Giving back nature

Giving back to nature

5:58 AM, 18th September 2017
Bhaskar Patil, PhD Candidate, Department of Chemical Engineering and Chemistry, Eindhoven University of Technology
Bhaskar Patil, PhD Candidate, Department of Chemical Engineering and Chemistry, Eindhoven University of Technology.

In an interview, Bhaskar Patil, PhD Candidate, Department of Chemical Engineering and Chemistry, Eindhoven University of Technology (TU/e), delves into his research on plasma assisted nitrogen fixation and the wonders if it can work for the world.

Insight into the research.

Our current research focuses on developing an alternative energy driven (such as plasma) chemical production, where energy is selectively delivered to the reaction channels which yields higher energy efficiency. It is based on innovations at three levels and guided by a holistic approach; material innovation, process innovation, and plant innovation. Material innovation addresses the need of catalyst and its combination with alternative energy source, process innovation aims to increase productivity and energy efficiency by selective activation of reaction channels, and finally plant innovation looks into distributed/ localized production platform via containerized plant such as “Evotrainer”.

‘Revolutionary reactor that coverts nitrogen from the atmosphere into Nox’

In our investigation we have developed an intensified gliding arc reactor, which operates at high frequency (kHz) as opposed to conventional 50 Hz operation, which enables high degree of non-equilibrium within the gliding arc region. Air is used as the only feed to obtained NOx (=NO + NO2) as the final product at relatively lower temperatures and at atmospheric pressure. We have produced ~ 2 vol% of NOx on an average and our modelling-simulation studies points out that this could be as high as 20 vol% per gliding arc cycle, which is much higher than the equilibrium concentration of 6 vol% at >3500 oC. Moreover the energy consumption was found to be as low as 2.5 MJ/mol, which is lowest among the plasma studies. This reactor is extremely flexible as it can be readily started and shut down, can operated at wide range of pressures and can easily be integrated in the proposed containerized plant. However, further improvement in this reactor geometry and operation is necessary to increase the product concentration and to further bring down the energy consumption below 0.5 MJ/mol N.

Cost effectiveness of the technology when scaled up for commercial processes

This is not the final version of the reactor and the technology, before it goes into commercial process; it needs to undergo few iterations to improve the performance and to get every bit from the reactor technology and the approach. The preliminary economic and life cycle analysis already shows promising results with the current performance. It is clear that when plasma reactor is used the overall reaction and separation sections would be greatly simplified, e.g. no need of compressors and the pre-heat exchangers, thanks to the proposed atmospheric and low temperature process. Cutting down on these expensive process equipment will not only yield savings in the capital cost but also save the inventories. Moreover, plasma process emerges as more environmentally friendly process when driven by renewable energy. The reactor tested on lab scale, operates already at quite higher capacity and can readily be scaled-up to commercial process by numbering-up strategy. Moreover, the gliding arc reactor is known for its flexibility in terms of operating pressure, processing capacity, and start-up/shut down time. The reactor technology can also be easily integrated with the existing renewable energy network.

Types of reactors used to produce key raw materials for fertilizers

We have been thoroughly researching 2 different possibilities to use non-thermal plasmas; without catalyst and in combination of catalyst using Gliding arc and Dielectric barrier discharge reactor, respectively.

A gliding arc reactor consisted of two diverging electrodes and an arc discharge is generated by applying high voltage (kV) across these electrodes. Feed gas (Air) entered from the bottom of the reactor and product together with unreacted feed leaves from the top. The high frequency arc discharge is ignited at the narrowest gap between these electrodes and then, under the influence of the gas flow, glided along the electrodes in the direction of gas flow. The arc extinguished when the applied voltage is not enough to sustain the discharge over a longer length. A cycle of arc ignition and extinction repeats with every gliding arc cycle. Gliding arc plasma is characterized by its strong non-equilibrium due to the continuous upward movement of the arc and its ability to vibrationally excite the reaction species, which found to be the most efficient reaction channel for NOx formation. A Gliding arc plasma reactor provided a blend of hot quasi-equilibrium plasma (lower part) and cold non-equilibrium plasma (upper part). The gas temperature is found to be lower than the thermal plasma, but generally higher than the conventional non-thermal plasma.

A catalytically packed dielectric barrier discharge (DBD) reactor consisted of two parallel electrodes in a co-axial configuration, separated by a gap of few millimeters. DBD plasma is generated within this discharge gap by applying alternating current (with frequency 1-40 kHz, occasionally with us pulses) across the electrodes. The dielectric barrier, made from quartz, was placed on one electrode. The discharge in a DBD reactor proceeds as separate current filaments referred to as microdischarges or as a single glow discharge, depending on the dielectric constant of the material packed within the discharge gap. The short duration of current flow in the microdischarges gives low heat dissipation and thus the DBD plasma reactor is an ideal tool for catalyst screening. Large number of catalyst supports and active metals and their combination were investigated for nitrogen fixation in the form of nitric oxide and ammonia.

Ways the benefit farmers and help tackle issues like limited land availability, food shortages and volatile weather conditions.

