Microfiltration and ultrafiltration membranes

A significant recent advance has been the development of microfiltration and ultrafiltration membranes composed of inorganic oxide materials. These are presently produced by two main techniques (a) deposition of colloidal metal oxide on to a supporting material such as carbon, and (b) as purely ceramic materials by high temperature sintering of spray-dried oxide microspheres. Other innovative production techniques lead to the... 

For relatively porous nanofiltration membranes, simple pore flow models based on convective flow will be adapted to incorporate the influence of the parameters mentioned above. The Hagen-Poiseuille model and the Jonsson and Boesen model, which are commonly used for aqueous systems permeating through porous media, such as microfiltration and ultrafiltration membranes, take no interaction parameters into account, and the viscosity as the only solvent parameter. It is expected that these equations will be insufficient to describe the performance of solvent resistant nanofiltration membranes. Machado et al. [62] developed a resistance-in-series model based on convective transport of the solvent for the permeation of pure solvents and solvent mixtures ... 

W.R. Bowen and A.O. Sharif, Hydrodynamic and colloidal interaction effects on the rejection of a particle larger than a pore in microfiltration and ultrafiltration membranes, Chem. Eng. Sci. 53 (1998) 879-890. 

Table 16.3 Advantages and limitation of various module configurations for microfiltration and ultrafiltration membranes.

Microfiltration and ultrafiltration membranes allow flow capacities of 150 to 500 liters/m per hour when operating on water. This is expressed as water flux for each membrane type. Naturally the flow capacity for juices is lower. After cleaning of a membrane the water flux should reach its original capacity and it serves as an indication whether the membrane was properly cleaned. It is also an indication for when a membrane needs replacement once it plugs over longer periods. 

The silicon nitride tip is used mostly for C-AFM. Measurements can be done in ambient air, controlled atmospheres, or in non-aggressive liquids. AFM also allows surface forces, and even molecular forces, to be directly quantified [23]. For example, the interaction forces between a silicon tip and microfiltration and ultrafiltration membranes in an electrolyte solution can be measured [24]. The geometry of the cantilever is not simple, and in some cases not even known, so comparison with theory is difficult. However, attaching a sphere to the cantilever instead of a tip enables the measurement of interaction between surfaces of known geometry [25]. This technique has been used to measure interactions between different materials in air... 

KJ. Howe, M.M. Clark, Fouling of microfiltration and ultrafiltration membranes by natural waters. Environ. Sci. Technol. 36 (16) (2002) 3571-3576. 

Table A1.21 Water Permeability for Assorted Microfiltration and Ultrafiltration Membranes (at 20°C)...

Inorganic microfiltration and ultrafiltration membranes have been used in a wide variety of processings. Typical applications were reported by Hsieh [2] and Bhave [3], and are summarized in Table 10.1.5. MF, which has pore sizes larger than 100 nm, can be applied to remove or concentrate particles or microorganisms, while UF membranes have been used for the separation of components, the sizes of which are from 2 to 100 nm, such as proteins and colloidal solutes. In this section, potential applications will be reviewed. 

MGmbranG Applications. Cellulose esters are effective in membrane applications. Ultrafiltration membranes based on cellulose nitrate were first described by Collander in 1924 (41). Cellulose nitrate films cast from mixtures of methyl acetate or acetone with glycerol and mixtures of ether and ethanol produce microfiltration and ultrafiltration membranes, respectively (42). Cellulose nitrate microfiltration membranes typically have 0.02-10 /um diameter pores and 4 X 10 - 15 cm /cm s atm permeability. Cellulose nitrate ultrafiltration membranes t5 ically have 0.003-0.03 )um diameter pores and (1-100) x 10 cm /cm s atm permeability (42). Nitrocellulose membranes are used in numerous biochemical and diagnostic applications and is discussed later. 

Keurentges, JTF Harbrecht, JG Brinkman, D Hanemaaijer, JH Cohen, MA Van t Riet, H. Hydrophobicity measurements of microfiltration and ultrafiltration membranes. 

Microfiltration and ultrafiltration membranes can be made from organic polymers or inorganic materials such as ceramic, glass, or metal or organic polymers. Materials used in MF and UF membrane fabrication are shown in Table 6.1. A number of different techniques are employed to prepare synthetic MF/UF membranes the most important are phase inversion, coating, sintering, and track etching. 

Furukawa, D. (2002). Global status of microfiltration and ultrafiltration membrane technology. Watermark (17). MEDRC (Newsletter). Muscat, Oman. 

As will always be the case, the actual purity achieved for a given purpose will be a compromise between the desire for absolute purity and the cost of achieving it. The appearance on the technical scene of membranes first of all, and now microfiltration and ultrafiltration membranes of reasonable cost, has made ultrapure water a practical goal. 

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