Hitoki Matsuda

Uptake of Fluoride by Al3+ Pretreated Low‐Silica Synthetic Zeolites: Adsorption Equilibrium and Rate Studies

Abstract The removal of fluoride from single component aqueous solution using Al3+‐ pretreated low‐silica synthetic zeolites (Al‐Na‐HUD, Al‐HUD, Al‐F9, and Al‐A4) was studied. The effects of adsorbent mass, initial solution pH, and initial concentration on fluoride removal in a batch system were evaluated. Equilibrium data were simulated using simple isotherms such as the Freundlich (F), Langmuir‐Freundlich (LF), Redlich‐Peterson (RP) and Dubinin‐Radushkevitch (DR) isotherms. From the DR model, initial pH effects and desorption studies, it was considered that the fluoride adsorption onto the zeolites proceeded by ion‐exchange or chemisorption mechanism. In interpreting the kinetic results, reaction kinetics (using Elovich equation) and mass transfer processes (both external mass transfer and intraparticle diffusion) were considered. Equilibrium and kinetic results of fluoride adsorption onto the adsorbents demonstrated the following order of performance: Al‐Na‐HUD>Al‐F9> Al‐HUD>Al‐A4.

Applicability of zeolite for CO2 storage in a CaO-CO2 high temperature energy storage system

Many reversible thermal dissociation reactions have been reviewed for storing thermal energy at very high temperatures, such as high temperature heat from power plants. Among them, dissociation of CaCO3 seems very promising as the material can dissociate at 1098 K under atmospheric condition and the reactants involved are free from toxicity. One of the dissociation products, CO2 gas, requires a storage system. Three CO2 storage systems are being considered and the thermal operating efficiencies, COP, of the respective CaO-CO2 energy storage systems are evaluated. It is found that the system with a zeolite adsorbent for CO2 storage becomes quite comparable to other systems when the adsorptivity of the adsorbent increases to higher values. The CO2 adsorption characteristics of zeolite 13X and super activated carbon under a temperature range 303–573 K are studied. Based on the adsorption data, it is found that zeolite 13X adsorbent can be used as a CO2 storage medium in a CaO-CO2 high temperature thermal energy storage system.

Chapter 1 Fluoride Removal from Water Using Adsorption Technique

Abstract Management of contaminants such as fluoride is a major public issue. Fluoride of geogenic origin in groundwater used as a source of drinking water is a major concern because fluoride content above permissible levels is responsible for human dental and skeletal fluorosis. Consequently, water sources containing elevated levels of fluoride have to be treated. Coagulation/precipitation, electrochemical, electrodialysis, reverse osmosis, adsorption and hybrid processes combining adsorption and dialysis are widely used defluoridation techniques. Currently, however, the development of cost effective and clean processes due to economic constraints and stringent environmental policies is desired. Adsorption technique is arguably one of the most versatile of all the defluoridation techniques due to a number of reasons such as cost, diverse end-uses, socio-cultural acceptance, regulatory compliance, environmental benignity and simplicity. For this technique, activated alumina, bone char and clay adsorption media are the most developed. During the past two decades, extensive research has focused on a number of alternative adsorbents, some exhibiting improved fluoride sorption performances while at the same time do not alter the quality of treated water. Studies have also shifted toward systematic modeling to approximate adsorber design parameters. In view of these, this review opens with a description of paradigm shifts in drinking water sources and highlights the genesis and toxicological effects of fluoride in drinking water as a means of defining the existing problem. Next, potential and established techniques for defluoridation are revisited. This is closely followed with a review of defluoridation adsorbents recognized by the World Health Organization and those novel defluoridation adsorbents reported in literature over the last two decades, with special reference to drinking water. Emphasis is laid on their availability, fluoride sorption capacity and mechanisms. In recognizing surface-tailored zeolite as a novel sorbent, detailed analysis of fluoride adsorption behavior is provided for this sorbent. Finally, defluoridation adsorption unit configurations, and challenges to and prospects for their implementation are briefly discussed.

