Wettability-based separators

The schematics of the phase separators used for liquid-liquid separation are depicted in Figure 7.17. Three principles are used geometrical modifications, wettability based separation, and gravity based separators. These are discussed in the following section. 

The wettability based separation of two immiscible liquids is explained in more detail for the membrane separator [72]. 

Figure 7.20 Schematics of wettability based separators, (a) Y-shaped separator. (Adapted with permission from Ref [54]. Copyright (2007) American Chemical Society.) (b) Membrane separator. (Adapted from Ref [72] with permission of The Royal Society of Chemistry.)...

Figure 2.14 Schematics of different types of flow spiitters for separation of iiquid-iiquid two-phase flow. (a) Geometrical modifications (e.g., Y-separator), (b) wettability-based separator (e.g., membrane separator), and (c) gravity-based separator (e.g., settler).

Different types of wettability-based separators have been used for separation of two immiscible liquids. Some of the examples are shown in Figure 2.17. The Y-shaped separator that was used for aqueous-organic systems comprised one inlet and two outlets. The splitter consists of a hydrophobic PTFE capillary with a steel needle having an internal diameter equal to the internal diameter of the Y-junction, being fitted into one of the outlets. The aqueous phase has a strong affinity toward... 

Solids separation based on density loses its effectiveness as the particle size decreases. For particles below 100 microns, separation methods make use of differences in the magnetic susceptibility (magnetic separation), elec trical conductivity (electrostatic separation), and in the surface wettability (flotation and selec tive flocculation). Treatment of ultrafine solids, say smaller than 10 microns can also be achieved by utilizing differences in dielectric and electrophoretic properties of the particles. 

Proper control of the properties of drilling mud is very important for their preparation and maintenance. Although oil-base muds are substantially different from water-base muds, several basic tests (such as specific weight, API funnel viscosity, API filtration, and retort analysis) are run in the same way. The test interpretations, however, are somewhat different. In addition, oil-base muds have several unique properties, such as temperature sensitivity, emulsion stability, aniline point, and oil coating-water wettability that require other tests. Therefore, testing of water and oil-base muds will be considered separately. 

The aqueous batteries use water based electrolytes (e.g., KOH electrolyte for NiCd and NiMH and H2-SO4 electrolyte for lead acid), which are less resistive then nonaqueous electrolytes. Polyolefin materials are generally suitable for use in the manufacture of separators for these batteries, but they are not inherently wettable by aqueous electrolytes. Such electrolytes are therefore unable to penetrate the pores of a separator formed from such a material, so that ion migration through the pores in solution will not occur without modification. This problem is sometimes overcome by treating the polyolefin material with a surfactant, which allows an aqueous electrolyte to wet the material. However, such surfactant can be removed from the surfaces of the polyolefin material when electrolyte is lost from the device, for example during charging and discharging cycles, and it is not subsequently replaced on the material when the electrolyte is replenished. 

The commonly used separator material now is the surface treated polypropylene. The surface treatment helps in making the polypropylene permanently wettable. Surface treatments involve the grafting of a chemical such as acrylic acid to the base fibers to impart wettability and is accomplished using a variety of techniques such as UV or cobalt radiation. Another method of imparting wettability to the polypropylene is a sulfonation treatment where the base fiber material is exposed to fuming sulfuric acid. The separator surface is designed to be made hydrophilic to the electrolyte. 

Froth flotation is an application of foams that is used to separate mineral components from each other based on their having different surface properties, typically their wettability and surface electrical charge. For example, froth flotation is the classic process used to separate copper from lead ore. The process involves having hydrophobic particles attach to gas bubbles which rise through a turbulent suspension to create a surface foam called a froth. Figure 10.2 shows an illustration of a mechanical flotation cell. This is the classic flotation device [53,91,625], First, the flotation feed particles are well dispersed into a particle suspension. Together with chemical flotation aids, such as collectors and frothers, this constitutes what is called the flotation pulp. In a mechanical flotation cell, air is fed in the form of fine bubbles and introduced near the impeller (see Figure 10.2). In addition to mechanical flotation cells, there are also pneumatic cells and cyclone flotation cells. Pneumatic... 

There exist a number of familiar procedures for effecting mineral separations, including sink-float methods based on density differences and froth flotation based on wettability. Because of the tendency of kerogen to swell and soften in the presence of organic liquids and thus possibly to mobilize trapped mineral particles, and because most minerals are water-wetted and thus extractable with water, we investigated a liquid-liquid (oil-water) pelletization method. 

The properties of water as a washing agent and a solvent can be enhanced with additives. Several types of additives include (i) surfactants that improve the wettability of the soil components and improve the solubility of lipophilic impurities (ii) complex-ing agents which convert heavy metals and their insoluble compounds into water-soluble compounds (iii) flotation agents (collectors and foamers), which convert certain insoluble substances into a separable phase and (iv) acids or bases for pH control which is necessary for the stability of compounds and for the selectivity of the flotation processes (Venghaus and Werther 1998 Wilichowski 2001). 

Froth flotation is an application of foams that is used to separate mineral components from each other based on their different surface properties, typically their wettability and surface electrical charge. For example, froth flotation is the classic process used to separate copper from lead ore. The process involves having... 

In order to separate the two phases online an in-house flow splitter was connected at the end of each test section (Fig. 3.6). The splitter had two side channels made of stainless steel and PTFE that have different wettabilities for the two liquids used. The internal diameter and the length of the side channels were chosen based on the pressure drop that was created on the flow splitter [similar to (Scheiff et al. 2011)]. With this configuration pure ionic liquid phase was obtained from the PTFE outlet and aqueous solution from the stainless steel outlet. However, at high mixture velocities the separation was not always 100 % efficient and a mixture of ionic liquid and aqueous solution was collected from the steel outlet. 

Figure 13.15 shows wettability improvanent of the separator by addition of Phoslyte. The wettability was analyzed by contact angle, base diameter, and volume change monitoring system. In general, conventional electrolytes have less ability for wettability to their electrode materials and separator. Phoslyte additive renders electrolytes more wettable to cell materials. Improvement of wettability by addition of Phoslyte was observed for cathode and anode as well. 

To circnmvent the low separator wettability and low electrolytic conductivity of single-solvent systems based on sulfone solvents as mentioned before, blending with a low-viscosity solvent such as EMC is a practical approach [170]. Based on this guideline, 1 mol dm" LiBF4 in TMS-ethyl acetate (50-50 yo. %)+2 vol.% VC was tested for Li/LiNii/2Mn3/204 cells. 

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