粉煤灰与硫酸氢铵焙烧反应动力学

提出了NH4HSO4法焙烧粉煤灰提取Al2O3的新方法,考察了焙烧温度、粉煤灰中Al2O3与NH4HSO4摩尔比对粉煤灰中Al反应率的影响,研究了粉煤灰与NH4HSO4焙烧反应动力学. 结果表明,粉煤灰与NH4HSO4焙烧反应受固体产物层扩散控制,300, 350, 400℃下的反应速率常数分别为1.25′10-3, 1.56′10-3, 1.89′10-3 min-1,反应活化能为17.19 kJ/mol,反应动力学方程为1-2/3a-(1-a)2/3=0.0422exp[-17190/(RT)]t,最佳工艺条件为：焙烧温度400℃,Al2O3与NH4HSO4摩尔比1:8,焙烧时间60 min;该条件下Al反应率达90%以上,主要产物为NH4Al(SO4)2和NH4Fe(SO4)2.     

膨化硝酸铵的热分解动力学研究

利用热重法测得了普通工业硝酸铵和膨胀化硝酸铵的热重曲线,计算到了普通肖酸铵和膨化硝酸铵的热分解活化能,研究了普通工业硝酸铵和膨化硝酸铵的热分解反应机理和动力学方程。     

Estimation of activation energies during hydrodesulfurization of middle distillates

Hydrodesulfurization (HDS) of different petroleum distillates was carried out in a batch reactor using commercial CoMo catalyst and reaction conditions similar to industrial practice. Various experiments (agitation, particle size and amount of catalyst tests) were conducted with different hydrocarbon feeds to assure the operation under kinetic regime. Reaction orders and activation energies for each feed were determined by two approaches (linear and non-linear regressions). Both kinetic parameters (n and E_A) were found to follow a direct relationship with sulfur content in the feed. Reaction orders ranged between 1.96 and 3.36 and activation energies from 21.49 to 41.96 kcal/mol, which were within the range of those reported in the literature. High values of reaction order were attributed to contributions of HDS reaction of each individual compound exhibiting very different reaction rate constants.     

Mixing and Crystallization Kinetics in Gas‐liquid Reactive Crystallization

A study of gas‐liquid reactive crystallization for CO₂‐BaCl₂‐H₂O system was performed in a continuous flow crystallizer. The influences of mixing on the crystallization kinetics of barium carbonate crystals were investigated. The mixing parameters are stirrer speed, feed concentration, gas‐flow rate, pH of solution, addition rate of NaOH solution, and mean residence time. Under pH‐stat operation, the crystallization mechanism can be assessed by the addition rate of NaOH solution, which acts as an indicator for the absorption rate of carbon dioxide. Assuming a size‐independent agglomeration mechanism, the nucleation rate, growth rate and agglomeration kernel can be obtained, simultaneously, at steady state, by the method of moments. Evidence shows that feed concentration, feed rate, gas‐flow rate, and stirrer speed have a significant influence on the nucleation rates and mean particle sizes. This shows the effect of micromixing. The crystallization mechanism tends to be reaction limited when the feed concentration of barium chloride solution is higher than 5 mM, while at lower stirrer speeds and feed concentrations, the mechanism tends to be both mixing and reaction controlled. The growth rate depends on the mean supersaturation value and the pH of the solution and the mass‐transfer resistance cannot be completely eliminated in this work. For a monodispersal collision model, in the viscous sub‐range of turbulence, the agglomeration kernel can be expressed as β ∝ d^{3 –1/4}, showing a low efficiency of collision. The result is also demonstrated by the agglomeration kernel expression. Comparison with a liquid‐liquid‐mixing reactive crystallization system is also discussed.     

亚硝酸钠与氯化铵反应动力学研究

研究了在盐酸催化的亚硝酸钠(NaNO2)与氯化铵(NH4C1)反应动力学,结果显示:亚硝酸钠与氯化铵在水中的反应为二级反应;其速率常数与该体系中氢离子的浓度成正比;活化能为50.26 kJ/mol;亚硝酸钠与氯化铵反应的动力学方程为dC/dt=-2.066×107CH+e-6045/TC2.     

