bluuebunny/crossref_metadata_2025 huggingface dataset:
Modeling Purchase Behavior at an E-Commerce Web Site: A Task-Completion Approach
Authors: Sismeiro Catarina , Bucklin Randolph E.
Published: July 2004

The authors develop and estimate a model of online buying using clickstream data from a Web site that sells cars. The model predicts online buying by linking the purchase decision to what visitors do and to what they are exposed to while at the site. To overcome the challenges of predicting Internet buying, the authors decompose the purchase process into the completion of sequential nominal user tasks and account for heterogeneity across visitors at the county level. Using a sequence of binary probits, the authors model the visitor's decision of whether to complete each task for the first time, given that the visitor has completed the previous tasks at least once. The results indicate that visitors' browsing experiences and navigational behavior predict task completion for all decision levels. The results also indicate that the number of repeat visits per se is not diagnostic of buying propensity and that a site's offering of sophisticated decision aids does not guarantee increased conversion rates. The authors also compare the predictive performance of the task-completion approach with single-stage benchmark models in a holdout sample. The proposed approach provides superior prediction and better identifies likely buyers, especially early in the task sequence. The authors also discuss implications for Web site managers.
Adsorption and Reaction of Methanol on Clean and Oxygen Precovered Cu(111)
Authors: Pöllmann S. , Bayer A. , Ammon Ch. , Steinrück Hans-Peter
Published: July 2004

The adsorption of methanol on the clean and oxygen precovered Cu(111) surface was studied by means of high resolution X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), and temperature programmed desorption (TPD). On clean Cu(111) methanol is adsorbed molecularly at 100 K. Only small amounts of methoxy are formed by heating to 160–180 K, whereas the main part of methanol desorbs molecularly. The formation of methoxy drastically increases on the oxygen precovered surface. In the UP spectra the peaks of molecular methanol disappear and the peaks of methoxy develop. TPD measurements show that methoxy desorbs dissociatively as formaldehyde and hydrogen with the rate maxima at around 430 K. The efficiency of the oxidation of methanol to formaldehyde depends on the amount of predosed oxygen, with a maximum methoxy coverage obtained for an oxygen precoverage of 0.18 ML. From the quantitative analysis we propose an additional reaction pathway involving not only the formation, but also the decomposition of an hydroxyl intermediate, parallel to the previously reported pathway, which leads to the desorption of water.
Hydrogen-Induced and Defect-Mediated Structural Transition (5×1)-hex → (5×1)-H on Ir(100)
Authors: Heinz Klaus , Hammer Lutz
Published: July 2004

Ir(100) is well known to exhibit a (5×1) periodic surface reconstruction denoted as (5×1)-hex. The atoms of the outermost layer are quasi-hexagonally arranged rather than being of quadratic order as the layers below and in the bulk. Accordingly, an excess of 20% of atoms is accommodated in the top layer and the surface is buckled with atomic rows protruding from the surface. It is shown by the combined application of atomically resolved scanning tunnelling microscopy (STM) and quantitative low-energy electron diffraction (LEED) that hydrogen adsorption at sufficiently high temperature induces the surface to restructure. The new phase, (5×1)-H, develops by the extraction of surface protruding and close packed atomic Ir wires from the hexagonal layer. The remaining atoms of the latter reassume quadratic order and the wires expelled reside on this layer. The extraction of the Ir wires proceeds in a zip-like process and starts preferentially at surface defects, in particular at step edges or domain boundaries. The wires’ lateral periodicity normal to their spatial orientation is again 5-fold, but only on average. The precise lateral arrangement depends sensitively on the details of preparation, in particular the amount of hydrogen exposure and the sample’s temperature during, or temperature treatment after, exposure.
Synthesis and Crystal Structure of Tetra(n-butyl)ammonium Hydroxomethoxophthalocyaninato(2-)iridate(III) Methanol Solvate
Authors: HÜCKSTÄDT HEINER , HOMBORG HEINER
Published: July 2004

Bis(phthalocyaninato(2-)iridium(II)) reacts in methanol with excess tetra(n-butyl)ammonium hydroxide to yield tetra(n-butyl)ammonium hydroxomethoxophthalocyaninato(2-)iridate(III). The complex salt crystallizes as a methanol solvate in the monoclinic space group P21/n(No. 14) with cell parameters a = 12.510(1) Å, b = 19.561(3) Å, c = 18.489(2) Å, = 90.42(1) °, Z = 4. The Ir atom is hexacoordinated with four isoindole N atoms ( N iso ) of the severely saddled pc ligand and two O atoms of the hydroxide ( O 1) and methoxide ( O2 ) ligand respectively in a mutual trans arrangement. The average Ir-N iso distance is 1.981(5) Å, the Ir-O1 distance 2.038(7) Å and the Ir-O2 distance 2.061(6) Å. The O atom of the solvate ( O3 ) is bound to O2 by a strong hydrogen bond with an O2 - O3 distance of 2.60(1) Å.
Naphthalene Oxidation by Peracetic Acid Catalysed by Mn(III) Porphine-like Complexes: Nature of Intermediates and Pathways of their Formation
Authors: BARKANOVA SVETLANA V. , KALIYA OLEG L.
Published: July 2004

