Effect of cake layer structure on colloidal fouling in reverse osmosis membranes

A series of reverse osmosis (RO) membrane filtration experiments was performed systematically in order to investigate the effects of various hydrodynamic and physicochemical operational parameters on a cake layer formation in colloidal and particulate suspensions. Bench-scale fouling experiments with a thin-film composite RO membrane were performed at various combinations of trans-membrane pressure (TMP), cross-flow velocity (CFV), particle size, pH, and ionic strength. In this study, silica particles with two different mean diameters of 0.1 and 3.0 μm were used as model colloids. Membrane filtration experiments with colloidal suspensions under various hydrodynamic operating conditions resulted that more significant permeate flux decline was observed as TMP increased and CFV decreased, which was attributed to the higher accumulative mass of particles on the membrane surface. Results of fouling experiments under various physicochemical operating conditions demonstrated that the rate of flux decline decreased significantly with an increase of the ionic strength as well as particle size, while the flux decline rate did not vary when solution pH changed. The experimentally measured cake layer thickness increased with a decrease in particle size and solution ionic strength. Furthermore, the model estimation of cake layer thickness by using a cake filtration theory based on the hydraulic resistance of membrane and cake layer was performed under various ionic strength conditions. The primary model parameters including accumulated mass and specific cake resistance were calculated from the cake layer resistance. This result indicated that the formation of cake layer could be closely related with solution water chemistry. The model estimated cake layer thickness values were in good agreement with the experimentally measured values.     

Component interactions and the stability of some pigment/polymer dispersions

The sedimentation behavior of rutile and selected organic pigments dispersed in polymer solutions has been interpreted in terms of acid-base interactions at the polymer/pigment interface. The acid-base information was obtained from inverse gas chromatography. Moderate strengths of acid-base interaction were beneficial to the stability of dispersions, whereas both the absence of and excessive interaction resulted in the rapid deposition of solids. The effect is associated with the orientation of adsorbed polymer molecules, which must provide an adequate steric (entropic) barrier for the aggregation and deposition of solids. Implicated is the balance of interaction forces at pigment/polymer and polymer/solvent contacts. Rheological data for the dispersions have been used to obtain a parameter related to the thickness of the adsorbed polymer layer, by way of amplifying on the state of the pigment/polymer interface. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67: 245–253, 1998     

絮凝沉淀-吸附两步法预处理松节油加工废水

采用絮凝沉淀-吸附两步法预处理松节油加工废水。筛选了絮凝剂和树脂类吸附材料,研究了吸附温度、时间、流量对吸附过程的影响,脱附剂及脱附液体积对解吸过程的影响。结果表明:常温下,pH值为7时,PAM为最佳的絮凝剂,废水中CODCr的去除率达36.1%;温度为30℃,pH值为7时,吸附流量为1 BV/h,聚氨酯为最佳的吸附材料,废水中CODCr的去除率可达35.7%;室温下依次以3 BV质量分数为6%的H2SO4溶液和2BV的水作为脱附剂,脱附流量为1 BV/h,脱附液体积为5 BV,脱附率可以达到92.3%;聚氨酯经过5次吸附-脱附后仍保持良好的吸附性能。     

温敏型聚合物在稠油污水中的絮凝作用探讨

稠油污水絮凝剂大都是阳离子聚丙烯酰胺(CPAM),但该絮凝剂在稠油污水中高分子长链的伸展受到高温和高矿化度的影响,絮凝效果大大降低。探讨了一种温敏型絮凝剂PA在不同浓度、温度、及不同浓度无机盐(NaCl和CaCl_2)条件下的絮凝作用并与CPAM进行对比。实验结果表明:温敏絮凝剂PA对稠油污水的乳化油和固相悬浮物的去除率较CPAM高,其主要原因是PA在较高温度下发生相分离使溶液亲水性降低、吸附能力增强;温度和无机盐(NaCl、CaCl_2)能促进温敏絮凝剂PA对稠油污水中乳化油和固相悬浮物的去除效果。     

Coagulation–flocculation of colloidal suspensions of kaolinite,bentonite, and alumina by chitosan sulfate

