鼓泡流化床稀相空间颗粒粒度分布的时变特性

鼓泡流化床稀相空间的催化剂颗粒粒度分布一方面与流化床流化速度有关，另一方面与流化床中藏量的细小颗粒跑损有关，即随着流化床操作的连续进行，流化床系统中的细颗粒不可避免的存在跑损，进而影响到稀相空间的颗粒粒度分布。由于这种跑损是连续发生的，因此稀相的颗粒粒度分布变化具有时变特性。选用催化裂化平衡催化剂和二维流化床，在连续流化操作过程中采集稀相空间中的颗粒样品，分析颗粒的粒度分布，考察稀相空间中颗粒粒度分布随流化操作时间的变化。结果表明：随着流化床系统中细颗粒的跑损，稀相颗粒粒度分布的中位粒径和峭度逐渐增加，稀相空间的颗粒逐渐粗化，经过一段流化操作时间后颗粒粒度分布变化趋于稳定。     

新型Pt基整体式催化剂的结构与催化性能

以堇青石蜂窝陶瓷(CHC)为载体,采用化学镀法制备Pt基整体式催化剂Pt-CHC,研究Pt-CHC催化剂在甲醛催化燃烧中的催化性能;对Pt-CHC催化剂在不同的甲醛初始浓度范围、较宽的空速范围与不同的进样相对湿度条件下进行活性测试,并进行扫描电镜和X射线能量色散谱表征。结果表明:Pt-CHC催化剂在Pt负载量较小(质量分数为0.24%)时,甲醛可在100℃时基本转化完全;活性组分Pt在蜂窝陶瓷载体表面选择性富集,Pt颗粒在催化剂中通孔道内部与孔口处均能基本维持均匀分布,颗粒粒径小于100 nm。     

甲醇制烯烃工艺催化剂再生过程的CFD-DEM模拟

为了合理控制甲醇制烯烃工艺系统(DMTO)中流化床催化剂再生器的积碳燃烧反应,利用计算流体力学(CFD)将再生化学反应动力学方程耦合到离散单元模型(DEM)中,使用CFD-DEM模型对催化剂再生过程进行了拟二维和三维数值模拟;分别从再生催化剂的颗粒流型、颗粒属性、积碳分布和再生器的气体组分等方面考察了不同进气气速对催化剂再生过程的影响。结果表明:随着进气气速的增大,再生催化剂颗粒的流化速度加快,积碳分布由宽变窄,颗粒整体的流化状态趋于均匀;再生催化剂的积碳量随着时间增加而减少,随进气气速的增大而减少速率加快;催化剂密度随反应时间的增加而略有减小;随着进气气速的增大,再生反应达到平衡状态所需的时间会大幅缩短;当进气气速大于0. 05 m/s时,氧气可以很快达到饱和。     

Pd-Ni双金属催化剂的研究进展

综述了Pd-Ni双金属催化剂的制备及应用研究进展,分析Pd-Ni双金属催化剂制备过程对催化剂结构和性能的影响及其应用研究现状,展望研究方向和趋势。浸渍法虽然操作简单、活性组分利用率较高,但存在颗粒分布不均匀、催化活性低的局限性;与浸渍法相比,化学沉淀法和置换法具有更高的分散度、催化活性及稳定性,是PdNi双金属催化剂制备的可行方法。电沉积法具有可以控制颗粒分布和晶核生长等优点,能大大提高催化剂的活性,是极具发展前景的研究方向。在传统制备方法中引入超声、微波辐照等手段的耦合法制备Pd-Ni双金属催化剂,能有效提高活性组分的分散度,是Pd-Ni双金属催化剂制备的趋势。     

