Jet loop reactors as a versatile reactor set up - Intensifying catalytic reactions: A review

Gas-Liquid mass transfer in a down flow jet loop reactor

Gas transfer and mixing were characterized in a 32-L bubble column reactor equipped with a commercially available rubber membrane diffuser. The performance of the membrane diffuser indicates that the slits in the membrane are best described as holes with elastic lids, acting as valves cutting off bubbles from the gas stream. The membrane diffuser thus functions as a one-way valve preventing backflow of liquid. Our design of the bottom plate of the reactor enabled us to optimize the aeration by changing the tension of the membrane. We thereby achieved mass transfer coefficients higher than those previously reported in bubble columns. A strong dependence of mass transfer on gas holdup and bubble size was indicated by estimates based on these two variables. The microalga, Rhodomonas sp. , sensitive to chemical and physical stress, was maintained for 8 months in continuous culture with a productivity identical to cultures grown in stirred tank reactors. Copyright 1998 John Wiley & Sons, Inc.

Characterization of gas transfer and mixing in a bubble column equipped with a rubber membrane diffuser

In this work, the traditional external loop, airlift bioreactor has been fitted with a spinning sparger. Baffles were located beyond the sparger circumference to prevent vortex motion throughout the bioreactor. The flat plate, spinning sparger had six orifices and was located below the downcomer connection to prevent the generation of a high shear environment inside the bulk medium as would be found in a stirred tank bioreactor. The spinning motion of the sparger produces smaller diameter bubbles with higher gas hold-ups and interfacial areas inside the bioreactor. Data and empirical correlations are presented for these features as well as liquid circulation velocity and mixing characteristics as functions of the spinning rate, superficial gas velocity and type of medium.



Dans ce travail, on a equipe le bioreacteur a air ascendant a boucle externe traditionnel ďun gicleur tournant. Des chicanes ont ete installees juste a ľexterieur du gicleur afin ďempěcher tout mouvement tourbillonnaire dans le reacteur. Le gicleur tournant a plateaux plats possedent six orifices et a ete place sous la connexion du trop plein pour empěcher la creation de cisaillement eleve dans le reacteur comme ce serait le cas dans un bioreacteur a reservoir agite. Le mouvement tournant du gicleur produit des bulles de diametre plus petit ainsi que des retentions de gaz et des surfaces interfaciales plus grandes dans le reacteur. Des donnees et des correlations empiriques sont presentees pour ces caracteristiques ainsi que pour la vitesse de circulation du liquide et les caracteristiques de melange, en fonction de la vitesse de rotation, de la vitesse de gaz superficielle et du type de milieu.

Hydrodynamic characteristics of a spinning sparger, external loop airlift bioreactor

Experiments were conducted in a modified reversed flow jet loop reactor having the liquid outlet at the top of the reactor to determine the gas holdup and overall volumetric mass transfer coefficient in the air-water system. The influence of gas and liquid flow rates, and the draft tube to reactor diameter ratio were studied. It was observed that both gas holdup and volumetric mass transfer coefficient increased with increased gas and liquid flow rates and were found to be significantly higher in the modified reactor compared to the conventional one. The optimum draft tube to reactor diameter ratio was found to be in the range of 0.4 to 0.5. Empirical correlations are presented to predict gas holdup and overall volumetric mass transfer coefficient in terms of operational and geometrical variables.



Des experiences ont ete menees dans un reacteur a boucle a jet d'ecoulement renverse modifie, dans lequel la sortie liquide est situee au sommet du reacteur, afin de determiner la retention de gaz et le coefficient de transfert de matiere volumetrique global dans le systeme air-eau. L'influence des debits liquides et gazeux et le rapport entre le tube d'aspiration et le diametre du reacteur ont egalement ete etudies. On a observe que la retention de gaz et le coefficient de transfert de matiere volumetrique augmentaient avec l'augmentation des debits liquides et gazeux et que, par ailleurs, ils etaient considerablement plus eleves dans le reacteur modifie que dans le reacteur conventionnel. On a trouve que le rapport optimal entre le tube d'aspiration et le diametre du reacteur se situait dans la gamme de 0,4 a 0,5. Des correlations empiriques sont presentees pour predire la retention de gaz et le coefficient de transfert de matiere volumetrique global en termes de variables geometriques et de fonctionnement.

A. Pavko

Papers

Volumetric gas-liquid mass transfer coefficients in a rectangular bubble column with a rubber aeration pad