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

The catalysis by coals of the oxidative dehydrogenation (ODH) of n-butane w as studied. The influence of oxygen and butane partial pressures, contact t ime, temperature and coal rank were investigated. The used coals were textu ral (surface area, mercury porosimetry, He picnometry, etc.) and chemically lash content, elemental analysis) characterized. Coals show an excellent c atalytic behaviour but the presence of gaseous O-2 is required. This fact l eads to the occurrence of two simultaneous processes: butane conversion, wh ich 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 degrees C, cracking and isomerisat ion reactions occur leading to a decrease in selectivity to dehydrogenation products (C-4's) The increase of contact time brings about a strong increa se in C-4's selectivity. The increase of the coal rank from lignite to by b ituminous coals also favours the butane conversion, however, coals with hig her rank lead to smaller conversions. The highest dehydrogenation yields we re obtained with an hv bituminous coal. When the reaction starts, butadiene is the main product formed in any experimental condition, but its formatio n is more affected by coal combustion than for butenes. (C) 1999 Elsevier S cience B.V. All rights reserved.