Influence of aromatic reactants and products involved in the two stage electrochemical oxidation on the voltammetric behaviour of Ce(IV)/Ce(III) redox couple

The redox behaviour of the Ce(IV)/Ce(III) couple in 1.0 M nitric acid, 1.0 M sulfuric acid, 1.0 M perchloric acid and in different concentrations of methane sulfonic acid was investigated on a glassy carbon electrode using cyclic voltammetry. Quasi reversible redox behaviour with low E _p value of 200 mV and below were observed in 1.0 M sulfuric acid and high concentrations of methane sulfonic acid. Anionic complexes apparently exist in this media. The reactants and products involved in the indirect oxidations are found to influence cerous/ceric redox behaviour in 2.0 M methane sulfonic acid in three distinct ways: (i) in the presence of cerous methane sulfonate organic compounds such as toluene, benzaldehyde and naphthaquinone do not exhibit substantial inhibitive effects; (ii) compounds such as p-xylene and p-tolualdehyde exhibit some inhibitive effect at higher concentrations; and (iii) compounds like naphthalene, p-ethoxy toluene and p-ethoxy benzaldehyde exhibit a fairly high level of inhibitive effect.     

Polymerization of acrylonitrile initiated by Ce(IV)-sucrose redox system: A kinetic study

The polymerization of acrylonitrile (M), initiated by the free radicals formed in situ in the Ce (IV)-sucrose redox system, was studied in aqueous sulfuric acid medium under nitrogen atmosphere in the temperature range of 30–60°C. The rate of polymerization is proportional to [M]^1.0, [R]^0.76, [Ce(IV)]^0.8, and [H⁺]^−0.46. The rate of Ceric ion disappearance and the rate of polymerization R_p have been measured. The effects of some water–miscible organic solvents, surfactants, ionic strength, and complexing agents on the rate of polymerization were investigated. The temperature-dependence of the rate was studied and the activation parameters were computed using the Arrhenius and Eyring plots. A mechanism consistent with the experimental data, involving Ce(IV)-sucrose complex formation, which generates free radicals, is suggested. The chain termination step of the polymerization reaction was determined. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Destruction of aniline by mediated electrochemical oxidation with Ce(IV) and Co(III) as mediators

Mediated electrochemical oxidation has been employed to test the feasibility of treating soluble organic wastes. We report Ce(IV)- and Co(III)-mediated electrochemical oxidation of aniline at various electrodes in acidic media as an example of organic waste. Aniline was oxidized by an electrogenerated electron transfer mediator, Ce⁴⁺ or Co³⁺, in the anolyte and carbon dioxide was produced as a final oxidation product. Carbon dioxide was collected by bubbling through a barium hydroxide solution. When a powerful oxidizing agent, Ce(IV) or Co(III), was used as an electron shuttling mediator, parameters affecting the coulombic efficiency for aniline oxidation were the standard oxidation potentials of the mediators, their concentrations and the reaction temperature. Intermediate species produced during the oxidation of aniline were identified by cyclic voltammetric and absorption spectroscopic measurements.     

Removal of Ce(IV) Ions from Aqueous Solutions Using Sawdust Coated by Electroactive Polymers

In this work, adsorption of the Ce(IV) ions onto polypyrrole (PPy) and polyaniline (PAn) conducting electroactive polymers as coated form on sawdust has been investigated. The effect of some important parameters such as initial concentration of the Ce(IV) ion adsorbent dosage, and contact time was studied. The experiments were carried out using both batch and column systems at room temperature. The equilibrium adsorption capacity of sawdust coated by polypyrrole and polyaniline for the removal of Ce(IV) ion was measured and extrapolated using linear Freundlich and Langmuir isotherms. It was found that sawdust modified by PPy and PAn improved the removal efficiency of Ce(IV) ions from aqueous solutions greatly.     