Mn ( III ) complexes of meso-tetra(o,o′-dichlorophenyl)porphyrin, tetra-tert-butyl-tetraazaporphine and 3,5-octanitrophthalocyanine are efficient catalysts of naphthalene oxidation by peracetic acid in acetonitrile solution. The pathways of the reaction and the nature of intermediates and final products depend on the catalyst structure. For meso-tetra(o,o′-dichlorophenyl)porphyrin MnCl and tetra-tert-butyl-tetraazaporphine MnCl the single primary oxidation product is 1-naphthol. For 3,5-octanitrophthalocyanine MnCl, two pathways of naphthalene oxidation yielding 1-naphthol (as the primary product) and 1,4-naphthoquinone are proposed. The pathway of 1,4-naphthoquinone formation in the 3,5-octanitrophthalocyanine MnCl -catalysed reaction seems to involve two intermediates, 1,4-endo-peroxy-1,4-dihydro- and 2,3-epoxy-1,4-endo-peroxy-1,2,3,4-tetrahydronaphthalene.
Macrocycle-Macrocycle Interactions within One-dimensional Cu Phthalocyanine Chains
Authors: GUO L. , ELLIS D. E. , MUNDIM K. C. , HOFFMAN B. M.
Published: July 2004

Interactions between planar Cu phthalocyanine molecules, CuPc , arranged in vertical stacking sequence are studied by first-principles density functional (DF) and semiempirical molecular dynamics (MD) methods. Dependence of electronic structure upon interplanar spacing and staggering angle is analyzed in order to interpret observed electrical conductivity and magnetic coupling behavior of partially oxidized Cu ( pc ) I . MD predictions of equilibrium structure of dimers and tetramers are in excellent agreement with experiment on the linear chain species. DF predictions of interaction energy of dimers are compared with MD and experiment.
Catalytic Properties of Cobalt Phthalocyanines Chemically Bonded to Polymer Anchored onto Silochrome Surface
Authors: BORISENKOVA S. A. , GIRENKO E. G. , GHERASSIMOV B. G. , MAZYARKINA L. M. , EROFEEVA V. P. , DERKACHEVA V. M. , KALIYA O. L. , LUKYANETS E. A.
Published: July 2004

Catalytic systems consisting of cobalt phthalocyanine grafted to maleic anhydride-styrene copolymer chemically linked with γ-aminopropylated silochrome have been prepared. In the process of sulfide oxidation with air oxygen the specific catalytic activity of these systems depends strongly on the phthalocyanine concentration in the catalyst. At low phthalocyanine concentrations (below 0.4 × 10−6 mol g−1) the catalytic activity is more than an order of magnitude larger than that of homogeneous catalysts and cobalt phthalocyanine adsorbed on a silochrome surface. The different ways of preparing the catalysts are reflected in the kinetic characteristics of the oxidation process.
On the Molecular Stereochemistry of the 21,22,23-trimethyl-5,10,15,20-Tetraphenylporphyrin Cation
Authors: SENGE MATHIAS O.
Published: July 2004

The crystal structure of the triflate salt of the title compound, [ Me 3 TPP ][ CF 3 SO 3], was investigated to obtain structural information on the conformation of N-trimethylated 5,10,15,20-tetraarylporphyrins. The molecular stereochemistry of the cation is characterized by an up/down/up arrangement for the three N-methyl groups with significant pyramidalization at the nitrogen atoms. The macrocycle is severely distorted with an average deviation from planarity of 0.438 Å. The distortion mode is an asymmetric saddle with deviations from the 4 N plane of the C b atoms at N-methylated pyrrole rings exceeding 1.1 Å. The out-of-plane displacements of pyrrole ring IV are significantly smaller than those of the methylated pyrrole rings.
Efficient Near-IR Sensitization of Nanocrystalline TiO2 Films by Zinc and Aluminum Phthalocyanines
Authors: NAZEERUDDIN MD. K. , HUMPHRY-BAKER R. , GRÄTZEL M. , WÖHRLE D. , SCHNURPFEIL G. , SCHNEIDER G. , HIRTH A. , TROMBACH N.
Published: July 2004

Several zinc(II) and aluminum(III) phthalocyanines substituted by carboxylic acid and sulfonic acid groups were anchored to nanocrystalline TiO 2 films. By irradiation with visible light the photovoltaic behavior of the electrodes containing LiI / LiI 3/propylene carbonate electrolyte was measured. Most efficient results were found using zinc(II) 2,9,16,23-tetracarboxyphthalocyanine, with a current conversion efficiency at 700 nm approaching 45%. It is shown that electron injection into TiO 2 occurs from the excited singlet state of the phthalocyanine derivatives. High stability of the cell performance under continuous irradiation was found.
Electron Transfer in the Reduction of Cobalt Porphyrin Incorporated into Nafion and Poly(4-vinylpyridine-co-styrene) Films
Authors: ZHAO FENG , ZHANG JIAN , ABE TOSHIYUKI , KANEKO MASAO
Published: July 2004

Potential step chronoamperospectrometry (PSCAS) measurement was carried out to investigate the one-electron transfer in the reduction of tetraphenylporphyrin cobalt(III) ([ Co III TPP (−2)]+) incorporated into a Nafion or poly(4-vinylpyridine-co-styrene) (P(VP-St)) film coated on an ITO electrode. The electron transfer of the redox centers in the two systems occurred by a physical diffusion mechanism. The fraction of the electroactive complex (R ct ) was independent of the CoTPP concentration in P(VP-St) but decreased with increasing CoTPP concentration in Nafion, especially at high concentrations. In both systems the apparent diffusion coefficient Dapp decreased with increasing CoTPP concentration. The Dapp value in Nafion (1.6 × 10−8 cm 2 s −1 at 0.02 M) was much higher than that in P(VP-St) (1.1 × 10−10 cm 2 s −1 at 0.02 M). The difference in the electron transfer process in the two systems was ascribed to the interaction of the redox center with the polymer framework, the morphology of the polymer matrix, the localization of the redox species in the hydrophilic/hydrophobic region, and the counterion migration under the potential step.
Absorption
Authors: Laso Manuel , von Stockar Urs
Published: July 2004

