Emulsion Filtration Through Surface Modified Ceramic Membranes

In this work we studied the influence of membrane hydrophobicity on the filtration of oil/water (O/W) emulsions with a dispersed phase content of 30% (V/V). The membrane filtration process was realized by using ceramic tubular hydrophilic or hydrophobic membranes with different mean pore size (0.2 pm, 1.2 pm, and 1.4 pm of mean pore radius). Hydrophobic character was obtained by modifying superficially the membrane surface with a very thin polymer layer. The results obtained showed that the emulsion viscosity and droplet size distribution depend on the shearing forces and transmembrane pressure. The operating conditions and the nature of the membrane surface/emulsion interaction are the main parameters which control the type and nature of emulsion changes, such as modification of the mean droplet size, concentration into oleic phase or breaking.     

表面作用力孔流通模型计算高分子滤过膜孔径大小及分布的方法

综述了一种建立在表面作用力孔流通模型基础上计算高分子多孔滤过膜孔径大小及分布的方法。     

泡压-滤速法研究聚丙烯微孔膜的孔径及其分布

膜科学与膜技术作为新兴的材料科学分支之一,在国民经济中发挥着越来越重要的作用．近年来,高分子微孔膜的研究与应用正引起人们日益增长的关注．采用双轴拉伸方法制备的聚丙烯微孔膜同时具备了良好的力学性能和透过性能［１］,克服了单轴拉伸方法各向异性的缺点,是一...     

Use of gas-liquid porometry measurements for selection of microfiltration membranes

The process of crossflow microfiltration is hindered by the significant problem of fouling due to a pore size which favours penetration of the solutes. This leads to an internal fouling (adsorption and pore obstruction) which reduces permeate flux and makes any regeneration difficult. This study outlines a method of choosing an appropriate microfiltration membrane. Choice of membrane nature and pore size has been made in accordance with rapid dead-end filtration tests and the use of liquid-gas permporometry. Measuring pore size by porometry allows a choice of material which is non-adsorbent with regard to specific solutions to be microfiltered. Moreover, the internal fouling can be detected quickly by backflush washing after several minutes of dead-end filtration, and by measuring pore size distribution of the fouled membrane. Thus, choice of pore size will tend towards a membrane which bears slight internal fouling. The methodology described in this paper has allowed an appropriate choice of microfiltration membrane for use in recycling alkaline cleaning solutions in the dairy products industry.     

Pore blocking mechanisms during early stages of membrane fouling by colloids

A method based on a simple linear regression fitting was proposed and used to determine the type, the chronological sequence, and the relative importance of individual fouling mechanisms in experiments on the dead-end filtration of colloidal suspensions with membranes ranging from loose ultrafiltration (UF) to nanofiltration (NF) to non-porous reverse osmosis (RO). For all membranes, flux decline was consistent with one or more pore blocking mechanisms during the earlier stages and with the cake filtration mechanism during the later stages of filtration. For ultrafiltration membranes, pore blocking was identified as the largest contributor to the observed flux decline. The chronological sequence of blocking mechanisms was interpreted to depend on the size distribution and surface density of membrane pores. For salt-rejecting membranes, the flux decline during the earlier stages of filtration was attributed to either intermediate blocking of relatively more permeable areas of the membrane skin, or to the cake filtration in its early transient stages, or a combination of these two mechanisms. The findings emphasize the practical importance of the clear identification of, and differentiation between mechanisms of pore blocking and cake formation as determining the potential for the irreversible fouling of membranes and the efficiency of membrane cleaning.     

Mesoporous silica composites containing multiple regions with distinct pore size and complex pore organization

Porous ceramics are of great interest for filtration, catalysis, and reactive separation processes. Performance in these applications is highly dependent on features such as pore size distribution and connectivity and wall composition. Here, we describe a method allowing the rational design and synthesis of mesoporous silica composites with controlled heterogeneous pore architectures and demonstrate its validity by producing structures with predetermined placement of regions having different pore size and pore organization.     

