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Composition analysis of the oil component of the Nigerian bitumen
Journal of African Earth Sciences, Vot. 12, No. 3, pp. 483-487, 1991.
0899-5362/91 $3.00 + 0.00 © 1991 Pergamon Press plc
Printed in Thailand
Composition analysis of the oil component of the Nigerian bitumen R. A. ODERmDEand E. O. ~ u n Departmentof Chemisu'y,Universityof Ibadan, Ibadan, Nigeria (Acceptedfor publication25th September, 1990) Abstract - The oil comtxmentwhich constitutes about 36 % of the Nigerian bitumen NBC-7 was fractionatedby elution-adsorptionchromatographyon silicagel. The most saturatedendthemost sromaticfractionswere subsequently firactionatedon activatedcharcoal. All the fractionswerecharacterizedby the densime~rictechnique. Resultsobtained indicate the oll component to be a complex smictural frameworkwith the firactionsexhibitingvarying degree of paraff'mic, naphthenic,aromatic, and h e ~ c character. The rings in the molecule are all polycyclic. Some physico-chemicalpropertiesand semi~mpiricalmeasurementswere determined,and results given.
INTRODUCTION
city, reliability, reproducibility, a n d rapidity. The r e s u R s so far reported in literature have b e e n described as quite sat/sfactory (Corbett, 1969; Y u s u f et aL, 1978). The d a t a obtained w o u l d elucidate t h e s t r u c t u r a l f r a m e w o r k of t h e oll c o m p o n e n t a n d provide useful i n f o r m a t i o n s for its c o m m e r c i a l exploration a n d exploitation.
T h e n e e d for t h e c o m p o s i t i o n a n a l y s i s of b i t u m e n s a n d their c o m p o n e n t s c a n n o t be overe m p h a s i z e d , since t h e data obtained would help in solving p r o b l e m s associated with t h e processing, t r a n s p o r t a t i o n , a n d u t i l i z a t i o n of t h e s e substances. There are a n u m b e r of m e t h o d s available in MATERIALS A N D A N A L Y r l C A L P R O C E D U R E S literature for t h e c o m p o s i t i o n analysis of b i t u m e n , b u t m o s t of t h e s e are quite laborious a n d detailed. M a t e f l a l s The u s e of spectroscopic t e c h n i q u e s h a s b e e n S a m p l e w a s collected from t h e NBC-7 well widely employed in t h e analysis of b i t u m e n s (Cyr located in Agbabu, Nigeria. C o m m e r c l a n y availet aL, 1987; Gorelysheva a n d R u d e n - s k a y a , 1971; able a n d a n a l a r grade solvents were used. The adThiel a n d Gray, 1988; Yang et aL, 1988). One of s o r b e n t s u s e d were B r o c k m a n n grade 1, a n d t h e the s h o r t c o m i n g s of t h e s e m e t h o d s is t h a t t h e y c o l u m n w a s m a d e of borosilicate tubing. are m o r e of qualitative r a t h e r t h a n quantitative, a n d in m o s t cases, they are employed in t h e S o l v e n t d e a s p h a l t e n i n g identification of functional g r o u p s p r e s e n t in t h e This aimed at precipitating t h e a s p h a l t e n e from components. t h e b i t u m e n . A b o u t 20g of t h e s a m p l e were reThe densimetric t e c h n i q u e is a n o t h e r m e t h o d fluxed with 2 0 0 m l o f p e n t a n e . The p e n t a n e extract that h a s also b e e n widely employed in t h e com- w a s collected as t h e m a l t e n e after solvent removal. position analysis of b i t u m e n (Corbett, 1964; Y u s u f The precipitated residue w a s filtered a n d t a k e n et al., 1978). T h i s m e t h o d w a s developed by as the a s p h a l t e n e . Corbett (1964) for characterizing asphalts, a n d requires only the e s t i m a t i o n of p e r c e n t carbon, P r e p a r a t i o n o f t h e o i l c o m p o n e n t p e r c e n t h y d r o g e n , a n d t h e m o l e c u l a r weight. This The rnaltene, principally, .composed of t h e r e s i n is t h e n followed by a calculation step, b a s e d u p o n a n d oll c o m p o n e n t s w a s fractlonated by elutionthe relationship b e t w e e n m o l a r v o l u m e a n d atomic a d s o r p t i o n c h r o m a t o g r a p h y o n a l u m i n a . T h e off, h y d r o g e n / c a r b o n ratio. being less polar t h a n t h e resin, c a m e o u t first a n d T h e c o m p o s i t i o n a n a l y s i s of t h e N i g e r i a n w a s eluted with p e n t a n e leaving t h e latter on t h e b i t u m e n or a n y of its c o m p o n e n t s h a s not b e e n c o l u m n . A s c h e m e s h o w i n g t h e p r e p a r a t i o n of t h e investigated a l t h o u g h there h a s b e e n a few reports off c o m p o n e n t is given in Fig. 1. on the properties of the b i t u m e n s (Adegoke a n d Ibe, 1982;Agagu, 1985; Ekwezor, 1985; Oshinowo F r a c t i o n a t i o n o f t h e Oil a n d Adediran, 1982). The oil w a s resolved into t h e s a t u r a t e d a n d In t h e p r e s e n t i n v e s t i g a t i o n , t h e d e n s i - a r o m a t i c f r a c t i o n s b y e l u t i o n - a d s o r p t i o n metric m e t h o d is employed b e c a u s e of its simpli- c h r o m a t o g r a p h y on activated silica gel u s i n g
483
484
R. A. ODER~e AND E . O . ~
Densimetric analysis
bitumen 100
The p e r c e n t c a r b o n a n d p e r c e n t hygrogen were d e t e r m i n e d in t h e microanalytical laboratory of t h e C h e m i s t r y D e p a r t m e n t , University of Ibadan. The m o l e c u l a r weights were d e t e r m i n e d according to the m e t h o d of Bevan et 02. (1965). The calculations were t h e n carried o u t according to Table 3.
i
Solvent~ a l t e n i n g
I
I
I J ~LraNt [. 74.73 i
Chromatography on nluminL elution with
I
I
Physlco-chemlcal properties, and semiempirical measurements
]Pent,..
