Direct Characterization of Kerogen by
X-ray and Solid-State 13C NMR Methods
26th Oil Shale Symposium
S. R. Kelemen, M. Afeworki, H. Freund M. L. Gorbaty, M. Sansone, M. Siskin, C.Walters
ExxonMobil Research and Engineering Company, Annandale, NJ, 08801
M. Solum, R. J. Pugmire
Departments of Chemical Engineering and Chemistry,
University of Utah, Salt Lake City, Utah, 84112
Background
• Understanding the chemistry of complex carbonaceous materials
is aided by developing representative chemical structural models
– Ideally want to link chemical structure models to reactivity models
• In the past, model development was aided by information gathered
using an indirect characterization strategy
– Mildly decompose the organic solid, separate, identify and quantify the
components using liquid and gaseous characterization methods
– Employ selective nondestructive chemical derivatization and analysis
• A large amount of chemical detail must be self-consistently
integrated in order to derive a molecular level model of organic
composition via indirect methods
– Approach has been used to elucidate chemical structure of the organic matter in
Green River and Rundle Ramsey Crossing Oil Shale
1
Original Organic Matter Models for Rundle and Green
River Oil Shale from Indirect Characterization
Rundle Organic Matter Model
Scouten, C. G.; Siskin,M.; Scouten, C. G.; Rose, K. D.; Axzel,T.;
Colgrove, S. G.; Pabst, R. E., Jr.; Prepr. Am. Chem. Soc.,
Div. Pet. Chem. 1989, 36 (1), 43
Green River Organic Matter Model
Siskin,M.; Scouten, C. G.; Rose, K. D.; Axzel,T.;
Colgrove, S. G.; Pabst, R. E., Jr.; in Geochemistry and
Conversion of Oil Shales, ed. By C. Snape, NATO
Series, 1995
2
Inherent Uncertainties with Indirect Characterization
• Mildly decompose the organic solid and analyze products
– Incomplete decomposition of the organic solid
– Chemical transformation during decomposition
• Chemical derivatization and analysis
– Non-selective, incomplete or destructive derivatization of organic matter
– Accuracy of methodologies to quantify derivatized products
• Combination of Indirect characterization with new direct
characterization methods can mitigate uncertainties
3
Direct Chemical State Probes for Carbonaceous Materials
• Significant advances made over the past decade for different direct
chemical state probes of complex carbonaceous samples
– Provides average chemical composition
• X-ray Photoelectron Spectroscopy (XPS)
– Heteroatom (N, S, O), higher energy/spatial resolution, non-conducting samples
• X-ray Absorption Near Edge Structure Spectroscopy (XANES)
– Sulfur, Carbon and Nitrogen
• Solid-State NMR Spectroscopy
–
13C
NMR for Carbon structures & oxygen functionalities, 15N NMR for speciation
• Multiple technique strategy developed to quantify the average
chemical structure of kerogen including Green River and Rundle oil
shale (Type I Kerogen)
4
Multiple Technique Strategy for Defining the
Organic Composition of Complex Carbonaceous Solids
Organic Forms of Oxygen
Carbon (H) Chemical/Skeletal Features
Feature
Approach
Feature
Approach
H/C
Elemental
Analysis
Average
Aromatic
Ring Size
13
Aliphatic C-O
O-CH3
13
Σ C-O
XPS
C=O
13
C=O, O-C-O
XPS
O=C-O, O=C-N
13
O=C-O, O=C-N
XPS
% Methyl
Carbon
13
C NMR
Average Aliphatic
Carbon Chain
Length
13
Fraction of
Aromatic Carbon
with Attachments
13
Alkyl Carbon Chain
Length Distribution
(Isomerization)
Indirect
Methods
C NMR
Organic Forms of Sulfur
Feature
Approach
Feature
Approach
R-S-S-R
XANES
XPS
S/C
Elemental Analysis
XANES
XPS
SO, SO 2, SO3
XANES
XPS
10-100 micron Spectroscopy (Yes)
C NMR
C NMR
O/C
XPS
Organic Forms of Nitrogen
Feature
Pyridinic
XPS
XANES
XPS
C NMR
C NMR
Amine
