TIUFaculty of Pharmacy

Pharmaceutical Technology II

Clarification and Filter Aids

3rd Grade

Lecture:1

2020-2021 Spring semester

Dr. Rozhan Arif Muhammed

Outlines

Definition and Terminology

Clarification Methods

Factors Affecting filtration Rate

Filter Media

Filter Aid

Filter Equipment

Definition

Filtration: It may be defined 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 is present in very low concentration, i.e., not exceeding 1.0% w/v, the process of its separation from liquid is called clarification.

Objectives

1.To remove unwanted solid particles from either a liquid product or from air.

2. To collect the solid as the product itself (e.g., following crystallization).

• The inadvertent introduction of foreign particle, the precipitation of undesirable materials during manufacture and the presence of impurities in the raw materials used to manufacture the preparation result in requirements for clarification of the preparation as the last stage in manufacture.

• Ultra-Filtration: Is a separation process usingmembranes with pore sizes in the range of 0.1 to 0.01micron. Typically, ultrafiltration will remove high molecular-weight substances, colloidal materials, and organic and inorganic polymeric molecules.

• Cake Filtration: If recovery of solid is desired, the process is called cake filtration.

Size of Filters

• Depending on the pore size, filter membranes can remove particles defined in the range :

1. microfiltration (0.1 to 2 µm, e.g., bacteria)

2. ultrafiltration (0.01 to 0.1 µm, e.g., virus)

3. nanofiltration (0.001 to 0.01 µm, e.g., organic

compounds in the molecular weight range of 300 to 1,000),

4. reverse osmosis (particles <0.001 µm).

Methods of Clarification

1) Settling

2) Filtration

3) Absorption and adsorption

1. Settling

It is the simplest method of clarification. It is done by allowing the liquid to stand in a suitable container until the suspended matter is settled down or risen to the top of the liquid.

Acceleration of settling can be done by centrifugation. In this process the liquid is rotated in a special container at high speed. The device used for centrifugation is called centrifuge.

The centrifugal forces developed inside the centrifuge drive the suspended particles to the bottom and sides of the device.

2. Filtration

• Filtration can be classified into the following categories depending on the physical state of the suspended matter and medium:

• Solid-liquid filtration

• Solid-gas filtration

• Liquid-liquid filtration

• Liquid-gas filtration

Filtration is the process by which the suspended matter is removed

from fluid by passing the mixture through porous, fibrous or granular

substances.

The specific procedures and equipment’s which may be used to achieve clarification are dependent on several factors are:

1- The particle size of the suspended matter: The state of subdivision of the suspended particles may range from the course (particles which may be seen by

eye) to the colloidal (particles which can be seen by ordinary microscope).

2- The physical state of the suspended matter: The clarification of aromatic waters and syrups often involves the removal of finely divided insoluble liquids

derived from the flavoring ingredients.

3-The quantity of suspended matter: the liquid to be clarified may be slurry (Contain a high concentration of colloidal dispersion).

4-The characteristics of the fluid medium: Viscosity, the temperature at which the fluid is to be clarified, the presence of

volatile constituents in solution, etc., require specific consideration.

5-The speed of the operation: This depend primarily on the quantity of liquid to be clarified.

• The theory of filtration involves consideration of the factors which influence the rate at which fluids can be passed through a porous medium. These factors are summarized in their simplest form in the following expression:

(Filter Area) (Pressure Drop)

• Rate of Filtration =

(Liquid Viscosity) (Filter Resistance)

• The rate of filtration, measured as the volume of liquid passed through the filter per unit time, will be reduced in proportion to the filter resistance and viscosity of the filtrate. It will be increased in proportion to the pressure drop across the filter and the filter area.

Filter Media

The filter medium used for clarification must have the following properties:

Capable of delivering a clear filtrate at suitable production rate.

It must withstand the mechanical stress which may be imposed on it without rupturing or being compressed significantly.

No chemical or physical interactions with the components of the filtrate should occur.

Types of Filter Media

There are two different types of filters:

1. Depth filters

2. Membrane filters

1. Depth Filters

• Depth filters retain suspended matter within the depth of the filter matrix.

• In this case, suspended particles must move through the tortuous path of the fiber matrix and eventually will collide with a fiber and separate from the medium.

• Due to the depth retention, such filters have a very high load capacity and can separate a high load of suspended matter of different sizes.

• Depth filter are fibrous materials: for example

• polypropylene, borosilicate, or glass fibre materials.

• Borosilicate and glass fibre materials are highly adsorptive and commonly used to remove colloidal substances, like iron oxide from water or colloidal particles from sugar solutions.

2. Membrane Filters

• Membrane filters are surface retentive filters and, therefore, have the distinct disadvantage to clog faster.

• In comparison to depth filters, membrane filters have a narrow pore size distribution, which results in a sharper retention rate.

• Another advantage of membrane filter is the fact that these are integrity testable. Therefore, flaws or defects can be detected, which is critical, due to the function of membrane filters, mainly in separating microorganisms from pharmaceutical solutions.

• Membrane filters are made in a wide variety of pore sizes

• The effective pore size for membranes varies, and membranes can be used in reverse osmosis (RO), nanofiltration (NF), ultrafiltration UF), and microfiltration (MF).

Examples of filter Media

a- Sheets of woven or felted material: These include wire screening; fabrics of cotton, wool, linen or synthetic Materials such as nylon; felt or muslin; and-filter paper.

Filter fabrics: They are commonly woven from natural fibers such as cotton and from synthetic fibers and glass.

Cotton fabric which is most common and widely used as a primarymedium.

