Cyanide Species Research Articles

Rate controlling reactions in fixed nitrogen conversion to N 2

Staged combustion approaches are used for controlling the emissions of NOx from combustion systems. Previous results1 have shown that the rate of conversion of total fixed nitrogen (TFN) species to N2 in the fuel rich combustion of methane with air can be accelerated towards equilibrium by increasing the temperature. The shift observed in the rate controlling mechanism for N2 formation from second order rate law behavior for TFN to first order decay of HCN after about 50–75 msec at 1850–1950 K suggested that the replenishment of the pool of free radical chain carriers (O+H+OH) in that reaction time range should be effective for accelerating the reaction. In the present work, this concept was studied both experimentally and theoretically. The experimental approach was to inject O2 about 50–100 msec downstream from the flame zone, in sufficiently low amouts not to alter bulk concentrations or temperature and flow fields. Typically, injection of 0.5% O2 based on total gas flow was shown to reduce TFN concentrations by 15–25%, between 1850 K and 1950 K. A detailed kinetic model of fixed nitrogen reactions decoupled from fuel oxidation produced predictions in good agreement with the experimental results for the dominant cyanide species. The agreement for amines and NO was affected by neglecting reactions of NO with hydrocarbon free radicals in the reaction mechanism. An analysis of the potential N2 forming reactions indicates that the reaction: NO+N→N2+O is the dominant path for N2 formation under high temperature, fuel rich conditions.

Evolved gas analysis of cobalt hardened gold plated films

Mass spectrographic evolved gas analysis was performed on Co hardened electrodeposited gold films. Two different rates of deposition were used. The abnormally high rate, 35 mA cm −2, gave rise to a much higher concentration of impurities including relatively large amounts of NH 3, H 2, HCN, and (CN) 2 which were around 400°C. Considerably smaller and compositionally different gaseous evolutions occurred near 600 and 800°C. The film deposited at the normal rate, 5 mA cm −2, evolved much less NH 3 and cyanide species and then at somewhat higher temperatures. The major evolution was around 800°C. This indicates that the normally deposited film occluded or codeposited fewer impurities and their higher temperature release probably resulted from the greater continuity of the film.

Nitric Oxide and Hydrogen Cyanide Formation in Laminar Methane/Air Diffusion Flames

Abstract Nitric oxide and hydrogen cyanide concentration distributions established in an unseeded, laminar, atmospheric methane-air diffusion flame have been analyzed in order to gain insight into the role nitrogen-containing species play in influencing NO formation in such flames. The experimental data indicate that HCN and NO formation are strongly dependent on the local stoichiometry within the flame region. Cyanide formation occurs only within the fuel-rich luminous flame core, presumably via reaction between hydrocarbon radicals and molecular nitrogen or nitric oxide. The cyanide species are subsequently partially converted to nitric oxide on the fuel-lean side of the primary reaction zone, contributing 15-30 percent of the total nitric oxide production by the flame. The nitric oxide concentration profiles peak on the fuel-lean side of the flame in the zone where the thermal production of NO by the extended Zeldovich mechanism occurs.

Effects of metal-ion binding on rhodanese activity

The stability constants for the calcium and magnesium complexes of rhodanese are >10 5 m −1 at both high and low substrate concentrations. The stoichiometry of alkaline earth metal ion binding totals close to 1 per 18,500 molecular weight. The usual assay reagents contain sufficient amounts of these metal ions to maintain added enzyme in its metal-complexed form. When reaction mixtures are treated with oxalate to remove calcium ions, inhibition of rhodanese activity is virtually complete under circumstances such that the contribution of magnesium ion is low. Zinc and a number of transition metal ions are inhibitors of rhodanese activity. Studies of the concentration dependence of these effects with zinc, copper, and nickel showed that: 1) Some cyanide complexes of these metals are competitive with the donor substrate, thiosulfate ion. The binding of the copper and zinc complexes is mutually competitive. 2) Another cyanide species of copper appears to combine with the free enzyme to form a functionally active complex. 3) The zinc cyanide species with a net positive charge is an inhibitor competitive with the acceptor substrate, cyanide ion. All of these observations are consistent with a model in which metal ions serve as the electrophilic site of rhodanese.

