Gas phase kinetics of voliteles from biomass pyrolysis. Note I: ketene, acetic acid and acetaldehyde

Biofuels obtained from biomass are considered an interesting alternative to fossil derived fuels and it has been estimated that they could provide about 25% of global energy requirements. A proper knowledge about their pyrolysis and combustion behavior and the formation of toxic intermediates is necessary. The problem involve a lot of chemical species, so that is has to be afforded systematically. Hydrocarbon pyrolysis and combustion has been mostly characterized but, especially for oxygenated species, such as aldehydes, acid, and alcohols, a lot of work is still to be done. No complete description is given for many secondary gas phase reactions involved in biofuels production. Oxygenated components are one of the major classes of tar compounds released from biomass pyrolysis [1]. Long vapour residence times and temperatures higher than 750 K cause secondary cracking of primary products reducing yields of organic liquids. Lower temperatures lead to condensation reactions and the subsequent formation of lower molecular weight liquids which can also react [2]. There is therefore a growing interest in the successive gas phase reactions of volatile species released from biomass pyrolysis [3]. The importance of molecular paths and four/six center reactions for oxygenated species is well proved by the actual research interest on these topics [4; 5; 6]. An existing and well known kinetic model [7] has been recently compared with experimental data regarding ketene, acetic acid, and acetaldehyde and thank to this activity it has been improved and validated. The importance of concerted path reactions, mainly at high temperatures, is pointed out. The comparison with experimental data is satisfactory.