Dense ceramic catalytic membranes and membrane reactors for energy and environmental applications

Catalytic membrane reactors which carry out separation and reaction in a single unit are expected to be a promising approach to achieve green and sustainable chemistry with less energy consumption and lower pollution. This article presents a review of the recent progress of dense ceramic catalytic membranes and membrane reactors, and their potential applications in energy and environmental areas. A basic knowledge of catalytic membranes and membrane reactors is first introduced briefly, followed by a short discussion on the membrane materials including their structures, composition and strategies for material development. The configuration of catalytic membranes, the design of membrane reaction processes and the high temperature sealing are also discussed. The performance of catalytic membrane reactors for energy and environmental applications are summarized and typical catalytic membrane reaction processes are presented and discussed. Finally, current challenges and difficulties related to the industrialization of dense ceramic membrane reactors are addressed and possible future research is also outlined.     

Characteristics of a zirconia composite membrane fabricated by a laser firing method

By a method of laser firing, a high zirconia containing (70%) composite membrane on porous ceramic tubing was successfully fabricated. The laser sintered composite membrane was characterized by gas separation/permeation experiments. In the separation experiment of a CO₂---CH₄ gaseous mixture, it was found that the separation factor of CH₄ over CO₂ was 1.15. In the pure gases permeation experiment, it was found that Knudsen diffusion is considered to be predominant in the permeation mechanism for pure gases H₂, He, CH₄, N₂, O₂, and CO₂, and the permeation mechanism of H₂O at lower temperature depends mainly on surface diffusion and on Knudsen diffusion at higher temperature.     

Pore surface fractal analysis of palladium-alumina ceramic membrane using Frenkel-Halsey-Hill (FHH) model

The alumina ceramic membrane has been modified by the addition of palladium in order to improve the H(2) permeability and selectivity. Palladium-alumina ceramic membrane was prepared via a sol-gel method and subjected to thermal treatment in the temperature range 500-1100 degrees C. Fractal analysis from nitrogen adsorption isotherm is used to study the pore surface roughness of palladium-alumina ceramic membrane with different chemical composition (nitric acid, PVA and palladium) and calcinations process in terms of surface fractal dimension, D. Frenkel-Halsey-Hill (FHH) model was used to determine the D value of palladium-alumina membrane. Following FHH model, the D value of palladium-alumina membrane increased as the calcinations temperature increased from 500 to 700 degrees C but decreased after calcined at 900 and 1100 degrees C. With increasing palladium concentration from 0.5 g Pd/100 ml H(2)O to 2 g Pd/100 ml H(2)O, D value of membrane decreased, indicating to the smoother surface. Addition of higher amount of PVA and palladium reduced the surface fractal of the membrane due to the heterogeneous distribution of pores. However, the D value increased when nitric acid concentration was increased from 1 to 15 M. The effect of calcinations temperature, PVA ratio, palladium and acid concentration on membrane surface area, pore size and pore distribution also studied.     

Low Temperature Sintering and Characterization of YSZ/Al Composite Coatings by Electrophoretic Deposition and Reaction Bonding Process

In practice, low temperature sintering is always the most desirable route to fabricate ceramic composites for industrial manufacturers and an economic way to produce ceramics with unique microstructure for technological applications. Normally the sintering temperature for dense YSZ coating is about 1500℃. Recently many studies have experimentally found that dense ceramic composites can be achieved at a sintering temperature lower by several hundred degrees Celsius for nano-sized powders than for coarse powders^[1-2]. Electrochemical processing is an attractive method for making ceramic films and powders because it offers the advantages of low temperature sintering, low cost and good control of the green forms^[3-4].     

