Extraction disperse phase, selection

Conventional methods of polymer extraction use large quantities of solvents as in shake-flask extraction or a Soxhlet extraction apparatus. For all classical extraction methods, solvent selectivity, in general, is low, i.e. solvents with high capacity tend to have low selectivity. In reflux extractions, which are still quite popular in polymer applications, the polymer is refluxed with a hot solvent, which disperses it to provide a solvent phase containing additives. In these conditions solvents are at their atmospheric boiling point. These methods are lengthy and labour intensive. Fractional extraction is based on solvents with increasing solvent power (cf. also [81]). 

Reductions ia mass transfer rates due to the presence of trace amounts of surfaee-active contaminants may be substantia). These effects have been measured for each of the two phases during drop formation, free fall, and coalescence and, although correlation was not achieved, at least those existing rdationshqre that came closest to the data in each case were identified. These observations were systematized by Skelland and Chadha 9 who also developed criteria for selection of the disperse phase in spray and plate extraction columns both in the presence and the absence of norfhce-active contamination. 

TSE at 165°C optionally with on-line microwave treatment to effect transreaction, or TSE at 165-200°C / morphology development along screw axis vs. processing conditions in three different extruders / rheology / TGA-GC / selective solvent extraction / SEM / mechanical properties / use to fix morphology of EVAc + E-MAc dispersed phase in PP matrix / dibutyltin oxide catalyst (0-4)... 

Yan H, Qiao F, Row KH, Molecularly imprinted-matrix solid phase dispersion for selective extraction of five fluoroquinolones in eggs and tissue. Anal. Chem. 2007 79 8242-8248. 

The proper selection of the dispersed phase is an essential prerequisite of efficient extraction processes. Often, this problem can only be solved by small-scale experiments. 

For solvent extraction want uniform and diameter that is a balance between surface area for mass transfer and settling velocity. Suitable drop size for dispersed phase is about 1 to 3 mm. The impeller should be selected for both pumping capacity and shear. If the impeller is primarily shear, then the drops close to the impeller will be very small and the drops far from the impeller will be very large. 

PA-6/HDPE/HDPE-g-MA Broad range of compositions/selective solvent extraction/SEM/rheology/finding of two dispersed phase sizes and its implications Argoud et al. 2014... 

Isopropanol vapor was used to dissolve the matrix in polymer blends [245]. Williams and Hudson [246] etched microtomed blocks of high impact polystyrene so that the rubber particles protruded from the matrix. Later, Kesskula and Traylor [130] removed rubber particles from Hire and ABS polymers by dissolving the matrix in a cyclohexane solution of osmium tetroxide and extracting the dispersed phase for SEM. Olefin particles were removed from impact modified nylon and polyester [6]. Selective etching of the polycarbonate phase with triethyl-amine in a mixture with styrene-acrylonitrile copolymer (SAN) revealed the nature of the blend [247]. 

Solid-phase sorbents are also used in a technique known as matrix solid-phase dispersion (MSPD). MSPD is a patented process first reported in 1989 for conducting the simultaneous disruption and extraction of solid and semi-solid samples. The technique is rapid and requires low volumes (ca. 10 mL) of solvents. One problem that has hindered further progress in pesticide residues analysis is the high ratio of sorbent to sample, typically 0.5-2 g of sorbent per 0.5 g of sample. This limits the sample size and creates problems with representative sub-sampling. It permits complete fractionation of the sample matrix components and also the ability to elute selectively a single compound or class of compounds from the same sample. Excellent reviews of the practical and theoretical aspects of MSPD " and applications in food analysis were presented by Barker.Torres et reported the use of MSPD for the... 

Solvent extraction carried out in conventional contactors like mixer-settlers and columns has certain limitations, including (a) controlling optimum dispersion and coalescence, (b) purifying both phases to ensure that stable emulsions are avoided (c) temperature control within a narrow band (d) high entrained solvent losses and related environmental and process economic effects and (e) large equipment dimensions and energy requirements when the density differential or selectivity is low. 

Liquid membranes of the water-in-oil emulsion type have been extensively investigated for their applications in separation and purification procedures [6.38]. They could also allow extraction of toxic species from biological fluids and regeneration of dialysates or ultrafiltrates, as required for artificial kidneys. The substrates would diffuse through the liquid membrane and be trapped in the dispersed aqueous phase of the emulsion. Thus, the selective elimination of phosphate ions in the presence of chloride was achieved using a bis-quaternary ammonium carrier dissolved in the membrane phase of an emulsion whose internal aqueous phase contained calcium chloride leading to phosphate-chloride exchange and internal precipitation of calcium phosphate [6.1]. 

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