Liquid-Membrane Fractionation

Nonselective membranes can assist enantioselective processes, providing essential nonchiral separation characteristics and thus making a chiral separation based on enantioselectivity outside the membrane technically and economically feasible. For this purpose several configurations can be applied (i) liquid-liquid extraction based on hollow-fiber membrane fractionation (ii) liquid- membrane fractionation and (iii) micellar-enhanced ultrafiltration (MEUF). 

In the short term, we do not expect chiral membranes to find large-scale application. Therefore, membrane-assisted enantioselective processes are more likely to be applied. The two processes described in more detail (liquid-membrane fractionation and micellar-enhanced ultrafiltration) rely on established membrane processes and make use of chiral interactions outside the membrane. The major advantages of these... 

Wardius [51] extended the advancing front model to be employed to multistage mixer-settler systems for liquid membrane operations. They presented a zero order solution to the perturbation equations based on the model developed by Ho et al. [29]. The emulsion globule residence time distribution in each mixer was assumed to be exponential and the fractional utilization of internal reagent was given by... 

Solid-infusion processes Emulsion liquid membranes Solid-supported liquid membranes Fnam fractionation Bubble fractionation... 

Accelerated solvent extraction (ASE), focused microwave soxhiet extraction (FMSE), immuno affinity cleanup (im-Cu), liquid-liquid extraction (LLE), low-temperature lipid precipitation (LTLP), matrix solid-phase dispersion (MSPD), microwave-assisted extraction (MAE), nanofiltration (NF), pressurized fluid extraction (PEE), single drop microextraction (SOME), solid-phase extraction (SPE), solid-phase microextraction (SPME), steam distillation (SD), stir bar sorptive extraction (SBSE), surpercritical fluid extraction (SFE), subcritical fluid extraction (ScFE), supported liquid membrane extraction (SLME), ultra-sonication (US), size exclusion chromatography (SEC), liquid chromatography-fraction collection (LC)... 

The host-guest selectivity of macrocyclic ligands as measured in homogeneous solution can translate effectively into multiphase separations systems such as IC and liquid membranes, even when macrocyclic structures must be modified to accommodate system demands. Separations scientists have applied this selectivity in novel ways to these two methodologies to effect separations that have potential or realized practical uses, both in analytical chemistry and preparative separations. To date, only a fraction of the macrocyclic structures that exhibit such potential have been studied, and to the degree that this line of research is pursued vigorously, many further innovations can be expected. 

Change in the volume fraction of internal phase in the emulsion leads to a variation of the specific interface. For each surfactant concentration, there is a different maximum in the dependence of the emulsion stability on the fraction of the disperse phase (Figure 3). The maximum stability corresponds to saturation of the adsorption layer by the surfactant. For a higher volume fraction of the internal phase at the specified surfactant concentration, the adsorption layer is unsaturated and the stability of the emulsion is diminished. For lower volume fractions of internal phase, the emulsion stability diminishes due to the presence of excess surfactant in the liquid membrane analogous to Figure 1. 

Kozlowski et al. [18] obtained the p CD polymers, which were prepared by crosslinking of 3-CD with 2-(l-docosenyl)-succinic anhydride derivatives in anhydrous N,N-dimethylformamide in the presence of NaH. It was established that the elongation of the hydrocarbon chain in the obtained 3-CD polymer in the reaction with 2-(l-docosenyl)-succinic anhydride results in the selectivity for Pb(ll) ions in the ion transport with the use of this ion carrier. At room temperature the dimmer was obtained, while at 100°C the polymers of 34kD and 13.5 kD fractions were received. The transport kinetics investigation on dependence of the carrier and Pb(II) concentrations have shown that the transport by the dimmer proceeded by the facilitated mechanism, typical for liquid membranes. The polymer however, has shown a linear increase of the transport flux in dependence on metal concentration in the source phase, this fact indicating that the polymer form of 3-CD prefers probably the fixed site mechanism of transport. PIMs containing dimmer and polymer of CD, in the transport of Zn(II), Cu(II) and Pb(Il) showed selectivity orders Pb(Il) Cu(II), Zn([]), and Pb(II) Cu(II) > Zn(II), respectively. The high selectivity factor for Pb(II)/Cu(II) equal to 163 for the dimmer was achieved (Table 1). 

Matsumoto, M. Mikami, M. Kondo, K. (2007). Selective Permeation of Organic Sulfur and Nitrogen Compounds in Model Mixtures of Petroleum Fraction through Supported Ionic Liquid Membranes. J. Chem. Eng. Japan, 40,1007-1010, ISSN 0021-9592. 

Refinery product separation falls into a number of common classes namely Main fractionators gas plants classical distillation, extraction (liquid-liquid), precipitation (solvent deasphalting), solid facilitated (Parex(TM), PSA), and Membrane (PRSIM(TM)). This list has been ordered from most common to least common. Main fractionators are required in every refinery. Nearly every refinery has some type of gas plant. Most refineries have classical distillation columns. Liquid-liquid extraction is in a few places. Precipitation, solid facilitated and membrane separations are used in specific applications. 

The retention efficiency of membranes is dependent on particle size and concentration, pore size and length, porosity, and flow rate. Large particles that are smaller than the pore size have sufficient inertial mass to be captured by inertial impaction. In liquids the same mechanisms are at work. Increased velocity, however, diminishes the effects of inertial impaction and diffusion. With interception being the primary retention mechanism, conditions are more favorable for fractionating particles in liquid suspension. 

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