活性污泥对管式多孔α-Al_2O_3陶瓷膜支撑体性能影响的初步研究

以剩余活性污泥作为支撑体的成孔剂,采用滚压成型及熔膜芯法制备管状多孔α-Al2O3陶瓷膜支撑体,研究了粘结剂羧甲基纤维素(CMC)和活性污泥的加入量对氧化铝陶瓷膜支撑体品质的影响。结果表明,随着成孔剂和粘结剂的增多,支撑体孔隙率和渗透通量呈增大趋势,孔隙率最大可达43.07%,纯水通量在0.4~1.0 MPa压力下变化范围为12 786.67~37 617.84 L/(m2·h·MPa)。     

活性污泥对管式多孔α-Al_2O_3陶瓷膜支撑体性能影响的初步研究

以剩余活性污泥作为支撑体的成孔剂,采用滚压成型及熔膜芯法制备管状多孔α-Al2O3陶瓷膜支撑体,研究了粘结剂羧甲基纤维素（CMC）和活性污泥的加入量对氧化铝陶瓷膜支撑体品质的影响。结果表明,随着成孔剂和粘结剂的增多,支撑体孔隙率和渗透通量呈增大趋势,孔隙率最大可达43.07%,纯水通量在0.4~1.0 MPa压力下变化范围为12 786.67~37 617.84 L/（m2·h·MPa）。     

气体分离用管状炭分子筛膜

以无机陶瓷管为支撑体、热塑性酚醛树脂为原料,经高温炭化制备了炭分子筛膜。用低温N2吸附的方法测定了炭分子筛膜的比表面积,用扫描电子显微镜对膜的形貌和厚度进行了表征。考察了膜的气体透过率以及气体的理想选择性随温度的变化关系:H2、CO2、O2、N2和CH4的透过率随温度的升高而增大;理想选择性α(H2/N2)、α(CO2/N2)、α(CO2/CH4)随温度的升高而减小,而α(O2/N2)随温度的升高先增大后减小,在90℃左右气体选择性达到最大。最后由阿累尼乌斯公式计算了气体透过炭分子筛膜的活化能,进一步说明气体透过机理为活化扩散。     

Preparation of alumina membranes for micro- and ultrafiltration applications

Abstract

A very thin disc type ceramic membrane (0·3-0·8 mm thickness, 25-30 mm diameter) made of pure alumina and suitable for microfiltration applications has been prepared by a tape casting process. A sol coating was applied to the disc to form an ultrafiltration membrane. T he pore size of the membrane could be varied in the range 0·1-0·7 μ m and porosity in the range 25-55% by optimising the ex perimental parameters. The most important factor for determining the pore size of the membrane was found to be the initial particle size distribution of the ceramic powder. Firing temperature and soaking time are other crucial parameters affecting volumetric porosity. Water permeability through the membrane under suction and under positive pressure is comparable with that of ceramic membranes prepared by conventional methods. In addition, a typical membrane shows a very narrow pore size distribution in the range 0·1-0·4 μm, with a median pore size of 0·28 μm. A very sharp drop in the pore size distribution pattern around 0·4 μm indicates that no pores larger than this exist. This implies that all particles with radius > 0·4 μm are trapped in the membrane, providing excellent separation efficiency. Results of microbial separation tests confirmed the possibility of micro-organism separation through these membranes.     

Elaboration and characterization of tubular macroporous ceramic support for membranes from kaolin and dolomite

A low cost macroporous support for ceramic membranes was prepared by in situ reaction sintering from local natural mineral kaolin with dolomite as sintering inhibitor. The characterization focused on the phase evolution, microstructure, pore structure, mechanical strength and water permeability at various compositions and sintering temperatures. The sintering of kaolin was improved with 5 wt% dolomite, but clearly inhibited with ≥10 wt% dolomite. For the 20 wt% dolomite samples, the crystalline phases were mainly composed of mullite, cordierite and anorthite after sintering between 1,150 and 1,300 °C. Moreover, both mean pore size and mechanical strength increased with increasing sintering temperature from 1,100 to 1,300 °C, but the water permeability and porosity decreased. The 1,250 °C sintered macroporous support with 20 wt% dolomite exhibited good performances such as porosity 44.6%, mean pore size 4.7 μm, bending strength 47.6 MPa, water permeability 10.76 m³ m⁻² h⁻¹ bar⁻¹, as well as good chemical resistance. This work provides opportunities to develop cost-effective ceramic supports with controllable pore size, porosity, and high strength for high performance membranes.     

