Showing papers on "Ammonia published in 2013"

Facile extraction of thermally stable cellulose nanocrystals with a high yield of 93% through hydrochloric acid hydrolysis under hydrothermal conditions

Abstract: A facile approach for extracting cellulose nanocrystals (CNCs) was presented through hydrochloric acid hydrolysis of cellulose raw materials under hydrothermal conditions. The influences of preparation parameters, such as reaction time, reaction temperature, and acid-to-cellulose raw material ratio, and different neutralization methods on the yield, microstructure and properties were studied. A high yield of up to 93.7%, crystallinity of 88.6%, and a maximum degradation temperature (Tmax) of 363.9 °C can be achieved by combining hydrochloric acid hydrolysis under hydrothermal conditions and neutralization with ammonia, compared with only 30.2%, 84.3% and 253.2 °C for sulfuric acid hydrolysis, respectively. More importantly, good stability of aqueous CNC suspensions can also be obtained due to the existence of ammonium groups, which can easily be removed through simple heat treatment before using the CNCs.

Synthesis of ammonia directly from air and water at ambient temperature and pressure

Abstract: The N≡N bond (225 kcal mol−1) in dinitrogen is one of the strongest bonds in chemistry therefore artificial synthesis of ammonia under mild conditions is a significant challenge Based on current knowledge, only bacteria and some plants can synthesise ammonia from air and water at ambient temperature and pressure Here, for the first time, we report artificial ammonia synthesis bypassing N2 separation and H2 production stages A maximum ammonia production rate of 114 × 10−5 mol m−2 s−1 has been achieved when a voltage of 16 V was applied Potentially this can provide an alternative route for the mass production of the basic chemical ammonia under mild conditions Considering climate change and the depletion of fossil fuels used for synthesis of ammonia by conventional methods, this is a renewable and sustainable chemical synthesis process for future

Catalytic Ammonia Synthesis: Fundamentals And Practice

Abstract: 1. The History of the Development of Ammonia Synthesis.- 2. Preparation and Activation of the Technical Ammonia Synthesis Catalyst.- 3. Elementary Steps in Ammonia Synthesis: The Surface Science Approach.- 4. A Surface Science and Catalytic Study of the Effects of Aluminum Oxide and Potassium on the Ammonia Synthesis Over Iron Single-Crystal Surfaces.- 5. Chemisorption at More Elevated Pressures on Industrial Ammonia Synthesis Catalysts.- 6. Kinetics of Ammonia Synthesis and Influence on Converter Design.- 7. Ammonia Synthesis: Commercial Practice.- 8. Deactivation of Synthesis Catalyst.- 9. Alternative Noniron Catalysts.- 10. What does the Future Hold? A Survey of Possible Technical Developments.- Appendixes.- Appendix 1. Production and Uses of Ammonia.- Appendix 2. Processes and Catalysts.- Appendix 3. Properties of Ammonia.- Appendix 4. Nomograph of Properties of Ammonia.- Appendix 5. Equilibrium Data on Ammonia Synthesis Reaction.- Appendix 6. Selected Patents on Ammonia Synthesis.- Appendix 7. Toxicology of Ammonia and Safety in Use.

Recent advances in electrocatalysts for electro-oxidation of ammonia

Abstract: The electro-oxidation of ammonia has attracted much attention in recent years since it addresses both the clean energy supply free of COx and environmental protection. However, the large-scale applications of ammonia electro-oxidation technologies have been strongly hindered by the insufficient performance and the high cost of the electrocatalysts related to the usage of high Pt loadings. Therefore, considerable effort has been devoted to developing electrocatalysts for ammonia electro-oxidation with improved activity and lower Pt loading over the past 10 years. From the initial focus on pure metal electrocatalysts, a wide range of Pt-based and Pt-free electrocatalysts for ammonia electro-oxidation have been investigated. This review begins with a brief discussion on the mechanism of the ammonia electro-oxidation with particular attention on the latest findings on the active intermediates and poisoning species, which is important for the fundamental understanding of the principles of improving the electrocatalyst performance for ammonia electro-oxidation. Typical types of electrocatalysts for ammonia electro-oxidation are next described, including pure metal, Pt alloy and Pt-free electrocatalysts. The various preparation methods are discussed and related to the resulting structures and electrocatalytic properties for ammonia electro-oxidation. The factors influencing the performance of the electrocatalysts are also highlighted for gaining fundamental insight into the optimization of the electrocatalyst performance. Based on the results achieved in this area, several future research directions are finally proposed and discussed.