HPF湿式氧化法焦炉煤气脱硫脱氰技术

介绍了HPF法脱硫脱氰工艺的原理、流程、特点以及实际操作数据。     

Mediated electrochemical oxidation of phenol in continuous feeding mode using Ag (II) and Ce (IV) mediator ions in nitric acid: A comparative study

Mediated electrochemical oxidation (MEO) process is one among the latest treatment technologies for the destruction of toxic organic pollutants under ambient temperatures and at atmospheric pressure. The process is a further extension of the conventional electrochemical treatment for the removal of toxic organics with powerful mediator oxidants in acidic medium. In this report the experimental results of using silver and cerium as mediator ions were compared with respect to their electro-oxidation behavior within the limitations of each mediator metal ion and their destruction efficiencies were compared for destructing phenol in continuous feeding mode. The following conclusions were drawn: (i) the optimum nitric acid concentration was found to be 8 and 3 M and the optimum temperature was found to be 60 and 80 °C for silver and cerium electro-oxidations, respectively; (ii) in the case of Ag (II)-MEO of phenol the maximum destruction efficiency achieved was 98% at 70 °C based on CO₂ evolved; (iii) for Ce (IV)-MEO of phenol the maximum destruction efficiency achieved was 93% at 90 °C based on CO₂. The results may provide baseline information on the use of suitable mediator metal ion in treating the target organic wastes by MEO process.     

焦炉煤气脱硫脱氰工艺的优化

通过对焦炉煤气脱硫系统中HCN分解装置的运行状况和存在的问题进行总结,找出了其堵塞原因,并在理论和实践分析的基础上对生产工艺进行改造、操作方法进行改进。经过改造后工艺实际生产效果明显改善,脱硫工序开工率、硫磺产量明显提高,取得了较好的经济效益和环境效益。     

Preparation of mesoporous MCM-41 supported zinc sorbents by microwave in-situ oxidation for H2S removal in coal gas

Zn-based MCM-41 supporter sorbents were prepared using the microwave in-situ oxidation method. Other sorbents were heated using a conventional heating method to contrast the performance for H₂S removal. The sorbents were tested at 500°C in fixed reactor and dried simulated Texaco coal gas was employed for the sulphurized atmosphere. The results show that sorbents prepared by microwave oxidation had a better toleration for the adsorption of H₂S. A 13.2% improvement occurred in the sulphur capacity of the sorbents heated by the microwave method. XRD, SEM with EDS-element mapping, TEM, N₂ adsorption, and XPS were used to characterize the properties of the sorbents. Due to the selective heating of the microwave and the superiority of the in-situ oxidation method, the sorbents heated by microwave exhibited more appropriate structures for sulphurization. Meanwhile, the even heating environment supplied by the microwave resulted in a more uniform distribution of the active component. The microwave also had an effect on the chemical bond and reduced the binding energy of the active component, which enhanced the reactivity between the H₂S and the sorbents. The preferable features generated by microwave in-situ oxidation accelerate the replacement of S to O, and therefore the Zn-based MCM-41 sorbents prepared by the microwave method have an increased capability for H₂S removal in high temperature coal gas.     

筛板塔Fe/Cu湿式催化氧化脱除H2S气体制硫磺的实验

阐述了筛板塔Fe/Cu湿式催化氧化脱除H₂S气体制硫磺流程,考察了操作空塔气速、液气比、起始pH值和H₂S入口浓度对H₂S脱除效率的影响及鼓风量、液柱高度对Fe^3＋氧化再生的影响;并进行了综合实验。结果表明,含120g/L的Cu²⁺、70g/L的Fe²⁺及70g/L的Fe³⁺的吸收体系即能对体积分数为1000×10^－6的H₂S废气近100％稳定脱硫,流程简短、能耗低,体系除消耗O₂外,过程不消耗原料,不产生二次污染,体系无降解问题。     

Novel method for removal of NO x and SO2 by sustainable electrochemical process using Ag(I)/Ag(II) redox mediator

The objective of this work was to develop a process for removal of industrial waste gases like NO, NO₂ and SO₂ by electrochemically generated Ag(I)/Ag(II) redox mediator system in aqueous nitric acid medium. 100% removal efficiencies were achieved in these studies for removal of NO _x and SO₂ with Ag(II) ions in room temperature and atmospheric pressure. This Ag(I)/Ag(II) redox mediator system can be regenerated continuously during the scrubbing process.     

