Yields Of NH3 Research Articles

Catalyst-Free Activation and Fixation of Nitrogen by Laser-Induced Conversion.

Ultrafast N2 fixation reactions are quite challenging. Currently used methods for N2 fixation are limited, and strong dinitrogen bonds usually need to be activated via extreme temperature or pressure or by the use of an energy-consuming process with sophisticated catalysts. Herein, we report a novel laser-based chemical method for N2 fixation under ambient conditions without catalysts, this method is called laser bubbling in liquids (LBL), and it directly activates N2 in water (H2O) and efficiently converts N2 into valuable NH3 (max: 4.2 mmol h-1) and NO3- (0.17 mmol h-1). Remarkably, the highest yields of NH3 and NO3- are 4 orders of magnitude greater than the best values for electrocatalysis reported to date. Notably, we further validate the experimental mechanism by using optical emission spectroscopy to detect the production of intermediate plasma and by employing isotope tracing. We also establish that an extremely high-temperature environment far from thermodynamic equilibrium inside a laser-induced bubble and the kinetic process of rapid quenching of bubbles is crucial for N2 activation and fixation to generate NH3 and NOx via LBL. Based on these results, it is shown that LBL is a simple, safe, efficient, green, and sustainable technology that enables the rapid conversion of the renewable feedstocks H2O and N2 to NH3 and NO3-, facilitating new prospects for chemical N2 fixation.

Tracking contaminants in the aqueous effluent during supercritical water gasification and oxidation of swine manure in the flow mode

Biomass waste processing is an area of great interest due to its potential for reducing environmental impact and recovering resources. The present work investigates for the first time the composition of products resulting from supercritical water (SCW) gasification and oxidation of swine manure (SM) continuously fed into a tubular reactor at a temperature gradient along its vertical axis of 390–600 °C and a pressure of 25 MPa. Special attention is paid to how the operating parameters, including SM flow rate (6.5–10.7 g/min), oxidation ratio (OR ≤ 1.78), and the presence of NaOH additive (1 wt%) influenced the composition and concentration of contaminants (phenols, N-bearing aromatics, polyaromatic hydrocarbons (PAHs), and ammonia) in the effluent collected at the reactor outlet. The results of gas chromatography-mass spectrometry indicate that water-soluble products comprise predominantly of phenols, pyridines, pyrroles, indoles, pyrazines, anilines, and quinolines. Increasing the reagent’s residence time during SCW gasification was observed to lower the amount of phenols in the effluent. In addition, the introduction of NaOH increases the yields of syngas and NH3 while lowering the concentration of N-bearing aromatics and PAHs. SCW oxidation of SM not only reduces contaminant levels in the effluent by several orders of magnitude, but also partially compensates for thermal inputs needed for the process implementation. Among N-bearing compounds, ammonia, pyridines, indoles, and quinolines display the highest resistance to oxidation. The paper explores the resource-saving and ecological benefits of SCW gasification and oxidation of SM.

Effect of NaCl/MgCl2 on generation of NOx precursors during aspartic acid pyrolysis: A experimental and theoretical study

This work studied the effect of NaCl/MgCl2 on the evolution of nitrogen during aspartic acid pyrolysis, focusing on the transformation pathways in molecular level. The generation of NOX precursors and other volatiles were detected by TG-FTIR, UV, and GC–MS. Notably, density functional theory was used to evaluate energy barrier and rate-determining step during pyrolysis. The yields of NH3, HCN, and HNCO were inhibited by NaCl/MgCl2 addition, especially on the second releasing stage (333–468 °C). The result of theoretical simulations showed that the rate-determining step in six pathways of aspartic acid pyrolysis was changed by NaCl/MgCl2 addition, especially for MgCl2, and the optimum generation pathway for nitrogen–containing products changed from NH3 formation to DKP formation. The highest energy barrier of NH3 and HCN generation increased to 327 kJ/mol and 432 kJ/mol after the addition of NaCl and MgCl2, respectively, leading to their lower release than raw aspartic acid. In addition, the presence of NaCl/MgCl2 decreased the energy barrier for the substitution of the amino group with the hydroxyl group, especially for NaCl, resulting in the fact that more nitrogen was retained in the char. The results first revealed how the NaCl/MgCl2 affected the nitrogen transformation during aspartic acid pyrolysis under molecular level.

