Kinetics of Vanillin Production from Kraft Lignin Oxidation

Abstract

Vanillin production from chemical oxidation of Pinus spp. Kraft lignin is investigated. At a temperature of 130 °C, an oxygen partial pressure of 3 bar, a total pressure of 9 bar, and a lignin concentration of 60 g/L in an alkaline medium of 2 N NaOH, a maximum vanillin yield of 10% is obtained. On the basis of experimental results in a batch reactor operated under various conditions of temperature, oxygen partial pressure, total pressure, initial lignin concentration and pH, a kinetic model is proposed to simulate vanillin production from oxidation of Kraft lignin. The reaction rate of vanillin production is, for pH > 11.5, rC = kNC[O2]1.75[L] − kCI[O2][C] and, for pH < 11.5, rC = kNC[O2]1.75[L] − Af(pH)[C]2. An attempt to predict pH variation during the reaction is also made. The overall flowsheet of the process is briefly addressed, and the recovery of vanillin by adsorption is discussed.