大尺寸陶瓷膜原子层沉积过程的CFD模拟

陶瓷膜具有耐高温、耐酸碱、强度高等优点,在液体分离领域得到了广泛应用。对陶瓷膜进行表面改性,可进一步提升其性能,但基于表面化学反应的改性方法工艺过程复杂,难于控制。原子层沉积(atomic layer deposition,ALD)是基于表面自限制化学反应过程的气固相薄膜沉积技术,可以在纳米尺度精确调控孔道结构,特别适用于多孔分离膜的改性和功能化。目前尚无适用于大尺寸陶瓷膜的ALD设备,需要对ALD过程进行专门的优化设计。通过CFD模型对1 m长的单通道陶瓷膜的ALD过程进行了研究,在数学模型中考虑了两种气体源交替进入腔体中所引发不同的表面反应,并考虑了脉冲边界的影响。模拟计算结果与实验比较平均相对误差为1.69%。在数值模拟的基础上,提出了双向交替旋转脉冲的ALD模式,为陶瓷膜的ALD沉积改性的装备设计和过程优化提供了理论依据。     

原子层沉积氧化锌功能化碳纳米管织物及其光催化特性

以二乙基锌和去离子水为前驱体,利用原子层沉积(ALD)在自支撑碳纳米管(CNT)织物上沉积氧化锌(ZnO)对其进行了功能化;考察了ALD沉积过程中功能化织物的微观形貌、晶型结构、表面性质及光催化性能.实验结果表明,ZnO最初在CNTs表面生长为纳米颗粒,随ALD循环次数的增加,逐渐形成包覆CNTs的保形生长层,改变AL...     

抗污染陶瓷膜改性及其在处理含油污水中的应用

陶瓷膜是处理含油污水最有前景的方法之一。膜污染是处理过程中不可避免的现象，导致能耗增加和寿命降低，因此提高陶瓷膜在含油污水处理中的抗污染性非常重要。首先总结了陶瓷膜的各种改性方法，对比了改性陶瓷膜的性能。除了传统的溶胶-凝胶法和浸涂法外，原子层沉积法在控制层厚度和调整孔径方面也有望用于陶瓷膜改性。增强表面亲水性和表面电荷是提高陶瓷膜处理含油污水性能的两种最常用策略。纳米金属氧化物，如TiO₂、ZrO₂和Fe₂O₃以及氧化石墨烯被认为是陶瓷膜改性的潜在候选物，用于提高通量和降低污染。被动抗污陶瓷膜，例如光催化和带电陶瓷膜，在污垢控制、油截留和通量增强方面展现出潜力。最后对陶瓷膜的市场规模和发展趋势进行了展望，指出必须加速高端抗污染陶瓷膜的研发，以满足更复杂的含油污水处理，例如油田含聚污水、压裂返排液等。     

润湿性对纳米多孔陶瓷膜输运性能的影响

为了实现复杂环境中高效回收水资源,采用先进的膜技术,基于建立的半连续超临界相反应改性实验装置对纳米多孔陶瓷膜分别进行亲水和疏水表面改性,通过接触角测量、微观结构观测等方法对润湿改性前后的纳米多孔陶瓷膜进行表征。基于单管管外水蒸气冷凝传热实验系统,对润湿改性前后的纳米多孔陶瓷膜进行了冷凝液输运特性的实验研究,揭示了混合气体温度、冷却水流速、跨膜压差和水蒸气体积分数等典型运行参数对纳米多孔陶瓷膜的冷凝液输运通量的影响规律与机理。同时,采用分子动力学方法,构建了水在不同润湿性纳米孔内输运模拟体系,研究水分子在不同润湿性纳米孔内的输运规律。     

润湿性对纳米多孔陶瓷膜输运性能的影响

为了实现复杂环境中高效回收水资源,采用先进的膜技术,基于建立的半连续超临界相反应改性实验装置对纳米多孔陶瓷膜分别进行亲水和疏水表面改性,通过接触角测量、微观结构观测等方法对润湿改性前后的纳米多孔陶瓷膜进行表征。基于单管管外水蒸气冷凝传热实验系统,对润湿改性前后的纳米多孔陶瓷膜进行了冷凝液输运特性的实验研究,揭示了混合气体温度、冷却水流速、跨膜压差和水蒸气体积分数等典型运行参数对纳米多孔陶瓷膜的冷凝液输运通量的影响规律与机理。同时,采用分子动力学方法,构建了水在不同润湿性纳米孔内输运模拟体系,研究水分子在不同润湿性纳米孔内的输运规律。     

