Comparing Crude Oils with Different API Gravities on a Molecular Level Using Mass Spectrometric Analysis. Part 1: Whole Crude Oil

Jandyson Santos,Marcos Eberlin,Alberto Wisniewski Jr.,Wolfgang Schrader

doi:10.3390/en11102766

Abstract

Different ionization techniques based on different principles have been applied for the direct mass spectrometric (MS) analysis of crude oils providing composition profiles. Such profiles have been used to infer a number of crude oil properties. We have tested the ability of two major atmospheric pressure ionization techniques, electrospray ionization (ESI(±)) and atmospheric pressure photoionization (APPI(+)), in conjunction with Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). The ultrahigh resolution and accuracy measurements of FT-ICR MS allow for the correlation of mass spectrometric (MS) data with crude oil American Petroleum Institute (API) gravities, which is a major quality parameter used to guide crude oil refining, and represents a value of the density of a crude oil. The double bond equivalent (DBE) distribution as a function of the classes of constituents, as well as the carbon numbers as measured by the carbon number distributions, were examined to correlate the API gravities of heavy, medium, and light crude oils with molecular FT-ICR MS data. An aromaticity tendency was found to directly correlate the FT-ICR MS data with API gravities, regardless of the ionization technique used. This means that an analysis on the molecular level can explain the differences between a heavy and a light crude oil on the basis of the aromaticity of the compounds in different classes. This tendency of FT-ICR MS with all three techniques, namely, ESI(+), ESI(−), and APPI(+), indicates that the molecular composition of the constituents of crude oils is directly associated with API gravity.

Highlights

Crude oils provide the most important energy source in the world, and consist of a wide assortment of compounds containing mostly hydrocarbons, with and without heteroatoms, such as sulfur, nitrogen, and oxygen, which vary widely in molecular weight (MW), polarity, volatility, specific gravity, and viscosity [1]
We have performed a detailed characterization of crude oils with different American Petroleum Institute (API) gravities on a molecular level from Fourier transform (FT)-ion cyclotron resonance (ICR) mass spectrometric (MS) data, using different ionization techniques
The molecular composition was obtained based on the most acidic (ESI(−)) and basic (ESI(+)) polar constituents of crude oils, as well as the less polar components, namely the aromatic hydrocarbons (APPI(+)), which shows the broadest composition of the crudes using FT-ICR MS analysis

Summary

Introduction

Crude oils provide the most important energy source in the world, and consist of a wide assortment of compounds containing mostly hydrocarbons, with and without heteroatoms, such as sulfur, nitrogen, and oxygen, which vary widely in molecular weight (MW), polarity, volatility, specific gravity, and viscosity [1]. Because of this highly complex chemical mixture, a detailed characterization of its constituents is essential in order to understand the underlying chemistry of crude oil refining, and to guide and improve the whole process [2]. These techniques are limited to the more volatile, less polar components with a MW < 400 Da [2]

Methods

Results

Conclusion