具有限域传质效应的碳基分离膜——从碳纳米管膜到石墨烯膜

限域传质是流体分子通过与其运动自由程相当的传质空间的过程,流体分子与限域壁面的作用与和流体分子间的相互作用决定了传质效率。当碳通道尺寸小于10 nm时,由于其壁面具有无摩擦效应,导致传质阻力小;因此,具有限域传质效应的碳基分离膜传质通量和选择性都高,有望成功突破渗透性和选择性的博弈效应。本文综述了近年来具有限域传质效应的碳基分离膜的研究进展,主要介绍了两类碳基分离膜,规整排列的碳纳米管膜和层层堆叠的石墨烯膜,概述了这两类膜的限域传质机理、构筑方法及其在水处理、脱水、脱盐、离子分离、气体分离等领域的应用。此外,展望了具有限域传质效应的碳基分离膜的发展及需要解决的问题。为创制新一代兼具高渗透性和高选择性的限域传质效应的分离膜的设计制备与应用提供了参考。     

限域传质分离机制初探：界面吸附层的“二次限域”效应

限域传质分离膜主要面向分子/离子水平的高精度分离过程，对解决CO₂分离、共沸物分离、盐湖提锂、海水淡化等重大应用需求具有重要意义。然而目前，这类膜的限域传质机制研究滞后，理论模型缺乏，已不能满足材料和化工等学科高速发展的需求。用介科学观点思考限域传质分离膜同时具有高通量和高选择性这一反常现象，即突破Trade-off效应，这是选择性机制与通量机制之间的竞争与协调导致的。纳微固液界面处流体分子在界面处会优先吸附，形成稳定的吸附层，基于此本文提出了“二次限域”的假说，即界面诱导的类固态新界面会对中间流体再次产生限域效应。通过对比限域传质分离膜的孔道尺寸与二次限域尺寸，进一步认知了二次限域的选择性机制，并结合选择性机制与通量模型对膜通量和选择性的定量预测进行了初探，以期为精密构建限域传质膜提供理论基础。     

智能膜对传质和反应与分离过程的调控

智能膜能响应外界刺激而改变自身的表面特性和膜孔大小,从而改变其选择性和渗透性等性能参数,是化工与材料等交叉学科领域的重要课题。综述了近年来有关智能膜用于跨膜传质过程的调控、亲和分离过程的调控、催化反应过程速率的调控等方面的研究。基于智能膜的传质、反应与分离过程具有条件温和、易于操控、易调控、高效等特点,为简单、高效的传质分离与反应操作提供了新途径和新方法。     

高效分离同碳数烃的先进微孔膜：现状与挑战

热法精馏分离同碳数烃混合物是当前石油化工行业中最耗能的过程之一。膜分离技术具有投资成本和操作费用低、节能降耗和集成度高等优点，可实现低能耗的膜法流程再造。以沸石分子筛和金属有机骨架材料（MOF）为代表的先进微孔膜较传统聚合物膜，具有更高的分离性能；渗透性和分离选择性可提升一至两个数量级，展现出优异的应用前景。本文综述了先进微孔膜在提升渗透性、分离选择性与分离过程稳定性3个方面的研究进展，深入探讨了膜层厚度、孔道取向、骨架柔性和晶间缺陷等微结构调控与同碳数烃分离性能间的构效关系。并且分析了面向同碳数烃高效分离应用的几种沸石膜和MOF膜面积放大制备的瓶颈问题，提出了晶种/成核位点均一性分布在先进微孔膜放大制备中的关键作用。最后对进一步加快新型先进微孔膜材料开发进程以应对石化行业多元化分离体系，以及加大膜工艺技术开发力度以匹配石化行业主流程工艺要求进行了展望。     

无机/有机复合分离膜研究与应用进展

无机/有机复合分离膜既具有聚合物膜的高选择性、高渗透性的优势，又具有无机膜的耐高温、抗腐蚀的优点。开发新型的无机/有机复合分离膜是膜材料领域的热点之一。介绍了无机/有机复合分离膜的特点、结构、制法以及提高复合分离膜渗透性能和选择性的途径。最后对复合分离膜的应用进展作了阐述。     

