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82
As discussed previously, stainless steel tubing contains a metal oxide
coating to prevent rusting, some of which could catalyze formaldehyde
generation under the right conditions. Once formaldehyde is formed, it can
react with an olefin (with the exception of ethylene) and produce a diene. In
the acidic zeolite environment, these dienes are highly reactive, combining
with olefins or other dienes, resulting in aromatic formation.
Table 3.4. Product selectivities from Figure 3.6
Methanol on unmodified
reactor
Methanol on reactor
with 8’ S.S. coil
Methanol conversiona 100% 100%
Ethylene to propeneb 0.28 0.72
Mole Carbon Selectivities
Ethylene 5.9% 12.6%
Propene 31.7% 26.3%
Butenes 19.2% 14.7%
Pentenes 8.7% 5.4%
Hexenes 9.7% 4.1%
Alkanesc 13.6% 9.2%
Toluene 0.9% 1.7%
Dimethylbenzenes 4.0% 9.3%
Trimethylbenzenes 4.0% 12.0%
Tetramethylbenzenes 1.0% 3.9%
a Mole carbon conversion. b Molar ratio. c Includes methane, isobutene, and
isopentane
3.5. Conclusion
In the MTO environment, formaldehyde will react with olefins to
produce dienes through a Prins reaction. Dienes have a variety of potential
reactions with olefins or other unsaturates, and the products of these
reactions lead to the formation of aromatic species. There is both a
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 93 |
| Contributing entity | University of Southern California |
| Repository email | cisadmin@lib.usc.edu |
| Full text | 82 As discussed previously, stainless steel tubing contains a metal oxide coating to prevent rusting, some of which could catalyze formaldehyde generation under the right conditions. Once formaldehyde is formed, it can react with an olefin (with the exception of ethylene) and produce a diene. In the acidic zeolite environment, these dienes are highly reactive, combining with olefins or other dienes, resulting in aromatic formation. Table 3.4. Product selectivities from Figure 3.6 Methanol on unmodified reactor Methanol on reactor with 8’ S.S. coil Methanol conversiona 100% 100% Ethylene to propeneb 0.28 0.72 Mole Carbon Selectivities Ethylene 5.9% 12.6% Propene 31.7% 26.3% Butenes 19.2% 14.7% Pentenes 8.7% 5.4% Hexenes 9.7% 4.1% Alkanesc 13.6% 9.2% Toluene 0.9% 1.7% Dimethylbenzenes 4.0% 9.3% Trimethylbenzenes 4.0% 12.0% Tetramethylbenzenes 1.0% 3.9% a Mole carbon conversion. b Molar ratio. c Includes methane, isobutene, and isopentane 3.5. Conclusion In the MTO environment, formaldehyde will react with olefins to produce dienes through a Prins reaction. Dienes have a variety of potential reactions with olefins or other unsaturates, and the products of these reactions lead to the formation of aromatic species. There is both a |
