Shin R. Mukai

Preparation and characterization of carbon cryogel microspheres

Abstract Carbon cryogel microspheres (CC microspheres) were successfully synthesized by an inverse emulsion polymerization of resorcinol with formaldehyde, followed by freeze drying and pyrolysis in an inert atmosphere. CC microspheres were characterized by scanning electron microscopy, elemental analysis and various gas adsorption measurements. By changing both the temperature for preparing the emulsion and pyrolysis temperature, it was possible to prepare both mesoporous microspheres and microspheres covered with ultramicroporous surfaces which pore sizes were smaller than the minimum molecular dimensions of ethane or carbon dioxide. Hydrophobicity of the obtained CC microspheres increased with the increase in pyrolysis temperature. The possibility of using the obtained mesoporous CC microspheres as column packing materials for high-performance liquid chromatography was also shown.

Modification of pore size of MFI-type zeolite by catalytic cracking of silane and application to preparation of H2-separating zeolite membrane

Abstract Catalytic cracking of silane (CCS) is proposed as a new method for modifying the effective pore opening of a zeolite. In this method, first silane compounds which can penetrate into the pores of the zeolite are introduced and are pre-adsorbed on active sites within the zeolite, such as acid sites and metal cations. Next, the adsorbed species are cracked catalytically on the sites, leaving coke that contains Si atoms on the active sites. By the calcination of the coked material, mono SiO 2 units are formed on active sites, thereby reducing the size of the pores. When this method is applied to powdery MFI-type zeolite, the adsorption capacity of benzene is markedly reduced, but that of CO 2 is maintained constant. Furthermore, the proposed CCS method was applied to reduce the pore diameters of an MFI-type zeolite membrane. By use of the membrane, experiments of separating H 2 from a mixture gas containing H 2 and N 2 or O 2 were conducted in a flow system. The membrane showed a high H 2 separation factor of about 90–140 (as compared with 1.4–4.5 for a non-treated MFI-type zeolite membrane).

Preparation of encaged heteropoly acid catalyst by synthesizing 12-molybdophosphoric acid in the supercages of Y-type zeolite

12-molybdophosphoric acid encaged in the supercages of Y-type zeolite was synthesized from molybdenum oxide and phosphoric acid, in a slurry mixture of Y-type zeolite crystals and deionized water. After thorough washing in hot water, the 12-molybdophosphoric acid was found to remain in the Y-type zeolite, at an amount estimated to be 0.09 g (g-support)−1. Catalysts thus obtained were found to show activity for the esterification of acetic acid with ethanol, indicating that this catalyst could be used as a solid acid catalyst in various liquid phase reactions which involve water.

Formation of monolithic silica gel microhoneycombs (SMHs) using pseudosteady state growth of microstructural ice crystals

Monolithic silica gel microhoneycombs, which have an array of straight macropores within their structure and developed micro/mesopores inside their walls, were prepared using pseudosteady state growth of ice crystals which occurs during the unidirectional freeze-gelation of freshly gelled aqueous silica hydrogels, followed by a pore-protecting drying method, freeze drying.

Porous properties of silica gels with controlled morphology synthesized by unidirectional freeze-gelation

Abstract In this work, the unidirectional freezing method was applied to a wide variety of silica gel precursors; from silica sols which do not readily gel, to thoroughly aged silica hydrogels. It was found that in addition to the well-known structure of fibers with polygonal cross-sections which are commonly obtained in the unidirectional freezing method, porous silica gels having unique morphologies such as honeycomb, lamellar and flat fiber structures could also be obtained by changing the state of the precursor sol or gel. The obtained silica hydrogels were freeze-dried after exchanging the water included in its structure to t -butanol, and finally dry samples maintaining their wet state structures were obtained. The morphology and the porous properties of the obtained silica gels were systematically analyzed and the influences of preparation conditions, including pH, aging time before freezing, SiO 2 concentration, freezing temperature, and storage time at the frozen state on both factors were examined in detail. It was found that the simultaneous controlling of both factors could be easily conducted by simply adjusting preparation conditions.

Gas adsorption on activated carbons from PET mixtures with a metal salt

Abstract Activated carbons were prepared from carbonized PET by steam activation via pretreatment by mixing PET with a metal salt [Ca(NO 3 ) 2 ·4H 2 O, Ca(OH) 2 , CaCO 3 , ZnO, and AlNH 4 (SO 4 ) 2 ·12H 2 O], and with acid treatment after carbonization. The porous properties of the activated carbons were determined by the nitrogen adsorption method. The adsorption isotherms of CO 2 , C 2 H 6 , nC 4 H 10 and iC 4 H 10 at 298 K on the prepared activated carbons were measured to determine practical applications and to obtain a better understanding of the porous structure of the prepared carbons. Steam-activated carbons via pretreatment have a larger mesoporosity than carbons with no pretreatment. The metal salt used in the pretreatment for steam activation has no influence on the microporous structure, but it does influence the mesoporous structure of the prepared carbons. Activated carbons prepared via pretreatment show a large adsorption capacity for nC 4 H 10 and iC 4 H 10 . These carbons are suitable as adsorbents for canisters, etc. Application of the potential theory to adsorption data for the prepared carbons suggests that the pretreatment contributes to the formation of pores larger than 0.50 nm at high burnoff.

