里川 重夫

Selective CO methanation was carried out over 10 wt%Ni/TiO2 and 0.5 wt%Ru-10 wt%Ni/TiO2, and the durability was examined. During the long-term test, both catalysts abated CO concentration from 0.25% (dry base) to less than 0.05% above ca. 175 degrees C with CO2 methanation suppressed. Ru-Ni/TiO2 exhibited the high activity of CO methanation compared to Ni/TiO2 during the test. Furthermore, for more than 5500 h, Ru-Ni/TiO2 maintained a wide temperature window for selective CO methanation (>50 degrees C), where CO and CH4 concentrations were <0.05% and <1%, respectively, at a high gas hourly space velocity of 10,000 h(-1). Over Ni/TiO2 and Ru-Ni/TiO2, CO2 methanation activity was initially enhanced, and then stabilized. The initial promotion of CO2 methanation activity is possibly due to the reduction of NiO which remained unreduced after the prereduction by H-2 at 450 degrees C. (C) 2014 Elsevier B.V. All rights reserved.

Selective CO methanation over Ru/Ti02, Ru-Ni/Ti02, Ru-Co/Ti02, Ru-Fe/Ti02, Ru-La/Ti02, Ru-K/Ti02, and Ru-Ni-La/TiO2 was investigated as a CO removal method from reformate gas for polymer electrolyte fuel cell applications, and the selectivity and activity were examined. The addition of Co and La to Ru/TiO2 improved both CO and CO2 methanation, while the addition of Ni raised only the activity for CO methanation. The addition of La increased the electron density in the Ru species, which likely enhanced the dissociation of the C-0 bond of CO on Ru probably due to back donation of electrons from Ru to CO. This led to high CO methanation activity over Ru-Laffi02. The trimetallic catalyst Ru-Ni-La/TiO2 showed the highest CO methanation activity among the prepared catalysts, resulting in a wider temperature range for selective CO methanation at low temperatures compared to Ru/Ti02. Crown Copyright 2013 Published by Elsevier B.V. All rights reserved.

The removal of CO from hydrogen-rich gas produced by steam reforming of hydrocarbons by selective CO methanation was investigated over xwt% Ru-ywt% Ni/TiO2 ( x = 0, 0.2, 0.3, 0.4, y = 0, 5, 9). The bimetallic catalyst Ru-Ni/TiO2 exhibited higher activity of CO methanation at low temperatures and lower activity of CO2 methanation at high temperatures than Ru/TiO2. Especially, 0.2 wt% Ru-9 wt% Ni/TiO2 was the most suitable catalyst for selective CO methanation. As for the prepared Ru-Ni/TiO2 catalysts, the reverse water gas shift ( RWGS) reaction was accelerated with an increase in the Ru loadings. Consequently the 0.2 wt% Ru-9 wt% Ni/TiO2 produced little CO due to the low activity of RWGS reaction, resulting in rapid abatement of CO at low temperatures and low production of CH4 at high temperatures compared to 0.3 wt% Ru-9 wt% Ni/TiO2 and 0.4 wt% Ru-9 wt% Ni/TiO2. (c) 2014 Elsevier Ltd. All rights reserved.

Various types of zeolites were evaluated for the adsorptive separation of ethanol and gasoline in ethanol blended gasoline. Mixed solution of ethanol and n-heptane was used as a model fuel. Adsorption selectivities of zeolites for ethanol and n-heptane were measured by a pulse testing method at 80 degrees C. These properties were dependent on the framework structures, exchangeable cations and Si/Al atomic ratios of zeolites. The adsorption capacities of zeolites for ethanol and n-heptane were evaluated by a continuous flow adsorption testing method at 80 degrees C. Zeolites with the FAU type structure (Na-Y and H-Y) showed higher adsorption capacities compared to the other types of zeolites. Adsorption strength of ethanol on zeolites was evaluated by a temperature programmed desorption method. Ethanol molecules adsorbed on Na-Y and H-Y were desorbed by heat treatment at around 300 degrees C, but ethanol adsorbed on H-Y was partially dehydrated because of zeolite acidity.