Nitrogen Reduction to Ammonia by a Phosphorus-Nitrogen PN 3 P-Mo(V) Nitride Complex: Significant Enhancement via Ligand Postmodification

Nitrogen Reduction to Ammonia by a Phosphorus-Nitrogen PN ³ P-Mo(V) Nitride Complex: Significant Enhancement via Ligand Postmodification

The effects of alkali metals and alkaline earth metals on the mechanism of N-containing gases production during glutamic acid pyrolysis

Biomass contains Alkali and Alkaline Earth Metals (AAEMs) which, during the pyrolysis process of biomass, can affect the production of harmful gases such as NH3, HCN and HNCO. In this study, the effect of AAEMs on the mechanisms of amino acid pyrolysis was analysed with a combination of Thermogravimetric- Fourier Transform Infrared Spectroscopy (TG-FTIR) experiments and Density Functional Theory (DFT) calculations. Moreover, the four most abundant metals in biomass (K, Ca, Na and Mg) were selected, and glutamic acid (Glu), which accounts for the largest proportion of plant proteins, was studied. The results showed that all four metal chlorides had an inhibitory effect on the production of N-containing gases, while promoted the char formation. Sodium was the most effective in reducing the yields of NH3, HCN and HNCO. The alkaline earth metals (Ca and Mg) could influence the temperature range for gas release. Diketopiperazines (DKP) were produced from the pyrolysis of amino acids, and the precursor of HCN and HNCO. This study explained the effect of AAEMs on nitrogen conversion mechanisms during biomass pyrolysis and provided theoretical support for controlling the nitrogen element transfer.

The Steric Effect in Preparations of Vanadium(II)/(III) Dinitrogen Complexes of Triamidoamine Ligands Bearing Bulky Substituents.

The reactions of newly designed lithiated triamidoamines Li3LR (R = iPr, Pen, and Cy2) with VCl3(THF)3 under N2 yielded dinitrogen–divanadium complexes with a μ-N2 between vanadium atoms [{V(LR)}2(μ-N2)] (R = iPr (1) and Pen (2)) for the former two, while not dinitrogen–divanadium complexes but a mononuclear vanadium complex with a vacant site, [V(LCy2)] (R = Cy2 (3)), were obtained for the third ligand. The V–NN2 and N–N distances were 1.7655(18) and 1.219(4) Å for 1 and 1.7935(14) and 1.226(3) Å for 2, respectively. The ν(14N–14N) stretching vibrations of 1 and 2, as measured using resonance Raman spectroscopy, were detected at 1436 and 1412 cm–1, respectively. Complex 3 reacted with potassium metal in the presence of 18-crown-6-ether under N2 to give a hetero-dinuclear vanadium complex with μ-N2 between vanadium and potassium, [VK(LCy2)(μ-N2)(18-crown-6)] (4). The N–N distance and ν(14N–14N) stretching for 4 were 1.152(3) Å and 1818 cm−1, respectively, suggesting that 4 is more activated than complexes 1 and 2. The complexes 1, 2, 3, and 4 reacted with HOTf and K[C10H8] to give NH3 and N2H4. The yields of NH3 and N2H4 (per V atom) were 47 and 11% for 1, 38 and 16% for 2, 77 and 7% for 3, and 80 and 5% for 4, respectively, and 3 and 4, which have a ligand LCy2, showed higher reactivity than 1 and 2.

Influence of stoichiometry air ratio on char characteristics and nitrogen conversion in circulating fluidized bed with post-combustion

