HYDROCRACKING REACTIVITIES OF PRIMARY COAL EXTRACTS PREPARED IN A FLOWING-SOLVENT REACTOR

Structural changes taking place during the hydrocracking of coal Lique faction extracts prepared in a newing-solvent reactor (FSR) have been studied. Preparation of coal extracts in this type of reactor allows d etermination of hydrocracking reactivities in isolation from secondary effects associated with long product residence times during the coal dissolution step. Parallel hydrocracking experiments have been carried out with a pilot-plant (PP) extract which had a different process his tory. A TGA (thermogravimetric analysis)-based method for determining boiling point distributions of heavy coal-derived liquids has been des cribed. The method has proved useful for mixtures not amenable to gas chromatography based simulated distillation. Products have also been c haracterized by size exclusion chromatography and UV-fluorescence spec troscopy using 1-methyl-2-pyrrolidinone as the solvent. Comparison wit h results obtained from these two techniques using tetrahydrofuran (TH F) as solvent has indicated partial loss of sample in THF, due to poor er solubility. Compared to the pilot-plant extract, a higher proportio n of the +450 degrees C bp material present in the FSR extract was fou nd to break down in the hydrocracking stage. Parts of the +450 degrees C bp material in the extracts appear to convert to chemically more st able, large molecular-mass structures with increasing intensity and le ngth of processing. At hydrocracking temperatures between 440 and 460 degrees C, the most significant structural changes in the FSR extracts have been observed during the first 30 min. Analogous structural diff erences between the PP extract and its hydrocracking products during t he first 30 min were somewhat smaller. Progressively smaller changes i n boiling point distributions, SEC chromatograms, and UV-F spectra hav e been observed between 30 and 150 min. The data do not allow distingu ishing between diminishing sample reactivity and a drop in catalyst ac tivity, but at least part of the slow-down in conversion appears due t o progressive reduction in the reactivity of the extracts.