Liquid Phase Hydrocarbon Oxidation E. R. BOOSERI AND M. R. FENSKE T h e Pennsylvania State College, State College, Pa.
L
IQUID phase oxidation of hydrocarbons has been the subject of many investigations. These have been summarized up to about 1944 by the surveys of Zuidema (18) and MeArthur (14). The previous studies have presented some rates of oxidation, established some oxidation mechanisms for pure hydrocarbons, and suggested possible mechanisms involved in the oxidation of petroleum lubricants. In the present work a further study was made of hydrocarbon oxidation as related to the deterioration of lubricating oil and the oxidation mechanism. For this purpose the oxidation characteristics of a number of pure hydrocarbons typical of some of the structures believed to be present in the higher boiling petroleum fractions were examined. These were then compared with the results found with two hydrocarbon mixtures, a condensed ring aromatic concentrate and a composite paraffinic neutral and its portions separated by silica gel treatment. The oxygen absorption studies were made with 200-gram samples in a closed circulatory system using commercial oxygen a t a pressure of about 720 mm. and a t constant temperatures in the range of 110' to 190' C. The apparatus employed, a modification of that used by Dornte ( 7 ) , was previously described in the literature ( 9 ) . Metal wire catalysts were employed which consisted of polished coils either of 200 em. of No. 20 iron wire or 40 cm. of Xo. 24 copper wire. The approximate surface area of this length of iron wire is 51 square em. and that of the copper wire is 6.4 square em. The different quantities of the two catalysts were employed because of the great difference in the activity of the two metals. With some modifications the analytical schemes used for chemical analysis of the oxidation products were the same as those used in similar studies (9, 13). Water was collected by condensation in a cold trap and by absorption with anhydrous calcium sulfate. Volatile acids were collected with the water and were determined by titration. Carbon dioxide was measured by absorption with potassium hydroxide-coated asbestos; carbon monoxide, after oxidation in a copper oxide furnace, was also determined by absorption as carbon dioxide. In the nonvolatile product organic acids were determined using an equal volume of butanol-toluene mixture as solvent and the methyl red-fluorescein indicator suggested in the procedure outlined by Hersh et al, (1%). Saponifiable material was determined by refluxing the sample with the butanol-toluene solvent for 1 hour with excess sodium butylate and then back t'itrating with hydrochloric acid, again using the methyl red-fluorescein indicator. The hydroxylamine hydrochloride method of Bryant and Smith ( 3 )was employed for carbonyl analysis and acetyl chloride ( 1 7 ) was used to determine hydroxyls. S o analysis was made for peroxides. An estimation of the portion of the original hydrocarbon charge that was oxidized during each run was made by extraction of the oxidation products. Concentrated sulfuric acid was used with saturated hydrocarbons in a 5 to 1 volume ratio of acid to oil and with a 1-hour shaking period in a Babcock bottle. An 88 weight yosulfuric acid solution %-asused Kith aromatic materials. While most oxidation products are extracted by t'his strength of acid, Matson ( 1 5 ) found that benzene derivatives 1 Present address, Thoinson Laboratory, General Electric Co ., Lynn, hfaes.
