Korekazu Ueyama

Synthesis of ordered mesoporous carbons with channel structure from an organic–organic nanocomposite

Mesoporous carbons with ordered channel structure (COU-1) have been successfully fabricated via a direct carbonization of an organic-organic nanocomposite.

Synthesis of defect-free zeolite-alumina composite membranes by a vapor-phase transport method

Abstract The value of pH for gel preparation has a significant influence on the compactness of a dry gel. A compact gel was prepared at high pH of ca. 12. An amorphous dry gel on a porous alumina support was crystallized by a vapor-phase transport (VPT) method. Membranes of low silica zeolites, analcime (ANA) and mordenite (MOR), were formed because alumina was partly dissolved and incorporated into the framework of zeolite. Coating of the alumina support with colloidal silica depressed the dissolution of alumina. On the alumina support coated with colloidal silica, ferrierite (FER) and ZSM-5 (MFI) membranes were obtained. Compactness of the MOR membrane was examined by a permeation test of 1,3,5-triisopropylbenzene (TIPB) at room temperature. Since no permeation of TIPB was detected, it was concluded that there existed no pinholes and cracks in the MOR membrane. The pervaporation test of a benzene/ p -xylene mixture of which the molar ratio was 0.860, was carriee out. The separation factor ((benzene/ p -xylene)permeate/(benzene/ p -xylene)feed) exceeded 160. Thus some shape selectivity appeared at the pore mouths of MOR. The formation process of the MOR membrane was studied by using SEM and XRD. The gel which penetrated in the alumina pores crystallized to MOR and formed a defect-free MOR-alumina composite layer.

Synthesis of zeolites under vapor atmosphere: Effect of synthetic conditions on zeolite structure

Abstract The present study found that aluminosilicate gels were crystallized to ZSM-5, ferrierite, KZ-2 or analcime under a vapor atmosphere. The structure and crystallinity of the resultant zeolite significantly depended on the composition of the organic vapor as well as that of the parent gel.

Crystallization of high silica BEA by dry gel conversion

Abstract Zeolite with BEA structure was prepared using a new crystallization method called ‘Dry Gel Conversion Technique’. This dry gel conversion technique is a convenient method to prepare zeolites and enables one to synthesize zeolite BEA with SiO2/Al2O3 ratios from 30 to infinity using tetraethylammonium hydroxide (TEAOH) as a structure directing agent. Zeolite BEA with SiO2/Al2O3 ratios from 30 to 730 were rapidly crystallized in 3 and 12 h, respectively. The 27Al NMR spectrum for BEA with SiO2/Al2O3 ratio of 30 confirmed the absence of octahedrally coordinated aluminum. The crystallization rates were higher for BEA with low SiO2/Al2O3 ratios than for those with high SiO2/Al2O3 ratios. BEA crystallized by this method had uniform particles of about 60 nm. Higher Na+ ion concentrations in the gel promoted the formation of high silica BEA. Elimination of occluded TEA cations took place at lower temperatures (around 623 K) in high silica BEA than that in BEA with low SiO2/Al2O3 ratios (around 900 K). This method also allowed to synthesize BEA in the form of self-bonded pellets.

Synthesis of BEA by dry gel conversion and its characterization

Abstract Zeolite BEA with SiO2/Al2O3 ratios ranging from 30 to 740 were crystallized at 413 and 453 K by the dry gel conversion technique. The particle size of the products increased with increasing SiO2/Al2O3 ratio as well as with increasing crystallization temperature. In as-synthesized BEA, the TEA+ ions interacting with Si-O− decomposed between 473 and 673 K and those interacting with Al-O− were cleaved between 673 and 798 K. During their elimination, the TEA+ ions interacting with Al-O− underwent higher degradation than those interacting with Si-O−. Chemical compositions showed the least influence on the fractions of decomposition product during the elimination between 473 and 673 K. The framework of H-BEA and NH4-BEA zeolites with SiO2/Al2O3 ratios ranging from 400 to 740 were stable even at 1373 K, whereas H-BEA with SiO2/Al2O3 = 30 was stable only up to 1173 K and became amorphous when calcined at 1373 K. After calcination at 1373 K, Na-BEA with SiO2/Al2O3 = 400 and 730 were transformed to tridymite (dense phase) whereas that with SiO2/Al2O3 = 30 became amorphous. The elimination of Na+ ions is necessary to have a BEA remain stable above 1173 K.

