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40
In the early 1990s, Kolboe began work with Ivar Dahl conducting
isotopic labeling studies on HSAPO-34 using 13C-methanol and alcohols
which would immediately dehydrate to alkenes on the catalyst.20,21 Dahl and
Kolboe were able to determine that neither ethylene nor propene react with
the 13C-methanol to a great extent based on the isotopic content of the
ethylene and propene. In fact, ethylene showed little reactivity at all on
HSAPO-34, thus the researchers determined it was an inert primary
product.22 Based on these results, Kolboe and Dahl proposed a mechanism,
illustrated in Scheme 2.8, centered around a ‘pool’ of hydrocarbons
(represented as (CH2)n) that were methylated to product olefinic products
alkanes, and aromatic species; however the researchers did not specify the
exact nature of these pool species.
2.6.4. The Paring Reaction
An additional concept that has influenced indirect mechanisms is the
‘paring’ contraction-expansion reaction published by Sullivan et al. in 1961.23
This reaction, depicted in Scheme 2.9, involves a ring contraction of
hexamethylbenzene to a methylated cyclopentadiene with an isopropyl
substituent. Loss of the isopropyl group yields propene and the resulting
cyclopentadienyl cation undergoes ring expansion to produce a
trimethylbenzene.
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 51 |
| Contributing entity | University of Southern California |
| Repository email | cisadmin@lib.usc.edu |
| Full text | 40 In the early 1990s, Kolboe began work with Ivar Dahl conducting isotopic labeling studies on HSAPO-34 using 13C-methanol and alcohols which would immediately dehydrate to alkenes on the catalyst.20,21 Dahl and Kolboe were able to determine that neither ethylene nor propene react with the 13C-methanol to a great extent based on the isotopic content of the ethylene and propene. In fact, ethylene showed little reactivity at all on HSAPO-34, thus the researchers determined it was an inert primary product.22 Based on these results, Kolboe and Dahl proposed a mechanism, illustrated in Scheme 2.8, centered around a ‘pool’ of hydrocarbons (represented as (CH2)n) that were methylated to product olefinic products alkanes, and aromatic species; however the researchers did not specify the exact nature of these pool species. 2.6.4. The Paring Reaction An additional concept that has influenced indirect mechanisms is the ‘paring’ contraction-expansion reaction published by Sullivan et al. in 1961.23 This reaction, depicted in Scheme 2.9, involves a ring contraction of hexamethylbenzene to a methylated cyclopentadiene with an isopropyl substituent. Loss of the isopropyl group yields propene and the resulting cyclopentadienyl cation undergoes ring expansion to produce a trimethylbenzene. |