I I~SINS 38.43
The percents ash, sediment, neutralization value, softening point, specific gravity, a n d aniline p o i n t s were d e t e r m i n e d as described in t h e IP s t a n d a r d s (1976}. The refractive indices, n D were m e a s u r e d on a n Abbe refractometer.
on 36.30
Fig. I. Scheme show/ng the preparation and we/ght composiUons (%) of components of the NBC-7 bitumen.
I OIL 36.30 I
i
Chromatography on silica gel, elution with
I
,I
Methylcyclo hexane
I
Chromatography on Charcoal, elution with
, Pentane
Chromatography on Charcoal, elution with
, Toluene
[
Tol ene
(
Methylcyclohexane
Methylcyclohexane
, Carbon
O's and S's denote the oil fractions obtained from elution-absorption chromatography on silica gel and charcoal respectively Fig. 2. Scheme showing the preparation and weight compositions (%} of the various oil fractions. methylcyclohexane and toluene respectively as eluents. The s a t u r a t e d fraction w a s divided into six p o r t i o n s : 0 t, ---- 06 o n t h e b a s i s of their refractive indices, a n d t h e aromatic fraction m a d e u p t h e s e v e n t h portion 07 . The m o s t saturated fraction 04 w a s f u r t h e r c h r o m a t o g r a p h e d on activated charcoal u s i n g p e n t a n e a n d toluene respectively as e l u e n t s to give S t a n d S 2 fractions. Similarly, t h e m o s t aromatic fraction 07 w a s resolved u s i n g m e t h y l c y c l o h e x a n e , methylcycloh e x a n e - t o l u e n e , a n d c a r b o n tetrachloride respectively as e l u e n t s giving S 3, S 4 a n d S s fractions. A s c h e m e showing' t h e p r e p a r a t i o n of the various oil fractions is given in Fig. 2.
RESULTS AND DISCUSSION The p r e s e n t Investigation a i m e d at c h a r a c t e r izing t h e oil c o m p o n e n t of t h e NBC-7 bitumel~ This w a s achieved by e l u t i o n - a d s o r p t i o n c h r o m a t o g r a p h i c f r a c t i o n a t i o n of t h e oil followed bl d e n s i m e t r i c a n a l y s i s . T h e p r o p e r t i e s of t h b i t u m e n a n d its oil are s u m m a r i z e d in Tables a n d 2. The proportion of t h e oil c o m p o n e n t of the te~¢ s a m p l e is 36.30 %. This value is h i g h e r t h a n mo~, of t h e values reported for o t h e r s a m p l e s of th s a m e origin (Adegoke a n d Ibe, 1982; Ekwezo~ 1985; Oshinowo a n d Adediran, 1982), a l t h o u g the d i s c r e p a n c y Is n o t so great. The values, so fa
Composition analysis of the oil component of the Nigerian bitumen Table I. Properties of the NBC-7 b i t u m e n
Property
Bitumen Property Bitumen
2.24 Neutralization value Softeningpoint, *C 52-56 Specific gravity, 25"C/250C 1.063 748 Molecular weight % Sediment 0.18
%C %H %N % (S + O) % ash
81.54 12.20 1.13 5.13 0.84
Table 2. Properties of the oil fractions of NBC-7 bitumen. Fractions
%C
%1
O1
88.59 89.55 89.26 88.23 86.24 85.38 84.10 87.04 87.68 89.69 90.11 89.58
9.80
02 O,
o, O, O, O, St
$2 $3 $4 $5
9.77 9.68 11.51
9.46 8.86 7.37
8.62 8.79 9.21
8.69 8.83
Aniline
MW 357 390 366 391 420 410 404 373 381 413 388 432
r~ 1.4536 1.4568 1.4573 1.4689 1.4765 1.4792 1.5120 1.4126 1.4188 1-5016 1_5023 1_5067
Point *C 72.10 71.80 70.80 70.60 68.70 65.40 41.50 71.20 70.90 49.50 49.20 48.70
Table 3. Calculation of test parameters by the densimetrie method
By Measurement: MW = %C = %H =
Molecularweight Weightpercent carbon Weightpercent hydrogen
d = #/C = Me/d = (Mc/d)c = =
density=1.4673-0.0431 (% H) hydrogenicarbonratio = 1.92 (% I-I/%C) atomicmolar volume = 1201/d.% C Molarvolume corrected for heteroatoms Mc/d- 6.0 (100 - % C - % H) %C fractionaromatic= 0.09 (Mc/d)c-1.15 (#/C) + 0.77 averagenumberof carbonatoms= (% C.MW)/1200 Condensationindex = 2 - I-[/C - fa total number of rings/tool. = #C(C.I.)/+ 1 numberof carbon atoms in aromaticring = fa.(#C) numberof aromaticringshnol. = #Ca-2)/4 numberof naphthenic rings/mol.= R - Ra
fa #(2 C.[. R #Ca Ra Rn
= = = = = = =
reported, r a n g e b e t w e e n 20 % a n d 40 %. The v a l u e is also less t h a n t h e 51.5 % a n d 3 9 . 6 % r e p o r t e d b y Ells (1914) for t h e oil c o m p o n e n t s of t h e Alberta a n d B e r m u d e z b i t u m e n s respectively. F u r t h e r m o r e , B o y d a n d M o n t g o m e r y (1962) r e p o r t e d 33 % a s t h e p r o p o r t i o n of t h e oil c o m p o n e n t of t h e A t h a b a s c a b i t u m e n of Alberta. S o m e of t h e r e a s o n s a d d u c e d for t h e s e v a r i a t i o n s i n c l u d e t h e c r u d e s o u r c e a n d t h e m e t h o d of a n a l y s i s (Corbett, 1969).
