Physico-chemical aspects of polyethylene processing in an open mixer. Part 26: Formal kinetics of aldehyde and carboxylic acid formation at a constant rate

Formation of carboxylic acids at a constant rate can be easily explained. It seems to result from the formation and decomposition of α,γ-keto-hydroperoxides. Formal kinetics based on formation and decomposition of these structural units is in agreement with the experimental findings. The activation energy deduced from the calculations is negligible, in agreement with the experimental data showing the constant rate to be practically temperature independent. Comparison of the acids with the hydroperoxides and ketones formed initially shows that the rate of oxygen addition to alkyl radicals is significantly smaller than in low molecular mass liquids. The same conclusion is reached on comparing directly the acids formed on decomposition of α,γ-keto-hydroperoxides in polyethylene melt and in hexadecane. The rate of oxygen addition in polyethylene melt is closer to 2 × 10⁵ than to 6 × 10⁵ (s⁻¹) that is valid in hexadecane.It is possible to attribute the relatively small amount of aldehydes that might be formed at a constant rate to different reactions of alkoxy radicals that are not in a cage with other radicals. These alkoxy radicals result from the addition of peroxy radicals to unsaturated bonds. This addition is followed mainly by epoxide formation and simultaneous release of an alkoxy radical.     

Catalytic hydrolysis of phosphate esters in microemulsions

We have continued our kinetics investigation of the iodosobenzoate (IBA) catalysis of the hydrolysis of p-nitrophenyl diphenyl phosphate (PNDP), in microemulsion media composed of hexadecane in water stabilized by cetyltrimethylammonium bromide and 1-butanol over a range of water mass fractions. We have examined two iodosobenzoic acid derivatives (5-nitro-2-iodosobenzoic acid and 5-octyloxy-2-iodosobenzoic acid) as catalysts. In addition, we have determined by³¹P FT-NMR techniques that the major product of the hydrolysis of PNDP, both in IBA catalyzed and in uncatalyzed media, is diphenylphosphate.     

Decomposition of oxalic acid with nitric acid

Oxalic acid or oxalate is widely used as a precipitant and a detergent in the field of nuclear energy. The present work aimed at developing a method of decomposing oxalic acid with HNO₃ in the presence of Mn²⁺ ion. The use of Mn²⁺ ion as low as 10^?3 mol/l facilitated the complete decomposition of oxalic acid, and the acidity of the resulting solution became as low as 0.1 eq/1 under the optimum conditions. The decomposition of oxalic acid is a first order reaction and proceeds at temperatures above 80°C; the activation energy of the reaction is 18.6 kcal/mol. This decomposition method is applicable to the dissolution of an oxalate precipitate.     

Molecular hydrogen-originated protonic acid site as active site on solid acid catalyst

The protonic acid sites are formed from hydrogen molecules on Pt/SO₄ ^2--ZrO2 , and the resulting protonic acid sites act as active sites for acid-catalyzed reactions. Promotion of molecular hydrogen on the activities is observed not only for the Pt/SO₄ ^2--ZrO2, but also for the other catalysts such as a physical mixture of Pt/SiO2 and H-ZSM5, and Co.Mo/SiO2-/Al2O3 . A molecular hydrogen-originated protonic acid site is proposed as a widely applicable concept for an active site on solid acid catalysts.     

Determination of liquid-liquid partition data for hydrazoic acid between tributylphosphate-alkane/nitric acid solutions using gas-liquid chromatography

The gas chromatographic technique of elution by characteristic point (ECP) has been used to determine partition data for HN₃ at finite concentrations with tributyl phosphate (TBP) in hydrocarbon (hexadecane) solution in the presence of nitric acid and uranyl nitrate. The data are used to derive predictive equations for calculating gas-liquid and liquid-liquid partition coefficients for varying temperature and varying concentrations of TBP, HNO₃, UO₂(NO₃)₂, and HN₃ in hydrocarbon solvents simulating nuclear fuel reprocessing flow sheets. The chromatographically derived partition data presented, being based on more precise measurements than were previously possible using conventional methods, allowed demonstration and quantification of the logarithmic temperature effect expected, but previously unobservable.     

