A novel low-cost method for Hg0 removal from flue gas by visible-light-driven BiOX (X = Cl,Br, I) photocatalysts

BiOX (X = Cl, Br, I) photocatalysts were synthesized by a simple coprecipitation method and were characterized by SEM, TEM, HRTEM, XRD, TG, DRS, PL, and ESR techniques. The photocatalytic activity of Hg⁰ removal and the effects SO₂ and NO were investigated under fluorescent light. The Hg⁰ removal performance was in the sequence of BiOI > BiOBr > BiOCl. Compared with BiOBr, BiOI showed much excellent SO₂ resistance on Hg⁰ removal. In the BiOBr reaction system, h⁺ and O₂⁻ could play key roles in Hg⁰ removal, while for BiOI photocatalytic system, I₂ might be an important species for higher Hg⁰ removal.     

Optimization of desulphurization of Artvin–Yusufeli lignite with acidic hydrogen peroxide solutions

In this study in which the Taguchi method was used, the optimization of sulphur removal by H₂O₂/H₂SO₄ solutions was carried out over lignite with higher content of sulphur from Artvin/Yusufeli, Turkey. In experiments, the ranges of experimental parameters were between 0.25 and 6.0 mol L⁻¹ for H₂O₂ concentration, 0.25–4 mol L⁻¹ for H₂SO₄ concentration, 10–60 °C for reaction temperature, 0.01–0.08 g mL⁻¹ for solid-to-liquid ratio, 15–120 min for reaction time, 200–300 rpm for stirring speed and 710–120 μm for particle size. The optimum conditions for these parameters have found to be 60 °C of temperature, 0.06 g mL⁻¹ of solid-to-liquid ratio, 60 min of reaction time, 250 rpm of stirring speed and −250 + 180 μm of particle size.A statistical experimental arrangement, L₂₅(5⁶) was prepared to determine optimum sulphur removal and ash removal ratios. The obtained yields were 97.85% in removal of total sulphur, 56.54% in removal of pyritic sulphur, 21.33% in removal of organic sulphur and 61.52% in removal of ash. According to variance analysis, it was seen that all parameters were effective in removal of pyritic and total sulphur, reaction temperature, solid-to-liquid ratio, reaction time, stirring speed, H₂O₂ and H₂SO₄ concentrations in removal of organic sulphur, and other parameters except acid concentration in removal of ash.     

Development of iron-based sorbents for Hg0 removal from coal derived fuel gas: Effect of hydrogen chloride

Laboratory studies were conducted to develop an elemental mercury (Hg⁰) removal process based on the reaction of H₂S and Hg⁰ using iron-based sorbents for coal derived fuel gas. It is well known that hydrogen chloride (HCl) is present in fuel gases derived from some types of coal, but the effect of HCl on the Hg⁰ removal performance of iron-based sorbents in coal derived fuel gas is not yet well understood. In this study, the effects of HCl on the removal of Hg⁰ from coal derived fuel gases over iron-based sorbents such as iron oxide (Fe₂O₃), supported iron oxides on TiO₂, iron oxide–Ca(OH)₂, and iron sulfides were investigated. The Hg⁰ removal experiments were carried out in a laboratory-scale fixed-bed reactor at 80 °C using simulated fuel gas. In the case of iron oxide (Fe₂O₃), the presence of HCl suppressed the Hg⁰ removal rate. In the case of Fe₂O₃ (2 or 5 wt%)/TiO₂, the presence of HCl did not suppress the Hg⁰ removal rate and the activity was stable. The Hg⁰ removal performance of reagent FeS₂ was higher than that of the iron oxide, and not affected by the presence of HCl. The Hg⁰ removal rate of iron oxide–Ca(OH)₂ was not effected by the presence of HCl, because HCl was captured by Ca(OH)₂. The reagent FeS₂ showed higher Hg⁰ removal activity than that of FeS₂ ore. However, the Hg⁰ removal performance of ground and kneaded FeS₂ ore was comparable to that of reagent FeS₂ probably due to the increase in porosity of the FeS₂ ore by grinding and kneading.     

