1 1 1 1 1 *1

1 1

1

c o c o c o c o c o c o ' co co co -^ co ^

Xaphthene.

1 1 2 * 2 * I I 1 I I I I I M i l 1 1 1 S 1 ! I l 12 1 I I I I I I I M S I

Aromatic.

¿ "

0

V.G.C. 0-792 0-794 0-788 0-787 0-781 0-779 0-801 0-779 0-903 0-805 0-781 0-896 0-808 0-782

K.V.I.

1 - s s l S I I I I

1

131

Refractive Index. ü O u(M®ClC5COlMCDnN üOOCDflOOONNNO O H N O O O , , 'tOCOOOrfiGOOO

— 1

1

0

— 1

H H H H H H H H H H H H rH H H H H H H H H H H H H H H H H H H H H H H

Viscosity.

R

0

<N 13-46 13-61 12-85 12-63 12-62 12-80 17-46 14-48 166-5 21-02 17-35 217-2 28-50 21-75

100°P. 136-5 142-0 123-6 118-1 114-6 112-4 219-7 136-3 306-7 179-4 492 252 2

Mol. wt.

lOOOONTti i

1

10

1

1 1

1

1

1

3

Aniline point, ° c. 121-8 120-9 124-6 126-8 128-2 130-0 88-5 119-9 132-0 87-5 118-8 134-5 93-3 119-9 136-9

t—< rR d o l o

Í/

20

0

Oil. LR10-7d . LR10-8d . LR10-9. LR10-10k LR10-11 k LR10-Rk. LR11-1. LR11-2. LR11-3. LR11-4. LR11-5. LR11-6. LR11-7. LR11-8. LR11-9. LR11-10. LRU-11k LR11-R. LR12-1. LR12-2-, LR12-3. LR12-4. LR12-5. LR12-6. LR12-7. LR12-8. LR12-9. LR12-10k LR12-R. LR13-1. LR13-2 LR13-3. LR13-4. LR13-5. LR13-6. LR13-7. LR13-8. LR13-9. LR13-10. LR13-R.

TableI—continued.

O X ID A T IO N S U S C E P T I B I L IT Y O F L U B R IC A T IN G O IL C O M P O N E N T S . 465

¿Jga S ° _a d'5,03 2}

> .

£ x_{O <D}

C .

i=i co fl'Oo

M i l M I I I I

CO OS 0 4 Q 0(N i f CO CO lO 0 0 CO

‘ ‘ LO tKt* vO vO

I I I I I I M SI I I CO " f CO Cf f 04 I I I I I I r f 0 4 ib 04 04 CO I I I I I I

11 I £ II I I SI II I S I S * “ * I m i i m i m i

<? II “ II II ? I II

COvOGOI>04 04COCO C O H O O O O C O O D c o c o c o g o o o i > i f

o o o o o o o o 11OOOOGOOOGOCfOOCO

o o o o o o o o

1 1 11

II I M II I

M i l l I I I I ' I I !

^vOOCONiOiO

I ^¿l>(OMNHO I O 0 5 r-i CM 0 5 0 4 CO vO 04 04 04 rH 04 04 vO

II I I I I M i l 11Tfi i—l CO O CO r—I VO CO i i i i I i i i CO 0 4 VO 0 4 CO I> O r-H

0 5 1> CO 0 5 t> CO C- I I I 1 I I I I

I I

N O O J i f l O i O O ^ C O ,

HHiOCONt'OOM

0 0 0 5 0 0 5 0 0 0 0 0 1 I 111 l§ l I lj

( N O O O O N H f tH I 04 04 CO 0 0 05 04 05 CO CO

I O r-l 04 04 04 CO CO I 1

I ll

C 0 0 4 N H O C 4 H C 0 H 1 0 m i o o o ^ c o o o o ' i i N

© vO C O r -lO O O G O O O C O O O O O O O O O O O C O G O

i H O O O O O O O O O 1—1 0 0 0 0 0 0 0 0 0

■GMCO' ^vOCOr ' OOO C4 C O ^ v O © t f C 0 0 5 pH r -4 04 CO vO CO I> 00 O pH

^ ri< tJ< T* 4 Ti< rh ¿ ¿ ¿ ¿ ¿ ¿ ¿ ¿ ¿ P i S S S S 2 S 3 S S S £3pHp3p3p3P3p3p3pH MM

