Filtration.pptx
- 1. FILTRATION PRESENTED BY- MS.HEERA VINAYAK KAREMORE ASSISTANT PROFESSOR M.PHARM (PHARMACEUTICAL CHEMISTRY) 1
- 2. Contents: 1. Definition 2. Mechanism of filtration 3. Types of filtration 4. Theories of filtration 5. Factors influencing filtration 6. Classification of filtration Pressure filtration – 1) plate and frame filter press 2) Meta filter 2
- 3. Definition Filtration It may be define as a process of separation of solids from a fluid by passing the same through a porous medium that retains the solids but allows the fluid to pass through. Clarification When solid are present in very low concentration i.e. not exceeding 1.0% w/v, the process of its separation from liquid is called clarification. 3
- 4. Terms used in Filtration 4
- 5. Mechanism of Filtration Straining Impingement Entanglement Attractive Forces Similar to sieving i.e. particles of larger size can’t pass through smaller pore size of filter medium. Solids having the momentum move along the path of streaming flow and strike (impinge) the filter medium. Thus the solids are retained on the filter medium. Particles become entwined (entangled) in the masses of fibers (of cloths with fine hairy surface or porous felt) due to smaller size of particles than the pore size. Thus solids are retained within fiber medium. Solids are retained on the filter medium as a result of attractive force between particles and filter medium, as in case of electrostatic filtration. 5
- 6. Types of Filtration Surface/screen filtration It is a screening action by which pores or holes of medium prevent the passage of solids Mechanism involved: straining and impingement For this, plates with holes or woven sieves are used Efficacy is defined in terms of mean or maximum pore size Depth filtration In this slurry penetrates to a point where the diameter of solid particles is greater than that of the tortuous void or channel Mechanism: Entanglement The solids are retained with a gradient density structure by physical restriction or by adsorption properties or medium 6
- 7. Theories of Filtration The flow of liquid through a filter follows the basic rules that govern the flow of any liquid through the medium offering resistance The rate of flow may be expressed as- Rate= driving force/resistance The rate of filtration may be expressed as volume(liters) per unit time(dv/dt) Driving force=pressure upstream – pressure downstream Resistance is not constant It is increase with an increase in the deposition of solids on the filter medium Therefore filtration is not a steady state 7
- 8. The rate of flow will be greatest at the beginning of filtration process, since the resistance is minimum After forming of filter cake, its surface acts as filter medium and solids continuously deposit adding to thickness of the cake Powder or granule bed visualized as a bundle of capillaries Upstream pressure, P1 Surface area Length (L) Downstream pressure, P2 Viscosity flow rate: m3/unit time Fig.: Filtration process parameters Resistance to flow is related to several factors given in fig. Resistance to movement=(pressure upstream – pressure downstream)/length of capillaries 8
- 11. Permeability may be defined quantitatively as the flow rate of a liquid of unit viscosity across a unit area of cake having unit thickness under a pressure gradient of unity This equation is valid for liquids flowing through sand, glass beds and various porous media This model is applied to filter beds or cakes and other types of depth filter This equation is further modified by including characteristics of K by Kozeny- Carman 11
- 13. Factors influencing filtration Properties of solid Temperature Objectives Properties of solids in slurry Properties of liquids • Particle shape • Particle size • Particle charge • Density • Particle size distribution • Rigidity or compressibility of solids under pressure • Tendency of particle to flocculate or adhere together • Density • Viscosity • Corrosiveness • Rate of formation of filter cake especially in early stages of filtration • Whether the solids or liquid or both are to be collected • Temperature of suspension 13
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- 15. Pressure Filtration Pressure filters can apply a large pressure differential across the septum to give economically rapid filtration with viscous liquids or fine solids. Due to the formation of cakes of low permeability, many types of slurry require higher pressure difference for effective filtration than can be applied by vacuum techniques. Pressure filters are used for such operations. However, high operational pressures, may prohibit continuous operation because of the difficulty of discharging the cake while the filter is under pressure. Example is plate and frame filter press, meta filter, etc. 15
- 16. Principle: According to Kozeny-Carman equation, rate of filtration is directly proportional to the overall pressure drop across filter medium and filter cake. The most common method of obtaining a pressure difference is applying pressure on the surface of the slurry i.e. pumping the slurry onto the filter. However, in the early stages of filtration, pressure difference should be less. This is to prevent the pores of the filter medium from clogging or plugging, which subsequently increases resistance to the flow. 16
