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Optical properties of carbon (HTT 873 K) from pre-oxidized vitrinites carbonized under pressures of about 200 MPa
Letters
to the Editor
Optical properties of carbon (HTT 873 K) from pre-oxidized under pressures of about 200 MPa
vitrinites
carbonized
Fariborz Goodarzi” and Harry Marsh *Fuel Research Laboratories, University of Technology, Esfahan, Iran Northern Carbon Research Laboratories, School of Chemistry, University Newcastle upon Tyne, NE1 7RU, UK (Received 7 August 1978; revised 29 November 1979)
The influence of pre-oxidation of vitrinites upon their carbonization behaviour at atmospheric pressure is reasonThere occurs a pronounced loss ably well understood1-3. of plasticity and a marked variation with heat-treatmenttemperature (HTT) of the optical properties, particularly refractive-index and bireflectance, of cokes from preoxidizedvitrinites. With progressive pre-oxidation there also occurs a pronounced change in the optical texture or microstructure, i.e. shape and size of anisotropic units3 seen in polished section, using polarized-light optical microscopy. Carbonization under high pressures produces carbons with optical textures different from those produced at atmospheric pressure4. The optical properties of these carbons produced at high pressures, e.g. reflectivity are also significantly affected. The objective of the present study is to extend our understanding of the mechanism of oxidation of softening vitrinites and modification of their carbonization properties by further examination of the optical properties of progressively pre-oxidised vitrinites carbonized at a pressure of one atmosphere, under nitrogen, and at pressures of about 200 MPa 4. The optical textures of the cokes and chars (collectively called carbons) examined here for optical properties have been described previously4,‘.
of Newcastle
upon Tvne.
6.0 -
5.0 -
10
15 Extent
20 of
25
oridatmn
30
35
40
(days)
Figure 1 Variation of maximum oil reflectivity with extent of oxidation at 378 K of Parkgate Yorkshire f) and Northumbrian f- - -1 vitrinites carbonized at one atmosphere pressure to 873 K at 5 K min-1
t
EXPERIMENTAL Two bituminous vitrinites (Table I) were hand-picked and ground to pass 72 BS mesh sieve (<21Opm diameter). The vitrinites were oxidized at 378 K in air for periods from 1 to 40 days. The pre-oxidized vitrinites were carbonized at a rate of heating of 5 K min-l with one hour soak period as follows: (1) in a tube furnace to 873 K + 2 K under nitrogen; (2) in a sealed gold tube under hydraulic pressure of 170 to 310 MPa at temperatures of 873 K f 5 K; the details of the pressurized carbonization procedures are Tab/e I Analyses of vitrinites
C
H
Vitrinite Parkgate (Yorkshire) 85.4 (caking) Unnamed (Northumbria) 87.9 (coking)
N+Oa
S (wt % dafl
Remax
Rernin
5.3
1.0
8.3
1.08
0.20
5.3
1.1
5.7
1.24
0.25
awt % N+O by difference 0016-2361180/040266-6282.00 0 1980 IPC Business Press
266
Oil Bireflecreflectance tivity (%I Romax-
FUEL, 1980, Vol 59, April
I 5
I
I
10
15 Extent
20 of
day
25 oxldotion
30
35
LO
(days1
Fiwre 2 Variation of oil bireflectance with extent of oxidation at 378 K of Parkgate Yorkshire () and Northumbrian (- - -) vitrinites carbonized at one atmosphere pressure to 873 K at 5 K min-1
given elsewhere6. A Leitz microscope photometer fitted with a polarizing strain-free objective (N.A. 0.95/x60) was used for reflectance measurements. Reflectivities in oil (noi1 = 1 S16 at 546 nm) of 50 separate particles on polished relief surfaces of each carbon were measured. Mean maximum reflectivities (Ro ax) o f eat h car b on were calculated as described7 and bireqectances were determined according to Marshall, Murchison and Goodarzia9.
RESULTS The variation of optical properties of the carbons from both
Letters to the Editor Third stage (9-40
vitrinites, with the extent of oxidation, shows three stages of oxidation identifiable with the optical texture and morphology of carbons from the vitrinites as reported earlier4. First stage (O-l day) The optical properties of carbon from both vitrinites prepared at atmospheric (Figures 1 and 2) and under hydraulic pressure (Figures 3 and 4) show a distinct decrease during this stage of minimum oxidation. Second stage (1-9 days) The variation of reflectivity with extent of oxidation for carbon prepared from both vitrinites, at 873 K, when carbonized at one atmosphere pressure shows after one day an increase with extent of oxidation; with further increase in extent of oxidation the reflectivities either remain constant or decrease slightly (Figure I). The bireflectance values of carbons from the Yorkshire (caking) vitrinite maintain the same level as in the First stage throughout, whereas the values of carbons from Northumbrian (coking) vitrinite increase continuously throughout this stage (Figure 2). The oil reflectivities and oil bireflectance values for carbons from both vitrinites when carbonized under hydraulic pressure increase continuously throughout this stage (Figures 3 and 4).
