Pharmaceutical Technology II PD515 Fall 2024 Lecture 8 - Centrifugation PDF

PHARMACEUTICAL TECHNOLOGY II PD515 FALL 2024 LECTURE (8) “CENTRIFUGATION” DR. WALEED MOHAMMED KHATTAB PHD. IN PHARMACEUTICAL TECHNOLOGY, 2020. MSC. IN PHARMACEUTICS, 2014. BSC. IN PHARMACEUTICAL SCIENCES, 2008. By the end of...

PHARMACEUTICAL TECHNOLOGY II PD515 FALL 2024 LECTURE (8) “CENTRIFUGATION” DR. WALEED MOHAMMED KHATTAB PHD. IN PHARMACEUTICAL TECHNOLOGY, 2020. MSC. IN PHARMACEUTICS, 2014. BSC. IN PHARMACEUTICAL SCIENCES, 2008. By the end of this lecture, the student will be able to: Understand the meaning of centrifugation and its importance in pharmaceutical industry. Recognize different types of centrifugation equipment. Identify the construction and process of filtration centrifuges. Identify the construction and process of sedimentation centrifuges. Identify the construction and process of continuous centrifuges. Waleed M. Khattab, PhD. Fall 2024 2  CENTRIFUGATION Centrifugation is a technique of separating substances which involves the application of centrifugal force. The particles are separated from a solution according to their size, shape, density, viscosity of the medium and rotor speed. Separation is achieved by spinning a vessel containing material at high speed; the centrifugal force pushes heavier materials to the outside of the vessel. A centrifuge is a laboratory device or an industrial scale equipment which is employed for separation of different phases (Solid/Liquid or Liquid/Liquid). Waleed M. Khattab, PhD. Fall 2024 3  CENTRIFUGATION IMPORTANCE Centrifugation, clearly, plays an important role in the pharmaceutical industry in the production of bulk drugs, biological products, and determination of molecular weight of colloids and in the evaluation of suspensions and emulsions. Waleed M. Khattab, PhD. Fall 2024 4  CENTRIFUGATION PRINCIPLE Centrifugation is used to separate all types of particle based upon their sedimentation properties. The sedimentation properties of particles are separated primarily on the basis of either their density or size. The density affect sedimentation to a much lesser extent than size. In centrifugation it is important to differentiate between the speed of centrifugation (r.p.m.) and the relative centrifugal force (RCF or G) since these are often confused. Waleed M. Khattab, PhD. Fall 2024 5  CENTRIFUGATION PRINCIPLE The centrifugal force generated by a centrifuge can easily be calculated using the corresponding equation. R is the distance from the center of rotation in centimeters; that is, the centrifugal force increases as the particles move down the centrifuge tube. As a general rule, the greater the centrifugal force the shorter the separation time. Waleed M. Khattab, PhD. Fall 2024 6  CENTRIFUGATION PRINCIPLE APPLICATIONS High centrifugal force is required if the particles in suspensions are very small. Toseparate such small particles from suspensions the centrifuge is designed to be small in size that can operate at very high speed of rotation. If a large amount of material is to be separated and a low centrifugal effect is sufficient to separate the suspension then the diameter of the centrifuge is increased and speed is kept low. Waleed M. Khattab, PhD. Fall 2024 7  INDUSTRIAL-SCALE CENTRIFUGES Waleed M. Khattab, PhD. Fall 2024 8  FILTRATION CENTRIFUGES (1) Perforated Basket Centrifuge: Construction: Batch type bottom driven centrifuge consists of a rotating basket placed on a vertical shaft and driven by a motor from bottom. The sides of the basket are perforated and are also covered with a screen or filter cloth on the inside. Surrounding the basket is a stationary casing that collects the filtrate. 9 Waleed M. Khattab, PhD. Fall 2024  FILTRATION CENTRIFUGES (1) Perforated Basket Centrifuge: 10 Waleed M. Khattab, PhD. Fall 2024  FILTRATION CENTRIFUGES (1) Perforated Basket Centrifuge: Operation: When the basket rotates, the product enters centrally is thrown outside by centrifugal force and held by filter cloth. The filtrate is forced through the cloth and is removed through liquid outlet. The solid material is remained on the cloth. The cake can be washed-off by water to get filtrate. Advantages: Compact – Rapid – Concentrated slurries – Final Product low moisture content – The dispersed solids are separated as a cake. Disadvantages: Batch-type process – Lengthy operation forms hard cake – Wear and Tear. Waleed M. Khattab, PhD. Fall 2024 11  FILTRATION CENTRIFUGES (2) Semi-continuous Centrifuge (Short cycle automatic batch centrifuge): Principle: Semi-continuous centrifuge is a filtration centrifuge. The separation is done on the basis of difference in the densities of the solid and liquid. This separation occurs through a perforated wall. The bowl contains a perforated side-wall. During centrifugation, the liquid phase passes through the perforated wall, while solid phase retains in the bowl. The solid is washed and removed by cutting the sediment using a blade. Waleed M. Khattab, PhD. Fall 2024 12  FILTRATION CENTRIFUGES (2) Semi-continuous