Thermal cracking of coal residues: Kinetics of asphaltene decomposition

An asphaltenic residue from a synthetic crude obtained by coal liquefaction was processed by thermal cracking. The kinetics of formation of oil + gas and coke (toluene-insoluble) from conversion of the asphaltenic fraction were determined. A three-lump model is proposed which considers parallel reactions for oil + gas and coke formation. Conversion data fitted second-order kinetics throughout for asphaltene conversion and oil + gas and coke formation. Delplot analysis indicated that under the most severe experimental conditions, asphaltenes and oils participated in secondary coke-forming reactions which are not included in the model. The activation energies ranged from 63.94 to 86.13 kJ mol(-1), the highest being that for asphaltene conversion. The highest asphaltene conversion, 55.9 wt%, was obtained at 475 degrees C and 40 min reaction time. At short reaction times, the asphaltenic fraction converted to coke (similar to 30 wt%) was much less than that converted to oil (similar to 70 wt%) at the four temperatures used, whereas at long reaction times this trend was reversed, especially at 475 degrees C. Structural analysis showed lower aromaticity and higher WC and N/C ratios in the oil from the products than from the feed. (C) 1997 Elsevier Science Ltd.