Preparation and characterization of low-cost ceramic microfiltration membranes for the removal of chromate from aqueous solutions

Low-cost ceramic microfiltration membranes were prepared using clay of IIT Guwahati. Two membranes were prepared by paste casting followed by sintering at different temperatures, the first one from clay only (membrane A) and the second one from clay with small amounts of sodium carbonate, sodium metasilicate and boric acid (membrane B). Both the membranes were characterized by TGA, SEM, XRD, water permeability test and acid–base treatment. With the increase of sintering temperature, pore size as well as permeability and flexural strength were increasing while porosity and pore density were decreasing. The overall performance of membrane B was better than membrane A. The average pore size, porosity, pore density and flexural strength of membrane B sintered at 1000 °C were 4.58 μm, 0.42, 2.06 × 10¹⁰ m^− 2 and 11.55 MPa respectively. This membrane was used for the removal of chromate from aqueous solutions by micellar enhanced microfiltration (MEMF) using cetylpyridinium chloride (CPC). 100% rejection of chromate ions were obtained at a feed ratio (CPC/chromate) of 10. Based on raw material prices, the membrane cost was estimated to be $19/m². The prepared low-cost membrane showed good promise for the treatment of wastewater containing such heavy metals.     

多孔氧化铝支撑体的制备与表征

以α-Al2O3粉末为骨料,采用塑性挤压成型技术和固态粒子烧结法制备Al2O3多孔陶瓷支撑体。研究了粘结剂和成孔剂的种类对支撑体性能的影响。研究结果表明:通过选用合适的粘结剂和成孔剂,可制得孔径分布窄、孔隙率高的支撑体。     

Preparation and characterization of supported ordered nanoporous carbon membranes for gas separation

Supported ordered nanoporous carbon membranes (ONCM) were prepared by coating a membrane‐forming solution of resorcinol‐formaldehyde (RF) resin on plate support through solvent evaporation and pyrolysis. The membrane solution was formed by the organic‐organic assembly of RF resin with Pluronic F127 in the presence of triethyl orthoacetate and catalyst hydrochloric acid. The thermal stability of precursor, the microstructure, functional groups, and morphology and porous structure of resultant support and ONCM were investigated by the techniques of thermogravimetry, X‐ray diffraction, Fourier transformed infrared spectroscopy, scanning electron microscopy/transmission electron microscopy and nitrogen adsorption‐desorption, respectively. Results have shown that the as‐obtained ONCM has well‐developed porous regularity with bi‐modal narrow pore size distribution. ONCM is tightly adhered to the adopted phenolic resin‐based carbon support. Gases permeating through the ONCM are dominated by molecular sieving mechanism. The ideal gas separation factor of the supported ONCM can be reached to 46.4, 4.7 and 3.3 for H₂/N₂, CO₂/N₂ and O₂/N₂, respectively. The supported ONCM obtained in this work exhibits most promising application for permanent gas separation. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39925.     

Effect of CTAB as a foaming agent on the properties of alumina ceramic membranes

Alumina-ceramic membranes were prepared by gelcasting process using CTAB as a foaming agent. To increase the fineness, the starting alumina powder was milled for 1 h in a ball mill before the casting process. Particle size distribution and surface area measurements of the as-received and milled alumina powder were examined. The casted alumina membranes were sintered at 1500 °C. Sintering parameters in terms of bulk density (BD) and apparent porosity (AP) were determined by the Archimedes method. Pore size distribution of the sintered porous alumina membranes was measured using mercury porosimeter. Microstructure of sintered membranes was investigated by scanning electron microscope (SEM). Cold crushing strength (CCS) of the sintered specimens was also evaluated. The result revealed that the properties of porous ceramics such as porosity, average pore size, pore size distribution and cold crushing strength could be controlled by adjusting the preparation conditions e.g. solid loading, sintering temperature and foaming agent. The open porosity, cold crushing strength and average pore size of the alumina ceramics sintered at 1500 °C were around 58.35%, 18 MPa and178 nm, respectively.     

