KINETIC-PARAMETERS OF THE CRACKING REACTION OF TAR FROM WOOD PYROLYSIS - COMPARISON OF DOLOMITE WITH INDUSTRIAL CATALYSTS

From the equation of the curves showing the time required for tar to be pyrolysed (up to 97.5% of completion as a function of reaction temperatures), it has been possible, by a theoretical development, to determine kinetic parameters. These parameters are the activation energies E(c), the rate constants k(v), k(w) and k(s), and the corresponding pre-exponential factors A(v), A(w) and S(s) i.e. the unit volume accessible to gas, the mass unit and unit surface of catalyst respectively. Comparison of these kinetic parameters for several potential catalysts of the tar formation from wood cracking reactions gave some interesting results. Decarbonated and recarbonated dolomites have the same types of sites (identical E(c) and A(s)) and the most efficient catalytic surface (highest A(s)). The differences in their catalytic activity is mainly due to differences in specific surface areas. Among all the catalysts studied, dolomite presents the most active surface; the high activity of activated charcoal can be attributed to its very high specific surface area. The differences in activity for dolomite and the more active of the silico-aluminate type catalysts, bentonite, is due to a lower A(s) for bentonite.