Capillary disc filter

The capillary disc filter looks like any other standard rotary vacuum disc filter, as can be seen in Figure 3.25, but the filter medium is a finely porous ceramic disc, which draws filtrate through the disc material by capillary action, under the applied vacuum. The filter discs are made of sintered alumina with uniform micropores less than 1 pm in size, which allows only liquid to flow through it. Despite an almost absolute vacuum, no air penetrates the filter material. The disc material is inert,... 

An interesting extension of the range of vacuum filters is the capillary disc filter (Figure 4.26). This is a continuously operating, capillary action, ceramic dewatering filter, which eliminates the need for separate filter cloths. The filter medium is a disc, formed from two circles of sintered alumina, joined at their circumferences. The filter has several such discs mounted on a central horizontal shaft. The medium is practically inert in most solutions, and may be used in a broad range of water-based and solvent-based slurries. In operation, as the microporous ceramic discs rotate through... 

The bubble point test, while popular, has some deficiencies that must be realized. First, there is variation in the operator detection of the test end point that is, the first appearance of gas bubbles rising in the liquid. Some operators are able to see smaller bubbles than others. In a recent study, a panel of seven observers recorded the initial detection of a steady stream of air bubbles rising from a capillary held under water as the air pressure was gradually increased. The observers, who had received different degrees of training, identified the simulated bubble point as occurring at air flows of 5 to 50 mL/min corresponding to air pressures of 34 and 38 psi, respectively, for a 90-mm disc filter membrane [56]. 

Although disc-type vacuum Alters are not normally well suited for cake washing (because the wash water runs too quickly off the surface of the cake), the capillary action filter has proved the exception. Wash liquid is sprayed on the cake solids, to remove additional filtrate or impurities. This displacement washing is not susceptible to the difficulties of conventional filtration systems, where cake cracking, channelling or uneven distribution occurs. 

Capillary filtration can provide for a high product output capacity with the produced filter cake having a very low water content. Disc filters of this type are considered to be energy efficient, using up to 90% less energy than other vacuum filters, because no air passes through the plates. 

This also is known as the Rutter technique. The spot is placed in the center of a filter paper disc containing a slit from the center to the perimeter. By means of this "wick", solvent is fed to the paper by capillary action, and resolution occurs as circles rather than spots. The chamber can be a petri dish or a desiccator (Figure... 

If the amount of solid is small in relation to the amount of liquid and the crystals do not settle readily, the apparatus shown in Figure 16b may be used a disc of hardened filter paper is wetted with the solvent and then placed in the upper part of the filtration capillary. Jena glass frits (12 G 3, 15 G 3,... 

BASF in Germany considered the use of the capillary gap cell (see Fig. 2.16 in Chapter 2) for this electrolysis. The cell consists of a stack of carbon discs closely spaced by 0.2 mm thick strips of an insulator. The electrolyte is pumped through the inter-electrode gaps and a voltage is applied to endplates so that a bipolar cell is formed. The cell design is compact, simple and cheap compared with a filter press cell and the tetraalkylammonium concentration could be reduced to below 0.5% without loss of yield and with an energy consumption below 3000 kWh ton . ... 

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