Pyrolysis of carbazole: Experimental results and kinetic study

Abstract

Contents and types of organic nitrogen compounds (ONCs) in crude oil can critically affect the quality and the economic viability of oil products. In this article, anhydrous thermal cracking of carbazole was carried out using an autoclave at 425–525°C, and heating times ranging from 187.5 to 237.5h. The pyrolysis products were qualitatively and quantitatively characterized by gas chromatograph- thermal conductivity detector-flame ionization detector, gas chromatography–mass spectrometry and elemental analyzer. Reaction mechanism and kinetics were investigated on the basis of the experimental data. The results show that primary reaction products are aromatic hydrocarbons, N-containing compounds as well as CH4 and H2; whereas NH3, HCN and C2H6 are minor products. At elevated temperatures degradation of carbazole undergoes simultaneously decomposition and condensation, involving cracking of CN bonds and CC bonds and forming of polycarbazole.Carbazole pyrolysis was demonstrated 0.8-order, and associated Arrhenius parameters of [E (KJ/mol), A (s−1)]=[321.628, 1.832×1017] were determined. In comparison with dibenzothiophene, thermal stability of carbazole seems to be more unstable during thermal processing of residual oil. The present study may further improve our understanding of the evolution of complex ONCs in heavy oil refining.