The post-combustion technology was one of the most promising de-NOx technologies, while the impact of stoichiometry air ratio in the furnace (λCFB) on char characteristics and nitrogen conversion under reduction atmosphere was not fully understood yet. Three different λCFB (0.75, 0.85 and 0.95) and two kinds of fuels, namely Fugu bituminous (FB) and its semi-coke (FS), were selected for this experiment when the combustion temperature maintained 960 °C. The results of Raman spectra indicated that the char reactivity had different degrees of improvement comparing with raw fuels. The char had the best reactivity when the λCFB was 0.85. Besides, the BET specific surface area and the BJH pore volume of FB char also reached maximum values of 4.99 m2/g and 13.43 mm3/g when the λCFB was 0.85. FS char also had the best reactivity and the most developed pore structure with the λCFB of 0.85. As λCFB decreasing, more fuel nitrogen (fuel-N) would remain in char rather than releasing into the gas phase. Simultaneously, even if fuel-N was released into the gas phase, it would exist in the form of NH3 and HCN instead of N2. Moreover, the yields of NH3 were always higher than HCN. Since the optimum char characteristics and appropriate fuel-N migration when the λCFB was 0.85, the NOx conversion ratios of FB and FS were the lowest, which were 2.81% and 3.81%, respectively. This study offered some useful information for the industrial application of post-combustion technology.

Multistep Functional Embellishment for p-ZnTe as a Cathode to Boost the Faraday Efficiency of Nitrogen Conversion.

An electrochemical N2 reduction reaction (N2RR) is a selective sustainable approach to obtain NH3 at mild conditions and has been proposed as an alternative to the full-blown Haber-Bosch process. However, achieving high yields of NH3 and high faraday efficiency (FE) at a low overpotential remains a big challenge but has high expectations for the electrocatalytic N2RR. Herein, a novel p-ZnTe cathode multistep embellished with NiOx and ZnO thin films was prepared for boosting faraday efficiency to 9.89% for N2RR at -0.2 V vs reversible hydrogen electrode (RHE), about 12 times of p-ZnTe@ZnO. All components within the NiOx@p-ZnTe/ZnO electrode work cooperatively. A N source was determined through a 15N isotopic-labeling experiment. Using steady-state photoluminescence, electrochemical impedance spectroscopy, and control experiments, a possible model of charge transformation is built. In particular, a NiOx layer has an important impact on increasing interfacial contact between a bare fluorine-doped tin oxide (FTO) glass and p-ZnTe and further reinforcing interfacial electron transfer. This work provides a practical application and a feasible strategy to develop highly efficient catalysts for N2 reduction and also affords a guideline for the fabrication of a flat electrode.

Tripodal P3XFe-N2 Complexes (X = B, Al, Ga): Effect of the Apical Atom on Bonding, Electronic Structure, and Catalytic N2-to-NH3 Conversion.

Terminal dinitrogen complexes of iron ligated by tripodal, tetradentate P3X ligands (X = B, C, Si) have previously been shown to mediate catalytic N2-to-NH3 conversion (N2RR) with external proton and electron sources. From this set of compounds, the tris(phosphino)borane (P3B) system is most active under all conditions canvassed thus far. To further probe the effects of the apical Lewis acidic atom on structure, bonding, and N2RR activity, Fe-N2 complexes supported by analogous group 13 tris(phosphino)alane (P3Al) and tris(phosphino)gallane (P3Ga) ligands are synthesized. The series of P3XFe-N2[0/1-] compounds (X = B, Al, Ga) possess similar electronic structures, degrees of N2 activation, and geometric flexibility as determined from spectroscopic, structural, electrochemical, and computational (DFT) studies. However, treatment of [Na(12-crown-4)2][P3XFe-N2] (X = Al, Ga) with excess acid/reductant in the form of HBArF4/KC8 generates only 2.5 ± 0.1 and 2.7 ± 0.2 equiv of NH3 per Fe, respectively. Similarly, the use of [H2NPh2][OTf]/Cp*2Co leads to the production of 4.1 ± 0.9 (X = Al) and 3.6 ± 0.3 (X = Ga) equiv of NH3. Preliminary reactivity studies confirming P3XFe framework stability under pseudocatalytic conditions suggest that a greater selectivity for hydrogen evolution versus N2RR may be responsible for the attenuated yields of NH3 observed for P3AlFe and P3GaFe relative to P3BFe.

