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81 the catalysts treated with formaldehyde and dimethoxymethane, but were not found in the methanol baseline. These results indicate these oxygenates accelerate aromatic formation by generating butadiene, which, in turn, speeds deactivation of the catalyst. 3.4.5. In-situ Formaldehyde Generation from Methanol Formaldehyde has been shown to be deactivating, but its formation under MTO conditions has not been observed. Figure 3.6 depicts the formation of formaldehyde in an MTO study by inclusion of additional stainless steel tubing to the regular bench-top reactor system described previously. Methanol conversion data and product selectivities are presented in Table 3.4. The most notable result of this experiment was the increase in aromatic species observed upon the addition of stainless steel tubing. The overall aromatic selectivity nearly tripled with the added tubing, increasing from 10% on the unmodified reactor to 27% on the modified reactor. In addition, ethylene selectivity doubled on the modified reactor and the ethylene to propene ratio increased from 0.3 to 0.7. Collectively, the selectivity of the C4 to C6 alkenes roughly decreased by half on the modified reactor, from 38% to 24%. Alkane selectivity also decreased on the modified reactor but only slightly.
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 92 |
Contributing entity | University of Southern California |
Repository email | cisadmin@lib.usc.edu |
Full text | 81 the catalysts treated with formaldehyde and dimethoxymethane, but were not found in the methanol baseline. These results indicate these oxygenates accelerate aromatic formation by generating butadiene, which, in turn, speeds deactivation of the catalyst. 3.4.5. In-situ Formaldehyde Generation from Methanol Formaldehyde has been shown to be deactivating, but its formation under MTO conditions has not been observed. Figure 3.6 depicts the formation of formaldehyde in an MTO study by inclusion of additional stainless steel tubing to the regular bench-top reactor system described previously. Methanol conversion data and product selectivities are presented in Table 3.4. The most notable result of this experiment was the increase in aromatic species observed upon the addition of stainless steel tubing. The overall aromatic selectivity nearly tripled with the added tubing, increasing from 10% on the unmodified reactor to 27% on the modified reactor. In addition, ethylene selectivity doubled on the modified reactor and the ethylene to propene ratio increased from 0.3 to 0.7. Collectively, the selectivity of the C4 to C6 alkenes roughly decreased by half on the modified reactor, from 38% to 24%. Alkane selectivity also decreased on the modified reactor but only slightly. |