Absorption, or gas absorption, is a unit operation used in the chemical industry to separate gases by washing or scrubbing a gas mixture with a suitable liquid. One or more of the constituents of the gas mixture dissolves or is absorbed in the liquid and can thus be removed from the mixture. In some systems, this gaseous constituent forms a physical solution with the liquid or the solvent, and in other cases, it reacts with the liquid chemically. The purpose of such scrubbing operations may be gas purification, eg, removal of air pollutants from exhaust gases; product recovery; or production of solutions of gases for various purposes. Gas absorption is usually carried out in vertical countercurrent columns. The solvent is fed in at the top of the absorber, the gas mixture from the bottom. The absorbed substance is washed out by the solvent, which is often recovered in a subsequentstrippingor desorption operation. The absorber may be a packed column, plate tower, or simple spray column, or a bubble column. The fundamental physical principles underlying the process of gas absorption are the solubility of the absorbed gas and the rate of mass transfer. Information on both must be available when sizing equipment for a given application. In standard packed absorption columns, a gas mixture travels up through a gas absorption tower and the solute is transferred to the liquid phase and thus gradually removed from the gas. The liquid accumulates solute on its way down through the column. Multicomponent mass‐transfer effects, nonisothermal gas absorption, and axial dispersion effects result in considerable departures from ideal flow assumptions. Neglect of axial dispersion results in an overestimation of the driving forces and may lead to an unsafe design. Bubble tray absorption columns may be designed graphically based on a so‐called McCabe‐Thiele diagram. The required number of actual plates, however, is larger than the number of theoretical plates. The computation of nonisothermal gas absorption processes is difficult because of all the interactions involved. A computer is normally required to establish the correct concentration and temperature profiles through the tower.
Acetaldehyde
Authors: Hagemeyer H. J.
Published: July 2004

Acetaldehyde is a product of most hydrocarbon oxidations. It occurs in trace amounts in all ripe fruits that have a tart taste before ripening. Acetaldehyde is also an intermediate product of fermentation. It may form in wine and other alcoholic beverages after exposure to air, imparting an unpleasant taste. Acetaldehyde occurs in trace quantities in blood. Acetaldehyde is a colorless, mobile liquid having a pungent, suffocating odor that is somewhat fruity and quite pleasant in dilute concentrations. It is a highly reactive compound undergoing numerous condensation, addition, and polymerization reactions. The liquid‐phase oxidation of ethylene is the process of choice for the manufacture of acetaldehyde. Acetaldehyde appears to paralyze respiratory muscles, causing panic. When breathed in high concentration, it causes headache and sore throat. Demand for acetaldehyde has decreased as a result of less consumption for acetic acid manufacture.
Acetylene‐Derived Chemicals
Authors: Hort Eugene V. , Taylor Paul
Published: July 2004

Acetylene, C2H2, is an extremely reactive hydrocarbon, principally used as a chemical intermediate. Because of its relatively high price, there have been continuing successful efforts to replace acetylene with cheaper raw materials. The name ethynylation was coined by Reppe to describe the addition of acetylene to carbonyl compounds. Principal Reppe acetylene chemicals include propargyl alcohol, butynediol, butenediol, butanediol, and butyrolactone. Butynediol is principally consumed in manufacture of butenediol and butanediol. Butanediol is consumed in manufacture of butyrolactone and tetrahydrofuran. Large amounts are also used as a monomer for polyesters and polyurethanes. Butyrolactone is principally used as an intermediate for manufacture of pyrrolidones. Propargyl alcohol is a primary skin irritant and severe eye irritant, highly toxic by all means of ingestion. Catalytic vinylation, in which a labile hydrogen compound adds to acetylene, forming a double bond, has been applied to a wide range of alcohols, phenols, thiols, and carboxylic acids. Vinyl ethers are used in the manufacture of glutaraldehyde and as monomers.
Acetone
Authors: Howard William L.
Published: July 2004

Acetone [67‐64‐1] (2‐propanone, dimethyl ketone, CH3COCH3), molecular weight 58.08 (C3H6O), is the simplest and most important of the ketones. It is a colorless, mobile, flammable liquid with a mildly pungent, somewhat aromatic odor, and is miscible in all proportions with water and most organic solvents. Acetone is an excellent solvent for a wide range of gums, waxes, resins, fats, greases, oils, dyestuffs, and cellulosics. It is used as a carrier for acetylene, in the manufacture of a variety of coatings and plastics, and as a raw material for the chemical synthesis of a wide range of products such as ketene, methyl methacrylate, bisphenol A, diacetone alcohol, methyl isobutyl ketone, hexylene glycol (2‐methyl‐2,4‐pentanediol), and isophorone. World production of acetone in 1999 was about 4.27 million metric tons per year, of which ∼1.4 million was made in the United States. Most of the world's manufactured acetone is obtained as a coproduct in the process for phenol from cumene and most of the remainder from the dehydrogenation of isopropyl alcohol. Numerous natural sources of acetone make it a normal constituent of the environment. It is readily biodegradable.
Acetal Resins
Authors: Starr John B.
Published: July 2004

The term “acetal resins” commonly denotes the family of homopolymers and copolymers whose main chains are completely or essentially composed of repeating oxymethylene units