Removal of elemental mercury from simulated coal-combustion flue gas using a SiO2–TiO2 nanocomposite

A novel silica–titania (SiO₂–TiO₂) nanocomposite has been developed to effectively capture elemental mercury (Hg⁰) under UV irradiation. Previous studies under room conditions showed over 99% Hg⁰ removal efficiency using this nanocomposite. In this work, the performance of the nanocomposite on Hg⁰ removal was tested in simulated coal-fired power plant flue gas, where water vapor concentration is much higher and various acid gases, such as HCl, SO₂, and NO_x, are present. Experiments were carried out in a fix-bed reactor operated at 135 °C with a baseline gas mixture containing 4% O₂, 12% CO₂, and 8% H₂O balanced with N₂. Results of Hg speciation data at the reactor outlet demonstrated that Hg⁰ was photocatalytically oxidized and captured on the nanocomposite. The removal efficiency of Hg⁰ was found to be significantly affected by the flue gas components. Increased water vapor concentration inhibited Hg⁰ capture, due to the competitive adsorption of water vapor. Both HCl and SO₂ promoted the oxidation of Hg⁰ to Hg(II), resulting in higher removal efficiencies. NO was found to have a dramatic inhibitory effect on Hg⁰ removal, very likely due to the scavenging of hydroxyl radicals by NO. The effect of NO₂ was found to be insignificant. Hg removal in flue gases simulating low rank coal combustion products was found to be less than that from high rank coals, possibly due to the higher H₂O concentration and lower HCl and SO₂ concentrations of the low rank coals. It is essential, however, to minimize the adverse effect of NO to improve the overall performance of the SiO₂–TiO₂ nanocomposite.     

Effect of Al Content on the Isomerization Performance of Solid Superacid Pd–S2O82−/ZrO2 –Al2O3

The effect of Al content on the performance of the Pd–S₂O₈²⁻/ZrO₂ –Al₂O₃ solid superacid catalyst was studied using n-pentane isomerization as a probe reaction. The catalysts were also characterized by X-ray diffraction (XRD), Fourier transform Infrared (FTIR), specific surface area measurements (BET), thermogravimetry–differential thermal analysis (TG–DTA), H₂-temperature programmed reduction (TPR) and NH₃ temperature-programmed desorption (NH₃-TPD). The Pd–S₂O₈²⁻/ZrO₂ –Al₂O₃ catalyst made from Al₂O₃ mass fraction of 2.5% exhibited the best performance and its catalytic activity increased by 44.0% compared with Pd–S₂O₈²⁻/ZrO₂. The isopentane yield reached 64.3% at a temperature of 238 °C, a reaction pressure of 2.0 MPa, a space velocity of 1.0 h ^− 1 and a H₂/n-pentane molar ratio of 4.0. No obvious catalyst deactivation was observed within 100 h.     

Two trimeric tri-TiIV-substituted Keggin tungstogermanates based on tetrahedral linkers

Two trimeric nine-Ti^IV contained tungstogermanates K₁₄{K ⊂ [(Ge(OH)O₃)(GeW₉Ti₃O₃₈H₂)₃]} · 42H₂O 1 and K₁₀{K ⊂ [(SO₄)(GeW₉Ti₃O₃₈H₃)₃] · 40H₂O 2 have been conventionally synthesized and characterized by elemental analysis, IR, TG and single-crystal X-ray diffraction. They were constructed from three tri-substituted A-α-[GeW₉Ti₃O₃₈] and GeO₄/SO₄ tetrahedral linker. They display the first example of trimeric titanium-substituted tungstogermanates, which contain both Ti–O–Ti and Ti–O–Ge/Ti–O–S bridges.     

Synergetic catalytic removal of Hg0 and NO over CeO2(ZrO2)/TiO2

A series of CeO₂(ZrO₂)/TiO₂ monolith catalysts were investigated for catalytic oxidation of Hg⁰ and NH₃-SCR of NO. Effect of flue gases components on catalytic oxidation of Hg⁰ was mainly studied. Results showed that the CeO₂(ZrO₂)/TiO₂ catalyst exhibited high efficiency for catalytic oxidation of Hg⁰ at 240–400 °C without adding other oxidant, and its catalytic performance for NH₃-SCR of NO was not affected. NH₃ had slight inhibitory effect while SO₂ and NO had no influence on catalytic oxidation of Hg⁰, but O₂ obviously improved catalytic oxidation of Hg⁰ for its oxidation susceptibility.     