485
The u s e of a l u m i n a a s a d s o r b e n t in t h e elutlonadsorption chromatography ofbltumens and other related s u b s t a n c e s h a s b e e n widely r e p o r t e d in l i t e r a t u r e (Gradler, 1942; Middleton, 1952; Savin et aL, 1955). O t h e r s u b s t a n c e s s u c h as silica gel a n d fuller's e a r t h h a v e also b e e n d e s c r i b e d as s u i t a b l e a d s o r b e n t s (Boyd a n d M o n t g o m e r y , 1962; F u c h s a n d N e t t e s h e i m , 1957; V e m o n , 1920). In m o s t cases, t h e r e s u l t s h a v e b e e n d e s c r i b e d as satisfactory. The m e t h o d of Boyd a n d M o n t g o m e r y (1963) w a s e m p l o y e d in t h e f r a c t i o n a t i o n of t h e oil, a l t h o u g h w i t h a slight modification. The s a t u r a t e s of t h e p r e p a r e d off a c c o u n t for a l m o s t 70 % of t h e total oil fractions. T h i s is h i g h e r t h a n t h e 60 % r e p o r t e d for t h e oil of t h e A t h a b a s c a b i t u m e n (Boyd a n d Montgomery, 1963). This s h o w s t h e oil is largely s a t u r a t e d w i t h s o m e d e g r e e of a r o m a t i c i t y (Boyd a n d M o n t g o m e r y , 1963; Corbett, 1969). The s a t u r a t e s of s o m e s a m p l e s of Nigerian b i t u m e n h a v e b e e n s h o w n to r a n g e b e t w e e n 55 % a n d 80 % (Adegoke a n d Ibe, 1982; Agagu, 1985; Ekwezor, 1985; O s h i n o w o a n d A d e d i r a n , 1982). It is p e r t i n e n t to m e n t i o n t h a t different m e t h o d s h a v e a l w a y s b e e n e m p l o y e d in m o s t cases. T h i s m i g h t be a r e a s o n for the variations. Twelve f r a c t i o n s were i s o l a t e d f r o m t h e off of t h e t e s t s a m p l e a n d all were c h a r a c t e r i z e d b y t h e d e n s i m e t r i c t e c h n i q u e . R e s u l t s of t h e d e n s i m e t r i c a n a l y s i s are p r e s e n t e d in T a b l e s 4 a n d 5. The p a r a m e t e r s u s e d in identifying the average c h e m i c a l s t r u c t u r e s p r e s e n t in t h e off are t h e fraction of a r o m a t i c c a r b o n s fa, t h e n u m b e r of a r o m a t i c rings p e r m o l e Ra; t h e s e two p a r a m e t e r s are indicative of t h e a r o m a t i c c h a r a c t e r ; t h e Rn v a l u e w h i c h r e p r e s e n t s t h e n u m b e r of n a p h t h e n i c r i n g s p e r mole i n d i c a t e s t h e n a p h t h e n i c c h a r a c t e r ; while t h e c o n d e n s a t i o n index, C.I. d i c t a t e s t h e n a t u r e of t h e rings In t h e molecule. If t h e C.I. is positive, t h i s m e a n s t h e r i n g s are polycyclic (Corbett 1964, 1969; Y u s u f et al., 1978). All t h e off f r a c t i o n s exhibit similarities in t h e i r average c h e m i c a l s t r u c t u r e s p r e s e n t w i t h s o m e s l i g h t v a r i a t i o n s . T h e f r a c t i o n 04 is t h e m o s t n a p h t h e n i c b u t least a r o m a t i c , while 0v is t h e least •n a p h t h e n i c b u t m o s t a r o m a t i c of all t h e oil fractions. All t h e o t h e r f r a c t i o n s exhibit intermediate characteristics between these two (Tables 4 a n d 5). A p a r t from t h e above p a r a m e t e r s , t h e H / C ratio also p l a y s a n I m p o r t a n t role in d e t e r m i n i n g t h e a r o m a t i c c h a r a c t e r of a p a r t i c u l a r fraction. For e x a m p l e , t h e 07 f r a c t i o n r e g a r d e d a s t h e m o s t a r o m a t i c h a s t h e least H / C ratio (1:04), c o m p a r e d with 1.56 of t h e f r a c t i o n 04 (leas[ aromatic). All t h e oil fractions, except 04 , c o n t a i n m o r e t h a n f o u r rings p e r mole in t h e i r average c h e m i c a l
486
R. A. ~
,~,~v E . O . ~
Table 4. Denstmetric analysts of oil fractions chromatographed on silica gel. Fractions Property d
#/C Mc/d (Mc./d~ fa C.I. R
Rn
O1
02
1.046 1.30" 12.82 12.78 0.43 0.27 29.10 4.92 12.51 2.63 2.29
1.045 1.32 12.97 12.86 0.41 0.27 26.36 4.56 10.81 2.20 2.36
03
o,
05
0 6
o,
1.050 1.29 12.81 12.74 0.43 0.28 27:22 4.81 11.70 2.43 2.38
1.9712 1.56 14.01 13.99 0.24 0.20 28.74 3.87 6.90 1.23 2.64
1.060 1.31 14.01 12.84 0.42 0,27 30.18 5.07 12.68 2.67 2.40
1.085 1.24 13.14 12.56 0.47 0.29 29.17 5.23 13.71 2.93 2.30
1.150 1.04 12A2 11.81 0.64 0.32 28.31 5.53 18.12 4.03 1.50
Table 5. Dermimetric analysis of oil fractions chromatographed on charcoal.
REFERENCES
Fractions Property d
H/C Mc/d (Mc/d) c fa C.L #C R #Ca Ra Rn
S!
