Bulletin 050

Bulletin 050

BUL 050

Petrographic studies of coals from Alberta plains

Author(s) Parkash, S. Date 1985-01-01

Eleven coal regions in the Alberta plains, identified suitable as feedstock for on-site conversion by liquefaction and pyrolysis, were analyzed for their petrographic composition and rank determination by reflectance analysis. Four lignites, two from Saskatchewan and one each from Texas and North Dakota, were studied for comparison. Petrographically, the eleven subbituminous coals could be divided nto two populations: one with high huminite and liptinite contents 90 percent) and one with substantially lower contents (70 to 75 percent). On a geological formation basis, the average huminite (vitrinite) content in coals from the Horseshoe Canyon Formation (88 percent) was higher compared to coals from the Paskapoo Formation (72 percent). The abundance of semifusinite in coals from the Paskapoo Formation (for example, Highvale and Ardley coals) suggested swamp conditions during the coalification which accelerated oxidation on the accumulating vegetation. The two American lignites showed huminite plus liptinite contents of less than 70 percent while the Saskatchewan lignites were somewhat higher. Reflectance measurements on the subbituminous coals showed a range of 0.36 to 0.47 with a reasonable correlation to the ASTM rank designations of these coals. Reflectivities determined on the lignites were generally lower.

To investigate the precise role of different organic coal components in technical processes, maceral concentrates from subbituminous and lignite coals were fractionated by the float-and-sink method using liquids differing in specific gravity. Lighter fractions showed nrichment of huminite and liptinite, but inertinite and mineral atter were in the heavier splits. The chemical composition of pure macerals computed from petrographic analyses of maceral concentrates showed that the huminite macerals were relatively rich in oxygen, whereas the liptinite macerals were relatively rich in hydrogen and the intertinite macerals were hydrogen deficient but relatively rich n carbon. To isolate relatively pure macerals from subbituminous coals, a density gradient centrifugation technique (DGC) was developed to obtain macerals of greater than 90 percent purity. A major limitation of the DGC maceral separation procedure was the mall amount of material obtained in a single DGC run. For maceral eactivity studies, where somewhat larger quantities were needed, multistage float-and-sink tests followed by density gradient centrifugation were suggested for isolating pure macerals from tests in microreactors. To obtain larger quantities of macerals (a few grams), a compromise between quality and quantity was the solution. An examination of the relationship between liquefaction yields and petrographic composition showed a rough positive correlation with huminitic-liptinitic content.

In order to follow the progressive alteration and resolidification of coal components during liquefaction, liquefied coal residual materials from both batch autoclave tests and continuous runs were xamined. This examination was based on three main categories: relatively unaltered organic components, thermally altered components (vitroplast, cenospheres, semicoke and granular residue), and norganic components. Microscopic examinations of liquefaction residues from optimum conditions suggested total conversion of liptinite, extensive conversion of huminite and possible partial onversion and reactivity of the semifusinite maceral of the nertinite group. An investigation of coal maceral morphology changes upon progressive hydroliquefaction provided some new insights into the role of different macerals in coal liquefaction in a semiquantitative manner. Because of the extremely complex catalytic ole of mineral matter in coal, it was not possible to predict the liquefaction of a coal from its maceral composition alone. It was not confirmed whether comparative studies of maceral composition and rank ith those of the relevant hydrogenation residues should enable conversion rates and efficiencies to be assessed for the various coals. The assessment of coal hydrogenation performance using microscope techniques might not be very efficient. It appeared essential to pool results from both chemical and microscopic nvestigations to derive a better understanding of the hydroliquefaction process.

Parkash, S. (1985): Petrographic studies of coals from Alberta Plains; Alberta Research Council, ARC/AGS Bulletin 50, 53 p.