and many alkyl naphthalenes are unaffected. Silica gel was used to separate the unreacted olefin I-hexadecene from its oxidation products. As a measure of the insoluble products formed during oxidation, isopentane-insoluble material was determined by the method outlined by Hersh et al. ( 1 2 ) . The degree to which the oils darkened in color w m determined by use of the ASTM Union colorimeter (1). The weight increase of a 1 x 3 inch glass microscope slide suspended in the oil sample during oxidation was taken as an indication of the tendency to form lacquer and surface deposits. Viscosities aere dctermined with the Cannon-Fenske viscometer (2). PURE HYDROCARBONS
The pure hydrocarbons included in this survey were a normal and a branched chain paraffin, an olefin, a naphthene, a benzene derivative, an alkylnaphthalene, and phenanthrene, Data for the source, properties, and purity of these hydrocarbons are given in Table I. Results of the oxidations are summarized in Table 11. The extent of oxidation, distribution of absorbed oxygen, and the nature of the products are given for tests made a t the indicated temperatures with and without the presence of metal wire catalysts. The rates of oxygen absorption are indicated in the curves of Figures 1 to 7 , inclusive. A wide variation was found in the stability and in the nature of the oxidation products formed from the various hydrocarbon structures. With the seven pure hydrocarbons studied, over a thousandfold difference in stability was observed in going from the least stable 1-hexadecene up through increasingly stable 1methyl-4-isopropylbenzene, czs-Decalin, tetraisobutane, hexadecane, and I-methylnaphthalene, to the most stable phenanthrene. These stabilities are summarized in Table I11 in terms of the time required for 100 millimoles of oxygen absorption per mole of hydrocarbon a t 150" C. Where the rate at 150" C. was not available for a compound, the uncatalyzed rate at the nearest temperature was converted to 160' C. for this comparison by using a rate coefficient of 2.0 per 10" C. temperature rise. Catalytic rates were then estimated roughly by assuming that the catalysts would have proportionately the same effect a t 150" C. as at the temperature a t which they were actually employed. Other observations are of interest in the data of Table I1 and in the absorption curves of Figures 1 to 7 . The paraffins, hexadecane and tetraisobutane, oxidized autocatalytically to form colorless, soluble products with water, carbonyl, and acid formation predominating. Branching of the paraffin carbon skeleton in tetraisobutane led to decreased stability and to a greater tendency for fission of the carbon skeleton to give larger quantities of volatile acids, water, and carbon dioxide. Unsaturation of the aliphatic skeleton in 1-hexadecene gave a very reactive material, with fission apparently taking place a t the double bond to give somewhat larger quantities of carbon dioxide than were produced with the paraffins. The formation of carbonyls, hydroxyls, and acids predominated. In general the oxidation charadteristirs of this olefin, other than the increased reactivity, appeared quite similar to those of the paraffins.
850
INDUSTRIAL AND ENGINEERING CHEMISTRY
August 1952
1851
X HEXADECANE 4 CIS-DECALIN
0 5 0 WT. % MIXTURE
0 190 'C,CU
WIRE
15
OXIDATION Figures 1-10. 1. Hexadecane Tetraisobutane 1-Hexadecene
2. 3.
4.
5. 6.
20
TIME, H O U R S
Oxygen Absorption Curves for Hydrocarbons
cis-Decalin 1-Methyl-4-is0 ropylbenzene 1-Methylnapht%alene
'
7. 8.
Phenanthrene Condensed ring aromatics (from aromatie cracking)
9. Hexadecane, cis-Decalin, and 50-50 mixture 10. Hexadecane, l-methylnaphthalene, and 50-60 mixture
INDUSTRIAL AND ENGINEERING CHEMISTRY
1852
Val. 44, No. 8
TABLEI. PUREHYDROCARBOSS USED IK OXIDATIONSTUDIES Refractive Index, n
Viscosity, CS.a t 100' F.
Hexadccane
1 4347
3 09
Du Eont, silica gel extraction
9s
Tetrai-obutane
1 4401
3 59
Standard Oil Development C o fractionation
98
Connecticut Hard Ruhher Cw, (Humphrey-Wilkinson; Du Poiit. fractionation
0 i$.
B.P., c. at 760 M m ,
Skeleton Formula
1-Iiaxadecene
c
cII-C=C
cis-Decalin
c
b
Phenanthrene
C
Source and A n y Additional Purification
Estm. Purit,y,
70
+
274
1 1413
3 OB
19:. 7
1 1810
2.64
1 4902
0 814
Semport Indnstrie,. f r a c r i u n a tion
$1 5
140
1 BOGi,
2 00
Reilly T a l and Cheniical C ' o r p , fractionation
0i
335
..
, .
Reilly T a r and Chemical Cor!,,
YO
l-l\lethyl--f-isoi?ropylbenzene
1-3Iethylnaphthalene
so
+
95
a Mixture of isomers.
