Extraction processes agitators

In liquid-solid extraction (LSE) the analyte is extracted from the solid by a liquid, which is separated by filtration. Numerous extraction processes, representing various types and levels of energy, have been described steam distillation, simultaneous steam distillation-solvent extraction (SDE), passive hot solvent extraction, forced-flow leaching, (automated) Soxh-let extraction, shake-flask method, mechanically agitated reflux extraction, ultrasound-assisted extraction, y -ray-assisted extraction, microwave-assisted extraction (MAE), microwave-enhanced extraction (Soxwave ), microwave-assisted process (MAP ), gas-phase MAE, enhanced fluidity extraction, hot (subcritical) water extraction, supercritical fluid extraction (SFE), supercritical assisted liquid extraction, pressurised hot water extraction, enhanced solvent extraction (ESE ), solu-tion/precipitation, etc. The most successful systems are described in Sections 3.3.3-3.4.6. Other, less frequently... 

The characteristic velocity k is a function of droplet size, density difference, viscosity, etc. Thus, the holdup tends to increase either as the superficial flow velocities Uc and Ud are increased or as the characteristic velocity is reduced (e.g., by increasing agitation). A point is eventually reached where the increase in holdup becomes unstable (typically when = 0.3-0.4). This phenomenon is known as flooding, and it imposes a limit on the flow rates and agitation levels that can be used in countercurrent extraction processes. 

From a commercial point of view, soybean is the most important source for lecithin however, lecithin production from sunflower (180) and rapeseed (181-183) wet gum has also been successful. Wet gum is removed during the first refining step of crude oil that is the degumming process. Traditionally, crude oil obtained from solvent-extraction process is agitated with 1-3% water at elevated temperatures (70-80°C). Under these conditions, phosphohpids and glycohpids start to swell and become insoluble in the oil. The hydrated mass is removed via centrifugation, and the dehydration is carried out under vacuum until the residual moisture is below 1%. 

Following emulsification, the emulsion is dispersed by mechanical agitation into the external feed phase containing the solute to be extracted. The efficiency of this extraction process is dependent on several parameters as discussed below. 

The classical techniques for the solvent extraction of materials from vegetable sources are based upon the correct choice of solvent coupled with the use of heat and/or agitation. The extraction of organic compounds contained within the body of plants and seeds by a solvent is significantly improved by the use of power ultrasound. The mechanical effects of ultrasound provide a greater penetration of solvent into cellular materials and improves mass transfer. There is an additional benefit for the use of power ultrasound in extractive processes which derives from... 

SDE can be used in static and dynamic modes. When working in the static mode, steps in the extraction process are (a) the magnetic stirrer is switched on to agitate the aqueous sample solution ... 

SPME consists of two steps extraction and desorption. In the extraction process the fiber is immersed into the sample with a syringe, vigorous stirring is applied, and the organic micropollutants are retained in the fiber depending on their distribution coefficients. Then, using the holder, the fiber is transferred to the analytical instrument for desorption, separation and quantification. The method has been automated and commercial systems are available which will extract, agitate, and inject the sample into a GC system. In HPLC the sample is extracted directly into the eluent stream rather than thermally desorbed." ... 

Commonly used agitated columns in extraction processes are shown in Table 6-10. 

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