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100
achieved by isomerization of the oxygenate to the aldehyde, but the
mechanism is not investigated further in this study. Previous, it was
suggested that an undesirable alkene could be converted to an aldehyde
then recycled into the reactor. This experiment suggests the undesirable
alkene can be converted into any oxygenate isomeric to an aldehyde and
recycled into the reactor resulting in an impact on the amount of ethylene
produced.
4.4.2. Effect of Acid Site Density and Temperature on Ethylene
Selectivity
Knowing aldehydes are able boost ethylene production, it is
interesting to investigate to what extent ethylene selectivity can be increased.
First, the effect of acid site density on the conversion of a methanol-acetaldehyde
solution is investigated using HZSM-5 (Si/Al = 40) and HZSM-5
(Si/Al = 140). In addition, the acid site density of HZSM-5 (Si/Al = 140) is
further decreased by steaming the zeolite prior to catalysis. The FID
chromatograms depicting these results are shown in Figure 4.4, with the
respective product selectivities shown in Table 4.4.
HZSM-5 (Si/Al = 40) has the highest acid site density (0.406 mmol of
acid sites per gram of catalyst) and, under these reaction conditions, it had
nearly 100% methanol conversion. The ethylene to propene ratio was
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 111 |
| Contributing entity | University of Southern California |
| Repository email | cisadmin@lib.usc.edu |
| Full text | 100 achieved by isomerization of the oxygenate to the aldehyde, but the mechanism is not investigated further in this study. Previous, it was suggested that an undesirable alkene could be converted to an aldehyde then recycled into the reactor. This experiment suggests the undesirable alkene can be converted into any oxygenate isomeric to an aldehyde and recycled into the reactor resulting in an impact on the amount of ethylene produced. 4.4.2. Effect of Acid Site Density and Temperature on Ethylene Selectivity Knowing aldehydes are able boost ethylene production, it is interesting to investigate to what extent ethylene selectivity can be increased. First, the effect of acid site density on the conversion of a methanol-acetaldehyde solution is investigated using HZSM-5 (Si/Al = 40) and HZSM-5 (Si/Al = 140). In addition, the acid site density of HZSM-5 (Si/Al = 140) is further decreased by steaming the zeolite prior to catalysis. The FID chromatograms depicting these results are shown in Figure 4.4, with the respective product selectivities shown in Table 4.4. HZSM-5 (Si/Al = 40) has the highest acid site density (0.406 mmol of acid sites per gram of catalyst) and, under these reaction conditions, it had nearly 100% methanol conversion. The ethylene to propene ratio was |
