Removing nitric oxide from flue gases by catalytic reduction

A Ti-W-V catalyst has been proposed for removing NO by means of ammonia reduction from flue gases from power stations and boiler systems operating with natural gas; it contains 10% W0₃ and 5% V₂O₅ deposited on anatase. The optimum NH₃/NO ration is 0.8. oxygen at levels of 0.1–7.8 vol. % does not affect the reduction of the NO. Industrial tests in flue gas from a power station show that the reduction of the NO is 96% at 240–270°C. The basic technological parameters have been determined.State Research and Development Institute for the Nitrogen Industry and Organic Synthesis Products, Moscow. Translated from Teoreticheskaya i Eksperimental'naya Khimiya, Vol. 27, No. 5, pp. 595–598, September–October, 1991. Original article submitted July 5, 1991.     

The reaction of methoxy radicals with nitric oxide and nitrogen dioxide

By allowing dimethyl peroxide (10^?4M) to decompose in the presence of nitric oxide (4.5 × 10^?5M), nitrogen dioxide (6.5 × 10^?5M) and carbon tetrafluoride (500 Torr), it has been shown that the ratio k₂/k_2′ = 2.03 ± 0.47: CH₃O + NO → CH₃ONO (reaction 2) and CH₃O + NO₂ → CH₃ONO₂ (reaction 2′). Deviations from this value in this and previous work is ascribed to the pressure dependence of both these reactions and heterogeneity in reaction (2). In contrast no heterogeneous effects were found for reaction (2′) making it an ideal reference reaction for studying other reactions of the methoxy radical. We conclude that the ratio k₂/k_2′ is independent of temperature and from k₁ = 10^10.2±0.4M^?1 sec^?1 we calculate that k_2′ = 10^9.9±0.4M^?1 sec^?1. Both k₂ and k_2′ are pressure dependent but have reached their limiting high-pressure values in the presence of 500 Torr of carbon tetrafluoride. Preliminary results show that k₄ = 10.^9.0±0.6 10^?4.5±1.1/ΘM^?1 sec^?1 (Θ = 2.303RT kcal mole^?1) and by k₄ = 10^8.6±0.6 10^?2.4±1.1/ΘM^?1 sec^?1: CH₃O + O₂ → CH₂O + HO₂ (reaction 4) and CH₃O + t-BuH → CH₃OH + (t-Bu) (reaction 4′).     

Ultrasound-induced aqueous removal of nitric oxide from flue gases: effects of sulfur dioxide, chloride, and chemical oxidant

The effects of sulfur dioxide (SO(2)), sodium chloride (NaCl), and peroxymonosulfate or oxone (2KHSO(5).KHSO(4).K(2)SO(4) with active ingredient, HSO(5)(-)) on the sonochemical removal of nitric oxide (NO) have been studied in a bubble column reactor. The initial concentration of NO studied ranged from about 500 to 1040 ppm. NaCl in the concentration range of 0.01-0.5 M was used as the electrolyte to study the effect of ionic strength. At the low NaCl concentration (0.01 M), the percent fractional removal of NO with initial concentration of 1040 ppm was enhanced significantly, while as the NaCl concentration increased, the positive effects were less pronounced. The presence of approximately 2520 ppm SO(2) in combination with 0.01 M NaCl further enhanced NO removal. However, with a NO initial concentration of 490 ppm, the addition of NaCl was detrimental to NO removal at all NaCl concentration levels. The combinative effect of sonication and chemical oxidation using 0.005-0.05 M oxone was also studied. While the lower concentrations of HSO(5)(-) enhanced NO removal efficiency, higher concentrations were detrimental depending on the initial concentration of NO. It was also demonstrated that in the presence of ultrasound, the smallest concentration of oxone was needed to obtain optimal fractional conversion of NO.     

A new electrochemical analyser for nitric oxide and nitrogen dioxide

Individual sensors employing Teflon-bonded diffusion electrodes have been developed to measure nitric oxide and nitrogen dioxide separately, simultaneously, and continuously at part-permillion levels. The NO sensor was biased at 1.5V and that for NO₂ at 0.8V, both relative to the hydrogen electrode. The crucial factor in the virtual elimination of response from carbon monoxide, a relatively abundant air-pollutant, was the use of gold electrodes for both detectors. At 0.8 V NO does not react on gold. Although NO₂ does oxidize at 1.5 V it was removed quantitatively from NO/NO₂ mixtures by triethanolamine on firebrick. The NO₂ reduction signal and the NO oxidation signal were stable and reproducible.     