A method of calculating adsorption enthalpy distribution using ammonia temperature-programmed desorption spectrum under adsorption equilibrium conditions

Abstract A method, called the ac -TPD method, was presented for calculating the density distribution function of the adsorption enthalpy of ammonia by utilizing the temperature-programmed desorption (TPD) spectrum of ammonia from solid catalysts measured under complete adsorption equilibrium conditions. TPD spectra were measured using a gas stream containing ammonia, at a relatively large concentration compared to the amount of ammonia desorbed from the catalyst. Under these conditions, the concentrations of ammonia both inside the catalyst particles and in the gas phase are kept almost constant during the experiment. This situation meant that the amount of ammonia remaining on the catalyst was at an equilibrium state and dependent on the temperature and concentration of ammonia. Therefore, it could be assumed that the adsorption equilibrium of ammonia on acid sites can be expressed by a Langmuir-Hinshelwood type equation, which has an adsorption enthalpy and a pre-exponential adsorption equilibrium constant corresponding to the strength of an acid site. The overall TPD spectrum is represented by the sum of the spectra from acid sites with different acid strengths. Under these assumptions, the desorption temperature was related to the adsorption enthalpy of ammonia, and a relationship was derived between the overall TPD spectrum and the density distribution function of the adsorption enthalpy. The distribution function obtained by this method can be used for evaluating acidic properties of solid catalysts. The heat flux required for the desorption of ammonia from acid sites during the TPD experiment was calculated using the obtained distribution. The value was found to agree well with that directly measured by a differential scanning calorimetric apparatus. The density distribution of the adsorption enthalpy ( Q ) was compared to the distribution of activation energy for desorption of ammonia ( E ) by a method, called dc -TPD, which was reported previously by us. This comparison gave the relationship between Q and E , and it was found that the Q value was smaller than the E value by about 15 kJ mol −1 .

Preparation of monolithic SiO2–Al2O3 cryogels with inter-connected macropores through ice templating

Macroporous monoliths of SiO2–Al2O3 cryogels were prepared. Macropores were generated by using ice crystals as the template, while the walls which surround the macropores were tailored as porous cryogels by freeze drying. Macropores and walls formed honeycomb-like structures, which were confirmed from scanning electron microscopy images of cross-sections of the samples. It was confirmed that the sizes of the macropores and the wall thicknesses were respectively in the ranges of 10–20 µm and 200–500 nm. Al mapping analysis by energy dispersive X-ray diffractometry showed that Al atoms were homogeneously dispersed throughout the samples without local aggregation. Moreover, Raman spectroscopy and 27Al NMR spectroscopy indicated that Al atoms were incorporated into the silica framework by forming an Al–O–Si polymeric network. Nitrogen adsorption–desorption measurements indicated that the walls were micro/mesoporous with high BET surface areas (>700 m2 g−1) and large pore volumes (>0.45 cm3 g−1). Moreover, NH3-TPD measurements revealed that the samples had acid sites, which allowed this material to be used as a solid acid catalyst.

A theoretical study on storage states of Li ions in carbon anodes of Li ion batteries using molecular orbital calculations

Abstract Semi-empirical molecular orbital calculations were carried out to clarify storage states of Li ions in amorphous carbon anodes of Li ion batteries. Storage states of Li ions between two graphene sheets were investigated and a favorable structure for a carbon anode to produce large reversible and small irreversible capacities is discussed. A polycyclic hydrocarbon molecule, C 54 H 18 , was used as a model of a graphene sheet. Relations between the interlayer distance of two graphene sheets and the storage state of Li ions were investigated, and preferable interlayer distances for specific numbers of Li ions were estimated. In particular, storage states with all Li ions on the basal area were treated, because the amount of basal carbons should be larger than that of edge carbons. The charge distribution of Li ions was also investigated. Calculated results suggested that a storage state in which a double Li ion layer was formed was preferable to achieve a larger capacity than the theoretical maximum capacity of graphitic carbons (372 mAh/g) and to reduce hysteresis in the charge–discharge process. Moreover, suitable distance between edges of graphene sheets to prevent the intercalation of electrolyte species was discussed. A recommended structure of carbon anodes suitable for the double Li ion layer storage and prevention of the intercalation of electrolyte species is proposed.

Chemical recycling of mixture of waste plastics using a new reactor system with stirred heat medium particles in steam atmosphere

A new reactor system was developed for recovery fuels from the waste plastic mixture in steam atmosphere. Firstly, the degradation mechanisms of eight kinds of plastics, two polyolefins (polyethylene and polypropylene), two polyamide resins (nylon-6 and nylon-6,6), polystyrene and three polyesters (polycarbonate, poly(butylene terephthalate) and poly(ethylene terephthalate), were investigated both in nitrogen and steam as the carrier gas. Plastics except for polyesters were degraded without any influences of the kinds of the carrier gas, leaving negligibly small amount of carbonaceous residue. Polyesters, which were degraded with producing large amount of the residue in nitrogen, were succeeded to be hydrolyzed at high reaction rates in steam with producing hardly the carbonaceous residue. Secondly, a mixture of the waste plastics was continuously degraded to produce heavy oil in steam atmosphere by using a new reactor system. This system was composed of three kinds of reactors connected in series. One was a reactor filled with stirred heat medium particles, which enabled the high heat transfer rate, the high holdup and the good contact of the melted plastics with steam. The second was a tank reactor. The last one was a fixed bed reactor with FeOOH catalyst particles, which showed the catalysis in steam for the decomposition both of a wax and sublimate materials generated by the degradation of plastics. Furthermore, the oil produced from the proposed reactor system was continuously upgraded to produce gasoline and kerosene over Ni-REY catalyst in steam atmosphere.