酸法还原浸出电解锰渣中锰和铁的工艺条件和动力学分析

研究酸法还原浸出电解锰渣中锰、铁的影响因素和动力学机制,并初步分析了反应机理.结果表明:增加反应温度、浸出时间均有助于锰、铁浸出率的提高.在85℃、4mL/g液固比、1.67mol/LH2SO4、0.2mol/LH2C2O4、120min浸出时间的条件下,锰、铁浸出率分别为99.9％和79.3％.反应机理为电解锰渣中难溶物Mn2O3、CaMn2O4、Fe(OH)3在酸性溶液中与H2C2O4发生还原反应形成易溶组分.锰、铁的浸出过程符合内扩散控制模型,表观活化能分别为21.6kJ/mol和17.9kJ/mol.     

Catalytic properties in deNOx and SO2–SO3 reactions

SCR-deNO_x reaction and SO₂–SO₃ oxidation tests were carried out by different research groups over fresh and used EUROCAT oxide samples in order to characterize the reactivity of the catalysts and to compare data obtained in several laboratories (Politecnico of Milan, Università of Salerno, ENEL of Milan, Boreskov Insitute of Catalysis).

Data are presented which indicate that the used EUROCAT catalyst is slightly more active both in the deNO_x reaction and SO₂–SO₃ oxidation than the fresh sample.

An analyses of data collected over honeycomb catalysts by means of a 2D, single-channel model of the SCR monolith reactor has been performed to evaluate the intrinsic kinetic constant of the deNO_x reaction; a satisfactory comparison has been obtained between estimation of the intrinsic kinetic constant and estimation of the intrinsic catalyst activity from data collected over powdered catalysts. A good agreement has been found in the experimental results collected in the different labs, both for the deNO_x reaction and SO₂–SO₃ oxidation.     

The influence of temperature and the concentration of MNSO4 on the simultaneous absorption and reaction of mixtures of SO2 and O2

We have studied the simultaneous absorption of gaseous mixtures of SO₂ and O₂ in solutions of MnSO₄ up to 0.75 mol/L and at temperatures between 10 and 40°C. The reactor used was operated continuously for the gas phase and batchwise for the liquid. The liquid phase was saturated in SO₂ at the first sampling after one hour. The absorption of O₂ was the controlling step in the process, with reaction order of 0 and 1 for SO₂ and O₂, respectively, and a fast reaction regime for MnSO₄ at concentrations of more than 0.025 mol/L. As far as manganese is concerned, our results show that the reaction order varies according to its concentration and we have obtained an equation which relates the kinetic constant to temperature and the concentration of the catalyst.     

钛铁矿硫酸浸出动力学研究

研究了攀枝花钛铁矿在硫酸溶液中浸取反应的动力学行为,发现在温度为１００℃－１９８℃、酸矿比为５００：１５时,钛精矿在８５％硫酸溶液中的反应速率同时受矿粒表面反应和表面产物层传质阻力影响,表观反应活化能约６８．４ｋＪ／ｍｏｌ。浸出反应动力学方程为ｔ＝「０．００７６６／（２．７４＊１０＾７ｅ＾－６８４００／ＲＴ）」「１－ｘ）＾１／３」｛１＋（１１－０．０１６Ｔ）「１＋（１－ｘ）＾１／３－２（１－ｘ）＾２／３」｝在酸矿比更低的非等温和准绝热实验中,该方程式可以很好地模拟反应的动力学特性。     

SO2和H2O对Y掺杂Mn/TiO2选择性脱除NO的影响

采用溶胶-凝胶法制备了Y掺杂的TiO₂载体,负载硝酸锰构成了Y掺杂的Mn-Y/TiO₂催化剂。考察了焙烧温度、空速对其催化还原NO性能的影响,并对催化剂的抗SO₂、H₂O毒化性能进行了考察。结果表明,催化剂的最佳焙烧温度为500 ℃,催化剂的活性随空速的降低而升高,XRD分析Y掺杂抑制了锐钛矿晶相的转移,有利于催化剂活性组分的分散,从而提高催化剂的活性。Mn-Y/TiO₂的抗毒化性能优于Mn/TiO₂,在反应温度180 ℃、空速14000 h^－1、氧含量为3%、NO浓度600 mL/L及NH₃/NO为1的条件下,同时通入200 mL/L SO₂和4% H₂O,NO转化率从非掺杂的Mn/TiO₂的48.2%上升到57.6%,Y掺杂提高了催化剂的抗毒化能力;FTIR分析表明催化剂中毒是由于生成了铵的硫酸盐或者锰、钇的硫酸盐。     

