Selective separation

Gas molecule, like hydrogen, that have a small size can permeate through smaller pores, which are inaccessible to larger gas molecules like nitrogen. 

CO2 as a byproduct during the combustion of fuels in industrial plants and automobiles is a major contributor to global warming. Hence, the selective capture of carbon dioxide requires special attention from the scientific community. The principle sources of CO2 that cause harm to the environment are contaminated natural gas, containing a mixture of methane and CO2 (known as pre-combustion), and exhaust gas generated in industiy or from automobiles (post-combustion). Separate physical conditions are needed for CO2 capture from pre- and post-combustion mixtures, and a variety of porous polymer networks, both soluble and insoluble, have been involved in CO2 capture with consideration of their pore dimensions.  

4-benzenedimethanol (HCP-BDM) and HCP-ben l alcohol (HCP-BA) networks synthesized by the Friedel-Crafts self-condensation method have shown high selectivity for CO2 over N2, measured by nitrogen adsorption isotherm at two different temperatures, 273 and 298 Nonlocal density functional theory (NLDFT) calculations confirmed the pore sizes to be below 2 nm for both of the networks. Such small pore sizes, as well as the high ojq gen content in both the polymers, is most probably tbe reason for the strong interactions with polar CO2 rather than N2, making these good candidates for the selective separation of CO2 from N2. 

In comparison to other polymer membranes, soluble porous networks hold an advantage in gas separations in the form of thin solution-cast films. Linear PIMs are soluble and thus good candidates in this regard. The introduction of triazole groups in PIMs (TZPIMs) by post-synthetic modification favors CO2 uptake and greater selectivity for gas separation. TZPIM membranes exhibit exceptional selective permeation as polymeric membranes for gas mixtures like CO2 and N2. 

A chiral PIM based on a binaphthalene monomer has been functionalized by incorporation of polyimide with binaphthalene and 4,4-(9-fluor-enylidene)dianiline. The polymeric film of this network demonstrates selective gas uptakes to separate CO2 from H2.  

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Polymers containing 8-hydroxyquinoline appear to be selective adsorbents for tungsten in alkaline brines (95). In the presence of tartrate and citrate, quinaldic acid [93-10-7] allows the separation of zinc from gallium and indium (96). Either of these compounds can selectively separate lead and zinc from oxide ores as complexes (97). It is also possible to separate by extraction micro quantities of rhenium(VII), using quinoline in basic solution (98). The... 

Finally, selective separation and dewatering of one suspended substance in a slurry containing different minerals or precipitates is possible by selectively adsorbing a magnetic material (usually hydrophobic) onto a soHd that is also naturally or chemically conditioned to a hydrophobic state. This process (Murex) was used on both sulfide ores and some oxides (145). More recently, hydrocarbon-based ferrofluids were tested and shown to selectively adsorb on coal from slurries of coal and mineral matter, allowing magnetic recovery (147). Copper and zinc sulfides were similarly recoverable as a dewatered product from waste-rock slurries (148). 

Cross-belt magnetic separators are based on the same principle as lifting magnets. Although these units have relatively low capacities, the same unit can produce selective separations with different products by using different pole gaps and field strengths. (See Fig. 19-42.)... 

The chemical propjerties of the contaminants have to be considered when selecting separation techniques. Some of the liquids are absolutely immiscible in water, and if the process stream involves water and the contamination is liquid/liquid, then the separation technique can greatly reduce the volume of contaminated water. For example, if acetone is the contaminant of concern, a simple vap>or stripping technique can be effective in making a separation. In the case of refined oil, which has a solubility limit of approximately 50 ppm, one of the oil/water separation techniques could be effective. Some general guidelines to consider are ... 

The selective separation range of the S-500/S 1000-system for glucans is shown for hybrid starch Triticale T22. This mixture of scb and nb/lcb glucans contains components in the range between approximately dp 50-300,000 glucose monomers (Fig. 16.11). The degree of polymerization distribution obtained from dextran-based calibration was computed as well in terms of... 

In accordance with expectations, the branching index classifies the major partition of the investigated sample as nb/lcb glucans. On CL 2B, as well as on S-1000, the major percentage of components was eluted in the selective separation range, and a minor amount of high dp scb glucans in both systems was eluted at the exclusion limit. 

The selective separation range of P-6/S-200 was determined with Blue Dextran (Vexdi exclusion limit) and fructose (V,o total permeation limit). Molecular weight (degree of polymerization) calibration (Fig. 16.22) was established with dextran standards and low dp pullulans (dp 3, 6, 9, 12, 15, 18) formed by the controlled hydrolysis of high dp pullulan. 

As an illustration for the improved performance of P-6/S-200 compared to P-6 solely, highly purified inulin was separated on both systems. Obviously, the high dp inulin components could not be resolved on P-6 (Fig. 16.25), whereas all of the inulin components were eluted within the selective separation range of the P-6/S-200 system (Fig. 16.26). 

M NaCl eluent. Because of the good performance of the TSK PW system in the low dp range, DMSO was shifted outside the selective separation range > 50 ml) and aqueous eluent-dissolved starch components could he analyzed in terms of absolute degree of polymerization distributions (mass m ... 

The second example is the SE-HPLC analysis of recombinant hGH. In this example, SE-HPLC is used for both a purity and a protein concentration method for bulk and formulated finished products. This method selectively separates both low molecular weight excipient materials and high molecular weight dimer and aggregate forms of hGH from monomeric hGH, as shown... 

Naphthalenedisulfonate-acetonitrile as the only mobile phase with a silica column coated with a crosslinked aminofluorocarbon polymer has proven to be an effective combination for the separation of aliphatic anionic surfactants. Indirect conductivity and photometric detection modes are used to monitor these analytes. The retention of these surfactants is found to depend on both the ionic strength and the organic solvent content of the mobile phase. The mechanism of retention is considered to be a combination of both reverse phase and ion exchange processes. Selective separation of both alkanesulfonates and... 

The selectivity (separation capability) of an HPLC system is dependent upon the combination of mobile and stationary phases. Since ions are being generated directly from the mobile phase by electrospray, its composition, including the identity and concentration of any buffer used, and its flow rate are important considerations. 

The solubilization of enzymes and proteins in water-containing reversed micelles has attracted a great deal of interest for their selective separation, purification, and efficient refolding and for bioreactions involving a wide class of polar, apolar, and amphiphilic reactants and products [13,44,162-164]. 

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