Chemical Engineering Science, 145: 31-44 (link)
In the search for advanced biofuels, microorganisms have been developed that make and secrete long chain hydrocarbons, resulting in a four phase fermentation mixture (cells, aqueous liquid, organic product, and (produced) gas). The product immiscibility offers the potential for a straightforward recovery, but surface active components in the fermentation broth emulsify the product droplets. In the current process, multiple centrifugation steps with chemical de-emulsifiers are used for product recovery, posing economic and environmental burdens on the process. In this paper, an alternative separation method is presented, in which gas bubbles induce coalescence of the emulsified oil droplets, obtaining a continuous oil layer. The oil layer formation was influenced by the gas flow rate, nozzle diameter, column geometry, and emulsion properties, offering the possibility for process optimisation. The developed gas bubble induced oil recovery method does not require chemical additives, uses mild process conditions, and can potentially be integrated with the fermentation, giving a low cost alternative for the conventional recovery method. Using this technology, another step can be made towards economically feasible production of advanced biofuels.