The aromatics varied greatly in their nature, depending o n the type of ring structure. The alkyi benzene, 1-methyl-4-isopropylbenzene, was quite reactive in forming soluble but somewhat colored oxygenated products. The oxygen vas consumed in the forinat'ion of preponderant quant,ities of carbonyls and hydrosyls. I n contrast, the condensed ring aromatics, 1-methylnaphthalene and phenanthrene, were relatively stable to oxygen absorption. Wit'h the naphthalene derivative, highly colored oxygenated products were formed which tended t o produce surface deposits aiid insoluble matter. The absorbed oxygen showed up in n-ater, carbon dioxide, and hydroxyl formation. I n the case of phenanthrene the oxygen absorption \vas too lo!v for accurate analysis of products. In order to obtain further infoimation on the condensed ring aromatics, for which phenanthrcne and l-met,hylnapht,haleneindicated a great oxidation st'ability, a ~ i a r r fraction o~ of a t'hermal cracking residue x a s studied. The phypical properties of this aromatic concentrate are given in Table IV. The -357 viscosit'y index and 1.691 refractive index indicate the highly aromatic nat,ure of this material. h molecular .i&&t of 216 and an aromatic ring structure of 85 weight yo in the concentrate %-ere estimated from statistical relationships derived from boiling pointrefract,ive index data for pure hydrocarbons ( 1 6 ) . Sulfur analysis indicated that any sulfur prescnt in the original gas oil had heen removed by the cracking operation. The aromatic concentrate had a stability somewhat less than the tn-o condensed ring aromatic hydrocarbons, as will be noted from the comparisons of Table 111 and the absorption curve in Figure 8. . T h e oxidation product i w s a black sirupy mass almost completely insoluble in isopentane and over 200 times as viscous as the starting material. The distribution of the absorbed oxygen among the various types of oxidation products 11-as similar t,o that found IT-ith 1-methylnaphthalene. These results indicate that condensed ring aromatic hydrocarbons are relatively stable to oxygen absorption, but other deterioration factors, such as the forination of insolublematter, areindicatiae of undesirable properties for many types of lubrication service. The oxygen dist,ributioii found x i t h some of the hydrocarbons can be expressed in the form of cheniical equations for the portion of the hydrocarbon charge undergoing oxidat,ion. This is illus-
trated by the following equation calculated for the noncatalytic oxidation of n-hesadecane at 150" C. for 5 . 5 hours:
'0:3--COOH 71-C 6H34 2.202 --+d o.2 1.0 =C=O 0.6 -('--OH
-
1
+
Siniilar equations for other oxidations are
sum^
I-. To obtain these equations the acid extract'ion data given in Table TI were used along wit'h the total quantity of nonvolatile material remaining after the osidations t o determine the quaiitity of hydrocarbon convert,ed t o oxygenated product's in each case. The amount of oxygen entering into t'he react'ions and the proport,ions of the oxygen going to the different types of products \\-ere also taken from Table 11. For simplicit'ythe coefficients n'ere adjusted t,o tmhebasis of one molecule of hydrocarbon oxidized, and all products that were then represented by less than 0.1 mole mere omitted. Sirice the amount of 0x1-gen found by thc analysis of the products seldom equaled 100% of the tothi oxygen consumed during the oxidation, the equations do not represent a strict oxygen balance. Molecular sizcs of the liquid oxidation products also are not knon-n. The equations are of interest in indicating the nature of the reactions and the average number of oxygenated groups formed per hydrocarbon molecule oxidized uiider the conditions specified. For a given hydrocarbon oxidized t,o thc same extent, the amount of oxygen reacting per mole of hydrocarhon oxidized autl t h e aiiiount,s of the products formed appeared t o be indcpendent oi t,emperat,ureand catalyst. Thus, the equations recorded in Table 5' for hexadecane, oxidized to the extent of about 0.5 mole of osygeii per mole of hydrocarbon charge, were essentially the s a i i i ~ r h e n the oxidations were conducted at 150" or a t 130" C. iir the presence or absence of iron aiid copper catalytic surfaces. h similar conclusion is indicat.ed by the equations for 1-methyl-4-isopropylbenzene, oxidized lo about 0.3 mole of oxygen per mole of hydrocarbon charge. I n the case of cis-Dccalin the oxidations a t 110" C. were conducted t o about 0.3 mole of osygen per mole of hydrocarbon charge, n-hile the oxidation at 130" C. x-as continued t o about' 0.5
