This report was prepared as an account of work sponsored by an agency of the United States Government.

Low-temperature catalytic pretreatment is a promising approach to the development of an improved liquefaction process. This work is a fundamental study on effects of pretreatments on coal structure and reactivity in liquefaction. The main objectives of this project are to study the coal structural changes induced by low-temperature catalytic and thermal pretreatments by using spectroscopic techniques; and to clarify the pretreatment-induced changes in reactivity or convertibility of coals in the subsequent liquefaction. This report describes the recent progress of our work. Substantial progress has been made in the spectroscopic characterization of structure and pretreatment-liquefaction reactions of a Montana subbituminous Coal (DECS-9), and thermochemical analysis of three raw and reacted bituminous coals. Temperature programmed liquefaction has been performed on three low-rank coals both in the presence and absence of dispersed molybdenum sulfide catalyst. We also performed a detailed study of the effects of mild thermal pretreatment-drying in air and in vacuum-on thermal and catalytic liquefaction of a Wyodak subbituminous coal. Important information on structure andstructural transformation during thermal pretreatment and liquefaction reactions of low-rank coals has been derived by applying solid-state CPMAS 13C NMR and flash pyrolysis-GC-MS (Py-GC-MS) for characterization of the macromolecular network of a Mon:ana subbituminous coal and its residues from temperature-programmed and nonprogrammed liquefaction (TPL and N-PL) at .al temperatures ranging from 300 to 425°C in Hdonor and non-donor solvents. The results revealed that this coal contains significant quantities of oxygen-bearing structures, corresponding to about 18 O-bound C per 100 C atoms and one Obound C per every 5 to 6 aromatic C. The oxygen-bearing components in the coal include catechollike structures, which seem to disappear from the liquefaction residues above 300°C; carboxyl groups, which almost disappear after 350'_C; and phenolic structures, which are most important in the original coal but diminish in concentration with increasing temperature. These results point to the progressive loss of oxygen functional groups and aliphatic-rich species from the macromolecular network of the coal during programmed heat-up under "/'PL conditions. The higher conversions in TPL runs in H-donor tetralin (relative to the conventional N-PL runs) suggest that the removal of carboxylic and catechol groups from the coal and the capping of the reactive sites by H-transfer from H-donors during low temperature (<_350°C) pretreatments have contributed to minimizing the retrogressive crosslinking at higher temperatures. Quantitative calculation of NMR data and mathematical correlation were also attempted in this work. For 24 liquefaction residues derived under significantly different conditions, linear correlations between C-distribution and reaction temperature (_>300°C)have been found, which can be expressed by a simple equation, Ci = 0t fi + 13T, where fi and C...

In this quarter, progress has been made in the following two aspects: 1) spectroscopic and chemical reaction studies on the effects of drying and mild oxidation of a Wyodak subbituminous coal on its structure and pretreatment/liquefaction at 350°C; and 2) effects of dispersed catalyst and solvent on conversion and structural changes of a North Dakota lignite. 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 non-catalytic low-severity liquefaction at 350°C for 30 min under 6.9 MPa 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 catechollike structure. Increasing air drying time or temperature increases oxidation to form more oxygen functional groups at the expense of aliphatic carbons. For non-catalytic 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 non-donor 1-methylnaphthalene (1-MN) solvent. Catalytic runs were performed using impregnated ammonium tetrathiomolybdate (ATI'M) 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 2h) 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 both in 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 crosslink 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. A North Dakota lignite (DECS-1) coal was studied in this quarter for its behaviors in non-catalytic and catalytic liquefaction. Reactions were carried out at temperatures between 250°C and 450°C. Regardless the reaction solvents and the catalyst being used, the optimum temperature was found to be 400°C. The donor solvent has a significant effect over the conversion especially at temperatures higher than 350°C. The A'l"FM-derived catalyst can increase the conversions remarkably. When tetralin was applied as the reaction solvent, "he catalyst enhances the conversion slightly indicating that the maximum value has been reached. At high temperatures, i.e. 450°C, the conversions of catalytic reactions dropped because of the dehydrogenation effect of this catalyst. Therefore the optimum temperature for the catalyst is 400°C. In the future research, the products,...

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Finally, the effects of reaction conditions were investigated on conversion of low-rank coals using a Texas subbituminous coal. To find the optimum reaction conditions which can minimize the retrogressive reactions while enhancing hydrogenation, several reaction conditions such as single-staged liquefaction (SSL) and temperature-programmed liquefaction (TPL) were compared. The effect of reaction solvents on the liquefaction was also studied using hydrogendonor solvents (e.g. tetralin and decalin), a non-donor solvent (e.g. 1-methylnaphthalene) and a recycle solvent (Wilsonville middle distillate). Ammonium tetrathiomolybdate (ATTM) was chosen as the catalyst precursor. Three impregnation methods, including preswelling, incipient wetness and slurrying were applied to investigate the effect of impregnation methods on the activity of the catalyst for liquefaction of the Texas subbituminous coal.