Super Centrifuge.

 Super Centrifuge.

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Centrifuge:

• The equipment used for the process of centrifugation is called a Centrifuge.

• The centrifuges are of two types as following,

1. Sedimentation centrifuge:L

• It is a centrifuge that produces sedimentation of solids based on the difference in the densities of two or more phases of the mixture. 

2. Filtration centrifuge:

•  It is a centrifuge in which solids pass through the porous medium based on the difference in the densities of the solid and liquid phases.

Super Centrifuge. 

•  Super Centrifuge is a continuous centrifuge used for separating two immiscible liquid phases.

Principle:  

• It is a sedimentation centrifuge. 

• The separation is based on the difference in the densities between two immiscible liquids. 

• Centrifugation is done in the bowl of a small centrifuge. 

• During centrifugation, the heavier liquid is thrown against the wall, while the lighter liquid remains as an inner layer. 

• The two layers are simultaneously separated using modified weirs. 

Construction:  

• It consists of a long hollow cylindrical bowl of small diameter. 

• It is suspended from a flexible spindle at the top and guided at the bottom by loose-fit bushing. 

• Two liquid outlets are provided at different heights at the top of the bowl, for simultaneous recovery of the separated liquids using modified weirs.  

Working:  

• The centrifuge is allowed to rotate on its longitudinal axis at a high frequency usually about 2000 revolutions per minute with the help of drive-assembly. 

• The feed is introduced from the bottom of the centrifuge using a pressure system. 

• During centrifugation, two liquid phases separate based on the difference in their densities. 

• The heavier liquid is thrown against the wall, while the lighter liquid forms an inner layer. 

• Both liquids rise to the top of the vertical bowl. 

• The liquid-liquid interface (the so-called neutral zone) is maintained by a hydraulic balance. 

• These two layers are simultaneously separately removed from different heights through modified weirs. 

• Thus the super centrifuge can work for continuous separation of immiscible liquid phases.

Uses:  

1. It is used for separating liquid phases of emulsions in food and pharmaceuticals. 

Commonly Asked Questions.

1. Write a short note on Super Centrifuge.

Non-Perforated Basket Centrifuge.

 

Centrifuge:

• The equipment used for the process of centrifugation is called a Centrifuge.

• The centrifuges are of two types as following,

1. Sedimentation centrifuge:L

• It is a centrifuge that produces sedimentation of solids based on the difference in the densities of two or more phases of the mixture. 

2. Filtration centrifuge:

•  It is a centrifuge in which solids pass through the porous medium based on the difference in the densities of the solid and liquid phases.

Non-Perforated Basket Centrifuge.

Principle:  

• This is a sedimentation centrifuge. 

• The separation is based on the difference in the densities of solid and liquid phases without a porous barrier. 

• The bowl contains a non-perforated side-wall. 

• During centrifugation, solid phase is retained on the sides of the basket, while the  liquid remains at the top, which is removed by a skimming tube.

Construction:  

• It consists of a basket, which may be made of steel or any other suitable metal. 

• The basket is suspended on a vertical shaft and is driven by a motor using a suitable power system. 

Working:  

• The suspension is fed continuously into the basket. 

• During centrifugation, the solid phase is retained on the sides of the basket, while liquid remains on the top. 

• The liquid is removed over a weir or through a skimming tube. 

• When a suitable depth of solids has been deposited on the walls of the basket, the operation is stopped. 

• The solids are then scraped off by hand or using a scraper blade.   

Uses:  

1. Non-perforated basket centrifuge is useful when the deposited solids offer high resistance to the flow of liquid.  

Commonly Asked Questions.

1. Write a short note on Non-Perforated Basket Centrifuge.

Perforated Basket Centrifuge.

 

Centrifuge:

• The equipment used for the process of centrifugation is called a Centrifuge.

• The centrifuges are of two types as following,

1. Sedimentation centrifuge:L

• It is a centrifuge that produces sedimentation of solids based on the difference in the densities of two or more phases of the mixture. 

2. Filtration centrifuge:

•  It is a centrifuge in which solids pass through the porous medium based on the difference in the densities of the solid and liquid phases.

Perforated Basket Centrifuge.

Principle:  

• Perforated basket (bowl) centrifuge is a filtration centrifuge.  

• The separation is through a perforated wall based on the difference in the densities of solid and liquid phases. 

• The bowl contains a perforated side-wall.  

• During centrifugation, the liquid phase passes through the perforated wall, while the solid phase is retained in the bowl.  

• The solid is removed after cutting the sediment by a blade after stopping the centrifuge. 

Construction:  

• It consists of a basket, made of steel (sometimes covered with vulcanite or lead) or copper or monel or any other suitable metal.  

• The basket may have a diameter of 0.90 meters and a capacity of 0.085 meter cube.  

• The basket is suspended on a vertical shaft and is driven by a motor using suitable power systems such as belt pulleys, water turbines and electric motors.  

• Surrounding the basket, a casing stationary is provided which collects the filtrate and discharges it at the outlet.

Working:  

• The material is kept in the basket when the basket is stationary.  

• Power is applied to rotate the basket and maximum speed must be attained quickly. 

• The basket runs at 1000 revolutions per minute.  

• During centrifugation, the liquid passes through the perforated wall, while the solid phase remains in the basket. 

• The liquid leaves the basket and is collected at the outlet.  The cake is then spun to dry as much as possible.  

• After a definite period of time, the power is turned off. By applying a brake the centrifuge is stopped.  The basket is brought to rest. 

• The solid cake is cut using a blade and then unloaded manually.  