Sa
$1
S4
Ss
1.096 1.18 12.59 12.29 0.52 0.30 27.05 5.06 14.07 3.02 2.04
1.088 1.19 12.58 12.35 0.51 0.36 27.84 6.01 14.20 3.05 2.96
1.070 1.22 12.51 12.44 0.49 0.29 30.87 5.48 15.13 3.28 2.20
1.093 1.15 12.19 12.11 0.54 0.31 29.14 5.52 15.74 3.44 2.08
1.087 1.17 12.33 12.22
0.52 0.31 32.35 6.00 16.77 3.69 2.31
s t r u c t u r e s . T h i s o b s e r v a t i o n is Justified b y t h e R value, w h i c h r e p r e s e n t s t h e total n u m b e r of rings p e r mole, a n d t h e C.I. v a l u e s . The R v a l u e of all t h e f r a c t i o n s is g r e a t e r t h a n 4.5, except 04 (3.87). However, t h e C.I. is positive for all t h e f r a c t i o n s (Tables 4 a n d 5). In a d d i t i o n to these, all t h e f r a c t i o n s c o n t a i n h e t e r o a t o m i c - c o n t a i n i n g c o m p o u n d s as indicated by their molar volumes, M c / d a n d (Mc/d)c (Tables 4 a n d 5). All t h e a b o v e i n f o r m a t i o n s indicate t h e oil to b e a c o m p l e x s t r u c t u r a l f r a m e w o r k with varying degree of paraffinic, n a p h t h e n i c , a r o m a t i c a n d h e t e r o a t o m i c c h a r a c t e r s . No a t t e m p t w a s m a d e to isolate t h e s e v a r i o u s c o m p o u n d s s i n c e t h e a i m of the s t u d y is J u s t to identify t h e average c h e m i c a l s t r u c t u r e s p r e s e n t in t h e off. It is w o r t h m e n t i o n i n g t h a t we a r e n o t a w a r e of a n y p r e v i o u s r e p o r t of t h e s e d a t a o n this partic u l a r off. S i n c e t h e NBC-7 b i t u m e n is a r e p r e s e n t ative of t h e Nigerian b i t u m e n , t h i s report would, t h u s , serve a s guideline for p r o s p e c t i v e w o r k e r s w h o m a y w i s h to u n d e r t a k e similar s t u d i e s in the near future.
Axiegoke, O. S. and Ibe, E. S. 1982. The tar sands and heavy crude resources of Nigeria. Proc. First International Conf., 15-20. Agagu, K. O. 1.985. A geologic guide to bltwninous deposits in South-Western Nigeria, In: (Ibadan Univ. Press), 1-22. Be'van, C. W. L., Red Head, J., and Foley, A. J. 1965. Intermediate Practical Chemistry. Nelson, London, England, 64-5. Boyd, M. L. and Montgome~-, D. S. 1962. Structural group analysis of the asphaltene and resin components of the Athabasca bitumen. Fue/, 41, 335-50. Boyd. M. L. and Montgomery, D. S. 1963. A study of the oil component of the Athabasca bitumen. J. Inst. Petrol.. 49, 345-52. Corbett, L. W. 1964. Densimetrlc method for characterIzing asphalts. Anal. Chem., 38, 1967-71. Corbett, L. W. 1969. Composition of asphalt and densimetric characterization. Anal. Chem., 41, 57. Cyr, N., Mclntyre, D. D., Toth, G. and Strausz, O. P. 1987. Hydrocarbon Structural group analysis of Athabasca asphaltene and its GPC fractions by carbon-13 NMR. Fue/, 8812, 1309-14. Ekwezor, C. M. 1985. Nigerian tar sands, bitumen c h e m i c a l p r o p e r t i e s a n d . t h e i r a p p l i c a t i o n to origin, production, and processing: Twenty-first annual Conf. of the Nig. Minir@ and C,eosclences Soc., 26-40. Ells, E. C. 1914. Preliminary report on the bituminous sands of Northern Alberta. Cannd~ dept. Mines Publ., 281, 86-90. Fuchs, W. and Nettesheim, G. 1957. Analysis and identification of asphaltic petrdeumprod~_~ts. ErdoL U. Koh/e, I0, 15-20. Gorelysheva, L. A. and Rudenskaya, I. M. 1971. Infra red spectroscopic study of bitumen. Netteperer~ Nettekhlm, 5, 10-12. Grader, R. 1942. A method of separating asphalts into group of substances. Oel U. Kohle, 38, 86778.
Composition analysis of the oil component of the Nigerian bitumen IP Standards for petroleum and its products. Methods for analysis and testing. 1976, Section I, Parts 1 and 2. Middleton, W. R. 1952. Adsorption m e t h o d for characterizing asphalts: Am. Chem. Soc., DW. Petrol Chem., Preprints, 3, 2, 445-52. Oshinowo, T. A. B. and Adediran, A. S. 1982. Bituminous tar sands of Nigeria. J. Nkj. Soc. Chem. Eng., I, 44-8. Savin, A. IC, Voreb'ev, S. D. and Monozon, A. M. 1955. Use of Chromatography in the investigaUon of bitumens. Referat Zhur. ~ 8234.
487
Thlel, J. and Gray, M. R. 1988. NMR Spectroscopic CharactertsUcs of Alberta bitumens. AOSTRA J. Res, 41. 63-73. Vernon, I~ K. and WUliam, F. S. 1920. A chemical investigation of the asphalt in the tar sands of Northern A]beria. J. Am. Chem. Soc., 43, 1337-49. Yang, P. W., Mantsch, H. H., Kotlyar, L S. and Woods, J. R. 1988. Characterization of Athabasca tar sands maltenes by diffuse reflectance infra red spectrometry. Energy Plw/s, 21, 26-31. Yusuf, A. A., Nizar, I~ E. and Khalrya, A. A. 1978. Studies of Kuwait Crudes. Ind. Eng. Chem- Prod. Res. Dev., 1712, 165-70.
