铁矿微粉低温快速氢还原实验研究

通过实验进行了铁矿微粉在输送过程中低温(180~570℃)、低压(<0.2 MPa)条件下用氢预还原的可行性研究. 分别考虑了反应温度、矿粉粒径、固气比、反应时间等参数对矿粉还原率的影响. 结果表明,粒径为61.7 mm的矿粉在加热温度570℃、固气比0.22 g/L、反应时间40 s时,还原率可达39.2%. 对还原样品粉末进行X射线衍射分析表明,铁矿粉中的Fe2O3已还原为Fe3O4并开始出现金属铁.     

钒钛磁铁矿的煤粉还原过程

对煤粉还原钒钛磁铁矿过程中产生的铁氧化物和钛铁化合物进行热力学分析,得出工艺还原过程中的反应热力学数据,进一步采用高温炉在还原温度1350℃、配碳比1.0、还原煤粒度小于75μm的条件下,考察还原时间对工艺指标的影响和还原过程,得出不同还原时间下产物的定量结果和物相成分.结果表明,还原时间为60min时,还原产物的全铁、金属铁、金属化率均达最大值,分别为68.60%,65.81%和95.93%,钒钛磁铁矿中铁氧化物的还原过程为Fe2O3→Fe3O4→FeO→Fe,钛铁化合物的还原过程为Fe2TiO5→Fe2TiO4→FeTiO3→FeTi2O5.     

水滑石焙烧产物脱除低浓度SO2的研究

研究了水滑石焙烧产物吸附低浓度SO2的性能和还原情况。实验表明：在大于600℃吸附温度下,焙烧的水滑石具有较好吸附性能。吸附剂本身制备条件对脱硫性能影响明显。负载Fe2O3后的复合金属氧化物吸附剂Fe2O3／Mg(Al)O吸附性能整Mg(Al)O有明显提高。氢还原是再生吸附剂的合理和可靠的方法。     

针状铁黄热处理研究进展

磁粉是磁记录介质的关键原料，γ－Fe2O3磁粉的制备包括铁黄合成、铁黄脱水、αFe2O3。还原和Fe3O4氧化等几大过程。本文针对铁黄脱水、还原和氧化，概述了铁黄热处理过程特征及其研究进展     

磁载光催化剂TiO2/SiO2/Fe3O4的制备及其性能

以微米级Fe3O4作为载体,用一种改进的溶胶一凝胶法制得TiO2／SiO2／Fe3O4包覆型光催化剂。采用振动样品磁强计（VSM）、X射线衍射仪（XRD）和透射电镜（TEM）分别对该催化剂的磁性能、晶体结构和微观形貌进行了表征,并通过对Cr^6＋水溶液的光催化还原对其催化活性进行了测试。结果表明,TiO2／SiO2／Fe3O4是由中间层SiO2和外壳TiO2组成的双层包覆粒子,通过与未包覆SiO2粒子TiO2／Fe3O4的比较,可知采用此种溶胶一凝胶过程制得的TiO2／SiO2／Fe3O4具有较好的磁性能和较高的光催化还原活性。     

微球状a-Fe2O3还原动力学

采用连续共沉淀和喷雾干燥相结合的方法制备出平均颗粒直径15.3 mm的微球状a-Fe2O3颗粒粉体,利用H2-TG还原实验手段结合Hancock-Sharp方法,研究了微球状a-Fe2O3在563~583 K温度范围内等温还原为Fe3O4的还原行为和还原动力学. 结果表明,随等温还原温度的升高,还原速率增大,在还原度a<0.8的还原阶段由a-Fe2O3转化为Fe3O4的还原反应是由相转变反应机理控制的,578 K以上恒温还原时,还原后期会发生部分Fe3O4的进一步还原. 在相转变机理控制的还原反应范围内,还原反应活化能为152.44 kJ/mol.     