Removal of Ammonia from Water by Ozone Microbubbles

Abstract: Ammonia is a major source of water pollution. One of the most common methods for removal of ammonia from water is oxidation. In this work, ozonation of ammonia using microbubbles was studied in a pilot plant. The experimental results indicate that ozone microbubbles were quite effective in oxidizing ammonia. Oxidation of ammonia was effective at high pH and high ozone generation rates. Ozonation was found to occur by direct reaction of ozone with ammonia at the higher pH. However, the hydroxyl radicals were also involved at the lower pH. Bromide ions acted as a catalyst in the ozonation process, and a faster rate of oxidation of ammonia and lower yield of nitrate was observed. The volumetric mass transfer coefficient of ozone in water was determined. It increased with the increasing rate of ozone generation and the pH of the medium.

Adsorption of ammonium ion by coconut shell-activated carbon from aqueous solution: kinetic, isotherm, and thermodynamic studies

Abstract: Ammonium ions are one of the most encountered nitrogen species in polluted water bodies. High level of ammonium ion in aqueous solution imparts unpleasant taste and odor problems, which can interfere with the life of aquatics and human population when discharged. Many chemical methods are developed and being used for removal of ammonium ion from aqueous solution. Among various techniques, adsorption was found to be the most feasible and environmentally friendly with the use of natural-activated adsorbents. Hence, in this study, coconut shell-activated carbon (CSAC) was prepared and used for the removal of ammonium ion by adsorption techniques. Ammonium chloride (analytical grade) was purchased from Merck Chemicals for adsorption studies. The CSAC was used to adsorb ammonium ions under stirring at 100 rpm, using orbital shaker in batch experiments. The concentration of ammonium ion was estimated by ammonia distillate, using a Buchi distillation unit. The influence of process parameters such as pH, temperature, and contact time was studied for adsorption of ammonium ion, and kinetic, isotherm models were validated to understand the mechanism of adsorption of ammonium ion by CSAC. Thermodynamic properties such as ∆G, ∆H, and ∆S were determined for the ammonium adsorption, using van't Hoff equation. Further, the adsorption of ammonium ion was confirmed through instrumental analyses such as SEM, XRD, and FTIR. The optimum conditions for the effective adsorption of ammonium ion onto CSAC were found to be pH 9.0, temperature 283 K, and contact time 120 min. The experimental data was best followed by pseudosecond order equation, and the adsorption isotherm model obeyed the Freundlich isotherm. This explains the ammonium ion adsorption onto CSAC which was a multilayer adsorption with intraparticle diffusion. Negative enthalpy confirmed that this adsorption process was exothermic. The instrumental analyses confirmed the adsorption of ammonium ion onto CSAC.

Achieving pH control in microalgal cultures through fed-batch addition of stoichiometrically-balanced growth media