Flow-injection spectrophotometric determination of ascorbic acid by reduction of vanadotungstophosphoric acid

Ascorbic acid may be determined spectrophotometrically at 360 nm based on reduction of vanadotungstophosphoric acid using flow-injection analysis. The carrier stream was distilled water and the reagent streams were buffer solution (pH 3.0), 1.735 × 10^?3 M dodecatungstophosphoric acid and 1.735 × 10^?3 M sodium vanadate. The injection rate was 80 h^?1. The calibration graph was linear up to 80 μg ml^?1 ascorbic acid and the relative standard deviation for the determination of 20 μg ml^?1 ascorbic acid was 1.5% (n=10). The detection limit was 1.0 μg ml^?1 ascorbic acid, based on an injection volume of 250 μl. The system was applied to the determination of ascorbic acid in vitamin C tablets.     

Dispersion of TiO2 on high‐surface‐area mesoporous silica: functionalization with tungstophosphoric acid and application in solvent‐free,aerobic oxidation of n‐hexadecane

Imidazole type ionic liquid, 1‐hexadecyl‐3‐methylimidazolium chloride, was used to template the synthesis of high‐surface‐area mesoporous silica under acidic conditions and crystalline titanium dioxide (TiO₂) nanoparticles of anatase phase were inserted utilizing a solvent evaporation‐induced method. The surface area of more than 700 m² g^?1 was obtained after TiO₂ impregnation. Further, the polyoxometalate, 12‐tungstophosphoric acid (PW₁₂) was dispersed on the surface of TiO₂ to form PW₁₂–TiO₂–silica hybrid catalytic materials. The catalytic activity of this hybrid material was tested for solvent‐free, aerobic oxidation of n‐hexadecane. The experimental investigation shows that PW₁₂–TiO₂ nanocrystals did not block the pore channels and gave good conversion. Copyright © 2012 John Wiley & Sons, Ltd.     

Synthesis and Characterization of Hexadecaaniline‐Grafted Comb‐like Poly(maleic acid‐alt‐1‐octadecene)

Highly soluble hexadecaaniline (A₁₆)‐grafted polyolefin derivatives poly(maleic acid‐hexadecaanilinamide‐alt‐1‐octadecene) (PMAO‐A₁₆) in a comb‐like configuration with alternate linear hexadecane and A₁₆ side‐chains were synthesized and characterized. The structure of PMAO‐A₁₆ was substantiated by infrared and UV‐Vis spectra showing high intensity of characteristic absorption peaks corresponding to a high degree of A₁₆ attachments. Covalent grafting of hexadecaanilines onto the polymer backbone of PMAO was confirmed by the detection of a new amide [–(C[dbnd]O)–NH–] absorption band appearing at 1661 cm^?1 accompanied with the full disappearance of anhydride carbonyl absorptions. Based on the comparison between TGA profiles of PMAO‐A₁₆ and hexadecaaniline, a 12.5% wt loss at 365–600°C was accounted for full elimination of aliphatic side‐chains that matches approximately with the weight percentage of total hexadecane arms (12.7%). The data revealed a nearly quantitative yield of A₁₆ grafting on anhydride subunits leading to complete conversion of PMAO into PMAO‐A₁₆. Furthermore, preliminary ¹H‐NMR study of PMAO‐A₁₆ indicated its capability to undergo molecular self‐assembly in DMSO where A₁₆s were dispersed in the solvent phase with hexadecane side‐chains located in a phase‐separated domain.     

CB‐TE2A+·Cl−·3H2O: a short intermolecular hydrogen bond between zwitterionic bicyclo[6.6.2]tetraamine macrocycles

