Tomohiko Tagawa

Degradation of dissolved diazinon pesticide in water using the high frequency of ultrasound wave.

This article aims to apply the ultrasound technique in the field of clean technology to protect environment. The principle of sonochemistry is conducted here to degrade pesticides in simulated industrial wastewater resulted from a factory manufacturing pesticides namely diazinon. Diazinon pesticide selected in this study for degradation under high frequency ultrasound wave. Three different initial concentrations of diazinon (800, 1200, and 1800 ppm), at different solution volumes were investigated in to degrade dissolved diazinon in water. Ultrasound device with 1.7 MHz, and 0.044 cm diameter, was used to study the degradation process. It is found that as the concentration of diazinon increased, the degradation is also increasing, and when the solution volume increases, the ability to degraded pesticides decreases. The experimental results showed an optimum condition achieved for degradation of diazinon at 1200 ppm as initial concentration and 50 ml solution volume. Kinetic modeling applied for the obtained results showed that the degradation of diazinon by high ultrasound frequency wave followed a pseudo-first-order model with apparent rate constant of around of 0.01 s(-1).

Study of the oxidative dehydrogenation of ethylbenzene: I. Catalytic behavior of SnO2P2O5

Abstract The oxidative dehydrogenation of ethylbenzene to styrene on SnO2P2O5 catalyst was investigated and the effects of catalyst composition and calcination temperature were studied. Elimination of phosphoric acid from SnO2P2O5 catalyst by nitric acid treatment and phosphoric acid treatment of the SnO2 surface result in an increase of activity and selectivity. The catalytic behavior of SnO2P2O5 catalysts is compared with that of crystalline tin(IV) phosphate. The interdependence of catalytic activity and selectivity, catalyst crystalline structure, and BET surface area is also discussed. These indicate that a type of tin-phosphorus compound is the active component. Also an increase in activity with reaction time and by calcination is explained. A mechanism consisting of the abstraction of hydrogen from ethylbenzene by surface oxygen to form styrene and the regeneration of oxygen from gas phase to the catalyst surface is proposed, with consideration of the role of tin and phosphorus, on the basis of kinetic data in a differential flow reactor.

Suppression of carbonaceous depositions on nickel catalyst for the carbon dioxide reforming of methane

Abstract A new pretreatment of catalyst, deposition–removal (D–R) treatment, is proposed to suppress carbonaceous depositions on Ni/Al2O3 catalyst for carbon dioxide reforming of methane. This treatment is based on the hypothesis that active cores forming carbon whiskers are different from surface active sites for the main reaction. In the deposition step, active cores of nickel are detached from the bulk nickel surface as growing cores in carbon whiskers. In the removal step, the carbon whiskers are removed from the nickel surface. These two steps are repeated by flowing pure methane gas and then pure carbon dioxide gas. The thermogravimetric (TG) measurements showed that the repeated D–R treatments reduced the carbonaceous deposition. Carbon monoxide adsorption measurements showed that the nickel surface area was decreased by the treatments. The reaction rate and the turnover frequency were increased by the treatments. The increase in the activity was explained by the development of active sites on newly exposed nickel layers which strongly interacted with the support.

Theoretical study on the synthesis of methyl acetate from methanol and acetic acid in pervaporation membrane reactors: effect of continuous-flow modes

Abstract The synthesis of methyl acetate (MeOAc) from methanol (MeOH) and acetic acid (HOAc) in pervaporation membrane reactors (PVMRs) is discussed in this paper. Three modes of PVMR operation, i.e. semi-batch (SB-PVMR), plug-flow (PF-PVMR) and continuous stirred tank (CS-PVMR) were modeled using the kinetic parameters of the reaction over Amberlyst-15 and permeation parameters for a polyvinyl alcohol (PVA membrane). Both of the reaction and permeation rates are expressed in terms of activities. The PVA membrane shows high separation factors for HOAc and MeOAc but very low for MeOH. The simulation results of SB-PVMR mode show quite good agreement with the experimental results. The study focused on comparing PVMR performances between two modes of continuous-flow operation for various dimensionless parameters, such as Damkohler number ( Da ), the rate ratio ( δ ), the feed composition and the membrane selectivity. Flow characteristic within the reactors arisen from different operation modes affects the reactor performance through its influences on the reaction and permeation rates along the reactor. There are only some ranges of operating conditions where CS-PVMR is superior to PF-PVMR.

