Plasma-assisted Nitrogen Fixation Research Articles

Energy Intensified Nitrogen Fixation Through Fast Modulated Gas Discharge from Pyramid-shaped Micro-electrode

Plasma-assisted nitrogen fixation has emerged as a promising alternative to conventional nitrogen fixation methods. In this study, we investigate the feasibility of plasma-assisted nitrogen fixation using an AC-driven dielectric barrier discharge generated from the micro-tips of a specially designed fast-modulated pyramid-shaped electrode. The obtained result is compared with the conventional flat electrode. Our results demonstrate that pyramid-shaped micro-tip electrodes can excite more nitrogen molecules than flat electrodes. Thus, pyramid electrodes have 58% more nitrogen oxides yield efficiency at 32% less energy cost. The highest nitrogen fixation is attained at 60% to 70% of oxygen concentration in nitrogen-feeding gas. These findings suggest that discharge through microtip is a promising and viable technology that could play a significant role in reducing the energy cost of the plasma-assisted nitrogen fixation method to meet the growing demand for sustainable nitrogen-based fertilizers.

Nitrogen Oxidation in a Multi-Pin Plasma System in the Presence and Absence of a Plasma/Liquid Interface

The recent energy crisis revealed that there is a strong need to replace hydrocarbon-fueled industrial nitrogen fixation processes by alternative, more sustainable methods. In light of this, plasma-based nitrogen fixation remains one of the most promising options, considering both theoretical and experimental aspects. Lately, plasma interacting with water has received considerable attention in nitrogen fixation applications as it can trigger a unique gas- and liquid-phase chemistry. Within this context, a critical exploration of plasma-assisted nitrogen fixation with or without water presence is of great interest with an emphasis on energy costs, particularly in plasma reactors which have potential for large-scale industrial application. In this work, the presence of water in a multi-pin plasma system on nitrogen oxidation is experimentally investigated by comparing two pulsed negative DC voltage plasmas in metal–metal and metal–liquid electrode configurations. The plasma setups are designed to create similar plasma properties, including plasma power and discharge regime in both configurations. The system energy cost is calculated, considering nitrogen-containing species generated in gas and liquid phases as measured by a gas analyzer, nitrate sensor, and a colorimetry method. The energy cost profile as a function of specific energy input showed a strong dependency on the plasma operational frequency and the gas flow rate, as a result of different plasma operation regimes and initiated reverse processes. More importantly, the presence of the plasma/liquid interface increased the energy cost up to 14 ± 8%. Overall, the results showed that the presence of water in the reaction zone has a negative impact on the nitrogen fixation process.

Mechanisms of reducing energy costs for nitrogen fixation using air-based atmospheric DBD plasmas over water in contact with the electrode

In this study, a plasma-assisted nitrogen fixation (NF) process, using dielectric barrier discharge (DBD) air and N2 plasmas ignited over a water surface is presented. We describe the influential factors on the plasma properties through plasma diagnostics such as electrode spacings, applied voltages, and feedstocks to reduce the energy cost for NF. In order to maximize the energy yield and reduce the energy cost for NF as NO3-, the gas phase NOx emitted through the gas outlet is trapped into water. Plasma diagnostics is performed to explain the underlying mechanisms for NOx formation with a reduced energy cost. The analyzed results suggest that decreasing the electrode gap over water surface can effectively reduce the energy cost for NF, and that this can be attributed to the increased number of distributed microdischarges instead of more intense plasma filaments that dominate at higher gaps. This system offers a promising result in NO3− synthesis, with a selectivity of 98 %, and an energy cost of 20.7 MJ/mol.

In situ probing of atmospheric-pressure warm air glow discharge for nitrogen fixation by multiple laser spectroscopies

The fixation of atmospheric nitrogen into valuable compounds through reactive plasma processes has attracted intense interests due to its easy operation and compatibility with distributed renewable energy sources. However, practical implementation of plasma-assisted nitrogen fixation is hampered because of its relatively low throughput, which is dominantly limited by the unclear underlying mechanisms. In this study, effort was focused on the in situ production of key species in a DC-driven warm air glow discharge at atmospheric pressure with the help of advanced laser spectroscopic diagnostics. Laser Rayleigh scattering was applied to determine the gas temperature distribution in the discharge column. And mid-infrared quantum cascade laser absorption spectroscopy and one/two-photon absorption laser-induced fluorescence were performed on molecular nitric oxide (NO), atomic oxygen and nitrogen (O, N) for their absolute densities in the discharge. It is found that the spatial distributions of gas temperature, O and N atoms show peaks in the hot discharge center. In contrast, a hollow ‘doughnut’ shape characterized by the NO molecule was observed, particularly under conditions of high discharge current but low airflow rate. The steady-state simulation shows that the hollow pattern of NO is dominantly induced by the radial diffusion of species due to the steep spatial gradient of gas temperature in the discharge cross-section. Moreover, the reverse conversion by atomic N leads to a negative effect on the NO synthesis, especially at the discharge center where the N density and gas temperature are high. From the steady-state modeling, a similar hollow distribution of NO2 was depicted in the air glow discharge. These results demonstrate the strong dependence on atomic O for the major formation process of NO, and the importance of suppressing the reverse paths dominated by atomic N for higher NO production in the studied warm air plasma.