This article reports on the removal of colloidal suspensions of kaolinite, bentonite, and alumina using chitosan sulfate (ChS). ChS was synthesized by partial introduction of sulfate groups in the chitosan (Ch) structure. The polyampholyte (chitosan sulfate) shows variable charge depending on the pH of the solution. ChS was characterized by FTIR, ¹³C‐NMR, elemental analysis, and potentiometric titrations. The ChS coagulation–flocculation capacity for kaolinite, bentonite, and alumina aqueous suspensions was systematically studied. The coagulation–flocculation process was carried out at various pH values and ChS concentrations. The pH range in which the largest ChS removal capacity was observed depended on particle type (4.5–5.5 for kaolinite, 4.5–7.0 for bentonite, and 7.0–8.0 for alumina). The removal of colloidal particles is explained by charge neutralization due to electrostatic interactions between ChS and particles and particle entrapping when the polyelectrolyte precipitates. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Adsorption of a weakly charged polymer on an oppositely charged colloidal particle: Monte Carlo simulations investigation

Monte Carlo simulations were used to investigate the conformational and electrical properties of isolated weak polyelectrolytes in the presence of an oppositely charged particle. Titrations curves were calculated to get an insight into the role of pH on the degree of ionization and conformation of isolated chains. The effect of ionic concentration and polyelectrolyte length on the titration curves was also investigated. The complex formation between the isolated polyelectrolyte and the oppositely charged particle was considered at different pH and ionic concentration values. The adsorption/desorption limit was calculated and the effect of the polyelectrolyte adsorption on the titration curves investigated. In particular, it was demonstrated that the presence of an oppositely charged particle clearly increases the degree of ionization of the weak polyelectrolyte and that ionic concentration plays a subtle role by increasing/reducing both the attractive energy between the polyelectrolyte and the particle and the polyelectrolyte degree of ionization.     

A population balance model for flocculation of colloidal suspensions by polymer bridging

A detailed population balance model for flocculation of colloidal suspensions by polymer bridging under quiescent flow conditions is presented. The collision efficiency factor is estimated as a function of interaction forces between polymer coated particles. The total interaction energy is computed as a sum of van der Waals attraction, electrical double layer repulsion and bridging attraction or steric repulsion due to adsorbed polymer. The scaling theory is used to compute the forces due to adsorbed polymer and the van der Waals attraction is modified to account for presence of polymer layer around a particle. The irregular structure of flocs is taken into account by incorporating the mass fractal dimension of flocs. When tested with experimental floc size distribution data published in the literature, the model predicts the experimental behavior adequately. This is the first attempt towards incorporating theories of polymer-induced surface forces into a flocculation model, and as such the model presented here is more general than those proposed previously.     

磁絮凝强化技术处理厌氧消化污泥脱水液

为满足后续生物处理单元对固体悬浮物（SS）和铁浓度的进水要求,采用磁絮凝强化技术对厌氧消化污泥脱水液进行预处理。通过正交试验和单因素试验,本文考察了混凝水力条件、聚合氯化铝（PAC）投加量、聚丙烯酰胺（PAM）投加量、磁粉投加量及药剂投加顺序对磁絮凝效果的影响。试验结果表明：磁絮凝强化技术在快搅300r/min（2min）、慢搅100r/min（15min）、静置10min时,依次投加磁粉（40mg/L）、PAC（30mg/L）、PAM（4mg/L）时处理效果最好。在此运行条件下,SS和Fe³⁺去除率分别为97.61%、98.24%、絮凝指数（FI值）取得最大值、zeta电位绝对值最小,絮凝效果最佳。与对照相比,磁絮凝强化技术对SS和Fe³⁺去除率分别可提高3.70%和10.82%,同时絮体最大沉降速度可提高33%。磁絮凝技术处理后的出水不仅可以满足后续生物处理单元对SS和铁浓度的要求,还可以有效提高磁絮凝体的沉降速度,减小沉淀时间,具有较好的实用价值。     

