Increasing prices of crude oil derived transportation fuels ascended the
researches on seeking alternative fuels, in last decades. Moreover, the increasing rate
of global warming, because of high greenhouse gas emissions initiated new research
for environment-friendly clean alternative fuels. Due to its low NOx emission, good
burning characteristics and high cetane number, dimethyl ether (DME) attracted
major attention as a transportation fuel alternative. Two possible pathways have been
proposed for DME production. One of these pathways is DME synthesis through
conventional methanol dehydration. More recently, direct DME synthesis in a single
step has attracted significant attention of researchers and fuel producers. Catalysts
having two active sites are required for direct DME synthesis from synthesis gas.
The aim of this work was to synthesize novel bifunctional direct DME
synthesis catalysts and test their activity in a high pressure fixed bed flow reactor.
Bifunctional mesoporous catalysts were synthesized by using one-pot hydrothermal
synthesis, impregnation and physical mixing methods. These materials were characterized by XRD, EDS, SEM, N2 physisorption and diffuse reflectance FT-IR
(DRIFTS) techniques.
Characterization results of the catalysts synthesized by one-pot hydrothermal
synthesis procedures in basic and acidic routes showed that pH value of the synthesis
solution was highly effective on the final physical structure and chemical nature of
the catalysts. Increase in the pH value promoted the incorporation of Cu, Zn and Al
into the mesoporous MCM-41 structure. Also, effects of Na2CO3 addition on the
catalyst structure during the hydrothermal synthesis procedure were investigated.
The characterization results showed that metals were incorporated into the catalyst
structure successfully. However, surface area results showed that loaded metals
blocked the pores of MCM-41 and decreased the surface area of the catalysts. Effects
of zirconium (Zr) metal with different weight ratios were also investigated. Results
showed that Zr loading increased the surface area of the catalyst.
A high pressure fixed bed flow reactor was built and the catalyst testing
experiments were performed between the temperature range of 200-400° / C, at 50
bars. The activity results of the catalyst synthesized by impregnation method showed
that no DME was formed over this catalyst / however it showed promising results for
production of methanol and ethanol. Selectivity values of these alcohols were
between 0.35 and 0.2. Formation of methane and CO2 indicated the occurrence of
reverse dry reforming reaction. Incorporation of Zr into the catalyst structure at
neutral synthesis condition caused significant activity enhancement, giving CO
conversion values of about 40% at 400° / C. Product distribution obtained with this
catalyst indicated the formation of DME, ethanol, methanol as well as CH4 and CO2.
Highest DME selectivity (60%) was observed with the catalyst prepared by physical
mixing of commercial methanol reforming catalyst with silicotungstic acid
incorporated methanol dehydration catalyst having W/Si ratio of 0.4.
| Identifer | oai:union.ndltd.org:METU/oai:etd.lib.metu.edu.tr:http://etd.lib.metu.edu.tr/upload/3/12611490/index.pdf |
| Date | 01 February 2010 |
| Creators | Arinan, Ayca |
| Contributors | Dogu, Timur |
| Publisher | METU |
| Source Sets | Middle East Technical Univ. |
| Language | English |
| Detected Language | English |
| Type | M.S. Thesis |
| Format | text/pdf |
| Rights | To liberate the content for public access |
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