We report the structural evolution of zeolitic imidazolate framework-8 (ZIF-8) as a function of time at room temperature. We have identified the different stages of ZIF-8 formation (nucleation, crystallization, growth, and stationary periods) and elucidated its kinetics of transformation. We hypothesize that the observed semicrystalline-to-crystalline transformation may take place via solution- and solid-mediated mechanisms, as suggested by the observed phase transformation evolution and Avrami's kinetics, respectively. A fundamental understanding of ZIF-8 structural evolution as demonstrated in this study should facilitate the preparation of functional metal-organic framework phases with controlled crystal size and extent of crystallinity.

ZIF-8 membranes, a type of zeolite imidazolate framework, were synthesized by secondary seeded growth on tubular alpha-Al(2)O(3) porous supports. The presence of small, highly crystalline, microporous crystals with narrow particle size distribution led to continuous thin membranes. The synthesized novel ZIF-8 membranes displayed unprecedented high CO(2) permeances and relatively high separation indexes for equimolar mixtures of CO(2) and CH(4).

The catalytic activity of zeolitic imidazole framework-8 (ZIF-8) and amine-functionalized ZIF-8 catalysts in the synthesis of chloropropene carbonate from CO2 and epichlorohydrin is demonstrated. In contrast to hitherto known catalysts, ZIF-8 catalysts displayed high epoxide conversions and moderate to high selectivities to chloropropene carbonate at reaction temperatures as low as 70 °C. No cocatalysts or solvents were required during the reaction. The incorporation of ethylenediamine in ZIF-8 enhanced its catalytic performance as a result of the higher CO2 adsorption capacity of the amine-functionalized samples. The ZIF-8 catalysts, however, lost their distinctive crystalline structure and superior catalytic performance when attempts were made to recycle them after use.

SAPO-34 membranes were prepared by in situ crystallization on alpha-Al2O3 porous supports. The crystal size of the seeds was effectively controlled in the 0.7 to 8.5 micron range by employing different structure-directing agents. Seeds smaller than 1 micron produced membranes with CO2/CH4 separation selectivities higher than 170 and unprecedented CO2 permeances as high as 2.0 x 10(-6) mol/m2.s.Pa at 295 K and a feed pressure of 224 kPa. The membranes effectively separated CO2/CH4 mixtures up to 1.7 MPa.

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Herein we demonstrate that chabazite zeolite SAPO-34 membranes effectively separated Kr/Xe gas mixtures at industrially relevant compositions. Control over membrane thickness and average crystal size led to industrial range permeances and high separation selectivities. Specifically, SAPO-34 membranes can separate Kr/Xe mixtures with Kr permeances as high as 1.2 × 10 (-7) mol/m(2) s Pa and separation selectivities of 35 for molar compositions close to typical concentrations of these two gases in air. In addition, SAPO-34 membranes separated Kr/Xe mixtures with Kr permeances as high as 1.2 × 10 (-7) mol/m(2) s Pa and separation selectivities up to 45 for molar compositions as might be encountered in nuclear reprocessing technologies. Molecular sieving and differences in diffusivities were identified as the dominant separation mechanisms.

Carbon dioxide is a significant impurity in many natural gas wells, with CO 2 concentrations as high as 70 %. The CO 2 must be removed in order to utilize the natural gas; CO 2 reduces the energy content of the gas, and it is acidic and corrosive in the presence of water. Ideally, the CO 2 should be removed while maintaining the natural gas at high pressure to save on recompression costs. Moreover, removing CO 2 without large energy expenditures is also desirable, and thus membranes that preferentially permeate CO 2 with high selectivities can significantly impact utilization of these gas wells by reducing the costs of natural gas purification.[1] Carbon dioxide is also an impurity in hydrogen synthesized by steam reforming of hydrocarbons, and separating CO 2 from H 2 by a membrane could be an energy-efficient approach. Polymeric membranes can separate CO 2 /CH 4 mixtures, but the high CO 2 pressures can plasticize them and decrease their separation ability.[2] A recent study by Lin et al., [3] however, reported that CO 2 pressures up to at least 1.7 MPa increased permeabilities and selectivities for highly-branched, cross-linked poly(ethylene oxide) membranes. Since natural gas wells can be at 7 MPa and higher pressures, membranes that are not changed by CO 2 at these pressures are desired. Zeolite membranes [4][5][6][7][8][9][10][11] potentially have significant advantages over polymeric membranes. These membranes, which were prepared with TEAOH (tetraethyl ammonium hydroxide) as the structure-directing agent, [13] were selective and stable in the presence of H 2 O, N 2 , C 2 H 4 , C 3 H 8 , and n-C 4 H 10 impurities.[8] Adsorption isotherms showed that CO 2 adsorbs more strongly than CH 4 on SAPO-34 crystals, and thus preferential adsorption accounts in part for the high selectivities.[9] Although these results are promising, higher permeances are desired in order to reduce the number of membrane tubes required and thus reduce the cost. The morphology and size of the zeolite crystals that comprise polycrystalline membranes affect the non-zeolite pathways, which decrease selectivity, and thicker membranes are often needed in order to minimize transport through these non-zeolitic pathways. The correlation between microstructure and perfomance has been demonstrated for separations of n-hexane/dimethylbutane, n/i-butane, and p/o-xylene mixtures. [14] In this study, SAPO-34 membranes were prepared by seeding SAPO-34 crystals on porous stainless steel supports. By using combinations of structure directing agents (SDAs) for both seed and membrane preparation, membranes with higher fluxes and high selectivities were prepared. Tetraethylammonium hydroxide (TEAOH) was used as the main SDA, and dipropylamine (DPA) and cyclohexylamine (CHA) were used as secondary SDAs. A recent patent showed that adding small amine molecules can help crystallize silicoaluminophosphates. [15] In the current study, SAPO-34 crystals were formed with multiple SDAs and these crystals were then used as seeds to synthesize the membranes. The co...