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94
Converting the olefinic pool to the aromatic pool would also increase
ethylene selectivity, thus the presence of water conflates the effects of the
Prins reaction and must be eliminated. The best alternative is 1,3,5-trioxane,
as it will readily decompose into three molecules of formaldehyde under the
reactor conditions.
One measure of used to compare the effect of various reagents on the
MTO product selectivity is the molar ethylene to propene ratio. In Chapter 3,
butadiene was generated from the reaction of formaldehyde with propene;
hence, comparison of the ethylene to propene ratio when employing
formaldehyde is artificially skewed by the consumption of some of the
propene. In addition, propene is still a valuable MTO product, so an
aldehyde that is less reactive would be preferable.
The FID chromatograms of several aldehyde alternatives are
compared to formaldehyde in Figure 4.2, and the relative product selectivities
are shown in Table 4.2. The methanol conversion is corrected to account for
the aldehyde additives and is nearly 100% in each case. There is a gradual
decrease in the ethylene to propene ratio as the carbon backbone of the
aldehyde lengthens. The relative selectivity for ethylene also deceases with
the lengthening carbon backbone, as does the selectivity for aromatics.
Additionally, more C4-C6 species are observed.
These results are consistent with the decreasing activity of the
aromatic pool and the reassertion of the HZSM-5 native pool. As the carbon
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 105 |
| Contributing entity | University of Southern California |
| Repository email | cisadmin@lib.usc.edu |
| Full text | 94 Converting the olefinic pool to the aromatic pool would also increase ethylene selectivity, thus the presence of water conflates the effects of the Prins reaction and must be eliminated. The best alternative is 1,3,5-trioxane, as it will readily decompose into three molecules of formaldehyde under the reactor conditions. One measure of used to compare the effect of various reagents on the MTO product selectivity is the molar ethylene to propene ratio. In Chapter 3, butadiene was generated from the reaction of formaldehyde with propene; hence, comparison of the ethylene to propene ratio when employing formaldehyde is artificially skewed by the consumption of some of the propene. In addition, propene is still a valuable MTO product, so an aldehyde that is less reactive would be preferable. The FID chromatograms of several aldehyde alternatives are compared to formaldehyde in Figure 4.2, and the relative product selectivities are shown in Table 4.2. The methanol conversion is corrected to account for the aldehyde additives and is nearly 100% in each case. There is a gradual decrease in the ethylene to propene ratio as the carbon backbone of the aldehyde lengthens. The relative selectivity for ethylene also deceases with the lengthening carbon backbone, as does the selectivity for aromatics. Additionally, more C4-C6 species are observed. These results are consistent with the decreasing activity of the aromatic pool and the reassertion of the HZSM-5 native pool. As the carbon |
