Formic acid as flexible CO and H₂ source in synthesis gas production

Titelangaben

Glowienka, Kevin ; Thiessen, Johannes ; Kern, Christoph ; Jess, Andreas:
Formic acid as flexible CO and H₂ source in synthesis gas production.
2015
Veranstaltung: ESCRE 2015 - European Symposium on Chemical Reaction Engineering , 27.-30.10.2015 , Fürstenfeldbruck, Deutschland.
(Veranstaltungsbeitrag: Kongress/Konferenz/Symposium/Tagung , Vortrag )

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Abstract

With the Directive 2009/28/EC the European Union intends to increase the proportion of biofuels up to 10 % in the transport sector until 2020 [1]. One of the major problems with biofuels is the low energy density and the local availability of biomass. Thus, the usage of biomass is only economically and ecologically reasonable within a small radius around the production sites. To increase the efficiency of transportation the biomass needs to be converted into intermediates of higher energy density. Wölfel et al. showed that different kinds of biomass can be converted into aqueous formic acid (FA) under very mild conditions with high selectivity [2].[2] This work concentrates on the question whether FA can be used as an intermediate for the production of second-generation biofuels. As FA is known to decompose either to hydrogen and carbon dioxide (dehydrogenation) or carbon monoxide and water (dehydration) it is a promising candidate both as carbon source that is free of catalyst poisons and hydrogen source. The objective of this work is to find a switchable reaction system that selectively produces CO or a mixture of CO and H2 and hence allows the combination with further hydrogen sources from renewable energy like solar and wind power.
To evaluate the concept experimentally, the activity and selectivity of the thermal and catalytic decomposition of formic acid in aqueous solution is investigated in gas and liquid phase. In this context, a suitable catalyst for the dehydration has to be found. This is against the modern trend in research with FA, as that is focused on the production of high purity hydrogen for applications like for fuel cells [3].
To examine the decomposition in the gas phase a continuous tubular fixed-bed reactor in combination with a saturator is used. Selective formation of CO can be achieved by using a TiO2 or a zeolite beta catalyst in the gas phase reaction. However, compared to supported noble metal catalysts like Au/TiO2, which can be used for hydrogen production, the activity is relatively low.
For the decomposition in liquid phase a semi-batch autoclave with a reflux condenser is used at a pressure of around 20 bar. Even though formic acid decomposes thermally to carbon monoxide and water in liquid phase, the rate of decomposition decreases significantly with rising water content in the mixture even at low water concentrations. Here catalysts which accelerate the reaction at high CO selectivity are being examined.
Finally, the potential of formic acid as intermediate for the production of synthesis gas from biomass will be evaluated.
References
[1] European Parliament and the Council, on the promotion of the use of energy from renewable sources: Directive 2009/28/EC, 2009.
[2] R. Wölfel, N. Taccardi, A. Bösmann, P. Wasserscheid, Green Chem 13 (2011) 2759–2763.
[3] A. Gazsi, T. Bánsági, F. Solymosi, J. Phys. Chem. C 115 (2011) 15459–15466.