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A Study of the Structure of Petroleum Asphaltenesand Related Substances by Proton Nuclear MagneticResonanceTeh Fu Yen a , Wen Hui Wu a & George V. Chilingar aa School of Engineering University of Southern California, Los Angeles, CaliforniaVersion of record first published: 12 Jul 2010.

To cite this article: Teh Fu Yen , Wen Hui Wu & George V. Chilingar (1984): A Study of the Structure of Petroleum Asphaltenesand Related Substances by Proton Nuclear Magnetic Resonance, Energy Sources, 7:3, 275-304

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A Study of the Structure ofPetroleum Asphaltenes andRelated Substances by ProtonNuclear Magnetic Resonance

Teh Fu Yen, Wen Hui Wu*, and George V.ChilingarSchool of EngineeringUniversity of Southern CaliforniaLos Angeles, California

Abstract The distribution of hydrogen according to struc­tural type in a series of representative asphaltic materials wasinvestigated by proton nuclear magnetic resonance (NMR). De­termination of the fraction of total hydrogens, which are satu­rated, hs' by using the NMR technique was shown to be moreaccurate than by infrared spectrophotometry. Also, by utilizingdata on the diameter of the aromatic sheets, La' obtained by x­ray diffraction, the shape of the aromatic centers was shown tovary but, on the whole, to be highly condensed and in no casechainlike in nature. Approximately 48 to 70 percent of the po­sitions on the edge of the aromatic centers are substituted byatoms other than hydrogen. While the presence of naphthenicgroups was confirmed, lack of reference data did not permit de­termination of size, shape, or degree of substitution. For thefractions prepared from crude oils, approximately 29 to 66 per­cent of the terminal carbons are in methyl or ethyl groups at-

Wen Hui Wu is 8 visiting scholar from the Research Institute of Petroleum Processing; Ministry ofPetroleum, P.O. Box 914, Beijing, People's Republic of China.

Energy Sources. Volume 7. Number 30090-8312/84/010275-00$02.0010Copyright © \984 Crane, Russak & Company, Inc.

275

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276 Teh Fu Yen, Wen Hui Wu, and George V. Chilingar

tached to the aromatic centers. NMR results confirmed theconclusion reached previously that mild thermalcracking resultsin the cleaving of chainsand dehydrogenation of the naphthenicstructures to aromatic structures.

IntroductionThe dark-colored, high-molecular-weight, nonhydrocarbon por­tion of crude oils and related bitumens is referred to as the as­phaltic fraction. For a given bitumen the asphaltic fraction isbelieved to consist of structurally similar molecules varying mainlyin molecular weight. In crude oils the asphaltic fraction may rep­resent less than the limit of detection, or as much as 50 percentof the total. Much larger amounts of asphaltic material, partic­ularly of high molecular weight and consequently having poor sol­ubility, are found in the source rocks in which the bitumen isbelieved to have originated. In studying the asphaltic fraction ofcrude oils, it is usually divided into two fractions based on solu­bility in n-pentane, the soluble portion being known as resin andthe insoluble portion as asphaltene.

The average structure of the molecules making up the asphalticfraction of crude oils and related bitumens has been under studyby the writers, using methods that have proved useful for the elu­cidation of the structure of polymers and other complex mole­cules. Densimetric, NMR, and infrared data have indicated acarbon-atom-to-total-ring ratio of about 6 [16]. The X-ray dif­fraction data have indicated aromaticities ranging from 0.2 to 0.6;diameters of the aromatic sheets, from 8.5 to 15 A; intersheet dis­tances from 3.55 to 3.70 A; stacking of sheets to the extent of 4 or5; and a spacing between saturated structural units of 5.5 to 6.0A [17]. Studies of rates of oxidation with permanganate have in­dicated that theheteroatoms, 0, N, and S occur in chemicallystable configurations, probably rings [8]. Infrared data indicatedthat naphthenic groups are present as well as aromatic and par­affinic ones. Electron spin resonance (ESR) data has shown thatthe unpaired electrons (free radicals) are located in the aromaticsheets [18]. In conjunction with metalization studies, ESR inves­tigation also showed that the sites for the unpaired electrons as

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Structure oj Petroleum Asphaltenes 277

well as for metal coordination are probably "imperfections" or"holes" in the aromatic sheets caused by the loss or replacementof internal carbons with heteroatoms such as nitrogen Pl.

These studies provided little or no quantitative information con­cerning the shape of the aromatic sheets, the extent of substitutionof the aromatic sheets and naphthenic groups, and the location ofmethyl groups relative to the condensed ring systems. In order toinvestigate these structural features, as well as to obtain indepen­dent values for certain other structural features previously deter­mined, a study was carried out using proton NMR. This methodwas selected because of its capacity to distinguish between hydro­gens in different structural environments within a molecule andto provide data for each in terms of the total number of hydro­gens.