This work investigated magnetization changes in NiFe2O4 nanoparticles induced by the adsorption of a series of carboxylic acids. The application of formic acid resulted in a significant 8.6% decrease in the magnetization of NiFe2O4 nanoparticles at 18,000Oe. With increasing carbon bond number in the saturated carboxylic acids, reductions in the magnetization of NiFe2O4 nanoparticles became around 4%. All unsaturated carboxylic acids produced approximately equivalent reductions in the magnetization, regardless of their double bond content. Based on these results, the observed NiFe2O4 magnetization changes appear to depend on either the polarity or the molecular size of the carboxylic acids and are believed to be caused by canting or pinning of spins in the vicinity of particle surfaces following adsorption of the acids. © 2014 The Ceramic Society of Japan and the Korean Ceramic Society.

The removal of CO from reformate streams by selective CO methanation was investigated over TiO2 supported Ru-Ni bimetallic and monometallic catalysts. The combination of Ru and Ni enhanced CO methanation at low temperatures. The introduction of Ni into Ru/TiO2 decreased the CO2 conversion rate at 260 degrees C from 10 to 7.3 mu mol min(-1) g(cat)(-1). The use of Ru and Ni, thus, expands the temperature range of selective CO methanation. Transmission electron microscopy and temperature programmed reduction by H-2 confirmed that Ru species were in close proximity to Ni species on Ru-Ni/TiO2, indicating a decrease in direct contact between Ru and TiO2. Fourier transform infrared spectroscopy techniques revealed that the decomposition of the formate species, formed during CO2 methanation, is slow over Ru-Ni/TiO2, in contrast to Ru/TiO2. (C) 2013 Elsevier B.V. All rights reserved.

Selective CO methanation in the reformate gas over Ni/TiO2 catalyst was carried out. Nickel metal salts (nitrate, sulfate, acetate, chloride and formate) used as a precursor of nickel, calcination temperatures (400-700 degrees C), reduction temperatures (350-650 degrees C) and nickel contents (1-30 wt%) affected to the CO methanation activity and CO/CO2 selectivity over the obtained Ni/TiO2 catalysts. The appropriate nickel precursors were nitrate and acetate and suitable calcination and reduction temperatures were 400-500 degrees C and 450-550 degrees C, respectively. An increase of nickel contents in the Ni/TiO2 catalysts improved to the CO methanation activity. Reverse water gas shift reaction activity was extremely low regardless of nickel contents. As a result, temperature window of Ni/TiO2 catalyst was constant and it could be shifted to desired position by changing nickel content. (C) 2012 Elsevier B.V. All rights reserved.

ニッケル-チタニア触媒の調製法の違いによるCO選択メタン化反応への影響

Vermiculite was subjected to mechanochemical treatment using a vibration mill. The treated samples were characterized by XRD, FE-SEM, N-2-adsorption, FT-IR and Si-29-MAS NMR. The mechanochemical treatment led to a reduction in the particle size and a significant increase in the surface area. Surface hydroxyl (silanol, magnesiol and aluminol) groups, located on the clay particle edges and amorphous silica phase, were also generated. The mechanochemical treatment of vermiculite gave a dramatic improvement in the lead (II) adsorption capacity. (C) 2012 Elsevier B.V. All rights reserved.

Woody biomass samples were pyrolized at different temperatures and heating rates in a fluidized bed reactor (FBR). Only under the conditions of rapid pyrolysis between 600 and 1000 degrees C, porous alumina particles as the bed material adhered on the surface of the obtained char. The amount of particles adhering on the char derived from softwood was larger than that derived from hardwood.

Recently, the photocatalytic activity of titania has attracted considerable attention for solving various environmental problems. Photocatalysis is considered to be effective in air purification, water purification, and used for dealing with various types of environmental pollution. The smaller the particle size of titania, the faster the photocatalysis proceeds. Since our previous study revealed that the modification of synthesis process reduced the particle size of silica, we attempted to apply this process to synthesise titania, with an objective of obtaining titania with high photocatalytic activity. This paper describes an unconventional gas-phase synthetic method involving high-temperature hydrolysis. Copyright © 2012 Inderscience Enterprises Ltd.