有机框架膜在气体分离中的研究进展

高渗透性、高选择性和高稳定性的膜材料是决定膜分离过程效率的关键。有机框架膜（organic framework membranes,OFMs）具有孔隙率高、孔道长程有序、易于官能化修饰、稳定性强等特点,在气体膜分离领域具有重要发展前景。综述了有机框架膜的化学组成、结构特征、制备方法及其在二氧化碳捕集与分离、烯烃/烷烃分离及稀有气体分离等气体分离过程中的应用。最后,对有机框架膜在气体分离领域的机遇和挑战进行了总结,并对其发展方向进行了展望。     

气/液膜接触分离过程及其膜材料研究

新型气液膜接触器是很多具有共同特点膜过程的总称,它使用高分子膜将两流体分隔开,膜孔为两流体提供有效传质的场所,与传统分离器相比具有许多独特的优点,日益成为分离科学研究的热点。简述膜接触器在不同气/液分离体系中的应用,针对膜吸收、膜蒸馏、膜结构填料等三种典型的气/液界面膜接触分离过程,从结构、膜材料、传质、分离效率等方面详细进行了分析和比较。着重介绍了近年来相关领域膜材料学的研究进展,如高分子膜材料、成膜方法以及膜材料的改性方法(等离子体改性法、紫外辐照法和表面涂覆改性法等)等。     

离子液体支撑液膜应用研究进展

离子液体作为一种新型绿色介质,受到研究学者的广泛关注。离子液体具有不易燃、无味、无污染、无蒸汽压、可循环使用等独特性质,被广泛应用于化学化工过程中。离子液体用于膜分离技术具有不易挥发、稳定性好的特点,近来对离子液体在支撑液膜方面的研究备受关注,离子液体支撑液膜在污染性气体的吸收分离方面具有高选择性、高渗透性等优势,在有机物的分离方面具有分离效果明显、耐用性强等优势,在化学反应方面具有催化效率高、可循环使用等优势,本文介绍了离子液体支撑液膜的常用制备方法和膜基材料的选择,探讨了离子液体支撑液膜的稳定性和分离选择性的影响因素,对离子液体支撑液膜在气体分离、有机物的分离、化学反应等方面的应用研究进行了综述。     

6FDA-BAPM/DABA聚酰亚胺混合基质膜的制备及其对CO_2分离性能的研究

为了解决聚酰亚胺膜易塑化且渗透性低的问题,利用单体设计和共聚的方法制备了大体积侧基型聚酰亚胺膜[6FDA-BAPM/DABA,n(BAPM)∶n(DABA)为3∶1],并测试了其对CO_2/CH_4等多种气体体系的分离性能。结果表明,所制备的膜具有良好的性能和抗塑化作用。在此基础上通过掺入中空多孔碳纳米球的方法制备了混合基质膜,以获得同时具有高选择性和高渗透性的气体分离膜。结果表明,掺入0.7%填料的膜具有最优性能,CO_2渗透系数达到122.85 Barrer,CO_2/CH_4选择性为63.84。     

分子印迹膜分离技术进展

分子印迹膜是分子印迹技术与膜分离相结合的一种新型的分离膜，具有高度的特异性分子识别能力，在分离工程中有着巨大的潜能。本文介绍了分子印迹技术的基本原理和分子印迹膜的结构特点，分析了分子印迹膜的两种传质机理，“延迟”效应和“促进”效应，简介了当前的研究及应用进展，包括了制备组成的优化手段，实现自组装的主要的合成方法、复合材料的开发以及在药物分离中的应用，提出了分子印迹膜当前存在的问题，最后对其发展进行了展望。     

Preliminary study on mechanism of confined mass transfer and separation: “secondary confinement” effect of interfacial adsorption layer

The confined mass transfer separation membrane is mainly for the high-precision separation process at the molecular/ion level, which is of great significance to solve the application needs of CO₂ separation, azeotrope separation, lithium extraction from salt lake, desalination of seawater and so on. However, at present, the research of the confined mass transfer mechanism of this kind of membrane is lagging behind, and the theoretical models of confined mass transfer are lacking, which can no longer meet the needs of the rapid development of materials and chemical engineering. From the perspective of meso-science, the abnormal phenomenon of high flux and high selectivity of the confined mass transfer separation membrane is considered, that is, breaking through the trade-off effect, which is governed by compromise-in-competition between the selectivity mechanism and the flux mechanism. It is found that the fluid molecules will preferentially adsorb at the interface and form a stable adsorption layer. Based on this, the hypothesis of “secondary confinement” is put forward, that is, the surface induced new solid-like interface will have confinement effect on the intermediate fluid again. By comparing the pore size and the secondary confined size of the confined mass transfer separation membrane, the selective mechanism of the secondary confinement is further confirmed, and the quantitative prediction of the membrane flux and selectivity is preliminarily explored by combining the selective mechanism and the flux model, which may provide a theoretical basis for the precise construction of the limited area mass transfer membrane.     

