Surface separation methods

Lindsey [3] prepared phosphono-substituted porphyrin derivatives, (II), for attachment to metal oxide surfaces for use as a chromatographic column packing agent. Surface separation methods using 9-borabicycIo[3.3.I]nonane derivatives, (III), are described by Lindsey [4]. 

Gas is produced to surface separators which are used to extract the heavier ends of the mixture (typically the components). The dry gas is then compressed and reinjected into the reservoir to maintain the pressure above the dew point. As the recycling progresses the reservoir composition becomes leaner (less heavy components), until eventually it is not economic to separate and compress the dry gas, at which point the reservoir pressure is blown down as for a wet gas reservoir. The sales profile for a recycling scheme consists of early sales of condensate liquids and delayed sale of gas. An alternative method of keeping the reservoir above the dew point but avoiding the deferred gas sales is by water injection. 

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. 

Principle The adsorptive-bubble separation methods, or adsub-ble methods for short [Lemlich, Chem. Eng. 73(21), 7 (1966)], are based on the selective adsorption or attachment of material on the surfaces of gas bubbles passing through a solution or suspension. In most of the methods, the bubbles rise to form a foam or froth which carries the material off overhead. Thus the material (desirable or undesirable) is removed from the liquid, and not vice versa as in, say, filtration. Accordingly, the foaming methods appear to be particularly (although not exclusively) suited to the remov of small amounts of material from large volumes of hquid. 

The separation methods routinely employed in the laboratory inelude the various chromatographic and electrophoretie techniques, whose seleetivity is eontinually being increased by the introduetion of new adsorbents, e.g. with ehemieally modified surfaces (Fig. 1). 

The hydrophilic surface characteristics and the chemical nature of the polymer backbone in Toyopearl HW resins are the same as for packings in TSK-GEL PW HPLC columns. Consequently, Toyopearl HW packings are ideal scaleup resins for analytical separation methods developed with TSK-GEL HPLC columns. Eigure 4.44 shows a protein mixture first analyzed on TSK-GEL G3000 SWxl and TSK-GEL G3000 PWxl columns, then purified with the same mobile-phase conditions in a preparative Toyopearl HW-55 column. The elution profile and resolution remained similar from the analytical separation on the TSK-GEL G3000 PWxl column to the process-scale Toyopearl column. Scaleup from TSK-GEL PW columns can be direct and more predictable with Toyopearl HW resins. 

A more complex but more versatile separation method is chromatography, a technique widely used in teaching, research, and industrial laboratories to separate all kinds of mixtures. This method takes advantage of differences in solubility and/or extent of adsorption on a solid surface. In gas-liquid chromatography, a mixture of volatile liquids and gases is introduced into one end of a heated glass tube. As little as one microliter (10-6 L) of sample may be used. The tube is packed with an inert solid whose surface is coated with a viscous... 

Separation methods, multichromato-graphic la 56 Serine la 246,356 lb 132 Serotonin la 70,76,239,240,262,355, 380 lb 37-39,231,243,348 Serotonin metabolites lb 327 Serum lipids la 89 Serum proteins la 74 Sesquiterpene derivatives lb 239,446 Sesquiterpene esters lb 239 Sesquiterpene glucosides la 327 Sesquiterpene lactones lb 448 Sevin lb 387-389 Si 50 000, specific surface area la 91 Silica gel, caffeine-impregnated la 85 -, surface modified la 3 Silica gel 60, specific surface area la 91... 

The electrostatic separation method is the exclusive choice in some specific situations, for example in the cases of rutile and ilmenite deposits. These deposits generally contain minerals of similar specific gravities and similar surface properties so that processes such as flotation are unsuitable for concentration. The major application of electrostatic separation is in the processing of beach sands and alluvial deposits containing titanium minerals. Almost all the beach sand plants in the world use electrostatic separation to separate rutile and ilmenite from zircon and monazite. In this context the flowsheet given later (see Figure 2.35 A) may be referred to. Electrostatic separation is also used with regard to a number of other minerals. Some reported commercial separations include those of cassiterite from scheelite, wolframite from quartz, cassiterite from columbite, feldspar from quartz and mica, and diamond from heavy associated minerals. Electrostatic separation is also used in industrial waste recovery. 

