- Email: [email protected]
Comments on the reactivity of low-rank coals in liquefaction
Short
reported that for the studied. Wallis” simple ethers (l), only the methyl ether (la) was quantitatively converted into phenol on treatment with ethanolamine at 200°C for 90 h. The ethyl (lb) and isopropyl (lc) ethers were stable under these conditions, while benzyl phenyl ether (Id) was partially cleaved (60% after 66 h).
dissolution of brown coals by amines. However, in view of the study of Wallis”, it is hard to explain all our results (for example, the 68 o/oconversion with octylamine at 200°C for 1 h) in terms of ether bond cleavage alone, and ester bond cleavage appears to be a more probable explanation.
/\ o-
CONCLUSIONS
E. S. and Diehl, J. W. Am. Chem. Sot. 1985,30(3), 130 Wender, I., Heredy, L. A., Neuworth, M. B. and Drvden. I. G. C. ‘Chemistry of Coal Utilization’, (Ed. M. A. Elliotj, 2nd Suppl. Vol., Wiley, New York,
Dia. Fuel Chem., Prepr.
8
1981, Chapter 8 Vahrman, M. Fuel 1970, 49, 5
9
Marzec, A., Juzwa, M., Betlej, K. and Sobkowiak, M. Fuel Process. Technol.
10
1979, 2, 35
Barton, W. A., Lynch, L. J. and Webster, D. S. Fuel 1984, 63, 1262 Grint, A., Mehani, S., Trewhella, M. and Cook, M. J. Fuel 1985,64, 1355 Redlich, P., Jackson, W. R. and Larkins, F. P. Fuel 1985, 64, 1383 Bartle. K. D.. Martin. T. G. and Williams, D. F. Fuel 1975, 54, 227 Kershaw, J. R. and Jezko, J. Sep. Sci. Technol. 1982, 17, 151 Squires, T. G., Aida, T., Chem, Y.-Y. and Smith, B. F. Am. Chem. Sot. Div.
11
0 OR
R = Me
b
R =
C
R=/-Pr
d
R = benzyl
Et
-
I
CH~H
$=o
High conversions were obtained for extraction of brown coals with supercritical fluid mixtures which contained amines or alcohols. The results can be explained in terms of ester bond cleavage and give indirect evidence for the importance of these bonds in brown coal, which may also have implications for future liquefaction strategies with lowrank coals. Unfortunately, spectroscopic evidence for the presence of significant amounts of esters in brown coals is limited.
Blessing,
Jezko, J., Gray, Fuel Process.
The lignin model 2 was unaffected by treatment with ethanolamine (200°C 48 h), though it was cleaved by 2 M NaOH (200°C 17 h)“. However, the keto analogue 3 did break down on prolonged treatment (200°C 114 h) with ethanolamine”. It is therefore possible that scission of b-aryl ether linkages with an adjacent carbonyl function (e.g., compound 3) may contribute to the
Comments
Frank
on the
Derbyshire
and
13 14 15 16
Fuel Chem.,
Ross, D. S. Am. 1978, 71, 171 D. and Kershaw, J. R.
Kershaw,
Technol.
1982, 5, 229 Technol.
J. R. Fuel Process.
19
20
1982, 5, 241
Vasilakos, N. P., Dobbs, J. M. and Parasi, A. S. Id. Em. Chem. Process Des. Der. 1985, 24, 121 Kershaw, J. R. Liquid Fuels Technol.
21
22
1984, 2, 385
J. R. and Bagnell, L. J. Am. Dir. Fuel Chem., Prepr. 1985, 30(3), 101 Swanson, M. L., Dollimore, J., Olson, Kershaw, Chem.
reactivity
23
Sot.
of low-rank
coals
Prepr.
1983, 28(4),
228
van Bodegom, B., van Veen, J. A. R., van Kessel, G. M. M. and SinnigeNijssen, M. W. A. Fuel 1984, 63, 346 Patai, S. (Ed.) ‘The Chemistry of Carboxylic Acids and Esters’, Wiley Interscience, New York, 1969 A. and Serjeant, E. P. Albert, ‘Ionization Constants of Acids and Bases’, Methuen, London, 1962 Wallis, A. F. A. Cellulose Chem. Technol. 1976. 10. 345 Kudchadker, A. P., Alani, G. K. and Zwolinsky, B. J. Chem. Rec. 1968, 68, 729 Engineering Sciences Data Items, London Perry, R. H. and Green, D. W. (Eds.) Chemical Engineers’ ‘Perry’s Handbook’, 6th Edn. McGraw-Hill, New York, 1984
17
J. E. and
Chem. Sot. Symp. Ser.
