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Electron microprobe analyses were made of the residual ash particles remaining after combustion in air at 1200 K of samples of representative coals used in thermal power plants and of samples of Northern Ireland lignite. Local associations of sulphur and calcium in the small areas analysed (c. 10 μm) were ascribed to the formation of the relatively stable CaSO 4 . This correlation was not linear and it was concluded that locally CaO reacted preferentially with the acidic oxides of silicon and aluminium to form calcium alumino-silicates. We recommend, therefore, that in assessing the amount of CaCO 3 or Ca(OH) 2 that must be added to a given fuel to achieve effective desulphurisation, due account must be taken of the ability of the constituent oxides in that coal to react with the additive

The primary interest of this work is to determine the effect of floc concentration on ferric floc particle interactions and hence, rheology. In accordance with established theory, ferric floc viscosity exhibits a non-linear increase with solids content, with the viscosity increasing sharply above a concentration of 12 000 ppm. Shear effectively breaks down floc structure, and thus reduces viscosity, the extent of which is independent of solids content. The effect of shear is also observed to diminish over time and can be adequately characterised by a power law model. Addition of aluminium nitrate to ferric floc increases the quantity of water bound within the floc, and thus produces suspensions which are more viscous in nature. Copyright © 2003 Society of Chemical Industry

The primary interest of this work was to determine the processing conditions which will provide the most water removal from the precipitate after freezing and thawing. The work examined the effect of variables such as freezing time, freezing temperature, and pre-treatment steps, e.g. agitation or concentration, on the freeze thaw process of ferric precipitates. The extent of dewatering of freeze thawed samples was not significantly affected by freezing rate or curing time, provided the floc was completely frozen. However, a pre-concentration step was found to produce a more concentrated residual. The relatively low degree of structure within the ferric flocs makes them particularly suitable for freeze-thaw conditioning. Only a slight increase in leach out of contaminant from the floc was observed. Thus, the experiments indicate that this is a very simple and effective method of dewatering precipitates, which does not require the use of additional additives.

Flocculative wastewater residues present a serious threat to the environment and a costly disposal problem to industry. The composition of the sludges makes them a particularly intractable problem due to the need for either recovery or permanent isolation of the bound contaminant. The primary interest of this work was to determine the effect of conditioning processes such as shear and washing on the retention of heavy metal contaminants (nickel, cadmium, copper, zinc) within ferric flocs. Shear was found to produce an increase in the leach-out of certain heavy metals, including cadmium and nickel. Copper and nickel were unaffected by the application of shear. The extent of contaminant leaching, due to shear, increased with increasing contaminant to floc ratio. Repeated washing of the floc readily removed sodium ions, however, contaminant metal ions reformed an equilibrium with the washwater and the floc with every washing. © 2002 Society of Chemical Industry

The adsorption of ca. millimolar concentrations of cadmium(II) on freshly precipitated aluminium(III) hydroxide is enhanced, at pH values of below 8, in the presence of ethylenediaminetetraacetate, EDTA, via stabilisation of the adsorbed cation. At levels where the hydroxide phase is in large excess to the cadmium(II), the addition of stoichiometrically equivalent concentrations of EDTA will enhance its adsorption to approximately 95%. In the presence of EDTA, cadmium adsorption increases with pH despite the fact that 99.9% of the dissolved cadmium is present as an anionic cadmium(II) EDTA complex. The adsorption observed has been modelled using the measured values of the solubility of aluminium hydroxide and its adsorption of EDTA, the normal and the EDTA-enhanced cationic binding of cadmium(II) and the accepted equilibrium constants for EDTA complexation of cadmium(II) and aluminium(III). The structures of the dissolved and adsorbed complexes have been inferred from XAFS and Al27 NMR spectroscopy.