A Modified Fokker-Planck Approach for a Complete Description of Vibrational Kinetics in a N2 Plasma Chemistry Model.

The Fokker-Planck (FP) approach for the description of vibrational kinetics is extended in order to include multiquanta transitions and time dependent solutions. Due to the importance of vibrational ladder climbing for the optimization of plasma-assisted nitrogen fixation, nitrogen is used as a test case with a comprehensive set of elementary processes affecting the vibrational distribution function (VDF). The inclusion of the vibrational energy equation is shown to be the best way to model transient conditions in a plasma reactor using the FP approach. Results are benchmarked against results from the widely employed state-to-state (STS) approach for a wide parameters range. STS and FP solutions agree within ∼10% for the lowest vibrational levels, while time dependent VDFs are in agreement with the STS solution within a ∼ 5% error. Using the FP approach offers the possibility to parametrize drift and diffusion coefficients in energy space as a function of vibrational and gas temperature, providing intuitive and immediate insights into energy transport within the vibrational manifold.

Frequency-Selective MHz Power Amplifier for Dielectric Barrier Discharge Plasma Generation

Plasma-assisted nitrogen fixation at atmospheric pressure is a clean and decentralized method for fertilizer production. Among many different plasma discharge types, dielectric barrier discharge (DBD) is one of the few that can generate high output of nitrogen compounds at atmospheric conditions for fertilizer usage. Most DBD generators operate at kHz switching frequencies, however, previous research has found that discharge activities occur at the intervals of the greatest voltage slew rate. The finding implies that operating at higher frequencies can lead to more discharge activities and higher plasma generation. This paper presents a MHz Class E power amplifier with frequency selection to generate DBD plasma at two distinct frequencies. The power amplifier achieves a peak efficiency of 91.5% and outputs 600 W at frequencies of 12.4 MHz and 15.5 MHz.

Plasma-assisted nitrogen fixation: the effect of water presence

This study compares dry plasma and plasma/liquid systems in terms of their energy efficiencies for guiding researchers and engineers in selecting reactors and intensifying the plasma-based “zero CO2” nitrogen fixation process toward NOx production.

Review of low-temperature plasma nitrogen fixation technology.

Nitrogen fixation is essential for all forms of life, as nitrogen is required to biosynthesize fundamental building blocks of creatures, plants, and other life forms. As the main method of artificial nitrogen fixation, Haber–Bosch process (ammonia synthesis) has been supporting the agriculture and chemical industries since the 1910s. However, the disadvantages inherent to the Haber–Bosch process, such as high energy consumption and high emissions, cannot be ignored. Therefore, developing a green nitrogen fixation process has always been a research hotspot. Among the various technologies, plasma-assisted nitrogen fixation technology is very promising due to its small scale, mild reaction conditions, and flexible parameters. In the present work, the basic principles of plasma nitrogen fixation technology and its associated research progress are reviewed. The production efficiency of various plasmas is summarized and compared. Eventually, the prospect of nitrogen fixation using low-temperature plasma in the future was proposed.

A novel energy efficient path for nitrogen fixation using a non-thermal arc.

Plasma-assisted nitrogen fixation is a promising sustainable and clean alternative to the classical Haber–Bosch process. However, the high energy consumption and low production rate of plasma-assisted nitrogen fixation limit its application. This study shows that the non-thermal (non-equilibrium) enhancement of the arc plasma significantly reduces the energy consumption of nitrogen fixation. The highest energy efficiency with high NO selectivity is observed with a low specific energy input (SEI). However, the highest production rate is reached at a high SEI. The studied process offers high NO selectivity (up to 95%) with low energy consumption (∼48 GJ per tN) at 0.1 kJ L−1 SEI, which is much lower than the previously reported value of plasma-assisted atmospheric nitrogen fixation and is close to that of the Haber–Bosch process.

