Changes in Asphaltene Microenvironments Evidenced by Fluorescence Solvatochromism

Abstract

This work involved the study of Cold Lake asphaltenes' behavior in toluene and o-dichlorobenzene. The changes in asphaltene microenvironments with the increase in asphaltene concentration were observed using fluorescence solvatochromism. The reporter molecule chosen was the environmentally sensitive fluorophore PRODAN. This procedure represents a novel and sensitive method to study asphaltene solutions, and might bring additional information to the existent database of asphaltene properties.A pre-aggregation model was developed to explain the experimental observations, and a definition for the critical aggregation concentration was proposed. The model is valid for low asphaltene concentrations and is supported by direct measurements of refractive indices for asphaltene solutions. Atomic force microscopy was used to image asphaltene entities. The size distribution indicated that asphaltene particles do not change significantly with the increase in concentration. The appearance of larger aggregates in solutions with concentrations above CAC might support the validity of the model.

Asphaltene aggregation in organic solvents

“…They interpreted the shift to occur at a critical aggregation concentration (CAC) (range 0.2-1.5 g/l) and suggested that the CAC was caused by the formation of larger asphaltene molecular aggregates from the smaller asphaltene molecular aggregates. The CAC values reported by Pietaru and Cramb [19] were close to the MCP values measured by Priyanto et al [18]. Both MCP and CAC, nevertheless, are close to CMC values reported in the literature.…”

“…It is believed that there is a change in the rate of aggregation at this point. In this study, henceforth, this point is called the critical aggregation concentration (CAC), the same terminology employed by Pietaru and Cramb [19]. The surface tension decreases observed were relatively small in the range of 36.1-35.5 mN/m.…”

“…Their first transition point may be related to a molecular association phenomenon while the second may indicate CMC-like aggregation. Pietraru and Cramb [19] found fluorescence spectral shifts at asphaltene concentrations higher than those observed by Groenzin and Mullins [16]. They interpreted the shift to occur at a critical aggregation concentration (CAC) (range 0.2-1.5 g/l) and suggested that the CAC was caused by the formation of larger asphaltene molecular aggregates from the smaller asphaltene molecular aggregates.…”

Effect of Precipitating Conditions on Asphaltene Properties and Aggregation

“…51,52 FL spectra of aromatic moieties are fundamentally related to the aromatic fluorophores' sizes and conjugation; the appearance of new bands, shifts in emission wavelengths and FL intensity have been correlated with changes surrounding these fluorophores, like the bathochromic red shifts caused by intermolecular aggregation. [53][54][55] One problem with asphaltenes is their color;…”

Behavior of fluorescent molecules bound to the interior of silica nanocapsules in various solvents

“…That is, the fluorescence solvatochromism was observed in the nanocapsule. The fluorescence intensity depended on the polarity parameter [19] of the solvent as shown in Fig. 6b: 1697 RFU for ethanol (0.289), 1028 RFU for 2-propanol (0.273), and 925 RFU for DMSO (0.263).…”