Ni-Mo-Al_2O_3催化剂覆碳改性对其加氢脱硫性能的影响

在催化剂制备的不同阶段引入碳物质,制备3种覆碳改性的NiMo-Al_2O_3加氢脱硫催化剂,采用低温氮静态容量吸附-脱附法、X射线衍射、H_2程序升温还原和高分辨透射电子显微镜对3种催化剂进行表征,并考察催化剂的加氢脱硫性能。结果表明:引入碳物质能够提高催化剂的加氢脱硫活性;采用前覆碳法即在载体上负载活性组分前引入碳前躯物,或采用共浸渍法即将活性组分与碳前躯物共同浸渍到载体上制得的催化剂,都能够增加八面体Mo物种的数量;采用共浸渍法制得催化剂活性组分分散性良好,MoS_2纳米颗粒堆垛层数多,其脱硫率比未覆碳改性催化剂的高6.8%;采用前覆碳法制得催化剂的金属分散性良好,其脱硫率比未覆碳改性催化剂的高5.1%;与未覆碳改性的催化剂相比,采用后覆碳法即在已负载活性组分的Ni-Mo-Al_2O_3催化剂上引入碳前躯物制得催化剂的脱硫率提高程度不大。     

铂基催化剂对甲醛的室温催化净化性能

采用直接沉淀还原法制备了新型Ti O_2负载型铂基催化剂,并对该催化剂在甲醛室温完全催化氧化净化反应中的活性、稳定性和适用性进行研究。结果表明:当铂负载量(质量分数)仅为0.10%时,制备的催化剂即可在室温使甲醛净化率达到97%,而且在50 h的稳定性测试中,甲醛净化率始终维持在95%以上;同时该催化剂在甲醛质量浓度为3~50 mg/m3和空气湿度为36%~90%较大变化范围内,也可使甲醛室温净化率始终在90%以上。通过表面形貌和粒径分布分析可知,催化剂中活性组分铂颗粒以2~5 nm粒径尺度在Ti O_2载体表面均匀分散,这应该是该催化剂表现出优越甲醛室温催化净化能力的主要原因。     

PtMo合金催化剂氧还原反应催化性能研究

采用乙二醇还原法和后续的热处理工艺制备了Pt-Mo合金催化剂。使用透射电子显微镜、X射线衍射、电感耦合等离子体发射光谱、X射线光电子能谱等方法对样品进行了形貌、结构和组分的表征。通过电化学测试方法，探究了不同催化剂的电催化活性和稳定性。结果表明：合适的热处理温度不仅提高了Pt-Mo纳米颗粒的合金化程度，而且改变了催化剂颗粒表面的电子结构和成分。所以，经过400℃热处理的PtMo/C-400催化剂表现出较好的氧还原性能，其电催化活性和稳定性均与商业J01-Pt/C催化剂相当。     

用于质子交换膜燃料电池的高活性、高稳定性PdCo/C合金催化剂

利用乙酸钴和双氰胺在不同温度下制备了碳包覆钴样品,并将其作为载体,利用液相还原法和真空热处理制备了PdCo/C合金催化剂。采用多种测试技术对样品进行了结构、形貌及组分的表征,研究了不同载体和不同热处理温度的样品的催化性能。实验结果表明,平均粒径为1.9nm的钯纳米颗粒能够均匀负载到含氮的石墨化程度较低的碳包覆钴载体上。热处理带来的合金化作用能够极大地提高催化剂的氧还原活性和稳定性,经过900℃热处理的样品其氧还原活性和稳定性都优于传统商业Pt/C催化剂。     

大颗粒纳米晶TiO2催化剂的制备及光催化性能研究

以钛酸丁酯为前驱体,采用溶胶-凝胶法制备出了大颗粒易分离的粉末二氧化钛催化剂,运用TG-DTA、XRD、SEM等方法表征它的物质性质,并以典型的偶氮染料甲基橙为目标污染物,研究了焙烧温度以及使用次数等对大颗粒二氧化钛光催化剂活性的影响.将自制的大颗粒TiO2催化剂与P25和工业钛白粉进行了对比催化活性实验研究.结果表明纳米晶粒径为17nm,TiO2颗粒的粒径分布于1～10μm之间.自制大颗粒TiO2催化剂催化活性优于P25和工业钛白粉,容易分离回收,而且具有较好的重复使用性能.     

