GAS–Liquid Interfacial Area in the Oxygen Absorption to Oil-in-Water Emulsions in an Airlift Reactor D.G´ omez-D´ ıaz, 1 *N.Gomes, 2 J.A.Teixeira 2 andI.Belo 2 1. Department of Chemical Engineering, University of Santiago de Compostela, Campus Sur, Santiago de Compostela E-15782, Spain 2. IBB-Institute for Biotechnology and Bioengineering, Center of Biological Engineering, University of Minho, Campus de Gualtar, Braga 4710-057, Portugal Thepresentworkincludesanexhaustivestudyaboutgas–liquidinterfacialareabetweengasphaseandliquidheterogeneousmediumgenerated inanairliftbioreactor.Thesystemstudiediscomposedbywater,methylricinoleate(MR),andTween-80,sinceitisthebaseofthemediumused for the production of  -decalactone, a peach-like aroma compound of industrial interest that can be produced biotechnologically through the biotransformationofricinoleicacid,bytheyeast Yarrowia lipolytica.Experimentalresultsallowdescribingthehydrodynamicbehaviourofthegas phaseintothebiphasicmedium. Le travail actuel comprend une ´ etude approfondie sur la zone interfaciale gaz-liquide entre la phase gazeuse et le milieu h´ et´ erog` ene liquide produit par un bior´ eacteur ` a agitation par circulation d’air. Le syst` eme ´ etudi´ e se compose d’eau, de ricinol´ eate de m´ ethyle et de Tween 80, puisqu’il constitue la base du milieu utilis´ e pour la production de  -decalactone, un compos´ ed’arˆ ome semblable ` alapˆ eche d’int´ erˆ et industriel que l’on peut produire de fac ¸on biotechnologique par la biotransformation de l’acide ricinol´ eique (un important constituant du ricinol´ eate de m´ ethyle), par la levure Yarrowia lipolytica. Les r´ esultats exp´ erimentaux permettent de d´ ecrire le comportement hydrodynamique de la phase gazeuse dans le milieu biphasique. Keywords: airlift bioreactor, methyl ricinoleate, emulsion, gas–liquid interfacial area INTRODUCTION G as–liquid–liquid systems are encountered in many reac- tions and have gained special interest in chemical engineering with the introduction of homogeneous bipha- sic catalysis. Mass transfer modelling in biphasic media has been done by several authors using as a model, systems in which the second liquid phase (organic) is an additional inert and external compound (like perfluorocarbons and silicone oils, among others) added to the system on the purpose to improve mass transfer from the gas to the liquid aqueous phase (Dumont and Delmas, 2003). These systems are encountered in some biochemical applications where a hydrophobic compound with higher oxygen solubility than water is used to improve the oxygen transfer rate to the cul- ture media. However, numerous biotechnological processes are based on the development of microorganisms within a biphasic medium formed by an oil-in-water emulsion where the oil is the substrate to be degraded. In these cases, the organic substrate can retard the gas–liquid mass transfer, thus limiting the overall productivity. The system herein presented is an emulsion of water and methyl ricinoleate (MR), stabilised by Tween-80, which constitutes the medium used in the production of  -decalactone (a peach-like aroma compound of industrial interest) through the biotrans- formation of ricinoleic acid (major constituent of MR) by the yeast Yarrowia lipolytica (Aguedo et al., 2005). The biochemical ∗ Author to whom correspondence may be addressed. E-mail address: diego.gomez@usc.es Can. J. Chem. Eng. 88:561–564, 2010. © 2010 Canadian Society for Chemical Engineering DOI 10.1002/cjce.20307 Published online 5 May 2010 in Wiley InterScience (www.interscience.wiley.com) | VOLUME88,2010. | | THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING | 561 |