Nitrogen Migration Research Articles

A review on nitrogen transformation and conversion during coal pyrolysis and combustion based on quantum chemical calculation and experimental study

• Review of nitrogen migration and transformation based on quantum chemistry and experiment. • Summarized the mechanism and regulation of nitrogen migration and transformation. • Emphasized the importance of N 2 formation during pyrolysis. The emission of NO x during coal combustion contributes to the formation of acid rain and photochemical smog, which would seriously affect the quality of atmospheric environment. Therefore, the decrease of NO x is of great importance for improving the efficient utilization of coal. The present review comprehensively summarized the influence factors and mechanisms of migration and transformation of nitrogen during the coal pyrolysis and combustion based on experimental study and quantum chemical calculation. Firstly, in the process of pyrolysis: the occurrence state and transformation of nitrogen were concluded. The influence of temperature, atmosphere, heating rate and catalyst on formation of NO x precursor and nitrogen migration path at the molecular level were summarized; Secondly, during the process of combustion: the influence of temperature, ambient oxygen concentration, physical structure of coal char, catalyst on heterogeneous oxidation of char (N) were summarized; The effects of char surface properties, catalyst and ambient atmosphere on heterogeneous reduction of NO x were also concluded. Based on the quantum chemical calculation, the reaction path of heterogeneous oxidation of char-N and heterogeneous reduction of NO x were described in detail. Current studies focus more on the generation of HCN and NH 3 , but in order to reduce the pollution of NO x from the source, it is necessary to further improve the process conditions and the optimal formula of producing more N 2 during pyrolysis, as well as clarify the path of the generation of N 2 . Experiments study and quantum chemistry calculation should be combined to complete the research of directional nitrogen reduction during pyrolysis and denitration during combustion.

Hydrogen production by supercritical water gasification of methylhydrazine in continuous system

Supercritical water gasification technology has ability to process unsymmetrical dimethylhydrazine (UDMH) wastewater derived from launching spacecraft, missile or satellite realizing both harmless treatment and resource utilization due to its unique property. Owning advantages such as compact structure, highly reduced reactor volume, improved heat transfer efficiency and fully mixed reactants, a spiral continuous reactor was proposed based on the characteristics of UDMH wastewater. Methylhydrazine (MMH) was used as model compound on account of UDMH’s commercial unavailability. The degradation of MMH in supercritical water is determined as an apparent first-order reaction using initial rate method. The effect of different parameters including temperature (450–550 °C), feeding flow rate (10–75 g/min), feeding concentration (5–30 %), and catalyst type on gasification were systematically investigated and subsequently the migration of carbon and nitrogen was also concerned. Results showed that addition of KOH could make the carbon gasification efficiency approach 100 % with the maximum hydrogen yield up to 21.6 mol/kg under the condition of 500 °C, 23 MPa, feeding flow rate of 30 g/min, feedstock concentration of 10 %. The proportion of organic carbon in total carbon tended to decrease with the increase of temperature. Most of nitrogen (up to 99.7 % at most) was gasified within our experimental range.

Pyrolysis behaviors of antibiotic fermentation residue and wastewater sludge from penicillin production: Kinetics, gaseous products distribution, and nitrogen transformation

Antibiotic fermentation residue (AFR) and wastewater sludge (AFS) were dangerous wastes from penicillin fermentation, and pyrolysis kinetics, gaseous products distribution, and nitrogen transformation of the two were investigated. The content of C/H/N/O/S in AFR was 93.52 %, with good pyrolysis performance and an average activation energy of 230.13 kJ/mol; the content of Fe/O in AFS reached 67.64 %, with poor pyrolysis performance and a high activation energy of 323.77 kJ/mol in the first stage. Monocyclic aromatic hydrocarbons and nitrogenous organics were main gaseous products of AFR pyrolysis, while monocyclic aromatic hydrocarbons and alcohols were main gaseous products of AFS pyrolysis. Pyridine- and pyrrole-nitrogen predominated in the biochar produced by AFR and AFS pyrolysis when the temperature was above 600 °C. The reactions of nitrogen migration and transformation during pyrolysis were summarized. This work provides insights for the pyrolysis potential and the highly concerned nitrogen conversion in AFR and AFS during pyrolysis.

