Electrochemical treatment of ammonia in wastewater by RuO<Subscript>2</Subscript>–IrO<Subscript>2</Subscript>–TiO<Subscript>2</Subscript>/Ti electrodes

This study investigated the removal of ammonia in wastewater by an electrochemical method using titanium electrodes coated with ruthenium and iridium (RuO₂–IrO₂–TiO₂/Ti) with low chlorine evolution over-voltage. The effects of operating parameters, including chloride ion concentration, current density and initial pH, were also investigated. The results were evaluated primarily by considering the efficiency of the elimination of NH₄⁺-N. The removal of ammonia by electrochemical oxidation mainly resulted from the indirect oxidation effect of chlorine/hypochlorite produced during electrolysis. The direct anodic oxidation efficiency of ammonia was less than 5%, and the current efficiency was less than 10%. The ammonia removal followed pseudo-first-order kinetics. The electrochemical process can be applied successfully as a final polishing step, or as an alternative method to biological nitrification. The process seems to be most beneficial for small coastal cities     

Efficient electrochemical reduction of nitrate to nitrogen using Ti/IrO2-Pt anode and different cathodes

Electrochemical reduction of nitrate using Fe, Cu, and Ti as cathodes and Ti/IrO₂-Pt as anode in an undivided and unbuffered cell was studied. In the presence of appropriate amount of NaCl, both cathodic reduction of nitrate and anodic oxidation of the by-products of ammonia and nitrite were achieved by all cathodes under a proper condition. Both in the absence and presence of NaCl, the order of nitrate removal rate was Fe > Cu > Ti. The nitrate removal was 87% and selectivity to nitrogen was 100% in 3 h with Fe cathode in the presence of NaCl. Ti/IrO₂-Pt anode played an important role during nitrate reduction, especially in the presence of NaCl, at which by-products could efficiently be oxidized. Moreover, atomic force microscopy (AFM) investigation shown Ti/IrO₂-Pt anode was suitable for nitration reduction and the surface roughness of all cathodes increased. The concentrations of Fe, Cu, and Ti in the electrolyte were less than 0.15, 0.12 and 0.09 mg/L after 3 h electrolysis, respectively.     

The physical solubilities and diffusivities of N<Subscript>2</Subscript>O and CO<Subscript>2</Subscript> in aqueous ammonia solutions on the additions of AMP,glycerol and ethylene glycol

Carbon dioxide (CO₂) is a major greenhouse gas, the emissions of which should be reduced. There are various technologies for the effective separation of CO₂. Of these, chemical absorption methods are generally accepted as the most effective. The monoethanolamine (MEA) process is an effective way to remove CO₂, but is an expensive option for the separation of CO₂ from massive gas-discharging plants. Therefore, ammonia solution, which is less expensive and more effective than MEA, was used for the removal of CO₂. In this study, the physical solubility of N₂O in (ammonia+water), (ammonia+2-amino-2-methyl-1-propanol+water), (ammonia+glycerol+water) and (ammonia+ ethylene glycol+water) was measured at 293, 303, 313, 323 K. Additive concentrations of 1, 3, and 5 wt% AMP, glycerol and ethylene glycol were added for each 9 wt% ammonia solution. A solubility apparatus was used to investigate the solubility of N₂O in ammonia solutions. The diffusivity was measured with a wetted wall column absorber. The “N₂O analogy” is used to estimate the solubility and diffusivity of CO₂ in the aqueous ammonia solutions. OriginPro 7.5 was used to correlate the solubility and diffusivity of N₂O in ammonia solutions. The parameters of the correlation were determined from the measured solubility and diffusivity.     

DSA electrochemical treatment of olive mill wastewater on Ti/RuO<Subscript>2</Subscript> anode

The electrochemical oxidation of olive mill wastewater (OMW) over a Ti/RuO₂ anode was studied by means of cyclic voltammetry and bulk electrolysis and compared with previous results over a Ti/IrO₂ anode. Experiments were conducted at 300–1,220 mg L⁻¹ initial chemical oxygen demand (COD) concentrations, 0.05–1.35 V versus SHE and 1.39–1.48 V versus SHE potential windows, 15–50 mA cm⁻² current densities, 0–20 mM NaCl, Na₂SO₄, or FeCl₃ concentrations, 80 °C temperature, and acidic conditions. Partial and total oxidation reactions occur with the overall rate being near first-order kinetics with respect to COD. Oxidation at 28 Ah L⁻¹ and 50 mA cm⁻² leads to quite high color and phenols removal (86 and 84%, respectively), elimination of ecotoxicity, and a satisfactory COD and total organic carbon reduction (52 and 38%, respectively). Similar performance can be achieved at the same charge (28 Ah L⁻¹) using lower current densities (15 mA cm⁻²) but in the presence of various salts. For example, COD removal is less than 7% at 28 Ah L⁻¹ in a salt-free sample, while addition of 20 mM NaCl results in 54% COD reduction. Decolorization of OMW using Ti/RuO₂ anode seems to be independent of the presence of salts in contrast with Ti/IrO₂ where addition of NaCl has a beneficial effect on decolorization.     

