Search

Asphaltenes are a complex mixture of molecular structures with a variety of functionalities, which in turn impacts their physical properties. Discriminating between asphaltenes that are strongly and weakly interfacially active is providing a new direction to mitigate asphaltene-related problems. Whole asphaltenes (WA) were extracted from a South American heavy crude oil, further fractionated into interfacially active asphaltenes (IAA) and remaining asphaltenes (RA), and molecularly characterized by positive-ion (+) atmospheric pressure photoionization (APPI) using a 9.4 T Fourier transform ion cyclotron mass spectrometer (FT-ICR MS). The IAA fraction was found to contain a greater abundance of heteroatoms with >50% of IAA containing two or more heteroatoms as compared to ∼30% for RA. The IAA fraction was enriched in oxygen-containing species, more specifically higher-order Ox and OxSy groups that were predominantly of low DBE. Gas-phase fragmentation of RA and IAA precursor ions (m/z 650) by infrared multiphoton dissociation (IRMPD) revealed an abundance of multi-core motifs in IAA, while RA was found to be a mixture of single-core and multi-core structures. Analysis of the fragmented ions showed a prevalence of nitrogen-containing species of high DBE (aromatic molecular structures), while oxygen-containing species were most likely associated with aliphatic side chains. Extrography fractionation of RA and IAA verified the abundance of multi-core motifs in IAA, which were highly polar and of low DBE and carbon number. These “atypical” structures of IAA are classified as asphaltenes as a result of their functionality and polarity rather than high aromaticity.

Using the extended-SARA method to fractionate asphaltenes based on their interfacial activity, the current study reports the first results on the estimated size and shape of interfacially active asphaltene (IAA) and remaining asphaltene (RA) nanoaggregates. These fractions have been reported to exhibit distinctly different chemical architectures that influence the size of asphaltene clusters in good and poor solvents. However, little is known about the building blocks, commonly referred to as nanoaggregates, which form these clusters and how those subtle differences in chemical architecture impact aggregation of asphaltenes. The nanoaggregate size and shape of IAA and RA was measured using small-angle neutron scattering (SANS). The characteristic length and asymptotic power-law exponent of whole asphaltenes (WAs) extracted from heavy crude oil and dispersed in deuterated toluene were 28.0 ± 0.2 A and 2.86 ± 0.01, respectively, showing negligible variations with changing asphaltene concentration, source of asphaltenes (bitumen and heavy crude oil), and solvent aromaticity. For RA fractions, which account for 98.5 wt % of WA, the characteristic length and power-law exponent of 28.8 A and 2.86 were comparable to that of WA but in contrast to 59.7 A and 2.20 for IAA. A ∼100% increase in the characteristic length and reduced power-law exponent of the IAA fraction confirms that these two asphaltene subfractions form dissimilar nanoaggregate structures.

Whole asphaltenes were fractionated by extended-saturates, aromatics, resins, and asphaltenes (E-SARA) analysis into four asphaltene subfractions: toluene-extracted interfacially active asphaltenes (T-IAA), toluene-extracted remaining asphaltenes (T-RA), Heptol 50/50-extracted interfacially active asphaltenes (HT-IAA), and Heptol 50/50-extracted remaining asphaltenes (HT-RA). The aggregation kinetics of fractionated asphaltenes measured by dynamic light scattering (DLS) showed that decreasing solvent aromaticity promoted asphaltene aggregation for all subfractions. In a given solvent, T-IAA exhibited the strongest aggregation tendency, followed by HT-IAA, then T-RA, and HT-RA. Such differences were attributed to the higher oxygen and sulfur contents (highlighted in sulfoxide content) in IAA subfractions than RA subfractions, as confirmed by elemental analysis and X-ray photoelectron spectroscopy (XPS). The interaction forces between immobilized fractionated asphaltenes were measured using an atomic force microscope (AFM) to obtain a fundamental understanding of asphaltene interactions in organic media of varying aromaticity. The results showed that decreasing solvent aromaticity reduced steric repulsion and increased adhesion between asphaltenes with asphaltenes adopting a more compressed conformation. IAA subfractions, in particular T-IAA, exhibited higher adhesion forces than RA subfractions during separation of two asphaltene films in contact. The results of AFM colloidal force measurements were in good agreement with the DLS data. In spite of the small sulfoxide content in asphaltenes, the sulfoxide groups are believed to play a critical role in enhancing asphaltene aggregation in the bulk oil phase.

The thin liquid film (TLF) technique equipped with Scheludko-Exerowa cell has been demonstrated to be a valuable tool for studying stability of dispersed systems of soft matter such as emulsions and foams. Many industrial applications involve the addition of various chemical aids to obtain desired properties or resolve technical problems. One of the examples is the use of chemical demulsifiers to remove emulsified water from petroleum emulsions. To study the role of chemicals in this process, a TLF technique with a dosing system is required to add demulsifiers into already formed thin liquid films stabilized by interfacial layers formed from indigenous surface active molecules. Herein, we present a modified design of the Scheludko-Exerowa cell with a dosing mechanism which allows for addition of desired chemicals to the intervening organic liquid film that is already formed. The stability of the water-in-oil emulsions and the mechanisms of their chemical destabilization were studied by determining the thinning process of intervening thin oil films before and after dosing a controlled amount of demulsifiers into the film. Dosing of a biodegradable polymer demulsifier (EC300) into the intervening oil film converted a stable film formed by asphaltene-in-heptol solutions into an unstable film with lifetimes of less than 20 s. The observed change in the film drainage rate and stability is related to the disruption of asphaltene network formed at the oil-water interface by EC300 demulsifiers. The experiments with the modified TLF cell also revealed the overdosing effect of EC300 demulsifier, forming more stable films at high EC300 concentrations. A comparison of the experimental results between a dosed system and a premixed system confirmed the value of the modification in the current TLF technique to study the stabilization/destabilization processes of water-in-oil emulsions that mimic more closely the real petroleum emulsions. The modified TLF technique allows for a better understanding of the underlying demulsification mechanisms.