Sampling and analysis of flue gases from a plasma incinerator

A system is described for monitoring flue gases from a plasma incinerator for polychlorinated biphenyls (PCBs), polychlorinated dibenzodioxins and polychlorinated dibenzofurans. The system is composed of three basic units: sampler/preconcentrator, gas chromatograph and mass-selective detector. The sampler operates by solid sorbent trapping and thermal desorption. The use of two adsorbers allows sampling at a high flow rate (～1 1 min^?1) and subsequent capillary gas chromatographic analysis without the need for cold traps. A sample trapped on the first adsorber is thermally desorbed and transferred by a carrier stream of 40 cm³ min^?1 to a second smaller adsorber and retrapped. It is then thermally desorbed and injected into the capillary column by a carrier gas at an appropriate flow rate. A sequential valve-minder activates the electric actuators of the two six-port valves used in the design and also controls the power required for heating the adsorbers. Operation of the sampler is automated and is initiated by a single push-button switch. In simulation, the system allowed the separation of the major compounds of interest from possible interferences in <15 min and afforded unambiguous identification of the hazardous compounds and their quantification. For a sample volume of 20 1, the minimum detectable concentration of PCBs is 25–50 ng m^?3.     

The determination of ammonia in flue gas from the selective catalytic reduction of nitric oxide with ammonia

The emission of NO_x from coal-fired boilers can be limited by means of the selective catalytic reduction of NO_x with ammonia. The amounts of unreacted ammonia downstream should be low to avoid processing and environmental problems. Continuous measurement of the ammonia in the flue gas is needed. The determination of ammonia and flue gas sampling techniques are discussed. Measurements of ammonia in exhausts of a laboratory reactor and of a pilot plant for the selective catalytic reduction of NO_x with ammonia are presented. Ammonia was determined by mass spectrometry and chemiluminescence in the gas phase, and by spectrophotometric (Nessler and Berthollet reactions) or potentiometry in aqueous solution, in low (<5 μl l^?1) and high (<1000 μl l^?1) concentration ranges.     

Spectrophotometric determination of nitrogen dioxide in air

Summary A sensitive spectrophotometric method for the determination of trace amounts of nitrogen dioxide, after fixing it as nitrite in alkaline sodium arsenite solution, is described. The reaction is based on the diazo-coupling of p-nitroaniline with chromotrophic acid in acetate medium (pH 6±0.5). The azo dye formed has its absorption maximum at 515 nm, with a molar absorptivity of 3.7×10⁴ l mol^–1 cm^–1. Beer's law is obeyed over the range 0–20 g of nitrite. The relative standard deviation is 2.5% for ten determinations of 10 g of nitrite. The effect of interfering gases and ions on the determination is discussed. The method has been applied to the determination of residual nitrogen dioxide in a laboratory fume cupboard and the results are compared with those obtained by the widely used sulphanilamide — NEDA method. Down to 0.5 g of nitrite can be determined.     

Reactions of dioxygenyl hexafluoroantimonate with water,carbon monoxide,methane, sulfur dioxide,nitric oxide,and nitrogen dioxide

The following gaseous products are released, in addition to oxygen, in reactions of O₂SbF₆ with water, CO, CH₄ and SO₂, respectively: O₃, COF₂, CHF₃ and SO₂F₂. Nitrogen dioxide forms the solid complex NO₂SbF₆, and nitric oxide forms a mixture of NOSbF₆ and NO₂SbF₆. No reaction of CO₂ with O₂SbF₆ has been observed.     

Hydrazyl,Nitronyl-, and imino-nitroxides: Synthesis,properties and reaction with nitric oxide and nitrogen dioxide

Ten novel and stable free radicals of nitronyl-, imino-nitroxide and hydrazyl type compounds were synthesized and their physico-chemical properties investigated. UV-Vis and ESR spectroscopic data, as well as the lipophilicities and specific hydrophobic areas of the compounds are compiled. The reaction of these radical compounds with nitric oxide and nitrogen dioxide was also investigated. The radicals synthesized, show selectivity in their reaction with these nitric oxides, depending on their structure (nitronyl-nitroxide radicals react with NO, while hydrazyl radicals react with NO₂). The processes are easily monitored by UV-Vis or ESR spectroscopy.     

