Molecular accessibility in oxidized and dried coals. Quarterly report

The objective of this research project is to determine the molecular and structural changes that occur in swelled coal as a result of oxidation and moisture los both in the presence and absence of light using our newly developed EPR spin probe method. The proposed study will make it possible to deduce the molecular accessibility distribution swelled, {ital oxidized} APCS coal for each rank as a function of (1) size (up to 6 nm) and shape, (2) the relative acidic/basic reactive site distributions, and (3) the role of hydrogen bonding as a function of swelling solvents. The advantage of the EPR method is that it permits molecules of selected shape, size and chemical reactivity to be used as probes of molecular accessible regions of swelled coal. From such data an optimum catalyst can be designed to convert oxidized coal into a more convenient form and methods can be devised to lessen the detrimental weathering process. This quarter we have continued to examine the effect of exposure of light before alkylation versus after O-alkylation of the coal structure. The variation in uptake of spin probe VII (amine group) is depicted in figure 1 for Wyodak-Anderson. Before O-alkylation, a significant decrease occurred in the uptake of VII with increasing exposure to ambient light. This suggests that partial break-up of the hydrogen bond network occurs, making it possible to wash out more of the spin probes. This effect was eliminated if the coal was O-alkylated after exposure to sunlight (Figure 2). The removal of the source of hydrogen bonding is responsible for the lack of spin probe up-take variation with time of exposure to light. Further experiments have shown that the data in Figures 1 and 2 is reproducible with a deviation of less than {+-} 10%. It has also been observed that if Wyodak-Anderson coal is exposed to sunlight before swelling, the oscillatory up-take of spin probe VII as a function of percent pyridine is essentially removed