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. The polymers are derived chiefly from formaldehyde or methanal, either directly or through its cyclic trimer, trioxane or 1,3,5‐trioxacyclohexane. The many commercially attractive properties of acetal resins are due in large part to the inherent high crystallinity of the base polymers, which contributes significantly to their excellent resistance to most chemicals, including many organic solvents. Stiffness, creep resistance, fatigue resistance, and excellent lubricity are properties of acetal resins which have contributed significantly to their commercial success. Acetal resins are generally stable in mildly alkaline environments. Properly end‐capped acetal resins are relatively thermally stable. Formaldehyde polymerizes by both anionic and cationic mechanisms. Copolymerization of trioxane with cyclic ethers or formals is accomplished with cationic initiators. All acetal resins contain various stabilizers introduced by the supplier. Acetal resins are most commonly fabricated by injection molding. They are used in conveying devices, gears, automotive parts, and household appliances.
Acetic Anhydride
Authors: Wagner Frank S.
Published: July 2004

Acetic anhydride (CH3CO)2O, is a mobile, colorless liquid that has an acrid odor. It is the largest commercially produced carboxylic acid anhydride. Its chief industrial application is for acetylation reactions in the production of cellulose acetates. It is also used in many other applications in organic synthesis. Manufacturing processes include the acetic acid process, the acetaldehyde oxidation process, and methyl acetate carbonylation. Acetic anhydride penetrates the skin, forming burns and blisters.
Acrylonitrile
Authors: Brazdil James F.
Published: July 2004

Acrylonitrile (also called acrylic acid nitrile, propylene nitrile, vinyl cyanide, and propenoic acid nitrile) is among the top 50 chemicals produced in the United States as a result of the tremendous growth in its use as a starting material for a wide range of chemical and polymer products. Acrylic fibers remain the largest use of acrylonitrile; other significant uses are in resins and nitrile elastomers and as an intermediate in the production of adiponitrile and acrylamide. Acrylonitrile (C3H3N, mol wt=53.064) is an unsaturated molecule having a carbon‐carbon double bond conjugated with a nitrile group. Acrylonitrile is miscible in a wide range of organic solvents, including acetone, benzene, carbon tetrachloride, diethyl ether, ethyl acetate, ethylene cyanohydrin, petroleum ether, toluene, some kerosenes, and methanol. Acrylonitrile undergoes a wide range of reactions at its two chemically active sites, the nitrile group and the carbon‐carbon double bond. Acrylonitrile is transported by rail car, barge, and pipeline. Department of Transportation (DOT) regulations require labeling acrylonitrile as a flammable liquid and poison. Acrylonitrile is highly toxic if ingested. It is moderately toxic if inhaled. Acrylonitrile is categorized as a cancer hazard by OSHA. Acrylonitrile will polymerize violently in the absence of oxygen if initiated by heat, light, pressure, peroxide, or strong acids and bases. It is combustible and ignites readily, producing toxic combustion products. Federal regulations (40 CFR 261) classify acrylonitrile as a hazardous waste. Uses of acrylonitrile include acrylic fiber, acrylonitrile–butadiene–styrene (ABS) resins, elastomers, and styrene‐acrylonitrile resins (SAN).
Acrylamide
Authors: Habermann C. E.
Published: July 2004

Acrylamide (NIOSH No. A533250) has shown steady growth since the mid‐1950s, but is still considered a small‐volume commodity. It is by far the most important member of the series of acrylic and methacrylic amides. Water‐soluble polyacrylamides have the most important applications, including as a dewatering aid for sludge in the treatment of effluent from municipal wastewater plants and in industrial processes. Acrylamide, C3H5NO, is a difunctional monomer containing a reactive electron‐deficient double bond and an amide group. It undergoes reactions typical of those two functionalities. The current routes to acrylamide are based on the hydration of inexpensive and readily available acrylonitrile. Contact with acrylamide can be hazardous and should be avoided.
Acrylamide Polymers
Authors: Huang Sun‐Yi , Lipp David W. , Farinato Raymond S.
Published: July 2004

This article presents an up‐to‐date, broad overview of acrylamide polymers covering the physics, chemistry, synthesis, and technology. Acrylamide polymers constitute a major segment of the global water‐soluble polymers market. The physics and chemistry of acrylamide polymers and copolymers in both the solid and solution states are discussed. Chemical properties and synthetic methods for acrylamide polymerization, copolymerization, and polymer derivatization are throughly covered, as are commercial manufacturing processes. The principal applications of acrylamide polymers are discussed, and there is coverage of modern methods of polymer analysis as applied to these materials. Safety and economic issues are considered.
Aluminum Oxide (Alumina), Activated
Authors: Pearson Alan
Published: July 2004

The activated aluminas comprise a series of nonequilibrium forms of partially hydroxylated aluminum oxide, Al2O3. The chemical composition can be represented by\documentclass{article}\usepackage{amssymb}\pagestyle{empty}\begin{document}${{\rm{Al}}{_{2}}{\rm{O}} _{{(}3-x{)}}}$\end{document}(OH)2xwherexranges from about 0 to 0.8. They are porous solids made by thermal treatment of aluminum hydroxide precursors and find application mainly as adsorbents, catalysts, and catalyst supports. Activated alumina, for purposes of this discussion, refers to thermal decomposition products (excluding α‐alumina) of aluminum trihydroxides, oxide hydroxides, and nonstoichiometric gelatinous hydroxides. The term “activation” is used to indicate a change in properties resulting from heating (calcining). In general, as a hydrous alumina precursor is heated, hydroxyl groups are driven off, leaving a porous solid structure of activated alumina. The physical properties of the material are set by the choice of precursor, the forming process, and the activation conditions. Activated alumina is a relatively innocuous material from a health and safety standpoint. It is nonflammable and nontoxic. Normal precautions associated with handling of nuisance dusts should be taken. Activated alumina is normally shipped in moisture‐proof containers because of its strong desiccating action.
Adhesives
Authors: Yorkgitis Elaine M.
Published: July 2004

