• Korean Chemical Engineering Research
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• v.43 no.6
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• pp.691-695
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• 2005

Zeolite membranes on various supports such as filter paper, cotton fiber, and glass fiber filter were prepared by secondary growth hydrothermal synthesis. First, zeolite NaA (${\approx}0.5{\mu}m$) and silicalite-1 (${\approx}0.2{\mu}m$) crystals were synthesized as zeolite seed crystals, and they were attached to the surfaces of the supports via chemical bonding. Zeolite NaA or silicalite-1 membranes could be synthesized on the supports coated with the seed crystals. The prepared zeolite membranes were observed by scanning electron microscope and analyzed by X-ray diffraction.

• Korean Chemical Engineering Research
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• v.44 no.3
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• pp.243-247
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• 2006

MFI zeolite membranes were prepared on anodic alumina (Anodisc) as support. First, silicalite-1(${\approx}1.2{\mu}m$) seed crystals were attached to the surface of the support via chemical bonding, and the a- and b-axis oriented zeolite membranes could be synthesized on the support coated with the monolayer of the seed crystals by secondary growth hydrothermal synthesis. The zeolite membranes prepared were characterized using scanning electron microscope and analyzed by X-ray diffraction.

• Bulletin of the Korean Chemical Society
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• v.32 no.5
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• pp.1443-1454
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• 2011

Methods to prepare novel second-order nonlinear optical (2O-NLO) materials composed of all-silica zeolite (silicalite-1) and a series of 2O-NLO molecules having high second order hyperpolarizability constants (${\beta}$ values) are reviewed. These methods include the development of novel methods to incorporate a series of hemicyanine (HC) molecules into the channels of silicaite-1 films in uniform orientations. The first method is to incorporate HC molecules tethered with long alkyl chains (octadecyl or longer) into the silicalite-1 channels with the long alkyl chain side first through the hydrophobic-hydrophobic interaction between the long alky chains and the silicalite-1 channels. The second method is to incorporate the HC molecule tethered with a medium length alkyl chain (nonyl) into the silicalite-1 channels with the medium length alkyl chain side first through hydrophobic-hydrophobic interaction between the medium length alky chain in the photoexcited state and the silicalite-1 channels. The third method is to incorporate the HC molecule tethered with propionic acid into the silicalite-1 channels with the propionic acid side last mediated by a tetrabultylammonium cation ion-paired to the propionate unit. A method to prepare a novel third-order nonlinear optical (3O-NLO) material composed of zeolite-Y and PbS or PbSe quantum dots is also reviewed. This Account thus describes a promising new direction to which the search for highly sensitive 2O-NLO and 3O-NLO materials has to be conducted and a new direction to which zeolite research and applications have to be expanded.

• Membrane Journal
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• v.13 no.4
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• pp.229-238
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• 2003

Pervaporation is mainly used to separate liquid mixtures because it exhibits a high selectivity compared with traditional distillation processes and it is known to be an energy saying separation process. Zeolite membranes show better thermal. mechanical, chemical stability than polymer membranes and especially silicalite-1 membrane can effectively separate organic compounds from water because of its high hydrophobicity. In this study, volatile organic compounds of ketone are separated by pervaporation using silicalite-1 membrane. As a feed concentration of acetone and MEK increases, a permeation flux of acetone and MEK increases while a selectivity decreases.

• Korean Chemical Engineering Research
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• v.49 no.6
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• pp.816-822
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• 2011

Pervaporation is known to be a low energy consumption process since it needs only an electric power to maintain the permeate side in vacuum. Also, the pervaporation is an environmentally clean technology because it does not use the third material such as an entrainer for either an azeotropic distillation or an extractive distillation. In this study, Silicalite-1 particles are hydrothermally synthesized and polydimethylsiloxane(PDMS)-zeolite composite membranes are prepared with a mixture of synthesized Silicalite-1 particles and PDMS-polymer. They are used to separate n-butanol from its aqueous solution. Pervaporation characteristics such as a permeation flux and a separation factor are investigated as a function of the feed concentration and the weight % of Silicalite-1 particles in the membrane. A 1,000 $cm^3$ aqueous solution containing butanol of low mole fraction such as order of 0.001 was used as a feed to the membrane cell while the pressure of the permeation side was kept about 0.2~0.3 torr. When the butanol concentration in the feed solution was 0.015 mole fraction, the flux of n-butanol significantly increased from 14.5 g/ $m^2$/hr to 186.3 g/$m^2$/hr as the Silicalite-1 content increased from 0 wt% to 10 wt%, indicating that the Silicalite-1 molecular sieve improved the membrane permselectivity from 4.8 to 11.8 due to its unique crystalline microporous structure and its strong hydrophobicity. Consequently, the concentration of n-butanol in the permeate substantially increased from 0.07 to 0.15 mole fraction. This composite membrane could be potentially appliable for separation of n-butanol from insitu fermentation broth where n-butanol is produced at a fairly low concentration of 0.015 mole fraction.