August 1952
INDUSTRIAL AND ENGINEERING CHEMISTRY
:w%o:
1853
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INDUSTRIAL AND ENGINEERING CHEMISTRY
1854
Vol. 44, No. 8
oxidation after oxidation started, except in the case of copper on
TABLE111. COMPARATIVE STABILITIESOF PUREHYDROCAR- 1-methylnaphthalene (Figure 6). In no case was there appreBONS, HYDROC-4RBON hIIXTURES, B N D COMPOSITE OILS ciable corrosion of the metals, the average loss of the metal cataMaterial 1-Hexadecene 1-Methyl-4-isopropylbenzene &-Decalin Tetraisobutane Hexadecane 1-Methylnaphthalene Phenanthrene Condensed ring aromatic concentrate Hexadecane-cis-Decalin 50 wt. %
Hr. for 100 hIillimoles of 02 Absorption/hlole of Hydrocarbon a t 150' C. NO Iron Copper catalyst catalyst catalyst 0.26 0.19 0 35 0.42 0.42 0.55 1.1 0.74 1.1 1.8 .. .. 2 3 2.9 1.8 124 127 203 >440 .. >730
Hexadecane-1-hf ethyldphthalene, 50 wt., 7'0 Paraffinicneutral Over-all Paraftin-naphthene portion Aromatic portion
54
1.4
..
..
..
..
>48 41 0.39 8
TABLE IV. PROPERTIES OF CONDEXSED RING AROMATIC CONCENTRATE FRACTIOKATED FROM A THERMAL CRACKIXG RESIDUE Viscosity a t 100' F.,
S.U.S.
CS.
Viscosity a t 210' F., cs. S.U.S. Viscositv index Refracti-ve index, n'," Boiling point range, F. a t 760 nim Molecular weightQ Color N P.A. Sui& cdntent. wt. % Hydrocarbon type analysisa Condensed aromatic rings, wt. %J Paraffin chains, wt. % No rings per molecule I n formula CnHm + z
56.49 261.3 4.26 40.2 - 357 1.691 683 to 717 216 8+ 0 01
HYDROCAREON MIXTURES AND OILS
85 15 3.2 -19.2 16.8
X
n
a From boiling point-refractive index and molecular weight-refractive index relationships (f6).
mole of oxygen per mole of charge. Temperature effect, as shown previously, can be neglected. The moles of oxygen per mole of hydrocarbon oxidized increased from 0.8 to 1.2, indicating a greater attack per mole of hydrocarbon oxidized with prolonged oxidation. This is supported by the data on the products formed, the tendency being merely to increaee end products such as acids, esters, carbon dioxide, and carbon monoxide. The amounts of carbonyl and hydroxyl compounds remain essentially unchanged. The effect of temperature variations on the rate of uncatalyzed oxidation of some of the hydrocarbons is given in Table VI. The average temperature coefficient was found t o be 2.0 per 10" C. temperature rise, with the corresponding average activation energy as given by the Arrhenius equation being 22,500 calories per gram mole. Judging from the oxygen absorption curves shown in Figures 1 to 7, inclusive, the effect of the catalysts was to shift the induction period without exerting an appreciable influence on the rate of
TABLEV. EQUATION FOR
Hexadecane
Tetreisobutane 1-Hexadecene cis-Deoalin
I -Methyl-4-isopropylbenzene
150 130 130 130 130 110 130 110 110 110 130 110 110 110
5,s 28.3 30.0 21.9 18.6 17.6 11.0 26.9 26 8 21.0 6.7 31.7 27.1 27.0
None None Fe Cu None None Pione None Fe cu None Kone Fe Cu
0.512 0.512 0.501 0.511 0,534 0.506 0.526 0.315 0.300 0.294 0.302 0.301 0,294 0.292
THE
2.2 2.3 2.1 2.2 3.3 1.0 1.2 0.8 0.8 0.8 1.4 1.4 1.3 1.3
lysts being only 0.4 mg. of iron and 0.7 mg. of copper. Analysis for metal content of the oxidized products, however, was not completed. Since the catalysts appeared to have an effect only in the early &ages of the oxidatione-Le., on the induction periods-it is of interest to compare in Table 1% bot'h the elapsed time necessary for 10 millimoles oxygen absorption per mole of charge and the estimated rate of absorption a t the point where the total absorption had reached 10 niillimoles per mole of hydrocarbon charge. This point was usually near the induction period, Copper increased t.he absorption rate in every case in amounts from 16 t o 147% and it correspondingly reduced the time necessary t o attain 10 millimoles of total oxygen absorption from 35 to 83% of the values found in the noncatalytic oxidations. Iron had little effect on the initial oxidations of 1-methylnaphthalene and cisDecalin, but increased the induction period for hexadecane, although the absorption rate after oxidation started was increased over that of the uncatalyzed oxidations. In other cases iron acted as a milder catalyst than copper.