Adhesives comprise one of the chief classes of polymer‐based products. Adhesive bonding is the method of choice for joining many materials, and their use can be expected to expand on a yearly basis because of their versatility and cost‐effectiveness. The market economics of adhesives is summarized and updated. The many ways in which adhesives can be classified is covered with an emphasis on their physical forms and types. The various chemistries used to make pressure‐sensitive, hot‐melt, solvent‐ and water‐based, structural, and natural product adhesives are described in some detail relative to the major constituents commonly used in each as well as the various minor constituents. The general advantages of each class of adhesive are provided. General comments on formulation and the role of the formulator in bringing adhesives to market conclude the article.
Adhesion
Authors: Pocius Alphonsus V.
Published: July 2004

Adhesion is a complex phenomenon that is studied and described by three scientific disciplines: surface science, engineering mechanics, and polymer physics and chemistry. This article provides an overview of the science of adhesion based in those three disciplines. Adhesion is described primarily from the viewpoint of making and breaking an adhesive bond although the basic concepts also apply to coatings. This article describes adhesion from the viewpoint of intermolecular forces and ties those concepts into strength of materials as well as surface energy. Methods by which adhesive bonds can be tested are also described. The article ends with a discussion that attempts to tie together fundamental forces at interfaces to the strength of an adhesive bond via the polymer physics of the adhesive.
Adipic Acid
Authors: Oppenheim Judith P. , Dickerson Gary L.
Published: July 2004

Adipic acid, hexanedioic acid, 1,4‐butanedicarboxylic acid, mol wt 146.14, HOOCCH2CH2CH,CH2COOH, is a white crystalline solid with a melting point of about 152°C. Little of this dicarboxylic acid occurs naturally, but it is produced on a very large scale at several locations around the world. The majority of this material is used in the manufacture of Nylon‐6,6 polyamide, which is prepared by reaction with 1,6‐hexanediamine. Adipic acid is a colorless, odorless, sour‐tasting crystalline solid that undergoes reactions including esterification, amidation, reduction, halogenation, salt formation, and dehydration. It also undergoes several industrially significant polymerization reactions. Adipic acid historically has been manufactured predominantly from cyclohexane. However, much research continues to be directed to alternative feedstocks, especially butadiene and cyclohexene, as dictated by shifts in hydrocarbon pricing. Air quality regulations may exert further pressure for alternative routes as manufacturers seek to avoid NOxabatement costs. When dispersed as a dust, adipic acid is subject to normal dust explosion hazards. The material is an irritant, especially upon contact with the mucous membranes. Protective goggles or face shields should be worn when handling the material. The material should be stored in corrosion‐resistant containers, away from alkaline or strong oxidizing materials. Adipic acid is a very large‐volume organic chemical and is one of the top 50 chemicals produced in the United States in terms of volume, although demand is highly cyclic. Adipic acid for nylon takes ∼60% of U.S. cyclohexane production. Adipic acid is relatively nontoxic.
Adsorption, Liquid Separation
Authors: Gembicki Stanley A. , Rekoske James , Oroskar Anil , Johnson James
Published: July 2004

Nearly every chemical manufacturing operation requires the use of separation processes to recover and purify the desired product. Liquid‐phase adsorption has long been used for the removal of contaminants present at low concentrations in process streams such as in deodorization of water, decolorization of sugar, and ion exchange of fermentation broth. Liquid‐phase simulated moving bed (SMB) processes are being increasingly used for bulk separation of a whole range of molecules whose molecular properties are very similar. Examples arep‐xylene from C8aromatics, normal paraffins from iso‐paraffins, fructose from glucose, and chiral molecules in the pharmaceutical industry. When it comes to the separation of close boiling molecules, SMB processes generally provide a better alternative to other conventional means of separation from both operating and capital costs point of view.

This article reviews the application of liquid‐phase adsorption processes in the hydrocarbon, industrial chemicals, food, and pharmaceutical industry. Special emphasis is given to the class of processes referred to as SMB processes including fundamental SMB principles , and the general applicability and guidelines for SMB design. The paper also illustrates several examples of SMB applications in the petrochemical industry and its recent growth in the pharmaceutical and biotech industry.
Aerogels
Authors: Ko Edmond I.
Published: July 2004

Aerogels are low‐density and high‐porosity materials that are most commonly prepared by removing the pore liquid from a wet gel with supercritical extraction. The most extensively studied and characterized are silica aerogels, which can be prepared in the density range of 3 to 500 kg/m
3
through a proper control of preparative variables. The unusual properties of these materials, such as high surface area and pore volume, low thermal conductivity, and low dielectric constant, make them attractive for applications in diverse areas including thermal insulation, detection of high energy particles, and catalysis. The challenge is to produce them in a cost‐competitive process, which means exploring options that do not involve supercritical drying. Recent results show that with surface modification, aerogel‐like materials can indeed be produced at ambient conditions. Other ongoing research has been directed at the preparation and characterization of nonsilicate aerogels, as well as organic and inorganic–organic hybrid materials in an attempt to define their properties and to identify potential applications.
Chromatography, Affinity
Authors: Hage David S.
Published: July 2004