Williams in 1958 [14] and in 1959 [13] was one of the first touse NMR to study petroleum fractions. As early as 1960, Brownand Ladner [2, 3] studied the low-temperature vacuum carboni­zation products from coals. Despite difficulties stemming fromthe presence of large amounts of phenolic hydrogen, they wereable to make a separation into three hydrogen types equivalent tothose of Williams. From these they were able to approximate thenumber of substitutable positions on the edge of the aromaticsheets, the degree of substitution, and the aromaticity. Oth et al.[11] examined several solvent extracts of coal and calculated thevalues for the ratio of aromatic to saturated hydrogen. Sebor etal. [5] used NMR spectroscopy to characterize an asphalt-resinfraction. The aromaticity increased from maltenes to asphalt toasphaltenes with increasing fraction molecular weight. High-tem­perature proton NMR was reported by Yokeno et al. [6] for eth­ylene tar .pitch. Pyrolysis depolymerization and polycondensationcan be monitored by the high-temperature technique.

Recently, Gillet et al. [9] used NMR spectroscopy to study somecrude oil and petroleum products and proposed some rules forobtaining reliable structural parameters. A method has been sug­gested to approximate the aliphatic and naphthenic saturated car­bons.

Several petroleum-derived materials have been characterizedstructurally by Dickinson [10]. The structures of petroleum resi-

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278 Teh Fu Yen, Wen Hui Wu, and George V. Chilingar

dues were compared by constructing hypothetical average mole­cules based on these average parameters.

ExperimentalSamples

The preparation of the asphaltene fractions of the crude oils; gil­sonite, and Kuwait visbreaker tar is described in a paper by Erd­man and Ramsey [8], and of the resin fraction in a paper by Yenet al.[I7].

The reference polymers were prepared in the laboratory. Thepolyacenaphthylene, poly-o-vinylanaphthalene, poly-2,5-dime­thylstyrene, poly-2-methyl-4-t-butylstyrene, and poly-2,6-di­methyl-4-t-butylstyrene were obtained from Drs. E. H. Gleasonand E. C. Hurdis, both associated with the Research Laboratoriesof the Koppers Co., Inc. The polybenzyl was. prepared by inter­facial polymerization of benzene and formaldehyde. The poly-a­methyl-styrene, polyindene, and poly-p-vinyltoluene were pre­pared by anionic polymerization of the monomers using n-butyl­lithium.

Instrumentation and Methods

Two Varian NMR spectrometers were used. The early portion ofthe study, involving some of the synthetic polymers and asphal­tene substances, was carried out using an A-60 or T-60 NMR,whereas the latter portion was carried out using an HR-IOO NMR.For studies at elevated temperatures, a Varian variable tempera­ture probe and closed loop temperature controller were used inconjunction with the A-60 NMR spectrometer.

Carbon disulfide and deuterated chloroform, and in some casesperdeuterated pyridine, were used as standard solvents. For as­phaltenes and resin, the concentration in the solvent was 10 per­cent. Owing to their limited solubility, the polymers were used atsaturation.

Where resonance bands overlapped, the areas were separatedusing the method of Brown et al. [3]. The areas were measured

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Structure of Petroleum Asphaltenes 279

repeatedly with a planimeter until good reproducibility was at­tained.

DiscussionThe NMR spectra of petroleum asphaltenes are qualitatively sim­ilar. A typical curve is shown in Figure I. The region of strongerresonance between () = 8.0 to 6.5 ppm is assigned to hydrogensattached to aromatic ring systems. The absence of absorption be­tween these regions rules out the presence of hydrogens attachedto carbons of isolated olefinic bonds. In the following discussion,the designation of the hydrogen types will be abbreviated to sat­urated, aromatic, and so on.

Qualitatively, a spectrum of asphaltics, for example, the Bax­terville resin, is very similar to that of a polymer, such as poly (2­methyl-4-t-butylstyrene). Figure 2 serves as an illustration, al­though there are no naphthenic protons in the polymer.

Inasmuch as in proton NMR the area under a peak is directlyproportional to the number of hydrogens contributing to the peak,the fraction of the total number of hydrogens that are saturated,i.e., Hsl H or b« [15], can be obtained from the areas under thecurve in the respective regions of resonance. In this respect, thecalculation is essentially the same as that used previously by theauthors to determine hs from infrared data [15]. The NMR valuesof hs for eight native petroleum asphaltenes, a petroleum resin, agilsonite asphaltene, and an asphaltene prepared from a refinerybottom producer are listed in the. third column of Table 1: .Thevalues, averaging a little above 0.9, are close to those obtained forthe same samples from infrared data. The h, values are shown inthe second column of Table 2.