面向过程工业的陶瓷膜制备与应用进展

陶瓷膜具有优异的化学稳定性、机械稳定性及分离性能,在过程工业中获得了成功应用,成为我国膜领域中最有国际竞争力的膜品种之一。本文基于面向应用过程的膜材料设计的理论框架,系统概述了陶瓷膜的定量制备技术、面向应用体系的陶瓷膜选择与设计方法以及膜应用过程中污染控制的研究进展,并对未来我国陶瓷膜领域的发展态势进行了分析和研讨。     

陶瓷膜制备低成本化途径的研究进展

本文从原材料的选择,新型成型工艺的使用以及降低烧结成本等方面综述了降低多孔陶瓷膜的制作成本的方法,综合分析了陶瓷膜低成本化研究的各种途径。在此基础上,本文还分析了如何通过陶瓷分离膜的表面修饰改性方法,提高陶瓷膜的选择性与渗透性。在降低陶瓷膜成本的同时,提高膜的分离性能,有利于加快我国陶瓷膜工业应用的发展。     

陶瓷纳滤膜制备与应用研究进展

陶瓷纳滤膜以其优良的热稳定性、化学稳定性和机械强度等特性,在涉及高温、酸碱、有机溶剂等苛刻环境的过程工业领域具有广阔的应用前景。因此,陶瓷纳滤膜材料的制备研究已引起众多科研工作者的关注。本文综述了陶瓷纳滤膜在制备及应用方面的研究进展,着重介绍了溶胶-凝胶法、化学气相沉积法、原子层沉积法及表面接枝等陶瓷纳滤膜制备方法。溶胶-凝胶法反应温度低、操作过程相对简单且精确可控,是目前国内外陶瓷纳滤膜制备的常用方法;化学气相沉积法及原子层沉积法则需借助气相化学反应在多孔基底表面进行材料沉积,从而修复缺陷,减小平均孔经;表面接枝技术可改变陶瓷膜表面亲疏水性,同时将陶瓷基膜孔径减小至纳滤范围。此外简单介绍了陶瓷纳滤膜的应用,并对未来陶瓷纳滤膜研究方向提出了建议,指出陶瓷纳滤膜微结构参数与分离性能之间的关系建立,以及探讨陶瓷纳滤膜在溶剂体系中的分离机理将成为今后一段时间内的研究热点。     

使用陶瓷膜蒸馏法水脱盐

通常,陶瓷膜是由金属氧化物,如氧化铝,二氧化锆,或二氧化钛制成的。由于在这些材料的表面存在羟基,而使它们的表面产生亲水性,因此,孔中很容易吸附很多水。在陶瓷膜领域,一般是将其表面进行改性,使市场购得的陶瓷膜的孔减小以避免气体混合物,或低分子量液体分离中的亲水行为,或者改变膜的吸附性质。     

陶瓷膜超疏水改性及其膜蒸馏性能研究

以聚苯乙烯(PS)和四氢呋喃(THF)的混合溶液为铸膜液,无水乙醇(Et OH)为非溶剂,通过非溶剂致相分离(NIPS)法在亲水性陶瓷膜表面构造超疏水性PS微孔膜,得到超疏水性陶瓷膜。考察PS与Et OH比例、浸渍时间对陶瓷膜疏水性和膜结构的影响,并通过浸没式真空膜蒸馏(SVMD)研究超疏水性陶瓷膜的脱盐性能。结果表明,超疏水改性后,PS沉积在陶瓷膜表面,减小了膜的平均孔径;当PS与Et OH的质量比为1:4,浸渍时间为3 min时,改性膜的水接触角达到152°,滚动接触角达到8°,达到超疏水效果,且在SVMD中的渗透通量最高,保持在1.57 kg/(m~2·h)左右,脱盐率高于99.5%。     

Atomic layer deposition of Al2O3 on porous polypropylene hollow fibers for enhanced membrane performances

