Effects of electromagnetic irradiation on low-molecular-weight fraction of fluidized catalytic cracking decant oil for synthesis of pitch precursor

[Display omitted] •Low-molecular-weight decant oil treated with microwave or electron beam radiation.•Both types of irradiation caused color and viscosity changes to the samples.•Efficacy of irradiation energy related to radical generation/recombination energies. We examined the effects of different energies of electromagnetic irradiation on the molecular size increase in the low-molecular-weight fraction of fluidized catalytic cracking decant oil (LMFD), which was fractionated from the original fluidized catalytic cracking decant oil. Microwave (MW) radiation was employed as a relatively low-energy source, and an electron beam (EB) was employed as a high-energy source. Variations in viscosity, color, molecular weight, and functional groups of the LMFD were examined before and after irradiation to illuminate the LMFD reaction mechanism. The viscosity increased from 43.17cP for LMFD to 3978cP after 3h of MW irradiation (MW3h) and to 1136cP after 1000kGy EB irradiation (EB1000). The reddish-brown color of the LMFD changed to black for the MW3h sample, whereas the EB1000 sample changed to a dark brown. As evaluated by matrix-assisted laser desorption ionization time-of-flight mass spectrometry, the molecular weights of the MW-irradiated samples increased more than those of the EB samples. The results can be related to the activation energies for radical formation and recombination. MW irradiation is considered to have an effective energy source for both radical formation and recombination, whereas EB irradiation exhibits an energy too high for radical recombination.