In order to compare the accuracy of the two methods .of deter­mining hs, nine polymers of known structure with hs values rang­ing from 0.25 to 0.90 were studied by both NMR and infraredmethods. The true values of hs as determined from the formulas,the values obtained from NMR, and the values indicated by in­frared analysis are listed in Table 3 and plotted relative to eachother in Figure 3. The asphaltic materials have been plotted onthe basis of the two methods of determination. The data for the

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Structure oj Petroleum Asphaltenes

BAXTERVILLE RESIN

281

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Structure of Petroleum Asphaltenes 285

a::

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PolymersG NMR vs. true<:> Infrared vs. true

ASRhaltenes and RelatedSubstances 6

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Numbers Correspond to those in the First Column of Table 3.)

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286 Teh Fu Yen, Wen Hui Wu, and George V. Chilingar

polymers, as shown in the table and the figure, indicate that NMRvalues of hs are approximately three times as accurate as thoseobtained by using infrared analysis.

In Figure I it is evident that the structure in the saturated andthe aromatic regions, particularly the former, is complex. For ref­erence and comparison, the chemical shift values for the hydro­gens of a number of compounds of known structure are listedacross the top of the figure. Williams [13] and Brown and Ladner[2] have investigated the structure of certain petroleum and coalfractions by grouping the hydrogen types according to chemicalshift and-correlating these data with the spectrum for the bitumenfraction. In each case, the saturated region of the spectrum wasdivided into two parts. For the petroleum asphaltenes and relatedbituminous substances under study, the complexity of the satu­rated hydrogen resonance seemed to justify a more comprehensiveanalysis. Accordingly, the saturated region was broken down intofour subgroups:

h =S

HexH

+ +

The assignments are given in Table 4, whereas the numerical val­ues are·presented in the last four columns of Table 1.

In order to evaluate the above terms, it is assumed that the ab­sorption corresponding to each subgroup is a symmetrical curve,or conversely, that the observed curve between 0 = 3.5 and 0.5may be considered as a composite of four symmetrical curves. Ac­cordingly, the curves recorded at 60 Mc/s for each of the asphalticsubstances resolved into four symmetrical peaks as shown in Fig­ure 1. This step was carried out following a procedure describedby Brown and Ladner, whereby the amplitude is deduced fromthe slope on the high field side of the observed resonance. Thegeometric procedure for resolving the experimental curve into itsfour symmetrical components is considered to be accurate to 5percent or better.

In the following discussion, the values of H N , H R , and HsM,areassumed to be due to the major contributors, i.e., to naphthenic,

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hele

tters

a~nd

Pin

dic

ate

po

siti

on

srela

tiv

eto

ana

rom

ati

cri

ng

.

~ 'I

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288 Teh Fu Yen, Wen Hui Wu, and George V. Chilingar

paraffinic methylene other than those 0 or fJ to an aromatic ring,and paraffinic methyl similarly other than 0 or fJ, respectively. Theprincipal departure-from this assumption comes from the fusedring naphthenic contributions to H R and H SMe' Whereas data onsuch compounds are as yet meager, the spectra for the decalins(II indicate that when bridge hydrogens are in the cis-configura­tion, the entire hydrogen resonance concentrates essentially in asingle peak at 0 = 1.41, i.e., within the range assigned to H N •

When the bridge hydrogens are in the trans-configuration, how­ever, about one third of the resonance is spread out to lower 0values concentrating mainly in the range assigned to Hs Me ' No dataare known to exist for more highly condensed naphthenic ring sys­tems, particularly where internal as well as peripheral bridge meth­ine groups are present. Thus, it has been assumed that thenaphthenic contribution to H SMe and H R will be no more than thatof an equivalent 1:1 mixture of cis- and transdecalin, i.e., H N maybe low by as much as 1/6 H N (or 18 percent) and H SMe may behigh by as much as 1/6 H N that, for the asphaltic materials understudy, would range from 13 percent to 20 percent. The effect onH R also would be such as to make the values high, but only by afew percent.

In the experiment described below, a sample of known com­position was examined and its spectrum correlated with theamounts of the several hydrogen types present, namely, H A , H a ,

HN , H R , and H SMe ' There is considerable difficulty in locating asample of fused-ring naphthenics; a natural hormone has servedthis purpose. Inasmuch as H; is required for this model, smallamounts of H A are also necessarily introduced. Thus, the modelmixture selected has to contain aromatic (HA ) , methyl and meth­ylene substitution (Ha ) , naphthenic (HN ) , paraffinic methylene(HR ) , and paraffinic methyl substitution (HSMe) groups. The sys­tem selected is a mixture of cholestane (I), o-tocopherol (II), andpentamethylbenzene (III) (Figure 4). Experimentally, in order toobtain a mixture whose hydrogen types are close to those of thepetroleum asphaltics, a molar ratio of 5:10:3 for 1:11:111 was used.For this particular experiment, the weights of I, II, and III were0.166 g (0.3 mole), 0.386 g (0.6 mole), and 0.0399 g (0.18 mole),respectively. The detailed calculation was tabulated in Table 5,

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Structure of Petroleum Asphaltenes

Me

MeMe

289

¢Me Me

lUI) . s-: IMe::::-" Me

Me

Me

Figure 4. A Blend of Model Compound for the Simulation of Petroleum As­phaltene, I, Cholestane, II, a-Tocopherol, III, Pentamethylbenzene.

from which the actual hydrogen-type ratios of the blend can beobtained.

