Analysis of the Nitrogen Content of Distillate Cut Gas Oils and Treated Heavy Gas Oils Using Normal Phase HPLC, Fraction Collection and Petroleomic FT-ICR MS Data

Abstract

The determination of the nitrogen content of petroleum products is important because nitrogen compounds decrease product quality and can be difficult to remove through processes such as hydrotreating. In recent years, Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) has been used to study the nitrogen species present in petroleum samples (petroleomics), with the goal of identifying hydrotreatment resistant species. While open column separations of petroleum samples are common, there has been little work done that employs a high-performance liquid chromatography (HPLC) separation prior to FT-ICR MS analysis. In this work, distillate cut and treated gas oils are separated on a commercially available dinitrophenyl “DNAP” column and the fractions are collected offline and analyzed by FT-ICR MS. HPLC separations on the “DNAP” column are shown, along with separations on a custom synthesized HPLC column (HC-Tol). Four peak regions are identified on the “DNAP” chromatograms, and the nitrogen species identified in each fraction using positive and negative electrospray ionization are discussed. It was found that pyridines are present in the first three fractions, while pyrroles are present in fractions 2 and 3. Acids are isolated in fraction 4. Alkylation of nitrogen species decreases their level of retention on the “DNAP” column, and the HPLC chromatograms can be used to qualitatively compare nitrogen content between samples. A comparison of HPLC fraction data to MS analysis of unfractionated gas oils found that fraction data are not adequate for quantitative comparisons of carbon number and double bond equivalents between samples.