Manufacture and characterization of ultra and microfiltration ceramic membranes by isostatic pressing

This paper describes the manufacture of tubular UF and MF porous and supported ceramic membranes to oil/water emulsions demulsification. For such a purpose, a rigorous control was realized over the distribution and size of pores. Suspensions at 30 vol.% of solids (zirconia or alumina powder and sucrose) and 70 vol.% of liquids (isopropyl alcohol and PVB) were prepared in a jar mill varying the milling time of the sucrose particles, according to the pores size expected. The membranes were prepared by isostatic pressing method and structurally characterized by SEM, porosimetry by mercury intrusion and measurements of weight by immersion. The morphological characterization of the membranes identified the formation of porous zirconia and alumina membranes and supported membranes. The results of porosimetry analysis by mercury intrusion presented an average pore size of 1.8 μm for the microfiltration porous membranes and for the ultrafiltration supported membranes, pores with average size of 0.01-0.03 μm in the top-layer and 1.8 μm in the support. By means of the manufacture method applied, it was possible to produce ultra and microfiltration membranes with high potential to be applied to the separation of oil/water emulsions.     

Preparation processes and characterizations of alumina-coated alumina support layers and alumina-coated natural material-based support layers for microfiltration

Recently, porous ceramic membranes have become a subject of significant interest due to their outstanding thermal and chemical stability. To reduce the high manufacturing costs of these porous ceramic membranes, recent research has focused on the utilization of inexpensive natural materials. However, there have not been any well-established direct comparisons of the membrane properties between typical alumina-based membranes and novel natural material-based membranes. Therefore, we compared alumina-coated alumina support layers (with average pore sizes ranging from 0.10 µm ~0.18 µm), alumina-coated diatomite-kaolin composite support layers (with an average pore size of 0.12 µm), and alumina-coated pyrophyllite-diatomite composite support layers (with an average pore size of 0.11 µm) via the dip-coating method and subsequent heat treatment ranging from 1200 °C–1400 °C for 1 h. The pure water permeability of the alumina-coated diatomite-kaolin composite support layer and the alumina-coated pyrophyllite-diatomite composite support layer was found to be approximately 2.0×10² L m⁻² h⁻¹ bar⁻¹, which is similar to that of an alumina-coated alumina support layer. Therefore, we suggest that the average pore size of an alumina-coated natural material-based support layer can be effectively controlled while exhibiting acceptable water permeability.     

Preparation and characterization of alumina hollow fiber membranes

With the rapid development of membrane technology in water treatment, there is a growing demand for membrane products with high performance. The inorganic hollow fiber membranes are of great interest due to their high resistance to abrasion, chemical/thermal degradation, and higher surface area/volume ratio therefore they can be utilized in the fields of water treatment. In this study, the alumina (Al₂O₃) hollow fiber membranes were prepared by a combined phase-inversion and sintering method. The organic binder solution (dope) containing suspended Al₂O₃ powders was spun to a hollow fiber precursor, which was then sintered at elevated temperatures in order to obtain the Al₂O₃ hollow fiber membrane. The dope solution consisted of polyethersulfone (PES), Nmethyl-2-pyrrolidone (NMP) and polyvinylpyrrolidone (PVP), which were used as polymer binder, solvent and additive, respectively. The prepared Al₂O₃ hollow fiber membranes were characterized by a scanning electron microscope (SEM) and thermal gravimetric analysis (TG). The effects of the sintering temperature and Al₂O₃/PES ratios on the morphological structure, pure water flux, pore size and porosity of the membranes were also investigated extensively. The results showed that the pure water flux, maximum pore size and porosity of the prepared membranes decreased with the increase in Al₂O₃/PES ratios and sintering temperature. When the Al₂O₃/PES ratio reached 9, the pure water flux and maximum pore size were at 2547 L/m²·h and 1.4 μm, respectively. Under 1600dgC of sintering temperature, the pure water flux and maximum pore size reached 2398 L/(m²·h) and 2.3 μm, respectively. The results showed that the alumina hollow fiber membranes we prepared were suitable for the microfiltration process. The morphology investigation also revealed that the prepared Al₂O₃ hollow fiber membrane retained its’asymmetric structure even after the sintering process.     

