- Email: [email protected]
Electron spin resonance studies of some Canadian coals
Short Communications
Electron
spin resonance
studies
of some Canadian
coals
Kailash C. Khulbe, Armen Manoogian *, Bei Wah Ghan*, Ranveer S. Mann and John A. MacPhee’ Department of Chemical Engineering and *Department of Physics, University of Ottawa, Ottawa, Ontario, KIN 984, Canada t Department of Energy, Mines and Resources, CANMET, Energy Research laboratories, Ottawa, Ontario, KIA OGl, Canada (Received 26 July 1962; revised 3 March 1963)
Nine Canadian coals of different rank and composition were studied by electron spin resonance. For percentage of fixed carbon in the range of 43 to 78 wt%, the free radical g values were found to increase with decreasing carbon content, and did not level off for the low rank coals. The free radical linewidths are attributed to atomic species such as oxygen and not to protons of hydrogen. (Keywords:
coal; free radicals; electron
spin resonance)
Electron spin resonance (e.s.r.) measurements were made of the free radical g value, linewidth and concentration in nine Canadian coals of different rank and composition. The results were correlated with the chemical analysis of the coals, namely the percentage of total carbon, fixed carbon, hydrogen and ash. Eight of the coals were from western Canada and one from eastern Canada (Row Minto). Coals from western Canada had a low sulphur content (< 1 wt%), while the Row Minto coal contained 6.8 wt% S. The amount of fixed carbon in the coals varied from 43 to 78 wt% total carbon from 6085 wt%. Most of the previously reported resonance results’ - ’ were for coals with a total carbon content of 65-95 wt%, so that the results presented here extend the data to the low carbon region. The measurements were carried out at X-band microwave frequency and at room temperature, for coals under vacuum and in air. All the coals produced a sharp e.s.r. line due to a free radical, and the g values as a function of carbon content are plotted in Figure 1. The g values are observed to increase with decreasing carbon content, and they approach the free spin value of2.0023 for the high rank coals. This result is similar to that reported by Retcofsky’j for coals with carbon content in the range of 65-85 wt%, but for coals with carbon content ~65 wt% Retcofsky indicated that the g values tended to achieve a constant value. However, the present results show that the g values generally increased even down to 45 wt% carbon content. Allowance was made for the coal with high sulphur content (Row Minto), and its data were ignored when drawing the curves of Figure 1, otherwise the curves would indeed tend to level off in the low carbon region. From the rectilinear plot of Figure 1 the following relation is obtained for the g value in terms of percentage fmed carbon, C: 0016-2361/83/08097342S3.00 @ 1983 Butterworth & Co. (Publishers) Ltd
g=2.0055-45
x 10-6 c
(1)
The concentration of the paramagnetic centres in the coals was obtained from the area of the integrated e.s.r. line compared with that of a standard DPPH sample. It was observed that the number of spins increased with increasing carbon content, and the effect of a vacuum was to cause a further increase for the high rank coals. The latter result indicates that atomic species such as oxygen may be important in affecting the coals. Linewidths are affected by dipole-dipole interactions between the paramagnetic centre and neighbouring atoms. Atomic species interacting with the free radical that are likely to cause line broadening include oxygen and hydrogen. Figure 2, a plot of the e.s.r. line half-width vs hydrogen content of the coals, shows a slight decrease in linewidth with increasing
2.0050
t 2.0040 t
30
40
50
60
70
60
90
100
% Carbon
Figure 1 Plot of g value of coals vs percentageof fixed and total carbon, for the samples in the presence of air. R, Row Minto coal
FUEL, 1983, Vol62,
August
973
Short Communications
species, such as oxygen, are important linewidths in the coals.
in effecting the
ACKNOWLEDGEMENT The authors thank the Department of Energy, Mines and Resources for a grant under the Research Agreement Program No.184/2/81, which enabled this investigation to be carried out.
31
3
”
8
3
’ 4
a
8
13
”
“‘1
5 %
REFERENCES
6
Retcofsky, H. L., Stark, J. M. and Friedel, R. A. Anal. Chem. 1968,&J, 1699 Elofson, R. M. and Schultz, K. F. in ‘Spectrometry of Fuels’, (Ed. R. A. Friedel), Plenum Press, New York, 1970, 202 Retcofsky, H. L., Stark, J. M. and Friedel, R. A. Chem. Znd. (Ion&n) 1967, 1372 Toyoda, S., Sugawara, S. and Honda, H. J. Fuel Sot. Japan 1966,45, 876 Toyoda, S. and Honda, H. Carbon 1966,3,527 Retcofsky, H. L. in ‘Chemistry of Coal Utilization’, Second Supp. Vol., (Ed. M. A. Elliot), John Wiley, New York, 1981, 241
Hydrogen
Figure 2 Half-width of the free radical e.s.r. lines vs percentage of hydrogen in the coals, for the samples in the presence of air
hydrogen content, which is opposite to that expected for the effect of hydrogen. Hence, it appears that other atomic
Ruthenium tetroxide catalysed representative hydrocarbons
oxidation
of Illinois
No.6 coal and some
Leon M. Stock and Kwok-tuen Tse Department of Chemistry, The University of Chicago. Chicago, IL 60637, USA (Received 30 December 1982; revised 4 March 1983)
The use of ruthenium tetroxide for the catalytic oxidation of coal molecules under mild conditions has been examined. The selectivity of the reagent for aromatic nuclei has been assessed by a study of the oxidation of selected benzene, naphthalene and phenanthrene derivatives. The catalysed oxidation of Illinois No.6 coal has been studied. The preliminary results described in this report suggest that this oxidant is effective for the selective oxidation of the aromatic structures in this coal. (Keywords:
catalytic
oxidation,
selective
oxidation;
coal structure)
Hayatsu, Scott and Winans recently reviewed the methods suitable for the selective oxidation of coal’. They point out that a variety of reagents are useful for the oxidation of the aliphatic network of these substances, but only one procedure is available’for the oxidation of the aromatic structural components. In this reaction, coal is oxidized in a mixture of hydrogen peroxide and trifluoroacetic acid under refluxzp4. These rather severe conditions are not appropriate for the oxidation of many potentially interesting coal structures and the limitations of this method for the elucidation of the composition of coal have been discussed5T6.
