Trapping of Paraffin and Other Compounds by Asphaltenes Detected by Laser Desorption Ionization−Time of Flight Mass Spectrometry (LDI−TOF MS): Role of A1 and A2 Asphaltene Fractions in This Trapping

Abstract

Trapping of compounds by asphaltenes in guest-host complexes (GHC) is an important phenomenon relevant to many properties of the system, such as asphaltene structure, swelling and solvent trapping, geochemical impact, as well as the trapping of metalloporphyrins, free radicals, resins, and other crude oil components, such as, e.g., paraffin. Several trapping mechanisms, such as adsorption and occlusion, during asphaltene separation from crude oil can be considered, but most interest is attracted to GHC, in which the guest is firmly bound and cannot be completely liberated from the host by solvent extraction. An example of such trapping is presented, with the guest being paraffinic and other resin-like compounds hereafter called trapped compounds (TCs). TCs were isolated from asphaltenes by the partition of the asphaltene sample in fractions A1 (toluene insoluble) and A2 (toluene soluble). A small quantity (about 8%) of a heptane-soluble TC fraction was isolated along with the A2 fraction. The presence of TCs in asphaltenes and their absence in fractions A1 and A2 were detected by means of laser desorption ionization-time of flight mass spectrometry (LDI-TOF MS) in the 450-600 molecular-mass range. These finding suggests that the TC sample is probably trapped in a network formed by both A1 and A2 fractions.

Waxes in asphaltenes of crude oils and wax deposits

“…In other words, the waxes are isolated from the oil system from which the asphaltenes have been removed beforehand [from maltenes (Branthaver et al 1983;Elsharkawy et al 2000;Fazeelat 2006;Alcazar-Vara and Buenrostro-Gonzalez 2011) or saturates (Yang and Kilpatrick 2005;Lu et al 2008)]. However, the traditional methods used to isolate asphaltenes by adding 40 volumes in excess of low boiling point paraffin hydrocarbons can produce a fraction which is contaminated with a significant amount of waxes (Chouparova and Philp 1998;Thanh et al 1999;Liao et al 2006;Acevedo et al 2009;Coto et al 2011). The presence of paraffin hydrocarbons in asphaltenes can be explained by their coprecipitation as a result of low solubility in low molecular weight n-alkanes (Thanh et al 1999;Coto et al 2011), by interaction between the alkyl lateral chains (C 7 -C 10 ) of asphaltenes with high molecular weight n-alkanes (Garcia and Carbognani 2001;Stachowiak et al 2005;Ganeeva et al 2014), and by their adsorption and/or occlusion inside asphaltene aggregates (Liao et al 2005(Liao et al , 2006Acevedo et al 2009;Gray et al 2011).…”

“…However, the traditional methods used to isolate asphaltenes by adding 40 volumes in excess of low boiling point paraffin hydrocarbons can produce a fraction which is contaminated with a significant amount of waxes (Chouparova and Philp 1998;Thanh et al 1999;Liao et al 2006;Acevedo et al 2009;Coto et al 2011). The presence of paraffin hydrocarbons in asphaltenes can be explained by their coprecipitation as a result of low solubility in low molecular weight n-alkanes (Thanh et al 1999;Coto et al 2011), by interaction between the alkyl lateral chains (C 7 -C 10 ) of asphaltenes with high molecular weight n-alkanes (Garcia and Carbognani 2001;Stachowiak et al 2005;Ganeeva et al 2014), and by their adsorption and/or occlusion inside asphaltene aggregates (Liao et al 2005(Liao et al , 2006Acevedo et al 2009;Gray et al 2011). Now, it is well-known that the asphaltenes exist as three-dimensional aggregates due to the strong intermolecular forces such as hydrogen bonding and p-bonding (Murgich 2002) and even at very low concentration as 50-150 mg/L in a good solvent such as toluene (Mullins et al 2012).…”

Effect of alumina and silica–alumina supported NiMo catalysts on the properties of asphaltenes during hydroprocessing of heavy petroleum

“…With the value of the H/C ratio the aromatic character of the asphaltenes can be established that is the higher the H/C ratio the lower the aromaticity [12][13][14], this indicates that the asphaltene structure becomes more aromatic as the reaction temperature is increased, which is further confirmed by the aromaticity factor. Asphaltenes obtained from the silica-alumina catalyst are less aromatic than those recovered from the NiMo/Al 2 O 3 catalyst.…”

Laser desorption ionization FT-ICR mass spectrometry and CARSPLS for predicting basic nitrogen and aromatics contents in crude oils

“…MALDI became an established mass spectrometry method for macromolecular compounds. LDI/MALDI coupled to time of flight mass spectrometry (TOF) has been applied in petroleomics for the characterization of petroporphyrins [12], crude oils [13], and their fractions [14,15], in addition to the determination of the molecular-weight distributions (MWDs) of asphaltenes [16][17][18][19][20][21].…”