Preparation of microporous silica membranes for gas separation

Microporous silica membranes for hydrogen separation were prepared on a γ-alumina coated α-alumina tube by sol-gel method. The reactants of sol-gel chemistry were tetraethoxysilane (TEOS) and methacryloxypropyl-trimethoxysilane (MOTMS). The silane coupling agent, MOTMS, was added as a template in order to control the pore structure to the silicon alkoxide, TEOS. In particular, the microporous membranes were prepared by changing the molar ratio of MOTMS with respect to other substances, and their pore characteristics were analyzed. Then, the effects of thermal treatment on the micropore structure of the resulting silica membranes were investigated. The pore size of the silica membrane prepared after calcination at 400–700 ‡C was in the range of 0.6–0.7 nm. In addition, permeation rates through the membranes were measured in the range of 100–300 dgC using H₂, CO₂, N₂, CH₄, C₂H₆, C₃H₆ and SF₆. The membrane calcined at 600 ‡C showed a H₂ permeance of 2×10^-7-7×10^-7 molm^-2s^-1Pa^-1 at permeation temperature 300 ‡C, and the separation factors for equimolar gas mixtures were 11 and 36 for a H₂/CO₂ mixture and 54 and 132 for a H₂/CH₄ mixture at permeation temperatures of 100 ‡C and 300 ‡C, respectively.     

Processing,structural characterization and performance of alumina supports used in ceramic membranes

Although there are various commercially available methods for the separation and capture of gas species such as CO₂ and H₂, they are energy expensive and in some cases environmentally unfriendly. The membrane separation process presents advantages such as its relative simplicity, ease of use, low energy consumption, and application in the separation of both liquid and gas mixtures. For these reasons, the membrane technology has achieved in the last years a great commercial and strategic importance. In this work we present a structural characterization of an alumina support, before and after the deposition of a titania film on its surface. The obtained asymmetric membranes are intended to be used in gas separation processes. The alumina supports and titania coatings were prepared by dry-pressing and sol–gel process, respectively. The processed samples were characterized by X-ray diffraction (XRD), nitrogen sorption, scanning electron microscopy (SEM), and X-ray microtomography (μ-CT). In order to evaluate the membranes performance, single-gas permeation experiments were performed at room temperature with nitrogen, helium, and carbon dioxide. We observed that although the alumina supports obtained in this work have not been submitted to any surface finishing procedure, the obtained membranes have potential application in gas separation processes. We observed that increasing the pressure feed leads to improving their separation capacity.     

Preparation and gas separation properties of asymmetric polysulfone membranes by a dual bath method

Defect-free skinned asymmetric gas separation membranes were prepared by a dual bath coagulation method that is a wet/wet phase inversion technique. The membranes were cast from a polysulfone/N,N-dimethylacetamide solution. In two sequent nonsolvent baths, the first bath using iso-propanol (IPA) leads to the formation of a dense skin top layer and the second bath using water makes the actual polymer precipitation. The top skin layer thickness was governed by changing the immersion time of the first IPA bath. We suggest that the growth rate of the skin layer is to be determined by a diffusion process.     

Preparation and characterization of polyvinylidene fluoride hollow fiber membranes for ultrafiltration

Polyvinylidene fluoride (PVDF) hollow fiber membranes were prepared using the solvent spinning method. N,N-dimethylacetamide was the solvent and ethylene glycol was employed as non-solvent additive. The effect of the concentration of ethylene glycol in the PVDF spinning solution as well as the effect of ethanol either in the internal or the external coagulant on the morphology of the hollow fibers was investigated. The prepared membranes were characterized in terms of the liquid entry pressure of water measurements, the gas permeation tests, the scanning electron microscopy, the atomic force microscopy, and the solute transport experiments. Ultrafiltration experiments were conducted using polyethylene glycol and polyethylene oxides of different molecular weights cut-off as solutes. A comparative analysis was made between the membrane characteristic parameters obtained from the different characterization techniques.     

Preparation and characterization of PVDF-PFSA flat sheet ultrafiltration membranes

High performance polyvinylidene fluoride (PVDF) flat sheet ultrafiltration (UF) membranes have been prepared by an immersion precipitation phase inversion method using perfluorosulfonic acid (PFSA) as a pore former and as a hydrophilic component of the membranes and polyethylene glycol (M_w = 400) (PEG400) as a pore forming agent. The effects of the presence of PEG and the concentration of the PFSA on the phase separation of the casting solutions and on the morphologies and performance of UF membranes including their porosity, water flux, rejection of bovine serum albumin (BSA) protein, and anti-fouling property were investigated. Phase diagrams, viscosities and the phase separations upon exposure to water vapor showed that both PEG400 and PFSA promoted demixing of the casting solution. Scanning electron microscopy measurements showed that the PVDF-PFSA blend membranes had more macropores and finger-like structures than the native PVDF membranes. The PVDF-PFSA membrane (5 wt-% PEG400+ 5 wt-% PFSA) had a pure water flux of 141.7 L/m²·h, a BSA rejection of 90.1% and a relative pure water flux reduction (RFR) of 15.28%. These properties were greatly superior to those of the native PVDF membrane (pure water flux of 5.6 L/m²·h, BSA rejection of 96.3% and RFR of 42.86%).     

