Continuous production and in situ extraction of isovaleraldehyde in a membrane bioreactor

Bioconversions are generally low productivity processes when compared to chemical synthetic reactions. The productivity of a bioconversion can be maximized if it is carried out in the presence of substrate/product concentrations at which the biocatalyst shows optimal activity and stability. One way to achieve this is to develop a process with continuous addition of the substrate and selective removal of the product. The microbial oxidation of isoamyl alcohol to isovaleraldehyde by a newly isolated Gluconobacter oxydans strain has been reported recently. High conversion yields (>90%) and good rates (maximum yield after 90 min) were obtained in a batch mode. With this strain, although aldehyde dehydrogenase(s) leading to acid formation are present, further oxidation of the aldehyde to acid is significantly slower so that transient accumulation of the aldehyde is possible. The productivity of this bioconversion can be improved by setting up a continuous process with addition of substrate at an adequate flow rate. In situ removal of the aldehyde is imperative to avoid acid production and to reduce evaporation of the product. This chapter describes a membrane-based extractive procedure to achieve an in situ, nondispersive recovery of the aldehyde.