Abstract
Drying and oxidation of Wyodak subbituminous coal at 100–150 °C have been shown to have significant effects on its structure and on its catalytic and noncatalytic low-severity liquefaction at 350 °C for 30 min under 6.9 MPa of H2. Spectroscopic analyses using solid-state 13C NMR, pyrolysis-GC-MS, and FT-IR revealed that oxidative drying at 100–150 °C causes the transformation of phenolics and catechol into other related structures (presumably via condensation) and high-severity air drying at 150 °C for 20 h leads to disappearance of catechol-like structure. Increasing air drying time or temperature increases oxidation to form more oxygen functional groups at the expense of aliphatic carbons. For noncatalytic liquefaction at 350 °C, raw coal gave higher conversion and oil yield than the dried coals, regardless of the solvent. Compared to the vacuum-dried coal, the coal dried in air at 100 °C gave a better conversion in the presence of either a hydrogen-donor tetralin or a nondonor 1-methylnaphthalene (1-MN) solvent. Catalytic runs were performed using impregnated ammonium tetrathiomolybdate (ATTM) precursor. In the presence of either tetralin or 1-MN, however, the runs using ATTM impregnated on air-dried coal (dried at 100 °C for 2 h) afford better conversions and oil yields than using vacuum-dried coal. Upon drying in air at 150 °C for 20 h, the conversion of air-dried coal decreased to a value significantly lower than that of the vacuum-dried coal in both the thermal and catalytic runs at 350 °C. Such a clearly negative impact of severe oxidation is considered to arise from significantly increased oxygen functionality which enhances the cross-link formation in the early stage of coal liquefaction. Physical, chemical, and surface physicochemical aspects of drying and oxidation and the role of water are also discussed.
Original language | English (US) |
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Pages (from-to) | 301-312 |
Number of pages | 12 |
Journal | Energy and Fuels |
Volume | 8 |
Issue number | 2 |
DOIs | |
State | Published - Mar 1 1994 |
All Science Journal Classification (ASJC) codes
- General Chemical Engineering
- Fuel Technology
- Energy Engineering and Power Technology