混配柴油凝点及溶解度参数的分子模拟研究

石化柴油中添加少量生物柴油调配混配柴油是当前研究的一个热点.分别用单组分、3组分和5组分正构烷烃构建石化柴油模拟系统,以亚油酸甲酯（ML）构建单组份生物柴油模拟系统.按2％、4％、6％、8％和10％物质的量比添加ML于石化柴油模拟系统中构建不同比例的混配柴油系统.利用分子动力学方法对各种系统的凝点区间及溶解度参数进行了模拟计算.利用热容等4个性质联合判断出各系统的模拟凝点区间,发现,随着ML的添加,系统的凝点总体呈下降趋势,说明生物柴油确具有明显的降凝效果,添加生物柴油可以使柴油的低温流动性增加.相比较而言,采用3组分正构烷烃构建石化模拟系统更为合适.通过对293 K时3组分石化柴油系统添加不同比例的ML构成的混配柴油系统的溶解度参数进行分析,得出了当添加比例为4％时两种油品的相容性最佳的结论.     

枝向量矩阵反馈环算法的MATLAB实现*

找到系统中的全部反馈环是系统动力学模型分析的基础。针对这一问题,比较了几种常见的反馈环计算方法,得出在时间复杂度上矩阵算法优于行列式算法。在计算机上用MATLAB实现了基于流率基本入树和强简化流率基本入树枝向量矩阵计算所有反馈环的矩阵算法,分析了算法的复杂性,并给出了相应的算例。     

四氢萘催化裂化研究进展

加氢处理油中含有一定量的环烷基单环芳烃,研究四氢萘催化裂化有利于加强对更多环数环烷基单环芳烃催化裂化的认识。综述了四氢萘催化裂化过程的反应机理,认为四氢萘主要遵循单分子裂化机理;从反应活化能、扩散、吸附等动力学角度对四氢萘裂解行为进行了解释;催化剂适宜的孔径和BrØnsted酸强度有利于四氢萘开环;随着反应温度升高、剂/油质量比增大、质量空速减小,四氢萘反应活性增强,同时氢转移反应愈发明显。适宜的催化剂孔径和Brnsted酸强度、反应温度、剂/油质量比以及质量空速有利于四氢萘裂化生成低碳烯烃。     

A computational approach to characterize formation of a passivation layer in lithium metal anodes

Li metal anode is the “Holy Grail” material of advanced Lithium-ion-batteries (LIBs). However, it is plagued by uncontrollable dendrite growth resulting in poor cycling efficiency and short-circuiting of batteries. This has spurred a plethora of research to understand the underlying mechanism of dendrite formation. While experimental studies suggest that there are complex physical and chemical interactions between heterogeneous solid-electrolyte interphase (SEI) and dendrite growth, most of the studies do not reveal the mechanisms triggering these interactions. To deal with this knowledge gap, we propose a multiscale modeling framework which couples kinetic Monte Carlo and Molecular Dynamics simulations. Specifically, the model has been developed to account for (a) heterogeneous SEI, (b) dendrite-SEI interactions, and (c) effect of electrolyte on Li electrodeposition and potential dendrite formation. This allows the proposed computational model to be extended to various electrolytes and SEI species and generate results consistent with previous experimental studies.     

Effects of Al:Si and (Al + Na):Si ratios on the properties of the international simple glass,part II: Structure

High-alumina containing high-level waste (HLW) will be vitrified at the Waste Treatment Plant at the Hanford Site. The resulting glasses, high in alumina, will have distinct composition-structure-property (C-S-P) relationships compared to previously studied HLW glasses. These C-S-P relationships determine the processability and product durability of glasses and therefore must be understood. The main purpose of this study is to understand the detailed structural changes caused by Al:Si and (Al + Na):Si substitutions in a simplified nuclear waste model glass (ISG, international simple glass) by combining experimental structural characterizations and molecular dynamics (MD) simulations. The structures of these two series of glasses were characterized by neutron total scattering and ²⁷Al, ²³Na, ²⁹Si, and ¹¹B solid-state nuclear magnetic resonance (NMR) spectroscopy. Additionally, MD simulations were used to generate atomistic structural models of the borosilicate glasses and simulation results were validated by the experimental structural data. Short-range (eg, bond distance, coordination number, etc) and medium-range (eg, oxygen speciation, network connectivity, polyhedral linkages) structural features of the borosilicate glasses were systematically investigated as a function of the degree of substitution. The results show that bond distance and coordination number of the cation-oxygen pairs are relatively insensitive to Al:Si and (Al + Na):Si substitutions with the exception of the B-O pair. Additionally, the Al:Si substitution results in an increase in tri-bridging oxygen species, whereas (Al + Na):Si substitution creates nonbridging oxygen species. Charge compensator preferences were found for Si-[NBO] (Na⁺), ^[3]B-[NBO] (Na⁺), ^[4]B (mostly Ca²⁺), ^[4]Al (nearly equally split Na⁺ and Ca²⁺), and ^[6]Zr (mostly Ca²⁺). The network former-BO-network former linkages preferences were also tabulated; Si-O-Al and Al-O-Al were preferred at the expense of lower Si-O-^[3]B and ^[3]B-O-^[3]B linkages. These results provide insights on the structural origins of property changes such as glass-transition temperature caused by the substitutions, providing a basis for future improvements of theoretical and computer simulation models.     