Study on reaction kinetics and selective precipitation of Cu, Zn, Ni and Sn with H2S in single-metal and multi-metal systems

Determination of reaction kinetics and selective precipitation of Cu, Zn, Ni and Sn with H(2)S in single-metal and multi-metal systems were studied to develop a process of metal recovery from plating wastewater. As samples, single-metal model wastewaters containing Cu, Sn, Zn or Ni, and multi-metal model wastewater containing Cu-Zn-Ni or Sn-Zn mixtures were used. In both single-metal and multi-metal systems, the pH value was precisely controlled at a value of 1.5 for CuS and SnS precipitation, 4.5 for ZnS precipitation and 6.5-7.0 for NiS precipitation. Subsequently, the sulfidation of Cu, Sn, Zn and Ni was evaluated. It was found that an amount of H(2)S equimolar to a given metal was sufficient to achieve almost complete precipitation of the particular metal. Further, the selectivity of metal precipitation was found to be higher than 95% in the Cu-Zn-Ni multi-metal system and higher than 91% in the Sn-Zn system. It was also found that the sulfidation reaction proceeded in accordance with Higbies penetration theory and reaction rate constants and mass-transfer coefficients under various experimental conditions were determined. Finally, the reaction rate constants obtained in single-metal and multi-metal systems were found to be almost the same indicating that the precipitation of a particular metal was not significantly affected by the presence of other components.

FORMATION MECHANISM OF Tio2 FINE PARTICLES PREPARED BY THE SPRAY PYROLYSIS METHOD

ABSTRACT Fine particles of Tio2 were prepared from titanyl sulfate solution by the Spray pyrolysis Method( SPM) The reaction tube was divided into four zones: drying, dehydration, pyrolysis 1 and pyrolysis 2 zones. Under various reaction temperature and carrier gas flow rate, the mean size and the size distribution of particles collected at different sampling positions along the axial direction of the reactor were compared. The effects of operating conditions of drying, dehydration and subsequent pyrolysis steps on the formation mechanism of Tio2 fine particles were discussed

Ultrasound assisted extraction and decomposition of Cl-containing herbicide involved in model soil

This work focused on ultrasound assisted extraction and decomposition of MCPA [(4-chloro-2-methylphenoxy) acetic acid] from model soil under argon atmosphere. In the experiments, 10 g model soil containing 1.75 x 10(-5) mol MCPA mixed with 90 g of de-aired water was used. For a comparison, the experiments were also carried out using MCPA aqueous solution of which the concentration was adjusted to 1.75 x 10(-4) mol/l. The results showed that complete MCPA decomposition was achieved after 120 min in the case of MCPA aqueous solution. Meanwhile, in the case of model soil, the MCPA decomposition ratio of 0.9 was obtained after 600 min. This result was attributed to combined effect of MCPA adsorption on kaolin and to attenuation of ultrasound by solid particles of kaolin. To evaluate ultrasound attenuation in the presence of solid particles, experiments with slurry consisting of alumina particles and MCPA solution were carried out at alumina particles concentration range of 0.1-100g/l. The results showed that the MCPA initial decomposition rate significantly decreased with an increase in alumina particles concentration. Thus, it was concluded that the solid particles reduced the MCPA decomposition ratio by reducing the formation of reactive species such as hydroxyl radicals which are know to be necessary for MCPA decomposition.

Enhanced dechlorination of chlorobenzene and in situ dry sorption of resultant Cl-compounds by CaO and Na2CO3 sorbent beds incorporated with Fe2O3.