硼铁精矿含碳球团还原过程数学模型

通过等温热重实验分析CO/CO2/N2气氛中硼铁精矿还原和无烟煤气化的动力学特性,求得Fe3O4→Fe O和Fe O→Fe两个还原阶段及碳素溶损反应的活化能分别为74.72,65.74与194.72 k J/mol.建立了硼铁精矿含碳球团还原过程数学模型,并通过实验验证了模型的准确性.考察了球团尺寸、孔隙率、反应活化能对金属化率的影响,结果表明,球团尺寸从φ16 mm×8 mm增加至φ32 mm×16 mm,前期还原速率降低,但最终金属化率从85%上升至99.4%;球团孔隙率对还原过程影响较小;碳素溶损反应活化能上升抑制还原进行,但对最终金属化率没有影响,而当界面还原活化能从初始值的0.95倍上升至1.05倍时,不仅反应速率下降,最终金属化率也从99.59%降低至94.81%.从活化能对还原过程影响推断,反应前期还原过程受碳气化和铁氧化物还原联合控制,后期为铁氧化物还原反应控制.     

添加Fe2O3对碳热还原含钛高炉渣的影响

以攀枝花含钛高炉渣为原料,针对碳热还原含钛高炉渣的还原产物TiC晶粒粒径较小而难以分离的问题,在原料中添加不同比例的Fe2O3促进TiC与渣相分离. 结果表明,原料中加入Fe2O3后,还原产物中Fe在渣中呈弥散分布,渣中TiC晶粒依附Fe相生长. Fe2O3添加量为5wt%时,依附于Fe相形核长大的TiC明显沉降,富集于还原产物底部,含钛高炉渣还原产物中TiC初步富集.     

钙钛矿型复合氧化物对甲烷的部分氧化及在混合太阳能氧化还原过程的应用

利用固相法合成了3种钙钛矿型复合氧化物Fe2O3-CaTixM1?xO3,研究了其结构、晶型和氧化还原活性。在固定床反应器中考察了该氧化物对两步法甲烷催化氧化制合成气及水分解制氢的活性及选择性。X射线衍射结果表明3种钙钛型复合氧化物均由正交晶系钙钛矿相和赤铁矿相组成。3种钙钛矿复合氧化物对甲烷的氧化活性顺序为Fe2O3-CaTi0.85Ni0.15O3Fe2O3-CaTi0.85Co0.15O3Fe2O3-CaTi0.85Fe0.15O3。固定床反应结果表明,以Fe2O3-CaTi0.85Ni0.15O3为氧载体催化剂,CH4转化率可达96%,CO和H2产率达71%,同时水分解反应的转化率为40%。利用Aspen Plus?对Fe2O3-CaTi0.85Ni0.15O3在混合太阳能氧化还原过程的效率及合成油和H2产率进行了模拟。模拟计算结果证明基于复合氧化物的混合太阳能氧化还原过程可以有效提高CH4利用率。     

QHB催化剂制备工艺

该催化剂的制备过程采用新的Fe－Cr共沉淀工艺，生成Fe〔Fe（Cr）O2〕2·xH2O类水合沉淀，改变了沉淀物的相态，改善了沉降和洗涤等性能；整个过程不需高温煅烧；成品中氧化铁主相为Fe3o4；三价铬离子进入氧化铁晶格，无游离态氧化铬存在，并使晶胞参数减少、晶格扭曲歧变；催化剂具有易还原的特点；使用性能良好，升温还原时间较短，操作弹性较大，床层温度容易控制，吨氨蒸汽消耗较低。     

Influence of the hydrogen reduction time and temperature on the morphology evolution and hematite/magnetite conversion of spindle-type hematite nanoparticles

We report on the transformation via hydrogen reduction of spindle-type hematite nanoparticles into hematite/magnetite hybrid iron oxide particles. The transformation process consists of the reduction of nanoparticles powder in an autoclave using hydrogen gas at a fixed pressure of 11 bars. Both temperature and time of reduction are varied between 300 °C to 360 °C and 0 to 45 h. X-Ray powder diffraction data on the obtained powder and corresponding Rietveld refinement allow the amount of reduced hematite to be determined as a function of these two parameters. Kinetics parameters are measured and an estimation of the activation energy is obtained through linearization of the Arrhenius equation. While reduction is dramatically accelerated at higher temperature, the morphology of the nanoparticles only remain qualitatively unchanged at 300 °C as seen from transmission electron microscopy images. The mechanisms underlying morphology changes are still under study and seem to be closely related to reactor pressure.     