0899-5362/91 $3.00 + 0.00 © 1991 Pergamon Press plc
Printed in Thailand
Composition analysis of the oil component of the Nigerian bitumen R. A. ODERmDEand E. O. ~ u n Departmentof Chemisu'y,Universityof Ibadan, Ibadan, Nigeria (Acceptedfor publication25th September, 1990) Abstract - The oil comtxmentwhich constitutes about 36 % of the Nigerian bitumen NBC-7 was fractionatedby elution-adsorptionchromatographyon silicagel. The most saturatedendthemost sromaticfractionswere subsequently firactionatedon activatedcharcoal. All the fractionswerecharacterizedby the densime~rictechnique. Resultsobtained indicate the oll component to be a complex smictural frameworkwith the firactionsexhibitingvarying degree of paraff'mic, naphthenic,aromatic, and h e ~ c character. The rings in the molecule are all polycyclic. Some physico-chemicalpropertiesand semi~mpiricalmeasurementswere determined,and results given.
INTRODUCTION
city, reliability, reproducibility, a n d rapidity. The r e s u R s so far reported in literature have b e e n described as quite sat/sfactory (Corbett, 1969; Y u s u f et aL, 1978). The d a t a obtained w o u l d elucidate t h e s t r u c t u r a l f r a m e w o r k of t h e oll c o m p o n e n t a n d provide useful i n f o r m a t i o n s for its c o m m e r c i a l exploration a n d exploitation.
T h e n e e d for t h e c o m p o s i t i o n a n a l y s i s of b i t u m e n s a n d their c o m p o n e n t s c a n n o t be overe m p h a s i z e d , since t h e data obtained would help in solving p r o b l e m s associated with t h e processing, t r a n s p o r t a t i o n , a n d u t i l i z a t i o n of t h e s e substances. There are a n u m b e r of m e t h o d s available in MATERIALS A N D A N A L Y r l C A L P R O C E D U R E S literature for t h e c o m p o s i t i o n analysis of b i t u m e n , b u t m o s t of t h e s e are quite laborious a n d detailed. M a t e f l a l s The u s e of spectroscopic t e c h n i q u e s h a s b e e n S a m p l e w a s collected from t h e NBC-7 well widely employed in t h e analysis of b i t u m e n s (Cyr located in Agbabu, Nigeria. C o m m e r c l a n y availet aL, 1987; Gorelysheva a n d R u d e n - s k a y a , 1971; able a n d a n a l a r grade solvents were used. The adThiel a n d Gray, 1988; Yang et aL, 1988). One of s o r b e n t s u s e d were B r o c k m a n n grade 1, a n d t h e the s h o r t c o m i n g s of t h e s e m e t h o d s is t h a t t h e y c o l u m n w a s m a d e of borosilicate tubing. are m o r e of qualitative r a t h e r t h a n quantitative, a n d in m o s t cases, they are employed in t h e S o l v e n t d e a s p h a l t e n i n g identification of functional g r o u p s p r e s e n t in t h e This aimed at precipitating t h e a s p h a l t e n e from components. t h e b i t u m e n . A b o u t 20g of t h e s a m p l e were reThe densimetric t e c h n i q u e is a n o t h e r m e t h o d fluxed with 2 0 0 m l o f p e n t a n e . The p e n t a n e extract that h a s also b e e n widely employed in t h e com- w a s collected as t h e m a l t e n e after solvent removal. position analysis of b i t u m e n (Corbett, 1964; Y u s u f The precipitated residue w a s filtered a n d t a k e n et al., 1978). T h i s m e t h o d w a s developed by as the a s p h a l t e n e . Corbett (1964) for characterizing asphalts, a n d requires only the e s t i m a t i o n of p e r c e n t carbon, P r e p a r a t i o n o f t h e o i l c o m p o n e n t p e r c e n t h y d r o g e n , a n d t h e m o l e c u l a r weight. This The rnaltene, principally, .composed of t h e r e s i n is t h e n followed by a calculation step, b a s e d u p o n a n d oll c o m p o n e n t s w a s fractlonated by elutionthe relationship b e t w e e n m o l a r v o l u m e a n d atomic a d s o r p t i o n c h r o m a t o g r a p h y o n a l u m i n a . T h e off, h y d r o g e n / c a r b o n ratio. being less polar t h a n t h e resin, c a m e o u t first a n d T h e c o m p o s i t i o n a n a l y s i s of t h e N i g e r i a n w a s eluted with p e n t a n e leaving t h e latter on t h e b i t u m e n or a n y of its c o m p o n e n t s h a s not b e e n c o l u m n . A s c h e m e s h o w i n g t h e p r e p a r a t i o n of t h e investigated a l t h o u g h there h a s b e e n a few reports off c o m p o n e n t is given in Fig. 1. on the properties of the b i t u m e n s (Adegoke a n d Ibe, 1982;Agagu, 1985; Ekwezor, 1985; Oshinowo F r a c t i o n a t i o n o f t h e Oil a n d Adediran, 1982). The oil w a s resolved into t h e s a t u r a t e d a n d In t h e p r e s e n t i n v e s t i g a t i o n , t h e d e n s i - a r o m a t i c f r a c t i o n s b y e l u t i o n - a d s o r p t i o n metric m e t h o d is employed b e c a u s e of its simpli- c h r o m a t o g r a p h y on activated silica gel u s i n g
483
484
R. A. ODER~e AND E . O . ~
Densimetric analysis
bitumen 100
The p e r c e n t c a r b o n a n d p e r c e n t hygrogen were d e t e r m i n e d in t h e microanalytical laboratory of t h e C h e m i s t r y D e p a r t m e n t , University of Ibadan. The m o l e c u l a r weights were d e t e r m i n e d according to the m e t h o d of Bevan et 02. (1965). The calculations were t h e n carried o u t according to Table 3.
i
Solvent~ a l t e n i n g
I
I
I J ~LraNt [. 74.73 i
Chromatography on nluminL elution with
I
I
Physlco-chemlcal properties, and semiempirical measurements
]Pent,..