Removal of Hg0 from containing‐SO2/NO flue gas by ultraviolet/H2O2 process in a novel photochemical reactor

A novel photochemical spray reactor is first developed and is used to remove Hg⁰ and simultaneously remove Hg⁰/SO₂/NO from flue gas by ultraviolet (UV)/H₂O₂ process. The effects of several parameters (UV wavelength, UV power, H₂O₂ concentration, Hg⁰ inlet concentration, solution temperature, liquid–gas ratio, solution pH, SO₂ concentration, NO concentration, and O₂ concentration) on removal of Hg⁰ by UV/H₂O₂ process were investigated. Removal mechanism of Hg⁰ is proposed and simultaneous removal of Hg⁰, NO, and SO₂ is also studied. The results show that the parameters, UV wavelength, UV power, H₂O₂ concentration, liquid–gas ratio, solution pH, and O₂ concentration, have significant impact on removal of Hg⁰. However, the parameters, Hg⁰ inlet concentration, solution temperature, SO₂ concentration, and NO concentration, only have small effect on removal of Hg⁰. Hg²⁺ is the final product of Hg⁰ removal, and Hg⁰ is mainly removed by oxidations of H₂O₂, ·OH, · O, O₃, and photoexcitation of UV. © 2014 American Institute of Chemical Engineers AIChE J, 60: 2275–2285, 2014     

Assessment of soil washing for Zn contaminated soils using various washing solutions

Bench-scale soil washing experiments were conducted to remove Zn from contaminated soils. Various washing solutions including hydrochloric acid (HCl), nitric acid (HNO₃), sodium hydroxide (NaOH), oxalic acid (HOOCCOOH·2H₂O), sulfuric acid (H₂SO₄), phosphoric acid (H₃PO₄), and tartaric acid (C₄H₆O₆) were used. The concentration of the washing solutions used in this study ranged from 0.1 M to 2 M with a liquid to solid ratio of 10. The soil washing results showed the following order of washing solution decreasing effectiveness for the removal of Zn: HCl > HNO₃ > H₂SO₄ > H₃PO₄ > C₄H₆O₆ > HOOCCOOH·2H₂O > NaOH.     

Spectroscopic studies on bis(1-amidino-O-alkylurea) copper(II) sulfate complexes where alkyl = methyl,ethyl, n-propyl or n-butyl: EPR evidence for binuclear complexes

Four new Cu(II) Complexes viz. [Cu(II)(1-amidino-O-methylurea)₂]SO₄·2H₂O (1), [Cu(II)(1-amidino-O-ethylurea)₂](SO₄)₂·2H₂O (2), [Cu(II)(1-amidino-O-n-propylurea)₂] SO₄·2H₂O (3), [Cu(II)(1-amidino-O-n-butylurea)₂]₂(SO₄)₂·2H₂O (4) have been synthesized and characterized. EPR spectrum of complex 4 at RT consisted of fine-structure transitions (ΔMs = ±1) with zero-field splitting (ZFS) of 0.0485 cm^?1 and a half-field signal (ΔMs = ±2) at ca. 1600 G, revealed formation of binuclear complex (S = 1). Whereas EPR spectrum of complex 2 in DMSO showed a mixture of mononuclear and binuclear complex in the ratio 0.75:1.0 with ZFS of 0.0385 cm^?1. From the temperature dependence of the EPR signal intensity, the isotropic exchange-interaction constant J was evaluated.     

A fluorescein derivative FLTC as a chemosensor for Hg2 + and Ag+ and its application in living-cell imaging

FLTC was synthesized and used as a fluorescent chemosensor to detect Hg^2 +. It showed high selectivity toward Hg^2 + over many heavy metal ions in an ethanol–H₂O (3:2, v/v, HEPES buffer, 0.5 mM, pH 7.15) solution with a detection limit of 0.21 μM. After complexation with Hg^2 +, FLTC showed extremely high selectivity toward Ag⁺ with a detection limit of 0.009 μM. Therefore, detection of Hg^2 + and Ag⁺ could be realized using FLTC and the FLTC–Hg^2 + complex, respectively. Cytotoxicity assays and fluorescence microscopy analysis showed that FLTC could be used as a fluorescent probe to detect Hg^2 + and Ag⁺ in L-02 human liver cells.     

Mn/Mg/Al-spinels as catalysts for SOx abatement: Influence of CeO2 incorporation and catalytic stability

Mg,Mn,Al-oxides with spinel structure, Al/(M²⁺ + Al) molar ratio of 0.25 and 0.50 and an Mn/Mg molar ratio of 0.30 have been evaluated as catalysts for SO_x removal under conditions similar to those found in FCC units. The best performance was that of the sample with the higher aluminium content. The incorporation of CeO₂ in this sample favored SO_x uptake for short reaction times as well as the reduction of the sulfated catalysts. When the regeneration was started at 530 °C, only H₂S was observed as reaction product, but when this step started at 650 °C, the release of SO₂ preceded that of H₂S, regardless of the chemical composition of the sample. As to the additive performance for successive reaction–regeneration cycles, the incorporation of CeO₂ produced a less efficient catalyst with regard to the removal of the SO₂ along the process, but with a higher regeneration efficiency and a lower formation of SO₂ as regeneration product.     