Abstract: Lack of accounting for proton uptake and secretion has confounded interpretation of the stoichiometry of photosynthetic growth of algae. This is also problematic for achieving growth of microalgae to high cell concentrations which is necessary to improve productivity and the economic feasibility of commercial-scale chemical production systems. Since microalgae are capable of consuming both nitrate and ammonium, this represents an opportunity to balance culture pH based on a nitrogen feeding strategy that does not utilize gas-phase CO2 buffering. Stoichiometry suggests that approximately 36 weight%N-NH4+ (balance nitrogen as NO3-) would minimize the proton imbalance and permit high-density photoautotrophic growth as it does in higher plant tissue culture. However, algal media almost exclusively utilize nitrate, and ammonium is often viewed as ‘toxic’ to algae. The microalgae Chlorella vulgaris and Chlamydomonas reinhardtii exclusively utilize ammonium when both ammonium and nitrate are provided during growth on excess CO2. The resulting proton imbalance from preferential ammonium utilization causes the pH to drop too low to sustain further growth when ammonium was only 9% of the total nitrogen (0.027 gN-NH4+/L). However, providing smaller amounts of ammonium sequentially in the presence of nitrate maintained the pH of a Chlorella vulgaris culture for improved growth on 0.3 gN/L to 5 gDW/L under 5% CO2 gas-phase supplementation. Bioreactor pH dynamics are shown to be predictable based on simple nitrogen assimilation as long as there is sufficient CO2 availability. This work provides both a media formulation and a feeding strategy with a focus on nitrogen metabolism and regulation to support high-density algal culture without buffering. The instability in culture pH that is observed in microalgal cultures in the absence of buffers can be overcome through alternating utilization of ammonium and nitrate. Despite the highly regulated array of nitrogen transporters, providing a nitrogen source with a balanced degree of reduction minimizes pH fluctuations. Understanding and accommodating the behavior of nitrogen utilization in microalgae is key to avoiding ‘culture crash’ and reliance on gas phase CO2 buffering, which becomes both ineffective and cost-prohibitive for commercial-scale algal culture.

Electrochemical synthesis of ammonia directly from air and water using a Li+/H+/NH4+ mixed conducting electrolyte

Abstract: Ammonia has been successfully synthesised directly from air and water using an electrochemical cell based on an H+/Li+/NH4+ mixed conducting membrane and Pt/C electrodes. It is found that the Nafion 211 membrane exhibits mixed H+/Li+ conduction after exchanging in 0.1 M Li2SO4 solution. The ionic conductivity of the mixed conductor is slightly lower than that of H+-form Nafion 211. The introduction of Li+ ions to the cell did not improve the ammonia formation rates in our experiments. Reasonably higher temperature may favour ammonia formation and the highest ammonia formation rate (9.37 × 10−6 mol m−2 s−1) and Faraday efficiency (0.83%) was obtained at 80 °C when a voltage of 1.2 V was applied. The ammonia formation rate decreased when 0.1 M Li2SO4 solution instead of water was used in the cell. Under the applied potential, the presence of Li+ ions might have a blocking effect on the transfer of protons resulting in a lower current at higher applied voltage, particularly at lower temperatures.

Influence of pig slurry characteristics on ammonia stripping efficiencies and quality of the recovered ammonium-sulfate solution.

Abstract: BACKGOUND Proper treatment technologies are required to address the environmental issues associated with increasing volumes of slurries. Ammonia stripping reduces the nitrogen content of the slurries and allows for its recovery in a valuable form. Herein the influence of pig slurry characteristics on ammonia stripping efficiency and the quality of the recovered ammonia solution were assessed. RESULTS Substrates characterized by low organic matter content, below 10 g COD L-1, resulted in ammonia stripping efficiencies greater than 80%. Changing slurry pH to 9.5 significantly improved the process, even though high COD contents kept the efficiencies below 70%. Ammonium sulfate solutions could be concentrated up to nitrogen contents greater than 40 g N L-1, while maintaining low organic contamination. Introducing a basic trap (pH > 12) before the acid one, allowed for the retention of more than 60% of the stripped organics with less than 3% of the stripped ammonia. CONCLUSIONS Ammonia stripping coupled with absorption proved to be a suitable technical solution for the recovery and valorization of the nitrogen contained in pig slurries. Clear enhancements in process efficiency were observed in the case of slurries with low organic matter content. The introduction of a basic trap, together with a slight increase in the operational pH level, further increased organics abatement. © 2012 Society of Chemical Industry

Comparison on the Performance of α-Fe2O3 and γ-Fe2O3 for Selective Catalytic Reduction of Nitrogen Oxides with Ammonia

Abstract: γ-Fe2O3 catalyst showed higher catalytic activity than α-Fe2O3 in 150–300 °C. Both NH3 and NO x species adsorbed and reacted easily on γ-Fe2O3. However, NH3 adsorbed on α-Fe2O3 and then reacted with gaseous NO x . Gaseous NO x was more easily adsorbed on α-Fe2O3 than gaseous NH3, consequently, stable nitrates formed and blocked the active sites, which affected the SCR reaction badly.

