Characterization of SiC ceramics with complex porosity by capillary infiltration: Part B – Filling by molten silicon at 1500 °C

In Part A of this study, infiltrations experiments of porous SiC samples by hexadecane with pore-size distributions comprising small and large pores were realized. Two successive stages were identified during the filling of these samples corresponding to the infiltration of the two types of pores. The experimental data were successfully treated with a new analytical function. In Part B, it was found that this function can also be applied to the analysis of the mass gain during molten silicon infiltration at 1500 °C. Prior to silicon infiltration, it was found that the operating temperature induces a shift of the pore size distributions towards larger values. A dissolution-recrystallisation mechanism can also occur during the infiltration of silicon. During the first stage, liquid silicon fills rapidly larger pores than hexadecane. The kinetics are significantly larger with liquid silicon. Consequently, the durations for the complete filling are very short with molten silicon.     

Modeling of sequence length distribution for olefin copolymerization with vanadium-based catalyst

Some thermodynamic and mechanical properties of a polyolefin, such as the melting temperature and the rigidity, are dependent on the nature of its sequence distribution. Accurate modeling of sequence length distribution (SLD) is important in precisely tuning and optimizing the properties of polymers produced. In this article, we proposed a model to predict the molecular weight distribution (MWD) and SLD for olefin copolymerization with vanadium-based catalyst. Due to the 2,1-insertion of α-olefin with vanadium-based catalyst, the SLD is expressed by uninterrupted methylene sequence distribution instead of conventional triad sequence distribution. To obtain a reliable model, parameter estimation with experimental data is first conducted. The SLD model along with the estimated kinetic parameters can be used to predict unmeasurable sequence length fraction. For the experimental conditions studied, the average methylene sequence length is predicted to change from 10 to 4 units as the propylene/ethylene mole feed ratio increases from 1.1 to 3.4.     

Formation mechanism and microstructure evolution of Ba2Ti9O20 ceramics by reaction sintering method

Ba₂Ti₉O₂₀ single-phase ceramics were prepared by reaction sintering method using TiO₂ and BaCO₃ as raw materials after heat treating at 1150°C for 10 hours. Furthermore, the formation mechanism and microstructure evolution of Ba₂Ti₉O₂₀ ceramics prepared by reaction sintering method were investigated. The formation behavior of Ba₂Ti₉O₂₀ phase was analyzed from the perspective of diffusion, where the reaction activation energy required for the process was calculated to be about 386.17 kJ/mol. Combined with the scanning electron microscopy and the energy dispersive spectrometer, it was revealed that the pores on Ba₂Ti₉O₂₀ grains in the process of reaction sintering might be caused by the absence of oxygen element. Meanwhile, the reason for the roughness of ceramic surface was that the local inhomogeneous distribution of barium on the surface of Ba₂Ti₉O₂₀ grain leaded to the enrichment of titanium.     

Investigations on Selectivity of Gas-Liquid Reactions in Capillaries

Biocatalysis offers a broad spectrum of possible ecological and economic advantages over conventional chemical catalysis processes, e.g., lower energy consumption and high enantio selectivity. The focus of this work is on gas-liquid reactions. These are of great importance in the chemical and biochemical industry and subject of current research since they are often limited by mass transfer or show low selectivity. Different suitable biocatalytically gas-liquid reaction systems were tested in capillary reactor designs in order to obtain information about the interaction between reaction and fluid mechanics. Furthermore, an optical measuring method was established. The experiments were performed in batch mode in a glass beaker with a flow cuvette for UV/Vis measurement of product concentration.     

Enantioselective esterification of (R,S)-2-(4-methylphenyl) propionic acid via Novozym 435: Optimization and application

This paper reports on the resolution of(R,S)-2-(4-methylphenyl) propionic acid(MPPA) enantiomers by enzymatic esterification in organic solvent. Novozym 435(CALB) has the best catalytic performance compared with other lipases. Of the alcohols screened, n-hexanol is the best acyl acceptor and gives the highest enzyme activity and enantioselectivity in n-hexane. Response surface methodology(RSM) was used to evaluate the influence of the factors, such as temperature, enzyme amount, substrate concentration and reaction time on the substrate conversion(c) and enantiomeric excess(ee). The correlation coefficient R~2 for enantiomeric excess and the conversion are 0.9827 and 0.9910, respectively, indicating that can accurately predict the experimental results. By simulation and optimization, the optimal conditions were obtained, involving 600 mmol·L~(-1) MPPA concentration(0.60 mmol), 850 mmol·L~(-1) hexanol concentration(0.85 mmol), 58 mg enzyme amount, 75 ℃ temperature and 4.5 h reaction time, respectively. Under the optimized conditions, the experimental values of conversion and enantiomeric excess were 89.34% and 97.84%, respectively, which are in good agreement with the model predictions.     