Evaluation on nitrogen conversion during biomass torrefaction and its blend co-combustion with coal

In this work, biomass torrefaction was combined with coal co-combustion to illustrate the differences in biomass performance and the mechanisms of migration and transformation of nitrogen over the entire course of thermal treatments. XPS analysis illustrated that torrefaction in CO2 suppressed the conversion of pyrrole-N (N-5) to quaternary-N (N-Q), whereas the trend for an O2 atmosphere moved in the opposite direction. During co-combustion, the impact on NO emission reduction shifted from positive to negative as the pretreatment temperature was raised, which is closely related to the six elementary reactions involving the intermediacy of NCO and NH, as well as to heterogeneous reduction of NO with char. In addition, torrefaction in a N2/O2 atmosphere at a lower temperature of 250 °C improved the properties of biomass and achieved the lowest NO emission during co-combustion, which provides the supporting theory needed for using effluent in power plants as a torrefaction medium.

Effects of crab disturbance on nitrogen migration and transformation in a coastal tidal flat wetland.

The influence of crab disturbances on nitrogen migration and the transformations of pore water and overlying water in a coastal tidal flat wetland were investigated at the lab scale, and the nitrogen exchange flux at the sediment-water interface was calculated. The results showed that crabs, combined with tidal effects, had significant effects on the microtopography of the studied crab box. In addition, there was no significant difference in the concentrations of NH4+-N, NO3--N, or TN between two points in the horizontal direction (P > 0.05), and there were significant differences in the concentrations of NH4+-N and TN in the vertical direction (P < 0.05); the NO3--N concentration difference was not obvious (P > 0.05). The NO3--N concentration in the surface pore water of the crab box had a downward trend with time. Furthermore, the NH4+-N and TN contents in the overlying water in the crab box were significantly higher than those of the control box, indicating that crab disturbances also had significant effects on the concentrations of NH4+-N, NO3--N, and TN in the overlying water. The existence of crab caves greatly promoted the nitrogen exchange flux at the sediment-water interface, and the mean exchange fluxes of NH4+-N, NO3--N and TN were 51.40 mmol (m2 day)-1, -13.44 mmol (m2 day)-1 and 39.74 mmol (m2 day)-1, respectively (much higher than those measured in the control box), implying that NH4+-N and TN were released from the sediment to the overlying water, while NO3--N was released from the overlying water to the sediment.

Migration of Sulfur and Nitrogen in the Pyrolysis Products of Waste and Contaminated Plastics

The most advantageous way of managing plastics, according to circular economy assumptions, is recycling, i.e., reusing them. There are three types of plastics recycling: mechanical, chemical and energy recycling. The products of the pyrolysis process can be used for both chemical and energy recycling. Possibilities of further use of pyrolysis products depend on their physicochemical parameters. Getting to know these parameters was the aim of the research, some of which are presented in this article. The paper presents the research position for conducting the pyrolysis process and discusses the results of research on pyrolysis products of waste plastics. The process was conducted to obtain the temperature of 425 °C in the pyrolytic chamber. Such a value was chosen on the basis of my own previous research and literature analysis. The focus was on the migration of sulfur and nitrogen, as in some processes these substances may pose a certain problem. Studies have shown high possibilities of migration of these elements in products of pyrolysis process. It has been shown that the migration of sulfur is similar in the case of homogeneous and mixed waste plastics—it immobilizes mainly in pyrolytic oil. Different results were obtained for nitrogen. For homogeneous plastics, nitrogen immobilizes mainly in char and oil, whereas for mixed plastics, nitrogen immobilizes in pyrolytic gas.

Effect of Na on the migration and release of pyridine nitrogen during coal pyrolysis

Based on density functional theory (DFT) and transition state theory, the effect of alkali metal Na on the formation mechanism and path of NH3 and HCN during coal pyrolysis was studied at the M06-2X/6-311G(d) level. The seven membered ring containing pyridine was selected as the coal model, and the adsorption structure of Na on the coal surface was used as the coal model containing Na. The results show that the presence of Na significantly strengthens the bonding between N and C atoms in pyridine ring, which makes the stripping of N atom from benzene ring requires higher activation energy, thus inhibiting the formation of HCN. However, Na can improve the surface activity of coal, and the energy barrier of NH3 formation rate determination step in the presence of Na is 271.35 kJ/mol lower than that in the absence of Na, which significantly promotes the formation of NH3.

