Large-Scale Clarification and Filtration Process Flashcards
Dr. Ubani
What is clarification?
Clarification is the process of separating a solid from a liquid or a fluid from another fluid.
There are two main reasons for clarification pharmaceutics, which are:
To remove impurities and recover desired products
To separate solvents from intermediates and APIs
Filtration can be broadly divided into:
- Solid-fluid filtration
- Fluid-fluid filtration.
What is solid-fluid filtration?
This can be defined as the separation of an insoluble solid from a fluid by means of a porous medium that retains the solid but allows the fluid to pass.
Solid-fluid filtration can be subdivided into:
- solid-liquid filtration: involves the separation of an insoluble material from a liquid.
- Solid-gas filtration: separation of a solid from air or gas.
List 5 applications of solid-liquid filtration.
- Improvement of product appearance.
- Removal of potential irritants.
- Water purification for pharmaceutical formulation
- Recovery of desired solid material from a suspension.
- Recovery of solvents from drug substance manufacturing processes.
- Sterilization of thermolabile products.
- Recovery or detection of microorganisms in filtrates after filtration.
List 2 applications of solid-gas filtration.
- Removal of suspended solid material from air to supply purified air in manufacturing rooms or processing equipment.
- Removal of particulate matter from the environment during manufacturing operations.
Mention 2 applications of fluid-fluid filtration.
- It can be employed to improve the clarity of the pharmaceutical product by removal of dispersed oils.
- Removal of entrained oil or water droplets from compressed air.
Mention three uses of compressed air.
- Bottle cleaning
- Film coating
- Fluid energy mills
Mention 4 mechanisms of filtration.
- Seiving/Straining
- Impingement
- Filtration by attractive forces
- Autofiltration
Discuss Sieving/Straining.
Membrane filters are used to strain or sieve out solid materials from a liquid using filters with pore sizes that are smaller than the filtrand.
This technique is used when the contaminant volume is low or small volumes need to be filtered.
An example is the removal of bacteria and fibres from parenteral preparations or the removal of contaminants before quantitative analysis.
Filtration occurs on the surface of a thin filter.
Discuss impingement.
This has to do with the retainment of suspended particles between the fibers of a filter medium.
It occurs as a result of the attractive force between the fiber and the suspended particle.
If the pores between filter fibers are larger than the suspended material, some particles will not be retained.
To enhance retainment, filter media used must be sufficiently thick to ensure optimal removal of unwanted materials.
Filters used in this filtration process are referred to as depth filters e.g. air filters, oil filters and fuel filters.
Discuss filtration by attractive forces.
Electrostatic forces can exert sufficient hold on particles and retain them on a filter medium.
For example, air can be freed of dust particles in an electrostatic precipitator by passing the air between highly charged surfaces which attract dust particles.
Discuss autofiltration.
This refers to a situation where filtered media (cake) acts as its own filter medium.
Here filtered particles accumulate to form residues of varying thickness, referred to as filter cake. The residue then acts as a filter for subsequent liquid.
This filtration mechanism is also known as cake filtration.
Mention 4 factors that can affect the rate of filtration.
- Area available for filtration
- Pressure difference across the filter bed
- Viscosity of the fluid passing through the filter
- Thickness of the filter medium and any deposited cake
State Darcy’s equation.
v/t = (KAΔP)/μL
Where:
v/t = rate of filtration ( volume of filtred material (m ³) per unit time (s))
K = proportionality constant
A = area available for filtration (m²)
ΔP = pressure difference across filter bed (Pa)
μ = viscosity (Pa.s)
L = thickness of the medium (m)
The proportionality constant, K, expresses the permeability of the filter medium and cake and will increase as the porosity of the bed increases.
K = e² / (5(1-e)²S²)
- e is the porosity of the cake and S is the surface area of the particles making up the cake.
How do you increase filtration rate?
- Increase the area available for filtration
- Increase the pressure difference across the filter bed
- Decrease the viscosity of the filrate
- Decrease the thickness of the filter cake
- Increase the permeability of the cake