Filtration of deformable emulsion droplets

Oil-in-water (o/w) emulsions of different droplet size were filtered on membranes of various pore sizes to investigate the growth and behaviour of o/w filter cakes. The cake desorptivity S and the filter membrane resistance R were measured at various filtration pressures P. The variation of S with P shows that filter cake oil droplets of radius a are effectively rigid for P < gamma/a and fully deformable for P > gamma/a, where gamma is the oil-water interfacial tension. For the largest P, when S became P-independent, the filter cake remained water-permeable as expected from theory.     

Effects of nanoparticles on the ultrafiltration of surface water

The effects of nanoparticles on the fouling behavior of UF membranes were investigated by filtering river water containing natural organic matter (NOM). Self-dispersible carbon black (70–200 nm) was employed to model nanoparticles in natural water. The presence of nanoparticles transformed the mode of initial fouling from internal pore adsorption of NOM to intermediate pore blocking, which caused a significant flux reduction. The use of powdered activated carbon to adsorb organic micromolecules reduced internal pore fouling, but this effect on initial fouling mode did not much mitigate the overall flux decline. As filtration proceeded, cake filtration became the dominant fouling mode. The resistance-in-series model revealed that boundary-layer resistance contributed significantly to increased filtration resistance in the filtration of river water. The nanoparticles nullified boundary-layer resistance plausibly by removing organic macromolecules from river water, but aggravated cake resistance, which required chemical cleaning. Addition of calcium significantly increased the aggregate size of nanoparticles from 0.18–0.35 μm to 3.4 μm, and thus reduced pore blocking and total cake resistance.     

大孔FCC催化剂的制备及裂化性能研究

利用聚苯乙烯(PS)颗粒和脱油残渣(VR)乳液为模板剂制备了大孔重油催化裂化催化剂,与未加模板的参比催化剂相比,比表面积分别增加了38.0%和46.2%,孔体积分别增加了20.6%和35.8%,平均孔径分别增加了54.5%和27.3%。微反评价结果表明,大孔催化剂活性较高,对重油的转化率分别提高了9.8%和12.2%,总液收分别提高了10.2%和7.3%。与参比催化剂相比,积炭后PS颗粒和VR乳液模板大孔催化剂的活性有一定程度的降低,但是当积炭量相同时,大孔催化剂的重油转化率和总液体产物收率都比参比催化剂要高,且两类大孔催化剂的数据比较接近。催化剂的基质经模板扩孔后,由于具有微孔-介孔-大孔的梯度孔分布,孔径分布更加合理,重油分子在催化剂孔道内的扩散速率更快,容炭能力更强,所以大孔催化剂具有较好的裂化性能。     

Crossflow microfiltration of oily water

Two α-alumina ceramic membranes (0.2 and 0.8 μm pore sizes) and a surface-modified polyacrylonitrile membrane (0.1 μm pore size) were tested with an oily water, containing various concentrations (250–1000 ppm) of heavy crude oil droplets of 1–10 μm diameter. Significant fouling and flux decline were observed. Typical final flux values (at the end of experiments with 2 h of filtration) for membranes at 250 ppm oil in the feed are ≈30–40 kg m⁻² h⁻¹. Increased oil concentrations in the feed decreased the final flux, whereas the crossflow rate, transmembrane pressure, and temperature appeared to have relatively little effect on the final flux. In all cases, the permeate was of very high quality, containing <6 ppm total hydrocarbons. The addition of suspended solids increased the final membrane flux by one order of magnitude. It is thought that the suspended solids adsorb the oil, break up the oil layer, and act as a dynamic or secondary membrane which reduces fouling of the underlying primary membrane. Resistance models were used to characterize the type of fouling that occurs. Both the 0.2 μm and the 0.8 μm ceramic membranes appeared to exhibit internal fouling followed by external fouling, whereas external fouling characterized the behavior of the 0.1 μm polymer membrane from the beginning of filtration. Examination of the external fouling layer showed a very thin hydrophobic oil layer adsorbed to the membrane surface. This oil layer made the membrane surface hydrophobic, as demonstrated by increased water-contact angles. The oil layer proved resistant to removal by hydrodynamic (shear) methods. By extracting the oil layer with tetrachloroethylene, followed by IR analysis, its average thickness at the end of a 2 h experiment under typical conditions was determined to be 60 μm for the 0.2 μm ceramic membrane and 30 μm for the 0.1 μm polymer membrane. These measured amounts of oil associated with the membrane at the end of the experiments are in good agreement with those determined from a simple mass balance, in which it is assumed that all of the oil associated with the permeate collected is retained on or in the membrane, indicating that the tangential flow did not sweep the rejected oil layer to the filter exit.     

