“…However, Wyoming Eagle Butte, Wyoming Black Thunder, and Texas Bottom all show a general trend of decreasing percent conversion with increasing percentage of water removed. These results are in agreement with the results obtained by others. ,,,, …”
Section: Results
and
Discussionsupporting
confidence: 94%
“…The rapid increase in temperature after removal of about 80% of the moisture seems to be a general characteristic of microwave heating of subbituminous coals. This behavior was also observed by Silver and Frazee, , who also noted a decreased reactivity toward liquefaction for greater than 75% moisture removal. 2 Plot of coal temperature vs percentage of moisture removed by microwave drying.…”
Section: Results
and
Discussionsupporting
confidence: 80%
“…These results are in agreement with the results obtained by others. 3,4,6,7,10 Chemical drying increased the conversion yields by as much as 18% as in the case of Illinois No. 6 coal.…”
Section: Resultsmentioning
confidence: 89%
“…However, there is considerable evidence to show that some methods of drying have a detrimental effect on the liquefaction behavior of coals. − Silver and Frazee 3 dried a Clovis Point subbituminous coal using a variety of methodsdifferent atmospheres, solvent drying, vacuum drying, and microwave drying. In all cases, the reactivities of the completely dried coals were lower than the reactivity of the original coal.…”
Different methods of drying coal were investigated to determine if drying can be accomplished without altering the coal structure and reactivity toward liquefaction. Coal-drying methods included thermal and microwave drying at elevated temperatures and chemical drying at low temperature. Six coals from lignite to high volatile bituminous rank were studied. Laboratoryscale liquefaction experiments were carried out on premoisturized and dried coals to determine the effects of different drying methods on liquefaction yields. Solid-state nuclear magnetic resonance (NMR) and swelling measurements were made to assess any changes in coal structure brought about by the different methods of drying. The NMR measurements showed that, in general, there were no major structural changes in coals dried thermally or with microwaves other than partial decarboxylation. Chemically dried coals exhibited increased resolution in the aliphatic carbon region that was attributed to adsorbed methanol, which was a reaction product as well as solvent for the chemical drying method. The swelling ratios of thermally dried and microwave-dried coals were lower than those of premoisturized coals, indicating a greater degree of cross linking in coals dried using these methods. The swelling ratios of the chemically dried coals were greater than those of the premoisturized coals. Coals that were dried or partially dried thermally and with microwaves had lower liquefaction conversions than coals containing equilibrium moisture contents. However, chemically dried coals had conversions ranging from 11 to 60% greater than the premoisturized coals. The conversion behavior is consistent with changes in the physical structure and cross-linking reactions because of drying. Thermal and microwave drying appeared to cause a collapse in the pore structure, thus preventing donor solvents from contacting reactive sites inside the coals. Chemical dehydration did not appear to collapse the pore structure.
“…However, Wyoming Eagle Butte, Wyoming Black Thunder, and Texas Bottom all show a general trend of decreasing percent conversion with increasing percentage of water removed. These results are in agreement with the results obtained by others. ,,,, …”
Section: Results
and
Discussionsupporting
confidence: 94%
“…The rapid increase in temperature after removal of about 80% of the moisture seems to be a general characteristic of microwave heating of subbituminous coals. This behavior was also observed by Silver and Frazee, , who also noted a decreased reactivity toward liquefaction for greater than 75% moisture removal. 2 Plot of coal temperature vs percentage of moisture removed by microwave drying.…”
Section: Results
and
Discussionsupporting
confidence: 80%
“…These results are in agreement with the results obtained by others. 3,4,6,7,10 Chemical drying increased the conversion yields by as much as 18% as in the case of Illinois No. 6 coal.…”
Section: Resultsmentioning
confidence: 89%
“…However, there is considerable evidence to show that some methods of drying have a detrimental effect on the liquefaction behavior of coals. − Silver and Frazee 3 dried a Clovis Point subbituminous coal using a variety of methodsdifferent atmospheres, solvent drying, vacuum drying, and microwave drying. In all cases, the reactivities of the completely dried coals were lower than the reactivity of the original coal.…”
Different methods of drying coal were investigated to determine if drying can be accomplished without altering the coal structure and reactivity toward liquefaction. Coal-drying methods included thermal and microwave drying at elevated temperatures and chemical drying at low temperature. Six coals from lignite to high volatile bituminous rank were studied. Laboratoryscale liquefaction experiments were carried out on premoisturized and dried coals to determine the effects of different drying methods on liquefaction yields. Solid-state nuclear magnetic resonance (NMR) and swelling measurements were made to assess any changes in coal structure brought about by the different methods of drying. The NMR measurements showed that, in general, there were no major structural changes in coals dried thermally or with microwaves other than partial decarboxylation. Chemically dried coals exhibited increased resolution in the aliphatic carbon region that was attributed to adsorbed methanol, which was a reaction product as well as solvent for the chemical drying method. The swelling ratios of thermally dried and microwave-dried coals were lower than those of premoisturized coals, indicating a greater degree of cross linking in coals dried using these methods. The swelling ratios of the chemically dried coals were greater than those of the premoisturized coals. Coals that were dried or partially dried thermally and with microwaves had lower liquefaction conversions than coals containing equilibrium moisture contents. However, chemically dried coals had conversions ranging from 11 to 60% greater than the premoisturized coals. The conversion behavior is consistent with changes in the physical structure and cross-linking reactions because of drying. Thermal and microwave drying appeared to cause a collapse in the pore structure, thus preventing donor solvents from contacting reactive sites inside the coals. Chemical dehydration did not appear to collapse the pore structure.