Physiological and toxicological aspects of combustion of natural and synthetic materials: Past, present and future

Normally one expects that flame contact is the major cause of injury and death during fires. Analysis of the factors involved in numerous fires has revealed that most deaths were not due to flame contact, but were a consequence of the production of carbon monoxide, nitrogen oxides, and other combustion products, such as aldehydes, ketones, low-molecular-weight alcohols, hydrogen cyanide, and other noxious species. The major emphasis within the scope of this paper relates to the physiological and toxicological aspects of smoke produced during the combustion of natural and synthetic materials. Special emphasis is directed towards the development of a laboratory protocol to determine the qualitative and quantitative analysis of smoke, factors pertaining to smoke development, and the evaluation of the animal's ability to escape from the survive a fire. This methodology incorporates both an assessment of animal behavior and a bioassay technique to classify the physiological status of the animal. Finally, a review is presented of the pathological changes common to humans involved in “real fires” as well as an analysis of the pathological changes observed in test animals following exposure to carbon monoxide and other combustion products resulting from the thermal decomposition of natural and synthetic materials.

The chemistry of some group VIII metals in molten cyanide. Part II. Ni, Pd and Pt

The chemistry of nickel, palladium and platinum in quenched (Na, K)CN eutectic melts has been investigated by diffuse-reflectance and infrared measurements. Nickel, when added as Ni(II), displays the characteristic spectra of Ni(II), and Ni(0) cyanide species. Only the latter species is formed when Ni(I) is added to the melt. A Ni(I) complex, Ni 2(CN) 4− 6 is formed when Ni(II) and Ni powder is added to the melt. Palladium, when added as Pd(II), displays the characteristic spectra of Pd(II) and Pd(I) cyanide compounds. A Pd(0) cyanide complex formed when sodium cyanamide (reducing agent) is added to the latter melt. Three species, characterised as Pt(II), Pt(I) and Pt(0) cyanide complexes are formed when Pt(II) compounds are added to the melt. The concentration of the Pt(0) species is increased by adding sodium cyanamide to the melt, while the concentration of the Pt(I) species is increased upon he addition of sodium dicyanamide (oxidising agent). The preparation and identification of a palladium cyanohydride complex is also described.

A study of nitric oxide formation in fuel-rich hydrocarbon flames: Role of cyanide species, H, OH and O

The object of this paper is to clarify the mechanism of prompt NO formation in the premixed methane-oxygen-nitrogen flame. To achieve this object, an accurate comparative study of theoretical and experimental results was carried out. In the experiment, a premixed steady one-dimensional laminar flame at about 0.1 atm pressure was chosen. The concentrations of O and H were measured by ESR together with NO, O 2 , HCN, etc. for several stoichiometric ratios between 0.88 and 1.42. The measured concentrations of H, O, cyanide species and stable species were compared with the results obtained by numerical calculation of species conservation and reaction equations for 20 components. It was found experimentally that the O atom concentration determined by ESR is not high enough to explain the mechanism of prompt NO formation by the Zeldovich mechanism and super-equilibrium concentration of O atoms. HCN was found to form prior to the formation of prompt NO, and the measured concentration of prompt NO was about ten times the maximum HCN concentration. Comparing the measured and calculated concentrations of the components, the rate-controlling reaction of methane oxidation was found to be CH 2 O+ M =CO+H 2 + M , and the rate constant of this reaction is k f .11 =2.1×10 15 exp (−17620/T) mol −1 cm 3 s −1 . The 40 elementary reactions and their reaction rates for 20 components were selected to predict the formation of prompt NO and behavior of the intermediate HCN. The concentration distributions obtained from the experiment and the numerical calculation based on the measured temperature distribution were compared and found to be in good agreement for NO and HCN for =1.26. For =0.88, the measured concentration of prompt NO and maximum concentration of HCN were 19 ppm and 1.1 ppm, respectively, while the calculated values were 26 ppm and 3.1 ppm, respectively. It was concluded that the NO formation mechanism in the wide range of stoichiometric ratio from fuel-lean to fuel-rich can be predicted by the 40 elementary reactions proposed in this paper.

