Immobilized Enzyme Reactors – Batch & continuous

Presented by – Abhishek GiriM.Sc. (Part – II), SEM – IV,P-VR.K.Talreja College UNR-03

Topics to be Covered

Introduction Types of Reactors Batch reactors Continuous reactors Advantages Disadvantages Applications References

What is a bioreactor?Bioreactor :- device, usually a vessel, used to direct the activity of a biological catalyst to achieve a desired chemical transformation.Fermenter : -Type of bioreactor in which the biocatalyst is a living cell.

Introduction

Immobilization of enzymes refers to the technique of confining/anchoring the enzymes in or on a inert support for their stability & functional reuse.

GOOSE WITH A GOLDEN EGG Retains structural conformation necessary for catalysis. Techniques for immobilization of enzymes are – adsorption,

entrapment, microencapsulation, covalent binding, & cross-linking.

Immobilized enzymes are broadly of two types - batch reactors & continuous reactors.

Choice of reactor depends on the cost of a predetermined product.

Types of an Enzyme Reactor

6 TYPES Stirred tank batch reactor. Continuous flow stirred tank reactor. Batch membrane reactor. Continuous flow ultra filtration membrane reactor. Packed bed reactor. Fluidized bed reactor.

Batch Reactor

Common when soluble enzymes are used. Fitted with fixed baffles that improve the stirring efficiency. Entire product is removed. Enzymes & Substrate molecule have identical residence time. Enzymes are not separated & not re-used. Operation costs of batch reactors are higher than for continuous

processes. Expensive & in some cases are not productive also labor & service

demand increases. Small scale experimental studies

Batch reactor – Stirred tank [STR]

Simplest form.. Good mixing, ease of temperature & pH

control. Loss of some enzyme activity may occur. Modified form – Basket Reactor. Basket reactor – enzymes are retained

over the impeller blades or baffles of the tank reactor.

Both have a well mixed flow pattern. High shear forces may damage cells. Requires high energy input.

Application :- free & immobilized enzyme reactions..

Recovery of products produced by enzymes like lipase, glucose isomerase & B-galactosidase.

Batch reactor – Plug flow [PFR]

Alternative to flow pattern type of reactors.

Flow rate controlled by a plug system. Plug flow – Packed bed or Fluidized

bed Used when inadequate product

formation in flow type reactors. Advantage – external mass transfer

effects can be reduced by the operational high fluid velocities.

Application :- used for obtaining kinetic data on the reaction systems.

Batch reactor – Packed-bed [PBR]

Modified form, Widely used. When equipped with external

heating & cooling coils is also called as PFR

Substrate stream flows at same velocity, parallel to reactor with no back-mixing.

3 substrate flow possibilities – downward flow method, upward, & recycling method.

Packed-bed reactors are used with immobilized or particulate biocatalysts.

Medium can be fed either at the top or bottom & forms a continuous liquid phase.

Batch reactor – Fluidised-bed [FBR] Intermediate between CSTRs & PBRs. Consist of a bed of immobilized

enzymes which is fluidized by rapid upwards flow of the substrate or in combination with a gas or Secondary liquid stream.

Fluidization requires large power input. Heating & cooling coils are located

outwards. Baffles are used to decrease stirring

efficiency. Useful if the reaction involves the

utilization or release of gaseous material.

Disadvantage – difficulty in scaling-up these reactors.

Continuous reactors Substrate added continuously & product removed simultaneously. Certain advantages over batch reactors. Control over the product formation, convenient operation of the

system & easy automation of the entire process. 2 types – Continuous stirred tank reactor (CSTR) & Plug flow reactor

(PFR). Choice of continuous reactor is based on the Kinetic considerations. CSTR is ideal for good product formation.

Continuous reactor – CSTR Continuously operated version of STR. Degree of conversion is independent of

the position in the vessel, as complete mixing is obtained with stirring & conditions within CSTR is same as the outlet stream.

Readily obtained. Requires more enzyme. More favorable than PFR if substrate

inhibition occurs. Enzymes are covalently linked to a

carrier by cyanogen bromide activation.