Uses:  

1. Performed basket centrifuge is extensively used for separating crystalline drugs (such as aspirin) from the mother liquor. 

2. Free flowing product can be obtained because mother liquor is removed completely.  

3. It is also used for removing unwanted solids from a liquid. For example, precipitated proteins are removed from insulin.  

Advantages:  

1. The centrifuge is very compact and it occupies very little floor space.  

2. It can handle slurries with a high proportion of solids and even those having a paste-like consistency.  

3. The final product has very low moisture content.  

4. In this method, the dissolved solids are separated from the cake.  

5. The process is rapid. 

Disadvantages:  

1. The entire cycle is complicated, resulting in considerable labor costs.  

2. It is a batch process.  

3. If the machine is adapted for prolonged operation, there is considerable wear and tear of the equipment.  

Commonly Asked Questions.

1. Write a short note on Perforated Basket Centrifuge.

Centrifugation: Introduction.

Definition:

• Centrifugation is a process involving the use of the centrifugal force for the sedimentation of heterogeneous mixtures with an instrument called a centrifuge, used in industry and in laboratories. 

• This process is used to separate two immiscible liquids. 

• More-dense components of the mixture migrate away from the axis of the centrifuge,  while less dense components of the mixture migrate towards the axis. 

• Centrifuge is a device for separating particles from a solution according to their sizes, shapes, densities, and viscosities of the medium. 

Applications of centrifugation:

• Production of bulk drugs.

• Production of biological products. 

• Biopharmaceutical analysis of drugs.

• Evaluation of suspensions and emulsions. 

• Determination of molecular weight of colloids. 

Theory of centrifugation:

• The centrifuge works on sedimentation. 

• Spinning samples at a high speed. 

• The components of a mixture are subjected to centrifugal force, Dense particles migrate away from the axis of rotation and lighter ones move towards it. 

Relative Centrifugal Force (RCF):

• RCF is the ratio of the centrifugal acceleration at a specified radius and the speed to the standard acceleration of gravity. 

• Relative Centrifugal force is defined as 

f=Mω2 r

• Where, 

• F= intensity of centrifugal force 

• M= mass of particle 

• ω= angular velocity of rotation 

• R= distance of migrating particles from central axis of rotation. 

• The RCF value for any centrifuge may be calculated from the following equation: 

RCF = 1.18 × r × (rpm) 2 ×10-5

• Where, 

• 1.18×10-5 = An empirical factor

• r is the radius in cm from the center of the centrifuge shaft to the external tip of the centrifuge tube. 

• rpm is the number of revolutions per minute of the centrifuge rotor.

• The time required to separate particles depends on the rotor speed, radius of rotor and effective path length traveled by sedimented particles. 

• The following formula is useful for the calculation of the speed required for a rotor with a radius that differs from the radius with which a prescribed, 

R.P.M. = 1000× √RCF/1.18×r 

• The length of time of centrifugation also can be calculated so that running with an alternative rotor of a different size is equivalent to running with an original rotor. 

Commonly Asked Questions.

1. Define “Centrifugation”? Give its applications in the Pharmacy,

2. Write a short note on theory of Centrifugation.

 

Vacuum Dryer.

 

Principle:

• Vacuum drying is generally used for the drying of substances which are hygroscopic and heat sensitive, and is based on the principle of creating a vacuum to decrease the chamber pressure below the vapor pressure of the water, causing it to boil. 

• Hence, water evaporates faster, and the rate of drying increases.

Construction:

• The oven is divided into hollow trays which increases the surface area for heat conduction.

• The oven door is locked airtight and is connected to a vacuum pump to reduce the pressure.

• The materials to be dried are kept on the trays inside the vacuum dryer and pressure is reduced by means of vacuum pump.

• The enclosed space ( approximately 1.5 meter cube ) is divided in to a number of portions by means of 20 hollow shelves, which are part of the jacket. 

• These shelves provide a larger surface area ( about 45 to 50 meter square ) for conduction of heat. 

• Over the shelves, metal trays are placed for keeping the material. 

• The oven door can be locked tightly to give an airtight seal. 

• The oven is connected to a vacuum pump by placing a condenser in between.

Working:

• The trays that are present in the dryer are used to dry the material that is placed in the shelves and the pressure is reduced to 30 to 60 Kps by vacuum pump.

• The door closes firmly and steam passes through the jacket space and the shelves.

• So the heat transfer is carried out by the conduction mechanism.

• When evaporated under vacuum, the water is evaporated from the material at 25 - 30℃.

• The vapor goes to the condenser.

• After drying, the vacuum line is disconnected.

• Then the materials are collected from the tray.

Uses:

1. Vacuum dryer can be used for drying of following:

1. Heat sensitive materials, which undergo decomposition.

2. Dusty and hygroscopic material.

3. Drugs containing toxic solvents. These can be separated in to closed containers.

4. Feed containing valuable solvents. These are recovered by condensation.

5. Drugs which are required as porous end products.

6. Friable dry extracts.

Advantages:

1. Material handling is easy.

2. Hollow shelves which are electrically heated can be used.

3. It provides a large surface area. So the heat can be easily transferred through the body of the dryer and the last drying action takes place.

4. Hot water can be supplied through the dryer, which help in drying process at the desired temperature.

Disadvantages:

1. Batch type process.

2. Low efficiency.

3. More expensive.

4. Labour cost is too high.

5. High maintenance.

6. Danger of overheating due to the vacuum.

Commonly Asked Questions.

1. With a well labeled diagram describe construction and working of Vacuum Dryer.

2. Write a short note on Vacuum Dryer.