Gas desulphurization by sorption of SO2 on CuO/Al2O3 solid sorbent in a counterflow multistage fluidized bed reactor: Experimental analysis and modelling of the reactor

This paper gives a review of several works performed in the Laboratory of Chemical Engineering of Toulouse (France) on the desulphurization of gas mixtures by chemical sorption of sulphur dioxide on cupric oxide deposited on porous alumina particles in a counterflow multistage fluidized bed reactor. The first part of the paper presents experimental results concerning effects of gas and solids flow rates, hold up of solids in the reactor, temperature and concentrations of SO₂ and other gases (CO₂, H₂O and NO _x ). Desulphurization yields exceeding 90% were obtained using a four-stage reactor and sulphur dioxide content could be reduced from 3000 ppm to less than 300 ppm with a small gas pressure drop. The presence of other components in the flue gas led to slight changes in the desulphurization yield. This could be corrected by a better choice of the operating conditions. The second part of the article presents the modelling of the reactor by taking into account the residence time distribution of the solid particles through it. Comparison between the model predictions and experimental results showed that the assumptions of Davidson and Harrison are sophisticated enough to describe reactor operation under steady state conditions. This paper is dedicated to Dr L K Doraiswamy on his sixtieth birthday.     

Long-term exposure of bacterial and protozoan communities to TiO2 nanoparticles in an aerobic-sequencing batch reactor

Abstract

Titanium dioxide (TiO₂) nanopowders at different concentrations (0–50 mg L^?1) were injected into an aerobic-sequencing batch reactor (SBR) to investigate the effects of long-term exposure to nanoparticles on bacterial and protozoan communities. The detection of nanoparticles in the bioflocs was analyzed by scanning electron microscopy, transmission electron microscopy, and energy-dispersive x-ray spectroscopy. The SBR wastewater experiments were conducted under the influence of ultraviolet light with photocatalytic TiO₂. The intrusion of TiO₂ nanoparticles was found both on the surface and inside of the bioflocs. The change of microbial population in terms of mixed liquor-suspended solids and the sludge volume index was monitored. The TiO₂ nanoparticles tentatively exerted an adverse effect on the microbial population, causing the reduction of microorganisms (both bacteria and protozoa) in the SBR. The respiration inhibition rate of the bacteria was increased, and the viability of the microbial population was reduced at the high concentration (50 mg L^?1) of TiO₂. The decreasing number of protozoa in the presence of TiO₂ nanoparticles during 20 days of treatment with 0.5 and 1.0 mg L^?1 TiO₂ is clearly demonstrated. The measured chemical oxygen demand (COD) in the effluent tends to increase with a long-term operation. The increase of COD in the system suggests a decrease in the efficiency of the wastewater treatment plant. However, the SBR can effectively remove the TiO₂ nanoparticles (up to 50 mg L^?1) from the effluent.     

Role of Brassica juncea (L.) Czern. (var. Vaibhav) in the phytoextraction of Ni from soil amended with fly ash: selection of extractant for metal bioavailability

A pot experiment was carried out to study the potential of the plant of Brassica juncea for the phytoextraction of metal from fly ash amended soil and to study correlation between different pool of metals (total, DTPA, CaCl(2) and NH(4)NO(3)) and metal accumulated in the plant in order to assess better extractant for plant available metals. The results of total metal analysis in the soil revealed the presence of Cr, which was found below detection limit (BDL) in the plants. The fly ash (FA) amendments and soil samples were extracted with different extractants and the level of metal vary from one extractant to another. The regression analysis between total and extractable metals showed better regression for all the tested metals except Mn (R(2)=0.001) in DTPA extraction. Correlation coefficient between metal accumulation by the plant tissues and different pool of metals showed better correlation with DTPA in case of Fe, Zn and Ni, whereas, Cu was significantly correlated with NH(4)NO(3) and other metals (Pb, Mn) with CaCl(2). The soil analysis results revealed that the mobility and plant availability of metals (Fe, Mn, Zn, Ni) within the profiles of amended soils was influenced by the change in pH, however, Pb and Cu was not affected. The metal accumulation in total plant tissues was found in the order of Fe>Ni>Zn>Mn>Cu>Pb and its translocation was found more in upper part. The plants grown on soil amended with 25%FA have shown significant increase in plant biomass, shoot and plant height, whereas, no significant effect was observed in root length. The cluster analysis showed 10%FA behave differently on the basis of physico-chemical properties and metal behavior. Thus, it may be concluded that B. juncea can be used for phytoextraction of metals, especially Ni in fly ash amendment soil.     

