Analysis of the organic matter in five oil shales

Analysis shales S. R. Palmer,

of the organic

A. F. Gaines

matter

in five oil

and A. W. P. Jarvie

Department of Chemical Engineering and Applied Chemistry, Triangle, Birmingham B4 7ET, UK (Received 4 January 1989; revised 18 May 7989)

Aston

University,

Aston

The organic matter in five oil shales (three Kimmeridge clays, one Oxford clay and one from the Julia Creek deposits in Australia) was concentrated by acid demineralisation and then further degraded, first by reduction with LiAIH, then by oxidation with perTFA and/or KMnO,. At each stage, products were separated into soluble and insoluble fractions by solvent extraction. The fractions were analysed using a range of appropriate techniques, including solution and solid state ‘H and i3C n.m.r., FT-i.r., g.p.c. and g.c.-m.s.. These analyses confirmed previous observations that oil shales, like coals, consist of a mobile and a rigid phase. In addition, it was found that a close relation existed between chemical structures present in the bitumens and in their associated kerogens, and that one of the kerogens differed from the other four in that isoprenoid chains predominated over straight chains throughout the system. Oxidation with perTFA gave residues that were predominantly aliphatic in character. PerTFA appeared to be a better oxidant than KMnO, for structural analysis in that it gave fewer secondary products. (Keywords:

demineralization;

solvent extraction;

oil shale)

A previous paper’ reported the application of methods commonly used in the analysis of coals to the structural analysis of two oil shales, a Kimmeridge clay (KCY) and an Oxford clay (OC). This study has now been extended to three further oil shales (two others (KCDl and KCD2) from the Kimmeridgian sequence and one (JC) from the Julia Creek deposits in Australia), with the addition of stepwise permanganate oxidation2 and Deno3-’ oxidation (H,O,/CF,CO,H) to the range of techniques used in the systematic breakdown of the complex oil shales into more amenable soluble materials. Inorganic materials were dissolved out of the shales the conventional HF/HCl mixture6,7. The using acid-treated products were analysed and the pyridineinsoluble kerogens were reduced with LiAlH,. The organic products from each stage of the breakdown process (Figure 1) were extracted with pyridine because this had previously been found to be the most effective solvent. To facilitate analysis, the pyridine extracts were fractionated into chloroform-solubles and -insolubles. So far investigations have been limited to the chloroformsoluble fractions and the pyridine-insoluble reduced kerogens. The five reduced, pyridine-extracted kerogens were oxidised with KMnO, and/or perTFA (H,O,/CF,CO,H) according to Figure 2. Alkaline KMnO, is probably the most widely used oxidant for the analysis of carbonaceous materials8T9; perTFA, on the other hand, has been extensively used in coal studies3p5 but there are few reports of its application to kerogens. Permanganate belongs to a group of traditional oxidants (e.g. chromate, oxygen, nitric acid) that attack benzylic positions in alkyl aromatics”, whereas perTFA selectively attacks aromatic positions in such molecules leaving the benzylic positions useful information has been intact’ ‘. Since much obtained from oxidation of coal with perTFA, it was thought worthwhile to carry out comparative investi0016-2361/89/lOl234-09S3.00 0 1989 Butterworth & Co. (Publishers)

1234

Ltd.

FUEL, 1989, Vol 68, October

gations of permanganate and Deno oxidation of the kerogens. Both procedures gave a residue insoluble in base, and after methylation a methylated humic acid-like fraction (MHA) and a dichloromethane-soluble fraction.

Powdered

I Acid deminerallsed Analysis

4-1

rock HF. HCI organic matter Py extraction

So*ble Bitumens CHCI,

CHCI,

bitumens

(11, 7, 4, 3, 41

Kerogens extraction

Py bitumens

i)

LIAIH,

ii)

H,O

reduction quench

I

(17. “,a

Aqueous

solution

I Quench

CHCI,

Reduced

residue

extraction

extract

(< 0.01)

Reduced

kerogen

Py extract (20.1.

lO,l,l)

I CHCI,

CHCI,

A

soluble

CHCI,

extraction

insoluble

110.1,4,1,1)

Figure 1 Pyridine extracts of organic products from each stage of the breakdown process. Figures in brackets represent the percentage soluble based on the original acid-treated kerogen, in the order KCY, JC, OC, KCDl, KCD2

Analysis

Deno oxidation

CHCI,

Residue

in five oil shales:

S. R. Palmer

of the Kimmeridgian

+ aqueous base layers

Precipitate

Demineralized kerogens (before extraction with pyridine)

CHCI, + aqueous layer CHCI,

I

extraction

KCY JC

QC Aqueous layer

KCDl KCD2

Reduced kerogens (before extraction with pyridine)

H/C ratios

Ash (%)

Pyrite (%)

H/C ratios

0.91 1.09 1.29 1.19 1.19

40 20 18 14 19

56 18 28 14 13

0.98 1.31 1.30 1.31 1.32

Before oxidation, the reduced residues with pyridine (Soxhlet) until no further discernible (usually 10 days).