Two new tetrazamacrocycle based Cu(II) complexes with 2D → 0D single-crystal to single-crystal transformation

Two new tetrazamacrocycle based compounds, namely, [Cu₆L₃(SO₄)₂]·SO₄·8H₂O (1) and [Cu₂L(SO₄)(H₂O)]^.2H₂O (2), have been prepared at different temperatures (H₂L = 10,21-dimethyl-3,6,14,17-tetraazatricyclo[17.3.18,12]tetracosa-1(23),8,10,12(24),19,21-hexaene-23,24-diolate). In 1, each SO₄^2 − anion bridges three [Cu₂L]^2 + cations to yield a hexagonal network, whereas in 2 each SO₄^2 − anion only links one [Cu₂L]^2 + cation to afford a discrete binuclear structure. Remarkably, the 2D network structure of 1 was transformed into the 0D structure of 2 in a single-crystal to single-crystal (SC–SC) fashion at room temperature.     

Mercury oxidation by hydrochloric acid over TiO2 supported metal oxide catalysts in coal combustion flue gas

Mercury oxidation by hydrochloric acid over the metal oxides supported by anatase type TiO₂ catalysts, 1 wt.% MO_x/TiO₂ where M = V, Cr, Mn, Fe, Ni, Cu, and Mo, was investigated by the Hg⁰ oxidation and the NO reduction measurements both in the presence and absence of NH₃. The catalysts were characterized by BET surface area measurement and Raman spectroscopy. The metal oxides added to the catalyst were observed to disperse well on the TiO₂ surface. For all catalysts studied, the Hg⁰ oxidation by hydrochloric acid was confirmed to proceed. The activity of the catalysts was found to follow the trend MoO₃ ~ V₂O₅ > Cr₂O₃ > Mn₂O₃ > Fe₂O₃ > CuO > NiO. The Hg⁰ oxidation activity of all catalysts was depressed considerably by adding NH₃ to the reactant stream. This suggests that the metal oxide catalysts undergo the inhibition effect by NH₃. The activity trend of the Hg⁰ oxidation in the presence of NH₃ was different from that observed in its absence. A good correlation was found between the NO reduction and the Hg⁰ oxidation activities in the NH₃ present condition. The catalyst having high NO reduction activity such as V₂O₅/TiO₂ showed high Hg⁰ oxidation activity. The result obtained in this study suggests that the oxidation of Hg⁰ proceeds through the reaction mechanism, in which HCl competes for the active catalyst sites against NH₃. NH₃ adsorption may predominate over the adsorption of HCl in the presence of NH₃.     

Study effect of different parameters on the sulphate sorption onto nano alumina

The aim of this research work is to investigate sorption characteristic of modified nano alumina (n-Al) for the removal of SO₄^2? from aqueous solutions and wastewater. The sorption of SO₄^2? by batch method is carried out. The optimum conditions of sorption were found to be: a sorbent dose of 0.3 g in 100 ml of SO₄^2?, contact time of 35 min, pH = 5. In optimum condition, removal efficiency was 85.6% for the SO₄^2?. Three equations, i.e. Morris–Weber, Lagergren and pseudo second order have been tested to track the kinetics of removal process. The Langmuir, Freundlich and D–R are subjected to sorption data to estimate sorption capacity. It can be concluded that n-Al has potential to remove SO₄^2? ions from aqueous solutions at different concentrations. It was found that the temperature has positive effect on the process and negative ΔG values indicated thermodynamically feasible and spontaneous nature of the sorption. Positive value of ΔS reveals the increased randomness at the solid–solution interface during the fixation of the ion on the active sites of the sorbent. The effect of other anions was studied and it was found the existence of them in the solution has considerable effect on the sulphate removal.     

Construction of two 2D 3d-4f coordination complexes based on the linkages of left-and right-handed helical chains

Two transition-lanthanide metal-organic coordination polymers, {[CoLn₂(Himdc)₂(SO₄)₂(H₂O)₄]·H₂O}_n [Ln = Yb (1), Ho (2)] (H₃imdc = imidazole-4, 5-dicarboxylic acid), have been synthesized by the hydrothermal reactions of lanthanide oxides, CoSO₄·7H₂O, H₃imdc and H₂O. Single-crystal X-ray diffraction analysis reveals that the isostructural complexes 1 and 2 possess unusual 2D wave-like heterometallic layers with 1D (Ln₂O₂CoO₂)_n and [Ln₂(SO₄)₂]_n inorganic chains constructed by the assembly of 1D left-/right-handed helical L–Ln₂Co–L (L = Himdc) chains and SO₄^2? anions, while a 3D framework is formed via hydrogen-bonding interactions interlayer.     