The reproducibility of the area measurements was within 5 per­cent. There is fair agreement between experimental and true valuesfor HA> H sM e, and H.; however, the HOi and H N agreement wasonly qualitative. The true value is also subject to certain experi­mental uncertainties, such as weighing, evaporation, and so on,but these are thought to be minor. Purity, however, is not knownand may introduce an appreciable error.

From the area under the component peaks, it is possible to es­timate values for H,", HI> i.e., the average number of carbon at­oms directly attached to an aromatic sheet divided by the numberof hydrogens that would be attached if the aromatic sheet weretotally unsubstituted. Expressed in another manner, C,", HI ratiois the degree of substitution of the aromatic sheets. The derivationis based on the assumption that for a unit of structure, C," is ap­proximately equal to one half of the number of o-hydrogens, HOi,i.e.,

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Tab

le5

Foun

dan

dT

rue

Val

ues

of

Hyd

roge

nT

ypes

of

aP

hy

sical

Ble

nd

.I

IIII

IB

len

dFo

und

Mol

esin

ble

nd

0.3

0.6

0.1

81

.08

Mol

arR

atio

510

3H

IH--

-0

.13

0.1

70

.30

0.2

4H

N/H

0.1

60

.02

---

0.1

80

.14

HR

/H0

.05

0.2

9--

-0

.34

0.3

6H

SMe/

H0

.09

0.1

4--

-0

.23

0.2

5H

A/H

---

---0

.01

0.0

10

.01

~ ;;;l ::- ;p ~ ::s ~ ::s ~ -. ~ § ~ ~ oa "' ~ 9 -, :::- i'

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Structure of Petroleum Asphaltenes

C =(l/2)Ha,su

andHI = H +(1/2)HA a

291

Hence:Csu»: =

The C,u IH, values obtained for the native asphaltenes and relatedsubstances are provided in the second column of Table 6. For thenative asphaltenes the degree of substitution on the edge of thearomatic sheets range from a low of 0.48 to a high of 0.70. Theresin cut of the Baxterville crude oil shows a higher degree of sub­stitution than does the corresponding asphaltene, i.e., 0.70 versus0.62. The degree of substitution for the asphaltene fraction of gil­sonite centers in the range of the native petroleum asphaltenes,which provides another indication of the close structural similarityof gilsonite and the asphaltic fraction of crude oils. The value forthe asphaltene from Kuwait visbreaker tar is about the same asfor the Burgan (Kuwait) crude oil, indicating that light crackinghas not affected the degree of substitution on the edge of the ar­omatic sheets.

Data from NMR also permit the estimation of the Csi C,u ratio,the average number of carbon atoms attached to a position on theedge of an aromatic sheet. Alternately defined, it is the total num­ber of saturated carbon atoms, Cs, divided by the number of car­bon atoms attached to the edge of the aromatic sheet:

HR

+ EN HSMe

Cs = Csu + 2 + -3-

= 1 +(Hn -tHN) /2 + H"&..'Je/3

H /2a

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Tab

le6

Va

lues

for

Str

uctu

ra

lP

ara

met

ers

of

Pet

role

um

Asp

ha

lten

esan

dR

ela

ted

Su

bst

an

ces

Ca

lcu

late

dfr

omNH

RD

ata

!e

Sam

ple

Cs

u/1I

1C

S/C

su

III/

CA

IIN/C

NC

SMe/

CM

e~

Pet

role

um

Asp

ha

lten

es;:0

-

~B

ax

terv

ille

0.6

24

.00

.34

---

0.>

0L

ag

un

illa

s0

.71

3.2

OJ,3

l.25

0.4

7~

8u

rga

n0

.51

3.6

0.5

20

.97

0.4

22'-

Wah

.N

o.A

-l0

.61

4.1

0.4

21

.09

0.4

2M

ara

0.4

85

.60

.38

0.9

80

.71

~W

afr.

No.

170

.60

3.4

0.5

30

.98

0.3

4R

aud

hat

ain

0.5

73

.70

.48

0.8

20

.42

::sR

ag

us

ta0

.70

4.8

0.4

01

.01

0.6

3

~P

etro

leu

mR

esin

s-.

