Solids and Suspensions

Figure 15-2. HPLC chromatogram obtained for drug product in solid and suspension dosage forms.

Ramsden W 1903 Separation of solids In the surface layers of solutions and suspensions Proo. R. Soo. 72 156-64... 

A suspension of 3.90 g (19.6 mmol) of p-(bromomethyl)benzaldehyde (2.8) and 4.00 g (31.7 mmol) of sodium sulfite in 40 ml of water was refluxed for two hours, after which a clear solution was obtained. The reaction mixture was cooled on an ice bath resulting in precipitation of some sodium sulfite. After filtration, the solvent was evaporated. Ethanol was added to the remaining solid and the suspension was refluxed for 10 minutes. After filtering the hot solution, the filtrate was allowed to cool down slowly to -18 °C whereupon sodium (p-oxomethylphenyl)methylsulfonate (2.9) separated as colourless crystals. The extraction procedure was repeated two more times, affording 2.29 g (10.3 mmol, 53%) of the desired product. H-NMR (200 MH D2O) 5(ppm) =4.10 (s,2H) 7.44 (d,2H) 7,76 (d,2H) 9.75 (s,lH). 

The chlorine and ethane are brought together in a fluid bed of finely divided, inert, solid heat-transfer medium, eg, sand, at 380—440°C the linear velocity of the gas is sufficient to maintain the finely divided solid in suspension within the reactor (26). 

In selec ting the machines of choice, the use of specific speed and diameter best describe the flow. Figure 10-67 shows the characteristics of the three types of compressors. Other considerations in chemical plant service such as problems with gases which may be corrosive or have abrasive solids in suspension must be dealt with. Gases at elevated temperatures may create a potential explosion hazard, while air at the same temperatures may be handled qmte normally minute amounts of lubricating oil or water may contaminate the process gas and so may not be permissible, and for continuous-process use, a high degree of equipment rehability is required, since frequent shutdowns for inspec tion or maintenance cannot be tolerated. 

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 Dorr agitator (Coulson and Richardson, loc. cit.) consolidates in one unit the principles of the thickener and the Pachuca tank. Resembling a rake-equipped thickener, it differs in that the rake is driven by a hollow shaft through which the solids-liquid suspension is lifted and circulated by an air stream. The rake moves the pulp to the center, where it can be entrained by the air stream. The unit may be operated batchwise or continuously. 

Some contrasting characteristics of the main lands of three-phase reactors are summarized in Table 23-15. In trickle bed reactors both phases usually flow down, the liquid as a film over the packing. In flooded reactors, the gas and hquid flow upward through a fixed oed. Slurry reactors keep the solids in suspension mechanically the overflow may be a clear liquid or a slurry, and the gas disengages from the... 

Listing of solid wastes, quantities, analyses and physical form (e.g. solid, slurry, suspension, sludge) toxicity and flammability. Checking the reliability and legality of waste disposal options, including any transportation offsite. Record keeping. 

Note that filter aid selection must be based on planned laboratory tests. Guidelines for selection may only be applied in the broadest sense, since there is almost an infinite number of combinations of filter media, filter aids, and suspensions that will produce varying degrees of separation. The hydrodynamics of any filtration process are highly complex filtration is essentially a multiphase system in which interaction takes place between solids from the suspension, filter aid, and filter medium, and a liquid phase. Experiments are mandatory in most operations not only in proper filter aid selection but in defining the method of application. Some general guidelines can be applied to such studies the filter aid must have the minimum hydraulic resistance and provide the desired rate of separation an insufficient amount of filter aid leads to a reduction in filtrate quality — excess amounts result in losses is filtration rate and it is necessary to account for the method of application and characteristics of filter aids. 

Determine the amount of wet cake obtained from filtering 10 m of suspension with a relative specific weight of 1.12. The suspension is 20% by weight solids and the cake wetness is 25%. 

We wish to separate titanium dioxide particles from a water suspension. The method chosen is centrifugation. The unit is a continuous solid-bowl type with a bowl diamter of 400 mm, a length to width ratio of 3.0, and the unit operates at 2,000 rpm. The feed contains 18 % (weight basis) solids and is fed to the unit at 2,500 Liters/hr at a temperature of 95° F. The average particle size is 65 /tm. (a) Determine the amount of solids recovered per hour (b) Determine the solids concentration in the centrate (c) Determine the horsepower requirments for the centrifuge (d) Size a graviy settler to remove an additional 15 % of the solids. 

Aeration The process of adding air to water. In wastewater treatment, air is added to freshen wastewater and to keep solids in suspension. 

In eertain eases, the primary proeess objeetive is to keep solid partieles in suspension. Areas of applieation involve eatalytie reaetions, erystallization, preeipitation, ion exehange, and adsorption. Axial flow and pitehed-blade turbines are best suited in providing the essential flow patterns in a tank to keep the solids in suspension. The suspended solid is eharaeterized by two parameters ... 

Each stage of particle formation is controlled variously by the type of reactor, i.e. gas-liquid contacting apparatus. Gas-liquid mass transfer phenomena determine the level of solute supersaturation and its spatial distribution in the liquid phase the counterpart role in liquid-liquid reaction systems may be played by micromixing phenomena. The agglomeration and subsequent ageing processes are likely to be affected by the flow dynamics such as motion of the suspension of solids and the fluid shear stress distribution. Thus, the choice of reactor is of substantial importance for the tailoring of product quality as well as for production efficiency. 

The centrifugal separation of solid impurities is adopted either as an alternative to filtration or combined with it. For example, having fixed-element filters that arrest larger particles, and a centrifuge system that removes the finer solids in suspension together with any water contained in the oil can clean a lubricant circulating system. 

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