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Carbonizations under pressure of chloroformsoluble material of coking vitrinite
Carbonizations under pressure of chloroformsoluble material of coking vitrinite
Krystyna
Bratek*
and Harry Marsh
Northern Carbon Research Laboratories, School of Chemistry, University of Newcastle upon Tyne, Newcastle upon Tyne, NE1 7RlJ, UK *Instytut Chimii i Technologii, Nafty i Wegia, Politechnika Wroclawskiej, Wroclaw, ul. Gdanska 7/9, Poland. (Received 5 September 1979)
Chloroform-soluble material from a Polish coking coal was prepared by extracting the coal after heating it initially to 673 K for 15 min. The soluble material was carbonized in sealed gold tubes to 800 K and 873 K at 200 MPa pressure and to 800 K, 1000 K and 1200 K at atmospheric pressure. Coke morphology was assessedby SEM with optical texture (micro-texture) being assessedby polarizedlight microscopy of polished surfaces. Cokes from the pressure carbonizations ( IOOwt % yield) showed coalescing spherule morphology, 10 to 20 pm diameter, and are totally anisotropic. The material normally lost as volatiles thus contributes totally to the formation of mesophase and anisotropic coke. Coke from the carbonization of the soluble material at one atmospheric pressure (41 w-t % yield) is composed mainly of anisotropic fine-grained mozaics in the range l-5 pm. Carbonization under pressure extends the range of sizes of optical texture in cokes from this chloroform-soluble material. Applications may exist in graphite manufacture.
Studies of thermosolvolysis of coais were initiated by Illingworth’. Preheated coals give higher yields of soluble material than raw coals. Chloroform is a good solvent particularly if the coal is heated to its softening point and then quickly cooled to 273 K before extraction29. Preheating lowers the softening point of the coal extractions, which from coking coal have high volatile matter (53 to 72 wt %), and carbon and hydrogen contents of 80.4 to 86.6 wt % and 5.3 to 6.7 wt % respectively4. The presence of the chloroform-soluble material in coking coal is essential to its coking properties. The chloroforminsoluble material has no coking capabilities. The role of the chloroform-soluble materials was interpreted by early workers in terms of bitumen molecules acting as a solvent and plasticizer for huminssT6. Chermin and van Krevelen’ suggest that what they term ‘metaplast’ controls the behaviour of coal in the plastic stage. Within recent years the recognition that the anisotropic components of cokes from coals are formed via growth mechanisms of nematic liquid crystals and mesophase from within the fluid phase of coal has clarified our understanding of the carbonization process’. We are now aware, but cannot describe precisely, the importance of certain physical and chemical properties of the pyrolysing system in the control of the size and shape (optical texture or microtexture) of the anisotropic carbon in coke’. These considerations are relevant to cokes made from both coal and petroleum feedstocks. Mochida et al. lo extensively studied the carbonization of soluble and insoluble materials of SRC pitches and petroleum pitches. They found that carbonization properties of pitches can be restored by co-carbonizing the soluble and insoluble materials, while Bratek and GerusPiasecka4 working with coking vitrinites found that the 0016-2361/80/050339~4$2.00 @ 1980 IPC Business
Press
coking properties of the vitrinite cannot be restored by cocarbonization of the chloroform-soluble and -insoluble materials. Evidently, after extraction, the soluble material is unable to disperse the molecular components of the insoluble material to their former state. Cokes from the chloroform extracts of coals generally contain a larger size of anisotropic optical texture than do the cokes from the parent coal, (e.g. using extracts from coking coals, the resultant cokes contain fine-grained mozaics (1 pm), coarse-grained mozaics (a5 pm) and flow-type anisotropy (~20 pm)‘). Always, cokes from insoluble material were isotropic under the polarized-light optical microscope4. It has been previously reported, mainly for pitches and model organic compounds, that carbonization under high pressure (e300 MPa) influences the optical texture of cokes11’12. The objective of our paper is to study the optical texture of cokes from chloroform-soluble material of coking coal using high-pressure carbonization techniques. Such cokes, because of absence of mineral matter, may have applications in graphite manufacture.
