molecules
Article
Research on the Composition and Distribution of
Organic Sulfur in Coal
Lanjun Zhang 1,2 , Zenghua Li 1,2, *, Yongliang Yang 1,2 , Yinbo Zhou 1,2 , Jinhu Li 1,2 , Leilei Si 1,2
and Biao Kong 1,2
1
2
*
Key Laboratory of Coal Methane and Fire Control, Ministry of Education, China University of Mining
and Technology, Xuzhou 221008, China; [email protected] (L.Z.); [email protected] (Y.Y.);
[email protected] (Y.Z.); [email protected] (J.L.); [email protected] (L.S.);
[email protected] (B.K.)
School of Safety Engineering, China University of Mining and Technology, Xuzhou 221116, China
Correspondence: [email protected]; Tel.: +86-516-8359-0598
Academic Editor: Derek J. McPhee
Received: 10 April 2016; Accepted: 10 May 2016; Published: 13 May 2016
Abstract: The structure and distribution of organic sulfur in coals of different rank and different
sulfur content were studied by combining mild organic solvent extraction with XPS technology.
The XPS results have shown that the distribution of organic sulfur in coal is related to the degree of
metamorphism of coal. Namely, thiophenic sulfur content is reduced with decreasing metamorphic
degree; sulfonic acid content rises with decreasing metamorphic degree; the contents of sulfate
sulfur, sulfoxide and sulfone are rarely related with metamorphic degree. The solvent extraction and
GC/MS test results have also shown that the composition and structure of free and soluble organic
sulfur small molecules in coal is closely related to the metamorphic degree of coal. The free organic
sulfur small molecules in coal of low metamorphic degree are mainly composed of aliphatic sulfides,
while those in coal of medium and high metamorphic degree are mainly composed of thiophenes.
Besides, the degree of aromatization of organic sulfur small molecules rises with increasing degree
of coalification.
Keywords: coal; XPS; organic solvent extraction; organic sulfur functional group
1. Introduction
S is one of the main harmful elements in coal, and SO2 emitted from the combustion of coal
causes serious environmental pollution. Thus, research on the geochemical properties, distribution,
form of occurrence, coal washing desulfurization and other aspects of sulfur have aroused people’s
attention. Since the 1960s, some industrialized countries have enacted a lot of strict regulations and
standards, limiting emissions of SO2 during the coal combustion process. These measures have greatly
promoted the development of desulfurization technology. Sulfur in coal can be classified into two
categories: inorganic sulfur and organic sulfur. Inorganic sulfur is present in the form of pyrite and
sulfate, of which pyrite is the major inorganic sulfur form in most coals. Conventional coal washing
technology can remove a large fraction of the inorganic sulfur in coal, but it has little influence on
organic sulfur. Organic sulfur in coal, a collective term describing sulfur-containing organic functional
groups, can be broadly divided into two types. One is sulfur-containing small molecule compounds
which can be extracted and separated by using an organic solvent, while the other is attached to
macromolecular skeleton forming C-S bonds and is difficult to separate from the coal matrix due to its
complicated chemical structure and composition [1–3]. Organic sulfur in coal mainly includes the forms
of mercaptans, disulphides, thioethers, sulfoxides, sulfones, thiophenes, sulfonates, etc. Because of the
rather complicated structure of organic sulfur in coal, people are still unable to directly determine the
Molecules 2016, 21, 630; doi:10.3390/molecules21050630
www.mdpi.com/journal/molecules
Molecules 2016, 21, 630
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content and form of organic sulfur in coal, and all kinds of analysis technologies cannot exactly describe
the structure of organic sulfur in coal [4,5]. Therefore, research on its structure and composition remains
a focus in the coal chemistry field all over the world. At present, XPS technology and solvent extraction
are two major methods adopted in research on the structure of organic sulfur in coal. XPS technology,
the most effective method of surface elemental analysis so far, is widely employed in the research on
the sulfur forms of coal. It works by analyzing the elements (except for element H and He) existing on
the sample surface and their modes of existence according to the different electron binding energy in
the photoelectron spectra of different elements and valence states, and then it infers the composition
and chemical structure of functional groups on the sample surface. This technology, due to its high
identification power, good sensitivity, capability to maintain samples intact and other advantages in
the speciation analysis of organic sulfur on coal surfaces, is the most effective coal surface analysis
method available today [6–8]. Solvent extraction is one of the most important methods in studying
coal structure. It releases soluble molecules in coal mainly by breaking intermolecular non-covalent
bonds such as intermolecular H bonds and through the charge transfer, π-π bond, van der Waals force,
electrostatic interactions, etc. From the conjoint analysis of solvent extraction and GC/MS, the existence
as well as the separation and precipitation rules of each constituent in coal can be clearly recognized,
resulting in advancement of coal structure research [9–12]. Mild solvent extraction methods can be
used to study the composition and characteristics of sulfur-containing polycyclic and heterocyclic
aromatic hydrocarbons of low molecular weight in coal, thus further obtaining relevant information
about the organic sulfur small molecules. By selecting coal samples of different rank and different
sulfur content and combining organic solvent mild extraction and XPS technology, this paper has
comprehensively analyzed the structure of organic sulfur in coal to obtain important information such
as the composition and distribution of organic sulfur functional groups in coal.
2. Results and Discussion
2.1. XPS Test Results and Analysis
Figure 1 shows the XPS fitting curves of elemental S in six raw coals; Table 1 shows the XPS
analysis results of the sulfur forms on the surface of six raw coal samples; Figure 2 is the contrastive
analysis figures of the relative content of different sulfur forms in six raw coals. In the XPS spectra
shown in Figure 1, the ordinate represents the strength of the electronic signal and the abscissa shows
the electron binding energy. The elements existing on the sample surface as well as their existing
forms can be analyzed through the electron binding energy, while their relative content can mainly be
determined through the height and area of the fitting peaks. We can see from Figure 1 that six S 2p
peaks can be fitted from the XPS spectrum of element S in each sample, wherein, the binding energy of
Peak 0, 163.1 eV, is attributed to sulfide (mercaptan and thioether) sulfur and pyritic sulfur. At present,
it is hard to distinguish mercaptan and thioether sulfide sulfur and pyritic sulfur using XPS technology
because their binding energies are similar. Besides, the binding energy of Peak 1 (164.2 eV) belongs
to thiophenic sulfur; Peak 2 (165.3 eV) to sulfoxide; Peak 3 (167.4 eV) to sulfone; Peak 4 (168.7 eV) to
sulfonate; Peak 5 (169.9 eV) to sulfate. Due to the differences in the content, forms and distribution of
organic sulfur and inorganic sulfur in various samples, their S 2p XPS spectra are also quite different.