XPS测定减水剂吸附层厚度

通过XPS谱图和XPS信息深度的计算方法测定了减水剂在胶凝颗粒表面的吸附层厚度。结果显示,木质素磺酸盐减水剂（LS）、改性木质素磺酸盐减水剂（GCL1-T）、萘系减水剂（FDN）和氨基磺酸盐减水剂（ASP）在水泥颗粒表面的吸附层厚度分别为8.70、10.87、1.50、7.26 nm;GCL1-T和FDN在粉煤灰表面的吸附层厚度分别为6.76 nm和0.95 nm。此方法可较准确描述减水剂在胶凝颗粒表面吸附层厚度的相对大小。由测定结果可进一步推断,FDN的分散机理以静电斥力效应为主;而空间位阻效应在LS、GCL1-T和ASP的分散机理中不可忽略。     

絮凝沉降-NaClO/活性炭氧化-吸附法处理采油污水实验研究

国内油田的采油污水绝大部分经处理后用于油田注水,但由于种种原因,还有一部分采油污水不能回注.这部分水外排至环境中,对环境产生一定的影响.作者以甘谷驿油矿采油污水为研究对象,采用絮凝沉降-NaClO/活性炭氧化-吸附法对该采油污水进行外排处理实验研究.考察了pH、NaClO投加量、氧化时间、吸附时间、活性炭投加量对CODCr去除率的影响.实验结果表明,该法可使原水含油质量浓度从93.1 mg/L降至5 mg/L以下,悬浮物从172 mg/L降至10 mg/L以下,CODCr从2 634 mgg/降至100 mg/L以下,出水各项指标均达到国家一级排放标准.     

The flocculation of kaolin by cationic polyacrylamides and the effect of cationic surfactant on this process

The flocculation of kaolin suspended in a dilute salt solution was studied as a function of the addition of cationic surfactant and cationic polyacrylamide (CPAM) added separately, consecutively, or simultaneously. Cationic polyacrylamide caused flocculation by bridging when added in low concentrations, but at higher concentrations, charge neutralization became the dominant mechanism and the flocculation rate was highly dependent on the charge density of the polymer. Adsorption of sufficient polymer or surfactant (cetyl pyridinium chloride) prevented immediate adsorption of the other, although surfactant could replace polymer after extended agitation. The adsorption of polymer was greatest when small flocs were formed by charge neutralization or by prolonged shaking. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2382–2389, 2002     

Enhanced electrochemical performance of Lithium-ion batteries by conformal coating of polymer electrolyte

This work reports the conformal coating of poly(poly(ethylene glycol) methyl ether methacrylate) (P(MePEGMA)) polymer electrolyte on highly organized titania nanotubes (TiO₂nts) fabricated by electrochemical anodization of Ti foil. The conformal coating was achieved by electropolymerization using cyclic voltammetry technique. The characterization of the polymer electrolyte by proton nuclear magnetic resonance (¹H NMR) and size-exclusion chromatography (SEC) shows the formation of short polymer chains, mainly trimers. X-ray photoelectron spectroscopy (XPS) results confirm the presence of the polymer and LiTFSI salt. The galvanostatic tests at 1C show that the performance of the half cell against metallic Li foil is improved by 33% when TiO₂nts are conformally coated with the polymer electrolyte.     

Cu/Ni colloidal dispersions stabilised by calcium and barium stearates for the amination of oxo-alcohols

Bimetallic Cu/Ni colloidal dispersions (the core catalyst) stabilised by a combination of calcium and barium stearates as protective colloids (catalyst C) showed a remarkable catalytic activity-several times higher than that of the core catalyst stabilised by barium stearate only (catalyst A) for the amination reaction of low reactive oxo-alcohols, having steric hindrance by branched alkyls, with dimethylamine to prepare N,N-dimethyl tertiary amines. Application of the catalyst C for the same amination reaction of dodecyl alcohol could be performed at a lower catalyst concentration of even 100 ppm based on copper at 220° C with a tertiary amine yield of 92% in a three hours' reaction. The reaction mixture containing catalyst C formed a gel at room temperature and formed a stable homogeneous solution with acetone as a polar solvent. It is postulated that water-repellency of calcium stearate and further incorporation of barium stearate as a second promoter yields a doubly stabilised structure for the core catalyst resulting in a remarkable increase in catalytic activity.     