To obtain some information as to how the oxidation characteristics of pure hydrocarbons compare with those of hydrocarbon mixtures and composite lubricants, some oxidation testa were conducted with a naphthene-paraffin mixture, a s aromatic-paraffm mixture, and finally a paraffinic neutral, and the portions separated from the neutral by silica gel extraction. Summary of the results of these oxidations is given in Table I1 and in the absorption curves of Figures 9, 10, and 11. With the hexadecane-cts-Decalin paraffin-naphthene mixture, the oxidation proceeded in an autocatalytic fashion a t an initial rate similar to that predicted irom a simple average of the data for the individual hydrocarbons, as is indicated in Figure 9 and the comparison shown in Table VIII. The considerably faster than average reaction in the later stages may have resulted a t least partially from a faster oxidation of the hexadecane here than was the case yhen it was free of the influence of the reactive czsDecalin. The refractive index of the portion of the hydrocarbon mixture remaining unoxidized indicated that the material oxidized was about 76 mole yoDecalin. The types of oxidation products were intermediate t o those which were obtained from hexadecane and cis-Decalin when oxidized individually. A very high degree of stability was found with a hexadecane1-methylnaphthalene mixture, quite similar to that of l-methylnaphthalene by itself. The appreciable discoloration and the chemical analysis of the oxidation products indicated that the attack may have centered on the 1-methylnaphthalene to give an
OXIDATION OF SOMEPUREHYDROCARBONS
1.1 1.1 0.8 0.9 2.9 0.3 0.2 0.1 0.1 0.2 0.3 0.4 0.3 0.4
0.1 0.1 0 0.1 0.3 0.1 0.1 0 0 0 0 0 0 0
0.1 0 0.1 0 0.3 0 0.1 0 0 0 0 0 0.1 0
0.3 0.3 0.4 0.4 0.6 0.1 0.2 0.1 0 0 0.1 0.1 0.1 0.1
0.2 0.2 0.1 0.2 0.2 0.1 0.2 0.1 0.1 0.1 0.1 0.1 0.1 0.1
1.0 1.0
0.6 0.4
1.2 0.7 0.6 0.5 0.6 0.6 0.5 1.0 0.8 1.0 0.9
0.5 0.4 0.4 0.4 0.4 0.4 0.4 0.8 0.7 0.8 0.7
1.1
0.5
92 79 84 88 98 87 80 80 81 79 91 89 101 96
August 1952
INDUSTRIAL AND ENGINEERING CHEMISTRY
PARAFFIN-NAPHTHENE
a:
30L-
w 20
= I,
0
1855
HEXADECANE AND I-METHYLNAPHTHALENE
I
~
10
E *
NEUTRAL
2a 6 8
4 cn3 W d
AROMATIC PORTION
1
OXIDATION TIME, HOURS Figure 11. Oxygen Absorption Curves for a Light Paraffinic Neutral and Portions Separated from the Neutral by Silica Gel Adsorption
LL
T e m p e r a t u r e of oxidation, 150° C., uncatalyzed
c
-
\
\
\
9
I- MET ti Y L- 4~soPROPYLBENZENE
cn inhibiting hydroxy compound. Oxygen absorption curves for PORTION this mixture are presented in Figure 10, and oxidation data are included in Table 11, where it will be noted that 54% of the abI 20 " ' 4I0 ' 6I 0 I 8I 0 100 sorbed oxygen was recovered in hydroxyl groups. To obtain further information as to how the oxidation of pure WEIGHT PER CENT AROMATICS hydrocarbons compares with that of a complete lubricant, the Figure 12. Oxygen Absorption Stability of Portions lower boiling or first 1570 of a conventional paraffinic neutral waB of a Light Paraffinic Neutral Compared