Page 78 |
Save page Remove page | Previous | 78 of 139 | Next |
|
small (250x250 max)
medium (500x500 max)
Large (1000x1000 max)
Extra Large
large ( > 500x500)
Full Resolution
All (PDF)
|
This page
All
|
67
At 20 minutes time on stream, methanol and DME were observed in
the reactor effluent and increased in selectivity throughout the remainder of
the experiment. The formaldehyde used in this study contained methanol as
a stabilizing agent to prevent polymerization thus methanol and DME were
not actual products of the reaction between propene and formaldehyde.
They were more like impurities in this case, but were included in the product
selectivity to demonstrate catalyst activity: the more methanol and DME in
the reactor effluent, the more deactivated the catalyst. The flow rate of the
methanol was 0.025-0.038 mL / hr, which corresponded to WHSVMeOH= 0.20
–0.30 hr-1. In a standard MTO experiment, the methanol flow rate was
between WHSV= 4 hr-1 and WHSV= 8 hr-1; thus the contribution of methanol
conversion to the overall product selectivity would be small but not negligible.
As previously discussed, the typical products of a Prins reaction were
alcohols, specifically diols or allylic alcohols. No alcohol other than methanol
was observed in the products from the reaction of propene and formaldehyde
on HSAPO-34; instead, butadiene was observed. An alcohol, be it a diol or
an allylic alcohol, produced in this acidic environment would be readily
dehydrated, the product of which would be a diene. Thus butadiene
formation was determined to occur through an acid-catalyzed dehydration as
it would be facile in the acidic zeolite environment.
Scheme 3.1 illustrated the mechanism of diene generation via the
Prins reaction. The first step (a) of this reaction was the protonation of
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 78 |
| Contributing entity | University of Southern California |
| Repository email | cisadmin@lib.usc.edu |
| Full text | 67 At 20 minutes time on stream, methanol and DME were observed in the reactor effluent and increased in selectivity throughout the remainder of the experiment. The formaldehyde used in this study contained methanol as a stabilizing agent to prevent polymerization thus methanol and DME were not actual products of the reaction between propene and formaldehyde. They were more like impurities in this case, but were included in the product selectivity to demonstrate catalyst activity: the more methanol and DME in the reactor effluent, the more deactivated the catalyst. The flow rate of the methanol was 0.025-0.038 mL / hr, which corresponded to WHSVMeOH= 0.20 –0.30 hr-1. In a standard MTO experiment, the methanol flow rate was between WHSV= 4 hr-1 and WHSV= 8 hr-1; thus the contribution of methanol conversion to the overall product selectivity would be small but not negligible. As previously discussed, the typical products of a Prins reaction were alcohols, specifically diols or allylic alcohols. No alcohol other than methanol was observed in the products from the reaction of propene and formaldehyde on HSAPO-34; instead, butadiene was observed. An alcohol, be it a diol or an allylic alcohol, produced in this acidic environment would be readily dehydrated, the product of which would be a diene. Thus butadiene formation was determined to occur through an acid-catalyzed dehydration as it would be facile in the acidic zeolite environment. Scheme 3.1 illustrated the mechanism of diene generation via the Prins reaction. The first step (a) of this reaction was the protonation of |
