Lecture Notes 6

Lecture Notes 6 - Concept question(s) for sedimentation...

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Concept question(s) for sedimentation centrifugation
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RVF video 2 http://www.youtube.com/watch?v=RuG4B6GBxag (Run from 45 sec time point to 1:40 sec) Basic sequence of steps 1. Add “body feed” (filter aid) to the product pool. 2. Pre-coat drum w filter aid cake. 3. Continuously feed the product pool to the RVF, continuously remove solids and filtrate. 4. Stop when precoat thickness reaches a minimum limit.
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Sterile filtration basics An absolute (membrane) filter To remove microorganisms (not viruses) from a fluid (liquid or gas) Standard: < 10 -6 chance for microbe to be in a patient dose Prove lab-scale filter can meet standard for highest expected bioburden level in feed Prove prodn filter and collection vessel are sterile beforehand Prove prodn filter is integral after filtration. Processing steps for liquid Steam through liquid and vent filter into tank to sterilize Filter the liquid into the tank Water flush and air integrity test the product vilter Liquid (product) filter Tank vent filter (flow in either direction is okay) T Steam trap V
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Archimedes discovers the principle that the buoyant force on a submerged object equals the weight of the liquid it displaces. A particle in a centrifugal field reaches terminal velocity in a wink. At this velocity the forces on the particle balance: F centrif = F bouyancy + F drag
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Terminal velocity of particles in a centrifuge v = terminal velocity of particle in radial direction; centifugal force and drag force on it are equal a = particle diameter ρ ρ 0 = density of particle - density of suspending medium μ = viscosity of suspending medium Applies to an idealized case of dilute suspension of spheres at Re < 1, but reveals important factors g = 2 G 2 ±² − ² 0 ³ 9 ´ µ 2 Coefficient (a property of the suspension) Driving force Velocity = particle flux / particle conc
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Some characteristic velocities (Harrison Table 5.1) item driving force Velocity* remark Yeast cell Gravity 0.5 cm/hr Too slow Yeast cell 1000 x gravity 500 cm/hr = 8 cm/min Practical in lab or prodn centrifuge Bacteria cell Gravity 0.02 cm/hr Way too slow Bacteria cell 1000 x gravity 20 cm/hr = 0.3 cm/min Practical in lab Protein molecule 10,000 x gravity 0.06 cm/hr Way too slow; opposed by Brownian motion Protein molecule 500,000 x gravity 3 cm/hr Practical in lab w ultracentrifuge * For dilute suspension in a medium with μ = 1 cp and ρ 0 = 1 g/cm 3 . Protein molecule are small, and strain the continuum assumption inside the terminal velocity eqn (assumption for the drag force)
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equilibrium concentration gradient Height, h colloid or particle concentration, C A B V particle ( ρ ρ 0 ) H g / kT = 0.01 << 1 H V particle ( ρ ρ 0 ) H g / kT = 1 What is the curve for suspension A in a cetrifugal field of 100 g ? diffusion
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Lecture Notes 6 - Concept question(s) for sedimentation...

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