Ba

xte

rvil

le0

.70

3.4

0.6

10

.81

0.4

8?

Gil

son

ite

Asp

ha

lten

es::. ::s

Tab

orv

ein

0.6

24

.30

.60

0.8

10

.55

I:l..

Ref

iner

yA

sph

alte

ne

~ CK

uwai

tv

isb

rea

ker

tar

0.5

22

.60

.39

1.1

40

.28

.~ ~ Q :::

; -. ~ ~

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Structure of Petroleum Asphaltenes

and

293

~SCsu

=hS - HSWe/3H

H /H.- Ct

As shown in Table I, the values of hs are approximately four anda half times those of H SMe ' and in the above equation HSMe is di­vided by three. The effect on Csi Csu of naphthenic contributionto H S M " therefore, can be at most only a few percent. In the aboveequations, however, the assumption is made that there are twohydrogens (HR, H N, or H a ) attached to each methylene carbon,i.e., that the groups attached to the aromatic sheet are straightchains. Inasmuch as branching at the a carbons would decreasethe denominator for H; below 2, the value of Csi Csu as given abovewould be high. Branching, including naphthenic structure not in­volving a carbons, would decrease the denominators for H R andH Nbelow 2; hence, the above value for CsIC," would be low. Theterm "branching" is used here to include naphthenic structure.For the time being, it is assumed that the effects on the value ofCslCsu induced by a and non-a branching will tend to cancel.

The values of Csi Csu ratio for the native petroleum asphaltenesand related substances are listed in the third column of Table 6.For the native asphaltenes and the resin, the values range from3.4 to 5.6, with the gilsonite asphaltene again falling well withinthis range. Comparison of the Kuwait visbreaker tar with the Bur­gan (Kuwait) crude oil shows a marked decrease in Csi Csu. Re­ferring again to Table I, it will be seen that there is a decrease inHRIHand H SM' IH and little change in HNIH. In an earlier paper[171, Yen et al. have shown that the aromaticity,f.. i.e., the frac­tion of carbon atoms that are aromatic, is higher for the asphal­tene from the visbreaker tar than for the corresponding Burgancrude oil. Taking into account the constancy of Csut H, ratio andthe fact that H decreases with increasing fa. it would appear thatlight cracking results mainly in the breaking of chains attached toaromatic rings. Further, inasmuch as HNIH does not increase, itis likely that dehydrogenation is taking place concurrently with thecleavage of paraffinic chains.

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294 Teh Fu Yen, Wen Hui Wu, and George V. Chilingar

The ratio of carbon to hydrogen of the saturated portion ofsample, fs/ hs, increases with increasing saturated chain length,C,I C.u , and with decreasing arornaticity, fa. As the carbon-to-hy­drogen ratio of the saturated portion increases, the ratio of carbonto hydrogen of total sample decreases (Figure 5).

Thus far, very little has been done to determine the shape ofthe condensed aromatic sheets in petroleum asphaltenes, althoughsome research of this type has been done for coals by Brown andLadner (2). It is evident that the value of the ratio of H, to thenumber of aromatic carbon atoms, CM will, for a sheet with agiven long dimension, increase as the degree of condensation orsymmetry decreases. This ratio was determined from NMR dataand from the carbon/hydrogen ratio in the following manner:

_ _C_. CA Ra/H H.NIH. BRIE. HStvle lE= -8--- + 2 + ---2--- + 2 + 3

8.

H

and

2H1=HalH + 2HAIH

H1 H. 18a

Values for HIC are provided in the third column of Table 2.Again, it can be observed that naphthenic contribution to HS Me

would lead to slightly low values of H/CA • For the asphaltic ma­terials under study, the error probably would not exceed 2 percent.

In order to derive the equation above, the assumption shouldbe made that there are two hydrogens attached to each carbon thatis a to aromatic ring or to each naphthenic carbon, i.e., HOI/ COl= 2, and HN/CN = 2. Figure 6 is the plot of two sets of H,/CA ,

which were calculated for different HOI/Ca and HN/CN values.The results signify that different values of HOI/COl and HN/CNdonot affect H,/CA value much. (See Figure 7.)

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f ~ ~ ~ a iii s:: s ~ ~ f2.

0I 1.8

I 1.6

I 1.4

I 1.2

I 1.0

HIe

I0

.8I

0.6

I0

.4

c:,10//

09

,/'"

~1~

.6)"

.

/°

24

Q//

0'

//

//

//

01 /

Io

0.2

1.0,

"I

0.8

1-

0.61

---

0.21

---

~ h S(N

MR

) 0.41

---

Figu

re5.

