The case for induced bond scission during coal pyrolysis

✍ Scribed by Donald F. McMillen; Ripudaman Malhotra; S.Esther Nigenda

• Publisher: Elsevier Science
• Year: 1989
• Tongue: English
• Weight: 989 KB
• Volume: 68
• Category: Article
• ISSN: 0016-2361
• DOI: 10.1016/0016-2361(89)90106-3

✦ Synopsis

Bond s&ions during coal pyrolysis are generally considered to result solely from the thermolysis of weak bonds in coal structures. Evidence is presented from published data showing that a significant amount of bond scission under pyrolysis cannot be due to simple thermolysis and must be induced by some other means. The evidence includes the following observations: 1, polymeric models consisting of no weak linkages are volatilized in the 450 to 550°C range; 2, polymeric coal models designed specifically to degrade by thermolysis of weak bibenzylic linkages show nonetheless a significant fraction of the cleavage of strong Car--Cal linkage; 3, under pyrolysis conditions bibenzyl type structures immobilized on silica yield benzene and ethylbenzene in addition to the expected toluene; 4, pyrolysis of 0-benzylated coals shows besides the expected cleavage of the benzyl ether linkage products from the scission of the strong phenyl-C bond. By analogy with coal liquefaction, the scission of strong bonds results from j?-scission of radical intermediates, and from hydrogenolysis engendered by either free H-atoms or cyclohexadienyl radicals. These reactive cyclohexadienyl radicals themselves may be formed from the scavenging of radicals (produced by weak-bond thermolysis) by dihydroaromatic structures or from reverse radical-disproportionation between aromatic and hydroaromatic structures. Finally, the importance of induced bond scissions was illustrated by showing how they help rationalize the observed selective production of oils as opposed to gas in the hydropyrolysis of coals when the pyrolysis temperature is maintained below a certain threshold.