Centrifuge (Short cycle automatic batch centrifuge): Construction: It consists of a rotating basket placed on a horizontal shaft and driven by a motor from side. The side of the basket is perforated. Surrounding the basket is a stationary casing that collects the filtrate. Waleed M. Khattab, PhD. Fall 2024 13  FILTRATION CENTRIFUGES (2) Semi-continuous Centrifuge (Short cycle automatic batch centrifuge): Construction: Slurry is introduced through a pipe that enters the basket through the center. To wash the crystal the wash-pipe is also introduced through the center of the basket. The layer of cake is removed by a chute fitted with a knife. The knife cuts down the cake within the basket. The knife-chute assembly is raised with the help of a hydraulic apparatus Waleed M. Khattab, PhD. Fall 2024 14  SEDIMENTATION CENTRIFUGES (1) Non-perforated Basket Centrifuge: Construction: It consists of a metallic basket. The basket is suspended on vertical shaft and is driven by a motor using a suitable power system. The basket contains a non-perforated side- wall that retains solid phase on its sides during centrifugation. The liquid that remains at the top is removed by a skimming tube. Waleed M. Khattab, PhD. Fall 2024 15  SEDIMENTATION CENTRIFUGES (1) Non-perforated Basket Centrifuge: Working: The suspension is fed continuously into the basket. During centrifugation, solid phase is retained on the sides of the basket, while liquid remains on the top. The liquid is removed 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: Useful when the deposited solids offer high resistance to M.the Waleed flow Khattab, PhD. of liquid. Fall 2024 16  SEDIMENTATION CENTRIFUGES (2) Super Centrifuge (Tubular Bowl Centrifuge): Principle: It is a solid bowl type continuous centrifuge used for separating two immiscible liquid phases. It is a sedimentation type of centrifuge in which during centrifugation the heavier liquid is thrown against the wall of the bowl while the lighter liquid remains as an inner layer. The two layers are simultaneously separated. Waleed M. Khattab, PhD. Fall 2024 17 (2) Super Centrifuge (Tubular Bowl Centrifuge): Construction: It consists of a long, hollow, cylindrical bowl which rotates at high speed to generate a settling acceleration of up to about 18,000 g (where, g is the acceleration due to gravity) for industrial models. The bowl is rotated on its vertical axis. Feed is introduced from the bottom through a nozzle. Two liquid outlets are provided at different heights. Inside the bowl there are three baffles to catch the liquid and force it to travel at the same speed of rotation as the bowl wall. Waleed M. Khattab, PhD. Fall 2024 18  SEDIMENTATION CENTRIFUGES (2) Super Centrifuge: (Tubular Bowl Centrifuge) Working: During centrifugation, two liquid phases separate based on their densities. The heavier liquid moves towards periphery and the lighter liquid forms an inner layer. Both the liquids climb-up to the top of the vertical bowl. These two layers are simultaneously separated and removed from different heights through modified outlets. Waleed M. Khattab, PhD. Fall 2024 19 SUPER CENTRIFUGE (TUBULAR BOWL CENTRIFUGE) Waleed M. Khattab, PhD. Fall 2024 20  SEDIMENTATION CENTRIFUGES (3) Conical Disk Bowl Centrifuge (Disk Stack Centrifuge): The disc stack centrifuge has a series of conical discs is used to remove solids (usually impurities) from liquids or to separate two liquid phases from each other by means of an enormously high centrifugal force. The denser solids or liquids which are subjected to these forces move outwards towards the rotating bowl wall, while the less dense fluids move towards the centre. Waleed M. Khattab, PhD. Fall 2024 21 (3) CONICAL DISK BOWL CENTRIFUGE (DISK STACK CENTRIFUGE): The special discs (known as disc stacks) increase the surface settling area which speeds up the separation process. The concentrated denser solid or liquid is then removed continuously, manually or intermittently, depending on the design of the disc stack centrifuge. This disc stack centrifuge is very suitable for clarifying liquids that have small proportion of suspended solids. Waleed M. Khattab, PhD. Fall 2024 22 CONICAL DISK BOWL CENTRIFUGE (DISK STACK CENTRIFUGE) Waleed M. Khattab, PhD. Fall 2024 23  CONTINUOUS PUSHER CENTRIFUGE (THREE PHASE DECANTER) Construction, Principle and Working: The feed (Solid particles suspended in two immiscible liquids) enters the decanter (rotating conical bowl or drum with conveyor screw and three outlets for solid phase, heavy liquid phase and light liquid phase) through feed tube and flows into the centrifugation space through the distributor. The conveyor screw transports the solids to the solids discharge. Separation of the two liquid phases takes place in the separation zone, whereby the light phase flows towards the bowl axis, and the heavy phase towards the bowl wall. Waleed M. Khattab, PhD. Fall 2024 24  CONTINUOUS PUSHER CENTRIFUGE (THREE PHASE DECANTER) Waleed M. Khattab, PhD. Fall 2024 25 Waleed M. Khattab, PhD. Fall 2024 27