Ammonia Process Research Articles

The aqueous chemistry of the copper-ammonia system and its implications for the sustainable recovery of copper

The dissolution of copper during the leaching of chalcopyrite in ammonia solutions is an attractive alternative to acid sulfate leaching in the treatment of ores with high consumption of acid. Despite considerable research into this complex leaching system, a lack of understanding of the fundamental chemical drivers has delayed the implementation of the ammonia process. In the present study, various ammonium salts solutions (chloride, sulfate, carbonate) have been used to study the effect of ion association on the dissociation constant of the ammonium ion at temperatures of 25 and 35 °C. Experimental and calculated solubilities of Cu 2+ have been obtained under different conditions and plotted in speciation distribution diagrams, in other to assess the accuracy of predictions using available thermodynamic properties. Ion association was found to significantly affect the dissociation constant of the ammonium ion in solutions containing sulfate, chloride and carbonate anions; thus, influencing the free ammonia concentration in solution. Increasing temperature from 25 to 35 °C was found to decrease the dissociation constant of the ammonium ion. These findings highlight the importance of using the correct anionic ligands for the ammonium ions and temperature in order to obtain high dissolution of copper. It has been established that solubility of copper in ammonia solution is affected by the anionic ligands, temperature and addition of chloride ions. The NH 3 ligand forms strong coordination compounds with cupric or cuprous ions depending on the anionic ligand, generating an increase in solubility between pH 8.5 and 10.0. The present study, therefore, identifies important constraints on the role of varying anion associated with ammonia, temperature, pH, and addition of chloride ions and the inter-dependence of these factors in controlling Cu 2+ solubility in ammoniacal systems. The results from the present study provides experimental pKa values and solubility constants of the various ammoniacal systems to provide commercial processing via ammoniacal routes the optimal conditions in which to maximise Cu recovery and maintain free ammonia at levels to minimise volatility and loss. The findings are directly beneficial to future commercial application employing effective ammonium-anion lixiviant strategies in the sustainable recovery of Cu. • Ion association affect pKa of the ammonium ion in solutions containing sulfate, chloride and carbonate anions. • Solubility of copper in ammonia solution is affected by the anionic ligands, temperature, and addition of chloride ions. • The findings are beneficial to commercial application employing ammonium-anion lixiviant in the sustainable recovery of Cu.

How does a resilient, flexible ammonia process look? Robust design optimization of a Haber-Bosch process with optimal dynamic control powered by wind

Ammonia can be an essential energy vector for storing excess renewable energy during the year and release this energy when demand is high. This storage during the year provides an essential part in the energy sector for moments when there is not enough wind and sun to cover the demand. Although the Haber-Bosch is a very mature process to synthesize hydrogen and nitrogen to ammonia, it is not flexible enough to match the erratic nature of renewables. This mismatch creates the need for large intermediate hydrogen buffer tanks. To reduce the capacity of the hydrogen storage tank, we need to optimize the dynamic power-to-ammonia process in a minute time scale while considering the uncertainties linked to renewables. Therefore, we coupled a stochastic wind power process to a dynamic Power-to-Ammonia process and performed a design optimization under uncertainties, i.e. a robust design optimization, for a three-hour wind scenario while considering optimal dynamic control. The robust design optimization showed significant trade-offs between the most productive, the most flexible, the most resilient, and robust power-to-ammonia plant designs. For the flexible and productive designs, the bypass fraction and buffer feed have essential roles in achieving these designs. In the future, we will use a stochastic process to consider the uncertainty of renewable power over more extended periods (days, weeks and months) coupled with the robust design optimization of the dynamic power-to-ammonia process and investigate its effect on the intermediate hydrogen buffer size and the plant’s cost.

Over 21.0% faradaic efficiency of ambient ammonia production: Photoelectrocatalytic activity of MOF-235

In recent years, the Haber-Bosh process's ammonia synthesis has shown a lot of energy consumption and significant CO2 emissions. In this sense, the photoelectrochemical production of NH3 via dinitrogen fixation has been showing a promising strategy. Thus, in this work, ammonia production under photoelectrocatalytic condition was carried out using the metal-organic iron terephthalate structure (MOF-235), obtained by a simple and low-cost process (solvothermal). The results indicated greater activity for the nitrogen reduction reaction (NRR) compared to the hydrogen reduction reaction (HRR), in addition to a high yield of NH3 0.716 µg h−1 cm−2 and Faradaic efficiency greater than 21.0% at - 0.2 V vs reversible hydrogen electrode in 0.1 mol L−1 Na2SO4 electrolyte. It is believed that the good results of MOF-235 during NRR are related to a high specific area of MOF, making available active sites of trinuclear-oxocentered iron in abundance. The material homogeneity in the electrode and the excellent light absorption were also decisive factors for the supply of high energy electrons necessary for ammonia production.