The kinetics of dehydration of lignite have been characterized by isothermal measurements of the water evolved under vacuum at 273–313 K. The rate of water release at low relative pressures is deceleratory and data are well expressed by the contracting volume rate equation. When the water vapour pressure, p, approaches the saturated value, po, the rate becomes controlled by the relative vapour pressure, β = p p o . These controls are combined in the kinetic analysis of the isothermal yield-time data. It is shown that the evaporation of water from lignite is satisfactorily expressed by the equation, dp dt = k(1 − α) 2 3 (1 − β) , where α is the fractional dehydration at time t. The activation energy was 35 ± 5 kJ mol−1 between 273 and 313 K. It was shown that the dehydration rates of different lignite samples were identical, and that they were the same as the rate of dehydration of a rehydrated reactant sample which had previously been dried. It is concluded that the low temperature drying of lignite occurs by the evaporation of liquid water previously immobilized within the continuous coherent carbonaceous matrix. The drying rate depends on the particle size, the rate of migration of the drying interface within the particles and on the ambient pressure of water vapour which tends to rehydrate the matrix.

Equimolar mixtures of iron sulfide, calcium carbonate and other selected additives were ignited in air at 1200 K, and it was shown that about 70% of the sulfur was retained in the residue as calcium sulfate. These reaction conditions were selected to represent those applicable when calcium carbonate is used in fluidized bed combustion. Calcium oxide is efficient in trapping sulfur oxides. It was further shown, however, that under the same well defined reaction conditions alumino-silicates react with CaSO 4 , to some extent, to release a proportion of the sulfur (~ 30%). This result is consistent with a previous conclusion that acidic oxides in coal reduce the efficiency of calcite for sulfur oxide removal from flue gases.

Stoichiometrically equivalent concentrations of ethylenediaminetetraacetate, EDTA, and of related chelating anions increase the adsorption of ca. millimolar concentrations heavy metal aqua-ions on amorphous precipitates of aluminium(III) or iron(III) hydroxide and, although higher concentrations decrease the adsorption, poly-EDTA, a polyelectrolyte containing EDTA functional groups, shows no such decrease.

The properties of water vapour have been investigated quantitatively between 0 and 10 Torr and at ambient temperature (295 K). Provided a satisfactory correction for surface adsorption is made, the deviation from ideal gas behaviour is not detectable within the accuracy of the corrected pressures (±3%). This is consistent with theoretical modelling calculations and also with experiments made at higher temperatures when they are extrapolated to ambient temperature. There was considerable adsorption of water vapour onto the glass of the apparatus which had previously been in constant use, up to ca. 20 monolayers and taking place in two distinct rate processes that were completed in ca. 5 and ca. 30 min. Very much less adsorption occurred on new Pyrex glass (ca. 1 monolayer). It was also shown that the measured equilibrium vapour pressures in the range 0–10 Torr were directly proportional (±8%) to the amount of water admitted.Both results are important in confirming the validity of the vacuum apparatus measurements when used to study rates of water release such as the dehydrations of solids which depend on this relationship. However as a consequence of water vapour adsorption, apparent yields were less by 32% than the values calculated using the ideal gas equation. Yield determinations therefore cannot be based on pressure and apparatus volume but must be obtained by direct calibration.

The dehydration of a homogeneous cubic sample of ‘woody’ lignite at ca. 290 K follows a modified contracting cube equation, dp/dt=k(1 –α)2/3(1 –β), in which k is a constant, α is the fraction of the sample dehydrated and β is the ratio of the vapour pressure of water at time t compared to its saturated value. The rate depends on the competitive evaporation and condensation of water via the dehydration interface. The system provides a satisfactory kinetic model for the rate of release of non-bonded water across a solid/gas interface.

