Ammonia

About: Ammonia is a research topic. Over the lifetime, 16217 publications have been published within this topic receiving 271940 citations. The topic is also known as: NH3 & azane.

Effects of temperature and carbon-nitrogen (C/N) ratio on the performance of anaerobic co-digestion of dairy manure, chicken manure and rice straw: focusing on ammonia inhibition.

Abstract: Anaerobic digestion is a promising alternative to disposal organic waste and co-digestion of mixed organic wastes has recently attracted more interest. This study investigated the effects of temperature and carbon-nitrogen (C/N) ratio on the performance of anaerobic co-digestion of dairy manure (DM), chicken manure (CM) and rice straw (RS). We found that increased temperature improved the methane potential, but the rate was reduced from mesophilic (30∼40°C) to thermophilic conditions (50∼60°C), due to the accumulation of ammonium nitrogen and free ammonia and the occurrence of ammonia inhibition. Significant ammonia inhibition was observed with a C/N ratio of 15 at 35°C and at a C/N ratio of 20 at 55°C. The increase of C/N ratios reduced the negative effects of ammonia and maximum methane potentials were achieved with C/N ratios of 25 and 30 at 35°C and 55°C, respectively. When temperature increased, an increase was required in the feed C/N ratio, in order to reduce the risk of ammonia inhibition. Our results revealed an interactive effect between temperature and C/N on digestion performance.

Removal of CO2 greenhouse gas by ammonia scrubbing

Abstract: This paper provides preliminary results on the novel study of ammonia scrubbing for the removal of carbon dioxide from flue gas. Experimental results indicated the potential of CO2 reduction by NH3 scrubbing is very promising. The overall CO2 removal efficiencies could be above 95% under proper operation conditions. The absorption capacity of NH3 was around 0.9 kg of CO2/kg of NH3 reagent being used. This should be higher than that by a MEA solution. The reaction products were analyzed and determined by X-ray diffraction analysis, SEM picture, and pH measurements. All the measurements indicated that an ammonium bicarbonate solution and its crystalline solids are the major products of reaction.

An FT-IR study of ammonia adsorption and oxidation over anatase-supported metal oxides

Abstract: The adsorption and the oxidation of ammonia over sub-monolayer TiO2-anatase supported chromium, manganese, iron, cobalt, nickel and copper oxides, has been investigated using FT-IR spectroscopy. These materials are models of catalysts active in the Selective Catalytic Reduction of NOx by ammonia (SCR process) and in the Selective Catalytic Oxidation of ammonia to dinitrogen (SCO process). For comparison, the adsorption of ammonia and hydrazine over the TiO2-anatase support has also been studied. CrOx TiO2 adsorbs ammonia both in a co-ordinated form over Lewis acid sites and in a protonated form over Bronsted acid sites, involving high-valence chromium (chromyl species). However, simple outgassing at r.t. causes the desorption of ammonia from Bronsted acid sites showing that they are very weak. All other catalysts do not present any Bronsted acidity. Co-ordinated ammonia gives rise to several oxidation products over Fe2O3 TiO2, CrOx TiO2, CoOx TiO2 and CuO TiO2, among which hydrazine is likely present. Other species have been tentatively identified as imido species, NH, nitroxyl species, HNO, and nitrogen anions,N−2. NiOx TiO2 and MnOx TiO2 appear to be even more active in ammonia oxidation, because the adsorbed species disappeared completely at lower temperature (473 K) than in the other cases. However, possibly just due to their excessive activity, no adsorbed species different from co-ordinated ammonia can be found in significant amounts over these surfaces. Based on these data, the mechanism of the SCR and SCO processes over these catalytic materials is discussed. In particular, it is concluded that Bronsted acidity is not a requirement for SCR and SCO activity.

Ammonia decomposition kinetics over Ni-Pt/Al2O3 for PEM fuel cell applications

Abstract: Due to the potential employment of ammonia as a hydrogen source for proton exchange membrane (PEM) fuel cell applications, an experimental study has been undertaken to determine the ammonia decomposition rates over a Ni-Pt/Al 2 O 3 catalyst under conditions likely to be employed in such an application. Using differential analysis of integral data, intrinsic rate data have been obtained between temperatures of 520 and 690 °C and at ammonia pressures between 50 and 780 Torr. It is shown that a first-order rate expression provides an adequate fit of the experimental data over the entire range of pressures and temperatures, although hydrogen inhibition effects may be significant at the lowest temperature. The activation energy was found to be on the order of 50 kcal/mol as opposed to the very low values (5–10 kcal/mol) obtained previously by others. The data are analyzed in the context of previous studies that were conducted under markedly different reaction conditions and differences are attributed to the types of catalysts employed and the fact that previous studies have primarily dealt with very low ammonia concentrations. Consequently, it does not appear as though NH bond cleavage is the rate determining step under these conditions. It is also shown that the rate expression is capable of predicting, to within 5%, the high ammonia conversions required for fuel cell applications.