(Invited) Plasma-Assisted Nitrogen Fixation By Water: Development and Evaluation of Hybrid Membrane Based Plasma-Electrochemical Reactor

The worldwide energy crisis and environmental issues have greatly driven the current research on exploring and efficiently utilizing the environmentally-friendly and sustainable energy sources1. Most sustainable sources such as solar and wind energy are in principle able to meet the global energy demand. Nevertheless, they are intermittent and require new concepts of conversion and storage of electricity. Chemical feedstock, i.e. storing energy in form of the binding energy of molecules, is an economically feasible option for long term (seasonal) storage. However, the main challenge is how to address the problem of developing an effective process for converting electrical energy into molecules of high energy for chemical feedstock.In this context, nitrogen fixation is unquestionably one of the most important chemical conversion process since it converts atmospheric nitrogen (low energy molecule) into molecules of high energy (e.g. NH3, NO)2,3.However, contemporary chemical industry for nitrogen fixation impose great concerns about the environmental sustainability in terms of immense energy consumption and burdened emissions profile. Nevertheless, plasma-technology that can be directly powered by renewable electricity, has been receiving renewed attention as an alternative “green” approach for N2 activation4 which is one of the fundamental requirement for NO or NH3 synthesis.Up to now solutions were mainly sought on material axis, however recent theoretical studies have revealed that there are intrinsic limitations of catalysis (i.e. scaling relationships) which keep the processes far from the optimum performance5. In this work, we will present a unique solution to the aforementioned limitations by employing a hybrid type reactor consisting of a plasma reactor and solid state water electrolysers with oxygen ion6 or proton conducting membranes. Unlike conventional plasma catalysis that requires the co-activation of reactants, in the proposed alternative approach, electrolysers provide reacting species on catalysts with a controllable manner while a radiofrequency plasma is used to increase the reactivity of nitrogen7. Such spatial separation of nitrogen dissociation and catalytic formation of the target molecules provides truely independent parameters to optimise the nitrogen fixation process. One aided benefit of the proposed approach is that both technologies, i.e. water electrolyser and plasma activation, utilize base molecules (N2 and H2O) and can be directly powered by renewable electricity. Such a scheme may be a stepping stone to zero carbon footprint processes. Moreover, the advantages of proposed approach will be also compared to conventional plasma catalysis or pure plasma processes.

Thermodynamic potential of a novel plasma-assisted sustainable process for co-production of ammonia and hydrogen with liquid metals

In the present article, the thermodynamic potential of a sustainable plasma-assisted nitrogen fixation process for co-production of ammonia and hydrogen is investigated. The developed process takes advantage of chemical looping system by using a liquid metal such as gallium to drive nitrogen fixation reaction using three reactors including reactor R1 to produce gallium nitride from gallium and nitrogen, reactor R2 to produce ammonia and hydrogen from gallium nitride, and plasma reactor R3 to convert gallium oxide to pure gallium. The results of the thermodynamic assessments showed that the proposed reactions are spontaneous and feasible to occur in the reactors. Likewise, the first two reactions are exothermic with ΔH=-230kJmol and ΔH=-239kJmol in the reactors R1 and R2, respectively with an equilibrium chemical conversion of 100%. The plasma reactor requires thermal energy to drive an endothermic reaction of gallium oxide dissociation withΔH=+870kJmol. Thermochemical equilibrium analysis showed that the molar ratio of steam to GaN, as well as the operating pressure and temperature of reactor R2 are the main operating parameters identifying the product composition in the reactor such that by increasing the temperature, the molar ratio of hydrogen to ammonia increases. However, by increasing the molar ratio of steam/GaN (φ value) from 0.1 to 1, the hydrogen content of the reactor increases from 45% to 70% at 400 °C. For φ > 1.0, the hydrogen content decreases while more hydrogen participate in the formation of NH3 thereby increasing the mole fraction of ammonia in the reactor. The equilibrium chemical conversion of all three reactors is expected to reach the completion point (χ = 100%) due to the highly negative Gibbs free energy of the liquid metal-based reactions together with a large thermal driving force supported by thermal plasma reactor. Finally, a scalability study points at a possible use of the new disruptive process design at small scale, and possible industrial transformation scenarios for a distributed production at a local site of consumption are depicted.

Plasma-assisted nitrogen fixation in water with various metals

Hydrogen generated from the reduction of hydrogen ions found in plasma-generated acid not only enhances the plasma-assisted ammonia synthesis rate by providing an additional hydrogen donor but also controls the acidity of plasma-activated water.