Selective CO methanation in the reformate gas over Ni/TiO2 catalyst was carried out. Nickel metal salts (ntrate, sulfate, acetate, chloride and formate) used as a precursor of nickel, calcination temperatures (400-700℃), reduction temperatures (350-650℃) and nickel contents (1-30 wt%) affected to the CO methanation activity and CO/CO_2 selectivity over the obtained Ni/TiO_2 catalysts.

In situ treatment technologies, including chemical treatment by Fenton's reaction, are expected to be effective for site remediation of polluted soil. To get basic data on the decomposition rate of trichloroethylene (TCE) by Fenton's reaction using iron powder, we investigated the influence of pH and dissolved Fe ion concentration on the decomposition rate of TCE in the presence and absence of buffer solution to maintain pH value. The decomposition rate depended on hydrogen peroxide concentration, and the maximum rate was observed around concentration of 88 mol/m(3). This finding was explained by the consumption of hydroxyl radicals by a competing reaction with hydrogen peroxide against TCE decomposition by the hydroxyl radicals produced from hydrogen peroxide. Under this condition, the most rapid dissolution rate of iron, i.e., the maximum increasing rate of Fe ion concentration, and the most rapid reduction in pH value were observed. The results with buffer solution showed that dissolution rate of iron was highly dependent on pH, and it was suggested that TCE decomposition was accelerated by the increase of Fe ions, rather than directly by the lowering of pH. The initial lag period in the TCE decomposition with iron powder, in contrast to the rapid initial reaction in the case of Fe solution, was also explained by the relatively slow dissolution of iron and relatively fast rate of Fenton's reaction with ferrous iron to produce hydroxyl radicals. The concentration of Fe ions was estimated and suggested to be much higher and the pH lower in the film around iron powder than in the body of the liquid. Also, the transfer of TCE from the liquid body to the reaction area in the film was suggested to be accelerated by its decomposition.

Transesterification of triolein with various alcohols like methanol, ethanol, 1-propanol, 2-propanol and 1-butanol over CaO catalyst was performed at atmospheric pressure and the temperature near to the boiling point of each alcohol with various catalyst dosages. High transesterification reaction rate was obtained by the reaction with methanol over CaO catalyst. However some amounts of the catalyst dissolved into the products during the transesterification reaction and the crystalline phase of catalyst changed to Ca(C3H7O3)(2) at the early stage of reaction. On the other hand, the moderate transesterification reaction rates were obtained by the reaction with higher alcohols like ethanol, 1-propanol and 1-butanol over CaO catalyst. Calcium was hardly dissolved into the product and the structure of catalyst was not changed until the triolein conversion reached to 100%. After all of the raw triolein converted to products, both calcium leaching and the formation of Ca(C3H7O3)(2) started. Some experiments and characterization implied that triolein suppressed the formation of Ca(C3H7O3)(2) by inhibiting the contact of glycerol with CaO in the absence of methanol and methanol seems to eliminate such inhibitory effect of triolein. (C) 2011 Elsevier B.V. All rights reserved.

Key factors controlling the thermal and redox-cycle stability of Ag/SnO2 catalyst were investigated to establish the design concept of "self-regenerative" soot oxidation catalysts. The effect of thermal aging (in air at 1000 degrees C) on the soot oxidation activity was tested for Ag catalysts supported on SnO2, CeO2, ZrO2, TiO2, and MgO and SnO2-supported Cu, Pd, Rh, Ru, and Pt. Ag/SnO2 is found to be the most effective catalysts in terms of both activity and thermal stability. XRD and EXAFS results showed that particle growth of metal or metal oxide by the thermal aging was the main reason of the decreased soot oxidation activity, and the supported Ag species on Ag/SnO2 showed high sintering-resistance owing to the Ag-O-Sn bonds at metal-support interface. The effect of redox aging at 800 degrees C on the soot oxidation activity and structure of Ag/SnO2 was also studied. H-2-reduction of Ag/SnO2 lead to the formation of the large (20 nm) particles of Ag3Sn, which were then redispersed by the reoxidation treatment to small Ag nanoparticles. This self-regenerative property lead to no catalyst deactivation of Ag/SnO2 after successive redox treatments. It is concluded that the strong chemical interaction between silver and tin species (metallic and oxidic Sn) under both reductive and oxidative environments at high-temperature enables the design of highly sintering resistant Ag-based oxidation catalysts. (C) 2011 Elsevier B.V. All rights reserved.