Mechanistic Insights into Electrocatalytic Nitrogen Reduction Reaction on the Pd‐W Heteronuclear Diatom Supported on C2N Monolayer: Role of H Pre‐Adsorption

The electrocatalytic N2 reduction reaction (eNRR) is a potential alternative to the Haber–Bosch process for ammonia (NH3) production. Tremendous efforts have been made in eNRR catalyst research to promote the practical application of eNRR. In this work, by means of density functional theory calculations and the computational hydrogen electrode model, we evaluated the eNRR performance of 30 single metal atoms supported on a C2N monolayer (M@C2N), and we designed a new thermodynamically stable Pd‐W hetero‐metal diatomic catalyst supported on the C2N monolayer (PdW@C2N). We found that PdW@C2N prefers to adsorb H over N2, and then, the pre‐generated hydrogen‐terminated PdW@C2N selectively adsorbing N2 behaves as the actual functioning “catalyst” to catalyze the eNRR process, exhibiting excellent performance with a low overpotential (0.31 V), an ultra‐low NH3 desorption free energy (0.05 eV), and a high selectivity toward eNRR over hydrogen evolution reaction (HER). Moreover, PdW@C2N shows a superior eNRR performance to its monomer (W@C2N) and homonuclear diatom (W2@C2N) counterparts. The revealed mechanism indicates that the preferential H adsorption over N2 on the active site may not always hamper the eNRR process, especially for heteronuclear diatom catalysts. This work encourages deeper exploration on the competition of eNRR and HER on catalyst surfaces.

A comparative techno-economic and sensitivity analysis of Power-to-X processes from different energy sources

In this paper, green hydrogen produced via water electrolysis and its conversion into three alternative fuels, such as methane, methanol, and ammonia, are considered. The four different Power-to-Fuel solutions are investigated and compared from both the technical and economic points of view aiming at providing a comprehensive overview of the Power-to-Fuel feasibility. At first, the global process efficiency, the storage capacity, the annual costs, and the production cost of the different fuels (in terms of mass, energy, and hydrogen content) are calculated for a reference scenario. Then, a sensitivity analysis is carried out analyzing the influence of many parameters (i.e. electricity cost, electrolyser CAPEX, operating hours, etc) on the economic viability of all the processes. Finally, map plots are developed reporting the fuel production cost for considering different renewable energy sources and their availability. They can be considered as a useful tool for pre-feasibility analysis of power to fuel processes enabling to analyze and compare the different solutions in different scenarios. It is found that the highest efficient process is the Power-to-Hydrogen (about 61.5%) followed by the methanol and ammonia processes and in the end the methane processes. In terms of energy storage and energy density by volume, the methanol resulted in the most suitable solution, while the ammonia resulted in the best H2 storage medium in terms of kg of H2 per m3 of storage (108 kgH2/m3). From the economic perspective, the annual cost breakdown showed that, in all the cases, the major expenditures are related to the electrical energy purchase and CAPEX and OPEX of the electrolyzer (around 90% of total costs), and a 50% reduction in electricity cost and electrolyzer CAPEX could lead to a reduction of about 30% and 18% on fuel production cost, respectively. The cheapest fuel in terms of mass and energy content are methanol (1.02 €/kg) and Hydrogen (0.16€/kWh), respectively. The ammonia production cost in terms of hydrogen content in mass resulted almost comparable with the Hydrogen one (5.76€/kgH2 and 5.31€/€/kgH2, respectively). The contribution of the co-produced oxygen sale has been estimated in around a 15% reduction of fuel production cost in all the cases.

