超细颗粒聚团流化的临界流化速度

在内径50 mm的流化床实验台上,测量SiO_2、Al_2O_3和TiO_2 3种超细颗粒原生粒径从30 nm增加到5μm的临界流化速度(Umf),并以Geldart A类颗粒(粒径45μm)为参照。结果表明:3种超细颗粒的Umf随粒径的变化规律一致,随原生粒径从30 nm增加到5μm,Umf逐渐增大;当颗粒粒径增加到45μm,Umf大幅度减小,其与原生粒径为30和200 nm时接近。对于不同材料,Umf由大至小的顺序依次为TiO_2、Al_2O_3、SiO_2。粉体安息角测量表明:对于同种材料颗粒,原生粒径对超细颗粒的Umf和安息角的影响规律一致,即5μm超细颗粒的安息角最大。聚团尺寸模型计算表明:稳定流化时,聚团尺寸随原生粒径的变化趋势以及随不同材料的变化趋势均与Umf的变化趋势一致。研究结果为超细颗粒流化临界速度预测研究奠定了基础。     

粒径及声场对SiO2超细颗粒流化行为的影响

采用内径为56 mm的玻璃管流化床,考察了平均粒径分别为5~10 nm(1#), 0.5 mm(2#)及10 mm(3#)的SiO2超细颗粒在无声场及声场存在下的流化行为. 无声场时,1#和2#颗粒可在较高的气速下形成稳定聚团,单位质量颗粒团间作用力与原生颗粒相比显著下降,因而可实现稳定的聚团流化,3#颗粒因颗粒间粘性力较大,无法实现稳定流化. 40~60 Hz的声场对3种超细颗粒的流化行为均可起到一定的改善作用,在此频率范围外,声场的作用不明显. 提高声压级,可以使1#和2#颗粒团发生一定程度的破碎,聚团尺寸减小,最小流化速度降低. 在实验范围内,添加声场无法使3#颗粒实现稳定流化.     

片状氧化铝的熔盐法制备关键参数

高径厚比片状Al₂O₃在高端珠光颜料片状基材应用方面潜力巨大,但是其制备技术为国外所垄断,开发片状Al₂O₃商用生产技术迫在眉睫。熔盐法是制备片状Al₂O₃的理想方法,目前尚无系统研究熔盐法关键工艺参数对片状Al₂O₃影响规律的报道。本文通过片状Al₂O₃的形成机理,系统研究了TiO₂添加剂、Na₃P₃O₉添加剂、煅烧温度和熔盐用量4种关键工艺参数对制备片状Al₂O₃的影响规律,并进一步优化制备工艺,提出最优工艺参数。利用扫描电子显微镜和X射线衍射仪分析Al₂O₃的形貌、粒度和物相。结果表明：采用熔融盐（Na₂SO₄-K₂SO₄）添加NaCO₃为凝胶剂,再加入质量分数分别为3.0%的Na₃P₃O₉和2.0%的TiO₂为添加剂,在煅烧温度为1200℃、保温时间5h时,所制得的六角片状Al₂O₃粉体具有优异的品质,其平均粒径约为4μm,厚度为50～200nm,径厚比为20～80。     

PFSA-PES-纳米颗粒复合纳米纤维的制备及催化性能

利用静电纺丝法制备了全氟磺酸(PFSA)-聚醚砜(PES)-纳米颗粒(SiO₂、TiO₂和Al₂O₃)复合纳米纤维,比较了SiO₂、TiO₂和Al₂O₃等不同纳米颗粒对磺酸基团在纤维表面分布的影响,并利用乙酸乙酯合成反应考察了纤维结构对表面磺酸基团活性的关系。结果表明:静电纺复合纳米纤维的比表面积可达85.6 m²·g^-1,纳米颗粒均匀分布在纤维表面,表面酸性中心占PFSA酸性基团总量最高达71.2%。酯化反应实验表明,复合纳米纤维具有很好的催化性能,纳米颗粒的存在可以提高酸中心的活性;同时,所得复合纳米纤维膜表现出很好的回收与可再生性能,有望作为一种对环境友好的固体酸催化剂。     

流化床垃圾焚烧炉飞灰沉积实验

在自行搭建的小型流化床积灰试验台上选用流化床垃圾焚烧炉对流管束浮灰,模拟焚烧炉烟气环境下开展飞灰沉积实验。首先分析浮灰理化特性,结果表明：随着粒径增大,浮灰中CaO和SO₃含量逐渐降低,而SiO₂和Al₂O₃的含量逐渐增加;碱金属Na和K以及卤素Cl的含量在粒径较小的浮灰中含量最高。其次重点研究了浮灰粒径、烟气温度和换热管表面温度对飞灰沉积特性的影响规律,结果表明：积灰中主要富含Ca、S、Si和Al等元素,积灰中CaO和SO₃含量比浮灰高,而Al₂O₃和SiO₂含量比浮灰低;积灰量随着烟气温度升高而增加;粒径对灰沉积影响作用显著,大粒径灰颗粒难沉积而小粒径灰粒易沉积;管壁温度在600℃时,积灰量最小。积灰中CaO和SO₃的含量随着管壁温度升高而减少,而难熔Al₂O₃和SiO₂的含量随着管壁温度升高而增加。     