“…Solvents have two main roles in coal dissolution: (1) donating hydrogen to stabilize free radicals generated upon heating of coal, (2) rendering coal molecules soluble. Both roles have been studied in the commonly used solvent 1,2,3,4-tetrahydroquinoline (THQ), [1][2][3][4] which is a highly efficient solvent for dissolving coal molecules and which provides a ready supply of hydrogen to stabilize radicals. However, it has been found difficult to examine these two roles independently; also, their inter-relationship is not well understood.…”
Solvents have two main roles in coal dissolution: (1) donating hydrogen to stabilize free radicals generated upon heating of coal, (2) rendering coal molecules soluble. Both roles have been studied in the commonly used solvent 1,2,3,4-tetrahydroquinoline (THQ), 1-4 which is a highly efficient solvent for dissolving coal molecules and which provides a ready supply of hydrogen to stabilize radicals. However, it has been found difficult to examine these two roles independently; also, their inter-relationship is not well understood.In our previous work, coals were heat-treated in various solvents at temperatures up to 300°C. The yields following dissolution in various hydrogen-donating solvents, such as 1,4,5,8,9,10-hexahydroanthracene (HHA), were found to correlate well with the total amount of hydrogen donated by each solvent. 5,6 After heat treatment in HHA at 300°C, the free radical concentration was found to be much lower than in the raw coal, 7 with hydrogen donation from HHA to the free radicals proving to be a key factor in promoting coal dissolution even at such a low temperature. We also found that a highly polar solvent N-methyl-2-pyrrolidinone (NMP) gave a higher dissolution yield in some low-rank coals than did hydrogen-donating HHA. Furthermore, a mixture of NMP with HHA gave an even higher dissolution yield for some coals than either HHA or NMP alone. 7 The dissolution mechanism in NMP would appear to be quite different from that in HHA, since NMP possesses a limited ability to donate hydrogen under the conditions of dissolution. Instead, NMP appears able to release noncovalent bonds via strong interactions at polar sites in coals. 7 Moreover, NMP interacts with free radicals and thus prevents them from recombining or taking part in further reactions. 8 However, the precise nature of the effect that NMP exercises on hydrogen-donating solvent to donate hydrogen is quite unclear. The goal of the present study was to clarify this solvent's role in hydrogen donation from hydrogen-donating solvent to coals and/or coal free radicals.Banko (Indonesia) coal, with a dry ash-free analysis of C%: 71.3; H%: 5.4%; N%: 1.2%; S%: 0.5%; O%: 21.6% (ash%: 2.4%), was used as the experimental sample, which was ground to <74 µm and dried in vacuo at 80°C for 24 h before use. The solvents employed in heat treatment were nonpolar 1-methylnaphthalene (1-MN), polar NMP, and hydrogen-donating 9,10-dihydroanthracene (DHA); they are from Wako Pure Chemical Industries, Ltd., Japan. Their purity is >97% for 1-MN and NMP, and >95% for DHA. Heat treatment of each coal sample was carried out in a 50-mL autoclave at 300°C for 1 h, as described before. 7 In each run, 1 g of coal and 5 g of solvent (either each independent solvent or various NMP/DHA mixtures) were charged into the autoclave, which was purged with nitrogen 3-5 times and finally pressurized with nitrogen to 5.0 MPa at room temperature. The autoclave was heated to 300°C within one to two minutes. Following heat treatment, the autoclave was cooled in an ice-water bath to roo...
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