Oxidation Of Hydrogen Cyanide Research Articles

Kinetic analysis on the hydrogen cyanide formation in the premixed methane/ammonia flame

Hydrogen cyanide (HCN) is a highly toxic trace emission that may be generated during ammonia (NH3) blended hydrocarbon combustion. In this study, a new kinetic model was developed and validated to predict HCN formation in NH3-blended combustion. Key rate coefficients for nitrogen-substituted hydrocarbon species were critically reevaluated. Using a one-dimensional freely propagating flame model, the formation of HCN in laminar premixed CH4/NH3/air flames was systematically analyzed under various conditions. Results indicate that HCN emission increases with increasing equivalence ratio (ϕ) and non-monotonically changes with NH3 blending ratio (α). Under lean conditions, HCN is primarily formed from the decomposition of imine radicals and oxidized by O/OH inside the flame front. While under rich conditions, the HCN oxidation takes place in the post-flame region, making the emissions at the outlet highly dependent on the reaction residential time. Consequently, attention should be paid to HCN emissions under high NH3 blending fraction (α > 50 %), and ultra-rich conditions (ϕ > 1.2) at normal temperature and pressure. The peak emission of HCN occurred at α = 0.7 and ϕ = 1.45, reaching a lethal concentration (310 ppm) in 1D premixed flame. Complex CHi and NHi interaction reactions are exhibited in the formation of HCN. The overall formation route can be divided into methylamine oxidation routes and radical combinations routes, and the former is dominant under all conditions. Independently increasing temperature or pressure will reduce the HCN emission due to the increased post-oxidation of HCN and diminished reaction characteristic time, respectively. More complicated changes in HCN were shown when temperature and pressure were increased at the same time. However, emissions will fall to a negligible level when temperature and pressure exceed 600 K and 2 atm, suggesting minimal concern for HCN emissions in CH4/NH3 combustion under elevated pressure and temperature conditions.

Insights into the differences in metal anchoring mechanisms and the impact on HCN catalytic oxidation performance

Hydrogen cyanide (HCN) is often produced in various industrial processes, such as metal smelting, carbon fiber production, etc. Due to its highly toxic nature, it has significant harm to the human body and the environment. Catalytic oxidation can convert HCN into non-toxic N2, CO2 and H2O. In this study, we conducted a comparative evaluation of the catalytic oxidation of HCN using Cu, Co and Mn as catalyst active centers, and used in situ DRIFTS to explore the reaction mechanism of HCN catalytic oxidation. The difference in the anchoring state of different metals on the hydroxyl groups on the Al2O3 surface, mainly the difference in anchoring strength and hydroxyl consumption, determines the difference in the metal dispersion state, which in turn affects the oxygen activation ability and HCN oxidation performance. Under high loading conditions, compared to Co and Mn, Cu species are more fully anchored due to lower hydroxyl consumption, exhibiting higher dispersion and redox properties, so the 10Cu/Al2O3 catalyst performs well HCN oxidation activity.

Experimental investigation and numerical modelling of CO and HCN release during the combustion of flexible polyurethane foam

The combustion of flexible polyurethane foam (FPUF) in fires releases relatively large amounts of carbon monoxide (CO) and hydrogen cyanide (HCN), threatening the lives of those exposed thereto. It is therefore necessary to use computational fluid dynamics method to explore the distribution of CO and HCN in a fire involving the combustion of FPUF. However, the release of CO and HCN varies significantly with the combustion conditions, which makes the numerical modelling challenging. In the present research, the yields of CO and HCN during the combustion of a non-flame-retardant FPUF were determined using a steady-state tube furnace (SSTF) facility, considering the effect of the ventilation condition. Meanwhile, a pyrolysis and combustion model of FPUF was constructed based on the fire dynamics simulator (FDS), and a four-step chemistry model was proposed to deal with the reactions in the gas phase. The experimental results showed that the yields of CO and HCN both increased with the limitation of ventilation, which was more pronounced in under-ventilated conditions. Meanwhile, the numerical simulation applying the four-step chemistry model predicted the variations in the yields of CO and HCN under ventilated conditions. In addition, when the appropriate kinetic parameters were applied to the reactions governing the oxidation of CO and HCN, the comparative results indicated that the global average deviations between the predicted and experimental yields could be reduced to 13.61 % (CO) and 8.19 % (HCN), respectively.