Exploring the sustainable production of ammonia by recycling N and H in biological residues: Evolution of fuel-N during glutamic acid gasification

In this work, the recycling of nitrogen and hydrogen from nitrogen-rich (N-rich) biological residues via autothermal gasification has been proposed as a process suitable for the sustainable production of ammonia (NH3). Two N-rich biological residues, sewage sludge and meat and bone meal, were used and analyzed in this work and glutamic acid was selected as the model compound of the protein-fuel-N in these residues. Glutamic acid gasification experiments were carried out in order to study the effect of temperature (800–900 °C) and steam-to-carbon ratio (0.5–1.0 g g−1) on the conversion of fuel-N into the most typical N-containing gasification products: NH3, molecular nitrogen (N2), hydrogen cyanide (HCN), nitrogen monoxide (NO), tar-N and char-N. Sewage sludge and meat and bone meal were also gasified under selected operating conditions with the main aim of assessing the NH3 production. The most abundant N-containing compounds obtained in the gasification of glutamic acid were NH3 (35–51% over fuel-N) and N2 (45–63% over fuel-N). The highest conversion of fuel-N to NH3–N in the glutamic acid gasification experiments (51%) was obtained at the lowest temperature (800 °C) and the lowest S/C ratio (0.5 g g−1). The increase in the temperature caused a decrease in the yield of NH3, as a consequence of its decomposition into N2. A similar fuel-N distribution was found when sewage sludge and meat and bone meal were gasified, obtaining joint yields of HCN–N, NO–N, tar-N and char-N lower than 5%, and being NH3–N (30–67%) and N2–N (28–68%) the majority products. The yields of NH3–N obtained from glutamic acid (51%), sewage sludge (30%), and meat and bone meal (67%) under the same gasification operating conditions were significantly different. These differences were attributed to the catalytic effect of the metals present in these residues and point to the need to optimize the operating conditions specifically for each residue. In summary, gasification of sewage sludge and meat and bone meal may be able to produce around 10% of the NH3 produced annually in Europe and between 102 and 262 GJ·ton−1 NH3 thanks to the combustion of the syngas generated.

Effects of calcium on the evolution of nitrogen during pyrolysis of a typical low rank coal

This study aims to investigate the effects of calcium on the migration of nitrogen in coal (coal-N) to N-containing gas species, particularly, NH3 and HCN (volatile-N) in volatiles, as well as the chemical transformation of the N in char during coal pyrolysis under different temperatures. The pyrolysis experiments of Shengli brown coal and its derived coal samples loaded with different contents of calcium were conducted under 600–800 °C in a novel fluidized bed reactor. The experimental results showed that during coal pyrolysis, the generation of NH3 is mainly derived from secondary reactions among volatiles, tar and char with the catalytic effect of mineral matter, especially calcium in coal. Increasing pyrolysis temperature from 600 to 800 °C could enhance the release of N in coal to volatiles. Meanwhile, the increased pyrolysis temperature could also inhibit the generation of NH3 while facilitating the formation of HCN. The release of HCN is more sensitive to pyrolysis temperatures. Specifically, under higher pyrolysis temperatures, more N-containing structures in coal would become thermally unstable and crack into HCN; On the other hand, higher pyrolysis temperature could also enhance the decomposition of N in coal to N-containing species in tar or N2, thus reducing the release of HCN and NH3. Nitrogen in tar could either undergo secondary decomposition reactions, generating NH3, HCN, N2 and other N-containing species in gas phase, or experience condensation polymerization by forming macromolecular structure and be retained in char at high pyrolysis temperatures. Calcium could significantly restrain the release of N from coal, thus reducing the yields of NH3 and HCN. During coal pyrolysis, calcium catalytically enhances the fracture and combination of chemical bonds, generating abundant free radicals. These free radicals could continuously attack N-containing structures and consequently release the N-containing gaseous products, such as NH3, HCN, N2 etc., resulting in the decrease of N in char. Calcium also plays important roles in nitrogen transformation in char during coal pyrolysis by catalytically intensifying the transformation of N in char from pyridinic nitrogen (N-6) and pyrrolic nitrogen (N-5) to quaternary type nitrogen (N-Q) during coal pyrolysis.

Fe-Mediated Nitrogen Fixation with a Metallocene Mediator: Exploring p Ka Effects and Demonstrating Electrocatalysis.

