Showing papers on "Ammonia published in 1993"

Thermophilic anaerobic digestion of livestock waste: the effect of ammonia

Abstract: Ammonia concentrations of 4 g N/l or more inhibited thermophilic digestion of cattle manure. A stable digestion of cattle manure could be maintained with ammonia concentrations up to 6 g N/l after 6 months of operation. However, the methane yield was reduced and the concentration of volatile fatty acids increased from 1 to 3 g/l as acetate, compared to controls with an ammonia concentration of 2.5 g N/l. The temporary strong inhibition following an one-step increase in ammonia concentration was reduced by applying a gradual increase. The specific methanogenic activity of ammonia-inhibited reactors (6 g N/l) with acetate or hydrogen as substrate was reduced by 73 and 52%, respectively. Tests of ammonia toxicity on the acetate- and hydrogen-utilizing populations showed a higher sensitivity of the aceticlastic compared to the hydrogenotrophic methanogens; the specific growth rate for the aceticlastic methanogens was halved at ammonia concentrations of 3.5 g N/l, compared to 7 g N/l for the hydrogenotrophic methanogens.

Prebiotic ammonia from reduction of nitrite by iron (II) on the early Earth.

Abstract: Theories for the origin of life require the availability of reduced (or 'fixed') nitrogen-containing compounds, in particular ammonia. In reducing atmospheres, such compounds are readily formed by electrical discharges, but geochemical evidence suggests that the early Earth had a non-reducing atmosphere, in which discharges would have instead produced NO. This would have been converted into nitric and nitrous acids and delivered to the early oceans as acid rain. It is known, however, that Fe(II) was present in the early oceans at much higher concentrations than are found today, and thus the oxidation of Fe(II) to Fe(III) provides a possible means for reducing nitrites and nitrates to ammonia. Here we explore this possibility in a series of experiments which mimic a broad range of prebiotic seawater conditions (the actual conditions on the early Earth remain poorly constrained). We find that the reduction by Fe(II) of nitrites and nitrates to ammonia could have been a significant source of reduced nitrogen on the early Earth, provided that the ocean pH exceeded 7.3 and is favoured for temperatures greater than about 25 degrees C.

Adsorption and reactions of co, no, hi and 0 1 on group viii metal surfaces

Abstract: Group VIII metals are used as catalysts for a number of reactions involving the molecules H2, CO, O2, NO and NH3. This paper will outline and discuss the differences in behaviour of the Group VIII metal surfaces in reactions of oxygen with hydrogen and carbon monoxide; nitric oxide with hydrogen and carbon monoxide; carbon monoxide with hydrogen; and ammonia with nitric oxide and oxygen. It will be shown that the differences in activity and selectivity of the various metals can be understood on the basis of the behaviour of these metals in the adsorption of the gases CO, NO, O2, H2 and NH3.

Potassium doping of vanadia/titania de-NOxing catalysts: Surface characterisation and reactivity study

Abstract: An investigation of the effect of K-doping on the surface and catalytic properties of sub-monolayer vanadia/titania de-NOxing catalysts is carried out Samples having different vanadium and potassium loadings have been investigated by means of Fourier-transform infrared spectroscopy (FT-IR), temperature-programmed desorption (TPD), temperature-programmed surface reaction (TPSR) and temperature-programmed reaction (TPR) techniques Isolated vanadyls and polymeric metavanadate species are present on the surface of undoped catalysts; both species increase on increasing the V2O5 loading in the range 028–53% w/w TPSR and TPR data provide evidence for a greater reactivity of polymeric metavanadate species as compared to isolated vanadyls Besides, a different type of isolated vanadyl appears to form at high loadings Ammonia is adsorbed at vanadium sites in the form of molecularly coordinated species and of ammonium ions Coordinated species show a higher thermal stability than ammonium ions Ammonia is also coordinated at titanium sites to give a more weakly held species Upon K-doping the stretching frequencies of surface vanadyls are lowered due to the production of strong oxide basic anions on the catalyst surface This reduces the Lewis acidity of vanadium ions IR and TPD experiments indicate that both molecularly chemisorbed ammonia and ammonium ions are present in much lower amounts and are less strongly held on K-doped samples TPD and TPSR data further indicate that the alkali dopant poisons preferentially Lewis acid sites associated with vanadium rather than with Ti4+ ions TPSR and TPR data show that alkali doping reduces markedly the nitric oxide conversion (associated with the number of active sites), but not the temperature threshold of the SCR reaction (associated with the intrinsic reactivity of the active sites) The lower number of active sites on alkali-doped catalyst can be related to the poisoning of both Bronsted and Lewis vanadium acid sites due to alkali addition, which results in a lower ammonia surface coverage

