Pharmaceutical Filtration Processes

Clarification and Filtration

• Clarification is the removal or separation of a solid from a liquid, or a fluid from another fluid.
• Fluids include both liquids and gases.
• Clarification can be achieved through filtration or centrifugation.
• Filtration is used to remove unwanted solid particles from liquids or gases.
• Centrifugation is used to separate fluids or collect solids.

Definitions

• Clarification: A process involving the removal or separation of a solid from a liquid or a fluid from another fluid. It includes liquids and gases.
• Filtration: A unit operation that separates particles from a liquid or gas by forcing it through a porous medium (filter). The particles are trapped in the filter, and the liquid or gas passes through, becoming the filtrate.
• Filter medium (filter): A porous material that separates particles from the liquid or gas.

Filtration: Definitions Continued

• Process of separating particles from a liquid by passing it through a permeable material.
• Permeable material is a porous material.
• Mixture of solids and liquid (feed), suspension, dispersion, influent, or slurry forced through a porous medium that acts as a filter.
• Solids trapped on the filter are known as the residue; they form a cake on the surface of the medium.

Application of Filtration in Pharmaceutical Processing

• Improves product appearance (sparkle, brightness).
• Removes potential irritants (e.g., from eye drops).
• Recovers desired solid material (e.g., from a suspension or slurry).
• Produces water of specific quality (e.g., Nanopure® water).

Application of Filtration in Pharmaceutical Processing (continued)

• Meets sterility specifications by removing microorganisms.
• Sterilizes solutions or suspensions, especially those that aren't stable under heat.
• Detects microorganisms in liquids by analyzing filters.
• Assesses the efficiency of added preservatives.
• Used for techniques like nanofiltration, ultrafiltration, and microfiltration to recover colloidal delivery systems.

Mechanisms of Filtration

• Surface straining/sieving: Particles larger than the filter medium's pores are trapped on its surface.
• Membrane filtration: Filtration occurs on the surface of the membrane, and particles larger than the pore size are trapped. Filters can become blocked if not designed properly or if high contaminant levels exist.
• Depth straining: Particles are trapped within the filter medium, typically due to their size and shape or their interaction with the medium or other particles already within it. Filter thickness is taken into consideration.
• Depth filtration (impingement): Particles are trapped in the filter's depth, even if they are smaller than the pore size, due to sticking to the pore walls, or other particles (entanglement).
• Cake filtration (auto-filtration): A layer of particles builds up on the filter, acting as its own filter medium; this continues until the process is stopped. It's particularly important where solid recovery is involved.

Filtration Equipment

• Classified by: The desired product (filtrate or cake solids), Method of operation (batch or continuous), Type of operation (non-sterile, sterile, centrifugation), Driving force (gravity, vacuum, pressure, centrifugation).
• Different types of filters exist, each utilizing varied methods for filtering (e.g., sand filters, rotary drums, filter presses, membrane filters).

Filter Selection

• Purpose determines filter type (e.g., sterilizing filters have specific pore sizes).
• Filter medium compatibility with the liquid or gas is crucial.
• Check chemical compatibility charts provided by vendors.
• Filtration surface area, flow rate, and pressure differences are assessed during selection.
• Filter selection must balance filter media, equipment, slurry characteristics, and final product quality (e.g., batch pressure filters).