Masatoshi Nagai

Poisoning effect of nitrogen compounds on dibenzothiophene hydrodesulfurization on sulfided NiMo/Al2O3 catalysts and relation to gas-phase basicity

Abstract The nature of hydrodesulfurization sites of sulfided NiMo Al 2 O 3 catalysts has been examined by selective poisoning studies using various nitrogen compounds. The reactions were carried out with a flow microreactor at 220–340 °C and 10.1 MPa total pressure. Major products were biphenyl and cyclohexylbenzene. The hydrogenation of biphenyl to cyclohexylbenzene rarely occurred at 260 °C in the presence of dibenzothiophene. Nitrogen compounds were effective poisons for dibenzothiophene hydrogenation but not for the desulfurization reaction at lower temperatures. The poisoning effect of nitrogen compounds was not correlated with their solution basicities but with their gasphase basicities. These results indicated that hydrogenation occurred on Bronsted sites that appeared on sulfided NiMo Al 2 O 3 Catalysts.

Selectivity of molybdenum catalyst in hydrodesulfurization, hydrodenitrogenation, and hydrodeoxygenation: Effect of additives on dibenzothiophene hydrodesulfurization

Abstract Kinetic studies of the hydrodesulfurization of dibenzothiophene on a presulflded molybdenaalumina catalyst were carried out in a high-pressure-flow microreactor. The mechanism discussed is based on selective poisoning studies, using various nitrogen, polyaromatic, sulfur, and oxygen compounds. The nitrogen compounds inhibited the hydrogenation of dibenzothiophene because they adsorbed more strongly than did dibenzothiophene at lower temperatures. At higher temperatures, the nitrogen compounds also hinder the desulfurization together with the hydrogenation of dibenzothiophene. The sulfur and the oxygen compounds retarded all reactions of the desulfurization of dibenzothiophene. The reactions of the desulfurization, the denitrogenation, and the deoxygenation proceed on one type of site and the hydrogenation reactions on another site.

Hydrodesulfurization of dibenzothiophene on alumina-supported molybdenum nitride

An alumina-supported molybdenum nitrided catalyst was prepared and tested to determine its activity and selectivity during the hydrodesulfurization of dibenzothiophene. The nitrided catalyst was extremely active for the selective C-S bond breakage of dibenzothiophene to produce biphenyl.

Preparation of uniform poly(lactide) microspheres by employing the Shirasu Porous Glass (SPG) emulsification technique

Abstract Relatively uniform biodegradable poly(lactide) (PLA) microspheres were prepared by employing a Shirasu Porous Glass (SPG) membrane emulsification technique. Poly(lactide) dissolved in co-surfactant (hydrophobic substance)/dichloromethane (DCM) was used as a dispersed phase (oil phase) and an aqueous phase containing poly(vinyl alcohol) (PVA) and sodium lauryl sulfate (SLS) was used as a continuous phase. The oil phase permeated through the uniform pores of the SPG membrane into the continuous phase by a pressure of nitrogen gas to form the droplets. Then, the solid polymer microspheres were obtained by simply evaporating DCM at room temperature for 24 h. The effects of the type and the amount of the co-surfactant, and PLA concentration on the size, size distribution, and the morphologies of the droplets and particles were investigated. A relatively uniform spherical PLA microsphere was obtained successfully by using lauryl alcohol (LOH) rather than hexadecane (HD) as a co-surfactant. PLA concentration was varied from 10 to 20 wt.%/vol., and the LOH/DCM ratio changed from 0.5:11.5 to 2:10 by volume. At the polymer concentration range used in this study (10–20 wt.%), variation of the droplet size was not so apparent when 2 ml of LOH was used, but the droplet size showed a minimum value at 15 wt.% when 0.5 or 1 ml of LOH was used. The variation of CV value (coefficient of variation) was smaller in the PLA concentration range of 10–15 wt.%, then the CV value became larger as the PLA concentration was increased from 15 to 20 wt.%. Although there was a tendency that the droplet size and the CV value decreased as the LOH/DCM ratio increased, the CV value of the particle after the evaporation of DCM showed the lowest value when the amount of LOH was 1 ml (LOH/DCM=1:11, by vol.). Therefore it was most adequate to use 1 ml of LOH to prepare the particles with a relatively narrow size distribution. Furthermore, it was clarified that the phase-separation between PLA and LOH was apparent and the surface of the particle obtained was wrinkled when the PLA concentration was lower after DCM was evaporated, while the particles with the smooth surface were obtained when the PLA concentration was higher. This method provides a unique technique to prepare uniform polymer microspheres composed of natural polymers, bio-degradable polymers, co-polymers or polymer blends, polyesters and those which can not be polymerized by the radical polymerization.

Preparation and Analysis of Uniform Emulsion Droplets Using SPG Membrane Emulsification Technique

Abstract A new technique for the preparation of uniform emulsion droplets using Shirasu porous glass (SPG) membranes was evaluated. The hydrophobicity of a dispersion phase and the concentration of the mixed surfactant, by which the interfacial tension between the continuous phase and the dispersion phase was changed, significantly affected the droplet size and size distribution. From the point of view that the difference in the interfacial energy affects the characteristics of the droplets, the effect of wettability of the dispersion phase on the thin layer of the continuous phase on the membrane surface was investigated by measuring the contact angle. It is understood that monodispersity of the droplets is controlled by the wettability of the dispersion phase for the continuous phase in contact with the SFG membrane. The droplet profiles at the initial stage and the final release shown in the schematic diagrams corresponded to the value of adhesional work as a scale of the wettability.