Catalytic combustion of methane over a highly active and stable NiO/CeO2 catalyst

In the last decades, many reports dealing with technology for the catalytic combustion of methane (CH₄) have been published. Recently, attention has increasingly focused on the synthesis and catalytic activity of nickel oxides. In this paper, a NiO/CeO₂ catalyst with high catalytic performance in methane combustion was synthesized via a facile impregnation method, and its catalytic activity, stability, and water-resistance during CH₄ combustion were investigated. X-ray diffraction, low-temperature N₂ adsorption, thermogravimetric analysis, Fourier transform infrared spectroscopy, hydrogen temperature programmed reduction, methane temperature programmed surface reaction, Raman spectroscopy, electron paramagnetic resonance, and transmission electron microscope characterization of the catalyst were conducted to determine the origin of its high catalytic activity and stability in detail. The incorporation of NiO was found to enhance the concentration of oxygen vacancies, as well as the activity and amount of surface oxygen. As a result, the mobility of bulk oxygen in CeO₂ was increased. The presence of CeO₂ prevented the aggregation of NiO, enhanced reduction by NiO, and provided more oxygen species for the combustion of CH₄. The results of a kinetics study indicated that the reaction order was about 1.07 for CH₄ and about 0.10 for O₂ over the NiO/CeO₂ catalyst.     

簇状分布的刚性双层植被明渠紊流特性分析

采用RNG k-ε 紊流模型,对簇状分布的刚性双层植被明渠水流进行了模拟和分析;根据时间及空间的双平均方法对植被明渠水流的流速及紊动参数进行了统计。结果表明:簇状分布的植被明渠水流可以分为植物区、间隙区及主流区,不同区域时均流速的大小和分布各异;双层植被明渠水流中,时均流速垂线分布在近床面、低植物顶部附近及高植物顶部附近均出现拐点,脉动强度和紊动能的最大值出现在高植物顶部附近。     

复吹转炉炼钢过程脱碳模型

通过分析复吹转炉脱碳过程的冶金机理,应用冶金热力学、动力学和传输理论,建立描述转炉脱碳过程的动力学模型,确定了模型的有关参数.模型的关键在于正确计算并比较钢液中[C]和[O]的传质速度,找到转炉冶炼脱碳过程的限制环节,并通过一系列热力学计算得到进入钢液的氧在各元素间的分配比例,从而得到转炉中脱碳反应的速度方程.将模型应用于本钢150 t转炉冶炼过程,模型在不同时刻的计算结果与现场实测值吻合较好.     

气体添加剂对热脱硝过程影响的实验和建模研究

An experimental study of thermal DeNOx process with different additives was performed in an electricity- heated tubular flow reactor, showing that CO is less effective to lower the optimum temperature than H2 and CH4. The maximum NO reduction is lowered with H2 added, while it is hardly affected by CO or CH4. The temperature window is widened appreciably with CH4 added, while it is narrowed slightly by H2 or CO. The disadvantage of CH4 is that it causes CO emission due to its incomplete oxidation, and the maximum conversion of CH4 to CO is more than 50%. In general, the calculation using a detailed chemical kinetic model predicts most of the process features reasonably well. The analysis on reaction mechanism shows that the effects of these additives on NO reduction are achieved principally by promoting the production of &;#8226;OH radical.     

催化氧化法处理红色基B废水的动力学研究

研究了催化氧化法处理红色基B生产过程所产生的工业废水的动力学。红色基B的工业废水COD值高达40 063 mg·L~(-1),含有大量有机物,颜色为红色且有强烈的刺激气味。废水处理过程中以FeSO_4为催化剂、H_2O_2为氧化剂,研究了催化氧化法处理废水的工艺路线及工艺条件,分析了影响因素,建立了动力学模型,研究了其催化氧化的动力学过程。结果表明,处理后的废水的COD值可降为4 mg·L~(-1)左右,去除率为90%;所建立的过氧化物催化氧化红色基B废水的动力学方程与实验数据拟合较好。其表观动力学方程为:-(dc)/(dt)=1.978 6exp(-(19 351)/(RT))[H_2O_2]_0~(0.979 6)c