Molecular Characterization of Aged Bitumen with Selective and Nonselective Ionization Methods by Fourier Transform Ion Cyclotron Resonance Mass Spectrometry. 2. Statistical Approach on Multiple-Origin Samples

Abstract

Bitumen is a very viscous and complex mixture primarily used as a binder for asphalt construction. During its service life, this binder is subjected to oxidative aging, which leads to asphalt stiffness and thermal cracking of the pavement structure. The behavior of bitumen toward oxidative aging is greatly dependent on its intrinsic properties and particularly on its content of nitrogen, oxygen, and sulfur functional groups. This is of fundamental importance as the origin of the crude will influence its resistance to oxidation after several years of use in a road. It is then essential to correlate the native composition of bitumen and their corresponding oxidized products to explain changes in the physicochemical behavior of asphalt binders. Pressure aging vessel is probably the most widely used technique to simulate long-time aging of bitumen. This artificial aging technique leads to accelerated aging under high-pressure and -temperature conditions. To understand such mechanisms, characterization at the molecular level is required. Nowadays, Fourier transform ion cyclotron resonance (FTICR) is the most-used technique for the analysis of petroleum products. Bitumen samples from three different origins were subjected to PAV aging and analyzed by FTICR-MS. Coupling of electrospray ionization (ESI) and atmospheric pressure photo ionization (APPI) sources were used to provide an exhaustive characterization of the samples. Principal component analysis (PCA), which is a multivariate statistical approach, was used to separate samples according to aging and origin. Indeed, ESI coupled to PCA allowed a significant separation of samples according to their PAV-aging on the PC1 axis. PC1 scores were then used as an intensity scale to carry out a modified double bond equivalent versus carbon number (DBE vs C#) mapping. This technique allowed the characterization of specific aging markers in O z and O z S y families for each bitumen sample. In addition, PC1 coordinates were used to develop a predictive model by principal component regression (PCR). Significant differences in sensitivity to oxidation were obtained for the three bitumen samples. Concerning APPI results, less significant differences were obtained for aging compared to those obtained by ESI. PCA coupled to APPI was also used for modified DBE vs C# maps, separating samples according to their origin. Significant differences were obtained in each bitumen sample in the different compound classes (HC, S 1 , N 1 , O 1 , etc.). Overall, this study demonstrates the great interest of coupling FTICR MS data to a PCA statistical approach to characterize oxidative aging of bitumen samples according to their origin.

Molecular Characterization of Aged Bitumen with Selective and Nonselective Ionization Methods by Fourier Transform Ion Cyclotron Resonance Mass Spectrometry. 3. Investigation on Molecular Fractions Obtained by Gel Permeation Chromatography

“…Only the O z S y family significantly increased in the three fractions with aging, and especially in the HMW fraction with more than 55% of increasing. This agrees with a previous study that presented O z S y family as the one that evolves the most with aging in bitumen of different origins . Surprisingly, the O z family decreased with aging in the HMW fraction while it increased in both other fractions and particularly in LMW with more than 30%.…”

“…Surprisingly, very few oxygenated species were observed in MMW fraction whether it is from native or PAV-72h bitumen. Overall, as expected, differences with aging seemed to be less significant than in ESI(−) because APPI­(+) corresponds to a nonselective ionization source that leads to the ionization of both low and high polarity molecules. , …”

“…This agrees with a previous study that presented O z S y family as the one that evolves the most with aging in bitumen of different origins. 30 Surprisingly, the O z family decreased with aging in the HMW fraction while it increased in both other fractions and particularly in LMW with more than 30%. It could thus be supposed that the compounds of the HMW fraction are protected from aging which could be due to their aggregation state.…”

“…Indeed, these markers appeared to be aldehydes with long alkyl chains and fatty acids. Occurrences of benzothiophenic acids and sulfonic acids were also evidenced for the O z S y compound family. , Atmospheric pressure photoionization (APPI) was also used for the characterization of PAV-aged samples, but no specific aging markers were evidenced due to the nonselective ionization of low polarity molecules. Nevertheless, APPI­(+) allowed to ionize molecules not observed by ESI(−) such as thiophenic compounds, furans, cycloalkanes, and polycyclic aromatic hydrocarbons …”

Characterization of Crude Oil Molecules Adsorbed onto Carbonate Rock Surface Using LDI FT-ICR MS

“…Therefore, a detailed molecular description of the species adsorbed to the rock surface should shed light on which factors of a crude oil-brine-rock system are important in improved oil recovery. Fourier transform ion cyclotron resonance mass spectrometry has been extensively used in petroleomics. − The outstanding resolving power and mass accuracy provided by Fourier-transform ion cyclotron resonance (FT-ICR) instruments enable the characterization of the incredibly complex mixtures found in the oil industry. However, reports of the ultrahigh-resolution mass spectrometry molecular characterization of crude oil species adsorbed onto rock surfaces are not abundant in the literature.…”