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44
methylation reactions in 200230 with the objective of differentiating between
these two pathways. The large pore aluminosilicate H-Beta was used in the
study due to topological restrictions of HZSM-5 and HSAPO-34. The
researchers examined the reaction of hexamethylbenzene alone and in the
presence of water on H-Beta, as well as solutions of 13C-methanol with the
aromatics toluene (5:1 methanol:toluene) and 1,2,4-trimethylbenzene (3:1
methanol:1,2,4-TMB) via GC-MS and compared the amount of olefins
produced in each case. They observed a greater amount of olefins produced
when in the solutions of methanol with aromatics than in the reactions of
hexamethylbenzene, results consistent with a side-chain alkylation
mechanism. If a Paring reaction were the dominant mechanism, similar
amounts of olefins would have been observed with hexamethylbenzene and
the solutions of aromatics and methanol. The following year, theoretical
calculations were published supporting the side-chain alkylation mechanism
in MTO catalysis.31
2.7.2. Support for the Hydrocarbon Pool Mechanism
After the works of Langner, Mole, and Kolboe, the idea of an indirect
mechanism for MTH catalysis became more favored then the direct
mechanisms. However, significant theoretical and experimental evidence for
these indirect mechanisms was not developed until nearly a decade later.
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 55 |
| Contributing entity | University of Southern California |
| Repository email | cisadmin@lib.usc.edu |
| Full text | 44 methylation reactions in 200230 with the objective of differentiating between these two pathways. The large pore aluminosilicate H-Beta was used in the study due to topological restrictions of HZSM-5 and HSAPO-34. The researchers examined the reaction of hexamethylbenzene alone and in the presence of water on H-Beta, as well as solutions of 13C-methanol with the aromatics toluene (5:1 methanol:toluene) and 1,2,4-trimethylbenzene (3:1 methanol:1,2,4-TMB) via GC-MS and compared the amount of olefins produced in each case. They observed a greater amount of olefins produced when in the solutions of methanol with aromatics than in the reactions of hexamethylbenzene, results consistent with a side-chain alkylation mechanism. If a Paring reaction were the dominant mechanism, similar amounts of olefins would have been observed with hexamethylbenzene and the solutions of aromatics and methanol. The following year, theoretical calculations were published supporting the side-chain alkylation mechanism in MTO catalysis.31 2.7.2. Support for the Hydrocarbon Pool Mechanism After the works of Langner, Mole, and Kolboe, the idea of an indirect mechanism for MTH catalysis became more favored then the direct mechanisms. However, significant theoretical and experimental evidence for these indirect mechanisms was not developed until nearly a decade later. |