Affinity chromatography is a liquid chromatographic technique that uses a biologically related ligand for the specific retention or analysis of a given target. The general theory of affinity chromatography is considered and several examples are given of its typical applications. A number of items to consider in the use of this method are discussed, including the choice of ligand, support material, immobilization method, and solvent conditions. Several types of affinity chromatography are then examined in more detail. Particular attention is given to the techniques of bioaffinity chromatography, immunoaffinity chromatography, boronate affinity chromatography, immobilized metal‐ion affinity chromatography, dye‐ligand affinity chromatography, and biomimetic affinity chromatography. The use of affinity chromatography in the measurement of thermodynamic and kinetic constants is also considered, as well as the use of this method in sample pretreatment, purification, and analysis. Other items that are discussed include recent developments in the use of molecular imprints as affinity ligands and the use of biosensors for the study of biological interactions.
Controlled Release Technology, Agricultural
Authors: Wilkins Richard M.
Published: July 2004

Controlled release formulations (CRFs) are intended to improve the delivery of pesticides and related biologically active substances. The consequent improvement in efficiency reduces losses in use and has many benefits, such as reduction in exposure to both workers and the environment, particularly in minimizing leaching and evaporation. This article introduces the advantages of CRFs and provides a theoretical rationale for their use based on pseudo‐first‐order loss kinetics, which are typical for pesticide dissipation in the environment. Thus, the greater the loss rate, especially for pesticides of short duration, the greater the potential for improvement in delivery to the target pest. As a consequence of this principle, reduced levels of pesticide delivered efficiently can be as efficacious as higher amounts of conventional formulations.

The types of CRFs are introduced and are classified as physical, chemical, or biological. The kinetics of release from CRFs is central to their successful use, and the mathematical basics of this are described. The mechanisms of release vary according to the type of formulation, and these are covered for physical and chemical types. Common release characteristics include first order, diffusion (square root of time) based, and zero order (constant). Release kinetics are usually measured under controlled laboratory conditions, but field determination are preferable.

Design of properties of CRFs then follow. The main groups of the physical‐type formulations, such as reservoirs with release‐rate controlling membranes and without membrane and the monolith or matrix structures, are those based on microencapsulated liquid cores in sprayable concentrate formulations, and polymeric matrix methods that are often fabricated as granules. The polymers used and the approaches employed for designing these types of CRFs are introduced with emphasis on encapsulation methods, such as phase separation and interfacial polymerization. In addition, other formulation types are included, such as laminates, coated granules, microparticles, matrix granules (swellable and nonswellable), matrix devices for animal and public health protection, plastic films, and mulches. The article closes with the recent biological approach to formulation based on living or dead genetically modified microorganisms containing proteinaceous toxins.
Air Pollution
Authors: Allen David T.
Published: July 2004

Air pollution is the presence of any substance in the atmosphere at a concentration high enough to produce an undesirable effect on humans, animals, vegetation, or materials, or to significantly alter the natural balance of any ecosystem. Air pollutants can be solids, liquids, or gases, and can be produced by anhropogenic activities or natural sources. Current concerns regarding air pollutants are on the effects of long term, chronic exposures to nonlethal concentrations of air pollutants, especially the pollutants defined in the Clean Air Act. These pollutants include: sulfur dioxide (SO
2
); carbon monoxide (CO); nitrogen dioxide, (NO
2
); ozone (O
3
); suspended particluates; volatile organic compounds (VOCs); and lead, (Pb). The impacts of indoor air quality on health, the effects of air pollution on global and regional climate, and the effects of air pollutants on global and regional atmospheric cycles (eg, stratospheric ozone depletion and acid deposition) have also emerged as concerns.
Alkanolamines from Olefin Oxides and Ammonia
Authors: Edens Martha R. , Lochary J. Fred
Published: July 2004

Ethylene oxide, propylene oxide, or butylene oxide react with ammonia to produce alkanolamines. Ethanolamines, NH3‐n(C2H4OH)n(C2HOH)n(\documentclass{article}\pagestyle{empty}\begin{document}${n=1,2,3}$\end{document}, mono‐, di‐, and tri‐), are derived from the reaction of ammonia with ethylene oxide. Isopropanolamines, NH3‐n(CH2CHOHCH3)n(mono‐, di‐, and tri‐), result from the reaction of ammonia with propylene oxide. Secondary butanolamines, NH3‐n(CH2CHOHCH2CH3)n(mono‐, di‐, and tri‐), are the result of the reaction of ammonia with butylene oxide. Mixed alkanolamines can be produced from a mixture of oxides reacting with ammonia. Ethanolamines have been commercially available for over 50 years and isopropanolamines, for over 40 years.sec‐Butanolamines have been prepared in research quantities, but are not available commercially. A variety of substituted alkanolamines are also available commercially, but have not reached the volume popularity of the ethanolamines and isopropanolamines. The freezing points of alkanolamines are moderately high. The ethanolamines are colorless liquids at or near room temperature. Alkanolamines are bifunctional molecules because of the alcohol and the amine functional groups in the same compound. This allows them to react in a wide variety of ways. Consumption of ethanolamines in the United States in chemical processing intermediates (captive use for ethyleneamine and surfactant applications) has increased significantly since the 1960s. Alkanolamines generally have low acute oral toxicity, but swallowing substantial quantities could have serious toxic effects. Exposure of the eye to undiluted alkanolamines can cause serious injury. Monoethanolamine and monoisopropanolamine are skin irritants, capable of producing serious injury in concentrations of 10% or higher. Alkanolamines and their derivatives are used in a wide variety of household and industrial applications. The amides are useful as foam stabilizers and aid cleaning in laundry detergents, dishwashing liquids, etc. Reaction of alkanolamines with a fatty acid at room temperature produces neutral alkanolamine soaps, found in cosmetics, polishes, household cleaners, and pharmaceuticals. Alkanolamine salts add to the surfactants line used in detergents, cosmetics, textiles, polishes, agricultural sprays, household cleaners, and metalworking compounds. Salts of alkanolamines and inorganic acids are useful chemical intermediates, and are used in corrosion inhibitors and antistatic agents, among other products.
Alkoxides, Metal
Authors: Horn M. , Horns U.
Published: July 2004