三相结构离子交换膜的构筑及应用研究

三相结构离子交换膜是一类具有惰性相、离子交换基团相和辅助功能基团相的特殊结构材料。传统两相结构离子交换膜受限于离子通量和选择性的相互制约,难以实现两者同步提升。因此,研究者开始关注新型三相结构,以改善离子传质路径。综述了离子交换膜从两相结构到三相结构的发展,介绍了微相分离离子交换膜、自具微孔离子交换膜、有机硅烷杂化离子交换膜和基于氧化石墨烯或金属有机框架的“三相”结构离子交换膜,讨论了离子膜介尺度中的相结构、孔道结构和缺陷等问题,并概述了三相结构在燃料电池、液流电池、一/二价离子分离和酸碱回收等领域所发挥的作用,以期给三相结构指导离子交换膜制备并提升性能提供策略参考。     

全钒液流电池膜离子选择性传导通道构建的研究进展

全钒液流电池（VFB）具有存储容量大、功率和容量可调、活性物质无交叉污染等优点，在大规模储能领域受到广泛的关注。商业化全氟磺酸膜成本高、离子选择性低的问题，制约了VFB的大规模应用。低成本非氟膜的研究成为主要的研究方向。迄今为止，替代膜面临着离子传导率与选择性之间的权衡问题，同时在强酸性和氧化条件下的化学稳定性也是一个挑战。通过构效关系优化膜内的离子选择性传导通道，是实现高离子选择性传导和高稳定性的关键。本文对基于传统亲水基团的离子选择性传导通道、基于孔径筛分效应的离子选择性传导通道、基于非传统亲水基团的离子选择性传导通道进行分析研究，较为全面阐述了当前VFB膜研究取得的进展及目前面临的问题，并提出了膜内离子选择性传导通道构建的研究方向。     

Tailoring the ionic transfer characteristics of polyvinyl chloride-based heterogeneous ion exchange membranes by embedding carboxy methyl cellulose in membrane channels

Polyvinyl chloride-based heterogeneous cation exchange membranes were modified by embedding carboxy methyl cellulose in ionic transfer channels of membrane. The effect of CMC to PVC blend ratios on properties of membranes was studied. SOM images showed uniform distribution and surfaces for prepared membranes relatively. The SEM images showed uniform and dense structure for the membranes. The XRD pattern also demonstrated amorphous structure for the membranes. Membrane water content was improved from 25 to 39 % by increase of CMC concentration up to 32 %wt. Similar trend was found for membrane surface hydrophilicity. The membrane ion exchange capacity, fixed ion concentration, membrane potential, charge density, transport number, permselectivity, and ionic flux were enhanced initially by increase of CMC ratio up to 16 %wt and then began to decrease by increase in CMC concentration from 16 to 32 %wt. The membrane oxidative stability and areal electrical resistance showed decreasing trends by utilizing of carboxy methyl cellulose in the membrane matrix. Membrane transport number and selectivity were also increased by increase of electrolyte concentration. Similar trend was found for the membrane electrical conductivity by increase of electrolyte concentration. Also prepared membranes showed higher transport number, selectivity, and areal electrical resistance at pH 7 compared to other pH values.     

Concave carrier molecules: selective transport of copper(II) and lead(II) nitrates through supported liquid membranes

Concave 1,10-phenanthrolines 1 are selective and efficient carrier molecules for membrane transport of copper(II) and lead(II) ions. With competitive membrane transport experiments the selectivity patterns of three concave 1,10-phenanthroline membrane carriers have been determined. Measurements with copper(II) and lead(II) nitrates confirmed the predicted selectivities and revealed high transport rates for 1a and 1b . While 1b shows a high preference for copper(II) nitrate, 1a transports lead and copper nitrates equally well, but with much higher flux. In bulk liquid membranes, the carrier mediated ion flux remained constant over an extended period, whereas it decreased significantly in reused supported liquid membranes, which indicates rapid loss of carrier from the membrane under these conditions.     