纳米粒子对CO2水合物导热性能的影响

试验研究了不同种类（Al₂O₃、Cu、SiO₂）、不同质量分数（0.05%、0.1%、0.15%）及不同粒径（10、30、50 nm）的纳米粒子对CO₂水合物热导率的影响。结果表明温度为-5~5℃时,纯CO₂水合物热导率为0.553~0.5861 W·m^-1·K^-1,具有玻璃体的变化特性。分散剂SDBS的加入,可改善CO₂水合物-纳米粒子体系的导热性能。在相同的质量分数和粒径下,纳米Cu粒子对CO₂水合物热导率的增强作用最好,但综合考虑水合物生成特性和溶液悬浮稳定性,选用纳米Al₂O₃粒子较合适。Al₂O₃粒子粒径越小,水合物热导率越大,15 nm比50 nm纳米粒子体系中CO₂水合物热导率的增长率平均提高了12.7%。此外,CO₂水合物热导率随Al₂O₃粒子质量分数的增大而增大,质量分数由0.05%增加到0.15%时,水合物热导率的增长率由4.2%提高到8.2%。     

纳米SiO2中添加大粒径组分的流化性能

以平均原生粒径为10nm的SiO2为原料，采用添加较大球形玻璃珠颗粒的方法，在内径为60nm的有机玻璃流化床中，考察了在不同添加量和不同添加颗粒粒径的情况下，纳米颗粒SiO2在流化性能。实验表明，纳米颗粒SiO2的流化经历了沟流、节涌破碎和聚团4个阶段，但当添加玻璃珠的量大于10：1或添加玻璃珠粒径不大于0．13mm时，SiO2的流化质量较好，并可采用床层压降曲线来表示其流化性能。     

生物质及其与惰性颗粒双组分体系的流化特性

采用MDMDY-300型全自动密度仪和体积法测量了生物质和3种惰性颗粒的颗粒密度和堆密度,在有机玻璃流化床内考察了生物质单组分及其与3种惰性颗粒双组分体系的最小流化空隙率和流化速度。结果表明,单组分颗粒密度随粒径的变化可以忽略,而堆密度却随粒径的增大有所减小;双组分体系的最小流化空隙率随细颗粒组分增加而出现先减小后增大的趋势,最小值出现在细颗粒组分体积分数为30%左右,且颗粒粒径差异越大变化趋势越明显;双组分体系的起始流化速度、最小流化速度和完全流化速度均随细颗粒组分含量增加呈现减小的趋势,当细颗粒体积分数达到30%左右后起始流化速度的下降趋势趋于平缓。     

涂层组分对堇青石脱硝催化剂性能的影响

为了探究涂层组分对整体式低温选择性催化还原（SCR）脱硝催化剂性能的影响，本文使用锰氧化物（MnO _x ）、氧化物涂层（TiO₂、SiO₂及Al₂O₃）、堇青石（CC）基体制备整体式涂层催化剂，考察催化剂牢固度以及脱硝活性。结果表明：在200℃ 时，对于MnO _x /Al₂O₃/CC催化剂，MnO _x 负载率为6%（质量分数）时脱硝效率最高为95%；对于MnO _x /TiO₂/CC，负载率为6%~12%时脱硝效率相差不大，为75%左右；对于MnO _x /SiO₂/CC，负载率12%时脱硝效率80%。样品牢固度排列顺序如下：MnO _x /Al₂O₃/CC > MnO _x /SiO₂/CC > MnO _x / TiO₂ /CC。通过BET、SEM、TG、Raman、H₂-TPR等测试与分析方法发现：影响催化剂性能的因素主要为活性组分MnO _x 状态以及载体性能的差异。Al₂O₃涂层比表面积适中，作为载体活性好；SiO₂涂层虽然比表面积大、牢固度好，但作为载体活性差；TiO₂作为涂层比表面积较小，溶胶中溶剂挥发快使得涂层表面不均匀。     

