Melt-treated coal

A weighed portion of dried product (referred to as melt-treated coal, MTC) was extracted to exhaustion sequentially with benzene and pyridine in an atmospheric Soxhlet apparatus. The extracts and residue were dried and weighed to determine the solubility of the MTC. 

In this Laboratory, several potential liquid-phase treating agents have been studied at 225-275°C—that is, at temperatures well below 325°C, which appears to be the initiation temperature for pyrolysis of the coals studied here. Working with Wyodak coal in a ZnC -water melt at 250°C, Holten and coworkers (2,3) discovered that addition of tetralin increased the pyridine solubility of product to 75%, compared to 25% without tetralin. About 10 wt-% of water is required in the melt, because pure ZnC melts at 317°C. 

Several bituninous coals have been treated with molten mixtures of NaOH plus KOH at 350-370 C in a 1 10 coal-to-caustic ratio for 1 hour and then washed with water, dilute acid, and finally with water again. By this procedure, which is similar to that of the TRW Gravi-melt Process, 80-90% of the ash and 70-80% of the total sulfur have been removed with a recovery of 80-90% of the coal on a moisture- and ash-free basis. The desulfurization could be improved by using a finer grind of coal, better washing procedures, or a recleaning step. 

An important aspect to this study was the determination of the system which most adequately describes the crystallization of the coal ash melts. The compositions of the three ashes studied have been normalized to the required number of components and plotted on the appropriate phase diagram. Normalization must be treated with care because, while only the major three or four components are assumed to be present, minor components may have a disproportionate effect on the crystallization. In the case of the eastern type ash the low CaO and MgO content reduced the need for plotting on the corresponding diagram. 

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