87 research outputs found
Gas-liquid mass transfer : a comparison of down-and up-pumping axial flow impellers with radial impellers
The performance of a down- and up-pumping pitched blade turbine and A315 for gas-liquid dispersion and mass
transfer was evaluated and then compared with that of Rushton and Scaba turbines in a small laboratory scale
vessel. The results show that when the axial flow impellers are operated in the up-pumping mode, the overall
performance is largely improved compared with the down-pumping configuration. Compared with the radial
turbines, the up-pumping A315 has a high gas handling capacity, equivalent to the Scaba turbine and is
economically much more efficient in terms of mass transfer than both turbines. On the other hand, the uppumping
pitched blade turbine is not as well adapted to such applications. Finally, the axial flow impellers in the
down-pumping mode have the lowest performance of all the impellers studied, although the A315 is preferred of
the pitched blade turbine
Liquid-liquid equilibria of UCON + (sodium or potassium) phosphate salt aqueous two-phase systems at 23 °C
Six phase diagrams for UCONâphosphate salt aqueous two-phase systems (ATPSs), at 23 °C, are presented. The ATPSs were obtained combining UCON (a random copolymer of 50 % ethylene oxide and 50 % propylene oxide) and a phosphate salt (KH2PO4, K2HPO4, potassium phosphate buffer pH = 7, NaH2PO4, Na2HPO4, and sodium phosphate buffer pH = 7). Among the salts used, Na2HPO4 proved to be the most effective in ATPS formation, providing the greatest heterogeneous region in the phase diagram. The previous established relation between the anion valence and the concentration needed to form a biphasic system was confirmed: higher valence requires lower concentration. Na+ salts require, in all cases, lower concentration to form ATPSs than the corresponding K+ salts. The size of the heterogeneous region in the phase diagrams increases with an increase of the pH value of the salt used in ATPS preparation.Fundação para a CiĂȘncia e a Tecnologia (FCT) - SFRH/BD/43439/2008Fundo Europeu de Desenvolvimento Regional (FEDER) - FEDER/POCI/201
The effect of salts on the liquidâliquid phase equilibria of PEG600 + salt aqueous two-phase systems
Six new ATPSs were prepared by combining polyethylene glycol PEG600 with potassium citrate, dipotassium hydrogen phosphate, sodium formate, potassium formate, sodium sulfate, and lithium sulfate. Complete phase diagrams, including the binodal curve and three tie-lines, were determined at 23 °C. The experimental data obtained for the binodal curve were successfully adjusted to the Merchuk equation, and the reliability of tie-line data was confirmed using the equations suggested by OthmerâTobias and Bancroft. The ability of each ion to induce ATPS formation was investigated. Na+ proved to be more effective in ATPS formation than K+ and Li+. For potassium salts, the order observed for the effectiveness of the anions was: HPO42â > C6H5O73â > HCO2â. Regarding the sodium salts, it was found that SO42â is clearly more effective than HCO2â. The position of the ions in the Hofmeister series and their free energy of hydration (ÎGhyd) were used to explain the ability of the ions to induce PEG salting-out. Furthermore, the effective excluded volume (EEV) of the salts was determined and the following order was found: Na2SO4 > K2HPO4 > Li2SO4 > K3C6H5O7 > NaCHO2 > KCHO2. Similar order was obtained when analyzing the size of the heterogeneous regions, suggesting the practical use of EEV as a comparison parameter between different ATPSs.This work is partially supported by project PEst-C/EQB/LA0020/2011, financed by FEDER through COMPETE-Programa Operacional Factores de Competitividade and by FCT-Fundacao para a Ciencia e a Tecnologia. Sara Silverio acknowledges her Ph.D. grant from FCT (SFRH/BD/43439/2008)
Applications of yeast flocculation in biotechnological processes
A review on the main aspects associated with yeast flocculation and its application
in biotechnological processes is presented. This subject is addressed following three
main aspects â the basics of yeast flocculation, the development of ânewâ flocculating yeast
strains and bioreactor development. In what concerns the basics of yeast flocculation, the
state of the art on the most relevant aspects of mechanism, physiology and genetics of yeast
flocculation is reported. The construction of flocculating yeast strains includes not only the
recombinant constitutive flocculent brewerâs yeast, but also recombinant flocculent yeast
for lactose metabolisation and ethanol production. Furthermore, recent work on the
heterologous ÎČ-galactosidase production using a recombinant flocculent Saccharomyces
cerevisiae is considered. As bioreactors using flocculating yeast cells have particular properties,
mainly associated with a high solid phase hold-up, a section dedicated to its operation is
presented. Aspects such as bioreactor productivity and culture stability as well as bioreactor
hydrodynamics and mass transfer properties of flocculating cell cultures are considered.
Finally, the paper concludes describing some of the applications of high cell density
flocculation bioreactors and discussing potential new uses of these systems.Fundação para a CiĂȘncia e a Tecnologia (FCT) â PRAXIS XXI - BD11306/97
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