1921–2021: A Century of Renewable Ammonia Synthesis

Synthetic ammonia, manufactured by the Haber–Bosch process and its variants, is the key to securing global food security. Hydrogen is the most important feedstock for all synthetic ammonia processes. Renewable ammonia production relies on hydrogen generated by water electrolysis using electricity generated from hydropower. This was used commercially as early as 1921. In the present work, we discuss how renewable ammonia production subsequently emerged in those countries endowed with abundant hydropower, and in particular in regions with limited or no oil, gas, and coal deposits. Thus, renewable ammonia played an important role in national food security for countries without fossil fuel resources until after the mid-20th century. For economic reasons, renewable ammonia production declined from the 1960s onward in favor of fossil-based ammonia production. However, renewable ammonia has recently gained traction again as an energy vector. It is an important component of the rapidly emerging hydrogen economy. Renewable ammonia will probably play a significant role in maintaining national and global energy and food security during the 21st century.

Tuning mobility of intermediate and electron transfer to enhance electrochemical reduction of nitrate to ammonia on Cu2O/Cu interface

• R-Cu 2 O/Cu/CF achieved high ammonia yield rate of 2.17 mg cm -2 h −1 with selectivity of 94.4%. • The faradaic efficiency of electrochemical reduction of nitrate to ammonia (ERNA) was 84.36%. • ERNA was dependent on surface mobility of adsorbed NO 2 - and electron transfer to NO 3 - . • Cu 2 O/Cu interface alleviated NO 2 - adsorption to improve surface diffusion of adsorbed NO 2 - . • Cu 2 O/Cu interface upshifted d band center of Cu to enhance electron transfer to NO 3 - . Compared to traditional haber–bosch process for synthetic ammonia, electrochemical reduction of nitrate to ammonia (ERNA) offers a promising and sustainable technology to generate ammonia at ambient temperature. However, the performance of ERNA is impeded by lacking of sound strategy for designing high-performance electrocatalyst. Here, a Cu based electrode with Cu 2 O/Cu interface was prepared by pulse electrodeposition and electroreduction, achieving the fast rate constant of 0.14 min −1 for reducing nitrate with a high ammonia yield rate of 2.17 mg cm -2 h −1 (faradaic efficiency: 84.36%) and ammonia selectivity of 94.4% at −0.25 V vs. RHE. Particularly, density functional theory (DFT) calculations for the adsorption energy indicated that Cu 2 O/Cu interface alleviated adsorption energy of NO 2 - from −2.02 eV (pure Cu) to −1.59 eV, improving surface diffusion of adsorbed NO 2 - . And DFT calculations for electronic structure implied that Cu 2 O/Cu interface upshifted the d band center of Cu (-2.25 eV vs. −2.48 eV of pure Cu), boosting electron transfer to NO 3 - . Additionally, in-situ infrared spectroscopic analysis confirmed vital intermediates of NO 2 - and NH 2 OH on Cu 2 O/Cu to identify reaction pathway and Gibbs free energy diagram clarified this interface decreased reaction barrier of crucial step (reducing *NO 2 to *NO) from 0.31 eV (pure Cu) to −0.77 eV for the enhancement of ERNA. Thereby, these findings demonstrated that Cu 2 O/Cu interface tunes mobility of NO 2 - and electron transfer to NO 3 - on Cu based electrocatalyst is an efficient method to promote performance of ERNA with high efficiency and rate.

Magnetic field-enhanced photocatalytic nitrogen fixation over defect-rich ferroelectric Bi2WO6

Photocatalytic N2 fixation is a promising and sustainable manufacturing process of ammonia (NH3); however, the NH3 production rate by this method is very low, thus severely restricting further application of this sustainable technology. Therefore, developing an efficient photocatalyst for N2 fixation under mild conditions is urgently required. Herein, ferroelectric Bi2WO6 materials with different surface oxygen defects were prepared, and the concentration of corresponding defects was controlled by adjusting the thermal reduction time. The abundant oxygen defects in Bi2WO6 can provide more reactive sites to promote the effective adsorption of N2, and the photogenerated charge carrier can be efficiently separated benefiting from the internal electric field. These would weaken the N2 triple bond and reduce the activation energy barrier for the conversion of N2 to NH3 under mild conditions. In the absence of sacrificial agents and cocatalysts, the optimized Bi2WO6 with oxygen defects shows an indigenous NH3 yield of 132.175 μmol·g-1·L-1·h-1, which is more than two times higher than that of the original Bi2WO6. Surprisingly, the Bi2WO6 with oxygen defects produced more than eight times NH3 (471.13 μmol·g-1·L-1·h-1) than that of the original Bi2WO6 when assisted by an external magnetic field, thus providing a new perspective for further enhancing the N2 fixation performance.

