Extraction apparatus, countercurrent

Step 1). A 100 L quantity of urine is adjusted by the addition of acid (hydrochloric acid is preferred but not essential) to a pH of 4 and extracted with a suitable solvent such as n-butyl alcohol, benzol, chloroform or ether in a continuous extraction apparatus. By using the countercurrent principle we find that this volume of urine may readily be extracted during one day s time and the active fraction transferred completely to a 4 L volume of butyl alcohol. This alcoholic solution is chilled and filtered from salts and other insoluble matter. 

Fig. 4-18. Countercurrent-extraction apparatus. (Courtesy of Dr. L. Craig and Interscience Publishers, Inc.)...

Figure 10.20 is a countercurrent extraction apparatus with both extract and... 

More elaborate multiple extractors based on a countercurrent principle have been developed that are capable of giving very efficient separations in favorable circumstances. For separating amounts greater than about 40 g, a counterdoublecurrent apparatus is preferable. With this apparatus, continuous rather than batchwise operation is possible, if a solvent system can be found such that the distribution coefficient of the desired substance is on one side of unity and those of all impurities are on the other side. Due to the cost of the apparatus (about 8000), the limited quantity of material that can be used (a maximum of about 40 g of substrate), the time necessary to find a suitable solvent system, and the problems associated with running and cleaning the apparatus, countercurrent extractors are usually employed as a last resort, i.e., after distillation, recrystallization, simple extraction, and liquid chromatography have failed to effect a satisfactory separation. 

Tbble 6-4. Classification of selected commercial extraction apparatus with countercurrent phase flow. 

Solid-liquid extraction [0.1, 0.8, 6.20, 6.77-6.80] is mainly applied as percolation extraction in cross-flow and countercurrent flow and as immersion extraction in discontinuous or continuous modes. With percolation extraction, the mechanically ground and decomposed solid is moved through the extraction apparatus from stage to stage and sprayed with solvent. In this case, the solvent is enriched with the key component. Percolation extraction may only be applied to solids which allow the throughflow of solvent in a packed bed state. When the permeability of the solid is too low, immersion extraction is used. Here the solid is suspended in the solvent or is intermediately... 

In order to explore the factors influencing the separation effect of spiral countercurrent extraction device, the experimental device is designed for the chromatographic elution studies, which is shown in Figure 1. For chromatographic spiral countercurrent extraction apparatus of the elution process, the separation process of equivalent as shown in Figure 2. 

If the distribution coefficient is sufficiently large, the simplest approach to liquid-liquid extraction is shaking the sample with an appropriate amount of an organic solvent. With smaller distribution coefficients or large sample volumes, continuous extraction or countercurrent extraction is required to achieve a complete separation. The apparatus for continuous extraction causes a liquid immiscible with the sample solution to circulate continuously and in finely divided form through the sample [171]-[173]. Extracted analytes are concentrated by distillation at appropriate times between individual extraction cycles. 

Hhen the distribution constant is very - f small continuous liquid-liquid extraction or f countercurrent distribution apparatus is required. 

Figure 8.5 Apparatus for liquid extraction. A, bubblers and iepingers B, lighter-than and heavy-than water continuous liquid-liquid extractors c, droplet countercurrent chronatograph.

An additional method of increasing the efficiency of liquid-liquid extraction is based on the countercurrent distribution principle [80-861 Early countercurrent distribution apparatus... 

Find, in a reference book, a description of the Craig countercurrent distribution apparatus and discuss its design as it relates to the description of countercurrent extraction presented in this chapter. 

Heterogeneously catalyzed hydrogenation reactions can be run in batch, semibatch, or continous reactors. Our catalytic studies, which were carried out in liquid, near-critical, or supercritical C02 and/or propane mixtures, were run continuously in oil-heated (200 °C, 20.0 MPa) or electrically heated flow reactors (400 °C, 40.0 MPa) using supported precious-metal fixed-bed catalysts. The laboratory-scale apparatus for catalytic reactions in supercritical fluids is shown in Figure 14.2. This laboratory-scale apparatus can perform in situ countercurrent extraction prior to the hydrogenation step in order to purify the raw materials employed in our experiments. Typically, the following reaction conditions were used in our supercritical fluid hydrogenation experiments catalyst volume, 2-30 mL total pressure, 2.5-20.0 MPa reactor temperature, 40-190 °C carbon dioxide flow, 50-200 L/h ... 

Figure 14.2. Laboratory-scale apparatus for catalytic reactions in supercritical fluids in combination with countercurrent extraction.

Separating funnels for batch extraction special glass apparatus for continuous extraction automatic shakers used for discontinuous countercurrent distribution. 

This type of operation is known as countercurrent operation. If equilibrium is attained between each stream at each stage in the apparatus, calculations can be carried out to relate the flow rates and concentration of products to the size and other design features of the apparatus. We shall illustrate how a material balance can be made for such type of equipment. The letter X stands for the weight concentration of solute in pounds of solute per pound of stream, solute-firee. The streams are assumed immiscible as in a liquid-liquid extraction process. 

Of course, it would be very laborious to perform such extractions separately. However, methods are now available for performing the extractions mechanically and this has made possible a new field of investigation. The name Countercurrent Distribution has been given to this type of extraction. Figure 2 is a photograph of one type of the apparatus. Its only function is the performance of large numbers of extractions in a systematic manner (2). 

In mass transfer apparatus one of two processes can take place. Multicomponent mixtures can either be separated into their individual substances or in reverse can be produced from these individual components. This happens in mass transfer apparatus by bringing the components into contact with each other and using the different solubilities of the individual components in the phases to separate or bind them together. An example, which we have already discussed, was the transfer of a component from a liquid mixture into a gas by evaporation. In the following section we will limit ourselves to mass transfer devices in which physical processes take place. Apparatus where a chemical reaction also influences the mass transfer will be discussed in section 2.5. Mass will be transferred between two phases which are in direct contact with each other and are not separated by a membrane which is only permeable for certain components. The individual phases will mostly flow countercurrent to each other, in order to get the best mass transfer. The separation processes most frequently implemented are absorption, extraction and rectification. 

The emergence of chemical engineering as a professional field of specialized knowledge was catalyzed to a major extent by the systematic classification of apparatus in terms of the Unit Operations. With further progress, the design methods evolved for particular apparatus types have proved equally applicable to other unit operations similar in physical arrangement, material and energy balances, rate behavior, and phase equilibrium. Thus there has been a very extensive development of parallel calculation methods for the separation operations conducted under countercurrent flow conditions—the fluid-fluid operations of distillation, absorption, and extraction. 

Many variations and special apparatus have been developed over the decades to solve specific problems and to do extractions more efficiently. Several of these are solvent heavier than water (Chapter 10) solvent lighter than water (Chapter 10) continuous countercurrent (Chapter 11) solid phase extraction (Chapter 12) liquid-solid extraction, microwave heated solvents (Chapter 10) and supercritical fluid extraction (Chapter 13). 

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