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65
3.4 Results and Discussion
3.4.1. Prins Reaction of Formaldehyde and Propene
The FID chromatograms from the reaction of formaldehyde with
propene are shown in Figure 3.1. Butenes were the dominant product after
five minutes time on stream, with nearly 80% product selectivity. Small
amounts of ethylene and pentenes were also observed; however, no
alcohols or other unusual MTO products were seen. After 10 minutes of
flowing propene and formaldehyde, ethylene became the main product,
increasing selectivity from 11% at five minutes to almost 50% at 10 minutes.
Butene selectivity was still high at this time but pentene selectivity decreased
by half with less than 5% selectivity at 10 minutes. A new product,
butadiene, was also observed but the selectivity was low, similar to that of
the pentenes. From 15 to 25 minutes time on stream, the ethylene selectivity
increased to nearly 60%. Butene and pentene selectivity decreased over
these times. More butadiene was observed, doubling from 10 to 15 minutes
and increasing slightly at 20 and 25 minutes. At 20 minutes, small amounts
of methanol and dimethyl ether (DME) were observed, and increased
consistently with additional time on stream. At 75 minutes, only small
amounts of ethylene, butanes, and pentenes were observed. Butadiene was
still observed in the product stream, but the selectivity decreased significantly
compared to the maximum selectivity seen at 25 minutes. Methanol and
DME were the main products after 75 minutes on stream.
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 76 |
| Contributing entity | University of Southern California |
| Repository email | cisadmin@lib.usc.edu |
| Full text | 65 3.4 Results and Discussion 3.4.1. Prins Reaction of Formaldehyde and Propene The FID chromatograms from the reaction of formaldehyde with propene are shown in Figure 3.1. Butenes were the dominant product after five minutes time on stream, with nearly 80% product selectivity. Small amounts of ethylene and pentenes were also observed; however, no alcohols or other unusual MTO products were seen. After 10 minutes of flowing propene and formaldehyde, ethylene became the main product, increasing selectivity from 11% at five minutes to almost 50% at 10 minutes. Butene selectivity was still high at this time but pentene selectivity decreased by half with less than 5% selectivity at 10 minutes. A new product, butadiene, was also observed but the selectivity was low, similar to that of the pentenes. From 15 to 25 minutes time on stream, the ethylene selectivity increased to nearly 60%. Butene and pentene selectivity decreased over these times. More butadiene was observed, doubling from 10 to 15 minutes and increasing slightly at 20 and 25 minutes. At 20 minutes, small amounts of methanol and dimethyl ether (DME) were observed, and increased consistently with additional time on stream. At 75 minutes, only small amounts of ethylene, butanes, and pentenes were observed. Butadiene was still observed in the product stream, but the selectivity decreased significantly compared to the maximum selectivity seen at 25 minutes. Methanol and DME were the main products after 75 minutes on stream. |
