Two thermal processing technologies have emerged for processing biomass into renewable
liquid products: pyrolysis and gasification/Fischer-Tropsch processing. The
work presented here will demonstrate oxidative pyrolysis of biomass as an alternative
process to avoid the intrinsic disadvantages of traditional pyrolysis. Additionally,
work has been conducted to examine the processing of biomass derived synthesis gas
to condensable products, which involves mitigating new challenges when compared
with the processing of conventional coal-based feedstocks during gasification/Fischer-
The research group of Professor Lanny D. Schmidt has pioneered autothermal
partial oxidation of a variety of gas and liquid feedstocks on noble metal catalysts to
synthesis gas with high selectivity, char-free operation, and on millisecond timescales
at temperatures of 600 - 1000 ◦C. More recently, cellulose has been shown to decompose
on the catalyst surface to also produce high selectivities to synthesis gas.
Chapter 2 discusses the discovery of an intermediate liquid phase during the autothermal
processing of cellulose particles over rhodium-based catalysts. Volatilization of
300 μm cellulose particles on a 700 ◦C catalytic surface were filmed using a high
speed camera capable of 1000 frames per second. The cellulose particles decomposed
through an intermediate liquid, which boiled to gaseous species that convected into
the catalyst bed. The high heat transfer rates made possible by the intimate contact
of the boiling liquid and the hot surface allowed rapid reactions without leaving char
residues. This unique insight allows new processes to be designed that exploit this
type of cellulose thermal decomposition.
Experiments were conducted to investigate the extension of catalytic partial oxidation
over noble metal catalysts to convert biomass to liquid pyrolysis products, termed
‘oxidative pyrolysis’. Model compounds were chosen to represent the lignin fraction
of lignocellulosic biomass to more easily and accurately study the proposed system.
Chapter 3 discusses the autothermal oxidative pyrolysis of monoaromatics over noble
metal catalysts. Benzene, toluene, ethylbenzene, cumene, and styrene were independently studied over five noble metal-based catalysts (Pt, Rh, Rh/
-Al2O3) while varying the carbon-to-oxygen feed ratio. Aromatic rings
were observed to be very stable in the reactor system, while homogeneous reactions
of the alkyl groups of ethylbenzene and cumene were prevalent.
Chapter 4 addresses the oxidative pyrolysis of microcrystalline cellulose particles
as a model for lignocellulosic biomass to yield liquid products. Cellulose was demonstrated
to autothermally convert to combustion, partial oxidation, and pyrolysis products
without char formation. The effects of support geometry, catalyst metal, and
hydrogen addition on product selectivities were studied. Platinum-coated alumina
spheres maximized the yield of pyrolysis products by favoring combustion chemistry
and minimizing reforming activities, as compared with rhodium-based catalysts. Up
to 60 % carbon selectivity to pyrolysis products could be achieved on a Pt catalyst
with hydrogen addition.
As mentioned, previous research in the Schmidt group has shown high selectivities
to synthesis gas by autothermal reforming of cellulose particles. However, utilizing
this biomass-derived syngas, as opposed to traditional coal-based syngas, is not well
studied. Biomass-derived synthesis gas presents a new set of inorganic impurities that
may affect catalyst performance during Fischer-Tropsch processing. Small quantities
(ppm) of typical biomass inorganics (Na, K, Li, and Ca) were loaded onto
supported Co-Re powder catalysts to study the effect on product selectivities (Chapter
5). The inorganic impurities were found to affect the reduction of Co and increase
CO2 and C5+ selectivities, which were largely attributed to electronic effects.
Chapter 6 proposes future research utilizing gas chromatography and mass spectrometry
to identify and quantify specific components within liquid pyrolysis products,
generally termed ‘pyrolysis oil’. This work will build on the research presented in
Chapter 4: the demonstration of oxidative pyrolysis of cellulose to produce up to 50 %
carbon selectivity to pyrolysis products. Further characterization of the pyrolysis oil
will involve pH and water fraction measurements. Preliminary work shows the presence
of several acids, alcohols, phenols, pyrans, among other small oxygenated species
in the pyrolysis oil. Levoglucosan was identified as being the largest carbon-based
fraction of the oil, up to 11 wt% under certain conditions. Additional experiments
extending oxidative pyrolysis to process polymer feedstocks are also proposed
University of Minnesota Ph.D. dissertation. July 2011. Major: Chemical Engineering. Advisor: Lanny D. Schmidt. 1 computer file (PDF); ix, 125 pages, appendix A.
Balonek, Christine Marie.
Autothermal oxidative pyrolysis of biomass feedstocks over noble metal catalysts to liquid products..
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