Kinetics of vanillin oxidation

Vanillin can be produced by oxidation of kraft lignin, with air, in alkaline medium. The optimal conditions for vanillin production strongly depend on pH and temperature. This paper addresses the effect of temperature and pH on vanillin degradation by oxidation. Experiments were carried out in a wide range of vanillin concentration, oxygen partial pressure, temperature and pH. Simple models are proposed to explain the observed rate of vanillin consumption under conditions of high alkalinity (pH > 12) and lower alkalinity (pH < 12). At pH > 12, the reaction rate of vanillin oxidation is first order in dissolved oxygen concentration [O-2] and in vanillin concentration [C], i.e., (-r(C))proportional to[O-2][C]; at pH < 12, the rate is zero order in oxygen concentration and second order in vanillin concentration, i.e., (-r(C)>proportional to f(pH)[C](2).