Pyrolysis behaviors of two coal-related model compounds on a fixed-bed reactor

• Caliph-Caliph bond rupture is the primary step for bibenzyl pyrolysis.
• Caliph-O bond rupture is the primary step for benzyloxybenzene pyrolysis.
• Products are mainly generated from the further reactions of the initial radicals.
• The initial radials should be stabilized in time to improve the liquid products.

The bibenzyl (BB) and benzyloxybenzene (BOB) were selected as coal-related model compounds, and their pyrolysis behaviors between 500 °C and 700 °C were investigated on a fixed-bed reactor. The pyrolysis products were analyzed by gas chromatography–mass spectrometer (GC–MS) and gas chromatography (GC), and the bond dissociation energy (BDE) was calculated with density functional theory (DFT) methods at B3LYP/6-31G (d) level. The results showed that the conversion in pyrolysis of BOB was higher than that of BB. The pyrolysis product distributions and BDE calculation indicate that Caliphatic–Caliphatic bond dissociation is the primary step for BB pyrolysis, while Caliphatic–O bond dissociation is the primary step for BOB pyrolysis. The differences in pyrolysis behaviors between BB and BOB indicate that the existence of oxygen atom will reduce the BDE thus being preferentially dissociated under pyrolysis. The initial radicals should be stabilized by some more reactive radicals, which lead to higher liquid yield.