Prestructured MXene fillers with uniform channels to enhance CO2 selective permeation in mixed matrix membranes

The packing pattern of two-dimensional (2D) sheet-like fillers in membranes is relatively random, leading to the unfavorable permeability from tortuous diffusion pathway. A new strategy that using prestructured materials with uniform channels as fillers was proposed. In this work, Ti₃AlC₂ is etched to prepare multilayered MXene (m-MXene), the channels aggregate as a whole unit, ensure the impossibility of ineffective packing compared with traditional individual sheets, largely facilitating the selective permeation. Then, the m-MXene/Poly (amide-6-b-ethylene oxide) (Pebax) MMMs are synthesized. SEM images demonstrate the accordion shaped structure of filler, which is the multi-channels laminates. Furthermore, the results of gas permeation test exhibit enhanced performance of m-MXene/Pebax MMMs. MMM with 0.5 wt.% m-MXene behaved best, CO₂ permeability of 86.22 Barrer as well as CO₂/N₂ selectivity of 104.85, transcending the Robeson upper bound (2008). Having distinct enhancement for CO₂ separation, the m-MXene/Pebax MMMs in this work offer prospective practical applications.     

Comparison of liquid-phase and methanol-swelling crosslinking processes of polyimide dense membrane for CO2/CH4 separation

To overcome the plasticization effect in polyimide membranes, many researchers have proposed crosslinking method. This can reduce an inter-segmental mobility by tightening and rigidifying the polymer chains. However, it is difficult to modify the whole polymer chains throughout the membrane because the reaction can be hindered by the diffusion rate of the crosslinker. In particular, it is hard for bulky crosslinker to penetrate a dense membrane with a small d-spacing. This study investigated the effect of crosslinking a dense Matrimid membrane with p-phenylenediamine (p-PDA) via two different crosslinking methods (i.e., methanol-swelling crosslinking process [M-SCP] and liquid-phase crosslinking process [L-PCP]). Most of the crosslinking reaction in M-SCP occurs on the membrane surface due to difficulty in penetration of the bulky p-PDA into the Matrimid dense membrane. In contrast, the L-PCP allows uniform crosslinking across the membrane. The membranes crosslinked using L-PCP showed excellent chemical resistance. Furthermore, the plasticization phenomenon was not observed in the membranes crosslinked using L-PCP with p-PDA more than 15%. Meanwhile, the membrane crosslinked using M-SCP exhibited poor plasticization and chemical resistance properties. These results showed that the L-PCP method can be more effective for the crosslinking of dense membrane to deliver both high plasticization and chemical resistance.     

Thin-film composite forward osmosis membrane prepared from polyvinyl chloride/cellulose carbamate substrate and its potential application in brackish water desalination

Synthesized by the reaction between α-cellulose and m-tolyl isocyanate (MTI), cellulose carbamate (CC) was blended with polyvinyl chloride (PVC) to fabricate substrates for thin-film composite (TFC) forward osmosis (FO) membranes. The introduction of CC into substrates improved both membrane structure and performance. The substrates exhibited higher porosity and hydrophilicity, and better connective pore structure; while rejection layer exhibited better morphology but limited cross-linked degree decrease after the introduction of CC. According to the results, the CC blend ratio of 10% was the optimal ratio. With this blend ratio, the TFC-10 membrane presented favorable water permeability (1.86 LMH/bar) and structure parameter (337 μm), which resulted in excellent FO performance (water flux with a value of 40.40 LMH and specific salt flux with a value of 0.099 g/L under rejection layer faces draw solution [DS] mode when 1 M NaCl and deionized water were utilized as DS and feed solution). In addition, the TFC-10 membrane showed good water flux and low-sulfate ion leakage in the potential application of brackish water desalination.     

Mechanochemically synthesized ZIF-8 nanoparticles blended into 6FDA-TrMPD membranes for C3H6/C3H8 separation

The mixed matrix membranes (MMMs) consisting zeolitic-imidazolate framework-8 (ZIF-8) nanoparticles in a polymer have been of considerable interest in separation applications. The fillers used are mostly synthesized using the solvothermal method. In this study, the ZIF-8 nanoparticles were synthesized using a solvent-less and salt-free mechanochemical method and were added to 6FDA-TrMPD polyimide to prepare MMMs. The single gas permeation of C₃H₆ and C₃H₈ through the MMMs was investigated. The C₃H₆ permeability and C₃H₆/C₃H₈ ideal selectivity of a 20 wt% mechano-synthesized ZIF-8/6FDA-TrMPD MMM were 70% and 32% higher than those of the neat polymer membrane at 0.1 MPa and 308 K, respectively. The C₃H₆/C₃H₈ separation performance of the mechano-synthesized ZIF-8 MMM was similar to that of the conventional solvothermal-synthesized ZIF-8 MMM. This separation performance was in good agreement with the Maxwell model. Temperature and pressure dependence analyses confirmed that the mechano-synthesized ZIF-8 nanoparticles acted as molecular sieves in the MMMs for the C₃H₆ and C₃H₈ permeation.     

