The Principle and Application of Ultrafiltration
The Principle and Application of Ultrafiltration
Introduction
The artificial permeable membrane used in the ultrafiltration process is generally made of polymer materials such as: cellulose acetate, cellulose acetate ester, polyethylene, polysulfone and polyamide and so on. Generally, to prefabricate various types of membrane modules such as tube type, plate type, roll type and capillary type, and then assemble several membrane modules so as to increase the filtration area and facilitate maintenance.
Ultrafiltration process
It is generally believed that ultrafiltration is a screening and separation process. Under static pressure difference as the driving force, the solvent and small solute particles in the stock solution pass through the membrane from the high-pressure side to the low-pressure side, generally it is called filtrate. However, the large particle components are blocked by the membrane, so that their concentration in the filtrate increases.
Separation mechanism
It is generally believed that the separation mechanism of ultrafiltration membranes is a screening and separation process, but the chemical properties of the membrane surface are also important factors affecting ultrafiltration separation. That is, solute interception in the ultrafiltration process has three methods: mechanical interception on the surface of the membrane, staying in the membrane pores and being removed, and adsorption on the surface of the membrane and in the pores.
Application
Separation, purification, concentration, desalination and dealcoholization of biochemical products (thymosin, heparin sodium, cytochrome C, etc.)
(2) Separation, purification, concentration and desalination of genetic engineering products (interferon, EPO, TPO, G-CSF, etc.)
(3) Separation, concentration and dealcoholization of plasma proteins (albumin, globulin, coagulation factors, etc.)
(4) Separation and concentration of cell culture products (viruses, antibodies, etc.)
(5) Buffer exchange before and after protein product chromatography or before lyophilization
(6) Collection of cells, bacteria and viruses
(7) Clarification of fermentation broth or culture broth, removal of bacteria and cell debris
(8) Depyrogenation of small molecule products (such as glucose, antibiotics, small peptides, etc.)
Selection of ultrafiltration cassette
(1)Selection of membrane material
Common membrane materials include polyethersulfone(PESU) and regenerated cellulose(RC), both of which have high rejection, high flux and are easy to clean.
• Polyethersulfone has excellent PH compatibility and is resistant to acid and alkali cleaning.
• Regenerated cellulose has high hydrophilicity, low protein adsorption, and is not resistant to strong alkali. So for regenerated cellulose, there are certain restrictions on cleaning and disinfection.
(2)Selection of membrane pore size
• If the target substance is expected to pass through the membrane pores, the molecular weight cut-off of the membrane is generally selected to be 5-10 times or more than the molecular weight of the target substance.
• If the target substance is expected to be fully intercepted. Generally, the molecular weight cut-off of the membrane is selected to be 1/3-1/5 of the molecular weight of the target substance
(3) Cleaning of ultrafiltration cassette
Cleaning of ultrafiltration cassette is mainly to remove membrane pollutants, maintain membrane performance and reduce batch-to-batch contamination. Contaminants include microorganisms, particles, proteins, pigments, etc. Therefore, it should select cleaning agents according to the nature of the pollutants and the tolerance of the membrane material. Common cleaning agents are acids (citric acid, acetic acid, phosphoric acid, etc.), alkalis (sodium hydroxide, sodium hypochlorite) and surfactants (SDS, Triton X100).