Selective CO methanation over Ru/Al(2)O(3) and Ru/TiO(2) was investigated as a CO removal method from reforming gas, and the effect of reduction treatment and the support materials on the selectivity and activity was examined. CO methanation activity was degraded over both Ru catalysts by raising reduction treatment temperature, which brought about Ru particle growth except for Ru/TiO(2) reduced at 600 degrees C. Ru/TiO(2) showed higher CO methanation activity than Ru/Al(2)O(3) due to smaller Ru particle size. A close correlation was found between CO(2) methanation rate and interfacial length of Ru particle and support, which indicates that the interface was identified as the reaction sites of CO(2) methanation in CO and CO(2) coexisting atmosphere. CO(2) methanation over Ru/TiO(2) was suppressed in spite of long length of the interface compared to Ru/Al(2)O(3), stemming from the small amount of CO(2) adsorbed onto Ru/TiO(2). Ru/TiO(2) catalyst exhibited wider temperature window for selective CO methanation than Ru/Al(2)O(3) catalyst. (C) 2011 Elsevier B.V. All rights reserved.

バイオエタノールをガソリンに10％混ぜたE10ガソリンが自動車燃料としてアメリカ、ブラジルを中心に主流になっている。しかし、エタノールとガソリンは物性が異なるため、分離して燃焼したほうが出力や燃費の面で優れていることがわかっている。そこで、本研究では車上でE10ガソリンからのエタノール分離が可能な吸着剤の開発を目的とし、種々のゼオライトを用いた吸着実験を行い、ゼオライトの物性と分離性能との関係を検討した。

改質ガス中の微量CO除去を目的とした、CO選択メタン化反応用Ni触媒担体として、TiO₂を適用すると高い選択性が得られる。本研究では担体効果について検討を行うため、TEMを中心としたキャラクタリゼーションを行った。その結果、Ni粒子は担体との相互作用を持たない独立したナノ粒子として存在し、CO₂メタン化反応の主要な活性点となる、金属―担体界面がほとんどないことが分かった。

The pervaporation performance of heat-treated PVA membranes with varying degrees of saponification was examined for the separation of ethanol from mixtures with n-heptane, which simulates the on-board separation of ethanol from gasoline containing bioethanol. All of the PVA membranes showed high permselectivity for ethanol against n-heptane. The ethanol selectivity decreased slightly, but the permeation flux increased with decreasing degree of saponification. The ethanol weight fraction in the permeate was higher than 98% for all feed compositions studied for PVA-417 membrane with a degree of saponification of 78-81%. High ethanol selectivity was observed irrespective of the heat-treatment time, and a maximum flux was observed at 3 min heat treatment at 75 degrees C. The flux decreased with increasing heat-treatment temperature. The PVA membrane showed high ethanol selectivity (96.8% in the permeate) and flux (12.2 g.m(-2).h(-1)) for commercially available E10 (10 wt % ethanol) gasoline.

Eucalyptus biomass char was produced by a fluidized bed reactor. The influence of pyrolysis temperature and heating rate on char yield was investigated. The pyrolysis temperature ranged between 673K-1673K. When rapid pyrolysis, char yield was almost constant at about 15%, between 773K-1173K, while was decreased to several % with increased temperature. When slow pyrolysis (10 K/min), char yield was almost kept at 22-17% between 1173K-1673K. Fixed carbon and ash yields in fast pyrolysis char were investigated by NC coder. Fixed carbon yield based on the dry biomass was monotonously decreased and ash yield gave the maximum in the vicinity of 1073K. SEM picture was also given to elucidate the effect on its structure of pyrolysis temperature and heating rate.

