Molecularly imprinted adsorbents for positional isomer separation.

2,4-Dihydroxybenzophenone (2,4-DHB) imprinted polymers were synthesized by surface imprinting technique, using allyl alcohol as the functional monomer. The polymers showed a very high selectivity for 2,4-DHB when compared with various positional isomers such as 2-HB, 2,2'-DHB, 4,4'-DHIB and 4,4'-DMB. Solvents were found to affect the selectivity as well as sorption capacity in the case of surface imprinted polymers. The selectivities decreased drastically when the imprint cavity was blocked. This validated the importance of the cavity and the rebinding interactions in governing the selectivity in the case of MIPs. The surface imprinted polymers also showed a high selectivity under non-equilibrium conditions thereby making them suitable adsorbents for industrial separations.     

Development of oxygen selective adsorbents for gas separation and purification

Development, characterization, and testing of oxygen selective chemical adsorbents (chemisorbents) for cyclic gas separation and purification applications using pressure cycling are described herein. Three structurally related compositions, designated IA-1, IA-2, and IA-3 offer high oxygen capacities and selectivities coupled with fast uptake kinetics. Extended lifetime tests for IA-3 indicate a half-life of 17 years with 0.01 % oxygen at 60 °F under cycling conditions. Hazard testing results are presented and these data impose some restrictions on handling and use. For practical applications using packed beds of adsorbent in pressure-swing cycles, agglomeration is required to produce larger particles using formulations and methods that minimize the impact on oxygen binding. Methods are described herein using polymeric binders that provide the necessary physical features while maintaining adequate adsorption performance characteristics. Proof of concept oxygen removal test results are also described.     

Selective mesoporous adsorbents for Ag+/Cu2+ separation

Three different approaches, including (1) manipulating the site chemistry, (2) controlling the spacing between neighbouring sites and (3) altering the adsorbates by the use of chelates, were successfully used to prepare MCM-41 adsorbents with excellent selectivity for silver adsorption from solutions containing copper.     

Characterization of synthetic adsorbents with fine particle sizes for preparative-scale chromatographic separation

Synthetic adsorbents with fine particle sizes (15-30 microm) were manufactured. These adsorbents are made of poly(styrenedivinylbenzene) and polymethacrylate, and have the same chemical structure as analytical- (5-10 microm) or industrial- (200-600 microm) grade synthetic adsorbents. Both of them have very similar porous structure to those of analytical or industrial sizes, so that they can adsorb compounds of various molecular masses. Chromatographic separation characteristics of newly manufactured fine-particle grades of synthetic adsorbents were evaluated and compared to those of analytical or industrial adsorbents. Reasonable dependency of separation performance on particle size of synthetic adsorbents was obtained. Hydraulic properties of fine-grade adsorbents had also been measured in view of column operations. Furthermore, scalability and applicability of these adsorbents for preparative-scale chromatographic separation of bioactive compounds was evaluated. Separation of soybean isoflavones and tea catechin derivatives had revealed that fine-grade synthetic adsorbents could be well applied with scalability under the same elution conditions used for analytical use. Scalability up to a 22400-fold loading amount was achieved from a small column packed with analytical-grade adsorbent used for method development to a scale-up preparative column packed with fine-grade adsorbent used for preparative purification. These results showed the usefulness of the fine-grade synthetic adsorbents for more precise purification of bioactive compounds, including pharmaceuticals and functional food additives with higher recovery.     

High-rate and high-density gas separation adsorbents and manufacturing method

High-rate and high-density gas separation adsorbents used in vacuum pressure swing adsorption (VPSA) processes are described. Agglomerated zeolite Li–LSX compositions made using colloidal silica binding agents and having improved nitrogen pore diffusivity compared to like compositions prepared with traditional clay binders, are also described. Preparation methods for the colloidal silica-bound adsorbents are described together with their characterization by mercury (Hg) porosimetry, scanning electron microscopy (SEM) and low dead-volume breakthrough testing, from which the pore diffusivity is obtained. In this article, we show how the location and dispersion of the colloidal silica binding agent within the agglomerated zeolite particle yields pore-architectures that resemble “state-of-the-art” binderless adsorbents. In addition, we use VPSA process simulations to show that the best process performance is achieved by the combination of high-rate and high-density adsorbent properties.     

Chiral and electrokinetic separation of amino acids using polypyrrole-coated adsorbents

An optically active and electroconductive polymeric adsorbent has been developed for the use in chromatographic resolution of nonderivatized amino acids. The chiral selectivity of the adsorbent is based upon ligand exchange of coordinated copper(II) complexes of D or L-amino acids and a molecular imprinting technique by modifying the resin surface with polypyrrole coating. Applying a potential difference of +/-1.5 V to the chiral and conductive column, racemic amino acids are separated according to their charge characteristics, and simultaneously resolved with respect to their optical isomerisms. A pH-controlled mixture of D,L-lysine and D,L-aspartic acid is resolved displaying enantioselectivity values of 1.19 and 2.08, respectively, and a baseline separation of the two amino acids is accomplished by alternating the polarity of the electric field. The synthesized adsorbent also exhibits size exclusion factor discriminating amino acids with larger side chains.     