聚乙烯基咪唑/陶瓷复合膜的渗透汽化性能

通过自由基接枝聚合反应在硅烷化处理的沉积有SiO2活性层的无机陶瓷微孔膜上接枝乙烯基咪唑（VI）,经质子化后,制备出一种聚电解质亲水性有机-无机复合膜。用FT-IR表征了接枝PVI前后化学组成的变化;用TGA 测定了单体在二氧化硅粉末上的接枝率;用SEM观察了接枝反应前后膜表面形态的变化;系统研究了操作条件对膜的渗透汽化分离性能的影响。结果表明,这种膜用于醇/水、酸/水等水溶液的分离有很好的选择性和渗透性,膜的渗透性随操作温度的变化表现异常,结合SEM的结果可以推断有机单体主要是在无机膜的孔内接枝形成活性分离层。     

锂离子电池用陶瓷聚烯烃复合隔膜

为改善聚烯烃微孔膜的耐热安全性,研究了用于锂离子电池的陶瓷聚烯烃复合隔膜ZrO2/SiO2/PP（聚丙烯）。 复合膜具有高度多孔性和良好液体电解液湿润性。 由于高的毛细吸附作用,通过吸附液态电解液,膜很易传导锂离子。 膜中ZrO2/SiO2的两性特征,将电解液中的酸性HF（氟化氢）消耗掉,而HF作为现在锂离子电池所用电解液中的杂质是不可避免的。 复合膜作为隔膜制备的碳/正极材料锂离子电池不仅具有优良的容量保持性、高温安全性,也显示良好的倍率放电性。     

Ceramic–glass composite high temperature seals for dense ionic-conducting ceramic membranes

A basic principle for selecting inorganic sealing materials for dense ionic-conducting ceramic membranes is described for high temperature permeation/reaction experiments. Based on this principle ceramic–glass composite seals consisting of the Pyrex glass and the ceramic powder of the membrane were developed and successfully used to seal a number of different dense ceramic membranes at high temperatures. The ceramic–glass composite seal is typically composed of 40–50 wt.% membrane material powder, 20–50 wt.% Pyrex glass and 5–20 wt.% additive such as sodium aluminate and boron oxide. The properties of ceramic–glass composite seal can be tailored to obtain suitable wettability, viscosity, chemical inertness, thermal expansibility, and bonding strength for good sealing results. A success rate for sealing these ceramic membranes of nearly 100% is possible using the ceramic–glass composite recipe if the correct sealing procedure, including seal paste preparation, is carefully followed.     

Modification of ceramic membranes by alcohol adsorption

This study aims at modifying ceramic membranes by means of alcohol chemisorption. Composite ceramic membranes with a skin layer of γ-alumina were used. First, the adsorption of several alcohol on powdered γ-alumina was investigated emphasising the thermal stability of the adsorbed compounds. Later, a commercial γ-alumina membrane was modified by alcohol adsorption. The permeability of water and several organic compounds was obtained for both the non-modified and modified ceramic membrane. Also, its isoelectric point was determined. The results prove that all the alcohol were readily adsorbed on powdered γ-alumina not only physically but also chemically forming an alkoxide. The chemisorbed alcohol was stable up to 200°C. Beyond this temperature, the alkoxide breaks up releasing the alcohol although the alkoxide also can react yielding an olefin or ether. The ceramic membrane was also successfully modified by alcohol adsorption. The layer of chemisorbed alcohol imparts hydrophobic characteristics to the membrane surface, so water permeability decreases significantly. This cannot be merely explained by pore size reduction due to the adsorbed layer. Thermal treatment at 250°C recovered original permeability with only minor damage to the membrane.     

Formatation of pore structure in tape-cast alumina membranes – effects of binder content and firing temperature

Disc type ceramic aluminium oxide membrane has been prepared by tape casting technique. Thickness of this single layer membrane is in the range 200–300 μm. Porosity and pore size distribution have been determined by mercury porosimetry. Polymeric binder content of the green tape and the firing temperature are found to have strong influence on the average pore size, pore size distribution and overall porosity. Higher binder content promotes agglomeration of the ceramic particles, which on firing leads to wider pore size distribution and formation of closed pores. Pore coarsening is observed with increasing firing temperature.     