Sharpless and his co-workers demonstrated that these deficiencies could be overcome by the use of a coordinating co-solvent, acetonitrile, for catalytic oxidation reactions*. This procedure has been adapted for the oxidation of coal. Preliminary experiments with Illinois No.6 coal established that it could be oxidized conveniently using a catalytic quantity of ruthenium(II1) chloride trihydrate in a mixture of water, acetonitrile and carbon tetrachloride at ambient temperature with excess sodium bromate, sodium periodate, periodic acid or sodium hypochlorite. The black reaction mixture acquired the appearance of pale green milk in -90 min.
USE OF RUTHENIUM
Tetroxide
TETROXIDE
An alternative method based upon ruthenium tetroxide is described in this report. While it has been known for some time that this oxidant is effective for the oxidation of aromatic structures, its usefulness has been limited by the low conversions realized in many reactions’. However, 0016236l/a3/oa0974-03S3.00 @ 1983 Butterworth & Co. (Publishers) Ltd 974
FUEL,
1983,
Vol62,
August
and representative
compounds
Typically, the compound (10 mmol) was suspension of sodium periodate (160 mmol, ruthenium(II1) chloride trihydrate (0.1 mmol, a mixture of carbon tetrachloride (20 ml), (20 ml) and water (30 ml) and the mixture
added to a 34.2 g) and 26.1 mg) in acetonitrile was stirred
Electron
spin resonance
studies
of some Canadian
coals
Kailash C. Khulbe, Armen Manoogian *, Bei Wah Ghan*, Ranveer S. Mann and John A. MacPhee’ Department of Chemical Engineering and *Department of Physics, University of Ottawa, Ottawa, Ontario, KIN 984, Canada t Department of Energy, Mines and Resources, CANMET, Energy Research laboratories, Ottawa, Ontario, KIA OGl, Canada (Received 26 July 1962; revised 3 March 1963)
Nine Canadian coals of different rank and composition were studied by electron spin resonance. For percentage of fixed carbon in the range of 43 to 78 wt%, the free radical g values were found to increase with decreasing carbon content, and did not level off for the low rank coals. The free radical linewidths are attributed to atomic species such as oxygen and not to protons of hydrogen. (Keywords:
coal; free radicals; electron
spin resonance)
Electron spin resonance (e.s.r.) measurements were made of the free radical g value, linewidth and concentration in nine Canadian coals of different rank and composition. The results were correlated with the chemical analysis of the coals, namely the percentage of total carbon, fixed carbon, hydrogen and ash. Eight of the coals were from western Canada and one from eastern Canada (Row Minto). Coals from western Canada had a low sulphur content (< 1 wt%), while the Row Minto coal contained 6.8 wt% S. The amount of fixed carbon in the coals varied from 43 to 78 wt% total carbon from 6085 wt%. Most of the previously reported resonance results’ - ’ were for coals with a total carbon content of 65-95 wt%, so that the results presented here extend the data to the low carbon region. The measurements were carried out at X-band microwave frequency and at room temperature, for coals under vacuum and in air. All the coals produced a sharp e.s.r. line due to a free radical, and the g values as a function of carbon content are plotted in Figure 1. The g values are observed to increase with decreasing carbon content, and they approach the free spin value of2.0023 for the high rank coals. This result is similar to that reported by Retcofsky’j for coals with carbon content in the range of 65-85 wt%, but for coals with carbon content ~65 wt% Retcofsky indicated that the g values tended to achieve a constant value. However, the present results show that the g values generally increased even down to 45 wt% carbon content. Allowance was made for the coal with high sulphur content (Row Minto), and its data were ignored when drawing the curves of Figure 1, otherwise the curves would indeed tend to level off in the low carbon region. From the rectilinear plot of Figure 1 the following relation is obtained for the g value in terms of percentage fmed carbon, C: 0016-2361/83/08097342S3.00 @ 1983 Butterworth & Co. (Publishers) Ltd
g=2.0055-45
x 10-6 c
(1)
The concentration of the paramagnetic centres in the coals was obtained from the area of the integrated e.s.r. line compared with that of a standard DPPH sample. It was observed that the number of spins increased with increasing carbon content, and the effect of a vacuum was to cause a further increase for the high rank coals. The latter result indicates that atomic species such as oxygen may be important in affecting the coals. Linewidths are affected by dipole-dipole interactions between the paramagnetic centre and neighbouring atoms. Atomic species interacting with the free radical that are likely to cause line broadening include oxygen and hydrogen. Figure 2, a plot of the e.s.r. line half-width vs hydrogen content of the coals, shows a slight decrease in linewidth with increasing
2.0050
t 2.0040 t
30
40
50
60
70
60
90
100
% Carbon
Figure 1 Plot of g value of coals vs percentageof fixed and total carbon, for the samples in the presence of air. R, Row Minto coal
FUEL, 1983, Vol62,
August
973
Short Communications
species, such as oxygen, are important linewidths in the coals.