It can be found in Table 1 and Figure 2 that after the removal of inorganic sulfur (iron sulfide
and sulfate) from the six coal samples, among the organic sulfur left, sulfide sulfur, thiophenic sulfur
and sulfonate have higher contents; sulfoxide and sulfone have lower contents. We can see from the
results that the change law of sulfide sulfur and pyrite content with the degree of metamorphosis
of the coal is not obvious (due to the interference of pyrite); thiophenic sulfur content is reduced
with decreasing degree of metamorphism of coal; sulfoxide and sulfone content shows no obvious
change rules; sulfonate content is raised with the decrease of metamorphic degree; and the content of
sulfate sulfur is rarely related with metamorphic degree, with all XPS results of sulfate sulfur being
significantly higher than the corresponding chemical analysis results. The relative content of iron
Peak Area
320.05
170.15
28.88
60.36
53.99
8.80
W(%)
49.83
26.49
4.50
9.40
8.41
1.37
Peak Area
186.07
122.45
65.42
109.03
216.06
141.01
TFF
W(%)
22.15
14.58
7.79
12.98
25.72
16.79
Peak Area
191.86
141.07
43.48
52.70
210.35
118.01
XCF
Molecules 2016, 21, 630
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W(%)
25.33
18.62
5.74
6.96
27.77
15.58
Peak Area
76.03
46.69
39.59
65.24
144.27
84.52
TKQ
W(%)
16.66
10.23
8.68
14.30
31.61
18.52
sulfide sulfur and sulfide sulfur ANW sample reaches up to 49.83% in the XPS results and that of
Peak Area
187.32
127.96
49.37
63.53
81.91
31.63
pyrite
DTR in this coal sample is 47.45% in the chemical analysis results, from which we can infer that
W(%)
34.58
23.62
9.11
11.73
15.12
5.84
the sulfide sulfur content of this coal is not high. The XPS analysis results show that the relative
Peak
Area
137.34
63.72
34.08
55.09
210.18
94.24
content of thiophenic sulfur in this coal is 26.49%, and the organic sulfur content of some other forms
CFH
W(%)
23.10
10.72
5.73
9.26
35.35
15.85
ANW
is relatively small.
800
1100
Peak0
Peak3
700
Peak1
Peak4
Peak2
Peak5
1000
Peak1
Peak4
500
400
300
800
700
600
ANW
200
100
160
162
164
TFF
500
166
168
170
400
160
172
162
164
166
1000
Peak0
Peak3
Peak1
Peak4
168
170
172
168
170
172
168
170
172
Binding Energy/eV
Binding Energy/eV
1100
Peak0
Peak3
900
Peak1
Peak4
Peak2
Peak5
1000
Peak2
Peak5
C ou n ts/s
900
C ou n ts/s
800
700
600
800
700
500
600
XCF
400
300
160
162
164
TKQ
500
166
168
170
400
160
172
162
164
166
Binding Energy/eV
Binding Energy/eV
800
1200
Peak0
Peak3
700
Peak1
Peak4
Peak2
Peak5
1100
Peak0
Peak3
Peak1
Peak4
Peak2
Peak5
1000
C ou n ts/s
600
C ou n ts/s
Peak2
Peak5
900
C ou n ts/s
C ou n ts/s
600
Peak0
Peak3
500
400
300
900
800
700
DTR
200
100
160
162
164
CFH
600
166
168
170
172
500
160
162
Binding Energy/eV
164
166
Binding Energy/eV
Figure1.1.The
TheXPS
XPSSS2p
2pfitting
fitting curve
curve of
Figure
of six
six raw
rawcoal
coalsamples.
samples.
Table 1. The XPS S 2p analysis of six raw coal samples.
Sample
Results
Pyritic Sulfur and
Sulphide Sulfur
Thiophene
Sulfoxide
Sulfone
Sulfonate
Sulfate
ANW
Peak Area
W(%)
320.05
49.83
170.15
26.49
28.88
4.50
60.36
9.40
53.99
8.41
8.80
1.37
TFF
Peak Area
W(%)
186.07
22.15
122.45
14.58
65.42
7.79
109.03
12.98
216.06
25.72
141.01
16.79
XCF
Peak Area
W(%)
191.86
25.33
141.07
18.62
43.48
5.74
52.70
6.96
210.35
27.77
118.01
15.58
TKQ
Peak Area
W(%)
76.03
16.66
46.69
10.23
39.59
8.68
65.24
14.30
144.27
31.61
84.52
18.52
DTR
Peak Area
W(%)
187.32
34.58
127.96
23.62
49.37
9.11
63.53
11.73
81.91
15.12
31.63
5.84
CFH
Peak Area
W(%)
137.34
23.10
63.72
10.72
34.08
5.73
55.09
9.26
210.18
35.35
94.24
15.85
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Molecules 2016, 21, 630
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50
45
Pyritic sulfur+Sulphide
Relative content/%
40
35
30
50
45
Thiophene
40
35
30
25
25
20
15
10
5
20
15
10
5
0
0
ANW
TFF
XCF
TKQ
DTR
A
50
45
40
ANW
CFH
Sulfoxide
35
30
35
30
25
25
20
15
10
5
20
15
10
5
0
TFF
XCF
TKQ
DTR
50
45
40
CFH
Sulfone
0
ANW
TFF
XCF
TKQ
DTR
50
45
40
35
CFH
Sulfonate
ANW
30
30
25
20
25
20
15
10
5
0
15
10
5
0
ANW
TFF
XCF
TKQ
DTR
CFH
TFF
XCF
TKQ
DTR
50
45
40
35
CFH
Sulfate
ANW
TFF
XCF
TKQ
DTR
CFH
Figure 2. The relative content of different sulfur on six coal samples surface.
Figure 2. The relative content of different sulfur on six coal samples surface.
Thus,ititcan
canbebeasserted
assertedthat
thatthiophenic
thiophenicsulfur
sulfur isis the
the main
main organic
organic sulfur
sulfur form of this coal. As
Thus,
As both
both
TFF
coal
and
XCF
coal
come
from
Weng’an
County,
Guizhou
Province,
they
are
formed
under
similar
TFF coal and XCF coal come from Weng’an County, Guizhou Province, they are formed under similar
geologicalconditions
conditionsand
andhave
havesimilar
similarcoal
coalproperties.
properties. Thus
Thus the
the distribution
distribution of various sulfur
geological
sulfur forms
forms
showninintheir
theirXPS
XPSanalysis
analysisresults
resultsisissimilar.
similar.The
The relative
relative content
content of iron sulfide sulfur
shown
sulfur and
and sulfide
sulfide
sulfurininthese
thesetwo
twocoals
coalsare
are22.15%
22.15%and
and25.33%,
25.33%, respectively,
respectively, in
in the
the XPS
XPS results, and those
sulfur
those of
of pyrite
pyrite
themare
are33.04%
33.04%and
and44.77%,
44.77%,respectively,
respectively,ininthe
thechemical
chemicalanalysis.
analysis. Differences
Differences can be recognized
ininthem
recognized
contrastingthe
theXPS
XPSresults
resultswith
withthe
thechemical
chemical analysis
analysis results.
results. The
bybycontrasting
The reason
reason for
for this
this phenomenon
phenomenonis,
is,
on
the
one
hand,
pyrite
on
the
surface
of
coal
particles
can
be
easily
oxidized
to
sulfate,
resulting
in
the
on the one hand, pyrite on the surface of coal particles can be easily oxidized to sulfate, resulting in
corresponding
decline
in pyrite
content.
