Continuous filtration

When the volume of mother liquor is large and the amount of crystals small, the apparatus of Fig. II, 32, 1 may be used. The large pear-shaped receiver is supported on a metal ring attached to a stand. When the receiver is about two-thirds fuU, atmospheric pressure is restored by suitably rotating the three-way stopcock the filtrate may then be removed by opening the tap at the lower end. The apparatus is again exhausted and the filtration continued. 

As a result, there is a growing trend to off-line clean reverse-pulse filters by using bags with multiple compartments. These sections allow the outlet-gas plenum serving a particular section to be closed off from the clean-gas exhaust, thereby stopping the flow of inlet gas. On the dirty-side of the tube sheet, the isolated section is separated by partitions from the neighboring sections where filtration continues. Sections of the filter are cleaned in rotation as with shaker and reverse-flow filters. 

Then, water is added continuously while the filtration continues at nearly constant flux. This latter filtration stage, when water is added to maintain a constant flux, is referred to as diafiltration. Proper choice of the diafiltration starting time can minimize the required membrane area, which is often the major part of the capital cost in an ultrafiltration process. 

Wash the precipitate in 6M guanidine HC1, Tris 0.3 M, pH 8.5. The polypeptide will appear in the filtrate. Continue washing with sufficient 6M guanidine HC1, Tris 0.3 M, pH 8.5, and add 10% 2-mercaptoethanol, to make an approx 30 mg/ml solution. 

After removal of the crude product, upon standing the ethyl acetate filtrate continues to deposit a dark yellow solid. This is not a second crop of the desired l,2,3-trimethyl-3-phenylindoleninium iodide it is, according to mp, UV, and NMR... 

In this and subsequent filtrations it is advantageous to use a rubber dam held in place by rubber bands (Org. Syn. 14, 25, Note 3). The use of the rubber dam is especially advantageous for a slow filtration continuing overnight. 

Good filtration practice requires careful regulation of the pressure at which the carbon-liquid mixture is delivered to the filter. At the start, the pressure should be low enough to permit a proper flow of clear liquid from the filter. Then as the filtration continues and the filter cake becomes thicker, the pressure from the pump should be increased to maintain the rate of flow but such an increase in pressure should be very gradual. 

Carbon can be placed on the filters by adding a carbon slurry to the filters after backwashing. Particles of carbon are thus distributed throughout the water on top of the filter and they then deposit on the sand surface of the filter. As the filtration continues, water passes through a layer of carbon, thus removing odorous materials. This is the point usually selected in small plants where feeding facilities do not exist. 

In the preparation of 2-methyl-l,3-cyclopentanedione from 4-oxohexanoic acid and pro-pionyl chloride a second fraction of the product is obtained by boiling the aqueous phase of the filtrate with charcoal, filtering, and extracting the filtrate continuously with ether. When the solvent is nitrobenzene the dione is obtained in 70% yield with m.p. 214-216°. 

Again, a priori, we would not have expected to get comparable results from techniques involving such different physical principles as filtration, continuous-flow centrifugation, and deposition. While filtration depends on particle size and deposition upon particle density, continuous-flow centrifugation adds in the possibility of flocculation into one or a few large particles. The three methods appear to achieve roughly similar results [118, 119], although filtration... 

The filtration continues until the precipitate of filtered particles has clogged the sand so that the flow rate drops. Then the flow is stopped and water introduced in the reverse direction so that it flows upward, backwashing the bed and carrying the precipitated solid away. This apparatus can only be used on precipitates that do not adhere strongly to the sand and can be easily removed by backwashing. Open tank filters are used in filtering municipal water supplies. 

The amount of sulphides may ho estimated by titrating the hot soda solution, to which ammonia has been added, with an ammoniacal silver nitrate solution, I c.c. of which corresponds to 0 005 gramme Na. S. As the titration proceeds, the precipitate is filtered off, and the addition of ammoniacal silver solution to the filtrate continued until a drop produces only a slight opacity. The presence of chloride, sulphate, hydrate, or carbonate does not interfere with the accuracy of this method. The ammoniacal silver nitrate solution is prepared by dissolving 13 345 grammes of pure silver in pure nitric acid, adding 250 c.c. liquor ammoniie fortis, and diluting to 1 litre. 

Liquid solutions, where the solute to be removed is adsorbed relatively strongly compared with the remainder of the solution, are treated in batch, semicontinuous, or continuous operations in a maimer analogous to the mixer-settler operations of liquid extraction (contact filtration). Continuous countercurrent cascades can be simulated or actually realized by use of such techniques as fluidized beds. 

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