限域传质分离膜

阐述了限域传质分离膜的研究背景及现状,分析了该领域面临的关键科学问题及研究思路,介绍了我国在此领域的研究进展,并提出了未来的发展方向。     

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。     

氧化石墨烯分离膜的性能调控及其传质机理研究进展

氧化石墨烯（GO）作为理想的膜构筑材料,因其蜂窝状的结构特点及表面分布大量含氧基团的特性,被广泛用于水处理分离膜的构筑。GO膜具有良好的物理特性、优异的化学稳定性和独特的二维层状结构,在污水处理、脱盐和离子筛分等水处理领域备受关注。在水处理中,GO膜对有机物和离子有较好的截留效果,但也存在水通量低、稳定性差等问题。本文分析了近年来GO膜在水处理领域的研究新进展;简单总结了GO膜的制备方法和水处理应用;重点阐述了GO水处理膜分离性能优化的方法和传质机理的研究进展;最后总结并展望了GO膜在结构调控和性能提升方面的发展方向。本文为设计和制备高性能GO水处理膜提供参考。     

功能化碳纳米管/聚合物复合分离膜

碳纳米管不仅具有优异的力学性质和超大的比表面积,同时具有优良的传输特性,将其添加到聚合物中制备复合分离膜,具有广阔的应用前景。通过化学改性将碳纳米管功能化,提高其在聚合物中的分散性,制备碳纳米管/聚合物复合膜。本文在介绍了碳纳米管功能化、碳纳米管/聚合物复合膜制备方法的基础上,综述了功能化碳纳米管的加入对复合分离膜亲水性、水通量、机械稳定性以及分离等性能的影响。总结了近年来对碳纳米管在聚合物膜内定向排列的研究进展及碳纳米管定向对复合膜相关性能的影响。由于碳纳米管材料的各向异性,利用电场、磁场及流场等对碳纳米管在聚合物膜内的分布进行定向,从而充分利用其优异的性能,是该类复合膜的研究方向。     

石墨烯基CO2分离膜通道微环境调控研究进展

石墨烯作为一种具有单原子层厚度的二维纳米片,凭借石墨烯基独特的物理性质,已成为高性能碳捕集膜的构筑单元。石墨烯基纳米片超薄的厚度有助于制备超薄膜以提升分离膜的通量,此外可调的物理化学性质赋予石墨烯二维通道内多样的微环境。以CO₂分离膜内多重传质机理为出发点,重点介绍近年来石墨烯基CO₂分离膜二维通道物理化学微环境精密调控的策略及进展,期望对石墨烯基CO₂分离膜的理性设计和可控制备提供清晰思路。     

磷酸三丁酯/煤油支撑液膜体系中苯酚的传质分离

研究了苯酚在以多孔聚丙烯平板膜(Celgard2500)为支撑体、磷酸三丁酯(TBP)为膜载体和煤油为膜溶剂的支撑液膜体系中的传质过程;用传统萃取法测定了TBP/煤油体系中苯酚络合物摩尔比为1∶1,同时得到25.0℃萃取平衡常数为96.72;考察了原料相pH值、初始质量浓度、膜二侧转速、载体浓度和反萃取相碱浓度对苯酚传质的影响,确定了该体系分离苯酚的最佳条件:原料相pH<9,苯酚初始质量浓度<1 000 mg/L,膜二侧转速>300 r/m in,载体浓度为0.55 mol/L,反萃取相碱浓度0.10 mol/L;根据双膜理论提出苯酚的传质动力学方程,采用直线斜率法计算了苯酚在TBP/煤油支撑液膜体系中的扩散层厚度和膜内扩散系数,计算结果表明动力学方程计算值能较好地与实验值吻合,平均相对误差在2%以内。     

聚多巴胺-氧化石墨烯-碳纳米管层状复合脱盐膜的制备及性能稳定性研究

二维纳米材料氧化石墨烯(GO)可通过层层堆叠成膜、构建层间毛细孔道,用于脱盐应用.然而,GO膜在运行过程中的渗透性能及其稳定性都有待提升.以亲水的碳纳米管(CNTs)为改性物,在聚多巴胺(PDA)修饰的基膜上交替喷涂多层GO(MLGO)和CNTs,制备出了多元层状复合脱盐膜.当MLGO-CNTs的单位面积质量为72 mg/m2时,复合膜在5 bar操作压力下对1 g/L Na2SO4溶液的盐截留率最高达到92.8%,水通量最高可达到4.8 L/(m2·h·bar),较PDA-MLGO膜提高了71.4%.在400 h的连续错流过滤实验中,复合膜的水通量稳定性高于PDA-MLGO膜.CNTs的管内空间和MLGO-CNTs组装间隙为复合膜引入了有效的渗透通道.     