In part 1 of this series of papers, the results of electron spray ionization mass spectrometry (ESI-MS) and molecular dynamics (MD) simulation revealed a close relationhsip between nanoaggregation of polyaromatic (PA) compounds and their chemical structures. In this paper, we present the results of investigating the flocculation of fractionated asphaltenes and synthesized PA molecules by dynamic light scattering (DLS). Together, these two papers complement one another and draw a full picture of asphaltene aggregation. Three asphaltene fractions were obtained on the basis of their different adsorption characteristics onto calcium carbonate. The DLS results suggest that the irreversibly adsorbed (Irr-Ads) asphaltenes containing the highest number of polar groups are the fraction of asphaltenes responsible for the observed flocculation in whole asphaltenes. To better understand the aggregation behavior of asphaltenes, flocculation of three synthesized PA compounds, N-(1-hexylhepyl)-N′-(5-carboxypentyl)peryle...

A gas chromatographic approach for the determination and quantification of trace levels of carbon oxides in gas phase matrices for in situ or near-line/at-line analysis has been successfully developed. Catalytic conversion of the target compounds to methane via the methanation process was conducted inside a metal 3D-printed jet that also acted as a hydrogen burner for the flame ionization detector. Modifications made to a field transportable gas chromatograph enabled the leveraging of advantaged microfluidic-enhanced chromatography capability for improved chromatographic performance and serviceability. The compatibility with adsorption chromatography technology was demonstrated with in-house constructed columns. Sustained reliable conversion efficiencies of greater than 99% with respectable peak symmetries were attained at 400°C. Quantification of carbon monoxide and carbon dioxide at a parts-per-million level over a range from 0.2 ppm to 5% v/v for both compounds with a respectable precision of less than 3% relative standard deviation for peak area (n = 10) and a detection limit of 0.1 ppm v/v was achieved. Linearity with correlation coefficients of R2 greater than 0.9995 and measured recoveries of >99% for spike tests were achieved. The 3D-printed steel jet was found to be reliable and resilient against potential contamination from the matrices owing to the in situ backflushing capability.

SARA fractionation separates crude oil into fractions of saturates (S), aromatics (A), resins (R), and asphaltenes (A) based on the differences in their polarizability and polarity. Defined as a solubility class, asphaltenes are normally considered as a nuisance in the petroleum industry mainly as a result of their problematic precipitation and adsorption at oil–water and oil–solid interfaces. Because a broad range of molecules fall within the group of asphaltenes with distinct sizes and structures, considering the asphaltenes as a whole was noted to limit the deep understanding of governing mechanisms in asphaltene-induced problems. Extended-SARA (E-SARA) is proposed as a concept of asphaltene fractionation according to their interfacial activities and adsorption characteristics, providing critical information to correlate specific functional groups with certain characteristics of asphaltene aggregation, precipitation, and adsorption. Such knowledge is essential to addressing asphaltene-related problems ...

Whole asphaltenes (WA) were fractionated by the E-SARA method according to their adsorption characteristics at oil−water interfaces from either toluene or heptol solutions. Heptol, a mixture of n-heptane and toluene at a 1:1 volume ratio, is a less aromatic solvent than toluene. The effect of solvent aromaticity on the composition of resulting asphaltene subfractions at oil−water interfaces was studied to determine the key functional groups that are critical to the asphaltene-induced stabilization of water-in-oil (W/O) petroleum emulsions. The interfacially active asphaltenes (IAA) were extracted as materials irreversibly adsorbed onto emulsified water droplets, while the asphaltenes remaining in the oil phase were considered as remaining asphaltenes (RA). Although toluene-extracted interfacially active asphaltenes (T-IAA) accounted for only 1.1 ± 0.3 wt % of WA, this subfraction of asphaltenes exhibited a greater interfacial activity and formed more rigid films at the oil−water interface than IAA extracted using heptol, known as HT-IAA which accounted for 4.2 ± 0.3 wt % of WA. The increased potential of T-IAA to stabilize W/O emulsions was attributed to their higher content of oxygen, resulting in a higher content of sulfoxide groups, as verified by elemental analysis, Fourier transform infrared (FTIR) spectroscopy, and X-ray photoelectron spectroscopy (XPS). Although the toluene-extracted remaining asphaltenes (T-RA) and heptol-extracted remaining asphaltenes (HT-RA) were shown to contain similar H/C ratios and nitrogen contents to those of T-IAA and HT-IAA, the two RA subfractions contained a much less amount of sulfur and oxygen, leading to a much reduced interfacial activity as compared with that of IAA subfractions. In spite of the small proportions in asphaltenes, oxygen-containing functional groups, in particular sulfoxides, were believed to contribute significantly to the increased stability of asphaltene-stabilized W/O petroleum emulsions.