Kinetic study of Cu(II) adsorption on nanosized BaTiO(3) and SrTiO(3) photocatalysts

In this study, nanoparticles with perovskite structure (nano-SrTiO(3) and nano-BaTiO(3)) were synthesized via a co-precipitation method, and their photocatalytic and adsorption characteristics were investigated. Both of them exhibited some photocatalytic activity and possessed a high adsorption capacity for copper ions. Further, the pseudo-first-order model was found to be more suitable to fit the experimental data. Moreover, it suggested that the Langmuir model was more adequate in simulating the adsorption isotherm. The maximum adsorption capacity was 370.4 mg/g and 200.0mg/g for nano-SrTiO(3) and nano-BaTiO(3), respectively. The negative apparent free energy confirmed that the Cu(2+) adsorption onto the nano-photocatalysts was a spontaneous process. The underlying mechanism of adsorption of Cu(II) onto nano-perovskites could be due to the ion exchange and surface complexation. From the results, SrTiO(3) and BaTiO(3) nanoparticles may be an effective material for Cu(2+) removal and, together with its photocatalytic activity, may be suitable for environmental remediation applications.     

Synthesis and electrochemical properties of Nb-doped Li3V2(PO4)3/C cathode materials for lithium-ion batteries

Li₃V_2−xNb_x(PO₄)₃/C cathode materials were synthesized by a sol-gel method. X-ray diffraction patterns demonstrated that the appropriate addition of Nb did not destroy the lattice structure of Li₃V₂(PO₄)₃, and enlarged the unit cell volume, which could provide more space for lithium intercalation/de-intercalation. Transmission electron microscopy and energy dispersive X-ray spectroscopy analysis illustrated that Nb could not only be doped into the crystal lattice, but also form an amorphous (Nb, C, V, P and O) layer around the particles. As the cathode materials of Li-ion batteries, Li₃V_2−xNb_x(PO₄)₃/C (x ≤ 0.15) exhibited higher discharge capacity and better cycle stability than the pure one. At a discharge rate of 0.5C, the initial discharge capacity of Li₃V_1.85Nb_0.15(PO₄)₃/C was 162.4 mAh/g. The low charge-transfer resistances and large lithium ion diffusion coefficients confirmed that Li₃V_2−xNb_x(PO₄)₃/C samples possessed better electronic conductivity and lithium ion mobility. These improved electrochemical performances can be attributed to the appropriate amount of Nb doping in Li₃V₂(PO₄)₃ system by enhancing structural stability and electrical conductivity.     

Reduction of Cu(II) to Cu(I) in solid CsCuCl3

The solid state reaction Cu + Cu²⁺ → 2Cu⁺ in CsCuCl₃ was studied at 499 K using a cell in which the Cu(II) sample was put between two copper discs. Mass changes, thickness of the product layer and the total electrical resistance of the cell were measured as a function of time, both with and without (spontaneous) applied voltage.     

Preparation and characterization of Ti/SnO(2)-Sb(2)O(3)-Nb(2)O(5)/PbO(2) thin film as electrode material for the degradation of phenol

In this work, a novel electrode of titanium substrate coated with mixed metal oxides of SnO(2), Sb(2)O(3), Nb(2)O(5) and PbO(2) was successfully prepared using thermal decomposition and electrodeposition. The surface morphology and the structure of the prepared thin film were characterized by scanning electronic microscopy (SEM) and X-ray diffraction (XRD), respectively. Experimental results showed that the structure of the prepared electrode might be described as a Ti/SnO(2)-Sb(2)O(3)-Nb(2)O(5)/PbO(2) thin film and its surface was mainly comprised pyramidal-shape beta-PbO(2) crystals. The modified electrode had higher oxygen evolution potential than that of other PbO(2) modified electrodes. Electrocatalytic oxidation of phenol in aqueous solution was studied to evaluate the potential applications of this electrode in environmental science. The phenol removal efficiency in an artificial wastewater containing 0.50g/L phenol could reach 78.6% at 20 degrees C and pH 7.0 with an applied electricity density of 20mA/cm(2) and treatment time of 120min. When 21.3g/L chloride was added to this wastewater, the removal efficiency could reach to 97.2%.     

