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Thermodynamics and reaction mechanism of urea decomposition

Tischer, Steffen; Börnhorst, Marion; Amsler, Jonas; Schoch, Günter; Deutschmann, Olaf

Abstract (englisch):
Selective catalytic reduction (SCR) for automotive applications depends on ammonia production from a urea-water solution by thermolysis and hydrolysis. In this process, undesired liquid and solid by-products are formed in the exhaust pipe. The formation and decomposition of these by-products have been studied by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC).
Based on a previously published reaction mechanism by Brack et al. [1], a new reaction scheme is proposed that emphasizes the role of thermodynamic equilibrium of the reactants in liquid and solid phases [2]. The observed phenomenon of liquefaction and re-solidification of biuret in the temperature range 193–230 °C can be explained by formation of a eutectic mixture with urea. According to DSC data, the direct decomposition of urea to ammonia and isocyanic acid can be ruled out. The dominant route is a self-polymerisation of urea to biuret and triuret. Biuret and triuret decomposition are dominated by thermodynamic equilibria with gaseous isocyanic acid. For this, thermodynamic data of triuret have been refined. The apparent melting point of biuret at 193 °C is explained by the formation of a eutectic mixture within the urea-biuret-triuret-cyanuric acid ensemble. ... mehr

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Volltext §
DOI: 10.5445/IR/1000104975
Veröffentlicht am 16.01.2020
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Zugehörige Institution(en) am KIT Institut für Katalyseforschung und -technologie (IKFT)
Institut für Technische Chemie und Polymerchemie (ITCP)
Publikationstyp Poster
Publikationsdatum 08.09.2019
Sprache Englisch
Identifikator KITopen-ID: 1000104975
HGF-Programm 37.03.01 (POF III, LK 01) Catalysts and Mechanisms
Veranstaltung 6th International Symposium on Modeling of Exhaust-Gas After-Treatment (MODEGAT VI 2019), Bad Herrenalb, Deutschland, 08.09.2019 – 10.09.2019
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