2
5.0
E :
:
4,o
s E ;
3.0
2 2.0'
I
1
5
10
15
20
25
Extent of oxidation Figure 3 Variation
of maximum
30
35
40
Idoysl
oil reflectivity
oxidation at 378 K of Parkgate Yorkshire ((- - -1 vitrinites carbonized under hydraulic 5 K min-’
with extent
of
1and
Northumbrian pressure to 873 K at
days)
The reflectivity values of carbons from the caking vitrinite, prepared at atmospheric pressure, decrease initially and then remain almost constant with further oxidation; values of carbons from the coking vitrinite maintain their maximum values of the Second stage for 13 days and then decrease slightly with further increase in oxidation (Figure 1). The bireflectance values of carbons from the caking vitrinite, prepared at atmospheric pressure, remain at the minimum value of the First stage; the bireflectance values of carbon from the coking vitrinite decrease initially and then remain constant after 15 days of oxidation (Figure 2). The oil reflectivity values of carbons from the caking vitrinite, carbonized under hydraulic pressure, continue to increase and then decrease slowly with further (20 days) of oxidation during this Third stage (Figure 3). The oil reflectivity values of carbons from the coking vitrinite, carbonized under hydraulic pressure, initially decrease sharply and then remain constant with further oxidation (Figure 3). The bireflectance values of carbons from both vitrinites decrease initially. There is a very small decrease for the carbons from the caking vitrinite and a very sharp decrease for the carbons from the coking vitrinite in this stage. The bireflectance values then remain constant with further oxidation, the bireflectance values of carbons from the caking vitrinite being now higher than the values of the carbons of the coking vitrinite (Figure 4). This study reveals that carbonization under 200 MPa pressure significantly influences the optical properties of carbon from coking vitrinites pre-oxidized for about 11 days (Figures 3 and 4). The reflectivity (6.3%) and bireflectance (6.1%) in oil after nine days of pre-oxidation represent maximum values recorded for carbons prepared at an HTT of 873 K 2,3. Thus, the effect of pre-oxidation reduces the facility, initially, of formation of anisotropic components in resultant carbons via the nematic liquid crystal and mesophase in the fluid phase of carbonization. Further oxidation preserves (or fixes) the inherent anisotropy of the vitrinite and this can be enhanced considerably by carbonization under high pressure when a type of in situ crystal growth must occur. It is also relevant to comment briefly upon some reflectivity and bireflectance values reported by Brown and Taylor” for some Antarctic coals. These values were exceptionally high. This study indicates the possibility that the coals examined by Brown and Taylor may have oxidized prior to further metamorphosis introduced by the geological conditions pertinent to Antarctica.
