Performance of two heat transfer fouling probes for various fluids

The predictions of two commonly used fouling monitoring devices, namely a heated rod in an annulus and a coiled wire in cross-flow are compared. As fouling fluids, heptane with dissolved styrene (to simulate chemical reaction fouling), heptane with suspended particles (to simulate particulate fouling) and Kraft pulp black liquor (where both the above fouling mechanisms may occur) have been used.     

New anion-exchange membrane resistant to organic fouling

An anion-exchange membrane was modified by sulfonating the surface of the base membrane, composed of styrene-divinylbenzene copolymer and polyvinylchloride, before its chloromethylation and the subsequent quarternization. The following three points are discussed: (1) effect of surface treatment with concentrated sulfuric acid to protect the membrane against organic fouling, (2) relation between sulfonating conditions at the membrane surface and the properties of the modified anion-exchange membrane, and (3) evaluation of the modified anion-exchange membrane.     

Regression analysis of a chemical reaction fouling model

A previously reported mathematical model for the initial chemical reaction fouling of a heated tube is critically examined in the light of the experimental data for which it was developed. A regression analysis of the model with respect to that data shows that the reference point upon which the two adjustable parameters of the model were originally based was well chosen, albeit fortuitously.     

反渗透膜有机污染的研究进展

介绍了反渗透进水中一些主要有机污染物质的污染机理以及操作条件、膜自身特性、溶液化学性质对于污染过程的影响,还综述了预处理技术、清洗方法以及通过膜的表面改性等措施来控制反渗透膜的有机污染,最后指出了目前研究中需关注的一些问题。     

Chemical control of colloidal fouling of reverse osmosis systems

Fouling of membranes by colloidal organic and inorganic particles continues to be documented as the most common and challenging obstacle in attaining stable continuous operation of reverse osmosis (RO) and ultrafiltration (UF) systems. Much current research is being conducted on physical parameters to mitigate such fouling. The focus has been on membrane synthesis and element design; microfiltration and ultrafiltration pretreatment; electromagnetic devices; correlation with physical factors such as Silt Density Index, zeta potential and critical flux; technique of direct observation of fouling process through a membrane; and classification of macromolecular organics for correlation with fouling characteristics. We report initial successes with chemical control of colloidal fouling. Through screening with a large number of observable coagulations of natural colloids, we have developed a group of proprietary anticoagulants and dispersants that would, at less than 10 ppm dosage to the RO feedwater, control various classes of colloidal foulants. Case studies of the control of humic matter, elemental sulfur and colloidal silicate in problematic RO systems that became stabilized are briefly presented. We conclude that a great need and potential exists in economically controlling the myriads of fouling interactions of colloidal particles during concentration within the brine channels of RO membrane elements. Low dosages of antifoulants can in many cases obviate the need for installation and maintenance of pretreatment unit or operations designed to remove such colloidal foulants from the process stream.     

A model fouling reaction in a zeolite catalyst

A zeolite catalyst became rapidly fouled when used for the alkylation of benzene by cyclohexene at temperatures below 245°C. At higher temperatures, the extent of fouling was limited and at 450° C, a steady rate of formation of cyclohexyl benzene was observed. The fouling material was identified as a mixture of di- and tri-alkyl benzene, trapped because of size in the void spaces of the zeolite crystal. A mathematical model based on the forms of Langmuir-Hinshelwood kinetics was used to describe the fouling phenomenon. The effect of the internal mass transport has also been investigated by means of a mathematical model. This model indicates that transport between the surface of the zeolite crystal and interior reaction sites is rapidly blocked by a layer of fouling material.     

超临界流体中的化学反应

超临界流体中的化学反应可分为两大类 ,即超临界流体作为反应介质的反应和超临界流体作为反应原料的反应 ,分别介绍了其研究进展 ,着重介绍了第一类反应中的酶催化反应、超临界水氧化、高分子合成     

A study of autoxidation reaction fouling in heat exchangers

The mechanism of autoxidation reaction fouling in single phase liquid heat transfer under turbulent flow conditions was studied using model solutions of indene in lube oil recirculated through a tubular fouling probe which permitted both thermal and mass deposition measurements. The fouling rate was initially constant, and then accelerated as polyperoxide gums reached their solubility limit. Deposit composition and morphology in the tubular device are compared with results obtained in an annular probe with a short heated length. The initial fouling data collected over surface temperatures of 180?255°C and flow velocities of 0.5–2.6 m/s (Re = 3000 ? 16000) gave reasonable agreement with a boundary layer reaction model.     

Optimal design of a heat exchanger undergoing reaction fouling

The design of heat exchangers which resist fouling is examined. It is shown that for asymptotic reaction fouling in a uniform wall temperature exchanger with outlet fluid temperature kept constant, it is possible to obtain an optimum combination of exchanger size and tube-side temperature. This optimum minimises the amount of fouling in the system. An equation which gives a good approximation to the optimum is derived, and its limitations discussed.     

