The use of coals as catalysts for the oxidative dehydrogenation of n-butane Original Research Article

The catalysis by coals of the oxidative dehydrogenation (ODH) of n-butane was studied. The influence of oxygen and butane partial pressures, contact time, temperature and coal rank were investigated. The used coals were textural (surface area, mercury porosimetry, He picnometry, etc.) and chemically (ash content, elemental analysis) characterized. Coals show an excellent catalytic behaviour but the presence of gaseous O2 is required. This fact leads to the occurrence of two simultaneous processes: butane conversion, which includes both ODH and deep oxidation, and coal combustion. The increase of the oxygen partial pressure and temperature favours butane conversion. However, at temperatures higher than 500°C, cracking and isomerisation reactions occur leading to a decrease in selectivity to dehydrogenation products (C4ʹs). The increase of contact time brings about a strong increase in C4ʹs selectivity. The increase of the coal rank from lignite to hv bituminous coals also favours the butane conversion, however, coals with higher rank lead to smaller conversions. The highest dehydrogenation yields were obtained with an hv bituminous coal. When the reaction starts, butadiene is the main product formed in any experimental condition, but its formation is more affected by coal combustion than for butenes.