Asphaltene Aggregation Behavior in Bromobenzene Determined By Small-angle X-ray Scattering

Abstract

Small-angle X-ray scattering (SAXS) analyses of an asphaltene (a heptane-insoluble fraction in Canadian oil sand bitumen (CaAs)), at various concentrations in bromobenzene (BB) were performed at a synchrotron facility. BB is the first trial medium in which the aggregation behavior of asphaltenes has been elucidated, and is considered to be one of the "best" pure solvents for CaAs when determining the Hansen Solubility Parameters (HSP). Although the aggregation behavior of the CaAs in toluene (TL) and toluene-pentane mixed solvent (TL-PT10, containing 10% pentane on a volume basis) was confirmed to be similar to that reported in previous SAXS studies, the behavior in BB was markedly different. The results indicated that aggregates with a soft boundary of ~30-60 Å in the radius of gyration (R g ), which were observable in TL and TL-PT10, disappeared in BB and larger aggregates with a clear boundary appeared simultaneously. This phenomenon supported a colloidal aggregation model, with HSP analyses suggesting that BB dispersed the colloid surface fraction at the molecular level and isolated the colloid core fraction, which led to the formation of a rigid aggregation of the core fraction. The HSP analyses enabled us to evaluate the aggregation behavior quantitatively, and the results obtained by SAXS were consistent with those obtained by Rayleigh scattering that we reported previously.

Experimental Investigation on the Interactions between Asphaltenes and Comb-like Octadecyl Acrylate (OA) Polymeric Flow Improvers at the Model Oil/Water Interface

“…McLean and Kilpatrick’s studies showed that asphaltene molecules could be bonded at the interface in the form of aggregates or gel-like structures . The observations accorded with the results of Morimoto et al who analyzed the structural properties of the layer by a small-angle X-ray method . However, discrepancies were proposed by Pauchard et al By fitting the dynamic interfacial tension (DIFT) into the adsorption model of asphaltenes, they considered that asphaltene molecules should adsorb irreversibly at the interface in the form of monomers .…”

Asphaltene Dispersion in Mixed Poor Solvents

“…SAXS data of CaAs at concentrations of 10,000 mg/L (~1 %) in BH-95/05, 83/17, 70/30, 60/40, and 50/50 were obtained at beamline BL6A 7) of the Photon Factory (PF) at the High Energy Acceleration Research Organization (KEK). The asphaltene concentration was lower than the maximum solubility determined and sufficiently low to prevent the effects of interparticle interference 3) . Prior to each measurement, the samples were shaken by hand, ultrasonicated for 10 min, and then allowed to stand for 1 week.…”

“…Fig. 2 includes the resulting fits for BH-95/5, 83/17, 70/30, 60/40, and 50/50, and the calculated R g values of aggregates were 1.4, 2.2, 2.9, 3.0, and 4.5 nm, respectively, smaller than those in toluene (~5 nm) at the same concentrations using the same asphaltene source 3) . It is interesting that aggregate size in a mixture of poor solvents can be much smaller than that in a good solvent.…”

“…These differences correspond to an R a as low as 1.3 MPa 0.5 . Small-angle X-ray scattering (SAXS) analyses showed that bromobenzene can disperse CaAs nanoaggregates 3) . Therefore, we may be able to identify a mixed solvent with the same set of HSPs as asphaltene.…”

Molybdenum Dialkyldithiophosphate as self-sulfurized catalyst precursor in Hydrocracking of Residue

“…Small-angle X-ray scattering (SAXS) was carried out for the particle size measurement of asphaltene aggregates, by a small angle scattering station (1W2A) in the Institute of High Energy Physics, Beijing. Data were processed using the software FIT2D and calculated according to the method reported in literature [12]. crystal were clearly identified.…”