Filtration-type methods

In the filtration-type methods (the first three techniques listed above), components accumulate as a steady-state (polarization) layer at a barrier or membrane [4] this occurs in much the same way as in field-flow fractionation or equilibrium sedimentation. However, there are several complications. First, fresh solute is constantly brought into the layer by the flow of liquid toward and through the filter. This steady influx of solute components can be described by a finite flux density term J0. Second, components can be removed from the outer reaches of the layer by stirring. Third, the membrane or barrier may be leaky and thus allow the transmission of a portion of the solute, profoundly affecting the attempted separation. In fact, one reason for our interest in layer structure is that leakiness depends on the magnitude of the solute buildup at the membrane surface. As solute concentration at the surface increases, more solute partitions into the membrane and is carried on through by flow. 

Aaltonen et al. (61) compared RRA and RIA for atropine. These workers obtained preparations of receptor from rat brain and lyophilized them to a stable, dry form, They used the tritium-labeled quinuclidinyl benzilate at 35 Ci/mmol. The affinity constant was 0.48 nM, and by analysis of 25- xL serum samples they could obtain a sensitivity down to 1.25 ng/mL in serum. Nonspecific binding was again quite reasonable (4%) and a filtration-type separation was used. The d isomer of an atropine did not bind, and therefore, the cross-reaction of the d,l compound was 50% that of the ( isomer. For comparison they used RIA developed by the method of Virtanen et al, (37). The immunogen was an /-hyoscyamine-bovine serum albumin conjugate, but the antiserum was sensitive to both d,l and I isomers. Racemic tritium-labeled atropine was used as the radioligand. 

Concepts Common household chemicals have different physical and chemical properties. Chemicals undergo changes in form, color, or texture when they are mixed together, separated, or heated. Some chemicals can be identified by their interaction with water, vinegar, iodine, red cabbage juice, and heat. Different types of mixtures, such as solutions or suspensions, are created when solids are combined with water. Evaporation and filtration are methods for separating mixtures of solids and liquids. Some chemicals can be classified as acids, bases, or neutral substances by their reactions with red cabbage juice. Observations... 

Adsorption of heavy metal ions on the ETS-10 sample was conducted using a batch-type method at room temperature (23 C). For kinetic measurement, I g of air-dried ETS-10 was added to 100 ml of solution pre-acidified by nitric acid under shaking so as to generate a solution of pH = 5.8. Then, 100 ml of 20 mmol/L Pb(N03)2 (or Cu(N03)2) solution was added to obtain a mixture with an initial Pb (or Cu concentration of approximately 10 mmol/L, a final pH value of about S.O and a batch fiictor (ratio of liquid volume to solid mass) of about 0.2 L/g. S ml of the mixture was withdrawn at an appropriate time interval by using a 5 ml syringe and rapidly filtered through a 0.2 pm nylon membrane filter. The filtrate was collected in a sample valve and analyzed for Pb (or Cu), Na and K concentrations using a spectrometer (Perkin-Elmer Analyst 300). The amount of metal adsorbed at time t (s), (mmol/g), was deduced from the mass balance between the initial concentration (Q) and concentration at time t (C,). The experimental data were fitted to pseudo-second-order equation ((/g, =1/Vq +//gj [8], where k (g/mmol/s) is the adsorption... 

Methods of Continuous Vacuum Filtration, Types of Design and Examples of Application 337... 

An obvious method of increasing the filtration area in the vessel is to stack several plates on top of each other the plates are operated in parallel. One design, known as the plate filter, uses circular plates and a stack that can be removed as one assembly. This allows the stack to be replaced after the filtration period with a clean stack, and the filter can be put back into operation quickly. The filter consists of dimpled plates supporting perforated plates on which filter cloth or paper is placed. The space between the dimpled plates and the cloth is coimected to the filtrate outlet, which is either into the hoUow shaft or into the vessel, the other being used for the feed. When the feed is into the vessel, a scavenger plate may have to be fitted because the vessel will be full of unfiltered slurry at the end of the filtration period. This type of filter is available with filtration areas up to 25 m and cakes up to 50 mm thick. 

Mechanical Cake Removal. This method is used in the American version of the dynamic filter described under cross-flow filtration with rotating elements, where turbine-type rotors are used to limit the cake thickness at low speeds. The Exxflow filter, introduced in the United Kingdom, is described in more detail under cross-flow filtration in porous pipes. It uses, among other means, a roUer cleaning system which periodically roUs over a curtain of flexible pipes and dislodges any cake on the inside of the pipes. The cake is then flushed out of the curtain by the internal flow. 

The success of a reverse osmosis process hinges direcdy on the pretreatment of the feed stream. If typical process streams, without pretreatment to remove partially some of the constituents Hsted, were contacted with membranes, membrane life and performance would be unacceptable. There is no single pretreatment for all types of foulants. Pretreatment methods range from pH control, adsorption (qv), to filtration (qv), depending on the chemistry of the particular foulant. Some of the pretreatment methods for each type of foulant are as foUow (43—45) ... 

Common names have been given to sodium sulfate as a result of manufacturiag methods. In rayon production, by-product sodium sulfate is separated from a slurry by filtration where a 7—10-cm cake forms over the filter media. Thus rayon cake was the term coiaed for this cake. Similarly, salt cake, chrome cake, phenol cake, and other sodium sulfate cakes were named. Historically, sulfate cakes were low purity, but demand for higher purity and controlled particle size has forced manufacturers either to produce higher quaUty or go out of busiaess. Sodium sulfate is mined commercially from three types of mineral evaporites thenardite, mirabilite, and high sulfate brine deposits (see Chemicals FROMBRINe). 

Preliminary Selections Assembling background information permits tentative selection of promising equipment and rules out clearly unsuitable types. If the material to be processed is a shiny or pumpable suspension of sohds in a hquid, several methods of mechanical separation may be suitable, and these are classified into setfiiug and filtration... 

Numerous application examples are related to gel filtration (e.g., see Hagel, 1989 Hagel and Janson, 1992 Pharmacia, 1991). A selected number of applications are discussed with respect to their goals and to types of methods and SEC media attributes, which impact the selection and or construction of a suitable SEC column. Specific examples of these various applications types are given later under Sections II,C and III. The optimization of running conditions to achieve the desired results are discussed in Section VI. 

The filtration, or superficial face, velocities used in fabric filters are generally in the range of 1 to 10 feet per minute, depending on the type of fabric, fabric supports, and cleaning methods used. In this range, pressure drops conform to Darcy s law for streamline flow in porous media, which states that the pressure drop is directly proportional to the flow rate. The pressure drop across the... 

An alternative method of manufacturing is to employ a coil of flat metal ribbon as the element, each turn spaced from the next by small lateral protuberances. The principle of filtration is the same. Porosity of both types are identical and cover a wide range, usually from 100 microns down to 0.5 microns. 

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