Dissertation/Thesis Abstract

The role of surface active agents on hydrate formation
by Lo, Chi Yuen, Ph.D., City University of New York, 2011, 138; 3444322
Abstract (Summary)

The goal of this study is to probe the mechanism for improving gas hydrate formation. Fast hydrate formation for gas storage requires the understanding of hydrate formation mechanism. However the formation kinetics is slow due to the low mass transfer rate of gas to hydrate growth regions. Past hydrate formation studies did not incorporate surface studies to investigate the formation mechanism. Our approach to solving this unknown mechanism is to use surface science techniques to probe the interface of hydrate and water.

From &zgr;-potential measurements, hydrate surface charge is negative due to bicarbonate ion adsorption. An ion exchange occurs upon adding SDS and DS- monomers replace the bicarbonate ions and a further negative charge confirms DS- adsorption. Pyrene fluorescence measures the micropolarity of the hydrate interface. Upon adding 50ppm SDS the hydrate interface's micropolarity decreases and indicates an admicelle formation.

Induction time measurements are correlated to the &zgr;-potential and Pyrene fluorescence measurements to show that reduced induction periods are due to a formation of an admicelle layer. This is first indication of a mechanism where an admicelle layer led to increased growth of hydrates.

Adsorption Isotherms of SDS and DTAB show similar L-S type adsorption. However, SDS, a hydrate promoter, would form a monolayer at lower surfactant concentrations than DTAB. DTAB, a possible anti agglomerate agent, shows a larger adsorption amount before forming a monolayer. The larger adsorption amount for DTAB indicates that a dense layer of surfactants would prevent hydrate particles from sticking to each other.

Raman spectroscopy reveals a blue shift for CP hydrate interface and a shoulder band. The shoulder implies of the aqueous CP around the hydrate interface. With the addition of SDS, the shoulder is blue shifted. Raman spectroscopy of the 1% CP in water shows the similar red shift for aqueous CP but upon adding 1mM SDS the vibrational band experiences a blue shift, indicating a hydrate-like environment. ATR-IR measurements of the hydrate interface expose that with 100ppm SDS bonded OH shifts from ice-like to water-like. This concentration is the same concentration of where a monolayer forms. A monolayer may loosen the hydrate's hydrogen bonding at the interface.

Indexing (document details)
Advisor: Lee, Jae W.
Commitee: Couzis, Alexander, Gilchrist, Lane, Jones, Camille, Morris, Jeffrey, Somasudaran, Ponisseril
School: City University of New York
Department: Engineering
School Location: United States -- New York
Source: DAI-B 72/05, Dissertation Abstracts International
Subjects: Chemical engineering
Keywords: Gas hydrates, Hydrate formation, Surface active agents, Surface enhancement, Surfactants
Publication Number: 3444322
ISBN: 978-1-124-51795-7
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