Reduction of hematite with hydrogen in fixed and fluidised beds

Reduction of hematite with hydrogen has been carried out in fixed and fluidised beds at identical gas flow rates. Influence of gas velocity and particle size has been ascertained. The performances of the two types of bed for the reduction of hematite with hydrogen have been compared. The observed difference in performance is considered to be primarily due to the solids movement characteristics of systems studied. This is also influenced by the bubbling phenomena occurring in fluidised systems.     

Effect of Mixing on Natural Gas Reburning

The purpose of this work is to understand the influence of the mixing process on reburning performance. Modeling is done in a one-dimensional approximation by utilizing a detailed chemical mechanism, staged addition of reactants, and mixture stratification. Natural gas is used as both the main fuel and the reburning fuel. The most important parameters that affect the efficiency of the reburning process are: the amount of the reburning fuel, the initial NO level, the initial temperatures of the injected reburning fuel and overfire air (OFA), temperature of flue gas at the points where reburning fuel and OFA are injected, and intensity of mixing of the reburning fuel and OFA with the stream of flue gases. It is shown that fuel stratification in the mixing zone improves reburning efficiency for small heat inputs of the reburning fuel and degrades reburning efficiency for large heat inputs. Initial temperatures of the reburning fuel and OFA affect NO reduction and can be optimized for deeper NO control. Reactions of N-containing species in the burnout zone play an important role in NO reduction for large heat inputs of the reburning fuel.     

Chemically Bonded Phosphate Ceramics: III, Reduction Mechanism and Its Application to Iron Phosphate Ceramics

In this, the last of a series of three papers, we discuss a method of forming iron phosphate ceramics by a reduction process. We report the formation of iron oxide ceramics by reducing hematite with iron in a phosphoric acid solution. The reaction results in a rapid-setting ceramic (at room temperature) with a compressive strength of 3700 psi and a density of 1.7 g/cm³. Although the exact mineral form of the binder is difficult to determine because it is mostly amorphous and hence is not amenable to X-ray diffraction analyses, this material is expected to consist of iron hydrophosphates. The reduction process is very useful in recycling several industrial wastes that are rich in hematite, including iron mine tailings, red mud (a caustic waste from the alumina industry), and machining swarfs. Formation of ceramics with red mud and swarfs is also discussed.     

Tribological characteristics of nanometer Si3N4 filled poly(ether ether ketone) under distilled water lubrication

Nanometer Si₃N₄ filled poly(ether ether ketone) (PEEK) composite blocks with different filler proportions were prepared by compression molding. Their friction and wear properties under distilled water lubrication, as well as under ambient dry conditions, were investigated on a block on ring machine by running a plain carbon steel (AISI 1045 steel) ring against the PEEK composite block. The worn surfaces of nanometer Si₃N₄ filled PEEK and the transfer film were observed by scanning electron microscopy (SEM) and electron probe microanalysis (EPMA). The results showed that distilled water could reduce the friction coefficient of nanometer Si₃N₄ filled PEEK but with the sacrifice of a large reduction in wear resistance. The SEM and EPMA pictures of the worn surfaces indicated that the wear mechanisms of nanometer Si₃N₄ filled PEEK under distilled water lubrication and ambient dry rubbing conditions were different. Under water lubrication, the dominant wear mechanism of the filled PEEK was severe abrasive wear with surface fracture. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1394–1400, 2001     