EXPERIMENTAL Vitrinite was hand-picked from a coking coal from the No. 1 Maja mine. The vitrinite was about 95 wt % pure with 2.4 wt % of fusinite, 1 wt % of micrinite, 0.6 wt % exinite and 1 wt % mineral matter. The vitrinite was preheated to 683 K under nitrogen for 15 min and extracted when cold with chloroform in a Soxhet extractor to give a 10.5 wt % yield of extract (thermobitumen) as in Table 1. The extracted material, after removal of chloroform, was carbon-
FUEL,
1980,
Vol 59, May
339
Pressurized carbonizations of chloroform-soluble material of coking vitrinite: K. Bratek and H. Marsh
Figure 7 Scanning electron micrograph material of 1 Maja mine coal (vitrinite)
of chloroform-soluble
figure 3 Scanning electron micrograph of coke of chloroformsoluble material of 1 Maja mine coal (vitrinite), 200 MPa, HTT 873 K
Figure 5 Scanning electron micrograph of coke of chloroformsoluble material of 1 Maja mine coal (vitrinite). 200 MPa, HTT’s 873 K and 1200 K
340
FUEL,
1980,
Vol 59, May
Figure 2 Scanning electron micrograph of coke of chloroformsoluble material of 1 Maja mine coal fvitrinite), 200 MPa, HTT 800 K
Figure 4 Scanning electron micrograph of coke of chloroformsoluble material of 1 Maja mine coal fvitrinite), 200 MPa, HTT’s 873 K and 1000 K
Figure 6 Scanning electron micrograph of coke of chloroformsoluble material of 1 Maja mine coal (vitrinite), 1 atmosphere pressure, HTT 800 K
Pressurized carbonizations of chloroform-soluble material of coking vitrinite: K. Bratek and Table 7 Chemical and coking properties
of vitrinite-
Determination
and chloroform-soluble
H. Ma&
material
Analysis (wt %I
Coking properties Dilatometric properties by Arnu-Audibert method
Moisture
C daf
H daf
Roga Index
Swelling Index
T2
Ash
VM daf
T1
Sample
(K)
(K)
T3 (K) ~-
Vitrinite from coking coal from 1 Maja mine
1 .o
0.9
28.0
88.4
5.0
77
9
667
700
756
Chloroformsoluble material
1 .o
0.5
59.1
64.4
6.3
60
-
-
7%)
28
274
-
-
Figure 8
Figure 7
Figure
Figure 9 Figures 7-10 Optical micrographs HTT’s 800 K, 873 K, 1000 K, 1200
-
a (%)
of optical textures K respectively
10
of cokes from chloroform-soluble
ized to 800 K or 873 K at 5 K min-l, with a 30 min soak, in sealed gold tubes under hydraulic pressures approaching 200 MPa as previously described1*>12. Subsequently, samples were carbonized, after removal from the gold tubes, to 1000 K and 1200 K at 5 K min-l at atmospheric pressure under nitrogen. The chloroform extract was also carbonized in a Gray-King furnace to 800 K, 1000 K and 1200 K, 5 min-l, under nitrogen. All cokes were mounted in a resin block, an optically smooth surface was prepared and optical textures were assessed. Scanning electron microscopy was
material
of 1 Maja mine coal fvitrinite),
used to assess the morphology
200 MPa,
of cokes.