The removal of chromium(VI) from dilute aqueous solution by activated carbon

The removal of chromium(VI) by activated carbon, filtrasorb 400, is brought by two major interfacial reactions: adsorption and reduction. Chemical factors such as pH and total Cr(VI) that affect the magnitude of Cr(VI) adsorption were investigated. The adsorption of Cr(VI) exhibits a peak value at pH 5–6. The particle size of carbon and the presence of cyanide species do not change the magnitude of chromium removal. The reduced Cr(VI), e.g. Cr(III) is less adsorbable than Cr(VI). The free energy of specific chemical interaction, ΔG chem was computed by the Gouy-Chapman-Stern-Grahame model. The average values of ΔG chem are −5.57 RT and −5.81 RT, respectively, for Cr(VI) and CN. These values are significant enough to influence the overall magnitude of Cr(VI) and CN adsorption. Results also indicate that HCrO − 4 and Cr 2O 2− 7 are the major Cr(VI) species involved in surface association.

Foam fractionation of cyanide complex anions of Zn(II), Cd(II), Hg(II) and Au(III)

An experimental investigation is presented of the batch foam fractionation of the cyanide complex anions of Zn(II), Cd(II), Hg(II) and Au(III) from 1.0 × 10 −5 M (metal concentration) alkaline aqueous solutions, with the cationic surfactant hexadecyltrimethylammonium chloride. The effects are established of the presence of CN − over the concentration range 2.5 × 10 −5M−1.0 M, of the presence of NO 3 − over the concentration range 0.05–0.75 M, and of interferences to metal foam fractionation provided by 0.50 M concentrations of NO 3 −, Br −, CN −, Cl − or SO 4 2−. Results are discussed in terms of the complex cyanide species of each metal that may have been present and in terms of the extent of hydration of the complex cyanide anions and of the potentially-interfering simple anions. The selectivity sequence, Au(CN) 4 −Hg(CN) 4 2−Cd(CN) 4 2−Zn(CN) 4 2− is established, both from data for single-metal solutions and for solutions containing equimolar concentrations of all four metals. A partial separation of the metals can be achieved in the presence of high concentrations of NO 3 −, which can be improved by taking maximum advantage of flotation rate differences.

Physiological and toxicological aspects of smoke produced during the combustion of polymeric materials.

Normally one expects that flame contact is the major cause of injury and death during fires. Analysis of the factors involved in numerous fires has revealed that most deaths were not due to flame contact, but were a consequence of the production of carbon monoxide, nitrogen oxides, and other combustion products, such as aldehydes, low molecular weight alcohols, hydrogen cyanide, and other noxious species. The major emphasis within the scope of this paper relates to the physiological and toxicological aspects of smoke produced during the combustion of materials. Special emphasis is directed toward laboratory procedures which have been developed to determine the qualitative and quantitative analysis of smoke, factors pertaining to smoke development, and to measure the response of laboratory animals exposed to smoke. The effects that fire retardants, incorporated into polymeric materials as a means of improving flammability characteristics, may have on smoke development, the mechanism of polymer degradation, and on the survival response of laboratory animals are also considered.

Physiological and Toxicological Aspects of Smoke Produced during the Combustion of Polymeric Materials

Normally one expects that flame contact is the major cause of injury and death during fires. Analysis of the factors involved in numerous fires has revealed that most deaths were not due to flame contact, but were a consequence of the production of carbon monoxide, nitrogen oxides, and other combustion products, such as aldehydes, low molecular weight alcohols, hydrogen cyanide, and other noxious species. The major emphasis within the scope of this paper relates to the physiological and toxicological aspects of smoke produced during the combustion of materials. Special emphasis is directed toward laboratory procedures which have been developed to determine the qualitative and quantitative analysis of smoke, factors pertaining to smoke development, and to measure the response of laboratory animals exposed to smoke. The effects that fire retardants, incorporated into polymeric materials as a means of improving flammability characteristics, may have on smoke development, the mechanism of polymer degradation, and on the survival response of laboratory animals are also considered.

Harmonic Frequencies and Potential Energy Distributions of Partially Deuterated Methyl Cyanide

Abstract Although the vibrational spectra and force constants of CH3CN and CD3CN have been thoroughly studied, partially deuterated methyl cyanide has received much less attention. The infrared spectrum of CD2HCN has only recently been reported1 and that of CH2DCN has not yet appeared. Normal coordinate analysis for neither partially deuterated species has appeared. We report here harmonic frequencies and potential energy distributions for both partially deuterated methyl cyanide species, CH2DCN and CD2HCN, based on force fields and structural parameters from CH3CN and CD3CN. The calculated frequencies for CD2HCN are compared with the observed infrared frequencies. The vibrational interaction of the relatively high CN stretching frequency and the CD stretching frequencies is also discussed.