Filtration Pharmacy Notes PPT PDF 2023

Filtration Pharmacy Notes PPT PDF

Introduction

• In pharmaceutical material processing removal of solids takes place by a number of mechanisms that include straining, flocculation, coagulation, sedimentation and surface capture.
• Filtration is a common operation widely employed in the production of sterile products, bulk drugs, and in liquid oral formulation, The suspension of solid and liquid to be filtered is known as the slurry.
• The porous medium used to retain the solids is described as the filter medium; the accumulation of solids on the filter is referred to as the filter cake, while the clear liquid passing through the filter is the filtrate.

Definition

Filtration is a unique unit mechanical or physical process of separating suspended and colloidal particles from fluids (liquids or gases) by interposing a medium through which only the fluid can pass.

Objectives

The main learning objective of filtration is to separate solids from liquid or gas medium The other objectives include:

1. To eliminate the contaminant particles so as to recover dispersing fluid.
2. To recover solid particles by eliminating the dispersing fluid.
3. To produce high-quality solvents and solids.
4. To purify air and pharmaceutically useful gases by removing particulate matter.
5. To sterilize thermolabile parenteral products.

Theory of Filtration

The flow of any liquid through any porous medium offers a resistance to its flow. The rate of filtration in such cases is expressed as:
Filtration Rate= (𝑫𝒓𝒊𝒗𝒊𝒏𝒈 𝑭𝒐𝒓𝒄𝒆)/ (𝑹𝒆𝒔𝒊𝒔𝒕𝒂𝒏𝒄𝒆 𝒃𝒚 𝒇𝒊𝒍𝒕𝒆𝒓 𝒎𝒆𝒅𝒊𝒖𝒎)
The net driving force in filtration is pressure above the medium minus pressure below the medium.
The resistance offered by filter medium is not constant over the period of filtration as it goes on increasing with time due to particle deposition on filter medium.
Rate is expressed as volume of filtrate per unit time (dv/c1t), Depending on dispersing (fluid) medium, filtration theory is divided in two parts.

Gas Filtration Theory

Gas filtration includes filtration of aerosol and lyosol. Membrane filters and nucleopore filters are used for gas filtration which works on the following mechanisms:
Diffusion Deposition
Direct Interception
Inertial Deposition
Gravitational Deposition
Electrostatic Deposition

Diffusion Deposition: In this mechanism the trajectories of individual small particles do not coincide with the streamlines of the fluid because of Brownian motion. With decreasing particle size, the intensity of Brownian motion increases and thus as a consequence, the intensity of diffusion deposition also increases.

Direct Interception: This mechanism involves finite size particles. These particles are intercepted as they approach the collecting surface to a distance equal to its radius.

Inertial Deposition: The presence of particles in the flowing fluid results in a curvature of the streamlines in the neighborhood of the body. Because of their inertia, the individual particles do not follow the curved streamlines but are projected against the body and may deposit there. It is obvious that the intensity of this mechanism increases with increasing particle size and velocity of flow.

Gravitational Deposition: Individual particles have a certain sedimentation velocity due to gravity. As a consequence, the particles deviate from the streamlines of the fluid and, owing to this deviation; the particles may touch a fiber.

Electrostatic Deposition: Both the particles and the fibers in the filter may carry electric charges. Deposition of particles on the fibers may take place because of the forces acting between charges or induced forces.

Liquid Filtration Theory

• The term filtration covers all processes in which a liquid containing suspended solid is freed of some or the entire solid when the suspension is drawn through a porous medium.
• Filtration is of two types namely; ‘Cake filtration’ where the proportion of solids in suspension is large and most of the particles are collected in the filter cake which can subsequently be detached from the medium and ‘Deep bed filtration’ where the proportion of solids is very small.
• For example, in water filtration, the particles are often considered as smaller than the pores of the filter medium and penetrate at a considerable depth for being captured.

Kozeny-Carman Equation

In the filtration as particles forming the cake are small and the flow through bed is slow, streamline conditions are almost invariably obtained.

At any instant it may be explained by Kozeny-Carman equation as:

Where,
U is flow rate,
A is filter area,
v is total volume of filtrate delivered,
t is filtration time,
∆P is pressure drop across cake and medium,
r is specific cake resistance,
µ is filtrate viscosity,
I is cake thickness and
L is thickness of cake equivalent to medium resistance.

Limitations:

Kozeny-Carman equation has certain limitations that it does not take into account the fact that depth of the granular bed is lesser than the actual path travelled by the fluid.
The actual path is not straight throughout the bed, but it is sinuous or tortuous.

