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1. FILTRATION It is the process in which particles are separated from a liquid by passing the liquid through a porous medium known as filter It separates particles from the liquid and allows the liquid to pass through it The suspension of solids and liquid to be filtered is known as feed or slurry and the solids collected on the filter medium form a cake called filter cake The clear liquid which passes through the filter is called filtrate

2. APPLICATIONS OF FILTRATION 1) Clarification of products to improve their appearance 2) To remove potential irritants e.g. from eye drop preparation applied to mucous membranes 3) For recovery of desired solid material from a suspension 4) Production of water of appropriate quality for pharmaceutical use 5) Meeting sterility specification to remove microbes 6) Sterilization of solutions and suspensions that are unstable

3. FACTORS AFFECTING RATE OF FILTRATION 1) AREA OF FILTER SURFACE 2) PARTICLE SIZE OF SOLIDS Rate of filtration is directly proportional to the particle size of solids to be removed 3) PORE SIZE OF FILTER MEDIA Rate of filtration is directly proportional to the pore size of filter media 4) RESISTANCE OF FILTER CAKE The rate of filtration will be greater at the beginning of process because there is minimum resistance But as the process proceeds, filter cake is formed and its thickness goes on increasing which slows down the rate of filtration   5) VISCOSITY OF THE LIQUID TO BE FILTERED 6) TEMPERATURE Increased temperature reduces the viscosity of thick liquids, so they can be filtered quickly 7) PRESSURE DIFFERENCE ACROSS FILTER The rate of filtration is directly proportional to the pressure difference across the filter bed

4. FILTER MEDIA The surface or medium upon which solids are retained in the process of filtration is called filter media PROPERTIES OF AN IDEAL FILTER MEDIUM It should be physically and chemically inert It should have high retention power for solids but allow maximum passage of liquids It should have sufficient mechanical strength to withstand It’s filtration pressure  It should offer minimum resistance during the filtration process It should not swell when it is in contact with the filtrate and washing liquid  It allows easy discharge of filter cake

5. SELECTION OF FILTER MEDIUM: The following factors must be considered while selecting the filter medium: 1) Size of the particles to be filtered 2) Amount of the liquid to be filtered 3) Nature of the substance to be filtered i.e. solution or suspension 4) Purpose of filtration i.e. to get clear preparation or a clear sterile preparation

6. FILTER MEDIA 1) FILTER CLOTH It is woven from either natural or synthetic fiber Cotton fabric is most common and widely used as a primary medium Nylon is often superior for pharmaceutical use, it is unaffected by molds, fungi, or bacteria It provides an extremely smooth surface for good cake discharge and has negligible absorption Both cotton and nylon are suitable in aseptic filtration Teflon is superior for most liquid filtration, as it is almost chemically inert, provides sufficient strength, and can withstand elevated temperatures 2) MEMBRANE FILTER MEDIA They are commonly used in the preparation of sterile solutions Membrane filters, classified as surface or screen filters, are made up of various esters of cellulose or from nylon , polyvinyl chloride ,

7. The filter is a thin membrane, about 150 micro meter thick, with 400 to 500 million pores per square centimeter of the filter surface The pores are extremely uniform in size and occupy about 80 % of filter volume 3) WOVEN WIRE CLOTH Particularly stainless steel is durable and easily cleaned Metallic filter media provide good surfaces for cake filtration and are usually used with filter aids Wire screens are particularly suitable, since they may be cleaned rapidly and returned to surface 4) POROUS STAINLESS STEEL FILTERS These are widely used for the removal of small amounts of unwanted solids from liquids Porous metallic filters can be easily cleaned and repeatedly sterilized

8. FILTER AIDS Filter aids are defined as the substances which when added to the liquid to be filtered , reduce the resistance of filter cake and increase filtration process These substances form a porous cake which can retain the solid particles but allow the liquid to pass through it These may be added directly to suspension to be filtered. Filter Aids ” is a group of inert materials that can be used in  filtration  pretreatment. ...  Filtration  without  filter aid , with precoat , and with precoat and body feed . The common  filter aids  are diatomaceous earth (DE), perlite , cellulose and others. CHARACTERISTICS FOR FILTER AID 1) Free of impurities 2) Inert to the liquid to be filtered 3) Should have a particle size distribution suitable for retention of solids as required 4) Should be able to remain suspended in the liquid 5) Should form a porous cake 6) Should be insoluble in the liquid to be filtered 7) Should be readily recoverable from the liquid

9. FILTRATION EQUIPMENTS

10.   1) PLATE AND FRAME FILTER PRESS( Filter Press) Various types of filter presses are used for large scale filtration but the PLATE AND PRESS is widely used in pharma industry It consists of a number of hollow frames and solid plates The plates have grooved surface to support the filter cloth Each plate has an outlet for the filtrate The frames are open with an inlet for the liquid to be filtered The plates and frames are assembled alternatively and each set works as a unit A number of such sets may be arranged horizontally or vertically Plates and frames may be made in various metals to provide resistance to corrosion or prevent metallic contamination of the product. Non-metals e.g. plastics is lighter, also varieties of wood are satisfactory materials of construction WORKING : The liquid to be filtered is allowed to enter the frame under pressure and passes through filter medium on to the surface of plate The filtrate drains out of the plate through the outlet The operation is continued till the frame is filled with filter cake WASHING: When the process is stopped filter cake is removed by washing from the frame and process is restarted

