Determination of Critical Aggregation Phenomena using Raman Spectroscopy

• Author / Creator

  Fournier, Geraldine A A

• The tendency of asphaltenes to aggregate in crude oil is observed at SATP and is enhanced at elevated temperatures. At these conditions, asphaltenes aggregation is a problem as it will ultimately lead to mesophase formation, a precursor of coke, known for causing plugging and fouling of pipelines and other equipment in refineries. It is becoming crucial to develop new technics using on-line sensors for characterization of heavy oil components in order to predict the onset of aggregation and prevent those shut downs. Previous studies have been done to determine the early stages of asphaltene aggregation, also called CNAC, in organic solvents using absorbance, fluorescence spectrometry, calorimetric titration or thermo-optical diffusivity. The ultimate goal of this work is to develop an in situ technique that is able to track aggregation at reaction conditions by using Raman spectroscopy, even though no structural information is available. This thesis describes the foundations of the in situ technique at ambient conditions. Aggregation of strongly associating model compounds such as surfactants was first investigated with Raman spectroscopy using a 785 nm laser. Intensity ratios as a function of the surfactant concentration showed progressive transitions which were interpreted as indicators of the critical micelle concentration. The good agreement with the literature encouraged the continued development of this method as an analytical tool to study the aggregation phenomena of highly complex associating compounds such as vacuum residue. Raman spectra of Athabasca VR solutions in toluene were observed in the concentration range between 0.1 wt. % and 0.0005 wt. % at room temperature and atmospheric pressure. Specific intensity ratios plotted versus the vacuum residue concentration showed a breakpoint around 0.006 wt. %. Such values were in agreement with the CNAC reported in previous articles. Therefore, Raman spectroscopy stands as an effective tool to detect and give reliable quantitative data for physical phenomena such as micellization and particles aggregation.

• Subjects / Keywords

  • Raman spectroscopy
  • Surfactants
  • Self-association
  • Micellization
  • Asphaltenes

• Graduation date

  Spring 2016

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/R3028PJ7D

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.