Servizio Comunitario di Informazione in materia di Ricerca e Sviluppo - CORDIS

Kinetics of the SCWG for several components of tar-water mixtures

Following the results on the quantification of tar compounds carried out for the SCWG tests, an analysis has been carried out aimed at individuating the chief reaction paths. Sugars, contributing in large amount to the initial tar composition in waste water, are promptly decomposed into furfurals (2-and 3-furaldehyde, (5H)-furan-2-one, 5-hydroxymethyl-2-furaldehyde, 5-methyl-(5H)-furan-1-one, ’x-butyrolactone, 5-methyl-2-furaldehyde).

The majority of these compounds present a high reactivity even at relatively low temperatures, thus giving rise to gases and short-chain aldehydes and acids. Complex phenols, such as 4-methylguaiacol and guaiacol, also present a high reactivity, producing simpler phenols (phenol, cresols, 2,4-dimethylphenol), which add to those initially present in the waste water sample.

These species appear to be the most difficult to be destroyed, although their concentrations are significantly dependent on both temperature and residence times. Acetic acid, which is the major contributor among the organic components polluting the waste water and also a rection intermediate, is scarcely reactive and not very sensitive to the residence time. Low reactivity is also shown by propanoic acid and 1,2-ethanediol. On the contrary 1-hydroxy-2-propanone, which is the third species in the quantitative composition of the tar sample considered in this study, undergoes complete conversion for temperatures slightly above 800K.

Given the complexity of the chemical composition of the tar-water mixture and the numerous reactions taking place, the interpretation of the decomposition kinetics by means of first-order Arrhenius kinetics for a set of species ((5H)furan-2-one, 2-hydroxy-3-methyl-2-cyclopentene-1-one 2-furaldehyde, guaicol,1-hydroxy-2-butanone, acetol) with mass fraction below one and limited to the temperature range where decreasing values should be considered empirical. The results report activation energies in the range 32 and 193 kJ/mol.

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