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1
Introduction
Zeolites have a wide range of applications but are specifically
important in the field of heterogeneous catalysis. Zeolites and zeotypes can
act as solid acids, and a wide range of topologies allow for shape-selective
catalysis. An overview of zeolite and zeotype structure and commercial
application is presented in Chapter 1, specifically focusing on those used in
this research.
Methanol-to-olefins (MTO) catalysis is a process that yields plastic-quality
olefins from a feedstock of methanol over acid zeolite catalysts. The
mechanism for this reaction is an indirect hydrocarbon pool scheme, where
organic reaction centers provide a scaffold for methylation. Olefins are
generated either through elimination from an aromatic reaction center or
cracking of an olefinic reaction center. The types of organic reaction present
depend on the zeolite topology being used, with HSAPO-34 primarily
employing aromatic reaction centers and HZSM-5 olefinic reaction centers.
Chapter 2 discusses the MTO reaction and mechanism in further detail,
exploring past work that has shaped current understanding of the
mechanism.
Industrial-scale catalysis is primarily preformed in stainless-steel
reactors, which contain several oxide compounds known to catalyze
methanol oxidation to formaldehyde. There are many potential reactions
available to formaldehyde in the MTO environment; but it has not previously
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 12 |
| Contributing entity | University of Southern California |
| Repository email | cisadmin@lib.usc.edu |
| Full text | 1 Introduction Zeolites have a wide range of applications but are specifically important in the field of heterogeneous catalysis. Zeolites and zeotypes can act as solid acids, and a wide range of topologies allow for shape-selective catalysis. An overview of zeolite and zeotype structure and commercial application is presented in Chapter 1, specifically focusing on those used in this research. Methanol-to-olefins (MTO) catalysis is a process that yields plastic-quality olefins from a feedstock of methanol over acid zeolite catalysts. The mechanism for this reaction is an indirect hydrocarbon pool scheme, where organic reaction centers provide a scaffold for methylation. Olefins are generated either through elimination from an aromatic reaction center or cracking of an olefinic reaction center. The types of organic reaction present depend on the zeolite topology being used, with HSAPO-34 primarily employing aromatic reaction centers and HZSM-5 olefinic reaction centers. Chapter 2 discusses the MTO reaction and mechanism in further detail, exploring past work that has shaped current understanding of the mechanism. Industrial-scale catalysis is primarily preformed in stainless-steel reactors, which contain several oxide compounds known to catalyze methanol oxidation to formaldehyde. There are many potential reactions available to formaldehyde in the MTO environment; but it has not previously |
