Molecular Changes in Asphaltenes within H₂ Plasma

Abstract

In the present work, the chemical changes in asphaltenes, solid residues, when they are treated with hydrogen plasma were analyzed. H 2 plasma was characterized by the presence of electrons, H + and H 2 + ions, at kinetic energies as low as 30 eV. These species can interact with the asphaltenes to produce changes in the chemical structure by different mechanisms such as bond cleavage, recombination, and condensation. Asphaltene samples were exposed to different treatment times (up to 120 min). The plasma was characterized by optical emission spectroscopy (OES) as well as by the different products created in the reactions of asphaltenes. The presence of C + , CH + , C 2 + , NH + , and V + was confirmed. Spectroscopic techniques such as Fourier transform infrared spectroscopy (FT-IR), matrix-assisted laser desorption ionization-time of flight-mass spectrometry (MALDI-TOF-MS), nuclear magnetic resonance spectroscopy ( 1 H NMR and 13 C NMR), and X-ray diffractometry (XRD) were used to characterize the chemical composition of asphaltenes at the different treatment times. Chemical changes were analyzed from the molecular structural parameters calculated by the above-mentioned spectroscopic techniques. Possible changes in the asphaltene cluster structures were analyzed using XRD. This work explores the application of plasma technologies to modify the chemical composition of asphaltenes and obtain valuable chemical products resulting from a plasma treatment process.

Impact of Thermal Treatment on Asphaltene Functional Groups

“…OPUS software (version 6.5) from Bruker was used to correct the base lines, determine the absorbance at specific wavenumbers, and integrate the areas between wavenumbers. The wavenumbers used in determining the functional groups in asphaltenes are reported in the literature. − The FTIR spectra were analyzed by comparing the ratios of intensities and/or the ratios of integrated areas within the same spectrum, and not between the spectra of different samples. Thus, our discussion is based on ratios and relative values, not on absolute quantitative values.…”

“…Many studies utilized the FTIR spectroscopic technique to study asphaltene molecules. − Coelho et al studied the linear relationship between the intensity ratios at 2927 and 2957 cm –1 and the ratios of n CH 2 / m CH 3 for carbon chains of alkyl-benzene to determine the aliphatic chains of asphaltenes and resins. They proposed a methodology for determining the functionality and calculating the percentage of single and paired hydrogen atoms attached to aromatic rings for asphaltene and resin .…”

Advances in Asphaltene Petroleomics. Part 1: Asphaltenes Are Composed of Abundant Island and Archipelago Structural Motifs

“…The evolution of the molecular view of the asphaltene structure is fraught with controversy and inconclusive debates. − For example, after 40 years of research, asphaltene molecular weight distributions still varied by more than an order of magnitude. − At some point, the debate focused on whether asphaltenes were monomers or polymers and how that affected molecular weight. Today, the consensus is that asphaltenes are monomeric, and techniques such as time-resolved fluorescence depolarization (TRFD) and mass spectrometry (MS) converged on molecular weights between ∼250 and 1200 g/mol, with an average of approximately 750 g/mol. − …”

Dealkylation of Aromatics in Subcritical and Supercritical Water: Involvement of Carbonium Mechanism

“…Regardless of the difference in reaction media, the asphaltenes resulting from the condensation of maltenes all share a similar FT-IR pattern. The absorption peaks at the wavenumbers 2921 and1455 cm –1 correspond to the methyl groups of the alkyl substitutes of aromatics, while those at 2851 and 1375 cm –1 result from the symmetrical bending and stretching vibrations of methyl groups. − Evidently, the intensity of the peaks relating to the alkyl substitutes of the asphaltenes formed under hydrothermal environments is much weaker than that of the asphaltenes formed under N 2 environments, suggesting that the dealkylation of aromatics under hydrothermal environments is significantly accelerated.…”