Char as catalyst for hot gas cleaning and upgrading : role of the oxygenated sites on the char surface

Abstract : Some recent researches have investigated the use of char in catalytic applications of hydrocarbons cracking [1]. Up to now textural properties as surface area, porosity and presence of minerals on its surface have been the main explanations of the catalytic performances of the chars. However literature and methane cracking tests have highlighted that oxygenated groups may play a role [2]. The goal of this study is to investigate the oxygenation of the char surface in terms of selectivity and efficiency. Then the catalytic performances of the functionalized chars will be evaluated through methane cracking tests. The oxygenation process has been done at 280°C for different duration times (1h, 2h, 4h, and 8h) under a 45 mL/min flow rate of a mixture composed of 8% O 2 / 92% N 2. Raw chars and oxygenated chars have been analysed by FTIR and TPD. Methane cracking experiments have been carried out at 700°C over a bed of raw chars and oxygenated chars in a Chembet Instrument. The output gas has been analyzed continuously during the experiments via a micro-GC. The O 2 gas phase oxygenation process has shown good results since the global amount of oxygenated groups at the surface has been enhanced. In particular groups such as anhydride, ether, phenol and lactone groups have been increased. The longest the oxygenation process was, the highest amount of oxygenated groups has been added. Thus it emphasizes that a functionalization of the char surface using a mixture of 8% O 2 / 92% N 2 is possible. First results of methane cracking confirmed the catalytic performances of chars since methane decomposed to hydrogen at a lower temperature than that for regular cracking. The efficiency is evaluated as regards to hydrogen production and the impact of oxygenated groups. However methane cracking experiments conducted on chars oxygenated did not lead to a clear increase in the hydrogen production. Oxygenated groups which have been increased seem to have been desorbed before reaching the temperature of methane cracking. Further investigation on the impact of the oxygenation on the textural properties need to be carried out.
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Marion Ducousso, Elsa Weiss-Hortala, Marco J. Castaldi, Ange Nzihou. Char as catalyst for hot gas cleaning and upgrading : role of the oxygenated sites on the char surface. WasteEng 2014 - 5th International Conference on Engineering for Waste and Biomass Valorisation, Aug 2014, Rio de Janeiro, Brazil. p.713-724. ⟨hal-01742998⟩

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