Tetraethoxysilane (TEES) is produced as a major by-product from the disproportionation of triethoxysilane (TRES) during the non-halogen process to produce monosilane SiH₄ for polycrystalline silicon manufacturing. In this study, the hydrolysis of TEES was carried out to produce silica fines in the gaseous phase as an effective use of the TEES by-product. We expected to attain higher conversion under lower temperature than in the case of tetramethoxysilane TEMS. One-hundred percent conversion was obtained under 923 K and above, and such temperature is relatively low compared to the 100% conversion temperature of TEMS, which was more than 1123 K.

Selective methanation of CO was performed over Ni/TiO2. CO in reformate gas was completely removed at 150-300 degrees C. The CH4 concentration in the outlet gas could be maintained below 1% in the entire temperature region because Ni/TiO2 suppressed the CO2 methanation reaction. It can be considered that the formation of CO by the reverse water-gas-shift reaction is blocked by the application of TiO2 to the support of Ni catalyst and that it results in the high CO/CO2 selectivity of Ni/TiO2.

Selective methanation of CO in the reformate gas (CO/CO(2)/H(2)/H(2)O = 0.175/17.9/70.9/11.1) proceeded over Ru catalysts supported on metal oxides and zeolites. CO was selectively methanated at wide temperature ranges (200-275 A degrees C) over Ru/gamma-Al(2)O(3), Ru/TiO(2) Ru/H-Y and Ru/H-beta catalysts. Higher Ru contents in Ru/gamma-Al(2)O(3) improved the selective CO methanation rate.

Layered materials of zinc hydroxychloride (ZHC), zinc hydroxynitrate (ZHN) and zinc hydroxysulfate (ZHS) were prepared by the precipitation method. The products were highly crystalline. The pH buffering capacities of the products are high in the pH range from 3 to 10. The zinc hydroxyl salts have a high capacity for adsorbing chromate ions. (C) 2010 Elsevier B.V. All rights reserved.

銀アルミナ触媒を用いたプロパンを還元剤としたNO選択還元反応において、反応ガス中にオゾンを添加することでNOを窒素に変換する反応温度領域は450℃付近から300℃付近まで低温側にシフトすることを見出した。本反応の律速段階は炭化水素の活性化であると考えられており、オゾンはプロパンの酸化を促進することで、低温でのNO選択還元活性の向上をもたらしたと考えた。オゾンによるプロパンの酸化反応は無触媒でも進行するが、窒素の生成には触媒が必要であり、NO選択還元反応は触媒上で進行すると考えた。また、銀アルミナ以外でもNO選択還元活性のあるアルミナ系触媒であればいずれも低温活性の向上効果が認められた。

PEFC用水素製造プロセスにおける微量のCO除去方法として、COメタン化反応が注目を集めている。しかし改質ガス中に共存するCO₂が同時にメタン化すると熱暴走する危険性があることが問題である。そこでCOメタン化選択性を向上させる必要がある。今までにCOメタン化反応に対する担体効果を調べており、Ru/TiO₂触媒が高いCOメタン化選択性を示した。今回は活性種に金属を添加することで、COメタン化選択性の高い担持二元金属触媒を開発する。

改質ガス中の微量CO除去を目的とし、Al₂O₃及びTiO₂を担体とした卑金属（Ni、Fe、Co）触媒を用いたCO選択メタン化反応を検討した。その結果、Ni/TiO₂が特異的に高活性、高CO/CO₂選択性を示し、従来の商業用Ru/Al₂O₃触媒以上に使用可能な温度域が広がることが分かった。本触媒では逆水性ガスシフト反応が著しく抑制され、その結果として高いCO/CO₂選択性が得られたものと推察した。種々のキャラクタリゼーションを行い、TiO₂担体が活性、選択性に与える影響について検討した。