Fabrication of indium tin oxides (ITO)-supported poly(3,4-ethylenedioxythiophene) electrodes coated with active IrO<Subscript>2</Subscript> layer for morphine electrooxidation

Novel indium tin oxides (ITO)/PEDOT/IrO₂ composite electrodes were fabricated by dipping IrO₂ colloids onto poly(3,4-ethylenedioxythiophene) (PEDOT)-coated ITO substrate for morphine electrooxidation. Scanning electron microscopy (SEM) image showed that the active IrO₂ layer was dispersed more uniformly at PEDOT intermediate layer than at bare ITO substrate. Voltammetric measurements indicated that the as-prepared IrO₂ colloids are very active for both the oxygen evolution reactions (OER) and for reversible valance transition between lower and higher oxides. ITO/PEDOT/IrO₂ electrodes perform enhanced electrochemical activity towards the oxidation of morphine, as compared with the un-modified ITO-based PEDOT electrodes (ITO/PEDOT) or the ITO electrodes directly coated with IrO₂ (ITO/IrO₂), suggesting that the composite electrode materials are one of the potential candidates for morphine detection.     

Application of an electrochemical-ion exchange reactor for ammonia removal

A new concept for ammonia removal from aqueous solution by zeolites followed by electrochemical oxidation/regeneration was studied in this work. In the first mode, (NH₄)₂SO₄ solution is passed through an ion exchange column where ammonium is concentrated in the zeolite. During the second mode (electrochemical oxidation/regeneration), the absorbed ammonia is harmlessly removed by electrochemical oxidation in the presence of sodium chloride (NaCl) and simultaneously the zeolite is regenerated. Continuous experiments were carried out for 172 h with five loading and four regeneration cycles without finding the loss of ammonia removal capacity of the zeolite. With electrochemical oxidation/regeneration, the conversion rate of ammonia adsorbed by the zeolites into nitrogen gas was more that 98%, and the conversion rate to nitrate was less than 2%; no ammonia or nitrite was detected in the regenerated solution. The regeneration solution can be repeatedly reused over a long period of time with 2.0 g/L NaCl added to the regeneration solution, saving both water resources and the chemical reagent. Moreover, approximately five times less energy was consumed with the present method than that of the direct electrochemical oxidation of ammonia.     

Selective oxidation of H<Subscript>2</Subscript>S to ammonium thiosulfate and elemental sulfur using mixtures of V-Bi-O and Sb<Subscript>2</Subscript>O<Subscript>4</Subscript>

The selective oxidation of hydrogen sulfide in the presence of excess water and ammonia was investigated by using vanadium-bismuth based mixed oxide catalysts. Synergistic effect on catalytic activity was observed for the mechanical mixtures of V-Bi-O and Sb₂O₄. Temperature programmed oxidation (TPO), X-ray photoelectron spectroscopy (XPS), and two separated bed reactivity test results supported the role of Sb₂O₄ for reoxidizing the reduced V-Bi-O during the reaction. This paper is dedicated to Professor Hyun-Ku Rhee on the occasion of his retirement from Seoul National University.     

A Highly Selective Pd(OAc)<Subscript>2</Subscript>/Pyridine/K<Subscript>2</Subscript>CO<Subscript>3</Subscript> System for Oxidation of Terpenic Alcohols by Dioxygen

Abstract  

Molecular sieves, complex organic bases and radical oxidants are commonly used in alcohols oxidation reactions. In this work, we have evaluated the beneficial effects of addition of K₂CO₃ to Pd(II)-catalyzed oxidation alcohols, which resulted in a remarkable increase in the oxidation reaction rates without selectivity losses. Herein, in a metallic reoxidant-free system, terpenic alcohols (β-citronellol, nerol and geraniol) were selectively converted into respective aldehydes from Pd(II)-catalyzed oxidation reactions in presence of dioxygen. High conversions and selectivities (greater than 90%) were achieved in the presence of the Pd(OAc)₂/K₂CO₃ catalyst and pyridine excess. The exogenous role of others auxiliary anionic and nitrogen compounds was appraised.     