Var

iatio

no

fC

,IH

,O

ver

the

Ran

geof

Hie

ofA

spha

lten

esas

Stud

ied

byN

MR

(h.)

and

X·R

ay(f

J.'" ~

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296 Teh Fu Yen, Wen Hui Wu, and George V. Chilingar

~"u/ U::E ::Ii

II> II>IU

NII

a:1 noIU

II

z\ 2-IU 0.4If)

NII

"'I tlIU

-------HI ..IU

Figure 6. Effect of Variation of HOt/COt and HN/CNvalues on H,IC, ratio.

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1.0

1;1) -., ;: ...,

I-/

-;: ~

0.8

1-

/~

/~ -

II/

., <:)

'iI~

0.6

1-

4E"

;: s5.

6~32

;.

(Ha

HN

HR

HS

Me)

H~

r-7

'iI'iI

'iI1--+

-+

-+

---

fa(N

MR

)

.:jf!/

82H

2H2H

3HC

~

(H

aH

N'

HR

HSM

.)H

~

0.4

1-

10l::

l'iI

.:.

•::;:

-'iI

01

-2

.5H

+H

+2

H+

3HC

""0

°0

..

:::c

I-

0(H

aH

NH

RH

sMe)

Ha

8~

00

1-

2H+

H+

2H+

3'H

C0

.21

-/.

(h

s)

H•

1-/

•1-

1.65

c:-O

l/I

II

II

II

II

Ia

0.2

0.4

0.6

0.8

i.Ofa

(X-r

oy)

Figu

re7.

Eff

ect

ofV

aria

tions

ofD

iffe

rent

Ass

umed

Coe

ffic

ient

son

thef.

de­

term

ined

byN

MR

Met

hod

and

X-r

ayA

naly

sis.

~ '1

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298 Teh Fu Yen, Wen Hui Wu, and George V. Chilingar

The calculated values of H,I CA are listed in the fourth columnof Table 6. In Figure 8, these values are plotted against the recip­rocal of the layer diameter, L., calculated from X-ray data by themethod of Diamond and reported by Yen et al. [17J. The referencelines represent the values calculated for the two extremes of sym­metry: a circular sheet and a linear katacondensed band. Theequations for these lines were derived as follows:

Circular

HI = (6CA)1/2

Linear BandCA

HI =~ + 3

'« =43r( CA - .z. )4 2

hence4

for an infinite hexagonal net (16)

t. 33/2. r, ..a.~cA--:1=-/=2- = -----:;--- = 1. 62

hence

HI=c;: 3.95 t: -1

·a

where r is the bond distance of the hexagons (r = 1.42..\). It canbe seen from Figure 8 that for the asphaltic materials under study,the average probable symmetry varies, but in no case approachesthat of a linear katacondensed band.

Referring to Table 2, it can be seen that the asphaltenes pre­pared from Lagunillas and Burgan crude oils both have the sameL. value but, according to Figure 9, vary considerably in sym­metry. In order to get a better picture of the average. aromaticsheet in each of these asphaltenes, the H,I CA values were calcu­lated for all possible ring arrangements that would give the closestlong axis, or L., value. The results are shown in Figure 9, whereit is evident that the average aromatic sheet for the Lagunillas as­phaltene corresponds closely to ovalene (m), while the average

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Structure of Petroleum Asphaltenes 299

1.0r--------------------~

o -Native Petraleum AsphalteneYJ - Refinary Asphalteneci-Gilsanite Asphaltene[J - Native Petroleum Resin• - Typicol Aromotic HydrocarbonI I

0.10 0.15 0.2CL -I

o

I0.05

0.2-

------~ ...---..-- -- TerpMnyl _____Links, __ ., ...-

07 t- -- >- Quint:uiot.enyl ~·5 Anthracene /'

• -- -- ~.'II Coeranthen! /~ r Tetracene . ;

PIUr.e .y 9 • u Tnangulene

061- kala -Band ........--""- 10~h [J em ./,... Pyrene

';' I HEnIP~r"flfnE Rubicene Benlfluoranlhene. Perytene..........- • Ttr)'lene z 6-... "

,.........- '.J'Clanthfenf e... 9 .0· 30 \:) JAntr,anlhrene

A 5~ QU2rt.:~yleni' .Anlhro\tlanClUlene. c /' .0• 0 70 k Coronene

Tt'rpher.yllfrylene n 4 ...d ~nthrodianthrene. e:::> v ovatene

ClftUfficintl1rene e~8 2......50' .~ IIYJ

Pentccinexaene b 1 tlisletranrenelOy:" Dinapt",tho avalene

0.3 - . C' I /' Oianthrocircumanlhreneperi- IrCU or

Disk"", .:

»:/

0.11- /

V/°O~-----;::-:~-----;:::-~-----;:::-~-----;::;-;'

0.8f-

0.4 -

0.91-

Figure 8. Estimation of Degree of Ring Condensation of the Aromatic Sheets.The Lines Represent the Theoretical Extremes for Fused Ring Systems.(The open points represent the values for the asphaltic fractions. Thesolid circles represent typical PNA.)