1,4,8,11‐Tetraazabicyclo[6.6.2]hexadecane‐4,11‐diacetic acid (CB‐TE2A) is of much interest in nuclear medicine for its ability to form copper complexes that are kinetically inert, which is beneficial in vivo to minimize the loss of radioactive copper. The structural chemistry of the hydrated HCl salt of CB‐TE2A, namely 11‐carboxymethyl‐1,8‐tetraaza‐4,11‐diazoniabicyclo[6.6.2]hexadecane‐4‐acetate chloride trihydrate, C₁₆H₃₁N₄O₄⁺·Cl⁻·3H₂O, is described. The compound crystallized as a positively charged zwitterion with a chloride counter‐ion. Two of the amine groups in the macrocyclic ring are protonated. Formally, a single negative charge is shared between two of the carboxylic acid groups, while one chloride ion balances the charge. Two intramolecular hydrogen bonds are observed between adjacent pairs of N atoms of the macrocycle. Two intramolecular hydrogen bonds are also observed between the protonated amine groups and the pendant carboxylate groups. A short intermolecular hydrogen bond is observed between two partially negatively charged O atoms on adjacent macrocycles. The result is a one‐dimensional polymeric zigzag chain that propagates parallel to the crystallographic a direction. A second intermolecular interaction is a hydrogen‐bonding network in the crystallographic b direction. The carbonyl group of one macrocycle is connected through the three water molecules of hydration to the carbonyl group of another macrocycle.     

Interfacial Behavior of Naphthenic Acids and Multivalent Cations in Systems with Oil and Water. I. A Pendant Drop Study of Interactions Between n‐Dodecyl Benzoic Acid and Divalent Cations

Abstract

Dynamic interfacial tension (IFT) measurements were used to investigate the interactions between a dissociated model naphthenic acid (p‐(n‐dodecyl) benzoic acid) and various divalent metallic cations (Mg²⁺, Ca²⁺, Sr²⁺, and Ba²⁺) across a toluene/hexadecane–water interface. The measurements were performed by using the pendant drop technique. The results obtained, plotted as IFT vs. time gave curves with similar shapes but different slopes and levels of the equilibrium IFT, depending upon the acid and salt concentrations and the type of cation added. Due to differences in degree of hydration of the various cations, the products of the reaction between dissociated acid monomers and the cations showed differences in solubility, which, in turn, affected the IFT. Based on the shapes of the curves, the mechanisms of the reactions involved in the process are discussed.     

Natural radionuclide-free phosphoric acid production

High-uranium phosphate rock from Itataia, Brazil, was milled for wet-process phosphoric acid production using the dihydrate method. Uranium contained in the phosphoric acid was recovered by solvent extraction. The distribution of long-lived natural radionuclides of the ²³⁸U and ²³²Th decay series involved in these operations was evaluated. ²²⁶Ra, ²²⁸Ra and ²¹⁰Pb were found to predominate in the phosphogypsum, while ²²⁸Th, ²³⁰Th and ²³²Th in the uranium-free phosphoric acid. Thorium is removed from the phosphoric acid by solvent extraction to produce a NORM-free phosphoric acid.     

Changes in hydrocarbon emulsification specificity of the polymeric bioemulsifier emulsan: effects of alkanols

The biopolymer emulsan, which forms stable emulsions with mixtures of aliphatic and cyclic (or aromatic) hydrocarbons in water, does not emulsify aliphatic hydrocarbons alone [1–4]. Monohydric primary alcohols from hexanol to dodecanol were shown to enhance the formation of pure aliphatic hydrocarbon/water emulsions under conditions of mild agitation. Enhancement was a function of emulsan concentration and was proportional to alkanol concentration (5×10^–5 M to 2.5x10^–4 M) at constant bioemulsifier concentration (0.05 mg/ml). Enhancement of emulsification was also found when aqueous solutions of diethanolamine and phenethyl alcohol (5 to 30×10^–3 M) were substituted for the primary alcohols. None of these substances emulsified hexadecane or othern-alkanes in the absence of the biopolymer. The strongest enhancement of emulsification (3-fold) was observed with tetra- and hexadecane. At alkanol concentrations optimal for enhancement of emulsification, no significant lowering of hexadecane/ emulsan/water interfacial tension was observed. The possibility of a direct association of alkanols with the emulsan in solution, resulting in altered conformation of biopolymer and modification of its specificity toward hydrocarbons, is discussed.Preliminary results of this work were presented at the 57th Colloid and Surface Science Symposium, 1983, Toronto, Canada.     

