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110 produced more C3 to C6 hydrocarbons and little ethylene. However, these results show that even a small amount of aldehyde combined with the methanol can cause large increases in ethylene selectivity, in this case doubling the ethylene to propene ratio to as compared to methanol alone under similar conversion. 4.4.3. Catalyst Deactivation with Aldehydes A catalyst lifetime study was conducted on HZSM-5 (Si/Al = 40) using a solution of methanol and 1,3,5-trioxane. The results are presented in Figure 4.7, with the corresponding product selectivity data shown in Table 4.7. After five minutes time on stream, methanol conversion was nearly full conversion, and the ethylene to propene ratio indicated equal molar production of the olefins. Aromatic content was the main component of the product selectivities with 37%. Propene and the C4 to C6 hydrocarbons had similar selectivities at 22% and 20% respectively. Ethylene had the lowest hydrocarbon selectivity at 17%. At 30 minutes time on stream, methanol conversion had dropped to 82% but the ethylene to propene ratio increased slightly to 1.4. Aromatic content was still the main component of the product selectivities, decreasing only 2% as compared with five minutes. Ethylene, propene, and the C4 to C6 hydrocarbons all had similar selectivities between 15 % and 17%, and all decreased in selectivity as compared to five minutes. The catalyst showed essentially complete deactivation after 60 minutes time
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 121 |
Contributing entity | University of Southern California |
Repository email | cisadmin@lib.usc.edu |
Full text | 110 produced more C3 to C6 hydrocarbons and little ethylene. However, these results show that even a small amount of aldehyde combined with the methanol can cause large increases in ethylene selectivity, in this case doubling the ethylene to propene ratio to as compared to methanol alone under similar conversion. 4.4.3. Catalyst Deactivation with Aldehydes A catalyst lifetime study was conducted on HZSM-5 (Si/Al = 40) using a solution of methanol and 1,3,5-trioxane. The results are presented in Figure 4.7, with the corresponding product selectivity data shown in Table 4.7. After five minutes time on stream, methanol conversion was nearly full conversion, and the ethylene to propene ratio indicated equal molar production of the olefins. Aromatic content was the main component of the product selectivities with 37%. Propene and the C4 to C6 hydrocarbons had similar selectivities at 22% and 20% respectively. Ethylene had the lowest hydrocarbon selectivity at 17%. At 30 minutes time on stream, methanol conversion had dropped to 82% but the ethylene to propene ratio increased slightly to 1.4. Aromatic content was still the main component of the product selectivities, decreasing only 2% as compared with five minutes. Ethylene, propene, and the C4 to C6 hydrocarbons all had similar selectivities between 15 % and 17%, and all decreased in selectivity as compared to five minutes. The catalyst showed essentially complete deactivation after 60 minutes time |