Nylon is often superior for pharmaceutical use, since it is unaffected by molds, fungi, or bacteria; provides extremely smooth surface for good cake discharge; and has negligible absorption properties.

Teflon is superior for most liquid filtrations because it is almost chemically inert, provides sufficient strength and can with stand elevated temperature.

b- Porous plates: these include perforated metal or rubber plates, natural porous materials, i.e., stone, porcelain and other ceramics. Unlike other media they can be reused after cleaning.

c- Membrane filters:

▪ These are made by casting, exemplified by the Millipore filters is prepared from cellulose esters and is a thin porous membrane.

▪ Since sizes of the pores can be controlled with a high degree of precision, these membranes may be used in a wide variety of clarification operations.

d- Unwoven fibrous materials: These include cotton, asbestos fibers and paper pulp and are employed with woven or felted material or porous plates used as supports.

Skin layer structure of a UF membrane Porous structure of cellulose acetate

PTFE membrane structure(Polytetrafluoroethylene)

Filter Aid

• They are special type of filter media that form a fine surface deposit that screens out all solids and preventing them from contacting and plugging the supporting filter medium.

• Usually, the filter aid acts by forming a highly porous, and noncompressible cake that retains solids as does any depth filter.

• Filter aids are insoluble adsorbent materials that may be added toliquid prior to its filtration to increase the efficiency of filtration.

Using of Filter Aids

• They can be used as a precoat before the slurry is filtered. This will prevent gelatinous-type solids from plugging the filter medium andalso give a clearer filtrate.

• They can also be added to the slurry before filtration. This increases the porosity of the cake and reduces resistance of the cake during filtration.

• The use of filter aids is usually limited to cases where the cake is discarded or where the precipitate can be separated chemicallyfrom the filter.

Characteristics of Filter Aids

• It should have a structure that permits the formation of porous and non-compresable cake (not dense),

• It should have a particle size distribution suitable for the retention of solids as required,

• It should be able to remain suspended in the liquid to be filtered (low sp-gr)

• It should be free of impurities,

• It should have high adsorption capacity,

• It should be inert to the liquid being filtered,

• It should be free of moisture in cases where the addition of moistureto the liquid is undesirable.

Examples

• Purified talc: Nonabsorbent, chemically inert, reasonable particle size.

• Diatomite: is the naturally occurring fossilized remains of diatoms. The most important use relative of high-ÿ quality diatomite is as a filtering media. The naturally occurring fossilized remains of diatomshave innate filtering characteristics due to their unique honeycomb structure.

• Charcoal: Good absorbent but not used for colouredpreparations, alkaloids or glycosides.

•Perlite: It is aluminum silicate of light weight, inert, impart no taste or odor to liquids being filtered, and are virtually insoluble in mineral and organic acids at all temperatures.

•Chalk: Reacts with acids, not for general use.

Effect of Absorption & Adsorptionon Clarification

• Filter media can affect clarification through absorption and adsorption processes in addition to their sieving effect.

• In absorption, the foreign particles are trapped within the medium, while in adsorption, the foreign substances adhere to the surface of the media.

• Frequently, filter aids provide the absorption and adsorption functions.

Filtration Equipments

• 1- FILTER FUNNEL

• Made up of Glass, Aluminum, Polythene, Stainless steel or any other suitable material.

• Neutral Glass made funnel are most used.

• White filter paper of suitable pore size is folded in such away that it fits in the funnel.

BUCHNER FUNNEL

• Made up of porcelain.

• It has a perforated plate.

• Used for filtration under reduced pressure

HOT WATER FUNNEL:

• These are doubled wall funnels made up of metals.

• Viscous substances such as liquid paraffin

• Glycerin, Castor oil and fatty substances like wool fat, bees wax, ointments and cream etc are filtered easily from this filter.

• Boiling water or steam is circulated in jacketed funnel.

Seitz Filter

• Lower part fitted with a perforated plate overwhich compressed asbestos pad is placed.

• Upper part has a value through whichpressure can be applied.

• Both parts joined together by winged nuts

• Advantages:

• No risk of contaminating the filtrate.

• Apparatus is very simple to use.

• For viscous solution they are more suitable.

• Disadvantages: Asbestos may shed loose fibersand Pad may absorb enoughproduct.

Filter Press

• It consists of hollow frames and solid plates

• Plates have grooved surface to support the filter cloth.

• Each plate has an outlet for filtrate.

• Frames are opened with an inlet for the liquid to be filtered.Advantages:

• Construction is very simple.

• Used for coarse to fine filtration.

• Operation and maintenance is easy.

• Filter cloth can be easily replaced.

Disadvantages

• Not economical for filtration of small quantities

• Leakage between the plates may take place

Rotary Filters

• They are used when the proportion of solid content in slurry is 15 to 30%.

• It consists of perforated matter drum wrapped with filter cloth

• Drum is partially immersed in the tank containing the materialsto be filtered

• • Drum rotates at the slow speed and creates vacuum due towhich filtrate enters the drum.

• Filter cake deposits on outer surface of the filter media.

• Cake is removed by scrapping with a knife.

• Advantages

• Area of filtration is very high.

• Thickness of the filtration cake is controlled by altering with the speedof rotation of drum.

• Disadvantages: Very expensive and Can’t be used for slurriescontaining low percentage of solid

Vacuum Filtration

• Vacuum filtration is used primarily tocollect a desired solid.

• Vacuum filtration uses a Buchnerfunnel and a side- arm flask.

• Vacuum filtration is faster than gravity filtration, because the solventor solution and air is forced throughthe filter paper by the application ofreduced pressure.