铁矿石孔隙度对其还原和碳化铁生成的影响

在1023 K温度下用热重法结合XRD和EDX分析研究了70%H2-30%CH4混合气体还原铁矿石制备碳化铁的过程,测定了原矿和还原中间产物的微孔分布. 结果表明,相同反应条件下微观结构不同的铁矿石其还原速率和碳化速率有较大差别,巴西块矿、澳大利亚块矿及南非球团矿在50 min内都可以全部还原,此后生成碳化铁;而南非块矿则需90 min才能基本还原,此后没有碳化铁生成. 疏松多孔的铁矿石较致密铁矿石的还原速率快,生成的还原铁结构疏松,有利于碳化反应的进行. 铁矿石还原后,0.5~3.5 nm微孔孔容积率约提高2倍,分布规律与原矿石相似,3.5~13 nm的微孔孔容积提高显著,这些对还原速率和碳化铁的生成反应有较大影响.     

水泥分解炉高CaO/CO2环境CO还原NO机制

通过流化床反应器模拟水泥分解炉高CaO/CO_2环境,并结合分子动力学广义梯度密度泛函理论,研究了CaO对CO还原NO的催化特性和CO_2促使CaO催化失效规律。在900℃、体积分数15%CO_2下,CaO催化作用可使NO脱除效率提高18%左右。在900℃时,当CO_2体积分数由5%升至30%,CO对NO还原率由97.0%降低到23.4%,且随反应时间增长CaO对CO还原NO的催化作用不断减弱。基于广义梯度密度泛函理论计算,CO_2,CO,NO在CaO表面活性位点的吸附能依次为CO_2(-1.869 eV)>NO(-0.781 eV)>CO(-0.669 eV),随着CO_2体积分数升高或反应时间增长,吸附在CaO表面的CO和NO减少,高体积分数CO_2促使CaO催化作用失效。CO还原NO的反应势垒(10.84 eV)大于CaO表面CO还原NO反应势垒(2.06 eV),CaO易催化CO还原NO。     

CO2沉淀法制取高补强白炭黑

以CO2 混合气体和水玻璃为原料 ,在助剂作用下 ,采用CO2 沉淀法制取高补强白炭黑 ,并得到其最佳工艺条件为水玻璃浓度 3 5g/L ,反应温度 70℃ ,助剂质量分数为 0 .7% ,反应时间 6 0min。对使用该白炭黑补强后的橡胶样品物理性能检测显示 ,此样品的扯断力达到 1 2 .3MPa。     

用H_2-CH_4气制备碳化铁的反应过程

用Ｈ２－ＣＨ４混合气制备碳化铁实验结果表明：铁矿粉还原生成碳化铁的过程由氧化铁的还原、甲烷的裂解和金属铁的碳化三个步骤组成为建立铁矿粉还原制备碳化铁的动力学模型提供了实验依据     

水对乙腈溶液中光催化还原CO_2性能促进的研究

文章研究了水对乙腈溶液中光催化还原CO2反应性能的影响。证明在相同的实验条件下,水能极大地提高乙腈体系中光催化还原CO2的效率;结果显示,水的体积占总体积10%时具有最佳的催化效果。另外,本研究对水对体系粘度和电导率影响进行测试,初步讨论了它们对光催化还原CO2反应中的影响。     

氨水吸收CO_2及固体产物的热分解

测试了氨水吸收CO2反应过程中CO2的脱除率和反应溶液pH值随吸收时间的变化,选择氨水质量分数分别为5%,10%,气体流速为540 mL/min,CO2体积分数为13.7%,研究了氨水溶液对CO2脱除率,结果表明:质量分数为10%的氨水溶液在反应初期对CO2脱除率能达到90%,随反应时间的延长,脱除率有所下降。对反应产物进行冷凝、结晶、干燥后的XRD分析结果显示氨水吸收CO2的产物主要为NH4HCO3。对氨水吸收CO2的反应产物进行了热质量损失实验,结果表明:在455 K时NH4HCO3可以达到100%分解,且升温速率为10 K/min时,最大分解速度对应的温度为416 K。     

