老化对钴铈基催化剂催化氧化丙烷的影响

采用柠檬酸络合法合成Co-CeO_x多活性中心催化剂,在不同温度进行加速老化处理,测试新鲜和老化后催化剂对丙烷的催化氧化性能,同时对其结构和性质进行表征.结果表明,当加速老化温度低于650℃时,丙烷转化率达50%的温度变化幅度小于10℃;加速老化温度高于750℃时,催化剂氧化丙烷的性能快速下降.表征结果显示,Co-CeO_x催化剂主要表现为尖晶石结构,老化后晶粒尺寸显著增大,Co³⁺的含量减少,氢还原峰温度升高.加速老化处理对Co-CeO_x催化剂物理结构的影响进而抑制了其化学特性及催化活性.测试Co-CeO_x催化剂对丙酮和甲苯的催化氧化性能,分别在179和244℃达到90%的脱除效率.因此,Co-CeO_x多活性中心催化剂具有良好的氧化性能,且表现出一定的稳定性.     

间二异丙苯一次氧化产物失控反应特性研究

间二异丙苯与空气发生一次氧化反应,是间二异丙苯氧化法制备间苯二酚的关键技术,采用DSC差式扫描量热仪和VSP2绝热量热仪等,研究间二异丙苯与空气反应生成一次氧化产物的热稳定性和绝热失控特性。结果显示:间二异丙苯与空气反应生成一次氧化产物的起始放热温度(T0)为129℃,绝热温升(ΔT ad)为222℃,最高失控压力(P max)为4.05 MPa,最大反应速率到达时间为24 h对应的温度(T D24)为49.6℃。在工业化实施时应优化工艺流程,在操作过程中严格控制反应温度,优化操作条件,以保证安全生产。     

紫外辐射对腐殖酸化学稳定性影响机制研究

腐殖酸广泛存在于各类地表水体中,分子结构对其物化性质有着显著影响.为探明紫外辐射过程对腐殖酸化学稳定性的影响途径,本研究采用光谱学和电化学技术考察了酚羟基和羧基等活性位点含量、胶体Zeta电位及其平均粒径等结构参数在辐射前后的变化特征.研究发现,未经辐射的水样,混凝过程对腐殖酸无明显去除效果.随着辐射时间的增加,腐殖酸的去除率大幅提高.照射3 h后,腐殖酸的去除率在80%以上.光谱分析结果表明,紫外辐射后腐殖酸分子中部分具有荧光效应的基团可能发生脱落或重排,但其芳香结构并未发生明显变化.胶体的Zeta电位和平均粒径均呈下降趋势,不利于腐殖酸的聚集沉淀;然而,腐殖酸分子中的羟基含量在辐射后略有下降,并伴随羧基和羰基等官能团的形成.活性位点数量及其反应活性的改善是腐殖酸化学稳定下降的主要原因.     

汶川8.0级地震路堑墙震害特征及机理分析

通过对2005年竣工的都江堰至映秀的三级公路的调查,分析了路堑墙的汶川8.0级地震震害模式;以浆砌片石典型解体崩毁工点为例,将基于抗震设计规范的验算与实震情况比较,认为现行抗震规范是按照刚性挡土墙进行设计的,对于"柔性挡土墙"并不完全适用;通过拟静力法进行计算认为墙后坡度越大,挡墙稳定性越差,未超过一定坡度时主动土压力系数增长缓慢,当超过一定坡度时,主动土压力系数急剧增长。     

山区公路边坡地质灾害数据库及统计分析

边坡稳定性受多种内外因素的综合影响,正确地认识各影响因素的特征及其对公路边坡稳定性的影响程度,有助于对边坡进行合理的评价,并采取经济有效的防护措施.本文在现场工程地质调查和文献调研的基础上,搜集了622个典型山区公路边坡的地质资料及灾害资料,建立了山区公路边坡地质灾害数据库,统计了各影响因素与边坡失稳频度的关系.统计结...     