Application :- used for obtaining kinetic data on the reaction systems.

Continuous reactor – PFR Degree of conversion is dependent on

the length of the reactor as no mixing device exist & the conditions within the reactor are never uniform.

Difficult to obtain. Requires less enzyme to obtain the

same degree of conversion as in CSTR.

Application :- used for obtaining kinetic data on the reaction systems.

Diagrams of various important enzyme reactor types.

a. Stirred tank batch reactor (STR), which contains all of the enzyme and substrates until the conversion is complete.

b. batch membrane reactor (MR), where the enzyme is held within membrane tubes which allow the substrate to diffuse in and the product to diffuse out. This reactor may often be used in a semi continuous manner, using the same enzyme solution for several batches.

c. packed bed reactor (PBR), also called plug -flow reactor (PFR), containing a settled bed of immobilised enzyme particles.

d. continuous flow stirred tank reactor (CSTR) which is a continuously operated version of (a);

e. continuous flow membrane reactor (CMR) which is a continuously operated version of (b);

f. fluidised bed reactor (FBR), where the flow of gas and/or substrate keeps the immobilised enzyme particles in a fluidised state.

Reactor Comparison

Batch High operating costs Batch-to-batch variations

PFR Difficult to control pH and Temperature

CSTR Simple pH, Temperature control Simple catalyst charging and replacement

Choice of reactor Form & characteristics of immobilized enzyme preparation. Operational requirements. Ex – Penicillin acylase (pH control), the CSTR or BSTR is more

suitable than PFR reactors. due to possible disintegration of support through mechanical

shearing, only durable preparation of immobilized enzymes should be used in CSTR.

With Small immobilized enzymes particles, problems such as high pressure drop & plugging arise in PFR reactors. Hence, FPR should be used..

Reactant characteristics can also influence the choice of reactor. Insoluble substrate and product & highly viscous fluids are

preferably processed in FBR or CSTR, where no plugging occurs.

Advantages of immobilized enzymes

High Stability. Reusable. Products are enzyme free. Ideal for multi-enzyme reaction systems. Controls of enzyme function is easy. Suitable for industrial & medical use. Minimize effluent disposal problems..

Disadvantages

Possible loss of biological activity of an enzyme during immobilization or while it is in use

Immobilization is expensive technique requires sophisticated equipment

Examples of Immobilized enzymes

Immobilized glucosidase & glucose isomerase are used in production of fructose from starch.

Immobilized L-Aminoacylase which resolves a mixture of D- and L- amino acids.

Immobilization of Microbial cells.

Applications of Enzyme Reactor

Used in a variety of therapeutic applications. As a drug or toxin removal system. To produce a desired product of commercial importance on a large

scale. In the degradation of toxic compounds.

Name of Reactor Application

Dehydrogenase reactor Conversion of lactate to pyruvate.

11-β-hydroxylase Synthesis of prednisolone (therapeutic & ISD).

Β-galactosidase Lactose hydrolysis in food industry.

Cellulase Used in paper industry.

Reactor Sizing

Reactor Sizing

Conversion of 99.25% 120 L reactor required

Increase conversion by 0.5% to 99.75% 360 L reactor required

Reactor Design Considerations

Temperature control pH control Level control Sterilizable Wire-mesh sieve Sample port

Simplified Reactor Schematic

Final Reactor Schematic

• U. Satyanarayan, Biotechnology, 2007 Reprint, Uppala Author Publisher Interlink.

• Colin Rateledge and Bjorn Kristiansen, Basic Biotechnology, 2nd Edition, Cambridge Univ. Press

• T. Devasena, Enzymology,2010, Oxford University press.

References - BOOKS

• www1.lsbu.ac.uk/water/enztech/reactors.htm• en.wikipedia.org/wiki/Batch_reactor• en.wikipedia.org/wiki/continuous_reactor• en.wikipedia.org/wiki/Immobilized_enzyme

References – Web-links

Thank You