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15
Phosphoric acid (17.5 g) was added drop wise and the mixture was stirred
for 10 to 15 minutes. The templating agent, tetraethylammonium hydroxide
(100mL) was added, and the resulting solution was stirred for an addition
three hours. The gel was transferred to a Teflon-lined autoclave, sealed and
heated at 473 K for 48 hours. Upon cooling, the supernatant liquid was
decanted and the HSAPO-34 precipitate was thoroughly washed with water.
The product was dried in an oven at 393 K for several hours. Prior to use in
catalysis, HSAPO-34 was calcined in air overnight at 873 K and stored in a
glove box under nitrogen to prevent hydrolysis.
1.5. Mordenite
Mordenite is a natural aluminosilicate with MOR topology discovered
in 1864.1 It has elliptical one-dimensional channels with large 12 T-atoms
pores 0.65 to 0.7 nm in diameter. Figure 1.7 illustrates the MOR topology.
One significant drawback to a one-dimensional zeolite is ease of
deactivation. When a channel is blocked at any single point, the whole
channel becomes inactive, thus accelerating deactivation of the catalyst.
Synthetic mordenite can be purchase from Zeolyst International in
three acid site densities: Si/Al = 6.5, Si/Al =10, and Si/Al = 45. Catalytic
applications for mordenite or mordenite-based catalysts include C5/C6
naphtha and xylene isomerization, petroleum dewaxing, NOx control and
selective olefin hydrogenation.10 In the work presented in Chapter 4,
Object Description
| Title | Modification of methanol-to-olefin hydrocarbon pool species by oxygenates on acidic zeolites |
| Author | Hayman, Miranda Jeanette |
| Author email | mirandah@usc.edu; mirandahayman@gmail.com |
| Degree | Doctor of Philosophy |
| Document type | Dissertation |
| Degree program | Chemistry |
| School | College of Letters, Arts and Sciences |
| Date defended/completed | 2011-02-11 |
| Date submitted | 2011 |
| Restricted until | Unrestricted |
| Date published | 2011-04-26 |
| Advisor (committee chair) | Haw, James F. |
| Advisor (committee member) |
Flood, Thomas C. Jessen, Kristian |
| Abstract | The mechanism of methanol-to-olefin (MTO) catalysis employs organic reaction centers, both aromatic and olefinic, to generate olefins on acid zeolites. Generally, propene is the favored MTO olefin on most zeolite catalysts, but ethylene is a more desirable olefin due to its prevalence in consumer plastics. Much research has been conducted to alter the MTO product selectivities to favor ethylene. This focus of this dissertation is selective modification of the olefinic reaction centers, converting them into aromatic reaction centers known to be responsible for the majority of ethylene production.; Formaldehyde reactivity was studied on HSAPO-34, and found to react with propene through a Prins reaction to form butadiene, which readily cyclized to aromatic species. Evidence of formaldehyde formation was observed from methanol oxidation on the stainless-steel surface of the reactor tubing. This reaction was then studied in HZSM-5 where olefinic reaction centers dominate the hydrocarbon pool. The olefinic reaction centers were converted to aromatic species, and a significant increase in ethylene selectivity was observed. Other oxygenated species, such as acetaldehyde, were also studied in conjunction with methanol on HZSM-5 and an improvement in ethylene selectivity was noted. The consequence of the increased ethylene selectivity however was an increase in the rate of deactivation due to the accelerated formation of aromatic species. |
| Keyword | MTO; methanol-to-olefins; zeolite; heterogeneous catalysis; hydrocarbon pool; HZSM-5 |
| 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-m3780 |
| Contributing entity | University of Southern California |
| Rights | Hayman, Miranda Jeanette |
| Repository name | Libraries, University of Southern California |
| Repository address | Los Angeles, California |
| Repository email | cisadmin@lib.usc.edu |
| Filename | etd-Hayman-4358 |
| Archival file | uscthesesreloadpub_Volume23/etd-Hayman-4358.pdf |
Description
| Title | Page 26 |
| Contributing entity | University of Southern California |
| Repository email | cisadmin@lib.usc.edu |
| Full text | 15 Phosphoric acid (17.5 g) was added drop wise and the mixture was stirred for 10 to 15 minutes. The templating agent, tetraethylammonium hydroxide (100mL) was added, and the resulting solution was stirred for an addition three hours. The gel was transferred to a Teflon-lined autoclave, sealed and heated at 473 K for 48 hours. Upon cooling, the supernatant liquid was decanted and the HSAPO-34 precipitate was thoroughly washed with water. The product was dried in an oven at 393 K for several hours. Prior to use in catalysis, HSAPO-34 was calcined in air overnight at 873 K and stored in a glove box under nitrogen to prevent hydrolysis. 1.5. Mordenite Mordenite is a natural aluminosilicate with MOR topology discovered in 1864.1 It has elliptical one-dimensional channels with large 12 T-atoms pores 0.65 to 0.7 nm in diameter. Figure 1.7 illustrates the MOR topology. One significant drawback to a one-dimensional zeolite is ease of deactivation. When a channel is blocked at any single point, the whole channel becomes inactive, thus accelerating deactivation of the catalyst. Synthetic mordenite can be purchase from Zeolyst International in three acid site densities: Si/Al = 6.5, Si/Al =10, and Si/Al = 45. Catalytic applications for mordenite or mordenite-based catalysts include C5/C6 naphtha and xylene isomerization, petroleum dewaxing, NOx control and selective olefin hydrogenation.10 In the work presented in Chapter 4, |