Pd-YSZ cermet membranes with self-repairing capability in extreme H2S conditions

A Pd-YSZ cermet membrane that performs coupled operations of hydrogen separation from a mixed-gas stream and simultaneous hydrogen production by non-galvanic water-splitting, and have high sulfur tolerance is fabricated. It is proved that in H₂S containing atmosphere the Pd-YSZ membrane has self-repairing capability, originating mainly from the conversion of Pd₄S back to metallic Pd and SO₂ by ambipolar-diffused oxygen obtained from water-splitting. The performance of membrane was analyzed at different temperatures in high H₂S containing (0–4000 ppm H₂S) mixed gas feed during the operation as a hydrogen separation membrane as well as during the coupled operation of hydrogen separation and hydrogen production. At 900 °C with the feed-stream having ≥2000 ppm H₂S, the hydrogen flux was severely affected due to the formation of some liquid phase of Pd₄S, resulting in the segregation of hydrogen permeating Pd-phase at the membrane surface. But at 800 °C, though the membrane was affected by the Pd₄S formation in high H₂S environment (up to 1200 ppm H₂S), its self-repairing capability and additional hydrogen production by water-splitting is capable of maintaining the hydrogen flux around ~1.24 cm³ (STP)/min.cm², a value expected by the same membrane while performing only the hydrogen separation function in H₂S-free environment.     

Ionic conductivity of Mn2+ doped dense tin pyrophosphate electrolytes synthesized by a new co-precipitation method

Mn²⁺-doped Sn_1−xMn_xP₂O₇ (x = 0–0.2) are synthesized by a new co-precipitation method using tin(II)oxalate as tin(IV) precursor, which gives pure tin pyrophosphate at 300 °C, as all the reaction by-products are vaporizable at <150 °C. The dopant Mn²⁺ acts as a sintering aid and leads to dense Sn_1−xMn_xP₂O₇ samples on sintering at 1100 °C. Though conductivity of Sn_1−xMn_xP₂O₇ samples in the ambient atmosphere is 10⁻⁹–10⁻⁶ S cm⁻¹ in 300–550 °C range, it increases significantly in humidified (water vapor pressure, pH₂O = 0.12 atm) atmosphere and reaches >10⁻³ S cm⁻¹ in 100–200 °C range. The maximum conductivity is shown by Sn_0.88Mn_0.12P₂O₇ with 9.79 × 10⁻⁶ S cm⁻¹ at 550 °C in ambient air and 2.29 × 10⁻³ S cm⁻¹ at 190 °C in humidified air. It is observed that the humidification of Sn_1−xMn_xP₂O₇ samples is a slow process and its rate increases at higher temperature. The stability of Sn_1−xMn_xP₂O₇ samples is analyzed.     

UV/S2O82− process for degrading polyvinyl alcohol in aqueous solutions

This investigation evaluates the effectiveness of the UV/S₂O₈²⁻ process in the degradation of polyvinyl alcohol (PVA) in aqueous solutions without adjusting their pH. The effects of UV wavelength and Na₂S₂O₈ dosage on the efficiency of degradation of PVA were examined. The efficiency of degradation of PVA under UV-254 nm exceeded that under UV-365 nm. A larger Na₂S₂O₈ dosage was associated with a higher efficiency of degradation of PVA under UV-254 nm irradiation. However, an excessive Na₂S₂O₈ dosage inhibited the degradation of PVA by the UV-365 nm/S₂O₈²⁻ process. Both UV-254 nm/S₂O₈²⁻ and UV-365 nm/S₂O₈²⁻ processes exhibited pseudo-first-order kinetics. SO₄⁻ was detected by performing quenching studies using specific alcohols, revealing that SO₄⁻ was found to be the predominant radical in the UV-254 nm/S₂O₈²⁻ process. Additionally, the presence of inorganic anions with various effects inhibited the degradation of PVA by the UV-254 nm/S₂O₈²⁻ process. Complete degradation of PVA (20 mg/L) was achieved within 5 min under UV-254 nm using an Na₂S₂O₈ dosage of 0.12 g/L in the absence of inorganic anions, indicating that UV irradiation to activate S₂O₈²⁻ promotes the degradation of PVA in aqueous solutions without adjusting their pH.