REFERENCES 1 2 3 4 5 5
10
15 Extent
20 of
oxidation
25
30
35
40
(days)
Figure 4 Variation of oil bireflectrance with extent of oxidation ) and Northumbrian (- - -) 378 K Parkgate Yorkshire (---vitrinites carbonized under hydraulic pressure to 873 K at 5 K min-*
at
6 7 8 9 10
Devries, H. A. W., Habets, P. J. and Bokhoven, C. Brennest. Chem. 1964,49, 105 Goodarzi, F. and Murchison, D. G. Fuel 1973, 52, 164 Goodarzi, F. and Murchison, D. G. Fuel 1976,55, 141 Goodarzi, F., Hermon, G., Iley, M. and Marsh, H. Fuel 1975, 54, 105 Marsh, H. and Goodarzi, F. Abstracts 12th Conf. on Carbon, Pittsburgh, USA, 1975, p. 81 Marsh, H., Dachille, F., Melvin, J. M. and Walker, P. L. Jr. Carbon 1971,4, 159 Goodarzi, F. and Murchison, D. G. Fuel 1972,51, 322 Marshall, R. J. and Murchison, D. G. Fuel 1971, 50, 4 Goodarzi, F. and Murchison, D. G. Fuel 1978,57,273 Brown, H. R. and Taylor, G. H. Fuel 196 1,40,2 11
FUEL, 1980, Vol 59, April
267
to the Editor
Optical properties of carbon (HTT 873 K) from pre-oxidized under pressures of about 200 MPa
vitrinites
carbonized
Fariborz Goodarzi” and Harry Marsh *Fuel Research Laboratories, University of Technology, Esfahan, Iran Northern Carbon Research Laboratories, School of Chemistry, University Newcastle upon Tyne, NE1 7RU, UK (Received 7 August 1978; revised 29 November 1979)
The influence of pre-oxidation of vitrinites upon their carbonization behaviour at atmospheric pressure is reasonThere occurs a pronounced loss ably well understood1-3. of plasticity and a marked variation with heat-treatmenttemperature (HTT) of the optical properties, particularly refractive-index and bireflectance, of cokes from preoxidizedvitrinites. With progressive pre-oxidation there also occurs a pronounced change in the optical texture or microstructure, i.e. shape and size of anisotropic units3 seen in polished section, using polarized-light optical microscopy. Carbonization under high pressures produces carbons with optical textures different from those produced at atmospheric pressure4. The optical properties of these carbons produced at high pressures, e.g. reflectivity are also significantly affected. The objective of the present study is to extend our understanding of the mechanism of oxidation of softening vitrinites and modification of their carbonization properties by further examination of the optical properties of progressively pre-oxidised vitrinites carbonized at a pressure of one atmosphere, under nitrogen, and at pressures of about 200 MPa 4. The optical textures of the cokes and chars (collectively called carbons) examined here for optical properties have been described previously4,‘.
of Newcastle
upon Tvne.
6.0 -
5.0 -
10
15 Extent
20 of
25
oridatmn
30
35
40
(days)
Figure 1 Variation of maximum oil reflectivity with extent of oxidation at 378 K of Parkgate Yorkshire f) and Northumbrian f- - -1 vitrinites carbonized at one atmosphere pressure to 873 K at 5 K min-1
t
EXPERIMENTAL Two bituminous vitrinites (Table I) were hand-picked and ground to pass 72 BS mesh sieve (<21Opm diameter). The vitrinites were oxidized at 378 K in air for periods from 1 to 40 days. The pre-oxidized vitrinites were carbonized at a rate of heating of 5 K min-l with one hour soak period as follows: (1) in a tube furnace to 873 K + 2 K under nitrogen; (2) in a sealed gold tube under hydraulic pressure of 170 to 310 MPa at temperatures of 873 K f 5 K; the details of the pressurized carbonization procedures are Tab/e I Analyses of vitrinites
C
H
Vitrinite Parkgate (Yorkshire) 85.4 (caking) Unnamed (Northumbria) 87.9 (coking)
N+Oa
S (wt % dafl
Remax
Rernin
5.3
1.0
8.3
1.08
0.20
5.3
1.1
5.7
1.24
0.25
awt % N+O by difference 0016-2361180/040266-6282.00 0 1980 IPC Business Press
266
Oil Bireflecreflectance tivity (%I Romax-
FUEL, 1980, Vol 59, April
I 5
I
I
10
15 Extent
20 of
day
25 oxldotion
30
35
LO
(days1
Fiwre 2 Variation of oil bireflectance with extent of oxidation at 378 K of Parkgate Yorkshire () and Northumbrian (- - -) vitrinites carbonized at one atmosphere pressure to 873 K at 5 K min-1
given elsewhere6. A Leitz microscope photometer fitted with a polarizing strain-free objective (N.A. 0.95/x60) was used for reflectance measurements. Reflectivities in oil (noi1 = 1 S16 at 546 nm) of 50 separate particles on polished relief surfaces of each carbon were measured. Mean maximum reflectivities (Ro ax) o f eat h car b on were calculated as described7 and bireqectances were determined according to Marshall, Murchison and Goodarzia9.
RESULTS The variation of optical properties of the carbons from both
Letters to the Editor Third stage (9-40
vitrinites, with the extent of oxidation, shows three stages of oxidation identifiable with the optical texture and morphology of carbons from the vitrinites as reported earlier4. First stage (O-l day) The optical properties of carbon from both vitrinites prepared at atmospheric (Figures 1 and 2) and under hydraulic pressure (Figures 3 and 4) show a distinct decrease during this stage of minimum oxidation. Second stage (1-9 days) The variation of reflectivity with extent of oxidation for carbon prepared from both vitrinites, at 873 K, when carbonized at one atmosphere pressure shows after one day an increase with extent of oxidation; with further increase in extent of oxidation the reflectivities either remain constant or decrease slightly (Figure I). The bireflectance values of carbons from the Yorkshire (caking) vitrinite maintain the same level as in the First stage throughout, whereas the values of carbons from Northumbrian (coking) vitrinite increase continuously throughout this stage (Figure 2). The oil reflectivities and oil bireflectance values for carbons from both vitrinites when carbonized under hydraulic pressure increase continuously throughout this stage (Figures 3 and 4).
