MOLECULAR APPROACH TO UNDERSTANDING RESIDUUM CONVERSION

Athabasca bitumen residuum was reacted under nitrogen, hydrogen, or hy drogen in the presence of a residuum hydrotreating catalyst for varyin g times which produced between 40 and 90 % residuum conversion. There was little difference among the relative rates of conversion for the t hree series. The data suggest that the first 30-40 % of residuum conve rsion mainly involves breaking of labile carbon-to-carbon bonds to pro duce distillate. It is suggested that additional conversion results fr om the formation of an aromatic-carbon aliphatic-carbon biradical inte rmediate, which is formed from hydroaromatic structures. Hydrogen tran sfer to the aromatic-carbon radical center is sufficient to prevent co ndensation leading to coke formation. The hydrogen radical produced as part of the hydrogen-transfer process can attack a condensed aromatic center, leading to gas and distillate formation from large aromatic m olecules. The initially formed aliphatic-carbon radical can preferenti ally undergo fragmentation to produce gas and distillate.