Atmospheric distribution of HCN from satellite observations and 3-D model simulations

Abstract. Hydrogen cyanide (HCN) is an important tracer of biomass burning, but there are significant uncertainties in its atmospheric budget, especially its photochemical and ocean sinks. Here we use a tracer version of the TOMCAT global 3-D chemical transport model to investigate the physical and chemical processes driving the abundance of HCN in the troposphere and stratosphere over the period 2004–2016. The modelled HCN distribution is compared with version 4.1 of the Atmospheric Chemistry Experiment Fourier transform spectrometer (ACE-FTS) HCN satellite data, which provide profiles up to around 42 km, and with ground-based column measurements from the Network for the Detection of Atmospheric Composition Change (NDACC). The long-term ACE-FTS measurements reveal the strong enhancements in upper-tropospheric HCN due to large wildfire events in Indonesia in 2006 and 2015. Our 3-D model simulations confirm previous lower-altitude balloon comparisons that the currently recommended NASA Jet Propulsion Laboratory (JPL) reaction rate coefficient of HCN with OH greatly overestimates the HCN loss. The use of the rate coefficient proposed by Kleinböhl et al. (2006) in combination with the HCN oxidation by O(1D) gives good agreement between ACE-FTS observations and the model. Furthermore, the model photochemical loss terms show that the reduction in the HCN mixing ratio with height in the middle stratosphere is mainly driven by the O(1D) sink with only a small contribution from a reaction with OH. From comparisons of the model tracers with ground-based HCN observations we test the magnitude of the ocean sink in two different published schemes (Li et al., 2000, 2003). We find that in our 3-D model the two schemes produce HCN abundances which are very different to the NDACC observations but in different directions. A model HCN tracer using the Li et al. (2000) scheme overestimates the HCN concentration by almost a factor of 2, while a HCN tracer using the Li et al. (2003) scheme underestimates the observations by about one-third. To obtain good agreement between the model and observations, we need to scale the magnitudes of the global ocean sinks by factors of 0.25 and 2 for the schemes of Li et al. (2000) and Li et al. (2003), respectively. This work shows that the atmospheric photochemical sinks of HCN now appear well constrained but improvements are needed in parameterizing the major ocean uptake sink.

Mid-infrared Frequency Modulation Detection of HCN and Its Reaction with O Atoms behind Shock Waves.

Hydrogen cyanide (HCN) is the primary cyanide species in combustion processes and plays a key role in the formation of NOx in the combustion of fossil fuels, nitrogen-containing biofuels, and blended hydrocarbon-ammonia mixtures. Robust, sensitive, and time-resolved in situ laser diagnostic methods are needed to gain insight into the combustion chemistry of HCN. Mid-infrared frequency modulation spectroscopy (MIR-FMS) has recently been established as such a quantitative technique for HCN detection behind shock waves. With a minimum detectable fractional absorption of 2 × 10-4 at a time resolution of 5 μs, an improved spectrometer design enabled the detection of HCN behind shock waves down to the ppm mole fraction level. An Allan noise analysis revealed that a further improvement toward shot-noise limited detection should be possible when fast mid-infrared photodetectors with a higher saturation limit will become available. HCN kinetic profiles in the presence of O(3P) atoms from thermal N2O decomposition have been measured in the temperature range 1448 K < T < 1954 K. The determined total rate constants for the key HCN oxidation reaction HCN + O, k/(cm3 mol-1 s-1) = 1.88 × 1014 exp(-64.5 kJ mol-1/RT)(+28%, -37%), turn out to be largely consistent with previous measurements. These data complete the set of available rate constant studies, by now covering the temperature range 450 K < T < 2500 K and relying on the detection of almost all feasible reactant and product species.

