Extraction rate

If the solute is uniformly distributed through the soHd phase the material near the surface dissolves first to leave a porous stmcture in the soHd residue. In order to reach further solute the solvent has to penetrate this outer porous region the process becomes progressively more difficult and the rate of extraction decreases. If the solute forms a large proportion of the volume of the original particle, its removal can destroy the stmcture of the particle which may cmmble away, and further solute maybe easily accessed by solvent. In such cases the extraction rate does not fall as rapidly. 

Any one of the five basic processes may be responsible for limiting the extraction rate. The rate of transfer of solvent from the bulk solution to the soHd surface and the rate into the soHd are usually rapid and are not rate-limiting steps, and the dissolution is usually so rapid that it has only a small effect on the overall rate. However, knowledge of dissolution rates is sparse and the mechanism may be different in each soHd (1). 

Temperature. Both the solubility of the material being extracted and its diffusivity usually increase with temperature, and higher extraction rates are obtained. In some cases the upper limit for the operating temperature is deterrnined by factors such as the need to avoid undesirable side reactions. 

The integral values of effective interfacial area can thus be obtained by measuring the reaction (extraction) rate and using physico-chemical properties of the reactants. A reaction satisfying the above conditions consists of hydrolysis of hexyl formate (11) ... 

The use of an extractant depends on loading capacity, extraction rate, pH range, and the cost of the reagent and the diluent. Loss of the extractant must be minimised because of its high cost. Organic losses to the aqueous phase are also undesirable because of the deleterious effect on cathode deposits. Advances in SX—EW processes are described in Reference 38. 

Prediction methods attempt to quantify the resistances to mass transfer in terms of the raffinate rate R and the extract rate E, per tower cross-sectional area Af, and the mass-transfer coefficient in the raffinate phase and the extract phase times the interfacial (droplet) mass-transfer area per volume of tower a [Eqs. (15-32) and (15-33)]. 

Mass Transfer Extraction rates for packed towers are usually excellently correlated for a given situation on the coordinate system of Fig. 15-35. Treybal [Chem. Eng. Prog., 62(9), 67 (1966)] nas suggested means whereby overall Hto s may be resolved into constituent... 

Perforations are usually 0.32 to 0.64 cm Vh to Vi in) in diameter, set 1.27 to 1.81 cm to Vi in) apart, on square or triangular pitch. There appears to be relatively httle effect of hole size on extraction rate, except that with systems of high interfacial tension smaller holes will... 

FIG. 15-38 Extraction rates for sieve-plate and modified biihhle-plate columns. System benzoic acid-water-toliiene, except where noted. To convert feet to meters, multiply by 0.3048 to convert inches to centimeters, multiply by 2.54. [Alletion, Strom, and Treyhal, Trans. Am. Inst. Cbem. Eng., 39, 361 (1943) Row, Kojfolt, and Withrow, ihid., 37, 559 (1941) Treyhal and Dumoulin, Ind. Eng. Cbem., 34, 709(1942).]... 

Refer to Fig. 15-39. The tower is formed into compartments by horizontal doughnut-shaped or annular baffles, and within each compartment agitation is provided by a rotating, centrally located, horizontal disk. Somewhat similar devices have been known for some time. The features here are that the rotating disk is smooth and flat and of a diameter less than that of the opening in the stationaiy baffles, which facihtates fabrication and apparently improves extraction rates. The typical proportions of the internals of the RDC are as follows ... 

In wet spinning, the solvent extraction rate can be influenced by changing several processing variables including the type and concentration of coagulation fluid, the... 

Controlling the extraction rate is vital because the shape and texture of the resultant fiber is directly influenced by the solvent removal rate. As the solvent is extracted from the surface of the fiber, significant concentration gradients can form. These gradients may result in a warping of the desired eircular shape of the fiber. For example, if the solvent is removed too quickly, the fiber tends to collapse into a dog-bone shape. Additionally, the solvent extraction rate influences the development of internal voids or flaws in the fiber. These flaws limit the tensile strength of the fibers. 

Partial enclosure allows small openings for charging/removal of apparatus and chemicals. The requisite air velocity to prevent dust or fumes leaking out determines the air extraction rate, e.g. 

Polymerization to Cg and CJj olefins is the chief side reaction. Polymerization increases with extraction temperature and with the hold-up time in the extraction section. It limits the temperature used to obtain high extraction rates. 

Bramley, A.S., Hounslow, M.J. and Ryall, R.L., 1996a. Aggregation during precipitation from solution A method for extracting rates from experimental data. Journal of Colloid and Interfacial Science, 183, 155-165. 

The unit of heat is the watt. However, the imperial unit should be understood, as it will still be met, particularly outside Europe. The ton of refrigeration is derived from an ability to remove sufficient heat from a short ton (2000 lbs) of water at 32°F to turn it to ice at the same temperature in the course of 24 hours. This amounts to a heat extraction rate of 3.517kW. 

R- CHt is more stable than H/C. Consequently, the hydrogen extraction rate of R- CH2 is lower than that of the methyl radical. 

As can be seen from Equation (135), the only effective way to increase the extraction rate is by increasing the phase contact area. This can be achieved by... 

Reactor electrical heat input(l) Coil/jacket heat balance Condenser heat extract rate (1) Reactor heat loss... 

The two BCs of the TAP reactor model (1) the reactor inlet BC of the idealization of the pulse input to tiie delta function and (2) the assumption of an infinitely large pumping speed at the reactor outlet BC, are discussed. Gleaves et al. [1] first gave a TAP reactor model for extracting rate parameters, which was extended by Zou et al. [6] and Constales et al. [7]. The reactor equation used here is an equivalent form fi om Wang et al. [8] that is written to be also applicable to reactors with a variable cross-sectional area and diffusivity. The reactor model is based on Knudsen flow in a tube, and the reactor equation is the diffusion equation ... 

The extraction rate of mepanipyrim with refluxing was higher than that with shaking (30 min) and sonication (Ultrasonic, 600 W, 28 kHz, 30 min). For the solvent system, acetone and acetonitrile showed almost similar extraction efficiencies. Methanol was found to be a less effective extraction solvent. Mepanipyrim was unstable in the acidic solution and alkaline solution under reflux conditions at 80 °C. The extraction rate of mepanipyrim under these conditions decreased to about 50% and 20%, respectively. Therefore, neutral solution was used as the extraction solvent in this method. 

The absorbance data enabled the determination of extraction rate constants. For a pseudo-first-order reaction, the following equation describes the extraction process ... 

Extraction rates of zinc (II) and nickel (II) with ethyldithizone, butyldithizone, or hexyldithizone in an organic phase (chloroform, CCI4, w-heptane, or benzene) showed a first-order dependence on the ligand and metal ion concentration and an inverse-first-order dependence on the proton concentration. The results were explained by chelate formation in the interfacial region [59]. The effects of stirring on the distribution equili-... 

The extraction system which was measured by the HSS method for the first time was the extraction kinetics of Ni(II) and Zn(II) with -alkyl substituted dithizone (HL) [14]. The observed extraction rate constants linearly depended on both concentrations of the metal ion [M j and the dissociated form of the ligand [L j. This seemed to suggest that the rate determining reaction was the aqueous phase complexation which formed a 1 1 complex. However, the observed extraction rate constant k was not decreased with the distribution constant Kj of the ligands as expected from the aqueous phase mechanism. 

Thus, the extraction rate constant k is related to kj and a dissociation constant by... 

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