The dechlorination of C(6)H(5)Cl and the in situ dry sorption of Cl-compounds produced by C(6)H(5)Cl decomposition in an alkaline sorbent of CaO or Na(2)CO(3) incorporated with Fe(2)O(3) were studied. A sample gas containing C(6)H(5)Cl at an initial concentration of 500 ppm balanced by either N(2), O(2) (5%)-N(2) or H(2)O (10%)-N(2) carrier gas was introduced into a lab-scale quartz tube reactor where CaO or Na(2)CO(3) sorbent was packed with Fe(2)O(3). Subsequently, the effect of Fe(2)O(3) addition to CaO or Na(2)CO(3) on the removal of C(6)H(5)Cl, achieved by the decomposition of C(6)H(5)Cl as well as the dry sorption of Cl-compounds produced by C(6)H(5)Cl decomposition, was investigated. It was found that the decomposition of C(6)H(5)Cl in CaO or Na(2)CO(3) sorbent bed incorporated with Fe(2)O(3) occurred in the lower temperatures, compared to the case when only CaO or Na(2)CO(3) sorbent bed was used. Thus, Fe(2)O(3) was found to play a catalytic role in the oxidative decomposition of C(6)H(5)Cl. Further, the decomposition of C(6)H(5)Cl in a bed containing only Fe(2)O(3) was promoted by the presence of O(2) and H(2)O in the reaction atmosphere. Moreover, a higher amount of Cl was absorbed in the combined CaO/Fe(2)O(3) and Na(2)CO(3)/Fe(2)O(3) beds, compared to the absorption of Cl-compounds in only CaO or Na(2)CO(3) sorbent bed. Finally, the comparison of CaO and Na(2)CO(3) sorbents showed that the decomposition of C(6)H(5)Cl and the in situ dry sorption of the resultant Cl-compounds in the combined Na(2)CO(3) and Fe(2)O(3) beds were higher than those in the combined CaO and Fe(2)O(3) beds.

Convective heat transfer of exothermic reactive gas flowing across a heating cylinder coated with platinum catalyst in a narrow duct

Abstract The effect of a catalytic surface reaction on the convective heat transfer is studied for a cross flow to a cylinder. Platinum catalyst is coated on the surface of the cylinder which is set horizontally in a rectangular duct. The fluid is a mixture of SO 2 and O 2 and the following exothermic reaction takes place on the surface of the cylinder: SO 2 +1/2 O 2 = SO 3 +99 kJ/mol . The cylinder is uniformly heated electrically from the inside by the DC power supply, and the reactant gas flows through a small clearance between the cylinder and the duct wall. The heat transfer coefficient is determined based on the temperature difference between the inlet gas and the forward stagnant point of the cylinder. The heat transfer coefficient for the non-reacting gas is at least about two times higher than the conventional correlation because of the effect of natural convection and small clearance. When the reaction takes place, the heat transfer coefficient rises by 4–16%. The effect of the enhancement is proportional to the reaction rate. The same correlation of the convective heat transfer as the SO 2 –O 2 reaction system is observed for the reaction system: CH 4 +2O 2 =CO 2 +2H 2 O, which proceeds faster without volume change of the gas than the former reaction.

NO reduction and the formation of nitrogen compounds over a metal-supported three-way catalyst

Abstract The fundamental characteristics of NO reduction and the formation of nitrogen compounds such as N 2 O, NH 3 and HCN were investigated on a metal-honeycomb-supported three-way catalyst. Experiments were carried out in a quartz glass tube reactor by flowing simulated gas mixtures in the NO/H 2 /Ar, NO/CH 4 /Ar and NO/CO/Ar systems. In the NO/H 2 /Ar system, NO reduction began at the lowest temperature of all the systems examined. In any system, the conversion ratio of NO reduction was over 90% at gas temperature higher than 900 K. However, depending on temperature, NO reduction resulted in nitrogen-compound formation as NH 3 in the NO/H 2 /Ar system, HCN in the NO/CH 4 /Ar system, and N 2 O in all systems. In particular, N 2 O formation was dominant at relatively low temperature. The effect of the coexistence of the oxygen on NO reduction was also examined and a sufficient conversion was observed if the O 2 concentration was less than 1 vol%.

Heat storing/releasing characteristics of a chemical heat storage unit of electricity using a Ca(OH)2/CaO reaction

The applicability of the Ca(OH)2/CaO thermochemical reaction for heat storage derived from night-time electricity was studied. The heat releasing rate, heat output, and thermal efficiency were investigated experimentally by using a laboratory/scale heat storage unit incorporated with a fin-type heat exchanger. It was found that, during the heat-releasing step, when water vapor at an ambient temperature of around 300K was introduced into the reactor, the temperature of the CaO reactant bed was increased to around its equilibrium temperature of 610 K. The hydration heat was then recovered by the heat exchanger medium (city water) the temperature of which was rapidly increased to above 343 K. The amount of the heat recovered from the CaO packed bed was about four times higher than that which might be recovered if the energy storage was carried out by the latent heat of water of the same volume.