Percolation extraction

Extraction and work-up. Of the standard methods of alkaloid extraction, percolation with methanol has been especially favoured by Australian workers, followed by removal of the solvent and dilute acid extraction. Besides alkaloids, methanol dissolves large amounts of other plant constituents which hamper the acid extraction. One strategy used to overcome this was to completely dissolve the residue left after removal of the methanol in a minimal quantity of warm glacial acetic acid, an excellent solvent for most plant constituents. The solution was then diluted with water until no more precipitate formed if the evaporation of the methanol had been carried out in a pilot plant-scale rotary evaporator, the whole operation could be done in the same slowly rotating vessel. After separation of the precipitate, most of the dilute acid could be removed in vacuo in the same equipment to give an aqueous solution of crude alkaloid acetates largely free from non-basic materials 70). 

Extract percolation on solid phases such as silica gel, alumina, alumina silicate, which retain interfering substances by adsorption mechanism ... 

Various types of leaching can be undertaken - direct extraction, percolation, pulsed flow extraction, and countercurrent extraction. 

In the French Oil Machinery Co. stationary basket extractor (Fig. 10.3-5), extract percolates through beds of solids contained in a circular array of sector-shaped compartments with perforated bottoms and drains into sumps positioned below the beds. Unlike crossflow extractors, the solids do not move." Instead, the solid feed spout and solids discharge zone rotate about the circle and the extract feed and discharge connections are switched periodically. These extractors are like automated diffusion batteries in which downflow is used but, because extract backmixes in each sump, the extract concentration leaving a stage is somewhat different from that entering the next stage. 

In the pharmaceutical field, PFE has also been used for two primary purposes, namely to extract pharmacologically active substances from plants and, especially, for quality control of tablets and medical foods. In this field, PFE clearly surpasses classical extraction methods such as those endorsed by pharmacopeias (which use as official standards techniques such as Soxhlet extraction, percolation, maceration, digestion, extraction under reflux, and steam distillation) and others based on ultrasonica-tion or turboextraction. PFE is a firm candidate for use in high-throughput screening programs for natural product discovery, where large numbers of small-scale extractions have to be performed in an efficient, reproducible manner. 

Due to the formation of emulsions, the liquid-liquid extraction of nonionic surfactants, e.g., APEO is restricted to their less surface-active metabolites, i.e., APEO with 1-3 ethoxy units, alkylphenoxy carboxylates (APEC) and alkylphenols (AP). Noncontinuous liquid-liquid extraction of water samples with methylene chloride using a separatory funnel has been applied for NP and NPEO (1-3 ethoxy units) [3132]. Also an ultrasonic bath has been shown to be suitable for the liquid-liquid extraction of APEO and AEO from water samples [33]. Continuous liquid-liquid extraction (percolation) has been successfully used for the concentration of short-chained APEO and AP too [31]. Steam distillation/ solvent extraction using an apparatus designed by Veith and Kiwus [34] is a sophisticated method of concentrating steam-distillable AP and APEO (1-3 ethoxy units) from water samples [2,35]. AEO have been efficiently extracted by combination of reflux hydrolysis with sulfuric acid and steam distillation with a "Karlsruhe Apparatus" [36]. 

The sohd can be contacted with the solvent in a number of different ways but traditionally that part of the solvent retained by the sohd is referred to as the underflow or holdup, whereas the sohd-free solute-laden solvent separated from the sohd after extraction is called the overflow. The holdup of bound hquor plays a vital role in the estimation of separation performance. In practice both static and dynamic holdup are measured in a process study, other parameters of importance being the relationship of holdup to drainage time and percolation rate. The results of such studies permit conclusions to be drawn about the feasibihty of extraction by percolation, the holdup of different bed heights of material prepared for extraction, and the relationship between solute content of the hquor and holdup. If the percolation rate is very low (in the case of oilseeds a minimum percolation rate of 3 x 10 m/s is normally required), extraction by immersion may be more effective. Percolation rate measurements and the methods of utilizing the data have been reported (8,9) these indicate that the effect of solute concentration on holdup plays an important part in determining the solute concentration in the hquor leaving the extractor. 