For example,
the sulfate
content
of TFFofcoal
the
corresponding
decline
in pyrite
content.
For example,
the sulfate
content
TFFrises
coalfrom
rises0.58%
from
in
the
chemical
analysis
results
to
16.79%
in
the
XPS
results.
On
the
other
hand,
XPS
is
a
surface
0.58% in the chemical analysis results to 16.79% in the XPS results. On the other hand, XPS is a surface
analysistechnology
technology which
which only
only detects
detects the
the top
top 2–20
analysis
2–20 molecular
molecular layers
layers on
on the
the coal
coal surface,
surface, so
so XPS
XPS
results
are
often
quite
different
from
phase
analysis
results.
In
addition,
no
dashing
treatment
results are often quite different from phase analysis results. In addition, no dashing treatment has
has
been
conducted
to
the
coal
samples
before
the
XPS
tests,
so
the
particle
effect
of
minerals
in
coal
will
been conducted to the coal samples before the XPS tests, so the particle effect of minerals in coal will
alsohave
havesome
someinterference
interferenceon
onthe
thetest
testresults
results [9,13,14].
[9,13,14]. It
It can
can also
also be
be seen
seen from
from the
also
the results
results that
that the
the
main
organic
sulfur
form
of
TFF
and
XCF
coal
is
thiophene;
sulfide
sulfur
content
is
small;
among
main organic sulfur form of TFF and XCF coal is thiophene; sulfide sulfur content is small; among
the
the
different
oxidized
forms
of
sulfur,
the
sulfonate
content
is
highest,
while
the
relative
contents
of
different oxidized forms of sulfur, the sulfonate content is highest, while the relative contents of sulfone
sulfone and sulfoxide is lower. Among organic sulfur in TKQ coal, sulfonate accounts for the highest
and sulfoxide is lower. Among organic sulfur in TKQ coal, sulfonate accounts for the highest relative
relative content, which is 31.61%. Since the chemical analysis results have shown that this coal only
content, which is 31.61%. Since the chemical analysis results have shown that this coal only contains
contains trace amounts of pyritic sulfur, the relative content of sulfide sulfur in this coal can be
trace amounts of pyritic sulfur, the relative content of sulfide sulfur in this coal can be approximately
approximately regarded as 16.66%. The relative content of thiophenic sulfur, sulfone and sulfoxide
regarded as 16.66%. The relative content of thiophenic sulfur, sulfone and sulfoxide shows a decreasing
shows a decreasing order. The XPS analysis results of sulfate sulfur are far higher than its chemical
order. The XPS analysis results of sulfate sulfur are far higher than its chemical analysis results. This,
analysis results. This, in addition to the reasons mentioned above, may also result from large errors
in addition to the reasons mentioned above, may also result from large errors in the analysis results,
in the analysis results, because this coal has a low sulfur content of only 0.6%. The relative contents
because this coal has a low sulfur content of only 0.6%. The relative contents of iron sulfide sulfur
of iron sulfide sulfur and sulfide sulfur DTR coal is 34.58%, while the chemical analysis results show
and sulfide sulfur DTR coal is 34.58%, while the chemical analysis results show that pyrite is rarely
that pyrite is rarely contained in this coal. Therefore, it can be inferred that sulfide sulfur is the main
contained in this coal. Therefore, it can be inferred that sulfide sulfur is the main organic sulfur form
organic sulfur form in this coal, followed by thiophenic sulfur; and the contents of sulfonic acid,
in this coal, followed by thiophenic sulfur; and the contents of sulfonic acid, sulfoxide and sulfone
sulfoxide and sulfone are the least. In the CFH coal sample, sulfonate accounts for the highest
are the least. In the CFH coal sample, sulfonate accounts for the highest relative content, which is
relative content, which is 35.35%, followed by sulfide sulfur and pyrite whose relative amount is
Molecules 2016, 21, 630
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Molecules 2016, 21, 630
5 of 13
35.35%, followed by sulfide sulfur and pyrite whose relative amount is 23.10% in total; the relative
contentinoftotal;
sulfate
is content
as highof
assulfate
15.85%sulfur
which
is far
higher
thanwhich
the sulfate
contentthan
obtained
23.10%
thesulfur
relative
is as
high
as 15.85%
is far higher
the
using the
chemical
analysis
method;
the relative
contentmethod;
of thiophenic
sulfur, content
sulfone, of
andthiophenic
sulfoxide is
sulfate
content
obtained
using
the chemical
analysis
the relative
relatively
scarce.
sulfur,
sulfone,
and sulfoxide is relatively scarce.
2.2. GC/MS
GC/MSResults
Resultsand
andAnalysis
AnalysisofofTHF
THFExtract
Extract
2.2.
GC/MSanalysis
analysisofofthe
theextract
extractwas
wascompleted
completedon
onan
anAgilent
Agilent6890/5975
6890/5975
Gas
Chromatography
GC/MS
Gas
Chromatography
and
Mass
Spectrometer
(Agilent
Technologies,
Santa
Clara,
CA,
USA)
located
at
the
Center
of Modern
and Mass Spectrometer (Agilent Technologies, Santa Clara, CA, USA) located at the Center
of
AnalysisAnalysis
of Nanjing
University,
with with
a DB-5
capillary
column
(30.0
mmˆ× 0.25
mm ׈0.25
0.25
µm),
Modern
of Nanjing
University,
a DB-5
capillary
column
(30.0
0.25 mm
μm),
the carrier
carriergas
gasbeing
beinghelium,
helium,flow
flowrate
rate
mL/min,
split
ratio
of 5:1,
injection
temperature
the
ofof
1.01.0
mL/min,
split
ratio
of 5:1,
injection
portport
temperature
of
˝ C injection volume of 2 µL, ionization methods of E1, source ionization voltage of 70 eV,
of
300
300 °C injection volume of 2 μL, ionization methods of E1, source ionization voltage of 70 eV, ion
˝ and mass (Ar) scan range of 30~650 amu. Computer retrieval
ion source
temperature
source
temperature
of 230of°C230
and C
mass (Ar) scan range of 30~650 amu. Computer retrieval and data
and
data
comparisons
are
conducted
to themethod
PBM method
and
the mass
spectrometry
comparisons are conducted accordingaccording
to the PBM
and the
mass
spectrometry
data data
of
of
compounds
in
the
NIST
chromatogram
library,
and
then
the
structure
of
the
compounds
compounds in the NIST chromatogram library, and then the structure of the compounds cancan
bebe
determined based
basedon
ontheir
theirconfidence
confidenceor
orsimilarity.
similarity.
determined
2.2.1. Yangzhuang
Yangzhuang Lean
LeanCoal
Coal(YZS)
(YZS)from
fromHuaibei
Huaibei
2.2.1.
