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43
Methylbenzene aromatic signals emerged 8 s after the methanol pulse. Two
hours after the methanol pulse, the methyl signals attributed to the
methylbenzene decreased, and olefinic products were observed by GC
analysis. The researchers attributed this to aging of the methylbenzenes to
polycyclic aromatic hydrocarbons, as illustrated in Scheme 2.10.
The researchers concluded methylbenzenes were the organic reaction
centers that composed the hydrocarbon pool on HSAPO-34. To test their
hypothesis, Haw and co-workers designed a double pulse study28 wherein
methylbenzenes were generated by a single 20 μL pulse of 13C-methanol
followed six minutes later by a second 20 μL pulse of natural abundance
methanol. The first pulse showed very little methanol conversion with only
14% converted to olefinic products, a common result obtained during the
induction period. The second pulse had 100% conversion of methanol, and
the olefinic products had 13C incorporation consistent with a side-chain
alkylation mechanism. Methylnaphthalenes were also observed to act as
organic reaction centers on HSAPO-34 and they were more selective for the
formation of ethylene, but they were overall less active as compared to
methylbenzenes.29
With the identification of the hydrocarbon pool species, focus shifted
to determining how olefins were produced from these aromatic species. Both
a Paring mechanism and side-chain alkylation were proposed as potential
routes for olefin generation. Haw and co-workers studied aromatic
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 54 |
| Contributing entity | University of Southern California |
| Repository email | cisadmin@lib.usc.edu |
| Full text | 43 Methylbenzene aromatic signals emerged 8 s after the methanol pulse. Two hours after the methanol pulse, the methyl signals attributed to the methylbenzene decreased, and olefinic products were observed by GC analysis. The researchers attributed this to aging of the methylbenzenes to polycyclic aromatic hydrocarbons, as illustrated in Scheme 2.10. The researchers concluded methylbenzenes were the organic reaction centers that composed the hydrocarbon pool on HSAPO-34. To test their hypothesis, Haw and co-workers designed a double pulse study28 wherein methylbenzenes were generated by a single 20 μL pulse of 13C-methanol followed six minutes later by a second 20 μL pulse of natural abundance methanol. The first pulse showed very little methanol conversion with only 14% converted to olefinic products, a common result obtained during the induction period. The second pulse had 100% conversion of methanol, and the olefinic products had 13C incorporation consistent with a side-chain alkylation mechanism. Methylnaphthalenes were also observed to act as organic reaction centers on HSAPO-34 and they were more selective for the formation of ethylene, but they were overall less active as compared to methylbenzenes.29 With the identification of the hydrocarbon pool species, focus shifted to determining how olefins were produced from these aromatic species. Both a Paring mechanism and side-chain alkylation were proposed as potential routes for olefin generation. Haw and co-workers studied aromatic |
