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Downstream Processing

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Presentation on theme: "Downstream Processing"— Presentation transcript:

1 Downstream Processing

2 Introduction Desired products are separated and purified after successful fermentation or enzyme reactions This step is up to 60% of total cost, not including the purchase of raw materials Products may be dilute in aqueous medium, temperature sensitive, have multiple items to separate, and/or have properties similar to contaminants Products may require high purification and homogeneity

3 Solid-Liquid Separations
Products may be biomass, extracellular, or intracellular Purpose: to separate insolubles from fermentation broth Cell sizes vary widely, from 1µm (bacteria) to 40µm (suspension plant cells)

4 Filtration The separation of particles by forcing the fluid through a filtering medium Based on particle size and pressure drop Filters are either based on pressure principle or vacuum

5 Rate of Filtration A= area of filter
Rate of filtration: (dvf/dt) = ΔP · A/ µ(L/K) A= area of filter K= filter’s permeability L= thickness of the filter cake Filtration time (t)= M∞Pc/2ΔP(Vf/A)2

6 Centrifugation 2 types: tubular and disk
Disk used in continuous operations: Has a short, wide bowl 8-20 inches in diameter which turns on a vertical axis Cone-shaped disks with uniform spacing are placed inside the bowl to separate suspended solids Terminal velocity= vt = dp2(ρs-ρ)a/18µ

7 Recovery Fermentation broth consists of dilute aqueous solution from which products have to be recovered and purified. Overlaps exist between recovery and purification Extraction and adsorption are exclusively classified as recovery

8 Extraction (liquid-liquid separation)
Separation of solutes from the feed by contact with another insoluble liquid (solvent) The effectiveness of the solvent increased with: optimum pH addition of counterions (acetate or butyrate)

9 Types of Extractions Single stage extraction- either in batch or continuous mode Overall material balance for the mixer-settler is F + S = R + E and the material balance for the solute is FxF + Sys = Rx + Ey Multistage extraction Crosscurrent extraction- use continuously or in batch Counter-current extraction- more efficient but cannot be operated in batch mode

10 Adsorption (physical and chemical)
This is effective from separation of very dilute dissolved substances 1- Conventional adsorption -based on intermolecular forces of attraction (Vander Waals force) between the molecules of solid and substance (activated carbon used to purify water) - process is mixing of fruit pits and calcium chloride

11 Adsorption (continued)
2- Ion Exchange -components include: polymeric network, ionic functional group attached to network and counter ion 3- Affinity adsorption involves chemical interactions between solute and ligand attached to surface of carrier particle

12 Purification Methods include precipitation, chromatography, and electrophoresis, and membrane separation Precipitation- Used for recovery of proteins and is induced by salt, organic solvent, or heat addition Chromatography- include a mobile phase with solutes to be separated and a stationary phase which may be adsorbent, ion-exchange resin, gel, or porous solid packed in cylindrical column Electrophoresis- separation of charged species according to migration rates in electrical field

13 Purification (continued)
Membrane Separation Microfiltration- separation of suspended material based on pore size of 0.02 to 10 µm Ultrafiltration- if separation is achieved at the molecular level, most commonly 100 to 200 Å Reverse osmosis- to separate suspended and dissolved material using high pressure to reverse flow across semipermeable membrane

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