RESULTS AND DISCUSSION The chloroform-soluble material was pitch-like, breaking with a conchoidal fracture (Figure 1). Scanning electron micrographs of cokes from the high-pressure carbonizations (Figures 2 and 3), show the development of botryoidal morphology”>” of anisotropic carbon of spherule size about 10 to 20 pm diameter. The spherules are less distinct (more
FUEL,
1980,
Vol 59, May
341
Pressurized carbonizations of chloroform-soluble material of coking vitrinite: K. Bratek and H. Marsh
Figure 11 Optical micrograph of optical texture of coke from chloroform-soluble material of 1 Maja mine coal (vitrinite), 1 atmosphere pressure, HTT 1200 K
coalesced) at 800 K than at 873 K. On heating to 1000 K and 1200 K at atmospheric pressure the morphology of the anisotropic spheroidal (botryoidal) carbon becomes more distinct (Figures 4 and 5). The coke prepared from the chloroform-soluble fraction in the Gray-King apparatus is without spheroidal morphology (Figure 6). Optical microscopy of polished surfaces of cokes shows that the size of optical texture is larger in the cokes of the pressure carbonizations, on average 10 to 20 pm diameter but showing sizes of 100 fin-r (Figures 7-10). The optical textures of cokes from the Gray-King apparatus (HTT 800 K, 1000 K, 1200 K) are independent of the carbonization temperatures, being about 1 to 5 pm, i.e. fine- to medium-grained mozaics. Thus, carbonization under pressure produces cokes with larger optical texture than those produced at atmospheric pressure. The principal reason for this is because the coke is produced in about 100 wt% yield. The 59 wt% of material which is lost in the Gray-King carbonization is retained within the gold tubes. This could act as a solvent to extend the temperature range of fluidity of the system so enhancing the facility for mesophase growth and coalescence. The spheroidal morphology results from the effect of high pressure which increases the viscosity of mesophase so prevent-
342
FUEL,
1980,
Vol
59,
May
ing complete coalescence and allowing retention of the spheroidal morphology of mesophase growth. In these experiments the high pressure of 200 MPa ensures spheroidal morphology and complete carbonization of the chloroformsoluble material and prevents the bursting of the gold tubes by evolved hydrogen. Much lower pressures may be equally effective in properly designed pressure reactors. The direct comparison of optical textures of cokes from chloroform-soluble material of vitrinites indicates that carbonization under pressure, by preventing loss of volatile matter, enables this to be totally incorporated into the mesophase to form cokes with anisotropic optical textures of size about 10 to 20 pm diameter. Optical textures of cokes of lower yield (about 40 wt %) prepared at one atmosphere pressure are much smaller, 1 to 5 pm, with a preponderance of the smaller sizes. The pressure carbonization can be used to enhance the size of optical texture and presumably the graphitizability and macrocrystallinity of any artefacts. Flexibility exists in terms of morphology and coalescence by manipulation of the conditions of pressure and carbonization temperature. If the ‘coke’ from the pressure carbonization exhibits plastic properties on reheating, then it could be manipulated to desired shapes either in a mould or with a suitable binder. These studies support the view that material in coal must be capable of forming the anisotro ic texture of cokes via liquid crystals and mesophase”’ P.
REFERENCES 1 2 3
4 5 6 1 8 9 10 11 12
Illingworth, f:.J. Sot. C/rem. Ind. 1914, 23, 389; 1920, 39, 14 Dryden, I. G. C. and Parkhurst, K. S. Fuel 1955,34,363 Miroszniczenko, A., Kaszirskaja, L. P., Czerniejew, J. I., Nesterenko, L. L. and Szlachowa, N. E. Koks i Chimiju 1964, 7,12 Bratek, K. and Germ+Piasecka, 1. 1977, unpublished results Brown, H. R. and Waters, P. L. Fuel 1966,45,41 Nadziakiewicz, J. Fuel 1958, 37, 361 Chermin, H. A. G. and van Krevelen, D. W. Fuel 1957, 36,85 Marsh, H. Fuel 1973,52, 205 Mochida, I., Marsh, H. and Grint, A. Fuel 1979,58, 803 Mochida, I., Amamoto, K., Maeda, K., Takeshita, K. and Marsh, H. Fuel 1979,58,482 and references therein Marsh, H., Dachille, F., Melvin, J. and Walker, P. L. Jr. Carbon 1971,9, 159 Marsh, H., Foster, J. M., Herman, G., Iley, M. and Melvin, J. Fuel 1973,52, 243
Krystyna
