OXIDATION OF O-XYLENE TO PHTHALIC-ANHYDRIDE OVER V2O5 TIO2 CATALYSTS .4. MATHEMATICAL-MODELING STUDY AND ANALYSIS OF THE REACTION NETWORK/

Results previously obtained for the oxidation of o-xylene and o-tolual dehyde over a 1% V2O5/TiO2 catalyst have been subjected to mathematica l modelling, using comprehensive ''rake'' networks which incorporate a dsorbed intermediates, a variety of routes to CO2, and provision for t he formation and removal from the surface of a ''residue'' formed at l ow conversion by both reactants. Equations representing yields of prod ucts as a function of reactant conversion are presented; these contain series of parameters that are complex functions of the rate constants for the individual steps, their values being obtained by regression a nalysis. The modelling confirms that phthalic anhydride is formed thro ugh a sequential process involving adsorbed forms of o-tolualdehyde an d phthalide as intermediates, but it is not formed by direct conversio n of o-xylene and o-tolualdehyde. At high conversion, phthalic anhydri de selectivity generally passes through a maximum, showing that it can undergo further oxidation to CO2. The selectivity for the ''residue'' (S-R) also passes through a maximum as it is removed from the surface ; moreover, the initial slopes of S-R VS conversion curves show that t he ''residue'' is formed early in the reaction network. (C) 1996 Acade mic Press Inc.