Study of combustion and NO chemical reaction mechanism in ammonia blended with DME

Ammonia (NH3) has been supposed to be the potential alternative energy source towards carbon neutrality. However, it has several unfavorable combustion characteristics, such as the slow combustion rate, poor combustion stability, high ignition energy and so on. As a renewable fuel, dimethyl ether (DME) is also considered to be a favorable carbon–neutral fuel, which can improve the combustion process of ammonia. To investigate the combustion and emission mechanism for the NH3/DME dual-fuel combustion, a detailed chemical reaction mechanism with 221 species and 1597 reactions was developed based on the previous relevant work. The laminar burning velocity (LBV) and ignition delay time (IDT) of ammonia, DME and NH3/DME combustion under a wide range of initial conditions were validated in 0-D and 1-D models. The process of NO formation and reduction reaction was also studied under the laminar burning combustion and ignition model, and it was found that fuel NOx still dominates the total NOx production in NH3/DME combustion, and the DME addition in ammonia up to 50% promotes the NO formation reaction, producing more NO. In order to analyze the effect of DME addition on NO formation mechanism, the analyses of chemical reaction pathway, sensitivity analysis on NO, typical active radical evolution behaviors and rate of production (ROP) were conducted in detail. In comparison with D50 (50%NH3/50%DME), D25(75%NH3/25%DME) with higher ammonia content generates more NH and NH2 radicals, and therefore, promoting the NO reduction reaction. Lower DME content in D25 also generates less H/O/OH active radicals, which inhibits the generation of NO. It is reduced by 9% approximately in total at equivalence ratio of 0.7. In addition, CH3 generated from DME could also partly promote the conversion of HNO and NO2 to NO, slightly increasing the NO production.

Modeling and Bayesian Uncertainty Quantification of a Membrane-Assisted Chilled Ammonia Process for CO2 Capture

Modeling and Bayesian Uncertainty Quantification of a Membrane-Assisted Chilled Ammonia Process for CO₂ Capture

Selective catalytic oxidation of ammonia to nitric oxide via chemical looping

Selective oxidation of ammonia to nitric oxide over platinum-group metal alloy gauzes is the crucial step for nitric acid production, a century-old yet greenhouse gas and capital intensive process. Therefore, developing alternative ammonia oxidation technologies with low environmental impacts and reduced catalyst cost are of significant importance. Herein, we propose and demonstrate a chemical looping ammonia oxidation catalyst and process to replace the costly noble metal catalysts and to reduce greenhouse gas emission. The proposed process exhibit near complete NH3 conversion and exceptional NO selectivity with negligible N2O production, using nonprecious V2O5 redox catalyst at 650 oC. Operando spectroscopy techniques and density functional theory calculations point towards a modified, temporally separated Mars-van Krevelen mechanism featuring a reversible V5+/V4+ redox cycle. The V = O sites are suggested to be the catalytically active center leading to the formation of the oxidation products. Meanwhile, both V = O and doubly coordinated oxygen participate in the hydrogen transfer process. The outstanding performance originates from the low activation energies for the successive hydrogen abstraction, facile NO formation as well as the easy regeneration of V = O species. Our results highlight a transformational process in extending the chemical looping strategy to producing base chemicals in a sustainable and cost-effective manner.

Microbial Nitrification Paradox: A Paradigm Shift on Nitrogen Uptake by Rice

Nitrogen fertilization is an integral agronomic practice to increasing productivity and profitability in agriculture. But the poor nitrogen use efficiency (NUE, about < 40%) causes many economic and environmental challenges. The microbial oxidative process of converting ammonia to nitrite to nitrate (nitrification) is the rate-limiting step in the N loss. The century-old, conventional theory of nitrification with the involvement of two functionally different bacterial groups as ammonia-oxidizing bacteria and nitrite-oxidizing bacteria has been upturned by the recent discoveries of archaeal members involved in ammonia oxidation (Ammonia-oxidizing archaea, AOA), anaerobic ammonia-oxidizing bacteria (Anammox bacteria) and complete ammonia oxidizing bacteria (Comammox bacteria) in the last two decades, largely due to the advances in molecular and metagenomic methods introduced to study the microbial ecology. What is interesting to know is that nitrate-transporters of host plants, as in rice, are involved in the assembly of the microbiome associated with roots. Besides, rice plants produce the biological nitrification inhibiting (BNI) compounds released through root exudates. Involvement of diverse microbiome members and the plant genome through nitrate transporters on the rice rhizosphere microbiome assembly necessitates the reappraisal of the nitrogen fertilization management options. This paper also highlights the need for gathering new knowledge on the plant-microbe interactions, from the genome to metabolite levels, and conserving these resources for sustainable rice cultivation.

