RESUMO
In the present study, we established a statistical distribution pattern of indigenous sulfur, nitrogen, and oxygen species in Arabian Heavy crude oil and its distilled fractions: naphtha, gas oil, and vacuum gas oil (VGO) using chemical derivatization with methyl iodide and subsequent characterization by positive electrospray Fourier transform mass spectrometry. It was observed that sulfur species for naphtha and gas oil were accumulated at lower double bond equivalent values and at lower carbon numbers compared to VGO, whereas crude oil encompassed a complete range of the sulfur species detected in all distilled fractions. Moreover, the use of alumina column chromatography and ligand exchange chromatography (LEC) on a palladium-bonded silica stationary phase revealed additional structural features of sulfur heterocycles in terms of condensed and non-condensed thiophenes. During LEC separation, in addition to sulfur heterocycles, interesting results were obtained for oxygen-containing compounds. Ortho-substituted alkyl phenols were separated from meta- and para-substituted alkyl phenols on a palladium-bonded silica stationary phase.
RESUMO
The heavy polycyclic aromatic hydrocarbons (HPAHs) cause detrimental effects to hydrocracker operations by deactivating the catalysts and depositing in the downstream of the reactor/ exchangers. Therefore, it is essential to continuously monitor the accumulation of HPAHs in a hydrocracker unit. To accurately measure the concentration of HPAHs, the development of a fast and reliable analytical method is inevitable. In this work, an analytical method based on non-aqueous reversed phase chromatography in combination with high resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) was developed. As a first step, five different types of stationary phases were evaluated for the separation of HPAHs in non-aqueous mode and the best suited phase was further used for the fractionation of HPAHs in a fractionator bottom sample obtained from a refinery hydrocracker unit. The eight major fractions or peaks obtained from the separation were further characterized by UV spectroscopy and FT-ICR MS and the compounds in the fractions were tentatively confirmed as benzoperylene, coronene, methylcoronene, naphthenocoronene, benzocoronene, dibenzoperylene, naphthocoronene and ovalene. The developed liquid chromatography method can be easily adapted in a refinery laboratory for the quantitation of HPAHs in hydrocracking products. The method was further tested to check the interference of sulfur aromatics and/or large alkylated aromatic hydrocarbons on the determination of HPAHs in hydrocracking products.