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39
regenerated. Many similarities exist between this mechanism and the
current favored MTO mechanism that will be discussed in Section 2.7.
2.6.3. The Hydrocarbon Pool
The work of Stein Kolboe on the MTO mechanism began in the 1980s.
In a 1986 letter,19 Kolboe detailed his studies on the effect of alkenes
administered prior to methanol. When HZSM-5 was pre-treated at 493 K
with a small amount of butene (1 mL per gram catalyst) before the methanol
stream, the catalyst had immediate activity for the conversion of methanol to
olefinic products at the same temperature; without pre-treatment, the catalyst
yielded no olefinic products. The effect of the butene was still present even
when the system was flushed with nitrogen for an extended period of time
before the methanol introduction.
Scheme 2.8. The Hydrocarbon Pool
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 50 |
| Contributing entity | University of Southern California |
| Repository email | cisadmin@lib.usc.edu |
| Full text | 39 regenerated. Many similarities exist between this mechanism and the current favored MTO mechanism that will be discussed in Section 2.7. 2.6.3. The Hydrocarbon Pool The work of Stein Kolboe on the MTO mechanism began in the 1980s. In a 1986 letter,19 Kolboe detailed his studies on the effect of alkenes administered prior to methanol. When HZSM-5 was pre-treated at 493 K with a small amount of butene (1 mL per gram catalyst) before the methanol stream, the catalyst had immediate activity for the conversion of methanol to olefinic products at the same temperature; without pre-treatment, the catalyst yielded no olefinic products. The effect of the butene was still present even when the system was flushed with nitrogen for an extended period of time before the methanol introduction. Scheme 2.8. The Hydrocarbon Pool |