微纳米SiO2颗粒的粒径调控技术研究进展

微纳米SiO₂颗粒是一种重要的无机非金属材料,同时也是组装具有功能特性纳米结构材料的理想构建基元,在橡胶、光子晶体、生物医学、化妆品等领域扮演着重要的角色。目前,研究人员对其粒径调控技术进行了大量的研究。然而,如何更有效地调控SiO₂的粒径仍有待进一步发展。为此,文章着重论述了SiO₂颗粒制备过程中的粒径调控机理及其影响因素,包括反应物的含量、催化剂种类和浓度、溶剂极性、合成工艺等因素。研究进展表明：基于St?ber法的SiO₂颗粒粒径调控技术可在10 nm～4.5μm范围内可调;基于微乳液法的SiO₂颗粒粒径调控技术可在20～100 nm范围内可调;基于沉淀法的SiO₂颗粒粒径调控技术可制得最小粒径为2 nm的SiO₂颗粒。最后,指出了微纳米SiO₂颗粒粒径调控技术中存在的问题及其发展方向,旨在为其在相关领域的应用提供一定的参考。     

Microstructure and flexure creep behaviour of SiC-particle reinforced Al2O3 matrix composites

The flexure creep behaviour of monolithic Al₂O₃ and 10 vol% SiC-particle reinforced Al₂O₃ matrix composites was investigated in air atmosphere at 1160 to 1400 °C and under a stress of 40 to 125 MPa. Two kinds of SiC particles with different particle sizes and oxygen contents were used in the composites, one having an average size of 0.6 μm with 1.7 vol% SiO₂ impurities and the other of average size 2.7 μm with 3.4 vol% SiO₂ impurities. Compared with the creep behaviour of monolithic Al₂O₃ the strain rate of the composites with 0.6 μm SiC particles did not decrease; however, the composites with 2.7 μm SiC particles exhibited excellent creep resistance. Microstructure analysis showed that the Al₂O₃ grains in the composites with 0.6 μm SiC particles were mainly equiaxed with most of the SiC particles lying at the grain boundaries or triplegrain junctions, whereas the grain features of the composites with 2.7 μm SiC particles were irregular and elongated and most of the SiC particles were entrapped into Al₂O₃ matrix grains. It was revealed that the entrapment of 2.7 μm SiC particles into Al₂O₃ matrix grains was related to the high SiO₂ impurity content on SiC particle surfaces, and the change of grain morphology and the good high-temperature oxidation resistance were responsible for the creep resistance increase of the composites with 2.7 μm SiC particles.     

TiO2与SiO2掺杂对Al2O3相转变的研究

通过球磨混合法,制备TiO2、SiO2和TiO2+SiO2掺杂的Al2 O3粉体,经不同温度煅烧后进行X射线衍射(XRD)测试,比较研究这三种掺杂对Al2 O3粉体相转变温度的影响.研究结果表明,TiO2、SiO2掺杂对γ-Al2 O3向α-Al2 O3的相转变均有促进作用.在掺杂质量分数为0.5％的情况下,二者可分别...     

Photocatalytic oxidation of methanol using titania-based fluidized beds

Experiments determined methanol removal and catalyst elutriation rates during photocatalytic oxidation (PCO) of fluidized and packed beds of various titania-based catalysts. The study developed elutriation-resistant catalysts in which TiO₂ was precipitated from solution (p-TiO₂), or was coated on an Al₂O₃ support (TiO₂/Al₂O₃) and compared them to Degussa P-25 TiO₂. Although Degussa P-25 TiO₂ oxidized methanol effectively, it elutriated at a rate that was two orders of magnitude greater than those of p-TiO₂ and TiO₂/Al₂O₃. In addition, TiO₂/Al₂O₃ removed methanol at a significantly greater rate than did P-25, with p-TiO₂ being the least active. Fluidized beds produced greater PCO rates than did packed beds of P-25 and TiO₂/Al₂O₃. Fluidization enhancers, such as vibration and incorporation of a static mixer, improved the performance of the P-25 fluidized bed, but did not change the effectiveness of TiO₂/Al₂O₃ or p-TiO₂. The activity of TiO₂/Al₂O₃ decreased with increasing calcination temperature (over the temperature range 673–873 K). The optimum TiO₂ loading for TiO₂/Al₂O₃ was 30 wt.%.     

恒热流直管中纳米流体对流传热的实验研究(英文)

In this work, the laminar convective heat transfer performance and the pressure drop of water-based nanofluids containing Al2O3, TiO2 and SiO2 nanoparticles flowing through a straight circular tube were experimen-tally investigated. The experimental results showed that addition of small amounts of nano-sized Al2O3 and TiO2 particles to de-ionized water increased heat transfer coefficients considerably, while the SiO2 nanofluids showed the opposite behavior attracting the authors’ interests. An average of 16%and 8.2%increase in heat transfer coefficient were observed with the average of 28%and 15%penalty in pressure drop for Al2O3 and TiO2 nanofluids.     

