Showing papers on "Ammonia published in 1991"

Dinitrogen photoreduction to ammonia over titanium dioxide powders doped with ferric ions

Abstract: The production of ammonia from dinitrogen and water vapor at mild conditions of temperature and pressure on Fe{sup 3+}-doped titanium dioxide powders under UV radiation has been studied in a continuous photoreactor working in the gas-solid regime. A net activity decline was observed after a few hours of irradiation; this decline did not depend on the reactor temperature, the powder composition, or the amounts of produced ammonia. The highest activity is found when no excess iron is segregated at the surface; overall turnover numbers for dinitrogen reduction as high as six electrons per iron atom can then be reached before powder deactivation, showing the catalytic character of the participation of Fe in this process. An IR investigation of the active and spent specimens revealed that the irradiation determines the almost complete disappearance of the OH groups from the powder surface. Furthermore, an ESR study of all the powders showed that bulk Fe{sup 3+} ions are better electron traps than Ti{sup 4+} ions so that, when a UV photon generates a hole-electron pair, the electron can be stabilized on the iron ions.

Oxidation kinetics of ammonia and ammonia-methanol mixtures in supercritical water in the temperature range 530-700.degree.C at 246 bar

Abstract: Oxidation of industrial chemical and metabolic wastes in a supercritical water medium is an effective method for the treatment and disposal of these materials. Partial oxidation of nitrogen-containing organics in supercritical water leads to the formation of ammonia, which is the rate-limiting step in the overall oxidation to nitrogen. In this study, the oxidation kinetics of ammonia and ammonia-methanol mixtures in supercritical water were experimentally determined in a packed and unpacked tubular plug flow reactor. The oxidation of ammonia was found to be partially catalyzed by the Inconel 625 (a nickel-chromium alloy) reactor walls. In the unpacked reactor, the activation energy was 38 kcal/mol over temperatures ranging from 640 to 700 °C. Oxidation of ammonia in the packed reactor gave an activation energy of 7.1 kcal/mol over the temperature range 530–680 °C and a reaction rate approximately 4 times larger than the tubular reactor data. A power law model and a catalytic model were tested, and the catalytic model was found to represent the data well. In experiments with ammonia-methanol mixtures, the oxidation of ammonia was unaffected by the presence of methanol for experiments conducted in the tubular reactor and retarded by the presence of methanol for packed bed experiments. These observations are consistent with the hypothesis that ammonia oxidation proceeds predominantly as a catalytic reaction in the packed bed reactor at the temperatures investigated. Competitive adsorption of methanol and ammonia reduces the oxidation rate of ammonia in the packed bed reactor. © 1991, American Chemical Society. All rights reserved.

Colon mucosal cell damage by ammonia in rats.

Abstract: Colons of male Sprague-Dawley rats were perfused, in situ, with ammonium (NH4+) or sodium (Na+) and acetate (CH3COO-) or chloride (Cl-) to determine the effects of the cations and anions or their interactions on the colon mucosa. Solutions simulating ileal fluid were delivered at 0.4 mL/min at 38 degrees C via cannulae inserted at the cecal-colonic junction. Effluents were collected by cannulae inserted in the anus. In the first experiment, perfusion with the control solution or with the control solution having 35 mmol/L NaCl replaced by equimolar amounts of ammonium acetate, ammonium chloride or sodium acetate showed that only ammonium-containing solutions caused histological damage, loss of mucus, and significant losses of carbohydrate and DNA (P less than 0.05). The losses of carbohydrate and DNA expressed in microgram.cm-1.30 min-1 were as follows: control, 13.4 and 1.0; ammonium acetate, 31.8 and 1.6; sodium acetate, 16.0 and 0.6; ammonium chloride, 24.1 and 1.3, respectively. In the second experiment, perfusion with control fluid containing 35 or 70 mmol/L ammonium acetate at pH 6.8, 7.4 or 8.0 increased carbohydrate and DNA losses into the effluents compared with the pretest period (P less than 0.05), without significant effects related to influent pH. These studies are consistent with the concept that the life span of colon cells is shortened by concentrations of ammonia found in the colon under normal conditions and that ammonia enhances cell proliferation in the colon mucosa.

Process and device for selective catalytic NOx reduction in exhaust gases containing oxygen

Abstract: For the operation of an SCR catalyst (5) for nitrogen oxide reduction, it is proposed to spray urea solution finely from a container (8) onto a heated vaporiser/catalyst (3) and, if necessary, to carry out an aftertreatment by means of a downstream hydrolysis catalyst (4). The result is that the reduction catalyst is subjected only to the ammonia eliminated from the urea and to the waste gas (12) to be purified, and the formation of other pollutants and contamination of the catalyst are thus avoided.