Nitrogen removal by different riparian vegetation buffer strips with different stand densities and widths

Abstract The migration of nitrogen (N) from farmland to lake aggravates eutrophication. Riparian buffer strips (RBSs) are crucial in alleviating nitrogen into water bodies. This study examined the impacts of different RBS patterns on nitrogen removal. The effects of different RBSs of various widths (5, 15, 30, and 40 m), with different vegetation types (Taxodium hybrid ‘Zhongshanshan’, poplar (Nanlin-95), and a mixed forest of T. hybrid ‘Zhongshanshan’ and poplar) and at different densities (400, 1,000, and 1,600 plants·hm−2) on the TN, NH4+-N and NO3−-N removal rates in different depths of runoff water were studied. The results showed that the 15 m-wide RBS removed nitrogen the most effectively, with average removal rates of NH4+-N, NO3−-N and TN reaching 67.79%, 65.93% and 65.08%, respectively. Among the RBSs with different vegetation types, the poplar forest RBS removed the most NH4+-N (74.28%) and NO3−-N (61.71%). The mixed-forest RBS removed the most TN (65.57%). The RBS with 1,000 plants·hm−2 was more suitable in terms of the removal of NH4+-N (74.25%), NO3−-N (71.08%) and TN (62.67%). The conclusion can provide the basis of vegetation and width optimization for the design and construction of an RBS for maximum eutrophication nutrient removal.

Nitrogen process in stormwater bioretention: the impact of alternate drying and rewetting on nitrogen migration and transformation.

Nitrogen migration and transformation in the stormwater bioretention system were studied in laboratory experiments, in which the effects of drying-rewetting were particularly investigated. The occurrence and distribution of nitrogen in the plants, the soil, and the pore water were explored under different drying-rewetting cycles. The results clearly showed that bioretention system could remove nitrogen efficiently in all drying-rewetting cycles. The incoming nitrogen could be retained in the topsoil (0-10 cm) and accumulated in the planted layer. However, the overlong dry periods (12 and 22 days) cause an increase in nitrate in the pore water. In addition, nitrogen is mostly stored in the plants' stem tissues. Up to 23.26% of the inflowing nitrogen can be immobilized in plant tissues after a dry period of 22 days. In addition, the relationships between nitrogen reductase activity in the soil and soil nitrogen content were explored. The increase of soil TN content could enhance the activity of nitrate reductase. Meanwhile, the activity of hydroxylamine reductase (HyR) could be enhanced with the increase of soil NO3- content. These results provide a reference for the future development of nitrogen transformation mechanism and the construction of stormwater bioretention systems.

Nitrogen Migration during Pyrolysis of Raw and Acid Leached Maize Straw

Solid biofuel is considered as a possible substitute for coal in household heat production because of the available and sustainable raw materials, while NOx emissions from its combustion have become a serious problem. Nitrogen-containing compounds in pyrolysis products have important effects on the conversion of fuel-N into NOx-N. Understanding these converting pathways is important for the environmentally friendly use of biomass fuels. The nitrogen migration during pyrolysis of raw and acid leached maize straw at various temperatures was investigated in this study. Thermal gravimetric analysis and X-ray photoelectron spectroscopy were used to investigate the performances of thermal decomposition and pyrolysis products from samples. The main nitrogen functional groups in biomass and biochar products were N-A (amine-N/amide-N/protein-N), pyridine-N, and pyrrole-N, according to the findings. The most common gaseous NOx precursor was NH3, which was produced primarily during the conversion of N-A to pyridine-N and pyrrole-N. The formation of HCN mainly came from the secondary decomposition of heterocyclic-N at high temperatures. Before the pyrolysis temperature increased to 650 °C, more than half of the fuel-N was stored in the biochar. At the same pyrolysis temperature, acid-leached maize straw yielded more gas-N and char-N than the raw biomass. The highest char-N yield of 76.39 wt% was obtained from acid-leached maize straw (AMS) pyrolysis at 350 °C. Low pyrolysis temperature and acid-leaching treatment can help to decrease nitrogen release from stable char structure, providing support for reducing nitrogenous pollutant emissions from straw fuel.

