Laboratory-scale Extractions

8-2 Schematic diagram of a small laboratory system for superheated water extraction. 

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Liquid-liquid extraction is a process by which one or more components of a mixture, usually in water, are selectively transferred to another, usually organic liquid. Liquid-solid extraction involves the use of a liquid to selectively remove components from a solid. The majority of laboratory scale extractions are batch extractions, involving separatory funnels. The theory and general techniques are discussed in Chapter 9. 

Several examples of laboratory-scale extractions follow. (1) SFE was used in a comparison of extraction methods for the determination of the apparent tannins in common beans. (2) Homogenates of shrimp meat were extracted with ethyl acetate followed by precolumn cleanup on a silica Sep-Pak cartridge to determine 4-hexylresorcinol, a processing aid. Two extraction procedures were compared to extract oil from olive foot cake with acidic hexane. An open-air method and exhaustive Soxhlet extraction with the latter removed about two times more oil. (3)... 

With a view to determining optimum conditions for each stage of this process, laboratory scale extractions of fresh Ascophyllum nodosum have been carried out under a variety of conditions, and the effect on the yield and quality of product has been assessed. 

To quantify the extraction capacity of carbon dioxide, the partition coefficient of MMA between the water and the C02-phase (m2) is a prerequisite. Since this partition coefficient is not reported in literature, m2 has been measured in a laboratory scale extraction unit at different temperatures and CO2 pressures and has also been predicted using the Peng-Robinson equation of state. 

In Timisia, the olive oil sector plays an important role in the economy, providing both employment and export revenues. Olive trees cover an area of 1.6 million ha with an annual oil production of 170 000 t (Rigane et al., 2011). The last decade, Timisian autochthonous varieties were extensively studied for their potential with regard to VOO quality characteristics. The oils obtained from healthy fruits using laboratory scale extraction, most of the time with the aid of an Abencor type mill and extractor (Oueslati et al., 2009). Thus, the amoimts of bioactive phytochemicals reported are rather high in comparison to what is reported for VOOs from the main producing coimtries. This illusive picture does not reflect necessarily the real content of this nutrient in the commercial products sold locally or of those exported. 

Liquid-liquid equilibria deserve our attention principally because of their widespread occurrence in industrial- and laboratory-scale extraction processes. They also play a role in assessing the effect of accidental spills of oil and organic solvents in lake and ocean waters. 

The characteristics of laboratory-scale extraction methods (e.g., time, extraction efficiency, extractant namre, working temperature) are poorly documented as researchers in this field have so far focussed on the determination of oleuropein and its derivatives [256,257], and the antioxidant activity of the phenolics extracted [231], but not on optimizing the extraction process itself. The extraction methods reported so far are complex and take hours or even days to complete. Sequential extraction of powdered leaves with 1 1 methanol-water, chloroform, and ethyl acetate was attempted by Savoumin et al. [256]. In any case, such toxic extractants should be avoided if the products are ultimately aimed at human use. 

In the simplest case, the feed solution consists of a solvent A containing a consolute component C, which is brought into contact with a second solvent B. Eor efficient contact there must be a large interfacial area across which component C can transfer until equiHbrium is reached or closely approached. On the laboratory scale this can be achieved in a few minutes simply by hand agitation of the two Hquid phases in a stoppered flask or separatory fuimel. Under continuous flow conditions it is usually necessary to use mechanical agitation to promote coalescence of the phases. After sufficient time and agitation, the system approaches equiHbrium which can be expressed in terms of the extraction factor S for component C ... 

The development of the novel Davy-McKee combined mixer—settler (CMS) has been described (121). It consists of a single vessel (Fig. 13d) in which three 2ones coexist under operating conditions. A detailed description of units used for uranium recovery has been reported (122), and the units have also been studied at the laboratory scale (123). AppHcation of the Davy combined mixer electrostatically assisted settler (CMAS) to copper stripping from an organic solvent extraction solution has been reported (124). 

In recent years researchers at West Virginia University have developed coal-derived pitches on a laboratory scale in quantities sufficient to make 1 kg samples of calcined coke for fashioning graphite test specimens. The pitches were derived by uhlizmg solvent extraction with N-methyl pyrrohdone (NMP). This solvent is able to isolate coal-based pitches m high yield and with low mineral matter content [13]. It is this work that will form the basis of the discussion for the later part of this chapter. 

Flash chromatography is widely employed for the purification of crude products obtained by synthesis at a research laboratory scale (several grams) or isolated as extracts from natural products or fermentations. The solid support is based on silica gel, and the mobile phase is usually a mixture of a hydrocarbon, such as hexane or heptane, with an organic modifier, e.g. ethyl acetate, driven by low pressure air. (Recently the comparison of flash chromatography with countercurrent chromatography (CCC), a technique particularly adapted to preparative purposes, has been studied for the separation of nonchiral compounds [90].)... 

The use of chemicals, essentially acid, is the method of choice for the extraction of pectins, at least at an industrial level (3,4). Enzymes such as "protopectinases", polygalacturonases, rhamnogalacturonases, have been tentatively used at a laboratory scale but their industrial interest is still an open question (4,5,6). There are only some reports on the use physical treatment such as various heat treatments. 

On a laboratory scale, generally an ultrasonic probe (horn) and an ultrasonic cleaner are used. The ultrasonic field in an ultrasonic cleaner is not homogeneous. Sonication extraction uses ultrasonic frequencies to disrupt or detach the target analyte from the matrix. Horn type sonic probes operate at pulsed powers of 400-600 W in the sample solvent container. Ultrasonic extraction works by agitating the solution and producing cavitation in the... 

HCN is the most preferred cyanide source in cyanohydrin synthesis. Besides HCN, several different cyanide sources, like potassium cyanide, are being used in biotransformation. Alternative methods for the safe handling of cyanides on a laboratory scale are, for instance, to use cyanide salts in solution. These solutions can be acidified and used as the aqueous layer in two-phase systems or the HCN can be extracted into the organic layer with the desired solvent for reactions in an organic phase. After the reaction, excess cyanide can readily be destroyed with iron(II) sulfate, or iron(III) chloride or bleach. Cyanide can also be presented in the form of organic cyano, such as acetone cyanohydrin [46] or cyanoformates. However, as claimed by Effenberger, some results could not be reproduced [47]. 

Robustness of the process. Many transition metal-catalyzed reactions function well at the laboratory scale, but on scaling up substrate and product inhibition may be an issue, and sensitivity to impurities may also become apparent. Increasing the SCR, which is often necessary for the economics of the process, also increases the impurity catalyst ratio. It is also very important to keep the number of components to a minimum, as extraction, crystallization and distillation are the only economic means of purification. Ligands can be a nuisance in this respect, particularly if they are used in amounts over 5 mol%. Reproducibility also is a stringent requirement. Thus, possible inhibition mechanisms should be recognized in order to avoid unwanted surprises during production. 

Conkerton EJ, Wan PJ, Richard OA. 1995. Hexane and heptane as extraction solvents for cottonseed A laboratory-scale study. J Am Oil Chem Soc 72 963-965. 

After a potential drug has been identified, it is subjected to additional experiments, such as different solvents, temperatnres, and pressures, to understand its specific behavior. Initial studies sought to identify the presence of different polymorphs, but the need to quantify the polymorphs naturally arose. Subsequent work tested the quantification models and probed how the polymorph concentration changes as a function of time or other variables. Kinetic or rate parameters often can be extracted. Studies were performed on the laboratory scale, such as under a microscope or in a bench crystallizer, up to large-scale manufacturing trials. 

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