The Role of Headwater Wetlands in Altering Streamflow and Chemistry in a Maine,USA Catchment1

Morley, Terry R., Andrew S. Reeve, and Aram J.K. Calhoun, 2011. The Role of Headwater Wetlands in Altering Streamflow and Chemistry in a Maine, USA Catchment. Journal of the American Water Resources Association (JAWRA) 1‐13. DOI: 10.1111/j.1752‐1688.2011.00519.x Abstract: Headwater wetlands, including hillside seeps, may contribute to downstream systems disproportionately to their relatively small size. We quantified the hydrology and chemistry of headwater wetlands in a central Maine, USA, catchment from 2003 to 2005 to determine their role in maintaining headwater streamflow and in affecting stream chemistry. A few of these headwater wetlands, commonly referred to as “seeps,” were characterized by relatively high groundwater discharge. During summer base flow, seeps were the primary source of surface water to the stream, contributing between 40 and 80% of stream water. Comparisons of groundwater and surface water dominant ion chemistry revealed only slight differences at the bedrock interface; however, significant changes occurred at the shallow groundwater‐surface water interface where we found decreases in total and individual cation concentrations with decreasing depth. Seep outflows significantly increased total cation and calcium concentrations in streams. Outflows at two seeps produced relatively high nitrate concentrations (88 ± 15 and 93 ± 15 μg/l respectively), yet did not correspond to higher nitrate in stream water below seep outflows (2 ± 1 μg/l). We demonstrate that small wetlands (< 1,335 m²) can contribute to headwater stream processes by linking groundwater and surface‐water systems, increasing the duration and magnitude of stream discharge, and by affecting stream chemistry, particularly during periods of base flow.     

Model for predicting hydroxylamine nitrate stability in plutonium process solutions

A mathematical model is described that may be used to determine the safety of hydroxylamine nitrate (HAN) solutions used in solvent extraction purification of plutonium. The most significant hazard associated with hydroxylamine use in processing plutonium is its rapid, autocatalytic reaction with nitric acid which can result in an explosion or pressurization of process vessels with radiological consequences to humans. In addition, heat is produced by the reaction that could potentially ignite process solvents. The HAN decomposition reaction can occur only under specific process conditions (temperature; HAN, plutonium and nitric acid concentrations) and the model is used to identify these conditions so that they can be avoided. A kinetics model has been developed using all of the known significant reactions that could occur in process solutions containing HAN and nitric acid as well as plutonium and iron. The reaction kinetics data (rate laws, rate constants, activation energies) used in the model were obtained from chemical literature sources. The model shows that the autocatalytic HAN reaction with nitric acid is very rapid and is catalyzed by Pu(III) and Fe(II) in process solutions. High temperatures and nitric acid concentrations also promote the reaction.     

形状在边坡稳定安全论证中的影响分析

将边坡结构简化成二维模型进行计算分析时,边坡形状对其简化结果产生影响,为此从边坡的平面形状和边坡高度2个方面着手,用三维数值模拟对边坡稳定性进行分析,计算结果表明:坡顶曲线半径对边坡稳定性影响较大。在进行边坡稳定性分析时,应首先根据坡顶曲线半径大小界定是否可以将边坡简化为二维模型。     

基于3DMINE-MIDAS-FLAC~(3D)耦合的残矿回采稳定性研究

残矿开采条件极为复杂,回采安全性差。为了保障残采安全,利用3DMINE,MIDAS/GTS,FLAC3D软件的耦合,对残采方案的稳定性进行数值模拟研究,根据残矿开挖后所形成空区的围岩位移、应力及塑性区状态判定回采危险区。选取某矿山浅部中段残采工程为例,研究结果表明:该矿山-47 m中段部分间柱采空区的帮壁和顶板因岩移过大、拉应力过大、拉伸塑性破坏或剪切塑性破坏,出现了11处危险区;顶柱采空区顶板因拉伸塑性破坏,出现了6处危险区。通过此3种软件的耦合可精细建立复杂的数值模型,提高数值模拟结果的合理性,危险区的判定有助于指导矿山残采过程中安全监测与支护措施的实施。