Moving-bed percolation systems are used for extraction from many types of ceUular particles such as seeds, beans, and peanuts (see Nuts). In most of these cases organic solvents are used to extract the oils from the particles. Pre-treatment of the seed or nut is usually necessary to increase the number of ceUs exposed to the solvent by increasing the specific surface by flaking or rolling. The oil-rich solvent (or misceUa) solution often contains a small proportion of fine particles which must be removed, as weU as the oil separated from the solvent after leaching. 

Immersion extraction systems are usefiil in handling finely ground material or when the percolation rate through the material to be extracted is too rapid to aUow effective diffusion from the soHds. These systems are appHed extensively in the sugar industry, in extraction from oilseeds having a high oil... 

Dosage forms of naturally occurring materials having therapeutic activity are prepared by extractive processes, especially percolation and maceration. Examples of such dosage forms have included certain tinctures, symps, fluid extracts, and powdered extracts. 

The flavor of instant coffee can be enhanced by recovering and returning to the extract or finished dry product some of the natural aroma lost in processing. The aroma constituents from the grinders, percolation vents, and evaporators may be added dkectly or in concentrated or fractionated form to achieve the deskable product attributes. 

Batch Percolators The batch tank is not unlike a big nutsche filter it is a large circiilar or rectangiilar tank with a false bottom. The solids to be leached are dumped into the tank to a uniform depth. They are sprayed with solvent until their solute content is reduced to an economic minimum and are then excavated. Countercurrent flow of the solvent through a series of tanks is common, with fresh solvent entering the tank containing most nearly exhausted material. In a typical ore-dressing operation the tanks are 53 by 20 by 5.5 m (175 by 67 by 18 ft) and extract about 8200 Mg (9000 U.S. tons) of ore on a 13-day cycle. Some tanks operate under pressure, to contain volatile solvents or increase the percolation rate. A series of pressure tanks operating with countercurrent solvent flow is called a diffusion battery. 

Leaching Cycle and Contact Method As is true generally, the choice between continuous and intermittent operation is largely a matter of the size and nature of the process of which the extraction is a part. The choice of a percolation or solids-dispersion technique depends principally on the amenability of the extraction to effective, sufficiently rapid percolation. 

Leachate in landfills. Leachate may be defined as hquid that has percolated through sohd waste and has extracted dissolved or suspended materials from it. In most landfills, the liqiiid portion of the leachate is composed of the liquid produced from the decomposition of the wastes and liquid that has entered the landfill from external sources, such as surface drainage, rainfall, groundwater, and water form underground springs. Representative data on chemical characteristics of leachate are reported in Table 25-72. 

Dimethylpentane/708-08-77 M 100.2, b 80.5 , d 0.763, n 1.3814, n 1.37882. Extracted repeatedly with cone H2SO4, washed with water, dried and distd. Percolated through silica gel (previously heated in nitrogen to 350°). Purified by azeotropic distn with EtOH, followed by washing out the EtOH with water, drying and distn. 

The organic layer is separated, evaporated on a steam bath, and the dark semicrystalline residue is distilled with steam to remove biphenyl. The contents of the steam-distillation flask are then extracted with ether (Note 3), and the ethereal layer is separated, dried over magnesium sulfate, and percolated through a short column of chromatographic alumina (Notes 4 and 5). Evaporation of the ethereal solution gives crude triphenylene which is sublimed at 175-180° and 0.1 mm. pressure. After rejection of an initial sublimate of impure biphenyl, the sublimed material forms nearly colorless crystals, m.p. 186-194° (Note 6). Yield 8-9 g. (53-59%). It may be further purified by recrystallization from a mixture of methylene chloride and pentane yielding colorless crystals, m.p. 199° (Note 7). 

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