几种粘土的孔隙结构与催化活性的研究

本文研究了五种不同产地的粘土在作为棉子油酸聚合反应催化剂时,其催化活性与孔隙结构的关系,采用气相流动色谱法,在液氮温度下测定粘土对氮气的吸附量,给出吸附及脱附等温线,确定其孔隙结构,对几种粘土作了差热分析及扫描电镜观察。研究结果表明:吉林粘土催化剂对棉子油酸聚合反应所得二聚酸的产率较高;所测样品均有较发达的中孔,孔径在30—40Å范围内的粘土对生成二聚酸有较好的选择性。     

Properties of protein adsorption onto pore surface during microfiltration: Effects of solution environment and membrane hydrophobicity

Properties of bovine serum albumin (BSA) adsorption onto pore surface during the filtration of BSA containing solution with the Sirasu porous glass membrane with a pore size of 0.1 μm were studied. The effects of pH, ionic strength, and surface modification on the flux decline and breakthrough curves were observed. The adsorption properties of BSA were estimated quantitatively by using the internal fouling model, which relates the filtration performance to the adsorption interaction, the adsorption capacity, and the thickness of the adsorption layer. The electrostatic interaction between BSA and pore surface was estimated by the streaming potential measurement. The BSA adsorption involved a rapid adsorption in the early stage of filtration followed by a slow multilayer adsorption that dominates the long-term filtration performance. The electrostatic repulsive force reduced the overall adsorption interaction but the electrostatic attractive force did not affect the adsorption interaction. The effect of ionic strength on the BSA adsorption could be explained in terms of the shift of the IEP of BSA toward lower pH with the increase in ionic strength. The hydrophobicity of membrane did not affect the adsorption properties except for the adsorption interaction in the early stage of the filtration.     

Study of Retention Ability of Nucleopore Membranes

The influence of pore sizes of nucleopore membranes and their shapes on the retention of polystyrene particles of 40–100 nm in size was studied. The interrelation between structural parameters of the nucleopore membranes found by various methods and the efficiency of filtration of calibrated particles were analyzed. The potential and limitations of the procedure for determining the efficiency of filtration of nanosized latex particles was demonstrated; the procedure was based on UV absorption spectroscopy.     

Demulsification of water-in-oil emulsion by using porous glass membrane

The hydrophilic porous glass membranes were used to demulsify water-in-oil emulsion, and demulsification efficiency can reach more than 96.2%. Effects of pore size of the membrane, transmembrane pressure and volumetric ratio of oil phase to internal aqueous phase in the emulsion on demulsification were investigated. It was found that pore size of membrane and transmembrane pressure can significantly affect demulsification efficiency. The smaller the pore size of the membrane, the better the demulsification efficiency. However, smaller pore size of the membrane has to be exerted a greater transmembrane pressure in order to make internal aqueous phase enter the membrane pore. Correspondingly, effect of transmembrane pressure on permeation flux of the droplets was also studied. In addition, recovered-oil phase by the demulsification were reused five times to extract cadmium from simulated aqueous waste. The results indicated that the extracting efficiency could arrive at 96.5%.     

