Thermodynamics Research Center / ThermoML | Journal of Chemical Thermodynamics

ABSTRACT

Nitrogen compounds in crude oil are known to cause several problems during refining including catalyst deactivation and gum formation. Industrially, nitrogen is removed by hydro-treating, which requires ring saturation prior to denitrogenation and makes hydro-treating an expensive process for heavy crude oils or coal liquids with high nitrogen content. Oxidative denitrogenation is an alternative method to hydro-treating, where the nitrogen compounds are oxidized to form nitrogen oxides, which can be separated from the oil by extraction with a polar solvent. During this separation process there is a loss of hydrocarbon material which can be between (10-20) wt% for an oil containing 1 wt% of N. The possibility to release nitrogen as NOx by thermal treatment and consequently recover the hydrocarbon portion from the N-oxide molecule is the topic explored in this work. The thermochemistry of the N-oxides of pyridine, 3-picoline, 2-mercaptopyridine, quinoline, 4-nitropyridine, 3,5-dimethylpyridine, picolinic acid, 4-picoline, 3-hydroxypyridine, nicotinic acid, isonicotinic acid, and nicotinamide was studied. The results showed that the N-oxides of pyridine and 3-picoline evaporated at atmospheric pressure while the other compounds decomposed after or during melting or during evaporation. Decomposition temperatures could be determined for all the N-oxides during thermal analysis at 5 MPa gauge. Infra-red spectroscopy of the residues after thermal treatment indicated that the compounds still contained nitrogen. The suggested chemistry taking place upon thermal decomposition in the liquid phase was discussed. N-oxides may form an oxaziridine intermediate, which results in formation of polymeric structures that still contain the nitrogen. Therefore, pyrolysis of the N-oxides subsequent to oxidation seems to be inefficient to liberate the nitrogen as NOx.