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93
Formaldehyde was introduced into the system in two forms: the
saturated solution of 37% in water and as 1,3,5-trioxane, a trimer of
formaldehyde, and the FID chromatograms for both are shown in Figure 4.1.
The methanol conversions for the methanol/formaldehyde and the
methanol/1,3,5-trioxane solutions were near identical, as were the product
selectivities. For this experiment, smaller catalyst bed was used (100 mg
versus 200 mg used in other experiments) to reduce the methanol
conversion so variances could more easily be identified.
More ethylene was observed in the presence of formaldehyde and
1,3,5-trioxane as compared to neat methanol as evidenced by the ten-fold
increase in the ethylene to propene ratio. This is congruent with results
previously discussed in Chapter 3. The drop in methanol conversion
observed compared to neat methanol is most likely due to one of the pool
species, the olefinic pool, being eliminated and converted into the aromatic.
Overall, these results justifying 1,3,5-trioxane as a valid alternative to the
37% solution of formaldehyde.
The benefit of using 1,3,5-trioxane over the saturated formaldehyde
solution is the elimination of water from the reaction, as well as the methanol
used as a stabilizing agent in the saturated solution. The methanol present
in the formaldehyde solution is an unknown quantity and would contribute to
methanol conversion. Previous studies show water can dealuminate the
catalyst through steaming11 and also increases ethylene selectivity.12
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 104 |
| Contributing entity | University of Southern California |
| Repository email | cisadmin@lib.usc.edu |
| Full text | 93 Formaldehyde was introduced into the system in two forms: the saturated solution of 37% in water and as 1,3,5-trioxane, a trimer of formaldehyde, and the FID chromatograms for both are shown in Figure 4.1. The methanol conversions for the methanol/formaldehyde and the methanol/1,3,5-trioxane solutions were near identical, as were the product selectivities. For this experiment, smaller catalyst bed was used (100 mg versus 200 mg used in other experiments) to reduce the methanol conversion so variances could more easily be identified. More ethylene was observed in the presence of formaldehyde and 1,3,5-trioxane as compared to neat methanol as evidenced by the ten-fold increase in the ethylene to propene ratio. This is congruent with results previously discussed in Chapter 3. The drop in methanol conversion observed compared to neat methanol is most likely due to one of the pool species, the olefinic pool, being eliminated and converted into the aromatic. Overall, these results justifying 1,3,5-trioxane as a valid alternative to the 37% solution of formaldehyde. The benefit of using 1,3,5-trioxane over the saturated formaldehyde solution is the elimination of water from the reaction, as well as the methanol used as a stabilizing agent in the saturated solution. The methanol present in the formaldehyde solution is an unknown quantity and would contribute to methanol conversion. Previous studies show water can dealuminate the catalyst through steaming11 and also increases ethylene selectivity.12 |
