Dilute continuous settling

Continuous Settling Dilute Systems. When apphed to continuous sedimentation the long tube test is used to model the settling of particles in an elemental vertical volume of liquid moving throu the length of the clarifier. The corresponding overflow rate Vc, of a continuous ideal basin is given by H/ta, where H is the sanq)le point depth. 

Cautiously add 250 g. (136 ml.) of concentrated sulphuric acid in a thin stream and with stirring to 400 ml. of water contained in a 1 litre bolt-head or three-necked flask, and then dissolve 150 g. of sodium nitrate in the diluted acid. Cool in a bath of ice or iced water. Melt 94 g. of phenol with 20 ml. of water, and add this from a separatory funnel to the stirred mixture in the flask at such a rate that the temperature does not rise above 20°. Continue the stirring for a further 2 hours after all the phenol has been added. Pour oflF the mother liquid from the resinous mixture of nitro compounds. Melt the residue with 500 ml. of water, shake and allow the contents of the flask to settle. Pour oflF the wash liquor and repeat the washing at least two or three times to ensure the complete removal of any residual acid. Steam distil the mixture (Fig. II, 40, 1 or Fig. II, 41, 1) until no more o-nitrophenol passes over if the latter tends to solidify in the condenser, turn oflF the cooling water temporarily. Collect the distillate in cold water, filter at the pump, and drain thoroughly. Dry upon filter paper in the air. The yield of o-nitrophenol, m.p. 46° (1), is 50 g. 

Dilute This is a fully expanded condition in which the solids particles are so widely separated that they exert essentially no influence upon each other. Specifically, the solids phase is so fuUy dispersed in the gas that the den sity of the suspension is essentially that of the gas phase alone (Fig. 12-29). Commonly, this situation exists when the gas velocity at all points in the system exceeds the terminal setthng velocity of the solids and the particles can be lifted and continuously conveyed by the gas however, this is not always true. Gravity settling chambers such as prilling towers and countercurrent-flow spray diy-ers are two exceptions in which gas velocity is insufficient to entrain the sohds completely. 

The extrapolation of this ratio to m2 = 0 is shown in Figure 17.2. The curve in Figure 17.2 should have a horizontal limiting slope. If an experimental curve does not have a horizontal limiting slope, the data have not been obtained in sufficiently dilute solution to show Henry s-law behavior. Very few data are available that satisfy this rigorous criterion [1]. We frequently settle for a condition in which the plot of 2/ 2 has a clear linear extrapolation to m2 = 0, as opposed to a continuing curvature that makes an extrapolation impossible. 

Palladium on barium sulphate (5% Pd) is prepared as follows. Dissolve 4.1 g of palladium chloride (1) in 10 ml of concentrated hydrochloric acid and dilute with 25 ml of water. Add all at once 60 ml of 3 m sulphuric acid to a rapidly stirred, hot (80 °C) solution of 63.1 g of barium hydroxide octahydrate in 600ml of water contained in a 2-litre beaker. Add more 3 m sulphuric acid to render the suspension just acid to litmus. Introduce the palladium chloride solution and 4 ml of 40 per cent formaldehyde solution into the hot mechanically-stirred suspension of barium sulphate. Render the suspension slightly alkaline with 30 per cent sodium hydroxide solution, continue the stirring for 5 minutes longer and allow the catalyst to settle. Decant the clear supernatant liquid, replace it by water and resuspend the catalyst. Wash the catalyst by decantation 8-10 times and then collect it on a medium-porosity sintered glass funnel, wash it with five 25 ml portions of water and suck as dry as possible. Dry the funnel and contents at 80 °C, powder the catalyst (48 g) and store it in a tightly stoppered bottle. 

Sample Solution Fill a 100-mL porcelain crucible halffull of ashless filter paper pulp. Place 2 g of the finished catalyst, in droplet or flake form and accurately weighed, on top of the paper pulp. Transfer the crucible to a muffle furnace set at room temperature, and slowly raise the temperature to 650° so that the stearine melts into the paper, and the organic mass bums and chars slowly. Continue heating at 650° for 2 h or until the carbon is burned off. Cool, add 20 mL of hydrochloric acid, quantitatively transfer the solution or suspension into a 400-mL beaker, and carefully evaporate to dryness on a steam bath. Cool, add 20 mL of hydrochloric acid, warm to aid dissolution (catalysts containing silica will not dissolve completely), transfer into a 500-mL volumetric flask, dilute to volume with water, and mix. Allow any solids to settle, pipet a clear, 50-mL aliquot into a 400-mL beaker, and dilute to 250 mL with water. (If there is suspended matter in the volumetric flask, filter a portion through a dry, medium-speed filter paper into a dry receiver, and pipet from the receiver.)... 

Wet classification is performed by filtration, settling, centrifugation, Sind hydrocyclones. When operated in conjunction with grinding equipment, the wet classification equipment must operate continuously and give a pumpable fluid. This is often accomplished in practice with hydrocyclones because the other methods are unsuitable (e.g., settlers and centrifuges are used for dilute suspensions, filters and screens produce a nonpumpable cake.)... 

---