Experimental and Theoretical Investigation on Three α,ω-Diarylalkane Pyrolysis

Abstract

Pyrolysis of three α,ω-diarylalkane compounds (biphenyl, diphenylmethane, and bibenzyl) was performed below 30 Pa between 573 and 1473 K. Vacuum ultraviolet single-photon ionization time-of-flight mass spectrometry was used to detect the reactants, radicals, and products. The relative concentration profiles of the pyrolysis species were estimated by a semi-quantitative analysis method. Experimental results indicated that the length of the C–C bridge bond plays an influential role in cracking of corresponding bonds in the α,ω-diarylalkane pyrolysis process. The C–H bond scission is dominant in pyrolysis of diphenylmethane at low temperatures, while the C–C bond scission competes with it when the temperature increases. The symmetrical homolysis of bibenzyl is a dominant reaction at low temperatures and will compete with the unsymmertrical cleavage reaction with increase of the temperature. In addition, the formation mechanism of fluorene, which plays a significant role in polycyclic aromatic hydrocarbon generation, during diphenylmethane pyrolysis was discussed by combining the experimental observation with the theoretical calculation. The theoretical calculation supported these experimental results at the mPW2PLYP level.