Preparation of Zeolite X Membranes on Porous Ceramic Substrates with Zeolite Seeds

Zeolite X membranes were investigated by in-situ hydrothermal synthesis on porous ceramic tubes precoated with zeolite X seeds or precursor amorphous aluminosilicate, and porous α-Al2O3 ceramic tubes with a pore size of 50 200 nm were employed as supports. Zeolite X crystals were synthesized by the classic method and mixed into deionized water as a slurry with a concentration of 0.2 0.5wt%, having a range of crystal sizes from 0.2 to 2μm. Crystal seeds were pressed into the pores near the inner surface of the ceramic tubes, and crystallization took place at 95℃ for 24-96 h. It was also investigated that Boehmite sol added with zeolite X seeds was precoated on ceramic supports to form a layer of γ-Al2O3 by heating, and hydrothermal crystallization could then take place to prepare the zeolite membranes on the composite ceramic tubes. The crystal species were characterized by XRD, and the morphology of the supports subjected to crystallization was characterized by SEM. The composite zeolite membranes have zeolitic top-layers with a thickness of 10-25 μm, and zeolite crystals can be intruded into pores of the supports as deeply as 100μm. The experimental results indicate that the precoating of zeolitic seeds on supports is beneficial to crystallization by shortening the synthesis time and improving the membrane strength. The resulting zeolite X membrane shows permselectivity to tri-n-butylamine((C4H9)3N) over perfluro-tributyl-amine ((C4Fg)3N), and a permeance ratio of 57 for ((C4Hg)3N to (C4F9)3N could be reached at 350℃. Permeances of BZ, EB and TIPB through the zeolite membrane were also measured and were found to slightly increase with temperature.     

高温水溶液pH值原位测量系统与机理

研制了以氧化钇稳定氧化锆(YSZ)陶瓷薄膜电极为pH电极、外置压力平衡式Ag/AgCl电极为参比电极的高温高压水溶液pH值原位测量系统,测量了H₃BO₃\LiOH水溶液在473.15~573.15 K范围内的pH值,并与热力学计算得到的pH值比较。 结果表明,当温度高于548.15 K时,测量系统可以实现pH值的准确测量;而低于此温度时,由于YSZ陶瓷膜内阻过大,测得的pH值与理论计算值存在偏差,且随温度的降低,测量偏差增大。 讨论了该系统的pH值测量机理。     

Sol-gel processing of inorganic membranes

Basic principles involved in sol-gel processing of ceramic membranes are described. This process has been applied to ceramic ultrafiltration membranes and is now investigated to prepare ceramic nanofilters. In this paper special emphasis is put on new developments concerning microporous zirconia membranes obtained by the polymeric route. A zirconium alkoxide precursor modified with an acetylacetone ligand has been used in order to control particle growth in the sols and pore size distribution in the membranes. N₂ adsorption and X-ray diffraction analysis have been performed on membrane materials showing the influence of process parameters (molar ratio r = acacH/Zr and sintering temperature T) on membrane structural evolution.     

Ceramic membranes modified with catalytic oxide films as ensembles of catalytic nanoreactors

Hybrid catalytic membrane systems have been produced by modifying porous ceramic membranes with metal oxide films. A two-layer cermet membrane consisting of a flexible stainless steel layer and an overlying porous TiO₂ ceramic layer and a ceramic titanium carbide membrane are examined. The membrane surfaces have been modified by the alkoxide method using colloidal organic solutions of metal complex precursors. Producing a tetragonal single-phase ZrO₂/Y₂O₃ coating on the cermet surface increases the abrasion strength of the ceramic layer. CO oxidation and the oxidative conversion of methane into synthesis gas and light hydrocarbons can be markedly intensified by modifying the membrane channels with Cu_0.03Ti_0.97O_2±δ and La + Ce/MgO catalysts, respectively. A method has been developed for depositing, onto the geometrical surface of a membrane, a film of the new single-phase oxide P_0.03Ti_0.97O_2±δ with an anatase structure and uniform pores of mean diameter 〈d〉 ～ 2 nm. Blocks of zeolite-like silicalite can be formed on the surface of the phosphorus-titanium oxide film. The resulting hybrid membrane is characterized by an anisotropic permeability depending on the flow direction. This property has an effect on conversion and selectivity in the nonoxidative dehydrogenation of methanol.     

