Sadao Araki

Preparation and CO2 adsorption properties of aminopropyl-functionalized mesoporous silica microspheres

Aminopropyl-functionalized mesoporous silica microspheres (AF-MSM) were synthesized by a simple one-step modified Stöber method. Dodecylamine (DDA) was used as the catalyst for the hydrolysis and condensation of the silica source and as the molecular template to prepare the ordered mesopores. The mesoporous silica surfaces were modified to aminopropyl groups by the co-condensation of tetraethoxysilane (TEOS) with 3-aminopropyltriethoxysilane (APTES), up to a maximum of 20mol.% APTES content in the silica source. The particle size, Brunauer-Emmet-Teller (BET) specific surface area, and mesoporous regularity decreased with increasing APTES content. It is believed that this result is caused by a decreasing amount of DDA incorporated into AF-MSM with increasing APTES content. It was also confirmed that the spherical shape and the mesostructure were maintained even if 20mol.% of APTES was added to the silica source. Moreover, AF-MSM was applied to the CO(2) adsorbent. The breakthrough time of the CO(2) and CO(2) adsorption capacities increased with increasing APTES content. The adsorption capacity of CO(2) for AF-MSM, prepared at 20mol.% APTES, was 0.54mmolg(-1). Carbon dioxide adsorbed onto AF-MSM was completely desorbed by heating in a N(2) purge at 423K for 30min.

Adsorption of carbon dioxide and nitrogen on zeolite rho prepared by hydrothermal synthesis using 18-crown-6 ether

Zeolite rho was prepared by hydrothermal synthesis using an 18-crown-6 ether (18C6) as a structure-directing agent, and the effects of the calcination temperature for removal of 18C6 on the physicochemical properties and CO(2)-adsorption properties were investigated. CO(2) adsorption on zeolite rho calcined at 150°C was lower than that on samples calcined at temperatures above 300°C. For samples calcined above 300°C, CO(2) adsorption increased with increasing calcination temperature up to 400°C. It is thought that the pore volume for adsorption of CO(2) increased as a result of 18C6 removal, resulting in increasing CO(2) adsorption. A decrease in CO(2) adsorption for calcination from 400°C to 500°C was observed. The particle size of zeolite rho increased with increasing 18C6 molar ratio. Particle sizes of 1.0-2.1 μm and 1.4-2.6 μm were found by field-emission scanning electron microscopy and dynamic light-scattering, respectively. The particle size is controlled in these regions by adjusting the 18C6 molar ratio. XRD showed that zeolite rho samples with 18C6 molar ratios of 0.25-1.5 had high crystallinity. The adsorbed amount of CO(2) is almost constant, at 3.4 mmol-CO(2)g(-1), regardless of the 18C6 molar ratio. However, CO(2) selectivity, which is the CO(2)/N(2) adsorption ratio, decreased. The amount of CO(2) adsorbed on zeolite rho is lower than that on zeolite NaX, but higher than that on SAPO-34. The CO(2)/N(2) adsorption ratio for zeolite rho was higher than those for SAPO-34 and zeolite NaX.

Autothermal reforming of biogas over a monolithic catalyst

Abstract This study focused on measurement of the autothermal reforming of biogas over a Ni based monolithic catalyst. The effects of the steam/CH4 (S/C) ratio, O2/CH4 (O2/C) ratio and temperature were investigated. The CH4 conversions were higher under all examined temperatures than the equilibrium conversion calculated using the blank outlet temperature, because the catalyst layer was heated by the exothermic catalytic partial oxidation reaction. The CH4 conversion increased with increasing O2/C ratio. Moreover, the CH4 conversion was higher than the equilibrium conversion calculated using the blank outlet temperature for O2/C>0.42 and reached about 100% at O2/C=0.55. However, the hydrogen concentration decreased for O2/C>0.45 because hydrogen was combusted to steam in the presence of excess oxygen. On the other hand, the hydrogen and CO2 concentrations increased and the CO concentration decreased with increasing S/C ratio. As a result, it was found that the highest hydrogen concentrations and CH4 conversions were attained at the O2/C ratios of 0.45-0.55 and the S/C ratios of 1.5-2.5. Moreover, the H2/CO ratio could also be controlled in the range from about 2 to 3.5 to give at least 90% CH4 conversion, by regulating the O2/C or S/C ratios.

Crystallization process of zeolite rho prepared by hydrothermal synthesis using 18-crown-6 ether as organic template.

There are many viewpoints on the formation mechanisms for zeolites, but the details are not clear. An understanding of the elementary steps for their formation is important for the development of large-scale membranes and efficient manufacturing processes. In this study, the effects of silicon, aluminum, and the incorporation of 18-crown-6 (18C6) ether, on the formation of zeolite rho, using 18C6 as the structure directing agent (SDA) have been investigated by using field emission scanning electron microscopy (FE-SEM), energy dispersive X-ray fluorescence spectrometry (EDX), nuclear magnetic resonance spectroscopy (NMR), thermo gravimetric analysis (TGA), and the pH measurement. These results suggested that a zeolite rho has four synthesis steps; (1) 0-3 h, the dehydration and condensation reaction between the silica and alumina to form amorphous aluminosilicates; (2) 3-20 h, the particle growth and aggregation process for the amorphous aluminosilicates; (3) 20-48 h, the crystallization and crystal growth of zeolite rho, with the incorporation of 18C6; and (4) 48-96 h, gentle growth with an increase in Na/Si ratio and a change in rate for the bounding state between the silica- and the alumina-based species. We consider the above to reflect the four steps for the formation of zeolite rho.

Water Gas Shift Reaction in a Membrane Reactor Using a High Hydrogen Permselective Silica Membrane

A membrane reactor (MR) for the water gas shift (WGS) reaction was developed by integrating a highly hydrogen permselective silica membrane. The membrane was prepared using an extended counter-diffusion chemical vapor deposition (CVD) method. A tetramethylorthosilicate (TMOS) silica source was fed from one side of the membrane support and oxygen gas fed from the other. The dense silica film was deposited on a porous support by pressurizing the side that TMOS is supplied. A high hydrogen permselective silica membrane was obtained by this method. A commercial Pt catalyst was used in the WGS reaction. Efficacy of the silica membrane toward the WGS reaction was investigated as a function of temperature (523-623 K), steam/carbon monoxide (S/C) ratio (1-3), differential pressure (0-100 kPa), and gas hourly space velocity (GHSV; 1800-5400 h−1). The CO conversion in the MR was higher than that for a fixed bed reactor (FBR) under all experimental conditions, and was also higher than the thermodynamic equilibrium conversion under almost all experimental conditions. This was due to the selective abstraction of hydrogen from the product stream by the silica membrane. At an S/C of 1.0, the CO conversion in the MR was superior to that in a FBR by 16.8%.

Synthesis of spherical porous cross-linked glutaraldehyde/poly(vinyl alcohol) hydrogels

Abstract Spherical glutaraldehyde cross-linked poly(vinyl alcohol) (PVA) hydrogels (G-PVA) were prepared in three steps: gelatification, cross-linking, and removal of alginate. Gelatification was carried out by dropping a solution of alginate, PVA, and glutaraldehyde into a calcium chloride solution to form calcium alginate. Calcium alginate gels were prepared at 20°C, 40°C, 60°C, and 80°C to study the effect of gelatification temperature on the formation of pores on the surface of G-PVA. The effect of the alginate content was studied. PVA and glutaraldehyde were cross-linked by immersion of the gels in a solution of H2SO4 and Na2SO4. The effect of sodium alginate and inorganic salts, such as MgSO4 and K2SO4, on the formation of pores on the surface of G-PVA was confirmed.