Comparative study of adsorbents performance in ethylene/ethane separation

Some potential adsorbents for ethylene/ethane separation are ethylene selective while the others are ethane selective. Among different adsorbents, i.e., zeolites and metal organic frameworks (MOFs), a comparative study is critical to find the more suitable adsorbent for the separation. In this paper, binary ethylene/ethane adsorption performances of zeolites and MOFs, i.e., equilibrium selectivities and adsorption capacities are investigated utilizing ideal adsorbed solution theory (IAST). IAST model is applied at different gas compositions (0.1–0.9 ethylene mole fractions) and pressures up to 100 kPa. The results revealed that the most selective adsorbent toward ethylene is 5A zeolite while MOFs have higher equilibrium adsorption capacities. Among zeolites and MOFs, 5A and Fe₂(dobdc) have the highest selectivity (27.4 and 13.6) and capacity (≈2.8 and 5.8 mmol ethylene/g) at 100 kPa and 298 K for a 50/50 mixture. Among ethane selective adsorbents, Silicalite-1 zeolite and UTSA-33a (MOF) have the highest selectivity and capacity (≈2.9 and ≈1.5 mmol ethane/g) at 100 kPa and 298 K for a 50/50 mixture, respectively. Investigation showed that adsorption capacity of ethylene selective adsorbents is higher than that of ethane selective ones.     

Solid state evidence for pi-complexation of sodium cation by carbon-carbon double bonds

Solid state evidence shows that neutral double bonds, attached to flexible sidearms of a lariat ether, serve as intramolecular pi-donors for a ring-bound Na+ cation.     

Advances in cyclodextrin polymers adsorbents for separation and enrichment: Classification,mechanism and applications

Over the past few decades, supramolecular chemistry has entered the field of scientific research and attracted extensive attention. Among supramolecular macrocycles, cyclodextrins(CDs) are widely applied in the field of adsorption due to their unique structure and properties. This review focuses on the important role of cyclodextrin polymers(CDPs) as adsorbents in the adsorption of different substances. It covers the category of CDPs adsorbents(including crosslinked CDPs, grafted CDPs, CD-based ...     

Advanced adsorbents for the separation of the ortho- and para-hydrogen spin isomers at cryogenic temperatures

Improved adsorbent types and compositions have been developed for the challenging separation of the ortho- and para-hydrogen spin isomers at 77 K. From a systematic study of commercially available adsorbent types, it has been found that zeolites of type X offer the largest capacity and selectivity towards ortho-hydrogen and that performance is significantly impacted by the cation type and the number of cations present in the zeolite. For the present separation improved performance was obtained with larger Group I cations, especially K and Cs. Another key property of the adsorbents addressed in the present work is the need to control the adsorbent composition to avoid unwanted catalytic conversion of the para- to ortho-hydrogen. A common source of unwanted catalytic activity in many adsorbent compositions was identified as the presence of unwanted transition metal impurities, especially iron associated with the natural clays, commonly employed as binding agents in the commercial agglomerated zeolite products. To avoid this, equivalent adsorbent compositions were agglomerated instead using colloidal silica binding agents which successfully minimize back conversion of the para- to ortho-hydrogen and produced adsorbents with higher capacities and selectivities for the ortho component at the test temperature of 77 K. These advanced adsorbents can be applied in more efficient hydrogen liquefaction processes.     

Metal organic frameworks as advanced extraction adsorbents for separation and analysis in proteomics and environmental research

Science China Chemistry - Human health is always under global spotlight, but now it suffers from severe environmental issue and various diseases. Developing highly selective and effective...     

Propylene epoxidation in the gas-phase oxidation of propane-propylene mixtures

Studies of propylene epoxidation in the gas-phase oxidation of propane-propylene mixtures at 633 K under static conditions indicate that epoxidation occurs by the reaction: C₃H₆+RO₂C₃H₆O+RO, with a rate constant of k=(1.7±0.2)×10⁷ cm³ mol^–1 s^–1.

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- T=633 . , C₃H₆+RO₂C₃H₆O+RO, =(1,7±0,2)×10^{7 3 –1 –1}.

     

New classes of selective separations exploiting magnetic adsorbents

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New extraction chromatographic material for rhenium separation

AbstractThree types of the extraction chromatographic materials, composed from Aliquat® 336 deposited in the polyacrylonitrile (PAN) beads and prepared by different procedures, were compared for extraction of rhenium. The best properties were exhibited when the solid extractant was prepared by impregnation of the ready-made PAN beads. Solid extractant prepared by direct coagulation of the beads from the suspension of Aliquat® 336 in solution of PAN in nitric acid differs only by lower capacity in dynamic conditions. Material prepared from the PAN solution in dimethylsulfoxide was the worst because Aliquat® 336 was washed out from the beads during coagulation of the polymer and the extraction capacity was low. As it is shown, the first two solid extractants are fully comparable with the commercial TEVA Resin.     

Adsorbent filled membranes for gas separation. Part 1. Improvement of the gas separation properties of polymeric membranes by incorporation of microporous adsorbents

The effect of the introduction of specific adsorbents on the gas separation properties of polymeric membranes has been studied. For this purpose both carbon molecular sieves and zeolites are considered. The results show that zeolites such as silicate-1, 13X and KY improve to a large extent the separation properties of poorly selective rubbery polymers towards a mixture of carbon dioxide/methane. Some of the filled rubbery polymers achieve intrinsic separation properties comparable to cellulose acetate, polysulfone or polyethersulfone. However, zeolite 5A leads to a decrease in permeability and an unchanged selectivity. This is due to the impermeable character of these particles, i.e. carbon dioxide molecules cannot diffuse through the porous structure under the conditions applied. Using silicate-1 also results in an improvement of the oxygen/nitrogen separation properties which is mainly due to a kinetic effect. Carbon molecular sieves do not improve the separation performances or only to a very small extent. This is caused by a mainly dead-end (not interconnected) porous structure which is inherent to their manufacturing process.