CO<Subscript>2</Subscript> capture using aqueous solutions of K<Subscript>2</Subscript>CO<Subscript>3</Subscript>+2-methylpiperazine and monoethanolamine: Specific heat capacity and heat of absorption

The specific heat capacity, heat of CCO₂ absorption, and CCO₂ absorption capacity of aqueous solutions of potassium carbonate (K₂CO₃)+2-methylpiperazine (2-MPZ) and monoethanolamine (MEA) were measured over various temperatures. An aqueous solution of K₂CO₃+2-MPZ is a promising absorbent for CCO₂ capture because it has high CCO₂ absorption capacity with improved absorption rate and degradation stability. Aqueous solution of MEA was used as a reference absorbent for comprison of the thermodynamic characteristics. Specific heat capacity was measured using a differential scanning calorimeter (DSC), and heat of CCO₂ absorption and CCO₂ absorption capacity were measured using a differential reaction calorimeter (DRC). The CCO₂-loaded solutions had lower specific heat capacities than those of fresh solutions. Aqueous solutions of K₂CO₃+2-MPZ had lower specific heat capacity than those of MEA over the temperature ranges of 303-353 K. Under the typical operating conditions for the process (CCO₂ loading=0.23mol-CCO₂·mol^?1-solute in fresh solution, T=313 K), the heat of absorption (?ΔHabs) of aqueous solutions of K₂CO₃+2-MPZ and MEA were approximately 49 and 75 kJ·mol-CO₂, respectively. The thermodynamic data from this study can be used to design a process for CCO₂ capture.     

Mechanism of electrochemical oxidation of ammonia

The electrochemical oxidation of ammonia has been studied in the most detail in alkaline solution at platinized platinum. Almost all work supports the essence of a mechanism first proposed by Gerischer and Mauerer (1970) [19], in which elemental nitrogen is formed at mildly positive potentials with near quantitative current efficiency through dimerization of partly dehydrogenated ammonia molecules NH_x(ads). The major intermediate, NH₂(ads), is formed at Pt(1 0 0) domains on the metal surface, where it dimerizes to hydrazine, and rapidly oxidizes to N₂. At somewhat more positive potentials, the formation of adsorbed nitrogen atoms poisons the anode, and nitrogen evolution ceases. At potentials where water is oxidized, the Pt anode is modified by a surface oxide; under these conditions, nitrogen evolution is accompanied by nitrogen oxides and oxyanions. Similar mechanisms are most probably followed on other noble metals and their alloys, although there is less experimental information. In the past decade there has been preliminary study of other anode materials, such as Ni/Ni(OH)₂, Ti/IrO₂, and boron-doped diamond, with a view to finding inexpensive and long-lasting anodes for ammonia oxidation, but so far, little is known about the mechanism of oxidation at these materials.     

Removal of tannins and polyhydroxy phenols by electro‐chemical techniques

The removal of tannins and their basic molecules such as catechol, pyrogallol, phloroglucinol and resorcinol was studied by electro‐flotation and electro‐oxidation techniques. Iron rods and triple oxide (TaO₂/RuO₂/IrO₂) coated titanium rods were used as electrodes for electro‐flotation and electro‐oxidation respectively. Interaction of tannins and polyhydroxy phenols with iron oxy‐hydroxide formed by anodic dissolution of iron was studied by UV‐Visible, FT‐IR and zeta‐potential measurements. GC–MS was used to identify the intermediate compounds formed during electro‐oxidation. Catechol, pyrogallol, phloroglucinol and resorcinol were found to be mineralized in the presence of triple oxide (TaO₂/RuO₂/IrO₂) coated titanium electrodes. Catechol and pyrogallol were found to form insoluble organo‐metal complexes while resorcinol and phloroglucinol were found to adsorb on iron oxy‐hydroxide. The sludge thus formed was simultaneously separated from the aqueous phase by hydrogen bubbles. It was observed that the power consumption is relatively high for electro‐oxidation compared with electro‐flotation. The effects of pH and reaction time on their removal were also studied and the results are discussed. Copyright © 2005 Society of Chemical Industry     

Analysis of the heat of reaction and regeneration in alkanolamine-CO<Subscript>2</Subscript> system