Crystallization of FER and MFI zeolites by a vapor-phase transport method

Abstract Dry aluminosilicate gels were crystallized to MFI and FER by a vapor-phase transport (VPT) method using ethylenediamine (EDA), triethylamine (Et3N) and water as vapor sources. The roles of water and amines in this crystallization were investigated. While Et3N and water encouraged crystallization, EDA acted as a structure-directing agent. A dry gel was crystallized to FER when no water was added. The 27Al and the 29SiNMR spectra indicated that all Al atoms were incorporated into the zeolitic framework in the early stage of crystallization and that the rest of the Si-rich phase gradually crystallized. Full crystallization of Si and Al atoms in dry gel was possible by selecting optimum synthetic conditions. FER was transformed to MFI with prolonged crystallization. The structure and crystallinity of zeolite significantly depended on the sort of support on which the dry gel was placed.

FER membrane synthesized by a vapor-phase transport method: Its structure and separation characteristics

Abstract The mechanism of formation of ferrierite (FER) membrane on an alumina support by a vapor-phase transport (VPT) method was studied using XRD, SEM, FE-SEM and EDX. The XRD measurement for a FER membrane after the removal of FER particles formed on the support showed that FER was formed in the pores of the alumina support, namely, a FER-alumina composite layer was formed. The FE-SEM image for the cross-sectional view of the FER-alumina composite layer showed that FER nanocrystals of about 50 nm diameter grew in the pores of the alumina support. Pervaporation tests for benzene/p-xylene mixtures were performed at 303 K. Even when the concentration of benzene in the feed solution was extremely small (0.5 mol%), the flux of benzene through the FER membrane was still greater than that of p-xylene. Therefore, a separation factor as high as 600 was obtained in the low feed concentration of benzene. Such a high selectivity for the benzene/p-xylene mixture suggested that the selectivity for the benzene/p-xylene mixture appears at the pore mouths of FER on the feed side of the FER-alumina composite layer.

Simultaneous chlorination and sulphation of calcined limestone

In order to analyze HCl and SO2 retention in fluidized bed combustors of coal and wastes, chlorination and sulphation of calcined limestone were investigated at 1023 K and atmospheric pressure using thermogravimetry. The rate of chlorination of calcined limestone slightly depended on its particle size and was kept almost constant against the progress of chlorination. In contrast, the rate of sulphation increased with decreasing particle size and steeply decreased with the progress of sulphation as commonly reported. It was found that the sulphation was markedly accelerated in the presence of HCl. Such acceleration of sulphation was remarkable for larger limestone. The level of conversion of CaO to (CaSO4 + CaCl2) always approached 100% in the simultaneous absorption of HCl and SO2. It was observed by SEM that in the chlorination a number of spherical aggregates and large voids were formed on the surface of limestone and that large aggregates with very flat surface and large voids have been formed in the course of the simultaneous chlorination and sulphation. These chlorination behavior and the acceleration of SO2 absorption in the presence of HCl can be due both to the formation of a mobile Cl− ion-containing phase and to the formation of voids playing a role of the diffusion paths for HCl and SO2 toward the interior of a limestone particle. Melting of a eutectic mixture of CaCl2 and CaSO4 might largely contribute to the promotion of SO2 absorption in the case of simultaneous absorption of HCl and SO2.

Preparation of a thin zeolitic membrane

The synthesis method to obtain a tight and thin zeolitic membrane was investigated. It was found that the most important factor to prepare a zeolitic membrane in a compact form was the pH to prepare the parent aluminosilicate gel. The aluminosilicate gel was supported on a porous alumina plate and treated in the vapor of templating reagents. It was found that a thin layer of ferrierite was formed on the surface of the plate. The rates of permeation of H 2 , He, CH 4 , O 2 , N 2 and CO 2 through the ferrierite membrane were measured. Permeation results indicated that the ferrierite membrane is formed in a compact form.

A DEFECT-FREE MORDENITE MEMBRANE SYNTHESIZED BY VAPOUR-PHASE TRANSPORT METHOD

A defect-free MOR membrane is synthesized on a porous alumina plate by a vapour phase transport method: shape selectivity is apparent in the pervaporation of a benzene–p-xylene mixture (the separation factor exceeded 160).