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50
were then compared that observed with methanol alone to determine the
composition of the HZSM-5 hydrocarbon pool. Their results are summarized
in Figure 2.2.
The inherent ethylene to propene ratio observed in the methanol/ p-xylene
mixture was extrapolated to 1.3, a ratio in agreement with typical
methylbenzene hydrocarbon pool pathways. The other solutions and
methanol alone had a very different intrinsic ethylene to propene ratio,
approximately 0.3. As the ethylene to propene ratio of methanol alone was
more closely related to that of 2-methyl-1-butene and p-xylene, an olefinic
pool was determined to operate in HZSM-5. The researchers suggested this
pool formed from dimerization of olefins though, not homologation as
proposed by Kolboe and co-workers. Scheme 2.11 illustrates formation of
this olefinic pool as well as methylation and cracking that produces more C3-
C6 alkenes. Haw and co-workers also suggested the aromatic pool was
responsible for nearly all ethylene production, particularly at the lower
reaction temperatures employed in this study.
Scheme 2.11. Olefin Production in an Olefinic Pool Mechamism.
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 61 |
| Contributing entity | University of Southern California |
| Repository email | cisadmin@lib.usc.edu |
| Full text | 50 were then compared that observed with methanol alone to determine the composition of the HZSM-5 hydrocarbon pool. Their results are summarized in Figure 2.2. The inherent ethylene to propene ratio observed in the methanol/ p-xylene mixture was extrapolated to 1.3, a ratio in agreement with typical methylbenzene hydrocarbon pool pathways. The other solutions and methanol alone had a very different intrinsic ethylene to propene ratio, approximately 0.3. As the ethylene to propene ratio of methanol alone was more closely related to that of 2-methyl-1-butene and p-xylene, an olefinic pool was determined to operate in HZSM-5. The researchers suggested this pool formed from dimerization of olefins though, not homologation as proposed by Kolboe and co-workers. Scheme 2.11 illustrates formation of this olefinic pool as well as methylation and cracking that produces more C3- C6 alkenes. Haw and co-workers also suggested the aromatic pool was responsible for nearly all ethylene production, particularly at the lower reaction temperatures employed in this study. Scheme 2.11. Olefin Production in an Olefinic Pool Mechamism. |
