Determination of asphaltene precipitation onsets and spectroscopic characterization of Argentinean crudes

PINZON, J.; VILTE, A.J.; CRAVERO, M.; ROMERO, MARCELO; CISMONDI DUARTE, M.

Buenos Aires

Congreso; 11th World Congress of Chemical Engineering; 2023

Asphalteneshave been under investigation for a long time, with efforts aimed at definingthe nature of asphaltenes based on their chemical composition, molecularstructures, aggregation properties, and phase behavior both in the context ofthe original crude and dilution in different solvents or precipitating agents.Different investigations have shown that the solubility of asphaltenes dependson the polarity, the molecular weight, as well as the characteristics of thesolvent.Inthe present work, the objective was to analyze seven crude samples(conventional and nonconventional), obtained from production fields in theArgentinean Patagonia. The samples were analyzed for the non-volatile fraction,since the volatile fraction was analyzed in a separate work, complementing theinformation on the identity of the crude. Crudeoil samples were characterized in terms of some physical and chemicalproperties using ASTM standards. Untreated and fractionated samples werecharacterized by FTIR spectroscopy. The precipitation of asphaltenes from thesamples was studied based on the so-called Indirect Method for thedetermination of asphaltene precipitation onsets, using n-pentane and n-heptaneas precipitating agents [1].Itwas found that the necessity of pretreatment of the crude oil, as well as theappropriate aging time, both depend on the composition or the type of crude.The maximum aging time used for the different crudes was 24 hours. The samplesanalyzed using the indirect method showed that precipitation begins in thedilution interval of 40 to 50% of the added volume of the precipitating agent.Theanalysis of the set of crude samples (C1-C7) through FTIR spectroscopy allowsthe identification of particular molecular vibrations  and differentiation between  compositions macroscopically similar. Thesamples C1 to C5 and C7 present similar characteristic signals of the IRspectrum with changes in relative peak areas and intensities. However, theinfrared spectrum of crude C6 exhibited a particular band at 3290 cm-1 corresponding to N-Hstretching  In all samples, we found theabsorption peaks around 2850 cm-1, 2920 cm-1 and 2970assigned to the stretching vibration of CH2 and CH3, andthe signal at 1710  cm-1 fromC=O stretching. The IR spectra showed signals near 1600 cm- 1identified as the vibration of the benzene ring, and signals at 1380 cm- 1and 1460 cm - 1 corresponding to CH3 bending.Additionally, absorption signals that appear at 1160 cm-1 and 1030cm-1 were assigned to the stretching vibrations of C=S and S=O,respectively. Therapid response and simplicity of the analytical procedures used in this work,provide interesting additional advantages for the analysis and investigation ofcrude oils and greatly facilitates the study of the influence of otherfractions (saturated, aromatic and resins) in the stabilization of asphaltenes.