NMR Spectroscopy Analysis of Asphaltenes

Abstract

In crude oil production and processing, asphaltene aggregation followed by precipitation is a major problem for the oil industry as it causes deactivation of catalysts, blocking pipelines, and deposition on the internal surface of the reservoirs, etc. Asphaltenes, a complex mixture of a broad distribution of molecules, consisting of aromatic cores bonded to aliphatics and porphyrin type molecules with heavy metals, are defined based on solubility. Molecular complexity along with varying molecular weight distribution makes asphaltenes a difficult scientific problem to characterize. Over several decades, many researchers have contributed to characterization, analysis, and determination of structural properties of asphaltenes by various analytical techniques. Nuclear magnetic resonance (NMR) spectroscopy and relaxometry are widely applied for characterizing the chemical structures of asphaltenes, interactions between asphaltenes and maltenes, and dynamical behaviors of asphaltenes in bulk and in confined states. The goal of the current review article is to give an insight into various aspects of asphaltene analysis by NMR spectroscopy and relaxometry. Following a short introduction on asphaltenes and theory of NMR technique, recent contributions on asphaltenes by NMR techniques are summarized and presented. Lessons learned and suggestions on possible future work conclude the present review article.

Characterization of the Interfacial Material in Asphaltenes Responsible for Oil/Water Emulsion Stability

“…Figure a shows that IM is rich in aliphatic and polycyclic aromatic groups whereas the diaromatic hydrogen peak and the aliphatic CH 2 and CH 3 peaks are sharp in both IM and asphaltenes. According to Ok and Mal, the aliphatic groups contain naphthenic, paraffinic, and olefinic groups . Peak intensity allowed an approximate comparison between IM and asphaltenes for each peak range, as presented in Table .…”

“…The similarity in proton aromaticity in IM and asphaltenes has led to probing carbon aromaticity by performing a 13 C NMR for which the spectra are depicted in Figure b. The aromatic carbons in 13 C NMR absorb at shifts greater than 105 ppm, while aliphatic carbons absorb at shifts smaller than 55 ppm . The sharp peak at 78 ppm results from the used solvent (CDCl 3 ).…”

“…The quantitative peak integration of the broad low-intensity peak from 110 to 150 ppm gives 69.2% carbon aromaticity for asphaltenes and 57% for IM. The peaks from 10 to 40 ppm are assigned to alicyclic and aliphatic CH, CH 2 , and CH 3 groups Table shows a rough comparison between the peaks in IM and those in asphaltenes based on peak intensities .…”

Quantifying Crude Oil Contamination in Sand and Soil by EPR Spectroscopy

“…Crude oil is a complex mixture of several tens of thousands of known compounds, a fact that needs to be taken into consideration if oil shall be identified by spectroscopic methods. Its 1 H NMR signature consists of a broad spectrum representing the unresolved sum of many resonance lines that have tentatively been separated into aromatic and aliphatic regions [16,17] The distinction of different types of crude oil has been attempted based on quantifying the individual spectral line groups, but the assignment of individual chemicals has not been achieved. It can be assumed that a 1 H spectroscopic separation of crude oil in natural soil, against the background of soil organic matter (SOM), is difficult at best [18].…”

Fractionation and Characterization of Petroleum Asphaltene: Focus on Metalopetroleomics

“…Petroleum, as the most important source of energy and raw chemical materials, is a complex but delicately balanced system that depends on the relationship of its constituent fractions to each other [1]. Hence, the disturbance of these interactions, such as recovery and refining, may cause sediment formation and asphaltene deposition [2,3], which brings about many negative effects to the petroleum industry, such as the deactivation of catalysts, blocked pipelines, and deposition on the internal surface of the reservoirs [4][5][6][7][8].…”