Plasmalysis
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Plasmalysis is a
Thermal/non-thermal plasma
Thermal plasmas.[1] can be technically generated, for example, by inductive coupling of high-frequency fields in the MHz range (ICP: Inductively coupled plasma) or by direct current coupling (arc discharges). A thermal plasma is characterized by the fact that electrons, ions and neutral particles are in thermodynamic equilibrium. For atmospheric-pressure plasmas, the temperatures in thermal plasmas are usually above 6000 K. This corresponds to average kinetic energies of less than 1 eV.
Technical aspects
To generate a nonthermal plasma at atmospheric pressure, a working gas (molecular or inert gas, e.g. air, nitrogen, argon, helium) is passed through an electric field. Electrons originating from ionization processes can be accelerated in this field to trigger impact ionization processes. If more free electrons are produced during this process than are lost, a discharge can build up. The degree of ionization in technically used plasmas is usually very low, typically a few per mille or less. The electrical conductivity generated by these free charge carriers is used to couple in electrical power. When colliding with other gas atoms or molecules, the free electrons can transfer their energy to them and thus generate highly reactive species that act on the material to be treated (gaseous, liquid, solid). The electron energy is sufficient to split covalent bonds in organic molecules. The energy required to split single bonds is in the range of about 1.5 - 6.2 eV, for double bonds in the range of about 4.4 - 7.4 eV and for triple bonds in the range of 8.5 - 11.2 eV . For gases that can also be used as process gases, dissociation energies are e.g. 5.7 eV (O2) and 9.8 eV (N2) [4]
Applications of atmospheric pressure plasmas
Dissociation mechanisms of gases and liquids
In the following section XH stands for any hydrogen compound, e.g. CH- and NH-compounds.
- Thermal dissociation: gaseous hydrogen molecules are being dissociated at temperatures above 3000 K e.g. in a plasma. At temperatures above 3500 K H2 und O2 are dissociated.
- electron impact dissociation:
The density of radicals scales with the electron density and higher gas and electron temperatures (thermal dissociation and electron impact).
- ion impact dissociation:
- dissociative electron attachment:
This process generates negative ions as well as neutral particles. The collision electron is captured by collision excitation. The energy difference between the ground state and the excited state dissociates the molecule. The electron-induced dissociation of water depends on the electron temperature, which influences the ratio of the OH density (n_OH) to the electron density (n_e) significantly. The maximum OH density is reached in the early afterglow when the electron temperature (T_e) is low.
- Photoionisation:
High-energy photons dissociate molecules - Solvated electrons:
Reducing agent in liquid [6]
Dissociation efficiency of different hydrogen sources
Water Electrolysis
Since the focus is always on the most energy-efficient dissociation of chemical compounds, the benchmark is the energy input of the electrolysis of distilled water (45 kWh/kgH2) as in the following reaction equation:
Methane-plasmalysis
A particularly efficient way of generating hydrogen (10 kWh/kgH2) is the methane plasmalysis.[8] In this process, methane (e.g. from natural gas) is decomposed in the plasma under oxygen exclusion, forming hydrogen and elemental carbon, as in the following reaction equation:
Methane plasmalysis offers, among other things, the possibility of decentralized decarbonization of natural gas or, if biogas is used, also the realization of a CO2 sink,[10] whereby, in contrast to the CCS process commonly used to date, no gas has to be compressed and stored, but the elemental carbon produced can be bound in product form.
This technology can also be used to prevent the flaring of so-called "
Wastewater-plasmalysis
The plasmalysis of wastewater and liquid manure enables hydrogen to be recovered from pollutants contained in the wastewater (ammonium (NH4) or hydrocarbon compounds (COD)). The plasma-catalytic decomposition of ammonia takes place as shown in the following reaction equation:
The treated wastewater is purified in the process. The energy requirement for the production of green hydrogen is approx. 12 kWh/kgH2.
This technology can also be used as ammonia cracking (chemistry) technology for splitting the hydrogen carrier ammonia.
Dissociation of hydrogen sulfide
Hydrogen sulfide - a component of crude oil and natural gas and a by-product in anaerobic digestion of biomass - is also suitable for plasma-catalytic decomposition to produce hydrogen and elemental sulfur due to its weak binding energy.
The energy requirement for the production of hydrogen from H2S is approx. 5 kWh/kgH2.
Reactor geometry
It is apparent that both the reactor geometry and the method by which the plasma is generated strongly influence the performance of the system.
References
- .
- doi:10.1016/j.sab.2005.10.003)
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: CS1 maint: multiple names: authors list (link - ^ Stellungnahme zum Einsatz von Plasmaverfahren zur Behandlung von Lebensmitteln; http://www.dfg.de/download/pdf/dfg_im_profil/reden_stellungnahmen/2012/sklm_plasmastellungsnahme_120525.pdf; 15. Oktober 2015
- ^ Stellungnahme zum Einsatz von Plasmaverfahren zur Behandlung von Lebensmitteln; http://www.dfg.de/download/pdf/dfg_im_profil/reden_stellungnahmen/2012/ sklm_plasmastellungsnahme_120525.pdf; 15. Oktober 2015
- ^ https://www.synreform.com/images/videos/Erklaervideo-Wasserreinigung-englisch.mp4
- ISBN 978-0-511-54607-5
- ISBN 978-1-107-62270-8, retrieved 2020-04-22
- ^ https://graforce.com/images/videos/Erklaervideo-Methan-Plasmalyse_englisch.mp4
- ISBN 978-3-658-14935-2, retrieved 2020-04-22
- ^ https://graforce.com/images/videos/Erklaervideo-CO2_englisch.mp4