Methylated

products Extraction

with CH,CI,

Solubles

MHA Figure 2 Oxidation of reduced, KMnO, and/or perTFA

pyridine-extracted

kerogens

with

The experimental procedures did not permit the recovery of carbon dioxide and highly polar water soluble acids. EXPERIMENTAL clay

Taken from the bottom of No. 2 pit of the London Brick Company at Calvert, Buckinghamshire (Grid Ref. SP 680 240)

KCY

Kimmeridge clay

Taken from the base of the cliff at Port Mulgrove, North Yorkshire (Grid Ref. NZ 790 170)

KCD 1

Kimmeridge clay

Taken 120cm below Rope Lake Headstone Band from the cliff at Clavell’s Hard, 1.5 km east of Kimmeridge Bay, Dorset (Grid Ref. SY 920 777)

Kimmeridge clay

Taken 60 cm above Rope Lake Headstone Band from the cliff at Clavell’s Hard, 1.5 km east of Kimmeridge Bay, Dorset (Grid Ref. SY 920 777)

KCD2

JC

samples

Rock samples were powdered, demineralised with HF/HCl and reduced with lithium aluminium hydride, as described previously’. Analytical data are shown below.

of NaOH to pH14

Acidify

Oil shale samples Oxford oc

et al.

Sample preparation

Total reaction product mixture Addition

matter

A more detailed description is available’2~‘3.

Reduced kerogen

I

of organic

Julie Creek

Sample supplied by Dr H. Stephenson, Marquarie University, New South Wales, Australia

Ash (%) 2.0 4.3 2.0 1.2 1.6 were extracted extraction was

Procedure for perTFA oxidationt4 The oxidation mixture (80 ml; CF,COOH + 30% aq H,O, + H,SO, in a volume ratio of 8:10:5) was added over a period of 15 min to 2 g of kerogen suspended in 100 ml of distilled CHCl,. This mixture was then refluxed for 5 h. After cooling, the reaction mixture was made alkaline (pH 14) by adding 20% w/v NaOH solution and then filtered at the pump. The filter cake (residue) was washed with distilled water and dried in a vacuum. The CHCl, and aqueous alkaline layers in the filtrate were then acidified with cone HCl to pH 1 and, after cooling overnight, filtered at the pump. The precipitate was washed, dried in vacua and retained for methylation. The remaining filtrate was then extracted with CHCl,; the extract was evaporated and the residue combined with the precipitated acids for methylation. The remaining aqueous solution was discarded. Methylation procedure The combined precipitated acids and CHCl, extracts were dried and then refluxed with 20ml of 14% BF, in experiments had methanol for three days15. Preliminary shown that this extended reaction time was necessary for complete reaction. The resulting mixture was then extracted with CH,Cl, and the insoluble material (MHA) isolated and dried. The CH,Cl, extract was washed with lOOm1 of saturated NaCl solution, and this aqueous phase was then extracted with CH,Cl, (2 x 35 ml). The combined CH,Cl, extracts were then washed with 100 ml of 10% aq Na,CO, and finally with lOOm1 of saturated NaCl solution. The final CH,Cl, solution was dried over MgSO, before evaporation in a rotary evaporator. These procedures are summarised in Figure2. Stepwise alkaline potassium permanganate oxidation’ Kerogens (0.5 g), distilled water (20 ml) and potassium permanganate stock solution (20 ml; 4.5 g KMnO, + 6.4 g KOH in 1OOOml distilled water) were reacted together at room temperature. When all colour of permanganate had disappeared from the reaction mixture it was filtered and the filter cake was treated with a further 20ml of

FUEL, 1989, Vol 68, October

1235

Analysis

of organic

matter

in five oil shales:

S. R. Palmer

stock solution. This was repeated 15 times; after this number of steps the consumption of permanganate, measured by the loss of colour, was found to be extremely slow even on heating to 60°C. All filtrates were combined and then acidified to precipitate the oxidised materials. These were methylated as above and extracted with dichloromethane. The H/C atomic ratios of the MHAs and the residues obtained by the two oxidation procedures are shown below. Residues KCY JC oc KCDl KCD2

