THERMAL-CRACKING OF COAL RESIDUES - KINETICS OF ASPHALTENE DECOMPOSITION

An asphaltenic residue from a synthetic crude obtained by coal liquefa ction was processed by thermal cracking. The kinetics of formation of oil + gas and coke (toluene-insoluble) from conversion of the asphalte nic fraction were determined. A three-lump model is proposed which con siders parallel reactions for oil + gas and coke formation. Conversion data fitted second-order kinetics throughout for asphaltene conversio n and oil + gas and coke formation. Delplot analysis indicated that un der the most severe experimental conditions, asphaltenes and oils part icipated 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 asp haltene conversion, 55.9 wt%, was obtained at 475 degrees C and 40 min reaction time. At short reaction times, the asphaltenic fraction conv erted 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 lon g reaction times this trend was reversed, especially at 475 degrees C. Structural analysis showed lower aromaticity and higher WC and N/C ra tios in the oil from the products than from the feed. (C) 1997 Elsevie r Science Ltd.