Green chemical pathway of plasma synthesis of ammonia from nitrogen and water: a comparative kinetic study with a N2/H2 system

This work demonstrates alternative green ammonia processing using nitrogen and water based non-thermal plasma without pure hydrogen supply which results in an enormous amount of CO2 emission.

AmmPower pilots new ammonia process in Michigan

AmmPower pilots new ammonia process in Michigan

Investigating the active sites in molybdenum anchored nitrogen-doped carbon for alkaline oxygen evolution reaction

Developing durable and efficient non-precious-metal based catalysts for oxygen evolution reaction (OER) is highly desirable in the field of electrocatalysis. In this work, a series of novel Mo anchored N-doped carbon catalysts (denoted as Mo/NC-T) were prepared starting from the zeolitic imidazolate framework 8 (ZIF-8) precursor. Firstly, Mo doped ZIF-8 precursor (Mo/ZIF-8) with a regular polyhedron structure was formed through a simple ion-exchange method process between molybdenum pentachloride (MoCl5) and ZIF-8. Afterward, Mo/ZIF-8 was converted to Mo/NC-T through a two-step calcination process in nitrogen (N2) and ammonia (NH3). The as-synthesized Mo/NC-T samples exhibited superior electrocatalytic OER properties. The optimal sample at 650 °C (Mo/NC-650) presented a low overpotential of 320 mV at 10 mA cm−2, a Tafel slope of 71 mV dec-1, and an outstanding long-term stability for 30 h in 1 M KOH solution. The remarkable OER activity of Mo/NC-T could be ascribed to the structural stability of carbon matrix and the synergistic effect between Mo3+ (derived from Mo-C bonds) and pyridinic N. This work provides a novel perspective on the roles of Mo species in the N-doped carbon electrocatalysts for OER.

A review on sensing and catalytic activity of nano-catalyst for synthesis of one-step ammonia and urea: Challenges and perspectives

One of the most significant chemical operations in the past century was the Haber-Bosch catalytic synthesis of ammonia, a fertilizer vital to human life. Many catalysts are developed for effective route of ammonia synthesis. The major challenges are to reduce temperature and pressure of process and to improve conversion of reactants produce green ammonia. The present review, briefly discusses the evolution of ammonia synthesis and current advances in nanocatalyst development. There are promising new ammonia synthesis catalysts of different morphology as well as magnetic nanoparticles and nanowires that could replace conventional Fused-Fe and Promoted-Ru catalysts in existing ammonia synthesis plants. These magnetic nanocatalyst could be basis for the production of magnetically induced one-step green ammonia and urea synthesis processes in future.

Adaptive changes in the ornithine cycle and amino acid synthesis in sheep liver with different meat productivity

The aim of the research was to study the ornithine cycle as the process of fixing ammonia and the formation of urea in the body of highly productive animals. In our experiments, we used a protein-deficient diet and urea as a nitrogen substitute for nitrogen-containing materials in the diet to reveal the mechanism of action of urea on animals, in particular on the biochemical processes of the ornithine cycle. There are some differences between Bukovinian sheep of the Askanian meat-wool breed and outbreds in terms of the ability to build muscle tissue. Our study reveals that the slaughter yield and the average daily gain consumption of Bukovinian-type meat of the Askanian meat-wool breed were higher in summer and in autumn, compare with purebred sheep. Sheep of the Bukovynian type of Askanian meat-wool breed have the intensity of enzymatic formation of urea in liver homogenates that is much higher in all experiments than in outbred sheep. A sharp drop in the activity of all stages of urea formation and glutamic acid synthesis in liver homogenates and significantly weakened urea formation was found in all experiments of the fourth series in comparison with the experiments in the third series. Increased muscle growth, high nitrogen deposition, and a much lower percentage of urinary excretion of ammonia and urea nitrogen, as well as higher activity of enzymes of the ornithine cycle and glutamic acid synthesis in the Bukovinian sheep type of Askanian meat-wool breed compared to outbreeds allow concluding that ammonia and urea in highly productive animals act less as finishing products of nitrogen metabolism than in low-productive animals.