Investigation of aggregation, breakage and restructuring kinetics of colloidal dispersions in turbulent flows by population balance modeling and static light scattering

Quantitative modeling of aggregating colloidal systems is the underlying problem in many industrial processes, such as micro and nanoparticle processing, crystallization or flocculation. Population balance models with various aggregation and breakage kernels have been proposed in order to describe aggregating systems, but they have been rarely validated against appropriate experimental data. Typically, model parameters are fitted against a single measured moment of the cluster distribution which can usually be equivalently described using several variations of the set of parameters underlying the relevant aggregation, breakage and restructuring kernels. In order to discriminate among alternative models we propose an approach based on measurement and quantitative modeling of multiple moments of the cluster mass distribution, such as those obtained from static light scattering measurements. This approach is applied to aggregation processes in turbulent conditions in order to test alternative kernels for aggregation, breakage, and restructuring kinetics. We present a detailed study on the sensitivity of measurables from static light scattering with respect to commonly used aggregation and breakage kinetic models. In particular, we analyze the dynamic and steady state behavior of two measurables: the average radius of gyration and the average zero angle intensity which represent two independent moments of the cluster mass distribution. In addition, we discuss the effect of cluster structure and mass distribution on the average structure factor and the apparent fractal dimension measured by static light scattering, in order to assess what structural information can be reliably extracted from such measurements.     

Enhanced performance and improved interfacial properties of polymer electrolyte membrane fuel cells fabricated using sputter-deposited Pt thin layers

For this study, catalyst layers for polymer electrolyte membrane fuel cells (PEMFC) were prepared by spraying and sputtering to deposit Pt amount of 0.1 and 0.01 mg cm⁻², respectively. These Pt layers were then assembled to fabricate membrane electrode assemblies (MEA) having either single- or double-layered catalysts. The PEM fuel cell with double layers showed a current density of 777 mA cm⁻² at a cell voltage of 0.6 V, which is a higher current density than state-of-the-art fuel cells at 643 mA cm⁻². These results indicate that Pt loading in state-of-the-art PEMFCs could be reduced by approximately 50% with no performance loss by using both spraying and sputtering method in the MEA fabrication process.     

Phase separation of polymer mixtures driven by photochemical reactions: current status and perspectives

Phase separation of polymer mixtures induced by photo‐crosslinking and photopolymerization is summarized from the viewpoint of competing interactions in polymeric systems. First, the kinetics of photo‐crosslinking and photopolymerization are reviewed with particular emphasis on the Trommsdorff ? Norrish effect in polymerization, which leads to the formation of a bimodal distribution of molecular weight at long irradiation time. The emergence of a very large molecular weight and the characteristic time for this effect to set in are utilized as a tool to control the temporal development of the resulting morphology. The shrinkage associated with the reaction and particularly its effect on the phase separation and the morphology are discussed together with the influence of the Trommsdorff ? Norrish effect. Experiments on polymerization‐induced phase separation extended from binary to ternary mixtures are described where the interfacial interactions give rise to a wide variety of morphologies. Taking advantages of light, experiments using spatial and temporal modulation have been performed to control and manipulate the phase separation. These experimental results are summarized and briefly discussed in relation to the elastic deformation induced by polymerization. Finally, an overview of theoretical studies and numerical simulation of reaction‐induced phase separation is given with some comments on the complexity of the phenomena. © 2016 Society of Chemical Industry     

