VFA recovery from fermented waste

VFA recovery from fermented waste-water streams and
integrated catalytic conversion to mixed ketone and vinyl ester
platform chemicals
This project focuses on the integrated recovery and catalytic conversion of
volatile fatty acids (VFAs) from fermentation streams that are obtained through
fermentation of (industrial) waste water. In a process that integrates separation
with catalytic conversion, the VFAs are transformed to the platform chemical
classes of mixed ketones and vinyl esters, which can find wide-spread
application in e.g. high performance resins, and as building blocks for fine and
bulk chemicals.
Stripping or distilling off the separated AA/PA/BA mixture allows for integrated
VFA conversion. Two such conversions routes are targeted here, i.e. the
alkyloxylation of ethylene to give vinyl esters of AA, PA and BA and the
ketonization of AA, PA and BA to give a mixture of ketones. The commercial
acetoxylation of acetic acid with ethylene for vinyl acetate synthesis is typically
conducted in the gas phase over supported bimetallic PdAu catalysts. The
conversion of the VFA mixture to a mixture of vinyl esters appears attractive
since three valuable bulk chemicals can be obtained which are easily separated
by distillation. Ethylene is of course readily obtained by ethanol dehydration,
making the products fully renewable. Whereas much is known for vinyl acetate
production, conversion of the mixture or pure PA and BA this way is relatively
unexplored. For vinyl acetate production, gradual deactivation of the catalyst by
restructuring, leaching or loss of components (KOAc) is well-known [1]. The
stability requirements for a catalyst capable to convert the VFA mixture will be
quite severe and studies of coking, sintering, leaching and poisoning of the
catalyst with substrates of increasing complexity, i.e. pure VFAs, VFA mixtures,
mixtures with added impurities and finally real feeds (by both extensive ex situ
as well as in situ catalyst characterization), will provide important insights into
the catalyst performance in terms of stability and activity. Volatilization of any
extracted salts will be limited, but influence of traces in the feed on catalytic
activity will be assessed. The supported bimetallic PdAu catalysts developed for
vinyl acetate synthesis will be taken as a starting point for the activity and
stability tests with mixtures of VFAs. Further improvements can be gained for
instance by changing or modifying the support (hydrophobicity/hydrophilicity
balance), the use of structural modifiers, or careful synthesis of the bimetal
active phase, e.g. we recently observed large effects of PdAu preparation on
activity in the hydrogenation of renewable acids. The effect of water, CO2, salts
and polar organics in the feed will be systematically addressed to assess 1)
concentrations that can be tolerated, 2) test possible regeneration processes and
3) guide the optimization of catalyst composition. Notably, the presence of water
has previously been shown to have a positive effect on vinyl acetate synthesis
[2].
Additionally, the gas phase conversion of the VFA to a mixture of ketones, i.e.
C3-C8 ketones obtained by homo- and cross-ketonization of the AA/PA/BA
mixture, will be targeted. In contrast to the ketonization of pure acetic acid, very
limited knowledge is available for the catalytic ketonization of VFA mixtures. The
product mixture is nonetheless a very valuable one, as the mixed ketones
platform can be converted to various end product classes, including lube oils [3]
or alkylated aromatics [4]. The alkylated aromatics can then subsequently be
conventionally processed to a large range of products, including BTX.
Ketonization catalysts typically are based on modified (mixed) oxides, such as
CeO2, TiO2, Al2O3 and ZrO2 for which the balance between strength and type of
(Lewis) acid and basic sites is crucial. For carboxylic acids larger than those of
the VFA platform, ceria-zirconia catalysts (CexZryO2) have shown considerable
promise and will be taken as a starting point [5]. The ketonization process is
typically operated at moderate temperatures (573-698K) and at atmospheric
pressure. The ketonization process produces CO2 and H2O as a coproducts [3]
and as a result more is already known about the influence of these expected
feed contaminants on kinetics of conversion and stability of the catalyst.
Importantly, ketonization can be efficiently operated in the presence of moderate
amounts of added water and in the presence of other functional-group
containing organics, such as alcohols and aldehydes [6]. Most reported studies
focus, however, on catalyst development with pure substrates and are not
concerned with long term stability under real-feed conditions. For both
conversion routes, emphasis will be placed on testing of long-term stability of
the different catalyst classes in gas-phase fixed bed reactors. In the Utrecht lab,
the (simultaneous) application of several techniques has been pioneered to
monitor such catalysts in situ, i.e. under operating conditions, and Raman,
DRIFTS, UV-Vis spectroscopic measurements are expected to give insight into
possible deactivation mechanisms and can even be used for automated
regeneration processes[7]. A plug-flow gas phase reactor combining on-line
activity measurements with simultaneous recording of in situ UV–Vis and Raman
spectroscopy complemented by in situ X-ray absorption studies previously
provided new insight into coke-formation and stability of a bimetallic catalyst, for
instance[8]. These studies will be complemented by extensive ex-situ
characterization studies using XRD, physi/chemisorption, Raman, FT-IR, XPS,
SEM and TEM analysis.
1. Pohl, M.-M., Radnik, J., Schneider, M., Bentrup, U., Linke, D., Brückner, A., and
Ferguson, E., Bimetallic PdAu–KOac/SiO2 catalysts for vinyl acetate monomer
(VAM) synthesis: Insights into deactivation under industrial conditions. Journal
of Catalysis, 2009. 262(2): p. 314-323.
2. Samanos, B., Boutry, P., and Montarnal, R., The mechanism of vinyl acetate
formation by gas-phase catalytic ethylene acetoxidation. Journal of Catalysis,
1971. 23(1): p. 19-30.
3. Kunkes, E.L., Gürbüz, E.I., and Dumesic, J.A., Vapour-phase C-C coupling
reactions of biomass-derived oxygenates over Pd/CeZrOx catalysts. Journal of
Catalysis, 2009. 266(2): p. 236-249.
4. Nomura, K., Ujihira, Y., Hayakawa, T., and Takehira, K., CO2 absorption
properties and characterization of perovskite oxides, (Ba,Ca) (Co,Fe) O3 - δ.
Applied Catalysis A: General, 1996. 137(1): p. 25-36.
5. Görtner, C.A., Serrano-Ruiz, J.C., Braden, D.J., and Dumesic, J.A., Catalytic
upgrading of bio-oils by ketonization. ChemSusChem, 2009. 2(12): p.
1121-1124.
6. Carlos Serrano-Ruiz, J. and Dumesic, J.A., Catalytic upgrading of lactic acid to
fuels and chemicals by dehydration/hydrogenation and C-C coupling reactions.
Green Chemistry, 2009. 11(8): p. 1101-1104.
7. Tinnemans, S.J., Kox, M.H.F., Nijhuis, T.A., Visser, T., and Weckhuysen, B.M.,
Real time quantitative Raman spectroscopy of supported metal oxide catalysts
without the need of an internal standard. Physical Chemistry Chemical Physics,
2005. 7(1): p. 211-216.
8. Iglesias-Juez, A., Beale, A.M., Maaijen, K., Weng, T.C., Glatzel, P., and
Weckhuysen, B.M., A combined in situ time-resolved UV-Vis, Raman and highenergy resolution X-ray absorption spectroscopy study on the deactivation
behavior of Pt and PtSn propane dehydrogenation catalysts under industrial
reaction conditions. Journal of Catalysis, 2010. 276(2): p. 268-279.

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