Atomic and micro-structure features of nanoporous aluminosilicate glasses from reactive molecular dynamics simulations

Long-term chemical durability of borosilicate glasses that makes them a widely accepted form of nuclear waste disposal is achieved through the formation of a porous aluminosilicate gel layer that provides passivity and limits the transport of water to the reaction front. Detailed understanding of the porous silicate gel layer is thus critical in elucidating the corrosion mechanism of these glasses and to design of new glass composition for waste immobilization and other applications. In this paper, we use the diffuse charge reactive potential to generate porous aluminosilicate glass structures with compositions equivalent to the gel layers formed at the glass-water interface with an aim to understand the processing condition on the microstructure and atomic structure of these systems. We demonstrate the use of the charge scaling techniques is an effective approach to generate these porous structures with controllable pore mophologies. After initial validation of the potentials and calcium aluminosilicate glass structures using neutron diffraction, we created gel structures with compositions similar to well-known model nuclear waste borosilicate glasses. The porosities and the pore size distribution bear a strong correlation to the processing temperature, as well as to the local atomic structure. Thus, by controlling the processing parameters, the generated porous structures can be customized to closely resemble gel structures due to borosilicate glass corrosion. These results provide insights of the micro- and atomic structure features of the porous aluminosilicate glasses and on the optimal procedure to generate porous structures that can be comparable to experimentally observed gel layer structures thus to elaborate on the correlations between the structure and phenomena in glass-water interactions.     

Pressure effects on shear deformation of borosilicate glasses

The shear behaviors of two multicomponent borosilicate glasses, Borofloat®33 (Boro33) and N-BK7® (N-BK7), under different pressures are investigated using molecular dynamics simulations. The addition of alkali ions lowers the yield stress and changes the pressure dependence of shear modulus. Shear-induced densification is observed in both glasses. It is found that the decreases of the oxygen-centered bond angle and the coordination number change of B are responsible for the density changes at low pressures, and the increase of 5-coordinated Si is the dominant mechanism for densification at high pressures. The average shear stresses experienced by Si and B decrease with pressure except that the flow stress of Si at the end of shear deformation in N-BK7. Moreover, the average shear stress of B is more sensitive to the applied pressures compared to Si, suggesting that B is able to relax mechanical stress more easily under pressurized-shear. By analyzing the nonaffine displacement of atoms, it is found that N-BK7 exhibits more localized plastic deformation compared to Boro33 at low pressures and the local rearrangements in both glasses become more homogeneous with increasing pressure. The mean squared nonaffine displacement curves show that alkali ions have the highest mobility induced by shear compared to the network formers and B is more mobile than Si for both glasses. We also observed that plastic deformation tends to take place around boron atoms for Boro33, whereas it occurs in the alkali-rich regions for N-BK7, indicating that these two glasses have different atomic-scale deformation mechanisms.     

Atomic-scale mechanisms of densification in cold-compressed borosilicate glasses

Knowledge of the underlying structural response during deformation processes is essential for understanding the macroscopic mechanical response of glass. Here we present results from cold compression-decompression molecular dynamics (MD) simulations of two multicomponent borosilicate glasses, Borofloat^®33 (Boro33) and N-BK7^® (N-BK7). Our results suggest that the densification of these two borosilicate glasses involves different types of structural changes. The fraction of permanent densification can be correlated to the change in intermediate-range structure. By performing Voronoi analysis, we quantify the contributions to densification from different cation types in these two multicomponent borosilicate glasses, finding that 3-coordinated cations facilitate the densification process. Higher-coordinated cations are relatively stable and can even show a slight expansion in their Voronoi volume.     

Effect of B2O3 on the structural and in vitro biological assessment of mesoporous bioactive glass nanospheres

In this paper, the boron-containing mesoporous bioactive glass (MBG) nanospheres have been successfully synthesized by modified sol-gel method assisted by surfactant, and the effect of boron substitution on structure and bioactivity was evaluated by combining experiments and ab initio molecular dynamics (AIMD) simulations. All of the samples exhibit regularly uniform mesoporous spherical microstructure with an average size of about 60 nm, and the boron-containing MBGs show higher specific surface area with the value up to 416.20 m²/g. The simulated body fluid (SBF) immersion test confirms that the deposited hydroxyapatite (HA) evidently increases with the increasing of boron content, indicating that the biological behavior has been significantly improved resulting from incorporation of boron. Additionally, our results also reveal that B₂O₃ substitution has positive impact on cell proliferation of human periodontal ligament cells (hPDLCs) at lower extracted concentration. Furthermore, AIMD simulation is employed to understand the relationship between structural changes and in vitro bioactivity in terms of structural information, especially the boron coordination number. The results illustrate that the boron-containing MBG nanospheres with excellent bioactivity are great potential for biomedical applications.     

Einfluss der Wechselwirkung von Reaktion und Fluiddynamik auf das Verhalten von Strahlschlaufenreaktoren

Jet loop reactors are used as apparatus to facilitate chemical or biological reactions. This type of apparatus is characterized by an internal circulation flow, essentially driven by the injection of liquid. The nozzle can also be used to inject and disperse gas. The internal fluid dynamics and thus the reactor behavior is significantly determined by the introduced momentum and by the internal gas distribution. To describe the mutual influence of a gas-consuming reaction and the internal fluid dynamics, a simplified model based on a momentum balance and a material balance was used. From the exemplary calculations, a critical range for non-selective reactions and for fluid dynamic stability is given.