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Intensive pyrolysis of unsaturated organic precursors over acidified oxide surfaces

Abstract : Carbon-like composite materials fabricated by non-catalytic heterogeneous pyrolysis (NCHP) of organic precursors over porous oxide supports are used in a variety of fields. The intensification of NCHP procedures for fabrication on a commercial scale is technically problematic. Direct intensification of operation parameters cannot be considered as the most effective method. For instance, an increase in support bed temperature often takes the pyrolysis process into the homogeneous reaction field, and greater gas space velocities and initial organic precursor concentrations lead to a rise in operating costs because of considerable losses of raw materials and increased power requirements. This paper describes an attempt to intensify non-catalytic heterogeneous pyrolysis procedures by optimizing the acid–base properties of the reaction agents (supports, precursors). A procedure of controlled acidification of the alumina support followed by thermal degradation of surface base salt was applied in order to cover the support surfaces with additional Lewis acid sites functioning as efficient host centres for precursor molecules. Unsaturated organic compounds, powerful Lewis bases, were used as the precursor agents. A probable elementary mechanism for non-catalytic heterogeneous pyrolysis of unsaturated organic precursors over an oxide surface reinforced by Lewis acids is proposed. The main characteristics of the composite hydrophobic materials produced by the NCHP technique using pre-acidified alumina samples—their chemical compositions, surface affinities to water, thermal stabilities in air, dynamic VOC adsorption and desorption capacities are presented and discussed. The elaborated composites are non-flammable in air until 600 °C, whereas the thermal stability limit of activated carbons is situated in the 250–300 °C range. As compared to activated carbons, these materials manifest really stable surface activities in VOC adsorption–desorption cycles.
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Laetitia Majoli, Alexei Evstratov, Jean-Michel Guillot, Jean-François Chapat, Jean-Luc Le Loarer. Intensive pyrolysis of unsaturated organic precursors over acidified oxide surfaces. Journal of Analytical and Applied Pyrolysis, Elsevier, 2005, 74 (1-2), pp.290-297. ⟨10.1016/j.jaap.2004.12.007⟩. ⟨hal-03482835⟩

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