Integrated fermentation and separation for the production of advanced biofuels

One of the latest innovations in biofuel research is the development of microorganisms producing and secreting diesel like molecules, so called advanced biofuels. These molecules are currently produced under aerobic conditions, using conventional fermentation technology. Subsequently, the product is recovered from the multiphase fermentation mixture by centrifugation. However, this process is too costly to produce advanced biofuels that can economically compete with conventional fuels. Clearly, improvements have to be made in different aspects of the process: at feedstock (e.g., cellulosic biomass), microorganism (e.g., anaerobic production) and process (e.g., low cost process technology) levels.

The latter can be achieved by integrating production and gravity separation of the product, lowering equipment costs and enabling continuous processing and cell reuse. Upon secretion by the microorganism, product droplets of about 1 μm are expected. To recover the biofuel, the droplets must coalesce first, reaching a size that is separated by gravity. Further droplet coalescence results in the formation a continuous oil phase. However, coalescence can be hindered by surface active components present in the fermentation medium or originating from the cells, leading to product emulsification. Hence, an integrated process should promote coalescence and prevent emulsion formation. In this contribution we show how these processes are influenced by the process conditions and scale. This analysis, together with literature and our own experimental data, results in a window of operation for integrated fermentation and product recovery. These results can be used for selection of an appropriate scale and equipment design for further piloting studies.