Reducing ammonia loss from cattle slurry by the use of acidifying additives: The role of the buffer system

Abstract: An 8-month-old cattle slurry was analysed titrimetrically and the major buffer components were found to be ammonium, bicarbonate and a solid phase of carbonates. A simulation model was developed which explained the experimental results. pH stability in response to addition of HCl, superphosphate, FeCl3, Ca(NO3)2 and CaCl2 in increasing levels was investigated. Upon aeration, pH rose quickly by 0.4 to 1.5 units for all additives and levels, except where HCl was added equivalently to the total alkalinity of the slurry, which then kept a stable pH of 4.2. Ammonia volatilisation in response to the addition of either HCl or CaCl2 was found to decrease with increasing amount of additive, HCl being more effective than CaCl2. This confirms that the total alkalinity is an important factor regulating the potential ammonia loss from cattle slurry. Addition of HCl or CaCl2 close to the total alkalinity resulted in a reduction of the potential ammonia loss to 0 and 15% of the untreated loss, respectively.

Intercalation of ammonia into zinc and cobalt phenylphosphonates

Abstract: Zn(O 3 PC 6 H 5 )•H 2 O and Co(O 3 PC 6 H 5 )•H 2 O can be easily dehydrated to yield structures that are isomorphous with the corresponding monohydrate. The dehydration is reversible since both derivatives quickly reabsorb moisture from the atmosphere. The dehydration reaction leaves an open coordination site on the metal allowing both anhydrous zinc and cobalt phenylphosphonates to intercalate ammonia upon exposure to a flow of ammonia gas, as evidenced by FTIR, elemental analysis, and TGA data

Ruminal Protein Fermentation: New Perspectives on Previous Contradictions

Abstract: Publisher Summary Ammonia has been recognized as both a rumen fermentation product and a substrate for microbial growth for more than 40 years. Nonprotein nitrogen sources such as urea are rapidly converted to rumen ammonia, but much of the ruminal ammonia arises from the fermentation of dietary protein. Large quantities can accumulate because the production rate of ammonia often exceeds the capacity of ammonia-utilizing species. Excess ammonia is absorbed across the rumen wall and is converted to urea. There is considerable interest in reducing ruminal protein degradation as proteins are the most expensive ingredient in ruminant diets. Protein degradation is a multistep process involving solubilization, extracellular hydrolysis, transport, deamination, and the formation of end products. It has been observed that (1) there are large differences in the amounts of nitrogen that can be precipitated from ruminal fluid by trichloroacetic and tungstic acids, (2) mixed cultures produces more ammonia than the best ammonia-producing isolates, and (3) ionophores decrease ammonia production as they have less effect on the most active ammonia-producing ruminal bacteria.

Inhibition by ammonia of methane utilization in Methylococcus capsulatus (Bath)

Abstract: The kinetics of methane uptake by Methylococcus capsulatus (Bath) and its inhibition by ammonia were studied by stopped-flow membrane-inlet mass spectrometry. Measurements were done on suspensions of cells grown in high- and low-copper media. With both types of cells the kinetics of methane uptake are hyperbolic when oxygen is in excess. The apparent K m and K max for methane uptake are both higher in low-copper cells than in high-copper cells. Ammonia is a simple competitive inhibitor of methane uptake in high-copper cells when the oxygen concentration is above a few μM. The findings agree with the assumption that ammonia is a week alternative substrate for particulate methane monooxygenase. In low-copper cells the effect of ammonia is complicated and cannot be explained in terms of current assumptions on the mechanism of soluble methane monooxygenase. Our data indicate that ammonia inhibition is likely to be a more serious problem in connection with cultivation in low-copper medium than in high-copper medium.

Method for converting urea to ammonia

Abstract: A method is provided for reducing NOx in a combustion exhaust gas stream from a boiler. The method includes the steps of converting an aqueous solution of urea to ammonia by heating the urea solution to a temperature of 350°-650° F. in an injection lance system. The urea solution is pressurized to the pressure required to keep urea reaction products in the liquid phase and is contacted for a selected time with a conversion catalyst selected from the group of metals, metal oxides, or metal compounds consisting of chromium or molybdenum to provide a converted urea solution. The converted urea solution is injected from the injection lance system into the combustion exhaust gas for reducing NOx.