I I~SINS 38.43
The percents ash, sediment, neutralization value, softening point, specific gravity, a n d aniline p o i n t s were d e t e r m i n e d as described in t h e IP s t a n d a r d s (1976}. The refractive indices, n D were m e a s u r e d on a n Abbe refractometer.
on 36.30
Fig. I. Scheme show/ng the preparation and we/ght composiUons (%) of components of the NBC-7 bitumen.
I OIL 36.30 I
i
Chromatography on silica gel, elution with
I
,I
Methylcyclo hexane
I
Chromatography on Charcoal, elution with
, Pentane
Chromatography on Charcoal, elution with
, Toluene
[
Tol ene
(
Methylcyclohexane
Methylcyclohexane
, Carbon
O's and S's denote the oil fractions obtained from elution-absorption chromatography on silica gel and charcoal respectively Fig. 2. Scheme showing the preparation and weight compositions (%} of the various oil fractions. methylcyclohexane and toluene respectively as eluents. The s a t u r a t e d fraction w a s divided into six p o r t i o n s : 0 t, ---- 06 o n t h e b a s i s of their refractive indices, a n d t h e aromatic fraction m a d e u p t h e s e v e n t h portion 07 . The m o s t saturated fraction 04 w a s f u r t h e r c h r o m a t o g r a p h e d on activated charcoal u s i n g p e n t a n e a n d toluene respectively as e l u e n t s to give S t a n d S 2 fractions. Similarly, t h e m o s t aromatic fraction 07 w a s resolved u s i n g m e t h y l c y c l o h e x a n e , methylcycloh e x a n e - t o l u e n e , a n d c a r b o n tetrachloride respectively as e l u e n t s giving S 3, S 4 a n d S s fractions. A s c h e m e showing' t h e p r e p a r a t i o n of the various oil fractions is given in Fig. 2.
RESULTS AND DISCUSSION The p r e s e n t Investigation a i m e d at c h a r a c t e r izing t h e oil c o m p o n e n t of t h e NBC-7 bitumel~ This w a s achieved by e l u t i o n - a d s o r p t i o n c h r o m a t o g r a p h i c f r a c t i o n a t i o n of t h e oil followed bl d e n s i m e t r i c a n a l y s i s . T h e p r o p e r t i e s of t h b i t u m e n a n d its oil are s u m m a r i z e d in Tables a n d 2. The proportion of t h e oil c o m p o n e n t of the te~¢ s a m p l e is 36.30 %. This value is h i g h e r t h a n mo~, of t h e values reported for o t h e r s a m p l e s of th s a m e origin (Adegoke a n d Ibe, 1982; Ekwezo~ 1985; Oshinowo a n d Adediran, 1982), a l t h o u g the d i s c r e p a n c y Is n o t so great. The values, so fa
Composition analysis of the oil component of the Nigerian bitumen Table I. Properties of the NBC-7 b i t u m e n
Property
Bitumen Property Bitumen
2.24 Neutralization value Softeningpoint, *C 52-56 Specific gravity, 25"C/250C 1.063 748 Molecular weight % Sediment 0.18
%C %H %N % (S + O) % ash
81.54 12.20 1.13 5.13 0.84
Table 2. Properties of the oil fractions of NBC-7 bitumen. Fractions
%C
%1
O1
88.59 89.55 89.26 88.23 86.24 85.38 84.10 87.04 87.68 89.69 90.11 89.58
9.80
02 O,
o, O, O, O, St
$2 $3 $4 $5
9.77 9.68 11.51
9.46 8.86 7.37
8.62 8.79 9.21
8.69 8.83
Aniline
MW 357 390 366 391 420 410 404 373 381 413 388 432
r~ 1.4536 1.4568 1.4573 1.4689 1.4765 1.4792 1.5120 1.4126 1.4188 1-5016 1_5023 1_5067
Point *C 72.10 71.80 70.80 70.60 68.70 65.40 41.50 71.20 70.90 49.50 49.20 48.70
Table 3. Calculation of test parameters by the densimetrie method
By Measurement: MW = %C = %H =
Molecularweight Weightpercent carbon Weightpercent hydrogen
d = #/C = Me/d = (Mc/d)c = =
density=1.4673-0.0431 (% H) hydrogenicarbonratio = 1.92 (% I-I/%C) atomicmolar volume = 1201/d.% C Molarvolume corrected for heteroatoms Mc/d- 6.0 (100 - % C - % H) %C fractionaromatic= 0.09 (Mc/d)c-1.15 (#/C) + 0.77 averagenumberof carbonatoms= (% C.MW)/1200 Condensationindex = 2 - I-[/C - fa total number of rings/tool. = #C(C.I.)/+ 1 numberof carbon atoms in aromaticring = fa.(#C) numberof aromaticringshnol. = #Ca-2)/4 numberof naphthenic rings/mol.= R - Ra
fa #(2 C.[. R #Ca Ra Rn
= = = = = = =
reported, r a n g e b e t w e e n 20 % a n d 40 %. The v a l u e is also less t h a n t h e 51.5 % a n d 3 9 . 6 % r e p o r t e d b y Ells (1914) for t h e oil c o m p o n e n t s of t h e Alberta a n d B e r m u d e z b i t u m e n s respectively. F u r t h e r m o r e , B o y d a n d M o n t g o m e r y (1962) r e p o r t e d 33 % a s t h e p r o p o r t i o n of t h e oil c o m p o n e n t of t h e A t h a b a s c a b i t u m e n of Alberta. S o m e of t h e r e a s o n s a d d u c e d for t h e s e v a r i a t i o n s i n c l u d e t h e c r u d e s o u r c e a n d t h e m e t h o d of a n a l y s i s (Corbett, 1969).