Drastically Increase in Atomic Nitrogen Production Depending on the Dielectric Constant of Beads Filled in the Discharge Space.

Nitrogen activation, especially dissociation (production of atomic nitrogen), is a key step for efficient nitrogen fixation, such as nitrogen reduction to produce ammonia. Nitrogen reduction reactions using water as a direct hydrogen source have been studied by many researchers as a green ammonia process. We studied the reaction mechanism and found that the nitrogen reduction could be significantly improved via efficient production of atomic nitrogen through electric discharge. In the present study, we focused on packed-bed dielectric barrier discharge (PbDBD) using dielectric beads as the packing material. The experimental results showed that more atomic nitrogen was produced in the nitrogen activation by the discharge in which the discharge space was filled with the dielectric beads than in the nitrogen activation by the discharge without using the dielectric beads. Then, it was clarified that the amount of atomic nitrogen increased as the dielectric constant of the beads to be filled increased, and the amount of atomic nitrogen produced increased up to 13.48 times. Based on the results, we attempted ammonia synthesis using water as a direct hydrogen source with the efficiently generated atomic nitrogen. When the atomic nitrogen gas generated by the PbDBD was sprayed onto the surface of the water phase and subsequently reacted as a plasma/liquid interfacial reaction, the nitrogen fixation rate increased by 7.26-fold compared to that when using the discharge without dielectric beads, and the ammonia production selectivity increased to 83.7%.

Modeling and optimization of ammonia process: Effect of hydrogen unit performance on the ammonia yield

The main object of this research is the development of a mathematical framework to simulate a commercial ammonia plant and obtaining the optimal operating conditions of process at steady state condition. The considered ammonia plant consists of steam and autothermal reforming reactors, low and high temperature shift converters, hydrogen purification section, methanation, and ammonia synthesis reactors. The catalytic reactors are heterogeneously modeled based on the mass and energy balance equations considering heat and mass transfer resistances in the gas and catalyst phases. In addition, an equilibrium model is applied to simulate the absorption column. Then, the accuracy of developed framework is investigated against plant data. The results show that the internal mass transfer resistance in the commercial catalyst limits the syngas production in the reforming section. In the second step, an optimization problem is formulated to enhance the ammonia production considering safety and operating limitations. The formulated optimization problem is handled employing the genetic algorithm. The results show that more syngas production in the optimized hydrogen unit is one of the main reasons for higher ammonia synthesis in the considered plant. Applying optimal conditions on the process increases ammonia production potential from 1890 to 2179 mol s−1.

Lithium‐based Loop for Ambient‐Pressure Ammonia Synthesis in a Liquid Alloy‐Salt Catalytic System

The Haber-Bosch process for ammonia (NH3 ) production in industry relies on high temperature and high pressure and is therefore highly energy intensive. In addition, the activity of the solid transition metal-based catalysts used is typically limited by the scaling relation between activation barrier for N2 dissociation and nitrogen-binding energy. Here, an innovative Li-based loop in a liquid alloy-salt catalytic system for ambient-pressure NH3 synthesis from N2 and H2 was developed. The looping process consisted of three reaction steps taking place simultaneously. The first step was the nitrogen fixation by Li in the liquid Li-Sn alloy to form lithium nitride (Li3 N), which floated up and dissolved into the molten salt. The second step was the hydrogenation of the Li3 N to produce NH3 and lithium hydride (LiH) in the molten salt. The third step was the decomposition of the LiH to regenerate Li in the presence of Sn. An average NH3 yield rate of 0.025 μg s-1 was achieved in an 81 h test at 510 °C and ambient pressure. The floating and dissolution of Li3 N realized in the liquid catalytic system enabled circumventing the scaling relation exerted on Li, and the remarkable properties of liquid alloy and molten salt offered extraordinary advantages for NH3 synthesis at ambient pressure.