Porous polypropylene hollow fiber (PPHF) membranes are widely used in liquid purification.However,the hydrophobicity of polypropylene (PP) has limited its applications in water treatment.Herein,we demonstrate that,for the first time,atomic layer deposition (ALD) is an effective strategy to conveniently upgrade the filtration performances of PPHF membranes.The chemical and morphological changes of the deposited PPHF membranes are characterized by spectral,compositional,microscopic characterizations and protein adsorption measurements.Al2O3 is distributed along the cross section of the PP hollow fibers,with decreasing concentration from the outer surface to the inner surface.The pore size of the outer surface can be easily turned by altering the ALD cycles.Interestingly,the hollow fibers become much more ductile after deposition as their elongation at break is increased more than six times after deposition with 100 cycles.The deposited membranes show simultaneously enhanced water permeance and retention after deposition with moderate ALD cycle numbers.For instance,after 50 ALD cycles a 17％ increase in water permeance and one-fold increase in BSA rejection are observed.Moreover,the PP membranes exhibit improved fouling-resistance after ALD deposition.     

Tungsten hexacarbonyl and hydrogen peroxide as precursors for the growth of tungsten oxide thin films on titania nanoparticles

W(CO)₆ and H₂O₂ were used in an atomic layer deposition (ALD)‐like process to grow thin WO_x films onto TiO₂ powders in a fluidized bed reactor. Carbonyl precursors are not widely used in this application, so that deviations from an ideal ALD process, previously not examined with W(CO)₆, were identified. The resulting WO_x films were a result of both ALD‐like and chemical vapor deposition‐based growth modes. A chemical reaction mechanism incorporating a combination of these two growth modes was inferred. As the move to expand the range of ALD precursors meets with the desire to scale up these processes, the simultaneous appearance of both these growth modes is likely to become more and more common, and so understanding the interaction of these two types of surface reactions is key to progress in the field. The films were observed to inhibit the anatase‐to‐rutile phase transformation in the TiO₂ powders upon high temperature annealing, while crystallization of the amorphous WO₃ was also not observed. Changes in the local bonding within the WO₃ were observed and associated with changes in the structural nature of the film and its interface to the substrate. © 2014 American Institute of Chemical Engineers AIChE J, 60: 1278–1286, 2014     

Ceramic Membranes for Novel Separations

Abstract

A number of advances have been made in the fabrication and performance of supported ceramic membranes. Improvements in techniques for the synthesis of particulate sols containing particles in the range of 4 to 10 nm in diameter are discussed. Several deposition techniques for the fabrication of supported ceramic membranes via solgel technology are examined, including slipcasting, filtration, coating, and permformation.

Supported titania membranes have been fabricated and both liquid phase permselectivity and gas phase permeability experiments have been performed. Results of the liquid phase separations indicate that these membranes are characterized by a molecular weight cutoff value of approximately 200. Gas phase permeabilities reveal that Knudsen diffusion is not the only mechanism of transport through these membranes.     

新型中空纤维陶瓷膜的制备方法

新型中空纤维陶瓷膜由于具有装填密度大、单位体积膜有效分离面积大、膜壁薄、渗透通量高和节省原料、易于实现分离设备小型化等独特优点而受到广泛关注,在用于多孔和致密陶瓷分离膜、固体氧化物燃料电池、微通道反应器、催化剂载体等方面都有着潜在的应用前景。本文在概括中空纤维陶瓷膜特点的基础上,综述了中空纤维陶瓷膜的制备方法及研究进展,着重分析比较了不同制备方法的优缺点。将相转化法应用于中空纤维陶瓷膜的制备,可实现通过一步成型制造具有自支撑非对称结构的复合陶瓷膜,有利于提高膜的渗透通量,简化膜制备工艺和显著降低制造成本。     

Mixing and solid‐liquid mass transfer characteristics in a three phase pulsed plate column with packed bed of solids in interplate spaces—a novel aerobic immobilized cell bioreactor