Sorption of carboxylic acid from carboxylic salt solutions at PHS close to or above the pKa of the acid, with regeneration with an aqueous solution of ammonia or low-molecular-weight alkylamine

Abstract: Carboxylic acids are sorbed from aqueous feedstocks at pHs close to or above the acids' pH a into a strongly basic organic liquid phase or onto a basic solid adsorbent or moderately basic ion exchange resin. the acids are freed from the sorbent phase by treating it with aqueous alkylamine or ammonia thus forming an alkylammonium or ammonium carobxylate which dewatered and decomposed to the desired carboxylic acid and the alkylamine or ammonia.

Ammonia translocation in cyanobacteria

Abstract: Ammonia is the inorganic nitrogen source preferentially used by most cyanobacteria. Moreover, even in nitrate utilizers or N2-fixers, ammonia is an obligate intracellular intermediate in nitrogen assimilation. It also affects the synthesis and the activation of several key enzymes in nitrogen metabolism such as nitrogenase, glutamine synthetase and nitrate reductase. The mechanism by which NH3/NH4+ enters different cyanobacteria (N2-fixers, non-fixers, neutrophilic) was thus studied. Using 14CH3NH3+, the convenient radioactive analog of ammonium, we have shown that the neutrophilic A. nidulans R-2 possibly possesses an active transport system for this cation. The conditions leading to repression and depression of this transport system have been studied; it appears that de novo protein synthesis is required for the acquisition of the transport ability. We have also provided evidence that methionine sulfoximine affects ammonium uptake only through its inhibition on glutamine synthetase, and found no support for the possible interaction of this inhibitor with the ammonium transporter. In the alkalophilic cyanobacterium Spirulina platensis, an active mechanism to translocate ammonium is probably not needed. Our data suggest that net uptake of ammonia to support optimal growth could be explained by a pH driven diffusion process. In all the different strains tested net ammonia uptake was observed only when conditions permit continuous amidation through the activity glutamine synthetase and inhibition of this enzyme by methionine sulfoximine caused the excretion of ammonia to the external medium. The weight of experimentation suggests that ammonia leaks from cells because of the inherent permeability of NH3, and that no specific carrier is involved in its release.

Process for the in-line hydrolysis of urea

Abstract: The present invention relates to a process for the in-line hydrolysis of urea. More particularly, the process involves heating an aqueous solution of urea while flowing through a conduit to a temperature and for a time effective to hydrolyze urea to produce hydrolysis products comprising ammonium carbamate, ammonium carbonate, ammonium bicarbonate, and ammonia. The hydrolysis products are useful for the reduction of nitrogen oxides in combustion effluents without the generation of substantial amounts of nitrous oxide.

Process for purification of aqueous solutions containing hydrogen sulfide, hydrogen cyanide, and ammonia

Abstract: Aqueous solutions which are contaminated by hydrogen sulfide, hydrogen cyanide, and ammonia are brought to a pH of about 3 or less after their formation and treated with an inert gas in a stripping column to remove the sulfide and cyanide. The pH of the solution is then increased to about 10 or more and the solution is again treated with an inert gas in a second stripping column to remove the ammonia.

Influence of additives on selective noncatalytic reduction of nitric oxide with ammonia in circulating fluidized bed boilers

Abstract: The application of selective noncatalytic reduction of nitric oxide with ammonia in circulating fluidized bed boilers is investigated. Special attention is directed to the use of additives to the ammonia so that the efficiency of the NO reduction at lower temperatures can be increased. Tests under realistic conditions in a research boiler and reaction kinetic calculations show that the type of additives used did not improve the process. On the other hand, it is shown that ammonia injection as such, when employed before the cyclone of the boiler, effectively reduces the NO emission to a level of 20-60 ppm, without significant negative effects such as ammonia bypass and an increased CO emission.

