(441c) Steam Reforming of Ethanol/Gasoline Mixtures: Deactivation, Regeneration and Stable Performance

Steam
reforming of ethanol/gasoline mixtures: deactivation, regeneration and stable
performance

Introduction

Increasing
concerns about environmental impacts of vehicles with gasoline powered
combustion engines have increased efforts to find technologies to reduce
emissions and fossil fuel consumption. Recently there has been an increased
focus on using renewable sources to generate
transportation fuels, such as utilizing agricultural waste to generate
ethanol.  Ethanol has a lower vapor pressure relative to gasoline and thus
ethanol/gasoline blends such as E85 (85% ethanol) are available rather than
100% ethanol within the current infrastructure.  Thus it is important to
understand the reforming capabilities of these mixed transportation fuels.
There has been extensive research on the reforming of pure ethanol, however,
literature on reforming ethanol-gasoline blends is limited.  For this study we
look at steam reforming of ethanol at less energy intensive conditions: 650°C
and steam/carbon ratio of 1.8 with a Rh/Pt catalyst (BASF RM-75ST) washcoated
on a ceramic monolith.  At these less energy intensive conditions, however,
catalyst deactivation due to either sulfur poisoning or carbon formation is
more favored.  The objective of this study is to understand sulfur-induced
catalyst deactivation and also potential catalyst regeneration methods in order
to develop a process reforming E85 or other sulfur containing liquid fuels at
less energy intensive conditions.

Results and
Discussion

The
catalyst deactivated after exposure to fuel containing 5 ppm sulfur after 22
hours on stream whereas the catalyst did not deactivate reforming a sulfur-free
fuel for at least 110 hours of continuous operation.  Although initially the
catalyst was able to achieve equilibrium product distributions with 100%
ethanol and gasoline conversion in both the sulfur-free and the 5 ppm sulfur
test condition the catalyst operating in the presence of sulfur deactivated to
an extent unsuitable for industrial hydrogen production, i.e. < 10 mole%
hydrogen production and < 21% ethanol conversion after 100 hours of
reforming.  After such significant levels of deactivation exposure to air for
one hour was able to restore initial catalyst activity.  Although initial
activity (100% ethanol and gasoline conversion and equilibrium hydrogen
production) was restored catalyst deactivation was measured after less time on
stream then with the fresh catalyst.  Successive air regenerations were also
performed after intermediate levels of deactivation as shown in Figure 1.

These
results show that some deactivation was reversible and thus initial activity
after air regeneration could be restored; however, an aspect of irreversible
deactivation also must have existed which shortened the period of stable
activity following the air treatment. Initial XPS results indicate that
extended periods of time on stream contribute to irreversible changes in
precious metal chemistry which may be attributed to the permanent loss in
performance shown in Figure 1. Coupling reactor studies with characterization
data it was found that these precious metal chemical changes may be avoided
with preemptive regeneration.  Preemptive regenerations extended the period of
stable performance during reactor studies.  These results imply that an
industrial process could be developed utilizing preemptive regenerations to
achieve stable activity while reforming a sulfur containing fuel.

Significance

In
industry, catalyst regenerations are performed more frequently as the catalyst
ages, however, the irreversible aspect of the catalyst deactivation is often
not understood.  The purpose of this study is to understand the difference in
the irreversible and reversible aspects of deactivation in order to optimize an
industrial process for reforming sulfur-containing fuels.

References

1.           
Swartz,
S.L., Matter, P.H., Arkenberg, G.B., Holcomb, F.H., Josefik, N.M.,  J. Power
Sources 188, 515 (2009)