A series of six-co-ordinate iron(II) complexes [FeIIL3]X2(X = ClO4 or BPh4) of the bidentate ligands 2,2′-bi-2-imidazoline (L3), 2,2′-bi-1,4,5,6-tetrahydropyrimidine (L4), 2,2′-bi-2-oxazoline (L5), and 5,5′-dimethyl-2,2′-bi-2-oxazoline (L6) have been prepared and characterised by their physical properties. In all cases co-ordination is via the α-di-imine group. Magnetic susceptibility and Mossbauer effect measurements as a function of temperature show that the complexes of L5 and L6 are fully high-spin (S= 2) over the temperature range 90–360 K, while for complexes of L3(X = ClO4 but not BPh4) and L4(X = ClO4 and BPh4) a 5T2⇌1A1 spin transition is observed in this temperature range. Electronic spectra of the corresponding nickel(II) complexes indicate a correlation between Dq(Ni) and the spin ground state of the iron(II) complexes. The iron(III) complex [FeIIIL33][ClO4]3 is high-spin (S= 5/2), while [FeL43][ClO4]3 has a 2T2 ground state but with a thermally accessible 6A1 excited state. Iron(III) complexes of L5 and L6 are unstable and could not be isolated. Reaction of the iron(II) complexes of L3 and L4 with dioxygen gave the iron(III) complexes [FeIIIL2(L – H)][ClO4]2 is good yield [(L – H)= monodeprotonated ligand] which may be reversibly converted to the [FeIIIL3]3+ species on treatment with one equivalent of HClO4. The temperature-dependent magnetic moments of the complexes [FeL2(L – H)][ClO4]2 are interpreted in terms of 2T2⇌6A1 spin equilibria.

The high-spin complex [FeII(2,2′-bi-2-imidazoline)3]2+ reacts with dioxygen in aprotic media to form water and an iron(III) complex in which one ligand molecule is mono-deprotonated; a mechanism involving proton transfer from the ligand to the partially reduced co-ordinated dioxygen is suggested.

Etude cinetique: il y aurait mise en jeu de l'intermediaire tres reactif Coen 2 (S 2 O 3 ) +

Buta-1,3-diene is catalytically hydrogenated to a mixture of butenes and butane by carbonylhydridotris(triphenylphosphine)iridium(I), IrH(CO)(PPh3)3, and by carbonyltrihydridobis(triphenylphosphine)iridium(III), IrH3(CO)(PPh3)2, at 50° in dimethylformamide. The rates observed could be predicted by the empirical rate equation, –d[C4H6]//dt=(1·86 × 10–3+ 0·681[PPh3])[Ir]0[C4H6]//( 1 + 1·42 × 104[PPh3]) where [Ir]0=[IrH(CO)(PPh3)3]+[IrH3(CO)(PPh3)2].This equation and additional spectrophotometric and kinetic studies of the individual steps in the catalytic cycle are quantitatively interpreted in terms of a mechanism based on the reductive elimination of butenes by Ir(σ-C4H7)H2(CO)(PPh3)2 formed from Ir(π-C4H7)(CO)(PPh3)2 produced by the initial reactions of buta-1,3-diene with both IrH(CO)(PPh3)3 and IrH3(CO)(PPh3)2. The intermediate Ir(π-C4H7)(CO)(PPh3)2 has been isolated and characterised. Rate data for the hydrogenation of ethylene catalysed by the same system have also been quantitatively interpreted by a fundamentally similar mechanism based on the formation of Ir(σ-C2H5)(CO)(PPh3)2 and its subsequent unimolecular decomposition.

The kinetics of the substitution of Cl– in [Co(CN)5Cl]3– by solvent H2O and by X–= NCS– or N3– may be quantitatively interpreted by a stepwise mechanism, equations (i) and (ii). High-performance liquid chromatographic analysis confirms the absence of direct chloride substitution by reaction (iii). These results support the view that the substitution occurs by an Id interchange mechanism. [Co(CN)5Cl]3–+ H2O →[Co(CN)5(OH2)]2–+ Cl–(i)[Co(CN)5(OH2)]2–+ X–→[Co(CN)5X]3–+ H2O (ii)[Co(CN)5Cl]3–+ X–→[Co(CN)5X]3–+ Cl–(iii)

High-performance liquid chromatography on unmodified silica or alumina columns either separately or in series has been compared with the ion-pair reversed-phase method for the analysis of pentacyanocobaltate(III) and bis(ethylenediamine)thiosulpnatocobalt(III) complexes.