多孔氧化铝陶瓷的制备、表征及性能研究

以蔗糖溶液为低温介质,采用冷冻干燥法和退火工艺制备多孔Al2O3陶瓷。研究了烧结温度和退火时间对多孔陶瓷孔隙结构、开孔率和力学性能的影响。结果表明,随着烧结温度的升高,试样的线性烧成收缩率有明显的升高,开孔率和维氏硬度先缓慢降低,当烧结温度为1600℃时迅速下降。平均晶粒尺寸是影响甚至决定多孔氧化铝陶瓷维氏硬度的主要原因。随着退火时间的延长,多孔陶瓷的孔径显著增大,多孔陶瓷开孔率范围为40.35%～64.58%,退火处理后的孔隙率比未退火处理提高了60.05%。多孔陶瓷的抗压强度随退火时间的延长而降低,而在最长的24h退火时间后,多孔陶瓷的抗压强度仍能达到25.9MPa,可以满足许多应用领域的强度要求。可以通过调节退火时间来控制多孔陶瓷的孔隙结构、开孔率和抗压强度。     

Preparation and characterization of novel ceramic membranes for micro-filtration applications

Porous microfiltration range ceramic membranes were prepared using kaolin and other suitable materials like feldspar, quartz, boric acid, activated carbon, sodium metasilicate and titanium dioxide following standard paste casting route. The membranes were casted as circular disks of 40 mm ID and 5 mm thickness. They were characterized using thermo gravimetric analysis (TGA), particle size distribution (PSD), X-ray diffraction (XRD) and scanning electron microscope (SEM) to evaluate the effect of maximum sintering temperature on the structure, porosity and mechanical integrity. The prepared membranes were initially dried at 120 °C and 250 °C for 24 h each and finally sintered at 850 °C, 900 °C and 950 °C for 6 h. Morphological parameters viz. pore size distribution, porosity, average pore size of the prepared membranes were determined and the membrane performance were evaluated by carrying out the permeation experiment with pure water. Results show that the average pore size of the membranes increases from 1.59 µm to 2.56 µm and porosity of the membrane supports decreases from 18.88% to 5.59% with increase in sintering temperature from 850 °C to 950 °C. The membrane corrosion resistance was also tested using acid and base and it is observed that there is no significant weight loss in the process. Based on market price of the inorganic precursors, the membrane cost was estimated to be $92/m² which can be considered low cost in the microfiltration range for industrial applications.     

Elaboration and properties of new ceramic microfiltration membranes from natural and synthesised apatite

In this work, we were interested in the development and the characterisation of new mineral microfiltration membranes coated on apatite macroporous supports which are prepared and characterised beforehand. The choice of material is based primarily on its low cost (considering its abundance in the Tunisian layers for natural apatite) and its thermal and chemical resistance. The active layers were prepared from lacunary hydroxyapatite synthesised (HA) and from natural apatite (AB). The membranes were deposited on the tubular support basing of natural apatite, already prepared by the “slip-casting” process. The thermal treatment consists of drying at room temperature for 24 h then a sintering at 600°C for the membrane with HA (MS) and at 750°C for the membrane with AB (MB). The surface and the cross-section morphologies observed through a scanning electron microscope (SEM) are homogeneous and do not present any macro defects (cracks, etc.). The average pore diameters of the active layer are approximately 0.25 μm and 0.2 μm for the MS and MB membrane respectively. The obtained membrane was used to treat cuttlefish effluents generated from the conditioning seawater product industry which consumes a great amount of water where the washing baths are discharged in the littoral of Sfax (Tunisia) (about 1000 m³/d). Cross-flow microfiltration was performed then, in order to reduce the turbidity and chemical oxygen demand (COD). The result showed a high retention of turbidity (99%), conductivity and COD (85%).