Impact of Thermal Treatment on Asphaltene Functional Groups

Abstract

The main objective of this study is to provide an in-depth analysis that reveals the impact of thermal treatment on the different functional groups that exist in asphaltene molecules. This contribution is important to further understand the nature of changes that take place in asphaltenes during distillation and thermal cracking processes. A slight increase was observed in the aromatic −CH groups, compared to aliphatic −CH groups, as crude oil is processed to atmospheric and vacuum residues. A slight decrease was also observed in the intensity ratio between methylene and methyl groups (CH 2 /CH 3 ) with distillation, which suggests a decrease in the average length of alkyl side chains for asphaltene molecules. The Fourier transform infrared (FTIR) results also suggest the possibility of thiophenic compounds oxidation during the atmospheric and vacuum distillations. More obvious differences were noted between asphaltenes exposed to thermal cracking, separated from the pitch samples, and their parent asphaltenes from the vacuum residues. Although the spectra of thermally treated asphaltenes have most of the features that belong to their parent asphaltenes, the results illustrate more aromatic structures as the reaction severity increases. In addition, the ratio of CH 3 to CH 2 groups shifted toward CH 3 with increasing reaction time and/or temperature due to the shortening of alkyl side chains. FTIR results have been further supported by 1 H and 13 C nuclear magnetic resonance (NMR) analysis, which confirmed the conclusion that thermal cracking of residual oils mainly affected the paraffinic side chains while the observed changes in the aromatic core appear to be relatively limited.

Effect of the Asphaltene Oxidation Process on the Formation of Emulsions of Water in Oil (W/O) Model Solutions

“…However, the band is weak and also appears in the untreated asphaltene. It can be observed from Figure 4b that a higher transmittance band is obtained for higher exposure time in the ranges 675-900 cm −1 corresponding to aromatic structures (C-O), 1365-1725 cm −1 corresponding to aromatic and aliphatic structures (C-H, C-C, and C=O), 1715 cm −1 band corresponding to the ketone group, and 2800-2900 cm −1 corresponding to aldehyde groups (RR'C=O and C-H) [33]. After oxidation at 1 and 5 h similar results are observed, but after 10 h an increase in the transmittance of approximately 10% is obtained.…”

“…Similarly, for fixed concentrations of 100 and 1000 mg/L, the formation of W/O emulsions shows an increase of 7% and 25%, and 37% and 66% for asphaltenes treatment temperatures of 373 and 473 K. These results indicate that as the asphaltenes concentration increased, the suitability of W/O phase formation increases. As the aromaticity increases, the decrease of side alkyl chains and the reduction of the alkyl chains ramification of the asphaltenes molecule can be responsible for the emulsions stabilization [33]. Also, the decreased solvency of treated samples, which decreases as treatment temperature increases, may lead to a higher preference of asphaltenes for being at the model solution-water interface than in bulk [25].…”

“…Different physicochemical properties of asphaltenes such as aromaticity, a short length of side alkyl chains, reduction of branching in aliphatic chains, an increase in the number of aromatic rings, and the presence of carbonyl groups show a clear trend for asphaltenes to form stable emulsions [29,32]. Hence, physicochemical changes in asphaltene structure during thermal EOR recovery processes may worsen the emulsification process [33,34]. In this way, in the field trial for ISC that was implemented in the Quifa Field located on the eastern plains of Colombia an emulsion problem was observed [35,36].…”

Slurry Phase Hydrocracking of Residue by Phosphomolybdic and Phosphotungstic Acids

“…FT-IR results also support that no olefinic hydrocarbon is produced during reaction in presence of acid catalysts. AlHumaidan et al [28] recently used FT-IR technique for detailed characterization of asphaltenes. The major IR peaks were found due to the saturated hydrocarbons as it was also observed in this study.…”

Pyrolysis of Asphaltenes Derived from Residual Oils and Their Thermally Treated Pitch

“… 4 The FTIR results suggested that thermal treatment mainly affects the paraffinic side chains in the molecular structure of asphaltenes, while changes in the aromatic core appear to be very limited. 4 In a more recent study, AlHumaidan et al 5 used NMR analysis to identify and quantify the structural parameters and the functional groups from which the hypothetical average structure of different asphaltene molecules were derived. The NMR analysis revealed several valuable findings and developed better understanding about the nature of structural changes that asphaltene molecules undergo during the thermal cracking of VRs.…”