Tsuneji Sano

Separation of acetic acid-water mixtures by pervaporation through silicalite membrane

Polycrystalline silicalite membranes were prepared on two kinds of porous supports by hydrothermal synthesis. The pervaporation performance of the silicalite membrane obtained was investigated using an acetic acid-water mixture as a feed. The silicalite membrane on the sintered stainless steel support selectively permeates acetic acid in the concentration of the feed acetic acid in the region of 5 to 40 vol%. However, the membrane on the porous alumina support showed no separation for the aqueous acetic acid solution. From the fact that the top layer of the membrane on the alumina support was not composed of pure silicalite but ZSM-5 zeolite crystals, which contained Bronsted acidic sites (Si(OH)Al) in the framework, it was suggested that the acidic sites associated with the framework aluminums play an important role in the separation of the acetic acid-water mixture. A long-term test of the pervaporation was also carried out to clarify the stability of the membrane.

Preparation and characterization of ZSM-5 zeolite film

The ZSM-5 zeolite film was prepared from a clear aqueous solution of a synthesis mixture with high H2O/SiO2. The large differences in morphology and SiO2/Al2O3 ratio between outer and inner sides of the films were observed.

Mesoporous materials prepared using coal fly ash as the silicon and aluminium source

Coal fly ash was converted into two types of porous materials, MCM-41 and SBA-15 (both of hexagonal structure), using the supernatant of the fly ash. It was found that most of the Si and Al components in the fly ash could be effectively transformed into mesoporous materials, depending on the hydrothermal conditions, and that fusion is essential. Investigation by 29Si and 27Al MAS NMR demonstrated that fusion plays an important role in enhancing the hydrothermal conditions for synthesis of these materials. A high concentration of Na ions in the supernatant of the fused fly ash was not found to be critical in the formation of Al-MCM-41 when prepared under controlled pH conditions. Pyridine adsorption experiments on Al-MCM-41 prepared from coal fly ash revealed the presence of Bronsted and Lewis acid sites. It was also found that the catalytic activity in the cumene cracking reaction is linked only to the accessible aluminium, and not to the total incorporated aluminium present in the Al-MCM-41.

Separation of methanolrmmethyl-tert-butyl ether mixture by pervaporation using silicalite membrane

The polycrystalline silicalite membrane was prepared on a porous sintered stainless steel support and its pervaporation performance was investigated using a MeOH/MTBE mixture as a feed. It was found that the MeOH selectivity of pervaporation is considerably higher than that of distillation. This indicates that the silicalite membrane permeates methanol preferentially. From the results of the competitive adsorption experiments and the temperature dependence of permeation rates of MeOH and MTBE, it was suggested that the selective sorption of MeOH into the membrane takes place and that the transportation of MTBE within the membrane is strongly suppressed as compared with that of MeOH.

Potentials of silicalite membranes for the separation of alcohol/water mixtures

Polycrystalline silicalite membranes were prepared on porous sintered stainless steel and alumina supports. The liquid separation potential of the membrane was investigated using various alcohol/water mixtures by pervaporation. The silicalite membrane showed a high alcohol permselectivity. Adsorption experiments of water and alcohols suggest that the high alcohol permselectivity is attributable to the selective sorption of alcohol into the silicalite membrane.

Characterization of AlSBA-15 prepared by post-synthesisalumination with trimethylaluminium

The mesoporous siliceous SBA-15 molecular sieve was synthesized and post-synthesis alumination was carried out using trimethylaluminium (TMA). It was found that the aluminium could be easily incorporated into the siliceous framework of SBA-15 without serious structure deformation. From detailed characterization of the prepared aluminium-containing SBA-15 (AlSBA-15) it was also found that it is difficult to keep the aluminium in the framework position after calcination. The hydrothermal stability of SBA-15 was considerably improved by the TMA processing. The results of the cumene cracking reactions and the pyridine adsorption experiments indicated that the Bronsted acid sites of AlSBA-15 are stronger than those of AlMCM-41 prepared by the same method.

Production of highly concentrated ethanol in a coupled fermentation/pervaporation process using silicalite membranes

The fermentation performance of a coupled fermentation/pervaporation process using silicalite membranes, which are ethanol permselective for an ethanol/water solution, was studied. The process exhibited about a 20% increase in an average glucose consumption rate as compared with that without the pervaporation unit. A strong correlation was observed between the membrane flux and the consumption rate. Ethanol concentrations in the permeates reached a maximum of 85% (v/v).

Concentration of fermented ethanol by pervaporation using silicalite membranes coated with silicone rubber

In order to stabilize the production of highly concentrated ethanol, a coupled fermentation/pervaporation process using ethanol permselective silicalite membranes coated with silicone rubber was studied. In case of the silicalite membrane without coating, the membrane flux and the ethanol concentration in the permeate decreased with the fermentation time. The completely recovered ethanol fermentation was 30% (w/w). This behavior partly resulted from the adsorption of succinic acid produced during the fermentation to the membrane. It was effective to coat a naked silicalite membrane with the silicone rubber in the production of concentrated fermented ethanol of constant concentration by pervaporation. During the fermentation, the ethanol concentration in the permeate was almost constant, about 70% (w/w) when the silicalite membrane coated with the silicone rubber was used. Even in the case of the fermentation/pervaporation using the coated silicalite membrane, the flux greatly decreased. It is suggested that the glycerol produced during the fermentation, which is not adsorbed by the membranes, might have affected the pervaporation fluxes.

Remarkable Charge Separation and Photocatalytic Efficiency Enhancement through Interconnection of TiO2 Nanoparticles by Hydrothermal Treatment.

Although tremendous effort has been directed to synthesizing advanced TiO2 , it remains difficult to obtain TiO2 exhibiting a photocatalytic efficiency higher than that of P25, a benchmark photocatalyst. P25 is composed of anatase, rutile, and amorphous TiO2 particles, and photoexcited electron transfer and subsequent charge separation at the anatase-rutile particle interfaces explain its high photocatalytic efficiency. Herein, we report on a facile and rational hydrothermal treatment of P25 to selectively convert the amorphous component into crystalline TiO2 , which is deposited between the original anatase and rutile particles to increase the particle interfaces and thus enhance charge separation. This process produces a new TiO2 exhibiting a considerably enhanced photocatalytic efficiency. This method of synthesizing this TiO2 , inspired by a recently burgeoning zeolite design, promises to make TiO2 applications more feasible and effective.

Estimation of dealumination rate of ZSM-5 zeolite by adsorption of water vapor

Adsorption isotherms of water were measured at 25°C for HZSM-5 zeolites with various SiO 2 / Al 2 O 3 ratios. From the analysis of the adsorption isotherms by the D-R method it was found that the micropore volume W 0 (H 2 O) accessible to water molecules increases linearly with an increase in the framework aluminums and that the number of water molecules associated with one framework aluminum is on average five. Based on these results, the number of the framework aluminums in HZSM-5 zeolites dealuminated by thermal treatment at 600–800°C was estimated. It was found that the rate of the dealumination of HZSM-5 zeolite by thermal treatment is apparently second order depending on the number of framework aluminums in the zeolite structure. It became clear that water molecules are able to be used to determine the number of framework aluminums of the dealuminated HZSM-5 zeolite.