Comparison of Nitrogen Loss Weight in Ammonia Volatilization, Runoff, and Leaching Between Common and Slow-Release Fertilizer in Paddy Field

Nitrogen (N) loss from paddy fields contributes to air and water pollution, which has been a serious challenge to agriculture and the environment. In situ field experiments were conducted to monitor ammonia (NH3) volatilization, surface runoff, and leaching loss in common nitrogen fertilizer and slow-release nitrogen fertilizer treatments. The total N loss by ammonia volatilization, leaching, and runoff was 38.27 ± 4.23~113.54 ± 7.66 kg ha−1 among the different treatments. Results indicated that slow-coated urea could reduce ammonia volatilization (24.69~29.54%), N surface runoff loss (20.05~25.37%), and leaching loss (21.86~38.05%) compared with common fertilizer. Of the different nitrogen loss pathways monitored in paddy fields, ammonia volatilization was the greatest (68.98~75.27% of the total N loss), followed by (in descending order) runoff (16.43~23.07%) and leaching (7.67~8.86%). Ammonia volatilization and N runoff loss were predominantly attributed to surface ammonium nitrogen (NH4+-N) concentration and precipitation. In addition, 42 ± 2.48% of N runoff loss was a result of wet deposition, while 58 ± 3.11% was attributed to nitrogen hydrolysis. There is obvious vertical nitrogen migration in the soil profile, among which NO3−-N leaching loss is the predominant form (69.94~90.12%).

Nitrogen migration in sewage sludge chemical looping gasification using copper slag modified by NiO as an oxygen carrier

In view of the high cost and failure of resource utilization of waste copper slag, the copper slag modified by NiO is used as an oxygen carrier in the chemical looping gasification, where the sewage sludge is converted into syngas through the oxidation of copper slag. Additionally, current studies on nitrogen migration in chemical looping are limited to the detection of nitrogen compounds in gas products, and there is little research on nitrogen migration from raw materials to solid-liquid-gas products. Therefore, under different oxygen equivalent coefficients (Ω), steam contents, reaction times, and cycle number, the nitrogen changes in gas (Gas-N), tar (Tar-N) and char (Char-N) were investigated in this paper. With increasing of Ω (0–0.78), the oxidation and catalytic cracking reactions of the NOx precursors, Char-N and Tar-N were promoted, and the yield of N2 increased from 52.49% to 91.98%. The addition of steam would lead to a significant increase in the yield of NOx precursors. The release of NH3 and HCN was mainly concentrated in the first 5 min. As the numbers of cycle increased, NH3-N and HCN-N both gradually decreased. Based on the above results, the distribution and migration mechanism of nitrogen species were also summarized.

Migration and transformation of nitrogen in sediment–water system within storm sewers

In the sediment–water system of storm sewers (e.g., sediments, interstitial water, and the water column), the migration of nitrogen and its biological transformation with different dissolved oxygen conditions were investigated. Results showed that in an aerobic segment, γ-proteobacteria, α-proteobacteria, and nitrospira, which are aerobic, grew actively in water column and interstitial water through ammonification and nitrification. In anoxic segment, ammonification depended mainly on clostridia, whereas nitrification was inhibited. Thus, after 20 days, the concentration of NH4+-N in the aerobic segment became noticeably lower (5.97 mg/L) than that in the anoxic segment (18.09 mg/L). In sediments, the biological transformation of organic nitrogen in the anoxic environment was more complete, resulting in elevating amino acid nitrogen and NH4+-N in the anoxic segment compared to the aerobic segment. Furthermore, the concentration gradient of NH4+-N between interstitial water and water column in aerobic and anoxic segments, thereby causing NH4+-N to migrate from interstitial water to the water column. In the sediment–water system, the different forms of nitrogen changes were the common result of biological transformation and material migration.