C_3H_8(CO_2)-CO(NH_2)_2-H_2O_2-H_2O四元体系相平衡及其应用

为了回收利用湿法合成过氧化尿素后母液中的H2O2和CO(NH2)2,提出了气体盐析法回收有用物质的方法。采用等温法测定了15℃时CO2-CO(NH2)2-H2O-H2O2四元体系在不同压力下的相平衡数据,结果表明,CO2没有盐析分离效应。实验测定5,10,15℃时C3H8-CO(NH2)2-H2O-H2O2四元体系相平衡数据表明,C3H8具有明显的盐析分离效应,且随着C3H8气体压强的增加,平衡液相中H2O2和CO(NH2)2的质量分数降低。湿法合成过氧化尿素后母液在15℃时加入C3H8气体,可继续使过氧化尿素结晶析出,H2O2的收率可提高26.54%。     

15℃时NaCl-CO(NH2)2-H2O2-H2O四元体系相平衡

为了改进过氧化尿素合成的生产工艺,采用等温法测定了15℃时NaCl-CO(NH2)2-H2O2-H2O四元体系及其三元子体系CO(NH2)2-H2O2-H2O和NaCl-CO(NH2)2-H2O的相平衡数据,依据所绘相图分析,结合热重和XRD表征,得出实验条件下NaCl和尿素能形成新的加合物CO(NH2)2×NaCl,其热稳定性比纯尿素高. 根据相图计算,15℃时CO(NH2)2-H2O2-H2O体系合成过氧化尿素的适宜条件范围较宽,在母液不利用的情况下H2O2的收率为58.08%;而在NaCl-CO(NH2)2-H2O2-H2O体系中,NaCl对过氧化尿素形成没有盐析效应.     

K2CO3-Na2CO3-H2O三元体系288 K相平衡研究

采用等温溶解平衡法研究了三元体系K2 CO3 -Na2 CO3 -H2 O 2 88K时的相平衡及平衡液相的主要物化性质 (密度 ,电导率 ,pH)。研究发现 :该三元体系有复盐NaKCO3 ·6H2 O形成 ,根据溶解度数据绘制了相图 ,相图中有 2个共饱点E、F ,三条单变度曲线AE、BF、EF ;平衡固相分别为K2 CO3 ·3/ 2H2 O、Na2 CO3 ·10H2 O、NaKCO3 ·6H2 O。实验结果表明K2 CO3 对Na2 CO3 有强烈的盐析作用 ;并简要讨论了实验结果。     

燃煤流化床飞灰湿法固定CO_2反应特性研究

为处理流化床飞灰堆积,实现CO2减排,以燃煤循环流化床锅炉飞灰作为碳捕获剂,进行了流化床飞灰湿法碳酸化固定CO2的工艺参数研究。考察了反应压力、反应温度、液固比对CO2单位固定量(每克飞灰固定的CO2质量)的影响。结果表明:反应压力只影响反应速率,不影响CO2固定量;在液固比为1 m L/g、反应温度70℃、反应压力3 MPa、搅拌转速300 r/min的条件下,最大CO2单位固定量为0.0879 g/g,碳酸化效率高达49.58%,说明流化床飞灰有较强的CO2固定能力。因此,利用燃煤流化床飞灰固定CO2具有一定的应用价值。     

搅拌流化床中超细氧化铁粉流态化及还原实验研究

在内径50 mm的搅拌流化床内进行了平均粒径239 nm的氧化铁粉的流态化及氢气还原实验. 结果表明,床中氧化铁颗粒以聚团鼓泡形式实现完全流化,最小流化速度为0.025 m/s,最大床层膨胀比为2.0. 在500℃下用氢气还原该氧化铁粉的反应过程为：Fe2O3?Fe3O4?Fe,Fe颗粒的粒径比Fe2O3小,有颗粒烧结现象,由Fe引起的颗粒烧结和粘结作用可能导致失流. 与普通流化床相比,搅拌能使流化时间由3 min延长至15 min,使失流时样品的金属化率由15%提高至76%.     

