Bitumen oxidation causes several physical and chemical changes that are related to bitumen hardening. In order to facilitate oxidative bitumen upgrading, the bitumen hardening process must be understood and overcome. The oxidation behaviors of different compound classes of the bitumen are different due to the presence of different functional groups. The typical H/C ratio (1.5) of bitumen indicates dominant naphthenic-aromatic character and low paraffinic character. The objectives of this study were to investigate the oxidative physical and chemical changes of naphthenic-aromatic part of bitumen, and to understand whether it is responsible for bitumen hardening or not.  Tetralin was used to represent naphthenic-aromatic part of the bitumen and it was oxidized at temperatures in the range 120-165 �C by using air as an oxidizing agent. Tetralin oxidized at 150 �C for 48 hours consumed approximately 7 wt% of oxygen that includes approximately 4.2wt% oxygen in oxidized tetralin, and approximately 0.2 wt% and 2.5 wt% present in CO2 and in H2O, respectively. Gas chromatography-mass spectrometry (GC-MS) and high performance liquid chromatography (HPLC) analyses confirmed the possible formation of heavier compounds due to the oxidation of tetralin.  The main oxygen-containing functional groups identified were: alcohols, ketones and carboxylic acids. Acid number of the tetralin increased from 0.01 mg KOH/g to 29.4 mg KOH/g and conductivity increased from 0 �S/cm to 0.011 �S/cm due to the oxidation at 165 �C for 48 hours. Various chemical changes cause some physical changes in tetralin such as change in colour and increase in density.  The oxidation of naphthenic-aromatic compounds bitumen will also result similar chemical changes that might lead to analogous physical changes in bitumen.

Oxidation of naphthenic-aromatic compounds in bitumen

248th National Meeting (2014)

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