Understanding the effect of CaO on HCN conversion and NOx formation during the circulating fluidized combustion process using DFT calculations

Hydrogen cyanide (HCN) is an important intermediate during the conversion of fuel nitrogen to NOx. The mechanism of HCN oxidation to NO, N2, and N2O on the CaO (100) surface model was investigated using density functional theory calculations to elucidate the effect of in-furnace SOx removal on HCN oxidation in circulating fluidized bed boilers. HCN adsorption on the CaO (100) surface releases as high as 1.396 eV and the HC bond is strongly activated. The CaO (100) surface could catalyze the oxidation of CN radical to NCO with the energy barrier decreasing from 1.560 eV for the homogeneous case to 0.766 eV on the CaO (100) surface. The succeeding oxidation of NCO by O2 forming NO is catalyzed by the CaO (100) surface with the energy barrier decreasing from 0.349 eV (homogeneous process) to 0.026 eV on the CaO (100) surface, while the reaction between NCO and NO forming either NO or N2 is prohibited in comparison with corresponding homogeneous routes. The rate constants of these reactions under fluidized bed combustion temperature range are provided, and the calculation results lead to the conclusion that CaO (100) surface catalyzes the HCN conversion and improves the NO selectivity during HCN oxidation in the HCN/O2/NO atmosphere, which could well explain previous experimental observations. Kinetic parameters of HCN oxidation on the CaO (100) surface are provided in the Arrhenius form for future kinetic model development.

Probing hydrogen–nitrogen chemistry: A theoretical study of important reactions in NxHy, HCN and HNCO oxidation

As an indirect storage medium of hydrogen, ammonia (NH3) has drawn significant attention from academia and industry. Understanding nitrogen combustion chemistry is a major challenge in applying ammonia for converting chemical energy to thermal energy. Diazene (N2H2), diazenyl radical (NNH), amidogen radical (NH2), hydrogen cyanide (HCN) and isocyanic acid (HNCO) are the crucial intermediate species in the combustion of NH3 or its mixtures with other hydrocarbons. In light of that, this study provides advanced theoretical treatment of 14 important reactions in the oxidation of these intermediates, including isomerization, dissociation and abstraction reactions. The rate constants of all these reactions, and the temperature-dependent thermochemistry of the species involved in the reactions, were calculated utilizing high level quantum chemical methods. Ro-vibrational properties of the reactants, products and stationary points were determined at the M06–2X/6–311++G (d,p) level of theory. Coupled cluster (CCSD(T)) methods were employed, with two large basis sets (cc-pVTZ and cc-pVQZ), and complete basis set of extrapolation techniques to compute the energies of the resulting geometries. All calculated results were compared with experimental and theoretical results in the literature. Finally, the implications of this work for combustion modeling were investigated, and the simulated species’ profiles of HCN and HNCO demonstrated the influence of the updated rate coefficients on kinetic model predictions.

Influence of Impurities on Sulfur Removal from Coke-Oven Gas

The extraction of hydrogen sulfide from coke-oven gas by means of alkaline aqueous solutions occurs in the presence of several acidic components, which dissolve to form acids with different degrees of dissociation. The relation between the acidic components of the gas depends on the batch composition and the corresponding coking conditions. The ratio H2S/CO2 decreases on coking coal with low sulfur content and elevated calcium content and with an elevated content of gas coal. There is little scope for slowing the CO2 absorption. The selectivity of H2S capture increases somewhat with increase in content of ballast salts. A general analysis of ballast-salt formation is proposed for circulatory and oxidative methods of sulfur removal. The influence of ballast salts on the activity of the absorbent solution in arsenic–soda sulfur removal is not critical. That may be explained in terms of As5+/As3+ conversion. The oxidation of hydrogen cyanide by strong acids produces compounds that cannot be regenerated; recommendations are made for slowing that process. The influence of organic contaminants on the removal of sulfur from coke-oven gas is considered.

On the Combination of fuel-rich/lean burner with MILD combustion for further NOx emission reduction

Moderate or Intensive Low-Oxygen Dilution (MILD) combustion as a newly developed technology has drawn much attention all over the world since it features the homogeneous combustion and extremely low NOx emission. Even though reduced NOx emission is reported in pulverized coal MILD combustion, its performance is not as comparable as that of gaseous and liquid fuels. In order to investigate the possibility of further reducing NOx emission in a MILD coal combustion furnace, horizontal fuel-rich/lean burner as another promising technology aiming to regulate NOx emission is employed in this study. Results have shown that fuel-rich/lean burner is able to further reduce NOx emission by about 4% when applied to a MILD coal combustion furnace. This is due to the combined effect of the reduction of thermal- and fuel-NO formation. Particles entrained in the fuel-rich stream is heated in a reducing atmosphere, so that the oxidation of hydrogen cyanide (HCN) and ammonia (NH3) released by volatile is hindered. Moreover, the NO released by char is reduced to molecular nitrogen. Thermal-NO is reduced because of the low local peak temperature in both streams.