to Pure studied. In addition, the neutral was separated by silica gel Hydrocarbons extraction into a saturated naphthene-paraffin portion and a n T e m p e r a t u r e of oxidation, 150' C., uncatalyzed aromatic portion. The extraction was carried out in a number of similar operations in each of which 260 grams of the neutral fraction were percolated through approximately 900 grams of 28- to ZOO-mesh Davison activated silica gel in a stainless steel tower of TABLEVI. EFFECT OF TEMPERATURE VARIATION ON UNCATALYZED RATEOF OXYGEN ABSORPTION 11/2-inch inside diameter. The paraffins and naphthenes were Temp. CoefActivation Endisplaced by washing with n-pentane, following which the aroTemp., ficient/lO" C. ergy, Cal./G. O c. Rise Mole matics were displaced with methanol and diethyl ether. The yields and properties of the neutral and its separate portions are indi1-Hexadeoene 110-130 1.9 19,500 1-Methyl-4-isopropylbenzene 110-130 2.2 24,000 cated in Table IX. cis-Decalin 110-130 1.9 20,000 The oxidation data obtained with the paraffinic neutral and its Hexadecane 130-150 2 3 28,000 LMethylnaphthalene 170-190 1.7 22,000 naphthene-paraffin and aro... 2 0 22,500 Average matic portions,are presented in Table I1 and in Figure 11. The oxidations were carried TABLE VII. EFFECTOF IRON A N D COPPERWIRE CATALYSTS IN THE EARLY STAGES OF out at different temperatures OXIDATION (Data estimated a t 10 millimoles of oxygen absorption per mole of hydrocarbon) in order t o give absorptions of 02 Absorption Rate, Elapsed Time for Total about 500 millimoles- of oxyMillimoles/Mole of Absor tion of 10 Millimoles of Hydrocarbon/Hr.a Ol/?Mole of Sample, Hr.6 gen per mole of hydrocarbon No . . NO charge in a reasonable length Temp., catacataof time. The stabilities of the Compound c. lyst Fee Cud lyst Fec Cud 6 . 7 (41g,) 3 . 7 (23%) 11.3 1 7 . 3 (-53%) 130 3.0 4 . 7 67%) three samples are also comHexadecane 110 8.3 13.2!59%) 20.5(147%) 3.0 1.5(50%) 0.5(83 0 ) pared in Table I11 in terms of ~~~~~~~~e 9.1 10.0 ( - 9 % ) 2 . 2 (76%) 3.3(6%) 4 . 5 (45%) 110 3.1 l-Methyl-4-isopropy1the time required at 150' C. benzene 110 5.0 6.8(36%) 9 . 2 (847) 2.6 2.0(23%) for 100 millimoles oxygen ab1-Methylnaphthalene 190 4.5 4.0(-11%) 5 . 2 (16%) 3.0 3.0(0%) sorption per mole. On this a Figures in parentheses indicate the per cent increase i.n rate effected by the catalysts. b Fi ures in parentheses indicate the per cent decrease In time required with the catalysts. basis the over-all neutral was 208 cm. of NO. 20 iron wire per ZOO grams of sample. about 105 times more stable d 40 om. of No. 24 copper wire per 200 grams of sample. 1 h a n i t s naphthene-paraffin 0
::i[i;Ri
INDUSTRIAL AND E N G I N E E R I N G CHEMISTRY
1856
Vol. 44, No. 8