Bratek*
and Harry Marsh
Northern Carbon Research Laboratories, School of Chemistry, University of Newcastle upon Tyne, Newcastle upon Tyne, NE1 7RlJ, UK *Instytut Chimii i Technologii, Nafty i Wegia, Politechnika Wroclawskiej, Wroclaw, ul. Gdanska 7/9, Poland. (Received 5 September 1979)
Chloroform-soluble material from a Polish coking coal was prepared by extracting the coal after heating it initially to 673 K for 15 min. The soluble material was carbonized in sealed gold tubes to 800 K and 873 K at 200 MPa pressure and to 800 K, 1000 K and 1200 K at atmospheric pressure. Coke morphology was assessedby SEM with optical texture (micro-texture) being assessedby polarizedlight microscopy of polished surfaces. Cokes from the pressure carbonizations ( IOOwt % yield) showed coalescing spherule morphology, 10 to 20 pm diameter, and are totally anisotropic. The material normally lost as volatiles thus contributes totally to the formation of mesophase and anisotropic coke. Coke from the carbonization of the soluble material at one atmospheric pressure (41 w-t % yield) is composed mainly of anisotropic fine-grained mozaics in the range l-5 pm. Carbonization under pressure extends the range of sizes of optical texture in cokes from this chloroform-soluble material. Applications may exist in graphite manufacture.
Studies of thermosolvolysis of coais were initiated by Illingworth’. Preheated coals give higher yields of soluble material than raw coals. Chloroform is a good solvent particularly if the coal is heated to its softening point and then quickly cooled to 273 K before extraction29. Preheating lowers the softening point of the coal extractions, which from coking coal have high volatile matter (53 to 72 wt %), and carbon and hydrogen contents of 80.4 to 86.6 wt % and 5.3 to 6.7 wt % respectively4. The presence of the chloroform-soluble material in coking coal is essential to its coking properties. The chloroforminsoluble material has no coking capabilities. The role of the chloroform-soluble materials was interpreted by early workers in terms of bitumen molecules acting as a solvent and plasticizer for huminssT6. Chermin and van Krevelen’ suggest that what they term ‘metaplast’ controls the behaviour of coal in the plastic stage. Within recent years the recognition that the anisotropic components of cokes from coals are formed via growth mechanisms of nematic liquid crystals and mesophase from within the fluid phase of coal has clarified our understanding of the carbonization process’. We are now aware, but cannot describe precisely, the importance of certain physical and chemical properties of the pyrolysing system in the control of the size and shape (optical texture or microtexture) of the anisotropic carbon in coke’. These considerations are relevant to cokes made from both coal and petroleum feedstocks. Mochida et al. lo extensively studied the carbonization of soluble and insoluble materials of SRC pitches and petroleum pitches. They found that carbonization properties of pitches can be restored by co-carbonizing the soluble and insoluble materials, while Bratek and GerusPiasecka4 working with coking vitrinites found that the 0016-2361/80/050339~4$2.00 @ 1980 IPC Business
Press
coking properties of the vitrinite cannot be restored by cocarbonization of the chloroform-soluble and -insoluble materials. Evidently, after extraction, the soluble material is unable to disperse the molecular components of the insoluble material to their former state. Cokes from the chloroform extracts of coals generally contain a larger size of anisotropic optical texture than do the cokes from the parent coal, (e.g. using extracts from coking coals, the resultant cokes contain fine-grained mozaics (1 pm), coarse-grained mozaics (a5 pm) and flow-type anisotropy (~20 pm)‘). Always, cokes from insoluble material were isotropic under the polarized-light optical microscope4. It has been previously reported, mainly for pitches and model organic compounds, that carbonization under high pressure (e300 MPa) influences the optical texture of cokes11’12. The objective of our paper is to study the optical texture of cokes from chloroform-soluble material of coking coal using high-pressure carbonization techniques. Such cokes, because of absence of mineral matter, may have applications in graphite manufacture.
