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51
3.2.3 Membrane characterization
The HT powders and the resulting membrane films were characterized by a
variety of techniques. The FTIR spectra of the HT were recorded using a Genesis II
(Mattson, FTIR) instrument; the experimental operating conditions were a scan-range
from 4000 cm-1 to 500 cm-1, scan numbers 50, and a scan resolution of 2 cm-1. XRD
analysis was carried out using a Rigaku X-ray diffractometer, with the Cu-Kα line used
for the X-ray source, with a monochromator positioned in front of the detector. Scans
were performed over a 2θ range from 5o to 75o with scan rate of 2°/min and a step rise
0.05. The surface area, the BJH (Barret-Joyner-Halenda), and the Horvath-Kawazoe (H-K)
pore volumes, and the pore size distribution (PSD) of the HT were calculated from N2
adsorption at 77 K using a Micrometrics ASAP 2010 instrument. The samples for
adsorption were pretreated by heating in vacuum overnight. The surface morphology of
the HT membrane films was investigated by scanning electron microscopy (SEM), using
a Philips/FEI XL-30 Field Emission Scanning Electron Microscope.
Transport properties of the HT membranes were measured using a Wicke-
Kallenbach type permeation apparatus using a bubble flow-meter to measure the flow,
and a mass spectrometer to measure the gas concentration. For the silicone-coated HT
membranes, their permeation characteristics were measured, using the constant volume
(or diffusion time-lag) method [Fielding, 1980] with the apparatus shown in Fig. 3.1. To
measure the gas permeance, the permeate side pressure was kept at ~1×10−2 Torr (1.33
Pa), while the feed side was maintained at a fixed pressure of either 30 or 40 psi
(206,842.7 or 275,790.3 Pa). Gas permeance ( r P [mol/m2 s Pa]) is calculated from Eqn
Object Description
| Title | Studies of transport phenomena in hydrotalcite membranes, and their use in direct methanol fuel cells |
| Author | Kim, Tae Wook |
| Author email | taewkim@usc.edu; kholy7@gmail.com |
| Degree | Doctor of Philosophy |
| Document type | Dissertation |
| Degree program | Chemical Engineering |
| School | Viterbi School of Engineering |
| Date defended/completed | 2006-06-09 |
| Date submitted | 2008 |
| Restricted until | Unrestricted |
| Date published | 2008-10-11 |
| Advisor (committee chair) | Tsotsis, Theodore T. |
| Advisor (committee member) |
Sahimi, Muhammad Bau, Robert |
| Abstract | Currently, the humanity is encountering two major crises: energy deficiency and global warming. In order to resolve these crises, we should consider maximizing energy efficiency and minimizing its usage. Furthermore, we should develop alternative energy sources (e.g. wind, solar, biomass), instead of hydrocarbon products. Moreover, we need to commercialize well-known techniques such as fuel cells, which are environment-friendly and high efficiency systems for various applications, such as power generation and transportation. In addition, we need to continue research on CO2 capture and separation processes.; This study presents the synthesis and characterization of hydrotalcite (HT) membranes with several techniques. In addition, this study explores the possibility of using HT materials as inorganic fillers for conductive membranes in direct methanol fuel cells (DMFC). Due to their properties, hydrotalcites also known as layered double hydroixde compounds, are a potentially good candidate as CO2-selective membranes and inorganic filler of conductive membrane.; Chapter 1 presents a general Introdcution to the various topics discussed in this Thesis. Chapter 2 describes the use of electrophoretic deposition as a new method for the preparation of HT thin films. The films are deposited on macroporous alumina substrates and on alumina substrates, which were previously coated by conventional dip-coating techniques using slurries of HT colloidal particles. Their permeation properties are investigated by single and mixed-gas permeation tests. The films are shown to be permselective towards CO2, consistent with the prior studies of these materials, which showed them to be effective CO2 adsorbents.; In Chapter 3 several methods are used for synthesis of effective CO2-selective HT membranes. Single gases and mixtures of gases are tested and their permeation is studied. Unfortunately, the dip-coating method results in mesoporous membranes with Knudsen flow. But the vacuum-suction method shows that the He/CO2 separation factor for these membranes is significantly higher than the corresponding Knudsen values, despite the fact that these membranes are not CO2-permselective. In order to decrease voids and pinholes, a silicone layer is coated by vacuum suction on the HT membranes. The silicone coating appears