MHAs

perTFA

KMnO,

perTFA

KMnO,

0.97 1.19 1.33 1.17 1.21

1.02 1.19 1.14 1.25 1.30

0.66 0.97 1.40 1.28 1.26

0.82 1.10 1.23 0.99 1.21

Instrumentation

Infrared spectra were recorded using a Perkin Elmer 1710 FT-i.r. spectrometer fitted with a Perkin Elmer 3600 data station, Solids were examined by the KBr disc method while the soluble materials were examined as thin films on NaCl plates. Carbon, hydrogen and nitrogen determinations were carried out using a Carlo Erba auto analyser model 1106. Each sample was analysed ten times and the average taken to reduce any problems due to the inherent heterogeneity of these systems. V,Os was added in some cases to assist combustion. ‘H and i3C n.m.r. spectrometry of the soluble materials was carried out using a Bruker AC series 300MHz n.m.r. spectrometer. TMS was added as the reference standard. Samples were dissolved in CDCl,. Solid state 13C n.m.r. spectra were obtained on the same instrument using magic angle spinning (4 KHz), proton decoupling (60 KHz) and cross polarisation (proton enhancement) with a contact time of 3ms. A recycle time of 4 s was used. Preliminary g.1.c. examination of soluble degradation products was carried out using a Pye Unicam gas chromatograph litted with a 1 m x OScm i.d. SE30 column. All g.c.-m.s. work was performed with a VG MM 12000 series quadrupole mass spectrometer, fitted with a 30m SE30 bonded phase fused silica column (0.3mm i.d.), which was programmed from 50°C to in the source (200°C) 300°C at 8°C min- ‘. Ionisation took place at 70eV and mass spectra were recorded every 2s using a Digital 200 data system. Solutions in chloroform (2% w/v) were examined by gel permeation chromatography using a Perkin Elmer series 10 liquid chromatograph fitted with a Perkin Elmer LC-85B spectrophotometric variable wavelength detector. The column was calibrated with n-alkanes as low molecular weight calibrants and polystyrene fractions with a

Table 1

Summary

of g.c.-m.s.

analysis

of CHCl,

et al. maximum molecular weight calibrants. RESULTS Analysis

weight of 6 x 10” as high molecular

AND DISCUSSION of demineralised

bitumens

Sample

Iso-alkane/n-alkane

n-Alkane C, 1-C,,

distribution

Pristane/phytane

Aliphatic/aromatic _

C

1.60

13.1 Il.4 7.1

n-Alkane

maxima

KCY

0.26

JC

0.81

C, i-C,*

CL

C,,

I .28

oc

0.22

C,,-C,,

C,,,

C,,

0.65

KCDI

0.65

C, 1-C,*

KCD2

6.61

C, ,-Cu

CI,, Cl,, C 14

1236

FUEL, 1989,

Vol 68, October

materials

Information obtained from g.c.-m.s. analysis of all five chloroform soluble bitumens is summarised in Table I, which includes a number of parameters that can be used to characterise bitumens and their origins. These parameters include the pristane/phytane ratio, the n-alkane distribution and the n-alkane maxima within these distributions. The distribution of n-alkanes in all of the samples is approximately C,,-C,,, and this, together with maxima at C,,-C,,, suggests a lower plant origin (cyanobacteria or algae) for the organic matter in these deposits 16-19 The KCDl and OC samples show maxima at C,, and C,, as well as at Cl,. Such bimodal n-alkane distributions have been noted previously for Kimmeridge clays, and it has been suggested that the higher alkanes originate from lower land plants such as mosses*’ In four of the bitumens n-alkanes predominate over branched chain species, whereas for the KCD2 bitumen the opposite is true. The high concentration of isoprenoid systems in the KCD2 sample may reflect a different source input but it may also be due to biodegradation. It is known that contact between crude oils and certain bacteria will lead to depletion of n-alkanes in the oils21,22. Degradation of isoprenoids also occurs but much more slowly. The pristane/phytane ratios of the five samples indicate that KCY and JC were deposited in oxidising environments and OC, KCDl and KCD2 in reducing environments23. The Northern Yorkshire Kimmeridge sample (KCY) has a pristane/phytane ratio of 1.6, which is higher than for the Dorset samples (KCDl and KCD2). Although high values have been observed previously for Yorkshire Kimmeridge clays, a satisfactory explanation of why there is such a difference between the Yorkshire and Dorset clays has not been forthcoming24. It may well be due to the greater maturity of the Yorkshire clays since it has been observed that as coalitication proceeds, the pristane/phytane ratio increases, possibly via the cracking of phytane to pristane. The FT-ir., ‘H and 13C n.m.r. analyses confirmed the observations from g.c.-m.s., that for all the samples this bitumen fraction was predominantly aliphatic in character and that the KCD2 sample was unique within the group. This sample showed significantly higher methyl/methylene peak ratios whether calculated from i.r. or n.m.r. data, and whereas for the other samples the major aliphatic peak in the 13C spectrum was at 29.8ppm, arising from the methylene groups of long linear chains, for the KCD2 sample the peak of greatest

C*,

0.91

2.1

0.75

10.2

Analysis of organic matter in five oil shales.. S. R. Palmer et al. intensity was the aliphatic peak at 37.6ppm, which can be attributed to the methylene groups (*CH,) shown belowz5 This sample also shows intense absorptions at 39.7 and 33.0 ppm; the former may be attributed to CH, groups near the terminus of an isoprenoid chain, and the latter to the methine groups (+CH) of an isoprenoid chainz6. +YH3