Poiseuille’s law

Poiseuille considered that filtration is similar to the streamline flow of a liquid under pressure through capillaries

Where, 
V = rate of flow, i.e., volume of liquid flowing per unit time
ΔP = Pressure difference across the filter, Pa
r = radius of the capillary in the filter bed, m
L = thickness of the filter cake (capillary length), m
Ƞ = viscosity of the filtrate

Darcy’s Equation

When using Poiseulle’s equation for filtration it is considered that capillaries in filter medium are highly irregular and non-uniform.
In order to approximate the flow rate the height of cake is taken as length of capillaries and a correction factors is introduced for the radius of capillaries.
This makes rate more simplified and is expressed as;

Where, U is flow rate, K is permeability coefficient, A is surface area of filter medium, ΔP is pressure difference across the filter, η is capillary radius in filter bed, L is capillary length.
The permeability coefficient (K) depends on porosity, specific surface area and compressibility of cake.

Membrane Filter

• A membrane is a thin layer of semi-permeable material that separates substances when a driving force is applied across the membrane.
• It works on the principle of physical separation. These are used for removal of bacteria, micro-organisms, particulates, and natural organic material, which can impart color, tastes, and odors to water and react with disinfectants to form disinfection byproducts.
• The membrane processes includes microfiltration, ultrafiltration, nanofiltration and reverse osmosis.

Principle

• The principle is quite simple that the membrane acts as a very specific filter that allows water to flow through, while it catches suspended solids and other substances.
• Membrane filter uses the sieving mechanism of the microfiltration membrane, driven by pressure, to trap particles with a diameter between 0.1-1 µm, such as suspended solids, bacteria, some viruses, and large-sized colloids.

Construction

• Membrane filters are plastic membranes based on cellulose acetate, cellulose nitrate or mixed cellulose esters with pore sizes in the micron or submicron range.
• They are very thin about 120 µ and must be handled carefully. They act like a sieve trapping particulate matter on their surface.
• Membrane filters are manufactured as flat sheet stock or as hollow fibers and formed into several different types of membrane modules.
• Module construction involves potting or sealing the membrane material into an assembly, such as with hollow-fiber module.
• These types of modules are designed for long-term use over the course of a number of years. Spiral-wound modules, are manufactured for long-term use.

Working

• The membrane separation process is based on the presence of semipermeable membranes.
• The principle is membrane acts as a very specific filter that will let water flow through, while it catches suspended solids and other substances,
• During use membrane filters are supported on a rigid base of perforated metal, plastic or coarse sintered glass.
• If the solution to be filtered contains a considerable quantity of suspended matter, preliminary filtration through a suitable depth filter avoids dogging of the membrane filter during sterile filtration.
• They are brittle when dry and can be stored indefinitely in the dry state but are fairly tough when wet.

Applications

• Membrane filtration is used as an alternative to flocculation, sediment purification techniques. adsorption (sand filters and active carbon filters, ion exchangers), extraction and distillation.
• It is used in dehydration, concentration/separation of substances or the treatment of residual liquids.
• It is in concentration of dissolved or suspended solids, and for obtaining a rejected liquid that contains a very low concentration of dissolved solids.
• It allows the isolation and enumeration of micro-organisms.
• It is used in removal of ammonium ions from potable water.
• It can also be used in the manufacture of dairy ingredients such as milk, whey and clarified cheese brine.

Sintered Glass Filter

• Sintered glass is a glass mesh used for filtration. It is available in different pieces of glassware.
• A suction funnel made of glass has its base made of very porous sintered glass_
• Sintered glass filters are more convenient to use than Buchner funnels because there is no filter paper to worry about, but they are harder to clean.

Principle

• The liquid to be filtered is poured into the sintered glass funnel and drawn through the perforations by vacuum suction,
• These flasks are attached to vacuum pump to carry out filtration under reduced pressure to allow for the suction and collection of the filtrate.

Construction

• Sintered glass filter available in different pore size are made of borosilicate glass.
• Borosilicate glass is finely powdered, sieved and particle of desired size are separated.
• It is then packed into a disc mould and heated to a temperature at which adhesion takes place between the particles to form porous structure.
• The disc is then fused to a funnel of suitable shape and size. Sintered filters are also made up of stainless steel which has a greater mechanical strength.
• However, these steel filters are very much liable to attack by the solutions passing through them.

Working

• The porous fritted glass disc in the middle allows filtrate to drain through leaving solids behind.
• The filtration may be carried out under reduced pressure.
• The suction flask traps vacuum to ensure that no fluids are carried over from the vacuum pump to the evacuated apparatus or vice versa

Applications

• It being permanent is used as an alternative to filter paper.
• For separation of viruses from bacteria.
• Sterilization of certain thermo-labile material.
• Filtration of broth cultures of bacteria.

FAQ’s

Filtration MCQ’s

Filtration MCQs refer to multiple-choice questions related to the process of filtration. These questions can cover a range of topics, including the principles of filtration, the equipment and methods used for filtration, and the applications of filtration in various industries.

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