Figure 33 is
is the
the total
total ion
ion chromatogram
chromatogram(TIC)
(TIC)ofofTHF
THFextract
extractofofYZS
YZScoal
coalsamples.
samples.After
After
Figure
thethe
contrastiveanalysis
analysisofofthe
thechromatogram
chromatogramlibrary,
library,asasshown
showninin
the
Table
can
determined
that
contrastive
the
Table
2, 2,
it itcan
bebe
determined
that
there
are
41
kinds
of
compounds,
as
well
as
three
compounds
whose
names
cannot
be
determined,
there are 41 kinds of compounds, as well as three compounds whose names cannot be determined,
namely, Peaks
Peaks14,
14,2727and
and28.28.
From
composition
of those
compounds,
be determined
namely,
From
the the
composition
of those
compounds,
it canitbecan
determined
that
that aromatic
hydrocarbons
containing
1 to represent
6 rings represent
the majority,
compounds
aromatic
hydrocarbons
containing
1 to 6 rings
the majority,
compounds
containingcontaining
oxygen,
oxygen, nitrogen
andalso
sulfur
also account
for a certain
proportion
the content
of saturated
aliphatic
nitrogen
and sulfur
account
for a certain
proportion
and and
the content
of saturated
aliphatic
hydrocarbons isisminimal,
minimal,The
Themononuclear
mononucleararomatics
aromaticsinclude
include1 1toto4 4methyl-substituted
methyl-substituted
compounds
hydrocarbons
compounds
and phenol.
phenol.Bicyclic
Bicyclicaromatic
aromatichydrocarbons
hydrocarbonsare
arecomposed
composedofofnaphthalene
naphthalene
and
methyl
substituted
and
and
itsits
methyl
substituted
derivatives,
biphenyl
and
its
methyl
substituted
compounds
as
well
as
diphenyl;
tricycloarenes
derivatives, biphenyl and its methyl substituted compounds as well as diphenyl; tricycloarenes
includes phenanthrene,
phenanthrene,its
itsmonomethyl
monomethyland
anddimethyl
dimethylsubstituted
substitutedderivatives,
derivatives,phenylnaphthalene
phenylnaphthalene
includes
and
substituted
derivatives,
and fluorene;
fluorene; tetracycloarenes
tetracycloarenesmainly
mainlyinclude
includetriphenylene
triphenyleneand
anditsitsmethyl
methyl
substituted
derivatives,
fluoranthene
and
itsits
methyl
substituted
fluorantheneand
andperylene;
perylene;pentacycloarenes
pentacycloarenescomprise
comprisebenzotetraphene
benzotetraphene
and
methyl
substituted
derivatives;
derivatives; hexacycloarenes
hexacycloarenesinclude
includenaphthotetraphene
naphthotetrapheneand
andother
othersubstances.
substances.Oxygen-containing
Oxygen-containing
compounds
compounds mainly
mainly include
includeesters,
esters,ketones
ketonesand
andphenols;
phenols;amide
amideisisthe
themajor
majornitrogen-containing
nitrogen-containing
compound;
Peak
41,
dibenzobenzodithiophene,
is
the
only
sulfur-containing
compound
compound; Peak 41, dibenzobenzodithiophene, is the only sulfur-containing compounddetected.
detected.
360
YZS
320
280
S
16
abundance(104)
S
240
41
14
200
33
160
120
34
31
8
1
15
3
80
6
2
40
45
0
11
7
5
21 23
17
10 13
9 12
10
19
18
36
26
22 24 28
20
25
27
29
32
30
15
retention time/min
20
35
37 38
25
39 40
41
45
30
Figure 3. Total ion chromatogram (TIC) of THF extract of YZS coal samples.
Figure 3. Total ion chromatogram (TIC) of THF extract of YZS coal samples.
Molecules 2016, 21, 630
6 of 13
Table 2. YZS tetrahydrofuran extraction GC/MS analysis results.
Number
1
2
3
4
5
6
7
8
9
10
11
12
13
15
16
17
19
19-1
19-2
20
21
22
23
24
25
26
29
30
31
31-1
32
33
34
35
36
37
38
39
40
41
42
Name
Molecular Formula
1,4-Dimethylbenzene
C8 H10
Ethenylbenzene
C8 H8
γ-Butyrolactone
C4 H6 O2
1,2,3-Trimethylbenzene
C9 H12
1,2,4-Trimethylbenzene
C9 H12
Naphthalene
C10 H8
1-(1,4-Dimethylcyclohex-3-en-1-yl)ethanone
C10 H16 O
1-Methylnaphthalene
C11 H10
2-Methylnaphthalene
C11 H10
2,6-Di-tert-butyl-4,4-dimethylcyclohexa-2,5-dien-1-one
C16 H26 O
Biphenyl
C12 H10
1,6-Dimethylnaphthalene
C12 H12
Diphenylmethane
C13 H12
2,6-Di-tert-Butylcyclohexa-2,5-diene-1,4-dione
C14 H20 O2
(2aR,4aR,7aS,7bR)-2,2a,4a,7a-Tetramethyl-2a,3,4,4a,6,7,7a,7b-octahydro
C15 H22 O
-5H-cyclopenta[cd]inden-5-one
4-Methylbiphenyl
C13 H12
2,6-Di-tert-butyl-4-ethylphenol
C16 H26 O
9H-Fluorene
C13 H10
4-tert-Butyl-2,6-di(propan-2-yl)phenyl acetate
C18 H28 O2
2,4,6-Tri-tert-butylphenol
C18 H30 O
3,5-Di-tert-butylbenzene-1,2-diol
C14 H22 O2
2,6-Di-tert-butyl-4-(hydroxymethyl)phenol
C15 H24 O2
Phenanthrene
C14 H10
Butyl 2-methylpropyl benzene-1,2-dicarboxylate
C16 H22 O4
1-Methylphenanthrene
C15 H12
2-Methylphenanthrene
C15 H12
2-Phenylnaphthalene
C16 H12
Hexadecanamide
C16 H33 C18 H35 NO
Octadec-9-enamide
C18 H35 NO
Triphenylene
C18 H12
2-Methyltriphenylene
C19 H14
4,41 -Ethane-1,2-diylbis(2,6-di-tert-butylphenol)
C30 H46 O2
Bis(2-ethylhexyl) decanedioate
C26 H50 O4
Benzo[pqr]tetraphene
C20 H12
Benzo[j]fluoranthene
C20 H12
10-Methylbenzo[pqr]tetraphene
C21 H14
3-Methylperylene
C21 H14
5,51 ,6,61 ,7,71 ,8,81 -Octahydro-2,21 -binaphthalene
C20 H22
Naphtho[7,8,1,2,3-nopqr]tetraphene
C22 H12
Dibenzo[d,d1 ]benzo[1,2-b:5,4-b1 ]bisthiophene
C18 H10 S2
Naphtho[1,2,3,4-pqr]tetraphene
C24 H14
2.2.2. Taifeng Fat Coal (TFF) from Guizhou
Figure 4 is the total ion chromatogram (TIC) of the THF extract of TFF coal samples. After the
contrastive analysis of the chromatogram library, as shown in the Table 3, it can be determined that
there are 31 kinds of compounds. Compared with YZS coal, the type and number of rings of aromatic
hydrocarbons are less, with only 1- to 3-cycloarenes detected. In the extract, monocycloarenes included
two kinds of trimethylbenzene derivatives and a kind of methyl- and butyl-substituted phenol;
the bicycloarenes contained more kinds, including naphthalene and its alkyl-substituted compounds;
tricycloarenes were mainly composed of phenanthrene, its monomethyl- and dimethyl-substituted
derivatives as well as methyl fluorene. The alicyclic hydrocarbons are mainly n-alkanes covering the
range from C11 to C17 (with the exception of C15 ). Besides, the cycloalkane trimethylcyclopentane is
also detected. Oxygen-containing compounds include furan and phenol; the only sulfur-containing
compound detected is dipropyl disulphide.