几种典型铁矿粉的流化特性

利用内径150 mm的D型有机玻璃流化床模型,对澳矿、巴西矿、北方矿和钒钛矿典型铁矿粉的流化特性进行了实验研究,获得了其流化特性曲线、初始流化速度和最大床层压降,并将初始流化速度的实测值和理论计算值进行了比较分析. 结果表明,矿粉粒度是影响其流化特性的最主要因素,粒径越大,床层所需要的初始流化速度越大,实测值和理论估算值基本相符;粒度小于0.125 mm钒钛矿流动性较差,在流化过程中易出现沟流现象;粒度范围较宽的矿粉,完全流态化时,细矿粉随气流夹带逸出明显;在粒度相同的情况下,几种不同的铁矿粉的开始流化速度接近,而床层压降有较大差异,巴西矿的床层压降明显大于其他三种铁矿粉. 最大床层压降的最小值均出现在粒度为0.25~0.425 mm,为铁矿粉流态化还原过程中较适宜的粒度范围.     

焦炉烟道废气-流化床式煤调湿技术的应用

利用焦炉烟道废气为热源及动力源,在流化床设备内对捣固焦炉配合煤进行预处理。生产应用表明,流化床煤调湿技术对配合煤调湿及分级作用明显,调湿后配煤水分降低2.2%,减少回炉煤气用量1474×104m3,CO2减排8750t,减少焦化废水处理量2万t,焦炉生产能力提高5%,排空废气粉尘含量〈50mg/m3。     

铁氧化物在流化床温度和CO气氛下的形态迁移及其对NO催化还原

利用小型固定床实验台实验研究了铁氧化物在典型流化床温度和CO还原性气氛下的形态迁移及其生成物对NO的催化还原作用,采用分级还原结合X射线衍射（XRD）表征分析,确定铁氧化物与CO和NO反应后生成物的价态及各种铁氧化物对NO的还原机制。结果表明,Fe₂O₃在实验条件下可依次被CO还原为Fe₃O₄、FeO和单质铁,反应过程中随着还原度的增加,还原速率逐级下降,从Fe₂O₃还原到Fe₃O₄的速率最高,FeO还原到Fe速率最低,在实验温度范围内,床温升高有利于提高Fe₂O₃到Fe₃O₄的还原速率和还原度。不同形态的铁氧化物对NO的催化还原特性不同,Fe₂O₃及其部分还原后生成的Fe₃O₄都不能直接与NO反应,Fe₂O₃对CO催化还原NO的效果很弱,而Fe₃O₄对CO还原NO的反应却有很强的催化作用,而进一步还原生成FeO与单质铁还可直接与NO反应。     

Simultaneous SO2/NOx removal by a powder-particle fluidized bed

Simultaneous dry removal of SO₂ and NO_x from flue gas has been investigated using a powder-particle fluidized bed. In a process of flue gas desulfurization by use of solid sorbents such as FeO (dust from a steel plant) and CuO, the smaller the particle size of sorbents, the higher the expected SO₂ conversion. In a powder-particle fluidized bed (PPFB), fine particles less than 40 μm in diameter fed into the bed are fluidized with coarse particles. But only the fine particles are entrained from the bed, and their residence time in the bed is remarkably long.

The reduction of NO_x with NH₃ in the fluidized bed is catalyzed by coarse particles or both coarse and fine particles. In this study, PPFB was applied to simultaneous dry SO₂/NO_x removal process, and several kinds of sorbents or catalysts were evaluated in a PPFB. Using the selected sorbents and catalysts, kinetic measurements were made in the temperature range of 300 to 600°C. SO₂ removal efficiencies were affected by reaction temperature, sorbent/S ratio, and static bed height. NO_x removal efficiencies in excess of 95% were achieved at NH₃/NO_x mole ratio of 1.0. When FeO was used as sorbent, SO₂ conversion increased with increasing temperature and reached 80% at 600°C.     

