氦气提纯技术发展现状与应用分析

为实现氦气资源的循环利用,有必要对氦气进行回收纯化。文中对目前国内外氦气的提纯技术发展现状进行了分析介绍,并综合分析比较了这些方法的应用原理、优缺点及发展趋势,针对各自的使用特点,给出了几种详细的提纯工艺实现方法,为促进我国氦气提纯技术的发展提供了新的思路。     

SELECTIVE ALKYLATION/ACYLATION OF DI- OR TRIANIONS: EXPEDITIOUS DERIVATIZATION OF ENDOTHELIN ANTAGONISTS[1]

ABSTRACT

Sitaxsentan sodium (1, TBC11251Na) is an ET_A selective endothelin antagonist under clinical development for pulmonary arterial hypertension and congestive heart failure. Second generation compounds, as exemplified by TBC2576 (2) are currently under development in our laboratories. To rapidly access analogs of 1 and 2, a route was developed for the selective alkylation or acylation of the corresponding di- or trianions derived from these two highly functionalized compounds. We report here on this straightforward, yet effective, procedure consisting of treating the di- or trianions with an excess amount of electrophiles, followed by a rapid quench. In this manner, selective alkylation or acylation of 1 and 2 was achieved with satisfactory yields.     

钼酸根阴离子印迹陶瓷膜的制备与吸附性能

以三氧化二铝陶瓷膜为载体,以钼酸根阴离子为模板离子,1-乙烯基咪唑为功能单体,1,6-二溴己烷为交联剂,采用表面印迹和接枝聚合方法制备了能选择性吸附Mo(Ⅵ)的新型印迹陶瓷膜(IIP-PVI/CM).采用红外光谱、X射线光电子能谱、热重分析及扫描电子显微镜等方法对陶瓷膜进行结构表征.研究了pH值对吸附性能的影响,当pH值范围为2~4时,IIP-PVI/CM具有良好吸附能力;动力学和热力学结果表明,IIP-PVI/CM对Mo(Ⅵ)的吸附符合准二级动力学模型和Langmuir吸附模型;当pH=4.0和温度为30℃时,IIP-PVI/CM对Mo(Ⅵ)具有良好选择性,Mo(Ⅵ)对W(Ⅵ)的选择性系数高达7.48;动态吸附结果表明,IIP-PVI/CM对W(Ⅵ)和Mo(Ⅵ)的吸附饱和时间分别为24和47 min,饱和吸附量分别为0.163和0.672 mmol/100 g,动态吸附时IIP-PVI/CM亦具有良好选择性;经9次吸附与解吸后,IIP-PVI/CM对Mo(Ⅵ)吸附容量仍可达到初始值的92%,再生和循环使用性能良好.     

Off-resonance frequency filtered magnetic resonance imaging

One of the main problems with rapid magnetic resonance imaging (MRI) techniques is the artifacts that result from off-resonance effects. The proposed off-resonance frequency filtered MRI (OFF-MRI) method focuses on the elimination of off-resonance components from the image of the observed object. To maintain imaging speed and simultaneously achieve good frequency selectivity, MRI is divided into two steps: signal acquisition and post-processing.     

Selective separation of lambdacyhalothrin by porous/magnetic molecularly imprinted polymers prepared by Pickering emulsion polymerization

Porous/magnetic molecularly imprinted polymers (PM‐MIPs) were prepared by Pickering emulsion polymerization. The reaction was carried out in an oil/water emulsion using magnetic halloysite nanotubes as the stabilizer instead of a toxic surfactant. In the oil phase, the imprinting process was conducted by radical polymerization of functional and cross‐linked monomers, and porogen chloroform generated steam under the high reaction temperature, which resulted in some pores decorated with easily accessible molecular binding sites within the as‐made PM‐MIPs. The characterization demonstrated that the PM‐MIPs were porous and magnetic inorganic–polymer composite microparticles with magnetic sensitivity (M_s = 0.7448 emu/g), thermal stability (below 473 K) and magnetic stability (over the pH range of 2.0–8.0). The PM‐MIPs were used as a sorbent for the selective binding of lambdacyhalothrin (LC) and rapidly separated under an external magnetic field. The Freundlich isotherm model gave a good fit to the experimental data. The adsorption kinetics of the PM‐MIPs was well described by pseudo‐second‐order kinetics, indicating that the chemical process could be the rate‐limiting step in the adsorption of LC. The selective recognition experiments exhibited the outstanding selective adsorption effect of the PM‐MIPs for target LC. Moreover, the PM‐MIPs regeneration without significant loss in adsorption capacity was demonstrated by at least four repeated cycles.     

