Increase in Extraction Yields of Coals by Water Treatment: Beulah-Zap Lignite

Abstract

In a previous paper, we have reported that water pretreatments of Argonne premium coals, Pocahontas No. 3 (PO), Upper Freeport (UF), and Illinois No. 6 (IL) at 600 K increased greatly the room-temperature extraction yields with a 1:1 carbon disulfide/N-methyl-2-pyrrolidinone (CS{sub 2}/NMP) mixed solvent. In this paper, the water treatment of Beulah-Zap (BZ) lignite has been carried out and the results obtained were compared with those for the three bituminous coals above. The extraction yields of BZ with CS{sub 2}/NMP increased from 5.5% for the raw coal to 21.7% by the water treatment at 600 K. Similar to the other three coals, the water treatments at 500 K gave little increase in the yields. The larger decrease in oxygen content and hydrogen-bonded OH and the increase in the methanol swelling ratio by the water treatment suggest that the yield enhancements for BZ are attributed to the removal of oxygen functional groups and the breaking of hydrogen bonds to a greater extent than that for IL. From the characterizations of the treated coals and the extraction temperature dependency of their extraction yields, it is suggested that, for high-coal-rank coals, PO and UF, the breaking of noncovalent bonds such as {pi}-{pi} interactionsmore » between aromatic layers and hydrogen bonds is responsible for the extraction yield enhancements. 14 refs., 3 figs., 2 tabs.« less