Evaluation of V2O5–WO3–TiO2 and alternative SCR catalysts in the abatement of VOCs

Two different commercial SCR catalysts belonging to the V₂O₅–WO₃–TiO₂ system, and different alternative catalysts based on Mn, Fe, Cr, Al and Ti oxides have been tested in the conversion of VOCs in excess oxygen in a temperature range typical of the SCR process (500–700 K). Propane, propene, isopropanol, acetone, 2-chloropropane and 1,2-dichlorobenzene have been fed with excess oxygen and helium. The industrial catalysts are poorly active in the conversion of propane, giving mainly rise to propene by oxy-dehydrogenation. The conversion of propene is higher with CO as the predominant product. In any case, the oxidation activity depends on the vanadium content of the catalyst. Isopropanol is mainly converted into acetone and propene, while acetone is burnt predominantly to CO. Mn- and Fe- containing systems are definitely more active in the conversion of hydrocarbons and oxygenates, giving rise almost exclusively to CO₂. 2-Chloropropane is selectively dehydrochlorinated to propene and HCl starting from 350 K, propene being later burnt to CO on the industrial V₂O₅–WO₃–TiO₂ catalysts, whose combustion activity is, apparently, not affected by chlorine. On the contrary, chlorine strongly affects the behavior of Mn-based catalysts, that are active in the dehydrochlorination of 2-chloropropane, but are simultaneously deactivated with respect to their combustion catalytic activity. The conversion of 1,2-dichlorobenzene gives rise to important amounts of heavy products in our experimental conditions with relatively high reactant concentration.     

Preparation of battery-grade manganese dioxide through disproportionation of partially oxidised hydrous manganese oxide in dilute sulphuric acid

Manganese hydroxide was precipitated from MnSO₄ and NH₄OH at controlled pH, partially oxidised by aeration and finally calcined at 573–623 K to yield manganese oxide with oxidation state between +3 and +4. When the calcined oxide was leached in dilute sulphuric acid, MnO₂ of high electrochemical activity was obtained. In order to improve the bulk or packing density of the product various oxidants were added during the aerial oxidation of the Mn(OH)₂ slurry and also during the leaching in dilute H₂SO₄. It was observed that the best results were obtained when active MnO₂ was added during the aerial oxidation of Mn(OH)₂ slurry.     

Enhanced activity of metal oxide-doped Ga2O3–Al2O3 for NO reduction by propene

Effect of additives, In₂O₃, SnO₂, CoO, CuO and Ag, on the catalytic performance of Ga₂O₃–Al₂O₃ prepared by sol–gel method for the selective reduction of NO with propene in the presence of oxygen was studied. As for the reaction in the absence of H₂O, CoO, CuO and Ag showed good additive effect. When H₂O was added to the reaction gas, the activity of CoO-, CuO- and Ag-doped Ga₂O₃–Al₂O₃ was depressed considerably, while an intensifying effect of H₂O was observed for In₂O₃- and SnO₂-doped Ga₂O₃–Al₂O₃. Of several metal oxide additives, In₂O₃-doped Ga₂O₃–Al₂O₃ showed the highest activity for NO reduction by propene in the presence of H₂O. Kinetic studies on NO reduction over In₂O₃–Ga₂O₃–Al₂O₃ revealed that the rate-determining step in the absence of H₂O is the reaction of NO₂ formed on Ga₂O₃–Al₂O₃ with C₃H₆-derived species, whereas that in the presence of H₂O is the formation of C₃H₆-derived species. We presumed the reason for the promotional effect of H₂O as follows: the rate for the formation of C₃H₆-derived species in the presence of H₂O is sufficiently fast compared with that for the reaction of NO₂ with C₃H₆-derived species in the absence of H₂O. Although the retarding effect of SO₂ on the activity was observed for all of the catalysts, SnO₂–Ga₂O₃–Al₂O₃ showed still relatively high activity in the lower temperature region.     

