The Echanism of the Formation of Hydantoins

Demineralization of coals and coal-derived chars is part of an effort to developalternative fuels from coal. Pyrolysis and some gasification processes yieldchars containing a large fraction of the calorific value of the feed coal andessentially all of its mineral matter. In the work reported here, three gasifi-cation chars produced from anthracite, bituminous, and subbituminous coals havebeen subjected to specific gravity separation to determine their yield-ashrelationships. Either low yields or high ash levels in the float products wereobserved. Also reported is preliminary work concerning the use of chemical con-ditioning to enhance the cleanability of coal prior to physical beneficiation.Conditioning of an IllinoisNo. 6 River King Mine coal with either supercriticalmethanol or cyclohexane resulted in an improved yield-ash relationship, whereassimilar treatment with supercritical toluene had a negative effect.INTRODUCTIONCurrently, there is increasing interest in the identification, development, andcharacterization of new coal-derived fuels which have application extending beyondtraditional electric utility markets into the commercial, industrial, residential,and transportation sectors of our economy. To penetrate these markets, new fuelsmust be low in both total sulfur and mineral matter. Emphasis is therefore beingplaced on the development of new processes to provide ultraclean coal having lessthan one percent mineral matter. In one recent example coal is subjected tophysical beneficiation, pyrolysis, and subsequent beneficiation of the char [ l ] .In this scheme, a portion of the char is combined with the pyrolysis liquids toproduce a heavy oil substitute. In order for the process to be profitable, how-ever, the excess char must be sold ata premium price, such as in the residentialheating market.Results from two different areas of research concerned with the development ofalternative fuels from coal will be presented in this paper. The first areainvolves beneficiation of chars produced from coal. Such chars may be a majorproduct of gasification and pyrolysis processes used to produce premium liquid andgaseous fuels. Since a large portion of the calorific value often ends up in thechar, the beneficiation of this material to produce a premium fuel can beimportant from a process economics standpoint.The second area of research is concerned with the use of a chemical pretreatmentto improve mineral matter liberation during subsequent physical beneficiation.Advantages of this reversal of the conventional order of treatment have been dis-cussed elsewhere 121. Reported here are preliminary results from the use ofsupercritical fluids in the initial chemical-pretreatment step.For reasons of clarity, the following discussion of methodology and results isdivided into two parts. The first section describes the beneficiation of thegasification chars, and the second the work on conditioning of coal prior to itsphysical beneficiation. After this, an overall conclusion section summarizes bothareas of research.