Highly Sensitive Ammonia Sensor with Organic Vertical Nanojunctions for Noninvasive Detection of Hepatic Injury

Abstract: We successfully demonstrate the first solid-state sensor to have reliable responses to breath ammonia of rat. For thioacetamide (TAA)-induced hepatopathy rats, we observe that the proposed sensor can detect liver that undergoes acute–moderate hepatopathy with a p-value less than 0.05. The proposed sensor is an organic diode with vertical nanojunctions produced by using low-cost colloidal lithography. Its simple structure and low production cost facilitates the development of point-of-care technology. We also anticipate that the study is a starting point for investigating sophisticated breath-ammonia-related disease models.

Photooxidation of Ammonia on TiO2 as a Source of NO and NO2 under Atmospheric Conditions

Abstract: Ammonia is the most abundant reduced nitrogen species in the atmosphere and an important precursor in the industrial-scale production of nitric acid. A coated-wall flow tube coupled to a chemiluminescence NOx analyzer was used to study the kinetics of NH3 uptake and NOx formation from photochemistry initiated on irradiated (λ > 290 nm) TiO2 surfaces under atmospherically relevant conditions. The speciation of NH3 on TiO2 surfaces in the presence of surface-adsorbed water was determined using diffuse reflection infrared Fourier transform spectroscopy. The uptake kinetics exhibit an inverse dependence on NH3 concentration as expected for reactions proceeding via a Langmuir–Hinshelwood mechanism. The mechanism of NOx formation is shown to be humidity dependent: Water-catalyzed reactions promote NOx formation up to a relative humidity of 50%. Less NOx is formed above 50%, where increasing amounts of adsorbed water may hinder access to reactive sites, promote formation of unreactive NH4+, and reduce oxidant le...

Electrochemical ammonia production on molybdenum nitride nanoclusters

Abstract: Theoretical investigations of electrochemical production of ammonia at ambient temperature and pressure on nitrogen covered molybdenum nanoparticles are presented. Density functional theory calculations are used in combination with the computational hydrogen electrode approach to calculate the free energy profile for electrochemical protonation of N2 and N adatoms on cuboctahedral Mo13 nanoparticles. Pathways for electrochemical ammonia production via direct protonation of N adatoms and N2 admolecules with an onset potential as low as −0.5 V and generally lower than −0.8 V on both a nitrogen covered or a clean Mo nanoparticle. Calculations presented here show that nitrogen dissociation at either nitrogen vacancies on a nitrogen covered molybdenum particle or at a clean molybdenum particle is unlikely to occur under ambient conditions due to very high activation barriers of 1.8 eV. The calculations suggest that the nitrogen will be favored at the surface compared to hydrogen even at potentials of −0.8 V and the Faradaic losses due to HER should be low.

Cobalt-based Catalysts for Ammonia Decomposition

Abstract: An effect of promoters such as calcium, aluminium, and potassium oxides and also addition of chromium and manganese on the structure of cobalt catalysts was examined. Studies of the catalytic ammonia decomposition over the cobalt catalysts are presented. The studies of the ammonia decomposition were carried out for various ammonia-hydrogen mixtures in which ammonia concentration varied in the range from 10% to 100%. Co(0) catalyst, promoted by oxides of aluminium, calcium, and potassium, showed the highest activity in the ammonia decomposition reaction. Contrary to expectations, it was found that chromium and manganese addition into the catalysts decreased their activity.