Pore Modification in Porous Ceramic Membranes With Sol-Gel Process and Determination of Gas Permeability and Selectivity

Summary: The aim of the study was to investigate the variation in total surface area, porosity, pore size, Knudsen and surface diffusion coefficients, gas permeability and selectivity before and after the application of sol-gel process to porous ceramic membrane in order to determine the effect of pore modification. In this study, three different sol-gel process were applied to the ceramic support separately; one was the silica sol-gel process which was applied to increase porosity, others were silica-sol dip coating and silica-sol processing methods which were applied to decrease pore size. As a result of this, total surface area, pore size and porosity of ceramic support and membranes were determined by using BET instrument. In addition to this, Knudsen and surface diffusion coefficients were also calculated. After then, ceramic support and membranes were exposed to gas permeation experiments by using the CO₂ gas with different flow rates. Gas permeability and selectivity of those membranes were measured according to the data obtained. Thus, pore surface area, porosity, pore size and Knudsen diffusion coefficient of membrane treated with silica sol-gel process increased while total surface area was decreasing. Therefore, permeability of ceramic support and membrane treated with silica sol-gel process increased, and selectivity decreased with increasing the gas flow rate. Also, surface area, porosity, pore size, permeability, selectivity, Knudsen and surface diffusion coefficients of membranes treated with silica-sol dip coating and silica-sol processing methods were determined. As a result of this, porosity, pore size, Knudsen and surface diffusion coefficients decreased, total surface area increased in both methods. However, viscous flow and Knudsen flow permeability were detected as a consequence of gas permeability test and Knudsen flow was found to be a dominant transport mechanism in addition to surface diffusive flow owing to the small pore diameter in both methods. It was observed that silica-sol processing method had lower pore diameter and higher surface diffusion coefficient than silica-sol dip coating method.     

Transport of binary water–ethanol mixtures through a multilayer hydrophobic zeolite membrane

Transport of water–ethanol mixtures through a hydrophobic tubular ZSM-5 (Si/Al = 300) zeolite membrane during pervaporation was studied experimentally and theoretically. The zeolite membrane was deposited on a support made of pure titania coated with three intermediate ceramic titania layers. The influence of feed concentration, feed temperature and permeate pressure on permeate fluxes and permeate concentrations was investigated in a wide range. Dusty gas model parameters of the support and all ceramic intermediate layers were calculated on the basis of gas permeation data. Mass transfer resistances and pressure drops in the different membrane layers during pervaporation were calculated for several process conditions. In particular the influence of the undesired but unavoidable pressure drop in the support and the intermediate layers on the effective driving force for pervaporation was evaluated and found to be relevant for predicting the overall process performance. The membrane prepared was found to be suitable for the recovery of highly concentrated ethanol from feed mixtures of relatively low ethanol concentrations at relatively low feed temperatures.     

