LIQUEFACTION OF LIGNITE CONTAINING CATION-EXCHANGED IRON

A significant enhancement of the liquefaction yields and desirable products from two lignites has been achieved by incorporating iron in the lignites by an ion-exchange process. The total conversion of iron ion-exchanged Hagel and Beulah lignites was found to increase by up to 25% and the oil yield by 10% relative to the untreated lignites. The ion-exchanged lignites were prepared by stirring a slurry mixture of the lignite and ferric acetate [Fe(OOCCH3)3] in a 10-L fermenter. The ion-exchange process, in which iron was exchanged primarily for calcium, yielded a highly dispersed catalytic iron species for coal liquefaction. Fe-57 Mossbauer and X-ray absorption fine structure (XAFS) spectroscopies were used to characterize this iron species after both the ion-exchange and the liquefaction processes. The results indicate that added iron is initially present in bimodal form. A significant fraction of the iron species is in particles finer than 30 angstrom in diameter but with the majority of the iron particles in the form of oxyhydroxide (alpha-FeOOH) ranging from 30 to 100 angstrom in diameter. The former size category includes molecularly dispersed ferric ions at the ion-exchange (carboxyl) sites. With sufficient sulfur present in the system, the iron is rapidly transformed to pyrrhotite (Fe1-xS) during liquefaction.