The authors have so far demonstrated that production of fine TiO₂ powder is possible by gas phase hydrolysis of titanium tetraisopropoxide (TTIP). In this paper, the effects are discussed of the shape of reactor and operational condition, such as mixing condition on the produced particle properties especially particle diameter of produced TiO₂ fines.<BR> Our originally designed reactor was used, in which the steam vapor was fed from the bottom of the reactor then transported through an internal thin tube in the heated part of the reactor, and then mixed with TTIP fed from the top of the reactor without heating. The TiO₂ fines were produced by 1.00 ml/min of TTIP gas flow (RC I) at 200, 300, 400 and 500°C of the reactor temperature with 10.0 ml/min (at 25°C) of TTIP gas flow (RC II).<BR> The particle diameter of TiO₂ produced by gas phase synthesis was the smallest at 200°C, while the produced TiO₂ showed increased crystallinity and photochemical activity with increased reaction temperature. The photocatalytic activity of TiO₂ fines produced at 500°C was around 1/10, while that of the calcinated TiO₂ fines produced at 200°C under RC II was 1/4 compared with that of JRC-TIO-4, respectively. The results of the photocatalytic activity tests suggested the activity is expected to be increased not only with increased crystallinities but also with decreased particle size.

The TiO2/SiO2/Fe3O4 (TSF) photocatalyst was used for the treatment of synthetic dyes wastewater. Different operating conditions such as catalyst load, pH and dye concentration were investigated in order to determine the optimum operating conditions. The optimum operating conditions were found to be 2500 ppm TiO2 photocatalyst dose and pH 3. More catalyst dose led to reduction in rate of reaction due to aggregation of photocatalyst as well as increasing of opacity inside photoreactor. Acidic medium favored adsorption of studied dyes on photocatalyst, and hence increased the rate of reaction. Under optimum conditions, complete decolourization and degradation of the organic dyes could be achieved within less than 45 min. Kinetic studies indicated that rate of reaction depends on three parameters: photocatalyst load, dye concentration and transmittance inside photoreactor. TSF photocatalyst could be used several times with nearly the same efficiency. The reuse of the photocatalyst is supposed to decrease the final cost of the treatment process.

The new methacrylic monomer, 3,5-dimethoxyphenyl methacrylate (DMOPM) was synthesized by reacting 3,5-dimethoxyphenol dissolved in ethyl methyl ketone (EMK) with methacryloyl chloride in presence of triethylamine as a catalyst. The homopolymer and copolymers of DMOPM with glycidyl methacrylate (GMA) were synthesized by free radical polymerization in EMK solution at 70 +/- 1 degrees C using benzoyl peroxide as a free radical initiator. The copolymerization behaviour was studied in a wide composition interval with the mole fractions of DMOPM ranging from 0.15 to 0.9 in the feed. The homopolymer and the copolymers were characterized by FT-IR, (1)H NMR and (13)C NMR spectroscopic techniques. The solubility was tested in various polar and non-polar solvents. The molecular weight and polydispersity indices of the polymers were determined using gel permeation chromatography. The glass transition temperature of the copolymers increases with increase in DMOPM content. The thermogravimetric analysis of the polymers showed that the thermal stability of the copolymer increases with DMOPM content. The copolymer composition was determined using (1)H NMR spectra. The monomer reactivity ratios were determined by the application of conventional linearization methods such as Fineman-Ross (r(1) = 0.520, r(2) = 2.521), Kelen-Tudos (r(1) = 0.629, r(2) = 2.554) and extended Kelen-Tudos methods (r(1) = 0.600, r(2) = 2.502). (C) 2009 Elsevier Ltd. All rights reserved.

A novel acrylic monomer, 4-cyanophenyl acrylate (CPA) was synthesized by reacting 4-cyanophenol dissolved in methyl ethyl ketone with acryloyl chloride in the presence of triethylamine as a catalyst. Copolymers of CPA with methyl methacrylate (MMA) at different composition was prepared by free radical solution polymerization at 70 +/- 1 A degrees C using benzoyl peroxide as an initiator. The copolymers were characterized by FT-IR, (1)H-NMR and (13)C-NMR spectroscopic techniques. The solubility tests were checked in various polar and non polar solvents. The molecular weight and polydispersity indices of the copolymers were estimated by using gel permeation chromatography. The glass transition temperature of the copolymers increases with increases MMA content. The thermal stability of the copolymer increases with increases in mole fraction of CPA content in the copolymer. The copolymer composition was determined by using (1)H-NMR spectra. The monomer reactivity ratios determined by the application of linearization methods such Fineman-Ross (r (1) = 0.535, r (2) = 0. 0.632), Kelen-Tudos (r (1) = 0.422, r (2) = 0.665) and extended Kelen-Tudos methods (r (1) = 0.506, r (2) = 0. 0.695).

