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29
synthetic gasoline production was discontinued though, due mainly to the
drop in gasoline prices, but also out of concern for the environment.
Aromatic species are abundant in the synthetic gasoline produced via MTG,
and gasoline technology had moved to eliminate aromatics from the fuel to
create a cleaner burning fuel source.
2.4. Methanol-to-Olefin Catalysis
The methanol-to-olefin (MTO) process was developed through a
refinement of MTG. Looking back at Scheme 2.1, MTO favors the products
propene and ethylene as opposed to larger olefins like pentenes and
aromatics. To accomplish this feat, the reaction conditions are altered and
the catalyst is switched from the aluminosilicate HZSM-5 to the silico-aluminophosphate
HSAPO-34. The principle reason for the shift in product
selectivity is due to the topology of HSAPO-34. HSAPO-34 has small pores,
preventing the diffusion branched hydrocarbons and aromatics. Another
contributing factor is the weaker acid strength of HSAPO-34, which limits the
possible side reactions of olefinic products. Figure 2.1 shows MTO product
selectivities on HZSM-5 and HSAPO-34 at 100% methanol conversion.
2.5. Direct Mechanisms in MTO Catalysis
The fundamental question of MTO (and MTG) catalysis in its early
years was regarding the formation the first carbon-carbon bond, which
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 40 |
| Contributing entity | University of Southern California |
| Repository email | cisadmin@lib.usc.edu |
| Full text | 29 synthetic gasoline production was discontinued though, due mainly to the drop in gasoline prices, but also out of concern for the environment. Aromatic species are abundant in the synthetic gasoline produced via MTG, and gasoline technology had moved to eliminate aromatics from the fuel to create a cleaner burning fuel source. 2.4. Methanol-to-Olefin Catalysis The methanol-to-olefin (MTO) process was developed through a refinement of MTG. Looking back at Scheme 2.1, MTO favors the products propene and ethylene as opposed to larger olefins like pentenes and aromatics. To accomplish this feat, the reaction conditions are altered and the catalyst is switched from the aluminosilicate HZSM-5 to the silico-aluminophosphate HSAPO-34. The principle reason for the shift in product selectivity is due to the topology of HSAPO-34. HSAPO-34 has small pores, preventing the diffusion branched hydrocarbons and aromatics. Another contributing factor is the weaker acid strength of HSAPO-34, which limits the possible side reactions of olefinic products. Figure 2.1 shows MTO product selectivities on HZSM-5 and HSAPO-34 at 100% methanol conversion. 2.5. Direct Mechanisms in MTO Catalysis The fundamental question of MTO (and MTG) catalysis in its early years was regarding the formation the first carbon-carbon bond, which |