CO_2甲烷化Ni基分子筛催化剂的研究进展

综述了镍基分子筛催化剂在CO_2甲烷化反应中的研究进展,系统总结了不同分子筛催化剂对CO_2甲烷化反应性能的影响,分析了不同分子筛载体结构与活性组分之间的相互作用及其对活性组分Ni的分散度、颗粒尺寸、抗烧结性之间的关系,阐释了不同孔结构分子筛催化剂的构效关系及其抗烧结和抗积碳的反应机理,展望了Ni基分子筛催化剂在甲烷化反应的应用前景。     

Study of the Theophylline Content of Single Coated Particles by Gas Chromatography/Mass Spectrometry

The aim of the present study was to determine by gas chromatography/mass spectrometry (GC/MS) the content uniformity of single theophylline microcapsules of different particle size ranges. Microencapsulation was carried out in a laboratory fluidized bed system using Eudragit L30D aqueous dispersion. Scanning electron microscopy was applied for the characterization of the surface morphology of the prepared theophylline microcapsules of two different particle size ranges. The theophylline content of single particles was determined by GC/MS analysis. It was found that the particle size of microcapsules greatly influenced their theophylline content. The GC/MS analysis was successfully applied to indicate the changes in the content uniformity and thus the interparticular coating distribution of single theophylline microcapsules in the presence of several excipients.     

Study of the Theophylline Content of Single Coated Particles by Gas Chromatography/Mass Spectrometry

The aim of the present study was to determine by gas chromatography/mass spectrometry (GC/MS) the content uniformity of single theophylline microcapsules of different particle size ranges. Microencapsulation was carried out in a laboratory fluidized bed system using Eudragit L30D aqueous dispersion. Scanning electron microscopy was applied for the characterization of the surface morphology of the prepared theophylline microcapsules of two different particle size ranges. The theophylline content of single particles was determined by GC/MS analysis. It was found that the particle size of microcapsules greatly influenced their theophylline content. The GC/MS analysis was successfully applied to indicate the changes in the content uniformity and thus the interparticular coating distribution of single theophylline microcapsules in the presence of several excipients.     

镁-镍合金催化剂制备及纳米碳管生长模式研究

采用多元醇法制备镁-镍合金纳米粉末,并以此为催化剂制备纳米碳管,利用比表面和孔径分布测定仪、X射线衍射仪和透射电镜,研究镁-镍合金催化剂的性能和纳米碳管的生长模式。结果表明:Mg∶Ni值对镁-镍合金催化剂特性影响较大,其中Mg∶Ni为1的催化剂颗粒比表面积较大且平均粒径较小;聚乙烯吡咯烷酮(PVP)用量增大,有利于提高催化剂颗粒的比表面积、减小平均粒径,但用量过大不利于Mg2Ni合成。在以镁-镍合金为催化剂制备碳纳米管的过程中,首先在催化剂表面形成碳膜,随后形成的碳膜将前期形成的碳膜及催化剂颗粒向外推挤,催化剂颗粒移动后遗留下中空隧道,最终形成碳管,由于纳米碳管尖端的催化剂颗粒反应后失去催化活性,碳管的生长动力主要来自碳管根部。     

Investigation of hydrodynamics of gas-solid fluidized beds using cross recurrence quantification analysis

Hydrodynamics of gas-solid fluidized bed was investigated by analyzing its pressure fluctuations using cross recurrence quantification analysis (CRQA). Pressure fluctuations were measured in a lab scale fluidized bed of various particle sizes at different gas velocities. First, the CRQA was applied to a number of well-known dynamic systems and the results demonstrated that it is a powerful method to detect similarities between nonlinear signals. Then, it was shown that graphical structures within the cross recurrence plot of pressure fluctuations of a fluidized bed vary with both superficial gas velocity and particle size. It was found that determinism and cross recurrence rate of non-normalized data initially decrease and then increase with increasing the gas velocity. When the signal is initially normalized, determinism and entropy do not change with the superficial gas velocity while cross recurrence rate is sensible to changes in the superficial gas velocity. It was concluded that entropy can be used for detecting changes of particle size and if a proper reference state is chosen, entropy can be a powerful index for detecting changes in the size of particles in a fluidized bed.     