Application of Porous Microspheres Prepared by SPG (Shirasu Porous Glass) Emulsification as Immobilizing Carriers of Glucoamylase (GluA)

Fairly uniform spheres of crosslinked polystyrene (PS) and polymethyl methacrylate (PMMA), prepared by a particular emulsification process using SPG (Shirasu Porous Glass) membranes and subsequent suspension polymerization, were applied for immobilizing carriers of Glucoamylase (GluA). A mixture of monomers, solvents, and oil-soluble initiator was allowed to permeate through the micropores of SPG, suspended in an aqueous solution of poly(vinyl alcohol), and polymerized while retaining the narrow size distribution during polymerization. A small amount of acrylic acid or glycidyl methacrylate (GMA) was incorporated for the immobilization of GluA via covalent bonding. Although GluA has been regarded as being difficult to retain its activity after the immobilization process, a porous structure of the carriers definitely favored the immobilization, and a maximum 55% relative activity (RA) was obtained by the physical adsorption to PMMA spheres. The reaction of epoxide in GMA with 6-aminocaproic acid provided a spacer arm for the carboxyl group. An improvement of activity was expected by the incorporation of the spacer arms; however, barely noticeable activity was observed for PMMA carriers either by the physical adsorption or by the covalent bonding. A slight improvement was observed for PS carriers with spacers compared to the carriers without them. The diffusion process of oligosaccharides in the porous carriers seemed to retard the rate of hydrolysis in the case of largest carriers, 60 μm PS-DVB-AA spheres. The activity of immobilized GluA was retained during a long storage period of more than 150 days, some of them even increasing gradually, while the activity of native GluA dropped to zero after 100 days.

Activity of alumina-supported molybdenum nitride for carbazole hydrodenitrogenation

The alumina-supported molybdenum nitride catalyst was extremely active in the hydrodenitrogenation of carbazole at 553–633 K and 10.1 MPa total pressure when compared with the sulfided and reduced catalysts.

Synthesis of uniform microspheres with higher content of 2-hydroxyethyl methacrylate by employing SPG (Shirasu porous glass) emulsification technique followed by swelling process of droplets

Relatively uniform microspheres containing a hydrophilic monomer, 2-hy- droxyethyl methacrylate (HEMA), were prepared by employing a swelling method of uniform seed droplets. A uniform seed emulsion composed mainly of styrene (St) was prepared by the Shirasu porous glass (SPG) membrane emulsification technique; this was mixed with a secondary emulsion composed mainly of HEMA/St or HEMA/MMA (methyl methacrylate) prepared by a homogenizer for swelling. The swollen droplets obtained were polymerized at 757C under a nitrogen atmosphere. The uniform mi- crosphere with a higher content of HEMA was obtained successfully by the swelling method while it failed by a direct emulsification method. The effects of the composition of the oil phase and the inhibitor in the continuous phase on the incorporated fraction of HEMA, the morphology of particles, and monomer conversion were investigated. It was found that the incorporated fraction of HEMA increased with increasing its feed fraction, and more HEMA was incorporated into the microsphere when HEMA/MMA was used as the oil phase of the secondary emulsion rather than HEMA/St. Although the final conversion was very low when the feed fraction of HEMA was higher, it can be increased to more than 80% by using an adequate amount of ethylene glycol dimethacrylate (EGDMA) as a crosslinker and NaNO2 as an inhibitor in the aqueous phase. Various microspheres with different morphologies such as spherical, snow- manlike, and popcornlike were observed, depending on composition of the oil phase. Furthermore, the porous microsphere with a high content of HEMA was obtained by employing hexanol (HA) as a porogen. q 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 1325-1341, 1997

Preparation and characterization of alumina-supported molybdenum carbide

Abstract Molybdenum carbide on alumina was studied by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and temperature-programmed surface reaction (TPSR) with hydrogen. The molybdenum carbide was prepared by nitridation of 12.5 wt% MoO 3 /Al 2 O 3 in a flow of NH 3 at 700°C, followed by carburization in a flow of 20% CH 4 /H 2 also at 700°C for 3 h. The sample was compared to an unsupported material prepared from MoO 3 in the same manner. The CH 4 formation profile during TPSR was deconvoluted into three peaks with maxima at 490°C, 690°C, and 810°C. The peak at 490°C was assigned to reduction of carbidic carbon, and the peaks at 690°C and 810°C were assigned to the removal of pyrolytic and graphitic carbon, respectively, as indicated by XPS and XRD measurements. Overall, the results suggest that molybdenum carbide was formed on the alumina supported by the carburization treatment at 700°C, in the same manner as with an unsupported reference sample. Prenitridation before carburization resulted in the formation of a carbide with a larger surface area and less free carbon, compared to the carbide formed by direct carburization.

PdO/Al2O3 in catalytic combustion of methane: stabilization and deactivation

In the recently developed catalytically assisted combustors for gas turbines using natural gas, deactivation of the palladium oxide (PdO) catalyst needs to be prevented. The effects of additives such as lanthanum and neodymium in PdO/Al 2 O 3 on the catalytic durability at 1123 K were studied using a conventional fixed-bed flow reactor at atmospheric pressure. The surface properties of the catalysts were investigated using CO chemisorption, XRD, and TPD after CH 4 adsorption. The catalyst deactivation during CH 4 oxidation followed the equation Φ=r 1 [1/(1+α 1 t)] n1 +r 2 [1/(1+α 2 t)] n2 , where r, α and n are constants, subscripts 1 and 2 are the rapid and slow deactivation species, respectively, and t is time on stream. The PdO/Al 2 O 3 catalyst was rapidly deactivated by the transformation of PdO to metallic Pd and slowly deactivated by the particle growth of PdO. The addition of Nd 2 O 3 and La 2 O 3 to PdO/Al 2 O 3 prevented the particle growth of PdO as well as the transformation of PdO to Pd up to high temperature.