Molecules 2016, 21, 630
7 of 13
also detected. Oxygen-containing compounds include furan and phenol; the only sulfur-containing
Molecules 2016, 21, 630
7 of 13
compound
detected is dipropyl disulphide.
140
4
1
abundance（104)
21
TFF
130
S
3
110
H3C
8
S
CH3
90
70
50
30
2
10
2
5
18
25
13 14 19
24
17
7 10 12 16 20 2223 26 27 29 30 31
28
6 8 9 11
15
6
10
14
18
retention time/min
22
26
30
Figure
4. Total
chromatogram(TIC)
(TIC) of
of the
TFF
coal
samples.
Figure
4. Total
ionion
chromatogram
the THF
THFextract
extractofof
TFF
coal
samples.
Table 3. TFF tetrahydrofuran extraction GC/MS analysis results.
Table 3. TFF tetrahydrofuran extraction GC/MS analysis results.
Number
Name
Molecular
Formula
Number
Name
Molecular
Formula
1
Tetrahydro-2-furanol
C4 H
1
Tetrahydro-2-furanol
C84O
H28O2
2
1,1,3-Trimethylcyclopentane
C8 H
2
1,1,3-Trimethylcyclopentane
C168H16
3
Dihydrofuran-2(3H)-one
C4 H6 O2
3
Dihydrofuran-2(3H)-one
4
Tetrahydro-2-furanmethanol
C5 HC104H
O26O2
4
Tetrahydro-2-furanmethanol
5
1,3,5-Trimethylbenzene
C9CH5H
12 10O2
6
1,2,4-Trimethylbenzene
C9 H
5
1,3,5-Trimethylbenzene
C129H12
7
Undecane
C11 H24
6
1,2,4-Trimethylbenzene
C9H12
8
Dipropyl disulfide
C6 H14 S2
7
Undecane
9
Naphthalene
C10C
H118H24
Dodecane
C12CH6H
8 10
Dipropyl
disulfide
26 14S2
11
Undecane,4,5-dimethylC
H
13
28
9
Naphthalene
C10H8
12
Tridecane
C13 H28
10 13
Dodecane
C
H26
2-Methylnaphthalene
C11 H12
10
11 14
Undecane,4,5-dimethyl1-Methylnaphthalene
C11C
H13
10H28
2-Ethenylnaphthalene
C12C
H13
10H28
12 15
Tridecane
16
Tetradecane
C14 H30
13
2-Methylnaphthalene
C11H10
17
2-Ethylnaphthalene
C12 H12
14 18
1-Methylnaphthalene
H10
2,3-Dimethylnaphthalene
C12C
H11
12
1,7-Dimethylnaphthalene
C12C
H12
15 19
2-Ethenylnaphthalene
12H10
1,4-Dimethylnaphthalene
C12C
H14
12H30
16 20
Tetradecane
2,6-di-tert-Butyl-4-methylphenol
C15 H24 O
21
17 22
2-Ethylnaphthalene
H12
2,3,6-Trimethylnaphthalene
C13C
H12
14
18 23
2,3-Dimethylnaphthalene
C
12
1,6,7-Trimethylnaphthalene
C13 H14H12
24
1,4,6-Trimethylnaphthalene
C13C
H12
14H12
19
1,7-Dimethylnaphthalene
25
1,4,5-Trimethylnaphthalene
C13 H14
20
1,4-Dimethylnaphthalene
C12H12
26
Hexadecane
C16 H34
21 27 2,6-di-tert-Butyl-4-methylphenol
CH1536
H24O
Heptadecane
C17
2-Methyl-9H-fluorene
C14C
H13
22 28
2,3,6-Trimethylnaphthalene
12H14
29
Phenanthrene
C
H
14C13
10H14
23
1,6,7-Trimethylnaphthalene
30
1-Methylphenanthrene
C15 H12
24 31
1,4,6-Trimethylnaphthalene
C
13H14
2,5-Dimethylphenanthrene
C16 H14
25
1,4,5-Trimethylnaphthalene
C13H14
26
Hexadecane
C16H34
27
Heptadecane
C17H36
28
2-Methyl-9H-fluorene
C14H12
29
Phenanthrene
C14H10
30
1-Methylphenanthrene
C15H12
31
2,5-Dimethylphenanthrene
C16H14
Molecules 2016, 21, 630
8 of 13
2.2.3. Chifeng Lignite (CFH) from Inner Mongolia
Figure 5 is the total ion chromatogram (TIC) of the THF extract of CFH coal samples. After the
contrastive analysis of the chromatogram library, as shown in the Table 4, it can be determined
that there are 30 kinds of compounds, as well as three compounds whose names cannot be
determined, namely, Peaks 9, 11 and 20. Aromatic hydrocarbons, aliphatic hydrocarbons and
heteroatom compounds are detected. Compared with the above two samples, less kinds of aromatic
hydrocarbons are detected in CFH coal and most of them are bicycloarenes. In the monocycloarene
class, only methyl- and butyl-substituted phenol and methylbenzoic acid are detected; similar the
bicycloarene in the above two samples, those in CFH coal mainly include naphthalene and its
mono- to tetramethyl-substituted compounds, biphenyl, indene, etc.; the only tricycloarene detected
is N-phenylnaphthalene-2-amine; the only tetracycloarene detected is quaterphenyl. Aliphatic
hydrocarbon levels are mainly high and medium length carbon chain n-alkanes which continuously
distribute from C23 to C31 . There are many kinds of oxygen-containing compounds, including
furans, alcohols, ketones, acids, phenols, etc.; N phenylnaphthylamine is the only nitrogen-containing
compound detected; the only sulfur-containing compound is dipropyldisulphide.
Table 4. CFH tetrahydrofuran extraction GC/MS analysis results.