3
12
18
REFERENCES 2
Communicat;ons
in liquefaction
Peter Stansberry
Fuel Science Program, Department of Materials Science University, University Park, PA 16802. USA (Received 13 March 1987; revised 20 May 1987)
and Engineering,
Ihis communication discusses the subject of the relative reactivities liquefaction. Accounts given by several researchers have provided explanation is presented to reconcile these opposing views.
The Pennsylvania
State
of low-rank and bituminous coals in seemingly contradictory results. An
(Keywords: liquefaction of coal; reactivity; effect of rank)
For some time there has been conflicting evidence in the literature concerning the relative ease of liquefaction of subbituminous coals and lignites compared with that of mid-rank bituminous coals. It is generally agreed that coals with carbon contents greater than about 89 % (maf) are, to all intents and purposes, unreactive in liquefaction, and that bituminous coals of carbon content in the approximate range 85-88’~ can be
001662361/87/121741-02$3.00 0 1987 Butterworth & Co. (Publishers)
Ltd.
converted readily to soluble products. However, it has been reported variously that low-rank coals are liquefied with greater’ m3 or less difficulty4,5 than bituminous coals. A discussion of the influence of coal structural properties on liquefaction has recently been given”. The observation that the low-rank coals require more severe reaction conditions to achieve the same levels of conversion as bituminous coals contrasts
with the known behaviour of low-rank coals in other areas of coal utilization, such as combustion and gasification where experience has shown them to be more reactive than coals of higher rank’. Generally, lower-rank coal liquids are of lower molecular weight and more volatile than the equivalent bituminous coal liquids, irrespective of their relative ease of productionsx9. These factors attest to the known
FUEL,
1987,
Vol 66, December
1741
Short
Communications
differences in coal structure with increasing rank. Namely, that coals of low-rank consist of structural units that are less condensed and are joined by a higher proportion of weak cross-links than coals of higher rank. The apparent discrepancy concerning the reactivity of low-rank coals in liquefaction is considered to be related to their thermally sensitive nature. Neavel” has discussed the formation of oxygen cross-links in subbituminous coals through the input of mild thermal or mechanical energy. These oxygen crosslinks may be further modified at higher temperatures, through the elimination of oxygen, to form stronger carbon
1742
FUEL, 1987,
Vol 66, December
It is proposed that the cause of the reported low reactivity of low-rank coals is due to cross-linking reactions that can occur during coal preparation (oxidation or drying) or during heat-up to reaction temperature, when even the presence of donor solvent may be insufficient to inhibit these reactions. Once substantial cross-linking has taken place, the conditions subsequently required to affect coal liquefaction must be of higher severity to reverse this process of crosslinking, and to break down the coal structure into lower molecular weight fractions. In other words, events occurring during the initial stages of the render process can liquefaction much more subsequent processing difficult if they are not properly controlled. In the presence of an active hydrogenation catalyst, provided that the rate of heat-up to temperatures greater than about 400°C is not too rapid, the tendency for cross-linking reactions to take place is effectively countered. In such systems, low-rank coals have been found to be readily liquefied4,16. The implications of the foregoing are that relevant coal structural characteristics and behaviour should be taken into account in coal liquefaction (or any coal utilization process) and exploited to advantage. Often, this may mean adopting more subtle approaches than have been used in the past. Historically, low-rank coals have been regarded feedstocks. liquefaction as poor However, the evidence suggests that, under conditions where coal dissolution is catalytically controlled, these coals may be more suitable for distillate production than coals of higher rank. Furthermore, thermal reactions alone do not provide the most efficient route to liquefy coals, since the only available means of controlling the competitive and processes of hydrogenation condensation, in a given system, are by adjusting the reaction temperature and, to some extent, the hydrogen pressure. Appropriate catalysis can provide an
