Influence of α′‐/α‐crystal polymorphism on properties of poly(l‐lactic acid)

Poly(l ‐lactic acid) (PLLA) is a biodegradable and biocompatible thermoplastic polyester produced from renewable sources, widely used for biomedical devices, in food packaging and in agriculture. It is a semicrystalline polymer, and as such its properties are strongly affected by the developed semicrystalline morphology. As a function of the crystallization temperature, PLLA can form different crystal modifications, namely α′‐crystals below about 120 °C and α‐crystals at higher temperatures. The α′ modification is therefore of special importance as it may be the preferred polymorph developing at processing‐relevant conditions. It is a metastable modification which typically transforms into the more stable α‐crystals on annealing at elevated temperature. The structure, kinetics of formation and thermodynamics of α′‐ and α‐crystals of PLLA are reviewed in this contribution, together with the effect of α′‐/α‐crystal polymorphism on the properties of PLLA. © 2018 Society of Chemical Industry     

基于数值计算方法计算最大反应速率到达时间

最大反应速率到达时间(TMR_ad)是化工工艺热风险评估中一个十分重要的参数。一般计算TMR_ad的方法是基于N级模型的分析。但对于复杂的反应过程统一采用N级模型分析计算可能会引起较大偏差甚至得到错误的评估。因此,提出运用基于反应类型的数值计算方法进行TMR_ad和T_D24的评估,通过分别代表N级反应和自催化反应的20% DTBP甲苯溶液和CHP的ARC测试分析表明：对于N级反应,该方法能可靠地用于TMR_ad和T_D24的求取;而对于自催化反应,尽管拟合效果很好,原有方法计算偏差很大,原因是不同模型下动力学参数不同,还进行偏差大小分析。由此可知该数值计算方法有广泛的适用性,对于放热曲线,需在了解其反应类型的基础上利用该方法进行TMR_ad和T_D24的评估,由此评估的结果更为可靠准确。     

悬浮床加氢脱硫尾气水蒸气转化制氢热力学

以悬浮床加氢脱硫尾气为水蒸气转化制氢原料,采用改进的原子序数矩阵法构建了包含6个独立反应的化学反应体系。分别考察各个独立反应在不同反应温度下,标准摩尔反应焓、吉布斯自由能变及平衡常数的变化规律;借助HYSYS流程模拟软件中的GIBBS反应器,研究反应器出口温度、反应压力及水碳物质的量之比对产物平衡组成的影响。热力学研究结果表明：烷烃碳数越高,水蒸气转化反应的平衡常数、吉布斯自由能变和标准摩尔焓对温度的敏感性越高,达到相同转化效果所需的反应温度越低。HYSYS模拟确定该体系下最适宜的反应条件为反应器出口温度700℃、反应压力100kPa、水碳物质的量之比4。     

PS-HQD树脂吸附废水中Cu~(2+)的动力学与热力学研究

为进一步探讨8-羟基喹哪啶树脂(PS-HQD)吸附废水中Cu~(2+)的吸附机理,用静态法研究了PS-HQD吸附Cu~(2+)的动力学与热力学规律等吸附性能。结果表明:在实验条件下,ΔH0、ΔS0说明PS-HQD对Cu~(2+)的吸附过程为吸热的熵增过程,ΔG0表明吸附过程能够自发进行,准二级动力学Lagergren方程更适合描述此吸附过程。PS-HQD第5次吸附的再生效率仍可达到83.84%,说明PS-HQD对Cu~(2+)的吸附具有良好的再生性能。     

Exergy：热力学第二定律的实践者

大多数研读热力学的学生都对熵抽象的观念感到痛苦。尤其甚者,他们对热力学第二定律的陈述及如何应用都觉得困惑。这篇短文借着Smith等人著名热力学教科书上的范例阐述有效能量（Exergy）的观念,并进而彰显热力学第二定律的意涵。     