CO_2 methanation over TiO_2–Al_2O_3 binary oxides supported Ru catalysts

TiO_2 modified Al_2O_3 binary oxide was prepared by a wet-impregnation method and used as the support for ruthenium catalyst. The catalytic performance of Ru/TiO_2–Al_2O_3catalyst in CO_2 methanation reaction was investigated. Compared with Ru/Al_2O_3 catalyst, the Ru/TiO_2–Al_2O_3catalytic system exhibited a much higher activity in CO_2 methanation reaction. The reaction rate over Ru/TiO_2–Al_2O_3 was 0.59 mol CO_2·(g Ru)1·h-1, 3.1 times higher than that on Ru/Al_2O_3[0.19 mol CO_2·(gRu)-1·h-1]. The effect of TiO_2 content and TiO_2–Al_2O_3calcination temperature on catalytic performance was addressed. The corresponding structures of each catalyst were characterized by means of H_2-TPR, XRD, and TEM. Results indicated that the averaged particle size of the Ru on TiO_2–Al_2O_3support is 2.8 nm, smaller than that on Al_2O_3 support of 4.3 nm. Therefore, we conclude that the improved activity over Ru/TiO_2–Al_2O_3catalyst is originated from the smaller particle size of ruthenium resulting from a strong interaction between Ru and the rutile-TiO_2 support, which hindered the aggregation of Ru nanoparticles.     

高岭土原位合成高硅铝比小晶粒NaY分子筛

以不同温度焙烧的苏州高岭土为原料,采用原位晶化法合成高硅铝比小晶粒NaY分子筛,考察晶种胶添加量、陈化温度、晶化温度和m(高土)∶m(偏土)对晶化过程和产物性质的影响。结果表明,m(高土)∶m(偏土)=1时,在晶种胶添加质量分数15%、陈化温度90℃和晶化温度100℃条件下,以普通高岭土为原料原位合成NaY样品的相对结晶度约为80%,骨架硅铝比(SiO2与Al2O3物质的量比)为6.4,平均粒径约500nm。调整原料中m(高土)∶m(偏土)可以控制原位晶化样品中的分子筛含量。以细化高岭土为原料合成的NaY分子筛(平均约445nm)粒径小于普通高岭土合成的样品。骨架硅铝比高于6.0的原位晶化样品的骨架坍塌温度高于950℃,具有很高的结构稳定性。     

Effects of porous oxide layer on performance of Pd-based monolithic catalysts for 2-ethylanthraquinone hydrogenation

Pd/oxide/cordierite monolithic catalysts(oxide = Al_2O_3, SiO_2 and SiO_2\\Al_2O_3) were prepared by the impregnation method. The results of ICP, XRD, SEM–EDX, XPS and N_2 adsorption–desorption measurements revealed that the Pd penetration depth increased with increasing the thickness of oxide layer, and the catalysts with Al_2O_3 layers had the larger pore size than those with SiO_2 and SiO_2\\Al_2O_3 layers. Catalytic hydrogenation of 2-ethylanthraquinone(eA Q), a key step of the H_2O_2 production by the anthraquinone process, over the various monolithic catalysts(60 °C, atmosphere pressure) showed that the monolithic catalyst with the moderate thickness of Al_2O_3 layer(about 6 μm) exhibited the highest conversion of e AQ(99.1%) and hydrogenation efficiency(10.0 g·L~(-1)). This could be ascribed to the suitable Pd penetration depth and the larger pore size, which provides a balance between the distribution of Pd and accessibility of active sites by the reactants.     

Catalytic removal of perchloroethylene (PCE) over supported chromium oxide catalysts

The oxidation of perchloroethylene (PCE) was investigated over chromium oxide catalysts supported on SiO₂, SiO₂–Al₂O₃, activated carbon, mordenite type zeolites, MgO, TiO₂ and Al₂O₃. Supported chromium oxide catalysts were more active than any other metal oxide catalysts including noble metal examined in the present study. PCE removal activity of chromium oxide catalysts mainly depended on the type of supports and the content of metal loaded on the catalyst surface. TiO₂ and Al₂O₃ containing high surface areas were effective for the high performance of PCE removal, since the formation of well dispersed Cr(VI) active reaction sites for the present reaction system, was enhanced even for the high Cr loading on the catalyst surface. CrO_x catalysts supported on TiO₂ and Al₂O₃ also exhibited stable PCE removal activity at a low feed concentration of PCE of 30 ppm up to 100 h at 350°C. However, significant catalyst deactivation was observed at high PCE concentration of 10 000 ppm. CrO_x/TiO₂ revealed stronger water tolerance than CrO_x/Al₂O₃ due to the surface hydrophobicity.