Fast Pyrolysis of Pulverized Coal at High Temperatures and Fuel Nitrogen Migration Characteristics in a Wire Mesh Reactor

Fast Pyrolysis of Pulverized Coal at High Temperatures and Fuel Nitrogen Migration Characteristics in a Wire Mesh Reactor

Structural Characterization of Fine γ′-Fe4N Nitrides Formed by Active Screen Plasma Nitriding

The paper presents the structural characterization of γ′-Fe4N nitrides produced by active screen plasma nitriding (ASPN) processes. Experiments were performed on the Fe-Armco model material at 693, 773, and 853 K for 6 h. Investigation of the properties of the substrate was realized using scanning electron microscopy (SEM, SEM–EBSD/Kikuchi lines), energy-filtered transmission electron microscopy (TEM-EFTEM), X-ray diffraction (GID, grazing incidence diffraction, micro-XRD), and secondary ion mass spectroscopy (SIMS). Results have confirmed that the γ′-Fe4N nitrides’ structure and morphology depend considerably on the nitriding process’s plasma conditions and cooling rate. In addition to that, γ′-Fe4N nitrides’ formation can be correlated with the surface layer saturation mechanism and recombination effect. It has been shown that the γ′-Fe4N structure depends considerably on several phenomena that occur in the diffusive layer (e.g., top layer decomposition, nitrogen, and carbon atoms’ migration). Our research proves that the nitrogen concentration gradient is a driving force of nitrogen migration atoms during the recombination of γ′-Fe4N nitrides. Finally, realized processes have allowed us to optimize active screen plasma nitriding to produce a surface layer of fine nitrides.

Conversion and transformation of N species during pyrolysis of wood-based panels: A review.

Understanding the migration and conversion of nitrogen in wood-based panels (WBPs) during pyrolysis is fundamentally important for potentially transforming the N-containing species into valuable material-based products. This review firstly summarizes the commonly used methods for examining N evolution during the WBPs pyrolysis before probing into the association between the wood and adhesives.The potential effects of wood-adhesive interaction on the pyrolysis process are subsequently analyzed. Furthermore, the controversial statements from literature on the influence of adhesives on wood pyrolysis behavior are discussed, which is followed by the detailed investigation into the distribution and evolution of N-containing species in gas, liquid and char, respectively, during WBPs pyrolysis in recent studies. The differences in N species due to the heating sources (i.e. electrical heating vs microwave heating) are particularly compared. Finally, based on the characteristics of staged pyrolysis, co-pyrolysis and catalytic pyrolysis, the converting pathways for WBPs are proposed with an emphasis on the production of value-added chemicals and carbon materials, simultaneously mitigating NOx emission.

Molecular dynamic investigation on nitrogen migration during hydrogen production by indole gasification in supercritical water

Hydrogen production by supercritical water gasification of biomass has broad application prospects. The migration and regulation mechanism of nitrogen in supercritical water is one of the key issues in biomass utilization. As a nitrogen-containing model compound of biomass, indole was used to study the mechanism of nitrogen migration during supercritical water gasification from a molecular perspective by using reactive empirical force fields (Reaxff) combined with Density functional theory (DFT) method. The pyrrole ring cracking was the first stage and then most of the nitrogen atoms left the carbon skeleton to form ammonia precursor radicals after being attacked by H or OH free radicals in supercritical water. The overall activation energy of each pyrrole ring opening way was calculated. The dominant way for pyrrole ring opening was analyzed and the competitive relationship among the different ring-opening ways was specified by comparing the activation energies of transition states and relative energies of intermediates. Compared with pyrolysis conditions, supercritical water molecules greatly promoted the separation of nitrogen atoms from the carbon skeleton to form NH3 and inhibited the formation of HCN. The higher temperature could facilitate the indole conversion and the hydrogen generation, but it also increased the possibility of char formation, causing part of the nitrogen to re-enter the organic structure. This study revealed the mechanism from the view of microscopic atoms, and provided theoretical support for the nitrogen regulation in supercritical water gasification of biomass.

