Mikihiro Nomura

Alkali-treatment technique — new method for modification of structural and acid-catalytic properties of ZSM-5 zeolites

Abstract ZSM-5 zeolite having a SiO2/Al2O3 molar ratio of 39.4 was treated in a NaOH alkali solution and the changes in structural and acidic properties were investigated. A siliceous species was selectively dissolved from the framework of zeolite, although a lower amount of Al was also eluted. In this procedure, mesopores with a uniform size were formed on the zeolite, while the microporous structure remained. The acidic property was changed very little quantitatively or qualitatively, even though the catalytic activity for cracking of cumene was enhanced by the alkali-treatment. This can be explained by the facts that adsorptive and diffusive properties of cumene through micropores of the ZSM-5 are increased by the creation of mesopores.

Conversion of dry gel to microporous crystals in gas phase

Recently the dry gel conversion (DGC) technique, where a hydrogel is dried and the resultant dry gel is converted into microporous crystals in steam or in a mixed vapor of steam and organic structure-directing agents (SDAs), has been developed. It has been shown that a wide variety of microporous crystals, pure silica microporous crystals, aluminosilicates, metallosilicates, and aluminophosphates, can be synthesized using the DGC method. Remarkable results have been reported in the synthesis of BEA types zeolites, namely aluminosilicate, titaniumsilicate, zincosilicate, and borosilicate with BEA topology, using tetraethylammonium hydroxide, a commercially available SDA. It has also been found that zeolite OU-1, probably analogous to SSZ-31 and NCL-1, is formed via phase transformation from BEA. Dense zeolite coatings like membranes are possible using this method. Characteristics of the DGC method are discussed in detail.

Ethanol/water transport through silicalite membranes

Transport mechanism of ethanol/water mixtures by pervaporation and vapor permeation through silicalite membrane was investigated. The activities of both ethanol and water in feed were controlled independently by vapor permeation to study the feed composition effects quantitatively. Also, adsorption experiments of single component and binary mixtures were carried out to measure the adsorbed mixture composition in the silicalite membrane. Ethanol permeance was independent of water concentration in feed. Water permeance, however, seriously decreased by the presence of ethanol in feed, and water permeation was restricted by ethanol. The adsorption–diffusion model was considered for the transport mechanism through the silicalite membrane. Ethanol selectively adsorbed to silicalite membrane from ethanol/water vapor. The diffusion coefficients of water and ethanol were calculated based on the adsorption–diffusion model, and the results showed almost the same diffusivity between the single component and mixture feed case. Thus, high ethanol selective permeation through the silicalite membrane was explained by the ethanol selective adsorption to the silicalite membrane.

Selective ethanol extraction from fermentation broth using a silicalite membrane

Abstract The selective extraction of ethanol from ethanol fermentation broth through a silicalite zeolite membrane was investigated. Ethanol (98.2 wt.%) at permeate side which is above the azeotropic composition, was continuously obtained from the fermentation broth having a 20 wt.% ethanol concentration. The separation factor of ethanol over water was 218, which is higher than that from water–ethanol mixtures. This high ethanol selectivity was due to the salts that are contained in fermentation broth. The high ethanol selectivity was maintained for 48 h.

Transport phenomena through intercrystalline and intracrystalline pathways of silicalite zeolite membranes

Abstract Zeolite membranes are, generally, polycrystalline structures. Penetrant molecules pass through zeolite crystals (intracrystalline pathways) and intercrystalline pathways. The transport phenomena of ethanol through intracrystalline and intercrystalline pathways of silicalite membranes were separately examined. An intercrystalline–intracrystalline model (i–i model) is proposed for quantitative discussion of fluxes through intercrystalline and intracrystalline pathways. The concentration in the interface of the intracrystalline region is of the Langmuir type, and the concentration in the intercrystalline region is proportional to the activity on the outside of the membrane. This i–i model was investigated using silicalite membranes and silicalite membranes modified by chemical vapor deposition (CVD). CVD modification was carried out using a tetramethylorthosilicate (TMOS)/O3 counter-diffusion CVD technique. The i–i model can quantitatively explain the permeate properties of ethanol transport both through the silicalite membrane and the CVD modified membrane. According to this model, ethanol is permselective from ethanol/water mixtures through intercrystalline pathways.

Effects of preparation method on oxygen permeation properties of SrFeCo0.5Ox membrane

It was investigated that the effects of preparation methods and conditions for SrFeCo 0.5 O x dense membrane on their oxygen permeability. Three different methods, a solid-state reaction method, an evaporation-to-dryness method, and a combined citrate and EDTA complexing method, were applied for the preparation of parent powder. The oxygen flux through membrane at 900°C was increased in the order listed above. The oxygen flux could be greatly improved by repeated calcination and grinding of parent powder. The membrane sintered at a temperature as high as 1200°C showed a higher oxygen flux (0.22 cm 3 (STP)/cm 2 .min).

Preparation of thin porous titania films on stainless steel substrates for heat exchange (HEX) reactors

A porous titania film with pores of few micrometer sizes was prepared on a stainless steel support for a composite material of metal and inorganic oxide. The combination of a porous catalyst layer and a metal support improves the thermal conductivity compared with a traditional inorganic powder catalyst by an aid of a metal support. A porous titania film was obtained on a stainless steel support by the electrostatic sol-spray deposition (ESSD) method. Water in the parent sol was a key factor to obtain porous films. These porous films were cracked by a rapid temperature change during the cooling procedure after the deposition by the difference of the thermal expansion rate of stainless steel and titania. The parent sol was aged before a deposition to obtain a flexible structure to keep its structure. The obtained porous films comprised an aggregation of fibrous titania with few micrometer pores by SEM observation. This film was stable for a rapid temperature change. A porous titania film without any cracks were obtained on a stainless steel substrate using the ESSD method by an aging of the parent sol.

Development of an all-ceramic module with silica membrane tubes for high temperature hydrogen separation

Abstract Heat resistant hydrogen selective membranes are desired for use as membrane reactors in low-temperature hydrogen production via the steam reforming of hydrocarbons, which are usually operated over 1000 K. In addition, developing a multi-tubular type of membrane unit that can process more reactants is becoming more and more important in order to realize the practical use of membrane reactors. In this study, an all-ceramic module consisting of 6 silica membrane tubes with a comparatively large membrane area of around 0.04 m2 was fabricated by a counter-diffusion chemical vapor deposition technique. As a result, the H2/N2 ideal separation factor and the H2 permeance of the module were 1300 and 1.9 × 10−7 mol·m−2s−1Pa−1 at 873 K, respectively. In a 1000-hour thermal stability test for the silica membrane module, it was found that the H2 permeance initially decreased by about 30% and then became steady under ΔP = 0.95 MPa at 773 K.