Fabrication of Pebax/SAPO mixed matrix membranes for CO2/N2 separation

Mixed matrix membranes (MMMs) were prepared by solvent evaporation method using Pebax-1074 polymer as matrix and inorganic zeolite SAPO-23 as dopant. The morphology, surface functional groups, microstructure, thermal stability, and separation performance of MMMs were analyzed by scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, thermogravimetric analysis, and gas permeation, respectively. The effects of dopant loading amount, permeation temperature, and permeation pressure on the structure and properties of MMMs were investigated. The results showed that the introduction of SAPO zeolite reduced the crystallinity of the MMMs and improved the CO₂/N₂ selectivity. Under the conditions of 30°C and 0.15 MPa, the MMMs prepared by incorporating with 5% SAPO zeolite in content exhibited the highest CO₂/N₂ selectivity of 72.0 together with the CO₂ permeability of 98.2 Barrer.     

Viscoelastic properties and flow instabilities of aqueous suspensions of cellulosic fibers: Effects of a gelation agent on dispersion,rheology, and flow stability

Processing of concentrated lignocellulosic biomass suspensions typically involves the conversion of the cellulose into sugars and sugars into ethanol. Biomass is usually pretreated via methods like comminution or steam explosion to form fine cellulosic fibers to be dispersed into an aqueous phase for further treatment. The resulting cellulose suspensions need to be pressurized and pumped into and out of various processing vessels without allowing the development of flow instabilities that are typically associated with “demixing”, that is, the segregation of the cellulosic biomass from the aqueous phase via the formation of mats of cellulosic fibers and the filtration of the aqueous phase. Such demixing can prevent continuous processing at high rates. Here, the development of flow instabilities via the demixing effect for cellulose suspensions is demonstrated using capillary and compressive squeeze flows. It is shown that the use of a gelation agent, hydroxypropyl guar gum, at the critical concentration of 0.5 wt% or higher significantly affects the viscoelastic material functions of cellulosic suspensions, improves the dispersive mixing of the fibers within the aqueous phase, and results in the elimination of the flow instabilities and associated demixing effects that are ubiquitously observed during the pressurization and processing of cellulosic suspensions.     

聚酯型聚氨酯乳液的合成及性能

以异佛尔酮二异氰酸酯（ IPDI）、六亚甲基二异氰酸酯（HDI）和聚己二酸 1,4-丁二醇酯二醇（ PBA）为主要原料制备系列水性聚氨酯乳液（ WPU）。采用红外光谱仪、差式扫描量热仪、 X-射线衍射仪、电子拉力机等对 WPU进行结构表征;为了从聚集状态上对聚氨酯结晶性有更深层次的探究,对 WPU进行了定伸情况下的测试。结果显示：随着硬段含量的增加,硬段 -软段间的氢键相互作用减小,微相分离程度增加,结晶性能降低;随着伸长率的增加,氢键相互作用和结晶性能都表现出先减小后增大的趋势。当硬段含量为 14. 73%时,聚氨酯胶膜拉伸强度达到 40. 11 MPa,剥离强度为 93. 7 N/（25 mm）。     

中频条件下真空灭弧室的纵向磁场仿真

该文研究了中频400～800Hz条件下纵磁真空灭弧室内的磁场特性,利用Ansys Maxwell求解了三维瞬态纵向磁场分布.由计算结果可知:在电流变化的过程中,中心区域纵向磁场的变化明显滞后于其他区域.电流峰值时在触头片开槽交错放置的位置有磁场峰值区域,电流过零时中心区域有明显剩磁.当频率增加时,涡流效应更明显,使纵向磁场的磁感应强度值减弱.对中心点,频率提高导致过零时剩磁增加,磁场滞后相位更明显,影响电弧扩散.增加触头片开槽数可以减弱涡流效应,而增加触头杯座槽旋转角,触头中间平面磁感应强度的最大值近似线性增加.文中通过分析电弧形态和电压等实验结果验证了磁场滞后对真空灭弧室的开断能力的影响.     

基于复合磁性槽楔的PMLSM推力波动抑制

永磁直线同步电机(permanent magnet linear synchronous motor,PMLSM)存在齿槽力,影响电机的控制性能。 本文提出一 种基于软磁、硬磁材料混搭的新型复合磁性槽楔结构(composite magnetic slot wedge,CMSW),能有效抑制 PMLSM 推力波动。 首 先,分析了单一磁性槽楔的材料、尺寸和空间位置分布对 PMLSM 输出推力和推力波动的变化规律。 然后,研究新型复合磁性 槽楔的软磁、硬磁材料配比和位置分布,对电机输出推力、推力波动和齿槽力等电磁性能的影响。 以最大推力和推力波动最小 为优化目标,利用正交优化法对复合磁性槽楔的尺寸进行优化。 研究表明,采用新型复合磁性槽楔可有效降低推力波动和损 耗,推力波动降低 79. 4%,而平均推力基本不变,为 PMLSM 推力波动抑制提供新的技术途径。     

Fe3O4@TiO2@SiO2@Ag光催化剂的制备及其光催化活性研究

采用溶剂热法和溶胶-凝胶法合成了磁性Fe₃O₄@TiO₂@SiO₂复合光催化剂,再通过巯基改性,使二氧化硅表面原位合成银纳米颗粒,最终形成目标光催化剂。利用XRD、FT-IR、XPS、SEM、VSM等分析测试手段对该催化剂的组成、结构、形貌及其磁学性能进行表征。通过光催化降解40 mL罗丹明B溶液(pH 5.3,30 mg/L),催化剂按1 g/L加入反应体系,光照120 min时,罗丹明B溶液的降解率达96.22%。相同条件重复循环实验10次,罗丹明B溶液降解率仅下降4.32%,表明Fe₃O₄@TiO₂@SiO₂@Ag磁性光催化剂具有出色的光催化活性和循环使用性。