Mechanism of extraction and desulfurization of coals with alcohols: Final report, March 1--December 31, 1987

Eleven Illinois coals were used in desulfurization studies involving ethanol and methanol. Eight of these coals were subjected to supercritical methanol conditions both without and with pretreatment with KOH. The percentage sulfur removed by supercritical methanol treatment is largest for the lowest rank coal (lignite) and is progressively less as the rank increases until it is smallest for the highest rank coal (low-volatile bituminous). Prior treatment with KOH/MeOH usually improves sulfur removal during subsequent supercritical methanol treatment. Also, three Illinois coals were subjected to mixtures of ethanol or methanol and radical initiators. The presence of O/sub 2/, NO, or N/sub 2/O improves desulfurization with both ethanol and methanol. Finally, experiments designed to examine why pyrite reduces faster within the coal matrix than without compared the effects of different mixtures and sequential arrangements of pyrite and graphite during ethanol reduction of pyrite. Graphite increase the rate of pyrite reduction when it is intimately mixed with pyrite or precedes pyrite in a flow reactor. The results show that ethanol or methanol treatments of coals greatly reduce total sulfur (both pyritic and organic) by forming principally hydrogen sulfide. One mechanism of organic sulfur removal is to cycle it through the reduced iron sulfidesmore » within the coal matrix before reduction to hydrogen sulfide. Supercritical and radical-inducing conditions enhance sulfur removal and demonstrate that a variety of conditions can facilitate alcohol desulfurization of coals. Alcohols furnish hydrogen within the coal matrix either by iron sulfide (pyrrhotite or troilite) catalyzed decomposition or by radical-induced decomposition through interaction with radical initiators and/or with internal radicals generated by heating the coal matrix. 5 refs., 14 figs., 4 tabs.« less