Number
Name
Molecular Formula
1
2
3
4
5
6
7
8
10
12
13
14
15
16
17
18
19
21
22
23
24
25
26
27
28
29
30
31
32
33
Tetrahydro-2-furanol
2-Methyl-2-pentenal
Dihydrofuran-2(3H)-one
Dipropyl disulfide
3-Methylbenzoic acid
1-Methylnaphthalene
Biphenyl
2,3-Dimethylnaphthalene
2,6-Di-tert-butylcyclohexa-2,5-diene-1,4-dione
2,6-Di-tert-butyl-4-methylphenol
4,4,6,7-Tetramethyl-3,4-dihydronaphthalen-1(2H)-one
1,4,6-Trimethylnaphthalene
1-Methyl-7-(propan-2-yl)naphthalene
1,4,5-Trimethylnaphthalene
5-tert-Butyl-1,1-dimethyl-2,3-dihydro-1H-indene
1,6-Dimethyl-4-(propan-2-yl)naphthalene
1,4-Dimethyl-6-(propan-2-yl)naphthalene
3,8-Dimethyl-5-(propan-2-yl)naphthalen-2-ol
N-phenylnaphthalen-2-amine
Tricosane
Tetracosane
Pentacosane
1-(2-{1-[(2-Ethylhexyl)oxy]ethenyl}phenyl)ethenol
Hexacosane
Heptacosane
Octacosane
Nonacosane
1,11 :41 ,111 :411 ,1111 -Quaterphenyl
Triacontane
Hentriacontane
C4 H8 O2
C6 H10 O
C4 H6 O2
C6 H14 S2
C8 H8 O2
C11 H10
C12 H10
C12 H12
C14 H20 O2
C15 H24 O
C14 H18 O
C13 H14
C14 H16
C13 H14
C15 H22
C15 H18
C15 H18
C15 H18 O
C16 H13 N
C23 H48
C24 H50
C25 H52
C18 H26 O2
C26 H54
C27 H56
C28 H58
C29 H60
C24 H18
C30 H62
C31 H64
Molecules 2016, 21, 630
Molecules 2016, 21, 630
9 of 13
9 of 13
0
4
1
28
130
12
CFH
abundance(104)
110
H3C
30
S
90
29
27
3
70
1
50
22
30
CH3
4
25
18
S
2
5
4
5
10
15
26
32
31
33
21
20
25
retention time/min
30
35
0
4
10
11
9 13
8 10 15 17 19 20
16
7
14
6
23
24
Figure5.5.Total
Totalion
ionchromatogram
chromatogram(TIC)
(TIC)of
ofthe
theTHF
THFextract
extractof
ofCFH
CFHcoal
coalsamples.
samples.
Figure
2.3.
2.3.Discussion
Discussion
The
resultsshow
showthat
thatamong
among
organic
sulfur
compounds
thesamples,
coal samples,
the
The XPS results
thethe
organic
sulfur
compounds
in theincoal
the content
content
of (mercaptans
sulfide (mercaptans
and thioether)
sulfur, thiophene
and sulfonate
sulfurwhile
is higher,
while
of sulfide
and thioether)
sulfur, thiophene
and sulfonate
sulfur is higher,
the content
the
content ofand
sulfoxide
and
sulfone
sulfur is
lower;
the distribution
of organic
sulfur
is related
of sulfoxide
sulfone
sulfur
is lower;
the
distribution
of organic
sulfur in
coalin
is coal
related
to the
to
the degree
of metamorphosis
of the
coal.
The rules
change
rules of(mercaptan
sulfide (mercaptan
and thioether)
degree
of metamorphosis
of the coal.
The
change
of sulfide
and thioether)
sulfur and
sulfur
pyrite
content
with the metamorphic
coal
is not (due
obvious
(due
to the interference
pyriteand
content
with
the metamorphic
degree ofdegree
coal is of
not
obvious
to the
interference
effect of
effect
of thiophene
pyrite); thiophene
sulfur is
content
is reduced
with decreasing
of coal metamorphosis;
pyrite);
sulfur content
reduced
with decreasing
degree ofdegree
coal metamorphosis;
sulfoxide
sulfoxide
andcontent
sulfoneshows
contentnoshows
no change
obviousrules;
change
rules; sulfonate
raised
the
and sulfone
obvious
sulfonate
content iscontent
raised iswith
the with
decrease
decrease
of metamorphic
degree;
the content
of sulfur
sulfateissulfur
rarely related
with metamorphic
of metamorphic
degree; and
the and
content
of sulfate
rarelyisrelated
with metamorphic
degree.
degree.
All the
XPS of
results
of sulfur
sulfatewere
sulfur
were significantly
higher
its corresponding
All the XPS
results
sulfate
significantly
higher than
its than
corresponding
chemicalchemical
analysis
analysis
results. Thiophenic
sulfur
is the
form sulfur
of organic
sulfur
inand
ANW
coal,
and sulfur
other
results. Thiophenic
sulfur is the
major
formmajor
of organic
in ANW
coal,
other
organic
organic
content
is Thiophene
relatively less.
Thiophene
is of
also
main sulfur
form of
in the
TFF
content sulfur
is relatively
less.
is also
main form
organic
in organic
the TFF sulfur
and XCF
samples;
and
XCF samples;
the content
ofstate
sulfonate
oxidation
state
is higher,
while(mercaptan
the contents
sulfide
the content
of sulfonate
oxidation
is higher,
while the
contents
of sulfide
andofthioether)
(mercaptan
andand
thioether)
sulfur,
sulfone
and sulfoxide
are less. In
TKQ coal,
sulfonate
content
sulfur, sulfone
sulfoxide
are less.
In TKQ
coal, the sulfonate
content
is thethe
highest,
followed
by
issulfide
the highest,
followed
sulfide (mercaptan
and
thioether)sulfur,
sulfur,sulfone,
while thiophenic
sulfur,
sulfone,
(mercaptan
andby
thioether)
sulfur, while
thiophenic
and sulfoxide
content
are
and
sulfoxide
content are
reduced
in sequence.
Organic
in DTR coalofshows
predominance
of
reduced
in sequence.
Organic
sulfur
in DTR coal
showssulfur
a predominance
sulfidea sulfur
(mercaptan
sulfide
sulfur (mercaptan
and thioether),
while sulfur,
the content
of thiophenic
sulfonate,
sulfoxide
and thioether),
while the content
of thiophenic
sulfonate,
sulfoxide sulfur,
and sulfone
is less.
In CFH,
and
sulfone is
less. InofCFH,
the relative
content
of highest,
sulfonatefollowed
in the coal
the highest,
followed
sulfide
the relative
content
sulfonate
in the coal
is the
by is
sulfide
(mercaptan
and by
thioether),
(mercaptan
and thioether),
the and
thiophenic
sulfur,
sulfone,
and sulfoxide contents are less.
while the thiophenic
sulfur,while
sulfone,
sulfoxide
contents
are less.
