Solvent filtration

The dry-extmsion process consists of four operations dissolution of the polymer in a volatile solvent filtration of the solution to remove insoluble matter extmsion of the solution to form fibers and lubrication, yam formation, and packaging. 

For these reasons, an understanding of the purification conditions and materials used is useful. For example, on using one solvent, impurities could crystallize under the same conditions as the compound of interest, but on using another solvent, the impurities may be left in the solution. Use of a relatively nonvolatile solvent may lead to residual amounts, which are difficult to eliminate. If the drug substance is dissolved in a solvent, filtration is an effective method of removing particulate matter. 

A hyperfiltration process developed by Mobil Oil, now ExxonMobil, for this separation is illustrated in Figure 5.28(b). Polyimide membranes formed into spiral-wound modules are used to separate up to 50 % of the solvent from the dewaxed oil. The membranes have a flux of 10-20 gal/ft2 day at a pressure of 450-650 psi. The solvent filtrate bypasses the distillation step and is recycled directly to the incoming oil feed. The net result is a significant reduction in the refrigeration load required to cool the oil and in the size and energy consumption of the solvent recovery vacuum distillation section. 

Metal oxides, used for manufacturing of ceramic nanofiltration membranes, are intrinsically hydrophilic. This limits the use of these membranes to polar solvents filtration of nonpolar solvents (n-hexane, toluene, cyclohexane) usually yields zero fluxes. Attempts have been made to modify the pore structure by adding hydrophobic groups, for example, in a silane coupling reaction [38, 43]. This approach is similar to modifications of ultrafiltration and microfiltration membranes... 

Classical separations by open column chromatography with different stationary phases (silica gel, reversed-phase C-18 or C-8, polyamide, cellulose) and elution with appropriate solvent mixtures are also useful for flavonoid fractionation and purification. Different column systems can be used. The classical open column chromatography uses relatively large particle sizes (0.2-6 mm), with limited resolution, and solvent filtration through the column proceeds by the pressure of the solvent column placed on top of the stationary phase. In other cases, smaller... 

Fluorous biphasic catalysis without fluorous solvents (filtration of a ther-momorphic fluorous catalyst). This can be used when a fluorous catalyst exhibits significantly different solubility in an organic solvent upon changing the temperature of the system. 

Guizard C, Ayral A, and Julbe A. Potentiality of organic solvents filtration with ceramic membranes. A comparison with polymer membranes. Desalination 2002 147 275-280. 

Polytetrafluoroethylene Gas, air, and solvent filtration Good for chromatographic applications and when protein binding is not an issue. ++++ ++... 

Numerous methods for the generation of imidazole carbenes have been reported. For example, starting from an imidazolium halide, the use of systems such as sodium hydride in ammonia or dimethylsulphoxide (DMSO), sodium in ammonia, alkali metals in tetrahydrofuran (THF), metal ferf-butoxides in THF or DMSO, etc. Recently, Seddon and Earle reported a simple procedure for the generation of the imidazolium carbene 2 in 90-95% yield from an imidazolium chloride 1 which does not require solvents, filtrations, or produce noxious waste products (Scheme 4) [40],... 

Figure 5.2. (a) All-glass solvent filtration flask using 0.45-pm membrane filters. (Legends 1. funnel, 2. clamp, 3. filter holder, 4. vacuum flask), (b) Kontes microfiltration system, which can also be used as a mobile phase reservoir. Mobile phase can be pulled into the flask from the Teflon tube without having to pour in from the top in traditional vacuum filtration flask. 

The most distinctly different approach to SPE is the use of a disc, not unlike a common filter paper. This SPE disc format is referred to by its trade name of Empore (discs). The 5-10 pm sorbent particles are intertwined with fine threads of PTFE which results in a disc approximately 0.5 mm thick and a diameter in the range 47 to 70 mm. Empore discs are placed in a typical solvent filtration system and a vacuum applied to force the solvent-containing sample through (Figure 8.7). To minimize the dilution effects that can occur, it is necessary to introduce a test-tube into the filter flask to collect the final extract. Manifolds are commercially available for multiple sample extraction using such Empore discs. 

Solvent filtration apparatus equipped with a 0.45 pm Teflon filter (Such as Ultra-ware filter apparatus 300/1,000 mL from Kontes glass company and 0.45 pm Teflon filters from Millipore Corp.). 

Insoluble solid in solvent filtration (or, if a fine precipitate, centrifugation)... 

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