Source of Groundwater Nitrate in Luanping Basin Based on Multi-environment Media Nitrogen Cycle and Isotopes

The multi-environment media of water, surface soil and vadose zone soil samples were collected in the upstream of Miyun Reservoir, in the Luanping Basin of Chengde City, Hebei Province. The aim was to identify the pollution source, ratio, spatial distribution, migration, and transformation characteristics of nitrogen in groundwater. Hydrogeochemistry, soil total nitrogen, and dissolved nitrate nitrogen of vadose zone soil analysis and a multi isotope tracer technique of δ15 N-NO3 and δ18O-NO3, δ34S-SO4 and δ18O-SO4, δ14 C, combined with land-use type analysis and geostatistics, were used in the study. The results showed that nitrate was the main form of nitrogen in the groundwater of the Luanping Basin. The NO3- concentration of groundwater was significantly correlated with the land-use types of residential land and cultivated land where the nitrate pollution of shallow groundwater was mainly distributed. Of the groundwater samples, 13.79% exceeded the National Standard Ⅲ for Groundwater (GB/T 14848-2017) of NO3- concentration value, while the excess multiple was 1.04-3.86, and 37.93% of the groundwater samples exceeded the World Health Organization NO3- concentration standard value. The excess multiple was 1.08-6.83. The spatial variation of groundwater NO3- concentration, soil total nitrogen and surface soil dissolved nitrate nitrogen of vadose zone was affected by the combination of natural structural factors and anthropogenic factors. The source of groundwater nitrate was mainly from livestock manure and domestic sewage, followed by chemical fertilizer leaching. The nitrogen cycle in the aeration zone-groundwater-dominated nitrogen circulation in the groundwater runoff area of the piedmont basin was nitrification. These findings are highly significant for the prevention and remediation of groundwater pollution when viewing the basin system as an independent unit, and for studying the sources and fate of nitrate pollution in the water environment.

Investigation of the nitrogen migration characteristics in sewage sludge during chemical looping gasification

Increasing attention has been given to the control of nitrogen pollutants during the process of using sewage sludge. In this paper, the gasification characteristics and the law of nitrogen migration in the process of chemical looping gasification (CLG) of sewage sludge were explored. Copper slag calcined at 1100 °C (1100CS), FeAl (Fe2O3+Al2O3), NiFeAl (NiFe2O4+Al2O3), and NiAl (NiO + Al2O3) were used as oxygen carrier. The addition of an oxygen carrier could increase the carbon conversion rate and decrease the low heating value. NOx precursors (HCN and NH3) were the main nitrogen-containing gas pollutants (∼40%). The sum yield of char nitrogen and tar nitrogen was only ∼10%. Nitrile nitrogen, heterocyclic nitrogen and amide nitrogen were the main nitrogenous compounds in tar nitrogen. Increasing the oxidative activity of the oxygen carrier could significantly promote the oxidative transformation of N2 from the NOx precursors, tar nitrogen, char nitrogen. Additionally, the migration of fuel nitrogen includes synchronous autothermal pyrolysis (stage Ⅰ) and oxidative pyrolysis of the three-phase product under the action of [O] (stage Ⅱ). Finally, this research realizes the energy utilization of sludge and reduces the release of nitrogen pollutants.

Electrochemical ammonia accumulation and recovery from ammonia-rich livestock wastewater

High levels of ammonia inhibit microbial activities and lead to process instability of traditional wastewater treatment. Nitrogen recovery via ammonia stripping is the best developed method, but this approach requires large amounts of alkaline chemicals and substantial energy for stripping. In this study, we designed a simple electrochemical system that allows the facile accumulation of a neutral species of ammonia (NH3), resulting in much lower overall stripping costs. In batch operation treatment of synthetic livestock wastewater (LW), the energy efficiency for total ammonia nitrogen (TAN) migration was found to be the best at a current density of 93.8 mA cm−2. Fed-batch operation, using synthetic or real LW, resulted in very high degrees of TAN accumulation (10,158 mg-N L−1 for synthetic and 17,704 mg-N L−1 for real LW) in catholyte after 400 min. It was found that TAN migration was responsible for 0.221 and 0.492 of total charge migration for synthetic and real LW, respectively. The nitrogen flux across a cation exchange membrane was 5975 g-N m−2 d−1 with an energy input of 28.2 kWh (kg-N)−1 when using real LW. All this supported the conclusion that an electrochemical approach such as this makes it possible to achieve highly desirable ammonia recovery from wastewater in a sustainable manner.