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106
Table 4.5. Mole carbon product selectivities for Figure 4.5.
623 K 648 K 673 K
Methanol
conversiona 84% 86% 97%
Ethylene to
Propeneb 1.9 1.7 1.1
Mole Carbon Selectivities
Ethylene 28% 25% 20%
Propene 22% 22% 28%
C4-C6
c 16% 18% 24%
Aromaticsd 23% 24% 24%
MeOH,
DMEe 12% 10% 4%
a Mole carbon conversion. b Molar ratio. c Includes C4 to C6 alkanes and
alkenes. d Includes benzene, toluene, and di- to tetramethylbenzenes. e Sum
of methanol and dimethyl ether product selectivities.
The standard temperature for MTO in this contribution is 648 K, but
industrially MTO is often carried out at higher temperatures. Typically,
increasing temperature results in a higher ethylene to propene ratio on
HZSM-5; however, increasing the temperature in the presence of
acetaldehyde has the opposite effect, decreasing the ethylene to propene
ratio. There is a higher conversion of methanol at the elevated temperature,
thus more organic reaction centers are being generated. As previously
proposed, the decrease in the ethylene to propene ratio may be due to 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 117 |
| Contributing entity | University of Southern California |
| Repository email | cisadmin@lib.usc.edu |
| Full text | 106 Table 4.5. Mole carbon product selectivities for Figure 4.5. 623 K 648 K 673 K Methanol conversiona 84% 86% 97% Ethylene to Propeneb 1.9 1.7 1.1 Mole Carbon Selectivities Ethylene 28% 25% 20% Propene 22% 22% 28% C4-C6 c 16% 18% 24% Aromaticsd 23% 24% 24% MeOH, DMEe 12% 10% 4% a Mole carbon conversion. b Molar ratio. c Includes C4 to C6 alkanes and alkenes. d Includes benzene, toluene, and di- to tetramethylbenzenes. e Sum of methanol and dimethyl ether product selectivities. The standard temperature for MTO in this contribution is 648 K, but industrially MTO is often carried out at higher temperatures. Typically, increasing temperature results in a higher ethylene to propene ratio on HZSM-5; however, increasing the temperature in the presence of acetaldehyde has the opposite effect, decreasing the ethylene to propene ratio. There is a higher conversion of methanol at the elevated temperature, thus more organic reaction centers are being generated. As previously proposed, the decrease in the ethylene to propene ratio may be due to a |
