Motoaki Kawase

Increased esterification conversion by application of the simulated moving-bed reactor

Abstract A new simultaneous reaction and separation process using a simulated moving-bed apparatus was proposed. β-Phenethyl acetate was produced from acetic and β-phenethyl alcohol. Proton-type ion-exchange resin was used both as a catalyst and as an adsorbent for chromatography. By application of the simulated moving-bed reactor, the esterification conversion was increased to more than 99%, far beyond the equilibrium conversion of 63%. Experimental and numerical simulation results were in good agreement. It was proved that flow rates and temperature were the most important factors to achieve almost 100% conversion.

The reduction of copper oxide thin films with hydrogen plasma generated by an atmospheric-pressure glow discharge

The reduction of copper oxide thin films by a hydrogen plasma generated by an atmospheric-pressure glow (APG) discharge was investigated. The copper oxide films were prepared by heating the sputtered copper films to C in the air (heat-formed copper oxide) or by sputtering (sputtered copper oxide). Both films were composed of . The reduction occurs first on the surface, then the interface gradually shifts from the surface into the inner region and finally the whole layer is reduced to metallic copper. This process is approximately explained by assuming that the diffusion of the atomic hydrogen in the reduced layer is the rate-deyermining step. By transmission electron microscopic (TEM) observation, a layer of 3 - 5 nm thickness composed of many microcrystals was observed along the surface of the heat-formed copper oxide. After the APG hydrogen plasma treatment, the crystal layer disappeared and the crystalline lattice was re-arranged to form large crystal Cu grains.

The simulated moving-bed reactor for production of bisphenol A

Abstract Bisphenol A was produced from acetone and phenol over an ion-exchange resin catalyst at 50–90°C. Phenol was used as solvent. The reaction proceeded under the excess phenol condition. The reaction rate was proportional to the acetone concentration in the initial period of the reaction. After the acetone conversion exceeded approximately 50%, the reaction rate became lower than expected by the first-order reaction rate. This was ascribed to water adsorption onto the resin. Batch adsorption and breakthrough experiments showed that water was adsorbed approximately seven times stronger than acetone and that bisphenol A was not adsorbed. Using the reaction rate equation for bisphenol A production, the adsorption isotherms and overall mass transfer coefficients of the components, the numerical simulation of the 3-zone-type simulated moving-bed reactor was carried out. High resin flow rate was required in order to remove water out of the reaction zone, and a high liquid flow rate was also required to desorb water from the resin in the recovery zone. As far as the flow rates were set appropriately, water was successfully removed to prevent the catalyst deactivation and the long-term stable production of BPA was allowed.

Lactosucrose production using a simulated moving bed reactor

Abstract The feasibility of a new reaction system with five components for the simulated moving bed reactor (SMBR) was investigated. In this reaction, an oligosaccharide, lactosucrose (lactosylfructoside), was produced from sucrose and lactose using an enzyme, β -fructofuranosidase from Arthrobacter sp. K-1. Numerical simulation of the batch process showed that the performance of the reaction process is improved by product removal. The adsorption equilibrium of each component had been determined and SMBR experiments had been carried out. Lactosucrose and glucose were well separated in the SMBR and the lactosucrose yield was increased compared to the conventional batch reaction. The expected optimum lactosucrose yield was not attained due to strong product hydrolysis around the raffinate port.

Methanol to olefins using ZSM-5 zeolite catalyst membrane reactor

A ZSM-5 zeolite catalyst membrane without pinholes was successfully prepared by synthesizing ZSM-5 zeolite layer on the outer surface of a cylindrical alumina ceramic filter. In the preparation of the membrane, to enhance the smoothness of the outer surface of the filter, a filter with pores of 0.1 μm in diameter was employed. Furthermore, the hydrothermal synthesis was repeated using the same samples. The obtained zeolite membrane showed a molecular sieving effect for the permeation of gaseous xylene and diethylbenzene isomers. The ratio of the permeability of the para-isomer to the meta-isomer was about 2.7 for xylene and 6.0 for diethylbenzene, respectively. The membrane was used as a catalytic membrane reactor to recover olefins from methanol. By adjusting the diffusion rate to the chemical reaction rate for producing olefins within the ZSM-5 zeolite layer, olefins were successfully produced at a high selectivity (about 80-90%) from methanol at high conversions of 60-98%.

