大孔树脂吸附南五味子总三萜的动力学和热力学分析

目的:考察大孔树脂吸附南五味子总三萜的动力学与热力学特征,为该类化合物的分离纯化提供参考。方法:以吸附率、洗脱率为综合评价指标,通过静态吸附-洗脱试验从11种大孔树脂中筛选最适合纯化南五味子总三萜的大孔树脂类型,建立AB-8型树脂纯化南五味子总三萜的吸附动力学模型和等温吸附模型,并计算热力学参数。结果:选择AB-8型树脂,该树脂对南五味子总三萜在0~50 min为快速吸附阶段,50~200 min为缓慢吸附阶段,200 min后为吸附饱和阶段。AB-8型树脂对南五味子总三萜的吸附行为符合准二级吸附动力学方程,吸附速率由液膜扩散和颗粒内扩散共同控制;平衡吸附数据符合Freundlich等温方程,属于多分子层吸附;高温有利于吸附。结论:AB-8型树脂对南五味子总三萜的吸附为熵推动过程,固-液界面上分子运动更为混乱,有更多水分子杂乱地由固体表面向溶液中运动,为南五味子总三萜的纯化工艺优选具有一定指导意义。     

异鼠李素的平衡溶解度及溶解热力学分析

目的:测定异鼠李素在水及正辛醇中的溶解度,计算热力学参数,为异鼠李素剂型设计与体内过程预测提供依据。方法:采用HPLC测定不同温度下异鼠李素在水、正辛醇中的平衡溶解度,测定常温下该成分在正辛醇-水中的表观油水分配系数,流动相甲醇-0.1%甲酸水溶液(70∶30),检测波长370 nm。结果:异鼠李素水溶性差,易溶于正辛醇中,采用Apelblat经典模型对异鼠李素溶解度数据进行拟合,在水、正辛醇中的溶解度拟合方程为lnx_(cal)=879.18-53 895.05/T-126.30ln T(r=0.999 7),lnx_(cal)=-1.32-2 699.36/T+0.35lnT(r=0.999 8),表明该模型拟合结果与实验数据吻合良好。异鼠李素在水和正辛醇中的溶解过程均为吸热和熵增加的过程,常温下异鼠李素的表观油水分配系数P为5 163(lgP=3.71)。结论:异鼠李素为脂易溶性化合物,水溶性较差,通过优化制剂工艺等方法增加其水溶解度可能会提高其口服吸收效率及生物利用度。     

Synthesis and Aqueous Solution Properties of Block Copolyethers with Latent Chemical Functionality

Three series of polyglycidol‐poly(allyl glycidyl ether)‐polyglycidol (PG‐PAGE‐PG) triblock copolymers with ranging PG contents and fixed molar masses of the middle PAGE block are prepared. The copolymers are analogous to the Pluronic, poly(ethylene oxide)‐poly(propylene oxide)‐poly(ethylene oxide) (PEO‐PPO‐PEO), block copolymers in which the chemically inert PEO and PPO are substituted by PG and PAGE, respectively, exhibiting latent chemical functionality. They are prepared by solvent‐free sequential anionic polymerization of allyl glycidyl ether and ethoxyethyl glycidyl ether followed by cleavage of the protective groups. In aqueous solution the block copolymers self‐associate. According to the thermodynamic data, the self‐association is enthalpically favored with a small entropy contribution, which is fundamentally different from that of Pluronic block copolymers. The nanostructures are parameterized by dynamic and static light scattering and visualized by transmission electron microscopy. Data indicate formation of relatively large particles that are identified as compound particles held together by strong hydrogen bonding promoted by the numerous hydroxyl groups from the PG moieties.

