141
Hydrothermal Processes in Subcritical Water
subsequent donor solvent liquefaction process. Significant changes were, however,
observed in the composition and molecular weight distributions of the liquid
products of the liquefaction process due to water pretreatment. The pretreatments
were carried out at 250°C and 38 atm pressure. The coal liquefaction was carried out
at 400°C and 500 psi H 2 pressure for 20 min in the tetralin solvent.
5.5.2 CoAl liqueFACTion in high-PreSSure And high-TemPerATure WATer
A number of studies [52,120–124] have examined the coal liquefaction in water at
high temperature and pressure. Mikita et al. [52] and Blaustein et al. (Blaustein et al.,
2012, pers. comm.) found tetrahydrofuran (THF) conversion of Illinois No. 6 coal in
water to be about 67%, in water and solvent-refined coal (SRC) II solvent about 87%,
and in water and 1000 ppm of Mo about 90% for reactions at 385°C, 1200 psig H 2
pressure, and 30 min residence time. A synergism was observed at low ratios (≤0.5)
of donor solvent to coal upon combination of SRC II distillate and water. A similar
effect was not observed when cyclododecane replaced water. The addition of Mo
catalyst precursors to the water allowed a complete elimination of donor solvent
without loss in conversion.
Yoneyyama et al. [120] examined noncatalytic hydrogenation of several bituminous and subbituminous coals with or without water addition at 400°C. By comparison, similar experiments in nitrogen or undecane (n-C 11 ) were also carried out. In
nitrogen or hydrogen atmosphere, water promoted coal conversion, but the addition
of undecane neither changed nor decreased the conversions. For higher rank coal,
undecane inhibited coal conversion in nitrogen. The conversion of coals using nitrogen and water increased with increasing carbon content of coals. However, when
hydrogen and water were used, there existed no clear relationship between the coal
conversion and the carbon content of coals. Under pressurized hydrogen, coals containing pyrites gave significantly larger conversions implying their catalytic role in
the conversion process. A synergistic effect existed between hydrogen and water on
the conversion of coals, and the effect was more obvious for the coals containing
larger amount of pyrite.
Ross and Blessing [121] and Ross et al. [122,123] found that for Illinois No. 6 coal
in the CO/H 2 O system at 4000–5000 psig pressure and 400°C (under supercritical
conditions), better toluene solubles were achieved than for tetralin under the same
conditions. The CO/H 2 O system was more effective than the H 2 /H 2 O system and
the latter system was not very effective for demineralized coal. The results were
explained in terms of an ionic mechanism involving the initial formation of formate
ion by which hydrogen is donated to the coal.
Recently, Anderson [124] examined hydrothermal dissolution of coal and found
that at high temperature and pressure, coal dissolution is rapid and can be taken to
completion. Breaking cross-linking structures will convert high-molecular-weight
structures into low-molecular-weight products that can be processed and used as
high-value chemical feedstock. Product is a pumpable liquid that can be further
processed. Up to 90% of the original carbon is recoverable as water-soluble product. Finally, inorganic components (pyrites, calcite) are readily converted to soluble
products that can be recovered and/or treated in the liquid phase.
Hydrothermal Processes in Subcritical Water
subsequent donor solvent liquefaction process. Significant changes were, however,
observed in the composition and molecular weight distributions of the liquid
products of the liquefaction process due to water pretreatment. The pretreatments
were carried out at 250°C and 38 atm pressure. The coal liquefaction was carried out
at 400°C and 500 psi H 2 pressure for 20 min in the tetralin solvent.
5.5.2 CoAl liqueFACTion in high-PreSSure And high-TemPerATure WATer
A number of studies [52,120–124] have examined the coal liquefaction in water at
high temperature and pressure. Mikita et al. [52] and Blaustein et al. (Blaustein et al.,
2012, pers. comm.) found tetrahydrofuran (THF) conversion of Illinois No. 6 coal in
water to be about 67%, in water and solvent-refined coal (SRC) II solvent about 87%,
and in water and 1000 ppm of Mo about 90% for reactions at 385°C, 1200 psig H 2
pressure, and 30 min residence time. A synergism was observed at low ratios (≤0.5)
of donor solvent to coal upon combination of SRC II distillate and water. A similar
effect was not observed when cyclododecane replaced water. The addition of Mo
catalyst precursors to the water allowed a complete elimination of donor solvent
without loss in conversion.
Yoneyyama et al. [120] examined noncatalytic hydrogenation of several bituminous and subbituminous coals with or without water addition at 400°C. By comparison, similar experiments in nitrogen or undecane (n-C 11 ) were also carried out. In
nitrogen or hydrogen atmosphere, water promoted coal conversion, but the addition
of undecane neither changed nor decreased the conversions. For higher rank coal,
undecane inhibited coal conversion in nitrogen. The conversion of coals using nitrogen and water increased with increasing carbon content of coals. However, when
hydrogen and water were used, there existed no clear relationship between the coal
conversion and the carbon content of coals. Under pressurized hydrogen, coals containing pyrites gave significantly larger conversions implying their catalytic role in
the conversion process. A synergistic effect existed between hydrogen and water on
the conversion of coals, and the effect was more obvious for the coals containing
larger amount of pyrite.
Ross and Blessing [121] and Ross et al. [122,123] found that for Illinois No. 6 coal
in the CO/H 2 O system at 4000–5000 psig pressure and 400°C (under supercritical
conditions), better toluene solubles were achieved than for tetralin under the same
conditions. The CO/H 2 O system was more effective than the H 2 /H 2 O system and
the latter system was not very effective for demineralized coal. The results were
explained in terms of an ionic mechanism involving the initial formation of formate
ion by which hydrogen is donated to the coal.
Recently, Anderson [124] examined hydrothermal dissolution of coal and found
that at high temperature and pressure, coal dissolution is rapid and can be taken to
completion. Breaking cross-linking structures will convert high-molecular-weight
structures into low-molecular-weight products that can be processed and used as
high-value chemical feedstock. Product is a pumpable liquid that can be further
processed. Up to 90% of the original carbon is recoverable as water-soluble product. Finally, inorganic components (pyrites, calcite) are readily converted to soluble
products that can be recovered and/or treated in the liquid phase.