Study of the oxidative dehydrogenation of ethylbenzene: II. Catalytic activity and acid and base properties of NaSiO2 · Al2O3

The oxidative dehydrogenation of ethylbenzene on a series of SiO2 · Al2O3 catalysts has been carried out by continuous flow reaction. The addition of sodium has resulted in an increase of activity and a maximum yield of styrene was observed at the value of 17 μmol of Na exchanged/g-cat. The same increase in activity was observed in the pulse reaction. The pulse reaction shows that ethylbenzene is adsorbed reversibly on the catalyst and that active oxygen species is also reversibly adsorbed. Such changes in oxidation activity have been explained by the cooperative effect of the acid and base sites of the catalyst. The acid-base titration shows that the addition of one Na ion increases the number of new acid (1.5 > H0 > −5.6) and base (17.2 < pKa < 26.5) sites tremendously. The acid sites of H0 between 1.5 and −5.6 are proven to be the active sites to adsorb ethylbenzene reversibly, whose oxidation, on the other hand, occurs on the base sites of pKa between 17.2 and 26.5. The pulse and flow reactions indicate that these acid-base sites are still effective even after carbonaceous materials have deposited.

Fuel cell type reactor for Chemicals-energy co-generation

In order to produce valuable chemicals and electric energy at the same time, a bifunctional reaction system has been proposed. By applying a principle of solid oxide fuel cell system, a membrane reactor for selective oxidation has been designed. The selective oxidation of methane with this reactor could produce valuable chemical such as ethene, ethane and carbon monoxide with high selectivity. The free energy change of the oxidation reaction has been directly converted into electric power with high efficiency.

Study of the oxidative dehydrogenation of ethylbenzene: III. Mechanism for styrene formation

Abstract The reaction mechanism of oxidative dehydrogenation of ethylbenzene has been investigated using the pulse technique, isotope exchange reaction, and ESR measurement. Collecting the effluents of the pulse reaction has shown the reversible adsorption of ethylbenzene. The deuterium exchange reaction has shown that the adsorbed intermediates of ethylbenzene are dissociated at the α position. Neutrally adsorbed molecular oxygen species and O − species are observed on the prereduced SiAl catalysts by the ESR measurement, showing the ability of the catalysts to activate gaseous oxygen. The reaction of the oxygen species with ethylbenzene has shown the active oxygen species to be O − species. The O − species consumed by the reaction are supplied from gaseous oxygen through O 2ad species. The reversible adsorption of ethylbenzene and the correlation between the turnover frequency and basicity suggest that the rate of the overall reaction at above 723 K is determined by the reaction of adsorbed ethylbenzene species and O − in abstracting the β-hydrogen. From the above results, a reaction mechanism is proposed as follows: the acid site of H 0 between 1.5 and −5.6 adsorbs ethylbenzene, reversibly abstracting the α-hydrogen at the basic OH adjacent to the acid site, and the base site of p K a between 17.2 and 26.5 activates gaseous oxygen to form O − which abstracts the β-hydrogen.

Design of electrode for solid oxide fuel cells reactor

Abstract A solid oxide fuel cell type reactor was tested for producing ethane and ethene as well as electric power by direct oxidation of methane. The design strategy of an anode catalyst was proposed. In order to evaluate the activity of surface oxygen species, Temperature Programmed Desorption (TPD) technique and pulse reaction technique were applied. The designed anode catalyst was La 1.8 Al 0.2 O 3 with Yttria Stabilized Zirconia (YSZ) as a solid electrolyte and La 0.85 Sr 0.15 MnO 3 as a cathode. The designed fuel cell type reaction system (air/La 0.85 Sr 0.15 MnO 3 /YSZ/La 1.8 Al 0.2 O 3 /methane) produced both ethene and ethane and electric power effectively. From the viewpoint of energy conversion, this can be regarded as CO 2 free combustion of methane. The nebulizer method, one of the direct preparation methods of fine powders from a mist of solution of raw materials, was proposed for the efficient preparation of the electrode structure.

Mechanistic aspects of oxidative coupling of methane over LaAlO3

Mechanistic aspects of the oxidative coupling reaction of methane over an LaAlO3 catalyst (La:Al = 1 : 1) prepared by the mist decomposition method have been studied, using both continuous-flow and pulsed-flow techniques. The delayed pulse technique together with temperature-programmed desorption reveal that an adsorbed oxygen species is effective in the formation of the C2 compounds, while a gaseous or weakly adsorbed oxygen species is involved in the combustion reaction. Methane cannot stay on the surface stably. Comparing these results with those obtained using the continuous flow reactor, mechanistic aspects are considered from the viewpoint of oxygen activity. The stability of this catalyst is also discussed.

Phenol synthesis by liquid-phase oxidation of benzene with molecular oxygen over iron-heteropoly acid

Abstract The phenol synthesis by liquid-phase oxidation of benzene with molecular oxygen over iron-heteropoly acid (HPA) system was studied. When iron salts were used with H 3 PW 12 O 40 , the highest activity was obtained. Spectroscopic studies showed that the state of the iron ion was changed after interaction with heteropoly acid (HPA) while the Keggin structure of HPA remained. The acidic nature of HPA activated benzene to form cationic species. Insoluble iron ion-exchanged heteropoly acid was obtained by partial ion exchange method, which also showed high activity on oxidation of benzene with molecular oxygen. The effects of reaction conditions were studied and the mechanism of deactivation was discussed. For the regeneration of catalytic activity, the addition of l -ascorbic acid as a reducing agent was suggested.