     

Microstructure and Thermal Analysis of Metastable Intermetallic Phases in High-Entropy Alloy CoCrFeMo0.85Ni

CoCrFeMoNi high entropy alloys (HEAs) exhibit several promising characteristics for potential applications of high temperature coating. In this study, metastable intermetallic phases and their thermal stability of high-entropy alloy CoCrFeMo_0.85Ni were investigated via thermal and microstructural analyses. Solidus and liquidus temperatures of CoCrFeMo_0.85Ni were determined by differential thermal analysis as 1323 °C and 1331 °C, respectively. Phase transitions also occur at 800 °C and 1212 °C during heating. Microstructure of alloy exhibits a single-phase face-centred cubic (FCC) matrix embedded with the mixture of (Co, Cr, Fe)-rich tetragonal phase and Mo-rich rhombohedron-like phase. The morphologies of two intermetallics show matrix-based tetragonal phases bordered by Mo-rich rhombohedral precipitates around their perimeter. The experimental results presented in our paper provide key information on the microstructure and thermal stability of our alloy, which will assist in the development of similar thermal spray HEA coatings.     

Arsenate Adsorption on Fly Ash,Chitosan and Their Composites and Its Relations with Surface,Charge and Pore Properties of the Sorbents

One of the ways to recycle millions of tons of fly ash and chitin wastes produced yearly is their utilization as low-cost sorbents, mainly for heavy metal cations and organic substances. To improve their sorption efficiency, fly ashes have been thermally activated or modified by chitosan. We aimed to deeply characterize the physicochemical properties of such sorbents to reveal the usefulness of modification procedures and their effect on As(V) adsorption. Using low temperature nitrogen adsorption, scanning electron microscopy, mercury intrusion porosimetry, potentiometric titration and adsorption isotherms of As(V) anions, surface, pore, charge and anion adsorption parameters of fly ash activated at various temperatures, chitosan, and fly ash modified by chitosan were determined. Arsenate adsorption equilibrium (Langmuir model), kinetics (pseudo-second order model) and thermodynamics on the obtained materials were studied. Neither temperature activation nor chitosan modifications of fly ash were necessary and profitable for improving physicochemical properties and As(V) adsorption efficiency of fly ash. Practically, the physicochemical parameters of the sorbents were not related to their anion adsorption parameters.     

Underpotential lithium plating on graphite anodes caused by temperature heterogeneity

Rechargeability and operational safety of commercial lithium (Li)-ion batteries demand further improvement. Plating of metallic Li on graphite anodes is a critical reason for Li-ion battery capacity decay and short circuit. It is generally believed that Li plating is caused by the slow kinetics of graphite intercalation, but in this paper, we demonstrate that thermodynamics also serves a crucial role. We show that a nonuniform temperature distribution within the battery can make local plating of Li above 0 V vs. Li⁰/Li⁺ (room temperature) thermodynamically favorable. This phenomenon is caused by temperature-dependent shifts of the equilibrium potential of Li⁰/Li⁺. Supported by simulation results, we confirm the likelihood of this failure mechanism during commercial Li-ion battery operation, including both slow and fast charging conditions. This work furthers the understanding of nonuniform Li plating and will inspire future studies to prolong the cycling lifetime of Li-ion batteries.

