Membrane procedure

Fig. 6.1 Scheme of the membrane procedure for producing caustic and chlorine. 

On-blot digestion is another method used for proteins blotted onto nitrocellulose or PVDF membranes. Procedure is similar to in-gel digestion with the exception of elution from the membrane surface. 

Ci8 derivatized silica as the sorbent, while a diphasic dialysis membrane procedure was employed for the isolation of chloramphenicol residues from milk constituents using ethyl acetate as the extraction solvent (68). 

Separation of the polymer-target product from non-bound species using membrane procedures... 

Dawidowicz, A. L., Kalityhski, R., Trocewicz, J., Nestorowicz, A., Pijalkowska, A., Trela-Stachurska, K. (2002). Investigation of propofol renal elimination by HPLC using supported liquid membrane procedure for sample preparation. Biomed. Chromatogr., 16, 455-8. 

Comparative potencies of novel pentapeptides in displacing [3H]NPY from rat brain membranes (procedure as described in Table 1). Ac, acetyl Nle, norleucine. 

A new membrane procedure was tested with field tests in Port Hueneme (Cahfornia). By means of special hollow fibre membranes (HEM) and the additional creation of a vacuiun on the exterior of the membranes MTBE can be transferred into the gas phase and destroyed by thermal procedures, for example. The efficiency of the technology strongly depends on the vacuum applied, the water temperature and the retention time. Very good results were obtained with low flow rates of 4 L min [ 14]. 

The complex often loses its activity to bind a gaseous molecule rapidly after fixation in a dry polymer. A solvent or a polymer residue occupies the sixth-coordination site (binding site) of the complex during the solid-state polymer preparation (e.g., casting to form a membrane) procedure or after the immobilization. A permeate molecule has to displace the occupant, and the reaction becomes very slow. If the gaseous molecule-binding site of the complex is kept vacant after the dry polymer preparation, this complex very rapidly reacts as a carrier, even in the solid state. Solid membranes have been successfully prepared by a combination of specific cobalt-porphyrins and polymer attachment of the complex [27-29]. 

Saito described a quantitative spectrophotometric procedure for iron based on a solid-phase extraction using bathophenanthroline in a poly(vinyl chloride) membrane. ... 

PVDF-based microporous filters are in use at wineries, dairies, and electrocoating plants, as well as in water purification, biochemistry, and medical devices. Recently developed nanoselective filtration using PVDF membranes is 10 times more effective than conventional ultrafiltration (UF) for removing vimses from protein products of human or animal cell fermentations (218). PVDF protein-sequencing membranes are suitable for electroblotting procedures in protein research, or for analyzing the phosphoamino content in proteins under acidic and basic conditions or in solvents (219). 

One report (13) describes the procedure for spinning dry asymmetric ceUulose acetate fiber with a bore skin. Such fibers are spun in a modified dry-spinning process in which a volatile Uquid (methyl formate) is used as the ceUulose acetate solvent. The bore coagulating Uquid is isopropyl alcohol, which is subsequentiy removed. The advantages of these dry fibers over most ceUulose acetate membranes are that they can be stored dry, they are wet-dry reversible, they can be sterilized and packed dry, and they are ready for use without removal of preservatives. 

Membrane Sep r tion. The separation of components ofhquid milk products can be accompHshed with semipermeable membranes by either ultrafiltration (qv) or hyperfiltration, also called reverse osmosis (qv) (30). With ultrafiltration (UF) the membrane selectively prevents the passage of large molecules such as protein. In reverse osmosis (RO) different small, low molecular weight molecules are separated. Both procedures require that pressure be maintained and that the energy needed is a cost item. The materials from which the membranes are made are similar for both processes and include cellulose acetate, poly(vinyl chloride), poly(vinyHdene diduoride), nylon, and polyamide (see AFembrane technology). Membranes are commonly used for the concentration of whey and milk for cheesemaking (31). For example, membranes with 100 and 200 p.m are used to obtain a 4 1 reduction of skimmed milk. 

Thermoplastics. There are five elastomeric membranes that are thermoplastic. Two materials, chlorinated polyethylene (CPE) and polyisobutylene (PIB), are relatively obscure. Thermoplastic materials can be either heat-fused or solvent-welded. In contrast to Hypalon and uncured EPDM, this abiHty to fuse the membranes together remains throughout the life of the material. However, cleaning of the membrane surface after exposure to weather is required. Correct cleaning procedures for specific membranes are available from the individual manufacturer. 

Procedures for trapping accelerant vapors in the headspace of a closed container on charcoal that is either encased in a porous pouch or impregnated into a flexible membrane have been described (124). Trace amounts of explosive compounds can be trapped from hplc effluents onto a porous polymer microcolumn for confirmatory gc examination (125). 

The subsequent improvement of the physical and chemical characteristics of these membranes, their incorporation into machines, and the development of procedures to prevent or clean surface-fouling films were the principal areas of significant advancement. By 1990, the industrial ultrafiltration market had grown to an estimated (90-100) x 10 . ... 

Gleaning. Fouling films are removed from the membrane surface by chemical and mechanical methods. Chemicals and procedures vary with the process, membrane type, system configuration, and materials of constmction. The equipment manufacturer recommends cleaning methods for specific apphcations. A system is considered clean when it has returned to >75% of its original water flux. 

Flux response to concentration, cross flow or shear rate, pressure, and temperature should be determined for the allowable plant excursions. Fouling must be quantified and cleaning procedures proven. The final design flux should reflect long-range variables such as feed-composition changes, reduction of membrane performance, long-term compaction, new foulants, and viscosity shifts. 

A membrane filter technique can also be used to determine the presence of fecal coliforms, and this procedure is said to be 93% accurate (20). A sample is passed through a membrane filter, and this filter is placed in a petri dish containing an enriched lactose medium. The dishes are incubated at... 

Pretreatment For most membrane applications, particularly for RO and NF, pretreatment of the feed is essential. If pretreatment is inadequate, success will be transient. For most applications, pretreatment is location specific. Well water is easier to treat than surface water and that is particularly true for sea wells. A reducing (anaerobic) environment is preferred. If heavy metals are present in the feed even in small amounts, they may catalyze membrane degradation. If surface sources are treated, chlorination followed by thorough dechlorination is required for high-performance membranes [Riley in Baker et al., op. cit., p. 5-29]. It is normal to adjust pH and add antisealants to prevent deposition of carbonates and siillates on the membrane. Iron can be a major problem, and equipment selection to avoid iron contamination is required. Freshly precipitated iron oxide fouls membranes and reqiiires an expensive cleaning procedure to remove. Humic acid is another foulant, and if it is present, conventional flocculation and filtration are normally used to remove it. The same treatment is appropriate for other colloidal materials. Ultrafiltration or microfiltration are excellent pretreatments, but in general they are... 

Membrane Characterization The two important characteristics of a UF membrane are its permeability and its retention characteristics. Ultrafiltration membranes contain pores too small to be tested by bubble point. Direc t microscopic observation of the surface is difficult and unreliable. The pores, especially the smaller ones, usually close when samples are dried for the electron microscope. Critical-point drying of a membrane (replacing the water with a flmd which can be removed at its critical point) is utihzed even though this procedure has complications of its own it has been used to produce a Few good pictures. 

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