木头基纤维素/石墨烯分离膜制备及污染物分离性能

利用酸性亚氯酸钠和氢氧化钠溶液,脱除巴沙木中木质素和半纤维素,制得纤维素薄膜,研究该薄膜微观结构、元素分布与组成、浸润性等方面性能。结果表明,经化学法剥离后的纤维素吸附剂对染料亚甲基蓝的吸附容量可达120.0mg/g,与Langmuir和Temkin模型均能较好地符合。随着膜孔径的收缩和氧化石墨烯（GO）的负载,纤维素膜对抗生素的截留性能大大增强。在0.3MPa通液压力下,纤维素/GO膜的纯水通量提高至原通量的13.5倍[由56.5L/（m²·h）到764.1L/（m²·h）];纤维素/GO膜对环丙沙星的截留率可达65.6%（纤维素膜对环丙沙星截留率为50.9%）。     

氧化石墨烯/碳纳米管水泥基复合材料的抗冻性研究

氧化石墨烯和碳纳米管都是碳基纳米材料,具有强度极高、比表面积极大和导电性能极好等优异性能.通过试验研究了不同掺量的氧化石墨烯和碳纳米管对水泥基复合材料抗冻性的影响;结果表明:300次冻融循环后试件的质量损失率和强度损失率揭示了氧化石墨烯和碳纳米管在改善水泥基复合材料抗冻性的作用,氧化石墨烯掺量为0.08％碳纳米管掺量为0.15％的试件在300次冻融循环后有最小的质量损失率和强度损失率;并用图形分析软件Image Pro Plus对试件的孔结构进行了定量分析,从孔结构的优化和水泥石强度增大等方面解释了作用机理.     

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.     

碳纳米管填充PDMS膜的渗透汽化性能

将碳纳米管（CNTs）填充到PDMS中制备出CNTs/PDMS杂化膜,并将其用于乙醇/水体系的分离,发现由多壁碳纳米管制备的膜分离性能优于单壁碳纳米管填充膜,在40℃下,进料乙醇浓度为5%（质量分数）时,膜的分离因子可由8.3提高到10.0,渗透通量为206.2 g·（m²·h）^-1;采用十二烷基三氯硅烷对多壁碳纳米管进行修饰,并对修饰前后碳纳米管的性能进行表征,研究表明修饰后碳纳米管表面形成疏水层,碳纳米管的疏水性增强;将修饰后的碳纳米管填充到PDMS中,可进一步提高杂化膜对乙醇的选择性,膜的分离因子可提高到11.3,渗透通量为130.9 g·（m²·h）^-1。     

Effect of Raw Multi-Wall Carbon Nanotubes on Morphology and Separation Properties of Polyimide Membranes

Raw multi wall carbon nanotubes (r-MWCNTs) were embedded as fillers inside the polyimide (PI) matrix and PI/r-MWCNTs mixed matrix membranes were fabricated by the phase inversion method. The TEM images and permeation results using helium as test gas showed that r-MWCNTs were generally closed ended and acted as impermeable nano particles. Gas permeation tests using CO₂ and CH₄ showed that the addition of r-MWCNTs into the dope solution increased the CO₂/CH₄ separation factor while decreasing the carbon dioxide and methane permeances. When the r-MWCNTs content was increased from 0% to 6 wt.%, permeance of CO₂ in the flat sheet mixed matrix membranes decreased from 9.15 GPU to 5.49 GPU and CO₂/CH₄ separation factor increased from 19.05 to 45.75. Identical to flat sheet mixed matrix membranes, the addition of 2 wt.% r-MWCNTs into a spinning dope increased the CO₂/CH₄ separation factor from 46.61 to 72.20. The glass transition temperature of the mixed matrix flat sheet membranes increased with an increase in the r-MWCNTs content. This implies a good segmental-level attachment between the two phases that forms a rigidified polymer region at the polymer/r–MWCNTs interface. FESEM images showed well dispersed r-MWCNTs in the polymer matrix at a loading of 2 wt% r-MWCNTs.