Comparison of temperature effect on electroreduction of tert-butyl chloride and tert-butyl bromide—Theoretical study

An effect of temperature on kinetics and mechanism of the reaction RX + e → R + X⁻ is studied using molecular dynamics simulations method for two molecules: t-BuCl and t-BuBr in two different solvent viscosities γ_x = 2 ps⁻¹ and γ_x = 40 ps⁻¹. The potential surfaces used in the simulations are two-dimensional and depend on the solvent generalized coordinate x and the C–X bond elongation y, the latter part based on quantum calculations. For both systems the transfer coefficient α is found to decrease with temperature and this effect is stronger in the more viscous solvent. For γ_x = 40 ps⁻¹ the following α values are reported: at T = 278 K 0.234 (t-BuCl) and 0.264 (t-BuBr), while at T = 398 K 0.208 (t-BuCl) and 0.222 (t-BuBr). In identical conditions and for the same height of the energy barrier, α(t-BuCl) is always lower than α(t-BuBr). The results are interpreted as an effect of the saddle point avoidance phenomenon.     

Effect of crack width on chloride diffusion coefficients of concrete by steady-state migration tests

The purpose of the present study is to explore the diffusion characteristics of cracked concrete according to the width of cracks. Major test variables include crack width, concrete strength, fly ash addition, and maximum aggregate size. The diffusion characteristics have been measured by steady-state migration test. The present study indicates that the diffusion coefficients do not increase with increasing crack widths up to the so-called “threshold crack width.” The threshold crack width for diffusion is found to be around 55–80 μm. Above this threshold value, the diffusion coefficients start to increase with crack width. A composite model with the introduction of “crack geometry factor” was derived to identify the diffusion coefficient in cracked concrete. It was shown that the crack geometry factor ranges from 0.067 to 0.206. Finally, the effects of concrete strength, fly ash addition and maximum aggregate size on diffusion coefficients are also discussed.     

Restricted diffusion of residual molecules in catalyst pores under reactive conditions

The restricted diffusion of residual molecules under catalytic conversion conditions was investigated using commercial catalysts. The effectiveness factor, η, and the effective diffusion coefficient, D_e, for residual molecules were evaluated and explicitly compared based on a pseudo-first-order reaction kinetic model and the Thiele modulus. The experimental results showed that the restrictive diffusion of heavy oil molecules is affected by the joint functions of several factors, such as the operating conditions, the size and configuration of the reactant molecules, and the average pore diameter of the catalyst. The reaction temperature has a greater influence on restrictive diffusion than the other operating factors, and the ratio of reactant molecular size to catalyst pore size is the most critical factor that determines the degree of restrictive diffusion. Moreover, a mathematical expression was derived for the restrictive factors in order to describe the relationship between the effective diffusivity and ratio of molecule-to-pore size.     

Heat transfer in trickle bed column with constant and modulated feed temperature: Experiments and modeling

Heat transfer was investigated in an insulated packed bed column with co-current downflow of gas and liquid under constant and periodically modulated gas–liquid feed temperature. Bed temperatures at three axial positions were assessed at steady state for different insulating systems, different gas and liquid flow rates and system pressure. The experimental profiles recorded were modeled with a dynamic pseudo-homogeneous one parameter model to analyze the effect of operating conditions and to deduce coefficients of overall (U) and bed to wall (h_W) heat transfer. It appears that the heat transfer is strongly affected by the system pressure, whereas the liquid flow rate has a smaller influence. The experimental data of h_W were correlated with the operating conditions leading to a small average error of 7% in the correlation. Condensation of water vapor occurring in the column seems to contribute to the heat transfer inside the packed bed. Several dynamic experiments modulating the feed temperature were also conducted and described with the help of the dynamic model. Predictions with the fitted values of U were in good agreement with experiments and give confidence to apply this model in the investigation of the catalytic wet air oxidation of phenol over carbon conducted in a trickle bed reactor under temperature feed modulation.     

萃取法测定混配配合物稳定常数的新方法

提出一种萃取法测定饱和配位数为2的混配配合物稳定常数的新方法.利用了有机相中混配配离子最大分布系数的性质,测定原理简单,且能得到满意的结果.     

焦化原料泵机封失效分析及改进

惠州炼油焦化装置螺杆原料泵机械密封在使用过程中出现频繁泄漏。使用寿命非常短,严重影响装置的平稳生产。为彻底解决此问题,文章通过对机械密封泄漏原因进行分析并提出了改进方案,彻底解决泄漏问题。     

梅花电气石改性PBT回收料研究

将梅花电气石用作聚对苯二甲酸丁二醇酯(PBT)回收料的填充改性剂,制成梅花电气石/PBT复合材料.研究了不同梅花电气石含量对PBT回收料热变形温度和负离子释放性能的影响,并利用电子显微镜对梅花电气石粉体和梅花电气石改性PBT回收料的断面形貌进行观察.研究表明,梅花电气石存在着类似梅花状的微观结构,其粉体微粒易团聚在一起形成大致为0.6 μm的微粒簇,电气石颗粒均匀地分散在PBT基体中,且界面结合性能良好,电气石的加入提高了PBT的热变形温度和负离子释放能力,当梅花电气石质量分数为8％时,负离子平均释放量达到了1458个/cm3.     

交联聚四氟乙烯的耐磨性能研究

采用电子束高温辐照制备交联聚四氟乙烯（XPTFE）,利用环-环立式万能摩擦磨损试验机在干摩擦条件下研究了PTFE和XPTFE的摩擦磨损性能变化规律。结果表明：与PTFE的摩擦系数相比,XPTFE的摩擦系数随剂量的增加而增加。随剂量的增加,XPTFE的耐磨性增大,当吸收剂量为150 kGy时,XPTFE耐磨性提高了近1 000倍。PTFE磨损表面光滑,磨屑为波浪形带状物;XPTFE的磨损表面形成摩擦棱,磨屑为粉状颗粒。XPTFE的三维网状交联结构导致其耐磨性能明显提高。     

地铁车站冷水机组应用臭氧冷却水处理技术的性能测试与分析

该文主要介绍在地铁车站的大型集中式空调系统中应用臭氧技术对冷水机组冷却水系统进行处理的实际效果,通过长期的测试数据分析,讨论了冷水机组的实际性能变化情况及影响因素.针对地铁站空调运行期长、气象环境变化跨度大,所造成的冷水机组实际工况多变不定、难以直接衡量其性能变化等问题,采取以实际性能系数与该工况下理想换算性能系数之间...     

中压安注注射管线压降系数计算及误差分析

中压安注注射管线的平均压降系数（L／D）。对于核电站的安全非常重要,文章计算了某核电站中压安注系统的（L／D）。以及其误差A（L／D）m,结果表明（L,D）m=586．40,（L／D）m＋A（L／D）m。608．10,（L／D）m—A（L／D）m=564．70,压降系数及误差符合核电相关的安全准则要求,该系统可以实现其安全功能。