EXPERIMENTAL Vitrinite was hand-picked from a coking coal from the No. 1 Maja mine. The vitrinite was about 95 wt % pure with 2.4 wt % of fusinite, 1 wt % of micrinite, 0.6 wt % exinite and 1 wt % mineral matter. The vitrinite was preheated to 683 K under nitrogen for 15 min and extracted when cold with chloroform in a Soxhet extractor to give a 10.5 wt % yield of extract (thermobitumen) as in Table 1. The extracted material, after removal of chloroform, was carbon-
FUEL,
1980,
Vol 59, May
339
Pressurized carbonizations of chloroform-soluble material of coking vitrinite: K. Bratek and H. Marsh
Figure 7 Scanning electron micrograph material of 1 Maja mine coal (vitrinite)
of chloroform-soluble
figure 3 Scanning electron micrograph of coke of chloroformsoluble material of 1 Maja mine coal (vitrinite), 200 MPa, HTT 873 K
Figure 5 Scanning electron micrograph of coke of chloroformsoluble material of 1 Maja mine coal (vitrinite). 200 MPa, HTT’s 873 K and 1200 K
340
FUEL,
1980,
Vol 59, May
Figure 2 Scanning electron micrograph of coke of chloroformsoluble material of 1 Maja mine coal fvitrinite), 200 MPa, HTT 800 K
Figure 4 Scanning electron micrograph of coke of chloroformsoluble material of 1 Maja mine coal fvitrinite), 200 MPa, HTT’s 873 K and 1000 K
Figure 6 Scanning electron micrograph of coke of chloroformsoluble material of 1 Maja mine coal (vitrinite), 1 atmosphere pressure, HTT 800 K
Pressurized carbonizations of chloroform-soluble material of coking vitrinite: K. Bratek and Table 7 Chemical and coking properties
of vitrinite-
Determination
and chloroform-soluble
H. Ma&
material
Analysis (wt %I
Coking properties Dilatometric properties by Arnu-Audibert method
Moisture
C daf
H daf
Roga Index
Swelling Index
T2
Ash
VM daf
T1
Sample
(K)
(K)
T3 (K) ~-
Vitrinite from coking coal from 1 Maja mine
1 .o
0.9
28.0
88.4
5.0
77
9
667
700
756
Chloroformsoluble material
1 .o
0.5
59.1
64.4
6.3
60
-
-
7%)
28
274
-
-
Figure 8
Figure 7
Figure
Figure 9 Figures 7-10 Optical micrographs HTT’s 800 K, 873 K, 1000 K, 1200
-
a (%)
of optical textures K respectively
10
of cokes from chloroform-soluble
ized to 800 K or 873 K at 5 K min-l, with a 30 min soak, in sealed gold tubes under hydraulic pressures approaching 200 MPa as previously described1*>12. Subsequently, samples were carbonized, after removal from the gold tubes, to 1000 K and 1200 K at 5 K min-l at atmospheric pressure under nitrogen. The chloroform extract was also carbonized in a Gray-King furnace to 800 K, 1000 K and 1200 K, 5 min-l, under nitrogen. All cokes were mounted in a resin block, an optically smooth surface was prepared and optical textures were assessed. Scanning electron microscopy was
material
of 1 Maja mine coal fvitrinite),
used to assess the morphology
200 MPa,
of cokes.
