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4.2. Introduction
Methanol-to-olefin (MTO) catalysis1,2 on acidic zeolites represents a
key step in the conversion of natural gas to light olefins, and could
significantly impact future plastic production. The MTO process converts
inexpensive methanol to more desirable light olefins, such as ethylene and
propene, which are in high demand as starting materials for many varieties of
plastics. Currently, light olefins are produced as by-products in petroleum
refining.
The overall accepted mechanism for the MTO process is an indirect
hydrocarbon pool mechanism wherein organic reaction centers act as a
scaffold for reaction with methanol and olefins are produced via cracking.3,4
On HSAPO-34 and HBeta, the organic reaction centers have been well
characterized as methylbenzenes, with the most active species being penta-and
hexamethylbenzene in HSAPO-345 and the heptamethylbenzenium
cation6 in HBeta.
Recent work by Kolboe and co-workers 7,8,9 determined these same
species were not active in producing olefins in HZSM-5. In fact, the
researchers found mechanistic separation in the MTO olefinic products
through isotopic labeling studies. Ethylene had similar isotopic content as
the aromatic reaction centers, specifically di- and trimethylbenzenes, while
propene shared isotopic compositions with the C4 and C5 alkenes. The
researchers concluded separate mechanisms, thus different organic reaction
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 98 |
| Contributing entity | University of Southern California |
| Repository email | cisadmin@lib.usc.edu |
| Full text | 87 4.2. Introduction Methanol-to-olefin (MTO) catalysis1,2 on acidic zeolites represents a key step in the conversion of natural gas to light olefins, and could significantly impact future plastic production. The MTO process converts inexpensive methanol to more desirable light olefins, such as ethylene and propene, which are in high demand as starting materials for many varieties of plastics. Currently, light olefins are produced as by-products in petroleum refining. The overall accepted mechanism for the MTO process is an indirect hydrocarbon pool mechanism wherein organic reaction centers act as a scaffold for reaction with methanol and olefins are produced via cracking.3,4 On HSAPO-34 and HBeta, the organic reaction centers have been well characterized as methylbenzenes, with the most active species being penta-and hexamethylbenzene in HSAPO-345 and the heptamethylbenzenium cation6 in HBeta. Recent work by Kolboe and co-workers 7,8,9 determined these same species were not active in producing olefins in HZSM-5. In fact, the researchers found mechanistic separation in the MTO olefinic products through isotopic labeling studies. Ethylene had similar isotopic content as the aromatic reaction centers, specifically di- and trimethylbenzenes, while propene shared isotopic compositions with the C4 and C5 alkenes. The researchers concluded separate mechanisms, thus different organic reaction |