Importance of the Hydrogen Isocyanide Isomer in Modeling Hydrogen Cyanide Oxidation in Combustion

Hydrogen isocyanide (HNC) has been proposed as an important intermediate in oxidation of hydrogen cyanide (HCN) in combustion, but details of its chemistry are still in discussion. At higher temperatures, HCN and HNC equilibrate rapidly, and being more reactive than HCN, HNC offers a fast alternative route of oxidation for cyanides. However, in previous modeling, it has been required to omit the HNC subset partly or fully in the reaction mechanisms to obtain satisfactory predictions. In the present work, we re-examine the chemistry of HNC and its role in combustion nitrogen chemistry. The HNC + O2 reaction is studied by ab initio methods and is shown to have a high barrier. Consequently, the omission of this reaction in recent modeling studies is justified. With the present knowledge of the HNC chemistry, including an accurate value of the heat of formation for HNC and improved rate constants for HNC + O2 and HNC + OH, it is possible to reconcile the modeling issues and provide a satisfactory prediction o...

Computational study on the mechanism and thermodynamic of atmospheric oxidation of HCN with ozone

Oxidation of hydrogen cyanide with ozone on the singlet potential energy surface is carried out using the MP2 and CCSD(T)//MP2 theoretical approaches in connection with the 6-311++G(d,p) basis set. In this reaction, energy barrier of transition states are low, so the reaction of HCN with ozone can occur easily at atmospheric condition. With variety of pre-reactive complex, five types of products are obtained at the MP2 method which four types of them have enough thermodynamic stability at the standard condition. CO2 + HNO are final adducts in a process that is computed to be exothermic by −132.605 kcal/mol in standard enthalpy and spontaneous by −144.166 kcal/mol in Gibbs free energy of reaction. In kinetic viewpoint, the production of OCN + HO2 adducts path with one low level transition state is the most favored path.

A combined experimental and theoretical study of micronized coal reburning

Micronized coal reburning (MCR) can not only reduce carbon in fly ash but also reduce NOx emissions as compared to the conventional coal reburning. However, it has two major kinetic barriers in minimizing NOx emission. The first is the conversion of NO into hydrogen cyanide (HCN) by conjunction with various hydrocarbon fragments. The second is the oxidation of HCN by association with oxygen-containing groups. To elucidate the advantages of MCR, a combination of Diffuse Reflection Fourier Transform Infrared (FTIR) experimental studies with Density Functional Theory (DFT) theoretical calculations is conducted in terms of the second kinetic barrier.

95/01747 Mechanism and modelling of hydrogen cyanide oxidation in a flow reactor

95/01747 Mechanism and modelling of hydrogen cyanide oxidation in a flow reactor

Mechanism and modeling of hydrogen cyanide oxidation in a flow reactor

The oxidation of hydrogen cyanide under flow reactor conditions (atmospheric pressure, 900–1400 K) has been examined. The study is based mainly on experimental data from the literature on the effect of NO and CO on HCN oxidation, emphasizing N 2O formation. However, additional experiments were conducted during the present work in order to investigate the importance of HNCO as an intermediate. The experimental data are compared with model predictions, using a revised reaction mechanism for HCN oxidation. Recent advances in our knowledge of thermodynamic properties for CN, NCO, and HNCO, as well as of the mechanism and rate constants for a number of key reactions have reduced the uncertainty in the model considerably: now model predictions are in good agreement with the experimental data. Compared with the previous HCN oxidation models, particularly the prediction of N 2O is significantly improved, aided by better knowledge about the NCO + NO reaction. Under the conditions investigated, the main oxidation route for HCN proceeds through NCO, formed by the reaction the sequence HCN+OH→CN+H 2O, CN+O 2 →NCO+O. The subsequent reactions of NCO determine the fate of the nitrogen atom. Depending on the gas composition and temperature, NCO is converted to HNCO (by reaction with H 2O or HCN), N 2O/N 2 (by reaction with NO) or NO (by reaction with O). Both HNCO and N 2O are important intermediates in HCN oxidation under these conditions. The present results are significant for understanding the fate of reactive nitrogen in fluidized bed combustion and staged combustion, particularly the formation and destruction of N 2O.