Flotation is certainly the major separation method based on the surface chemistry of mineral particles. It is, however, not the only method. Selective flocculation and agglomeration may be mentioned as other methods used commercially to a limited extent. The former is for hematite, while the latter is for coal and finely divided metallic oxide minerals. Both processes use the same principles as described for flotation to obtain selectivity. In selective flocculation, polymeric flocculants are used. The flocculants selectively adsorb on the hematite, and the hematite floes form and settle readily. Thereby separation from the sili-... 

Flotation. In many cases, contaminants adsorbed on the surface of clay particles, or contaminants occurring in soil as discriminate particles, have different surface properties to clean soil particles. By adding special chemical substances, the formation of a hydrophobic surface on the contaminated particles is possible. Pulp aeration results in the attachment of hydrophobic contaminated particles to the surface of the small bubbles that are formed. In this way, selective flotation of these particles is achieved. Contrary to the gravimetric separation methods, flotation offers the possibility to separate contaminated and noncontaminated particles of the same grain size and density but with different surface properties. 

High polarity is one of the reasons why both the ionic and amphoteric surfactants, and especially their metabolites, are difficult to detect. This property, however, is important for the application tasks of surface-active compounds, but is also the reason for their high water solubility. Due to this fact, their extraction and concentration from the water phase, which can be carried out in a number of very different ways, is not always straightforward. Furthermore, they are often not volatile without decomposition, which thus prevents application of gas chromatographic (GC) separation techniques combined with appropriate detection. This very effective separation method in environmental analysis is thus applicable only for short-chain surfactants and their metabolites following derivatisation of the various polar groups in order to improve their volatility. 

In a previous section, the effect of plasma on PVA surface for pervaporation processes was also mentioned. In fact, plasma treatment is a surface-modification method to control the hydrophilicity-hydrophobicity balance of polymer materials in order to optimize their properties in various domains, such as adhesion, biocompatibility and membrane-separation techniques. Non-porous PVA membranes were prepared by the cast-evaporating method and covered with an allyl alcohol or acrylic acid plasma-polymerized layer the effect of plasma treatment on the increase of PVA membrane surface hydrophobicity was checked [37].The allyl alcohol plasma layer was weakly crosslinked, in contrast to the acrylic acid layer. The best results for the dehydration of ethanol were obtained using allyl alcohol treatment. The selectivity of treated membrane (H20 wt% in the pervaporate in the range 83-92 and a water selectivity, aH2o, of 250 at 25 °C) is higher than that of the non-treated one (aH2o = 19) as well as that of the acrylic acid treated membrane (aH2o = 22). 

Electropolishing is well established as a simple, in situ method to separate porous silicon layers from the silicon electrode. By switching the anodic current density from values below JPS to a value above JPS, the PS film is separated at its interface to the bulk electrode. The flatness of a PS surface separated by electropolishing is sufficient for optical applications, as shown in Fig. 10.10. 

Normal-phase liquid chromatography is thus a steric-selective separation method. The molecular properties of steric isomers are not easily obtained and the molecular properties of optical isomers estimated by computational chemical calculation are the same. Therefore, the development of prediction methods for retention times in normal-phase liquid chromatography is difficult compared with reversed-phase liquid chromatography, where the hydrophobicity of the molecule is the predominant determinant of retention differences. When the molecular structure is known, the separation conditions in normal-phase LC can be estimated from Table 1.1, and from the solvent selectivity. A small-scale thin-layer liquid chromatographic separation is often a good tool to find a suitable eluent. When a silica gel column is used, the formation of a monolayer of water on the surface of the silica gel is an important technique. A water-saturated very non-polar solvent should be used as the base solvent, such as water-saturated w-hexane or isooctane. 

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