The portion of the oxidation product uiiextracted with 88 weight % sulfuric acid was assumed to rcprcsent the unosygenated portion of the charge. This assumption appeared justified since the Absorption, AIillimoles 0 d M o I e original over-all neutral had an unchanged refractive index after Average of 50 Wt. 70 treatment with the acid. The decrease in refractive index would liexadecane hexadecane Time Hr. and cis-Decacis-Decalin thus indicate that either aromatics or naphthenes, or both, had a t 136' C.' Hexadecane cis-Decalin lin mixture been oxidized in preference to paraffins. Since there was but very little change in the refractive index of the naphthene-paraffin concentrate when it \vas oxidized by it,self, however, it appears that the aromatics were preferentially oxidized in the over-all neutral. Calculation of the reaction necessary to give the above refractive 50 Wt. % hexa.I\.erage of hevadecane decane 1index data indicate that about 32 weight yoof the aromatics origiand 1-methylmetliylnaphnally present in the neutral had been oxidized, while only about, 1-Methylnaphthalene thalene mixAt 150' C. Hexadecane naphthalene' ture 10% of the naphthene-paraffin portion underwent oxidation. The oxidation stabilities of the light paraffinic neutral and its separate portions are compared in Figure 12 x i t h data for some of the pure hydrocarbons studied. Thc high reactivity of the naphthene-paraffin portion would seein t o indicate the presence of Estimated f r o m data a t 170' C. using temperature coefioient of 2.0 per some highlj- branched molecular structures viith reactive tertiary 10" C. rise. carbon atoms. Thus, the reactivity of this concentrate is similar to t,hat report>edby Larsen et al. ( 1 3 ) for t'he highly branched TABLE Ix. PHYSIC.4L P R O P E R T I E S O F LIGHTP A R A F F I l v I C NEUnaphthene, 9,lO-diisobutylperhydroanthracene. The effect of T R A L .%XU P O R T I O N S SEPARATED BY S I L I C A GEL TREATXEST differences in ring content, however, should be investigated. Paraffin-Saph.4romatic Over-all then? Portion Portion Keutral The aromat,ic concentrate \vas less stable than t,he condensed Tieight Yo of neutral 100 82.9 17.1 ring aromatics studied, but it \ws more stable than the benzene T'iscosity at 100" F., cs. 12.20 10.60 49.39 derivative, l-meth~-l-4-isopropylberizene. Other studies of the 66.6 60.9 228.6 S.U.S. Viscosity a t 210' F., cs. 2.86 2.71 4.65 oxidation of' hydrocarbon mixtures have indicated a similar in35.8 32.3 41.5 S.U.S. 103 -I36 hibiting effect by condensed ring aromatics ( 4 , 10, 11, 13, 18). 85 Viscosity index 0.8378 0.9734 0,8584 Density, d 2 O The oxidation characteristics of mixed-type compounds such as Refractive index, n %' 1 4767 1.4630 1,5535 naphthene-aroniat,ic compounds viould be of interest in this conCotbrell boiling point, converted t o 760 mm., ' F. nection. iZlthough stability has also been attributed to other Initial 668 .... .... 678 .... naturally contained inhibitors in petroleum lubricants (6,13, 1 8 ) , 50 % 267 ' Molecular weight' 300 305 the effect' and structures of such inaterials are unfortunately not Color, N.P..4. 1I/? n'ater-n.hite 6 Aniline point, ' C. 88.2 98. 3 0.4 as yet well defined. Sulfur content, wt. 70 0 05h 0 006 0.27
TABLEVIII. COMPARISON O F O X Y G E N b B S O R P T I O S FOR MIXTURES WITH THOSE OF INDIVIDUAL HYDROCARBON^
.
