Formation of silica particles and stabilization of asphaltene colloids in apolar media using amphipiles and polymers.
Chang, Chia-Lu
1995
Abstract
This project is comprised of two research topics both involving the stability of colloids in apolar media. The topics are: (1) the formation of silica particles through the hydrolysis of tetraethyl orthosilicate (TEOS) in aliphatic-based nonionic W/O microemulsions and (2) the stabilization of asphaltene colloids (from crude oil) in aliphatic media using amphiphiles and polymers. In pure hydrocarbon alkane media, both asphaltenes and silica particles are unstable and coagulate through the acid-base interaction among their polar groups. However, both colloidal particles can be stabilized in the apolar media by the amphiphilic-like molecules, such as surfactants. These amphiphiles attach the surface of particles with the polar groups and sterically stabilize particles in the media with the tail groups. Our objectives were to understand the key features of silica particle formation and asphaltene colloid stabilization in aliphatic media as a function of the molecular structure of amphiphilic stabilizers, the type of oil, and the composition of solution. In both silica and asphaltene systems, the molecular interaction, the molecular association structure and the colloidal particle dimension were characterized using molecular spectroscopy, scattering techniques and electron microscopies. From this characterization, we elucidated the mechanism of the nucleation and growth of silica particles in microemulsions and clarified the behavior of the stability of asphaltene colloids in the presence of amphiphiles (or polymers). In the study of the formation of silica particles in W/O microemulsions, it was found that the growth of silica in nonionic microemulsions is rate-limited by the hydrolysis of tetraethyl orthosilicate (TEOS). Kinetics studies showed that the rate of TEOS hydrolysis was affected by the concentrations of aqueous ammonia and surfactant. The analysis of silica particle size distributions showed that the growth of silica particles behaved as a reaction-controlled process where the shape of size distributions was preserved during the growth of particles. The size and dispersity of synthesized silica particles were determined in the particle nucleation period by the stability of hydrolyzed polymeric silica species in microemulsion droplets and by the compartmentalization of these species in the aqueous phase of microemulsions. In the study of asphaltene stabilization in aliphatic media, it was found that asphaltenes can be stabilized in alkane by alkylbenzene-derived amphiphiles with a sufficiently polar head groups and a sufficiently long alkyl tail groups. The spectroscopic analysis of asphaltene-amphiphile interactions indicated that the hydrogen-bonding capacity of asphaltenes was approximately 1.6-2.0 mmole per gram of asphaltenes. It was also found that polymeric molecules with multiple polar groups could associate with multiple asphaltene particles to form the hetero-aggregates between asphaltenes and polymers in the solution.Other Identifiers
(UMI)AAI9610092
Subjects
Engineering, Chemical
Types
Thesis
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