additional degree of freedom by which to promote hydrogenation reactions, and to enhance the selectivity of the reaction products towards liquids. REFERENCES 1
McLean, J. B., Comolli, A. G. and Smith, T. 0. Am. Chem. Sot., Div. Fuel Chrm., Prep. 1986. 31 (4), 268
2
in Whitehurst, D. D. ‘Coal Fundamentals’, Am. Liquefaction Chem. Sot. Symposium Series 139, 1979, p. 133 Longanbach, J. R. in ‘New Approaches in Coal Chemistry’, Am. Chem. Sot. Svmnosium Series 169. 1980. P. 131 Da&, A., Derbyshire, F. J., Stansberry, P. G. and Terrer, M.-T. Fuel Proc. Tech. 1986, 12, 127 Wu, W. R. K. and Starch, H. H. US Bureau of Mines Bulletin 1968, No. 633 Snape, C. E. Fuel Proc. Tech. 1987,15, 257 Soledade, L. E. B., Mahajan, 0. P. and Walker, P. L., Jr. Fuel 1978, 57, 56 Trachte, K. in ‘Liquefaction of Wyoming Subbituminous Coal with the EDS Process’, Proceedings of EPRI Contractor’s Conference on Coal Liquefaction, Palo Alto, CA, 8-10 May 1979, p. 13-l Becker, M., Bendoraitis, J. G., Bloch, M. G. and Cabal, A. V. in ‘Analytical Studies for the H-Coal Process’, prepared for DOE by Mobil Research Corp. under Development and contract no. EF-77-C-01-2676, 1979 Neavel, R. C. in ‘Coal Science’, (Eds. M. L. Gorbaty, J. W. Larsen and I. Wender), Academic Press, New York, 1982, Vol. 1, p. 1 Suuberg, E. M., Lee, D. and Larsen, J. W. Fuel 1985, 64, 1668 ‘Lignite Nowacki, P. (Ed.) in Technology’, Noyes Data Corp., NJ, 1980 Senftle, J. T. and Davis, A. Int. J. Coal Geol. 1984, 3, 375 Ignasiak, B. S., Chugston, D. M. and Montgomery, D. S. Fuel 1972,51, 76 Tomlinson, G., Gray, D. and Neuworth, M. Proceedings of the International Conference on Coal Science, Sydney, 1985, p. 3 Derbyshire, F. J., Davis, A., Epstein, M. and Stansberry. P. G. Fuel 1986.65. 1233
3
4
9
10
11 12
13 14 15
16
reported that for the studied. Wallis” simple ethers (l), only the methyl ether (la) was quantitatively converted into phenol on treatment with ethanolamine at 200°C for 90 h. The ethyl (lb) and isopropyl (lc) ethers were stable under these conditions, while benzyl phenyl ether (Id) was partially cleaved (60% after 66 h).
dissolution of brown coals by amines. However, in view of the study of Wallis”, it is hard to explain all our results (for example, the 68 o/oconversion with octylamine at 200°C for 1 h) in terms of ether bond cleavage alone, and ester bond cleavage appears to be a more probable explanation.
/\ o-
CONCLUSIONS
E. S. and Diehl, J. W. Am. Chem. Sot. 1985,30(3), 130 Wender, I., Heredy, L. A., Neuworth, M. B. and Drvden. I. G. C. ‘Chemistry of Coal Utilization’, (Ed. M. A. Elliotj, 2nd Suppl. Vol., Wiley, New York,
Dia. Fuel Chem., Prepr.
8
1981, Chapter 8 Vahrman, M. Fuel 1970, 49, 5
9
Marzec, A., Juzwa, M., Betlej, K. and Sobkowiak, M. Fuel Process. Technol.
10
1979, 2, 35
Barton, W. A., Lynch, L. J. and Webster, D. S. Fuel 1984, 63, 1262 Grint, A., Mehani, S., Trewhella, M. and Cook, M. J. Fuel 1985,64, 1355 Redlich, P., Jackson, W. R. and Larkins, F. P. Fuel 1985, 64, 1383 Bartle. K. D.. Martin. T. G. and Williams, D. F. Fuel 1975, 54, 227 Kershaw, J. R. and Jezko, J. Sep. Sci. Technol. 1982, 17, 151 Squires, T. G., Aida, T., Chem, Y.-Y. and Smith, B. F. Am. Chem. Sot. Div.
11
0 OR
R = Me
b
R =
C
R=/-Pr
d
R = benzyl
Et
-
I
CH~H
$=o
High conversions were obtained for extraction of brown coals with supercritical fluid mixtures which contained amines or alcohols. The results can be explained in terms of ester bond cleavage and give indirect evidence for the importance of these bonds in brown coal, which may also have implications for future liquefaction strategies with lowrank coals. Unfortunately, spectroscopic evidence for the presence of significant amounts of esters in brown coals is limited.
