Extended characterization of petroleum aromatics using off-line LC-GC-MS

Abstract

Characterization of crude oil remains a challenge for analytical chemists. With the development of multi-dimensional chromatography and high-resolution mass spectrometry, an impressive number of compounds can be identified in a single sample. However, the large diversity in structure and abundance makes it difficult to obtain full compound coverage. Sample preparation methods such as solid-phase extraction and SARA-type separations are used to fractionate oil into compound classes. However, the molecular diversity within each fraction is still highly complex. Thus, in the routine analysis, only a small part of the chemical space is typically characterized. Obtaining a more detailed composition of crude oil is important for production, processing and environmental aspects. We have developed a high-resolution fractionation method for isolation and preconcentration of trace aromatics, including oxygenated and nitrogen-containing species. The method is based on semi-preparative liquid chromatography. This yields high selectivity and efficiency with separation based on aromaticity, ring size and connectivity. By the separation of the more abundant aromatics, i.e., monoaromatics and naphthalenes, trace species were isolated and enriched. This enabled the identification of features not detectable by routine methods. We demonstrate the applicability by fractionation and subsequent GC-MS analysis of 14 crude oils sourced from the North Sea. The number of tentatively identified compounds increased by approximately 60 to 150% compared to solid-phase extraction and GC × GC-MS. Furthermore, the method was used to successfully identify an extended set of heteroatom-containing aromatics (e.g., amines, ketones). The method is not intended to replace traditional sample preparation techniques or multi-dimensional chromatography but acts as a complementary tool. An in-depth comparison to routine characterization techniques is presented concerning advantages and disadvantages.

Effect of Isopropanol on the Fluorescence of Crude Oil-in-Water Dispersions

“…Aromatic contents of these oils are in the range of 25 wt % while asphaltene content is less than 0.5 wt %. The aromatic composition of this crude oil type (same reservoir) is represented in the work by Huynh et al…”

“…Aromatic contents of these oils are in the range of 25 wt % while asphaltene content is less than 0.5 wt %. The aromatic composition of this crude oil type (same reservoir) is represented in the work by Huynh et al 12 First, stock dispersions containing 100, 400, 700, and 1000 mg L −1 of crude oil were prepared in water, isopropanol, or mixtures of both. Subsamples from these stock dispersions were taken, to which either water or isopropanol was added at regular intervals creating a series of samples with decreasing oil concentration and/or a change in the isopropanol-to-water fraction.…”