Polymerization kinetics of methylmethacrylate by oxidation: Reduction system using cerium(IV)/lactic acid in aqueous medium

The kinetics of polymerization of methylmethacrylate initiated by cerium(IV)–lactic acid redox system was studied in an aqueous medium in the temperature range of 25–50°C. The rate of polymerization (R_p) and the rate of cerium(IV) disappearance have been measured. The effects of some water‐miscible organic solvents, cationic, anionic, nonionic surfactants, and complexing agents on the rate of polymerization were investigated. The temperature dependence of the rate was studied, and the activation parameters were computed using the Arrhenius and Eyring plots. The effects of inorganic and organic solvents on polymerization were also investigated. All of them depressed both the initial rate and limiting conversion. A mechanism consistent with the experimental data, involving cerium(IV)–lactic acid complex formation, which generates free radicals, is suggested. The chain termination step of the polymerization reaction is by mutual interaction of the growing macromolecules. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3498–3505, 2007     

海水介质下铁基液相催化氧化法脱除硫化氢的实验研究

以天然碱性海水为反应介质,采用Fe基液相催化氧化法,针对质量浓度为10g/m3左右H2S的气体进行了模拟海上钻井平台脱除H2S的实验研究。主要考察了配方溶液、空气过剩因子(ε)、温度、溶液初始pH等工艺参数对脱硫效果的影响,并对反应产生的固体物含水硫磺进行了X射线衍射(XRD)、电子扫描电镜(SEM)表征。通过分析实验结果确定了最佳催化氧化脱除H2S的条件。并发现了产生的固体物质大颗粒硫磺,易于固液分离。     

A new sol‐gel route alumina for selective oxidation of H2S to sulphur

In this study, a new synthesis method was developed for the production of modified sol‐gel alumina (SG‐M) for the selective oxidation of H₂S to elemental sulphur. The catalytic activity of this modified alumina without any active metal incorporation was then compared with the activity of commercial alumina (alumina‐com) for H₂S selective oxidation. The N₂ adsorption‐desorption isotherm showed that the SG‐M alumina synthesized in this work has a mesoporous structure with well‐defined hysteresis loops. Both alumina materials showed a γ‐Al₂O₃ crystalline phase with an amorphous structure in their crystal structure. The surface acidity of the alumina materials was determined using pyridine‐adsorbed FTIR analyses, and both alumina showed Lewis acid sites on their surfaces. The catalytic activity tests were performed at 250°C using a feed ratio of O₂/H₂S:0.5. The complete conversion of H₂S over SG‐M was achieved during 400 minutes of reaction time. However, the commercial alumina lost its activity at earlier reaction times. Lewis acid sites and surface hydroxyl groups caused the alumina to be active in H₂S selective catalytic oxidation, and the formation of Al‐S bonds, observed when the H₂S conversion fell, caused a decrease in the catalytic activity of the alumina materials. A high sulphur yield (≥95%) was obtained over SG‐M, even though there was no active metal incorporation and even in the presence of excess oxygen. Considering the catalytic activities, the new sol‐gel alumina synthesized in this work is superior to commercial alumina. It was concluded that, as a catalyst without any active metal, SG‐M is a promising catalyst in H₂S selective oxidation to sulphur.     

Synthesis and characterization of a thermally stable strongly acidic Cd(II) ion selective composite cation-exchanger: Polyaniline Ce(IV) molybdate

A polymer supported organic-inorganic composite and strongly acidic cation-exchanger polyaniline Ce(IV) molybdate was chemically synthesized and demonstrated to be an excellent ion-exchange material due to its high selectivity for Cd(II), thermal stability and fast elution of an exchangeable H⁺ ion. The material was characterized for its ion exchange properties to study its cation-exchange behavior. Cd(II) selectivity depends upon the distribution coefficient in several solvent systems. The selectivity of this material varied depending upon its composition and the composition of the eluting solvent. Its selectivity was examined and some important binary separations such as Cd(II)-Pb(II), Cd(II)-Hg(II), Cd(II)-Zn(II) and Cd(II)-Ni(II) were also achieved. The physico-chemical properties of the material were also studied using C, H, N elemental analysis, ICP-MS, FTIR, TGA-DTA, X-ray and SEM studies.     