Blessing,
Jezko, J., Gray, Fuel Process.
The lignin model 2 was unaffected by treatment with ethanolamine (200°C 48 h), though it was cleaved by 2 M NaOH (200°C 17 h)“. However, the keto analogue 3 did break down on prolonged treatment (200°C 114 h) with ethanolamine”. It is therefore possible that scission of b-aryl ether linkages with an adjacent carbonyl function (e.g., compound 3) may contribute to the
Comments
Frank
on the
Derbyshire
and
13 14 15 16
Fuel Chem.,
Ross, D. S. Am. 1978, 71, 171 D. and Kershaw, J. R.
Kershaw,
Technol.
1982, 5, 229 Technol.
J. R. Fuel Process.
19
20
1982, 5, 241
Vasilakos, N. P., Dobbs, J. M. and Parasi, A. S. Id. Em. Chem. Process Des. Der. 1985, 24, 121 Kershaw, J. R. Liquid Fuels Technol.
21
22
1984, 2, 385
J. R. and Bagnell, L. J. Am. Dir. Fuel Chem., Prepr. 1985, 30(3), 101 Swanson, M. L., Dollimore, J., Olson, Kershaw, Chem.
reactivity
23
Sot.
of low-rank
coals
Prepr.
1983, 28(4),
228
van Bodegom, B., van Veen, J. A. R., van Kessel, G. M. M. and SinnigeNijssen, M. W. A. Fuel 1984, 63, 346 Patai, S. (Ed.) ‘The Chemistry of Carboxylic Acids and Esters’, Wiley Interscience, New York, 1969 A. and Serjeant, E. P. Albert, ‘Ionization Constants of Acids and Bases’, Methuen, London, 1962 Wallis, A. F. A. Cellulose Chem. Technol. 1976. 10. 345 Kudchadker, A. P., Alani, G. K. and Zwolinsky, B. J. Chem. Rec. 1968, 68, 729 Engineering Sciences Data Items, London Perry, R. H. and Green, D. W. (Eds.) Chemical Engineers’ ‘Perry’s Handbook’, 6th Edn. McGraw-Hill, New York, 1984
17
J. E. and
Chem. Sot. Symp. Ser.
3
12
18
REFERENCES 2
Communicat;ons
in liquefaction
Peter Stansberry
Fuel Science Program, Department of Materials Science University, University Park, PA 16802. USA (Received 13 March 1987; revised 20 May 1987)
and Engineering,
Ihis communication discusses the subject of the relative reactivities liquefaction. Accounts given by several researchers have provided explanation is presented to reconcile these opposing views.
The Pennsylvania
State
of low-rank and bituminous coals in seemingly contradictory results. An
(Keywords: liquefaction of coal; reactivity; effect of rank)
For some time there has been conflicting evidence in the literature concerning the relative ease of liquefaction of subbituminous coals and lignites compared with that of mid-rank bituminous coals. It is generally agreed that coals with carbon contents greater than about 89 % (maf) are, to all intents and purposes, unreactive in liquefaction, and that bituminous coals of carbon content in the approximate range 85-88’~ can be
001662361/87/121741-02$3.00 0 1987 Butterworth & Co. (Publishers)
Ltd.