The efficiency of nucleophiles, (N3–, NCS– and Me2SO) in combining with the intermediate [Co(CN)5]2–depends on the ion from which the intermediate is formed, [Co(CN)5(OH2)]2–, [Co(CN)5Cl]3–, or [Co(CN)5(N3H)]2–, thereby suggesting that the substitution of these ions takes place by dissociative interchange, Id.

At 25°C with a pH of 7–8 and in concentrations of ca. 10–2M, [Co(CN)6]3– competes successfully with solvent H2O in the substitution of Cl– in trans-[Co(en)2Cl2]+ to give mainly [Co(en)2Cl(µ-CN)Co(CN)5]–(en = ethylenediamine); at higher temperatures polymeric species are also formed.

The relative nucleophile efficiencies predicted for NH3, CH3NH2 and CN− from their rates of reaction with trans-Co(CN)4(SO)3(OH2)3− are confirmed by competition experiments with similar nucleophiles (NH3-CH3NH2) but not by experiments with contrasting nucleophiles (NH3-CN−). This system, though substantially dissociative in mechanism, (D), possesses some interchange properties, (Id).

(–)-trans-4-Bromo-3-hydroxy-1,2,3,4-tetrahydrochrysene has been obtained from the chromatographic separation and cleavage of the corresponding menthyloxyacetyl (MOA) diastereoisomer. The (–)-enantiomer of this bromohydrin has been assigned (3R,4R)absolute stereochemistry and used in the synthesis of (+)-(3S,4R)-chrysene 3,4-oxide. Thermal racemization studies on this arene oxide gave a barrier to racemization (Ea) of 25.15 kcal mol–1 and an activation entropy (ΔS‡) of 0.7 cal mol–1 K–1, in accord with PMO predictions.

The kinetics of substitution of [Co(CN)5Cl]3– by water and by dimethyl sulphoxide (dmso) may be quantitatively interpreted by the mechanism in equations (i)–(iii). High-performance liquid [CO(CN)5Cl]3–+ H2O [graphic omitted] [Co(CN)5(OH2)]2–+ Cl–(i), [Co(CN)5Cl]3–+ dmso [graphic omitted] [Co(CN)5(dmso)]2–+ Cl–(ii), [Co(CN)5(OH2)]2–+ dmso [graphic omitted] [Co(CN)5(dmso)]2–+ H2O (iii) chromatographic analysis confirms the direct formation of a single, probably sulphur-bonded, isomer of [Co(CN)5(dmso)]2– from [Co(CN)5Cl]3– as well as via[Co(CN)5(OH2)]2–. The kinetics suggests the participation of the dissociatively formed intermediate [Co(CN)5]2–, but charged nucleophiles (NCS– or N3–) react more slowly with [Co(CN)5]2– than do the uncharged nucleophiles (dmso and water) when the leaving group is Cl– compared to the case when the leaving group is OH2. These results support the view that the substitution occurs by an Id interchange mechanism.

The rapid absorption of one mol of dioxygen by one mol of a bi-CuI macrocyclic complex in MeCN is followed by a slower anaerobic oxidative dehydrogenation of the ligand by the bound dioxygen to regenerate the CuI centres so that the cycle may be repeated, at least once again although more slowly.

Activated olefins, HR1CCR1H (R1= CO2Me or COPh), are reduced rapidly and stoicheiometrically by some alkyl phosphines, PR32, (R2= Et, Prn, or Bun), both free and initially bound to cobalt, in anhydrous methanol; the reaction proceeds by the formation of an ylide.

