8/13/2019 Down Streaming Updated

1/13

8/13/2019 Down Streaming Updated

2/13

Introduction Desired products are separated and purified after

successful fermentation or enzyme reactions

This step is up to 60% of total cost, not including thepurchase 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

8/13/2019 Down Streaming Updated

3/13

Solid-Liquid Separations Products may be biomass, extracellular, or intracellular

Purpose: to separate insolubles from fermentation

broth Cell sizes vary widely, from 1m (bacteria)to 40m

(suspension plant cells)

8/13/2019 Down Streaming Updated

4/13

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

8/13/2019 Down Streaming Updated

5/13

Rate of FiltrationRate of filtration: (dvf/dt) = P A/ (L/K)

A= area of filter

K= filters permeability

L= thickness of the filter cake

Filtration time (t)= MPc/2P(Vf/A)2

8/13/2019 Down Streaming Updated

6/13

Centrifugation 2 types: tubular and disk

Disk used in continuous operations:

Has a short, wide bowl 8-20 inches in diameter whichturns on a vertical axis

Cone-shaped disks with uniform spacing are placedinside the bowl to separate suspended solids

Terminal velocity= vt= dp2

(s-)a/18

8/13/2019 Down Streaming Updated

7/13

Recovery Fermentation broth consists of dilute aqueous solution

from which products have to be recovered andpurified.

Overlaps exist between recovery and purification

Extraction and adsorption are exclusively classified asrecovery

8/13/2019 Down Streaming Updated

8/13

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)

8/13/2019 Down Streaming Updated

9/13

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

8/13/2019 Down Streaming Updated

10/13

Adsorption (physical and chemical) This is effective from separation of very dilute

dissolved substances

1- Conventional adsorption-based on intermolecular forces of attraction (VanderWaals force) between the molecules of solid andsubstance (activated carbon used to purify water)

- process is mixing of fruit pits and calcium chloride

8/13/2019 Down Streaming Updated

11/13

Adsorption (continued)2- Ion Exchange

-components include: polymeric network, ionic

functional group attached to network and counter ion3- Affinity adsorption

involves chemical interactions between solute andligand attached to surface of carrier particle

8/13/2019 Down Streaming Updated

12/13

Purification Methods include precipitation, chromatography, and

electrophoresis, and membrane separation

Precipitation- Used for recovery of proteins and isinduced by salt, organic solvent, or heat addition

Chromatography- include a mobile phase with solutesto be separated and a stationary phase which may be

adsorbent, ion-exchange resin, gel, or porous solidpacked in cylindrical column

Electrophoresis- separation of charged speciesaccording to migration rates in electrical field

8/13/2019 Down Streaming Updated

13/13