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4
In this reactor set-up, high purity helium is used as a carrier gas and it
is further purified by an Alltech All-Pure Helium Purifier rated at less than
three parts per billion non-methane hydrocarbons. The flow rate of helium is
controlled using an MKS Mass-flo controller, and flow rates are stated in
standard cubic centimeters per minute (sccm). The helium carrier gas
travels through a pre-heating zone, where quartz pieces heat the gas to a
minimum of 473 K using an Omegalux heating tape. A short transfer line
connects the pre-heating zone to a Valco six-port 1/16 inch air-actuated
valve, which is used to introduce small amounts of reagents in pulse
experiments. The valve housing is purged with dry nitrogen to prevent air
from entering the system through the rotor assembly.
Further downstream is a Swagelok T-junction which allows for larger
quantities of reagents to be introduced into the system in a continuous flow.
A Harvard Apparatus PHD 2000 syringe pump is used to regulate the
reagent flow in these types of experiments. Reagent flow rates are
expressed in terms of reagent mass versus catalyst mass per unit time,
known as weight hourly space velocity (WHSV).
The actual reactor in this set-up is a vertical 1/4 inch quartz tube,
which houses the catalyst. Quartz pieces surround the catalyst to regulate
the temperature and quartz wool is used to separate the catalyst from the
quartz pieces as well as support all components within the reactor. Two
Swagelok 1/8 inch H-Series valves are used to isolate the reactor from
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 15 |
| Contributing entity | University of Southern California |
| Repository email | cisadmin@lib.usc.edu |
| Full text | 4 In this reactor set-up, high purity helium is used as a carrier gas and it is further purified by an Alltech All-Pure Helium Purifier rated at less than three parts per billion non-methane hydrocarbons. The flow rate of helium is controlled using an MKS Mass-flo controller, and flow rates are stated in standard cubic centimeters per minute (sccm). The helium carrier gas travels through a pre-heating zone, where quartz pieces heat the gas to a minimum of 473 K using an Omegalux heating tape. A short transfer line connects the pre-heating zone to a Valco six-port 1/16 inch air-actuated valve, which is used to introduce small amounts of reagents in pulse experiments. The valve housing is purged with dry nitrogen to prevent air from entering the system through the rotor assembly. Further downstream is a Swagelok T-junction which allows for larger quantities of reagents to be introduced into the system in a continuous flow. A Harvard Apparatus PHD 2000 syringe pump is used to regulate the reagent flow in these types of experiments. Reagent flow rates are expressed in terms of reagent mass versus catalyst mass per unit time, known as weight hourly space velocity (WHSV). The actual reactor in this set-up is a vertical 1/4 inch quartz tube, which houses the catalyst. Quartz pieces surround the catalyst to regulate the temperature and quartz wool is used to separate the catalyst from the quartz pieces as well as support all components within the reactor. Two Swagelok 1/8 inch H-Series valves are used to isolate the reactor from |
