Chemistry Reference
In-Depth Information
Processes in space
P
el
Active zone
Passive zone
Reactants
T
e
T
g
T
e
≈
T
g
Stable
products
(a)
A
1
A
2
A
1
A
2
Hot electrons
A
k
Elementary reactions
Dissociation,
excitation,
etc.
Recombination,
de-excitation,
etc.
A
k
A
l
P
el
Active phase
Time τ
Passive phase
Processes in time
(b)
FIGURE 4.1
Scheme of a plasma chemical flow reactor (a) and of a closed reactor (b),
respectively (with
P
el
electrical power input,
T
e
kinetic temperature of electrons,
T
g
gas
temperature).
containing the input species (
A
1
...
A
l
). The
double zone structure of every nonthermal plasma chemical flow reactor is well
known. But very often the specific role of the PZ and its great importance for the
final gas composition is underestimated.
There are conditions, namely in low-pressure plasmas, in which desired com-
pounds originate nearly complete in the PZ. In this case a suitable control scheme for
the manipulation of the PZ (e.g., by gas temperature control) considerably increases
the efficiency of the whole reactor similar to the quench of an isothermal reac-
tor. The quite different functions of the AZ and PZ especially in connection with
so-called reversible chemical quasi-equilibrium states will be outlined in Section 4.3.
The basis particle component of the AZ which guarantees the energy input in the
reactant mixture is the hot electron gas. Hot electrons are produced by the different
types of electrical discharges as glow discharges (DC, AC, RF, microwave) includ-
ing hollow cathode discharges as well as barrier discharges, corona discharges, and
plasma jets, see Section 3.8.
A
k
) but also new components (
A
k
+
1
...