+VH3

-CH,-XCH,-CH2CH,-CH2~CH2-CH~CH,-

Thef, values calculated from 13C n.m.r. data and from ‘H measurements using the Brown-Ladner equation” are given in Table2. Although there are large variations between f, values obtained using the two methods, the trends within the bitumen series are consistent. Both

Table 2

Calculated

f, values for chloroform

bitumens

Sample

C/H

f” .a

X3”

KCY JC oc KCDl KCD2

0.91 0.65 0.51 0.49 0.46

0.55 0.32 0.22 0.10 0.00

0.27 0.18 0.20 0.18 0.14

“Calculated ‘Calculated

Table 3

from ‘H measurement using the Brown-Ladner from 13C n.m.r. data

G.p.c.

data for the chloroform

Sample

Detector

KCY

ri

bitumens Polydispersity

M,

M,

equation

MW Range”

UV

930 650

6760 6960

7.2 10.5

140 00&20 8OOOG12

JC

rc uv

1350 930

4300 4450

3.1 4.7

50 000-60 50 000-60

oc

ri “V

600 420

8370 18940

13.9 44.6

23OOOG12 180000@12

KCDl

ri uv

660 630

9950 7170

14.9 11.4

70000@12 23000@12

KCD2

ri uv

1710 1200

9640 10570

5.6 8.8

230 O&60 230 00&30

_ “The lower MW values are clearly erroneous of suitable calibrants for the g.p.c. column ri, Refractive index; uv, ultraviolet

Table 4

Distribution

of carbon

and arise because

environments

of lack

methods indicate that aromaticity follows the order The discrepancies KCY > JC > OC > KCDl > KCD2. between the the values from the two methods probably arise from errors in the assumptions made in the Brown-Ladner calculations and from the uneven enhancement of 13C nuclei due to the nuclear Overhauser effect. G.p.c. analysis of the bitumens revealed much higher molecular weights than g.c.-m.s. (Table3), with M, typically in the 10000-4000 range and M, in the 2000400 range. In general, molecular weights ranged from several hundred thousand to 12. Obviously the low end of the molecular weight distribution is in error, and illustrates the problem of not having a suitable calibrant for bitumens. In the case of the OC sample, a bitumen component having a molecular weight of 1.8 x lo6 was detected by the U.V. detector; this value is exceptionally high, and may be due to aggregate formation. The polydispersity figures show that these systems are all highly heterogeneous, which would be expected considering the nature and the source of the bitumens. Analysis of the kerogens was restricted to solid state techniques. FT-i.r. spectrometry provided a functional group analysis of each kerogen, which, together with elemental analyses and the n.m.r. data (Tab/e#), showed that apart from the KCY sample, the kerogens consisted predominantly of aliphatic material with various amounts of carboxylic, alcoholic, phenolic and other units. The greater aromaticity of the KCY sample establishes its greater maturity, as indicated by the high pristane/phytane ratio found in the KCY bitumen. Both FT-i.r. and n.m.r. showed the KCD2 kerogen to contain more isoprenoid structures than the other kerogens. Analysis of LiAlH,-reduced materials The FT-i.r., ‘H and i3C n.m.r. spectra of the chloroform-soluble reduction products were very similar to those of the corresponding bitumens, with only minor differences. As would be expected, the OH peaks were slightly stronger and sharper and the >C=O peaks weaker. These residual > C=O absorptions probably arise from reoxidation of samples during work-up. The chloroform-soluble reduced materials generally gave well-resolved spectra. This was particularly true of the 13C n.m.r. spectrum of the KCDl sample, the aromatic region of which clearly showed two sets of three carbon

in the kerogens Contribution

Carbon

Range

1

21G170

carbonyl”

2

170-129

subs + bridgehead

3

129-100

protonated

4

1OC-60

5

(ppm)

KCY

environment

Region

of each carbon

JC

oc

_

environment

(%)

KCDl

KCD2

_

_

34

25

20

17

17

19

20

14

14

11

alcoholsethers

1

3

9

2

6

6G50

methoxy

5

4

8

6

7

6

50-24

methylene-methine

35

41

42

49

47

7

244

methyl

6

I

I

12

12

0.53

0.45

0.34

aromatic

aromatic

f,” “Carbonyls could not be determined aromatic carbon signal “f,=_ total carbon signal

because

of the spinning

0.31

0.28

side band subtraction

FUEL,

1989,

Vol 68, October

1237

Analysis Table 5 Sample

of organic Summary

matter

of g.c.-ms.

in five oil shales:

analysis

of chloroform-soluble

Iso-alkane/n-alkane

n-Alkane

JC

0.09

CNC,, C,,-C,0

oc

0.13

C,,-C**

KCY

KCDl KCD2

Table 6

0.50

Distribution

of oxidation

S. R. Palmer

products

reduction

et al. products

distribution

Pristane/phytane

Aliphatic/aromatic -_-__

C

_

18.4

C::? C,,

1.07

0.26

C 19

0.31

4.51

C,g-C,,

C 24

_

4.35

C,&,*

C 23

0.44

0.21

from perTFA

n-Alkane

and KMnO,

Sample

perTFA

-.