On the difference in material structure and fatigue properties of nylon specimens produced by injection molding and selective laser sintering

This paper describes the influence of dynamic tension/compression loading on notched and unnotched nylon specimens fabricated by Injection Molding (IM) and Selective Laser Sintering (SLS). The main objective of this work is to analyze and describe the differences in material structure and fatigue properties of as-built nylon parts produced by IM and SLM from the same polyamide 12 powder. The differences in dimensional quality, density, surface roughness, crystal structure and crystallinity are systematically measured and linked to the mechanical fatigue properties. The fatigue properties of the unnotched SLS specimens are found to be equal to those of the unnotched IM specimens. The presence of pores in the sintered samples does not lead to rapid failure, and the microvoid coalescence failure mechanism is delayed. The notched specimens show more brittle failure and increased fatigue resistance which is caused by local notch-strengthening. The results enable improved understanding of the difference in material structure and fatigue behavior of selective laser sintered and injection molded polyamide.     

Ni基催化剂催化燃油重整耦合选择性催化还原NOx反应

分别以La₂O₂CO₃, CeO₂, ZrO₂和Al₂O₃为载体, 采用浸渍法制备了Ni基重整催化剂, 并以正十二烷模拟车载燃油进行催化重整反应以同时制备小分子碳氢化合物(HCs)和H₂, 考察了其在4wt%Ag/Al₂O₃上选择性催化还原(HC-SCR)氮氧化物(NO_x)的性能. 采用N₂吸附-脱附、X射线粉末衍射、H₂程序升温还原和热重等手段对Ni基催化剂进行了表征. 结果表明, 随着重整催化剂氧化还原性能增强, 产物中H₂浓度增加, 可参与SCR反应的HCs含量减少, 从而导致重整-SCR耦合体系上NO_x净化活性温度窗口向低温移动, NO_x最高转化率降低. Ni/ZrO₂+Ag/Al₂O₃耦合体系中H₂/HCs符合SCR反应所需的最优比例, 在柴油车典型排气温度范围内表现出良好的NO_x净化能力. 同时, 在Ni/ZrO₂+Ag/Al₂O₃耦合体系上考察了其燃油重整-SCR的活性稳定性. 结果显示, 重整催化剂的耐久性有待进一步提高.     

Ammonium Determination in Water Samples by Using Opa-Nac Reagent: A Comparative Study with Nessler and Ammonium Selective Electrode Methods

A selective and sensitive method based on the ammonium derivatisation with o -phthaldialdehyde (OPA) and N -acetyl-cysteine (NAC) has been developed for ammonium determination in real water samples. The proposed procedure has been compared with ammonium reference methods such as Nessler reagent method and ammonium selective electrode. All procedures have been chemometrically tested and compared in terms of the main analytical properties. These procedures have been used to determine ammonium in unknown water samples. The OPA-NAC reagent method does not present any systematic error (proportional or constant), while Nessler reagent presents both of them for some samples assayed. The ammonium selective electrode is free of corrigible systematic errors, however presents amine interference. The OPA-NAC ammonium method is able to achieve a detection limit (LOD) of 0.07 mg/L in the sample, with a linear dynamic range up to 1.4 mg/L of ammonium.     

On Resin Modification of Monosaccharides

Ellman's dihydropyran resin was used for selective protection of monosaccharide thioglycosides and glycosides. Following on‐resin acylation and subsequent cleavage of the polymer‐bound intermediates, product components having selectively unblocked hydroxyl functions could be obtained.      

MnOx/Al-SBA-15的结构性质及低温NH3选择性催化还原NOx

采用后合成法制备MnO_x/Al-SBA-15催化剂, 考察了催化剂的低温NH₃选择性催化还原(SCR)NO_x的性能. 利用傅里叶透射红外变换(FTIR)光谱、N₂吸附-脱附、X射线衍射(XRD)、扫描电镜(SEM)、拉曼光谱(Raman)、X射线光电子能谱(XPS)及NH₃程序升温脱附(NH₃-TPD)的表征手段, 对催化剂的结构性质和SCR性能进行了系统分析. 结果表明, 适量Al的掺杂能提高MnO_x/SBA-15催化剂的SCR活性, 当硅铝摩尔比为50时, 催化剂活性最佳. 表征结果显示, Al掺杂后, 催化剂仍保持良好的骨架结构, 较大比表面、孔容和孔径, 并且Mn在催化剂表面富集, 由低价态转化为高价态, MnO₂为催化剂的主要活性相. 此外, Al的掺杂使MnO_x在催化剂表面高度分散, 表面酸性增强, 从而提高了催化剂的SCR活性.