Reaction Kinetics and Modeling of the Enzyme-catalyzed Production of Lactosucrose using β-Fructofuranosidase from Arthrobacter sp. K-1

Lactosucrose synthesis from sucrose and lactose was carried out by using β-fructofuranosidase from Arthrobacter sp. K-1. The transfructosylation mechanism was found to be of an ordered bi-bi type in which sucrose was bound first to the enzyme and lactosucrose was released last. Hydrolysis side-reaction experiments indicated that the reactions were uncompetitively inhibited by glucose and lactose, while no inhibition by fructose was apparent. The overall reaction rates were formulated. The reaction rate constants, equilibrium constant, and dissociation and Michaelis constants were determined at 35°C and 50°C by fitting the experimental concentration changes with the calculated values by a nonlinear least-square method. The average relative derivation for the concentrations was 9.67%. The kinetic parameters were also calculated for 43°C and 60°C by assuming the Arrhenius law, and the course of reaction was predicted. The obtained reaction rate equations well represented the concentration changes during the experiment at all temperatures.

Effective diffusivities of lighter hydrocarbons in Cu- and Co-MFI-type zeolite catalysts

Abstract Intracrystalline and effective diffusivities of ethane, propane, ethylene and propylene were measured for several kinds of MFI-type zeolite, such as silicalite-1, H-MFI, Cu- and Co-MFI-type zeolites at temperatures ranging from 323 to 823 K . The intracrystalline diffusivity represents the mobility of molecules within zeolite crystals, and was found to be reduced to 1/100 for paraffins and 1/1000 for olefins by the existence of active sites (proton, Cu and Co ions), as compared with silicalite-1. The effective diffusivity was evaluated by multiplying the intracrystalline diffusivity by a partition factor. Although the intracrystalline diffusivity of olefins was about 1/10 to 1/100 of that of paraffins, the effective diffusivity of olefins was almost equal to that of paraffins. The calculated effective diffusivity of ethylene within Cu-MFI was in good agreement with those evaluated by the kinetic analysis of the catalytic decomposition of NO with ethylene over Cu-MFI catalyst.

Measurement of Intracrystalline Diffusivities of Hzsm-5 Zeolite At Higher Temperatures and Predictions of Shape Selectivity

Abstract A model is developed which describes the activity and the shape selectivity of methylation of toluene to produce xylenes over HZSM-5 zeolite catalysts by taking account of both intracrystalline diffusion and acid strength distributions inside and outside the crystallite. The shape selectivity is strongly affected by the relative rates of intracrystalline diffusions of hydrocarbon molecules. Uptake curves of amounts of benzene, toluene and xyleneisomers adsorbed on high-silica HZSM-5 zeolites, which have no catalytic activities, were measured in the range of temperature from 373–673 K. Effective intracrystalline diffusivities were calculated from the uptake curves over the temperature range. The ratio among the diffusivities of para-, meta-and ortho-xylene was about 10:1:1 in the above temperature range. Each acid strength distribution of acid sites inside and outside the crystallite was measured by combining the two methods developed by us. Rate constants of methylation and isomerizations of xylenes inside and outside the crystallite were estimated by performing these reactions over two kinds of the catalysts: one has acid sites only inside the crystallite, the other only outside the crystallite. Using these values, the proposed model was found to predict well the apparent shape selectivity. A chart based on the proposed model was also presented which provides a guide in preparing more highly selective HZSM-5 catalysts for the methylation of toluene.

Numerical simulation of the thermal-gradient chemical vapor infiltration process for production of fiber-reinforced ceramic composite

Abstract A numerical model was developed in order to describe the thermal-gradient chemical vapor infiltration (CVI) for the production of SiC W /Al 2 O 3 composite. The proposed model considered reaction, diffusion and deposition of alumina within the porous preform. The cubic array of disconnected cylinders model was proposed in order to represent the porous structure of the preform and the composite. The experimental results of CVI were in good agreement with the calculated results. The effects of total pressure, heating temperature and initial surface temperature on the final residual porosity and the infiltration time were investigated. The heating temperature and the initial surface temperature had a larger effect on the porosity and the infiltration time than did the total pressure. In order to produce a dense composite, the initial surface temperature must decrease with increasing heating temperature.

Fine particle synthesis by continuous precipitation using a tubular reactor

Abstract —A new continuous precipitation process using a tubular reactor with a T-mixer was applied to the production of nanometer-to-micrometer particles of several kinds of inorganic salts. A reactor tube was placed in two constant-temperature baths at different temperatures for separating the particle formation and growth stages. This enabled good monodispersity and high yield simultaneously. Another reactor setup using a reactor tube of submillimeter diameter with a rapid particle sampler was applied for investigating particle growth in the initial stage. By varying the residence time from 0.4 ms to 120 s over six orders of magnitude, lanthanum phosphate particles of diameter 3 nm to 1 μm were obtained. At 0.4 ms, the particle size widely ranged from 3 to 200 nm since the nucleation was continuing. After the nucleation practically ended at arround 10 ms, the particle grew uniformly by crystal growth. The shape became spherical and the size distribution became more monodisperse. The typical final geometric standard deviation was 1.1. Using the thin tubular reactor, the quality of the resulting particles was improved as well as the observation of particle growth in the initial stage being made possible.