PhD opportunities

Conversion of hydrogen for nitrogenous compounds synthesis by plasma-catalysis

Thesis proposal

Area of expertiseEnergtique et gnie des procds
Doctoral SchoolSystems Engineering, Materials, Mechanics, Energy
SupervisorM. Vandad ROHANI
Co-supervisorM. Frdric FABRY
Research unitEnergy and Processes
Starting dateOctober 1st 2020
KeywordsHydrogen, Ammonia, Nitrogenous compounds, Physical chemistry, Chemical kinetics, Non-equilibrium media
AbstractCONTEXT AND CHALLENGE OF THE PHD
Hydrogen is a compound attracting more and more interest in the context of the energy transition due to an oxidation producing only water. Until now mainly produced for chemical applications (70 MtH2/year) A great part of the global hydrogen production being used for the synthesis of ammonia (170 MtNH3/year), a molecule essential for agriculture (fertilizers), polymers (plastics) and weapons (explosives) it is now expected to become a leading energy vector. Nevertheless, its weakness is that it is a gas with a very low density making its storage, transport, and on-board use very difficult. Converting hydrogen to a denser gas or a liquid is a relevant solution to solve that. A promising path would be the use of nitrogen (abundant element and relatively low cost) to produce a heavier hydro-nitrogenous compound such as an azane (ammonia, hydrazine, etc.). Thus, in this context also considering the conversion of hydrogen to ammonia could be very interesting. In its gaseous form (NH3) or its aqueous form (NH4OH), would then appear as a new vector, of transition (hydrogen vector) or of substitution (energy vector), with physical characteristics comparable to hydrocarbons. The problem is that this conversion, although exothermic, has high energy and economic costs. The thermo-catalytic Haber-Bosch process which currently produces more than 90% of the world's ammonia destined for chemistry suffers from a low chemical yield per cycle and requires particularly energy-consuming operating conditions (high pressure and temperature). Despite numerous research and development works carried out during this last century the 2007 Nobel Prize in Chemistry, Gerhard Ertl, devoted part of his career to seek to understand its fundamental heterogeneous chemical mechanisms the energy and economic costs of the process remain high. However, significant scientific efforts continue to be invested in an attempt to improve the process, improvement which to date is one of the scientific challenges with the greatest industrial interest and benefits. Among the possible solutions for improvement, the one consisting in replacing thermo-catalysis by non-equilibrium plasma-catalysis is particularly interesting. Thanks to new reaction paths followed in a medium far from the equilibrium, this could lead to greatly reducing the energy and economic costs of the process by bringing the operating conditions of pressure and temperature close to the ambient ones while gaining in chemical yield. Moreover, its electrification by this way would also place this process, if associated with water electrolysis or bio-methane plasma cracking for example, as a credible Power-to-X solution.

OBJECTIVES OF THE PHD
The specific objective of the thesis will be to develop a non-equilibrium plasma-catalytic reactor of synthesis exploiting a non-thermal plasma with a high degree of energy control operating under quasi-ambient pressure and temperature conditions for converting hydrogen and nitrogen into azanes. The objective on a more fundamental level will be to understand the physicochemical mechanisms, their interconnections and their kinetics, taking place in this new way of synthesis, with the aim to robustly optimize the chemical and energy yields of this plasma-catalytic process. Ammonia being the simplest azane, this thesis will mainly focus on it. But, it will also address the study on synthesis of higher azanes, even other nitrogenous compounds, from hydrogen, nitrogen and eventually an additional reactant.

METHODOLOGY
The proposed thesis will be part of the work carried out over the last ten years on this subject at the PERSEE research center of Mines ParisTech and will include two parallel components that will communicate together: (i) an experimental component consisting in designing and studying a plasma-catalytic reactor of synthesis based on the previous works of the team and using a set of physical and chemical analysis devices that the PhD candidate will appropriate, (ii) a theoretical part consisting in proposing and then validating a chemical model of plasma-catalytic synthesis of ammonia firstly, and secondly of higher azanes, from hydrogen and nitrogen under the chosen reaction conditions based on the experimental results acquired and the existing literature. Regarding the distribution of the tasks, the strong synergistic coupling between the plasma and the catalyst will imply an equal distribution of efforts between the study of non-thermal plasma and that of heterogeneous catalysis.
ProfileTypical profile for a thesis at MINES ParisTech: Engineer and / or Research Master: Physics or Chemistry.

Prerequisites (specific skills for this thesis): Physical Chemistry (in particular Thermochemistry and Chemical Kinetics), Synthetic Chemistry, Out of equilibrium Thermodynamics, Electrokinetics.
English:> B2 either 750 at TOEIC or 550 at TOEFL
French FLE: A2 / B1

To apply, please send CV, transcript of engineering diploma or research master and cover letter to:
vandad-julien.rohani@mines-paristech.fr or frederic.fabry@mines-paristech.fr
FundingConcours pour un contrat doctoral