2 Characterization
of
Alkanes
in
Extracts
of
Coals,
Lignites, and Related Fuels K. D. BARTLE
Downloaded by UNIV OF CALIFORNIA SAN DIEGO on March 9, 2016 | http://pubs.acs.org Publication Date: November 12, 1982 | doi: 10.1021/bk-1982-0205.ch002
University of Leeds, Department of Physical Chemistry, Leeds LS2, 9JT, England
D. W. JONES and H. PAKDEL University of Bradford, School of Chemistry, Bradford BD7, 1DP, England 1
13
The application of H and C N.M.R. spectroscopy, gas chromatography (G.C.) and mass spectrometry (M.S.) in the separation and identification of alkanes extracted from fossil fuels is illustrated with three Turkish lignites (including one extracted by supercritical gas), coal tar and petroleum crude. Elution of hydrocarbons from a silica-gel column may be monitored byHN.M.R. and molecular-sieve sub-fractionation into normals and branched/cyclics by G.C., together with C N.M.R. T measurements. G.C. (e.g. with a eutectic packed column) can enable individual normal, isoprenoid and cyclic alkanes, valuable as geochemical indicators, to be identified. C N.M.R. chemical shifts are consistent with G.C.-M.S. identifications of acyclic isoprenoids in several fuels. 1
13
1
13
Alkanes in Fossil Fuels. Sedimentary rocks, which range in age from Recent (MO* years) to the pre-Cambrian period (^3 χ 10 years), contain the major reservoir of organic (and reactive) carbon in the crust of the earth, deposited as fossil fuels: these include oil shale, coal, petroleum, tar sands, natural asphalts and natural gas. The organic matter in fossil fuels contains, in addition to carbon, several percent each of hydrogen and oxygen; coals and related fuels typically also include 1-5$ nitrogen and 1—10% sulphur (and small amounts of many other elements). These complicated coal materials are thought to have been generated by anaerobic degradation of plant and animal materials by micro organisms in a reducing environment. From asphaltites to highrank coals, the carbon content increases and hydrogen content decreases (Table I); crude oils, to which some reference will also be made here, have higher hydrogen contents (and much lower mineral contents) than the solid fuels. 1
0097-6156/82/O205-0O27$06.0O/O © 1982 American Chemical Society
Fuller; Coal and Coal Products: Analytical Characterization Techniques ACS Symposium Series; American Chemical Society: Washington, DC, 1982.
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COAL AND COAL PRODUCTS
28
Table I Alkane Content o f Hydrocarbon Minerals and Other
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Source
Recent sediments Crude o i l s O i l shales Turkish asphaltites Bituminous c o a l s Lignites T u r k i s h Montan Wax
Sediments
Atomic H/C R a t i o o f Organic Matter
% Alkanes i n Organic Matter
1.7-1.9 1.5-2.0 1.3-1.6 1.3 0.5-0.7 0.7-1.0 0.80
0.8-36.9 30-1+5 6 ^-10 0.U-0.7 0.01-1.0 0.05
Saturated hydrocarbons amount t o 30 or k0% o f petroleum crudes and are thus o f d i r e c t economic importance. Although the much s m a l l e r p r o p o r t i o n s o f alkanes i n c o a l s represent very l i t t l e d i r e c t commercial v a l u e , a knowledge o f the alkanes e x t r a c t e d from c o a l l i q u i d s can be o f c o n s i d e r a b l e h e l p i n determining the behaviour d u r i n g p r o c e s s i n g o f commercial f u e l products, as w e l l as i n organic geochemical i n v e s t i g a t i o n s o f the nature and o r i g i n o f f u e l s . The alkanes are g e n e r a l l y present as a multi-component mixture o f (a) a c y c l i c s - n o r m a l s (predominant), singly-branched (iso and anteiso), and m u l t i p l y branched (mainly a c y c l i c i s o p r e n o i d s ) — and (b) c y c l i c s ( n a p h t h e n i c s ) — mono-, d i - , t r i - , t e t r a - , and p e n t a c y c l i c s , i n c l u d i n g isoprenoids (Table I I ) . A n a l y t i c a l Spectroscopy and Spectrometry o f F o s s i l F u e l s . I n v e s t i g a t i o n o f the composition and s t r u c t u r e o f f u e l s has f o r long p r o v i d e d one o f the major f i e l d s o f i n d u s t r i a l a p p l i c a t i o n of molecular spectroscopy (J_). More r e c e n t l y , the demand f o r d e t a i l e d s t r u c t u r a l analyses o f f o s s i l - f u e l e x t r a c t s has been stimulated both by i n c r e a s e d i n t e r e s t i n energy sources i n g e n e r a l , e s p e c i a l l y t h e i r organic geochemistry and the e n v i r o n mental consequences o f combustion, and, a l s o , f o r c o a l i n p a r t i c u l a r , by the need f o r i n f o r m a t i o n on the chemical s t r u c t u r e of the s t a r t i n g m a t e r i a l and o f subsequent stages o f new c o a l conversion processes. A wide range of s p e c t r o s c o p i c methods ( 2j , i n c l u d i n g n u c l e a r magnetic resonance (N.M.R.) ( i n s o l u t i o n and i n s o l i d ) , e l e c t r o n s p i n resonance (E.S.R.), i n f r a r e d ( I . R . ) , u l t r a v i o l e t (U.V.), X-ray and luminescence, has been a p p l i e d t o the s t r u c t u r a l a n a l y s i s o f f o s s i l f u e l s . However, f o r m a t e r i a l s as complex as c o a l s , p r e l i m i n a r y s u b d i v i s i o n o f e x t r a c t s i s an e s s e n t i a l p r e - r e q u i s i t e f o r s u c c e s s f u l e x p l o i t a t i o n o f these spectroscopic techniques (3.). Thus, when alkanes have been i s o l a t e d , t h e i r f u r t h e r s u b - f r a c t i o n a t i o n i n t o η and branchedc y c l i c alkanes may be achieved by 5^ m o l e c u l a r - s i e v e a d s o r p t i o n , a method which we g e n e r a l l y p r e f e r t o t h i o u r e a - or urea-adduction.
Fuller; Coal and Coal Products: Analytical Characterization Techniques ACS Symposium Series; American Chemical Society: Washington, DC, 1982.
2.
BARTLE ET AL.
Characterization of Alkanes
29
TABLE II Saturated Hydrocarbons
Typical
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Type (a)
Carbon S t r u c t u r e
Formula
acyclic
(i)
Normal
(ii)
Iso
n 2n+2
C
H
C H n
n
n
(iii)
n
Z
CH
Acyclic isoprenoid
n
Singlybranched
2 n + 2
Z
C H
Ante-iso
(b)
Group
+
9 a n
9
+
Z
Singlybranched
9 d
9
Ζ η
~
ά
Polybranched
cyclic
(iv)
Monoterpane
C^
C H
Q
(Sesquiterpene C |
Monocyclic
0
η en
n 2n-2
C 5
H
Dicyclic
(v) C H
(Diterpane (vi)
Diterpane
(vii)
Sterane
(viii)
Triterpane
« D i cJ y c l i c
η 2n-2 0
n 2n-4
C
H
CH
η Zn-o
R C
0
c
n 2 -8 H
n
Τ Η