'
Hydrocarbon type analysisa Aromatic rings, wt. % Naphthene rings, wt. 70 Paraffin chains, wt. 70 STurnber of rings I n formula CnHmT i
n
z a
10 26 64 1.3 21.6 -2.9
56
0 31
44' ' 2.1
69
1.1
20.0 -14.2
21.8 -0.2
From boiling point-refractive index relationships ( 1 6 ) . Assuming all sulfur t o he in aromatic portion ( 6 ) .
portion and about five times as stable as its aromatic portion. This higher stability of the over-all neutral corresponds to the result,s obtained in a previous study (8) with portions separated by distillation and ertraction from a light mineral oil. Table I1 shows that the original neutral gave the lowest viscoaity increase, but it formed the greatest amount of surface deposits and gavc a highly colored product,. The aromatic concentrate gave the greatest viscosity increase, highest isopentane insolubles, and a black product. The product of t8henaphthene-paraffin port,ion was allnost colorless and free of insoluble matter, but it was the most acidic of the three oxidation products. There TTere several indications t,hat the aromatics were preferent,ially attacked in the oxidation of the composite neutral despite the twentyfold greater stability of t,he aromatics as compared t o the naphthenes-paraffins when t,aken individually. The distribution of the oxidation product,s with the aromatic portion !\-as more similar to that of the over-all neutral than to that of the naphthene-paraffin portion. The following refractive index data also indicate a preferential attack on the aromatics: Refractive Index, n%O Over-all neutral Neutral remaining unoxidized Saphthene-paraffin portion Aromatic portion
1,4767 1.4736 1.4630 1,5535
LITERATURE CITED
(1) Ani. Soc. Testing Materials, "Standards on Petroleum Products and Lubricants," p. 84, -4STM D 155-45T, Philadelphia, Pa.,
1950. (2) Ibid., p. 185, ASTM D 445-367'. ( 3 ) Bryant, W.M. D., and Smith, D. &I., J . ,4m. Chern. SOC.,57, 57 (1935). (4) Chemozhukov, N. I., C o n g r . mondinl pCtToZe. 2 me C o n g ~ . .11, See. 2, 797 (1937). (5) Denison, G. H., IND. ENG.CHGM.,36, 477 (19413). (6) Dinneen. G. U., Bailey, C. IT., Smith, J. R., and Ball, J. S., AmZ. Chnn., 19, 992 (194i). (7) Dornte, R. W., IXD.ESG. CHCM., 28, 26 (1936). (8) Fenske, M.R., Stevenson, C. E., Lawson, S . D., Herbolsheimer, G., and Koch, E. F . , Ihid.. 3 3 , 5 1 6 (1941). (9) Fenske, 31. R. et d.,I X D . ENG. CHEM.,A N A L . E D . , 13, 51 (1941). (10) Fuchs, G. H. Ton, and D i a m o n d , R., 1x1).ENG.C H m f . . 34, 927
(1942). (11) George, P., and Robertson, :I., J . I n s f . Petroleum, 32, 400 (1946). (12) Ilersh, R. E., Lawson, K. D., Koch, E. F., a n d Fenske, M. R . , Petroleunz Rejiner, 22, 197 (1943).
Larsen, R. G., Thorpe, R.E.. and Armfield, 1;. A,. I r n . ENC. CHEY., 34, 183 (1942). (14) hIcA%rthur, D. S.,Natl. Research Council Can.. R e p t . MO-1049 (1945). (15) hlatson, 13. J., M.S.t,hesis, T h e Pennsylvania S t n t c College, 194T. (16) Petroleum Refining Laboratory. J . I n s f . Petrole7~rn,36, 624-68
(13)
(1950).
Smith, D. %I., arid Bryant, JT-. M. D . , J . A m . Chem. SOC., 5 7 , 61 (1935). (18) Zuidema, H. €I., Chem. R e t s . , 38, 197 (1946). (17)
RECEIVED ior review September 18, 1 Q j l . ACCI:PTEDApril 2 8 , 1952. Condensed from a thesis submitted b r E . R . Rooscr to tho faculty of the Graduate School oi The Pennsylrania State College in partial fiilfil!ment of the requirements of the degree of doctor of philosophy.