Complexes of morin and quercetin with boric acid and oxalic acid in acetic acid medium. Fluorimetric determination of boron

The binary and ternary fluorescent complexes of morin or quercetin with boric acid and oxalic acid in an anhydrous acetic acid medium are described. The physico-chemical and spectral properties and chemical composition of these complexes have been established. The ternary complexes are suitable for fluorimetric determinations of boron. The limits of detection are 0.1 ng B ml^-1 and 0.3 ng B ml^-1, for the morin and quercetin complexes, respectively, and calibration graphs are linear up to 10 μg B ml^-1.     

Flow-coulometric detector for uric acid in human urine

A novel flow-coulometric detector integrating an immobilized uricase reactor and an electrolytic cell was fabricated and used for the determination of uric acid in human urine. The procedure is based on the measurement of the total charge with and without passing the sample through an enzyme reactor which allows the complete conversion of the electro-active uric acid in electro-inactive products. The amount of uric acid is linearly related to the difference between the two total charges. The current efficiencies for 1 × 10^?4-1 × 10^?3 M uric acid were found to be nearly 100% (r.s.d. < 1%).     

基于纳米结构的电化学传感器用于伏安法测定苄丝肼、尿酸和叶酸(英文)

A carbon paste electrode modified with carbon nanotubes and ferrocene was fabricated.An electrochemical study of the modified electrode and an investigation into its efficiency for the electrocatalytic oxidation of benserazide,uric acid and folic acid were undertaken.The electrode was also used to study the electrocatalytic oxidation of benserazide using cyclic voltammetry,chronoamperometry,and square wave voltammetry(SWV).We found that the oxidation of benserazide at the surface of the modified electrode occurs at a potential about 285 mV lower than that of unmodified carbon paste electrode.SWV gave a linear dynamic range from 8.0×10-7 to 7.0×10 4 mol/L.The detection limit was 1.0×10-7 mol/L for benserazide.This modified electrode was used for the determination of benserazide,uric acid,and folic acid in an urine sample.     

A small angle neutron scattering study of the interface between solids and oil-continuous emulsions and oil-based microemulsions

We have measured the small angle neutron scattering (SANS) from slurries of powder in contact with surfactant solutions and emulsions to determine the fluid/solid interfacial structure. The slurry solids consisted either of graphite or pyrites particles; and the fluids were hexadecane containing the robust commercial polyisobutylenesuccinamide (PIBSA) surfactant, or a high internal phase emulsion of aqueous ammonium nitrate in hexadecane stabilised by PIBSA. To resolve the interfacial structure for both systems, combinations of deuterated and protonated materials were used.At low concentration in hexadecane, PIBSA forms a complete monolayer on graphite with a footprint per molecule of 103 Å² and a layer thickness of 19 Å. At higher concentrations, the complete monolayer of footprint is 61 Å² and 30 Å thick indicating compression of the PIBSA chain coil structure. Geometric exclusion effects caused by the stacking of the graphite particles also results in an excess of oil for ca. 160 Å above the surfactant monolayer.For pyrites in contact with surfactant in hexadecane, the oxidised surface layer, while smooth at the oil interface, is diffuse and/or rough at the interface with the bulk sulphide below. There is again a complete monolayer of surfactant adsorbed at the oxide surface, in a relatively compressed state with a footprint of 70 Å², more tightly bound than on graphite. The excess of oil phase above the adsorbed surfactant monolayer is observed for samples with larger pyrites particle sizes but not for a sample with smaller particles. This suggests that the oil excess does arise from purely geometric solid particle packing, but that the local particle surface curvatures are significantly higher than the overall particle size would suggest.The scattering from the pyrites/emulsion interface was modelled by a 30 Å thick monolayer of surfactant coating an oxide surface with a molecular footprint of 123 Å². For the larger particle size samples, there is a 30 Å thick layer of oil above the pyrites particle surface before a bulk emulsion/pyrites mixture is reached.These results extend previous reflectometry experiments on the silicon/emulsion interface, indicating that for stable emulsions the structures are qualitatively similar for three dissimilar solid surfaces. They show that useful results on surfactant structure and emulsion layering at the solid/emulsion and other solid/fluid interfaces can be simply obtained by SANS on powder samples variously contrasted by deuteration. SANS can be applied to a much greater range of solid interfaces than reflectometry since large neutron-transparent single crystals are not required, although the variety of faces in a powdered material degrades the quality of the information.     

