<p></p><p>Biomass and shale gas have been proposed as alternate
sources of liquid hydrocarbon fuels. Traditional petroleum refining, however,
is not capable of directly converting either the highly oxygenated molecular
structure of lignocellulosic biomass or the low molecular weight alkanes of
shale gas into liquid fuels. In this work, we investigate two processes to
generate fuels by upgrading low molecular weight species present in biomass
pyrolysis vapors and in shale gas via carbon-carbon coupling reactions of low
molecular weight species present in biomass pyrolysis vapors and shale gas. </p>
<p>In the first process, fast pyrolysis and hydrodeoxygenation
are used to convert woody biomass into hydrocarbons. However, 22% of the carbon
in this process forms C<sub>1</sub>-C<sub>3</sub> species which are unsuitable
for use as liquid fuels. Aldol condensation has been proposed as a means of leveraging
carbonyl groups present in the pyrolysis product distribution prior to
hydrodeoxygenation in order to couple low molecular weight species such as
glycolaldehyde to transform the C<sub>1</sub>-C<sub>3</sub> fraction into C<sub>4+</sub>
species. We demonstrate that aldol condensation of fast pyrolysis vapors
results in a large (10%) reduction in carbon yield to C<sub>6</sub> species and
only a small (5%) reduction in carbon yield to C<sub>1</sub>-C<sub>3</sub>
species to form C<sub>7+</sub> products, suggesting that higher molecular
weight species undergo significant reaction over the aldol condensation
catalyst. We demonstrate a pathway by which levoglucosan can be converted into
levoglucosenone, which then forms C<sub>7+</sub> species through self-aldol condensation
and condensation with light oxygenates. </p>
<p>In the second process, light olefins in shale gas,
consisting primarily of ethane and propane, are dehydrogenated and oligomerized
into higher molecular weight species. Ni cation sites exchanged onto microporous
materials catalyze ethene oligomerization to butenes and heavier oligomers, but
also undergo rapid deactivation. The use of mesoporous supports has been
reported in the literature to alleviate deactivation in regimes of high ethene
pressures and low temperatures that cause capillary condensation of ethene
within mesoporous voids. Here, we reproduce prior literature findings on
mesoporous Ni-MCM-41 and report that, in sharp contrast, reaction conditions
that nominally correspond to ethene capillary condensation in microporous
Ni-Beta or Ni-FAU zeolites do not mitigate deactivation, likely because
confinement within microporous voids restricts the formation of condensed
phases of ethene <a>that are effective at solvating and
desorbing heavier intermediates that are precursors to deactivation</a>.
Deactivation rates are found to transition from a first-order to a second-order
dependence on Ni site density in Ni-FAU zeolites with increasing ethene
pressure, suggesting a transition in the dominant deactivation mechanism
involving a single Ni site to one involving two Ni sites, reminiscent of the
effects of increasing H<sub>2</sub> pressure on changing the kinetic order of
deactivation in our prior work on Ni-Beta zeolites.</p><br><p></p>
| Identifer | oai:union.ndltd.org:purdue.edu/oai:figshare.com:article/17152895 |
| Date | 19 December 2021 |
| Creators | Richard S. Caulkins (5930567) |
| Source Sets | Purdue University |
| Detected Language | English |
| Type | Text, Thesis |
| Rights | CC BY 4.0 |
| Relation | https://figshare.com/articles/thesis/Catalysis_of_Carbon-Carbon_Coupling_Reactions_for_the_Formation_of_Liquid_Hydrocarbon_Fuels_from_Biomass_and_Shale_Gas_Resources/17152895 |
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