Simple Extractors

Unlike absorption or stripping, extraction does not involve vaporization or condensation or the heat that accompanies these processes. For this reason extraction is nearly an isothermal process, although some temperature variation could occur as a result of heat of solution. 

This number of variables is matched by process constraints and performance specifications. The feed and solvent compositions and thermal conditions are constrained at values determined by the sources of these streams. Also, the stage pressures are not truly independent because once the pressure is set at one stage (by pumping capacity, etc.), the pressure profile is determined by the column hydraulics. The stage heat loads are constrained at values determined by heat losses if no controlled heat addition or removal exists at the stages. A listing of all these constraints follows  

At the design phase, three independent variables are available to satisfy perfor- 

The independent variables are the feed rate, the solvent rate, and the number of stages. For a given feed rate, the engineer must determine the solvent rate and the number of stages required to satisfy two specifications the recovery of the extract component from the feed, and the concentration of the extract component in the extract or raffinate. 

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The simple box-type mixer—settler (113) has been used extensively in the UK for the separation and purification of uranium and plutonium (114). In this type of extractor, interstage flow is handled through a partitioned box constmction. Interstage pumping is not needed because the driving force is provided by the density difference between solutions in successive stages (see Plutoniumand plutonium compounds Uraniumand uranium compounds). 

The De Danske Sukkerfabriker (DDS) diffuser extractor (Fig. 6) is a relatively simple version of this family of machines, employing a double screw rotating in a vessel mounted at about 10° to the horizontal. The double screw is used to transport the soHds up the gradient of the sheU, while solvent flows down the gradient. Equipment using a single screw in a horizontal sheU for countercurrent extraction of soHds under pressure has been described (19). 

Ash is a measure of residual sodium acetate. A simple method consists of dissolving the PVA in water, diluting to a known concentration of about 0.5 wt %, and measuring the electrical conductivity of the solution at 30°C. The amount of sodium acetate is estabUshed by comparing the result to a cahbration curve. A more lengthy method involves the extraction of the PVA with methanol using a Soxhlet extractor. The methanol is evaporated and water is added. The solution is titrated using hydrochloric acid in order to determine the amount of sodium acetate. 

Spray Towers These are simple gravity extractors, consisting of empty towers with provisions for introducing and removing liquids at the ends (see Fig. 15-32). The interface can be run above the top distributor, below the bottom distributor, or in the middle, depending on where the best performance is achieved. Because of severe axial back mixing, it is difficult to achieve the equivalent of more than one or two theoretical stages or transfer units on one side of the interface. For this reason they have only rarely been applied in extraction applications. 

Percolation In addition to being applied to ores and rock in place and by the simple technique of heap leaching (usually on verv large scale see Wadsworth, loc. cit.) percolation is carried out in batcJi tanks and in continuous or dump extractors (usually on smaller scale). 

If the desired product is fairly water soluble, simple extraction into organic solvents may not be an efficient means of recovery. In that case, continuous extraction of the aqueous solution with an organic solvent may be necessary to effect the recovery. Either of two types of apparatus are normally employed, and the correct design depends on the density of the organic solvent. For solvents less dense than water, the apparatus should be set up as in Fig. A3.11a. The barrel of the extractor is charged with the... 

EQEX - Simple Equilibrium Stage Extractor System... 

Considering the processes in the simple spray column (Fig. 9.1), the main questions that a chemical engineer must answer about the design of an extractor can be listed. 

Fig. 13.10 T3fpical FIA extraction manifolds. Injection in front of the extractor components (a) simple (b) multiextraction and (c) injection after the extraction has been carried out. (Based on systems from Refs. 178, 179.)...

Yamamoto has examined a number of catalyst systems for the reaction. A simple process using HfCI< in a soxhlet extractor has shown useful characteristics ... 

The adaptation of supercritical fluid extraction (SFE) in routine residue and metabolism analysis as well as other extraction/separation laboratories and applications has been slow. This is despite the demonstrated feasibility of using SFE for the removal of sulfonylureas, phenylmethylureas and their metabolites from soil and plant materials (1-2), as well as widespread demonstrated use of supercritical fluid extraction for other applications (3-6). The reason for this is simple. Although automated, SFE extraction apparatus typically only analyzes a single sample at a time. The technique could not compete effectively with the productivity of an experienced technician performing many sample extractions simultaneously. In essence, with a one vessel automated supercritical fluid extractor, operator attendance is high and throughput is about the same or even less than current conventional liquid-liquid and solid-liquid extraction techniques. 

Contactors have a number of advantages compared to simple liquid/gas absorb-er/strippers or liquid/liquid extractors. Perhaps the most important advantage is high surface area per volume. The contact area of membrane contactors compared to traditional contactor columns is shown in Table 13.2. Membrane contactors provide 10-fold higher contactor areas than equivalent-sized towers. This makes membrane... 

Continuous glycerin washing of soap produced by saponification has been demonstrated in a countercurrent centrifugal extractor (38). The device achieves phase separation with as little as 0.02 specific gravity difference and accomplishes up to 10 theoretical stages of extraction. Some of the advantages over prior operations reportedly include flexibility in feed, low holdup, less waste due to more efficient separation, simple operation, rapid startup, and small space requirements. 

Consider a simple mixer for extraction. In minimal entropy production, size I. time t. and duty J are specified and the average driving force is also fixed. We can also define the flow rate Q and the input concentration of the solute, and at steady state, output concentration is determined. The only unknown variables are the solvent flow rate and composition, and one of them is a decision variable specifying the flow rate will determine the solvent composition. Cocurrent and countercurrent flow configurations of the extractor can now be compared with the... 

Refer to Fig. 15-41. The extractor is an extension of the simple baffled mixing vessel into a multistage column. Although commercial application has been made, data are scarce and are limited to towers of small diameter. The preferred proportions are Z, = 0.5d, d, > d,. 

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