in effecting the
ACKNOWLEDGEMENT The authors thank the Department of Energy, Mines and Resources for a grant under the Research Agreement Program No.184/2/81, which enabled this investigation to be carried out.
31
3
”
8
3
’ 4
a
8
13
”
“‘1
5 %
REFERENCES
6
Retcofsky, H. L., Stark, J. M. and Friedel, R. A. Anal. Chem. 1968,&J, 1699 Elofson, R. M. and Schultz, K. F. in ‘Spectrometry of Fuels’, (Ed. R. A. Friedel), Plenum Press, New York, 1970, 202 Retcofsky, H. L., Stark, J. M. and Friedel, R. A. Chem. Znd. (Ion&n) 1967, 1372 Toyoda, S., Sugawara, S. and Honda, H. J. Fuel Sot. Japan 1966,45, 876 Toyoda, S. and Honda, H. Carbon 1966,3,527 Retcofsky, H. L. in ‘Chemistry of Coal Utilization’, Second Supp. Vol., (Ed. M. A. Elliot), John Wiley, New York, 1981, 241
Hydrogen
Figure 2 Half-width of the free radical e.s.r. lines vs percentage of hydrogen in the coals, for the samples in the presence of air
hydrogen content, which is opposite to that expected for the effect of hydrogen. Hence, it appears that other atomic
Ruthenium tetroxide catalysed representative hydrocarbons
oxidation
of Illinois
No.6 coal and some
Leon M. Stock and Kwok-tuen Tse Department of Chemistry, The University of Chicago. Chicago, IL 60637, USA (Received 30 December 1982; revised 4 March 1983)
The use of ruthenium tetroxide for the catalytic oxidation of coal molecules under mild conditions has been examined. The selectivity of the reagent for aromatic nuclei has been assessed by a study of the oxidation of selected benzene, naphthalene and phenanthrene derivatives. The catalysed oxidation of Illinois No.6 coal has been studied. The preliminary results described in this report suggest that this oxidant is effective for the selective oxidation of the aromatic structures in this coal. (Keywords:
catalytic
oxidation,
selective
oxidation;
coal structure)
Hayatsu, Scott and Winans recently reviewed the methods suitable for the selective oxidation of coal’. They point out that a variety of reagents are useful for the oxidation of the aliphatic network of these substances, but only one procedure is available’for the oxidation of the aromatic structural components. In this reaction, coal is oxidized in a mixture of hydrogen peroxide and trifluoroacetic acid under refluxzp4. These rather severe conditions are not appropriate for the oxidation of many potentially interesting coal structures and the limitations of this method for the elucidation of the composition of coal have been discussed5T6.
Sharpless and his co-workers demonstrated that these deficiencies could be overcome by the use of a coordinating co-solvent, acetonitrile, for catalytic oxidation reactions*. This procedure has been adapted for the oxidation of coal. Preliminary experiments with Illinois No.6 coal established that it could be oxidized conveniently using a catalytic quantity of ruthenium(II1) chloride trihydrate in a mixture of water, acetonitrile and carbon tetrachloride at ambient temperature with excess sodium bromate, sodium periodate, periodic acid or sodium hypochlorite. The black reaction mixture acquired the appearance of pale green milk in -90 min.
USE OF RUTHENIUM
Tetroxide
TETROXIDE
An alternative method based upon ruthenium tetroxide is described in this report. While it has been known for some time that this oxidant is effective for the oxidation of aromatic structures, its usefulness has been limited by the low conversions realized in many reactions’. However, 0016236l/a3/oa0974-03S3.00 @ 1983 Butterworth & Co. (Publishers) Ltd 974
FUEL,
1983,
Vol62,
August
and representative
compounds
Typically, the compound (10 mmol) was suspension of sodium periodate (160 mmol, ruthenium(II1) chloride trihydrate (0.1 mmol, a mixture of carbon tetrachloride (20 ml), (20 ml) and water (30 ml) and the mixture
added to a 34.2 g) and 26.1 mg) in acetonitrile was stirred