document3
DESCRIPTION
fgdsgfte5364567i8TRANSCRIPT
Motivation
•Consider two different modes of a continuous process involving enzymatic reactions as shown below
S,E
S,E,P S,P
S
(a) (b)
Immobilized Enzyme
Advantages of method (b)
•Reusability of enzyme•Reduced separation costs• Some enzymes are more stable if they are immobilized. (Many native
enzymes are “immobilized” in the cell.)
Definitions
•Enzyme Immobilization • Enzyme immobilization may be defined as a process of confining the
enzyme molecules to a solid support over which a substrate is passed and converted to products.
• Immobilized Enzyme• An immobilized enzyme is one whose movement in space has been restricted
either completely or to a small limited region.
Ideal Characteristics of Supports
• Inert.
•Physically strong and stable.
• Cost effective.
• Possibility to regenerate.
•Reduction in product inhibition.
Immobilization Techniques
Immobilization TechniquesPhysical methods
Adsorption
Entrapment
Encapsulation
Chemical methodsSupport
Copolymerization
Cross Linking
Effect of Mass-Transfer Resistance
•Due to the large particle size of immobilized enzyme or due to inclusion of enzyme in polymeric matrix.
External Mass Transfer Resistance
•Enzymes are immobilized on surface of uncharged, nonporous flat plate.•Entire surface is uniformly accessible to substrate in adjacent fluid.•At steady state product and substrate do not accumulate at the
surface and rate of mass transfer equals rate of reaction
Concentration profiles
Distance from the surface
Conc
entr
atio
n
Distance from the surface
Conc
entr
atio
n
Reaction Limited Mass Transfer Limited
Rate of Reaction Vs Concentration
Concentration
rate
of r
eact
ion
rate
of r
eact
ion
Reaction LimitedMass Transfer Limited
Concentration
Internal Mass Transfer Resistance
•Enzymes are immobilized to a porous support having large internal surface areas.
Effective Diffusivities in Biological gels
•The gel structure increases the path length for diffusion, and asa result decreases the diffusion rate.•One of the most reliable techniques is the thin-disk method
• A diffusion cell with two compartments divided by a thin gel. • Each compartment contains a well-stirred solution with different solute
concentrations.
•Effective diffusivity can be calculated from the mass flux verses timemeasurement