Continuous oxidation of aromatic aldehyde to aromatic carboxylic acid by Burkholderia cepacia TM1 in a cell-holding reactor

The continuous oxidation of aromatic aldehydes to the corresponding aromatic carboxylic acids was performed. In the continuous oxidation of aromatic aldehydes by Burkholderia cepacia TM1 in a cell-holding reactor, the concentration of the aromatic aldehyde in the reactor was kept extremely low by appropriately adjusting the initial turbidity of the cells in the reactor, the feeding rate of the aromatic aldehyde to the reactor and the average residence time. Thus, the feeding concentration at the inlet of vanillin, p-hydroxy-benzaldehyde, or syringaldehyde was 20.0, 20.0, or 4.0 g/l, respectively. Under the indicated reaction conditions, the steady state of the reaction continued for approximately 650 h, 450 h, and 160 h, respectively, for vanillin, p-hydroxybenzaldehyde and syringaldehyde as the substrate. The molar yield of vanillic acid, p-hydroxybenzoic acid and syringic acid in the steady state was, respectively, approximately 95, 80 and 96%, and the productivity was, respectively, 0.770, 0.350 and 0.160 (g/l.h). Moreover, since the recovered reaction solution consisted almost predominantly of only one type of aromatic carboxylic acid, separation and purification of the product was considered to be unnecessary. To prevent a decrease in the pH of the reaction solution and to maintain a high solubility of the substrate and the product, a phosphate buffer (pH 7.2) is better than distilled water as a reaction solution for feeding.