Layer filtration

Another scheme for methylxanthine isolation involves the extraction of the dried ground plant with 10% ammonium hydroxide chloroform (1 10). A large proportion of the extraction mixture is used, relative to the sample, to ensure complete extraction of any theobromine. Caffeine and theophylline will be extracted easily under these conditions.20 After removing water from the organic layer, filtration, and solvent removal, any methylxanthines present will be in the residue together with some impurities. An approach to finally isolating these methylxanthines from this... 

Aldushin, A. R, Merzhanov, A. G., and Khaikin, B. I., Conditions for the layer filtration combustion of porous metals. Dokl. Phys. Chem., 215,295 (1974). 

Kralingen, Netherlands [83] Surface water Meuse River Coagulation Sedimentation Ozonation Dual layer filtration Carbon filtration Safety chlorination Protection against periodic taste/odor and toxic substances Removal of THM s produced by chlorination Removal of matter produced by or unsuccessfully removed by ozonation Particle size 0.8 mm Bed deptli 4 m Bed diameter 6 m Volume per filter 116 m" Contact time 12 min. 

In some types of processing, the carbon and liquid are not premixed before filtration instead a layer of carbon is preformed in the filter through which the liquid to be purified is passed continuously.2,3 Layer-filtration is practiced in systems that contain a liquid phase which serves to pick up any impurities produced by the operation, e.g., dry cleaning and electroplating. An accumulation of impurities is avoided by recycling the liquid phase through the carbon layer. 

Carbon generally is applied as a suspension, but in Europe some study has been devoted to layer filtration. In this, the sugar liquors are pumped through, a layer of activated carbon previously deposited in the filter. In a two-stage operation, a partially purified batch of liquor is passed through a layer of virgin activated carbon after which this layer is used to decolorize partially a dark liquor. 

InTjurope, three" stages ot countercurrent are recommended.12 The fresh carbon is applied to the thick liquor, the once-used carbon to the thin liquor, and the twice-used carbon is added to the neutralized converter juice. To avoid rehandling the carbon filter cake, some manufacturers use a modification of layer filtration. In this procedure, after the thick liquor has been filtered, the thin liquor is pumped through the once-used carbon on the filter. Success in the operation depends on placing a carbon layer of uniform thickness on the filter. -— ------------------------- ---------... 

The metal-ion permselective properties were examined as follows metal ion solutions containing Fe(N03)3 and FeCh with 2 ppm concentration were prepared, respectively. Before and after the formation of ESA layers, filtration measurement of the metal ion solution through sample membranes was carried out by using an ultrafiltration cell (Amicon 8010, 50 ml volume). The metal-ion rejection (R) was defined by the following equation ... 

Decolorization of sugar solutions using powdered active carbons can be carried out by two methods contact batch method and the continuous layer filtration method. There is a third method, which is a combination of both the methods. 

Continuous layer filtration involves filtering the sugar syrup through a layer of activated carbon. Several types of filters are used, such as pressure leaf filters with metal frames on which a filter cloth that may be cotton, polyamide, or wire mesh is fixed rotary leaf filters or bed filters in which the filtering medium is a ceramic or sintered plate, wire mesh, or finely perforated metal plate. The latter filters are usually coated with a layer of filter aid that may be a diatomaceous earth. A suspension of active carbon in water or liquor is passed through the filter until a uniform layer of active carbon bed 10 to 15 mm thick builds up. The filter is then ready for filtration of the liquor that must flow to the filter at a uniform rate to avoid breaking the layer. 

It is worth mentioning here that each of the two methods described above requires different activated carbons with different properties. For example, in the contact batch method, the active carbons used should have good filtering properties, because the flow rates here are about 10 times higher than in the continuous layer filtration... 

Kozinski A.A. and Lightfoot E.N., 1972. Protein ultrafiltration a general example of boundary layer filtration, AIChEJ, 18, 1030. 

Teng et al. [236] prepared a three-layered membrane consisting of Col/HAp and CS in a sandwich structure using a layer-by-layer filtration process. SEM results showed that both the surface and cross-section of the three-layered membranes exhibited a porous structure with a pore size of tens to hundreds of micrometers. 

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