Studies on adsorption, desorption and biodegradation of pentachlorophenol by the anaerobic granular sludge in an upflow anaerobic sludge blanket (UASB) reactor

PCP-degrading anaerobic granular sludge could be formed in an upflow anaerobic sludge blanket (UASB) reactor that was seeded with anaerobic sludge acclimated to chlorophenol. When hydraulic retention time (HRT) was 20-22 h and PCP loading rate was 200-220 mgL(-1)d(-1), the wastewater containing 170-180 mgL(-1) PCP could be treated effectively in UASB reactor, and PCP removal rate reached up to 99.5%. PCP adsorption and desorption by anaerobic granular sludge follow Freundlich isothermal equation and part of adsorption capacity was not reversible. And the isothermal equation could well describe the variation law of PCP adsorption and desorption by anaerobic granular sludge. The results indicated that the principal removal mechanism of PCP was biodegradation by anaerobic granular sludge, but not adsorption or volatilization.     

Facile synthesis and electrochemical properties of Mn3O4 nanoparticles with a large surface area

Mn₃O₄ nanoparticles were prepared by a novel oxidation-precipitation method at a low temperature. The crystal phase, microstructure, surface area and electrochemical properties of the products were characterized by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), N₂ adsorption-desorption isotherms and cyclic voltammetry (CV). The results indicate that the addition of citric acid and tartaric acid remarkably reduced the particle size and increased the specific surface area of Mn₃O₄ nanoparticles. The samples prepared by the addition of citric acid and tartaric acid have a narrow particle size distribution of 5-10 nm, a surface area of 119 and 122 m²/g, and a capacitance of 171 and 172 F g⁻¹, respectively.     

Selective removal of Pb(II), Cd(II), and Zn(II) ions from waters by an inorganic exchanger Zr(HPO3S)2

The present study reported synthesis of a new inorganic exchanger, i.e., zirconium hydrogen monothiophosphate [Zr(HPO₃S)₂, denoted ZrPS] and its selective sorption toward Pb(II), Cd(II) and Zn(II) ions. ZrPS sorption toward all the three metals is dependent upon solution pH due to the ion-exchange nature. As compared to another inorganic exchanger zirconium phosphate [Zr(HPO₄)₂, denoted ZrP], ZrPS exhibits highly selective sorption toward these toxic metals from the background of calcium ions at great levels. Such sorption preference is mainly attributed to the presence of –SH group in ZrPS, as further demonstrated by FT-IR analysis and XPS study. Moreover, ZrPS particles preloaded with heavy metals could be efficiently regenerated with 6 M HCl for multiple use without any noticeable capacity loss. All the experimental results indicated that ZrPS is a promising sorbent for enhanced heavy metals removal from contaminated water.     

Synthesis and electrochemical properties of Ti doped Li3 − xFe2 − xTix(PO4)3/C cathode materials

Li_3 − xFe_2 − xTi_x(PO₄)₃/C (x = 0-0.4) cathodes designed with Fe doped by Ti was studied. Both Li₃Fe₂(PO₄)₃/C (x = 0) and Li_2.8Fe_1.8Ti_0.2(PO₄)₃/C (x = 0.2) possess two plateau potentials of Fe³⁺/Fe²⁺ couple (around 2.8 V and 2.7 V vs. Li⁺/Li) upon discharge observed from galvanostatic charge/discharge and cyclic voltammetry. Li_2.8Fe_1.8Ti_0.2(PO₄)₃/C has higher reversibility and better capacity retention than that of the undoped Li₃Fe₂(PO₄)₃/C. A much higher specific capacity of 122.3 mAh/g was obtained at C/20 in the first cycle, approaching the theoretical capacity of 128 mAh/g, and a capacity of 100.1 mAh/g was held at C/2 after the 20th cycle.     