RESULTS AND DISCUSSION The chloroform-soluble material was pitch-like, breaking with a conchoidal fracture (Figure 1). Scanning electron micrographs of cokes from the high-pressure carbonizations (Figures 2 and 3), show the development of botryoidal morphology”>” of anisotropic carbon of spherule size about 10 to 20 pm diameter. The spherules are less distinct (more
FUEL,
1980,
Vol 59, May
341
Pressurized carbonizations of chloroform-soluble material of coking vitrinite: K. Bratek and H. Marsh
Figure 11 Optical micrograph of optical texture of coke from chloroform-soluble material of 1 Maja mine coal (vitrinite), 1 atmosphere pressure, HTT 1200 K
coalesced) at 800 K than at 873 K. On heating to 1000 K and 1200 K at atmospheric pressure the morphology of the anisotropic spheroidal (botryoidal) carbon becomes more distinct (Figures 4 and 5). The coke prepared from the chloroform-soluble fraction in the Gray-King apparatus is without spheroidal morphology (Figure 6). Optical microscopy of polished surfaces of cokes shows that the size of optical texture is larger in the cokes of the pressure carbonizations, on average 10 to 20 pm diameter but showing sizes of 100 fin-r (Figures 7-10). The optical textures of cokes from the Gray-King apparatus (HTT 800 K, 1000 K, 1200 K) are independent of the carbonization temperatures, being about 1 to 5 pm, i.e. fine- to medium-grained mozaics. Thus, carbonization under pressure produces cokes with larger optical texture than those produced at atmospheric pressure. The principal reason for this is because the coke is produced in about 100 wt% yield. The 59 wt% of material which is lost in the Gray-King carbonization is retained within the gold tubes. This could act as a solvent to extend the temperature range of fluidity of the system so enhancing the facility for mesophase growth and coalescence. The spheroidal morphology results from the effect of high pressure which increases the viscosity of mesophase so prevent-
342
FUEL,
1980,
Vol
59,
May
ing complete coalescence and allowing retention of the spheroidal morphology of mesophase growth. In these experiments the high pressure of 200 MPa ensures spheroidal morphology and complete carbonization of the chloroformsoluble material and prevents the bursting of the gold tubes by evolved hydrogen. Much lower pressures may be equally effective in properly designed pressure reactors. The direct comparison of optical textures of cokes from chloroform-soluble material of vitrinites indicates that carbonization under pressure, by preventing loss of volatile matter, enables this to be totally incorporated into the mesophase to form cokes with anisotropic optical textures of size about 10 to 20 pm diameter. Optical textures of cokes of lower yield (about 40 wt %) prepared at one atmosphere pressure are much smaller, 1 to 5 pm, with a preponderance of the smaller sizes. The pressure carbonization can be used to enhance the size of optical texture and presumably the graphitizability and macrocrystallinity of any artefacts. Flexibility exists in terms of morphology and coalescence by manipulation of the conditions of pressure and carbonization temperature. If the ‘coke’ from the pressure carbonization exhibits plastic properties on reheating, then it could be manipulated to desired shapes either in a mould or with a suitable binder. These studies support the view that material in coal must be capable of forming the anisotro ic texture of cokes via liquid crystals and mesophase”’ P.
REFERENCES 1 2 3
4 5 6 1 8 9 10 11 12
Illingworth, f:.J. Sot. C/rem. Ind. 1914, 23, 389; 1920, 39, 14 Dryden, I. G. C. and Parkhurst, K. S. Fuel 1955,34,363 Miroszniczenko, A., Kaszirskaja, L. P., Czerniejew, J. I., Nesterenko, L. L. and Szlachowa, N. E. Koks i Chimiju 1964, 7,12 Bratek, K. and Germ+Piasecka, 1. 1977, unpublished results Brown, H. R. and Waters, P. L. Fuel 1966,45,41 Nadziakiewicz, J. Fuel 1958, 37, 361 Chermin, H. A. G. and van Krevelen, D. W. Fuel 1957, 36,85 Marsh, H. Fuel 1973,52, 205 Mochida, I., Marsh, H. and Grint, A. Fuel 1979,58, 803 Mochida, I., Amamoto, K., Maeda, K., Takeshita, K. and Marsh, H. Fuel 1979,58,482 and references therein Marsh, H., Dachille, F., Melvin, J. and Walker, P. L. Jr. Carbon 1971,9, 159 Marsh, H., Foster, J. M., Herman, G., Iley, M. and Melvin, J. Fuel 1973,52, 243