2
5.0
E :
:
4,o
s E ;
3.0
2 2.0'
I
1
5
10
15
20
25
Extent of oxidation Figure 3 Variation
of maximum
30
35
40
Idoysl
oil reflectivity
oxidation at 378 K of Parkgate Yorkshire ((- - -1 vitrinites carbonized under hydraulic 5 K min-’
with extent
of
1and
Northumbrian pressure to 873 K at
days)
The reflectivity values of carbons from the caking vitrinite, prepared at atmospheric pressure, decrease initially and then remain almost constant with further oxidation; values of carbons from the coking vitrinite maintain their maximum values of the Second stage for 13 days and then decrease slightly with further increase in oxidation (Figure 1). The bireflectance values of carbons from the caking vitrinite, prepared at atmospheric pressure, remain at the minimum value of the First stage; the bireflectance values of carbon from the coking vitrinite decrease initially and then remain constant after 15 days of oxidation (Figure 2). The oil reflectivity values of carbons from the caking vitrinite, carbonized under hydraulic pressure, continue to increase and then decrease slowly with further (20 days) of oxidation during this Third stage (Figure 3). The oil reflectivity values of carbons from the coking vitrinite, carbonized under hydraulic pressure, initially decrease sharply and then remain constant with further oxidation (Figure 3). The bireflectance values of carbons from both vitrinites decrease initially. There is a very small decrease for the carbons from the caking vitrinite and a very sharp decrease for the carbons from the coking vitrinite in this stage. The bireflectance values then remain constant with further oxidation, the bireflectance values of carbons from the caking vitrinite being now higher than the values of the carbons of the coking vitrinite (Figure 4). This study reveals that carbonization under 200 MPa pressure significantly influences the optical properties of carbon from coking vitrinites pre-oxidized for about 11 days (Figures 3 and 4). The reflectivity (6.3%) and bireflectance (6.1%) in oil after nine days of pre-oxidation represent maximum values recorded for carbons prepared at an HTT of 873 K 2,3. Thus, the effect of pre-oxidation reduces the facility, initially, of formation of anisotropic components in resultant carbons via the nematic liquid crystal and mesophase in the fluid phase of carbonization. Further oxidation preserves (or fixes) the inherent anisotropy of the vitrinite and this can be enhanced considerably by carbonization under high pressure when a type of in situ crystal growth must occur. It is also relevant to comment briefly upon some reflectivity and bireflectance values reported by Brown and Taylor” for some Antarctic coals. These values were exceptionally high. This study indicates the possibility that the coals examined by Brown and Taylor may have oxidized prior to further metamorphosis introduced by the geological conditions pertinent to Antarctica.
REFERENCES 1 2 3 4 5 5
10
15 Extent
20 of
oxidation
25
30
35
40
(days)
Figure 4 Variation of oil bireflectrance with extent of oxidation ) and Northumbrian (- - -) 378 K Parkgate Yorkshire (---vitrinites carbonized under hydraulic pressure to 873 K at 5 K min-*
at
6 7 8 9 10
Devries, H. A. W., Habets, P. J. and Bokhoven, C. Brennest. Chem. 1964,49, 105 Goodarzi, F. and Murchison, D. G. Fuel 1973, 52, 164 Goodarzi, F. and Murchison, D. G. Fuel 1976,55, 141 Goodarzi, F., Hermon, G., Iley, M. and Marsh, H. Fuel 1975, 54, 105 Marsh, H. and Goodarzi, F. Abstracts 12th Conf. on Carbon, Pittsburgh, USA, 1975, p. 81 Marsh, H., Dachille, F., Melvin, J. M. and Walker, P. L. Jr. Carbon 1971,4, 159 Goodarzi, F. and Murchison, D. G. Fuel 1972,51, 322 Marshall, R. J. and Murchison, D. G. Fuel 1971, 50, 4 Goodarzi, F. and Murchison, D. G. Fuel 1978,57,273 Brown, H. R. and Taylor, G. H. Fuel 196 1,40,2 11
FUEL, 1980, Vol 59, April
267