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300 Teh Fu Yen, Wen Hui Wu, and George V. Chilingar

I~

OAJ ------DXir-LOgunillaS 1m!

04at-_ @........ '<,

I

(nl

Figure 9. Comparison of the H,/CA Values of Lagunillas and Burgan Asphal­tenes with Those for Condensed Aromatic Ring Systems with an Ap­proximately Equal Long Axis or L. Value.

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Structure of Petroleum Asphaltenes 301

value for the Burgan asphaltene falls close to anthro- 3' , 5/, I,10 -tetracenyl (k) or 2,3-benznaphtho- 2/, 7/, 1,8 anthryl [I].Whereas it is recognized that these correlations represent the av­erage structure, it should be pointed out that, for the Lagunillasasphaltene at least, it would take nine naphtho- 2/ , 7', 1, 13 ­ovalene (n) nuclei to permit the existence of one tetracene band(a). These findings seem to confirm earlier conclusions [15,17] thatthe aromatic sheets of petroleum asphaltenes approach the shapeof discs in contrast to coals, where the aromatic structure is be­lieved to exist largely in the bent or branched katacondensedbands.

Turning now to the naphthenic portion of the molecule, datafrom NMR and X-ray permit an estimation .of HN/CN, i.e., theratio of the number of naphthenic hydrogens to naphthenic car­bons. One assumption, however, is necessary, i.e., that on the av­erage each paraffin carbon is linked to two hydrogens, i.e., Cpl H;= 112. Accordingly,

R'N H Rp .JLHS H-- -.-+-..- - H.H C H C C

Hp .Cp HN HCN (s

-- -+ f{ =r;C Hp C fIN

C tc = 1 fa ' and-s .

HN!tNIH

= t;I!:{ 1 - H- HS/2H + NIHwe 2 - hs

Values for fa as determined by X-ray analysis are provided in thefourth column of Table 2.

The values calculated for the HNI CN ratio using the above equa­tion are listed in the fifth column of Table 6. Structural iriterpre­tation of H N I CN is made difficult at this time because, as pointedout previously, there is uncertainty concerning the effect of bothperipheral and internal bridge hydrogens on the NMR spectrum

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302 Teh Fu Yen, Wen Hui Wu, and George V. Chilingar

of condensed polynuclear naphthenes. If it is assumed that theaverage naphthenic group contains the same number and arrange­ment of rings as exist in the aromatic sheets and that H N representsonly naphthenic methylene hydrogens, then the extent of sub­stitution could be estimated by comparing the observed HNI CN

values with those for methylene of the unsubstituted naphthenicgroups, which would be given by 2H,I CA. Comparison of the val­ues given in Table 6 shows that in a number of instances HNI CN

> 2H,I CA. Consequently, either the assumption that the na­phthenic and aromatic groups are comparable in number and ar­rangement of rings or that H N can be assumed to represent onlythe methylenic hydrogens of a condensed naphthenic group is in­correct. Studies involving the progressive dehydrogenation of as­phaltenes, as well as a better understanding of NMR spectra ofcondensed naphthenic molecules, should permit verification of oneor rejection of both of the above assumptions and permit a clear­cut structural interpretation.

The last feature to be investigated by NMR was CSMJCM" theratio of the total number of methyl groups that are neither Ci nor{3 to an aromatic ring to the total number of methyl groups. Thisratio can be evaluated quite easily by means of the following equa­tion:

=

where HM,lHs is determined from infrared absorption data [15].Values for HM,IH s are provided in the fifth column of Table 2,whereas those for CSM'I CM, are presented in the sixth column ofTable 6. It is evident that the full effect of transnaphthenic con­tribution to H S M ' will be reflected in the values of CSM'I CM, ratio;hence, the values of the latter may be high by some 15 or 20 per­cent. The values listed in Table 6 for the native petroleum as­phaltenes, the petroleum resin, and the gilsonite asphaltene suggestthat from 1/3 to more than 2/3 of the methyl groups are moreremote than {3 to the aromatic sheets. The low value of 0.28 forthe asphaltene from the Kuwait visbreaker tar compared to 0.42for the asphaltene fraction of the equivalent Burgan crude oil again

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Structure of Petroleum Asphaltenes 303

suggests that mild cracking results in breaking off from the aro­matic sheets of relatively long chains and/or the dehydrogenationof naphthenic groups to which methyls or ethyls are attached.

