Metal Supported Zeolite for Heavy Aromatics Transalkylation Process

Aiming at improving the catalytic activity, benzene product purity, and catalyst stability during heavy transalkylation processes, strategies invoking startup procedures and catalyst system designs are summarized and discussed in this review. In particular, recent advances in the developments and catalytic performances of the on-line sulfiding technique, the selective pre-coking startup procedure, and a versatile dual-bed catalyst system design were compared and discussed.     

Influence of calcium on cracking of steel during the welding or casting process

The influence of calcium on the brittle–ductile transition temperature is studied for the solidification range. The test bars were cast from carbon steel with and without the addition of calcium. Mechanical properties at different temperatures around the solidus were evaluated. The fractured surfaces were examined using a scanning microscope coupled with a Kevex analyser. For the modified steel, the liquid phase appears (on heating) for higher temperature while the temperature range within which fracture can nucleate, during casting or welding, is markedly narrowed. In medium-carbon steel, calcium changes the manner of fusion of the grains. The inclusions of the liquid phase form at the triple points and the surfaces of grains remain solid above the solidus temperature.     

双相不锈钢在水溶液中之腐蚀疲劳与动态应变时效

本研究主要探讨 2 2 %Cr双相不锈钢在含氯离子水溶液中之腐蚀疲劳裂缝成长行为 ,以及在慢应变速率拉伸试验过程中所发生的动态应变时效现象 .同时以 31 6L沃斯田体系不锈钢及4 30肥粒体系不锈钢作为比较 ,藉以探讨不同晶体结构对腐蚀疲劳及动态应变时效行为的影响 .实验结果显示 ,在 80℃ ,3.5wt%NaCl水溶液中 ,3种不锈钢并未发生应力腐蚀破裂 ,但其中 31 6L沃斯田体系不锈钢及 2 2 %Cr双相不锈钢却发生动态应变时效 ,且动态应变时效的发生与温度 ,应变速率及沃斯田体相的组织有关 .在NaCl水溶液中 ,采用预裂试片量测疲劳裂缝生长速率 ,其结果表明 ,4 30肥粒体系不锈钢之疲劳裂缝生长速率最快 ,而氢脆是加快裂缝生长速率的主因 ,就双相不锈钢而言 ,腐蚀疲劳裂缝的生长主要与该不锈钢所含之肥粒体相的氢脆现象有关     

Cohesive zone modelling of anodic dissolution stress corrosion cracking induced by corrosion product films

Damage mechanics based on the cohesive zone model were applied to study the anodic dissolution stress corrosion cracking (SCC) in flat and U-shaped edge-notched specimens. The simulation results show that corrosion product films (CPFs) facilitate crack initiation in SCC due to the CPF-induced stress and CPF rupture. In the flat specimen, SCC susceptibility increases with the CPF thickness and CPF Young’s modulus, while it decreases with CPF fracture strength. For the U-shaped edge-notched specimen, the normalised threshold stress intensity factor K_ISCC/K_IC decreases with the CPF thickness and notch depth.     

Initiation and propagation of complex 3D networks of cracks in heterogeneous quasi-brittle materials: Direct comparison between in situ testing-microCT experiments and phase field simulations

We provide the first direct comparisons, to our knowledge, of complex 3D micro cracking initiation and propagation in heterogeneous quasi-brittle materials modelled by the phase field numerical method and observed in X-ray microtomography images recorded during in situ mechanical testing. Some material parameters of the damage model, including the process zone (internal) length, are identified by an inverse approach combining experimental data and 3D simulations. A new technique is developed to study the micro cracking at a finer scale by prescribing the local displacements measured by digital volume correlation over the boundary of a small sub-volume inside the sample during the numerical simulations. The comparisons, performed on several samples of lightweight plaster and concrete, show a remarkable quantitative agreement between the 3D crack morphology obtained by the model and by the experiments, without any a priori knowledge about the location of the initiation of the cracks in the numerical model. The results indicate that the crack paths can be predicted in a fully deterministic way in spite of the highly random geometry of the microstructure and the brittle nature of its constituents.     