l-P l-P t-P H-11—1 H-l h i 1-3 l-i 1-3 t-3 l"3 1-^ t-3 1-3 t-3 I—11-3

V, «.2 05^ 05 5 "S.fi.2

.cpj

-7! .£ o g -f m

cs 42 OT) (U^i O

of th e e x tra c t cu t from th e distillate first indicated. T he d istillate series are begun a t th e m ore volatile end, an d th e e x tra c t series a t th e m ore soluble end. F o r exam ple, fractio n LR 8-9 is th e n in th e x tra c t from th e eighth distillate. The stock itself is indicated b y 0, an d residue from ex tractio n or distillation by R.

Chemical Constitution.

W aterm an analyses,9 calculated from th e physical properties shown, are also presented in Table I, to g eth er w ith values for kinem atic viscosity index (K .V .I.) 4 an d viscosity-gravity co n stan t (V.G.C.).6

This experim ental w ork was com pleted a n d th e calculations m ade several years ago. Since t h a t tim e several papers have ap p eared giving im proved correlations betw een chem ical co n stitu tio n a n d physical pro­

p erties.2 The W aterm an analysis, th o u g h now recognized as som ew hat inaccurate, has th e a d v an tag e of being widely know n an d used. U ntil m uch m ore is learned ab o u t th e chem ical co n stitu tio n of oils, it will p rob­

ably rem ain th e best m ethod of characterizing close-cut oil fractions, even if regarded only as em pirical. Consequently th e resu lts a t h an d are presented a t th is tim e ra th e r th a n to delay th e p re p a ratio n of th is paper by th e d eterm ination of oth er properties an d by calculation along more m odern lines.

The W aterm an analyses are reported, n o t conventionally as percentages of carbon atom s in arom atic, n ap h th en e an d paraffin stru ctu res, b u t as num ber of carbon atom s in th e respective stru ctu res. This effectively introduces a th ird param eter, th e m olecular w eight ; th e device is con­

venient in com paring different fractions.

Several conclusions m ay be draw n from th e calculated results. The stock appears to be a ty p ica l w ide-cut, ra th e r highly paraffinic lubricating- oil fra ctio n ; its paraffinic co n ten t rem ains rem ark ab ly c o n stan t a t about 73 per cent, th ro u g h o u t th e distillation range. T he arom atic content is ra th e r high, as is to be expected in an unrefined oil, an d increases slightly tow ards th e high end of th e distillation range.

The W aterm an analyses o f th e e x tra cts show several ra th e r surprising characteristics of th e stock (Fig. 4). F ractio n s L R 4 an d L R 10, th e in ter­

m ediate “ key ” distillates, all th e ex tra c ts of w hich were exam ined com­

pletely, appear to have pure arom atics as th e lim iting s ta r t of th e extract series; both th e paraffin an d n ap th en e co n ten ts a p p a re n tly ex trap o late to zero, an d th e arom atic to 100 per cent. T he presence of even traces of u n alk y lated arom atics in a high-m olecular-w eight oil w hich h a d u n d er­

gone essentially no chemical change is a t least som ew hat rem arkable.

This is definitely n o t tru e of th e lig h test distillate exam ined, LR1 ; in it, th e lim iting com position is arom atic, naphthene-free b u t strongly alkylated.

The heaviest fraction, LR 15, could n o t be com pletely exam ined in this w ay, because th e range of th e m ethod of W aterm an has n o t been extended to m aterials of such high m olecular weight an d arom atic content.

