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The conversion of polysaccharides to hydrogen gas. Part II: The catalytic decomposition of formaldehyde in the aqueous phase
Author(s) -
Hill S. P.,
Winterbottom J. M.
Publication year - 1988
Publication title -
journal of chemical technology and biotechnology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.64
H-Index - 117
eISSN - 1097-4660
pISSN - 0268-2575
DOI - 10.1002/jctb.280410206
Subject(s) - catalysis , formaldehyde , chemistry , inorganic chemistry , hydrogen , aqueous solution , methanol , carbonium ion , decomposition , reaction rate , organic chemistry
Abstract The aqueous phase decomposition of formaldehyde, to hydrogen gas, catalysed by platinum—copper chromite, has been carried out in the temperature range 20–60°C, at a solution pH of 12. The production of hydrogen was favoured by intermediate temperatures (40–50°C) and an activation energy of 22.2 kJ mol −1 (5.3 kcal mol −1 ) was recorded. The rate of reaction was first order with respect to OH − ion concentration at low alkali concentrations and was first order with respect to HCHO concentration at all concentrations. At high alkali concentrations the reaction should become zero order with respect to OH − ion concentration, but initial rates actually decrease under these conditions having passed through a maximum. The rate of reaction was directly proportional to catalyst weight at low catalyst loading, but the relationship became non‐linear at high catalyst loadings. Conversions of formaldehyde to hydrogen gas were substantially less than theoretical. The decomposition reaction has to compete with a number of side reactions such as polymerization of formaldehyde at low temperatures (<40°C) and at higher temperatures with the Cannizzano reaction, aldol condensation, and possibly formaldehyde hydrogenation to methanol. In addition hydrogen loss may occur due to copper chromite reduction. A reaction mechanism is proposed involving a surface formate intermediate.