As further insight into the assignment to the HN band, the NMRspectra of a large number of perhydropolynuclear aromatic hy­drocarbons have been obtained. For most pericondensed na­phthenic systems (even for pure compounds) the signal wandersthrough a wide range in the space of NMR spectra. This is due tospin-spin interaction of protons in a mixture of conformers. Na­phthenics whose signal concentrates in the {) = 1.8 - 1.4 ppmrange are those of kata type, especially the stearane type. Inas­much as a number of terpenoids and related compounds have beenfound in petroleum, this may imply that the naphthenic structurein asphaltic fraction is perhaps similar to the structure of stearaneduring the course of diagenesis.

Finally, it is always dangerous to propose the application ofNMR analysis for structural elucidation of such complex classesof substance as petroleum asphaltics. For example, if a proposedhypothetic structure is adopted, at least most of the structure pa­rameters, such as cun; cue: HI/CA , HN/CN, CSMe/CMe, f ..and so on, have to be very close. In many cases, more than onetool should be used to derive such a structure.

Acknowledgment

A portion of this paper originally appeared in the preprint of theAmerican Chemical Society, 7(3): 99, 1962, issued by the Divisionof Petroleum Chemistry. The original version has completelymodified into the present form and some errors have been cor­rected.

References

I. American Petroleum Institute Research Project 44. 1978. Selected NuclearMagnetic Resonance Spectral Data. Serial No. 14 and 15.

2. Brown, J. K., and Ladner, W. R. 1960. Hydrogen distribution in coal-likematerial by high-resolution nuclear magnetic resonance spectroscopy, II. Acomparison with infrared measurement and the conversion to carbon struc­ture. Fuel, 39: 87-%.

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304 Teh Fu Yen, Wen Hui Wu, and George V. Chilingar

3. Brown, J. K., Ladner, W. R., and Sheppard, N. 1960. Hydrogen distribu­tion in coal-like material by high-resolution nuclear magnetic resonancespectroscopy, I. The measurement and interpretation of the spectra. Fuel,39: 79-86.

. 4. Bhacca, N. S., Johnson, L. F., and Shoolery, J. N. 1962. NMR SpectraCatalog. Varian Associates.

5. Seber, G., Lang, I., Hajek, M., Weiser, 0., and Mosteeky, J. 1977. ProtonNMR structure analysis of asphaltene-resin petroleum fractions. Chem.Prum., 27(9): 455-459.

6. Yokono, J., Miyazawa, K., Sanada, Y., Yamada, E., and Shimokawa, S.1979. High temperature 'H NMR of ethylene-tar pitch. Fuel, 58(3): 237-238.

7. Erdman, J. G., and Harju, P. H. 1963. Capacity of petroleum asphaltenesto complex heavy metals. .[. Chem. Eng. Data, 8: 252-258.

8. Erdman, J. G., and Ramsey, V. G. 1961. Rates of oxidation of petroleumasphaltenes and other bitumens by alkaline perrnanganate. Geochim. et Cos­mochim. Acta, 25(3): 175-188.

9. Gillet, S., Rubini, P., Delpuech, Jean-Jacques, Escalier, Jean-Claude, andValentin; P. 1981. Quantitative carbon-13 and proton nuclear magnetic res­onance spectroscopy of crude oil and petroleum products, I. Some rules forobtaining a set 'of reliable structure parameters. Fuel, 60(3): 221-225.

10. Dickinson, E. M. 1980. Structure comparison of petroleum fraction usingproton and »c NMR spectroscopy. Fuel, 59(5): 290-294.

II. Oth, J. F. M., De Ruiter, E., and Tschamler, H. 1961. Hydrogen in coaland coal extracts, I. The ratio of aromatic to aliphatic hydrogen from pro­ton-spin resonance and infrared measurements. Brennstaff-Chem., 42:378-380.

12. Sadder Research Laboratories, Inc. 1978. The Sadtler Handbook of ProtonNMR Spectra.

13. Williams, R. B. 1959. Nuclear Magnetic Resonance. Spectrochem. Acta, 14:24-44.

14. Williams, R. B. 1958. Characterization of hydrocarbon in petroleum by nu­clear magnetic resonance spectrometry. A STM Spectral Technical Publica­tion No. 224: 168-194.

15. Yen, T. F., and Erdman, J. G. 1962. Investigation of the structure of pe­troleum asphaltenes and related substance by infrared analysis. Arn. Chem.Soc., Div. Pet. Chem., Preprints 7(1): 5-18.

16. Yen, T. F., Erdman, J. G., and Hanson, W. E. 1961. Reinvestigation ofdensimeter methods of ring analysis. J. Chern. Eng. Data, 6: 443-448.

17. Yen, T. F., Erdman, J. G., and Pollack, S. S. 1961. Investigation of thestructure of petroleum asphaltenes by X-ray diffraction. Anal. Chem., 33:1587-1594.

18. Yen, T. F., Erdman, J. G., and Saraceno, A. J. 1962. Investigation of thenature of free radicals in petroleum asphaltenes and related substances byelectron spin resonance. Anal. Chem., 34: 694-700.

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