Cu–Mn mixed oxides for low temperature NO reduction with NH3

Cu–Mn mixed oxides were prepared by a co-precipitation method and applied for low temperature NO reduction with NH₃ in the presence of excess oxygen. Effects of [Cu]/[Mn] ratio and calcination temperatures on NOx conversions were investigated. Cu–Mn oxide catalysts containing small amounts of copper showed the complete NOx conversion in a wide range of reaction temperature from 323 to 473 K. This catalyst showed a reversible deactivation due to the presence of water vapor and SO₂. Different catalytic activities of Cu–Mn mixed oxides could be attributed mainly to surface areas and the crystalline nature.     

微硅粉中SiO2在稀碱液中的溶解行为及动力学

研究了微硅粉中SiO2在稀碱溶液中的溶解行为及溶解动力学,考察了反应时间、NaOH初始浓度及反应温度对SiO2浸出率的影响,并分析了原料和浸出渣的物相. 结果表明,SiO2的浸出率随碱初始浓度和反应温度增加而增加. 微硅粉中无定型SiO2在NaOH稀碱液中的溶解表观活化能为18 kJ/mol,说明该溶解反应由扩散控制.     

Grain growth in TiO2-added ZnO–Bi2O3–CoO–MnO ceramics prepared by chemical processing

The effect of TiO₂ on the grain growth of the ZnO–Bi₂O₃–CoO–MnO ceramic system prepared by chemical coprecipitation, was studied between 1150 and 1300 °C in air. Bi₂O₃ melts during firing, and then TiO₂ dissolves into Bi₂O₃-rich liquid. TiO₂ initially reacts with Bi₂O₃ to form Bi₄Ti₃O₁₂. Above ≈1050 °C, Bi₄Ti₃O₁₂ reacts with ZnO to form Zn₂TiO₄ spinel phase. The kinetic study of grain growth carried out using the expression Gⁿ–G_oⁿ=K_o·t·exp(−Q/RT) gave grain exponent (n) value as 6 and the apparent activation energy (Q) as 226.46 kJ/mol. 1.00 mol% TiO₂ addition increased the grain growth exponent value from 6 to 7 and apparent activation energy with 1.00 mol% TiO₂ addition was found to be 197.10 kJ/mol. The ZnO grain size gradually increases with increasing TiO₂ content. Addition of TiO₂ may increase the reactivity of the Bi₂O₃-rich liquid towards the ZnO grain, thus affecting the ZnO grain growth.     

利用反应动力学分析硫磺制酸转化器设计参数的选择

根据 SO2 转化试验研究建立的动力学模型 ,并用转化器操作数据进行校正 ,从而得到完整反应动力学方程。运用反应动力学方程编制的程序 ,着重对转化器进口 SO2 浓度的选择、各段进口温度的选择、压力对最终转化率的影响进行讨论     

Viscosity measurements and empirical predictions for fluxed Australian bituminous coal ashes

Recent interest in the suitability of Australian bituminous coals for use in integrated gasification-combined cycle (IGCC) technologies has provided the opportunity to determine viscosity data for a range of coal ashes slags fluxed with limestone at the tapping temperatures of entrained flow gasifiers. Experimental viscosity measurements have been made over a range of slag compositions covering the anorthite region at the 0–2.5, 2.5–5, 5–7.5 and 7.5–10 wt% FeO levels of the quaternary SiO₂–Al₂O₃–CaO–FeO system. Contour plots of viscosities at 1450°C for the four FeO ranges are presented as an example for predicting slag behaviour in entrained flow gasifiers. The viscosity measurements have also been fitted empirically using a modified Urbain treatment to give separate models for the four FeO levels. Polynomial expressions are given for the evaluation of viscosities covering the temperature range 1400–1550°C for slags within the compositional range used in the derivation.     