oxidations Recovery”

Residues

maxima

(wt%)

MHA KMnO,

perTFA

Solubles KMnO,

perTFA

Total product KMnO,

perTFA

KMnO,

KCY

36.5

49.2

14.1

11.1

13.5

12.0

64.1

JC

53.0

29.3

8.7

19.8

16.6

22.3

19.3

71.4

oc

19.0

2.2

30.4

13.1

26.6

30.7

76.0

46.0

72.3

KCDl

37.5

32.5

44.1

25.5

9.3

8.3

101.5

66.3

KCD2

61.3

44.2

8.1

9.7

46.3

20.8

115.7

74.7

“All weight percentages The oxidation products

are expressed in terms of the dry, ash-free parent contained very little inorganic matter (ash ~2%)

resonances. The first set, at 129.7, 128.4 and 127.2ppm, is attributable to unsubstituted benzene ring carbons and the second set, at 145.7, 141.3 and 169.6ppm, to aromatic carbons substituted with a CH,OH group. There was also a peak at 64.0ppm, which can be attributed to the carbon atom of -CH,OH. These observations indicate that benzoic acid groups in the kerogens had been reduced to benzyl alcohols by LiAlH,. Despite the increased alcoholic character of the reduction products, only very low concentrations of alcohols and diols in general, and no benzyl alcohols in particular, were detected by g.c.-m.s., and it must be concluded that the alcohol units were attached to larger non-volatile fragments. Although only insignificant concentrations of volatile alcohols were detected, reduction with LiAlH, did release relatively high concentrations of other volatile products, n-alkanes being the prominent species. The distributions of n-alkanes in the chloroform-soluble fractions differ slightly from those of the original bitumens (Table 5). In general maxima occur at higher carbon numbers and pristane/phytane ratios are significantly lower. In both cases this may be due to the fact that the lower carbon number materials would be preferentially released in the earlier extractions. As with the original bitumens and kerogens,the KCD2 reduction products contained significantly higher concentrations of isoprenoid species. Other compound classes detected in all these extracts were alkylbenzenes, alkoxybenzenes, branched and cyclic alkanes and small quantities of alkylnaphthalanes. Alkyl esters of phthalic acids were found in high concentrations in the JC, OC and KCD2 extracts. In addition, the JC and KCD2 samples both contained significant quantities of two components which could not be identified. The first of these was a benzene derivative, since it gave a very strong peak at m/z77. Consultation of the eight peak index plus a computer search yielded diphenyl ether as the best, yet poor, lit. The second component had a molecular weight of 350 and a base

1238

FUEL, 1989, Vol 68, October

kerogen

peak of 251, but likewise could not be identified by either a computer search or from the eight peak index. The high concentrations of phthalates and the first of the unknowns are the factors responsible for the very low aliphatic/aromatic ratios observed for the JC and KCD2 samples (Table 5). It has been observed’ that treatment with LiAlH, of the OC and KCY samples, which contained large proportions of pyrite, increased their solubility by about 10 and 20% respectively. Reduction had a much smaller effect on the other samples, which had low pyrite contents, and enhanced their solubility by only z l-2%. These observations provide further evidence to support the contention that much of the dissolution achieved by LiAlH, reduction is due to release of materials trapped within the pyrite framework. The FT-i.r. and solid state 13C n.m.r. spectra of the reduced kerogens were very similar to those obtained from the parent kerogens, apart from enhanced -OH absorptions and reduced >C=O absorptions. In the case of the OC and the KCY samples this means that removal of 10% and 20% respectively of the organic content appears to have little effect on their overall structure assessed by FT-i.r. and solid state n.m.r.. Analysis

of oxidised

materials

The total product recoveries, together with the yields of base-insoluble residues, humic acid fractions (MHA) and dichloromethane soluble fractions, from the perTFA and KMnO, oxidations, are given in Table6. Total product yields varied from 115% to 64%; yields below 100% indicate the degradation of the kerogen into carbon dioxide and water-soluble acids, which are lost, while yields above 100% can be accounted for by the addition of oxygen to the kerogen. Since perTFA can oxidise aromatic rings to carbon dioxide it might be expected that product yield would decrease as aromatic content increased, and indeed for the perTFA system a rough correlation exists between f, values of the parent kerogens

Analysis

of organic

matter

in five oil shales:

S. R. Palmer

et al.