The paraffin contents of all th e m em bers of th e e x tra c t series increase regularly in th e direction of percentage extra cted , b u t a t a ra p id ly decreas­

ing rate , levelling off very uniform ly a t ab o u t 85 per cent. This fa c t gives excellent confirm ation of th e now generally accepted view 7 t h a t wax-free oils are quite free of acylic hydrocarbons. The present w ork allows an 466 K A P F F , B O W M A N , A N D L O W Y : C H E M IC A L C O N S T IT U T IO N A N D

even stronger state m en t : a single n ap h th en e ring ap p aren tly cannot hold m ore th a n ab o u t fo rty carbon atom s in aliphatic side-chains.

A dditional support for th e absence of pure paraffins is th e fact th a t w ithin th e experim ental error no fraction showed less th a n five cyclic carbon atom s per molecule.

O X ID A T IO N S U S C E P T I B I L IT Y O F L U B R IC A T IN G O IL C O M P O N E N T S . 467

Fi g. 4.

C O M P O S IT IO N O P E X T R A C T S F R O M K E Y D I S T I L L A T E S .

F o r all th e ex tra c t series, th e n aphthene content extrapolates to zero a t th e more soluble end. In th e case of th e low-molecular-weight distillates, th is finding is n o t surprising, for these m aterials m ay not contain more th a n one ring per molecule, an d if both naphthenes and arom atics are present, th e y m u st occur in different com ponent compounds. U nfortunately, the

converse cannot be verified e x p e rim e n ta lly ; slightly a lk y lated n a p h th en es cannot be sep arated from strongly alk y lated arom atics of th e sam e m olecular weight by th e fra ctio n atio n m ethods used in th is work.

The n ap h th en e c o n ten t passes th ro u g h a broad b u t definite m axim um in each e x tra c t series; th is m axim um occurs a t a b o u t th e 25 per cent, ex tra c te d p o in t a n d am ounts to ab o u t 25 p er cent, n ap h th en es. T he peak is n o t unexpected, because th e solubilities of th e n ap h th en es are in te r­

m ediate betw een those of th e arom atics an d th e paraffins of th e same m olecular w eight, a n d therefore th e y should co n cen trate a t an in term ed iate p o in t in th e series. The fa c t t h a t th e p eak is b ro ad on th e less soluble side indicates t h a t m uch of th e n a p h th en e co n ten t is stro n g ly alk y lated .

The analyses show rem arkable hom ogeneity for th e less soluble halves of th e distillate fractions. T hus th e re is a definite lim it to th e paraffinicity of oils obtainable from such a stock by physical m ethods, as is well know n in refinery practice. Oils of extrem e high V .I. can be produced only by drastic chem ical m ethods.

Oxidation Tests.

U n fo rtu n ately none of th e m a n y te sts described for ox id atio n suscepti­

b ility of oils is suitable for th e ex am ination of th e close-cut fractions 468 K A P F F , B O W M A N , A N D L O W Y : C H E M IC A L CON ST.LT U TiUJM Anu

Fi g. 5.

O X I D A T IO N T E S T T H E R M O S T A T .

obtained in th is work, because all require relativ ely large sam ples. The final fractions were so sm all in volum e t h a t a semi-micro m eth o d was d eveloped;

it will be described in detail.

Method o f Oxidation. The sam ples were oxidized in a specially built th e rm o stat, illustrated, w ith th e cover rem oved, in Fig. 5. I ts essential p a rt is a solid alum inium block having th irty -tw o holes, drilled p a r t way in to it, to accom m odate th e sam ples, an d “ Chrom alox ” strip heaters bolted to its sides. T em perature control is provided b y th e expansion of th e block itself; a “ K o v ar ” rod, having a low coefficient o f th erm al expansion, passes th ro u g h a hole in th e axis of th e block, an d th e difference in expansion actu ates contacts w hich control th e v oltage applied to th e heaters th ro u g h an electronic relay. A differential screw is p rovided for ad ju stm en t. The whole assem bly is enclosed in a n air-b ath .

The tem p eratu res in th e holes used were found to be th e sam e to w ithin