Distribution of pyrochlore phase in Pb(Mg1/3Nb2/3)O3-PbTiO3 films and suppression with a Pb(Zr0.52Ti0.48)O3 interfacial layer

Thin films of the relaxor ferroelectric Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃ (PMN-PT) on Pt/Ti/SiO₂/Si (Pt/Si) substrates both with and without a Pb(Zr_0.52Ti_0.48)O₃ (PZT) interfacial layer were investigated. Perovskite and pyrochlore coexistence was observed for PMN-PT thin films without a PZT interfacial layer. Interestingly, most of the pyrochlore phase was observed in single-coated films and in the first layer of multi-coated films. The pyrochlore phase exhibited grains with an average size of about 25 nm, which is smaller than those of the perovskite phase (about 90 nm). In contrast, for PMN-PT thin films grown on a PZT interfacial layer, the formation of a pyrochlore phase at the interface between PMN-PT layers and the substrate is completely suppressed. Moreover, small grains are not observed in the films with a PZT interfacial layer. The measured polarization-electric field (P-E) hysteresis loops of PMN-PT films with and without PZT layers indicate that enhanced electrical properties can be obtained when a PZT interfacial layer is used. These enhanced properties include an increase in the value of remanent polarization P_r from 2.7 to 5.8 μC/cm² and a decrease in the coercive field E_c from 60.5 to 28.0 kV/cm.     

Thermal and FTIR spectral characterization of diammonium tetrachloromanganate (II) monohydrate crystals

Crystals of the new compound, diammonium tetrachloromanganate (II) monohydrate, were grown by slow evaporation solution growth method at room temperature. The compound was characterized through thermogravimetric, low temperature differential scanning calorimetric methods and Fourier Transform infrared spectroscopy. The elemental analysis and the thermal studies confirm the stoichiometry of the compound. The thermal anomalies observed in differential scanning calorimetric curve at − 9.8 °C and − 20.4 °C in the cooling cycle indicate a first order transition. The phase transition is attributed to the gradual ordering of NH₄⁺ and MnCl₄²⁻ ions at low temperatures. The infrared spectrum of the compound characterizes the various chemical bonding and water molecules in the compound.     

Investigation of Cu(In,Ga)Se2/In2S3 diffuse interface by Raman scattering

The CIGSe/In₂S₃ interface is known to be highly diffuse because of the migration of Cu from the CIGSe into the In₂S₃. Most of the analytical techniques allowing the determination of composition profiles throughout this interface involve ion etching either during the samples preparation or during data acquisitions. In the present work, we have explored the potential of the Raman scattering for the characterization of such interfaces. This technique is non destructive and provides information on both the composition and the structure of the materials that are probed. Three CIGSe/In₂S₃ structures have been investigated; the parameter varying being the substrate temperature during the In₂S₃ deposition. For the first time we could demonstrate that at high temperature, the CuInS₂ Cu-Au phase is formed at the CIGSe/In₂S₃ interface. Furthermore, the thickness of the ordered defect compound at the CIGSe surface increases with the deposition temperature. All of the new knowledge collected during this work shows the relevance of using the Raman scattering technique for the characterization of the CIGSe/In₂S₃ interface.     

Importance of H(2)O(2)/Fe(2+) ratio in Fenton's treatment of a carpet dyeing wastewater

The effectiveness of the Fenton's reagent (H(2)O(2)/Fe(2+)) in the treatment of carpet dyeing wastewater was investigated under different operational conditions, namely, H(2)O(2) and FeSO(4) concentrations, initial pH and temperature. Up to 95% COD removal efficiency was attained using 5.5 g/l FeSO(4) and 385 g/l H(2)O(2) at a pH of 3, temperature of 50 degrees C. The H(2)O(2)/Fe(2+) ratio (g/g) was found to be between 95 and 290 for maximum COD removal. It was noteworthy that, keeping H(2)O(2)/Fe(2+) ratio constant within the range of 95-290, it became possible to decrease FeSO(4) concentration to 1.1 g/l and H(2)O(2) concentration to 96.3 g/l, still achieving nearly the same COD removal efficiency. The relative efficiencies of Fenton's oxidation and coagulation stages revealed that Fenton's coagulation removed organic compounds which were not removed by Fenton's oxidation, indicating that the Fenton's coagulation acted as a polishing step.     

Thermal conductivity of gaseous CFCl3 (Freon 11) and CF2Cl2 (Freon 12) and their mixtures with N2 at 292K

Thermal conductivity of the gases CFCl₃ (Freon 11), CF₂Cl₂ (Freon 12), and their binary mixtures with nitrogen have been measured at 292 K. The results for the mixtures are compared with various theoretical models, which give the thermal conductivity as a function of concentration using properties of the pure components. From the experimental results, the mutual diffusion coefficients for the two systems are calculated.     