Substrate selectivity in reductive multielectron/proton catalysis with small molecules such as N2, CO2, and O2 is a major challenge for catalyst design, especially where the competing hydrogen evolution reaction (HER) is thermodynamically and kinetically competent. In this study, we investigate how the selectivity of a tris(phosphine)borane iron(I) catalyst, P3BFe+, for catalyzing the nitrogen reduction reaction (N2RR, N2-to-NH3 conversion) versus HER changes as a function of acid p Ka. We find that there is a strong correlation between p Ka and N2RR efficiency. Stoichiometric studies indicate that the anilinium triflate acids employed are only compatible with the formation of early stage intermediates of N2 reduction (e.g., Fe(NNH) or Fe(NNH2)) in the presence of the metallocene reductant Cp*2Co. This suggests that the interaction of acid and reductant is playing a critical role in N-H bond-forming reactions. DFT studies identify a protonated metallocene species as a strong PCET donor and suggest that it should be capable of forming the early stage N-H bonds critical for N2RR. Furthermore, DFT studies also suggest that the observed p Ka effect on N2RR efficiency is attributable to the rate and thermodynamics of Cp*2Co protonation by the different anilinium acids. Inclusion of Cp*2Co+ as a cocatalyst in controlled potential electrolysis experiments leads to improved yields of NH3. The data presented provide what is to our knowledge the first unambiguous demonstration of electrocatalytic nitrogen fixation by a molecular catalyst (up to 6.7 equiv of NH3 per Fe at -2.1 V vs Fc+/0).

A Synthetic Single-Site Fe Nitrogenase: High Turnover, Freeze-Quench (57)Fe Mössbauer Data, and a Hydride Resting State.

The mechanisms of the few known molecular nitrogen-fixing systems, including nitrogenase enzymes, are of much interest but are not fully understood. We recently reported that Fe-N2 complexes of tetradentate P3(E) ligands (E = B, C) generate catalytic yields of NH3 under an atmosphere of N2 with acid and reductant at low temperatures. Here we show that these Fe catalysts are unexpectedly robust and retain activity after multiple reloadings. Nearly an order of magnitude improvement in yield of NH3 for each Fe catalyst has been realized (up to 64 equiv of NH3 produced per Fe for P3(B) and up to 47 equiv for P3(C)) by increasing acid/reductant loading with highly purified acid. Cyclic voltammetry shows the apparent onset of catalysis at the P3(B)Fe-N2/P3(B)Fe-N2(-) couple and controlled-potential electrolysis of P3(B)Fe(+) at -45 °C demonstrates that electrolytic N2 reduction to NH3 is feasible. Kinetic studies reveal first-order rate dependence on Fe catalyst concentration (P3(B)), consistent with a single-site catalyst model. An isostructural system (P3(Si)) is shown to be appreciably more selective for hydrogen evolution. In situ freeze-quench Mössbauer spectroscopy during turnover reveals an iron-borohydrido-hydride complex as a likely resting state of the P3(B)Fe catalyst system. We postulate that hydrogen-evolving reaction activity may prevent iron hydride formation from poisoning the P3(B)Fe system. This idea may be important to consider in the design of synthetic nitrogenases and may also have broader significance given that intermediate metal hydrides and hydrogen evolution may play a key role in biological nitrogen fixation.

Bipolar membrane electrodialysis for generation of hydrochloric acid and ammonia from simulated ammonium chloride wastewater

Simulated ammonium chloride wastewater was treated by a lab-scale bipolar membrane electrodialysis for the generation of HCl and NH3·H2O and desalination. The influence of initial concentration of NH4Cl, current density, salt solution volume, initial concentration of acid and base and membrane stack structure on the yields of HCl and NH3·H2O was investigated. The current efficiency and energy consumption were also examined under different conditions. The results showed that, at the current density of 48 mA/cm2, the highest concentration of HCl and NH3·H2O with initial concentration of 110 g/L NH4Cl was 57.67 g/L and 45.85 g/L, respectively. Higher initial concentration of NH4Cl was favor to reduce unit energy consumption and increase current efficiency of the BMED system. The membrane stack voltage of BMED increased quickly under constant current when the concentration of NH4Cl contained in the solution of salt compartment was depleted below the “inflection point concentration” about 8000 mg/L. It means that the concentration of NH4Cl below 8000 mg/L was no longer suitable for BMED because of higher energy consumption. The HCl and NH3·H2O concentration increased more quickly following the increase of current density. When increasing the volume of NH4Cl, the concentration of HCl and NH3·H2O also increased. The high initial concentration of acid and base could improve the final concentration of them, while the growth rate was decreased. Compared with the BMED system with three compartments, the growth rate of HCl concentration with the two compartments was higher and its unit energy consumption was lower. It meant that the performance of the BMED system could be improved by optimizing operation conditions. The application feasibility of the generation of HCl and NH3·H2O and desalination of ammonium chloride wastewater by BMED was proved.