• Applied Chemistry for Engineering
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• v.2 no.2
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• pp.97-107
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• 1991

Highly-siliceous dealuminated zeolite, silicalite(end member of ZSM-5) was synthesized from a batch composition of 2.55 $Na_2O-5.0$ TPABr-$100SiO_2-2800H_2O $ at $180^{\circ}C$ and at times ranging from one to seven days of reaction time. Autoclaves containing the synthesis mixture were centrifuged within the specially-equipped convection oven to provide an elevated gravitational force field like 30 and 50 G. Tests were also conducted at normal gravity. For synthesis performed under elevated gravities, average and maximum crystal sizes were substantially greater than those synthesized under normal gravity and product yields were also found to be affected by elevated gravity ; that is, product yields were substantially enhanced under elevated gravity from 4 % to 55 % with respect to normal gravity. The average crystal sizes of silicalite synthesized at normal gravity were 50 to $70{\mu}m$ over an entire range of reaction time, one to seven days while the average crystal sizes synthsized under elevated gravities, 30 and 50 G, were 160 to $190{\mu}m$ respectively. For the elevated gravity, in particular, two separate nucleations and growths were observed. For examples, at 50G, large crystals of $200{\mu}m$ were produced through the second growing stage after 5 days of reaction following the rapid first growing stage where fairly large crystals of $135{\mu}m$ were produced only in 2 days of reaction. The maximum crystal sizes obtained through the above two growing stages were 190 and $300{\mu}m$, respectively. A discussion of how elevated gravity affects nucleation, growth, yield and crystal size of silicalite is presented.

• Membrane Journal
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• v.25 no.5
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• pp.422-430
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• 2015

The present study announces that the pH value of seed coating solution makes a significant effect on the microstructure of silicalite-1 zeolite layer formed on ${\alpha}$-alumina support. Seed with an average diameter of 75 nm was dispersed in ethanol to prepare three kinds of seed coating solutions with different pH values, and dip-coated on the support. The pH value was controlled to be 2.2, 7.0, and 9.3, respectively. In the secondary growth process, pH 7 seed solution resulted an uniform, 3 to $4{\mu}m$ thick, completely covered, and 100 nm grained silicalite-1 zeolite separation layer. The uniformity and completeness were explained by a uniform, closely packed, multi-layered, and completely covered seed coating in the pH 7 condition. In the condition, ${\alpha}$-alumina support and seed are oppositely charged: support is positively charged (8.4 mV) and seed, negatively (-1.7 mV). The opposite charging induced a strong electrostatic attraction between seed and support, which made the good seed coating state. On the other hand, pH 2.2 and pH 9.3 seed solutions resulted non-uniform, partially covered, and around $1{\mu}m$ grained zeolite separation layer, since seed and support are the same sign charged in the conditions. The same sign charging induced a strong electrostatic repulsion between seed and support which caused a low coverage of seed. It could be concluded that the pH value of seed coating solution is a key parameter to determine the microstructure of silicalite-1 zeolite separation layer.

• Applied Chemistry for Engineering
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• v.25 no.3
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• pp.286-291
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• 2014

In this study, nanosized TPA-silicalite-1 was synthesized with a suitable molar composition of TPAOH: $SiO_2$: $H_2O$ for the development of zeolite ceramic membranes to utilize as gas separation. As silica sources, TEOS, LUDOX AS-40 and CAB-O-SIL were used with the starting material of TPAOH. $NaH_2PO_4$, and a variety of acids and bases were used as promoters after TPAOH, $SiO_2$, $H_2O$ gel synthesis. To decrease synthesis time, a two step temperature change method was applied to the synthesis of TPA-silicalite-1 at a low temperature. TPA-silicalite-1 synthesized was analyzed with XRD, SEM, BET and TGA. As a result, TPA-silicalite-1 powders with a particle size of 100 nm and a specific surface area of $416m^2/g$ were obtained as optimum synthesis conditions when the two stage temperature change method was used with $NaH_2PO_4$ as promoter.

• Korean Chemical Engineering Research
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• v.51 no.4
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• pp.476-481
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• 2013

Ethylbenzene (EB) which has a similar physical properties with p-xylene (pX) was separated from EB/pX mixture by using MFI-type zeolite (TS-1, ZSM-5, and Silicalite-1) coated membranes. The zeolites were synthesized by microwave method to reduce the synthesis time and uniformly formed zeolite particles were coated on the ${\alpha}$-almina tubular support with a thickness of $3-4{\mu}m$. Separation factor and permeation flux of the synthesized zeolite coated membranes were measured to survey the best performance of ethylbenzene separation from different composition of EB/pX mixtures. When the EB/pX mixture of 5:5 molar ratio applied for the separation experiment, it represented the highest separation factor. We also have studied about the effect of the atomic composition of zeolites on the separation performance within the temperature range from 160 to $220^{\circ}C$. TS-1 showed the highest permeation flux of $1,666mol/m^{2*}s^*Pa$ and Silicate-1 showed the highest separation factor of 1.73 at $200^{\circ}C$ respectively.

• Journal of the Korean Ceramic Society
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• v.33 no.9
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• pp.1064-1072
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• 1996

The synthetic conditions and characteristics of ZSM-5 type zeolites (ZSM-5/silicalite) for the preparation of the zeolite composite membranes for gas separation were investigated. ZSM-5 zeolites could be synthesized by the hydrothermal treatment of the mixture of colloidal silica sol aluminum nitrate sodium hydroxide and TPABr at a temperature range of 150-17$0^{\circ}C$ in the autoclave. Silicalties were done from the solution of water glass water and TPABr. Their crystalline structures transformed from orthorhombic to monoclinic from and their pore structures of three-dimensional channels were opened as TPABr filling channels was burned off at the calcination temperature of 50$0^{\circ}C$. The specific surface area of the calcined zeolite was about 360 m3/g and its surface property was hydrophobic. Crystal sizes of ZSM-5 and silicalite were 0.5-1.0${\mu}{\textrm}{m}$ and 8-10${\mu}{\textrm}{m}$ respectively having no change due to the calcination. In particular the shape and the size of the ZSM-5 type zeolite were sensitively varied with silica sources and concentrations of reaction solutions/sols.