BACKGROUND: The pulsed plate column (PPC) with packed bed of solids in the interplate spaces finds use as a three phase aerobic bioreactor and is a potential heterogeneous catalytic reactor. Good knowledge of the extent of mixing in the liquid phase and solid‐liquid mass transfer coefficient are essential for modeling, design and optimization of these columns. The present work aims at the study of liquid phase mixing and solid–liquid mass transfer characteristics in a three phase PPC. RESULTS: Residence time distribution studies were performed. Dispersion number was found to increase with increase in liquid superficial velocities, frequency of pulsation, amplitude of pulsation and the vibrational velocities. Increase in frequency and amplitude of pulsation, and hence increase in vibrational velocity, resulted in increase of the solid–liquid mass transfer coefficient. CONCLUSIONS: The mixing behaviour in this contactor approximated a mixed flow behaviour. The three phase PPC was found to outperform many other kinds of three phase contactors in terms of solid liquid mass transfer characteristics. Empirical correlations developed can be used for the determination of solid–liquid mass transfer coefficients for three phase PPC and hence can facilitate the design, scale‐up and modeling of these columns, when used as chemical or biochemical reactors. Copyright © 2011 Society of Chemical Industry     

Recent Advances in MRI Studies of Chemical Reactors: Ultrafast Imaging of Multiphase Flows

NMR has long been established as an in situ technique for studying the solid-state structure of catalysts and the chemical processes occurring during catalytic reactions. Increasingly, pulsed field gradient (PFG) NMR and magnetic resonance imaging (MRI) are being exploited in chemical reaction engineering to measure molecular diffusion, dispersion and flow hydrodynamics within reactors. By bringing together NMR spectroscopy, PFG NMR and MRI, we are now able to probe catalysts and catalytic processes from the angstrom-to-centimeter scale. This article briefly reviews current activities in the field of MRI studies applied to catalysts and catalytic reactors. State-of-the-art measurements, which can already be used in real reactor design studies, are illustrated with examples of single-phase flow with and without chemical reaction in a fixed-bed reactor. The ability to obtain high spatial resolution (< 200μm) in images of the internal structure and flow field within reactors is demonstrated, and the potential uses of these data in reactor design and understanding bed fouling phenomena are discussed. In particular, MRI has produced the first detailed measurements of the extent of heterogeneity in the flow field within fixed-bed reactors. The example of a fixed-bed esterification process is used to show how NMR spectroscopy and MRI techniques can be combined to provide spatially resolved information on both hydrodynamics and chemical conversion within a process unit. The emerging area of ultrafast MRI is then highlighted as an area of particular interest. Recent advances have demonstrated that it is possible to record 2D images over timescales of ～100ms in the magnetically heterogeneous environments typical of heterogeneous chemical reactors. These advances open up opportunities to image many unsteady state processes for the first time. Examples are given of real-time visualization of bubble-train flow in a ceramic monolith and exploring the stability of the gas–liquid distribution as a function of liquid flow rate in a trickle-bed reactor.     

多相搅拌槽内宏观混合研究进展

多相搅拌槽反应器广泛应用于化工、冶金等过程工业中,而多相混合状态对于多相搅拌槽反应器的设计、优化和放大具有重要意义.混合时间是表征其宏观混合过程的一个重要参数.文中从实验和数值模拟二方面对多相搅拌槽反应器的液相混合时间研究进行综述,对气液、液固、液液、气液固4种体系的多相搅拌槽进行了分类总结,讨论了分散相、桨型、转速、...     

Numerical simulation of atomic layer deposition for thin deposit formation in a mesoporous substrate

ZnO deposition in porous γ-Al₂O₃ via atomic layer deposition (ALD) is the critical first step for the fabrication of zeolitic imidazolate framework membranes using the ligand-induced perm-selectivation process (Science, 361 (2018), 1008–1011). A detailed computational fluid dynamics (CFD) model of the ALD reactor is developed using a finite-volume-based code and validated. It accounts for the transport processes within the feeding system and reaction chamber. The simulated precursor spatiotemporal profiles assuming no ALD reaction were used as boundary conditions in modeling diethylzinc reaction/diffusion in porous γ-Al₂O₃, the predictions of which agreed with experimental electron microscopy measurements. Further simulations confirmed that the present deposition flux is much less than the upper limit of flux, below which the decoupling of reactor/substrate is an accurate assumption. The modeling approach demonstrated here allows for the design of ALD processes for thin-film membrane formation including the synthesis of metal–organic framework membranes.     

Wetting of Ceramics by Liquid Metals

A linear relation is established between the cosine of the contact angle and the temperature of a liquid metal sessile drop resting on a ceramic substrate. This relation is demonstrated for many liquid metal/ceramic systems. The work of adhesion and the effects of surface roughness, porosity, chemical reactions, and structural transformations in the substrate surface are also discussed.