Activity and selectivity control in iron catalyzed Fischer-Tropsch synthesis

We present results of a catalyst structure-function study that supports a CO hydrogenation model with -olefins formed as the principal primary products and n-paraffins formed during secondary hydrogenation reactions. The interplay of catalyst composition and reaction environment controls the extent of secondary reactions. Catalysts that contain mainly oxidic phases or carbides with large concentrations of excess matrix carbon favor secondary reactions. The relative concentrations of oxide and carbide phases depends on the ease of reduction of the catalyst, which can be changed by cation substitutions. For example, cobalt substitution into Fe₃O₄ lowers the reduction temperature by 20 ° C. Excess matrix carbon has been intentionally introduced (by treatment in high temperature H₂/CO) into model iron carbide catalysts produced by laser synthesis. Increased paraffin selectivity as matrix carbon is introduced suggests the influence of the diffusion constraints on product selectivity. Alkali promotion will affect secondary hydrogenation pathways. We illustrate how catalysts with low levels of alkali become increasingly more selective to paraffins at high conversions (and high effective H₂/CO ratios).Reaction environment also controls catalyst composition and selectivity. Mossbauer spectroscopy on spent catalysts suggests that oxide/carbide phase formation in iron catalysts are sensitive to reactor configuration (extent of backmixing). In integral fixed bed reactors, catalysts partition into carbide phases in the front of the bed but show increasing amounts of oxide near the exit, whereas the catalysts in the stirred tank reactor remain all carbides. Product selectivities reflect the phase differences.Other examples illustrating secondary hydrogenation phenomena will be presented.     

MAGNETICALLY STABILIZED FLUIDIZATION PART I GAS AND SOLIDS FLOW

A fluidized bed of magnetic particles, such as iron or magnetite, can be stabilized by applying an external magnetic field, as was shown earlier by Rosensweig and coworkers. The stabilization results in a suppression of bubble formation, little solids mixing and a much narrower residence time distribution of the gas flow; the gas flow rate in the dense phase is increased. In this experimental study the axial and radial mixing coefficients in the gas flow were determined as functions of several variables, such as gas flow rate and magnetic field strength. It appeared that the radial mixing coefficient is comparable to that in a fixed bed, and the axial mixing coefficient was greater than in a fixed bed but smaller than in a fluidized bed without stabilization. The axial mixing is the result of some channelling.

The mixing of the solids is very low, and if there is a continuous solids flow through the bed, deviations from plug flow can be reduced by increasing the magnetic field strength.

Apparently, the magnetically stabilized fluidized bed is well suitable for countercurrent gas-solid operations.     

Effect of phosphorus addition on the hydrotreating activity of NiMo/Al2O3 carbide catalyst

A series of phosphorus promoted γ-Al₂O₃ supported NiMo carbide catalysts with 0–4.5 wt.% P, 13 wt.% Mo and 2.5 wt.% Ni were synthesized and characterized by elemental analysis, pulsed CO chemisorption, BET surface area measurement, X-ray diffraction, near-edge X-ray absorption fine structure, DRIFT spectroscopy of CO adsorption and H₂ temperature programmed reduction. X-ray diffraction patterns and CO uptake showed the P addition to NiMo/γ-Al₂O₃ carbide, increased the dispersion of β-Mo₂C particles. DRIFT spectra of adsorbed CO revealed that P addition to NiMo/γ-Al₂O₃ carbide catalyst not only increases the dispersion of Ni-Mo carbide phase, but also changes the nature of surface active sites. The hydrodenitrogenation (HDN) and hydrodesulfurization (HDS) activities of these P promoted NiMo/γ-Al₂O₃ carbide catalysts were performed in trickle bed reactor using light gas oil (LGO) derived from Athabasca bitumen and model feed containing quinoline and dibenzothiophene at industrial conditions. The P added NiMo/γ-Al₂O₃ carbide catalysts showed enhanced HDN activity compared to the NiMo/γ-Al₂O₃ catalysts with both the feed stocks. The P had almost no influence on the HDS activity of NiMo/γ-Al₂O₃ carbide with LGO and dibenzothiophene. P addition to NiMo/γ-Al₂O₃ carbide accelerated CN bond breaking and thus increased the HDN activity.     

难选铁矿流态化磁化焙烧研究进展与发展前景

我国有大量常规选矿方法难以利用的铁矿石资源,实现其利用可增加我国铁矿石资源可利用量,缓解铁矿石供应紧张的局面,提高铁矿石供应安全的保障程度。磁化焙烧-磁选是难选铁矿石利用的重要方法,流态化磁化焙烧是近年来研究的热点。本文综述了磁化焙烧原理、竖炉及回转窑磁化焙烧的技术现状及存在问题,介绍了流化床磁化焙烧发展历史和研发现状,着重总结了低温流态化磁化焙烧在焙烧动力学、过程强化、反应器模拟、关键技术研发及产业化示范方面的研究进展,分析了其在褐铁矿、菱铁矿、赤铁矿及含铁尾渣利用方面的发展前景。