Experimental and numerical investigation of catalytic PM combustion in a fluidized bed type PM removal device for low-temperature continuous regeneration

A fluidized bed filter can perform highly efficient PM collection and low-temperature continuous regeneration. However, to further reduce continuous regeneration temperature, a rough surface bed particle was selected herein. It is expected that the rough surface increases and stabilizes doped catalyst on bed particle even in fluidized bed. This bed particle can stably support 9.48 g-catalyst/kg-bed particle of doped catalyst versus 1.58 g-catalyst/kg-bed particle in previous research. This increase in catalyst amount increases the probability of good PM-catalyst contact, and collection efficiency can easily maintain its initial value due to catalytic PM combustion. PM combustion also depends on fluidization. Thus, combustion kinetics in a fluidized bed was investigated via a newly developed thermogravimetric analyzer that considered PM-gas relative velocity, and a constructed kinetic model was applied to numerical simulation. PM combustion obeyed an Arrhenius relationship, and the effect of PM-gas relative velocity was included in the kinetic model as a mass transfer term. A continuous regeneration experiment was conducted under optimal conditions, and the continuous regeneration temperature is 330 °C. As water vapor occurs in combustor exhaust, we added 10 vol% water vapor and found that the continuous regeneration is further reduced to 300 °C.     

流化床中颗粒尺寸的模糊测量模型

本建立了一种对流化床中颗粒尺寸进行的模糊模型，在实验室条件下对气－固流化床的颗粒进行了测量，通过功率谱密度对所获得的压力波动进行了分析，并订对颗粒尺寸与压力波动动及其它影响参数的关系进行了研究。     

Effect of particle size on gas holdup in three-phase reactors

Gas holdups were measured in a batch three-phase cocurrent column in which glass beads ranging from 17 to 5000μm were suspended up to 20 vol %. The effect of particle size on gas holdup was found to be different in three types of reactors such as the gas-sparged slurry reactors, three-phase bubble columns and three-phase fluidized beds. An increase of particle size reduced gas holdup in three-phase bubble columns, while raising it in gas-sparged slurry reactors and three-phase fluidized beds. The maximum and minimum gas holdup were observed respectively for particle size of about 88–250μm and 500μm, but the values of particle size were dependent on solid content and gas velocity. This paper is dedicated to Dr L K Doraiswamy on his sixtieth birthday.     

The effect of pretreatment in a fluidized bed upon diamond synthesis on particles by chemical vapour deposition

Diamond synthesis was carried out on non-diamond particles (single- and poly-crystal silicon, quartz and SiC) by microwave plasma-enhanced chemical vapour deposition. Fine diamond particles were deposited on the non-diamond particle surface. The particle deposition density on the untreated particle substrates was strongly dependent on the surface characteristics of the particle substrates. The value ranged from 10–10⁵ mm^–2 for each particle. Particle substrates were pretreated in a gas-solid fluidized bed, and these were then used for the deposition of diamond. The pretreatment of the surface of the particle substrate in the fluidized bed greatly enhanced the nucleation of diamond. A deposition density of about 10⁷ mm^–2 was obtained on single-crystal silicon particles pretreated for 15 h. The effectiveness of the fluidized bed pretreatment on the deposition density was observed to be appreciable for the four kinds of particle examined.     

Synthesis of multi-walled carbon nanotubes using Co–Fe–Mo/Al2O3 catalytic powders in a fluidized bed reactor

The effects of the metal loading (30–70 wt.%), metal molar ratio (Co/Fe, 1–5) and mass ratio of citric acid to the catalyst (0–0.6) on the productivity and mean diameter of the multi-walled carbon nanotubes (MWCNTs) in a gas–solid fluidized bed reactor (with an inner diameter of 0.056 m and a height of 1.0 m) were determined. Liquefied petroleum gas (LPG) was used as the carbon source. X-ray diffraction (XRD) was used to characterize the catalysts synthesized using a combustion method. MWCNTs synthesized in the fluidized bed reactor were characterized by field emission scanning electron microscopy (FE-SEM) to observe their morphologies and measure their diameters. Productivity was increased by increasing both the metal loading and the mass ratio of citric acid to the catalyst. A high productivity, up to 2000%, was obtained. The catalyst transition metal particle grain size decreased in the range of 8–17 nm with an increasing citric acid mass ratio to the catalyst and the mean diameter of the MWCNTs decreased with increasing the metal molar ratio, however the correlation between the grain size in the catalyst and the mean diameter of MWCNTs remains unclear.