掺入粉煤灰提高碾压混凝土耐久性的试验研究

试验采用在碾压混凝土中掺入粉煤灰(其掺量占胶凝材料总量的10%～45%)的方法来提高碾压混凝土耐久性(包括强度、干缩、耐磨性和抗冻性)。试验结果表明:(1)粉煤灰掺量小于30%时能提高碾压混凝土强度但影响度不大;(2)随着粉煤灰掺量的增加,碾压混凝土的干缩呈直线降低,且抗磨性和抗冻融能力明显提高;(3)粉煤灰能有效提高碾压混凝土的耐久性,且在试验条件下的最佳掺量为30%。     

粉煤灰低温蒸压煅烧提取氧化铝的试验研究

介绍一种粉煤灰提取氧化铝的新方法.分析蒸压和煅烧两阶段主要影响因素对氧化铝提取率的影响,初步探讨低温蒸压和低温煅烧反应机理,确定蒸压和煅烧两阶段的最佳工艺条件.     

气体再燃低NO_x燃烧中NO与NH反应研究

对气体再燃低NOx燃烧过程进行分析,采用量子化学密度泛函理论研究了NH自由基与NO反应的机理,优化了反应过程中反应物、中间体、过渡态和产物的几何构型,并计算了它们的能量,同时进行振动分析,以确定中间体和过渡态的真实性。对NH自由基与NO反应机理与实验结果进行了验证和比较,并通过模拟NH自由基与NO的反应,得出反应通道,对认识再燃脱硝的本质和主要过程具有重要的理论参考价值和实践指导意义。     

Modeling of Mixing and Precipitation Using CFD and Population Balances

Simulations of particle size distributions in technical precipitation reactors require the consideration of turbulent mixing and precipitation kinetics. For that, spatially resolved population balances have to be evaluated. In turbulent flows these balances cannot be solved directly, instead either Reynolds averaging or Large Eddy Simulations have to be applied, while unresolved fluctuations need to be modeled. Reynolds averaging of the population balance leads to a turbulent growth dispersion term which has to be modeled. As no theoretically founded approach is available, an assumption was made in analogy to the turbulent diffusion, which improves the prediction of the size distribution shape compared to experiments.     

双螺杆中啮合块、螺杆元件混合过程及混合性能的研究

以双螺杆挤出机中的啮合块、螺杆元件作为研究对象,对其混合过程及混合性能进行研究,分析物料与添加剂的相互运动及变化过程。利用网格重叠技术和Ployflow软件对啮合块、螺杆元件的混合性能进行仿真,研究螺杆元件及不同转速下啮合块对应流体区域内的最大剪切应力,粒子在流体区域内的停留时间分布、分布指数、分离尺度等。结果表明:在啮合块流道内的混合过程中,啮合区域的两种粒子进行分布混合,其他区域的粒子在轴向运动到第2片啮合块时开始被带入啮合区,与另一种粒子进行分布混合;在相同转速下,啮合块的混合性能优于螺杆元件,随着转速的提高,啮合块的分散混合性能逐渐增强。     

水玻璃激发粉煤灰、矿粉活性的试验研究

以水泥为主要胶凝材料,掺加工业废渣粉煤灰、矿粉作为替代物,同时添加一定量的水玻璃激发剂,研究其对矿物掺合料的激发机理及合理掺量。结果表明:水玻璃对矿物掺合料的活性激发效果表现良好,改善了水泥基材料的强度,实现了保护环境和节约经济的目的。     

Hydrolysis Kinetics of 2-Pyridinecarboxamide, 3-Pyridinecarboxamide and 4-Pyridinecarboxamide in High-Temperature Water

abstract A kinetic study is reported here on hydrolysis of three pyridinecarboxamides in high-temperature water in the temperature range of 190-250 °C at 8 MPa. 2-Pyridinecarboxamide, 3-pyridinecarboxa...     

A Model of Drying Kinetics of Acacia mangium Wood at Different Temperatures

The objective of this study was to determine the isothermal drying kinetics of Acacia mangium wood blocks by employing a relative humidity-controlled drying chamber. A model was developed based on solution of Fick's second law and evaluated through the coefficient of determination (R ² ), sum of square error (SSE), root mean square error (RMSE), and reduced chi-square (χ ² ). This model was compared to semi-theoretical models which are commonly used to describe the drying behavior of biomass in previous studies. The porosity and shrinkage characteristics of dried specimens were also evaluated. Based on the findings in this work, it was determined that the proposed model resulted in an excellent fit with experimental data for all four drying temperature levels of 30, 35, 40, and 45 ^° C to describe the isothermal drying kinetics of Acacia mangium . It appears that volumetric shrinkage of the samples decreased quadratically with decreasing moisture ratio. The activation energy of the drying process was determined to be 41.07 kJ/mol.     