100 9

.s? >

go-

5 a ii z I-

80-

t;

7060 50 A

I

I

0.2

0.3

Figure 3 the parent

I 0.4 fa value

Plot of total yields of oxidised products kerogen: 0, perTFA; A, KMnO,

I

I

0.5

0.6

versusf,

value of

and total product yields. No such relation is found for KMnO, systems (Figure3). Apart from the highly aromatic KCY sample, yields from KMnO, oxidation were substantially lower than from perTFA oxidation. This may be because in the former system long-chain molecules are converted by secondary oxidation to shorter-chain water-soluble products that are not recovered. There is no apparent correlation between the yield of each product fraction and the f, value of the kerogen. Since both oxidants attack aromatic centres, albeit in different ways, one might have expected some sort of relation between yield of soluble product and kerogen aromaticity and, since perTFA does not attack aliphatic centres, that residue yields would increase with aliphatic content. This is in fact the opposite to results reported recently for a series of Australian coals: Verheyen et al.” reported that as the rank, and therefore aromaticity, of the coals increased, so did the quantity of residue remaining after perTFA oxidation. The H/C ratios of the oxidation products are generally lower than those of the parent kerogen. These ratios suggest, but in no way establish, that aromaticity increases on oxidation. More precise information on aliphatic/aromatic ratios can be obtained from n.m.r. analysis. The solid state r3C n.m.r. spectra of the KCY and KCD2 perTFA residues and MHAs were compared with those of the parent kerogens (Figure4). These particular samples were chosen because they have the highest and lowest aromatic contents respectively. The KCY residue has anf, value of 0.24 compared with 0.53 for the original kerogen, and the KCD2 residue a value of 0.12 compared with 0.28 for the original kerogen. It appears that perTFA oxidation of these kerogens yields an insoluble residue that is predominantly aliphatic, not aromatic as found for coals. According to Verheyen et a1.28, the presence of residual aromatic material after perTFA oxidation may be due to: lack of a reactive site; insufficient penetration by the oxidant; or deactivation of the substrate by -CO,H substitution. Since the residues are resistant to further attack by perTFA, the second suggestion appears to be an unlikely explanation for the lack of aromatic reactivity. The observation of

I

I

100

200

pm

KCD2

kerogen

I

100 mm Figure 4 Solid state 13C n m.r. spectra: a, reduced kerogen; b, MHA from perTFA oxidation of ieduced kerogen; c, residue from perTFA oxidation of reduced kerogen

FUEL,

1989,

Vol 68, October

1239

Analysis

of organic

matter

in five oil shales:

S. R. Palmer

aI

6

h 9

8

.I

B

d

Jk F

G

, _._ 30

0

RT mins Figure 5 Total ion current traces of soluble perTFA oxidation products from a, JC and b, KCD2 reduced kerogens: 1-14, C,0-C24 n-chain monomethyl esters (methyl ester group not included in carbon number); A, 2,6,10-trimethylundecanoic acid (methyl ester); B, 3,7,1 I-trimethyldodecanoic acid (methyl ester); C, 4,8,12-trimethyltridecanoic acid (methyl ester); D, 5,9,13-trimethyltetradecanoic acid (methyl ester); E, 2,6,10,14-tetramethylpentadecanoic acid (methyl ester); F, 3,7,11,1Stetramethylhexadecanoic acid (methyl ester); G, 4,8,12,16-tetramethylheptadecanoic acid (methyl ester)

enhanced >C=O adsorption in the 13C n.m.r. spectra of the residues compared with the original kerogen spectra suggests that deactivation is the more likely explanation. In contrast to the residues, the MHAs have aromatic contents similar to those of the original kerogens. Since they are soluble in base they must contain high concentrations of -CO,H groups and the 13C n.m.r. spectra of the MHAs show by far the strongest >C=O absorptions. These materials would appear to be derived from kerogen units that are less crosslinked and of lower molecular weight than those leading to the residues. Like the residues they are resistant to further oxidation by TFA, probably due to deactivation by -CO,H substitution. Analysis by solid state n.m.r. of the residues and MHAs obtained from KMnO, oxidation of the KCY and KCD2 kerogens, gave spectra similar to those obtained from the TFA oxidation products. As expected, the KMnO, residues were more aromatic than the perTFA residues. The dominating feature in the g.c.-m.s. traces of the methylated soluble fractions from both the TFA and KMnO, oxidation was a series of saturated monomethyl esters. In the case of the KCD2 sample isoprenoid esters predominated, whereas for all the other systems the straight chain esters were the major volatile species. The total ion current traces for the KCD2 sample, and for