Metal alkoxides are compounds in which a metal is attached to one or more alkyl groups by an oxygen atom. Alkoxides are derived from alcohols by the replacement of the hydroxyl hydrogen by metal. The metal alkoxides exhibit great differences in physical properties. Many metal alkoxides are soluble in the corresponding alcohols, but magnesium alkoxides are practically insoluble. The most outstanding property of the metal alkoxides is the ease of hydrolysis, used for sol–gel applications. Metal alkoxides catalyze the Tishchenko condensation of aldehydes, the transesterification of carboxylic esters, and other enolization and condensation reactions. Commercial alkoxides include alkali metal alkoxides (sodium methylate, sodium ethylate, sodiumtert‐butylate, sodiumtert‐amylate, potassium methylate, potassium ethylate, and potassiumtert‐butylate), alkaline‐earth metal alkoxides (magnesium methylate, magnesium ethylate, and calcium methylate and ethylate), aluminum alkoxides (aluminum isopropylate and aluminumsec‐butylate), transition‐metal alkoxides (titanium alkoxides, zirconium alkoxides, and vanadium alkoxides), and antimony trialkoxides. Metal alkoxides are strongly caustic requiring the use of protective glasses and gloves. Metal alkoxides are mainly used as catalysts (in Ziegler‐Natta polymerization, transesterifications, and condensations); in coatings for plastics, textiles, glass, and metals; in additives for adhesives and paints; for sol–gel applications; for synthesis of minerals capable of safely enclosing radioactive nuclear waste; and for the cross‐linking or hardening of natural and synthetic materials. Alkali metal alkoxides find their principal use in organic synthesis where they act as strong bases.
Allyl Chloride
Authors: Kneupper Chris , Saathoff Lester
Published: July 2004

A history of allyl chloride production and alternative technologies is presented. The properties needed for use of this material are given and common reactions and reaction products are discussed. Manufacture and processing of allyl chloride is covered including discussion of the high temperature propylene chlorination reaction mechanism, significant reaction by‐products, reaction conditions, industrial reactor design, product recovery through fractional distillation, and materials of construction. Techniques for maintenance of product integrity during storage and shipment are discussed, and transport equipment to maximize safety and minimize potential environmental impact is mentioned. Current production facilities for allyl chloride are listed. Most production is used for captive use as raw material for epichlorohydrin production. Sales specifications, statistical quality control parameters and analytical methods are briefly covered. Health hazards, exposure limits, personal protective equipment, and emergency response information are given. Current commercial products manufactured from allyl chloride are discussed.
Allyl Alcohol and Monoallyl Derivatives
Authors: Nagato Nobuyuki
Published: July 2004

The technology of introducing a new functional group to the double bond of allyl alcohol was developed in the mid‐1980s. Allyl alcohol is accordingly used as an intermediate compound for synthesizing raw materials such as epichlorohydrin and 1,4‐butanediol, and this development is bringing about expansion of the range of uses of allyl alcohol. Allyl alcohol is a colorless liquid having a pungent odor; its vapor may cause severe irritation and injury to eyes, nose, throat, and lungs. It is also corrosive. Allyl alcohol is freely miscible with water and miscible with many polar organic solvents and aromatic hydrocarbons. It forms an azeotropic mixture with water and a ternary azeotropic mixture with water and organic solvents. Hydroformylation of allyl alcohol is a synthetic route for producing 1,4‐butanediol, a raw material for poly(butylene terephthalate), an engineering plastic. The CC double bond of allyl alcohol undergoes epoxidation by peroxide, yielding glycidol, applied in manufacturing glycidol as an intermediate for industrial production of glycerol. There are two processes for industrial production of allyl alcohol being used industrially at present: isomerization of propylene oxide, and a new process developed by Showa Denko K. K. The monoallyl derivative allyl chloride (AC) is a transparent, mobile, and irritative liquid produced by chlorination of propylene at high temperature. It is used mostly as an intermediate compound for producing epichlorohydrin. Allyl acetate is produced mostly for manufacturing allyl alcohol. Allyl methacrylate (AMA) is used mostly as a raw material for silane coupling agents. Allyl glycidyl ether is used mainly as a raw material for silane coupling agents and epichlorohydrin rubber. Dimethylallylamine is used in the production of insecticides and pesticides. Most allyl compounds are toxic and many are irritants. Precautions should be taken at all times to ensure safe handling.
Aluminum Sulfate and Alums
Authors: Darragh K. V. , Ertell C. A.
Published: July 2004