to improve the separation characteristics of these membranes.; Chapter 4 describes preparation of a miniature-type micromembrane using silicon wafers and stainless steel (SS) foils as templates. Silicon-based micromembranes show the potential for application for microreactor systems, but their pressure resistance is not high enough to carry out the permeation test. HT micromembranes, prepared by coated HT colloid solution with 0.1~0.2 μm diameter on SS substartes, are characterized by several analytical techniques and by single-gas permeation experiments. Most of the HT micro-membranes exhibit Knudsen transport behavior with He and N2-transport being favored when compared to CO2. Some of the HT micromembranes turned out to be CO2-selective, however.; Chapters 5 and 6 demonstrate how both hybrid and in-situ hydrotalcite-SPEEK (sulfonated polyetheretherketone) membranes are synthesized and investigated for the possibility of making a conductive membrane in direct methanol fuel cell. Our study's goal is to develop a new, cost-effective membrane with superior methanol barrier properties, and reasonable proton conductivity in order to replace commercial Nafion® membranes. We prepare HT-SPEEK membranes by incorporating HT particles into SPEEK and by in-situ sulfonation polymerization from PEEK and HT. The hybrid HT-SPEEK membranes exhibit good resistance for methanol permeability and reasonable proton conductivity.Their properties depend strongly on the sulfonation degree of the polymer matrix, and on the fraction of the HT present in the hybrid membranes. Therefore, HT-SPEEK membranes are potentially viable candidates for replacing Nafion® membranes. Moreover, the in-situ membrane's properties depend on the reaction time, and the fraction of hydrotalcite initially added to the PEEK materials prior to sulfonation. The MeOH permeability for the in-situ membranes is 3 ~ 5 times smaller than the one for the commercial Nafion®115 film. |
| Keyword | adsorbent; carbon dioxide; conductive membrane; fuel cell; hydrotalcite; membrane |
| Language | English |
| Part of collection | University of Southern California dissertations and theses |
| Publisher (of the original version) | University of Southern California |
| Place of publication (of the original version) | Los Angeles, California |
| Publisher (of the digital version) | University of Southern California. Libraries |
| Provenance | Electronically uploaded by the author |
| Type | texts |
| Legacy record ID | usctheses-m1657 |
| Contributing entity | University of Southern California |
| Rights | Kim, Tae Wook |
| Repository name | Libraries, University of Southern California |
| Repository address | Los Angeles, California |
| Repository email | cisadmin@lib.usc.edu |
| Filename | etd-Kim-2407 |
| Archival file | uscthesesreloadpub_Volume26/etd-Kim-2407.pdf |
Description
| Title | Page 66 |
| Contributing entity | University of Southern California |
| Repository email | cisadmin@lib.usc.edu |
| Full text | 51 3.2.3 Membrane characterization The HT powders and the resulting membrane films were characterized by a variety of techniques. The FTIR spectra of the HT were recorded using a Genesis II (Mattson, FTIR) instrument; the experimental operating conditions were a scan-range from 4000 cm-1 to 500 cm-1, scan numbers 50, and a scan resolution of 2 cm-1. XRD analysis was carried out using a Rigaku X-ray diffractometer, with the Cu-Kα line used for the X-ray source, with a monochromator positioned in front of the detector. Scans were performed over a 2θ range from 5o to 75o with scan rate of 2°/min and a step rise 0.05. The surface area, the BJH (Barret-Joyner-Halenda), and the Horvath-Kawazoe (H-K) pore volumes, and the pore size distribution (PSD) of the HT were calculated from N2 adsorption at 77 K using a Micrometrics ASAP 2010 instrument. The samples for adsorption were pretreated by heating in vacuum overnight. The surface morphology of the HT membrane films was investigated by scanning electron microscopy (SEM), using a Philips/FEI XL-30 Field Emission Scanning Electron Microscope. Transport properties of the HT membranes were measured using a Wicke- Kallenbach type permeation apparatus using a bubble flow-meter to measure the flow, and a mass spectrometer to measure the gas concentration. For the silicone-coated HT membranes, their permeation characteristics were measured, using the constant volume (or diffusion time-lag) method [Fielding, 1980] with the apparatus shown in Fig. 3.1. To measure the gas permeance, the permeate side pressure was kept at ~1×10−2 Torr (1.33 Pa), while the feed side was maintained at a fixed pressure of either 30 or 40 psi (206,842.7 or 275,790.3 Pa). Gas permeance ( r P [mol/m2 s Pa]) is calculated from Eqn |