1240

FUEL,

comparison the OC sample, are shown in Figure5. The KMnO, oxidations generally produced a shorter range of acids with the maxima in their distributions shifted to lower carbon numbers. A difference of one carbon in the corresponding maxima for the two oxidations would be expected, since KMnO, attacks at the benzylic position whereas perTFA attacks the benzene ring itself. The decrease in the maxima by more than one carbon is presumably due to the more extensive secondary oxidation occurring within the KMnO, systems4. Since secondary oxidation occurs to only a minor extent in perTFA systems 5, it is fairly certain that the distribution of fatty acids obtained from TFA oxidation represents the distribution of alkyl chains within the part of the kerogen that is rendered soluble. The distributions of n-chain esters produced by perTFA and KMnO, oxidation of the KCDl and JC samples are shown in Figure 6. Low concentrations of n-chain dicarboxylic acids (l-SO/ of total acid concentrations) were also found in all five perTFA oxidised samples. Since it is known that dicarboxylic acids >C, are stable in TFA media’, it can be concluded that long alkyl chain bridges between aromatic units are rare in these kerogen systems. The KMnO, samples generally contained higher concentrations of dicarboxylic acids, again presumably due to some secondary oxidation of fatty acids to dicarboxylic acids. Benzene dicarboxylic acids were also present in all five samples from both oxidations. The occurrencez9 of these compounds in perTFA-oxidised coal products has been attributed to the presence of dihydrobenzene ring systems such as 9,12_dihydronaphthacene. Presumably such structures are also present in the kerogens. Other materials found in all five samples included a series of n-chain alkanes. The alkanes are unreactive towards perTFA and presumably result, as in the previous LiAlH, reduction step, from release of trapped material after the break-up of the kerogen network. N.m.r. analysis, which gives a more general picture of composition than g.c.-m.s., established that the soluble fractions were highly aliphatic; the strongest peaks in both the ‘H and 13C n.m.r. spectra of all samples were those due to long methylene chains. The KCD2 sample had the highest CH,/CH, peak ratio and its 13C n.m.r. spectrum the strongest absorptions in the 32-40ppm region, attributed usually to carbon atoms at and next to branching sites. The observation of the high concentrations of isoprenoid species in all the KCD2 breakdown products suggested a certain uniformity of structure within the system. To determine whether this uniformity persisted even in the final residue, the KCD2 perTFA residue was further degraded by stepwise KMnO, oxidation; this gave small amounts of a secondary residue, some l&15% of the starting weight, virtually no MHA material and a soluble of the fraction. The 13C solid state n.m.r. spectrum secondary residue showed a very strong aromatic peak, a strong carbonyl peak and a relatively weak aliphatic peak, which suggests a heavily carboxylated aromatic structure with a few aliphatic groups attached. From a mass balance consideration it would appear that virtually all of the aromatic material from the original perTFA residue was retained in this second residue. This indicates that the permanganate oxidation has cleaved the aromatic/aliphatic bonds that the perTFA left intact. It was established from g.c.-ms. analysis that the methylated soluble material derived from this secondary

1

5

A

et al.

1989,

Vol 68, October

Analysis

a

perTFA

$ .-

80

.: 5 $

60 40 20 0

1112

1314

120

2 ,-

80 60

z

40

1718

IllIll 19 20 21 2223

24 25 262728 oxidation

:,ji1,1,,

20 0

11 12 1314

1516

17181920 Carbon

21 22 2324

25262728

number

perTFA

5 ‘F

CONCLUSION

Permanganate

.Y ; 100

.9 z

Il-l

1516

oxidation

120

80

.-T 5 2

60 40

1617181920212223242' i

120

Permanganate

.E 100 (u 80 .-z .-’ !! :

The observation of high concentrations of alkanes and other hydrocarbons in the relatively volatile soluble products obtained at each stage of the dissolution process confirmed the previous observation that oil shales, like coals, are made up of mobile and rigid phases. As might be expected, the sample oil shales were heterogeneous and possessed a variety of chemical structures. The results presented in this investigation revealed these structures in some detail. Analysis of insoluble material by FT-i.r. and n.m.r. as well as examination of oxidation products showed that there was a striking similarity between the chemical structures in the bitumens and in their associated kerogens. Thus, the distribution of alkyl chains as soluble alkanes and as monomethyl esters obtained by perTFA oxidation of kerogens, was nearly identical. Oxidation with perTFA is superior to oxidation with KMnO, as a structural probe in that it produces fewer secondary products and gives a more precise definition of alkyl group distribution within the system. The residues obtained from oxidation of kerogens, unlike those from coals, are predominantly aliphatic in character. In coals, oxidation of aromatic structures by perTFA leaves intractable condensed aromatic ring systems, while oxidation of the less aromatic kerogens apparently leaves a cross-linked aliphatic network. One of the KC samples differed from the others in that isoprenoid structures predominated over straight chain structures throughout the system.

ll_-llL

100

.!

et al.

that the aliphatic composition of the perTFA residue is somewhat similar to the aliphatic material already dissolved from it, and that there is a uniformity of structure throughout the whole kerogen.

oxidation

120 .$ 100

of organic matter in five oil shales: S. R. Palmer

60 40 20 0 67

I l-l ll 891011

1

I

oxidation

REFERENCES

I

121314151617181920212223242526 Carbon

number

Figure 6 A comparison of the distribution esters produced by perTFA and permanganate b, KCDl reduced kerogens

of n-chain oxidations

monomethyl of a, JC and

oxidation contained an abundance of methyl esters of macro carboxylic acids, the most prominent species being a set of isoprenoid chain mono-methyl esters similar to those found in the original perTFA solubles from this kerogen. Also present in significant concentrations were a set of n-chain mono-methyl esters (C,,&,,), a set of dicarboxylic acid methyl esters (C,&,,), and dimethyl phthalate, together with dibutyl and diethyl phthalates. A significant single component detected could not be identified fully, but had a fragmentation pattern similar to that of polycyclic aliphatic structures such as the triterpanes. It did not have the characteristic m/z peaks at 191 or 217, but instead there were peaks at 171, 201 and 215 in this region. The predominance of the isoprenoid and n-chain esters in this fraction suggests