[(C_2H_5)_4N]_2｛Fe_4S_4[S_2CN(C_2H_5)_2]_4｝的晶体和分子结构

本文报导含类立方烷型簇核Ｆｅ４ｓ４的金硫配位化合物［（Ｃ２Ｈ５）４Ｎ］２｛Ｆｅ４Ｓ４［Ｓ２ＣＮ（Ｃ２Ｈ５）２］４｝的合成、晶体和分子结构测定的结果。     

溶胶-凝胶法制备KZnLa（PO_4）_2：Ce,Tb及其荧光性能研究

采用溶胶-凝胶法合成KZnLa（PO4）2：Ce,Tb,并对其荧光性能进行研究,利用XRD、SEM对产物的物相结构、形貌进行研究,用荧光光度计对荧光粉的激发光谱和发射光谱测试,研究不同浓度的激活剂和敏化剂对荧光强度的影响。研究结果表明：制备的荧光粉粒径约200nm,为单斜向磷酸盐结构;改变La3＋,Ce3＋,Tb3＋浓度,将对相对荧光强度产生影响,且（KZn）0.3La0.45PO4∶0.2Tb,0.05Ce时,相对荧光强度最大。     

Cerium(IV)-mediated electrochemical oxidation process for destruction of organic pollutants in a batch and a continuous flow reactor

The mediated electrochemical oxidation (MEO) process with Ce(IV) and nitric acid as the oxidizing medium was employed for the destruction of various model organic pollutants in batch and continuous organic feeding modes. A near complete destruction was observed for all the model organic pollutants studied. The effects of organic concentration, temperature, concentration of Ce(IV), concentration of nitric acid and feeding time on the organic destruction efficiency were investigated. Under the experimental conditions of 80 °C and 0.95 M Ce(IV) in 3 M nitric acid, nearly 90% destruction was achieved based on CO₂ production and 95% based on TOC and COD nearly for all the organic compounds studied in batch organic addition. In the case of continuous organic addition with in situ electroregeneration of Ce(IV) by the electrochemical cell a good destruction efficiency was obtained. For long term organic feeding (120 min) the destruction efficiency was found to be 85% based on CO₂ evolution and 98–99% based on TOC and COD analyses. A model was proposed for calculating the CO₂ formation constant during the continuous process of organic addition. The model predicted a steady state CO₂ evolution pattern for the destruction process during continuous organic feeding. The experimental results obtained confirmed the predicted trends for the destruction process. The changes in enthalpy, entropy, activation energy and free energy for EDTA degradation were found to be 26.7 kJ/mol, −230 J/(mol·K), 29.7 kJ/mol, and 118 kJ/mol respectively.     

Kinetics,degradation pathway and reaction mechanism of advanced oxidation of 4‐nitrophenol in water by a UV/H2O2 process

Photooxidation of 4‐nitrophenol (4‐NP) in water by the UV/H₂O₂ advanced oxidation process was carried out in order to investigate the kinetics and pathway of 4‐NP degradation. The experimental results showed that the photodegradation of 4‐NP accorded well with pseudo‐first order kinetics. The effects of different parameters, such as H₂O₂ dosage, pH value and various anion scavengers on the degradation of 4‐NP have been investigated in detail. It was found that acidic conditions are more favorable to the degradation of 4‐NP but many anions, such as HCO₃^?, NO₃^? and Cl^?, slow down the photooxidation rate of 4‐NP. Hydroquinone, 1,2,4‐trihdroxybenzene, 4‐nitropyrogallol, and 4‐nitrocatechol were tentatively identified as the intermediates of 4‐NP degradation by GC/MS after samples were derivatized by N,O‐bis(trimethylsilyl)‐trifluoroacetamide (BSTFA). A degradation pathway was proposed to account for the observed intermediates produced during 4‐NP degradation by the UV/H₂O₂ process. Copyright © 2003 Society of Chemical Industry     

均相共沉淀法制备草酸铈固溶体

以草酸二乙酯、Ce(NO3)3.6H2O、Y(NO3)3.6H2O为初始原料,以尿素为pH值调节剂,实现了Ce3 、Y3 的均相共沉淀。利用热重分析(TG-DTA)从多方面证实了n=0～35.5(n为尿素与草酸二乙酯的摩尔比)范围内得到的沉淀物为草酸铈的固溶体。经扫描及透射电子显微镜观察,生成的草酸盐固溶体沉淀颗粒尺寸随着n值的增大而减小,由n=0时约10μm下降到n=35.5时约0.5μm,沉淀物热分解后得到的氧化物经X射线衍射分析及晶格常数计算表明了为Y固溶CeO2,其结晶粒径约10 nm。