This research is mainly directed toward the development of hardness of glass ceramic by adding different amounts of ZrO2 to the glass and by applying different heat-treatments. Differential thermal analysis (DTA), X-ray diffraction (XRD) and Scanning electron microscope (SEM) were used to study the crystallization behaviour of the glass samples. The only observed crystalline phases were tetragonal and monoclinic zirconia. Hardness was found to increase by increasing time and temperature of heat-treatment due to the formation of monoclinic phase as a result of the martensitic reaction. This transformation opposes crack opening. (C) 2008 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

The sorption performance of a modified carbon black was explored with respect to arsenic removal following batch equilibrium technique. Modification was accomplished by refluxing the commercial carbon black with an acid mixture comprising HNO(3) and H(2)SO(4). Modification resulted in the substantial changes to the inherent properties like surface chemistry and morphology of the commercial carbon black to explore its potential as sorbent. The suspension pH as well as the point of zero charge (pH(pzc)) of the material was found to be highly acidic. The material showed excellent sorption performance for the removal of arsenic from a synthetic aqueous solution. It removed similar to 93% arsenic from a 50 mg/L solution at equilibration time. The modified carbon black is capable of removing arsenic in a relatively broad pH range of 3-6, invariably in the acidic region. Both pseudo-first-order and second-order kinetics were applied to search for the best fitted kinetic model to the sorption results. The sorption process is best described by the pseudo-second-order kinetic. It has also been found that intra-particle diffusion is the rate-controlling step for the initial phases of the reaction. Modelling of the equilibrium data with Freundlich and Langmuir isotherms revealed that the correlation coefficient is more satisfactory with the Langmuir model although Freundlich model predicted a good sorption process. The sorption performance has been found to be strongly dependent on the solution pH with a maximum display at pH of 5.0. The temperature has a positive effect on sorption increasing the extent of removal with temperature up to the optimum temperature. The sorption process has been found to be spontaneous and endothermic in nature, and proceeds with the increase in randomness at the solid-solution interface. The spent sorbent was desorbed with various acidic and basic extracting solutions with KOH demonstrating the best result (similar to 85% desorption). (C) 2008 Elsevier B.V. All rights reserved.

Natural mordenite (NM), natural clinoptilolite (NC), HDTMA-modified natural mordenite (SMNM) and HDTMA-modified natural clinoptilolite (SMNC) have been proposed for the removal of As(V) from aqueous solution (HDTMA = hexadecyltrimethylammonium bromide). Influence of time on arsenic sorption efficiency of different sorbents reveals that NM, NC, SMNM and SMNC require about 20, 10, 110 and 20 h. respectively to reach at state of equilibrium. Pseudo-first-order model was applied to evaluate the As(V) sorption kinetics on SMNM and SMNC within the reaction time of 0.5 h. The pseudo-first-order rate constants, k are 1.06 and 0.52 h(-1) for 1 and 0.5 g of SMNM, respectively. The observed k values 1.28 and 0.70 h(-1) for 1 and 0.5 g of SMNC. respectively are slightly high compared to SMNM. Surfactant surface coverage plays an important role and a significant increase in arsenate sorption capacity could be achieved as the HDTMA loading level on zeolite exceeds monolayer coverage. At a surfactant partial bilayer coverage, As(V) sorption capacity of 97.33 and 45.33 mmol kg(-1) derived from Langmuir isotherm for SMNM and SMNC, respectively are significantly high compared to 17.33 and 9.33 mmol kg(-1) corresponding to NM and NC. The As(V) uptake was also quantitatively evaluated using the Freundlich and Dubinin-Kaganer-Radushkevich (DKR) isotherm models. Both SMNM and SMNC removed arsenic effectively over the initial pH range 6-10. Desorption performance of SMNM and SMNC were 66.41% and 70.04%, respectively on 0.1 M NaOH regeneration solution. (C) 2008 Elsevier B.V. All rights reserved.