Ar-S-Ar(H)
Elemental Analysis
Indirect
Methods
Aromatic/
Naphthenic Ring
Size Distribution
Thiophenic
Approach
13
C NMR
XPS
XANES
XPS
Feature
Aromatic C-O
13
R-S-R(H)
Approach
C NMR
% Aromatic/
Aliphatic
Carbon
C NMR
Feature
Amide
Pyrrolic
Approach
15
N NMR
XPS, XANES
15
N NMR
XPS, XANES
15
N NMR
XPS, XANES
15
N NMR
XPS, XANES
Feature
N/C
NO, NO2
Pyridinic
(O-Environment)
Quaternary
(Amonium Salt)
(Pyridinum ion)
(Ar-Bridgehead)
Approach
Elemental Analysis
XPS
15
N NMR
XPS, XANES
15
N NMR
XPS, XANES
15
N NMR
XPS, XANES
5
Van Krevelen Diagram for Kerogen and Rock-Eval Data
180
Hydrogen (per 100 C)
160
Green River
Type I
Type II
120
100
Type III
80
60
40
Type I
Type II
Type IIIC
20
0
5
Kerogen
Type
Green River
Rundle
Duvernay (A)
Duvernay (B)
Duvernay (C)
Duvernay (D)
Oxford Clay
Paradox
Malm
Draupne
Bakken
Monterey
Gippsland (A)
Gippsland (B)
Proprietary (A)
Proprietary (B)
Proprietary (C)
Fruitland
I
I
II
II
II
II
II
II
II
II
II
IIS
IIIC
IIIC
IIIC
IIIC
IIIC
IIIC
Rundle
140
0
Sample
10
15
Organic Oxygen (per 100 C) XPS
Rock-Eval
Hydrogen
Tmax (°C)
Index
(mg/g)
446
739
444
995
414
532
438
439
443
242
479
22
413
577
438
401
420
670
424
581
419
580
411
621
415
251
436
226
427
295
453
235
479
120
424
237
• Lacustrine source rocks from the Green
20 River and Rundle formations contain
hydrogen-rich algal kerogen (Type I) derived
primarily from cyanobacteria or various
6
Chlorophyta and dinoflagellates, respectively
Complimentary XPS and 13C NMR Data for Aromatic Carbon
Hydrogen (per 100 Carbon)
200
175
Rundle
Green River
150
Type I (XPS)
Type II (XPS)
Type IIIC (XPS)
Type I (NMR)
Type II (NMR)
Type IIIC (NMR)
• The amount of aromatic
carbon, measured by both 13C
NMR and XPS, increases with
decreasing H/C
– Surface composition
comparable to the bulk
– XPS percent aromatic carbon
from calibrated carbon (1s) π
to π* Signal (1)
125
100
75
50
25
0
20
40
60
80
Aromatic Carbon (Percent)
100
• Green River and Rundle
Kerogen (Type I) have less
aromatic carbon than other
organic matter types at
comparable levels of maturity
(1) S. R. Kelemen et.al. Applied Surf. Sci., 1993, 64,167
7
XPS Carbon (1s) Spectra of Kerogen
and Curve Resolution into Different Components
C
Rundle
Type I
Kerogen
C
Duvernay (B)
Type II
Kerogen
C-O
C-O
C=O
O=C-O
C=O
O=C-O
Binding Energy (eV)
Binding Energy (eV)
8
Organic Oxygen Forms Quantified using XPS
Org. Oxygen
C-O
(286.3 eV)
Mole Percent
C=O
(287.5 eV)
O-C=O
2x (289.0 eV)
5.1
11.1
9.7
5.9
5.0
4.7
13.7
3.9
10.0
4.1
8.6
14.9
15.4
10.6
11.1
6.6
4.0
9.3
3.8
4.6
5.0
4.2
3.5
4.7
8.7
2.2
6.8
3.3
6.5
10.1
9.5
8.3
6.8
6.6
4.0
7.1
0.5
1.7
3.4
0.8
0.8
0.0
2.4
0.6
2.8
0.6
1.8
2.0
2.8
1.6
2.2
0.0
0.0
1.9
0.8
4.7
1.3
0.8
0.7
0.0
2.6
1.1
0.4
0.3
0.3
2.8
3.1
0.7
2.1
0.0
0.0
0.3
Per 100 C
Total
Sample
Green River
Rundle
Duvernay (A)
Duvernay (B)
Duvernay (C)
Duvernay (D)
Oxford Clay
Paradox
Malm
Draupne
Bakken
Monterey
Gippsland (A)
Gippsland (B)
Proprietary (A)
Proprietary (B)
Proprietary (C)
Fruitland
Low
High
9
XPS Nitrogen (1s) Spectra of Kerogen
and Curve Resolution into Different Components
Draupne
Type II
Pyrrolic
Pyrrolic
Monterey
Type IIS
Amine
Quaternary
Quaternary
Amine
Pyridinic
Pyridinic
Binding Energy (eV)
Gippsland (B)
Type IIIC
Pyrrolic
Pyridinic
Binding Energy (eV)
Prop. (C)
Type IIIC
Pyrrolic
Pyridinic
Quaternary
10
Binding Energy (eV)
Binding Energy (eV)
XPS Nitrogen (1s) Spectra of Type I Kerogen and
Curve Resolution into Different Components
Green River
Type I
Kerogen
Pyrrolic
Rundle
Type I
Kerogen
Pyrrolic
Quaternary
Pyridinic
Quaternary
Amine
Amine
Pyridinic
Binding Energy (eV)
Binding Energy (eV)
11
Nitrogen Forms Quantified using XPS
Total
Sample
Green River
Rundle
Duvernay (A)