Mild
MildTHF
THFsolvent
solventextracts
extractsmainly
mainlycontain
containfree
freeorganic
organicsulfur
sulfursmall
smallmolecules
moleculeswhose
whosedistribution
distribution
and
and content
content are
are closely
closely related
related to
to the
the degree of metamorphosis of the coal. That
That is,
is, when
when the
the
metamorphic
sample is
is higher,
higher,there
thereisisaacorresponding
correspondingincrease
increaseininthe
thecontent
content
ratio
metamorphic degree
degree of a coal sample
ratio
as
as
well
as
kinds
of
aromatic
hydrocarbons,
while
the
relative
content
of
aliphatic
hydrocarbons
well as kinds of aromatic hydrocarbons, while the relative content of aliphatic hydrocarbons drops;
drops;
the chemical
structure
of extracts
simple
withnumber
a smallofnumber
of substituent
the chemical
structure
of extracts
is simpleiswith
a small
substituent
groups; thegroups;
content the
and
content
kinds of heteroatom
are fewer.
carbon
content ofhydrocarbons
aliphatic hydrocarbons
kinds ofand
heteroatom
compoundscompounds
are fewer. The
carbonThe
content
of aliphatic
in extracts
in
extracts
direct
link to the metamorphic
degree
of coal,
too. That
with lower metamorphic
has
a directhas
linka to
the metamorphic
degree of coal,
too. That
is, with
loweris,metamorphic
degree of coal,
degree
of of
coal,
the ratio of
high-carbon
alkanesgrows
in thehigher.
extractThe
grows
freesmall
organic
sulfur
the ratio
high-carbon
alkanes
in the extract
freehigher.
organicThe
sulfur
molecules
small
molecules
in coal of lowdegree
metamorphic
degree
are mainly
composed
of aliphatic
while
in coal
of low metamorphic
are mainly
composed
of aliphatic
sulfides,
while sulfides,
those in coal
of
those
in coal
medium
and high degree
metamorphic
degree
are mainly
composed ofBesides,
thiophenes.
Besides,
medium
andofhigh
metamorphic
are mainly
composed
of thiophenes.
the degree
of
the
degree of of
aromatization
of the
organic
sulfur
small
rises
with rising Thiophenic
degree of
aromatization
the organic sulfur
small
molecules
rises
withmolecules
rising degree
of coalification.
coalification.
Thiophenic
was
notextracts
detected
mild
THF
extracts
of TFF and
CFHthe
coal
samples,
sulfur was not
detected sulfur
in mild
THF
ofinTFF
and
CFH
coal samples,
while
XPS
results
while
results
of TFF showed
and CFH
coal samples
showed
a certain sulfur,
proportion
thiophenic
of TFFthe
andXPS
CFH
coal samples
a certain
proportion
of thiophenic
whichofsuggests
that
sulfur,
which
suggests sulfides
that aliphatic
hydrocarbon
arecompared
more likely
to be
dissolvedsulfur.
compared
aliphatic
hydrocarbon
are more
likely to besulfides
dissolved
with
thiophenic
It can
with
sulfur.
It can also be seen
fromthat
the aforementioned
resultsofthat
small number
also thiophenic
be seen from
the aforementioned
results
only a small number
freeonly
and asoluble
organic
of free and soluble organic sulfur small molecules are detected in the extract. This is because most
organic sulfur is attached to the macromolecular skeleton of coal by C-S bonds, making them hard to
Molecules 2016, 21, 630
10 of 13
sulfur small molecules are detected in the extract. This is because most organic sulfur is attached to the
macromolecular skeleton of coal by C-S bonds, making them hard to separate from the coal matrix,
and leading to the small ratio of soluble organic matter. In addition, since GC/MS can only detect
compounds with a relative molecular weight of less than 500, most of the soluble organic sulfur small
molecules exceed the GC/MS detection range. Therefore, only very low amounts of organic sulfur
small molecules can be detected.
3. Experimental Section
3.1. XPS Experimental Method and Coal Sample Selection
XPS measurement was conducted on an ESCALAB250 X-ray photoelectron spectrometer
(Thermo Fisher, Waltham, MA, USA) at the Advanced Analysis and Computation Center of the
China University of Mining and Technology. Al K alpha anode was employed; the power was 200 W,
and the probe diameter was 900 µm. The full scanning transmission was 100 eV with step size being
1.000 eV; the narrow scanning transmission was 20 eV with step size being 0.05 eV; the basic vacuum
was 10´7 Pa. C 1 s (284.6 eV) was taken as the calibration standard to conduct the check. In the
XPS spectra, the ordinate represents the strength of the electronic signal, and the abscissa shows the
electron binding energy. The S 2p XPS spectra obtained were peak fitted by using XPSPEAK 4.1 special
software (Advanced Analysis & Computation Center of China University of Mining & Technology,
Xuzhou, China), with the fitting parameters set as Shirley Background, 0% Lorentzian-Guaussian and
FWHM 1.2 eV. Among the binding energies of sulfur compounds, 163.1 eV corresponds to sulfide
sulfur (mercaptan and thioether) and pyritic sulfur, 164.2 eV to thiophenic sulfur, 165.3 eV to sulfoxide,
167.4 eV to sulfone, 168.7 eV to sulfonate, and 169.9 eV to sulfate [15–18].
Temperature, pressure, and time, the physical and chemical influence the degree of metamorphosis
of the coal. In the coal metamorphism process, its physical characteristics, chemical composition and
process performance undergo regular changes. According to the degree of coal metamorphosis, coal
can be divided into three categories which are lignite, bituminous and anthracite. Six coal samples of
different sulfur content and different metamorphic degree were selected as research objects. They were
Anning anthracite (ANW) from Guizhou, Taifeng fat coal (TFF) from Guizhou, Xingcheng fat coal
(XCF) from Guizhou, Tangkou gas coal (TKQ) from Shandong, Datong weakly caking coal (DTR) from
Shanxi and Chifeng lignite (CFH) from Inner Mongolia, respectively. The bulk analysis, elemental
analysis and analysis of various sulfur forms of the six coal samples are shown in Tables 5 and 6.
The proximate analyses and elemental analyses of the coal were in accordance with the Chinese
national standards GB/T 30732-2014 and GB/T 31391-2015. The experimental samples were taken out
from the sealed bags where they were stored, put into a 50 ˝ C vacuum oven to dry for 12 h, and then
cooled to room temperature. Two g of each dry coal sample was taken out and smashed to less than
74 µm to conduct the XPS tests.
Table 5. The proximate and ultimate analysis of the six coal samples.
Sample
ANW
TFF
XCF
TKQ
DTR
CFH
Proximate Analysis (wt % as Received)
Ultimate Analysis(wt % Daf)
Mad
Aad
Vad
FCad
Odaf
Cdaf
Hdaf
Ndaf
1.84
1.22
1.39
2.32
2.86
15.32
7.91
17.38
16.61
9.83
7.90
13.89
6.90
29.69
32.94
34.85
21.80
31.88
83.35
51.71
49.06
53.00
67.44
38.91
2.90
5.55
7.11
10.21
8.94
18.58
91.05
83.59
83.11
82.24
85.59
74.63
3.23
5.29
5.47
5.18
4.08
4.47
1.34
1.42
1.43
1.63
0.74
0.86
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Table 6. The sulfur forms of six coal samples.
