Catalytic Cracking of Pyrolytic Vapors of Low-Rank Coal over Limonite Ore

Low-grade natural iron ore, limonite, is proposed as an inexpensive catalyst to increase the light liquid production from coal pyrolysis. Experiments were conducted at a pyrolyzer combined with gas chromatography/mass spectrometry (Py-GC/MS). It is found that limonite favors the formation of light aromatic hydrocarbons, while the aliphatics and oxygenated compounds in tar are significantly reduced. Tests with model compounds (C-19 alkane and o-cresol) indicate that the increased light aromatics could result from the conversions of either oxygenated compounds or aliphatics promoted by limonite. Gaseous products are determined with online gas chromatography (GC). A strong correlation between COx and light aromatics is revealed in the catalytic pyrolysis process, indicating that COx could be seen as an index of light aromatic formation. There is a maximum value for the yield of liquids when the temperature is increased, which is quite different from the tests without limonite. It is postulated that pyrolytic water is decreased with the temperature because the total tar yield exhibits an increasing trend.