hide
Free keywords:
-
Abstract:
In modern society the usage of crude oil serves multiple purposes and forms the basis for many products. The transportation sector is probably the most oil-dependent sector at the time. The chemical industry also requires oil as feedstock for a wide product range. These branches of industry rely on a stable quality of the raw material. However, the global energy consumption has nearly exhausted conventional oil resources. This led to the exploitation of heavier accessible feedstocks. The formation and maturation of crude oil increases the complexity regarding its constituents. Including isomeric possibilities consequently leading to the remarkable amount of several million structurally different compounds in a single oil sample.
In order to guarantee the continuous quality of products, deeper knowledge about this new type of feedstock is required. Bulk features only provide a limited amount of information. Structural information on a molecular level will be better suited to characterize the raw material and to adapt the industrial process to it. In the recent past it has become possible to identify single compound compositions by the usage of high-resolution mass spectrometry (HRMS). Furthermore, structural elucidation of single compounds is feasible by applying tandem mass spectrometry (MS/MS). However, the complexity of crude oil makes a simplification of the sample imperative. Chromatographic approaches for sample simplification are heavily limited due to the nature of the sample. Two examples are ligand exchange chromatography (LEC) using a silver impregnated stationary phase and size-exclusion chromatography (SEC), both of which have been utilized in order to pre-separate the sample before MS measurement.
In the course of this study these two chromatographic approaches were combined and followed by HRMS analysis of different fractions. In detail, maltenes (Saturates, Aromatics and Resins) and asphaltenes of a bituminous oil were compared. Firstly, these SARA fractions were offline separated by molecular size using SEC. The following HRMS analysis revealed deeper insights onto the corresponding fractions utilizing spectral stitching. Secondly, the resulting fractions underwent an online separation by argentation chromatography (ARG) with MS analysis. As it turned out, the silver-(I)-mercaptopropyl silica based stationary phase was capable of separating NOS-compounds according to their heteroatom content rather than separating by aromaticity, which is the minor separation mechanism. Fragmentation experiments (MS2) were carried out online by using HRMS and successfully revealed molecular features of different isomers at defined mass windows.