A computational analysis of the bonding in boron trifluoride and boron trichloride and their complexes with ammonia

Abstract: Complexation energies for the interactions of BF 3 and BCl 3 with NH 3 have been calculated at the ab initio Hartree-Fock and MP2 levels of theory, using large polarized basis sets. The formation of H 3 N-BCl 3 is found to be favored by 4.27 kcal/mol over H 3 N-BF 3 3 at the MP2 level. This is in agreement with the experimental observation that the Lewis acidities of the boron trihalides increase in the order BF 3

Field investigations of ammonia exchange between barley plants and the atmosphere. I. Concentration profiles and flux densities of ammonia

Abstract: The exchange of ammonia between the atmosphere and the canopy of spring barley crops growing at three levels of nitrogen application (medium N, high N and excessive N) was studied over two consecutive growing seasons by use of micrometeorological techniques. In most cases, ammonia was emitted from the canopy to the atmosphere. The emission started around 2 weeks before anthesis, and peaked about or shortly after anthesis. The volatilization of ammonia only took place in the daytime. During the night-time, atmospheric ammonia was frequently aborbed by the canopy. Occasionally, plants in the medium and high N treatments also absorbed ammonia from the atmosphere during the daytime. Daytime absorption of ammonia never occurred in the excessive N canopy. The loss of ammonia from the canopy amounted in both years to 0.5–1.5 kg NH3-N ha−1 and increased with the N status of the canopy. In agreement with the small losses of ammonia, the content of 15N-labelled nitrogen in the plants did not decline during the grain-filling period. The experimental years were characterized by very favourable conditions for grain dry matter formation, and for re-utilization of nitrogen mobilized from leaves and stems. Consequently, a very high part of the nitrogen in the mature plants was located in grain dry matter (80–84% in 1989; 74–80% in 1990). The efficient re-utilization of nitrogen may have reduced the volatilization of ammonia.

AMMONIA AND UREA EXCRETION IN LAHONTAN CUTTHROAT TROUT (ONCORHYNCHUS CLARKI HENSHAWI) ADAPTED TO THE HIGHLY ALKALINE PYRAMID LAKE (pH 9.4)

Abstract: Earlier studies have reported that acute exposure to alkaline pH strongly inhibits ammonia excretion in freshwater rainbow trout, but the Lahontan cutthroat trout thrives in Pyramid Lake, Nevada, at pH 9.4. We investigated the rates and mechanisms of ammonia and urea excretion in this species in Pyramid Lake water to determine whether special strategies are employed to excrete nitrogenous wastes in an environment unfavourable for ammonia excretion. The majority of nitrogen wastes (N-wastes) were excreted as ammonia (56 % through the gills, 10 % through the kidney), while urea excretion accounted for 34 % (32 % gills, 2 % kidney). Ammonia excretion was dependent on the NH3 partial pressure gradient (deltaPNH3) across the gills and independent of Na+ influx and acidification of the gill water boundary layer. Acute exposure to more alkaline water (pH 10) decreased ammonia excretion by 52 %, while exposure to neutral water (pH 7.6) increased ammonia excretion by 200 %. When fish were held in a ‘closed system’ for 8 h, ammonia excretion decreased as water ammonia levels increased over the first 6 h. However, after 6 h a marked increase in ammonia excretion occurred which may have been associated with an increase in the PNH3 gradient and/or activation of a carrier-mediated transporter. We conclude that Lahontan cutthroat trout, adapted to pH 9.4 water, maintain N-waste excretion by modifying mechanisms common to other teleosts. These modifications include lower rates of ammonia excretion, a higher ratio of urea excretion to ammonia excretion, a higher rate of renal ammonia excretion, greater plasma pH and greater total ammonia level (increased plasma PNH3), which facilitate the diffusive excretion of NH3 across the gills, and a lack of dependence of ammonia excretion on Na+ influx.