Lithium (Li)-ion batteries with graphite anodes and Li metal oxide cathodes are the dominant commercial battery chemistry for electric vehicles (EVs) (1). However, their cycle lifetime and operational stability still demand further improvements (2–5). During long-term cycling, Li-ion batteries undergo irreversible capacity decay due to decreased utilization of anode/cathode active materials, metallic Li plating, electrolyte dry-out, impedance build-up, or excessive heat generation (6–9). Some of these issues also lead to battery shorting and thermal runaway (10, 11). To enable mass adoption of EVs, increasing efforts have been made to realize the fast charging of Li-ion batteries (12). Under this condition, all of the detrimental factors mentioned above are aggravated (6, 7, 13), further compromising the battery cycling life and safety. As a result, a clear understanding of the failure mechanisms of Li-ion batteries is crucial for their future development.Plating of metallic Li on graphite anodes is a major cause of the capacity decay of Li-ion batteries (6, 7, 12, 14–17). Significant amounts of solid electrolyte interphase (SEI) and dead Li form and remain inactive, leading to an accelerated loss of Li inventory. It is generally believed that the slow kinetics of Li ion intercalation into graphite causes metallic Li plating (14). Three-electrode measurements (18–25) showed that the potential of graphite anodes shifted negatively under increased charging rates and finally dropped below 0 V vs. Li⁰/Li⁺, reaching Li-plating conditions. However, Li-plating phenomenon on graphite anodes is still not fully understood. Firstly, the actual onset potential of Li plating is still unclear, which is not necessarily below 0 V vs. Li⁰/Li⁺ (18). Furthermore, few studies explained why Li plated on graphite in spatially inhomogeneous patterns (7, 14, 17). Most importantly, in some reports, Li plates even under a moderate charging rate below 1.5 C (6, 7). Under these conditions, three-electrode measurements indicate that the anode potential does not drop below 0 V vs. Li⁰/Li⁺ (18). Kinetic arguments alone are not sufficient to resolve these problems, so we hypothesize that previously neglected thermodynamic factors may also play crucial roles in Li plating.It is well-known that the equilibrium electrode potential of a redox reaction shifts with temperature (26–35). Exothermic reactions and joule heating during cycling raise the temperature of batteries (10), which can also build up an internal temperature gradient. Simulations (7, 36–42) and experimental studies (41, 43–49) showed intensified heating under increased cycling rates, and temperature differences of 2 K to nearly 30 K within the batteries (10). This spatial variation in temperature leads to a heterogeneous distribution of the equilibrium potential for both Li plating and graphite intercalation on the anode, which could make Li plating thermodynamically favorable at certain locations.In this paper, we discover that temperature heterogeneities within Li-ion batteries can cause Li plating by shifting its equilibrium electrode potential. We first introduce a method to quantify the temperature dependence of the equilibrium potential for both Li plating and graphite intercalation. Then, we correlate the shift of the equilibrium potential to Li plating using a Li-graphite coin cell with an intentionally created heterogeneous temperature distribution and explain the observation with thermal and electrochemical simulations. Finally, the effects under fast charging conditions are examined. The data explicitly show that metallic Li can plate above 0 V vs. Li⁰/Li⁺ (room temperature) on a graphite anode. The temperature dependence of the equilibrium potential likely participates in the capacity decay of commercial Li-ion batteries, which can be increasingly severe during fast charging conditions. This research brings insights into a key failure mechanism of Li-ion batteries, highlights the importance of maintaining homogeneous temperature within batteries, and will inspire future development of Li-ion batteries with improved safety and cycle lifetime.     

二氟二氯甲烷-1,1-二氟乙烷二元系恒温汽液平衡的研究

用带观察窗的静态平衡器测定了二氟二氯甲烷、1,1-二氟乙烷在常沸点以上的蒸汽压以及该二元系在29.81℃、39.90℃和49.86℃下的加压汽液平衡,获得了温度T、总蒸汽压p、系统总组成Z、系统总量n_T以及汽相体积V~(?)的数据。以物料衡算与由T,p、x推算y的方法相结合,求得了平衡相组成x、y。并进一步用修正的PR及修正的SRK状态方程成功地关联了数据。     

关联高压相平衡的模型比较

用TRK状态方程,采用可调的振荡参数,对48个二元系进行了相平衡关联,并将其准确度分别与a)修正的SRK方程,b)基于对应状态原理的SRK方程及c)利用Huron-Vidal局部组成混合规则的SRK方程相比较。结果发现:TRK方程用了本文改进的计算方法后不仅能加快运算速度,避免发散,且能适用于更多类型的二元系相平衡数据关联;k_(12)(?)k_(21)时的TRK方程与a)、b)、c)相比,占明显优势。     

静态蒸汽总压法研究中压汽液平衡

建立了一套用文题方法测定中压汽液平衡的装置、测压范围为0～7MPa。采用了液体物料集中脱气、液相转移物料、连续进料、以数字式精密压力计测量溶液总蒸汽压的实验方法,每次实验可完成二分之一全浓度范围的测定工作。使用此装置测定了甲醇、丙酮、正戊烷、二氟二氯甲烷(Freon 12)四种纯组分在常沸点以上的蒸汽压以及甲醇-丙酮、二氟二氯甲烷-正戊烷、二氟二氯甲烷-丙酮三对二元系的汽液平衡,获得了温度T、压力P以及系统总组成Z的数据。并进一步用物料衡算与RK状态方程相结合的方法求得了完整的T、p、x、y汽液平衡数据。