植被护坡中植物根系的阻裂增强机理研究

本文从复合材料的角度对植物根系的加固机理进行了分析,将含根系的岩土体看成一特殊的复合材料,其中岩土体为基体相材料,根系为增强相材料,根系犹如纤维,将对根土复合体起到阻裂增强作用.并运用能量原理对根系的阻裂增强作用进行了分析研究,得出根土复合体中某点的抗剪强度增量的计算公式及该点处根系的抗拔力和最大拔出长度的计算公式,得出某点抗剪强度增量主要与该点处根的面积比、面密度、长径比、抗拉强度、根士间的黏聚力及摩擦系数有关,及如果根系深入某点以下锚同段长度大于该点处的最大拔出长度,根系将被拉断的结论.     

催化裂化过程中含硫化合物转化规律的研究

选择丁硫醚、叔丁硫醚、四氢噻吩和乙基苯基硫醚作为模化合物,在模拟固定床催化裂化微反装置上考察含硫化合物转化和分布规律,在催化裂化过程中,烷基硫醚可以完全转化,转化产物为硫化氢,反应条件对转化程度没有明显影响;环状含硫化合物的转化程度与反应条件、溶剂性质有关,转化产物主要为硫化氢和汪量噻吩,生产的噻吩可进一步发生烷基化反应,反应温度升高,溶剂供氢能力增强,硫化氢的收率增加;乙基苯基硫醚也可以完全转化,转化产物主要为硫化氢和苯硫酚,生成的苯硫酚可进一步发生烷基化反应,反应温度升高,溶剂供氢能力增强,硫化氢的收率增加。     

有机硅橡胶裂解产物气相色谱-质谱联用分析

以室温硅橡胶和高温硅橡胶产品的边角废料及次品作为实验原料,进行到催化和碱催化裂解,将裂解产物进行气相色谱－质谱（ＧＣ－ＭＳ）联用分析,经过质谱数据检索,确定了两种酸催化产物的组成,高温橡胶的酸催化裂解产物主要是环状化物合;室温橡胶的酸催化一妥产物中有太和链状两类化合物,该实验为硅像胶废料利用提供了依据。碱催化产物太复杂,产物利用存在困难。     

Aging kinetics of porous media due to freezing-thawing cycles

The two-dimensional Ausloos et al. model of fluid invasion, freezing and thawing in a porous medium is elaborated upon and investigated in order to take into account the pore volume redistribution and conservation during freezing. The results are qualitatively different from previous work, since the damaged pore sizes are found to be much less than the possible maximum value and is reached after a large number of invasion-freezing-thawing cycles, e.g. the material is “slowly damaged”. The pore size distribution is thus found in better agreement with expected practical findings. The successive invasion percolation clusters are still found to be self-avoiding with aging. The cluster size decreases with a power law as a function of invasion-frost-thaw iterations. The aging kinetics is also discussed through the normalized totally invaded pore volume. Received 24 September 1999 and Received in final form 5 January 2000     

Numerical comparison of two modes of gas-solid riser operation: Fluid catalytic cracking vs CFB combustor

Two modes of gas-solid riser operation, i.e., fluid catalytic cracking (FCC) and circulating fluidized bed combustor (CFBC), have been recognized in literature; particularly in the understanding of choking phenomena. This work compares these two modes of operation through computational fluid dynamics (CFD) simulation. In CFD simulations, the different operations are represented by fixing appropriate boundary conditions: solids flux or solids inventory. It is found that the FCC and CFBC modes generally have the same dependence of solids flux on the mean solids volume fraction or solids inventory. However, during the choking transition, the FCC mode of operation needs more time to reach a steady state; thus the FCC system may have insufficient time to respond to valve adjustments or flow state change, leading to the choking. The difference between FCC and CFBC systems is more pronounced for the systems with longer risers. A more detailed investigation of these two modes of riser operation may require a three-dimensional full loop simulation with dynamic valve adjustment.