Publication: Research › Ph.d. thesis – Annual report year: 2010
The main focus of this thesis is zeolite catalyzed conversion of oxygenates to hydrocarbon fuels and
chemicals. Furthermore, conversion of ethane to higher hydrocarbons has also been studied.
After a brief introduction to the concept of “the methanol economy” in the first chapter, the second
chapter is a literature study of Mobil’s “methanol to hydrocarbons” (MTH) process, giving an overview
of the history of the process, the nature of the employed catalysts, and the reaction mechanism.
In the third chapter, a series of experiments concerning co conversion of ethane and methanol over a
commercial H-ZSM-5 zeolite impregnated with gallium and/or molybdenum is described. The object was
to investigate if the presence of methanol in the feed could enhance the conversion of ethane, but in all
cases the opposite is observed; the presence of methanol actually suppresses the conversion of ethane.
This suppression of ethane conversion is most likely due to simple composition for the active sites.
Isotopic labeling studies performed with 13C labeled methanol and unlabeled ethane showed that in the
very first minutes of the reaction, large amounts of carbon atoms from ethane are incorporated into the
products. This observation is attributed to a stoichiometric reaction between ethane and the metal
oxide species in the catalyst, leading to the oxidation of ethane to ethene, which is readily converted
and incorporated into the products.
Conversion of methanol, ethanol, 2-propanol, and 1 butanol to hydrocarbons over various zeolite
catalysts is studied in Chapter 4. When 2-propanol or 1-butanol is converted over H-ZSM-5, the total
conversion capacities of the catalyst are more than 25 times higher than for conversion of methanol and
ethanol. Furthermore, for conversion of C3+ alcohols, the selectivity shifts during the experiment, and
after around one third of the total run time, the product mixture consists almost exclusively of alkenes,
which is in stark contrast to conversion of methanol and ethanol where the catalyst produces large
amounts of aromatics until full deactivation. When zeolite H Beta is employed, the conversion capacities
for all four alcohols are markedly lower than for H-ZSM-5, and H Beta has higher conversion capacity for
methanol than the other alcohols. Furthermore, conventional and mesoporous H Ga MFI was employed
in the conversion of methanol and 2 propanol. These catalysts showed a lower selectivity towards
aromatics than H-ZSM-5 and the mesoporous H-Ga-MFI deactivated extremely slowly during the
conversion of 2-propanol and only very small amounts of coke were deposited on the gallium based
zeolites compared to H-ZSM-5.
In the fifth chapter the direct zeolite catalyzed production of hydrocarbons from other oxygenates such
as glycerol, methyl lactate, and acetic acid is studied. In general, very fast deactivation due to coke
deposition is observed, but dilution of the reactants in methanol has a distinct positive effect on this,
and reasonable conversion capacities are achieved in this way. The incorporation of the carbon atoms
from the oxygenates into the hydrocarbon products was confirmed by isotopic labeling experiments.
More than 25 different oxygenates are converted over H-ZSM-5 as 10 % solutions in methanol, and the
effect of the H/C atomic ratio of the dehydrated reaction mixture and the specific functional groups in
the reactant on the catalyst lifetime, product selectivity, and formation of coke is addressed.
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