Interaction of ammonia with Broensted acid sites in different cages of zeolite Y as studied by proton MAS NMR

Abstract: Ammonia adsorption onto acidic Y zeolites is studied with 1H MAS NMR (at 295-320 K). The influence of the amount of adsorbed ammonia is investigated in the presence of sodium or cesium as exchangeable cations and for different framework compositions (Si/Al = 2.4-12). The Bronsted sites in unloaded or partially loaded zeolites are observed near δ = 3.9 for protons in supercages and near δ = 4.6 for protons in sodalite cages. Ammonium ions under condition of no proton-exchange resonate at δ = 8.1. These species are detected as such only in the sodalite cages. In the supercages, a signal at δ = 6.9 is observed, which is ascribed to an exchange involving NH4+ (δ = 8.1), H+ (δ = 3.9), and NH3 (δ = 0.8). Furthermore, in the sodalite cages, a signal at δ = 6.5 is observed, which is ascribed to an exchange involving NH4+ (δ = 8.1), H+ (δ = 4.6), and NH3 (δ = 0.8), but with different relative residence times. Additionally, ammonium-ammonia signals are found at δ = 5.3-5.9 and at a position determined by the NH3/NH4+ ratio in the zeolite (δ = 7-1). For the ammonium-ammonia species proton-exchange between ammonium and ammonia is fast compared to the time scale of the NMR experiment. For at least two ammonium species proton-exchange with the Bronsted protons is fast, and consequently the lines are shifted to δ = 6.9 and 6.5. This implies that ammonium ions observed at δ = 8.1 have the lowest basicity and the ammonium ions at δ = 6.5 have the highest basicity. However, for the temperature range used, ammonia reacts statistically with the Bronsted sites of different acid strength.

Distribution of aqueous chlorine with nitrogenous compounds: chlorine transfer from organic chloramines to ammonia

Abstract: A kinetic model for chlorine transfer in the aqueous chlorine/ammonia/organic nitrogen system was constructed and used to explain the distribution of the chlorine species over time. Observed second-order rate constants for chlorine transfer from organic chloramines to ammonia were found to be 3.84×10 -2 M -1 s -1 for N - chloroglycine, 1.55×10 -2 M -1 s -1 for N-chloroglycylglycine, and 5.85×10 -3 M -1 s -1 for N-chloromethylamine (pH 6.8). Chlorine transfer from organic chloramines to ammonia was found to be significant under simulated conditions of wastewater disinfection

Development of ammonium-saponites from gels with variable ammonium concentration and water content at low temperatures*

Abstract: Ammonium-saponite is hydrothermally grown at temperatures below 300°C from a gel with an overall composition corresponding to (NH4)0.6Mg3Si34Al0.6O10(OH)2. The synthetic saponite and coexisting fluid have been characterized by means of X-ray powder diffraction, X-ray fluorescence, Induced Coupled Plasma-Atomic Emission Spectroscopy, thermogravimetric analysis, transmission electron microscopy, CEC determination using an ammonia selective electrode, and pH measurement. In the crystallization model developed, crystallization started with the growth of individual tetrahedral layers with an aluminum substitution not controlled by the A1IV/A1VI ratio in the gel and hydrothermal fluid, on which the octahedral Mg layers can grow. During the synthesis, individual sheets stacked to form thicker flakes while lateral growth also took place. The remaining A1VI partly replaced ammonium as the interlayer cation.

Catalytic effect of iron wires on the syntheses of ammonia and hydrazine in a radio-frequency discharge

Abstract: The catalytic effect of iron wires on plasma syntheses of ammonia and hydrazine has been studied in the nitrogen-hydrogen plasma prepared using rf discharge at a pressure of 650 Pa (5 Torr). The product was mainly ammonia including a small amount of hydrazine. When iron wires were placed in the plasma downstream of the gas flow, the yields of both products increased, about two times in ammonia and two orders of magnitude in hydrazine. The yields increased with increasing number of wires (the surface area of the catalyst). The dissociative adsorption of nitrogen molecules and/or molecular ions on the iron surface and the formation of NHx by the reaction with hydrogen in the plasma followed by the formation of NH3 or N2H4 are considered as a reaction scheme. This is supported by the identification of NH3 with XPS of the surface of iron wires.

Determination of ammonium ion in rainwater and fogwater by flow injection analysis with chemiluminescence detection

Abstract: Reaction between ammonia and hypobromite in alkaline solution was found to give chemiluminescence. The maximum wavelength of the chemiluminescence is ∼710 nm. This chemiluminescence reaction has been used for the determination of ammonium ion concentration in rainwater and fogwater with a flow injection analysis system. The detection limit of ammonium ion was 6.1×10 -6 mol/dm 3 (3 RSD). The dominant components in rainwater such as NO 3 - , SO 4 2- and Cl - , do not interfere with the determination, but humic acid and urea do

Solubility of ammonia in aqueous solutions of sodium sulfate and ammonium sulfate at temperatures from 333.15 K to 433.15 K and pressures up to 3 MPa

