Thermal decomposition of asphaltenes Speros E. Moschopedis, Sat Parkash and James G. Speight Fuel Sciences Division, Alberta Research Council, 11315 - 87 Avenue, Edmonton, Alberta, Canada T6G 2C2 (Received 15 August 1977) The thermal decomposition of Athabasca asphaltene at relatively low (<35O”C) temperatures is believed to proceed by elimination of groups situated on peripheral sites of the asphaltene. More severe degrad- ation of the asphaltene structure does not occur until elevated (>350°C) temperatures are attained. Bitumens and petroleums are predominantly hydrocarbon in nature; they do, however, contain appreciable amounts of organic non-hydrocarbon constituents, mainly nitrogen-, oxygen- and sulphur-containing compounds. These consti- tuents usually appear throughout the entire range of bitu- men fractions but tend to concentrate mainly in the heavier fractions and in the non-volatile residues’9. Although their concentration in the various fractions may be quite small, their influence is nevertheless quite important. Of special importance is the asphaltene fraction in which the non- hydrocarbon constituents tend to concentrate3 and which appears to be responsible for a large proportion of the coke produced during a thermal operation. It was therefore of interest to expand the investigations described earlier on the thermal cracking of the Athabasca bitumen4p5. The pre- sent communication describes the thermal treatment of the asphaltene fraction from Athabasca bitumen and attempts to determine the course of the thermal reaction by investi- gating the nature and production of the gaseous materials and the non-volatile residue. EXPERIMENTAL Weighed amounts of dried (7O”C/2.7 kPa/SO h) demineral- ized asphaltenes (ca. 2.5 g), separated from Athabasca bitumen in the manner described elsewhere6, were placed in a silica tube, in a conventional tube furnace, flushed by a stream of dry nitrogen (>99.9% purity) raised to the desig- nated temperature at 5’C min-l and maintained at that temperature for 1.5 h. The composition of the gaseous products was determined using a Fischer Gas Partitioner equipped with two columns - one 183 cm x 6.4 mm (6 ft x l/4 in) packed with di-2ethylhexylsebacate on 60-80 mesh Chromosorb P and the other 198.3 cm x 9.5 mm packed with 40-60 mesh molecular sieve - maintained at 70°C using dry helium as the carrier (40 ml min-l) gas. The proportions of propane and butane in the gaseous pro- ducts were estimated by means of a gas chromatograph equipped with a silica-gel column (305 cm x 9.5 mm) and a thermal-conductivity cell. Non-volatile products were con- 0016-2361178/5707-0431801 zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA .OO 0 1978 IPC Business Press tinuously extracted (Soxhlet) with pentane and then with benzene until all extracts were colourless (ca. 24 h). The experimental technique did not allow estimation of the sulphur dioxide which is known to be produced during the thermal decomposition of asphaltenes’. Elemental analyses were determined by the Alfred Bern hardt Microanalytical then, West Germany. RESULTS Laboratory, Elba& uber Engelskir- The thermal decomposition of the asphaltenes occurred readily at a variety of temperatures to yield products vary- ing from low-molecular-weight gases on the one hand to presumably high-molecular-weight, benzene-insoluble mate- rial on the other. The data presented in zyxwvutsrqponmlkjihgfedcbaZYXWVU Table 1 show that gases are re- leased from the asphaltene at low temperatures, and that there is a significant increase in the amounts of these pro- ducts over the temperature range 200-600°C. The product distributions are markedly different at temperatures above 350°C. For example, the yields of the Cl-C4 paraffins rise from 8 1.5 mmol/ 100 g asphaltene to 185.5 mmol/ 100 g asphaltene at 400°C. Similarly, at temperatures above 35O”C, hydrogen sulphide is an important component of the gaseous products, there being only 5 mmol/ 100 g asphal- tene at 300°C but rising to 24.5 mmol H$S/lOO g asphaltene at 400°C. It is also significant that the gaseous products contain substantial proportions of the oxygen and sulphur originally present in the asphaltenes (Table 2). The evolution of gases (CH4, C$-I6, CO and 02) from the asphaltene at low (<3OO”C) temperatures is at first sur- prising, but it is known that first condensed.aromatics and then alkyl derivatives will produce hydrocarbon gases at moderate temperatures’v8 and the oxygen-containing gases could conceivably arise from the facile decomposition of the various oxygen functions that are reputed to be present in the asphaltenes 9~10 . Indeed, gases of this type have been shown to be present in the oil sand at formation tempera- FUEL, 1978, Vol 57, July 431