The estimation of regeneration heat of absorbent is important because it is a key factor that has an effect on the process efficiency. In this study, thermal stability and regeneration heat of aqueous amine solutions such as monoethanolamine (MEA), 2-amino-2-methyl-1-propanol (AMP), N-methyldiethanolamine (MDEA), and 1,8-diamino-pmenthane (KIER-C3) were investigated by using TGA-DSC analysis. The thermal characteristics of the fresh and CO₂ rich amine solutions were estimated. The CO₂ rich amine solutions were obtained by VLE experiments at T=40 °C. The regeneration heat of aqueous MEA solution was 76.991–66.707 kJ/mol-CO₂, which is similar to heat of absorption. The reproducibility of the results was obtained. The regeneration heat of aqueous KIER-C3 20 wt% solution (1.68 M) was lower than that of aqueous MEA 30 wt% solution (4.91 M). Therefore, the KIER-C3 can be used as an effective absorbent for acid gas removal.     

Electrochemical synthesis of ammonia from water and nitrogen catalyzed by nano-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> and CoFe<Subscript>2</Subscript>O<Subscript>4</Subscript> suspended in a molten LiCl-KCl-CsCl electrolyte

Nano-Fe₂O₃ and CoFe₂O₄ were suspended in molten salt of alkali-metal chloride (LiCl-KCl-CsCl) and their catalytic activity in electrochemical ammonia synthesis was evaluated from potentiostatic electrolysis at 600 K. The presence of nanoparticle suspension in the molten chloride resulted in improved production of NH₃, recording NH₃ synthesis rate of 1.78×10^?10 mol s^?1 cm^?2 and 3.00×10^?10 mol s^?1 cm^?2 with CoFe₂O₄ and Fe₂O₃, which are 102% and 240% higher than that without the use of a nanocatalyst, respectively. We speculated that the nanoparticles triggered both the electrochemical reduction of nitrogen and also chemical reaction between nitrogen and hydrogen that was produced from water electro-reduction on cathode. The use of nanocatalysts in the form of suspension offers an effective way to overcome the sluggish nature of nitrogen reduction in the molten chloride electrolyte.     

Influence of operating temperature on CO<Subscript>2</Subscript>-NH<Subscript>3</Subscript> reaction in an aqueous solution

Although aqueous ammonia solution has been focused on the removal of CO₂ from flue gas, there have been very few reports regarding the underlying analysis of the reaction between CO₂ and NH₃. In this work, we explored the reaction of CO₂-NH₃-H₂O system at various operating temperatures: 40 °C, 20 °C, and 5 °C. The CO₂ removal efficiency and the loss of ammonia were influenced by the operating temperatures. Also, infrared spectroscopy measurement was used in order to understand the formation mechanism of ion species in absorbent, such as NH₂COO⁻, HCO₃⁻, CO₃²⁻, and NH₄⁺, during CO₂, NH₃, and H₂O reaction. The reactions of CO₂-NH₃-H₂O system at 20 °C and 40 °C have similar reaction routes. However, a different reaction route was observed at 5 °C compared to the other operating temperatures, showing the solid products of ammonium bicarbonates, relatively. The CO₂ removal efficiency and the formation of carbamate and bicarbonate were strongly influenced by the operating temperatures. In particular, the analysis of the formation carbamate and bicarbonate by infrared spectroscopy measurement provides useful information on the reaction mechanism of CO₂ in an aqueous ammonia solution.     

Catalytic performance of CuCl<Subscript>2</Subscript>-modified V<Subscript>2</Subscript>O<Subscript>5</Subscript>-WO<Subscript>3</Subscript>/TiO<Subscript>2</Subscript> catalyst for Hg<Superscript>0</Superscript> oxidation in simulated flue gas

CuCl₂-SCR catalysts prepared by an improved impregnation method were studied to evaluate the catalytic performance for gaseous elemental mercury (Hg⁰) oxidation in simulated flue gas. Hg⁰ oxidation activity of commercial SCR catalyst was significantly improved by the introduction of CuCl₂. Nitrogen adsorption, XRD, XRF and XPS were used to characterize the catalysts. The results indicated that CuCl₂ was well loaded and highly dispersed on the catalyst surface, and that CuCl₂ played an important role for Hg⁰ catalytic oxidation. The effects of individual flue gas components on Hg⁰ oxidation were also investigated over CuCl₂-SCR catalyst at 350 oC. The co-presence of NO and NH₃ remarkably inhibited Hg⁰ oxidation, while this inhibiting effect was gradually scavenged with the decrease of GHSV. Further study revealed the possibility of simultaneous removal of Hg⁰ and NO over CuCl₂-SCR catalyst in simulated flue gas. The mechanism of Hg⁰ oxidation was also investigated.     