Sample
ANW
TFF
XCF
TKQ
DTR
CFH
Sp.d /%
St.d /%
Ss.d /%
So.d /%
Absolute
Absolute
Relative
Absolute
Relative
Absolute
Relative
1.37
3.42
2.39
0.67
0.60
1.25
0.65
1.13
1.07
0.03
0.04
0.40
47.45
33.04
44.77
4.48
6.67
32.00
0.01
0.02
0.03
0.00
0.04
0.05
0.73
0.58
1.26
0.00
6.67
4.00
0.70
2.27
1.29
0.64
0.51
0.80
51.09
66.37
53.97
95.52
85.00
64.00
St.d —total sulfur; Sp.d —iron sulfide; Ss.d —sulfate; So.d —organic sulfur.
Forms of sulfur in samples were analyzed in accordance with the Chinese national standard
GB/T215-2003, Determination of Forms of Sulfur in Coal. The results are shown in Table 6. The rough
contents of organic sulfur, iron sulfide sulfur and sulfate sulfur can be obtained with this method.
According to Chinese national standard GB/T15224.2-2004, coals with different sulfur content are
divided into six grades, namely special low sulfur coal with total sulfur less than or equal to 0.5%,
low sulfur coal (0.51% to 1.00%), low and medium sulfur coal (1.01% to 1.50%), medium sulfur coal
(1.51% to 2.00%), medium and high sulfur coal (2.01% to 3.00%) and high sulfur coal more than 3.00%.
Based on the above criteria, TFF coal can be classified as high sulfur coal, XCF coal as medium and
high sulfur coal, ANW coal and CFH coal as low and medium sulfur coals, and TKQ coal and DTR
coal as low sulfur coals. Organic sulfur occupies a dominant position in low sulfur coal (TKQ coal and
DTR coal), with very tiny content of other forms of sulfur. However, in addition to the predominant
organic sulfur, there are also a certain amounts of iron sulfide and sulfate in medium-sulfur coal and
high-sulfur coal (the other four samples).
3.2. THF Solvent Extraction Experimental Methods and Procedures
In the extraction experiments, tetrahydrofuran (THF) was selected as solvent, and Yangzhuang
lean coal, Taifeng fat coal and Chifeng lignite were extracted by means of microwave assisted extraction.
Taifeng fat coal and Chifeng lignite information has been introduced in above, that was not repeated
here, Yang Zhuang thin coal coal quality analysis results are shown in Table 7. The extracts were
analyzed by GC/MS to study the composition and structure of the organic sulfur small molecules
in coal. The main instruments of the experiment include a CW-2008 multifunctional microwave
reaction/extraction apparatus produced by Shanghai Xintuo Instruments Technology Co., Ltd.
(Shanghai, China) and a RE-52AA rotary evaporator produced by Yarong Biochemical Instrument
Factory (Shanghai, China). Forty g coal samples with particle size of 180~380 µm were taken out and
put into the extractor, and then 400 mL tetrahydrofuran was added to the extractor. After the container
was installed in accordance with the operating requirements, the circulating water was turned on.
Then, the power supply of the equipment was started after making sure that experimental system was
correctly connected. During the extraction, the pressure was set to normal pressure, the temperature
to 50 ˝ C and the extraction time to 4 h. After the end of extraction, suction filtration was applied to
the coal and solvent mixtures in the container using a vacuum suction device, so as to separate the
residual coal (coal samples after extraction) and extract. The RE-52AA rotary evaporator was used to
concentrate the extract under the conditions of 30 r¨ min´1 and 60 ˝ C until the extract was concentrated
to 8 mL. Then, it was transferred to a sealed glass bottle for sealing and preservation and sent to the
laboratory for GC/MS analysis.
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Table 7. The proximate and ultimate analysis of YZS coal samples.
Sample
YZS
Proximate Analysis (wt % as Received)
Ultimate Analysis (wt % Daf)
Mad
Aad
Vad
FCad
Odaf
Cdaf
Hdaf
Ndaf
1.58
46.16
5.30
40.86
2.50
89.0
4.12
3.3
4. Conclusions
In this paper, XPS analysis tests and a THF microwave assisted extraction method are adopted to
study the structure of organic sulfur in coal. By conducting XPS analysis tests on coal of different sulfur
content and different degrees of metamorphosis and in combination with GC/MS analysis of mild
THF microwave extracts of the coal samples, this paper comprehensively analyzed the distribution
rules of organic sulfur in coal. The following conclusions can be drawn:
(1)
(2)
Among the organic sulfur in coal samples, the contents of sulfide (mercaptan and thioether) sulfur,
thiophenic sulfur and sulfonate are higher, while the contents of sulfoxide and sulfone are lower.
The change rule of sulfide sulfur (mercaptan and thioether) and pyrite content with the degree of
metamorphosis of coal is not obvious (due to the interference of pyrite); thiophenic sulfur content
is reduced with decreasing metamorphic degree of coal; sulfoxide and sulfone content shows
no obvious change rule; sulfonate content is raised with the decrease of metamorphic degree;
and the content of sulfate sulfur is rarely related with metamorphic degree.
The distribution and content of free organic sulfur small molecules in coal are closely related to the
degree of metamorphosis of coal. That is, with a higher metamorphic degree of a coal, the content
ratio as well as the kinds of aromatic hydrocarbons in its extracts increase correspondingly,
while the relative content of aliphatic hydrocarbons drops; the chemical structure of extracts
is simple, with a small number of substituent groups; the content and kinds of heteroatomic
compounds are lower. The content of aliphatic hydrocarbon compounds in extracts has a direct
link to the metamorphic degree of coal, too. That is, with a lower degree of coal metamorphosis,
the ratio of high-carbon number alkanes in the extract increases. The free organic sulfur
small molecules in coal of low metamorphic degree are mainly composed of aliphatic sulfides,
while those in coals of medium and high metamorphic degree are mainly thiophenes. Besides,
the aromatization degree of organic sulfur small molecules rises with rising degree of coalification.
Acknowledgments: This study is supported by the National Natural Science Foundation of China (No. 51304189,
No. U1361213, No. 51074158), the Program for Innovative Research Team in University of Ministry of Education
of China (IRT13098) and a project funded by the Priority Academic Program Development of Jiangsu Higher
Education Institutions (PAPD).
Author Contributions: Lanjun Zhang conducted the experiments and analyzed the data. Zenghua Li conceived
the study, participated in its design and coordination, and helped to draft the manuscript. Yongliang Yang,
Yinbo Zhou, Jinhu Li, Leilei Si and Biao Kong drafted the manuscript. All the authors read and approved the
final manuscript.
Conflicts of Interest: The authors declare no conflict of interest.
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Sample Availability: Not Available.
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