Aluminum sulfate octadecahydrate,\documentclass{article}\usepackage{amssymb}\pagestyle{empty}\begin{document} $ {{\rm{Al}}{_{2}}{(}{\rm{SO}}{_{4}}{)}_{3}{\rm{{\cdot{}}}}18{\rm{H}}{_{2}}{\rm{O}}} $ \end{document}, and its aqueous solutions are used primarily in the paper industry for sizing and as a flocculating agent in water and wastewater treatment. This material is often called papermakers' alum or alum and is sometimes referred to as cake alum or patent alum. The solid commercial hydrate also called dry alum, ground or lump. Anhydrous aluminum sulfate, Al2(SO4)3, is a specialty item used in food applications. Over 50 acidic, basic, and neutral aluminum sulfate hydrates have been reported. Commercial dry alum is likely not a single crystalline hydrate, but rather it contains significant amounts of amorphous material. In the United States, aluminum sulfate is usually produced by the reaction of bauxite or clay with sulfuric acid. Unfortunately, the term alum is now used for several different materials. Papermakers' alum or simply alum refers to commercial aluminum sulfate. Common alum or ordinary alum usually refers to potash alum which can be written in the form\documentclass{article}\usepackage{amssymb}\pagestyle{empty}\begin{document} $ {{\rm{K}}{_{2}}{\rm{SO}}_{4}{\rm{{\cdot{}}}}{\rm{Al}}_{2}{(}{\rm{SO}}_{4}{)}_{3}{\rm{{\cdot{}}}}24{\rm{H}}{_{2}}{\rm{O}}} $ \end{document}, or it can refer to ammonium alum, ammonium aluminum sulfate. The term is also applied to a whole series of crystallized double sulfates having the same crystal structure as the common alums. Some examples of alums are cesium alum,\documentclass{article}\usepackage{amssymb}\pagestyle{empty}\begin{document} $ {{\rm{CsAl}}{(}{\rm{SO}}{_{4}}{)}_{2}{\rm{{\cdot{}}}}12{\rm{H}}{_{2}}{\rm{O}}} $ \end{document}; iron alum,\documentclass{article}\usepackage{amssymb}\pagestyle{empty}\begin{document} $ {{\rm{KFe}}{(}{\rm{SO}}{_{4}}{)}_{2}{\rm{{\cdot{}}}}12{\rm{H}}{_{2}}{\rm{O}}} $ \end{document}; chrome alum,\documentclass{article}\usepackage{amssymb}\pagestyle{empty}\begin{document} $ {{\rm{KCr}}{(}{\rm{SO}}{_{4}}{)}_{2}{\rm{{\cdot{}}}}12{\rm{H}}{_{2}}{\rm{O}}>} $ \end{document}; and chromoselenic alum\documentclass{article}\usepackage{amssymb}\pagestyle{empty}\begin{document} $ {{\rm{KCr}}{(}{\rm{SeO}}{_{4}}{)}_{2}{\rm{{\cdot{}}}}12{\rm{H}}{_{2}}{\rm{O}}} $ \end{document}. In industrial practice it is generally the aluminum content of alums that is important. Because aluminum sulfate is widely available, other alums are more in the nature of specialty items.
Aluminates
Authors: Keller Robert J. , Len Joseph J.
Published: July 2004

Among industrial users of sodium aluminate are producers of paper, paint pigments, silica, alumina or alumina‐based catalysts, dishwasher detergents, molecular sieves, concrete, antacids, and others. Sodium aluminate is used in removal of phosphates from municipal and industrial waste waters and for clarification of industrial process and potable water. Commercial sodium aluminate products are available as liquids, and to a lesser degree, in solid form. The formula of anhydrous sodium aluminate is variously given as NaAlO2(aluminum sodium oxide),\documentclass{article}\usepackage{amssymb}\pagestyle{empty}\begin{document}${{\rm{Na}}{_{2}}{\rm{O}}{\rm{{\cdot{}}}}{\rm{Al}}{_{2}}{\rm{O}}{_{3}}}$\end{document}, or Na2Al2O4. Commercial sodium aluminates are not accurately represented by these formulas because the products contain more than the stoichiometric amount of sodium oxide, Na2O. The amount of excess caustic in commercial products is indicated by ratios of Na2O/Al2O3. Commercial quantities of sodium aluminate are made from hydrated alumina, in the form of aluminum hydroxy oxide, AlO(OH), or aluminum hydroxide, Al(OH)3, a product of the Bayer process which is used to refine bauxite, the principal aluminum ore. In addition to treatment of industrial and municipal water supplies, sodium aluminate is used in large quantities in papermaking where it improves sizing, filler retention, and pitch deposition. Sodium aluminate is also widely used in the preparation of alumina‐based catalysts.
Aluminum Carboxylates
Authors: McKenna Arthur L.
Published: July 2004

Aluminum salts of carboxylic acids, aluminum carboxylates, may occur as aluminum tricarboxylates (normal aluminum carboxylates), Al(OOCR)3; monohydroxy (monobasic) aluminum dicarboxylates, (RCOO)2Al(OH); and dihydroxy (dibasic) aluminum monocarboxylates, RCOOAl(OH)2. Aluminum carboxylates are used in three general areas: textiles, gelling, and pharmaceuticals. Derivatives of low molecular weight carboxylic acids have been mainly associated with textile applications; those of fatty carboxylic acids are associated with gelling salts; and more complex carboxylates find applications in pharmaceuticals. Commercial products can be combinations of mono‐, di‐, and tricarboxylates and not just the individual species. Some aluminum carboxylates of commercial interest are monobasic aluminum acetate, C4H7AlO5; dihydroxyaluminum aminoacetate, C2H6AlNO4; aluminum monostearate, C18H37AlO4; aluminum distearate, C36H71AlO5; and aluminum tristearate, C54H108AlO6.