- 17. Advantages 1. Cakes are obtained with very low moisture content. 2. Cakes may be disposed and flattened in layers provided they are not thixotropic and sufficiently stable to support a tractor. 3. Intensive soluble recovery or removal of contaminants from the cake may be achieved. 4. Clean filtrates may be produced by recirculating the filtrate for 1-2 minutes or by precoating if a clear filtrate is required right from the start. 5. Solutions may be polished to a high degree of clarity. 6. The filter bodies and internals may be constructed from a wide variety of alloys including synthetic materials for filter presses. 7. Pressure Filters are available in a wide level of automation from labor intensive operator controlled up to fully automatic machines. 17
- 18. Disadvantages 1. Cloth washing is difficult and if the solids are sticky a 3 mm precoat from diatomite or perlite is required. - This adds another step prior to filtration and if not done carefully and a too thin precoat is formed it may leave areas with exposed cloth which will blind rapidly. Conversely, if a too thick precoat is formed since the operator seeks to be on the safe side, such a precoat consumes effective cake volume. 2. The operator can hardly see the forming cake and is unable to carry out an inspection while the filter is in operation. 3. The internals are difficult to clean and this may be a problem with food grade applications. 18
- 19. 1. Plate and Frame Filter Press A filter press contains a set of plates designed to provide a series of chambers or compartments in which solids may collect. The plates are covered with a filter medium such as canvas. Slurry is admitted to each compartment under pressure; liquor passes through the canvas and out a discharge pipe, leaving a wet cake of solids behind. Construction • Consist of plates and frames assembled alternately with a filter cloth over each side of the plates • The plates have channels cut in them so that clear filtrate liquid can drain down along each plate • The feed slurry is pumped into the press and flows through the duct into each of the open frames so that slurry fills the frames • The filtrate flows through the filter cloth and the solids build up as a cake on the frame side of the cloth 19
- 20. • The filtrate flows between the filter cloth and the face of the plate though the channels of the outlet • The filtration proceeds until the frames are completely filled with solids Fig. Filter press. Assembly of plates and frame 20
- 21. Working : The slurry enters the frame from the feed channel The filtrate passes through the filter medium on to the surface of the plate while the solids form a filter cake in the frame. The filtrate then drained down the surface of the plate , between the projections on the surface and escapes from the outlet. Filtration is continued until the frame is filled with filter cake, when the process is stopped , the frame emptied, and the cycle re- started. 21
- 22. Advantages &disadvantages Advantages: 1. Construction is very simple and a wide variety of materials can be used. 2. It provides a large filtering area in a relatively small floor space. 3. It is versatile, the capacity being variable according to the thickness of the frames and the number used. 4. The construction permits the use of considerable pressure difference. 5. Efficient washing of the cake is possible. 6. Operation and maintenance is straightforward , because there no moving parts, filter cloths are easily renewable and, because all joints are external, any leaks are visible and do not contaminate the filtrate. 22
- 23. Disadvantages: 1. It is a batch filter, so it is a time consuming. 2. The filter press is an expensive filter, the emptying time, the labor involved, and the wear and tear on the cloths resulting in high costs. 3. Operation is critical, as the frames should be full, otherwise washing is inefficient and the cake is difficult to remove. 4. The filter press is used only for slurries containing less about 5 % solids 23
- 24. 24 Principal- • Mechanism is surface filtration • In this , metal rings contain semicircular projection, which are arranged as a nest to form channel on the edges. • This channel offers resistance (strainer) to the flow of solids (course particals). • The clear liquid is collected into receiver from the top. Meta filter
- 25. 25 Construction- • Meta filter consist of a series of metal rings. • These are threaded so that a channel is formed on the edges. • It contains agrooved drainage column on which a series of metal rings are packed. • These rings are usually made up of stainless steel and have dimensions of about 15.0mm internal diameter and 22.0mm external diameter. • Each metal ring has a number of semicircular projection (0.8 mm in thickness) on the side of surface. • The projections are arranged as a next to form channel on the edges. • These rings are tightened on the drainage column with a nut. • Meta filter are know as edge filter.
- 26. 26 Uses- • Perticularly useful for preparation of perticulate free solutions for parenteral and opthalmic uses. Working-
- 27. 27 Advantages- • The rotary filter is automatic and is continues in operations , so that the labour cost are very low. • The filter has large capacity,so it is suitable for the filtration of highly concentrated solutions. • Variation of the speed of rotation enable the cake thickness to be controlled. • Pre coat of filter aid couled used to accelerate the filtration rate. • Filter has large surface area.
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