Intermittent extraction

Soxtherm , FEXTRA and intermittent extractions. The newer methods (SFE, ASE , MAE) invariably operate at pressures above atmospheric. Micromethods of solvent extraction have also been described [57,58]. 

Principles and Characteristics In boiling under reflux procedures a small amount of ground polymer (typically 3g) is placed in a headspace jar (typically 100 mL) and solvent (typically 30 mL) is added. After sealing, the jar is placed in an oven at a temperature where the solvent slowly refluxes. The solvent is, therefore, at the highest temperature possible without applying an external pressure. Consequently, reflux extractions tend to be much faster than Soxhlet extractions. Examples are Soxtec , Soxtherm , FEXTRA and intermittent extraction. Whilst, in theory, partitioning of the analyte between the polymer and solvent prevents complete extraction, this hardly ever constitutes a problem in practice. As the quantity of solvent is much larger than that of the polymer, and the partition coefficients usually favour the solvent, very low additive levels in the polymer result at equilibrium. Any solvent or solvent mixture can be used. 

Figure 3.3 Apparatus for intermittent extraction of solids 1, boiler vessel 2, extraction vessel 3, cooler 4, heating coil 5, transformer 6, contact-block 7, timer. Reproduced by permission of DSM Research, Geleen...

Advantages of intermittent extraction are similar to those of solid-fluid-vortex extraction. A disadvantage is caking of the polymer in the case of a high polymer concentration in the extract or by loss of extraction fluid. Interlaboratory comparison is restricted. 

Applications The method is in use for the determination of water extractable organics in PA6 and PA4.6, and for alkane extraction of waxes from HDPE (in nitrogen atmosphere to prevent oxidation) [156]. Ethylene-bis-stearamide (EBA) can be extracted from ABS in 30 min using intermittent extraction in this case quantitative Soxhlet extraction was not possible. Nelissen [157] has used intermittent extraction with MTBE for the analysis of the flame retarder system of Tribit 1500 GN30. 

The carbonaceous material and foreign materials for liqnefaction are intermittently extracted from the bottom of the reactor with a part of the reaction mixtnre and cooled as residne. The pyrolysis gas emerging is carried to a distillation colnmn and condensed as light, medium and heavy fractions. 

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. 

In vitro cytotoxicity assays using isolated cells have been applied intermittently to cyanobacterial toxicity testing over several years." Cells investigated for suitability in cyanobacterial toxin assays include primary liver cells (hepatocytes) isolated from rodents and fish, established permanent mammalian cell lines, including hepatocytes, fibroblasts and cancerous cells, and erythrocytes. Earlier work suggested that extracts from toxic cyanobacteria disrupted cells of established lines and erythrocytes," but studies with purified microcystins revealed no alterations in structure or ion transport in fibroblasts or erythrocytes,... 

The intermittent method involved a repeated succession of extractions and titrations of one sample the other involved titrations of different samples of the same material, extracted for different lengths of time, until a constant titration value was reached. 

A solvent-free strategy for the synthesis of thiazoles involved mixing of thioamides with a-tosyloxy ketones in a clay-catalyzed reaction (Scheme 7). The typical procedure entailed mixing of thioamides and in situ produced a-tosyloxy ketones with montmorillonite K-10 clay in an open glass container. The reaction mixture was irradiated in a microwave oven for 2-5 min with intermittent irradiation and the product was extracted into ethyl acetate to afford 2-substituted thiazoles in 88-96% yields [8]. 

The intermittent solid-fluid-vortex extraction method [153] consists of four stages ... 

Flow injection analysis (F1A). In this technique, introduced by Ruzicka and Hansen, a small amount of sample is injected into a liquid flow (see Fig. 5.16), which apart from being automated is normally continuous, but can include the use of stopped-flow, merging zones extraction techniques in addition to FIA scanning and methods based on intermittent pumping89. The principles of FIA and the versions just mentioned will now be briefly discussed on the basis of the excellent review of Ruzicka and Hansen89 in order to understand the appli-cational possibilities of electrochemical detection in this technique. 

This paper is a review of methods for estimating releases of chemicals into the environment in the course of extraction of raw materials, manufacturing, use, storage, transportation, and disposal, as well as by accidents or natural processes. It discusses source types, forms of substances released (solids, liquids, and gases), receiving media (air, water, soil), time pattern of release (continuous versus intermittent, cyclic versus random), and geographic patterns of release (point, line, area, and volume sources). 

Prepared cottonseed meats containing 35 per cent of extractable oil are fed to a continuous countercurrent extractor of the intermittent drainage type using hexane as the solvent. The extractor consists of ten sections and the section efficiency is 50 per cent. The entrainment, assumed constant, is 1 kg solution/kg solids. What will be the oil concentration in the outflowing solvent if the extractable oil content in the meats is to be reduced by 0.5 per cent by mass ... 

For cogifitive function, total daily doses of 120 to 240 mg divided into 2 or 3 doses of ginkgo leaf extract are recommended. For intermittent claudication, 240 mg a day would be preferable. 

Potential applications for this technology include the treatment of airstreams contaminated with volatile organic compounds (VOCs) from air stripping, soil vapor extraction, industrial air emissions, and for the cleaning of air in closed environments. PCO is best suited for waste streams with low concentrations of contaminants, and with low to medium flow rates. The AIR-11 process can operate consistently in conditions where flow rates and VOC concentrations are highly variable, even intermittent. 

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