Determination of pipemidic acid based on flow-injection chemiluminescence due to energy transfer from peroxynitrous acid synthesized on-line

A flow-injection chemiluminescence (CL) method for the determination of pipemidic acid is described. It is based on energy transfer from excited state peroxynitrous acid to pipemidic acid, in which the excited state peroxynitrous acid is synthesized on-line by the mixing of acid hydrogen peroxide with nitrite in a flow system and the CL is from two excited states of pipemidic acid. The proposed method allows the measurement of pipemidic acid over the range of 2.0×10^–7–2.0×10^–5 mol l^–1 . The detection limit is 6.3×10^–8 mol l^–1, and the relative standard deviation for 2.0×10^–6 mol l^–1 pipemidic acid (n= 9) is 0.9%. This method was evaluated by the analysis of pipemidic acid in pharmaceutical preparations.     

Kinetics and mechanism of oxidation of malonic acid by permanganate and manganese dioxide in acid perchlorate medium

Summary The kinetics of oxidation of malonic acid by both [MnO₄]^– and MnO₂ have been studied in an HClO₄ medium. The oxidation product of the organic acid was found to be glyoxylic acid. A reaction mechanism assuming complexation between MnO₂ and malonic acid is suggested. The rate is independent of [H⁺].     

On-line preconcentration of perfluorooctanoic acid and perfluorooctanesulfonic acid by nonaqueous capillary electrophoresis

Separation of major environmental pollutants as perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS) by capillary electrophoresis is reported for the first time. It is not possible to resolve the solutes in an aqueous media. However, the use of methanol and acetonitrile as the background electrolyte (BGE) solvents allowed their rapid separation in an uncoated capillary. A major effort was put into BGE optimization in respect to both separation efficiency and detection for further on‐line preconcentration. 5 mmol.L^?1 naphthalene‐1‐sulfonic acid and 10 mmol.L^?1 triethylamine dissolved in ACN/MeOH (50:50 v/v) provided best separation and detection conditions. Next, the large‐volume sample stacking and the field‐amplified sample injection were applied and compared. Large‐volume sample stacking improved limits of detection (LODs) with regard to the standard injection by 69 times for PFOA and 143 times for PFOS with LODs of 280 and 230 nmol.L^?1, respectively. Field‐amplified sample injection improved LODs 624 times for PFOAand 806 times for PFOS with LODs 31 and 40 nmol.L^?1, respectively. Both preconcentration methods showed repeatabilities of migration times less than 1.2% RSD intraday and 6.6% RSD interday. The method was applied on PFOA and PFOS analysis in a sample of river water treated with solid‐phase extraction, which further improved LOD toward 5.6 × 10^?10 mol.L^?1 for PFOS and 6.4 × 10^?10 mol.L^?1 for PFOA and allows the method to be used for river water contamination screening or decomposition studies.     

THE SURFACE PROPERTIES OF A HYDROPHOBIC TRANSPOSON (Tn-5) MUTANT OF RHIZOBIUM ETLI

The physicochemical surface characteristics of a Tn-5 induced hydrophobic mutant (CE3003) of Rhizobium etli CE3 were investigated. The wild type CE3 was very hydrophilic with low contact angles for polar liquids, while the Tn-5 induced mutant had a surface that was moderately hydrophobic, with polar liquid contact angles in the 50–60° range. As a result, the polar surface free energy components (γ ⁺ and γ ^-) that constitute the acid-base component (γ ^AB) of surface tension, were greatly reduced on THE surface of the hydrophobic mutant. This decreased electron donicity of the mutant' surface caused an almost five fold increase in the magnitude of the acid-base component of the interfacial interaction free energy between the mutant and hexadecane. The increased adhesion to hexadecane reported earlier is probably attributable to this interaction free energy change and not to any alteration in zeta potential, which was similar for CE3 and CE3003 at pH 7. X-ray photoelectron spectroscopy showed CE3OO3 to have less surface carbon and nitrogen and more surface oxygen than CE3 with alterations in the (C-C,H) and (C-O,N) components being observed.