Two-gap superconductivity in R2Fe3Si5 (R=Lu,Sc) and Sc5Ir4Si10

R₂Fe₃Si₅ (R= Sc, Y, Lu) contains nonmagnetic iron and has a relatively high superconducting transition temperature T_c among iron-containing superconductors. An anomalous temperature dependence of specific heat C(T) has been reported for polycrystalline samples down to 1 K. We have grown R₂Fe₃Si₅ single crystals, confirmed the anomalous C(T) dependence, and found a second drop in specific heat below 1 K. In Lu₂Fe₃Si₅, we can reproduce C(T) below T_c, assuming two distinct energy gaps 2Δ ₁/k_BT_c = 4.4 and 2Δ ₂/k_BT_c = 1.1, with nearly equal weights, indicating that Lu₂Fe₃Si₅ is a two-gap superconductor similar to MgB₂. Hall coefficient measurements and band structure calculation also support the multiband contributions to the normal-state properties. The specific heat in the Sc₂Fe₃Si₅ single crystals also shows the two-gap feature. R₅Ir₄Si₁₀ (R = Sc, rare earth) is also a superconductor where competition between superconductivity and the charge-density wave is known for rare earths but not for Sc. We have performed detailed specific heat measurements on Sc₅Ir₄Si₁₀ single crystals and found that C(T) deviates slightly from the behavior expected for weak-coupling superconductors. C(T) for these superconductors can also be reproduced well by assuming two superconducting gaps.     

Two-gap superconductivity in R2Fe3Si5 (R=Lu,Sc) and Sc5Ir4Si10

Abstract

R₂Fe₃Si₅ (R= Sc, Y, Lu) contains nonmagnetic iron and has a relatively high superconducting transition temperature T_c among iron-containing superconductors. An anomalous temperature dependence of specific heat C(T) has been reported for polycrystalline samples down to 1 K. We have grown R₂Fe₃Si₅ single crystals, confirmed the anomalous C(T) dependence, and found a second drop in specific heat below 1 K. In Lu₂Fe₃Si₅, we can reproduce C(T) below T_c, assuming two distinct energy gaps 2Δ ₁/k_BT_c = 4.4 and 2Δ ₂/k_BT_c = 1.1, with nearly equal weights, indicating that Lu₂Fe₃Si₅ is a two-gap superconductor similar to MgB₂. Hall coefficient measurements and band structure calculation also support the multiband contributions to the normal-state properties. The specific heat in the Sc₂Fe₃Si₅ single crystals also shows the two-gap feature. R₅Ir₄Si₁₀ (R = Sc, rare earth) is also a superconductor where competition between superconductivity and the charge-density wave is known for rare earths but not for Sc. We have performed detailed specific heat measurements on Sc₅Ir₄Si₁₀ single crystals and found that C(T) deviates slightly from the behavior expected for weak-coupling superconductors. C(T) for these superconductors can also be reproduced well by assuming two superconducting gaps.     

Metastable states of the 2223 phase in the Bi(Pb)SrCaCuO system

By the magnetically modulated microwave absorption method (MAMMA) we observed the modifications induced by different calcination temperatures (between 830°C and 870°C) on the 2223 phase formed in a system sintered at (855±5)°C with the starting composition Bi_1.7Pb_0.3Sr₂Ca₂Cu₃O _y . The presence of the 2223 phase in almost distinct states (consequently, multiple 2223 phases) in the same sample was observed. As the calcination temperature was increased up to 850°C, the highest temperature state of the 2223 phase intensified. Higher calcination temperatures resulted in the enhancement of other lower-temperature states. The homogeneity of the 2223 phase was greatly improved by annealing the samples at, 800°C for 5 min in a flowing nitrogen atmosphere. We labeled as metastable the lower-temperature states having excess oxygen, which, by easily losing the supplementary oxygen under the above annealing procedure, were shifted to higher temperatures.     

Photoluminescence and radioluminescence of pure and Ce activated Na3Gd(PO4)2

The spectroscopic properties of Na₃Gd(PO₄)₂ and Na₃Gd(PO₄)₂:Ce³⁺ phosphors in the VUV-UV spectral range were investigated. Five excitation bands of Ce³⁺ ions at Gd³⁺ sites are observed at wavelengths of 205, 246, 260, 292, and 321 nm. Doublet Ce³⁺ 5d → 4f emission bands are observed at 341 and 365 nm with a decay constant τ_1/e around 26 ns. The X-ray excited luminescence of Na₃Gd_0.99Ce_0.01(PO₄)₂ at room temperature shows a photon yield of ∼17,000 photons/MeV of absorbed X-ray energy.