Extraction processes dispersed phase selection

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)... 

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. 

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. 

The term contactor systems present only membrane devices, mosdy hollow-fiber, but not processes. The membrane in a contactor acts as a passive (not selective) barrier and as a means of bringing two immiscible fluid phases (such as gas and hquid, or an aqueous hquid and an organic hquid) in contact with each other without dispersion. The phase interface is immobihzed at the membrane pore surface, with the pore volume occupied by one of the two fluid phases that are in contact. Contactor devices are used in many of the above-mentioned BLM systems (HLM, HFCLM, HFLM, FLM, pertraction, membrane-based extraction, MHS) as construction units. Sometimes, selective hydrophobic, hydrophihc, or ion-exchange membranes are used as barriers for additional selective separation in the devices similar to contactors. 

The separation of the products from the IL catalytic mixture can be performed in various cases by simple decanting and phase separation or by product distillation. In this respect, a continuous-flow process using toluene as extractant has been appHed for the selective Pd-catalyzed dimerization of methyl acrylate in ILs [136]. However, in cases where the products are retained in the IL phase, extraction with supercritical carbon dioxide can be used instead of classical liquid-liquid extractions that necessitate the use of organic solvents, which may result in cross-contamination of products. This process was successfully used in catalyst recycling and product separation for the hydroformylation of olefins employing a continuous-flow process in supercritical carbon dioxide-IL mixtures [137]. Similarly, free and immobilized Candida antarctica lipase B dispersed in ILs were used as catalyst for the continuous kinetic resolution of rac-l-phenylethanol in supercritical carbon dioxide at 120°C and 150°C and 10 Mpa with excellent catalytic activity, enzyme stability and enantioselectivity levels (Fig. 3.5-11). 

Interestingly, in multiphase catalytic processes the primary products can be extracted during the reaction thus modulating the product selectivity (using different substrates and reaction products solubility with the catalyst containing phase, such as dienes/monoenes and arenes/cycloalkenes). Indeed, this approach can constitute a suitable method for avoiding consecutive reactions of primary products and has been used in the partial hydrogenation of dienes and arenes by transition-metal NPs dispersed in ILs. 

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