Stationary states of hydrogen‐producing reactions in nonequilibrium plasma

Abstract

In this work, stationary states of hydrogen-producing reactions in nonequilibrium plasmas are explored, namely the water splitting and water gas shift reactions. For both reactions, the effluent from the reactor at long residence times in the plasma was found to be independent of the influent speciation. In other words, feeding the reactor either 0.1H 2 O or 0.1H 2 + 0.05O 2 by mole produced the same effluent composition, and similarly, feeding the reactor 0.1CO + 0.1H 2 O produced nominally the same effluent as 0.1CO 2 + 0.1H 2 . For both reactions, the effluent from the plasma was found to be very far from local equilibrium at the total pressure and background temperature of the plasma and shifted in the endothermic direction relative to the local equilibrium speciation. This work further demonstrates that special attention must be paid to the recombination zone in plasmachemical processes. The recombination zone tends to drive the gas composition from plasma stationary states back towards local equilibrium.

Polynitrogen High Energy Density Materials Synthesized by Nonequilibrium Plasma

“…The endothermic CO 2 splitting reaction involves an enthalpy change of approximately 284 kJ mol –1 . Similarly, the water splitting reaction H 2 O → H 2 + 1 / 2 O 2 , involving an enthalpy of reaction of approximately 242 kJ mol –1 , can be promoted by nonequilibrium plasma at low temperature under vacuum where it is not favorable from the perspective of equilibrium thermodynamics . Similar results have been obtained for association reactions involving N 2 chemistries, where high mole fractions of nitric oxide and hydrazine have been realized under conditions where they are unexpected in systems governed by thermodynamic equilibrium .…”

“…Since the nonthermal plasma reaction medium is not constrained by local equilibrium, , product mixtures can be synthesized that are not expected at any temperature for the reactor pressure . For long reaction times, the product mixtures are usually, but perhaps not always, shifted in the endothermic direction relative to the equilibrium composition. ,, In other words, the preponderance of empirical experimental evidence suggests nonequilibrium plasma is most effective at promoting endothermic overall reactions past the equilibrium composition to obtain product distributions that are not expected for any temperature at the system pressure, which again is typically from vacuum to near ambient.…”

Plasma‐catalytic synthesis of acrylonitrile from methane and nitrogen

“…At the feed conditions, this gas is nominally in the equilibrium state at ambient temperature and the reactor pressure. Based on previous results in other chemical systems, in the discharge, the gas gets activated and eventually at long residence times reaches a stationary speciation that is stable only in the nonequilibrium plasma 12–14 . As soon as the gas leaves the plasma, the time evolution is governed by the equilibrium state at the local temperature and pressure, and the chemical composition that was previously stable in the plasma becomes unstable and relaxes to a metastable state through a process termed recombination.…”

Planetary Energy Flow and Entropy Production Rate by Earth from 2002 to 2023

“…The extremum principle is expected to be general to systems in the nonlinear regime of thermodynamics. For example, the author has also applied this idea to describe chemical reactions in a different type of system that operates far from local equilibrium, specifically low-temperature plasma reactors [39][40][41].…”