Pyrolysis of coal and iron oxides mixtures. 2. Reduction of iron oxides

The reduction of iron oxides during the pyrolysis of blends of coal and iron oxides on a laboratory scale, has been studied. The pyrolysis of blends of bituminous coal and 30 wt% of magnetite or hematite has been studied by thermogravimetry and analysis of gases, using a heating rate of 3.2 K min^?1. The state of iron in ferrocoke has been established by X-ray diffraction. A primary reduction by hydrogen and carbon monoxide of the hematite has been observed at between 400 °C and 500 °C, but hidden in thermogravimetric measurements by primary volatilization of the coal. At ≈600 °C magnetite is progressively reduced to wustite and then to iron. This reduction starts a little earlier if the heating rate is slow and the coal rank is low and progresses more rapidly when using hematite. Except for higher heating rates in the coal-magnetite blends, the reduction is complete at 1000 °C. The reductants are H₂ and CO, with production of H₂O and CO₂. When the temperature is increased the reduction by CO becomes of increasing importance, being mainly produced from the coke by the Boudouard reaction. The consumption of coke for the reduction of iron oxides is therefore more important at higher temperatures. Lignite is clearly a better reducing agent than the other coals, because of larger quantities of CO produced from the start of its pyrolysis, and the good reactivity of its char towards CO₂ and H₂O.     

铬酸钠氢还原反应动力学

引言 铬为重要战略资源,铬及其化合物在国民经济中有不可替代的广泛应用.Cr2O3为铬盐工业主要产品之一,广泛有于、颜料、磨料、治金原料、耐火材料、有机合成催化剂、热喷涂材料等领域.     

Computational study of staged membrane reactor configurations for methane steam reforming. II. Effect of number of stages and catalyst amount

The present work complements part I of this article and completes a computational analysis of the performances of staged membrane reactors for methane steam reforming. The influence of the number of stages and catalyst amount is investigated by comparing the methane conversion and hydrogen recovery yield achieved by an equisized‐staged reactor to those of an equivalent conventional membrane reactor for different furnace temperatures and flow configurations (co‐ and counter‐current). The most relevant result is that the proposed configuration with a sufficiently high number of stages and a significantly smaller catalyst amount (up to 70% lower) can achieve performances very close to the ones of the conventional unit in all the operating conditions considered. This is equivalent to say that the staged configuration can compensate and in fact substitute a significant part of the catalyst mass of a conventional membrane reactor. To help the interpretation of these results, stage‐by‐stage temperature and flux profiles are examined in detail. Then, the quantification of the performance losses with respect to the conventional reactor is carried out by evaluating the catalyst amount possibly saved and furnace temperature reduction. © 2009 American Institute of Chemical Engineers AIChE J, 2010     

多晶硅金刚线切割废料制备Al-Si合金过程中的热力学和动力学分析

通过X射线衍射仪、X射线荧光光谱分析仪、傅里叶变换红外光谱仪分析了金刚线切割多晶硅废料的组分及其体系中存在的硅氧化物，研究了铝与切割废料合金化过程中可能存在的化学反应过程，采用HSC Chemistry 6.0软件对其反应体系进行了热力学分析，利用差热分析法研究了铝热还原切割废料中SiO2的动力学过程，对金刚线切割多晶硅废料进行了掺铝制备铝硅合金的实验研究。结果表明，金刚线切割多晶硅废料和铝粒按不同铝硅摩尔比兑掺后，在电磁搅拌的作用下，合金化的温度范围为800~1600℃，铝热反应可将废料中少量的SiO2杂质还原成单质Si，铝热还原二氧化硅的活化能为364.1 kJ/mol，反应级数为0.91，实验样品的EPMA和XRD等表征结果表明合金成分和渣相与热力学分析完全吻合，合金化效果明显。     

Ex situ hydrolytic degradation of sulfonated polyimide membranes for fuel cells

Ex situ hydrolytic stability of sulfonated polyimide (s-PI) membranes for fuel cells was studied depending on structural and external parameters including the ion exchange capacity, the block character, the temperature and the hydrogen peroxide concentration. Infrared spectroscopy was used to identify and quantify the chemical modifications such as the loss of imide functions and of ionic monomers. The decrease in ion exchange capacity due to the elution of sulfonated oligomers was confirmed by sulfur content analysis. A complete hydrolysis of some of the imide functions is observed leading to polymer chain scissions and to the loss of the mechanical properties. It is shown to be a thermo activated process and the activation energy (60 kJ/mol) is found in good agreement with the value determined from fuel cell lifetimes. The degradation in fuel cell conditions is similar but faster than in pure water. The same kinetic can be reproduced ex situ by addition 0.05% of hydrogen peroxide.