Self‐Assembled Isoporous Block Copolymer Membranes with Tuned Pore Sizes

The combination of nonsolvent‐induced phase separation and the self‐assembly of block copolymers can lead to asymmetric membranes with a thin highly ordered isoporous skin layer. The effective pore size of such membranes is usually larger than 15 nm. We reduced the pore size of these membranes by electroless gold deposition. We demonstrate that the pore sizes can be controlled precisely between 3 and 20 nm leading to a tunable sharp size discrimination in filtration processes. Besides fractionation of nanoparticles and biomaterials, controlled drug delivery is an attractive potential application.     

Microfiltration membranes prepared from polyethersulfone powder grafted with acrylic acid by simultaneous irradiation and their pH dependence

Polyethersulfone (PES) powder was grafted with acrylic acid (AAc) by simultaneous γ-ray irradiation. The kinetics of the radiation induced graft polymerization was studied and the grafted PES powder was characterized. Then, microfiltration (MF) membranes were prepared from PES-g-PAAc powder with different degrees of grafting (DG) under phase inversion method. The swelling behavior and the mean pore size of MF membranes were measured, and the filtration property was tested. The results showed that the pore size and the flux of MF membranes increased with the increase in DG. And, MF membranes’ properties were dependent on the pH value.     

Influence of the Pore Structure of a Catalyst for Demetallization of Petroleum Feedstock on the Process Results

Demetallization of a mixture of vacuum gas oil with heavy coker gas oil on CoMo/γ-Al₂O₃ catalysts with different pore structures was studied, and the influence of the catalyst pore structure on the process results was demonstrated. For the demetallization catalysts to be effective, their pore size should be restricted not only from below but also from above. When using samples with broad pores, effects of the hydrodesulfurization and hydrodemetallization inhibition can arise owing to adsorption of supramolecular structures of heavy residues, in particular, of asphaltenes.

     

A novel polypropylene microporous film

The structure and properties of a polypropylene microporous film prepared by biaxial stretching of non-porous polypropylene film of high β-crystal content were investigated. The porosity of these films can be as high as 30–40%, and the average pore size was around 0.05 μm. The films were found to have the structure of a two-phase interpenetrating network; both the polypropylene and the pore regions were three-dimensionally continuous. The advantages of the biaxially stretched microporous films are the combination of high permeability to fluids with good mechanical properties and almost circular pore shape with narrow pore size distribution. The application of this microporous film for battery separators, filtration membranes and substrates of functional polymer composites is discussed.     

Effect of particle shape on crossflow filtration flux

In an effort to further increase the understanding of crossflow filtration, experiments were performed on the influence of particle shape on permeation flux. Five particles of similar density and size distribution but of different shapes were used to test the influence of particle shape, while varying experimental parameters such as crossflow velocity, filtration pressure, solids concentration, membrane morphology and pore size. Particle shape was found to influence the equilibrium flux by the structure of the cake layer formed. Irregularly shaped particles such as branched carbon particles provided higher fluxes due to the high voidage cakes. More regularly shaped particles such as glass spheres resulted in lower fluxes. Platelet aluminium particles had relatively high filtration rates due to the gaps between the plates. The effects of the other experimental parameters typically showed results consistent with previous publications. Using the measured cake mass, a theoretical model based on D'Arcy and Kozeny gave reliable filtration flux compared to the experimental results.     

油田水中烷基酚的胶束电动色谱分离

采用硼酸盐-十二烷基硫酸钠胶束电动色谱对油田水中存在的烷基酚进行了分离分析。考察了影响分离的各种不同因素：缓冲液浓度、体系的pH值、胶束溶液浓度、分离电流、管住温度及有机添加剂β-环糊精等。在恒流100μA下,38min内可分离20种烷基酚。采用Cl－TBP萃淋树脂对油田水样进行了浓缩富集预处理。