Membrane preparation technology

However, as with the conventional bulk MIP materials, the limited accessibility of MIP binding sites due to a random distribution inside and on the surface of the bulk polymer phase remains one of the major unsolved problems. Thus, the advantage of membrane preparation technology to provide well-defined pore structures is not yet fully exploited for the preparation of self-supported micro and macroporous MIP membranes. 

Since selective formation of a specified pore size has been achieved at a considerable level in the present membrane preparation technology, one important key to further extend spread of the membrane filtration in the fumre is economic efficiency. The key to increase the economic efficiency will be reduction of clogging and increasing mechanical and chemical strength. In this coimeclion, a membrane superior in thermal resistance is advantageous because it can expand the range of application. In the field of pharmaceutical application, for example, steam sterilization resistance may be required. 

Based on Table 5.3, technical trends of MF/UF membranes will be reviewed from the following two viewpoints (1) membrane materials and (2) membrane preparation technology. 

Membrane Preparation Technology As is apparent from Table 5.3, the most important method in membrane preparation is phase separation. The phase separation method has been widely utilized due to the following advantages ... 

Larbot, A., J. A. Alary, C. Guizard, L. Cot and J. Gillot. 1987. New inorganic ultrafiltration membranes Preparation and characterization. Int. J. High Technology Ceramics 3 145-51. 

Most ultrafiltration membranes are porous, asymmetric, polymeric structures produced by phase inversion, i.e., the gelation or precipitation of a species from a soluble phase. See also Membrane Separations Technology. Membrane structure is a function of the materials used (polymer composition, molecular weight distribution, solvent system, etc) and the mode of preparation (solution viscosity, evaporation time, humidity, etc.). Commonly used polymers include cellulose acetates, polyamides, polysulfoncs, dyncls (vinyl chlondc-acrylonitrile copolymers) and puly(vinylidene fluoride). 

This book provides a general introduction to membrane science and technology. Chapters 2 to 4 cover membrane science, that is, topics that are basic to all membrane processes, such as transport mechanisms, membrane preparation, and boundary layer effects. The next six chapters cover the industrial membrane separation processes, which represent the heart of current membrane technology. Carrier facilitated transport is covered next, followed by a chapter reviewing the medical applications of membranes. The book closes with a chapter that describes various minor or yet-to-be-developed membrane processes, including membrane reactors, membrane contactors and piezodialysis. 

The technology to fabricate ultrathin high-performance membranes into high-surface-area membrane modules has steadily improved during the modem membrane era. As a result the inflation-adjusted cost of membrane separation processes has decreased dramatically over the years. The first anisotropic membranes made by Loeb-Sourirajan processes had an effective thickness of 0.2-0.4 xm. Currently, various techniques are used to produce commercial membranes with a thickness of 0.1 i m or less. The permeability and selectivity of membrane materials have also increased two to three fold during the same period. As a result, today s membranes have 5 to 10 times the flux and better selectivity than membranes available 30 years ago. These trends are continuing. Membranes with an effective thickness of less than 0.05 xm have been made in the laboratory using advanced composite membrane preparation techniques or surface treatment methods. 

Wilhelm, F.W. (2000) Bipolar membrane preparation, in Bipolar Membrane Technology (ed. A.J.B. Kemperman),... 

In order to maintain the advantage of the microfabrication approach which is intended for a reproducible production of multiple devices, parallel development of membrane deposition technology is of importance. Using modified on-wafer membrane deposition techniques and commercially available compounds an improvement of the membrane thickness control as well as the membrane adhesion can be achieved. This has been presented here for three electrochemical sensors - an enzymatic glucose electrode, an amperometric free chlorine sensor and a potentiometric Ca + sensitive device based on a membrane modified ISFET. Unfortunately, the on-wafer membrane deposition technique could not yet be applied in the preparation of the glucose sensors for in vivo applications, since this particular application requires relatively thick enzymatic membranes, whilst the lift-off technique is usable only for the patterning of relatively thin membranes. 

The wall-thickness of 2 mm provides the CC tubes with sufficient mechanical strength to withstand gas and liquid pressures that are common in membrane technology. The measured pore diameters of 120 and 184 nm are well in the range used for mesoporous membrane preparation and it is expected that y-alumina layers can be applied on the supports by conven-... 

There are many different modifications of the method, early technology used membrane preparations, modem methods use solubilized receptors and receptor of constructs which enable fast signal detection. 

Nevertheless, the availability of procedures allows the preparation of zeolite membranes and layers with sufficient quality, reproducibility, and reliability only up to a few hundred square centimeters in surface, delaying the industrial implementation of zeolite membrane-based technology. To be realistic, the lack of module reliability under extreme temperature cycling or harsh environment and the necessary raw material cost reductions (supports and chemicals) are two of the main challenges toward which strong efforts must be targeted. 

The high cost, limited lifetime, and low permeability are relevant limits of Pd and Pd-alloy membranes. To overcome these drawbacks, many studies have been carried out for the preparation of supported metallic membranes in which a thin metallic layer is supported on a thicker sublayer. However, the preparation technology of metalhc membranes is still today not sufficiently mature and more work is necessary to produce defect free and stable membranes at acceptable costs. 

When discussing membrane preparation, not only must the physical structure be considered, but one must also consider the membrane form or shape. In an effort to combat concentration polarization and membrane fouling and to maximize the membrane surface area per unit module volume, membranes are produced in the form of flat sheets (used either In plate-and-frame or spiral wound modules), supported and unsupported tubes, and hollou fibers. Although much of the technology associated with membrane development and membrane production Is closely guarded as proprietary Information, some of the details are beginning to appear in the literature (6,9-13,16-20). 

Technologies Membrane preparations Fluorescence Cell-based fluorescence... 

---