Introduction to Filtration Chapter 31

Principles of Filtration Filtrate (permeate) – is the fluid and particles that pass through the filter Retentate – is the material trapped by the filter Basic set up: Filter and filter support Vessel for filtrate Driving force for the filtration

Issues with filtration Clogging Extractables – impurities from the filter Binding Adsorption – component binds to the surface of a medium Absorption – liquids are taken up into the entire depth of the material (sponge)

Types of filtrations and filters Macrofilters (filters, depth filters) – used to separate particles of m10 m or larger Microfilters are used to separate particles from 0.1 mm to m10 m. Bacteria and cells Ultra filters are used to separate macromolecules on the basis of their molecular weight (proteins)

Macrofiltration Known as depth filters because they trap material throughout their depth. Filters Quantitative grade leave little ash when burned Qualitative grade leaves significant ash when burned Hardened grade are stronger than other filters to aid in vacuum filtrations

Microfiltration Microfilters are called membranes and are manufactured to have a particular pore size. Pore size (absolute) means that 100% of particles above that size will be retained by filter Pore size (nominal) 90-98% retention.

Factors in choosing microfilter Pore size Resistance to organic solvents Surface smoothness (smooth for micro scope) Extractables Wetting properties (hydrophilic or phobic) Rate of flow, resistance to heat and tear

Applications of microfiltration Removal of bacteria, yeast, and fungi to aid in sterilizing of liquids and gases May remove mycoplasma, E. coli, fungi, yeast May be used to monitor coliform bacteria in drinking water

HEPA Filters HEPA – High Efficiency Particulate Air filters are used to remove particulates including microorganisms from air Are depth filters made of glass microfibers that form a flat sheets are pleated to increase overall surface area. May be used to protect lab animals from infections

Ultrafiltration Ultrafilters are membranes that separate samples on the basis of molecular weight Size is 1 to 100 Angstroms Weights of 1000 to 1,000,000 Molecular weight cutoff, MWCO- is the lowest molecular weight solute that is generally retained by the membrane

Applications of ultrafiltration Fractionation is the separation of larger particles from smaller ones Proteins of different sizes DNA from nucleotides Concentration – solvent is forced through a filter while solute is retained. Initial volume is reduced and high molecular weight species are concentrated above the filter

Dialysis and Reverse Osmosis Are separation processes that use membranes similar to ultrafiltrtion Dialysis is based on differences in the concentration of solutes between one side of the membrane and the other. Driving force is the difference in solute concentration Desalting is an example of this technique

Continued Reverse Osmosis, RO – is used to remove very low molecular weight materials, including salts, from a liquid, (usually water). RO is important in water purification systems In RO, water under pressure flows through a thin film. Water goes through impurities don’t

Filtration Systems Small Scale Large scale Syringe filter devise Spin filtration Large scale Hollow-fiber ultrafilters Tangential or cross-flow filtration