Duvernay (B)
Duvernay (C)
Duvernay (D)
Oxford Clay
Paradox
Malm
Draupne
Bakken
Monterey
Gippsland (A)
Gippsland (B)
Proprietary (A)
Proprietary (B)
Proprietary (C)
Fruitland
Per 100 C
Pyridinic
398.6 eV
2.2
1.8
2.9
2.0
2.1
2.1
2.4
3.1
2.3
2.3
3.5
3.3
0.8
1.9
1.7
1.1
1.1
1.7
20
5
27
19
18
15
17
23
15
10
20
16
18
34
31
35
36
30
High
Low
Mole Percent (XPS)
Amine
Pyrrolic
399.4 eV
400.2 eV
9
9
4
4
0
0
15
5
9
8
7
5
0
0
0
0
0
0
57
52
52
59
65
62
53
59
54
65
52
62
62
56
57
57
64
57
Quaternary
401.4 eV
13
35
18
18
17
23
15
13
22
17
21
17
20
10
11
7
0
13
12
Plot of Relative Amounts of Nitrogen Forms for Kerogen
80
398.6 eV + 401.4 eV
399.4 eV
400.2 eV
Pyrrolic
(400.2 eV)
60
Mole Percent
Green River
Rundle
40
Pyridinic (398.6 eV) +
Quaternary (401.4 eV)
Amine
(399.4 eV)
20
0
0
20
40
60
Percent Aromatic Carbon (XPS)
80
13
XPS Sulfur (2p) Spectra of Kerogen and
Curve Resolution into Different Components
SO4
2P
3/2
Duvernay (C)
Type II
Oxford
Type II
Aliphatic
2P
1/2
Aliphatic
Aromatic
Aromatic
FeS2
Binding Energy (eV)
SO4
FeS2
Binding Energy (eV)
14
Sulfur Forms Quantified using XPS
Sample
Green River
Rundle
Duvernay (A)
Duvernay (B)
Duvernay (C)
Duvernay (D)
Oxford Clay
Paradox
Malm
Draupne
Bakken
Monterey
Gippsland (A)
Gippsland (B)
Proprietary (A)
Proprietary (B)
Proprietary (C)
Fruitland
Total
Org. S
Aliphatic
Sulfide
Aromatic
(Thiophenic)
Sulfoxide
Sulfate
Pyrite
0.5
0.6
1.4
1.2
0.6
1.0
3.2
1.4
1.9
2.1
2.2
2.7
2.7
0.5
0.2
0.2
0.1
0.4
17
15
33
16
11
5
37
16
22
19
25
39
36
31
24
22
8
37
10
9
28
20
13
20
23
22
16
20
32
21
44
58
33
58
56
51
9
4
13
5
0
5
10
2
7
8
10
4
8
0
0
0
0
0
50
66
25
46
69
66
17
45
45
52
30
16
10
11
42
20
36
12
14
6
2
13
7
4
13
15
10
1
2
20
2
0
0
0
0
0
High
Low
15
Aromatic
FeS2
Aliphatic
2465
2470
2475
Absorbance
Energy (eV)
2465
2470
2475
Energy (eV)
Spectrum
Fit
Spectrum
Fit
2480Aliphatic
Aromatic
Sulfoxide
Sulfite
Pyrite
2480
Third Derivative Absorban
Oxford
Type II
2485
Spectrum
Fit
Duvernay (A)
Type II
Aromatic
FeS2
Aliphatic
2485
Spectrum
2465
2470
2475
2480Fit
2485
2465
2470
2475
2480
2485
Absorbance
Third Derivative Absorbance
S-XANES Absorbance and
Third Derivative Absorbance Spectra of Kerogen
Energy (eV)
Aliphatic
Arom atic
Sulfite
Sulfoxide
Sulfate
Pyrite
16
Combined S-XANES and XPS Results for Sulfur Forms
.
Aliphatic/(Aromatic + Aliphatic)
Mole % Aromatic S (Non Ox. Org. Basis)
100
80
60
40
20
S-XANES 3rd Der. Abs.
S-XANES Abs.
XPS
0
1.0
Type I
Type II
Type IIIC
Type II (Mat. Seq.)
Type IIIC (Mat. Seq.)
0.8
Rundle
0.6
Green
River
0.4
0.2
0.0
0
20
40
60
80
Percent Aromatic Carbon
100
0
20
40
60
80
Percent Aromatic Carbon17
100
Summary
• A direct characterization strategy is used to quantify the average chemical
structure of kerogen (mitigates indirect approach uncertainties)
– Solid-state 13C NMR, XPS and S-XANES
– Wide range of organic matter types and maturities
– Basis for developing specific chemical structural models of kerogen
linked to reactivity models
• Total amounts of organic nitrogen and sulfur vary among kerogen, however,
patterns emerge for the relative abundances of nitrogen and sulfur forms
– The relative amount of aliphatic sulfur decreases with increasing aromatic carbon
+ High aliphatic sulfur levels for Green River and Rundle kerogen
– The majority of nitrogen exists as pyrrolic nitrogen in all kerogens
+ Pyridinic, amine and quaternary found in Green River and Rundle kerogen
• Green River and Rundle Kerogen (Type I) have more hydrogen than other
kerogen organic matter types (at equivalent levels of maturity)
– Both 13C NMR and XPS show aromatic carbon increases with decreasing H/C
18
– Carbon structural features from solid-state 13C NMR appear in a companion poster