Control of organic fouling at two seawater reverse osmosis plants

Organic fouling of seawater Reverse Osmosis (RC) membranes is a phenomenon not well understood; it can result in a loss of membrane productivity and salt rejection properties. Two seawater RO plants using DuPont B-10 hollow fiber permeators had experienced organic fouling and were studied.The two plants used different sources of feedwater; one RO plant at Culebra, Puerto Rico, used open seawater; while the other RO plant at Grand Cayman Island, British West Indies, used a sea well. Both feed water sources possessed high concentrations of soluble organics (40–80mg/1) which were mainly humic acids. In an attempt to remove these organics with in-line cationic polyelectrolyte coagulation, the plants experienced organic fouling which caused excessive loss of productivity and salt rejection; both plants initially failed their acceptance tests.It was discovered that the fouling was actually caused by interactions between the humic acids and in-line cationic, polyelectrolyte coagulants which were not removed by in-dedth and cartridge filtration. Rather than remove the humic acid material, acid addition was initiated and in-line cationic coagulants use discontinued to keep the humic acids soluble. It should be noted that with the open seawater intake ferrous sulfate was still used to remove colloidal material and reduce the SDI. Both plants subsequently have passed their 720-hour acceptance test.Culebra and Grand Cayman plants have now exceeded design specification for both productivity and salt rejection. The aramid hollow fiber permeators on acidified feed have shown 100% rejection of these organics at both 25% and 50% conversion and organic fouling has not been evident.     

超临界流体在非催化反应中的应用

依据超临界流体自身的特点,在反应中既作为溶剂又作为催化剂,从一个全新的角度介绍了超临界流体在非催化反应中的新成果、新动向。主要阐述了包括超临界水、甲醇、二氧化碳在有机反应中的应用,并与传统催化反应进行了比较,同时探讨了国内外研究现状、应用前景和发展趋势。     

A contribution to fouling in hyperfiltration induced by chemical reaction

The foulant iron hydroxide is formed by condensation reaction using hydrolyzable iron (III)-salt solutions. This occurs in the bulk as well as in the concentration polarization layer. As steady state conditions are difficult to obtain, cobalt and lithium salts are used to study the relationship of competitive transport of different coions through the membrane. It could be shown that at low pH values the most mobile ions permeate, and when condensation by hydrolysis may occur, the reaction will start.     

Measurement of rate of anion exchange and the effect of organic fouling

A method has been developed for the examination of rates of reaction of a strongly basic ion-exchange resin with a large organic anion. The results indicate that an organically fouled resin reacts at a slower rate than an unfouled one under standard conditions, and the possibilities of using the method as an aid to solving the problem of organic fouling are discussed.     

Natural organic matter fouling due to foulant–membrane physicochemical interactions

An extended DLVO (XDLVO) force analysis was introduced to predict natural organic matter (NOM) fouling in ultrafiltration (UF) membrane processes. Ultrafiltration membrane fouling experiments were performed using two NOM extracts from real waters and two commercial polymeric UF membranes. The hydrodynamic force by permeation drag and three interfacial forces of XDLVO (van der Waals, electrostatic, acid–base energy) were used for the force analysis. Acid–base interaction forces between NOM and UF membranes were dominant in short range (separation distances < 5 nm) and appear to determine the potential of NOM deposition. Relative extents of flux decline were successfully predicted using the short-range force analyses.     

腐殖酸类物质对反渗透膜的污染研究

通过单一污染物实验,分析了不同浓度的腐殖酸类有机物对反渗透膜的污染过程,明确了膜表面沉积的腐殖酸类有机污染物总量是导致系统膜通量降低与脱盐率升高的主要因素.腐殖酸与钙离子的复合污染实验表明,钙离子的存在加快了腐殖酸的沉积速率,且两者在膜表面的沉积使膜通量与脱盐率下降,而腐殖酸在膜上的沉积量是通量变化的决定因素.     

Preparation of macroreticular anion exchange membrane and its behavior relating to organic fouling

Base membranes were prepared by coating a monomer mixture consisting of styrene–divinylbenzene–polybutadiene–t-amyl alcohol onto a polypropyrene cloth and subsequently by polymerizing the monomers. The resultant base membranes were chloromethylated and then quaternized. Thus, macroreticular anion exchange membranes were prepared and their properties were investigated. Furthermore, the organic fouling of the membranes was studied by using Na dodecylbenzenesulfonate as a foulant. The resistibility of the membranes was dependent on the balance between the porosity of the membranes and the foulant quantity.     

Chemical recycling of plastics using sub- and supercritical fluids

The development of chemical recycling of waste plastics by decomposition reactions in sub- and supercritical fluids is reviewed. Decomposition reactions proceed rapidly and selectively using supercritical fluids compared to conventional processes. Condensation polymerization plastics such as polyethylene terephthalate (PET), nylon, and polyurethane, are relatively easily depolymerized to their monomers in supercritical water or alcohols. The monomer components are recovered in high yield. Addition polymerization plastics such as phenol resin, epoxy resin, and polyethylene, are also decomposed to monomer components with or without catalysts. Pilot scale or commercial scale plants have been developed and are operating with sub- and supercritical fluids.     

A Comparative study of organic fouling in hollow fiber and spiral wound membranes

The occurrence of flux decline in brackish water reverse osmosis (RO) plants due to dissolved organics is a topic of ongoing research. This type of organic fouling has also been found in seawater RO plants. A study was undertaken to compare organic fouling in hollow fiber and spiral wound membranes using a seawater feed that possessed a high concentration of huraic acid. This study was undertaken at an RO plant on Grand Cayman Island, British West Indies. The feed water came from a sea well and possessed a concentration of humic acid that varied between 35 and 60 mg/l.The hollow fiber membrane was operated at a recovery of 25% while the recovery with the spiral wound membrane varied between 5 and 25%. The performance data which included permeate flow, salt rejection, pressure drops across the membrane and analysis of the membranes for organic fouling were undertaken. This study compared the performance data and organic fouling between the hollow fiber and spiral wound meembranes.     

有机合成中的氰化反应

氰基化合物因具有独特的性质被人们广泛的应用在医药、农药、材料等领域。系统地介绍了有机合成中的加氰反应,对不同类型的氰化反应进行了综述。