9 10 11 12

13

14 15

Palmer, S. R., Gaines, A. F. and Jarvie, A. W. P. Fuel 1987, 66, 499 Djuricic, M. V. V., Murphy, R. C., Vitorovic, V. and Biemann, K. Geochemica et Cosmochemica Acta 1971, 35, 1201 Deno, N. C., Greigger, B. A. and Stroud, S. G. Am. Chem. Sot. Dia. 01 Fuel Chem. Prepr. 1978, 23, 54 Deno, N. C., Greigger, B. A. and Stroud, S. G. Fuel 1978,57,455 Deno, N. C., Greigger, B. A., Jones, A. D., Raktiky, W. G. and Stroud, S. G. Spec. Rep. Electr. Power Res. 1979, No. AF-960 Durand, B. and Nicaire, G. in ‘Kerogen’ (Ed. B. Durand), Editions Technip, Paris, France, 1980, p. 35 Dancy, T. E. and Giedroye, V. J. J. Inst. Petroleum 1950,36,593 Hayatsu, R., Scott, R. G. and Winans, R. E. in ‘Oxidation in Organic Chemistry’ (Ed. W. S. Trahonovsky), Academic Press, London, UK, 1982, Part D Vitorovic, D. in ‘Kerogen’ (Ed. B. Durand), Editions Technip, Paris, 1980, p. 301 House, N. 0. in ‘Modern Synthetic Reactions’ 2nd Edn., W. A. Benjamin, 1972 Deno, N. C., Greigger, B. A. Jones, A. D. et al. Tet. Let. 1977, 1703 Gallois, R. W. ‘A Pilot study of shale oil occurrences in the Kimmeridge clay’ Institute of Geological Sciences, 1978, Report No. 78/13 Cox, B. M. and Gallois, R. W. ‘The stratigraphy of the Kimmeridge clay of the Dorset type area and its correlation with other Kimmeridge sequences’, Institute of Geological Sciences 1980, Report No. 80/4 Shadle, L. J., Jones, A. D., Deno, N. C. and Given, P. H. Fuel 1986,65, 611 Verheyen, T. V. and Johns, R. B. Anal. Chem. 1983, 55, 1603

FUEL, 1989, Vol 68, October

1241

Analysis 16 17 18 I9 20

21

22

1242

of organic matter in five oil shales: S. R. Palmer et al.

Blumer, M., Guillard, R. R. L. and Chase, T. Marine Biology 1971, 8, 183 Gelpi, E., Schneider, H., Mann, J. and Oro, T. Phyrochemistry 1970, 9, 603 Youngblood, W. H. and Blumer, M. Marine Biology 1973, 21, 163 Youngblood, W. H., Blumer, M., Guillard, R. R. L. and Florc, F. Marine Biology 1971, 8, 190 Williams, P. F. V. and Douglas, A. G. in ‘Advances in Organic Geochemistry 1979’ (Eds. A. G. Douglas and J. R. Maxwell), Pergamon Press, Oxford, UK, 1980, p. 531 Deroo, G., Tissot, B., McCrossan, R. G. and Der, F. ‘Oil Sands Fuel of the Future Memoir 3’ Can. Sot. Pet. Geol., 1974, pp. 148, 184 Connan, J., LeTran, K. and Van der Weide, B. ‘Proc. 9th World

FUEL, 1989,

Vol 68, October

23 24 25 26 27 28 29

Pet. Congr. Tokyo’, Applied Science Publications, London, UK, 1975, n. 171 Poweli, T. and McKinIy, D. M. Nature 1973, 203, 37 Williams, P. F. V. and Douglas, A. G. in ‘Advances in Organic Geochemistry’ (Ed. M. Biorov). Wilev. London, UK. 1979 Levy, G. C. in ‘Topics in Car&-13 irnr Spectroscop;‘. Wiley, London, UK, 1979 Nietzel, D. A., McKay, D. R., Heppner, R. A. et al. Fuel 1981, 60, 307 Brown, J. K. and Ladner, W. R. Fuel 1960, 39, 87 Verheyen, T. V., Pandolfo, A. G., Johns, R. B. and Mackay, G. H. Geochimia et C~smochimn Acta 198_5,49, 1603 Painter, P. C., Snyder, R. W., Starsinic, M. rr al. Applied Spectroscopy

30

1981, 35, 475

Deno, H. C., Curry, K. W., Greiger,

B.A. et al. Fuel 1980,59,694