棉花模板Zn/Ti/Fe-LDO吸附水中硝酸盐机制

通过共沉淀-焙烧法制备以棉花为模板的Zn/Ti/Fe焙烧态类水滑石（YLDO）和无棉花模板的Zn/Ti/Fe焙烧态类水滑石（NLDO）,运用SEM、N₂吸附法、FTIR和XRD对其进行表征,考察YLDO和NLDO对水中硝酸盐的吸附机制及其紫外光催化再生的机理。结果表明,YLDO在形态中引入棉花的遗迹,比表面积增大为74.8 m²·g^-1,大孔数量增加;在化学成分上引入了C元素,提高了吸附性能;形成磁性物质,可通过磁性分离回收。pH为7、298 K时,YLDO对水中硝酸盐的最大吸附量为66.57 mg·g^-1,比NLDO增加了22.6%。YLDO和NLDO吸附硝酸盐的吸附等温线符合Langmuir方程,吸附动力学可用准二级动力学方程来描述,吸附热力学研究表明吸附过程为自发吸热过程。吸附饱和的YLDO和NLDO可在紫外光照射下再生,5次再生循环后仍保持较高的吸附性能。YLDO可通过吸附-磁分离-紫外光催化再生工艺有效去除水中硝酸盐,不产生二次污染,在硝酸盐废水处理中具有潜在的应用前景。     

Kinetic,thermodynamic parameters and in vitro digestion of tannase from Aspergillus tamarii URM 7115

Tannase is an enzyme used in various industries and produced by a large number of microorganisms. The aim of this study was to evaluate tannase production to determine the biochemical, kinetic, and thermodynamic properties and to simulate tannase in vitro digestion. The tannase-producing fungal strain was isolated from “jamun” leaves and identified as Aspergillus tamarii. Temperature at 26°C for 67?h was the best combination for maximum tannase activity (6.35-fold; initial activity in Plackett–Burman design—15.53?U/mL and average final activity in Doehlert design—98.68?U/mL). The crude extract of tannase was optimally active at 40°C, pH 5.5 and 6.5. Moreover, tannase was stimulated by Na⁺, Ca²⁺, Mg²⁺, and Mn²⁺. The half-life at 40°C lasted 247.55?min. The free energy of Gibbs, enthalpy, and entropy, at 40°C, was 81.47, 16.85, and ?0.21?kJ/mol?·?K, respectively. After total digestion, 123.95% of the original activity was retained. Results suggested that tannase from A. tamarii URM 7115 is an enzyme of interest for industrial applications, such as gallic acid production, additive for feed industry, and for beverage manufacturing, due to its catalytic and thermodynamic properties.     

Ultrastable Host–Guest Complexes and Their Applications

This review describes monovalent synthetic receptor–ligand (or host–guest) pairs with extremely high binding affinity, comparable to that of the biotin–avidin pair, and their applications. Cucurbit[7]uril (CB[7]), a member of the host family cucurbit[n]uril (CB[n], n=5–8, 10), forms ultrastable host–guest complexes with ferrocene-, adamantane- or bicyclo[2.2.2]octane-based molecules having ammonium groups properly positioned to interact with the carbonyl oxygens at the portals of CB[7]. The extremely high affinity is achieved by a large enthalpic gain arising from the near perfect size/shape complementarity between the rigid CB cavity and the rigid core of the guest molecules, with the critical assistance of the positive entropy change due to the extensive dehydration of the host and guest. The high stability of the complexes allowed us and others to explore several biological applications such as immobilization of biomolecules on a solid surface, protein isolation, triggering intracellular events, and regulating enzymatic activities. These complexes with their exceptional affinity, chemical robustness, simple preparation, biocompatibility, and easy handling may replace the biotin–(strept)avidin system in diverse areas of research, including affinity chromatography, high throughput biochemical assays, imaging, and sensor technologies.     

Computational screening of metal‐organic frameworks for xenon/krypton separation

A variety of metal‐organic frameworks (MOFs) with varying linkers, topologies, pore sizes, and metal atoms were screened for xenon/krypton separation using grand canonical Monte Carlo (GCMC) simulations. The results indicate that small pores with strong adsorption sites are desired to preferentially adsorb xenon over krypton in multicomponent adsorption. However, if the pore size is too small, it can significantly limit overall gas uptake, which is undesirable. Based on our simulations, MOF‐505 was identified as a promising material due to its increased xenon selectivity over a wider pressure range compared with other MOFs investigated. © 2010 American Institute of Chemical Engineers AIChE J, 2011