Bioactive and degradable organic–inorganic hybrids

CaO–SiO₂–poly(vinyl alcohol) (PVAL) and CaO–P₂O₅–SiO₂–PVAL organic–inorganic hybrids were obtained as monoliths and characterized before and after be soaked in a solution mimicking human plasma. The hybrids were obtained by adding PVAL (0.9, 1.8 and 3.6 wt.%) to three CaO–(P₂O₅)–SiO₂ gel glasses with 25 mol% of CaO and 0, 2.5 and 5 mol%, respectively of P₂O₅. The influence of PVAL and P₂O₅ on the monoliths obtaining and on their textural properties and in vitro behavior was analyzed. Additions of PVAL favored the synthesis of cracked-free monoliths able to be coated with bone-like apatite after be soaked in Kokubo's simulated body fluid (SBF), i.e. to present in vitro bioactivity. Increasing P₂O₅ contents made the hybrids syntheses difficult and decreased their in vitro bioactivity. In addition, the in vitro degradation of hybrids increased with the increasing of PVAL and P₂O₅. Thus, hybrids with the highest amounts of both components showed so high degradation in SBF that the apatite layer formation was impeded. Organic–inorganic hybrids in these systems could be clinically used as bone defect fillers in non load bearing applications or as matrices in controlled release systems.     

Improvement of catalytic activity and sulfur-resistance of Ag/TiO2–Al2O3 for NO reduction with propene under lean burn conditions

Ag-based catalysts supported on various metal oxides, Al₂O₃, TiO₂, and TiO₂–Al₂O₃, were prepared by the sol–gel method. The effect of SO₂ on catalytic activity was investigated for NO reduction with propene under lean burn condition. The results showed the catalytic activities were greatly enhanced on Ag/TiO₂–Al₂O₃ in comparison to Ag/Al₂O₃ and Ag/TiO₂, especially in the low temperature region. Application of different characterization techniques revealed that the activity enhancement was correlated with the properties of the support material. Silver was highly dispersed over the amorphous system of TiO₂–Al₂O₃. NO₃⁻ rather than NO₂⁻ or NOx reacted with the carboxylate species to form CN or NCO. NO₂ was the predominant desorption species in the temperature programmed desorption (TPD) of NO on Ag/TiO₂–Al₂O₃. More amount of formate (HCOO⁻) and CN were generated on the Ag/TiO₂–Al₂O₃ catalyst than the Ag/Al₂O₃ catalyst, due to an increased number of Lewis acid sites. Sulfate species, resulted from SO₂ oxidation, played dual roles on catalytic activity. On aged samples, the slow decomposition of accumulated sulfate species on catalyst surface led to poor NO conversion due to the blockage of these species on active sites. On the other hand, catalytic activity was greatly enhanced in the low temperature region because of the enhanced intensity of Lewis acid site caused by the adsorbed sulfate species. The rate of sulfate accumulation on the Ag/TiO₂–Al₂O₃ system was relatively slow. As a consequence, the system showed superior capability for selective adsorption of NO and SO₂ toleration to the Ag/Al₂O₃ catalyst.     

烟气氧硫比对软锰矿浆烟气脱硫体系浸锰过程及脱硫产物的影响

基于烟气中氧气与二氧化硫浓度之间的关系对软锰矿浆烟气脱硫反应的影响机理分析,提出用氧硫比(氧气与二氧化硫的摩尔比)作为关联烟气含氧量与二氧化硫浓度的参数,考察了烟气氧硫比对软锰矿浆烟气脱硫体系锰浸出率及脱硫产物的影响,据此探讨了提高锰浸出率与硫酸锰产量的方法.结果表明,氧硫比是体系pH值变化的指针因子,并通过改变体系的...     