Hydrolysis and oxidation of hydrogen cyanide over limestone under fluidized bed combustion conditions

A kinetic study was conducted for hydrolysis and oxidation of HCN over limestone at 1123 K with a fixed bed reactor. In the absence of O 2 , HCN was hydrolyzed to mainly NH 3 . However, the reaction rate of hydrolysis was far lower than that of oxidation. In the presence of O 2 at concentrations higher than 0.5%, oxidation of HCN was dominant and most of HCN was oxidized to NO, while only a small amount of NH 3 was produced. Conversion of HCN to N 2 O for oxidation over limestone was far lower than the conversions which had been reported for homogeneous oxidation of HCN

The atmospheric chemistry of hydrogen cyanide (HCN)

Since 1981, three groups have reported spectroscopic detections and measurements of hydrogen cyanide in the atmosphere. HCN concentrations (volume mixing ratios) of (1.5–1.7) × 10−10 appear to characterize the stratosphere and the northern hemisphere's nonurban troposphere. In this paper we explore the atmospheric behavior of HCN by examining its chemical and photochemical properties. Its principal sinks are reactions with atmospheric OH and O(1D); precipitation appears to be a negligible sink. In the stratosphere, vacuum UV photons also attack HCN. Atmospheric model calculations show that HCN should be relatively well mixed in the troposphere and that its concentration decreases slowly with altitude in the stratosphere. Its atmospheric residence time appears to be about 2.5 years, although 1–5 years is a possible range. To maintain the observed atmospheric burden of HCN, an annual source of about 2 × 10−11 g nitrogen as HCN is required; we speculate as to the identity of these sources. Oxidation of HCN by OH, while the major sink for atmospheric HCN, is not simple or direct. Instead, oxidation proceeds from the HCN·OH adduct formed in HCN + OH reactions. These pathways and their uncertainties are outlined here.

Oxidation of hydrogen cyanide in shock waves. Formation of nitrogen monoxide

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTOxidation of hydrogen cyanide in shock waves. Formation of nitrogen monoxideTetsuo Higashihara, Ko Saito, and Ichiro MurakamiCite this: J. Phys. Chem. 1983, 87, 19, 3707–3712Publication Date (Print):September 1, 1983Publication History Published online1 May 2002Published inissue 1 September 1983https://doi.org/10.1021/j100242a026RIGHTS & PERMISSIONSArticle Views87Altmetric-Citations8LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (612 KB) Get e-Alerts

The oxidation of hydrogen cyanide in fuel-rich flames

The decay of hydrogen cyanide in the burnt gases of a number of fuel-rich flames has been investigated with a view to establishing the mechanism of decay and reconciling discrepant results reported in the literature. At least two parallel rate-controlling steps have been identified: one which is first order in OH, possibly reaction (12′) or some kinetically equivalent process: (12) HCN+ OH→( HOCN+ H) . The other step, which is second order in OH has been identified as: (5) HCN+ OH⇒ CN+ H 2 O , (15) CN+ OH→( OCN+ H) . Over the temperature range 1950 to 2380 K, the rate constants k (12′) = (2.0 ± 0.2) × 10 8 m 3/kgmole-sec and k (15) = (5.6 ± 0.7) × 10 10 m 3/kgmole-sec have been obtained. The relative contributions of reactions (12′) and (15) vary markedly with temperature, with reaction (15) dominating at temperatures above 2300 K. It is proposed that rupture of the OCN linkage in the products of reactions (12′) and (15) may then give rise to amine (NH) species which are the measured products of HCN decay: HOCN→ HNCO → +H NH 2+ CO , OCN+ H→ NH+ CO . No evidence for any HCN-removing reactions involving CO 2, NO or NH 3 has been obtained.