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114
After five minutes time on stream, the H-Ferrierite catalyst was fully
deactivated, converting only 3% of the methanol. The ethylene to propene
ratio was quite high at 2.9 but these olefins constituted less than 1% of the
product selectivities combined. The only appreciable amount of any product
was methane, which had a selectivity of 2%, in agreement with previous work
showing methane production increased zeolite deactivation.14 The FER
topology of H-Ferrierite readily deactivated, most likely due to larger aromatic
species blocking the smaller 8 T-atom channel. In addition, the Ferrierite
used had a high acid site density, which allowed rapid conversion of the
methanol to the large aromatic species that coked the catalyst.
For H-Beta, methanol conversion was 46% after five minutes time on stream,
indicating advanced deactivation. The ethylene to propene ratio was 1.4.
Aromatic species, mostly penta- and hexamethylbenzene, comprised the
main component of the product selectivities at 20%. Propene and ethylene
accounted for 11% and 10% of the product selectivities, respectively, while
the C4 to C6 hydrocarbons had the lowest selectivity at 7%. The Beta
topology is a fairly large pore size and allows diffusion of the large
methylbenzenes, as evidenced by the large amounts of penta- and
hexamethylbenzene shown in Figure 4.8. However, the smaller channel
system of Beta has approximately the same diameter as ZSM-5, which would
only permit diffusion of smaller than 1,2,4,5-tetramethylbenzene. Larger
aromatics could form at the intersections with the larger channel system and
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 125 |
| Contributing entity | University of Southern California |
| Repository email | cisadmin@lib.usc.edu |
| Full text | 114 After five minutes time on stream, the H-Ferrierite catalyst was fully deactivated, converting only 3% of the methanol. The ethylene to propene ratio was quite high at 2.9 but these olefins constituted less than 1% of the product selectivities combined. The only appreciable amount of any product was methane, which had a selectivity of 2%, in agreement with previous work showing methane production increased zeolite deactivation.14 The FER topology of H-Ferrierite readily deactivated, most likely due to larger aromatic species blocking the smaller 8 T-atom channel. In addition, the Ferrierite used had a high acid site density, which allowed rapid conversion of the methanol to the large aromatic species that coked the catalyst. For H-Beta, methanol conversion was 46% after five minutes time on stream, indicating advanced deactivation. The ethylene to propene ratio was 1.4. Aromatic species, mostly penta- and hexamethylbenzene, comprised the main component of the product selectivities at 20%. Propene and ethylene accounted for 11% and 10% of the product selectivities, respectively, while the C4 to C6 hydrocarbons had the lowest selectivity at 7%. The Beta topology is a fairly large pore size and allows diffusion of the large methylbenzenes, as evidenced by the large amounts of penta- and hexamethylbenzene shown in Figure 4.8. However, the smaller channel system of Beta has approximately the same diameter as ZSM-5, which would only permit diffusion of smaller than 1,2,4,5-tetramethylbenzene. Larger aromatics could form at the intersections with the larger channel system and |