Hydroisomerization and hydrocracking of long chain n-alkanes on Pt/amorphous SiO2–Al2O3 catalyst

The hydroisomerization and hydrocracking of n-hexadecane, n-octacosane and n-hexatriacontane on a 0.3% platinum/amorphous silica–alumina (MSA/E) catalyst was investigated in a stirred microautoclave at 345, 360 and 380°C and between 2 and 13.1 MPa hydrogen pressure. For each n-paraffin, the reaction pathway and the kinetic parameters were determined. The results were used to elucidate the effect of chain length and operating conditions on isomerization and cracking selectivity. The conversion of the n-paraffins lead to the formation of a mixture of the respective isomers, as the main product, together with cracking products. At every temperature, the iso-alkane/n-alkane ratio of cracking products increased considerably with increasing conversion degree. At the same conversion level, higher reaction temperatures lead to cracking products characterized by a lower iso-alkane/n-alkane ratio. The conversion rate constants showed a considerable increase between n-C₁₆ and n-C₂₈, whereas a slight decrease between n-C₂₈ and n-C₃₆ was observed. The hydroisomerization selectivities showed a decrease as a function of chain length and with increasing conversion levels. The increase in reaction temperature leads to a small decrease in the isomerization selectivities only at low-medium conversion degrees and at the highest temperature investigated, while the effect of this parameter on the maximum yields achievable in iso-C16, iso-C28 and iso-C36 was negligible. The results indicate that the conversion of the n-paraffins follows a first-order kinetic in hydrocarbon while the order in hydrogen pressure was −1.1 ± 0.21 for n-C₁₆ and −0.66 ± 0.15 for n-C₂₈. Furthermore, an increase in hydroisomerization selectivity at higher hydrogen pressure for n-C₂₈ conversion was observed.     

H2O和SO2对Mn-Fe/MPS催化剂用于NH3低温还原NO的影响

研究了H2O和SO2对Mn-Fe/MPS催化剂低温下选择性催化NH3还原(SCR)NO的影响. 结果表明,Mn-Fe/MPS催化剂具有良好的催化活性,在空速为20000 h-1、反应温度433 K时,NO的SCR转化率达99.1%. 在反应温度低于413 K时,水蒸汽(10%, j)在一定程度上降低了催化活性;超过433 K时,这种影响可完全消除,NO的SCR转化率达到97.8%以上. 低浓度SO2(100′10-6)存在条件下,443 K时催化效率仍可稳定在97.2%. 在水和SO2共存的情况下,生成的硫酸盐和亚硫酸盐沉积在催化剂表面导致催化剂逐渐失活,FT-IR测试也表明伴随SCR反应生成了硫酸铵. 提高反应温度可以延缓催化剂的失活. 此外还研究了不同活化温度对催化剂活性恢复的影响,结果表明,当活化温度达到773 K时,催化剂活性可以完全恢复. 本研究中的催化剂的综合性能优于目前文献报道的其他催化剂.     

CO_2加氢反应的基础研究进展

对通过CO_2加氢反应合成烃类和含氧化合物的研究近来获得重要进展,主要表现在催化剂的研制和反应动力学及反应机理方面的研究上。本文在大量有关文献的分析基础上概述了这些进展,为今后的进一步工作做了一些理论准备。     

亚微米LiFe0.05Mn1.95O4正极材料的制备及电化学性能

采用固相燃烧法合成了亚微米单晶多面体LiFe_0.05Mn_1.95O₄正极材料。借助XRD、FE-SEM、TEM、XPS和恒电流充放电等手段对样品的结构、形貌、物相组成和电化学性能进行测试。结果表明,Fe掺杂未改变尖晶石型LiMn₂O₄的立方晶系结构,其{400}和{440}衍射峰相对应的晶面出现显著的择优生长,形成了形貌为{111}、{110}和{100}晶面的单晶去顶角八面体晶粒。LiFe_0.05Mn_1.95O₄正极材料表现出比纯LiMn₂O₄材料更为优异的电化学性能,在1C和5C时有着114.7mA·h/g、104.7mA·h/g首次放电比容量,10C倍率下经1000次循环后,容量保持率为83.9%。循环伏安与阻抗分析得出掺杂后的样品有着较大的锂离子扩散系数与较小的活化能。对5C倍率循环1000次后Fe掺杂样品的极片分析发现,其晶体结构基本无变化,适量的Fe掺杂能够有效抑制尖晶石型LiMn₂O₄在充放电循环过程中的Jahn-Teller效应以及Mn的溶解,提升材料的结构稳定性与容量保持率。