混炼工艺对NBR/PVC发泡材料性能的影响

研究了密炼和开炼两种混炼方式及不同的密炼温度对丁腈橡胶(NBR)/聚氯乙烯(PVC)发泡材料性能的影响。结果表明,混炼温度相同时,密炼工艺比开炼工艺的塑化共混效果更好,胶料的门尼黏度更高,发泡材料性能更优;在130～160℃的密炼温度范围内,密炼温度为150℃时得到的发泡材料密度最低、硬度较高。     

反应注射成型设备混合系统的类型与性能

介绍了反应注射成型设备的撞击混合式、旋转混合式以及旋转Kenics混合器等混合系统的结构特点,并对工作性能进行了分析     

Thermal Degradation Kinetics of Carotenoids in Palm Oil

In the present work, a detailed study is performed for carotene thermal degradation in palm oil at four temperatures ranging from 170 to 230 °C. The heating process was carried out with injection of nitrogen, and the samples were collected every 20 min during a total heating period of 140 min. HPLC analysis was conducted to monitor the carotenoids and tocols variations over the heating time at each temperature. The experimental data were then compared to literature data concerning carotenoids thermal degradation. The thermal degradation kinetics of carotenoids in palm oil followed an order superior to 1. The dependence of constant rates with temperature obeyed the Arrhenius relationship. The activation energy for the carotenoids thermal degradation in palm oil was found to be 109.4 kJ/mol.     

Effect of Temperature on Phase and Alumina Extraction Efficiency of the Product from Sintering Coal Fly Ash with Ammonium Sulfate

A new developed technology for extracting alumina from coal fly ash was studied in this paper. In this technology, coal fly ash is first sintered with ammonium sulfate, forming ammonium aluminum sulfate in the resultant product, where alumina can be easily leached without using any strong acid or alkali. The products obtained under different sintering conditions were characterized by X-ray diffractometry. Alumina extraction efficiency of these products was also investigated. The results show that the sintering temperature and time substantially influence the phase composition and alumina extraction efficiency of sintered products, while the heating rate has little influence. The optimal sintering condition is 400 °C for 3 h in air with a heating rate of 6 °C·min^− 1. Under the optimal sintering condition, the alumina extraction efficiency from as-sintered coal fly ash can reach 85% or more.     

大掺量粉煤灰烧结砖焙烧过程及机理探讨

目前对大掺量粉煤灰烧结砖焙烧过程及机理的研究，基本是将粉煤灰作为均质材料来进行的。本文基于组成粉煤灰的各颗粒成分的“颗粒特性”存在较大的差异，而具有不同的烧结特性这一事实，对大掺量粉煤灰烧结砖的焙烧过程及机理进行探讨。     

Polythiophene oxidation: Rate coefficients, activation energy and conformational energies

Polythiophene films reduced by prepolarization at different cathodic potentials were used as the initial states for their potentiostatic oxidation. At the chronoamperometric maxima the oxidation occurs under chemical kinetic control. The oxidation kinetic characteristics: rate coefficient (k), activation energy (E_a) and the reaction order of the oxidation reaction, change as a function of the cathodic potential of prepolarization. That means that k and E_a for the oxidation are functions of the oxidation overpotential, as for any oxidation kinetics, and of the cathodic potential of prepolarization. Rising cathodic potentials of prepolarization promote decreasing rate coefficients, k, and increasing E_a. Those variations are described by the electrochemical relaxation model. The activation energy includes two components: the constant activation energy of the electrochemical reaction and the conformational activation energy of the initial packed conformations that increases as the prepolarization potential rises.     

Evaluation of Thermodynamic Parameters for Separation of Hexavalent Chromium by Fly Ash

Abstract

Kinetics and thermodynamic parameters of Cr⁶⁺ separation by fly ash from aqueous solution has been evaluated. It was found that the separation process is partly diffusion controlled and endothermic in nature. The mass transfer coefficient increases with an increase in temperature. The activation energy and change of enthalpy were also evaluated and found to be 17.5 kJ/mol and 14.47 kcal/mol, respectively. The free energy of the process was small but positive, and it decreases with an increase of temperature. The change of entropy was found to be small and remains unchanged over the 30 to 50°C temperature range. This process follows the Langmuir isotherm model where Q _o and b were also determined at different temperatures.