Combustion of hazardous biological waste derived from the fermentation of antibiotics using TG–FTIR and Py–GC/MS techniques

The combustion characteristics for three kinds of antibiotics residue (AR) materials were investigated by TG–FTIR and Py–GC/MS technique. The TG results indicated that AR combustion involved three stages, and correlation between the H/C atomic ratio of the raw materials and peak temperature of weight loss for the second stage was obtained. The FTIR spectra identified evolving gaseous products as CO2, CH4, HCNO, NH3, HCN, and NO. An AR material with a low H/C ratio promoted the formation of CO2 and HCN, but suppressed the yields of NH3 and CH4. The Py–GC/MS results suggested that abundant volatiles can be produced, including alkenes, benzene, phenols, furans, acid, and heterocyclic-N, nitrile-N and amine-N compounds, and confirmed the FTIR absorption characteristics in the low temperature range. A possible pathway for the AR combustion was also tentatively presented.

Co-pyrolysis between microalgae and textile dyeing sludge by TG–FTIR: Kinetics and products

In this work, the kinetic behavior and evolution characteristics of the gaseous products of microalgae (MA) and textile dyeing sludge (TDS) blends during co-pyrolysis were investigated using TG–FTIR. The TDS was blended with MA in the range of 10–90wt.%, and then heated from 105°C to 900°C at 10, 20 and 40°C/min under N2 atmosphere with a flow rate of 80ml/min. The initial decomposition temperature of TDS was lower than MA, but the pyrolysis intensity of MA was higher than TDS. The co-pyrolysis of MA and TDS could avoid the drawbacks with each other and improve their pyrolysis performance. The synergistic interaction between MA and TDS was mainly due to the flowing and sticky bio-oil and alkali metals catalytic effect. Two iso-conversional methods of Ozawa–Flynn–Wall (OFW) and Kissinger–Akahira–Sunose (KAS) were used to calculate the activation energy, and low average activation energy was obtained when the blending ratio of MA was 80%. CO2, H2O, CH4, CO, HNCO, NH3, HCN, SO2, CH, CO and CO groups were the main gaseous products observed from the FTIR spectrums during co-pyrolysis. The origin of CO2, H2O, CH4, CO, HNCO, NH3, HCN, SO2, CH, CO and CO groups was analyzed combined with the decomposition order of the components in MA and TDS. The evolution of the gaseous products was consistent with the weight loss of the blends during co-pyrolysis. The yields of CO2, CH, CO, CO, CO, HNCO, NH3, HCN and SO2 did not monotonically change with the increasing blending ratio of MA, attributed to the synergistic interaction between MA and TDS. The blending ratio of MA reached 80% would obtain the highest yield of desired products. In order to get the low average activation energy and more desired products, the potential global optimum blending ratio of MA for co-pyrolysis of the blends was 80%.

Evaluating molecular cobalt complexes for the conversion of N2 to NH3.

Well-defined molecular catalysts for the reduction of N2 to NH3 with protons and electrons remain very rare despite decades of interest and are currently limited to systems featuring molybdenum or iron. This report details the synthesis of a molecular cobalt complex that generates superstoichiometric yields of NH3 (>200% NH3 per Co-N2 precursor) via the direct reduction of N2 with protons and electrons. While the NH3 yields reported herein are modest by comparison to those of previously described iron and molybdenum systems, they intimate that other metals are likely to be viable as molecular N2 reduction catalysts. Additionally, a comparison of the featured tris(phosphine)borane Co-N2 complex with structurally related Co-N2 and Fe-N2 species shows how remarkably sensitive the N2 reduction performance of potential precatalysts is. These studies enable consideration of the structural and electronic effects that are likely relevant to N2 conversion activity, including the π basicity, charge state, and geometric flexibility.