Abstract: As part of an ongoing project dealing with experimental and theoretical work on phase equilibria in aqueous solutions containing weak electrolyte gases like ammonia, hydrogen cyanide, sulfur dioxide, or carbon dioxide, the solubility of ammonia in aqueous solutions of sodium sulfate and ammonium sulfate was measured by a synthetic method in the temperature range from 333.15 to 433.15 K at total pressures up to 3 MPa. The model proposed by Edwards et al. is used to correlate the data. That model is extended to include the formation of one or more solid phases. Experimental results and the correlations are reported and compared with literature data and other correlations

Effect of Mineral Nutrients on the Kinetics of Methane Utilization by Methanotrophs

Abstract: The effect of different mineral nutrients on the kinetics of methane biodegradation by a mixed culture of methanotrophic bacteria was studied. The substrate factors examined were ammonia, iron, copper, manganese, phosphate, and sulphide. The presence of iron in the growth medium had a strong effect on the yield coefficient. Yield coefficients up to 0.49 mg protein per mg methane were observed when iron was added at concentrations of 0.10–5.0 mg/l. Iron addition also increased the maximum methane utilization rate. The same effect was observed after addition of ammonium to a medium where nitrate was the only nitrogen source. The observed Monod constant for methane utilization increased with increasing concentration of ammonia. This shows that ammonia is a weak competitive inhibitor as observed by other researchers. Relatively high levels of both ammonia (70 mg/l) and copper (300 µg/l) inhibited the methane degradation, probably due to the toxic effect of copper-amine complexes.

Effect of water vapour and ammonia on the solid-solid interaction of Cu oxide with Y-type zeolite: preparation of catalyst for reduction of nitric oxide with ammonia at low temperature.

Abstract: The solid-solid interaction between copper oxide and NH4-Y zeolite has been followed to determine changes in the number of bridging framework OH groups, water evolved during the heating process, zeolite structural stability and changes in the state of the Cu ions, manifested in their reducibility and catalytic activity in the selective reduction of NO with ammonia. The interaction of CuO with NH4-Y results in copper oxide deaggregation and incorporation of single copper ions and/or Cu-O species into the zeolite cationic sites via their exchange with the zeolite bridging OH groups. The process is enhanced by increasing temperature and the presence of water vapour or ammonia in the gaseous phase, by coordination of water or ammonia molecules to copper ions, stimulating their movement into the zeolite bulk. These changes in the state of copper are reflected in the dramatic increase of the system's catalytic activity in the NO+NH3+O2 reaction. The catalytic activity of CuO/zeolite mixtures treated in this way, at temperatures above 470 K, approaches a high activity level of the Cu-exchanged Y zeolite containing single Cu ions. Thus, a method is suggested for the preparation of highly active Cu-zeolite catalyst, which avoids the employment of a huge amount of water solution containing a Cu salt.

An integrated process for making methanol and ammonia

Abstract: An integrated process for making methanol and ammonia from a hydrocarbon feed stock and air is disclosed. An air separation unit is used to produce substantially pure oxygen and nitrogen gas streams. The oxygen gas is used in the secondary reformer to increase the operating pressure of the reformers so that compression to methanol synthesis pressure may be done by a single stage compressor. The nitrogen gas is used to remove carbon oxides impurities from a ammonia synthesis feed stream in a nitrogen wash unit in addition to supplying the nitrogen reactant in the ammonia synthesis gas. Use of nitrogen wash obviates the need for steam shift and methanation reactions used in prior art processes.

Effect of crystal morphology in selective catalytic reduction of nitric oxide over V2O5 catalysts

Abstract: Structural specificity of vanadium pentoxide catalysts was investigated in the selective catalytic reduction (SCR) of nitric oxide. Catalysts were prepared by different temperature-programmed methods to obtain particles having preferential exposure of different crystal planes. Catalyst samples were characterized using the BET surface area technique, X-ray diffraction, laser Raman spectroscopy. X-ray photoelectron spectroscopy, scanning electron microscopy and 3-D imaging techniques. A steady-state fixed-bed reactor system was used for activity and selectivity measurements. Identification and quantification of reaction effluents were achieved using an analytical scheme that combined gas chromatography, chemiluminescence, gas chromatography-mass spectroscopy and wet chemistry techniques. Samples that preferentially exposed the (010) basal planes were found to promote direct oxidation of ammonia more readily than nitric oxide reduction as evidenced by the differences in nitric oxide and ammonia conversions and in nitrogen and nitrous oxide yields. The difference in catalytic activity and selectivity was related to the relative abundance of V O sites exposed on the catalyst surface and the competing reactions that are involved in SCR and direct ammonia oxidation reaction schemes.