Characterization of the Interfacial Material in Asphaltenes Responsible for Oil/Water Emulsion Stability

Abstract

This study aimed at a better understanding of the structure and properties of the most interfacially active asphaltenes responsible for the stability of oil/water emulsions. Interfacial material (IM) was extracted from three different crude oils using a modified solvent washing procedure. Structural parameters of IM were analyzed and compared to those of a parent asphaltene. High-resolution microscopy imaging was performed to correlate IM microstructure to their interfacial properties. Although IM and asphaltene fractions had comparable molecular weights, IM species had a smaller aromatic core than asphaltenes with at least one linear fatty acid chain containing a sulfinic or carboxylic group. This subtle difference conferred them with an amphiphilic character that promoted their self-assembly into 2–6 nm thick worm-like aggregates in solution instead of spherical clusters. IM molecules interacted with water through their fatty acid chains while simultaneously π–π stacking with adjacent molecules. These two types of interactions favored their multilayer growth and the formation of stable interfacial films around water droplets that significantly lowered the oil/water interfacial tension. High-resolution microscopy imaging of the interfacial films revealed the presence of flexible nanosheets that are 10–50 nm thick. The nanosheets provided a large surface area on which asphaltene clusters (smaller than 20 nm) and fine clay particles (100–200 nm) adsorbed. Even though multiple washings were performed to extract IM, there were still traces of asphaltenes present in this fraction as well as 10–30 wt % of clays, depending on the type of crude oil. The latter induced some artifacts when analyzing the properties of the most interfacially active asphaltenes.

Low-Temperature Graphene Growth and Shrinkage Dynamics from Petroleum Asphaltene on CuO Nanoparticle

“…However, after the heating reaction (Figure b), the Raman spectra of nanoparticles became significantly different. Besides the sharp G peak at 1580 cm –1 , a relatively broad D peak at 1350 cm –1 was observed for the CuO nanoparticles, which represents an ordered molecular boundary structure . A very weak G′ (or 2D) peak at 2700 cm –1 was also found for CuO nanoparticles, indicating a multilayer structure of graphene.…”

“…The asphaltenes were recovered from the filter cake by dissolution in toluene and then dried after solvent evaporation. The elemental composition of the asphaltene is shown in Table …”

Nanoscale Characterization of Thin Films at Oil/Water Interfaces and Implications to Emulsion Stability

“…The carbon, hydrogen, nitrogen, sulfur, and oxygen (CHNS/O) contents were analyzed using a FlashSmart elemental analyzer (Thermo Scientific, USA) using two reactor columns, a thermal conductivity detector, and appropriate calibration standards. More details of these experimental procedures can be found elsewhere …”

“…Significant progress has been made over the past decade to isolate and characterize the interfacial material (IM) responsible for the stability of o/w emulsions. Centrifugation studies revealed that the IM may constitute less than 2 wt % of the total asphaltenes present in oil or bitumen. , Asphaltenes are a polydisperse mixture of the heaviest and most polarizable fraction of crude oil and contain thousands of molecules with different structures . Even though IM species are a subfraction of asphaltenes, their concentration is so low that they do not affect the average properties of asphaltenes in bulk solution.…”

“…Even though IM species are a subfraction of asphaltenes, their concentration is so low that they do not affect the average properties of asphaltenes in bulk solution. However, they exhibit a greater interfacial activity than asphaltenes due to the abundance of acidic oxygen and sulfur-containing species. − With a relatively high hydrogen-to-carbon ratio, the molecular structure of IM components may be comparable to that of naphthenic acids with a small polycyclic moiety and a long fatty acid chain. ,, As a result, they tend to accumulate as stacked molecules oriented perpendicular to the o/w interface. ,, The latter would further undergo conformational changes to form a protective film that stabilizes emulsions …”