Caking properties of coal residues after extraction with mixed solvents

Abstract

The caking properties of nine bituminous coals were measured after their soluble parts were extracted with mixed solvents. The extraction yields of the soluble components could be arbitrarily controlled up to ≈60 wt% at room temperature by varying the composition of the mixed solvents. The variations of the crucible swelling number (CSN) and Roga index with the extraction yield were classified into four patterns. Pattern 1: both CSN and Roga index decrease rapidly with extraction yield; i.e. all the soluble parts act as ‘caking components’. Pattern 2: CSN and Roga index remain constant for ≈10 wt% of extraction yield, followed by rapid decreases. Pattern 3 (Shin-Yubari coal): CSN is invariant with extraction yield; even after low molecular weight materials are extracted, caking components may be produced from the residue during heat treatment. Pattern 4 (Zao Zhuang coal): CSN increases with extraction yield up to 28% and then begins to decrease. The presence of a maximum CSN, and the observations for Gieseler fluidity, suggest that there is an optimum fluidity for swelling character. Soxhlet extraction with chloroform revealed that the chloroform soluble substances, which have often been regarded as ‘caking components’, in fact form only a fraction of the caking components.