The kinetics of the substitution of Cl– in [Co(CN)5Cl]3– by solvent H2O and by X–= NCS– or N3– may be quantitatively interpreted by a stepwise mechanism, equations (i) and (ii). High-performance liquid chromatographic analysis confirms the absence of direct chloride substitution by reaction (iii). These results support the view that the substitution occurs by an Id interchange mechanism. [Co(CN)5Cl]3–+ H2O →[Co(CN)5(OH2)]2–+ Cl–(i)[Co(CN)5(OH2)]2–+ X–→[Co(CN)5X]3–+ H2O (ii)[Co(CN)5Cl]3–+ X–→[Co(CN)5X]3–+ Cl–(iii)

The dinitrone derivatives (5a, b) of 2,2,4,4-tetramethylcyclobutane-1,3-dione were synthesised by peroxyacid oxidation of the corresponding di-imines (3a, b). X-Ray crystallographic analysis of di-imine (3a) and the hydroxyimino nitrone isomers (6a, b) indicate a marked buttressing effect leading to an exclusive preference for the trans geometry in di-imine (3a) and dinitrone (5a). Thermal elimination reactions of the N-But substituted nitrones (5a), (6a), and (8a) to yield oximes and 2-methylpropene have been investigated by u.v. kinetic studies. The results are consistent with a concerted mechanism involving a five-membered cyclic transition state.

The acid-catalysed substitution of [Co(CN)5(N3)]3– by NCS– in water yields [Co(CN)5(OH2)]2–, [Co(CN)5(SCN)]3–, and [Co(CN)5(NCS)]3–. Spectroscopic and high-performance liquid chromatographic analytical data are quantitatively consistent with an acid-catalysed dissociative mechanism [equations (1)–(5)], in which K1= 4.47 ± 0.22 dm3 mol–1, k2=(3.46 ± 0.17)× 103 s1, [Co(CN)5(N3)]3–+ H3O+ [graphic omitted] [Co(CN)5(N3H)]2–+ H2O (1)[Co(CN)5(N3H)]2– [graphic omitted] [Co(CN)5]2–+ HN3(2)[Co(CN)5(OH2)]2– [graphic omitted] [Co(CN)5]2–+ H2O (3)[Co(CN)5]2–+ H2O [graphic omitted] [Co(CN)5(OH2)]2–(4)[Co(CN)5]2–+ NCS [graphic omitted] [Co(CN)5(SCN)]3–(5a)[Co(CN)5]2–+ NCS [graphic omitted] [Co(CN)5(NCS)]3–(5b)K3= 6.07 × 104 s1, (K5a+K5b)/K4[H2O]= 0.14 ± 0.02 dm3 mol–1, and K5/K5b≈ 4 at 40 °C and unit ionic strength. Equilibrium spectroscopic measurements of K1(4.67 ± 0.09 dm3 mol1) agree with the fitted kinetic result.

Chrysene 3,4-oxide, a major initial mammalian metabolite of chrysene, now synthesised in optically active form and configurationally assigned, has been found to racemize thermally with an activation energy of 25·2 kcal mol–1, consistent with an earlier perturbational molecular orbital calculation-predicted oxepin intermediate mechanism.

The substitution of pentacyanohydroxocobaltate(III), [Co(CN)5(OH)]3–, by azide ion is shown to take place by the reaction of aquopentacyanocobaltate(III), [Co(CN)5(OH2)]2–, in equilibrium with it. Deviations from simple second-order rate laws for the substitution of azide, thiocynate, and cyanide into [Co(CN)5(OH2)]2– at unit ionic strength and 40 °C are sufficiently small to be comparable with effects due to ionic activity variation and should not be accepted as evidence of a dissociative (D) mechanism. The reactions are reliably assigned to this class on the basis of activation volumes, solvent effects, and nucleophile competition experiments.