11. Plate and Frame Press

12. ADVANTAGES The construction is very simple and a number of materials from wood to stainless steel may be used for its construction Large filtering area It is most versatile filter press because filter media can be varied to suit a particular requirement It can be used for coarse to fine filtration The operation and maintenance is easy The filter cloth can be easily replaced USES: Used for removal of protiens ppt from insulin liqours Bacteria removal by usin aesbestos or cellulose filtering medium DISADVANTAGES This filter press is for batch filtration and filtration of small quantities are not economical This filter press is quite costly including labor cost Leakage between plates may take place through faulty assembly

13. 2) FILTER LEAF It consists of a frame in which a drainage screen is enclosed The whole unit is covered with a cloth which acts as a filter medium The inside of frame is fitted with an outlet and an attachment to connect to a vacuum pump The frame of filter may be of any shape i.e. round, square or rectangular The leaf is immersed in the container having slurry to be filtered and the vacuum system is connected to the filtrate outlet When the vacuum is created, the filtration will start and the filtrate will go on collecting in the receiver The cake will be deposited on the outer surface of filter cloth which can be easily washed with water or Removed by backward flow of air through the unit This method has the advantage that the liquid can be filtered from any vessel and the deposited cake can be removed simply by washing or By blowing air in the reverse direction through the system USES: This is most satisfactory method if the solid contents in the liquid are not more than 5% The labor cost involved in operating the filter leaf are also comparatively low DISADVANTAGE: life of leaf is short. May rupture

14. Filter Leaf Principle Filter Leaf consist of longitudinal drainage screen covered with a filter cloth. Mechanism is surface filtration and act as a sieve or strainer Vacuum or pressure can be applied to increase the rate of filtration. Filter is used for filtration of slurries with low solid content, e.g., dilute suspensions, where the solid content is less than 5 %.

15. ADVANTAGES In order to increase the filtration surface area, a number of unit can be connected in parallel The operation of filter leaf is relatively inexpensive because t he labor cost involved in operating the filter leaf are also comparatively low Cleaning is highly effective . Any vessel can be used to filter the slurry. DISADVANTAGES This filter press is for batch filtration In most cases it is used when there are less than 5% solids in the liquid to be filtered.

16. 3) ROTARY FILTER When the proportion of the solid contents in the slurry is in the range of 15-30% and it is not possible to filter them by filter leaf or filter press, then rotary drum filter is used It is a continuous process and is used in pharmaceutical industries for large scale operation This filter works on the principle like that of filter leaf Rotary drum filter consists of a perforated metal drum wrapped with filter cloth or other suitable material to act as filter medium The drum is partially immersed in the tank containing the material to be filtered The drum is rotated at a slow speed i.e. less than one revolution per minute and vacuum is created As soon as vacuum is create d, the filtrate will enter into the drum through the filter medium The filter cake will be deposited on the outer surface of the filter medium The cake is then removed by scraping with a knife just before the rotating drum repeats another cycle The above mentioned operation continues till the slurry gets exhausted

17. ROTARY FILTER

18. ADVANTAGES The area of filtration is very high, so a large quantity of slurry can be filtered at a time It is a continuous process and is used in pharmaceutical industries for large scale operation DISADVANTAGES This filter is very expensive This process can not be used for slurries containing low percentage of solids

19. 4) META FILTER The meta filter consists of a grooved drainage rod on which is packed a series of metal rings These rings are usually of stainless stee l, are about 15 mm inside diameter 22 mm outside diameter 0.8 mm in thickness

20. Construction With a number of semicircular projections on one surface The height of projections and the shape of ring are such that when rings are packed together and tightened on drainage rod with a nut, channels are formed One or more of these packs is mounted in a vessel c ontaining the slurry and the filter may be operated by pumping in the slurry under pressure When vacuum is created , liquid passes through the pack into drainage rod and then to the receiver The pack of rings serves as a base on which the true filter medium is supported The ability to separate very fine particles means that meta filter is used exclusively for clarification purposes The strength of meta filter permits the use of high pressures making the method suitable for viscous liquids

21. ADVANTAGES : Meta filter has considerable strength and high pressures can be used, with no danger of bursting the filter medium It is very economical filter meta filter can be made from materials that can provide excellent resistance to corrosion and avoid contamination of most sensitive product Removal of cake is effectively carried out by flushing water DISADVANTAGE: The small surface area of the meta filter restricts the amount of solid that can be collected Uses The clarification of syrups Injection solutions and Products such as insulin liquors

22. 5) Filter Funnel A  filter funnel  is a laboratory funnel used for separating solids from liquids via the laboratory process of filtering. In order to achieve this, a cone-like shaped piece of filter paper is usually folded into a cone and placed within the funnel. The suspension of solid and liquid is then poured through the funnel. The solid particles are too large to pass through the filter paper and are left on the paper, while the much smaller liquid molecules pass through the paper to a vessel positioned below the funnel, producing a filtrate. The filter paper is used only once. If only the liquid is of interest, the paper is discarded

23. 6) Buchner Funnel A  Buchner funnel  is a piece of laboratory equipment used in filtration. It is traditionally made of  porcelain , but  glass  and  plastic  funnels are also available. On top of the funnel-shaped part there is a cylinder with a fritted glass disc/perforated plate separating it from the funnel. 7) Hot Filtration Funnel Hot  filtration  funnel  is a less commonly seen  funnel  where the  funnel  is jacketed, and surrounded by a heated fluid.