M-MOF-74吸附分离H2/He混合物的分子模拟研究

为了探究有机金属框架MOF-74能否作为一种优良的固体吸附剂,分离H₂/He混合物中H₂,并达到提纯He的目的,采用分子模拟的手段研究了H₂、He及H₂/He混合物在M-MOF-74（M=Mg、Co、Ni、Cu、Zn）上的吸附性能及吸附机理。结果表明,在1 bar（1 bar=10⁵ Pa）压力和25℃条件下,纯H₂对纯He在Ni-MOF-74上的选择性达6.58,而Mg-MOF-74对H₂的吸附量最大,其值为0.19 mmol·cm^-3,为He吸附量的6.46倍。当H₂/He混合物的浓度发生变化时,对其在M-MOF-74上的吸附分离因子没有较大影响,说明浓度变化不会影响M-MOF-74上吸附位点容纳H₂和He的能力。吸附位点和吸附热分析表明,MOF-74上的金属离子未饱和位点能够显著增强其对H₂的吸附能力。其结果对判断M-MOF-74是否具有分离H₂/He混合物的潜力,以及定量分析MOFs金属未饱和位点对H₂/He混合物分离的贡献提供了一定的理论基础。     

M-MOF-74吸附分离H2/He混合物的分子模拟研究

为了探究有机金属框架MOF-74能否作为一种优良的固体吸附剂,分离H₂/He混合物中H₂,并达到提纯He的目的,采用分子模拟的手段研究了H₂、He及H₂/He混合物在M-MOF-74（M=Mg、Co、Ni、Cu、Zn）上的吸附性能及吸附机理。结果表明,在1 bar（1 bar=10⁵ Pa）压力和25℃条件下,纯H₂对纯He在Ni-MOF-74上的选择性达6.58,而Mg-MOF-74对H₂的吸附量最大,其值为0.19 mmol·cm^-3,为He吸附量的6.46倍。当H₂/He混合物的浓度发生变化时,对其在M-MOF-74上的吸附分离因子没有较大影响,说明浓度变化不会影响M-MOF-74上吸附位点容纳H₂和He的能力。吸附位点和吸附热分析表明,MOF-74上的金属离子未饱和位点能够显著增强其对H₂的吸附能力。其结果对判断M-MOF-74是否具有分离H₂/He混合物的潜力,以及定量分析MOFs金属未饱和位点对H₂/He混合物分离的贡献提供了一定的理论基础。     

Separation of He/N2/CH4 ternary mixtures by a triple-reflux pressure swing adsorption process

Conventional pressure swing adsorption (PSA) processes can only produce one high purity product in a single stage, whereas the state-of-art dual-reflux PSA (DR-PSA) can produce two high purity products simultaneously. However, multicomponent gas separation is often required in the industry, targeting at recovering several valued products at the same time. In this study, we propose a novel adsorption process, namely triple-reflux PSA (TR-PSA), to separate three components simultaneously. A middle product outlet and a middle reflux stream were introduced to the adsorption columns of a conventional DR-PSA process to separate ternary mixtures of nitrogen, methane, and helium. Nonisothermal dynamic models were built to investigate the impacts of operating parameters particularly the location of the middle reflux/product stream and the middle reflux flow rates. Results showed that the TR-PSA process successfully separated ternary mixtures obtaining three enriched products simultaneously in a single stage, yielding a separation performance comparable to that of the double-stage DR-PSA with significantly lower capital and energy cost.     

The influence of the ionic concentration, concentration of the polymer, degree of neutralization and chain extension on aqueous polyurethane dispersions prepared by the acetone process

There are many variables in the preparation of aqueous polyurethane (PU) dispersions. Chemical and compositional variables such as carboxylic acid concentration, concentration of the polymer, degree of pre/post-neutralization of the carboxylic acids and chain extension that all impact solution properties such as particle size and viscosity. Another variable is the method by which the dispersion is prepared; two primary methods are currently employed in industrial manufacture, the prepolymer mixing process and the acetone process. This study evaluates the impact of the chemical variables on a given PU dispersion formulation prepared by the acetone process. Changes in carboxylic acid concentration, degree of pre/post-neutralization and chain extension were found to have the expected impacts on dispersion solution properties. Increased ionic concentration, and degree of pre-neutralization led to lower particle size and higher viscosity, increased degree of chain extension led to larger particle size and lower viscosity, increased post-neutralization increased both particle size and viscosity, and increased concentration of the polymer led to a viscosity increase without any change in particle size.