High-performance liquid chromatography on unmodified silica or alumina columns either separately or in series has been compared with the ion-pair reversed-phase method for the analysis of pentacyanocobaltate(III) and bis(ethylenediamine)thiosulpnatocobalt(III) complexes.

The complex chlorocarbonylbis(triphenylphosphine)iridium(I), IrCl(CO)(PPh3)2, has been found to catalyse the hydrogenation of olefins, (RHCCHR), in dimethylformamide at 50°(R = H) and at 80°(R = CO2Me or CO2H), at a rate which increases to a maximum value during an initial induction period. The induction period does not occur in hydrogenations carried out in toluene at 80°(R = CO2Me), and may be removed in dimethylformamide by addition of p-methoxyphenol. In the presence of basic cocatalysts in dimethylformamide, the catalyst is converted into trihydridocarbonylbis(triphenylphosphine) iridium (III), IrH3(CO)(PPh3)2, during the induction period. The induction period in the absence of cocatalyst is attributed to the involvement of an iridium–olefin intermediate in a radical chain process depending on the solvent or its impurities. The mechanism of the reactions is discussed in terms of an iridium–olefin intermediate, the concentration of which is determined partly by the equilibria existing between the stable iridium complexes present and partly by the kinetic competition of the reactions forming and removing the intermediate.

Buta-1,3-diene is catalytically hydrogenated to a mixture of butenes and butane by carbonylhydridotris(triphenylphosphine)iridium(I), IrH(CO)(PPh3)3, and by carbonyltrihydridobis(triphenylphosphine)iridium(III), IrH3(CO)(PPh3)2, at 50° in dimethylformamide. The rates observed could be predicted by the empirical rate equation, –d[C4H6]//dt=(1·86 × 10–3+ 0·681[PPh3])[Ir]0[C4H6]//( 1 + 1·42 × 104[PPh3]) where [Ir]0=[IrH(CO)(PPh3)3]+[IrH3(CO)(PPh3)2].This equation and additional spectrophotometric and kinetic studies of the individual steps in the catalytic cycle are quantitatively interpreted in terms of a mechanism based on the reductive elimination of butenes by Ir(σ-C4H7)H2(CO)(PPh3)2 formed from Ir(π-C4H7)(CO)(PPh3)2 produced by the initial reactions of buta-1,3-diene with both IrH(CO)(PPh3)3 and IrH3(CO)(PPh3)2. The intermediate Ir(π-C4H7)(CO)(PPh3)2 has been isolated and characterised. Rate data for the hydrogenation of ethylene catalysed by the same system have also been quantitatively interpreted by a fundamentally similar mechanism based on the formation of Ir(σ-C2H5)(CO)(PPh3)2 and its subsequent unimolecular decomposition.

The complex trishydridocarbonylbis(triphenylphosphine)iridium(III), IrH3(CO)(PPh3)2, has been found to hydrogenate ethylene catalytically and stoicheiometrically in dimethylformamide at 50°. The rates observed were predicted by equation (i) which could be deduced from a similar equation established previously for the catalyst hydridocarbonyltris(triphenylphosphine)iridium(I), IrH(CO)(PPh3)3, where [IrH3(CO)(PPh3)2]0 represents the initial concentration of IrH3(CO)(PPh3)2. –d[C2H4]//dt=0·01[IrH3(CO)(PPh3)2]0[C2H4]//1 + 828[H2]+ 247[PPh3](i) The reaction of ethylene with IrH3(CO)(PPh3)2 controls the rate of ethylene activation while the inhibitory effect of hydrogen and triphenylphosphine is thought to originate in subsequent competition between reactions of the ethylene intermediate giving ethane and those with hydrogen and phosphine reforming ethylene. The inhibition cannot be explained solely by the effect of the equilibria (ii) and (iii). IrH3(CO)(PPh3)2⇌ IrH(CO)(PPh3)2+ H2(ii), IrH(CO)(PPh3)3⇌ IrH(CO)(PPh3)2+ PPh3(iii)