生物接触氧化法去除微污染水源水中的氨氮

采用生物接触氧化法对北京某水库的微污染水源水进行了除氨效果研究。结果表明,生物接触氧化法具有较好的除氨效果,生物接触氧化原水氨氮的质量浓度在不大于0.234mg/L时,氨氮的月平均去除率为30.8%~72.9%,进水氨氮的质量浓度人工增加至0.126~2.080mg/L时,氨氮去除率最高可达97.4%,平均去除率为71.2%。同时探讨了水温及进水氨氮的质量浓度对氨氮去除效果的影响。     

Selective oxidation of hydrogen sulfide over LaCoO<Subscript>3</Subscript> and LaSrCoO<Subscript>4</Subscript> mixed oxides

Perovskite LaCoO₃ and perovskite-like LaSrCoO₄ mixed oxides were prepared by polyglycol gel method, and their catalytic performance was compared for the selective oxidation of hydrogen sulfide in a stream containing excess amount of ammonia and water for the first time. These samples were investigated by using XRD, BET, O₂-TPD and XPS. The catalytic activity and the selectivity to solid products (ammonium thiosulfate and elemental sulfur) of LaCoO₃ were better than those of LaSrCoO₄, and this is explained in terms surface contents of oxygen and cobalt, oxidation state of cobalt, and BET surface area.     

Modelling NH<Subscript>3</Subscript> volatilisation within a urine patch using NZ-DNDC

Urea concentrations in urine patches deposited during animal grazing can be over ten times higher than typical fertiliser application rates, potentially leading to large ammonia (NH₃) losses. The process-based NZ-DNDC model was modified to better simulate soil pH changes and ammonia (NH₃) emissions following urine application using data collected from a New Zealand field trial. After modification, simulated 30-day NH₃ emissions decreased from 506 to 117 kg N ha^?1 compared to measured emissions of 78 ± 3 kg N ha^?1 (mean ± standard error) and the Nash–Sutcliffe Efficiency (NSE) for daily NH₃ emissions increased from ?7.11 to +0.97 for the parameterisation dataset. However, modified model correctly estimated the cumulative emissions for the first 7 days. Using the same parameterisation on an independent dataset from a nearby site gave cumulative 18-day NH₃ emissions of 84 kg N  ha^?1 compared to the measured 48 ± 2 kg N ha^?1 (mean ± standard error). However, the NSE for daily NH₃ emissions was ?0.71, indicating site specific parameterisation might be needed. The sensitivity of NH₃ emissions to ±5 and ±10% errors in 4 model parameters was tested. The sensitivities ranged from ?0.36 to +0.71. The highest sensitivity was to the rate of NH₃ transfer from the soil solution to the atmosphere and the lowest sensitivity was to the rate of urea hydrolysis.     

Natural Micas Intercalated with Al<Subscript>2</Subscript>O<Subscript>3</Subscript> and Modified with Transition Metals as Catalysts of the Selective Oxidation of Ammonia to Nitrogen

Natural cationic layered clays—vermiculite and phlogopite—pretreated with acids were intercalated with alumina pillars. In next step, transition metals were deposited on the surface of pillared interlayer clays (PILC) by a liquid ion exchange method. The catalyst samples were characterized with respect to: composition (EPMA), structure (XRD), texture (BET), surface acidity (NH₃-TPD) and coordination of deposited transition metals (UV–vis-DRS). The modified clays were tested in the role of catalyst for the selective oxidation of ammonia to nitrogen. In a series of the studied samples the best catalytic performance presented alumina pillared vermiculite modified with copper.     

Modified carbon nitride as an efficient adsorbent for ammonia nitrogen with low concentration

The adverse effects of excessive ammonia on aquatic ecosystem have provoked the development of efficient methods for its removal. Here, we present a thermal copolymerization of melamine and sodium hydrogen carbonate and successfully introduce oxygen groups into the structure of g-C₃N₄, which is applied to low-concentration ammonia removal. Oxygen groups are introduced into g-C₃N₄ and increase its surface electron negativity. When the initial concentration of ammonia nitrogen is 18.74 mg L⁻¹, the lowest concentration of it after adsorption is 1.43 mg L⁻¹, and the ammonia nitrogen removal efficiency is 92.3%. The main reason for our material high performance on adsorption ammonium may be ascribed to deprotonated carboxylic acid, which has the ability to adsorb positively charged ammonium ions.