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Downstream Processes

Downstream Processes. BIE/CEE 5930/6930 Spring 2008. Ultrafiltration and Microfiltration. Microfiltration 0.1 to 10 μ m filter sizes Used to separate cells Ultrafiltration MW range 2000 to 500,000 (2 to 500 kilo Daltons (kD)) Used to concentrate or sieve proteins based on size

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Downstream Processes

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  1. Downstream Processes BIE/CEE 5930/6930Spring 2008

  2. Ultrafiltration and Microfiltration • Microfiltration • 0.1 to 10 μm filter sizes • Used to separate cells • Ultrafiltration • MW range 2000 to 500,000 (2 to 500 kilo Daltons (kD)) • Used to concentrate or sieve proteins based on size • Anisotropic membranes • A thin membrane with small pores supported by a thicker membrane with larger pores • Low MW solutes pass through the filter and high MW solutes are retained • Pressure driven process • Can result in concentration polarization and gel formation at membrane surface

  3. Ultrafiltration and Microfiltration • At steady state: • Rate of convective transport of solute towards membrane = rate of diffusive transport of solute in opposite direction Gel polarization equation

  4. Ultrafiltration and Microfiltration Cross flow or tangential flow filtration • Pressure applied parallel to membrane instead of perpendicular to it • Fluid flows parallel to membrane and prevents accumulation of solute at the surface

  5. Ultrafiltration and Microfiltration Pressure drop given by: Hagen-Poiseuille Equation for laminar flow in a pipe Modified Hagen-Poiseuille Equation for turbulent flow in a pipe These expressions relate pressure drop due to linear flow of fluid through the pipe

  6. Ultrafiltration and Microfiltration

  7. Ultrafiltration and Microfiltration • Filtration flux (J) is a function of • Transmembrane pressure drop (ΔPM) • Gel layer concentration (CG) • Mass transfer coefficient (K) • Bulk solute concentration (CB) • If no solute is present, then Flux is a function of ΔPM only. • If solute is present and RG is constant, flux still increases linearly with ΔPM • If gel polarization occurs, RG is not constant and flux will no longer be a function only of ΔPM } From Gel polarization eq.

  8. Ultrafiltration and Microfiltration • ΔPM may be applied in two ways • Increasing inlet pressure (Pi) • Decreasing ΔP by increasing Po (Back-pressure) • Pi is constrained by pumps available or membrane properties • If Pi is constant, applying a little back pressure is good because we get higher ΔPM • If too much back pressure is applied, • ΔP decreases and thereby velocity • Gel polarization starts to occur • Lower velocity decreases mass transfer rate • If velocity is too high, we get high pressure drop (ΔP) and low ΔPM again resulting in low flux

  9. Ultrafiltration and Microfiltration

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