Over the past century, the Haber-Bosch process has gone through many changes and operational optimizations, which have pushed this process very close to the thermodynamic limit in terms of the energy consumption. However, the Haber – Bosch process still consumes ~1% of the world’s total energy use, ~3-5% of the world’s total natural gas output and emits over 300 million metric tons of CO2. Therefore it comes with no surprise that ammonia has been identified by the International Energy Agency (IEA) as one of 18 chemicals, which contribute 80% to the total energy demand of the chemical industry and 75% of GHG emissions. Thus, a sustainable route for production of nitrogen containing chemicals is indispensable.

Looking at the future, world population is rapidly growing and it is expected to cross 9 billion by 2050, so that demand in food will also grow much more, which will correspondingly increase the dependency on fertilizer use to increase the food production. Thus, the CO2 emission from fertilizer production via the Haber-Bosch process will become an alarming factor in view of global warming. Interestingly, new opportunities in the renewable energy production/cost and innovative process design concepts have been established recently.

These new developments opens a new paradigm of localized and small-scale sustainable production of nitrogen containing compounds, for which the Haber-Bosch process will not be economically and environmentally attractive, because of its CO2 footprint and required harsh process conditions. Therefore, we think that plasma assisted nitrogen fixation is an innovative and alternative sustainable route for nitrogen fixation, which can be driven by alternative energy sources such as solar or wind. It would also facilitate production of nitrogen containing products close to the point of use (e.g. fertilizer at farmland for African countries) and at the point of energy production (near wind mill or solar farm in Germany/ Norway), which is feasible by employing container plants. Moreover, the preliminary life cycle analysis shows that this process will achieve considerable reductions in environmental footprint.

Comparing with other ongoing researches.

In last one century, a huge amount of research efforts have been put in to develop an alternative process routes for currently employed Haber-Bosch process; such as biological, alternative energy driven, homogeneous catalyst, electro and photo catalytic nitrogen fixation. However, none of the alternative processes are anywhere close to the performance of Haber-Bosch process’ energy consumption. It is evident that it is highly unlikely to have an alternative process which would be more energy efficient than the Haber-Bosch process. However, the efforts are in direction to reduce the environmental footprint of Haber-Bosch process by developing an alternative “green” nitrogen fixation process. This is where, alternative energy (plasma) assisted nitrogen fixation route holds great potential for the future. Comparing to the research done in the field of plasma assisted nitrogen fixation, we have obtained one of the best product concentration and energy consumption numbers till date using gliding arc reactor. Moreover, we have been able to demonstrate that the nitric oxide route could lead to higher energy efficiency than the ammonia route (mainly because of different thermodynamic barriers). As pointed out above, we have achieved ~ 2 vol% of NOx on an average and the energy consumption was found to be as low as 2.5 MJ/mol, which is lowest among the plasma studies.

Commercializing the technology

Several efforts are put in to further investigate and thoroughly understand the plasma assisted nitrogen fixation process under the flagship project “Fertilizing with Wind”. We are exploring other possibilities to extend this technology for example in hydroponics, aquaponics, etc. It is further investigated for commercialization in African countries and that is the business case currently under discussion. Several research proposals, such as Leap-Agri call from EU, are submitted and under scrutiny to further exploit the knowledge and the expertise gained in this research work.

Collaboration with Evonik  

This collaboration was a result of the European Union funded project “MAPSYN”, requiring intense industry-academic collaboration. We are furthering our collaboration with Evonik to transfer learnings from the lab environment to the demonstration scale plant. We cannot comment on the specific details because of the confidentiality.

Plans for future research.

Our future research plan revolves around developing thorough understanding of plasma assisted nitrogen fixation without and with catalyst. In without catalyst studies, we would like to vibrationally excite the nitrogen molecule by employing non-equilibrium plasmas to lower the energy demand. For catalyst studies, plasma-catalyst interaction and synergy are important aspects, which require systematic catalyst and various integration concept screening. Our ultimate goal is to develop localized nitrogen fixation plants, which can fit in a container and can be taken anywhere either to utilize the surplus renewable energy (e.g. in Germany/Norway, etc) or to produce fertilizer or other fixed nitrogen products at the point of use (e.g. remote and fertilizer deprived places such as African countries). 

Adoption of research in emerging countries 

It would be very beneficial for emerging regions, especially because of the higher importance given to the renewable energy generation, as it aims to utilize in-situ the electricity produced from the renewable sources. In developing regions such as African countries, farmers lack access to the sufficient amount of fertilizers and the cost is unusually high. “Fertilizing with the wind” will enable farmers living in the developing regions and stranded regions to produce their own fertilizers and will make them self-reliant.

Challenges faced

The Plasma assisted reactions are extremely challenging field and needs multidisciplinary collaborations between great numbers of field of science such as plasma physics, catalysis, chemical engineering, electrical engineering, high voltage and plasma ignition, plasma diagnostics, and many more. Therefore, this work was carried out by working in a multi-national, multi-disciplinary, public-private-partnership team in the framework of a large-scale European project- “MAPSYN”. Achieving an ambitious project goal of developing an innovative technology and a demonstration scale plant for it, starting from scratch, in a limited time period and communication with partners speaking different technical language were extremely challenging things. On a positive note, the understanding of the plasma-catalyst interaction, plasma generation and plasma-surface reactions has been advanced like never before, which gives renewed push to pursue non-equilibrium plasma assisted nitrogen fixation.

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