离子交换膜的发展态势与应用展望

基于离子交换膜的电膜技术,由于其独特的离子传递特性,可以用于离子物系的分离、分级,在清洁生产、节能减排、能量转换等方面有着广泛的应用前景。本文综述了离子交换膜的制备、应用过程以及组件设计等方面的前沿性进展,并对亟待解决的问题和未来的发展方向作了展望。关于膜的制备,提出了从二相到三相、从致密到微孔的新型离子交换膜结构,开发了电纳滤膜并用于一价或多价离子的分离,通量和选择性均得到提高,实现了膜功能的多样化。在应用过程中,实现了扩散渗析和电渗析过程的集成,分离效果优越,生产成本降低。同时对膜组件进行优化,设计开发出新型的卷式组件,克服了传统板式组件的诸多缺陷。值得一提的是,离子分离膜的应用领域也由初级水处理扩展到复杂物料的分离与纯化。以上研究成果将为离子交换膜的发展提供指导,加快其工业化进程。     

Carbon nanotube-nanoporous anodic alumina composite membranes with controllable inner diameters and surface chemistry: Influence on molecular transport and chemical selectivity

This work presents the fabrication of carbon nanotube composite membranes with controllable nanotube dimensions (inner diameters and lengths) and surface chemistry and explores their influence on the transport properties and chemical based transport selectivity. These membranes were prepared by growing of vertically aligned multiwalled carbon nanotubes (MWCNTs) inside nanoporous anodic alumina membranes (NAAMs) through a catalyst-free chemical vapour deposition (CVD) approach. The deposition time during CVD process and the length of NAAMs were used to control nanotube dimensions. The thermal annealing and wet and dry oxidation processes were used to control the surface chemistry of inner walls of nanotubes from highly graphitic-hydrophobic to oxygen rich and hydrophilic. The structural features and chemical composition of the prepared membranes are characterised by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. The influence of the nanotube dimensions and surface chemistry on molecular transport properties of prepared membranes are assessed by analysing the transport of two models molecules with different hydrophilic–hydrophobic and charge properties. The obtained results reveal that the diffusional flux of model molecules through CNTs-NAAMs can be controlled by nanotube dimensions and surface chemistry of graphitic surface and these parameters can be used to tailor their chemical based molecular separation for specific applications.     

Modeling ideal selectivity variation in nanoporous membranes

A parallel resistance transport model has been developed to describe variations in separation ability (quality) of nanoporous carbon membranes. The model considers transport through high-selectivity, high-resistance nanopores in combination with low-selectivity, low-resistance defect pores. Although few in number or small as a percentage of membrane area, these low-selectivity pores exert a disproportionate influence on permeation. The predictive qualities of the model are demonstrated using permeation data from the literature. Using flux ratios of oxygen to nitrogen, we can predict the area fraction (α) of defect pores. At an area fraction of only 10⁻⁹ defect pores, the oxygen-to-nitrogen ratio falls to near unity—indicating no selectivity for oxygen. Although developed for nanoporous carbon membranes, the approach will work for zeolitic and other forms of nanoporous membranes.     

Pervaporation separation of water/ethanol mixture using asymmetric ion‐exchange membranes containing aluminum ions

The asymmetric aluminum ion exchange polysulfone membranes have successfully been prepared for the dehydration of ethanol‐water mixture. The relationship between the membrane morphology, separation performance, and the ion content of membranes were discussed in this study. The experimental results showed that the separation performance of those membranes was increased upon increasing the degree of aluminum ion exchange in polysulfone membranes. Both permeation rate and separation factors of those membranes increased with increasing the degree of ion exchange. The increase in separation performance of aluminum ion exchange membranes was mainly attributed to ion crosslinking in polymer network and the hydration effects of exchanged ion in membranes. On the other hand, the operating temperature in the PV process showed a significant influence on the dehydration of water molecules in the permeate. An increase in temperature increased the permeation flux of permeate but slightly decreased its selectivity. The aluminum asymmetric ions in membranes showed a strong influence on permselectivity of asymmetric ion exchange membranes. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007