Thermogravimetry–Mass Spectrometry Analysis of Nitrogen Transformation during Oxy-fuel Combustion of Coal and Biomass Mixtures

The nitrogen transformation during the oxy-fuel combustion of coal and biomass mixtures was studied through thermogravimetry–mass spectrometry (TG–MS). Influence factors, such as atmosphere and biomass share, were selected to study the release of four nitrogenous gases HCN, HNCO, NH3, and NO. With the presence of ≥20% O2, the combustion of Datong coal and biomass mixtures releases less HCN, NH3, and NO and more HNCO in the O2/CO2 atmosphere compared to the O2/N2 atmosphere. HCN and HNCO compete mutually during the formation of nitrogenous gases. The mixtures of Datong coal and biomass release more nitrogenous gases than Datong coal alone in both O2/CO2 and O2/N2 atmospheres during the devolatilization. With the O2 concentration in the O2/CO2 atmosphere increasing from 20 to 100%, the relative yields of NH3, HCN, and HNCO produced from the mixtures decrease, while the NO yield increases. The HNCO yield changes greatly with the increase of the O2 concentration because of the oxidation by OH. Increasing the biomass share in the mixtures improves the relative yields of nitrogenous gases. The biomass share can greatly affect the HCN and HNCO yields, owing to the different forms of N-containing structures between coal and biomass.

Effects of Solid Residence Time and Inherent Metal Cations on the Fate of the Nitrogen in Coal during Rapid Pyrolysis

Six coals with carbon contents ranging from 69 to 80 wt % dry ash-free (daf) were rapidly pyrolyzed at 1300 °C under a stream of high purity He in a free fall-type graphite reactor incorporating a graphite filter to control the residence time of coal particles. In this manner, the effects of both residence time and inherent mineral contents on N2 formation from char-N following devolatilization were examined. At a residence time of zero, 20–30% of the coal-N was released as volatile-N species, such as tar-N, HCN and NH3, while <15% was transitioned to N2 and the remainder (60–80%) was retained in the char. When the residence time was increased to 120 s, the yields of tar-N, HCN and NH3 were almost unchanged, irrespective of the coal type, although the N2 yield increased and the char-N decreased with increasing residence times, with the changes in yields of both species being roughly equal. When an Indonesian char sample already devolatilized at 1000 °C was pyrolyzed again by applying a slow heating rate o...

Characterization of an Intermediate in the Ammonia-Forming Reaction of Fe(DMeOPrPE)2N2 with Acid (DMeOPrPE = 1,2-[bis(dimethoxypropyl)phosphino]ethane)

The reactivity of Fe(DMeOPrPE)2N2 with water and acid was explored. (DMeOPrPE is the bidentate phosphine 1,2-[bis(dimethoxypropyl)phosphino]ethane.) The complex reacts with acid to form trans-[Fe(DMeOPrPE)2(N2)H](+) and small amounts of ammonia and hydrazine. When reacted with H2O, cis-Fe(DMeOPrPE)2(H)2 is formed. To increase the yields of ammonia and hydrazine, we investigated the effect of anion, solvent, and acid addition rate on the yields of ammonia. Of these parameters, only the properties of the anion (i.e., of the acid) had a significant impact on the yields of ammonia. The highest yields of NH3 occurred with the largest/least-coordinating anion (triflate). A short-lived purple intermediate (τ1/2 < 5 s at 23 °C) was observed in the reaction of Fe(DMeOPrPE)2N2 with triflic acid. Because the structure of this purple species could potentially provide valuable insights into the mechanism of ammonia formation, a method was developed for independently synthesizing and stabilizing the complex. Spectroscopic characterization of the purple species identified it as the paramagnetic [((DMeOPrPE)2Fe)2(μ-N2)](2+) complex (1). This purple dimer (1) exists in equilibrium with yellow, monomeric, paramagnetic [Fe(DMeOPrPE)2N2](+) (2). The role of 1 in the formation of hydrazine and ammonia was probed by reacting 1 with acid.