converted readily to soluble products. However, it has been reported variously that low-rank coals are liquefied with greater’ m3 or less difficulty4,5 than bituminous coals. A discussion of the influence of coal structural properties on liquefaction has recently been given”. The observation that the low-rank coals require more severe reaction conditions to achieve the same levels of conversion as bituminous coals contrasts
with the known behaviour of low-rank coals in other areas of coal utilization, such as combustion and gasification where experience has shown them to be more reactive than coals of higher rank’. Generally, lower-rank coal liquids are of lower molecular weight and more volatile than the equivalent bituminous coal liquids, irrespective of their relative ease of productionsx9. These factors attest to the known
FUEL,
1987,
Vol 66, December
1741
Short
Communications
differences in coal structure with increasing rank. Namely, that coals of low-rank consist of structural units that are less condensed and are joined by a higher proportion of weak cross-links than coals of higher rank. The apparent discrepancy concerning the reactivity of low-rank coals in liquefaction is considered to be related to their thermally sensitive nature. Neavel” has discussed the formation of oxygen cross-links in subbituminous coals through the input of mild thermal or mechanical energy. These oxygen crosslinks may be further modified at higher temperatures, through the elimination of oxygen, to form stronger carbon
1742
FUEL, 1987,
Vol 66, December
It is proposed that the cause of the reported low reactivity of low-rank coals is due to cross-linking reactions that can occur during coal preparation (oxidation or drying) or during heat-up to reaction temperature, when even the presence of donor solvent may be insufficient to inhibit these reactions. Once substantial cross-linking has taken place, the conditions subsequently required to affect coal liquefaction must be of higher severity to reverse this process of crosslinking, and to break down the coal structure into lower molecular weight fractions. In other words, events occurring during the initial stages of the render process can liquefaction much more subsequent processing difficult if they are not properly controlled. In the presence of an active hydrogenation catalyst, provided that the rate of heat-up to temperatures greater than about 400°C is not too rapid, the tendency for cross-linking reactions to take place is effectively countered. In such systems, low-rank coals have been found to be readily liquefied4,16. The implications of the foregoing are that relevant coal structural characteristics and behaviour should be taken into account in coal liquefaction (or any coal utilization process) and exploited to advantage. Often, this may mean adopting more subtle approaches than have been used in the past. Historically, low-rank coals have been regarded feedstocks. liquefaction as poor However, the evidence suggests that, under conditions where coal dissolution is catalytically controlled, these coals may be more suitable for distillate production than coals of higher rank. Furthermore, thermal reactions alone do not provide the most efficient route to liquefy coals, since the only available means of controlling the competitive and processes of hydrogenation condensation, in a given system, are by adjusting the reaction temperature and, to some extent, the hydrogen pressure. Appropriate catalysis can provide an
additional degree of freedom by which to promote hydrogenation reactions, and to enhance the selectivity of the reaction products towards liquids. REFERENCES 1
McLean, J. B., Comolli, A. G. and Smith, T. 0. Am. Chem. Sot., Div. Fuel Chrm., Prep. 1986. 31 (4), 268
2
in Whitehurst, D. D. ‘Coal Fundamentals’, Am. Liquefaction Chem. Sot. Symposium Series 139, 1979, p. 133 Longanbach, J. R. in ‘New Approaches in Coal Chemistry’, Am. Chem. Sot. Svmnosium Series 169. 1980. P. 131 Da&, A., Derbyshire, F. J., Stansberry, P. G. and Terrer, M.-T. Fuel Proc. Tech. 1986, 12, 127 Wu, W. R. K. and Starch, H. H. US Bureau of Mines Bulletin 1968, No. 633 Snape, C. E. Fuel Proc. Tech. 1987,15, 257 Soledade, L. E. B., Mahajan, 0. P. and Walker, P. L., Jr. Fuel 1978, 57, 56 Trachte, K. in ‘Liquefaction of Wyoming Subbituminous Coal with the EDS Process’, Proceedings of EPRI Contractor’s Conference on Coal Liquefaction, Palo Alto, CA, 8-10 May 1979, p. 13-l Becker, M., Bendoraitis, J. G., Bloch, M. G. and Cabal, A. V. in ‘Analytical Studies for the H-Coal Process’, prepared for DOE by Mobil Research Corp. under Development and contract no. EF-77-C-01-2676, 1979 Neavel, R. C. in ‘Coal Science’, (Eds. M. L. Gorbaty, J. W. Larsen and I. Wender), Academic Press, New York, 1982, Vol. 1, p. 1 Suuberg, E. M., Lee, D. and Larsen, J. W. Fuel 1985, 64, 1668 ‘Lignite Nowacki, P. (Ed.) in Technology’, Noyes Data Corp., NJ, 1980 Senftle, J. T. and Davis, A. Int. J. Coal Geol. 1984, 3, 375 Ignasiak, B. S., Chugston, D. M. and Montgomery, D. S. Fuel 1972,51, 76 Tomlinson, G., Gray, D. and Neuworth, M. Proceedings of the International Conference on Coal Science, Sydney, 1985, p. 3 Derbyshire, F. J., Davis, A., Epstein, M. and Stansberry. P. G. Fuel 1986.65. 1233
3
4
9
10
11 12
13 14 15
16