Investigating the operation parameters for ammonia synthesis in dielectric barrier discharge reactors

Plasma-assisted nitrogen fixation has been considered a potential green alternative for conventional Haber–Bosch process and has recently received a lot of attention. Ammonia synthesis in nonthermal plasma reactors at atmospheric pressure has been investigated in this research with a 5% Ru/α-Al2O3 catalyst. The operating parameters including feed molar ratio, flow rate, applied voltage, discharge power and argon dilution were investigated to provide information for optimization of NH3 concentration and energy consumption. Difference between the blank reactor and the catalyst-packed reactor were presented with a discussion on their own optimal parameters. The optimal feed gas ratio (N2:H2) for blank reactor and the catalyst-packed reactor are 1:3 and 2:1 correspondingly. Higher flow rate resulted in a lower NH3 concentration and energy consumption in both blank reactor and the catalyst-packed reactor. Ammonia concentration of 1.49% was achieved in a catalytic DBD reactor with 120 ml min−1, 2:1 N2/H2 feed gas ratio and 38.4 W discharge power, corresponding to the energy consumption of 32.39 MJ mol−1. The discharge power and the reactor temperature is important to the synthesis of ammonia in catalytic DBD reactor and the effect of heat build-up in the reactor on NH3 concentration was observed. Argon addition improved the conversion of nitrogen and hydrogen at a cost of energy consumption and production rate in both blank and catalyst-packed reactor, but it is more beneficial for increasing the conversion of reactants in the case of catalytic DBD reactor.

Sustainable Non-Thermal Plasma-Assisted Nitrogen Fixation-Synergistic Catalysis.

In this Minireview, the multiple chemical synergies present in catalytic non-thermal plasma-assisted nitrogen fixation (NTPNF) are uncovered through a critical exploration of the underlying mechanisms, during which the catalyst, plasma, and reactants play different roles. For the gas-phase NTPNF, the synergies consist of different aspects of the catalytic pathways such as electron-impact dissociation; Zeldovich mechanism in the PNO interactions; and Eley-Rideal, Langmuir-Hinshelwood, surface adsorption, and diffusion mechanisms for the plasma-catalyst interactions. The synergies within the gas-liquid NTPNF involve contributions of plasma and UV excitation to the gas-phase reactions and the UV excitation of molecules at the liquid-surface interface, which improves synthesis of aqueous nitrate, nitrite, and ammonium products. Based on the various synergistic mechanisms during NTPNF, future potential applications are proposed for how NTPNF could benefit the sustainable nitrogen fixation industry.

Recent Progress of Plasma-Assisted Nitrogen Fixation Research: A Review

Nitrogen is an essential element to plants, animals, human beings and all the other living things on earth. Nitrogen fixation, which converts inert atmospheric nitrogen into ammonia or other valuable substances, is a very important part of the nitrogen cycle. The Haber-Bosch process plays the dominant role in the chemical nitrogen fixation as it produces a large amount of ammonia to meet the demand from the agriculture and chemical industries. However, due to the high energy consumption and related environmental concerns, increasing attention is being given to alternative (greener) nitrogen fixation processes. Among different approaches, plasma-assisted nitrogen fixation is one of the most promising methods since it has many advantages over others. These include operating at mild operation conditions, a green environmental profile and suitability for decentralized production. This review covers the research progress in the field of plasma-assisted nitrogen fixation achieved in the past five years. Both the production of NOx and the synthesis of ammonia are included, and discussion on plasma reactors, operation parameters and plasma-catalysts are given. In addition, outlooks and suggestions for future research are also given.

Life Cycle Assessment of the Nitrogen Fixation Process Assisted by Plasma Technology and Incorporating Renewable Energy

The importance of nitrogen fixation is evident in every aspect of a human being’s life, from the synthesis of vital for all organisms nutrients and, in turn, the ecosystem conservation to the production of fertilizers, plastics, and many other daily usage products. However, increasing concerns about the environmental sustainability of contemporary chemical industry seem to impose, nowadays, great challenges to the industrial nitrogen fixation which is linked to immense energy consumption and burdened emissions profile. Upon these considerations, it becomes imperative to adopt a holistic approach toward the development of novel “green” process technologies for the synthesis of fixed nitrogen. A considerable effort to that direction has been made by means of plasma technology mainly at the laboratory scale. Although research studies have shown promising results, little attention has been placed on conceptualizing plasma-assisted nitrogen fixation at an industrial scale and evaluating its environmental footp...

Energy Considerations for Plasma-Assisted N-Fixation Reactions

In a time of increasing concerns about the immense energy consumption and poor environmental performance of contemporary processes in the chemical industry, there is great need to develop novel sustainable technologies that enhance energy efficiency. There is abundant chemical literature on process innovations (laboratory-scale) around the plasma reactor itself, which, naturally, is the essential part to be intensified to achieve a satisfactory process. In essence, a plasma process needs attention beyond reaction engineering towards the process integration side and also with strong electrical engineering focus. In this mini-review, we have detailed our future focus on the process and energy intensification of plasma-based N-fixation. Three focal points are mainly stressed throughout the review: (I) the integration of renewable energy; (II) the power supply system of plasma reactors and (III) process design of industrial plasma-assisted nitrogen fixation. These different enabling strategies will be set in a holistic and synergetic picture so as to improve process performance.