485
The u s e of a l u m i n a a s a d s o r b e n t in t h e elutlonadsorption chromatography ofbltumens and other related s u b s t a n c e s h a s b e e n widely r e p o r t e d in l i t e r a t u r e (Gradler, 1942; Middleton, 1952; Savin et aL, 1955). O t h e r s u b s t a n c e s s u c h as silica gel a n d fuller's e a r t h h a v e also b e e n d e s c r i b e d as s u i t a b l e a d s o r b e n t s (Boyd a n d M o n t g o m e r y , 1962; F u c h s a n d N e t t e s h e i m , 1957; V e m o n , 1920). In m o s t cases, t h e r e s u l t s h a v e b e e n d e s c r i b e d as satisfactory. The m e t h o d of Boyd a n d M o n t g o m e r y (1963) w a s e m p l o y e d in t h e f r a c t i o n a t i o n of t h e oil, a l t h o u g h w i t h a slight modification. The s a t u r a t e s of t h e p r e p a r e d off a c c o u n t for a l m o s t 70 % of t h e total oil fractions. T h i s is h i g h e r t h a n t h e 60 % r e p o r t e d for t h e oil of t h e A t h a b a s c a b i t u m e n (Boyd a n d Montgomery, 1963). This s h o w s t h e oil is largely s a t u r a t e d w i t h s o m e d e g r e e of a r o m a t i c i t y (Boyd a n d M o n t g o m e r y , 1963; Corbett, 1969). The s a t u r a t e s of s o m e s a m p l e s of Nigerian b i t u m e n h a v e b e e n s h o w n to r a n g e b e t w e e n 55 % a n d 80 % (Adegoke a n d Ibe, 1982; Agagu, 1985; Ekwezor, 1985; O s h i n o w o a n d A d e d i r a n , 1982). It is p e r t i n e n t to m e n t i o n t h a t different m e t h o d s h a v e a l w a y s b e e n e m p l o y e d in m o s t cases. T h i s m i g h t be a r e a s o n for the variations. Twelve f r a c t i o n s were i s o l a t e d f r o m t h e off of t h e t e s t s a m p l e a n d all were c h a r a c t e r i z e d b y t h e d e n s i m e t r i c t e c h n i q u e . R e s u l t s of t h e d e n s i m e t r i c a n a l y s i s are p r e s e n t e d in T a b l e s 4 a n d 5. The p a r a m e t e r s u s e d in identifying the average c h e m i c a l s t r u c t u r e s p r e s e n t in t h e off are t h e fraction of a r o m a t i c c a r b o n s fa, t h e n u m b e r of a r o m a t i c rings p e r m o l e Ra; t h e s e two p a r a m e t e r s are indicative of t h e a r o m a t i c c h a r a c t e r ; t h e Rn v a l u e w h i c h r e p r e s e n t s t h e n u m b e r of n a p h t h e n i c r i n g s p e r mole i n d i c a t e s t h e n a p h t h e n i c c h a r a c t e r ; while t h e c o n d e n s a t i o n index, C.I. d i c t a t e s t h e n a t u r e of t h e rings In t h e molecule. If t h e C.I. is positive, t h i s m e a n s t h e r i n g s are polycyclic (Corbett 1964, 1969; Y u s u f et al., 1978). All t h e off f r a c t i o n s exhibit similarities in t h e i r average c h e m i c a l s t r u c t u r e s p r e s e n t w i t h s o m e s l i g h t v a r i a t i o n s . T h e f r a c t i o n 04 is t h e m o s t n a p h t h e n i c b u t least a r o m a t i c , while 0v is t h e least •n a p h t h e n i c b u t m o s t a r o m a t i c of all t h e oil fractions. All t h e o t h e r f r a c t i o n s exhibit intermediate characteristics between these two (Tables 4 a n d 5). A p a r t from t h e above p a r a m e t e r s , t h e H / C ratio also p l a y s a n I m p o r t a n t role in d e t e r m i n i n g t h e a r o m a t i c c h a r a c t e r of a p a r t i c u l a r fraction. For e x a m p l e , t h e 07 f r a c t i o n r e g a r d e d a s t h e m o s t a r o m a t i c h a s t h e least H / C ratio (1:04), c o m p a r e d with 1.56 of t h e f r a c t i o n 04 (leas[ aromatic). All t h e oil fractions, except 04 , c o n t a i n m o r e t h a n f o u r rings p e r mole in t h e i r average c h e m i c a l
486
R. A. ~
,~,~v E . O . ~
Table 4. Denstmetric analysts of oil fractions chromatographed on silica gel. Fractions Property d
#/C Mc/d (Mc./d~ fa C.I. R
Rn
O1
02
1.046 1.30" 12.82 12.78 0.43 0.27 29.10 4.92 12.51 2.63 2.29
1.045 1.32 12.97 12.86 0.41 0.27 26.36 4.56 10.81 2.20 2.36
03
o,
05
0 6
o,
1.050 1.29 12.81 12.74 0.43 0.28 27:22 4.81 11.70 2.43 2.38
1.9712 1.56 14.01 13.99 0.24 0.20 28.74 3.87 6.90 1.23 2.64
1.060 1.31 14.01 12.84 0.42 0,27 30.18 5.07 12.68 2.67 2.40
1.085 1.24 13.14 12.56 0.47 0.29 29.17 5.23 13.71 2.93 2.30
1.150 1.04 12A2 11.81 0.64 0.32 28.31 5.53 18.12 4.03 1.50
Table 5. Dermimetric analysis of oil fractions chromatographed on charcoal.
REFERENCES
Fractions Property d
H/C Mc/d (Mc/d) c fa C.L #C R #Ca Ra Rn
S!
