Flux Limiting Factors in Cross-flow Ultrafiltration of Invertase through an Asymmetric Inorganic Membrane

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Abstract
Here the flow versus pressure characteristics of 0.1 to 5% w/w aqueous solutions of invertase, with a molecular weight of 270,000 dalton, are studied when they are tangentially filtered at 298 K through an inorganic asymmetric membrane of nominal pore radius 0.02 μm, with pressures going from 5 to 100 kPa, while the recirculation speed in the retentate loop is kept constant at 0.48 m/s. In such conditions, all these solutions are totally retained. The mass transfer coefficient is calculated, within the frame of the film layer theory for the concentration polarization phenomenon, by studying the volume flow as a function of concentration for several constant pressures in the above mentioned range. For low applied pressures, the concentrations giving zero volume flows can be interpreted as corresponding to osmotic pressure differences that balance the applied ones, and a power dependence of these pressures on concentration is proposed. For higher pressures the zero flow concentration is almost constant, probably due to a predominant gelification process.