Sorption selective

An interesting consequence of selective sorption is that conditions for partition chromatography arise which may enhance the normal ion exchange separation factors. This aspect has been utilised by Korkisch34 for separation of inorganic ions by the so-called combined ion exchange-solvent extraction method (CISE). 

The thermodynamic analysis of these systems played an important role in the interpretation of these data and of the high selectivity. It was found that selective sorption of complex organic ions is accompanied by an increase in the entropy of the system (Table 6). 

Selective sorption by the filler sorption of one of the matrix components (residual monomer, low molecular homologs, various impurities) may lead to plasticization of the boundary layers and appearance of soft interphases [115,116]. 

Methods of EGA using selective sorption, condensation of effluent gases, infrared absorption and thermoparticulate analysis have been reviewed by Lodding [144]. The use of simple gas burette systems should not be forgotten and an Orsat gas analysis apparatus can provide useful measurements in studies of the decomposition of formates [169]. Problems have been encountered in the determination of water released Kiss et al. [170—172] have measured the formation of this compound from infrared analyses of the acetylene evolved following reaction of water with calcium carbide. Kinetic data may be obtained by wet methods ammonia, determined by titration after absorption in an aqueous solution, has been used to measure a—time values for the decomposition of ammonium salts in a fluidized bed [173],... 

Fischer-Tropsch synthesis products contain also high quantities of n-a-olefins that can be recovered by selective sorption processes with suitable molecular sieves [19]. A large-scale Fischer-Tropsch synthesis plant operates in South Africa [20]. Another plant was started in Indonesia in 1993 [21]. 

The attractive (80) features of MOFs and similar materials noted above for catalytic applications have led to a few reports of catalysis by these systems (81-89), but to date the great majority of MOF applications have addressed selective sorption and separation of gases (54-57,59,80,90-94). Most of the MOF catalytic applications have involved hydrolytic processes and several have involved enantioselec-tive processes. Prior to our work, there were only two or three reports of selective oxidation processes catalyzed by MOFs. Nguyen and Hupp reported an MOF with chiral covalently incorporated (salen)Mn units that catalyzes asymmetric epoxidation by iodosylarenes (95), and in a very recent study, Corma and co-workers reported aerobic alcohol oxidation, but no mechanistic studies or discussion was provided (89). 

Novel manufacturing technologies are needed to address modem separation and reaction challenges. ZeoUtes possess molecular sieving, selective sorption properties and catalytic activity, as well as enhanced thermal and chemical stabiUty which make them good candidates for these applications. Future focus needs to address the processing methods and theoretical understanding of these materials so their potential for commercial appUcation can be realized. 

If the specifications for diesel fuels become even more strict in the future and sulfur levels less than 0.05% S (500 ppm) must be achieved, it may be more reasonable to remove the sulfur by means other than hydrotreating. At the level of 500 ppm, selective stoichiometric reactions or selective sorption may be worth considering, even if the sorptions are irreversible. It should be recalled that benzene was for many years freed of thiophene by stoichiometric removal by Raney nickel, as pointed out by Startsev (2). 

Functionalized polymers are of interest in a variety of applications including but not limited to fire retardants, selective sorption resins, chromatography media, controlled release devices and phase transfer catalysts. This research has been conducted in an effort to functionalize a polymer with a variety of different reactive sites for use in membrane applications. These membranes are to be used for the specific separation and removal of metal ions of interest. A porous support was used to obtain membranes of a specified thickness with the desired mechanical stability. The monomer employed in this study was vinylbenzyl chloride, and it was lightly crosslinked with divinylbenzene in a photopolymerization. Specific ligands incorporated into the membrane film include dimethyl phosphonate esters, isopropyl phosphonate esters, phosphonic acid, and triethyl ammonium chloride groups. Most of the functionalization reactions were conducted with the solid membrane and liquid reactants, however, the vinylbenzyl chloride monomer was transformed to vinylbenzyl triethyl ammonium chloride prior to polymerization in some cases. The reaction conditions and analysis tools for uniformly derivatizing the crosslinked vinylbenzyl chloride / divinyl benzene films are presented in detail. 

Poly(vinylbenzyl chloride) (VBC) is an ideal starting material onto which a variety of functional groups can be attached through relatively simple reactions and mild reaction conditions. Functionalized polymers are of interest in a variety of applications including but not limited to fire retardants, selective sorption resins, chromatography media, controlled release devices and phase transfer catalysts. An example of the wide applicability of functionalized polymers is provided by trimethyl ammonium functionalized poly(VBC). 

Sorption Properties. Sorption isotherms were determined of n-hexane and 2,3-dimethylbutane on variously pretreated samples of zeolite by a gravimetric method using a Cahn electrobalance. No shape-selective sorption was observed for these sorbates, which bespeaks a pore size greater than about 0.5 nm. The sorption capacity of S2 was appreciably lower than that of zeolite X, Y, or mordenite. Routine sorption capacities were determined by a simple procedure of pore filling with benzene at room temperature after calcination of the samples at various temperatures. 

Quite apart from this molecular sieving effect, zeolites are also effective in selectively sorbing particular components from a mixture of molecules all individually capable of penetrating the entire zeolite. Some liquid phase sorption equilibria studies have been reported for both the small-pore 5A molecular sieve (1 ) and the large-pore faujasite NaY zeolite (2). With the recent synthesis of intermediate pore sTze zeolites such as ZSM-5 and ZSM-11(3), a study of the selective sorption properties of these zeolites was initiated. 

Selective Sorption of Alcohols from Aqueous Solution... 

Highly selective sorption of aromatic compounds from paraffin-containing solutions has been reported for the faujasites NaX, NaY, and HY under equilibrium conditions (2). Thus, benzene is preferentially adsorbed relative to n-hexane or n-decane, p-xylene relative to n-octane, and naphthalene relative to n-decane. The measured separation factors in these systems are so large (K>700) that essentially only one species exclusively occupies the internal volume of the zeolites. 

In distinct contrast to the faujasites, the intermediate-pore zeolites ZSM-5 and ZSM-11 exhibited a marked preference for n-paraffins relative to aromatics. As can be seen from Table II, both H-ZSM-5 and H-ZSM-11 preferentially sorbed n-nonane from mixtures of nonane and p-xylene dissolved in an inert, non-sorbable solvent, 1,3,5-tri-isopropylbenzene. Selectivity factors greater than 40 were observed, despite the fact that both compounds were readily sorbed when higher zeolite/sorbate ratios were used. Highly selective sorption of n-heptane relative to naphthalene, and n-tetradecane relative to 1-phenyloctane, was also observed with H-ZSM-5. 

Iso-paraffins too can be separated from aromatics on H-ZSM-5, a process that cannot be accomplished with either the small-pore or large-pore zeolites, such as A and Y. While the selectivity is not nearly as large as it is for n-paraffins, selective sorption of 2-methylheptane relative to p-xylene (selectivity factor = 6.7) was nevertheless observed. 

Selective Sorption of Xylene Isomers from Solution... 

The high hydrophobicity of ZSM-5 permits the selective sorption of organic compounds dissolved in water. A high (1670 1) silica/alumina ratio ZSM-5 preferentially sorbed n-butyl alcohol (90.7% sorbed) from iso-butyl alcohol (17.3% sorbed) and tert-butyl alcohol ( 0% sorbed), all dissolved in water. 

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