Preparation and Chiral Selectivity of BSA-Modified Ceramic Membrane

Chirality plays an important role in the function of biological processes. For isolating only the desired enantiomer, various methods have been developed, such as high performance liquid chromatography and capillary electrophoresis1. But with these method…     

Facile synthesis of mesoporous silica sublayer with hierarchical pore structure on ceramic membrane using anionic polyelectrolyte

A facile method for introducing mesoporous silica sublayer onto the surface of a ceramic membrane for use in liquid-phase separation is described. To reduce the electrostatic repulsion between the mesoporous silica sol and the ceramic membrane in highly acidic conditions (pH < 2), thus facilitating the approach of hydrolyzed silica sol to the surface of the membrane, poly(sodium 4-styrenesulfonate) (Na+PSS-, denoted as PSS-) was used as an ionic linker. The use of PSS- led to a significant reduction in positive charge on the ceramic membrane, as confirmed by experimental titration data. Consistent with the titration results, the amount of mesoporous silica particles on the surface of the ceramic membrane was low, in the absence of PSS- treatment, whereas mesoporous silica sublayer with hierarchical pore structure was produced, when 1 wt % PSS- was used. The results show that mesoporous silica grows in the confined surface, eventually forming a multistacked surface architecture. The mesoporous silica sublayer contained uniform, ordered (P6 mm) mesopores of ca. 7.5 nm from mesoporous silica as well as macropores ( approximately mum) from interparticle voids, as evidenced by transmission electron microscopy and scanning electron microscopy analyses. The morphologies of the supported mesoporous silica could be manipulated, thus permitting the generation of uniform needlelike forms or uniform spheroid particles by varying the concentration of PSS-.     

一种新型的亲水性聚丙烯酸-陶瓷复合膜

通过化学气相沉积和丙烯酸(AA)在大孔陶瓷膜表面的接枝共聚制备了一种新型的亲水性PAA-陶瓷复合膜. 用FT-IR、SEM、EDS、表面接触角等方法对复合膜接枝层的化学组成、表面形态、元素分布和亲水性进行了表征. 通过系统研究气相沉积和接枝反应的主要条件对膜的渗透汽化性能的影响, 发现当TEOS用量为5 mL, 汽化温度为175 ℃时进行气相沉积, 然后在丙烯酸浓度为7.5%的溶液中进行接枝聚合, 制得的复合膜对醇水混合物显示了优良的分离性能.     

Synthesis of lithium ferrite by precursor and combustion methods: A comparative study

The thermal decomposition of lithium hexa(carboxylato)ferrate(III) precursors, (Li₃[Fe(L)₆]·xH₂O, L = formate, acetate, propionate, butyrate), has been carried out in flowing air atmosphere from ambient temperature upto 500 °C. Various physico-chemical techniques, i.e., TG, DTG, DTA, XRD, SEM, IR, Mössbauer spectroscopy, etc., have been employed to characterize the intermediates and end products. After dehydration, the anhydrous complexes undergo decomposition to yield various intermediates, i.e., lithium oxalate/acetate/propionate/butyrate, ferrous oxalate/acetate and α-Fe₂O₃ in the temperature range of 185–240 °C. A subsequent decomposition of these intermediates leads to the formation of nanosized lithium ferrite (LiFeO₂). Ferrites have been obtained at much lower temperature (255–310 °C) as compared to conventional ceramic method. The same nano-ferrite has also been prepared by the combustion method at a comparatively lower temperature (400 °C) and in less time than that of conventional ceramic method.     

Impurity partitioning in Nafion and ceramic separators used for purification of spent chromium plating solutions

Cationic partitioning (Cu(II), Ni(II), and Fe(III)) into Nafion and ceramic membranes equilibrated with different salt solutions was investigated in this study. Both single-ion and multicomponent partitioning in a Nafion-117 membrane in a 2.12 M chromic acid solution was well characterized with the Freundlich isotherm. The affinity for the Nafion membrane was Fe(III)>Ni(II)>Cu(II). The partition coefficients of the divalent cations in multicomponent partitioning experiments were similar to those in single-ion experiments whereas the partition coefficients of the trivalent cation decreased. Among the factors investigated, pH had the most significant influence on the partition coefficients, especially in the pH range of about 0.5–1.5. In contrast, temperature in the range of 25–55 °C had an insignificant effect. The ceramic diaphragm had partition coefficients equal to the porosity (0.4) of the ceramic for all of the species implying that cations were not adsorbed to its surface.