Ammonia combustion engine

Abstract: PURPOSE: To improve combustibility by providing an ammonia decomposition reacting means which decompose ammonia by the exhaust gas after combustion in an ammonia combustion engine which obtains driving force by combusting ammonia gas. CONSTITUTION: The ammonia gas in an ammonia tank 22 is introduced to a combustion chamber mixed with the air in an intake pipe 14. Since ammonia gas is incombustible in the combustion chamber 24, gas such as hydrogen gas is introduced in a sub-combustion chamber 64 to perform initial combustion. Since in the beginning of combustion in the combustion chamber 24, the temperature of the exhaust gas introduced in an ammonia decomposition reactor 38 is also low, a heat exchanger 42 is heated by an auxiliary heater 52 to decompose the ammonia gas into nitrogen and hydrogen. This hydrogen is sent to the combustion chamber 24 and a hydrogen occluding means 58. In the case of lacking in hydrogen supply amount in starting an ammonia combustion engine 10 and rapid acceleration, the hydrogen reserved by the hydrogen occluding means 58 is supplied to the sub-combustion chamber 64. This improves the combustibility of ammonia. COPYRIGHT: (C)1993,JPO&Japio

Pilot-scale experiments with ammonia and urea as reductants in selective non-catalytic reduction of nitric oxide

Abstract: Comparative studies of ammonia and urea as reductants of nitric oxide have been carried out in a pilot-scale reactor, in the injection temperature range from 1023 K to 1373 K. The reactor has a temperature gradient of about 200 K/s. The efficiency of the two reductants and the emissions of CO, N 2 O, HCN and NH 3 have een measured. The optimum temperature was found to be 1223 K with ammonia, 1273 K with urea. No significant difference in reducing capacity was found. At a molar ratio NH i /NO of 1.3, 70% reduction was achieved with either reductant at their optimum temperatures. The emissions of nitrous oxide (N 2 O) and carbon monoxide turned out to be the major problem with the use of urea, especially at lower temperatures. At a temperature of 1223 K, a maximum of 85 ppm of N 2 O was found. With ammonia, no more than 18 ppm was measured at any temperature. With urea, the emission of carbon monoxide rose to 95 ppm at 1223 K. With ammonia, a maximum of 55 ppm was found at 1123 K. An explanation for the observations, based on NCO as an intermediate in the decomposition of urea, is discussed. With methylamine as an exception, hydrocarbons, amines, and alcohols as additives to ammonia generally shift the active temperature window as well as the maximum degree of reduction toward lower values. The emission of HCN was nearly zero with no additive to the reductant, less than 8 ppm with most additives, but in special cases over 200 ppm with dimethylamine.

Lithotrophic growth and hydrogen metabolism by Clostridium magnum.

Abstract: Clostridium magnum, originally described as a non-autotrophic homoacetogenic bacterium, was found to be able to grow with H2/CO2, formate, or methanol with stoichiometric acetate formation, provided that the growth medium contained at least 0.025% (w/v) yeast extract. Hydrogen was also formed as a byproduct of glucose fermentation, and was consumed again after glucose consumption. Hydrogen formation from glucose was independent of growth conditions and reached similar maximal concentrations in mineral media with or without ammonia added as well as in non-growing cultures or in the presence of carbon monoxide.

Role of countercurrent multiplication in renal ammonium handling: regulation of medullary ammonium accumulation.

Abstract: Ammonium (NH3 plus NH4+), produced predominantly in the proximal tubule, is transferred to the final urine by a process involving countercurrent multiplication of ammonium which generates an ammonium concentration gradient in the renal medulla. It was hypothesized that if urinary ammonium excretion rates are controlled in part by the medullary ammonium gradient, changes in hydration and acid-base state should cause changes in the medullary ammonium gradient consistent with expected changes in urinary ammonium concentrations. To test that hypothesis, rats were subjected to water diuresis, water deprivation, water deprivation plus furosemide, and dietary acid and base loads and corticomedullary ammonium gradients in their kidneys were then measured. Sections were cut along the corticomedullary axis to yield slices of cortex, outer stripe of outer medulla, inner stripe of outer medulla, and three levels of the inner medulla. The total ammonia content of homogenized slices was measured by either a membrane ammonia electrode or an enzymatic technique. Kidneys from water-deprived animals showed a distinct ammonium gradient along the corticomedullary axis, with the highest contents found at the tip of the papilla. The gradient was attenuated by water diuresis and abolished by furosemide. Acid loading enhanced the gradient, and base loading abolished it. These results indicate that the corticomedullary ammonium gradient is regulated in response to changes in hydration and acid-base state.

Aqueous ammonia injection scheme

Abstract: An improved process for reducing nitrogen oxide emissions to the atmosphere comprises the injection of ammonia vapor, formed by the vaporization of an aqueous ammonia solution (5), into a combustion effluent. A dilute aqueous ammonia phase, produced by such vaporization, may also be injected, either in vapor or liquid form, into a combustion effluent (19). Temperature and pressure control of such vaporization may be used to maintain the desired concentration of ammonia injected into the com-bustion effluent.