centrifugation, its types, principle, functions, applications

 

DEFINATION:

“Centrifugation is a process which involves the use of the centrifugal force for the sedimentation of  heterogeneous mixtures with a centrifuge, used in industry and in laboratory settings”.

PRINCIPLE:

 The centrifuge works using the sedimentation principle, where the centripetal acceleration causes denser substances and particles to move outward in the radial direction. At the same time, objects that are less dense are displaced and move to the center. In a laboratory centrifuge that uses sample tubes, the radial acceleration causes denser particles to settle to the bottom of the tube, while low-density substances rise to the top.

CENTRIFUGAL  FIELD:

“ It  is the apparent force that draws a rotating body away from the center of rotation. It is caused by the inertia of the body”.

 EQUATION  OF  CENTRIFUGAL  FORCE:

The equation for centrifugal force are as follows:

INSTRUMENT  COMPONENTS:

The instrument components of centrifuge are as follows:

·        Rotor

·        Motor

·        Imbalance  detector

·        Tachometer

·        Safety  lid

·        Braking  system

·        Refrigerator

TYPES  OF  CENTRIFUGE:

There are four types of centrifuge which are as follows:

·        Small Benchtop

·        Microcentrifuges

·        High speed centrifuge

·        Ultracentrifuges

  SMALL  BENCHTOP:

The characteristics of small benchtop are as follows:

·        With or without refrigeration

·        Slow speed (eg up to 4000 RPM)

·        Common in clinical labs (blood/plasma/serum sepration)

·        can take approx (up to) 100 tubes, depending on diameter

 MICROCENTRIFUGE:

The characteristics of microcentrifuge are as follows:

·        Take tubes of small vols (up to 2 mL)

·        Very common in biochemistry/molecular biology/biological labs

·        Can generate forces up to ~15,000 x g

·        With or without refrigeration

HIGH  SPEED  CENTRIFUGE:

The characteristics of high speed centrifuge are as follows:

• ·        15,000 – 20,000 RPM
• ·        Large sample capacity depending on rotor
• ·        Normally refrigerated
• ·        Research applications
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  ULTRACENTRIFUGE:

The characteristics of ultracentrifuge are as follows:

• Limited lifetime
•   Expensive
•     Require special rotors
•     Care in use – balance critical!
•     Research applications
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  FUNCTIONS:

There are several process functions using centrifuges in biotech separation. These are listed below:

1. SEPARATION:

 Centrifugation can be used for solid-liquid separation provided the solids are heavier than the liquid. Centrifuge can also be used to separate a heavy phase, and two lighter liquid phases, with one of the lighter phases being lighter than the other. As discussed, solids can be lighter than liquid and separation is by flotation of the dispersed solid phase.

 2. CLARIFICATION- MINIMAL SOLIDS IN LIQUID PRODUCT:

 Centrifuge can be used to clarify the discharged separated lighter liquid phase. The objective is to minimize the discrete suspended solids in the light continuous phase. Usually, only fine submicron biosolids are left uncaptured by centrifugation and they escape with the discharged light phase.

 3. CLASSIFICATION -SORT BY SIZE AND DENSITY:

 Centrifuge is used to classify solids of different sizes. One of the several possible applications is to classify crystals of different size range, with the finer submicron sizes leaving with the light phase and retaining only the larger sizes in the separated heavy phase. Either of the separated solids can be the product. For example, the larger crystals can be the product crystals while the finer crystals are returned to the crystallizer to grow to larger crystals. Another similar application is to classify smaller size cell debris in the light liquid phase from the heavier products after homogenizing cells.

  4. DEGRITTING – REMOVE OVERSIZED AND FOREIGN

   PARTICLES:

Degritting is similar to classification where unwanted particles, larger or denser, are rejected in the sediment, with product (smaller or less dense) overflowing in the lighter liquid phase. Another situation is where smaller unwanted particles are rejected in the light liquid phase, and valuable heavier solids are settled with the heavier phase.

 5. THICKENING OR CONCENTRATION- REMOVE  LIQUID

    CONCENTRATE SOLIDS:

 Centrifuge is frequently used to concentrate the solid phase by sedimentation and compaction, removing the excess liquid phase in the overflow or centrate. This reduces the volume of the product in downstream processing.

 6. SEPARATION  AND REPULPING – REMOVE IMPURITIES BY WASHING AND DILUTING:

With a concentrated suspension containing contaminants such as salts and ions, it is diluted and washed so that the contaminants are dissolved in the wash liquid. Subsequently, the suspension is sent for centrifugation to remove the spent wash liquid with dissolved contaminants or finely suspended solids. Subsequently, the product can be further concentrated by centrifugation.

 PREVENTIVE  CARE  FOR  CENTRIFUGE:

The preventive care for centrifuge are as follows:

·        Carefully read manual before using centrifuge.

·        Select proper operating conditions.

·        Check rotor for cleanliness and for damage.

·        Select proper rotor of definite size.

·        Be sure that rotor is clean and undamaged.

·        Keep accurate record of centrifuge and rotors.

·        Carefully clean rotors for centrifugation.

·        Verify that alarms are working properly.

 

COMMON  FAILURES:

The common failures that occurs in centrifuge are as follows:

·        Machine will not start.

·        Power supply is faulty.

·        Safety switch or timer not working properly.

·        Motor not working properly.

·        Motor making noise.

·        Rotor is broken.

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