Sa
$1
S4
Ss
1.096 1.18 12.59 12.29 0.52 0.30 27.05 5.06 14.07 3.02 2.04
1.088 1.19 12.58 12.35 0.51 0.36 27.84 6.01 14.20 3.05 2.96
1.070 1.22 12.51 12.44 0.49 0.29 30.87 5.48 15.13 3.28 2.20
1.093 1.15 12.19 12.11 0.54 0.31 29.14 5.52 15.74 3.44 2.08
1.087 1.17 12.33 12.22
0.52 0.31 32.35 6.00 16.77 3.69 2.31
s t r u c t u r e s . T h i s o b s e r v a t i o n is Justified b y t h e R value, w h i c h r e p r e s e n t s t h e total n u m b e r of rings p e r mole, a n d t h e C.I. v a l u e s . The R v a l u e of all t h e f r a c t i o n s is g r e a t e r t h a n 4.5, except 04 (3.87). However, t h e C.I. is positive for all t h e f r a c t i o n s (Tables 4 a n d 5). In a d d i t i o n to these, all t h e f r a c t i o n s c o n t a i n h e t e r o a t o m i c - c o n t a i n i n g c o m p o u n d s as indicated by their molar volumes, M c / d a n d (Mc/d)c (Tables 4 a n d 5). All t h e a b o v e i n f o r m a t i o n s indicate t h e oil to b e a c o m p l e x s t r u c t u r a l f r a m e w o r k with varying degree of paraffinic, n a p h t h e n i c , a r o m a t i c a n d h e t e r o a t o m i c c h a r a c t e r s . No a t t e m p t w a s m a d e to isolate t h e s e v a r i o u s c o m p o u n d s s i n c e t h e a i m of the s t u d y is J u s t to identify t h e average c h e m i c a l s t r u c t u r e s p r e s e n t in t h e off. It is w o r t h m e n t i o n i n g t h a t we a r e n o t a w a r e of a n y p r e v i o u s r e p o r t of t h e s e d a t a o n this partic u l a r off. S i n c e t h e NBC-7 b i t u m e n is a r e p r e s e n t ative of t h e Nigerian b i t u m e n , t h i s report would, t h u s , serve a s guideline for p r o s p e c t i v e w o r k e r s w h o m a y w i s h to u n d e r t a k e similar s t u d i e s in the near future.
Axiegoke, O. S. and Ibe, E. S. 1982. The tar sands and heavy crude resources of Nigeria. Proc. First International Conf., 15-20. Agagu, K. O. 1.985. A geologic guide to bltwninous deposits in South-Western Nigeria, In: (Ibadan Univ. Press), 1-22. Be'van, C. W. L., Red Head, J., and Foley, A. J. 1965. Intermediate Practical Chemistry. Nelson, London, England, 64-5. Boyd, M. L. and Montgome~-, D. S. 1962. Structural group analysis of the asphaltene and resin components of the Athabasca bitumen. Fue/, 41, 335-50. Boyd. M. L. and Montgomery, D. S. 1963. A study of the oil component of the Athabasca bitumen. J. Inst. Petrol.. 49, 345-52. Corbett, L. W. 1964. Densimetrlc method for characterIzing asphalts. Anal. Chem., 38, 1967-71. Corbett, L. W. 1969. Composition of asphalt and densimetric characterization. Anal. Chem., 41, 57. Cyr, N., Mclntyre, D. D., Toth, G. and Strausz, O. P. 1987. Hydrocarbon Structural group analysis of Athabasca asphaltene and its GPC fractions by carbon-13 NMR. Fue/, 8812, 1309-14. Ekwezor, C. M. 1985. Nigerian tar sands, bitumen c h e m i c a l p r o p e r t i e s a n d . t h e i r a p p l i c a t i o n to origin, production, and processing: Twenty-first annual Conf. of the Nig. Minir@ and C,eosclences Soc., 26-40. Ells, E. C. 1914. Preliminary report on the bituminous sands of Northern Alberta. Cannd~ dept. Mines Publ., 281, 86-90. Fuchs, W. and Nettesheim, G. 1957. Analysis and identification of asphaltic petrdeumprod~_~ts. ErdoL U. Koh/e, I0, 15-20. Gorelysheva, L. A. and Rudenskaya, I. M. 1971. Infra red spectroscopic study of bitumen. Netteperer~ Nettekhlm, 5, 10-12. Grader, R. 1942. A method of separating asphalts into group of substances. Oel U. Kohle, 38, 86778.
Composition analysis of the oil component of the Nigerian bitumen IP Standards for petroleum and its products. Methods for analysis and testing. 1976, Section I, Parts 1 and 2. Middleton, W. R. 1952. Adsorption m e t h o d for characterizing asphalts: Am. Chem. Soc., DW. Petrol Chem., Preprints, 3, 2, 445-52. Oshinowo, T. A. B. and Adediran, A. S. 1982. Bituminous tar sands of Nigeria. J. Nkj. Soc. Chem. Eng., I, 44-8. Savin, A. IC, Voreb'ev, S. D. and Monozon, A. M. 1955. Use of Chromatography in the investigaUon of bitumens. Referat Zhur. ~ 8234.
487
Thlel, J. and Gray, M. R. 1988. NMR Spectroscopic CharactertsUcs of Alberta bitumens. AOSTRA J. Res, 41. 63-73. Vernon, I~ K. and WUliam, F. S. 1920. A chemical investigation of the asphalt in the tar sands of Northern A]beria. J. Am. Chem. Soc., 43, 1337-49. Yang, P. W., Mantsch, H. H., Kotlyar, L S. and Woods, J. R. 1988. Characterization of Athabasca tar sands maltenes by diffuse reflectance infra red spectrometry. Energy Plw/s, 21, 26-31. Yusuf, A. A., Nizar, I~ E. and Khalrya, A. A. 1978. Studies of Kuwait Crudes. Ind. Eng. Chem- Prod. Res. Dev., 1712, 165-70.