The determination of carbon,nitrogen and oxygen in gases by neutron time-of-flight spectrometry

Carbon, nitrogen and oxygen were determined in gases by time-of-flight spectrometry of prompt neutrons from the respective reactions¹²C(d, n)¹³N,¹⁴N(d, n)¹⁵O and¹⁶O(d, n)¹⁷F, produced by a pulsed beam of deuterons of 2 MeV (for nitrogen) or 3 MeV. The analysis is non-destructive and requires about 15 min. per sample. The relative standard deviation for all three elements was about ±3%. Detection limits, using a total irradiation current of 20 millicoulombs, for carbon, nitrogen and oxygen, respectively, were 6·10⁻⁸ g, 2·10⁻⁷ g and 1.7·10⁻⁷ g per cm² cross-sectional area of irradiating beam.     

Formation of nitrous acid and nitric oxide in the heterogeneous dark reaction of nitrogen dioxide and water vapor in a smog chamber

The dark reaction of NO_x and H₂O vapor in 1 atm of air was studied for the purpose of elucidating the recently discussed unknown radical source in smog chambers. Nitrous acid and nitric oxide were found to be formed by the reaction of NO₂ and H₂O in an evacuable and bakable smog chamber. No nitric acid was observed in the gas phase. The reaction is not stoichiometric and is thought to be a heterogeneous wall reaction. The reaction rate is first order with respect to NO₂ and H₂O, and the concentrations of HONO and NO initially increase linearly with time. The same reaction proceeds with a different rate constant in a quartz cell, and the reaction of NO₂ and H₂¹⁸O gave H¹⁸ONO exclusively. Taking into consideration the heterogeneous reaction of NO₂ and H₂O, the upper limit of the rate constant of the third-order reaction NO + NO₂ + H₂O → 2HONO was deduced to be (3.0 ± 1.4) × 10^?10 ppm^?2-min^?1, which is one order of magnitude smaller than the previously reported value. Nitrous acid formed by the heterogeneous dark reaction of NO₂ and H₂O should contribute significantly to both an initially present HONO and a continuous supply of OH radicals by photolysis in smog chamber experiments.     

Electrochemical determination of nitric oxide and of its derivatives

Nitric oxide (NO) is one of the simplest odd electron species. Furthermore, it is relatively hydrophobic, which is consistent with its role as a diffusible intracellular messenger or as an immune effector. NO is generated in biological systems and plays important roles as a regulatory molecule. The main problem in NO analysis is its extreme reactivity; in aerated water solution it is transformed into nitrite and nitrate, inactive biological forms. Moreover, it may lose an electron forming the NO⁺ ion, involved in the synthesis of nitrosothiols (RSNOs). The main problems encountered in the analytical determination of free NO and of RSNOs in biological systems are the low stability and the very low concentration of these compounds. The determination of nitrates and nitrites may also be difficult when their concentration is in the nmolar range. We describe an electrochemical assay for the determination in the same sample of free NO and of its derivatives in nmolar range. Owing to its high sensitivity, the procedure could also be applied to environmental analyses     

二氧化碳中一氧化氮气体标准物质研制

研制二氧化碳中一氧化氮气体标准物质。以高纯二氧化碳和一氧化氮气体标准物质为原料,采用称量法制备二氧化碳中一氧化氮气体标准物质,用气体分析仪对制备的标准物质浓度进行检测,并对该标准物质定值结果的不确定度进行评定。研制的二氧化碳中一氧化氮气体标准物质中一氧化氮的浓度为5,25,50 μmol/mol,相对扩展不确定度为3.0% (k=2)。该气体标准物质具有良好的均匀性和稳定性,可用于食品级二氧化碳分析方法的确认和评价。     

Water permeability of bilipid membranes in presence of nitric acid and nitrogen dioxide

Summary The water permeabilities of phosphotidyl choline bilipid membranes have been measured in absence and presence of nitric acid and N02 respectively. The permeability coefficients increase on addition of nitric acid but decrease eventually to zero on addition of nitrogen dioxide. These results have a bearing on respiration processes involving membranes of the alveoli in the lung and also membranes of blood capillaries.

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Zusammenfassung Die Permeabilitäten von Wasser für Phosphotidyl Choline Bilipid Membranen wurden in Abwesenheit und Gegenwart von Salpetersäure und Stickstoffdioxyd gemessen. Die Permeabilitäts-Koeffizienten nehmen in Gegenwart von Salpetersäure zu, aber sie nehmen ab, wenn Stickstoffdioxyd hinzugefügt wird. Diese Resultate sind wichtig für Atmungsprozesse, an welchen die Membranen von Alveolen der Lunge und auch Membranen der Blutkapillaren teilnehmen.

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